A New Step Towards Solid Base Catalysis: Azidoproazaphosphatranes Immobilized in Nanopores of Mesoporous Silica

Abstract

International audienceHeterogeneous basic catalysts derived from proazaphosphatranes, known as Verkade’s superbases, were prepared for the first time by covalent immobilization onto SBA-15 silica. In order to introduce the tether to the surface, three siloxane-containing azido derivatives of the proazaphosphatranes were first synthesized (2a–c) which after post-synthetic grafting onto silica support led to the formation of hybrid materials of different basicity and steric properties, 2a–c@SBA-15. These latter were fully characterized using a wide variety of molecular and solid-state techniques to determine their structural and textural properties. These new solid base catalysts were then evaluated in the Diels–Alder reactions of anthrone and 3-hydroxy-2-pyrone with two electron-deficient dienophiles, N-methylmaleimide and dimethyl fumarate. In general, high activity and selectivity were obtained depending on the catalytic species, the performance decreasing in the order methoxybenzyl>neopentyl>methyl azidophosphatrane. Catalyst recycling was studied for the best catalyst, the methoxybenzyl derivative, 2c@SBA-15, and it was shown that the catalyst could be re-used up to 3 cycles before any loss of activity could be detected

Design and fabrication of mesoporous heterogeneous basic catalysts

“…149 Three siloxane-containing azido derivatives of the proazaphosphatranes (1a-c) were immobilized on SBA-15, leading to the construction of heterogeneous basic catalysts 1a-c@SBA-15 with different basic and steric properties (Fig. 128 TG results showed that the amount of functional groups was 0.8, 0.55, and 0.47 mmol g À1 of silica for 1a@SBA-15, 1b@SBA-15, and 1c@SBA-15, respectively. 128 TG results showed that the amount of functional groups was 0.8, 0.55, and 0.47 mmol g À1 of silica for 1a@SBA-15, 1b@SBA-15, and 1c@SBA-15, respectively.…”

“…18). 128 The deactivation may be caused by leaching of some active species and/or plugging of some pores with reactants and products. This is also in good agreement with phosphorus elemental analysis, pointing out that a lower loading (around 50%) for the more sterically hindered neopentyl and methoxybenzyl bases.…”

Recyclable organocatalysts based on hybrid silicas

“…49 Simple reactions such as peptide formation 50 or addition of alcohols 51,52 or amines 53 on silylated isocyanates have also been used to form proline or prolinamide-based precursors. The use of (3-azidopropyl)triethoxysilane (AzPTES) upholsters growing interest, either to form P=N linkages through the Staudinger reaction, 54 or to create strong triazole linkers by the reaction with organic alkynes through the copper-catalyzed azide-alkyne cycloaddition reaction (termed CuAAC). This new methodology enables a very fast preparation of organo(alkoxy)silanes in high yield thanks to microwave activation.…”

“…High activities and endo/exo selectivities have been found, and M118c was reused up to 3 cycles without loss of activity. 54 Scheme 24 Diels-Alder cycloadditions with urea/thiourea-functionalized MSN Scheme 25 Diels-Alder cycloadditions with supported bases…”

Fabrication of ordered mesoporous solid super base with high thermal stability from mesoporous carbons

“…The second strategy involves modification of mesoporous materials by the introduction of basic species on the surface of mesoporous hosts. Basic guests can be introduced by post-synthetic modification or direct synthesis; for example, organic basic species can be introduced into mesoporous silica using such methods [25][26][27][28].…”