Reaction of alkynes with [RuCp(CO)(CH3CN)2]+ and [RuCp*(CO)(CH3CN)2]+.: Convenient synthesis of ruthenium cyclopentadienone complexes

The mono-carbonyl complexes [RuCp(CO)(CH3CN)(2)]PF6 (1) and [RuCp*(CO)(CH3CN)(2)]PF6 (2) react with terminal and internal alkynes to afford the cationic complexes [RuCp(eta (4)-cyclopentadienone)(CH3CN)]PF6 (3) and [RuCp*(eta (4)-cyclopentadienone)(CH3CN)]PF6 (4), respectively, in high yields. These reactions are highly selective, yielding in the case of terminal alkynes only one regioisomer with the substituents exclusively in the alpha,alpha' positions of the cyclopentadienone moiety. In contrast, the reaction of 1 with PhC=CPh yields no cyclopentadienone complex but instead the sandwich complex [RuCp(eta (6)-C6H5PhC=CPh)](+) and the bis-carbonyl complex [RuCp(CO)(2)(CH3CN)](+) in a 1:1 ratio. X-ray structures of representative complexes are reported.