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 AlMe3 with L-1 (N,N '-bis(benzylidine)-o-phenylenediamine) and L-2 (N,N '-bis(2-thienylmethylene)-o-phenylenediamine) gave the complexes (LAlMe3)-Al-1 (1) and (LAlMe2)-Al-2 (2), respectively, which involved two types of reaction mechanisms: one was proton transfer and ring closure, and the other was alkyl transfer. Complexes (LAlMe2)-Al-3 (HL3 = 4-chlorobenzylidene-o-aminothiophenol) (3), (LAlMe2)-Al-4 (HL4 = 2-thiophenecarboxaldehyde-o-aminothiophenol) (4), (LAlH)-Al-3(NMe3) (5), (LAlH)-Al-4(NMe3) (6) and (LAlH)-Al-5(NMe3) (HL5 = 4-methylbenzylidene-o-aminothiophenol) (7) were prepared by reacting HL3-5 with equimolar AlMe3 or H3Al. NMe3, respectively. Compounds 3-7 feature an organic-inorganic hybrid containing CNAlSC five-membered ring. All complexes were characterized using H-1 NMR and C-13 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.