Ring-opening metathesis polymerization of norbornene and norbornadiene by tungsten(II) and molybdenum(II) complexes

Abstract

The reaction of norbornene (NBE) and norbornadiene (NBD) in the presence of seven-coordinate tungsten(II) and molybdenum(II) complexes of the [(CO) 4M(μ-Cl) 3M(SnCl 3)(CO) 3] and [MCl(M′Cl 3)(CO) 3(NCMe) 2] (M=W, Mo; M′=Sn, Ge) types leads to ring-opening metathesis polymerization (ROMP) and to the formation of high molecular weight polymers. The geometric structure of these polymers was determined by means of 1 H - and 13 C -NMR spectroscopy. The monitoring of the reaction between cyclic olefins and the metal complex by means of 1 H -NMR spectroscopy allowed us to observe the coordination of NBD to metal atoms in the initiation step of the polymerization process. Compounds of the [MCl(SnCl 3)(CO) 3(η 4-NBD)] type prepared directly from [(CO) 4M(μ-Cl) 3M(SnCl 3)(CO) 3] or [MCl(M′Cl 3)(CO) 3(NCMe) 2] (M=W, Mo) in the presence of an excess of NBD initiate the ROMP reaction immediately. The detection of the first-formed products in the reaction between the metal complex and cyclic olefins provides valuable information concerning the nature of the initiating species.