title: One-step synthesis of a highly homogeneous SBA-NHC hybrid material: en route to single-site NHC-metal heterogeneous catalysts with high loadings.
abstract: The one-step synthesis of a mesoporous silica of SBA type, functionalized with a 1-(2,6-diisopropylphenyl)-3-propyl-imidazolium (iPr2Ar-NHC-propyl) cation located in the pore channels, is described. This material was obtained by the direct hydrolysis and co-condensation of tetraethylorthosilicate (TEOS) and 1-(2,6-diisopropylphenyl)-3-[3-(triethoxysilyl)propyl]-imidazolium iodide in the presence of Pluronic P123 as a non-ionic structure-directing agent and aqueous HCl (37%) as an acid catalyst. Small-angle X-ray diffraction measurements, scanning and transmission electron microscopies, as well as dinitrogen sorption analyses revealed that the synthesized material is highly mesoporous with a 2D hexagonal arrangement of the porous network. (13)C and (29)Si CP-MAS NMR spectroscopy confirmed that the material contains intact iPr2Ar-NHC-propyl cations, which are covalently anchored via silicon atoms fused into the silica matrix. Moreover, comparison of the latter data with those of an analogous post-synthetic grafted SBA-NHC material allowed us to establish that, as expected, (i) it is most probably more homogeneous and (ii) it shows a more robust anchoring of the organic units. Finally, elemental mapping by energy dispersive X-ray spectroscopy in the scanning electron microscope demonstrated a very homogeneous distribution of the imidazolium units within the one-pot material, moreover with a high content. This study thus demonstrates that a relatively bulky and hydrophilic imidazolium unit can be directly co-condensed with TEOS in the presence of a structure-directing agent to provide in a single step a highly ordered and homogeneous mesoporous hybrid SBA-NHC material, possessing a significant number of cationic NHC sites.
authors.affiliation: Laboratoire de Chimie Organométallique Appliquée, UMR CNRS 7509, Ecole européenne de Chimie, Polymères et Matériaux, Université de Strasbourg, 25 rue Becquerel, 67087 Strasbourg, France. vritleng@unistra.fr.
authors.forename: Mansuy
authors.initials: M
authors.lastname: Rocquin
authors.forename: Mickaël
authors.initials: M
authors.lastname: Henrion
authors.forename: Marc-Georg
authors.initials: MG
authors.lastname: Willinger
authors.forename: Philippe
authors.initials: P
authors.lastname: Bertani
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Chetcuti
authors.forename: Benoît
authors.initials: B
authors.lastname: Louis
authors.forename: Vincent
authors.initials: V
authors.lastname: Ritleng