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The chemistry of some trifluoromethyl-phosphines Beg, Mirza Arshad Ali 1961

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THE CHEMISTRY of SOME TRIPLUOROMETHYL-PHOSPHINES . by MIRZA ARSHAD ALI BEG B..Sc.(Hons.)f M.Sc. (Karachi), 1955» A thesis submitted i n p a r t i a l f u l f i l m e n t of the requirements f o r the degree of DOCTOR OF PHILOSOPHY i n the Department of Chemistry. We accept t h i s thesis as conforming to the required standard© THE UNIVERSITY OP BRITISH COLUMBIA June, 1961. In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication' of this thesis for financial gain shall not be allowed'without my written permission. Department of ^^R^+^C&&^ The University of British Columbia, Vancouver 8, Canada. Date Af*Ql.tfc% /9£f GRADUATE STUDIES Field of Study: Inorganic Chemistry Topics in Inorganic Chemistry H. C. Clark H. G. Heal Topics in Organic Chemistry L. D. Hayward D. E. McGreer A. Rosenthal R. Stewart Radiochemistry D. R. Wiles Seminar in Chemistry : R. Stewart Related Studies: . Atomic Physics K. L. Erdman ! Geophysics '. J. A. Jacobs Structure of Metals II V. Griffiths j E. Teghtsoonian PUBLICATIONS 1. Chemistry of the Trifluoromethyl Group, Part I, Complex For-mation by Phosphines containing the trifluoromethyl group. M. A. A. Beg and H. C. Clark, Can. J. Chem., 38, 119, 1960. 2. Chemistry of the Trifluoromethyl Group, Part II, Nickel(II) Complexes of Trifluoromethyl-phosphines. M. A. A. Beg and H. C. Clark, Can. J. Chem., 39, 595, 1961. 3. Chemistry of the Trifluoromethyl Group, Part III, Phenylbistri-fluoromethylphosphine and related Compounds. M. A. A. Beg and H. C. Clark, Can. J. Chem., 39, 564, 1961. Wqp Pntuersttg of ^ rtttsii Columbia FACULTY OF GRADUATE STUDIES PROGRAMME OF THE F I N A L O R A L E X A M I N A T I O N FOR T H E D E G R E E OF D O C T O R O F P H I L O S O P H Y of M. ARSHAD A. BEG B.Sc. (Hons), M.Sc. (Karachi) FRIDAY, JULY 28th, 1961 at 2:30 p.m. IN ROOM 342, CHEMISTRY COMMITTEE IN CHARGE Chairman: D. M. MYERS W. A. BRYCE J. A. JACOBS H. C. CLARK J. P. KUTNEY j. A . C R U M B c. A . MCDOWELL J. HALPERN R. STEWART L. G. HARRISON E. TEGHTSOONIAN External Examiner: H. J. EMELEUS, C.B.E., Ph.D., D.Sc, A.R.C.S., F.R.S. University Chemical Laboratory, Cambridge, England ABSTRACT CHEMISTRY OF SOME TRIFLUOROMETHYL-PHOSPHINES One particular aspect of the chemistry of the trifluoromethyl group is its high electron-withdrawing power which reduces the donor properties of normally strong bases. This investigation has been concerned with the chemistry of some phosphines containing this group. For this purpose, substituted phosphines containing methyl or phenyl and trifluoromethyl groups have been prepared. For the study of their donor properties, a series of addition compounds with boron trifluoride, platinum(II) chloride and nickel(II) salts have been prepared. The reported methods for preparing the methyl-trifluoromethyl-phosphines do not produce a good yield; therefore, an attempt has been made towards a better understanding of the reactions. The phenyl-trifluoromethyl-phosphines have been prepared by reacting trifluoroiodomethane with a phosphorus compound containing a P-P bond. Thus, a reaction with tetraphenylcyclotetraphosphine gives phenylbistrifluoromethylphosphine and phenyltrifluoromethyliodo-phosphine, and reaction with tetraphenlydiphosphine gives diphenyl-trifluoromethylphosphine. The latter has also been prepared by re-action of trifluoroiodomethane with either triphenylphosphine or diphenylchlorophosphine. These new phosphines are colorless liquids (except phenyltri-fluoromethyliodophosphine which is reddish-brown) of high boiling point. They are stable in air and cannot be hydrolysed with acid or water, except the iodophosphine C(.HSCF3PI, which reacts with water to give phenyltrifluoromethylphosphinic acid, a new oxyacid. Phenyl-bistrifluoromethylphosphine can be hydrolysed with aqueous alkali to give fluoroform and phenylphosphonous acid. Diphenyltrifluoro-methylphosphine, on the other hand, cannot be hydrolysed by aqueous alkali, but reacts slowly with alcoholic potassium hydroxide to give' fluoroform and diphenylphosphinic acid. The phosphines form a further series of new compounds by reaction with halogens. Phenylbistrifluoromethylphosphine reacts with iodine to form trifluoroiodomethane, but forms phenylbistri-fluoromethyldibromophosphorane with bromine. This compound al-so gives phenyltrifluoromethylphosphinic acid on aqueous hydrolysis, as obtained in the case of phenyltrifluoromethyliodophosphine. Be-sides forming the dibromophosphorane, diphenyltrifluoromethylphos-phine is the first trifluoromethyl-phosphine known to form a diiodo-phosphorane. It is interesting to note that diphenyltrifluoromethyl-phosphine is difficult to hydrolyse, whereas the phosphoranes can be hydrolysed easily, giving fluoroform and diphenylphosphinic acid. By reaction with methyl iodide, this phosphine also forms a new phosphonium compound, methyldiphenyltrifluoromethylphosphonium iodide which is readily hydrolysed by cold water with the loss of the trifluoromethyl group. In general, phosphines containing one trifluoromethyl group show similar properties to those of their parent compounds, tri-methylphosphine and triphenylphosphine, while those containing two trifluoromethyl groups are very similar in their behaviour to tristri-fluoromethylphosphine. The phosphines containing more than one CF 3 group do not form addition compounds with boron trifluoride. The phenyl-tri-fluoromethyl-phosphines form more stable complexes than the methyl-trifluoromethyl-phosphines. The phosphines containing up to two trifluoromethyl groups form complexes with platinum(II) chloride. A complex with tristri-fluoromethylphosphine could not be obtained. Except dimethyltri-fluoromethylphosphine, which forms mainly a cis isomer, the other phosphines, CHa(CF3)2P, C6H5(CF3).,P, and (C 6H 5) 2CF 3P form main-ly trans isomers. The non-occurrence of the tristrifluoromethylphos-phine complex and the production of mainly trans isomers of the above-mentioned phosphines has been interpreted in terms of steric phenomenon. The phosphines containing more than one CF S group do not form complexes with nickel(II) salts. The nitrate complexes of trimethylphosphine and dimethyltrifluoromethylphosphine are para-magnetic, while the dichloro, dibromo, diiodo, and dithiocyanato complexes are diamagnetic. A correlation of the various properties, for example boiling points and heats of vaporization, has shown that the trifluoromethyl substituted phosphines are not anomalous in the general family of phosphines. An attempt has also been made towards a study of the infrared spectra of the phosphines and their compounds, and towards a cor-relation with the spectra of other phosphorus compounds. Finally, an approximate estimate of the "electronegativities" of a wide range of substituted phosphines gives values which are in good agreement with the observed order of reactivities of the phosphines studied, and assists in correctly placing the trifluoromethylphosphines in such a range, of compounds. ( i ) ABSTRACT One p a r t i c u l a r aspect of the chemistry of the t r i -fluoromethyl group i s i t s high electron-withdrawing power which reduces the donor properties of normally strong bases* This i n v e s t i g a t i o n has been concerned with the chemistry of some phosphines containing t h i s group. For t h i s purpose, substituted phosphines containing methyl or phenyl and t r i -fluoromethyl groups have been prepared. For the study of t h e i r donor properties, a series of addition compounds with boron t r i f l u o r i d e , platinum(Il) chloride and n i c k e l ( I I ) s a l t s have been prepared. The reported methods f o r preparing the methyl-trifluoromethyl-phosphines do not produce a good y i e l d ; therefore, an attempt has been made towards a better under-standing of the reactions. The phenyl-trifluoromethyl-phosphines have been prepared by reacting t r i f l u o r o i o d o -methane with a phosphorus compound containing a P-P bond. Thus, a reaction with tetraphenylcyclotetraphosphine gives phenylbistrifluoromethylphosphine and phenyltrifluoromethyl-iodophosphine, and reaction with tetraphenyldiphosphine gives diphenyltrifluoromethylphosphine. The l a t t e r has also been prepared by reaction of trifluoroiodomethane with either triphenylphosphine or diphenylchlorophosphine. ( i i ) \ These new phosphines are colorless l i q u i d s (ex-cept phenyltrifluororaethyliodophosphine which i s reddish-brown) of high b o i l i n g point. They are stable i n a i r and cannot be hydrolysed with acid or water, except the iodo-phosphine C H CP PI, which reacts with water to give phenyl-6 5 3 trifluoromethylphosphinic acid, a new oxyacid. Phenylbis-trifluororaethylphosphine can be hydrolysed with aqueous a l k a l i to give fluoroform and phenylphosphonous acid. Di-phenyltrifluoromethylphosphine, on the other hand, cannot be hydrolysed by aqueous a l k a l i , but reacts slowly with alco-h o l i c potassium hydroxide to give fluoroform and diphenyl-phosphinic acid. The phosphines form a further series of new com-pounds by reaction with halogens. Phenylbistrifluoromethyl-phosphine reacts with iodine to form trifluoroiodomethane, but forms phenylbistrifluororaethyldibromophosphorane with bromine. This compound also gives phenyltrifluoromethyl-phosphinic acid on aqueous hydrolysis, as obtained i n the case of phenyltrifluoromethyliodophosphine. Besides forming the dibromophosphorane, diphenyltrifluoromethylphosphine i s the f i r s t trifluoromethyl-phosphine known to form a diiodo-phosphorane. I t i s in t e r e s t i n g to note that d i p h e n y l t r i -fluoromethylphosphine i s d i f f i c u l t to hydrolyse, whereas the phosphoranes can be hydrolysed e a s i l y , g iving fluoroform and ( i i i ) diphenylphosphinic acid. By reaction with methyl iodide, t h i s phosphine also forms a new phosphonlum compound, methyldiphenyltrifluoromethylphosphonium iodide, which i s re a d i l y hydrolysed by cold water with the loss of the t r i -fluoromethyl group. In general, phosphines containing one t r i f l u o r o -methyl group show s i m i l a r properties to those of t h e i r parent compounds, trimethylphosphine and triphenylphosphine, while those containing two trifluoromethyl groups are very s i m i l a r i n t h e i r behaviour to tristrifluoromethylphosphine. The phosphines containing more than one CP group 3 do not form addition compounds with boron t r i f l u o r i d e . The phenyl-trifluoromethyl-phosphines form more stable complexes than the methyl-trifluoromethyl-phosphines. The phosphines containing up to two t r i f l u o r o -methyl groups form complexes with platinum(Il) chloride. A complex with tristrifluoromethylphosphine could not be obtained. Except dimethyltrifluoromethylphosphine, which forms mainly a c i s isomer, the other phosphines, CH^(GP^)^P, C H (CP ) P, and (C H ) CP P form mainly trans isomers. The 6 5 3 2 6 5 2 3 non-occurrence of the tristrifluoromethylphosphine complex and the production of mainly trans isomers of the above-mentioned phosphines has been interpreted i n terms of s t e r i c phenomenon. (iv) The phosphines containing more than one CF_ group j do not form complexes with n i c k e l ( I I ) s a l t s . The n i t r a t o complexes of trimethylphosphine and dimethyltrifluoromethyl-phosphine are paramagnetic, while the dichloro, dibromo, diiodo, and dithiocyanato complexes are diamagnetic. A c o r r e l a t i o n of the various properties, f o r ex-ample b o i l i n g points and heats of vaporization, has shown that the trifluoromethyl substituted phosphines are not anomalous i n the general family of phosphines. An attempt has also been made towards a study of the infra-red spectra of the phosphines and t h e i r compounds, and towards a c o r r e l a t i o n with the spectra of other phos-phorus compounds. F i n a l l y , an approximate estimate of the " e l e c t r o n e g a t i v i t i e s " of a wide range of substituted phos-phines gives values which are i n good agreement w i t h the observed order of r e a c t i v i t i e s of the phosphines studied, and a s s i s t s i n c o r r e c t l y placing the trif l u o r o m e t h y l -phosphines i n such a range of compounds. ACKNOWLEDGEMENT To Dr. H. C. Clark f o r his immeasurable advice and continual encouragement throughout the course of this work, I am p a r t i c u l a r l y indebted. My thanks are due to Dr. W. R. Cullen and Dr. C. J. W i l l i s , f o r t h e i r interest and discussions. I am obligated to Prof. C. A. McDowell for his personal i n t e r e s t , and to the other members of the Department f o r t h e i r assistance. In addition, ray gratitude i s extended to the Council of S c i e n t i f i c and Ind u s t r i a l Research, Pakistan, and to the Colombo Plan Administration i n Canada, for the award of a scholarship, held during the period of th i s research programme. (v) CONTENTS Chapter Page INTRODUCTION 1 SECTION I PREPARATION AND' CHEMISTRY OP THE PHOSPHINES 1. Preparation of Methyl-trifluoromethyl Phosphines 7 2. Preparation of Phenyl-trifluoromethyl Phosphines 21 3. Properties of Phenyl-trifluoromethyl Phosphines 39 SECTION I I PREPARATION AND STUDY OP THE ADDITION COMPOUNDS 4. Formation of Boron T r i f l u o r i d e Complexes 59 5. Formation of Platinum(Il) Chloride Complexes 66 6. Formation of Complexes with Nickel Salts 82 SECTION I I I GENERAL DISCUSSION 7. Comparison of Phosphines with and without CF Group 90 3 8. Hydrolysis of the Trifluoromethyl-Phosphorus Compounds 116 9. Infra-Red Spectra of the Phosphines and Related Compounds 129 10. Conclusions 157 EXPERIMENTAL I. Experimental Methods 161 (vi) EXPERIMENTAL Page I I . Preparation of the Phosphines 163 Preparation of CP I 168 3 Preparation of Trimethylphosphine 169 Preparation of Dimethyltrifluoromethyl-phosphine 171 Preparation of Tr i s t r i f l u o r o m e t h y l -phosphine 174 Preparation of MethyIbistrifluoromethyl-phosphine 177 IIIA. Preparation of Phenyl-Trifluoromethyl-Phosphines 179 Preparation of Phenylbistrifluoromethyl-phosphine 179 Interaction of Trifluoroiodomethane and Tetraphenylcyclotetraphosphine 181 Characterization of Fractions 184 Preparation of Diphenyltrifluoromethyl-phosphine 187 Interaction of Trifluoroiodomethane and Tetraphenyldiphosphine 190 Reaction of Trifluoroiodomethane and Triphenylphosphine 192 Reaction of Trifluoroiodomethane and Diphenylchlorophosphine 193 IIIB. Properties and Reactions of Phenyl-Trifluoromethyl-Phosphines 196 Phenylbistrifluoromethylphosphine 196 ( v l i ) Page Physical Properties 196 Reactions: Hydrolysis 197 Reaction with Halogens 199 Reaction with CF^I 201 Reaction with OH I 202 3 Phenyltrifluoromethyliodophosphine 202 Hydrolysis 203 Reaction with CP I 204 3 Reaction with CP I and Hg 204 Diphenyltrifluoromethylphosphine 205 Physical Properties 205 Hydrolysis Reactions 206 Reaction with Halogens 207 Reaction with CP,I 209 3 Reaction wi th CH,I 210 3 IV. Complexes of the Phosphines 212 Boron T r i f l u o r i d e Complexes 212 Reaction with: Trimethylphosphine 212 Dimethyl t r i f luoromethylphosphine 213 Me thylb i s t r i fluo rome thylpho s phin e 215 Tristrifluoromethylphosphine 215 Phenylbistrifluoromethylphosphine 215 Diphenylbi s trifluoromethylpho sphine 215 Triphenylphosphine 217 ( v i i i ) Page Platinum(II) Chloride Complexes 218 Bis(trimethylphosphine)dichloroplatinum(II) 219 Bis(dimethyltrifluoromethylphosphine)-dichloroplatinum(II) 221 Bis(methylbistrifluoromethylphosphine)-dichloroplatinum(II) 221 Reaction of Tristrifluoromethylphosphine with Platinum(Il) Chloride 225 B i s(phenylbi s t r i fluorome thylpho sphi ne)-dichloroplatinum(II) 227 Bis(diphenyltrifluoromethylphosphine)-dichloroplatinum(II) 229 Determination of Dipole Moments 232 Complexes of the Nickel Salts 233 Trimethylphosphine Complexes 233 Dimethyltrifluoromethylphosphine Complexes 237 Reaction with other Phosphines 240 REFERENCES 241 TABLE OP ILLUSTRATIONS Page F i g . A. Plate No. Pi g . F i g . - P l o t of 1« M 3 ^ R Vs. B o i l i n g Point (Observed) 93 1. Phenyltrifluoromethyliodophosphine 2 . Phenyltrifluoromethylphosphinic Acid Plate No. 2 , F i g . F i g . F i g . F i g . Plate No. Fi g . F i g . P i g . P i g . 3 * Dimethyltrifluoromethylphosphine 4. Methylbi s t r i fluoromethylpho sphine 5• Phenylbistrifluoromethylphosphine 6. Diphenyltrifluorome thylpho sphine 7. 8. 9. 101 Plate No. 4< P i g . P i g . Pig. Pig. Plate No. Pig. Pig. P i g . 1 1 . 12. 13. 14 . 5 . 15 . 16 . 1 7 . 141 141 141 141 141 141 Methyldiphenyltrifluoromethylphosphonium iodide Methyltriphenylphosphonium iodide Methyldiphenylphosphine oxide Dime t h y l b i s t r i fluoromethylpho sphonium iodide Trimethylphosphine-boron t r i f l u o r i d e Dimethyltri fluorome thylpho sphine-boron t r i f l u o r i d e Diphenyltrifluoromethylphosphine-boron t r i f l u o r i d e Triphenylpho sphine-boron t r i f l u o r i d e Bis(diphenyltrifluoromethylphosphine)di-chloroplatinum(II) Bis(phenylbistrifluoromethylphosphine)die chloroplatirium(II) Bis(phenylbistrifluoromethylphosphine)di-chlorodibromoplatinum(ITC) 147 147 147 147 150 150 150 150 154 154 154 Plate No. 6. P i g . 18 . Bis(trimethylphosphine)dichloroplatinum(II) 154 P i g . 19. Bis(dimethyltrifluoromethylphosphine)di-chloroplatinum(II) 154 F i g . 20 . Bis(methylbistrifluoromethylphosphine)di-chloroplatinura(II) 154 I N T R O D U C T I O N Pluorocarbon chemistry can r i g h t l y claim to have developed more ra p i d l y than almost any other branch of chemistry. War acted as a catalyst i n i t s rapid growth V i r t u a l l y nothing was known of the chemistry of fluorocar-bons i n mid 1941> yet the necessary amount of the desired fluorocarbons was available when the f i r s t d i f f u s i o n sepa-r a t i o n of UPg went into operation at Oak Ridge i n 1943* Many chemists then quickly r e a l i z e d that this was a f i e l d which i n the near future would span p r a c t i c a l l y a l l branch of chemistry. The fluorocarbons are characterized- by t h e i r great thermal s t a b i l i t y and resistance to chemical action. Compared with hydrocarbons, they are completely r e s i s t a n t to oxidation and do not burn. They are extremely i n e r t and both they and t h e i r derivatives have been found to be most useful compounds. A further development of wide - 2 -i n t e r e s t commenced with the discovery that when the fluoro-carbon iodides are heated or exposed to u l t r a v i o l e t l i g h t , fluorocarbon r a d i c a l s are produced. This i n t e r e s t i n g pro-perty has been applied to the preparation of a large number of fluorocarbon derivatives with functional groups and of fluorocarbon m e t a l l i c or metalloidal compounds. The most studied reactions are those using trifluoroiodomethane. In most cases, the reaction involves simple treatment of t h i s compound with an organic compound, or i f a trifluoromethyl-metalloid i s desired then the metalloid or one of i t s com-pounds i s used. The development of fluorocarbon chemistry has therefore been on two main l i n e s : the preparation of the perfluorocarbon compounds- containing functional groups, and the preparation of perfluorocarbon metallic or metalloidal compounds. The f i r s t comprises a large and i n t e r e s t i n g section of organic chemistry and the second started by the B r i t i s h school i s s t i l l passing through i t s formative stage. The perfluorocarbon derivatives, or more s p e c i f i -c a l l y , the trifluoromethyl compounds of a large number of metalloids and a few metals are now known. However, i n t e r e s t i s currently centred on the trifluoromethyl derivatives of boron, t i n , phosphorus, arsenic and sulphur. I t i s observed that the main features of the chemistry of the hetero atoms - 3 -(metal or metalloid) are retained on the introduction of the trifluoromethyl group but there i s a profound change from the properties of t h e i r a l i p h a t i c analogues. This trend r e s u l t s from the highly electronegative nature of the trifluoromethyl group. tives of the metalloids were being prepared, quite a large amount of information was already available regarding the organic compounds of phosphorus. The chemistry of the organo' phosphorus compounds i s an old subject and was developed i n the l a s t century, mainly i n Germany by Michaelis and his students, and l a t e r by Arbuzov i n Russia. These workers con-centrated on the systematic synthesis of a wide variety of compounds. However, there are s t i l l many gaps i n the l i s t of characterized organo-phosphorus compounds. For instance, the phosphines and halophosphines react i n general with halogens to form the phosphoranes — R^PX,. B u t t h e a l k y l -phosphoranes were unknown u n t i l recently. Also, i t i s ex-pected that the s t a b i l i t y of the phosphoranes should increase tablished i n many cases. In most cases, the diiodophospho-ranes are unknown. knowledge i n organophosphorus chemistry. The r e a c t i v i t y and t o x i c i t y of the compounds may be one of the reasons, but the At the time when the f i r s t trifluoromethyl deriva-i n the order I but t h i s has not been es There may.be a number of reasons for t h i s lack of - 4 -use of vacuum manipulation now provides a unique technique whereby reactive substances can be handled e a s i l y and safely. This technique not only provides a method of handling re-active substances out of contact with a i r , but also allows for the f r a c t i o n a t i o n and preparation of pure samples. For instance, the preparation of trimethylphosphine has always presented a problem since i t reacts r e a d i l y i n a i r and furthermore, the usual method of preparation gave a very low y i e l d . The use of vacuum techniques and modified method of preparation leads to a high y i e l d of the pure, phosphine. The a v a i l a b i l i t y of physical instruments e.g. the infra-red spectrophotometer etc. provides another means of tes t i n g the pu r i t y of the substances. With these- techniques, we are now i n a better p o s i t i o n to investigate organo-phosphorus com-pounds than was possible previously. I t i s also clear that even i f the fluorocarbons had been known to the workers of the past century, they would have been severely handicapped by the. lack of suitable techniques. P r a c t i c a l l y a l l the substituted phosphines were known by the l a s t h a l f of this century. With the discovery of the reaction of perfluoroalkyl iodides with phosphorus, a new chapter was opened and a series of compounds containing trifluoromethyl groups were prepared. The work was, however, directed towards the preparation of the analogues of the known organo-phosphorus compounds. The f i r s t i n the series - 5 -was tristrifluoromethylphosphine and the two iodophosphines (CF,) 0PI and CF PI • The hydrocarbon analogues of only the the remaining two are the chlorides (CH,)0PC1 and CH-PCl ing iodoaryl compounds have not yet been reported. The trifluoromethyl-phosphines are found to be quite d i f f e r e n t from the methyl and phenyl phosphines i n both physical and chemical properties. Thus tristrifluoromethylphosphine b o i l s at a lower temperature than the methyl analogue and much lower than triphenylphosphine which i s of comparable mole-cular weight. Tristrifluoromethylphosphine inflames spon-t a n e o u s l y i n a i r and unlike the a l k y l or a r y l phosphines can be hydrolysed with the cleavage of the P-C bond. This reaction can be considered a c h a r a c t e r i s t i c reaction of the t r i f l u o r o -methyl compounds of phosphorus and i n most cases can be adopted for the i d e n t i f i c a t i o n of these compounds. Another major d i f -ference from the methyl or phenyl phosphines i s the inertness of the lone p a i r electrons on phosphorus. preparative i n nature and the stage has been reached for more detailed studies. The present investigation i s therefore concerned with the study of the r e a c t i v i t y of the t r i f l u o r o -methy-lphosphines towards standard reactants p a r t i c u l a r l y with respect to t h e i r donor properties. For a reasonably wide which have been reported only recently. 3'2*" (2 2> ) 3 2 The correspond-Hox^ever, most of the work so f a r reported i s mostly - 6 -study of the effect of the trifluoromethyl group i t seems necessary to examine i t s chemistry i n the environment of both methyl and phenyl groups. This has been done by pre-paring phosphines of the type RCCF^JgP and RgCF^P, where R i s methyl or phenyl. The preparations of the methyl-trifluoro-methyl phosphines ( C H J ) 2 C F J P and CH^tCF ) G P have been des-cribed previously but t h e i r r e a c t i v i t y has not been reported. The phenyl-trifluoromethyl phosphines (CgH^JgCF^P and CgH^CF^gP have been prepared during this i n v e s t i g a t i o n by making use of the r e a c t i v i t y of the P-P bonds. These sub-s t i t u t e d phosphines have been made to react with boron t r i f l u o r i d e , platinum (II) chloride and a series of n i c k e l s a l t s . The whole subject has been divided into three sec-tions. The f i r s t one deals with the preparation and the chemistry of the phosphines, the second i s concerned with the preparation of the addition compounds, and the t h i r d deals with the general effect of the trifluoromethyl group on the chemistry of the class of compounds ca l l e d phosphines. S E C T I O N I PREPARATION AND CHEMISTRY OP THE PHOSPHINES C H A P T E R I PREPARATION OP METHYL-TRIFLUOROMETHYL PHOSPHINES The preparation of methyl-trifluoromethyl phos-phines has been carried out by the exchange methods,described (12) by previous workers. ' The exchange of a methyl group i n trimethylphosphine for the trifluoromethyl group i n t r i f l u o r o -iodomethane gives dimethyltrifluoromethylphosphine and l i k e -wise, the exchange of a trifluoromethyl group i n t r i s t r i -fluoromethyl phosphine with the methyl group i n methyl iodide gives methylbistrifluoromethylphosphine. The reactions may be represented by the following equations: 2 (CH,)_ P +- CP_I > (CH_)_CF_P + (CH_) PI (1) JO 0 3 2 3 ' 3 4 ( C F 3 ) 3 P + CH 3I > C H ^ C F ^ P -hCF 3I (2) These exchange reactions require the preparation of trimethylphosphine and tristrifluoromethylphosphine. The (3) former has been prepared by the Grignard reaction and the l a t t e r by the di r e c t reaction of trifluoroiodomethane on (4-) phosphorus. The preparation of methyl-trifluoromethyl phosphines i s quite involved and does not always give a satisfactory y i e l d , since frequently side reactions occur which consume much of the s t a r t i n g material. In the present inv e s t i g a t i o n the methods have been modified to improve the y i e l d s . An attempt has also been made to gain a better understanding of the mechanisms of the reactions. Trimethylphosphine: The reaction of phosphorus t r i c h l o r i d e with methyl magnesium iodide at room temperature occurs with violence and produces l a r g e l y tetramethylphos-15) phonium chloride and phosphorus diiodide. . 3PC1 5 + 4 CH3MgI > ( C H ^ P C H - P ^ 4- 4 MgCl 2 (3) This indicates that a large excess of the Grignard reagent (33) i s necessary and that only low yields can be expected. By s t i r r i n g the reaction mixture vigorously and cooling i t o i n t e n s i v e l y to - 78 , the violence of the reaction and the formation of phosphorus iodide can be reduced, as i s evi-denced by the absence of the orange colour of the iodide. These conditions also prevent the escape of the phosphine as i t i s formed. To reduce the loss of the phosphine during d i s t i l l a t i o n , the d i s t i l l a t e may be received i n a cooled f l a s k . By taking these precautions, a y i e l d of 60% of t r i -methylphosphine has been obtained. _ 9 -Dimethyltrifluoromethylphosphine; The reaction of trimethylphosphine with trifluoroiodomethane gives dimethyl-trifluororaethylphosphine, tetramethylphosphonium iodide and a small amount of a white s o l i d which probably i s dimethyl-bistrifluoromethylphosphonium iodide. The reaction starts much below room temperature with a rapid deposition of white s o l i d . After about an hour, equilibrium appears to tee es-tablished, but further slow formation of the white s o l i d continues. The y i e l d of the phosphine (CH^JgCF^P i s not higher than 33% and hence i t i s desirable to elucidate the probable mechanism of t h i s reaction. Ik few observations, i n addition to those ci t e d e a r l i e r are relevant i n this connection. 1. Tetramethylphosphonium iodide does not react with t r i -fluoroiodomethane. 2. Dimethyltrifluoromethylphosphine and trifluoroiodomethane formaan intimate and inseparable mixture i n the gas phase. This probably indicates the formation of a molecular complex. 3» In the l i q u i d phase, this mixture gives a reasonable amount of a white s o l i d which melts at 60 and which sublimes into the vacuum system. The hydrolysis of t h i s s o l i d gives fluoroform, corresponding approximately to the loss of two trifluoromethyl groups from what may be dimethylbistrifluoromethylphosphonium iodide. The infrared spectrum of this s o l i d i s also consistent with t h i s i d e n t i f i -cation. 4. Trimethyltrifluoromethylphosphonium iodide which - \ - 10 -Is a l i k e l y product of this reaction i s not found among the products. 5» The quaternary compound j(CH^^CF^ljl i s soluble i n l i q u i d trifluoroiodomethane and ethanol and i s insoluble i n carbon tetrachloride and trimethylphosphine. 6. When the reaction i s carried out i n carbon tetrachloride, the product i s a mixture of trimethyltrifluoromethylphos-phonium iodide and tetramethylphosphonium iodide. 7« The treatment of trimethyltrifluoromethylphosphonium iodide with trimethylphosphine i n ethanol gives some tetramethylphos-phonium iodide. The above facts may now be considered i n the l i g h t of the mechanisms proposed by the e a r l i e r workers who predicted the i n i t i a l formation of the quaternary compound (CH,) CF,PJ +I. This i s then suggested to react i n either L 3 3 3 of the following ways. (a) By d i s s o c i a t i o n to the phosphine (CH^JgCF^P and methyl iodide. The methyl iodide so formed reacts further with trimethylphosphine to give tetramethyl-phosphonium iodide. ( C H 3 ) 3 P +- CF 3 I > [ ( C H 3 ) 3 C F 3 P ) V > ( C H 3 ) 2 C F 3 P + C H I CH_I + (CH ) P > [ ( C H ) P]V 3 3 3 L 3 4 J (b) By nucleophilic attack of the trimethylphosphine on a methyl group of the quaternary compound { ( C H 3 ) 3 C F 3 P ] + I . (CH 3) 3P: CH. 3-P-CF 3 ^Xm.^)^ + {Wj^^! CH3 CH3 - 11 -F i r s t of a l l , i t may be pointed out that the phos-phonium s a l t {(CH^^CF^pj + I i s quite stable and has been found to be unaffected by trifluoroiodomethane and trimethyl-phosphine. In view of i t s high s t a b i l i t y towards these re-agents, i t i s surprising that i t i s not found i n the reaction products. A simple mechanism for t h i s reaction would be that of an acid-base type. That trimethylphosphine i s quite basic i s shown by i t s immediate reaction with boron t r i f l u o r i d e and (<o) s i m i l a r compounds. The o v e r a l l reaction appears to be a simple metathetical step. (CH,)_P + CF I » (CH ) CP P + CH I (4) •> J 3 3.2 3 3 However, such a reaction must involve the formation of some type of intermediate, probably from the nucleophilic attack of trimethylphosphine on the iodine atom of t r i f l u o r o -iodomethane. The electron withdrawing tendency of the t r i -fluoromethyl group gives a p o s i t i v e character to iodine and makes i t susceptible to nucleophilic attack. Such attack on iodine may give the intermediate? P^cO-I'^'^-.PCCH^)^—>jj(CH 3) P l f c F ^ } (5) This intermediate i s vulnerable to further nucleophilic attack and may lead to the formation of a second intermediates (CH 3) 3P: | C H 3 ) 3 P I ] + O F " ] — ^ C H ^ P l j ^ C H ^ P C p J " (6) The formation of such compounds has been proposed by other workers i n the study of the e l e c t r i c a l conductance of the - 12 -(58 59) phosphoranes ' • In the present case the attack may b e - l i k e l y because of the negative nature of the t r i f l u o r o -methyl group. The next step w i l l be the formation of a stable pentavalent compound. This may be done by (1) the transfer of a methyl group from anion to cation which would give J( CH3 ) 3 P I J + J( C H 3 ) 2 P'— C P J " » CH^) Pj * i" -f- (CH^) 2CF^P (7) or (2) the transfer of the iodine from the cation to the anion which would give ^ ) 3 P j f ^ C ^ P C P 3 ] " - > [ ( C H ^ C F ^ P J V + C C H ^ P (8) However, since there i s no evidence for the occurrence of the compound j ( C H 3 ) 3 C F 3 P J + I as a reaction product, i t i s clear that (1) i s the favoured route. This mechanism i s supported by the observation (1) that trimethylamine and trifluoroiodomethane give fluoroform and tetramethylammonium iodide and no dim e t h y l t r i f l u o r o -methylamine i s obtained. The small size of nitrogen allows easy access of the CF 3 group to the protons i n the anion according to the above mechanism. This would give fluoro-form and tetramethylammonium iodide according to route (1). Added support also comes from the observation (7) noted above. This may be represented by the following scheme: |(CH3 ) 3 CF 3PJ + 1 " :P (CH3 ) 3 > GH3) 3 C P 3 P J + 1 ( ) ^ P l j ~ I > J ( C H 3 ) 4 P J + l " + (GH 3) 2CF 3P ) (9) - 13 -I t should also be pointed out that further solvo-l y t i c action of. trifluoroiodomethane with the intermediate [ ( C H ^ P l ] * £ ( C H J ) J P C F J J ~ would lead to the formation of the quaternary compound |( C H 3 ^ ( C F 3 ) g P j + I which has been found i n the present i n v e s t i g a t i o n . This may be represented as follows: | [ ( C H 3 ) 3 P l J + C H 3 ) 3 C F 3 P j " | ^ j( G H 3 ) 4PJV-f-j( C H 3 ) G ( C F 3 ) 2 P J V (10) The second quaternary compound being a derivative of a phos-phine which i s a much weaker base than trimethylphosphine may then be extensively dissociated at room temperature. [ ( C H 3 ) 2 ( C F 3 ) 2 P J + I " ^ = ^ ( C H 3 ) 2 C F 3 P + C F 3 I (11) Such d i s s o c i a t i o n would explain the ready sublimation of the white s o l i d (CH,.)„(CF,).PI i n vacuo. The above considerations lead to the conclusion that the formation of two quaternary compounds £ ( C H 3 ) ^ p j l and £ ( C H 3 ) 2 ( C F ^ ^ P ] I would consume a large amount of the o r i g i n a l phosphine ( C H 3 ) 3 P and hence the y i e l d of the desired phos-phine ( C H 3 ) 2 C F 3 P would not be high. Methylbistrifluoromethylphosphine: This phosphine i s prepared by heating tristrifluoromethylphosphine with methyl iodide to 240 . A y i e l d of 54% i s reported v but i t can be s l i g h t l y improved by using a small excess of methyl iodide. Although t h i s excess tends to react with the phos-phine ' C H 3 ( C F 3 ) 2 P forming the quaternary compound | ( C H 3 ) 3 C F 3 P J + I - 14 -and trifluoroiodomethane, i t does insure complete reaction of the tristrifluoromethylphosphine, thus increasing the y i e l d to 60% and at the same time avoiding the cumbersome separa-t i o n of the phosphines with close b o i l i n g points. o Below 235 tristrifluoromethylphosphine and methyl o iodide react only slowly, but heating to 235 or above, pro-duces trace amounts of free'iodine and a small amount of a white s o l i d which has been i d e n t i f i e d as the phosphonium com-pound I J C H ^ ^ C P ^ P J I . Some phosphorus trliodide and a black carbonaceous material are also obtained, the quantity of these two being considerably increased when the reaction i s performed at higher temperature or for a longer period of time. The carbonaceous material contains no C - P bonds, sug-gesting that i t possibly i s the r e s u l t of pyrolysis of hydrocarbons. Methylbistrifluoromethylphosphine has also been prepared by the reaction of methyl iodide and t e t r a k i s t r i -0 (7) fluoromethyldiphosphine by heating the two at 150 . I t can also be prepared by heating tristrifluoromethylphosphine (2) o and methyl mercuric iodide at 220 . The mechanism proposed by the previous authors involves the i n i t i a l formation of the quaternary compound jcH^CCF^J^pj I, which then undergoes pyrolysis to give methylbistrifluoromethylphosphine and trifluoroiodomethane. However, since this hypothetical compound has mixed ligands, i t would be expected to give a mixture of products (74). ^ n - 15 -this case, equal amounts of methylbistrifluoromethylphosphine and dimethyltrifluoromethylphosphine together with a mixture of trifluoroiodomethane and methyl iodide would be obtained. But, when equimolar quantities of the reactants are taken, there i s no evidence of the formation of dimet h y l t r i f l u o r o -methylphosphine. On these considerations therefore the pos-tulated mechanism i s a l i t t l e doubtful. The high temperature at which this reaction i s performed and the fact that methylbistrifluoromethylphosphine can also be prepared by heating (CP^J^P and methyl mercuric iodide suggest that some consideration must be given to a free r a d i c a l mechanism. The homolytic f i s s i o n of the C - I (8) bond i n methyl iodide gives methyl radicals which would react with tristrifluoromethylphosphine. Further i n t e r a c t i o n of the methyl and trifluoromethyl radicals would produce fluor o -form and polymeric carbonaceous material. Free iodine would be formed i n the course of this reaction which would react with the phosphines to give phosphorus iodide. The reaction . may be described by the following scheme. •CK3I > - C H 3 + I -(CF 3) 3P+-CH 3 > CH 3(CF 3) 2P-(- - C F 3 (12) • C P 3 4 - C H 3 I > C F 3 C H 3 -h I- (13) •CH3+ C P 3 C H 3 = > C F 3 H + - C 2 H 5 (14) CH3I-f- > higher hydrocarbons I - (15) - 16 -A comparison of bond energies shows that the G-C bond i n CF^CH^ i s weaker than the C-H bond i n CF^-H (90 and 102 kcals respectively) ^43) a o that; by a r a d i c a l attack mechanism, equation (14) would proceed favourably. Also since the trifluoromethyl r a d i c a l can abstract hydrogen from methane the l a t t e r would not be found among the products. This mechanism i s borne out from the comparison with an analogous reaction of t r i s t r i f l u o r o m e t h y l a r s i n e and methyl (75) iodide. The reaction has been carried out by heating and also by i r r a d i a t i n g the mixture with u l t r a v i o l e t l i g h t . The products obtained are analogous to those obtained for the phosphine under consideration. Tristrifluoromethylphosphine: The reaction of red or white phosphorus with trifluoroiodomethane t r i s t r i -fluoromethylphosphine, bistrifluoromethyliodophosphine and (4,9) trifluoromethyldiiodophosphine . The y i e l d of the phos-phines depends on the r a t i o of the reactants and also on the nature of phosphorus (white or red). A few observations are relevant i n th i s connection: (1) Hexafluoroethane or higher fluorocarbons are not usually formed. But, i t has been found that hexafluoroethane and phosphorus t r i f l u o r i d e ( s i l i c o n t e t f a f l u o r i d e i s also present i f the reaction i s carried out i n a glass tube) are formed when the temperature of the reaction i s very high (^ 270 ) or when the quantity of phosphorus i s considerably increased. Higher temperatures - 17 -also give tetrafluoromethane. (2) The presence of iodine either free or i n the form of trifluoroiodomethane appears to be essential f o r the reaction. Thus s i l v e r t r i f l u o r o a c e t a t e o and red phosphorus do not react at 250 , except to produce t r i f l u o r o a c e t i c anhydride; but i n the presence of iodine, trifluoromethyl-iodo-phosphines are re a d i l y formed. (3) Re-action occurs smoothly between trifluoroiodomethane and a mixture of phosphorus and phosphorus t r i i o d i d e . (4) The reaction of tristrifluoromethylphosphine with iodine and the disproportionation of the iodophosphines gives a mixture of the phosphine, iodophosphines, phosphorus t r i i o d i d e and t r i -fluoroiodomethane . These facts suggest that the reaction requires the i n i t i a l formation of a phosphorus iodide. The most e a s i l y formed iodide of phosphorus i s the phosphorus d i i o d i d e . ( P l g ) ^ ^ A k i n e t i c study of the reaction between phosphorus and iodine shows the phosphorus diiodide to be formed through the follow-ing steps:^76) 4-1 >P l _ P I >P I f P P I 4-P > P I 4- P 4 2 4 2 4 2 2 2 2 2 2 4 4 2 2 P 2 4 - I 2 - ^ P 2 I 2 P 2I 24- I 2 - ^ P 2 I 4 2 P 2 I 2 — » P 2 I 4 + P 2 The diiodide ( ? 2 I ^ ) 3 0 formed i s possibly the reactive species i n the reaction under consideration. The attack on the re-active P-P bond by trifluoroiodomethane would give t r i f l u o r o -methyl-diiodophosphine and phosphorus t r i i o d i d e . - IS -P4 4 - 4 I 2 ~ * 2 ^ ~ P - t . ( 1 6 ) I. J-P P -h CP I \ CF PI -r- PI (17) i \ 3 f 3 2^ 3 Trifluororaethyldiiodophosphine appears to be the main reac-t i o n intermediate i n the formation of the phosphine (CF^^P, as i s evidenced by the small quantity of the former i n the products and also by the reactions carried out at lower temperatures Q200 ) when only the iodophosphines are the major products. Further reaction of trifluoroiodomethane with trifluoromethyldiiodophosphine would form an i n t e r -mediate (CF-) PI which has not been isolat e d but whose 0 d. 3 chlorine analogue (CF,)_PC1„ i s known. The reaction of this J d 3 intermediate with a further quantity of phosphorus would give bistrifluoromethyliodophosphine and phosphorus diiod i d e . —P 2CP3PI2-H 2CP 5I > [ 2 ( C P 3 ) 2 P I 3 ] 2 ( C F 3 ) 2 P I + ( P I 2 ) 2 (18) Trifluoromethyldiiodophosphine may also react further with phosphorus to give tristrifluoromethylphosphine and phosphorus diiodide. 3(CF,)PI_-f- P >(CF_)P +- 3PI 0 (19) 3 2 3 3 2 The reaction of bistrifluoromethyliodophosphine with CF 3I would give another unstable pentavalent compound ( C P 3 ) 3 P I 2 which again has not been is o l a t e d but might form as a reaction intermediate. The reaction of this interme-diate with phosphorus would give tristrifluoromethylphosphine* 2 ( CF 3 ) 2PI + 2CF 3I—-> 2 [( CF 3 ) 3 P I 2 ] _ Z ! i _ > 2 (CF 3 ) ^ + ( P ^ ) g (20) 1 - 19 -Bistrifluoromethyliodophosphine may also react with phosphorus (as i s the case with recycling) to give t r i s t r i f l u o r o m e t h y l -phosphine and trifluoromethyldiiodophosphine. 2(CP 3) 2PI-hP 4(CP 3) P + CP P I 2 (21) The above consideration shows that the sets of re-actions (16) to (21) are a l l occurring i n equilibrium with one another and may be represented as: I 2P — P I 2 + CP 3I C P 3 P I 2 ^ e ( CP 3 ) 2 F I ^ = i (CP 3) P-f-12 (22 ) I t i s also l i k e l y that only disproportionation re-actions are occurring and giving r i s e to the above sets of e q u i l i b r i a . Such reactions would involve r a d i c a l intermediates. I t i s observed that heating of the iodophosphines individu-a l l y gives the same mixture of products. Hence for the f o r -mation of the r a d i c a l intermediate, i t i s possible that the i n i t i a l reaction involves the breaking of the P-I bond (P-C being stronger than P-I): CP„PI0 » CP^PI + I- (25) 3 2 3 Since ordinary l i g h t can l i b e r a t e free iodine from the iodo-phosphines, t h i s formulation may be correct. The reaction of iodine would then be two-fold: (1) to react with phos-phorus to form the phosphorus iodides and (2) to react with trifluoromethyl groups to give trifluoroiodomethane. Prom (1) the trifluoromethyl radical(s);:; may be obtained which might s t a r t the above series of reactions. - 20 -CF_PI 0+ I »-CF„+-(PI0)0 or PI (24a) 3 2 3 2 2 3 CP.PL+ I >CFI-t-'PI (24b) 3 2 3 2 These might be followed by the e q u i l i b r i a represented by (22) Such e q u i l i b r i a have been noted i n the case of f u r y l ^ " ^ phenyl and trifluoromethyl arsenicals. In general mixed t r i h a l i d e s of phosphorus decompose to give i t s simple t r i h a l i d e s . As concluded i n the case of phenyl ar-(12) senicals, i t i s l i k e l y that e q u i l i b r i a are attained by opposing bimolecular processes. However, only detailed equilibrium studies would establish the true mechanism. - 21 -C H A P T E R I I PREPARATION OP PHENYL-TRIFLUOROMETHYL-PHOSPHINES The phenyl-trifluoromethyl-phosphines have been prepared by reacting trifluoroiodomethane with phenyl phosphines having a P-P bond and one or two phenyl groups attached to each phosphorus atom; v i z . , tetraphenyl-diphosphine ;^^-p—p 0 -> and tetraphenylcyclotetra-C^ -Hc Ji phosphine b P—P 5 5 • v I I ' ^ P - P 6 5 6 5 The former gives diphenyl t r i f luoromethylphosphine (C.-H,- )0CP_P 15 D <L 3 and the l a t t e r gives phenylbistrifluoromethylphosphine. Phenylb i s trifluoromethylpho sphine Tetraphenylcyclotetraphosphine has been known f o r a long time but i t s reactions have not been f u l l y studied. - 22 -The c y c l i c structure has been established only r e c e n t l y ^ ^ , and u n t i l 1958 i t was known as phosphobenzene.(or phosphoro-(15) benzene) CgH 5P=PCgH 5 . ' Tetraphenylcyclotetraphosphine i s prepared "from phenyldichlorophosphine and phenylphosphine: 2 C 6H 5PC1 2 + 2 C 6H 5PH 2 ^ C ^ P ) +4HC1 , ' ( 2 5 ) Phenyldichlorophosphine i s prepared by the Friedel-Crafts reaction. By re f l u x i n g an excess of phosphorus t r i c h l o r i d e with a mixture of benzene and aluminium chloride and treating the mixture with phosphorus oxychloride, a satisfactory y i e l d of phenyldichlorophosphine i s obtained. Phenylphosphine os-(C,H PH0) may be obtained by the reduction of phenylph o 5 <- (20 21) phonous acid * , obtained by the hydrolysis of phenyl-dichlorophosphine. This i s not a very s a t i s f a c t o r y method (22) since the y i e l d i s often poor .... The method i n current / Q"Z OA \ use involves the reduction of phenyldichlorophosphine with a suspension of l i t h i u m aluminium hydride i n ether. The reaction of phenylphosphine and phenyldichlorophosphine has been carried out by re f l u x i n g the ether solution of the rea.ctants. Tetraphenylcyclotetraphosphine i s deposited o after some time as a white s o l i d melting at 148 - 150 . Trifluoroiodomethane does not dissolve tetraphenyl-cyclotetraphosphine at room temperature and there i s no re-action u n t i l the tetraphosphine has melted. The s o l i d d i s -- 23 -solves at this temperature (150 ) and the reaction occurs slowly. Unreacted phosphine c r y s t a l l i z e s when this solution i s cooled. Heating to 185 gives an i n v o l a t i l e mixture of phenylbistrifluoromethylphosphine, phenyltrifluoromethyl-iodophosphine and phenyldiiodophosphine. The v o l a t i l e pro-ducts, besides trifluoroiodomethane, consist of small amounts of fluoroform, hexafluoroethane, and free iodine which always seems to be present. The above reaction also occurs on i r r a d i a t i o n with u l t r a v i o l e t l i g h t . The process i s slow as might be expected from reactions between heterogeneous phases. However, the products are the same as obtained by the heating of the re-actants. The reaction most probably depends on the r e a c t i v i t y of the P-P bond. I t may be worthwhile considering b r i e f l y the r e a c t i v i t y of the metal-metal or metalloid-metalloid bond (M-M bond). The M-M bond i s l i m i t e d to elements con-taining less than seven electrons i n their'valence s h e l l . The other elements which come close to carbon i n forming such bonds are s i l i c o n , phosphorus and sulphur. The s t a b i l i t y of the M-M bond decreases with i n -creasing atomic number of M, for a series of elements i n the same periodic group. Thus the diplumbanes are the least stable i n group IV, while ethane i s the most stable. S i m i l a r l y dibismuthine i s unknown whereas phosphorus forms the - 2 4 -d i - , poly- and cyclopoly-phosphines, and some oxyacids are also known to have long P-P chains. These differences can be related to the bond energies which also decrease with i n -creasing atomic number. The cleavage of the M-M bond i s much easier than that of the C-G bond. The difference may be due to the following factors: (1) The atoms are much larger than car-bon. (2) They are .less electronegative. (3) They are capable of a much higher coordination number. (4) The bond energy of the M-M linkage i s less than that of C-C. In fact the M-M bond energy i s lower than f o r most M-X bonds, as (27 28) shown by the values reported i n the l i t e r a t u r e ' . This indicates that i n the event of an attack by X-Y, the bonds M-X and M-Y would be formed p r e f e r e n t i a l l y . Thus the M-M bond is a p o t e n t i a l point of attack by a reactive species. The r e a c t i v i t y of the M-M bond must be l a r g e l y due to the presence of an appreciable amount of pi-bonding. Such pi-bonding i s possible i n M-M bonds, for elements other than those i n the f i r s t periodic row, since use can be made (33) of available higher o r b i t a l s . The attack by a reactive species X-Y at the M-M bond can then r e a d i l y lead to the f o r -mation of a fourth single bond on each M atom. Such a qua-druply bonded state i s very common i n phosphorus compounds ^ Subsequent rearrangement of this intermediate and cleavage of the remaining M-M single bond leads to the formation of the M-X and M-Y products. The following consideration bears out the above statement, Tetraraethyldiarsine reacts with halogen to give dimethylhaloarsine and with a l k y l halides to give t e t r a -(32) methylarsonium iodide and dimethylhaloarsine . A compari-son of bond energies from the following table indicates that the As-As bond i s much weaker and would be p r e f e r e n t i a l l y attacked i n order to form the more stable As-halide and As-C bonds, As-As As-F As-Cl As-Br As-I As-H As-C 34.5 111.9 73.0 57.6 42.6 58.6 57 The tetraphenyldiphosphine i s s i m i l a r l y known to react r e a d i l y with hydrochloric acid to give diphenylphosphine and diphenyl-chlorophosphine. Here again a comparison of bond energies shows that the P-H and P-Cl bonds are stronger than the P-P bonds, so that the l a t t e r would be p r e f e r e n t i a l l y cleaved i n order to form more stable bonds. P-P P-F P-Cl P-Br P-I P-H P-C 50.0 114 78.5 63.7 49 76.4 62 The mechanism of such an attack may be explained (35) by the so-called four-centre type reaction , the best ex-ample of which i s the reaction of hydrogen iodide to give hy-drogen and iodine. H H H H H — H I 4- I I \ -+- (26) i i i i i — i - 2 6 -Thus there i s only a change of configuration of the atoms of the reactants to give the products and no electron transfer or ion formation i s involved. Such a mechanism may we l l occur i n the above reaction of tetramethyldiarsine. .CH \ CH, 'As—As 4- S CHX — I j OIL (CH 3) 2As As(CH 3) 2 I CH; (CH ) As 5.3 (CH_) A s l 3 2 The trimethylarsine so formed would react further with methyl iodide and would form tetramethylarsonium iodide. The re-action of tetraphenyldiphosphine with hydrochloric acid may be represented s i m i l a r l y : ( C 6 H 5 ) 2 P - P ( C 6 H 5 ) 2 _ H —-CI < C 6 V 2 ? f ( ° 6 H 5 l H CI =±(C6H5)2PC1 +(C 6H 5) 2PH The above discussion of the cleavage of the M-M bond may now be applied to the reaction of t r i f l u o r o i o d o -methane and tetraphenylcyclotetraphosphine. Two mechanisms are possible: (1) The reaction may proceed through a four-centre type mechanism i n the following way: C/-H — P—P—C^-Hj- CF, C 6 H 5 - P - P - C 6 H 5 I y C 6 H 5 C 6 H 5 - [ ~ f 9 * 3 C^HC P—P i 5 \ C 6 H 5 /°6 H5 C 6H 5^P-P-GF 3 C 6 H 5 - P - P : (27) - 2? -/°6E5 6 5 C 6 H 5 ~ P ^ P s C F 3 — I ° 6H 5 C 6 H 5 - B - B C 5H 5-P--P N , C 6 H 5 CF, CF-4--I C.Hp-3 6 j C 6H 5 - P - P ° 6 H 5 - I CF. , ° 6 H 5 CF, (28) + C 6 H 5 ~ P I 2 C 6H 5 C 6 H 5 - P - P - P ^ CF 3 •+-CF3-I .CF, C 6 H 5 / C 6 H 5 CF, CF—-I C F 3 C 6 H 5 ° 6 H 5 CF. P— P X ^CF3 (29) -f C 6H 5CF 3I C 6 H 5 X / / C 6 H 5 CF, P-P CF, + CF 3-I C 6 H 5 CF' \ / 6 5 p P \ CF. C F 3 - I C 6H 5(CF 3) 2P -» 4-C 6H 5CF 3PI (3Q) Phenyltrifluoromethyliodophosphine disproportionates incompletely under the conditions of the experiment giving phenylbistrifluoromethylphosphine, phenyldiiodophosphine and some phenyltrifluoromethyliodophosphine. I t may be thought l i k e l y that the diphosphine (C^H^CF^^ would be present* Whether th i s or the triphosphine i s present has not been deter-mined; but a polymeric substance i s obtained when the iodophos-phine C5H5CF3PI i s treated with mercury and a large excess of - 28 -trifluoroiodomethane. This requires further i n v e s t i g a t i o n . (2) The reaction has been shown to occur on u l t r a -v i o l e t i r r a d i a t i o n of the reactants. The reaction may there-fore be thought of as proceeding through a free r a d i c a l mechanism. The simultaneous breaking of the four P - P bonds i s not energetically possible and hence the following scheme i s suggested. CF — I h v > -CF H- I-3 3 CJK - P - P — C H +- -GF -+- I > C H _ - P — P . D 5 6 5 , ( 6 5 3 6 5 V C F C J L - - P - P - C . r L . ( M L . - P - P - I 3 6 5 6 5 6 5 ^ c H ( 3 1 ) b 5 \ H 5 C6?5 I - P - P - P - P — CF„ -t- CF I —*C_.H - P - P - C X + C H (CP ) P+C H P I / / 3 3 6 5 • • o 5 6 5 3.2 6 5 2 C H C H 6 5 6 5 • * P P O P , I C H (CF L P + - C H PI -r-/ / 3 6 5 3 2 6 5 2 0 H _ C H (32) >• 6 5 6 5 The d i r a d i c a l C J i P — P C H_ would either recombine 6 5* - 6 5 to form tetraphenylcyclotetraphosphine or would react further with trifluoroiodomethane to give the phosphine and iodo-phosphine. This mechanism does not require the formation of the diphosphine ( C , H CP P) as i n equation (30), and also gives the same approximate r a t i o of phenylbistrifluoromethylphos-phine and phenyltrifluoromethyliodophosphine as the experi-mental value of 2:1. The r a t i o would be of this order i f the experimentally observed disproportionation of p h e n y l t r i f l u o r o -methyliodophosphine i s taken into consideration. Diphenyltrifluoromethylphosphine There are two possible methods f o r the preparation of this phosphine: (1) Reaction involving the cleavage of P-P bond with each phosphorus having two phenyl groups attached to i t : i . e . , reaction with tetraphenyldiphosphine. (2) Ex-change reaction involving the exchange of a phenyl or any other group f o r the CF^ group. Such an exchange takes place between triphenylphosphine or diphenylchlorophosphine with CF^I. I t may be pointed out that an analogous reaction to prepare phenylbistrifluoromethylphosphine i s not successful. No reaction takes place between iodobenzene and t r i s t r i f l u o r o -methylphosphine. In view of t h i s , the formation of diphenyltrifluoromethylphosphine from triphenylphosphine, although only i n very low y i e l d , i s i n t e r e s t i n g . An a l t e r -native exchange reaction i s that between diphenylchloro-phosphine and trifluoroiodomethane, where the chlorine atom i s exchanged for a trifluoromethyl group. Since a convenient method f o r the preparation of diphenylchlorophosphine i s now available, the phosphine (CgH^^CF^P has been prepared l a r g e l y by t h i s method. - 30 -Diphenylchlorophosphine: This compound i s prepared by a v a r i e t y of methods, but they a l l give very low y i e l d . (37) ° Pyrolysis of phenyldichlorophosphine at 300 for f i v e days gave a 4% y i e l d of the desired product (CgH^gPCl. The reac-t i o n i s slow and the process has to be repeated a number of times. In th i s connection i t i s s i g n i f i c a n t to note that triphenylphosphine and phosphorus t r i c h l o r i d e do not dispro-portionate to give diphenylchlorophosphine, but rearrange-(38) ment does occur with the corresponding arsenic compounds . The reaction of triphenylphosphine with phosphorus t r i i o d i d e also does not y i e l d the corresponding diphenyl-product. The reaction of phenyldichlorophosphine with l i t h i u m phenyl (using molar quantities) does not give diphenylchlorophos-phine, but produces triphenylphosphine instead. Diphenylchlorophosphine i s obtained i n good y i e l d (39) from diphenylphosphinodithioic acid . The acid i s prepared by r e f l u x i n g a mixture of phosphorus pentasulphide, benzene and aluminium chloride. The hydrolysis of the product so obtained gives diphenylphosphinodithioic acid, which separates into the benzene layer as a green solution. Chlorine i s passed through t h i s green solution when diphenyltrichloro-phosphorane separates as orange yellow c r y s t a l s . Red phos-(40) phorus i s added. to the s o l i d c r y s t a l l i n e product and slowly heated to d i s t i l off the solvent and phosphorus t r i c h l o r i d e . Vacuum d i s t i l l a t i o n of the residual mixture gives diphenyl-- 31 -chlorophosphine of high p u r i t y i n excellent y i e l d . I f the heating i n the l a s t stage i s carried out too vigorously, the phosphorane disproportionates to give phenyldichlorophosphine and hence heating has to be done only slowly, so that the phosphorane does react with phosphorus. The reactions may be represented as follows: A1C1_ V l O + C 6 H 6 2^ ( 0 6H 5) 2PSSH (33) (C H ) PSSH4-3CL > (C H ) PCL+S G14-HC1 (34) 6 5 2 2 65_2 3 2 3(C CH LHC14-2P > 3(C HJPC1-T-2PC1 (35) 6 5 2 3 6 5 2 3 Diphenylphosphine: This compound i s prepared by (41) the reduction of diphenylchlorophosphine with l i t h i u m metal . (42) The previously described method involves the treatment of diphenylchlorophosphine with zinc and subsequent hydrolysis of the product with water. This gives a low y i e l d of the phosphine (C-H ) PH. The effectiveness of l i t h i u m , compared 6 5 2 with zinc, i s probably because the reaction with l i t h i u m occurs at room temperature but that with zinc has to be carried out at elevated temperatures. Further, the hydrolysis of the more polarised L i - P bond would occur more r e a d i l y than that of the Zn-P bond. Tetraphenyldiphosphine: This phosphine i s prepared by the d i r e c t reaction of diphenylphosphine and diphenyl-(41,42) chlorophosphine . - 32 -( C . H K P H - M C H ) PCI 9- (C H ) P - P ( C H ) + HC1 ( 3 6 ) 6 5 2 6 5 2 6 5 2 6 5 2 The reaction i s preferably carried out i n a high b o i l i n g s o l -vent, since r e f l u x i n g the mixture of reactants seems to be necessary to obtain a better y i e l d of the pure product. Tetraphenyldiphosphine i s obtained as a white c r y s t a l l i n e o s o l i d melting at 1 2 0 . The thermal decomposition of tetraphenylcyclotetra-(14*15) phosphine i s reported to give tetraphenyldiphosphine, but i n both reports, the l a t t e r has not been is o l a t e d and only i n d i r e c t evidence of i t s formation i s c i t e d . I t has (43) recently been reported that phenyldichlorophosphine reacts with l i t h i u m metal to give the d i l i t h i u m adduct C ^ R - P — P C J E L , o 5 | | 6 5 L i L i the intermediate product being tetraphenylcyclotetraphosphine. The l a s t compound also gives a disodiura adduct(•'•^^which has (23) been used for the preparation of diphenyldimethyldiphosphine. In the present i n v e s t i g a t i o n t h i s method has been studied i n an attempt to obtain the diphosphine (C L ) . P - P ( C H ) , by 6 5 2 6 5 2 treating the sodium adduct with iodobenzene but no p o s i t i v e results have been obtained. The d e t a i l s of the procedure have been described i n the experimental section. Interaction of trifluoroiodomethane and tetraphenyl- diphosphine : Trifluoroiodomethane reacts with the diphosphine only at elevated temperatures. Like tetraphenylcyclotetra-phosphine, the diphosphine i s also insoluble i n t r i f l u o r o i o d o -methane at room temperature and no reaction occurs below the melting point of the diphosphine. The reaction i s slow even o above this temperature u n t i l about 185 • Heating at t h i s temperature produces diphenyltrifluoromethylphosphine and diphenyliodophosphine. The products are i n v o l a t i l e l i q u i d s which can be separated from one another by extraction with petroleum ether which dissolves diphenyltrifluoromethylphos-phine only and leaves the diphenyliodophosphine as a thick red l i q u i d . Among the v o l a t i l e products of reaction are small amounts of fluoroform and free iodine, besides un-reacted trifluoroiodomethane. The reaction has also been performed by i r r a d i a t i n g the two reactants with u l t r a v i o l e t l i g h t . The reaction i s slow but the products are the same as obtained above. The reaction may be represented by equation (37 ) . ( C 6 H 5 ) 2 P - P ( C 6 H 5 ) 2 " + " C F 3 I ~ > ( C 6 H 5 ) 2 C P 3 P 4 " ( C 6 V 2 P I ( 3 ? ) The mechanism of the reaction appears to be a simple four-centre type, as discussed previously. W z * r P ( 0 6 H 5 , 2 ' > CF^-I < C 6 H 5 ) 2 ; P f ( C 6 H 5 ) 3 (C 6H 5) 2CF 5P (C 6H 5) 2PI (37a The reaction may also proceed by a free r a d i c a l mechanism. The energy of u l t r a v i o l e t r a d i a t i o n i s much larger than the P-P bond energy, so the i n i t i a l step i n the reaction may be the breaking of the P-P bond to give the radicals (C,rHt-)0P*. b 5 <~ - 34 -Trifluoroiodomethane also undergoes homolytic f i s s i o n of the C-I bond under these conditions. The reaction would then proceed by the intercombination of the radicals as shown by the following scheme. CP,— I ^ v >.CF,+ I-3 3 6 5 2 3 6 5 2 3 6 5 2 A comparison of bond energies shows why the t r i -fluoromethyl r a d i c a l would combine with phosphorus rather than recombine with iodine. The same reason may explain why the phosphorus r a d i c a l (CJi_ )0P« does not recombine to give 0 5 the P-P bond. P - P P - C P - I C - I 50 62 48 55 Thus the P-C bond energy being higher than P-P, diphenyl-trifluoromethylphosphine would be formed p r e f e r e n t i a l l y and the remaining r a d i c a l s (CgH^JgP-and I -would form diphenyl-iodophosphine. Interaction of trifluoroiodomethane and triphenyl- phosphine: As mentioned e a r l i e r diphenyltrifluoromethyl-phosphine can also be prepared by the reaction of t r i f l u o r o -iodomethane and triphenylphosphine. The reactants mix re a d i l y at room temperature without reacting. This solution - 35 -o becomes yellow on gradual heating and, on heating to 185 for four hours, diphenyl t r i f luoromethylphosphine i n 20%' y i e l d , diphenyliodophosphine and some trifluoromethylbenzene are pro-duced. The l a s t named compound i s separated i n vacuum and the phosphine (CgHp-^CF^P i s extracted with petroleum ether. o At higher temperatures: e.g., 215 * only diphenyliodophosphine and trifluoromethylbenzene are obtained. The reaction most probably proceeds by a free r a d i -c a l mechanism. The reaction may be i n i t i a t e d by the attack of the CF_ r a d i c a l on one of the P-phenyl bonds and may then 3 proceed as shown by equations 38 - 3 8 b . CF 3 — I A vCF^ •+• I-( C 6 H 5 ) 2 P — C 6H 5+CF 5 > (C 6H 5) 2CF 5P4- -CgH (38) •C6H54-CF3 I ^C 6H 5CF 3 + I- (38ai> ( C 6 H 5 ) 2 P — C 6H 54- I > (C 6H 5) 2PI + .C6H5 ( 3 8 b ) A C-C bond being stronger than a P-C bond, r a d i c a l attack would give trifluoromethylbenzene and reactions 38a and 38b would be favoured. This may be the reason why the y i e l d of' diphenyltrifluoromethylphosphine i s p a r t i c u l a r l y low at higher temperatures. The other possible mechanism would be the formation of the quaternary compound (C.H_)„CF P + I as an intermediate. I 6 5 3 3_j This does not seem very l i k e l y i n view of the products which have been obtained. The formation of iodobenzene which would be very l i k e l y according to this mechanism has not been ob-served. Moreover, i t does not explain the formation of t r i -fluoromethylbenzene. The formation of diphenyliodobenzene alone and no (CgH^^CF^P at higher temperatures i s also not explained by this mechanism. Interaction of trifluoroiodomethane and diphenylchlo- rophosphine: The reaction of diphenylchlorophosphine with trifluoroiodomethane also produces diphenyltrifluoromethyl-phosphine. Diphenylchlorophosphine i s soluble i n t r i f l o r o -iodomethane but reaction does not occur unless the reactants are heated to a high temperature. In these investigations, o the reaction was conducted at 205 for 12 hours. The reaction i s slow, f o r at the end of t h i s period some diphenylchloro-phosphine i s recovered. The reaction occurs i n an approxi-mate r a t i o of 1:1 of the reactants, the major products being diphenyltrifluoromethylphosphine, diphenyliodophosphine and phenyltrifluoromethylchlorophosphine. Reasonable amounts of trifluorochloromethane and trifluoromethylbenzene and traces of hexafluoroethane and fluoroform are also obtained. The required phosphine i s separated by extracting : with petroleum ether, but f i n a l p u r i f i c a t i o n by vacuum d i s t i l l a t i o n i s not s a t i s f a c t o r y and, i n the present investigation, has been effected by vapor phase chromatography. - 37 -The formation of trifluorochloromethane has been found to be suppressed by using a large excess of t r i f l u o r o -iodomethane. Longer heating gives lower y i e l d of diphenyl-trifluoromethylphosphine and^increase i n the y i e l d of phenyltrifluoromethylchlorophosphine and trifluoromethyl-benzene. The reaction probably proceeds by a free r a d i c a l mechanism. Of the three ligands attached to phosphorus i n diphenylchlorophosphine, the P-Cl bond, because of i t s higher p o l a r i t y , would be the centre of attack by a t r i f l u o r o -methyl r a d i c a l . The reaction may then proceed by the follow-ing scheme. CP^—I ^ vCF^-f- I-(C.H_)_P— Cl-h«CF_ MC^H_) 0P —CF,+ C1- (39) 6 5 2 3 6 5 2 3 CI- -+- CF^I - - ^ CF^Cl -h !• (39a) (C 6H 5) 2PC14-CF 3 _ > C6H5'CP3+C6H5PC1 (40) CgH 5PCl -+-CP31 — > CgH5 (CP 3 ) PCI + I • (40a) (CgH 5) 2PCH-CF 3I -> CP 3CH-(CgH 5) 2PI (41) The l a s t step (41) i s a four-centre type reaction and possibly i s much faster than the other possible reactions, hence the observation that the diphenyliodophosphine i s always found i n f a i r l y large amounts. Prolonged heating might also involve the d i s s o c i a t i o n of trifluorochloromethane and hence suppress the formation of the phosphine (CgHc) 2CF 3P by equation (39)« - 38 -I t i s also possible that the reaction proceeds through the formation of an intermediate quinquevalent compound. The intermediate, having mixed ligands, would dissociate i n more than one way. (C 6H 5) 2PC1 H- CFjI CI ( C 6 H 5 ) 2 P — I T F 3 CI I ^ 1 C 6 H 5 CF, C F 3 I (CgHgJgCF^P + CFjCl + Ig A A * (C 6H 5)CF 3PCl-f C 6 H 5 C ^ I 2 ^ ( C 6 H 5 ) 2 P I CF3C1 (41) (42) (43) I t i s d i f f i c u l t to say which of these reactions would be favoured. However, experimental observations show that reaction (43) occurs under a l l conditions, whereas reactions (41) and (42) depend on p a r t i c u l a r experimental conditions. In these reactions trifluorochloromethane also enters into reaction, and hence the quantity obtained i s r e l a t i v e l y small. " ! - 39 -C H A P T E R I I I  PROPERTIES OF PHENYL-TRIFLUOROMETHYL PHOSPHINES PHENYLBISTRIFLUOROMETHYLPHOSPHINE Physical properties: Phenylbistrifluoromethylphosphine i s o a colourless o i l y l i q u i d which b o i l s at 148-50 . I t s vapor pressure equation i s given by log P(ram) - 7 . 5 6 0 6 - 1 9 8 5 , (I) ~ ^ -1 whence the latent heat of vaporization i s 9054 c a l mole and the Trouton's constant i s 2 1 . 3 7 . This l a s t value i s normal and shows that the phosphine i s not associated. o The b o i l i n g point i s 42 below that of the methyl analogue o CgH 5(CH 3) 2P and i s 10 below the phosphine CgH^PHg. The compound i s unaffected by a i r and moisture and i s quite stable on heating to high temperatures i n a sealed tube. The pyrolysis of the phosphine i s slow at o o 200 but somewhat faster at 300 . The products of pyrolysis - 40 -are s i l i c o n t e t r a f l u o r i d e , trifluoromethylbenzene and traces of fluoroform. The presence of trifluoromethylbenzene i n -dicates that the decomposition s t a r t s x^ith the f i s s i o n of the P-CF^ bond to give the trifluoromethyl group and the subsequent reaction of this r a d i c a l on the P-phenyl bond gives trifluoromethylbenzene. S i l i c o n t e t r a f l u o r i d e i s usually found i n the pyrolysis of the trifluoromethyl com-(63) pounds . Phenylbistrifluoromethylphosphine i s not d i s -solved by water even at high temperatures. I t i s , however, soluble i n organic solvents from which i t can be recovered unchanged. Chemical Properties: 1. Hydrolysis: (a) P h e n y l b i s t r i -fluoromethylphosphine i s quite stable towards water. How-ever, prolonged heating at 110 gives fluoroform, phenyl-o (44.) phosphonous acid M.Pt.69 and traces of benzene. The reaction i s extremely slow and may be represented by equation ( 4 4 ) . C,H_(CF„)oP-r-2Ho0 > C,H_PH( 0) 0H+ 2CF_H (44) 6 5 3 2 2 o 5 3 The traces of benzene are possibly due to pyrolysis rather than hydrolysis. (b) The phosphine i s remarkably stable towards acid hydrolysis. I t does not react at a l l with hydrochloric o o acid up to 110 ; but prolonged heating at 185 gives fluoro-form i n traces. This might again be due to pyrolysis rather than hydrolysis. - 41 -(c) Phenylbistrifluoromethylphosphine can be hydro-lysed e a s i l y with aqueous sodium hydroxide. The rate of evolution of fluoroform decreases a f t e r some time and the o reaction i s best carried out at elevated temperatures (80 ). The products of hydrolysis are fluoroform and the sodium s a l t of phenyl phosphonous acid. A solution of the l a t t e r , when a c i d i f i e d gives phenylphosphonous acid CgHpjPH(0)0H. This reaction has been discussed at length i n chapter 8 0 The s t a b i l i t y of phenylbistrifluoromethylphosphine i n a i r , compared with tristrifluoromethylphosphine which i n -flames i n a i r , i s of interest since only one phenyl group i s responsible for t h i s difference. The oxidation of t r i s -trifluoromethylphosphine i n a i r is rapid but t r i s t r i f l u o r o -(45) methylphosphine oxide i s not a reaction product . In i t s oxidation i n a i r , tristrifluoromethylphosphine resembles trimethylphosphine (which i s also oxidized r e a d i l y but gives the oxide.J The ready oxidation of phosphines can be related to t h e i r b a s i c i t i e s which decrease w i t h the su b s t i t u t i o n of electronegative groups. As this s ubstitution takes place, the lohe p a i r electrons become decreasingly available. Thus, whereas trimethylphosphine forms an oxide by reacting with atmospheric oxygen, trichloromethylphosphine (CI^ClXP does (46) not . S i m i l a r l y , phenyldiethylarsine CJL^ C0EL )^As 0 5 2 5 2 - 42 -gives the arsine oxide, but the phenylbis(2-cyanoethyl)-arsine CrEc(CnH.CN)_As i s not affected by atmospheric a i r . o p d 4 .2 The s t a b i l i t y of the cyanoarsine has been ascribed to the (46) inductive effect of the CgH^CN group and t h i s might be extended to most compounds of this type. Extension of this explanation to p h e n y l b i s t r i -(47) fluoromethylphosphine and arsine would indicate that the trifluoromethyl group being more electronegative should be responsible for their s t a b i l i t y . The r e a c t i v i t y of t r i s t r i -fluoromethylphosphine, however, contradicts t h i s . I t i s possible that some factor other than the inductive effect i s responsible f o r the i n s t a b i l i t y of the t r i s t r i f l u o r o -methylphosphine i n a i r . An answer to t h i s probably l i e s i n the structure of the phosphines. The P-C bond distances i n trimethylphosphine and tristrifluoromethylphosphine are 1 .87 and 1.92A r e s p e c t i v e l y ^ ^ ] Since the bond energy de-(30) creases with increasing interatomic distances, the P-C bond i n tristrifluoromethylphosphine may be somewhat more sus-ceptible to attack than the bond i n trimethylphosphine. Furthermore, the suppressed a v a i l a b i l i t y of the phosphorus lone p a i r electrons might cause p r e f e r e n t i a l attack on the P-C bond i n tristrifluoromethylphosphine rather than forming an oxide. I t i s also quite l i k e l y that the difference i n r e a c t i v i t y of the two phosphines may be related to the small amount of pi-bonding character present i n the P-C bond i n - 43 -(CH_) P. This has been calculated to be 0-1 pi-bond per 3 3 sigma bond or 0-3 pi-bond per phosphorus atom i n the phos-(34) phine . This pi-bond character i s l o s t with increasing interatomic distance and may therefore not be present i n tristrifluoromethylphosphine. Hence the s t a b i l i t y of phenylbistrifluoromethylphos-phine may be related to the reduced b a s i c i t y of the phosphine r e s u l t i n g from the presence of the electronegative t r i f l u o r o -methyl groups, together with the conjugation effect of the (54) phenyl group . This l a t t e r allows some pi-bond character to the P-C bonds and confers additional s t a b i l i t y to the compound. Its s t a b i l i t y can be compared with the much higher r e a c t i v i t y of methylbistrifluoromethylphosphine where no conjugation i s possible. The reaction with hydrochloric acid can be explained on the same l i n e s . Both tristrifluoromethylphosphine and phenylbistrifluoromethylphosphine are unaffected by hydro-c h l o r i c acid even at high temperatures. These two phosphines are very weak bases and hence reaction with acid might not be expected. In the reaction with hydrochloric acid, i t would be the nucleophilic attack on the proton that would st a r t the reaction. The reduced a v a i l a b i l i t y of the un-shared electrons would r e s t r i c t such an attack. I t has been shown that the b a s i c i t y towards proton and trimethylbdron i s (53) of the same order . As w i l l be shown l a t e r , p h e n y l b i s t r i -- 44 -fluoromethylphosphine and tristrifluoromethylphosphine f a i l to form any complex with boron t r i f l u o r i d e . I t i s therefore not very surprising that hydrochloric acid does not af f e c t the two phosphines. (The same argument may be extended to methylbistrifluoromethylphosphine.) 2. Reaction with halogens; (a) Reaction with iodine: Phenylbistrifluoromethylphosphine does not react with iodine at room temperature. The usual method of re-acting a phosphine and a halogen i n a carbon tetrachloride solution does not give phenylbistrifluoromethyldiiodo-o phosphorane. No reaction occurs up to 150 but the iodine vapor appears to react slowly above th i s temperature. The trifluoromethyl groups are almost q u a n t i t a t i v e l y cleaved giving trifluoroiodomethane and phenyldiiodophosphine. Traces of benzene, fluoroform and crystals of phosphorus t r i i o d i d e are also present among the products. The reaction may be represented as • C-H (CF_)P-h2l » C H PI + 2CP I (45) 6 5 3 2 2 6 5 2 3 The presence of fluoroform and benzene i s most l i k e l y due to the presence of moisture on iodine. The absence of phenyltrifluoromethyliodophosphine among the reaction products i s inte r e s t i n g since i t shows that the formation of this compound i n the reaction of t e t r a -phenylcyclotetraphosphine and trifluoroiodomethane i s not due - 45 -to secondary reaction between phenylbistrifluoromethylphos-phine and iodine and t h i s gives support to the mechanism postulated e a r l i e r * (b) Reaction with bromine: P h e n y l b i s t r i f l u o r o -methylphosphine reacts r e a d i l y with bromine and forms phenylbistrifluoromethyldibromophosphorane which i s an orange yellow c r y s t a l l i n e s o l i d . C 6H 5(CP 3) 2P-hBr 2 > C 6H 5(CP 3) 2PBr 2 (46) This compound i s very reactive towards moisture but i s quite stable i n a dry atmosphere. But when i t i s treated with water, one equivalent of fluoroform i s evolved and a white s o l i d i s formed. This s o l i d has been i d e n t i f i e d as phenyltrifluoromethylphosphinic acid €gH^(CP3)P(0)OH o which melts at 8 4 - 8 6 . C f oH 5(CF 3 )APBrA-+- 2H0H—^ C^H^CF^ ) P( 0) OH + CF3 H-t- 2HBr (47) The formation of dihalophosphoranes by t r i f l u o r o -methyl phosphines i s i n t e r e s t i n g since they do not react with hydrochloric acid and do not form an oxide r e a d i l y . I t may be noted that phosphines as a class form phosphoranes. This indicates that the r e a c t i v i t y i n terms of b a s i c i t y of the phosphines i s not related to the ease of phosphorane formation. I t i s possible that this phenomenon i s due to the d i f f e r e n t mechanism of reaction. The difference i n reaction mechanism seems to be - 46 -obvious from the nature of the attacking species. The hydro-chloride formation would involve the nucleophilic attack of the phosphines on the protons, whereas phosphorane formation involves the e l e c t r o p h i l i c attack of the halogen atom on the lone p a i r electrons of phosphorus. Thus the reduced a v a i l a -b i l i t y of the lone p a i r electrons would not give a hydro-chloride but would not be concerned i n the event of an e l e c t r o p h i l i c attack. The reaction might proceed through an intermediate tetrahedral structure formation. Such a structure i s incap-able of independent existence and i s more susceptible to further e l e c t r o p h i l i c attack and to the ultimate formation of the phosphorane. This type of structure has been postu-lated i n various reaction mechanisms: e.g., i n the reaction (55) between a phosphite (RO)„P and a l k y l halide and i t s sub-sequent d e a l k y l a t i o n ^ ^ . The primary step i s suggested to be the formation of the intermediate phosphonium compound and the subsequent approach of the anion from behind, as i n Walden inversion, i s responsible f o r dealkylation. These res u l t s are also confirmed by the e l e c t r i c a l conductivity of (57) the compounds PCl^ and PBr^ i n nitrobenzene • S i m i l a r l y the conductance of (C,-Hr-0)„PBro has been shown to involve o 0 $ d species such as (C 6H 50) 3PBr + and ( C 6 H 5 0 ) 3 P B r 5 - ( 5 8 , 5 9 ) The non-occurrence of phenylbistrifluoromethyldi-iodophosphorane CgH^CF^^P^ i s i n accord with the general - 47 -s t a b i l i t y of the phosphoranes. I t may be pointed out that phosphorus pentaiodide i s not known. This might be because of the larger size of the anions and the lower bond energy of the P-halogen bond. Moreover, the electronegativity d i f -ference between phosphorus and iodine i s too small to allow the attainment of the maximum covalency of phosphorus. I f electron-withdrawing groups are present, the P-halogen bonds i n the phosphoranes become weaker ( i n the order p \ c i ^ B r ^ I ) (61) as i n the case of trifluoromethyl-bromophosphoranes . Consequently the tristrifluoromethyldiiodophosphorane i s not known. I t i s , however, possible that such a phosphorane i s formed as an intermediate which by the usual mode of decom-po s i t i o n gives trifluoroiodomethane, since the attack of iodine on the P-CF^ bond seems less l i k e l y . The formation of a stable phenylbistrifluoromethyl-dibromophosphorane i s as would be expected. The hydrolysis reactions of t h i s phosphorane provide an in t e r e s t i n g l i n k between the trifluoromethyl and a r y l phosphines. Alkaline hydrolysis of phenylbistrifluoromethyldibromophosphorane gives fluoroform and phenylphosphonic: acid but the aqueous hydrolysis gives phenyltrifluoromethylphosphinic acid, C„H (CF )P(0)OH. The loss of only one trifluoromethyl group 6 5 3 by aqueous hydrolysis i s observed i n the case of t r i s t r i f l u o -romethylphosphine oxide and tristrifluoromethyldichlorophos-phorane. - 48 -(CP ) PO+-H 0 ^ (CP ) P(0)OH f CP H 3 3 2 3 2 3 (CP ) PCI 4-H 0 > (CF ) P(0)OH •+- CP H 3 3 2 2 3 2 3 The mechanism of hydrolysis w i l l be discussed l a t e r but i t i s i n t e r e s t i n g to note the s t a b i l i t y of the other trifluirrro-methyl group i n the phosphinic acid towards aqueous hydrolysis. The hydrolysis of the aryl-dihalophosphoranes gives (62) the corresponding oxide . The difference between the phenyl and trifluoromethyl phosphines i s therefore obvious. This reaction leads to the conclusion that the behaviour of phenylbistrifluoromethyldibromophosphorane i s more l i k e that of tristrifluoromethyldichlorophosphorane rather than that of the arylphosphoranes, and i s i n conformity with the general conclusions derived l a t e r . The i n f r a - r e d spectrum of the acid shows that phenyltrifluoromethylphosphinic acid i s a f a i r l y weak acid. The weaker a c i d i t y of this acid, compared with b i s t r i f l u o r o -methylphosphinic acid, might be due to the presence of the phenyl group. The electron-withdrawing tendency of the t r i -fluoromethyl group i s satisfied- to some extent due to the d r i f t of electrons from the phenyl r i n g and hence the acid i s not strong. 3 . (a) Reaction with methyl iodide: P h e n y l b i s t r i -fluoromethylphosphine does not react with methyl iodide at o room temperature nor up to 100 . The two compounds, however, - 49 -o are miscible. Decomposition occurs on heating to 2 3 0 and the products are trifluoroiodomethane and fluoroform, and a black i n v o l a t i l e product which might be due to carbonization. How-ever, neither methylphenyltrifluoromethylphosphine nor d i -methylphenyltrifluoromethylphosphonium iodide i s among the reaction products. This observation i s i n accord with the b a s i c i t y of the phosphine, since stable phosphonium compounds are formed by f a i r l y basic phosphines. (b) Reaction with trifluoroiodomethane:. Phenyl-bis t r i f luoromethylphosphine does not react with t r i f l u o r o -o iodomethane when the two are heated to 230 . Among the re-action products are fluoroform and trifluoromethyl-benzene, but no tristrifluoromethylphosphine i s formed. The absence of tristrifluoromethylphosphine can be attributed to the poor b a s i c i t y of the phosphine CgH^CF^JgP, whereby the nucleophilic attack on iodine i s not l i k e l y . However, as noted above, the pyrolysis of t h i s phosphine starts above 200 . This cleaves the phenyl group which i n turn reacts with trifluoroiodomethane to form trifluoromethylbenzene. One noted feature of this reaction i s the conversion of both trifluoroiodomethane and the phosphine into fluoroform. PHENYLTRIFLU0R0METHYLI0D0PH0SPHINE Physical properties: Phenyltrifluoromethyliodophosphine i s o a reddish brown l i q u i d b o i l i n g at 112-114 at 20 mm. I t i s not very stable i n a i r , p a r t i c u l a r l y moist a i r i n which i t - 50 -fumes. I t dissolves i n the common organic solvents and also i n water. The aqueous solution i s highly a c i d i c . I t reacts with most of the polar solvents since i t cannot be recovered on evaporation of these solutions. At high temperatures there o i s extensive disproportionation. When heated to 220 i t gives phenylbistrifluoromethylphosphine and traces of t r i -fluoroiodomethane, benzene, fluoroform and phosphorus t r i i o d i d e . Chemical properties: 1. Hydrolysis with a l k a l i ; P h enyltri-fluoromethyliodophosphine reacts r e a d i l y with an al k a l i n e solution and gives fluoroform and sodium phenylphosphonate. C,-H (CF„ )PI+- JNaOH ^CrHr.P0(0Na)o+- CF,HHTaI+- Ho0 ( 4 7 ) o 5 3 o 5 «- 3 d. Hydrolysis with water; Phenyltrifluoromethyliodo-phosphine reacts with water to give an acidic solution. Evaporation of this solution gives phenyltrifluoromethyl-phinic acid and a small amount of phenyltrifluoromethyl-phosphine according to equation (48). 2C H (CF )PI+2 HOH >2 6 5 3 L s 5 3 C^ H (CF_)P(0H) > C CH_(CF_)P(0)0H + C,.H1_(CF,)PH+2HI (48) o 5 3 6 5 3 The acid so obtained i s i d e n t i c a l with the phosphinic acid obtained on hydrolysis of phenylbistrifluoromethyldibromo-o phosphorane ( i t s M.Pt. is.84-86 and i t s s i l v e r s a l t melts o at 294-96 ). Phenyltrifluoromethylphosphine (CgH^CF^JPH), formed i n the hydrolysis, has been characterized only by i t s i n f r a -red spectrum which showed strong absorption at 2300 cm"! this being c h a r a c t e r i s t i c f o r a P-H bond. The other absorptions - 51 -c h a r a c t e r i s t i c of the phenyl and trifluoromethyl groups were of course present. The formation of the phosphinic acid CJE._(CF,)P(0)0H o 5 j and the phosphine CJEL (CF,)PH'is consistent with the reactions o 5 j of the h a l o p h o s p h i n e s I t i s the spontaneous oxidation-reduction of the apparently unstable intermediate phosphinous acid which leads to the formation of the observed products. 2. Reaction with trifluoroiodomethane: The iodo-phosphine CgH^CF^JPI dissolves i n trifluoroiodomethane. There i s extensive disproportionation of the iodophosphine o at 200 and phenylbistrifluoromethylphosphine and phosphorus triiodide are formed, and trifluoroiodomethane i s recovered quan t i t a t i v e l y . The other products are small amounts of benzene and fluoroform. 5. Reaction with trifluoroiodomethane and mercury: Phenyltrifluoromethyliodophosphine reacts with t r i f l u o r o -iodomethane (large excess) i n the presence of mercury. The products obtained are phenylbistrifluoromethylphosphine and a thick l i q u i d . This could not be characterized properly but i t contains no iodides. The deta i l s of the attempts to characterize i t appear i n the experimental section, from which i t appears to be a polymerised product of phosphorus containing the phenyl and trifluoromethyl groups. - 52 -DIPHENYLTRIFLUOROMETHYLPHOSPHINE Physical properties: This phosphine i s a thick o i l y l i q u i d * I t s odour, unlike other phosphines i s not too obnoxious. I t o b o i l s at 255-57 • The vapor pressure i s given by the equation: Log P = 7-781 - 2598 (II) (mm; —FJT— whence the latent heat of vaporization i s 11,850 c a l mole and the Trouton's constant i s 22-3, 'showing i t to be non-o associated. The b o i l i n g point i s 28 below the methyl analogue o and 24 below the secondary phosphine (CgH^JgPH. Diphenyltrifluoromethylphosphine i s heavier than water and insoluble i n i t . I t dissolves i n organic solvents and can be recovered unchanged from i t s solutions. I t i s quite stable i n a i r and moisture, and i s not decomposed ea s i l y on heating i n a sealed tube. I t suffers only p a r t i a l o decomposition on heating to 300 for 24 hours. Only mild carbonization takes place, and small amounts of s i l i c o n t e t r a -f l u o r i d e , fluoroform and benzene are formed, with 85% recovery of the phosphine. Chemical properties: 1. (a) Hydrolysis:. D i p h e n y l t r i f l r u o r o -o methylphosphine does not react with water even up to 120 . o I t also does not react with hydrochloric acid (up to 150 ) which shows that the b a s i c i t y of th i s phosphine i s also low. I t cannot be hydrolysed with aqueous sodium hydroxide even up o to 80 . Only a trace of fluoroform i s obtained when the o a l k a l i n e solution i s heated with the phosphine to 100 . - 53 -1. (b) Hydrolysis with alcoholic potassium hydroxide; The phosphine can be hydrolysed with al c o h o l i c potassium hydroxide. The reaction, however, i s slow (even 6 at 80 ) and i s only 78% complete i n 96 hours. The residual solution from t h i s reaction gives diphenylphosphinic acid o (M.Pt .193 ) on a c i d i f i c a t i o n . The reaction may be repre-sented by equation (49)« (C,HC L CP„P-|-20H > 6 5 £ 3 (C 6H 5) 2CP 5P(0H) 2 ^(C 6H 5) 2P(0)OH -f CF3H (49) 2. Reaction with halogens: (a) with iodine: Diphenyltrifluoromethylphosphine reacts with iodine to give diphenyltrifluoromethyldiiodophosphorane (CgH^) 2CF 3PI 2, which i s a t h i c k brown-black o i l y l i q u i d , stable i n a i r and x-jater. o i t i s not decomposed by heating up to 200 . Trifluoroiodo-methane, the expected product of decomposition (as i n the case of CgH r(CP 3) 2P i s not obtained. Hydrolysis of this com-pound by aqueous sodium hydroxide gives fluoroform quanti-t a t i v e l y and sodium diphenylphosphinate. (C 6H 5) 2CF 3P-f-I 2 >• ( C 6 H 5 ) 2 C P 3 P I 2 (50) (C6H5)2CF3PI2+-2NaOH > ( CgH^ ) 2?( 0) 0H+CF 3H + 2NaI (51) 2(b) Reaction with bromine: Diphenyltrifluoro-methylphosphine reacts vigorously with bromine and the reaction i s exothermic. Diphenyltrifluoromethyldibromophosphorane (OgHpj)2CF3PBrv>-.is obtained as an orange coloured o i l which - 54 -i s not affected by a i r and moisture. I t i s insoluble i n water and hydrochloric acid and does not react with them up to 80 . However, i t can be readily hydrolysed with aqueous sodium hydroxide and evolves fluoroform q u a n t i t a t i v e l y . The other product of t h i s hydrolysis i s also diphenylphosphinic acid which i s obtained on a c i d i f y i n g the alkaline s o l u t i o n . The reactions are s i m i l a r to those represented by equations ( 5 0 ) and ( 5 1 ) . The ready hydrolysis of the phosphoranes with a l k a l i n e solutions i s i n t e r e s t i n g i n view of the reluctance observed i n the case of the phosphine (CgHpj ^ CF-^P. This has been discussed i n chapter 8 on the basis of formation of a t r i g o n a l bipyramidal intermediate. The formation of the diiodophosphorane i s not surprising since the corresponding triphenyldiiodophosphorane i s known^ 6 8! Th e s t a b i l i t y of the iodophosphoranes decreases i f the iodine content i n the phosphorane i s raised, p a r t i c u -l a r l y i f electron a t t r a c t i n g groups are present. Thus (CF^J^P does not form (CF^J^P^ and (CgH^JgPI^ Is not yet known. The s t a b i l i z i n g influence should therefore be that of the electron-releasing groups l i k e the a l k y l group or the conjugation effect of the phenyl group. Thus the properties of diphenyl-trifluoromethylphosphine are determined more by the presence of the phenyl groups than by the character of the t r i f l u o r o -- 55 -methyl group. This i s further revealed by the s t a b i l i t y of the dibromo-phosphorane'; towards water which should have given the phosphinic acid i f the trifluoromethyl-"character was predominant. 5(a) Reaction with trifluoroiodomethane: Diphenyl-trifluoromethylphosphine i s not miscible with GP^I at low temperatures, but they form a homogeneous solution at room o temperature. There i s no reaction up to 200 except that traces of fluoroform are obtained, and a small amount of diphenyliodophosphine separates from the reaction mixture. The reaction i s extremely slow. This observation i s i n accord with the expected be-haviour of a poorly basic phosphine. Since the phosphine does not react with hydrochloric acid, i t might indicate that a nucleophilic attack on the iodine atom of CF^I i s not very l i k e l y . I t may be pointed out again that the b a s i c i t y of such phosphines demands the attack of e l e c t r o p h i l i c groups which could use the lone pa i r electrons. Apparently CP^I f a i l s to f u l f i l this condition. However, i f a high enough temperature i s employed pyrolysis might give some of the observed products. 5(b) Reaction with methyl iodide: Diphenyltri-fluoromethylphosphine i s miscible with methyl iodide at room temperature but no reaction occurs unless the mixture i s - 56 -heated to 100 . At this temperature, an orange colored o i l slowly separates. This o i l can be c r y s t a l l i z e d by diss o l v i n g i n ethanol and treating this solution with a large excess of ether. Methyldiphenyltrifluoromethylphosphonium iodide so obtained i s a yellow c r y s t a l l i n e s o l i d melting at 123-26 , and i s quite stable i n a i r . Methyldiphenyltrifluoromethylphosphonium iodide reacts r e a d i l y with cold water to lose the trifluoromethyl group qu a n t i t a t i v e l y . The re s u l t i n g aqueous solution i s highly a c i d i c , due to the formation of hydriodic acid, accord-ing to equation (53). Treatment of the aqueous solution with s i l v e r oxide precipitates s i l v e r iodide and evaporation of the f i l t r a t e gives methyldiphenylphosphine oxide. (C 6H 5) 2CF 3+CH 3I f OH (CJI ) CF P 3 6 5 2 5 I (52) CH_(C.H ) CF P 3 6 5.2 3 V-t-HOH >CH,(C H ) P04-CF H+-HI (53) 3 6 5.2 3 The reaction with methyl iodide seems in t e r e s t i n g since the phosphine does not react with hydrochloric acid, and these two reactions have been correlated with the basi-c i t y of the p h o s p h i n e s ^ \ i t i s l i k e l y that the difference arises because of the nature of the attacking group. I t has been suggested by Baker and Ingold that the primary step i n the reaction of a l k y l halides i s the anionization of the halogen atom R-CH^^^Hal. The methylene group so obtained provides a reactive centre and i s compar-able with the halogens i n i t s tendency to capture an electron. - 57 -This type of anionization i s not possible for t r i f l u o r o -methyl halides since i n their case the reaction occurs by a nucleophilic attack on the r e l a t i v e l y p o s i t i v e iodine atom0 The non-occurrence of a hydrochloride of diphenyl-trifluoromethylphosphine can be explained i f i t i s noted that the phenylphosphines form only weak hydrochlorides which can be r e a d i l y hydrolysed, and the trifluoromethylphosphines do not form any hydrochlorides. I t may therefore be said that the co r r e l a t i o n of b a s i c i t y with the reaction of phos-phines with a l k y l halides does not hold i n the case of phenyl-trifluoromethyl-phosphines. This r e l a t i o n w i l l be discussed i n d e t a i l i n chapter 7« The aqueous hydrolysis of methyldiphenyltrifluoro-me thyphosphoniurn iodide resembles that of the aryl-phos-phonium compounds. Thus methyltriphenylphosphonium iodide on hydrolysis with potassium hydroxide gives benzene, methyldiphenylphosphine oxide and potassium iodide. CH (C H ) P 3 >6v 5 3 _ + I + KOH > C H + CH (C H ) PO-J-KI (54) 6 6 3 6 5.2 Phenoxydiphenylmethyl- and phenoxydiphenylbenzylphosphonium iodides are hydrolysed by heating with water, and the more (67) electronegative phenoxy group forms phenol . C^H CH C H 6 5 X / ,.2 6 5 C 6 H 5 ^ O C 6 E 5 I T HOH >(C CH_.) 0(C CH_GH ')P0: -j-GcE OH-f-HI 6 5 ' 6 5 2-' 6 5 ( 5 5 ) - 58 -C H CH 6 5 \ / 3 X P C^ H •r oc H 6 5 - 6 5 f-f HOH- -CH (C H ) P04-C H OH-HHI (56) 3 6 5 . 2 6 5 The electronegative nature of the trifluoromethyl group i s very much apparent when i t i s found that the phosphonium compound CH (C^H) CF P L 3 6 5 2 3 I hydrolyses at room temperature. Equation (53) may be represented by the following scheme. CH C H 3 X / 6 5 P. CF. C H 6 5 t 1 + HOH-CH C H 3 X / 6 5 CH CCH_ \ / 6 5 P. CF. CJS 6 5 + OH CF C H 6 5 ->CH -3 C H • 6 5 C H 6 5 OH^ + HI J PO 4- CF H 3 The i n s t a b i l i t y Of the intermediate hydroxide gives the observed products. Thus i n the hydrolysis of phosphonium compounds, the CF^ group i s more ea s i l y hydro-lysed than a phenoxy group and the order of ease of hydrolysis i s CF^) O 0 g H 5 ) C g H 5 ^ C H ) C 6 H 5 C H 2 e S E C T I O N I I PREPARATION AND STUDY OP THE ADDITION COMPOUNDS - 59 -CHAPTER IV FORMATION OF BORON TRIFLUORIDE COMPLEXES In the previous chapters the r e l a t i o n between the a v a i l a b i l i t y of the lone p a i r of electrons on the phosphorus atom and the b a s i c i t i e s of the phosphines has been discussed. The b a s i c i t y could be further examined by studying the ease of formation of t h e i r addition compounds with strong electron acceptors such as boron t r i f l u o r i d e and platinum (II) chloride. The study of the reactions with the l a s t two compounds pro-vides an insight into the coordination chemistry of these bases. The addition compounds of phosphines with boron com-pounds (Lewis acids) r e s u l t from sigma-bond formation be-tween phosphorus and boron. On the other hand, the bond between phosphorus and platinum i n the products of the re-actions between the phosphines and platinum (II) chloride i s multiple i n character and involves dn-d-jTbonding i n addi-t i o n to the P-Pt sigma-bond. - 60 -The ease of formation of the addition compounds formed by Lewis acids depends on more than one factor, i^uite a few cases are complex and involve the inductive, s t e r i c as w e l l as the hybridization effects. Whereas electro-negativity demands i n agreement with most observations that boron t r i f l u o r i d e be a better acceptor than the other boron halides ( B F ^ BCT ^ BBr ), i t has been shown that r e l a t i v e acid strength increases i n the order BF / BC1 C BBr„ towards < B I < : a base l i k e pyridine ( 7 0 ) ijh^g ^ a s frQen explained on the basis of increasing pi-bonding i n the B-X bond i n the series BF^, BCl^ and BBr^. This would place BF^ i n the same posi-ti o n as BH i n acid strength, as i s shown by t h e i r acid 3 strength towards trimethylamine. Thus coordination chemistry becomes very involved i f a l l acceptors are considered at once, since frequently th e i r acid strengths show unusual relationships which cannot be explained by one single e f f e c t . Since a monotonic series of generalized acids and bases (73) cannot be established , the usual practice i s to take one of the acids as a reference acid and to study the r e l a t i v e s t a b i l i t y of i t s addition compounds*' *' . Boron t r i f l u o r i d e has been chosen as the reference acid f o r the present investigation. The addition compounds have been prepared by combining the reactants i n molar r a t i o s and allowing them to react slowly. In most cases, reaction occurred below room temperatur-e. - 61 -The r e l a t i v e s t a b i l i t i e s have been estimated by measuring the saturation pressures of the compounds, since (73) according to Brown , the less stable compound,compared with another of closely s i m i l a r structure and molecular weight, exhibits the higher saturation pressure. The results . are only q u a l i t a t i v e but for establishing r e l a t i v e s t a b i l i -( 7 D t i e s such results have been considered adequate Trimethylphosphine-boron t r i f l u o r i d e : This com-(6) pound has been previously reported . I t i s ea s i l y prepared by the d i r e c t reaction of trimethylphosphine and boron t r i -f l u o r i d e . The reaction i s spontaneous and occurs much below room temperature. Trimethylphosphine-boron t r i f l u o r i d e i s a o white c r y s t a l l i n e s o l i d , which melts at 126-130 . I t i s easily decomposed i n moist a i r and by polar solvents giving trimethylphosphine. As i s true of the other boron t r i f l u o r i d e addition compounds, the trimethylphosphine complex i s not soluble i n non-polar solvents. The saturation pressure of the compound i s given by equation(i11) . Log P(mm) = 8.460 - 2627 (III) T Dimethyltrifluoromethyl-boron t r i f l u o r i d e : This compound i s also obtained e a s i l y when the phosphine reacts with boron t r i f l u o r i d e . When so prepared i t i s a thick o i l . This compound i s more e a s i l y decomposed i n a i r , absorbing water, - 62 -and by polar solvents, than i t s trimethylphosphine analogue. The saturation pressure of the compound i s given by the equation (iv)l log P(mm) = 10.354 - 2146 (IV) T Diphenyltrifluoromethylphosphine-boron t r i f l u o r i d e : This compound i s formed by the i n t e r a c t i o n of the phosphine (CgHj-JgCF^P and boron t r i f l u o r i d e , but the reaction i s slow and occurs at room temperature when the former has melted. The reaction can be carried out i n a non-polar solvent with the deposition of the complex i n the form of an o i l . This complex i s quite stable at room temperature but i s decom-posed slowly by moisture - and r e a d i l y by polar solvents. The saturation pressure of th i s addition compound i s given by equation log P(mm) = 6.609 - 1755 (v) T Triphenylphosphine-boron t r i f l u o r i d e : The reaction has been carried out by passing boron t r i f l u o r i d e through a petroleum ether solution of triphenylphosphine, with the i n -stantaneous deposition of triphenylphosphine-boron t r i f l u o r i d e i n the form of a white c r y s t a l l i n e s o l i d which melts at 128-o 130 . This compound i s quite stable i n a i r and shows the same s o l u b i l i t y behaviour toward polar and non-polar solvents as i t s analogues. - 63 -The saturation pressure of this compound i s given by equation (VI). Log p(ram) = 3.840 - 972 (VI) T Boron t r i f l u o r i d e does not react with t r i s t r i f l u o r o -methylphosphine, methylbistrifluoromethylphosphine, and phenylbistrifluoromethylphosphine. The reactions have been attempted at -78 by d i r e c t treatment of the reactants, but i n a l l cases reactants were r.ecovered q u a n t i t a t i v e l y . phosphorus and boron i s a sigma-bond, and that i t i s i n -fluenced by more than one factor. One of the factors, which has been found very important i n the present investigation, i s the electronegativity of groups attached to the Lewis base. As mentioned e a r l i e r , electron withdrawing electro-negative groups would reduce the a v a i l a b i l i t y of the lone p a i r electrons. The high electronegativity of the t r i f l u o r o -methyl group has already been discussed. Thus i t would be expected that as the b a s i c i t y and consequently the a v a i l a -b i l i t y of the lone p a i r electrons decreases with the i n t r o -duction of trifluoromethyl groups, the s t a b i l i t y of the boron t r i f l u o r i d e addition compounds would decrease. The r e l a t i v e v o l a t i l i t i e s given by the vapour pressure equations show the following order of s t a b i l i t y : (CH ) P.BP \ trifluoromethyl series, while i n the phenyl-trifluoromethyl o I t has already been' said that the bonding between (CP ) 3 3 series - 64 -J c J I f C F LP.BF \ (CF ) P.BF i . The same equations give 1 6 5 V 3 2 3 / 3 3 3 J the following order for the a l k y l and a r y l - t r i f l u o r o m e t h y l -phosphines : (C 6H 5) 3P.BF 3^ (CH 5) 3P.BF 3^> (CgH JgCF P . B F ^ (CH3) 2 CF 3P. BF 3 ) { C ( C F 3 ) 2P. B F ^ CH3 ( CF 3) g P. B F ^ (CF^)^. B F ^ The above comparison shows that the phenyl-phosphines form more stable complexes than the methyl-phosphines. This order i s d i f f e r e n t from that expected from the b a s i c i t i e s of the phosphines. Thus, whereas the methyl-phosphines form a hydrochloride and a quaternary s a l t r e a d i l y , the phenyl-phosphines do i t with d i f f i c u l t y . However, i n both the phenyl and methyl series, the replace-ment of a trifluoromethyl group with negative inductive effect w i l l greatly reduce the b a s i c i t y of the phosphine and hence lower the s t a b i l i t y of the addition compound. The pi-character of the P-C bonds discussed e a r l i e r i s gradually l o s t as the more electronegative t r i f l u o r o -methyl group i s introduced, and i s almost absent i n t r i s t r i -fluoromethyl-phosphine. This effect leads to the decreased a v a i l a b i l i t y of the lone pair electrons. I t i s therefore not surprising that the boron t r i f l u o i d e complexes of phos-phines with more than one trifluoromethyl group have not been found. Added confirmation of t h i s view comes from the finding that the adduct (CF^J^P.BH^ a l s o d o e s n o t e x i s t ^ ? ) r^ h e borine adducts, i t may be pointed out, are more stable than those of boron t r i f l u o r i d e . - 65 -Ste r i c effects may also be thought of as being responsible for the non-occurrence of the complexes of phosphines with more than one trifluoromethyl group. S t e r i c interactions would be greatest i n tristrifluoromethylphosphine, o for which the CPC angle has b een found to be 100 with a l l the CE^ groups on the same side of the phosphorus atom. I t i s known that a certain amount of rearrangement occurs from the planar configuration of BP to the tetrahedral environ-5 ment of B i n an addition compound of BF,. Hence, the s t e r i c interference of the CF, group with F atoms on B must be quite small. For phosphines having two trifluoromethyl groups t h i s i n t e r a c t i o n would be smaller s t i l l . Although the amount of such interference i s d i f f i c u l t to determine quantitatively, i t c e r t a i n l y would be very small i n the case of trifluoro-methyl-phosphines, and i s u n l i k e l y to be responsible f o r the non-occurrence of the adducts under consideration. - 66 -C H A P T E R V FORMATION OF PLATINUM(II) CHLORIDE COMPLEXES I t has already been said at the beginning of this section that the bond between phosphorus and platinum i n phosphine-platinum(II) chloride complexes w i l l be multiple i n character, involving d-n-C/TT bonding i n addition to sigma-bonding. This w i l l give considerable additional s t a b i l i t y , and hence phosphines which are otherwise poor donors towards boron t r i f l u o r i d e may form stable compounds with platinum(Il) chloride. The preparation of these compounds has been effected either by d i r e c t reaction of the phosphine with (78) platinura(Il) chloride or by the method of Jensen , which consists of treating an aqueous solution of potassium c h l o r o p l a t i n i t e , K^PtCl^, with an alcoholic or acetone solution of the phosphine. The r a t i o of phosphine to p l a t i -num(II) chloride usually taken for reaction has been 2:1. - 67 -Bis(trimethylphosphine)dichloroplatinum( XL ): (79) This compound has been reported previously and has been shown to occur i n two forms, c i s and trans. The dir e c t re-action i s a slow process i n this p a r t i c u l a r preparation. The s o l i d obtained i s usually a mixture of yellow and white s o l i d s , trans and c i s isomers, which can be separated easily by extracting with ether, which does not dissolve the white s o l i d . The formation of the yellow isomer can be checked by using an excess of trimethylphosphine. The preparation proceeds more ra p i d l y i n benzene solution, and i n this case the formation of the yellow isomer can be suppressed by excess of phosphine. The y i e l d i n both these cases, however, i s low. I t can be improved by treating the phosphine with potassium c h l o r o p l a t i n i t e , when only the white isomer i s obtained and i n 41$ y i e l d . The bis(trimethylphosphine)dichloroplatinum( JH. ) so obtained i s the cis isomer as shown by i t s high dipole o moment of 13.1D. I t melts at 324-326 with decomposition. o I t dissociates rapidly above 200 . Its d i s s o c i a t i o n pressure i s given by the equation log Pmm = 6 .510 - 2108 (17TT) T ; The heat of d i s s o c i a t i o n i s obtained as 9*59 kcal mole-'*'. (CH ) P 3 3 PtCl i s not very stable 2 2 The compound and seems to decompose on standing i n a i r , p a r t i c u l a r l y i n moist a i r . Treatment with water, i n which i t i s insoluble, causes slow decomposition and evolution of trimethylphos-phine. I t i s insoluble i n ether and non-polar solvents, but i s f a i r l y soluble i n polar solvents. Heating an alcoholic solution also decomposes the compound. Bis(dimethyltrifluoromethylphosphine)dichloro- platinum(II): This compound i s prepared by reacting p l a t i -num^ II") ) chloride with dimethyltrifluoromethylphosphine i n the r a t i o of' 1:2. The reactio.h i s sloitf but gives an excel-lent y i e l d of the addition compound which i s pale yellow. R e c r y s t a l l i z a t i o n gives white needle-shaped crystals and a small amount of a pale yellow product. The white needle-shaped crystals of bis(dimethyl-trifluoromethylphosphine)dichloroplatinum(II) have a dipole moment of 9.2 D showing the compound to be the cis isomer. (The small amount of the yellow product i s possibly the trans isomer.) This compound, with decomposition which i s rapid above the melting point. The d i s s o c i a t i o n pressure of the compound i s given by equa-tio n ( V I I I ) : log P(rnm) = 7.969 - 2438 (VIIK) T . . . . whence the heat of di s s o c i a t i o n i s 11.31 kcal mole (CH, ) CP P L PtCl , 3 2 3 J 2 2* (CH ) CF P 3 2 3 PtCl , melts at 188-190 2 2 - 69 Bis(dimethyltrifluoromethylphosphine)dichloro-platinum (II) i s quite stable i n a i r and i s not affected by moisture. I t dissolves i n polar solvents which do not react with i t , but is insoluble i n ether, carbon t e t r a -chloride, and benzene. Gold water does not react with i t . Treatment with b o l l i h g xtfater does not give the phosphine (CH^CF^P as i n the case of (CH ) P -PtCl , but gives 3 3 \2. 2" fluoroform instead. The evolution of fluoroform i s slow and not quantitative, even a f t e r 2 4 hours. Hydrolysis with a l k a l i gives fluoroform almost quan t i t a t i v e l y . This may be contrasted with the reaction of the phosphine (CH ) CF P i t s e l f , which i s not hydrolysed by a l k a l i . The 3 2 3 complex dissolves i n methyl iodide, but can be recovered un-changed. This may be contrasted with most of the mercury iodide complexes of the phosphines and arsines, which on ( 8 0 ) treatment with methyl iodide form quaternary compounds. I t i s also unaffected by trifluoroiodomethane. Bi s(methylb i s t r i fluo rome thylpho sphin e)di chloro- platinum ( I I ) : This compound i s prepared by the d i r e c t re-action of methylbistrifluoromethylphosphine and dichloro-platihum ( I I ) . JThe reaction i s slow, but takes place more quickly i n the presence of excess phosphine, preferably i n the l i q u i d phase. The reaction product i s extracted with carbon tetrachloride, which on evaporation deposits fin e yellow crystals of the addition compound CH (CF ) 0P 3 3 d. - 7 0 -The complex so obtained i s the trans isomer as determined by the dipole moment which i s 0.0D. I t melts at 0 85-87 and i s s l i g h t l y dissociated below i t s melting point. o The d i s s o c i a t i o n Is very rapid above 140 . (.This, therefore furnishes a good method of obtaining the pure phosphine.) The d i s s o c i a t i o n pressure i s given by the equation log P(mm) = 4,885 - 1258 (TJC) T whence the heat of d i s s o c i a t i o n i s 5»76 k c a l mole"-1-. The compound is soluble i n organic solvents and only s l i g h t l y so i n b o i l i n g water. I t i s quite stable to-wards water, unlike the addition compounds of the other rnethyl-phosphines. Treatment with aqueous sodium hydroxide gives only 50/&fluoroform. I t dissolves i n methyl iodide and trifluoroiodomethane but i s recovered unchanged i n each case. Tristrifluoromethylphosphine does not react with dichloroplatinum (II) at room temperature nor when heated o to 200 . Reaction of the two i n methanol or butanol gives a golden.yellow solution and some colourless crystals which are yery unstable and cannot be i s o l a t e d . Evaporation of the solvent gives a resinous product but not the addition compound ( C P 3 ) 3 P 2 P t c i 2 . Bis(phenylbis trifluoromethylphosphine)dichloro- platinum ( I I ) ; This compound can be prepared by d i r e c t trea ment of the phosphine CgH^CF^gP with platinum (II) c h l o r i d - 71 -at room temperature but the process i s slow. I t can be o accelerated by heating the reactants at 100 i n a sealed tube. The reaction produces greenish c r y s t a l s which ban be r e c r y s t a l l i z e d from acetone. This product i s completely soluble i n non-polar solvents suggesting that i t i s homo-geneous and just one isomer. However, the reaction of an acetone solution of the phosphine CgH^CF^^P with an aqueous solution of potassium c h l o r o p l a t i n i t e gives a small amount of an insoluble white s o l i d on extraction of the product with non-polar solvents. The two products also d i f f e r i n their melting points. The main component (greenish o solid) melts at 134-36 , and i s the trans.isomer as deter-mined by i t s dipole moment which i s found to be 0.0D. The small amount of white s o l i d on the other hand melts with decomposition above 300 . From i t s s o l u b i l i t y and melting point i t may be said, by analogy, that the l a t t e r has the cis configuration. Bis(phenylbistrifluoromethylphosphine)dichloro-platinum (II) i s a very stable s o l i d . I t i s not affected by water;;- or organic solvents. I t i s soluble i n methyl iodide and trifluoroiodomethane, producing a yellow solution, but i s recovered unchanged from these solutions. I t can, how-ever, be hydrolysed e a s i l y with aqueous sodium hydroxide which gives fluoroform q u a n t i t a t i v e l y . - 72 -C 6H 5(CP 3) 2P P t C l 0 reacts The addition compound with halogens to give new s o l i d products. Two equivalents of the halogen are absorbed i n the reaction. The bromo-compound which results i s an orange coloured substance, and the iodo-compound i s brown. Both are quite stable i n a i r , insoluble i n non-polar solvents, but soluble i n polar solvents. Hydrolysis of the bromo-compound gives two equi-valents of fluoroform, and thermal decomposition produces pure phosphine. By analogy with the reaction of the t r i -ethylphosphine derivative (CQ^H^J^P^PtClg w ni°h takes up , two equivalents of ammonia to give |Ptj(C2H^ ^PJ-gCNH^)^ Gig* the compounds under consideration may be Jpt-£(CgH,_) (CF^^PJvjB^J C l 2 and Pt{< ( C c H ( C F j 0 P k l Cl„. However further study i n t h i s '6XV 3 2 J 2 2j 2' connection i s needed i n order to elucidate t h e i r structure. Chemical reactions have sometimes been used to prove the structures of platinum complexes. They are known to be e f f e c t i v e i n the case of bis(triphenylphosphine)dichloropla-, s ( 8 3 ) (c78) tinum (II) which has been obtained only i n the cis form . This proof of structure i s less ambiguous for complexes con-taining two strongly trans d i r e c t i n g groups l i k e the phos-phines, and the other two ligands having a weak trans effect (82) l i k e chlorine • However, the r e s u l t s must be treated with caution, and physical methods are s t i l l better suited f o r the • elucidation of the configuration. - 73 -The chemical method consists i n treating the complex (R^PjgPtCl^ with a bidentate ligand: e.g., ethylenediammine, which would form a complex only i f the positions are a v a i l -able f o r chelate formation. This i s better suited f o r com-plexes with a c i s structure and would not be effective f o r those with a trans configuration. This method was applied to the p h e n y l b i s t r i f l u o r o -methylphosphine complex but no complex of the type jpt£cgH^(CP^ )gP^2 e n Gig w a s obtained. From this observation and the dipole moment value of 0.0D, i t may be concluded that the compound has a trans configuration. Bis(diphenyltrifluoromethylphosphine)dichloro- platinum ( I I ) : This compound i s prepared by reacting an acetone solution of diphenyltrifluoromethylphosphine with an aqueous solution of potassium c h l o r o p l a t i n i t e . The product so obtained i s a resinous substance which can be c r y s t a l -l i z e d by treatment of i t s acetone solution with a large excess of water. Bis(diphenyltrifluoromethylphosphine)-dichloroplatinum (II) i s thus obtained as a pale yellow powder. Extraction with ether ^ives a small amount (r^5%) of white s o l i d , and from i t s s o l u b i l i t y and colour t h i s i s possibly the c i s isomer, o The main product (pale yellow) melts at 63-65 and from i t s dipole moment, which i s found to be 0.0D, i t has the trans configuration. I t i s quite stable to a i r and moisture. I t i s soluble i n p r a c t i c a l l y a l l organic solvents, but i s insoluble i n water. I t i s not affected by b o i l i n g water nor by cold aqueous a l k a l i . The compound, however, i s slowly hydrolysed by heating with alcoholic potassium hydroxide. I t also dissolves i n methyl iodide and trifluoroiodomethane, but the two iodides do not seem to react with the complex which is recovered unchanged.. Bis(diphenyltrifluoromethylphosphine)dichloro-platlnum(II ) reacts with two equivalents of bromine to give a yellow s o l i d . The reaction i s analogous to that of the phenylbistrifluoromethylphosphine complex, and the product i s possibly bis(diphenyltrifluoromethylphosphine)-dibromo.dichloroplatinum^n).This compound can be r e a d i l y and quan t i t a t i v e l y hydrolysed with aqueous a l k a l i . This may be contrasted with the. d i f f i c u l t y , of hydrolysis of the phosphine ( C 6 H 5 ^ 2 C P 3 P and i t s addition compound (CgH^CF^P gPtClg, and may be compared with the ready hydrolysis of diphenyl-trifluoromethyldibrpmophosphorane. Thermal decomposition of bis(diphenyltrifluoromethylphosphine)dibromodichloro-platinum(I2L ) gives the phosphine (CgH^ ^CF-^P, and also supports the above formulation. Treatment of the addition compound j( CgH,- ^CF^P 2 P t c i 2 with iodine gives the corresponding iodo-compound which i s a brown s o l i d . This compound also can be hydrolysed e a s i l y and qu a n t i t a t i v e l y by a l k a l i , and i n a l l respects i s s i m i l a r to - 75 -(0 6H 5) 2CP 3P 2 P t C 1 2 the analogous halogen compounds described above. Treatment of the addition compound with ethylenediammine as the chemical test f or the structure of the complex caused no reaction, showing ( i f the test i s applicable) that the pale yellow s o l i d i s a trans isomer. As has already been stated, these studies with platinum( J U L ) chloride would further reveal the donor proper-t i e s of the phosphines. This i s because platinum enjoys a favourable p o s i t i o n i n coordination chemistry, this property being due to the following factors: (1) Pi-bonding i s f a c i l e since the 5d levels are close to 6s and 6 p . This gives additional s t a b i l i t y to the complexes. (2) Hybridization of 6p and 5d o r b i t a l s produces p i -x xz type o r b i t a l s which form the pi-bond. Platinum i s therefore i n a better p o s i t i o n than boron t r i -f l u o r i d e to form complexes. Thus even phosphines of highly electronegative character which do not form an addition com-pound with boron t r i f l u o r i d e may do so with platinum( XL,) c'hloride. Phosphorus t r i f l u o r i d e i s an example of this type of phosphorus derivative. An examination of phosphorus t r i f l u o r i d e , which behaves s i m i l a r l y to the above phosphines i n i t s reaction towards boron t r i f l u o r i d e and platinum( XL. ) chloride, seems - 7 6 -useful. I t Is known that phosphorus i n phosphorus t r i -f l u o r i d e uses i t s 3d and 3d o r b i t a l s to form A-rr-drr zy yz bonds with metals. The formation of such a bond i s further supported by the symmetry of the PF^ molecule (C37//)> i n which the two o r b i t a l s 3d and 3d are i n a doubly de-generate system of pi-symmetry . The molecules of t r i -methylphosphine and tristrifluoromethylphosphine (and hence probably the other phosphines) have been shown to have the same symmetry^ 8] I t is therefore quite surprising that no complex formation i s observed i n the case of t r i s t r i -fluoromethylphosphine. An examination of the mechanism of formation of these complexes seems desirable. The bonding i n complexes of the type (R P) PtCT 3 2 2 consists of a sigma-bond formed by the donation of lone p a i r electrons from phosphorus to platinum, and a pi-bond which i s the r e s u l t of the overlapping of the d-or dp-hybrid o r b i -t a l of platinum with the vacant d - o r b i t a l of phosphorus. From the properties of the tristrifluoromethylphosphine i t i s apparent that the sigma-bond w i l l be very weak. The complex, i f i t forms, would be s t a b i l i z e d by strong p i -bonding only. The formation of the square planar complexes of platinum(lt. ) s a l t s has been suggested to occur through a (354 trigonal-bipyramidal activated complex . This t r a n s i t i o n state i s s t a b i l i z e d by the ligands with pi-bond character. I t would therefore be expected that the phosphines, which have some pi-bonding character already, would s t a b i l i z e - l i -the t r a n s i t i o n state more than those which have none. In platinum(H.V) complexes, the greatest degree of pi-bonding i s attained wien the pi-bonding ligands are c i s (133)/ to one another ,. Thus i f the phosphines are cis to one another, they compete with the chloro groups for the d or b i t a l s (d and d taking P-Pt-P as the y axis) of p l a t i -xy yz num. However, when they are trans, the same d o r b i t a l (dy Z) would be used: i . e . , the phosphines would compete with one another. Since chlorine has a smaller tendency to form a pi-bond than phosphorus, the cis isomer of the platinum compound would be more stable than the trans. However, among the a l k y l phosphines, as the series i s ascended from methyl to n-propyl, the trans isomer becomes increasingly stable. The s t a b i l i z a t i o n of the trans isomer has been attributed to s t e r i c effects The larger trifluoromethyl groups may also be giving r i s e to the same phenomenon, and hence i t may be expected that the trifluoromethyl-phosphines would give mainly trans isomers. Thus, whereas electro-negativity demands that a cis structure be more stable (since the pi-bond strength i s increased as i n phosphorus t r i -(87) (78) f l u o r i d e and triphenylphosphlne ,) s t e r i c effect would give a trans isomer for tristrifluoromethylphosphine. The compound very unstable as i s revealed by the comparison of the heat of di s s o c i a t i o n of the complexes, (CF ) P 3 3 . PtCl would, however, be 2 2 kcal mole 1 and CH (CF ) P . 3 3 2 (CH ) CF P 3 2 3 -ptci , A H = 11.3 2 2' P t C l 2 , AH = 5 . 8 kcal mole'-l. - 78 -The value of AH i s seen to decrease with substitution of trifluoromethyl groups. Extrapolation of this value would indicate that the AH for low, and hence i t i s not surprising that i t has not been is o l a t e d by the common methods. I t might, however, be use-f u l to t r y a displacement reaction: (CF ) P - . 3 3 . PtCl^ would be much too 2 2 (R P) PtCl + 2(CF ) P. 3 2 2 3 3 (CF ) P 3 3 0 P t C l -f- 2R P 2 2 3 i n order to establish the non-occurrence of the complex. From the results already mentioned, i t i s found that a l l trifluoromethyl substituted phosphines, except dimethyltrifluoromethylphosphine, give the trans isomers. The1 s t a b i l i t y of c i s (CH,) P 3 3 (CH )_,CF P 3 2 3 ^PtClg as compared with cis PtCl i s as would be expected on the basis of 2 2 electronegativity. Thus, the replacement of one methyl group by a more electronegative trifluoromethyl group appears to give.greater s t a b i l i t y to the complex by causing a greater increase i n pi-bonding than i s o f f s e t by the reduction i n strength of the sigma-bond. This may be seen by a reduction i n the dipole moment by the substitution of one t r i f l u o r o -methyl group, (CH ) P 3 3 PtCl ,A =13.1 D, 2 2 (CH ) CF P 3 2 3 PtCl >Lb =9.2 D 2 2 As the number of trifluoromethyl groups i s increased, s t e r i c effect which i s absent i n (CH,)_CF„P becomes more im-3 2 3 portant, and hence only the trans isomer i s obtained for CH (CF ) P 3 3 2 PtCl . S t e r i c effect and not the reduced 2 2 b a s i c i t y of the phosphine i s possibly the main reason for the s t a b i l i t y of the trans isomer. Thus a comparison with phosphorus t r i f l u o r i d e shows that c i s (PF ) PtCl i s more . - 3 2 • 2 stable than the trans isomer. Whereas phosphorus t r i f l u o r i d e (88) forms Ni(PF ) , tristrifluoromethylphosphine replaces only two carbon monoxide molecules from n i c k e l carbonyl v . The formation of the platinum(II) chloride complex thus seems to be independent of the basic character of the phos-phine, and depends on s t e r i c effects instead. In the case of the phenyl phosphines i t i s known that triphenylphosphine gives only the c i s compound. Data on mixed phosphines (RgR'P) i s unfortunately lacking* How-ever, t r i - n - b u t y l a r s i n e gives a trans isomer, but phenyldi-n-butylarsine s h i f t s the equilibrium towards c i s structure - . This i s explained as p a r t l y due to s t e r i c effects and p a r t l y to electronic effects. The phenyl group, being r i g i d , occupies l e s 3 space i n the immediate neighbourhood of M (M = P,As) than an a l k y l group. Hence when the s t e r i c effect i s not operative, the more stable c i s structure w i l l be obtained. The s t a b i l i t y w i l l be enhanced by the electro-negativity of the phenyl group, which w i l l increase the strength of the pi-bond between phosphorus and platinum. - 30 -I t i s somewhat surprising to f i n d that i n the case of phenyl-trifluoromethyl-phosphines, mostly the trans isomers are obtained. This indicates that the replacement of a phenyl group by a CP group s h i f t s the equilibrium towards 3 the trans isomer. The s t a b i l i t y of the trans isomer would increase with the number of trifluoromethyl groups by the consideration of the larger size of the CF, group. The c i s -3 trans isomerization equilibrium studies indicate that the trans isomer of bis(triphenylphosphine)dichloroplatinum (II) i s unstable. In this connection, i t i s • inte r e s t i n g to notethat the melting point of the complexes increases with the number of trifluoromethyl groups—the complex o mel s at 65 whereas (C H (CF ) P L 6 5 3 2 J (C H ) CF P . 6 5 2 3 _ PtCl melts at 1 3 4 - 1 3 6 . 2 2 2 P T C 1 2 I t may therefore be concluded that the replacement of a phenyl or methyl group by a trifluoromethyl group r e s u l t s mainly i n the formation of a trans isomer. The p o s s i b i l i t y of phosphine-catalyzed isomerization (85) may not be ruled out . This depends on the mechanism of attack of the phosphine on the intermediate t r i g o n a l -bipyramidal structure. The f i r s t step i n this mechanism i s the replacement of a chloro group by the catalyst phosphine, and the second, which i s through the ;same, intermediate, gives the appropriate isomer and the catalyst . The occur-rence of the c i s or the trans isomer would, however, depend on the s t a b i l i t y of the structure and the trans effect of the phosphine. - 81 -The conclusion from the above discussion i s that the s u b s t i t u t i o n of trifluoromethyl group tends to favour the formation of the trans isomer. Explanation on the basis of s t e r i c phenomenon i s the more probable one. Any tendency towards the formation of even a weak sigma-bond would give a complex with platinum( ZEE ), and the s t e r i c effect of the large trifluoromethyl groups would favour the placing of the phosphines trans to one another. - 82 -C H A P T E R V I FORMTION OF COMPLEXES WITH NICKEL SALTS I t was pointed out i n the l a s t chapter that platinum( H ) forms complexes with a v a r i e t y of ligands (145) because the double bonding postulated by Chatt et. a l . i s p a r t i c u l a r l y f a c i l i t a t e d due to the closeness of the energy l e v e l 5d to 6s and 6p. Nickel, however, does not enjoy this favourable p o s i t i o n and hence the amount of double bonding i s not at a l l comparable. Whereas the con-f i g u r a t i o n of platinum and palladium complexes Is i n v a r i a b l y planar, that of n i c k e l i s either planar or tetrahedral, depending on the ligands. The former structure i s much more common than the l a t t e r which i s quite rare. The t e t r a -hedral structure i s produced by the more electronegative ligands, since i n these cases the "purely i o n i c " bonds - 83 -formed with the co-ordinated ions w i l l lead to a structure i n which there i s the greatest separation of charge. Thus as the bonds become more io n i c they w i l l more l i k e l y give r i s e to the tetrahedral structure. I t Is therefore found that the attachment of the ligands to n i c k e l through four oxygens tends to be tetrahedral whereas a planar structure i s found f o r the ligands attached through sulphur, the difference being due to the higher electronegativity of (90) oxygen , The energy difference between the o r b i t a l s giving r i s e to the two configurations i s quite small and hence the balance between the two i s very d e l i c a t e l y poised. Thus small s t r u c t u r a l differences In the ligands and changes i n environment may lead to a change i n configuration. In most cases, however, n i c k e l forms an octa-hedral structure, either through co-ordination with the solvent i f i n solution or through polymerisation i f i n a (94) s o l i d state . This has been explained on the basis of c r y s t a l f i e l d theory which shows a gain of 1 5 - 3 0 kcals i n (134) going from a tetrahedral configuration to octahedral • This also explains why the tetrahedral structure i s so rare. In the case or triphenylphosphine < 9 1> however, i t has been shown that n i c k e l does form tetrahedral com-plexes, S t e r i c effect i s supposedly responsible for pre-venting an octahedral configuration ( s t e r i c repulsion of (C_H ) P molecules would prevent polymerization) and the 6 5 3 weak c r y s t a l f i e l d strength of triphenylphosphine w i l l not give a planar structure. Some d i s t o r t i o n of the t e t r a -- 84 -hedron would be expected according to Jahn-Teller effect, (91) however t h i s d i s t o r t i o n would not be large . While discussing the formation of complexes be-tween trifluoromethyl-phosphines and platinum (II) chloride, i t has been found that the electronegativity and s t e r i c effect of the CF group were mainly responsible for the 3 d i f f e r e n t observations. The same factors of size and elec-tronegativity have been noted above as being responsible f o r the occurrence of tetrahedral complexes of n i c k e l . I t might therefore be expected that the trifluoromethyl-phosphines would also form tetrahedral n i c k e l complexes. An examination of the reactions of (CH ) P, 3 3 (CH ) CF P, CH (CF ) P, C H (CF ) P and (CF ) P 3 2 3 3. 3 2 6 5 3 2 3.3 has shown that only the f i r s t two form stable complexes and the remaining phosphines do not react with n i c k e l ( I I ) s a l t s , NiX , where X i s CI", Br", I", SCN*, and No The compounds have been prepared by d i r e c t reaction i n the presence of excess phosphine. The complexes with dimethyl-trifluoromethylphosphine are not as stable as those of trimethylphosphine, and hence have been used without p u r i -f i c a t i o n f o r further study. Trimethylphosphine complexes were r e c r y s t a l l i z e d from butanol. The reaction i n both cases occurs i n the r a t i o of 1:2 of NiX to phosphine. - 85 -The properties of the phosphine complexes are given i n the following table: Compound Magnetic Moment Colour Absorption Maxima (Me P) Ni(NO ) 3 2 3 2 (Me 5P) 2NiCl 2 (Me P) NiBr 3 2 2 (Me P) N i l 3 2 2 (Me P) NI(SCN) 3 2 2 (Me2CP P ) 2 N I X N 0 3 ) 2 (Me 2CP 3P) 2NiCl^ (Me2CP P ) 2 N 1 B p 2 (Me 2CP 3P) 2NiI 2 3 . 1 7 Diamagnetic Dark red Crimson Dark brown 4850(m 3325(s 5320(s 3650(m 5400 (m 2700(s 5175(m 2850(v Orange yellow 4600(sh),3550(vs), (Me 2CP^P) 2Ni(SCN) 2 2,93 Dark red Diamagnetic Pink " Black " Dark brown " Yellow 2975(s 5550(w 4150(s 4800(w 3450 ('s 4875(s 2625(s 3750(m 3140(m , 3 6 7 5(vs), 2550(s) N.Bo s = strong; w = weak; vs = very strong; sh = shoulder. 4600(m 2550(s , 3950 ( s ) , ,3880(m), , 2 6 5 0 ( s ) . ,3800(m), ,2425(w). ,3875(W"), ) , 2600(a ) . , 2 6 0 0 ( B ) . , 4850 ( s ) , , 3 2 7 0(s). ,4050(m), , 2 5 5 0(s). , 3950(a ) , , 2400(a ) . ,3550(m), , 2280(a ) . D i n i t r a t o n i o k e l ( I I ) Complexes: The i s o l a t i o n of the di n i t r a t o complexes of both the phosphines i s d i f f i c u l t since they cannot be precipitated from their solutions and hence they have been studied only i n soluti o n . These n i t r a t o com-- 86 -plexes are very reactive towards moisture and are r e a d i l y decomposed by Xi/ater and other solvents. Warming the bis ( d i -methyl t r i f luoromethylphosphine)dinitrato-nickel( II) with water gave traces of fluoroform and the phosphine (CH ) CF P. 3 2 3 Warming of the trimethylphosphine analogue with water gave trimethylphosphine. D i c h l o r o n i c k e l ( I l ) Complexes: The dichloro complexes of the phosphines (CH ) P and (CH )„CF P are more 3 3 3 2 3 stable than the n i t r a t o analogues. The reaction with dimethyltrifluoromethylphosphine i s slow and i s d i f f i c u l t to carry out i n solution, since the solvents hydrolyse the phosphine (CH„) CF P. Trimethylphosphine, on the other hand, 3 2 3 reacts r e a d i l y and the complex can be r e c r y s t a l l i z e d from suitable solvents. There i s a change i n colour i n d i f f e r e n t solvents which i s probably due to co-ordination i n solution. The aqueous solution i s pink but the colour fades gradually on standing, with the evolution of the phosphine (CH ) P. 3 3 Dibromonickel(II) Complexes: The dibromo complexes of (CH ) P and (CH ) CF P are somewhat more stable than t h e i r 3 3 3 2 3 dichloro analogues, as judged by t h e i r behaviour* towards water and other solvents. Bis(dimethyltrifluoromethylphosphine) dibromonickel(II) shoxi/s the same behaviour as the dichloro compound i n that i t i s formed slowly and i s decomposed r e a d i l y by moisture and other solvents. The bis(trimethylphosphine) - 37 -dibromonickel, however, i s quite stable and decomposes only slowly i n moist air ;. : Diiodo- and Dithiocyanatonickel(II) Complexes: The diiodo and dithiocyanato complexes of these phosphines are quite stable and are unaffected by moist a i r and cold water i n which they are p r a c t i c a l l y insoluble. The complexes d i s -solve on inarming with water but the corresponding phosphines are slowly given o f f . The behaviour of the iodo complexes as well as of the other s a l t s (chloride, bromide, thiocyanate, and n i t r a t e ) towards acids and bases are i n t e r e s t i n g i n that the colour of the solution which i s usually pink i s l o s t i n acid solutions but i s restored when neutralized by bases. Their colours are stable i n neutral solutions only. The' above observations, though q u a l i t a t i v e , reveal the general trend of the s t a b i l i t y of the complexes which i s i n the order NO <^  CI ^ Br ^ I ^SCN. A s i m i l a r 3 (92) relationship has been noted i n the case of palladium complexes I t has been explained on the basis of an increasing amount of pi-bonding i n the Ni-X bond. Another factor noticeable i n the above order of s t a b i l i t y i s the decreasing ^electronegativity of the anion. As was pointed out i n the beginning, electronegativity d i f f e r -ences are l i k e l y to cause differences i n configuration. Since the n i t r a t e ion i s more electronegative than the other anions - 38 -studied, i t (NO. ) i s l i k e l y to form a more io n i c bond. The 3 net effect would be an arrangement with greatest separation of l i k e charges given by a tetrahedral structure. In terms of c r y s t a l f i e l d theory the n i t r a t e ion does not have enough perturbing power to cause spin p a i r i n g and thus give r i s e to diamagnetic compounds. On the other hand, the halo-gen and the thiocyanate ions have s u f f i c i e n t l y high ligand f i e l d strength and hence the complexes are diamagnetic. This i s i n keeping with the empirical relationship between the magnetic properties and the structure of compounds of (93) t h i s type . I t may be mentioned that magnetic moment though not the best guide to the structure i s one of the best c r i t e r i a for a tetrahedral configuration, since s a l t s with t h i s structure are paramagnetic and those with planar structure are diamagnetic. However, the reverse i s not true; i . e . , a l l paramagnetic complexes of n i c k e l are not tetrahedral since octahedral complexes also exhibit para-magnetism. I t i s therefore necessary that the structure be d e f i n i t e l y established, usually by X-ray methods. In the present investigation, the d i n i t r a t o com-olexes of the phosphines (CH ) P and (CH ) CP P have been 3 3 ' 3 2 3 found to be paramagnetic. Since the other d i n i t r a t o complexes (95) (of t r i e thy Iphosphine and triphenylphosphine)have been es-tablished to have tetrahedral configuration i t i s reasonable - 89' -to assume that the above complexes have a tetrahedral structure ..also. The fact that no complexes of the n i c k e l s a l t s , with methylbistrifluoromethylphospbine, p h e n y l b i s t r i f l u o r o -phosphine, and tristrifluoromethylphosphine could be ob-tained i s consistent with the observation that n i c k e l ( I I ) with a larger difference between the 3<i and the 4s and 4p l e v e l s i s not i n a p o s i t i o n to form pi-bonds as.easily as would platinum(II). Since the s t a b i l i t y of the complexes i s enhanced by such bonding, phosphines with reduced a v a i l a -b i l i t y of the lone p a i r electrons do not give any complexes at a l l . This s t a b i l i t y relationship can be seen from a comparison of the s t a b i l i t y of the complexes of (CH^^P and (CH K CF P. I t i s seen that the replacement of one methyl 3 2 3 J group by a trifluoromethyl group reduces the s t a b i l i t y of the complexes considerably. I t i s therefore not surprising that the complexes of phosphines with more than one t r i -fluoromethyl group have not been obtained. S E C T I O N I I GENERAL DISCUSSION CHAPTER VII COMPARISON OP THE PHOSPHINES WITH AND WITHOUT CP, GROUPS Physical Properties: The phosphines as a class are reactive substances. They are a l l malodourous. The trifluoromethyl group produces a change i n odour and i t i s found that phenylbistrifluoromethylphosphine and diphenyl-trifluoromethylphosphine are not so obnoxious as the corres-ponding phenylphosphines. Phosphines occur i n a l l the three physical states: the hydrides, i . e . , the primary and secondary phosphines (lower a l k y l and trifluoromethyl sub-stituted) are gases, the t e r t i a r y phosphines containing the lower a l k y l , trifluoromethyl, and some a r y l groups are o i l y l i q u i d s , and those with higher a l k y l and/or a r y l groups are c r y s t a l l i n e s o l i d s . P r a c t i c a l l y a l l of them s o l i d i f y into a glass when cooled i n l i q u i d nitrogen,x^hich i s c h a r a c t e r i s t i c of most phosphorus compounds. Usually the b o i l i n g points of substances increase with increasing molecular weight, but i n the case of polar compounds this relationship between molecular weight and b o i l i n g point does not seem to hold. This i s p a r t i c u l a r l y true f o r the perfluoro compounds. I t has been found that the b o i l i n g point i n these cases i s correlated with p o l a r i z -a b i l i t y rather than molecular weight^-^l An excellent re-latio n s h i p i s given by the equation: % T b = KM  Rm where T^ i s the b o i l i n g point, M i s the molecular weight, R i s the molar r e f r a c t i v i t y and K Is a constant depending m ° on the p a r t i c u l a r class of compound. The following table (97) gives some values of K C - OH N - - CI - Br - I K 11 .6 12.3 12.75 13.6 15.05 The value of K can be found from the above r e l a -tionship but unfortunately no data i s available for the phos-phines. However from the values of triethylphosphine - 1.446 and d - 0,801), phenyldiethylphosphine ( C 9 H J o C A p < " l f t s 1.5458, d = 0.954) and (C H ) (4-MeC H )P ^ 5 2 6 5 D 2 5 2 6 4 = 1.5428, d = 0.9373). - 9 2 -R i s found from Lorentz-Lorentz equation: m • R ^ *D - ' M M = : • -3-" D + 2. and hence an average value of 11.8 for K can be calculated, Assuming the value of K = 11.8, the r e f r a c t i v i t y equivalent of the di f f e r e n t groups may be calculated. The following table gives the values of R m for the di f f e r e n t groups» H CH, C H P 3 6 5 Equivalents 1.1 5 . 6 5 2 2 . 5 7 .1 ( 9 - 5 f o r PH,,' PH , - 3 2 and PH) From these values the equivalent for the t r i f l u o r o -(97) methyl group may be calculated . I t i s found to be 37«9 for one CF group, 4 2 . 9 for two and 47*4 for three groups. ' • 3 I t may be mentioned that the r e f r a c t i v i t y of an element i s a consti t u t i v e property and hence depends on the environment. The values obtained above are therefore very approximate but give close agreement with the observed b o i l i n g points. The following table shows t h i s . Phosphine B o i l i n g Point Phosphine B o i l i n g Point Calculated Observed Calculated Observed (CH3) P 37.0 37.8 ( ° 6 H 5 ) 3 P 360 360 (CH ) 2PH 24 21.1 (C 6H 5) 2PH 289 280 (CH )PH 3 2 - 10 -14 ,C 6H 5PH 2 155 160 - 93 -Phosphine B o i l i n g Point Phosphine B o i l i n g Point Calculated Observed Calculated Observed P H 3 - 87 -87 CH (C H ) P 3 6 5 2 305 283 (CP 3) 2PH - 2 1.0 (CH,) C H P 3 2 6 5 195.9 192 (CP )PH 2 - 28 -25.5 CE 3(CH 3) 2P 38 46.9 (CF 3) 3P 17 17.0 (CP ) CH P 3 2 3 26 35.2 C P 3 ( C 6 H 5 ) 2 P 257 255 (CF,) C J i P 3 2 6 5 159 150 The agreement between the calculated and the ob-served values i s found to deviate within reasonable l i m i t s . This may be expected obviously from the nature of the approxi-mation — p a r t i c u l a r l y the value of atomic r e f r a c t i v i t y of the d i f f e r e n t groups. This i s found to vary widely and obviously requires further examination. However, for the present i t i s s u f f i c i e n t to say that the b o i l i n g points of the phosphines are not a function of molecular weight alone but depend on the p o l a r i z a b i l i t y of the groups attached to i t . A p l o t 3 / . of M 'c/ R^ against the observed b o i l i n g points gives a straight l i n e as shown i n f i g . ( A )• The deviations may again be attributed to environmental effe c t s . The relationship discussed above i s excellent i n that i t correlates the methyl, phenyl, and trifluoromethyl groups, at the same time i n d i c a t i n g that the trifluoromethyl-phosphines are not uniquely d i f f e r e n t from other phosphines but, rather, f i t the general pattern. The low b o i l i n g points of the fluorocarbons are thought to be due to low intermole-cular f o r c e s ^ ^ a n d large intramolecular forces. Such forces -93-3/2 F l g * A * P l o t of M ~/Rm Vs. B o i l i n g Point (Observed). 14. (CP ) CH P 15. CP (C H ) P 16. (CF ) C_H P - 94 -make the fluorocarbon molecules i n f l e x i b l e and therefore prevent free rotation* This r e s t r i c t i o n would be responsible for lowering the b o i l i n g points. The same might be true of the trifluoromethyl-phosphines i n which the trifluoromethyl group would be responsible f o r the low intermolecular forces, r e s u l t i n g i n t h e i r higher vapor pressure compared with the methyl analogues. The other properties of the phosphines are also related i n a s i m i l a r manner. Thus the latent heat of vapori-zation i s lower for the trifluoromethyl-phosphines than the methyl- or phenyl-phosphines. The following table gives the values of the latent heats for the phosphines: Phosphines Lv (cal/mole) Phosphines Lv (cal/mole) PH 3489 P(CF ) CH 6310 3 3 2 3 PH(CH L 6270 PCF (CH ) 6950 3 2 3 3 2 P(CH^) 6943 PtCF^CgH 9054 P(CF ) 5890 PCF (C H ) 11850 3 3 3 6 5 2 Unfortunately the values for a l l the phosphines are not reported and so i t i s d i f f i c u l t to correlate t h i s property. However, i t i s possible to say a l i t t l e about the trifluoromethyl-phosphines whose values are known. Since the heat of vaporization i s a measure of the forces acting between the molecules of the same species, i t i s possible to understand the low vapor pressures exhibited by trifluoromethyl-phosphines . - 95 -The heat of vaporization i s empirically related to p o l a r i z a b i l i t y of the s u b s t a n c e T h e force preventing a molecule from leaving the surface of the l i q u i d does not depend on the mass and hence i t i s possible to see why the heat of vaporization would not depend on the molecular weight. Larger molecules are e a s i l y deformed. Their effective area i s greater and hence the energy required for transformation into vapor would be large. Thus heat of vaporization would depend on the molecular size and the deformability of the molecule, both of these factors being a measure of p o l a r i z -a b i l i t y . The fluorocarbons have been considered as " s t i f f molecules" ^ "^and hence the molecular size would not enter into the o v e r a l l deformability of the fluorocarbons. The large trifluoromethyl groups may behave likewise and hence the properties would be si m i l a r * The lower heat of vaporization of the t r i f l u o r o -methyl-phosphines may also be explained on the basis of the concept of i n t e r p e n e t r a t i o n ^ ^ ] according to which the hydrocarbon molecules interpenetrate one another,whereas fluorocarbons do not do so or do i t to a n e g l i g i b l e amount. Thus f o r vaporization of interpenetrated molecules energy would be required: (1) to free the molecules from t h e i r interpenetrated condition and, (2) f o r transformation of the phase; i . e . , f o r bringing i t from the l i q u i d surface to a i - 9 6 -vapor state. In the case of non-interpenetrated molecules only ( 2 ) would be involved and hence the energy of vaporization would be low. Extension of this phenomenon to the t r i f l u o r o -methylphosphine would show that this concept applies very w e l l . The trifluoromethyl group i s large, compact, and more electronegative. The f i r s t two factors would prevent i n t e r -penetration and the electronegativity would cause repulsion, so that the net effect would be a lower heat of vaporization. I t i s s i g n i f i c a n t i n th i s connection to notice the close values of AH^ of trimethylphosphine and dimet h y l t r i f l u o r o -methylphosphine (6943 and 6950 cal/mole). This indicates that some amount of interpenetration has been promoted by the re-pulsive action of the trifluoromethyl group which causes intermeshing of the methyl groups. This effect would be absent i n the phosphine with two trifluoromethyl groups. This also explains the higher b o i l i n g point of dime t h y l t r i -fluoromethylphosphine compared with trimethylphosphine. concept of interpenetration to the phosphines would suggest that the trifluoromethyl phosphines would not be associated and would have the normal values of Trouton's constant. The above discussion of the application of the Phosphine' ( C F „ ) P Z 3 ' 3 Trouton's Constant 2 0 . 3 (CF )CH P CF (CH,)-P (CH7) P 3 ^ 3 3 ^ ^ -> 3 2 0 . 5 2 1 . 7 2 2 . 3 Phosphine (CH ) PH 3 2 Titojaton • s Cons tant 2 1 . 2 1 8 . 7 ( C P 3 ) 2 C 6 H 5 P C P 3 ( C 6 H 5 ) P 2 1 . 3 22 - 97 -Although the values are not s i g n i f i c a n t l y d i f f e r e n t , the above table shows that progressive replacement of the di f f e r e n t groups gradually lowers the Trouton's constant. Thus tristrifluoromethylphosphine and methylbistrifluoromethyl-phosphine have normal values. Trimethylphosphine and phenyl-bistrifluoromethylphosphine are probably associated more than dimethyltrifluoromethylphosphine, phenylbis trifluoromethyl-phosphine, and dimethylphosphine. I t i s interesting to note that the values f o r CF^CH^gP and (CE^)^P are quite c l o s e , showing that the former i s associated,and t h i s might be the reason for i t s higher b o i l i n g point, compared with the l a t t e r . Chemical Properties: The phosphines i n general are insoluble i n water under normal conditions, thus showing no tendency towards hydration. They are, however, soluble i n organic solvents. The primary and the secondary phos-phines dissolve to a small extent i n water. The t r i f l u o r o -me thylpho sphines conform with the general behaviour of the phosphines towards solvents under ordinary conditions, but at high temperatures they usually react with the solvent and lose the trifluoromethyl group. The loss of the t r i f l u o r o -methyl group w i l l be considered later,but for the present,it i s s u f f i c i e n t to say that the P-CP bond i s i n some way more 3 susceptible to attack. Phosphines as a class are basic i n nature. How-ever, phosphine PH i s very weakly basic. The b a s i c i t y r i s e s 3 with the degree and type of substitution. The order of - 9 8 -b a s i c i t y i s primary ^secondary <^  t e r t i a r y I For the t e r t i a r y phosphines, introduction of electron-withdrawing groups reduces i t . Thus the order of b a s i c i t y i s a l k y l ^ a r y l ^ trifluoromethyl. This can be seen from the reaction with hydrochloric acid and the ease of hydrolysis of the s a l t so formed. Thus CH PH forms c r y s t a l l i n e s a l t s with HC1 3 2 and HI; C H PH i s sparingly soluble i n HC1 but forms a s a l t 6 5 2 with HI. The same i s the case with secondary phosphines. The s a l t of (CH ^PH and HC1 i s stable,but that of (CgH^PH i s decomposed e a s i l y by water. The same order i s applicable to the t e r t i a r y phosphines: (CH ) P-HC1 i s quite stable, 3 3 (C H ) P»HC1 i s decomposed on d i l u t i n g the acid solution and 6 5 3 tristrifluoromethylphosphine does not form a s a l t at a l l . However, this possibly r e f l e c t s the s t a b i l i t y of the hydro-chloride rather than the r e a c t i v i t y of the phosphine. The phosphines In general show additive properties. The lower members (hydrides and a l k y l substituted) can be oxidized r e a d i l y i n a i r . The a r y l phosphines are o x i d i z e d only by strong o x i d i z i n g agents or i n the presence of c a t a l y s t s . The trifluoromethyl-phosphines do not form an oxide d i r e c t l y and l i k e the a r y l phosphines require an intermediate compound. Direct reaction with atmospheric oxygen breaks the P - CP 3 bond and does not give any oxide. The possible explanation for this phenomenon has been given previously with respect to the reduced amount of pi-bonding character, which i s exhibited i n t h e i r reactions mentioned i n SectionH. - 99 -The mixed methyl phosphines RR^P have properties e.g. ( C H ^ P and intermediate between the two extremes (CF ) P , exhibiting the properties of the predominant j J> J group. Thus methylbistrifluoromethylphosphine resembles tristrifluoromethylphosphine rather than trimethylphosphine, and dimethyltrifluoromethylphosphine resembles trimethyl-phosphine rather than tristrifluoromethylphosphine. Dimethyl-fluoromethylphosphine and trimethylphosphine react slowly with a i r t o give the oxide, but tristrifluoromethylphosphine and methylbistrifluoromethylphosphine inflame i n a i r and no oxide i s formed i n the presence of excess a i r . The mixed phenyl-phosphines, on the other hand, r e t a i n the inductive and mesomeric effects of the benzene r i n g . Thus the presence of one phenyl group i s s u f f i c i e n t to s t a b i l i z e the phosphine C^H^CF^^P completely so that i t does not react with atmospheric oxygen. The effect can also o be noted i n the r i s e In the b o i l i n g point from 17 f o r t r i s -trifluoromethylphosphine to 150 f o r phenyIbistrifluoro-methylphosphine. The s t a b i l i t y has been considered i n Section I and has been thought to be due to the conjugation effect together with the electron-withdrawing tendency of the t r i -methyl group. The effect may be represented as: F F P _ c O p D c — F 15 F - 100 -Thus,the electron-withdrawing tendency being s a t i s f i e d by thee d r i f t of electrons from the phenyl groups, the pi-bonding character i s restored to a certain extent and the P-CF, bond 3 i s s t a b i l i z e d . I t may be worthwhile estimating this e f f e c t . I t has been shown previously i n Chapter 2 that an increase i n the bond distance increases the r e a c t i v i t y , and the bond lengths i n P-CH, and P-CF have been noted as 1 .87 and 1 .93 3 3 respectively. The bond shortening has been attributed to (3D pi-bonding . I t has been shown that for the formation of such bonds, the r e l a t i v e electronegativities of the bound (102) atoms or groups are not c r i t i c a l . An estimate can be (101) made of the bond shortening due to pi-bonding . This gives a bond shortening of 0 . 0 5 4 A for 0 . 1 pi-bond or for a 10% pi-bonding character. This i s just the amount of bond lengthening observed i n (CF ) P I t would therefore be 3 3 expected that the P-CF, bond energy would be short of 10% J (-3] of the pi-bonding energy (50 kcal) attributed to phosphorus giving a value of 57 kcal mole - 1 for the P-CF bond. The 3 t o t a l loss of energy due to the presence of CF groups would .1 3 then be 15 kcal mole , which i s s u f f i c i e n t l y s i g n i f i c a n t to a l t e r the character of. the phosphine concerned. A reaction which i s common to a l l phosphines i s the reaction with halogens. This i s surprising i n view of the - 1 0 1 -fact that some of the phosphines react only r e l u c t a n t l y with hydrochloric acid. As has been said previously, this i s possibly because of the mechanism of reaction. In the case of reaction with hydrochloric acid a nucleophilic attack of the lone pair on the proton i s involved, whereas i n the case of the reaction with halogens an e l e c t r o p h i l i c attack of the halogens on the lone p a i r electrons takes place. The phosphines usually react vigorously with the halogens and form the phosphoranes R^PX^• The formation of phosphoranes i s possible only under controlled conditions; otherwise a replacement reaction occurs i n which one of the groups i s substituted by the halogen atom forming a halo-phosphine. The mechanism of formation of the halophosphine, however, involves the formation of a phosphorane: R P+X -3 2 (R XP) 3 + -X uncontrolled > (R XP)+X 3 -> R XP+ RX The ease of reaction with the halogens i s i n the order (P) ^  CI ^  Br ^  I. (The' f l u o r i n e compounds have not been f u l l y studied,) The chlorides are the most stable, whereas the iodides are i n most cases quite unstable and are not known. The non-occurrence of most iodophosphoranes i , i s possibly due to s t e r i c factors as well as to the lower electronegativity of iodine. The promotion energy to match - 102 -the s-, p-, and d- o r b i t a l s demands that the ligands be electro-negative. Large ligands have high p o l a r i z a b i l i t y ; consequently, t h e i r size would prevent a close packing. This i s possibly the reason why PI does not occur. However, the iodo-phos-5 phoranes of the phosphines with a certain amount of pi-bonding would be expected to be formed. The a l k y l and a r y l phosphines (68) ( t e r t i a r y ) are found to give the cUiodophosphorane . The trifluoromethyl-phosphines do not form the iodo-compounds (except ( C J E L ) 0 C F P ) and t h i s gives further support to the o 5 2 3 argument that they are devoid of any pi-character. I t has already been said that the formation of halo-phosphines takes place through the formation of an i n t e r -mediate phosphorane. This reaction may be considered a decomposition of the phosphorane since i t takes place only on heating, with a rearrangement of bonds such that more stable compounds are formed. This type of reaction occurs probably because i t Is i r r e v e r s i b l e ; i . e . , reactions of the type R P X + R X — - * R P X do not take place. ( ;Obviously the addition 2 3 2 reactions with phosphorus tr-ihalides are not possible. How-ever, gradual replacement of the halogen atom increases the tendency towards addition reaction and with diphenylchloro-phosphine and benzyl halide we do get ( C H ) C H P C I . ) 6 5 2 7 7 2 The phosphoranes are an i n t e r e s t i n g series of com-pounds. In t h e i r reactions they resemble the phosphonium compounds. Their conductivity i n solutions indicate that they - 103 -are ion i c i n nature with the structure R„PX" + R PX •3 — - 3 3 PX X 4, I easil Ly or They can be hydrolysed e with the f o r -mation of an "oxide R^PO. The trifluoromethyl-phosphoranes d i f f e r from the others i n this respect. Their aqueous hy-(103) d r o l y s i s usually produces an acid . ( C F ) P C I 3 3 2 ( C F 5 ) 3 P C 1 2 ( C P 3 ) 2 P C I 3 H20 (CF ) P(0)0H+ CF H 3 2 3 NaOH J£a > ( C F )P(0)(0Na) + 2CF H 3 2 3 2H90 d ' > (CF ) P(0)0H + 3HC1 The mixed phosphoranes R2R PX 2 exhibit intermediate properties. (C.H LCF PBr i s re s i s t a n t to aqueous hydro-6 5 2 3 2 l y s i s and i n this respect resembles (CgH^J^PBr^ showing that the effect of the phenyl groups i s s t i l l predominant. C H (CF LPBr on the other hand gives C H (CF )P(0)0H on 6 5 3 2 2 6 5 3 aqueous hydrolysis and i s s i m i l a r to the hydrolysis of (CF ) PCI . The methyl-trifluoromethyl-phosphoranes have 3 3 2 not.been prepared but they are expected to behave s i m i l a r l y . The a l k a l i n e hydrolysis of the phosphoranes (other than trifluoromethyl) invariably gives the oxide. The trifluoromethyl-phosphoranes, however, give acids, de-pending upon the number of trifluoromethyl groups displaced. Thermal-decomposition of the phosphoranes gives a halophosphine and an a l k y l or a r y l or trifluoromethyl halide. - 104 -R PX > R PX +• RX 3 2 2 R 2PX 3 > RPX2 +- RX RPX > PX 4- RX 4 3 ^ These reactions suggest that a structure with more (61) X than R i s more stable ; i . e . , R„PX„ should be more stable 2 3 than R PX^. A detailed study has not been made i n this con-3 2 (60) nection but whatever evidence i s available, suggests that R_PX i s covalent and R PX„ i o n i c i n nature. 2 3 3 2 The thermal cleavage of R from R^ R PX^ possibly depends on the nature of the group, the weakly bonded group being cleaved more ea s i l y . Thus i n (C H ) CP PBr , t r i -6 5 2 3 2 fluoromethylbromide i s l o s t e a s i l y . This i s comparable with the analogous arsenic compounds. The formation of halophosphines on reaction of the phosphine with halogens Is an i n t e r e s t i n g reaction since these compounds are w e l l suited f o r the synthesis of other compounds, and t h e i r polymers. This reaction may be com-pared with the formation of a phosphorane and i t s subsequent decomposition into halophosphine and a halide of the attached group. The hydrogen of the primary and secondary phosphine (69b) can be replaced e a s i l y by halogens . Tertiary phosphines have to be heated In order to produce the halophosphine. Irifluoromethyl-phosphines d i f f e r from the other phosphines i n t h e i r reactions with iodine. They react with iodine cleaving a l l the trifluoromethyl groups to give t r i f l u o r o -iodomethane. - 105 -The halophosphines are reactive compounds, due to the presence of the halogen atom. Thus most of t h e i r re-actions are simi l a r to those of the t r i h a l i d e s of phosphorus. (104) The R PX compounds are more reactive than RPX^ . The 2 2 reactive group being halogen, the halophosphines can easil y be oxidized i n a i r . I f the other groups attached to phos-phorus are also reactive, oxidation occurs explosively. The trifluoromethyl-iodo-phosphines decompose i n t h i s manner since the bond energies of P-I and P-CF are both lower than P-0. However, i n the presence of s t a b i l i z i n g groups l i k e the higher a l k y l and phenyl groups, they are quite stable. The oxidation of such halophosphines gives the corresponding phosphonyl halides RPOXg or RgPOX. The hydrolysis reactions are discussed i n the next chapter, but i t i s s u f f i c i e n t to say here that the t r i f l u o r o -methyl-halo-phosphines give fluoroform and phosphorous acid whereas the other halophosphines give the corresponding phosphine and the acid. Like the phosphines, the halophosphines add halogens to give the pentavalent compounds. RPX + X >• RPX R PX + X > R PX 2 2 4 2 2 2 3 The monohalophosphines being more l i k e the ter-t i a r y phosphines, show a greater tendency towards such reactions than the dihalophosphines, which behave more l i k e the t r i h a l i d e s of phosphorus. - 106 -The r e a c t i v i t y of the halogen atoms i n the halo-phosphines can be seen from t h e i r replacement by the other halogen or pseudo-halogen atoms. The exchange of a halogen atom with an organic group by reacting with organoraetallic compounds i s u t i l i z e d for the preparation of higher sub-s t i t u t e d halophosphines. Another important reaction u t i l i z -ing t h i s property i s the Wurtz reaction. The metals usually employed f o r t h i s reaction are l i t h i u m , sodium, and mercury. The phosphines react with a l k y l halides to form quaternary compounds. The formation of the quaternary com-pound depends on the b a s i c i t y of the phosphine. However, the s t a b i l i t y of the quaternary compound does not depend only on the base strength of the phosphine. The two pro-perties depend on d i f f e r e n t factors, the strength depending on polar effects while s t a b i l i t y can depend to a large ex-(66) tent on stereochemical effects . Thus the lower members react spontaneously whereas with bulky groups heating i s necessary f o r formation of the quaternary compound. The s t a b i l i t y also depends on the p o l a r i t y of the bond. A hydrochloride w i l l be hydrolyzed eas i l y i f the p o l a r i t y of P-H i s greater than the other bonds. In the case of groups with p o s i t i v e inductive effect -j-I, (e.g., the a l k y l groups) the p o l a r i t y would be lower than for groups with negative inductive effect. Consequently, the hydrochloride of t r i -- 1 0 7 -phenylphosphine would not be as strong as that of trimethyl-phosphine. S i m i l a r l y , phosphines with two trifluoromethyl groups have not been found to form quaternary s a l t s , but quaternary salts for phosphines with one trifluoromethyl group have geen i s o l a t e d . The phosphonium sa l t s undergo thermal decomposition giving the organic halide R X and the phosphine R P . The -,. 3 decomposition of a phosphonium compound with mixed groups [ R R ' ^ ' . I i n several ways. I t i s S u f f i c i e n t here to say that the ease "**X i s much more complicated i n that i t may occur of elimination of the various ra d i c a l s depends on t h e i r (74) r e l a t i v e a f f i n i t y f o r a negative charge . On this basis the electron a t t r a c t i n g groups head the scale. Thus In a phosphonium s a l t with mixed groups the more electronegative groups w i l l cleave more e a s i l y . However i t has been found that the decomposition of such compounds gives a mixture of halides of the d i f f e r e n t radicals present i n i t . The posi-t i o n i n the scale for the trifluoromethyl group cannot be determined at t h i s stage since the thermal decomposition of . + -(CH ) CP P I has not been studied, but the decomposition 3 3 3 of the phosphonium compound CH,(C H ) 0CF P I gives a mix-• -> 6 5 2 3 ture of methyl iodide, fluoroform, and benzene. The formation of complexes i s a c h a r a c t e r i s t i c property of the phosphines. A large variety of such com-- 108 -plexes are known. The simplest are the carbon.disulphide and p-benzoquinone adducts. For the formation of such an adduct i t i s desirable that the carbon atom be i n a conjugated sys-O S tem (such as i n p-benzoquinone (u) and carbon disulphide C ). 6 s I t i s imperative that attached atoms are such that they create an electron deficiency on the carbon atom. Thus carbon d i -oxide does not form an adduct nor does dimethyl- y p y r o n e ^ ^ ) However the chief c r i t e r i o n i s the a v a i l a b i l i t y of the lone pai r electrons. The a l k y l phosphines form carbon disulphide and p-benzoquinone adducts. Triphenylphosphine does not form a CS^ adduct but forms a p-benzoquinone addition com-pound. The difference i s due possibly to the structure factors (108) and to the mechanism of reaction • The mixed phosphines with more a l k y l groups (Alk C II P) form CS„ adducts but no 2 6 5 2 compound with p-benzoquinone i s reported. The phosphines Alk(CgH,-)2P have also been reported as not forming CS^ or p-benzoquinone adducts. The trifluoromethyl-phosphines do not form any compound with carbon disulphide. The phosphines form a series of addition compounds with metal halides, p a r t i c u l a r l y mercury halides, but also with copper, s i l v e r , gold, cadmium, zinc, boron, aluminium, t i n , cobalt, n i c k e l , palladium, platinum, and various other t r a n s i t i o n metals. A discussion of complex formation with the metal halides mentioned above would become very involved i f they were discussed i n d i v i d u a l l y . Since i n a l l cases ;. - 109 -the Influence of the electronegative ligand on coordinating property of the phosphine i s apparent, i t w i l l be easier to st a r t with strong acceptors—boron and aluminium h a l i d e s — and then consider the other metals. However, a f u l l d i s -cussion i s handicapped by the lack of information about the trifluoromethyl-phosphines. The formation of complexes with boron t r i f l u o r i d e has been discussed i n chapter 4 where I t was shown that the Inductive, s t e r i c , and hybridization effects were a l l res-ponsible for t h e i r formation and s t a b i l i t y . The Inductive and s t e r i c effects were considered mainly responsible for the occurrence of the complexes discussed, and the s t e r i c factor would be ignored i n those cases. The s t e r i c and hy-b r i d i z a t i o n effects do play an important part i n the chemi-str y of the other phosphine-boron compounds. I t i s known that the change of the group can cause a change i n h y b r i d i -zation of the phosphorus or boron atoms. Substitution of hydrogen by methyl on the phosphine i s an example. The elec-tron releasing methyl group would cause higher hybridization effect; i n other words trimethylphosphine would be more highly hybridized than phosphine. Since trimethylphosphine would not require as much energy as phosphine to be promoted to the completely hybridized state, the l a t t e r would be a (109) weaker base . The effect Is related to the bond angles which are: - 110 -Phosphine: PR, P(GH ) P(CP ) 3 o V 3 3 o Bond angle: 93.5 100.4 99.6^2,5 The acid-base reaction involves (1) the promotion energy to a state of complete tetrahedral hybridization and (2) energy for the formation of the sigma-bond. The d i f f e r -ence in hybridization energy is seen to explain the behaviour of phosphine and trimethylphosphine, but does not explain the Inertness of the lone pair electrons of (CF^j^P where the inductive effect is now much more important. It was pointed out earlier that the different reference acids would indicate different s t a b i l i t y relation-ships and since a raonotonic scale of such relationships i s d i f f i c u l t to establish the different acids should be con-sidered separately. Some of the obvious differences are: PP.BP i s not known but F,P.BH has been prepared. BH 3 3 3 3 3 i s , however, a very strong acceptor. Phosphine (PH ) forms 3 1:1 complex and also 1:2 complex with BP^, PH^BP^, and PH (BP ) . It forms 1:1 complexes with boron trichloride, 3 3 2 tribromide, borane, BH^ and boron trimethyl. Dimethylphosphine (CH )0PH forms a complex with 3 2 BH . This addition compound (CH ) PH.BH loses hydrogen at 3 o r 3 2 3 150 and forms a dirtier „ and a tetramer 2 [<CH3)2BBH2J UCH^J^P.BH 1 ^ . These polymers are very stable compounds. Methylphosphine (CH )PH also forms a 1:1 complex CH PH .BH • 3 2 3 2 3 - I l l -Triphenylphosphines form complexes with most of the boron compounds but they have not been inve s t i g a t e d — o n l y the compounds with BG1 ^ 1 1 5^and B(CiI ) ^ 1 1 6^have been reported 3 6 5 3 and the compound with BP has been prepared during this 3 i n v e s t i g a t i o n . The addition compounds with phosphines bearing mixed groups have also not been reported so that a co r r e l a t i o n with respect to the phosphines cannot be attempted beyond whatever has been mentioned already. The study with the aluminium s a l t s has also not been explored f u l l y . Complexes of only the raethyl-phosphines have been prepared showing the general trend that the elec-tron releasing a l k y l groups increase the donor properties of the phosphines. Compounds of gallium, indium and thallium a l k y l s have also been prepared but not with a variety of phosphines. The application of the above study to the tran-s i t i o n metal halides would also show the same trend—the electronegative groups would decrease the donor properties of the phosphine. In the case of t r a n s i t i o n metals the noted difference i s the a b i l i t y to form a dir- dir bond. Such bonding alloi^s complex formation by a wide range of phosphines. The addition compounds of the phosphines with the dihalides of the various metals are generally of two types: the rationof the phosphine to the metal halide may be 1:1 or 2:1, The 1:1 complexes are usually dimers with bridged structures. In the case of copper and s i l v e r (Cu(l), Ag(l)) i t - 112 -has been shown that the 1:1 complexes are four-fold macro-(110,111) 4 The above complexes are known only f o r a small molecules of the formula R P —>MI 3 group of the a l k y l phosphines. The data on phenyl-phosphines i s scanty. However ;dimethylphenylpbosphine and diethylphenyl-phosphine have been studied. The former gives both 2 : 1 and 1:1 complexes whereas the l a t t e r gives only 1:1 complexes with copper(l)and s i l v e r ( l ) . The t r i f luoromethyl-phosphines do not form any complexes with s i l v e r iodide, except dimethyl-trifluoromethylphosphine which gives an unstable 1:1 complex. However complexes with d i e t h y l p-trifluoromethylphenylphos-phine have been prepared and they are 1:1 for copper(l) iodide and 2 : 1 for s i l v e r iodide . These 2 : 1 complexes are more stable than the 1 : 1 . This i s considered to be due to the s o l u b i l i t y and concentration of the complex i n the medium. However, i t has been shown i n the case of platinum(II) chloride that electronegative ligands on the t e r t i a r y phosphines en-hance the pi-bonding character since there would be a d r i f t of electrons towards the ligand therefore forming stronger bonds. This increased amount of pi-bonding might be res-(113) ponsible f o r making a 2 : 1 complex more stable . The t r i -fluoromethylphosphines have no tendency to form even a weak sigma-bond wfth these metal halides and hence the question of the s t a b i l i z i n g influence of 7r-bonding does not a r i s e . - 1 1 3 -The complexes of the phosphines with the halides of mercury, p a r t i c u l a r l y mercuric iodide and chloride have been studied much more extensively than the other metal halides of the same group. P r a c t i c a l l y a l l phosphines with even a s l i g h t amount of pi-character seem to give a mer-curic iodide complex. The trifluoromethyl-phosphine com-plexes have not been is o l a t e d but q u a l i t a t i v e tests show that unstable complexes can be produced for dime t h y l t r i -fluoromethylphosphine and diphenyltrifluoromethylphosphine. The other trifluoromethylphosphines (CF^) P, (CF^CH^P and (CF ) C H P do not seem to react w i t h mercuric iodide 3 2 6 5 but this would require a systematic study. Further c o n f i r -mation of the strong coordination tendency of mercury halides towards the phosphines comes from the stable com-plexes of diethyl-p-trifluoromethylphenylphosphines. Since the electron-withdrawing tendency of a p-trifluoromethyl-phenyl group would be approximately comparable to the trifluoromethyl group i t s e l f , i t i s reasonable to conclude that complex formation by phosphines i s possible i f there i s some amount of pi-bonding character present. This view would be found to be generally applicable. Knowledge of the complexes of the phosphines with other t r a n s i t i o n metals i s extremely scattered and not - 114 -much, i s known about them. However n i c k e l , palladium, and platinum form a group of important complexes. The unique p o s i t i o n of platinum compared with palladium and n i c k e l has already been mentioned. The compounds of metals of higher t r a n s i t i o n series are invariably planar since elec-tron p a i r i n g , according to ligand f i e l d theory, can occur .readily. The other factors governing the configuration are the s t e r i c effect, electronegativity, and the Jahn-T e l l e r e f f e c t . The addition compounds of the trialkyl-phosphines with platinum(II) and palladium(II) occur both i n 2:1 and 1:1 r a t i o . For platinum(II) the phenyl-phosphines and trifluoromethyl-phosphines have been reported to form only the 2:1 type of compounds. The complexes with phenyl-phosphines and palladium have not been reported. The com-plexes of the 1:1 type are bridged through the halogen a toms: R P CI CI 3 \ / \ / Pt _Pt CI CI PR^ Their configuration permits them to exhibit geo-metrical isomerism. Thus both types, v i z . 2:1 and 1:1, occur i n c i s and trans forms. According to the generaliza-t i o n made i n chapter 5» phosphines with higher a l k y l and/or - 115 -trifluoromethyl groups give mainly trans-isomers. The phenyl and/or lower a l k y l substituted phosphines give mainly c i s -isomers. I t would be observed from the above discussion that the trifluoromethyl group exhibits the properties of a pseudo-halogen. The high electronegativity makes i t resemble the halogens but because of i t s volume i t does not quite f i t into that series. The main difference i s that, unlike the halide ions, the trifluoromethyl anion does not exist as a stable entity. - 116 -C H A P T E R V I I I HYDROLYSIS OF THE TRIFLUOROMETHYL-PHOSPH0RUS COMPOUNDS Trifluoromethyl compounds as a class are suscep-t i b l e to hydrolytic attack. The hydrolysis reaction usually goes to- completion with the quantitative l i b e r a t i o n of fluoroform. Several trifluoromethyl compounds are, however, known i n which the M-CF bond Is res i s t a n t to hydrolytic 3 attack. Only one compound of phosphorus, trifluoromethyl-phosphonic acid, i s known i n which the fluoroform i s not lib e r a t e d easily, - although i t i s evolved slowly on heating o to 150 . I t has been proposed that the lengthening of the M-CF^ bond i s responsible for the ease of hydrolysis as r 11,7; r-observed i n the case of the trifluoromethyl compounds of the group V elements ^ " ^ l In the other cases where hydrolysis i s d i f f i c u l t , as f o r example i n pe r f l u o r o a l k y l halides, the bonds are either normal or shorter than those observed for the corresponding a l k y l compounds. However, instances to the contrary are also known i n which the M-CP bond i s 3 longer than the corresponding M-CH bond and s t i l l the hydro-3 l y s i s i s d i f f i c u l t . One such compound i s CF,SF . The follow-3 5 ing observations are relevant i n the discussion of the ease of hydrolysis as observed i n the case of P-CF compounds. 3 -1. The P-CP bond lacks pi-character thus reducing the 3 bond energy of t h i s bond compared with P-CH and P-CHH . 3 6 5 2. The trifluoromethyl group acts as a pseudohalogen group, so that i t s behaviour i n the case of phosphorus com-pounds would be l i k e the t r i h a l i d e s . 3 . The behaviour as a pseudohalogen group i s supported by i t s high electronegativity and high electron-withdrawing (142) effe c t , obtained from the o~ value given by Taft . The following table gives the values of electronegativity of groups and t h e i r o~ value and shows i t s s i m i l a r i t y to the other electronegative groups. Group Electron-withdrawing Electro-power negativity CH . 0.00 2 . 3 4 b 3 H 0.49e 2.10° CCH 0.60® 2.70 d 6 5 I 3 OCH M.46 a 2 . 9 2 a - 118 -Group Electron-withdrawing Electro-power <fn' negativity O C 6 H 5 2.38 3 . 10 I 2 . 3 8 2 . 6 8 Br 2.80 2 . 9 4 01 2 . 9 4 3 .19 CP 3 2.81 f 3.3^ P 3.08 3.93 CC1 2 . 6 5 f 2 . 8 5 b 3 f « ^ t> CBr 2 . 5 0 2 . 6 3 a calculated from (142a) by multiplying with 2 . 8 . b ( 1 4 0 ) , C C&Q), d ( 5 h ) , e ( 1 4 2 ) , f (105), g (106) 4« The ease of hydrolysis for the phosphorus halides i s known to increase as the electronegativity of the halogens decreases. However, the above table would indicate that the ease of hydrolysis would be better understood i f the electron-withdrawing power i s also taken into consideration. 5. whereas the bond energy and the electronegativity values do not d i f f e r e n t i a t e between the ease of hydrolysis of P-CP and P-I on the one hand and P-CH and P-C H on the 3 3 6 5 other, the electron-withdrawing power does Indicate the d i f f i -c u lty that could a r i s e i n the hydrolysis of the l a t t e r bonds. This difference i s further seen by the comparison of the heat of formation of the various compounds that might be expected i n the hydrolysis reactions. - 119 -Compound AH CH 17.88 4 a CF 220 4 CF H I69 a 3 C^ H , 19-82 6 . § CO— 161.63 H F ( a q ) 78.66 NaF 135.9 (aq) PH 2.21 3 H , P O, x 232.2 3 3(aq) CF 117a 3 a = (143) The above table indicates why the methyl and the phenyl groups would be d i f f i c u l t to hydrolyse l whereas the hydrolysis of the CF, group would be easy. This table also indicates the 3 p o s s i b i l i t y of a closely s i m i l a r reaction by which a flu o r i d e and a carbonate could be formed. There are quite a few t r i -fluoromethyl compounds which hydrolyse In t h i s manner. This difference has been attributed to a di f f e r e n t mechanism ^ (118) of reaction . In the case of substituted phosphines i t has been Observed that t h e i r hydrolysis i s much easier when they are oxidized to the pentavalent state. This i s possibly because of the structure of the quinquevalent compound; v i z . , t r i g o n a l bipyramidal. Radioactive exchange studies indicate that the - 120 -equatorial positions i n the phosphoranes are d i f f e r e n t i n (119-121) behaviour from the apical positions . The difference i s indicated by the hydrolysis of t r i s t r i f l u o r o m e t h y l d i -chlorophosphorane and bistrifluoromethyltrichlorophosphorane. The trifluoromethyl groups of the former are supposed to be i n the equatorial p o s i t i o n and can be hydrolysed e a s i l y , but i n the l a t t e r they are i n the a p i c a l p o s i t i o n so that hydro-l y s i s does not remove the trifluoromethyl groups and the P-Cl bonds are replaced instead. However, these examples are meant to reveal only the difference i n behaviour due to p o s i t i o n of the group. I t i s observed from the reactions of the phosphoranes that unless points of more favourable attack are present i n the equatorial p o s i t i o n , the a p i c a l positions are f i r s t attacked giving an unstable intermediate. PX + 2H 0 > [PX (OH) 1 +- 2HX I f groups l i k e methyl or phenyl are present, this intermediate i s s t a b i l i z e d by l o s i n g a water molecule and forming an oxide, PX 3(OH) 2 X P0 4- H 0 3 ^ 2 but i f electron withdrawing groups are present, the reaction goes further and such groups are l o s t . X P(0H) 3 2 -> X 2P0(0H)+HX The foregoing mechanism i s supported i n p a r t i c u l a r by the observation that (1) phosphoranes formed from phos-phines which cannot be hydrolysed e a s i l y are themselves rapi d l y hydrolysed with the loss of the more electron with-drawing groups, and (2) hydrolysis of the phosphines usually - 121 -gives phosphorus i n the pentavalent state. The l a t t e r obser-vation therefore outlines the general mechanism of hydrolysis of the phosphines:. 1. Promotion to the intermediate penta-valent state, followed by (2) Rearrangement to give a stable structure. • This mechanism may now be considered i n the l i g h t of experimental f a c t s . 1. Phosphines: (a) Tristrifluoromethylphosphine i s not hydrolysed by water at room temperature but can be hydrolysed at high tem-peratures or by al k a l i n e solutions. The CF groups are 3 probably replaced step by step, l o s i n g one CF„ at a time. 3 The reaction i s base-catalysed since an excess of base i s not necessary f o r the completion of the reaction. The reac-ti o n possibly proceeds through the formation of an i n t e r -mediate of the. type (CP ) PH(OH) 3 3 which being an unstable compound loses a CP group and forms bi s t r i f l u o r o m e t h y l -3 phosphinous acid (CF^^POH. The l a t t e r i s unstable i n water and gives fluoroform and trifluoromethyl-phosphonous acid CP P(OH) which i n turn i s hydrolysed by water to give fluoro-3 2 form and phosphorous acid. The reaction may be respresented (118) as follows : OH (CP ) P + H- OH > 3 3 (CP ) PH(OH) 3.3 •(CF ) POH+CP H 3 2 3 (CP ) POH - — " ( CP ) P(0)H4-H0H — > 3 2 3.2 - 122 -(CP ) P H H 0 OH CP P(OH) -t-CP H CF,P = 0 +• C 3 V 0 H 3 <-H OH' (CP ) P OH + H 3.2 \ 0 H20 CP P(OH) + CPH 3 2 3 CP,P=0 H2 ( 3 ^OH CP_H + 3 •> H3PO The intermediates postulated above would be ob-tained only in the presence of weak alkaline solution or with water, but when strong alkaline solutions are used fluoroform Is liberated immediately and quantitatively, since i n this case the nucleophilic attack would proceed more rapidly. (b) Diphenyl-tri fluorome thylpho sphlne and Dimethyltrifluoromethylphosphine: These phosphines are not hydrolysed easily. It i s interesting to note that the hydrolysis of diphenyl-trifluoromethylarsine i s also d i f f i -(47) cult « It is possible that the pi-bonding character due to the presence of two methyl or phenyl groups stabilizes the P-CP bonds in the above compounds, making i t more 3 d i f f i c u l t to remove the CP group. However, when the lone 3 pair of electrons on the phosphorus atom is used for the formation of a coordinate bond or to give a pentavalent compound, i t i s found that the CP„ group is easily l o s t . 3 - 123 -Thus In the case of dimethyltrifluoromethylphosphine, hydro-lysi s i s f a c i l i t a t e d by the addition of bromine to i t . Similarly, hydrolysis of bis(dimethyltrifluoromethylphosphine)-dichloroplatinum(II) gives fluoroform almost quantitatively«, The reaction of diphenyltrifluoromethyldibromophosphorane gives diphenylphosphinic acid and so does the platinum com-plex (C,_H ) CP P PtCl 6 5 2 3 J2 2 The reactions of these phosphines most probably occur by the following scheme: (C H ) CF P +- 2 (OH)" > (C H ) CP P(OH) -> CF H4- ( C X )_P(0)OH 6 5 2 3 6 5 * 3 2 3 o 5 The formulation of the intermediate as (CgH ^CF^PfOH^ i s consistent with the fact that the reaction does not occur unless there i s an excess of a l k a l i present. (This may be contrasted with the hydrolysis of (CF_) P where the Inter-^H 3 3 mediate is formulated as (CF,)_P since in this case the 5 3 ^GH reaction i s base-catalysed and requires only one equivalent of the alkaline solution.). It i s significant that the phosphorane ( Cg H^ ) 2 C F 3^ B r 2 i S n ° * ' ^ ^ v o ^ 3 e < 3 i b 7 water* The hydrolysis of the platinum compound (CH^CF^P PtCl by water to give fluoroform Is Interest-2 2 Ing. The corresponding reaction does not occur with the complex of the phenyl-phosphine (C H ) CP P. Probably this 6 5 2 3 i s due to the cis structure of the complex and'the higher basicity of the phosphine which allows the coordination with water forming the transition complex - 124- -{ < ° V 2 o y } 2 p t c l 2 and give the penta-which would s p l i t off a This intermediate would be quite unstable valent compound (CH )_CP P L 3 2 3 N 0 H _ molecule of Eluorofomu The phosphine (C H ) CP P on the 6 5 2 3 other hand forms a trans complex and i t s weaker basicity would not permit the above reaction. (c) Phenylbj s t r i fluo romethylpho sphine and Me thylb i s t r i fluorome thylpho sphi n e: These phosphines are not hydrolysed by water at ordinary temperatures, but the lat t e r o i s hydrolysed slowly above 110 giving fluoroform and phenylphosphonous acid. Since the reaction product i s the same as that obtained from the hydrolysis of t r i s t r i f l u o r o -methylphosphine, the reaction may be represented by the same scheme: C H (CP ) p+HOH-6 5 3 2 /H C H (CP ) P 6 5 3 2 N)H C^H^ (CF^ JPOHJ -j- CP^H CgH (CP^) P (OH) C^ H (CP^) P (0) H H HOH H / C H (CP )P:0 : 6 5 3 * OH / ±: C H (CP )P-0H 6 5 3 V OH / H C H P=0 ^ = ± C H P(0H) 4- CP H 6 5 v • 6 5 2 3 OH 125 -The above scheme is supported by the fact that the phosphinous acids are usually unstable and rearrange. It i s not necessary that the reaction must proceed through the formation of the phosphinous acid and i t Is equally l i k e l y that after the formation of the intermediate, the attack on the P-CF„ bond 3 Is much more fa c i l e and hence fluoroform i s eliminated by the following scheme: CCH_(CF ) P4-H0H 6 5 3 2 >C H P=0 -h 2CF H 6 5 S0H 3 This reaction would take place particularly in the alkaline solutions. The hydrolysis of the phosphorane C H (CF ) PBr 6 5 3 2 2 has already been mentioned as proceeding through the forma-tion of the intermediate C H (CF ) P(OH) and HBr and the 6 5 3 2 2 disproportionation of the intermediate gives the phosphinic acid C H (CF )P(0)OH. In the presence of a l k a l i , the hydro-6 5 3 lysis product w i l l be phenylphoaphonic acid C H PO(GH) . 6 5 2 C H (CF )P(0)ONa + NaOH—^C H PO(ONa) + CF H 6 5 3 6 5 2 3 A similar product has been obtained from the hydrolysis of bis t r i f luorome thyl phosphinic acid.. C H (CF ) P 6 5 3 2 NQH HOH C H (OH) P 6 5 H OH - 126 -The hydrolysis of methylbistrifluoromethyldihalo-phosphorane has not been reported, but It is of interest to find that the hydrolysis of bis(raethylbistrifluoromethyl-phosphine )dichloroplatinura( II ) gives only one equivalent of fluoroform. The products have not been f u l l y investigated but since no fluorides are obtained, i t is possible that the reaction gives the phosphinic acid CH CP P(0)OH which might 3 3 be stable to a l k a l i . 2 . Halophosphines: (a) Alkyl and Aryl-halophosphines: These compounds hydrolyse to give, by simultaneous oxidation-reduction, two products—a secondary phosphine and a phosphinic acid. This can be explained on the basis of the above mechanism as follows: (J) R PX4-H 0 > 2 2 R P — O H 2 ^ X ->R POH + HX 2 (II) R POH >R PH -f- R P(0)OH 2 2 2 In this connection i t may be noted that in halophosphines the i n i t i a l attack i s on the P-halogen bond with the elimin-ation of a hydrogen halide, this being due to the higher electronegativity of the halogens. The second step i s a rearrangement leading to the self-oxidation-reduction process and hence the observed products. It Is only in rare cases that the phosphinous acid R P(OH) is obtained (69c) since they usually are unstable. - 127 -(b) Trifluoromethylhalophosphinea: The high electron-withdrawing power of the trifluoromethyl group gives a positive character to the iodine atom, thus making the l a t t e r more susceptible to attack, whereas in the case of the more electronegative halogen atoms the reaction i s the same as observed for the alkyl halophosphines. By contrast with the hydrocarbon analogues the trifluoromethylhalophos-phines hydrolyse to give the phosphinous acid as required by the f i r s t step above. The st a b i l i t y of the phosphinous acid has been attributed to the high electron-withdrawing power of the trifluoromethyl group which reduces the ten-(122) dency of the lone pair electrons to bond with a proton , and hence the second step does not occur. However, the hydrolysis of this acid has been shown to take place under (123) certain conditions and has been discussed above in connection with the hydrolysis of (CP ) P. 3 3 (c) Phenyl t r i f luoromethyliodophosphine: No members of the alkyltrifluoromethylhalophosphlne have so far been reported. However, phenyltrifluoromethyliodophosphine, prepared during this investigation, hydrolyses with water according to the mechanism postulated under (2a) and gives the phosphinic acid CJK (CP )P(0)OH. However, as expected, 6 5 3 the hydrolysis with a l k a l i produces the phosphonic acid C J PO(OH) according to the following mechanism: 6 5 2 C H (CF )PI+30H-6 5. 3_ F C OH \ / C H-lP-OH 6 5 \ |_ OH •C H PO(OH) +- CF H-PHI 6 5 ,2 3 The phosphoniura compounds containing alkyl or aryl groups yield a hydrocarbon containing the more electro-negative group and the corresponding phosphine oxide. Of the two phosphoniura compounds containing one CF group, + - 3 the hydrolysis of only one, studied and has been discussed already. CH (C H ) CF P 3 6 5 2 3 I , has been - 129 -C H A P T E R I X INFRA-RED SPECTRA OF THE PHOSPHINES  AND RELATED COMPOUNDS The study of the infra-red spectra of organo-phosphorus compounds is of recent origin, and hence most of the assignments are only in the tentative stage. How-ever, the spectra of a large number of such compounds have been listed i n this investigation, and an attempt w i l l therefore be made in this chapter to give an approximate correlation of observed absorption bands. It i s well known that the different modes of vibration of a molecule give rise to characteristic group - 130 -frequencies^^ 4] A detailed study of the vibration spectra within a group R, in compounds R-X, shows that a regular shift in wavelength i s obtained as the electronegativity and the position in the periodic table of X changes^^5) A comparison for the different elements can be found in the ie shi; (126) literature^^*^but the following table shows th shift in the C-F stretching frequency of CF -X compounds 3 CF CF 01 CF Br CF I CF H 4 3 3 3 3 Frequency 1265 1210 1207 1185 1160 Electro-negativity of X 4.0 3.0 2,8 2.5 2.1 Such shifts are sufficiently consistent and from these the structure of compounds can often be deduced, Trimethylphosphine and tristrifluoromethylphos-phine both have C symmetry, so that i f the frequencies 3v of one of them are assigned those of the other can at least approximately be assigned. Fortunately the spectra of (127) trimethylphosphine has been thoroughly investigated , and is supported by the assignment of the frequencies for (128) phosphine and dimethylphosphine (CH ) PH • The sym-metry of the (CH ) P molecule requires 22 fundamental 3 3 vibrations. Of these, half would be doubly degenerate (E) and of the other half of the A species, four are forbidden (A^). The remaining seven consist of two P-C skeletal modes which take care of the stretching and bending of - 131 -this bond and the other five are the methyl group modes. Out of the eleven E type vibrations, two are skeletal and the remaining are methyl group modes. The following table (127) gives the complete assignment of the frequencies . Species A CH asymmetric stretching 2970 T?2 CH symmetric stretching 2850 CH asymmetric bending 1417 CH symmetric bending 1310 v_ CH rocking or wagging 960 5 3 Vg P-C symmetric stretching 652 P-C symmetric bending v0-v,, species A , forbidden o M 2 Species E V,av/3 CH asymmetric stretching 2970 vIH_ CH symmetric stretching 2920 vlev/c CH asymmetric bending 1430 V,7 CH symmetric bending 1298 v,9 CH rocking or wagging 1067 3 v/tf CH^ rocking or wagging 947 •Vju P-C asymmetric stretching 717, 707 T^, P-C asymmetric bending VA^ CH^  twisting - 132 -The choice between symmetric and asymmetric modes is only tentative. However the interesting conclusion is that the absorption near 700 cm 'has been assigned to P-C asymmetric stretching vibration. For some time in the past, this assignment was tentative only although i t was thought (129) to occur in this region . However, since C-C vibration occurs at 1100 cm ' and Si-C occurs near 800 cm"' , i t is certain that P-C would occur above 800 cm"' . This is borne out by the above assignment. In order to make' correlations for the trifluoro-methylphosphines, i t i s necessary to know the assignments for the trifluoromethyl compounds. Fortunately some of the trifluoromethylhalides have been worked oxxt^^l These halide molecules have C, symmetry^and would give rise 3v to six infra-red active fundamental bands. Three vibra-tions would be of the species and would consist of symmetrical stretching vibration of the CE group, the 3 stretching vibration of the C-X bond and the symmetrical deformation of the CF group. The other three would be the 3 doubly degenerate vibrations of the E species and consist of the antisymmetrical CF stretching mode and two rocking 3 or bending modes. The following table gives the detailed assignments for CF I. 3 - 133 -Band Strength Assignment Band Strength Assignment 265 (calc) v E 1443 ¥- 2v A, 2 3 1 286 (()calc) v 3 A l 1605 ¥ t fV. E 1 5 449,456,461 W- v 2 - v 3 A x 1724 W 540 M v 5 E 1818 ¥ V * 2 A l 562,572,576 M 2v 3 A l 1868 ¥- 2 v 2 + V 3 A l 777 W vrv3 ^ 1855 ¥-735,741,747 S v 2 A l 1916 W V V 2 E 808 w V 5 + V 6 A 1 + A 2 + E 1961 ¥ = v 4 + v r v 3 E 918 ¥ W l + V E 2137 W 2 V 1 A l 1067,1073 2096 ¥- v^-V^V A 1078 S-b v l A i L j k 2242 ¥ V A + V 1 E 1019,1026 4 J -1030 S 2203 W- W ^ 3 E 1193 W 2V 2-V 3 A x 2231 " ¥ 2 v 4 A 1 +E 1185 St T 4 E 2433 ¥- 2 v i " V 3 A l 1269 M V v 5 E 3401 W- ^ l A i " E 1332 ¥ v +- E 1 6 3496 W- 3 v 4 A 1 + A 2 + E 1359 W V v 3 A l The fundamental hands are at 265, 286, 540, 743, 1076 and - i 1185 cm « The last two correspond to the symmetrical and antisymmetrical stretching vibrations of the CP group. The 3 vibrations at 540 and 743 are due to CP deformation and the 3 calculated absorption at 265 and 286 would be for C-I stretching. - 134 -Before considering the trifluoromethylphosphines, the CP group i t s e l f may be considered in the light of the 3 above. The CP group i t s e l f gives rise to four fundamental 3 vibrations: two symmetrical vibrations corresponding to stretching and deformation, and two antisymmetrical vibra-tions corresponding to similar modes. The atom or group bonded to the CP group would also give rise to two vibra-3 tions — symmetrical stretching of. CP - X and the rocking of • s-r 3 the X against CP . The result of the study of the CP -X 3 3 stretching vibrations shows that the interaction between the two modes of vibrations i s small and hence i t is con-cluded that the CP group is a "stiff or r i g i d group^3"*"! 3 This would imply that the fundamental vibrations- due to a CF group would not be greatly different from molecule to 3 molecule. This i s indeed found to be the case in most of the compounds studied. Since for a f u l l treatment of the spectra, the mathematical discussion becomes very involved, approximations have been suggested. The following table gives the observed bands. (CH,j P Strength (CH ) P Strength 3 3 3 3 2970 (M) 1298 (W) 2920 (M) 1067 (W) 2850 (M) 960 (M) 1430 (M) 947 (W) 1417 (M) 653 (M) 1310 (M) - 135 -(4) CP P I 3 2 Abs. Strength 1272 M 1157 S 1142 S 1111 s 1072 M 737 S (4) ( C F ) 2P I Abs. Strength Abs. Strength 2252 M 1119 M 2217 S 1029 M 1273 M 951 W 1256 ¥ 854 W 1203 S 798 M 1183 M 748 S 1162 S 746 S 1131 S 714 W (4) ( C P ) P -3 3 Abs. Strength Abs. Strength 2444 W 1492 ¥ 2298 M 1390 M 22 42 M 1345 M 1934 ¥ 1308 M 1904 ¥ 1277 M 1798 ¥ 1230 S 1751 M 1183 S 1680 ¥ 1153 S 1647 W 1127 S 1587 ¥ - 136 -(CP ) P 3 3 (Continued) Abs. Strength Abs. Strength 1041 M 844 W 1023 M 797 W 966 M 754 S 923 M 726 M As i n trimethylphosphine, the trifluoromethylphos-phines w i l l have vibrations corresponding to the s k e l e t a l and trifluoromethyl group stretching and bending vibrations* Since the P-I stretching v i b r a t i o n l i e s outside the scale of the common instruments 300 cm , the diiodophosphine CP PI might serve as the best s t a r t i n g point. In t r i f l u o r o -3 2 iodomethane, the absorptions at 1076 and 1185 are considered as the symmetrical and antisyrametrical vibrations of the CP group. By analogy, the absorption at 1111 cm 'in 3 CP^PI^ may be assigned to the symmetrical vibrations and tKose at 1142 and 1157 may be taken as corresponding to the doubly degenerate v i b r a t i o n at 1185 observed i n CP I. The - 137 -- I absorption at 737 cm may be taken as due to the CP defor-3 mation mode, since the same appears in compounds other than those containing phosphorus. However, the P-C stretching vibration is also expected to appear in this same range. A detailed study is necessary to settle this point but the presence of this vibration in a large number of compounds not containing phosphorus does indicate that i t is a CF 3 deformation mode. The remaining absorptions observed in CF,PI_ are possibly the combination modes. 3 2 As more trifluoromethyl groups are attached to phosphorus, the spectra w i l l become complicated because the skeletal vibrations would come into play. Moreover a s p l i t -ting of the characteristic frequency would be expected because of the presence of two equivalent groups. Such spl i t t i n g is observed in molecules with two or more equi-valent bonds. The split t i n g depends on the resonance or coupling between the equivalent bonds. And, in general, the larger the coupling the larger i s the sp l i t t i n g . In the case of trimethylphosphine the characteristic stretch-ing frequencies occur at 2970, 2920 and 2850 cm 1 Similar - 138 -s p l i t t i n g would be expected in the case of bistrifluoro-mehtyl and tristrifluoromethyl-phosphines. It i s observed that for two CF, groups the s p l i t t i n g is into three bands, 3 and for three CF groups i t i s s p l i t into four bands. In 3 the absence of mathematical treatment, i t is d i f f i c u l t to assign a particular band to a definite mode. A l l that can be said is that the bands at 1203, 1162 and 1131 cm"'ob-served for (CF,) PI are due to the stretching vibrations of the CF, group. Similarly, in the case of (CF ) P there are 3 3 3 four strong absorption maxima at 1230, 1183, 1153 and 1127, and again these are due to the stretching vibrations of three CF groups. 3 _i The absorption for (CF,) P at 754 cm i s strong 5 3 and may be attributed to the antisymmetric deformation mode. Since the difference in the symmetric and antisymmetric deformation modes i s quite large and since calculations for the branching of a parallel deformation band does not indi-cate a spl i t t i n g into submaxima of more than 15 to 20 cm ' , the other band of medium intensity at 726 may be attributed to the P-C stretching vibration. The rest of the bands may be connected with the different combination bands, as shown in the case of CF_I. 3 The above discussion of the vibration spectra of CF^PIg, (CF^JgPI and ( C F ^ P simplifies the correlation for - 139 -the methyl-trifluoromethyl phosphines. Since (CH^) P and (CF,) P both have the same symmetry, the other phosphines, 5 , 3 v i a . , (CH ) CF P and CH (CF ) P, are also expected to have 3.2 3 ,3 3.2 the same symmetry, and hence the same relations should apply. The following table gives the absorption maxima of the methyl-trifluoromethyl phosphines. (CH 3) 3P Abs. Intensity Abs. Intensity 2970 M 1298 ¥ 2920 M 1067 M 2850 M 960 M 1430 M 947 ¥ 1417 M 940 ¥ + 1310 M 653 M Abs. Intensity Abs. Intensity 2995 M 1175 VS 2934 • M 1125 VS 2840 M 1118 VS 2290 ¥ 955 M 2240 •w 906 M r+" 1440 M 876 M 1425 W 755 ¥ 1378 ¥ 745 W 1310 ¥ 725 M 1305 ¥ 680 ¥ 1295 - 140 -CH (CP ) P 3 3.2 Abs. Intensity Abs. Intensity 2985 W 1203 VS 2934 ¥ 1167 VS 2825 ¥ 1143 s 2290 ¥ 1115 vs 1465 M 912 M 1375 M 892 1307 M 821,836 ¥ 1283 M 750,745 M 705 M One of the ch a r a c t e r i s t i c features of the spectra of these phosphines i s that the shapes of the bands at 900-960 i n the three phosphines i s the same; for(CH ) P 3.3 at 960 and 947, f o r (CH ) CP P at 955 and 906, and f o r • 3.2 3_| CH (CF ) P at 912 and 892 cm i This has been attributed • ' - ' ^ - — - - -s - - -the stretching modes of the trifluoromethyl group are as expected from the above consideration. Thus f o r the phos-phine (CH ) CF P the bands at 1118 and 1125 may be a t t r i -3.2 3 buted to symmetrical stretching, and the bands at 1175 (by analogy with CF I) to the antisymmetrical mode. 3 S i m i l a r l y f o r CH (CF ) P, the bands at 1115, 1167 and _| 3 3.2 1203 cm may be attributed to s p l i t t i n g , due to two CF 3 groups. The asymmetric deformation of the trifluoromethyl groups occur for ( C H ^CF P at 725, and f o r CH (CF ) P-at 745 and 750 cm"1. - 141 -A third feature which is noticeable i s the shifting of the P-C stretching vibration with successive introduction of the CP groups. These bands are well marked, and can be 3 easily distinguished from the CP^ deformation vibrations. Thus for (CH ) P, i t is at 653, for (CH )_CP P at 680, and 3 3 3 2 3 for CH (CP ) P at 705. Another feature of the spectra of 3 3 2 these phosphines is the diminution in the intensity of the CH stretching frequency with the successive replacement of 3 groups, as would be expected. For the phenyl-trifluoromethyl phosphines, the same methods may be applied. However the behaviour of the phenyl group is somewhat different from the methyl group, in that the former has more than one characteristic absorp-tion. In general, the vibrations characteristic of the aromatic ring remain unaltered when attached to another element, and hence the presence of the ring can be easily established. For the phenyl ring the C-H stretching vibration occurs at 2940 cm ', and the C-H deformation vibration at 1470-1370. In the phosphorus compounds studied during this investigation, the deformation fre-quency Is invariably at 1435-1445 i n the form of an intense sharp band, and Is accompanied by two other sharp bands of weaker intensity—one at 1490 and the other at 1590 cm '. The prominent feature of these two absorptions i s that their - 141 -Plate No. 1. Pig. No. 1. Phenyl t r i f luorome thyl iodopho sphine,, Pig. No. 2. Phenyltrifluoromethylphosphinic Acid. Plato No. 2 . _ 141 _ F i g . No. 3 . Dimethyltrifluoromethylphosphine. F i g . No. 4. Methylbistrifluoromethylphosphine. F i g . No. 5. Phenylbistrifluoromethylphosphine. i ! i - 142 -intensity (and usually not their position) varies from molecule to molecule, and is found to depend in some way on the other substituents on phosphorus. These two vibra-tions consist of a "lateral dilation and contraction of the ring 9 produced mainly by stretching and compressing of the C-H bond"^"^l The absorption which is said to be very sen-sitive to the substituent on the phenyl ring (phosphorus (136) in this case) i s said to occur at 1045-1185 • However there are three bands appearing i n this region: (1) 995" 1005, (2) 1030, (3) 1070 cm"; each of them due to a different mode. These are found to be constant both for the compounds (129) studied here and for those reported elsewherev i The other absorptions due to the phenyl ring also appear at.constant frequencies: e.g., those at 690, 770-740 are due to out of plane vibration and hence need not be discussed further. There are however some weak absorptions between 1050 and 1175 due to hydrogen bending vibrations. These appear in practically a l l P-phenyl compounds with varying intensity. In trifluoromethyl compounds however they are probably hidden by the strong CF, stretching vlbra-3 tions and are not observed. The superposition of the phenyl group frequencies on those of the trifluoromethyl group allows a correlation of the spectra of the phenyl-trifluoromethyl phosphines. - 143 -The following table gives the absorption maxima of these phosphines: *C H CP PI 6 5 3 Abs. Intensity Abs. Intensity Abs. Intensity Abs. Intens: 3060 W + 1690 W + 1335 ¥ 1025 M 2900 W 1675 ¥ 1310 ¥ 1000 M 2340 ¥ + 1660 ¥ 1270 ¥ 830 ¥ • 1880 W r 1585 W + 1210 M 745 S 1800 W- 1490 W+ + 1150 S+. 715 ¥ 1725 w- 1740 M 1115 s + - 690 S 1710 ¥- 1385 ¥ 1070 M ( C 6 H 5 ) CP P 2 3 3060 w +• 1585 ¥ +- 1150 S + 845 ¥ 3000 V 1570 ¥ - 1105 S + 800 ¥ 2910 w - 1485 W + +- 1070 M 745 S 2240 W = 1440 M 1027 W-H + 720 ¥ 1965 ¥ 1385 ¥ 1000 ¥ + 695 S 1880 W 1325 ¥ 970 W 1810 ¥ 1310 ¥ 915 ¥ 1660 ¥ 1275 ¥ 875 W C 6H 5(CF 3) 2P 3080 1870 ¥ 1730 1660 ¥ 2920 ¥ 1835 ¥- 1715 ¥ 1645 ¥ 2320 W + 1810 ¥- 1695 ¥ 1635 ¥ 2220 W = 1770 ¥- 1680 ¥ 1615 ¥ 1980 tf ~ 1745 ¥- 1670 ¥ 1590 ¥ + - 144 -e H (CP ) p 6 5- 3-2 (Continued) Abs. Intensity Abs. Intensity Abs. Intensity 1575 W- 1390 ¥ - 1030 tf+ 4-1570 W= 1330 ¥ + - 1000 M 1555 ¥= 1265 ¥' 875 W + 1540 ¥- 1190 S + 8 0 5 M 1507 ¥ 1170 s 750 S 1490 W + 1140 s + 745 s 1475 ¥- 1100 s H- 690 s 1445 M 1070 M 700 M (sho 675 ¥ The best compound to consider f i r s t is the iodo-phosphine C H (CP )PI, since further substitution either 6 5 3 with CF or phenyl gives more complex spectra. The spec-3 trum of this compound i s not markedly different from what would be expected of a combination of trifluoromethyl and phenyl group frequencies* There are two strong bands at 1150 and 1115 cm 1 corresponding to the stretching fre-quencies of the CF group. The absorption at 1115 cm 1 may 3 be assigned to the symmetrical stretching and that at 1150 to the asymmetric mode, by analogy with CF,I. The stretch-3 ing and deformation frequencies of the aromatic C-H are unaltered and so are those for the out of plane vibrations, which occur at 745 and 690 cm -1 The remaining maxima may - 145 -be assigned to the various combination modes, except the P-C vibration which appears as a weak absorption at 715 om '. A fact which is conspicuous in this spectra is the predomi-nance of the phenyl group frequencies. Thus a l l the absorp-tions characteristic of a monosubstituted benzene ring are present here, but those of the trifluoromethyl group are not observable except, of course, the CP stretching* The 3 CF deformation vibration is missing, possibly overlapped 3 with the out of plane vibrations of the benzene ring. The C-F overtone which is quite marked in other trifluoromethyl phosphines appears as a.very weak absorption. The spectrum of diphenyltrifluoromethylphosphine similarly shows strong absorptions characteristic of the phenyl group. Thus,except the CF stretching vibrations 3 at 1105 (due to symmetric mode) and 1150 (due to asymmetric mode), the remaining maxima resemble those of triphenyl-phosphine. Most of the maxima have even the same shape as (41) that of triphenylphosphine • The CF overtone occurs as - I 3 a weak absorption at 2300 cm and the P-C stretching and CF^ deformation vibrations do not appear in the range studied. One marked feature of the spectrum of this com-pound, and also of the other phenyl-trifluoromethyl-phos-phines, is the absence of the P-C stretching vibration from the observed range. This w i l l be discussed later. - 146 Phenylbistrifluoromethylphosphine may be expected to show most of the frequencies of the trifluoromethyl group. The spectrum consists of a series of weak maxima, some of which can be traced back to the CP group, as 3 seen in the case of CP I. Thus the C-F overtone appears -! 3 at 2320 cm , the CP^ stretching frequencies are of course present and appear at 1190, 1140 and 1100. The second of these maxima is diffuse and is actually a doublet. The deformation frequency of the CP group does not appear again, 3 and,since i t has not been found in any of the phenylphos-be phines considered so far, i t mayAconcluded that It i s ob-scured by other bands. The P-C stretching vibration, which for the phenylphosphines appears at 715* also cannot be detected In the spectrum. It has been suggested that the shifting of the P-C to higher frequency is similar to the shift of P-0 with electronegative substituents. Thus It is not observed in triphenylphosphine,also. The common feature of the phenyl-trifluoromethyl-phosphines may be described as the predominance of the aromatic ring vibrations. This may be compared with the spectrum of CH (CF ) P, in which the intensity of C-H 3 3 2 stretching is of a low intensity. The shapes of the bands - I in the 1470 to 1370 cm region is worth noting. In phenyl-trifluoromethyliodophosphine and diphenyltrifluoromethyl-phosphine the intensity of the band at 1590 i s greater than at 1490 cm ', but In phenylbistrifluoromethylphosphine they are comparable. A similar reversal takes place i n the - 147 -case of substitutions of more electronegative groups: e.g., in phenyldichlorophosphine G _H PCI and benzenephosphonic 6 5 2 acid C H PO(OH) . This i s particularly true of pentavalent 6 5 .2 phosphorus compounds: e.g., (C H )P(0)C1, triphenyl 6 5. phosphate, etc. The spectra of the phosphonium compounds has not been treated separately so far. The infra-red studies for these compounds appear to be quite interesting, since there is usually a marked shift from the parent phosphines. This would be expected from the change in -the structure of the ,(137) compounds. The phosphonium compounds have a tetragonal structure with a D symmetry. As observed in other struc-4h ture changes, the tendency would be a shift towards shorter wave-length. In the case of PH I and PH , the fundamental 4 3 -I P-H frequencies are observed at 2372 and 2280 cm , and 2421 and 2327 cm ' respectively. The following table gives the spectra of some of the phosphonium compounds prepared during this investigation. (CH ) PI * 3 4 Abs. Intensity Abs. Intensity 2970 M 1280 W 2920 W 1150 W-2850 W 1045 w-2050 w 970-940 S (diffuse) 1545 w 860 W . 1450 M 780 w 1375 M 770 M * Nujol Mull **KBr Pellet Plate No. 5 . - 147 -Pig. No. 7. Methyldiphenyltrifluororaethylphos-phoniura iodide. Pig. No. 8. Methyltriphenylphosphonium iodide. F i g . No. g. Methyldiphenylphosphine oxide. F i g . No. 10. Dimethylbistrifluoromethylphosphonium iodide. (CH ) (CP ) PI 5 2 5 2 Abs. - 148 -Intensity Abs. Intensity Abs. Intensity 3020 M 1350 M 2970 ¥ + 1300 M*- 980 s 2320 ¥ 1210 M 920 M 2220 ¥ 1180 St 890 Shou] 1500 ¥ 1150 M 850 ¥ 1450 M 765 M 745 S ;H (c H ) P I 3 6 5 3 Abs. Intensity Abs. Intensity Abs. Intensity 3020 ¥ 1685 W 1305 W 2980 ¥ 1640 ¥ 1180 ¥ + 2910 W-f- 1610 ¥ 1160 ¥ + -<-2860 ¥ -f 1580 M 1110 S 2720 ¥ - 1570 ¥-•- 1070 2325 ¥ 1555 ¥ 1025 ¥ 2300 ¥ 1535,1545 ¥- 995 M 2200 ¥ 1480 ¥ + ->- 920 M + 1830 W 1465 ¥ 915,905 M +• 1815 ¥ 1435 M +• 855 ¥ 1780 ¥ 1395 ¥ + + 785 M 1725 ¥ 1335 ¥+ 750 S 1705 ¥ 1325 W + 715 M 690 S CH,(C^H )^CP P I ^ * -3 6 5 2 3 Abs. Intensity Abs. Intensity Abs. Intensity 3120 ¥ 1680 ¥ 1300 ¥ 3000 ¥ 1665 ¥ 1180) S 2920 M 1640 ¥ 1170) S 2860 ¥ + 1616 ¥ 1105 s 2320 ¥ 1585 ¥+-+- 1110 M + 2250 ¥ 1570 ¥- 1095 W-f-2200 ¥ 1555 ¥ 1030 ¥ 2000 ¥ 1535,1530 ¥ 995 1835 ¥ 1505 W 920 M + 1825 ¥ 1485 ¥ + 915 M + 1805 ¥ 1470,1465 W 795 W+4-1765 ¥ 1440 M 755 •M 1715 ¥ 1405 ¥ 745 M 1710 ¥ 1340 ¥+ 725 ¥-H 1690 ¥ 1325 ¥ + 685 M + Hujol Mull * * K B r P e l l e t - 149 -It can be seen from the above table that the characteristic frequencies have shifted to shorter wave lengths. This is particularly apparent In the phenyl-phosphonium compounds. The C-H (aliphatic), C-H (aroma-tic) stretching frequency, the phenyl group out of plane vibrations, and also the trifluoromethyl stretching fre-- I quency are shifted 10-30 cm to shorter wavelength. One of the most characteristic features of the phosphonium compounds, or in general the quadruply connected aromatic phosphorus compounds, is that the P-C stretching fre-- I quency appears as a strong band at about 720 cm • The band at 725 cm' in CH (CH ) CP PI and at 715 cm"' in 3 6 5 2 3 CH -(C-H,.) PI are attributed to this absorption. A simi-3 6 5 3 l a r effect is noted in the case of triphenylphosphine oxide and methyldiphenylphosphine oxide, for which this absorption occurs at 720 and 710 respectively (observed during this investigation). It is known that the electronegativity of the sub-stituents markedly shifts a particular characteristic absorp-tion. This has been illustrated for the phosphoryl group P^O. With three highly electronegative substituents, the P=)0 frequency l i e s at 1300 (for (CP ) PO i t occurs at -I 5 3 1325 cm ). For two electronegative substituents, i t occurs - 150 -at 1260; and for one i t occurs at 1230, e.g., i n (C H ) P0C1. 6 5.2 For substituents such as phenyl and methyl groups, i t occurs -I (129) at 1190 and 1176 cm respectively . For methyldiphenyl-phosphine oxide i t occurs at 1175, and f o r s i l v e r phenyl-trifluoromethylphosphinate i t occurs at 1225 cm\ Since the a c i d i t y of substituted phosphorus acids depends on the electron-withdrawing effect of the substituents, I t would appear that phenyltrifluoromethylphosphinic acid with one phenyl group i s not a strong acid, compared with t r i f l u o r o -methylphosphonic acid whose P = 0 occurs at 1300, Rather, i t s a c i d i t y would be comparable with the a r y l or a l k y l phosphinic acids. I t may be mentioned that the P-C stretch-ing frequency appears at 715 cm1 although i t is, absent i n CJL_('CF ) P. 6 5 . 3 . 2 The question of the appearance of additional frequencies with the .expansion of valence s h e l l brings us to the consideration of the spectra of the complexes. This i s indeed observed to be the case, f or i n the phenyl phos-phine complexes of platinum(Il) chloride and boron t r i -f l u o r i d e a new band appears i n the expected region. The following table shows the P-C (aromatic) absorption of the complexes. Pig. No. 11. Trimethylphosphine-boron t r i f l u o r i d e . Pig. No. 14. Triphenylphosphine-boron t r i f l u o r i d e . - 151 -C H (CP ) P PtCl 6 5 3 2 2 ; 2 705 700 (C H ) CP P.BF 6 5 2 3 3 700 715 /I C H CP_P.BP 6 5 3 715 3 This absorption may therefore be taken as the characteristic of the quadruply connected phenyl-phosphorus compounds. This i s borne out from a comparison of the spectra of the twenty-one phenyl phosphorus compounds (quadruply connected) reported by Daasch and Smith, twenty containing sharp and strong maxima, while the remaining one has not been com-pletely studied. The trivalent compounds reported have - I . weak or no absorption i n this region (700 cm )• are as follows: the boron trifluoride complexes of the phosphines have a l l the absorptions characteristic of the phosphines but do not have any corresponding to those of boron tr i f l u o r i d e . A strong and broad band appears i n the region 1175-1200 cm '. That the strong absorption results from the change of symmetry due to complex formation and not to a reaction with any of the groups on phosphorus is suggested by the following facts: The other observations regarding the complexes -152-1. '-' The phosphine can be liberated from the complex on treatment with water. In the case of trifluoromethyl substituted phosphines fluoroform i s evolved on such treatment. 2. The CP^ stretching frequency would be shifted to longer wave lengths as observed in the case of reaction with trimethyltrifluoromethyltin which gives CP3BP5 and whose C-F stretching frequency is shifted to 962 from imn . n , - 1 ( 1 5 8 ) 1100 cm • 3. The I.R. spectrum does not reveal any RVjO ab-sorption. It is therefore l i k e l y that the strong absorp-tion may be due to a change of symmetry of the boron trifluoride molecule. In the case of ketone-BP^ complexes also, similar bands have been noted (139) and have been interpreted as due to the coordinate bond B-*0. A com-parison of the spectrum of the phosphine complexes from the following table (which gives only the Important maxima) shows that most of the features are common. (CH 3) 3P.BP 3 3000w 2900w 1 4 2 5 W I310w,+V I300w- 1125s 1085s 1060s 1037s (1125-1037) 970m 785w+- 772w 705w 675w Strong and broad (CH 3) 2CP 3P.BF 3 3100W+- 3000W4- 2300w- 1430w+ 1320m 1240W+-1175s (1175-1025 strong and broad) 970m 925ra 885m 820W+ 780w 765w 750w 725w 705ra 675m - 153 -3150W 3050w + 295OW 2300w 1975w 1900w 1800w 1590w 1530W- 1475* 1440w 1315w-t-1220m 1175m + 1150s 1125s 1095s (broad) 1070m + 1030m 995m 900m + 870-835 (broad) 790w 745s 700m + 690s I ) P.BP 5 3 3 3250m 3150w +• 3050w 2400w 2325w 1950w 1875w 1800w 1700w 162 5w 1575w + 1475w + 1435m 132 5w 1300w 1235w 1180w + 1160w + 1110a 1075-1085s IO3O-IO5OS 1000m 910m-t- 885ra 770s (755w,750w) 740s 725w 715m 695s 680ra The above table shows/_th'at the C-H a l i p h a t i c or aro-matic i s shi f t e d to lower wavelength. The P-C stretch-j ing frequency for the methyl phosphines remains approximately the same. The best resolution f o r the strong absorption at 1100 cm-' i s that f o r the compound (CH ) 0CP P.BP , which 6 5 2 3 3 gives three maxima, 1 1 5 0 , 1125 and 1 0 9 5 . The CF, frequencies 3 do not seem to have changed and an overlapping absorption seems to have come i n . The spectrum of (C H ) P.BF shows an _l . 6 5 3 3 absorption at 1110 cm . A comparison with the methyl phos-phines shows that they also absorb strongly at 1125. There are other frequency s h i f t s which occur i n the boron t r i f l u o -r ide complexes. The weak absorption at 785 cm ', f o r instance, i s common i n a l l phosphine complexes, but appears neither i n boron t r i f l u o r i d e nor i n the phosphines themselves. This may be at t r i b u t e d to the P-*B bond. -5-54-The spectra of the platinum(II) chloride complexes do not d i f f e r very much from those of the parent phosphines. The following table l i s t s the absorption maxima of the complexes studied. [(CH 3) 3P] v PtClr 2960w 2985w 2810w- I428w+ 1420w + 1315W+ 1298m 1283w-»- 975m 956m + 862 , 868w + 745w+ 731w 680,670w [(CH 3) 2CP 3P] 2PtCl 2 2995w 2915w-«- 2850w- 1 4 4 5 w - 1 4 3 0 w + 1405w+ 1315w+ 1293w-«-+ 1182s 1 1 3 5 , 1 1 2 0 s 866m 758w + 965m $22m + [ C H 3 ( C F 3 ) 2 V t C l 2 748W+ 720w + 3010w 2920w 1308w + 1287w 913m +• 898m 2840w - 2 3 2 0 w - 14l2w + 1202s 1170s 1130s 760,755w 740w I t i s observed that for'(CHj) P and (CH 3) 2(CF 3)P complexes no s h i f t i n the C-H stretching frequency occurs, but f o r CH_(CF,) P a s h i f t of 30 cm"1 occurs towards 3 3 2 shorter wave-length. The CF 3 stretching frequency i s un-altered. The CH3 rocking frequency s h i f t s to shorter wave-length i n the case of (CPL) P and (CH ) CF P by 3 3 3 2 3 J 16-30 and 10-16 respectively, but i s unchanged f o r CH,(CF_) P. The P-C stretching frequency i s found to be 3 3 2 shi f t e d to shorter wavelength i n a l l cases. For (CH,) P 3 3 i t i s sh i f t e d by 2 5 , for ( C H 5) CF P by 40, and for 1 2 3 CH 3(CF 3) 2P by 35 cm" . F i g . No. 1 5 . Bis(diphenyltrifluoromethylphosphine)dichloro-platinum(II). F i g . No. 16. Bis (phenylbis trifluoromethyl phosphine )dichloro-platinum(II). F i g . No. 17. Bis(phenylbistrifluoromethylpbosphine)dichloro-dibromoplatinum(IV). -155-The following table gives the spectra of the phenyl-trifluororaethyl-phosphine complexes. _(C 6H 5) 2CP gP J 2 P t c i 2 3075w 2940w + 2350w 1960w - 1900w -1825w- 1725w 1660w 1600w + 1590w +-1550w 1480w + 1430m 1390w + 1325w + 1280w + 125 5w 1170s 1130s 1105m + 1075m 1060m 1035w + 1020w +• 995w-t-970w- 900w - 835w + 805w -t- 745m 715m 690m + Pi PtCl J2 2 3075w 2985w- 2350w - 1960w- 1890w-1800w- 1590w- 1475W4- 1430m 1370w 1315w + 1300w 123 5w 1150s 1120s 1095s 1065m 1030m 1020m 995m 970w 925w 840w 785w 740m + 705m 685s I t i s observed that inthe l a s t case there i s a s h i f t i n the CF^ stretching frequency. For diphenyl-trifluoromethylphosphine the s h i f t is 25 cm"l towards shorter wave-length, and f o r phenylbistrifluoromethyl-phosphine the s h i f t i s 40 cra~l towards longer wave-length. -156-The eff e c t may possibly be due to interactions of the substituent groups. The other c h a r a c t e r i s t i c frequencies of the phenyl groups are found to remain unchanged. This i s i n contrast with tile methyl-phosphines where the CF^ frequencies are unaltered and the methyl vibrations suffer a change. The other i n t e r e s t i n g feature of these complexes i s the appearance of the P-C (phenyl) absorption which has already been pointed out. -157-Q a A | J | R |X CONCLUSIONS It is clear from the foregoing discussion that one effect alone does not explain a l l the properties of the phosphines under study. Among the various effects that have been called upon to explain the different properties, electronegativity, the Inductive effect, and the steric effect of the CF^ group have been considered as factors responsible for the many observations. Per-haps the most Important of these is the inductive effect of the electronegative trifluoromethyl group, which decreases the ava i l a b i l i t y of the lone pair electrons on the phosphorus atom. In effect this increases the "electronegativity" of the complete phosphine molecule. - 1 5 8 -Kagarise ^^'^has used an empirical equation for the c a l c u l a t i o n of the electronegativity of groups. His equation f o r a group A(x,y,z) containing three atoms (x,y,z) attached to a central atom A i s of the type: x ( e f f , = ^ + _ i _ ( X x + x ^ X z ) Extension of this equation to the phosphines would give a rough estimate of the "electronegativity" of the phos-phines. Such values have been calculated f o r the phos-phines studied during t h i s i n v e s t i g a t i o n , and are reported i n the following table. In preparing t h i s table, the electronegativity of the trifluoromethyl, phenyl, and (|0<b) (5-0 O+o) methyl groups has been taken as 3«3> 2.7, and 2 . 3 . Phosphine Electronegativity Phosphine Elec tronegatIvi ty (CF 5) 3P 2.70 (CH 3) 3P 2.25 (CP5)CH3P 2.53 (C 6H 5) 3P 2.40 (CP 3) 2C 6H 5P 2. 60 PP 3 3.05 CF 3(CH 3) 2P 2.37 PCI 3 2.55 CP 3(C 6H 5) 2P 2.50 PH3 2.10 This approximation shows that the phosphines with electronegative substituents such as the phenyl and trifluoromethyl groups w i l l behave l i k e the t r i h a l i d e s of phosphorus. This i s Indeed found to be the case. Such electronegative groups w i l l also affect the electron density on the central atom. A rough estimate of th i s factor can be obtained from the e l e c t r o n e g a t i v i t i e s of the - 159 -atom A and the substituent'X attached to A by assuming that the bonding electrons w i l l be divided between A and X in the ond (141) ratio of their electronegativities • For a single bond the number of electrons on A in A-X would be given by; ? *A + % ' and for A in A(x,y,z) by: XA *X ^A^^Y XA*XZ The following table gives the number of bonding electrons n in the three covalent bonds on P in the various phosphines. Phosphine n Phosphine n (CF ) P 3,3 2.33 (CH 3) 3P 2.86 (CF ) CH P 3 2 3 2.51 (C 6H 5) 3P 2.62 (CF 3) 2C 6H 5P 2.43 PF 3 2.06 GF3('CH ) 2P 2.69 PCI, 3 2.47 CF 3(C 6H 5) 2P 2.53 3.00 It w i l l be seen from the above tables that general trend of reactivity is borne out. It may be general-ised that phosphines with an electronegativity higher than 2.50 would not normally be reactive towards Lewis acids. Deviations from this generalisation may be explained on the basis of the various effects enumerated earlier. The anomalous behaviour of phosphine PH, has been explained 3 as due to the difference In the degree of hybridization (142) of the phosphorus atom , and has been considered earlier i n explaining the reactivity of the above-mentioned phos-phines with boron tri f l u o r i d e . Similarly the unexpected -160-r e a c t i v i t y of the other phosphines towards Lewis acids can be explained on the basis of the pi-bonding charac-t e r . The a b i l i t y of PCI and PF to form compounds 3 3 PCl_.BBr_ and PP_.BH, i s an example of t h i s type. Hence 3 3 3 3 t h i s generalisation concerning the r e l a t i o n between electronegativity and r e a c t i v i t y of the phosphines must be , used with Caution. Many of the properties of the t r i -fluoromethyl-phosphines e.g. complex formation must be explained dn terms of s t e r i c effects together with the p o s s i b i l i t i e s of pi-bond formation. I t i s clear then that the per f l u o r o a l k y l groups and the trifluoromethyl group i n p a r t i c u l a r , because of t h e i r unique combination of s i z e and electronegativity, impart i n t e r e s t i n g and unusual properties to the molecules of which they form a part. I t can be seen from the fore-going discussion and also from the calculated electronega-t i v i t y that with the gradual introduction of the t r i f l u o r o -methyl group, the a v a i l a b i l i t y of the lone p a i r electrons i s reduced and hence donor properties of phosphorus are diminished. Much further study, p a r t i c u l a r l y of a quan-t i t a t i v e nature i s needed to f u l l y understand these char-a c t e r i s t i c s . E X P E R I M E N T A L - 161 -I EXPERIMENTAL METHODS 1. General Techniques Most of the compounds studied were v o l a t i l e i n nature and i n many cases reacted with a i r and moisture. Consequently they were manipulated i n a conventional vacuum system. The system was of Pyrex glass and consisted of a number of traps for f r a c t i o n a l d i s t i l l a t i o n , large bulbs f or storage, cold finger, molecular weight bulb, manometer, and several i n l e t points. A "Duo Seal Hi Vac" pump was used i n conjunction with a mercury d i f f u --4-sion pump to give a vacuum of 10 mm, which was s a t i s f a c -tory f o r most purposeso A v o l a t i l e compound was introduced into the system by freezing i t i n l i q u i d nitrogen, pumping off the a i r within the tube or container holding the material, and then allowing the compound to slowly expand into the system. For fra c t i o n a t i o n , mixtures of v o l a t i l e compon-ents were passed through a series of traps which were cooled to d i f f e r e n t temperatures. The cooling was effected by surrounding each trap with a slush bath, which was pre-pared by cooling an appropriate organic solvent to i t s freezing point with l i q u i d nitrogen. For a sa t i s f a c t o r y f r a c t i o n a t i o n by this method, i t i s necessary that the v o l a t i l e mixture passes at a pressure of 1 - 5 mm and -162-o that the b o i l i n g points are at l e a s t 20 apart. In most cases separation had to be repeated a number of times to obtain a pure product. Molecular weights of gases were obtained by Regnault's method. The gases were allowed to expand into a bulb of known volume (208 ml) and the pressure was noted from the manometer. The molecular weight was calculated from the mass, volume, pressure, and temp-erature by applying the gas law. Most of the reactions were carried out i n Garius tubes which were constructed with a thick-walled c a p i l l a r y at one end. Afte r evacuation of the tube, the reactants were condensed into I t by freezing the end of the tube i n l i q u i d nitrogen, and the c a p i l l a r y was sealed. When the reaction was complete, the t i p of the Carius tube was broken inside an evacuated length of rubber pressure tubing, and the v o l a t i l e components fractionated into the vacuum system. Pinal p u r i f i c a t i o n was frequently effected by d i s t i l l i n g the products i n a s t i l l of approximately 5 ml capacity and 8™ column outside the vacuum system i n an atmosphere of nitrogen. The appropriate fractions were p u r i f i e d f o r -J63-analytical purposes by vapour phase chromatography using a 10' column of "Ucon polar", a silicone type packing. A small amount (10 ml) of the d i s t i l l e d sample was i n -jected for a test run on to the column which had been heated to the required temperature. The flow of the different components was recorded and the elution time of the main component was determined. A large amount (0.25 ml) of the sample was then injected and the main component(i); ; collected in a cooled collector. By control-l i n g the temperature of the column at about the boiling point of the desired product and maintaining a steady flow of helium, complete separation of the components was effected. Melting points were recorded by direct obser-vation under a magnifying glass. Boiling points were determined by the inverted capillary method, and also by plot-ting the vapour pressure against the inverse of temper-ature (•VT) a n (* extrapolation to a pressure of 760 mm, taking values close to the boiling point. The vapour pressure was obtained by using an isoteniscope and re-cording- the pressure from manometers. An effective control of temperature is therefore necessary. The constant tem-perature bath for the isoteniscope was of paraffin o i l -164-heated with an e l e c t r i c immersion heater. The heat was o controlled t o i l by using a thermal regulator. Substances which were reactive towards a i r and moisture were prepared In the bulb of the isoteniscope. For the manipulation of i n v o l a t i l e substances reactive towards a i r and moisture, a dry box was used. A steady stream of nitrogen swept through the box i n which a fresh surface of phosphorus pentoxide was l e f t exposed. 2 . A n a l y t i c a l Methods 2 a . Analyses f o r carbon, hydrogen, f l u o r i n e , and phosphorus were made by microchemical methods ( by Dr. A l f r e d Barnhardt). Determinations of the halogen contents of the platinum(Il) halide complexes and of the t t <o n i c k e l complexes were carried out by standard methods.v Platinum was determined by heating the complex gradually u n t i l i t decomposed, and by f i n a l l y i g n i t i n g i t i n a hydrogen atmosphere. Where the platinum complex was v o l a t i l e or did not decompose as expected, the estimation was made by p r e c i p i t a t i n g i t as ammonium chloroplatinate. 2 b . The trifluoromethyl group of the phosphorus compounds can be ea s i l y hydrolysed to give fluoroform q u a n t i t a t i v e l y . This was frequently used as a method of , i d e n t i f i c a t i o n of the compounds as well as for analysis. -165-20 ml of 10 -20$ aqueous sodium hydroxide were placed i n a Pyrex tube and the dissolved air removed, by pumping i n vacuum. The sample was then weighed and sealed in small evacuated tubes, which were sealed with the alkali solut-ion and broken inside the large tube. In most cases the o reaction tube was heated to 80 for 24 hours. The fluoro-form was then purified by fractionation and weighed i n the molecular weight bulb. The infra-red spectrum and the molecular weight were considered sufficient for the iden-t i f i c a t i o n of fluoroform. Acidification of the remaining alkaline solution usually gave an acid or i t s salt which was Identified by i t s melting point and from i t s infra-red spectrum. 5. Infra-red Spectra The determination of infra-red spectra was a very convenient means of identification of the compounds and/or mixtures. The presence of a trifluoromethyl group for instance was indicated by the strong absorption in the 8 -9/o region. Since the spectra of the different com-pounds differ from one another in this finger print region, impurities ( e.g. fluoroform in trifluoroiodomethane ) could easily be identified. The spectra of the purified compounds were -166-recorded on a Perkin Elmer model 21 recording spectro-photometer, while f o r preliminary i d e n t i f i c a t i o n use was made of the "Infracord". Both are double beam instruments, f i t t e d with rock s a l t optics. The spectra of the v o l a t i l e compounds were taken by enclosing the sample at a known pressure i n an evacuated 10 cm gas c e l l , and those of l i -quids by pressing them between rock salt discs to give a c a p i l l a r y f i l m . For s o l i d s , either a mull was prepared with nujol or hexachlorobutadiene, or a potassium bromide ( 1 2 4 ) p e l l e t was used. The p e l l e t technique was preferred, since only a small sample was needed. 4* U l t r a - v i o l e t Spectra Absorption spectra i n the v i s i b l e and u l t r a -v i o l e t regions were recorded on a Cary model 14 spectro-photometer. The c e l l s were of fused quartz and t h e i r absorption path lengths were either 1 or 10 mm. A l l s o l -vents were of A.R. grade. For solutions which decomposed on standing, the recording was taken f i r s t with a more concentrated solution f or a test run and the d i f f e r e n t absorption bands were resolved by taking d i l u t e solutions. 5. Magnetic S u s c e p t i b i l i t y ^ 1 7 ^ These measurements were made on a Gouy magnetic balance which was sensitive to changes of ±0.00002 g. The -167-current through the electromagnet was. regulated within 0.001$. The s u s c e p t i b i l i t i e s were measured at room tem-perature.; only. Solid, samples were f i n e l y ground and packed to a height of 2.5 to 4 cm i n tubes of 3*5 ram diameter and 15 cm i n length. With careful packing, the packing error was reduced to less.than 3%* The apparatus was calibrated with benzene. 6. Dipole Moment These measurements were made with.a simple Slbarch d i e l e c t r i c constant meter. Standard solutions were prepared by dissolving the compounds i n reagent grade solvents which were dried by the standard methods• The solvents used were chloroform, benzene, and carbon tetrachloride. Chloroform was dried over calcium chloride, benzene over phosphorus pentoxide, and carbon tetrachlor-ide over potassium sulphate. The dipole moment of the compound was calculated to an accuracy of ±0.5 D from the d i e l e c t r i c constant of the solution and the solvent. -168-I I PREPARATION OF THE PHOSPHINES 1 a. Preparation of Trifluoroiodomethane For the preparation of s i l v e r t r i f l u o r o a c e t a t e , s i l v e r oxide (lOOg) was treated with a 50% aqueous s o l -ution of t r i f l u o r o a c e t i c acid (100 g). Aft e r the un-reacted s i l v e r oxide had been removed by f i l t r a t i o n , the solution was concentrated i n vacuo and the s o l i d f i n a l l y dried over phosphorus pentoxide. The y i e l d was quanti-t a t i v e (180 g). 1 b« S i l v e r t r i f l u o r o a c e t a t e (110 gj was intimately mixed with an excess of iodine (330 g). The mixture was placed i n a round bottom f l a s k , f i t t e d with an a i r and water condenser and connected to a tower containing sodium hydroxide p e l l e t s . This was connected by means of rubber tubing to a trap, cooled i n a dry ice-alcohol mixture, followed by two traps cooled i n l i q u i d nitrogen. The l a s t trap was connected to a calcium chloride tube to protect the product from atmospheric moisture. The reaction was i n i t i a t e d by heating the mix-ture at the upper edge with a free flame, avoiding ex-cessive heating. The gases evolved during the reaction consisted of trifluoroiodomethane,and carbon dioxide. -169-Sorae iodine also sublimed but t h i s was condensed by the water and a i r condensers. Most of the COg was removed by -the sodium hydroxide tower. The vapours of t r i f l u o r o -iodomethane condensing into the traps s t i l l contained some carbon dioxide and iodine as impurities. The product was therefore fractionated i n the vacuum system, the trifluoroiodomethane condensing i n the trap cooled to -132 • This f r a c t i o n was recycled through a long tube packed with sodium hydroxide, and a f t e r another f r a c t i o n -ation, was s u f f i c i e n t l y pure. The p u r i t y was tested by molecular weight measurements and by the infra-red spectrum. A f t e r p u r i f i c a t i o n , i t was stored i n the large bulb (painted black) attached to the vacuum system or sealed i n Carius tubes. Trifluoroiodomethane has now become commercially available, i n most cases containing only a trace of fluoroform as an impurity. Later i n the work, therefore, i t was d i r e c t l y condensed from the cylinders and was fractionated only when a p a r t i c u l a r l y pure sample was desired. 2, Preparation of Trimethylphosphine This compound was prepared by the Grignard Method. The reaction was c a r e f u l l y carried out i n an -170-i n e r t atmosphere by reacting methyl iodide and Magnesium turnings. The methylraagnesium iodide (1 Mole) so obtained was cooled vigorously by placing the reaction f l a s k i n a mixture of dry ic e and alcohol, and a solution of phos-phorus t r i c h l o r i d e ( 22.4 g, 0.16 mole ) i n 50 ml ether was added cautiously with vigorous s t i r r i n g . In these reactions i t was observed that when the Grignard reagent was not cooled to these temperatures, an orange s o l i d was deposited. I f the s t i r r i n g was not vigorous, i t was found that l o c a l reaction set i n with explosive violence. The addition of phosphorus t r i c h l o r i d e was therefore slow and took about two and one ha l f hours. The f l a s k was then allowed to warm to room temperature, and waa heated d i r e c t l y to d i s t i l l off the phosphine and ether. When necessary more ether was added to f l u s h out the phosphine, and d i s -t i l l a t i o n resumed, th i s time u n t i l no d i s t i l l a t e was obtained. The d i s t i l l a t e was kept cool and a solution of s i l v e r iodide i n a saturated aqueous solution of potassium iodide ( 5 nil ) was added. The mixture was shaken v i g -orously f o r two hours. sj_ Ver iodide adduct of trimethylphosphine separated and was f i l t e r e d out, washed f i r s t with potassium iodide solution then with water, -171-and f i n a l l y dried over phosphorus pentoxide. (Total yield 32 g or 62%) To regenerate the phosphine from the silver iodide adduct, the la t t e r was genfLy warmed and the vapours allowed to pass through traps cooled with melting carbon tetrachloride,, dry ice-alcohol mixture, and liquid nitro-o gen. The pure phosphine collected in the -78 trap, 3 a. Preparation of Dimethyltrifluoromethylphosphine -Trimethylphosphine (2 g, 0,0Z£> mole) and t r i -fluoroiodomethane (4«1 g, 0.21 mole) were sealed in a Garius tube. That the reaction started much below room temperature was apparent from the rapid deposition of a white solid. This solid dissolved in liquid trifluoro-iodomethane and reappeared as the tube warmed up. The deposition of white solid continued but after one half hour the reaction slowed down considerably. The tube was l e f t for 24 hours and was opened into the vacuum system for fractionation of the products. The phosphine o was condensed at -78 bath, trifluoroiodomethane by the o pentane bath (-132 ), and fluoroform passed on to the; liquid nitrogen trap. The quantities of the three products were 0.95 S (7.37 mmole), 0.75 g (3.8 mmole), and 0.073 g (0.1 mmole) respectively. The white solid in the tube consisted of tetramethyl phosphonium iodide and a volatile -172-white solid which was found to sublime into the vacuum system. 3 b . To obtain a larger quantity of the phosphine, 4 g (0.05mole) trimethylphosphine and 20 g (0.1 mole) trifluoroiodomethane were sealed. The rapid reaction at low temperature could be readily seen in this large scale experiment. In order to speed up the reaction, the tube was shaken for six hours, and after a total of 18 hours of reaction the reactants and products were separated. The yield was very poor. Prom a series of fractionations only 0.875 g (6.7 ram°le) of pure phosphine was obtained* The phosphine was separated from traces of CF^I by con-densing the mixture on to a large excess of silver iodide. The phosphine forms an unstable adduct and so CP I can be separated. The adduct decomposes above 5 & n (i gives pure phosphine. By repeating the process of forming the silver iodide adduct and decomposing i t , pure phospnine could be obtained. However only 8.43 g(°-G>3 mole) of t r i -fluoroiodomethane could be recovered. 3 c. The amount of trifluoroiodomethane consumed did not exactly correspond with the expected stoichiometry, and hence the volatile white solid was analysed for the trifluoromethyl groups. The solid (0.472 g) was treated with 20%, sodium hydroxide (5 ml) at room temperature. After 60 hours, fractionation gave fluoroform (0.235 g ? -173-3.36 mmole) identified from i t s molecular weight. (Found 71.0, calculated 70.0) This corresponds with the loss of two trifluoromethyl groups from what might be dimethyl -bistrifluoromethylphosphonium iodide ( CF^, found49.8$; calculated for (CH^) g(CF^ ) 2 P I , 42.3$) • Evaporation of the pale yellow hydrolysis solution gave a solid whose infra-red spectrum showed the absence of trifluoromethyl groups and corresponded with that of sodium salt of dimethylphosphlnic acid. o The original solid melted at 60 C and absorbed strongly i n the 8 - 9/i- region of the infra-red , indicatin the presence of trifluoromethyl groups. On standing over a long period, fluoroform was evolved, leaving a red hygroscopic solid of unknown composition. 3 d. To further characterize this compound, two experiments were performed. 1. Tetramethylphosphonium iodide (O.I367 g) was sealed with trifluoroiodomethane (0..5 g)» There was no immediate reaction although liquid trifluoroiodomethane seemed to dissolve the solid. On opening the tube after 72 hours, the trifluoroiodomethane was recovered quantitatively. 2. Dimethyltrifluoromethyl phosphine (0.1 g) was sealed with trifluoroiodomethane o (0.2 g). There was no reaction in the gas phase at 25 nor at lower temperatures. However, on the removal of a l l -174-o v o l a t i l e material at -78 , a white s o l i d formed which could be sublimed to cooler parts of me tube and appeared to be s i m i l a r t o the white s o l i d thought to be dimethyl-bistrifluoromethylphosphonium iodide. The separation of the reactants was d i f f i c u l t and no s o l i d sublimed into the system. The infra-red spectrum of the v o l a t i l e products showed the presence of fluoroform, probably due to d i s -sociation of the above phosphonium iodide. 3 e. Since the reaction i n the gas phase was slow, this reaction was performed i n the l i q u i d phase by treat-ing 0.1232 g of -the phosphine with 2 . 0 g of t r i f l u o r o -iodomethane. Fractionation a f t e r 120 hours l e f t behind a small amount of the white s o l i d which was spectrosco-p i c a l l y i d e n t i c a l with the o r i g i n a l white s o l i d . 4 a. Preparation of Tristrifluoromethylphosphine The method used was the same as reported e a r l i e r , i . e . by heating red or white phosphorus with t r i f l u o r o -iodomethane i n sealed Pyrex tubes o r i n an autoclave. Varying proportions of phosphorus to iodide, and d i f f e r e n t conditions of temperature were studied. Typical r e s u l t s are shown i n the following table. When white phosphorus was used,'it \tfas f i r s t reduced to powder form, by vigor-ous shaking of molten phosphorus under di s t i l l e d water. Successive treatments removed most of the impurities and -175-the l a s t traces of water were removed i n vacuo. However the yields of the required phosphine were s t i l l rather low, this being attributed to the presence of small amounts of phosphorus oxide. When red phosphorus and t r i f l u o r o -methyl iodide, i n the r a t i o of 1:2 by weight, were heated, the y i e l d of phosphine was again low although r e c y c l i n g of the iodides with more trifluoromethyl iodide increased the y i e l d somewhat. The highest y i e l d s were obtained when small amounts of free iodine were present. A l l of the trifluoromethyl iodide was then u t i l i s e d to give a higher r a t i o of the phosphine to iodides. Under these conditions there was also formed i n small amounts an o i l y , yellow l i q u i d of unknown composition which was immiscible with the iodides, and which was i n v o l a t i l e at room tem-perature. The yie l d s shown i n the following table are (4) much higher than those reported o r i g i n a l l y * , and com-(9) pare favourably with those of Burg and Mahler* • Wt. of Phosphorus Wt. of CP3I Conditions Products Y i e l d fo o 2 g. white 2 g 225 f o r 48 hr P ( C F 3 ) 3 32 P ( C F 3 ) 2 I 13 P C P 3 I 2 3 C P 3 I 30 CP^H 9 13 g white 13 g red 5 g red -176-8 g 216° P ( C F 3 ) 3 40 P ( C F 3 ) 2 I 10 PCF 3I 2 2 CF 3I 25 CF3H 8 8 g P ( C F 3 ) 5 26 after r e c y c l i n g of the iodides 39 10 g 0 216 for 48 hr P(CF,), •> 3 47 + 0.5 g I 2 P ( C F 3 ) 2 I 15 P ( G F 3 ) I 2 2 GF 3I 0.3 CF3H 7o3 -t-unknown l i q u i d In a l l these experiments the residue i n the tube was a red s o l i d which was i d e n t i f i e d as a mixture of phosphorus t r i i o d i d e and phosphorus diiod i d e . 4 b. In order to elucidate the mechanism of these reactions, a reaction was performed i n which there was no iodide present. .6.7 g s i l v e r t r i f l u o r o a c e t a t e , 0.5 g red phosphorus, and a trace of iodine were heated i n a o Carius tube to 250 for 12 hours. The only v o l a t i l e product obtained was t r i f l u o r o a c e t i c anhydride (molecular weight observed 212, calculated 210). Since the compound does not contain any phosphorus, t h i s experiment shows that -177-there i s no reaction between silvei&trifluoroacetate and phosphorus. However i n the presence of excess of iodine the phosphines have been obtained. Another experiment o carried out i n an autoclave at 285 did not produce tristrifluoromethylphosphine or fluoroform, but gave phosphorus t r i f l u o r i d e and carbon t e t r a f l u o r i d e instead. 5 a» Preparation of Methylbistrifluoromethylphosphine Tristrifluoromethylphosphine (1.3 g, 5*46 mmole) was sealed with methyl iodide (0.83 g, 5»8 mmole) and o - o heated to 230 for 12 hours, and at 235 for a further 20 hours. The two reactants, which o r i g i n a l l y formed separate layers at room temperature, af t e r reaction formed a homo-geneous solution. The completion of reaction could be seen by cooling the reaction tube i n l i q u i d nitrogen ..,('; and allowing i t to slowly warm up. I f the reaction was not complete, the solution would not remain homogeneous and would separate Into two layers on reaching room tem-perature. The separation of the products was very tedious and required, a series of fractionations to i s o l a t e the pure phosphine. The v o l a t i l e products from the above reaction consisted of methylbistrifluoromethylphosphine (0.615 g, 3*34 mmole) corresponding to a. y i e l d of 60$ based on the amount of tristrifluoromethylphosphine -178-eonsumed, trifluoroiodomethane 11%, and fluoroform !%• There was also an involatile residue in the tube. This consisted of some insoluble carbonaceous matter which was not identified, but definitely did not contain a CF^ group as shown by the infra-red spectrum. The residue also contained a white solid which was found to be t r i -(2) methyltrifluoromethylphosphonium iodide . When equimolar quantities were used, a l l the methyl iodide was used up but some tristrifluoromethyl-phosphine was l e f t unreacted. Tristrifluoromethylphos-phine (0.67 g, 2.81 mmole) and methyl iodide (0.39 g* o 2.75 mmole) were heated to 230 for 48 hours. There was less carbonisation but the two phosphines were d i f f i -cult to separate. 5 b. Methylbistrifluoromethylphosphine was also prepared by heating tristrifluoromethylphosphine (0.56g) o with methyl mercuric chloride (0.40 g) to 220 for 16 hours. The solid methyl mercuric chloride was found to carbonise slightly. The reaction was slow and the phosphi were found to be difficult',:»to separate. -179-I I I PHENYL-TRIFLUOROMETHYL-PHOSPHINES A 1. Preparation of Phenylbistrifluoromethylphosphine a* Preparation of Phenyldichlorophosphine This compound was prepared by the F r i e d e l -Crafts reaction, o r i g i n a l l y reported by Michaelis. However, modifications of the method have been described by Buchner and Lockhart* ' and these were employed. 165 S phosphorus t r i c h l o r i d e , 23.4 g benzene, and 53 g aluminium t r i c h l o r i d e anhydrous were refluxed, at f i r s t slowly and then vigorously f o r one and one h a l f hours or u n t i l the evolution of HC1 ceased. The heating was then stopped and 62 g phosphorus oxychloride were added drop by drop while the mixture was s t i l l hot. The AlCl'POCl, 3 J complex precipitated as awhite granular s o l i d . The l i q u i d layer was extracted with 6 - 8 portions each of 100 ml of petroleum ether. The residue was f i l t e r e d and the f i l t r a t e along with the extract was subjected to vacuum d i s t i l l a t i o n . The product d i s t i l l i n g over between 107 -0 112 was coll e c t e d . The infra-red spectrum of the product corresponded with that reported* » b. Preparation of Phenylphosphine The method of Michaelis was attempted but found un-sa t i s f a c t o r y . The phosphine was prepared by the reduction of -180-phenyldichlorophosphine with l i t h i u m aluminium hydride. 18.8 g phenyldichlorophosphine i n 100 ml d i e t h y l ether was added cautiously to a wel l s t i r r e d suspension of l i t h i u m aluminium hydride (3 g) i n 100 ml ether. The reaction was vigorous and was carried out at 0 C. After the addition of phenyldichlorophosphine was complete, the mixture was refluxed f o r 3 0 minutes and 5 ml of d i s -t i l l e d water were added dropwise. This mixture was re-fluxed f o r an hour and then d i s t i l l e d d i r e c t l y . The o phenylphosphine d i s t i l l e d at 160 but was contaminated with water. I t was therefore dissolved i n ether, and a f t e r siphoning out the water, the ether solution was dried with calcium chloride. I t was then d i s t i l l e d i n a s t i l l of 2 5 ml capacity and 8" column. The r e s u l t i n g product was pure phenylphosphine. The infra-red spectrum of this compound has not been reported but the sharp band at 2300 cm"-'", ch a r a c t e r i s t i c of the P-H bond, ea s i l y i d e n t i f i e d the product. c. In another preparation, the reaction was carried out i n n-butyl ether i n order to slow down the reaction, the same quantities being used. The reaction was smooth but the separation by d i s t i l l a t i o n was not very e f f e c t i v e , possibly because of the close b o i l i n g points of the phosphine and ether. -181-d. Preparation of Tetraphenylcyclotetraphosphine This compound was prepared by the reaction of phenyldichlorophosphine and phenylphosphine. 2C 6H 5PC1 2+ 2C 6H 5PH 2 * ( C 6 H 5 P ) 4 + ^Cl In a three necked f l a s k , which had been flushed with nitrogen and which was f i t t e d with a s t i r r e r and con-denser, was placed a 50 ml ether solution of 18 g phenyl-dichlorophosphine, and while t h i s solution was being s t i r r e d , a 50 ml ether solution of l l g phenylphosphine was slowly added. The solution gradually turned yellow but a s o l i d was not deposited immediately. After the addition was complete, the solution was refluxed for three hours during which time a white s o l i d was deposited and the evolution of HG1 ceased. The ether solution was decanted o f f , and the remaining s o l i d was washed with ether and then dried. The yiel d , of tetraphenylcyclo-tetraphosphine was S0%» The compound was characterized o by i t s melting point 148 - 150 and i t s infra-red spect-rum.*1*) e. Interaction of Tetraphenylcyclotetraphosphine  and Trifluoroiodomethane Tetraphenylcyclotetraphosphine (1.0 g) was sealed with trifluoroiodomethane (2.025 g) and l e f t at room temperature f o r 24 hours. The s o l i d phosphine i s -182-insoluble i n trifluoroiodomethane, and f l o a t s on the l i q u i d CF_I. The tube containing the reactants was heated to 70 f o r 24 hours but no reaction occurred. o I t was then heated to 150 f o r 12 hours. On cooling, the s o l i d phosphine separated i n the form of yellow c r y s t a l s . The trifluoroiodomethane also changed i t s colour, becoming s l i g h t l y reddish, i n d i c a t i n g that some s l i g h t reaction had occurred. The reaction was then o conducted at 185 for 12 hours, when a dark red I n v o l a t i l e l i q u i d was obtained and 0.558 g trifluoroiodomethane was recovered. The dark red l i q u i d was shaken with mer-cury and the remaining l i q u i d extracted with ether. After removal of ether, 0.45 g of a l i q u i d of low v o l a t i l -i t y was obtained and was i d e n t i f i e d as p h e n y l b i s t r i f l u o r o -methylphosphine. (Pound C, 39.35%; H, 2.10%; P, 45.40$; P, 12.30$. Calculated f o r C_H_FJP, C,39.03$; H, 2.03$; o 5 o P, 46.36$; P, 12.60$) In order to investigate the mechanism of the reaction of trifluoroiodomethane and tetraphenylcyclote-traphosphlne, and also to characterize the other reaction products, the following experiments were performed. £. Tetraphenylcyclotetraphosphine (1 g) and o trifluoroiodomethane ( 2 g ) were heated at 165 f o r 20 hours. The mixture became dark red and no s o l i d separated -183-on cooling. D i s t i l l a t i o n under vacuum gave phenylbis-triluoromethylphosphine (0.3 g), showing that the reaction can be carried out above the melting point of the phos-phine. gr. Tetraphenylcyclotetraphosphine (2 g) and trifluoroiodomethane. (5 g) were sealed i n a pyrex tube and i r r a d i a t e d with u l t r a - v i o l e t l i g h t from a 200 watt U.V. lamp at a distance of 20 cm. The r a d i a t i o n was concentrated on the l i q u i d CF^I and the r e s t of the tube was wrapped with aluminium f o i l so that the vapour phase was not i r r a d i a t e d . The reaction was slow, possibly because of the heterogeneous phases. The l i q u i d phase became darker as the reaction proceeded, and after 15 days of i r r a d i a t i o n , f r a c t i o n a t i o n of the products gave phenylbistrifluoromethylphosphine (0.899g) and unreacted trifluoroiodomethane (2.192 g). The consumption of 2.803 g of the l a t t e r i s about one gram i n excess of what i s required f o r the production of the above amount of phosphine. h. In order to account f o r the above loss of CF,I, the other products were analysed. The r e s t of the 5 products were the unreacted tetraphenylcyclotetraphosphine and a thick reddish syrup. The infra-red spectrum of t h i s syrup indicated strong absorption i n the 8 - 9/t region, -184-c h a r a c t e r i s t i c of CF, groups. Treatment of a small amount j of t h i s substance with sodium hydroxide solution evolved fluoroform. 0.32 g of th i s reddish l i q u i d gave 0.012 g or 3*7$ fluoroform, which was not a quantitative amount to correspond with the analysis of a possible compound. i . Tetraphenylcyclotetraphosphine (1.5 g) and trifluoroiodomethane were sealed i n a Carius tube add o heated to 185 f o r 12 hours. The v o l a t i l e compounds were fractionated through -78, -132 , and -196 baths. A small amount of phosphine d i s t i l l e d over and collected o i n the -78 bath. Trifluoroiodomethane was collected i n o the -132 bath, whereas fluoroform and hexaf luoroethane were condensed i n the l i q u i d nitrogen trap. The t r i -fluoroiodomethane which was recovered weighed 5»5 g and the other v o l a t i l e products were only 0.022 g. The l a t t e r were i d e n t i f i e d by t h e i r i n f r a - r e d spectra. The remaining l i q u i d was subjected to f r a c t i o n a l d i s t i l l a t i o n outside the vacuum system under a pressure of 20 mm. Two fractions were obtained, one b o i l i n g at o o 62 - 65 (4.9 g) and the other b o i l i n g at 112 - 116 (3.8 g). A thick l i q u i d , which s o l i d i f i e d on standing, remained i n the d i s t i l l a t i o n f l a s k . j . Characterization of the Fractions The f r a c t i o n b o i l i n g at 62 - 65° was i d e n t i f i e d -185-as phenylbistrifluoromethylphosphine from the Infra-red spectrum of the l i q u i d . The phosphine was s l i g h t l y coloured, possibly because of the presence of traces of iodine. I t was therfore p u r i f i e d by shaking with mercury for 24 hours, followed by d i s t i l l a t i o n i n an atmosphere of nitrogen. Two fractions were obtained, o o one b o i l i n g at 84 - 86 and the other at 148 - 150 • The Infra-red spectrum of the f i r s t f r a c t i o n indicated the presence of a P-H bond by the c h a r a c t e r i s t i c absorp-t i o n at 2300 cm"-'-. Since the quantity of this f r a c t i o n was not very s i g n i f i c a n t (ca. 0 . 1 g) i t was not inves-tigated further. o The other f r a c t i o n b o i l i n g at 148 - 150 was further p u r i f i e d by vapour phase chromatography. The o temperature of the furnace was maintained at 120 and the column used was "Ucon polar". The spectrum showed a wide gap between the small amount of impurity and the phosphine, showing that the l a t t e r a f t e r d i s t i l l a t i o n was 98$ pure. The phosphine p u r i f i e d this way was used f o r further inve s t i g a t i o n . o k. The f r a c t i o n b o i l i n g at 112 - 114 (at 20 ram) was i d e n t i f i e d as phenyltrifluoromethyliodophosphine. (Pound 1,41.2$ Calculated f o r C H P PI; I, 41.78$) The 7 5 3 -186-inf r a - r e d spectrum ( f i g . 1 ) showed two strong bands i n the region associated with C-F stretching frequencies corresponding to one trifluoromethyl group. I t was ob-served that on cooling, t h i s f r a c t i o n deposited needle-shaped crystals which were s i m i l a r to and i d e n t i f i e d by t h e i r melting point as phosphorus t r i i o d i d e . The presence of phosphorus t r i i o d i d e was possibly due to the dispro-portionation of the idophosphine as shown l a t e r . 1. The f r a c t i o n remaining i n the s t i l l s o l i -d i f i e d on cooling into a resinous mass. Treatment with water gave a strongly acid solution but did not p r e c i p i -tate any s o l i d . The solution was brown and contained free iodine and iodides. The o r i g i n a l material was i n -soluble i n petroleum ether, but seemed p a r t i a l l y soluble i n acetone. The s o l i d recovered from the acetone solution did not show any absorption f o r the C-F stretching f r e -quency region, but did contain a phenyl group. Analysis showed i t to be an iodide, possibly phenyldiiodophosphine. m. In another experiment, the l i q u i d (15 g) remaining i n the tube a f t e r d i s t i l l a t i o n of the phosphine was sealed with trifluoroiodomethane (25 g) and mercury (80 g). The mixture was shaken f o r 48 hours. After f r a c t i o n a t i o n of the v o l a t i l e products, the mixture was extracted with ether. The evaporation of the solvent -187-l e f t a thick pale yellow l i q u i d (20 g). Prom analysis i t was shown not to contain any iodides, and from the infra - r e d spectrum was found to contain trifluoromethyl groups. 0.322 g of this substance was treated with a 20$ sodium hydroxide solution and th i s gave 0.0428 g or 13.28$ fluoroform. 2. Diphenyltrifluoromethylphosphine a. Preparation of Diphenylchlorophosphine The preparation of this compound was attempted by the disproprtionation of phenyldichlorophosphine (37 ) # 75 g of the l a t t e r were heated i n three sealed tubes f o r f i v e days. The decomposition reaction was slow and mostly incomplete, f o r at the end of t h i s period only 1 g of a f r a c t i o n b o i l i n g over 300 was obtained. The rest of the products consisted of phosphorus t r i c h l o r i d e and unreacted phenyldichlorophosphine• b. The preparation was attempted by tre a t i n g phenyldichlorophosphine with l i t h i u m phenyl. Lithium phenyl was obtained commercially as a 0.75 molar suspen-sion i n pentane. The suspension (70 ml, 0.052 mole) was placed i n a three-necked f l a s k which was flushed with nitrogen, and phenyldichlorophosphine (9 g,0.05 mole)was added dropwise. The reaction was vigorous and the f l a s k had to be cooled i n an Ice bath. At the end of the reaction -188-th e pentane solution was evaporated i n vacuo, and this gave o a s o l i d , melting at 85 , which was i d e n t i f i e d spectroscop-i c a l l y , t o be triphenylphosphine. The reaction was carried 0 out at -78 , but the product s t i l l was triphenylphosphine. No diphenylchlorophosphine could be obtained. c. Diphenylchlorophosphine was prepared by the ( 4 0 ) . method of Steube, LeSuer, and Norman a To a w e l l - s t i r r e d mixture of phosphorus pentasulphide (208 g, 0.47 mole) arid benzene (224 g» 3»18 mole), aluminium chloride (222 g, 1.66 mole) was gradually added at such a rate that the benzene did not b o i l . The mixture was refluxed f o r f i v e hours, and a f t e r standing f o r three hours was poured onto crushed i c e . The dark green l i q u i d so obtained was separated, washed with more water, then dried with magnesium sulphate. The same volume of benzene was added to the above solution of diphenylphosphinodithioic acid, and while this solution was cooled i n an ice bath and s t i r r e d , a rapid stream of chlorine was passed through i t . Di-phenyl t r i chl or ophospho ran e separated as an o i l which soon s o l i d i f i e d to give orange yellow c r y s t a l s . 200 ml of petroleum ether was added to t h i s mixture. A f t e r an hour the supernatent l i q u i d was decanted and the s o l i d residue was washed with more petroleum ether. Red phosphorus (15*5 g» 0.5 mole) was added to this mixture ( s o l i d and -189-1 o petroleum ether) and heated slowly on an o i l bath to 180 0 When the more v o l a t i l e products, phosphorus t r i c h l o r i d e and petroleum ether, d i s t i l l e d over, the residual mixture o was vacuum d i s t i l l e d and the f r a c t i o n b o i l i n g at 178 at 20mm was collected. This gave 64 g or 63% y i e l d of d i -phenylchlorophosphine. d. Diphenylphosphine was prepared by adding an ethereal solution of diphenylchlorophosphine (22 g, 0.1 mole) to a suspension of l i t h i u m metal (0.3 g) i n ether. The reaction was controlled by cooling the react-ion f l a s k i n an i c e bath. After the addition was complete, the mixture was refluxed and treated with water. At the end of this reaction, the precipitated l i t h i u m chloride was f i l t e r e d o f f and the ether solution was d i s t i l l e d . A fter the ether was d i s t i l l e d o f f , diphenylphosphine was d i s t i l l e d i n vacuo. e. Preparation of Tetraphenyldiphosphine An ethereal solution of diphenylphosphine (9 g, 0 .05 mole) Was added gradually to another ether solution of diphenylchlorophosphine (11 g, 0 .05 mole). The r e s u l t -ing mixture was refluxed f or two hours when tetraphenyl-diphosphine separated as a white s o l i d . The s o l i d was washed with ether and dried, and then sealed with t r i -fluoroiodomethane f o r further reaction. -190-f. The preparation of this compound jCCgH^JgPJ^ was also attempted through the formation of the dlphenyl-diphosphinebisodium adduct. To a well-stirred mixture of freshly cut softium pieces (3 g) and tetrahydrofuron (100 ml), phenyldichlorophosphine (17»9 g* 0.1 mole) was added in a nitrogen atmosphere. The reaction was vigo-rous and the flask had to be cooled. The colour of the solution changed to yellow and f i n a l l y became bright red. The unreacted sodium was separated and iodobenzene (20.4 g, 0.1 mole) was added gradually. Sodium iodide was seen to separate, but the solution on evaporation did not leave any residue corresponding to tetraphenyldiphosphine. The solid residue l e f t after d i s t i l l a t i o n did, however, i n -dicate the presence of P-CgH^ bond by i t s infra-red spec-trum. The preparation of tetraphenyldiphosphine by the above method was repeated by using powdered sodium in xylene, and also by using lithium. Positive results could not, however, be obtained. g. Interaction of Tetraphenyldiphosphine  and Trifluoroiodomethane Tetraphenyldiphosphine (1.2 g, 3.2 mmole) and an excess of trifluoroiodomethane (12.2 g, 62.2 mmole) o were heated in a Pyrex tube to 185 for 12 hours. After -191-fractie-nation of Hie products, trifluoroiodomethane (11.5 g> 58• 5 mmole) and a small amount of fluoroform (0.004 g) were obtained as the v o l a t i l e products, and the residue i n the tube was a thick red l i q u i d . The loss of trifluoroiodomethane indicated that some reaction had occurred. The i n v o l a t i l e red l i q u i d was therefore treated with petroleum ether to extract the phosphine, much of the former being insoluble i n this solvent. Infra-red spectrum of the remaining red l i q u i d did not indicate the presence of a CP^ group, and analysis showed i t to be an iodo-phosphine containing free iodine and probably was d i -phenyliodophosphine. Evaporation of the petroleum ether extract i n vacuum l e f t an i n v o l a t i l e l i q u i d (0.4 g) whose i n f r a -red spectrum had two strong bands i n the C-F stretching frequency region, and also the c h a r a c t e r i s t i c frequenc-ies of the phenyl group. Treatment of this l i q u i d with alcoholic potassium hydroxide gave fluoroform. Analysis of a pure sample ( p u r i f i e d by vapour phase chromatography o using a s i l i c o n e column i t a; temperature of 230 with helium flowing at a pressure of 7 p.s.i.) showed i t to be diphenyltrifluoromethylphosphine. (Found C, 60 .86$; H, 4 .25$; F, 2 2 . 6 9 $ ; P, 11 .79$. Calculated f o r C, ,H F,P; C, 13 10 o 61 .41$; H, 3 . 9 4 $ ; P, 2 2 . 4 5 $ ; P, 12.21$) -192-h. To elucidate the reaction mechanism t e t r a -phenyldiphosphine (1.0 g, 2.7 mmole) and t r i f l u o r o i o d o -methane (10 g, 51 mmole) were i r r a d i a t e d with u l t r a -v i o l e t l i g h t for seven days. The diphosphine [(OgH,-JgPJ 2 was insoluble i n CF,I, but as the reaction proceeded, the colour of the l i q u i d became darker. Fractionation of the v o l a t i l e products gave trifluoroiodomethane (9*6 g) and extraction of the residue with petroleum ether l e f t an insoluble red l i q u i d whose infra-red spectrum corresponded with the one obtained on heating the two reactants. The petroleum ether extract gave diphenyltrifluoromethylphos-phine (0.15 g), i d e n t i f i e d from i t s infra-red spectrum ( f i g . 6 )„ Some of the unreacted diphosphine was also found with the i n v o l a t i l e residue., I• Reaction of Triphenylphosphine with  Trifluoroiodomethane Triphenylphosphine (2.5 g, 9«54 mmole) was heated with excess trifluoroiodomethane (14.0 g, 71«4 mmole) to 185 f o r four hours. The s o l i d phosphine (CgHj-J^P i s e a s i l y soluble i n the l i q u i d CF^I at room temperature and as the tube Is gradually heated, the solution becomes yellow, orange, and f i n a l l y reddish brown. Fractionation of the v o l a t i l e products gave trifluoroiodomethane (10.6 g, 75.7$), fluoroform (0.4628 g, 9»25%) and a small amount of trifluoromethylbenzene -193-(0.0434 g» 0.42$). A thick reddish brown mass was l e f t i n the reaction tube and was extracted with petroleum ether. Vacuum d i s t i l l a t i o n of this extract gave diphenyl-trifluoromethylphosphine (0.2 g), which was i d e n t i f i e d from i t s infra-red spectrum ( f i g . 6 ). The infra-red spectrum of the residual reddish brown l i q u i d was iden-t i c a l with that obtained from the reaction of tetraphenyl-diphosphine and trifluoroiodomethane. The reaction of triphenylphosphine and t r i f l u o r o iodomethane at lower temperatures, 70 and 110 f o r 24 hours each, gave back the CP I q u a n t i t a t i v e l y , and at o J 214 gave a reddish brown resinous substance which could not be i d e n t i f i e d . However 12$ of the trifluoroiodometh-ane was consumed. j . Reaction of Diphenylchlorophosphine  and Trifluoroiodomethane Diphenylchlorophosphine (5«6 g)or(25..5 mmole) and trifluoroiodomethane (12.5 g, 63.7 mmole) were heated o 205 f o r 12 hours. The reactants were miscible at room temperature and formed a pale yellow solution. A f t e r reaction, the solution which became reddish brown was fractionated i n the vacuum system. A mixture of hexa-fluoroethane and fluoroform was obtained i n trace amounts. The other v o l a t i l e products were trifluorochloromethane -194-(1.24 g, 14*8$), unreacted trifluoroiodomethane (8.79 g» 10*3%)* and a small amount of trifluoromethylbenzene (0.0438 g). The i n v o l a t i l e l i q u i d was extracted with petroleum ether. The residual red l i q u i d was i d e n t i f i e d as diphenyliodophosphine from i t s infra-red spectrum, and was s i m i l a r i n a l l respects to the red l i q u i d i n reactions HI'gig), HE 2(h), and HI 2 ( i ) . k. In another experiment employing the same conditions and the same amount of diphenylchlorophosphine but a larger excess of trifiluoroiodomethane (17*0 g) than i n HI 2 ( j ) , 5.0 g of crude diphenyltrifluoromethyl-phosphine by extracting with petroleum ether and only a small amount of trifluorochloromethane (0.1 g) were ob-tained. D i s t i l l a t i o n of the crude phosphine under vacuum o gave a f r a c t i o n (3»5 g) b o i l i n g at 112 - 130 , and an i n v o l a t i l e residue which was i d e n t i f i e d as diphenylchloro-phosphine. o The f r a c t i o n b o i l i n g at 112 - 130 was f u r t h e r p r u i f i e d by vapour phase chromatography to give three f r a c t i o n s . The infra-red spectra of the three fractions showed them to be trifluoromethylbenzene, p h e n y l t r i f l u o r o -methylchlorophosphine, and diphenyltrifluoromethylphosphine. 1. The i n v o l a t i l e reddish brown l i q u i d , i d e n t i -f i e d spectroscopically as (C^-H[-)9PI, was shaken with t r i --195-fluoroiodomethane (23.7 g) and mercury (168.5 g) f o r 120 hours. At the end of th i s period, trifluoroiodomethane was recovered qu a n t i t a t i v e l y (23.3 g) from the reaction mixture, showing that the expected reaction giving ( C 6 H 5 ^ 2 C P 3 P d i d n o t o c c u r » -196-B PROPERTIES AMD REACTIONS OF PHENHJ-TRIFLUOROMETRYL-PHOSPHINES 1« .Phenylbigtrifluoromethylphosphine a* Physical Properties Phenylbistrifluoromethylphosphine i s a colour-less o i l y l i q u i d whose odour i s not as obnoxious as those of other phosphines. I t s b o i l i n g point, determined by o the inverted c a p i l l a r y method, i s 148 - 150 , and i t s vapour pressure was found to be as follows. T VT IO~3 P log P 26 0.33 44 17 I.2304 33 0.3268 20 1.3010 41 0.3185 25 1.3979 51 0.3086 35 1.5441 61 0.2994 46 1.6628 71 0.2907 63 1.7997 77 0.2857 77 1.8865 81 0.2825 90 1.9542 86 0.2726 110 2.0414 90 0.2755 123 2.0899 94 0.2725 139 2.1430 96 0.2710 150 2.1761 100 0.2681 165 2.2175 105 0.2646 204 2.3096 108 0.2625 223 2.3483 -197-Th e vapor pressure follows the equation: log P(mm) = 7.5606- 1985 10 r j T -The latent heat of vaporization calculated from the above - I -data i s 9054 kcal mole and the Trouton's constant i s 21.37. 1 (b). The phosphine i s stable In a i r and i s o unchanged on heating up to 200 . Phenylbistrifluoromethyl-o phosphine (1.058 g) was heated to 210 for 48 hours. The phosphine was recovered q u a n t i t a t i v e l y (1.004 g), and only traces of fluoroform and s i l i c o n t e t r a f l u o r i d e could be i d e n t i f i e d spectroscopically. The phosphine (0.639 g) was o then heated to 300 f o r 48 hours. The tube walls were etched but the phosphine was not a l l pyrolyzed and most of i t (0.48 g) was recovered unchanged. The other v o l a t i l e materials were fluoroform, s i l i c o n t e t r a f l u o r i d e and some trifluoromethylbenzene. This shows that the phosphine i s o only 25$ pyrolyzed when heated at 300 for 48 hours. 1 ( c ) . . Reactions6fPtienylbistrifluoromethy 1 -phosphine: The phosphine does not react with s i l v e r iodide, a s o l u t i o n of s i l v e r iodide i n potassium iodide, or with car-bon disulphide. 1 (d). Hydrolysis with water: The phosphine (0.277 g, 1.12 cummole) was sealed with water' (1.28 g). The reaction tube was l e f t at room temperature for 48 hours. The reactants formed two separate layers. On opening the tube, the phosphine was recovered q u a n t i t a t i v e l y . Heating - 198 -the reaction tube to 80 f o r 24 hours gave only a trace of fluoroform, i d e n t i f i e d spectroscopically. The reactants o were then heated to l l O for J2 hours. This gave a small amount of fluoroform (0.038 g, 0.92 mmole). A c r y s t a l l i n e residue was l e f t i n the tube when the reactants were pumped off and was i d e n t i f i e d as phenylphosphonous acid, melting o "(44) at 69 (reported M.Pt. 70-71 ) 1(e) Hydrolysis with a l k a l i : The phosphine (0.273 g, 1.11 mmole) was sealed with 5 ml of 20% a l k a l i s o lution (sodium hydroxide). The reaction was slow at room temperature and evolution of fluoroform continued slowly. o The reaction was carried out at 80 for 24 hours. When the tube was opened, fluoroform was recovered almost quantita-t i v e l y (0.149 g, 2.13 mmole). This hydrolysis accounted f o r 96.4$ of the trifluoromethyl groups JCF^ found as fluoroform 54.8$; calculated f o r CgH^CF ^P, 56.1$.] The s o l i d r e s i -due obtained on evaporation of the a l k a l i n e s olution was found to contain the sodium s a l t of phenylphosphonous acid. o A c i d i f y i n g t h i s s a l t gave the acid, M.Pt. 69 • 1(f) Hydrolysis with acid; The phosphine (0.372 g, 1.51 mmole) was heated to 80° f o r 24 hours with 36 N hydrochloric acid (2 g). The reactants formed separate layers and did not seem to react. They were then heated to o 110 for 48 hours. Fractionation did not give any fluoroform. - 1 9 9 -o They were f i n a l l y heated to 185 f o r 120 hours. This gave a trace amount of fluoroform (0.0022 g). The phosphine and acid s t i l l formed two layers and the former was recovered / q u a n t i t a t i v e l y . REACTION Op;PHENYLBISTRIFLUOROMETHYLPHOSPHINE WITH HALOGENS: 1(g) Reaction with iodine: P h e n y l b i s t r i f l u o r o -methylphosphine (0.4736 g, 1.93 mmole) was treated with iodine (0.508 g, 2.0 mmole). At room temperature, the mix-ture formed a brown l i q u i d but did not seem to react. No o reaction occurred when the mixture was heated f i r s t to 80 , o o o then 110 and to 150 • After heating at 185 f o r 48 hours, the products were a small amount of fluoroform (0.028 g, 0.4 mmole), trifluoroiodomethane (0.382 g, 1.96 mmole), phosphorus t r i i o d i d e and some unreacted phosphine. The amount of trifluoroiodomethane was only 50$ of the expected quantity. In a second experiment using excess iodine (1.163 g, 4.58 mmole), the phosphine (0.3899 g, 1.58 mmole) o was heated to 185 f o r 48 hours to give trifluoroiodomethane (0.481 g, 2.47 mmole) and fluoroform (0.032 g, O.46 mmole). A small amount of benzene (0.055 g) and traces of unreacted phosphine were also present among the reaction products. The conversion into fluoroform and trifluoroiodomethane accounted f o r 91*5% of the trifluoromethyl groups. The f o r -mation of fluoroform and benzene might be due to the small traces of moisvture on iodine which i s not removed even on ex-- 200 -tensive drying* 1(h) Reaction with bromine; The phosphine (0.695 g» 283 mmole) was reacted with bromine (0.450 g, 2.83 mmole). The reaction was vigorous and an orange-yellow s o l i d was immediately deposited. The reaction could, however, be controlled by carrying out the reaction i n car-bon tetrachloride solution. The completion of the reaction was marked by the coloration of the solution and by the p r e c i p i t a t i o n of the phosphorane. Washing with small amounts of carbon tetrachloride to remove excess bromine and then pumping o f f the solvent gave pure p h e n y l b i s t r i -fluoromethyldibromophosphorane (Found Br 38>93#, calcu-lated f o r C QH CF-PBr , Br 39.41$). o 0 o d. l ( i ) The phosphorane reacted very r e a d i l y with water with the loss of one equivalent of CF and formation 3 of a white s o l i d . The dibromophosphorane (O.324 g, 0.798 mmole) was sealed with water (1 . 0 g) and l e f t a t room temperature overnight. Fluoroform (0.060 g, 0 .85 mmole) was evolved corresponding to the loss of one CF per mole. 3 (Found CF,, 18 . 4 $ . Calculated f o r C H F PBr ; CF , 3 4 . 5 $ ) . 2 8 5 6 2 3 A white s o l i d was obtained when the l i q u i d was pumped o f f . I t was r e c r y s t a l l i z e d from water and dried over phosphorus pentoxide. The s o l i d was i d e n t i f i e d spectroscopically as phenyltrifluoromethylphosphinic acid CJl (CF )P (0)0H. The o 6 5 3 . acid melted at 84-86 . The s i l v e r s a l t of t h i s acid was - 201 -obtained by trea t i n g the aqueous solution of the acid with s i l v e r oxide, f i l t e r i n g o f f any excess of the oxide and evaporating the s o l i d i n vacuo* The re s u l t i n g s o l i d was dried over phosphorus pentoxide. The s i l v e r s a l t C H (CP )P(0)0Ag (Found Ag, 33.81%; calculated for C H F P0 Ag; Ag, 34.06$) 7 5 3 2 was a c r y s t a l l i n e s o l i d melting at 2 9 4 - 9 6 and was very sen-s i t i v e to l i g h t . The s i l v e r s a l t was e a s i l y prepared, however, by treating the mixture of the phosphorane C H_(CF ) PBr and ^ 6 5 3 2 2 water with s i l v e r oxide. The precipitated s i l v e r bromide was f i l t e r e d out along with the excess s i l v e r oxide, and the evaporation of the solution gave a product i d e n t i c a l with that obtained from the reaction with the acid. l ( j ) Reaction with trifluoroiodomethane: Phenyl-bis t r i f luoromethylphosphine (O .4I5 g, 1 .69 mmole) was treated with trifluoroiodomethane (1.151 g, 5»91 mmole). The reac-tants were miscible at room temperature. They were heated o to 230 for 10 hours. Fractionation of the products gave fluoroform (0 . 1902 g, 2 . 7 2 mmole) trifluoroiodomethane (0 . 8 8 4 8 g, 4 . 5 4 mmole) and unreacted phosphine C H (CF ) P 6 5 3 2 (0 . 1743 g» 0.708 mmole). Trifluoromethylbenzene was i d e n t i -f i e d among the products spectroscopically but the same method did not indicate the presence of tristrifluoromethylphosphine. The reaction tube was covered with charred material and con-tained some phosphorus t r i i o d i d e . - 202 -l ( k ) Reaction with methyl iodide: P h e n y l b i s t r i -fluoromethylphosphine (0,627 g, 2,55 mmole) and methyl iodide o (1.031 g, 7»26 mmole) were heated to 230 • The reactants were miscible at room temperature but did not seem to react. After heating f o r 10 hours, trifluoroiodomethane (0.087 g» 0.446 mmole) and fluoroform (0.0589 g, 0.84 mmole) and a mix-ture of methyl iodide and trifluoroiodomethane (0.180 g>) were obtained as the v o l a t i l e products. The residual l i q u i d was a black carbonized product consisting of a mixture of methyl iodide and phenylbistrifluoromethylphosphine. The expected products (CH )C H (CF )P or [(CH )C H (CF ) plVwere not 3 6 5 3 L 3. 6 5 3 2 J i d e n t i f i e d among the products. . 2. Phenyltrifluoromethyllodophosphine 2 (a) Physical properties: P h e n y l t r i f l u o r o -methyliodophosphine i s a reddish-brown l i q u i d (perhaps due o to traces of free iodine) which b o i l s at 112-114 at 20 mm pressure. I t fumes i n a i r and reacts with moisture. I t dissolves i n water and the solution so obtained i s highly a c i d i c . I t also reacts with organic solvents; e.g., acetone from which i t cannot be recovered unchanged. 2 (b) I t i s unstable at high temperatures and undergoes disproportionation. The iodophosphine (2 .003 g) o was heated i n a sealed tube at 220 f o r 12 hours. The v o l a t i l e products were small amounts of fluoroform (0.02 g), trifluoroiodomethane (0.06 g) and traces of benzene. The i n v o l a t i l e products were phenylbistrifluoromethylphosphine, - 203 -some unreacted iodophosphine C H (CP )PI and phosphorus 6 5 3 t r i i o d i d e . 2(c) Hydrolysis with a l k a l i : P h e n y l t r i f l u o r o -methyliodophosphine (0.334 g, 1.1 mmole) was reacted with 5 ml of 20$ sodium hydroxide so l u t i o n . There was immediate reaction at room temperature and fluoroform was evolved. However, t h i s evolution was not quantitative. The reaction was therefore carried out at 100 f o r 15 hours, when 0.0694 g (0.99 mmole) fluoroform was evolved. (CF, found 3 as CF H, 20.75$; calculated for C H F PI, 23.03$.) The 3 7 5 3 hydrolysis was only 90$ complete. The residue a f t e r evapo-r a t i o n of water contained a hygroscopic sodium s a l t whose infra- r e d spectrum corresponded with that of sodium phenyl-phosphonate. 2(d) Hydrolysis with water: Phen y l t r i f l u o r o -methyliodophosphine (0.334 g) was treated with 0.125 g water and l e f t i n a sealed tube overnight. On pumping off the l i q u i d , a white s o l i d was obtained. The M.Pt. of th i s o s o l i d was 84-86 and i n a l l respects was s i m i l a r to the compound obtained from the aqueous hydrolysis of the phos-phorane C H (CF ) PBr i n l ( . i ) . I t s s i l v e r s a l t was also 6 5 3 2 2 prepared by reacting the iodophosphosphine with water, tr e a t i n g the aqueous solution with s i l v e r oxide and f i l t e r -ing out the s i l v e r iodide and excess s i l v e r oxide. The solu t i o n was concentrated i n vacuo and the needle-shaped i. - 204 -c r y s t a l l i n e s o l i d dried over phosphorus pentoxide. The s i l v e r s a l t was i d e n t i f i e d a n a l y t i c a l l y (Pound Ag, 33*80$, calcu-lated for CCE (CP )P(0)0Ag, 34.06$), by i t s melting point o 6 5 3. of 294-96 and also by i t s infra-red spectrum ( f i g . Z ) . The aqueous hydrolysis also gave a small amount of a l i q u i d whose infra-red spectrum showed the presence of P-H, P-C^ Ht- and P-CP bonds showing the probable formation o b 3 of phenyltrifluoromethylphosphine C H (CP )PH. 6 5 3 2(e) Reaction with trifluoroiodomethane: The iodophosphine (2«347 g, 7.72 mmole) was heated with t r i f l u o r o -o iodomethane (2.299 g, 11.8 mmole) to 200 fo r 12 hours. The reactants formed a homogeneous solution at room temperature but a f t e r reaction crystals of phosphorus t r i i o d i d e could e a s i l y be recognised. Fractionation gave t r i f l u o r o i o d o -methane qu a n t i t a t i v e l y (96.1$) (2.210 g, 11.33 mmole), and traces of fluoroform. Among the other products which, pre-sumably resulted from disproportionation of the iodophosphine were phenylbistrifluoromethylphosphine (0.617 g, 2.51 mmole), some benzene, phosphorus t r i i o d i d e and unreacted iodophosphine. 2(f) Reaction w i t h trifluoroiodomethane and mercury: Phenyltrifluoromethyliodophosphine (2.8g, 9»21 mmole) was sealed with an excess of trifluoroiodomethane(10 g, 51•3 mmole) and mercury (54 g) i n a Pyrex tube and shaken f o r 24 hours. Fractionation after the reaction gave t r i f l u o r o i o -domethane (8 .9 g» 45«6 mmole) and phenylbistrifluoromethyl-- 205 -phosphine (1.5 g, 6.1 mmole). Extraction of the solid product with ether gave a thick liquid which was found to be identi-cal with the one obtained in IK l(m) (Reaction with residual liq.+ CP I + Hg). 3 3 . Diphenyltrifluoromethylphosphine 3(a) Physical properties: Diphenyltrifluoro-methylphosphine is a colourless o i l y liquid. Like phenyl-bis t r i f luoromethylphosphine, i t s odour i s not obnoxious. I f boils 0 at 255-57 . Its vapor pressure was found to be 1 follows: T I / T x i o 3 P log P 327 0.3058 16 1.2041 347 0.2882 19 1.2788 368 0.2718 23 1.3617 381 0.2625 27 1.4314 392 0.2551 31 1.4914 404 0.2475 38 1.5798 415 0.2410 44 1.6435 425 0.2352 53 1.7243 435 0.2299 64 1.8062 441 0.2267 78 1.8921 446 0.2242 87 1.9395 455 0.2198 104 2.0170 461 0.2169 140 2.1461 466 0.2146 162 2.2095 471 0.2123 184 2.2648 476 0.2101 210 2.3222 480 0.2083 233 2.3674 485 0.2062 265 2.4232 490 ^ 0.2041 301 2.4786 495 0.2020 339 2.5302 The above data gives the following equation for vapor. ;pres sure: Log P(mm) a . 7.781 - 2598 T - 206 -- l whence the latent heat of vaporization i s 11850 cals mole and the Trouton's constant i s 22.93* 3(b) Diphenyltrifluoromethylphosphine i s quite a stable i n a i r . In a sealed tube i t could be heated to 200 without any s i g n i f i c a n t change. When i t was heated to 300 for 24 hours, only mild carbonisation took place and 85$ phosphine was recovered. The v o l a t i l e products were s i l i c o n t e t r a f l u o r i d e , fluoroform and benzene. REACTIONS OF DIPHEimiTRIFLUOROMETHYLPHOSPHINE: 3(c) Reaction with water: The phosphine i s immiscible and does not react with water even at high tem-peratures. The phosphine (0.223 g) was sealed with water (1.2 g) and heated to 120 for 48 hours. Fractionation did not give any fluoroform and the phosphine was recovered q u a n t i t a t i v e l y . 3(d) Reaction with hydrochloric acid; Diphenyl-trifluoromethylphosphine (0.344 g) was sealed with 36 N hydro-o c h l o r i c acid (2.4 g) and heated to 150 • At the end of the reaction period, the phosphine was s t i l l immiscible with the acid and was recovered unchanged. 3(e) Reaction with aqueous a l k a l i ; The phos-phine (0.242 g) was sealed with 5 ml of 20$ sodium hydrox-ide s o lution. There was no reaction at room temperature. The o reactants were heated to 80 f o r 24 hours but at the end of thi s period the phosphine s t i l l remained as an immiscible - 207 -l i q u i d . The reaction tube was then heated to 100 f o r 24 hours. No reaction seemed to have occurred and only a trace of fluoroform was recovered. 3(f) Reaction with alcoholic potassium hydroxide: The hydrolysis was attempted by sealing the -phosphine (0.2137 g, 0 .84 mmole) with alcoholic potassium hydroxide (5 ml of 20$ s o l u t i o n ) . The reaction was very o slow at room temperature and hence was conducted at 70 f o r 96 hours. Fractionation gave fluoroform (0.046 g, 0.657 mmole). (CF found 21 .5$ ; calculated f o r (CH ) CF P, 3 6 5.2 3 27 .16$. ) The hydrolysis was only 78$ complete. The residual solution was evaporated to dryness and after d i s s o l v i n g i n water was a c i d i f i e d with hydro-c h l o r i c acid. This gave a white p r e c i p i t a t e which was washed with water and dried over phosphorus pentoxide. The o melting point of 193 and the infra - r e d spectrum of this substance showed i t to be diphenylphosphinic acid (CCH_)_P(O)OH. ( 2 6 ) o 5 c. REACTION WITH HALOGENS: 3(g) Reaction with iodine: A carbon t e t r a -chloride solution of diphenyltrifluoromethylphosphine (0.1788 g, 0.70 mmole) was added tp an iodine (0.18 g, 0.71 mmole) solution i n the same solvent. After standing f o r an hour, a brown-black o i l separated. The supernatant l i q u i d was decanted and the o i l washed, and f i n a l l y the l a s t traces of the solvent were removed i n vacuo. The - 208 -thick o i l y l i q u i d was i d e n t i f i e d as diphenyltrifluoromethyl-diiodophosphorane (Pound 1^ , 49*32$; calculated for (C H ) 0CF PI , 50.0$). 0 5 ^ 3 2 3(h) Diphenyltrifluoromethyldiiodophosphorane (0.123 g, 0.24 mmole) was sealed with 2.5 ml of 20$ aqueous sodium hydroxide solution. Fluoroform was immediately evolved and to complete the reaction the reaction tube was o heated to 80 . A f t e r 24 hours, 0.0155 g (0.22 mmole) fluoroform was obtained representing 91*7$ hydrolysis. 3(i) Diphenyltrifluoromethyldiiodophosphorane i s stable towards water. The phosphorane (0.254 g, 0.5 mmol o was heated with water to 80 f o r 24 hours. Fractionation a f t e r t h i s period did not produce any fluoroform. 3(j) Diphenyltrifluoromethylphosphine (0.1782 g, 0.70 mmole) and excess of iodine (0 .50 f, 1.97 mmole) o were heated to 200 for 24 hours. Fractionation of the products gave only traces of fluoroform and no t r i f l u o r o -iodomethane was obtained, showing the s t a b i l i t y of the phos-phorane at t h i s temperature. 3(k) Reaction with bromine; To a carbon tetrachloride solution of the phosphine (0.1658 g, 0.65 mmole) was added a solution of bromine (0.105 g, 0.66 mmole) i n the same solvent. An orange-coloured o i l separated to-wards the end of the reaction. The product (0.2694 g, O.65 mmole) was washed, and aft e r removal of excess solvent i n vacuo was i d e n t i f i e d as diphenyltrifluoromethyldibromo-- 209 -phosphorane (Pound Br, 38.07$; calculated for (C^H^CF^PBr^ 38 .64$). 3(1) Diphenyltrifluoromethyldibromophosphorane (0.2723 g, 0.66 mmole) was treated with aqueous sodium hy-droxide (5 ml of 20$ s o l u t i o n ) . There was immediate reaction and fluoroform (0.0436 g, 0.62 mmole) was evolved, represent-ing 96.1$ hydrolysis. The r e s u l t i n g solution was a c i d i f i e d with hydrochloric acid, which gave a white p r e c i p i t a t e of 0 (26) diphenylphosphinic acid (M.Pt. 194 )• The dibroraophosphorane was treated with excess 36 N hydrochloric acid and heated to 80 but no reaction occurred. There was also no reaction when the phosphorane o was heated with water to 80 • 3(m) Reaction with trifluoroiodomethane: Diphenyltrifluoromethylphosphine (0.2178 g, 0.86 mmole) was sealed with trifluoroiodomethane (0.8557 g, 4.36 mmole). The two reactants were immiscible at low temperatures and there was no reaction at room temperature. The mixture was o heated to 100 f o r 24 hours. The solution remained color-less and the trifluoroiodomethane was recovered q u a n t i t a t i v e l y . o The reaction was then conducted at 200 f o r 24 hours. The so l u t i o n was colored s l i g h t l y brown and a small amount of thick black l i q u i d appeared to be separating. Fractionation of the reactants gave 95«4$ trifluoroiodomethane (0.8179 g, 4.173 mmole) and traces of fluoroform ( i d e n t i f i e d spectro-s c o p i c a l l y ) . The infra-red spectrum of the small amount of black l i q u i d did not indicate the presence of  CF - 210 -group and a q u a l i t a t i v e analysis showed i t to be a phenyl-iodo-phosphine, most probably diphenyliodophosphine. 3(n) Reaction with methyl iodide: Diphenyl-trifluoromethylphosphine (0.2337 g, 0.92 mmole) was treate with methyl iodide (0.2693 g» 1.89 mmole). The reactants were miscible at room temperature. They were heated o gradually to 100 f o r 12 hours. An orange colored o i l slowly separated. The o i l was cooled i n l i q u i d nitrogen and allowed to warm up slowly. This gave a s o l i d product. Excess methyl iodide (0.1391 g> 0.977 mmole) was removed from the s o l i d and the l a t t e r dissolved i n ethyl alcohol. On treatment with a large excess of ether, a yellow powder was obtained. This was i d e n t i f i e d as methyldiphenyltri-fluoromethylphosphonium iodide (Pound: C, 42.4$; H, 3.3$; P, 14.2$; P, 7 .6$. Calculated f o r C H P PI: C ,42.6$; 14 13 3 H, 3.3$; P, 14.3$; P, 7.9$.) 3(o) The phosphonium compound melted at 123-o 26 and was quite stable i n a i r . With water i t reacted slowly to give fluoroform q u a n t i t a t i v e l y . The phosphonium iodide (0.127 g, 0.32 mmole) was treated with an excess of water (3.5 g) to give 99.1$ fluoroform (0.0223 g, 0.318 mmole) (CF found 17.56$; calculated for CH (C H ) CP P I 3 3 6 5,2 3 17.68$). The water solution was highly a c i d i c . On eva-poration of water, an o i l was obtained. The l a t t e r was p u r i f i e d by treating i t s benzene solution with s i l v e r oxid - 211 -Evaporation of the benzene solution gave a s o l i d melting at o 111-112 and was i d e n t i f i e d as methyldiphenylphosphine oxide. The i d e n t i t y of the l a t t e r compound was confirmed (36) by preparing i t by standard methods and comparing the infra-red spectra 0 - 212 -IV COMPLEXES OF THE PHOSPHINES 1. Borontrlfluorlde Complexes Boron t r i f l u o r i d e was obtained commercially, and was p u r i f i e d by f r a c t i o n a t i o n i n the vacuum system. The reaction with the phosphines was carried out by condensing the two i n an evacuated tube. Since the complexes were re-active towards moisture, study of the properties of the complexes was carried out i n the glove box, through which a steady stream of dry nitrogen was passing. 1(a) Trimethylphosphine: The phosphine (0.1995 g» 2.62 mmoles) was reacted with a s l i g h t excess of boron t r i f l u o r i d e (0.1927 g, 2.79 mmoles) i n a sealed a tube. The reaction occurred 78 and a white s o l i d was obtained. Aft e r 48 hours, excess boron t r i f l u o r i d e (0.0031 g, 0.05 mmole) was removed giving a r a t i o of phosphine:to boron t r i f l u o r i d e of 1 :1 .05. Trimethylphosphinerborontrifluoride i s a white o c r y s t a l l i n e s o l i d melting at 126-130 with decomposition. The compound decomposed slowly i n moist a i r . I t decomposed on treatment w i t h water, giving trimethylphosphine. Other polar solvents; e.g., acetone and alcohol, reacted In the same manner. I t Is only s l i g h t l y soluble i n chloroform and insoluble i n carbon tetrachloride and carbon disulphide. - 213 -The saturation pressure of the compound was ob-served to be as follows: T I/T x 10 5 P log P 30S - 0.3247 3 0.4771 333 0.3003 4 0.6021 348 0.2873 11 1.0414 363 0.2755 17 1.2304 368 0.2718 21 1.3222 373 0.2681 26 1.4150 378 0.2646 30 1.4771 383 0.2611 39 1.5911 388 0.2578 49 1.6902 393 0.2545 59 1.7709 398 0.2512 72 1.8573 403 0.2481 91 1.9590 408 0.2450 111 2.0453 413 0.2421 142 2.1523 418 0.2392 174 2.2405 423 0.2365 217 2.3365 428 0.2336 288 2.4594 The plot o'f log P against l/T showed a break near the melting point. The saturation pressure of the solid i s given by the equation log Pmm = 8.460 - 2627 10 rp o in the range 35-100 whence the heat of sublimation is -1 11.98 kcal mole • 1(b) Dimethyltrifluoromethylphosphine: Diraethyltrifluoromethylphosphine (0.2952 g, 2.27 mmole) was sealed with boron trifluoride (0.1617 g* 2.37 mmole). As the phosphine melted, a thick liquid was found to separate. The reaction was complete when the tube reached room tempera-ture. The amount of boron trifluoride recovered (0.0028 g - 214 -corresponding to a reaction with 0.1589 g or 2.33 mmole) gave a r a t i o of 1:1.03. The product was p u r i f i e d by treat-ment with carbon tetrachloride. The compound was obtained as a colourless o i l y o l i q u i d which s o l i d i f i e d ^ 25 into a glass and the l a t t e r o softened at approximately~S • The complex i s easily de-composed by a i r and moisture. Water li b e r a t e d the phosphine o and heating i n moist a i r at 150 gave traces of fluoroform. The complex showed the same behaviour toward polar and non-polar solvents as the trimethylphosphine analogue. The saturation pressure of the compound was as follows: T l/T x 105 P log P . 22 6 0.4425 8 0.9081 229 0.4367 12 1.0792 233 0.4292 14 1.1461 235 0.4255 17 1.2304 238 0.4202 22 1.3424 241 0.4149 28 1.4472 243 0.4115 33 1.5185 245.5 0.4074 41 1.6128 247.5 0.4041 49 1.6902 250 0.4000 59 1.7709 252 0.3968 69 1.8388 254 0.3937 74 1.8692 256 0.3906 98 1.9912 257.5 0.3883 114 2.0569 259 0.3861 130 2 . I I 3 9 260.5 0.3839 149 2.1732 262.5 0.3810 178 2.2 504 264.5 0.3781 215 2.3324 266 0.3759 245 ' 2.3892 267.5 0.3738 282 2.4502 269.5 0.3710 331 2.5198 271.5 0.3683 353 2.5478 - 215 -The saturation pressure follows the equation l o g . . P(mm) = 10.354 - , 2146 whence the heat of vaporization i s 9*68 kcal mole • 1(c) MethyIbistrifluoromethylphosphine (0.2690 g, I . 4 6 mmole) was sealed with boron t r i f l u o r i d e (0.0938 g, 1.38 mmole). There was no perceptible reaction but on cooling o below -78 , the mixture of the reactants s o l i d i f i e d . On warming up, a very v o l a t i l e gas ( i d e n t i f i e d as BP_) 3 v o l a t i l i s e d . The reaction tube was kept at room tempera-ture f o r 120 hours but no complex separated. The tube was o cooled to -78 and the v o l a t i l e s were separated. Boron t r i f l u o r i d e was recovered q u a n t i t a t i v e l y showing that no reaction had occurred. 1(d) Tristrifluoromethylphosphine (0.3106 g, I . 3 0 mmole) was sealed with boron t r i f l u o r i d e (0.1934 g» o 2.84 mmole) and kept at -112 . The two compounds were mis-c i b l e at t h i s temperature, but when warmed to room tempera-ture did not give any complex. The v o l a t i l e s were separated by keeping the reaction tube at -112 and f r a c t i o n a t i n g i n the vacuum system. Boron t r i f l u o r i d e was recovered quanti-t a t i v e l y , showing that no reaction occurred. 1(e) Phenylbistrifluoromethylphosphine: The phos-phine (0.3562 g, 1.587 mmole) was sealed with boron t r i -f l u o r i d e (0.1331 g, 1.96 mmole). The reaction did not seem to occur at room temperature, whereupon the tube was cooled o to —78 • A s o l i d was deposited but f r a c t i o n a t i o n as des-- 216 -cribed above, gave back boron t r i f l u o r i d e q u a n t i t a t i v e l y , and the spectrum of the residual products did not show any of the ch a r a c t e r i s t i c absorptions corresponding to the phosphine-boron t r i f l u o r i d e complex. 1(f) Diphenyltrifluoromethylphosphine (0.254 g, 1 mmole) was reacted with excess of boron t r i f l u o r i d e (0.136 g, 2 mmole). At f i r s t no reaction appeared to take place. The tube was then cooled to -78 and warmed up slowly. A thick o i l deposited. This was i s o l a t e d by pumping off the excess of boron t r i f l u o r i d e (0.063 g» 0.93 mmole), which showed that the complex formed with the r a t i o of 1:1.07 of phosphine: boron t r i f l u o r i d e . The compound was p u r i f i e d by treating i t with carbon tetrachloride i n which i t was i n -soluble. Diphenyltrifluoromethylphosphine-boron t r i f l u o r i d e i s a colourless o i l y l i q u i d , which i s very reactive towards moisture. Treatment with water, alcohol and acetone decom-poses the compound and gives the phosphine. Similar to other phosphine complexes, i t i s insoluble i n non-polar solvents. The complex i s quite stable i n dry a i r at room o temperature but dissociates completely above 100 . The saturation pressure of the compound was found to be as f o l -lows : - 217 -T I/T x 1 b 3 P Log P 312 0 . 3 2 0 5 6 0 .7782 323 0 . 3 0 9 6 12 1 .0792 328 0 . 3 0 4 9 15 1 . 1761 338 0 . 2 9 5 9 27 1 .4314 343 0 . 2 9 1 5 32 1 . 5 0 5 1 349 0 .2865 39 1 .5911 354 . 0 .2825 46 1 .6628 360 0 . 2 7 7 7 55 1 . 7 4 0 4 364 0 . 2 7 4 7 62 1 . 7 9 2 4 368 0 . 2 7 1 7 70 1 .8451 372 0 .2688 80 1 . 9 0 3 1 377 0 . 2 6 5 3 94 1 . 9 7 3 1 381 0 . 2 6 2 5 111 2 . 0 4 5 3 The saturation pressure follows the equation: log P(ram) = 6.609 - 1753 whence the heat of vaporization i s 8 .O4 kcal mole . •1(g) Triphenylphosphine: Boron t r i f l u o r i d e was passed i n a solution of triphenylphosphine (0.3682 g, 1 . 4 0 5 mmole) i n petroleum ether. A white s o l i d was im-mediately p r e c i p i t a t e d . The s o l i d was p u r i f i e d by washing with petroleum ether and f i n a l l y pumping off the l a t t e r i n vacuum. This gave triphenylphosphine-boron t r i f l u o r i d e (O.464O g, 1 . 4 0 5 mmole) and was confirmed by analysis. (Found C, 63.5$; H, 5 . 0 2 $ . Calculated for (C rH ) P.BF : 6 5 3 3 C, 6 4 . 6 $ ; H, 4 . 7 $ . ) Triphenylphosphine-boron t r i f l u o r i d e i s o a white s o l i d melting at 120-130 . I t i s stable i n a i r but polar solvents decompose i t . Like the other phosphine com-plexes t h i s i s also insoluble i n non-polar solvents. - 218 -The saturation pressure of the compound was found to be as follows: T i/T x 1 0 3 P log P 353 0.2833 10 1.0000 376 0.2660 17 1.2304 386 0.2591 21 1.3222 400 0.2500 26 1.4150 406 O.2463 28 1.4472 411 0.2433 30 1.4771 419 0.2387 33 1.5185 424 0.2360 35 1.5441 430 0.2326 38 1.5798 437 0.2290 42 1.6232 441 0.2268 45 1.6532 446 0.2242 64 1.8062 The saturation pressure equation calculated from the above data i s ; P(mm) = 3.840 - 972 10 "IF" whence the heat of sublimation i s 4*43 k c a l mole . 2. PLATINUM(II) CHLORIDE COMPLEXES Platinum(II) chloride was prepared by heating o c h l o r o p l a t i n i c acid (obtained commercially) to 325 i n an (117) atmosphere of nitrogen . The complexes were prepared by reacting the phosphine d i r e c t l y with the s o l i d platinum(II) chloride i n which case the reaction was slow, or by react-ing In the presence of a solvent. The reaction i n the l a t t e r case was also slow but had the advantage of giving a homogeneous c r y s t a l l i n e product. The complex was also prepared by treating an aqueous solution of potassium - 219 -c h l o r o p l a t i n i t e , prepared by the standard method ( l a t e r ob-tained commercially) with an alcoholic or acetone solution of the phosphine. The i d e n t i t i e s of the compounds were determined from the r a t i o of reactants as well as from standard methods of analysis. 2(a) Bis(trimethylphosphine)dichloroplatinum(II): Trimethylphosphine (0.220 g, 2.89 mmole) was sealed with platinum(Il) chloride (0.2556 g, 0 .96 mmole). Complex f o r -mation was favoured when the phosphine was i n the l i q u i d phase. The reaction, however, did not go to completion and unreacted phosphine (0.1272 g, 1.67 mmole) was recovered a f t e r seven days. The mixture of the complex and platinum(II) chloride was extracted with methyl alcohol to give white crystals of the complex. The reaction occurred more ra p i d l y i n a benzene .suspension but s t i l l the y i e l d was low. Trimethylphosphine, (0.195 g* 2.5:6,' mmole) shaken f o r 2 4 hours with platinum(II) chloride (0.3345 g, 1 .26 mmole) i n 2.5 ml benzene, gave only 0.10 g of the complex, representing a 20$ y i e l d . . Better yields of the complex were obtained by shaking an aqueous solution of potassium c h l o r o p l a t i n i t e (1.20 g, 2.89 mmole) with the phosphine (0.43 g» 5.66 mmole). The mixture was heated on a steam bath for 30 minutes and the white complex was f i l t e r e d and washed with water, alcohol - 220 -and ether. Recrystallization from methanol gave a yield of 0.51 g» or 41$ of bistrimethylphosphine-dichloroplatinum(II). (Pound Pt, 45.5$; CI, 17.0$. Calculated for [(CH <) P1 PtCl i L 3,3 2 , 2 Pt 44.7$; CI 16.1$) The complex dissolves readily in chloroform, i s sparingly soluble in ethanol and almost insoluble in ether, 1 benzene and carbon tetrachloride. In polar solvents, par-tic u l a r l y water, heating causes decomposition and free phos-phine i s evolved. The complex melted at 324-326 (with decomp.) and the dissociation pressure was found to be as follows i T _3 i/T x 10 P log P 341 0.2933 4 0.602 357 0.2801 7 0.8451 377 0.2653 14 1.1461 387 0.2584 19 * 1.2788 400 0.2500 26 1.4150 408 0.2451 30 1.4771 413 0.2421 33 1.5185 428 0.2336 40 1.6021 433 0.2309 45 1.6532 438 0.2283 50 1.6990 443 0.2257 57 1.7559 448 0.2232 64 1.8062 453 0.2208 72 1.8573 458 0.2183 80 1.9031 463 0.2160 91 1.9590 468 0.2137 103 2.0128 473 0.2114 116 2.0645 478 O.2092 134 2.1271 483 0.2070 165 2.2175 488 0.2049 200 2.3010 493 0.2028 238 2.3766 o The dissociation is more rapid above 200 • The o dissociation pressure in the range of 155-190 is given - 221 -by the equation: log P(mra) = 6.510 - 2108 10 rj-i -1 whence the heat of di s s o c i a t i o n i s 9.59 kcals mole . 2(b) Bis(dimethyltrifluoromethylphosphine)dichloro- platinum(II): Dimethyltrifluoromethylphosphine (0.412 g, 3*17 mmole) was reacted with platinum(II) chloride (O.425 g, 1.59 mmole). A f t e r 48 hours at room temperature no phos-phine was recovered and a,pale yellow s o l i d was obtained which was p u r i f i e d by r e c r y s t a l l i z a t i o n from methanol to give white, needle-shaped crystals of b i s ( d i m e t h y l t r i f l u o r o -me thylphosphine) dichloroplatinum( I I ) . (Pound Pt 37«2$; d l .13.-256. Calculated f or CI 13.5$). The complex melted at 188-190 with decomposition. The dis s o c i a t i o n pressure was found to be as follows: (CH ) CP P 3.2 3 PtCl : Pt 37.1$; 2 2 T I/T x 10 5 P Log P 365 O.274O 21 1.3222 371 0.2695 26 1.4150 379 0.2639 34 1.5315 384 0.2605 42 1,6232 391 0.2558 54 1.7324 394 0.2538 59 I.7709 397 O.2519 67 1.8261 400 0.2500 75 1.8751 407 0.2457 87 1.9395 413 0.2421 97 1.9868 425 0.2353 110 2.0414 439 0.2278 119 2.0755 449 0.2227 125 2.0969 468 0.2137 163 2.2122 473 0.2114 196 2.2923 478 0.2092 229 2.3598 483 0.2070 311 2.4928 - 222 -The d i s s o c i a t i o n pressure i n the range of 90-130 i s given by the equation Log P(ram) = 7.969 - 2438 10 ip -1 whence the heat of d i s s o c i a t i o n i s 11.31 kcals mole . As the compound i s heated gradually i t becomes black due to decomposition. The white crystals darken completely^, 150 • Decomposition i s more rapid a f t e r the o complex has melted. The d i s s o c i a t i o n above 150 i s i r r e -v e r s i b l e , which was found by allowing the phosphine (iden-t i f i e d as such spectroscopically) to be i n contact with the s o l i d . There was no reaction and the phosphine did not con-dense. When heated i n a i r the phosphine,evolved due to decomposition, caught f i r e * Bis(dimethyltrifluoromethylphosphine)dichloro-platinum(II) i s quite stable i n a i r and i s not affected by moisture. I t i s soluble i n alcohol and chloroform, but not i n carbon tetrachloride and ether. I t i s not soluble i n cold water, but reacts slowly with hot water to evolve fluoroform. The complex (0.094 g, 0.18 mmole) was added to 1 ml of water and heated to b o i l i n g for two hours. Frac-tionation of the products gave only 65$ fluoroform (0.016 g, 0.23 mmole). The reaction i n a sealed tube at 100 f o r 24 hours was much slower and gave only 45$ fluoroform. In both cases a black residue was deposited. - 223 -The complex gave fluoroform on treatment with a l k a l i . The compound ( 0 . 0 9 5 8 g, 0.182 mmole) was heated o to 80 with a 25$ aqueous sodium hydroxide, and a 90$ y i e l d of fluoroform (0.0230 g, 0.328 mmole) was obtained. The complex (0.102 g) was sealed with t r i f l u o r o -iodomethane ( 1 . 0 0 g) i n a small Carius tube. I t was kept o at - 7 8 for 72 hours and at room temperature f o r seven days. Fractionation at the end of this period gave t r i -fluoroiodomethane (0 . 9 8 8 g) qua n t i t a t i v e l y , showing that no reaction occurred. The complex ( 0 . 1 2 0 g) was treated with methyl iodide ( 1 . 1 .g) i n which i t dissolved but evaporation of methyl iodide gave almost unchanged reactants and a. trace of fluoroform." 2(c) BlsX'methylbis t r i f luoromethyl phosphine ) d i - chloroplatinum(II); Methylbistrifluoromethylphosphine (O.729O g, 3 . 9 5 6 mmole) was sealed with platinum(II) chlor-ide ( 0 . 5 2 2 g, 1;.'96 mmole) at room temperature. A f t e r 24 hours 0 . 3 1 4 8 g ( 1 . 7 1 mmole) phosphine had reacted. The reaction product was extracted with carbon tetrachloride and on evaporation of the solvent a yellow c r y s t a l l i n e s o l i d (O.45O6 g, 0.71 mmole) was obtained. This was iden-t i f i e d as bis(methylbistrifluoromethylphosphine)dichloro-platinum(Il)o (Found Pt 2 9 . 9 $ ; 61 1 1 . 2 $ . Calculated f o r - 224 -CH (CP ) P 3. 3-2 to prepare PtCl : Pt 30.7$; CI 11.2$). In other attempts 2 2 the compound by keeping the reactants at lower temperatures and f o r longer periods, unreacted phosphine was always recovered. Bis(methylbistrifluororaethylphosphine)dichloro-o platinum(II) melted at 85-87 and the di s s o c i a t i o n pressure was recorded.as follows: T l/T x 10 5 P log P 333 0.3003 9 0..9542 344 0.2907 16 1.2041 354 0.2825 22 1.3424 366 0.2732 27 1.4314 377 0.2653 34 1.5315 386 0.2591 41 1.6128 399 0.2506 55 1.7324 410 0.2439 74 1.8692 418 0.2392 98 1.9912 432 O.2315 143 2.1553 435 0.2299 175 2.2430 438 0.2283 209 2.3201 442 0.2262 254 2.4048 445 0.2247 295 2.4698 447 0.2237 345 2.5378 449 0.2227 386 2.5866 The d i s s o c i a t i o n pressure i n the range of 80-140 may be expressed by the equation: log P(mm) = 4.885 - 1258 10 TJT' whence the heat of d i s s o c i a t i o n Is 5*76 kcals mole'1'. The o complex decomposes i r r e v e r s i b l y above 150 since the d i s -sociated phosphine ( i d e n t i f i e d spectroscopically) does not - 225 -condense on cooling to form the complex again. The complex i s soluble i n carbon tetrachloride, ether, acetone and alcohol, but i s insoluble i n cold water. I t i s s l i g h t l y soluble i n b o i l i n g water but no decomposition occurs. Treatment with aqueous sodium hydroxide (0.105 g» 0.166 mmole complex with 2.5 ml of 20$ a l k a l i solution) at o 80 for 24 hours gave 50$ fluoroform (0.023 g, 0.328 mmole). The reaction was slow at room temperature and the solution became yellow a f t e r the reaction. The compound dissolved i n trifluoroiodomethane and methyl iodide to give a yellow solution, but the reactants were recovered qu a n t i t a t i v e l y with traces of fluoroform i n each case. 2(d) Reaction of Tristrifluoromethylphosphine with  Platinum(II) Chloride: Tristrifluoromethylphosphine (0.175 g> 0.866 mmole) was sealed with platinum(II) chloride (0.132 g, 0.496 mmole) i n a small tube and l e f t at room temperature f o r 120 hours. No reaction seemed to occur; hence the tube was o warmed to 80 f o r 12 hours. At the end of t h i s period the phosphine was recovered qu a n t i t a t i v e l y , showing that no re-action had occurred. Another attempt was made by passing the phosphine i n a stream of nitrogen over platinum(II) chloride heated to o 200 , but no reaction appeared to have occurred. - 226 -Tristrifluoromethylphosphine (0.243 g, 1.02 mmole) was sealed with a suspension of platinum(II) chloride (0.12 g, 0.45 mmole) i n methyl alcohol (1 ml). Methanol developed a golden yellow colour, and i f more concentrated solutions were taken the colour was darker. The tube was l e f t at room temperature f o r 96 hours. During t h i s time i t was observed that a few colourless crystals were deposited on the tube w a l l . Fractionation of the products gave fluoroform (0.0207 g, 0.295 mmole) and a mixture of methanol and t r i s -trifluoromethylphosphine which was d i f f i c u l t to separate. However, a yellow resinous product was obtained on pumping off the alcohol. The cry s t a l s which had appeared i n the tube could not be i s o l a t e d a f t e r evaporating the alcohol. Further treatment with alcohol gave a small amount of a pale yellow s o l i d contaminated with platinum chloride. This yellow s o l i d was hydrolysed with aqueous sodium hy-• I -droxide and 13$ fluoroform was obtained. The a l k a l i n e residue s t i l l contained a trifluoromethyl group as observed from the in f r a - r e d spectrum. • The above experiment was repeated, using butanol instead of methanol i n order to f a c i l i t a t e separation. The products were 75$ of the unreacted phosphine, 5$ fluoroform and a small amount of yellow resinous material as obtained above. The infra-red spectrum of th i s substance showed - 227 -strong absorptions i n the 8-9/fregion corresponding to the C-P stretching frequency. There were three broad bands in this region for this substance, whereas the phosphine shows four sharp ones. 2(e) Bi3(phenylbis trifluoromethylphosphine)di-chloroplatinum(II)s Phenylbi s trif1uoromethylpho s phine (0.7925 g, 3.22 mmole) was heated with platinum(II) chloride o (0.5079 g» 1.16 mmole) to 100 for seven days. The reaction was slow at room temperature and a grey product was obtained under these conditions. Heating accelerated the process and greenish-yellow crystals lere deposited. At the end of the reaction period excess phosphine (0.206 g, 0.84 mmole) was recovered and the greenish solid was recrystallized from acetone. This was identified as bis(phenylbistri-fluoromethylphosphine)dichloroplatinum(II). (Pound C, 25.6$; H, 1.36$; P, 29.44$. Calculated for c 1 g H 1 0 F 1 2 P 2 P t C 1 2 8 C, 25.4$; H, 1.37$; P, 30.1$.) Treatment of a solution of phenylbistrifluoro-.methylphosphine in acetone with an aqueous solution of potassium chloroplatinite gave a small amount of a sol i d > o a 300 besides the one melting at 134-36 • It was insoluble in non-polar solvents and was possibly the cis isomer. Since i t was not obtained i n any large proportion i t was not investigated. The main component, melted at o 134-136 , was soluble in most organic solvents, and was not affected by boiling water. It was also soluble i n t r i -- 223 -fluoroiodomethane and methyl iodide, giving a yellow solution but no reaction was observed to take place. The complex (0.129 g, 0.17 mmole) was treated with aqueous sodium hydroxide (2 .5 ml of 20$ s o l u t i o n ) . Re-action commenced immediately the reactants came i n contact, and to complete the reaction, the mixture was heated to 80 for 12 hours. This gave 93*5$ fluoroform (0.0439 g, 0.627 mmole). Bis(phenylbistrifluoromethylphosphine)dichloro-platinum(Il) (0.271 g, 0.357 mmole) was dissolved i n carbon tetrachloride, and a small excess of a d i l u t e solution of bromine i n the same solvent added to i t . On standing, an orange coloured p r e c i p i t a t e was obtained. The solvent and excess bromine were pumped o f f , and a product corresponding to the addition of two equivalents of bromine (0.328 g, o 0i.357, mmole) was obtained as an orange s o l i d melting at 73 • I Thermal decomposition of this substance gave pure phosphine, suggesting that the reaction with bromine had produced bis(phenylbistrifluoromethylphosphine)dichlorodibromo-platinum(IV)• 1 This compound was characterised by hydrolysing i t with aqueous a l k a l i . 0.128 g (0.139 mmole) of the substance o on heating with a l k a l i n e solution to 80 gave 0.037 g» (0.556 mmole) or 96.2% fluoroform. The inf r a - r e d spectrum of the compound (fig.17 ) - 229 -showed that only monosubstituted phenyl group was present, and there was, a s h i f t i n the C-P absorption as compared with the phosphine. A s i m i l a r compound was obtained by treating a solution of bis(phenylbistrifluoromethylphosphine)dichloro-platinum(II) (O.I44 g, 0.19 mmole) i n carbon tetrachloride with an iodine solution i n the same solvent. A brown s o l i d was obtained (0.192 g, 0.19 mmole). The gain i n weight of the s o l i d corresponded with the formation of bis(phenyl-bistrifluoromethylphosphine)dichlorodiiodoplatinum(IV)• To estab l i s h the structure of b i s ( p h e n y l b i s t r i -fluoromethylphosphine)dichloroplatinum(II), i t was treated with ethylenediamine. A large excess of ethylenediamine and a mixture of water and the complex were heated with shaking to effect p a r t i a l s o l u t i o n . After cooling this solution, a concentrated aqueous solution of potassium c h l o r o p l a t i n i t e was added. The p r e c i p i t a t e so obtained was found,spectroscopically, not to contain any phenylbis t r i f luoromethylphosphine, s turning that the struc-ture was not c i s . 2(f) Bis(diphenyltrifluoromethylphosphine)di- chloroplatinum(II): Diphenyltrifluoromethylphosphine (O.254 g» 1 mmole) i n acetone was added to an aqueous solu-t i o n of potassium c h l o r o p l a t i n i t e (0.21 g, O.5O6 mmole) and the mixture was heated for 50 minutes. A reddish-orange C H (CP ) P 6 5 3.2 PtCl 2 2 - 230 -l i q u i d separated as the acetone v o l a t i l i s e d . This l i q u i d became a resinous mass when cooled. I t s acetone solution was treated with animal charcoal and a f t e r f i l t r a t i o n the yellow solution so obtained was treated with a large excess of water. A pale yellow s o l i d was obtained and was iden-t i f i e d as bis(diphenyltrifluoromethylphosphine)dichloro-platinum(II). The complex was analysed for fluoroform by treating i t with bromine. (Pound CF^, 16 .9$. Calculated fo r (CgH^CF P 2 P t C l 2 : CFy 17.8$.) The compound so obtained was treated with ether. A small amount was found to be insoluble i n this solvent. o The main component melted at 63-65 and was i d e n t i f i e d as the trans isomer (see l a t e r ) . The small f r a c t i o n melted at 230 and probably was the c i s isomer. The main component was soluble i n most organic solvents but insoluble i n water. I t was not affected by b o i l i n g water nor by cold aqueous a l k a l i . Alcoholic potas-sium hydroxide evolved fluoroform slowly at room tempera-ture. The complex (0.216 g, 0.279 mmole) was heated to 80 with potassium hydroxide f o r 36 flours. The reaction was , . >x quite "slow even at t h i s temperature since only 85$ f l u o r o -form (0.0327 g, 0.478 mmole) was evolved. The complex was soluble i n trifluoroiodomethane and methyl iodide, but they effected no change on i t . - 231 Reaction of bis(diphenyltrifluoromethylphosphine dichloroplatinum(Il) (0.128 g, 0.165 mmole) with a carbon tetrachloride solution of bromine gave a yellow p r e c i p i t a t Evaporation of solvent and excess bromine gave a yellow s o l i d (0.154 g» 0.165 mmole)—which corresponded to the addition of two moles of bromine and possibly was b i s ( d i -phenyl t r i f luoromethylphosphine)dichlorodibromoplatinum(ISO The substance i s soluble i n water and other polar solvents Hydrolysis of this.compound (0.144 S» 0.154 mmole) with a l k a l i gave fluoroform (0.021 g, 0.33 mmole) immediately. (Pound CP^ 14.5$. Calculated for UCgHLj^F^P PtCl B r n 2 2 2 14.7$). Bis(diphenyltrifluoromethylphosphine)dichloro-platinum(II) (0.142 g, 0.183 mmole) was treated with a solution of Iodine i n carbon tetrachloride to give an addi t i o n product (0.188 g, 0.183 mmole). A dark brown s o l i d was prec i p i t a t e d and the gain i n weight corresponded with the formation of bis(diphenyltrifluoromethylphosphine)-dichlorodiiodoplatinum(IV). The elucidation of the structure of the main component from the preparation of the complex was carried out by trea t i n g with ethylenediamine. No p r e c i p i t a t e con-taining the phosphine and ethylenediamine was obtained (as found spectroscopically), showing that bis(diphenyl-trifluoromethylphosphine)dichloroplatinum(Il) was probably a trans isomer. - 232 -DETERMINATION OF DIPOLE MOMENTS Accurate determination of the dipole moment was not possible i n most cases because (1) of low s o l u b i l i t y i n solvents of low d i e l e c t r i c constant and (2) of th e i r tendency ( i n the case of trimethylphosphine and dimethyl-trifluoromethylphosphine complexes) to decompose slowly i n the presence of moisture. The ca l c u l a t i o n of t h i s con-(146) stant was therefore done by using Jensen's formula - for such cases. The dipole moments of the compounds were found to be as l i s t e d i n the following table. Molar concentration soln. P i^(D) m ^ (CH ) P PtCl measured i n chloroform: benzene (1:1) solu-L 3.3 J2 2 t i o n (£ mix = 3.380) 0.000466 3.426 3320 13.1 ± 0 . 5 0.000977 3.441 3780 (CH ) CP P 3 2 3 PtCl measured i n chloroform solution 2 2 ( £ CHC1 = 4 ' 9 4 7 ) 0.00108 4.982 1667 0.00189 5.007 1806 9.2 ± 0 . 5 (CH (CP ) P 3, 3-2 PtCl measured i n carbon tetrachloride solution 2 2 ( £ c c i = 2- 2 6 1> 4 0.00297 2.261 0.00525 2.261 0.0 r(C H ) CP P 6 5 2 3 2 PtCl measured i n chloroform solution 2 2 ( 6 CHC1 = 4 -955) 3 0.00132 4.955 0.00391 4.955 0.0 - 233 -Molar concentration s o l n . P M>CD) m (C H (CF ) P n 6 5 3.2 J2 PtCl measured i n chloroform solution ^CHClj = 4-955) 0.00142 4.955 0.00495 4.955 0.0 3* Complexes of the Nickel Salts The complexes were prepared by reacting anhydrous n i c k e l s a l t s (except n i c k e l n i t r a t e , which was used as the hexahydrate) with phosphines i n 1:2 r a t i o i n sealed evacu-ated tubes,and were p u r i f i e d by r e c r y s t a l l i z a t i o n from butanol. Use of the glove box was necessary since a l l the compounds were sensitive towards moisture. Unless other-wise stated, carbon tetrachloride solution was used i n measurements of absorption spectra. A. TRIMETHYLPHOSPHINE COMPLEXES (a) Bis(trimethylphosphine)dichloronickel(II): Nickel chloride (0.2233 g, 1 .72 mmole) was reacted with trimethylphosphine (0.3485 g, 4*58 mmole). The reaction started at room temperature with the development of a purple colour. The reaction was complete i n one-half hour arid the product at t h i s stage was black v i o l e t . When the reaction tube was cooled i n l i q u i d nitrogen the product assumed a pink colour (only i n the presence of excess phosphine). A f t e r removing the excess phosphine (0.098 g, 1.28 mmole) - 234 -the s o l i d was r e c r y s t a l l i z e d from butanol to give crimson red c r y s t a l s . This was i d e n t i f i e d as his(trimethylphos-phine )dichloronickel( I I ) . (Pound Ni 20.05$, CI 25.14$. Calculated f o r f(CH ) P L 3.3 J The complex was sensitive to moisture. Water NiCl : Ni 20.56$, CI 25.27$.). 2 2 gave a pink solution which decomposed e a s i l y with the f o r -mation of a transient blue colour and with evolution of phosphine. Acids e a s i l y faded the colour but a d i l u t e alka-l i n e solution returned i t . I t i s e a s i l y soluble i n polar solvents but only s l i g h t l y so i n non-polar solvents. The colour i n the various solvents i s d i f f e r e n t . In non-polar sol v e n t s , l i k e carbon tetrachloride and benzene,it i s pink. I t i s v i o l e t i n chloroform, orange i n d i e t h y l ether and petroleum ether, and deep blue i n acetone. The colour of these solutions faded gradually,giving the n i c k e l s a l t and the phosphine, 3(h) Bis(trimethylphosphine)dibromonickel(II): Nickel bromide (0.732 g, 3»36 mmole) was reacted with t r i -methylphosphine (0.5141 g, 6.76 mmole). Reaction started at room temperature with the formation of dark v i o l e t s o l i d . However, the reaction did not go to completion a f t e r 24 hours and most of the phosphine (0.343 g) was recovered. The s o l i d and unreacted phosphine- were then refluxed for 30 minutes,when crimson red crystals were obtained. This was - 235 -(CH ) P D 3 NiBr : 2 2 i d e n t i f i e d as bis(trimethylphosphine)dibromonickel(II)• (Pound Ni 16.01%, Br 42.7$. Calculated f o r Ni 15.68$, Br 43.24$.) The compound was slowly decomposed by moisture. I t was soluble i n polar solvents with easy decomposition. The solutions i n p r a c t i c a l l y a l l solvents were usually pink. 3(c) Bis(trimethylphosphine)di i o d o n i c k e l ( I I ) : Nickel iodide (1.1193 g> 3*65 mmole) was sealed with t r i -methylphosphine (0.545 g> 7.17 mmole). The reaction was slow and a f t e r 48 hours a small amount of phosphine (0.0694 g) was s t i l l l e f t , a dark brown s o l i d also being formed. The pure product (dark brown) was obtained from hot butanol and was i d e n t i f i e d as bis(trimethylphosphine)diiodonickel(II). (Pound Ni 11.85$, I 0 54-30$. Calculated f o r f(GH_) p| NiCl : [ 3 3 2 2 Ni 12.50$, i 2 54.72$.) The compound i s . not affected by moisture. I t d i s -solves i n warm water, giving a pink solution.which i s de-colorized on a c i d i f i c a t i o n . The color i s returned when the solut i o n i s neutralised again with d i l u t e a l k a l i . The solu-tions i n most solvents are pink. 3(d) Bis(trimethylphosphine)dithiocyanatonickel(II)t Nickel thiocyanate (0.4223 g, 2.43 mmole) was treated with trimethylphosphine (O .484I g, 6«37 mmole). The reaction tube was opened a f t e r seven days and unreacted phosphine (0.2987 g, 3.93 mmole) was recovered. This gave a r a t i o of 1:1 f o r the - 236 -reactants. The product at this stage was blue-black. On re-fluxing with butanol and an excess of phosphine the crystals obtained were orange yellow and were identified as b i s ( t r i -methylphosphine)dithiocyanatonickel(II). (Pound Ni 11,27%, (SCN)" 34.45$. Calculated for Ni 17.79$, (SCN)~ 34.60$.) The compound was not affected by moisture; in fact i t was only slightly soluble in cold water. It dis-solved in warm water with decomposition. It was only spar-ingly soluble in ether, but was f a i r l y soluble in benzene and carbon tetrachloride. 3(e) Bis(trimethylphosphine)dinitratonickel(II); Trimethylphosphine (0,1992 g, 2.62 mmole) was sealed with nickel nitrate hexahydrate (0.381 g, 1.31 mmole). The re-action occurred at room temperature with the formation of a dark red sticky substance. Only traces of phosphine mixed with water were recovered. Attempts were made to obtain a crystalline product,; by (1) heating the hexahydrate to o 120 to drive off as much of the water as possible, and (2) by refluxing the mixture of nickel nitrate hexahydrate and phosphine with acetic acid, butanol, and tetrahydro-furan, but without any satisfactory results. For analyti-cal and magnetic measurements, nickel nitrate hexahydrate was heated to 120 and condensed with an excess (CH ) P 3 3 Ni(SCN) 2 2 - 237 -of phosphine and butanol. A f t e r a homogeneous solution was obtained by warming, the butanol was pumped o f f . Next i t was treated with a larger excess of phosphine (to serve as solvent). The complex so obtained was taken up i n butanol, and was i d e n t i f i e d as bis(trimethylphosphine)dinitrato-n i c k e l ( I l ) . (Pound Ni 17.33$. Calculated for [(CH ) Pi Ni (NO ) : I 3.3 J2 3.2 Ni 17.37$). The compound was very sensitive towards moisture and was easil y decomposed by water. B. -DIMETHYLTRIFLUOROMETHYLPHOSPHINE COMPLEXES The reaction with dimethyltrifluoromethylphosphine had to be carried out i n anhydrous conditions. The hydrated n i c k e l s a l t s on being warmed with solvents gave off fluoro-form. R e c r y s t a l l i z a t i o n was also not possible for this reason. Direct reactions were therefore carried out i n a l l cases. 3(f) B i s ( d i m e t h y l t r i f l u o rome thylpho s phi n e)di chlo- r o n i c k e l ( I I ) : Nickel chloride (0.2336 g, 1.81 mmole) was allowed to react with dimethyltrifluoromethylphosphine (0.5850 g, 4«5 mmole) for seven days. When fre s h l y sealed the complex was scar l e t red and turned blue oh cooling (only i n excess phosphine), but when l e f t f o r a long period i t became green. The recovery of excess phosphine (0.1949 g> - 238 -1.50 mmole) showed that the reaction had occurred i n the r a t i o of 1:2 (of n i c k e l chloride to phosphine) and the pro-duct was i d e n t i f i e d as bis(dimethyltrifluoromethylphos-phine )dichloronickel( II) . (Found Ni 14 .72$, CI 13 .15$. Calculated f or ["(CH ) CF Pi NiCl : Hi 14*91$, CI 13.25$..) L 3 2 3 J 2 2 This compound i s soluble i n polar solvents but decomposes e a s i l y . The absorption spectrum was measured from a f r e s h l y prepared methanol soluti o n . 3(g) Bis(dimethyltrifluoromethylphosphine)di-bromonickel(Il): Nickel bromide (0.1920 g, 0 .88 mmole) was sealed with dimethyltrifluoromethylphosphine (0.2306 g, 1.77 mmole). The reaction was slow but was complete i n 15 days giving a d u l l black s o l i d and only traces of phos-phine. This was i d e n t i f i e d as b i s ( d i m e t h y l t r i f l u o r o -methylphosphine )dibromonickel( II) . (Found Ni 11 .84$, Br 3 4 . 1 0 $ . Calculated for Br 3 3 . 4 7 $ . ) The compound decomposed easil y i n moist a i r but was quite stable i n a dry atmosphere. I t was decomposed ea s i l y by most polar solvents i n which i t was soluble. 3(h) Bis(dimethyltrifluoromethylphosphine)di- i o d o n i c k e l ( I I ) : Dimethyltrifluoromethylphosphine (0.2439 g, 1.87 mmole) was reacted with n i c k e l iodide (0.311 g, 1 mmole). The reaction was slow and the r e s u l t i n g product (CH ) CF Pi NiBr : Ni 12 .14$, . . 3 2 3 J 2 2 - 239 -ttfas a dark brown s o l i d which was i d e n t i f i e d as bis(dimethyl-t r i f luoromethyl)diiodonickel(II). (Pound Ni 9.74$, I g 43.80$. Calculated for (CH ) CF P 3 .2 3 N i l : Ni 10.14$, 2 2 1,44.40$.) The compound was p r a c t i c a l l y insoluble i n cold water and on warming with i t , gave off the phosphine. The complex dissolved i n benzene and carbon tetrachloride, but was soluble with immediate decomposition i n most other s o l -vents. 3(i) Bis(dimethyltrifluoromethylphosphine)dithio- cyanato-nickel(II): Diraethylbistrifluoromethylphosphine (0.340 g, 2.61 mmole) was treated itfith n i c k e l thiocyanate (0.2281 g, 1.31 mmole). Only traces of unreacted phosphine were recovered and a yellow s o l i d was obtained. This could be p u r i f i e d by r e f l u x i n g with butanol,and was i d e n t i f i e d as bis(dimethyltrifluoromethylphosphine)dithiocyanatonickel(II). (Pounds Ni 13.42$; (SON)" 26 .25$. Calculated f o r (CH 3) 2CP 3P 2Ni(SCN) : Ni 13.36$; (SON)"" 26.73$.) This compound was stable i n moist a i r and was soluble i n warm water with slow decomposition. I t was soluble i n most organic solvents but the polar ones decom-p o s e i i t more e a s i l y . - 240 -3 ( j ) Bis(dimethyltrifluoromethylphosphine)di-n i t r a t o n i c k e l ( I I ) : Various experiments (as for trimethyl-phosphine) were conducted to i s o l a t e a stable c r y s t a l l i n e complex with n i c k e l n i t r a t e , but the best re s u l t s were ob-tained by f i r s t heating the s a l t (0.222 g, 0.76 mmole) to 120 and then condensing a large excess of phosphine (0.52 g, 4.0 mmole) i n a small tube (so that the phosphine i s i n a l i q u i d phase). S l i g h t warming was s u f f i c i e n t to make the product homogeneous. The dark red s t i c k y sub-stance was taken up i n butanol and was i d e n t i f i e d as bis(dimethyltrifluoromethylphosphine)dinitratonickel(II). .(Pound Ni , 1 3 . 2 2 $ . Calculated f o r l~(CH ) CF P~| Ni (NO ) : L 3 2 3 J 2 5 2 Ni,13.12%) C. REACTION WITH OTHER PHOSPHINES The n i c k e l s a l t s were treated with m e t h y l b i s t r i -fluoromethylphosphine, phenylbis trifluoromethylphosphine and tristrifluoromethylphosphine but no compound formation was observed. The treatment was attempted both with and without solvents. When performed i n the presence of s o l -vents, the recovered phosphines were contaminated with fluoroform. Preliminary experiments with d i p h e n y l t r i -fluoromethylphosphine showed that the complexes were form-ing, but these have not been studied i n d e t a i l . - 241 -I REFERENCES 1. . Haszeldine, R.N. and West, B.O. J. Chem. S o c , 3631, 1956. 2 . Haszeldine, R.N. and West, B.O. J. Chem. S o c , 3880, 1957. 3. Mann, F.G-. and Wells, A.F. J. Chem. Soc. ,702, 1938. 4. Bennett, F.W., Emeleus, H.J., and Haszeldine, R.N. J. Chem. S o c , 1565, 1953. 5. Auger and B i l l y . Compt. Rend., 139, 597, 1904. 6. Brown, H.C. J. Chem. S o c , 1248, 1956. 7. Cullen, W.R. Can. J. 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Ste r i c Effects i n Organic Chemistry, edited by Newman^ John Wiley and Sons, New York, 1 9 5 6 , p p . 6 1 3 - 6 2 0 . 1 4 2 a . Taft. p . 5 9 5 . 143« Parmer, J.B., Henderson, I.H.S., Lossing, F.P., and Marsden, D.G.H. J. Chem.. Phys., 2 £ , 352, 1 9 5 2 . 144 « Jensen, K.A. Z. Anorg. Allgem. Chem., 2 2 9 , 2 2 5 , 1 9 3 6 . 145« Chatt, J., Duncanson, L.A., and Venanzi, L.M., J. Chem. S o c , 4 4 5 6 , 1955. I460. Jensen, K.A. and Nygaard, B« Acta, Chlm. Scand.,. 3 , 4 7 9 , 1 9 4 9 . C H E M I S T R Y O F T H E T R I F L U O R O M E T H Y L G R O U P PART I. COMPLEX FORMATION BY PHOSPHINES CONTAINING THE TRIFLUOROMETHYL GROUP 1.2 M . A . A . BEG AND H . C. CLARK ABSTRACT The formation of co-ordination compounds of (CH 3) 3P, (CH 3) 2PCF 3 , CH 3 P(CF 3 ) 2 , and P(CF 3) 3 > with boron trifluoride and platinum (II) chloride has been studied. The properties of the new compounds (CH 3 ) 2 PCF 3 .BF 3 , [(CH 3) 2PCF 3] 2PtCl 2, [CH ?P(CF 3) 2] 2PtCl 2 are described, and it is hence concluded that the stabilities of the boron trifluoride compounds decrease in the order (CH,),P.BF, > (CH 3 ) 2 PCF 3 .BF 3 > (CH 3 P(CF 3 ) 2 BF 3 > P(CF 3 ) 3 .BF 3 ), while for the platinum (II) complexes the order of stability is [(CH 3) 3P] 2PtCl 2 < [(CH 3) 2PCF 3] 2PtCI 2 > [CH 3P(CF 3) 2] 2PtCI 2 > ([P(CF3)3]2PtCl2). These two orders are related to the electronegativity of the trifluoromethyl group and its influence on the bonding properties of the phosphorus atoms. INTRODUCTION While a range of organometallic and organometalloidal trifluoromethyl compounds has been prepared, little quantitative information is so far available for the trifluoromethyl group. Since its electronegativity will differ widely from that of a normal alkyl or aryl group, these organometalloidal compounds may be expected to show unusual properties. A study has therefore been made of the effect of the trifluoromethyl group on the donor properties of substituted phosphines. Two types of addition products may be formed: (a) those containing-only a <r-bond from phosphorus to the acceptor atom, as for example in F3P.BH3, and (b) those in which both a- and ir-bonding occurs, usually between phosphorus and a transition metal, e.g. (R 3 P)2PtCl2. The effect of the electronegative trifluoromethyl group on the formation of a- and x-bonds will vary and may be investi-gated by examining the properties of these two classes of compounds. E X P E R I M E N T A L Preparation of the Phosphines Trimethylphosphine was prepared by the method of Mann and Wells (1). This reaction normally gives low yields, but it was found that, with strong cooling of the reaction vessel in an acetone - solid C O 2 mixture, yields of 60% could be regularly obtained. The phosphine was isolated as the silver iodide complex, which, when warmed in vacuo, readily evolved the phosphi'ne. The reaction of trimethylphosphine with trifluoroiodomethane, as described by Haszeldine and West (2), was used to prepare dimethyl trifluoromethylphosphine, but yields higher than 33% based on CF3I could not be obtained. The reaction appeared to commence below —78° and was virtually complete after the mixture had stood at room temperature for about 30 minutes. Apart from the desired product and an involatile residue of tetramethylphosphonium iodide, a volatile white solid identified as dimethyl bis(trifluoromethyl)phosphonium iodide, m.p. 60°, was also found. The latter compound (0.472 g) reacted with excess aqueous sodium hydroxide at room temperature to give fluoroform (0.235 g) corresponding to the loss of two C F 3 groups. Purification of the "^Manuscript received August 20, 1959. Contribution from the Chemistry Department, University of British Columbia, Vancouver 8, B.C. 'Presented at the International Conference on Co-ordination Chemistry, London, April 1959. Can. J . Chem. Vol. 38 (1960) 119 120 C A N A D I A N J O U R N A L OF C H E M I S T R Y . V O L . 38, 1960 dimethyl trifluoromethylphosphine was best achieved by thermal decomposition of its silver iodide complex as described by Haszeldine and West. Methyl bis(trifluoromethyl)phosphine was prepared by reacting tris-trifluoromethyl-phosphine with methyl iodide as described by Haszeldine and West (3).. The-preparation of t-ris(trifluoromethyl)phosphine from phosphorus and trifluoroiodo-methane followed the methods of earlier workers (4). Commercial boron trifluoride was used after purification by vacuum distillation. Platinum (II) chloride was prepared by heating chloroplatinic acid to 325° in an atmos-phere of nitrogen. The complexes described below were prepared by reacting the phos-phines with boron trifluoride or platinum (II) chloride in sealed, evacuated tubes. The identities of the boron trifluoride derivatives were determined from the ratios of the reactants and those of the platinum (II) chloride complexes by standard methods of analysis. Saturation pressures were measured with an isoteniscope, the boron trifluoride compounds being prepared directly in its bulb in order to avoid decomposition with moisture. Compounds with Boron Trifluoride (a) Trimethylphosphine.—The phosphine (0.1995 g, 2.60 mmoles) reacted immediately with boron-trifluoride (0.1927 g, 2.79 mmoles) to give a white solid. The recovery of excess trifluoride (0.0031 g) gave a ratio phosphine:boron trifluoride of 1:1. The com-pound ( C H 3 ) 3 P . B F 3 has been reported previously (5) but few of its properties have been described. It is decomposed slowly in moist air, and rapidly in water, acetone, and ethanol. It is only slightly soluble in chloroform and insoluble in carbon tetrachloride and carbon disulphide. The melting point is 126-130° (decomp.) and the saturation pressure is given by the equation logio p (mm) = 8.460 — (2627/ T) in the range 25 o -100° , whence the heat of sublimation is 11.98 kcal mole - 1 . (b) Dimethyl trifluoromethylphosphine.—The phosphine (0.2952 g, 2.27 mmole) reacted with boron trifluoride (0.1589 g, 2.27 mmole) to give a white solid which melted below room temperature to a viscous liquid. The compound showed the same behavior towards moist air and polar solvents as its trimethylphosphine analogue. The melting or freezing point could not be precisely determined since supercooling to a glass occurred. Softening of the glass took place at approximately —9° C. The vapor pressure of the compound is given by the equation logio p (mm) = 10.354— (2146/T) whence the heat of vaporization is 9.68 kcal mole - 1 . (c) Methyl bis(trifluoromethyl)phosphine.—In this case, no reaction occurred after 120 hours at room temperature between the phosphine (0.2690 g) and boron trifluoride (0.0938 g). Cooling to —78° still allowed the boron trifluoride to be recovered and there was no sign of complex formation. Similarly, the treatment of t r i s t r i f luoromethyl-phosphine (0.3106 g) with boron trifluoride (0.1934 g) failed to reveal the formation of any complex. Compounds with Platinum (II) Chloride (a) Trimethylphosphine.—The complex [ ( C H 3 ) 3 P ] 2 P t C l 2 has been prepared previously (6) but it was here prepared for comparison with its trifluoromethyl analogues. Direct reaction between the phosphine and platinum (II) chloride in the absence of a solvent was very slow. In a benzene suspension, reaction was more rapid although the yield was still low. Thus trimethylphosphine (0.195 g) shaken for 24 hours with platinum (II) chloride (0.3345 g) in benzene gave only 0.10 g of the complex, a 20% yield. Higher yields could be obtained by using the method described by Jensen (7) for the preparation of the B E G A N D C L A R K : T R I F L U O R O M E T H Y L GROUP 121 corresponding triethylphosphine complex. This involved shaking an aqueous solution of potassium chloroplatinite (1.20 g) with the phosphine (0.43 g). The mixture was heated on a steam bath for 30 minutes, and the white complex was filtered, and washed with water, alcohol, and ether. Recrystallization from methanol gave a yield of 0.51 g, a 4.1% yield of bis(trimethylphosphine)dichloroplatinum (II). Found: Pt, 45.5; CI, 17.0. Calc. for [ ( C H 3 ) 3 P ] 2 P t C l 2 : Pt , 44.7; CI, 16.1%. The melting point is 324-326° and the dissociation pressure in the range 155-190° is given by the equation logio p (mm) = 6.510—(2108/T), whence the heat of dissociation is 9.59 kcal mo le - 1 . The complex dissolves readily in chloroform, is sparingly soluble in ethanol, and almost insoluble in ether, benzene, and carbon tetrachloride. In water, particularly when heated, decomposition occurs and the free phosphine is evolved. {b) Dimethyl trifluoromethylphosphine.—The reaction of the phosphine (0.412 g, 3.17 mmoles) with platinum (II) chloride (0.425 g, 1.59 mmoles) at room temperature for 48 hours in a sealed tube gave a pale yellow product, which was recrystallized from methanol to give white, needle-shaped crystals of bis(dimethyl (trifluoromethyl) -phosphine)dichloroplatinum (II). Found: Pt, 37.2; CI, 13.2. Calc. for [ ( C H 3 ) 2 P C F 3 ] 2 P t C l 2 : Pt, 37.1; CI, 13.5%. The complex melted at 188-190° with decomposition and the dissocia-tion pressure over the range 90-130° is given by the equation logio p (mm) = 7.969 — (2438/T) whence the heat of dissociation is 11.31 kcal mole - 1 . It is soluble in alcohol, chloroform, and carbon disulphide and insoluble in ether, benzene, and carbon tetra-chloride. It is not soluble in cold water, but reacts slowly with hot water to evolve fluoroform. Almost complete conversion (90%) to fluoroform is obtained on heating to :80° with 25% aqueous sodium hydroxide. (c) Methyl bis{trifluoromethyl)phosphine.—This phosphine and platinum (II) chloride in a 2:1 ratio reacted only slowly and unreacted phosphine was always recovered from the re-action tubes. Extraction of the solid reaction product with carbon tetrachloride or methanol and evaporation of the extract gave yellow crystals of bis(methyl bis(trifluoromethyl)-phosphine)dichloroplatinum (II). Found: Pt, 29.9; CI, 11.2. Calc. for [ C H 3 P ( C F 3 ) 2 ] 2 -P t C l 2 : Pt, 30.7; CI, 11.2%. The melting point is 85-87° and the dissociation pressure in the range 80-140° may be expressed as logio/' (mm) = 4.885 — (1258/T) whence the heat of dissociation is 5.76 kcal mole - 1 . The complex is soluble in carbon tetrachloride, ether, acetone, and alcohol, but is insoluble in water. Hydrolysis (50% approx.) to fluoroform occurs with 25% aqueous sodium hydroxide at 80°. (d) Tris(trifluoromethyl)phosphine.—The following experiments were performed in attempts to prepare a platinum (II) complex. In all cases the reactants were completely recovered and no sign of complex formation was observed, (i) Direct reaction of the phosphine (0.175 g) and platinum (II) chloride (0.132 g) at room temperature, (ii) The passage of the phosphine in a stream of nitrogen over platinum (II) chloride heated to 200°. {Hi) Reaction of the phosphine and platinum (II) chloride in methanol. Several experiments were performed under this last set of conditions and in all cases the methanol acquired a yellow color and a few colorless crystals appeared to be formed. A l l attempts to isolate a product were unsuccessful, apparently because of decomposition. Dipole Moments Because of the low solubility of the platinum complexes and also their tendency, in certain cases, to decompose slowly in the presence of moisture, accurate dipole moments were not calculated. The dielectric constants were measured with a simple Ebarch dielectric constant meter and dipole moments were calculated using Jensen's formula (8) for dilute solutions. The accuracy of the dipole moments is ± 0 . 5 D . 122 C A N A D I A N J O U R N A L OF C H E M I S T R Y . V O L . 38, 1960 TABLE Molar concentration c a o i n Pm n (D) [(CH3)3P]2PtCl2 measured in chloroform:benzene (1:1) solution (emiX = 3.380) 0.000466 3.426 - 3320 0.000977 3.441 3780 13.1 ±0 .5 [(CH3)2PCF3]2PtCl2 measured in chloroform solution (ecHcia = 4.947) 0.00985 4.982 1667 0.00189 . 5.007 1806 9.2±0.5 [CH3P(CF3)2]2PtCl2 measured in carbon tetrachloride solution (eccu = 2.261) 0.00297 2.261 0.00525 2.261 0 DISCUSSION The addition compounds formed by phosphines with boron trifluoride result from dative c-bond formation from phosphorus to boron. Smaller secondary effects such as back co-ordination may also be involved but these are of only minor importance. Evidence from other series of B F 3 derivatives (9), comparable to that described here, reveals that a decrease in the electron-donating power of the co-ordinating base produces a correspond-ing decrease in the stability of the molecular addition compound. As a qualitative measure "of stability, we have here employed relative volatilities. The vapor pressure equations quoted above show thedower volatili ty and greater stability of ( C H 3 ) 3 P . B F 3 as compared with (CHs)2PCF3.BF3. The trifluoromethyl group thus markedly reduces the donor properties of the phosphorus atom. This is in accordance with a higher electronegativity and a smaller inductive effect for the trifluoromethyl in contrast to the methyl group. Since the adduct (CF3)3P.BH 3 does not exist (10) and since borine adducts are generally more stable than their boron trifluoride analogues, it is not surprising that methyl bis(trifluoromethyl)phosphine- and tris(trifluoromethyl)phosphine-boron tri-fluoride adducts could notbe isolated. The possibility that steric interaction by the much larger C F 3 group is responsible for the observed decrease in stability jnust also be considered, although the extent of such interaction is difficult to determine accurately. The steric requirements will certainly be greatest for tris(trifluoromethyl)phosphine for which Bowen (11) has shown the C P C angles to be 100° and the C F 3 groups all to lie on the same side of the phosphorus atom. Also since there is some rearrangement of the planar B F 3 molecule towards a tetrahedral configuration on formation of the co-ordinate bond, it would appear that steric interaction between the C F 3 groups and F atoms must be comparatively small. For the other phos-phines with fewer C F 3 groups, steric interactions will be of even less significance. The observed decrease in stability of the B F 3 adducts is therefore not due to. steric effects. The infrared spectra of ( C H 3 ) 3 P . B F 3 and ( C H 3 ) 2 P C F 3 . B F 3 could not be completely resolved so that full interpretation is not possible. However, in both cases the B — F stretching frequencies at 1450 and 1505 c m - 1 in B F 3 were shifted to the 1175-1200 c m - 1 . This is similar to the shifts observed for ke tone-BF 3 complexes by Susz et al. (12). There is also a considerable shifting of bands in the 650-750 c m - 1 region. Since both the B F 3 bending and P — C (aliphatic) stretching frequencies occur in this region and since no other similar spectra are available for comparison, assignments have not been made. In phosphine - platinum (II) co-ordination compounds, in addition to the formation of dative c-bonds from phosphorus to platinum, strong ^7r-(f7r-bonding.is also possible and appears to be of considerable importance in determining,relative stabilities. As an extreme B E G A N D C L A R K : T R I F L U O R O M E T H Y L GROUP 123 case, consider bis(trifluorophosphine)dichloroplatinum (II) ( F 3 P ) 2 P t C l 2 (1/3) .-.Here the highly electronegative fluorine atoms reduce the electron donor properties of phosphorus, but at the same time cause considerable 7r-bonding which appears to involve the unshared rf-electron pairs of platinum and the vacant 3d orbitals of the phosphorus atoms. The extent of this electron drift from platinum back to phosphorus is shown by the small dipole moment of 4.4 D . This indicates a cM-configuration and must be compared with values of 11-12 D for the cis-isomers of bis(trialkylphosphine)dichloroplatinum (II) complexes. Similarly, the substitution of trifluoromethyl for methyl groups may tend to give increased ir-bonding between platinum and phosphorus although not to the same extent as phosphorus trifluoride. The configurations of the complexes described earlier can be deduced from their colors, solubilities in polar and non-polar solvents, and their dipole moments. Bis(trimethylphos-phine)dichloroplatinum (II) and bis(dimethyl trifluoromethylphosphine)dichlorop!ati-num (II) are obtained as the cis-isomers since they are white solids and have large dipole moments. Bis(methyl bis(trifluoromethyl)phosphine)dichloroplatinum (II) is isolated in the trans-iorm which is yellow-orange and has a zero dipole moment. It must be empha-sized that these are the major components of reaction products prepared and recrystallized under the same conditions. In all three cases there were indications that the other isomer was also formed but only to the extent of less than about 5%. Since it is known that the isomer obtained under a given set of conditions may depend to some extent on relative solubilities, it would clearly be necessary to study in detail the cis-trans equilibria in order to determine unambiguously the relative stabilities of the isomers of the various com-plexes. However, since all our complexes could be prepared under identical conditions in the absence of solvents, the fact that different isomers are obtained with dimethyl trifluoromethylphosphine and methyl bis(trifluoromethyl)phosphine is significant and is discussed later. The relative stabilities of these new phosphine complexes may be examined in several ways. Chemically, the trimethylphosphine complex appears the least stable since decom-position always occurs to a small extent during recrystallization from methanol, and to a much larger extent on reaction with warm water. Also, the solid compound always smells strongly of the free phosphine. In contrast the other two complexes were odorless solids which could be recrystallized without decomposition and which reacted only slowly with hot water. A n accurate index of thermal stability is seen in the heats of dissociation calculated from the observed dissociation pressures, the values being 6.7 kcal m o l e - 1 for « s - [ ( C H 3 ) 3 P ] 2 P t C l 2 , 11.3 kcal m o l e - 1 for c « - [ ( C H 3 ) 2 P C F 3 ] 2 P t C l 2 , and 5.8 kcal m o l e - 1 for / raras-[CH 3 P(CF 3 ) 2 ] 2 PtCl 2 . The process of dissociation probably involves the loss of a phosphine molecule and the formation of a dimeric bridged complex, 2(phosphine)2PtCl2 —» 2phosphine + (phosphine)2Pt2Cl4 but it could alternatively result in the simultaneous loss of both phosphine molecules to give free platinum (II) chloride. Although the actual course of dissociation is unknown, the above values are considered a reasonable guide to relative stabilities of the platinum complexes and they show the order to be (CH,),P < (CH3)2PCF3 > CH3P(CF3)2[ > P(CF,),]. Points of particular interest are: (a) the increase and then decrease in stability in the series as C F 3 is substituted for C H 3 ; (6) the non-existence, under the conditions so far studied, of a Pt(II) complex of tris(trifluoromethyl)phosphine; and (c) the fact that, under 124 C A N A D I A N J O U R N A L O F C H E M I S T R Y . V O L . 38, 1900 the same conditions, dimethyl (trifluoromethyl)phosphine gives the cw-isomer, while methyl bis(trifluoromethyl)phosphine produces the trans-isomer. In platinum (II) com-plexes the greatest degree of x-bonding is obtained when the two x-bonding ligands are cis to one another (14). Substitution of the first methyl group by the more electronegative C F 3 group thus appears to give greater stability to the complex by causing a greater increase in x-bonding than is offset by the reduction in strength of the cr-bond. This can also be seen by a comparison of the dipole moment of 13.1 D for [ ( C H 3 ) 3 P ] 2 P t C l 2 with that of 9.2 D for [ ( C H 3 ) 2 P C F 3 ] 2 P t C l 2 . For the complex of methyl bis(trifluoromethyl) phosphine there might be expected to occur one of only two possibilities: (a) introduction of the second C F 3 group on each phosphine might produce even greater stability; or (b) the reduction in strength of the tr-bond may more than offset any increase in x-bonding so as to give a less stable complex. In either case, one might expect that the cw-isomer would be obtained. The occurrence of the trans-isomer is therefore unexpected, and can satisfactorily be explained, together with the non-existence of a t r i s t r i f luoromethyl-phosphine complex, in terms of steric hindrance. When models are drawn using the usual values of atomic radii, it can be shown that 2 trimethyl(or indeed any alkyl)phosphine molecules can be placed cis to one another about a platinum atom, but not 2 tristrifluoro-methylphosphine molecules. The observed effects are certainly not just due to the decreased donor properties of the phosphines since the cw-isomer of bis(trifluorophosphine)-dichloroplatinum (II) is known and is more stable than its <ro«5-isomer. The importance of steric effects for the trifluoromethylphosphines is also shown by the fact that nickel carbonyl derivatives have been obtained (15) in which no more than 2 of the carbon mon-oxide molecules can be replaced by tris(trifluoromethyl)phosphine. In contrast, the more electronegative and more weakly electron-donating but much smaller P F 3 molecule can occupy all four positions to give N i ( P F 3 ) 4 (16). Although these stability orders for the boron trifluoride and platinum (II) chloride derivatives might well be investigated further by the determination of thermodynamic values, particularly the thermodynamic differences between cis- and trans-isomers, the present information does emphasize the high electronegativity of the trifluoromethyl group, as well as the importance of x-bonding in transition metal complexes. ACKNOWLEDGMENTS We gratefully acknowledge the support of the National Research Council , and one of us ( M . A . A . B.) expresses thanks for a scholarship received from C. S. I. R . (Pakistan) under the auspices of the Colombo Plan. REFERENCES 1. M A N N , F. G . and WELLS, A. F. J. Chem. Soc. 702 (1938). 2. HASZELDINE, R. N . and WEST, B . O. J. Chem. Soc. 3631 (1956). 3. HASZELDINE, R. N . and WEST, B . O. J. Chem. Soc. 3880 (1957). 4. BENNETT, F. W. , EMELEUS, H. J., and HASZELDINE, R. N . J. Chem. Soc. 1565 (1953); BURG, A. B . and MAHLER, W . J. Am. Chem. Soc. 79, 247 (1957). 5. GRAHAM, W . A. G . and STONE, F. G . A. J . Inorg. & Nuclear Chem. 3, 164 (1956). 6. CAHOURS, A. Ann. 156, 302 (1870). 7. JENSEN, K. A. Z. anorg. Chem. 229, 225 (1936). 8. JENSEN, K. A. and NYGAARD, B . Acta Chem. Scand. 3, 479 (1949). 9. STONE, F. G. A. Chem. Rev. 58, 101 (1958). 10. BURG, A. B . and BRENDEL, G. J . Am. Chem. Soc. 80, 3198 (1958). 11. BOWEN, H. J . M . Trans. Faraday Soc. 50, 463 (1954). 12. CHALANDON, P . and Susz, B . P . Helv. Chim. Acta, 41, 697 (1958). 13. CHATT, J . and WILLIAMS, A. A. J . Chem. Soc. 3061 (1951): 14. CHATT, J . and WILKINS, R. G. J . Chem. Soc. 273 (1952). 15. EMELEUS, H. J . and SMITH, J . D. J . Chem. Soc. 527 (1958). 16. WILKINSON, G. J . Am. Chem. Soc. 73, 5501 (1951). C H E M I S T R Y O F T H E T R I F L U O R O M E T H Y L G R O U P PART II. N I C K E L (II) C O M P L E X E S OF T R I F L U O R O M E T H Y L PHOSPHINES M . A . A . B E G AND H . C . CLARK Reprinted from CANADIAN JOURNAL OF CHEMISTRY 39, 595 (1961) CHEMISTRY OF THE TRIFLUOROMETHYL GROUP PART II. NICKEL (II) COMPLEXES OF TRIFLUOROMETHYL PHOSPHINES* M . A . A . B E G AND H . C. CLARK The ability of tr i-alkyl and -aryl phosphines to form co-ordination compounds with transition metal salts is well established. However, this abili ty is considerably modified when the phosphine contains the highly electronegative trifluoromethyl group. This has been shown in the reactions of methyl-trifluoromethyl-phosphines with boron trifluoride and platinum (II) chloride (1), where the results have been interpreted in terms of the effect of the electron-withdrawing power of the trifluoromethyl group on the donor properties of the phosphines, and of the large steric requirements of the trifluoromethyl group. These two factors of the perturbing power or ligand field strength of the phosphines, and their steric requirements are just those that have been considered important in producing tetrahedral nickel (II) complexes (2). The first example of an apparently tetrahedral complex was ( P E t 3 ) 2 N i ( N 0 3 ) 2 (3), although the lack of a full structure determination left room for alternative configurations. For the triphenylphosphine complexes ( P P h 3 ) 2 N i X 2 where X = N 0 3 ~ , C I - , Br~ , I - , detailed studies (4) leave no doubt that they possess tetrahedral structures. Other examples of tetrahedral nickel (II) complexes are now known (5). It therefore seemed of interest to examine the nickel (II) complexes of ( C H 3 ) 3 P , ( C H 3 ) 2 P C F 3 , C H 3 P ( C F 3 ) 2 , and P ( C F 3 ) 3 wherever stable com-pounds could be isolated. Only the first two of these phosphines gave stable complexes and there were no indications of reaction between nickel (II) salts and either methyl -bistrifluoromethylphosphine or tristrifluoromethylphosphine. The complexes of diniethyl-trifluoromethylphosphine were considerably less stable than those of trimethylphosphine. The properties of the newly prepared compounds are shown in the table. Magnetic moment Compound (B.M.) Color Absorption maxima (Me 3P) 2Ni(N0 3) 2 (Me 3P) 2NiCl 2 (Me3P)2NiBr2 (Me 3P) 2NiI 2 (Me 3P) 2Ni(SCN) 2 (Me 2PCF 3) 2Ni(N0 3) 2 (Me 2 PCF 3 ) 2 NiCl 2 (Me 2PCF 3) 2NiBr 2 (Me2PCF„)2NiI2 (Me 2PCF 3) 2Ni(SCN) 2 3.17 Diamagnetic 2.93 Diamagnetic Dark red 4850(m), 3950(s), 3325(s) Crimson 5320(s), 3880(m), 3650(m), 2650(s) Crimson 5400(m), 3800(m), 2700(s), 2425(w) Dark brown 5175(m), 3875(w), 2850(vs), 2600(s) Orange-yellow 4600(sh), 3550(vs), 2975(s), 2600(s) Dark red 5550(w), 4850(s), 4150(s), 3270(s) Pink 4800(w), 4050(m), 3450(s), 2550(s) Black 4875(s), 3950(s), 2625(s), 2400(s) Dark brown 3750(m), 3550(m), 3140(m), 2280(s) Yellow 4600(m), 3675(vs), 2550(s) The trimethylphospine complexes have not been reported previously and it is not surprising that the nitrate is paramagnetic and like its triethylphosphine analogue may be considered to be tetrahedral. The halogen and thiocyanate complexes are diamagnetic in accordance with the greater ligand strengths of these anions. The complexes of dimethyltrifluoromethyl phosphine are very similar to the trimethylphosphine compounds, only the nitrate is paramagnetic and possibly tetrahedral. *From part of a thesis submitted by M.A.A.B. in partial fulfillment of the requirements for the Ph.D. degree. C a n . J . C h e m . V o l . 39 (19G1) 595 59G C A N A D I A N J O U R N A L O F C H E M I S T R Y . V O L . 39, 1961 The intensity of the colors of the solid compounds and of the observed absorption bands suggest that charge-transfer transitions are involved. The fact that a nickel (II) complex of tristrifluoromethyl phosphine could not be obtained is consistent with its inability to give a platinum (II) compound (1). The smaller size of the nickel atom compared with platinum may explain why the latter but not the former can give a complex with methylbistrifluoromethyl phosphine.. E X P E R I M E N T A L v The methyl-trifluoromethyl-phosphines were prepared as described previously (1). A l l nickel salts were prepared in the anhydrous state, except the nitrate which was used as the hexahydrate. The trimethylphosphine complexes were prepared by direct reaction of the phosphines with the nickel salts in 2:1 ratio in sealed evacuated tubes, and were purified by refluxing with butanol for about 30 minutes when crystals of the complexes separated. In the case of nickel nitrate, the product could not be crystallized satisfactorily and solutions of the complex were used where necessary. For the dimethyltrifluoromethyl-phosphine complexes, crystallization was not possible owing to their instability. The preparations in these cases were therefore performed in the presence of excess phosphine which acted as a solvent and gave reasonably pure products. The analyses of the compounds are given in the table. % Ni % X Calc. for Calc. for Compound Found NiX 2 (PR 3 ) 2 Found NiX 2 (PR 3 ) 2 (PMe 3 ) 2 Ni(N0 3 ) 2 17.33 17.37 — — . (PMe 3) 2NiCl 2 20.05 20.56 25.14 25.27 (PMe 3) 2NiBr 2 16.01 15.68 42.70 43.24 (PMe 3) 2NiI 2 11.85 12.50 54.30 54.72 (PMe 3) 2Ni(SCN) 2 17.27 17.79 34.45 34.60 (Me 2 PCF 3 ) 2 Ni(N0 3 ) 2 13.22 13.12 — — (Me 2PCF 3) 2NiCl 2 14.72 14.91 ' 18.15 18.25 (Me 2PCF 3) 2NiBr 2 H . 8 4 12.14 34 .10 33.47 (Me 2PCF 3) 2NiI 2 9.76 10.14 43.80 44.40 (Me 2PCF 3) 2Ni(SCN) 2 13.42 13.36 26.25 26.73 A l l the complexes except the iodides and thiocyanates decomposed in the presence of moisture. Although stable in dry solvents, wet polar solvents caused decomposition. Magnetic measurements were made on a Gouy magnetic balance, using powdered samples except for the nitrates for which solutions were used. Spectra were determined in carbon tetrachloride or methanol solutions using a Cary model 14 spectrophotometer. ACKNOWLEDGMENTS The financial support of the National Research Council is gratefully acknowledged as is the award of a Colombo Plan scholarship to M . A . A . B . 1. M . A. A. BEG and H . C. CLARK. Can. J . Chem. 38, 119 (I960). 2. L. M . VENANZI. J . Inorg. & Nuclear Chem. 8, 137 (1958). 3. K. A. JENSEN. Z. anorg. u. allgem. Chem. 229, 225 (1936). 4. L. M . VENANZI and H . M . POWELL. Proc. Chem. Soc. 6 (1956). 5. N. S. GILL and R . S. NYIIOLM. J . Chem. Soc. 3997 (1959). RECEIVED DECEMBER 5, 1960. CHEMISTRY DEPARTMENT, UNIVERSITY OF BRITISH COLUMBIA, VANCOUVER, B . C . C H E M I S T R Y O F T H E T R I F L U O R O M E T H Y L G R O U P PART III. PHENYLBISTRIFLUOROMETHYLPHOSPHINE A N D RELATED COMPOUNDS M . A . A . B E G AND H . C. CLARK Reprinted from CANADIAN JOURNAL OF CHEMISTRY 39, 564 (1961) C H E M I S T R Y O F T H E T R I F L U O R O M E T H Y L G R O U P PART III. PHENYLBISTRIFLUOROMETHYLPHOSPHINE AND RELATED COMPOUNDS M. A. A. B E G AND H. C. CLARK C H E M I S T R Y O F T H E T R I F L U O R O M E T H Y L G R O U P PART III. PHENYLBISTRIFLUOROMETHYLPHOSPHINE AND RELATED COMPOUNDS1 M. A. A. B E G AND H. C. CLARK ABSTRACT The reaction of trifluoroiodomethane with tetraphenylcyclotetraphosphine leads to the formation, of phenylbistrifluoromethylphosphine and phenyltrifluoromethyliodophosphine. The mechanism of the reaction is discussed and the physical and chemical properties of these compounds are reported. Bromine reacts with phenylbistrifluoromethylphosphine to form phenylbistrifluoromethyldibromophosphorane which is hydrolyzed to phenyltrifluorb-methylphosphinic acid, C6H5(CF3)P(0)0H. INTRODUCTION In previous papers in this series, the donor properties of methyl-trifluorom ethyl -phosphines were studied by the investigation of their ability to form complexes with boron trifluoride and platinum (II) chloride (1), and with a series of nickel (II) salts (2). Since much is known of the corresponding complexes of aryl phosphines, it seemed worth-while to study the donor properties of aryl-trifluoromethyl-phosphines. Unlike the methyl-trifluoromethyl-phosphines which have been known for some time (3, 4, 5), the phenyl-trifluoromethyl-phosphines had not been previously reported, although their arsine analogues had been prepared (6). We now report the preparation of phenylbistri-fluoromethylphosphine. DISCUSSION AND RESULTS Phenylbistrifluoromethylphosphine has been prepared by the reaction of trifluoroiodo-methane with tetraphenylcyclotetraphosphine, the properties of which have been reported by other workers (7, 8, 9). The reaction was performed at 185°, above the melting point of the tetraphosphine, and the other reaction products, besides phenylbistrifluoromethyl-phosphine, are phenyltrifluoromethyliodophosphine, which is a very involatile reddish brown liquid, and small amounts of fluoroform and hexafluoroethane. The mechanism of this reaction, involving the interaction of a perfluoroiodoalkane with a four-membered phosphorus ring is of some interest. A free-radical mechanism involving fission of phosphorus-phosphorus bonds by the attack of C F 3 radicals seems probable. This is supported by the fact that the reaction wi l l occur thermally or on ultra-violet irradiation of the tetraphosphine with trifluoroiodomethane. Since the simultaneous breaking of four P — P bonds is unlikely, the following reaction scheme may be suggested. CeH& I C 6H 5P—PC 6H 5 -CF 3 C6H6P—P—CF3 CF3I C6H5P-• | | + • » I * I + C8H5P(CF3)2 + C6H6PI2 C 6H 5P—PC 6H 5 -I C6H5P—P—I C6H5P-CF.Ij C 6 H 6 | + 2C6H6(CF3)PI CeHgP • 2C6H6(CF3)PI C6H6P(CF3)2 + C6H6PI2. 'Manuscript received December 5, 1960. Contribution from the Department of Chemistry, University of British Columbia, Vancouver, B.C. From part of the thesis presented by M.A.A.B. in partial fulfillment of the requirements for the Ph.D. degree. Can. J . Chem. Vol. 39 (1961) 564 B E G A N D C L A R K : T R I F L U O R O M E T H Y L GROUP 565 This scheme is supported by the observation that the reaction products contain phenylbistrifluoromethylphosphine and phenyltrifluoromethyliodophosphine in an ap-proximately 2:1 ratio, and also by the results of a separate experiment which indicated extensive disproportionation of the iodophosphine at 200° as indicated above. Phenylbistrifluoromethylphosphine is a colorless liquid boiling at 148-150°; it is stable at 200° and prolonged heating to 300° causes only partial decomposition. It is not hydro-lyzed by acids, but reacts very slowly with water at 100° and much more rapidly with aqueous sodium hydroxide at 80°. The hydrolysis products are fluoroform and either phenylphosphonous acid C6H5PO2H27, or its sodium salt. Phenylbistrifluoromethylphosphine does not react with iodine at room temperature, but at 185° the trifluoromethyl groups are cleaved as trifluoroiodomethane. There is no evidence of the formation of the diiodophosphorane, C 6 H 6(CF 3 ) 2 P l 2 . However, the phosphine reacted vigorously with bromine at room temperature to form phenylbistri-fluoromethyldibromophosphorane. This is in agreement with the usual decrease in stability for dichloro-, dibromo-, and diiodo-phosphoranes. Phenylbistrifluoromethyl-dibromophosphorane is readily hydrolyzed by water losing only one of the two tr i -fluoromethyl groups per molecule as fluoroform and producing phenyltrifluoromethyl-phosphinic acid, C 6 H 6 ( C F 3 ) P ( 0 ) O H . Phenyltrifluoromethyliodophosphine is a reactive liquid which is readily hydrolyzed. Whereas alkaline hydrolysis produced fluoroform and the sodium phenylphosphonate, treatment with water gives phenyltrifluoromethylphosphine and phenyltrifluoromethyl-phosphinic acid, C 6 H 5 ( C F 3 ) P ( 0 ) O H . The production of phenyltrifluoromethylphosphinic acid from the aqueous hydrolysis of phenylbistrifluoromethyldibromophosphorane provides an interesting link between the trifluoromethyl- and aryl-phosphorus compounds. Whereas hydrolysis of tr iaryl-dichlorophosphoranes yields phosphine oxides (10), hydrolysis of tristrifluoromethyl-dichlorophosphorane (11) gives bistrifluoromethylphosphinic acid and one equivalent of fluoroform. H20 (CF3)3PC12 > [(CF3)3P(OH)2] - (CF3)2P(0)OH + CF3H The hydrolysis of phenylbistrifluoromethyldibromophosphorane shows that the inter-mediate compound C 6 H B ( C F 3 ) 2 P ( O H ) 2 is unstable. H20 C6H6(CF3)2PBr2 > [C6H5(CF3)2P(OH)2] C6H5(CF3)P(0)OH + CF 3H The trifluoromethyl groups behave in the same way as in the hydrolysis of tristrifluoro-methyldichlorophosphorane and the phenyl group shows its customary resistance to hydrolytic attack. The formation of phenyltrifluoromethylphosphinic acid from the hydrolysis of phenyl-trifluoromethyliodophosphine is consistent with the general reactions of halophosphines (12). The spontaneous oxidation-reduction of the apparently unstable hydrolysis product leads to the production of phenyltrifluoromethylphosphine and phenyltrifluoromethyl-phosphinic acid. H20 2C6H5(CF3)P1 -> [2C6Hs(CF3)POH] -> C6H6(CF3)PH + C6H6(CF,)P(0)OH The infrared spectra of these phenyl-trifluoromethylphosphorus compounds show the expected features. Absorption associated with the strong carbon-fluorine- stretching vibrations occurred in the 1100-1200 c m - 1 region. However, it is of interest to notice 566 C A N A D I A N J O U R N A L OF C H E M I S T R Y . V O L . 39, 1901 that the spectrum of silver phenyltrifluoromethylphosphinate, C 6 H 5 ( C F 3 ) P ( 0 ) O A g , showed absorption at 1225 c m - 1 corresponding to the P : 0 vibration. This absorption occurs in the same region for the aryl and a lkyl phosphinic acids R .2P (0)OH, which are weak acids. For the strong acid, trifluoromethylphosphonic acid, this vibration is shifted to the higher frequency of 1300 c m - 1 (13, 14). This might suggest that phenyltrifluoro-methylphosphinic acid is a fairly weak acid. E X P E R I M E N T A L The preparations of the starting materials were carried out in a nitrogen atmosphere. Reactions with trifluoroiodomethane were carried out in sealed evacuated Pyrex tubes and the products and reactants were manipulated by standard vacuum techniques, out of contact with air and moisture. Preparation of Tetraphenylcyclotetraphosphine Phenyldichlorophosphine was obtained by the method of Buchner and Lockhart (15). The preparation of phenylphosphine by the Michaelis method (16, 17) is very cumbersome and gives a low yield. A much easier method (9, 18) is by reduction of phenyldichloro-phosphine with lithium aluminum hydride. Phenyldichlorophosphine (18.8 g) dissolved in 100 ml diethyl ether was added cautiously to a well-stirred suspension of l i thium aluminum hydride (3 g) in 100 ml ether. The reaction was vigorous and cooling was necessary. After the addition of phenyldichlorophosphine had been completed, the mixture was refluxed for 30 minutes and 5 ml of water were added dropwise. After being refluxed for an hour, the mixture was distilled and the resulting phenylphosphine, distilling at 160°, was dried over calcium chloride (yield 55%). The preparation of tetraphenylcyclotetraphosphine by the Michaelis ' method (19) is not convenient and the compound was prepared by adding phenylphosphine (11 g) in 50 ml ether to a well-stirred solution of phenyldichlorophosphine (18 g) in 50 ml ether. The solution gradually turned yellow but solid was not immediately deposited. After the addition was complete, the solution was refluxed for 3 hours during which time a white solid was deposited. The ether solution was decanted and the remaining solid was washed and dried. The yield of tetraphenylcyclotetraphosphine (m.p. 149-50°) was 90%. Reaction of Tetraphenylcyclotetraphosphine with Trifluoroiodomethane Tetraphenylcyclotetraphosphine (1.0 g) was sealed with trifluoroiodomethane (2.025 g) and left at room temperature for 24 hours. The solid phosphine was insoluble in tr i -fluoroiodomethane. N o reaction occurred at 70° C over 24 hours, nor at 150° C for 12 hours, but on heating at 185° C for 12 hours a dark-red involatile liquid was obtained and 0.558 g of unreacted trifluoroiodomethane was recovered. The dark-red liquid was shaken with mercury and the remaining liquid extracted with ether. After removal of the ether, a liquid (0.45 g) of low volati l i ty was obtained and identified as phenylbistri-fluoromethylphosphine (Found: C , 39.35%; H , 2.10%; F , 45.40%; P , 12.30%. Calculated for C 8 H 6 F 6 P : C, 39.03%; H , 2.03%; F , 46.36%; P , 12.60%). Phenylbistrifluoromethylphosphine is a colorless oily liquid whose odor is not as obnoxious as those of other phosphines. It boils at 148-150° and its vapor pressure is given by the equation log ^ = 7.5606 — (1985/T), whence the latent heat of vaporiza-tion is 9054 cal m o l e - 1 and the Trouton's constant is 21.37. It is stable in air and does not react with water up to 100° C. It does not react with silver iodide, a solution of silver iodide in potassium iodide, or with carbon disulphide. B E G A N D C L A R K : T R I F L U O R O M E T H Y L GROUP 567 Two separate experiments were performed to investigate the mechanism of the above reaction and to characterize the other reaction products. (1) Tetraphenylcyclotetraphosphine (2 g) was sealed with trifluoroiodomethane (5 g) in a Pyrex tube and was irradiated with ultraviolet radiation from a 200-watt U . V . lamp. The reaction was slow (possibly because of the heterogeneous phases), but after 15 days phenylbistrifluoromethylphosphine (0.899 g) and unreacted trifluoroiodomethane (2.192 g) were obtained. The rest of the product was a thick reddish syrup which showed strong absorption in the I .R. between 8-9 ju, characteristic of C — F stretching frequencies. This was not identified. (2) Tetraphenylcyclotetraphosphine (7.5 g) was sealed with 18 g trifluoroiodomethane and heated at 185° C for 12 hours. A volatile mixture of hexafluoroethane and fluoro-form (0.022 g), and 5.5 g of unreacted trifluoroiodomethane were recovered. The remaining liquid was subjected to fractional distillation under 20 mm pressure. Two fractions were obtained, one boiling at 62-65° (4.9 g) and the other boiling at 112-116° (3.8 g). A thick liquid which solidified on standing remained in the distillation flask. This showed strong absorption in the I.R., corresponding to the C — F stretching frequencies. Another experiment to identify this completely involatile liquid showed that i t contained some iodides, including phosphorus triiodide. When treated with a large excess of trifluoroiodo-methane and mercury, some pure phenylbistrifluoromethyl phosphine was obtained, but the main product was a very viscous pale-yellow liquid, presumably polymeric. The liquid distilling at 62-65° was identified as phenylbistrifluoromethylphosphine and the fraction distilling at 112-114° was identified as phenyltrifluoromethyliodophos-phine. (Found: I, 41.2%. Calculated for C 7 H 6 F 3 P I : I, 41.78%.) Reactions of Phenylbistrifluoromethylphosphine (a) Hydrolysis Phenylbistrifluoromethylphosphine (0.277 g) was sealed with water (1.28 g). There was no reaction at room temperature and the reactants formed two separate layers. After heating at 80° for 24 hours, only a trace of fluoroform was obtained, while after 36 hours at 110°, 0.038 g fluoroform was evolved. Traces of benzene were also identified spectro-scopically. There remained a white crystalline solid which melted at 69° and was identified as phenylphosphonous acid. Phenylbistrifluoromethylphosphine (0.273 g) was sealed with 5 ml of 20% aqueous sodium hydroxide solution. The reaction was slow at room temperature with the evolution of fluoroform. The tube was heated to 80° for 24 hours. The production of 0.149 g fluoro-form (mol. wt. obtained 70.0, calculated 70.0) showed that the hydrolysis was 96.4% complete ( C F 3 obtained as C F 3 H : 54.8%; calculated for C 6 H 6 P ( C F 3 ) : 56.1%). The solid obtained on evaporation of the solution was identified spectroscopically as the sodium salt of phenylphosphonous acid. Phenylbistrifluoromethylphosphine (0.372 g) and 36 N hydrochloric acid (2 g) were sealed. There was no reaction at room temperature and the reactants formed separate layers. There was no reaction at 80° for 24 hours and at 110° for 48 hours. The tube was finally heated to 185° for 120 hours. A t the end of this period the amount of fluoroform evolved was only 0.0022 g and the phosphine was recovered almost quantitatively. (b) Reaction with Halogens (1) Iodine.—Phenylbistrifluoromethylphosphine (0.389 g) and iodine (1.163 g) did not react at room temperature, nor after heating at 150° for 24 hours. The mixture was finally heated to 185° for 48 hours. The products obtained, were fluoroform (0.032 g), 568 C A N A D I A N J O U R N A L OF C H E M I S T R Y . V O L . 39, 1961 trifluoroiodomethane (0.481 g), (mol. wt. 194, calculated 196), benzene (0.055 g), and traces of unreacted phosphine. The conversion into fluoroform and trifluoroiodomethane accounted for 91.5% of the trifluoromethyl group. The formation of fluoroform and benzene may be due to the presence of small traces of moisture on the iodine which is not removed even on extensive drying. The. solid- left in the tube, after pumping off the volatiles, contained phosphorus triiodide and no phenyltrifluoromethyliodophosphine. (2) Bromine.—Phenylbistrifluoromethylphosphine (0.6965 g) and bromine (0.450 g) were combined. The ensuing vigorous reaction was controlled by performing the experi-ment in carbon tetrachloride solution and pumping off the volatiles after the reaction was complete. This was marked by the persistence of the bromine color. The reaction gave an orange-yellow solid which was very reactive towards moisture and was identified as phenylbistrifluoromethyldibromophosphorane (Found: Br , 38.93%. Calculated for C 8 H 6 F 6 P B r 2 : Br , 39.41%). On reacting the dibromophosphorane with water, one equiva-lent of C F 3 was lost and a white solid was left. The dibromophosphorane (0.324 g) was sealed with water (1.0 g) and left at room temperature overnight. Fluoroform (0.060 g) was evolved corresponding to a loss of one equivalent of C F 3 per mole (Found: C F 3 , 18.4%. Calculated for C 8 H 5 F 6 P B r 2 : C F 3 , 34.5%). A white solid was obtained by pumping off the liquids, recrystallizing the residue from water, and finally drying over phosphorus pentoxide. The solid was identified spectroscopically as phenyltrifluoromethylphosphinic acid, C 6 H 5 ( C F 3 ) P ( 0 ) O H . The acid melted at 84-86°. The silver salt of the acid was obtained as needle-shaped crystals by treating the aqueous solution of the acid with silver oxide. The same salt could also be obtained from the reaction mixture of phenyl-bistrifluoromethyldibromophosphorane and water which had stood overnight and had lost one equivalent of C F 3 . The silver salt C 6 H B ( C F 3 ) P ( 0 ) O A g (Found: A g , 33.81%. Calculated for C 7 H e F 3 P 0 2 A g : Ag , 34.06%) melted at 294-96° and was very sensitive to light. (c) Pyrolysis of the Phosphine Phenylbistrifluoromethylphosphine (1.058 g) was heated to 210° for 48 hours; 1.004 g of the phosphine and traces of fluoroform and silicon tetrafluoride (identified spectro-scopically) were obtained. Phosphine (0.639 g) was heated to 300° for 48 hours. The tube walls were etched but the phosphine was not all pyrolyzed: 0.48 g was recovered unchanged. The other volatile materials were fluoroform, silicon tetrafluoride, and some benzene trifluoride. Reactions of Phenyltrifluoromethyliodophosphine Phenyltrifluoromethyliodophosphine is a reddish-brown liquid which boils at 112-114° at 20 mm. It fumes in air and reacts slowly with water. The solution obtained by absorp-tion of water is highly acidic. It disproportionates on heating. (a) Hydrolysis Phenyltrifluoromethyliodophosphine (0.334 g) was treated with 5 ml of 20% sodium hydroxide. There was immediate reaction at room temperature. The tube was heated to 100° for 15 hours. Fluoroform (0.0694 g) (mol. wt. found 69.8, calculated 70.0) was evolved ( C F 3 found, 20.75%; calculated for C 7 H 6 F 3 P I , 23.03%). The hydrolysis was only 90% complete. The residue contained a hygroscopic sodium salt whose I .R. spectrum corresponded with that of sodium phenylphosphonate. Phenyltrifluoromethyliodophosphine (0.334 g) was treated with 0.125 g water and left in a sealed tube overnight. When water and other liquids were removed, a white solid was left. The melting point was 84-86° and in all respects the compound was similar to B E G A N D C L A R K : T R I F L U O R O M E T H Y L GROUP 569 that obtained from the hydrolysis of phenylbistrifluoromethyldibromophosphorane. The silver salt was also prepared by reacting more of the iodophosphine with water and pre-cipitating the iodide as silver iodide. The solution was concentrated in vacuo and the solid dried over P 2 0 6 . The silver salt was identified analytically (Found: A g , 33.80%. Calculated: A g , 34.06%) by its melting point of 294-96°, and also spectroscopically. The above treatment of the iodophosphine also gave a small amount of a liquid whose I.R. spectrum showed the presence of P — H , P—CeHs, and P — C F 3 bonds. The hydrolysis with water therefore appears to give some phenyltrifluoromethylphosphine. (b) Reaction with Trifluoroiodomethane The iodophosphine (2.347 g) was heated with trifluoroiodomethane (2.299 g) at 200° for 12 hours. Trifluoroiodomethane (2.210 g, 96.1%) was recovered and the main products of reaction, presumably from the disproportionation of the iodophosphine, were phenyl-bistrifluoromethylphosphine (0.617 g), phosphorus triiodide, and benzene. Some of the unreacted iodophosphine was also identified among the products. (c) Reactions with Trifluoroiodomethane and Mercury The iodophosphine (2.8 g) and trifluoroiodomethane (10 g), with 54 g mercury, were sealed in a tube and shaken for 24 hours. Trifluoroiodomethane (8.9 g) was recovered and phenylbistrifluoromethylphosphine (1.5 g) was obtained. The loss of 1.1 g of trifluoroiodo-Hg methane indicated that the reaction C 6 H 6 P C F 3 I + C F 3 I ——> C6Ff5(CF 3 ) 2 P had occurred. Besides the phosphine, some polymers were also obtained as mentioned earlier. Pyrolysis of phenyltrifluoromethylphosphine iodide: The iodophosphine (2.003 g) was heated in a sealed tube to 220° for 12 hours. Fluoroform (0.02 g) and trifluoroiodomethane (0.06 g) were obtained as the volatile products and there remained phenylbistrifluoro-methylphosphine, benzene, phosphorus triiodide, and some unreacted phenyltrifluoro-methyl iodophosphine. The I .R. spectra were taken on a Perkin-Elmer model 21 double-beam instrument with rock salt optics. L iqu id films were used for liquids and K B r pellets for solids. The following absorption bands were noted for the compounds mentioned. Phenylbistrifluoromethylphosphine 3080 (w) 2920 (w) 2320 (w) 1980 (w) 1870 (w) 1835 (w) 1810 (w) 1770 (w) 1745 (w) 1730 (w) 1670 (w) 1645 (w) 1590 (w) 1490 (w) 1445 (m) 1330 (w) 1265 (w) 1190 (s) 1140 (s) 1100 (s) 1070 (m) 1030 (w) 1000 (m) 875 (w) 805 (w) 750 (m) 745 (m) 690 (m) Phenyltrimioromethyliodophosphine 3060 (w) 2900 (w) 2340 (w) 1880 (w) 1800 (w) 1725 (w) 1710 (w) 1690 (w) 1675 (w) 1660 (w) 1585 (w) 1490 (w) 1440 (m) 1385 (w) 1335 (w) 1310 (w) 1270 (w) 1210 (m) 1150 (s) 1115 (s) 1070 (m) 1025 (m) 1000 (m) 830 (w) 745 (s) 715 (w) 690 (m) Silver phenyltrifluoromethyl phosphinate 3080 (w) 2900 (w) 2300 (w) 1860 (w) 1815 (w) 1725 (w) 1710 (w) 1690 (w) 1756 (w) 1640 (w) 1630 (w) 1590 (w) 1555 (w) 1485 (w) 1440 (m) 1335 (w) 1225 (s) 1200 (m) 1140 (s) 1110 (s) 1045 (m) 1015 (m) 995 (m) 970 (m) 870 (w) 760 (w) 740 (m) 715 (m) 695 (m) 570 C A N A D I A N J O U R N A L O F C H E M I S T R Y . V O L . 39, 1901 ACKNOWLEDGMENTS We gratefully acknowledge the support of the National Research Council , and one of us ( M . A . A . B ) expresses thanks for a scholarship received from C.S. I .R. (Pakistan) under the auspices of the Colombo Plan. REFERENCES 1. M . A. A. B E G and H. C. CLARK. Can. J. Chem. 38, 119 (1960). 2. M . A. A. B E G and H. C. CLARK. Can. J. Chem. This issue. 3. R. N. HASZELDINE and B. O. WEST. J. Chem. Soc. 3631 (1956). 4. R. N. HASZELDINE and B. O. WEST. J. Chem. Soc. 3880 (1957). 5. A. B. BURG and G. BRENDEL. J. Am. Chem. Soc. 80, 3198 (1958). 6. W. R. CULLEN. Can. J. Chem. 38, 445 (1960). 7. J. W. B. REESOR and G. F. WRIGHT. J. Org. Chem. 22, 385 (1957). 8. W. KUCHEN and H. BUCHWALD. Chem. Ber. 91, 2296 (1958). 9. P . R. BLOOMFIELD and K . PARVIN. Chem. & Ind. 541 (1959). 10. G. M . KOSOLAPOFF. Organophosphorus compounds. John Wiley & Sons, Inc., New York. 1950. p. 70. 11. H. J. EMELEUS, R. N . HASZELDINE, and R. C. PAUL. J. Chem. Soc. 563 (1955). 12. G. M . KOSOLAPOFF. Organophosphorus compounds. John Wiley & Sons, Inc., New York. 1950. p. 137. 13. L . W. DAASCH and D . C. SMITH. Anal. Chem. 23, 853 (1957). 14. F. W. BENNETT, H. J. EMELEUS, and R. N . HASZELDINE. J. Chem. Soc. 3598 (1954). 15. B. BUCHNER and L . B. LOCKHART. J. Am. Chem. Soc. 73, 755 (1951). 16. A. MICHAELIS. Chem. Ber. 7, 6 (1874). 17. A. MICHAELIS. Ann. 265, 181 (1876). 18. T. WEIL, B. PRIJS, and H. ERLENMEYER. Helv. Chim. Acta, 35, 616 (1952). 19. A. MICHAELIS and H. KOHLER. Chem. Ber. 10, 807 (1877). 

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