The cleavage of strong carbon-sulfur bonds by transition metal complexes: Homogeneous models of the hydrodesulfurization reaction.

摘要

Reaction of [(dippe)NiH]2 (1) (dippe = 1,2-bis-(di- i-propylphosphino)ethane) with dibenzothiophene at room temperature affords the C-S insertion product (dippe)Ni(eta2-C,S-dibenzothiophene) ( 2), which has been structurally characterized. At room-temperature in THF, 2 undergoes a desulfurization reaction which is believed to proceed via the intermediacy of a terminal sulfido complex of nickel, namely (dippe)Ni=S (3). Kinetic and structural evidence for the chemical feasibility of 3 was found by independent experiments. Thermolysis of (dcpe)Ni(SH)(Ph) (dcpe (1,2-bis-(dicyclohexylphosphino)ethane) leads to the formation of [(dcpe)Ni(mu-S)]2. The kinetics of this reaction are consistent with a unimolecular rate-determining step involving loss of benzene and formation of a transient sulfido complex. This sulfido complex can be trapped with nitrones, and an adduct of 3,4-dihydroisoquinoline N-oxide has been structurally characterized.; Hydride-dimer 1 also reacts with thiophene, benzothiophene, and alkylated aibenzothiophenes, and the salient features of these reactions are discussed in detail. A related hydride dimer, [(dippe)PtH]2 (4) was found to react with dibenzothiophene, 4-methyldibenzothiophene, and 4,6-dimethyldibenzothiophene leading to insertion complexes which have all been structurally characterized. This work includes the first preparation of a series of adducts of dibenzothiophenes substituted in the 4 and 4,6 positions, and provides a route into complexes which can be used to study the problems of "deep" hydrodesulfurization (the production of gas oils with less than 0.05% sulfur content by weight).; Homogeneous rhodium, iridium complexes were also found to activate the strong carbon-sulfur bonds in thiophenes, and their chemistry is described in detail.