Kinetics and mechanism of the reaction of photogenerated eta(1)-(tetrachloromethane)pentacarbonylmetal(0) complexes, (eta(1)-(CCl4)M(CO)(5); M=Mo, W) with 1-hexene: The initial steps in the creation of olefin methathesis catalysts

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 nucleophils, 1-hexene (hex), this species affords (eta(2)-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. (C) 1997 Elsevier Science S.A.