Molybdenum(VI) bis-imido Complexes of Dipyrromethene Ligands.

We report the synthesis of high-valent molybdenum(VI) bis-imido complexes - with dipyrromethene (DPM) supporting ligands of the general formula (DPM)Mo(NR')Cl (R, R' = mesityl (Mes) or -butyl (Bu)). The electrochemical and chemical properties of - reveal unexpected ligand noninnocence and reactivity. N NMR spectroscopy is used to assess the electronic properties of the imido ligands in the -butyl complexes and . Complex is inert toward ligand (halide) exchange with bulky phenolates such as KOMes or amides (e.g., KN(SiMe)), whereas the use of the lithium alkyl LiCHSiMe results in a rare nucleophilic β-alkylation of the DPM ligand. While the reductions of the complexes occur at molybdenum, the oxidation is centered at the DPM ligand. Quantum-chemical calculations (complete active space self-consistent field, density functional theory) suggest facile (near-infrared) interligand charge transfer to the imido ligand, which might preclude the isolation of the oxidized complex in the experiment.