The Supramolecular-Templating Approach

The preparation of mesoporous carbon materials with ordered open-pore structures by the supramolecular-templating approach is extremely difficult in solution and remains challenging, owing to the intrinsic characters of organic molecules and the high formation energy of C—C bonds. 

More recently, Dai and coworkers successfully prepared ordered mesoporous carbon films with open-framework structures by using resorcinol and formaldehyde as carbon sources and diblock copolymer polystyrene-poly(4-vinylpyridine) (PS-P4VP) as a template [72]. Similar results were reported by Tanaka et al. [73], in which the same carbon precursor and triblock copolymer F127 (EO106PO70EO106) were used for organic-organic self-assembly. Triethyl 

High Curvature mtiDduced by increasing the ratio of phcnoVleniplate and the PEO/PPO segment in tribiock copotymer 

Inherent to the surfactant-templating approach, the interactions on surfactant/precursor species interfaces and inside species themselves play important roles on the polymer and carbon mesostructures. Several issues should be addressed  

SDAs Block copolymers with one block sufficiently compatible with a thermosetting resin and one other block sufficiently repulsive are good SDAs. 

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For the inclusion of functional moieties, control of the location and the orientation of the guest species within the host architecture is of considerable importance. The supramolecular templating approach allows the in situ controlled placement of molecules due to the formation of reservoirs of different polarity (the hydrophobic interior of the micelles, the hydrophilic compartment, the inorganic framework) during the synthesis.However, the synthesis conditions must be carefully chosen because the mesostructure formation involves a delicate interplay between micelle formation, condensation of the inorganic framework, and the formation of the film. 

These results show unambiguously that templates are an attractive alternative to the tedious precursor synthesis commonly used for the preparation of shape-persistent macrocydes. They allow the preparation of symmetrically and even of nonsymmetrically functionalized PAMs in high yields. Moreover, the increased amount of the shape-persistent macrocyde in the crude product simplifies the purification procedure in most cases. However, both the supramolecular and the covalent template approach require the presence of appropriate functional groups that bind (are bound) to the template. 

Roelfes s supramolecular assembly is one of the most efficient enan-tioselective catalysts for aqueous Michael additions. The DNA template approach has also been used for enantioselective Friedel-Crafts reactions in water, with outstanding results in terms of conversion and enantioselectivities (110). All these results confirm the impressive potential of DNA-based enantioselective catalysis. 

One of the most successful approaches to the synthesis of metalla-supramolecular systems has been by templated self-assembly processes. Most of the templating agents used by synthetic chemists are either cationic or neutral species. Anions, on the other hand, have only fairly recently been successfully utilized as templates. The new metalla-macrocycles [Pd2Ni2(atu)4(PPh3)4X]3+ (atu = deprotonated amidinothiourea, X = C1, Br, I) have been prepared using anion templated syntheses. Only in the presence of each of these three halides are the metalla-macrocycles... 

Very recently, MacGillivray et al. succeeded in the supramolecular construction of molecular ladders in the solid state using a linear template approach [48]. They designed the cocrystals 1,3-benzenediol (resorcinol) or a derivative with an all-trans-bis(4-pyridyl)butadiene or hexatriene, in which two resorcinol molecules preorganize two polyene molecules through two hydrogen bond interactions, for [2-1-2] photoaddition (Scheme 5). In this design, two polyenes would... 

Most of the systems described in Chapter 5 contain small- or medium-sized or multinuclear benzenoid and non-benzenoid arenes. In Chapter 6, Hoger gives an overview over the mastery of the synthesis of macro- and megacycles. He shows different approaches towards shape-persistent macrocycles and carefully examines and discusses selected examples that display the advantages and disadvantages of macrocycle synthesis under kinetic and thermodynamic control. The template approach (both supramolecular and covalent) towards functionalized rings is also discussed and introduces a strong motif of supramolecular chemistry, which is much further developed but in a more polymer-oriented topic, in the next chapter. 

The synthesis of interlocked molecules has become commonplace over the past 25 years with the gradual development of a number of highly facile template methods for their construction. What were once laboratory curiosities have now taken a prominent place in the broad field of supramolecular chemistry, especially regarding their uses and further potential as molecular switches and machines [1], We present here an overview of the main synthetic approaches to these molecules, with a focus on methods in which macrocyclization reactions result in interlocked products. The analysis is by no means meant to be comprehensive or exhaustive in detail, but rather to convey the variety and utility of the selected synthetic strategies in generating abiotic rotaxane and catenane superstructures. 

The metastable, 2-D packing motif presented by some Pcs adsorbed on Ag(l 11) has also prompted the utilization of such ensembles as templates for the organization of complementary guest molecules such as fullerenes [193] or corannulenes [194], giving rise to the formation of two-component, 2-D architectures. More recently, a similar approach has been used to prepare a surface-supported, three-component system. In fact, the immersion of an Au substrate into a solution containing both a ZnPc and a Zn porphyrin led to the formation of a highly ordered, 2-D arrangement of both Pc and porphyrin which can act as a bimolecular chessboard toward the supramolecular assembly of a third component (i.e., C6o fullerene) which is selectively trapped in the open spaces (Fig. 25) [195],... 

The classical thermochemical approach has also already been applied to special template-assisted chemical reactions like the template-directed synthesis of oligonucleotides [260], for which a detailed system of kinetic elementary steps has been derived and solved. Other examples are the thermochemical model for the assessment of cooperativity in self-assembly processes proposed in Ref. [261, 262] and for the quantitative description of multicomponent self-assembly processes of polymetallic helicates [263, 264]. More thermochemical approaches applied within particular fields of supramolecular chemistry will be mentioned in the following. 

A. W. Kleij, J. N. H. Reek, Ligand-template directed assembly an efficient approach for the supramolecular encapsulation of transition-metal catalysts, Chem. Eur. J., 2006,12, 4218. 

As an alternative to the two-step approach, mesoporous silica with organic moieties covalently linked to their internal surface could be obtained in a single-step cocondensation of siloxane and organosiloxane precursors using similar supramolecular templating techniques as those for the synthesis of pure silica. Successful one-step syntheses of MCM-41 silicas modified with alkyl, phenyl, vinyl. cyanoethyL amine, thiol, and propylsulfonic acid moieties were reported in the literature.Similar preparations were extended to MCM-48 silica and to meso-... 

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