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Unsaturated ditertiary arsine derivatives of some metal carbonyls Mihichuk, Lynn Michael 1974

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UNSATURATED DITERTIARY ARSINE DERIVATIVES OF SOME METAL CARBONYLS By LYNN MICHAEL MIHICHUK B.Sc. ( H o n s . ) , U n i v e r s i t y o f W a t e r l o o , 1970 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n t he Department o f CHEMISTRY We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA September, 197^ In presenting th i s thesis in par t i a l fu l f i lment of the requirements for an advanced degree at the Univers i ty of B r i t i s h Columbia, I agree that the L ibrary sha l l make it f ree ly ava i lab le for reference and study. I further agree that permission for extensive copying of th i s thes is for scho lar ly purposes may be granted by the Head of my Department or by his representat ives. It is understood that copying or pub l i ca t ion of th i s thes i s f o r f i nanc ia l gain sha l l not be allowed without my written permission. Department of 0 H & ff\ I S ' f The Univers i ty of B r i t i s h Columbia Vancouver 8, Canada Date NOV flllH ABSTRACT The meso and racemic forms of the new d i t e r t i a r y arsine, c i s - 2 , 3 - b i s ( m e t h y l p h e n y l a r s i n o ) - 1 , 1 , 1 , k , k h e x a f l u o r o b u t - 2 -ene (L-L) , were prepared "by the reaction of hexafluorobutyne-2 with 1,2-dimethyl-l,2-diphenyldiarsine i n hexafluoroacetone. The two diastereomers were i s o l a t e d and reacted with i r o n pentacarbonyl a f f o r d i n g (L-L)'Fe(CO)^ and ( L - L ) ' F e 2 ( C 0 ) g . Two of the three possible geometric isomers of the l a t t e r were obtained and t h e i r properties allowed assignment of the con-f i g u r a t i o n of the s t a r t i n g ligands. Minor amounts of the symmetric and asymmetric forms of FegtCCO^AstCH^) (C^H,.)^ were also obtained through loss of fluorocarbon. The complexes F e 2 ( C O ) 6 [ E ( R 1 ) ( R £ ) ] 2 (E = As, P; R x = R 2 = CHy R-j_ = CH^, Rg = £5^5) were prepared and studied by "*"H and 13 1 ^C nmr spectroscopy. Variable temperature H nmr studies indicate the hexacarbonyl complexes are f l u x i o n a l with respect to the [ F e - E ] 2 c l u s t e r . A c t i v a t i o n parameters were calculated 13 f o r the motion and possible mechanisms are discussed. The J<Z nmr spectra of the carbonyl groups at 25° and -70° suggest an independent intramolecular scrambling of the carbonyl groups about the i r o n atom. Reactions of (L-L) and the related d i t e r t i a r y arsine ligand, cis-2,3-bis(dimethylarsino)-1,1,1,h,b,4-hexafluorobut-2-ene (L-L), with the Group VI metal hexacarbonyls gave the chelate complexes ( L - L ) ' M C C O ) ^ and ( L - L ) M ( C O ) ^ . The (L-L)M-(CO)jt^ complexes were i r r a d i a t e d with the 450W lamp i n the presence of excess (L-L), giving four d i f f e r e n t types of complexes: f a c - ( L - L ) b ( L - L ) m M ( C O ) 3 and fac-(L-L) b(L-L)™ r a n gM(CO) (where b and m denote bidentate and monodentate ligand respec-t i v e l y ) , c i s - ( L - L ) 2 M ( C 0 ) 2 and trans-(L-L) 2M(CO)g. The seven-coordinate complexes (L-L) M(C0 ) y ( 2 and (L-L)-M(C0)^X 2 (M = Mo, Wj X = Br, I ) were prepared and characterized and "^C nmr spectra at 25° and -70° suggest the complexes are nonrigid. S i m i l a r l y "*"H nmr studies indicate the seven-coordinate (L-L)LMo(C0) 2Br 2 complexes are also nonrigid at 25° and -70°. The (L-L)L 2Mo(C0)Br 2 complexes (L i s a monodentate phosphite or phosphine) are r i g i d at 25° and nonrigid at higher temperatures. A c t i v a t i o n parameters were cal c u l a t e d f o r the motion of two of the complexes. F i n a l l y , two novel Group VII metal carbonyl complexes of (L-L) of formula C l 6H l 8As^F^0gMn 2 and C^HgAsFgO^Re are described. The former contains a f l u o r i n a t e d n - a l l y l group bonded to one manganese atom and the l a t t e r a CH 20 fragment o"-bonded to rhenium. - i v -TABLE OF CONTENTS Page ABSTRACT i i LIST OF TABLES x i LIST OF FIGURES x i v ACKNOWLEDGEMENTS xvi o CHAPTER I INTRODUCTION 1 1. Six-Coordinate Group VI Metal Carbonyl Complexes 1 A. Preparative Methods 1 B. Infrared ( i r ) Studies 3 C. Bonding i n Metal Carbonyls ^ D. Nuclear Magnetic Resonance (nmr) Studies... 7 E. Mass Spectrometric Studies 9 F. Reaction Mechanisms 10 2. Seven-Coordinate Group VI Metal Carbonyl Complexes 1^ A. Preparative Methods Ik B. Conductometric Studies 15 C. Crystallographic Studies 15 D. I r Studies 17 E. Nmr Studies 17 3. This Work 20 -V-Page CHAPTER II EXPERIMENTAL 21 1. General Techniques and Physical Measurements 21 2. S t a r t i n g Materials 23 3» Preparation of the Diarsines and Diphosphine 25 A. 1 ,2-Dimethyl -1 ,2-Diphenyldiarsine.... 25 B. Tetramethyldiarsine 26 C. Tetramethyldiphosphine 26 Preparation of the Ligands 27 A. Cis - 2 , 3 - B i s ( m e t h y l p h e n y l a r s i n o ) - 1 , 1 , -1,4,^,4-Hexafluoro"but-2-ene (L-L)'... 27 B. Cis - 2 , 3-Bis(dimethylarsino) - 1 , 1 , 1 , 4 - , -^-,4-Hexaf luorobut-2-ene (L-L) 28 5- Reactions of Cis -2 ,3-Bis(methylphenyl-arsino) - 1 , 1 , 1 , H- ,k, ^-Hexafluorobut-2-ene (L-L) with T r a n s i t i o n Metal Carbonyls.... 30 A. Reactions of (L-L) with Iron Pentacarbonyl 30 B. Reactions of (L-L) with Group VI Metal Hexacarbonyls 31 C. Preparation of the Diastereomeric ( L - L ) ' M ( C 0 ) 3 X 2 Complexes (M = Mo, W; X - Br, I) kO - v i -Page 6. Reactions of C i s - 2 , 3 - B i s ( d i m e t h y l -a r s i n o ) -1,1,1,4-, 4,4-Hexafluorobut-2-ene (L-L) w i t h T r a n s i t i o n Metal Carbonyls 4-4-A. Reaction of (L-L) w i t h T r i i r o n Dodecacarbonyl. 4-4-B. Reaction of (L-L) w i t h Group VI Metal Hexacarbonyls 45 C. Reactions of (L-L)M(CO)^ and M(CO) 6 (M = Cr, Mo, W) w i t h Excess (L-L) 4-5 D. P r e p a r a t i o n of the (L-L)M(C0)^X 2 Complexes (M = Mo, W; X = Br, I ) 48 E. P r e p a r a t i o n of the ( L - L ) L M o ( C 0 ) 2 B r 2 Complexes (L = a Mondentate Li g a n d ) . . 59 F. P r e p a r a t i o n of the ( L - L ) L 2 M o ( C 0 ) B r 2 Complexes 59 G. Reaction of (L-L) w i t h Dimanganese Decacarbonyl and Dirhenium Decacar-bonyl. 69 i . R e action of (L-L) w i t h Diman-ganese Decacarbonyl 69 i i . R eaction of (L-L) w i t h Dirhenium Decacarbonyl 70 7. Reactions of T e t r a m e t h y l d i a r s i n e w i t h I r o n Pentacarbonyl and Dimanganese Decacarbonyl. 72 - v i i -Page A. Tetramethyldiarsine and Iron Pentacarbonyl 72 B. Tetramethyldiarsine and Dimanganese Decacarbonyl 72 8. Reaction of Tetramethyldiphosphine with Iron Pentacarbonyl 73 9. Reactions of 1,2-Dimethyl-l,2-Diphenyl-diarsine with Iron Pentacarbonyl and Dimanganese Decacarbonyl. 73 A. 1,2-Dimethyl-l,2-Diphenyldiarsine and Iron Pentacarbonyl 73 B. 1,2-Dimethyl-l,2-Diphenyldiarsine and Dimanganese Decacarbonyl 7^ CHAPTER III RESULTS AND DISCUSSION 76 1. The Ligands 76 2. The Stereomutation of Arsenic and Phosphorus 81 A. General Discussion 81 B. Separation and I d e n t i f i c a t i o n of the Stereoisomers of D i t e r t i a r y Arsines... 83 3. Iron Carbonyl Complexes of (L-L) and (L-L)'... 8k A. (L-L)Fe(CO) 3 and (L-L) ' Fe (CO) ^  8** 'B. (L-L)Fe 2(CO) 6 and (L-L)'Fe 2(C0) 6 87 - v i i i -Page C. F e 2 ( C O ) 6 [ A s ( C H 3 ) ( C 6 H 5 ) ] 2 91 4. Stereochemical Nonrigidity of the Fe^CO)^-[ E ( R 1 ) ( R 2 ) ] 2 Complexes (E = As, % = R 2 = CH^( R x = CKy R 2 = C6H^; E - P, R± = R £ = CH 3) 93 5- A Description of the Method Used i n the Calculation of Thermodynamic Parameters f o r Nonrigid Molecules 102 CHAPTER IV RESULTS AND DISCUSSION. 105 1. (L-LMCO)^ and ( L - L ) ' M C C O ) ^ Complexes (M = Cr, Mo, W) 105 A. Preparation 105 B. Spectroscopic Results 106 C. Possible Mechanism of Formation 110 2. Fac-(L-L) b(L-L)" 1M(CO) and Fac - ( L - L ) b -0 j (L-L) IjM(C0) 3 Complexes (M = Cr, Mo, W) 112 A. Preparation 112 B. Characterization 113 C. Chemical Properties 120 3. C i s - ( L - L ) 2 M ( C 0 ) 2 (M =' Cr, Mo, W) and Trans -(L-L) 2M(C0) 2 Complexes (M = Cr, Mo) 125 A. Preparation 125 B. Characterization 126 C. Trans to Cis Isomerization.. 130 - i x -Page 4. Summary 131 CHAPTER V RESULTS AND DISCUSSION 133 1. (L-L)M(CO) 3X 2 and ( L - L ) ' M C C O ) ^ Complexes (M = Mo, W; X = Br, I) 133 A. Preparation and Chemical Properties... 133 B. Characterization 135 2. (L-L)LMo ( C 0) 2Br 2 Complexes (L = Monodentate Ligand) 140 A. Preparation and Chemical Properties... 140 B. Spectroscopic Results 14-0 3. (L-L)L 2Mo ( C 0)Br 2 Complexes 144-A. Preparation and Chemical Properties... 144 B. Stereochemical Nonrigidity 14-5 C. I r Spectra 160 4. Summary. 160 CHAPTER VI RESULTS AND DISCUSSION l6Z 1. Reactions of (L-L) with Dimanganese Decacarbonyl and Dirhenium Decacarbonyl.... 162 A. (L-L) and Dimanganese Decacarbonyl,... 163 B. (L-L) and Dirhenium Decacarbonyl 166 2. Reaction of 1 , 2-Dimethyl-l,2-Diphenyl-diarsine with Dimanganese Decacarbonyl 169 -x-Page SUGGESTIONS FOR FUTURE INVESTIGATIONS 17 2 BIBLIOGRAPHY 173 - x i -LIST OF TABLES Table Page I Purchased Chemicals and Suppliers....... 23 II Reactions of Iron Pentacarbonyl with (L-L) 32 III A n a l y t i c a l Data f o r Iron Carbonyl Complexes Of (L-L)' 3k IV l r Spectra (2100-1900 cm - 1), f o r Iron Carbonyl Complexes of (L-L) 35 V Nmr Data f o r Iron Carbonyl Complexes of (L-L) .... 36 VI A n a l y t i c a l and Preparative Data f o r Diastereomeric Group VI (L-L)'M(CO)^ Complexes 37 VII l r Spectra (2100-1900 cm - 1) f o r Diastereomeric Group VI (L-L)'M(CO)^ Complexes 38 VIII Nmr Data f o r Diastereomeric Group VI (L-L)'M(CO)^ Complexes 39 IX A n a l y t i c a l and Preparative Data f o r Diastereomeric (L-L)'M(C0) 3X 2 Complexes (M = Mo, W; X = Br, I ) . . . kl X l r Spectra (2100-1900 cm - 1) f o r Diastereomeric (L-L)'M(C0 ) y C 2 Complexes (M = Mo, W; X = Br, I) k2 XI Nmr Data f o r Diastereomeric (L-L)'M(C0)^X 2 Complexes (M = Mo, W; X = Br, I) k3 XII A n a l y t i c a l and Preparative Data f o r Group VI (L-L)M(CO)^ Complexes ^6 XIII l r Spectra (2100-1900 cm"1) f o r Group VI (L-L)M-(C0)^ Complexes k7 XIV Nmr Data f o r Group VI (L-L)M(C0) / L Complexes k7 - x i i -Table Page XV Reactions of (L-L)M(CO)^ and M(CO) 6 (M = Cr, Mo, W) with Excess (L-L) 4-9 XVI A n a l y t i c a l Data f o r (L-L) Derivatives of M(C0)g (M = Cr, Mo, W) 53 XVII l r Spectra (2000-1800 cm"1) f o r (L-L) Derivatives of M(C0) 6 (M = Cr, Mo, W) 5^ XVIII Nmr Data f o r (L-L) Derivatives of M(C0) 6 (M = Cr, Mo, W) 55 XIX A n a l y t i c a l and Preparative Data f o r (L-L)M(CO)^-X 2 Complexes (M = Mo, W; X = Br, I) 57 XX l r Spectra (2100-1900 cm"1) f o r (L-L)M(C0)^X 2 Complexes (M = Mo, W; X = Br, I) 58 XXI Nmr Data f o r (L-L)M(C0)^X 2 Complexes (M = Mo, W; X = Br, I ) . 58 XXII A n a l y t i c a l and Preparative Data f o r (L-L)LMo-( C 0 ) 2 B r 2 Complexes 60 XXIII l r Spectra (2000-1800 cm"1) f o r (L-L)LMo(C0) 2Br 2 Complexes 6 l XXIV Nmr Data f o r (L-L)LMo(C0) 2Br 2 Complexes 62 XXV A n a l y t i c a l and Preparative Data f o r (L-L)L 2Mo-(C0)Br 2 Complexes 65 XXVI l r Spectra (1900-1700 cm"1) f o r (L-L)L 2Mo(C0)Br 2 Complexes 66 XXVII Nmr Data f o r (L-L)L 2Mo(C0)Br 2 Complexes 67 XXVIII Thermodynamic Parameters f o r Bridging Phosphido and Arsenido D i i r o n Hexacarbonyl Complexes....... 96 - x i i i -Table Page XXIX 1 3 C Nmr Data 101 XXX Temperature Dependence of l/t8cw f o r the Asymmetric Isomer of Fe 2 (C0) 6[As(CH^)(CgH^)] 2... 103 XXXI l r Spectra (2100-1800 cm - 1) f o r Some Group VI Chelate Complexes 110 XXXII l r Spectra (1900-1700 cm - 1) f o r Some Group VI Cis Dicarbonyl Complexes 129 XXXIII l r Spectra (2100-1900 cm"1) f o r Some Group VI Halotricarbonyl Complexes 139 XXXIV Thermodynamic Parameters f o r (L-L)L 2Mo(C0)Br 2 Complexes 151 XXXV l r Spectra (2100-1900 cm - 1) f o r Some Manganese Complexes 171 -xiv-LIST OF FIGURES Figure Page 19 1 The 7 F nmr spectrum of the products of equation [XVIl] (R = C^H^) (a) i n the absence of hexafluoroacetone and (b) i n the presence of hexaf luoroacetone 79 2 C r y s t a l structure of ( f f a r s ) F e 2 ( C 0 ) 6 . 88 3 Variable temperature "Hi nmr spectra i n benzene i n the arsenic methyl region of the asymmetric isomer of Fe 2(CO) 6[As(CH 3) ( C ^ ) ] 2 95 4- Variable temperature "*"H nmr spectra i n benzene of F e 2 ( C O ) 6 [ A s ( C H 3 ) 2 ] 2 97 5 Temperature dependence of l/c 8 UJ f o r the asymmetric isomer of Fe 2(CO) 6[As(CH 3) (C^H^)] 2 . . 104-6 The normal carbonyl v i b r a t i o n a l modes of the Group VI (L-L)M(CO)^ and (L-L)'M(CO)^ complexes 108 7 The normal carbonyl v i b r a t i o n a l modes of Group VI mer and fac isomers of (L-L) b(L-L) mM ( C 0 ) 3 . . . 115 8 The carbonyl i r spectrum i n cyclohexane of an isomer of (L-L) l 3(L-L) mMo (C0 ) 3 117 9 The carbonyl i r spectra i n cyclohexane of c i s -(L-L) 2Mo (C0) 2 (A) and trans-(L-L) 2Mo(CO) 2 (B).. 127 10 The carbonyl i r spectrum i n cyclohexane of a mixture of (L-L)W(CO)^ (A), fac-(L-L) b(L-L)™-W(C0)3 (B), and cis-(L-L) 2W ( C 0 ) 2 (C) 132 11 C r y s t a l structure of (L-L)W(CO) „I„ 136 -XV-Figure Page 12 Variable temperature "^H nmr spectra i n benzene i n the arsenic methyl region of (L-L)[p(0CH 3) 3] 2Mo(C0)Br 2 1^7 13 Variable temperature Hi nmr spectra i n benzene i n the methoxy methyl region of (L-L)[P(0CH 3) 2(C 6H^)] 2Mo(C0)Br 2. A and D are the phosphorus decoupled spectra and B and C are the normal spectra. 150 14 Variable temperature Hi nmr spectra (methyl region) i n benzene of (L-L)[P(CH 3) 2(CgH^)] 2-Mo(C0)Br 2. A i s the normal spectrum and B, C, D, E are the phosphorus decoupled spectra... 156 15 C r y s t a l structure of Mn2 (CCOgAs^CH-^F^C^ 164 16 The Hi nmr spectrum of the rhenium complex (a) i n the absence of Eu(F0D) 3 and (b) i n the presence of Eu(FOD)^ 168 - x v i -ACKNOWLEDGEMENTS I am extremely g r a t e f u l to Dr. W.R. Cullen f o r his valuable guidance and assistance during the course of t h i s work. My thanks also to: Dr. F.W.B. E i n s t e i n and Dr. J . Trotter f o r t h e i r i n t e r e s t i n the X-ray c r y s t a l structure of a manganese and tungsten complex. Dr. E. Koster, Miss P. Watson, and Mr. W. Lee f o r running the nmr spectra. Mr. P. Borda f o r performing microanalyses. Drs. R. Pomeroy, A. Fenster, J . Price, G. Spendjian, D. Patmore, L.S. Chia, A. Wu, and F.L. Hou f o r help received during the course of t h i s work. A very s p e c i a l thanks to my wife, Mary, f o r the typing of th i s t h e s i s . F i n a l l y , I am indebted to the National Research Council of Canada and t h i s Department f o r f i n a n c i a l support, - 1 -CHAPTER I INTRODUCTION This thesis i s concerned with the preparation, characterization, and general chemistry of some d i t e r t i a r y arsine complexes of t r a n s i t i o n metal carbonyls with the emphasis on complexes of the Group VI metal carbonyls. Thus, the general introductory discussion i s r e s t r i c t e d to work on related s i x and seven-coordinate Group VI metal carbonyl complexes. 1. Six-Coordinate Group VI Metal Carbonyl Complexes A . Preparative Methods The general preparative methods f o r metal carbonyl complexes of chromium, molybdenum, and tungsten can be divided into two major routes as follows: ( 1 . ) Direct displacement of carbon monoxide by a donating g r o u p — The displacement can be effected by r e f l u x i n g the metal carbonyl and ligand i n an appropriate solvent e.g. equation [ i ] 1 , heating the reactants i n a sealed tube e.g. equation [ i l ] ^ , or by u l t r a v i o l e t i r r a d i a t i o n of the reactants e.g. - 2 -equation [ill]-^. Mo(CO) 6 + f 6 f o s * ^ ^ e l n > ( f 6 f o s ) M o ( C 0 ) 4 [ i ] Mo(CO) 6 + ( C 2 H 5 ) 2 P C A P ( C 2 H 5 ) 2 > [ I I ] (C 2H 5) 2PC 2H^P(C 2H 5) 2Mo(CO) J [ j f Mo (C0 ) 6 + NCCH3 (NCCH 3) 2Mo(C0)^ [ill] (2 . ) Displacement of substituent groups from p a r t i a l l y substituted complexes by the desired ligand—-This route i s useful f o r the preparation of s p e c i f i c complexes not obtainable through d i r e c t carbon monoxide replacement e.g. equations [iv]^  and [v]\ Cr ( C 0) 3(mesitylene) + diphos** tube"6** > [IV] trans-(diphos) 2Cr(CO) 2 Mo(CO)j(toluene) + piperazine > (piperazine) 3Mo ( C 0 ) 3 [V] + toluene P u r i f i c a t i o n of the products i s achieved by chromatog-raphy, r e c r y s t a l l i z a t i o n , or vacuum sublimation. Thermal s u b s t i t u t i o n reactions of the Group VI metal carbonyls can generally be ca r r i e d out between 50 and 150° providing a strong donor ligand i s present. However, c e r t a i n f 6 f o s =(C 6H 5) 2PC = C P ( C 6 H 5 ) 2 ( C F 2 ) 3 diphos - (C- 6H 5) 2PCH 2CH 2P(C 6H 5) 2 -3-metal carbonyl derivatives (see Chapter IV) do not undergo thermal reaction even at very high temperatures. The maximum temperature which can be used f o r thermal s u b s t i t u t i o n i s l i m i t e d by the range of s t a b i l i t y of s t a r t i n g materials and f i n a l products. In the photochemical reaction of metal carbonyl derivatives i t i s possible to i s o l a t e r e l a t i v e l y unstable s u b s t i t u t i o n products (at or below room temperature) not obtainable by the thermal method. Thus, a wide range of new compounds have become accessible by the photochemical procedure. B. Infrared ( i r ) Studies I r spectroscopy has proven to be a valuable t o o l i n studies of Group VI carbonyl reactions, both i n characterizing the complexes and i n monitoring the reactions. The number of i r - a c t i v e carbonyl stretching fundamentals f o r geometrical isomers of the octahedral, derivatives L xM(C0)^_ X can be derived (using group theory) on the basis of the l o c a l symmetry of the carbonyl groups undisplaced from the o r i g i n a l octahedral array by substituent groups ( i . e . only interactions among the carbonyl groups need be considered). This so-called "energy-factoring" approach^ i s possible because the v i b r a t i o n a l frequencies of carbonyl groups are so well separated from other v i b r a t i o n a l frequencies. Thus the number and i n t e n s i t y of carbonyl stretching vibrations have been used p r i m a r i l y to d i f f e r e n t i a t e between Group VI metal c i s 2 , 6 , 7 and t r a n s 2 , 8 dicarbonyl, f a c 2 , 7 , 9 , 1 0 and m e r 7 , 1 1 t r i c a r b o n y l , and c i s 2 , 6 , 7 , 1 2 and t r a n s 7 , 1 3 tetracarbonyl complexes. The following section i s concerned with a des c r i p t i o n of the widely accepted bonding mechanism i n metal carbonyl complexes (which i n turn i s r e f l e c t e d i n the carbonyl i r stretching frequencies). A knowledge of the bonding scheme i s e s s e n t i a l to understand the r e a c t i v i t y of the metal-carbon bond ( i n Group VI metal carbonyl complexes) with varying degrees of su b s t i t u t i o n . C. Bonding i n Metal Carbonyls Carbon monoxide forms stable complexes with t r a n s i t i o n metals such as chromium, molybdenum, and tungsten, i n which the metal i s i n a low oxidation state. The s t a b i l i z a t i o n r e s u l t s from the f a c t that the carbon atom i n carbon monoxide possesses vacant TT o r b i t a l s i n addition to a lone p a i r . Bonding i s thought to involve the formation of a and TT bonds. The o bond r e s u l t s from the donation of the lone pa i r of electrons on the carbon atom to a vacant metal o r b i t a l as i l l u s t r a t e d i n 1. The TT bond r e s u l t s from back donation of electrons from the f i l l e d nonbonding d o r b i t a l s on the metal to the low-lying TT antibonding o r b i t a l s of the carbon monoxide as i l l u s t r a t e d i n 2. The metal-carbonyl bond would be quite weak i f the bond i s formed merely through donation of the lone p a i r since the n u c l e o p h i l i c i t y of carbon monoxide i s considered to be quite low. -5-© < © ) + >C = Q: > M C = 0 : 1 CO >M a bond formation C - 0 2 M >C0 dn-prf "back bonding" 2 M >E dn-pn "back bonding" E = arsenic or phosphorus The two modes of bonding are mutually r e i n f o r c i n g or synergic since the charge removal from the metal through rr "back bonding" increases the electron density on carbon, which then strengthens i t s o bond formation. This then increases the electron density on the metal and strengthens i t s rr bond formation. In metal carbonyl complexes two types of "back bonding" mechanisms are possible: (1.) dn-pn "back bonding" and (2.) drr-drr "back bonding". Ligands such as carbon monoxide accept charge through dn-pn "back bonding" since they have low-lying pn o r b i t a l s . Other -6-ligands such as arsines and phosphines accept charge through drr-dn "hack bonding" ( i l l u s t r a t e d i n _3_), since the coordinating atom, arsenic or phosphorus, possesses vacant d o r b i t a l s . The degree of "back bonding" f o r these ligands varies as a function of the e l e c t r o n e g a t i v i t i e s of substituents on the donor atom. Replacing some of the carbon monoxide groups of the parent carbonyl (e.g. Group VI metal hexacarbonyls) with ligands of lower TT-acceptor a b i l i t y causes the remaining carbon monoxide groups to accept drr electrons from the metal to a greater extent, to prevent accumulation of charge on the metal atom. This produces a decrease i n the carbonyl stretching frequency with corresponding increases i n metal-carbon stretching frequencies. As the degree of s u b s t i t u t i o n of carbon monoxide with poorer TT-acceptor ligands increases, the metal-carbon bond strength further increases making the ease of carbon monoxide displacement more d i f f i c u l t . Complete displacement of carbon monoxide from the Group VI metal hexacarbonyls has been achieved with trifluorophosphine, ' 1 6 a ligand that i s quite 17 s i m i l a r to carbon monoxide i n n-accepting a b i l i t y . ' There appears to be d i f f e r i n g schools of thought as to whether the change i n the carbonyl stretching frequencies f o r a series of derivatives i s a function of the r e l a t i v e a or TT 18 bonding a b i l i t i e s of the ligands i n the complex. Cotton has proposed that changes i n the carbonyl stretching f r e -quencies depend only on the n-accepting a b i l i t y of the ligand -7-while Bigorg,ne±y believes the v(CO) changes are affected by the CT-donating a b i l i t y of the donor atom. This i s s t i l l a cont r o v e r s i a l subject; s u f f i c e i t to say both e f f e c t s i n -17 fluence the carbonyl stretching frequencies. An important feature i n the determination of stereo-chemistry and r e a c t i v i t y of metal carbonyl derivatives i s the trans e f f e c t . Two carbonyl groups trans to each other compete across the metal atom f o r the same metal TT bonding o r b i t a l s , whereas a carbonyl group trans to a weaker t r-acceptor ligand i s p r i m a r i l y responsible f o r the d e r e a l i z a t i o n of the charge on the metal atom. Thus, i n a reaction of a . carbonyl derivative and a donor ligand, one of the trans carbonyl groups i s the more l a b i l e and i s usually displaced. D. Nuclear Magnetic Resonance (nmr) Studies The cha r a c t e r i z a t i o n of many Group VI metal carbonyl derivatives has been based mainly on "*"H nmr spectroscopy. In metal complexes containing arsine or phosphine ligands, the protons i n the ligands are deshielded and the "*"H resonance peaks move downfield, providing a c r i t e r i o n of complex formation. The "*"H methyl resonance patterns of some t e r t i a r y 20 21 phosphine disubstituted Group VIII metal complexes ' have been shown to be usef u l i n determing the stereochemistry cf the phosphine ligands, c i s phosphines gi v i n g a well defined 1:1 doublet and trans phosphines a well defined 1:2:1 " t r i p l e t " . 22 However, Shaw and coworkers have shown, i n some t e r t i a r y -8-phosphine disubstituted Group VI metal carbonyls, that the '''H methyl resonance pattern i s not generally useful i n determining the stereochemistry of these complexes. Intermediate patterns ( i . e . a broad resonance flanked by a 1:1 doublet) are observed f o r complexes i n which the phosphine ligands are i n c i s or trans positions rather than the well defined doublet or " t r i p l e t " patterns. 13 YC nmr studies have been applied to a v a r i e t y of Group VI metal carbonyl d e r i v a t i v e s . Gansow et a l . J studied 13 the JC nmr spectra of a series of monosubstituted LW(CO)^ complexes and found a l i n e a r c o r r e l a t i o n between the carbonyl chemical s h i f t s and the carbonyl stretching force constants. This was taken to suggest that changes i n metal-carbon-oxygen 13 TT bonding exert a dominant influence on yC chemical s h i f t s . 24-Very recently, Bodner and Todd found a c o r r e l a t i o n between 13 the nmr carbonyl chemical s h i f t s and the carbonyl stretching frequencies f o r a series of (n-arene) t r i c a r -bonylchromium complexes. From the sign of the c o r r e l a t i o n they postulate that changes i n the carbonyl chemical s h i f t with varying substituents on the arene r i n g can be explained i n terms of changes i n the extent of metal to carbonyl TT back donation. 31 P nmr studies on phosphine substituted Group VI metal carbonyl derivatives have yielded further information on the 2 *i bonding and structure i n these compounds. Grim et a l . have shown i n Group VI metal complexes of the type (L)(L )M(CO)^ (L and L are a t e r t i a r y phosphine and organophosphite or two d i f f e r e n t t e r t i a r y p h o s p h i n e s ) c o n t a i n i n g phosphorus 31 31 atoms i n c i s p o s i t i o n s , the J P- P s p i n - c o u p l i n g c o n s t a n t i s c o n s i d e r a b l y s m a l l e r t h a n f o r the c o r r e s p o n d i n g compounds 2 6 w i t h t r a n s phosphorus atoms. Grim e t a l . have a l s o f o u n d t h a t i n complexes of the t ype ( R n P h 3 _ n P ) W ( C 0 ) ^ where R i s a l k y l , n i s 0-3, t h e s i z e of. the 1^^W--^1P s p i n - c o u p l i n g c o n s t a n t appeared t o be a measure o f t h e r r - a c c e p t o r a b i l i t y of t h e phosphorus compound. E. Mass S p e c t r o m e t r i c S t u d i e s The mass s p e c t r a o f Group VI m e t a l c a r b o n y l d e r i v a t i v e s are r o u t i n e l y used i n c o n j u n c t i o n w i t h nmr and i r s p e c t r a i n t h e e l u c i d a t i o n o f m o l e c u l a r s t r u c t u r e . A t y p i c a l s p e ctrum u s u a l l y g i v e s a peak a t t r i b u t e d t o t h e p a r e n t i o n as w e l l as peaks due t o t h e c o n s e c u t i v e l o s s o f c a r b o n y l groups. Thus, the number of c a r b o n y l groups p r e s e n t i n a m e t a l complex can g e n e r a l l y be deduced from i t s mass spectrum; however, c a u t i o n must be e x e r c i s e d i n t h e i n t e r p r e t a t i o n o f the mass s p e c t r a l d a t a o f Group VI c a r b o n y l complexes s i n c e the p a r e n t i o n i s n o t always o b t a i n e d . The f r a g m e n t a t i o n p a t t e r n has been u s e d as a t o o l t o 27 d i f f e r e n t i a t e between complexes k and , j5_ e x h i b i t i n g no monomeric i o n s o f t h e t y p e [ (CO ^ M P ^ C H ^ ] * o r [ C C O ^ M P f C H ^ g ] (M=Cr, Mo, W; n=0-4). A p a r t from i t s use i n s t r u c t u r a l e l u c i d a t i o n , mass s p e c t r o s c o p i c s t u d i e s on Group VI c a r b o n y l complexes have y i e l d e d o t h e r i n f o r m a t i o n . The mass s p e c t r a and i o n i z a t i o n -10-(CH 3) 2 CH^ CH 3 (CO)^M P P M(CO)^ CH 3 CH 3 M = Cr , Mo , W (CO)^M M(C0)^ ( C H 3 ) 2 p o t e n t i a l s of some Group VI LM(CO)^ complexes, where L represents 28 a s e r i e s of monodentate ligands, have been reported. Variations i n the donor-acceptor a b i l i t y of the ligands were found to influence molecular i o n i z a t i o n potentials and cracking patterns. The molecular i o n i z a t i o n potentials were found to depend on the metal and the ligand. Mass spectrometric studies of the e f f e c t of a l k y l sub-stit u e n t s i n benzene rings on the metal-ligand bond strength i n a series of substituted dibenzenechromium derivatives» have shown the chromium-ligand bond to be strengthened by i n -29 creased donor a b i l i t y of the r i n g a l k y l substituents. F. Reaction Mechanisms The Group VI metal hexacarbonyls show no detectable exchange of carbon monoxide i n solut i o n at room temperature. However, at elevated temperature i n the gas phase exchange 30 occurs and the rate of exchange i s independent of carbon monoxide concentration suggesting a d i s s o c i a t i v e process of the type represented by equation [ v i ] . Studies conducted -11-M(CO) 6 * M(CO) 5 + CO " [ V I ] M = Cr, Mo, W 30 w i t h s u b s t i t u t e d d e r i v a t i v e s of chromium and molybdenum^ show that exchange of carbon monoxide i s slower w i t h the s u b s t i t u t e d complexes than w i t h the parent hexacarbonyls. This i s i n agreement w i t h an in c r e a s e i n the metal-carbon bond s t r e n g t h w i t h i n c r e a s e d s u b s t i t u t i o n . There have been no r e p o r t s of k i n e t i c s t u d i e s of s u b s t i t u t i o n of the Group VI metal hexacarbonyls by bidentate l i g a n d s . However, some data are a v a i l a b l e f o r the s u b s t i t u t i o n of Group VI metal hexacarbonyl d e r i v a t i v e s by bidentate l i g a n d s . 31 32 Connor et a l . have i n v e s t i g a t e d the c h e l a t i o n r e a c t i o n s of some Group VI pentacarbonyl complexes c o n t a i n i n g p o t e n t i a l l y b i dentate l i g a n d s t h a t are monocoordinated. T h e i r k i n e t i c s t u d i e s suggested the mechanism of c h e l a t i o n i s concerted although the chromium r e a c t i o n s appeared to have more d i s s o c i a t i v e or S ^ l c h a r a c t e r i n t h i s concerted process. 33 Basolo et a l . ^ have s t u d i e d the r e a c t i o n of diphos w i t h a s e r i e s of c i s - a n d trans-l^Mo(CO)^ complexes where L i s a phosphine or phosphite and have found t h a t the r a t e s do not depend.on the c o n c e n t r a t i o n of diphos. A p o s s i b l e mechanism i n accord w i t h t h e i r f i n d i n g s can be represented as f o l l o w s ; -12-O c xo .M N. CO c o o c .CO .IY1 CO C o slow -L f a s t -L CO L M CO CO CO f a s t + P-P O C .CO P B-.M CO c o P-P = diphos [ V I I ] 34 Dobson and coworkers have examined bidentate ligand replacement i n some disubsti t u t e d Group VI metal tetracarbonyl complexes with such bidentate ligands as (CH^gNCHgCHgNCCrl^),,, CH^SCHgCHgSCH^35 and ( C ^ ^ A s C H g A s t C g H ^ . 3 6 The bidentate ligands were completely displaced i n a l l cases and there was no evidence f o r the ring-opened complex i n which only one end of the ligand was coordinated. Kinetic r e s u l t s suggested ring-opening was rate determining but the ring-opened intermediate r a p i d l y l o s t the ligand to give the observed product. 37 Recently, A n g e l i c i and Knebel^' have investigated chelate ring-opening reactions of a series of Group VI (P N)M(CO)^ complexes with carbon monoxide, givi n g the monocoordinated ligand complex (P N)M(CO)^ (P~N i s a phosphorus-nitrogen donor bidentate ligand). They found the - 1 3 -rates of the reaction to be dependent upon the bulkiness of the groups on the nitrogen donor group of the ligand and the size of the chelate ring. Their k i n e t i c studies provide some evidence that the reaction proceeds v i a a ring-opened five-coordinate intermediate according to the following mechanism: (CO)^M^p) s (CO)^M-P~N (CO)5M-P~N [ v i l l ] The reactions of the Group VI metal hexacarbonyls with t e r t i a r y phosphines and phosphites have been extensively "38-^-1 studied. I t has been found that chromium hexacarbonyl usually favours reactions by a d i s s o c i a t i v e mechanism (S^jl) while molybdenum and tungsten hexacarbonyls react v i a d i s s o c i a t i v e and associative mechanisms ( S N 1 and S N 2 ) . Equations [IX] and [X] i l l u s t r a t e the d i s s o c i a t i v e and associative processes respectively. M ( c o ) 6 i I 57 * M ( c o ' s ffet> L M< C 0>5 M = Cr, Mo, W M ( C 0 ) 6 + L LMo(CO) 6 LM(CO) 5 M = Mo, W [IX] [x] -14-2. Seven-Coordinate Group VI Metal Carbonyl Complexes This discussion i s concerned with substituted halocarbonyls of molybdenum (II) and tungsten ( I I ) . A. Preparative Methods There are two p r i n c i p a l methods of preparing substituted halocarbonyls of molybdenum (II) and tungsten ( I I ) . The f i r s t general method developed by Lewis and coworkers can be represented by the general equation [ x i ] . M(CO) 6 ^ L 2M(C0)^ ^ L 2M(C0) 3X 2 [XI] M = Mo, W; X = C l , Br, I In the equation L i s a monodentate ligand, but the reaction 44 45 works equally well i f L 2 i s bidentate. Nyholm and coworkers ' have investigated the oxidation reactions of ( L 2 ) 2 M ( C 0 ) 2 ( L 2 i s bidentate) and have found that complexes of d i f f e r i n g metal oxidation state were formed depending on the halogen. The second general method of preparation of the t i t l e compounds involves preparation of the parent halocarbonyls followed by reaction with the appropriate ligand, as i l l u s t r a t e d i n equation [ X i i ] where L i s a monodentate ligand. M(C0) 6 M(C0)^X 2 ^ L 2M(C0) 3X 2 [XII] M = Mo, W; X = C l , Br, I This method developed exclusively by Colton and associates - 1 5 -involves the preparation of derivatives of monodentate^ 6 -^ 0 SI- S3 and bidentate ligands. J J Dicarbonyl derivatives of bidentate ligands-^"--^ represented by the general formula (ligand) 2M(CO) 2X 2 (M = Mo, W; X = C l , Br, I) have also been prepared by Colton and associates. B. Conductometric Studies Molar conductivity studies show that the complexes of the type (bidentate ligand) M ( C 0 ) 3 X 2 (M = Mo, W; X = C l , Lh, h< SI-S3 Br, I) are a l l nonelectrolytes, ' J J whereas the dicarbonyl complexes can be formulated as e i t h e r 1:1 bf\\ 4-S S2 S1-S4-e l e c t r o l y t e s ' -^ '^  or nonelectrolytes. v C. Crystallographic Studies For coordination number seven, three basic polyhedral geometries are possible: pentagonal bipyramid, capped octahedron, and capped t r i g o n a l prism. Recently X-ray s t r u c t u r a l determinations have been performed on four substituted Group VI metal halocarbonyl d e r i v a t i v e s . These are b r i e f l y described below. The complex bis[bis(diphenylarsino)methane]dibromo-d i c a r b o n y l m o l y b d e n u m ( I I ) i s best described as a d i s t o r t e d capped octahedron with a carbonyl group i n the unique capping p o s i t i o n ; one of the arsine ligands i s b i - and the other monodentate. The tungsten atom i n dibromotricarbonylbis[bis(diphenyl-arsino )methane]tungsten(II)^ has a d i s t o r t e d capped octahedral -16-e n v i r o n m e n t , a c a r b o n y l group o c c u p y i n g t h e u n i q u e c a p p i n g p o s i t i o n . Both l i g a n d s are monodentate. I t i s s i g n i f i c a n t t h a t t h e capped o c t a h e d r a l c o n f i g u r a t i o n i n t h i s complex and t h e one d e s c r i b e d i n t h e p r e c e d i n g p a r a g r a p h a r e v e r y s i m i l a r even though a c a r b o n y l group has been r e p l a c e d i n the t u n g s t e n complex by the b u l k y and l e s s e l e c t r o n e g a t i v e d i p h e n y l a r s i n o group i n t h e molybdenum complex. I n t h e complex d i b r o m o t r i c a r b o n y l [ l , 2 - b i s ( d i p h e n y l -p h o s p h i n o ) e t h a n e ] m o l y b d e n u m ( I I ) - l - a c e t o n e - ^ the molybdenum atom has a s l i g h t l y d i s t o r t e d capped o c t a h e d r a l e n v i r o n m e n t w i t h a c a r b o n y l group a g a i n o c c u p y i n g the u n i q u e c a p p i n g p o s i t i o n . The c o o r d i n a t i o n sphere o f t h e molybdenum atom i n d i c a r b o n y l c h l o r o b i s - [ o - p h e n y l e n e b i s ( d i m e t h y l a r s i n o ) ] -m o l y b d e n u m ( l I ) t r i - i o d i d e - b i s c h l o r o f o r m i s a capped t r i g o n a l p r i s m , the c h l o r i n e atom o c c u p y i n g t h e c a p p i n g p o s i t i o n . The p r i s m s k e l e t o n i s i l l u s t r a t e d i n 6 where As~As i s the d i t e r t i a r y a r s i n e l i g a n d . -17-I t appears t h a t the choice of polyhedron f o r a given s u b s t i t u t e d Group VI metal halocarbonyl i s d i c t a t e d by such f a c t o r s as l i g a n d - l i g a n d r e p u l s i o n s , s t e r i c c o n s t r a i n t s of multid e n t a t e l i g a n d s , e l e c t r o n i c s t r u c t u r e of the metal, and c r y s t a l packing energies. D. I r Studies l r s p e c t r a have been used to d i s t i n g u i s h between the Group VI metal h a l o t r i c a r b o n y l and h a l o d i c a r b o n y l 44,45,51-54 complexes; ~" ^  ^ the former e x h i b i t i n g three s t r o n g carbonyl absorptions and the l a t t e r two st r o n g c a r b o n y l absorptions. I r s t u d i e s have been a p p l i e d to detect carbon monoxide 51 53 c a r r y i n g systems-' ' J J represented by the gene r a l equation [ X I I I ] . ( l i g a n d) 2 M(GO) 3X 2 ^ (ligand) 2M(CO) gX C 0 M = Mo, W; X = C l , Br, I O 2 2 The d i f f e r e n c e i n carbonyl s t r e t c h i n g f r e q u e n c i e s has been a p p l i e d to d i f f e r e n t i a t e between an i o n i c and covalent bromotricarbonyl c o m p l e x . ^ E. Nmr Studies [ X I I I ] Nmr s t u d i e s have been used p r i n c i p a l l y to study the modes of c o o r d i n a t i o n of p o t e n t i a l l y bidentate l i g a n d s i n Group VI metal h a l o c a r b o n y l complexes. 5 1 - 5 ^ + I n t h e s e s t u d i e s i n f o r m a t i o n - 1 8 -i s d e r i v e d from the chemical s h i f t of the methylene protons si n c e the l i g a n d s employed are of the type (C£H^) 2E(CH 2) n~ E ( C 6 H 5 ) 2 (E = As, P, n = 1; E = P, n = 2 ) ; l i t t l e i n f o r m a t i o n can he obtained from the chemical s h i f t s of the phenyl groups. Equation [XIV] i l l u s t r a t e s a unique e q u i l i b r i u m - ^ t h a t has been s t u d i e d by nmr as each complex d i f f e r s i n the mode of c o o r d i n a t i o n of the bidentate l i g a n d Lv , . L 2 M o ( C 0 ) 3 I 2 + L 2 N ( L 2 ) 2 M o ( C 0 ) 3 I 2 ( L 2 ) 2 M o ( C 0 ) 2 I 2 + CO L2 = ( C 6 H 5 ) 2 A s C H 2 A s ( C 6 H 5 ) 2 [XIV] V a r i a b l e temperature nmr s t u d i e s have been p a r t i c u l a r l y u s e f u l i n demonstrating stereochemical n o n r i g i d i t y i n some Group VI metal h a l o c a r b o n y l complexes. A v a r i a b l e temperature nmr study of the d i c a r b o n y l complexes [ ( C 6 H 5 ) 2 A s C H 2 A s ( C 6 H ^ ) 2 ] 2 M ( C O ) 2 X 2 5 9 (M = Mo, W; X = C l , Br, I ) shows t h a t , near room temperature, exchange occurs between the nonequivalent l i g a n d molecules i n the manner depi c t e d i n [XV], The exchange ceases at lower temperature. This nmr study represents the f i r s t r e p o r t e d example of the n o n r i g i d c h a r a c t e r of a seven-coordinate Group VI metal h a l o c a r b o n y l complex. Very r e c e n t l y , R i x et al.^° reported a v a r i a b l e temperature nmr study of the c a t i o n i c species (P~P) 2Mo(CO) 2I (M = Mo, W; P~P = (CH 3) 2PCH 2CH 2P(CH 3) 2) f u r t h e r demonstrating the - 1 9 -M = Mo, W; X = C l , Br, I [XV] n o n r i g i d c h a r a c t e r of s e v e n - c o o r d i n a t e Group VI metal h a l o c a r b o n y l s . The l i m i t i n g low temperature nmr s p e c t r a are c o n s i s t e n t w i t h a monocapped t r i g o n a l p r i s m a t i c s t r u c t u r e 7_. The n o n r i g i d i t y at h i g h e r temperatures i s e x p l a i n e d by a p o l y t o p a l rearrangement, p o s s i b l y by r a p i d m i g r a t i o n of i o d i n e over the f i v e f a c e s of the prism. Z M = Mo, W; the l i g a n d o c c u p i e s b i t e s a -20-3. This Work Chapter II of t h i s thesis i s devoted e n t i r e l y to describing the preparation of the d i t e r t i a r y arsine ligands cis-2 ,3-bis (methylphenylarsino) -1,1,1,4-, 4-,4—hexaf luorobut-2-ene (denoted as (L-L)) and cis-2,3-bis(dimethylarsino)-l,1,1, 4-,4-,4-hexafluorobut-2-ene (denoted as (L-L)) and t h e i r t r a n s i t i o n metal carbonyl complexes. A n a l y t i c a l and spectroscopic data f o r the ligands and metal complexes are also included. Chapter III i s concerned with a discussion of the two ligands (L-L) and (L-L) and some of t h e i r i r o n carbonyl complexes. Chapter IV presents a discussion on some Group VI metal carbonyl complexes of (L-L) and (L-L) . Chapter V i s concerned with a discussion on some seven-coordinate Group VI metal halocarbonyl derivatives of (L-L) i and (L-L) with the emphasis on the nonrigid character of these complexes. Chapter VI includes a discussion on some novel manganese and rhenium carbonyl complexes of (L-L). The bridging methylphenylarsenido manganese carbonyl complex i s also described. -21-CHAPTER II EXPERIMENTAL This chapter describes the various synthetic procedures used i n the preparation of the d i t e r t i a r y arsine ligands and t h e i r t r a n s i t i o n metal carbonyl complexes. A n a l y t i c a l and spectroscopic data f o r a l l new complexes are given i n tabular form where applicable. 1. General Techniques and Physical Measurements A i r - s e n s i t i v e s t a r t i n g materials were handled i n a nitrogen atmosphere. A l l p y r o l y s i s and photochemical (200W) reactions were c a r r i e d out i n sealed evacuated thick-walled Carius tubes. A standard vacuum system was used f o r the manipulation of v o l a t i l e reactants. Infrared ( i r ) spectra were recorded on a Perkin-Elmer 457 double beam spectrophotometer and c a l i b r a t e d using polystyrene and cyclohexane. Nuclear magnetic resonance (nmr) spectra were run on Varian T-60, HA-100, XL-100, and CFT-20 spectrometers with chemical s h i f t s given i n ppm downfield from i n t e r n a l TMS f o r 1 13 H and spectra, and u p f i e l d from i n t e r n a l CFC1 0 f o r -22-J" 7F spectra. Heteronuclear decoupling experiments with noise modulation u t i l i z e d instrumentation already described i n the 6l l i t e r a t u r e . Temperature studies were ca r r i e d out on the HA-100 and XL-100 instruments using a Varian V-4-34-3 variable temperature u n i t which was c a l i b r a t e d against an ethylene g l y c o l standard sample. Mass spectra were measured with an AEI MS-9 spectrometer with d i r e c t introduction of the s o l i d sample. Melting pqints were determined i n open c a p i l l a r i e s using a Gallenkamp melting point apparatus and are uncorrected. Unless otherwise stated a l l u l t r a v i o l e t i r r a d i a t i o n s were performed using a 200W Hanovia 654-A-36 lamp situated 20 cm from the reaction tube. The tube was continuously shaken and cooled by an a i r stream. In some cases i r r a d i a t i o n s were performed using a 4-50W Hanovia lamp placed i n a water cooled quartz jacket. This was inserted into a la r g e r glass jacket containing the so l u t i o n to be i r r a d i a t e d . Nitrogen was bubbled through the solut i o n during the course of the reactions. Microanalyses were performed by P. Borda of t h i s department. -23-2. Sta r t i n g Materials The following chemicals were obtained commercially and used without further p u r i f i c a t i o n . Table I Purchased Chemicals and Suppliers Chemical Suppliers deuterochloroform dg-methylene chloride d^-benzene dimethylarsinic acid dimethyl s u l f a t e benzenearsonic acid hexafluorobutyne-2 hexafluoroacetone chromium hexacarbonyl molybdenum hexacarbonyl tungsten hexacarbonyl dimanganese decacarbonyl dirhenium decacarbonyl iron pentacarbonyl triphenylphosphine dimethylphenylphosphine methyldiphenylphosphine Merck, Sharp, and Dohme of Canada Ltd. Merck, Sharp, and Dohme of Canada Ltd. Merck, Sharp, and Dohme of Canada Ltd. F i s h e r S c i e n t i f i c Co. Eastman Organic Chemicals Eastman Organic Chemicals Peninsular Chemresearch Inc. Peninsular Chemresearch Inc. Strem Chemical Co. Strem Chemical Co. Strem Chemical Co. Pressure Chemical Co. Strem Chemical Co. A l f a Inorganics Inc. Eastman Organic Chemicals Strem Chemical Co. Strem Chemical Co. -2k-Table I (Continued) Chemical Suppliers dimethyl phenylphosphonite Strem Chemical Co. trifluorophosphine Strem Chemical Co.. trimethylphosphite Eastman Organic Chemicals triethylphosphite Eastman Organic Chemicals -25-3. Preparation of the Diarsines and Diphosphine 62 63 A. 1,2-Dimethyl-l,2-Diphenyldiarsine ' Benzenearsonic acid (100 g, 495 mmol) was dissolved i n 240 ml of warm concentrated hydrochloric acid with a trace (0.1' g) of potassium iodide being added. Sulphur dioxide was passed through the soluti o n f o r 1 h producing crude dichlorophenylarsine (106 g, 96%) as a dense yellow o i l . The dichloroarsine (106 g, 475 mmol) was slowly added with s t i r r i n g to a solution of sodium hydroxide (92 g, 2.3 mol) i n water (200 ml). A cloudy white s o l u t i o n resulted. This was cooled and placed i n a 3-necked f l a s k equipped with condenser, s t i r r i n g bar, and dropping funnel. Dimethyl sulfate (75 g» 590 mmol) was added, dropwise, with s t i r r i n g , keeping the temperature between 20 and 30°. After s t i r r i n g overnight, the temperature was raised to 80° f o r 1 h. The pre c i p i t a t e d s a l t s were f i l t e r e d o f f , the f i l t r a t e evaporated to 250 ml and made neutral to litmus paper with sulphuric acid (18N). The solution was treated with absolute ethanol (250 ml) and f i l t e r e d . The f i l t r a t e was made acid to congo red paper with sulphuric acid (18N), the p r e c i p i t a t e d s a l t s removed, and the re s i d u a l s o l u t i o n concentrated to 200 ml. After d i l u t i o n with absolute ethanol (600 ml), the s a l t s which separated were f i l t e r e d and the ethanol solution evaporated to dryness. The s a l t f r a c t i o n s were washed out with acetone and then dried i n vacuo y i e l d i n g white c r y s t a l s of methylphenylarsinic acid (85 g, 90$). - 2 6 -Methylphenylarsinic acid ( 2 1 . 7 g, 1 0 9 mmol) with 3 8 . 3 g ( 5 8 0 mmol) of aqueous 5 0 $ hypophosphorous acid and 2 9 0 ml of absolute ethanol were refluxed f o r 6 h under nitrogen. The system r a p i d l y became murky. Upon cooling, the ethanol was removed from the suspension of white c r y s t a l s . The s o l i d residues were extracted from the acid layer with 3 0 0 ml of degassed petroleum ether (bp 6 5 - 1 1 0 ° ) . The extract was f i l t e r e d and cooled to - 2 0 ° , y i e l d i n g a i r - s e n s i t i v e white needles of 1 , 2-dimethyl-l, 2-diphenyldiarsine ( 1 0 g, 5&f°) > The nmr spectrum (CCl^ solution) showed two s i n g l e t s at 1.20 (CH^Marea 6 ) and I.30 (CH^Marea 6 ) , and a multiplet centred at 7 - 3 0 (CgH^)(area 2 0 ) . B. Tetramethyldiarsine Tetramethyldiarsine was prepared by the reduction of dimethylarsinic acid i n 2 M hydrochloric acid with hyphophosphorous 64-acid; the diarsine was used without further p u r i f i c a t i o n . C. Tetramethyldiphosphine Tetramethyldiphosphine was obtained v i a a sulphur 6 S 66 exchange between tetramethyldiphosphine disulphide -)' and tributylphosphine. °^ -27-4. Preparation of the Ligands A. Cis-2,3-Bis(methylphenylarsino)-1,1,1,4,4,4--Hexafluorobut-2-ene (L-L) 1,2-dimethyl-l,2-diphenyldiarsine (8 g, 24 mmol), dissolved i n 25 ml of petroleum ether (bp 30-60°) and excess hexa-fluoroacetone (14 g, 84 mmol) were sealed under vacuum i n a Pyrex tube and allowed to stand (with occasional shaking) f o r 4 h at 20°. The tube was then opened and hexafluorobutyne-2 (6 g, J6 mmol) was added. The tube contents were allowed to react at 20° f o r 5 days with periodic shaking. Excess v o l a t i l e s t a r t i n g materials and solvent were taken into the vacuum system leaving a viscous yellow l i q u i d (8 g, 67%) to which hexane (50 ml) was added u n t i l the solut i o n turned cloudy. Upon cooling i n dry i c e , white a i r - s t a b l e c r y s t a l s of the racemic isomer of cis-2,3-bis(methylphenyIarsino)-l,l,l,4,4,4-hexafluorobut-2-ene were i s o l a t e d (mp 79-81°). The nmr spectra (CCl^ solution) consisted of a s i n g l e t at 1.20 (CH-j), a multiplet centred at 7.40 (CgH^), and a si n g l e t at 53.2 (CF^). Anal. Calcd. f o r cj_8 H l 6 F 6 A s2 : c» ^3-6; H, 3.2. Found: C, 43.6; H, 3 .1. The solvent was removed under reduced pressure leaving a yellow a i r - s t a b l e l i q u i d which was warmed to 3^° at 0.1 mm to remove a small amount of impurity. The s u b s t a n t i a l l y pure meso isomer of cis-2,3-bis(methylphenylarsino)-!,!,1,4,4,4--28-hexafluorobut-2-ene remained. I t was not possible to d i s t i l l the product without decomposition. The nmr spectra (CCl^ solution) consisted of a broad s i n g l e t at 1.50 (CH^), a multiplet centred at 7.20 (C^H^) and a s i n g l e t at 53-0 (CF^). Traces of the trans-adduct (containing the meso and racemic diastereomers) were also present i n t h i s f r a c t i o n , as indicated by the presence of absorptions at 50.0 and 50.8 i n the 1 9 F spectrum. Anal. Calcd. f o r c 1 8 H i 6 F 6 A s 2 : °' H ' 3 , 2 • F°und: C, 43.5; H, 3.1. The i r spectrum of both diastereomers showed the following bands ( l i q u i d f i l m ) : 3071(w), 3 0 5 K w ) , 2955(w), 2923(m), 1565(m), I483(s), l 4 3 5 ( s ) , 1377(w), 1333(w), 1305(w), 1230(vs,br), l l 4 5 ( v s , b r ) , 1077(m), 1025(m), 995(m), 855(m), 837(m), 7 3 K s ) , 689(s), 645(m) cm"1.* B. Cis-2 ,3-Bis (dimethylarsino) -1,1,1,4-, 4,4-Hexa-fluorobut-2-ene 6 7 (L-L) Tetramethyldiarsine (14- g, 67 mmol) and excess hexa-fluoroacetone ( 3 0 g, 180 mmol) were sealed under vacuum i n a Pyrex tube and allowed to stand (with occasional shaking) f o r 2 h at 20°. The tube was opened and hexafluorobutyne-2 (18 g, 108 mmol) was added. After resealing the tube vs = very strong, s = strong, m = medium, w - weak, br = broad -29-th e contents were allowed to react at room temperature f o r 2 days. Excess v o l a t i l e s t a r t i n g materials were taken into the vacuum system leaving a yellow l i q u i d . The nmr spectra (CCl^ solution) showed a s i n g l e t at 1.32 (CH^) and a s i n g l e t at 53-2 (CF^). The i r spectrum showed the following hands ( l i q u i d f i l m ) : 2990(w), 2915(w), 1570(w), l425(m), I300(w), 1230(vs), 1175(sh,s), H52(vs), 1135(vs), 897(w), 867(w), 852(w), 652(m) cm"1. -30-5. Reactions of Cis-2,3-Bis(methylphenylarsino)-1,1,1,4,4,4-Hexafluorobut-2-ene (L-L) with T r a n s i t i o n Metal Carbonyls » A. Reactions of (L-L) with Iron Pentacarbonyl A number of reactions between iron pentacarbonyl and the meso and racemic forms of (L-L) are given i n tabular form i n Table I I . In a l l cases the crude reaction mixture was evaporated to dryness and the residue was chromatographed on F l o r i s i l (100-200 mesh) using nitrogen saturated solvents as eluents as indicated i n Table I I . A n a l y t i c a l and spectroscopic data f o r the products of a l l these reactions are l i s t e d i n Tables I I I , IV, and V. The following gives the detailed experimental conditions f o r a t y p i c a l reaction between ir o n pentacarbonyl and (L-L) . Iron pentacarbonyl (5 g> 25-5 mmol) and rac-(L-L) (1 g, 2.0 mmol) i n 20 ml of benzene were sealed i n an evacuated thick-walled Carius tube, and heated at 150° f o r 2 days. The f i n a l s o l u t i o n ( i n i t i a l l y yellow) was dark brown-red. The tube was opened and v o l a t i l e material removed under reduced pressure. The r e s u l t i n g dark o i l was dissolved i n a minimum of methylene chloride and chromatographed on F l o r i s i l . Petroleum ether (bp 30-60°) eluted a brown band which upon solvent removal and r e c r y s t a l l i z a t i o n (from petroleum ether) at dry ice temperature, yielded brown c r y s t a l s of rac-(L-L) Fe{C0)^ (0.19 g» 15$)i mp 142-143° (with decomposition). A 5% d i e t h y l ether, 95$ petroleum ether mixture eluted -31-an orange band which upon solvent removal and r e c r y s t a l l i z a t i o n from the same solvent mixture at dry ice temperature, afforded dark red-brown c r y s t a l s of rac-(L-L) Fe 2(C0)^ (0.55 g» 35$); mp 173-175°. ' B. Reactions of (L-L) with Group VI Metal Hexacarbonyls A l l reactions between (L-L)' and M(C0) 6 (M = Cr, Mo, W) were performed at 150° f o r the time indicated i n Table VI. A n a l y t i c a l , preparative, and spectroscopic data f o r the diastereomeric (L-L) M(C0)^ products are given i n Tables VI, VII, and VIII. The following experimental d e t a i l s are given f o r a t y p i c a l reaction between (L-L) and chromium hexacarbonyl. The hexacarbonyl (0.2 g, 0.91 mmol) and rac-(L-L) (0.5 g, 1.0 mmol) i n 15 ml of benzene were sealed i n an evacuated Carius tube and heated at 150° f o r 29 h. The f i n a l s o l u t i o n ( i n i t i a l l y pale yellow) was deep amber. A f t e r removal of suspended s o l i d material the solvent was evaporated under reduced pressure and the r e s u l t i n g o i l y residue r e c r y s t a l l i z e d from hexane at 0° y i e l d i n g amber c r y s t a l s of rac-(L-L)'cr(C0) i t (0.33 g, 55$); mp 148-14-9°. Table II i Reactions of Iron Pentacarbonyl with (L-L) No F e ( C 0 ) e (L-L) Conditions Products Yi e l d P u r i f i c a t i o n 5 g 25 mmol 5 g 25 mmol 5 g 25 mmol 5 g 25 mmol 5 g 25 mmol rac 1 g Uv i r r a d i a t i o n 2 i n benzene (25 ml) mmol f o r 3 days rac 1 g Pyrol y s i s i n 2 benzene (20 ml) at mmol 150° f o r 2 days rac 1 g Pyro l y s i s i n 2 benzene (20 ml) at mmol 150O f o r 3 days meso 1 g Uv i r r a d i a t i o n 2 i n benzene (25 ml) mmol f o r 3 days meso 1 g Pyrol y s i s i n 2 benzene (20 ml) at mmol 150° f o r 2 days rac-(L-L)'Fe(C0) 3 40 C (1) rac-(L-L)'Fe 2(C0) 6 10 c (3) rac-(L-L)'Fe(C0) 3 15 c (1) r a c - ( L - L ) ' F e 2 ( C 0 ) 6 35 c (3) F e 2 ( C 0 ) 6 [ A s ( C H 3 ) ( C 6 H 5 ) ] 2 10 c (1) r a c - ( L - L ) ' F e 2 ( C 0 ) 6 15 c (2) F e 2 ( C 0 ) 6 [ A s ( C H 3 ) ( C 6 H 5 ) ] 2 trace c (1) meso-(L-L)'Fe(C0) 3 25 c (2) F e 2 ( C 0 ) 6 [ A s ( C H 3 ) ( C 6 H 5 ) ] 2 10 c (1) meso-(L-L)'Fe«(C0)^ 15 c (2) Table II (Continued) No Fe(CO) 5 (L-L)' Conditions Products Yiel d $ * P u r i f i c a t i o n 6 5 g 25 mmol meso 1 g 2 mmol Pyro l y s i s i n benzene (20 ml) at 150° f o r 3 days F e 2 ( C 0 ) 6 [ A s ( C H 3 ) ( C 6 H 5 ) ] 2 * * meso-(L-L)'Fe o (C0)^ 35 15 C (1) C (2) C indicates chromatography i n F l o r i s i l . The arabic numeral indicates th? solvent required to elute the product: ( l ) i s 100$ petroleum ether (bp 30-60°), (2) i s 98$ petroleum ether, 2$ d i e t h y l ether, (3) i s 95$ petroleum ether, 5$ d i e t h y l ether. In each case a f t e r chromatographing, the solvent was removed and r e s u l t i n g s o l i d (or o i l ) r e c r y s t a l l i z e d at dry i c e temperature i n the same solvent mixture used f o r elution. This i s mainly the symmetric isomer with trace amounts of the asymmetric one. Table III i A n a l y t i c a l Data f o r Iron Carbonyl Complexes of (L-L) Analysis Compound Colour Mp(°C) Calcd. Found C H C H F e 2 ( C O ) 6 [ A s ( C H 3 ) ( C 6 H 5 ) ] 2 (symmetric) orange 162-164 39.20 2. 62 39-00 2 .81 F e 2 ( C O ) 6 [ A s ( C H 3 ) ( C 6 H 5 ) ] 2 (asymmetric) orange 93-95 39.20 2. 62 39.4-9 2 .75 rac-(L-L)'Fe(C0) 3 brown 142-14-3* 39.62 2. 52 39-39 2 • 51 meso-(L-L)'Fe(C0) o brown 117-120* 39.62 2. 52 39-33 2 .49 rac - ( L - L ) ' F e 2 ( C 0 ) 6 red-brown 173-175* 37.12 2. 06 37.39 2 • 32 meso-(L-L)'Fe 2(C0) 6 red-brown 144-146 37.12 2. 06 37.38 2 .20 With decomposition -35-Table IV Ir Spectra (2100-1900cm L) f o r Iron Carbonyl Complexes of (L-L)' Compound v ( C 0 ) ( c m - 1 ) * P e 2 ( C O ) 6 [ A s ( C H 3 ) ( C 6 H 5 ) ] 2 . (symmetric). 2052(s), 2009(vs), I979(vs), 1965(vs), 1955(m) F e 2 ( C O ) 6 [ A s ( C H 3 ) ( C 6 H 5 ) ] 2 (asymmetric) 2052(s), 2007(vs), 1977(vs) • 1965(vs), 1955(m) rac-(L-L)'Fe(CO) 3 2003(vs), 1937(s), I919(vs) meso-(L-L) Fe(CO)-^ 2003(vs), 1939(s), 1921(vs) r a c - ( L - L ) ' F e 2 ( C 0 ) 6 206Mm), 2023(s), 1999(m), 1985(m), 1971(w), 1959(w) meso-(L-L)'Fe^(CO)^ 2064(m), 2023(s), 1995(m), 1983(m), I967(w), 1955(w) * C6H12 s o l u t i o n -36-Table V Nmr Data f o r Iron Carbonyl Complexes of (L-L) Compound H 1 9 , F e 2 ( C O ) 6 [ A s ( C H 3 ) ( C 6 H 5 ) ] 2 (symmetric) F e 2 ( C O ) 6 [ A s ( C H 3 ) ( C 6 H 5 ) ] 2 (asymmetric) rac-(L-L) Fe(CO). meso-(L-L) Fe(CO). rac-(L-L) F e 2 ( C 0 ) 6 meso-(L-L) Fe 2(C0)^ Singlet at 1.93 (CH 3). M u l t i p l e t centred at 6.93 (C 6H 5) Singlets at .0.93 and 2.0 (CH^). M u l t i p l e t s centred at 6.93 and 7.4 (C 6H 5) Sin g l e t at 2.27 (CH 3). Singlet, at 7-50 (C 6H 5) Singlet at 2.23 (CH 3). Si n g l e t at 7.53 (C 6H 5) Singlets at 1.22 and 2.57 (CH 3). M u l t i p l e t s centred at 7-0, 7-5. and 7-9 (C 6H 5) Singlet at 2.57 (CH 3). M u l t i p l e t centred at 7-0 Singlet at 51.0 (CF 3) Singlet at 51.8 (CF 3) Quartets centred at 41.0 and 46.8 (CF 3) J(F,F) = 11.3 Hz Singlet at 44.5 (CF 3) ( C 6 H 5 ) CDC1 3 solution Table VI A n a l y t i c a l and Preparative Data f o r Diastereomeric Group VI (L-L)'M(COK Complexes Reaction Analysis Compound Colour Mp( C) Time Y i e l d Calcd. Found h % C H C H rac-(L-L) ' c r(CO)^ amber 148-14-9 29 60 40.00 2 .43 40.12 2 • 29 meso-(L-L) 'cr(CO)^ amber 158-161 25 55 4o.oo 2 .43 40.11 2 .44 rac-(L-L)'MO(CO)^ yellow 1*1-0-143 19 75 37.50 2 .28 37-21 2 .27 meso-(L-L)'MO(CO)^ yellow 164-166* 17 75 37.50 2 .28 37.49 2 .45 rac-(L-L) ' w(CO)^ yellow 156-158 47 90 33.33 2 .02 33.45 2 .00 meso-(L-L) 'w(CO)^ yellow I66-I69 4-6 90 33-33 2 .02 33.05 1 .95 With decomposition -38-Table VII Ir Spectra (2100-1900 cm"1) f o r Diastereomeric Group VI (L-L) M(C0)K Complexes Compound V (CO)(cm _ 1 )* rac-(L-L)'cr(CO)^ 2021(m), 1935(s), 1913(vs) meso-(L-L) Cr(CO)^ 2021(m), 1937(s), 1911(vs) rac-(L-L)'MO(CO)^ 2C40(m), 19^7(s), 1925(vs) meso-(L-L)'MO(CO)^ 2C40(m), 19^7(s), 1923(vs) rac-(L-L)'w(CO)^ 2036(m), 1935(s), 1913(vs) meso-(L-L)'w(CO)^ 2032(m), 1937(s), 1915(vs) ^6^12 s o l- u" T Jion -39-Table VIII f Nmr Data f o r Diastereomeric Group VI (L-L) M(CO),, Complexes Compound 1 H 19F rac-(L-L)'cr(CO)^ Singlet at 2.15 Singlet at 50 .6 (CH 3). Mu l t i p l e t (CF 3) centred at 7.40 meso-(L-L) 'Cr(CO)J!+ (C 6H 5) Singlet at 2.13 Singlet at 51 .4-(CH 3). Mu l t i p l e t (CF 3) centred at 7..40 rac-(L-L)'MO(CO)^ (C 6H 5) Singlet at 2.18 Singlet at 50 .8 (CH 3). M u l t i p l e t (CF ) centred at 7-4-0 meso-(L-L)'MO(CO)^ (C 6H 5) Singlet at 2.15 Singlet at 51 .0 (CH 3). M u l t i p l e t (CF ) centred at 7-4-0 rac-(L-L) 'wCCO)^ (C 6H 5) Singlet at 2.30 Singlet at 50 • 3 (CH 3). M u l t i p l e t (CF 3)' centred at 7-40 meso-(L-L) 'w(CO)^ (C 6H 5) Singlet at 2.28 Singlet at 50 • 3 (CH 3). Mu l t i p l e t (CF„) centred at 7-4-3 j (C 6H 5) CS 0 s o l u t i o n -40-C. Preparation of the Diastereomeric (L-L) MtCOV-Xg Complexes (M = Mo, W; X = Br, I) The (L-L) M(C0) i + complexes (M = Mo, W) i n degassed methylene chloride (25 ml) were treated slowly with an equimolar amount of the halogen (bromine, iodine) i n degassed methylene chloride (25 ml) under nitrogen, at 0° , with e f f i c i e n t s t i r r i n g to avoid l b c a l concentration of the halogen. The solu t i o n was then s t i r r e d f o r 3 h at room temperature and f i l t e r e d . Upon concentration of the methylene chloride at reduced pressure, addition of degassed hexane, and cooling to -20° the c r y s t a l l i n e 1 (L-L) M(C0)JX.^ complexes separated. They were washed with hexane and dried i n vacuo. A n a l y t i c a l , preparative, and spectroscopic data f o r the diastereomeric (L-L) M{C0)complexes are given i n Tables IX, X, and XI. It was found that a higher y i e l d of the t r i c a r b o n y l complexes could be obtained by doing the halogen addition at 0° , then warming the solution to room temperature rather than performing the entire reaction at room temperature. The l a t t e r method appeared to give the required complex as well as substantial amounts of other species probably r e s u l t i n g from the replacement of more than one carbonyl group by the halogen. Table IX A n a l y t i c a l and Preparative Data f o r Diastereomeric (L-L) M(CO) x2' Complexes (M = Mo, W; X = Br, I) C ompound Colour Y i e l d Calcd. C H Analyses X C Found H X rac-(L-L) Mo(C0) 3I 2  meso-(L-L) Mo(C0) 3I 2 rac-(L-L)'Mo(C0) 3Br 2  meso-(L-L) Mo(C0) 3Br 2 rac-(L-L) ' w(CO) 3I 2  meso-(L-L) ' w ^ C O ) ^ rac-(L-L) ' w(C0) 3Br 2 meso-(L-L) W(C0) 3Br 2 orange 75 27.09 1.72 27.3KD 27.10 1. 90 27.20(1) orange 75 27.09 1.72 27.3KD 27.40 1. 80 27.06(1) yellow 42 30.14- 1.91 19.14(Br) 30.42 2. 10 l8.95(Br) yellow 45 30.14- 1.91 19.l4-(Br) 30.25 2. 05 19.00(Br) orange 65 24-.76 1.57 24.95(1) 24-.65 1. 75 24-.70(1) orange 57 24.76 1.57 24.95(1) 24-. 97 1. 77 25.12(1) yellow 60 27.27 1.73 17.31(Br) 27.35 1. 85 17.20(Br) yellow 60 27.27 1.73 17.31(Br) 27.40 1. 90 17-10(Br) A l l complexes decomposed without melting above: 120°. -42-Table X I r Spectra (2100-1900 cm - 1) f o r Diastereomeric (L-L)'M(C0)^X Complexes (M = Mo, W; X = Br, I) Compound v(CO)(cm 1 ) * rac- (L-L)'MO(C0 ) 3I 2 2056(s), 1989(vs), I937(s) meso - ( L - L ) ' M O ( C O ) 3 I 2 2056(s), 199Kvs), 1937(s) rac- (L-L)'Mo(CO) 3Br 2 2076(s), 1989(vs), 1927(s) meso -(L-L)'Mo(C0) 3Br 2 2076(s), 1997(vs), 1933(s) rac- (L-L ) 'w ( C0) 3I 2 2048(s), 197Kvs), 1919(s) meso -(L - L ) ' w ( C O ) 3 I 2 2048(s), 1977(vs), 1923(s) rac- (L-L ) 'w(CO) 3Br 2 2068(s), 197^(vs), 1923(s) meso -(L-L ) 'w (C0) 3Br 2 2068(s), I971(vs), 1925(s) CH 0C1„ s o l u t i o n -43-Table XI Nmr Data f o r Diastereomeric (L-L)'M(CO)^X^ Complexes (M = Mo, W; X = Br, I ) Compound 1 * 19 F* rac-(L-L)'Mo(CO) 3I 2 Singlet at 2.64 (CH^). Singlet at 50 .4 Singlet at 7.55 (CgH^) (CF 3) meso-(L-L)'MoCCO^Ig Singlet at 2.87 (CH^). Singlet at 50 .8 M u l t i p l e t centred at (CF.) 7.40 (C 6H 5) j rac-(L-L)*Mo(CO) 3Br 2 Singlet at 2.43 (CH 3). Singlet at 51 .0 meso-(L-L)'MotCO^Br. Singlet at 7-58 (CgH^) (CF 3) Singlet at 2.63 (CrU). Singlet at 51. .2 M u l t i p l e t centred at (CF„) 7.40 (C 6H 5) j rac-(L-L)'w(C0) 3I 2 Singlet at 2.63 (CH^). Singlet at 50, ,8 meso-(L-L)'w(CO) 3I^ Singlet at 7-53 (CgH^) (CF 3) Singlet at 2.90 (CH.) Singlet at 51.2 M u l t i p l e t centred at (CF.) 7-38 (C 6H 5) j rac-(L-L)'w(CO) 3Br 2 Singlet at 2.50 (CH^). Singlet at 51. 2 meso-(L-L)'wtCO^Br. Singlet at 7-58 (CgH^) (CF 3) Singlet at 2.70 (CH^). Singlet at 51. 6 M u l t i p l e t centred at (CF.) 7-50 (C 6H 5) j CDC1. solut i o n -44-6. Reactions of Cis-2,3-Bis(dimethylarsino)-1,1,1 ,4,4,4-Hexafluorobut-2-ene (L-L) with T r a n s i t i o n Metal Carbonyls A. Reaction of (L-L) with T r i i r o n Dodecacarbonyl The d i t e r i a r y arsine (L-L) (1.1 g, 0.30 mmol) and t r i i r o n dodecacarbonyl (1.9 g» 0.38 mmol) i n acetone solu t i o n (20 ml) were i r r a d i a t e d with u l t r a v i o l e t l i g h t f o r 24 h. The solvent was removed under reduced pressure and chromatography of the s o l i d residue on F l o r i s i l gave two bands which were eluted with petroleum ether. The f i r s t band off the column gave a red-brown s o l i d i d e n t i f i e d as (L-L)Fe(C0) 3 (1.0 g, 66$). The mass spectrum showed a parent ion followed by loss of three carbonyl groups. The carbonyl i r spectrum (C^H^ 2 solution) consisted of three bands at 2001(s), 1933(s), 1917(vs) cm"1. Anal. Calcd. f o r G 1 1 H 1 2 A s 2 F 6 F e ° 3 ! C ' 2 5 ' 8 ; H ' 2 , 3 ' F, 22.3. Found: C, 25-8; H, 2.3; F, 22.4. The second band gave a yellow-red s o l i d of (L-L)Fe 2(C0)g (0.1 g, 5$)' The mass spectrum showed a parent ion followed by loss of s i x carbonyl groups. The carbonyl i r spectrum showed the following absorptions: 2062(m), 2024(s), 1996(m) 1986(m), I968(w), 1956(w) cm"1. Anal. Calcd. f o r c 1 4 H 1 2 A s 2 F 6 F e 2 ° 6 : c » 2 5 -8 ; H, 1.8. Found: C, 26.0; H, 1.7. -45-B. Reaction of (L-L) with Group VI Metal Hexacarbonyls The following general method was used f o r the preparation of a l l new (L-L)M(CO)^ complexes (M = Cr, Mo, W) from the reaction of (L-L) with the Group VI hexacarbonyls. A benzene solution (15-20 ml) containing a 1:1 mole r a t i o of ligand to hexacarbonyl was heated at 150° i n an evacuated Carius tube f o r 19-42 h. At the end of the reaction period the solution ( i n i t i a l l y pale yellow) was dark yellow (except f o r (L-L)Cr(CO)^ which was amber). The solvent was removed under reduced pressure and the r e s u l t i n g s o l i d residue chromatographed on F l o r i s i l . Petroleum ether eluted a yellow band which upon r e c r y s t a l l i z a t i o n from a methylene' chloride-hexane mixture afforded the (L-L)M(C0)i]_ complexes. A n a l y t i c a l , preparative, and spectroscopic data f o r the new complexes are l i s t e d i n Tables XII, XIII, and XIV. C. Reactions of (L-L)M(CO)^ and M(C0)g (M = Cr, Mo, W) with Excess (L-L) A number of reactions between M(C0)^ and the (L-L)M(CO)^ complexes (M = Cr, Mo, W) with (L-L) are given i n tabular form i n Table XV. A l l p y r o l y s i s reactions were performed i n evacuated Carius tubes; u l t r a v i o l e t i r r a d i a t i o n s (200W) were performed i n evacuated quartz tubes. In a l l cases the crude reaction mixture was evaporated to dryness and the residue was chromatographed on F l o r i s i l using nitrogen saturated solvents as indicated i n Table XV. A l l complexes were r e c r y s t a l l i z e d Table XII A n a l y t i c a l and Preparative Data f o r Group VI (L-L)M(CO)^ Complexes Compound Colour Mp(°C) " Reaction Time h Y i e l d * Analyses Calcd. Found C H C H (L-L).Cr(C0) 4 amber 138-140 27 82 26.87 "2.24 26.80 2. 30 (L-L)Mo(CO)^ yellow 141-143 19 80 24.83 2.07 25.08 2. 20 (L-L)W(CO)^ yellow 155-157 42 70 21.56 1.80 21.76 1. 95 - 4 7 -Table XIII I r Spectra (2100-1900 cm"1) f o r Group VI ( L - L ) M ( C 0 ) I ) > Complexes Compound V (C0)(cm~ 1 ) * (L-L)Cr(CO)^ 2020(m) , 1 9 3 K s ) , 1 9 1 1(vs) (L-L)Mo(CO)^ 2036(m), 1939(s), 1921(vs) (L-L)W(CO)^ 2036(m), 1 9 3 K s ) , 1 9 H ( v s ) * C 6 H 1 2 s o l u " t i ° n Table XIV Nmr Data f o r Group VI (L-L)M(COK Complexes Compound 1 * 19 F« * (L-L)Or(CO)^ Singlet at 1. 85 (CH 3) Singlet at 50. ,2 (CF 3) (L-L)Mo(CO)^ Singlet at 1. 85 (CH 3) Singlet at 50. ,6 (CF 3) (L-L)W(CO)^ Singlet at 1. 97 (CH 3) Singlet at 50. ,6 (C'F3) CS 0 solution -48-from a degassed methylene chloride-hexane mixture at - 2 0 . A n a l y t i c a l and spectroscopic data f o r the new complexes are l i s t e d i n Tables XVI, XVII, and XVIII. D. Preparation of the (L-L)M(C0) 3X 2 Complexes (M = Mo, W; X = Br, I) The new complexes were prepared by slow addition of the halogen (bromine, iodine) i n methylene chloride to a vigorously s t i r r e d methylene chloride s o l u t i o n of an equimolar amount of (L-L)M(CO)^ (M = Mo, W) under a nitrogen atmosphere. Halogen addition to the (L-L)W(CO)^ species was performed at 0 ° ; a f t e r the addition, the ice-water bath was removed and solu t i o n s t i r r e d f o r 1 h at room temperature. Iodination of the (L-L)Mo(CO)^ complex was performed e n t i r e l y at 0 ° and bromination e n t i r e l y at dry ice temperature. In a l l cases the s o l u t i o n was f i l t e r e d and concentrated. Addition of degassed hexane, and cooling to - 2 0 ° yielded the c r y s t a l l i n e ( L - L ) M ( C 0 ) 3 X 2 complexes. A n a l y t i c a l , preparative, and spectroscopic data f o r the new halogen derivatives are l i s t e d i n Tables XIX, XX, and XXI. Table XV Reactions of (L-L)M(CO)^ and M (C0) 6 (M = Cr, Mo, W) with Excess (L-L) No Carbonyl (L-L) Conditions Products •it- Y i e l d P u r i f i c a t i o n 1 C r ( C 0 ) 6 0.2 g 0.90 mmol 0.82 g P y r o l y s i s i n 2.2 benzene (15 ml) at mmol 195° f o r 22 h (L-L)Cr(CO)^ 70?o C (1) 2 (L-L)Cr(CO)^ 0.82 g 0.3 g . 0.56 2.2 mmol mmol 3 (L-L)Cr(CO)^ 4.5 g 1.2 g 12.0 2.2 mmol mmol 4 (L-L)Cr(CO)^ 2.3 g 0.6 g , 1.1 6 mmol mmol Pyroly s i s i n benzene (15 ml) at 190° f o r 46 h Uv i r r a d i a t i o n (450W) i n benzene (350 ml) f o r 85 min Uv i r r a d i a t i o n (450W) i n benzene (350 ml) f o r 20 min (L-L)Cr(CO)^ c i s - ( L - L ) 2 C r ( C 0 ) 2 (L-L)Cr(CO)^ c i s - ( L - L ) ? C r ( C 0 ) L fac-(L-L) fac-(L-L) b(L-L)™Cr(C0) (L-L)^Cr ( C 0 ) 3 (L-L)Cr (C0) i ( < c i s - ( L - L ) 2 C r ( C 0 ) 2 fac-(L-L)P(L-L)^Cr ( C 0 ) 3 f a c - ( L - L ) b ( L - L ) ? C r ( C 0 ) o 0.060 g C (1) trace C (2) trace . c (1) 32$ c (2) 3% c (4) trace c (3) 0.030 g c (1) 26$ c (2) 9% c (4) trace c (3) Table XV (Continued) No Carbonyl (L-L) Conditions Products Y i e l d P u r i f i c a t i o n 0.70 g Pyroly s i s i n (L-L)Mo(CO)^ 46$ c (1) 1.88 benzene (15 ml) at cis-(L-L) 2Mo(C0) 2 30$ C (2) mmol 175° f o r 23 h 0.24 g Pyroly s i s i n (L-L)Mo(C0)i[j< trace C (1) 0.62 benzene (15 ml) at cis-(L-L) 2Mo(C0) 2 36$ C (2) mmol 175° f o r 20 h 2.8 g Uv i r r a d i a t i o n (L-L)Mo(CO)^ trace C (1) 7. 60 (200W) i n benzene cis-(L-L) 2Mo(C0) 2 trace C (2) mmol (15 ml) f o r 266 h fac-(L-L)b(L-L) mMo(CO). 0 j 20$ C (4) 3-0 g Uv i r r a d i a t i o n cis-(L-L) 2Mo(C0) 2 26$ C (2) 8.0 (4-50W) i n benzene fac-(L-L) b(L-L)^Mo(C0) 3 19$ C (4) mmol (300 ml) f o r 65 fac-(L-L)b(L-L)1j?Mo(C0)„ 3$ C (3) min 4 g Uv i r r a d i a t i o n (L-L)Mo(CO)^ trace C (1) 10.8 (450W) i n benzene cis-(L-L) 2Mo(C0) 2 15$ C (2) mmol (350 ml) f o r 1.5 h fac-(L-L) b(L-L) mMo(C0) 3 33$ C (4) fac-(L-L) b(L-L) 1jMo(C0) 3 3$ C (3) 5 Mo(C0) 6 0.2 g O.76 mmol 6 (L-L)Mo(C0) 4 0.36 g 0.62 mmol 7 Mo(C0) 6 0.4 g 1.52 mmol 8 (L-L)Mo(CO)^ 1 g 1.7 mmol 9 Mo(C0) 6 0.6 g 2.3 mmol Table XV (Continued) No Carbonyl (L-L) Condi t i o n s Products Y i e l d P u r i f i c a t i o n 10 w(co), 0.4 g 1.1 mmol 1.0 g P y r o l y s i s i n 2.8 benzene (10 ml) at mmol 185° f o r 69 h (L-L)W(CO)^ 70$ C (1) 11 (L-L)W(CO)^ 0 . 1 2 0 . 2 g 0 . 3 0 0 . 3 0 mmol mmol P y r o l y s i s i n benzene (15 ml) at 195° f o r 66 h P y r o l y s i s i n benzene (15 ml) at 210° f o r 48 h (L-L)W(CO)^ c i s - ( L - L ) 2 W ( C 0 ) 2 0.1 g trac e Complete Decomposition C (1) C (2) 12 (L-L)W(C0) Z | > 1.1 g 0.4 g 2.9 0.6 mmol mmol Uv i r r a d i a t i o n ( 2 0 0 W ) i n benzene (15 ml) f o r 141 h (L-L)W(CO)^ 0.15 g fac-(L-L)b(L-L)>(C0)„ 17$ C C (1) (4) 13 w(co)6 0.6 g 1.7 mmol 2.7 g Uv i r r a d i a t i o n 7.3 • (450W) i n benzene mmol (350 ml) f o r 29 h (L-L)W(CO)^ cis-(L-L) ?W(C0) f a c - ( L - L ) ' f a c - ( L - L ) b ( L - L ) m W ( C 0 ) 3  b(L-L)!JW(C0) 3 9$ 2$ 20$ 6$ C C C C (1) (2) (4) (3) Table XV (Continued) No Carbonyl (L-L) Conditions * Products Y i e l d P u r i f i c a t i o n 14 (L-L)W(CO)Zj> 2 g Uv i r r a d i a t i o n (L-L)W(CO)^ trace c (1) 1 g 5.4 (4-50W) i n benzene cis-(L-L) 2W(C0) 2 10$ C (2) 1.5 mmol mmol (300 ml) f o r 6.5 h fac-(L-L) b(L-L) mW(CO) 3 13$ C (4) fac-(L-L) b(L-L)mw(CO) 3 2$ C (3) Not including excess ligand which was recovered i n each experiment. Refluxing f a c - ( L - L ) _ (L-L)Jvio(C0) 3 with a 25 molar excess of ( L - L ) i n benzene f o r 16 h gave ( L - L ) 2 [ A s ( C H 3 ) 2 ] 2 -Mo 2(C0)^ which was eluted by a 50$ petroleum ether, 50$ d i e t h y l ether solution. I r r a d i a t i o n (450W) of c i s - ( L - L ) 2 C r ( C 0 ) 2 f o r 85 min gave t r a n s - ( L - L ) 2 C r ( C O ) 2 and i r r a d i a t i o n (450W) of C J L S - ( L - L ) 2 M O ( C 0 ) 2 f o r 3«5 h gave t r a n s - ( L - L ) 2 M o ( C 0 ) 2 . In each case, the trans-isomer was r e c r y s t a l l i z e d from a methylene chloride-hexane mixture at -20°. C i s - ( L - L ) p W ( C O ) 2 did not isomerize. ( L - L ) B denotes bidentate ligand; ( L - L ) ™ denotes monodentate ligand i n a c i s configuration and ( L - L ) ™ monodentate ligand i n a trans configuration. C indicates chromatography on F l o r i s i l . The arabic numeral indicates the solvent required to elute the product: (1) i s 99$ petroleum ether (bp 30-60°), 1$ d i e t h y l ether, (2) i s 98$ petroleum ether, 2$ d i e t h y l ether, (3) i s 95$ petroleum ether, 5$ d i e t h y l ether, (4) i s 90$ petroleum ether, 10$ d i e t h y l ether. Table XVI A n a l y t i c a l Data f o r ( L - L ) Derivatives of M(C0) A (M = Cr, Mo, W) Compound Colour Mp(°C) Analyses Calcd. Found C H C H f a c - ( L - L ) B ( L - L ) m C r ( C O ) 3 f a c - ( L - L ) B ( L - L ) m C r ( C O ) 3 c i s - ( L - L ) 2 C r ( C 0 ) 2 t r a n s - ( L - L ) 2 C r ( C O ) 2 f a c - ( L - L ) B ( L - L ) m M o ( C 0 ) 3 f a c - ( L - L ) B ( L - L ) m M o ( C 0 ) 3 c i s - ( L - L ) 2 M o ( C 0 ) 2 trans-(L-L) 2Mo(CO) 2 ( L - L ) 2 [ A S ( C H 3 ) 2 ] 2 M O 2 ( C O ) ^ f a c - ( L - L ) B ( L - L ) m W ( C 0 ) 3 f a c - ( L - L ) B ( L - L ) m W ( C 0 ) 3 c i s - ( L - L ) 2 W ( C 0 ) 2 pale orange 150- 155 25.91 2.73 25.98 2. 91 orange 115-•118 25.91 2.73 25.60 2. 79 brown-red 168-•170 . 25.35 2.82 25.50 3- 00 brown-red l4 l -•14-3 •170 25.35 2.82 25.21 3. 02 yellow 167- 24.67 2.60 24.45 2. 72 orange 118-•120 24.67 2.60 24.66 2. 81 orange 160-•162 24.11 2.68 24.33 2. 76 orange 152-•154 2'4.11 2.68 24.28 2. 86 yellow 116- 118 •170 22.90 2.86 23.26 3. 00 yellow 168- 22.53 2.37 22.30 2. 31 orange 136- 137 22.53 2.37 22.43 2. 55 red-orange 177- 179 21.95 2.44 21.70 2. 61 * Complex melted with decomposition. -54-Table XVII I r Spectra (2000-1800 cm - 1) f o r (L-L) Derivatives of M(C0) (M = Cr, Mo, W) Compound v(C0)(cm~ 1) f a c - ( L - L ) b ( L - L ) ^ C r ( C 0 ) 3 1 9 5 3(vs), 1 8 7 3 ( s ) , 1 8 6 3 ( s) fac-(L-L) b(L-L)!JCr(C0) 3 1953(vs), I 8 7 3 ( s ) , 1 8 6 3 ( s) c i s - ( L - L ) 2 C r ( C 0 ) 2 I 8 8 3 ( v s ) , 1 8 2 9(s) trans-(L-L)^Cr(CO)„ 1 8 2 9 fac-(L-L) b(L-L)^Mo(C0) 3 1 9 6 3(vs), 1 8 8 5 ( B ) , 1 8 7 3 ( s) fac-(L-L) b(L-L)!jMo(C0) 3 1 9 6 3(vs), 1 8 8 5 ( s ) , 1 8 7 3 ( s) c i s - ( L - L ) 2 M o ( C 0 ) 2 I 8 9 9 ( v s ) , 1845(s) trans-(L-L)^Mo(CO)^ 1845 ( L - L ) 2 [ A s ( C H 3 ) 2 ] ? M o 2 ( C 0 ) ^ 1 9 6 3 ( s ) , I 8 8 l ( s , br) f a c - ( L - L ) b ( L - L ) m W ( C 0 ) 3 1959(vs), I 8 7 9 ( s ) , 1867 ( s) fac-(L-L) b(L-L)!Jw(C0) 3 1 9 5 9(vs), I879(s), 1867 ( c i s - ( L - L ) 2 W ( C 0 ) 2 I 8 9 0 ( v s ) , 1839(s) C/-H, 0 s o l u t i o n -55-Table XVIII Nmr Data f o r (L-L) Derivatives of M{CO), (M = Cr, Mo, W) Compound 1 * 19 ** F fac-(L-L) b(L-L) mCr(CO)„ f a c - ( L - L ) b ( L - L ) I J C r ( C O ) 3 c i s - ( L - L ) 2 C r ( C 0 ) 2 trans-(L-L) 2Cr(CO) 2 fac-(L-L) l 3(L-L) i nMo(CO)„ fac-(L-L)°(L-L)™Mo(C0) Singlets at 1.33. 1.68, and 1.80 (CH 3) Singlets at 1.31, 1.70, and 1.82 (CF 3) Singlet at 52.0 Quartets centred at 53-6 and 5 .^6 (CF^) J(F,F) = 12.0 Hz (CH 3) Singlets at 1.30, 1.70, 1.82, and 1.88 (CH 3) (CF 3). Singlet at 51-6 Quartets centred at 50.4 and 52.0 (CF 3) J(F,F) = 2.2 Hz Singlet at 50.6 (CF 3) Singlet at 1.83 Singlet at 49.8 (CH 3) Singlets at 1.33, 1.70, and 1.82 (CH 3) Singlets at 1.30, 1.68, and 1.80 (CH 3) (CF 3) Singlet at 50.8 Quartets centred at 52.9 and 53.0 (CF 3) J(F,F) = 11.3 Hz (CF 3). Singlet at 50.2 (CF 3). Quartets centred at 49.2 and 50.3 (CF ) J(F,F) = 2.3 Hz -56-> Table XVIII (Continued) Compound 1 * 19F** cis-(L-L) 2Mo(CO) 2 Singlets at 1.37, Singlet at 50.6 1.70, 1.83 and (CF 3) 1.90 (CH 3) trans-(L-L) 0Mo( CO) Singlet at 1 .87 Singlet at 49.6 (CH 3) (CF 3) (L-L) 2[As(CH 3) 2] 2Mo 2 (C0) i | / Singlets at 1.67 Singlet at 50.8 and 1.93 (CH : 3 > (CF 3) f a c - ( L - L ) b ( L - L ) m W ( C 0 ) 3 Singlets at 1.33, Singlet at 50.8 1.77, 1-83, and (CF 3). Quartets 1.93 (CH ) centred at 52.7 and 53-0 (CF„) J(F,F) = = 13-5 Hz fac-(L-L) b(L-L) mW(C0) Singlets at 1.27, Singlet (br) at 1.72, 1.77, and 50.8 (CF ). 1.90 (CHo) Quartet centred at 49.6 (CF 3) J(F,F) = = 2.2 Hz cis-(L-L) 2W(C0) 2 Singlets at 1.43, Singlet at 50.2 1.80, 1.97, and (CF ) 2.05 (CH 3) CDC10 s o l u t i o n CH2C12 s o l u t i o n Table XIX A n a l y t i c a l and Preparative Data f o r (L-L)M(C0) 3X 2 Complexes* (M = Mo, W; X = Br, I) Analyses Compound Colour Y i e l d Calcd. Found C H X C H X (L-L)Mo(CO) 3I 2 orange 70 16.38 1.49 3 1 . 5 K D 16.20 1.61 31.28(1) (L-L)Mo(CO) 3Br 2 yellow 73 18.54 I.69 22.47(Br) 18.62 1.71 22.35(Br) (L-L)W(CO) I 2 orange 72 14.76 1.35 28.41(1) 14.64 1.21 28.25(1) (L-L)W(C0) 3Br 2 yellow 50 16.50 1.50 20.00(Br) 16.54 1.53 20.05(Br) A l l complexes decomposed without melting above 120°. -58-Table XX I r Spectra (2100-1900 cm - 1) f o r (L-L)M(CO) X Complexes ( M = Mo, W; X = Br, I) Compound v(C0)(cm" 1 )* (L-L)Mo(C0) 3I 2 2056( s ) , 1985(vs), 1927(£ 0 (L-L)Mo(C0) 3Br 2 2076( s), 1993(vs), I925(s) (L-L)W(C0) 3I 2 2052( s), 1971(vs), 19170 3) (L-L)W(C0) 3Br 2 2068( s ) , 1977(vs), 19H(£ 0 CHgClg solut i o n Table XXI Nmr Data f o r (L-L)M(C0) 3X 2 Complexes (M = Mo, W; X = Br, I) C ompound * 19F (L-L)Mo(C0) 3I 2 Singlet at 2 •17 (CH 3) Singlet at 51 .1 (CF 3) (L-L)Mo(C0) 3Br 2 Singlet at 2, .05 (CH 3) Singlet at 52 .6 (CF 3) (L-L)W(CO) I 2 Singlet at 2, .23 (CH 3) Singlet at 52 .k (CF 3) (L-L)W(C0) 3Br 2 Singlet at 2, ,10 (CH 3) Singlet at 53 .2 (CF 3) CDC1„ solut i o n -59-E. Preparation of the (L-L)LMo(C0) 2Br 2 Complexes (L = a Monodentate Ligand) The following general procedure represents the method used to synthesize the (L-L)LMo(C0) 2Br 2 complexes. The dicarbonyl complexes were prepared by the addition of ' L to an equimolar amount of (L-L)Mo(C0) 3Br 2 i n methylene chloride (5 ml) at room temperature under a nitrogen atmosphere. The orange solut i o n was f i l t e r e d and concentrated under a reduced pressure. Addition of degassed hexane, and cooling to -20° afforded the c r y s t a l l i n e (L-L)LMp(C0) 2Br 2 complexes. A n a l y t i c a l , preparative, and spectroscopic data f o r the new "mixed" seven-coordinate species are l i s t e d i n Tables XXII, XXIII, and XXIV. F. Preparation of the (L-L)L 2Mo(C0)Br 2 Complexes A l l reactions between excess L and (L-L)Mo(CCO^Brg were car r i e d out i n r e f l u x i n g benzene (for the time indicated i n Table XXV) under a nitrogen atmosphere, except f o r ( L - L ) 2 ~ Mo(C0)Br 2 which was synthesized by warming a benzene so l u t i o n (50°) of ( L - L ) b ( L - L ) m M o ( C 0 ) 2 B r 2 f o r 30 min. A n a l y t i c a l , preparative, and spectroscopic data f o r the new (L-L)L 2Mo(C0)Br 2 complexes are given i n Tables XXV, XXVI, and XXVII. Attempts to produce other complexes of the type * In the general formula L i s a monodentate ligand; however, the formula also applies to complexes where L 0 i s bidentate. Table XXII A n a l y t i c a l and Preparative Data f o r (L-L)LMo(CO) 9Br c > Complexes Analyses Compound Colour Y i e l d Calcd. Found $ C H Br C H Br (L-L) b(L-L) mMo(CO)„Br ** (L-L)(C 5H 5N)Mo(C0) 2Br 2 pale yellow 60 20.46 2. 27 15.15 20.50 2. 40 14. 87 yellow 60 23.59 2. 23 23.52 2. 42 (L-L)[P(0CH 2CH_) 3]Mo(C 0 ) 2 B r 2 (L-L)[p(C 6H 5) 3JMo(CO) 2Br 2 yellow 59 22.59 3. 18 18.82 22.76 3- 40 19. 10 orange 65 35-52 2. 85 16.91 35-35 2. 73 16. 70 (L-L)[P(CH 3)(C 6H 5) 2]Mo(CO) 2Br 2 yellow 54 31.22 2. 83 18.09 31.40 3- 06 17. 87 (L-L)[P(CH 3) 2(C 6H 5)]Mo(CO) 2Br 2 yellow 58 26.28 2. 80 19.46 26.34 2. 88 19. 14 (L-L)[P(0CH 3) 3]Mo(C0) 2Br 2 yellow 59 19.31 2. 60 19.80 19.21 2. 70 19. 60 (L-L)[P(OCH 3) 2(C 6H 5)]Mo(CO) 2Br 2 yellow 56 25.29 2. 69 18.74 25.44 2. 70 18. 46 A l l complexes decomposed without melting above 120°. (L-L) designates (CH.J 2As(CF.JC = C ( C F j A s ( C H J 2 acting as a bidentate ligand and ( L - L ) b the same ligand acting i n a monodentate^manner. Analysis f o r $N gave 1.82 (Calcd. 1.83$). -61-Table XXIII I r Spectra (2000-1800 cm ) f o r (L-L)LMo(C0) 2Br 2 Complexes Compound v(C0)(cm - 1)* (L-L) '(L-L) mMo(C0) 2Br 2 (L-L)(C 5H 5N)Mo(C0) 2Br 2 (L-L)[P(OCHgCH^) 3]Mo(CO) 2Br 2 (L-L)[P(C 6H 5) 3]Mo(CO) 2Br 2 (L-L)[P(CH 3)(C 6H 5) 2]Mo(C0) 2Br 2 (L-L)[P(CH 3) 2(C 6H 5)]Mo(C0) 2Br 2 (L-L)[P(0CH 3) 3]Mo(C0) 2Br 2 (L-L)[p(0CH 3) 2(C 6H 5)]Mo(C0) 2Br 2 198l(vs), 1957(vs), 1959(vs), 195l(vs), 195Kvs), 195Kvs), 1965(vs), 1957(vs), 1913(s) I883(s) 1879(s) I869(s) I 8 6 9(s) I 8 6 7(s) I 8 8 3(s) 1875(s) * CH 0C1 0 s o l u t i o n Table XXIV Nmr Data f o r (L-LjLlVMCO), Complexes Compound 1 * 19 ** x y F (L-L) b(L-L) mMo(C0) 2Br 2 (L-L)(C 5H 5N)Mo(CO) 2Br 2 (L-L)[P(0CH 2CH 3) 3]Mo(C 0 ) 9 B r 2^2 (L-L)[P(C 6H 5) 3]Mo(C0) 2Br 2 (L-L)[P(CH 3)(C 6H 5) 2]Mo(C0) 2Br 2 (P-0CH2CH^) J(H,H) = 7.0 Hz. Singlets at 2.47 and 2.25 (As-CH 3) Singlet at 2.08 (As-CH 3). Mul t i p l e t s centred at 7.47, 7-82, and 9-02 (C^H^N) Singlet at 1.98 (As-CH 3). T r i p l e t centred at 1.33 Pentet centred at 4.25 (P-0CH2CH3) J(H,H) = 7-0 Hz J(H,PT~= 7-0 Hz Singlet at 1.87 (As-CH^). Multipl e t s centred at 7.40 and 7.83 (P-CgH^) Singlet at 1.70 (As-CH^). Doublet centred at 2.48 (P-CH3) J(H,P) = 10.0 Hz. Singlet at 51.2 (CF^) Singlet at 51.2 (CF^) Singlet at 51.6 (CF 3) Singlet at 51-4 (CF^) Singlet at 51.4 (CF 3) Table XXIV (Continued) C ompound 1 * 19 F** ( L - L ) [ P ( C H 3 ) 2 ( C 6 H 5 ) ] M o ( C 0 ) 2 B r 2 (L-L)[P(OCH 3) 3]Mo(CO) 2Br 2 (L-L)[P(0CH 3) 2(C 6H 5)]Mo(C0) 2Br 2 M u l t i p l e t s centred at 7 • 50 and 7-80 (P-CgH^) Singlet at 1.83 (As-CH^). Doublet centred at 2.12 (P-CH3) J(H,P) = 11.0 Hz. Multiple t s centred at 7.43 and 7-80 (P-CgH^) Singlet at I . 9 8 (As-CH^). Doublet centred at 3-88 (P-0CH3) J(H,P) = 11.2 Hz Singlet at 1.85 (As-CH^). Doublet centred at 3«80 (P-0CH3) J(H,P) = 11.5 Hz. Multiple t s centred at 7.47 and 7-80 (P-CgH^) Singlet at 51.4 (CF^) Singlet at 51-2 (CF^) Singlet at 51.6 (CF^) * C D C 1 3 s o l u t i o n ** C H 2 C 1 2 s o l u t i o n -64-(L-L)L 2Mo(C0)Br 2 f a i l e d f o r ligands such as triphenylphosphine, pyridine, trichlorophosphine, trifluorophosphine, methyl-diphenylphosphine, methyl diphenylphosphinite, bis(diphenyl-phosphino)methane, and bis(diphenylphosphino)ethane. The following experimental d e t a i l s are given f o r a t y p i c a l ! reaction between (L-L)Mo(C0) 3Br 2 and excess trimethylphosphite. (L-L)Mo(C0),jBr 2 (0.30 g, 0.4l mmol) and trimethylphosphite (0.120 g, O.96 mmol) i n dry, degassed benzene (15 ml) were.. refluxed under nitrogen f o r 75 min. The i r spectrum of the solution indicated complete reaction of (L-L)Mo(C0) 3Br 2. The deep red-orange solu t i o n ( i n i t i a l l y orange) was f i l t e r e d and the benzene removed under reduced pressure. R e c r y s t a l l i z a t i o n of the red o i l from a degassed methylene chloride-hexane mixture at -20° afforded orange plates of (L-L)[P(0CH 3) 3] 2Mo(C0)Br, (0.24 g, 63$); mp 150° (decomposes). Table XXV A n a l y t i c a l and Preparative Data f o r (L-L)L pMo(C0)Br ? Complexes Reaction Analyses Compound time Y i e l d Calcd. Found h % C H Br C H Br (L-L) 2Mo(C0)Br 2 0.5 60 19.84 2. 34 15. 56 19. 87 2. • 56 15. 28 (L-L)[P(0CH 2CH„) 3] 2Mo(C0)Br 2 14 72 25-51 4. 25 16. 19 25. 48 4, .10 15. 86 (L-L)[P(0CH 3) 3J 2Mo(CO)Br 2 1.25 63 19.91 3. 32 17. 55 19. 93 3. .61 17. 70 (L-L)[P(OCH 3) 2(C 6H 5)] 2Mo(CO)Br 2 24 60 30.12 3- 41 16. 06 30. 23 3. • 50 15. 80 (L-L)[P(CH 3) 2(C 6H 5)] 2Mo(CO)Br 2 24 51 32.19 3. 65 17. 15 32. 47 3-• 76 17. 00 A l l complexes decomposed without melting above 120°. (L-L) 2Mo(C0)Br 2 was brown and a l l other complexes were orange. -66-Table XXVI I r Spectra (1900-1700 cm - 1) f o r (L-L)L 2Mo(C0)Br 2 Complexes Compound v(CO)(cm ) (L-L) 2Mo(C0)Br 2 l 8 2 9 (L-L)[P(OCH 2CH ) 3] 2Mo(C0)Br 2 1841 (L-L)[P(0CH 3) 3J 2Mo(C0)Br 2 18^3 (L-L)[P(OCH 3) 2(C 6H 5)] 2Mo(CO)Br 2 1829 (L-L)[P(CH 3) 2(C 6H 5)] 2Mo(CO)Br 2 1792 CH 0C1 0 s o l u t i o n Table XXVII Nmr Data f o r (L-L)L 2Mo(CO)Br 2 Complexes Compound 1 * (L-L) 2Mo(C0)Br 2 (L-L)[P(0CH 2CH 3) 3] 2Mo(C0)Br, (L-L)[P(0CH 3) 3] 2Mo(C0)Br 2 (L-L)[p(0CH 3) 2(C 6H 5)] 2Mo(C0)Br 2 Singlet at I . 9 8 (As-CH 3) Singlets at 2.07 and I . 5 0 (As-CH^). T r i p l e t centred at 1.28 (P-OCHgCH^). M u l t i p l e t centred at 4 . 2 5 (P-0CH2CH3) (see Chapter V f o r coupling constants) Singlets at 2.08 and I . 5 0 (As-CH^). Intermediate pattern centred at 3 » 9 0 (P-0CH3) |j(H,P) + j'(H,p')l = 10.0 Hz Singlets at 1.88 and I . 5 3 (As-CH^). Intermediate pattern centred at 3 - 4 4 (P-0CH3) |J(H,P) + j'(H,p')| = 10.5 Hz and 3 - 5 9 (P-0CH3) |J(H,P) + j'(H,p')| = 10.0 Hz. Multip l e t s centred at 7 . 3 7 and 7 . 7 0 (P-CgH^) Singlet at 5 0 . 8 (CF^) Singlet at 5 2 . 4 (CF^) Singlet at 5 2 . 2 (CF^) Singlet at 5 2 . 4 (CF^) Table XXVII (Continued) Compound •LH F ( L - L)[P(CH 3) 2(C 6H^)] 2Mo(CO)Br 2 Quartets centred at 2.32 (As-CH^) Quartets centred at J(H,F) = 2.5 Hz and 0.907 (As-CH 3) 51.4 and 53-2 (CF^) J(H,F) = 2.0 Hz. Singlet at 1.00 J(F,F) = 15.0 Hz (As-CH-j). Doublets centred at 2.07 (P-CH 3) J(H,P) = 9.75 Hz, 1.85 (P-CH3) J(H,P) = 8.25 Hz, 1.27 (P-CH3) J(H,P) = 7.75 Hz, and 0.912 (P-CH^) J(H,P) = 8.75 Hz. Multip l e t s centred at 7-12 and 7-85 (P-CgH^) * Spectra of a l l complexes obtained from CDC1 3 solution except f o r the spectrum of ( L - L)[P(CH 3) 2(C^H^)] 2Mo(C0)Br 2 which was obtained from C^D^ solution. Intermediate pattern refers to a broad c e n t r a l resonance l y i n g between a 1:1 doublet. |J(H,P) + J (H,P )|= the separation of the 1:1 doublet. ** C H 2 C 1 2 s o l u t i o n -69-G. Reaction of (L-L) with Dimanganese Decacarbonyl  And Dirhenium Decacarbonyl A number of d i f f e r e n t reactions (photolytic and thermal) between (L-L) and Group VII metal carbonyls were attempted. I t was found that the reaction of (L-L) with dimanganese decacar-bonyl gave a d i f f e r e n t product from that formed i n the reaction of (L-L) with dirhenium decacarbonyl. i . Reaction of (L-L) with Dimanganese Decacarbonyl Dimanganese decacarbonyl (0.6 g, 1.6 mmol) and (L-L) (2.2 g, 5-95 mmol) i n 15 ml of degassed toluene were refluxed under an atmosphere of nitrogen f o r 100 min. The reaction was monitored by observing the disappearance of the dimanganese decacarbonyl. The f i n a l s o l u t i o n was dark brown-red ( i n i t i a l l y yellow). The toluene was removed under reduced pressure and the brown ta r r y o i l chromatographed on F l o r i s i l under nitrogen. A 0-2$ d i e t h y l ether, 100-98$ petroleum ether mixture eluted a yellow band which afforded yellow c r y s t a l s . R e c r y s t a l l i z a t i o n from a methylene chloride-hexane mixture at -20° gave yellow c r y s t a l s of formula C^H^gAs^F^O^Mng (0.1 g, 9$); mp 190° (decomposes); sublimes at 105° (0.1 mm). The mass spectrum gave a parent ion peak followed by a peak due to the loss of three carbonyl and a peak due to the loss of s i x carbonyl groups. The i r spectrum i n the carbonyl region (CgH-^ solution) showed the following absorptions: 2036(m), 2009(vs), 1977(m), 1949(s), 194l(w), 1933(m) cm"1. Carbon-fluorine bands -70-(CCl^ solution) were seen at 1277(sh), 1269(s), 1195(s), 1131(s), 1093(s) cm - 1. The Hi nmr spectrum (C^H^ solution) showed s i n g l e t s at 1-357, 1-302, 1.252, 1.112 (CH^) and doublets centred at 1.272 (CH 3) J(H,F) = 2.0 Hz and 1.04-7 (CH^) J(H,F) = 6.0 Hz. The 1 D /F nmr spectrum (CH^Clg.solution) consisted of a C-CF^ doublet centred at 4-2.5 JCCF^.F) = 26 Hz, a broad C-F doublet centred at 60.86 J(F,F) = 121 Hz, and another C-F doublet of quartets centred at 67.78 J(H,F) = 121 Hz, JtCF^.F) = 26 Hz. Anal. Calcd. f o r C^H^As^FgO^Mng: C, 26.09; H, 2.4-4-; Mn, 14-.95; mol wt 736. Found: C, 26.10; H, 2.65; Mn, 15-10; mol wt 736 (mass spec). The i d e n t i c a l complex was also obtained using the following reaction conditions i n which a three to four molar excess of ligand was employed: ( l ) r e f l u x i n g i n benzene f o r 22 h (8$) (2) p y r o l y s i s i n benzene at 110° f o r 3-5 h i n a thick-walled Carius tube (23$) (3) u l t r a v i o l e t i r r a d i a t i o n (200W) i n benzene f o r 73 h (2$). U l t r a v i o l e t i r r a d i a t i o n using the 4-50W lamp prdduced no complex as complete decomposition occurred. i i . Reaction of (L-L) with Dirhenium Decacarbonyl Dirhenium decacarbonyl ( l g , 1.5 mmol) and (L-L) (l .7g , 4.5 mmol) i n 375 ml of degassed benzene were i r r a d i a t e d with the 4-50W lamp f o r 85 min. The reaction was monitored by observing the disappearance of the dirhenium decacarbonyl. The f i n a l solution was dark orange ( i n i t i a l l y c o l o u r l e s s ) . The benzene was removed under reduced pressure and the red o i l -71-chromatographed on F l o r i s i l under nitrogen. Petroleum ether eluted a pale yellow band of unreacted ligand (0.5 g)• A 2-10$ d i e t h y l ether, 98-90$ petroleum ether mixture eluted an orange band which afforded o i l y orange c r y s t a l s . Recrystal-l i z a t i o n from a methylene chloride-hexane mixture at -20° gave dark orange a i r - s t a b l e c r y s t a l s of formula C^^HgAsF^O^Re (0.4 g, 22$); mp 151-1520 (sealed evacuated c a p i l l a r y ) . The mass spectrum showed peaks due to the parent ion followed by loss of four carbonyl groups. The i r spectrum (CgH-j^ solution) gave carbonyl frequencies at 2100(m), 202l(s), 1995(s,br), 198l(vs) cm"1. The XH nmr spectrum (CDCl^ solution) showed a s i n g l e t at 2.13 (shoulder on the low f i e l d side at 100 MHz). The 1 9 F nmr spectrum (CH^Clg solution) consisted of quartets centred at 53.2 and 59-1 (CF^) J(F,F) = 12.4 Hz. Anal. Calcd. f o r C ^ H g A s F ^ R e : C, 22.18; H, 1.34; F, 19-12; mol wt 596. Found: C, 22.02; H, 1.10; F, 18.90; mol wt (mass spec) 596. Reaction between dirhenium decacarbonyl and excess (L-L) i n r e f l u x i n g toluene or xylene resulted i n complete decomposition as no stable complexes were i s o l a t e d . -72-7. R e a c t i o n s o f T e t r a m e t h y l d i a r s i n e w i t h I r o n P e n t a c a r b o n y l  and Dimanganese D e c a c a r b o n y l A. T e t r a m e t h y l d i a r s i n e and I r o n P e n t a c a r b o n y l T e t r a m e t h y l d i a r s i n e and e x c e s s i r o n p e n t a c a r b o n y l i n benzene were h e a t e d a t 150° f o r 19 h i n a s e a l e d e v a c u a t e d C a r i u s t u b e . Chromatography on F l o r i s i l u s i n g benzene as t h e e l u t i n g s o l v e n t and r e c r y s t a l l i z a t i o n f r o m a benzene-heptane m i x t u r e a t - 2 0 ° gave dark r e d - o r a n g e c r y s t a l s o f F e 2 ( C 0 ) £ -[ A s ( C H 3 ) 2 ] 2 . The nmr spectrum, i r spectrum, and mp were i d e n t i c a l w i t h t h o s e o f a u t h e n t i c F e 2 ( C O ) 6 [ A s ( C H 3 ) 2 ] 2 . 0 B. T e t r a m e t h y l d i a r s i n e and Dimanganese D e c a c a r b o n y l An e q u i m o l a r amount o f dimanganese d e c a c a r b o n y l and t e t r a m e t h y l d i a r s i n e i n t o l u e n e (30 ml) were r e f l u x e d f o r 20 h under an atmosphere o f n i t r o g e n . Chromatography on F l o r i s i l u s i n g p e t r o l e u m e t h e r and r e c r y s t a l l i z a t i o n f r o m a methylene c h l o r i d e - h e x a n e m i x t u r e a f f o r d e d y e l l o w c r y s t a l s o f M n 2 ( C 0 ) 8 [ A s ( C H 3 ) 2 ] 2 . S p e c t r o s c o p i c p r o p e r t i e s were i n agreement w i t h t h o s e of a u t h e n t i c M n 2 ( C 0 ) 8 [ A s ( C H 3 ) 2 ] 2 . 6 9 -73-8. Reaction of Tetramethyldiphosphine with Iron Pentacarbonyl Tetramethyldiphosphine and excess i r o n pentacarbonyl i n benzene were heated at 14-0° f o r 24- h i n a sealed evacuated Carius tube. Chromatography on F l o r i s i l using petroleum ether and r e c r y s t a l l i z a t i o n from a methylene chloride-hexane mixture afforded orange c r y s t a l s of F e 2 ( C 0 ) ^ [ P ( C H 3 ) 2 ] 2 whose "4l nmr spectrum, i r spectrum, and mp were i n agreement with the l i t e r a t u r e v a l u e s . 6 8 9. Reactions of 1,2-Dimethyl-l,2-Diphenyldiarsine with  Iron Pentacarbonyl and Dimanganese Decacarbonyl A. 1,2-Dimethyl-l,2-Diphenyldiarsine and Iron  Pentacarbonyl Iron pentacarbonyl (4- g, 20 mmol) and 1,2-dimethyl-l,2-diphenyldiarsine (2 g, 6 mmol) i n benzene (25 ml) were heated at 150° f o r 3 days i n a sealed evacuated Carius tube. The f i n a l s o l u t i o n was dark brown. The benzene and excess i r o n pentacarbonyl were removed under reduced pressure and the residual orange s o l i d chromatographed on F l o r i s i l under nitrogen. Petroleum ether eluted a yellow band which a f t e r solvent removal and r e c r y s t a l l i z a t i o n from petroleum ether at -20° gave orange c r y s t a l s of asymmetric Fe 2(C0)^[As(CH 3)-( C 6 H 5 ) ] 2 (0.2g, 5%); mp 93-96°. A second orange band eluted by a 5$ d i e t h y l ether, 95$ petroleum ether mixture gave a f t e r r e c r y s t a l l i z a t i o n from -74-the same s o l v e n t m i x t u r e a t -20°, orange c r y s t a l s o f symmetric F e 2 ( C 0 ) 6 [ A s ( C H 3 ) ( C 6 H 5 ) ] 2 (1.2 g, 33$); mp 162-164°. A n a l y t i c a l and s p e c t r o s c o p i c d a t a f o r b o t h i s o m e r s were p r e v i o u s l y g i v e n i n T a b l e s I I I , I V , and V. B. 1 , 2 - D i m e t h y l - l , 2 , D i p h e n y l d i a r s i n e and Dimanganese  D e c a c a r b o n y l Dimanganese d e c a c a r b o n y l (1.3 g, 3«3 mmol) and 1,2-d i m e t h y l - 1 , 2 - d i p h e n y l d i a r s i n e (1.1 g, 3-3 mmol) i n t o l u e n e (30 ml) were r e f l u x e d f o r 20 h under a n i t r o g e n atmosphere. The f i n a l s o l u t i o n was d a r k brown-red. The t o l u e n e was removed under reduced p r e s s u r e and the o i l y s o l i d chromatographed on F l o r i s i l under n i t r o g e n . P e t r o l e u m e t h e r e l u t e d a y e l l o w band c o n t a i n i n g 0.1 g o f u n r e a c t e d dimanganese d e c a c a r b o n y l . A 1$ d i e t h y l e t h e r , 99$ p e t r o l e u m e t h e r m i x t u r e e l u t e d two y e l l o w bands. The f i r s t band o f f t h e column gave a y e l l o w s o l i d w h i c h was r e c r y s t a l l i z e d f r om a methylene c h l o r i d e - h e x a n e m i x t u r e a t -20° and i d e n t i f i e d as M n 2 ( C 0 ) g [ A s ( C H 3 ) ( C g H ^ ) ^ ( i s o m e r A) ( 0 . 5 5 g, 27$) mp 158-160° ( s e a l e d e v a c u a t e d c a p i l l a r y ) . The mass spectrum showed a peak due t o the p a r e n t i o n f o l l o w e d by the l o s s of e i g h t c a r b o n y l g r o u p s . The i r spectrum (C^H^,, s o l u t i o n ) showed c a r b o n y l f r e q u e n c i e s a t 2 0 4 8 ( s ) , 1995(s), 1985(vs), 196l(vs) cm" 1. The XH nmr spectrum ( C D C l ^ s o l u t i o n ) gave an a r s e n i c m e t h y l s i n g l e t a t 1 .92 and a r s e n i c p h e n y l m u l t i p l e t s c e n t r e d at 7.42 and 7-68. -75-Anal. Calcd. f o r c 2 2 H l 6 A s 2 ° 8 M n 2 ! C ' 39-52; H, 2.40; mol wt 668. Found: C, 39-55; H, 2.6lj mol wt (mass spec) 668. The second band gave a yellow s o l i d which was i d e n t i f i e d as Mn 2(CO)g[As(CH 3)(C 6H 5)] 2 (isomer B) (0.55 g, 27$); mp 199-201° (sealed evacuated c a p i l l a r y ) . The mass spectrum showed a parent ion followed by loss of eight carbonyl groups. The i r spectrum (£5*^2 solution) gave carbonyl frequencies at 2048(s), 1985(vs), 196l(vs) cm"1. The 1H nmr spectrum (CDCl^ solution) consisted of an arsenic methyl s i n g l e t at 1.83 and arsenic phenyl multiplets centred at 7.45 and 7-75. Anal. Calcd. f o r C 2 2 H l 6 A s 2 ° 8 M n 2 ! C ' 3 9 ' $ 2 5 H * 2m**°'> m o 1 wt 668. Found: C, 39-70; H, 2.60; mol wt (mass spec) 668. - 7 6 -CHAPTER III RESULTS AND DISCUSSION This chapter i s divided into f i v e major sections. The f i r s t section i s concerned with the preparation and characterization of the two ligands employed i n t h i s study. A short discussion on the stereomutation of arsenic and phosphorus i s given i n the second section. Section 3 i s concerned with the preparation and c h a r a c t e r i z a t i o n of some i r o n carbonyl complexes. In section 4 the n o n r i g i d i t y of the F e 2 ( C 0 ) ^ [ E ( R 1 ) ( R 2 ) l 2 complexes (E = As, R x = R 2 = CH 3, R1 = CHy R 2 = C ^ ; E = P, R± = R g = CH^) i s discussed. Section 5 i s concerned with a d e s c r i p t i o n of the method used i n the computation of a c t i v a t i o n parameters f o r the nonrigid complexes. 1. The Ligands Hexafluoroacetone and tetramethyldiarsine react at 2 0 ° to give a compound containing two sets of inequivalent methyl.groups and equivalent trifluoromethyl groups as shown by nmr spectros-70 copy. This compound (R = CH^) dissociates to some extent at 2 0 ° as indicated i n [XVl]. -77-(R)(CH 3)AsAs(CH 3)(R) + ( C F 3 ) 2 C 0 ( ) 2 ( R) ^  . ( ^ ^CO [XVI] The complex i s assigned s t r u c t u r e 8a or 8b i n which one a r s e n i c atom, a c t i n g as a donor, i s fo u r - c o o r d i n a t e and the other, a c t i n g as an acceptor, i s f i v e - c o o r d i n a t e (R = CH 3) ( i f the lone p a i r i s thought of occupying one s i t e ) . ( C F 3 ) 2 C 0 < > ( C F 3 ) 2 C 0 (R)(CH 3)As As(CH )(R) + 8a ( R ) ( C H 3 ) A s = A s ( C H 3 ) ( R ) 8b When t e t r a m e t h y l d i a r s i n e r e a c t s w i t h hexafluorobutyne-2 at 20°, f a c i l e q u a n t i t a t i v e a d d i t i o n across the t r i p l e bond occurs w i t h the formation of an approximate 1:1 mixture of the c i s - and trans-isomers of 2 , 3 - b i s ( d i m e t h y l a r s i n o ) - l , l , l , 4 , 4 , 4 -hexafluorobut-2-ene £ (R = CH 3) and 10 (R = C H 3 ) . 7 1 However, C H 3 ^ C H 3 C F 3 ^ C F 3 (CH 3)RAs C F 3 As-As + C F 3 C H C C F 3 —=> X C = C ^ + ^ C^C^ R R (CH3)RAs As(CH 3)R C F 3 As(CH 3)R 1 10 [XVII] - 7 8 -when excess hexafluoroacetone i s used as solvent and i f the diarsine i s f i r s t allowed to mix with the solvent before the acetylene i s added, the product i s exclus i v e l y the cis-adduct. The s t e r e o s p e c i f i c i t y i s thought to be due to the i n i t i a l formation of a complex such as 8a, 8b (R = CH^) which allows attack of the acetylene on only one side of the arsenic-arsenic 70 bond. Other workers have evidence f o r the existence of s i m i l a r 72 adducts.' The related 1,2-dimethyl-l,2-diphenyldiarsine reacts s i m i l a r l y with hexafluoroacetone and hexafluorobutyne although no nmr parameters were obtained f o r the hexafluoroacetone adduct. Figure 1(a) shows the 1 9 F nmr spectrum of the reaction product obtained i n the absence of hexafluoroacetone. Figure 1(b) shows the spectrum of the product obtained when hexa-fluoroacetone i s present. The two low f i e l d peaks i n the spectra can be assigned to the meso and racemic forms of the trans-adduct 10 (R = CgH^) and the two high f i e l d peaks to the meso 11 and racemic 12 forms of the cis-adduct £ (R = C^H^). The e f f e c t of the hexafluoroacetone i s to change the r a t i o from CF 3 CF 3 , CF, CF 3 CeH^ C=C ^C 6H 5 CH 3 C ^ C C 6H 5 - A B ; . > A S ^ \ S / > A S « < C H 3 ^ C H 3 cpf ' ' ^ C H 3 meso 11 racemic 12 -79-(a) (b) 49 50 51 52 53 54 ppm F i g u r e 1. The 1 9 F nmr spectrum of the products of equation [XVII] (R = C 6H^) (a) i n the absence of hexa-f l u o r o a c e t o n e and (b) i n the presence of hexa-f l u o r o a c e t o n e . -80-55$ trans: 4-5$ c i s i n i t s absence to 12$ trans: 88$ c i s i n i t s presence, presumably due to the formation of a s i m i l a r adduct 8a, 8b (R = C ^ ) . The meso•and racemic isomers of the cis-adduct can be separated by virt u e of t h e i r d i f f e r e n t s o l u b i l i t y i n hexane. One isomer which i s obtained as a pure s o l i d and i d e n t i f i e d as the racemic isomer .12 (see section 3 of t h i s chapter) i s 19 1 responsible f o r the - 7F s i n g l e t at 53-2 and the H s i n g l e t at 1.20. The other isomer, obtained as an o i l and i d e n t i f i e d as the meso isomer 11 can be obtained free of the racemic form but i t i s usually contaminated with traces of the two forms of the trans-adduct 10 (R = C^H^). Its 1 9 F spectrum i s thus comprised of s i n g l e t s at 50.0, 50.8 (trans-adduct), and 53.0 (cis-adduct), while the H nmr spectrum shows a broad peak at 1.50. The cis-diastereomers 11 and 12, once separated, are stable. The c i s configuration allows them to act as monometallic bidentate (chelating) ligands or as b i m e t a l l i c tridentate ligands since the double bond can also act as a coordination s i t e . Examples of both types of behaviour w i l l be presented i n the following sections of t h i s chapter and the following chapters. I d e n t i f i c a t i o n of complexes formed from the reactions of £ (R = CH^ or 0^H^) with various metal carbonyls are based, to a large extent, on the nmr spectra of the products. Simple chelate complexes formed by replacing two carbonyl groups of the metal carbonyl by the ligand show arsenic methyl signals -81-s h i f t e d downfield from the free ligand value. This deshielding e f f e c t arises because the arsenic lone p a i r s are no longer available f o r s h i e l d i n g of the methyl groups since they are involved i n coordination to the metal. Similar deshielding e f f e c t s are observed f o r the trifluoromethyl groups. A further deshielding of trifluoromethyl groups occurs i n complexes u t i l i z i n g the double bond as an a d d i t i o n a l coordination s i t e . The carbon-fluorine stretching region i n the i r ( 1 3 0 0 -1 0 0 0 cm - 1) f o r complexes possessing normal chelate structures are nearly i d e n t i c a l with those of the free ligand. Any loss of symmetry would have resulted i n obvious changes i n band number and d i s t r i b u t i o n . Complexes containing fragmented ligand show a d r a s t i c change i n the carbon-fluorine stretching region. 2. The Stereomutation of Arsenic and Phosphorus > A. General Discussion The pyramidal inversion of configuration about a c e n t r a l atom, such as arsenic or phosphorus, surrounded by three substituents and a lone p a i r i s i l l u s t r a t e d i n [XVIII]. X Y •> x—E: [ X V I I I ] E = As or P -82-Arsenic and phosphorus are well known to have high h a r r i e r s 7ij._78 to inversion,' these b a r r i e r s being influenced by such factors as s t e r i c and conjugation ( ( p - d ) n conjugation) e f f e c t s . As the s t e r i c requirement of a substituent increases the pyramidal ground state i s d e s t a b i l i z e d r e l a t i v e to the les s crowded t r a n s i t i o n state, with a resultant decrease i n the b a r r i e r to inversion. The difference i n s t e r i c requirements of a methyl group and a t-butyl group i s r e f l e c t e d i n the d i f f e r e n t inversion rates f o r a methyl substituted and t-b u t y l substituted phosphetane, the rate being much slower f o r the 73 methyl d e r i v a t i v e . The e f f e c t of s t e r i c requirements on the inversion rate i s also r e f l e c t e d by the behaviour of the \ 79 two ligands ethylene-1,2-bis(n-butylphenylarsine) 7 and 80 ethylene-1,2-bis(methylphenylarsine), rapid inversion occurring i n the n-butyl derivative and no inversion occurring i n the methyl der i v a t i v e . During the inversion process, the hy b r i d i z a t i o n of the bonding o r b i t a l s at the arsenic or phosphorus atom i s regarded 3 2 as changing from sp to sp , and that of the lone p a i r of electrons from sp^ to p. Thus rr d e r e a l i z a t i o n of the lone pa i r favours the rehybridization process and lowers the b a r r i e r to inversion. In phosphines the e f f e c t of a r y l s u b s t i t u t i o n -173 i s to lower the b a r r i e r by 2-3 kcal mol .' y The lowering of inversion b a r r i e r s i n the diarsine and diphosphine systems i s thought to be due to d e r e a l i z a t i o n of the lone p a i r electrons into empty d o r b i t a l s by (p-d) n conjugation. In the t r a n s i t i o n state to inversion the lone p a i r of electrons offers the best -83-geometry f o r overlap to empty 3d o r b i t a l s on an adjacent phosphorus or arsenic atom. Nmr experiments performed on 1,2-dimethyl-l,2-diphenyl-diarsine and 1,2-dimethyl-l,2-diphenyldiphosphine give b a r r i e r s to inversion of 27 and 26 kcal mol" res p e c t i v e l y . The collapse of the two methyl peaks i n the XH nmr spectrum over a high temperature range i s thought to be due to the stereomutation of the arsenic and phosphorus atoms causing rapid interconversion of the two diastereomeric forms. Equation [XIX] i l l u s t r a t e s the interconversion of the meso and racemic forms f o r 1,2-dimethyl-1,2-diphenyldiarsine. ° 6 H 5 <CH3 C 6 H 5 7K inversion CH-3 -As' CH C 6 H 5 CH 3 .. 3%. ,-C6H5 rotation ~ As' > "•As^  CH 3 C 6H 5 ^-As y \ C 6H 5 CH 3 racemic [xix] B. Separation and I d e n t i f i c a t i o n of the Stereoisomers of D i t e r t i a r y Arsines The i d e n t i f i c a t i o n of the geometrical isomers of d i t e r t i a r y arsines involves the formation of the metal complexes which may be separated by column chromatography followed by res o l u t i o n of the racemic modification 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 . Some ligands such as ethylene-l,2-bis(n-butylphenylarsine)^°' are a c t u a l l y s t a b i l i z e d by complex formation. Once the ligands -84-are set free, the two diastereomeric forms r a p i d l y interconvert "by pyramidal inversion about the arsenic atom, whereas other 8 0 8 2 ligands ' do not interconvert i n the free form. The d i t e r t i a r y arsine £ (R = ^ 5 ^ 5 ) c a n ^e separated into the meso and racemic forms 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 without any apparent interconversion of the two forms; the two isomers are stable to heat at 1 5 0 ° . Once separated, they are reacted with various metal carbonyls g i v i n g diastereomeric deri v a t i v e s . In p a r t i c u l a r , reaction with i r o n pentacarbonyl affords a complex (L-L) Fe 2(C0)£ as one of the re a c t i o n products. The properties of the geometric isomers of (L-L)' Feg(CO)^ allow assignment of the configuration of the s t a r t i n g ligands. 3. Iron Carbonyl Complexes of (L-L) and (L-L) The reaction of i r o n pentacarbonyl or t r i i r o n dodeca-carbonyl with c i s - 2 , 3 - b i s ( d i m e t h y l a r s i n o ) - ! , 1 , 1 , 4 , 4 , 4 - h e x a -fluorobut - 2-ene (L-L) and c i s - 2 , 3 - b i s ( m e t h y l p h e n y l a r s i n o ) -l , l , l , 4 , 4 , 4 - h e x a f l u o r o b u t - 2 - e n e (L-L) affords two major carbonyl derivatives; (L-L)Fe(C0) 3, ( L - L ) ' F e { C 0 ) ^ and (L-L)Fe 2(C0) 6, (L-L)'Fe 2(C0) 6. A. (L-L)Fe(C0) 3 and (L-L)'Fe(C0) 3 The t r i c a r b o n y l complexes are best prepared by u l t r a v i o l e t i r r a d i a t i o n . When heated at 1 5 0 ° with i r o n pentacarbonyl the corresponding (L-L)Fe 2(CO)^ and (L-L) Fe 2(C0)^ derivatives are produced. Prolonged heating of i r o n pentacarbonyl and -85-(L-L) or (L-L) (3 days) d r a s t i c a l l y lowers the y i e l d of the (L-L)Fe(C0) 3 or (L-L) Fe{CO)^ complexes. Thus they seem to be the intermediates i n the thermal production of (L-L)Fe 2(C0)£ and (L-L) Fe 2(C0)^. This conversion process has also been o r> observed f o r a v a r i e t y of other ligands. J Mass spectra (which show peaks corresponding to the parent ion (ligand)Fe(CO)* and stepwise loss of three carbonyl groups) and the a n a l y t i c a l data suggest the formula (ligand)Fe(CO) 3. The ''"H nmr spectra of these t r i c a r b o n y l species indicate that both arsenic atoms are coordinated symmetrically since only one lower f i e l d arsenic methyl s i n g l e t i s observed. In the 19 7 F spectra the presence of only one trifluoromethyl s i n g l e t also indicates a symmetrical structure. The i r spectra i n the carbonyl region show three terminal carbonyl bands i n d i c a t i v e of e i t h e r an equatorial-equatorial substituted t r i g o n a l bipyramid (C^)^ or an e q u a t o r i a l - a x i a l substituted t r i g o n a l * 84 bipyramid (C ). The a x i a l - e q u a t o r i a l substituted species, i f r i g i d i n solution, would give two arsenic methyl absorptions i n the "'"H nmr spectrum whereas the equatorial-equatorial substituted species would only give one arsenic methyl s i g n a l . Other structures consistent with the i r spectrum are: (1) 84 an a x i a l - e q u a t o r i a l substituted square pyramid (C ); (2) s 84 3 8 an equatorial-equatorial substituted square pyramid (C ). In view of the f a c t that five-coordinate t r a n s i t i o n metal d Q £ compounds generally adopt trigonal-bipyramidal configurations and since iron pentacarbonyl i t s e l f has the same con-f i g u r a t i o n , the t r i g o n a l bipyramidal structures are more favoured. - 8 6 -However, the l a t t e r would require the ligand to subtend an angle of ca. 120° at the iro n atom and angles of ca. 90° have usually been found i n chelate c o m p l e x e s 8 7 - 8 9 corresponding to ligand s u b s t i t u t i o n at an a x i a l and equatorial p o s i t i o n . In the s o l i d , the ligands are probably coordinated at an a x i a l and equatorial p o s i t i o n as i s reported f o r (diars)Fe(CO) 3, 9° diars = o-C^H^As^CH-^g^. In solution, the t r i c a r b o n y l complexes, l i k e other ( l i g a n d ) F e ( C O ) a n d ( l i g a n d ) R u ( C 0 ) 3 9 2 complexes are probably undergoing p o s i t i o n a l exchange, ^ whereby a x i a l and equatorial substituents are exchanging as depicted i n [XX]. Recently Odom9^ and coworkers provided OC-As. Fe CO C O oc-.As, C O (L-L) or (L-L) 1 CO [xx] further evidence f o r the n o n r i g i d i t y of these five-coordinate 13 13 complexes u t i l i z i n g -^C nmr spectroscopy. The VC nmr spectrum of the carbonyl groups i n tricarbonyl-l , 2-bis(dimethylphosphino-ethane)iron(O) exhibits only one peak at 25° and - 8 0 ° , and i s •consistent with the molecule having a nonrigid structure on the nmr time scale due to rapid intramolecular exchange. The spectroscopic r e s u l t s f o r the diastereomeric (L-L) Fe(CO). complexes do not allow a decision to be made regarding the -87-structure of the i n i t i a l ligand (L-L) i . e . , whether i t i s racemic or meso, since the complexes are too symmetrical; one having methyl groups c i s with respect to the chelate r i n g (the meso complex) and the other trans (the racemic complex). B. (L-L)Fe 2(C0) 6 and (L-L)'Fe 2(CO) 6 The dinuclear complexes are best prepared by heating the iron carbonyl with eit h e r (L-L) or (L-L)' at 150°. (L-L)Fe 2(C0)^ c r y s t a l l i z e s as a yellow-red s o l i d whereas the diastereomeric (L-L) Fe(CO)^ complexes c r y s t a l l i z e as dark red-brown s o l i d s . A l l complexes are soluble i n polar organic solvents (such as di e t h y l ether, chloroform, and acetone), but only s l i g h t l y soluble i n the nonpolar solvents (such as cyclohexane and petroleum ether). They can be heated at 150° f o r 6 days without any noticeable decomposition occurring. The mass spectra (which show peaks corresponding to the parent ion and a stepwise loss of s i x carbonyl groups) and the a n a l y t i c a l data suggest the formula (ligand)Fe 2(CO)^. The i r spectra i n the carbonyl region are very s i m i l a r to those reported*7"^ f o r other (ligand)Fe 2(C0)^ complexes whose structures 96 97 96 are well established. ' 7 The c r y s t a l s t r u c t u r e 7 of ( f f a r s ) F e 2 ( C 0 ) ^ i s shown i n Figure 2. The molecule consists A B A of two inequivalent i r o n atoms Fe and Fe . Fe i s approximately octahedrally coordinated to three carbonyl groups, two arsenic B B atoms, and Fe ; Fe i s coordinated to the C=C bond of the cyclobutene r i n g , three carbonyl groups, and Fe"^ (acting as a donor). Thus the coordination around Fe can be regarded -88--89-as eit h e r a d i s t o r t e d t r i g o n a l bipyramid (with the C=C bond occupying one s i t e ) or a d i s t o r t e d octahedron (with the two carbon atoms occupying two s i t e s ) . Since the (L-L)Fe 2(C0)^ and (L-L) Fe^CO)^ complexes resemble the reported (ligand)Fe 2(CO)g complexes i n nearly every respect, i t i s reasonable to propose an analogous structure 13_ (R = CH^ or C^H^). (CO)3Fe 12* I f i t i s assumed that no interconversion of the meso and i racemic forms of (L-L) occurs during the reaction with i r o n pentacarbonyl ( t h i s assumption seems j u s t i f i e d since no interconversion i s observed i n other metal carbonyl reactions with (L-L) ; see Chapter IV), the racemic isomer should give i one (L-L) Fe 2(C0)^ complex 14 and the meso could give two (L-L) Fe 2(C0)^ isomers 2J5 and 16. The c r y s t a l l i n e ligand affords a Fe 2(C0)^ complex whose nmr spectrum shows two arsenic methyl and two tr i f l u o r o m e t h y l absorptions (the trifluoromethyl groups are deshielded with respect to the free ligand value due to coordination of the C=C moiety to an i r o n * For R = C^H^ t h i s diagram i s not intended to represent a s p e c i f i c diastereomer. - 9 0 -16 atom). The two trif l u o r o m e t h y l groups belong to the same molecule since there i s spin-spin coupling between them (J(F,F) = 11.3 Hz). Such a spectrum would be expected only f o r V± and thus the s o l i d s t a r t i n g ligand i s the racemic form of (L-L) . The nmr spectrum of the Fe 2(C0)g complex obtained from the o i l y ligand shows only one type of arsenic methyl group to be present and only one tri f l u o r o m e t h y l group. Such a spectrum would be possible f o r ei t h e r lj5 or 16, but not from a mixture of both. Thus the o i l y ligand i s the meso form of (L-L) and gives the same product, probably lj5, on heating, and u l t r a v i o l e t i r r a d i a t i o n . The reason f o r p r e f e r r i n g 15_ i s that phenyl-phenyl repulsions appear to be l e s s than methyl-methyl i n t h i s sort of system (see section 4 of t h i s chapte -91-C. F e 2 ( C O ) 6 [ A s ( C H 3 ) ( C 6 H 5 ) ] 2 Prolonged thermal reaction of ( L - L ) with i r o n pentacarbonyl (3 days) also, y i e l d s , i n addition to the Fe 2(C0)g complexes, a compound having the empirical formula FetCCO^AstCH^)(C^H^). This proved to be i d e n t i c a l with the product obtained by heating i r o n pentacarbonyl with l,2-dimethyl-l,2-diphenyldiarsine: lower y i e l d s are obtained on i r r a d i a t i o n . The meso ligand i s a better source of the fluorocarbon-eliminated product. In f a c t the y i e l d i s almost that which i s obtained by t r e a t i n g i r o n pentacarbonyl with the diarsine under i d e n t i c a l conditions. The ( L - L ) F e 2 ( G 0 ) ^ complexes are stable by themselves i n benzene soluti o n f o r at l e a s t 5 days (150°) so they are not the unique source of the arsenido bridged complexes. The reaction mixture i s very complex and i t i s d i f f i c u l t enough to e s t a b l i s h when the fluorocarbon i s l o s t , l e t alone r a t i o n a l i z e the differences i n behaviour between the two ligands. There i s spectroscopic evidence f o r the existence of t e t r a k i s ( t r i f l u o r o -methyl )cyclopentadienoneiron t r i c a r b o n y l i n sol u t i o n . This would be formed by reaction of the free acetylene with i r o n 98 pentacarbonyl. y The reaction of 1,2-dimethyl-l,2-diphenyldiarsine with i r o n pentacarbonyl gives two isomeric products which can be e a s i l y separated by c a r e f u l chromatography by virt u e of t h e i r d i f f e r i n g s o l u b i l i t i e s . The major product i s assigned structure 17 (E = As). The nmr spectrum shows only one type of arsenic methyl; hence the structure i s symmetrical ( C 9 i r ) . The lower - 9 2 -11 v o l a t i l i t y and s o l u b i l i t y of t h i s isomer, compared with the other isomer, are also i n accord with t h i s formulation. The carbonyl i r frequencies are very s i m i l a r to the phosphorus analogue" which, i n the s o l i d state, has the two phenyl groups that the arsenic analogue would be i s o - s t r u c t u r a l . The minor product of the reaction of the diarsine with i r o n pentacarbonyl i s an isomer of 17_ (E = As) which has the asymmetric structure 18 since the "Hf nmr spectrum shows two d i s t i n c t s i n g l e t s i n the arsenic methyl region. One of these resonances i s at r e l a t i v e l y high f i e l d ( 0 . 9 3 ) and t h i s can be assigned to the methyl group which i s adjacent to the phenyl group on the other arsenic atom (the s h i f t to high f i e l d i s a x i a l as i n 17_ (E = P) 100 and i t i s thus reasonable to believe C H 3 (COL F e C •3 ..-FeCCOL 18 -93-due to through-space sh i e l d i n g of the methyl group by the phenyl group). The i r spectra of 17_ (E = As) and 18 i n the v(CQ) region are i d e n t i c a l as i s the case f o r the two phosphorus go analogues. 7 7 4. Stereochemical Nonrigidity of the Fe 2(CO) 6[E(R ] L) ( R 2 ) l 2  Complexes (E = As, = R g = CH^, R-L = CH^, R g = C^H^;  E = P, R ± = R 2 = CH 3) A recent s t r u c t u r a l determination of the symmetric analogue of Fe 2(CO)^[P(CH 3)(C^H^)] 2 has shown i t to have a folded structure c o n s i s t i n g of two octahedrally coordinated iron atoms (assuming a "bent" i r o n - i r o n bond) with bridging phosphido groups as i n 17_ (E = P): the two phenyl groups are a x i a l . I t i s l i k e l y that the F e 2 ( C 0 ) 6 [ p ( C H 3 ) 2 ] 2 and Fe 2(CO) 6-[ A s ( C H 3 ) 2 ] 2 complexes possess s i m i l a r skeletons as depicted i n 19a and l£b respectively. As stated i n section 3-C, 17 (E = As) and 18 are probably the structures of the symmetrical and asymmetrical isomers of Fe 2(CO)^[As(CH 3)(C^H^)] 2, A t h i r d isomer of t h i s complex 19c was not formed presumably because of repulsion between the two a x i a l methyl groups. ?3 R a E = P, R = R_ = R = R, = CH Q R I 1 R ~ 1 2 3 4 3 4 \ r J I / 2 b E = As, R^ = R 2 = R^ = R^ = CH^ ( C 0 L F e ^ ^ F e ( C 0 ) 3 * E = A s ' R l = R3 = C H 3 ' R2 = H = C 6 H 5 1?_ -94-When a benzene solution of 18 (the asymmetric form) i s heated at 150° 17_ (E = As) (the symmetric form) i s produced and an equilibrium i s established a f t e r 15 h with the r a t i o of 17_ (E = As) to 18 being 6:1. The same equilibrium i s attained a f t e r 90 h at 150° s t a r t i n g with the symmetric isomer. This process [XXI] of necessity involves bond breaking CH, &H5 '6 5 CH. (C0) 3Fe-r; Fe(C0)3 CH 3 \ | 6 5>>CH, 150* >s As' (C0)3Fe<__ ..--Fe(C0)3 [xxi At temperatures below 120° the nmr spectrum of the symmetric isomer i s independent of temperature. However the asymmetric isomer has a temperature dependent XH nmr spectrum and t h i s i s shown i n Figure 3- As the temperature i s increased the two i n i t i a l l y sharp s i n g l e t s broaden, collapse, and coalesc into a single l i n e which sharpens as the temperature i s further increased. This indicates that at the higher temperature a l l the methyl groups are equivalent on the nmr time scale and suggests that the molecule i s f l u x i o n a l i n the manner indicated i n [XXII] (E = As, R± = = CH^, R g = R^ = CgH^). The two methyl resonances of the dimethylarsino compound 19b behave i n the same manner v/hen the sample i s heated suggesting that -95-1 2 2 °C 1 0 4 °C Figure J. Variable temperature H nmr spectra i n benzene i n the arsenic methyl region of the asymmetric isomer of Fe 2(CO) 6[As(CH ) ( C 6 H 5 ) ] 2 . - 9 6 -R3 R 4 \ , R. (C0)3Fe^" ^ F e ( C 0 ) 3 'R2 ^ V < ^ R , R1 (CO) Fe^T ..--FetCOL . D 3 3 R 2 R4 the molecule i s f l u x i o n a l i n the manner indicated i n [XXIl] (E =As, = Rg = = = CH^). The temperature dependence of the "^H nmr spectrum of t h i s compound i s shown i n Figure 4. Thermodynamic parameters were calculated f o r the motion using the procedure of Gutowsky and Holm10"'" (see section 5 of t h i s chapter f o r an outline of the method). The parameters are l i s t e d i n Table XXVIII which also contains the values obtained f o r the dimethylphosphino analogue 19a i n i t i a l l y studied by Dessy and coworkers. 1 0 2 Table XXVIII Thermodynamic Parameters f o r Bridging Phosphido and Arsenido D i i r o n Hexacarbonyl Complexes Compound AH t( kcal mol" 1) AS^(eu) T p(°K)* F e 2 ( C 0 ) 6 [ A s ( C H 3 ) 2 ] 2 16.1+0.6 -3.7+1.5 347+2 F e 2 ( C 0 ) 6 [ P ( C H 3 ) 2 ] 2 15-0+0.6 :2.1+0.2 -6.6+1.2 ** -4-5+1 347+3 338+2 Fe (CO) 6[As(CH ) ( C 6 H J ] asymmetric J D 17.4+0.9 -3.8+1.5 373+4 ** Values from reference 102. -97-64.5 °C 42 °C 30 °C F i g u r e 4. V a r i a b l e temperature XH nmr s p e c t r a i n benzene of F e 2 ( C O ) 6 [ A s ( C H 3 ) 2 ] 2 . -98-The phosphorus decoupled spectrum was used i n the variable temperature study of F e 2 ( C C O ^ C P C C H ^ g ] ^ and the temperature dependent behaviour of the r e s u l t i n g two si n g l e t s (otherwise two v i r t u a l l y coupled t r i p l e t s ) i s very s i m i l a r to the arsenic analogues. No explanation can be given f o r the discrepancy i n the values but those values determined during the present i n v e s t i g a t i o n make a consistent set and are i n agreement with the values obtained from a study of the motion of a related complex C 0 2 ( C 0 ) 6 [ G e ( C H 3 ) 2 ] 2 . 1 0 3 The motion of the bridging arsenido and phosphido species i s characterized by a high a c t i v a t i o n enthalpy and a small negative a c t i v a t i o n entropy suggesting the intermediate or t r a n s i t i o n state of the " b u t t e r f l y " motion i s of comparable entropy to the s t a t i c forms. In order to account f o r the high temperature nmr r e s u l t s various mechanisms can be postulated f o r the motion: one could involve d i s s o c i a t i o n to an intermediate such as (CO^R^gE^e-FetER^R^) (CO)^ and others could involve no bond breaking. The d i s s o c i a t i v e mechanism seems u n l i k e l y since an intermediate such as that indicated above could allow r o t a t i o n about the Fe-E and Fe-Fe bonds. Consequently i n the case of the bridging methylphenylarsenido compounds 17_ (E = As) and 18, interconversion of the symmetric and asymmetric isomers would occur. However t h i s interconversion only happens at much higher temperatures (150°) no conversion occurring at 100°. Another f a c t which seems to eliminate a d i s s o c i a t i v e mechanism i s that the bridging dime.thylphosphido derivative remains v i r t u a l l y -99-coupled over the entire temperature range. A doublet might be expected i n the high temperature region f o r the phosphorus methyl groups i f bond d i s s o c i a t i o n occurred. The other type of mechanism to account f o r the motion and which appears more l i k e l y i s a nondissociative mechanism. Two l i k e l y intermediates 102 103 have been suggested by other workers ' and have the C o V l and D O V l skeletons shown i n 20 and 2_1 res p e c t i v e l y . Neither of these intermediates has been detected by nmr spectroscopy 102 since they are very s h o r t - l i v e d . Dessy and coworkers suggest the " b u t t e r f l y " motion proceeds.through the highly symmetrical intermediate 2_1 because of the large negative entropy value they f i n d . But t h i s value now appears to be incorrect (Table XXVIII) and there i s no means of deciding i n favour of e i t h e r 20 or 21 or any other intermediate on the basis of the data at hand. This has been pointed out by Klemperer 1 0^ i n an analysis based on t o p o l o g i c a l representations. In an attempt to gain more information concerning the 13 motion of these f l u x i o n a l molecules, the ^C nmr spectrum of 19a and 19b was determined. Chemical s h i f t s and coupling -100-* constants are l i s t e d i n Table XXIX. 1 13 In agreement with the H nmr spectrum, the nmr spectrum of the arsenic compound 19b consists of two s i n g l e t s f o r the dimethylarsino groups; however, only one s i n g l e t i s observed f o r the carbonyl groups at 25° and -70°. S i m i l a r l y the spectrum of the phosphorus compound 19a at 25° consists of two " t r i p l e t s " f o r the dimethylphosphino groups and one " t r i p l e t " f o r the carbonyl groups which remains as one " t r i p l e t " at -70°. The single resonance associated with the carbonyl groups indicates that a carbonyl scrambling process i s taking place which i s s t i l l f a s t at -70° on an nmr time scale and which takes place v i a an intramolecular pathway since x 3C-31p coupling i s maintained. Rapid interchange of the carbonyl groups has also been observed i n such molecules as ( p o l y o l e f i n ) -F e 2 ( C 0 ) 6 , 1 0 8 ( C 8 H 8 ) F e ( C 0 ) 3 , 1 0 9 R h ^ ( C 0 ) 1 2 , 1 1 0 and RhCo 3(C0) 1 2 13 Note that the C spectra are obtained from CDC13 solutions containing a trace amount of C r ( a c a c ) 3 [ t r i s ( a c e t y l a c e t o n a t o ) chromium(III)] using a Fourier transform technique. Long pauses between successive pulses i n the Fourier transform technique are required since carbonyl carbons have long s p i n - l a t t i c e relaxation times. However, the addition of a paramagnetic compound reduces the length of T, so that a 10 5 shorter accumulation time (machine time) i s required. J An e f f e c t i v e paramagnetic reagent that has been employed i n the studies of organometallic molecules i s C r ( a c a c ) ^ . ' When C r ( a c a c ) 3 i s used i n our work, a two-fold increase i n i n t e n s i t y of the carbonyl peak of 19b resulted which i s equivalent to a twenty-fold decrease i n the time needed to obtain the spectrum. -101-Table XXIX 1 3 C Nmr Data Compound 13 * •L-?c F e 2 ( C 0 ) 6 [ A s ( C H 3 ) 2 ] 2 F e 2 ( C 0 ) 6 [ P ( C H 3 ) 2 ] 2 Singlet at 212.8 (CO). Singlets at 16.7 and 13.5 (CH 3) " T r i p l e t " centred at 213.0 (CO) |J(C,.P) + j ' (C,p' ) | = 10.0 Hz. " T r i p l e t s " centred at 23.4 |J(C,P) + j ' (CP* ) | = 40.0 Hz. and 17.4 |J(C,P) + j'(C,p')l = 20.0 Hz (CH 3) Spectra from CDC13 solutions (with XH decoupling) i n the presence of a trace amount of C r ( a c a c ) 3 < The |J(C,P) + J (C,P )| r e f e r s to the separation of the two outer peaks of the " t r i p l e t " . Another p o s s i b i l i t y to account f o r the single carbonyl resonance at room temperature i s that the equatorial and a x i a l carbonyl 13 31 carbons have the same chemical s h i f t and -'C- P coupling 13 constant. In view of the great s e n s i t i v i t y of chemical 24 112-114 s h i f t s with respect to t h e i r environment, ' as demonstrated, for example, by the observation that the c i s and trans chemical s h i f t s of the carbonyl carbons i n [(C^H^) 3P]Cr(C0)^ 2^ d i f f e r by 4.8 ppm, i t i s u n l i k e l y that accidental superposition of 13 31 chemical s h i f t s and ^C- P coupling constants are responsible for the single carbonyl " t r i p l e t " . -102-I t i s apparent that the " b u t t e r f l y " motion of the [Fe-E]^ skeleton and the scrambling of the carbonyl groups are independent processes. Thus i t seems f r u i t l e s s to attempt to explain the 103 b u t t e r f l y motion i n terms of the properties of intermediates such as 2_0 and 21. 5. A Description of the Method Used i n the C a l c u l a t i o n of  Thermodynamic Parameters f o r Nonrigid Molecules Gutowsky and Holm x 0 x have developed mathematical expressions that can be applied to the nmr method f o r processes that interchange protons between two s i t e s . When the temperature dependence of an exchange process i s being studied, the separation of the two l i n e s under conditions where the exchange process i s slow (at lower temperatures) i s f i r s t determined. Then as the sample i s heated, the two l i n e s begin to come clos e r and c l o s e r together and r can be calculated at each temperature where T = T. TQ/(TA f T D) (T A and -r are the average A B A B A B l i f e t i m e s of the protons at each d i f f e r e n t s i t e A and B) using expression [ X X I I l ] : T(SOJ 2- hu?) = 2 if TSOJ> VT [ xx in ] e Sex) i s the separation of the two peaks i n radians s e c ~ x assuming no interchange and 8 u J e i s the experimentally measured peak separation (radians sec~ x) at each d i f f e r e n t temperature. This s i m p l i f i e d equation can only be used when the width of the signals i s small i n comparison with the separation of the two -103-signals; otherwise a more detailed expression must be used. Table XXX l i s t s the data used i n the c a l c u l a t i o n of thermo-dynamic parameters f o r the asymmetric isomer of F e 2 ( C 0 ) ^ -[ A s ( C H 3 ) ( C 6 H 5 ) ] 2 . The data of Table XXX are plotted i n Figure 5 Table XXX Temperature Dependence of zOOJ f o r the Asymmetric Isomer of F e 2 ( C O ) 6 [ A s ( C H 3 ) ( C 6 H 5 ) ] 2 T(°K) h x 10 3 (°K _ 1) . ScJ e(rad sec" 1) l / rSa^rad - 1) 3^ 5 2.90 568.3 0.07 350 2.86 565.2 0.11 355 2.82 555.8 0.16 360.5 2.77 540.1 0.22 362.5 2.76 533.8 0.26 365 2.74 515.0 0.31 as l o g 1 0 (rScu) versus ^/^. Using equation [XXIV], the slope and intercept of the graph then give the a c t i v a t i o n energy E 3. and the frequency f a c t o r V q r e s p e c t i v e l y . l°g 1 0 ( r S c d ) = log 1 0(2v o / S a j)-E a/2.3RT [XXIV] The frequency f a c t o r i s related to AS^ through expression [XXV] where the symbols have t h e i r usual s i g n i f i c a n c e . A§ + ekbTe R [XXV] vo = h -104-2.70 2.80 2.90 (1/T)x 10 Figure 5- Temperature dependence of l/TcWfor the asymmetric isomer of Fe 2(C0)^[As(CH 3)(C^H^)] 2. (Semilog p l o t ) -105-CHAPTER IV RESULTS AND DISCUSSION This chapter i s concerned with the preparation, charac-t e r i z a t i o n , and general chemistry of some Group VI metal carbonyl complexes of cis -2 ,3-bis(dimethylarsino)-!,1,1 ,4 ,4 ,4 -hexafluorobut-2-ene (L-L) and cis - 2 ,3-bis(methylphenylarsino)-l,l,l ,4 ,4 ,4-hexafluorobut -2-ene (L-L) . Section 1 discusses some tetracarbonyl complexes; section 2, some t r i c a r b o n y l complexes; and section 3, some dicarbonyl complexes. Section 4 summarizes the preceding three sections. 1. (L-L)M(CO)^ and ( L - L ) ' M ( C O ) ^ Complexes (M = Cr, Mo, W) A. Preparation Reaction of the Group VI metal hexacarbonyls with an equimolar amount of eithe r (L-L) or (L-L) (150 , benzene) f o r 1-2 days i n a sealed evacuated Carius tube, y i e l d s i n the usual manner,^'^' 1 1^ the disubsti t u t e d chelate complexes (L-L)M(CO)^ and (L-L)'M(C0)^S -106-( L - L ) 150° ( L - L ) M ( C O ) ^ + 2C0 (L-L)'M(CO),. + 2C0 M (C0 ) A + • ( L - L ) benzene M = Cr, Mo, W [XXVI] The complexes are yellow (except f o r the chromium derivative which i s amber), a i r - s t a b l e , c r y s t a l l i n e s o l i d s moderately soluble i n nonpolar organic solvents and very soluble i n polar organic solvents. B. Spectroscopic Results The mass spectra of the chelate complexes show a peak due to the parent ion (ligand)M(CO)^ + as well as peaks due to the stepwise loss of four carbonyl groups. The ~*"H and 1 9 F nmr spectra show one arsenic methyl s i n g l e t and one trifluoromethyl s i n g l e t . This suggests that e i t h e r the five-membered r i n g (determined by the metal, two arsenic, and two carbon atoms of the ligand) i s planar i n solut i o n as i n 22 ( i . e . a symmetric structure), or the r i n g i s involved i n a conformational change that i s rapid, on an nmr time scale, at room temperature i n the manner indicated i n [XXVIl]. • A s ^ < M = Cr, Mo, W 22 -107-[xxvn' The chemical s h i f t of the arsenic methyl groups of the meso- and racemic-(L-L) MtCO)^ complexes d i f f e r s by only ca.' 0 . 0 2 ppm; however, the diastereomeric (L-L) M ( C 0 ) ^ complexes are considerably s h i f t e d to lower f i e l d (ca. 0.3 ppm) i n comparison with the (L-L)M(CO)^ complexes. The deshielding of the methyl groups i n the free ligands as well as t h e i r chelate complexes can be a t t r i b u t e d to the replacement of a methyl group on an arsenic atom by the more electronegative phenyl group. The nmr r e s u l t s f o r the Group VI diastereomeric (L-L) M(C0)^ complexes do not allow a decision to be made regarding the i n i t i a l configuration of the ligand (L-L) since the complexes are too symmetrical; the meso complex having methyl groups c i s with respect to the chelate r i n g and the racemic complex having methyl groups trans with respect to the chelate r i n g . The tetracarbonyl chelate complexes 2 J exhibit Cg v l o c a l symmetry of the carbonyl groups f o r which four i r - a c t i v e carbonyl stretching modes are expected ( 2 A ^ + B.^  + Bg) as shown i n Figure 6 . 1 1 6 The i n t e n s i t y of the highest frequency -108-A x ( 2 ) B 2 As-As = ( L - L ) or ( L - L ) ' Figure 6. The normal carbonyl v i b r a t i o n a l modes f o r the Group VI ( L - L ) M ( C O ) ^ and ( L - L ) ' M ( C O ) ^ complexes. - 1 0 9 -o c .CO A s - " " , "CO C o 2J M = Cr, Mo, W; As-As = (L-L) or (L-L) mode A-j_(l) i s enhanced i n the spectra of these complexes possibly because of coupling with the A^(2) mode or because of d i s t o r t i o n of the molecule from i d e a l C 2 V symmetry. The tetracarbonyl o ry complexes usually show the expected four bands, ' '' although accidental superposition of two of the lower frequency bands 117 can occur. A s i m i l a r superposition i s observed i n the spectra of the ( L - L ) M ( C O ) ^ and ( L - L ) ' M ( C O ) ^ complexes. A comparison of the carbonyl stretching frequencies of the ( L - L ) M ( C O ) ^ complexes with those Group V I chelate complexes of the rela t e d l e s s electronegative d i t e r t i a r y arsine ligand cis - 1 , 2-bis(dimethylarsino)ethylene (cis-edas) i s given i n Table X X X I . The frequencies of the complexes of ( L - L ) are somewhat higher than those of t h e i r cis-edas counterparts. This trend i s consistent with the expected greater amount of metal-arsenic double bonding i n the complexes of ( L - L ) . The more electronegative trifluoromethyl groups i n ( L - L ) increase the amount of TT donation from the metal to the arsenic ligand r e l a t i v e to cis-edas. This leads to a decrease i n TT "back bonding" between the metal and carbonyl groups with subsequent -110-Table XXXI I r Spectra (2100-1800 cm - 1) f o r Some Group VI Chelate Complexes Chelate Complex v(C0)(cm _ 1) (L-L)Cr(COk* (cis-edas)Cr(C0) 2 j < 2020, 2010, 1931. 1911 1935, 1900, 1880 (L-L)Mo(CO)^* (cis-edas)Mo(CO)^ 2036, 2020, 1939. 1921 1905, 1890, 1870 (L-L)W(COk* (cis-edas)W(CO) i j > 2036, 2009, 1931, 1911 1903, 1873, 1852 * This work, C^H-^ solvent. ** Reference 118, KBr disk. strengthening of the carbon-oxygen bond and higher carbonyl stretching frequencies. Further evidence that the complexes possess a normal chelate structure i s obtained from the carbon-fluorine stretching region i n the i r . In t h i s region (1300-1000 cm - 1) the spectra of the metal complexes are nearly i d e n t i c a l with those of the free ligands; any loss of symmetry would have resulted i n changes i n the number and i n t e n s i t y of the bands. C. Possible Mechanism of Formation The d i t e r t i a r y arsine ligands, (L-L) and (L-L) , probably react with the Group VI metal hexacarbonyls i n the manner - I l l -indicated i n equations [XXVIIl] and [XXIX]. M(CO) 6 + As-As > (As-As)M(CO)^ + CO [XXVIIl] (As-As )M( CO )^ 5> (As-As)M(CO)^ + CO [XXIX] M = Cr, Mo, W; As-As = (L-L) or (L-L)' The f i r s t step involves the formation of a pentacarbonyl complex i n which one arsenic atom of the bidentate ligand i s coordinated and the second step involves the coordination of the other arsenic atom with simultaneous loss of carbon monoxide. The chromium reactions probably occur v i a a d i s s o c i a t i v e process (S^jl) while the molybdenum and tungsten reactions occur v i a an associative process (S^2) or a combination of the two 31,32,38-41 processes. '^ Carbonyl bands att r i b u t e d to the pentacarbonyl intermediates are seen i n the i r spectra of the reaction mixtures; however, the M(C0)^ species have not been i s o l a t e d . Ward 7 has i s o l a t e d pentacarbonyl intermediates of the type shown i n [XXVIIl] from reactions of the Group VI metal hexacarbonyls and related d i t e r t i a r y arsine ligands. -112-2. Fac-(L-L) b(L-L) mM(CO) 3 and Fac-(L-L) b(L-L)™M(CO) 3 Complexes ( M = Cr, Mo, W)* A. Preparation The t r i c a r b o n y l complexes are best prepared by photolysing a benzene solut i o n of the parent hexacarbonyl or tetracarbonyl derivative and excess (L-L) (pyrolysis at temperatures of 150-200° apparently does not y i e l d the t r i c a r b o n y l d e r i v a t i v e ) : M(C0) A or hv ° + excess (L-L) > (L-L) (L-L) mM(CO)- + (L-L)M(CO)^ benzene ^ (L-L) b(L-L)™M(C0) 3 [XXX] M = Cr, Mo, W The p h o t o l y l i s reaction i s performed using a 200W and 4-50W lamp (for the molybdenum and tungsten derivatives only; the chromium reaction i s performed using the 4-50W lamp). The 4-50W reaction gives the t r i c a r b o n y l derivative i n a much shorter time than does the 200W reaction. For example, the photolysis (200W) of a benzene solut i o n of molybdenum hexacarbonyl and excess (L-L) affords, a f t e r 266 h, a 20$ y i e l d of the molybdenum t r i c a r b o n y l d e r i v a t i v e , whereas performing the same photolysis using a 4-50W lamp gives, a f t e r 1.5 h a 36$ y i e l d of the same product. The shorter reaction time with the 4-50W lamp can be * (L-L) denotes bidentate ligand and ( L - L ) m the ligand i n a c i s configuration acting i n a monodentate manner and (L-L)™ the ligand i n a trans configuration acting i n a monodentate manner. - 1 1 3 -attributed to: ( l ) increase i n the f l u x and (2) greater e f f i c i e n c y of the reaction apparatus - the carbon monoxide that i s evolved i s constantly removed from the reaction s o l u t i o n by the nitrogen and the lamp i s situated very close to the so l u t i o n ( 3 0 mm) which completely surrounds the quartz jacket containing the lamp. Hitherto no t r i c a r b o n y l complex containing two bidentate ligands has been reported from the reaction of a Group VI metal hexacarbonyl with an excess amount of a p o t e n t i a l l y bidentate ligand. However, the l i t e r a t u r e r e l a t i n g to complexes of the type ( L 2 ) ( L ) M ( C 0 ) 3 (M = Cr, Mo, W; L 2 i s a bidentate ligand and L i s a monodentate ligand) has been well documented. x x' x x°'' x^ B. Characterization Two isomeric t r i c a r b o n y l derivatives are obtained from the 450W photochemical reaction and one t r i c a r b o n y l derivative from the 200W reaction. A n a l y t i c a l data suggest the formula (L-L^MtCO)^. Therefore, from a consideration of the " e f f e c t i v e atomic number" rule (which most organometallic molecules obey), the coordination sphere about the metal atom consists of three carbon monoxide groups, one bidentate, and one monodentate ligand (L-L). The i r spectra of the two isomers are i d e n t i c a l i n the carbonyl region; hence, the configuration of the carbonyl groups i s probably the same i n both isomers. However, f o r molecules of the type ( L - L ) b ( L - L ) m M ( C 0 ) 3 two basic configurations are possible: one having a l l carbonyl groups c i s to each other and -Un-designated as the fac isomer 2 4 , and the other having two carbonyl groups trans to each other and designated as the mer isomer 25-As As 'As As-M : ,CO CO O c 'As. M As 1 -As As C O C O C O 24 2J M = Cr, Mo, W; As-As = (L-L) The fac isomer 24 exhibits C^ v l o c a l symmetry of the carbonyl groups and two i r - a c t i v e bands are expected. However, 1 1 9 Dobson and Houk 7 found that i n complexes of the type f a c -M^COyCgY (where i s a bidentate ligand and Y i s a monodentate ligand) where the net charge-releasing a b i l i t y of the ligands i s expected to be i n the order X g > Y, the lowest frequency mode i s s p l i t into two components (C symmetry). The more d i s s i m i l a r the bonding properties of Xg and Y the greater the s p l i t t i n g of the mode. These three v i b r a t i o n a l s t r e t c h i n g modes, indicated i n Figure 7, involve a change i n dipole moment and are expected to r e s u l t i n strong absorptions. The mer isomer 2J? exhibits Cg v l o c a l symmetry of the carbonyl groups f o r which three i r - a c t i v e carbonyl stretching modes are also expected. The normal v i b r a t i o n a l modes are shown i n Figure 7- Modes A and C involve a change i n dipole moment of the molecule and are expected to r e s u l t i n strong absorptions! -115-Mer: Figure 7- The normal carbonyl v i b r a t i o n a l modes f o r Group VI mer and fac isomers of ( L - L ) b -(L-L) mM(CO) 3 0 -116-however, mode B does not involve a change i n dipole moment and t h i s v i b r a t i o n should r e s u l t i n a weak absorption. T , , ," „ 11,119-122 , 11,121,122 Indeed, reported fac- 7 and mer-IVKCO^XgY complexes do show the d i s t i n c t i v e carbonyl patterns described above. Both isomers of (L-L) b(L-L) mM(C0) 3 show three strong bands i n the v(CO) region i n d i c a t i v e of a fac configuration. A sample spectrum i n the v(C0) region of one of the two isomers i s shown i n Figure 8. The lowest frequency band of the t r i -carbonyl derivatives i s s p l i t into a doublet, the separation being ca. 10-12 cm~x. The s p l i t t i n g i s i n agreement with the 119 findings of Dobson et a l . 7 since the bidentate ligand has a larger net charge-releasing a b i l i t y than the monodentate ligand. The production of isomers possessing a fac configuration i s not unreasonable because a carbonyl group trans to another carbonyl group i n (L-L)M(CO)^ i s more l a b i l e than a carbonyl trans to an arsenic atom and i s more l i k e l y to be displaced by (L-L). Dobson and Houk x x have found that the geometry of the t r i c a r b o n y l product seems to also depend on the s t e r i c requirements of both the incoming ligand and the chelate. The basic difference i n the nmr spectra of the two isomeric f a c - ( L - L ) b ( L - L ) m M ( C 0 ) 3 complexes i s the magnitude of the 19 19 7 F - 7 F coupling constant. This and other data previously discussed suggest the two isomers d i f f e r i n the configuration of the monodentate ligand since the bidentate ligand i n each isomer must possess a c i s configuration to form a chelate complex. -117-Figure 8. The carhonyl i r spectrum i n cyclohexane of an isomer of (L-L) b(L-L) mMo(CO)„. -118-The major chromium and molybdenum t r i c a r b o n y l product shows three arsenic methyl s i n g l e t s ( r e l a t i v e area 1:2:1 i n order of increasing f i e l d ) and the tungsten complex four equal area arsenic methyl s i n g l e t s i n the XH nmr spectra. I t appears that there i s an accidental superposition of two 19 absorptions i n the chromium and molybdenum spectra. Their F nmr spectra a l l consist of a t r i f l u o r o m e t h y l s i n g l e t ( r e l a t i v e area 2) followed, at s l i g h t l y higher f i e l d , by two t r i f l u o r o -methyl quartets (each of r e l a t i v e area 1; J(F,F) = 12.0 Hz f o r chromium, 11.3 Hz f o r molybdenum, and 13-5 Hz f o r tungsten). 19 19 The magnitude of the 7F- 7F coupling constants suggests the 123 124 two t r i f luoromethyl groups are c i s •Jl to each other i n the monodentate ligand. Hence the major derivative i s designated as fac-(L-L) b(L-L)^M(C0) . The minor t r i c a r b o n y l product i s assigned the fac structure i n which the two trifluoromethyl groups i n the monodentate ligand are trans to each other. The XH nmr spectrum should consist of four equal area arsenic methyl s i n g l e t s . This i s observed f o r the tungsten d e r i v a t i v e but the chromium and molybdenum derivatives show three arsenic methyl s i n g l e t s ( r e l a t i v e area 1:2:1 i n order of increasing f i e l d ) presumably due to an accidental superposition of two absorptions. The 19 corresponding 7F spectra should consist of a trifluoromethyl s i n g l e t ( r e l a t i v e area 2) f o r the f l u o r i n e atoms of the bidentate ligand and two trifluoromethyl quartets (each of r e l a t i v e area 1) f o r the f l u o r i n e atoms of the monodentate ligand. The chromium and molybdenum derivatives exhibit a quartet ( r e l a t i v e -119-area 1; J(F,F) = 2.2 Hz f o r chromium and 2.3 Hz fo r molybdenum) followed by a higher f i e l d s i n g l e t ( r e l a t i v e area 2) and another quartet ( r e l a t i v e area 1; same coupling constants as the lower f i e l d quartet). However, the tungsten derivative shows a quartet ( r e l a t i v e area 1; J(F,F) =2.2 Hz) followed, at s l i g h t l y higher f i e l d , by a broad s i n g l e t ( r e l a t i v e area 3)- The si n g l e t contains absorptions due to the chelate r i n g trifluoromethyl groups and one trifluoromethyl group of the monodentate ligand. The smaller J(F,F) observed i n these complexes i s i n agreement 12 3 with the assignment of a trans configuration J i n the mono-dentate ligand. Hence the minor product i s designated as fac-(L-L) b(L-L)™M(CO) 3. The source of the trans ligand i n fac-(L-L) b(L-L) mM(CO) 3 i s an isomerization of (L-L) that occurs i n the 4-50W photo-chemical reaction such that the c i s and trans forms of the ligand are i n equilibrium., with the r a t i o of c i s to trans being 9s 1 19 as shown by 7 F nmr spectroscopy. No apparent ligand isomerization occurs i n the 200W reaction. The 200W reaction y i e l d s the fac-(L-L) b(L-L) mM(CO)~ complexes c J whose spectroscopic properties are i d e n t i c a l with the c i s isomer ( i . e . monodentate ligand i n a c i s configuration) obtained from the 4-50W reaction. The 1 9 F nmr data of (L-L)b(L-L)I!!M(CO) ^  and (L-L) b(L-L) mM(CO) „ also support the assignment of a fac configuration since the two trifluoromethyl groups of the chelating ligand are chemically equivalent. I f the complexes adopted a mer configuration the two trifluoromethyl groups would be chemically inequivalent and -120-two a d d i t i o n a l quartets f o r the f l u o r i n e atoms of the bidentate ligand should appear. It i s not possible to determine whether the five-membered chelate r i n g i n the two isomeric t r i c a r b o n y l complexes i s planar i n s o l u t i o n or undergoing conformational changes that are rapid on an nmr time scale at room temperature, s i m i l a r to that discussed f o r the tetracarbonyl complexes i n the preceding section. C. Chemical Properties Fac-(L-L) l 3(L-L)" 1M(C0) „ c r y s t a l l i z e as yellow needles (except f o r fac-(L-L) b(L-L) mCr(CO)„ which gives pale orange V\ TYl needles) and fac-(L-L) (L-L)^.M(C0) 3 c r y s t a l l i z e as large orange plates. The lower s o l u b i l i t y of f a c - ( L - L ) b ( L - L ) ^ M ( C 0 ) . compared c J with fac-(L-L) b(L-L)^M(CO) 3 allows a f a c i l e separation of the two isomers by column chromatography. The t r i c a r b o n y l complexes are unstable i n nondegassed solvents but i n d e f i n i t e l y stable i n the s o l i d state. A nondegassed deuterochloroform s o l u t i o n of e i t h e r fac-(L-L) -(L-L)^Mo(C0) 3 or fac-(L-L) b(L-L) IjMo(CO) 3 produces a brown p r e c i p i t a t e of unknown composition and the (L-L)Mo(CO)^ complex a f t e r ca. 15 min. Decomposition i s slower i n benzene, The s t a b i l i t y of the complexes, which decreases i n the order tungsten > molybdenum » chromium, i s considerably enhanced i n nitrogen saturated solvents. The monodentate ligand i n the two isomeric t r i c a r b o n y l derivatives i s e a s i l y displaced by carbon monoxide, r e s u l t i n g -121-i n the formation of the tetracarhonyl complexes,.according to the general equation [XXXl]. f a c - ( L - L ) ( L - L ) M ( C O ) 3 + CO — > (L-L)M(CO)^ +. ( L - L ) [XXXl] M = Cr, Mo, W I r r a d i a t i o n of the fa c - ( L - L ) L 3 ( L - L ) m M ( C O ) complexes gives the corresponding tetrasubstituted dicarbonyl derivatives (see following section), suggesting the t r i c a r b o n y l species are intermediates i n the photochemical production of the dicarbonyl d e r i v a t i v e s . Refluxing a benzene solution of eithe r t r i c a r b o n y l isomer r e s u l t s i n the formation of (L-L)M(CO)^ (M = Mo, W) which appears to a t t a i n an equilibrium concentration as judged by the i r spectra of the reaction mixture. When the t r i c a r b o n y l species i s refluxed i n the presence of excess ligand, ca. ten molar, no (L-L)M(CO)^ forms. Possibly, at t h i s temperature the t r i c a r b o n y l complex exists i n an equilibrium with uncomplexed ligand as shown i n equation [XXXIl]. Decomposition by the evolution of carbon monoxide can give (L-L)M(CO)^. 80° f a c - ( L - L ) ( L - L ) M ( C 0 ) 3 ; * ( L - L ) M ( C 0 ) 3 + ( L - L ) [XXXIl] M = Mo, W However, r e f l u x i n g a benzene solut i o n of ei t h e r of the fac molybdenum isomers with a very large excess of the ligand, ca. twenty-five molar, slowly gives a new product of empirical formula ( L - L ) [ A S ( C H - J ? ] M O ( C O ) ? . Nmr, ir, and mass spectroscopic -122-data are consistent with a dimeric structure 26 i n which the two metal centres are linked by a metal-metal bond and two bridging dimethylarsenido groups. 26 As-As•= (L-L); R = CH, The trans carbonyl complex 26 possesses C 2^ symmetry f o r which three i r - a c t i v e carbonyl bands are expected. The i r spectrum i n the carbonyl region shows two bands, the low frequency band being broad possibly due to an accidental superposition of two absorptions. The ''"H nmr spectrum shows a s i n g l e t f o r the arsenic methyl groups of the bidentate ligand and a s i n g l e t at s l i g h t l y higher f i e l d f o r the bridging dimethylarsenido groups. The 19 7F spectrum shows one trifluoromethyl s i n g l e t . The geometry of the four-membered [MogASg] r i n g , with the metal-metal bond i n the plane of the r i n g , appears s i m i l a r to that of M o 2 ( C 0 ) 8 [ A s ( C H 3 ) 2 ] 2 . 6 8 A possible source of the bridging arsenido groups i n 2_6 i s tetramethyldiarsine formed from the decomposition of (L-L). Similar decomposition of the related (L-L) ligand i n a thermal - 1 2 3 -reaction giving 1,2-dimethyl-l,2-diphenyldiarsine, has been suggested to account f o r the formation of a dimeric i r o n 124-complex with bridging methylphenylarsenido groups (see Chapter I I I ; section 4.C). Refluxing a benzene solution of fac_-(L-L) b(L-L) mMo(CO)» c J with a good n-acceptor ligand such as diphenylacetylene, gives (L-L)Mo(CO)^ and cis-(L-L) 2Mo(C0) 2 (discussed i n section 3 of t h i s chapter). Note, that merely r e f l u x i n g a benzene soluti o n of fac-(L-L) b(L-L) mMo(CO) 3 does not give c i s - ( L - L ) 2 -Mo(C0) 2. A possible mechanism to account f o r i t s formation based on an i n i t i a l ligand d i s s o c i a t i o n (S^l) i s outlined i n [XXXIIl]-[XXXVII], Coordination of the acetylene followed by elimination of a carbonyl group from the acetylene complex, (where a carbonyl group would be more l a b i l e than i n fac-(L-L) b(L-L) mMo(CO)~), and attack by the more nucleophilic ligand (L-L) gives cis-(L-L) 2Mo(C0) 2. fac-(L-L) b(L-L) mMo(CO) 3 (L-L) bMo(CO) 3 + (L-L) [XXXIIl] (L-L) bMo(C0) 3 + acetylene * (L-L) bMo(CO) 3(acetylene) [XXXIV] (L-L) bMo(CO) 3(acetylene) ; ^ (L-L) bMo(C0) 2(acetylene) [xxxv] + CO (L-L) bMo(C0) 2(acetylene) + (L-L) (L-L) b(L-L) mMo(CO) 2(acetylene) [XXXVl] -124-(L-L) b(L-L)^Mo(C0) 2(acetylene) > cis-(L-L)jyio(C0) 2 [ x x x v u ] + acetylene i Another possible mechanism based on the i n i t i a l formation of a complex between f a c -(L-L) b(L-L) mMo(CO)and the acetylene c J (S^2), followed by elimination of carbon monoxide and co-ordination of the free arsenic atom of the monodentate ligand with concomitant loss of the acetylene, i s outlined i n [XXXVIII]-[XL]. fac-(L-L) b(L-L)^Mo(CO) 3 + acetylene [XXXVIII] (L-L) b(L-L)™Mo(C 0)-(ac etylene) c j (L-L) b(L-L)^Mo(CO) 3(acetylene) ; k [xxxix] (L-L) b(L-L)^Mo(C0) 2(acetylene) • + CO (L-L) b(L-L)^Mo(C0) 2(acetylene) >cis-(L-L) 2Mo(CO) 2 + acetylene [XL] In eit h e r case, the formation of an acetylene complex f a c i l i t a t e s the loss of a carbonyl group. There i s no spectro-scopic evidence ( i r ) f o r the existence of any of the postulated intermediates. Unlike the molybdenum and tungsten derivatives, a r e f l u x i n g benzene so l u t i o n of fac-(L-L) (L-L) Cr(CO)~ shows carbonyl absorptions i n the i r c h a r a c t e r i s t i c of the tetracarbonyl and dicarbonyl complexes. However, i t does not appear that -125-the complexes a t t a i n an equilibrium concentration. In the presence of a very large ligand excess the i r shows a pattern s i m i l a r to that seen f o r the molybdenum reaction, suggesting the presence of ( L - L ^ C A s C C H ^ ^ C r ^ C O ) ^ . However t h i s product was not i s o l a t e d . 3. C i s - ( L - L ) 2 M ( C 0 ) 2 (M = Cr, Mo, W) and Trans-(L-L)gM(CO) 2 Complexes (M = Cr, Mo) A. Preparation The c i s dicarbonyl complexes are best prepared by i r r a d i a t i n g (4-50W) a benzene s o l u t i o n of the tetracarbonyl complex and excess ligand (L-L): (L-L)M(CO)^ + excess (L-L) c i s - ( L - L ) 2 M ( C 0 ) 2 + 2 C 0 M = Cr, Mo, W [XLI] Heating the reactants at 175° y i e l d s the molybdenum dicarbonyl complex: trace amounts of the chromium and tungsten derivatives are obtained at higher temperatures (190-210°) a f t e r prolonged heating and occasional removal of the accumulated carbon monoxide. Further i r r a d i a t i o n (4-50W) of c i s - ( L - L ) 2 M ( C 0 ) 2 (M = Cr, Mo) gives the isomeric trans-(L-L) 2M(CO) 2 d e r i v a t i v e : c i s - ( L - L ) 2 M ( C 0 ) 2 h V > trans-(L-L) 2M(CO) 2 [XLII] M = Cr, Mo -126-Other related d i t e r t i a r y arsine and d i t e r t i a r y phosphine Group VI metal c i s dicarbonyl complexes have been prepared by heating the corresponding tetracarbonyl derivative with the ligand at temperatures > 200°. 2 ' ^ There does not appear to be any report of the existence of d i t e r t i a r y arsine trans dicarbonyl complexes. However, trans-(diphos) ?M(CO) ? complexes (M = Cr, Mo; diphos = (C^H,.), The ca t i o n i c species [(diphos) 2M(C0) 2] L' 2 (M = Cr, Mo, W) are prepared by chemical oxidation of the corresponding neutral observed and i n others trans to c i s or c i s to trans rearrangements occur. B. Characterization The c i s complexes have a configuration 2y_ with the two carbonyl groups i n r e l a t i v e c i s positions (C 2 symmetry) f o r which two i r - a c t i v e carbonyl bands are expected and observed. The spectra are consistent with other characterized Group VI metal 2 6 7 c i s dicarbonyl complexes. ' '' A sample spectrum i n the v(CO) region of cis-(L-L) ?Mo(CO) ? appears i n Figure 9(a). The PCH 2CH 2P(C 6H 5) 2) have been described. 2,8 complexes. 42,125-127 In some cases retention of isomerism i s \ ^ A s 27 M = Cr, Mo, W; As-As = (L-L) -127-e o t r e q a o s q y o 00 rH I 6 o CD e CD > o o o\ rH CM O O O CM Hi I l-l I w O <4H o CD CTJ CD ,C O rH O >> O •H -— Hi CM •P O O O CD ft O CQ S CM I H H i >» — O rH CO o CQ CD E H C3 ON a o u B q a o s q y CD u -128-carbonyl frequencies of c i s - ( L - L ) Q M ( C O ) Q are lowered considerably with respect to ( L - L ) M ( C O ) ^ . I t i s apparent that the two remaining carbonyl groups are able to share a much greater proportion of the available metal d-electrons; the r e s u l t i n g strong bonding to the metal explains t h e i r resistance to further s u b s t i t u t i o n . The carbonyl stretching frequencies of cis-(L-L)oM(CO) 2 and other c i s dicarbonyl complexes are l i s t e d i n Table XXXII. The higher carbonyl frequencies of the ( L - L ) derivatives are compatible with the expected greater amount of metal-arsenic double bonding due to the presence of the electronegative trifluoromethyl groups. The "*"H nmr spectra of the tetrasubstituted complexes show four arsenic methyl s i n g l e t s of equal area i n accordance with the c i s dicarbonyl structure. The 1 9 F nmr spectra show a trifluoromethyl s i n g l e t rather than two quartets as i s expected, presumably due to the f a c t that the trifluoromethyl groups are i n s e n s i t i v e to the d i f f e r e n t methyl environments about each arsenic atom. The trans complexes have a configuration 28 with the two carbonyl groups i n r e l a t i v e trans p o s i t i o n s . O C c o 28 M = Cr, Mo; As-As = ( L - L ) -129-T a b l e XXXII I r Spectra (1900-1700 cm"1) f o r Some Group VI Cis Dicarbonyl Complexes Compound v(CO)(cm 1 ) ( L - L ) 2 C r ( C 0 ) 2 * (diphos) 2Cr(C0) 2** ( d i a r s ) 2 C r ( C 0 ) 2 *** 1883, 1829 1848, 1708 1845, 1771 (L-L) ?Mo(CO) * (diphos) 2Mo(CO) 2 (diars) 2Mo(CO) 2 *** 1899, 1845 1852, 1786 1859, 1786 (L-L) ?W(CO) * (diphos) 2W(C0) 2 (diars) 2W(CO) 2 *** 1890, 1839 1847, 1782 1850, 1774 This work, C^H^ solvent. Data taken from reference 2, CICHgCHgCl solvent; diphos = ( C 6 H 5 ) 2 P ( C H 2 ) 2 P ( C 6 H 5 ) 2 . Data taken from reference 6, CHCl^ solvent; diars = o-C 6H^[As(CH 3) 2] 2. These complexes possess C 2^ symmetry f o r which two carbonyl stretching vibrations (A + ) are expected, one (B~ ') being i r - a c t i v e . The i r spectra of the trans derivatives show the expected one carbonyl band. A sample spectrum of trans-(L-L) 2Mo(C0) 2 i s seen i n Figure 9(b). 1 19 The H nmr and yF nmr spectra of both trans complexes--130-show one arsenic methyl and one trifluoromethyl s i n g l e t . C. Trans to Cis Isomerization The c i s complexes are thermodynamically more stable than the isomeric trans complexes. Complete trans to c i s isomerization occurs f o r the molybdenum derivative upon r e f l u x i n g i n benzene f o r 44 h and the chromium derivative upon r e f l u x i n g f o r 1.5 h:. t r a n s - ( L - L ) p M ( C O ) o n e a t > cis- ( L - L ) 2 M ( C 0 ) 2 [XLIII] M = Cr, Mo Presumably methyl-methyl int e r a c t i o n s are greatest i n the trans de r i v a t i v e , these interactions being greater f o r chromium due to i t s smaller atomic s i z e . Trans to c i s isomerization i s also found when the molybdenum and chromium derivatives are chromatographed on F l o r i s i l . The trans chromium derivative even isomerizes i n the s o l i d state. The trans-(diphos)J(CO) complexes (M = Cr, Mo) are known to undergo f a c i l e isomerization i n s o l u t i o n giving 2 8 128 the c i s isomer. V Bond et a l . have recently shown that c y c l i c voltammetry i s an extremely useful technique f o r r -i 0 4-1 +2 studying isomerism of the L(diphos) 2M(C0) 2J ' ' complexes (M = Cr, Mo, W). The c i s - t r a n s isomerization processes of necessity involve bond breaking. Perhaps, a five-coordinate intermediate i s involved, as indicated i n [XLIV]. - 1 3 1 -O [XLIV] O 4. Summary Pyro l y s i s ( 1 5 0 ° ) of M(C0) 6 (M = Cr, Mo, W) and ( L - L ) or ( L - L ) i n benzene affords the tetracarbonyl chelate complexes (L-L)M(CO)^ and ( L - L ) ' M ( C O ) ^ (M = Cr, Mo, W). U l t r a v i o l e t i r r a d i a t i o n (450W) of the Group VI (L-L)M(CO)^ d e r i v a t i v e s and excess ( L - L ) i n benzene yie l d s f a c - ( L - L ) L 3 ( L - L ) ^ M ( C 0 ) . , f a c - ( L - L ) B ( L - L ) ™ M ( C 0 ) 3 ( where one ligand functions i n a bidentate manner and another, i n e i t h e r a c i s or trans configuration, functions i n a monodentate manner), and c_is-(L-L) 2M(C0) 2 (M = Cr, Mo, W). Prolonged i r r a d i a t i o n of c i s - ( L - L ) 2 M ( C 0 ) 2 y i e l d s t r a n s - ( L - L ) 2 M ( C O ) 2 (M = Cr, Mo) which can be thermally reconverted into the c i s form, A l l reactions were monitored by observing the c h a r a c t e r i s t i c carbonyl bands of the substituted products. Figure 10 shows a t y p i c a l spectrum of a reaction mixture where a l l bands can be assigned. Further characterization of the complexes, once is o l a t e d , was aided by nmr spectroscopy. -132-(A) 2000 1900 1840 Wavenumber (cm - 1) Figure 10. The carbonyl i r spectrum i n cyclohexane of a mixture of (L-L)W(CO)^ (A), f a c - ( L - L ) b -( L - L ) % ( C 0 ) 3 (B), and cis-(L-L) 2W(CO) 2 (C). -133-CHAPTER V RESULTS AND DISCUSSION This chapter examines some seven-coordinate Group VI metal halocarbonyl complexes of cis-2 ,3-"bis(dimethylarsino)-l,l,l ,4-,4,4-hexafluorobut-2-ene (L-L) and ci s - 2 , 3-bis(methyl-phenylarsino ) - l , 1,1,4-,4,4—hexafluorobut-2-ene (L-L) , with the emphasis on the stereochemical n o n r i g i d i t y of these 1 13 19 complexes as revealed by nmr studies of the H, -a), 7F, 31 and J P n u c l e i . Section 1 concerns some hal o t r i c a r b o n y l complexes; section 2, some bromodicarbonyl complexes; and section 3» some bromomonocarbonyl complexes. Section 4-summarizes aspects of the preceding three sections. 1. (L-L)M(C0). 3X 2 and (L-L) ' M ( C O ) ^ Complexes (M = Mo, W; X = Br, I) A. Preparation and Chemical Properties The general method of preparation of the halogen derivatives (L-L)M(C0) qX ? and (L-L)'M(C0)^X 9 can be represented as follows; -134-(L-L)M(CO)^ > (L-L)M(CO) 3X 2 + CO ( L - L ) ' M ( C O ) ^ 2 > ( L - L ) ' M ( C O ) 3 X 2 + CO [ X L V ] M = Mo, W; X = Br, I Slow dropwise addition of a s o l u t i o n of the halogen to a vigorously s t i r r e d methylene chloride s o l u t i o n of the metal complex i s es s e n t i a l i n order to prevent l o c a l accumulation of the halogen. The conditions f o r the production of the h a l o t r i c a r b o n y l complexes are found to depend on the metal, ligand, and halogen (see Chapter II; sections 5'C and 6.D). In general the preparation of the ( L - L ) M ( C 0 ) 3 X 2 complexes r requires lower temperatures than does the ( L - L ) M ( C 0 ) 3 X 2 complexes. Possibly t h i s r e f l e c t s a greater s t a b i l i t y of the ( L - L ) species, since the replacement of two methyl groups i n ( L - L ) by two phenyl groups i n ( L - L ) r e s u l t s i n reduced methyl-halogen i n t e r a c t i o n s . The halogen complexes are c r y s t a l l i n e orange or yellow nonionic s o l i d s considerably more soluble i n polar solvents than i n nonpolar ones. They appear to decolourize i n the s o l i d state a f t e r a few months and are quite unstable i n oxygenated solvents. The s t a b i l i t y of these complexes which i s enhanced * For example, (L-L)Mo(CO)^I 9 has a molar conductivity of 0.9 - 1 2 ohm cm i n nitrobenzene; 1:1 e l e c t r o l y t e s show cond u c t i v i t i e s -1 2 44 of 20-30 ohm cm i n the same solvent. Refluxing a sample of (L-L)Mo(C0) 3Br 2 i n methylene chloride under a nitrogen atmosphere f o r 6 h r e s u l t s i n complete decomposition; s i m i l a r r e s u l t s are observed a f t e r s t i r r i n g a s o l u t i o n at room temperature f o r 39 h, -135-i n nitrogen saturated solvents, decreases i n the order tungsten » molybdenum; iodine » bromine. B. Characterization The c r y s t a l structure of (L-L)W(C0) 3I 2, which i s very s i m i l a r to that of ( C 6 H 5 ) 2 P ( C H 2 ) 2 P ( C 6 H 5 ) 2 M o ( C O ) 3 B r 2 , 5 7 i s shown i n Figure 11. The tungsten atom i s seven-coordinate with a d i s t o r t e d capped octahedral environment , the capping group being a carbonyl. The capped face consists of the two remaining carbonyl groups and one of the arsenic atoms from the bidentate ligand, while the uncapped face consists of the two iodine atoms and the remaining arsenic atom. The capping group exhibits close nonbonded contacts with the other three atoms i n the capped face. The angle subtended at the tungsten atom by the bidentate ligand i s 75-9° which i s considerably decreased from the angles subtended by s i m i l a r chelating ligands i n octahedral complexes.^ The two tungsten-arsenic bonds are s i g n i f i c a n t l y shorter o than a normal tungsten-arsenic single bond by ca. 0.19 A. This shortening i s thought to be due to some metal-arsenic double bond character caused by drr-drr back donation from the tungsten atom. There i s also a s i g n i f i c a n t difference between the two metal-arsenic bond lengths, the metal-arsenic bond trans to an iodine atom being shorter than the metal-arsenic bond trans to a carbonyl group. Since an iodine i s expected to be a * The choice of the capped octahedron appears to describe the observed geometry more exactly. - 1 3 7 -weaker dir-acceptor than a carbonyl group, there i s a greater amount of back donation to the arsenic atom trans to the halogen. In f a c t , i t appears as though the halogen has no apparent n-acceptor properties, the tungsten-iodine bond length being e s s e n t i a l l y the sum of t h e i r single bond r a d i i . The nmr spectra of the tungsten complex are not i n accordance with i t s X-ray c r y s t a l structure. The "'"H nmr spectrum at room temperature and -70° exhibits one arsenic methyl s i n g l e t c h a r a c t e r i s t i c of chelating (L-L) and the 1 9 F 13 nmr spectrum one trifluoromethyl s i n g l e t . The nmr spectrum at room temperature consists of one s i n g l e t f o r the dimethylarsino groups ("*"H decoupled), one quartet f o r the trifluoromethyl groups (J(C,F) = 285 Hz), a broad absorption f o r the o l e f i n i c carbons (due to long range coupling to the f l u o r i n e atoms), and one s i n g l e t f o r the carbonyl groups. No s t a t i c polyhedron can e x i s t that i s i n agreement 1 19 13 with a l l the nmr data. Thus the H, 'F, and JQ> nmr data suggest that i n solution the molecule has a nonrigid structure 1 19 at room temperature on an nmr time scale; the H and 7F nmr spectra are consistent with the molecule having t h i s nonrigid structure down to -70°. Rapid exchange of the three carbonyl groups could possibly explain the appearance of one carbonyl 13 absorption i n the nmr spectrum; however, t h i s would not 1 19 explain the H and 7F nmr spectra since the two arsenic atoms would s t i l l be i n an asymmetric environment. A more l i k e l y mechanism to explain the n o n r i g i d i t y , consistent with a l l the nmr data, i s a drastic rearrangement process involving rapid -138-scrambling of the carbonyl groups and iodine atoms, and simultaneous migration of the capping group over the faces of the [ASgCglg] octahedron. This process can proceed v i a an intramolecular rearrangement or a carbonyl d i s s o c i a t i v e process forming a six-coordinate intermediate. The s o l i d - s t a t e structure may correspond to the low temperature form of the molecule but t h i s l i m i t was not reached at - 7 0 ° . 1 19 The H and 7F nmr spectra of the other halot r i c a r b o n y l derivatives are very s i m i l a r to that of (L-L)W(C0) 3I 2 suggesting they also are nonrigid i n s o l u t i o n i n the manner discussed above. Note that i n the meso-(L-L) M{C0)^X^ complexes a multipl e t i s observed i n the XH nmr spectra i n deuterochloroform f o r the phenyl protons whereas i n the rac-(L-L) M(C0) 3X 2 complexes a s i n g l e t i s seen f o r the phenyl protons. Presumably the singlet, i s due to an accidental superposition of peaks since the racemic isomers exhibit a multiplet f o r the phenyl protons i n deuterobenzene. A feature of the "hi nmr spectra of the (L-L)M(C0) 3X 2 com-plexes i s that f o r a given metal, as X changes from Br to I, the arsenic methyl absorption moves downfield. This trend i s also observed f o r a given metal and ligand configuration i n the diastereomeric (L-L) M(C0) 3X 2 complexes. A further unique feature of the diastereomeric complexes i s that f o r a given metal and halogen, the arsenic methyl sig n a l i n rac-(L-L) -M(C0) 3X 2 i s considerably more shielded than i n meso-(L-L) --139-M(C0) 3X 2 < This could r e f l e c t a difference i n the r e l a t i v e conformations of the five-membered chelate r i n g i n the two types of diastereomeric complexes. The i r spectra of the t r i c a r b o n y l complexes i n the carbonyl region, which consist of three bands, are s i m i l a r to other seven-coordinate Group VI metal t r i c a r b o n y l derivatives (Table XXXIII). Table XXXIII I r Spectra (2100-1900 cm - 1) f o r Some Group VI Halotricarbonyl Complexes Compound v(C0)(cm _ 1 ) (L-L)Mo(C0) 3I 2* 2056, 1985. 1927 (dam)Mo(C0) 3I 2** 2040, 1975, 1920 (diphos)Mo(CO) 3I 2*** 2036, 1986, 1925 (diars)Mo(C0) 3I 2**** 2053, 1982, 1925 (L-L)W(C0) 3Br 2* 2068, 1977, 1911 (diphos)W(C0) 3Br 2*** 2050, 1965, 1910 * This work, C^H-^ solvent. Data taken from reference 53, KBr disk; dam = ( C^H^) 2~ AsCH 2As(C 6H 5) 2. *** Data taken from reference 52, KBr disk; diphos = ( C 6 H 5 ) 2 P ( C H 2 ) 2 P ( C 6 H 5 ) 2 . **** Data taken from reference 44, nujol mull; diars = o-C 6 H 4 [ A s ( C H 3 ) 2 ] 2 . -14-0-2. (L-L)LMo(C0) 2Br 2 Complexes (L = a Monodentate Ligand) • A. Preparation and Chemical Properties The addition of a methylene chloride s o l u t i o n of L to a methylene chloride solution of (L-L)Mo(C0) 3Br 2 under a nitrogen atmosphere, r e s u l t s i n the f a c i l e replacement of a carbonyl group by L giving (L-L)LMo(C0) 2Br 2s 2^° (L-L)Mo(C0) 3Br 2 + L (L-L)LMo(C0) 2Br 2 + CO [XLVI] The dicarbonyl complexes are seven-coordinate yellow (except f o r (L-L)[p(C 6H^) 3]Mo(C0) 2Br 2 which i s orange) c r y s t a l l i n e s o l i d s considerably more stable and more soluble than the parent (L-L)Mo(C0) 3Br 2 complex. These complexes do not melt but only decompose on heating i n an open c a p i l l a r y tube. B. Spectroscopic Results For the (L-L)LMo(C0) 2Br 2 complexes i n which L i s a monodentate t e r t i a r y phosphine or phosphite, the nmr spectra show an arsenic methyl s i n g l e t i n the region associated with chelating (L-L) and absorptions due to substituents on the 19 phosphine or phosphite. The 7 F nmr spectra exhibit a trifluoromethyl s i n g l e t f o r (L-L). The complex ( L - D f X o C H ^ ] -Mo(C0) 2Br 2 shows one arsenic methyl s i n g l e t i n the "*"H nmr spectrum at 25° and -80°. Thus, the nmr spectra of the dicarbonyl complexes (L-L)LMo(C0) ?Br ? i n the (L-L) region -141-are very s i m i l a r to those of the (L-L)M(CO) 3X 2 complexes suggesting they too are nonrigid i n s o l u t i o n . I f the dicarbonyl complexes adopt an asymmetric octahedral co n f i g u r a t i o n ' ( s i m i l a r to (L-L^CCO^Ig v/ith L replacing a carbonyl group), the XH nmr spectra could be accounted f o r by a scrambling process of L, the carbonyl groups, and bromine atoms as well as a simultaneous rapid migration of the capping group over faces of the octahedron. E q u i l i b r a t i o n of the arsenic methyl groups by rapid migration of the capping group over faces of the octahedron would dictate a s t a t i c octahedral configuration 2_9_ ( i r suggests carbonyl groups are c i s ) with L i n the capping p o s i t i o n . Connor et al.^° have recently reported a f l u x i o n a l seven-coordinate molybdenum and tungsten iododicarbonyl complex. They explain the f l u x i o n a l i s m by a polytopal rearrangement, possibly by rapid migration of the iodine over the faces of a s t a t i c t r i g o n a l prism. Br 2 9 As-As = (L-L) -142-The (L-L) b(L-L) mIVIo(C0) 2Br 2 complex (where (L-L) 1 3 denotes bidentate ligand and ( L - L ) m monodentate ligand) provides an i n t e r e s t i n g example where the nmr data suggest three d i f f e r e n t types of processes are occurring i n s o l u t i o n . The nmr spectrum shows two equal area arsenic methyl s i n g l e t s , while 19 the 7F nmr spectrum exhibits one trifluoromethyl s i n g l e t . I f scrambling between the carbonyls, bromine atoms, and ( L - L ) m and rapid migration of the capping group over the octahedral faces are occurring, the resultant "'"H nmr spectrum should give an arsenic methyl s i n g l e t ( r e l a t i v e area 2) f o r the bidentate ligand and two arsenic methyl s i n g l e t s (each of r e l a t i v e area 1) f o r the monodentate ligand; one of the s i n g l e t s f o r ( L - L ) m would also have a chemical s h i f t c h a r a c t e r i s t i c of 19 a uncoordinated arsenic atom. The 7F spectrum should give a trifluoromethyl s i n g l e t f o r the f l u o r i n e atoms of the bidentate ligand ( r e l a t i v e area 2) and two trifluoromethyl quartets (each of r e l a t i v e area 1) f o r the monodentate ligand with a c h a r a c t e r i s t i c coupling constant f o r c i s trifluoromethyl 123 124 groups. •7' It appears that i n addition to a scrambling and migration process, exchange i s also occurring between the coordinated and uncoordinated arsenic atoms of the monodentate ligand thereby e q u i l i b r a t i n g the methyl groups of t h i s ligand. Scrambling and ligand exchange appear to be f a s t on an nmr time scale at -80°. An exchange process between the chelated and monodentate ligands would probably r e s u l t i n the appearance of a single arsenic methyl absorption. Colton et a l . have reported -143-a variable temperature XH nmr study of the seven-coordinate complexes [(C 6H^) 2AsCH 2As(C 6H^) 2] 2M(C0) 2X 2 (M = Mo, W; X = C l , Br, I ) , containing one chelated and one monodentate d i t e r t i a r y arsine ligand. Their study shows that, near room temperature, exchange occurs between the nonequivalent ligands, r e s u l t i n g i n the appearance of one methylene absorption, and at lower temperatures t h i s exchange ceases, r e s u l t i n g i n the appearance of two d i f f e r e n t methylene absorptions. They suggested the t r a n s i t i o n state f o r the exchange process has configuration 30» X X As. \ / As v H 2 C C H 2 OC CO 20 M = Mo, W; X = C l , Br, I The i r pattern i n the carbonyl region of a l l the (L-L)LMo-( C 0 ) 2 B r 2 complexes i s very s i m i l a r suggesting the carbonyl groups have i d e n t i c a l r e l a t i v e configurations. The presence of two strong carbonyl absorptions indicates the carbonyl groups possibly possess a c i s o r i e n t a t i o n . ^ 0 The carbonyl frequencies vary as a function of the rr-acceptor a b i l i t y of L, the better the rr-acceptor the higher the carbonyl frequency. Thus the phosphite complexes give higher carbonyl frequencies than the phosphine complexes. -144-3- (L-L)L 2Mo(CO)Br 2 Complexes A. Preparation and Chemical Properties The seven-coordinate monocarbonyl complexes are prepared "by r e f l u x i n g the parent (L-L)Mo(CO) 3Br 2 species i n benzene with an excess amount of the monodentate ligand L. (L-L)Mo(C0) QBr o + excess L - — 8 ° ° >(L-L)L 0Mo(CO)Br 0 J £ benzene <~ [XLVII] + 2C0 (L-L) 2Mo(C0)Br 2 i s prepared by warming the ( L - L ) b ( L - L ) m -Mo(C0) 2Br 2 complex i n benzene to 50°s (L-L) b(L-L) mMo(C0) 2Br 2 >(L-L) 2Mo(C0)Br 2 + CO [XLVIIl] The bromomonocarbonyl complexes are orange (except f o r (L-L) 2Mo(C0)Br 2 which i s brown) c r y s t a l l i n e s o l i d s , stable i n the s o l i d - s t a t e but unstable i n nondegassed solvents, g i v i n g the corresponding (L-L)LMo(C0) 2Br 2 complex as one of the decomposition products. The complexes show a great tendency to c r y s t a l l i z e as methylene chloride adducts, but the solvent of c r y s t a l l i z a t i o n i s r e a d i l y removed i n vacuo, They, l i k e the (L-L)M(C0) 3X 2 and (L-L)LMo(C0) 2Br 2 d e r i v a t i v e s , do not melt on heating. A l l the (L-L)L 2Mo(C0)Br 2 complexes containing monodentate phosphines or phosphites are carbon monoxide c a r r i e r s : CO N (L-L)L Mo(C0)Br ? ; (L-L)LMo(C0)„Br 9 + L [XLIX] -145-Th e (L-L) 2Mo(C0)Br 2 complex does not appear to react' with carbon monoxide at room temperature. B. Stereochemical Nonrigidity The nmr r e s u l t s of the (L-L)L 2Mo(C0)Br 2 complexes (L i s monodentate) indicate the species are r i g i d at room temperature and are nonrigid at higher temperatures on an nmr time scale. This i s i n contrast to the (L-L)M(CO) 3X 2 and (L-L)LMo(C0) 2Br 2 derivatives which appear to be nonrigid at room temperature. The ( L - L ) [ P ( 0 C H 3 ) 3 ] 2 M o ( C 0 ) B r 2 and ( L - L ) [ P ( O C H 3 ) 2 ( C 6 H 5 ) ] 2 -Mo(C0)Br 2 complexes are examples of H ^ P P and H ^ P P spin systems. The theory of nuclear spin systems of the type H PP'H ' has been developed by H a r r i s 1 ^ 0 ' 1 3 1 who has shown that a simple 1:2:1 " t r i p l e t " resonance w i l l be observed f o r H n when | J ( P , P ' ) | » | J ( H , P ) + j'(H,p')| ( i . e . when 31p_31p c o u p l i n g i s strong). When 31p_31p c 0 u p l i n g i s small a 1:1 doublet 31 31 should be observed. However, when J P - P coupling i s intermediate several methyl absorption resonances are expected and appear as an unresolved, broad resonance l y i n g between a 1:1 doublet of separation |J(H , P ) + J^H.p')! .130.131 T h e two monocarbonyl complexes exhibit the l a t t e r type of resonance pattern f o r the methyl and methoxy groups. Henceforth t h i s type of resonance absorption i s referred to as an intermediate pattern. The XH nmr spectrum of (L-L ) [ P(OCH 3) 3] 2Mo(CO)Br 2 at room temperature consists of two equal area arsenic methyl s i n g l e t s -146-and a phosphite methyl intermediate pattern; the yF nmr spectrum shows a trifluoromethyl s i n g l e t . When phosphorus i s decoupled the phosphite methyl proton absorbance appears as a single sharp l i n e i n d i c a t i n g a l l s i x methyl groups are equivalent. These spectra can be interpreted i n terms of a seven-coordinate capped octahedral structure 2~L (P = PCOCH^)^) with a carbonyl group i n the capping p o s i t i o n above the [P 2Br] face. The arsenic methyl groups on one side of the [A.s^Pg] plane experience a d i f f e r e n t environment from those on the other side. 21 (P = PCOCH^)^) has a temperature dependent XH nmr spectrum shown i n Figure 12. As the temperature i s increased the two i n i t i a l l y sharp arsenic methyl s i n g l e t s broaden, collapse, and coalesce into a single l i n e which sharpens as the temperature i s further increased. This indicates that at the higher temperatures a l l the arsenic methyl groups are equivalent on an nmr time scale and suggests that the molecule Br Br 21 As-As = (L-L) -147-- 1 4 8 -i s f l u x i o n a l i n the manner indicated i n [ L ] (P = P(OCH^)„). An intramolecular polytopal rearrangement from a capped octahedral geometry through a pentagonal bipyramid intermediate to another capped octahedral geometry, pos s i b l y by rapid migration of the carbonyl group over the two [PgBr] faces, would lead to an averaging of the two types of arsenic methyl environments. Rather than r e s t r i c t i n g the migration to the two faces as shown i n [ L ] , migration of the carbonyl group over a l l the faces would also lead to an averaging process. A polytopal rearrangement process as depicted i n [ L ] (P = PCOCH^)^) but invo l v i n g a phosphite d i s s o c i a t i o n forming a six-coordinate intermediate can be eliminated by the fa c t that the phosphite methyl groups remain v i r t u a l l y coupled over the entire temperature range. I f bond d i s s o c i a t i o n occurred a doublet might be expected f o r the phosphite methyl groups. The room temperature nmr spectra of (L-L)[P(OCH^) ?(C^H^)]^--149-MoCCCOBrg indicate the molecule has configuration J l (P = P(OCH^g(C^H^)). Thus, the XH nmr spectrum shows two equal area arsenic methyl s i n g l e t s followed, at lower f i e l d , by two methoxy methyl intermediate patterns and phosphorus phenyl multiplets. The intermediate patterns collapse to two sharp 19 s i n g l e t s with phosphorus decoupling. The 7F nmr spectrum 31 consists of a trifluoromethyl s i n g l e t . Since the P nmr spectrum indicates the two phosphorus n u c l e i are chemically equivalent, the two intermediate patterns are assigned to the 132 diastereotropic J methoxy methyl groups on each phosphorus atom. The intermediate patterns r e s u l t from v i r t u a l l y coupled H^PP H-j spin systems. S i m i l a r l y the (L-L)[P(0CH 3) 2(CgH^)] 2Mo(C0)Br 2. complex has a temperature dependent XH nmr spectrum i n d i c a t i n g i t i s f l u x i o n a l . The two arsenic methyl s i n g l e t s broaden, collapse, and coalesce as the temperature i s increased. However, there i s no e q u i l i b r a t i o n of the two diastereotropic methoxy methyl resonances. Figure 13 shows the two intermediate patterns f o r the methyl groups, with and without phosphorus decoupling, at room temperature and the temperature corresponding to coalescence of the arsenic methyl absorptions. The high temperature spectra appear to be best accounted f o r by a process [ L ] (P = PfOCH^JgCCgH^)) which would lead to an e q u i l i b r a t i o n of the arsenic methyl resonances but not the diastereotropic methoxy methyl resonances. Thermodynamic parameters were calculated f o r the f l u x i o n a l motion using the method of Gutowsky and Holm. x 0 x - 1 5 0 -95< D 950 A ^ ' A ^ ^ ^ v ^ ^ 25 25c 2 Hz Figure 1 3 . Variable temperature 1H nmr spectra i n benzene i n the methoxy methyl region of ( L - L ) [ p ( O C H 3 ) 2 ( C 6 H 5 ) ] 2 Mo(C0)Br 2. A and D are the phosphorus decoupled spectra. B and C are the normal spectra. -151-The parameters f o r t h i s complex and (L-L)[P(0CH 2CH 3) 3] 2Mo(C0)Br are l i s t e d below i n Table XXXIV. Table XXXIV Thermodynamic Parameters f o r (L-L)L 2Mo(C0)Br 2 Complexes Compound A H ^ k c a l m o l - 1) AS"*"(eu) T c(°K)* (L-L)[P(OCH 3) 2(C 6H 5)] 2Mo(CO)Br 2 6.7 + 0.6 -29 + 2 368+3 (L-L)[P(0CH 2CH 3) 3] 2Mo(C0)Br 2 4.9 + 0.6 -35 ± 2 368+3 T = coalescence temperature of the arsenic methyl resonances, c (L-L)[P(0CH 3) 2(C 6H 5)] 2Mo(C0)Br 2 i s characterized by a low a c t i v a t i o n enthalpy and a very large negative a c t i v a t i o n entropy suggesting the intermediate or t r a n s i t i o n state of the f l u x i o n a l motion i s of considerable less entropy than the s t a t i c forms. Process [ L ] , involving the formation of a pentagonal bipyramid as the intermediate i s i n accord with the entropy value of Table XXXIV, since t h i s symmetrical intermediate should have a smaller entropy than e i t h e r of the s t a t i c forms. Thus the capped octahedral ground state configuration i s des t a b i l i z e d r e l a t i v e to the less crowded t r a n s i t i o n state, r e s u l t i n g i n a low b a r r i e r f o r the motion. The thermodynamic parameters do not favour a polytopal rearrangement process with d i s s o c i a t i o n g i v i n g a six-coordinate intermediate. D i s s o c i a t i o n of the phosponite can also be -152-eliminated by the f a c t that the methoxy methyl groups remain v i r t u a l l y coupled over the entire high temperature range. Di s s o c i a t i o n of one end of the chelate ligand (L-L) to form a six-coordinate intermediate followed by recombination would probably require a much higher b a r r i e r than i s observed . For •. 133 example, Meaker et a l . report an a c t i v a t i o n energy of 12.8 kcal m o l _ ± f o r an exchange process involving d i s s o c i a t i o n of one end of a d i t e r t i a r y alkylphosphine ligand i n a seven-coordinate tantalum carbonyl complex. They note that a polytopal rearrangement could occur but would possibly have a much lower b a r r i e r than observed. The nmr spectra of (L-L)[P(0CH 2CH 3) 3] 2Mo(C0)Br 2 at room temperature d i f f e r from those of the other monocarbonyl complexes suggesting i t has a d i f f e r e n t r e l a t i v e configuration. The XH nmr spectrum exhibits two equal area arsenic methyl s i n g l e t s , an apparent t r i p l e t f o r the methyl protons of the ethoxy group, and a multip l e t structure f o r the methylene protons of the ethoxy group due to coupling to the methyl protons and 19 phosphorus atom; the 7F nmr spectrum consists of a t r i f l u o r o -methyl s i n g l e t . A more det a i l e d examination of the XH nmr spectrum of the phosphite group shows, that with proton decoupling, the methylene absorption collapses to two doublets with 1H--7"LP coupling constants of 6.0 and 4.0 Hz. I t i s not possible to say whether the two d i f f e r e n t sets of methylene protons are further coupled across the molybdenum centre to the other -153-phosphorus atom. With broad band phosphorus decoupling, the methylene multiplet collapses to two equal area quartets (J(H,H) = 7.0 Hz). The decoupling experiments indicate there are two chemically inequivalent sets of methylene protons. In 31 accordance with these observations the P nmr spectrum indicates the two phosphorus atoms are i n an asymmetric environment. There appears to be an accidental superposition of two absorptions i n the methyl resonance since one t r i p l e t i s seen; furthermore, the methyl protons do not appear to be coupled to the phosphorus atom. These spectra can be interpreted i n terms of a seven-coordinate capped octahedral structure 3_2 (P = PCOCHgCH^)^) with the phosphite groups i n a trans p o s i t i o n . A carbonyl group occupies the capping p o s i t i o n above the [PBrg] face. There i s a d i f f e r e n t environment on each side of the [ASgBrg] plane, so that arsenic methyl groups on one side of the plane have a d i f f e r e n t chemical s h i f t from those on the other side; s i m i l a r l y the two phosphite groups are i n an asymmetric environment. P 22 As-As = (L-L) -154-J2 (P = PCOCHgCH^)^) has a temperature dependent XH nmr spectrum i n d i c a t i n g i t also i s f l u x i o n a l . As the temperature i s increased the two arsenic methyl si n g l e t s broaden, collapse, and coalesce i n a manner analogous to Jl (P = T{0CHj)y or P ( O C K j ) ^ { C ^ ) ) . S i m i l a r l y the two methylene quartets (phosphorus decoupled) collapse into one quartet at the temperature corresponding to coalescence of the arsenic methyl s i n g l e t s . Since the chemical s h i f t difference between the two methylene quartets i s so small (1.5 Hz) the collapse may be a temperature e f f e c t rather than i n d i c a t i n g an e q u i l i b r a t i o n of the methylene groups* The high temperature spectra can be s a t i s f a c t o r i l y explained by an intramolecular polytopal rearrangement process [ L i ] (P = PtOCHgCH-j)^) which leads to an averaging of the two types of arsenic methyl and ethoxy methylene environments. Thermodynamic parameters were calculated (Table XXXIV) f o r the motion and are very s i m i l a r to those of 31 (P = P ( 0 C H . J , ( C A i c ) ) , -155-suggesting the two complexes behave i n an analogous manner at high temperatures. The nmr spectra of (L-L)[P(CH 3) 2(C 6H 5)] 2Mo'(CO)Br 2 d i f f e r considerably from the other seven-coordinate monocarbonyl complexes. At room temperature the "*"H nmr spectrum i n the (L-L) region consists of an arsenic methyl quartet ( r e l a t i v e area 1; (J(H,F) = 2.5 Hz), followed at higher f i e l d by an arsenic methyl s i n g l e t ( r e l a t i v e area 2) and an arsenic methyl quartet ( r e l a t i v e area 1; (J(H,F) = 2.0 Hz). The 1:2:1 arsenic methyl r a t i o i s presumably due to an accidental superposition of peaks i n benzene since four equal area absorptions appear i n deuterochloroform. The phosphine ligand exhibits four phosphine 1 31 methyl doublets (each of r e l a t i v e area 1) a r i s i n g from H- P coupling and two phosphine phenyl multiplets (each of r e l a t i v e area 1.7)- With broad band phosphorus decoupling, the phosphine methyl doublets collapse to four s i n g l e t s . The room temperature "*"H nmr spectrum of t h i s complex with and without phosphorus decoupling i s shown i n Figure 14. 19 The y F nmr spectrum gives two equal area trifluoromethyl quartets (J(F,F) = 15.0 Hz); the 1 9 F - 1 9 F coupling constant 1 2 3 1 2 4 31 indicates the trifluoromethyl groups are c i s . J ' The J P nmr spectrum at room temperature suggests the two phosphorus atoms are i n an asymmetric environment. Possible configurations f o r (L-L)[P(CH 3) 2(C 6H 5)] 2Mo(C0)Br 2 consistent with the room temperature nmr spectra are shown i n 22 and 3_4 (P = P ( C H 3 ) 2 ( C 6 H 5 ) ) . In eith e r configuration the capping carbonyl group i s above the [AsPBr] face such that -156-Figure 14. Variable temperature H nmr spectra (methyl region) i n benzene of (L-L)[p(CH 3) 2(C 6H 5)] 2Mo(CO)Br 2. A i s the normal spectrum and B, C, D, E are the phosphorus decoupled spectra. -157-the two arsenic atoms are i n an asymmetric environment and a l l four arsenic methyl groups are inequivalent. S i m i l a r l y the two d i f f e r e n t phosphorus atoms produce two d i f f e r e n t p a i r s of 132 diastereotropic ^ phosphine methyl groups. (L-L)[P(CH 3) 2(C^H^)] 2Mo(CO)Br 2 has a temperature dependent 1 19 1 H and 7F nmr spectrum. The variable temperature H nmr spec-trum i s shown i n Figure 14. I t was not possible to. obtain a l i m i t i n g high temperature spectrum; thus the spectrum i s not as defined at high temperatures as those of the other monocarbonyl complexes. As the temperature i s increased i t appears that there i s broadening of the arsenic methyl and phosphine methyl resonances. Since the two types of methyl resonances are not as well separated as i n the phosphite and phosphonite complexes, overlap of the resonances can occur. The broad resonance observed at high temperatures possibly i s due to arsenic and phosphine methyl absorptions. At high temperatures there i s no e q u i l i b r a t i o n of the two phosphorus atoms. However, as the temperature i s increased -158-the two t r i f l u o r o m e t h y l q u a r t e t s "broaden, c o l l a p s e and c o a l e s c e i n t o a s i n g l e b r o a d peak w h i c h sharpens as the t e m p e r a t u r e i s f u r t h e r i n c r e a s e d , i n d i c a t i n g the t r i f l u o r o m e t h y l groups a r e e q u i v a l e n t on an nmr time s c a l e a t h i g h t e m p e r a t u r e s . I n v o k i n g a p o l y t o p a l rearrangement p r o c e s s a t h i g h t e m p e r a t u r e s i n v o l v i n g c a r b o n y l m i g r a t i o n o v e r f a c e s of t h e o c t a h e d r o n such as t o e q u i l i b r a t e the t r i f l u o r o m e t h y l groups b u t n o t the phosphorus atoms, s u g g e s t s t h e complex has c o n f i g u r a t i o n 3_4 (P = 7{CK^)Z ( C ^ H ^ ) ) . R a p i d m i g r a t i o n o f a c a r b o n y l o v e r the [ A s P B r ] , [ P B r 2 ] , and [ A s P B r ] f a c e s , i l l u s t r a t e d i n [ L I l ] , would e q u i l i b r a t e the t r i f l u o r o m e t h y l groups b u t n o t the phosphorus atoms. A l i m i t i n g f a s t exchange h i g h t e m p e r a t u r e nmr sp e c t r u m f o r t h i s t y pe o f p r o c e s s s h o u l d c o n s i s t o f two a r s e n i c m e t h y l r e s o n a n c e s and f o u r p h o s p h i n e m e t h y l r e s o n a n c e s . As-As = ( L - L ) [ L I l ] A s i m i l a r type of motion f o r 13_ (P = ~P{CE^)2 ( C 6 H ^ ) ) would eq u i l i b r a t e the trifluoromethyl groups and the phosphorus atoms. -159-Had i t been possible to calculate thermodynamic parameters f o r 2k ( p = P ( C H 3 ) 2 ( C 6 H 5 ) ) , they may have yielded further information concerning the f l u x i o n a l motion. The 1H nmr spectrum of (L-L) 2Mo(C0)Br 2 at 25° and -70° exhibits one arsenic methyl s i n g l e t i n the region associated with coordinated arsenic; the 1 9 F nmr spectrum at 25° consists of a trifluoromethyl s i n g l e t . No s t a t i c polyhedron can be drawn to account f o r the nmr data, suggesting the complex i s f l u x i o n a l i n solu t i o n at 25° and -70°. Since a l i m i t i n g slow exchange low temperature spectrum was not obtained, i t i s only possible to speculate on possible mechanisms to account f o r the motion. One such process, s i m i l a r to that postulated f o r the other seven-coordinate monocarbonyl complexes, i s a polytopal rearrangement by rapid migration of a carbonyl group over the faces of an [As^Br,] octahedron. This process would dictate the complex having a r e l a t i v e configuration 25. (omitting the capping carbonyl), Rapid migration of a carbonyl over the faces of an octahedron i n which the two bromine atoms are c i s to each other as i n 36, would not lead to an averaging of the arsenic methyl groups, since As(l) w i l l always be d i f f e r e n t from As(2). 15 As-As = (L-L) 2k As(l)-As(2) = (L-L) -i6o-C. I r Spectra Each of the (L-L)L 2Mo(C0)Br 2 complexes shows one carbonyl band i n the i r spectrum. The carbonyl frequency of ( L - L ) L 2 -Mo(C0)Br 2 (1843-1792 cm - 1) i s considerably lowered compared with (L-L)LMo(C0) 2Br 2 (1981-186? cm"1) and (L-L)Mo ( C 0) 3Br 2 (2076-1925 cm - 1), r e f l e c t i n g the f a c t that the remaining carbonyl group i s able to share a much greater proportion of the available metal d-electrons. From a consideration of the carbonyl frequency of the (L-L)L 2Mo(C0)Br 2 complexes, the T T-acceptor properties of L decrease i n the order trimethyl-phosphite c= triethylphosphite > dimethyl phenylphosphonite > dimethylphenylphosphine. 4. Summary Halogen oxidation of (L-L)M(CO)^ and (L-L ) 'M(CO ) ^ (M = MO, W) y i e l d s the seven-coordinate complexes (L-L)M(CO) 3X 2 and (L-L)'M(CO) 3X 2 (M = Mo, W; X = Br, I) which appear to be nonelectrolytes. Nmr spectra suggest the complexes are stereo-c h e m i c a l ^ nonrigid at room temperature. F a c i l e replacement of a carbonyl group i n (L-L)Mo(CO) 3Br 2 by a monodentate ligand L y i e l d s (L-L)LMo(C0) 2Br 2 which appear to be best described as seven-coordinate molecules also non-r i g i d at room temperature„ Heating the (L-L)Mo(CO) 3Br 2 complex with excess L (L i s a phosphine, phosphite, or phosphonite) gives (L-L)L 2~ Mo(C0)Br 2; heating (L-L) b(L-L) mMo(C0) 2Br 2 gives (L-L) 2Mo(C0)Br 2. -161-The complexes are seven-coordinate, the former "being r i g i d at room temperature and nonrigid at higher temperatures, while the l a t t e r appears to be nonrigid at room temperature and - 7 0 ° . The nmr spectra at room temperature f o r the monocarbonyl complexes containing phosphorus ligands can be s a t i s f a c t o r i l y interpreted i n terms of a s t a t i c seven-coordinate capped octahedral structure with a carbonyl group i n the capping po s i t i o n ; at higher temperatures the spectra are consistent with a polytopal rearrangement by rapid migration of the carbonyl group over octahedral faces. The d i f f e r e n t r e l a t i v e configurations postulated f o r the monocarbonyl complexes are probably dictat e d l a r g e l y by s t e r i c i n t e r a c t i o n s such as that experienced between a capping group and other groups i n the capped face. In conclusion, t h i s work represents some of the f i r s t reported examples of n o n r i g i d i t y i n seven-coordinate Group VI halocarbonyl complexes where hitherto only two reports have appeared;^'^° however, there have been a few reports of t h i s phenomena being observed i n other seven-coordinate complexes.133-135 -162-CHAPTER VI RESULTS AND DISCUSSION In section 1 two novel compounds obtained from the reaction of (L-L) with dimanganese decacarbonyl and dirhenium decacarbonyl are examined. In section 2 the Mn 2(CO)g[As(CH 3)(CgH^)] 2 complexes are discussed. 1. Reactions of (L-L) with Dimanganese Decacarbonyl and  Dirhenium Decacarbonyl Although the reactions of fluorocarbon-bridged d i t e r t i a r y arsines with metal carbonyl species usually afford complexes i n which the ligand remains intact,!36-139 some i n t e r e s t i n g cleavage reactions have recently been discovered. For example, the ligand f ^ f a r s , (CH-^AsC = CAs(CH 3) 2CF 2CF 2, when treated with t r i i r o n d o d e c acarbonyl,dimanganese or dirhenium deca-l 4 l carbonyl, forms complexes i n which one arsenic-carbon bond of the ligand has been replaced by a metal-carbon bond; the displaced dimethylarsino group appearing elsewhere i n the r e s u l t i n g product. However, unusual ligand reactions are not confined to fluorocarbon-bridged donors (e.g. references 142-14-5). -163-The reaction of (L-L) with dimanganese decacarbonyl and dirhenium decacarbonyl gives a d i f f e r e n t product f o r each metal carbonyl species i n which ligand cleavage has occurred. A. (L-L) and Dimanganese Decacarbonyl Pyr o l y s i s of (L-L) and dimanganese decacarbonyl i n benzene at 110° i n a sealed evacuated Carius tube gives a yellow a i r -stable compound of formula C^H^gAs^F^O^Mng as determined by microanalysis and mass spectrometry. The i d e n t i c a l complex i s obtained upon r e f l u x i n g the above reactants i n benzene or toluene or photolysing the reactants (200W); however, the y i e l d s are considerably decreased from that of the p y r o l y s i s reaction. 14-6 14-7 An X-ray s t r u c t u r a l determination of the complex ' ' indicated the presence of a novel f l u o r i n e substituted T T - a l l y l fragment. A view of the molecule showing a l l atoms except the methyl groups i s given i n Figure 15. The coordination around Mn(l) i s c l o s e l y octahedral, having three arsenic atoms ( c i s to each other) and three carbonyl carbon atoms within i t s inner coordination sphere. The coordination around Mn(2) i s d i s t o r t e d octahedral and includes a bridging arsenic atom, three carbonyl carbon atoms, and three a l l y l carbon atoms C ( l l ) , C(12), and C(l6). The a l l y l carbon atoms occupy two adjacent s i t e s and form part of an asymmetrically substituted n - a l l y l system which i s linked to Mn(l) v i a two manganese-arsenic bonds. A further l i n k between the two manganese atoms i s provided by the -164--165-bridging dimethylarsenido group. o The carbon-carbon distances (C(ll)-C(12) = 1.39 ± 0.03 A, o C(ll)-C ( l 6 ) = 1.38 + 0.03 A) of the n - a l l y l group f a l l i n the 14-8 14-9 range of carbon-carbon distances previously reported. The angle subtended at the c e n t r a l carbon atom (C (12)-C(ll)-C(l6) = 122 + 2°) has the expected value. Although the l i t e r a t u r e i s well documented on hydrocarbon n - a l l y l derivatives of t r a n s i t i o n metals, e.g., TT-C^H^COCCO^) n-C^MnCCO)^, 1 5 1 ( n - C y ^ P d B r ) 2 , 1 5 2 ( r r - C ^ N i B r ) 2 , 1 5 3 t h i s study appears to be the f i r s t reported example of'a f l u o r i n a t e d n - a l l y l t r a n s i t i o n metal d e r i v a t i v e . However, the existence of a long-lived f l u o r i n a t e d a l l y l cation has been reported i n 1 4^ a communication by Chambers et a l . J In accord with the X-ray c r y s t a l structure of the manganese complex, the ^H nmr spectrum shows s i x inequivalent arsenic methyl resonances. Four resonances appear as s i n g l e t s and two 1 19 appear as doublets due to H- 7 F coupling. Since two d i f f e r e n t f l u o r i n e decoupling frequencies are required to collapse the doublets to single sharp l i n e s , each of the two arsenic methyl groups are coupled to a d i f f e r e n t f l u o r i n e atom (either F(4) or F(5)). Possibly, coupling involves the methyl groups on As(2) rather than As(3) as the coupling i s transmitted through one le s s bond. The 1 9 F nmr spectrum consists of a t r i f l u o r o -methyl doublet (J(CF 3,F) = 26 Hz) followed at higher f i e l d by a broad carbon-fluorine doublet (J(F,F) = 121 Hz) and another carbon-fluorine doublet of quartets (J(F,F) = 121 Hz, J(CF.j,F) = 26 Hz). The t r i f luoromethyl group appears to be -166-coupled to e i t h e r F(4) or F(5). The large geminal 1 9 F - 1 9 F coupling constant i s i n accord with other reported geminal 154-156 f l u o r i n e coupling constants. ^ J The chemical s h i f t s of the two f l u o r i n e atoms (60.86 and 67.78) are at higher f i e l d than the trifluoromethyl group (42.5) due to s h i e l d i n g by the a l l y l linkage. The i r spectrum indicates s i x terminal carbonyl groups, consistent with the C symmetry of the complex. s The T T - a l l y l manganese complex i s the r e s u l t of a ligand rearrangement reaction as a carbon-fluorine bond has been cleaved g i v i n g the a l l y l fragment. The complex also contains a bridging dimethylarsenido group, presumably r e s u l t i n g from the cleavage of an arsenic-carbon bond i n the ligand (L-L). Stone et a l . have reported the preparation of fluorocarbon complexes obtained by n u c l e o p h i l i c displacement of a f l u o r i d e ion from h e x a f l u o r o b u t y n e - 2 , f l u o r o - o l e f i n s 1 " ^ or poly-fluoroaromatic compounds ^ by carbonylmetal anions. B. (L-L) and Dirhenium Decacarbonyl Reaction of (L-L) with dirhenium. decacarbonyl on u l t r a -v i o l e t i r r a d i a t i o n (450W, benzene solution) affords an orange a i r - s t a b l e s o l i d of formula C^HgAsF^O^Re (22$) as determined by microanalysis and mass spectrometry. Thermal reaction of the carbonyl and ligand does not appear to y i e l d any stable complex. The i r spectrum of the rhenium complex i n the terminal carbonyl region consists of four bands, i n d i c a t i n g a Re(CO)^ -167-fragment (mass spectrum shows the loss of four carbonyl groups). The C=C frequency i s increased to 1608 cm - 1, compared with 1569 cm - 1 found i n the free ligand. 19 The 7 F nmr spectrum consists of two trifluoromethyl quartets (J(F,F) = 12.4 Hz), the 1 9 F - 1 9 F coupling constant 123 124 being i n d i c a t i v e of c i s trifluoromethyl groups. The "*"H nmr spectrum consists of a s i n g l e t with a shoulder (fl u o r i n e decoupled) on the low f i e l d side at 100 MHz. These data best f i t the structures 37a or 37b. Addition of the s h i f t reagent, tris(2,2-dimethyl -6,6,7»7.8,8,8-hepta-fluoro -3»5-octanedionato)europium(Tll) (commonly referred to as Eu(F0D) 3), to a s o l u t i o n of the rhenium complex, separated the methylene resonance from the dimethylarsino s i g n a l , confirming i t s presence. O C oc 0 r F C C f c 1 KH3)2 / 3 R ^ c - o ^ C -H 2 C 0 •^3 O C O C 0 r f_ C £ E i ( C H 3 ) 2 / 3 A s — a Re. ^.C ^ 0 — - c H 2 C 0 C F 3 37b The e f f e c t of adding the s h i f t reagent i s shown i n Figure 16. The separation and s h i f t of the two peaks also confirm the presence of the oxygen atom since i t i s our experience that terminal carbonyl groups do not i n t e r a c t with s h i f t reagents. -168-a) b) 1 1 1 1 S(ppm) 3 2 5 2 F i g u r e 16. The H nmr spectrum of the rhenium complex (a) i n the absence of EufFOD)^ and (b) i n the presence of Eu(FOD)~. -169-19 Under high resolution, the low f i e l d 7 F quartet i s s p l i t 159 further "because of coupling to the dimethylarsino group J 7 "but the high f i e l d quartet shows no t r i p l e t structure expected f o r 37P. Thus 37a i s preferred. The o r i g i n of the methylene group i n the rhenium tetracarbonyl complex i s unknown but i t does not come from the solvent as the i d e n t i c a l product was produced using benzene-d^ as solvent. Although paramagnetic lanthanide complexes have found a wide a p p l i c a t i o n i n organic nmr studies (e.g. references 160-163), there do not appear to be any reports concerning the use of a lanthanide s h i f t complex i n e l u c i d a t i n g an organometallic structure. A preliminary account has appeared showing the e f f e c t of added s h i f t reagent on some i r o n complexes; however, the d i f f e r e n t proton signals were resolvable i n the 164 absence of the lanthanide reagent. 2. Reaction of 1,2-Dimethyl-l,2-Diphenyldiarsine with  Dimanganese Decacarbonyl The diarsine reacts with dimanganese decacarbonyl i n re f l u x i n g toluene with cleavage of the arsenic-arsenic bond, giving two isomers of formula Mn 2(CO)g[As(CH 3)(C^H^)]^ as determined by microanalysis and mass spectrometry. I t should be noted that i r o n pentacarbonyl reacts with the same diarsine with cleavage of the arsenic-arsenic bond, r e s u l t i n g i n the formation of two isomeric Fe 2(C0)^[As(CH 3)(C^H^)] 2 complexes (see Chapter I I I ; section 3-C). -170-Spectroscopic properties of the two manganese isomers are The two isomers d i f f e r i n the configuration about the arsenic atom, one having two methyl and two phenyl groups opposite each other (symmetric) and one having a methyl and phenyl group opposite each other (asymmetric). However, the spectroscopic properties do not allow a decision to be made regarding the configuration of the two isomers. Both species exhibit an arsenic methyl s i n g l e t i n the "*"H nmr spectrum. The i r spectrum i n the carbonyl region of isomer A (which eluted faster) consists of four bands as expected 12 f o r a c i s M(C0)^L 2 complex; isomer B exhibits three carbonyl bands, presumably due to an accidental superposition of two s i m i l a r to other reported Mn 2(C0)g[E.(R) 2] 2 complexes (E = As or 69 P; R = CH^ or C^H^) 7 i n d i c a t i n g they possess a s i m i l a r skeleton 3_8 with bridging methylphenylarsenido groups. C C 0 0 28 -171-absorptions. The spectra of other known Mn 2(C0)g[E(R) 2] 2 complexes (E = As or Pj R = CH^ or C^H^) also show only three of the expected four bands, (Table XXXV). Table XXXV I r Spectra (2100-1900 cm - 1) f o r Some Manganese Complexes Compound v(C0)(cm~ 1) Mn 2(C0)g[As(CH 3)(C 6H 5)] 2* A Mn 2(C0)g[As(CH 3)(C 6H 5)] 2* B Mn 2(C0) 8[As(CH 3), 2] 2 : Mn 2(C0)g[As(C 6H 5) 2] 2 7 Mn 2(C0)g[P(CH^) o], > l3'2 J2 Mn 2(C0)g[P(C 6H ) 2 ] 2 2048, 1995, 1985, 1961 2048, 1985, 1961 2039, 1975, 1952 2050, 1987, 1955 2044, 1978, 1955 2053, 1992, 1957 * This work, C^H 1 2 solvent; A and B are the isomers, ** Data taken from reference 69, CICHgCHgCl solvent. -172-SUGGESTIONS FOR FUTURE INVESTIGATIONS The r e a c t i o n of f a c - ( L - L ) b ( L - L ) m M o ( C O ) 3 w i t h s t r o n g n a c c e p t o r l i g a n d s warrants f u r t h e r study. By v a r y i n g the ac-c e p t o r p r o p e r t y of the added l i g a n d , i t should be p o s s i b l e to s p e c t r o s c o p i c a l l y i d e n t i f y a complex between i t and the t r i -c a r b o n y l s p e c i e s . The u l t i m a t e f a t e of the added l i g a n d should a l s o be determined s i n c e the r e a c t i o n has p o s s i b l e c a t a l y t i c u t i l i t y . An attempt to determine the mechanism o f t r a n s to c i s i s o m e r i z a t i o n i n the chromium and molybdenum d i c a r b o n y l com-plex e s c o u l d be made by performing the i s o m e r i z a t i o n i n the presence of carbon monoxide. F u r t h e r s t u d i e s of the r e a c t i o n of ( L - L ) M o ( C O ) w i t h d i t e r t i a r y phosphine l i g a n d s t o produce complexes of the type ( L - L ) ( d i t e r t i a r y phosphine)Mo(CO)2 B r2 c o u l d l e a d t o f u r t h e r i n f o r m a t i o n c o n c e r n i n g the n o n r i g i d i t y of the d i c a r b o n y l cora-31 p l e x e s , e.g. by examining the P nmr spectrum of the product. 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