Addition of acetylenes to olefins. Oxidative coupling versus [2+2] cycloaddition to a vinylidene intermediate

The reaction of [RuCp (kappa(1)(P),eta(2)-PPh2CH2CH2CH=CH2)( CH3CN)] PF6 (1 ) with HC equivalent to CPh in the absence of base results in the formation of the eta(4)-butadiene complexes [RUCp(kappa(1)(P),eta(4)-(3Z,5E)-PPh2CH2 CH2CH=CH-CH=CHPh)]PF6 (2a) and [RuCp(kappa(1)(P),eta(4)-(3Z)-PPh2CH2CH2CH=C H-CPh=CH2)]PF6 (2b). When the reaction is carried out in the presence of ba se (NaOEt), in addition to 2a and 2b, the eta(3)-butadienyl complex RuCp(ka ppa(1)(P),(3,4,5-eta)-PPh2CH2CH2CHCHCCHPh) (2c) is obtained. The C-C coupli ng reactions take place also with internal alkynes (RC)-C-1 equivalent to C R2 (R-1= R-2 = Ph, Et; R-1=Ph, R-2 = Et) to give the eta 4-butadiene comple xes [RuCp(kappa(1)(P),eta(4)-(3Z,5Z)-PPh2CH2CH2CH=CH-CR1 equivalent to CHR2 )]PF6 (3-5). In the case of terminal acetylenes two distinct reaction modes are observed proceeding via either metallacyclopentene complexes or the su ccessive intermediacy of vinylidene and metallacyclobutane complexes. With internal alkynes, the metallacyclopentene route is followed. X-ray structur es of representative complexes are reported.