Bimetallic C–C Bond-Forming Reductive Elimination from Nickel

详细信息    查看全文

• 作者：Hongwei Xu ; Justin B. Diccianni ; Joseph Katigbak ; Chunhua Hu ; Yingkai Zhang ; Tianning Diao
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：April 13, 2016
• 年：2016
• 卷：138
• 期：14
• 页码：4779-4786
• 全文大小：612K
• 年卷期：0
• ISSN：1520-5126

文摘

Ni-catalyzed cross-coupling reactions have found important applications in organic synthesis. The fundamental characterization of the key steps in cross-coupling reactions, including C–C bond-forming reductive elimination, represents a significant challenge. Bimolecular pathways were invoked in early proposals, but the experimental evidence was limited. We present the preparation of well-defined (pyridine-pyrrolyl)Ni monomethyl and monophenyl complexes that allow the direct observation of bimolecular reductive elimination to generate ethane and biphenyl, respectively. The sp³–sp³ and sp²–sp² couplings proceed via two distinct pathways. Oxidants promote the fast formation of Ni(III) from (pyridine-pyrrolyl)Ni-methyl, which dimerizes to afford a bimetallic Ni(III) intermediate. Our data are most consistent with the subsequent methyl coupling from the bimetallic Ni(III) to generate ethane as the rate-determining step. In contrast, the formation of biphenyl is facilitated by the coordination of a bidentate donor ligand.