Regiochemical selectivity in the Carbon-Sulfur bond cleavage of 2-methylbenzothiophene: Synthesis, characterization, and mechanistic study of reversible insertion into a C-S bond

Article abstract of DOI:10.1021/ja00152a011

Thermolysis of (C₅Me₅)Rh(PMe₃)(Ar)(H) (Ar = Ph or 3,5-xylyl) with 2-methylbenzothiophene at early reaction times yields a C-H activation compound and a single C-S insertion product resulting from insertion of rhodium into the S-C bond adjacent to the methyl substituent, 2k. Prolonged heating results in the conversion of 2k to the isomer in which the metal has inserted into the C-S bond adjacent to the aryl group via an intramolecular pathway, 2t. Both 2k and 2t were characterized by ¹H, ³¹P, and ¹³C NMR spectroscopies and by single crystal X-ray diffraction. The kinetic product crystallized as a racemic twin in the orthorhombic space group P2₁2₁2₁, with a = 8.5438(1) ?, b = 12.8079(2) ?, c = 19.3021(3) ?, Z = 4, and V = 2112.19(5) ?3, while the thermodynamic product crystallized in the triclinic space group P1 with a = 8.669(6) ?, b = 8.86(1) ?, c = 15.8(1) ?, α = 76.42(9)°, β = 86.66(7)°, γ = 74.46(9)°, Z = 2, and V = 1091.5(1.9) ?³.