C(sp2)‒Halide activation for efficient Ullmann-type C‒O coupling in water by in situ reduction of supramolecular Cu(II) species stabilized on a modified GO nanosheets support

Abstract

In the present research, the new supramolecular Cu(II) species immobilized on a magnetic benzotriazole-grafted GO nanosheets (CuO/mGO-TA-Me-BTA), with appropriate geometry of ligands for stronger chealation, was fabricated by using the Click Chemistry concept as a new magnetic nanocomposite. The obtained nanomaterial was characterized by using different spectroscopic, microscopic or analytic techniques and methods such as FT-IR, EDX, XRD, FESEM, elemental mapping, TGA-DTG, AAS and VSM. Furthermore, an attempt has been made for efficient synthesis of diverse derivatives of diaryl ethers in the presence of in situ produced heterogeneous Cu(I) species supported on the modified GO nano-structured catalyst by using 10 mol% loading of sodium ascorbate (NaAsc) in water. In situ reduction of heterogeneous Cu(II) species was found to exhibit exceptional catalytic activity for the activation of C(sp2)‒I and C(sp2)‒Br and even less reactive C(sp2)‒Cl bonds in the Ullman-type C‒O coupling of various substituted phenols and iodo/bromo/chloro arenes in the presence of cesium carbonate and water. Moderate to excellent yields (78 % up to 93 %) of the corresponding diaryl ethers were formed under mild conditions for chloro‑ and bromo/iodo- arenes, respectively. High performance as well as easy recoverability and reusability for at least five times make the reduced CuO/mGO-TA-Me-BTA a robust catalytic system in comparison with other conventional heterogeneous and homogeneous catalysts containing Cu or palladium species. To the best of our knowledge, this is the first application of in situ reduction of heterogeneous Cu(II) species in the C‒X activation for the Ullman-type C‒O coupling reaction. It can address the problem of residual transition metals remaining in the synthesis of diaryl ethers, especially the biologically active compounds.