Coordinatively unsaturated ruthenium allenylidene complexes: highly effective, well defined catalysts for the ring-closure metathesis of α,ω-dienes and dienynes

The well defined, conveniently accessible and coordinatively unsaturated allenylidene complexes [RuCl2(=C=C= CPh2)(PCy3)2] and [Ru2Cl4(=C=C=CPh2)(PCy3)(η-MeC6-H4Pri-4)] are highly effective catalysts for the ambient temperature ring-closure metathesis of α,ω-dienes and dienynes, illustrated by the facile and high yielding formation of variously functionalised 5, 6, 7, 8, 15, 16 and 18 membered mono- and bi-cyclic ring systems