Synthesis, structure and catalytic study of chloro-bridged two-core ruthenium carbene complexes

The reaction of a ruthenium carbide complex RuCl2(C:) (PCy3)2 with [H(Et2O)x]+[BF4]− at a molar ratio of 1:2 produced a two-core ruthenium carbene complex {[RuCl(double bond; length as m-dashCHPCy3)(PCy3)]2(μ-Cl)3}+·[BF4]− (8) in the form of a yellow–green crystalline solid. After a ligand exchange reaction of 8 with LiBr, a bromide ruthenium carbene complex {[RuBr(double bond; length as m-dashCHPCy3)(PCy3)]2(μ-Cl)3}+·[BF4]− (9) was obtained as a crystalline solid. Catalytic studies showed that both 8 and 9 are selective catalysts for ring closing metathesis of unsubstituted terminal dienes. More importantly, no isomerized byproduct was observed when 8, or 9 was used as the catalyst at an elevated temperature (137 °C), indicating that both 8 and 9 are chemo-selective catalysts for ring closing metathesis reactions.