Ruthenium-acetylide-mediated catalytic dimerization of RC CH (R=Ph, CO2Me) and the formation of the new ruthenium eta(3)-butadienyl complex C5Me5Ru(PPh3)[eta(3)-PhCHCHC=C(Ph)C CCPh]

The in-situ-generated ruthenium-acetylide species C5Me5Ru(PPh3)C equivalent to CPh (1) was found to catalyze the dimerization of RC equivalent to CH to give predominantly the head-to-head dimers trans-RCH=CHC equivalent to CR (R = Ph (3), TON = 607 h(-1); R = CO2Me (4), TON = 975 h(-1)). A new ruthenium eta(3)-butadienyl complex C5Me5Ru(PPh3)(eta(3)-PhCHCHC=C(Ph)C equivalent to CPh) (5) was isolated at the end of the catalytic dimerization of PhC equivalent to 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 C5Me5Ru(PPh3)-(Cl)=C=CHPh (2) with the dimer 3 in the presence of NEt3. The formation of an intermediate eta(2)-alkyne complex C5Me3Ru(PPh3)(eta(2)-PhCH=CHC equivalent to CPh)(C equivalent to CPh) (6) was observed during the reaction.