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)(η 6 -p-cymene)} 2 ](1)/ AcOH, under cooperative transition metal/Brønsted 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(η 6 -pcymene)(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 most active and selective procedures for the dimerization of terminal alkynes in a protic medium. The linear coupling of three molecules of phenylacetylene affords an organometallic ruthenium complex featuring a butenynyl ligand which has been characterized by X-ray crystallography.

Transition Metal Vinylidene- and Allenylidene-Mediated Catalysis in Organic Synthesis

“…The head-to-head homodimerization of terminal alkynes has been carried out using a variety of catalytic systems including ruthenium half-sandwich complexes, − Grubbs’ catalyst, a thiolate-bridged dimeric ruthenium­(III), a ruthenium-P,N system, ruthenium-P 4 and osmium P 4 systems, , ruthenium-P,O and osmium-P,O systems, − a Rh­(III) catalyst, and iridium systems (Chart ). , …”

DLPNO-CCSD(T) and DFT study of the acetate-assisted C–H activation of benzaldimine at [RuCl2(p-cymene)]2: the relevance of ligand exchange processes at ruthenium(ii) complexes in polar protic media

“…Dalton Transactions evidence reported by Bassetti et al 45 indicates that this process should be initiated by ruthenium-chloro bond breaking, release of chloride and the formation of a cationic intermediate (see B 0+ in Scheme S2 of the ESI †). Such a dissociation process was calculated to be endergonic by 2.7 [0.9] kcal mol −1 and showed an activation energy of 20.2 [18.9] kcal mol −1 .…”

Rhenium-catalysed reactions in chemical synthesis: selected case studies

“…[50][51][52][53] These activation pathways are also often invoked in many associated transitionmetal-catalysed reactions employing alkyne substrates. [54][55][56][57] Jia and co-workers demonstrated the first example of C-C bond cleavage of internal propargyl alcohols to access rhenium viny-lidene complexes in 2018 (Scheme 1B). 58 It was found that tris (dppm)rhenium(I) iodide complex 6a reacts with tertiary, secondary and primary propargyl alcohols in the presence of 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU) to deliver rhenium(I) vinylidene complex 6c.…”