The Template Method

As we considered above, one of the fundamental problems associated with the preparation of macrocyclic ligands is concerned with the orientation of reactive sites such that they give intramolecular (cyclic) rather than intermolecular (acyclic) products. This is associated with the conformation of the reactants and the reactive sites, and so we might expect that judicious location of donor atoms might allow for metal ion control over such a cyclisation process. This is known as a template synthesis, and the metal ion may be viewed as a template about which the macrocyclic product is formed. This methodology was first developed in the 1960s, and has been very widely investigated since that time. At the present, template reactions usually prove to be the method of choice for the synthesis of many macrocyclic complexes (with the possible exceptions of those of crown ethers and tetraazaalkanes). When the reactions are successful, they provide an extremely convenient method of synthesis. 

Template reactions are not limited to those involving a single organic component and a single metal ion. Consider the reaction shown in Fig. 6-6. The two open chain precur- 

Naturally, more than two reactant species could be envisaged, as could the introduction of donor atoms into two or more of the reactants. It is not always necessary to isolate the metal complexes of the reactants, and it is often possible to simply mix all of the reactants together in a suitable solvent. 

To further exemplify this methodology, let us take a typical example of the application of a template reaction as seen in the synthesis of a mixed N2S2 donor macrocyclic ligand 6.11. This compound is of interest to the co-ordination chemist as it possesses a potentially square-planar array of soft (sulfur) and harder (nitrogen) donor atoms. What sort of co-ordination chemistry is it likely to exhibit Will the hard or the soft characteristics dominate The most obvious route for the synthesis of 6.11 would involve the reaction of the dithiol 6.10 with l,2-bis(bromomethyl)benzene (Fig. 6-7). 

Unfortunately, this macrocycle cannot be prepared as a free ligand by this method. The starting diimine 6.10 could apparently be prepared from 2-aminoethanethiol and biacetyl. However, we saw in Fig. 5-79 that the direct reaction of 2-aminoethanethiol with 1,2-dicarbonyls leads to a range of cyclic and acyclic products, rather than to products such as 6.10. However, we also saw in Fig. 5-78 that the nickel(n) complex (6.12) of the 6.12 could be obtained if the reaction was conducted in the presence of an appropriate salt. 

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The latter method, the template method, involves a reaction to produce a transition state similar to the desired product using a template. The template should have a shape similar to the space of the product. The template interacts with the substrate by forming noncovalent bonds such as coordination bonds (Fig. 3). The representative and most successful examples are found in crown ether chemistry. In the chemistry, alkali metals act as templates to create a crown-ether-like transition state with an ethylene glycol substrate by using metal-oxygen coordination bonds. 

The template methods have also been used for the synthesis of a number of substituted Ln di(naphthalocyanine) complexes, LnNc2 [82-88]. Apart from thermal fusion by conventional heating processes, complexation has been initiated by microwave radiation, although only a few publications are devoted to the template synthesis of lanthanide bis(phthalocyanine) complexes by this method [89, 90]. The use of microwave radiation (MW) reduces the reaction time from several hours to several minutes. Unsubstituted complexes LnPc2 (Ln = Tb, Dy, Lu) were prepared [90] by irradiation (650-700 W) of a mixture of phthalonitrile with an appropriate lanthanide salt for 6-10 min (yields >70%). 

For an inheritance-based design, the template method (see Section 11.3.1.2, Framework-Style Reuse and the Template Method) forms the basis of plug-ins. This design style, common initially, has now fallen somewhat out of favor. 

The template method involves using the pores in a microporous solid as nanoscopic beakers for the synthesis of nanoparticles of the desired material [1,3,10]. A wide variety of materials are available for use as template materials [1,10,14-19]. Pore diameter sizes range from Angstroms to many p,m. Several of the more common materials used as templates are reviewed below. 

In order to explore the effects of small electrode size, we have used the template method to prepare ensembles of disk-shaped nanoelectrodes with diameters as small as 10 nm. We have shown that these nanoelectrode ensembles (NEEs) demonstrate dramatically lower electroanalytical detection limits compared to analogous macroelectrodes. The experimental methods used to prepare these ensembles and some recent results are reviewed below. 

A new approach for preparing microstructured Li ion battery electrodes was demonstrated here. This approach entails using the template method... 

A variety of nanomaterials have been synthesized by many researchers using anodic aluminum oxide film as either a template or a host material e.g., magnetic recording media (13,14), optical devices (15-18), metal nanohole arrays (19), and nanotubes or nanofibers of polymer, metal and metal oxide (20-24). No one, however, had tried to use anodic aluminum oxide film to produce carbon nanotubes before Kyotani et al. (9,12), Parthasarathy et al. (10) and Che et al. (25) prepared carbon tubes by either the pyrolytic carbon deposition on the film or the carbonization of organic polymer in the pore of the film. The following section describes the details of the template method for carbon nanotube production. 

By the template technique using anodic oxide films and pyrolytic carbon deposition, one can prepare monodisperse carbon tubes. Since the length and the inner diameter of the channels in an anodic oxide film can easily be controlled by changing the anodic oxidation period and the current density during the oxidation, respectively, it is possible to control the length and the diameter of the carbon tubes. Furthermore, by changing the carbon deposition period, the wall thickness of the carbon tubes is controllable. This template method makes it possible to produce only carbon tubes that are not capped at both ends. Various features of the template method are summarized in Table 10.1.1 in comparison with the conventional arc-discharge method. 

Encapsulation of other material into carbon nanotubes would also open up a possibility for the applications to electrodevices. By applying the template method, perfect encapsulation of other material into carbon nanotubes became possible. No foreign material was observed on the outer surface of carbon nanotubes. The metal-filled uniform carbon nanotubes thus prepared can be regarded as a novel onedimensional composite, which could have a variety of potential applications (e.g novel catalyst for Pt metal-filled nanotubes, and magnetic nanodevice for Fe304-filled nanotubes). Furthermore, the template method enables selective chemical modification of the inner surface of carbon nanotubes. With this technique, carbon... 

The template method will be able to produce various types of unique carbon nanotubes and one-dimensional carbon composites, and such unique materials would provide a variety of potential applications. 

Template Method Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. The Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm s structure. 

A few abstract protected methods are left to the concrete mapper object to implement. They are declared in AbstractMapper so that they can be called by the Template Methods to maximize code reuse. 

The template method may be extended to derivatives of imines, and hence to the synthesis of cyclic hydrazones. An example of a templated cyclisation leading to a cyclic hydrazone is shown in Fig. 6-13. 

The physical and chemical activation methods are effective in preparing the microporous carbons with high surface area. However, the pore structures of the carbons are not easily controlled by the activation processes and the size of the pores generated by the activation processes is limited to the micropore range only. Under these circumstances, the templating method which will be considered in the following Section II.2 has recently... 

FIGURE 3.8 The formation process of CNT by the template method using an AAO film. (From Chmiola, J., et al., Science, 313, 1760, 2006. With permission.)... 

In order to obtain Au/Pt nanoparticle-covered BCN nanotube brushes, the nanotubes obtained by the template method described earlier were soaked in 2 mL of 5 mM aqueous solutions of hydrogen hexachloroplatinatc (rv) or hydrogen tetrachloroaurate (III) for 12 h. The nanotubes were washed with distilled water twice followed by a washing with 10 mM sodium borohydride solution before drying at 40 °C for an hour. The resulting products were examined by electron microscopy. 

The nickel ) complex of 92 cannot be prepared directly via the template method, but can be prepared by a transmetallation procedure. Synthesis of the macrocycle in the presence of one of the metal ions known to be effective as a template is followed by a metal exchange process in solution to insert the nickel ) ion. This cation exhibits a strong preference for the square planar, square pyramidal, and octahedral geometries 79). Thus the failure of the nickel ) cation to behave as a template ion in the synthesis of 92 is probably due to the disinclination of the metal to accommodate the pentagonal array of donor nitrogen atoms necessary for reaction to occur. 

The template method is the most general, since it can be accomplished a priori with all the strategies. 

The simplest, but not necessarily the best, way of evaluating elastomeric finishes is the template method. The fabric is stretched by hand with, it is to be hoped, constant force in both warp and fill or weft and wale directions. The residual elongation is determined by the fabric s dimensional change. This method suffers from difficulties in repeatability owing to the variable stretching forces. 

The template method is a general approach for preparing nanomaterials that entaU synthesis or deposition of the desired material within the cylindrical and monodisperse pores of a nanopore membrane or other solid [20-22]. Cylindrical nano-strucmres with monodisperse diameters and lengths are obtained, and depending on the membrane and synthetic method used, these may be solid nano wires or hollow nanombes. This method has been used to prepare nano wires and nanombes composed... 

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