Transformations and agostic interactions of hydrocarbyl ligands bonded to the sulfur-rich dimolybdenum site Mo2Cp2(μ-SMe) 3: Chemical and electrochemical formation of μ-alkyl and μ-vinyl compounds from a μ-alkylidene derivative

Abstract : A series of chemical and electrochemical transformations of systems in which a Mo2Cp2(μ-SMe)3 core is bridged by a μ-C2HnR ligand (n = 0-4) are described in this paper. The reaction of the alkylidene complex [Mo2Cp2(μ-SMe) 3(μ-η1:η2-CHCH2Tol)] (BF4) (1) with LiBun at 0°C produces the μ-σ,π-vinyl complex [Mo2Cp2(μ-SMe) 3(μ-η1:η2-CH=CHTol] (2) in good yield. The molecular structure of 2 has been confirmed by X-ray analysis. Upon treatment with NaBEL4 1 is readily converted into the semibridging alkyl species [Mo2Cp2(μ-SMe)3(μ-CH 2CH2Tol)] (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 η1 α-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 μ-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 [Mo2Cp 2(μ-SMe)3(μ-C2HnR] z- complexes (n = 0-4 and z = 0, 1), including 1-3. © 2005 American Chemical Society.