Partially Fluoride-Substituted Hydroxyapatite as a Suitable Support for the Gold-Catalyzed Homocoupling of Phenylboronic Acid: An Example of Interface Modification

Abstract

Interface modification of hydroxyapatite-supported nanogold by fluoride ion improved the activity of the catalyst toward aerobic homocoupling of phenylboronic acid. In the aerobic homocoupling reaction of PhBF 3 K catalyzed by hydroxyapatite-supported gold nanoclusters (Au:HAP), a study on the reactivity and reusability of the Au:HAP catalyst showed an unusual yield profile for the reaction. Intensive characterization of the catalyst by X-ray diffraction, transmission electron microscopy, and energy-dispersive X-ray spectroscopic analysis exhibited that the structure of the metal oxide support undergoes transformation from HAP to fluorapatite (FAP) and finally to calcium fluoride (CaF 2 ) during the course of these cycles of homocoupling of PhBF 3 K. Investigations of the interactions of Au:HAP with PhBF 3 K and of the fluoride ion-induced structural changes in both the support and the AuNCs, indicating that partially fluoride-substituted HAP (F-HAP) is the optimal support for the homocoupling of PhB(OH) 2 . This is effective both as a stabilizer for AuNCs through the phosphate moiety and in activation of C–B bond transmetalation through B–F interactions. The results strongly suggest that fine-tuning of the structure of the interface between metal clusters and their support (namely, surface modification) might be important in developing chemo-selective catalysts.