Redox Reactions between Halides and Reducing Metal Complexes in Non-aqueous Solution: Part 1.—Derivatives of Tetrakis(triphenyl phosphite)nickel(O)

Abstract

Tetrakisftriphcnyl phosphite)nickel(O) (Ni(tp)4) undergoes ligand exchange with electron donors such as methyl methacrylate (mma) to form complexes of the type Ni(tp)3(mma) which enter into redox reactions with organic halides to generate free radicals. Three techniques are described for determining the absolute rate coefficients of these latter processes. In two methods, concentrations of Ni(tp)3(mma) are monitored spectrophotometrically, while in the third the rate of radical generation is deduced from observations of the rate of the ensuing free-radical polymerization of (mma). Reactions of CHBr3, CBr4, CH2Br2, CCl3COOEt, CHCBCOOEt, CHClj, CH2C12 are reported in this paper. In general, bromides are much more reactive than the corresponding chlor ides, and the rate of reaction increases with the number of halogen atoms attached to a single carbon. Further, introduction of an electronegative group into the halide molecule greatly increases the rate of reaction. It is concluded that the electron-affinity of the halide and solvation of the transition com plex play important roles in determining the rate coefficients and activation parameters. The reactivities of the halides in these redox processes and in chain transfer reactions arc compared.