Novel aluminium compounds derived from Schiff bases: Synthesis, characterization and catalytic performance in hydroboration

Seven novel aluminium complexes supported by Schiff base ligands derived from o-diaminobenzene or o-aminothiophenol were synthesized and characterized. The reactions of AlMe ₃ with L ¹ (N,N′-bis(benzylidine)-o-phenylenediamine) and L ² (N,N′-bis(2-thienylmethylene)-o-phenylenediamine) gave the complexes L ¹ AlMe ₃ (1) and L ² AlMe ₂ (2), respectively, which involved two types of reaction mechanisms: one was proton transfer and ring closure, and the other was alkyl transfer. Complexes L ³ AlMe ₂ (HL ³  = 4-chlorobenzylidene-o-aminothiophenol) (3), L ⁴ AlMe ₂ (HL ⁴  = 2-thiophenecarboxaldehyde-o-aminothiophenol) (4), L ³ AlH(NMe ₃ ) (5), L ⁴ AlH(NMe ₃ ) (6) and L ⁵ AlH(NMe ₃ ) (HL ⁵  = 4-methylbenzylidene-o-aminothiophenol) (7) were prepared by reacting HL ^3–5 with equimolar AlMe ₃ or H ₃ Al⋅NMe ₃ , respectively. Compounds 3–7 feature an organic–inorganic hybrid containing CNAlSC five-membered ring. All complexes were characterized using ¹ H NMR and ¹³ C NMR spectroscopy, X-ray crystal structure analysis and elemental analysis. The efficient catalytic performances of 1–7 for the hydroboration of carbonyl groups were investigated, with compound 4 exhibiting the highest catalytic activity among all the complexes.