Silica surface functionalization is often done through the condensation of functional silanes on silanols, silica surfaces’ terminal groups. APTES, aminopropyltriethoxysilane, is widely used due to its assumed high reactivity with silanols, kinetically promoted by the catalytic action of the terminal amine function. Here, we revisit, based on a quantitative analysis by solid-state 29Si NMR, the assembly of this silane on silica surfaces to investigate whether its presence results from grafting, i.e., hetero-condensation with silanol groups or from homo-condensation of silane molecules in solution leading to polycondensates physisorbed on silica. We investigate the interaction of APTES with a crystalline layered silicate, ilerite, and with amorphous nonporous silica. We also studied a second silane, cyanopropyltrichlorosilane (CPTCS), terminated with a nitrile group. Our results undoubtedly prove that while CPTCS is grafted on the silica surface, the presence of APTES on silica and silicate materials is only marginally associated with silanol consumption. The analysis of the signal related to silicon atoms from silanes (T n species) and those from silica (Q n species) allowed for the accurate estimation of the extent of homo-condensation vs grafting based on the ratio of T-O-T/Q-O-T siloxane bridges. These findings deeply question the well-established certainties on APTES assembly on silica that should no longer be seen as grafting of alkoxysilane by hetero-condensation with silanol groups but more accurately as a homo-condensed network of silanes, predominantly physisorbed on the surface but including some sparse anchoring points to the surface involving less than 6% of the overall silanol groups.
The syntheses of the novel silicon‐bridged tris(tetraorganotin) compounds MeSi(CH2SnPh2R)3 (2, R=Ph; 5, R=Me3SiCH2) and their halogen‐substituted derivatives MeSi(CH2SnPh(3−n)In)3 (3, n=1; 4, n=2) and MeSi(CH2SnI2R)3 (6, R=Me3SiCH2) are reported. The reaction of compound 4 with di‐t‐butyltin oxide (t‐Bu2SnO)3 gives the oktokaideka‐nuclear (18‐nuclear) molecular diorganotin oxide [MeSi(CH2SnPhO)3]6 (7) while the reaction of 6 with sodium hydroxide, NaOH, provides the trikonta‐nuclear (30‐nuclear) molecular diorganotin oxide [MeSi(CH2SnRO)3]10 (8, R=Me3SiCH2). Both 7 and 8 show belt‐like ladder‐type macrocyclic structures and are by far the biggest molecular diorganotin oxides reported to date. The compounds have been characterized by elemental analyses, electrospray mass spectrometry (ESI‐MS), NMR spectroscopy, 1H DOSY NMR spectroscopy (7), IR spectroscopy (7, 8), and single‐crystal X‐ray diffraction analysis (2, 7, 8).
Es wird über die Synthesen der neuartigen siliciumverbrückten tris‐tetraorganozinnverbindungen MeSi(CH2SnPh2R)3 (2, R=Ph; 5, R=Me3SiCH2) und ihrer halogensubstituierten Derivative MeSi(CH2SnPh(3−n) In)3 (3, n=1; 4, n=2) und MeSi(CH2SnI2R)3 (6, R=Me3SiCH2) berichtet. Die Reaktion von Verbindung 4 mit Di‐tert‐butylzinnoxid, (t‐Bu2SnO)3 liefert das oktokaideka‐nukleare (18‐nuklear) molekulare Diorganozinnoxid [MeSi(CH2SnPhO)3]6 (7), während aus der Umsetzung von 6 mit Natriumhydroxid, NaOH, das trikonta‐nukleare (30‐nuklear) molekulare Diorganozinnoxid [MeSi(CH2SnRO)3]10 (8, R=Me3SiCH2) erhalten wurde. Sowohl 7 und 8 zeigen gürtelartige Leiter‐Typ makrocyclische Strukturen und sind die bei weitem größten bekannten molekularen Diorganozinnoxide. Die Verbindungen wurden mittels Elementaranalysen, Elektrospray‐Massenspektrometrie (ESI‐MS), NMR‐Spektroskopie, 1H‐DOSY‐ NMR‐Spektroskopie (7), IR‐Spektroskopie (7, 8) und Einkristallröntgenstrahlbeugungsanalyse (2, 7, 8) charakterisiert.
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