INSERTION OF RHODIUM INTO THE CARBON SULFUR BOND OF THIOPHENE - MECHANISM OF A MODEL FOR THE HYDRODESULFURIZATION REACTION

The reaction of (C5Me5)Rh(PMe3)(Ph)H with thiophene leads to the elimination of benzene and oxidative addition of the thiophene C-S bond across the Rh(I) center, giving (C5Me5)activatedRh(PMe3)(SCH = CHCH = CH). Similar reactions occur with 2-methylthiophene, 3-methylthiophene, 2,5-dimethylthiophene, benzothiophene, and dibenzothiophene. Selectivity studies performed with these complexes are consistent with the coordination of sulphur to rhodium prior to C-S bond cleavage. Reversible reductive elimination of thiophene occurs at approximately 80-degrees-C. The diene portion of the C-S insertion ligand undergoes a Diels-Alder reaction with dimethyl acetylenedicarboxylate to give dimethyl phthalate as a major product. The dimethylthiophene complex (C5Me5)activatedRh(PMe3)(SCMe = CHCH = CMe) was structurally characterized, crystallizing in the monoclinic space group P1BAR with a = 8.707 (8) angstrom, b = 14.157 (15) angstrom, c = 8.637 (5) angstrom, alpha = 100.90 (8)-degrees, beta, = 106.07 (6)-degrees, gamma = 87.85 (8)-degrees, V = 1004 (3) angstrom-3, and Z = 2.