Strongly Polarized Iridium δ− –Aluminum δ+ Pairs: Unconventional Reactivity Patterns Including CO 2 Cooperative Reductive Cleavage
Résumé
The iridium tetrahydride complex Cp*IrH 4 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*IrH 3 Al(i Bu)(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*IrH 3 Al(i Bu)-(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 CO 2 and AdNCO, leading to CO (trapped as Cp*IrH 2 (CO)) and the alkylaluminum oxo ([(iBu)(OAr)Al(Py)] 2 (μ-O) (3)) and ureate ({Al(OAr)(i Bu)[κ 2-(N,O)AdNC(O)-NHAd]} (4)) species, respectively. The bridged amidinate species Cp*IrH 2 (μ-CyNC(H)NCy)Al(i Bu)(OAr) (5) is formed in the reaction of 2 with dicyclohexylcarbodiimine. Mechanistic investigations via DFT support cooperative heterobimetallic bond activation processes.
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