Palladium cluster ions

In 2007, negative-ion ESI-MS was used to detect the boron species responsible for transmetallation in the Suzuki reaction [PhB(OCH3)3] (Fig. 4D) [46]. Soon after, ESI-MS allowed the in situ observation of small catalytically active palladium clusters during a Suzuki reaction that could be precursors to catalytically active palladium nanoparticles. [(lL)sPd3(H20)], [(lL)3Pd3(H20)7] and the... 

The Reactivity of Free Palladium Clusters and Atomic Metal Ions... 

It is noteworthy that besides highly dispersed palladium clusters, ionic Pd was also detected by ESR in Pd/Li-AbOa catalysts prepared by anchoring PdCb onto alumina modified with butyl lithium. These catalysts were highly active and selective in the hydrodechlorination of substituted aromatic compounds. The coexistence of Pd and Pd° in the Pd/Li-AbOa catalysts suggests the possible formation of mixed metal ion - metal nanocluster ensemble sites. 

Other suitable reaction solvents are aqueous tetrahydrofiiran, 1,2-diraethoxyethane or acetonitrile [28]. The same result was obtained by the method G, whereas 4-nitro-chlorobenzene was also coupled, in almost quantitative yield, within 2 h at 100 °C, or 87 h at room temperature. However, in the presence of tetra-n-butylammonium bromide (5 mol%), a soluble source of bromide anions, the SM reactions of aryl bromides have been effected in ethanol at room temperature in the presence of palladium(II) acetate or chloride (2 mol%) and potassium phosphate (2 eq.) as the base, even under exposure to air [55]. Palladium salts are reduced in situ with arylboronic acids to form catalytically active nano-sized palladium clusters (2-5 nm). The latter are stabilized by adsorbtion of one-layer bromide ions at the surface of each palladium-particle. Otherwise, the unstable nano-sized palladium-clusters are aggregated to the micro-sized catalytically inactive palladium black. In this manner, 2-bromonaphthalene (268) was reacted with 2-methoxyphenylboronic acid (269) to fiimish the biaryl 270 in 98% yield [55], respectively. Scheme 17. 

In this section we shall try to review available data on catalytic properties of electron-deficient palladium on supported catalysts. The term electron deficient we shall consider to mean very small clusters of Pd on various supports, and/or palladium ions stabilized by virtue of their presence in an appropriate chemical environment. 

The most frequently used metallic catalysts for acyldiazo- and (alkoxycarbonyl)dia-zomethanes are complexes or salts of rhodium, palladium and copper. Alkenylboronic esters A-silylated allylamines and acetylenes are successfully cyclopropanat-ed with diazocarbonyl compounds under catalysis of one of those metal derivatives. Newly developed metallic catalysts for diazoacetic esters include polymer-bound, quantitatively recoverable Rh(II) carboxylate salts ", Cu(II) supported on NATION ion exchange poly-mer ruthenacarborane clusters, Rh2(NHCOCH3)4 which produces cyclopropanes with substantially enhanced trans (anti) selectivity as shown below and (rj -CsHs)... 

The reaction of palladium acetate with dppm and CO affords the trinuclear dicationic cluster [Pd3(/x-dppm)3(/u, -CO)] + (13), which contains a planar triangular Pd3 (/r-dppm)3 framework. The selective attachment of halide ions gives (14) (equation 9), closely related to (15), which is obtained by disproportionation of [Pd2Cl2(/tr-dppm)2] in the presence of PP3. 1... 

A Mdssbauer investigation of the reduction of iron oxide (0.05 wt % Fe) and iron-oxide-with-palladium (0.05 wt % Fe, 2.2 wt % Pd), carried upon 7 -Al203, reveals that supported ferric ion alone, under hydrogen, yields ferrous ion only at 500—700 °C this reduction takes place at room temperature with the bimetallic catalyst and proceeds to form a PdFe alloy at 500 °C. Similar effects are found in reduction by carbon monoxide, which yields iron-palladium metal clusters at 400 °C. The view is taken that migration over T7-A1203 is not involved but that activated hydrogen transfers only at bridgeheads on the contact line between the metal and iron oxide. 

In a similar vein, Sakai, Takenaka and Torikai produced Nafion/metal microcomposites by reducing palladium, rhodium, platinum and silver ion-exchanged membranes with H, at high temperatures (100-300°C) (26). The affected metal clusters, distributed homogeneously, were about 50 A in size. As in Risen s work, a polymer matrix template effect appears to be operative. These systems were considered and evaluated within the context of gas separations technology. 

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