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.

Graphical abstractCyclic voltammetry and spectroscopic studies of tungsten nitrosyl alkoxides have been reported. We also described the synthesis and characterisation of the first example of a chelate complex containing an α,ω-alkanediolate attached to the {W(NO)(TpMe2)}2+ centre. All these complexes efficiently catalyse the cathodic reduction of chloroform. The presence of the chloro(ethoxide) lowers the energy barrier in this process (the overpotential) by more than 1000 mV.Figure optionsDownload full-size imageDownload as PowerPoint slide