DOI: 10.1002/anie.201101993
Heterogeneous Catalysis
Catalytic Oxidation of Silanes by Carbon Nanotube–Gold
Nanohybrids**
Jubi John, Edmond Gravel, Agnꢀs Hagꢀge, Haiyan Li, Thierry Gacoin, and Eric Doris*
The selective oxidation of silanes has attracted wide interest
as silanols are key synthons for the production of silicon-
containing materials[1] and nucleophilic partners in organo-
metallic cross-coupling reactions.[2] Silanes are classically
converted into silanols using strong oxidizing agents such as
osmium tetroxide,[3] permanganate,[4] ozone,[5] peracids,[6] or
peroxides.[7] However, under these reaction conditions, sig-
nificant amounts of siloxanes and toxic by-products are
formed. To overcome these drawbacks, catalytic systems
involving water and oxygen have been recently devised. They
offer the advantage of cleanly producing silanols along with
hydrogen gas as the only by-product. While initial catalytic
silane oxidation studies relied on homogeneous transition
metals,[8] heterogeneous catalytic systems have emerged as
very promising alternatives.[9,10] Indeed, the latter are more
efficient (high conversion rate), recyclable, selective (little to
no siloxane by-product formation), and usually operate under
milder conditions.[11] Amongst heterogeneous catalysts for
silane oxidation, recent elegant examples include nanoporous
gold by Asao, Yamamoto, and co-workers,[9a] and hydroxya-
patite-supported silver or gold nanoparticles by Kaneda and
co-workers.[10]
silane oxidation. Our approach involves layer-by-layer (LBL)
assembly of gold nanoparticles on carbon nanotubes
(CNTs).[12] Nanotubes provide high specific surface area and
excellent nanoparticle (NP) dispersion. In addition, nano-
tubes are electronically active[13] and stabilization of transient
higher oxidation states of gold are anticipated by collabo-
rative interactions with the metal.[14] To the best of our
knowledge, this is the first report on silane oxidation by CNT-
supported catalysts.
The preparation of the CNT–gold nanohybrid (see the
Supporting Information for details) started with aqueous self-
assembly of amphiphilic nitrilotriacetic diyne lipids
(DANTA) on multiwalled carbon nanotubes[15] (Figure 1) to
Herein we report an alternative strategy which has led to
the discovery of the most efficient catalytic system to date for
Figure 1. Schematic representation of the AuCNT nanohybrid:
a) AuNP; b) PDADMAC layer; c) DANTA nanorings; (d) polymerized
region (green); e) multiwalled CNT.
[*] Dr. J. John, Dr. E. Gravel, Dr. E. Doris
CEA, iBiTecS, Service de Chimie Bioorganique et de Marquage
91191 Gif-sur-Yvette (France)
E-mail: eric.doris@cea.fr
Dr. A. Hagꢀge
CEA, iBEB, Service de Biochimie et de Toxicologie Nuclꢁaire
30207 Bagnols-sur-Cꢀze (France)
and
CEA, iBEB, CNRS-UMR 6191
13108 Saint Paul-les-Durance (France)
yield a stable suspension. As previously described, DANTA
self-organized as hemimicelles on the nanotube, thus giving
rise to nanoring-like structures.[16,17] While the hydrophobic
portion of DANTA is adsorbed onto the CNTs through van
der Waals interactions, its hydrophilic anionic head is oriented
toward the aqueous phase.[17a] To promote additional stability
of the rings, the diyne motif incorporated in the lipophylic
chain was photopolymerized by UV irradiation at 254 nm.
Polymerization takes place within individual half-cylinders
and reinforces cohesion of the assembly.[18] After UV
irradiation, the DANTA-decorated nanotubes became resist-
ant to dialysis against water and to ethanol washes, thus
indicating that the lipid assemblies were polymerized.[16a] The
second layer was thereafter deposited by stirring the sus-
pended nanotubes with cationic poly(diallyldimethylammo-
nium chloride) (PDADMAC) which adsorbed to the surface
of the tube through electrostatic interactions with the primary
anionic layer. The twice-coated CNTs were then recovered by
centrifugation before a solution of freshly prepared colloidal
gold nanoparticles (AuNPs) was added.[19] The metallic NPs
Dr. H. Li
State Key Laboratory of Physical Chemistry for Solid Surfaces and
National Engineering Laboratory for Green Chemical Productions of
Alcohols, Ethers, and Esters, Department of Chemistry, College of
Chemistry and Chemical Engineering, Xiamen University
Xiamen 361005 (China)
Dr. T. Gacoin
Laboratoire de Physique de la Matiꢀre Condensꢁe, CNRS UMR
7643, ꢂcole Polytechnique
91128 Palaiseau (France)
[**] This research was partly supported by the ANR (Nanorings
imaging) and by the CEA-Eurotalents program. We are grateful to
the TEM Team (CEA, iBiTecS), and Dr. W. L. Ling (CEA, iBS) for TEM
images. Dr. S. Perruchas (CNRS, UMR 7643) is acknowledged for
helpful discussions.
Supporting information for this article is available on the WWW
Angew. Chem. Int. Ed. 2011, 50, 7533 –7536
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
7533