THERMAL FRAGMENTATION OF ACYL THIOLATO COMPLEXES TO REACTIVE METAL SULFIDO INTERMEDIATES - STRUCTURE OF RU(ETA(6)-SC(3)ME(3)COME)(PPH(3))(2)

This study deals with the thermal decomposition of acylbutenethiolate (SC(3)Me(3)COMe) complexes derived from the base hydrolysis of tetramethylthiophene complexes [(ring)M-(C(4)Me(4)S)](2+) (M = Ru, ring = p-cymene, C(4)Me(4)S; M = Os, ring = p-cymene; M = Rh, Ir, ring C(5)Me(5)), (cymene)Ru(SC(3)Me(3)COMe) (1) and (C(4)Me(4)S)Ru(SC(3)Me(3)COMe) undergo thermal fragmentation, affording tetramethylfuran and insoluble ruthenium sulfides. The thermal decomposition of both 1 and (cymene)Os(SC(3)Me(3)COMe) (2) follows first-order kinetics. Two intermediates were observed in the thermal decomposition of 2. These intermediates are clusters containing inequivalent cymene groups as the only H-1 NMR detectable ligands. The second, more stable, intermediate was isolated and identified as (cymene)(3)Os3S2 (4). The complex Ru(eta(6)-SC(3)Me(3)COMe)(PPh(3))(2) (5) is obtained when 1 is thermolyzed in the presence of PPh(3). Crystallographic analysis confirmed the structure of 5, in which the eta(6)-acyl thiolate is bound through the four carbon atoms as well as the O and S atoms. The formation of 5 is first order in [1]. At high [PPh(3)]-the rate is zero order in [PPh(3)], while at low [PPh(3)] a bimolecular ([PPh(3)][Ru]) pathway is indicated. These results are explained in terms of a preequilibrium whereby the acyl thiolate in one isomeric form of 1 reversibly binds in an eta(6) mode. Thermal decompositions of (C(5)Me(5))M(SC(3)Me(3)COMe) (M = Rh (6), Ir (7)) occur unimolecularly to give tetramethylfuran and [(C(5)Me(5))MS](4). Thermolysis of 6 in the presence of PPh(3) still gives tetramethylfuran, but the Rh product is spectroscopically identified as (C(5)Me(5))(2)Ru-2(mu(2)-S)(2)(PPh(3)).