Tetrakis(triphenyl phosphite)nickel(0)+ maleic anhydride: ligand exchange and free-radical formation

Abstract

Tetrakis(triphenyl phosphite)nickel(0)(Ni(tp)₄) reacts reversibly with maleic anhydride (man) in methyl methacrylate (mma) or styrene (st) solution to form the species Ni(tp)₂(man)(III). Kinetic studies based on absorbance measurements are consistent with a rate-determining dissociation of Ni(tp)₄; the intermediate compound Ni(tp)₃(man)(formed by complexing of Ni(tp)₃ and man) reacts by an S_N1 process to generate the final product(III). The equilibrium constant for the overall ligand exchange has been evaluated.

Reaction between Ni(tp)₃ and man generates free-radicals capable of initiating the copolymerization of man and mma or st; the efficiency is extremely low on account of the predominance of competitive ligand exchange reactions. The copolymerization has been studied over a range of conditions and rates of initiation have been calculated by a method that does not involve a knowledge of the monomer reactivity ratios.

The kinetics of both ligand exchange and initiation reactions have been examined and there is satisfactory agreement with experiment under a variety of conditions.