Towards applications of metal–organic frameworks in catalysis: C–H direct activation of benzoxazole with aryl boronic acids using Ni2(BDC)2(DABCO) as an efficient heterogeneous catalyst

Abstract

A crystalline porous metal–organic framework Ni₂(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 Ni₂(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 Ni₂(BDC)₂(DABCO) exhibited significantly higher catalytic activity than that of other Ni-MOFs such as Ni₃(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 Ni₂(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.