Niobium tetrachloride complexes with thio-, seleno- and telluro-ether coordination – synthesis and structures

Abstract

NbCl₄ reacts with the dithioethers MeS(CH₂)_nSMe (n = 2 or 3), ⁱPrS(CH₂)₂SⁱPr or o-C₆H₄(CH₂SEt)₂ in a 1 : 1 molar ratio in CH₂Cl₂ or toluene over several days, to give red or orange, paramagnetic complexes, [NbCl₄(dithioether)]. Their X-ray crystal structures confirm distorted octahedral geometries with chelating dithioether. MeS(CH₂)₂SMe, alone, also forms an [NbCl₄{MeS(CH₂)₂SMe}₂] complex based upon eight-coordinate Nb(IV) in a square antiprismatic geometry. Similar six-coordinate cis-[NbCl₄(diselenoether)] are formed by MeSe(CH₂)_nSeMe (n = 2 or 3) and ⁿBuSe(CH₂)₃SeⁿBu. The monodentate ligands Me₂S, Me₂Se and ⁿBu₂Se form [NbCl₄(R₂E)₂] (E = S, Se) which are unstable in solution, losing R₂E to form complexes with a 1 : 1 stoichiometry, which are shown to be diamagnetic dimers, [(Me₂E)Cl₃Nb(μ-Cl)₂NbCl₃(Me₂E)], with single Nb–Nb σ-bonds. Tellurium ligands tend to decompose in these reactions, but reaction at room temperature of Me₂Te and NbCl₄ formed [NbCl₄(Me₂Te)₂], the X-ray structure of which revealed an eight-coordinate dimer, [Nb₂Cl₄(μ-Cl)₄(Me₂Te)₄]. The new complexes have been characterised by microanalysis, IR, UV-visible spectroscopy and magnetic measurements. X-ray crystal structures are reported for [NbCl₄(L–L)] (L–L = MeS(CH₂)_nSMe, n = 2 or 3, ⁱPrS(CH₂)₂SⁱPr, o-C₆H₄(CH₂SEt)₂, MeSe(CH₂)₃SeMe), [Nb₂Cl₈(Me₂Te)₄], [Nb₂Cl₈(Me₂S)₂] and [Nb₂Cl₈(Me₂Se)₂]. The complexes are very sensitive to moisture and dioxygen, and some also readily undergo C–E bond cleavage. Two ligand fragmentation products were identified –[Nb₂Cl₄(μ-S)₂{MeS(CH₂)₃SMe}₂] and [Nb₂Cl₄(μ-Se)₂{o-C₆H₄(CH₂)₂Se}₄]. X-ray crystal structures are also reported for the oxidation/hydrolysis products [NbOCl₃(Me₂S)] and [NbOCl₃{MeS(CH₂)₂SMe}].