Several ruthenium-based olefin metathesis catalysts of the formula (PR3)2X2Ru=CHCHCPh2 have been synthesized, and relative catalyst activities were determined by monitoring the ring-closing metathesis of the acyclic diene diethyl diallylmalonate. The following order of increasing activity was determined: X = I < Br < Cl and PR3 = PPh3 << P(i)Pr2Ph < PCy2Ph < P(i)Pr3 < PCy3. Additional studies were conducted with the catalyst (PCy3)2-Cl2Ru=CH2 to probe the mechanism of olefin metathesis by this class of catalysts. The data support a scheme in which there are two competing pathways: the dominant one in which a phosphine dissociates from the ruthenium center and a minor one in which both phosphines remain bound. Higher catalyst activities could be achieved by the addition of CuCl to the reaction.
ASJC Scopus subject areas
- Colloid and Surface Chemistry