Kang Xing, Wu Xiaowei, Han Xing, Yuan Chen, Liu Yan, Cui Yong
School of Chemistry and Chemical Engineering, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University Shanghai 200240 China
Chem Sci. 2019 Dec 19;11(6):1494-1502. doi: 10.1039/c9sc04882k.
Covalent organic frameworks (COFs) show great promise as heterogeneous photocatalysts, but they have not yet been explored for asymmetric photocatalysis, which is important for the sustainable production of pharmaceuticals and fine chemicals. We report here a pair of twofold interpenetrated 3D COFs adopting a rare (3,4)-connected topology for photocatalytic asymmetric reactions by imine condensation of rectangular and trigonal building blocks. Both COFs containing a photoredox triphenylamine moiety are efficient photocatalysts for the cross-dehydrogenative coupling reactions and asymmetric α-alkylation of aldehydes integrated with a chiral imidazolidinone catalyst. Under visible-light irradiation, the targeted chiral products are produced in satisfactory yields with up to 94% enantiomeric excess, which are comparable to those of reported reactions using molecular metal complexes or organic dyes as photosensitizers. Whereas the COFs became amorphous after catalysis, they can be recrystallized through solvent-assisted linker exchange and reused without performance loss. This is the first report utilizing COFs as photocatalysts to promote enantioselective photochemical reactions.
共价有机框架（COFs）作为多相光催化剂显示出巨大的潜力，但尚未用于不对称光催化，而不对称光催化对于药物和精细化学品的可持续生产至关重要。我们在此报告了一对通过矩形和三角形结构单元的亚胺缩合形成罕见的（3,4）连接拓扑结构用于光催化不对称反应的双重互穿三维COFs。两种含有光氧化还原三苯胺部分的COFs都是用于交叉脱氢偶联反应和与手性咪唑啉酮催化剂结合的醛的不对称α-烷基化反应的高效光催化剂。在可见光照射下，目标手性产物以令人满意的产率生成，对映体过量高达94%，这与使用分子金属配合物或有机染料作为光敏剂的报道反应相当。虽然COFs在催化后变成无定形，但它们可以通过溶剂辅助的连接体交换进行重结晶并重复使用而不损失性能。这是首次利用COFs作为光催化剂促进对映选择性光化学反应的报告。
