Formation of β-Ruthenium-Substituted Enones from Propargyl Alcohols

The reaction of the dienone ruthenium dicarbonyl dimer {[2,5-Ph-3,4-Tol(eta(5)-C4CO)]Ru(CO)(2)}(2) (7) with propargyl alcohol at room temperature gave a high yield of beta-ruthenium-enal (E)-[2,5-Ph-3,4-Tol(eta(5)-C4COH)]Ru(CO)(2)(CH=CHCHO) (8E), which was characterized spectroscopically and by X-ray crystallography. Reaction of 7 with pent-2-yn-l-ol led to the kinetic formation of the E-isomer (E)-[2,5-Ph-3,4-Tol(eta(5)-C4COH)]Ru(CO)(2)[C(CH2CH3)=CHCHO (10E-Et), which isomerized to an equilibrium mixture of Z- and E-isomers upon heating. The intramolecular nature of the 1,2-hydrogen shifts involved in these reactions was established by the absence of crossover products in the reaction of 7 with a mixture of PhC CCH2OH and PhC CCD2OH. A primary deuterium isotope effect (k(H)/k(D) approximate to 11) was seen on the product-forming step in the reaction of 7 with PhC CCHDOH. The reaction of PhC CCH3 with 7 produced the alkyne complex [2,5-Ph-2-3,4-Tol(2)(eta(5)-C4COH)]Ru(CO)(2) (eta(2)-PhC CCH3) (14). The key step in the mechanism of the reaction of 7 with propargyl alcohols is proposed to be an in-plane 1,2-hydrogen migration to an electrophilic carbon of a complexed alkyne.