Transformations and Agostic Interactions of Hydrocarbyl Ligands Bonded to the Sulfur-Rich Dimolybdenum Site {Mo_2Cp_2(mu-SMe)}3}: Chemical and Electrochemical Formation of mu-Alkyl and mu-Vinyl Compounds from a mu-Alkylidene Derivative

摘要

A series of chemical and electrochemical transformations of systems in which a {Mo_2Cp_2-(mu-SMe)_3} core is bridged by a mu-C_2H_nR ligand (n = 0-4) are described in this paper.The reaction of the alkylidene complex [Mo_2Cp_2(mu-SMe)_3(mu-eta~1:eta~2-CHCH_2Tol)](BF_4) (1) with LiBu~n at 0 deg C produces the mu-sigma,pi-vinyl complex [Mo_2Cp_2(mu-SMe)_3((mu-eta~1:eta~2-CH=CHTol] (2) in good yield.The molecular structure of 2 has been confirmed by X-ray analysis.Upon treatment with NaBH_4 1 is readily converted into the semibridging alkyl species [Mo_2Cp_2(mu-SMe)_3-(mu-CH_2CH_2Tol)] (3),which is also formed by electrochemical reduction of 1 in acidic medium.NMR and X-ray diffraction studies of 3 are consistent with,but do not definitively establish,the presence of a eta~1 alpha-agostic interaction.Density functional theory has been used to confirm the presence of agostic interactions in both 1 and 3 and also to explore the exchange pathways for these hydrocarbyl dimolybdenum systems.Electrochemical transformation of the mu-alkylidene complex 1 gives 3 as the major product when acid is present and a mixture of 2 and 3 when acid is absent,production of 2 being favored by low initial concentrations of 1.Theoretical,spectroscopic,and diffraction data are used to explain the formation and structures of closely related [Mo_2Cp_2(mu-SMe)_3(mu-C_2H_nR]~(z+) complexes (n = 0-4 and z = 0,1),including 1-3.