Synthesis, structural characterisation and bonding in an anionic hexavanadate bearing redox-active ferrocenylgroups at the periphery

Abstract

Amide FcCONHC(CH₂OH)₃ (1; Fc = ferrocenyl), prepared from fluorocarbonylferrocene and tris(hydroxymethyl)methylamine, reacts with (Bu₄N)₃[H₃V₁₀O₂₈] in N,N-dimethylacetamide to afford a salt containing a bis(triolato) capped hexavanadate anion bearing two ferrocenyl groups at its periphery, (Bu₄N)₂[{FcC(O)NHC(CH₂O)₃}₂V₆O₁₃] (2). Compounds 1 and 2 were characterised by elemental analysis, spectroscopic methods (IR, NMR, and MS) and by cyclic voltammetry; the crystal structures of 1·1/2CH₃CO₂Et and (Bu₄N)₂[{FcC(O)NHC(CH₂O)₃}₂V₆O₁₃]·2Me₂NCHO were determined by X-ray diffraction analysis. Single-point DFT calculations performed for the isolated hexavanadate anion revealed the presence of 3-centre 4-electron (3c4e) O–V–O bonds on the hexavanadate cage, which are responsible for the high energy of the occupied frontier orbitals. The upper eleven occupied molecular orbitals including the HOMO are all delocalized over the hexavanadate cage and, therefore, any electrochemical oxidation can be expected to occur preferentially at the hexavanadate anion without affecting the pendant ferrocene moieties.