Molybdenum Oxo−Imido Aryloxide Complexes:  Oxo Analogues of Olefin Metathesis Catalysts

The novel 16-electron molybdenum oxo−imido bis(aryloxide) complexes [Mo(N^tBu)(O)(2,6-Me₂C₆H₃O)₂(py)] (1) and [Mo(N^tBu)(O)(2,6-ⁱPr₂C₆H₃O)₂(py)] (2) have been prepared by the salt elimination reactions of [Mo(N^tBu)(O)Cl₂(DME)] with the appropriate lithium aryloxide and from the cycloaddition reactions of tert-butyl isocyanate with the appropriate molybdenum dioxo bis(aryloxide) complex [Mo(O)₂(OAr)₂(py)_n]. Complexes 1 and 2 are the first isolable and crystallographically characterized molybdenum oxo−imido aryloxide complexes. The geometry around the metal in complexes 1 and 2 is best described as a distorted trigonal bipyramid, with the imido and pyridine ligands occupying the axial positions and the oxo and aryloxide ligands in the equatorial plane. X-ray and IR data have confirmed that the imido ligand is the dominant π donor in the complexes, resulting in an Mo−O bond order of less than 2.5. Reaction of [Mo(N^tBu)(O)Cl₂(DME)] with Li(OCH₂^tBu) instead gave the novel complex [Mo(N^tBu)(OCH₂^tBu)₃Cl(py)] (3).