Six-coordinate aluminium cations: Synthesis, characterization and catalysis

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.