Mechanistic Investigation of Carbon-Carbon Bond Formation in the Reduction of Alkyl Halides by Organonickel Complexes in Aqueous Solution

Article abstract of DOI:10.1021/ja00264a024

The macrocyclic alkylnickel(II) complexes, RNi(tmc)⁺ (R = C2H5, C3H7, and CH2-c-C5H9; tmc = (1R,4R,8S,11S)-1,4,8,11-tetramethyl-1,4,8.11-tetraazacyclotetradecane), react with alkyl halides R'X (R'= CH3, C2H5, 1-C3H7, 2-C3H7, and PhCH2) in alkaline aqueous solutions, yielding combination and disproportionation products of R and R'.The reactivity of R'X increases in the order methyl < primary < secondary and Cl < Br < I.In the case R = R' = C2H5, the product distribution compares with that deternined independently for ethyl radicals in aqueous solution.The proposed one-electron reduction of alkyl halide by the alkylnickel complexes in the rate-determining step produces an organonickel(III) complex and the alkyl halide radical anion.Both products rapidly eliminate ethyl radicals whose self-reactions yield the final products.Alkyl halide/alkyl radical exchange reactions effectively compete with radical self-reactions.The rate constant for the reaction C2H5^. + 2-C3H7I -> 2-C3H7^. + C2H5I in aqueous solution was determined by competition with V(H2O)6²⁺.The value k_2-PrI ca. 6E5 M^-1s^-1 is significantly higher than in aprotic solvents.