Hydrovinylation and [2+2] Cycloaddition Reactions of Alkynes and Alkenes Catalyzed by a Well-Defined Cationic Ruthenium−Alkylidene Complex

Abstract

The cationic ruthenium−alkylidene complex [(PCy3)2(CO)(Cl)RuCHCHC(CH3)2]+BF4- (1) was found to catalyze both hydrovinylation and [2+2] cycloaddition reactions of alkynes and alkenes. The reaction of R‘C⋮CR‘ ‘ (R‘ = H, Ph, n-Pr; R‘ ‘ = Ph, n-Pr, p-Tol, SiEt3, CH2CH2OH) with ethylene in the presence of 1 (3 mol %) produced the hydrovinylation products 2 and 3. The analogous reaction of dimethyl acetylenedicarboxylate (R‘ = R‘ ‘ = CO2Me) with ethylene and norbornene resulted in the formation of the [2+2] cycloaddition products 4. Based on the experimental evidence, a plausible mechanism of the hydrovinylation reaction has been proposed via a sequential insertion of alkyne and ethylene to the hydride complex 7.