Pd-chelated 1,3,5-triazine organosilica as an active catalyst for Suzuki and Heck reactions

Abstract

Design of novel functional periodic mesoporous organosilica with molecular level control finds applications in several fields of energy and environmental research including adsorption, catalysis, nanotechnology, and energy harvesting. Herein we present a melamine (1,3,5-triazine) functionalized periodic mesoporous silica (MPMO) by self-assembly of N2,N4,N6-tris(3-(triethoxysilyl)propyl)-1,3,5-triazine-2,4,6-triamine (TTET) with tetraethylorthosilicate (TEOS) via cocondensation strategy. The TTET silsesquioxane precursor was synthesized by the condensation reaction between cyanuric chloride and 3-aminopropyl triethoxysilane. The resultant MPMO material serves as an effective solid chelating agent through amine and triazine functionalities for Pd(II) to provide Pd-MPMO. The Pd-MPMO material was thoroughly characterized by a small-angle XRD, HRTEM, N2 sorption, 13C CP-MAS NMR, 29Si CP-MAS NMR, and ICP analyses. The Pd-MPMO serves as an active catalyst for CC bond formation reactions by Suzuki- and Heck cross-coupling methodologies under ligand- and cocatalyst-free conditions. Notably, the present catalytic protocol demonstrates a wide spectrum of substrate scope towards Suzuki coupling between aryl halides (I−, Br−, Cl−) and aryl boronic acids with high turn-over-number (TON) in aqueous phase under air ambience. Whereas for Heck-coupling reaction, the phenyl iodides furnished high TON than the other aryl halides. Investigation of Pd-leaching by a hot filtration test as well as reusability experiments confirms the true heterogeneous nature of present Pd-MPMO and its robustness in terms of substrate scope, catalyst stability, and durability.