Ruthenium, rhodium, and iridium complexes of thiophene and benzo[b]thiophenes: models for catalytic hydrodesulfurization

摘要

Ru, Rh, and Ir complexes of [pi]-bound thiophene (T) and benzo (b) thiophenes (BTs), which serve as models for the adsorption of thiophenes on hydrodesulfurization (HDS) catalysts, have been synthesized. The Rh and Ir compounds are the first dicationic transition metal complexes of either T or BTs. The BT ligands are bound to the transition metal centers via the benzene ring. The first X-ray structural characterization of a BT complex, (([eta]-C[subscript]5H[subscript]5)Ru([eta][superscript]6-BT)) BF[subscript]4 is reported;These model complexes react with a variety of nucleophiles (H[superscript]-, MeO[superscript]-, (MeO[subscript]2C)[subscript]2CH[superscript]-, EtS[superscript]- and phosphines). The BT compounds yield the first isolable transition metal cyclohexadienyl complexes derived from fused ring aromatic ligands; four isomers of each cyclohexadienyl complex are produced. The isomers result from addition at the four tertiary carbons on the benzene ring; for the nucleophiles studied, addition occurred preferentially at the carbon closest to the sulfur atom, C7. This isomer of CpRu(BT·H) has been characterized by an x-ray structure determination;The T complexes react with phosphines to produce (Cp*Ir([eta][superscript]4-T·PR[subscript]3)][superscript]2+. Double nucleophilic addition reactions (H[superscript]- and MeO[superscript]-) of (Cp*Ir(BT)) [superscript]2+ and (Cp*Ir(3-MeBT)) [superscript]2+ are also discussed. Reaction of either NaBEt[subscript]3H or Cp[subscript]2Co with (Cp*Ir(T)) [superscript]2+ results in a 2e[superscript]- reduction of the Ir complex. On the basis of [superscript]1H NMR data and by analogy to related complexes, this product is identified as Cp*Ir([eta][superscript]4-T);Both (CpRu(BT)) [superscript]+ and (CpRu(3-MeBT)) [superscript]+ undergo base-catalyzed deuterium exchange of H2 and H7 in KOH/CD[subscript]3OD solutions which follows the rate law, rate = k (Ru complex) (OH[superscript]-). The mechanism is proposed to involve rate-determining proton abstraction from either (CpRu(BT)) [superscript]+, or (CpRu(3-MeBT)) [superscript]+, followed by addition of D[superscript]+ from the CD[subscript]3OD solvent to give the deuterated BT complex. Heterogeneous reactor studies of deuterium exchange of BT over several HDS catalysts (PbMo[subscript]6.2S[subscript]8, 1% Pt-10% Re/[gamma]-Al[subscript]2O[subscript]3, Co[subscript]0.25MoS, and 5% Re/[gamma]-Al[subscript]2O[subscript]3) and [gamma]-Al[subscript]2O[subscript]3 indicate that BT is activated to exchange at the 2- and 3-positions over the catalysts. These results suggest that deuterium exchange of BT over HDS catalysts does not occur when BT is [pi]-bonded through its benzene ring. ftn*DOE Report IS-T-1322. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.