Bimetallic Oxidative Addition in Nickel-Catalyzed Alkyl–Aryl Kumada Coupling Reactions

Abstract

The mechanism of alkyl-aryl Kumada coupling catalyzed by the nickel pincer complex Nickamine was studied. Experiments using radical-probe substrates and DFT calculations established a bimetallic oxidative addition mechanism. Kinetic measurements showed that transmetalation rather than oxidative addition was the turnover determining step. The transmetalation involved a bimetallic pathway.3

Computational Studies of Synthetically Relevant Homogeneous Organometallic Catalysis Involving Ni, Pd, Ir, and Rh: An Overview of Commonly Employed DFT Methods and Mechanistic Insights

“…Tertiary halides were shown to be unreactive due to a prohibitively high barrier of reductive elimination relative to the most stable triplet Ni(II) intermediate. 305 The authors concluded that the aryl−alkyl coupling involved a Ni(I)/Ni(III) catalytic cycle, in which the transmetalation was deduced to be the turnover-determining step. The authors also suggested that the transmetalation may involve a bimetallic pathway, in which two Ni(II) complexes are required to supply two electrons to the alkyl halide.…”

Advances in Stereoconvergent Catalysis from 2005 to 2015: Transition-Metal-Mediated Stereoablative Reactions, Dynamic Kinetic Resolutions, and Dynamic Kinetic Asymmetric Transformations

“…75 sp 2 -Hybridized electrophiles 55 undergo oxidative addition selectively and rapidly in the presence of nickel(0) species such as 56 , thereby producing nickel(II) complex 57 . Bimetallic oxidative addition 76 of alkyl halide 58 leads to transient nickel(III) species 59 . Rapid reductive elimination then produces nickel(I) intermediate 60 and the C sp 3 -C sp 2 product 61; 60 is then reduced to the active nickel(0) catalyst 56 by a low-valent metal reducing agent to complete the catalytic cycle.…”

Circumventing Intrinsic Metal Reactivity: Radical Generation with Redox‐Active Ligands

“…In contrast with nickel's well‐known affinity towards radicals, generation of radical species by nickel complexes is less documented but has been implicated in nickel‐catalyzed cross‐coupling reactions ,,. Metal‐centered redox transfers are involved in these examples but possible implication of a bipyridine ligand by delocalization of electronic density was reported in the nickel‐based formation of carbon‐centered radicals from an alkyl halide .…”