Addition of benzenethiol to terminal alkynes catalyzed by hydrotris(3,5-dimethylpyrazolyl)borate–Rh(III) bis(thiolate) complex: Mechanistic studies with characterization of the key intermediate

Abstract

The Rh(III)–thiolate complex [Tp ∗Rh(SPh) 2(MeCN)] ( 2; Tp ∗ = hydrotris(3,5-dimethylpyrazolyl)borate) readily undergoes substitution of MeCN by XyNC (Xy = 2,6-dimethylphenyl) to give the isocyanide complex [Tp ∗Rh(SPh) 2(XyNC)] ( 3), whereas reaction of 2 with terminal alkynes results in the formation of the rhodathiacyclobutene complex [Tp ∗Rh(SPh){η 2-CH CR(SPh)}] ( 4; R = aryl, alkyl). Molecular structures of 3 and 4 (R = CH 2Ph) have been determined by single crystal X-ray diffraction. Complex 2 as well as [Tp ∗Rh(cyclooctene)(MeCN)] have been found to catalyze regioselective addition of benzenethiol to terminal alkynes RC CH at 50 °C to give R(PhS)C CH 2 in moderate to high yields. The above products are selectively formed when R = CH 2Ph and n-C 6H 13, while cis-RCH CHSPh and RC(SPh) 2CH 3 are also obtained as by-products when R = p-MeOC 6H 4. Catalytic cycle involving 2 and 4 is proposed based on the mechanistic studies using NMR measurement.