Thio-, seleno- and telluro-ether complexes of aluminium(iii) halides: synthesis, structures and properties

Abstract

The reaction of AlCl₃ with Me₂E (E = S, Se or Te) or ⁿBu₂E (E = Se or Te) in CH₂Cl₂ under rigorously anhydrous conditions gave the pseudo-tetrahedral complexes [AlCl₃(R₂E)]. The [AlX₃(Me₂E)] (X = Br or I, E = S; X = Br, E = Te) were made from toluene solution since attempted syntheses in CH₂Cl₂ resulted in substantial chloride incorporation. The synthesis of [(AlCl₃)₂{o-C₆H₄(CH₂SEt)₂}], in which the ligand bridges two tetrahedral aluminium centres, and of the six-coordinate trans-[AlX₂{MeE(CH₂)₂EMe}₂][AlX₄] (X = Cl or Br, E = S, and X = Cl, E = Se) and cis-[AlI₂{MeS(CH₂)₂SMe}₂][AlI₄] are reported. The tripodal thioether forms [AlCl₃{MeC(CH₂SMe)₃}], which is a chain polymer with κ²-coordinated ligand and a tbp arrangement at Al(III). Chalcogenoether macrocycle complexes [AlCl₃([9]aneS₃)], [AlCl₂([14]aneS₄)][AlCl₄] and [AlCl₂([16]aneSe₄)] [AlCl₄] are also described. All complexes were characterised by microanalysis, IR and multinuclear NMR (¹H, ²⁷Al, ⁷⁷Se or ¹²⁵Te) spectroscopy as appropriate. In CH₂Cl₂ solution [AlCl₃(Me₂S)] with added Me₂S forms [AlCl₃(Me₂S)₂], and the [AlX₂{MeS(CH₂)₂SMe}₂][AlX₄] exist as mixtures of cis and trans isomers which undergo rapid exchange at ambient temperatures. X-Ray crystal structures are reported for [AlCl₃(Me₂Se], [AlX₃(Me₂Te)] (X = Cl or Br), trans-[AlCl₂{MeE(CH₂)₂EMe}₂][AlCl₄] (E = S or Se), cis-[AlI₂{MeS(CH₂)₂SMe}₂][AlI₄], [AlCl₃{MeC(CH₂SMe)₃}], and for the sulfonium salt [Me₂SH][AlCl₄]. The aluminium halide chalcogenoether chemistry is compared with the corresponding gallium and indium systems, and the relative Lewis acidities of the metals discussed. Attempts to use [AlCl₃(ⁿBu₂E)] (E = Se or Te) as LPCVD reagents to form aluminium chalcogenide films were unsuccessful.