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. Reaction between MoN(OtBu)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 they can be reversible 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-OtBu & 2-OtBu), perfluoro-tert-butanolate (1-OtBuF9 & 2-OtBuF9), tritylate (1-OCPh3 & 2-OCPh3), mesitylate (1-OMes & 2-OMes), thio-tert-butanolate (1-StBu), thiotritylate (1-SCPh3 & 2-SCPh3) and thiomesitolate complexes (1-SMes). The electrochemical properties of all complexes are evaluated and compared. All complexes isolated are characterized by multinuclear and multidimensional NMR spectroscopy and (if applicable) by EPR spectroscopy. Furthermore, the reactivity of 1-Cl and 2-Cl in the present of protons is investigated, which shows facile extrusion of ammonia in the presence of excess protons and decamethylcobaltocene yielding diamagnetic bis-molybdenum(III) complexes (3 & 4).