Syntheses, molecular structures, and dynamic solution behavior of nitrido (oxo) molybdenum(VI) siloxides
摘要:
Cocondensation reaction of MoO3 with hexamethyldisilazane, followed by work-ups produced the nitrido molybdenum(VI) compounds, [MoN(OSiMe3)(3)(NH3)](2) (1), [MoN(OSiMe3)(3)(py)] (2), and a very unusual mu(2)-oxo-mu(2)-nitrido tetranuclear molybdenum(VI) compound, [Mo2N2O(OSiMe3)(4)(py)(2)](2). 2py (3). When 1 is reacted with excess methanol it results in another oxonitrido Mo(VI) compound, Mo4N4O2(OH)(8)(H2O)(MeOH)(3) (4). The compounds were characterized by elemental analyses, FT-IR, H-1 and C-13 NMR, mass spectrometry, and by single-crystal X-ray diffraction for 1 and 3. Compound 1 is dimeric in the solid state with two bridging siloxo groups; however, in toluene solution and at ambient temperature, the dimer readily dissociates into the monomer. The molecular geometry changes rapidly via a pseudorotation process as deduced from the variable temperature H-1 and 13C NMR Study However, as the temperature is lowered, monomer<->dimer equilibrium is attained. The Delta G(not equal) for the pseudorotation of 1 is 13.1 kcal mol(-1) and Delta G(not equal) for the monomer<->dimer association is 9.9 kcal mol(-1). Compound 2 is also fluxional, but remains monomeric in toluene solution down to 190 K. The Delta G(not equal) for the pseudorotation of 2 is 12.2 kcal mol(-1). In contrast, 3 is tetranuclear in the solid state and is not fluxional in solution. Instead, it is slowly disproportionated to 2 and, presumably, an oxonitrido Mo(VI) pyridine adduct. (C) 2000 Elsevier Science Ltd. All rights reserved.
Formation of mononuclear nitrido complexes of chromium(<scp>VI</scp>) and molybdenum(<scp>VI</scp>); syntheses and X-ray crystal structures of NCr(OBu<sup>t</sup>)<sub>3</sub>and NMo(OSiMe<sub>3</sub>)<sub>3</sub>(py)
Mononuclear nitrido complexes of Cr and Mo, N=Cr(OBu(t))(3) and N=Mo(OSiMe(3))(3)(py), are synthesized; the chromium complex has an idealized C-3v symmetry while the molybdenum complex has a distorted square-pyramidal geometry with the nitrido ligand at apical position; the N-Cr distance is 1.538(5) Angstrom while the average N-Mo distance is 1.627 Angstrom.