Other Synthetic Techniques

Several other synthetic techniques have also been described. Redistribution polymerization was outlined in COMC II (1995) (chapter Organopolysilanes, p 99) and proceeds by phosphonium salt-catalyzed redistribution of chlorodisilanes.133 Disproportionation polymerization, which is a similar process, has been described for the formation of polymers by ethoxide-catalyzed disproportionation of alkoxydisilanes via silyl anion intermediates.134 These procedures give rise to network polymeric products of rather low molecular weight (see below, Section 3.11.7.1). 

The Wurtz-type coupling reactions, which were one of the original methods for the formation of Ge-Ge bonds, are still in use.337 Various other synthetic techniques have been developed and improved upon in recent years as well. 

Application of other synthetic techniques, predominantly metal vapor methods, have added other cluster stoichiometries to this list, which presently includes Au5, Au , Aug, Aug, and Aun. The few examples for Au2 (3, 69), Au3 (30), and Am (36, 76) will not be considered here, since they do not involve gold in unusual oxidation states. The sections are ordered according to the cluster size, although, historically, the Aun moiety was the first to be detected (65). 

Other synthetic techniques, described below, are applied to produce pseudohalide complexes, for example reactions of exchange of perchlorate anion to... 

Solvothermal techniques have been extensively developed for the synthesis of metal oxides [149-152]. Unlike many other synthetic techniques, solvothermal synthesis concerns a much milder and softer chemistry conducted at low temperatures. The mild and soft conditions make it possible to leave polychalcogen building-blocks intact while they reorganize themselves to form various new structures, many of which might be promising for applications in catalysis, electronic, magnetic, optical and thermoelectronic devices [153-155]. They also allow the formation and isolation of phases that may not be accessible at higher temperatures because of their metastable nature [156, 157]. 

This carbene insertion reaction has been used in a variety of syntheses, and is especially attractive when coupled with other synthetic techniques. Taber et al. used carbene cyclopropanation in several synthetic endeavors. In one example, the diazoketone was treated with bis-A-tert-butylsalicylaldiminato copper(II) [Cu(TBS)2, 388] to induce the carbene cyclopropanation reaction. The diazoketone was prepared by treating 386 with mesyl azide to give 387 in 82% yield, which was followed by treatment with the Cu(TBS)2 reagent to produce 389 in 80% yield in Taber and co-workers synthesis of (-i-)-isoneonepatelactone.308... 

Vinyl esters of carboxylic acids, which are not amenable to preparation by other synthetic techniques, are readily prepared by transvinylation. As depicted in equation (39),... 

ADMET is quite possibly the most flexible transition-metal-catalyzed polymerization route known to date. With the introduction of new, functionality-tolerant robust catalysts, the primary limitation of this chemistry involves the synthesis and cost of the diene monomer that is used. ADMET gives the chemist a powerful tool for the synthesis of polymers not easily accessible via other means, and in this chapter, we designate the key elements of ADMET. We detail the synthetic techniques required to perform this reaction and discuss the wide range of properties observed from the variety of polymers that can be synthesized. For example, branched and functionalized polymers produced by this route provide excellent models (after quantitative hydrogenation) for the study of many large-volume commercial copolymers, and the synthesis of reactive carbosilane polymers provides a flexible route to solvent-resistant elastomers with variable properties. Telechelic oligomers can also be made which offer an excellent means for polymer modification or incorporation into block copolymers. All of these examples illustrate the versatility of ADMET. 

The introduction of new synthetic techniques has led to the discoveries of many new electronic materials with improved properties [20-22]. However, similar progress has not been forthcoming in the area of heterogeneous catalysis, despite the accumulation of considerable information regarding structure-reactivity correlations for such catalysts [14-19]. The synthetic challenge in this area stems from the complex and metastable nature of the most desirable catalytic structures. Thus, in order to minimize phase separation and destruction of the most efficient catalytic centers, low-temperature methods and complicated synthetic procedures are often required [1-4]. Similar challenges are faced in many other aspects of materials research and, in general, more practical synthetic methods are required to achieve controlled, facile assembly of complex nanostructured materials [5-11]. 

In 1972, we reported a general procedure for the preparation of highly reactive metal powders. The basic procedure involved the reduction of a metal salt in a hydrocarbon or ethereal solvent. The reductions are most generally carried out with alkali metals such as potassium, sodium, or lithium. A wide range of methods have been developed to carry out the reductions. The reactivities of these resulting black powders exceed other reports in the literature for metal powders. This high reactivity has resulted in the development of several new synthetic techniques and vast improvements in many older, well established reactions. This review concentrates on the metals Mg, Ni, Zn, Cd, Co, Cu, Fe, and U. 

In other studies, Lehn and coworkers have produced a range of mixed-donor cryptands using direct synthetic techniques (usually at high... 

As recently recognized by the Nobel Chemistry award committee, the conceptualization, development, and commercial application of enantioselective, homogeneous hydrogenation of alkenes represents a landmark achievement in modem chemistry. Further elaboration of asymmetric hydrogenation catalysts by Noyori, Burk, and others has created a robust and technologically important set of catalytic asymmetric synthetic techniques. As frequently occurs in science, these new technologies have spawned new areas of fundamental research. Soon after the development of... 

Therefore, the chiral cyanohydrins are valuable and versatile synthons as their single hydroxyl asymmetric centre is accompanied by at least one other chemical functionality. Thus with careful functional group protection, differential and selective chemical transformations can be performed. Such synthetic techniques lead to production of interesting bioactive compounds and natural products. These products include intermediates of j3-blockers 15 1117], j3-hydroxy-a-amino acids 16 [118],chiral crown ethers 17 [lll],coriolic acid 18 [120], sphingosines 19 [121], and bronchodilators such as salbutamol 20 [122] (Fig. 3). 

Sulfonation is easily reversible. Simply diluting the fuming sulfuric acid leads to the removal of the -SO3H. This is an important synthetic technique for protecting certain sites from reaction. Sulfonation can act as a placeholder while other reactions are performed, and then the easy removal of the sulfonic acid group makes the site available for reaction in a later step in a series of reaction steps. 

Enzymatic polymerizations have been established as a promising and versatile technique in the synthetic toolbox of polymer chemists. The applicability of this technique for homo- and copolymerizations has been known for some time. With the increasing number of reports on the synthesis of more complex structures like block copolymers, graft copolymers, chiral (co)polymers, and chiral crosslinked nanoparticles, its potential further increases. Although not a controlled polymerization technique itself, clever reaction design and integration with other polymerization techniques like controlled radical polymerization allows the procurement of well-defined polymer structures. Specific unique attributes of the enzyme can be applied... 

The subject matter covered below is divided into sections according to the structure of the redox unit(s). This review is restricted primarily to materials for which well-defined redox behavior has been repiorted, usually involving cyclic voltammetric studies and other electrochemical techniques in solution. Unraveling the electron transfer processes in laiger macromolecules which contain multiple redox sites can be very challenging, thus for some systems model branched oligomers have been studied in detail, and this work will be discussed. Selected synthetic schemes are included to acquaint the reader with the building blocks which are available for the construction of new derivatives, and with the synthetic steps involved. 

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