REGIOCHEMICAL SELECTIVITY IN THE CARBON-SULFUR BOND-CLEAVAGE OF 2-METHYLBENZOTHIOPHENE - SYNTHESIS, CHARACTERIZATION, AND MECHANISTIC STUDYOF REVERSIBLE INSERTION INTO A C-S BOND

Thermolysis of (C(5)Me(5))Rh(PMe(3))(Ar)(H) (Ar = Ph or 3,5-xylyl) wit h 2-methylbenzothiophene at early reaction times yields a C-H activati on compound and a single C-S insertion product resulting from insertio n 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 wh ich the metal has inserted into the C-S bond adjacent to the aryl grou p via an intramolecular pathway, 2t. Both 2k and 2t were characterized by H-1, P-31, and C-13 NMR spectroscopies and by single crystal X-ray diffraction. The kinetic product crystallized as a racemic twin in th e orthorhombic space group P2(1)2(1)2(1), with a = 8.5438(1) Angstrom, b = 12.8079(2) Angstrom, c = 19.3021(3) Angstrom, Z = 4, and V = 2112 .19(5) Angstrom(3), while the thermodynamic product crystallized in th e triclinic space group <P(1)over bar> with a = 8.669(6) Angstrom, b = 8.86(1) Angstrom, c = 15.18(1) Angstrom, alpha = 76.42(9)degrees, bet a = 86.66(7)degrees, gamma = 74.46(9)degrees, Z = 2, and V = 1091.5(1. 9) Angstrom(3).