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

Abstract

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)-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.