Phosphine free SBA-15–EDTA–Pd highly active recyclable catalyst: synthesis characterization and application for Suzuki and Sonogashira reaction

Abstract

Phosphine obstructed highly efficient and reusable SBA-15–EDTA–Pd(11) has been synthesized by anchoring a Pd–EDTA complex over the surface of organo-functionalized SBA-15. The physiochemical properties of the organo-functionalized catalyst were analyzed by elemental analysis, ICP-OES, XRD, N₂ sorption measurement isotherms, TGA and DTA, solid state ¹³C, ²⁹Si NMR spectroscopy FT-IR, XPS DRS UV-visible, SEM and TEM. The XRD and N₂ sorption analyses of the synthesized catalyst confirm that the ordered mesoporous channel structure was retained even after the multistep synthetic procedures. The (100), (110) and (200) reflections in SBA-15 provide a good structural stability, an the existence of a long range order and high pore wall thickness. The TGA-DTA results reveal that the thermal stability of the synthesized catalyst SBA-15–EDTA–Pd(11) was maintained at higher temperature. The organic moieties anchored over the surface of the SBA-15 and inside the pore wall were demonstrated by solid state ¹³C NMR and FT-IR spectroscopy. Further, solid state ²⁹Si NMR spectroscopy provides information about the degree of functionalization of the surface silanol groups, of the SBA-15 with organic moieties. The electronic environment and oxidation state of the Pd metal in the SBA-15–EDTA–Pd(11) were monitored by XPS, and DRS UV-visible techniques. Moreover, the morphologies and topographic information of the synthesized catalyst were confirmed by SEM and TEM spectroscopy. The synthesized catalyst SBA-15–EDTA–Pd(11) was screened for the Suzuki and Sonogashira coupling reactions and shows a higher catalytic activity with higher TON (turn over number). The anchored solid catalyst can be recycled efficiently and reused five times, without a major loss in the reactivity.