Promotion of reductive elimination reaction of diorgano(2,2'-bipyridyl)nickel(II) complexes by electron-accepting aromatic compounds, Lewis acids, and Bronsted acids.

Reductive elimination of R-R from dialkyl(2,2'-bipyridyl)nickel(n), [NiR2(bpy)] 1 (R = CH3 (1a), C2H5 (1b), n-C3H7 (1c)), caused by pi-coordination of electron-accepting aromatic compounds and reductive elimination of Ar-Ar from [NiAr2(bpy)] 2 (Ar = C6F5 (2a) and pyrazolyls (2b and 2c)) promoted by electron-accepting aromatic compounds, Lewis acids, and Bronsted acids have been investigated. H-1-NMR and kinetic data indicate that pi-coordination of the electron-accepting aromatic compound to [NiR2(bpy)] leads to the reductive elimination of R-R. The rate of the reductive elimination obeys the second-order rate law, -d[l]/dt = k[l][electron-accepting aromatic compound]. Plots of log k vs la, of the electron-accepting aromatic compound give a line with a slope of 1.8. Bronsted acids cause reductive elimination of Ar-Ar from 2 selectively under several reaction conditions (e.g., 2a with CF3COOH in air and 2b with HBr). The reductive elimination reaction of 2a caused by CF3COOH obeys the second-order rate law, -d[2a]/dt = k'[2a][CF3COOH], in air. The reaction of 2b with H2SO4 requires O-2, giving the rate equation, -d[2b]/dt = k[2b](2)[O-2]; e increases with [H2SO4], reaching a maximum value at a high [H2SO4]. UV-vis spectroscopy reveals the presence of the following equilibrium: 2b + H(2)SO(4)reversible arrow2b.H2SO4, and the equilibrium constant K-a is evaluated as K-a = [2b.H2SO4]/([2b][H2SO4]) = 47 M-1 at 300.5 K. UV-vis data give information about the electronic states of 2 and the 2b-Bronsted acid adduct. Poly(6-hexylpyridine-2,5-diyl) with a higher molecular weight has been prepared according to the basic information.