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 (n)Bu2E (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 κ(2)-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 ((1)H, (27)Al, (77)Se or (125)Te) 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((n)Bu2E)] (E = Se or Te) as LPCVD reagents to form aluminium chalcogenide films were unsuccessful.

Phosphine complexes of aluminium(iii) halides – preparation and structural and spectroscopic systematics

“…This arises from the ability of the aluminium halides to promote reaction with CH 2 Cl 2 , as seen in other systems. 5,18 In these cases toluene was used for the syntheses. Once isolated, the pure complexes with AlBr 3 and AlI 3 react only slowly with CH 2 Cl 2 , and it remains the NMR solvent of choice since it is very weakly coordinating and freezes at 176 K, with data collected immediately from freshly prepared solutions.…”

“…The NMR spectra are essentially invariant over the temperature range 295-233 K, in contrast to those of the corresponding thioether or selenoether complexes, which show fast dissociative ligand exchange is present at ambient temperatures. 5 27 Al resonance of the anion (δ = −26.5 (s)) is observed. The loss of coupling and then the loss of the cation resonance along the series X = Cl → Br → I can be ascribed to increasing quadrupolar relaxation rates as the electric field gradients around the Al nucleus increase with the changing donor sets.…”

“…27 In a study of complexes with Group 16 donor ligands, we found that for comparable complexes, d(M-X) and d(M-E) (E = S, Se, Te) were very similar for M = Al or Ga and typically ∼0.2 Å longer for M = In. 5 DFT calculations predict that the bond lengths involving neutral ligands for a fixed metal (Al, Ga or In) generally increase (for gas phase molecules) Cl < Br < I, reflecting decreasing Lewis acidity down the series. 5,[7][8][9] However, in some cases solid state effects ( packing effects, intermolecular interactions, hydrogen bonding or interaction with solvent molecules) can mask this trend.…”

“…5 DFT calculations predict that the bond lengths involving neutral ligands for a fixed metal (Al, Ga or In) generally increase (for gas phase molecules) Cl < Br < I, reflecting decreasing Lewis acidity down the series. 5,[7][8][9] However, in some cases solid state effects ( packing effects, intermolecular interactions, hydrogen bonding or interaction with solvent molecules) can mask this trend. 9 In order to explore the issue of size between Al and Ga centres, we compared d(M-X) (X = Cl, Br or I) for the fourcoordinate [MX 4 ] − ions, with data taken from the Cambridge Structural Database.…”

“…4 Complexes of aluminium halides with neutral soft-donor ligands have received much less attention and current knowledge is not systematic. 3 We recently reported 5 complexes with thio-, seleno-and telluro-ether ligands, including examples of four-coordinate [X 3 Al(ER 2 )] (X = Cl, Br or I; E = S, Se or Te; R = alkyl) and [(AlCl 3 ) 2 {o-C 6 H 4 (CH 2 SEt) 2 }], as well as six-coordinate [AlX 2 {MeE(CH 2 ) 2 EMe} 2 ][AlX 4 ] (E = S or Se). The isolation of the latter was unexpected since gallium(III) halides gave only four-coordinate complexes with the bidentate chalcogenoethers.…”