Synthesis, characterization and electrochemical behavior of oxo-bridged (arylimido)[tris(3,5-dimethylpyrazolyl)borato] molybdenum(V) complexes

Reaction of the oxo-molybdenum(V) precursor [MoTp*(O)Cl2] [Tp* = hydrotris(3,5-dimethyl-1-pyrazolyl)borate] with H2NC6H4R-4 (R = OEt; OPr) in refluxing toluene in the presence of Et3N afforded the binuclear oxo-bridged oxo(arylimido) molybdenum(V) complexes [Tp*Mo(O)Cl](μ-O)[Tp*Mo(NC6H4OR-4)Cl]. Surprisingly, a similar reaction between [MoTp*(O)Cl2] and C6H5NH2 yielded the previously reported compound [{MoTp*(O)Cl}2(μ-O)] as the only product. The new compounds were characterized by microanalytical data, mass spectrometry, IR and 1H NMR spectroscopy. Cyclic voltammetric studies of the new compounds, of the previously reported compounds [Tp*Mo(O)Cl](μ-O)[Tp*Mo(NAr)Cl] (Ar = C6H4OMe-4, C6H4F-3, C6H4Cl-4, C6H4Br-4, and C6H4I-3), and of [{MoTp*(O)Cl}2(μ-O)] revealed a reversible one-electron oxidation process that is little affected by the nature of the substituent on the aryl group, whereas it is greatly affected by replacement of the imido ligand with an oxo ligand. The [{MoTp*(O)Cl}2(μ-O)] compound also shows a one-electron reduction process.