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

摘要

NbCl4 reacts with the dithioethers MeS(CH2)(n)SMe (n = 2 or 3), (PrS)-Pr-i(CH2)(2)(SPr)-Pr-i 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)(2)SMe, alone, also forms an [NbCl4{MeS(CH2)(2)SMe}(2)] complex based upon eightcoordinate Nb(IV) in a square antiprismatic geometry. Similar six-coordinate cis-[NbCl4(diselenoether)] are formed by MeSe(CH2)(n)SeMe (n = 2 or 3) and (BuSe)-Bu-n(CH2)(3)(SeBu)-Bu-n. The monodentate ligands Me2S, Me2Se and (Bu2Se)-Bu-n 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(mu-Cl)(2)NbCl3(Me2E)], with single Nb-Nb sigma-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(mu-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)(n)SMe, n = 2 or 3, (PrS)-Pr-1(CH2)(2)(SPr)-Pr-i, o-C6H4(CH2SEt)(2), MeSe(CH2)(3)SeMe), [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(mu-S)(2){MeS(CH2)(3)SMe}(2)] and [Nb2Cl4(mu-Se)(2){o-C6H4(CH2)(2)Se}(4)]. X-ray crystal structures are also reported for the oxidation/hydrolysis products [NbOCl3(Me2S)] and [NbOCl3{MeS (CH2)(2)SMe}].