A wide range of chiral ligands based on the 2,2′-bipyridine scaffold were designed and synthesized. In complexation with metal Lewis acids, the reactivity and stereoselectivity of the prepared chiral ligands were examined in asymmetric catalytic direct aldol reactions, thus providing the desired products with high stereoselectivities.

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Key indicatorsSingle-crystal X-ray study T = 113 K Mean (C-C) = 0.002 Å R factor = 0.040 wR factor = 0.097 Data-to-parameter ratio = 11.1For details of how these key indicators were automatically derived from the article, see

A series of amino-salicylaldimine ligands, 5-tert-butyl-3-(R-1-ylmethyl)-salicylaldimine (L1-4, R = morpholine, piperidine, pyrrolidine, 4-methylpiperazine) have been synthesised and structurally analysed. The molecular structure of compound (L1, R = piperidine) has been determined by single-crystal X-ray diffraction. These ligands reacted with [CrCl 3 (THF) 3 ] in THF to form chromium complexes, which were isolated in high yields as stable green solids and characterised by means of IR and elemental analysis. Activated with methylaluminoxane (MAO), these complexes showed moderate catalytic activities for ethylene oligomerisaton.Scheme 1 Synthesis of amino-salicylaldimine ligands L1-4 and their Cr (III) complexes C1-4. Fig. 1 Molecular structure of ligand 2. Hydrogen atoms are omitted for clarity.