Strongly Polarized Iridiumδ−–Aluminumδ+ Pairs: Unconventional Reactivity Patterns Including CO2 Cooperative Reductive Cleavage

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(iBu)­(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(iBu)­(OAr)­(Py)] (2). Spectroscopic, crystallographic, and computational data support the description of these heterobimetallic complexes 1 and 2 as featuring strongly polarized Al­(III)δ+–Ir­(III)δ− 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(μ-O) (3)) and ureate ({Al­(OAr)­(iBu)­[κ2-(N,O)­AdNC­(O)­NHAd]} (4)) species, respectively. The bridged amidinate species Cp*IrH2(μ-CyNC­(H)­NCy)­Al­(iBu)­(OAr) (5) is formed in the reaction of 2 with dicyclohexylcarbodiimine. Mechanistic investigations via DFT support cooperative heterobimetallic bond activation processes.