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. NbF5reacted with equi-molar 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)-OC6H4CHNHC6H3(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)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.