Unusual Nonoctahedral Geometry with Molybdenum Oxoimido Complexes Containing η2-Pyrazolate Ligands

The preparation and oxygen-atom-transfer (OAT) reactivity of oxoimido complexes [MoO­(N-t-Bu)­(t-Bu2-4-Rpz)2] [where R = H (1), Br (2), and Me (3); t-Bu2pz = 3,5-di-tert-butylpyrazolate] are reported. The reaction of the potassium salt of the respective pyrazolate ligands and the molybdenum oxoimido precursor, [MoO­(N-t-Bu)­Cl2(dme)] (dme = dimethoxyethane), in toluene afforded complexes 1–3 in good yields. The complexes were fully characterized by 1H and 13C NMR and IR spectroscopy, mass spectrometry, elemental analysis, and single-crystal X-ray crystallography. The solid-state structures reveal that, in each case, the molybdenum center is coordinated by one oxo, one N-t-Bu group, and two sterically demanding pyrazolate ligands via their two adjacent nitrogen atoms in an η2 fashion. Coordination around the metal center is severely distorted from octahedral and might be seen as closely approaching a distorted trigonal-prismatic geometry, which is relevant to the active site of dimethyl sulfoxide reductase in its oxidized form. The potential utility of all of the complexes 1–3 for OAT reactivity toward PMe3 at room temperature is examined, and plausible mechanistic pathways are explored by density functional theory calculations. Furthermore, the complexes reported here open a new and convenient entry into mixed oxoimidomolybdenum complexes.