Templating cation

Dale improved this procedure by conducting the cyclooligomerization in the presence of certain templating cations paired with non-nucleophilic counterions (e.g.,... 

Tire first C—O bond formation is probably not influenced strongly by the presence of a templating cation. Since it is not crucial for one end of the chain to meet the other rather than reacting with a different molecule, it is not necessary to superimpose either a template or dilution condition on the reaction to prejudice the statistics. In the second step, however, such a prejudicial condition is required. This is available in the form of an... 

Newkome and co-workers have demonstrated the operation of a template effect in the formation of a pyrido-ester-crown. In the reaction shown in Eq. (2.8), they treated 2-clTloronicotinoyl cliloride with either the disodium or dipotassium salt of pentaethylene glycol. TJie two reactions were conducted under identical conditions except for the presence of sodium vs. potassium cations. Since the product is a six-oxygen macrocycle, its formation would be expected to be favored by K" rather than Na" counter ions for the glycolate. In fact, the yields of crown-lactone were 30% and 48% respectively when Na" and K" were the templating cations. 

More recently, Dale and Daasvatn have shown that the product composition can be influenced by adding a templating cation (see Sect. Addition of copper... 

Chiral-at-metal cations can themselves serve as chirality inducers. For example, optically pure Ru[(bipy)3] proved to be an excellent chiral auxihary for the stereoselective preparation of optically active 3D anionic networks [M(II)Cr(III)(oxalate)3]- n (with M = Mn, Ni), which display interesting magnetic properties. In these networks all of the metalhc centers have the same configuration, z or yl, as the template cation, as shown by CD spectroscopy and X-ray crystallography [43]. 

The kinetics and mechanisms of template reactions are rarely studied in depth - they are often merely assumed to be genuine template reactions rather than a metal-activated reaction at a coordinated ligand. The best evidence for a true template mechanism is the isolation and characterization of intermediates with both reactants and with the macrocyclic product complexed with the template cation. 

Use of organic templates In the current preparation of a new series of microporous crystals, organic templates are often used. Organic chemicals are also used in the preparation of pillared clays to control the pore sizes and the porosity as follows The interlayer cations of silicate layer are exchanged with positively charged sol particles, and then a part of the sols are exchanged with organic template cations such as octadecyl trimethyl ammonium (OTMA). 

Figure 3.45 shows the results of kinetic studies of the template synthesis of benzo [18] crown-6 according to the reaction shown, as a function of the templating cation. Clear rate enhancements... 

Acid catalyzed Sehiff base condensation of 2,6-diformyl-p-cresol and TETA (triethylenetetraamine) with Pr3+ as the template cation (in methanol) afforded a 1 1 product containing a tetraclinching alcohol (Eq. 9b, Table 9) [132]. One of the carbonyl groups was acetylated under mild acidic conditions. The 10-coord-ination around Pr3 + achieved by one aryloxide site, one imine and three amino nitrogen, two bidentate nitrate anions and one molecule of methanol is best described as a bicapped square antiprism. 

Reinhoudt and co-workers (101-105) have reported a series of Schiff base macrocyclic polyether ligand complexes prepared via barium cation-templated Schiff base condensation of the appropriate polyether dialdehyde with a diamine, in the presence of a transition metal or uranyl acetate, followed by removal of the Ba2+ template cation on subsequent addition of guanidinium sulfate (Scheme 19). The copperdl) and nickeldl) complexes (62) and (63) exhibit reversible redox couples... 

PURELY SILICEOUS HFI-tvoe ZEOLITES. Among the templating cations which were uaed, P R proved to be the moat efficient for easy and fast crystallization. In Table IT are given the crystallographic oharacteriatica of the obtained siliceous HFI-type zeolites (16) aa a function of the template. 

Reaction of Cu(I)-complexed [3]-rotaxane 86 with either Zn(OAc)2 2H2O (2 equiv) or [Au(tht)2]BF4 (6 equiv tht = tetrahydrothiophene) afforded the [3]-rotaxanes 87 and 88 respectively, in 83% and 42% isolated yields. Subsequent reaction of 88 with a slight excess of KCN afforded the free [3]-rotaxane 89 in 62% yield. Surprisingly, the same reaction performed on 87 resulted in the removal of only one of the two template cations, affording the Cu(I) complex 90 in essentially quantitative yield. 

Template cations are still needed in the second step in order to produce [M]-OMS-1 materials where [M] signifies incorporation of M into the framework. 

P.A. Barrett and R.H. Jones, The Pore-size Modification of a Layered Aluminophosphate [A13P4016C9H24N3] by Rational Selection of the Intercalated Template Cation. J. Chem. Soc., Chem. Commun., 1995, 1979-1980. 

Moreover, recently DES of choline chloride/urea (or malonic acid) have been used as solvents in the synthesis of new coordination polymers, Zn(O30PCH2CO2)NI-E, of open-framework iron oxaphosphates and alumino-phospate zeolite analogues. Generally, the ionic medium not only acts as a solvent but also provides the template cations around which the inorganic frameworks order. 

Removal of the Cu" template cation of compound (135) with KCN produced [2]-rotaxane (138) (Figure 45). As observed in some other cases, the demetallation reaction is accompanied with a pirouetting of the macrocycle placing its dpp chelate outside the cleft formed by the porphyrinic stoppers [126, 132]. 

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