Six-coordinate aluminium cations: synthesis, characterization and catalysis
Abstract
The present work details the synthesis and structural characterization of six-coordinate aluminium cations derived from the single starting material, Salen(tBu)AlCl 1 [Salen(tBu) = N,N′-ethylenebis(3,5-di-tert-butylsalicylideneimine)]. They are of formula [Salen(tBu)Al(base)2]+X– and contain various combinations of base and counter anion; H2O, Cl– 2, MeOH, Cl– 3, MeOH, BPh4– 4, MeOH, OTs– 5. With thf as base and OTs– as the anion, the neutral complex, Salen(tBu)Al(thf)(OTs) 6 is obtained. MeOH can be added to 6 to displace the thf and produce 5. In contrast the addition of acetophenone to 2 does not displace the H2O but produces the hydrogen-bonded complex 2· · ·2(acetophenone) 7. All of the compounds were characterized spectroscopically and, in the case of 3, 5 and 7, by X-ray crystallography. Compounds 1–3 were examined for activity as oxirane polymerization catalysts.