Strongly Polarized Iridium(delta-)-Aluminum(delta+) Pairs: Unconventional Reactivity Patterns Including CO2 Cooperative Reductive Cleavage

摘要

The iridium tetrahydride complex Cp*IrH4 reacts with a range of isobutylaluminum derivatives of general formula Al(iBu)(x)(OAr)(3-x) (x = 1, 2) to give the unusual iridium aluminum species Cp*IrH3Al(Bu-i)(OAr) (1) via a reductive elimination route. The Lewis acidity of the Al atom in complex 1 is confirmed by the coordination of pyridine, leading to the adduct Cp*IrH3Al(Bu-i)(OAr)(Py) (2). Spectroscopic, crystallographic, and computational data support the description of these heterobimetallic complexes 1 and 2 as featuring strongly polarized Al(III)(delta+)-Ir(III)(delta-) interactions. Reactivity studies demonstrate that the binding of a Lewis base to Al does not quench the reactivity of the Ir-Al motif and that both species 1 and 2 promote the cooperative reductive cleavage of a range of heteroallenes. Specifically, complex 2 promotes the decarbonylation of CO2 and AdNCO, leading to CO (trapped as Cp*IrH2(CO)) and the alkylaluminum oxo ((iBu)(OAr)Al(Py)(2)(mu-O) (3)) and ureate ({Al(OAr)(Bu-i)kappa(2)-(N,O)AdNC(O)-NHAd} (4)) species, respectively. The bridged amidinate species Cp*IrH2(mu-CyNC(H)NCy)Al(Bu-i)(OAr) (5) is formed in the reaction of 2 with dicyclohexylcarbodiimine. Mechanistic investigations via DFT support cooperative heterobimetallic bond activation processes.