Highly dispersed Pd-nanoparticles in vanadium oxide supported zeolite-Y for C-C coupling reaction through C-Cl bond activation

Abstract

The current study provided evidence on the contribution of the Lewis acid center (V^4 +/V⁵⁺) at the aluminosilicate framework in facilitating the C-Cl bond activation during the Suzuki Miyaura cross-coupling (SMCC) reaction. To accomplish such process five catalysts with different palladium (Pd) to vanadium (V) ratios were synthesized on zeolite-Y and were duly characterized. The formation of low dimensional Pd nanoparticles (1–4 nm) on vanadium oxide supported zeolite-Y (VO_x-Y) and the Pd/V ratio was found to be dependent on the type of amino acids (proline, cysteine, serine, and threonine) used during synthesis. Particularly, the presence of thiol group in cysteine helped in stabilizing the Pd nanoparticles, while zeolite-Y, being a hard templating agent, controlled their fine distribution. Lewis acid sites V⁴⁺/V⁵⁺ created at the aluminosilicate framework helped in weakening the C-Cl bond of aryl chloride through Vⁿ⁺---Cl (n = 4,5) interaction which was proved by the Density Functional Theory (DFT) calculations and experimentally through Raman studies. The cysteine-modified zeolite-Y supported Pd/PdO-VO_x-Y_Cys catalyst activated the C-Cl bond of aryl chlorides, resulting in high % yield (up to 93 %) of the biaryls with large substrate scopes. The Pd and V loading, Pd/V, Pd⁰/Pd²⁺, V⁵⁺/V⁴⁺ ratios, and the interaction of Pd and V highly influenced the activity of the catalysts.