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

Abstract

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 L1 (N,N′‐bis(benzylidine)‐o‐phenylenediamine) and L2 (N,N′‐bis(2‐thienylmethylene)‐o‐phenylenediamine) gave the complexes L1AlMe3 (1) and L2AlMe2 (2), respectively, which involved two types of reaction mechanisms: one was proton transfer and ring closure, and the other was alkyl transfer. Complexes L3AlMe2 (HL3 = 4‐chlorobenzylidene‐o‐aminothiophenol) (3), L4AlMe2 (HL4 = 2‐thiophenecarboxaldehyde‐o‐aminothiophenol) (4), L3AlH(NMe3) (5), L4AlH(NMe3) (6) and L5AlH(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 1H NMR and 13C 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.

Molecular Main Group Metal Hydrides

“…901,902 In both cases, turnover is proposed to proceed via initial hydroalumination of the CC or CC bond followed by formal σ-bond metathesis between the resultant alkyl or alkenyl aluminum species and HBpin. Since these early reports, the hydroboration of aldehyde and ketone substrates has been shown to be catalyzed by a range of other aluminum hydride complexes including N-heterocyclic iminatoaluminum(III) hydrides [(IPr=N)AlH 2 ] 2 (553) and [(IMes=N)AlH 2 ] 2 (703), 903 β-diketiminate-stabilized diazo compounds, 904 and Schiff-base complexes, 905 and in a cooperative fashion involving the Li and Al centers in lithium amidoaluminates of the types L n Li{ i Bu 2 Al(H)(TMP)} (L = THF, PMDTA, DABCO, diglyme (706−709)) 906 and L n Li-[{(Me 3 Si) 2 N} 2 AlH 2 )] (L = THF, 12-crown-4, PMDTA, TMEDA, Me 6 TREN (710−714)). 907 A number of these systems have also been probed for their capabilities in the hydroboration of alkynes.…”

Recent Advances in Aluminum Compounds for Catalysis

“…Z. Yang et al [24] researched series of aluminum complexes supported by Schiff base ligands, L 3 AlMe 3 (HL 3 = (N,N'bis(benzylidine)-o-phenylenediamine)) (6), L 4 AlMe 2 (HL 4 = (N,N'bis(2-thienylmethylene)-o-phenylenediamine)) (7), L 5 AlMe 2 (HL 5 = 4-chlorobenzylideneoaminothiophenol) (8), L 6 AlMe 2 (HL 6 = 2-thiophenecarboxaldehydeoaminothiophenol) (9), L 5 AlH(NMe 3 ) (10), L 6 AlH(NMe 3 ) (11) and L 7 AlH(NMe 3 ) (12) (HL 7 = 4methylbenzylideneo-amino-thiophenol) (Scheme 1). The high-efficiency catalytic performance of 6-12 for the hydroboration of carbonyl group was studied, and compound 9 had the highest catalytic activity (25 °C, 1 hour, 99 % yield).…”

s-Block Metal Catalysts for the Hydroboration of Unsaturated Bonds

“…In this regard, several aluminum-based catalysts active for the reduction of CO bonds have been developed (Scheme ). − Compared with Group 1 and Group 2 catalysts, however, application of aluminum catalysts (group 13) is still in its infancy. A comparison of β-diketiminate magnesium 5 with its aluminum analogue 93 demonstrates that the magnesium complex 5 showed higher activities toward aldehyde and ketone hydroboration.…”