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)2Se(n)Bu and MeTe(CH2)3TeMe (L-L) also produce complexes with 4-coordinate gallium centres, [(GaX3)2(mu-L-L)], confirmed by the crystal structures of [(GaI3)2(mu-MeS(CH2)2SMe)], [(GaCl3)2(mu-PhS(CH2)2SPh)] and [(GaCl3)2(mu-nBuSe(CH2)2Se(n)Bu)]. 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(mu-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 ditelluroether o-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.