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

The Rh(III)-thio late 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)l (3), 4 whereas reaction of 2 with terminal alkynes results in the formation of the rhodathiacyclobutene complex [Tp*Rh(SPh){eta(2)-CH = CR(SPh)}] (4; R = aryl, alkyl). Molecular structures of 3 and 4 (R = CH2Ph) 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 degrees C to give R(PhS)C = CH2 in moderate to high yields. The above products are selectively formed when R = CH2Ph and n-C6H13, while cis-RCH = CHSPh and RC(SPh)(2)CH3 are also obtained as by-products when R = p-MeOC6H4. Catalytic cycle involving 2 and 4 is proposed based on the mechanistic studies using NMR measurement. (c) 2006 Elsevier B.V. All rights reserved.