Attachment of metal complexes

Pyrenes appear to be once again amongst the most useful linkers, and the attachment of metal-complexed porphyrins has already been discussed in the section on small aromatic molecules. Porphyrin rings bearing a metal center can also be directly adsorbed on the CNTs sidewalls, and they have been shown to exhibit an increased charge transfer from the metal to the tubes, presumably mediated by the aromatic moieties [100]. A similar behavior is exhibited by the phthalocyanine-based complexes [101]. Other aromatic molecules can be used for appendages, including triphenylphos-... 

In addition to imprinted acid-base catalysts [49-55], attempts to imprint metal complexes have been reported and constitute the current state of the art [46, 47]. In most cases of metal-complex imprinting, ligands of the complexes are used as template molecules, which aims to create a cavity near the metal site. Molecular imprinting of metal complexes exhibits several notable features (i) attachment of metal complex on robust supports (ii) surrounding of the metal complex by polymer matrix and (iii) production of a shape selective cavity on the metal site. Metal complexes thus imprinted have been appHed to molecular recognition [56, 57], reactive complex stabilization [58, 59], Hgand exchange reaction [60] and catalysis [61-70]. 

Brown, A.P. and Anson, F.C. (1977). Molecular anchors for the attachment of metal complexes to graphite electrode surfaces./. Electroanal. Chem., 83, 203-7. 

Covalent bonding refers to the materials made in which the transition metal is bonded directly to the resin through an organometallic bond. Two different approaches can be used to covalently attach metal complexes to polymer supports (i) synthesis of appropriate functional monomers and their (co)polymerization to form catalytically active polymers (Scheme 11.1) or (ii) attachment of metal complexes to preformed functional polymer supports by chemical reactions. Following these approaches, both soluble and cross-linked chiral polymeric metal complexes can be prepared. An example of an organometallic tin catalyst suitable for transesterification was reported by workers at Rohm and Haas Company [3]. 

The attachment of metal complexes to the polymer most often occurs via coordinating functional groups (ligands) boimd to the polymer in a covalent fashion as outlined in the earlier chapters of this book, but various types of noncovalent attachment are also well documented. The latter can be achieved, for instance, by means of electrostatic interactions, physisorption by amphiphilic polymer micelles (either as common association micelles or as unimolecular micelles), by hydrogen bonding, or by specific interactions of proteins with a molecule (Figure 14). 

Heterogeneous catalysis are bi- or multi-phased they have dominated the industrial sector even though the fundamental principles involved are largely unknown. Advancements in analytical instrumentation, however, are allowing increased understanding of the catalytic phenomena in these systems. An important aspect of heterogeneous catalysis is the synthesis of active sites via attachment of metal complexes with a given chemical composition to the support surfaces (4). 

Porous crystalline materials should be investigated as supports because they offer special advantages through their well-defined geometrical sites for the attachment of metal complexes. 

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