Homogeneous Catalytic Dimerization of Terminal Alkynes by C5Me5Ru(L)H3 (L = PPh3, PCy3, PMe3)

The ruthenium hydride complexes C 5 Me 5 Ru(L)H 3 (L = PPh 3 ( 1a ), PCy 3 ( 1b ), PMe 3 ( 1c )) were found to catalyze the dimerization reaction of terminal alkynes RC⋮CH (R = Ph, t -Bu, SiMe 3, CH 2 Ph, C 4 H 9 ) to produce cis - and trans -1,4-disubstituted enynes RCH CHC⋮CR and 1,3-disubstituted enynes CH 2 C(R)C⋮CR. The selective product formation was effected by modulating both the catalyst environment and the alkyne substrates. A rare form of dimer, cumulene PhCH 2 CH C C CHCH 2 Ph ( 5d ), was cleanly obtained from the dimerization of HC⋮CCH 2 Ph with 1b . A mechanistic interpretation is presented on the basis of the product distribution.