Phosphonic acid functionalized ordered mesoporous material: a new and ecofriendly catalyst for one-pot multicomponent Biginelli reaction under solvent-free conditions

Abstract

We report a new ordered 2D hexagonal mesoporous organosilica material (PAFMS-1) bearing phosphonic acid functionality at the surface. This hybrid material showed high Brunauer-Emmett-Teller surface area (565 m(2) g(-1)) and ordered assembly of mesoporoes with an average pore diameter of ca. 2.1 nm. This novel hybrid mesoporous material has been synthesized via cocondensation of (triethoxysilyl)(propyliminomethyl)biphenylmethyl phosphoester (PEFOS) and tetraethyl orthosilicate (TEOS) in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB) at 373 K. The phosphoester-functionalized organosilane (PEFOS) precursor has been synthesized for the first time by a simple SN2 reaction followed by Suzuki coupling and a Mannich reaction. The material has been characterized by powder X-ray diffraction, N2 sorption, and transmission electron microscopy image analysis, whereas the presence of organic moieties (an aromatic biphenyl ring and an aliphatic side chain), phosphrous, and silicon in the pore wall of the material have been characterized by solid-state magic-angle-spinning NMR, X-ray photoelectron, and Fourier transform infrared (FT-IR) spectroscopic tools. Further, the surface acid strength of the hybrid material has been determined by FT-IR analysis of the samples via temperature-programmed pyridine adsorption studies. The material has been utilized as a reusable heterogeneous catalyst for the synthesis of biologically important and value added multifunctionalized 3,4-dihydropyridin-2-1H-(ones)/3,4-dihydropyridin-2-1H-(thiones) (DHPMs) through a multicomponent Biginelli condensation reaction under solvent-free conditions at 333 K. The phosphonic acid functionalized 2D hexagonal mesoporous material showed much higher catalytic activity in this multicomponent condensation reaction over sulfonic acid functionalized mesoporous silica (MCM-41-SO3H) bearing an aliphatic chain in the hybrid framework.