Hydrovinylation and [2+2] cycloaddition reactions of alkynes and alkenes catalyzed by a well-defined cationic ruthenium-alkylidene complex

The cationic ruthenium-alkylidene complex [(PCy3)(2)(CO)(Cl)Ru=CHCH=C(CH3)( 2)]+BF4- (1) was found to catalyze both hydrovinylation and [2+2] cycloaddi tion 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 analogou s reaction of dimethyl acetylenedicarboxylate (R' = R" = CO2Me) with ethyle ne and norbornene resulted in the formation of the [2+2] cycloaddition prod ucts 4. Based on the experimental evidence, a plausible mechanism of the hy drovinylation, reaction has been proposed via a sequential insertion of alk yne and ethylene to the hydride complex 7.