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Hybrid multidentate ligands : amido phosphine complexes of the Group VIII metals MacNeil, Patricia Ann 1983

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<r .1 HYBRID MULTIDENTATE LIGANDS: AMIDO PHOSPHINE COMPLEXES OF THE GROUP VIII METALS by PATRICIA ANNE MACNEIL B.Sc. (Honours), St. Mary's University, 1977 M.Sc, University of Toronto, 1979 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE DEPARTMENT OF CHEMISTRY We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA April ,1983 © P a t r i c i a Anne MacNeil, 1983 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of C h e m i s t r y  The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date A p r i l ?1 , 1Q3^ - i i -Abstract The hybrid ligands HN(SiMe 2CH 2PPh 2) 2 and HN(CgH 5CH 2)(SiMe 2CH 2-PPh 2) react readily with n-butyl lithium to y i e l d the corresponding lithium s a l t s . Metathesis of Group VIII t r a n s i t i o n metal halides with LiN(SiMe 2CH 2PPh 2) 2 produces a variety of amido phosphine complexes. For the nickel t r i a d , these derivatives have the formula [MCIN(SiMe 2CH 2PPh 2) 2] (M = N i , Pd, P t ) ; a variety of rhodium and iridium complexes [M(L)N(SiMe 2-CH 2PPh 2) 2] (M = Rh, I r ; L = CO, ^-CgH^C^.PMe^PPI^) and [M(C0D)N(C6H5-CH 2)(SiMe 2CH 2PPh 2)] (M = Rh, I r ; COD = 1,5-cyclooctadiene) have also been prepared and characterized. Single crystal x-ray structural analysis of [NiClN(SiMe 2CH 2PPh 2) 2] indicates that i t adopts a distorted square planar stereochemistry, whereas the palladium analogue [PdClN(SiMe 2CH 2PPh 2) 2] i s almost perfectly square planar. Based primarily on spectral data, a l l of these Group VIII amido phosphines are assigned square planar geometries with mutually trans phosphines, with the tridentate ligand coordinated to the metal through the amide nitrogen and both phosphine centres. The amino phosphine dichlorides, [MCI 2NH(SiMe 2CH 2PPh 2) 2] (M = Ni, Pd, Pt) are prepared from the free ligand. The nickel derivative, [NiCl 2NH(SiMe 2CH 2PPh 2) 2], has been shown by crystallographic analysis to have a very distorted tetrahedral geometry; no interaction between the NH moiety and the nickel centre i s observed. Reaction of these amino phosphines with t r i e t h y l amine cleanly produces the corresponding amido phosphines. [NiClN(SiMe 2CH 2PPh 2) 2] reacts at low temperatures with Grignards or alkyl lithium reagents to y i e l d a series of hydrocarbyl complexes - i i i [Ni(R)N(SiMe 2CH 2PPh 2) 2] (R = Me, a l l y l , v i n y l , phenyl). These a l k y l (aryl) complexes react readily at room temperature under one atmosphere of carbon monoxide to give Ni(0) species, [Ni (C0) 2N(C0R)(SiMe 2CH 2PPh 2) 2], in which the ligand chelates in a bidentate fashion (through the phos-phines) owing to migration of the acyl group to the amide nitrogen. For the methyl and phenyl derivatives, the intermediate Ni(.II) acyl complexes have also been iso l a t e d . As shown by crystal structural analysis, inser-tio n of CO into the nickel vinyl bond results in an n -acryloyl Ni(0) species in which the hybrid ligand has undergone further rearrangement to an imidate structure. Some of the rhodium and iridium amidophosphines, lM(L)N(SiMe 2CH 2-PPh 2) 2] (M = Rh, L = n 2-C 8H 1 4,PPh 3; M = I r , L = n 2-C gH 1 4, C ^ ) and [M(COD)N(C 6H 5CH 2)(SiMe 2CH 2PPh 2)] (M = Rh.Ir) are catalyst precursors for the homogeneous hydrogenation of simple ol e f i n s under mild conditions (1 atm. H 2, 22°C). For the rhodium amido phosphines, o l e f i n isomerization is a competing process with hydrogenation, whereas with I l r ( .n -CgH^4)N(.Si-Me 2CH 2PPh 2) 2] only straightforward reduction i s observed. A number of irid i u m ( I I I ) amido phosphine hydrides has been prepared The five-coordinate, 16-electron complex [Ir(H) 2N(SiMe 2CH 2PPh 2) 2], formed 2 from [Ir(n -C gH 1 4)N(SiMe 2CH 2PPh 2) 2] under dihydrogen, reacts readily with neutral ligands to stereoselectively produce mer cis-nHH^CUNfSiMeo-PPh 2) 2] (L = CO, PMe3). Oxidative addition of dihydrogen to [Ir(L)N(SiMe 2-CH 2PPh 2) 2] (L = PMe3, PPh 3) produces hydride derivatives in which the tridentate ligand i s coordinated f a c i a l l y . X-ray analysis of fac c i s -[Ir(H) 2(PMe 3)N(SiMe 2CH 2PPh 2) 2] has provided conclusive evidence for this iv -f a c i a l stereochemistry. The amine trihydrides fac and mer_-IIr(H).3NH(Si-Me 2CH 2PPh 2) 2] have been characterized; their formation formally corres-ponds to a ligand-assisted heterolytic cleavage of dihydrogen. - V -Table of Contents Page Abstract i i Table of Contents v L i s t of Figures v i i i L i s t of Tables Glossary of Abbreviations x i i i Acknowledgement xv Introduction 1 Chapter I 3 Transition Metal Dialkyl Amides and Bis(Trimethyl s i l y l ) 3 Amides: Synthesis, Structure and Bonding Hybrid Amido Phosphine Ligands 15 Amido Phosphine Complexes of the Nickel Triad 20 Amido Phosphines of Rhodium and Iridium 35 Chapter II 41 Migratory Insertion of Carbon Monoxide into Metal-Carbon 41 Bonds Migratory Insertion of Carbon Monoxide into N i c k e l ( I I ) - 45 Carbon Bonds An c i l l a r y Ligand Rearrangements Promoted by the Migratory 47 Insertion of Carbon Monoxide into Nickel(II)-Carbon Bonds Migratory Insertion of Carbon Monoxide into Palladium(11)- 69 Carbon Bonds - v i -Page Chapter III 72 Homogeneous Catalytic Hydrogenation of Olefins 72 Employing Rhodium and Iridium Complexes: General Principles Di hydride Catalysts 76 Monohydride Catalysts 80 Homogeneous Catalytic Hydrogenation using Rhodium and 82 Iridium Amido Phosphines Chapter IV 94 Oxidative Addition of Dihydrogen to Square-Planar Iridium(I) 94 Complexes Stereoselective Formation of Iridium(III) Amides and 102 Ligand-Assisted Heterolytic S p l i t t i n g of Dihydrogen Stereoselective Ligand Additions to [Ir(H) 2N(SiMe 2CH 2PPh 2) 2] 112 Oxidative Addition of Dihydrogen to [IrLN(SiMe 2CH 2PPh 2) 2] 116 (L = CO, PMe3, PPh3) Spectral Trends in the Stereochemical Assignment of 123 Iridium(III) Amido Phosphine Hydrides Hydrido Intermediates Involved in Catalytic Hydrogenations 126 using Rhodium and Iridium Amido Phosphines Chapter V Experimental: General Information 128 Preparation of the Hybrid Ligands 130 - v i i -Page Amido Phosphine Complexes of the Nickel Triad 133 Conversion of N i ( I I ) , Pd(II), and Pt(II) dichloro amino 136 diphosphines to the corresponding chloro amido diphosphines ATKyl Derivatives of the Ni(II) and P(11) Amido Phosphines 136 Carbonylation Reactions 139 Amido Phosphine Complexes of Rhodium and Iridium 142 Hydrogenation Procedure 147 Iridium(III) Amido Phosphine and Amine Trihydrides 147 References 155 Appendix: Crystallographic Data 163 - vi i i -Li s t of Figures page Fig. 1.1 Transition metal complexes incorporating bis(trimethyl 5 s i l y l ) amide ligands; shaded areas represent metals for which these derivatives have been characterized. Fig. 1.2 -rr-Bonding in a transition metal dialkyl amide complex. 9 Fig. 1.3 Structure of [Cr(NPr 2) 3] (reproduced with permission). 12 Fig. 1.4 Structure of [Mn{N(SiMe 3) 2) 2THF (reproduced with 14 permi ssion). Fig. 1.5 Structure of [Mn{N(SiMe 3) 2> 2] 2 (reproduced with 14 permi ssion). Fig. 1.6 Structure of [NiN(SiMe 3) 2(PPh 3) 2] (reproduced with 14 permission). Fig. 1.7 Structure of { L i N ( S i M e 3 ) 2 ) 3 (reproduced with 18 permi ssion). Fig. 1 .8 ]HNMR (100 MHz) spectrum of [NiC1N(SiMe 2CH 2PPh 2) 2] 22 in CyDg. Fig. 1 .9 X-ray crystal structure of [NiClN(SiMe 2CH 2PPh 2) 2]. 23 Fiq. 1.10 Proposed conformational f l i p p i n g of ligand backbone of 25 [NiC1N(SiMe 2CH 2PPh 2) 2] i n solution. Fig. 1.11 X-ray crystal structure of [PdClN(SiMe 2CH 2PPh 2) 2]. 27 Fig. 1.12 ]HNMR (80 MHz) spectrum of [PtClN(SiMe 2CH 2PPh 2) 2] 30 in C 5D 5. Fig. 1.13 X-ray crystal structure of [NiC1 2NH(SiMe 2CH 2PPh 2) 2]. 32 Fig. 1.14 a) Structure of [PdCl 2( tBu) 2P(CH 2) r,P( tBu )\i • 34 b) Possible dimeric structure of [PdCI ?NH^,SiMe?CH?-PP h 2 ) 2 ] . Fig. 1.15 ]HNMR (100 MHz) spectrum of [Rh(C 2H 4)N(SiMe 2CH 2PPh 2) 2] 37 in C 6D 6. Fig. 1.16 ]HNMR (400 MHz) spectrum of [Rh(C0D)N(C 6H 5CH 2)(SiMe 2- 4 0 CH 2PPh 2)] in C 6D 6. - ix -H^NMR (80 MHz) spectrum of [Ni(CH 3)N(SiMe 2CH 2PPh 2) 2 in C 7D g. ]HNMR (80 MHz) spectrum of [Ni(CH=CH 2)N(SiMe 2CH 2PPh 2) 2] in C 6D 6 H^NMR (80 MHz) spectrum of [Ni (CO^NtCOCH^SiMe^H^ PPh 2) 2] in CyDg. IR(KBr disc) spectrum of [Ni(C0) 2N(C0CH}(SiMe 2CH 2 P P h 2 ) 2 ] . H^NMR (80 MHz) spectrum of [Ni(C0Cf-H[-)N(SiMe?CH?-PPh 2) 2] in C 6D 6. a) H^NMR (80 MHz) spectrum of [Ni(C0CH 3)N(SiMe 2CH 2-PPh 2) 2] in C 7D g at 298°K. b) ''HNMR (80 MHz) spectrum of [Ni(C0CH 3)N(SiMe 2CH 2-PPh 2) 2] in C 7D g at 243°K. H^NMR (400 MHz) spectrum of [Ni(C0)N(C0C 2H 3)(SiMe 2CH 2-PPh 2) 2] in C 6D 6. a) Vinyl proton region (400 MHz HNMR) of [Ni(C0)N-(C0C 2H 3)(SiMe 2CH 2PPh 2) 2] b) Spectral simulation of vinyl proton ABCXY pattern: J i 3 = 11.72, Jo 3 = 7.57, J-| P l = 6.59, Vpg = 1.46, J 3 ; P 1 = 13.92, J 3 j P 2 = 3.17, J 2 ) P 2 = 4.15. X-ray crystal structure of [Ni(C0)N(C0C 2H 3)(SiMe 2CH 2-P P h 2 ) 2 ] . (alternate chelate ring conformation i s indicated by unshaded thermal e l i p s o i d s ) . TT-system of the Ni(0) n -acryloyl complex ( imidate tautomer ). Orbital representation of dihydrogen activation by a tr a n s i t i o n metal complex. Hydrogenation p r o f i l e for reaction of 1-hexene with [Rh(PPh 3)N(SiMe 2CH 2PPh 2) 2] (1 atm. H 2, 22°C). Hydrogenation p r o f i l e for reaction of 1-hexene with [Ir(.C0D)N(C 6H 5CH 2)(SiMe 2CH 2PPh 2) 2] (1 atm. H 2, 22°C). Hydrogenation p r o f i l e for reaction of 1-hexene with [Ir(C0E)N(SiMe 2CH 2PPh 2) 2] (1 atm. H 2, 22°C). - x -Page Fig. 4.1 General mechanism for oxidative additions involving 98 Vaska-type complexes, [Ir(CO)CI(PR 3) 2]. Fig. 4 .2 Proposed mechanism for the oxidative addition of 100 dihydrogen to [Ir ( C 0)(o-carb)(PPh 3) 2]. Fig. 4 .3 ]HNMR (80 MHz) spectrum of [Ir(H) 2N(SiMe 2CH 2PPh 2) 2] 103 in C 6D 6. Fig. 4.4 ]HNMR (270 MHz) spectrum mer-[Ir(H) 3NH(SiMe ?CH ?- 105 PPh 2) 2] in C 6D 6. Fftg. 4 .5 a) 1HNMR (400 MHz) spectrum of fac-[Ir(H) 3NH(SiMe 2- 107 CH 2PPh 2) 2 in C 6D 6. b) Hydride region (400 MHz ]HNMR) of fac-[Ir(H)-NH- 107 (SiMe ?CH ?PPh ?) ?j. 10 7 c) Spectral simulation of hydride AA'MXX' pattern: 2JA,A'= 2.2, 2j A M = 2 j r „ = 5 . 5 2 J = = "19.0. ZJM.X = £ J M = 1 4 - 0 ' 2 J A X = 2 j r j X = i 3 o . o , 2 j X i j r = i . u : x Fig. 4.6 H^NMR (400 MHz) spectrum of mer cis_-[Ir(H)?('PMeo)N- 114 (SiMe 2CH 2PPh 2) 2] in CgDg. Fig. 4.7 a) Hydride region (400 MHz ^ HNMR) of f a c - [ I r ( H ) 2 - 118 (PMe3)N(S1Me2CH2PPh2)2]. b) Spectral simulation of hydride AA'XX'Y pattern: 118 2JA,X = 2JA-,X' = "21.0, 2j A Y = 2j . Y = 2 1 . 0 , 2JA XX = 2JA^,X = 1 4 7-°> 2 jA,A- = 4.0, 2 j x Y = 9.0, 2 j x ,x - =4-0. Fig. 4.8 X-ray crystal structure of fac-[Ir(H) 2(PMe 3)N(SiMe 2- 119 CH 2PPh 2) 2] Fig. 4 .9 Proposed mechanism for the oxidative addition of d i - 122 hydrogen to [Ir(L)N(SiMe 2CH 2PPh 2) 2] . - xi -L i s t of Tables page Table I Crystallographic data for the Group VIII metal 29 bis (trimethyl s i l y l ) amides and amido phosphines 1 151 Table II HNMR data for: (Ph 2PCH 2SiMe 2) 2NH LiN(SiMe 2CH 2PPh 2) 2 [MClN(SiMe 2CH 2PPh 2) 2] (M = N i , Pd, Pt) [Ni(R)N(SiMe 2CH 2PPh 2) 2] (R = CH3, C 2H 3, C 3H 5, C 6H 5) [Pd(R)N(SiMe 2CH 2PPh 2) 2] (R = CH3, C 3H 5) [Ni(CN)N(SiMe 2CH 2PPh 2) 2] 1 152 Table III HNMR data for: [Ni(C0) 2N(C0R)(SiMe 2CH 2PPh 2) 2] (R = CH3, C 2H 3, C 3 H 5 ' C 6 H 5 ) [Ni(COR)N(SiMe 2CH 2PPh 2) 2] (R = CH3, C gH 5) [Ni(C0)N(C0C 2H 3)(SiMe 2CH 2PPh 2) 2] [Pd(COCH 3)N(SiMe 2CH 2PPh 2) 2] 1 153 Table IV HNMR data for: [Ir(L)N(SiMe 2CH 2PPh 2) 2] (L = CO, C 2H 4, C 8H 1 4, PMe3, PPh 3) [Rh(L)N(SiMe 2CH 2PPh 2) 2] (L = CO, C 2H 4, C gH 1 4, PMe3, PPh3) [M(C gH 1 2)N(SiMe 2CH 2PPh 2) 2] (M = Rh, Ir) - x i i -page Table V H^NMR data f o r : [ I r (H) 2 N(SiMe 2 CH 2 PPh 2 ) 2 ] mer and fac- [ I r (H) o NH(SiMe 0 CH 0 PPh 0 ) 0 ] mer c i s - [ I r (L ) (H) 9 N(S iMe 9 CH 9 PPh 2 ) 2 ] (L = CO, PMeJ mer t rans- [ I r (H) 2 (CO)N(SiMe 2 CH 2 PPh 2 ) 2 ] fac c is - [ I r (H) 0 (PMe 3 )N(S iMe 2 CH 2 PPh 9 ) 2 ] 1 54 Table VI Bond lengths for [NiClN(SiMe 2 CH 2 PPh 2 ) 2 ] 164 Table VII Bond lengths for [PdClN(SiMe 2 CH 2 PPh 2 ) 2 ] -C 7 Hg 165 Table VIII Bond lengths for [NiCl 2 NH(SiMe 2 CH 2 PPh 2 ) 2 ] 1 66 Table IX Bond lengths for [Ni(C0)N(C0C 2 H 3 ) (SiMe 2 CH 2 PPh 2 ) 2 ] 1 67 Table X Bond lengths for fac- [ I r (H) 2 (PMe 3 )N(SiMe 2 CH 2 PPh 2 ) 2 ] 168 Table XI Bond angles for [NiCIN(SiMe 2 CH 2 PPh 2 ) 2 ] 1 69 Table XII Bond angles for [PdCINCSiMe 2 CH 2 PPh 2 ) 2 ]*C ? H 8 1 70 Table XIII Bond angles for [NiCl 2 NH(SiMe 2 CH 2 PPh 2 ) 2 ] 1 71 Table XIV Bond angles for [Ni(C0)N(C0C 2 H 3 ) (SiMe 2 CH 2 PPh 2 ) 2 ] 1 72 Table XV Bond angles for fac- [ I r (H) 2 (PMe 3 )N(SiMe 2 CH 2 PPh 2 ) 2 ] 1 73 - x i i i -Glossary of Abbreviations o _8 A angstrom unit, 10 cm br broad n-Bu n-butyl cm~^  wave number COA cyclooctane, CgH-j g COE cyclooctene, CgH^ COD cyclooctadiene, CgH-^ Cp pentamethyl cyclopentadienyl.(CH^JgC^ d doublet dec decomposition diphos 1,2-bis(diphenylphosphino)ethane, dppe DME dimethoxyethane dmpe 1,2-bis(dimethylphosphino)ethane d n formal d-electron configuration dt doublet of triplets Et ethyl, C 2H 5 fac facial gem geminal {H} proton decoupled (NMR) HOMO highest occupied molecular orbital Hz hertz, sec"^ IR infra-red J coupling constant - xiv -J „ apparent coupling constant ( v i r t u a l coupling) app L a neutral unidentate ligand LUMO lowest unoccupied molecular o r b i t a l m moderate int e n s i t y (IR) multiplet (NMR) M the central metal atom in a complex Me methyl, CH3 mer meridional ml m i l l i i i t r e NMR nuclear magnetic resonance ol o l e f i n Ph phenyl, C gH 5 ppm chemical s h i f t in parts per m i l l i o n py pyridine quart quartet quint quintet R an alky! group t t r i p l e t THF tetrahydrofuran v stretching frequency ( i n cm~^) X an anionic ligand (usually halide) s strong in t e n s i t y (IR) singlet (NMR) w weak int e n s i t y - XV -Acknowledgement I would l i k e to express my appreciation to my research supervisor, Dr. Michael Fryzuk, for his encouragement, enthusiasm, patience, and instruction which have provided a productive and enjoyable atmosphere in which to work. A special thanks to Dr. Axel Westerhaus for his interesting ideas and discussions, and especially, for his refreshing perspective on chemistry. -1-Introduction Since even subtle variations in ligand design can be manifested in drastic steric and electronic changes in their transition metal complexes, a great deal of research has been devoted to the synthesis of new ligands. As a result, many different ligands possessing a wide range of donor atoms (C, 0, H, P, N, S etc.) are known. A rather useful, i f somewhat inaccurate, means of ligand classifi-cation, involves designation (on the basis of the donor atom(s)) as either "hard" or "soft". According to the hard-soft acid-base theory (HSAB)1, hard bases prefer to bind to hard acids and soft bases to soft acids. Generally, transition metals foilow this rule as evidenced by the fact that soft tertiary phosphines form relatively few derivatives of the hard, early transition metals 2' 3' 4' 5 (Ti, Zr, Hf, V, Nb, Ta). In contrast, phosphine complexes of the later transition metals are legion 6' 7' 8. However, the hard amido ligand is quite common for the early metals, whereas few stable Group VIII amides are known9. An alternative ligand system is the hybrid ligand. The term "hybrid" has been previously used by Sacconi-10 and others-1-1'-12 to describe mixed donor ligands containing both phosphine and amine centres. However, in this account "hybrid" is used in a slightly different context, referring to the fact that the target ligands possess both hard and soft donor atoms arranged in a chelating fashion. Two such possible metal chelates are illustrated below in structures ^ and £. The tridentate hybrid ligand ^ can be formally classified as a uninegative six-electron donor and, as such, 5 can be likened to the ubiquitous cyclopentadienyl group, n -CgHg . - 2 -R2 R2 Si Si f \ . . / \ N I / U - * M « - : L R : 1 2 S i m i l a r l y , the bidentate £ resembles the a l l y l ligand, n^-C^H^-, in that both are uninegative four-electron donors. In these examples, the amido function acts as the hard donor while L represents a variety of soft donors, such as t e r t i a r y phosphines, arsines, o l e f i n s , thioethers, and isocyanides. The impetus to the design of these hybrid ligands l i e s in t h e i r dual character of donor types. It would be expected that such ligands would be acceptable for a wide range of t r a n s i t i o n metals. Use of the chelate e f f e c t 1 3 should ensure m u l t i d e n t i c i t y , especially where mismatching of hard/soft pairs i s concerned. In addition, new r e a c t i v i t y should be observed in th e i r t r a n s i t i o n metal derivatives, as compared to the analo-gous complexes of the monodentate donors. These proposals have indeed proven to be correct. Although t h i s account i s concerned only with hybrid amido phosphine complexes of the Group VIII metals, the coordination chemistry and r e a c t i v i t y of zirconium and hafnium amido phosphines have also been i n v e s t i g a t e d 1 1 * ' 1 5 . - 3 -Chapter I Transition Metal Dialkyl Amides and Bis(Trimethy1si 1yi) Amides  Synthesis Although isoelectronic with the ubiquitous alkyl group, the amide donor (-NR2) has achieved far less prominence as a t r a n s i t i o n metal ligand. I t would appear that this i s ' i n part due to the significance of t r a n s i t i o n metal alkyls as reactive intermediates in many important c a t a l y t i c processes (for example, Fischer-Tropsch reactions, hydroformylation, Monsanto's acetic acid synthesis). However, stable amide complexes have been obtained for most of the elements. The majority are molecular compounds containing the basic structural unit shown below in 3. R ../ M N \ R* 3 The f i r s t t r a n s i t i o n metal amide, [Ti(NPhg)^]> was prepared by Dermer and Fernelius- 1 7 in 1 935 via the metathesis reaction outlined in equation 1 . T i C l 4 + 4KNPh2 • [Ti(NPh 2) 4]+ 4 KC1 (1) -4-In f a c t , most t r a n s i t i o n metal amides are prepared by such a metathetical exchange between an a l k a l i amide and a metal halide (equation 2). This MXn + nM'NR2 • [M(NR 2) ] + nM'X (2) (M1 = Li,Na,K) route has been employed to synthesize amide complexes for p r a c t i c a l l y the entire t r a n s i t i o n series. The extensive use of t h i s preparative method l i e s in the f a c i l e formation of the required a l k a l i amides; in particular l i t h i o d i a l k y l amides and b i s ( t r i m e t h y l s i l y l ) amides are readily prepared from the corres-ponding amine and n-butyllithium (equation 3 ) . Most of the alkyl and aryl lithium salts are stable, colorless solids which have low s o l u b i l i t y HNR2 + n-BuLi •* LiNR 2 + C 4H ] 0 + (3) in organic solvents; in contrast, the b i s ( t r i m e t h y l s i l y l ) analogues are very soluble in a variety of organic solvents. It should be noted that one of the most extensively used methods for the formation of tr a n s i t i o n metal al k y l s also involves a metathetical exchange between the corresponding lithium al k y l or Grignard reagent and a metal halide. Metathesis, as in equation 2, was employed by Burger and Wannagat18 in 1965 to synthesize the f i r s t t r a n s i t i o n metal bis(trimethylsilyl)amide - 5 -derivatives, having the formula [M{ N(SiMe 3) 2) 3] (M = Cr.Fe) and [M{N(SiMe3)2>2] (M = Mn,Co,Ni). Since then, bis(trimethylsilyl)amides of irrost of the transition metals have been obtained (Fig. 1.1) ' J\' ' / ' / ' / ' / ' / / s / , / / ' / > • ' s / ' ' ' ' / ' / / ' / ' ' / , ' / , / ; > , /—1 ' ' ' ' / ? > ; > 1 ' / MrfV ' / / / , / / / , r / / S / 7~> > > . / / F e v ' * ' s / / / / / / > > > / / / / / ' 21' / {/ C6/ ' / / / . / / / / / / / / / / S •'Ay. ' / / / ' (,<,<, ,>>'•>, / / / / , 41 Nb 42 Mo 43 Tc s ' S ' ' / / / / ,Ru ' , / / / ' ' / ' '' JPlh', / / / / / / / ' / y , 46 Pd / *v, ' / / A g / ' ' ', '>:*/. •M'/ / / / / / / / / / ','!*/ . ' ' i - / / , / 74 W 75 Re 76 Os ' ' ' / A/1/ -' ' ' / < / , s 78 Pt ' / ' '' / X9' / y / / ' ', Fig. 1 .1 Transition metal complexes incorporating bis(trimethyl silyl) amide ligands; shaded areas represent metals for which these derivatives have been characterized - 6 -In some cases, metathetic synthesis of t r a n s i t i o n metal amides produces surprising r e s u l t s , such as a valency change of the metal or the formation of metal imides. An example of the former was reported by B r a d l e y 1 9 in 1972; upon reaction of LiN(SiMe 3) 2 with a Ni(II) halide, an unexpected Ni(I) species was isolated and c r y s t a l l o g r a p h i c a l l y characterized (equation 4). Another interesting r e s u l t i s the formation of a tantalum [ N i C l 2 ( P P h 3 ) 2 ] + LiN(SiMe 3) 2 • [Ni(PPh 3) 2N(SiMe 3) 2] (4) i m i d e 2 0 upon reaction of LiNEt 2 with TaClg (equation 5). Although the TaCl 5 + LiNEt 2 ^ P e n t a n e > [Ta(NEt 2) 3(NEt)J (5) <35% mechanism of t h i s decomposition has not been f u l l y elucidated, i t i s believed to occur via release of a diethyl amino radical from the expected pentakis compound, which then attacks the unstable quadrivalent Ta(NEt) 4 to produce the imide, diethyl amine, and ethylene (equation 6). Ta(NEt 2) 5 •Ta(NEt 2) 4+ -NEt2 >. EtN=Ta(NEt 2) 3 +. HNEt2 + C 2H 4 (6) An alternative preparative route to t r a n s i t i o n metal amides involves reaction of a metal halide with an amine, with concommitant formation of amine hydrohalide. This method has been mainly applied to the early -7-2 1 transition metals in higher oxidation states. An example is the formation of the manganese complex [Mn(CO)5(NHMe)(NH2Me)] (equation 7). [Mn(C0)5Br] + 3 MeNH2 P e n t a n e > [Mn(CO)5(NMe)(NH2Me)] + MeNH3+-Br" (7) Another possible, although seldom used, route to amido complexes is a type of "transamination" reaction, in which the more volatile amine is usually displaced (equation 8 ) . However, the degree of displacement is largely controlled by steric factors. The synthesis of [TiNMe2(NPr)3] 22 serves to illustrate the utility of this method (equation 9) M(NR2)n + HNR2 (xs) >M(NR2 ) n_ m(NR 2) m + HNR2 (8) (m = o-m) 3HNPr [Ti(NMe2)4] 2->[TiNMe2(NPr2)3] (9) Structure and Bonding One useful classification of transition metal dialkylamides and bis (trimethylsilyl) amides involves designation as either homoleptic or hetero-leptic. The former category include those derivatives containing only one type of ligand (eg. [Cr(NPr 2) 3]) while the latter are complexes having amide as well as other donor ligands (eg. [Co{N(SiMe3)2}2PPh3]). For the early transition metals, there are numerous examples of homoleptic species; - 8 -however, heterolepic complexes are far less common, a rather surprising fact in view of the wide variety of a n c i l l a r y ligands possible. I t i s interesting to note that the exact opposite trend i s observed for t r a n s i t i o n metal a l k y l s . For both categories of amide complex, there are comparatively few examples of stable derivatives towards the right hand side of the t r a n s i t i o n series. This trend may be explained in part by noting that a po t e n t i a l l y unfavorable bonding situation arises upon interaction of the "hard" amido 2+ 1 + function with a "soft" t r a n s i t i o n metal, such as Pd or Rh On the basis of the hard-soft acid-base theory" 1, i t i s not surprising that amide com-plexes of the l a t e r t r a n s i t i o n metals would be destabilized, at least in comparison to those involving the early, "hard" t r a n s i t i o n metals (for example, Z r * V , Nb^). However, incorporation of s i l y l groups at nitrogen makes the amido ligand more polarizable. In f a c t , the bis(.trimethylsilyl) amido ligand forms stable complexes with a number of t r a n s i t i o n metals in low oxidation states. Other rational izations for the paucity of amides of the l a t e r t r a n s i -tion metals have centred on the bonding properties of the amide ligand. Three bonding modes can be envisioned for a o-bonded alkylamido ligand. One p o s s i b i l i t y i s approximately sp hybridization of the nitrogen, resulting in Ft \ / M N R M 4 5 6 - 9 -a pyramidal geometry (4). A l t e r n a t i v e l y , d-n-p-n bonding of the nitrogen lone pair with metal d-orbitals of correct symmetry results in a t r i g o n a l -planar geometry at nitrogen (5). There are also amide derivatives in which the bridging structure (6) i s involved, although t h i s type of bonding may be prevented by using bulky R groups at nitrogen. Since the amide moiety acts as both a two electron a-donor as well as a two electron n-donor (Fig. 1.2), i t would seem reasonable that the electron deficient early t r a n s i t i o n metals, which possess vacant d - o r b i t a l s , should form stronger metal-amide bonds than the electron r i c h metals towards the right of the periodic table. The importance of ^-bonding i s supported by the observation that bis (trimethylsilyl)amido derivatives of the l a t e r t r a n s i t i o n metals are s i g n i f i -cantly more stable than t h e i r dialkylami do analogues. Substantial evidence i n -dicates'that, for Si-N compounds, there i s s i g n i f i c a n t delocalization of the nitrogen lone pair into empty s i l i c o n d - o r b i t a l s , resulting in contraction o of the Si-N bond length from the expected value of ^1.82 A, for a Si-N a-bond, to the observed values of 1.65 - 1.75 A. In addition, the structural data for HN(SiH 3) 2, HN(SiMe 3) 2 > and F 2 B N ( S i H 3 ) 2 2 3 indicate that a l l contain Fig. 1.2 TT-Bonding in a t r a n s i t i o n metal di a l kyl amide complex -1 0-nitrogen in a planar, rather than pyramidal environment; planarity of the NSi2 fragment would be necessary in order to maximize ir-backbonding. As a consequence, i t would be expected that the decreased IT-donor a b i l i t y of bis(trimethylsilyl)amides, as compared to dialkylamides, should tend to be more favorable for coordination with electron r i c h metals. In addition to thermodynamic considerations, the inherent i n s t a b i l i -ty of amides of the late t r a n s i t i o n metals can be seen to be a result of available pathways for decomposition ( i e . k i n e t i c i n s t a b i l i t y ) . I t has long been known that, for al kyl groups possessing B-hydrogens, Bi-el imination of t r a n s i t i o n metal alkyls i s a dominant, and often troublesome, mode of decomposition. The corresponding reaction with t r a n s i t i o n metal amides, resulting in formation of metal hydride and imine, had previously been considered as an i n s i g n i f i c a n t process, since the amides of the early metals are a l l thermally stable at room temperature. In f a c t , p u r i f i c a t i o n i s usually carried out by d i s t i l l a t i o n or sublimation at high temperatures. However, dialkylamides of rhodium do indeed decompose via B-elimination of the metal amide bond (equation I O ) 2 4 ; as a r e s u l t , rhodium dialkylamides have yet to be i s o l a t e d . This decomposition route can be blocked through RhCl(PPh 3) 3 + LiNMe2 »RhH(PPh 3)3 + CH2=NMe (10) the incorporation of an amido group having no g-hydrogens; thus, Lappert 2 5 isolated the f i r s t rhodium amide by coordination with the b i s ( t r i m e t h y l s i l y l ) amido ligand (equation 11). - 1 1 -RhCl(PPh3)3 + LiN(S1Me 3) 2 — » Rh(PPh3)2N(SiMe3)2 (11) Even so, at room temperature, this complex loses hexamethyldisilazane, probably via an ortho metallation/reductive elimination sequence. In addition to the amide's ability to form both a and TT bonds, the steric requirements of the substituents at nitrogen greatly influence the structures of transition metal amides. Homoleptic and heteroleptic derivatives having coordination numbers ranging from two to six have been prepared, the stoichiometry depending largely on the steric bulk of the ligand. Monomeric, four-coordinate complexes, [M(NR2)4] (M = Ti,V,Mo), can even be obtained with the least sterically demanding dimethylamido l igand 2 6 . However, the analogous complexes of Z r ^ and Hf^ are believed to be polymeric, both in solution and in the solid state, although the metal's exact coordination number is not known. The unstable dimethyl-amide derivatives of Ti(III), V(.III), and Cr(III) are believed to be d i m e r i c 2 7 ' 2 8 ' 2 9 , at least in solution. Higher coordination numbers have been observed, especially for the second and third row metals. X-ray diffraction analysis of Nb(NMe2)^ has shown it to have a square pyramidal geometry whereas Ta(NEt2)g is trigonal bipyramidal , undoubtedly a mani-festation of the more bulky ethyl (vs. methyl) groups. A regular octa-31 hedral WNg core is observed for the complex lW(NMe2)5] 32 The structure of the Cr(III) complex , given in Fig.1.3, is repre-sentative of a monomeric homoleptic dialkylamide. Note the planarity in all three amide units, as well as the fact that the Cr-N bond lengths - 1 2 -(^1.87 A) are s i g n i f i c a n t l y shorter than predicted (VI.97 A). Fig. 1.3 As expected on the basis of both thermodynamic and kine t i c consi-derations, bis(trimethylsilyl)amides of the la t e r t r a n s i t i o n metals are considerably more robust than their dialkylamido analogues. Although not exactly ubiquitous, representative complexes include those of Mn(II), F e ( I I I ) , Ru(II), Co(I), Co(II), N i ( I ) , N i ( I I ) , Rh(I), I r ( I ) , Cu(I), Ag(I), and Au(I). In a l l c a s e s , these d e r i v a t i v e s are prepared v i a reaction of an appropriate metal halide precursor with the lithium amide. In contrast, attempts at preparing simple dialkylamides of these metals have largely been unsuccessful. However, i f the amido function i s substituted with electron-withdrawing groups, such as in " NC12 or " N(CN) 2, iso l a b l e species of Mn(II), F e ( I I ) , Co(II), N i ( I I ) , Pt(IV), and Cu(II) are obtained. Once again, t h i s would appear to be a r e s u l t of the reduced a-basicity and/or tr-donor a b i l i t y of the amide nitrogen. The Cr(III) complex shown in Fig. 1.3 also i l l u s t r a t e s how a bulky amido ligand can be used to s t a b i l i z e low coordination numbers. Especially remarkable in t h i s regard is the bis(trimethylsilyl)amido ligand, N(SiMe 3) 2. Although typical coordination numbers for the lanthanides are eight through ten, monomeric three-coordinate complexes having the formula [Ln{N(SiMe 3) 2} 3] (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Ho, Yb and L u f 3 have been characterized. X-ray analysis has shown that the erbium and ytterbium derivatives have pyramidal LnN 3 units, as compared to the trigonal-planar arrangement observed in three-coordinate t r a n s i t i o n metal amides. In f a c t , the most common coordination number for the t r a n s i t i o n metal bis(trimethylsilyl)amides i s the rather unusual three coordination. 314 The pink Mn(II) complex, [Mn{N(SiMe3)2>2THF] (Fig. 1.4) i s one such ex-ample; although quite thermally stable, the THF may be removed by heating at 35 120°C in vacuo, y i e l d i n g a dimeric species, [{MnN(SiMe 3) 2> 2] ( F i g . 1.5). X-ray crystallographic analysis of the Fe(III) species, [Fe{N(SiMe 3) 2) 3], has 3 6 shown i t to have a trigonal-planar structure . Bradley and Hursthouse have also elaborated the structures of the related three-coordinate complexes, [Co{N(SiMe 3) 2) 2PPh 3] 1 9, [CoN(SiMe 3) 2(PPh 3) 2] 3 7, and [ N i N ( S i M e 3 ) 2 ( P P h 3 ) 2 ] 1 9 ( F i g . 1.6). It i s reasonable to assume that the Cu(I) complex, [CuN(SiMe 3) 2-( P P h 3 ) 2 ] , has a very si m i l a r geometry to i t s Ni(I) and Co(I) analogues Two coordinate bis(trimethylsilyl)amides are also known. Burger and -1 4-Fig. 1.4 Structure of [Mn{N(SiMe 3) 2} 2THFj (reproduced with permission) Fig. 1.5 Structure of [Mn{N(SiMe 3) 2) 2] 2 (reproduced with permission) 1.70(1) 122.5(41. A30.AU) Fig. 1.6 Structure of lNiN(.SiMe 3) 2(PPh 3) 2] (reproduced with permission). -1 5-Wannagat°° have postulated a l i n e a r structure for the N i ( I I ) s i l y l amide, [Ni {N(SiMe 3) 2) 2] • Its i s o l a t i o n as a red o i l has precluded d e f i n i t i v e struc-tural characterization. On the basis of IR, NMR and UV spectral information, 3 3 [Co{N(SiMe 3) 2} 2], i s also linear . Likewise, the two-coordinate Au(I) deri -vatives, [AuN(SiMe 3) 2L] (L = PMe3, PPh 3, AsPh 3) are expected to be l i n e a r 4 0 . In summary, extensive x-ray crystal 1ographic data for a wide variety of t r a n s i t i o n metal dialkylamides, indicates a planar, or nearly planar NR2 unit; t h i s has been attributed to the contribution of d i r - p u bonding at the metal. For the related bis(trimethylsilyl)amido complexes, the Si'2N moiety i s invariably planar, probably as a consequence of s i m i l a r n-backbonding, Si-N, involving the s i l i c o n centres. In addition to modifying the electronic properties of the amide nitrogen, the incorporation of s t e r i c a l l y bulky s i l y l groups, having a necessarily planar arrangement, d r a s t i c a l l y affects the molecular geometry of i t s t r a n s i t i o n metal derivatives. As a r e s u l t , not only does the use of bis(trimethylsilyl)amides allow for the s t a b i l i z a t i o n of the l a t e r t r a n s i t i o n metal M-N bond, but also gives r i s e to complexes of unusually low coordination number. Hybrid Amido Phosphine Ligands S t a b i l i z a t i o n of Group VIII t r a n s i t i o n metal amide M-N bonds can be achieved through the incorporation of the amide function as part of a hybrid ligand. We have synthesized several such ligands; the preparation of the tridentate ligand HN(SiMe 2CH 2PPh 2) 2, 7, i s outlined in Scheme 1.1. The synthesis i s p a r t i c u l a r l y a t t r a c t i v e i n that i t requires inexpensive, - 1 6 -readily available starting materials; the yields are very good (^80% o v e r a l l ) , and, even though care must be taken to exclude oxygen and traces of water, the procedure i s quite straightforward. Typically the ligand i s produced on a 50 g scale via this route. Scheme 1.1 CISiMe2CH2CI + NH4CI NEt, THF CISiMe2CH2CI Me2 Me2 ^Si S i ^ Et 20 C | H CI O'C LiPPh 2/THF Me2 Me2 Me2 Me2 Si Si w ~ . . ^Si Si ^ r ^ - \ . "-6"1-' r "\ p Li P hexane P H P Ph, Ph, Ph, Ph, 8 The reaction proceeds by the dropwise addition of 1,3-bis (chloro-methyl)tetramethyldisilazane to a cold THF solution of LiPPh 2. After work--1 7-up, the product i s r e c r y s t a l l i z e d from minimum hexanes at -30°C to give colorless c r y s t a l s . This compound, as well as those which w i l l be referred to l a t e r , has been f u l l y characterized by usual spectroscopic means, i . e . 1 1 3 31 H, C and PNMR as well as IR and elemental analysis. In parti c u l a r , the s i l y l methyl groups of 7 appear as a doublet ( 4 J H p = 1.0 Hz) due to long range coupling with phosphorous; t h i s feature has been observed by Schore and others in related systems 4 1' 4 2. The ligand i s readily deprotonated with n-butyllithium in hexane to give i t s c r y s t a l l i n e lithium s a l t , Molecular weight analysis of ^ 4 3 by the Signer method has indicated that i t i s trimeric in benzene solution. Although i t s structure has not been elucidated by X-ray c r y s t a l -lography, i t would seem reasonable that, in the s o l i d state, i t should resemble that observed for the closely related LiN(SiMe 3) 2 (Fig.1.7 ) . However, l i t h i o bis(trimethylsilyl)amide is dimeric in benzene; a compa-rison between these lithium s a l t s i s therefore somewhat tenuous. Spectros-1 31 1 copic analysis ( H and P{ H}NMR) of 8 has not been p a r t i c u l a r l y enlightening, except as a means of assigning purity, since the H^NMR and 31 1 H H} signals are rather broad. Bidentate hybrid ligands have also been prepared; Schemel .2 outlines the synthesis of HN(PhCH 2)(SiMe 2CH 2PPh 2), 9. High yie l d s of this derivative may be obtained by reaction of LiPPh 2 with C6H5CH2NH(SiMe2CH2C1) in THF. Once again, the colorless c r y s t a l l i n e lithium salt.l^O, i s readily formed upon treatment of 9^  with n-BuLi in hexane. However, this derivative d i f f e r s from the tridentate 8 in that i t i s very thermally sensitive. Although stable at -30°C for up to six months, storage at room temperature results in -1 8-Fig. 1.7 Structure of { L i N t S i M e . ^ ^ (reproduced with permission) Scheme 1-2 ClSiMe2CH2CI + (^H,JCH2NH2 Me, H CI LiPPh, Me2 Ph-v S i ^ Li P Phj 10 n-BuLi Ph Me2 H P Ph 2 9 decomposition to a mauve colored o i l . Signer analysis in benzene gives a molecular weight midway between a dimer and trimer. The H^NMR spectrum also implicates two dif f e r e n t forms of th i s lithium s a l t since there are two broad SiCH^ signals, two CH^P resonances and two broad PhCH^ absorptions upon heating to 80°C, only one species i s observed. - 2 0 -Amidophosphine Complexes of the Nickel Triad As expected on the basis of previous work by Bradley, Lappert, and others, these lithium amidophosphines are convenient starting materials for metathetical reactions with a variety of transition metal halides. The ligand, in these complexes of the Group VIII metals, acts as a uninegative six-electron donor, coordinating in a tridentate manner through the amide nitrogen and both phosphorous centres. The nickel amidell is most conveniently prepared from NiCl?-DME, since this starting material can be easily obtained completely anhydrous and is also slightly soluble in organic solvents (equation 12). The analogous reaction using anhydrous NiC^ or NiB^ proceeds in much lower yield, probably owing to their very low solubilities. Alternatively,!^ may be prepared from N i C ^ P f ^ ^ (R = Me or Ph); however, in the case of NiC^PPhg^j difficulties were encountered in recrystal 1 izing the product away from the involatile phosphine by-product (PPhg). The analytically pure, diamagnetic nickel amide is obtained, after recrystal1ization from toluene/hexane, as large diamond-shaped, deep-brown crystals. This complex is moderately air-sensitive and very hygroscopic; i t is soluble in a wide range of organic solvents, including benzene, toluene and acetone and is moderately soluble in cyclohexane. N i C l 2 D M E + L i N ( S i M e 2 C H 2 P P h 2 ) 2 11 ( 12 ) - 2 1 -As previously mentioned, the analogous reaction of Ni CI 2^ P R 3 ^ 2 (R = Et or Ph) with LiN(SiMe 3) 2 results in reduction of the starting Ni(II) complex to form a three-coordinate Ni(I) species, NiN(SiMe 3) 2-( P R 3 ) , , . This unexpected result has been rationalized as being due to combined s t e r i c and electronic factors. Presumably, the tr-acceptor a b i l i t y of the phosphines may help to s t a b i l i z e the low oxidation state at Ni. In addition, the large s t e r i c bulk of these ligands may prevent formation of the expected square-planar Ni(II) complex, Ni{N(SiMe 3) 2> 2-( P R 3 ) 2 . However, i t i s evident from t h i s result that electron transfer plays a s i g n i f i c a n t role in the formation of metal-amide bonds. The fact that we observe no such reduction may be explained by assuming that i n i t i a l coordination of the tridentate ligand's phosphine centres may serve to cage any radicals formed prior to metathesis and thus prevent a net reduction of the metal centre. A l i n e a r , tridentate ligand may coordinate to a t r a n s i t i o n metal in either a meridional, planar stereochemistry or a f a c i a l , pyramidal stereochemistry depending upon both the stereoelectronic constraints of the metal as well as the f l e x i b i l i t y of the ligand backbone. Spectros-copica'lly, the most d e f i n i t i v e means for establishing the mode of l i g a t i o n in these complexes i s from H^NMR data. The spectrum of 11 (Fig.1.8) w i l l serve to i l l u s t r a t e . A v i r t u a l t r i p l e t for the CH2P protons centred at 1.2 -> 1 .7 ppm i s indicative of a trans orientation of the chelating phosphines;J i s usually 5 - 6 Hz. Shaw has demonstrated that v i r t u a l app coupling arises in such A ?A 2J(X spin systems when J y y ' i s very large. -22-Ph, ;N-Ni-CI > ^ P h 2 Si(CH 3) : 3'2 Q-(C6H5)2P RZII] ~fc 6- 5 ) 2 p 5 ppm CH2P J Fig. 1 .8 1HNMR(lOOMHz)spectrum of lNiClN(Si.Me 2CH 2PPh 2) 2] in CyD (asterisk indicates residual solvent protons). For these amidophosphine complexes, the trans phosphines are strongly coupled; as a r e s u l t , an apparent A^X2 pattern i s observed for the CH2P protons. Another useful spectral correlation has been pointed out 46 by Moore and Robinson who noted that a chemical s h i f t difference of 0.6 1.0 ppm between the ortho and para/meta protons of the phosphine phenyl groups, when the spectrum i s recorded in deuterated aromatic solvents, i s also indicative of mutually trans diphosphines. -2 3 -That t h i s trans disposition persists in the s o l i d state has been demonstrated by X-ray crystallographic analysis of Vk As can be seen from Fig. 1,9, t h i s complex adopts a distorted square planar geometry; instead of the expected 90° value for the two Cl-Ni-P bond angles, the Fig. 1.9 X-ray crystal structure of lNiClN(„S1Me9CH9PPK9) J -2 4-observed values are 93.74(2)° and 95.40C2)0. Especially s i g n i f i c a n t i s the puckering of the chelate ring backbone: the planar ClNiNSi^ unit i s t i l t e d by approximately 40° with respect to the coordination plane of the nickel complex. As a r e s u l t , one s i l i c o n atom i s disposed 0.89 K above, and the other 1.25 i\ below, the coordination plane; in addition, the methyl groups on Si(1) are staggered with respect to the methyls of Si(2) in order to minimize unfavorable s t e r i c interactions. Since, in the s o l i d state, t h i s nickel complex has near symmetry, the s i l y l methyls should be diastereotopic in solution. S i m i l a r l y , the methylene protons should be diastereotopic. However, th i s would only be the case r f the chelate ring were r i g i d in solution. In a c t u a l i t y , only one SiCH^ signal i s observed in the H^NMR at ambient temperature. Two possible explanations for t h i s observation are accidental degeneracy or a very rapid conformational f l i p p i n g of the chelate ri n g . Variable tempera-ture H^NMR down to -78°C resulted in broadened peaks as well as a decrease (by 50 ± 5%) in peak i n t e n s i t y , as measured by integration versus residual 6 8 solvent protons (d -acetone or d -toluene). Surprisingly, at -80°C, the o r i g i n a l l y orange-brown solution, sealed in an NMR tube under nitrogen, turns bright green with no v i s i b l e p r e c i p i t a t e . O r i g i n a l l y we believed that t h i s color change and the decrease in peak intensity was due to the paramagnetic tetrahedral isomer of the nickel amide which was being sta-b i l i z e d at low temperature. Exchange of the axial and equatorial sit e s in the puckered rings could therefore be occurring via a square planar/ tetrahedral equilibrium (well known for Ni(II) phosphines) 4 7. However, low temperature v i s i b l e and near IR spectroscopy f a i l e d to support this - 2 5 -hypothesis; no absorptions attributable. to tetrahedral d° complexes could be observed. In addition, the Evans' method did not indicate any paramag-netic species in solution at low temperature. 4 8 Additional evidence that a tetrahedral isomer was not involved in thi s axial/equatorial exchange was given by the results of the following experiment. I t i s well known that strong f i e l d ligands tend to s t a b i l i z e low spin t r a n s i t i o n metal complexes. Therefore, i t would be expected that the cyano derivative, [Ni( CNjNfSiMegCHgPPI^^] > readily prepared from,1,1 and Me-jSiCN, should exist exclusively as the square planar, diamagnetic isomer. Exchange via a tetrahedral isomer could therefore be ruled out. However, the ^ HNMR of this complex, even down to -80°C, i s identical to that of i t s chloro analogue 11, Therefore, the required conformational f l i p p i n g of the ligand backbone i s very, l i k e l y occurring by a simple rotation of the planar NSi*£ fragment through the square plane of the complex ( F i g . l .10). Fig. 1.10 Proposed conformational f l i p p i n g of ligand backbone of [NiClN(SiMe ?CH ?PPh ?) ?] in solution -2 6-The corresponding reaction of LiN(SiMe 2CH 2PPh 2) 2 with PdCl 2(PhCN) 2 proceeds smoothly at -78°C to give the palladium amide ,12 in good y i e l d (equation 13). Like i t s nickel analogue, moisture and oxygen must be Ph, M e S i ^ P PdCI2(C6H5CN)2 + 8 P h C H 3 „ 2 \ | — Pd-CI (13) -78*C M * * ^ I e,Si 2 V p Ph2 12 rigorously excluded during the preparation; once formed, the s o l i d i s stable at room temperature under nitrogen for extended periods of time. Rec r y s t a l l i z a t i o n from toluene/hexane produces large orange blocks of this derivative as a toluene solvate. To our knowledge, t h i s i s the f i r s t example of a stable palladium amide; presumably, previous attempts to form Pd-N bonds resulted only in reduction to Pd(l) or palladium metal. In f a c t , i f t h i s reaction i s carried out at temperatures above 0°C, rapid darkening of the solution i s observed and the y i e l d of lj? i s very low. Thus, i t would appear that reduction poses a problem at ambient temperature. Once again, these observations point to the participation of electron transfer in the formation of metal amide bonds and the importance of coordination of the phosphine arms of the tridentate ligand prior to meta-thesis. The spectral features of thi s complex are very s i m i l a r to those of i t s nickel analogue. Diagnostic of a trans disposition of the chelating phosphines i s a v i r t u a l t r i p l e t in the H^NMR; the s i l y l methyls appear as -2 7-a sharp s i n g l e t . However, i t s s o l i d state structure i s quite different from that o f ^ (Fig. 1.11). Note the almost perfect square planar geometry Fig. 1.11 .X-ray crystal structure of lPdClN(.SiMe 2CH 2PPh 2). 2] at palladium, as demonstrated by the Cl-Pd-N and P-Pd-P bond angles of almost 180°. Instead of the puckering observed in the nickel complex, the NSi 2 unit of lj> i s v i r t u a l l y coplanar with the coordination plane of the -28-complex. This va r i a t i o n in structure i s undoubtedly a consequence of the longer Pd-P(2.3078(5), 2.3112(5) A) and Pd-N(2.063(2) K) as compared to Ni-P(2.2086(6), 2.1975(5) K) and Ni-N(l.924(2) A) bonds. As a r e s u l t , the SiMe 2 groups are eclipsed with respect to one another and the complex has near C 2 V symmetry. Thus, the solution and s o l i d state structures for 12are the same. Although only six amides of the Group VIII metals have been subjected to crystallographic structural analysis, i t i s interesting to note a number of trends (Table I ) . Not s u r p r i s i n g l y , l i t t l e contraction in the M-N bond lengths i s observed over the theoretical values, indicating a decreased n-donor a b i l i t y of the amide nitrogen. This i s probably a di r e c t consequence of delocalization of the nitrogen lone pair into Si d-o r b i t a l s , which is manifested in short N-Si bonds (theoretical value = O 1.88 A), planar NSi*2 units, and expanded Si-N-Si bond angles (as compared to the 120° value expected for sp hybridized nitrogen). Although there are two reports'* 9' 5 0 of simple platinum(II) amides, [PtCl(NHPh)(PEt 3) 2] and [ P t ( N P h 2 ) ( P E t 3 ) 2 C l ] , no such complex incorporating a bis(trimethylsilyl)amide has been prepared. However, we have isolated such a stable platinum complex which completes the series [MClN(SiMe2-CH 2PPh 2) 2] for the entire nickel t r i a d . Although t h i s derivative i s readily prepared in good y i e l d as fine yellow crystals from reaction of the lithium amide with Zeise's s a l t , [K{ PtCl 3( C 2H 4)}], (equation 14); l i t t l e , i f any, product was obtained with a variety of other platinum precursors (such as PtCl 2(C0D), trans-PtC1p(PR 3 )o , R = Ph or Et, P t C l 2 -(PhCN) 2, t r a n s - P t ( H ) C l ( P E t 3 ) 2 ) . Table I Crystallographic data for the Group VIII metal bis (trimethyl s i l y l ) amides and amido phosphines Compl ex M-N M-N (theor.) N-Si <SiNSi Co{N(SiMe 3) 2} 2PPh 3 1.934 1 .96 1 .70 (av) 125.5 CoN(SiMe 3) 2(PPh 3) 2 1.924 1 .96 1 .69 (av) 128.0 Ni{N(SiMe 3) 2}(PPh 3) 2 1 .870 1 .86 + 1 .71 126.4 Fe{N(SiMe 3) 2> 3 1.918 1 .95 1 .73 121 .24 NiClN(SiMe 2CH 2PPh 2) 2 1 .929 1 .86 1 .72 128.13 PdClN(SiMe 2CH 2PPh 2) 2 2.063 2.10 1" 1 .72 122.27 o Bond lengths, in A; bond angles in degrees. T" for sq. planar Ni ( t e t . = 1.91) ^ Bragg-Slater ( a l l other theoretical values are from covalent r a d i i ) . -30-K<Pt(C2H4)CI3} 8 PhCH3 O'C Ph, Me2Si | N—Pt —CI Me2Si I Ph2 13 (14) X-ray crystal!ographic analysis of this complex was obviated by the marked resemblance of i t s ''HNMR spectral characteristics to those of the corresponding nickel and palladium amidophosphines. The by now familiar v i r t u a l t r i p l e t for the CH2P protons i s further s p l i t into a 1:4:1 t r i p l e t by coupling with Pt-195 (Fig. 1.12) ( Pt, 33.5% natural abundance; 3 Pt = ^'® H z^' 1"S t n e r e f ° r e reasonable to assume that i t s structure i s very similar to that of the palladium amide. Ph, Me2Si | N — P t — C I Me2Si I Ph, p p m Fig. 1.12 ^NMRtSOMHz) spectrum of [PtClN(SiMe 2CH 2PPh 2) 2] in CgD6 - 3 1 -The amidophosphinesH, 13^  may be more readily prepared, and in higher y i e l d , from the corresponding aminophosphine dichlorides, [MCl 2NH(SiMe 2CH 2PPh 2) 2]. Not sur p r i s i n g l y , the free ligand being a potential neutral four-electron bidentate, readily coordinates to the metals of the nickel t r i a d . The nickel complex 1^4 is prepared at room temperature simply by s t i r r i n g a toluene solution of NiCl2*DME and HN(SiMe 2CH 2PPh 2) 2 for 30 minutes (equation 15). Upon removal of solvent from the resultant deep-red solution, a green s o l i d i s formed which, Me, Ph 2 S ^ P 2 /C I NiCI 2DME + 7 P h C H ? » HN Ni (15) R T - \ \ ^ P y x c i Me2 Ph 2 14 after r e c r y s t a l ! i z a t i o n from CH 2Cl 2/hexane forms blue-black blocks. Such drastic color changes are well known for Ni(II) complexes which undergo square planar/tetrahedral e q u i l i b r i a ; the H^NMR, which has many broad resonances between 0 and 20 ppm, also indicates the presence of paramagnetic and diamagnetic s p e c i e s 5 1 . The s o l i d state structure of 14^  displays a distorted tetrahedral geometry at nickel (Fig. 1.13). Note that t h i s molecule possesses no elements of symmetry. The Ni-Cl(2.2216(8) and 2.2058(8) A) and Ni-P (2.3180(7) and 2.3469(7) A)bond lengths are typical of tetrahedral Ni(II) complexes. Of most si g n i f i c a n c e , there appears to be no inter a c t i o n , either i n t e r - or intramolecular,between the N-H moiety and the Ni centre. Fig. 1.13 X-ray crystal structure of XNiCl 2NH(SiMe 2CH 2PPh 2). 2J This i s not too surprising in view of the fact that of this complex i s identical to that of the free ligand (3365 cm~^). Apparently, der-e a l i z a t i o n of the nitrogen lone pair into empty Si d-orbitals renders i t unavailable for coordination. This i s in sharp contract to the closely related molecule [ N i B r ^ H f C f ^ O ^ P P I ^ ^ ] which has a 5-coordinate, square-pyramidal s t r u c t u r e 5 2 with Ni-N bond length of 2.01(3) A\ - 3 3 -The corresponding reaction of the free ligand with PdClzCPhCN^  produces as large yellow plates; the analogous procedure using Zeise's s a l t gives the platinum aminophosphine as large colorless blocks (equation 16). It i s assumed that, on the basis of th e i r H^NMR spectra, these deri -atives are square planar with mutally c i s phosphines; the c h a r a c t e r i s t i -c a l l y broadened CH?P resonances indicate weakly coupled cis phosphines. PdCI2(C6H5CH2)2 + 7 Me2 Ph 2 HN S i ^ P CI Me2 Ph2 (16) K{Pt(C2H4)CI^ + 7 15 , M=Pd 16, M=Pt However, the extremely low s o l u b i l i t y might be indicative of a dimeric or polymeric form reminiscent of Pd and Pt complexes prepared and characterized by Shaw 5 3 ( F i g . 1.14). This may also help to explain the decrease in (3305 cm~^  for 1^; 3280 cm~^  for H ) in these complexes as compared to the free ligand. Possibly, t h i s i s a result of hydrogen bonding between the N-H groups and the chlorides. P h 2 / \ S i ^ H ^ S i ^ \ P h 2 b) S>d-C1'' 9 ^ p d _ . r i P h \ / X N T v Ph 2 Fig. 1.14 a) Structure of l P d C l 2 {R2P(.CH2).5PR2}J2 (R = tBu) b) Possible dimeric structure of £PdCl2NH(SiMe2CH2PPh2)2] As indicated e a r l i e r , these complexes can be used to prepare the corresponding amidophosphines. Reaction of 14^  with triethylamine at room temperature proceeds within minutes to give high yields of ^ (equation 17). However, this reaction i s much slower for the Pd and Pt derivatives, requiring 24 h to go to completion. Reaction of l j ^ and JJ5 W P ' N C . P h C H 3 Me2sf I Me2 Ph2 A ^ Ph 2 / NEt,.HCI Me2Si | ,CI ; N - - M— c i We 2SiV p Ph 2 17 with other bases, such as pyridine, was unsuccessful, resulting only in starting materials. The action of pyridine on 1^ gave only N i C l 2 ( p y ) 4 , whereas the poorly coordinating 2,4,6-trimethyl-pyridine gave no reaction at a l l . It i s p a r t i c u l a r l y s i g n i f i c a n t that the reaction of N i C l 2 ( P R 3 ) 2 and HN(SiMe 3) 2 with NEt 3 results in no_ amide formation; only starting materials were recovered. Thus, i t would seem that a plausible mechanism for the amide conversion involves i n i t i a l coordination of the phosphines followed by activation of the d i s t a l N-H ( s i m i l a r to the well-known cyclometallations involving ligand C-H a c t i v a t i o n 5 1 * ' 5 5 ' 5 6 ) . Although oxidative addition of the N-H group to form an intermediate of the type U i s quite probable, no evidence has as yet been obtained to support such a process. Amidophosphines of Rhodium and Iridium It would appear that reaction of LiN(SiMe 2CH 2PPh 2) 2 with a Group VIII metal halide i s a general route to stable amidophosphines, as evidenced by the i s o l a t i o n of a variety of Rh(I) derivatives by t h i s method (see Scheme 1.3). As for the complexes of the nickel t r i a d , a l l of these species are monomeric, a n a l y t i c a l l y pure, highly c r y s t a l l i n e solids which are very a i r and moisture sensitive. The carbonyl , phosphine, and ethylene derivatives may a l t e r n a t i v e l y be prepared in high y i e l d by reaction of with the desired neutral ligand (equation 1 8 ) . - 3 6 -Scheme 13 Ph 2 M e2 S L I N—Rh—L Ph, 18 19 20 21 22 L CO C 2 H 4 COE PMe3 PPh, Ph2 M e ^ t ^ l Me2sT 'j (18) N - Rh— L Me,Si 1 O P h C H 3 Me2Si I Ph2 Ph 2 L=CO,C2H4,PR3 In a l l of these complexes, the hybrid ligand i s coordinated in a tridentate manner, binding to the rhodium centre through hoth. phosphines and the N atom, resulting in square planar, 16-electron species. The - 3 7 -exclusive trans disposition of the chelating phosphines was once again established primarily from H^NMR data, in particular the CH2P v i r t u a l t r i p l e t at VI. 8 ppm ( J a p p ~5 Hz). A typical spectrum i s shown in (Fig. 1.15). The 3 1K 1H}NMR spectra are very straightforward A 2X patterns ''' i 11111 •  11, i 11111111 111 i. S 7 6 5 4 3 2 1 0 p p m Fig. 1 .15 ^NMROOOMHz). spectrum of lRh(C 2H 4)N(.$1Me 2CH 2PPh 2) 2] in CgDg for the cyclooctene, carbonyl, and ethylene derivatives and A2BX patterns 31 103 for the PMe, and PPh, complexes. The P- Rh coupling constants for the ligand's PPh2 groups are typically in the range of 130 - 140 Hz (normal values for Rh(I) species), while p for the ancillary PMe3 or PPh3 in 2JI and is somewhat higher (150 - 160 Hz), a reflection of 57 the weak trans influence of the amide group . It is rather remarkable that, prior to our efforts in this area, only one rhodium amide complex, [RhN(SiMe 3) 2(PPh 3) 2] 2 5, had been charac-terized. However, although this complex is stable under inert atmospheres in the solid state, decomposition, with concomitant elimination of HN(SiMe3)2, occurs in benzene solution at 25°C (t^ = 12 h). In contrast, deuterobenzene solutions of our rhodium amidophosphines, sealed in NMR tubes under nitrogen, show no decomposition, even after several months at 25°C. This is possibly a consequence of steric constraints imposed by the two five-membered chelate rings; ortho-metallation (and subsequent reductive elimination of the amide) of the phenyl substituents would be expected to be unfavorable on steric grounds. The analogous iridium derivatives 23- -»- 27 may be prepared in a similar manner or, more simply, via reaction of the iridium cyclooctene amide 2j^  with the required neutral ligand in toluene at room temperature (Scheme 1.4)(except for L = PPh3 which requires refluxing.in toluene for 24 h). In contrast to the previous preparations of the rhodium analogues, the solvent used in the synthesis of the iridium amides is crucial; when diethyl ether is employed inseparable mixtures of products are formed whereas the use of toluene results in high yields of the pure complexes. The H^NMR spectra of these derivatives indicate that all are square-planar - 3 9 -Scheme 14 {.r(COE)2Cl}2 + 8 P * ? " * > X ^ P Me2Si | 0 #C Ph 2 Me2Si | N— Ir— L Ph2 Me2Si PhCH3 N — I r — A Ph 23 24 MM* 25 26 27 L CO C 2H 4 PMe3 PPh3 complexes with trans phosphines. I t should be noted that only one other 5 8 iridium amide, [Ir(C0D)N(SiMe3) 2(PEt 3)], has been prepared to date . Rhodium and iridium amidophosphines have also been synthesized incorporating bidentate hybrid ligands. The preparation of the cyclo-octadiene derivatives [M(C0D)N(PhCH 2)(SiMe 2CH 2PPh 2)] i s very straight-forward (equation 19); carried out at room temperature, the products are obtained in v i r t u a l l y quantitative yields as a n a l y t i c a l l y pure c r y s t a l s . Although exceptionally a i r and moisture se n s i t i v e , these com-plexes, either as solids or in solution undergo no decomposition (via {M(COD)CI)2 + 10 PhCH3 R.T. Me2Si M V N (19) M = Rh.lr 28,29 - 4 0 -6-elimination) under inert atmospheres. Molecular weight measurements (Signer) indicate that these species are monomeric i n solution (benzene). The H^NMR (see Fig. 1.16) are quite straightforward, the most informative resonances being the sharp SiCH^ singlet at 0.04 ppm and the doublet ( J^ j p = 13.0 Hz) for the CH2P protons. Surprisingly, the COD ligand i s not readily displaced, so, as yet, a series of these complexes has not been prepared. Addition of either PMe^ or dmpe to a toluene solution of either 2JJ or 2j} results only in the i s o l a t i o n of starting materials. Carbon monoxide does displace the diene ligand but the stoichiometry of the resultant rhodium complex, isolated as deep red c r y s t a l s , has not been elucidated. Me2Si CH2P C6H5CH2 ,=CH J L _ J L 3 ppm Fig. 1.16 1HNMR(400MHz) spectrum of [Rh(C0D)N(C 6H 5CH 2)(SiMe 2CH 2PPh 2)] i n C6 D6 - 4 1 -Chapter II Migratory Insertion of Carbon Monoxide into Metal-Carbon Bonds 59 Due to i t s involvement in important c a t a l y t i c (hydroformylation, "Reppe" reactions, Monsanto's acetic acid process) and stoichiometric reactions 6 0(carbonylation of organic halides using Collman's reagent or N i ( C 0 ) 4 ) , the migratory insertion of carbon monoxide into t r a n s i t i o n 6 1 6 2 metal alkyl bonds has been the object of intensive research ' .The a b i l i t y of metal al k y l s to form acyl derivatives upon exposure to CO 6 3 was f i r s t reported by C o f f i e l d , Kozikowski, and Closson in 1957 (equation 2 0 ) . Since then, examples of this reaction have been observed for most t r a n s i t i o n metals. Although detailed k i n e t i c studies have not been carried out for most of these cases, analogy i s usually made to the prototypical MeMn(C0)g complex for which the reaction mechanism has been well elaborated. MeMn(C0)5 MeC0Mn(C0)5 (20) The basic feature of a migratory insertion reaction i s that an un-saturated group (Y) becomes inserted between two atoms o r i g i n a l l y bound together (M-X) as in equation 21. The unsaturated molecule may be CO, an o l e f i n , diene, acetylene, aldehyde, n i t r i l e , S0 2, or 0 2, while the ligand X may be H, a l k y l , a r y l , v i n y l , OR", NR2", NR3, OH", H20, halide or another metal. -4 2-M-Y + :X • M-X-Y (21) I t i s important to note the d i s t i n c t i o n between an oxidative addition and an insertion reaction since a reaction of the type shown in equation22 i s sometimes regarded as an insertion of M into an H-H bond. However, a migratory insertion reaction results in np_ net change in the metal's formal oxidation state whereas an oxidative addition (equation 22 ) involves a net two electron oxidation of the metal centre. Migratory insertions may be either intramolecular or intermolecular; the former class of reactions requires simultaneous coordination of the unsaturated group and the ligand X at the metal, while the l a t t e r proceed by external nucleophilic attack of Y on M-X. In some cases, especially with CO, reaction may be reversible; the reverse reaction of equation?! i s termed an "extrusion", "deinsertion", or a "decarbonylation" and may be promoted thermally, photo-l y t i c a l l y , or chemically (eg. using Rh(PPh^JgCl). In the case of al k y l —>-acyl migratory insertions, reaction occurs intramolecularly, usually in the presence of an external Lewis base ligand, which f i l l s the coordination _site l e f t vacant after insertion has taken place; usually phosphines, carbon monoxide, or amines serve t h i s purpose (equation 23), H LnM + H 2 (22) H Mn(C0) 5CH 3 + LMn(C0)4C0CH3 (23) -4 3-The most common cases of CO insertion involve t r a n s i t i o n metal carbonyl alk y l complexes i n which the inserting CO i s already coordinated, although there are a s i g n i f i c a n t number of examples of acyl formation using metal al k y l s having no carbonyl ligands. In the l a t t e r case, i t i s believed that the incoming CO coordinates prior to i n s e r t i o n . Thus a vacant s i t e cis to the al k y l group must be generated in order for reaction to occur S i m i l a r l y , i f the starting material i s a carbonyl al k y l complex, a car-bonyl ligand must be c i s to the al k y l group. The term "migratory i n s e r t i o n " i s best applied to these reactions since i t has been established (mainly through l a b e l l i n g studies) that, rather than a direct insertion of CO into the M-C bond, th i s process i s better considered as a 1,2-migration of an alkyl group to a c i s coor-dinated carbonyl l i g a n d 6 4 ' 6 5 5 6 6 . Although t h i s has only been firmly esta-blished for a few cases of CO migratory insertion (Notably the MeMn(C0)5 67 system), Hal pern has suggested that R group migration probably occurs in most, i f not a l l , cases of al k y l *acy1 transformations. A general two-step mechanism, involving a coordinatively unsaturated acyl i n t e r -mediate, is outlined in equation 24. R 0 L' 0 1 // \ ' x ft . L-M-CO • L-M-C L-M-C (24) ' | \ i \ L L R L R The r e a c t i v i t y of CO with t r a n s i t i o n metal a l k y l s i s often completely independent of the nature of the solvent; such is the case with [EtPt(CO)-( A s P h 3 ) C l ] 6 8 . However, for [CH 3Mn(C0) 5f 6,[CpFe(C0) 2CH 3] 6 9 , and [CpMo(C0)3-70 CH,] , i t has been shown that more highly coordinating and/or polar -44-solvents markedly increase the rate of CO insertion (the solvent-assisted pathway). This effect has been ascribed to a possible solvent-promoted breaking of the M-R bond, although l i t t l e s o l i d evidence has been provided as yet for a solvated acyl intermediate. When the solvent i s highly coordinating, competition occurs between reaction of L'(see equation 24) with the acyl intermediate and i t s reversion to the a l k y l . However, in non-polar solvents, reaction proceeds by direct attack of L on the acyl intermediate. Such an intermediate may be either a coordinatively unsat-urated, monohapto acyl or a coordinatively saturated dihapto a c y l . The l a t t e r p o s s i b i l i t y would seem quite feasible in view of the preponderance of t r a n s i t i o n metal alk y l derivatives for which the acyl moiety i s coordi-2 nated in an n -fashion. Based on studies using t r a n s i t i o n metal complexes with ch i r a l R groups, i t was found that CO migratory insertions are very stereospecific 7 ] 72 and usually proceed with retention of configuration at carbon ' . However, very l i t t l e extensive investigation has been made on the effect of the R group on the rate of these reactions. Generally, i t has been noted that electron-releasing groups tend to promote insertions whereas electron-withdrawing groups s i g n i f i c a n t l y decrease rates. Reaction of CO with RMn(C0)5 follows the sequence R=n-Pr>Et>Me»CH2Ph and CF 3 7 3. Si m i l a r l y the analogous reaction of CpMo(C0)3R with PPh 3 shows a decrease in the rate with R=Et>Me>CH2Ph>CH2CH=CH27'4. Thus i t would appear that the r e a c t i v i t y r e f l e c t s the strength of the M-R bond. In l i g h t of these observations, i t should not be surprising that - 4 5 -r e a c t i v i t y usually decreases upon descending a t r a n s i t i o n metal t r i a d since the heavier metals from stronger metal-carbon bonds. For example, whereas CO insertion into the rhodium methyl bond of [MeRhtCOHPtn-E^^" IX] (X=C1 or B r ) 7 5 and [MeRh(C0)(PMe 2Ph) 2Br 2] 7 6 occurs readily under one 75 7 7 atmosphere of CO, the corresponding iridium complexes 5 do not react under these conditions; in f a c t , [MeIr(CO)(PMe 2Ph) 2Br 2] does not undergo 7 ft insertion even under higher pressures of CO Migratory Insertion of Carbon Monoxide into Nickel (II)-Carbon Bonds Although a large variety of nickel (II) alkyl (and aryl) complexes i s known, the corresponding acyl derivatives are exceedingly r a r e 6 2 . Such species are presumed intermediates in a variety of N i ( l l ) carbony-79 l a t i o n reactions ; an example of such a reaction i s i l l u s t r a t e d in equation 25. < < / . . + C 0 1 f o ^ ^ V ^ r - O M e (25) 2 The i n s t a b i l i t y of Ni(II) acyls has been ascribed to dominant decarbonyla-tion "(equation 25) or C-C coupling r e a c t i o n s 8 0 (equations27 and 2 8 ) . Ni(II)-C „ N i ( l I ) R + CO (26) R / Ni(II) • Ni(0) + R'CR (27) R r o - 4 6 -0 Jt-R Ni(II) • Ni(0) + R'-C-C-R (28) \ n ll C-R' 0 0 // 0 The f i r s t example H J of a Ni(II) acyl species was reported in 1970. Reaction of [CpNi(a,Tr-cyclooctene)] with high pressures of CO resulted in an acyl derivative, [CpNi(COCgH-j3)]; however, attempts to isolate this complex were unsuccessful and characterization was based solely on mass spectrometric data. 82 8 3 However, Klein ' has isolated stable acetyl nickel complexes of the type [Ni(C0CH 3)X(PMe 3) 2] (X=Cl,Br). Single crystal x-ray structual analysis has established the trans square planar structure of these nickel acyl derivatives. Although moderately stable, these acetyl complexes slowly lose CO under inert atmospheres with concomitant regeneration of the sta r t i n g nickel a l k y l . S i m i l a r l y , reaction of [Ni(R)Cll_ 2] ( R= CH2CMe2Ph or CH 2SiMe 3 ; L=PMe3 or PMe2Ph) under one atmosphere CO at room temperature yielded the corresponding acyl complexes [Ni (C0R)C11_2] 8 \ X-ray crystal structure analysis of [Ni(C0CH 2SiMe 3)CI(PMe 3) 2] indicates a distorted square planar geometry with trans disposed phosphines. Surprisingly, these reactions a r e i r r e v e r s i b l e , even with prolonged heating. S a c c o n i 8 5 has reported the i s o l a t i o n of five-coordinate cationic nickel acyl complexes of formula [Ni(C0R)L]BPh 4 (R=CH3,C2H5,CH2Ph; L=tris (2-diphenylarsinoethyl)amine:(nas 3),tris(2-diphenylphosphinoethyl)amine: (nrP,)) from the alky l complexes [Ni(R)L]BPh d. For the methyl derivative, -4 7-an intermediate has been i d e n t i f i e d ; crystallographic analysis has shown thi s intermediate to be a " s o l i d solution" of the cationic acyl and a cationic carbonyl (equation29 ). The proposed reaction scheme involves an undetected intermediate in which the nitrogen i s no longer bound, in order to provide a coordination s i t e for the incoming CO. These acyl complexes are stable both in solution and i n the s o l i d state under an atmosphere of CO; however, under nitrogen or argon, gradual loss of CO reforms the starting a l k y l derivative. Fahey 8 6 has isolated a nickel benzoyl complex from the reaction of [ N i ( C 6 H 5 ) C l ( P E t 3 ) 2 ] with CO (1-2 atmospheres) at 25°C in hexane. The product, [Ni(C0CgH^)Cl(PEt 3) 2] was produced as orange c r y s t a l s . A number of other nickel acyl complexes has also been characterized; however, these species were prepared via oxidative addition of an a l k y l , v i n y l , or aryl halide to [Ni(PEt 3) 2(l,5-C0D)] rather than CO i n s e r t i o n . A n c i l l a r y Ligand Rearrangements Promoted by the Migratory Insertion of  Carbon Monoxide into Nickel(II)-Carbon Bonds As anticipated, reaction of [NiClN(SiMe 2CH 2PPh 2) 2] with Grignard -48-or al k y l lithium reagents produces the corresponding alkyl (or aryl) com-plexes in high yi e l d s (equation 30). The only r e s t r i c t i o n to this prepa-ration i s that the R group cannot have B-hydrogens; thus, the ethyl deri-vative, Ni(Et)N(SiMe2CH2PPh2)2» could not be isola t e d , presumably owing to rapid decomposition via a B-elimination mechanism. Typically, synthesis of these hydrocarbyl ( i e . a l k y l , a r y l , v inyl) derivatives i s Ph 2 Ph, X ^ P X ^ P 2 s N _ N i _ C l " f t * » ti — Ni — R Me2Sf I " 3 0 - C Me^f I <30) Ph, ^ P h , R s = C H 3 , C 3 H 5 , carried out at high d i l u t i o n (MO M in toluene, THF, or Et20) and low temperature (rb-30°C) in order to prevent reductive coupling r e a c t i o n s 8 7 , an often troublesome decomposition route for metal alkyls (equation 31) A . / 2 M-R —* Mv' %M • M + M • 2M + R-R ( 3 1 ) *R' R These nickel hydrocarbyls are isolated as highly c r y s t a l l i n e , a n a l y t i c a l l y pure sol i d s which are very a i r and moisture s e n s i t i v e ; however, under inert atmospheres they are stable for several months. Rec r y s t a l l i z a t i o n i s t y p i c a l l y carried out from neat hexane at -30°C, owing to the high s o l u b i l i t y of these derivatives in organic solvents. Structural characterization has been largely based on ^ HNMR data; the spectra of [Ni (CH 3)N(S1Me 2CH 2PPh 2) 2] (Fi g . 2.1) and [Ni(CH=CH 2)N(Si-Me 2CH 2PPh 2) 2] (Fi g . 2.2) serve as i l l u s t r a t i v e examples. The-virtual - 4 9 -Me2S^ | N — N i — C H 3 Me2Si I Ph 2 U C H / Ni-CH 3 p p m Fig. 2.1 N^MRCSO MHz) spectrum of [Ni (CH3)N(SiMe2CH2PPh2)2] in C7D£ Ph, Me2Si^ | N - N i - C ' Me,sf I *C I H» I H, J,.t 1 0 8 3 J , 3 17.5 2 J 2 .3 1-5 3Jp,, 6-3 *JP,2 3 5 4JR3 2.1 1 ppm Fig. 2.2 ^NMRCSO MHZ) spectrum of [Ni(CH=CH2)N(SiMe2CH2PPh2)2] in CgDg - 5 0 -t r i p l e t for the C^P protons i s once again diagnostic of a trans orien-tation of the chelating phosphines; such a conformation i s quite predict-able in l i g h t of the fact that aj_l_ known [NiX(R)(PR 3) 2] species have 8 8 s 8 9 square planar geometries with mutually trans phosphines . In addition, the methyl group of [Ni(CH-^NCSiMezCHzPPhz^l appears as a sharp t r i p l e t upfield of TMS owing to c i s coupling with the tridentate ligand's two phosphine centres ( J ^ p = 10.0 Hz). Although the vinyl derivative displays a complicated ABCX2 pattern for the vinyl protons, phosphorus decoupling s i g n i f i c a n t l y s i m p l i f i e d the spectrum so that analysis of the proton-proton coupling constants was possible. When R i s the a l l y l group, C^H^, the "*HNMR i s a c l a s s i c AX^ pattern for the a l l y l protons (phosphorus coupling merely broadens these signals ' s l i g h t l y ) . Since the syn and anti protons are equivalent, i t i s apparent that exchange i s occurring, presumably via rapid (at least on the NMR 3 1 time scale) 11 — • n interconversions. Upon cooling to -80°C, no changes were observed i n the a l l y l proton resonances. "Whenever an alkyl-metal complex i s produced, one i s almost obliged 9 0 to treat i t with CO to see i f i t w i l l undergo migratory insertion" . The r e a c t i v i t y of the nickel hydrocarbyl amido phosphines towards CO was therefore investigated. Indeed, a l l of these nickel species react readily under one atmosphere of carbon monoxide at room temperature to give nickel(0) derivatives in which the chelating mode of the ligand has been altered. With [Ni(CH3)N(SiMe2CH2PPh2)2]» carbonylation occurs very rapidly -51-Me2 Ph2 CH,CN Ni ° S i ^ p ' CO Me2 Ph2 o ik. 4 ppm Fig. 2.3 ""HNMFUSO MHZ) spectrum of [Ni (C0) 2N( C0CH3) (SiMe 2CH 2PPh 2) 2] in C7°8 - 5 2 -R_ 30 CH 3 31 C 3 H 5 32 C 6 H 5 33 C 2 H 3 to produce the Ni(0) species in v i r t u a l l y quantitative y i e l d (by NMR) (equation 32); the i n i t i a l l y gold-orange solution fades within seconds of exposure to CO and after f i v e minutes i s completely colorless. Colorless crystals of 30 are obtained from hexane; the chemical and mole-cular weight (Signer) analysis are consistent with the monomeric complex [Ni(C0) 2N(C0Me)(SiMe 2CH 2PPh 2) 2]. The ]HNMR (Fig. 2.3) displays a broad ^ P h 2 Me2 Ph2 N^ — Ni — P. 1 a t m C 0 . RC.N > Me2Si p R T 0 N S i ^ * P ^ N C 0 o (32) \ ^ p h 2 Me2 Ph 2 signal for the CH2P, indicative of weak coupling to two cis phosphines. 13 When the reaction i s carried out under CO, the sharp singlet due to 13 13 the acetyl protons ( COCH^) i s s p l i t into a doublet due to C coupling (J^l 13^ = 6.35 Hz). The most s i g n i f i c a n t structural information comes from the infra-red spectra o f 3 J j ( F i g . 2.4). In addition to the N-acetyl band at 1715 cm~\ two very strong terminal carbonyl stretches at 1995 and 1930 cm~\ indicative of two cis carbonyls, are also observed. These bands s h i f t appropriately (to 1680, 1955 and 1890 cm"\ respectively) upon incorporation of ^ CO. The absorption at 1715 cm~^  i s quite t y p i c a l 9 1 of organic amides, -NC0Rj which usually have vQQR values of 1625-1725 cm"^; however, th i s i s a rather high frequency stretch for nickel acyl Ni-COR _*| 82 — 8 6 groupings which absorb in the 1600-1650 cm" range - 5 3 -The 13C{1H}NMR of 1 3C enriched30 i s also consistent with the OA-proposed structural formulation in that the terminal carbonyls appear o as a t r i p l e t at 200.2 ppm due to c i s phosphorus coupling ( J_, = J l P j U c 2.4 Hz) while the amide carbonyl (Si 2NC0CH 3) i s a singlet at 161.9 ppm. These chemical s h i f t s are quite typical for t r a n s i t i o n metal carbonyl 92 Q o (M-CO) and amide carbonyl f u n c t i o n a l i t i e s . An identical reaction obtains for the nickel a l l y l derivative, [Ni (C 3H5)N(SiMe 2CH 2PPh 2) 2]; this reaction i s also complete in five minutes and the product i s obtained as colorless crystals in ^80% recrystal1ized y i e l d . Once again, the IR consists of two very strong terminal carbonyl stretches at 1 995 and 1935 cm~^, as well as a strong N-acyl band at 1715 cm"^. No other product is observed. The spectral and analytical data for31 indicate that, l i k e 30 i t i s a Ni (o) derivative in which the hybrid ligand i s coordinated in a bidentate fashion through the phosphine donors. 2 However, the nickel hydrocarbyls having the sp -carbon ligands, vinyl and phenyl, show somewhat different migratory insertion behavior: not only i s the reaction much slower but several products have been i d e n t i f i e d . After s t i r r i n g a toluene solution of [Ni(CgH 5)N(SiMe 2CH 2~ PPh 2) 2] under one atmosphere of CO for seven hours, a mixture of two products was obtained in an approximate 1:1 r a t i o (by NMR) (equation 33 ). Ide n t i f i c a t i o n of the benzoyl nickel complex 34 and the Ni(0) derivative 32 was made possible by recrystal1ization of the crude product from neat hexane followed by Pasteur type separation of the orange prisms of 34 from OA-the colorless crystals of 3^ 2. If th i s reaction i s monitored by ^ HNMR, i t -54-Me2 Ph2 PhCN Ni O x ^ • N  u S i ^ P CO Ph 2 Me2 Ph 2 / ^ P 32 M e 2 $ i i co * ~ y N — N i — P h • (33) Me2S* I Ph, x — p M e ^ | O ^ N - N i - C ' Me.Si I > h Ph 2 34 i s observed that the nickel benzoyl complex i s formed rapidly and quantitatively at room temperature (<30 minutes); the subsequent formation of the Ni(0) complex i s much slower, requiring several days. Pure34 can thus be ea s i l y obtained by exposing a solution of [Ni(C AHr)~ N(SiMe 2CH 2PPh 2) 2] to CO for only twenty minutes followed by r e c r y s t a l l i -zation from toluene/hexane; 32 is produced exclusively i f the solution i s OA, s t i r r e d under CO for three days. As expected, a CgDg solution of 34, sealed in an NMR tube under CO, slowly reacts to quantitatively form the Ni(0) complex 32. Interestingly, the ^ HNMR spectrum of 34 i s rather complex (Fig . 2.5), consisting of two sharp SiMe 3 peaks (of equal i n t e n s i t y ) , an -5 5-AB quartet of v i r t u a l t r i p l e t s for the CH2P protons and a complicated set of phenyl resonances. Upon heating to 80°C, the two s i l y l methyl P h . / ^ P M e £ i | O JH— Ni — C M e , S i I X P h P h , J 4 ppm Fig. 2.5 ]HNMR(80 MHz) spectrum of [Ni(C0C 6H 5)N(SiMe 2CH 2PPh 2) 2] in C gD 6 peaks collapse to a broad s i n g l e t . The spectral data are consistent with r e s t r i c t e d rotation of the NiCOPh group about the Ni-C bond, which i s probably a resu l t of s t e r i c interactions of the nickel benzoyl fragment with the tridentate ligand's phenyl substituents. A l t e r n a t i v e l y , this - 5 6 -could be explained as a consequence of multiple Ni-C bonding as shown in (equation 34). Ph 2 Ph2 y P y ^ p M62Si | O Me2Si | + O-/N— Ni — C ' * ^ N —Ni = C (34) Me2Si I N P h Me2Sl I N P h Ph 2 ^ Ph 2 35 The corresponding nickel acetyl compl ex 36can also be prepared by the stoichiometric addition of one equivalent of CO to a toluene solution of [Ni(CH 3)N(SiMe 2CH 2PPh 2) 2] ( e q u a t i o n ^ ) . The ""HNMR of thi s complex Ph 2 Ph, y ^ P y ^ - P 2 ) , _ N j _ C H 3 1 e<*™ C 0 . 2 N / N _ N J _ C * (35) Me Si I Me.sf I N C H , \ ^ P 2 p 3 Ph 2 Ph 2 36 consists of a broad singl e t for the SiMe 3 protons at room temperature which becomes a sharp doublet upon cooling to -30°C (Fig . 2.6). Once again, this i s consistent with r e s t r i c t e d rotation about the Ni-COCH^ bond. Both the benzoyl and acetyl derivatives 34 and 36 are stable, c r y s t a l l i n e solids but do evolve CO upon heating, to regenerate the starting hydrocarbyl complex. For the nic k e l - v i n y l starting material, reaction with CO i s complete in three hours, as indicated by the formation of a colorless solution of 33, v - — OA/ -5 7-7 6 5 4 3 2 1 0 ppm a) ^NMRCSOMHz) spectrum of lNi.(C0CH3).NC.Si.Me2CH.2PPh2)2] in C yD 8 at 298°K. b) 1HNMR(.80MHz) spectrum of [Ni(C0CH 3)N(SiMe 2CH 2PPh 2) 2J in C,D„ at 243°K. -5 8-Ph, Me2Si | H N — Ni — V ^ . H H Ph 2 Me2 Ph 2 H H CO S i ^P* Me2 Ph2 CO 33 M e „ S i - Q * Ni v H, » 2 P Ph„ CO (36) 37 However, the 1HNMR of the pale yellow o i l y residue, l e f t after solvent removal, indicates that, in addition to the expected N-acryloyl species 33(which i s the major product in ^90% y i e l d , by NMR), another Ni(0) product i s formed (equation 36). Although i n i t i a l l y a minor component of the product mixture, t h i s species may be se l e c t i v e l y separated as fine yellow crystals by repeated recrystal1izations from hexane. In fa c t , attempts to obtain pure 33 have been unsuccessful, since i t slowly loses a CO ligand in solution or under vacuum to produce 37. Thus the y i e l d of 37 can be increased to ^.90% (by NMR) by slow removal of CO under high vacuum over a two day period, as indicated by the gradual deepening of the solution to a clear yellow-orange color. The reversible nature of - 5 9 -t h i s reaction i s demonstrated by the fact that yellow CgDg solutions of a n a l y t i c a l l y pure ^ s e a l e d in NMR tubes under one atmosphere of CO, fade to colorless within minutes;33 i s the only observed species. Originally, 3 7 was formulated, on the basis of extensive spectral 2 data, as an n, -acryloyl complex wherein the rearranged ligand binds in a tridentate fashion through the ir-system of the vinyl group as well as the two phosphine centres. Since the coordinated o l e f i n of th i s complex, Me S i x O, P CO Ph 2 38 as depicted in structure 3J3, has enantiotopic faces, the SiMe3 groups are diastereotopic and should therefore give r i s e to four resonances in the H^NMR. This i s indeed the case, as shown by the 400 MHz spectrum i l l u s t r a t e d in Fig. 2 . 7 . In addition, the CHgP protons are also dia-stereotopic and display four sets of doublets of doublets. The o l e f i n i c protons are shifted u p f i e l d , as compared to the starting nickel-vinyl complex, and a r e s p l i t by two inequivalent phosphorous n u c l e i ; although complicated, simulation of t-his ABCXY pattern (Fig. 2.8) allows f u l l assignment of proton-proton and proton-phosphorus coupling constants. The infra-red data are also consistent with t h i s formulation owing to the single very strong terminal carbonyl absorption at 1950 cm"^  as well -1 2 as a strong band at 1 625 cm , ascribed to VQQQ H of the n -acryloyl " 2 3 - 6 0 -b) Fig. 2.8 a) Vinyl proton region (400 MHz ]HNMR) of £N1(C0)N(C0C2H3)-(SiMe 2CH 2PPh 2) 2] b) Spectral simulation of vinyl proton ABCXY pattern: J 1 3 = 11.72, J 2 j 3 = 7.57, J . ^ = 6.59, J 2 ^ = 5.62, J1,P2 = 1 - 4 6 ' J3,P1 = 1 3 ' 9 2 ' J3,P2 = 3 ' 1 7 ' J2,P2 = 4 J 5 - 6 1 -group. Further evidence is provided by the JIP{'H}NMR spectrum which consists of an AX doublet of doublets (6A = 16.38 ppm; SX = -1.38; A^X = ^7'^ H z^ c* u e t o t' i e ^ n e c l u i v a 1 ent phosphine centres. However, the x-ray crystal structure of 37 is slightly different than predicted (Fig. 2.9). Although the coordination about the nickel centre is correct as postulated for 38, with one terminal carbonyl, a Fig. 2.9 X-ray crystal structure of [Ni(.C0)NtC0C2H3)(S1Me2CH2PPh2)2] (alternate chelate ring conformation is indicated by unshaded thermal ellipsoids). - 6 2 -coordinated o l e f i n , and two phosphines, the hybrid ligand backbone has undergone a further rearrangement. A " s i l a t r o p i c s h i f t " of one of the s i l i c o n centres to the carbonyl oxygen of the N-acryloyl fragment results in the observed "imidate" structure. Nonetheless, a l l of the afore-mentioned spectral data are consistent with the s o l i d state structure of Fig. 2.9. Several questions are now raised by the crystallographic structural characterization of 37. Does t h i s s o l i d state structure persist in solution or i s i t merely a result of crystal packing effects? In the absence of X-ray crystallographic data for30,31, and32, i s t h i s type of amide —»• OA> ^A OA imidate isomerization also occurring with the other Ni(0) complexes? If not, why does only the acryloyl fragment rearrange? A l l spectral information acquired to date suggests that the s o l i d state structure of 37 i s identical to i t s structure in solution. The OA. infra-red spectra in solution ( C ^ C l g . toluene, or hexane) have identical values of VQQQ^H-^ (1625 cm~^) as observed for a KBr disc of Unfortu-nately, d i s t i n c t i o n cannot be made, on an IR basis, between the amide and the imidate tautomers, since the absorption ranges overlap (1625 - 1725 cm - 1 for the former versus 1600 - 1675 cm - 1 for the l a t t e r ) 9 1 . Although four s i l y l methyl resonances would be expected in the ^HNMR for both 37 and ,38, the large chemical s h i f t range of the SiCH_3 signals (-0.67 —»• +0.67 ppm) as well as the fact that only two of these peaks display phos-phorus coupling ( J ^ p = 0.98 Hz) would be more consistent with the imidate structure. -6 3-31 1 The P{ H}NMR indicates a rather large chemical s h i f t difference, of almost 18 ppm, between the two phosphine doublets. Although the phos-phines of 38 are diastereotopic, such a drastic s h i f t difference seems quite unreasonable; an AB quartet might be more appropriate. When the 31P{1H}NMR spectrum of 1 5N-labelled37 i s recorded, only the resonance at w — 1 5 -1.38 ppm displays phosphorus - N coupling. Once again, t h i s implies that the imidate 37^  i s the only form present in solution, since the three-•31 1 C IK bond P- N coupling in the NSiMe 2CH 2PPh 2 fragment should be greater 15 than the four-bond coupling in the N=C0SiMe2CH2PPh2 fragment. The unusually high chemical s h i f t value of -1.38 ppm (as compared to a l l of 31 1 the previously prepared Group VIII amido phosphines which have P{ H} signals in the 10 35 ppm range) might be explained in terms of ring 94 s t r a i n imposed by the coordination of the o l e f i n . Studies by Garrou 31 have shown that the P s h i f t value of a tr a n s i t i o n metal complex incor-porating a chelating phosphine i s s i g n i f i c a n t l y dependent upon the size of the metal-chelate r i n g . It i s quite possible that upon coordination of the o l e f i n in 37 the resulting chelate ring i s somewhat strained, thereby weakening one of the Ni-P bonds and giving r i s e to the r e l a t i v e l y high f i e l d 3 1 P s h i f t . 31 1 1 Although the P{ H}NMR, HNMR, and IR are somewhat inconclusive as to the solution structure of 37 i t would seem reasonable to postulate ing the imidate form. At present, the 2 9SiNMR of 1 5N-labelled37 i s beii investigated in hope of affirming t h i s proposal. In l i g h t of the well-documented l a b i l i t y of trimethyl s i l y l groups 95 96 2 in organic compounds ' , the imidate rearrangement of the nickel n --64-acryloyl should not be too surprising. This type of behavior has been extensively investigated for the popular s i l y l a t i n g agent bis (trimethyl 9 7 10 0 1 s i l y l ) acetamide " . The HNMR of this compound at room temperature (CDC13) indicates an approximate 1:1 r a t i o of the amide (N,N) and imidate (N,0) forms 39 and 40 j n contrast, the Si Me, OSiMe, / 3 | 3 CH.C-N CH,C=N 0 SiMe 3 SiMe 3 39 40 mono(trimethylsilyl) amides, such as N-methyl-N-trimethylsilylacetamide, have generally been accepted as having the amide structure. However, both the mono and bis s i l y l compounds show temperature dependent NMR behavior, which can be rationalized as either the result of hindered rotation about the C-N bond or SiMe3 group exchange 1 0 1. Other spectral s t u d i e s 1 0 2 , 13 29 involving C and SiNMR, has also confirmed the presence of both 1 2 tautomeric forms at room temperature for a variety of compounds R CONR S i -Me2R3 (R1 = CH3,C2H50; R2 = H ,CH3 ,CgH5 ,Si(CH 3) 3 ,p-CH3CgH4,p-ClCgH4, 3 p-CH30CgH4; R =CH3,CgH5 ,p-CH3CgH4,p-CH30CgH4). Generally, there i s a 29 Si s h i f t difference of ^ 9 ppm for an NSJ_ (6 = ^ 10 ppm) versus an OSi grouping (6^19 ppm); a s h i f t difference of ^ 15 ppm i s observed between 13 the amide and the imidate forms in the CNMR. By determining the re l a t i v e concentrations of the tautomers over a wide temperature range, i t was concluded that the amide form i s favored by electron donating groups at N and by decreasing temperature. -6 5-In contrast, the Ni(0) species 30,31 ,32 and33 show no evidence of 'Vb o/b 'Vb 'Vb tautomerism. The HNMR of 30 has only one singlet for the SiMe 2 protons even down to -80°C and up to 120°C. The broad signal for the CH2P protons does sharpen to a doublet at high temperatures, but t h i s i s probably a con-sequence of conformational changes in the eight-membered chelate ring. 31 1 The P{ H}NMR of 30 i s a singlet (an identical situation obtains for 31^,32, and 33)whereas the imidate form of 30 should give two peaks (a mixture of amide and imidates would, of course, complicate the spectra further). 13 1 S i m i l a r l y , the C{ HlNMR of the Ni(0) complexes indicates the presence of only one tautomer in solution at room temperature, although the chemical s h i f t values are not s u f f i c i e n t l y disparate to unequivocably distinguish 1 3 between the two possible structures ( C values for the COR unit of S j ^ ^ - ^ l i e in the range 162 - 158 ppm, whereas the chemical s h i f t for,37 i s 166 ppm). Molecular models of 37and 38 indicate that the formation of either V b ^ structure seems equally favorable on s t e r i c grounds. However, d e r e a l i z a -tion of electron density from the n i c k e l - o l e f i n i c bond into the C=N iT-system may be the driving force for the s i l a t r o p i c rearrangement bbserved for the n -acryloyl nickel complex ( f i g . ' 2.10); such an extended it-system i s not available in the amide form, or, of course, in those N-acyls having R groups other than v i n y l . Although the ligand rearrangement observed in the formation of the complexes [Ni(C0) 2N(C0R)(SiMe 2CH 2PPh 2) 2] (R = Me, a l l y l , v i n y l , phenyl) 1 31 may at f i r s t seem rather unusual, variable temperature H and P NMR as Si Fig. 2.10 ir-system of the nickel rr-acryloyl complex (imidate form) well as labelling experiments have suggested a possible mechanism. At low temperature, the acetyl complex36 forms immediately upon exposure of a CyDg solution of [Ni(CH3)N(SiMe2CH2PPh2)2] to CO. Upon warming to -40°C, the Ni(0) species is gradually formed, the reaction going to com-31 1 pletion in approximately two hours. The P{ H}NMR at -40°C contains only two singlets throughout the course of the reaction, one at 26.7 ppm (due to the starting material) and the other at 15.5 ppm (due to the acetyl complex36 and the Ni(0) derivative^, which have degenerate chemi-O/V Oft, cal shifts). No other species was detected. A possible mechanism could therefore involve initial insertion of CO into the nickel-carbon bond, resulting in a nickel-acyl (or aroyl) species which then undergoes -6 7-reductive elimination of the acyl group to the amide nitrogen. A plausible mechanism is outlined in Scheme 2.1. Scheme 2.1 Me,Si 2 \ Ph, P I N — Ni — R Me 2Si I Ph, C O Ph , / ^ P Me 2Si | O N _ N i — C ' Me,Si j , R 2 v - p P h 2 Ph, < O v R Me 2 Si | N — N i — C O Me 2 Si I P h 2 Ph, x ^ P 9 Me Si | jfc'-R — MejSi ' S C O Ph, C O M e 2 P h 2 S i ^ P C O R C N Ni ^ > \ i ^ P ^ N C O M e 2 P h 2 M e 2 S i — l E C ^ / P h > N i | f ^ - C O \ p / \ 0 Ph , -68-An alternative mechanism proceeding through an i n i t i a l insertion of carbon monoxide into the Ni-N bond to form an intermediate Ni(II) carbamoyl could conceivably produce the same results (Scheme2.2). Scheme 2.2 Ph 2 _ Ph2 y^p M e ^ | Me2Si | N—Ni — R ,NC,-Ni-R Mesl I Me2Si O [ ^ Ph, Ph2 P h 2 P h 2 ^ R S ^ P Me2Si | Me2Si | NC-Ni— CO «« , N £ ~ N L Me2Si 6 I Me2Si 0 ^CO Ph2 Ph2 CO Me2 P h 2 RCN N i ^ 0 ^ S i ^ P ^ CO Me2 Ph 2 However, the i s o l a t i o n of the acetyl complex 36 and the benzoyl d e r i v a t i v e ^ would seem to decrease the significance of th i s pathway. In addition, Marks 1 0 3has shown that for the alkyl dialkylamide complex [Th(Cp*) 2(NMe 2)-- 6 9 -CH^], CO insertion into the Th-C bond was observed, even though the dial kylamide [Th(Cp )2(^^2^Z^ rea<^^y forms the carbamoyl complex [Th(Cp )2(C0NMe2)2]• Thus, i t would seem that the migratory aptitude of an alky l group i s greater than for an amide, Nft,, ligand. F i n a l l y , the fact that the rhodium and iridium amido phosphines [ M L N l S i l ^ C ^ -PPh 2)2^ ( M = R n> L = COE, PPh 3) react in a straightforward manner under CO to give the corresponding carbonyl [ M ( C 0 ) N ( S i l ^ C ^ P P I ^ ^ l as the sole product, also implies that CO insertion into the M-N bond i s not a f a c i l e process with these Group VIII amido phosphines. Migratory Insertion of Carbon Monoxide into Palladium(II)-Carbon Bonds The alk y l derivatives [Pd(CH 3)N(SiMe2CH 2PPh 2)2] and [Pd(C 3H 5)N-(SiMe2CH2PPh2)2] are readily prepared via metathesis of [PdClN(SiMe 2CH 2~ PPh 2)2^ with Grignard reagents, in a similar manner as outlined for t h e i r nickel analogues. In contrast to the nickel a l l y l complex, [Pd(C 3H 5)N(SiMe 2CH 2PPh 2) 2] demonstrates only the n.1 mode of bonding at ambient temperatures (by ^HNMR). Upon increasing the temperature, the 31 a l l y ! resonances broaden; above 50°C, an AX^ pattern ( P decoupled) i s 3 1 observed, indicating rapid n —•n interconversions of the syn and anti a l l y l protons. Once again, these palladium a l k y l s are c r y s t a l l i n e , a i r and moisture sensitive solids which are very soluble in a wide variety of organic solvents. In view of the fact that square planar palladium(II) complexes of the type trans-[Pd(PR 3) 2(CH 3)X] (X = CI, Br; PR3 = PEt 3, PPh 3, PPh2Me) react readily with CO (1-3 atmospheres) at room temperature to give the - 7 0 -corresponding palladium acetyl d e r i v a t i v e s 1 0 4 " 1 0 6 , i t i s rather surprising that the palladium alkyl amido phosphines are completely unreactive to CO under these conditions. However, under 20 atmospheres CO, the palladium acyl 41^ i s the only ohseryed product, which i s obtained from hexane as a n a l y t i c a l l y pure red crystals (equation 37),. No further reaction with CO took place. The more robust nature of the palladium a l k y l s , as compared to their nickel analogues, p a r a l l e l s previous CO Ph2 Ph 2 Me2Si I Me2Si | P 2 NN _ p d - C H 3 2° a t m > > - P d - C * (37) Me2st I P h C H a Me2s1 \ \>H, ^ Ph2 Ph 2 41 migratory insertion r e a c t i v i t y patterns and is undoubtedly a consequence of increased Pd-C bond strength. The r e a c t i v i t y of the corresponding platinum derivatives could not be surveyed since iPtClNtSiMegCHgPPhg)^! does not undergo metathesis with Grignard or alkyl lithium reagents. A variety of reaction conditions was investigated as well as a number of different a l k y l a t i n g agents but only intractable mixtures or starting material were isolated. An alternate route using AgBF^ or AgClO^ in CHgC^ or CH^CH in an attempt to abstract the chloride resulted only in the formation of a s i l v e r mirror but no AgCl. A possible explanation for t h i s anomalous behavior i s that the Pt-Cl bond has been strengthened due to the weak trans influence of the amide nitrogen - 7 1 -This i s supported by the Pt-Cl stretching frequency at 317 cm" , indicating a very strong Pt-Cl bond. Similar behavior has been observed 10 8 in other platinum complexes containing a trans X-Pt-NP^ grouping -72-Chapter I I I Homogeneous Catalytic Hydrogenation of Olefins Employing Rhodium and  Iridium Phosphine Complexes. General Principles Since the discovery of Wilkinson's c a t a l y s t , RhCl(PPh 3) 3, in 1 965 1 0 9' 1 rhodium phosphine complexes have been employed extensively in c a t a l y t i c homogeneous hydrogenations of substrates containing o l e f i n i c or acetylenic bonds. In f a c t , these reactions have been more thoroughly studied than any other class of organometallic transformation. Obviously, t h i s i s in part due to the i r synthetic (and possible i n d u s t r i a l ) u t i l i t y . However, interest has also been spurred by the complexity of these reactions, which pose i n t r i c a t e mechanistic challenges, as well as the immense variation possible in the catalyst design. The general mechanistic picture for a l l homogeneous c a t a l y t i c hydro-genations can be broken down into three d i s t i n c t stages: dihydrogen a c t i -vation, substrate a c t i v a t i o n , and hydrogen transfer. The role of the t r a n s i t i o n metal catalyst in the reaction of dihydrogen with an unsaturated organic molecule i s mainly to circumvent the o r b i t a l symmetry r e s t r i c t i o n s (Woodward-Hoffman) presented by the concerted reaction of two diatomic, or pseudodiatomic, molecules such as 0 2, H 2, N 2, C 2H 4 (equation 38) J 1 1. A stepwise process would t h e o r e t i c a l l y be possible (equation 39),but since th i s involves high energy hydrogen atoms, reaction does not occur by t h i s route either. However, i f the hydrogen i s f i r s t bonded to one or two other atoms, such as a t r a n s i t i o n metal, addition of dihydrogen to an unsaturated -7 3-C-C: C^=c' + H-H • H-H (38) "C=CC + H- -H • > - C ^ 39) H -H carbon-carbon bond i s both thermodynamically and symmetry allowed. Since the d-orbitals of these t r a n s i t i o n metals are of correct symmetry to interact d i r e c t l y with H 2 (Fig.3.1), two metal-hydride bonds may be formed; the process i s thus a homolytic s p l i t t i n g of dihydrogen. Hydrogen transfer from this hydride complex to the o l e f i n i s now possible. Such a homolytic H 2 LUMO TM HOMO Fig. 3.1 Orbital representation of dihydrogen activation by a t r a n s i t i o n metal complex cleavage of H 2 requires a formal two electron oxidation of the t r a n s i t i o n metal, or one electron oxidation of two metal centres (equations 40-42). H in H n-2 M + H 2 • M X' (40) M-M + H 2 • 2 M-H (41) d n ,n-l 2 M + H 2 • 2 M-H (42) This explains in part why rhodium and iridium complexes, which readily undergo two electron transformations between the +1 and +3 oxidation states, are so effec t i v e and widely used in these c a t a l y t i c reactions. Another means of activating dihydrogen, which obviates a formal oxidation of the metal, involves heterolytic s p l i t t i n g 1 1 2 (equation 43). Often, this reaction i s promoted by addition of base, or by hydrogenolysis of an a n c i l l a r y alkyl ligand. Although t h i s process can also be envisioned as an oxidative addition of dihydrogen, followed by reductive elimination M - X + H 2 • M-H + HX (43) d n d n of HX (X = halide, alkyl or a r y l ) , heterolytic cleavage usually occurs only with metals in higher oxidation s t a t e s 1 1 2 . Both homolytic and heterolytic activation of H 2 require at least one free coordination s i t e . This may be achieved by use of an i n i t i a l l y coordinatively unsaturated complex or through ligand dissociation from a coordinatively saturated species. Substrate activation also requires an open coordination s i t e since t h i s i s usually accomplished by binding of the unsaturate to the metal centre to form a t r a n s i t i o n metal T i-olefin complex. Although the simultaneous coordination of hydrogen and substrate by the metal atom i s often necessary (except in the case of free radical mechanisms), the s a t i s f a c t i o n of t h i s c r i t e r i o n does not guarantee hydro-genation. A number of quite stable hydrido o l e f i n or diene complexes is -75-known, an example being c i s , trans-f.IrH 2(COD)(PMePh 2) 2]' r 1 1 3 ; t h e i r reluctance to undergo migratory insertion of the o l e f i n into the M-H bond has been ascribed to lack of the required coplanar arrangement of the metal, hydride, and o l e f i n TT-bond (.42). H — - C i II M C 42 I t has been demonstrated that, in a l l cases (except free r a d i c a l ) , hydrogen transfer proceeds in a stepwise manner to generate an intermediate 1 1 4 - 1 1 7 a-alkyl metal complex • As a r e s u l t , some of these systems also isomen'ze ol e f i n s and/or catalyze exchange of D2 and o l e f i n i c protons. Depending upon the metal complex, the f i n a l reductive elimination of saturated alkane may occur via an intramolecular or intermolecular mechanism (vide i n f r a ) . In broad terms, two major c a t a l y t i c pathways are available for a transition-metal catalyzed reduction of an unsaturate 1 1 8. The "hydride route" involves oxidative addition of H 2 to the metal centre, to form a metal-hydride, followed by substrate coordination. A l t e r n a t i v e l y , the "unsaturate route", which proceeds by the binding of substrate prior to dihydrogen a c t i v a t i o n , may be operative, although i t would appear that oxidative addition of H 2 to a metal-olefin complex should o r d i n a r i l y be less f a c i l e (due to the iT-acidity of the o l e f i n ) . Unfortunately, kinetic measurements alone cannot d i f f e r e n t i a t e between these two paths. Assign--76-ment of the "hydride" route i s usually based on the i s o l a t i o n , or spectral characterization, of metal hydride species. However, i f no hydrides are observed, but there i s evidence for metal-olefin derivatives formed during the reaction, the "unsaturate route" i s often invoked. Metal formation in the absence of substrate also infers this pathway. C l a s s i f i c a t i o n of catalyst precursors generally involves designation . as either a monohydride or a dihydride system, depending upon the nature of the proposed active hydride species generated at some point in the c a t a l y t i c cycle. In these cases, i d e n t i f i c a t i o n of the metal hydrides i s not necessarily d i r e c t , that i s , they are not always isolable or even detect-able spectroscopically; often their participation in the c a t a l y t i c cycle i s inferred by mechanistic studies, isotopic l a b e l l i n g experiments, or by analogy to related systems for which hydrido species have been unequivocably identi f i e d . I t should be noted that the term "catalyst precursor" refers to the synthesized t r a n s i t i o n metal complex (which i s not necessarily a pre-formed metal hydride); t h i s i s d i s t i n c t from the actual catalyst which may be present in only very low concentrations and thus undetectable under the particular reaction conditions. In f a c t , mechanistic studies by Hal pern have indicated that iso l a b l e or spectroscopically dominant species formed during the hydrogenation cycle are usually not involved in the k i n e t i c a l l y s i g n i f i c a n t c a t a l y t i c pathway 1 1 9' 1 2 0. Dihydride Catalysts The complexity of homogeneous c a t a l y t i c hydrogenation reactions has often precluded d e f i n i t i v e mechanistic analysis or has led to c o n f l i c t i n g -7 7-postulates of reaction pathways, depending upon interpretation of kinetic and spectral data. Even for the most extensively studied system, Wilkinson's catalyst, there is s t i l l some controversy. However, a number of key steps has been well documented and are generally accepted as applic-able to most dihydride catalysts. There are two major classes of rhodium phosphine dihydride catalyst precursors: neutral complexes of the type [RhL^X] (X = halide, L = tertiary phosphine or arsine) such as Wilkinson's catalyst, or cationic rhodium phosphines of the general form [Rhl_2(diene)] + , which have been extensively investigated by Shrock and Osborne, Brown and Halpern .In the former case, the necessary free coordination site(s) are generated through dissociation of phosphine at some point in the catalytic cycle, whereas for the latter case hydrogenation of the diene ligand results in an unsaturated (often solvated) reactive intermediate. The preponderance of phosphine ligands in these catalysts is due in part to their necessary lability as well as their stabilizing influence on the dihydride intermediate. The general mechanism is shown in Scheme 3.1. For these complexes, dihydrogen activation occurs via homolytic splitting; such an oxidative addition produces exclusively the cis dihydride 1 2 1*' 1 2 5. Often this step is reversible. Olefin coordination then occurs to form a dihydrido -rr-olefin complex. Alternatively, olefin coordination can precede oxidative addition of H^ , as is the case for strongly binding olefins or where the catalyst has chelating diphosphine ligands. Since the chelating phosphines must berautually cj_s, oxidative addition of H2 (also cis) would give an inter-mediate having hydrides trans to the phosphine centres. To overcome this unfavorable situation, reduction occurs instead by the "unsaturate route". -78-The oxidative addition of H 2 to the metal-olefin derivative i s thought to be rate-determining for this pathway. H H a) M + H , , M RH \ H H * \ 1/ H M * M sw ol b) M + ol . M / \ • / \ RH I R | H M - M I I ol Scheme 3.1 General mechanism for hydrogenation of o l e f i n i c substrates using t r a n s i t i o n metal dihydride cataly s t s : a) hydride route b) unsaturate route Regardless of the sequence of the f i r s t two steps, an intermediate dihydrido o l e f i n metal complex i s generated; the next step in the c a t a l y t i c cycle involves a migratory insertion of the o l e f i n into a cis metal hydrogen bond. For systems operating by the "hydride" route, i t i s believed that this step i s rate-determining. The resulting cis-hydrido o-alkyl then -79-r a p i d l y , and i r r e v e r s i b l y , reductively eliminates to give the saturated alkane product. Since t h i s step i s so f a s t , ci_s hydrido alk y l species are rare l y observed. These dihydride catalysts are highly stereospecific, resulting in overall c i s addition of dihydrogen. The stereochemistry of reduction by Rh(PPh 3) 3Cl was elegantly demonstrated by Wilkinson, who showed that c a t a l y t i c deuteration of maleic and fumaric acids in benzene/ethanol gave meso-2,3-dideuterosuccinic acid and d_,£-2,3-dideuterosuccinic acid , res-p e c t i v e l y 1 2 6 - O r i g i n a l l y , these results were interpreted as being due to a simultaneous transfer of both deuterium atoms. However, i t i s now clear that this transfer i s indeed stepwise but that the high rate of the product-forming reductive-elimination-step, as compared to the migratory insertion reaction, usually precludes o l e f i n isomerization or H2/D2 exchange. 12 7 Many of these catalysts are very selective »showing a decrease in r e a c t i v i t y with increasing substitution at the o l e f i n i c bond. This would appear to be a result of s t e r i c interference by bulky phosphine groups, thereby impeding the coordination of i n t e r n a l , versus terminal, olefins and/or by slowing the migratory insertion step. For the highly unsaturated complex [Rh(diphos)] +, s t e r i c i n h i b i t i o n would be expected to be i n s i g n i f i c a n t ; i n f a c t , t h i s complex e f f i c i e n t l y hydrogenates sub-sti t u t e d o l e f i n s and even aromatic r i n g s , such as benzene, toluene and xylenes. Generally, i t i s observed that most second-row metal complexes are more reactive towards hydrogenation than t h e i r third-row congeners. This i s undoubtedly a result of the increased s t a b i l i t y of higher oxidation - 8 0 -states of the t h i r d row metals due, in part,to the increased strength of their metal-hydride bonds. However, Crabtree has reported a number of catalysts of the type [Ir(C0D)l-2] + which are more effective in the reduc-12 8 tion of olefins and dienes than the i r rhodium analogues • Comparison of reaction pathways for these iridium catalysts to typical rhodium dihydride systems i s rather tenuous at t h i s point. Monohydride Catalysts Two possible mechanistic pathways for monohydride systems are out-lined in Scheme 3.2. Owing to the paucity of kinetic data, i t i s d i f f i c u l t to assign either pathway with any certainty. The major cloudy area concerns the product-forming reductive elimination; this presumably may occur via either an intramolecular mechanism or a binuclear reductive elimination with a second mole of M-H. Once again, overall c i s addition of dihydrogen to the o l e f i n i c bond is observed. An i n t e r e s t i n g , although often troublesome, feature of these cata-lysts,such as [RhH(C0)(PPh 3) 3] and[IrH (C0)2(PPh3)2]» i s their tendency to promote o l e f i n isomerization and isotopic exchange between D2 and o l e f i n i c 129 130 protons . This can occur via B-elimination of the coordinated al k y l intermediate (equation 44 ) i f the reductive elimination i s slow r e l a t i v e to al k y l formation. Possibly, this i s a consequence of the slow oxidative addition of H 2 to the metal-alkyl intermediate (intramolecular path). Olefin isomerization sometimes occurs via monohydride catalysts in the absence of hydrogen; such a process involves oxidative addition of the - 8 1 -1 3J. o l e f i n to form a i r - a l l y ! hydride derivative , which can then reductively eliminate in two possible ways, one of which leads to isomerized o l e f i n (equation 45). However, few examples of o l e f i n isomerization by this pathway are well, documented. H \ / a) M + ol / \ X R H \ H H M H 2 \ / M / \ ol \ / M / \ M H, ol M - M + RH MH \ / M / \ H ol \ / M / \ Scheme 3.2 General mechanism for hydrogenation of o l e f i n i c substrates using t r a n s i t i o n metal monohydride catalysts: (a) intramolecular pathway (b) intermolecular pathway - 8 2 -Monohydn'de catalysts show a very pronounced preference towards reduction of terminal versus internal o l e f i n s ; in fact. [HRh(C0)(PPh 3) 3] i s completely ineffectual for the hydrogenation of cyclohexene 1 3 2. Once again, this presumably i s a result of s t e r i c i n h i b i t i o n by the bulky phosphine ligands. CH, i J MH + CH2 = CHCH2CH3 • M-CH • MH + CH3CH = CHCH3 (44) CH2CH3 H CHCH, M + CH2 = CHCH2CH3 • M —^CH •M + CH3CH = CHCH3 (45) CH2 Homogeneous Catalytic Hydrogenation using Rhodium and Iridium Amido  Phosphines It i s not surprising, in view of their structural resemblance to Wilkinson's catalyst 43^that some of the rhodium and iridium amido diphos-phines, [M(L)N(SiMe 2CH 2PPh 2) 2] (M = Rh, L = COE, PPh 3; M = I r , L = COE, C 2 H ^ ) are catalyst precursors for the homogeneous hydrogenation of simple ole f i n s under very mild conditions. Like [RhCl(PPh 3) 3], these species are 16 electron complexes having l a b i l e ligand(s) which, upon dissociation, generate the required vacant coordination s i t e s . The comparison between these systems i s especially apt for [Rh(PPh 3)N(SiMe 2CH 2PPh 2) 2] 22, which bas i c a l l y d i f f e r s from Wilkinson's catalyst in the replacement of a chloride (Cl~) by an amide (~NR?) ligand (both weak trans influence ligands). -83-P P h 3 S N _ R h — P P h , Me 2 S i I C I — R h — P P h , I 3 P P h 3 43 2 2 In order to be an effective homogeneous hydrogenation c a t a l y s t , a t r a n s i t i o n metal complex must: 1) have good thermal s t a b i l i t y , 2) have s u f f i c i e n t s o l u b i l i t y in a wide range of solvents, 3) be able to be easily separated from i t s reaction products, and 4) be substrate se l e c t i v e . For the rhodium and iridium amido phosphine complexes, thermal s t a b i l i t y poses no problem since these derivatives are stable in benzene at temperatures up to 120°C. These complexes are exceptionally soluble in almost a l l organic solvents; in f a c t , most hydrogenation runs were carried out in neat o l e f i n (at 22°C, 1 atmosphere H2), employing a substrate to catalyst r a t i o of approximately 1000:1. Catalyst separation is also straightforward since the v o l a t i l e reduction products can be vacuum-transferred away from the i n v o l a t i l e metal complex prior to analysis. The iridium complexes demonstrate a pronounced preference for terminal versus internal o l e f i n s ; however, in the case of the rhodium amidophosphines s e l e c t i v i t y i s , s u r p r i s i n g l y , rather poor. As previously indicated, most rhodium phosphine dihydride catalysts show very l i t t l e , i f any, tendency toward o l e f i n isomen*zation. Assuming that for the rhodium amido phosphines hydrogenation proceeds, in analogy to Wilkinson's c a t a l y s t , through a dihydride intermediate (via either the - 8 4 -"hydride" or "unsaturate" route), only straightforward reduction of o l e f i n i c substrates would be expected. However, product analysis by H^NMR and, more accurately, by GLC indicates an unexpectedly high percen-tage of isomerized o l e f i n . When either [Rh(n -CgH 1 4)N(SiMe 2CH 2PPh 2) 2] or [Rh(PPh 3)N(SiMe 2CH 2PPh 2) 2] is employed as catalyst precursor, the turnover number 1 3 3for isomerization of 1-hexene to cis/trans-2-hexene (^O/h) i s higher than for hydrogenation to hexane (^50/h). Similar behavior obtains for the rhodium and iridium bidentate amido phosphines; with [Ir(C0D)N(CgH 5CH 2)(SiMe 2CH 2PPh 2)], the turnover number for hydroge-nation i s approximately 120/h as compared to MO/h for isomerization (the rhodnlum analogue i s about four times slower). These results are i l l u s t r a t e d by the hydrogenation p r o f i l e graphs in Fig.3.2 and 3.3. Since JTO isomerization i s observed in the absence of H 2, t h i s process i s c l e a r l y not occurring via oxidative addition of the o l e f i n to form an a l l y l hydride intermediate (which can then reductively eliminate to produce internal o l e f i n s ) . The anomalous r e a c t i v i t y of these rhodium catalysts i s further demonstrated by the observation that internal o l e f i n s , such as 2-hexene, are hydrogenated as rapidly as terminal ones; t h i s i s in contrast to the preference of terminal versus internal o l e f i n s exhibited by c l a s s i c a l Wilkinson-type hydrogenation systems. With 2-hexene as sub-st r a t e , isomerization also occurs; an i n i t i a l 50/50 mixture of cis/trans-2-hexenes is rapidly isomerized to give a 10:90 ra t i o of cis/trans isomers, which are then hydrogenated at normal rates. To complicate matters further, the [Ir(n -CgH 1 4)N(SiMe 2CH2PPh2) 2] derivative shows no_ evidence of isomerization but only straightforward - 8 5 -10(M TIME (h) Fig. 3.2 Hydrogenation p r o f i l e for reaction of 1-hexene with [Rh(PPh 3)N(SiMe 2CH 2PPh 2) 2] (1 atm. H 2, 22°C) -86-100, TIME (h) Fig. 3.3 Hydrogenation p r o f i l e for reaction of 1-hexene with [Ir(C0D)N(C 6H 5CH 2)(SiMe 2CH 2PPh 2) 2] (1 atm. H 2, 22°C) -87-reduction of o l e f i n s to alkanes under identical hydrogenation conditions (Fi g . 3.4);the turnover number, using 1-hexene as substrate, i s comparable to that of i t s rhodium congener (^70/h). In contrast to t h e i r rhodium ana-logues, hydrogenation of 2-hexene i s extremely slow (^ 2 turnovers per hour) when using either [Ir ( n 2-C gH 1 4(N(SiMe 2CH 2PPh 2) 2] or [Ir(C0D)N(C gH 5CH 2)-(SiMe 2CH 2PPh 2)] as catalyst precursor. In f a c t , after three hours under 1 atmosphere of H 2 in neat 2-hexene, the iridium cyclooctene complex loses i t s hydrogenation a c t i v i t y e n t i r e l y and a c a t a l y t i c a l l y inactive t r i h y d r i d e , [Ir(H)2NH(SiMe 2CH 2PPh 2) 2], precipitates out of solution (see next chapter). Although the mechanistic details of these systems have not been elucidated as yet, analogy to Halpern's conclusions regarding Wilkinson's catalyst would, at least s u p e r f i c i a l l y , seem reasonable. Since the "unsaturate" route would be expected to be comparatively i n e f f i c i e n t , i t would appear that, for the rhodium and iridium tridentate amido phosphines, hydrogenation should operate via the "hydride" route. For the case of the [Rh(PPh2)N(SiMe 2CH 2PPh 2) 2], two p o s s i b i l i t i e s are then presented: oxidative addition of dihydrogen can occur to generate an 18 electron cis-dihydride, which then loses PPhg to produce an unsaturated c a t a l y t i c a l l y active i n t e r -mediate (equation 46 ). Ph 2 Ph2 > - R h - L > - R h - H Si L Si L ' I " S ^ h , ™ 2 L=PPh 3 2 22 44 45 (46) - 8 8 -1004 o TIME (h) Fig. 3.4 Hydrogenation p r o f i l e for reaction of 1-hexene with rirCCOE)N(SiMe 2CH 2PPh 2) 2] (.1 atm. H 2, 22°C) - 8 9 -Although4£and have not been i d e n t i f i e d for the rhodium c a t a l y t i c systems, t h e i r iridium analogues have been isolated and f u l l y characte-rized (see next chapter). Coordination of the o l e f i n then occurs (equation 47 ). Migratory insertion would then produce a ci s o-alkyl P h 2 P h 2 > - f K , + > < = ^ > - " h - H M e 2 S l X H H^i (47) P h 2 P h 2 45 46 hydride which then rapidly reductively eliminates alkane (equation 48 ). Oxidative addition of dihydrogen to the highly unsaturated Rh(I) species48 . P h z , _ P h 2 M e ^ i |/nqr M e ^ I v / (48) 46 5==- N — Rh I ' *> > — R h — + -C-CX MeuSi I MeJSi I H H P h 2 P h 2 47 4 8 would re-form45and hence start the cycle over again. I t i s possible that 4J£, 46,47and 48are solvated, but since no s i g n i f i c a n t effect i s observed in either toluene, diethylether, or THF (versus neat o l e f i n ) , i t would appear that such a solvent ligand i s very weakly bound and eas i l y displaced. A l t e r n a t i v e l y , loss of PPh^ prior to oxidative addition of H 2 could also occur to produce the same results (equation 49 ). At some point, however, a coordination s i t e must be opened up. The fact that the amido phosphine complexes [M(L)N(SiMe 2CH 2PPh 2) 2] (M = Rh, I r ; L = CO, PMe3) do - 9 0 -not hydrogenate olefins i s probably a result of the reluctance of the carbonyl and PMe3 ligands toward dissociation. With the n -cyclooctene rhodium and iridium c a t a l y t i c precursors, i t would appear that the cyclooctene ligand i s displaced rather than under 1 atm H 2, show free cyclooctene. With the bidentate complexes [M(C0D)N(CgH 5CH 2)(SiMe 2CH 2PPh 2)] (M = Rh, I r ) , i t i s reasonable to assume that a c a t a l y t i c a l l y active i n t e r -mediate i s generated by uptake of two equivalents of dihydrogen, with concomitant formation of cyclooctene. On the basis of Hal pern's work13*4 with the isoelectronic [Rh(C0D)(diphos)] + system, the following mechanism (Scheme 3.3)seems plausible. Note that the bidentate amido phosphines would be expected to operate by the "unsaturate" route in order to circumvent Scheme 3.3 (49) hydrogenated, since C^Ds solutions of these complexes, sealed in NMR tubes - 9 1 -formation of an intermediate having a hydride trans to a phosphine centre (equation 50). ' B l . 1 1 3Hz - MejSi * V Ol etc (50) Although these postulated mechanisms (equations46—• 49, Scheme 3.3 ) seem quite acceptable at f i r s t glance, a number of questions remain unanswered. Most perplexing i s the high isomerization a c t i v i t y of the rhodium amido phosphines. Presumably, for these systems, g-elimination of the coordinated alkyl i n t e r m e d i a t e ^ to form internal olefins i s a competing process with reductive elimination of the saturated alkane. Possibly this i s a result of the ligand stereochemistry. As w i l l be discussed in the following chapter, a f a c i a l coordination of the t r i -dentate ligand has been observed. Therefore, i t i s conceivable that the rhodium complexes require a f a c — • mer isomerism during the c a t a l y t i c cycle so that reversible £-elimination can occur. Such a process may either be unnecessary for the iridium amidodiphosphines or may be fast enough to preclude isomerization. Another p o s s i b i l i t y i s that the dihydride intermediate45 undergoes reductive elimination of the metal amide bond to form a monohydride amino phosphine species 49 which then acts as the active catalyst (equation 51).). -92-Ph 2 Ph 2 MejSi | .,H Me2Si | ; N - R h ' H.N-*Rh-H (51) Ph 2 Ph 2 45 49 #»•»• M M As previously discussed, olefin rearrangement is often a competing process with olefin reduction when employing rhodium monohydride catalysts. The iridium congener to 4J5 [IrtH^NjSif^CHgPPhg^]. shows no such behavior (even under partial vacuum) but this would seem reasonable in view of the increased stability of the +3 oxidation state for iridium versus rhodium complexes. This could also explain the fact that the iridium cyclooctene complex does not isomerize olefins. Assuming the participation of such an intermediate 49, a possible catalytic cycle is outlined in Scheme 3.4. Scheme 3.4 p h 2 Ph2 p / ^ P M e ^ | M e ^ | ,M H N —*R h — H HN -•Rh , M e ^ l M^ST I Ph2 Ph2 H h 2 P h 2 Me Si | 2 > - R h ' ' . M*2K I W Ph2 V 2 H Me Si H P h 2 - 9 3 -This cycle would seem to be more f a c i l e than for those involving conven-tional monohydride catalysts since neither a second oxidative addition of H 2 nor a dinuclear reductive elimination (with a second mole of M-H) i s necessary. Rather, the product-forming step could be made possible by a prior re-oxidative addition of the N-H group. Although the process depicted in equation 51, and i t s importance to the c a t a l y t i c cycle, might, at f i r s t glance, appear to be somewhat speculative, comparisoncan be made to Shrock and Osborn's wel1-documented [Rh(diene)(PMe 2Ph) 2] + c a t a l y s t 1 3 5 w h i c h , in addition to being effective as an hydrogenation catalyst for simple o l e f i n s , also catalyzes o l e f i n isomeri-zation. This a c t i v i t y has been ascribed to an equilibrium in solution between the cationic dihydride species and a neutral monohydride (equation 52 ). Rh(H) 2CPMe 2Ph) 2 + ^ RhH(PMe2Ph)2 + H + ( 5 2 ) I t has been determined that the monohydride i s an extremely active isomeri-zation and a good hydrogenation c a t a l y s t , whereas the dihydride i s a poor hydrogenation cat a l y s t , and possibly inactive toward isomerization. Mono-hydride formation, as shown in equations 51 and 52, i s not r e a l l y too remarkable but rather,further examples of the well-known heterolytic s p l i t t i n g of H 2. The s t r i k i n g feature of these systems i s that an equilibrium can exist between the monohydride and dihydride intermediate, and thus affect the r e a c t i v i t y during the c a t a l y t i c cycle. -94-Chapter IV Oxidative Addition of Dihydrogen to Square-Planar Iridium(I) Complexes Owing to t h e i r significance in a variety of homogeneous c a t a l y t i c transformations (such as hydrosilation, hydrogenation, hydroformylation, Monsanto's acetic acid synthesis, oxygenation), oxidative addition reactions (equation 53) have been, and continue to be, the focus of intense 136 investigation The most extensive study has involved the interaction of 8 square-planar d iridium(I) complexes, particulary [Ir(CO)CI(PPI^^] (Vaska's complex) and i t s c l o s e l y related derivatives with a number of 224137 reactant molecules (XY) ' These reactions are often rev e r s i b l e ; the res u l t i n g MLn + XY (XY)MLn (.53) I r ( I I I ) species vary in s t a b i l i t y , depending largely upon the nature of the addendum (XY). The tendency of a particular t r a n s i t i o n metal towards oxidative addition of a covalent molecule i s influenced by both the nature of the 13 7 A 2 k metal complex as well as the reactant: . A combination of the electronic and s t e r i c properties of the metal complex plays a decisive role in deter-mining the course of these reactions. Generally, t h i r d row metals are more reactive than the i r second row congeners. I t has been observed that electron donating ligands promote oxidative additions, whereas 7T-acid ligand (such as CO or o l e f i n ) retard these processes. Thus, increased b a s i c i t y at the metal centre tends to favour these reactions. The s t e r i c bulk of the ligand system i s also important; very bulky ligands (such as P(t-Bu]g. can sometimes e f f e c t i v e l y block oxidative additions. Usually the metal complex must be coordinatively unsaturated or, i f saturated, - 9 5 -capable of losing a ligand. It has also been demonstrated that the local symmetry at the metal centre is critical since four-coordinate d cobalt(I) and iridium(I) complexes having anon-planar structure do not add dioxygen whereas their square planar analogues are very reactive. A systematic survey of the oxidative addition behavior of Vaska's complex with a variety of reactants (XY=. 0 .^ CH^I, H 2 , I 2 , B r 2 , CI2» HC1) has indicated that the thermodynamic stability of the adduct is directly proportional to the addendum's acidity (that i s , the degree of electron transfer from M to XY). Thus, the Ir(III) species formed via reaction of [Ir(CO)CI(PPh3)2] with C l 2 , Br 2 , or I2 are more stable than those formed from 0 2 or H 2 ; in fact, the former oxidative additions are irreversible whereas the latter are easily reversible. The structure of the adduct i s , not surprisingly, greatly depend-ent upon the nature of the addendum'. In general terms, two categories of reactant molecules can be recognized: those which dissociate (eg. H2) upon addition to a metal complex, or those which remain intact (eg. 0 2 ) . For the former case, reaction with Vaska's complex generates an octahedral complex 50 in which both atoms (or groups) X and Y are individually bon-ded to the metal centre. For the latter case, the adduct has a distorted octahedral geometry (51J, with a Cl-Ir-CO bond angle of approximately 100°. - 9 6 -P R 3 C O ^ | ^ H 50 51 As outlined in Chapter III, activation of dihydrogen by a transition metal complex can occur either via homolytic splitting by one or two metal centres, resulting in a two electron oxidation of the metal centre or two one electron oxidations. Alternatively, heteroly-tic splitting can take place under appropriate conditions; although the overall reaction cannot be regarded as an oxidative addition, such g a process may occur at some stage. For coordinatively unsaturated d metal complexes, homolytic cleavage has been established as the dominant mechanism. Addition of dihydrogen to square-planar iridium derivatives has been shown, both in solution and in the solid state, to be stereo-specifically c is . The cis orientation of the two hydrides has been primarily established by spectral methods. In .fact, stereochemical assignment by physical methods has been more extensive for iridium hydrides than for any other group of transition metal hydrides, owing to their proliferation,their reasonable stabil ity, and the possibility of several isomeric forms 1 2 5. In particular, NMR has provided conclusive information as to the structures of complexes of the form [Ir(H) 2(C0)Cl(PR 3) 2]. For the case where PR3=PPhMe2> Shaw has observed -9 7-two hydride resonances in CfiDg at -18.36 ppm ( t d , J,, p = 14.1 Hz, chemical s h i f t i s characteristic of hydrides of the later t r a n s i t i o n metals (0 to -50 ppm, with most in the -20 -* -30 range) while the coupling constants are typical of a hydride coupling to a c i s phosphine (10 40 Hz). The trans orientation of the phosphines i s demonstrated by a v i r t u a l t r i p l e t centred at 1.89 ppm (J app = 3.8 Hz). Infrared data ("thin f i l m " - neat o i l ) for [Ir(H) 2(C0)Cl(PPhMe 2) 2] also support the cis assignment of the hydrides since there are two hydride absorptions (2169, 2067 cm"^) due to the two different HIrL groupings. I t should also be noted that the sterochemistry of dihydrogen addition to [Ir(CO)CI(PR 3) 2] i s insensitive to the nature of the solvent. With one possible exception139»a11 oxidative additions of dihydrogen to d metal complexes proceed, or are assumed to proceed ( i n the absence of detectable hydrides), i s such a c i s fashion. Harrod's report of a supposedly trans oxidative addition o f H 2 to [Ir(D)C0(PPh 3) 2] (minor isomer) has met with skepticism since isomerization of an i n i t i a l l y formed c i s adduct would also be consistent with the results (equation 5 4 ) . D D * l r - P CO major (54) CO H P=PPh3 CO | S P -98 -The general observation of ci s dihydrides formed i n these 1 4 0 reactions has led to interpretation in terms of a concerted mechanism involving a r e l a t i v e l y non-polar, three-centre t r a n s i t i o n state 53 (equation 55). PR 3 .CI C O ^ ^ PR, H, (PR3)2Cl(CO)lr;;^ (55) 52 53 Another interesting feature of oxidative additions to Vaska-type iridium(I) complexes i s that the adduct [Ir(XY)(C0)C1(PR 3) 2] almost invariably has the two phosphines in mutually trans positions. A 1 2 4 generalized mechanism which has been postulated to explain these results i s depicted in Fig.4.1. Approach of the reactant molecule along the Cl-Ir-CO bond axis results in a decrease in the adduct's Cl-Ir-CO bond angle (from i t s original 180°). Thus, the two phosphine ligands retain t h e i r c o l l i n e a r relationship to the metal. H PR3 PR3 \ .CI Cl^ I ,H C O ^ ^ PR3 c o I H ^ PR, Fig. 4.1 General mechanism for oxidative additions involving Vaska-type complexes, [Ir(.C0)Cl(PR 3) 2] -99-However, recently i t has been reported that an alternative stereo-chemical course for the oxidative addition of dihydrogen can be followed . Although a complete study has not been carried out as yet, i t would appear that the nature of the anionic ligand ( X ) i s highly i n f l u e n t i a l in deter-mining the stereochemistry of the adduct. Bresadola 1 4 1 has observed that when X i s a bulky carborane ( B I Q C ^ H I Q R - ) , several isomers can be detected depending upon the solvent. I f carried out in polar solvents (eg. CH^CN), the unusual dihydride 5j[ i s formed whereas in non-polar solvents (eg. CH,C10 or CoH.Cl 0) a mixture of isomers 55 and 56 i s formed. Once again, assignment of these structures has been primarily based on H^NMR and IR spectral data. On the basis of the mechanism of Fig.4.1.structure 55, r\J\j having c i s dihydrides and trans phosphines would be the expected product. P P h 3 P P h 3 CO C O I carb | P P h 3 I , H PPhg | N H CO I ^ H P P h 3 | ^ H carb P P h 3 carb 54 55 56 M M > * * * * Isomer 5Jj, although unexpected, can be rationalized to be a result of s t e r i c crowding of the bulky carborane ligand, causing a deformation of the iridium complex from an idealized square-planar geometry. The phosphines therefore migrate to positions trans to the incoming dihydrogen molecule, with the carborane and carbonyl ligands remaining c o l l i n e a r with the metal (F i g . 4.2). The formation of the anomalous isomer 54 has yet to be s a t i s f a c t o r -—1 00— i l y explained, but i s presumed to be due to either a thermodynamic solvent effect or the presence of solvated intermediates. CO PR3 I .-H PR3 I ^ carb Fig. 4.2 Proposed mechanism for the oxidative addition of dihydrogen to I I r(C0)(a-carb)(PPh 3) 2] Since this report, another case of a dihydride adduct having c i s phosphines has been documented1 2. Reaction of H 2 with [Ir(CO)(CH 2CN)-(PPh,) 9] yields i n i t i a l l y exclusively isomer 57 which gradually isomerizes in hydrogen-saturated CH 2C1 2 to form a mixture of 57 and 5^. Thus, the thermodynamically stable isomer 58 i s the expected product on the basis of CO PPh3 I ^ PPh 3 I^H CH2CN 57 the"normal" (F i g . 4.1)oxidative-addition of H 2 to Vaska-type complexes. However, the k i n e t i c a l l y stable isomer57 presumably forms via the process outlined in Fig. 4.2. I t would appear that t h i s i s due to an especially favorable trans conformation of the C0-Ir-CH2CN u n i t , owing to the high H PR j carb ZQT ^ PR, PPh3 CHXN I pph3 58 -101-o-dorvor ability of the CH2CN in combination with the ir-acidic character of the carbonyl ligand. The mechanism of interconversion of isomers 57and 58has not been elaborated as yet. -102-Stereoselective Formation of I r i di um(111) Amides and Ligand-Assisted  Heterolytic S p l i t t i n g of Dihydrogen As previously described (Chapter 3), some of the rhodium and iridium anido phosphine complexes [MLN(SiMe 2CH 2PPh 2) 2] (M = Rh, L = COE, PPh^; M=Ir, K O E . C ^ ) act as e f f i c i e n t catalyst precursors for the homogeneous hydrogenation of simple o l e f i n s . In an ef f o r t to delineate the mechanism of these processes and to i s o l a t e possible c a t a l y t i c intermediates, a number of oxidative reactions was carried out and studied. Although the rhodium amido phosphines [RhLN(SiMe 2CH 2PPh 2) 2] (L = CO, PMe3, PPhg, COE, C ^ ) showed no reaction under four atmospheres of dihydrogen, the analogous iridium derivatives (with the exception of the carbonyl complex) react readily and stereoselectively under one atmosphere of hydrogen to y i e l d a variety of stable iridium(III) hydrides. It i s noteworthy that these complexes are the f i r s t examples of iridium (III) amides reported to d a t e 1 4 3 . The novel five-coordinate iridium dihydride [Ir(H) 2N(SiMe 2CH 2PPh 2) 2], 5^, i s prepared by s t i r r i n g a toluene solution of [Ir(CgH^)N(SiMe 2CH 2~ PPh 2) 2] under one atmosphere of dihydrogen for one hour (equation 56 ) . Removal of excess dihydrogen and solvent followed by r e c r y s t a l l i z a t i o n from toluene/hexane gives a n a l y t i c a l l y pure orange c r y s t a l s . The infrared of 5J") (KBr) has one moderate intensity V j r _ ^ band at 2200 cm~^  ; the 31 1 1 Pi H}NMR consists of one sharp singlet at 23.9 ppm. The HNMR spectrum (Fig. 4.3), which i s invariant down to -80°C, has a single sharp Si(C^)3 -10 3-Ph 2 Ph2 y^P y^P Me2Si | Me2Si | ,H , N - l r - A ± J h ^ >_lr' (56) Ph 2 K ^ P h 2 ,P P\59 resonance, a v i r t u a l t r i p l e t (J gpp = 5.2 Hz) for the CH2P protons and, of most i n t e r e s t , a sharp t r i p l e t at -24.9 ppm (integral value = 2 H). The high upfield chemical s h i f t of th i s hydride resonance i s typical of iridium(III) hydrides and the phosphorus -hydride coupling constant (J D = 13.2 Hz) l i e s within the range normally observed for c i s H,P H, r couplings 1 2 5.Although no other five-coordinate iridium-dihydrides have Ph 2 Me2Si | , ,H } l - l r ' Me^Si P S H ^ ^ P h , • 24.9 4 ppm Fig. 4.3 'HNMR(80MHZ) spectrum of [Ir(H) 2N(SiMe 2CH 2PPh 2) 2] in CGD6 -104-been noted in the l i t e r a t u r e , the spectral data and chemical analysis support this structural formulation for 5j^. Since no ^ HNMR spectral changes are observed upon cooling to -80°C, i t would appear that t h i s trigonal bipyramidal structure i s stereochemically r i g i d . Further support for this proposal i s provided by the completely stereoselective ligand addition reactions of 59 (vide i n f r a ) . Surprisingly, i f the reaction i l l u s t r a t e d in equation(56) i s monitored under excess H 2 ( i n a sealed NMR tube), formation of the dihydride i s not observed. Rather, the product has been assigned, on the basis of spectral data, to have the structure 60, an iridium amine trihydride (equation 57 ). Consistent with t h i s formulation are the three hi g h - f i e l d multiplets at -8.97, -9.69, and -24.6 ppm ( F i g . 4.4) in the H^NMR corresponding to the three different Ir-H moieties. The down-f i e l d region i s also informative as the two Si-CH 3 singlets and the AB quartet of v i r t u a l t r i p l e t s for the CH2P protons indicate that the two faces of the iridium complex are inequivalent. Although normally obscured by other s i g n a l s , the N-H peak can be observed when the starting iridium-(57) 60 -105-cyclooctene complex i s N-labelled; a doublet ( J l t - = 70 Hz) at l0N-H 0.10 ppm has been assigned to the coordinated amine hydrogen. ~ i 1 1 1 ~ 5 4 3 2 1 ppm Fig. 4 .'4 ]HNMR(270 MHz) spectrum of mer-[Ir(H) 3NH(SiMe 2CH 2PPh 2) 2] in CgDg In addition , the IR(CgDg solution under H 2) has two moderate inte n s i t y bands at 2175 cm"1 and 1705 cm"1, attributed to V j r _ H ; the lower energy absorption i s typ i c a l of a trans H-M-H grouping 3 k h. The weak N-H stretch occurs at 3210 cm"1. When the reaction i s carried out under an atmosphere of deuterium, the IR bands s h i f t appropriately. —106— The ^ 'K 'H}NMR of 60 i s a singlet at 1-1.44 ppm; no signal due to the dihydride 5j9 (at 23.9 ppm) i s observed under excess H2. Removal of dihydrogen from solutions of ,6^0 quantitatively generates 59. The reversible nature of this reaction i s i l l u s t r a t e d by the fact that when CgDg solutions of 59 are sealed under ^ 1 atmosphere of H 2, the amine trihydride 60 i s formed instantaneously. When carried out on a larger scale in Schlenck-type glassware, formation of 60 i s indicated by the bright yellow coloration of the solution; removal of excess H 2  in vacuo immediately produces a deep orange solution, which turns bright yellow again upon exposure to dihydrogen. It would appear that formation of t h i s unusual species (6J3) i s f a c i l i t a t e d by the use of a starting material having a dissociable ligand. When [Ir(COE)N(SiMe 2CH 2PPh 2) 2] i s sealed in an NMR tube under hydrogen, free cyclooctene i s observed, which i s slowly hydrogenated to cyclooctane. A similar reaction obtains for the ethylene derivative, [Ir(C 2H 4)N(SiMe 2-CH 2PPh 2) 2]; under one atmosphere of dihydrogen, the mer amine trihydride 6J^ i s rapidly formed and free ethylene is observed i n the ^ HNMR. In the absence of dissociation ( i e . for [IrLN(SiMe 2(CH 2PPh 2) 2] 2, L = PPh 3, PMe 3), only straightforward oxidative addition occurs (vide i n f r a ) . In an attempt to iso l a t e 6j), a concentrated pentane solution of [Ir(C0E)N(SiMe 2CH 2PPh 2) 2] was s t i r r e d under one atmosphere of H 2 (equa-tion 58);after approximately two hours, a fine yellow precipitate formed (in ^70% yiel d ) which was f i l t e r e d and washed with cold pentane. The spectral and analytical data are consistent with the f a c i a l isomer of 6^. Ph 2 y^p H N — l r — H -107-3 p p m b). •8.5 I C) Fig. 4.5 a) ^ HNMR (400 MHz) of fac-Elr(H)3NH(S1Me2CH2PPh2)23 in CgDg. b) Hydride region (400 MHz ]HNMR) of fac- I I r(H) 3NH(SiMe 2CH 2-PPh 2) 2] c) Spectral simulation of hydride AA'MXX' pattern: JA,A' = 2- 2' 2jA,M = JA',M = 5 - 5 i JA,X = JA' X = ~19'°' "JM,X = 2 J M . X - = 1 4 - O 2 J A , X - = 2 J A ' , X = 1 3 0 - 0 ' J x , r = 1 - ° -108-Ph, P h 2 Me Si I Me,Si | ,H 2 \ _ r _ A H ? > 2 H N - J r - H (58) N - l r pentane MeJSi^ S\ Ph 2 61 Most s i g n i f i c a n t l y , the 'HNMR has a complex symmetrical second-order multiplet centred at -8.5 ppm (Fig.4.5a)which i s the c h a r a c t e r i s t i c 125 pattern for two magnetically inequivalent hydrides trans to two phosphine centres. The resulting AA'MXX' pattern has been simulated (Fig.4.5b) in order to obtain the appropriate coupling constants. The hydride trans to the amine centre appears as a t r i p l e t of t r i p l e t s at -24.3 ppm. In addition, the IR(KBr) has two Ir-H stretching bands at 2180 cm"1 and 2115 cm"1 and a weak N-H stretch at 3200 cm"1. In contrast to i t s meridional isomer, 61 is stable in the s o l i d rv\, state even under high vacuum for extended periods of time. However, in solution under N 2 (in a sealed NMR tube), the fac amine trihydride slowly decomposes to give a mixture of the dihydride 59^and the mer trihydride I t would seem conceivable that this process occurs via loss of H 2 from 61 to give 59^which then adds H2 to give the mer-tri-hydride (Scheme 4.1). The formation of the fac and mer amine trihydrides can be viewed as an example of an overall h e t e r o l y t i c - s p l i t t i n g of dihydrogen 1 1* 5. In this case, the ligand's amide centre f a c i l i t a t e s the reaction, acting in a similar manner to the external base normally involved in_reactions -1 09-Scheme 4.1 Phj Me2Si | > - l r -Me2Si I Ph2 1» Ha/PhCHs 2> vac Ph, Me2S^ x N - l r ' Me sf [ N H 2 v- p Ph2 pentane H, Ph2 Me^i | H c . H N — l r — H 2 ^ P Ph. I H PhCH PhCH, H, Me.Si 2 \ N 2/PhCH 3 — 2 \ , Ph. \/ lr — H H MeJSi y i p Ph, of this type. The novel feature of this reaction as compared to most heterolytic s p l i t t i n g s of H£, i s that the protonated anionic group remains coordinated in the iridium product. It i s not clear at this point whether formation of 6J3 and occurs in a concerted process, or in a stepwise manner involving oxidative addition to form an intermediate Ir(V) species which then reductively eliminates (Scheme 4.2). Isolation of the fac isomer from pentane i s undoubtedly a result of i t s expected lower s o l u b i l i t y in pentane than the mer isomer (dipole moment measure-- M o -ments for a series of iridium t r i hydrides indicate a much higher u^ , value for the fac versus the mer isomer J 1 4 6 ; the fac amine trihydride 61^ i s therefore 'milked 1 out of solution. E q u i l i b r i a involving an Ir(V) intermediate could also account for the observed isomerization of61.^ in toluene; however, no such species has been i d e n t i f i e d as yet. Scheme 4.2 Me 2 s J I . u , M e2s ,v p P h 2 Me2Si , / /yi P h 2 Ph, ^ e n t a n e ^XP*»„ H N - U — H , H ^ N - - l r — H ^ p h 2 ^ P h , In an attempt to gain some insight into the formation of these unusual iridium t r i h y d r i d e s , l a b e l l i n g experiments were carried out. -111-A CgDg solution of [Ir(D) 2N(SiMe 2CH 2PPh 2) 2] was sealed under one atmos-phere of dihydrogen. Only the mer trihydride 60 was observed; no deuterium-labelled product was detected. Furthermore, a CgDg solution of [Ir(H) 2N(SiMe 2CH 2PPh 2) 2] sealed under one atmosphere of D2 yielded only the f u l l y deuterated product [Ir(D) 3ND(SiMe 2CH 2PPh 2) 2]; no hydride resonances were observed. It i s d i f f i c u l t at th i s point to explain these results but i t i s conceivable that an Ir(V) species i s once again im p l i -cated. A rapid equilibrium between the starting dihydride (or dideuteride) and an intermediate iridium(V) species could result in scrambling (equation 5 9 ) . In l i g h t of the fact that the iridium(V) hydrides [ I r H 5 L 2 ] (L = PEt 3, PEt 2Ph, P M e ^ 7 and [IrH 4{ Bu^PCH2CHCHRCH2PBu|}]I'+8 have magnetically equivalent hydrides (even down to -100°C), an iridium (V) intermediate of the type shown in equation59 would be expected to be highly fluxional and scambling would therefore be expected to be fa s t . A l t e r n a t i v e l y , i f reaction i s occurring by direct heterolytic cleavage at the iridium amide bond, 5J3 and 60 must be rapidly interconverting under dihydrogen (equation 60). Ph2 • Ph 2 • Ph2 s^P ^ P H y^p Me2Si | ,D Me2Si , . • M e £ i | H > - l r ' ^ — H ^ N - l r ' - H (59) Me2Si I N D Me2Si ^ M e ^ l Ph 2 Ph 2 P n 2 -112-Ph 2 ^ Ph 2 P ^ 2 > - . r ^ ^ J f — D ^ j ' - D (60) Me2Si p > H M e 2 S ^ P Ph 2 Ph2 Another unusual aspect of these iridium amine trihydrides i s thei r rapid r e a c t i v i t y with CH2C12- It "is well known that CCl^ and even CHC13 149 often react with t r a n s i t i o n metal hydrides to form chloride derivatives ; however, most are inert to CH 2C1 2. However, in th i s solvent, both the mer and fac-trihydrides react (under H2) to form exclusively another hydride; i t i s believed that t h i s species i s c i s - [ I r C l (H) 2NH(SiMe 2CH 2-PPh 2) 2] although i t has not been i s o l a t e d . For the mer tr i h y d r i d e , this transformation i s complete in ^ 0.5 hour whereas the analogous reaction with fac-61 takes Mh. Stereoselective Ligand Additions to [Ir(H) 2N(SiMe 2CH 2PPh 2 ) p ] . In l i g h t of the fact-that the iridium dihydride i s a coordinati-vely unsaturated, formally 16-electron iridium(III) derivative, i t i s not surprising that addition reactions with neutral ligands are f a c i l e . When PMe^ i s added to a toluene solution of 5^, the or i g i n a l orange-colored -113-solution fades to a pale yellow within minutes. Upon work-up and r e c r y s t a l l i z a t i o n from neat hexane at -30°C, off-white needles of 62^ are obtained (equation 61). The ^HNMR (Fig . 4.6)consists of two sharp Si-CHg peaks of equal i n t e n s i t y , two sets of doublets of v i r t u a l t r i p l e t s for the CH2P, and a complex pattern characteristic of a meridionally coordinated tridentate amidophosphine ligand for the phenyl protons 4 7 Ph 2 _ Ph 2 Me,Si I \\ o u _ Me£ i , ^PMe 3 P 2 *^N — I r > " > - l V ^ H " (61) • " - 2 - N ^ P ^ Ph 2 Ph 2 62 ( i n CgDg). Most informative i s the hydride region which i s comprised of a doublet of t r i p l e t s of doublets (dtd) at -10.21 ppm for the hydride trans to the PMe^ ligand, and a doublet of quartets at -19.96 ppm for the hydride trans to the amide nitrogen. Analysis of these data, in con-junction with IR and P{ H"}NMR spectral information as well as chemical analysis,confirms the structure of 62 to be as depicted,with two mutually ci s hydrides and the hybrid ligand coordinated in the usual iwer stereo-chemistry. A similar reaction obtains for [Ir(H) 2N(SiMe 2CH 2PPh 2) 2] with CO; when a toluene solution of 5£ is s t i r r e d under one atmosphere of carbon monoxide, the solution becomes v i r t u a l l y colorless within seconds (equation 62). The downfield region of the H^NMR of the product i s reminiscent of that of i t s PMe^ analogue £2 while the hydride region consists of two doublets of t r i p l e t s at -7.86 and -16.09 ppm. It i s evident from the spectral information that ,63 i s isostructural with oZ, -114-P h 2 MBjSi H P P h 2 ppm -Try**" -10.21 - I .19.96 Fig. 4.6 ^HNMR(400MHz) spectrum of mer cis-IIr(H) 2CPMe 3)N(S1Me 2CH 2PPh 2) 2] in C 6D 6 Ph2 Me2Si | ,,H N - l r ' Me2Si l > H Ph 2 CO Ph2 > P Me2S^ | ,.CO N — l r ' — H M e 2 S f ^ l Ph 2 63 (62) -11 5-having cis-dihydrides and a meridonially bound amidophosphine ligand. It should be noted that no other isomer of §2 or 6j£ i s observed under these reaction conditions. In order that the product of mer c i s stereochemistry be formed from ,59, the ligand L must approach 59. c i s to the iridium amide bond; approach of L trans to the iridium amide bond to y i e l d the mer trans isomer i s , for some reason, disfavored. I t i s arguable that such an isomer i s formed i n i t i a l l y but rearranges to y i e l d the mer c i s product. However, t h i s has been shown not to occur by the following observations. The m^ tr^n£-IIr(H) 2(.C0)N(SiMe 2CH 2PPh 2) 2] complex 64, although undetected in the previous experiment, can be prepared, a l b e i t by a very different route. Upon vigorously s t i r r i n g a suspension of [Ir(C0E)N(Si-Me 2CH 2PPh 2) 2] and paraformaldehyde in toluene for 24 hours, followed by extraction with hexane, 64^  i s formed in v i r t u a l l y quantitative y i e l d (NMR). Recrystal!ization from toluene/hexane gives a n a l y t i c a l l y pure pale yellow c r y s t a l s . Although the ^ HNMR cl e a r l y indicates a trans dihydride derivative (owing to the sharp t r i p l e t at -6.00 ppm), unequi-vocal evidence for this structural assignment i s provided by the IR spectrum which has one strong V j r _ ^ absorption at 1725 cm ^ . Clearly t h i s product i s formed via i n i t i a l oxidative addition of HCHO to form an hydrido formyl species which then undergoes d e i n s e r t i o n 1 5 0 of the formyl carbonyl to give 6^4 (equation 63 ). Solutions of 64 do not isomerize to the mer c i s isomer 63 , even after extended periods of time 'VXJ under one atmosphere CO. >—P % y^p - y^p M p c i i . x Me,SJ | .H Me 2 Si | ,H / I ( S - C O E M e S< l^c*° U e S i u ^ l 2 V p V V . H V - p ^ P h 2 P h 2 P h 2 64 It has been shown that for certain iridium(I) complexes, reaction with paraformaldehyde leads to formation of iridium(III) hydrido formyl species 1 5- 1. As anticipated, such derivatives can be isolated from iridium amidophosphines in which ligand dissociation does not occur; such i s the case for the reaction of (HCH0)n with [Ir(PMe 3)N(SiMe 2CH 2PPh 2) 2]. How-ever, t h i s reaction yields as inseparable mixture of two isomers, the ra t i o of which appears to depend upon reaction time. Although the H^NMR (400 MHz) i s extremely complicated, i t appears that the structures of the products, £5 and ,66 • are as shown below. P h 2 y^J1^2 P 66 ^ P P M e 3 2 \ > p ^ p h 2 P n 2 65 Oxidative Addition of Dihydrogen to [IrLN(SiMe 2CH 2PPh 2) 2] (L = CO, PMe3, PPh 3). In l i g h t of the exclusive mer stereochemistry of the hybrid ligand in a l l of i t s N i ( I I ) , Pd(II), P t ( I I ) , Rh(I), and I r ( I ) complexes, the formulation of the fac stereochemistry for 6^ and 65^ may seem question-able. However, unequivocal evidence has been provided that coordination of the tridentate ligand in a f a c i a l manner i s indeed possible. Within -117-minutes of s t i r r i n g a toluene solution of [Ir(PMe^NCSif^CI^PPf^^] under one atmosphere of H 2, the color rapidly fades u n t i l the solution is almost colorless (equation 64). Large, off-white blocks of 6^ are P h 2 P h 2 S~^P y^p Me 2 Si | Me 2 Si | , H > - r P M 6 3 w _ P M e 3 67 obtained from hexane. Although the downfield of the 1HNMR spectrum of £7 is s i m i l a r to isomeric J^2, the hydride region'is very d i f f e r e n t (Fig.4.7)being comprised of a complex, symmetrical multiplet centred at -11.04 ppm. This hydride pattern remains invariant regardless of the spectrometer's operating frequency indicating that i t i s a si n g l e , non f i r s t order hydride resonance and that t h i s complex has two chemically equivalent, but magnetically inequivalent, hydrides. Combined with spectral simulation of th i s AA'XX'Y pattern, analysis of the downfield 1 3 1 1 region of the HNMR, IR, P{ H}NMR, and chemical analysis, i t was con-cluded that 67 contained a f a c i a l l y coordinated amidophosphine ligand, with the two hydrides trans to the ligand's phosphine donors. Confirmation of th i s fac c i s stereochemistry was provided by X-ray crystal structure analysis ( F i g . 4.8). The P-|-Ir-P2 angle of 109.58c c l e a r l y indicates a s l i g h t l y distorted f a c i a l geometry. I t i s also interesting to note that the Si2N-Ir unit i s non-planar (the metal i s 3.9° out of the NSi 2 coordination plane), a surprising r e s u l t in view of the exclusive planarity of the Si 2NM fragment in a l l other t r a n s i t i o n metal-bis ( s i l y l ) amido complexes reported to date. The SiNSi angle i s -118-11.04 Fig. 4.7 a) ]HNMR (10.0 MHz) of fac-£lr(H).,(,PMe3) N (_S iMe, CH, PP h,)_2J in CgDg b) Hydride region (400 MHz ]HNMR) of fac-IIr(H) 2(PMe 3)N(SiMe 2-PPh 2) 2] c) Spectral simulation of hydride AA'XX'Y pattern: 2 jA,)( = °A',)(' = " Z 1-°» JA,Y = JA',Y = 2 1 JA,X' =  2 jA',X = 1 4 7 ' ° ' 2 jA,A' = 4-°> 2 jX,Y = 9'°> 2 jX,X' = 4-° -119-Fig. 4.8 X-ray crystal structure of fa£-[Ir(H)2(.PMe3)N(SiMe2CH2PPh2)2] o also much larger (131.4°) than expected for sp hybridized nitrogen. Possibly, these facts are a consequence of steric constraints imposed by the facial orientation of the tridentate ligand. The product of the oxidative addition of dihydrogen to [Ir(PPh3)-N(SiMe2CH2PPh2).2J is also a fa£ dihydride. Once again, reaction occurs rapidly at one atmosphere of H2 at room temperature to yield exclusively fac c1s-[Ir(H)2(PPh3)N(S1Me2CH2PPh2)2], 5^8 (equation 65). However, at -1 20-Ph 2 Ph 2 y^p y^P Me Si | Me2Si^ | ,H \ _ , r _ p p h 3 ^ _ H 2 > N - i r ' - p p h (65) Me/. p M ^ ^ l N s / P h 2 80°C, 68 isomerizes (>90% in 1 hour) in solution to y i e l d mer c i s -' w [Ir(H 2)(.PPh 3)N(SiMe 2CH 2PPh 2) 2J (equation 65). In contrast, 67 shows no such isomerization, when heated at 120°C for 24 hours. Rearrangement of ^8 to 69 is therefore probably occurring by i n i t i a l loss of PPh^ at high Ph 2 y^p M Q C . ^ N - Ir — P P h . • ' > - l ' r : ' (66) ^ i S p ' A _ P P h 3 • ^ P h 2 H Ph2 y^p Me2Si | ,PPh 3 , N - l r - H P h 2 - 1 2 1 -temperature to form 5| which then re-adds PPh 3 ( r e c a l l that L approaches 59 c i s to the iridiurtiramide bond) to give the meridional cis dihydride i \ r \ —— isomer 69 (equation 66). Presumably t h i s route i s not open to PMe3 analogue,^dee to i t s reluctance toward PMe3 d i s s o c i a t i o n . The fac c i s complex i s also unique from the other iridium dihydrido amido phosphines in that the oxidative addition of dihydrogen i s reversible. A l l of the complexes 5^6^,6^,6^,6^ are exceptionally stable, c r y s t a l l i n e materials, both in solution and in the s o l i d state. However,,68 gradually loses dihydrogen under vacuum, or after several hours under N 2 in solu t i o n , to regenerate [Ir(PPh 3)N(SiMe 2CH 2PPh 2) 2]• It can be seen from the stereochemistry of the kinetic products of the oxidative addition of H 2 to the iridium(I) amido phosphines [IrLN(SiMe 2CH 2PPh 2) 2] (L = PMe3, PPh 3) that reaction does not_ occur in a manner analogous to Vaska's complex. In other words, the dihydrogen mole-cule approaches along the P-Ir-P bond a x i s , rather than the L-Ir-X axis (for Vaska's complex, L = CO and X = CI) (Fig.4.9 ). I t i s an interesting coincidence that the complexes mer cis-[IrL(H) 2NSiMe 2CH 2PPho) 2], prepared via the addition of L (= CO, PMe3, PPh 3) to , have the stereochemistry expected on the basis of the "normal" Vaska-type oxidative addition of Hp (mechanism as in Fig. 4.1). The disparity in r e a c t i v i t y between the -1 2 2 -H. 'H PPh2 J „ L N, PPh„ L= PMe3, PPh3 H v i ^ | N H ^_PPh 2 C Fig. 4.9 Proposed mechanism for the oxidative addition of dihydrogen to [Ir(.L)N(SiMe 2CH 2PPh 2) 2] iridium amidophosphines and [Ir(C0)Cl(PPh3) 3] i s further emphasized by the fact that [Ir(C0)N(SiMe 2CH 2PPh 2) 2], which basically d i f f e r s from Vaska's complex in the substitution of a chloride by an amide centre, does not react with H 2, even under four atmosphere pressure. It would therefore appear that, to a large extent, the stereo-chemistry of the dihydrogen-iridium(III) adduct, and even the r e a c t i v i t y of the i n i t i a l iridium(I) complex, i s largely dependent upon the nature of the anionic ligand X in the starting d square planar complex. As discussed previously, when X = H, carborane, CH2CN, and amide, the k i n e t i c a l l y stable isomer i s either mainly (in the former two cases) or exclusively ( i n the l a t t e r two cases) the one having c i s dihydrides which -12 3-are trans to c i s diphosphines. It i s therefore arguable that Vaska's complex shows " t y p i c a l " r e a c t i v i t y with dihydrogen but rather, may be the exception to the ru l e . Spectral Trends in the Stereochemical Assignment of Iridium(III)  Amidophosphine Hydrides As mentioned e a r l i e r , stereochemical analysis of iridium(III) hydrides has been largely made by spectrochemical means. Where complex s t a b i l i t y and crystal 1 i n i t y permit, x-ray crystal structure and neutron d i f f r a c t i o n analysis have been invaluable; however, these methods are, as yet, very expensive and appropriate only for s o l i d samples. For the iridium(III) anido phosphine hydride systems, the bulk of stereochemical information has been obtained from the H^NMR spectra. In p a r t i c u l a r , analysis of the upfield region ( i e . 6< 0/ppm) in terms of chemical s h i f t s and coupling patterns has usually precluded x-ray crystal structure analysis. Selective homodecoupling, phosphorus decoupling, and variable temperature experiments have also been very helpful diagnos-t i c a l l y . A number of trends has been noted in the H^NMR hydride resonances of the iridium amido phosphine hydrides; their.chemical s h i f t s and coupling constants are given in Table V (page 154). Hydrides trans to the tridentate ligand's amide (or amine) centre t y p i c a l l y resonate at -20 -*• -25 ppm (upfield of TMS). For a hydride trans to a phosphine (either as part of the tridentate ligand or a unidentate t e r t i a r y -124-phosphine), the chemical s h i f t range i s -8.5 •*• -11.5 ppm. For the single example of a hydride trans to a carbonyl group, the signal appears at -7.86 ppm. In the complex, mer trans-[Ir(H)2(CO)N(SiMe2CH2PPh2)2]» in which the two hydrides are mutually trans, the chemical s h i f t i s -6.00 ppm. Not surprisingly, the order of chemical s h i f t values p a r a l l e l s the trans influence order (of the group trans to the hydride), i e . H>C0>P>N % NH 1 0 7. The coupling constants are quite typical of other I r ( I I I ) hydrides 2 2 with p (c i s ) in the range 12.5 ->• 21 Hz while J H p (trans) are much larger (130-150 Hz). Couplings between chemically or magnetically inequi-valent hydrides are approximately 2 5.5 Hz. Although the P{ H}NMR spectra of these complexes are not quite as informative, an interesting pattern i s observed for the octahedral d i - and trihydrides. For those derivatives i n which the tridentate ligand i s coordinated meridionally, the chemical s h i f t of the PPh 2 centre i s normally %11.00 ppm. Such a s h i f t i s well within the normal 10-35 ppm range observed i n a l l of the Ni(0), N i ( I I ) , Pd(II), P t ( I I ) , Rh(I) and Ir( I ) amido phosphines prepared to date. However, for the complexes in 31 i which the ligand i s bound f a c i a l l y , the H H} signal (for the PPh 2 groups) i s observed much further u p f i e l d , (< O.ppm). Once again, this may r e f l e c t the fact that for the dihydrides 67^ and 68^. the PPh 2 centres are trans to hydrides (a strong trans influence ligand) whereas in the other complexes the PPh 2 i s trans to another PPh 2 (moderate trans i n f l u -31 ence). A si m i l a r trend i n P values has been noted by others for a wide 57 152 variety of metals ' -1 2 5-The high ^'p^H} chemical s h i f t o f fac cis-[Ir(H ) 2 L N(SiMe 2CH 2-PPh 2) 2] may also be a function of the r e l a t i v e l y unusual stereochemistry of the tridentate ligand. Meek57 and others 9 4 have noted that upon coordination to a t r a n s i t i o n metal, a phosphine ligand usually resonates downfield as compared to the free ligand. Such i s the case for a l l of 31 the Group VIII amidophosphines. Since the P for the free ligand, H N(SiMe 2 C H 2PPh 2) 2, i s a singet at -23.2 ppm, the chemical s h i f t differen-ce A, defined as 6P(coordinated)-5P(free l i g a n d ) 5 7 , i s t y p i c a l l y in the 31 range of 30 -»• 60. However, i t has also been observed that the P values of t r a n s i t i o n metal complexes incorporating chelating phosphines show a 94 dependency upon the size of the metal chelate ring ; this contribution has been designated A^ and r e f l e c t s the ring s t r a i n involved upon coor-dination. Thus, i t i s quite probable that the unusually high chemical s h i f t observed for the f a c i a l amido phosphines may indicate a more strained conformation of the two five-membered chelate rings, as compared to the mer stereochemistry. Infra-red spectral correlations also follow the trans influence series. The iridium-hydride stretching frequency for hydride trans to an amino group (as in fa£ and mer-[Ir(H) 3NH(SiMe 2CH 2PPh 2) 2]) i s 2175-2180 cm"1, which i s s l i g h t l y higher than for the corresponding absorption when the hydride i s trans to an amide (2075-2110). For hydride trans to a phos-phine centre, V j p _ H i s in the range 2065-2115 cm"1; when trans to CO, t h i s band s h i f t s down to 1925 cm"1. An even more drastic effect i s noted for trans H-Ir-H groupings; i n t h i s case, v I r _ H i s in the region 1705-1725 -126-cm"1. Although V j r _ ^ values have been well correlated for iridium com-plexes having trans phosphine, carbonyl, and hydride 1igands 1 k h (and the iridium amidophosphine hydrides absorb within these quoted ranges), no such assignment has previously been made for hydrides trans to amides. However, i t would seem that, on the basis of the amide's weak trans influence character, the high energy absorptions observed (for H-Ir trans to N) are quite reasonable. Hydrido Intermediates Involved in Catalytic Hydrogenations using Rhodium  and Iridium Amido Phospines As discussed in Chapter 3, the mechanism of o l e f i n hydrogenation and isomerization catalyzed by a number of rhodium and iridium amido-phosphines i s , as yet, largely speculation. However, the results of the oxidative addition reactions of dihydrogen with iridium amidophosphines have been somewhat informative. I t would appear reasonable that for the [Ir(COE)N(SiMe 2CH 2PPh 2) 2] system, the active catalyst i s probably [ I r ( H ) 2 N ( S i M e 2 C H 2 P P h 2 ) 2 ] , 59. Coordination of the substrate should then proceed to give mer c i s - { I r ( H ) 2 ( o 1 ) N ( S i M e 2 C H 2 P P h 2 ) 2 ) , analogous to formation of mer cis-[Ir(H) 2LN(SiMe 2CH 2PPh 2)o] (L = CO, PMe3). The following steps, migratory insertion and reductive elimination, should proceed in a straightforward manner to y i e l d the saturated alkane. Involvement of either the fac or mer trihydrides 6^, 6^ should be suppressed i n the presence of excess substrate, since i t i s reasonable to assume that o l e f i n coordination to the coordinatively unsaturated, 16-electron complex -12 7-should be more f a c i l e than a second oxidative addition to an I r ( I I I ) centre (or a heterolytic cleavage of H 2). The fact that [IrLN(SiMe 2 C H 2PPh 2) 2] (L = PPh 3, PMe3) do not hydrogenate ol e f i n s i s undoubtedly a consequence of the i n a b i l i t y of the dihydrogen adduct to dissociate a phosphine ligand (at least at room temperature); the required coordination s i t e for o l e f i n binding i s therefore not generated. The i n a c t i v i t y of [Ir(C0)N(SiMe 2CH 2PPh 2) 2] towards o l e f i n hydrogenation i s also understandable in l i g h t of the fact that t h i s complex does not even oxidatively add H2. As far as the isomerization a c t i v i t y of some of the amido phos-phine complexes, i t has been proposed that t h i s may indicate the presence of an amine monohydride in the c a t a l y t i c cycle. That such a species can form via reductive elimination of the metal-amide bond has been lent credence by the i s o l a t i o n of the iridium amine trihydrides 60 and 61^. Note that formation of Rh .(H)NH(SiMe 2CH 2PPh 2) 2", l i k e 50 and 6 J . , corresponds to an overall heterolytic s p l i t t i n g of H 2 (equation 67 ). Ph2 Ph2 Me2Si | Me2Si , / l - R h — L ^ • HN — Rh —H (67) Me.Si I ~ L MeJSi I Ph2 ^ Ph2 L=COE, PPh3 Chapter V Experimental —T28— General Information: A l l manipulations were performed under pre-purified nitrogen in a Vacuum Atmospheres HE-553-2 glove box equipped with a M0-40-2H p u r i f i e r , or i n standard Schlenk-type glassware. Palladium dichloride was purchased from Ventron and used as received to prepare PdCl 2 ( CgH,-CN)2 by a l i t e r a t u r e method 1 5 3. Potassium tetrachloro-platinate was also obtained from Ventron and r e c r y s t a l l i z e d from hot ethanol prior to use in the preparation of K [ P t C l 3 ( C 2 H 4 ) ] 1 5 1 + Pt(COD)Cl 2 1 5 5, PtC1 2(C 6H 5CN) 2 1 5, 6trans-PtCl 2(PR 3) 2 (R=Ph 5 7or Et 1 5 8),and trans-Pt(H) CI ( P E t 3 ) 2 1 5 8 . Rhodium t r i c h l o r i d e hydrate and iridium t r i c h l o r i d e hydrate were obtained on loan from Johnson-Mathey and used d i r e c t l y in the synthesis of { R h ( C 8 H u ) 2 C l } 2 1 5 9 , { R h ( C 2 H 4 ) 2 C l } 2 1 6 0 , { R h ( C 0 ) 2 C l } 2 1 6 1 , R h ( P M e 3 ) 4 + C l ' 1 6 2 , Rh(PPh 3) 3Cl I 6 3 , {Rh(C0D)Cl) 2 1 6 \ {Ir(COD)CI >2 1 6 5 , and {Ir(CgH ] 4) 2C1 >2 1 6 6 . L i P P h 2 1 6 7 was prepared by the dropwise addition of n-butyl1ithium in hexane (1.6 M, Aldrich) to a hexane solution of HPPh 2 < After several washings with hexane, the resultant lemon-yellow powder was used d i r e c t l y in the preparation of (Ph 2PCH 2SiMe 2) 2NH. Methylene chloride (CH 2C1 2), cyclohexane, t r i e t h y l amine and benzyl-amine were pur i f i e d by d i s t i l l a t i o n from CaH2 under argon. Toluene, hexanes, and diethyl ether were dried and deoxygenated from sodium benzo-phenone ketyl under argon. Acetone was dried by refluxing over « 2C0 3 for several days followed by d i s t i l l a t i o n under argon. Tetrahydrofuran (THF) was predried by refluxing over CaH2 and then d i s t i l l e d from sodium benzo-phenone ketyl under argon. 1 3C0 (90 atom % 1 3C) was purchased from MSD and used without further p u r i f i c a t i o n . 1 5NH 4C1 (99 atom % 1 5N) was obtained from MSD and dried at -12 9-120°C for 24 h prior to use. The hydrogenation substrates (1-hexene and cis/trans-2-hexenes) were purchased from Aldrich (Gold Label) and dried over 4 & molecular sieves, va-cuum transferred, and freeze-pump-thawed several times. Any trace peroxides were removed by passing the driedolefins through a short column of activated alumina (Fisher 80-200 mesh). Melting points were determined on a Mel-Temp apparatus in sealed ca-p i l l a r i e s under nitrogen and are uncorrected. Carbon, hydrogen, nitrogen analyses were performed by Mr. P. Borda of this department. H^NMR were recorded on one of the following instruments, depending upon the complexity of the particular spectrum: Varian EM-360L, Bruker WP-80, Varian XL-100, Nicolet-Oxford H-270, and Bruker WH-400. (Spectral simulations were performed using the Bruker Aspect 2000 computer system with the UBCPANIC program (PANIC = parameter Adjustment in NMR by rteration and Calculation) ). 31P{1H}NMR spectra were run at 32.442 MHz on the Bruker WP-80 in 10 mm tubes 13 1 f i t t e d with inserts for the internal standard P(0Me) 3. C{ H}NMR spectra were run at 20.1 MHz and 100 MHz on the Bruker WP-80 and WH-400, respectively. Infrared spectra were recorded either on a Pye-Unicam SP-1100 or a Perkin-Elmer 598 as KEr discs or in solution. Gas l i q u i d chromatographic analyses were performed using a Varian Vista 6000 GC (with a 4oi Computer Data System) equipped with a flame ionization detector (FID). The following column specifications apply to a l l sample analyses: 60/80 Chromosorb P(AW)/20% t r i - o - c r e s y l phosphate; 20 f t x 1/8" ss; Col. temp.: 40°C; sample s i z e : 0.5 y l . CgDg, (CD 3) 2C0, C 7D g, CD 2C1 2, and CDC13 were purchased from Aldrich; the CgDg, (CD 3) 2C0, CD 2C1 2, and C 7D g were dried over activated 4 & -1 30-molecular sieves and vacuum transferred, while the CDClg was dried by refluxing over CaH2 followed by vacuum transferral . The Grignard reagents methylmagnesium chloride ( i n THF) and vinyl -magnesium chloride ( i n THF) were purchased from Ventron; phenylmagnesium bromide (in Et 20) was obtained from A l d r i c h . A l l y l magnesium chloride was prepared from freshly d i s t i l l e d a l l y l chloride and excess magnesium turnings in THF, f i l t e r e d through cotton wool, and standardized using a gas buret (with 0.1 N HC1). Note: A l l recorded infra-red absorptions are given in cm"^; a l l chemical 1 13 31 s h i f t s ( H, C, P) are in ppm with the coupling constants expressed i n Hz. A l l ^ HNMR were recorded in CgDg at room temperature (referenced to CgDgH at 7.15 ppm) unless otherwise noted. Preparation of the hybrid ligands. (C1CH 25iMe 2) 2NHand (CI CH^SiNe,,),,15NH 1,3-bis(chloromethyl)tetramethyldisilazane, (CICH 2SiMe 2) 2NH, was prepared as described by Osthoff and K a n t o r 1 6 8 . However, for i t s ^N-labelled analogue, a modification of this method was employed. This prepa-ration was carried out in a 250 ml heavy-walled flask f i t t e d with a Kontes 9 mm needle-valve i n l e t . To a suspension of finely-crushed 1 5NH 4C1 (1.09 g, 0.02 mol) in THF (100 ml) was added ClCH 2SiMe 2Cl (5.7 g, 0.04 mol). The mixture was cooled to 0°C. Triethylamine (6.1 g, 0.06 mol) was added, via syringe, and the suspension was then s t i r r e d vigorously at room temperature for 7 days. -1 31-The solvent was removed in vacuo and the product extracted with hexanes, f i l t e r e d and pumped down. D i s t i l l a t i o n of the resultant yellowish o i l (b.p. 103°/10 mm) gave the product in ^60% y i e l d as a c l e a r , colorless 15 l i q u i d . The synthesis of the N-labelled tridentate ligand was carried 14 out in an identical manner as described below for i t s N analogue. (Ph 2PCH 2SiMe 2) 2NH. To a cooled solution (-4°C) of LiPPh 2 (9.6 g, 0.05 mol) in THF (50 ml) was added (CICH 2SiMe 2) 2NH (5.35 g, 0.025 mol) dropwise with s t i r r i n g . The i n i t i a l l y clear red solution gradually decolourized to a very pale yellow when a l l of the s i l y l chloride had been added. The solution was s t i r r e d at room temperature for 0.5 h; the THF was then removed in vacuo. The residue was extracted with pentane (50 ml) and f i l t e r e d through a medium porosity f r i t . Removal of the pentane in vacuo yielded a pale yellow o i l which was immediately taken up in hexane (10 ml), f i l t e r e d and cooled to -30°C. Fine white needles of the product formed; these were f i l t e r e d and washed with cold hexane. Y i e l d : 10.2 g (77%). m.p. 45-46°C. Anal. Calcd. for C 3 Q H 3 7 N P 2 S i 2 : C, 68.05; H, 6.99 ; N, 2.65. Found: C, 68.33; H, 7.25; N, 2.55. IR (KBr): v N _ H = 3365 (w) . 3 1 P{ ]H}NMR (CgDg ):-22 .45 ( s ) . LiN(SiMe 2CH 2PPh 2) 2. To a vigorously s t i r r e d solution of freshly r e c r y s t a l -l i z e d (Ph 2CH 2SiMe 2)NH (5.3 g, 0.01 mol) in pentane (50 ml) at room tempera-ture, was slowly added n-BuLi in hexane (1.6 M, 8 ml, 0.016 mol). A fine white precipitate immediately formed. After s t i r r i n g at room temperature for 0.5 h, the white s o l i d was f i l t e r e d and washed with pentane. Y i e l d : 3.8 g (71%). Although the product i s s u f f i c i e n t l y pure at t h i s stage to be used in metathetical reactions with t r a n s i t i o n metal s a l t s , i t may be r e c r y s t a l l i z e d from toluene/hexane to give colorless plates, m.p. 120°C -1 32-(decomp.). Anal. Calcd for C 3 o H 3 6 L l N P 2 S i 2 : C* 6 7 - 2 9 " H» 6- 7 3* N> 2- 6 1-Found: C, 67.00; H, 6.78; N. 2.48. Molecular weight (Signer): theoretical (monomer), 535; found, 1516. 31P{1H}NMR (CgDg): -23.20 ( s ) . (CICH^SiMep)(CgHgCHp)NH. The apparatus for t h i s reaction consisted of a l£ 3-necked round-bottom flask to which was attached a 250 ml addition funnel. To a solution of benzylamine (21.4 g, 0.20 mol) in hexane (200 ml) was slowly added ClCH^SiMe^l (14.3 g, 0.10 mol) in hexane (150 ml). Immediately, a white granular precipitate (benzylamine hydrochloride) formed. After addition of the s i l y l chloride was completed (%3 h), the mixture was s t i r r e d vigorously for several hours at room temperature and then f i l t e r e d under argon. The precipitate was washed with copious quanti-t i e s of hexane. The combined hexane fractions were then pumped down, yielding an almost colorless o i l . D i s t i l l a t i o n gave the product as a color-less l i q u i d (b.p. 76-80°C/l mm). Y i e l d : 16 g (76%). (PhgPCHpSiMe2)(CgHgCHg)NH. Preparation of t h i s bidentate ligand was carried out in a manner d i r e c t l y analogous to that described for (Ph 2PCH 2SiMe 2) 2NH (vide supra) from (CICH2SiMe2)(CgHgCh^NH (2.1 g, 0.01 mol) and LiPPh 2 (1.9 g, 0.01 mol) in THF (25 ml). Work-up (as previously outlined) resulted in a yellowish o i l which was d i s t i l l e d (b.p. 140°C/1 mm) as a colorless l i q u i d . Y i e l d : 3.0 g (83%). IR(hexane): v N _ H = 3380 (w). 31P{1H}NMR (CgDg): -22.31 (s ) . LiN(CgH 5CH 2)(SiMe 2CH 2PPh 2) . Formation of t h i s lithium s a l t proceeded smoothly using n-BuLi and the ligand (Ph 2CH 2SiMe 2)(CgH 5CH 2)NH in hexane at room tempe-rature (see above preparation of LiN(SiMe 2CH 2PPh 2). R e c r y s t a l l i z a t i o n at -30°C from hexanes resulted in colorless crystals of the product. This -1 33-complex i s very thermally sensitive and must be stored at -30°C (storage at room temperature results in decomposition to a mauve o i l ) . Y i e l d : 92%. Anal. Calcd. for C 2 ?_H 2 5LiNPSi: C, 71.54; H, 6.78; N, 3.79. Found: C, 71.53; H, 6.80; N, 3.78. Molecular weight (Signer): theoretical (monomer), 369; found, 943. 3 1 P{1H}NMR(C6D6): -23.54 (,br s ) . Amido Phospine Complexes of the Ni Triad [NiClN(SiMe 2CH 2PPh 2) 2]. Method 1. A solution of LiN(SiMe 2CH 2PPh 2) 2 (1.34 g, 2.5 mmol) in Et 20 (25 ml) was added dropwise with s t i r r i n g to a cooled (0°C) solution of [ N i ( P M e 3 ) 2 C l 2 ] I G 9 (0.7 g, 2.5 mmol) in THF (30 ml). The i n i t i a l l y clear deep red solution immediately became dark brown in colour. After s t i r r i n g at 0°C for 0.5 h, the solution was s t i r r e d at room temperature for 1 h. The solvent was removed in vacuo and the resultant brown o i l extracted with cyclohexane. Upon f i l t r a t i o n through a medium porosity f r i t , a clear deep brown solution was obtained; the cyclohexane was then removed in vacuo. Re c r y s t a l l i z a t i o n from toluene/hexane yielded diamond-shaped brown prisms, m.p. 153-155°C. Anal. Calcd. for C 3 0 H 3 6 C 1 N N i P 2 S 1 2 : C' 5 7 - 8 3 » H» 5 - 7 8 ' N> 2- 2 5-' Found: C, 57.71; H , 5.87; N, 2.23. Y i e l d : 1.01 g (65%). 31P{]H}NMR(CgDg): 14.76 ( s ) . Method 2. To a suspension of NiCl 2-DME J l 7 Q(0.22 g, 1.0 mmol) in toluene (30 ml) was added a solution of (Ph 2PCH 2SiMe 2) 2NH (0.53 g, 1.0 mmol) in toluene (10 ml). Immediately, a clear deep-red solution formed and, upon s t i r r i n g at room temperature for 0.5 h, green shiny needles began to precipi-tate. An excess of triethylamine (0.15 g, 1.5 mmol) was added dropwise, producing a deep brown solution. After s t i r r i n g at room temperature for 1 h, the solution was f i l t e r e d through C e l i t e . Removal of the solvent in vacuo yielded large brown prisms of a n a l y t i c a l l y pure [NiClN(SiMe 2CH 2PPh 2) 2]. Y i e l d : 0.55 g (88%). [PdC1N(S1Me2CH2PPh,) 23. A solution of LiN(SiMe 2CH 2PPh 2) 2 (0.54 g, 1.0 mmol) in Et 20 (10 ml) was slowly added to a cooled (-78°C) solution of freshly prepared (CgH 5CN) 2PdCl 2 (0.39 g, 1.0 mmol) in THF (30 ml); the mixture was s t i r r e d at -78°C for 0.5 h. The clear orange-gold solution was then s t i r r e d at 0°C for 1 h and f i n a l l y at room temperature for an additional hour. The solvent was removed in vacuo and the product extracted with cyclohexane. Rec r y s t a l l i z a t i o n from toluene/hexane gave orange blocks of the palladium amide, which contains one mole of toluene as solvent of c r y s t a l l i z a t i o n . Anal. Calcd. for C 3 ?H 4 4C1 MP2jPdSi 2: C, 58.26; H, 5.7?; N, 1.83. Found: C, 58.27; H, 5.96; N, 1.81. m.p. 136-137°C. Y i e l d : 0.40 g (60%). The com-plex may also be recrystal1ized from acetone/hexane, yie l d i n g orange rod-l i k e c r y s t a l s , m.p. 140°C. Anal. Calcd. for C3QH36C1NP2PdSi2: C' 5 3 - 7 2 ' H, 5.37; N, 2.07. Found: C, 53.73; H, 5.54; N, 2.04. 3 1 P{1H}NMR((CD3)2C0) : 18.71 ( s ) . [PtClN(SiMe 2CH 2PPh 2) 2]. To a cooled (0°C) solution of freshly prepared Zeise's s a l t , K [ P t C l 3 ( C 2 H 4 ) ] , (0.37 g, 1.0 mmol) in THF (25 ml) was slowly added a solution of LiN(SiMe 2CH 2PPh 2) 2 (0.54 g, 1.0 mmol) in Et 20 (10 ml). The o r i g i n a l l y clear lemon-yellow solution did not undergo any noticeable colour changes during the addition. The solution was s t i r r e d at 0°C for 0.5 h and then at room temperature for 4 h. The solvent was removed in vacuo the product was then extracted with cyclohexane, f i l t e r e d , and pumped down to a fine yellow glass. Upon r e c r y s t a l l i z a t i o n from toluene/hexane, shiny yellow plates of the platinum amide were obtained. Y i e l d : 0.48 g (63%). m.p. 147-149°C. Anal. Calcd. for C 3 7 H g 4 C l N P 2 P t S i 2 : C, 52.23; H, 5.18; N, 1.65. Found: C, 52.10; H, 5.27; N, 1.61. 31P{]H}NMR (CgDg): 34.27 ( t , 2 J p t j R = 2690.0). -1 35-[NiC1oNH(SiMeoCH2PPh2)o]. A solution of freshly r e c r y s t a l l i z e d (Ph 2PCH 2SiMe 2) 2NH (0.53 g, 1.0 mmol) in THF (10 ml) was added to a suspension of NiCI2•DME (0.22 g, 1.0 mmol) in THF (25 ml). The solution immediately became clear deep red in colour and, upon s t i r r i n g at room temperature for 0.5 h, green crystals began to form. After an additional 0.5 h, the solvent was removed in vacuo. Recrystal1ization of the green s o l i d from CH 2C1 2/ hexane produced f l u f f y green crystals which, upon standing, gradually re-formed as shiny blue-black prisms. Y i e l d : 0.58 g (88%). m.p. 185-187°C. Anal. Calcd. for C 3 QH 3 7C1 2NNiP 2Si 2: C, 54.65; H, 5.66; N, 2.12. Found: C, 54.43; H, 5.67; N, 2.00. IR(KBr): = 3365 (w). [PdCl 2NH(SiMe 2CH 2PPh 2) 2]. A solution of PdCl 2(C gH 5CN) 2 (0.38 g, 1.0 mmol) and (Ph 2PCH 2SiMe 2) 2NH (0.53 g, 1.0 mmol) in THF (35 ml) was s t i r r e d at room temperature for two days. Removal of the solvent in vacuo yielded a gold-coloured o i l which was then r e c r y s t a l l i z e d from CH 2Cl 2/cyclohexane to give yellow prisms of the product. This complex contains one mole of cyclohexane as solvent of c r y s t a l l i z a t i o n , m.p. 140°C. Anal. Calcd. for C 3 g H 4 9 C l 2 N P 2 P d S i 2 : C, 54.68; H, 6.20; N, 1.77. Found: C, 55.06; H, 6.39; N, 1.75. 3 1P{ ]H}NMR((CD 3) 2C0): 21.86 ( s ) . IR(KBr): vNH = 3305 (w). [PtCl 2NH(SiMe 2CH 2PPh 2) 2], Pt(COD)CI2(0.19 g, 0.5 mmol) and (.Ph2PCH2SiMe2)2NH (0.27 g, 0.5 mmol) were dissolved in THF (20 ml). Upon r e f l u x i n g , the milky solution gradually became clear lemon-yellow in colour; the solution was refluxed overnight. The solution was then cooled to room temperature and, upon addition of hexane (30 ml), a fine white s o l i d precipitated. The s o l i d was f i l t e r e d under nitrogen and r e c r y s t a l l i z e d from CH 2Cl 2/cyclohexane to give a colourless gel which, upon standing at room temperature overnight, -1 36-formed large colourless blocks. Y i e l d : 0.31 g (.78%). m.p. 220-222°C. Anal. Calcd. for C 3 ( ) H 3 7 C l 2 N P 2 P t S i 2 : C, 45.28; H, 4.65; N, 1.76. Found: C, 45.31; H, 4.65; N, 1.69. 3 1P{ ]H}NMR(CD 3) 2C0): 41.44 ( t , 1 J p t p = 3599.6). IR (KBr): \>NH = 3280 (w). Conversion of N i ( I I ) , Pd(II), and Pt(II) - dichloro amino diphosphines to  the corresponding chloro amido diphosphines. This reaction i s exemplified with the palladium complex. [PdCl 2NH(SiMe 2CH 2PPh 2) 2-C 6H 1 2] (0.15 g, 0.2 mmol) was dissolved in toluene (15 ml) at room temperature, forming a clear gold solution. An excess of t r i e t h y l amine (^0.5 ml) was added and the solution s t i r r e d for 24 h. The resultant deep orange solution was f i l t e r e d through Celite in order to remove the colourless granular NEt 3*HCl. Removal of the solvent in vacuo yielded the product as well-formed crystals (no further r e c r y s t a l l i z a t i o n necessary). In contrast to the palladium and platinum derivatives, the analogous reaction to form the nickel complex i s complete within one hour. Alkyl Derivatives of the Ni(II) and Pd(II) Amido Phosphines. [Ni(CH 3)N(S1Me 2CH 2PPh 2) 2]. To a cooled solution (-30°C) of [NiCIN(SiMe 2CH 2~ PPh 2) 2J (.62 mg, 0.1 mmol) in toluene (15 ml) was added CH3MgCl in THF (2.9 M, 35 y £ , 0.1 mmol). The i n i t i a l l y deep brown solution rapidly became deep orange in colour. After standing at -30°C for 0.5 h, the solvent was removed i n vacuo. The product was extracted with cyclohexane, f i l t e r e d through Celi t e and pumped down to y i e l d fine yellow-orange c r y s t a l s . Re-c r y s t a l l i z a t i o n from toluene/hexane at -30°C gave a n a l y t i c a l l y pure product, m.p. 134-136°C. Y i e l d : 44 mg (74%). Anal. Calcd. for C 3 l H 3 g N N i P 2 S i 2 : C, 61.80; H, 6.53; N, 2.33. Found: C, 61 .60; H, 6.43; N, 2.20. 3 1P{ 1H}NMR(C gD 6): 26.73 ( s ) . -1 37-[N1(CH,CH=CH2)N(S1Me2CH2PPho)2]. A l l y l magnesium chloride in THF (0.55 M, 91 vl, 0.05 mmol) was added to a cooled (-30°C) solution of [NiClN(SiMe 2CH 2PPh 2) 2] (31 mg, 0.05 mmol) in toluene (15 ml). The resultant deep red-brown solution was kept at -30°C for 0.5 h. After warming to room temperature, the solvent was removed in vacuo. Extraction and r e c r y s t a l l i -zation was carried out in the same manner as described for the methyl derivative, y i e l d i n g deep red-brown c r y s t a l s . Anal. Calcd. for C 3 3 H 4 1 N N 1 P 2 S i 2 : C ' 6 3 - 0 6 " H> 6 - 5 3 ' N> 2- 2 3- Found: C, 62.82; H, 6.80; N, 2.13. m.p. 130°C (decomp.). Y i e l d : 24 mg (78%)'. 3 1 P{1H}NMR(CgD6): 17.81 (br s ) . [Ni(CH=CH 2)N(SiMe 2CH 2PPh 2) 2]. Addition of vinyl magnesium bromide in THF (1.4 M, 72 u £ , 0.1 mmol) to a cooled (-30°C) solution of [NiClN(SiMe 2CH 2PPh 2) 2] (62 mg, 0.1 mmol) in Et 20 (60 ml) produced a cloudy pale yellow solution. After 5 minutes at -30°C, the solvent was rapidly removed in vacuo. Extraction with hexane, followed by f i l t r a t i o n through C e l i t e and solvent removal, yielded gold-yellow crystals of the vinyl d e r i -vative. Recrystal!ization from toluene/hexane at -30°C produces a n a l y t i c a l l y pure material. Y i e l d : 40 mg (65%). Anal. Calcd. for C 3 2 H 3 5 N N i P 2 S i 2 : C, 62.54; H, 6.35; N, 2.28. Found: C, 62.48; H, 6.44; N, 2.11. 3 1P{ 1H}NMR(C 6D 6): 21.00 ( s ) . [Ni(C 6H 5)N(SiMe 2CH 2PPh 2) 2]. To a cooled solution (-30°C) of [NiClN(SiMe 2CH 2PPh 2] (62 mg, 0.1 mmol) in THF (60 ml) was added phenyl mag-nesium bromide in Et 20 (3.0 M, 34 y£, 0.1 mmol). After 15 minutes at -30°C, the solvent was removed i n vacuo. Extraction with hexane gave gold coloured crystals of the phenyl derivative, m.p. 160-162°C (decomp.,). -Yield: 40 mg -1 38-(60%). Anal. Calcd. for C 3 6 H 4 ] N N i P 2 S i 2 : C, 65.06; H, 6.35; N, 2.28. Found: C, 65.58; H, 6.35; N, 2.06. 3 1P{ 1H}NMR(C 6Dg): 20.32 ( s ) . [Ni(CN)N(SiMe 2CH 2PPh 2) 2] . Freshly d i s t i l l e d Me 3SiCN 2 7 J (44 mg, 0.45 mmol) was added at room temperature to a solution of [NiClN(SiMe 2CH 2PPh 2) 2] (0.25 g, 0.4 mmol) in toluene (25 ml). After s t i r r i n g at room temperature for 45 minutes, the reaction mixture rapidly changed from i t s i n i t i a l deep brown colour to a clear orange. The solution was s t i r r e d at room temperature for an additional 2 h, after which time the solvent was removed in vacuo. Recrystal!ization of the resultant o i l from toluene/hexane yielded small orange blocks of the cyanide complex, m.p. 142-143°C. Y i e l d : 20 mg (83%). Anal. Calcd. for C 3 1 H 3 6 N 2 N i P 2 S l 2 : C ' 6 Q- 6 8> H> 5 - 8 7 ' N> 4- 5 6- F o u n d : C, 61.00; H, 6.00; N, 4.40. IR(KBr): v Q N = 2122 ( s ) . [Pd(CH 3)N(SiMe 2CH 2PPh 2) 2]. The synthesis of t h i s complex was performed in an identical fashion as outlined for i t s nickel analogue. Upon addition of the Grignard, the st a r t i n g gold-coloured solution became completely colourless. Recrystal 1 ization of the product from minimum hexane at -30°C yielded colorless plates. Anal. Calcd. for C 3 1H 3gNP 2PdSi 2: C, 57.28; H, 6.05; N, 2.15. Found: C, 57.17; H, 6.10; N, 1.82. Y i e l d : 48 mg (74%). 3 1P{ ]H}NMR(C 6D 6): 24.92 ( s ) . [Pd(CH 2CH=CH 2)N(SiMe 2CH 2PPh 2) 2]. Preparation of t h i s complex followed that of the corresponding nickel derivative. The product was obtained as pale yellow crystals from hexane. m.p. 90°C (decomp.). Y i e l d : 29 mg (86%). Anal. Calcd. for C 3 3H 4 1NP 2PdSi 2: C, 58.67; H, 6.07; N, 2.07. Found: C, 59.23; H, 6.42; N, 2.13. -1 39-Carbonylation Reactions 13 A l l reactions of the Ni(II) a l k y l s with CO and CO to produce the Ni(0) derivatives [Ni(C0) 2N(C0R)(SiMe 3CH 2PPh 2) 2l were performed at one atmosphere pressure at room temperature in toluene. T y p i c a l l y , 0.02 M solutions of the Ni complexes ,Ni(R)N(SiMe 2CH 2PPh 2) 2 (R = methyl, a l l y l , v i n y l , phenyl), were rapidly s t i r r e d under carbon monoxide. A typical preparation is given below. [Ni(C0) 2N(C0CH 3)(SiMe 2CH 2PPh 2) 2] . A solution of [Ni(CH 3)N(SiMe 2CH 2PPh 2) 2] (0.12 g, 0.20 mmol) i n toluene (10 ml) was s t i r r e d under 1 atm. carbon monoxide at room temperature. Within 5 minutes, the original gold-orange colour faded to a c l e a r , colourless solution. The solvent was removed in vacuo and the resultant o i l taken up in minimum hexanes. Colorless c r y s t a l l i n e clusters were f i l t e r e d and washed with cold hexanes. Yi e l d : 0.12 g (85%). m.p. 122°C. Anal. Calcd. for C 3 4 H 3 g N N i 0 3 P 2 S i 2 : C, 59.48; H . 5.68; N, 2.04. Found: C, 59.30; H, 5.73; N, 1.80. Molecular weight (Signer): t h e o r e t i c a l , 689; found, 698. IR(CH 2C1 2): v C Q = 1 995 (vs), vC0CH = 1 7 1 5 ( s ) * 3 1 p { l H > N M R ( C 6 D 6 ) : 15.10 (s ) . 13C{1H}NMR( CgDg: C_0CH3> 161.9 ( s ) ; Ni-CO, 200.2 ( t , 2J31p_13 c = 2.4). [Ni(C0) 2N(C0C3H 5)(SiMe 2CH 2PPh 2) 2]. The synthesis of t h i s complex was carried out in an identical manner as outlined for i t s acetyl analogue. Y i e l d : 80%. m.p. 138-140°C. Anal. Calcd. for C 3gH 4 1NNi0 3P 2Si 2: C, 60.67; H, 5.76; N, 1.97. Found: C, 60.66; H, 5.89; N, 1.80. IR(CH 2C1 2): v C Q = 1995 (vs), 1935 (vs); v c o c R = 1715 ( s ) . •— 3 5 [Ni(C0) 2N(C0C 2H 3)(SiMe 2CH 2PPh 2) 2]. Upon s t i r r i n g a toluene solution of [Ni(C 2H 3)N(SiMe 2CH 2PPh 2) 2] under CO for 3 h, followed by rapid removal of —140— solvent under reduced pressure, a mixture of two i d e n t i f i a b l e products was "obtained. [Ni (C0) 2N(C0C 2 H 3 ) (SiMe 2CH 2PPh 2') 2] was the major product (%90%) but has not yet been obtained a n a l y t i c a l l y pure due to contamination by [Ni(C0)N(C0C 2H 3)(SiMe 2CH 2PPh 2) 2] (vide i n f r a ) . IR(CH 2C1 2): v C Q = 1996 (vs), 1935 (vs); v c o c H = 1700 ( s ) . 3 1P{ 1H}NMR(C 6D 6): 15.01 ( s ) . 1 3C{ 1H}NMR(C gD 6) i C0C 2H 3, 157.4 ( s ) ; Ni-CO, 199.9 ( s ) . [Ni(C0)N(C0C 2H 3)(SiMe 2 CH 2PPh 2) 2]. The y i e l d of t h i s derivative can be i n -creased from M0% (vide supra) to greater than 90% by the following modifi-cation. After the above reaction mixture had become colorless (^ 3 h), the excess CO was removed i n vacuo and the solution s t i r r e d under p a r t i a l vacuum for an additional 24 h, gradually becoming yellow-orange in colour. The solvent was then removed and the product r e c r y s t a l l i z e d from hexane. m.p. 131 - 133°C- Anal. Calcd. for C 3 4 H 3 9 N N i 0 2 P 2 S i 2 : C, 60.89; H , 5.82; N, 2.09. Found: C, 60.86; H, 6.00: N, 1.82. IR(CH 2C1 2): v C Q = 1950 (vs); vC0C H = 1 6 2 5 ( S ) ' 3 1 P { 1 H > N M R ( C 6 D 6 ) : 16.38 (d, = 57.4); -1.38 (d). 1 3C{ 1H}NMR(C 6D 5):C0C 2H 3, 166.0 ( s ) ; Ni-CO, 205.2 (dd, p = 10.9, J l 3 C , P 2 = 6 - 3 ) -[Ni(C0) 2N(C0C 6H 5)(SiMe 2CH 2PPh 2) 2]. Although the preparation of t h i s d e r i -vative'was as described for the acetyl analogue, i t i s a much slower reaction, going to completion i n ^2 days. Y i e l d : 72%. m.p. 158°C. Anal. Calcd. for C 3 g H 4 1 N N i 0 3 P 2 S i 2 : C, 62.57; H , 5.48; N, 1.87. Found: C, 63.00; H, 5.73; N, 1.65. IR(KBr): v C Q = 1990 ( v s ) , 1930 (vs); v C O p h = 1680 ( s ) . 3 1P{ 1H}NMR(CgD 6): 15.09 ( s ) . 13C{]H}NMR(CgDg): COPh, 158.1 ( s ) ; Ni-CO, 200.2 ( s ) . -141-[Ni(CQCH3)N(SiMe2CH2PPh2)2]• Exactly one equivalent of carbon monoxide was added to a toluene (20 ml) solution of [Ni(CH3)N(S1Me2CH2PPh2)2] (0.12 g, 0.20 mmol) through the use of a calibrated gas bulb (25 ml, 0.18 atm). The solution was stirred under CO for 5^ h; no apparent color change took place during this time period. The solvent was removed in vacuo and the product recrystallized from toluene/hexane. Yield: 0.10 g (78%). Anal. Calcd. for C 3 2 H 3 g NNi0P 2 Si 2 : C, 60.95; H, 6.19; N, 2.22. Found: C, 61.06; H, 6.20; N, 2.14. IR(KBr): v C Q C H = 1615 (s). 3 1 P f 1 H}NMR(C?Dg): 15.60 (s). [Ni(C0C6H5)N(SiMe2CH2PPh2)2]. A solution of [Ni(CgH5)N(SiMe2CH2PPh2)2] (0.06 g, 0.10 mmol) in toluene (10 ml) was stirred under 1 atm. CO for 20 minutes. During this time period, the original gold-colored solution became clear deep orange. The solvent was pumped off and the product recrystallized as large orange blocks from toluene/hexane. Yield: 48 mg (70%). m.p. 163-165°C. Anal. Calcd. for C 3 7 H 4 1 NNi0P 2 Si 2 : C, 64.16; H, 5.92; N, 2.02. Found: C, 64.31; H, 5.98; N, 2.16. IR(KBr): v C Q p h = 1602 (m). 31P{1H}NMR(C6D6): 15.89 (s). [Pd(C0CH3)N(SiMe2CH2PPh2)2]. In a Parr Mini-Reactor (300 ml) was added a toluene (30 ml) solution of [Pd(CH3)N(SiMe2CH2PPh2)2] (0.13 g, 0.20 mmol). The reactor was sealed under N 2 , taken out to the vacuum l ine, evacuated and then f i l led with 20 atm CO. The solution was stirred magnetically for 5 h at room temperature. The excess CO was then vented and the reactor flushed with N 2 > The resultant orange-red solution was pumped down and the product recrystallized from toluene/hexane. Yield: 81 mg (60%). Anal. Calcd. for C 3 2H 3 9N0P 2PdSi 2: C, 56.72; H, 5.76; N, 2.07. Found: C, 57.03; H, 5.64; N, 2.41. IR(C6D6): v C Q C H ^ = 1640 (m). m.p. 153°C. —1 42— Amido1 Phosphine Complexes of Rhodium and Iridium [Rh(C sH. | /,)N(SiMe 2CH 2PPh 2) 2]. A solution of LiN(SiMe 2CH 2PPh 2) 2 (1.07 g, 2.0 mmol) in Et 20 (10 ml) was added dropwise to a s t i r r e d , cold (-78°C) solution of {Rh(C 2H 4) 2Cl} (0.72 g, 1.0 mmol) in Et 20 (80 ml). The o r i g i n a l clear orange solution darkened s l i g h t l y during the addition. After 1 h at -78°C, the solution was s t i r r e d at 0°C for an additional hour and then at room temperature for 2 h. Removal of the solvent yielded an o i l y residue which was extracted with hexanes, f i l t e r e d through C e l i t e , and pumped down. Re c r y s t a l l i z a t i o n from minimum hexanes gave gold-brown crystals which were washed with ^10 ml cold (-30°C) hexanes. Yi e l d : 0.48 g (65%). m.p. 188-191°C. Anal. Calcd. for C 3 8H 5 C )NP 2RhSi 2: C, 61.54; H, 6.75; N, 1.89. Found: C, 61.33; H, 6.66; N, 1.87. 31P{1H}NMR(CgDg, 50°C): 31.93 (br d, JRh,P = 1 4 0- 4>-[Rh(C0)N(SiMe 2CH 2PPh,) 23. Method 1. To a cold (-78°C) solution of {Rh(C0) 2Cl} 2 (0.20 g, 0.50 mmol) in Et 20 (60 ml) was added, dropwise with s t i r r i n g , a solution of LiN(SiMe 2CH 2PPh 2) 2 (0.53 g, 1.0 mmol) in Et 20 (10 ml). The mixture was s t i r r e d at -78°C for 30 minutes, warmed to 0°C for an hour, and f i n a l l y s t i r r e d at room temperature for 2 h. The o r i g i n a l l y clear yellow solution deepened to a murky orange during the course of t h i s reaction. The solvent was then removed in vacuo and the residue extracted with hexanes, f i l t e r e d and pumped down. The product was r e c r y s t a l l i z e d as yellow-orange needles from hexanes. Y i e l d : 0.47 g (71%). m.p. 128-130°C. Anal. Calcd. for C 3 1H 3 gN0P 2RhSi 2: C, 56.45; H, 5.46; N, 2.12. Found: C, 56.70; H, 5.50; N, 2.01. IR(CH 2C1 2): v c o = 1950 (vs). 31P{1H}NMR(CgDg): 30.92 (d, J R h > p = 129.4). -1 43-Method 2. A solution of lRh(CgH 1 4)N(SiMe 2CH 2PPh 2) 2] (0.12 g, 0.20 mmol) in toluene (20 ml) was stirred' under 1 atm. CO at room temperature for 30 minutes. During t h i s time period, the o r i g i n a l gold-coloured solution lightened rapidly to a clear yellow. The solvent was removed and the o i l y residue r e c r y s t a l l i z e d from hexanes. Y i e l d : 90%. [Rh(C 2H^)N(SiMe 2CH 2PPh 2) 2]. This complex was prepared by either Method 1, using {Rh(C 2H 4) 2Cl} 2 in E t 2 0 , or Method 2, from [Rh(CgH 1 4)N(SiMe 2CH 2PPh 2) 2] in toluene under 1 atm C ^ . The reaction conditions and work-up procedures for both methods were as described for the carbonyl derivative. Y i e l d : method 1, 70%; method 2, 83%. m.p. 156-158°C. Anal. Calcd. for C 3 2 H 4 0 N P 2 R n S i 2 : C' 5 8- 2 7> H» 6 - 0 7 ' N> 2- 1 2- F 0 L m d : c> 58.55; H, 5.95; N, 2.09. 3 1P{ 1H}NMR(C 6D 6): 32.48 (d, J R h p = 131.8). [Rh(PMe 3)N(SiMe 2CH 2PPh 2) 2]. Synthesis of t h i s derivative was carried out using Rh(PMe 3) 4 +Cl~ in Et 20 (Method 1); a l t e r n a t i v e l y , t h i s complex was more e a s i l y prepared via Method 2, using a s l i g h t excess of PMe3 , added to a toluene solution of [Rh(C gH 1 4)N(SiMe 2CH 2PPh 2) 2]. Y i e l d : method 1, 68%; method 2, 92%. m.p. 225-227°C. Anal. Calcd. for C 3 3H 4 5NP 3RhSi* 2: C, 56.01; H, 6.36; N, 1.98. Found: C, 56.35; H, 6.40; N, 1.91. 3 1P{ 1H}NMR(C gD 6): PPh 2, 33.42 (dd, J R h j P p h 2 = 144.3, J p p h 2 > ^ = 44.4); PMe3, -10.26 (dt, JRh> PMe3 = 1 4 8 - 0 ) -[Rh(PPh 3)N(SiMe 2CH 2PPh^) 2]. This complex was prepared via Method 1, from Wilkinson's c a t a l y s t , [Rh(PPh 3) 3Cl], in THF, or by means of Method 2, from [Rh(CgH-| 4)N(SiMe 2CH 2PPh 2) 2] and one equivalent r e c r y s t a l l ized PPh 3 in toluene. Y i e l d : method 1, 63%; method 2, 86%. m.p. 172-174°C. Anal. Calcd. for C 4 gH 5 1NP 3RhSi 2: C, 64.50; H, 5.71; N, 1.57. Found r C , 64.83; -144-H, 5.60; N, 1.49. 31P^rONMRCCgDg): PPl^, 50.00 (dt, J R h p p h 3 = 163.6, J p p n 2 , p p n 3 = 40.3); PPh 2, 31.94 (dd, = 142.8). [Rh(C 3H 1 2)N(C 6H 5CH 2)(SiMe 2CH 2PPh 2)]. To a solution of {Rh(CgH 1 2)Cl) 2 (0.10 g, 0.2 mmol) in toluene (40 ml) was added a solution LiN[CgH 5CH 2)-(SiMe 2CH 2PPh 2) (0.15 g, 0.4 mmol) in toluene (20 ml) at room temperature. The mixture was s t i r r e d at R.T. for 1 h; the solvent was then removed in  vacuo, the product extracted with hexanes, f i l t e r e d and pumped down. Recrystal1ization gave large gold blocks. Y i e l d : 0.20 g (88%). Molecular weight (Signer): t h e o r e t i c a l , 573; found, 522. Anal. Calcd. for C 3 QH 3 7NPRhSi: C, 62.83; H, 6.46; N, 2.44. Found: C, 62.99; H, 6.40; N, 2.54. 3 1P{ 1H}NMR(C gD 6): 32.36 (d, J R h p = 166.2). [ I r U o ^ 1)N(SiMe 2CH 2PPh 2) 2], A solution of {Ir( CgH] 4) 2C1 >2 (0.45 g, I. 0 mmol) in toluene (100 ml) was cooled to 0°C. Addition of LiN(SiMe 2-CH 2PPh 2) 2 (1.07 g, 2.0 mmol) in toluene (30 ml) was carried out in a drop-wise manner, via syringe. The solution was s t i r r e d at 0°C for 3 h and then gradually warmed to room temperature. The solvent was then removed and the resultant deep orange o i l y residue extracted with hexanes, f i l t e r e d through C e l i t e , and pumped down. Recrystal1ization from minimum hexanes gave large orange blocks. Y i e l d : 0.50 g (60%). m.p. 204-205°C. Anal. Calcd. for C 3 g H 5 0 I r N P 2 S i 2 : C, 54.94; H, 6.02; N, 1.69. Found: C, 54.78; H, 6.13; N, 1.59. 3 1P{^ H)NMR(CgDg): 18.95 (s, br). [Ir(C0)N(SiMe 2CH 2PPh 2) 2]. This complex was prepared in an identical fashion to that described for i t s rhodium analogue (Method 2 only) from [Ir(C gH 4)N(SiMe 2CH 2PPh 2) 2] i n toluene under 1 atm CO. Y i e l d : 95%. m.p. 138-139°C. Anal. Calcd. for C 3 1H 3gIrN0P 2Si 2: C, 49.73; H, 4.81; N, 1.87. Found: C, 49.96; H, 5.00; N, 1.76. IR(CH 2C1 2): v C Q = 1 930 (vs). 3 1P{ 1H}NMR(C 6D 6): 23.94 ( s ) . [Ir(CpH / [)N($iMe 2CH 2PPh 2) 2]. Preparation of this derivative was as outlined for i t s rhodium analogue (Method 2 only). Y i e l d : 74%. Anal. Calcd. for C 3 2 H 4 0 I r N P 2 S i 2 : C, 51.34; H, 5.35; N, 1.87. Found: C, 51.43; H, 5.45; N, 1.93. 3 1P{ 1H}NMR(C 6D 6): 21.95 ( s ) . [Ir(PMe 3)N(SiMe 2CH 2PPh 2) 2]. The synthesis of this complex was carried out as described for i t s rhodium analogue (Method 2). Yi e l d : 82%. Anal. Calcd. for C 3 3 H 4 5 I r N P 3 S i 2 : C, 49.75; H, 5.65; N, 1.76. Found: C, 49.77; H, 5.78; N, 1.68. 3 1P{ 1H}NMR(C 6D 6): PPh 2 > 24.10 (d, J p p n 2 ) p M e 3 = 28.4); PMe3> -51 .17 ( t ) . [Ir(PPh 3)N(SiMe 2CH 2PPh 2) 2] . A solution of [Ir(C gH 1 4)N(SiMe 2CH 2PPh 2) 2] (0.17 g, 0.2 mmole) and freshly recrystal1ized triphenylphosphine (52 mg, 0.2 mmole) in toluene (30 ml) was refluxed for 24 h under nitrogen. The deep orange solution was then allowed to cool to room temperature and the solvent removed in vacuo. Recrystallization from neat hexane yielded a n a l y t i c a l l y pure orange needles. Yield: 0.15 g (78%). Anal. Calcd. for C 4 8 H 5 1 I r N P 3 S i 2 : C' 5 8 - 6 6 ' H ' 5 - 1 9 ' N' 1 - 4 2 ' F o u n d : c» 58.74; H, 5.20; N, 1 .34. [Ir(C gH 1 2)N(CgH 5CH 2)(SiMe 2CH 2PPh 2)] . Preparation of the complex was carried out in an identical manner to that outlined for i t s rhodium analogue. Y i e l d : 91%. Anal. Calcd. for C 3 QH 3 7IrNPSi: C, 54.38; H, 5.59; N, 2.11. Found: C, 54.10; H, 5.36; N, 1.91. 3 1 P{ ] H}NMR( CgDg): 21.28 (s) . -1 46-[Ir(PMe 3)N(SiMe ?CH ?PPh ?) ?]. The synthesis of th i s complex was carried out as described for i t s rhodium analogue (Method 2). Y i e l d : 82%. Anal. Calcd. for C 3 3 H 4 5 I r N P 3 S i 2 : C, 49.75; H, 5.65; N,1 -76. Found: C, 49.77, H. 5.78; N, 1.68. 3 1P{ 1H}NMR(C 6D 6): PPH 2, 24.10 ( d , J p p h j P M e = 28.4); PMe3, -51.17(f) 2 3 -14 7-Hydrogenation Procedure A typical run was carried out in a 250 ml heavy-walled flask f i t t e d with a Kontes 9 mm needle-valve i n l e t , attached d i r e c t l y to a vacuum l i n e which had access to vacuum and puri f i e d hydrogen (passed through MnO on 17*"? vermiculite and activated molecular sieves ). Reaction temperature was maintained at 22°C through the use of a glass water-jacket attached to a Haake temperature c o n t r o l l i n g u n i t . Samples were withdrawn via syringe and separated from the catalyst (via vacuum transfer) prior to GLC analysis. Iridium(III) Amido Phosphine Dihydrides and Amine Trihydrides  [Ir(H) 2N(SiMe 2CH 2PPh 2) 2]. A solution of [Ir(C gH 1 4)N(SiMe 2CH 2PPh 2) 2] (0.17 g, 0.20 mmol) in toluene (20 ml) was s t i r r e d under 1 atm. dihydrogen for 1 h. During t h i s time period, the solution's o r i g i n a l deep orange color faded to a clear yellow. Upon removal of excess H 2 in vacuo, the solution immediately deepened to a clear orange color. The solvent was pumped o f f and the o i l y residue r e c r y s t a l l i z e d from toluene/hexane. Y i e l d : 0.12 g (87%). Anal. Calcd. for C 3 0 H 3 8 I r N P 2 S i 2 : C, 49.86; H, 5.26; N, 1.94. Found: C, 50.20; H, 5.56; N, 2.00. IR(KBr): v J r _ H = 2200 (m). 3 1P{ 1H}NMR(C gD 6):23.9 (s) . mer-[Ir(H) 3NH(SiMe 2CH 2PPh 2) 2]. Since t h i s trihydride derivative i s stable 1 31 only under dihydrogen, H and PNMR measurements were made by sealing C 6D 6 solutions of [Ir(C gH 1 4)N(SiMe 2CH 2PPh 2) 2] or [Ir(H) 2N(SiMe 2CH 2PPh 2) 2] (M0 mg) under 1 atm H 2 in NMR tubes. Infra-red spectra were recorded by tran s f e r r i n g , under H 2 , a sample (formed after s t i r r i n g -148-[Ir(CgH 1 4)N(SiMe 2CH 2PPh 2) 2] i n CgDg under 1 atm H 2 for 1 h) to a solution IR c e l l (NaCl, 0.1 mm). IR(CgDg): v N _ H = 3210 (w); v J r _ H = 2175 (m), 1705 ( s ) . 3 1 P ]H NMR(CgDg): 11.44 ( s ) . fac-[Ir(H) 3NH(SiMe 2CH 2PPh 2) 2]. The apparatus for t h i s reaction consisted of a Schlenck-type f r i t assembly to which was attached two 100 ml round bottomed f l a s k s . A l l manipulations were carried out on a high vacuum l i n e . A clear orange solution of [Ir(C gH 1 4)N(SiMe 2CH 2PPh 2) 2] (0.17 g, 0.20 mmol) in pentane (60 ml) (vacuum-transferred from sodium benzophenone ketyl d i r e c t l y into the reaction flask) was vigorously s t i r r e d for 3 h under 1 atm. H 2 > After ^1 h, the solution lightened in volor to a pale yellow and, after 2 h, a fine yellow precipitate formed. The precipitate was f i l t e r e d and washed several times with pentane. Y i e l d : 0.10 g (70%). Anal. Calcd. for C 3 0 H 4 Q I r N 0 2 S i 2 : C, 49.72; H, 5.52; N, 1.93. Found: C, 49.86; H , 5.66; N, 1.97. IR(KBr) : v N _ R = 3200 (w); v I r _ H = 2115 (m), 2180 (w). mer-cis-[Ir(H) 2(C0)N(SiMe 2CH 2PPh 2) 2]. A solution of [Ir(H) 2N(SiMe 2CH 2-PPh 2) 2] (0.07 g, 0.1 mmol) in toluene (10 ml) was s t i r r e d under 1 atm. CO for 15 minutes. The solution became almost colorless within seconds of exposure to CO. The solvent was removed in vacuo and the product r e c r y s t a l -l i z e d from hexanes. Y i e l d : 64 mg (86%). Anal. Calcd. for C 3 i H 3 g I r N 0 P 2 S i 2 : C, 49.60; H, 5.07; N, 1.87. Found: C, 49.90; H, 5.13; N, 1.90. IR(KBr): v I r _ H = 2075 ( s ) , 1 925 ( s ) ; v C Q = 1965 ( s ) . 31P{1H}NMR(CgDg) : 24.29 ( s ) . mer-trans-[Ir(H) 2(C0)N(SJMe 2CH 2PPh 2) 2]. To a solution of [ I r ( C g H 1 4 ) N ( S i -Me 2CH 2PPh 2) 2] (0.08 g, 0.1 mmol) in toluene (25 ml) was added s o l i d (HCH0)n (10 mg, 0.3 mmol). The suspension was s t i r r e d at room temperature -149 -for 24 h, during which time the original orange color faded to a pale yellow. The solvent was removed in vacuo. The product was extracted with hexanes, filtered through Celite, and pumped down. Recrystallization from hexanes produced small yellow crystalline clusters. Yield: 53 mg (71%). Anal. Calcd. for C 3-,H 3 8IrN0P 2Si 2: C, 49.60; H, 5.07; N, 1.87. Found: C, 50.00; H, 5.15; N, 1.88. IR(KBr): v C Q = 1990 (vs), v J r _ H = 1725 (s). 31P{1H}NMR(C6D6): 9.68 (s). mer-[Ir(H)2(PMe3)N(SiMe2CH2PPh2)2]. To a solution of [Ir(H)2N(SiMe2CH2-PPh2)2] (0.07 g, 0.1 mmol) in toluene (10 ml) was added an excess of PMe3 (10 y £ , 0.15 mmol) via syringe. The initial orange color faded slightly upon addition of the phosphine. After standing at room temperature for 15 minutes, the solvent was removed in vacuo and the product recrystallized from hexanes. Yield: 0.07 g (88%). Anal. Calcd. for C 3 3 H 4 7 I rNP 3 Si 2 : C, 49.62; H, 5.89; N, 1.75. Found: C, 50.00; H, 6.00; N, 1.74. IR(KBr): v I r _ H = 2110 (s, br). 31P{1H}NMR(C6D6): PPh2, 11.00 (d, 2 J p M e 3 > p p h 2 =19.0); PMe3, -56.83 (t, br). fac-[Ir(H)2(PMe3)N(5iMe2CH2PPh2)2]. A solution of [Ir(PMe3)N(SiMe2CH2-PPh 2) 2] (0.08 g, 0.1 mmol) in toluene (10 ml) was stirred under 1 atm. H2 for 0.5 h at room temperature. Within minutes, the solution had become virtually colorless. The solvent was pumped off, yielding a beige solid. Recrystallization from hexane resulted in off-white blocks. Yield: 64 mg (90%). Anal. Calcd. for C 3 3 H 4 7 I rNP 3 Si 2 : C, 49.62; H, 5.89; N, 1.75. Found: C, 49.91; H, 5.87; N, 1.84. IR(KBr): v J r _ H = 2065 (s), 2020 (s). 31P{1H}NMR(C6D6): PPh2, -1.67 (br d, 2 J p M e p p h = 9.0); PMe3, -51.62 (t). - 1 5 0 -fac^-[Ir(H)2(PPh3)N(SiMe2CH2PPh2)2] • T n i " s complex was prepared as outlined (vide supra) for its PPh3 analogue. Recrystallization from hexane produced colorless needles; the recrystallized yield was rather low (65%) owing to loss of H 2 in solution with re-formation of the starting material. Anal. Calcd. for C 4 8H 5 3 I rNP 3 Si 2 : C, 58.54; H, 5.39; N, 1.42. Found: C, 58.20; H, 5.39; N, 1.22. 3 1P}NMR(CgDg): PPh3, 10.50 (jnl; pph.2, -8.19 (ml. •tf »••• II en •tf o • •> en m C J • • o • US II n • i o • l l m r o C J II i n CM n II Q_ OJ C J F— " 3 *o • a . r o en *— fmm. C J .» m o r-«. • n < •> •""3 CM ( " • o C J C J • •« CTl i n — •>— • •« • II II I-. o • i n m i n CO f — •— •tf r— r— •> * II II i— r v II CM CO c o r o I' ll * r -> •> r o n r o n Q. * C J C J • CM * C J i — •* - 3 •"3 a. C J a. CO • r— r. — . ~3 •> •o •a •t r— • CM * •o _e E •o T3 •D E E E CO LT) C J i n r — CO cn •tf cr» o 00 o c o •-^  r o c n r o 00 c o i n i n •tf U 3 m i n «!• r o CM CO C J r o CM CO X 3 : 3 : 3 : X 3 C ZC C J / \ X OJ E E JQ c n CO a. a. cj CO , ^  ro +J OJ E O ro J= U 4-> ro i -a. O B E '— '—' m m cn U3 CO CM o 113 o m o o o o o m | h > o r o N i n c s j i c o II II it n n n n E CL E a- E Q- E cu * QJ - ai • OJ _ s i x cnx cn 3 ; cn C J C J C J ai o c j o CO o o II O-U3 •• t f o c j C J r o x CJ C J C J , C J II II a. Q. X X . . , •tf E * " C J . CO t en r-— C J • U3 • * "? i n •• 3 Z | X x l vi x l 1 0 <-> 0 <_) (-> 0 0 0 O u 0 O . s ro ro ro ra *-> 4-> 4-> 4-> Ol 01 o> OJ E '—• E — • E " E ^ — 0 O — O ^ 0 ro J= ra J= ra J= ro - C 1- -t-> i. 4-> ( . 4-> ra i - ro I . ro I- ro l -O . O O . 0 Q . 0 a. 0 E E E E E E E E C J C J i n 0 <M 1— C J -tf cn m C J 0 r— C J 0 r ~ U3 r-~ 00 r*. CO i n 0 r ~ cn i n r -. , ,—^ i n 0 >—-B 4-) • C J n ID u i • s- t. r — U3 ^3 J 3 11 11 11 E Q. a . II r o C J E a a O . cn CO cn ro ro Q. - 3 * 0 ro f— r— •> •« •!-> •!-> -a -z> •sr 0 i n i n co ' r -irt l / l tri r o O i. r— m •tf 0 r o J 3 0 * C J 0 O to 0 0 O 1 i C J C J J= 0 . C J C J 0 . C J C J C J C J X J= C J JZ 0 a. J= a. C J 0 . 0 . 0 . a i C J a . C J 3Z X C J X (_> X 0 on C J l_) C J 01 C J 01 . » sz 0J 5Z JZ £ T— 0 . 00 0 * ' » <-> z » - zr z z r o * . r o C J X J= X ^ (_> a. <-> 0 0 0 0 0 <-> 0 T J z z z Q. T a b l e J J . 1 HNMR Data (( a) recorded at 45°C) S1-CH 3 CH^P Other [ I r ( C 8 H l 4 ) N ( S 1 M e 2 C H 2 P P h 2 ) 2 ] * a ) 0.10 (s) 1.80 ( t , = 4.2) 7.08 (ra, 7.82 (m, para/meta) ortho) C ^ H . . : 1.25 (br m) 6 - 1 4 2.15 (br m) [ I r (CO)N(SiMe 2 CH 2 PPh 2 ) 2 ] 0.20 (s) 1 . 7 8 ( 1 , ^ = 5.9) 7.00 (m, 7.95 (m, para/meta) ortho) [ I r (PMe 3 )N(S1Me 2 CH 2 PPh 2 ) 2 ] 0.15 (s) 1.82 ( t , ^ p p = 5.0) 7.07 (m, 8.07 (m, para/meta) ortho) P(CH3) 3 : 0.80 (d , J P j C H = 8.6) [ I r (PPh 3 )N(S iMe 2 CH 2 PPh 2 ) 2 ] 0.20 (s) 1.82 ( t , = 4.5) 6.93 (m, 7.65 (in, para/meta) ortho) P ( C 6 H 5 ) 3 : 6.76 (m) [Rh(C g H 1 2 )N (C 6 H 5 CH 2 ) (S iMe 2 CH 2 PPh 2 ) ] 0.04 (s) 1 - 5 7 < d d ' ^ h , C H 2 = 0 - 9 8 ' ip.qfc = 1Z-7.) 7.05 (m, 7.60 (m, para/meta) ortho) C a J , , (endo/exo CH, ) : 2.02 (br m), 8 - 1 ' 2.17 (m), 2:28 (m). CgH 1 z (=CH): 2.97 (br s ) . 5.19 (br s ) . CH^CgHg: 4.60 (s) C H 2 C g H 5 : 7.09 (m), 7.25 (m). tIr (C g H 1 2 )N(C 6 H 5 CH 2 ) (S1Me 2 CH 2 PPh 2 ) ] -0.04 (s) 1-55 (d. - 12.7) 7.20 (m, para/meta) CgH_12 (endo/exo CH^: 1.74 (br m), 2.15 (m), 1.16 (m). C g H 1 2 (=CH): 2.55 (m), 4.83 (m). CH^CgHg: 4.95 ( s ) . O^CgHg: 7.37 (m). [Rh(C0)N(SiMe 2 CH 2 PPh 2 ) 2 ] 0.22 (s) 1 . 7 3 ( 1 , ^ = 5.0) 7.02 (m, 7.82 (m, para/meta) ortho) [Rh(CgH 1 4 )N(SiMe 2 CH 2 PPh 2 ) 2 ] 0.10 (s) 1-77 (d t , J^pp = 4 .2 , 7.09 (m, 7.81 (m, para/meta) ortho) 2.21 ( br m) 2.79 (br m) [Rh(C 2 H 4 )N(S iMe 2 CH 2 PPh 2 ) 2 ] 0.26 (s) 1.78 (t.Japp = 4.5) 7.11 (m, 7.78 (m, para/meta) ortho) C ^ : 2.24 ( d t , J R n > C 2 H 4 = 1.75, J p ^ H j = 4.0) [Rh(PMe 3 )N(S1Me 2 CH 2 PPh 2 ) 2 ] 0.11 (s) 1.82 ( t , ^ p p = 4.8) 7.10 (m, 7.99 (m, para/meta) ortho) P(CH3) 3 : 0.62 (dd, J p > c „ 3 = 8 . 1 , J„h,CH3 = ^ [Rh(PPh 3 )N(S' iMe 2 CH 2 PPh 2 ) 2 ] 0.24 (s) 1.92 ( t , ^ p p = 4.1) 7.00 (m, 7.66 (m, para/meta) ortho) PfCgHgJj: 6.86 (m) 1 r Ta bl e l L H^NMR Data SI-CH3 CHoP ( C g H ^ P Other Ir(H) 2N(S1Me 2CH 2PPh 2) 2 0.24 (s) 1.89 (t,J a p p=5.2) 7.02(m,para/meta) 7.92(m,ortho) Ir-H, -24.86 ( t , 2 J H p =13.2) mer-TfrH)3NH(S1Me2CH2PPh2)2 fac-TrTH)3NH(S1Me2CH2PPh2)2 -0.02 (s) 0.05 (s) 0.23 (s) 0.25 (s) 1.70 (dt ,J a p p = 4.9, 'gem ,=14.1) 2.36 (dt ,J a p p = 4.1) 1.91 (dd , 2 J H p=9.0, ' -14.1) "gem' mer-cis- 4 ° - 3 1 ^ TrTHT2TC0)N(SiMe2CH2PPh2)2 „ 3 4 ( s ) 2.09 (dd, 2J H > P=11.0) 1.80 (dt ,J a p p = 5.4 J„^=13.8) gem 2.09 (dt ,J a p p = 6.5) 6.99'.7.12(m,para/meta) 8.20,8.35(m,ortho) 6.98(m,para/meta) 8.28(m,ortho) 6.96,7.04(m,para/meta) 7.70,7.95(m,ortho) Ir-H, -8.99 ( td , 2 J p H =19 .5 , 2 J H H =5 .0 ) -9.69 (td, 2J PjH=18.0) -24.6 ( t t , 2 J p H =15.5) Ir-HA(trans to PPh 2), -8.5 (m, from spectral simulation of AA'MXX' pattern: 2 J A A ' = 2 . 2 ; 2 J A M = 2 J A ' j H = 5 . 5 ; -19.0; 2 J M i X - V x - ^ . O ; 2 J A > r = JA,X 2 j A ' . X ' 2 j A : x = 130.0; 2 J X ) X ' = 1.0) Ir-Hjy, (trans to NH), -24.3 (tt) Ir-H (trans to CO), -7.86 (dt , 2 J H , p =17.6, Z J H , H = 4 - 4 > Ir-H (trans to N), -16.09 (dt , 2 J H p =12.5) mer-trans-TrTHT2TC0)N(S1Me2CH2PPh2)2 0.18 (s) 0.18 (s) fac-cis , 0.53 (s) T7rH77rPMe3)N(SiMe2CH2PPh2)2 2 - ° 4 ( t - J a p p 3 5 - 7 5 1.79 (dt ,J a p p = 5.2, Jg O T=13.0) 2 - 2 2 ( d t , J a p p - 5.2) 6.98(m,para/meta) 7.87(m,ortho) 6.95,7.05(m,para/meta) 7.83,8.14(m,ortho) mer-cis T7THT^PMe 3 )N (S iMe 2 CH 2 PPh 2 ) 2 0.32 (s) 0.72 (s) 1.95 (m) 2.05 (m) 6.89(m,para/meta) 7.08(m,ortho) Ir-H, -6.00 ( t , 2 J H p=14.7) P(CH 3 ) 3 , 0.76 (d, 2 J H j P =8 .0 ) ' Ir-H (trans to PPH 2), -10.21 (ddt, 2 J H p ( c 1 s H 7 . 6 ; 2 J H p ( trans' 135.0; 2JH,H=5.D ? 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Crystals were mounted on an Enraf-flonius CAD4-F d iffractometer in non-specific orientations. Final u n i t - c e l l parameters were obtained by least-squares on 2 sin 6 /A values for 25 reflections measured with MoKa-j radiation (X = 0.70930 A). A l l structures, were solved by conventional heavy-atom techniques. The computer programs used include l o c a l l y written programs, for data processing and l o c a l l y modified versions of the following: AGNOST, absorption correction from Northwestern University, ORFLS, f u l l -matrix least squares, and ORFFE, function and errors, by W.R. Busing, K.O. Martin, and H.A. Levy; FORDAP, Patterson and Fourier synthesis, by A. Zalkin ; ORTEP I I , i l l u s t r a t i o n s , by C.K. Johnson. Corrected bond lengths appear along with the uncorrected values in Tables VI to X , an corrected bond angles are es s e n t i a l l y equal to the uncorrected values l i s t e d in Tables XI to XV. Stereoscopic views of these structures are given on pages 174 and 175. —1 64— Table VI o Bond lengths (A) with estimated standard deviations i n parentheses [NiClN(SiMe 2CH 2PPh 2) 2] Bond uncorr. corr. Bond uncorr. corr, Ni Ni Ni Ni PO) P(D P(D -CI -PO) -P(2) -N -C(l) -C(7) •C(13) P(2) -C(2) P(2) -C(19) P(2) -C(25) S i ( l ) - N S i ( l ) - C ( l ) Si(l)-C(3) Si(l)-C(4) Si(2)-N Si(2)-C(2) Si(2)-C(5) Si(2)-C(6) C(7) -C(8) C(7) -C(12) C(8) -C(9) 2.1703(6) 2.2086(6) 2.1 975(5) 1 .924(2 1 .816(2 1 .825(2 1.817(2 1 .807(2 1 .824(2 1 .813(2 1.710(2 1.887(2 1 .859(3 1 .867(3 1 .713(2 1 .893(3 1 .857(4 1 .860(4 1.381(3 1 .387(3 1 .386(4 2.172 C(9) - c o o) 2.212 c ( i o ) -COD 2.201 C ( l l ) -C(12) 1.929 C(13) -C(l4) 1 .819 C(13) -CO 8) 1.830 C(14) -C(15) 1.822 C(15) -C(16) 1.810 C(16) -C(17) 1 .828 C(17) -C(l8) 1 .818 C(19) -C(20 1 .716 C(19) -C(24) 1.895 C(20-•C(21) 1.868 C(21) -C(22) 1.876 C(22] -C(23) 1 .721 C(23] -C(24) 1 .904 C(25] -C(26) 1.867 0(25 ' -C(30) 1 .872 C(26 )-C(27) 1 .389 C(27 )-C(28) 1 .394 C(28 )-C(29) 1 .390 C(29 )-C(30) 1.368(4 1.363(4 1.387(3 1.371(3 1.384(3 1.381(4 1.357(4 1.357(4 1 .384(4 1.389(3 1.381(3 1 .381(4 1.374(4 1 .368(4 1 .390(4 1.371(3 1 .381(3 1 .381(4 1 .364(4 1 .349(4 1 .385(4 1.374 1 .371 1 .391 1.384 1.395 1.384 1 .367 1.371 1 .387 1 .394 1 .390 1 .383 1 .383 1 .373 1 .392 1.381 1.39.5 1 .384 1.379 1 .356 1 .389 Unit-c e l l parameters: a = 10.091(3) b = 10.224(3) c = 17.237(4) a = 81.06(2) 8 = 78.51(2) Y = 65.93(3) Z = 2 R = 0.029 space group = PI —165— Table VII Bond lengths (A) with estimated standard deviations in parentheses [PdClN(.SiMe 2CH 2PPh 2) 2]-CH 3C 6H 5 Bond uncorr. corr. Pd - P ( D 2.3078(5) 2.311 Pd -P(2) 2.3112(5) 2.314 Pd -CI 2.3143(6) 2.317 Pd -N 2.063(2) 2.069 P ( D - c ( D 1 .805(2) 1 .809 P ( D -C(7) 1 .821(2) 1 .827 P ( D -C(13) 1 .819(2) 1 .823 P(2) -C(2) 1.807(2) 1 .811 P(2) -C(19) 1 .816(2) 1 .821 P(2) -C(25) 1.820(2) 1 .825 S i ( l ) -N 1.713(2) 1 .719 S i ( D -CCD 1.885(3) 1 .891 Si (IP -CC3) 1.873(3) 1 .881 SI C D -C(4) 1 .871(4) 1 .879 Si (.2) -N 1 .711(2) 1 .717 Si(2) -C(2) 1.885(3) 1 .892 Si(2) -C(5) 1.872(3) 1 .881 Si(2) -C(6) 1 .855(3) 1 .863 C(7) -C(8) 1 .374(4) 1 .390 C(7) -C(12) 1.370(4) 1 .383 C(8) -CC9) 1.388(4) 1 .394 C(9) -C(10) 1 .345(6) 1 .357 C(10) -C(.ll) 1 .360(6) 1 .376 C(1D -C(12) 1.386(4) 1 .391 C(13) -C(14) 1 .388(4) 1 .399 Bond uncorr. corr. C(13 C(14 C(15 C(16 C(17 C('l 9 C('l 9 C(20 C(21 C(22 C(23 C(25 C(25 C(26 C(27 C(28 C(29 C( 31 C(31 C(31 C(32 C(33 C(34 C(35 -C(l 8). 1 .372(3) 1 .388 -C(! 5) 1 .384(4) 1 .389 -C(l6) 1 .355(6) 1 .372 -C(17) 1 .359(5) 1 .370 -C(18) 1 .380(4) 1 .384 -C(20) 1 .392(3) 1 .402 -C(24) 1 .376(4) 1 .388 -C(21) 1.390(4) 1 .395 -C(22) 1.354(5) 1 .366 -C(23) 1 .373(5) 1 .382 -C(24) 1 .383(4) 1 .388 -CC.26) 1.380(3) 1 .394 -C(30) 1 .379(4) 1 .391 -C(27) 1.385(4) 1 .388 -C(28) 1 .361(5) 1 .372 -C(29) 1 .361(5) 1 .376 -C(30) 1.385(4) 1 .389 -C(32) 1 .396(6) 1 .413 -C(36) 1.367(5) 1 .386 -C(37) 1 .49.2(7) 1 .503 -C(33) 1 .359.(8) 1 .374 -C(34) 1 .383(8) 1 .400 -C(35) 1 .352(7) 1 .367 -C(36) 1 .365(6) 1 .379 Uni t - c e l l parameters: a = 11.538(2) b = 15.366(2) c = 10.951(1) a = 92.91(1) 3 = 104.10(1) Y = 84.75(1) Z = 2 R = 0.022 space group = Pi -1 66-Table VIII o Bond lengths (A) with estimated standard deviations in parentheses [NiCl 2NH(SiMe 2CH 2PPh 2) 2] Bond uncorr. corr. Ni •ci(D 2.2216(8) 2.2251 Ni CI (2) 2.2058(8) 2.2081 Ni •P(D 2.3180(7) 2.3202 Ni •P(2) 2.3469(7) 2.3502 P(D -•C(l) 1 .815(3) 1 .817 P(D • -C(7) 1.814(3) 1 .817 P(D • -C(13) 1.826(3) 1 .832 P(2) • -C(2) 1.817(3) 1 .820 P(2) • •C(19) 1.826(3) 1 .831 P(2) • -C(25) 1 .824(3) 1 .829 si ( i ) -N 1.718(2) 1 .724 Si ( D -C(l) 1.885(3) 1 .891 s i d ) -C(3) 1.859(4) 1 .866 S i ( l ) -C(4) 1.848(3) 1 .854 Si(2) -N 1.718(2) 1 .723 Si(2) -C(2) 1.886(3) 1 .892 Si(2) -C(5) 1.861(3) 1 .868 Si(2) -C(6) 1.845(3) 1 .851 C(7) -C(8) 1 .390(4) 1 .397 C(7) -C(12) 1.382(4) 1 .388 C(8) -C(9) 1 .373(4) 1 .376 Bond uncorr. corr, C(9) -c(io) 1 .373(5) 1 .379 C(10) - C ( l l ) 1 .377(5) 1 .383 c(n) -C(12) 1 .390(4) 1 .392 C(13) -C(14) 1 .394(5) 1 .403 C(13) -C(18) 1 .373(5) 1 .382 C(14) -C(15) 1 .397(5) 1 .402 C(15) -C(16) 1 .360(7) 1 .370 C(16) -C(17) 1 .363(7) 1 .371 C(17) -C(18) 1 .389(4) 1 .393 C(19) -C(20) 1 .392(4) 1 .400 C(19) -C(24) 1 .389(4) 1 .396 C(20) -C(21) 1 .389(5) 1 .393 C(21) -C(22) 1 .376(6) 1 .382 C(22] -C(23) 1 .357(5) 1 .365 C(23] -C(24) 1 .390(4) 1 .394 C(25] -C(26) 1 .390(4) 1 .398 C(25 -C(30) 1 .384(4) 1 .395 C(26 -C(27) 1 .367(4) 1 .370 C(27 )-C(28) 1 .367(5) 1 .379 C(28 )-C(29) 1 .366(5) 1 .373 C(29 )-C(30) 1 .384(4) 1 .387 Unit-c e l l parameters: a = 10.224(7) b = 10.5769(8) c = 17.770(2) a = 72.978(6) @ = 78.424(6) Y = 61 .864(8) Z = 1 .356 R = 0.031 space group = Pl —167— Table IX Bond Lengths (A) with estimated standard deviations in parentheses [Ni(C0)N(C0C 2H 3)(SiMe 2CH 2PPh 2) 2] Bond Length(A) Ni -P(l) 2:214(3) Ni -P(2) 2.244(3) Ni -C(3) 1.731(15) Ni -C(9) 2.08(2) Ni -C(10) 2.083(13) P ( l ) - C ( l ) 1.838(11) P(D-C(11) 1 .842(13) P(D-C(17) 1.848(11) P(2)-C(2) 1 .798(11 ) P(2)-C(23) 1 .869(13) P(2)-C(29) 1.848(11) S i ( l )-N 1 .729(14) S i ( l ) - C ( l ) 1 .859(13) Si(l)-C(4) 1.862(15) Si (D-C(5) 1.847(15) Si(2)-0(1) 1.687(11) Si(2)-C(2) 1.911(13) Si(2)-C(6) 1.846(14) Si(2)-C(7) 1.806(15) 0(1)-C(8) 1.393(15) 0(2)-C(3) 1 .164(14) N -C(8) 1.31(2) C(8)-C(9) 1.46(2) C(9)-C(10) 1.35(2) Un i t - c e l l parameters: a = 16.2396 (3 = b = 11.5336 c = 19.0764 Bond Length(A) c( 11)-C(12) 1.346(15) c< n ) - c(i6) 1 .37(2) c( 12)-C(13) 1.39(2) c( 13)-C(14) 1 .32(2) c( 14)-C(15) 1.38(2) c( 15)-C(16) 1.39(2) c( 17)-C(18) 1 .423(13) c( 17)-C(22) 1.362(13) C( 18)-C(19) 1.41(2) c( 19)-C(20) 1.40(2) c 20)-C(21) 1.369(15) c( 21 )-C(22) 1.414(14) c( 23)-C(24) 1.385(15) c( 23)-C(28) 1 .343(1 5) c( 24)-C(25) 1.37(2) c( 25)-C(26) 1.35(2) c( 26-C(27) 1 .34(2) c( 27)-C(28) 1 .38(2) c( 29)-C(30) 1.424(15) c( 29)-C(34) 1.366(14) C' 30)-C(31) 1.40(2) c( 31)-C(32) 1 .31(2) C( 32-C(33) 1.41(2) c( 33)-C(34) 1.409(1 5) 392 space group = P2 ] /n Z = 4 R = 0.050 -1 68-Table X Bond lengths (A) with estimated standard deviations in parentheses fac-rir(H). 2CPMe 3lNCSiMe 2CH 2PPh 2) 2] Bond Uncorr, Bond Uncorr. Ir -P(D 2.366(2) l r -P(2) 2.343(3) I r -P(3) 2.235(3) Ir -N 2.211(8) P(l) -C(l) 1.806(9) P(D -C(7) 1.826(9) P(D -C(13) 1.846(9) P(2) -C(2) 1.847(10) P(2) -C(19) 1.839(12) P(2) -C(25) 1.843(10) P(3) -C(31) 1.802(12) P(3) -C(32) 1.82(-) P(3) -C(33) 1.813(15) Si ( D -N 1.705(9) SKI ) -C(l) 1.913(9) S i ( l ) -C(3) 1.864(11) si( i ) -C(4) 1.883(11) Si(2) -N 1.671(8) Si(2) -C(2) 1.892(10) Si(2) -C(5) 1.900(11) Si(2) -C(6) 1.873(12) C(7) -C(8) 1.400(14) C(7) -C(12) 1.391(13) C(8) CO) C(10 c(n C(13 C(13 C(14 C(15 C(16 C(17 C(19 C(19 C( 20 C(21 C(22 C(23 C(25 C(25 C(26 C(27 C(28 C(29 -C(9) -C(10) )-c(ii) )-C(12) )-C(14) )-C(18) )-C(15) )-C(16) )-C(17) )-C(18)" )-C(20) )-C(24) )-C(21) )-C(22) )-C(23) )-C(24) )-C(26) )-C(30) )-C(27) )-C(28) )-C(29) )-C(30) 1 .36(2 1 .36(2 1 .34(2 1 .392( 1.377( 1 .346( 1.39(2 1 .38(2 1 .38(2 1 .37(2 1 .40(2 1.37(2 1 .37(2 1 .42(2 1 .33(2 1 .43(2 1.41(2 1 .358( 1 .37(2 1 .39(2 1 .36(2 1 .37(2 5) 5) 4) 4) Uni t - c e l l parameters: a = 19.858(2) 6 = 112.330(4) Z = 4 b = 10.5744(5) R = 0- 0 3 0 c = 18.564(2) s P a c e 9 r 0 UP = C c -16 9-Table XI Bond angles (deg) with estimated standard deviations in parentheses lNiClN(SiMe 2CH 2PPh 2) 2] Bonds Angle(deg) Bonds Angle(.deg) CI -Ni -pd) 95.40(2) P(2) -c( .2) -Si(2) 104.36(12) CI -Ni -P(2) 93.74(2) P(.D -c( 7) -C(8) 124.1(2) CI -Ni -N 178.16(6) P(.D -c( 7) -C(12) 116.8(2) p(l) -Ni -P(2) 167.72(2) C(8) -c( 7) -C('12) 119.1(2) p(i) -Ni -N 85.96(6) C(7) -c( 8) -C(9) 120.1(3) P(2) -Ni -N 85.10(5) C(8) -c( .9) -C(10) 120.2(3) Ni -P(l) -cd) 102.96(9) C(9) -c( 10) - C ( l l ) 120.3(3) Ni -P(l) -C(7) 120.11(7) c(io) -c( 11) -C(12) 120.2(3) Ni -P(l) -C(13) 115.14(7) C(7) -c( 12) - C ( l l ) 120.1(2) cd) -P(l) -C(7) 105.73(10) P(D -c( 13) -C(14) 118.8(2) C(l) -p(i) -C(.13) 107.27(11) pd) -c( 13) -C(18) 123.0(2) C(7) -pd) -C(13) 104.67(10) C(14) -c( 13) -C(18) 118.2(2) Ni -P(2) -C(2) 106.98(8) C(13) -c( 14) -C(15) 120.3(2) Ni -P(2) -C(19) 121.29(7) C(14) -c( 15) -C(16) 121.0(3) Ni -P(2) -C(25) 106.46(7) C(15) -c( 16) -C(17) 119.7(3) C(2) -P(2) -C(19) 108.49(11) C(16) -C 17) -C(18) 120.0(3) C(2) -P(.2) -C(25) 108.56(11) C(13) -c( 18) -C(17) 120.9(3) C(19) -P(2) -C(25) 104.54(9) P(2) -c( 19) -C(20) 119.3(2) N - S i ( l ) -C(l) 104.15(9) P(2) -C( 19) -C(24) 122.1(2) N - S i ( l ) -C(3) 114.6(2) C(20) -c( 19) -C(24) 118.5(2) N - S i ( l ) -C(4) 114.87(15) C(19) -C( 20) -C(21) 121 .0(2) Ci (D - S i ( l ) -C(3) 107.4(2) C(20) -c( 21) -C(22) 119.9(2) c(D - S i ( l ) -C(4) 108.3(2) C(21) -C 22) -C(23) 119.9(3) C(3) - S i ( l ) -C(4) 107.2(2) C(22) -C{ 23) -C(24) 120.5(3) N -Si(2) -C(2) 105.15(9) C(19) -C( 24) -C(23) 120.2(2) N -Si(2) -C(5) 1.13.8(2) P(2) -c [25) -C(26) 118.1(2) N -Si(2) -C(6) 112.7(2) P(2) -c [25) -C(30) 123.5(2) C(2) -Si(2) -C(5) 108.6(2) C(26) -c .25) -C(30) 118.4(2) C(2) -Si(2) -C(6) 107.4(2) C(25 -c 26) -C(27) 121 .2(3) C(5) -Si(2) -C(6) 108.8(3) C(26) -c [27) -C(28) 119.6(3) Ni -N - S i ( l ) 118.02(9) C(27) -c [28) -C(29) 120.0(3) Ni -N -S1(2) 113.83(10) C(28) -c [29) -C(30) 121 .0(3) S K I ) -N -Si(2) 128.13(10) C(25) -c [30) -C(29) 119.7(3) P(D -cd) - S i ( l ) 105.70(12) -1 7 0 -Table XII Bond angles (deg) with estimated standard deviations in parentheses [PdClN(SiMe2CH2PPh2)2] -CHgCgHg Bonds Angle(deg) Bonds Angle(deg) P(2) -Pd -P(2) 177.11(2) C ,7) -c( 8) -c( 9) 119.9 [3) PO) -Pd -CI 90.56(2) C( 8) -C( 9) -c( 10) 121.0< 4) P(D -Pd -N 88.66(5) C( 9) -c( 10) -C 11) 120.1 [3) P(2) -Pd -CI 91.29(2) c( 10) -c( 11) -c( 12) 119.4( 4) P(2) -Pd -N 89.47(5) c( 7) -c( 12) -c( 11) 121.3( 3) CI -Pd -N 179.04(5) p( 1) -c( 13) -c( 14) 120.6 [2) Pd - P O ) -C(l) 106.77(8) p 1) -c( 13) - c ( 18) 121 .0 2) Pd -PO) -C(7) 120.39(7) c( 14) -C( 13) -c( 18) 118.4 2) Pd - P O ) -C(13) 111.94(7) c( 13) -C( 14) -c( 15) 120.3 ,3) C ( l ) -PO) -C(7) 108.28(11) c( 14) -c( 15) -c( 16) 120.4( 3) C ( l ) - P O ) -C(13) 104.93(11) c( 15) -c( 16) -c( 17) 119.7( 3) C(7) - P O ) -C(13) 103.52(11) c 16) -c( 17) -C 18) 120.9 3) Pd -P(2) -C(2) 105.88(8) c( 13) - c 18) -c( 17) 120.3( 3) Pd -P(2) -C(19) 115.27(8) p( 2) -c( 19) -c( 20) 121 .5 2) Pd -P(2) -C(25) 116.38(7) p( 2) -c( 19) -C( 24) 119.0( 2) C(2) -P(2) -C(19) 107.97(12) c( 20) -c( 19) -c( 24) 119.4( 2) C(2) -P(2) -C(25) 107.03(11) c( 19) -c( 20) -c( 21) 119.4( 3) C(19) -P(2) -C(25) 103.85(10) c( 20 -C( 21) -c( 22) 120.7( 3) N - S i O ] - C O ) 105.61(10) c( 21) -C( 22) -c( 23) 120.1( 3) N - S i ( l )-C(3) 113.59(15) c 22) -C( 23) -c( 24) 120.2 ,4) N - S i ( l )-C(4) 113.7(2) c( 19) -c( 24) -c( 23) 120.1 ,3) c(i) - S i ( l )-C(3) 109.2(2) p 2) -c( 25) -c( 26) 123.2 [2) c(D -S1(V -C(4) 106.1(2) P( 2) -c( 25) -CI 30) 118.6 [2) C(3) - s i ( i ; -C(4) 108.3(2) c( 26) -c( 25) -c( 30) 118.2 2) N - S i (2 )-C(2) 105.66(10) c( 25) -c( 26) -c( 27) 120.1( 3) N - S i (2 )-C(5) 112.90(15) c( 26 -c( 27) -c( 28) 121 .1( 3) N - S i (2 )-C(6) 113.36(14) c( 27) -c( 28) -c( 29) 119.4 3) C(2) - S i ( 2 ] -C(5) 105.9(2) c( 28) -c( 29) -c( 30) 120.2 3) C(2) - S i (2 )-C(6) 109.8(2) c( 25) -c( 30) -c( 29) 121 .0 .3) C(5) - S i ( 2 , >-C(6) 108.9(2) c 32) -c( 31) -Ci 36) 117.3( 4) Pd -N - S i ( l ) 119.34(10) c( 32) -c( 31) -c( 37) 120.7( 4) Pd -N - S i ( 2 ) 118.39(9) c( 36) -c( 31) -c( 37) 122.0( 4) S i O ) -N - S i ( 2 ) 122.27(11) c( 31) -c( 32) -c( 33) 120.2 ,5) P O ) - C O ) - S i ( l ) 106.90(12) c 32) -c( 33) -c( 34) 121.1( 5) P(2) -C(2) - S i ( 2 ) 107.22(12) c( 33) -c( 34) -C( 35) 119.0 [6) P O ) -C(7) -C(8) 121.1(2) Ci 34) -c( 35) -c( 36) 120.1 [6) P O ) -C(7) -C(12) 120.6(2) c( 31) -c( 36) -c( 35) 122.4 ,4) C(8) -C(7) -C(12) 118.2(3) -1 71-Table XIII Bond angles (deg) with estimated standard deviations in parentheses [NiCl 2NH(SiMe 2CH 2PPh 2) 2] Bonds Angle(deg) Bonds Angle(deg) C l ( l ) - N i -CI (2) C l ( l ) - N i -P(l) C l ( l ) - N i -P(2) Cl(2)-Ni -P(l) Cl(2)-Ni -P(2) P(l) -Ni -P(2) Ni -P(l Ni - P ( l Ni -P(l C( l ) - P ( l C ( l ) - P ( l C(7)-P(l Ni -P(2 Ni -P(2 Ni -P(2 C(2)-P(2 C(2)-P(2 C(19)-P(2)-C(25) N - S i ( l N - S i ( l N -Si(1 C(l)-Si(l C(l)-Si(l C(3)-Si(l N -Si(2 N -Si(2 N -Si(2 C(2)-Si(2 C(5)-Si(2 S i ( l ) - N P(D-C(1 P{2)-C(2 C(D -C(7) -C(13) -C(7) -C( 13) -C(13) -C(2) -C(19) -C(25) C(19) C(25) C(D -C(3) -C(4) -C(3) -C(4) -C(4) -C(2) -C(5) -C(6) -C(5) -C(.6) -C(6) (Si(2) - S i ( l ) -Si(2) 130.36(3) 98.89(3) 103.33(3) 102.40(3) 105.81(3) 116.99(2) 118.46(10) 119.59(9) 103.94(8) 104.85(12) 105.05(13) 1 02.92(12) 116.15(10) 118.86(8) 109.17(8) 106.59(1 3) 102.34(12) 101 .53(11) 109.87(12) 111.8(2) 108.8(2) 105.5(2) 112.42(14) 108.5(2) 111 .12(12) 111.5(2) 110.24(15) 106.01(15) 108.7(2) 109.2(2) 134.1(2) 118.85(14) 120.94(15) P(D -C(7) P(D -C(7) C(8) -C(7) C(7) -C(8) C(8) -C(9) C(9) -C(10 C(10)-C(ll C(7) -C(12 P(l) -C(13 P(l) -C(13 C(14)-C(13 C(13)-C(14 C(14)-C(15 C(15)-C(16 C(16)-C(17 C(13)-C(18 P(2) -C(19 P(2) -C(19 C(20)-C(19 C(19)-C(20 C(20)-C(21 C(21)-C(22 C(22)-C(23 C(19)-C(24 P(2) -C(25 P(2) -C(25 C(26)-C(25 C(25)-C(26 C(26)-C(27 C(27)-C(28 C(28)-C(29 C(25)-C(30 -C(8) -C(12) -C(12) -C(9) -C(10) )-C( l l ) )-C(12) )-C( l l ) )-C(14) )-C(18) )-C(18) )-C(15) )-C(16) )-C(17) )-C(18) )-C(17) )-C(20) )-C(24) )-C(24) )-C(21) )-C(22) )-C(23) )-C(24) )-C(23) )-C(26) )-C(30) )-C(30) )-C(27) )-C(28) )-C(29) )-C(30) )-C(29) 120.5(2 120.5(2 118.9(3 120.5(3 120.6(3 119.6(3 120.3(3 120.2(3 119.4(2 121.4(2 119.1(3 119.4(4 120.4(4 120.4(4 120.1 (4 120.5(4 123.5(2 118.0(2 118.6(3 120.5(3 119.9(3 120.1(3 120.9(4 120.0(3 120.9(2 121 .2(2 117.9(2 121.2(3 120.7(3 119.0(3 121 .2(3 120.1(3 -1 72-Table XIV Bond angles (deg) with estimated standard deviations in parentheses [Ni(C0)N(C0C2H3)(.SiMe2CH2PPh2)2] Bonds Angle(deg) Bonds Angle(deg) )-P(l)-Ni P(l)-Ni P(l)-Ni P(l)-Ni P(2)-Ni P(2)-Ni P(2)-Ni C(3)-Ni C(3)-Ni C(9)-Ni Ni -P(l Ni -P(l Ni -P(l C(l)-P(l C(D-P(1 C(ll)-P( Ni -P(2 Ni -P(2 Nu -P(2 C(2)-P(2 C(2)-P(2 C(23)-P(2) N -Si( N -Si( N -Si( C(l)-Si( C(l)-Si( C(4)-Si( . 0(1)-Si(2) 0(1)-Si(2) 0(1)-Si(2) C(2)-Si(2) C(2)-Si(2) C(6)-Si(2) Si(2)-0(1) Si(l)-N P(l)-C(l)-P(2)-C(2)-Ni -C(3) P(2) C(3) C O ) c ( io ) C(3) C(9) C(10) C(9) C(10) C(10) C O ) C ( l l ) C(17) C ( l l ) C(17) C(17) -C(2) -C(23) -C(29) -C(23) -C(29) -C(29) - C ( l ) -C(4) -C(5) -C(4) -C(5) -C(5) -C(2) -C(6) -C(7) -C(6) -C(7) -C(7) -C(8) -C(8) S i ( l ) S i (2 ) -0(2) 106.50(12) 0(1) -C(8) -N 105.9(4) 0(1) -C(8) -C(9) 94.0(5) N C(8) -C(9) 124.8(5) Ni C(9) -C(8) 106.2(4) Ni C(9) -C(10) 112.2(5) C(8) -C(9) -C(10) 115.0(5) Ni c ( io ) -C(9) 129.1(7) P(D • c ( n ) -C(12) 95.9(6) P(D -• c ( n ) -C(16) 37.7(6) C(12)-• c ( n ) -CO 6) 118.9(4) C(1D-•C(12) -C(13) 116.8(4) C(12)-•C(13) -C(14) 114.1(4) C(.13)-•C(14) -C(15) 102.1(6) C(14)--C(15) -C(16) 101 .6(5) C(1D-•C(16) -C(15) 100.7(5) P(D • -C(17) -C(18) 120.6(4) PO) • •C(17) -C(22) 112.4(4) C(18)-•C(17) -C(22) 116.3(4) C(17). -C(18) -C(19) 104.3(6) C(18) -C(19) -C(20) 100.7(5) C(19). -C(20) -C(21) 99.9(5) C(20-C(21)--C(22) 104.2(6) C(17) -C(22) -C(21) 122.9(7) P(2) -C(23) -C(24) 100.0(7) P(2) -C(23] -C(28) 112.6(6) C(24) -C(23] -C(28) 107.6(6) C(23) -C(24 )-C(25) 108.1(6) C(24) -C(25 )-C(26) 106.2(5) C(25) -C(261 -C(27) 98.4(6) C(26) -C(27 )-C(28) 120.4(7) C(23) -C(28 )-C(27) 114.0(6) P(2) -C(29 )-C(30) 110.1(7) P(2) -C(29 )-C(34) 107.5(7) C(30) -C(29 )-C(34) 119.4(9) C(29) -C(30 )-C(31) 123.4(13) C(30) -C(31 )-C(32) 118.8(6) C(31) -C(32 )-C(33) 117.4(6) C(32) -C(34 )-C(34) 178.1(13) C(29) -C(34 )-C(33) 117.2(14) 112.9(14) 129.9(15) 105.0(10) 71 .4(10) 132(2) 70.9(9) 125.6(11) 118.7(12) 115.6(13) 121 .9(15) 121(2) 120(2) 117(2) 124.2(15) 118.1(10) 121.7(9) 120.2(11) 117.4(11) 121.8(11) 118.6(1.1) 120.5(11) 120.9(11) 119.7(12) 120.3(11) 120.0(13) 120.4(14) 118.2(15) 121(2) 121.0(15) 118.8(13) 120.8(10) 119.9(9) 119.3(11) 118.4(11) .9(14) .8(13) 118.0(13) 120.7(12) 121 121 -1 7 3-Table XV Bond angles (deg) with estimated standard deviations in parentheses fac-[Ir(H) 2(PMe 3)N(SiMe 2CH 2PPh 2) 2] Bonds Angle(deg) Bonds Angle(deg) P(l) - I r -P(2) 109.58(9) Ir -N -Si(2) 111 .7(4) P(l) - I r -P(3) • 104.75(9) S i ( l ) - N -S1(2) 131 .4( 5) P(l) - I r -N 78.9(2) PO) -c( 1) - S i ( l ) 106.1( 4) P(2) - I r -P(3) 100.24(10) P(2) -C( 2) -SK2) 110.0( 5) P(2) - I r -N 85.6(2) P(D -c( 7) -C(8) 119.5( 8) P(3) - I r -N 171.4(2) , P(D -c( 7) -C(12) 122.4( 7) Ir -P(l) -C(l) 102.7(3) C(8) -C( 7) -C(12) 118.0( 9) Ir -P(l) -C(7) 122.9(3) C(7) -C( 8) -C(9) 120.0( ID Ir -P(l) -C(13) 121 .3(3) C(8) -C( 9) - c(io) 121 .0( 11) C(l) -P(l) -C(7) 104.5(4) C(9) -C( 10) - C ( l l ) 120.6( 10) C(D -P(l) -C(13) 102.0(4) C(10)-C( 11) -C(12) 120.3( 11) C(7) -P(l) -C(13) 100.5(4) C(7) -C( 12) - C ( l l ) 119.9( 10) Ir -P(2) -C(2) 107.4(3) P(l) -c( 13) -C(14) 119.9( 7) Ir -P(2) -C(19) 124.0(4) p(D -c( 13) -C(18) 121 .0( 8) Ir -P(2) -C(25) 114.9(3) C(14)-C( 13) -C(18) 119.1( 9) C(2) -P(2) -C(19) 104.5(5) C(13)-C( 14) -C(15) 120.3( 10) C(2) -P(2) -C(25) 104.3(5) C(14)-C( 15) -C(16) 120.0( 12) C(19)-P(2) -C(25) 99.8(5) C(15)-C( 16) -C(17) 118.4( 12) Ir -P(3) -C(31) 116.9(4) C(16)-C( 17) -C(18) 120.4( ID Ir -P(3] -C(32) 115.0(6) C(13)-C( 18) -C(17) 121 .5( ID Ir -P(3] -C(33) 121 .0(5) P(2) -C( 19) -C(20) 117.9( 9) C(31)-P(3] -C(32) 100.7(8) P(2) -C( 19) -C(24) 122.8( 9) C(31)-P(3] -C(33) 101.1(7) C(20)-C( 19) -C(24) 119.3( 11) C(32)-P(3] -C(33) 98.8(11) C(19)-C( 20] -C(21) 121 .0 12) N -Si(13 -C(l) 106.2(4) C(20)-C 21 ] -C(22) 118.5 13) N - S i ( V -C(3) 112.7(5) C(21)-C (22] -C(23) 121 .1 J 2 ) N - S i ( i ; -C(4) 115.2(5) C(22)-C ,23] -C(24) 119.9 [13) C ( l ) - S i ( l )-C(3) 105.5(5) C(19)-C [24] -C(23) 120.1 :i2) C ( l ) - S i ( l )-C(4) 107.4(5) P(2) -C [25] -C(26) 118.2 r7) C(3)-Si(l )-C(4) 109.1(5) P(2) -C [25] -C(30) 124.8 (8) N -Si(2 )-C(2) 104.8(4) C(26)-C (251 -C(30) 117.0 HO) N -Si(2 )-C(5) 115.3(5) C(25)-C (26 )-C(27) 121 .7 (11) N -Si(2 )-C(6) 114.5(5) C(26)-C (27 )-C(28) 119.2 (12) C(2)-Si(2 )-C(5) 111 .9(5) C(27)-C (28 )-C(29) 119.4 (10) C(2)-Si(2 )-C(6) 104.5(5) C(28)-C (29 )-C(30) 120.9 (ID C(5)-Si(2 )-C(6) 105.5(6) C(25)-C (301 )-C(29) 121 .8 (11) Ir -N -SKD 113.0(4) -1 74--1 7 5 -P u b l i c a t i o n s : 1. Fryzuk,M.D.; MacNeil,P.A. Organometallics, in press. " S t e r e o s e l e c t i v e Formation of I r i d i u m ( I I I ) Amides and L i g a n d - A s s i s t e d H e t e r o l y t i c S p l i t t i n g of Dihydrogen." 2. Fryzuk,M.D.; MacNeil,P.A. O r g a n o m e t a l l i c s , TJj)83,2_,355 . "Amides of Rhodium and I r i d i u m S t a b i l i z e d a s H y b r i d M u l t i d e n t a t e Ligands." 3. Fryzuk,M.D.; MacNeil,P.A. O r g a n o m e t a l l i c s , 3^,82,1/1540. " A n c i l l a r y L i g a n d Rearrangements Promoted by the M i g r a t o r y I n s e r t i o n of Carbon Monoxide i n t o N i c k e l (II) Carbon Bonds." 4. Fryzuk,M.D.; MacNeil,P.A.; R e t t i g , S . J . ; Secco,A.S.; T r o t t e r , J . O r g a n o m e t a l l i c s , 1 , 9 1 8 . " T r i d e n t a t e Amidophosphine D e r i v a t i v e s of the N i c k e l T r i a d : S y n t h e s i s , C h a r a c t e r i z a t i o n , and R e a c t i v i t y of N i c k e l ( I I ) , P a l l a d i u m ( I I ) , and Pl a t i n u m ( I I ) amide Complexes." 5. Fryzuk,M.D.; MacNeil,P.A. J.Am.Chem.Soc.,1981,103,3592. "Hybrid M u l t i d e n t a t e Ligands. T r i d e n t a t e Amidophosphine Complexes of N i c k e l ( I I ) and P a l l a d i u m ( I I ) . " 6. Bosnich,B.; MacNeil,P.A.; Roberts,N.K. J.Am.Chem.Soc., "Asymmetric S y n t h e s i s . Asymmetric C a t a l y t i c Hydrogenation Using C h i r a l C h e l a t i n g Six-Membered Ring Diphosphines." ,198^,103,2273. 

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