MONOMERIC (PENTAMETHYLCYCLOPENTADIENYL)IRIDIUM IMIDO COMPOUNDS - SYNTHESIS, STRUCTURE, AND REACTIVITY

The monomeric terminal imido complexes Cp*IrNR (Cp* = eta-5-C5Me5; 1a, R = t-Bu; 1b, R = SiMe2t-Bu; 1c, R = 2,6-Me2C6H3; 1d, R = 2,6-i-Pr2C6H3) were prepared from [Cp*IrCl2]2 (2) and 4 equiv of the corresponding lithium amide LiNHR in THF. In addition, the complexes Cp*Ir(RNH2)Cl2 (3a, R = t-Bu; 3d, R = 2,6-i-Pr2C6H3) were made from an amine and [Cp*IrCl2]2 (2) and dehydrochlorinated with KN(SiMe3)2 to provide an alternate route to 1a,d. Efficient exchange occurred between 1a and arylamines, leading to 1c,d and tert-butylamine. tert-Butylimido complex 1a, a weak nucleophile, reacted with MeI to form [Cp*IrI2]2 and Me3Nt-Bu+I-. Coupling of the imido ligand in 1a with CNt-Bu and CO gave Cp*Ir(t-BuNCNt-Bu)(CNt-Bu) (4) and Cp*Ir(t-BuNCO)(CO) (5a), respectively. Cp*IrPPh3(t-BuNCO) (5b) was formed from 1a, PPh3, and CO. The bridging imido complex Cp*IrNt-Bu(dppePt) (6, dppe = 1,2-bis(diphenylphosphino)ethane) was prepared from 1a and dppePt(C2H4). Complex 1a and CO2 gave the cycloadduct Cp*Ir(Nt-BuOCO) (7a), which added PPh3 to form Cp*IrPPh3(Nt-BuOCO) (7b). Two equivalents of dimethylacetylenedicarboxylate reacted with 1a to yield the pyrrole complex Cp(Ir(eta-4-RCCRNt-BuRCCR) (8, R = CO2Me). Maleic anhydride was added to 1a to give Cp*Ir[Nt-BuC(O)CH=CHCO2] (9a), which reacted with CO to yield Cp*Ir(CO)[Nt-BuC(O)CH=CHCO2] (9b). Compounds 1a-d, 7a, and 8 were structurally characterized by X-ray diffraction; imido complexes 1a-d have short Ir-N distances and nearly linear Ir-N-C(Si) angles, consistent with the presence of a metal-nitrogen triple bond.