title: Reductive Cleavage of CO2 by Metal-Ligand-Cooperation Mediated by an Iridium Pincer Complex.
abstract: A unique mode of stoichiometric CO2 activation and reductive splitting based on metal-ligand-cooperation is described. The novel Ir hydride complexes [((t)Bu-PNP*)Ir(H)2] (2) ((t)Bu-PNP*, deprotonated (t)Bu-PNP ligand) and [((t)Bu-PNP)Ir(H)] (3) react with CO2 to give the dearomatized complex [((t)Bu-PNP*)Ir(CO)] (4) and water. Mechanistic studies have identified an adduct in which CO2 is bound to the ligand and metal, [((t)Bu-PNP-COO)Ir(H)2] (5), and a di-CO2 iridacycle [((t)Bu-PNP)Ir(H)(C2O4-κC,O)] (6). DFT calculations confirm the formation of 5 and 6 as reversibly formed side products, and suggest an η(1)-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 η(1)-CO2 ligand leads to a carboxylate intermediate, which further reacts with the hydride ligand to give complex 4 and water.
authors.affiliation: Departments of †Organic Chemistry and ‡Chemical Research Support, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Moran
authors.initials: M
authors.lastname: Feller
authors.affiliation: Departments of †Organic Chemistry and ‡Chemical Research Support, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Urs
authors.initials: U
authors.lastname: Gellrich
authors.affiliation: Departments of †Organic Chemistry and ‡Chemical Research Support, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Aviel
authors.initials: A
authors.lastname: Anaby
authors.affiliation: Departments of †Organic Chemistry and ‡Chemical Research Support, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Yael
authors.initials: Y
authors.lastname: Diskin-Posner
authors.affiliation: Departments of †Organic Chemistry and ‡Chemical Research Support, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: David
authors.initials: D
authors.lastname: Milstein