Synthesis And Applications Of Chiral NCN And NNN Tridentate Pincer Ligands

The tridentate pincer ligands can coordinate with metal center to form stable complexes, which show excellent stability, reactivity and stereoselectivity. Great progress has been made for these compounds in synthesis, structure, reactivity and applications. Therefore, they were wildly used in all fields such as coordination chemistry, organic synthesis, heterogeneous catalyses and functional materials, becoming a hotspot for chemists.Coordination bond between the tridentate pincer ligands containing nitrogen and metal center is so strong that it's easy to improve the reactivity and selectivity via changing the metal center or the ligand. Based on the concept of chiral tridentate pincer ligands, we conducted the investigations including the following two sections.1. Two tridentate pincer ligands containing nitrogen:NCN (L1) and NNN (L2) pincer ligands were synthesized from chiral (R)-BINOL. According to our knowledge ligand NCN (L1) has not been reported up to now.2. Using asymmetric Henry reaction between p-nitrobenzaldehyde and nitromethane as the model reaction, the catalytic performance of the NNN ligand (L2) coordinated with several metal salts in situ at room tempreture was investigated. The system of NNN ligand /CuOTf (1:1) was proved to be potential catalyst in Henry reaction. Various solvents and bases were surveyed for the reaction subsequently. When the loading of catalyst was 10 mol%, it showed outstanding catalytic efficiency for the reaction in methanol with enantiomeric excess (up to 80%). With the assistance of (Me3Si)2MeN, the reaction was accelerated although enantiomeric excess was decreased to 67%. In addition, the catalyst showed moderate catalytic efficiency for Henry reaction between a variety of benzaldehydes and nitromethane to afford the expected products in moderate yields with good enantioselectivities (up to 75%).