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

Article abstract of DOI:10.1021/om980902x

The reaction of [RuCpOcKP)y-PPh2CH2CH2CH=CH2)(CH3CN)]PF6 (1) with HCCPh in the absence of base results in the formation of the ?/4-butadiene complexes [RiGp(icP),i]4(3Z,5￡)-PPh2CH2CH2CH=CH-CH=CHPh)]PF6 (2a) and [RuCp(1(P),?74-(3Z)-PPh2CH2CH2CH=CH-CPh=CH2)]PF6 (2b). When the reaction is carried out in the presence of base (NaOEt), in addition to 2a and 2b, the ?73-butadienyl complex RuCp(/c1(P),(3,4,5-?/)-PPh2CH2CH2CHCHCCHPh) (2c) is obtained. The C-C coupling reactions take place also with internal alkynes RCR2 (R1 = R2 = Ph, Et; R1 = Ph, R2 = Et) to give the ?;4-butadiene complexes [RuCp(1(P),?;4-(3Z)5Z)-PPh2CH2CH2CH=CH-CR1=CHR2)]PF6 (3-5). In the case of terminal acetylenes two distinct reaction modes are observed proceeding via either metallacyclopentene complexes or the successive intermediacy of vinylidene and metallacyclobutane complexes. With internal alkynes, the metallacyclopentene route is followed. X-ray structures of representative complexes are reported.