Modeling Aspects of Hydrodesulfurization at Molybdenum: Carbon−Sulfur Bond Cleavage of Thiophenes by Ansa Molybdenocene Complexes

Abstract

Hydrodesulfurization (HDS), the means by which sulfur is removed from crude petroleum feedstocks and fuels, has been cited as the largest volume and most important industrial catalytic application of transition metals. Of the sulfur impurities present in crude petroleum, thiophenes are among the most resistant towards HDS. A thorough understanding of the reactivity of thiophenes towards transition metal centers is, therefore, paramount to improving existing HDS technologies. The authors have, therefore, been prompted to investigate the reactivity of thiophenes towards molybdenum complexes in an effort to discover molybdenum chemistry of relevance to HDS. It was discovered that the ansa molybdenocene complexes, [Me{sub 2}Si(C{sub 5}Me{sub 4}){sub 2}]MoH{sub 2} and [Me{sub 2}Si(C{sub 5}Me{sub 4}){sub 2}]Mo(Ph)H, exhibit reactivity that models required aspects of the mechanism for thiophene HDS. Thus, upon photolysis, [Me{sub 2}Si(C{sub 5}Me{sub 4}){sub 2}]MoH{sub 2} is capable of inducing C -S bond cleavage of thiophene (T) to give [Me{sub 2}Si(C{sub 5}Me{sub 4}){sub 2}]Mo({mu}{sup 2}-C,S-T). The latter complex can also be obtained by the thermal reaction of [Me{sub 2}Si(C{sub 5}Me{sub 4}){sub 2}]Mo(PH)H with thiophene. These reactions are not only of significance because they represent the first examples of thiophene C-S bond cleavage by a molybdenum compound, but are also of interest inmore » view of the reports that the unsubstituted molybdenocene dihydride derivative, Cp{sub 2}MoH{sub 2}, does not achieve C-S bond cleavage of thiophene; in preference, Cp{sub 2}MoH{sub 2} reacts with the {alpha} C-H bond to give a thienyl complex, Cp{sub 2}Mo({mu}{sup 1}-C-SC{sub 4}H{sub 3})H.« less