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Conformational studies of some ditertiary arsine chelate complexes Ward, John Edward Henry 1972

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CONFORMATIONAL STUDIES OF SOME DITERTIARY ARSINE CHELATE COMPLEXES BY JOHN EDWARD HENRY WARD B.Sc. (Hons.), University of Alberta, 1968 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of CHEMISTRY We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA June, 1972 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . ) Department The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada - i i -ABSTRACT Several new ditertiary arsines, (CH^ ) 2ASCR.1R2CH2AS (CH^ ) 2 (R1 = Si(CH 3) 3, SiCl 3, F, CN, CI; R2 = H and \ = &2 = F ) a n d ^ C H3^2 A s C F H C F2 A' S ^ CH3^2 w e r e P r eP a r ed by the addition of tetramethyl-diarsine to an appropriately substituted olefin. When these ligands were reacted with Group VI hexacarbonyls or pentacarbonylmanganese halides, complexes were frequently obtained which contained a five-membered chelate ring. The nuclear magnetic resonance parameters derived from high resolution spectra of the ditertiary arsines and their chelate complexes were qualitatively interpreted in terms of their rotational and conformational behavior. In the complexes, a trimethylsilyl group was found to adopt an "equatorial" position on the two-carbon bridge of the chelate ring, while a fluorine substituent favored an "axial" orientation. Such extreme preferences were not indicated for cyano or chloro substituents. The chelate rings in the complexes of 1,2-bis(dimethylarsino)-l,1-difluoroethane probably undergo rapid conformational inversion. Changes in coupling constants due to transition metal variations in the chelate complexes were rationalized by a qualitative geometrical approach. However, the effects of substituting the arsenic atoms by phosphorus donor atoms could not be predicted by similar arguments. Nevertheless, variations in solvent, temperature, donor atoms, metal atoms, and their substituents did not drastically alter the conformations of the chelate rings. Apparently, the rotational behavior of the neat ditertiary arsines is partially dictated by the "bulky" dimethylarsino substituents. - i i i -TABLE OF CONTENTS Page CHAPTER 1. INTRODUCTION 1 I . Chemical I n v e s t i g a t i o n s 4 I I . T h e o r e t i c a l Studies 5 I I I . C r y s t a l l o g r a p h i c Determinations 7 IV. C i r c u l a r Dichroism Studies 8 V. I n f r a r e d Studies 8 VI. Nuclear Magnetic Resonance I n v e s t i g a t i o n s 8 A. Ethylenediamine Chelate Complexes 9 B. Propylenediamine Chelate Complexes 10 C. Butylenediamine Chelate Complexes 12 D. N-Substituted Diamine Chelate Complexes .... 13 V I I . This work 14 CHAPTER 2. EXPERIMENTAL 17 I. General Techniques 17 I I . S t a r t i n g M a t e r i a l s 19 I I I . P r e p a r a t i o n of the New D i t e r t i a r y A rsines 20 IV. P r e p a r a t i o n of the New Chelate Complexes 22 - i v -Page CHAPTER 3. RESULTS: CHARACTERIZATION AND MECHANISM 26 I. D i t e r t i a r y A r s i n e s 26 A. P r e p a r a t i v e Methods 26 B. A n a l y t i c a l R e s u l t s 29 C. I n f r a r e d Spectra JJ-D. Reaction Mechanisms 31 I I . Chelate Complexes 35 A. P r e p a r a t i v e Methods 35 B. A n a l y t i c a l Results 3 8 C. I n f r a r e d Spectra 41 D. Reaction Mechanisms 50 CHAPTER 4. NUCLEAR MAGNETIC RESONANCE RESULTS 55 I . New D i t e r t i a r y A rsines 55 I I . Chelate Complexes 63 CHAPTER 5. CONFORMATIONAL DISCUSSION 89 1. I n t r o d u c t i o n 89 A. L i m i t a t i o n s 89 B. D i h e d r a l Angle R e l a t i o n s h i p s 91 C. Chemical S h i f t s and Conformations 94 - V -Page I I . Chelate Complexes 95 A. Chelate Ring Conformations and V i c i n a l Coupling Constants 95 B. Chelate Ring Conformations and Chemical S h i f t s 100 C. Chelate Ring Conformations and the A r s e n i c -Methyl Groups 101 D. A l t e r a t i o n s i n the Geminal ^H-^H Coupling Constants 102 E. P e r t u r b a t i o n s and T h e i r E f f e c t on Chelate Ring Conformations 102 1. Solvent Changes 103 2. T r a n s i t i o n Metal V a r i a t i o n s 104 3. Donor Atom A l t e r a t i o n s 114 4. Halogen Substituent Changes 114 5. Temperature V a r i a t i o n s 115 F. D i p o l a r E f f e c t s 118 G. Analogous Systems 118 H. C r y s t a l l o g r a p h i c Results 119 I I I . D i t e r t i a r y A rsines 121 IV. Summary 122 BIBLIOGRAPHY 124 - v i -LIST OF FIGURES Figure Page 1 The i n f r a r e d spectrum of (CH 3) 2AsCH(CN) CH 2As ( C H ^ . . . 33 2 The carbonyl i n f r a r e d s p e c t r a of (CH 3) 2AsCHFCF 2~ A s ( C H 3 ) 2 C r ( C 0 ) A and (CH3> AsCF 2CH As(CH 3> Mn(CO) 3Br.. 44 3 Normal modes of C-0 s t r e t c h i n g v i b r a t i o n s f o r isomers of M n ( C 0 ) 3 ( L — L ) X 49 4 P a r t i a l "hi NMR spectrum (100 MHz) of neat ( C H ^ A s -C H ( S i ( C H 3 ) 3 ) C H 2 A s ( C H 3 ) 2 57 5 P a r t i a l *H NMR spectrum (100 MHz) of neat (CH 3) 2AsCH-( S i C l 3 ) C H 2 A s ( C H 3 ) 2 59 6 P a r t i a l 1H NMR spectrum (100 MHz) of neat (CH 3) 2AsCF 2~ CH 2As(CH 3) 2 62 7 1H NMR spectrum (100 MHz) of (CH 3) 2AsCH(Si(CH 3) 3>-CH 2As(CH 3) 2Cr(CO) 4 66 8 1H NMR s p e c t r a (100 MHz) of (CH ) ^ sCHFCH^s (CH3> 2 ~ C r ( C 0 ) 4 68 9 Expansion of the ^H NMR resonances of the methyl groups of (CH 3) 2AsCHFCH 2As(CH 3) 2Cr(CO) 4 69 10 P a r t i a l hi NMR spectrum (100 MHz) of (CH 3> 2PCHFCF 2~ P ( C H 3 ) 2 C r ( C O ) 4 71 11 P a r t i a l 1H NMR s p e c t r a (100 MHz) of (CH ) 2AsCH 2CF 2" As(CH 3) 2Mn(CO) 3Br 73 12 1 9 F NMR spectrum (94.077 MHz) of (CH3> 2AsCH 2CF 2" As(CH ) Mn(C0) 3Br 74 13 P a r t i a l 1H NMR s p e c t r a (100 MHz and 220 MHz) of (CH 3) 2AsCH(CN)CH 2As(CH 3) 2Cr(C0) 4 76 - v i i -LIST OF TABLES Table Page I S u p p l i e r s of the Chemicals Purchased 19 I I The New D i t e r t i a r y A r s i n e s 21 I I I Chelate Complexes Synthesized 25 IV A n a l y t i c a l and P r e p a r a t i v e Data f o r the New D i t e r t i a r y A r s i n e Ligands 30 V I n f r a r e d Absorption Frequencies f o r the D i t e r t i a r y A r s i n e s 32 VI A n a l y t i c a l and P r e p a r a t i v e Data f o r the New Chelate Complexes 39 VII Bond Lengths and Valency Angles i n (CH.^ ) 2ECRR* CF 2~ E(CH 3) 2M(CO) 4 Complexes 4 2 V I I I Carbonyl I n f r a r e d S t r e t c h i n g Frequencies f o r the Chelate Complexes 43 IX Carbonyl I n f r a r e d S t r e t c h i n g Frequencies of Some Hydrocarbon-bridged Chelate Complexes 45 X INDOR Responses of ( C H 3 ) 2 A s C H ( S i C l 3 ) C H 2 A s ( C H 3 ) 2 60 XI F i r s t - o r d e r Chemical S h i f t s f o r the Neat Ligands .... 64 XII F i r s t - o r d e r Coupling Constants f o r the Neat Ligands.. 65 X I I I F i r s t - o r d e r Chemical S h i f t s f o r the Chelate Complexes 78 XIV F i r s t - o r d e r Coupling Constants f o r the Chelate Complexes 83 XV F i r s t - o r d e r Phosphorus Coupling Constants f o r the Chelate Complexes 88 - v i i i -Table Page XVI F i r s t - o r d e r Coupling Constants f o r the T r i m e t h y l s i l y l Chelate Complexes 1 0 6 XVII Experimental and P r e d i c t e d Changes i n V i c i n a l Coupling Constants w i t h Changes i n the T r a n s i t i o n Metal HO XVIII F i r s t - o r d e r Coupling Constants f o r the D i f l u o r o Chelate Complexes 113 - ix ACKNOWLEDGEMENTS I am extremely g r a t e f u l to Dr. W.R. C u l l e n f o r the many frank and honest d i s c u s s i o n s during the course of t h i s work. Of a l l my experiences at U.B.C., I value these most h i g h l y . I a l s o appreciate the c o n t r i b u t i o n s of Dr. L.D. H a l l to t h i s work. I admire h i s i n s i g h t and understanding of conformational and NMR problems. F i n a l l y , I wish to acknowledge the help r e c e i v e d from the students of Dr. C u l l e n and Dr. H a l l : Dave Harbourne, Mark Waldman, John Crow, Ross Leeder, Greg Spendjian, Roland Pomeroy, Bob Johnson, Paul S t e i n e r , Ben Malcolm, and Ian Armitage. I a l s o wish to remember Roland Burton, P h y l l i s Watson, Hans Wyngaarden, Peter Borda, Ben C l i f f o r d , and Greg Snider. S p e c i a l thanks are extended to Beverly C u l l e n , R i c and Lynda S p r a t l e y , and my w i f e , Marney. - x -We are the other people, We are the other people, You're the other people too. F. Zappa - 1 -CHAPTER 1 INTRODUCTION The stereochemical aspects of chelate r i n g s are the subject of 1-5 6 s e v e r a l e x c e l l e n t reviews and books. Most of the research i n t h i s area has been performed on the t r a n s i t i o n metal complexes of diamines and amino acids although there are a few reports of conformational 7 8 stud i e s on chelate complexes w i t h sulphur donor atoms. ' This t h e s i s examines the conformational behavior of some d i t e r t i a r y a r s i n e chelate d e r i v a t i v e s of t r a n s i t i o n metal carbonyls, a t o p i c which has not been e x t e n s i v e l y considered before. Thus, of n e c e s s i t y , the i n t r o d u c t o r y d i s c u s s i o n i s r e s t r i c t e d to the experimental and t h e o r e t i c a l work on r e l a t e d diamine chelate complexes. Before 1933 i t was assumed that five-membered diamine chelate 1 9 rin g s were planar. However, i n that year i t was proposed that the bis(e t h y l e n e d i a m i n e ) p l a t i n u m ( I I ) c a t i o n could e x i s t i n four p o s s i b l e forms: A ( l ) , completely p l a n a r ; A ( 2 ) , c h a i r form; A(3 ) , trough form; and A ( 4 ) , angular form. I - 2 -(1) H 2 H 2 C - N H 2 C - N >: / H 2 N - C H 2 H 2 N - C H 2 (2) H 2 C H 2 C H -O I N ' C H . (4) F o l l o w i n g t h i s r e p o r t , Theilacker"*"^ noted that the chelate r i n g s themselves could be puckered. This avoids an e c l i p s e d conforma-t i o n of the hydrogen atoms and i s represented i n 13 and the Newman p r o j e c t i o n C. I f the chelate r i n g i s puckered, s u b s t i t u e n t s on the - 3 -atoms of the five-membered r i n g e x i s t i n " a x i a l " or " e q u a t o r i a l " o r i e n t a t i o n s . Bulky s u b s t i t u e n t s (R) on the ethane bridge carbon atoms were expected to show a preference f o r the " e q u a t o r i a l " p o s i t i o n on the chelate r i n g as i n D ( l ) r a t h e r than D(2). A consequence of the favored staggered conformations of the chelated ethylenediamine (en) molecule i s that such complexes have two enantiomeric forms, denoted 6 and A.,11 as i n E ( l ) and E(2). C (1) (2) This was f i r s t r e a l i z e d by Kobayashi and again noted i n 1953. However, an attempt to resolve the mono(ethylenediamine) c a t i o n [ C o ( e n ) ( N H 3 ) 4 ] 3 + f a i l e d , probably because of the r a p i d i n v e r s i o n of 14 the chelate r i n g between the S and X conformers. - 4 -On the other hand, compounds c o n t a i n i n g unsymmetrically s u b s t i t u t e d diamine l i g a n d s , such as propylenediamine (pn), are known to e x i s t i n two p r e f e r r e d enantiomeric forms i n which the methyl groups adopt " e q u a t o r i a l " o r i e n t a t i o n s "*""* as i n D( l ) . I. Chemical I n v e s t i g a t i o n s Considerable i n t e r e s t has centered on the i n t r a m o l e c u l a r i n t e r a c t i o n s of diamine chelate r i n g s . Numerous b i s - and t r i s - d i a m i n e chelate complexes have been prepared and examined by a v a r i e t y of methods. In the octahedral t r i s - c h e l a t e complexes, each puckered five-membered r i n g can adopt a conformation w i t h the carbon-carbon bond p a r a l l e l to the t h r e e - f o l d a x i s of the molecule as i n F ( l ) , or w i t h the carbon-carbon bond perpendicular to the t h r e e f o l d a x i s as i n F ( 2 ) . Moreover, F A888 AXXX these complexes e x i s t as o p t i c a l isomers d i f f e r i n g i n the c o n f i g u r a t i o n of the three chelate r i n g s about the metal i o n , designated as A or A, - 5 -according to the r e l a t i v e h e l i c i t y of the chelate r i n g s . 1 1 3+ In the [ t r i s ( e t h y l e n e d i a m i n e ) c o b a l t ] s p e c i e s , i t was thought 16—18 that form F ( l ) f o r a A c o n f i g u r a t i o n i s most p r e f e r r e d . This conclusion i s based on experiments i n which e q u i l i b r i u m mixtures of c o b a l t ( I I I ) t r i s - d i a m i n e compounds co n t a i n i n g the ions 3+ [ C o ( e n ) x ( p n ) 3 _ x ] (x = 1-3) were separated by paper chromatography and t h e i r r e l a t i v e r a t i o s determined s p e c t r o p h o t o m e t r i c a l l y . The methyl groups f i x the conformations of the propylene diamine l i g a n d , and t h i s , together w i t h the other evidence, enabled the r e l a t i v e s t a b i l i t i e s 19 of a l l isomers to be estimated. However, Sudmeier and Blackmer have considered these r e p o r t s , and w i t h t h e i r oxm NMR evidence concluded 3+ that the most abundant [ t r i s ( e t h y l e n e d i a m i n e ) c o b a l t ] isomer contains two chelate r i n g s i n the " p a r a l l e l " conformation as i n F ( l ) , and the remaining one i n the "perpendicular" o r i e n t a t i o n as i n F ( 2 ) , that i s A ( 6 6 X ) . In view of these and other r e s u l t s i t can be concluded that chemical s t u d i e s on the conformations of diamine chelate r i n g s have met w i t h only l i m i t e d success. I I . T h e o r e t i c a l Studies The theory that the five-membered chelate r i n g i s puckered was 20 elaborated by Mathieu. He derived the d i f f e r e n c e s i n non-bonded i n t e r a c t i o n s between the methyl groups i n the diastereoisomers of c i s -[Co(d-pn)]» i n an attempt to e x p l a i n why one isomer was formed p r e f e r e n t i a l l y . - 6 -2 1 In their classic paper, Corey and Bailar calculated the preferred conformations of an ethylenediamine chelate ring by a vector analysis method. They concluded that the chelate ring is significantly puckered, characterized by the dihedral angle <j> = 4 8 . 8 ° as in C. It was suggested that the methyl group in propylenediamine chelate complexes would favor an "equatorial" orientation. In addition, they proposed that this staggered geometry would occur for ethylenediamine chelate rings in octahedral, tetrahedral, and square planar complexes. Recently, more sophisticated calculations on the conformations * u i . • • • -. 2 2 - 2 4 A i 2 5 , 2 6 . . of chelate rings in simple and complex systems have been 2 2 - 2 4 attempted. Gollogly and coworkers have varied the molecular geometry of ethylenediamine type complexes in such a way as to minimize the sum of the various conformational energy terms. These studies indicate that a puckered five-membered chelate ring is very flexible and has a wide range of conformations of almost equal energy, including 2 1 unsymmetric ones not considered by Corey and Bailar, whose original view held that the ethylenediamine chelate ring is limited to two mirror image symmetrical conformations. From theoretical investigations of propylenediamine chelate 22 complexes, Gollogly and Hawkins concluded that the energy separation between the conformer with the "axial" methyl group and that with a preferred "equatorial" group is 0-3 kcal/mol. It was also shown that conformational distortion is the most effective way of alleviating the van der Waals interactions between the methyl substituent and the cis-"axial" substituent in octahedral chelate complexes. 24 In a recent paper in this series, these authors varied the metal-- 7 -n i t r o g e n bond lengths i n a h y p o t h e t i c a l ethylenediamine c h e l a t e r i n g . This i n v e s t i g a t i o n , which a l s o revealed that a v a r i e t y of the ch e l a t e r i n g geometries were almost e q u i v a l e n t i n energy, w i l l be discussed i n d e t a i l i n Chapter 5 of t h i s t h e s i s . III. C r y s t a l l o g r a p h i c Determinations The puckered arrangement i n the diamine chelate r i n g was f i r s t 27 28 v e r i f i e d by Scouloudi and C a r l i s l e . ' Th e i r examination of the X-ray data obtained from [Cu(en)^] [HgCSCN)^] showed th a t the chelate r i n g s have an asymmetric-skew c o n f i g u r a t i o n , w i t h one carbon atom o o 0.35 A ab ove the CuNN plane and the other 0.55 A below i t . The li g a n d s i n the complex adopt the s t a t i s t i c a l l y p r e f e r r e d 6X c o n f i g u r a -t i o n , which i s common i n many other t r a n s - b i s ( e t h y l e n e d i a m i n e ) c h e l a t e complexes. However, the observed range of asymmetric conformations suggests that the energy d i f f e r e n c e s between the che l a t e r i n g conformations are r e l a t i v e l y s m a l l , as proposed by G o l l o g l y and co-22-24 workers. X-ray r e s u l t s have a l s o been obtained from many stu d i e s 29—32 of t r i s ( e t h y l e n e d i a m i n e ) chelate complexes, r e v e a l i n g a l l the p o s s i b l e combinations of chelate r i n g conformations, 666, 66A, 6XX , and XXX, f o r a A c o n f i g u r a t i o n . Unfortunately X-ray c r y s t a l l o g r a p h i c determinations have shown that the conformations of the chelate r i n g s i n the s o l i d s t a t e are i n f l u e n c e d by the p e r t u r b i n g e f f e c t s of i n t e r m o l e c u l a r i n t e r a c t i o n s such as hydrogen bonding and c r y s t a l packing v a r i a t i o n s . Therefore, these systems cannot always be expected to behave i n s o l u t i o n as they do i n the s o l i d s t a t e . - 8 -IV. Circular Dichroism Studies The optical effects of chelate rings are manifest in the central transition metal or metal ion of chelate complexes. Although i t is difficult to determine the exact sources of the rotational strength in these systems, i t seems that the degree of puckering is the most 33 important effect. This assumption has been used to interpret much of the CD data obtained from propylenediamine chelate complexes of 3A 36 cobalt. Nevertheless, this technique has not been particularly fruitful in the determination of chelate ring conformations. V. Infrared Studies Infrared spectroscopy has been used rarely in the determination of chelate ring conformations.^ Such studies have been hampered by the low solubility of many transition metal chelate complexes in suitable solvents. Frequently i t was necessary to perform infrared experiments on samples in the solid state and like the X-ray determinations, the results obtained from these investigations must be interpreted with caution, since crystal packing effects and intermolecular hydrogen bonding can complicate the spectra. VI. Nuclear Magnetic Resonance (NMR) Investigations Prior to 1968, NMR provided l i t t l e information about the actual conformations of five-membered diamine chelate rings.^ Since that time - 9 -• * - ' - i , * «-• * *• 15,19,46-69 , a v a r i e t y of reports on the conformatxons of f i v e - and 37-45 six-membered r i n g s of mono-, b i s - , and t r i s - c h e l a t e complexes have appeared. The f o l l o w i n g summarizes the NMR s p e c t r o s c o p i c i n v e s t i g a t i o n s made on some five-membered r i n g diamine c h e l a t e complexes. A. Ethylenediamine Chelate Complexes A s i n g l e ethylenediamine chelate r i n g undergoes r a p i d conformational 46 i n v e r s i o n according to a report by Bramley and Johnson. These 1 3+ workers examined H NMR s p e c t r a of [Co(en)(NH^)^] and showed that the peak corresponding to the four methylene protons was broadened 59 by coupling w i t h the Co nucleus, the NH protons, and r a p i d r e l a x a t i o n . Bis(ethylenediamine) chelate complexes have been s t u d i e d more 47-51 thoroughly, but a l s o w i t h l i t t l e success. None of these a r t i c l e s report NMR s p e c t r a which could be completely solved by computer a n a l y s i s , and few conclusions were drawn from the chemical s h i f t data obtained. However, i t seems l i k e l y that the chelate r i n g s i n t h i s type of complex undergo conformational i n v e r s i o n as do the r i n g s i n the mono(ethylenediamine) complexes. 52-54 The t r i s ( e t h y l e n e d i a m i n e ) chelate complexes of r u t h e n i u m ( I I ) , p l a t i n u m ( I V ) , 5 4 ' 5 5 n i c k e l ( I I ) , 6 1 r h o d i u m ( I I I ) ) 5 9 ' 6 0 ' 6 2 i r i d i u m ( I I I ) , 6 2 19 54 56—59 and c o b a l t ( I I I ) ' ' have been the subject of many NMR 4 62 i n v e s t i g a t i o n s ' and the behavior of the c h e l a t e r i n g s i n these complexes i s now b e t t e r understood. The l i g a n d s r a p i d l y i n v e r t between the 6 and X conformers. Chemical s h i f t s , c o upling constants, and the temperature dependence of contact s h i f t s , i n d i c a t e that 60-75% of a l l - 10 -the l i g a n d s are i n the <S conformation f o r a A c o n f i g u r a t i o n . ^ ' ^ ' ^ The r e l a t i v e energies of the isomers l i k e l y are 66A < 666 ^ 6AA << AAA, f o r a A configuration.^»60 considerable d i f f e r e n c e s i n the NMR sp e c t r a of the complexes are a consequence of the l a r g e v a r i a t i o n s i n the chemical s h i f t separations between the " a x i a l " and " e q u a t o r i a l " 4 19 59 protons. ' By N d e u t e r a t i o n , Co decoupling, and/or by using a spectrometer w i t h a high f i e l d s t r e n g t h , many of the s p e c t r a could be s u f f i c i e n t l y r e s o l v e d to permit complete a n a l y s i s . No evidence was obtained f o r dynamic l i n e broadening or slow conformational i n v e r s i o n i n s o l u t i o n . B. Propylenediamine Chelate Complexes When the ethylenediamine l i g a n d i s replaced by propylenediamine, s i m i l a r r e s u l t s are obtained, except that the conformer i n which the methyl group adopts an " e q u a t o r i a l " p o s i t i o n i n the chelate r i n g i s p r e f e r r e d , r e s t r i c t i n g conformational i n v e r s i o n . For example, data obtained from the NMR spectrum of K[Co(CN)^(pn)] by using N d e u t e r a t i o n and homonuclear decoupling of the methyl r e s o n a n c e ^ confirmed that the methyl group occupies an " e q u a t o r i a l " o r i e n t a t i o n on the f i v e -1 1 membered chelate r i n g as i n J3, since the H- H coupling constants i n d i c a t e trans (J = 12.4 Hz), gauche ( J , =4.4 Hz), and trans -= gauche ' geminal (J = -12.4 Hz) p a i r s of protons. Very s i m i l a r values were geininal r J derived from the sp e c t r a of trans-bis(propylenediamine) complexes of platinum and palladium.''""' - 11 -H G H 3+ The spectrum of [Co(pn)(NH^)^] could not be solved due to the 3 extensive overlap of the methylene and methine proton resonances. Perhaps the use of decoupling experiments and a spectrometer which operates at a '''H resonant frequency of 220 or 251 MHz would s i m p l i f y the spectrum of t h i s compound. Chemical s h i f t arguments have enabled the assignments of the absolute c o n f i g u r a t i o n s of s e v e r a l propylenediamine chelate 63~65 63 complexes to be made. A study of the methyl and ethane b r i d g e 64 proton resonances i n Na[Co(pn)(oxalato) 2] showed d i s t i n c t chemical s h i f t and coupling constant d i f f e r e n c e s f o r the 6 and A c o n f i g u r a t i o n s . The isomer, found to correspond to the A absolute c o n f i g u r a t i o n , has an " a x i a l " geminal proton 0.11 ppm higher than the corresponding proton i n the or A isomer. The trans coupling constants of these " a x i a l " protons are a l s o d i f f e r e n t , being ca. 12 and 10 Hz r e s p e c t i v e l y . S i m i l a r r a t i o n a l e s were used to derive the absolute c o n f i g u r a t i o n s of tri s ( p r o p y l e n e d i a m i n e ) complexes of p l a t i n u m ( I V ) . ^ 54 Complete analyses were obtained f o r the s p e c t r a of r u t h e n i u m ( I I ) , 19 54 54 c o b a l t ( I I I ) , ' and platinum(IV) t r i s ( p r o p y l e n e d i a m i n e ) metal chelate complexes. A l l the parameters derived from these i n v e s t i g a t i o n s - 12 -agree w e l l w i t h the data.obtained from K [ C o ( C N ) ^ ( p n ) ] t h e methyl group thus p r e f e r s an " e q u a t o r i a l " o r i e n t a t i o n on the chelate r i n g s of tris(propylenediamine) complexes. C. Butylenediamine Chelate Complexes In t h e i r e x c e l l e n t paper on contact s h i f t i n v e s t i g a t i o n s of 66 nickel-butylenediamine chelate complexes, R e i l l e y and co-workers found that the meso isomer f r e e l y i n t e r c o n v e r t s between the 6 and A conformers as i n H. H On the other hand,in the racemic mixture,the conformer w i t h the two methyl groups i n an " e q u a t o r i a l " p o s i t i o n i s favored over the species w i t h the methyl s u b s t i t u e n t s i n an " a x i a l " o r i e n t a t i o n , as i n I_. - 13 -The authors were a l s o able to c a l c u l a t e the degree of puckering of the chelate r i n g , 72°, from the angular dependence of the h y p e r f i n e coupling constants. This d i h e d r a l angle v a r i e s from 52-61° according to c a l c u l a t i o n s based on the NMR s p e c t r a of ethylenediamine chelate 19 r i n g s i n tris(ethylenediamine) c o b a l t ( I I I ) complexes, w h i l e the angles 22 i n r e l a t e d compounds determined c r y s t a l l o g r a p h i c a l l y range from 43-53°. D. N-Substituted Diamine Chelate Complexes S u b s t i t u t i o n of the groups bonded to the n i t r o g e n donor atoms i n these chelate systems has provided s i g n i f i c a n t conformational data. 67 Haake and coworkers have measured the r a t e s of base c a t a l y z e d proton exchange at the n i t r o g e n atoms i n N,N'-dimethylethylenediamineplatinum(II) chelate complexes. I t was found that the r a t e of proton removal i s the l i m i t i n g f a c t o r on the r a t e of i n v e r s i o n at n i t r o g e n , which seems to depend on the trans l a b i l i z i n g e f f e c t of the other s u b s t i t u e n t s on the platinum atom. A b i s chelate cobalt complex of t h i s l i g a n d , r a c - t r a n s -[Co((CH 3)HNCH 2CH 2NH(CH 3)) 2(N0 2) 2] + has been r e c e n t l y reported to y i e l d an AA'BB' NMR spectrum which was s o l v e d , a f f o r d i n g parameters which are c o n s i s t e n t w i t h the chelate r i n g s i n gauche conformations (J = & & trans 68 10.7 Hz, J , = 4.3 and 4.6 Hz), gauche 69 F i n a l l y , v a r i a b l e temperature i n v e s t i g a t i o n s by Ho and R e i l l y r e v e a l that N - a l k y l s u b s t i t u e n t s p r e f e r the " e q u a t o r i a l " p o s i t i o n i n the f i v e -membered ethylenediamine r i n g . For example, the N methyl group i n 2+ [Ni(H 20) 4((CH 3)HNCH 2CH 2N(CH 3)H)] was found to favor the " e q u a t o r i a l " - I m -p o s i t i o n on the chelate r i n g by 0.43 kcal/mol. Few of these NMR i n v e s t i g a t i o n s j u s t described y i e l d e d coupling constant i n f o r m a t i o n of conformational s i g n i f i c a n c e . The general l a c k of t h e i r success can be a s c r i b e d to a number of causes, i n c l u d i n g the use of l i g a n d s which are b a s i c a l l y u n s u i t a b l e f o r NMR a n a l y s i s . For example, the s p e c t r a derived from the ethylenediamine d e r i v a t i v e s 4 described by B e a t t i e were solved only a f t e r a concerted e f f o r t by s e v e r a l research groups over a p e r i o d of four years. At b e s t , these l i g a n d s are expected to y i e l d AA'BB' type NMR s p e c t r a , which are r e l a t i v e l y d i f f i c u l t to s o l v e . The c l o s e p r o x i m i t y of the A and B resonances i s al s o a hindrance; f o r example, the c o b a l t - t r i s ( e t h y l e n e -diamine) complex y i e l d e d an NMR spectrum which was solved only when 59 t h i s s e paration was increased by using a 251 MHz spectrometer, w i t h Co decoupling. V I I . This T'Jork In t h i s study, l i g a n d s were d e l i b e r a t e l y chosen so that the NMR spect r a of t h e i r c h e l a t e complexes would be s u i t a b l e f o r uncomplicated s p e c t r a l a n a l y s i s . Since previous i n v e s t i g a t i o n s ^ ' ^ had demonstrated 19 1 that F NMR parameters are g e n e r a l l y more s e n s i t i v e than H parameters to changes i n stereochemical environment, s e v e r a l s p e c i a l l y f l u o r i n a t e d l i g a n d s were i n c l u d e d . For s i m p l i c i t y and s y n t h e t i c convenience,1,2-bis(dimethylarsino) ethane chelate d e r i v a t i v e s of metal carbonyls were chosen f o r t h i s study. Several new unsymmetrically s u b s t i t u t e d d i t e r t i a r y a r s i n e s - 15 -were obtained by r e a c t i n g t e t r a m e t h y l d i a r s i n e w i t h an a p p r o p r i a t e l y s u b s t i t u t e d o l e f i n . For NMR i n v e s t i g a t i o n s , the chelate complexes of these l i g a n d s have d i s t i n c t advantages over those complexes examined by other workers. Considerable chemical s h i f t d i f f e r e n c e s between the v a r i o u s protons on the chelate r i n g can be brought about by appropriate s u b s t i t u t i o n s of the ethane bridge protons. When these s u b s t i t u e n t s do not have nuclear s p i n s , simpler s p e c t r a w i l l be obtained. The use of a r s e n i c donor atoms i s a l s o important, f o r these do not s i g n i f i c a n t l y complicate the s p e c t r a of the v i c i n a l carbon s u b s t i t u e n t s by s p i n - s p i n i n t e r a c t i o n s . Once the d i t e r t i a r y a r s i n e l i g a n d s have been obtained, they can be used to prepare complexes i n which the b a s i c c h e l a t e r i n g framework can be a l t e r e d by a p p r o p r i a t e l y v a r y i n g the s u b s t i t u e n t s on the two-carbon b r i d g e , the donor atoms, the t r a n s i t i o n metal, or the s u b s t i t u e n t s on the t r a n s i t i o n metal. Thus, by the NMR method, i t should be p o s s i b l e to s y s t e m a t i c a l l y examine the conformational, s t e r i c , and e l e c t r o n i c r e l a t i o n s h i p s i n a s e r i e s of r e l a t e d c h e l a t e complexes. Chapter 2 of t h i s t h e s i s describes the p r e p a r a t i o n of the new d i t e r t i a r y a r s i n e s , which are obtained by the p h o t o l y t i c a d d i t i o n of t e t r a m e t h y l d i a r s i n e to s u b s t i t u t e d o l e f i n s . I t a l s o describes t h e i r c h e l a t e complexes, u s u a l l y synthesized by the s u b s t i t u t i o n of carbonyl groups by the ligands on s u i t a b l e metal carbonyl s u b s t r a t e s . - 16 -Chapter 3 presents the a n a l y t i c a l r e s u l t s obtained f o r these compounds and considers the p o s s i b l e mechanisms by which they may be formed. Chapter 4 i s devoted to a p r e s e n t a t i o n of the r e s u l t s obtained from the NMR s t u d i e s of the new d i t e r t i a r y a r s i n e s and t h e i r chelate complexes. F i n a l l y , Chapter 5 i n c l u d e s i n t e r p r e t a t i o n s of the NMR r e s u l t s i n terms of conformational and r o t a t i o n a l behavior of the complexes and l i g a n d s . The e f f e c t s of s e v e r a l p e r t u r b a t i o n s i n the che l a t e r i n g systems are a l s o described and discu s s e d , along w i t h comparisons w i t h the conformations derived from X-ray s t u d i e s of some of the chelate complexes. - 17 -CHAPTER 2 EXPERIMENTAL This chapter considers the s y n t h e t i c procedures used i n preparing the new d i t e r t i a r y a r s i n e ligands and t h e i r c helate complexes. The methods by which the p h y s i c a l , a n a l y t i c a l , and sp e c t r o s c o p i c p r o p e r t i e s of these compounds were obtained w i l l a l s o be described. I. General Techniques A l l r e a c t i o n s , u n l e s s otherwise noted, were c a r r i e d out i n sealed Pyrex Carius tubes. Decomposition of a i r - s e n s i t i v e s t a r t i n g m a t e r i a l s and products was avoided by working i n a n i t r o g e n atmosphere. V o l a t i l e compounds were manipulated i n a standard vacuum system, w h i l e i n v o l a t i l e l i q u i d samples were handled by s y r i n g e techniques. A 72 Swagelok f i t t i n g equipped w i t h an i n j e c t i o n gasket enabled the t r a n s f e r of a i r - s e n s i t i v e , i n v o l a t i l e l i q u i d s to the Carius tubes. Microanalyses were performed by Mr. Peter Borda of t h i s Department, or by the Schwarzkopf M i c r o a n a l y t i c a l Laboratory, Woodside, N.Y. Uncorrected m e l t i n g p o i n t s were determined w i t h a Gallenkamp melt i n g p o i n t apparatus. . Mass s p e c t r a were obtained w i t h an AEI MS-9 instrument w i t h d i r e c t i n t r o d u c t i o n of s o l i d samples. - 18 -I n f r a r e d s p e c t r a were measured on a Perkin-Elmer 457 spectrometer and were c a l i b r a t e d against polystyrene and/or cyclohexane. Spectra of the new d i t e r t i a r y a r s i n e l i g a n d s were obtained from l i q u i d f i l m s between potassium bromide or sodium c h l o r i d e p l a t e s . The i n f r a r e d s p e c t r a of the complexes were run on cyclohexane s o l u t i o n s i n calcium f l u o r i d e or potassium bromide c e l l s . The NMR s p e c t r a were obtained using a Va r i a n A-60, T-60, XL-100 or an e x t e n s i v e l y m o d i f i e d HA-100 spectrometer. The m a j o r i t y of these s p e c t r a were recorded i n the frequency sweep mode on c a r e f u l l y c a l i b r a t e d charts using the HA-100 instrument. A l l "4l chemical s h i f t s were recorded w i t h t e t r a m e t h y l s i l a n e as the i n t e r n a l reference. For 19 F measurements, the Var i a n HA-100 spectrometer was tuned to 94.07 MHz and ca. 20% of tr i c h l o r o f l u o r o m e t h a n e was used as the i n t e r n a l reference f o r chemical s h i f t c a l i b r a t i o n . Heteronuclear decoupling experiments w i t h noise modulation used instrumentation already 73 7 A 75 76 described i n the l i t e r a t u r e . ' The s p i n - t i c k l i n g and INDOR experiments have a l s o been described. Temperature s t u d i e s were c a r r i e d out on the Varian HA-100 spectrometer using a V a r i a n V-4343 v a r i a b l e temperature u n i t which was c a l i b r a t e d against ethylene g l y c o l and methanol samples. Computer analyses of the NMR s p e c t r a were obtained w i t h an IBM 360-67 computer and a modified v e r s i o n of the LA0C00N I I I program. 7 7 - 19 -I I . S t a r t i n g M a t e r i a l s The chemicals i n Table I were obtained commercially and used as rece i v e d . Table I . S u p p l i e r s of the Chemicals Purchased Chemical S u p p l i e r d i m e t h y l a r s i n i c a c i d chromium hexacarbonyl molybdenum hexacarbonyl tungsten hexacarbonyl dimanganese decacarbonyl 2,5-norbornadienetetra-carb onylmolyb denum deuterochloroform d,-benzene 6 d,-acetone 6 1,1-difluoroethylene t r i f l u o r o e t h y l e n e v i n y l f l u o r i d e v i n y l c h l o r i d e t r i m e t h y l v i n y l s i l a n e t r i c h l o r o v i n y l s i l a n e a c r y l o n i t r i l e t r i b u t y l p h o s p h i n e F i s h e r S c i e n t i f i c Co. Strem Chemicals Inc. Strem Chemicals Inc. Strem Chemicals Inc. Pressure Chemical Co. Strem Chemicals Inc. Merck, Sharp, and Dohme of Canada Ltd. Merck, Sharp, and Dohme of Canada L t d . S t o h l e r Isotope Chemicals Matheson of Canada L t d . P e n i n s u l a r Chem Research, Inc. Matheson of Canada L t d . Matheson of Canada L t d . P i e r c e Chemical Co. Pi e r c e Chemical Co. A l d r i c h Chemical Co. Columbia Organic Chemicals Co., Inc. - 20 -Tetrame t h y l d i a r s i n e was prepared by the re d u c t i o n of dimethyl-78 a r s i n i c a c i d i n 2M h y d r o c h l o r i c a c i d w i t h hypophosphorous a c i d ; the d i a r s i n e was used without f u r t h e r p u r i f i c a t i o n . Tetramethyldiphosphine was obtained v i a the sulphur exchange r e a c t i o n of tetramethyldiphosphine d i s u l p h i d e , 7 ^ ' ^ w i t h t r i b u t y l p h o s p h i n e . 7 ^ Pentacarbonylmanganese c h l o r i d e was obtained by bubbling c h l o r i n e gas through a s o l u t i o n of dimanganese decacarbonyl i n carbon 81 t e t r a c h l o r i d e at 0°. A s o l u t i o n of bromine i n carbon t e t r a c h l o r i d e added to dimanganese decacarbonyl i n the same solvent y i e l d e d penta-82 carbonylmanganese bromide. Pentacarbonylmanganese i o d i d e vas made by heating a mixture of i o d i n e and dimanganese decacarbonyl i n a 83 sealed Carius tube at 150° f o r 1.5 h. Before use these manganese complexes were sublimed and t h e i r p u r i t y checked by i n f r a r e d spectroscopy. III. P r e p a r a t i o n of the New D i t e r t i a r y A r s i n e s The f o l l o w i n g s y n t h e s i s i s a t y p i c a l example of the methods used i n preparing the new d i t e r t i a r y a r s i n e l i g a n d s . P r e p a r a t i o n of 1 , 2 - b i s ( d i m e t h y l a r s i n o ) - l - f l u o r o e t h a n e _3 A Carius tube (70 ml capacity) was evacuated, cooled i n l i q u i d n i t r o g e n , and charged w i t h t e t r a m e t h y l d i a r s i n e (5.0 ml, 7.3 g, 35 mmol ). Excess v i n y l f l u o r i d e (29 g, 64 mmol) was condensed i n t o the tube which was then sealed. The tube was i r r a d i a t e d f o r 48 h w i t h a 200 - 21 -watt Hanovia u l t r a v i o l e t lamp placed at a di s t a n c e of ca. 20 cm. The tube was continuously shaken, and cooled w i t h a stream of a i r . When the r e a c t i o n was completed, the tube was cooled i n l i q u i d n i t r o g e n , opened to a vacuum system, and the v o l a t i l e contents removed, l e a v i n g a residue (7.2 g, 82%) of the c o l o r l e s s , a i r - s e n s i t i v e , l i q u i d product, l , 2 - b i s ( d i m e t h y l a r s i n o ) - l - f l u o r o e t h a n e J3. By s i m i l a r procedures, a l l the new d i t e r t i a r y a r s i n e s l i s t e d i n Table I I were prepared. In those cases where the o l e f i n was a non-v o l a t i l e l i q u i d i t was syringed i n t o the Carius tube. Table I I . The New D i t e r t i a r y A r s i n e s 3 ( C H 3 ) 2 A s C ( l ) ( l ' ) C ( 2 ) ( 2 ' ) A s ( C H 3 ) 2 2 1 3 2 1 = S i ( C H 3 ) 3 ; 1', 2, and 2' = 1 = S i C l 3 ; 1', 2, and 2' = H 1 = F; 1', 2, and 2' = H H 4 1 = H; 1', 2, and 2* = F 5 1 and 1' = H; 2 and 2' = F r 6 1 = C l ; 1', 2, and 2' = H 7 1 = CN; 1', 2, and 2 * = H The diagram i s not intended to represent a f i x e d rotamer i n s o l u t i o n . - 22 -1,2-Bis(dimethylphosphino)-1,1,2-trifluoroethane was prepared by the p h o t o l y t i c a d d i t i o n of tetramethyldiphosphine to t r i f l u o r o -84 ethylene f o l l o w i n g the procedure of Haszeldine and coworkers. IV. P r e p a r a t i o n of the New Chelate Complexes The next three procedures represent the methods used to synthesize the d i t e r t i a r y a r s i n e and d i t e r t i a r y phosphine metal carbonyl chelate d e r i v a t i v e s . A. P r e p a r a t i o n of l , 2 - b i s ( d i m e t h y l a r s i n o ) - l - f l u o r o e t h a n e t e t r a -carbonylchromium 12 A Carius tube was charged w i t h chromium hexacarbonyl (1.0 g, 5 mmol), evacuated, and cooled i n l i q u i d n i t r o g e n . The l i g a n d , 1,2-bis-( d i m e t h y l a r s i n o ) - l - f l u o r o e t h a n e j3, (1.0 g, 5 mmol) was added followed by sodium-dried benzene (5 ml). The tube was sealed, allowed to warm to room temperature and then heated to 140° f o r 14 h. A f t e r c o o l i n g i n l i q u i d n i t r o g e n , the Carius tube was opened and warmed to room temperature. The benzene was removed under reduced pressure and the o i l y residue t r i t u r a t e d w i t h 5 ml of l i g h t petroleum ether (b.p. 40-60°). The r e s u l t i n g y ellow s o l i d was t r e a t e d w i t h two more 5 ml p o r t i o n s of the same s o l v e n t , d r i e d under reduced pressure, and then vacuum sublimed (120°, 10 mm). This produced a pure sample of 1,2-bis(dimethyl-arsino)-1-fluoroethanetetracarbonylchromium 12 (0.75 g, 39%). - 2 3 -B. P r e p a r a t i o n of 1 , 2 - b i s ( d i m e t h y l a r s i n o ) - 1 - c y a n o e t h a n e t e t r a -carbonylmolybdenum 2J5 A 1 0 0 ml round-bottomed f l a s k equipped w i t h a magnetic s t i r r e r , n i t r o g e n i n l e t , and r e f l u x condenser was charged w i t h reagent grade dioxane ( 3 0 ml) saturated w i t h n i t r o g e n . 2 , 5 - N o r b o r n a d i e n e t e t r a -carbonylmolybdenum ( 0 . 5 g, 1 . 6 6 mmol) and 1 , 2 - b i s ( d i m e t h y l a r s i n o ) - 1 -cyanoethane 1_ ( 0 . 4 4 g, 1 . 6 6 mmol) were added to the f l a s k and the mixture was r e f l u x e d f o r 1 5 minutes. A f t e r c o o l i n g and f i l t e r i n g the s o l u t i o n , the s o l v e n t was removed under vacuum and the product c r y s t a l l i z e d from a mixture of benzene and l i g h t petroleum e t h e r , y i e l d i n g pure 1 , 2 - b i s -(dimethylarsino)-l-cyanoethanetetracarbonylchromium 2 8 ( 0 . 3 8 g, 4 9 % ) . C. P r e p a r a t i o n of 1 , 2 - b i s ( d i m e t h y l a r s i n o ) - 1 , 1 - d i f l u o r o e t h a n e -tricarbonylmanganese c h l o r i d e 23> In a 1 0 0 ml round-bottomed f l a s k f i t t e d w i t h a magnetic s t i r r e r , n i t r o g e n i n l e t , and r e f l u x condenser was placed reagent grade benzene ( 5 0 ml). F o l l o w i n g s a t u r a t i o n of the sol v e n t w i t h n i t r o g e n , penta-carbonylmanganese c h l o r i d e ( 0 . 4 2 g, 1 . 8 2 mmol) was added to the benzene together w i t h the l i g a n d 1 , 2 - b i s ( d i m e t h y l a r s i n o ) - l , 1 - d i f l u o r o -ethane 5_ ( 0 . 5 g, 1 . 8 3 mmol). The r e a c t i o n mixture was r e f l u x e d f o r 1 h, cooled, and f i l t e r e d . A f t e r removal of the sol v e n t under reduced pressure, the r e s u l t i n g s o l i d was washed w i t h a sm a l l amount of l i g h t petroleum ether, d r i e d under a high vacuum, and then sublimed - 24 -( 1 3 0 ° , 10 mm), y i e l d i n g a pure sample of 1 , 2 - b i s ( d i m e t h y l a r s i n o ) - l , 1 -difluoroethanetricarbonylmanganese c h l o r i d e 2J3 (0 .51 g, 6 2 % ) . The chelate complexes prepared during t h i s i n v e s t i g a t i o n are presented i n Table I I I . A l l the chromium, molybdenum, and tungsten complexes were synthesized by a procedure s i m i l a r to A, except 1 , 2 - b i s -(dimethylarsino)-l-cyanoethanetetracarbonylmolybdenum which was obtained by method B. P r e p a r a t i o n C i s r e p r e s e n t a t i v e of the syntheses of the tricarbonylmanganese h a l i d e d e r i v a t i v e s . - 25 -Table III. Chelate Complexes Synthesized. (CH.)-EC(3)(3*)C(4)(4')E(CH_)9M(C0) X 5 1 5 I m n (K = Cr, Mo, W; m = 4, n = 0 M = Mn; m = 3; X = Cl, Br, I; n = 1) _8 3 = S i ( C H 3 ) 3 ; 3',4, and 4' = H; E = As; M = Cr £ 3 = S i ( C H 3 ) 3 ; 3',4, and 4" = H; E = As; M = Mo 10 3 = S i ( C H 3 ) 3 ; 3',4, and 4' = H, E = As; M = W 11 3 = S i C l 3 ; 3',4, and 4' = H; E = As; M = Cr 12 3'= F; 3,4, and 4' = H; E = As; M = Cr 13 3'= F; 3,4, and 4' = H; E = As; M = Mo 14 3 = H; 3',4, and 4' = F; E = As; M = Cr 15 3 = H; 3',4, and 4' = F; E = As; M = Mo 16 3 = H; 3!,4, and 4' = F; E = As; M = W 17_ 3 = H; 3',4, and 4' = F; E = As; M = Mn; m = 3; X = Br; n = 1 18 3 = H; 3' ,4, and 4' = F; E P; M = Cr 19 3 = H; 3',4, and 4' = F; E P; M = Mo 20 3 and 3' = H; 4 and 4' = F; E = As; M = Cr 21 3 and 3' = H; 4 and 4' = F; E = As; M = Mo 22 3 and 3' = H; 4 and 4' = F; E = As; M = W 23 3 and 3' = H; 4 and 4' = F; E = As; M = Mn; m = 3; X = C l ; n = 1 24 3 and 3' = H; 4 and 4' = F; E = As; M = Mn; m = 3; X = Br; n = 1 25 3 and 3' = H; 4 and 4' = F; E = As; M = Mn; m = 3; X = I ; n = 1 26 3 = C l ; 3',4, and 4' = H; E = As; M = Cr 27 3 = CN; 3' ,4, and 4' = H; E = As; M = Cr 28 3 = CN; 3',4, and 4' = H; E = As; M = Mo 29 3 = CN; 3',4, and 4' = H; E = As; M W The diagram i s not intended to represent a f i x e d conformer i n s o l u t i o n . - 26 -CHAPTER 3 RESULTS: CHARACTERIZATION AND MECHANISM This chapter i s concerned w i t h the general methods of preparing d i t e r t i a r y a r s i n e s and t h e i r c helate complexes. I t i s d i v i d e d i n t o two p a r t s which consider the d i t e r t i a r y a r s i n e s and t h e i r metal carbonyl chelate d e r i v a t i v e s s e p a r a t e l y . Each s e c t i o n w i l l review the previous s y n t h e t i c routes used to o b t a i n these compounds before d i s c u s s i n g t h e i r r e s p e c t i v e p h y s i c a l , a n a l y t i c a l , and s p e c t r o s c o p i c p r o p e r t i e s . The chapter excludes mention of those p r o p e r t i e s obtained from NMR measurements, which are the subject of l a t e r chapters. P o s s i b l e mechanisms f o r the formation of these compounds are a l s o described. I . D i t e r t i a r y A rsines A. P r e p a r a t i v e Methods D i t e r t i a r y a r s i n e s have been synthesized by a v a r i e t y of methods. The f i r s t compound i n t h i s c l a s s to be i n t e n s i v e l y i n v e s t i g a t e d was 85 1,2-bis(dimethylarsino)benzene, ( d i a r s ) , prepared by Chatt and Mann i n 1939 by the f o l l o w i n g route: - 27 -. A s ( C H 3 ) 2 ( D 4 C H 3 M g l - | | J A S ( C H 3 ) 2 Since that time d i t e r t i a r y a r s i n e s of the type R-jT^AsCE^CH^AsR.^ have been synthesized by Grignard r e a c t i o n s : CI R 2 A s C H 2 C H 2 A s R 2 C I + 2 R 1 M g B r »• R | R 2 A s C H 2 C H 2 A s R ^ R 2 86 87 O L85 n D L (2) Ri • C H 3 - C 2 H 5 • P h : R 2 P h R 1 = C 4 H 9 8 8 ; R - C 4 H 9 The compound where R^ = = Ph, 1,2-bis(diphenylarsino)ethane, has been prepared by s e v e r a l other routes. For example, i t was i s o l a t e d when a mixture of ethylene oxide and di p h e n y l a r s i n e were heated at 89 130 c I 1 130° 2 P h 2 A s H 4- C H 2 C H 2 0 - P h 2 A s C H 2 C H 2 A s P h 2 (3) 90 91 Reaction of Ph^AsK-2dioxane or Pt^AsNa w i t h 1,2-dichloroethane has a l s o y i e l d e d 1,2-bis(diphenylarsino)ethane. N a / N H 3 C I C H 2 C H 2 C I 2 P h 3 A s »• 2 P h 2 A s N a - P h 2 A s C H 2 C H 2 A s P h 2 (4) - 28 -Oc c a s i o n a l l y such methods have been unsuccessful because an e l i m i n a t i o n r e a c t i o n occurred w i t h the d i s u b s t i t u t e d ethane, y i e l d i n g an o l e f i n . Thus the r e a c t i o n of Pt^AsK.2dioxane w i t h 1,2-dibromoethane afforded 9 0 only ethylene and t e t r a p h e n y l d i a r s i n e . D i t e r t i a r y a r s i n e s u b s t i t u t e d ethylenes and acetylenes have been synthesized by s i m i l a r r e a c t i o n s . For example, c i s - and trans-1,2-b i s ( d i m e t h y l a r s i n o ) e t h y l e n e r e s u l t e d from the r e a c t i o n of sodium 92 93 dimethylarsenide and c i s - l , 2 - d i c h l o r o e t h y l e n e . ' The a d d i t i o n of secondary a r s i n e s to o l e f i n s has not been e x p l o i t e d i n the synth e s i s 9 4 of d i t e r t i a r y a r s i n e s . However, King and coworkers have used t h i s method to prepare "mixed" t e r t i a r y p h o s p h i n e - t e r t i a r y a r s i n e compounds, f o r example: P h 2 A s H + P h 2 P C H = C H 2 £ ^ +• P h 2 P C H 2 C H 2 A s P h 2 (5) A l k y l and a r y l s u b s t i t u t e d d i a r s i n e s have been added to o l e f i n s 95-97 or acetylenes according to three r e p o r t s . Thus 9"! 9 S ( C H 3 ) 2 A s C F 2 C F ( C F 3 ) A s ( C H 3 ) 2 , ( C H ^ A s C F B r C F ^ s ( C H j 2 > c i s - and 95 trans-(CH 3) 2AsC(CF 3)=C(CF 3) As ( C H 3 ) 2 , and c i s - and trans-Ph (CH^AsC-96 (CF 3)=C(CF 3)AsPh(CH 3) have been prepared by r e a c t i n g an o l e f i n or acetylene w i t h the appropriate d i a r s i n e , f o r example: o 50 ( C H 3 ) 2 A s A s ( C H 3 ) 2 -I- C F ( C F 3 ) = C F 2 — (6) ( C H ^ A s C F l C F ^ C F j A s i C H ^ - 29 -This l a s t route seemed the most a t t r a c t i v e way of preparing new d i t e r t i a r y a r s i n e s u b s t i t u t e d ethanes, s i n c e i t i s the only method reported i n which s u b s t i t u e n t s other than hydrogen and a r s e n i c atoms could be placed on the carbon atoms i n the ethane b r i d g e . The new d i t e r t i a r y a r s i n e s 1~7_ described i n Table I I were obtained according to t h i s general equation: ( C H 3 ) 2 A s A s ( C H 3 ) 2 + = C ^ , ^ > l C H 3 > 2 A s C - <^As lCH 3 ) 2 (7) These l i g a n d s appeared to be formed e a s i l y on p h o t o l y s i s , but not so r a p i d l y on heating . A l l the r e a c t i o n s were c a r r i e d out using excess o l e f i n , consequently the y i e l d s were c a l c u l a t e d on the b a s i s of the amount of t e t r a m e t h y l d i a r s i n e used. B. A n a l y t i c a l Results The r e a c t i o n c o n d i t i o n s and a n a l y t i c a l data f o r the new d i t e r t i a r y a r s i n e s _l-_7 are summarized i n Table IV. In most instances the y i e l d s are l i k e l y to be an accurate measure of the extent of the r e a c t i o n , although the p r e p a r a t i o n of 1 , 2 - b i s ( d i m e t h y l a r s i n o ) - 1 - ( t r i m e t h y l s i l y l ) -ethane _1 where both s t a r t i n g m a t e r i a l s were i d e n t i f i e d i n the r e a c t i o n mixture, d i d not go to completion. Thus the y i e l d quoted f o r t h i s product i s not accurate. I t i s a l s o much lower (60%) than those values (ca. 80-90%) reported f o r the other d i t e r t i a r y a r s i n e l i g a n d s 2_-6_. The a n a l y t i c a l data obtained f o r these l i g a n d s are s a t i s f a c t o r y , - 30 -Table IV. A n a l y t i c a l and P r e p a r a t i v e Data f o r the New D i t e r t i a r y A r s i n e Ligands 1-J7. Compound A n a l y s i s C a l c u l a t e d Found Reaction Time Y i e l d % C H C H h (CH 3) 2AsCH(Si(CH 3) )CH 2As(CH 3) 1 34.9 7.80 30.5 7.29 18 60 ( C H 3 ) 2 A s C H ( S i C l 3 ) C H 2 A s ( C H 3 ) 2 2 19.4 4.07 19.3 4.36 15 86 (CH 3) 2AsCHFCH 2As(CH 3) 2 3 i 28.2 5.91 25.6 6.06 48 82 (CH 3) 2AsCHFCF 2As(CH 3) 2 4 24.7 4.49 24.6 4.35 24 90 (CH 3) 2AsCH 2CF 2As(CH 3) 2 5 26.3 5.15 26.5 5.25 24 84 (CH 3) 2AsCHClCH 2As(CH 3) 2 6 26.5 5.55 26.4 5.69 12 94 (CH ) AsCH(CN)CH 2As(CH 3) 2 1_ 32.0 5.75 31.5 5.86 11 96 except f o r 1 , 2 - b i s ( d i m e t h y l a r s i n o ) - 1 - ( t r i m e t h y l s i l y l ) e t h a n e 1 and 1,2-b i s ( d i m e t h y l a r s i n o ) - l - f l u o r o e t h a n e _3. These p a r t i c u l a r d i a r s i n e s fumed v i g o r o u s l y and i g n i t e d when exposed to the a i r ; thus i t was d i f f i c u l t to o b t a i n a n a l y t i c a l l y pure samples of these l i q u i d s f r e e of decomposition products. A l s o , f a i l u r e of the r e a c t i o n s to go to completion i s probably s i g n i f i c a n t s i n c e , f o r example, contamination of the t r i m e t h y l s i l y l l i g a n d 1_ by the r e l a t i v e l y i n v o l a t i l e t r i m e t h y l v i n y l -s i l a n e and t e t r a m e t h y l d i a r s i n e precursors l i k e l y c o n t r i b u t e d to the poor a n a l y t i c a l r e s u l t s . However, the t r i m e t h y l s i l y l _! and monofluoro _3 - 31 -d i t e r t i a r y a r s i n e s have been adequately c h a r a c t e r i z e d by the e x c e l l e n t analyses obtained from t h e i r Group VI t e t r a c a r b o n y l c h e l a t e d e r i v a t i v e s (CH 3) 2AsCH(Si(CH 3) 3)CH 2As(CH 3) 2M(CO) 4 8-10 (M = Cr, Mo, W) and (CH 3) 2AsCHFCH 2As(CH 3) 2M(CO) 4 12-13 (M = Cr, Mo). C. I n f r a r e d Spectra Table V contains the i n f r a r e d a b s o r p t i o n frequencies f o r the neat d i t e r t i a r y a r s i n e s l-7_. The i n f r a r e d spectrum of 1,2-bis (dimethy 1-arsino)-l-cyanoethane 7 i s a t y p i c a l example and i s shown i n Figure 1. D. Reaction Mechanisms In the present i n v e s t i g a t i o n , as noted p r e v i o u s l y , i t has been found ftiat the a d d i t i o n of t e t r a m e t h y l d i a r s i n e to o l e f i n s proceeds more r a p i d l y under u l t r a v i o l e t i r r a d i a t i o n than on h e a t i n g , suggesting a f r e e r a d i c a l mechanism f o r t h i s r e a c t i o n . I t has been reported that r a d i c a l s of the type R 2As" and R 2P' is- u i u i . 98-100 , , . . 101. ,. _ , e x i s t . DiphenyIphosphorus and d i p h e n y l a r s e n i c f r e e r a d i c a l s have been produced by p h o t o l y s i s of tetraphenyldiphosphine and t e t r a p h e n y l -d i a r s i n e , r e s p e c t i v e l y , at 77°K and t h e i r ESR s p e c t r a measured. The phosphorus-phosphorus and a r s e n i c - a r s e n i c bond strengths i n diphosphine and d i a r s i n e are approximately equal being 43.7 and 44.7 k c a l / 102 mole r e s p e c t i v e l y . In comparison, the a r s e n i c - a r s e n i c bond strength i n t e t r a m e t h y l d i a r s i n e i s 38.3 kcal/mole, according to Mortimer and 103 Skinner. The corresponding bond strength f o r tetramethyldiphosphine - 32 -Table V. I n f r a r e d Absorption Frequencies f o r the D i t e r t i a r y A r s i n e s . D i t e r t i a r y A r s i n e Frequencies^ ( C H 3 ) 2 A s C H ( S i ( C H 3 ) 3 ) -CH 2As(CH 3) 2 1 2980(s), 2960(s), 2910(vs), 2815(m), 1420(br,s), 1248(vs), 1102(w), 1043(w), 1008(w), 887(s), 858(vs), 835(br,vs), 750(m), 685(m), 570 (w). ( C H 3 ) 2 A s C H ( S i C l 3 ) C H 2 -A s ( C H 3 ) 2 2 2980(vs), 2910(vs), 2815(m), 1418(br,vs), 1260(s), 1245(m), 1210-990(br,s), 890(s), 867(m), 845(s), 830(s), 790(s), 730(m), 700(s). (CH ) AsCHFCH As-( C H 3 ) 2 3 2980(s), 2910(vs), 2812(m), 1417(br.s), 1320(w), 1310(w), 1255(m), 1250(m), 1170(br,w), 1120(w), 1090(vw), 1049(m), 933(s), 890(s), 844(s), 828(s), 732(br,s), 570(w). (CH 3) 2AsCHFCF 2As-( C H 3 ) 2 4 2985(m), 2915(s), 2810(w), 1413(br,s), 1315(w), 1303(w), 1260(w), 1247(w), 1151(m), 1052(vs), 1010(vs), 978(w), 956(m), 896(m), 849(vs), 793(w), 725(br,s), 548(w), 515(w). (CH ) AsCF 2CH As-( C H 3 ) 2 5 2980(m), 2910(m), 2815(w), 1413(br,m), 1260(w), 1212(w), 1190(m), 1130(B), 1114(m), 1025(w), 1000(m), 965(br,vs), 893(m), 848(m), 724(w), 570(w). (CH 3) 2AsCHClCH 2As-( C H 3 ) 2 6 2980(s), 2915(B), 2810(w), 1420(B), 1410(s), 1255(s), 1240(m), 1188(w), 1100(w), 1022(w), 890(B), 862(m), 840(B), 786(w), 772(w), 700(br,w), 570(w). (CH 3) 2AsCK(CN)CH 2-A s ( C H 3 ) 2 1_ 2980(s), 2910(s), 2815(w), 2210(s), 1419(br,s), 1260(m), 1200(w), 1160(w), 1090(br,w), 920(m), 893(s), 849(br,s), 792(w), 748(w), 570 (w). Spectra measured on l i q u i d f i l m s using KBr or NaCl p l a t e s . w = weak,v = very, br = broad, s = str o n g , m = medium - 33 -O O in a D U o q j o s q y - 34 -is not known; however, i t is anticipated to be close to the value found for i t s arsenic analog. Thus similar reaction paths could be expected for related reactions involving these two species. 84 104 Haszeldine and coworkers ' have postulated that the addition of tetramethyldiphosphine to fluoroolefins could proceed by a radical combination mechanism, as shown in (8). i C H 3 ) 2 P P ( C H 3 ) 2 2 ( C H 3 ) 2 P -( C H 3 ) 2 P - + )C=CC " i C H 3 ) 2 p C " C - ( 8 ) ( C H 3 ) 2 P - + l C H 3 ) 2 P C - C - ( C H 3 ) 2 P C - C P ( C H 3 ) 2 84 104 By this method, (CH3)2PCHFCF2P(CHj) , (CH )2PCHFCH2P(CH ) , 104 104 (CH 3) 2PCF 2CH 2P(CH 3) 2, U (CH 3) 2PCH(CH 3)CH 2P(CH 3) 2, X U H and 104 (CH 3) 2PCH 2CH 2P(CH 3) 2 were prepared. The perfluoromethyl analogs of 104 these compounds were similarly obtained. Other mechanisms for the addition of tetramethyldiarsine to olefins are possible. The diarsine could react with the olefin via a four-centered process or the reaction could proceed through an activated olefin intermediate. Nevertheless, the indirect evidence seems to indicate that radical combination occurs in the addition of tetramethyl-104 diphosphine and tetramethyldiarsine to olefins. - 35 -I I . Chelate Complexes A. P r e p a r a t i v e Methods A host of t e r t i a r y phosphine, a r s i n e , and s t i b i n e d e r i v a t i v e s of t r a n s i t i o n metal carbonyls have been prepared i n the l a s t twenty years. i _ . _ 105-107 There are s e v e r a l e x c e l l e n t reviews on t h i s s ubject. D i t e r t i a r y a r s i n e chelate complexes of chromium, molybdenum, and tungsten carbonyl have u s u a l l y been produced by displacement of two carbonyl groups on the parent hexacarbonyl, at elevated temperatures. As an i l l u s t r a t i o n , the general equation f o r the formation of some 108 d e r i v a t i v e s of 1,2-bis(diphenylarsino)ethane i s shown below. °r P h 2 A s C H 2 C H 2 A s P h 2 + M ( c O j 6  O C P h 2 As ~f»2 M r e f l u x n h. QQ— , C H 2 M = C r , n = 2 4 £ P h 2 = M o , n = 4 O = W, n = 7 0 ( 9 ) The 1,2-bis(diphenylphosphino)ethane group VI t e t r a c a r b o n y l d e r i v a t i v e s were obtained i n much the same manner. Another convenient route to these chelate complexes i s to d i s p l a c e s u b s t i t u e n t s other than carbonyl groups from the t r a n s i t i o n metal. In t h i s way 1,2-bis(diphenylphosphino)ethanetetracarbonylmolybdenum was prepared by the replacement of 1,5-cyclooctadiene from 1,5-cyclo-octadienetetracarbonylmolybdenum. - 36 -O C P h 2 P ( C H 2 ) 2 P P h "2 + oc--Mo. C O 30 O C Ph, --Mo. C o p— P h 2 T H2 -CH 2 (10) + C 8 H ] 2 Two pentacarbonylmanganese h a l i d e s have been shown to react at moderate temperatures w i t h 1,2-bis(diphenylphosphino)ethane to y i e l d 112 the f ac s u b s t i t u t e d complexes. The r e l a t e d 1,2-bis (dimethylarsi.no)-P h , 'P-C M n l C O ) 5 X + P h 2 P C H 2 C H 2 P P h 2 ± . ^KrSSAi X = Br I I P h2 C O 113 benzene chelate complexes have been obtained by an analogous process. I t appeared that the new d i t e r t i a r y a r s i n e s l-7_ would react by such s t r a i g h t f o r w a r d paths to produce s i m i l a r f a c complexes and i n a s e r i e s of r e a c t i o n s d i r e c t l y r e l a t e d to ( 9 ) - ( l l ) , the p r e v i o u s l y described l i g a n d s were used to prepare the new d i t e r t i a r y a r s i n e chelate complexes 8-29. A l l the Group VI chelate complexes except 1,2-bis(dimethylarsino)-l-cyanoethanetetracarbonylmolybdenum 28^  were prepared by heating an equimolar mixture of the appropriate d i t e r t i a r y a r s i n e ( L — L ) and metal hexacarbonyl w i t h benzene at 135°-180° f o r 0.5-24 h: - 37 -O C -co M c o M O c X M C O Cr, Mo .W; L L = I ~ 7 2CO (12) A f t e r workup and p u r i f i c a t i o n by s u b l i m a t i o n , the chromium chelate complexes were obtained as yel l o w s o l i d s , w h i l e the molybdenum and. tungsten compounds were white s o l i d s . The 1,2-bis(dimethylarsino)-l-cyano-ethane complex28 was obtained, by displacement of 2,5-norbornadienetetra-carbonylmolybdenum: O C o c \ As- -As ref lux d ioxane ^ ^ A s C 7 H 8 C O c o (13) As As = \CH3)2AsCH(CN)CH2As ( C H 3 ) 2 , || j | = C 7 H 8 D e r i v a t i v e s of pentacarbonylmanganese h a l i d e s were synthesized by r e f l u x i n g equimolar mixtures of the l i g a n d and substrate i n benzene f o r 0.5-1.5 h. Fo l l o w i n g removal of the solvent and s u b l i m a t i o n of the r e s u l t i n g s o l i d , orange col o r e d fac c h e l a t e complexes were obtained. Mn(C0) 5 X + L — L J r e f l ux QQ L L = ( ,CH 3 ) 2 AsCHFCF 2 As ( C H 3 ) 2 ; X = Br C L L = ( c H 3 ) 2 A s C F 2 C H 2 A s ( C H 3 ) 2 ; X= Cl, Br, I o 2CO (14) - 38 -B. A n a l y t i c a l Results Table VI summarizes the r e a c t i o n c o n d i t i o n s and a n a l y t i c a l r e s u l t s f o r the new chelate compounds 8-29. A n a l y t i c a l samples of the d i t e r t i a r y a r s i n e and d i t e r t i a r y phosphine complexes were u s u a l l y obtained by s u b l i m a t i o n of the crude samples at el e v a t e d temperatures (100-180°). A few of the samples,(CHj) 2AsCH(CN)CH 2As(CHg) 2M(C0) 27, 28, and 23_ (M = Cr, Mo, W), would not sublime under these c o n d i t i o n s and were consequently r e c r y s t a l l i z e d from a pentane-acetone mixture and d r i e d under reduced pressure. Y i e l d s of the complexes v a r i e d considerably f o r s e v e r a l reasons. At the high r e a c t i o n and s u b l i m a t i o n temperatures used, some products decomposed. The y i e l d s were a l s o reduced by r e l u c t a n c e of the d i t e r t i a r y a r s i n e to chelate w i t h the metal. Frequently the major products were complexes i n which only one of the donor atoms of the l i g a n d was bonded to the metal atom. These compounds were removed by washing the r e a c t i o n mixture w i t h l i g h t petroleum ether. This problem was most troublesome i n the p r e p a r a t i o n of 1,2-bis(dimethylarsino)-l-chloroethanetetracarbonylchromium 26. In order to i s o l a t e the chelate complex i t was necessary to chromatograph the r e a c t i o n mixture on F l o r i s i l , s i n c e the unidentate complex was formed i n such high y i e l d . Mass spec t r a of the Group VI t e t r a c a r b o n y l d e r i v a t i v e s showed peaks corresponding to the parent i o n followed by the l o s s of four carbonyl groups. Other peaks f r e q u e n t l y encountered fn these s p e c t r a could be a t t r i b u t e d to the l o s s of a methyl group from the parent i o n or from the parent i o n l e s s one to four carbonyl groups. A l l mass sp e c t r a Table V I . A n a l y t i c a l and P r e p a r a t i v e Data f o r the New Chelate Complexes. Chelate Comnlexes A n a l y s i s React ion Reaction Y i e l d m.p. Chelate Complexes Calcula ted Found Time h Temp. °C % °C C H C H (CH 3) 0AsCH(Si(CH_).)CH„As(CH.) C r ( C O ) . 8 I 5 5 1 5 1 4 — -32.9 5.10 33.2 5.15 4 180 49 86-87 (CH 3] 2AsCH(Si(CH 3) 3)CH 2As(CHj) 2Mo(CO) 9 30.1 4.67 30.0 4.79 2.5 150 38 109-111 (CH 3) 2AsCH(Si(CH ) )CH 2As(CH ) 2W(C0) 10 25.8 3.99 25.6 3.90 6 135 32 127-128 (CH 3) 2 A s C H ( S i C l 3 ) C H 2 A s ( C H 3 ) 2 C r ( C 0 ) 4 11 22.4 2.82 22.3 2.79 5 140 74 135-138 b (CH 3) 2AsCHFCH 2As(CH 3) 2Cr(CO) 4 12 28.6 3.60 28.4 3.45 14 140 39 160-162 (CH 3) 2AsCHFCH 2As(CH 3) 2Mo(C0) 4 13 25.9 3.26 25.9 3.16 2 140 40 151-152 2AsCHFCF 2As(CH 3) 2Cr(C0) 4 14 26.3 2.87 26.5 2.90 6 150 65 194-195 (CH 3) 2AsCHFCF 2As(CH 3) 2Mo(C0) 4 15 24.0 2.62 23.9 2.51 2 150 64 162-166 (CH 3) 2AsCHFCF 2 A s(CH 3) W(C0) 4 16 20.4 2.23 20.8 2.15 24 150 33 197-198 (CH 3: 2AsCHFCF 2As(CH 3) 2Mn(CO) 3Br 17 21.2 2.56 21.2 2.79 1 e 74 173-187 (CH 3) 2PCHFCF 2P(CH 3) 2Cr(C0) 4 18 32.6 3.56 32.5 3.63 - 3 145 61 205-215 b ( C H 3 : 2PCHFCF 2P(CH 3) 2Mo(C0) 4 19 29.2 3.18 29.3 3.08 1.5 145 55 190-193 b ( C H 3 : 2AsCH 2CF 2As(CH 3) 2Cr(CO) 20 27.4 3.22 27.7 3.21 2 150 50 169-170 ( C H 3 : ) 2AsCH 2CF 2As(CH 3) 2Mo(C0) 4 21 24.9 2.93 24.9 2.99 2 150 77 151-154 b Table VI (Continued) (CH 3) 2AsCH 2CF 2As(CH 3) 2W(CO) 4 22 21.1 2.48 21.3 2.49 18 150 11 176-177 (CH 3) 2AsCH 2CF 2As(CH 3) 2Mn(CO) 3Cl 23 24.1 3.15 23.9 3.19 1 e 62 149-153 (CH ) 2AsCH 2CF 2As(CH 3) 2Mn(CO) 3Br 24 21.9 2.86 21.8 2.78 0.5 e 81 171-173 b (CH 3) 2AsCH 2CF 2As(CH 3) 2Mn(CO) 3I 25 20.0 2.61 20.0 2.70 1.5 e 74 201-202 (CH 3) 2AsCHClCH 2As(CH 3) 2Cr(CO) 4 26> 27.5 3.46 27.5 3.43 4 140 38 164-165 (CH ) 2AsCH(CN) CH 2As (CH ) 2 C r (CO) 2± 31.0 3.54 30.9 3.39 8 140 69 165-175 b (CH 3) 2AsCH(CN)CH 2As(CHg) 2Mo(CO> 4 28 28.1 3.21 28.1 3.22 0.25 f 49 161-163 (CH 3) 2AsCH(CN)CH 2As(CH )2W(CO) 29 23.6 2.71 23.5 2.66 14 150 39 186-188 Complexes were prepared as described i n Chapter 2. Compound melted w i t h decomposition. Compound was i s o l a t e d by chromatography on F l o r i s i l by e l u t i o n w i t h benzene. Compound was p u r i f i e d by c r y s t a l l i z a t i o n from a pentane-acetone mixture. Compound prepared i n r e f l u x i n g benzene s o l u t i o n . Compound prepared i n r e f l u x i n g dioxane s o l u t i o n . - 41 -obtained from the chelate complexes showed peaks corresponding to the fragments [ ( C H ^ A s ^ 4 " and [ (CH 3) 3 A s 2 ] + . Several of the new d i t e r t i a r y a r s i n e c h e l a t e complexes, (CH 3) 2AsCHFCF 2As(CH 3) 2M(CO) 4 14-15 (M = Cr, Mo), (CH ) 2PCHFCF 2P(CH 3) £-Mo(CO) 4 19, and (CH 3> 2AsCF 2CH 2As (CH 3) 2 C r ( C O ) 4 20_ have had t h e i r s t r u c t u r e s determined by X-ray crystallography."'""'" 4 The gross s t r u c t u r e s were as expected. A d i s c u s s i o n of the X-ray data i n Table VII w i l l appear i n Chapter 5. C. I n f r a r e d Spectra The i n f r a r e d absorption frequencies f o r the carbonyl groups of the complexes 8-29 are presented i n Table V I I I . Sample s p e c t r a of 1,2-b i s ( d i m e t h y l a r s i n o ) - l , l , 2 - t r i f l u o r o e t h a n e t e t r a c a r b o n y l c h r o m i u m 14_ and 1,2-bis(dimethylarsino)-1,1-difluoroethanetricarbonylmanganese bromide 24 appear i n Figure 2. Data obtained from the i n f r a r e d s p e c t r a of r e l a t e d hydrocarbon-bridged l i g a n d chelate complexes are presented i n Table IX. On the b a s i s of l o c a l carbonyl group symmetry, compounds of the type c i s - M ( C 0 ) 4 ( L — L ) , belong to the p o i n t group C 2 . When the unsymmetrical nature of the puckered five-membered chelate r i n g i s considered, these complexes belong to the p o i n t group C^. Both assignments p r e d i c t a maximum of four carbonyl absorptions i n the i n f r a r e d r e g i o n . The Group VI chelate complexes e x h i b i t e i t h e r three or four (as i n Figure 2A) absorptions i n the carbonyl s t r e t c h i n g r e g i o n of the i n f r a r e d spectrum. The three band p a t t e r n occurs as a r e s u l t of the a c c i d e n t a l degeneracy of two of the absorptions. - 42 -Table V I I . Bond Lengths (A) and Valency Angles (degrees) i n (CH 3) 2E CRR' C F 2 E ( C H 3 ) 2 M(C0) 4 Complexes 15 19 14 20 30 31 M Mo Mo Cr Cr Cr Mo E As P As As As As R F F F H F F R* H H H H C l CF 3 Mo-As 2.58 - - - - 2.57 Mo-P - 2.48 - - - -Cr-As - - 2.43 2.45 2.42 -Mo-C 2.00 2.03 - - - 1.94 Cr-C - - 1.88 1.89 1.90 -C-0 1.15 1.13 1.16 1.14 1.13 1.19 As-C 1.99 - 1.99 1.98 1.99 1.96 P-C - 1.89 - - - -E-M-E 82 82 84 84 85 82 Other Z . at M 88-94 89-93 89-92 88-93 88-94 87-95 M-C-0 178 179 178 178 177 177 M-X-CH3 121 120 121 120 122 121 Other z. at E 94-109 95-110 97-108 99-112 99-107 95-108 C-C (average) 1.50 C-F (average) 1.37 I. at C (average) 108 - 43 -Table V I I I . Carbonyl I n f r a r e d S t r e t c h i n g Frequencies (cm ) f o r the Chelate Complexes 8-29. Chelate Complex Frequencies ( C H 3 : ) 2AsCH(Si(CH 3) 3)CH 2As(CH 3) 2Cr(CO) 8 2006 1915 1892 (1892) ( C H 3 : 2AsCH(Si(CH 3) 3)CH 2As ( C R )2Mo(CO) 9 2020 1925 1906 1902 ( C H 3 ; 2AsCH(Si(CH 3) 3)CH 2As(CH 3) 2W(C0) 10 2016 1918 1896 (1896) ( C H 3 ; 2 A s C H ( S i C l 3 ) C H 2 A s ( C H 3 ) 2 C r ( C 0 ) 4 11 2011 1923 1900 (1900) ( C H 3 : 2AsCHFCH 2As(CH 3) 2Cr(C0) 4 12 2011 1923 1900 (1900) ( C H 3 : 2AsCHFCH 2As(CH 3) 2Mo(C0) 4 13 2018 1933 1913 (1913) ( C H 3 : 2AsCHFCF 2As(CH 3) 2Cr(C0) 4 14 2021 1931 1913 1907 (CH 3) 2AsCHFCF 2As(CH 3) 2Mo(CO) 4 15 2036 1937 1924 1917 (CH 3) 2AsCHFCF 2As(CH 3) 2W(C0) 4 16 2030 1934 1916 1913 (CH 3) 2AsCHFCF 2As(CH 3) 2Mn(C0) 3Br 17 2038 1973 1926 (CH 3) 2PCHFCF 2P(CH 3) 2Cr(CO) 4 18 2021 1936 1913 1909 (CH 3) 2PCHFCF 2P(CH 3) 2Mo(C0) 4 19 2032 1943 1922 1920 (CH 3) 2 A s C H 2 C F 2 A s ( C H 3 ) 2 C r ( C 0 ) 4 20 2016 1927 1903 (1903) (CH 3J 2AsCH 2CF 2As(CH 3) 2Mo(C0) 4 21 2032 1935 1917 1912 (CH 3) 2AsCH 2CF 2As(CH 3) 2W(C0) 4 22^  2024 1927 1906 (1906) (CH 3) 2AsCH 2CF 2As(CH 3) 2Mn(C0) 3Cl 23 2038 1970 1923 (CH 3) 2AsCH 2CF 2As(CH 3) 2Mn(C0) 3Br 24 2034 1967 1922 (CH 3) 2AsCH 2CF 2As(CH 3) 2Mn(CO) 3I 25 2030 1968 1924 (CH 3) 2AsCHClCH 2As(CH 3) 2Cr(C0) 4 26 2012 1923 1899 (1899) (CH 3) 2AsCH(CN)CK 2As(CH 3) 2Cr(C0) 4 27 2014 1928 1906 1903 (CH 3) 2As CH(CN)CH 2As(CK 3 ) Mo (CO) 4 28 2025 1935 1914 (1914) (CH 3) 2AsCH(CN)CH 2As(CH 3) 2W(CO) 4 29 2021 1928 1906 (1906) Cyclohexane s o l v e n t , 0.1 and 0.5 mm KBr c e l l s The e r r o r i n those frequencies above 2000 cm ^ i s + 4 cm \ -1 -1 i n those below 2000 cm i t i s + 2 cm - 44 -aoueqjosqv - 45 -Table IX. Carbonyl I n f r a r e d S t r e t c h i n g Frequencies (cm ) of Some Hydrocarbon-bridged Chelate Complexes. Chelate Complex Frequencies (cm 1 ) Ph 2AsCH 2CH 2AsPh 2Cr(CO) 4 a 2008 (1893) 1893 1869 Ph 2AsCH 2CH 2AsPh 2Mo(CO) * 2020 (1908) 1908 1879 Ph oAsCH oCH.AsPh oW(C0), a 2 2 2 2 4 2020 (1897) 1897 1872 Ph 2PCH 2CH 2PPti 2Cr (CO) ^ 2009 1914(sh) 1899 1877 Ph 2PCH 2CH 2PPh 2Mo(CO) 4 b' C 2020 1919(sh) 1907 1881 2028 1932 1919 1906 Ph 2PCH 2CH 2PPh 2W(CO) 4 b 2016 1912(sh) 1901 1876 cis-Ph 2PCH 2CH 2PPh 2Mn(CO) 3Br d 2022 1959 1918 cis-Ph 2PCH CH PPh 2Mn(CO) 3I d 2020 1958 1920 data taken from reference 108, dichloromethane s o l v e n t , data taken from reference 109, 1,2-dichloroethane s o l v e n t , data taken from reference 110, hydrocarbon s o l v e n t , data taken from reference 112, chloroform s o l v e n t . - 46 -In g e n e r a l , carbonyl group absorptions s h i f t to higher frequency as the t o t a l e l e c t r o n e g a t i v i t y of the s u b s t i t u e n t s bonded to a metal i n c r e a s e s . This trend i s expected on the b a s i s of simple bonding arguments. The more e l e c t r o n withdrawing a s u b s t i t u e n t , the l e s s TT donation by the f i l l e d d o r b i t a l s of the metal w i l l occur to the TT* o r b i t a l s of the carbonyl groups. This strengthens the carbon-oxygen bond and consequently the v i b r a t i o n a l frequency of these atoms w i l l i n c r e a s e . An examination of the data i n Table V I I I f o r a p a r t i c u l a r set of d e r i v a t i v e s , f o r example, the chromium complexes 8^ , 11, _12, 14, 18, 20, 26, and _2_7 i l l u s t r a t e s t h i s tendency. As expected, the t r i f l u o r o e t h a n e d e r i v a t i v e 14_ has the highest i n f r a r e d s t r e t c h i n g frequencies, f o l l o w e d by the d i f luoroethane d e r i v a t i v e 20_. The c h l o r o , cyano, f l u o r o , and t r i c h l o r o s i l y l d e r i v a t i v e s 26_, 27_, 12, and 1_1 y i e l d s p e c t r a w i t h almost i d e n t i c a l frequencies. Presumably t h i s i s a r e s u l t of the s i m i l a r e l e c t r o n e g a t i v i t i e s of these s u b s t i t u e n t s . Comparison of the data contained i n Tables V I I I and IX i n d i c a t e s that the i n f r a r e d s t r e t c h i n g frequencies are f a i r l y i n s e n s i t i v e to changes from a r s e n i c to phosphorus donor atoms. Thus there i s l i t t l e d i f f e r e n c e between the carbonyl s t r e t c h i n g frequencies of (CH 3) 2AsCHFCF 2As(CH 3) 2Cr(CO) 4 14 and (CH 3> 2PCHFCF 2P(CHg) 2Cr(CO) 4 18, or Ph 2AsCH 2CH 2AsPh 2Cr(C0) 4 and Ph 2PCH 2CH 2PPh 2Cr(CO) 4. For a given d i t e r t i a r y a r s i n e or phosphine Group VI metal carbonyl d e r i v a t i v e , the i n f r a r e d absorptions f o l l o w the frequency trend Mo > Cr > W, as i l l u s t r a t e d by the data i n Tables V I I I and IX. This behavior has been r a t i o n a l i z e d i n the parent hexacarbonyls by - 47 -con s i d e r i n g the consequences of the "lanthanide c o n t r a c t i o n " . This e f f e c t i s s a i d to cause gre a t e r donation of the 5d o r b i t a l e l e c t r o n density to the TT* o r b i t a l of a carbonyl group bonded to a tungsten atom, compared w i t h the amount of 3d or 4d o r b i t a l donation by chromium or molybdenum atoms. A molecule of the type fac-M(CO)^(L—L)X w i l l y i e l d a maximum of three carbonyl s t r e t c h i n g absorptions. The i n f r a r e d s p e c t r a of (CH 3) 2AsCFHCF 2As(CH 3) 2Mn(CO) 3Br 17 and (CHj) 2AsCH 2CF 2As(CHg) 2Mn(CO) 3X 23-25 (X = C l , Br, I) bear t h i s p r e d i c t i o n out. As an example, the spectrum of 1 , 2 - b i s ( d i m e t h y l a r s i n o ) - 1 , 1 - d i f l u o r o e t h a n e t r i c a r b o n y l -manganese bromide appears i n Figure 2B. D i t e r t i a r y a r s i n e s may chelate w i t h the pentacarbonylmanganese h a l i d e s u b s t r a t e to y i e l d e i t h e r a f a c i a l (fac) or m e r i d i a n a l (mer) product. (15) The fac complex J ( 1 ) , l i k e the mer compound J ( 2 ) , w i l l e x h i b i t a maximum of three carbonyl absorptions i n the i n f r a r e d r e g i o n : thus c o n s i d e r a t i o n of the number of bands i n the spectrum i s i n s u f f i c i e n t to make a d i s t i n c t i o n between these two isomers. 120 Abel and Wi l k i n s o n have examined t h i s fac-mer assignment problem i n r e l a t e d rhenium complexes. The formation of fac isomers has been - 48 -r a t i o n a l i z e d i n terms of the c i s l a b i l i z i n g e f f e c t of the halogen s u b s t i t u e n t on the carbonyls i n pentacarbonylrhenium h a l i d e s u b s t i t u i o n r e a c t i o n s w i t h p y r i d i n e . A d e t a i l e d examination of the symmetry of the carbonyl s t r e t c h i n g v i b r a t i o n a l modes f o r the fac and mer manganese complexes are shown i n Figure 3. For the mer isomer, modes A and C_ w i l l i n v o l v e a change i n the d i p o l e moment of the molecule and are expected to r e s u l t i n strong absorptions. On the b a s i s of l o c a l carbonyl group symmetry mode B_ does not i n v o l v e a d i p o l e change i n the complex and t h i s v i b r a t i o n w i l l l i k e l y r e s u l t i n a weak i n f r a r e d a b s o r p t i o n . On the other hand, a l l three v i b r a t i o n a l s t r e t c h i n g modes of the fac c h elate complex i n v o l v e a change i n d i p o l e moment and are expected to r e s u l t i n strong absorptions. Hence the fac complexes should y i e l d a maximum of three strong absorptions, w h i l e mer complexes should y i e l d one weak and two strong absorptions. Unfortunately experimental v e r i f i c a t i o n of these conclusions has not yet been p o s s i b l e due to the l a c k of s u i t a b l e isomers. Some i n d i r e c t support f o r these conclusions comes from a study of the i n f r a r e d s p e c t r a of the complexes 32 and 33. v i b r a t i o n s provides a more convincing s o l u t i o n . 121 The normal B r B r •Mn. - 49 -Mer-. Figure 3. Normal modes of C-0 s t r e t c h i n g v i b r a t i o n s f o r isomers of Mn(CO) 3(L—L)X. - 50 -Although the mer phenylphosphlte d e r i v a t i v e j32_ does not have the phosphorus atoms c i s to each other, the three s u b s t i t u e n t s as a group have the same stereochemical r e l a t i o n s h i p as i n the mer c h e l a t e complexes. I t e x h i b i t s one weak and two i n t e n s e a b s o r p t i o n s , w h i l e the fac isomer 33 produces three strong bands i n the i n f r a r e d r e g i o n . Comparison of the i n f r a r e d s p e c t r a of the manganese d e r i v a t i v e s i n Table V I I I w i t h the f a c - l , 2 - b i s ( d i p h e n y l p h o s p h i n o ) e t h a n e t r i c a r b o n y l -manganese h a l i d e s p e c t r a i n Table IX shows that they are very s i m i l a r , except that the a b s o r p t i o n bands of the c h e l a t e complexes s t u d i e d i n t h i s work are 5 to 15 cm higher i n frequency. This i s probably due to the d i f f e r e n c e s i n e l e c t r o n e g a t i v i t y caused by the f l u o r i n e s u b s t i t u e n t s i n the d i t e r t i a r y a r s i n e s . A l l t h i s evidence s t r o n g l y suggests that the M n ( C 0 ) 3 ( L — L ) X chelate complexes prepared i n t h i s work are indeed the fac isomers. The i n f r a r e d s p e c t r a of a l l the chelate complexes a l s o seem to i n d i c a t e that i n s o l u t i o n , the chelate r i n g remains i n t a c t and that the carbonyl s u b s t i t u e n t s remain bonded to the metal atom. D. Reaction Mechanisms The l i t e r a t u r e r e l a t i n g to the k i n e t i c s and mechanisms of the s u b s t i t u t i o n r e a c t i o n s of metal carbonyls and t h e i r d e r i v a t i v e s has 122 12 A been thoroughly documented. There have been no r e p o r t s of k i n e t i c s t u d i e s of the s u b s t i t u t i o n of the Group VI hexacarbonyls by b i d e n t a t e l i g a n d s . However, the r e a c t i o n s of these substrates at 100-125—129 170° w i t h t e r t i a r y phosphines and phosphites have been - 51 -e x t e n s i v e l y examined. I t has been concluded that such r e a c t i o n s proceed v i a intermediates of both reduced and increased c o o r d i n a t i o n number. Chromium hexacarbonyl r e a c t s predominantly by a d i s s o c i a t i v e mechanism wh i l e molybdenum and tungsten hexacarbonyls react v i a d i s s o c i a t i v e and a s s o c i a t i v e processes. The new d i t e r t i a r y a r s i n e l i g a n d s most l i k e l y r e a c t w i t h the Group VI hexacarbonyls by a two step r e a c t i o n : O C o. -co • M -o c o o c As • M As O A s - -As - C O M = C r , M o , W ; A s — A s = 1 - 7 O c As -c o o c A s (16a) •M \ A - - A s J C O (16b) Intermediates of type K have been i s o l a t e d from r e a c t i o n mixtures and i d e n t i f i e d by i n f r a r e d spectroscopy. From Table VI i t can be seen that the ease of s u b s t i t u t i o n of the various hexacarbonyls occurs i n the order Cr - Mo > W. This 129-131 125-trend a l s o a r i s e s i n carbonyl exchange and other s u b s t i t u t i o n r e a c t i o n s , where the rates f o r the tungsten congener are approximately ten times slower than f o r the chromium and molybdenum hexacarbonyls. - 52 -This behavior can a l s o be accounted f o r i n terms of the "lanthanide c o n t r a c t i o n " e f f e c t , described i n the previous s e c t i o n to r a t i o n a l i z e the trend i n the carbonyl i n f r a r e d s t r e t c h i n g frequencies of the Group VI hexacarbonyls."'""'"^ The s u b s t i t u t i o n of pentacarbonylrhenium h a l i d e s by 1,2-bis(dipheny1-phosphino)ethane and 1,2-bis(dimethylarsino)benzene has been 113 i n v e s t i g a t e d . K i n e t i c data i n d i c a t e that the r a t e of carbonyl s u b s t i t u t i o n i s f i r s t order i n s u b s t r a t e and independent of the l i g a n d and i t s c o n c e n t r a t i o n . The observed r a t e constants f o r the d i f f e r e n t l i g a n d s at 50° are c l o s e to one another, and the p o s i t i v e a c t i v a t i o n entropies are f u r t h e r evidence f o r the d i s s o c i a t i v e process which the authors propose. X - C O s l o w (17a) C X C O L (17b) - 53 -X X (17c) X =.CI, Br, I L L = 1 . 2 " bi s(diphenylphosphino) ethane, bipyridyl, or l,2-bis(dimeth y larsino)-benzene These workers have i n f r a r e d evidence f o r species i n the r e a c t i o n mixture; however, the rat e s at which i t i s formed and consumed are reported to be too f a s t to measure. I t i s l i k e l y that the formation of the manganese complexes i n the present study occurs by a d i r e c t l y 113 r e l a t e d process, but at a f a s t e r r a t e . The f i r s t order r a t e constants f o r the d i s s o c i a t i o n of a carbonyl group from pentacarbonylrhenium h a l i d e s decrease i n the order I < Br < CI. This i s expected on the b a s i s of a greater rhenium-carbon bond s t r e n g t h , r e s u l t i n g from a l e s s e l e c t r o n e g a t i v e i o d i n e atom compared w i t h bromine or c h l o r i n e s u b s t i t u e n t . The compounds 1 , 2 - b i s ( d i m e t h y l a r s i n o ) - 1 , 1 - d i f l u o r o e t h a n e t r i c a r b o n y l -manganese c h l o r i d e _2_3, bromide lk_ and i o d i d e 25_ probably form according to the same rate trend. 132 Basolo and coworkers have reported the only study which presents accurate r a t e s f o r both the formation of the i n i t i a l m e t a l - l i g a n d bond ( f o r example r e a c t i o n type 16a) and the r i n g c l o s u r e r e a c t i o n ( f o r - 54 -example r e a c t i o n 16b) i n metal carbonyl d e r i v a t i v e s . Here, k i n e t i c s t u d i e s of the r e a c t i o n s of 1,2-bis(diphenylphosphino)ethane w i t h d i c a r b o n y l d i n i t r o s y l i r o n and n i t r o s y l t r i c a r b o n y l c o b a l t showed that the rate constant f o r the second step (18b) i s much l e s s than the r a t e constant f o r the f i r s t step (18a). O C O N — F e o c o ° N - F e + P P P h 2 P C H 2 C H 2 P P h 2 4 0 " - C O 25 k, = 5.1 x 10' M ^ S e c - 1 ,-3 o P c / k 2 = 5.8 x 1 0 " 5 S e c - 1 P h 2 P C H 2 C H 2 P P h 2 (18a) O N -o C18b) Thus these workers were able to observe and i s o l a t e the intermediates Fe(NO) 2(CO)Ph 2PCH 2CH 2PPh 2 and Co(NO)(CO) 2Ph PCH 2CH 2PPh 2 which have only one phosphorus atom donating to the t r a n s i t i o n metal. Since the r e a c t i o n s were not st u d i e d as a f u n c t i o n of temperature, thermodynamic data were not obtained, and i t was not determined i f the two r e a c t i o n steps progressed by a s s o c i a t i v e or d i s s o c i a t i v e processes. This example p a r a l l e l s the observations made on the r e a c t i o n s of the Group VI hexacarbonyls w i t h the new d i t e r t i a r y a r s i n e s l_-_7. Thus f o r r e a c t i o n (16), i t i s probable that >> k . - 55 -CHAPTER 4 NUCLEAR MAGNETIC RESONANCE RESULTS The r e s u l t s of the NMR st u d i e s of the new d i t e r t i a r y a r s i n e s l_-7_ and the chelate complexes 8-29 are presented i n t h i s f o u r t h chapter. Normally the sp e c t r a were amenable to f i r s t - o r d e r assignments and could be solved by i t e r a t i v e computer a n a l y s i s . However, the chemical s h i f t s and coupling constants were not e a s i l y d erived from the NMR spe c t r a of s e v e r a l of these compounds and heteronuclear double resonance experiments f a c i l i t a t e d the d e t a i l e d analyses of these p a r t i c u l a r cases. I t was assumed that geminal c o u p l i n g constants are negative, 19 19 whi l e geminal F- F coupling constants were taken to have p o s i t i v e 133 1 1 1 19 sig n s . Furthermore, v i c i n a l H- H and H- F coupling constants were accepted as having p o s i t i v e signs.134 137 ^ n t n ^ s b a s i s , the 1 1 19 19 138 signs of s e v e r a l H- H and F- F coupling constants were determined. I. New D i t e r t i a r y A r s i n e s A common feature of the NMR sp e c t r a of the ligands J.-7 i s the presence of peaks a t t r i b u t a b l e to the arsenic-methyl groups. U s u a l l y these resonances are l o c a t e d close to one another and they f r e q u e n t l y - 56 -overlap. In s e v e r a l instances these peaks are complicated by coupling w i t h the f l u o r i n e atoms on the two-carbon b r i d g e . P a r t of the NMR spectrum of l , 2 - b i s ( d i m e t h y l a r s i n o ) - l - ( t r i m e t h y l s i l y l ) -ethane IL i s shown i n Figure 4. I t i s complicated by the presence of the peaks at 9.02 x and 10.00 x, which r e s u l t from the contamination of the sample by the s t a r t i n g m a t e r i a l s t e t r a m e t h y l d i a r s i n e and t r i m e t h y l v i n y l s i l a n e , r e s p e c t i v e l y . Ignoring these resonances, the NMR spectrum c o n s i s t s of a sharp s i n g l e t at 9.94 x ( ( C H ^ ^ S i ) , a quartet centered at 9.19 x ^ ( C H ^ ^ A s ) , a l e s s i n t e n s e quartet at 9.383 x (IH) , and a m u l t i p l e t from 8.30-8.60 x (2H). For a completely f i r s t - o r d e r spectrum, three separate resonances are expected to a r i s e from H^,, ^ and R^ , . However, the s t r u c t u r e of the downfield m u l t i p l e t suggests that the spectrum i s , „ , „ . , . - i n 139,140 1 , d e c e p t i v e l y simple , s i n c e only seven major peaks are present, when twelve are expected. Two of the c o u p l i n g constants were estimated from the s p l i t t i n g s i n the u p f i e l d q u a r t e t , nevertheless these spacings could not be r e a d i l y i d e n t i f i e d i n the m u l t i p l e t . Subsequent "*'H-{"'"H} INDOR e x p e r i -ments showed that l i n e s 1-7 (see Figure 4) were a c t u a l t r a n s i t i o n s . U n f o r t u n a t e l y , an unambiguous assignment based on these INDOR responses could not be made due to the low i n t e n s i t i e s of l i n e s 1, 2, 7, and 8, and the overlap of l i n e s 5 and 6. However, once the a c t u a l t r a n s i t i o n s were recognized, i t was a simple matter to i d e n t i f y the spacings generated by the t h i r d c o u p l i n g , and a l l the t r a n s i t i o n s were assigned to i n d i v i d u a l proton resonances. This provided s u f f i c i e n t data f o r an i t e r a t i v e computer a n a l y s i s of the spectrum, but i t was s t i l l necessary J l 2 5,6 9 1Q 11 i — 12 8.20 8.40 8.60 8.80 9.00 9.20 9.40 T F i g u r e 4. P a r t i a l H NMR spectrum (100 MHz) of neat (CH ) 2 A s C H ( S i ( C H 3 ) 3 ) C H 2 A s ( C H 3 ) ^ A r e p r e s e n t a t i v e f i r s t - o r d e r assignment i s given above the spectrum. - 58 -to determine which resonances corresponded to the methylene and methine protons. The r e l a t i v e signs of the three coupling constants were determined from the NMR spectrum as f o l l o w s . Lines 1, 3, 4, and 7 form a symmetrical sub-quartet i n the m u l t i p l e t . I f the int e n s e s i n g l e t comprised of l i n e s 5 and 6 came between l i n e s 3 and 4, the coupling constants of the u p f i e l d resonance would have opposite s i g n s . On the other hand, i f this s i n g l e t l a y outside the region bounded by l i n e s 3 and 4, 140 they would have the same r e l a t i v e s i g n s . The spectrum of the t r i m e t h y l s i l y l d i t e r t i a r y a r s i n e 1 f a l l s i n t o the l a t t e r category so the c o upling constants i n the h i g h f i e l d resonance have the same r e l a t i v e s i g n s . Hence, they must be v i c i n a l coupling constants and i t f o l l o w s that the geminal protons, B.^ A N & JL?'' 8^ v e r ^ s e t o t n e m u l t i p l e t , w h i l e the u p f i e l d quartet corresponds to H.. t. A n a l y s i s of the NMR spectrum of 1 , 2 - b i s ( d i m e t h y l a r s i n o ) - 1 - ( t r i c h l o r o -s i l y l ) e t h a n e 2^  a l s o presented c e r t a i n problems. The ^H spectrum of the ethane bridge protons i s shown i n Figure 5. Pa r t of the spectrum i s obscured by the presence of the broad peak at 8.42 x, which i s l i k e l y due to an im p u r i t y . Furthermore, the equal spacings of many of the t r a n s i t i o n s made i t d i f f i c u l t to propose t e n t a t i v e assignments. However, 1 1 H-{ H} INOOR study enabled the spectrum to be sol v e d ; the r e s u l t s of these experiments are presented i n Table X. I r r a d i a t i o n of l i n e s 1-4 (see Figure 5) showed that peaks 1-4 (A), 5-8 (B), and 9-12 (C) could be assigned to separate proton resonances. The INDOR responses a l s o i n d i c a t e d that and have opposite s i g n s . Hence A and B are H^ 75 133 and w h i l e C i s H^t . ' 8.00 8.20 8.40 8.60 T Figure 5. P a r t i a l """H NMR spectrum (100 MHz) of neat ( C H 3 ) 2 A s C H ( S i C l 3 ) C H 2 A s ( C H 3 ) 2 A r e p r e s e n t a t i v e f i r s t - o r d e r assignment i s given above the spectrum. - 60 -Table X. INDOR Responses of (CH 3) 2AsCH(SiCl 3)CH^As(CH 3> 2 2_.a,h Observe 1 2 3 4 5 6 7 8 9 10-11 12 1 2 3 JJ •H 4 to t 5 6 12 * R P R P * R P P R * P R R P * P R P R R P * R P R P * P R P R P R * R = r e g r e s s i v e t r a n s i t i o n , P = pr o g r e s s i v e t r a n s i t i o n , k * i n d i c a t e s i r r a d i a t i o n of t h i s t r a n s i t i o n . For the remaining d i t e r t i a r y a r s i n e s , excluding (CH 3) 2AsCF 2CH 2-A s ( C H 3 ) 2 5_, the lowest f i e l d resonance was i n t u i t i v e l y assigned to the methine proton, t h i s being the one which i s most deshielded by the e l e c t r o n e g a t i v e s u b s t i t u e n t s at C^. The spectrum of l , 2 - b i s ( d i m e t h y l a r s i n o ) - l - f l u o r o e t h a n e 3^  i s complicated by the s p i n - s p i n coupling from the f l u o r i n e s u b s t i t u e n t . 1 19 I t was s i m p l i f i e d by a H-{ F} heteronuclear decoupling experiment, 19 and t h i s spectrum, together w i t h that of the F resonance, provided data f o r a complete computer a n a l y s i s . 1 19 The H and F s p e c t r a of 1,2-bis(dimethylarsino)-1,1,2-19 L 1 19 t r i f l u o r o e t h a n e 4^  were analyzed w i t h the a i d of F-{"H} and H-{ F} heteronuclear decoupling experiments. The r e l a t i v e s i g n s of the 19 19 v i c i n a l F- F c o u p l i n g constants were not e x p l i c i t l y determined, but were assumed to have the same signs as the analogous c o u p l i n g constants i n the metal carbonyl chelate complexes of t h i s l i g a n d . The experiments 3 i n which the r e l a t i v e signs of the v i c i n a l J values were determined F F i n a chelate complex are described l a t e r i n t h i s Chapter. The spectrum of the r e l a t e d t r i f l u o r o d i t e r t i a r y phosphine, (CH 3) 2PCF 2CFHP(CH 3) 2, was s i m p l i f i e d and analyzed w i t h the a i d of "*"H-{^F}, ^ - { ^ ^ P } , "'"'F-'I^ H}, and ^Y-{^^"p} decoupling experiments. 19 U s u a l l y the spectrum of an ABX F s p i n system i s expected to c o n s i s t of a quartet of m u l t i p l e t s a r i s i n g from the geminal (AB) f l u o r i n e s , and a s i n g l e m u l t i p l e t due to the X f l u o r i n e atom, i f J A T ) >> J A V . and J . ^ , and 6AT> >> J A T > . In t h i s i n stance the geminal AB AA DA AD AB f l u o r i n e s were separated by a r e l a t i v e l y s m a l l chemical fehift d i f f e r e n c e , *AB ~ dAB* Consequently, the outer m u l t i p l e t s of the AB " q u a r t e t " were i n s u f f i c i e n t l y i ntense to observe, so i t was necessary to estimate SAB 19 19 the values of the chemical s h i f t d i f f e r e n c e 6 and the geminal F- F coupling constants J,„. AB The spectrum of the methylene protons of (CH 3) 2AsCH 2CF 2As (CH 3) 2 5_ i s shown i n Figure 6. The center line of the t r i p l e t i s s l i g h t l y s p l i t i n t o a doublet w i t h 0.6 Hz s e p a r a t i o n . Using t h i s spacing and estimates 19 19 1 1 of the geminal F- F and geminal H- H c o u p l i n g constants, 260 Hz 139 141 and -13.0 Hz r e s p e c t i v e l y , the spectrum was analyzed, ' . y i e l d i n g 3 1 19 the v i c i n a l J- values. F o r t u n a t e l y , the derived v i c i n a l H- F Hr I ON N> 7.60 7.80 8 . 00 8 . 20 T Figure 6. P a r t i a l ^ NMR spectrum (100 MHz) of neat (CH 3) 2AsCF 2CH 2As(CH 3) 2. - 63 -coupling constants are e s s e n t i a l l y independent of the estimates f o r 2 both of the geminal coupling constants. V a r i a t i o n s of + 15 Hz i n the J 2 value and of + 0.5 Hz i n the J value r e s u l t i n a change of only — nil 1 19 + 0.3 Hz i n the v i c i n a l H- F c o u p l i n g constants. Tables XI and X I I c o n t a i n the chemical s h i f t s and c o u p l i n g 1 19 constants derived from the H and F s p e c t r a of the neat d i t e r t i a r y a r s i n e s _l-7_* Data obtained from measurements on 1,2-bis(dimethy1-p h o s p h i n o ) - l , l , 2 - t r i f l u o r o e t h a n e are a l s o i n c l u d e d . I I . Chelate Complexes As noted f o r the new d i t e r i a r y a r s i n e s , a l l the NMR s p e c t r a of the chelate complexes 8-29 e x h i b i t peaks r e s u l t i n g from the a r s e n i c -methyl or phosphorus-methyl groups. These resonances u s u a l l y do not overlap w i t h the remainder of the t r a n s i t i o n s i n the s p e c t r a . The ^H NMR spectrum of 1 , 2 - b i s ( d i m e t h y l a r s i n o ) - l - ( t r i m e t h y l s i l y l ) -ethanetetracarbonylchromium 8^, shown i n Figure 7, i s t y p i c a l of those obtained f o r the chelate complexes 8-29. The intense s i n g l e t at 10.0 x can be a t t r i b u t e d to the ( C H ^ ^ S i group, w h i l e the quartet between 8.5 T and 9.0 x corresponds to the arsenic-methyl resonances. The s p e c t r a of the protons on the two-carbon bridge were assigned on a f i r s t - o r d e r b a s i s and presented no problems, beyond a d e c i s i o n as to which of the resonances were those of the geminal p a i r of protons. Thus the r e l a t i v e signs of the three coupling constants were determined by the s p i n - t i c k l i n g t e c h n i q u e . I r r a d i a t i o n of the lowest f i e l d t r a n s i t i o n of the H, quartet caused both of the lower f i e l d t r a n s i t i o n s 1 2 Table XI. F i r s t - o r d e r Chemical S h i f t s (x and <j> Values) f o r the Neat Ligands (CH 3) 2EC--CE(CH 3) 2. Compound 1 1' 2 2' Methyl Groups (CH 3) 2AsCH(Si(CH 3) 3CH 2As(CH 3) 2 1 9.383 8.517 8.438 9.156 9.186 9.198 9.226 (C H 3 ) 2 A s C H ( S i C l 3 ) C H 2 A s ( C H 3 ) 2 2 8.502 8.330 8.107 8.841 8.885 9.027 9.040 (CH 3) 2AsCH 2CHFAs(CH 3) 2 3 188.33 4.939 7.988 8.171 b (CH ) 2AsCHFCF 2As (CH 3) 2 4. 4.961 211.02 106.59 a 108.36 a b (CH 3) 2PCHFCF 2P(CH 3) 2 5.122 214.88 111 a ' d 113 a ' d b (CH 3) 2AsCH 2CF 2As(CH 3) 2 _5 7.939 7.939 90.76 90.76 8.870 8.870 8.940 8.940 (CH 3) 2AsCH 2CHClAs(CH 3) 2 6 5.152 7.923 7.999 b (CH ) 2AsCH 2CH--(CN)As(CH 3) 2 I 7.303 8.235 8.340 8.923 8.923 8.969 9.000 The stereochemical assignment was made a r b i t r a r i l y since the angular dependence of F- F coupling i s not w e l l known.138 Data are not reported due to complexity of methyl resonances. Phosphorus chemical s h i f t s were not determined. These are estimated values, see t e x t . 1 . 2 Table X I I . F i r s t - o r d e r Coupling Constants (Hz) f o r the Neat Ligands (CH ) E C 1 —CE(CH ) .'2' J 1 Compound J l l * J12 J12' J1'2 J1'2' J22' (CH 3) 2AsCH 2CH(Si CCH3) 3) As (CH.3) 2 1 9.1 5.2 -12.9 ( C H 3 ) 2 A s C H 2 C H ( S i C l 3 ) A s ( C H 3 ) 2 2 7.0 6.8 -13.4 (CH 3) 2AsCH 2CHFAs(CH 3) 2 3 49.5 14.0 39.3 10.1 4.9 -13.2 (CH 3) 2AsCHFCF 2As(CH 3) 2 4_ 47.5 13.1 21.5 -16.0 -23.7 265.6 (CH 3) 2PCHFCF 2P(CH 3) 2 47.2 17.0 14.7 -18.6 -20.0 ==261 a ' b (CH 3) 2AsCH 2CF 2As(CH 3) 2 5 -13. C 13.3 31.0 31.0 13.3 =260 (CH 3) 2AsCH 2CHClAs(CH 3) 2 6 10.1 5.7 -13.1 (CH 3) 2AsCH 2CH(CN)As(CH 3) 2 7_ 10.9 5.5 -12.8 Estimated value, computer a n a l y s i s i t e r a t e d to 0.150 RMS e r r o r . Phosphorus coupling constants are: J 2 3 = 6.0 Hz, = 50.5 Hz, J 2 ^ = 10.2 Hz, = 8.4 Hz, J 3 5 = 2.7 Hz, J 3 , 5 = 17.0 Hz, J 4 5 = 23.0 Hz, = 24.0. Estimated v a l u e , see t e x t . J44' J3"4 "4' J3'4' J44' 10.5 7.5 8.0 85 9.0 9.5 10.0 10.5 r Figure 7. H NMR spectrum (100 MHz) of ( C H 3 ) 2 A s C H ( S i ( C H 3 ) 3 ) C H 2 A s ( C H 3 ) 2 C r ( C 0 ) 4 i n benzene s o l u t i o n . A r e p r e s e n t a t i v e f i r s t - o r d e r assignment i s given above the spectrum. - 67 -of the H^, resonance to s p l i t i n t o doublets, thus e s t a b l i s h i n g that J^^, and J ^ T ^ I have the same r e l a t i v e s i g n s ; hence and H^, must be the geminal p a i r of protons. Assignments f o r the other s i l i c o n d e r i v a t i v e s (CH 3> 2AsCH(Si(CH 3) ^ CI^As (CH^MCCO) 4 £-10 (M = Mo, W) , and ( C H 3 ) 2 A s C H ( S i C l 3 ) C H 2 A s ( C H 3 ) 2 C r ( C O ) 4 11 were made f o l l o w i n g t h i s precedent. In the remaining chelate complexes, except the (CH 3) 2AsCF 2CH 2~ A s ( C H 3 ) 2 5_ d e r i v a t i v e s , the lowest f i e l d resonance was assigned to the methine proton, as was done f o r the d i t e r t i a r y a r s i n e l i g a n d s i n the preceding s e c t i o n . The normal NMR spectrum of 1,2-bis ( d i m e t h y l a r s i n o ) - l - f luoroethane-tetracarbonylchromium 12 i s shown i n Figure 8. In a d d i t i o n to the couplings w i t h the f l u o r i n e s u b s t i t u e n t , i t i s f u r t h e r complicated by the p a r t i a l obscuring of the u p f i e l d proton resonance by the a r s e n i c -13 methyl resonances and t h e i r C and spinning s i d e bands. The spectrum was convemen 1 19 t l y s i m p l i f i e d by a "H-{ F} decoupling experiment, 19 1 shown i n Figure 8B. Together w i t h the spectrum of the F resonance the H spectrum was e a s i l y analyzed. An expansion of the arsenic-methyl region of t h i s spectrum i s shown i n Figure 9. 1 19 A n a l y s i s of the H and F s p e c t r a of l , 2 - b i s ( d i m e t h y l a r s i n o ) - l , l , 2 -t r ifluoroethanetetracarbonylchromium 14 was a l s o s t r a i g h t f o r w a r d except 3 138 that i t was necessary to determine the r e l a t i v e signs of the J values r r 19 19 by s e l e c t i v e F- F double resonance experiments. This was f a c i l i t a t e d 19 by p r i o r removal of a l l proton couplings from the F spectrum by the 73 noise-modulated, heteronuclear decoupling method. The r e s u l t i n g 4 . 5 5 . 0 5 . 5 7 . 5 " 8 . 0 ' ' 8.5 " ' 9 . 0 " —a5~ Figure 8. "hi-NMR spec t r a (100 MHz) of (CH 3) 2AsCHFCH 2As(CH 3) 2Cr(CO) 4 i n benzene s o l u t i o n . A i s the normal spectrum. B i s the spectrum measured w i t h 19 simultaneous i r r a d i a t i o n at the F resonance (94.077949 MHz). Diagramatic representations of the e f f e c t of the decoupling f i e l d and of the f i r s t order assignment are a l s o given. - 69 -Figure 9. Expansion of the H NMR resonances of the methyl groups of <CH 3) 2AsCHFCH A s ( C H 3 ) 2 C r ( C O ) 4 > A shows the normal resonances while B shows them w i t h simultaneous i r r a d i a t i o n i q at the F resonance (94.077949 MHz). - 70 -spectrum c o n s i s t e d of two adjacent quartets and F^,, which e x h i b i t e d 19 19 the l a r g e geminal F- F coupling constant, and a quartet F^, much f u r t h e r u p f i e l d . I t was found that i r r a d i a t i o n of the second highest f i e l d component of the resonance caused the lowest f i e l d component of F^, to s p l i t i n t o a doublet, thus e s t a b l i s h i n g that J^- J T a n d have the same r e l a t i v e s i g n s . When the lowest f i e l d component of F^ was i r r a d i a t e d , the f i r s t and t h i r d highest f i e l d components of F^, were s p l i t . Hence the r e l a t i v e signs of J ^ t and J^t^t are opposite and 19 19 138 the v i c i n a l F- F coupling constants have negative s i g n s , s i n c e 19 19 geminal F- F cou p l i n g constants are normally taken to be p o s i t i v e . 19 19 Because the F- F coupling constants of (CH^ A s C H F C F ^ s ( C H 3 > 2 _4, and (CH„)0ECHFCF-E(CH.)„ M(C0) X 14-19 (M = Cr, Mo, W; E = As; m = 4, 3 2 I 5 1 m n < and n = 0 : M = Mn; E = A s ; m = 3 ; X = B r ; n = 1: M = Cr, Mo; E = P , m = 4; n = 0) are s i m i l a r i n magnitude to those determined f o r the t r i f l u o r o chelate complex 14, i t i s assumed that the v i c i n a l J values — j< £ i n the former compounds are a l s o negative. The NMR sp e c t r a of the phosphorus analogs were f u r t h e r s i m p l i f i e d 1 31 by the use of H-{ P}, and other decoupling experiments. Figure 10 contains an example of phosphorus decoupling (Figure 10B) of the spectrum of the methine proton i n the chromium d e r i v a t i v e (CH 3) 2PCHFCF 2P-( C H 3 ) 2 C r ( C O ) 4 18. The NMR sp e c t r a of the chelate complexes (CH 3) 2AsCF 2CH 2As(CH 3) 2M(C0)^ 20-22 (M = Cr, Mo, W) were not subjected to computer a n a l y s i s s i n c e the s p e c t r a of the methylene protons show no f i n e s t r u c t u r e i n the expected t r i p l e t . This presumably r e s u l t s from complete averaging of 4.70 4.90 5.10 5.30 5.50 Figure 10. P a r t i a l 1H NMR sp e c t r a (100 MHz) of (CH 3) 2PCHFCF 2P(CH 3) 2Cr(C0) 4 i n chloroform s o l u t i o n . A i s the normal spectrum. B was measured w i t h 31 simultaneous i r r a d i a t i o n at the P resonance (40.4840000 MHz). Representations of the f i r s t - o r d e r assignment f o r the s p e c t r a are a l s o shown. - 72 -1 19 the H- F c o u p l i n g constants. On the other hand, the s p e c t r a of the manganese che l a t e d e r i v a t i v e s (CH^) 2AsCF 2CH 2As(CH^) 2Mn(C0)23-25 (X = C l , Br, I) c o n t a i n much more d e t a i l and were completely solved by the usual methods. Figure 11 shows the methylene regions of the s p e c t r a of the bromide complex 24. The a n a l y s i s of these proton s p e c t r a were complicated by two f a c t o r s . Attempts to s i m p l i f y the s p e c t r a by complete f l u o r i n e decoupling f a i l e d , probably because of the l a r g e chemical s h i f t d i f f e r e n c e s between the geminal p a i r of f l u o r i n e atoms. Furthermore, 1 19 the H s p e c t r a are very s o l v e n t dependent. However, the F s p e c t r a 19 1 enabled the v i c i n a l F- H c o u p l i n g constants to be estimated, and t e n t a t i v e assignments of the t r a n s i t i o n s i n the "Si s p e c t r a were made. 19 The F spectrum of the d i f l u o r o manganese chelate complex 24_ (chloroform solvent) i s shown i n Figure 12. T r a n s i t i o n s i n the normal spectrum (Figure 12A) are broadened by i n t e r a c t i o n of the 19 1 arsenic-methyl groups w i t h the f l u o r i n e atoms. By F-{ H} n o i s e -modulated heteronuclear decoupling experiment, the spectrum i n F i g u r e 12B was obtained, i n which both the arsenic-methyl.and methylene proton i n t e r a c t i o n s have been removed. The proton s p e c t r a are r e l a t e d to the " d e c e p t i v e l y simple" case described i n the d i s c u s s i o n of the NMR spectrum of the t r i m e t h y l s i l y l l i g a n d 1. I f the J^4' a n d ^3'4' c o u P i i n g s were removed i n the spectrum i n benzene or chloroform s o l u t i o n , the spectrum would appear as the l i n e s d e p i c t i n g the geminal coupling constants J g y • These l i n e s are i n d i c a t e d by the a s t e r i s k s i n Figures 11A and 11C. This derived spectrum i s very s i m i l a r to the spectrum of the methylene - 73 -A i . i . i . i . i . i . i . i - — i 7.60 7.80 8.00 8.20 8.40 7.00 72 0 740 7.60 7 80 7.10 7.30 7.50 7.70 7.90 "£ Figure 11. P a r t i a l h NMR s p e c t r a (100 MHz) of (CH 3) 2AsCF 2CH 2As(CH 3) -Mn(C0) 3Br i n benzene (A), d^-acetone (B) , and chloroform (C). Representative f i r s t - o r d e r assignments are provided above each spectrum. 8.50 8.60 8.70 9.90 10.00 10.10 K H z Figure 12. F NMR spectrum (94.077 MHz) of (CH 3) 2AsCF 2CH 2As(CH 3) 2Mn(C0) 3Br i n chloroform s o l u t i o n . A i s the normal spectrum. B i s the spectrum measured w i t h noise-modulated simultaneous i r r a d i a t i o n of the proton resonances (99.9887400 MHz f o r the u p f i e l d f l u o r i n e and 99.9876400 MHz f o r the downfield f l u o r i n e ) . - 75 -re g i o n of the t r i m e t h y l s i l y l d i t e r t i a r y a r s i n e shown i n Figure 4. By a s i m i l a r argument, the cou p l i n g constants J - j ? ^ an& J34 a r e p r e d i c t e d 19 1 to have the same s i g n s . Since v i c i n a l F- HH co u p l i n g constants are X 3A X37 p o s i t i v e , t h i s provides f u r t h e r c o r r o b o r a t i o n of the assignment 19 1 that a n d J34 are F- H coupling constants w h i l e c o r r e s P o n d s to the geminal c o u p l i n g constant. This r a t i o n a l e of course depends on the f a c t that the r e l a t i v e l y s m a l l coupling constants, J - j i ^ t 19 1 and J34' are already assumed to be v i c i n a l F- H cou p l i n g constants. The NMR s p e c t r a pf the c h l o r o and cyano d e r i v a t i v e s , (CH 3) 2AsCHClCH 2~ A s ( C H 3 ) 2 C r ( C O ) 4 26 and (CH 3> 2AsCH(CN)CH 2As(CHg) 2M(CO) 4 27-29 (M = Cr, Mo, W) were u s u a l l y not d i f f i c u l t to s o l v e ; however, the cyano chelate d e r i v a t i v e s sometimes e x h i b i t unusual NMR s p e c t r a . One of the geminal proton resonances i s obscured by the arsenic-methyl peaks, w h i l e the t r a n s i t i o n s of the remaining two resonances overlap e x t e n s i v e l y . The "^H NMR spectrum (chloroform s o l v e n t ) of these two protons i n the cyano d e r i v a t i v e 27_ i s shown i n Figure 13. Since t h i s c helate complex i s not very s o l u b l e i n the s o l v e n t , i t was not p o s s i b l e to o b t a i n double resonance responses of s u i t a b l e magnitude. However, by running the sample at 220 MHz (Figure 13B) i t was p o s s i b l e to make an assignment of these t r a n s i t i o n s to e i t h e r H~, or H,. 3 4 V a r i a b l e temperature s t u d i e s performed on the t r i m e t h y l s i l y l j5, monofluoro JL2, d i f l u o r o j!£, t r i f l u o r o 1A^, and cyano 27_, d e r i v a t i v e s between -50°C and 120°C r e s u l t e d i n no app r e c i a b l e changes i n the coupling constants determined from these complexes. As a n t i c i p a t e d the chemical s h i f t s were observed to change w i t h the v a r i a t i o n s i n temperature, 142 - 76 -Figure 13. P a r t i a l H NMR s p e c t r a (100 and 220 MHz) of (CH 3) 2AsCH(CN)-CH 2As(CH 3) 2Cr(CO) 4 i n chloroform s o l u t i o n . A i s the spectrum measured at 100 MHz w h i l e B was measured at 220 MHz. Representations of the f i r s t - o r d e r assignments are given above the sp e c t r a . - 77 -The coupling constants i n the d i f l u o r o manganese bromide d e r i v a t i v e s (CH 3) 2AsCH 2CF 2As(CH 3) 2Mn(CO) 3Br 24 v a r i e d s l i g h t l y w i t h i n t h i s temperature 19 L. range. The v i c i n a l F - H coupling constants f o r the complex at 80°C are presented i n the Table described below. The chemical s h i f t s and coupling constants derived by i t e r a t i v e a n a l y s i s of the NMR s p e c t r a of chelate complexes 8-29 are summarized i n Tables X I I I , XIV and XV. p 0 r reasons discussed i n the next chapter, each compound was st u d i e d i n s e v e r a l d i f f e r e n t s o l v e n t s . Table X I I I . First-order 3 (CH3)2E C--Chemical Shifts (T qfE(CH3)2M(CO)nXm and <j> Values) for The Chelate Complexes 8-29^  Compound c Solvent 3 3' 4 4' Methyl Groups (CH )2AsCH(Si(CH3)3)CH2- C6 H6 10.187 7.953 9.310 8.673 8.767 8.827 9.003 As(CH3)2Cr(CO)4 8 CHC13 9.899 7.638 9.070 8.439 8.502 8.598 8.720 CH2C12 9.869 7.612 9.052 8.448 8.518 8.608 8.721 1 OO (CD3)2CO 9.85b 7.626 9.097 8.552 8.676 8.796 8.895 i C6H5N02 9.573 7.354 8.800 8.298 8.345 8.459 8.563 (CH3)2AsCH(Si(CH3)3)- C6 H6 10.176 8.041 9.299 8.723 8.848 8.872 9.064 CH As(CH3) Mo(CO)4 9 CHC13 9.838 7.677 9.017 8.424 8.509 8.577 8.700 (CD3)2CO 9.529 7.481 8.831 9.002 9.097 9.154 9.264 (CH3)2AsCH(Si(CH3)3)- C6 H6 10.196 8.137 9.330 8.630 8.774 8.774 8.984 CH2As(CH3)2W(CO)4 10 CHC13 9.828 7.732 9.019 8.316 8.406 8.465 8.587 (CD3)2CO 9.467 7.501 8.797 8.259 8.365 8.407 8.520 Table XIII (Continued) Compound c Solvent 3 3' 4 4' Methyl Groups (CH3)2AsCH(SiCl3)CH2- C6 H6 9.718 7.964 9.183 8.633 8.695 8.967 9.215 As(CH3)2Cr(CO)4 11 CHC13 9.164 7.434 8.810 8.226 8.371 8.417 8.612 CH2C12 9.106 7.395 8.773 8.278 8.362 8.413 8.610 (CD3)2C06 C6H5N02e (CH3)2AsCHFCH2As- C6 H6 5.503 192.91 8.103 9.435 8.838 8.933 8.974 9.205 i —. (CH3)2Cr(CO)4 12 CHC13 4.400 193.17 7.500 8.734 8.439 8.486 8.520 8.650 1 CH2C12 4.374 193.01 7.485 8.720 8.446 8.494 8.519 8.660 (CD3)2CO 4.101 191.65 7.337 8.414 8.416 8.458 8.504 8.579 C6H5N02 4.203 192.44 7.374 8.529 8.390 8.436 8.486 8.581 (CH^AsCHFCH As- CHC13 4.467 193.46 7.528 8.667 8.448 8.495 8.519 8.653 (CH3)2Mo(CO)4 13 (CD3)2CO 4.176 192.95 7.374 d - 80 -m <r ON CN ro ro oo oo CO p-3 o u o H fi CD ro 00 cs) 00 CN CM 00 OS rH oo fi fi fi ON rH fi fi rH ON CM rH 00 00 CO VO rH vO CO rH CM rH CM VO ON ON O O rH m CM ro m m 00 ON o- ON m r~-ON ON ON 00 oo oo vo o 00 o ON r~ vO CM CM CM CM CM CM CM ro CM CM rH CM CM CM CM rH i-H rH rH rH rH rH rH rH rH rH rH rH rH rH vO 00 ON o ON O O O CM 00 O VO 00 rH O ON r- rH VO m ON 00 <r <f o -d-O O ON O O ON o ON o <d- CM CM CM CM CM CM rH CM CM rH CM rH CM t-H rH CM CM CM CM rH rH rH rH rH rH rH rH rH rH rH rH rH rH rH <f m CM rH ON ON rH m rH ON O ON vO 00 vO 00 ro <f CM <f ro <f CM in <T rH ro ro o ON o CM O ON CM ON CM <r CM ON CM ON CM CM rH CM CM CM rH CM rH CM co CO rH CM rH CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM m VO VO ON 00 CM CO . rH 00 m rH . CO VO VO rH o O m -* VO rH ON ON ON CM 00 ON CM rH <f rH <T CM CM rH <f <!• <!• <r m m -j- in <r <r <f m o- m <f O o O o o o CJ CM CJ CJ CJ CJ CJ CM CM o CM CM CM CM CN CO rH •—^ 53 CO ,-—s CO CO •—\ ro ro /—\ VO rH CJ ro m rH ro rH ro rH CO rH ro rH c S3 C_) CM P 33 u P CJ P CJ p CJ P CJ p vO 33 33 CJ> vO 33 c_> 33 CJ 33 CJ 33 CJ 33 CJ CJ CJ CJ s CJ CJ — ' CJ >—' CJ V / CJ vv CJ T3 CJ 3 C a o CJ x CD rH fi rt H T3 c 3 O PA & o CJ 1 1 mi 1 VO| 1 oo ON j CO rH| CO rH 1 to rH| CD rH| --ll < < <ti U 1 1 CM CM CM CM pq PH PH PH PH PH CO CM CM a CJ /—N u CJ / N PH pH PH o o PH /—N Cn o CJ o CJ o 33 CJ 33 CJ 33 o 33 CJ CJ PH CJ CJ — a v—' CJ CJ CJ ^—' 33 *—^ 33 CO 5-1 CO c CO ^ ' CO CJ 5-1 CJ o < CJ <! S < < S PH CJ PH CM CM CM CM CM CM CM CM CM CM CM CM •—s ,—N CO CO ro CO CO CO CO CO CO CO CO CO 33 33 33 33 33 33 33 33 33 33 33 33 CJ CJ CJ CJ CJ O CJ CJ CJ CJ CJ U '—' ^—' Table X I I I (Continued) Compound c Solvent 3 3' 4 4' Methyl Groups (CH 3) 2AsCH 2CF 2As- C 6 H 6 9.22 9. 22 105.8 105.8 9.42 9.42 9.52 9.52f ( C H 3 ) 2 C r ( C O ) 4 20 (CH ) AsCH CF 2As- C 6 H 6 9.17 9. 17 — — 9.43 9.43 9.55 f 9.55 (CH 3) 2Mo(CO) 4 21 ( C H ^ A s C H CF As- C 6 H 6 9.28 9. 28 — — 9.42 9.42 9.51 f 9.51 (CH 3) 2W(C0) 4 22 (CH 3) 2AsCH 2CF 2As- CHC1 3 7.713 7. 549 92.06 107.06 8.357 8.357 8.357 8.430 (CH ) Mn(C0) 3Cl 23_ (CD 3) 2C0 7.670 7. 292 92.37 104.92 8.306 8.329 8.366 8.366 (CH 3) 2AsCH 2CF 2As- C 6 H 6 8.079 8. 197 91.45 106.42 8.530 8.660 8.806 8.959 (CH 3) 2Mn(C0) 3Br 24_ CHC1 3 7.673 7. 546 91.79 106.62 8.273 8.273 8.358 8.484 (CD 3) 2C0 7.607 7. 272 92.28 104.64 8.252 8.273 8.312 8.360 (CH 3) 2AsCH 2CF 2As- CHC1 3 7.635 7. 502 92.93 103.59 8.183 8.183 8.303 8.452 (CH 3) 2Mn(CO) 3I 25 (CD 3) 2C0 7.497 7. 178 91.96 106.09 8.111 8.111 8.274 8.320 Table X I I I (Continued) Compound c Solvent 3 3* 4 4' Methyl Groups (CH 3) 2AsCHClCH 2As- C 6 H 6 6.492 8.930 . 8.544 8.883 8.938 9.082 9.111 ( C H 3 ) 2 C r ( C O ) 4 26 CH 2C1 2 5.672 8.134 7.789 8.448 8.448 8.521 8.565 C 6H 5N0 2 5.522 8.042 . 7.711 8.425 8.425 8.477 8.528 (CH 3) 2AsCH(CN)CH 2As- C 6 H 6 a 8.932 9.008 9.082 9.244 (C H 3 ) 2 C r ( C O ) 4 27 CHC1 3 7.736 7.765 d 8.376 8.396 8.427 8.539 CH 2C1 2 7.643 7.800 8.334 8.287 8.299 8.326 8.434 o (CD 3) 2CO 6.985 7.622 8.034 8.351 8.362 8.390 8.466 C 6H 5N0 2 7.151 7.625 8.061 8.283 8.273 8.324 8.443 (CH 3) 2AsCH(CN)CH 2As- CHC1 3 7.644 7.832 8.334 8.386 8.400 8.430 8.538 (CH 3) 2Mo(CO) 4 28 (CD 3) 2CO 6.930 7.670 7.993 8.334 8.334 8.373 8.444 (CH 3 ) 2 A s CH(CN)CH 2 A s - CHC1 3 7.683 7.867 d 8.258 8.270 8.309 8.419 (CH 3) 2W(CO) 4 29 (CD 3) 2CO 6.853 7.679 d 8.218 8.218 8.265 8.329 The stereochemical assignment was made a r b i t r a r i l y s ince the angular dependence of F- F coupling i s not w e l l known. Data are not reported due to complexity of methyl resonances. In order of i n c r e a s i n g d i e l e c t r i c constant. d Proton resonance was obscured by the methyl resonances. The sample decomposed i n s o l u t i o n . ^ E x t e r n a l TMS • ? 4 Table XIV. F i r s t - o r d e r Coupling Constants (Hz) f o r The Chelate Complexes 8-29 (CH ) EC—C E(CH„)„M(CO) X j z ^ j ^ i j ^ c n in Compound Solvent '33* 34 '34« J3'4 J3'4* '44' ( C H 3 ) 2 A s C H ( S i ( C H 3 ) 3 ) -CH 2As(CH 3) 2Cr(CO) 4 8 (CH ) AsCH(Si(CH ) )-CH 2As(CH 3) 2Mo(CO) 4 9_ ( C H 3 ) 2 A s C H ( S i ( C H 3 ) 3 ) -CH 2As(CH 3) 2W(CO) 4 10 C 6 H 6 CHC1, CH 2C1 2 (CD 3) 2CO C 6H 5N0 2 C 6 H 6 CHC1, (CD 3) 2C0 C 6 H 6 CHC1, (CD 3) 2C0 5.1 5.2 5.3 5.0 5.2 4.5 4.5 4.4 4.5 4.6 4.5 15.9 16.1 15.9 16.1 15.9 15.7 15.9 16.0 15.9 16.0 16.0 -12.7 -12.8 -12.8 -12.8 -12.7 -13.0 -13.0 -12.9 -13.0 -12.9 -13.1 oo Table XlV(Continued) Compound c Solvent J 3 3 ' J34 J34' J3'4 J3'4' J44" ( C H 3 ) 2 A s C H ( S i C l 3 ) C H 2 - C 6 H 6 4.8 15.5 -12.5 A s ( C H 3 ) 2 C r ( C O ) 4 11 CHC1 3 5.3 15.4 -12.8 CH 2C1 2 5.2 15.5 -12.9 (CH 3) 2AsCHFCH 2- C 6 H 6 49.6 3.6 3.4 15.7 48.7 -13.9 A s ( C H 3 ) 2 C r ( C O ) 4 12 CHC1 3 49.7 3.6 3.4 15.5 48.3 -14.0 CH 2C1 2 49.7 3.6 3.4 15.8 48.8 -14.0 (CD 3) 2CO 49.6 3.5 3.2 16.2 50.8 -14.3 C 6H 5N0 2 49.6 3.4 3.3 15.9 49.6 -14.0 (CH 3) 2AsCHFCH 2- CHC1 3 49.1 4.5 2.9 14.0 48.2 -14.0 As(CH 3) 2Mo(CO) 4 13 (CD 3) 2CO 49.4 4.1 2.9 14.2 49.2 d -14.4 (CH 3) 2AsCHFCF 2As- C 6 H 6 49.0 5.5 15.1 -23.4 -15.8 266.9 ( C H 3 ) 2 C r ( C O ) 4 14 CHC1 3 49.1 5.3 14.8 -23.8 -15.9 267.9 CH 2C1 2 49.6 5.3 15.0 -23.6 -15.8 267.5 (CD 3) 2CO 48.3 5.6 17.3 -21.6 -15.0 264.7 C 6H 5N0 2 48.7 5.4 16.0 -22.6 -15.6 265.8 Table XIV(Continued) Comoound Solvent J33. J 3 4 '34' J3*4 J3'4' J44' (CH 3) 2AsCHFCF 2As-(CH 3) 2Mo(CO) 4 15 (CH 3) 2AsCHFCF 2As-(CH 3) 2W(CO) 4 16 (CH 3) 2AsCHFCF 2As-(CH 3) 2Mn(CO) 3Br 17 (CH 3) 2PCHPCF 2P-( C H 3 ) 2 C r ( C O ) 4 1 8 8 (CH ) PCHPCFgP-(CH 3) 2Mo(CO) 4 1 9 J (CH 3) 2AsCH 2CF 2As-( C H 3 ) 2 C r ( C O ) 4 20 (CH ) AsCH CFjAs-(CH 3) 2Mo(CO) 4 21 CHC1, (CD 3) 2C0 CHC1, (CD 3) 2CO CHC1. (CD 3) 2CO CHC1, (CD 3) 2CO CHC1, (CD 3) 2CO C 6 H 6 C 6 H 6 48.9 48.5 48.7 48.0 48.4 47.4 48.0 47.0 4.7 5.3 4.5 5.0 48.5 26.2 48.1 24.8 6.0 6.2 5.2 5.3 16.1 19.1 15.1 18.0 7.3 7.9 18.5 20.8 19.7 21.9 18.0 18.0 18.2 18.2 -23.2 -20.0 -23.6 -20.9 -10.6 -10.8 -17.6 -16.3 -16.8 -14.9 18.0 18.2 -16.3 268.4 -15.0 264.2 -16.4 269.9 -15.2 265.9 -13.2 251.4 -13.8 252.2 -15.5 269.5* -14.6 266.0 -15.4 269.8 -14.7 266.1 18.0 18.2 Table XlV(Continued) Compound Solvent J 3 3 ' J34 J34' J3*4 J3'4' J44' (CH 3) 2AsCH 2CF 2As- C 6 H 6 — 18.0 18.0 18.0 18.0 — (CH 3) 2W(CO) 4 22 (CH 3) 2AsCH 2CF 2As- CHC1 3 -13.1 44.9 6.7 12.7 7.0 248.5 .(CH ) Mh(CO) C l 23 (CD 3) 2CO -13.1 40.6 7.9 15.2 9.5 245.7 (CH ) AsCH CF 2As- C 6 H 6 -13.1 40.5 7.4 17.2 7.3 247.2 i (CH 3) 2Mn(CO) 3Br 24 CHC1 3 -13.2 42.0 7.0 14.9 7.2 248.4 oo ON 1 CHC13(80°C) -13.1 39.4 7.4 16.2 8.1 (CD 3) 2CO -13.3 39.9 7.9 15.0 9.5 246.2 (CH 3) 2AsCH 2CF 2As- CHC1 3 -13.1 40.5 7.7 14.5 8.2 245.1 (CH 3) 2Mn(CO) 3I 25 (CD 3) 2CO h -13.3 35.6 7.6 13.7 9.5 247.2 (CH 3) 2AsCHClCH 2As- C 6 H 6 5.2 7.5 -13.2 ( C H 3 ) 2 C r ( C O ) 4 26 CHC1 3 CH 2C1 2 (CD 3) 2CO C 6H 5N0 2 4.8 4.9 4.8 5.0 7.2 7.2 6.5 6.7 -13.4 -13.6 -13.6 -13.5 Table XlV(Continued) Compound Solvent J33« J34 J34' J3'4 • J3'4* J44* (CH 3) 2AsCH(CN)CK 2As- C6 H6 d ( C H 3 ) 2 C r ( C O ) 4 27 CHC1 3 5.8 11.4 -12.4 CH 2C1 2 6.0 11.1 -13.1 (CD 3) 2CO 6.1 10.2 -12.9 C 6H 5N0 2 6.1 10.2 -13.0 (CH 3) 2AsCH(CN)CH 2As- CHC1 3 5.4 11.1 -13.0 (CH 3) 2Mo(CO) 4 28 (CD 3) 2CO 5.4 10.1 -13.3 (CH 3) 2AsCH(CN)CH 2As- CHC1 3 5.4 11.8 -13.6 (CH 3) 2W(CO) 4 29 (CD 3) 2CO 5.7 9.8 -13.2 a-f See Table X I I I . 31 19 31 1 See Table XV f o r P- F and P- H coupling constants. h Values are approximate since the i t e r a t i o n proceeded only to 0.7 RMS e r r o r . Table XV. F i r s t - o r d e r Phosphorus Coupling Constants (Hz) f o r the Chelate Complexes. (CH 3) 3 4 PC—C P 1 V 4' (CH 3) 2M(CO) 4 1 Compound Solvent J 2 3 J 2 3 ' J24 J24' J 3 5 J3'5 J 4 5 J4'5 (CH 3) 2PCH?CF 2P- CHC1 3 7.9 =35.O3 9.9 2.1 0.8 = 2.0^ 34.2 35.6 ( C H 3 ) 2 C r ( C O ) 4 18 (CD 3) 2CO 6.2 31.0 11.8 1.3 1.2 2.8 32.0 38.8 (CH 3) 2PCHFCF 2P- CHC1 3 7.3 36.5 8.1 1.5 1.0 1.2 36.5 38.7 (CH 3) 2Mo(CO) 4 19 (CD 3) 2CO 6.1 33.8 9.9 0.8 1.3 1.9 34.0 42.5 J and J couplings are assumed to be l a r g e r than J and J couplings. These values are estimated at + 1 Hz. - 89 -CHAPTER 5 CONFORMATIONAL DISCUSSION This f i n a l chapter b r i n g s forward i n t e r p r e t a t i o n s of the NMR data i n terms of che l a t e r i n g conformations. The e f f e c t s of v a r i o u s p e r t u r b a t i o n s on these chelate systems are a l s o considered, and comparisons w i t h the X-ray r e s u l t s are made. The d i s c u s s i o n i s completed by con s i d e r i n g the NMR r e s u l t s obtained from the new d i t e r t i a r y a r s i n e s . I . I n t r o d u c t i o n A. L i m i t a t i o n s I t i s worthwhile to r e i t e r a t e the l i m i t a t i o n s inherent i n the conformational s t u d i e s of five-membered chelate r i n g s . C a l c u l a t i o n s by 22-24 G o l l o g l y and coworkers on ethylenediamine type complexes i n d i c a t e that a simple five-membered c h e l a t e r i n g i s very f l e x i b l e , having a wide range of conformations of e s s e n t i a l l y e q u i v a l e n t energy, i n c l u d i n g unsymmetrical puckered conformations not considered i n previous s t u d i e s . - 90 -Thus the barrier to the conformational inversion of five-membered 24 chelate rings is relatively small, like that in cyclopentane, which 143-145 has been calculated as 3-4 kcal/mol. Hence, a l l conformations determined by the NMR method will be subject to some degree of time averaging. Furthermore, the ground state energies of conformations which are close to one another on the pseudorotational cycle, where the angle of pucker rotates around the ring, are probably similar.22,23,146 ^ & result, the present study is necessarily limited to an evaluation of which section of the pseudorotational cycle is populated, and possibly, of the extent of that population. A single, specific conformation cannot be assigned, although i t may be that in some instances one section of the pseudorotational cycle is extensively populated. In the present work attention is confined to defining the sense of rotation about the C-C bond of the ethane moiety, as represented by the "twist" (T) and "envelope" (v) conformers shown in M. c — A s As-=^^yV\ As 3 8: 4 V \ V 3 C 3 * A , , / \ A S As-«-_ /hA As A s - M,-* -~=^ As A s - pA M S — Q 4 M C 4 X: Yi 3 T 4 3 V M - 91 -The numerical s u p e r s c r i p t s on "T" and "V" i n d i c a t e the atom d i s p l a c e d above the plane defined by the remaining r i n g atoms, w h i l e s u b s c r i p t s i n d i c a t e an atom which i s below the plane. These l i m i t a t i o n s are made more p e r t i n e n t by some recent s t r u c t u r a l s t u d i e s on some hydrocarbon-bridged d i t e r t i a r y phosphine complexes. They r e v e a l unsymmetrically puckered r i n g s i n c l u d i n g conformations w i t h both carbon 147-149 atoms of the ethane b r i d g i n g group l y i n g below the P-M-P plane. Results obtained from the X-ray determinations of _ t r a n s - b i s ( e t h y l e n e -diamine) complexes a l s o show that asymmetric puckering i s common and that a great v a r i e t y of conformations e x i s t i n the s o l i d s t a t e . B. D i h e d r a l Angle R e l a t i o n s h i p s The v a r i o u s dependences of coupling constants between n u c l e i bonded to adjacent s a t u r a t e d carbon atoms should a l s o be considered before 3 proceeding w i t h the main pa r t of the d i s c u s s i o n . J values may „ 134-138,150-153 -l^  . ... . , , u -r e f l e c t : 1) changes xn the d i h e d r a l angle between cou p l i n g n u c l e i , 2) v a r i a t i o n s i n the e l e c t r o n e g a t i v i t i e s of the s u b s t i t u e n t s attached to the carbon atoms, 3) p e r t u r b a t i o n s i n the bond angles between the coupling n u c l e i and the adjacent carbon atoms, or 4) a l t e r a t i o n s i n the carbon-carbon bond length of the ethane b r i d g e . Consequently, any s t r u c t u r a l a n a l y s i s based on the d i h e d r a l angle dependence of v i c i n a l c o upling constants must take i n t o account the v a r i a t i o n s i n a l l these f a c t o r s as a f u n c t i o n of the t o t a l molecular environment. Bearing these i n mind, q u a l i t a t i v e conformational preferences of the five-membered chelate r i n g s may be derived from the - 92 -f o l l o w i n g angular r e l a t i o n s h i p s . V i c i n a l ^H-^H coupling constants have been shown to obey a dependence on the d i h e d r a l angle (<j>) by the relationship^^''" 2 J„„ ~ Acos <fc + Bcoscb + C rirl 136 152 153 The value of C i s g e n e r a l l y taken to be s m a l l , ' * w h i l e the 153 s i g n of B i s u s u a l l y negative. Thus J u„ f o r cb = 180° i s higher nn than J U 1 J f o r cb = 0 ° . T y p i c a l l y , f o r cyclohexane type systems, trans rirl ~ ( a x i a l - a x i a l , <f) = 180°) "hl-^H c o u p l i n g constants are i n the range 9-13 Hz, w h i l e gauche ( a x i a l - e q u a t o r i a l or e q u a t o r i a l - e q u a t o r i a l , <j> - 60°) H- H co u p l i n g constants are between 2-4 Hz. Trans coupling constants have been reported as high as 15.0 Hz f o r five-membered r i n g diamine type c h e l a t e c o m p l e x e s . ^ 4 ' S i m i l a r angular dependences have • • i 1 9 r - l u •>• - - 134-137 . M been proposed f o r v i c i n a l F- H coupling constants, as i n N. N 0 20 40 eo 80 IOO 120 140 160 ISO D IHEDRAL A N G L E Some workers have formulated t h i s d i h e d r a l angle r e l a t i o n s h i p as 3 J U 1 7 = Dcos2<(> 0° < <J> < 90° HF = Ecos2<j) 90° < <f> < 180° - 93 -Both types of expressions y i e l d r e s u l t s s i m i l a r to those obtained from the ^H-"hl f u n c t i o n described p r e v i o u s l y , except that the c o e f f i c i e n t s 3 19 1 give r i s e to much higher J values. Trans F- H c o u p l i n g constants 13A —137 3 f a l l i n the range 25-60 Hz w h i l e gauche J^p values have been found to be approximately three times lower i n magnitude. ^'-^^ The curves shown f o r the d i h e d r a l angle r e l a t i o n s h i p s of v i c i n a l 19 1, F-TI coupling constants i n N a r i s e from the d i f f e r i n g e l e c t r o n e g a t i v i t i e s of the substituents bonded to the ethane bridge carbon atoms. An increase i n e l e c t r o n e g a t i v i t y of the s u b s t i t u e n t s r e s u l t s i n the lowering of the values of the c o e f f i c i e n t A i n the type of expression described 1 1 f o r v i c i n a l H- H coupling constants. Thus the upper curve, 1, 3 2 represents a p l o t of J vs. Acos <j> + BcosiJ> + C, where the sum of the Hr s u b s t i t u e n t e l e c t r o n e g a t i v i t i e s i s lower than those sums f o r curves 2 or 3. Related compounds i n s i m i l a r conformations e x h i b i t d i f f e r e n t coupling constants due to t h i s dependence on e l e c t r o n e g a t i v i t y . For 19 1 example, the c i s F- H c o u p l i n g constant i n 3i4_ i s 25.1 Hz w h i l e that coupling constant i n the g e o m e t r i c a l l y s i m i l a r compound 2I5_ i s 15.9 Hz. 134 34 35 I t i s a l s o noteworthy that a given absolute v a r i a t i o n i n coupling constants w i l l r e q u i r e a much greater v a r i a t i o n i n those d i h e d r a l angles near 0°, 90°, or 180°, compared w i t h more "intermediate" d i h e d r a l - 94 -angles, s i n c e the curves are " f l a t t e s t " near these angles. As an i l l u s t r a t i o n , a r e d u c t i o n of the d i h e d r a l angle between a proton trans to a f l u o r i n e atom by 10° would be expected to r e s u l t i n a c o u p l i n g constant change of about 1 Hz, w h i l e a 10° v a r i a t i o n f o r these s u b s t i t u e n t s i n a gauche o r i e n t a t i o n would produce a d e v i a t i o n of at l e a s t 3 to 4 Hz. S i m i l a r a l t e r a t i o n s f o r two protons would y i e l d , 70,134-137 smaller changes. 1 1 19 1 In summary, H- H and F- H coupling constants f o r angles near 0° or 180° are very s e n s i t i v e to changes i n s u b s t i t u e n t e l e c t r o n e g a t i v i t y , but they are r e l a t i v e l y i n s e n s i t i v e to minor f l u c t u a t i o n s i n the d i h e d r a l angle. The opposite e f f e c t s are observed f o r gauche ^H-^H and 19 1 F- H coupling constants. 19 19 V i c i n a l F- F coupling constants do not seem to f o l l o w the normal 2 cos <j> type r e l a t i o n s h i p s , and l i t t l e stereochemical i n f o r m a t i o n has been 138 derived from these parameters. In the present study, the i n t e r p r e t a t i o n of coupling constant data i s mainly dependent on the presence or absence of l a r g e trans ^H-"4l or "^F-^H coupling constants. By t h i s method, i t can be p r e d i c t e d whether or not c h e l a t e r i n g s favor conformations i n which c e r t a i n s u b s t i t u e n t s maintain a trans or gauche o r i e n t a t i o n to one another. C. Chemical S h i f t s and Conformations Chemical s h i f t data can a l s o provide i n f o r m a t i o n about the conformati of the chelate complexes. For "l o c k e d " six-membered r i n g organic compounds i t i s f r e q u e n t l y found that a x i a l protons have higher chemical - 95 -s h i f t s than e q u a t o r i a l ones. A s i m i l a r r e s u l t i s obtained f o r 19 15 154 many ethylenediamine and propylenediamine chelate ' complexes of s e v e r a l t r a n s i t i o n metals. I I . Chelate Complexes A. Chelate Ring Conformations and V i c i n a l Coupling Constants I t i s convenient to s t a r t the d i s c u s s i o n w i t h the t r i m e t h y l s i l y l d e r i v a t i v e s 8-10. I t seems l i k e l y that the r i n g conformations of these substances would be d i c t a t e d by the s t e r i c requirements of the "bulky" t r i m e t h y l s i l y l groups.^""^ The v i c i n a l ''"H-^ H coupling constants appear to agree w i t h t h i s a n t i c i p a t i o n , being ca. 16 and ca. 5 Hz i n magnitude. The former value c l e a r l y indicates"'""^ a trans r e l a t i o n s h i p between the two protons as shown i n 0_. A s i m i l a r c o n c l u s i o n seems obvious f o r the r e l a t e d t r i c h l o r o s i l y l d e r i v a t i v e 11. In both instances the c a r b o n - s i l i c o n bond p r o j e c t s toward the periphery of the molecule as i f i t had an " e q u a t o r i a l " o r i e n t a t i o n . ( C H 3 ) ~ W -As ( O C ) 4 M ' - .A s (CH3)2 S i ( C H 3 ) 3^ 3 H, H 3' 8 M = C r 9 M = M o . 10 M = W - 96 -The e l e c t r o p o s i t i v e nature of the t r i m e t h y l s i l y l and dim e t h y l a r s i n o s u b s t i t u e n t s a l s o seems to be an important f a c t o r c o n t r i b u t i n g to the unusually l a r g e value of the trans coupling constants. The data f o r the monofluoro d e r i v a t i v e s 12-13 i n d i c a t e unequi-v o c a l l y that the f l u o r i n e s u b s t i t u e n t s have trans r e l a t i o n s h i p s w i t h respect to v i c i n a l protons and hence that the c a r b o n - f l u o r i n e bonds have " a x i a l " o r i e n t a t i o n s as i n P_. Thus the v i c i n a l ^H-"4l coupling constants are both r e l a t i v e l y s m a l l (ca. 3.5 Hz) w h i l e one of the 19 1 v i c i n a l F- H coupling constants i s approximately three times the magnitude of the other (ca. 49 and ca. 16 Hz) 70,134-137 I Q C L M " ( C H 3 ) 2 «jU' 3 ' 12 M = C r . 13 M • M o This marked conformational preference of the f l u o r i n e s u b s t i t u e n t s had not been a n t i c i p a t e d . In order to check i t s g e n e r a l i t y , the t r i f l u o r o d e r i v a t i v e s 14-16 were synthesized and s t u d i e d . T h e i r NMR parameters i n d i c a t e a major preference f o r two of the c a r b o n - f l u o r i n e bonds to have an " a x i a l " o r i e n t a t i o n , as i n Q. This c o n c l u s i o n i s 19 1 based p r i m a r i l y on the magnitudes of the v i c i n a l F- H coupling 19 19 constants, although the v i c i n a l F- F coupling constants appear to 138 19 1 be i n accord. The l a r g e s t v i c i n a l F- H co u p l i n g constant (ca. 15-19 - 97 -Q 14 M = Cr, 15 M n M o , 16 M = W Hz) i s much l e s s than expected f o r a f l u o r i n e atom i n a trans p o s i t i o n to a v i c i n a l proton. The phosphorus d e r i v a t i v e s (CH 3) 2PCHFCF 2P(CH 3) 2M(CO)^ 18-19 (M = Cr, Mo) y i e l d NMR parameters much l i k e those of t h e i r a r s e n i c analogs and i t appears that a l l these compounds have s i m i l a r conformations i n s o l u t i o n . At t h i s time i t i s not appropriate to comment on the 31 1 31 19 magnitudes of the P- H and P- F coupling constants s i n c e l i t t l e i s known about the dependence of these parameters on v a r i a t i o n s i n d i h e d r a l angle, bond l e n g t h , bond angle, and s u b s t i t u e n t e l e c t r o -n e g a t i v i t i e s . 3 On comparisonwith the l a r g e s t v i c i n a l J„_ values (ca. 15-19 Hz) Hr 19 1 obtained from the Group VI t r i f l u o r o d e r i v a t i v e s 14-16, the F- H coupling constants i n the manganese t r i f l u o r o d e r i v a t i v e 17 (ca. 25 and 7 Hz) seem to i n d i c a t e a greater " a x i a l " preference f o r the hydrogen atom, a l l other things being equal. However, the e l e c t r o n i c and s t e r i c e f f e c t of changing the metal atom and i t s s u b s t i t u e n t s has not been d e l i n e a t e d , so i t i s unwise at t h i s time to a t t r i b u t e a l l these - 98 -coupling constant changes to p u r e l y conformational a l t e r a t i o n s . I t i s i n t e r e s t i n g to note that the NMR s p e c t r a of compound JL7 e x h i b i t peaks corresponding to only one isomer. P o s s i b l y only one of the chelate complexes R ( l ) or R(2) i s formed i n the r e a c t i o n . A s i m i l a r R NMR spectrum would r e s u l t i f the f l u o r i n e and hydrogen s u b s t i t u e n t s i n the two isomers had corresponding i d e n t i c a l chemical s h i f t s and c o u p l i n g constants. In t h i s case, the s o l u t i o n could c o n t a i n a mixture of both R ( l ) and R(2). With the present data i t does not seem p o s s i b l e to choose between these two p o s s i b i l i t i e s . NMR parameters f o r the d i f l u o r o Group VI complexes 20-22 imply that conformational e q u i l i b r i u m occurs r a p i d l y on the NMR time scale,as i n S_. 19 1 This accounts f o r the complete averaging of the v i c i n a l F- H coupling constants (ca. 18 Hz). - 99 -In the d i f l u o r o manganese d e r i v a t i v e s 23-25, the magnetic equivalence of the hydrogen (and f l u o r i n e ) atoms i s removed and an ABXY type spectrum r e s u l t s . These ch e l a t e complexes may e x i s t i n s o l u t i o n as an e q u i l i b r i u m mixture of two conformers T ( l ) and T(2). T (O (2) 23 X = Cl, 24 X = Br, 25 X = I U n f o r t u n a t e l y , both of these "locked" conformers are expected to 3 e x h i b i t l a r g e trans J u v a l u e s , t h e r e f o r e the data cannot be r e a d i l y r rl i n t e r p r e t e d i n terms of t h e i r r e l a t i v e p o p u l a t i o n s . The chloro 2j6 and cyano 27-29 chelate d e r i v a t i v e s were next - 100 -examined i n order to determine whether other p o l a r s u b s t i t u e n t s e x h i b i t e d the same strong preference as the f l u o r i n e s u b s t i t u e n t s . Keeping i n mind the d i f f e r e n c e i n e l e c t r o n e g a t i v i t y between the s u b s t i t u e n t s of the f l u o r o 12-13,14-16, ch l o r o 26_, and cyano 27-29 d e r i v a t i v e s , the v i c i n a l "^H-^ H coupling constants seem to i n d i c a t e that n e i t h e r the cyano nor the chloro s u b s t i t u e n t favors the " a x i a l " o r i e n t a t i o n to the same extent as the f l u o r o s u b s t i t u e n t . Thus the trans ''"H-'hl coupling constants of 26_ (ca. 7 Hz) and of 27-29 (ca. 10 Hz) are both s i g n i f i c a n t l y l a r g e r than that of the f l u o r o d e r i v a t i v e s 12-13 (ca. 3.5 Hz), and these chelate complexes l i k e l y e x i s t as an e q u i l i b r i u m mixture of two conf ormers, as shown i n U_. U o o 26 M = Cr, R - C l ; 27 M = Cr , R = C N ; 28 M = Mo , R = C N ; 29 M = W , R = C N B. Chelate Ring Conformations and Chemical S h i f t s  The chemical s h i f t data f o r the ethane bridge s u b s t i t u e n t s of chelate complexes 8-29 corroborate the i n t e r p r e t a t i o n s based on the d i h e d r a l angle dependences of the v i c i n a l coupling constants. In the complexes which have s u b s t i t u e n t s predominantly favored i n an " a x i a l " or " e q u a t o r i a l " p o s i t i o n , the chemical s h i f t of the " a x i a l " methylene - 101 -proton i s s i g n i f i c a n t l y higher than that of the " e q u a t o r i a l " methylene proton. Thus the " a x i a l " geminal proton H^, i n the t r i m e t h y l s i l y l d e r i v a t i v e 8^  occurs at ca. 9.0 T, while the " e q u a t o r i a l " proton resonance i s centered at ca. 7.6 T. The methylene protons i n the monofluoro d e r i v a t i v e s 12-13 behave i n a s i m i l a r manner. In c o n t r a s t , the d i f l u o r b 23-25 and cyano 27-29 chelate d e r i v a t i v e s , which do not appear to have such extreme conformational preferences, e x h i b i t r e l a t i v e l y s m a l l chemical s h i f t d i f f e r e n c e s between the geminal protons. Indeed, by changing the s o l v e n t , these protons are sometimes observed to exchange t h e i r order. The "^H NMR s p e c t r a of the d i f l u o r o manganese bromide complex 7A_ (Figure 11) i l l u s t r a t e t h i s phenomenon. In the spectrum i n benzene (Figure 11A), has a lower chemical s h i f t than H^,. This order i s reversed i n the s p e c t r a determined i n d^-acetone (Figure 11B) and chloroform (Figure 11C). C. Chelate Ring Conformations and the Arsenic-methyl Groups In thei r NMR s p e c t r a , the m a j o r i t y of the chelate complexes e x h i b i t three or four peaks corresponding to the arsenic-methyl s u b s t i t u e n t s . I t d i d not seem p o s s i b l e to a s s i g n these resonances to s p e c i f i c methyl groups; however, i n the f l u o r i n a t e d d e r i v a t i v e s unequal 19 1, F- a coupling constants w i t h the methyl protons were observed, implying some s t e r e o s p e c i f i c i t y i n the m e t h y l - f l u o r i n e i n t e r a c t i o n s . For example, the NMR spectrum of 1 , 2 - b i s ( d i m e t h y l a r s i n o ) - l - f l u o r o e t h a n e -tetracarbonylchromium L2 (Figure 9) shows coupling between the methyl groups and the f l u o r i n e atom, which i s removed when the f l u o r i n e atom i s - 102 -decoupled (Figure 9B). Perhaps, i f the angular dependences of FCAsCH and FCCAsCH coupling constants were known, specific assignments could be made, and conformational information could be derived from the methyl-fluorine coupling constants. D. Alterations in the Geminal Coupling Constants At this point, i t is convenient to consider the variations of the 1 1 2 geminal H- H coupling constants. Among other dependences, values have been shown to become more negative as the electronegativity of the vicinal and geminal substituents increases, in a series of related 152 compounds. Many of the chelate complexes 8-29 exhibit similar behavior. For example, the geminal H^-^ H coupling constant in 1,2-bis-(dimethylarsino)-1-(trimethylsilyl)ethanetetracarbonylchromium J3 is ca. -13 Hz, while for 1,2-bis(dimethylarsino)-1-fluoroethanetetracarbonyl-chromium this value is ca. -14 Hz. This difference could be a result of the variation in electronegativities of the fluoro and trimethylsilyl substituents. E. Perturbations and Their Effect on Chelate Ring Conformations By perturbing the five-membered chelate rings, i t was hoped that further information could be derived about their conformations in solution. This was carried out by: 1) changing the solvent, 2) varying the transition metal, 3) replacing the arsenic atoms by phosphorus donor atoms, 4) altering the halogen substituent on the manganese atom, - 103 -and 5) v a r y i n g the sample temperature. Each of these are considered i n d e t a i l i n the f o l l o w i n g s e c t i o n s . 1. Solvent changes In an attempt to evaluate the p o s s i b l e i n f l u e n c e s of d i p o l a r i n t e r a c t i o n s on the conformational preferences of 8-29, t h e i r NMR parameters were determined i n a number of solve n t s w i t h v a r y i n g d i e l e c t r i c constants. I t i s w e l l known that conformers (or rotamers) having the higher d i p o l e moment are more favored by so l v e n t s of 157—159 higher d i e l e c t r i c constant, and i t was hoped that some systematic changes might thereby be induced i n the conformations, and hence the NMR parameters of 8-29. From i n v e s t i g a t i o n s on the NMR s p e c t r a of d i f l u o r o e t h y l e n e s , I h r i g and Smith"''^ showed that geminal ^H-^H and "'"^ F-^ H c o u p l i n g constants 19 1 19 19 and v i c i n a l F- H, and F- F coupling constants vary w i t h changes i n the solvent i n which the spectrum was obtained. The absolute 19 19 19 L, v a r i a t i o n s are greatest f o r the v i c i n a l F- F and F-H coupling constants (ca. 3 Hz) and are n e g l i g i b l e f o r v i c i n a l ^H-^H coupling constants. Therefore, i t seems that f l u o r i n a t e d compounds which have r i g i d s t r u c t u r e s w i l l have inherent solvent v a r i a b l e coupling constants and chemical s h i f t s , i r r e s p e c t i v e of any gross conformational, r o t a t i o n a l , or other form of change i n geometry. Furthermore, i f an analogy can be drawn between the d i f l u o r o e t h y l e n e s and the chelate systems examined 19 L, 19 19 i n t h i s work, the v i c i n a l F-"TI and F- F coupling constants obtained from the chelate complexes w i l l be expected to d i f f e r w i t h solvent - 104 -changes, independently of the r e l a t i v e conformer p o p u l a t i o n s . The data i n Table XIV agree w e l l w i t h these a n t i c i p a t i o n s . The v i c i n a l "'"H-^ H cou p l i n g constants f o r those complexes thought to have one conformer h i g h l y favored vary i n a range of ca. 0.3 Hz. However, these ^H-^H coupling constants i n the chloro 2!6_ and cyano 27-29 d e r i v a t i v e s vary by as much as 2 Hz, probably because of the a l t e r a t i o n s i n conformer populations w i t h the changes i n solvent p o l a r i t y . The 19 L. 19 19 v i c i n a l F-"H and F- F coupling constants a l s o vary as expected, sometimes by as much as ca. 3 Hz, as i n the t r i f l u o r o chelate d e r i v a t i v e s 15 and 16. The l a r g e s t v a r i a t i o n s i n coupling constants (ca. 15-20%) occur i n the d i f l u o r o manganese chelate complexes 23-25. U n f o r t u n a t e l y , the r e l a t i v e conformer populations have not been determined f o r these chelate d e r i v a t i v e s , making i t d i f f i c u l t to draw s p e c i f i c conclusions about the solvent dependency of the coupling constants. C l o s e r s c r u t i n y of the chemical s h i f t data, and a d d i t i o n a l experiments could p o s s i b l y provide some in f o r m a t i o n about i n t e r m o l e c u l a r and s o l v e n t -155 s o l u t e i n t e r a c t i o n s . 2. T r a n s i t i o n Metal V a r i a t i o n s I t seemed f e a s i b l e that by v a r y i n g the s i z e of the metal atom i n the five-membered chelate r i n g , subsequent conformational changes would occur i n the r e s t of the r i n g , and these would be r e f l e c t e d i n the NMR parameters of the chelate d e r i v a t i v e s 8-29. However, f o r a given s o l v e n t , only s m a l l changes i n the coupling constants and chemical - 105 -s h i f t s were observed f o r chromium, molybdenum, and tungsten analogs. The data f o r the t r i m e t h y l s i l y l d e r i v a t i v e s 8-10 shown i n Table XVI are 1 1 a good i l l u s t r a t i o n of t h i s behavior. The v i c i n a l H- H c o u p l i n g constants, J o t , and J 0 i / t i n d i c a t e that the conformations i n the c h e l a t e 3 4 3 4 r i n g s are approximately the same. 24 G o l l o g l y and coworkers have demonstrated that a v a r i e t y of t h e o r e t i c a l ethylenediamine chelate r i n g geometries are e n e r g e t i c a l l y s i m i l a r , l y i n g w i t h i n 0.2 kcal/mol of each other. Some of t h e i r c a l c u l a t i o n s o i n v o l v e d changing the metal-nitrogen bond lengths from 2.0 to 2.3 A, which caused v a r i a t i o n s i n the d i h e d r a l angle about the carbon-carbon bond from 57.5° to 65°. Thus the expected a l t e r a t i o n i n the d i h e d r a l angle f o r a bond length increase of 14%, 100 x (2 x 0.3)/(2.0 + 2.3), would be the d i f f e r e n c e between these two angles, 65°-57.5° = 7.5°. I f the values of the c o e f f i c i e n t s i n the d i h e d r a l angle r e l a t i o n s h i p are obtained, the expected v a r i a t i o n s i n the coupling constants due to the metal atom s u b s t i t u t i o n s i n the d i t e r t i a r y a r s i n e chelate complexes can be roughly estimated. For s i m p l i c i t y , the d i h e d r a l angle r e l a t i o n s h i p to ^H-^H and ^F-^H coupling constants i s assumed to take the f o l l o w i n g form: 3 J = Acos2cj) 0° < <J> < 90° = Bcos2cJ) 90° < <j> < 180° In the chelate complexes s t u d i e d i n t h i s work, the l a r g e s t trans coupling constants obtained are ca. 16 Hz, i n the t r i m e t h y l s i l y l d e r i v a t i v e s (GH 3) 2AsCH(Si(CH 3) 3 ) C H ^ s (CH 3) 2M(C0) ^  ^-10 (M = Cr, Mo, W) Table XVI. F i r s t - o r d e r Coupling Constants (Hz) f o r the T r i m e t h y l s i l y l Chelate Complexes 8-10. Compound Solvent J 3 3 ' J34 J34' J3'4 J3'4' J44' ( C H 3 ) 2 A s C H ( S i ( C H 3 ) 3 ) - C 6 H 6 5.1 15.9 -12.7 CH 2As(CH 3) 2Cr(CO) Z i 8 CHC1 3 5.2 16.1 -12.8 (CD 3) 2co 5.0 16.1 -12.8 ( C H 3 ) 2 A s C H ( S i ( C H 3 ) 3 ) - C 6 H 6 4.5 15.7 -13.0 CH 2As(CH 3) 2Mo(C0) 4 9 CHC1 3 4.5 15.9 -13.0 (CD 3) 2CO 4.4 16.0 -12.9 ( C H 3 ) 2 A s C H ( S i ( C H 3 ) 3 ) - C 6 H 6 4.5 15.9 -13.0 CH 2As(CH 3) 2W(CO) 4 10 CHC1 3 4.6 16.0 -12.9 (CD 3) 2CO 4.5 16.0 -13.1 - 107 -Taking t h i s value to represent the coupling constant f o r a d i h e d r a l angle of 180° i n a l l the complexes, we o b t a i n B = 16. For both ^H-^H and "^F-^H cou p l i n g constants, the r a t i o of A to B i s ca. 2/3."^ Thus f o r the J values i n the present study, A = 2 / 3 x B = 1 0 and 3J—, = l d c o s 2 * 0°< cb ^ 90° rirl = 16cos2c() 90°< <b < 180° 19 1 The c o e f f i c i e n t s f o r the F- H r e l a t i o n s h i p can be derived from data 136 presented by G o v i l and are A = 36 and B = 54. Assuming that bond length changes i n the ethylenediamine chelate complexes p a r a l l e l those i n the d i t e r t i a r y a r s i n e complexes, these f u n c t i o n s can be used to c a l c u l a t e the expected d e v i a t i o n s i n the coupling constants of the complexes w h i l e changing from chromium to o o tungsten. T y p i c a l Cr-As and Mo-As bond l e n g t h s , 2.43 A and 2.58 A, have been presented i n Chapter 3. These do not seem to vary a p p r e c i a b l y from complex to complex. The W-As bond length i n o x o t e t r a c h l o r o - o -° 161 phenylenebis(dimethylarsine)tungsten(VI) has been found to be 2.67 A. Assuming the same value f o r the tungsten complexes i n t h i s work, the o o metal-arsenic bond length v a r i e s from 2.43 A to 2.67 A or 9.5%, 100 x (2 x 0.24)/(2.43 + 2.67). The v a r i a t i o n i n d i h e d r a l angle f o r t h i s bond length change might be expected to be 9.5%/14% x 7.5° = 5°. Now assuming a d i h e d r a l angle of 60° i n the chromium chelate complexes, the changes i n the angles of the ethane s u b s t i t u e n t s occur as i n V. - 108 -The a n t i c i p a t e d coupling constant changes are c a l c u l a t e d as f o l l o w s : 16cos2175° = 0.1 Hz 10cos255° = 0.8 Hz 10cos260° - 0.8 Hz 54cos2175° = 0.3 Hz 36cos255° = 2.8 Hz 36cos260° ~ 2.6 Hz As w e l l as p r o v i d i n g an approximate t h e o r e t i c a l measure of the magnitude of the changes expected on s u b s t i t u t i n g a chromium atom by a tungsten atom, these values can be used to p r e d i c t whether a coupling constant w i l l increase or decrease. The data f o r the t r i m e t h y l s i l y l d e r i v a t i v e s 8-10 shown i n Table XVI i l l u s t r a t e these "*"H-^ H Coupling Constants J = 16cos 2180 c trans J , = 10cos260° gauche 2 or = lOcos 65° 19 1 F- H Coupling Constants J = 54cos 2180 c trans J , = 36cos260° gauche 2 or = 36cos 65° - 109 -a l t e r a t i o n s . As p r e d i c t e d , the trans H- H coupling constants, J ^ , ^ , , which vary by only ca. 0.1 Hz f o r a given s o l v e n t , are not n e a r l y so s e n s i t i v e to changes i n the metal as the gauche ^H-^H coupling constants which change by ca. -0.6 Hz. These approximate v a r i a t i o n s , as w e l l as those f o r the remaining chelate complexes examined i n t h i s s e c t i o n , are presented i n Table XVII. The numbers i n brackets represent the magnitude of the p r e d i c t e d changes. A plus (+) s i g n i n d i c a t e s that the coupling constant increases w i t h the s u b s t i t u t i o n of chromium by tungsten, w h i l e a minus (-) s i g n i n d i c a t e s that a decrease i s observed and expected f o r that p a r t i c u l a r coupling constant w i t h the same s u b s t i t u t i o n o c c u r r i n g . The experimental v a r i a t i o n s u s u a l l y are l e s s than the p r e d i c t e d changes, and always i n the p r e d i c t e d d i r e c t i o n , except f o r the t r i f l u o r o chelate d e r i v a t i v e s 14-16 and 18-19. This discrepancy i s e a s i l y accounted f o r when i t i s r e c a l l e d that the o r i e n t a t i o n s of the geminal f l u o r i n e atoms i n those complexes could not be a b s o l u t e l y assigned, and were a r b i t r a r i l y assumed to take the stereochemical r e l a t i o n s h i p where F^, i s " a x i a l " w h i l e F^ takes the " e q u a t o r i a l " p o s i t i o n on the chelate r i n g . By exchanging the l a b e l i n g of these two f l u o r i n e atoms,the r e s u l t s i n Table XVII become e n t i r e l y c o n s i s t e n t . Thus i t appears that by r e l a t i v e l y naive geometrical arguments, the e f f e c t of the changes i n the metal atom can be roughly p r e d i c t e d . P r e v i o u s l y , i t was noted that the change from a Group VI t r a n s i t i o n metal to manganese atom apparently r e s u l t s i n a greater " a x i a l " preference f o r the hydrogen s u b s t i t u e n t i n the t r i f l u o r o manganese d e r i v a t i v e 1J_. In the b r i d g i n g dimanganese decacarbonyl d e r i v a t i v e - 110 -Table XVII. Experimental and P r e d i c t e d Changes i n V i c i n a l Coupling Constants (Hz) w i t h Changes i n the T r a n s i t i o n M etal. Chelate Complexes J34 J34' J 3 . 4 J3'4* (CH ) 2AsCH(Si(CH ) )CH 2- -0.6(-•0.8) -O.l(-O.l) As(CH 3) 2M(CO) 4 8-10 (CH 3) 2AsCHFCH 2As(CSL ) £ - 0.7(0.4) -0.4(-1.3) -1.8(- 1.3) -0 . K-0.2) M(C0) 4 12-13 3 (CH 3) 2AsCF 2CFHAs- -0.6(2.84) ? (-2.57) (CH 3) 2M(C0) 4 14-16 (CH 3) 2PCF 2CFHP(CH 3) 2-ou-M(C0) 4 18-19 -0.8(2.84) l . K - 2 . 5 7 ) (CH 3) 2AsCH(CN)CH 2As- -0.6(- 0.8) 0.0(-0.1) (CH 3) 2M(C0) 4 27-29 M = Cr and Mo only, thus the p r e d i c t e d changes have been reduced by ca. 50%. - I l l -o 175 (CH 3) 2AsC=CAs(CH 3) 2CF 2CF 2Mn 2(CO) 8' the Mn-As bond le n g t h i s 2.40 A, o only 0.03 A d i f f e r e n t from the Cr-As bond lengths described e a r l i e r . Thus i t would be expected that the coupling constant v a r i a t i o n s between the t r i f l u o r o chromium complex and i t s manganese analog 17_ would be very s m a l l , probably l e s s than 0.2 Hz. The a c t u a l changes are much l a r g e r than p r e d i c t e d on the b a s i s of t h i s s t r u c t u r a l r a t i o n a l e . I t appears that more in f o r m a t i o n about the s t e r i c and e l e c t r o n i c e f f e c t s of changing the metal atom and i t s s u b s t i t u e n t s must be obtained before a s e n s i b l e i n t e r p r e t a t i o n of t h i s data can be brought forward. F o r t u n a t e l y the NMR parameters of the d i f l u o r o complexes 20-25 can help d e l i n e a t e the e f f e c t s of these a l t e r a t i o n s . I f s o l u t i o n s of these c h e l a t e complexes conta i n e q u i l i b r i u m mixtures of only two; conformers, as i n W(l) and W(2), the sums of a l l the v i c i n a l c o upling constants i n conformer W(l) w i l l equal the sum of those coupling constants i n conformer W(2). assuming that the bond angles and bond M = C r . M o , W ; X = Y = C O M = M n ; X = C l , Br, I; Y = C O lengths are i d e n t i c a l f o r the two conformers. 19,60,162 Therefore, given any r e l a t i v e p r o p o r t i o n s of species W(l) and W(2), t h i s sum of - 112 -19 1 v i c i n a l F- H coupling constants i s independent of conformational preferences i n such an e q u i l i b r i u m . I t f o l l o w s , t h a t a comparison 3 of the sums of the v i c i n a l J„„ values between the d i f l u o r o Group VI Hr and manganese d e r i v a t i v e s , 20-22 and 23-25, would i n d i c a t e s i m i l a r i t i e s or d i f f e r e n c e s other than conformational preferences f o r e i t h e r of the two conformers. Table XVIII contains the coupling constants as w e l l as the sums of the v i c i n a l J„ v a l u e s , SJ-.^, f o r these chelate Hr HF complexes. I t i s immediately evident that f o r a given s o l v e n t , these sums are almost equal, f a l l i n g i n the range ca. 71-73 Hz. The data may be i n t e r p r e t e d i n s e v e r a l d i f f e r e n t ways. The changes i n s o l v e n t s , metal atoms, and metal atom s u b s t i t u e n t s i n d i c a t e t h a t s u b s t i t u e n t e l e c t r o n e g a t i v i t i e s , bond angles, and bond lengths: 1) do not vary, 2) cancel the e f f e c t of one another, or 3) vary, but i n s u f f i c i e n t l y to cause n o t i c e a b l e coupling constant changes. In any event, i t appears that changing from a Group VI metal atom to manganese atom does not r e s u l t i n any appreciable e l e c t r o n i c v a r i a t i o n s i n the c h e l a t i n g d i t e r t i a r y a r s i n e s . Consequently, i t seems the data may be compared and i n t e r p r e t e d on a conformational b a s i s . A s i m i l a r treatment of data derived from d i t e r t i a r y a r s i n e complexes w i t h six-membered chelate n 162-163 r i n g s , y i e l d s i d e n t i c a l r e s u l t s . Nevertheless, t h i s c o n c l u s i o n cannot be a p p l i e d to the d i f l u o r o manganese chelate complexes 23-25 because the NMR parameters f o r the "locked" conformers W(l) and W(2) are unknown. However, i t provides f u r t h e r evidence f o r the apparent greater " a x i a l " preference f o r the hydrogen atom i n the t r i f l u o r o manganese d e r i v a t i v e s 17_ compared w i t h the chromium, molybdenum, and tungsten analogs 14-16 and 18-19. Table X V I I I . First-.order Coupling Constants (Hz) f o r the D i f l u o r o Chelate Complexes 20-25. Compound Solvent J33* J34 J34« J3'4 J3'4' J44' Z J (CH 3) 2AsCH 2CF 2As(CHg) 2~ C 6 H 6 18.0 18.0 18.0 18.0 72.0 C r ( C 0 ) 4 20 (CH 3) 2AsCH 2CF 2As(CH ) - C 6 H 6 18.2 18.2 18.2 18.2 72.8 Mo (CO). 21 4 — i M (CH 3) 2AsCH 2CF 2As(CH 3) - C 6 H 6 18.0 18.0 18.0 18.0 72.0 M L O | W(C0) 4 22 (CH 3) 2AsCH 2CF 2As(CH ) - CHC1 3 -13.1 44.9 6.7 12.7 7.0 248.5 71.3 Mn(C0) 3Cl 23 (CD 3) 2C0 -13.1 40.6 7.9 15.2 9.5 245.7 73.2 (CH 3) 2AsCH 2CF 2As(CH 3) 2~ C 6 H 6 -13.1 40.5 7.4 17.2 7.3 247.2 72.4 Mn(CO) 3Br 24 CHC1 3 -13.2 42.0 7.0 14.9 7.2 248.4 71.1 (CD 3) 2C0 -13.3 39.9 7.9 15.0 9.5 246.2 72.3 (CH 3) 2AsCH 2CF 2As(CH ) - CHC1 3 -13.1 40.5 7.7 14.5 8.2 245.1 70.9 Mn(C0) 3I 25 - 114 -3. Donor Atom A l t e r a t i o n s A s t r u c t u r a l treatment s i m i l a r to that presented i n the s e c t i o n on t r a n s i t i o n metal v a r i a t i o n s would p r e d i c t t h a t the d i h e d r a l angle of the ethane moiety i n the ch e l a t e r i n g would decrease when the a r s e n i c atoms are s u b s t i t u t e d by phosphorus atoms si n c e the M-P and P-C bonds would be s h o r t e r . This would produce a decrease i n J„, and an 34 increase i n . However, the data do not change i n accordance w i t h these arguments, s i n c e both coupling constants i n c r e a s e i n changing to phosphorus donor atoms. For example, f o r s p e c t r a of the t r i f l u o r o d e r i v a t i v e s JL4 (chromium-arsenic) and 18. (chromium-phosphorus) obtained i n chloroform J 0 , and J ~ / T increase from 5.3 to 6.0 Hz and 34 34 14.8 to 18.5 Hz, r e s p e c t i v e l y . I t seems that such a donor atom change i n .the chelate complex causes more than simple geometric a l t e r a t i o n s i n the two-carbon br i d g e . E l e c t r o n i c e f f e c t s are a n t i c i p a t e d to be more important f o r t h i s s u b s t i t u t i o n , because the donor atoms are bonded d i r e c t l y to the ethane bridge carbon atoms, i n co n t r a s t w i t h v a r i a t i o n s i n the metal atom, which i n v o l v e changes f a r t h e r removed from that part of the chelate r i n g . I t seems that more i n f o r m a t i o n must be obtained on r e l a t e d l i g a n d s and complexes before the e l e c t r o n i c and s t e r i c e f f e c t s of donor atom s u b s t i t u t i o n can be determined. 4. Halogen Subs t i t u e n t Changes I t seemed that by v a r y i n g the c i s - " a x i a l " s u b s t i t u e n t on the t r a n s i t i o n metal atom, changes would occur i n the conformational - 115 -22 preferences of the chelate r i n g s . The data i n Table XVIII i n d i c a t e 19 1 l i t t l e v a r i a t i o n i n the v i c i n a l F- H coupling constants w i t h changes i n the halogen atom s u b s t i t u e n t i n the d i f l u o r o manganese d e r i v a t i v e 23-25. For a given s o l v e n t , there i s a s l i g h t tendency 3 f o r the trans J value to decrease i n the order I < Br < CI. With HF the data, i t does not seem p o s s i b l e to determine whether or not t h i s trend i s i n d i c a t i v e of any conformational preferences f o r conformer W(l) or W(2). The e f f e c t s of such s u b s t i t u e n t changes probably could be d e l i n e a t e d by using more s u i t a b l e l i g a n d s , such as meso-l,2-bis-. ( d i m e t h y l a r s i n o ) - l , 2 - d i f l u o r o e t h a n e . The c h e l a t e complexes of t h i s d i t e r t i a r y a r s i n e could adopt two conformations as i n X. V a r i a t i o n s i n the populations of the conformers could be e f f e c t e d by changing the s u b s t i t u e n t s on the t r a n s i t i o n metal, and observed by : f o l l o w i n g the changes i n the ^H-^H coupling constants. 5. Temperature V a r i a t i o n s , By v a r y i n g the temperatures of the NMR samples, i t was hoped that the r e l a t i v e populations of the v a r i o u s conformers could be changed. - 116 -This would enable estimates of the a c t i v a t i o n energies f o r conformational i n v e r s i o n of the chelate r i n g s to be obtained. Many treatments of v a r i a b l e temperature NMR s p e c t r a i n terms of dynamic processes r e l y on the assumption that the inherent chemical s h i f t s of protons or f l u o r i n e s i n the i n d i v i d u a l species undergoing the 164 process are themselves temperature i n v a r i a n t . G e n e r a l l y , t h i s assumption leads to no s e r i o u s e r r o r s i n the c a l c u l a t i o n of exchange r a t e s , provided that the protons or f l u o r i n e s s h i f t e q u a l l y . However, i t i s d i f f i c u l t to separate these inherent s h i f t s from those r e s u l t i n g from a l t e r a t i o n s i n the dynamic process. Thus, i t i s a n t i c i p a t e d that the chemical s h i f t s of the s u b s t i t u e n t s on the ethane bridge i n t h i s work w i l l vary w i t h temperature changes, i r r e s p e c t i v e of any conformational i n v e r s i o n already o c c u r r i n g . The NMR s p e c t r a of the t r i m e t h y l s i l y l , monofluoro, d i f l u o r o , ! t r i f l u o r o , and cyano chromium d e r i v a t i v e s j3, JL2_, 20_, 1_4, and 27 as > w e l l as the d i f l u o r o manganese che l a t e complex 24 were a l l observed i n the temperature range -50° to +120°. S i g n i f i c a n t l y , none of the coupling constants of the chromium d e r i v a t i v e s changed by more than a few percent i n t h i s temperature span. The t r ± m & t h y l s i l y l , monofluoro, and t r i f l u o r o d e r i v a t i v e s 8_, 12, and 14, which probably have h i g h l y favored conformations, would be expected to exhibit s m aller coupling constant v a r i a t i o n s w i t h . temperature changes than the d i f l u o r o and cyano c h e l a t e complexes 1Q_ and lh_y and 27, which do not seem to have such h i g h l y p r e f e r r e d conformations. - 117 -The results imply that the chelate r i n g s of a l l the complexes, excluding the d i f luoro d e r i v a t i v e s 20_ and \24, have s t r o n g l y favored conformations, i r r e s p e c t i v e of the energy b a r r i e r s to i n v e r s i o n 22 i n v o l v e d , which are l i k e l y more than 3 to 4 kcal/mol. A p o s s i b l e i n t e r p r e t a t i o n of the r e s u l t obtained f o r the cyano complex 27_ i s that the cyano s u b s t i t u e n t e x c l u s i v e l y p r e f e r s an " e q u a t o r i a l " o r i e n t a t i o n . This would imply that the trans "hn-^ H coupling constants i n these d i t e r t i a r y a r s i n e s u b s t i t u t e d compounds are, as a n t i c i p a t e d , very s e n s i t i v e to the e l e c t r o n e g a t i v i t y d i f f e r e n c e s i n s u b s t i t u e n t s bonded to the ethane bridge. Since only s m a l l changes r e s u l t e d i n the coupling constants of the d i f luoro chromium chelate complex 20_ when the temperature was v a r i e d , i t seems that the energy b a r r i e r f o r the e q u i l i b r i u m r e a c t i o n between conformers W(l) and W(2) i s s m a l l , or that the temperature dependences are the same f o r both conformers. I f the e q u i l i b r i u m r e a c t i o n were 4 -1 slowed to the NMR time s c a l e (k - 10 sec ) , an ABXY spectrum would be expected to r e s u l t from the "locked" conformers. 19 1 In the manganese d i f l u o r o chelate complex 2!4, the trans F- H coupling constant decreased from 42.0 Hz at probe temperature to 39.4 Hz at 80°, w h i l e the sums of the v i c i n a l c o upling constants remained at 71.1 Hz. Again, t h i s v a r i a t i o n seems to imply some change i n r e l a t i v e populations of conformers W(l) and W(2) although i t i s not known which i s favored w i t h the increase i n temperature. - 118 -F. D i p o l a r E f f e c t s While the p r e c i s e sources of the " a x i a l " f l u o r i n e preferences are not known, three d i f f e r e n t r a t i o n a l e s have been proposed, one being based on r e p u l s i v e d i p o l e - d i p o l e i n t e r a c t i o n s i n carbohydrate systems^"*'"^^ such as _36_; a second on the preference f o r adjacent d i p o l a r bonds to favor a "gauche" r e l a t i o n s h i p ; " ' " ^ and a t h i r d on p-p o r b i t a l overlap between f l u o r i n e p o r b i t a l s and those of some other 168 s u i t a b l y l o c a t e d atom. S i m i l a r preferences have been explained more r e c e n t l y by c o n s i d e r i n g the combined a t t r a c t i v e and r e p u l s i v e 169 i n t e r a c t i o n s i n a wide range of compounds. However, i t i s not obvious that any of these can be invoked to account f o r the conformational preferences discovered i n t h i s work. G. Analogous Systems Although there appears to be no precedent f o r the marked conformational preference of the c a r b o n - f l u o r i n e bond i n organometallic compounds, s e v e r a l instances are known i n o r g a n i c - h e t e r o c y c l e s . For example, the f l u o r i n e s u b s t i t u e n t of f l u o r i n a t e d carbohydrates such as 36^ "* >^ -70 has such a strong preference f o r the a x i a l o r i e n t a t i o n that the compound favors the a l l a x i a l conformation shown. S i m i l a r l y 5-fluoro-1,3-171 172,173 dioxane _37 and i t s d e r i v a t i v e s a l s o show a marked preference f o r that conformer having the f l u o r i n e a x i a l l y o r i e n t e d . - 119 -In the d i t e r t i a r y a r s i n e chelate complexes, the reduced preference f o r the c h l o r i n e s u b s t i t u e n t i n the " a x i a l " p o s i t i o n compared to the f l u o r i n e s u b s t i t u e n t s could be a n t i c i p a t e d from r e s u l t s obtained from 172,173 the 5-halo-l,3-dioxane system, ' where the f o r m a l l y analogous observation has been made tha t a c h l o r o s u b s t i t u e n t has a lower preference f o r an a x i a l o r i e n t a t i o n than a f l u o r o s u b s t i t u e n t . H. C r y s t a l l o g r a p h i c Results T r o t t e r and coworkers"'""'"4 116,174 ^ a v e i n v e s t i g a t e d the s o l i d s t a t e s t r u c t u r e s of s e v e r a l of these fluorocarbon-bridged d i t e r t i a r y a r s i n e and phosphine d e r i v a t i v e s of chromium and molybdenum hexacarbonyls. Although the i n i t i a l r e s u l t s i n d i c a t e d that t h e i r s t r u c t u r e s were abnormal,"'"''""' i t now seems that the s o l i d s are disordered and that the most chemically reasonable i n t e r p r e t a t i o n of the data r e q u i r e s each molecule to have normal geometries. The r e s u l t s confirm that "bulky" groups such as the t r i f l u o r o m e t h y l s u b s t i t u e n t i n ^ 31 occupies an 114 174 " e q u a t o r i a l " p o s i t i o n i n a puckered five-membered chelate r i n g . '" - 120 -O Furthermore, the hydrogen atom i n the ethane bridge of the t r i f l u o r o chromium chelate complex 14 i s i n the " e q u a t o r i a l " p o s i t i o n , as expected from the NMR r e s u l t s . Assuming that the s t r u c t u r e s of the chelate complexes i n the s o l i d s t a t e and s o l u t i o n are e s s e n t i a l l y the same, the X-ray r e s u l t s i n Table VII have some i n t e r e s t i n g i m p l i c a t i o n s . As a n t i c i p a t e d , o they show that the Mo-As bond length (2.58A) i n the t r i f l u o r o c h e l a t e o complex 15_ i s longer than the Cr-As d i s t a n c e (2.43 A) i n i t s chromium o analog 14_, and longer than the Mo-P bond length (2.48 A) i n the phosphorus t r i f l u o r o c helate complex 19. The metal-donor atom bond lengths i n t h i s s e r i e s of compounds seem to be f a i r l y independent o of the s u b s t i t u e n t s on the ethane b r i d g e . The W-As bond length (2.67 A) 161 i n C-H,(As(CH_)_).W0Cl„ al s o seems to be i n accord. Therefore, i t 6 4 3 2 2 3 appears that the chelate r i n g s i z e does vary w i t h changes i n the t r a n s i t i o n metal or donor atoms. This i s a l s o borne out by the f l u c t u a t i o n s of 82-85° obtained f o r the As-M-As angles. As shown • p r e v i o u s l y , the NMR data appear to r e f l e c t these s t r u c t u r a l v a r i a t i o n s w i t h a l t e r a t i o n of the t r a n s i t i o n metal. - 121 -Those c r y s t a l l o g r a p h i c parameters (Table VII) not d i r e c t l y i n v o l v e d i n the five-membered r i n g s are remarkably i n v a r i a n t , from complex to complex. The arsenic-carbon, carbon-oxygen, molybdenum-carbon, and chromium-carbon bond lengths and the M-C-0 and M-As-C angles do not a l t e r s i g n i f i c a n t l y . I I I . D i t e r t i a r y A r s i n e Ligands The vicinal ^H-^H and "^F-'Hi coupling constants of a l l the new d i t e r t i a r y a r s i n e l i g a n d s l-7_ i n d i c a t e a major p o p u l a t i o n of the rotamers having the two dimethylarsino s u b s t i t u e n t s i n an a n t i o r i e n t a t i o n , as i n Y. Trans ''"H-^ H coupling constants of ca. 7-11 Hz are obtained f o r the t r i m e t h y l s i l y l 1_, t r i c h l o r o s i l y l 2^ , monofluoro _3, chloro 6^ , and cyano 7_ l i g a n d s , w h i l e trans F- H cou p l i n g constants of the monofluoro _3 and t r i f l u o r o h_ d i t e r t i a r y a r s i n e s are 39.3 and 21.5 Hz r e s p e c t i v e l y . The phosphorus analog of the t r i f l u o r o d e r i v a t i v e h_ y i e l d s s i m i l a r NMR parameters. Thus i t seems that the ope r a t i o n of the conformational preferences of a f l u o r i n e s u b s t i t u e n t i s only e f f e c t i v e - 122 -in the chelate r i n g system. I t appears that s t e r i c requirements are important i n these d i a r s i n e s , as i s found i n the r e l a t e d s u b s t i t u t e d 159 ethanes, such as meso-2,3-dibromobutane, described by Abraham. Perhaps the r e s u l t s of v a r i a b l e temperature and solvent s t u d i e s could be i n t e r p r e t e d i n terms of the r e l a t i v e rotamer populations f o r these d i a r s i n e s . I t has been demonstrated i n r e l a t e d systems that the d i s t r i b u t i o n of r o t a t i o n a l isomers i s a f u n c t i o n of the p o l a r i t y of the solvent.^-' 9 In a d d i t i o n , bridged metal carbonyl complexes of these d i t e r t i a r y a r s i n e s would provide a p o s s i b l e method of determining the e f f e c t of the t r a n s i t i o n metal i n unchelated complexes. IV. Summary In s o l u t i o n , s i g n i f i c a n t conformational preferences are conferred on the d i t e r t i a r y a r s i n e c o n t a i n i n g five-membered c h e l a t e r i n g s by some r i n g s u b s t i t u e n t s . While a t r i m e t h y l s i l y l group p r e f e r s an " e q u a t o r i a l " o r i e n t a t i o n on the two-carbon bridge of the chelate r i n g , a f l u o r i n e s u b s t i t u e n t adopts an " a x i a l " p o s i t i o n . However, i n s e v e r a l complexes such strong preferences are not i n d i c a t e d , as i n the d e r i v a t i v e s (CH 3) 2AsCH 2CF 2As(CH 3> 2Mn(CO) 3X (X = CI, Br, I) which are thought to e x i s t as an e q u i l i b r i u m mixture of two conformers. In these cases the evidence i s i n s u f f i c i e n t to determine the exact nature of conformational behavior. Changes i n the che l a t e r i n g geometries due to metal atom v a r i a t i o n s are roughly p r e d i c t a b l e from the a l t e r a t i o n s i n the NMR parameters of these complexes. However, the e f f e c t s of donor - 123 -atom s u b s t i t u t i o n cannot be r a t i o n a l i z e d . V a r i a t i o n s i n s o l v e n t , temperature, metal atom, and i t s s u b s t i t u e n t s , and donor atoms do not d r a s t i c a l l y a l t e r the chelate r i n g conformational preferences. I t seems that the r o t a t i o n a l preferences i n the d i t e r t i a r y a r s i n e s examined i n t h i s work are p a r t i a l l y d i c t a t e d by the "bulky" d i m e t h y l -a r s i n o s u b s t i t u e n t s . - 124 -BIBLIOGRAPHY 1. R.D. G i l l a r d and H.M. I r v i n g , Chem. Rev., 65_, 603 (1965). 2. J.H. Dunlop and R.D. G i l l a r d , Advan. Inorg. Chem. Radiochem., 9_, 185 (1966). 3. A.M. Sargeson i n " T r a n s i t i o n Metal Chemistry" V o l . 3, R.L. 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