Yuan Chen, Fu Shiguo, Yang Kuiwei, Hou Bang, Liu Yan, Jiang Jianwen, Cui Yong
School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules and State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, P. R. China.
Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore 117585, Singapore.
J Am Chem Soc. 2021 Jan 13;143(1):369-381. doi: 10.1021/jacs.0c11050. Epub 2020 Dec 24.
While crystalline covalent organic frameworks (COFs) linked by C-C bonds are highly desired in synthetic chemistry, it remains a formidable challenge to synthesize. Efforts to generate C-C single bonds in COFs via de novo synthesis usually afford amorphous structures rather than crystalline phases. We demonstrate here that C-C single bond-based COFs can be prepared by direct reduction of C═C bond-linked frameworks via crystal-to-crystal transformation. By Knoevenagel polycondensation of chiral tetrabenzaldehyde of dibinaphthyl-22-crown-6 with 1,4-phenylenediacetonitrile or 4,4'-biphenyldiacetonitrile, two olefin-linked chiral COFs with 2D layered tetragonal structure are prepared. Reduction of olefin linkages of the as-prepared CCOFs produces two C-C single bond linked frameworks, which retains high crystallinity and porosity as well as high chemical stability in both strong acids and bases. The quantitative reduction is confirmed by Fourier transform infrared and cross-polarization magic angle spinning C NMR spectroscopy. Compared to the pristine structures, the reduced CCOFs display blue-shifted emission with enhanced quantum yields and fluorescence lifetimes, while the parent CCOFs exhibit higher enantioselectivity than the reduced analogs when be used as fluorescent sensors to detect chiral amino alcohols via supramolecular interactions with the built-in crown ether moieties. This work provides an attractive strategy for making chemically stable functionalized COFs with new linkages that are otherwise hard to produce.
虽然通过碳 - 碳键连接的结晶共价有机框架（COF）在合成化学中备受期待，但合成仍然是一项艰巨的挑战。通过从头合成在COF中生成碳 - 碳单键的努力通常得到无定形结构而非结晶相。我们在此证明，基于碳 - 碳单键的COF可以通过晶体到晶体的转变直接还原碳碳双键连接的框架来制备。通过将联萘 - 22 - 冠 - 6的手性四苯甲醛与1,4 - 苯二乙腈或4,4'-联苯二乙腈进行Knoevenagel缩聚反应，制备了两种具有二维层状四方结构的烯烃连接的手性COF。对所制备的CCOF的烯烃键进行还原，产生了两种碳 - 碳单键连接的框架，其在强酸和强碱中均保持高结晶度、孔隙率以及高化学稳定性。傅里叶变换红外光谱和交叉极化魔角旋转碳核磁共振光谱证实了定量还原。与原始结构相比，还原后的CCOF表现出蓝移发射，量子产率和荧光寿命增强，而当用作荧光传感器通过与内置冠醚部分的超分子相互作用检测手性氨基醇时，母体CCOF表现出比还原后的类似物更高的对映选择性。这项工作为制备具有难以产生的新连接的化学稳定功能化COF提供了一种有吸引力的策略。
