Ruthenium-mediated cyclotrimerization of alkynes utilizing the cationic complex [RuCp(CH3CN)3]PF6

The substitutionally labile cationic complex [RuCp(CH3CN)(3)](+) (as the PF6- salt) was tested with respect to its ability to catalyze the cyclotrimerization of terminal alkynes and diynes to afford benzene derivatives. Whereas [RuCp(CH3CN)(3)](+) is in fact promoting the catalytic cyclotrimerization of alkynes, the formation of stable and inert sandwich complexes of the type [RuCp(eta(6)- arene)](+) deactivates the catalyst and thus quenches the catalytic cycle. All new sandwich complexes were isolated and characterized spectroscopically. A proposal for a plausible catalytic cycle including possible degradation pathways of the catalyst is presented based on DFT calculations. As key intermediates several novel carbene complexes have been identified including metallacyclo-pentatriene and metallaheptatetraene species. (C) 2003 Elsevier B.V. All rights reserved.