title: Bimetallic C-C Bond-Forming Reductive Elimination from Nickel.
abstract: 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 sp(3)-sp(3) and sp(2)-sp(2) 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.
authors.affiliation: Department of Chemistry, New York University , 100 Washington Square East, New York, New York 10003, United States.
authors.forename: Hongwei
authors.initials: H
authors.lastname: Xu
authors.affiliation: Department of Chemistry, New York University , 100 Washington Square East, New York, New York 10003, United States.
authors.forename: Justin B
authors.initials: JB
authors.lastname: Diccianni
authors.affiliation: Department of Chemistry, New York University , 100 Washington Square East, New York, New York 10003, United States.
authors.forename: Joseph
authors.initials: J
authors.lastname: Katigbak
authors.affiliation: Department of Chemistry, New York University , 100 Washington Square East, New York, New York 10003, United States.
authors.forename: Chunhua
authors.initials: C
authors.lastname: Hu
authors.affiliation: Department of Chemistry, New York University , 100 Washington Square East, New York, New York 10003, United States.
authors.forename: Yingkai
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, New York University , 100 Washington Square East, New York, New York 10003, United States.
authors.forename: Tianning
authors.initials: T
authors.lastname: Diao