Reductive Cleavage of CO2 by Metal–Ligand-Cooperation Mediated by an Iridium Pincer Complex

详细信息    查看全文

• 作者：Moran Feller ; Urs Gellrich ; Aviel Anaby ; Yael Diskin-Posner ; David Milstein
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：May 25, 2016
• 年：2016
• 卷：138
• 期：20
• 页码：6445-6454
• 全文大小：567K
• 年卷期：0
• ISSN：1520-5126

文摘

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-κ_C,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.