Spirobifluorene-based three-dimensional covalent organic frameworks with rigid topological channels as efficient heterogeneous catalyst

Abstract

Although the past decade has witnessed tremendous progress in the development of covalent organic frameworks (COFs), three-dimensional (3D) COFs fabrications and characterizations are still much less studied compared with two-dimensional (2D) COFs, due to their complicated topology structures caused by interpenetration and limited choices of node-building blocks. In this work, we constructed a novel 3D COF (SP-3D-COF-BPY) successfully using orthogonal dual-planar spirobifluorene and bipyridine as building blocks. Also, we demonstrated the application of 3D COF-supported Pd(II) catalyst in heterogeneous catalysis. A sevenfold interpenetrated dia structure was revealed for SP-3DCOF-BPY by powder X-ray diffraction (PXRD) in conjunction with structural simulation and Pawley refinement. The bipyridine-linked frameworks bear one-dimensional (1D) unobstructed rigid channels and offer a high density of discrete coordination sites for chelating Pd(II) species. Very high loading of Pd(II) (∼15 wt %) was achieved in the asymmetric (as)-prepared Pd(II)@3D-COF-BYP. The generated highly ordered porous channels and easily accessible catalytic sites, such as COF-supported Pd(II) complex, serves as a highly active and stable microporous heterogeneous catalyst in Suzuki-Miyaura coupling reactions. The observed catalytic efficiency was high and the catalyst could be conveniently reused multiple times without any noticeable decay in catalytic performance.