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    Home > JACS: a new "Ark" of chiral catalysis -- Synthesis of chiral N-heterocyclic carbene metal complexes

    JACS: a new "Ark" of chiral catalysis -- Synthesis of chiral N-heterocyclic carbene metal complexes

    • Last Update: 2020-01-14
    • Source: Internet
    • Author: User
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    1、 Background: chiral N-heterocyclic carbene (NHCs) metal complexes have become a hot topic in the field of chiral catalysis due to their special topological structure and controllable steric hindrance around the metal Since the first asymmetric hydrogenation reaction induced by chiral NHCs was successfully realized in 2001, considerable progress and development have been made in this field Due to the convenient synthesis route of NHCs, many kinds of NHCs with different chiral elements have been successfully developed and applied Among them, the most representative is the NHCs metal complexes with C 2 or C 1 symmetry Because of the trans structure of carbene framework substituents and N-aryl substituents, this unique chiral environment has excellent chiral induction effect on a variety of chiral catalytic reactions In view of the important application value of chiral NHCs, more and more attention has been paid to their chiral synthesis pathway The traditional synthesis method uses chiral raw materials to synthesize chiral NHCs, which is expensive and difficult to maintain enantioselectivity How to use a simple synthesis path or separation method to realize the preparation of chiral NHCs is a hot topic in this field (photo source: J am Chem SOC.) 2 Recently, the research team of Professor Herve clavie of the University of Aix Marseille in France has successfully realized a new synthesis path for the preparation of chiral NHCs metal complexes from prochiral NHCs Relevant research work was published on J am Chem SOC (DOI: 10.1021 / JACS 9b12698) (photo source: J am Chem SOC.) 3 Computational chemistry is an outstanding representative in the field of chemical research in the 21st century In 2013, Martin kapras, Michael Levitt and ariye vascher won the Nobel Prize for chemistry for "creating multi-scale models for complex chemical systems" However, at present, computational chemistry is still playing the role of "supporting role" - to prove the feasibility of the reaction or to explore the reaction mechanism For this reason, the author first made a bold attempt to "theory guide practice" Firstly, the author selected the NHCs with C 1 symmetry structure and calculated the rotation of NHCs with three structures Each NHCs has two rotation modes: the rotation of carbene skeleton functional group and the rotation of N-aryl structure The calculation results of representative structure 3a-3c are as follows: for 3a, because the complexes in four chiral states have smaller activation energy difference, it means that they can easily achieve conversion and only get racemates, so they can not achieve the preparation of chiral complexes 3b structure has a large activation energy difference However, the activation energy difference of N-aryl rotation of 3C structure is small, so it is not feasible to prepare pure chiral metal complexes Based on the above theoretical research, the author has carried out experimental exploration and successfully prepared the chiral (+) - and (-) - NHCs CuCl metal complexes through the separation of chiral preparation chromatography The transition metallization of gold or palladium complexes of NHCs with AuCl · SME 2 or Pd (allyl) Cl 2 has also been successfully carried out (photo source: J am Chem SOC.) for the complex with C 2 symmetry structure, the author also made a detailed exploration and study, and found that it can also achieve the successful preparation of chiral metal complexes (photo source: J am Chem SOC.) 4 Research conclusion the research team of Herve clavie, University of Aix Marseille, France, has developed a new synthesis path for the preparation of chiral NHCs metal complexes from prochiral NHCs, and successfully prepared a variety of chiral NHCs metal complexes with C 1 or C 2 symmetry.
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