Theoretical and Spectroscopic Investigations of the Bonding and Reactivity of (RO)3M≡N Molecules, where M = Cr, Mo, and W

Abstract

The electronic structures of the molecules ((t)BuO)(3)M[triple bond]N (M = Cr, Mo, W) have been investigated with gas phase photoelectron spectroscopy and density functional calculations. It is found that the alkoxide orbitals mix strongly with the M[triple bond]N triple bond orbitals and contribute substantially to the valence electronic structure. The first ionization of ((t)BuO)(3)Cr[triple bond]N is from an orbital of a(2)(C(3v)) symmetry that is oxygen based and contains no metal or nitrogen character by symmetry. In contrast, the first ionizations of the molybdenum and tungsten analogues are from orbitals of a(1) and e symmetry that derive from the highest occupied M[triple bond]N sigma and pi orbitals mixed with the appropriate symmetry combinations of the oxygen p orbitals. In this a(1) orbital, the oxygen p orbitals mix with the highest occupied M[triple bond]N orbital of sigma symmetry. This mixing reduces the metal character, consequently reducing the metal-nitrogen overlap interaction in this orbital. From computational modeling, the polarity of the M[triple bond]N bond increases down the group such that W[triple bond]N has the highest charge separation. In addition to investigation of the effects of the metals, the electronic influences of substitution at the alkoxide ligands have been examined for the molecules (RO)(3)Mo[triple bond]N (R = C(CH(3))(2)H, C(CH(3))(3), and C(CH(3))(2)CF(3)). The introduction of CF(3) groups stabilizes the molecular orbital energies and increases the measured ionization energies, but does not alter the overall electronic structure. The bonding characteristics of the ((t)BuO)(3)M[triple bond]N series are compared with those of organic nitriles.