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The synthesis and characterization of some molybdenum, rhenium and rhodium complexes incorporating pyrazolylgallate… Cooper, David Arthur 1985

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THE SYNTHESIS AND CHARACTERIZATION OF SOME MOLYBDENUM, RHENIUM AND RHODIUM COMPLEXES INCORPORATING PYRAZOLYLGALLATE LIGANDS by DAVID ARTHUR COOPER B.Sc. (Honours), Southampton University, 1983 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CHEMISTRY We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA July, 1985 © David Arthur Cooper, 1985 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by h i s or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of Qk£ftA>l*SY The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 D a t e >') ></W • (3$$: i i ABSTRACT Several uninegative ligands based on a gallium core and incorporating p y r a z o l y l groups have been synthesized and t h e i r metathesis reactions with molybdenum, rhenium and rhodium halides have been studied. The bidentate p y r a z o l y l g a l l a t e ligand Et 2Gapz 2~ ( L 1 ) has been incorporated i n the complexes L 1Mo(n 3-allyl)(CO) 2(Hpz), (where ' T ^ - a H y l ' = C^H,, C 7H 7 and Hpz = pyrazole). The unsymmetric tridentate p y r a z o l y l g a l l a t e ligands Me 2Gapz(OCH 2pyr)~ ( L 2 ) , Me2Gapz(SCNCH2CH2NMe)- ( L 3 ) and Me2Gapz(OCH2CH2CH=CH2) (L*+) display a v a r i a b l e r e a c t i v i t y towards molybdenum, rhenium and rhodium precursors. Although no complexes incorporating V* were i s o l a t e d , L 2 and L 3 were shown to co-ordinate f a c i a l l y i n the octahedral complexes L 2Mo(C 7H 7)(CO) 2 and L 3Re(CO) 3. In addition, a meridional co-ordination geometry of L 2 has been s t r u c t u r a l l y characterized i n the square planar rhodium(I) complex, L 2Rh(CO). This co-ordinatively unsaturated rhodium(I) species was shown to undergo an i n t e r e s t i n g oxidative addition reaction with methyl iodide followed by a methyl migration reaction to give a rhodium(III) a c e t y l d e r i v a t i v e . Less predictable products have also been obtained i n t h i s study; these include the dimeric species [Mo(r) 3-allyl)(CO) 2(SCNCH 2CH 2NMe)] 2 formed from the reaction of NaL 3 with Mo(CH 3CN ) 2 ( T i 3-allyl)(CO) 2X ( ' n 3 - a l l y l ' = C3 H5» a n t * X = B r » ^ r e s P e c t i v e l y ) and also an unexpected chlorine-containing complex, [Me(Cl)Gapz(OCH 2pyr)]Rh(CO) from the reaction of NaL 2 and [Rh(CO) 2C1] 2. i i i ! 1 [Me 2Ga(SCNCH2CH2NMe)] 2» t n e product of the reaction between Me3Ga and i 1 'i -HSCNCH2CH2NMe (the precursor of L d ) has been s t r u c t u r a l l y shown to possess a novel eight-membered Ga-(N-C-S) 9-Ga r i n g . i v TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i v LIST OF TABLES i x LIST OF FIGURES x i LIST OF ABBREVIATIONS x i v ACKNOWLEDGEMENT x v i i CHAPTER I INTRODUCTION . 1 1.1 General Review 1 1.2 General Techniques 16 CHAPTER II MOLYBDENUM CARBONYL COMPLEXES INCORPORATING THE Et 2Gapz 2~ LIGAND 17 2.1 Introduction 17 2.2 Experimental 22 2.2.1 Starting Materials 22 2.2.2 Preparation of Na + [ E t 2 G a p z 2 ] ~ (NaL 1) 22 V Page 2.2.3 Preparation of [Et 2Gapz 2]Mo(C 7H 7)(C0) 2(Hpz), (L 1Mo(C 7H 7)(CO) 2(Hpz)) 23 2.2.4 Preparation of [Et 2Gapz 2]Mo(Ci tH 7)(CO) 2(Hpz), (L 1Mo(C kH 7)(CO) 2(Hpz)) 24 2.2.5 Attempted preparation of [Et 2Gapz 2]Mo(C 3H 5)(CO) 2(Hpz) (L 1Mo(C 3H 5)(CO) 2(Hpz)) . . . 24 2.2.6 Attempted preparations of [Et 2Gapz 2]Mo(r) 3-allyl)(CO) 2, ( L 1 M o ( n 3 - a l l y l ) ( C O ) 2 ) 25 2.3 Results and Discussion 29 2.3.1 [Et 2Gapz 2]Mo(r) 3-allyl)(CO) 2(Hpz) , (L 1Mo(r) 3-allyl)(CO) 2(Hpz)) where ' T ] 3 - a l l y l ' = C ^ , or C 7H 7 29 2.3.2 Mo(C 3H 5)(CO) 2(Hpz) 2Br 34 2.3.3 • ,[Et 2Gapz 2]Mo(r) 3-allyl)(CO) 2" 35 2.4 Summary 37 CHAPTER III REACTIONS OF MOLYBDENUM AND RHENIUM CARBONYL COMPLEXES WITH UNSYMMETRIC TRIDENTATE PYRAZOLYLGALLATE LIGANDS 38 3.1 Introduction 38 3.2 Experimental 42 3.2.1 Starting Materials 42 v i Page 3.2.2 Preparations of Na +[Me 2Gapz(OCH 2pyr)] - (NaL 2) Na+[Me2Gapz(s6NCH2CH2NMe)]- (NaL 3) and Na+[Me2Gapz(OCH2CH2CH=CH2)]- (NaL1*) 43 3.2.3 Preparation of [Me2Ga(SCNCH2CH2NMe)] 2 45 3.2.4 Preparation of [Me 2Gapz(SCNCH 2CH 2NMe)]Re(CO) 3, (L 3Re(CO) 3) . 45 3.2.5 Attempted preparations of [Me2Gapz(SCNCH2CH2NMe)]-M o ( n 3 - a l l y l ) ( C O ) 2 where n 3 - a l l y l = ( i ) C 3H 5, C^H, or ( i i ) C 7H 7 46 , 3.2.6 Attempted preparation of [Me 2Ga(OCH 2CH 2CH=CH 2)] 2 and reactions of Na +[Me 2Gapz(OCH 2CH 2CH=CH 2)]~, (NaL1*) 47 3.2.7 Preparation of [Me 2Gapz(0CH 2pyr)]Mo(C 7H 7)(C0) 2, (L 2Mo(C 7H 7)(CO) 2) 50 3.3 Results and Discussion 50 3.3.1 Reactions of Me3Ga with HSCNCH2CH2NMe and HOCH2CH2CH=CH2 50 3.3.2 Reactions of Na +[Me 2Gapz(SCNCH 2CH 2NMe)]" (NaL 3) . . 54 3.3.3 [Me 2Gapz(OCH 2pyr)]Mo(C 7H 7)(CO) 2, (L 2Mo(C ?H 7)(C0) 2) 64 3.4 Summary 67 v i i Page CHAPTER IV RHODIUM DERIVATIVES OF UNSYMMETRIC, TRIDENTATE PYRAZOLYLGALLATE LIGANDS 68 4*1 Introduction 68 4.2 Experimental 71 4.2.1 Starting Materials 71 4.2.2 Reaction of Na +[Me 2Gapz(OCH 2pyr)]" (NaL 2) and [Rh(CO) 2Cl] 2 71 4.2.3 Reactions of [Me 2Gapz(OCH 2pyr)]Rh(CO) (L 2Rh(CO)) 72 4.2.4 Attempted preparations of [Me 2Gapz(OCH 2pyr)]Rh(X) (L 2Rh(X)) where X = PMe3, PPh 3 , COE 76 4.2.5 Attempted preparations of [Me2Gapz(SCNCH2CH2NMe)]Rh(CO) (L 3Rh(CO)) and [Me2Gapz(OCH2CH2CH=CH2)]Rh(CO) (L l +Rh(CO)) 76 4.3 Results and Discussion 80 4.3.1 [Me 2Gapz(OCH 2pyr)]Rh(CO) (L 2Rh(C0)) 80 4.3.2 [Me(Cl)Gapz(OCH 2pyr)]Rh(CO) 89 4.3.3 Reactions of [Me 2Gapz(OCH 2pyr)]Rh(C0) (L 2Rh(C0)) . . 95 4.3.4 Attempted formation of [Me2Gapz(SCNCH2CH2NMe)]Rh(CO), (L 3Rh(C0)) and [Me 2Gapz(OCH 2CH 2CH=CH 2)]Rh(CO), (L l +Rh(C0)) 100 4.3.5 Attempted formations of [Me 2Gapz(OCH 2pyr)]Rh(X), (L 2Rh(X)) where X = PMe3, PPh 3, COE 101 4.4 Summary 102 v i i i Page CHAPTER V CONCLUSIONS AND PERSPECTIVES 103 REFERENCES 107 APPENDIX I STEREO DIAGRAMS, BOND LENGTHS AND BOND ANGLES OF SOME OF THE PREPARED COMPLEXES 113 APPENDIX II THEORETICAL INTENSITY PATTERNS FOR MASS SPECTROSCOPIC ANALYSIS 121 APPENDIX I I I MOLECULAR WEIGHT DETERMINATION 123 i x LIST OF TABLES Table Page I Micro-analyses and i r data of the complexes LMo(CO) 2(Hpz)Y 27 II -^H nmr data of the complexes LMo(CO) 2(Hpz)Y i n C 6D g s o l u t i o n 28 III Ir carbonyl stretching frequencies of [R 2Gapz 2]Mo(C 7H 7)(CO) 2(Hpz) (R = Et, Me) 29 IV Mass sp e c t r a l data for [Et 2Gapz 2]Mo(C 4H 7)(CO) 2(Hpz) . . . 33 V Micro-analyses and i r data of [Me 2Gapz(OCrl 2pyr)]Mo(C 7H 7)(CO) 2 and the complexes derived from (SCNCH2CH2NMe)_ 48 VI XH nmr data of [Me 2Gapz(OCH 2pyr)]Mo(C 7H 7)(CO) 2 and the complexes derived from (SCNCH2CH2NMe)~ 49 VII Mass sp e c t r a l data for [Mo(C 3H 5)(CO) 2(SCNCH 2CH 2NMe)] 2. . . 62 VIII Ir carbonyl stretching frequencies of some LMo(C 7H 7)(CO) 2 complexes (where L = p y r a z o l y l g a l l a t e ligand) 65 IX Micro-analyses and i r data of the rhodium derivatives prepared 78 X nmr data of the rhodium derivatives prepared (CgD 6 solution) 79 XI Ir carbonyl stretching frequencies for some LRh(CO) complexes where L = unsymmetric tridentate p y r a z o l y l -g a l l a t e ligand 82 X Table Page XII Mass spectral data for [Me 2Gapz(OCH 2pyr)]Rh(CO) 85 XIII Intermolecular Rh-Rh Interactions 88 XIV I r stretching frequencies of Ga-Cl bonds . . . 89 XV Mass sp e c t r a l data for [Me(Cl)Gapz(OCH 2pyr)]Rh(CO) . . . 92 XVI Ir carbonyl stretching frequencies of some LRh(CO)I 2 complexes 95 x i LIST OF FIGURES Figure Page 1 Pyrazole 1 2 Deprotonation of pyrazole 2 3 Examples of the co-ordination modes of pyrazole and the pyraz o l y l anion 3 4 Examples of polypyrazolylborate complexes 4 5 Di-deuteriopyrazolyl gallane dimer 5 6 Synthesis of Na +[Me 2Gapz 2]~ 6 7 Structures of [Me 2Gapz 2] 2Cu and [Me 2Ga(dmpz) 2] 2Cu . . . . 7 8 Examples of mono-bidentate p y r a z o l y l g a l l a t e complexes . . 8 9 [MeGaCdmpz^OHlWCC^KCO^ 10 10 Synthesis of Na +[Me 2Gapz(OCH 2CH 2NH 2)]" 11 11 Examples of unsymmetric tridentate monopyrazolylgallate ligands 12 12 The p y r a z o l y l g a l l a t e ligands NaL 1, NaL 2, NaL 3, and NaL 4 15 13 Molybdenum carbonyl derivatives of Me 2Gapz 2~ . . . . . . . 18 14 'Chair' conformation of the Ga-(N-N)2~Mo r i n g 19 15 [H 2B(dmpz) 2]Mo(C 7H 7)(CO) 2 and [Et 2Bpz 2]Mo(C 7H 7)(CO) 2 . . . 20 16 [Et 2Gapz 2]Mo(n 3-allyl)(CO) 2(Hpz) and "[Et 2Gapz 2]Mo ( n 3-allyl)(CO) 2" 21 17 Nujol and cyclohexane s o l u t i o n (inset) i r spectra of [Et 2Gapz 2]Mo(C l tH 7)(CO) 2(Hpz) 30 x i i Figure Page 18 80 MHz FT 1E nmr spectrum of [Et 2Gapz 2]Mo(C 7H 7)(C0) 2(Hpz) i n C 6D 6 s o l u t i o n (400 MHz FT inset) 31 19 Approximate hydrogen-molybdenum distances i n Et 2E-(N-N)-Mo, (E = Ga, B), systems 36 20 [Me 2Ga(0CH 2pyr)] 2 38 21 [Me 2Gapz(OCH 2CH 2NH 2)]Mo(C 7H 7)(CO) 2 and [Me 2Gapz(OCH 2CH 2SEt)]Re(CO) 3 39 22 Na +[Me 2Gapz(X ~ Y ) ] ~ 40 23 Na +[Me 2Gapz(SCNCH 2CH 2NMe)]- (NaL 3) 41 24 Na+[Me 2Gapz(OCH 2CH 2CH=CH 2)] - (NaL 4) 42 25 Syntheses of NaL 2, NaL 3 and NaL 4 44 26 X-ray c r y s t a l structure of [Me 2Ga(SCNCH 2CH 2NMe)] 2 . . . . 52 27 [Me 2Gapz] 2 and [Me 2Ga(SCNCH 2CH 2NMe)] 2 53 28 80 MHz FT lB. nmr spectrum of [Me 2Gapz(SCNCH 2CH 2NMe)]Re(CO) 3 *-n C 6D 6 55 29 Nujol and THF solu t i o n (inset) i r spectra of [Mo(C l tH 7)(CO) 2(SCNCH 2CH 2NMe)] 2 57 30 Proposed geometric isomerism i n [Mo ( Ch H y ) ( CO ) 2 ( SCNCH2CH2NMe ) ] 2 58 31 80 MHz FT *H nmr spectrum of [Mo(C 3H 5)(C0) 2(sdNCH 2CH 2riMe)] 2 i n d 6-acetone 61 32 Possible dimeric structures of [Mo(C 3H 5)(CO) 2(SCNCH 2CH 2NMe)] 2 63 33 80 MHz FT *H nmr of [Me 2Gapz(0CH 2pyr)]Mo(C 7H 7)(C0) 2 i n C 6D g 66 34 Rhodium p y r a z o l y l g a l l a t e complexes 69 x i i i Figure Page 35 Ir spectra of the reaction of [Rh(CO) 2Cl] 2 and Na+[Me 2Gapz(OCH 2pyr)]- i n THF 73 36 Ir spectra of the reactions of [Me 2Gapz(OCH 2pyr)]Rh(CO) with iodine and methyl iodide i n CH 2C1 2 74 37 Ir spectra of the reaction of [Rh(CO) 2Cl] 2 and Na +[Me 2Gapz(OCH 2CH 2CH=CH 2)]- i n THF 77 38 I r spectra and assignments of the reaction of [Rh(CO) 2Cl] 2 and Na+[Me 2Gapz(OCH 2pyr)]- i n THF 81 39 80 MHz FT *H nmr spectrum of [Me 2Gapz(OCH 2pyr)]Rh(CO) i n C 6D 6 s o l u t i o n (400 MHz FT inset) 84 40 X-ray c r y s t a l structure of [Me 2Gapz(OCH 2pyr)]Rh(CO). . . . 86 41 80 MHz FT lH nmr spectrum of [Me(Cl)Gapz(OCH 2pyr)]Rh(C0) i n C 6D 6 s o l u t i o n 91 42 X-ray c r y s t a l structure of [Me(Cl)Gapz(0CH 2pyr)]Rh(C0) . . 94 43 Reaction pathway for [Me 2Gapz(0CH 2pyr)]Rh(C0) + methyl iodide 97 44 80 MHz FT *H nmr spectrum of [Me 2Gapz(0CH 2pyr)]Rh(C0Me)I i n C 6D 6 s o l u t i o n 99 45 The four-membered ri n g required i n [Me2Gapz(SCNCH2CH2NMe)]Rh(CO) 100 46 Signer's apparatus for MWt Determination 123 x i v LIST OF ABBREVIATIONS A : angstrom a.m.u. : atomic mass uni t ( s ) br : broad °C : degrees Celsius Calcd. : calculated c f . : L. confer (compare) C 4H 7 : 2-methylallyl cm - 1 : wave number ( r e c i p r o c a l centimetres) COD : 1 , 5-cyclooctadiene COE : cyclooctene Co. : company Cp : r) 5-cyclopentadienyl ligand d : doublet dd : doublet of doublets dmpz : 3 , 5-dimethylpyrazolyl e.g. : L. exempli g r a t i a (for example) Et : e t h y l FT : Fourier transform g : gram(s) 1H : proton Hpz : pyrazole hrs. : hours Hz : hertz i . e . : L. i d est (that i s ) XV i r : i n f r a - r e d J : magnetic resonance coupling constant L : ligand(s) L 1 : Et 2Gapz 2~ L 2 : Me 2Gapz(OCH 2pyr)~ L 3 : Me 2Gapz(SCNCH 2CH 2NMe) _ L 4 : Me 2Gapz(OCH 2CH 2CH=CH 2) -L, : l i t r e ( s ) L t d . : Limited Me : methyl m/e : mass to charge r a t i o min : minutes ml- : m i l l i l i t r e ( s ) mpz : 3-methylpyrazolyl n : integer nmr : nuclear magnetic resonance ppm : parts per m i l l i o n pyr : p y r i d y l pz : p y r a z o l y l s : s i n g l e t t : t r i p l e t THF : tetrahydrofuran U.B.C. : University of B r i t i s h Columbia ~ : approximately x v i dihapto trihapto pentahapto nmr chemical s h i f t bridging i r stretching frequency indicates 'see footnote' x v i i ACKNOWLEDGEMENT I wish to express my sincere thanks to Dr. Alan Storr for h i s encouragement, guidance and support during the course of t h i s work. I t has been an enjoyable and rewarding experience. I am indebted to the members of the research group both past and present, i n p a r t i c u l a r Dr. Brenda Louie and Mr. Emmanuel Onyiriuka for t h e i r assistance and i n s p i r a t i o n . My thanks are extended to the Faculty and technical s t a f f of the Chemistry Department and e s p e c i a l l y I thank Dr. Steve Rettig for his excellence i n X-ray crystallography. I would also l i k e to thank Dr. P a t r i c i a MacNeil and Dr. Ian Butler for d i l i g e n t proof-reading. F i n a n c i a l support from the University of B r i t i s h Columbia i n the form of a Teaching Assistantship (1983-85) i s g r a t e f u l l y acknowledged. 1 CHAPTER I INTRODUCTION 1.1 General Review 4 Figure 1. Pyrazole. The fIve-membered diazole c y c l i c compound, pyrazole, was f i r s t c i t e d i n the l i t e r a t u r e i n the l a t e nineteenth c e n t u r y 1 * 2 . Subsequently, despite a sparse role i n nature, i t has been incorporated i n pharmaceuticals, dyes and polymers amongst other useful chemical a p p l i c a t i o n s . Although pyrazole e x i s t s as a tautomer, i n accordance to conventional het e r o c y c l i c nomenclature, the system can be numbered as shown in Figure 1. The odourless, c r y s t a l l i n e s o l i d i s h y d r o l y t i c a l l y and thermally very stable, due p a r t l y to i t s aromatic character, since i t can be considered a Huckel '4n + 2' system, where n = 1. Deprotonation can occur r e l a t i v e l y e a s i l y y i e l d i n g the resonance s t a b i l i z e d pyrazolyl anion as i n Figure 2. 2 H © H N - N N N Figure 2. Deprotonation of pyrazole. As a ligand, pyrazole can function as a neutral, monodentate, two-electron donor v i a the lone pair on nitrogen-2, allowing a wide range of complexes to be formed. Commonly with this type of co-ordination hydrogen bonding can also occur between the hydrogen on nitrogen-1 and a neigh-bouring anion 3 (Figure 3(a)). Of perhaps greater significance,however, are those complexes derived from the pyrazolyl anion, which has been found to co-ordinate i n three possible ways (Figure 3 ( b ) , ( c ) , ( d ) ) . Most reports involve the anion acting as an 'exobidentate' bridge between two metals or metalloids 1*. A l t e r n a t i v e l y i t has been shown that the pyrazolyl anion can serve as an n 2-endobidentate ligand as depicted by a recent X-ray c r y s t a l structure of a uranium (IV) s p e c i e s 5 . T h i r d l y , a monodentate co-ordination mode can exist as exhibited i n the renowned polypyrazolylborate and g a l l a t e anions and also with some select t r a n s i t i o n metals 6. 3 monodentate exobidentate T p-endobidentate Figure 3. Examples of the co-ordination modes of pyrazole and the p y r a z o l y l anion. Indeed of notable s i g n i f i c a n c e i n pyrazole chemistry has been the development of the polypyrazolylborate ligands. Since t h e i r discovery i n 1966 by Trofimenko, numerous publications and r e v i e w s 7 - 9 have i l l u s t r a t e d the v e r s a t i l i t y and co-ordinating a b i l i t i e s of these ligands (Figure 4). They can function as either bidentate or tridentate chelating ligands, and have provided a wealth of s t r u c t u r a l and spectroscopic i n t e r e s t as well as an impetus for the development of related ligands. 4 Figure 4. Examples of polypyrazolylborate c o m p l e x e s . 1 0 » 1 1 » V l » 5 These ligand systems can be modified by replacement of boron with another atom, perhaps most notable of these being those involving poly-p y r a z o l y l g a l l a t e ligands. Complexes incorporating p o l y p y r a z o l y l -a l k a n e s 7 » 1 4 » 1 5 , - phospines 1 6» 1 7 and -amines 1 8 have also been c i t e d . This thesis w i l l be p r i n c i p a l l y concerned with t r a n s i t i o n metal complexes derived from the g a l l a t e ligands. With the development of the boron systems i n hand i t was not u n t i l 1973 when the f i r s t gallium based pyrazolyl compound was formed 1 9. A mixture of pyrazole and trimethylamine-trideuteriogallane yielded the 'pyrazabole' 2 0 type analogue, a s o l i d d i-deuteriopyrazolyl gallane dimer. A symmetric 'boat' structure of a six-membered ring containing four nitrogens and two gallium atoms with planar pyrazolyl rings was X-ray c r y s t a l l o g r a p h i c a l l y established (Figure 5). In t h i s conformation, the pyrazolyl moieties r e t a i n t h e i r aromaticity. D D Figure 5. Di-deuteriopyrazolyl gallane dimer. The bidentate ligand, M e 2 G a P 2 2 ~ » (where pz - 1-pyrazolyl group), e a s i l y synthesised as shown i n Figure 6, has been su c c e s s f u l l y incorporated i n a number of t r a n s i t i o n metal complexes. 6 Figure 6. Synthesis of Na +[Me 2Gapz 2]~. Acting as a uninegative, four-electron donor, t h i s ligand can be likened and compared to the p-diketonate ion, d i f f e r i n g however, i n structure and i t s i n a b i l i t y to form t r i s - b i d e n t a t e chelates ( c f . Fe(acac) 3) and polynuclear species ( c f . Cu 2(acac) l t(H 2 0 ) 2 ). Nickel, copper and cobalt a l l form complexes of the general formula [Me 2Gapz 2] 2M, displaying varying structures and n o n - r i g i d i t y i n s o l u t i o n as evidenced i n t h e i r nmr spectra. The geometry of the orange, a i r stable n i c k e l complex i s c l e a r l y square planar about the n i c k e l centre, as shown by i t s X-ray c r y s t a l s t r u c t u r e 2 1 , whilst that of the cobalt d e r i v a t i v e i s t e t r a h e d r a l 2 2 . The copper compound was found to have a structure exhibiting a square planar arrangement i n the s o l i d state and a tetrahedral arrangement with the s u b s t i t u t i o n of the more s t e r i c a l l y demanding 3 , 5-dimethylpyrazolyl (dmpz) u n i t s 2 3 . 2 1 * (Figure 7). 7 Me Figure 7. Structure of [Me 2Gapz 2] 2Cu and [Me 2Ga(dmpz) 2] 2Cu. Quite unexpectedly the binuclear complex [Me3Ga^(mpz) 3CuO] 2 was formed from the 3-methyl substituted pyrazole (mpz) d e r i v a t i v e 2 5 . The reasons for t h i s contrast are not clear at present. 8 Numerous complexes bearing only one Me 2Gapz 2~ ligand are well documented. In a l l the complexes, the six-membered Ga-(N-N)2-M r i n g retains i t s 'boat' conformation as well as i t s c h a r a c t e r i s t i c n o n - r i g i d i t y i n s o l u t i o n . A series of manganese, molybdenum, tungsten and rhenium carbonyl derivatives with d i f f e r e n t a n c i l l a r y ligands were e a s i l y prepared i n THF and c r y s t a l l i n e products were o b t a i n e d 2 6 * 2 7 . Other cases involve ' a l l y l ' complexes of n i c k e l and p a l l a d i u m 2 8 , and more recent reports include complexes of i r i d i u m 2 9 , rhodium 3 0 and platinum 3 1 a l l of which display square planar t r a n s i t i o n metal geometries with a v a r i e t y of ligands; COD, CO and PPh 3 (Figure 8)• Me CO (P Figure 8. Examples of mono-bidentate p y r a z o l y l g a l l a t e complexes. 9 Formation of the t r i s - p y r a z o l y l substituted ligand, MeGapz3~, requires use of MeGaCl 2 since further heating of Me 2Gapz 2 - with pyrazole f a i l s to eliminate methane and give the desired l i g a n d . Functioning as a uninegative, s i x - e l e c t r o n donor with approximate symmetry, a tridentate co-ordination geometry of MeGapz3~ i s therefore possible with the ligand occupying f a c i a l p o s i t i o n s . The f i r s t row divalent halides of Mn •* Zn a l l react with MeGapz3~ giving complexes of the type [MeGapz 3] 2M** 3 2, while further studies have yielded numerous carbonyl derivatives of other m e t a l s 3 2 " 3 4 . Recent studies have been directed to the r e a c t i v i t y of molybdenum carbonyl anions based on the MeGapz3~ ligand system towards a v a r i e t y of t r a n s i t i o n and main group metal d e r i v a t i v e s 3 5 * 3 6 . As previously mentioned, s l i g h t v a r i a t i o n s i n the ligand can cause pronounced e f f e c t s i n the r e s u l t i n g t r a n s i t i o n metal complexes; further exemplification can be found i n the tridentate systems with t h e i r methyl substituted pyrazole counterparts. For example, the 3,5-dimethyl s u b s t i -tuted t r i s - p y r a z o l y l g a l l a t e ligand can prove too s t e r i c a l l y demanding to form complexes of the type ML 2. I t i s of note that where lesser s t e r i c constraints e x i s t , incorporation of a hydroxy moiety replacing a 3,5-dimethylpyrazolyl group can occur, thus y i e l d i n g the ligand, MeGa(dmpz)2OH- (Figure 9 ) 3 7 . 10 CO Figure 9. [MeGa(dmpz) 20H]W(C t tH 7)(C0) 2. The s u b s t i t u t i o n of methyl groups onto the p y r a z o l y l rings i s manifested i n the host ligand being a better a donor, creating a more 'elec t r o n - r i c h ' metal centre. This can be attributed to the p o s i t i v e inductive e f f e c t of the methyl groups relaying more e l e c t r o n i c charge to the metal, as evidenced by lower carbonyl stretching frequencies i n the i r spectra of the carbonyl d e r i v a t i v e s . As previously indicated,however, the e l e c t r o n i c s t a b i l i t y gained can often be o f f s e t by s t e r i c crowding stemming from the presence of the methyl groups. Thus, quite often,the t r i s -(3,5-dimethylpyrazolyl)gallate ligand w i l l fragment allowing the formation of a more stable dimeric species where the substituted pyrazolyl moieties merely form bridges between two metal c e n t r e s 2 9 * 3 0 . Generally, the substituted derivatives where formed, have an enhanced s t a b i l i t y i n comparison to the unsubstituted pyrazolyl ligands, since the methyl groups on the pyrazolyl rings can o f f e r some form of s t e r i c protection to the t r a n s i t i o n metal, rendering i t more stable against oxidation and h y d r o l y s i s . 11 A s i g n i f i c a n t deviation away from the related polypyrazolylborate ligands was the introduction of the unsymmetrical, tridentate p y r a z o l y l -g a l l a t e l i g a n d s 3 8 . This entailed a replacement of one of the py r a z o l y l units i n Me 2Gapz 2~ with a b i f u n c t i o n a l chelating moiety as shown i n Figure 10. + CH4 Figure 10. Synthesis of Na +[Me 2Gapz(OCH 2CH 2NH 2)] _. This c a p a b i l i t y , unique to the gallium d e r i v a t i v e s , has generated a further impetus for the development of new ligands since the scope of v a r i a t i o n of the donor atoms (oxygen and nitrogen i n Figure 10) and the supporting carbon fragment i s vast. Examples of co-ordinating ligands are shown i n Figure 11. 12 Figure 11. Examples of unsymmetric tridentate monopyrazolylgallate ligands. 13 Of s p e c i a l mention i s the fact that due to the f l e x i b i l i t y of the carbon skeleton between the donor atoms, these ligands can now co-ordinate with either a f a c i a l or meridional geometry. The chelation mode i s p r i m a r i l y determined by the p a r t i c u l a r metal and a n c i l l a r y ligands involved, but both mer and fac isomers have been observed for the complex [Me 2Gapz(OCH 2CH 2NH 2)] 2Ni 3 9. In l i g h t of the success encompassing the p y r a z o l y l g a l l a t e ligands, a comparison with t h e i r predecessors, the borate systems seems evident. Although for the most part t h e i r chemistries are expectedly s i m i l a r , several important differences have been noted. Preparative procedures are less forcing i n the g a l l a t e ligand syntheses and y i e l d hygroscopic, a i r se n s i t i v e s a l t s as opposed to the a i r stable borate d e r i v a t i v e s . In the bidentate systems, a more symmetric 'boat' conformation i s observed for the Ga-(N-N)2~M rings, shown unequivocally by X-ray s t r u c t u r a l studies, and th i s purports to the unequal bond lengths of Ga-N (~2.0 A) and B-N (~ 1.6 A ) . Consequently the 'boat' interconversion ' f l i p p i n g ' process as observed by variable temperature 1H nmr studies on [Me 2Epz 2] 2Ni, (E = Ga,B), were shown to be more f a c i l e for [ M e 2 G a p z 2 ] 2 N i 2 3 . E l e c t r o n i c f a c t o r s , o r i g i n a t i n g from the difference i n e l e c t r o -n e g a t i v i t i e s of gallium (1.82 ) and boron (2.01 ), render the g a l l a t e ligands more electron donating as evidenced by i r measurements of analogous carbonyl complexes 3 2. Thus the i n a b i l i t y to form t r a n s i t i o n metal Allred-Rochow e l e c t r o n e g a t i v i t e s . 14 complexes incorporating either H 2Gapz 2~ or HGapz 3~, has been attributed to the greater p o l a r i t y i n the Ga-H bond and the r e s u l t i n g increased r e a c t i v i t y 2 2 . Generally, the spectra of the complexes based on the g a l l a t e derivatives are easier to int e r p r e t than those of the i r borate analogues. In the *H nmr spectra, the Ga-Me moiety provides an excellent 'reporter group' i n i d e n t i f y i n g isomers as well as resonating i n a p o s i t i o n generally void of other s i g n a l s . In addition, the presence of the 1 0 B and isotopes and the complicating proton additions and losses common i n the mass spectra of the borates are absent i n the g a l l a t e s , leaving the clear isotope pattern of 6 9Ga (60.4%) and 7 1Ga (39.6%) easy to di s c e r n . The f i r s t part of th i s thesis deals e x c l u s i v e l y with the bidentate Et 2Gapz 2~ ligand ( L 1 ) and i t s co-ordination with molybdenum dicarbonyl ' a l l y l ' u n i t s . Experiments were undertaken with the aim of examining the geometry of the s t e r i c a l l y strained Ga-(N-N)2~Mo chelate r i n g and to investigate any possible C-H-Mo inte r a c t i o n s formed. Chapter I I I describes the syntheses of three unsymmetric tridentate p y r a z o l y l g a l l a t e ligands, Me 2Gapz(OCH 2pyr)- ( L 2 ) , Me 2Gapz(SCNCH 2CH 2NMe) - ( L 3 ) and Me2Gapz(OCH2CH2CH=CH2)~ (I>) (Figure 12) and the i r reactions with molybdenum dicarbonyl ' a l l y l ' and rhenium carbonyl precursors. F i n a l l y , i n an attempt to force a meridional co-ordination mode, an e f f o r t was made to obtain square-planar rhodium complexes incorporating these ligands. 15 Figure 12. The p y r a z o l y l g a l l a t e ligands NaL 1, NaL 2, NaL 3 and NaL 4. 16 1«2 General Techniques Since most of the compounds encountered were a i r and moisture s e n s i t i v e , experimental manipulations were ca r r i e d out i n a dry box (Vacuum Atmospheres Corporation), on a vacuum l i n e or i n nitrogen purged apparatus• The solvents used were dried by re f l u x i n g with the appropriate drying a g e nt 4 0 j 1 * 1 and d i s t i l l e d under nitrogen, (Linde U.S.P. Grade, Union Carbide Canada L t d . ) . Ir spectra were recorded on a Perkin Elmer 598 spectrometer, the 1601 cm - 1 bond of polystyrene being used for c a l i b r a t i o n purposes. Both Hujol mulls (KBr plates) and solu t i o n spectra i n dichloromethane, cyclohexane and THF (KBr and Cs l sol u t i o n c e l l s ) were employed. *H nmr spectra were performed by the U.B.C. nmr service on a Bruker WP80 or a Bruker WH400 using Fourier transform techniques. The nmr tubes were f i t t e d with a flame-seal c o n s t r i c t i o n and a B-10 q u i c k - f i t cone, enabling samples to be loaded i n a nitrogen atmosphere and sealed under vacuum. The required amount (~ 1 ml) of solvent (C gD 6, C 7D a, or d 6-acetone, Merck Sharp and Dohme of Canada Ltd.) was condensed into the tube using l i q u i d nitrogen on the vacuum l i n e . Chemical s h i f t s were measured r e l a t i v e to the re s i d u a l solvent protons where ir „ =2.84 ppm, Mass spectra were recorded by the U.B.C. mass spectrometry service using a Varian MAT CH4 or an AES MS 50. The i n t e n s i t i e s quoted refer to a pa r t i c u l a r i s o t o p i c combination of a fragment, where applicable, and are stated r e l a t i v e to the most intense peak of the spectrum. Toluene Me = 7.91 ppm, and % (CH 3) 2CO = 7.89 ppm. 17 CHAPTER II MOLYBDENUM CARBONYL COMPLEXES INCORPORATING THE Et 2Gapz 2~ LIGAND 2.1 Introduction E a r l i e r reports have d e t a i l e d the synthesis of the bidentate b i s - p y r a z o l y l g a l l a t e ligand, Me 2Gapz 2~, and i t s co-ordination chemistry towards several t r a n s i t i o n metal c e n t r e s , 2 6 - 3 1 . Those complexes involving molybdenum include the ' r ) 3 - a l l y l * (Figure 13(a)) and tetracarbonyl anion derivatives (Figure 1 3 ( b ) ) 2 6 . In these cases and indeed i n a l l of the previous reports incorporating the Me 2Gapz 2~ ligand, the six-membered, Ga-(N-N)2~M chelate r i n g (where M = t r a n s i t i o n metal) ex i s t s i n a 'boat' conformation. This s t r u c t u r a l arrangement allows the pyra z o l y l rings to remain planar and hence r e t a i n t h e i r s t a b i l i z i n g aromatic character. In order to investigate whether the geometry of the Ga-(N-N)2~M r i n g i s s t e r i c a l l y c o n t r o l l e d , greater s t e r i c constraints have been imposed on the complexes of the type shown i n Figure 13(a) by sub s t i t u t i n g the methyl group on the gallium with an ethyl group. 18 Figure 13. Molybdenum carbonyl derivatives of Me 2Gapz 2~ In order to r e l i e v e non-bonding i n t e r a c t i o n s , i t was suspected that the chelate ring might d i s t o r t into a possible 'chair' conformation, destroying the p l a n a r i t y of the sp 2 bonds about one of the nitrogen atoms i n each pyrazolyl ring (Figure 14). 19 Figure 14. 'Chair' conformation of the Ga-(N-N)2-Mo r i n g . A similar s i t u a t i o n i n the analogous pyrazolylborate ligand systems has been observed, forcing the corresponding B-(N-N)2-Mo ring into a shallow chair conformation i n the complex (Et 2Bpz 2)Mo(C 3H 5)(CO) 2 ( H p z ) 1 + 2 . In addition to the s t r u c t u r a l i n t e r e s t associated with the conforma-t i o n of the Ga-(N-N)2-Mo r i n g , related compounds with pyrazolylborate ligands have revealed the existence of novel three-centre, two-electron hydrogen bridge bonds, (Figure 15) j 1 * 3 »1+'4 • In view of the s i m i l a r i t y i n the chemistry of the pyrazolylborate and p y r a z o l y l g a l l a t e ligands, an in v e s t i g a t i o n into the p o s s i b i l i t y of analogous in t e r a c t i o n s i n the gallium-based ligands seemed warranted. Due to the inherent i n s t a b i l i t y of the H 2Gapz 2~ l i g a n d 2 2 , the C-H-Mo i n t e r a c t i o n was investigated using the Et ?Gapz 2~ ligand. 20 H T I 3 - C 7 H 7 C O C O C O Figure 15. [H 2B(dmpz) 2]Mo(C 7H 7)(CO) 2 and [Et 2Bpz 2]Mo(C 7H ?)(CO) 2. Reactions of the Et 2Gapz 2~ ligand ( L 1 ) and molybdenum carbonyl precursors with and without the addition of pyrazole were undertaken, with the aim of forming the complexes shown i n Figure 16(a) and 16(b). For the molybdenum centre to achieve an eighteen-electron configuration i n the l a t t e r s i t u a t i o n (Figure 16(b)), i t was thought that the alpha hydrogen of one ethyl group may engage i n a three-centre, two-electron C-H-Mo bonding i n t e r a c t i o n . 21 n-allyl <P CO (b) Figure 16. [Et 2Gapz 2]Mo(n 3-allyl)(CO) 2(Hpz) and " [ E t 2 G a p z 2 ] M o ( T i 3 - a l l y l ) ( C O ) 2 " . The complexes shown i n Figure 16(a) were formed (where ' r ) 3 - a l l y l ' = C^Hy, C 7H 7) and a c r y s t a l of the L 1 Mo(C 7H 7)(CO) 2(Hpz) complex has been submitted for X-ray c r y s t a l structure a n a l y s i s . Unfortunately no complexes of the formula L 1 M o ( n 3 - a l l y l ) ( C O ) 2 (Figure 16(b)) could be i s o l a t e d . 22 2.2 Experimental  2.2.1 Starting Materials Molybdenum hexacarbonyl (Strem Chemicals), sodium hydride (Alfa) and pyrazole (Aldrich) were used as supplied; t r i e t h y l g a l l i u m 1 * 5 , Mo(CH 3CN) 3(CO)3 1 + 6, Mo(CH 3CN) 2(C 1 +H 7)(CO) 2Cl, Mo(CH 3CN) 2(C 3H 5)(CO) 2Br' t 7, and Mo(C 7H 7)(CO) 2I l t 8 were prepared according to l i t e r a t u r e methods. Me t h a l l y l chloride and a l l y l bromide (Eastman Kodak Co.) were d i s t i l l e d before use. THF Na+H" + pzH rr-s-r »• Na+pz" + H, v room temp./18 hrs. * Sodium pyrazolide was formed from the deprotonation of pyrazole (2.001 g; 29.42 mmol) using sodium hydride (0.712 g; 29.67 mmol) i n THF; removal of the solvent i n vacuo q u a n t i t a t i v e l y yielded the white s a l t . 2.2.2. Preparation of Na+[Et 0Gapz 0]~, (NaL 1) Et.Ga + Na +pz~ TVE—3 • Na +[Et,Gapz]~ 3 + * room temp./15 mins. 1 3 v 1 T1TF Na+[Et 3Gapz]- + Hpz r e f l u x / 4 8 h r s . ' Na+[Et 2Gapz 2]" + EtH The Et 2Gapz 2~ ligand was f r e s h l y prepared by the reaction of t r i e t h y l g a l l i u m (1.536 g; 9.929 mmol) with sodium pyrazolide 23 (0.918 g; 10.20 mmol) i n THF at room temperature, followed by r e f l u x i n g with pyrazole (0.696 g; 10.23 mmol) for two days. The progress of the reaction was monitored by observing the disappearance of the N-H stretching frequency of free pyrazole i n the i r spectrum of the reactant s o l u t i o n . The cooled so l u t i o n was then d i l u t e d with THF to give a standard s o l u t i o n (0.0407 mol l " 1 ) of NaL 1, which was stored i n a nitrogen atmosphere. 2.2.3 Preparation of [Et ?Gapz ?)Mo(C 7H 7)(C0) ?(Hpz), (L 1Mo(C 7H 7)(CO) 0(Hpz)) Mo(C 7H 7)(C0) 2I + Hpz + NaL 1 _ THF room temp./20 hrs.' L 1Mo(C 7H 7)(C0) 2(Hpz) + Nal Equimolar amounts of the ligand (NaL 1), Mo(C 7H 7)(C0 2)I (0.103 g; 0.28 mmol) and pyrazole (0.018 g; 0.27 mmol) were s t i r r e d i n THF at room temperature for twenty hours. After removal of the solvent i n vacuo,the r e s u l t i n g dark brown residue was extracted with benzene, and the extracts f i l t e r e d . Addition of a small amount of n-hexane and slow evaporation of the mixed solvent from the f i l t r a t e afforded a i r stable red-brown, needle-like c r y s t a l s of L 1Mo(C 7H 7)(CO) 2(Hpz) (~ 46%). 24 2.2.4 Preparation of [Et 0Gapz 0]Mo(C^H 7)(CO) ?(Hpz), (L 1Mo(C, tH 7)(CO) ?(Hpz) Mo(CH 3CN) 3(CO) 3 + Hpz + C ^ C l + NaL 1 room THF temp./20 hrs."' L 1M°(^H 7)(CO) 2(Hpz) + NaCl + 3CH3CN + CO Mo(CH 3CN) 3(CO) 3 (0.119 g; 0.39 mmol), a s l i g h t excess of methallyl chloride (0.053 g; 0.58 mmol), NaL 1 (0.40 mmol) and pyrazole (0.027 g; 0.40 mmol) were added to THF. After s t i r r i n g at room temperature overnight the solvent was removed i n vacuo leaving a dark brown o i l y residue which was extracted with benzene. Slow evaporation of the solvent from the f i l t e r e d extracts yielded a i r - s t a b l e , l a r g e brown, p l a t e l e t s of L 1Mo(C l +H 7)(CO) 2(Hpz) (~ 23%). 2.2.5 Attempted preparation of [Et 2Gapz 2]Mo(C qH 5)(CO)2(Hpz), (L 1Mo(C,H K)(C0) o(Hpz)) Three routes were investigated i n an attempt to i s o l a t e the desired complex. In each case orange c r y s t a l s of Mo(C 3H 5)(CO) 2(Hpz) 2Br were obtained i n low y i e l d and there was no evidence for the formation of the expected product. The reaction of Mo(CH 3CN) 2(C 3H 5)(CO) 2Br with NaL 1 and Hpz at room temperature, and also a s i m i l a r pathway to that i n section 2.2.4 using Mo(CH 3CN) 3(CO) 3, both formed Mo(C 3H 5)(C0) 2(Hpz) 2Br as the only molybdenum-containing product i s o l a t e d . In addition,NaL 1 was refluxed with Mo(C0) 6 for forty-eight hours followed by s t i r r i n g at room temperature for 25 twenty hours with C 3H 5Br and Hpz. The usual work-up procedure of t h i s reaction mixture again only yielded Mo(C 3H 5)(CO) 2(Hpz) 2Br. 2.2.6 Attempted preparations of [Et 2Gapz 2]Mo ( r) 3-allyl)(CO) 2,  (L 1 M o ( T i 3 - a l l y l ) ( C O ) 0 ) ( i ) Where ' n 3 - a l l y l ' • C 7H 7 *[ Mo(C 7H 7)(C0) 2I + NaL 1 - a . TOF -3 ~ • "L 1Mo(C 7H 7)(C0) 9" + Nal 1 room temp. 28 hrs. and r e f l u x 16 hrs. ' ' 2 1 To a THF so l u t i o n of Mo(C yH 7)(CO) 2I (0.105 g; 0.28 mmol), an equimolar equivalent of NaL 1 was added and the r e s u l t i n g dark-blue mixture allowed to s t i r for twenty eight hours at room temperature followed by sixteen hours r e f l u x . Work-up of the reaction mixture resulted i n a black s o l i d which would not c r y s t a l l i z e , despite several attempts at room temperature, -10°C and -78°C with n-hexane, benzene, dichloromethane and several solvent mixtures. An n-hexane extraction of the black s o l i d yielded a compound, which by 1H nmr was i d e n t i f i e d as the dimeric species, [ E t 2 G a p z ] 2 4 9 , i n d i c a t i n g that some form of decomposition had occurred. Equations i n square brackets indicate the expected course of reactions. 26 ( i i ) Where ' T ) 3 - a l l y l ' = C,HR, C hH 7 Mo(CO) 6 + NaL x fluxM8 hrs. ' Na+[LlMo(C0) 4]- + 2C0 re [ (Na +[L 1Mo(CO) 4] - + C 4H 7C1 (or C 3H 5Br) _ THF room F temp./20 hrs.' " L ^ C W ( C O ) 2 " + NaCl + 2C0 ] The tetracarbonyl molybdenum anion was prepared by r e f l u x i n g molybdenum hexacarbonyl (0.270 g; 1.03 mmol) and an equimolar aliquot of the ligand (NaL 1) for two days. To th i s yellow s o l u t i o n , a s l i g h t excess of the a l l y l halide was added dropwise and the r e s u l t i n g mixture s t i r r e d for a further twenty hours at room temperature. The usual work-up procedure of solvent removal, extraction with benzene and f i l t r a t i o n afforded a dark green o i l . Persistent e f f o r t s to e f f e c t c r y s t a l l i z a t i o n with a va r i e t y of solvents at room temperature, -10°C, and -78°C were unsuccessful. Other routes using Mo(CH 3CN) 3(CO) 3, Mo(CH 3CN) 2(C 3H 5)(CO) 2Br and Mo(CH 3CN) 2(C l tH 7)(CO) 2Cl gave s i m i l a r i n t r a c t a b l e dark green o i l y residues. Table I. Micro-analyses and i r data of the complexes LMo(C0)9(Hpz)Y Compound Calcd. 0 S) Found (%) v C Q (cm-1) L Y C H N C H N in Nujol in solution Et 2Gapz 2 C HH 7 42.48 5.03 15.56 42.53 5.20 15.42 1935 , 1819 1941, 1854* Et 2Gapz 2 CyHy 46.09 4.71 14.66 46.30 4.38 14.59 1939 , 1861 1941, 1865* (Hpz)(Br) C 3 % 32.87 3.17 13.69 33.10 3.35 13.51 1920 , 1810 1941, 18421" = in cyclohexane = in dichloromethane. Table II. *H nmr data of the complexes LMo(CO)2(Hpz)Y in C 6D 6 solution Compc L >und Y Ga-Et2 • n 3 - a l l y l ' 'pyrazole' 'pyrazolyl' Et 2Gapz 2 9.81 (q) H 0 9.46 (q) H 0 9-21 (q) Hv 8.91 (q) H v 8.54 (s) anti 6.96 (s) syn 8.34 (s) Me 2.62 (d) 4.59 (dd) 3.90 (d) H 1.35 (br) H. A. 3.92 (t) HB 2.72 (d) Hy 1.94 (d) H6 Et 2Gapz 2 9.31 (q) H0 9.08 (q) 8.78 (t) 8.70 (t) Hv 4.74 (s) C 7H 7 2.36 (d) 4.56 (t) 4.08 (d) H 1.40 (br) ^ 3.84 (t) HB 2.44 (d) Hy 1.84 (d) H6 (Hpz)(Br) ^ 5 8.51 (br) anti 5.83 (br) syn 6.38 (br) unique 1.83 (br) 3.88 (br) H V 4.43 (br) H -1.63 (br) H s = singlet, d = doublet, t = triplet, q = quartet, dd = doublet of doublets, br = broad. See Figure 18 (page 31) for proton identification 29 2.3 Results and Discussion 2.3.1 [Et 0Gapz 0]Mo ( n 3-allyl)(CO) ?(Hpz) > (L 1Mo ( n 3-allyl)(CO) ?(Hpz))  where ' n 3 - a l l y l ' = C^ H-,, or C 7H 7 The a i r stable complexes of the above formula were characterized by micro-analyses, i r , nmr, and mass spectrometry. In the i r spectra, the observed two strong carbonyl bands of equal i n t e n s i t y are i n d i c a t i v e of a cis-carbonyl arrangement 5 0 as expected (Figure 17). The N-H st r e t c h at ~ 3400 cm - 1 (Nujol) of the pyrazole ligand i s also consistent with the predicted structures. In comparison with the analogous Me 2Gapz 2~ derived C 7H 7 compound 5 1, the carbonyl bands were observed at a lower stretching frequency for the ethyl d e r i v a t i v e (Table I I I ) . This may be a consequence of the s l i g h t l y greater inductive e f f e c t (+ I) of the ethyl groups, thereby creating a more 'e l e c t r o n - r i c h ' metal centre and a weaker C-0 bond due to the increased d + % back-bonding from the metal to the carbonyl l i g a n d . Table I I I . I r carbonyl stretching frequencies of [R 2Gapz 2]Mo(C 7H 7)(CO) 2(Hpz) (R - Et, Me). Compound i n cyclohexane (cm' reference (Et 2Gapz 2)Mo(C 7H 7)(C0) 2(Hpz) 1941, 1865 thi s work (Me 2Gapz 2)Mo(C 7H 7)(CO) 2(Hpz) 1949, 1874 26 32 In the XH nmr spectrum of L 1Mo(C 7H 7)(C0) 2(Hpz) (Figure 18) the signals due to the pyra z o l y l protons of the g a l l a t e ligand indicate that the two pyrazolyl groups are equivalent, thus the ' n 3 - a l l y l ' and pyrazole ligands must be trans to each other. The resonances of the two equivalent pyr a z o l y l groups can be distinguished from those of the pyrazole ligand by th e i r r e l a t i v e i n t e g r a l values ( 2 : 1 ) . In the 1H nmr spectrum of L 1Mb(C l tH 7)(CO) 2(Hpz) the 'syn' and ' a n t i ' protons of the methallyl ligand (C^Rj) are displayed as si n g l e t s which suggests t h e i r equivalence. This feature provides further support for the structure shown i n Figure 17, where the C 1 +H 7 group i s oriented so that the methyl moiety of the ••n3-a l l y l ' group i s d i r e c t l y opposite L 1 and thus the 'syn' and 'a n t i ' protons become equivalent. A 400 MHz *H nmr spectrum of L 1Mo(C 7H 7)(CO) 2(Hpz) c l e a r l y resolves the signals of the inequivalent ethyl groups of L 1 . I t i s proposed that the downfield methylene resonances correspond to the eth y l group i n a pseudo-axial p o s i t i o n , as t h i s p o s i t i o n renders the methylene protons s l i g h t l y closer to the metal c e n t r e 2 3 * 5 1 . The si n g l e t observed for the C 7H 7 group i n the spectrum indicates that t h i s ligand i s involved i n a rapid f l u x i o n a l process at room temperature. A series of low temperature 1H nmr spectra of the complex, L 1Mo(C 7H 7)(CO) 2(Hpz), showed the signal of the C 7H 7 group to separate out into several resonances at lower temperatures, as previously noted i n s i m i l a r TI 3-C 7H 7 containing complexes 5 2. 33 In the mass spectrum of L 1Mo(C 4H 7)(CO) 2(Hpz) (Table IV), a l l the p r i n c i p a l assignments were made with the aid of the expected i n t e n s i t y patterns for the possible i s o t o p i c combinations (appendix, page 120). In Table IV. Mass Spectral data for [Et 2Gapz 2]Mo(C 1 +H 7)(C0) 2(Hpz) m/ e Relative Intensity (%) Assignment 471 4 [(Et 2Gapz 2)Mo(C l tH 7)(C0) 2] + 443 3 t(Et 2Gapz 2)Mo(C l tH 7)(C0)]+ 415 46 [(Et 2Gapz 2)Mo(C l tH 7)] + 386 41 [(EtGapz 2)Mo(C t tH 7)] + 359 100 [ G a 2 p z 2 E t 3 ] + 331 63 [ G a 2 p z 2 E t 2 H ] + 301 46 [ G a 2 p z 2 E t ] + 165 15 [GapzEt]+ 127 8 [ G a E t 2 ] + 99 5 [GaEtH]+ 69 21 Ga+ 68 34 [Hpz]+ 56 3 [C„H 7]+ calculated with 6 9 G a and 9 8Mo. 34 add i t i o n to the sequential losses of pyrazole, carbon monoxide and ethene from the parent ion, the spectrum also showed the presence of the [ E t 2 G a p z ] 2 + dimer. In the proposed structure of the L 1Mo ( n 3-allyl)(CO) 2(Hpz) complexes, the a x i a l ' r ) 3 - a l l y l ' and pyrazole groups can exert a s t e r i c constraint on the ethyl moieties of E t j G a p Z j ^ L 1 ) . The extent of the inherent non-bonding interactions may force a f l a t t e n i n g of the normal 'boat* conforma-tio n of the Ga-(N-N)2-Mo chelate ring to the 'chair' conformation. I t should be noted,however, that the micro-analyses, i r and nmr data obtained could equally support the existence of either 'boat' or 'chair' conforma-tions of the chelate rings i n the complexes LAMo(T} 3-allyl)(CO) 2(Hpz). In order to unequivocally ascertain the correct structure, a c r y s t a l of I^MoCCyHy)(CO) 2(Hpz) has been submitted for an X-ray c r y s t a l structure determination which i s currently i n progress. 2.3.2 Mo(C,Hc;)(CO) 0(Hpz) 0Br The attempted incorporation of C 3H 5 as the ' f ) 3 - a l l y l ' group present i n (Et 2Gapz 2)Mo ( n 3-allyl)(CO) 2(Hpz) proved unsuccessful. Despite the several routes attempted, the c r y s t a l l i n e complex, Mo(C 3H 5)(CO) 2(Hpz) 2Br, was the only molybdenum carbonyl compound i s o l a t e d . This observation seems unusual i n view of the fact that no 'extra' s t e r i c or el e c t r o n i c constraints are imposed on the molecule by the C 3H 5 group compared to C 7H 7 or C^Hy. Moreover the f a c i l e formation of the analogous pyrazolylborate compound, (Et 2Bpz 2)Mo(C 3H 5)(CO) 2(Hpz) has been reported i n the l i t e r a t u r e 5 3 ' 3 5 The basis of t h i s unusual behaviour perhaps l i e s i n the order and nature of the addition of the reactants. Excess pyrazole,however, was shown to have no noticeable e f f e c t i n the formation of (Et 2Bpz 2)Mo(C 3H 5)(CO) 2(Hpz) 5 3. Several attempts at the synthesis of (Et 2Gapz 2)Mo(C 3H 5)(CO) 2(Hpz) v i a proven pathways for analogous compounds 2 6* 5 3 yielded only one i d e n t i f i a b l e molybdenum-containing product, Mo(C 3H 5)(CO) 2(Hpz) 2Br. 2.3.3 " [ E t 0 G a p z 0 ] M o ( r i 3 - a l l y l ) ( C O ) 0 " No compounds of the above formula were i s o l a t e d . Attempts using C^H, and C3Hg as the ' n 3 - a l l y l ' group gave i n t r a c t a b l e dark green gums while the reaction of Mo(C 7H 7)(C0) 2I and NaL 1 formed a black s o l i d which was found to contain the decomposition product [ E t 2 G a p z ] 2 4 9 . In contrast to the borate ligand systems, gallium derived complexes incorporating a three-centre, two-electron C-H-Mo bonding i n t e r a c t i o n could not be i s o l a t e d . A possible explanation of t h i s d i s s i m i l a r i t y may originate from the d i f f e r e n t bond lengths associated with each system. Figure 19 i l l u s t r a t e s the comparable s i t u a t i o n i n the two cases. The c r i t i c a l , longer Ga-N bond of ~ 2.0 A ( c f . B-N ~ 1.6 A) purports to a greater separation between the gallium and molybdenum atoms (~ 4.1 A) as compared to that between the boron and molybdenum atoms (~ 3.8 A). In so doing the gallium chelate ring may prove more f l e x i b l e for d i s t o r t i o n s , but the estimated proximity between the methylene hydrogens and the molybdenum 36 Figure 19. Approximate hydrogen-molybdenum distances i n Et 2E-(N-N) 2-Mo, (E = Ga,B), systems. 37 centre (~ 2.9 A) appears to be i n s u f f i c i e n t to allow any C-H-Mo bonding i n t e r a c t i o n . 2.4 Summary The a i r stable, 'eighteen-electron' complexes of the formula (Et 2Gapz 2)Mo(n 3-allyl)(CO) 2(Hpz) ( n 3 - a l l y l = C 4H 7, C 7H 7) have been formed. The X-ray c r y s t a l structure determination of the complex (Et 2Gapz 2)Mo(C 7H 7)(C0) 2(Hpz) i s currently i n progress and may reveal a 'chair' conformation of the Ga-(N-N)2~Mo chelate r i n g present i n t h i s complex. The ' r | 3 - a l l y l ' , C 3H 5, could not be incorporated into the compounds of the previous formula; but synthetic attempts instead yielded the complex, Mo(C 3H 5)(CO) 2(Hpz) 2Br. It i s proposed that the longer Ga-N bond distance as compared to the B-N bond distance i n the ligand E t 2 E p z 2 ~ (E *> Ga,B), prevents the formation of any C-H-Mo i n t e r a c t i o n i n the complexes ( E t 2 G a p z 2 ) M o ( n 3 - a l l y l ) C O ) 2 while the geometric requirements for t h i s i n t e r a c t i o n are f u l f i l l e d i n the borate systems. 38 CHAPTER III REACTIONS OF MOLYBDENUM AND RHENIUM CARBONYL COMPLEXES WITH UNSYMMETRIC TRIDENTATE PYRAZOLYLGALLATE LIGANDS 3.1 Introduction As mentioned i n Chapter I (page 11), c e r t a i n b i f u n c t i o n a l donor unsymmetrical tr i d e n t a t e , p y r a z o l y l g a l l a t e ligands. In addition, the reaction of the b i f u n c t i o n a l donor species with trimethyl gallium i s frequently investigated, the products of which are often dimeric with the gallium atoms assuming t e t r a h e d r a l 5 5 , or di s t o r t e d t r i g o n a l b i p y r a m i d a l 5 6 geometries. For example,the reaction of 2-pyridylcarbinol with trimethyl gallium yielded the dimer [Me 2Ga(OCH 2pyr)] 2 5 6, (Figure 20). species have been incorporated into the *Me2Gapz' moiety to form Me Me Figure 20. [Me 2Ga(0CH 2pyr)] 2. 39 The successful development of the unsymmetric, tridentate p y r a z o l y l g a l l a t e ligands can be p a r t l y attributed to th e i r co-ordinating a b i l i t y towards molybdenum dicarbonyl ' a l l y l ' and rhenium t r i c a r b o n y l units (Figure 21). Figure 21. [Me 2Gapz(OCH 2CH 2NH 2)]Mo(C 7H 7)(CO) 2 and [Me 2Ga(dmpz)(OCH 2CH 2SEt)]Re(CO) 3. 40 The v e r s a t i l i t y and s t a b i l i t y of these compounds are well documented and representative examples of these complexes have been s t r u c t u r a l l y c h a r a c t e r i z e d 5 7 * 5 8 . Consequently,the r e a c t i v i t y of more recently designed ligands, where the nature of the carbon skeleton and donor atoms (X and Y) are varied (Figure 22), towards appropriate molybdenum and rhenium carbonyl precursors are often investigated. Figure 22. Na +[Me 2Gapz(X ~~~~ Y ) ] _ . U n t i l now a l l the b i f u n c t i o n a l groups used i n these ligand systems have incorporated a two-carbon spacing between th e i r donor atoms (nitrogen, oxygen or sulphur). In order to e s t a b l i s h the s i g n i f i c a n c e of t h i s s t r u c t u r a l arrangement, Na +[Me 2Gapz(SCNCH 2CH 2NMe)] - (NaL 3) (Figure 23)was synthesized and i t s co-ordination properties studied. 41 Figure 23. Na+[Me2Gapz(SCNCH2CH2NMe)]" (NaL 3). These ligand systems were further extended to Na +[Me 2Gapz(OCH 2CH 2CH=CH 2)]~ (NaL 4), i n which co-ordination may be possible through an o l e f i n as one of the donor groups (Figure 24). 42 Figure 24. Na+[Me2Gapz(OCH2CH2CH=CH2)]- (NaL 4). 3.2 Experimental  3.2.1 Starting Materials Mo(CH 3CN) 2(C 3H 5)(CO) 2Br, Mo(CH 3CN) 2(C 4H 7)(CO) 2C1 4 7 and M o ( C 7 H 7 ) ( C 0 ) 2 I 4 8 were prepared as described by l i t e r a t u r e methods s t a r t i n g with molybdenum hexacarbonyl (Strem Chemicals). The a l l y l halides and 43 a c e t o n i t r i l e employed were d i s t i l l e d before use, the l a t t e r being dried by re f l u x i n g over phosphorus pentoxide (BDH Chemicals). [Re(CO) 1 +Cl] 2 was synthesized by the l i t e r a t u r e procedure 5 9, from rhenium hexacarbonyl (Strem Chemicals) and chlorine gas (Matheson). NaH + HSCNCH2CH2NMe THF In K i 1 •—• •••• i TXT—r- • Na +[SCNCH 0CH 0NMel _ + H 0 room temp./24 hrs. 1 2 2 ' 2 The sodium s a l t of 2-mercapto-l-methylimidazole was e a s i l y prepared by s t i r r i n g equimolar amounts of sodium hydride (1.152 g; 48.00 mmol) (Alfa) and the mercapto-imidazole (5.499 g; 48.23 mmol) (Aldrich) f o r twenty four hours at room temperature i n THF. Upon solvent removal i n  vacuo the desired white s a l t , Na+[SCNCH2CH2NMe]~ was recovered i n quantitative y i e l d . The hygroscopic nature of the compound necessitated storage i n a dry nitrogen atmosphere. 3.2.2 Preparation of Na+[Me 2Gapz(OCH 2pyr)]~ (NaL 2), Na+[Me2Gapz(SCNCH2CH2NMe)]- (NaL 3) and Na+[Me2Gapz(OCH2CH2CH=CH2)]- (NaL1*) The ligands were synthesized from the Na +[Me 3Gapz]~ p r e c u r s o r 3 8 and an equimolar amount of the alcohol ( i i and i i i ) or mercapto-Imidazole ( i ) (Figure 25). Refluxing the mixtures for f o r t y hours effected the 44 Figure 25. Syntheses of NaL 2, NaL 3 and NaL 4. 45 disappearance of the 0-H (~ 3450 cm - 1) and the S-H (~ 2800 cm"1) bands i n the i r spectra of the appropriate reacting s o l u t i o n s . The cooled solutions were then d i l u t e d to a known volume with THF and stored under nitrogen. 3.2.3 Preparation of [Me2GaSCNCH2CH2NMe]2 2Me3Ga + 2HSCNCH2CH2NMe THF « i r r - r • [Me0Ga(SCNCH0CHoNMe)]0 + 2 CH U room temp./3 hrs. 1 2 x 2 2 / J 2 4 2-Mercapto-l-methylimidazole (2.0 g; 18 mmol) and trimethylgallium (2.1 g; 18 mmol) were s t i r r e d i n THF at room temperature for three hours. After solvent removal i n vacuo the residue was extracted with benzene and l e f t to stand to allow slow evaporation of the solvent, which subsequently i i q u a n t i t a t i v e l y afforded colourless c r y s t a l s of [Me 2Ga(SCNCH 2CH 2NMe)] 2. 3.2.4 Preparation of [Me ?Gapz(SCNCH ?CH 2flMe)]Re(C0),, (L 3Re(C0),) [Re(C0)^Cl] 2 + 2NaL 3 reflux/19 hrs. » 2L 3Re(CO) 3 + 2NaCl + 2C0 46 A two molar equivalent amount of the ligand (NaL 3) was added to [Re(CO) 1 +Cl] 2 (0.292 g; 0.44 mmol) i n THF. A nineteen hour r e f l u x of the reactant s o l u t i o n effected the t o t a l disappearance of the carbonyl bands of the s t a r t i n g material i n the i r spectra of the reacting mixture. Following t h i s the normal work-up procedure on the cooled s o l u t i o n afforded small white c r y s t a l s from benzene, which were characterized as L 3Re(CO) 3 (~ 40%). 3.2.5 Attempted preparations of [Me 2Gapz(SCNCH 2CH 2NMe)]Mo(Ti 3-allyl)(CO) 2  where n 3 - a l l y l = c ^ h r > C l lH 7(i) or C 7 H 7 ( i i ) ( i ) 2Mo(CH 3CN) 2(C 3H 5)(CO) 2Br* + 2Na +[Me 2Gapz(SCNCH 2CH 2NMe)]~ THF I 1 „ , • [Mo(C,Hc)(CO),(SCNCH,CH,NMe)]9 + 2NaBr room temp./16 hrs. 1 v 3 5 / v ' 2 V 2 2 / J 2 + 4CH3CN + [Me 2Gapz] 2 Addition of an equimolar amount of NaL 3 to a clear orange THF sol u t i o n of Mo(CH 3CN) 2(r) 3-allyl)(CO) 2X (~ 0.34 mmol), immediately resulted i n p r e c i p i t a t i o n of a f i n e white s o l i d (presumably NaX), with concomitant s h i f t s i n the carbonyl stretching frequencies i n the i r spectra of the mixture. After s t i r r i n g the reaction mixture at room temperature f o r twenty hours, the solvent was removed i n vacuo and the residues extracted with benzene. Subsequent evaporation of the solvent from the f i l t e r e d * Similar equation for Mo(CH 3CN) 2(C 1 +H 7)(C0) 2Cl 4 7 solutions l e f t orange c r y s t a l s characterized as benzene solvate compounds. Heating at 70°C whilst under vacuum removed the res i d u a l benzene and gave a n a l y t i c a l l y pure samples of [Mo(n 3-allyl)(CO) 2(SclraL^CH^NMe)] 2 ('n 3-allyl'=C3H 5, C ^ ) (~ 60%). ( i i ) The ligand (NaL 3) was added to an equimolar amount of Mo(C 7H 7)(C0 2)I (0.088 g; 0.24 mmol) i n THF. The dark green mixture was then s t i r r e d at room temperature for eighteen hours. The usual work-up procedure on the r e s u l t i n g orange s o l u t i o n , extracting with dichloromethane or benzene afforded a dark purple solid,however, which proved u n i d e n t i f i a b l e . 3.2.6 Attempted preparation of [Me2Ga(OCH,CH?CH=CH?)]? and reactions with  Na +[Me 2Gapz(OCH 2CH 2CH=CH 2)]-, (NaL 4). Me3Ga (0.228 g; 1.98 mmol) and 3-butene-l-ol (0.144 g; 2.00 mmol) were refluxed i n THF for four hours. Work-up with a v a r i e t y of solvents yielded an insoluble white powder characterized as the tetrameric species, [Me 2GaO] 4. The appropriate molar aliquots of the ligand (NaL^) were reacted with [ R e ( C 0 \ C l ] 2 (0.122 g; 0.18 mmol) and Mo(CH3CN) 2 ( C 3 H 5 ) ( C O ) 2 B r (0.128 g; 0.36 mmol) at room and r e f l u x temperatures. The usual work-up procedure gave u n i d e n t i f i a b l e products, despite several attempts at p u r i f i c a t i o n with a v a r i e t y of solvents at room temperature, -10°C and -78°C. Table V. Micro-analyses and i r data of [Ms2Gapz(0CH2pyr)]M3(C7H7)(CD)2 and the complexes derived from (SCNQ^QyMe)-. Compound Calcd. (%) Found (%) vco ( a n - 1 ) C H N C H N In Nujol Other [Ma2Ga(SOOL.CH2»fe) ] 2 33.85 5.17 13.16 33.99 5.25 13.15 [M^GapzCSCNa^O^IMe) ]Re(CO)3 26.19 2.56 10.18 26.22 2.21 9.90 2010, 1900(br) ^OOS, 1910(br) [MoC^Hj )(03)2(SQOl2CH2»fe)] 2 35.18 3.26 9.12 35.54 3.39 8.43 1930, 1837 *1935(br),1872,1852 [Mo^H, )<a»2(Sany^Mfe)]2 37.62 3.76 8.78 37.46 3.89 8.83 1935(br),1865,1840 *1975,1939,1875,1854 tMe2Gapz(CCH2pyr)]M>(C7H7)(CO)2 46.36 4.25 8.11 46.25 4.23 7.99 1928, 1855 * 1940, 1861 in (lichloromethane in THF * in cyclohexane hr = broad Table VI. XH nnr data of pfe2Gapz(OCH2pyr)]^ C7H7)(OD)2 and the complexes derived from (SOO^Q^ttfer. Ocrapound Ga-Me S-Me H h% 'pyrazolyl* O-CHg-pyr 'allyl' H Y H anti H syn Other * [M^Ga(SCTOl2CH2Mfe)]2 10.22(a) 10.39(8) 6.44(a) 6.29(8) 2.72(br) 3.04(br) [Ma2Gapz(SQCH2CH2tWe)]Re(ao)3 10.12(a) 9.94(a) 7.49(8) 3.44(d) 4.34(d) 3.94(dd) 2.69(d) 2.12(d) * )(a»2(san^a^«MB)]2 6.83(8) 3.28(d) 3.18(d) 8.60(d) 8.68(d) (J-lOHz) 6.58(d) 6.60(d) (>7Hz) 6.18(br) H unique *[bfe(^H7)(a))2(stkH2ca2»fe)]2 6.80(8) 3.18(d) 3.23(d) 8.54(8) 8.90(8) 6.65(d) 7.05(d) (>3Hz) 8.28(8) allyl Me [I^(^(0(H2pyr)]M)(C7H7)(O3)2 10.12(8) 10.49(a) 3.99(t) 3.07(d) 2.02(d) A - 5.04(d) B = 5.34(d) (Jab=15 Ik) 4.62(8) <7»7 measured In dg-acetone (x acetone » 7.89 pan) measured in CgDg (t benzene » 2.84 ppm) s = single, d •» doublet, t - triplet, br » broad, dd ~ doublet of doublets See Figure 28 (page 55) for proton Identification 50 3.2.7 Preparation of [Me 2Gapz(0CH 2pyr)]Mo(C 7H 7)(C0) 2, (L 2Mo(C 7H 7)(C0) 2). Mo(C 7H 7)(C0) 2I + NaL THF room TT^-r • L 2Mo(C 7H 7)(C0) 9 + Nal. temp./18 hrs. > ' N 2 This complex was prepared by reacting an equimolar amount of the ligand (NaL 2) with Mo(C 7H 7)(C0) 2I (0.089 g; 0.24 mmol) i n THF at room temperature for eighteen hours, the colour of the reaction mixture changing from dark green to a red-brown. The usual work-up procedure of solvent removal, extraction i n benzene, f i l t r a t i o n and slow evaporation of the benzene afforded red-brown c r y s t a l s , characterized as L 2Mo(C 7H 7)(C0) 2 (~ 60%). 3.3 Results and Discussion 3.3.1 Reactions of Me?Ga with HSCNCH2CH2NMe and HOCH2CH2CH=CH2. The elimination of methane from trimethylgallium and 2-mercapto-l-methylimidazole i s i n accord with s i m i l a r reactions involving gallium a l k y l s and compounds containing an a c i d i c hydrogen 6 0. As shown by the X-ray c r y s t a l structure obtained (Figure 26), the complex formed exists as a dimer incorporating a novel eight-membered ring with the gallium atoms i n a tetrahedral geometry. This 'exobidentate' co-ordination of 'SCNCH2CH2NMe' can be considered analogous to the pyra z o l y l derived compound [Me 2Gapz] 2 (Figure 27) 1* 9. The 'boat' conformation of the 51 six-membered Ga-(N-N)2~Ga ring i n [Me 2Gapz] 2,however, can be contrasted to the eight- membered Ga-(N-C-S) 2~Ga rin g which adopts a 'chair' arrangement. Presumably t h i s 'chair' conformation allows for the minimum amount of non-bonding int e r a c t i o n s between the methyl groups present and allows the imidazole rings to remain planar. This planar arrangement allows d e r e a l i z a t i o n of the n-electrons i n each bridging ligand unit with a r e s u l t i n g increase In s t a b i l i z a t i o n energy. The Ga-N distances i n [Me 2Ga(SCNCH 2CH 2NMe)] 2 (2.02 A) are longer than the distance of 1.97 A normally observed i n four co-ordinate gallium compounds 6 1* 6 2. These weaker Ga-N bonds may be a consequence of the s t r a i n about the gallium atoms which are present i n a d i s t o r t e d tetrahedral environment. Quite unlike 2-mercapto-l-methylimidazole, 3-butene-l-ol did not form the expected product with trimethylgallium, the attempted syntheses y i e l d i n g only [Me2GaO] 1 + 6 3 » 6 4 . 53 Figure 27. [Me 2Gapz] 2 and [Me 2Ga(SCNCH 2CH 2NMe)] 2. 54 3.3.2 Reactions of Na+[Me2Gapz(SCNCH2CH2NMe)]" (NaL 3). The reaction of NaL 3 with [Re(CO) 4Cl] 2 yielded the product L 3Re(CO) 3, characterized by micro-analyses, i r and nmr. The i r spectra of L 3Re(CO) 3 suggests the presence of three carbonyl groups i n a f a c i a l arrangement. The spectra showed two carbonyl bands of equal i n t e n s i t y but the lower frequency band appeared r e l a t i v e l y broad. Several attempts at resolving t h i s broad band were unsuccessful. As shown i n other LM(CO) 3 compounds however, i t i s not uncommon for three carbonyl groups co-ordinated f a c i a l l y to display only two carbonyl bands i n th e i r i r s p e c t r a 5 0 . The inequivalent GaMe2 resonances i n the nmr (figure 28) rules out a possible meridional co-ordination of L 3 and i t i s therefore presumed that the remaining three f a c i a l s i t e s are occupied by the sulphur and the two nitrogen atoms from the ligand, thereby completing the expected octahedral geometry. In th i s proposed structure (Figure 28), the complex exhibits a co-ordinatively saturated, 'eighteen-electron' rhenium centre. Noteworthy i s the fact that the signal of the H proton of the pyrazolyl ring i n the P *H nmr spectrum appears as a doublet of doublets, coupling with the Inequivalent, neighbouring and protons. In the 1H nmr spectra of other p y r a z o l y l g a l l a t e ligand-containing complexes t h i s H s i g n a l i s P commonly displayed as an observed t r i p l e t . 55 56 L 3Re(CO) 3 thus represents the f i r s t reported case where an unsymmetric, tridentate p y r a z o l y l g a l l a t e ligand incorporates a sing l e carbon spacing between the sulphur and nitrogen donor atoms denoted as X and Y i n Figure 22. In contrast to the successful co-ordination of L 3 with the rhenium t r i c a r b o n y l u n i t , attempts with molybdenum dicarbonyl ' a l l y l ' precursors f a i l e d to give s i m i l a r octahedral complexes. Instead degradation of the ligand occurred enabling two free 'SCNCH2CH2NMe' anions to bridge two metal centres giving dimers of the form [Mo(n 3-allyl)(CO) 2(SCNCH 2CH 2tiMe)] 2 ( * T } 3 - a l l y l ' = C 3H 5, C 4H 7), which were characterized by micro-analyses, i r , *H nmr and mass spectrometry. The low s o l u b i l i t y of these compounds precluded an accurate molecular weight determination by either i s o p i e s t i c or cryoscopic methods. The i r spectra of [Mo(C kH 7)(CO) 2(SCNCH 2CH 2NMe)] 2 showed two pairs of carbonyl bands (Figure 29) which would be consistent with the existence of the geometric isomers shown i n Figure 30, where the C 4H 7 groups may be c i s or trans to each other. A l t e r n a t i v e l y , the exact structure of i r [Mo(Ci tH 7)(C0) 2(SCNCH 2CH 2NMe)] 2 may possess a symmetry point group which would lead to an expected four carbonyl bands. 57 58 Figure 30. Proposed geometric isomerism i n [Mo(C l tH 7)(CO) 2(SCNCH 2CH 2NMe)] 2. 59 The 1H nmr spectra (Figure 31) of these c r y s t a l l i n e products confirmed the absence of any GaMe2 or 'pyrazolyl' proton signals and showed i j only the presence of the ' n ^ - a l l y l ' and SCNCH2CH2NMe groups. The signals due to the 'ant i ' protons of the C 3H 5 group suggest two inequivalent 'anti' protons both coupling to the 'unique' p r o t o n 6 5 (J = 10 Hz); thus two doublets are observed. In the 'syn' proton region however, only one doublet i s displayed which would indicate two equivalent 'syn' protons coupling to the 'unique' proton ( J = 7 Hz). To c l a r i f y t his apparent contradiction, a double resonance experiment was performed where the 'unique a l l y l ' proton was i r r a d i a t e d , thus removing any coupling to thi s proton. As a consequence the two doublets of the 'ant i ' protons collapsed to give two broad s i n g l e t s , and the doublet due to the 'syn' protons appeared as two si n g l e t s with very s i m i l a r x values. In addition a 300 MHz spectrum of [Mo(C 3H 5)(CO) 2(SCNCH 2CH 2NMe)], without i r r a d i a t i o n , resolved the 80 MHz 'syn' proton doublet as being i n fact two doublets with very similar chemical s h i f t values. In view of these r e s u l t s the 'a n t i ' and 'syn' protons of the C 3H 5 are shown to be inequivalent, which i s i n accord with the structure shown (Figure 31). 60 The proposed dimeric form of the [Mo(n 3-allyl)(C0) 2(SCNCH 2Ol 2NMe)] 2 complexes would enable the molybdenum atoms to achieve a more s t a b i l i z i n g 'eighteen-electron' configuration. In order to f u l f i l t h i s requirement, a double bond between the molybdenum centres can be envisaged (Figure 31). Further supporting evidence for the dimer was found i n the mass spectrum of [Mo(C 3H 5)(CO) 2(SCNCH 2CH 2NMe)] 2 (Table VII) where i n addition to the appearance of the parent ion signal at m/e 612 a signal corresponding to the binuclear [Mo(SCNCH2CH2NMe)]2 fragment was also observed at 418 a.m.u. In addition, the 1H nmr spectrum obtained does suggest the presence of a dimer, since the monomeric complex of the same empirical formula would probably necessitate the existence of a paramagnetic, molybdenum ( I ) , d 5 species. I t i s well established that even a trace amount of a paramagnetic material can enhance the broadening of signals i n nmr spectra, often rendering t h e i r i n t e r p r e t a t i o n much more d i f f i c u l t 6 6 . 62 Table VII. Mass Spectral Data for [Mo(C 3H 5)(CO) 2(SCNCH 2CH 2NMe)] 2. m/e Relative Intensity (%) Assignment 612 0.53 [Mo 2(C 3H 5) 2(CO)^(SCNCH2CH2NMe) 2 ] + 584 0.95 [Mo 2(C 3H 5) 2(CO) 3(SCNCH 2CH 2NMe) 2]+ 515 2.50 [Mo 2(C 3H 5)(CO) 2(SCNCH 2CH 2NMe) 2] + 500 2.04 [Mo 2(C 3H 5) 2(SCNCH 2CH 2NMe) 2] + 459 11.47 [Mo 2(C 3H 5)(SCNCH 2CH 2NMe) 2] + 418 4.14 [Mo 2(SCNCH 2CH 2NMe) 2] + 308 24.50 [Mo(C 3H 5)(CO) 2(SCNCH 2CH 2NMe)] + 280 16.50 [Mo(C 3H 5)(CO)(SCNCH 2CH 2NMe)]+ 252 100.00 [Mo(C 3H 5)(SCNCH 2CH 2NMe)]+ Mo2 fragments based on Mo fragments based on 9 8Mo 63 A sim i l a r dimeric structure, also consistent with the micro-analyses, i r , nmr and mass spectra obtained, could be proposed, whereby only the sulphur atoms bridge the two molybdenum centres (Figure 32(a)). In th i s Figure 32. Possible dimeric structures of [Mo(C 3H 5)(CO) 2(SCNCH 2CH 2NMe)] 2. co-ordination mode a double Mo-Mo bond would be required to give each the two molybdenum centres an 'eighteen-electron' configuration. In a si m i l a r s i t u a t i o n the 'S-phenyl' group has been s t r u c t u r a l l y shown to bridge, v i a the sulphur atoms, two molybdenum c e n t r e s 6 7 * 6 8 . Several other reports have c i t e d sulphur atoms bridging between molybdenum atoms, but those incorporating the molybdenum i n a +1 oxidation state are r e l a t i v e l y uncommon69. 64 In view of the proven co-ordination of the mercapto-imidazole i n i i [Me2GaSCNCH2CH2NMe] however, the related structure (Figure 32(b)) with bridging nitrogen and sulphur atoms seems most probable. I t i s hoped that the exact structure of [Mo(C 3H 5)(CO) 2(SCNCH 2CH 2NMe)] 2 i n the s o l i d state w i l l be revealed by an X-ray c r y s t a l structure determination which i s currently i n progress. 3.3.3 [Me ?Gapz(0CH 2pyr)lMo(C 7H 7)(C0) o, (L 2Mo(C 7H 7)(CO) 0). An e a r l i e r report had shown the ligand, L 2 , to co-ordinate to Mo ( n 3-allyl)(CO) 2 u n i t s 5 6 (where ' r ^ - a l l y l ' = C^Ry, C 3 H 5 ) . This has now been extended to include C 7H 7 as the n 3 - a l l y l group. The product, obtained as red-brown c r y s t a l s , was characterized by micro-analyses, i r and *H nmr. As expected the i r spectra of L 2Mo(C 7H 7)(C0) 2 displayed two equally intense carbonyl bands suggesting the presence of two carbonyl ligands i n a cis-arrangement 5 0. The carbonyl stretching frequencies occur at a r e l a t i v e l y higher wavenumber i n comparison to those of rel a t e d p y r a z o l y l g a l l a t e complexes incorporating the Mo(C 7H 7)(C0) 2 unit (Table V I I I ) . This feature may be a r e f l e c t i o n of the n- a c i d i t y of the p y r i d y l ri n g i n L 2Mo(C 7H 7)(C0) 2, since t h i s would lead to a weaker back-bonding from the molybdenum to the carbonyl ligands due to competitive back-bonding to the TC system of the p y r i d y l r i n g . Consequently the C-0 bond i n the carbonyl groups of L 2Mo(C 7H 7)(C0) 2 are stronger and thus display higher stretching frequencies i n the i r spectra, as observed. 65 Table VIII. I r carbonyl stretching frequencies of some LMo(C 7H 7)(C0) 2 complexes (where L = tridentate unsymmetric p y r a z o l y l g a l l a t e l i g a n d ) . Compound v n„ i n cyclohexane (cm - 1) Reference — — — CjU — — — — — — [Me 2Gapz(0CH 2pyr)]Mo(C 7H 7)(C0) 2 1940, 1861 This work [Me 2Gapz(OCH 2CH 2SEt)]Mo(C 7H 7)(CO) 2 1933, 1857 70 [Me 2Gapz(OCH 2CH 2NH 2)]Mo(C 7H 7)(CO) 2 1932, 1855 52 [Me 2Gapz(OCH 2CH 2NMe 2)]Mo(C 7H 7)(CO) 2 1929, 1873 52 In the 1H nmr of L 2Mo(C 7H 7)(CO) 2 (Figure 33), two signals are observed for the GaMe_2 protons i n d i c a t i n g the existence of two inequivalent sets of methyl protons. This observation and also the appearance of the signals for the O-Cl^-pyr methylene protons as an 'AB quartet' i n the spectrum i s consistent with a f a c i a l coordination of L 2 to the molybdenum centre. The observation of one signal due to the r) 3-C 7H 7 group indicates that t h i s group i s involved i n a rapid f l u x i o n a l process at room temperature, whereby a l l seven protons appear equivalent on the nmr time-scale. In theory the C 7H 7 ligand could occupy any of three pos i t i o n s , opposite one of the two nitrogens or oxygen atoms of the donor set i n L 2 . St e r i c factors which influence the po s i t i o n of the C 7H 7 group were seen to 67 orient this group trans to the amino nitrogen i n the X-ray c r y s t a l structure of the related [Me 2Gapz(0CH 2CH 2NH 2)]Mo(C 7H 7)(C0) 2 complex 5 8. On th i s basis the structure shown i n Figure 33 of L 2Mo(C 7H 7)(C0) 2 seems most probable. 3.4 Summary Varying degrees of r e a c t i v i t i e s have been observed for the unsymmetric, tridentate p y r a z o l y l g a l l a t e ligands; NaL 2, NaL 3 and NaL 4, towards rhenium and molybdenum carbonyl precursors. In a d i r e c t contrast to Me 2Gapz(OCH 2pyr)~ ( L 2 ) and Me2Gapz(SCNCH2CH2NMe) ( L 3 ) , no complexes were iso l a t e d with the o l e f i n - c o n t a i n i n g ligand, Me2Gapz(OCH2CH2CH=CH2)~ ( L 4 ) . The reaction of trimethylgallium and 2-mercapto-l-methylimidazole yielded the dimeric complex, [Me 2Gapz(SCNCH 2CH 2NMe)] 2, which was X-ray c r y s t a l l o g r a p h i c a l l y shown to possess a novel eight-membered Ga-(N-C-S) 2-Ga r i n g . The tridentate p y r a z o l y l g a l l a t e ligand, Me2Gapz(SCNCH2CH2NMe)~, ( L 3 ) , derived from the mercaptan, was seen to co-ordinate i n a f a c i a l geometry i n the complex L 3Re(CO) 3. The reaction of NaL 3 with molybdenum dicarbonyl precursors,however, proceeded v i a the degradation of the ligand, ultimately y i e l d i n g the dimers [Mo(n 3-allyl)(CO) 2(SCNCH 2CH 2NMe)} 2 (where V - a l l y l ' - C 3H 5, Chn7). 68 CHAPTER IV RHODIUM DERIVATIVES OF UNSYMMETRIC TRIDENTATE PYRAZOLYLGALLATE LIGANDS 4.1 Introduction In contrast to the majority of t r a n s i t i o n metals which usually form eighteen-electron complexes, rhodium complexes can r e a d i l y assume a stable sixteen-electron configuration. Of p a r t i c u l a r i n t e r e s t are those complexes i n which the rhodium i s i n a +1 oxidation state (d 8) i n a square planar environment. In l i g h t of t h i s , the reactions of the unsymmetric, t r i d e n t a t e , p y r a z o l y l g a l l a t e ligands L 2 , L 3 and L 4 mentioned i n Chapter I I I , with rhodium precursors were studied with a view to forcing a meridional co-ordination of the ligands i n square planar rhodium(I) complexes. To date rhodium complexes have been reported which incorporate bidentate p y r a z o l y l g a l l a t e l i g a n d s 3 0 * 7 1 , the symmetric, tridentate p y r a z o l y l g a l l a t e ligand i n (MeGapz 3)Rh(|j.-CO) 3Rh(pz 3GaMe) 3 3, and also monocarbonyl rhodium compounds with some unsymmetric tridentate p y r a z o l y l -g a l l a t e l i g a n d s 7 2 (Figure 34). In addition a molybdenum-rhodium complex * L 2 = Me 2Gapz(OCH 2pyr)~, L 3 = Me2Gapz(SCNCH2CH2NMe)~, L 4 = Me2Gapz(OCH2CH2CH=CH2)~. 69 (X)(Y) = ( C 0 ) ( C 0 ) (C0 ) (PPhJ (PPh,)(PPh3) (COD) Figure 34. Rhodium p y r a z o l y l g a l l a t e complexes. 70 incorporating the MeGapz3~ ligand has also been s t r u c t u r a l l y c h a r a c t e r i z e d 3 5 . Of notable i n t e r e s t i s the a b i l i t y of square planar rhodium(I) complexes to catalyse c e r t a i n chemical reactions. Since the r e a l i z a t i o n of the c a t a l y t i c p o t e n t i a l of Rh(PPh 3) 3C1 7 3, the r e a c t i v i t y of s i m i l a r rhodium(I) complexes towards oxidative additions, a fundamental reaction step for most c a t a l y t i c c y cles, has been a subject of continual i n t e r e s t . In this regard, considerable attention has focussed on the r e a c t i v i t y of rhodium(I) complexes with methyl iodide, and a wealth of geometric and k i n e t i c information has been obtained 7 1*. Thus, as part of an ongoing i n v e s t i g a t i o n , the oxidative addition reactions of a rhodium(I) complex Incorporating the unsymmetric, tridentate p y r a z o l y l g a l l a t e ligand Me 2Gapz(OCH 2pyr)~ have been examined. This chapter d e t a i l s the reactions of NaL and [Rh(CO) 2Cl] 2 (where L = L 2 , L 3 , L 1*). The complex L 2Rh(C0) was formed and shown to undergo a f a c i l e oxidative addition reaction with methyl iodide followed by a methyl migration reaction to y i e l d a f i v e co-ordinate rhodium(III) a c e t y l d e r i v a t i v e , L 2Rh(C0Me)I. In addition the char a c t e r i z a t i o n of the unexpected side-product [Me(Cl)Gapz(OCH 2pyr)]Rh(CO) formed i n the rea c t i o n of NaL 2 and [ R h ( C 0 ) 2 C l ] 2 i s described. 71 4.2 Experimental 4.2.1 Starting Materials The ligands Na +[Me 2Gapz(OCH 2pyr)]" (NaL 2), Na+[Me2Gapz(SCNCH2CH2NMe)]- (NaL 3) and Na+[Me 2Gapz(OCH 2CH 2CH=CH 2)] - (NaL 4) were synthesized as described i n Chapter I I I , section 3.2.2. Methyl iodide (Fisher S c i e n t i f i c Chem. Co.) was dried over phosphorous pentoxide (BDH Chemicals), followed by d i s t i l l a t i o n . Rh(PPh 3) 3Cl (Strem Chemicals), iodine ( A l d r i c h Chem. Co.), hydrogen and hydrogen chloride (Matheson) were used as supplied. [ Rh(CO) 2C1] 2 7 5, [ R h ( C O E ) 2 C l ] 2 7 6 and Rh(PMe3) ^ C l - 7 7 were prepared as described i n the l i t e r a t u r e . 4.2.2 Reaction of Na+[Me ?Gapz(OCH ?pyr)]~ (NaL 2) and [Rh(CO) ?C1] 0. *[ R h ( C O ) 2 C l ] 2 + 2NaL 2 r e f l u x / i 8 hrs ' 2 l 2 r 1 i ( C 0 ) + 2 N a C 1 + 2 0 0 To a s t i r r e d s o l u t i o n of [Rh(CO) 2Cl] 2 (0.276 g; 0.70 mmol) i n THF at -78°C was added a two molar equivalent aliquot of the ligand (NaL 2) dropwise. The r e s u l t i n g mixture was warmed to room temperature and then refluxed for eighteen hours during which time the o r i g i n a l yellow so l u t i o n turned dark brown. The progress of the reaction was monitored by observing The reaction sequence leading to the formation of [Me(Cl)Gapz(0CH 2pyr)]Rh(C0) i s unclear. 72 the disappearance of i n i t i a l , and growth of new, carbonyl bands i n the i r spectra of the reaction mixture (Figure 35). Upon cooling to room temperature, the THF was removed i n vacuo and the r e s u l t i n g dark brown residue extracted with benzene. The f i l t e r e d extracts were then l e f t to allow slow evaporation of the benzene which afforded orange cube-shaped and yellow p l a t e l e t c r y s t a l s . The two a i r stable products were separated by f r a c t i o n a l c r y s t a l l i z a t i o n and were i n d i v i d u a l l y characterized as L 2Rh(CO) (orange, ~ 40%) and [Me(Cl)Gapz(OCH 2pyr)]Rh(CO) (yellow, ~ 10%). 4.2.3. Reactions of [Me 0Gapz(OCHppyr)]Rh(C0), (L 2Rh(C0)).  ( i ) With methyl iodide L 2Rh(C0) + Mel 7—- • L,Rh(C0Me)I x ' room temp./2 hrs. 2 ' A 1:1 mole r a t i o of L 2Rh(C0) (0.056 g; 0.14 mmol) and methyl iodide (0.020 g; 0.14 mmol) was s t i r r e d i n dichloromethane at room temperature. The o r i g i n a l yellow s o l u t i o n gradually changed to an orange colour with a concomitant disappearance of the carbonyl band at 1962 cm - 1 of L 2Rh(C0) and appearance of two new carbonyl bands at 2042 and 1714 cm - 1 i n the i r spectra of the reaction mixture (Figure 36). After two hours the reaction mixture was l e f t to stand to allow for the slow evaporation of the 73 Figure 35. Ir spectra of the reaction of [Rh(CO)2Cl] and Na+[Me2Gapz(OCH2pyr)]- in THF. 74 Iodine room temp Ihr 2095 c m Me 253" 1962 1100 tooo 1100 tOOO tBOO Methyl Iodide room temp 2 hrs 2042 (CHpi, eoln.) •In c m -i Figure 36. Ir spectra of the reactions of [Me 2Gapz(OCH 2pyr)]Rh(C0) with iodine and methyl iodide i n CH 2C1 2. 75 dichloromethane. Upon evaporation of the solvent, small orange c r y s t a l s were recovered and subsequently characterized as L 2Rh(COMe)I (~30%) ( v r n 1714 cm - 1). ( i i ) With iodine CH 2C1 2 [ L 2Rh(CO) + I 9 rr-z • L 2Rh(CO)I, 1 L v ' 2 room temp./l hr. 2 J A s l i g h t excess of iodine was s t i r r e d at room temperature with L 2Rh(CO) (0.043 g; 0.11 mmol) i n dichloromethane. After one hour the o r i g i n a l carbonyl band of L 2Rh(C0) i n the i r spectrum disappeared and was replaced by a new carbonyl band at a s i g n i f i c a n t l y higher frequency (Figure 36). A black s o l i d was i s o l a t e d but no a n a l y t i c a l l y pure samples could be obtained. ( i i i ) With hydrogen and with hydrogen chloride (1;1) A dichloromethane sol u t i o n of L 2Rh(C0) (0.030 g; 0.07 mmol) was s t i r r e d i n the presence of hydrogen gas at atmospheric pressure and room temperature for four hours. Quantitative recovery of L 2Rh(C0) from the solution indicated that no reaction had occurred. A benzene sol u t i o n of L 2Rh(C0) (0.059 g; 0.14 mmol) was s t i r r e d at room temperature i n the presence of an equimolar volume of hydrogen chloride gas for one hour. The i r and nmr data of the pale brown s o l i d obtained suggested some form of degradation of the s t a r t i n g material had occurred. 76 4.2.4. Attempted preparations of [Me 2Gapz(OCH 2pyr)]Rh(X), (L 2Rh(X)) where  X = PMe,, PPh,, COE. The appropriate molar equivalent of the ligand (NaL 2) was added to THF solutions of [Rh(COE) 2C1] 2 (0.108 g; 0.15 mmol), Rh(PMep^+Cl - 0.266 g; 0.60 mmol), and Rh(PPh 3) 3Cl (0.167 g; 0.18 mmol). S t i r r i n g the solutions i n reaction conditions of -78°C, room, and ref l u x temperatures followed by the usual work-up procedure and extraction with a v a r i e t y of solvents, f a i l e d to give the desired compounds. Instead u n i d e n t i f i a b l e products were obtained except i n the reaction using Rh(PPh 3) 3Cl where a small amount of [ R h ( P P h 3 ) 2 C l ] 2 was i s o l a t e d . 4.2.5 Attempted preparations of [Me 2Gapz(SCNCH 2CH 2NMe)]Rh(C0), (L 3Rh(C0))  and [Me 2Gapz(OCH 2CH 2CH=CH 2)]Rh(CO), (L 4Rh(C0)). Two molar equivalents of NaL 3 and NaL 4 were added to two separate THF solutions of [ R h ( C 0 ) 2 C l ] 2 (~ 0.20 mmol). The progress of the reactions were monitored by observing the carbonyl region i n the i r spectra of the reaction mixtures. A f t e r f o r t y hours at r e f l u x temperatures no s i g n i f i c a n t change from the carbonyl bands of [Rh ( C 0 ) 2 C l ] 2 was observed i n the reaction using NaL 3, but these bands were replaced by a single carbonyl band at 1993 cm - 1 for the reaction with NaL 4 (Figure 37). After solvent removal i n vacuo from the cooled solutions, the black residues were extracted i n benzene and f i l t e r e d . The s o l i d products obtained could not be i d e n t i f i e d , 77 [Rh(CO)2Cl]2 2063 g^ag 2060 2020 1993 + NaL room temp 40 hrs 1993 reflux 18 hrs i f c »loo cm Figure 37. Ir spectra of the reaction of [Rh(CO) 2Cl] 2 and Na +[Me 2Gapz(OCH 2CH 2CH=CH 2)] - i n THF. Table IX Micro-analyses and i r data of the rhodium derivatives prepared. Calcd. (%) Found (%) Compound C H N Cl C H N Cl i n Nujol i n CH 2C1 2 L 2Rh(CO) 35.49 3.70 10.35 35.09 3.75 10.35 1931 1962 [Me(Cl)Gapz(0CH2pyr)]Rh(C0) 30.97 2.82 9.85 8.33 30.95 2.86 9.85 8.00 1942 1968 L 2Rh(COMe)I 28.48 3.29 7.67 28.72 3.34 7.52 1694 1714 Table X XH nmr data of the rhodium derivatives prepared in C 6D g solution. Compound Ga-Me •l jyrazoly L' •pyrj Ldyl' -O-CHj-pyr 0 0 -C-Me H y H 6 H TI H 9 H L2Rh(C0) lO.OO(s) 3.95(t) 2.69(d) 2.32(d) 4.07(d) 4.15(t) 3.51(td) 1.90(dt) 5.46(a) [Me(Cl)Gapz(0CR2pyr)]Rh(C0) 9.84(a) 3.91(t) 2.68(d) 2.50(d) 3.97(d) 4.00(t) 3.38(td) 2.08(dt) A - 4.75(d) B - 5.93(d) JAB= 1 6 H z L2Rh(COMe)I 9.92(8) 10.12(8) 3.92(t) 2.76(d) 1.12(d) 3.84(B) 4.00(t) 3.40(td) 0.44(dt) A - 4.78(d) B - 5.24(d) JAB" 1 6 H Z 7.20(a) s « singlet, d - doublet, t • triplet, dt - doublet of triplets, td - triplet of doublets. See Figure 39 (page 84) for proton identification 80 despite persistent e f f o r t s at p u r i f i c a t i o n by c r y s t a l l i z a t i o n or s e l e c t i v e p r e c i p i t a t i o n with a v a r i e t y of solvents at room temperature, -10°C and -78°C. 4.3 Results and Discussion 4.3.1. [Me 0Gapz(OCH ?pyr)jRh(CO), (L 0Rh(CO)). L 2Rh(C0), a product of the metathesis reaction between [ R h ( C 0 ) 2 C l ] 2 and NaL 2 was f u l l y characterized by micro-analyses, i r , *H nmr, mass spectrometry, molecular weight determination and X-ray crystallography. Ir evidence suggests a dicarbonyl species (v = 2080, 2020 cm - 1 i n C»0 THF solution) probably of the form shown i n Figure 38, as a possible i n t e r -mediate i n the formation of t h i s complex. The reactions of other unsymmetric, tridentate p y r a z o l y l g a l l a t e ligands, such as Na+[Me2Gapz-(0CH 2CH 2NH 2)]~ with [ R h ( C 0 ) 2 C l ] 2 also implicated the transient existence of a dicarbonyl species and a tentative assignment of a square pyramidal structure seemed j u s t i f i e d 7 2 . Heating the reaction mixture effected the disappearance of the carbonyl bands of the 'dicarbonyl' species ( v C Q 2080, 2020 cm - 1) and the appearance of two new carbonyl bonds at 2018 and 1953 cm - 1 i n the i r spectra. I t i s suspected that the carbonyl stretching 81 [Rh(CO)2Cl]2 V r Me N-N O' N-N'-Me NaL2 CO rRh! .CO 2080 2020 " V f i 1950 TtSB-• in cm Figure 38, Ir spectra and assignments of the reaction of [Rh(CO) 2Cl] 2 and Na +[Me 2Gapz(OCH 2pyr)]- i n THF. 82 frequency at 1953 cm - 1 i s due to the monocarbonyl rhodium complexes formed i n t h i s reaction, but the o r i g i n of the band at 2018 cm - 1 remains unclear at this stage. It has been established that the two c r y s t a l l i n e products i s o l a t e d from the reaction, namely L 2RhC0 and [Me(Cl)Gapz(OCH 2pyr)]Rh(CO) display one carbonyl band each i n the i r i r spectra (Nujol, CH 2C1 2 and THF solution) (table XI). Table XI I r carbonyl stretching frequencies for some LRh(CO) complexes, where L = unsymmetric tridentate p y r a z o l y l g a l l a t e ligand Compound L 2Rh(C0) [Me(Cl)Gapz(0CH 2pyr)]Rh(C0) [Me 2Gapz(OCH 2CH 2NMe 2)]Rh(CO) [Me 2Gapz(OCH 2CH 2NH 2)]Rh(CO) v^Q(cm - 1) i n CHgClg Reference 1962 t h i s work 1968 this work 1958 72 1955 72 The higher carbonyl stretching frequency for L 2Rh(C0) i n comparison to [Me 2Gapz(OCH 2CH 2NR 2)]Rh(CO), (R = H, Me), may be a r e f l e c t i o n of the it - a c i d i t y of the p y r i d y l group as previously noted i n Chapter I I I , section 3.3.3. Metal back-bonding into t h i s group would lead to a weaker Ir i n THF solution of c r y s t a l l i n e samples of L 2Rh(C0) and [Me(Cl)Gapz(OCH 2pyr)]Rh(CO) gave v C Q = 1950 and 1960 cm - 1 r e s p e c t i v e l y . 83 back-bonding to the carbonyl group, hence the C-0 bond i s strengthened as observed i n the i r spectra. The s i n g l e t s observed i n the AH nmr spectra of L 2Rh(CO) (Figure 39) for the 'GaMe2' and '0-CH 9-pyr' moieties confirm that t h e i r protons are i n equivalent environments. This feature suggests a meridional co-ordination of L 2 to a square planar rhodium centre. In view of the secondary product, [Me(Cl)Gapz(OCH 2pyr)]Rh(CO), also obtained i n th i s reaction, i t i s worth mentioning that the r a t i o of the in t e g r a l s corresponding to the 'GaMe^' and 'O-CH^-pyr' resonances i n the nmr spectrum of L 2Rh(CO) are consistent with the expected r a t i o of 6:2. The positions of the p y r i d y l proton signals occur at s i m i l a r x values to those observed when L 2 i s co-ordinated i n a f a c i a l geometry (Figure 33, page 66). Figure 39. 80 MHz FT 1H nmr spectrum of [Me 2Gapz 2(OCH 2pyr^Rh(CO) in C 6D 6 (400 MHz inset). a 10 t (ppm) 85 The mass spectrum of L 2Rh(CO) (Table XII) displayed signals due to the parent ion (m/e = 405), as well as signals corresponding to the losses of methyl, carbonyl and pyrazolyl groups from the parent species. The most intense signal observed was that due to the [0CH 2pyr] + fragment. Table XII. Mass spectral data for [Me 2Gapz(OCH 2pyr)]Rh(CO). m/ e Relative Intensity (%) Assignment 405 11 [[Me 2Gapz(OCH 2pyr)]Rh(C0)] + 390 27 [[MeGapz(0CH 2pyr)]Rh(C0)] + 361 6 333 24 322 19 [[MeGa(0CH 2pyr)]Rh(C0)] + 294 13 [[MeGa(0CH 2pyr)]Rh]+ 192 5 [MeGa(OCH 2pyr)] + 181 12 [MeGapz(0CH2)] 108 100 [0CH 2pyr]+ 79 43 pyr+ 69 22 Ga+ 68 49 [Hpz]+ at 120°C calculated with 6 9 G a . 86 As i l l u s t r a t e d by the X-ray c r y s t a l structure (Figure 40), the plan a r i t y of the complex allows a weak Rh-Rh i n t e r a c t i o n of 3.54 A between pairs of molecules. I n t e r e s t i n g l y s i m i l a r i n t e r a c t i o n s have been observed i n other square planar rhodium complexes (Table XIII), but the related [Me 2Gapz(OCH 2CH 2NMe 2)]Rh(CO) was s t r u c t u r a l l y shown to exist as di s c r e t e monomeric molecules. Figure 40. X-ray c r y s t a l structure of [Me 2Gapz(OCH 2pyr)]Rh(CO). Rh 3.54 A Figure 40. (contd). 88 Table XIII Intermolecular Rh-Rh Interactions Rh....Rh (A) Reference Compound L 2Rh(CO) (acac) Rh(CO) 2 Rh(pzH)(CO) 2Cl (8-hydroxyquinolinato)Rh(C0) ( Rh-Rh (metal) ( Rh...Rh (sum of atomic r a d i i ) 3.54 t h i s work 3.27 78 3.45 79 3.10 80 2.68 81 ) 2.64 82 ) As shown i n Table XIII, the Rh-Rh i n t e r a c t i o n i n L 2Rh(C0) appears to be r e l a t i v e l y long i n comparison to s i m i l a r i n t e r a c t i o n s . This may be a consequence of the methyl groups on the gallium atoms which are oriented above and below the main plane of the molecule, thereby providing a s t e r i c constraint against a closer approach of the second molecule. The existence of a possible dimeric structure prompted a molecular weight determination, using the i s o p i e s t i c method (appendix, page 121). In benzene so l u t i o n , a molecular weight of 470 ± ~ 20 a.m.u. was calculated, which, although c o n s t i t u t i n g an error of 16% of that expected (406 a.m.u.), does at least indicate that the monomeric form of L 2Rh(C0) exists i n s o l u t i o n . 89 4.3.2 [Me(Cl)Gapz(OCH 0pyr)]RhCO. Accompanying the expected product of [Me 2Gapz(OCH 2pyr)]RhCO, yellow a i r stable p l a t e l e t c r y s t a l s of [Me(Cl)Gapz(OCH 2pyr)]Rh(CO) were also formed and f u l l y characterized. Despite the s i m i l a r i t y of the Nujol mull i r spectra of the two compounds only the chlorine de r i v a t i v e displayed a band at 360 cm - 1 i n the far i r region corresponding to the stretching frequency of the Ga-Cl bond. This frequency i s quite comparable to the values of v^ a ( ,^ reported i n other compounds containing a chlorine bonded to a four co-ordinate gallium centre (Table XIV). Table XIV I r stretching frequencies of Ga-Cl bonds. Compound [Me(Cl)Gapz(0CH 2pyr)]Rh(C0) GaCl 3(PPh 3) GaCl 3(NMe 3) GaH 2Cl(NMe 3) ^GaCl ( C m " 1 } 360 (C 6H 6) 391,352 (CH 2C1 2) 392,360 (Nujol) 345 (C 6H 6) reference t h i s work 83 84 85 The s l i g h t l y higher stretching frequency of the carbonyl band of [Me(Cl)Gapz(OCH 2pyr)]Rh(CO) ( v C Q = 1968 cm"1) compared to L 2Rh(C0) ( v C Q = 1962 cm - 1 CH 2C1 2 solution) (Table XI) may be a r e s u l t of the electron with-drawing, negative inductive e f f e c t of the chlorine atom ca r r i e d through the molecule, thereby weakening the metal to carbonyl backbonding. 90 In the lE nmr spectrum of the chloro derivative (Figure 41) the methylene protons of the '0-CH ?-pyr' moiety are displayed as a t y p i c a l 'AB' p a t t e r n 6 6 i n d i c a t i n g t h e i r inequivalence. Also i n contrast to the L 2Rh(C0) spectrum, the i n t e g r a l r a t i o showed the presence of only three Ga-Me protons to the two methylene protons of the 'O-CH^-pyr' u n i t . The difference i n the p o s i t i o n of the 'Ga-Me' protons i n the two complexes can be attributed to the deshielding e f f e c t of the chlorine atom 6 6 which lowers the x value of these protons i n [Me(Cl)Gapz(OCH 2pyr)]Rh(CO) compared to L 2Rh(C0). These features are i n f u l l accord to that expected where one of the two methyl groups of L 2 has been displaced by a chlorine atom i n [Me(Cl)Gapz(OCH 2pyr)]Rh(CO). The presence of the chlorine atom seems to have l i t t l e e f f e c t however, on the p o s i t i o n of the ' p y r i d y l ' and 'pyrazolyl' proton resonances since these are almost i d e n t i c a l i n the nmr spectra of both [Me(Cl)Gapz(0CH 2pyr)]Rh(C0) and L 2Rh(C0). The mass spectrum of [Me(Cl)Gapz(OCH 2pyr)]Rh(CO) (Table XV) displayed signals due to the parent ion at m/e = 426 which appeared i n the expected GaCl isotope pattern (appendix, page 121). Noteworthy i s the fact that the most intense signa l observed was that of the [ClGa(0CH 2pyr)] + ion, whereas in the mass spectrum of L 2RhC0 (Table XII) the [0CH 2pyr] + fragment appeared to be most abundant and the corresponding [MeGa(0CH 2pyr)] + s i g n a l weak (5%) . This suggests that the chlorine atom may provide a greater s t a b i l i t y when incorporated i n gallium-containing fragments as compared to those with a methyl group. Figure 41. 80 MHz FT *H nmr spectrum of [Me(Cl)Gapz(0CH 2pyr)]Rh(C0) i n C 6D g. Brnztnc j L I I I I I I I I I I I I 1 I I 1 1 2 3 4 5 6 7 8 9 10 T(ppm) 92 Table XV. Mass spectral data for [Me(Cl)Gapz(OCH 2pyr)]Rh(CO) m/ e Relative Intensity (%) Assignment 425 43 [Me(Cl)Gapz(OCH 2pyr)Rh(CO) ] + 397 45 [Me(Cl)Gapz(OCH 2pyr)Rh] + 390 43 [MeGapz(0CH 2pyr)Rh(C0)] + 353 83 333 54 322 27 [MeGa(0CH 2pyr)Rh(C0)] + 294 19 [MeGa(0CH 2pyr)Rh] + 212 100 [ClGa(OCH 2pyr)]+ 181 64 [MeGapz(0CH 2)] + 108 72 [0CH 2pyr]+ 79 50 pyr+ 69 42 Ga+ 68 77 [Hpz]+ 1 at 120°C * calculated with 6 9 G a and 3 5 C 1 . 93 An X-ray c r y s t a l structure determination of [Me(Cl)Gapz(OCH 2pyr)]Rh(CO) (Figure 42) ruled out the p o s s i b i l i t y of any Ga-Cl-Rh i n t e r a c t i o n and showed the chlorine In a p o s i t i o n i d e n t i c a l to that of the methyl group i t replaced i n L 2 . The absence of a Rh-Rh i n t e r a c t i o n i n t h i s complex may be a r e f l e c t i o n of an increased deviation from pl a n a r i t y r e l a t i v e to L 2Rh(CO) which allowed a weak i n t e r a c t i o n between pairs of molecules. The presence of the bulky chlorine atom, replacing a methyl group on the gallium i n o 1 * 1/RhCO, appears to d i s t o r t the five-membered RhNNGaO rin g (Figure 42), thus preventing a close approach of a second molecule. [Me(Cl)Gapz(OCH 2pyr)]Rh(CO) represents the f i r s t reported case where a methyl group of the 'Me2Ga' moiety of a p y r a z o l y l g a l l a t e ligand has been displaced by a chlorine atom. The mechanism by which t h i s occurs i s unclear at t h i s stage, but i t appears that a highly unstable methyl anion has been removed. I f the methyl group had been bonded to the rhodium centre at some stage i t i s conceivable that i t may have been l o s t as a reductive elimination product of perhaps methane, methyl chloride or ethane. A l t e r n a t i v e l y traces of moisture i n the THF solvent may have allowed the formation of hydrogen ch l o r i d e , which then could have displaced methane from the 'Ga-Me2' moiety by an a c i d o l y s i s r e a c t i o n 8 6 » 8 7 » 8 8 . Attempts to convert L 2Rh(CO) to [Me(Cl)Gapz(OCH 2pyr)]Rh(CO) using hydrogen chloride however, were unsuccessful. In order to begin to unravel the mechanism of the formation of [Me(Cl)Gapz(OCH 2pyr)]Rh(CO) however, a complete i s o l a t i o n and chara c t e r i z a t i o n of a l l the reaction products seems necessary. 9 4 Figure 42. X-ray c r y s t a l structure of [Me(Cl)Gapz(OCH 2pyr)]Rh(CO). 95 4.3.3 Reactions of [Me ?Gapz(OCH 0pyr)]Rh(CO) (L 2Rh(CO)). Although only a b r i e f study was undertaken, L 2Rh(CO) seemed susceptible to oxidative addition with iodine and methyl iodide, the l a t t e r reaction undergoing a further methyl migration reaction to y i e l d L 2Rh(COMe)I. The s h i f t of the carbonyl band of L 2Rh(CO) i n the i r spectra from 1952 to 2095 cm - 1 with the addition of iodine, suggests the formation of a stronger C-0 bond for the carbonyl ligand i n t h i s product. An oxidized rhodium centre (Rh(I)(d 8) •> R h ( I I I ) ( d 6 ) ) would have a weaker back-bonding contribution and thus be expected to strengthen t h i s bond since i t s antibonding character i s lessened. On t h i s basis i t seems l i k e l y that a si x co-ordinate, octahedral rhodium(III) iodine adduct had formed. Indeed, the carbonyl stretching frequency observed i s quite comparable to analogous products formed from s i m i l a r oxidative addition reactions of iodine with rhodium(I) centres, (Table XVI). Table XVI I r carbonyl stretching frequencies of some LRh(C0)I 2 complexes. L 2Rh(C0)I 2 [Me 2Gapz(OCH 2CH 2NH 2)]Rh(CO)I 2 [HB(dmpz) 3]Rh(CO)I 2 CpRh(C0)I 2 (PPh 3) 2ClRh(CO)I 2 Compound v C Q ( c m - l ) i n CH 0C1 ? 2095 reference t h i s work 2090 72 2090 89 2065 90 2085 91 i n Nujol 96 As observed i n Table XVI the C-0 bond i n L 2Rh(CO)I 2 appears to be r e l a t i v e l y strong which would suggest that L 2 i s less electron donating to the rhodium centre i n comparison to the other ligand systems considered. This trait,however, i s the reverse of that det a i l e d i n previous r e p o r t s 3 2 * 7 2 i . e . that the p y r a z o l y l g a l l a t e ligands are generally regarded to be better electron donors compared to cyclopentadienyl and pyrazolylborate ligands. The o r i g i n of these observed differences remains unclear but may be related to the n - a c i d i t y of the p y r i d y l moiety (page 64) The reaction of methyl iodide with L 2Rh(CO) formed the rhodium(III) a c e t y l complex, L 2Rh(COMe)I, possibly v i a the s i x co-ordinate intermediate, L 2Rh(CO)(Me)I. The i r spectrum of the reaction mixture showed the formation of two new carbonyl bands which are assigned as i n Figure 43. The oxidative addition of methyl iodide, presumably with t r a n s - a d d i t i o n 9 3 , would give a s i x co-ordinate, octahedral rhodium(III) species accounting for the carbonyl band at 2042 cm - 1 (Figure 36). The c i s - o r i e n t a t i o n of the terminal methyl and carbonyl groups i n t h i s complex can then permit an intramolecular migration of the methyl moiety to form a terminal a c e t y l group, (v_ = 1714 cm - 1). K i n e t i c studies on s i m i l a r reactions suggest the formation of LRh(C0)(Me)I as the fast step and the a l k y l to acyl conversion as the slow, rate-determining s t e p 9 3 . The only c r y s t a l l i n e material obtained from the reaction of L 2Rh(C0) and methyl iodide was i d e n t i f i e d as the a c e t y l d e r i v a t i v e , since a single carbonyl band corresponding to the a c e t y l group at 1694 cm - 1 was shown i n the i r spectrum (Nujol) of the orange s o l i d . Indeed the elusive nature of 97 Figure 4 3 . Reaction pathway for [Me 2Gapz(OCH 2pyr)]Rh(CO) and methyl iodide. 98 s i m i l a r LRh(CO)(Me)I complexes due to the acetyl-forming process has been previously n o t e d 7 2 > 9 4 » 9 5 . Further confirmation of the rhodium(III) a c e t y l complex emanates from the *H nmr spectrum of the product i n CgD6 s o l u t i o n (Figure 44). The pos i t i o n of the acetyl protons displayed i s consistent with s i m i l a r acetyl rhodium s p e c i e s 7 2 and no signal was seen i n the usual Rh-Me proton (~ 9t) r e g i o n 7 2 . In addition the presence of the iodide and a c e t y l ligands now render the Ga-Me? and the methylene (O-CH^-pyr) protons on L 2 inequivalent, thus they are displayed as two s i n g l e t s and an 'AB' quartet respectively In the *H nmr spectrum. Noteworthy Is the large s h i f t of the signals of the ' i * proton on the p y r i d y l ring and the '6' proton of the pyrazolyl group In comparison to th e i r positions In the spectrum of the s t a r t i n g material, L 2Rh(CO) (Figure 39). This may be attributed to the deshielding e f f e c t of the neighbouring c i s - i o d i d e group predicted i n the acetyl compound. The exact geometry of the complex however cannot be deduced from the *H nmr spectrum alone since other structures could i n theory give spectra s i m i l a r to that obtained. An X-ray c r y s t a l structure determination of a related compound, [Me2Gapz(OCH2CH2NMe2)Rh(COMe)I however, c l e a r l y showed the a c e t y l ligand i n the a p i c a l p o s i t i o n of a square-based pyramid 7 2, thus i t seems l i k e l y t h i s may be the geometry adopted i n L 2Rh(COMe)I. Figure 44. 80 MHz *H nmr spectrum of [Me2Gapz(0CH2pyr)]Rh(C0Me)I 100 4 . 3 . 4 Attempted formation of [Me 2Gapz(SCNCH 2CH ?NMe)]Rh(C0), (L 3Rh ( C 0 ) ) and [Me 2Gapz(OCH ?CH 0CH=CH 2)]Rh(CO) ) ( L ' + R M C O ) ) . The s t r a i n imposed on the Me2Gapz(SCNCH2CH2NMe)~ ligand i n a meridional co-ordination mode appeared to i n h i b i t the formation of the target complex, L 3Rh ( C 0 ) . This may be a consequence of the inherent i n s t a b i l i t y of the planar, four-membered heterocyclic ring which would be required i n th i s complex (Figure 4 5 )• I t i s conceivable that alternate Figure 4 5 . The four-membered ring required i n [Me2Gapz(SCNCH2CH2NMe)]Rh(CO). less strained products could have formed such as the ligand i n a bidentate co-ordinating mode or two Rh ( C 0 ) 2 units bridged with either pyrazolyl or 101 'SCNCHjCHjNMe' groups. No tractable products however were recovered and i n view of the i r spectra obtained on the reaction residues i t seemed that no s i g n i f i c a n t reaction had occurred. I n i t i a l l y the reaction between [Rh(CO) 2Cl ]2 and NaL 4 seemed to be promising, as evidenced by the i r spectra obtained of the reaction mixture (Figure 37). As expected, what appeared to be the formation of a mono-carbonyl rhodium complex was observed ( v r = 1993 cm - 1), presumably L 4Rh(C0), but on work-up of the reaction mixture no pure products were i s o l a t e d . 4.3.5 Attempted formations of [Me 2Gapz(OCH 2pyr)]Rh(X), (L 2Rh(X)) where .X = PMe,, PPh„, COE. None of the complexes of the above formula were i s o l a t e d as pure samples. Previous attempts at co-ordinating phosphine ligands to the fourth co-ordination s i t e of s i m i l a r rhodium p y r a z o l y l g a l l a t e complexes had also been u n s u c c e s s f u l 7 2 . In contrast to the n - a c i d i t y of the carbonyl group, phosphine ligands are generally known to be strong a d o n o r s 9 2 and this difference may well have a bearing on there being no phosphine counterparts of L 2Rh(C0). In view of the p l a n a r i t y of the L 2-Rh system i t seems the extra s t e r i c demands of the phosphine ligands would have l i t t l e e f f e c t i n d e s t a b i l i z i n g the 'L 2Rh(PR 3)' compounds. In cyclooctene (COE) complexes, bonding of the o l e f i n f u n c t i o n a l i t y to the metal p a r t i a l l y involves f i l l e d metal d - o r b i t a l s back-bonding to the vacant antibonding pit o r b i t a l s of the o l e f i n 9 2 . This i t-acidity, s i m i l a r 102 to the bonding of the carbonyl ligand, would then seem to favour the s t a b i l i t y of the complex L 2Rh(C0E). Unfortunately the course of the reaction could not be e f f e c t i v e l y monitored by i r since the ethylene stretching mode (~ 1500 cm - 1) appears weak and i s complicated by other C-H stretching bonds 9 2. Since no pure products were i s o l a t e d the formation of the expected complex remains unclear. 4.4 Summary The Me 2Gapz(OCH 2pyr)~ ligand ( L 2 ) was found capable of meridional co-ordination to a rhodium centre, the requirements of the fourth co-ordination s i t e being f u l f i l l e d by a carbonyl group. Attempts to form the complexes L 2Rh(X) (where X = PMe3, PPh 3, COE) and LRh(CO) (where L = L 3 , L1*) were unsuccessful. L 2Rh(C0) was shown to be susceptible to oxidative addition with iodine and methyl iodide, the l a t t e r reaction also undergoing a f a c i l e methyl migration reaction to form the rhodium(III) a c e t y l complex, L 2Rh(C0Me)I. In addition to L 2Rh(C0), the reaction of [Rh(CO) 2Cl] 2 and Na +[Me 2Gapz(OCH 2pyr)]~ (NaL 2) also yielded the complex [Me(Cl)Gapz(OCH 2pyr)]Rh(CO), which represents the f i r s t reported case of a chlorine atom sub s t i t u t i n g for a methyl group of the 'Me2Ga' moiety i n py r a z o l y l g a l l a t e ligands. 103 CHAPTER V CONCLUSIONS AND PERSPECTIVES The a i r stable complexes of the formula [Et 2Gapz 2]Mo ( n 3-allyl)(CO) 2(Hpz) (where '1)3-31171' = C^Hy, C 7H 7) have been formed whereas the corresponding compounds without pyrazole (Hpz) and incorporating a possible C-H-Mo in t e r a c t i o n could not be i s o l a t e d . An X-ray c r y s t a l structure determination of [Et 2Gapz 2]Mo(C 7H 7)(C0) 2(Hpz) i s currently i n progress and may reveal a novel 'chair' conformation of the Ga-(N-N)2-Mo chelate r i n g i n th i s complex. A further extension of th i s work could be directed towards the s u b s t i t u t i o n of the pyrazolyl (pz) groups i n the Et 2Gapz 2~ ligand by the more s t e r i c a l l y demanding 3,5-dimethylpyrazolyl (dmpz) groups. It would be i n t e r e s t i n g to compare the s t r u c t u r a l differences of the complexes i n LMo ( n 3-allyl)(CO) 2(Hpz) where L = Et 2Gapz 2~ and Et 2Ga(dmpz) 2~. The suspected i n a b i l i t y of the Et 2Gapz 2~ ligand to allow a C-H-Mo in t e r a c t i o n i n the complexes "[Et 2Gapz 2]Mo ( n 3-allyl)(CO) 2" i s thought to be a consequence of the r e l a t i v e l y longer Ga-N bond distance (~ 2.0 A), as compared to the B-N distance (~ 1.6 A) i n the s t r u c t u r a l l y characterized borate analogues of these complexes. In addition to the inherent s i z e differences of the E t 2 B p z 2 ~ and Et 2Gapz 2~ ligands, i r evidence suggests the l a t t e r are s l i g h t l y more electron donating towards molybdenum c e n t r e s 5 3 . Comparisons of Et 2Gapz 2~ to other uninegative four-electron donating ligands could include the 8-diketonate l i g a n d s 9 6 (planar six-membered 104 MoOCCCO chelate ring) and the oxine ligands'' (planar, five-membered MoOCCN chelate r i n g ) . As outlined i n Chapter I the 'pyrazolylgallate ligands' can also be extended to include the formally uninegative, s i x - e l e c t r o n donating , unsymmetric, tridentate ligand systems. Since t h e i r co-ordination to metal centres involves chelation v i a d i f f e r e n t donor atoms, they can be likened to the established P,0,P 9 8; P , N , P 9 9 « 1 0 0 ; and 0,N,S 1 0 1 donating ligand systems. In Chapters III and IV of this work the co-ordination a b i l i t i e s of the unsymmetric tridentate p y r a z o l y l g a l l a t e ligands Me 2Gapz(0CH 2pyr)~ ( L 2 ) , Me2Gapz(SCNCH2CH2NMe)~ ( L 3 ) , and Me2Gapz(OCH2CH2CH=CH2)~ ( L 4 ) towards molybdenum, rhenium and rhodium metal centres were investigated. The attempts at i s o l a t i n g complexes with L 4 were unsuccessful but those reactions with L 2 and L 3 formed i n t e r e s t i n g , i f not e n t i r e l y predictable products. Me2Gapz(SCNCH2CH2NMe)~ ( L 3 ) was shown to co-ordinate i n a f a c i a l geometry i n the complex L 3Re(CO) 3, which provides the f i r s t example of a single carbon-spacing between two of the l i g a t i n g atoms i n complexes incorporating unsymmetric tridentate p y r a z o l y l g a l l a t e ligands. Unexpected-l y the reaction of NaL 3 with molybdenum dicarbonyl ' a l l y l ' precursors proceeded v i a the degradation of the ligand forming the dimers [Mo (n 3-allyl)(CO) 2(SCNCH 2CH 2NMe)] 2 (where * n 3 - a l l y l ' = C 3H 5, C 4 H 7 ) . Attempts to i s o l a t e a meridional co-ordination of L 3 i n a square planar monocarbonyl rhodium (I) complex were unsuccessful. In l i g h t of this 105 'variable' r e a c t i v i t y observed for L 3 i t may be of i n t e r e s t to investigate the reactions of NaL 3 towards other t r a n s i t i o n metal precursors, p a r t i c u l a r l y with a view to forming tetrahedral or t r i g o n a l bipyramidal geometries. The reaction of trimethyl gallium and 2-mercapto-l-imidazole (the b i f u n c t i o n a l donor species used i n the synthesis of L 3 ) formed the dimeric i 1 complex, [Me2Ga(SCNCH2CH2NMe)]2,which was s t r u c t u r a l l y shown to possess a novel eight-membered Ga-(N-C-S)-Ga r i n g , with the gallium atoms assuming d i s t o r t e d tetrahedral geometries. The ligand Me 2Gapz(OCH 2pyr)~ ( L 2 ) was found capable of co-ordinating both f a c i a l l y , i n the octahedral complex L 2Mo(C 7H 7)(C0) 2, and meridionally i n the square planar complex L 2Rh(C0). These two possible co-ordination geometries of L 2 may well be a consequence of the f l e x i b i l i t y of the 'GaOCH2pyr' moiety incorporated i n t h i s ligand. The inherent p l a n a r i t y i n the square planar monocarbonyl rhodium de r i v a t i v e of Me 2Gapz(OCH 2pyr)~ ( L 2 ) allows a weak Rh-Rh i n t e r a c t i o n between pairs of molecules, as displayed i n an X-ray c r y s t a l structure of t h i s complex. Although t h i s i n t e r a c t i o n i s r e l a t i v e l y d i s t a n t , t h i s feature has not been observed i n the related [Me 2Gapz(OCH 2CH 2NMe 2)]Rh-( C O ) 7 2 . In addition L 2Rh(C0) was shown to be susceptible to oxidative addition with iodine and methyl iodide, the l a t t e r reaction undergoing a further methyl migration reaction to form the rhodium(III) a c e t y l d e r i v a t i v e L 2Rh(C0Me)I. Since only preliminary studies were undertaken i n i n v e s t i g a t i n g the r e a c t i v i t y of L 2Rh(C0) t h i s area warrants further 106 a t t e n t i o n . Although no reaction was observed with L 2Rh(C0) and hydrogen at room temperature and atmospheric pressure, more forcing conditions of increased hydrogen pressure or temperature may prove more succe s s f u l . In addition to L 2Rh(C0) the reaction of NaL 2 and [Rh(CO) 2Cl] 2 also yielded the chlorine-containing complex [Me(Cl)Gapz(OCH 2pyr)]Rh(CO). In view of t h i s unexpected r e s u l t the p o s s i b i l i t y of synthesizing halogen-containing ligands q u a n t i t a t i v e l y and studying t h e i r r e a c t i v i t y towards t r a n s i t i o n metal centres may be worth Investigating, e s p e c i a l l y since these ligands could^in theory,be capable of a tetradentate co-ordination. As exemplified i n t h i s study the chemistry of the p y r a z o l y l g a l l a t e ligands and t h e i r co-ordination complexes continues to provide s t r u c t u r a l and spectroscopic i n t e r e s t . Despite t h e i r seemingly exotic nature, the v e r s a t i l i t y and proven chelating a b i l i t i e s has f i r m l y established these ligand systems within organometallic co-ordination chemistry. 107 REFERENCES 1. E. Bucher, Chem. Ber. 22_, 842 (1889). 2. L. Knorr, Chem. Ber. 16, 2597 (1883). 3. C. Reimann, A. Santoro, and A.D. Mighell, Acta Cryst. Sect. B, 26, 521 (1970). 4. R.B. King and A. Bond, J . Organomet. 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Ga -s 2 .3697(8) 2 .374 N(1)-C(4) 1 .365(4) 1 .389 Ga -CO) 1 .970(3) 1 .975 N(2)-C(3) 1 .344(4) 1 .349 Ga -C(2) 1 .962(4) 1 .970 N(2)-C(5) 1 .385(5) 1 .390 Ga -N(1)' 2 .019(2) 2 .024 N(2)-C(6) 1 .473(5) 1 .479 S -C(3) 1 .733(3) 1 .739 C(4)-C(5) 1 .322(6) 1 .327 N(1)-C(3) 1.335(3) 1.340 114 Bond angles (deg) w i t h estimated standard d e v i a t i o n s i n parentheses Bonds Angle(deg) Bonds Angle(deg) s -Ga - C O ) 1 0 4 . 7 9 0 2 ) C(4) - N O )-Ga* 122.2(2) s -Ga -C(2 ) 1 0 8 . 0 5 0 2 ) C(3) - N ( 2 ) - C ( 5 ) 107.9(3) s -Ga - N O ) ' 100.90(7) C(3) - N ( 2 ) - C ( 6 ) 126.5(3) C O ) -Ga -C(2 ) 124.9(2) C(5) - N ( 2 ) - C ( 6 ) 125.7(3) C(1 ) -Ga - N O ) ' 104.0(2) S - C ( 3 ) - N O ) 127.0(2) C(2) -Ga - N O ) ' 111.46(14) S - C ( 3 ) - N ( 2 ) 123.6(2) Ga -S -C(3 ) 100.97(9) N O ) - C ( 3 ) - N ( 2 ) 109.4(2) C(3) -N(1) - C U ) 106.4(3) N O ) - C ( 4 ) - C ( 5 ) 109.6(3) C(3) - N O ) -Ga' 131.1(2) • N(2) - C ( 5 ) - C ( 4 ) 106.7(3) I n t r a - a n n u l a r t o r s i o n angles (deg) standard d e v i a t i o n s i n parentheses Atoms Value(deg) NO)'-Ga -S -C(3) 99.96(12) S -Ga -N(1)'-C(3)' -76.0(3) Ga -S -C(3)-N(1) -85.6(2) Ga' -NO)-C(3)-S 6.0(4) 115 Bond lengths i n v o l v i n g hydrogen atoms (A) w i t h estimated standard d e v i a t i o n s i n parentheses Bond Length(A) Cd)-H(la) 0.90(4) Cd)-H(lb) 1.00(5) C(l)-H(1c) 0.99(4) C(2)-H(2a) 1.02(5) C(2)-H(2b) 0.84(5) C(2)-H(2c) 1.12(4) Bond Length(A) C(4)-H(4) 0.83(4) C(5)-H(5) 0 .81(5) C(6)-H(6a) 0.91(6) C(6)-H(6b) 1.12(8) C(6)-H(6c) 1.02(5) Bond angles i n v o l v i n g hydrogen atoms (deg) w i t h estimated standard d e v i a t i o n s i n parentheses Bonds Angle(deg) Bonds Angle(deg) Ga -C(1)-H(1a) 116(3) H(2b)-C(2)-H(2c) 104(4) Ga -Cd)-H(lb) 115(3) N(1)-C(4)-H(4) 121(3) Ga -C(l)-Hdc) 111(2) C(5)-C(4)-H(4) 129(3) H(1a)-C(1 )-Hdb) 105(3) N(2)-C(5)-H(5) 122(4) H(1a)-C(1)-H(1c) 100(3) C(4)-C(5)-H(5) 131(4) Hdb)-C(l)-Hdc) 109(4) N(2)-C(6)-H(6a) 104(4) Ga -C(2)-H(2a) 122(3) N(2)-C(6)-H(6b) 116(4) Ga -C(2)-H(2b) 109(3) N(2)-C(6)-H(6c) 111(2) Ga -C(2)-H(2c) 115(2) H(6a)-C(6)-H(6b) 122(5) H(2a)-C(2)-H(2b) 124(4) H(6a)-C(6)-H(6c) 128(5) H(2a)-C(2)-H(2c) 73(3) H(6b)-C(6)-H(6c) 74(4) 116 T o r s i o n angles (deg) w i t h estimated standard d e v i a t i o n s i n parentheses Atoms Value(deg) C O ) C(2) NO) S C O ) C(2) Ga Ga C(4) C(4) Ga' Ga' C(3) Ga' C(5) C(5) C(6) C(6) C(3) C(6) NO) S s s C(2) C(2) C(2) NO) NO) NO) S s s C O ) C O ) C O ) NO) NO) NO) C(3) Ga' C(3) C(6) C(3) C(3) C(3) C(5) C(5) C(5) N O) H(4) H(4) -Ga -Ga '-Ga -Ga -Ga -Ga -S -S -NO)--NO)--NO)--NO )• -NO )• -NO)--N(2)--N(2)--N(2)--N(2)--N(2)--N(2)--C(4)--Ga -Ga -Ga -Ga • -Ga • -Ga • '-Ga '-Ga '-Ga -Ga • -Ga • -Ga -Ga --Ga • -Ga • '-Ga '-Ga '-Ga -NO)--N(D--N(2)--N(2)--N(2)--N(2)--N(2)--N(2)--N(2)--N(2)--C(4)--C(4)--C(4)-S S -S •NO NO NO C(3 C(3 C(3 C(3 C(3 C(3 C(4 C(4 C(3 C(3 C(3 C(3 •C(5 C(5 C(5 -CO -CO -CO -CO -CO -CO -C( -C( -C( -C(2 -C(2 -C(2 -C(2 -C(2 -C(2 -C(2) -C(2) -C(3) -C(3) -C(3) '-C(3)' '-C(3)' '-C(3)' -NO) -N(2) -S -N(2) -S -N(2) -C(5) -C(5) -S -NO) -S -NO) -C(4) -C(4) -N(2) -HOa) -HOb) -HOc) -HOa) -HOb) -HOc) )-HOa) )-H(1b) )-HOc) -H(2a) -H(2b) -H(2c) -H(2a) -H(2b) -H(2c) H(2a) H(2b) C(2)-H(2c) C(4)-H(4) C(4)-H(4) C(5)-H(5) C(5)-H(5) C(6)-H(6a) C(6)-H(6b) C(6)-H(6c) C(6)-H(6a) C(6)-H(6b) C(6)-H(6c) •C(5)-H(5) C(5)-N(2) C(5)-H(5) -152.2 -17.1 99 -76 175 3B -85 95.1 -179.9 0.6 6.0 -174.6 0.4 175.0 180.0 0.6 0.0 -179.4 0.4 179.6 0.0 -151(3 86(3 -38(2 84(3 -40(3 -163(2 -46(3 -169(3 67(2 -139(3 63(4 -54(2 -15(3 -174(4 70(2 111(3 -47(4 -164(2 -177(3 -2(3 171 (4 -9(4 79(4 -144(4 -62(3 -101(4 36(4 118(3 -170(5 177(3 7(6 96( 0 6 5 6 2) 2) 12) 3) 3) 3) 2) 2) 2) 3) 4) 2) 4) 2) 2) 3) 5) 4) 4) 4) 4) 117 [Me2Gapz(OCH2pyr)]Rh(CO) Bond lengths (A) w i t h estimated standard d e v i a t i o n s i n parentheses Bond Length(A) Bond Length(A) Rh -0(1) 2.038(3) N( i )-C(10) 1.327(6) Rh -N(2) 2.022(4) N(2)-C(12) 1.339(6) Rh -N(3) 2.038(3) N(3)-C(5) 1.350(5) Rh -C(1) 1.778(5) N(3)-C(9) 1.341(6) Ga -0(1) 1 .915(3) C(4)-C(5) 1.506(6) Ga -N(1) 1.984(4) C(5)-C(6) 1.380(7) Ga -C(2) 1.958(6) C(6)-C(7) 1.375(7) Ga -C(3) 1.976(5) C(7)-C(8) 1.387(8) 0( 1 )-CU) 1.397(5) C(8)-C(9) 1.368(8) 0(2)-C(1) 1.159(5) C(10)-C(11) 1.354(8) N(1 )-N(2) 1.377(5) C(1 1 )-C(12) 1 .376(7) 118 Bond angles (deg) w i t h estimated standard d e v i a t i o n s i n parentheses Bonds Angle(deg) 0(1 ) -Rh -N(2) 68 .73(14) 0(1 ) -Rh -N(3) 80 .61(14) 0(1) -Rh -CO ) 175 .1(2) N(2) -Rh -N(3) 169 .31(15) N(2) -Rh -CO ) 92 .2(2) N(3) -Rh -CO ) 98 .3(2) 0(1) -Ga -NO ) 89 .95(14) 0(1) -Ga -C(2) 110 .3(2) 0(1) -Ga -C(3) 110 .7(2) NO) -Ga -C(2) 110 .4(2) NO) -Ga -C(3) 109 .8(2) C(2) -Ga -C(3) 121 .3(2) Rh -0(1 -Ga 119 .4(2) Rh - 0 ( 1 -C(4) 116 .0(3) Ga -OO -C(4) 124 .2(3) Ga -NO -N(2) 122 .9(3) Ga -NO -COO) 130 .0(4) N(2) -NO -COO) 107 .0(4) Rh -N(2 -NO ) 118 .2(3) Rh -N(2 -C(12) 135 .0(3) NO) -N(2 -C(12) 106 .8(4) Rh -N(3 -C(5) 1 14 .6(3) Rh -N(3 -C(9) 127 .5(3) C (5) -N(3 -C(9) 117 .8(4) Rh - c o -0(2) 176 .2(5) 0(1 ) -C(4 -C(5) 1 1 1 .5(4) N(3) -C(5 -C(4) 1 17 .1(4) N(3) -C(5 -C(6) 121 .4(4) C(4) -C(5 -C(6) 121 .5(4) C (5) -C(6 -C(7) 120 .1(5) C (6) -C(7 -C(8) 118 .6(5) C(7) -C(8 -C(9) 118 .4(5) N(3) -C(9 -C(8) 123 .7(5) NO) -C(10)-C(11) 1 1 1 .7(5) C(10)-C(11)-C(12) 104 .1(5) N(2) -C(12)-C(11) 110 .5(5) 119 [Me(Cl)Gapz(OCH 2pyr)]Rh(CO) Bond lengths (A) w i t h estimated standard d e v i a t i o n s i n parentheses Bond Length(A) Bond Length(A) Rh -0(1) 2.046(5) N(1)-C(9) 1 .332( 1 1 ) Rh -N(2) 2.025(7) N(2)-C(11) 1 .339(10) Rh -N(3) 2.020(6) N(3)-C(4) 1 .362(9) Rh -C(1) 1.806(9) N(3)-C(8) 1 .336(10) Ga -CI 2.194(3) C(3)-C(4) 1 .475(12) Ga -0(1) 1.871(5) C(4)-C(5) 1.391 (11 ) Ga -N(1) 1.942(6) C(5)-C(6) 1 .362( 12) Ga -C(2) 1.932(9) C(6)-C(7) 1.386(13) 0(1)-C(3) 1.421(9) C(7)-C(8) 1 .369( 12) 0 ( 2 ) - C ( l ) 1.132(9) C(9)-C(10) 1 .378(14) N(1)-N(2) 1.361(9) C(10)-C(11) 1.353(13) 120 Bond angles (deg) w i t h estimated standard d e v i a t i o n s i n parentheses Bonds Angle(deg) Bonds Angle(deg) 0(1 ) -Rh -N(2) B7.B(2) Rh -N(2)-N(1) 119.2(5) 0(1) -Rh -N(3) 80.8(2) Rh -N(2)-C(11) 134.5(6) 0(1) -Rh -CO) 178.2(3) NO) -N(2)-CO 1 ) 106.2(7) N(2) -Rh -N(3) 168.7(2) Rh -N(3)-C(4) 115.0(5) N(2) -Rh -CO) 93.7(3) Rh -N(3)-C(8) 127.3(5) N(3) -Rh -CO) 97.6(3) C(4) -N(3)-C(8) 117.8(7) CI -Ga -OO) 104.5(2) Rh -CO)-0(2) 177.1(8) CI -Ga -NO) 106.9(2) 0(1) -C(3)-C(4) 112.0(7) CI -Ga -C(2) 113.5(3) N(3) -C(4)-C(3) 117.3(7) 0(1 ) -Ga -NO) 92.9(3) N(3) -C(4)-C(5) 121.4(8) 0(1 ) -Ga -C(2) 117.9(4) C(3) -C(4)-C(5) 121.2(8) N(1) -Ga -C(2) 118.5(4) C(4) -C(5)-C(6) 119.8(8) Rh -0(1) -Ga 115.7(3) C(5) -C(6)-C(7) 119.6(8) Rh -0(1 ) -C(3) 114.6(5) C(6) -C(7)-C(8) 117.9(9) Ga -0(1 ) -C(3) 125.3(5) N(3) -C(8)-C(7) 123.5(8) Ga -N(1) -N(2) 119.9(5) NO) -C(9)-C(10) 107.9(9) Ga -N(1) -C(9) 130.5(6) C(9) -COO)-C(II) 105.9(9) K(2) -NO ) -C(9) 109.6(7) N(2) -C( 1 1 )-CO0) 110.4(8) 121 APPENDIX II THEORETICAL INTENSITY PATTERNS FOR MASS SPECTROSCOPIC ANALYSIS 138 140 142 104 106 108 GaCI 6 9 71 Ga 92 94 95 96 97 9 8 100 Mo 122 161 163 164 165 166 167 168 169 171 MoGa 184 186 187 188 189 190 191 192 193 194 195 196 197 198 200 Mo2 123 APPENDIX III MOLECULAR WEIGHT DETERMINATION c Figure 46. Signer's Apparatus for MWt. determination The Signer ( i s o p i e s t i c ) technique for molecular weight determination was u s e d 1 0 2 . A solution of a standard compound (s) i s eq u i l i b r a t e d i n a closed, evacuated system with the sample sol u t i o n (x) at a constant temperature. Over a period of several days, the vapour pressures above each sol u t i o n are equalized with concomitant equalization of the mole fr a c t i o n s of s and x i n the s o l u t i o n . The f i n a l volume of each solution i s then used to calculate the molecular weight of x by employing the equation below. 124 G M V M - x 8 8 x G V s x where G x e weight of sample, x. G = weight of standard, s. s V = volume of sample s o l u t i o n , x V = volume of standard s o l u t i o n s M = molecular weight of standard, s. s The c r i t i c a l factor i n t h i s experiment i s the maintenance of the apparatus i n an isothermal condition. 125 

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