Alkyne Hydrothiolation Catalyzed by a Dichlorobis(aminophosphine) Complex of Palladium: Selective Formation of cis‐Configured Vinyl Thioethers

Abstract

Cis all round: Dichlorobis[1-(dicyclohexylphosphanyl)piperidine]palladium, [(P{(NC(5)H(10))(C(6)H(11))(2)})(2)Pd(Cl)(2)], is a highly efficient alkyne hydrothiolation catalyst and the first generally applicable system that selectively generates cis-configured anti-Markovnikov adducts in excellent yields within only a few minutes at 120 °C in the presence of only 0.05 mol % of the catalyst (see scheme).

Chemicals from Alkynes with Palladium Catalysts

“…97 The uncommon preferential anti-Markovnikov-type addition of thiols to terminal alkynes has been achieved recently using as catalyst a dichlorobis(aminophosphine) complex of palladium. 98 The use of Pd(OAc) 2 (2 mol%) showed to catalyze the hydroselenation of terminal alkynes with benzeneselenol in benzene as solvent at 80 ºC, leading to branched vinyl selenides. 99 However, small amounts of byproducts from double hydroselenation and isomerization are formed under these conditions, the selectivity to the final terminal alkene being achieved totally by using pyridine as solvent as exemplified in Scheme 38 with the preparation of 104 from 5-methylhex-1-yne.…”

Mechanism of the palladium-catalyzed hydrothiolation of alkynes to thioethers: a DFT study

“…In the original experimental paper [47], the authors employed Pd(PMe 3 ) 2 as the catalyst and used different substrates, which may have important effects on the reaction mechanism. To take further account of the effect of the reaction activity and reaction mechanism with the different substrates, the reaction of palladium-catalyzed hydrothiolation of phenyl mercaptan to propyne and phenylacetylene were calculated.…”

“…Thus, while thiol hydrothiolation with aromatic or aliphatic alkynes would appear to provide ideal substrates for their activation by the transition metals, there has been relatively little investigation of this aspect of their chemistry. Furthermore, an experimental and theoretical investigation of rhodium-catalyzed hydrothiolation of ligandcontrolled regioselectivity also been performed recently by Castarlenas et al [46], and Frech et al [47] studied palladium-catalyzed hydrothiolation of aromatic alkynes and aliphatic or aromatic thiols into cis-configured antiMarkovnikov-type vinyl thioethers with excellent yields within a few minutes at 120°C (Scheme 1).…”

“…To our knowledge, there are no detailed theoretical studies of this novel pathway other than the palladium-catalyzed hydrothiolation reported by the Frech group [47]. So, we present a detailed density functional theory (DFT) computational investigation of the mechanism and regioselectivity of the palladium-catalyzed hydrothiolation of thiols with aliphatic or aromatic alkynes resulting in cis-configured vinyl thioethers or Markovnikov-type products on the basis of the experimental evidence reported by Frech et al [47].…”

“…So, we present a detailed density functional theory (DFT) computational investigation of the mechanism and regioselectivity of the palladium-catalyzed hydrothiolation of thiols with aliphatic or aromatic alkynes resulting in cis-configured vinyl thioethers or Markovnikov-type products on the basis of the experimental evidence reported by Frech et al [47]. From the research results, we will gain knowledge of the factors that control the activation barriers of these reaction systems.…”