Kinetics and Mechanistic Insights into the Acetate-Assisted Dimerization of Terminal Alkynes under Ruthenium- and Acid-Promoted (RAP) Catalysis

Abstract

The mechanism of the dimerization of terminal aryl alkynes promoted by [{RuCl(μ-Cl)(η6-p-cymene)}2](1)/AcOH, under cooperative transition metal/Bronsted acid catalysis, has been investigated with regard to (i) the activation of the dinuclear ruthenium complex and (ii) the catalytic formation of the trans-1,4-diaryl-1,3-enyne products, by a detailed kinetic investigation of both processes. Complex 1 is subject to a slow solvolytic process in neat acetic acid or is transformed rapidly in the presence of sodium acetate to form the monomeric ruthenium(II) acetato complex [RuCl(η6-p-cymene)(OAc)]. The latter is the active catalytic species promoting the alkyne dimerization process, via initial π-alkyne coordination and intramolecular C–H abstraction by the acetate ligand, as key steps of the catalytic cycle. The presence of additive acetate salts allows for the reaction to proceed at room temperature with short reaction times and high trans/cis stereoselectivity, thus rendering this catalytic system among the ...