Formation of β-Ruthenium-Substituted Enones from Propargyl Alcohols

The reaction of the dienone ruthenium dicarbonyl dimer {[2,5-Ph-3,4-Tol(η5-C4CO)]Ru(CO)2}2 (7) with propargyl alcohol at room temperature gave a high yield of β-ruthenium-enal (E)-[2,5-Ph-3,4-Tol(η5-C4COH)]Ru(CO)2(CHCHCHO) (8E), which was characterized spectroscopically and by X-ray crystallography. Reaction of 7 with pent-2-yn-1-ol led to the kinetic formation of the E-isomer (E)-[2,5-Ph-3,4-Tol(η5-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 (kH/kD ≈ 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-Ph2-3,4-Tol2(η5-C4COH)]Ru(CO)2(η2-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.