Thiolato-bridged η-cycloheptatrienyl molybdenum complexes

Abstract

A new series of binuclear thiolato-bridged molybdenum complexes [(η-C₇H₃R₁⁴)Mo(µ-SR²)₃Mo(η-C₇H₃R₄¹)][BF₄](R¹= H or Me; R²= Et, Pr, Bu, Ph or CH₂Ph) have been prepared by treating the mixed-sandwich compounds [Mo(η-C₆H₅Me)(η-C₇H₃R₁⁴)][BF₄](R¹= H or Me) or [Mo(η-C₇H₇)(η-C₇H₉)][BF₄] with the corresponding thiols R²SH. Dynamic NMR studies reveal that all of these complexes (except for R²= Ph) are fluxional due to the inversion at the pyramidal sulfur centre. The activation free energy of this intramolecular process has been estimated by the coalescence temperature method. The values range from ΔG^‡= 52.9 to 58.1 kJ mol^–1 and increase in the order: R²= CH₂Ph < Bu < Pr < Et. Cyclic voltammetric studies of the binuclear compounds show that they undergo two reversible one-electron reductions and the ease of reduction is dependent on the electron-donating ability of the R¹ and R² groups.