Terminal‐Alkyne‐Induced Decomposition of a Phosphine‐Free Ruthenium Alkylidene Catalyst

Abstract

AbstractThe transformations of the third‐generation Grubbs catalyst [RuCl2(=CHPh)(3‐Br‐py)2(H2IMes)] (py=pyridine, H2IMes=1,3‐bis(2,4,6‐trimethylphenyl)imidazolidin‐2‐ylidene) in the presence of a terminal alkyne (phenylacetylene) were studied theoretically. The ruthenium η3‐vinylcarbene complex is the most probable product of the reaction between the 14‐electron ruthenium alkylidene species and phenylacetylene. Its subsequent transformation into the ruthenium vinylidene complex and stilbene, both being experimentally observed earlier, is possible. The former is believed to be the active species catalyzing the dimerization of terminal alkynes. The calculated pathway also predicts the formation of [RuCl2(H2IMes)] species, which might initiate the cyclotrimerization of terminal alkynes or transform into the experimentally detected [RuCl2(3‐Br‐py)3(H2IMes)] complex. An alternative mechanism of the Grubbs catalyst decomposition through an intermediate Ru species having alkylidene and vinylidene ligands in the coordination sphere of ruthenium is also proposed.