Activation of Mononuclear Arene Ruthenium Complexes for Catalytic Propargylation Directly with Propargyl Alcohols

Mononuclear complexes of the type [(p-cymene)RuX(CO)(PR3)][OTf] (R=Ph, Cy; X=Cl, OTf) promote the direct catalytic propargylation of furan with propargyl alcohols. These precursors are generated in situ from [(p-cymene)RuCl(OTf)(PR3)] by activation of the propargylic alcohol, leading to the carbonyl ligand formation via allenylidene and alkenyl-hydroxycarbene intermediates. The generation of the catalytically active species requires a short initial thermal activation to induce decoordination of the p-cymene ligand. The in situ generated catalyst has been applied to catalytic transformations of alkynes and propargylic alcohols: propargylation of furans, propargyl ether synthesis from internal and terminal propargylic alcohols with propargyl, homopropargyl and allyl alcohols, selective dimerization of phenylacetylene into E-enyne, and propargyl alcohol rearrangement into α,β-unsaturated aldehydes and ketones via the Meyer-Schuster rearrangement. The propargylation of propargylic alcohols containing internal C≡C bonds suggests an activation via the Nicholas-type intermediate, the metal-stabilized propargyl cation.