Polycondensation of benzyl chloride catalysed by ArCr(CO)₃

Arene chromium tricarbonyls were found to function as effective homogeneous catalysts for the polycondensation of benzyl chloride when they are thermally activated. The catalytic activity and induction period depended upon the nature of the arene attached to the metal. Their activity decreased and induction time increased with respect to the nature of the arene in the order: anisole, toluene, p-xylene and benzene. The alkylation products of a model reaction, catalysed by ArCr(CO)₃, were only ortho- and para-substituted. The degree of polybenzyl branching, determined by ¹H n.m.r. and DP, was found to increase with increasing reaction temperature and M ̄_n. Although there is experimental evidence that in the initiation step the arene ring remains loosely attached to the metal, a mechanism similar to that of polymerization by a Lewis acid catalyst is proposed.