Polymerization of 1-alkynes initiated by transition metal carbene complexes, 2. Kinetics and mechanism of the initiation reaction

A kinetic study of the initiation reaction of alkyne polymerization by a transition metal intramolecular coordinated carbene complex, was carried out. It showed that there is a slow disappearance of the initial carbene and simultaneously appearance of both active species and organic side-products. Their structures were determined by GC-MS. The apparent rate constants of both initiation and side-reactions were measured and the corresponding thermodynamic parameters established. According to the experimental results, a mechanism of the initiation reaction is proposed. In the first step a replacement of the intramolecular double bond of the initiator by the triple bond of a monomer molecule takes place and in the second step the insertion of the monomer. The resulting carbenic active species may lead either to organic products via cyclopropanation reaction or to a high-molecular-weight polymer.