Syntheses and Reactivity of Analogues of Grubbs" Second Generation Metathesis Catalyst with Fluorous Phosphines: A New Phase-Transfer Strategy for Catalyst Activation

Reactions of the bis(pyridine) complex (H₂IMes)(Py)₂(Cl)₂Ru(=CHPh), (H₂IMes=1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) and the highly fluorophilic phosphines [R_fn(CH₂)_m]₃P [1; m/n=a, 2/6; b, 2/8; c, 2/10; d, 3/8; R_fn=CF₃(CF₂)_n−1] give (H₂IMes){[R_fn(CH₂)_m]₃P}(Cl)₂Ru(=CHPh) (4a–d, 64–78 %), which are analogues of Grubbs’ second generation alkene metathesis catalyst. Complexes 4a,b are effective catalysts for conversions of 1,6-dienes to cyclopentenes under monophasic and biphasic conditions in CH₂Cl₂ and CH₂Cl₂/fluorous solvent mixtures. The latter generally exhibit rate accelerations, which are believed to arise from phase transfer of the dissociated fluorous phosphine, allowing the substrate to better compete for the fourteen valence-electron intermediate. Only modest effects are observed when Grubbs’ second generation catalyst is similarly reacted. The most fluorophilic catalyst, 4c, can be recycled by extracting the reaction mixtures with perfluoro(methylcyclohexane).