Advanced Surface Functionalization of Periodic Mesoporous Silica:  Kinetic Control by Trisilazane Reagents

Abstract

The surface reactions of mesoporous silica MCM-41 with a series of new trisilylamines (trisilazanes) (SiHMe2)2NSiMe2R and (SiMe2Vin)2NSiMe2R (R = indenyl, norpinanyl, chloropropyl, 3-(N-morpholin)propyl; Vin = vinyl), disilylalkylamine (SiHMe2)iPrNSiMe2(CH2)3Cl, and monosilyldialkylamines Me2NSiMe2R (R = indenyl, chloropropyl, 3-(N-morpholin)propyl) were investigated. 1H, 13C, and 29Si MAS NMR spectroscopy, nitrogen adsorption/desorption, infrared spectroscopy, and model reactions with calix[4]arene as a mimic for an oxo surface were used to clarify the chemical nature of surface-bonded silyl groups. The trisilylamines exhibited a comparatively slow surface reaction, which allowed for the adjustment of the amount of silylated and nonreacted SiOH groups and led to a stoichiometric distribution of surface functionalities. The 2:1 integral ratio of SiHMe2 and SiMe2R moieties of such trisilazanes was found to be preserved on the silica surface as indicated by microanalytical as well as 13C and 29Si MAS NMR spectroscopic data of the hybrid materials. For example, the reaction of MCM-41 with (SiHMe2)2NSiMe2(CH2)3Cl, (SiHMe2)iPrNSiMe2(CH2)3Cl, and Me2NSiMe2(CH2)3Cl provided bi- and monofunctional hybrid materials with one-third, one-half, or all chemically accessible silanol groups derivatized by chloropropyl groups, respectively. Thus, a molecular precursor strategy was developed to efficiently control the relative amount of three different surface species, SiHMe2 (or SiVinMe2), SiMe2R, and SiOH, in a single reaction step. The reaction behavior of indenyl-substituted monosilazanes and trisilazanes (R = Ind) with calix[4]arene proved that the indenyl substituent can act as a leaving group forming a dimethylsilyl species, which is anchored bipodally on the silica surface, that is, via two Si-O bonds.

Surface Organobarium and Organomagnesium Chemistry on Periodic Mesoporous Silica MCM‐41: Convergent and Sequential Approaches Traced by Molecular Models

“…[18] After partial dehydroxylation at 270 8C/10 À3 torr, the maximum silanol surface sites accessible for this parent material M1 (pore diameter d p,ads = 3.4 nm, BET surface a s = 1023 m 2 g À1 , pore volume V p = 0.99 cm 3 g À1 ; Table 1 and Figure 1) was determined to be 3.16 mmol per gram of SiOH by 1,1,3,3-tetramethyldisilazane silylation. [19] With the aim of generating alkylated alkaline earth metal surface species, two grafting strategies were pursued.…”

“…All solvents were stored in a glovebox. Compound MCM-41 (M1), [18] 1, [16] 2 [16] 3, [17c] and MgMe 2 [43] were synthesized according to literature procedures. TEA was purchased from ABCR and used as received.…”

Mesoporous Silica Nanoparticles: Their Projection in Nanomedicine

“…The postsynthesis or grafting method consists in grafting the functional groups after the surfactant removal, either by extraction or calcination, has been carried out [74]. This method offers a wide range of chances to allocate diverse functional groups in MSNPs and also allows to chemically attach delicate organic functions prone to hydrolysis and elimination reactions [75]. One of the major issues of postsynthesis method is the possible blocking of the mesopore openings by the functional groups, which would lead unavoidably to heterogeneous functionalization of the mesoporous matrix [76].…”

Modified silica nanoparticles with an Aminonaphthoquinone

“…In this case experiments were performed by using repetition times from 10 to 300 s based on literature data for similar samples. 28 The results obtained with commercial silica NPs indicated that the repetition time of 60 s could be used to obtain quantitative Si spectra with enough signal-to-noise ratio to integrate the spectra. The external references used for the chemical shifts were the CH 3 signal of hexamethylbenzene at 17.3 ppm for 13 C and the Q 3 Si sites of caulinite at -91.5 ppm for 29 Si.…”