TAGRA 2025

Catalytic carbonylation reactions can be performed under ambient or low pressures (≤5 bar). However, the use of carbon monoxide in organic synthesis remains limited due to difficulties in storage, handling, and the need for high-pressure equipment. To overcome these issues, several CO surrogates have been investigated for the preparation of carbonyl-containing compounds. Formic acid has emerged as an efficient, benign, and inexpensive carbonyl donor in Pd-catalyzed reactions. Homogeneous palladium-catalyzed carbonylations generally provide high yields and selectivity under mild conditions; however, their practical application is restricted by issues inherent to homogeneous catalysis, including catalyst separation, recycling difficulties, and residual metal contamination. To address these limitations, heterogeneous catalysts have been developed to enhance catalyst recovery, reusability, and environmental compatibility. Herein, a heterogeneous palladium catalyst, SBA-15@PHEN-Pd(II), was prepared by immobilizing a 5-amino-1,10-phenanthroline–Pd(II) complex onto SBA-15 via CPTES silylation and ligand grafting. 5-Amino-1,10-phenanthroline was synthesized by nitration of 1,10-phenanthroline in concentrated H2SO4/HNO3, followed by reduction of the nitro group using hydrazine hydrate in the presence of Pd/C. The catalyst was characterized by TGA, SEM, EDX, and BET analyses, showing a ligand loading of ~174 mg g-1 and a Pd content of 0.16 mmol g-1. The catalytic performance of SBA-15@PHEN-Pd(II) was evaluated in the carbonylation of haloarenes using formic acid/DCC as a CO surrogate. Optimization identified DMF as the preferred solvent, NaOH (1.5 eq.) as the optimal base, and 120 °C as the ideal temperature, affording up to 66% yield at 0.63 mol% Pd. Substrate scope studies revealed the reactivity trend Ar–I > Ar–Br > Ar–Cl, with electron-withdrawing substituents enhancing conversion. The catalyst retained activity over six cycles with minimal deactivation. Leaching tests, hot filtration, and control experiments indicated that the reaction proceeds via surface-immobilized Pd species. These findings demonstrate that SBA-15@PHEN-Pd(II) constitutes a stable and recyclable heterogeneous system for CO-free carbonylation of aryl halides.