Reductive Cleavage of CO2 by Metal–Ligand-Cooperation Mediated by an Iridium Pincer Complex
datasetposted on 28.04.2016, 00:00 authored by Moran Feller, Urs Gellrich, Aviel Anaby, Yael Diskin-Posner, David Milstein
A unique mode of stoichiometric CO2 activation and reductive splitting based on metal–ligand-cooperation is described. The novel Ir hydride complexes [(tBu-PNP*)Ir(H)2] (2) (tBu-PNP*, deprotonated tBu-PNP ligand) and [(tBu-PNP)Ir(H)] (3) react with CO2 to give the dearomatized complex [(tBu-PNP*)Ir(CO)] (4) and water. Mechanistic studies have identified an adduct in which CO2 is bound to the ligand and metal, [(tBu-PNP-COO)Ir(H)2] (5), and a di-CO2 iridacycle [(tBu-PNP)Ir(H)(C2O4-κC,O)] (6). DFT calculations confirm the formation of 5 and 6 as reversibly formed side products, and suggest an η1-CO2 intermediate leading to the thermodynamic product 4. The calculations support a metal–ligand-cooperation pathway in which an internal deprotonation of the benzylic position by the η1-CO2 ligand leads to a carboxylate intermediate, which further reacts with the hydride ligand to give complex 4 and water.