Strongly Polarized Iridium^δ−–Aluminum^δ+ Pairs: Unconventional Reactivity Patterns Including CO₂ Cooperative Reductive Cleavage

Abstract

The iridium tetrahydride complex Cp*IrH₄ reacts with a range of isobutylaluminum derivatives of general formula Al(<i>i</i>Bu)_<i>x</i>(OAr)_3-<i>x</i> (<i>x</i> = 1, 2) to give the unusual iridium aluminum species [Cp*IrH₃Al(ⁱBu)(OAr)] (<b>1</b>) via a reductive elimination route. The Lewis acidity of the Al atom in complex <b>1</b> is confirmed by the coordination of pyridine, leading to the adduct [Cp*IrH₃Al(^<i>i</i>Bu)(OAr)(Py)] (<b>2</b>). Spectroscopic, crystallographic, and computational data support the description of these heterobimetallic complexes <b>1</b> and <b>2</b> 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 <b>1</b> and <b>2</b> promote the cooperative reductive cleavage of a range of heteroallenes. Specifically, complex <b>2</b> promotes the decarbonylation of CO₂ and AdNCO, leading to CO (trapped as Cp*IrH₂(CO)) and the alkylaluminum oxo ([(<i>i</i>Bu)(OAr)Al(Py)]₂(μ-O) (<b>3</b>)) and ureate ({Al(OAr)(^<i>i</i>Bu)[κ²-(N,O)AdNC(O)NHAd]} (<b>4</b>)) species, respectively. The bridged amidinate species Cp*IrH₂(μ-CyNC(H)NCy)Al(^<i>i</i>Bu)(OAr) (<b>5</b>) is formed in the reaction of <b>2</b> with dicyclohexylcarbodiimine. Mechanistic investigations via DFT support cooperative heterobimetallic bond activation processes.