An active carbon support has been functionalized in order to introduce at its surface chelating phosphine groups. This has been done in several steps, which have each been studied in detail and optimized in turn. The first step consisted of increasing the number of oxygenated surface groups by oxidative treatment with HNO3. The second step involved the coupling of an amine with the surface carboxylic groups by formation of an amide bond. Various coupling agents were studied, of which SOCl2 was found to be the most efficient. Fluorinated and brominated amines were used as model amines (easier surface quantification by XPS thanks to the presence of heteroatoms such as F or Br), before reacting ethylenediamine. The pending arm of the diamine could then be further transformed into the desired bidentate phosphine in the last step. The success of the procedure was confirmed, and proof for actual surface chemical reactions was obtained. Two coordination compounds, Pd(dba)2 and Ru3(CO)12, were then incorporated on the starting carbon support and on the functionalized one. It was found that the presence of chelating phosphine groups at the surface of the functionalized support allowed to increase the yield of incorporation and the metallic dispersion at the surface, probably via a ligand exchange mechanism. Nanometer-sized Pd and Ru particles were evidenced by TEM.
Two mixed-metal clusters, [Ru 5 PtC(CO) 14 (COD)] (1) and [Ru 6 Au 2 C(CO) 16 (PPh 3 ) 2 ] (2), were anchored onto a prefunctionalized active carbon support (C PPh 2 ) with chelating phosphane groups on its surface. These clusters were also deposited onto the unmodified support (C SX+ ) for comparison. The incorporation of 1 and 2 on both supports was studied by a combination of SIMS and XPS. When the clusters were anchored onto the functionalized carbon support, SIMS spectra displayed characteristic patterns that were different from those obtained in the case of their deposition on the unmodified support. In the latter case, spectra corresponded to the results obtained with pure unsupported clusters. XPS analyses of the supported species seemed to indicate that the stoichiometry of the clusters was retained after anchoring and that their dispersion was better on C PPh 2 than on C SX+ . This indicates that the phosphanes act as anchors for noble metal compounds through a ligand exchange mechanism. The sup-
C 129 H 114 AuF 6 O 12 P 7 Pd 9 ,trigonal, R3 (no. 148), a =22.520(4) Å, c =39.433(7) Å, V =17319 Å 3 , Z =6, R gt(F) =0.047, wRref(F 2 ) =0.129, T =120 K. Source of materialSuitable crystals for X-ray diffraction analysis were obtained from the crude product resulting of the reaction of [Pd 3(CO)3(P-tBu 3)3]with [Au(PPh3)Cl] in presence of TlPF6.The crystals were grown by slow diffusion of diethylether in aCH 2 Cl 2 solution under carbon monoxide atmosphere at 4°C. Experimental detailsThe data were not corrected for absorption, but the data collection mode with high redundancy, partially takes the absorption phenomena into account (62 images, DF =2°, 29272 reflections measured for 7791 independent reflections). The PF 6 anion is disordered with aP-F bond on 3 axis. The solvent molecule is also disordered, the ring atoms were refined isotropically and constraints on bond lengths were applied. All the Hatoms were calculated with AFIX and included in the refinement with acommon isotropic temperature factor (U iso =0.065 Å 2 ). The Hatoms of the solvent molecules were not localized. DiscussionMolecular clusters are fascinating compounds of nanometrical size, comprising several metal atoms (from three to afew hundreds) surrounded by aligand shell, with potential applications in the nano field [1] and also in catalysis [2][3][4][5]. They can be used as such as homogeneous catalysts, or as heterogeneous catalysts if they are first deposited onto asupport and then activated to produce supported nanoparticles. In the latter area, the use of Au-Pd mixed metal clusters as precursors for mixed-metal nanoparticles is of particular interest because of the number of catalysed reactions by this alloy [6][7][8][9]. Nevertheless, only fifteen Au-Pd clusters were fully characterized, what is relatively poor compared to the Au-Pt analogues [10]. Thus, succeeding in obtaining the X-ray structure of such entities remains achallenge. In our attempts to synthesize Au-Pd clusters from homonuclear palladium clusters, the compound [Pd9Au(CO)9(PPh3)6](PF6)was obtained in very low yield. The synthesis of this cluster was based on the known preparation of [Pd14Au2(CO)9(PMe3)11](PF6)2 obtained by reacting [Pd8(CO)8(PMe3)7]w ith [Au(PCy 3 )Cl] in the presence of TlPF6 [11]. The cluster [Pd 9 Au(CO) 9 (PPh 3 ) 6 ](PF 6 )c rystallizes with three molecules of tetrahydrofuran by molecule of cluster (this solvent was used in the work-up of the reaction to obtain the crude product before crystallization). The structure of the metallic core of this cluster can be viewed as an octahedron of palladium atoms in which each bond of one triangular face is bridged by an additional Pd atom, the same face being also capped by the gold atom. Six terminally bounded PPh3 are observed with six bridging (m 2 )and three capping (m3)CO. The Pd-Au distance is 2.8369(7) Å.Due to the position of the gold atom, the Pd-Pd distances of the capped triangular face aree longated compared to the other Pd-Pdbonds of the octahedron (3.0917(9) Å vs. 2.750 Å (average)). ...
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