What is the Rate of the Csp 2-Csp 2 Reductive Elimination Step? Revealing an Unusually Fast Ni-Catalyzed Negishi-Type Oxidative Coupling Reaction

Although reductive elimination has been known for over 40 years and is an essential step in coupling reactions, 1-6 within the catalytic cycle, there are very few quantitative kinetic studies of the Csp 2-Csp 2 reductive elimination. 7,8 Investigation of stoichiometric reactions of biaryl Ni, Pd, and Pt complexes reveals valuable insight into the reductive elimination step. 9-11 The rate constants of the reductive elimination of Csp 2-Pd-Csp 2 and Csp 2-Pt-Csp 2 systems have been measured to be in the range of 10-3 to 10-5 s-1. 9,10 In sharp contrast, catalytic reactions for Csp 2-Csp 2 couplings appear to be much faster, as catalytic processes can occur at temperatures as low as-30 °C which indicates a much lower energy activation barrier. 12 Collman et al. in 1987 discussed that the rates of many reductive elimination reactions are very difficult to obtain because they are so exothermic and the corresponding oxidative addition is unknown. 13 In fact, until today, there are still few bis-aryl Ni and P