Catalytic transformation of phenylacetylene mediated by phosphine-free ruthenium alkylidene complexes

Phosphine-free ruthenium alkylidene complexes, [RuCl2(=CH-o-OiPrC6H4)(IMesH2)], [Ru(CF3CO2)2(=CH-o-OiPrC6H4)(IMesH2)], and [RuCl2(=CHPh)(3-Br-py)2(IMesH2)], were found as catalyst precursors for non-metathesis transformations of phenylacetylene, e.g. cyclotrimerization and dimerization. Selective product formation was affected by modulating the coordination sphere of the catalyst and temperature. An NMR study under various experimental conditions and DFT calculations taken together permitted the conclusion that the degradation of the alkylidene complex took place in the initial step, regardless of the manner of alkyne addition.