Arene Binding Affinities in [CpRu(η6-arene)]+ Complexes: Models for the Adsorption of Arenes on Hydrodesulfurization Catalysts

Product/reactant ratios (Y) were determined for the reactions CpRu(η6-DBT)+ + L ⇌ CpRu(η6-L)+ + DBT (where DBT is dibenzothiophene and L is a homo- or heterocyclic arene), which were conducted under UV photolysis conditions. In the photostationary state, the Y values for the different arenes decrease in the following order: mesitylene (17) > toluene (13) > indole (9.1) > carbazole (6.7) > benzene (5.9) > fluorene (5.1) > biphenyl (3.9) > DBT (1.0) > phenanthrene (0.65) > naphthalene (0.35). In general, alkyl-substituted arenes have a higher binding affinity than the parent arene, except for tert-butyl groups, which decrease the Y values. These trends in η6-arene binding to CpRu+ provide a basis for understanding competitive adsorption of arenes on metal sites of hydrotreating catalysts. Such arene components in petroleum feedstocks reduce the rates of hydrodesulfurization of dibenzothiophenes.