A crystallographic and DFT study on a NHC complex of niobium oxide trifluoride

The complex [NbOF3(Ipr)](2), 1, was afforded in crystalline form by reaction of NbF5 with the bulky NHC ligand 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) in toluene by slow contact with moisture air. The molecular structure of 1 was ascertained by X-ray diffraction, providing the first example of a dinuclear NbOF3 derivative and also a rare case of niobium compound with a monodentate NHC. A DFT investigation has shown that the Nb-C bond consists of a weak NHC to Nb sigma donation, reinforced by an electrostatic contribution presumably favored by the presence of the ancillary fluoride ligands. The computed enthalpy for the dissociation of one Ipr from 1 is ca. 36kcalmol(-1). The presence of bulky 2,6-diisopropylphenyl substituents on the carbene ligand has negligible influence on the Nb-C bond, as highlighted by DFT analyses on simplified models.[GRAPHICS]