Metal as template

METAL-BASED QUADRATIC NONLINEAR OPTICAL MATERIALS 

Role of the MLCT transition-. The cases of Fe 86 and Ru 87 are different these tm( bipyridine )metal complexes stabilise octahedral 

The particular case of yttrium is very useful to gain a deeper insight into this effect. Yttrium presents strong chemical similarities with lanthanides and its ionic radius (1.075 A) make it close to dysprosium (1.083 A) or erbium (1.062 A) on the other hand its electronic configuration (4f ) is identical to that of lanthanum. Plotting the variation of / vs the 

---

Kinetic aspects of the use of alkali metals as templates for the formation of other crowns have been studied in some depth (Mandolini Masci, 1984). The results of such investigations parallel the previous observations - namely, that the catalytic efficiency of such ions in promoting cyclization shows a strong tendency to parallel their strength of binding with the crown products (this in turn often correlates with the fit of the metal ion for the macrocyclic cavity in the product). 

This elegant synthesis has demonstrated the possibility of using a hydrogen bond-acceptor template to prepare template-free interlocked species (in a similar fashion to Sauvage s catenanes syntheses which make use of transition metals as templates). 

The use of metals as templates in the higher-order cycloadditions is similar to the [2 + 2]-cycloadditions of alkenes using Cu(I) catalysts. 

The selective reduction of steroid ketones by means of LiAlH4-activated template polymers can be carried out following the principle of an ion exchanger. Although the application of polymers in template syntheses is currently limited, and the reactions do not always run satisfactorily, this method appears to be a landmark for future rational syntheses. Microporous phases with three-dimensional lattice networks and defined pore structures and sizes can be obtained by the use of molecules or hydrated ions of alkali metals or alkaline earth metals as templates [73]. A concept developed by the Mobil Oil Company for the synthesis of porous materials employs a regular arrangement of molecules formed... 

SYNTHESIS OF INTERLOCKING RINGS USING TWO DIFFERENT TRANSITION METALS AS TEMPLATING AND CONNECTING CENTERS RuCu(20.4) -", RuZn(20.4), AND RuAg(20.4) CATENANES TEMPLATE SYNTHESIS OF A 5-COORDINATE ZINC(1I) CATENANE,... 

Macrocycles have been prepared by formation of macrocyclic imines as well as by using variations of the Williamson ether synthesis ". Typically, a diamine or dialdehyde is treated with its counterpart to yield the Schiff s base. The saturated macrocycle may then be obtained by simple reduction, using sodium borohydride, for example. The cyclization may be metal-ion templated. In the special case of the all-nitrogen macrd-cycle, 15, the condensation of diamine with glyoxal shown in Eq. (4.14), was unsuccess-ful ... 

The result of condensation of (3-dicarbonyl compounds with 3,4-diaminofurazan depends on the reaction conditions. With metal ions as templates, 14-membered rings 188 were formed exclusively (91MI2), whereas in the absence of these ions, only fused diazepines 189 were formed (Scheme 122) (89UKZ1064). 

Formation of artificial receptors by interaction of metal with macroheterocycles as templates 97CRV1669. 

Quaternary ammonium bromides and hydroxides (quats) are applied as templates in the synthesis of zeolites with relatively high Si/Al ratio. Examples will be given of the use of mon-, di-, poly- and associated quats as templates in zeolite growth. Templated zeolites of the MFI-type can be grown in a lateral or in an axial way onto metal supports, providing promising composite systems, for separation and catalysis, respectively. 

Douglas and coworkers were the first one that described a bottom-up approach based on S-layers as templates for the formation of perfectly ordered arrays of nanoparticles [128]. The S-layer lattice was used primarily to generate a nanometric lithographic mask for the subsequent deposition of metals. In this approach a thin Ta-W film was deposited... 

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. 

Electrochemical template-controlled sjmthesis of metallic nanoparticles consists of two steps (i) preparation of template and (ii) electrochemical reduction of metals. The template is prepared as a nano structured insulating mono-layer with homogeneously distributed planar molecules. This is a crucial step in the whole technology. The insulating monolayer has to possess perfect insulating properties while the template has to provide electron transfer between electrode and solution. Probably, the mixed nano-structured monolayer consisting of alkylthiol with cavities which are stabilized by the spreader-bar approach [19] is the only known system which meets these requirements. 

Gold electrodes coated by nanostructured self-assembled monolayer of TMPP and Cl2 are used as template for in situ synthesis of metallic nanoparticles (Figure 2). 

Gel-Type Cross-Linked Functional Polymers as Template in the Synthesis of Size Controlled Metal... 

In the reaction of unprotected uridine with tri(imidazolyl-l)phosphine (ratio 1 1.5) under mild conditions (THF, — 78° to 0 °C, 10 min) and subsequent oxidation with iodide, two types of polymers [(Up)n (n = 2-6) and (Up)nU (n = 2—5)] are formed. Additives such as metal cations or polynucleotides (poly U and poly A) acting as templates in the oxidation process showed a significant effect on the ratio of the 3, 5 -linked to 2, 5 -linked oligomer 17 177 ... 

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. 

Aza macrocycles have also been used as templating agents in the formation of zinc and other metal cation-containing aluminophosphates via hydrothermal synthesis.705 The zeolite-like structures have been formed in the presence of cyclam- and hexaaza-based macrocycles. 

---