Tsuji–Wacker Oxidation of Terminal Olefins using a Palladium–Carbon Nanotube Nanohybrid Simon Donck, [a, b] Edmond Gravel, [b] Nimesh Shah, [a] Dhanaji V. Jawale, [b] Eric Doris,* [b] and Irishi N. N. Namboothiri* [a] Palladium nanoparticles supported on carbon nanotubes were used in the Tsuji–Wacker oxidation. The palladium-based nano- hybrid was found to be very active in combination with cupr- ous chloride for the selective oxidation of terminal olefins into methyl ketones. The co-catalytic system operates under very mild and sustainable conditions (room temperature, atmos- pheric pressure, low catalyst loading), as opposed to previously reported catalysts, and can be recycled without any loss in activity. The Tsuji–Wacker oxidation is a practical method for the trans- formation of terminal olefins into ketones. It usually involves catalytic amounts of palladium together with stoichiometric amounts of cuprous salts under aerobic conditions. [1] Recent efforts have been devoted to improving the process by tuning the catalysts, [2] oxidants, [3] and/or solvents. [4] To recycle the costly palladium catalyst and to facilitate isolation of the prod- ucts, supported catalysis has also been investigated, including the use of palladium on iron oxide [5] or TiO 2 , [6] dendrimer–palla- dium complexes, [7] palladium on montmorillonite, [8] and palla- dium on charcoal. [9] Although efficient, these heterogeneous systems suffer from some drawbacks such as high tempera- tures and/or high catalyst loadings. With these critical features in mind, we sought to develop a catalyst that would operate under mild and sustainable con- ditions. Our laboratories recently reported supramolecular as- semblies of metallic nanoparticles on carbon nanotubes (CNTs). This protocol afforded densely coated CNTs that were used in the catalysis of various organic transformations. [10] In the course of our investigations, we demonstrated that CNTs acted as a synergistic support capable of boosting the performance of the catalytic metal, as nanotubes provide high specific sur- face area and excellent nanoparticle dispersion. In addition, nanotubes are electronically active, and stabilization of transi- ent higher oxidation states of Pd is anticipated. We therefore wanted to expand the use of CNT-supported palladium to the catalysis of the Tsuji–Wacker oxidation reaction (Figure 1). The supported palladium catalyst was prepared by using a layer-by-layer approach. [10b] First, carbon nanotubes were so- nicated in the presence of amphiphilic nitrilotriacetic-diyne (DANTA) surfactants in water, and this resulted in the formation of nanoring-like structures at the surface of the CNTs. The rings were then polymerized by UV irradiation, which reinforced the cohesion of the supramolecular assembly. In a second step, a polycationic polymer [i.e., polydiallyldimethylammonium chloride (PDADMAC)] layer was deposited on the primary coat- ing, and palladium nanoparticles (PdNPs) were added to afford the final hybrid (i.e., PdCNT). Although other anchoring meth- ods of PdNPs on CNTs are described in the literature, they usu- ally do not provide such a dense and homogeneous covering of the nanotube surface. [11] Blank experiments were conducted with either bare nanotubes or DANTA-coated nanotubes. How- ever, no PdNPs could be detected on the naked nanotubes and poor Pd-covering was observed with DANTA nanotubes. These control experiments highlight the importance of the layer-by-layer assembly, for which the polyammonium network provided robust anchoring and stabilization of the palladium nanoparticles. Transmission electron microscopy (TEM) indicated that the PdNPs were of spherical shape, and size evaluation by statisti- cal measurement gave a mean particle diameter of approxi- mately 2 nm (Figure S1, Supporting Information). The volume of the aqueous PdCNT suspension was adjusted to a Pd con- centration of 14 mm [as determined by inductively coupled plasma mass spectrometry (ICP-MS)]. X-ray photoelectron spec- troscopy (XPS) analysis indicated that the particles were com- posed of a mixture of palladium metal and palladium oxide in an approximate ratio of 1:1 (Figure S2). Figure 1. Overview of the Tsuji–Wacker oxidation over PdCNT. [a] S. Donck, Dr. N. Shah, Prof. Dr. I. N. N. Namboothiri Department of Chemistry, Indian Institute of Technology Bombay Mumbai 400 076 (India) E-mail : irishi@chem.iitb.ac.in [b] S. Donck, Dr. E. Gravel, Dr. D. V. Jawale, Dr. E. Doris CEA, iBiTecS, Service de Chimie Bioorganique et de Marquage 91191 Gif-sur-Yvette (France) E-mail : eric.doris@cea.fr ChemCatChem 2015, 7, 2318 – 2322 # 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2318 Communications DOI: 10.1002/cctc.201500241