Mo(CO)5Py as an Initiator of Polymerization

In a series of publications we have described the kinetics of free-radical formation from molybdenum carbonyl in association with organic halides in a number of electron-donating solvents. Radical formation involves the displacement of carbon monoxide from the carbonyl by the solvent or vinyl monomer in a rate-determining process giving rise to complexes of the type Mo(CO)5L (where L represents the solvent or monomer) which then react directly with the halide. This paper describes a study of the behaviour of Mo(CO)5Py in association with organic halides in methyl methacrylate solution. The results show that Mo(CO)5Py does not react directly with the halide but first undergoes activation by reaction with monomer, mainly with displacement of pyridine. The relative reactivities of complexes of the type Mo (CO) 5L are discussed. The mechanism previously proposed to account for the inhibition processes observed in Mo (CO)6-organic halide systems satisfactorily explains the extensive inhibition observed in the present work.