Synthesis, characterisation and structures of thio-, seleno- and telluro-ether complexes of gallium(iii)

Abstract

The reactions of GaX₃ (X = Cl, Br or I) with SMe₂, SeMe₂ and TeMe₂ (L) in non-coordinating solvents produces only the pseudo-tetrahedral [GaX₃L], which have been characterised by IR, Raman and multinuclear NMR (¹H, ⁷¹Ga, ⁷⁷Se or ¹²⁵Te) spectroscopy, and by the crystal structure of [GaCl₃(SeMe₂)]. The ⁷¹Ga NMR resonances show small low frequency shifts for fixed halides as the neutral donors change from S → Se → Te. Bidentate ligands including MeS(CH₂)₂SMe, PhS(CH₂)₂SPh, MeSe(CH₂)₂SeMe, ⁿBuSe(CH₂)₂SeⁿBu and MeTe(CH₂)₃TeMe (L–L) also produce complexes with 4-coordinate gallium centres, [(GaX₃)₂(μ-L–L)], confirmed by the crystal structures of [(GaI₃)₂{μ-MeS(CH₂)₂SMe}], [(GaCl₃)₂{μ-PhS(CH₂)₂SPh}] and [(GaCl₃)₂{μ-ⁿBuSe(CH₂)₂SeⁿBu}]. The structural data are consistent with the weaker Lewis acidity of the gallium as the halide co-ligands become heavier. Multinuclear NMR studies suggest that in chlorocarbon solutions partial dissociation of the ligands occur, which increases with the halide co-ligand Cl < Br < I. The o-xylyl dithioether, o-C₆H₄(CH₂SMe)₂, despite being pre-organised for chelation, also forms [(GaCl₃)₂(μ-L–L)]. The corresponding diselenoether complex decomposes in solution with C–Se bond cleavage to form the selenonium salt [o-C₆H₄CH₂Se(Me)CH₂][GaCl₄], which was structurally characterised. The ditelluroethero-C₆H₄(CH₂TeMe)₂ undergoes rapid C–Te bond fission and rearrangement upon reaction with GaCl₃, and the telluronium species [o-C₆H₄CH₂Te(Me)CH₂]⁺ and [MeTe{CH₂(o-C₆H₄)CH₂TeMe}₂]⁺ have been identified by ES⁺ mass spectrometry from their characteristic isotope patterns.