Homogeneous catalytic dimerization of terminal alkynes by C(5)Me(5)Ru(L)H-3 (L=PPh(3), PCy(3), PMe(3))

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, C4H9) to produce cis- and trans-1,4-disubstituted enynes RCH-CHC=CR and 1,3-disubstituted enynes CH2=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.