Characterization of the "Absent" Vanadium Oxo V(═O){N(SiMe)}, Imido V(═NSiMe){N(SiMe)}, and Imido-Siloxy V(═NSiMe)(OSiMe){N(SiMe)} Complexes Derived from V{N(SiMe)} and Kinetic Study of the Spontaneous Conversion of the Oxo Complex into Its Imido-Siloxy Isomer.

The synthesis and characterization of V(═O){N(SiMe)} (), V(═NSiMe){N(SiMe)} (), and V(═NSiMe)(OSiMe){N(SiMe)} () are described. Prior attempts to synthesize the vanadium(V) oxo complex via salt metathesis of VOCl with the lithium or sodium silylamide salt had yielded either the putative rearranged species V(═NSiMe)(OSiMe){N(SiMe)} () or the oxo-bridged, dimetallic {(μ-O)V[N(SiMe)]}. We now show that complex is available by treatment of the vanadium(III) tris(silylamide) V{N(SiMe)} with iodosylbenzene. The imido complex was obtained by treatment of V{N(SiMe)} with trimethylsilyl azide. Sublimation of formed complex , which was determined to be V(═NSiMe)(OSiMe){N(SiMe)}, on the basis of infrared, electronic, and H and V NMR spectroscopies. Crystallographic disorder precluded a complete structural characterization of , although a four-coordinate V atom, as well as severely disordered ligands, were apparent. Comparison of the vibrational spectra of and allowed an unambiguous assignment of the V-O (995 cm) and V-N (1060 cm) stretching bands. The vibrational spectrum of complex displayed strong absorbances at 1090 and 945 cm, indicative of its metal imide and metal siloxide moieties. The H NMR spectrum of in deuterated benzene showed overlapping signals for the ligand protons proximal and distal to the oxo moiety at 0.52 and 0.38 ppm. The H NMR spectrum of in deuterated methylene chloride displayed distinct signals for the imido (0.41 ppm) and amido (0.35 ppm) protons, whereas H NMR spectroscopy of showed three signals in an intensity ratio consistent with the formula V(═NSiMe)(OSiMe){N(SiMe)}. V NMR spectra of - revealed singlet resonances at -119 ppm (), -24 ppm (), and -279 ppm (). The electronic spectra of - displayed single absorbances in the charge transfer region, consistent with their d electron configurations. Kinetic studies of the spontaneous conversion of complex to were used to determine the rate constants (ca. 0.0002 s (63 °C), 0.0006 s (73 °C), 0.002 s (83 °C)) and activation energy (ca. 20 kcal/mol) of this first-order process.