Pseudohalides synthesis

The Heck reaction, a palladium-catalyzed vinylic substitution, is conducted with olefins and organohalides or pseudohalides are frequently used as reactants [15, 16], One of the strengths of the method is that it enables the direct monofunctionalization of a vinylic carbon, which is difficult to achieve by other means. Numerous elegant transformations based on Heck chemistry have been developed in natural and non-natural product synthesis. Intermolecular reactions with cyclic and acyclic al-kenes, and intramolecular cyclization procedures, have led to the assembly of a variety of complex and sterically congested molecules. 

The palladium-catalyzed Heck carbonylation reaction is a powerful means of generating amides, esters, and carboxylic acids from aryl halides or pseudohalides [28]. The development of rapid, reliable, and convenient procedures for the introduction of carbonyl groups is important for the development of high throughput chemistry in general and high-speed microwave-mediated chemistry in particular. Unfortunately, the traditional method of introducing carbon monoxide into a reaction mixture via a balloon or gas tube is not practical because of the special requirements of microwave synthesis. 

The synthesis of metalloporphyrins which contain a metal-carbon a-bond can be accomplished by a number of different methods(l,2). One common synthetic method involves reaction of a Grignardreagent or alkyl(aryl) lithium with (P)MX or (PMX)2 where P is the dianion of a porphyrin macrocycle and X is a halide or pseudohalide. Another common synthetic technique involves reaction of a chemically or electrochemically generated low valent metalloporphyrin with an alkyl or aryl halide. This latter technique is similar to methods described in this paper for electrosynthesis of cobalt and rhodium a-bonded complexes. However, the prevailing mechanisms and the chemical reactions... 

H. Cheradame, J. Habimana de la Croix, E. Rousset, and F.J. Chen, Synthesis of polymers containing pseudohalide groups by cationic polymerization. 9. Azido end-capped poly(2-methylpropene) by polymerization initiated by the system lewis acid-2-azido-2-phenylpropane, Macromolecules, 27(3) 631-637, January 1994. 

Salts of InCl2 and Ini2- (see Section 25.2.2.4) serve as the starting point for the synthesis of salts of [In(NCS)2], [In(NCO)2]- and [In(NCS)3]3 by metathesis in ethanol 13 the IR spectrum shows that both ligands are N-bonded in structures which are apparently bridged homopolymers in the solid state. No other pseudohalide compounds of indium(I) have been reported. 

As with indium, the literature contains a number of surveys of the general inorganic1 and organometallic chemistry of thallium,273 and the reviews of this element already cited are also concerned with the adducts of the halides and pseudohalides,5 and with other aspects of the coordination chemistry.6 A monograph by Lee provides a most useful treatment of the literature up to 1970.274 The application of thallium compounds in organic synthesis has been discussed.275 276... 

Tertiary phosphines form a wide range of complexes of the type PtX2(PR3)2 (X - halide, pseudohalide R = alkyl, aryl or mixed alkylaryl). Space limitations preclude this chapter becoming a compendium of known compounds, therefore for each individual complex the reader is directed to Chemical Abstracts, Gmelin or the book by McAuliffe which contains extensive tabulations of compounds.1225 In this chapter we outline the general methods of synthesis, the properties, and the structures and spectral features which we expect to be found with this class of compounds. 

There is considerable and widespread interest in the metal complexes of these anions and current research topics comprise for example (i) the spectroscopic study of the binding in these anions (linkage isomerism) and their complexes, (ii) the synthesis of regular polymers of their transition metal complexes and study of the semiconducting properties of these polymers, (iii) the use of the pseudohalides in pharmacological (e.g. low toxicity of —SCN) and biochemical studies (easy complexation of SCN- to metals), and (iv) the use of the activation of these triatomic anions by coordination to metals for their selective conversion in organic synthesis. 

A variety of preparative methods are available for the synthesis of metal pseudohalide complexes.202 209 The use of a large counterion like NEt4+, PPh4+ or (PPh3)2N+ is often important for the isolation of the water-free complexes. Furthermore, the presence of bulky counterions can have a stabilizing influence on the more or less explosive complexes containing azide anions. 

A simple and straightforward approach to their synthesis is the reaction between simple metal salts and the alkali metal or complex anion pseudohalides. Mixed ligand complexes can easily be made via addition of a neutral ligand to the anionic complex species (cf. preparation of trans-ML2(NCS)2, e.g. 103). However, all these methods have been well reviewed202 209 and representative examples can be found in the references of Section 13.5.5.3. 

A new line of studying the metal-pseudohalide complexes comprises on the one hand the synthesis of the pseudohalide in the coordination sphere of a metal. On the other hand a coordinated pseudohalide is used as a building block for a new molecule which thus is constructed in the metal coordination sphere. A short outline of the first aspect will be given below, while for examples of the second aspect the reader is referred to refs. 344-347. 

Palladium-catalyzed synthesis of aryl amines. Starting materials are aryl halides or pseudohalides (for example triflates) and primary or secondary amines. 

The most widespread method of synthesis of complex compounds of pseudohalide ions is through the immediate interaction of ligands with their corresponding metal salts (4.1) [44] ... 

Infrared and NMR-spectral analysis, and x-ray diffraction data, testify [42-54] that in case of complexes of the already discussed pseudohalide ions, the competitive coordination can be explained by the HSAB principle hard Pearson acids are bound with hard N-center, and soft acids with soft X- donor (S, Se) centers. This situation allows us to obtain directly the coordination compounds of pseudohalides with a definite localization mode of the coordination bond, i.e., to carry out the regioselective synthesis on the basis of the higher stability of complexes which are obtained as a result of hard-hard or soft-soft interactions [2]. 

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