/pdf/chemical-strategies-to-design-textured-materials-from-cb2un3cizv.pdf

Chemical strategies to design textured materials: from microporous and mesoporous oxides to nanonetworks and hierarchical structures.

Noncovalent interactions: a challenge for experiment and theory

Since the first reports in the late 1970s on transition metal complexes contain- ing pincer-type ligands—named after the particular coordination mode of these ligands—these systems have at- tracted increasing interest owing to the unusual properties of the metal centers imparted by the pincer ligand. Typical- ly, such a ligand comprises an anionic aryl ring which is ortho,ortho-disubsti- tuted with heteroatom substituents, for example, CH2NR2 ,C H 2PR2 or CH2SR, which generally coordinate to the met- al center, and therefore support the MC s bond. This commonly results in a terdentate and meridional coordina- tion mode consisting of two metalla- cycles which share the MC bond. Detailed studies of the formation and the properties of a large variety of pincers containing platinum group metal complexes have provided direct access to both a fundamental under- standing of a variety of reactions in organometallic chemistry and to a range of new applications of these complexes. The discovery of alkane dehydrogenation catalysts, the mecha- nistic elucidation of fundamental transformations (for example, CC bond activation), the construction of the first metallodendrimers for sustain- able homogeneous catalysis, and the engineering of crystalline switches for materials processing represent only a few of the many highlights which have emanated from these numerous inves- tigations. This review discusses the synthetic methodologies that are cur- rently available for the preparation of platinum group metal complexes con- taining pincer ligands and especially emphasizes different applications that have been realized in materials science such as the development and engineer- ing of sensors, switches, and catalysts.

Platinum Group Organometallics Based on “Pincer” Complexes: Sensors, Switches, and Catalysts

Dendrimers in Supramolecular Chemistry: From Molecular Recognition to Self-Assembly.

Dendron-mediated self-assembly, disassembly, and self-organization of complex systems have been investigated. The most ideal building blocks would need to display shape persistence in solution and in the solid state, since only this feature provides access to the use of complementary methods of structural analysis. Most supramolecular dendrimers are chiral even when they are constructed from nonchiral building blocks and are equipped with mechanisms that amplify chirality. This poses additional challenges associated with the understanding of the structural origin of chirality in different supramolecular structures through combinations of structural analysis methods. While many supramolecular structures assembled from dendrimers and dendrons resemble some of the related morphologies generated from block-copolymers, they are much more complex and are not determined by the volume ratio between the dissimilar parts of the molecule.

Dendron-Mediated Self-Assembly, Disassembly, and Self-Organization of Complex Systems

AT the interface between heterogeneous and homogeneous catalysis there is great scope for the development of new materials that combine the advantages and/or minimize disadvantages associated with each of these classes. In particular there is a need for homogeneous catalysts with properties that allow their ready removal from a product-containing solution. One approach to such materials is to anchor homogeneous catalysts to soluble polymer supports1; we have recently prepared such catalytic materials in which the active centre is an organometallic species2,3. One disadvantage encountered when anchoring catalytic metal sites to polymers is the difficulty of accurate control of the number and location of these sites. Here we report an alternative approach—the synthesis of polysilane dendrimers (highly branched macromolecules4–6) which are functionalized at their periphery with metal-containing catalytically active sites. These dendrimers show regiospecific catalytic activity for the Kharasch addition of polyhalogenoalkanes to carbon–carbon double bonds. It should be possible to remove the nanoscale catalytic macromolecules of this type from the solution of products using filtration methods.

/pdf/homogeneous-catalysts-based-on-silane-dendrimers-3ubo2bgyo3.pdf

Joan W. J. Knapen

Papers

Homogeneous Catalysts Based on Silane Dendrimers Functionalized with Arylnickel(II) Complexes