Ruthenium−Acetylide-Mediated Catalytic Dimerization of RC⋮CH (R = Ph, CO₂Me) and the Formation of the New Ruthenium η³-Butadienyl Complex C₅Me₅Ru(PPh₃)[η³-PhCHCHCC(Ph)C⋮CCPh]

Abstract

The in-situ -generated ruthenium−acetylide species C 5 Me 5 Ru(PPh 3 )C⋮CPh ( 1 ) was found to catalyze the dimerization of RC⋮CH to give predominantly the head-to-head dimers trans -RCH CHC⋮CR (R = Ph ( 3 ), TON = 607 h - 1; R = CO 2 Me ( 4 ), TON = 975 h - 1 ). A new ruthenium η 3 -butadienyl complex C 5 Me 5 Ru(PPh 3 )(η 3 -PhCHCHC C(Ph)C⋮CPh) ( 5 ) was isolated at the end of the catalytic dimerization of PhC⋮CH (81% based on Ru). The structure of the 1.5 benzene-solvated complex 5 ·1.5C 6 H 6 was established by X-ray crystallography. Complex 5 was independently prepared from the stoichiometric reaction of C 5 Me 5 Ru(PPh 3 )(Cl) C CHPh ( 2 ) with the dimer 3 in the presence of NEt 3 . The formation of an intermediate η 2 -alkyne complex C 5 Me 5 Ru(PPh 3 )(η 2 -PhCH CHC⋮CPh)(C⋮CPh) ( 6 ) was observed during the reaction.