Towards applications of metal-organic frameworks in catalysis: C-H direct activation of benzoxazole with aryl boronic acids using Ni-2(BDC)(2)(DABCO) as an efficient heterogeneous catalyst

A crystalline porous metal-organic framework Ni-2(BDC)(2)(DABCO) was synthesized and characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR), atomic absorption spectrophotometry (AAS), and nitrogen physisorption measurements. The Ni-2(BDC)(2)(DABCO) could be used as an efficient heterogeneous catalyst for the nickel-catalyzed direct heterocycle C-H arylation reactions between azoles and arylboronic acids forming 2-arylbenzoxazoles as the principal product. This approach avoids the use of hazardous aryl halides as well as the formation of halide byproducts in the synthesis of aryl-substituted benzoxazoles. The Ni-2(BDC)(2)(DABCO) exhibited significantly higher catalytic activity than that of other Ni-MOFs such as Ni-3(BTC)(2), Ni(HBTC)(BPY), and that of some common nickel salts such as NiCl2, Ni(NO3)(2), Ni2SO4, and Ni(OAc)(2). To the best of our knowledge, application of Ni-2(BDC)(2)(DABCO) in the field of catalysis as well as the C-C cross coupling reaction via direct C-H functionalization using a nickel heterogeneous catalyst have not previously been reported in the literature.