Palladium complexes chemical properties

Beside these catalytically active metallophosphine dendrimers (see above), preliminary studies on the chemical properties of phoshorus-based dendrimers complexed to metals such as platinum, palladium and rhodium have been described by Majoral, Caminade and Chaudret [21], They showed that these macromolecules (see Scheme 13) could be useful for the (in situ) generation of metallodendrimer catalysts. 

The discovery in the early 1980s that cationic palladium-phosphine complexes catalyse the copolymerisation of carbon monoxide with ethene or a higher a-olcfin to yield perfectly alternating polyketones has since attracted continuous increasing interest [1,2]. This is because the monomers are produced in large amounts at a low cost and because polyketones represent a new class of thermoplastics of physical-mechanical and chemical properties that have wide applications [3-6]. In addition, easy functionalisation can open the way to a large number of new materials [7]. The copolymerisation has... 

Polystyrene is the most frequently used polymeric support for the immobilization of palladium complexes [15]. The PS resins are well developed in the field of sohd-phase peptide synthesis. Therefore resins bearing various chemical functional groups, diameter size, loading value, degree of cross-finking, for example, are now commercially readily available to permit investigation of these variables on the catalytic property. The most widely used polystyrene in... 

The difference in solvent properties can affect the chemical potential of the catalyst complexes and monomers. The latter effect is expected to be small because of the absence of strong interactions between MA, CO2, and ethylene. A higher incorporation of MA in the copolymer in CO2 can be caused by an energetically more favorable catalyst-MA complex compared to the catalyst-ethylene complex. Another effect of the non-polar CO2 is that the local concentration of the polar MA is probably higher around the catalyst than in the bulk to stabihze the electrical charge of the cationic palladium complex and the counterion in... 

Metal Complexes. These catalysts are typically organometallic complexes they are used predominantly in homogeneous catalysis. Most of these reactions involve oxidative addition of reactants, reductive elimination of products, as well as rearrangements of atoms and chemical bonds in the coordination sphere of the complexed metal atoms (9). An extensive study by Zamaraev on the catalytic property of palladium complexes illustrates the application of these complexes to various chemical syntheses (10). 

A large number of heterogeneous catalysts have been tested under screening conditions (reaction parameters 60 °C, linoleic acid ethyl ester at an LHSV of 30 L/h, and a fixed carbon dioxide and hydrogen flow) to identify a suitable fixed-bed catalyst. We investigated a number of catalyst parameters such as palladium and platinum as precious metal (both in the form of supported metal and as immobilized metal complex catalysts), precious-metal content, precious-metal distribution (egg shell vs. uniform distribution), catalyst particle size, and different supports (activated carbon, alumina, Deloxan , silica, and titania). We found that Deloxan-supported precious-metal catalysts are at least two times more active than traditional supported precious-metal fixed-bed catalysts at a comparable particle size and precious-metal content. Experimental results are shown in Table 14.1 for supported palladium catalysts. The Deloxan-supported catalysts also led to superior linoleate selectivity and a lower cis/trans isomerization rate was found. The explanation for the superior behavior of Deloxan-supported precious-metal catalysts can be found in their unique chemical and physical properties—for example, high pore volume and specific surface area in combination with a meso- and macro-pore-size distribution, which is especially attractive for catalytic reactions (Wieland and Panster, 1995). The majority of our work has therefore focused on Deloxan-supported precious-metal catalysts. 

Ionic liquids can be used as replacements for many volatile conventional solvents in chemical processes see Table A-14 in the Appendix. Because of their extraordinary properties, room temperature ionic liquids have already found application as solvents for many synthetic and catalytic reactions, for example nucleophilic substitution reactions [899], Diels-Alder cycloaddition reactions [900, 901], Friedel-Crafts alkylation and acylation reactions [902, 903], as well as palladium-catalyzed Heck vinylations of haloarenes [904]. They are also solvents of choice for homogeneous transition metal complex catalyzed hydrogenation, isomerization, and hydroformylation [905], as well as dimerization and oligomerization reactions of alkenes [906, 907]. The ions of liquid salts are often poorly coordinating, which prevents deactivation of the catalysts. 

In 1942 the resolution of the microscope in the hands of James Hillier of the RCA Laboratories was 20 A. Now in the hands of Joseph H. Wall of the Brookhaven National Laboratory it is 2.5 A permitting visualization of the individual platinum atoms. A survey of catalysts made with the electron microscope in 1942(95) showed a diversity of size, shape and texture of catalytic substances. Many of the precious metals were large and consequently not very efficient—only a very small fraction of the atoms were available for surface reactions. However many of them were of colloidal size,(96) i.e. of one dimension at most of 2000A. The usual method of making the catalyst was to soak the support with a solution of the salt of the precious metal and then subject it to thermal treatment. The complex topoche-mical reactions that take place are difficult to control to obtain monodisperse particles of optimum size. Two questions arose in the 40 s and 50 s. What is the dependence of catalytic activity on particle size Is there a particle size below which there is no catalytic activity It was proposed to synthesize the metal particles in solution in colloidal form check their properties, both physical and chemical in solution then mount them on a suitable support to study their activity in heterogeneous catalytic reactions. However, the colloidal chemistry of platinum and palladium was complex, poorly understood and difficult to reproduce. 

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