Coordination complexes of NbX5 (X = F, Cl) with (N,O)- and (O,O)-donor ligands and the first X-ray characterization of a neutral NbF5 adduct

A variety of fairly air-stable complexes were prepared by straightforward reactions of NbX5 (X = F, Cl) with a series of potential bidentate (N,O)- and (O,O)-donor ligands in CH2Cl2. NbF5 reacted with equimolar amounts of 2-[(2,6-diisopropylphenyl)iminomethyl]phenol (dpimpH) and 2-benzoyl-6-hydroxy-6-phenylpentafulvene (bhpfH) to afford the mononuclear complexes NbF5[κ1(O)-OC6H4CH[double bond, length as m-dash]NHC6H3(CHMe2)2], 2, and NbF5[κ1(O)-bhpfH], 7, respectively. The 1:1 reactions of NbF5 with salicylaldehyde oxime (saoH2) and 2-phenylaminoethanol gave the hexafluoroniobato salts [NbF4{κ1(O)-ON(H)[double bond, length as m-dash]CHC6H4OH}2][NbF6], 3, and [NbF4{κ1(O)-OCH2CH2NH2Ph}2][NbF6], 6, respectively. The syntheses of 2, 3 and 6 are accompanied by oxygen to nitrogen intramolecular H migration, leading to the formation of metal–alkoxide moieties. The parallel chemistry of NbCl5 is characterised by HCl release. The 1:1 reactions with dpimpH, saoH2 and bhpfH yielded, respectively, the ionic complex [NbCl2{κ1(N):κ1(O)-dpimp}2][NbCl6], 4a, the neutral-dinuclear Nb2Cl7[κ1(O)-saoH][κ2(O)-sao], 5, and the mononuclear NbCl4[κ2(O)-bhpf], 8. The tantalum species [TaCl2{κ1(N):κ1(O)-dpimp}2][TaCl6], 4b, was prepared from TaCl5/dpimpH. The new products 2–8 were fully characterized by analytical and spectroscopic techniques. Moreover the solid state structures of 2 and 8 were ascertained by X-ray diffraction studies; the structure of 2 exhibits an intramolecular bifurcated N–H(O,F) hydrogen bond. DFT calculations were carried out in order to predict the lowest energy structures in the distinct cases, showing generally good agreement with the experimental data.