1462 zyxwvutsrqpo Organometallics 1991, 10, 1462-1479 Iridium Alkoxide and Amide Hydride Complexes. Synthesis, Reactivity, and the Mechanism of zyxw O-H and N-H Reductive Elimination David S. Glueck, Linda J. Newman Winslow, and Robert G. Bergman' Depertment of Chemistry, Univers& of California, Berkeley, California 94720 Received October 29. 1990 The ethoxy hydride complex Cp*IrPPh,(OEt)(H) (3, Cp* = q5-C5Me5) was prepared from Cp*IrPPh3C12 and sodium ethoxide in ethanol. Ethoxide 3 reacted with alcohols to form the alkoxy hyd,rides Cp*IrPPh,(OR)(H) (R = OCDzCD3, 6s; R = n-Pr, 6b; R = i-Pr; 6c; R = Ph, 6e) and with amines to give the amido hydrides Cp*IrPPh,(NHR)(H) (R = Ph, 8a; R = CH2Ph, 8b). The isopropoxide 6c! was characterized by X-ray diffraction (P2,lc; a = 11.7943 (13) A, zyxwvut b = 11.7467 (8) A, c = 20.3034 (27) A, B = 96.56 (l)O, zyxwvutsrqponmlkjihgfedcb V = 2794.5 (9) A,, 3642 unique data, 2979 for which P > 3a(P); R = 1.59%, R, = 2.08%, zy GOF = 1.378). Irradiation of complex 3 yielded ethanol and the phosphine-cyclometalated complex Cp*Ir- (PPh2C&)(H) (5a) in cyclooctane or a mixture of 5a and Cp*IrPPh,(Ph)(H) (5b) in benzene. The reaction of 3 with heterocumulenes afforded the products of insertion into the I d bond, Cp*IrPPh3(0C02Et)(H) (9), Cp*IrPPh,(S,COEt) (lo), and Cp*IrPPh3(RNC02Et) (R = Ph, lla; R = p-Tol, llb; R = Me, lllc). Similarly, CSz underwent insertion into the Ir-N bond of the amido hydrides 8a,b to form Cp*IrPPh3- (S2CNHR)(H) (R = Ph, 12a; R = CH2Ph, 12b). Reaction of MeNCO with 8a, however, gave Cp*IrPPh,(NPhC(O)NHMe)(H) (13b). The reaction of 3 with several two-electron donor ligands yielded ethanol and the Ir(1) compounds Cp*IrPPh,(L) (L = CO, 14; L = CzH4, 15; L = CN-t-Bu, 16; L = PPh, 17; L = PPh2Me, 18). The anilido hydride 8a underwent similar elimination reactions with these ligands to afford 14-18 and aniline; benzylamido hydride 8b reacted with PPh3 to give benzylamine and 17. Saturation kinetics were observed in all cases for the reaction of PPh, with 3 and 8a,b in toluene, suggesting that these alkoxy and amido hydride compoundsreversibly form an intermediate that is trapped by PPh3 to form 17 and alcohol or amine. Additional evidence is provided that supports the ring-slipped species (v3-C5Me5)IrPPh3(X)(H) (X = OEt, NHPh, NHCH2Ph) as the identity of this intermediate. Introduction The metal-carbon bond has by definition been the traditional focus of organometallic chemistry. Rational syntheses of metal alkyl complexes are now available; such fundamental processes as oxidative addition, reductive elimination, and migratory insertion have been extensively studied. Many homogeneous catalytic reactions that result in C-H or C-C bond formation proceed by combinations of such organometallic reactions.' Similarly, fundamental information on the preparation and reactivity of metal alkoxide and amide complexes is required to develop and understand catalytic processes resulting in the formation of H-heteroatom (0 or N) and C-heteroatom bonds. Alkoxy and amide coordination complexes and organo- metallic compounds of the early transition metals are well-known2 These species often contain robust M+ and M-N bonds, perhaps because of a favorable donor-ac- ceptor interaction between the heteroatom lone pair and an empty orbital of the metal.2 Bonds between low-valent late transition metals and 0 or N are less common; it has been proposed that the interaction between the hard ligand and the soft late metal is unfavorable and leads to weak metal-heteroatom bonds.' Studies of these complexes have also been hampered by their facile decomposition to metal hydrides by &elimination pathways. Indeed p- elimination of metal alkoxides is a classical route to hy- dride~.~ Recently, however, several stable late-transition- (1) Collman, J. P.; Hegedus, L. 5.; Norton, J. R.; Finke, R. G. zyxwvu Prin- ciples and Applicatiom of Organotranaition Metal Chemistry; Univer- sity Science Books: Mill Valley, CA, 1987; pp 279-669. (2) (a) Bradley, D. C.; Mehrotra, R. C.; Gaur, D. P. Metal Alkoxides; Academic Press: New York, 1978. (b) Lappert, M. F.; Power, P. P.; Sanger, A. R.; Srivastava, R. C. Metal and Metalloid Amides; Ellis Horwood: Chichester, U.K., 1980. (3) Chatt, J.; Shaw, B. L. J. Chem. SOC. 1962, 5075. (4) Recent review: (a) Alkoxides and amides: Bryndza, H.; Tam, W. Chem. Rev. 1988,88,1163. (b) Amides: Fryzuk, M. D.; Montgomery, C. D. Coord. Chem. Reo. 1989, 95, 1. metal alkoxide and amide complexes have been synthes- ized and their reactivity in~estigated;~ still, mechanistic information is sparse. We report here the preparation of $pentamethyl- cyclopentadienyl (Cp*) hydride complexes of iridium containing alkoxide and amide ligands, their wactivity, and mechanistic studies of their reductive elimination and in- sertion reaction^.^ These compounds, od the form Cp*IrPPh,(H)(X) where X = OR or NHR, enable direct comparison of the Ir-0 and Ir-N bonds to the corre- sponding Ir-C and Ir-H bonds in the complexes Cp*IrPR',(R)(H) (R' = Me, Ph), which have been exten- sively studied in our work on C-H activation of alkanes.s A few recent mechanistic studies have been carried out on late-metal alkoxide insertion reactions; almost nothing is known as yet about the mechanism of reactions of the late-transition-metal-amide bond. The alkoxiide investi- gations have focused largely on coordinatively unsaturated, square-planar da complexes. Atwood et al.'" investigated the Vaska-type complexes (PPh3)21r(CO)OR while Bryndzanvcexamined (dppe)Pt(Me)OR. In each case, the initial step of the insertions was postulated to involve coordination of a ligand at the vacant site. We expected that the coordinatively saturated iridium systenns consid- ered in this work might react by different patlhways. Results and Discussion Synthesis of Iridium Alkoxide Hydrides. hletathesis of metal halides with alkali-metal alkoxides is a classical route to metal alkoxides,8 but in organometallic chemistry (5) Synthesis of the alkoxy hydrides haa been published in preliminary form: Newman, L. J.; Bergman, R. G. J. Am. Chem. SOC. 1985,107,5314. (6) Bergman, R. G. Science 1984,223,902. (7) (a) Rees, W. M.; Churchill, M. R.; Fettinger, J. C.; At~vood, J. D. Organometallics 1986,4,2179. (b) Bryndza, H. E. Organometallics 1986, 4, 1686. (c) Bryndza, H. E. Organometallics 1985, 4, 406. (8) Reference 2a, pp 13-27. 0276-7333/91/2310-1462$02.50/0 0 1991 American Chemical Society