Reaction of W(CO)5THF with (triphos)Rh[è3-S(C6H4)CHdCH2] (1), obtained by insertion of the 16e- fragment [(triphos)RhH] into the C2-S bond of benzo[b]thiophene (BT), gives the dimer (triphos)Rh[è3-(CO)5WS(C6H4)CHdCH2] (2; triphos ) MeC(CH2PPh2)3). Unlike 1, the heterometal dimer 2 reacts with H2 (30 atm) above 70 °C in THF, undergoing the desulfurization of the C-S-inserted BT. As a result, a mixture of the hydrido carbonyl species (triphos)RhH(CO), ethylbenzene, and WSx (xav ) 1.5) is obtained. High-pressure NMR spectroscopy in the temperature range from 20 to 70 °C shows that the desulfurization step is preceded by the formation by the dimer (triphos)RhH(í-H)[í-o-S(C6H4)C2H5]W(CO)4 (5), in which the Rh and W centers are held together by bridging 2-ethylthiophenolate and hydride ligands. Complex 5 has been characterized in both the solid state (single-crystal X-ray analysis) and solution (multinuclear NMR spectroscopy). The desulfurization of 5 occurs also by thermolysis in THF at 120 °C under a nitrogen atmosphere. Reaction of 5 with CO (30 atm, 40 °C) gives the complex [(triphos)Rh(CO)2][(CO)5W(o-S(C6H4)C2H5)] (8), in which the thiolate ligand is è1-S bound to the tungsten atom in the complex anion [(CO)5W- (o-S(C6H4)C2H5)]-. The hydrogenation of 8 (30 atm of H2, >70 °C) gives exclusively free 2-ethylthiophenol. The carbonylation of 2 (30 atm of CO, room temperature) results in the formation of [(triphos)Rh(CO)2][(CO)5W(o-S(C6H4)CHdCH2)] (3), in which the 2-vinylthiophenolate ligand is è1-S bound to the tungsten atom. The possible similarity in the C-S bond cleavage mechanism in the desulfurization of 5 to those occurring in the HDS over promoted heterogeneous catalysts is discussed.
Mimicking the HDS Activity of Promoted Tungsten Catalysts. A Homogeneous Modeling Study Using a Two-Component Tungsten/Rhodium System
Bianchini Claudio;Meli Andrea;Moneti Simonetta;Vizza Francesco
1997
Abstract
Reaction of W(CO)5THF with (triphos)Rh[è3-S(C6H4)CHdCH2] (1), obtained by insertion of the 16e- fragment [(triphos)RhH] into the C2-S bond of benzo[b]thiophene (BT), gives the dimer (triphos)Rh[è3-(CO)5WS(C6H4)CHdCH2] (2; triphos ) MeC(CH2PPh2)3). Unlike 1, the heterometal dimer 2 reacts with H2 (30 atm) above 70 °C in THF, undergoing the desulfurization of the C-S-inserted BT. As a result, a mixture of the hydrido carbonyl species (triphos)RhH(CO), ethylbenzene, and WSx (xav ) 1.5) is obtained. High-pressure NMR spectroscopy in the temperature range from 20 to 70 °C shows that the desulfurization step is preceded by the formation by the dimer (triphos)RhH(í-H)[í-o-S(C6H4)C2H5]W(CO)4 (5), in which the Rh and W centers are held together by bridging 2-ethylthiophenolate and hydride ligands. Complex 5 has been characterized in both the solid state (single-crystal X-ray analysis) and solution (multinuclear NMR spectroscopy). The desulfurization of 5 occurs also by thermolysis in THF at 120 °C under a nitrogen atmosphere. Reaction of 5 with CO (30 atm, 40 °C) gives the complex [(triphos)Rh(CO)2][(CO)5W(o-S(C6H4)C2H5)] (8), in which the thiolate ligand is è1-S bound to the tungsten atom in the complex anion [(CO)5W- (o-S(C6H4)C2H5)]-. The hydrogenation of 8 (30 atm of H2, >70 °C) gives exclusively free 2-ethylthiophenol. The carbonylation of 2 (30 atm of CO, room temperature) results in the formation of [(triphos)Rh(CO)2][(CO)5W(o-S(C6H4)CHdCH2)] (3), in which the 2-vinylthiophenolate ligand is è1-S bound to the tungsten atom. The possible similarity in the C-S bond cleavage mechanism in the desulfurization of 5 to those occurring in the HDS over promoted heterogeneous catalysts is discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
