Transition metals supramolecular assembly

Sauvage, J.-P. Dietrich-Buchecker, C. O. Chambron, J.-C. Transition metals as assembling and templating species synthesis of catenanes and molecular knots. In Comprehensive Supramolecular Chemistry, Sauvage, J.-P. Hosseini, M.W., Ed., Publisher Elsevier, Oxford, UK 1996 Vol. 2, p 43. 

A supramolecular assembly of macromolecules bearing antenna dendron has been reported. Pyrazole-anchored PBE dendrons were synthesized to examine the coordination behavior to transition-metal cations (Cu, Au, Ag) [31]. Self-assembled metallacycles were found. The Cu-metallacycle further formed luminescent fibers about 1 pm in diameter. The luminescence (605 nm) occurred by the excitation of the dendron (280 nm) and the excitation spectrum was coincident with the absorption spectrum of the dendron, suggesting the antenna effect. Interestingly, the luminescence of the Cu-metallacycle fiber disappeared when the fiber was dissociated into the individual metallacycles in C2H2. 

A review13 with 53 references of the transition-metal mediated supramolecular self-assembly is presented. Focus is on the self-assembly of macrocycles, catenanes, and cages from (en)Pd(N03)2 and pyridine-based bridging ligands. 

Figure 84 Chiral structures—the first examples of transition-metal-based discrete supramolecular assemblies with controlled stereochemistry.

Fujita, M. Self-assembled macrocycles, cages and catenanes containing transition metals in their backbones. In Comprehensive Supramolecular Chemistry Sauvage, J.-P., Hosseini, M. W., Eds. Elsevier Oxford, 1996, Vol. 9, pp 253-282. 

Currently the main interest in template reactions lies in their key role in the controlled synthesis or the self-assembly of a variety of supramole-cular entities (449). One needs a combination of intuition, conjecture, and serendipity (450) a recent example of successfully combining serendipity and rational design is provided by the silver(I)-promoted assembly of one-dimensional stranded chains (451). One also needs an understanding of mechanism in order to optimize the selection and design of building blocks and templates for the generation of yet more sophisticated supramolecular structures references cited in this present review contain at least some kinetic or mechanistic information or speculation. Template routes to interlocked molecular structures have been reviewed (452), while a discussion of switching by transition metal contains a little about the kinetics and mechanisms of this aspect of template... 

The synthesis and structures of transition metal complexes of anionic cyclo-polypnictogen ligands, e.g. cyclo-P5, are discussed in Section 7.2.1 and 11.2. An exciting recent development involves the use of these complexes as building blocks for the construction of novel supramolecular assemblies, including one-dimensional (ID) and two-dimensional (2D) polymers and even soluble spherical fullerene-like aggregates.Complexes that have been used for this... 

Figure 1.16 Transition metal Rh-catalysts formed by self-assembly (a) Schematic representation of the self-assembly process, (b) Hydroformylation of styrene with supramolecular Rh-catalysts.

New Supramolecular Approaches in Transition Metal Catalysis Template-Ligand Assisted Catalyst Encapsulation, Self-Assembled Ligands and Supramolecular Catalyst Immobilization... 

The last of the important concepts that we will consider is self-assembly. Most chemists have, at some time in their careers, wondered why molecules cannot just make themselves. The process by which molecules build themselves is termed self-assembly and is a feature of many supramolecular systems. If the molecular components possess the correct complementary molecular recognition features and their interaction is thermodynamically favourable then simply mixing them could result in the specific and spontaneous self-assembly of the desired aggregate. This assumes that there is no significant kinetic barrier to the assembly process. The recognition features within the components may be any of the intermolecular bonding processes mentioned above, but we will be concerned with interactions between transition metal ions and polydentate ligands. 

Despite their solid appearance, within the gel the liquid component is mobile and is only held by capillary forces. The solid network can be either a covalent polymer or a supramolecular assembly of small molecules. The latter class of compound, termed low molecular weight gelators (LMWG) of which 14.11 14.15 are examples, is perhaps of most interest to supramolecular chemists. Perhaps the most well known gels are metal oxide based polymeric materials produced by the sol-gel process. The sol-gel process involves the hydrolysis and polycondensation of monomeric metal salts such as early transition... 

This last section deals with a few examples of the formation of self-assembly structures from lanthanide complexes, which are formed by using transition metal ions. This area of research is very novel and relatively few examples have been developed to date. While the lanthanide ions have been used to mediate the formation of supramolecular structures, such as helicates, many of which can have both/-/ mdf-d metal ions, etc. the focus here will be on the use of lanthanide complexes and ligand structures similar to those described above [170-173]. 

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