Kinetics and mechanism of the reaction of photogenerated (η1-(tetrachloromethane) pentacarbonylmetal(O) complexes, (η1-(CCl4)M(CO)5; M = Mo, W) with 1-hexene: The initial steps in the creation of olefin methathesis catalysts

Abstract

The initial steps in the formation of the heterogeneous olefin methathesis catalysts produced by photolysis of M(CO)6/CCl4 solutions (M = Mo, W) have been studied by pulsed laser flash photolysis with infrared and visible detection. In both systems, (Cl3CCl)M(CO)5 (datively bonded to M through a single Cl) is produced immediately after the flash. In the presence of the trapping nucleophile, 1-hexene (hex), this species affords (η2-hex)M(CO)5. For M = W, there is also a competitive unimolecular decay pathway which affords the solid catalyst. Infrared and rate data for (Cl3CCl)W(CO)5 and related complexes suggest that CCl4 bonds weakly to W and is a poor net donor of charge to the metal atom, which could promote fast oxidative addition of CCl4 to [M(CO)5]. The rate-determining step for the unimolecular pathway is envisioned to involve slow decomposition via CO loss of the possible oxidative addition product to afford the heterogeneous catalyst.