Redox and catalytic properties of alkoxides based on tris(3,5-dimethylpyrazolyl)borato tungsten nitrosyls

Previously we reported on the catalytic properties of species based on the {Mo(NO)(TpMe2)O2} moiety in the cathodic reduction of chloroform. Here, we have performed cyclic voltammetry and spectroscopic studies of the tungsten bis-alkoxide [W(NO)(TpMe2)(OEt)2], a novel chelate [W(NO)(TpMe2)O(CH2)4O], and a mono-alkoxide [W(NO)(TpMe2)Cl(OEt)] [TpMe2 = hydrotris(3,5-dimethylpyrazol-1-yl)borate]. All these complexes efficiently catalyse the cathodic reduction of chloroform which proceeds even at ca. −1.77 V versus Fc+/Fc in the presence of the chloro(ethoxy) complex. The chelate complex exhibits a quasi-reversible one-electron reduction at a potential 180 mV more anodic than its bis(ethoxy) counterpart. The UV–Vis spectrum of the former complex shows a red-shifted band (by 70 nm) in the visible region when compared with the latter.