Homocoupling reaction of p-tolylboronic acid with palladium-hydroxyapatite composite from chicken eggshell as the catalyst

Biaryl compounds, consist of two aromatic rings linked by a single bond, are crucial in the synthesis of antiviral drugs, antifungal agents, functional materials, and agrochemicals. Traditionally, these compounds are synthesized through cross-coupling reactions using two different types of aryl reagents. However, homocoupling reactions have emerged as a valuable alternative, enabling the production of symmetric biaryls from a single aryl substrate. This study explores the development of a heterogeneous palladium-hydroxyapatite (Pd-HAP) catalyst for the homocoupling of arylboronic acids. Hydroxyapatite, known for its hydroxyl-rich surface, high porosity, and strong acid-base sites, was selected as a cost-effective catalyst support. The research focused on optimizing solvent and temperature to maximize biaryl yields. Under optimal conditions ethanol as the solvent at 50 °C for 24 h, an 88 % yield of biaryl products was achieved. The recycled catalyst maintained a yield of 42 % after five reuses. These findings contribute to more sustainable and cost-effective approaches for biaryl synthesis.