Synthesis and electrochemical properties of molybdenum nitrido complexes supported by redox-active NHC and MIC ligands†

We report the synthesis of a series of molybdenum nitrido complexes supported by bis-phenolate N-heterocyclic and mesoionic carbenes (NHC & MIC). The reaction between MoN(O^tBu)₃ and the corresponding azolium salts [H₃L¹]Cl and [H₃L²]Cl (with L¹ = bis-phenolate triazolylidene and L² = bis-phenolate benzimidazolylidene) gives clean access to the corresponding NHC/MIC complexes 1-Cl and 2-Cl. Electrochemical investigations of these complexes showed that they can be reversibly reduced at potentials of −1.13 and −1.01 V vs. Fc/[Fc]⁺ and the reduced complexes [1-Cl]⁻ and [2-Cl]⁻ can be cleanly isolated after chemical reduction with one equivalent of decamethylcobaltocene. Exchange of the halide atoms is furthermore reported to give a series of nitrido complexes supported by tert-butanolate (1-O^tBu and 2-O^tBu), perfluoro-tert-butanolate (1-O^tBu^F9 and 2-O^tBu^F9), tritylate (1-OCPh₃ and 2-OCPh₃), mesitolate (1-OMes and 2-OMes), thio-tert-butanolate (1-S^tBu), thiotritylate (1-SCPh₃ and 2-SCPh₃) and thiomesitolate complexes (1-SMes). The electrochemical properties of all complexes were evaluated and compared. All isolated complexes were characterized by multinuclear and multidimensional NMR spectroscopy and (if applicable) by EPR spectroscopy. Furthermore, the reactivity of 1-Cl and 2-Cl in the presence of protons and decamethylcobaltocene was investigated, which shows facile extrusion of ammonia, yielding diamagnetic bis-molybdenum(III) complexes 3 and 4.