Hydrodesulfurization of Organosulfur Heterocycles by Metal Hydride-Nickel(0) Complexes: Accelerated Single-Electron Transfer in Carbon-Sulfur Bond Cleavage

Article abstract of DOI:10.1021/ja00284a045

The novel nickel complex, LiAlH2(THF)n.C10H8N2.Ni (2), which result from the interaction in a THF solution of (2,2'-bipyridyl)(1,5-cyclooctadiene)nickel (1) with LiAlH4 in a 1:1 molar ration is powerful desulfurizing agent in homogeneous solution for such aromatic sulfur heterocycles as dibenzothiophene (3), phenoxathiin (11), phenothiazine (12), and thianthrene(13).When employed in a 2:1 molar ratio with the heterocyclic substrate, 2 produces the corresponding ring-opened desulfurization products (biphenyl, diphenyl ether, diphenylamine, and benzene, respectively) in high yields.In contrast, 1 effects predominantly ring contraction during desulfurization and yields dibenzofuran, carbazole, and dibenzothiophene from 11, 12, and 13, respectively.From consideration of relative desulfurization rates for substituted dibenzothiophenes, deuterium labeling experiments, and the chemical reactivity differences for 1 and 2, it is concluded that these reagents desulfurize via single-electron-transfer mechanism and that radical anoins are crucial reactive intermediates.The greater reactivity of 2 is ascribed to its anionic nickel character.