IRIDIUM ALKOXIDE AND AMIDE HYDRIDE COMPLEXES - SYNTHESIS, REACTIVITY, AND THE MECHANISM OF O-H AND N-H REDUCTIVE ELIMINATION

The ethoxy hydride complex Cp*IrPPh3(OEt)(H) (3, Cp* = eta-5-C5Me5) was prepared from Cp*IrPPh3Cl2 and sodium ethoxide in ethanol. Ethoxide 3 reacted with alcohols to form the alkoxy hydrides Cp*IrPPh3(OR)(H) (R = OCD2CD3, 6a; R = n-Pr, 6b; R = i-Pr; 6c; R = Ph, 6e) and with amines to give the amido hydrides Cp*IrPPh3(NHR)(H) (R = Ph, 8a; R = CH2Ph, 8b). The isopropoxide 6c was characterized by X-ray diffraction (P2(1)/c; a = 11.7943 (13) angstrom, b = 11.7467 (8) angstrom, c = 20.3034 (27) angstrom, beta = 96.56 (1)-degrees, V = 2794.5 (9) angstrom 3, 3642 unique data, 2979 for which F2 > 3-sigma-(F2); R = 1.59%, R(w) = 2.08%, GOF = 1.378). Irradiation of complex 3 yielded ethanol and the phosphine-cyclometalated complex Cp*Ir-(PPh2C6H4)(H) (5a) in cyclooctane or a mixture of 5a and Cp*IrPPh3(Ph)(H) (5b) in benzene. The reaction of 3 with heterocumulenes afforded the products of insertion into the Ir-O bond, Cp*IrPPh3(OCO2Et)(H) (9), Cp*IrPPh3(S2COEt) (10), and Cp*IrPPh3(RNCO2Et) (R = Ph, 11a; R = p-Tol, 11b; R = Me, 11c). Similarly, CS2 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*IrPPh3(NPhC(O)NHMe)(H) (13b). The reaction of 3 with several two-electron donor ligands yielded ethanol and the Ir(I) compounds Cp*IrPPh3(L) (L = CO, 14; L = C2H4, 15; L = CN-t-Bu, 16; L = PPh3, 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 PPh3 with 3 and 8a,b in toluene, suggesting that these alkoxy and amido hydride compounds reversibly 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 (eta-3-C5Me5)IrPPh3(X)(H) (X = OEt, NHPh, NHCH2Ph) as the identity of this intermediate.