Monomeric (Pentamethylcyclopentadienyl)iridium Imido Compounds: Synthesis, Structure, and Reactivity

Article abstract of DOI:10.1021/ja00006a026

The monomeric terminal imido complexes Cp*IrNR (Cp* = η⁵-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(η⁴-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.