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Designing bifunctional acid–base mesoporous hybrid catalysts for cascade reactions

“…Upon the oxidation with H 2 O 2 , necessary to convert thiols to suphonic 30 groups, the peak at 27 ppm disappeared and contemporarily new signals at 54 ppm, due to C1, and at 18 ppm due to C2 adjacent to the -SO 3 H groups, appeared (curves c-e), suggesting a complete oxidation of thiols in -SO 3 H groups. 41,42,46,47 The signal due to sulfonic acids is also present after the grafting of the DMAN 35 organic base onto the mesoporous silica (curve e) and this confirms that the post-synthetic procedure used to graft the organic base does not affect the strong acid sites. Additionally, 29 Si MAS NMR spectra confirm that the DMAN fragments and MPTES are not only intact after the synthesis of 60 the bifunctional hybrids but are also incorporated covalently into the ordered and non-ordered porous network bounded to inorganic silica units.…”

“…The weight loss (TGA) and their respective derivates (DTA) for the 35 one-pot non-ordered DMAN-SO 3 H/SiO 2 -5-5 and ordered DMAN-SO 3 H/OMS-5-5 are reported in Fig. 3 Section A.…”

“…The 30 spatial isolation of incompatible active organic groups that cannot coexist in solution is the key to produce bifunctional acid-base heterogeneous hybrid catalysts. Recently, many examples of bifunctionalized mesoporous catalysts have been reported, 1 in which acid and base functional groups, with different strength, 35 are hosted into the silica matrix such as amines combined together with silanols, 2,3 thiols, 4,5 ureas, 6,7 heteropolyacids 8 or Lewis and Brønsted acids. [9][10][11] In most cases, the catalysts consist in bifunctionalized periodic mesoporous organosilica (PMO), [12][13][14] modified SBA-15 15 and mesoporous silica nanoparticles 40 (MSNs), 7,10,11,16 having acid groups within the framework walls and base groups into the channel pores or vice versa.…”

“…Synthesis of the silylated base precursor 1,8-bis(dimethylamino)naphthalene (DMAN) was functionalized with terminal silyl-alcoxide reactive groups, 34,35 (see Fig.1SI for NMR characterisation of the silyl derived DMAN), obtaining 50 mono and bi-silylated DMAN precursors. In fact, to graft DMAN onto the wall of mesoporous silica, a mono-silylated precursor (DMAN-1Sil) is necessary, whilst two terminal reactive silyl groups (DMAN-2Sil) are needed to integrate the base organocatalysts into the framework of mesoporous material 55 through one-pot synthesis with conventional monosilane precursors (TMOS or TEOS), used as additional silicon sources, through sol-gel or micellar routes.…”

Cooperative catalysis by silica-supported organic functional groups

“…The cooperative effect of silanol groups has been thought to improve the catalytic activity of mesoporous silica-supported amines in base-catalyzed reactions such as the nitroaldol (Henry) condensation, 22,23 Knoevenagel condensation 22,24,25 and Michael addition. 22 For instance, in the report by Bass et al, 22 amine-functionalized silica catalysts were prepared by bulk imprinting with protected amines.…”