Dinuclear niobium(III), tantalum(III) and tantalum(IV) complexes with thioether and selenoether ligands

Abstract

Magnesium reduction of MCl5 (M=Nb or Ta) in the presence of R2S (R=Me or nBu) affords the complexes [M2Cl4(R2S)2(μ-Cl)2(μ-R2S)]. The X-ray structures of those complexes where M=Nb or Ta, R=nBu2S, and of a new polymorph of [Ta2Cl4(Me2S)2(μ-Cl)2(μ-Me2S)], show that they have confacial bi-octahedral structures with MM double bonds. The reactions of [Nb2Cl4(R2S)2(μ-Cl)2(μ-R2S)] with MeSCH2CH2SMe, MeSeCH2CH2SeMe or MeSeCH2CH2CH2SeMe produce the edge-linked dimers [Nb2Cl4(MeSCH2CH2SMe)2(μ-Cl)2] and [Nb2Cl4{MeSe(CH2)nSeMe}2(μ-Cl)2], all with MM double bonds (M26+). The tantalum diselenoether complex, [Ta2Cl4(MeSeCH2CH2SeMe)2(μ-Cl)2], is similar. Two “dimer of dimers”, [{Nb2Cl4(μ-Cl)2(μ-Me2S)}2(μ-MeSeCH2CH2CH2SeMe)2] and [{Ta2Cl4(μ-Cl)2(μ-Me2S)}2(μ-nBuSeCH2CH2CH2SenBu)2], containing confacial bi-octahedra linked by diselenoether bridges, were obtained as minor by-products and were identified via their X-ray crystal structures. Under similar conditions the xylyl-linked diselenoether, o-C6H4(CH2SeMe)2, gave a complex mixture of products, including [Ta2Cl4{o-C6H4(CH2SeMe)2}2(μ-Se)2]. The complexes were characterised by microanalysis, IR and UV–visible spectroscopy. X-ray crystal structures are reported for [Nb2Cl6(nBu2S)3], [Ta2Cl6(nBu2S)3], [Ta2Cl8(Me2S)2], [Ta2Cl6(Me2S)3], [Ta2Cl4{o-C6H4(CH2SeMe)2}2(Se)2], [{Ta2Cl6(Me2S)(nBuSeCH2CH2CH2SenBu)}2] and [Ta2Cl4(Me2S)4(S)2].