Sorbonne Universités, UPMC Univ Paris 06, CNRS, Institut Parisien de Chimie Moléculaire, Equipe Chimie des Polymères , 4 Place Jussieu, F-75005 Paris, France.
Institute of Chemical Research of Catalonia (ICIQ) , Avgda. Països Catalans 16, 43007 Tarragona, Spain.
J Am Chem Soc. 2016 Apr 13;138(14):4908-16. doi: 10.1021/jacs.6b01306. Epub 2016 Mar 30.
For the first time, supramolecular helical rods composed of an achiral metal complex and a complementary enantiopure monomer provided a good level of enantioinduction in asymmetric catalysis. Mixtures containing an achiral ligand monomer (BTA(PPh2), 2 mol %) and an enantiopure ligand-free comonomer (ester BTA, 2.5 mol %), both possessing a complementary benzene-1,3,5-tricarboxamide (BTA) central unit, were investigated in combination with [Rh(cod)2]BArF (1 mol %) in the asymmetric hydrogenation of dimethyl itaconate. Notably, efficient chirality transfer occurs within the hydrogen-bonded coassemblies formed by BTA Ile and the intrinsically achiral catalytic rhodium catalyst, providing the hydrogenation product with up to 85% ee. The effect of the relative content of BTA Ile as compared to the ligand was investigated. The amount of chiral comonomer can be decreased down to one-fourth of that of the ligand without deteriorating the enantioselectivity of the reaction, while the enantioselectivity decreases for mixtures containing high amounts of BTA Ile. The nonlinear relationship between the amount of chiral comonomer and the enantioselectivity indicates that chirality amplification effects are at work in this catalytic system. Also, right-handed helical rods are formed upon co-assembly of the achiral rhodium complex of BTA(PPh2) and the enantiopure comonomer BTA Ile as confirmed by various spectroscopic and scattering techniques. Remarkably, the major enantiomer and the selectivity of the catalytic reaction are related to the handedness and the net helicity of the coassemblies, respectively. Further development of this class of catalysts built on chirally amplified helical scaffolds should contribute to the design of asymmetric catalysts operating with low amounts of chiral entities.
首次报道了由非手性金属配合物和互补的手性单体组成的超分子螺旋棒在不对称催化中提供了良好的手性诱导。研究了含有非手性配体单体（BTA(PPh2)，2mol%）和手性单体（酯 BTA，2.5mol%）的混合物，两者均具有互补的苯-1,3,5-三羧酸酰胺（BTA）中心单元，与[Rh(cod)2]BArF（1mol%）在马来酸二甲酯的不对称氢化反应中进行了组合。值得注意的是，在 BTA Ile 和内在非手性催化铑催化剂形成的氢键共组装体中发生了有效的手性转移，为氢化产物提供了高达 85%的对映体过量。研究了 BTA Ile 与配体的相对含量的影响。在不降低反应对映选择性的情况下，可以将手性单体的量减少到配体的四分之一，而对于含有大量 BTA Ile 的混合物，对映选择性降低。手性单体的量与对映选择性之间的非线性关系表明，在该催化体系中存在手性放大效应。此外，通过各种光谱和散射技术证实，在 BTA(PPh2)的非手性铑配合物和手性单体 BTA Ile 的共组装中形成了右手螺旋棒。值得注意的是，主要对映异构体和催化反应的选择性分别与共组装体的手性和净螺旋性有关。进一步开发基于手性放大螺旋支架的这类催化剂，将有助于设计使用少量手性实体的不对称催化剂。
