Synthesis metal-directed reactions

A typical example is seen in the addition of hydrogen cyanide to an imine to yield a cyanoamine (Fig. 4-29). Many of these reactions have been used to best advantage in the synthesis of macrocyclic ligands and complexes, and as such are considered in Chapter 6. A simple example of such a reaction is seen in the addition of HCN to the cobalt(m) complex indicated in Fig. 4-30. The starting complex is also readily prepared by a metal-directed reaction. 

Probably one of the commonest reactions encountered in the template synthesis of macrocycles is the formation of imine C=N bonds from amines and carbonyl compounds. We have seen in the preceding chapters that co-ordination to a metal ion may be used to control the reactivity of the amine, the carbonyl or the imine. If we now consider that the metal ion may also play a conformational role in arranging the reactants in the correct orientation for cyclisation, it is clear that a limitless range of ligands can be prepared by metal-directed reactions of dicarbonyls with diamines. The Tt-acceptor imine functionality is also attractive to the co-ordination chemist as it gives rise to strong-field ligands which may have novel properties. All of the above renders imine formation a particularly useful tool in the arsenal of preparative co-ordination chemists. Some typical examples of the templated formation of imine macrocycles are presented in Fig. 6-12. 

Bates, R. (2000) Organic Synthesis Using Transition Metals, Wiley-Blackwell, Oxford, UK. Describes how transition metals can act to catalyse or direct organic reactions, with some metal-directed reactions of relevance but more for the advanced student. 

Method of synthesis the direct reaction between silicon metal and methyl chloride in a fluid bed reactor yields a complex mixture of methyl chlorosilanes the chlorosilanes are distilled or purified, and the primary product - dimethyidichlorosilane, (CH3)2SiCl2 - is reacted with water (hydrolysis) to give poly(dimethylsiloxane) oligomers (Me SiOJ. ... 

Direct Process. The preparation of organosilanes by the direct process, first reported in 1945, is the primary method used commercially (142,143). Organosilanes in the United States, France, Germany, Japan, and the CIS are prepared by this method, including CH SiHCl, (CH2)2SiHCl, and C2H SiHCl2. Those materials are utilized as polymers and reactive intermediates. The synthesis involves the reaction of alkyl haUdes, eg, methyl and ethyl chloride, with siUcon metal or siUcon alloys in a fluidized bed at 250—450°C ... 

Alternatively, thermal cracking of acetals or metal-catalyzed transvinylation can be employed. Vinyl acetate or MVE can be employed for transvinylation and several references illustrate the preparation especially of higher vinyl ethers by such laboratory techniques. Special catalysts and conditions are required for the synthesis of the phenol vinyl ethers to avoid resinous condensation products (6,7). Direct reaction of ethylene with alcohols has also been investigated (8). 

Industrial use of HCl gas for the manufacture of inorganic chemicals includes the preparation of anhydrous NH4CI by direct reaction with NH3 and the synthesis of anhydrous metal chlorides by reaction with appropriate carbides, nitrides, oxides or even the free metals themselves, e,g, ... 

Directed orr/io-metallation—transition metal-catalyzed reaction symbiosis in heteroaromatic synthesis 99JHC1453, 99PAC1521. 

The general interligand C—C coupling reaction shown in Eq. (8) for (metalla-/3-diketonato)BF2 compounds also occurs directly with metalla-/3-diketonate anions, thereby precluding the need to prepare the neutral difluoroboron complexes (53). As a one-pot synthesis, metal carbonyl acetyl compounds can be converted to neutral 77-allyl complexes [Eq. (12)]. 

Although direct reaction of lanthanide mono-porphyrins with free phthalo-cyanine or its lithium derivatives is generally more efficient than the template synthesis, and gives rise to mixed-ligand complexes, the template strategy can also be applied for synthesis of phthalocyanine-porphyrin complexes, as in the case of unsymmetric bisphthalocyanine complexes (Scheme 8.2, B(b)) [106, 136, 145, 146]. Thus, metallation of free porphyrins with lanthanide salts in TCB or n-octanol leads to single-decker complexes, which then react with phthalonitriles under the action of DBU in alcoholic media to give the desired compounds. 

A different type of direct synthesis involves the reaction of the metal with an alkyl halide ... 

A diverse group of secondary and tertiary amines are readily synthesized from the reaction of primary and secondary amines with allylic carbonates in the presence of preformed iridium metalacycles, but the direct synthesis of primary amines via iridium-catalyzed allylic amination requires the use of ammonia as a nucleophile. The asymmetric allylation of ammonia had not been reported until very recently, and it is not a common reagent in other metal-catalyzed reactions. Nonetheless, Hartwig and coworkers developed the reactions of ammonia with allylic carbonates in the presence of la generated in situ [89]. Reactions conducted in the initial work led exclusively to the products from diallylation (Scheme 16). Further advances in... 

Oxazoline-directed aromatic substitution and addition reactions provide synthetic chemists with powerful tools for the construction of complex aromatic compounds. Since the last authoritative review by Meyers, these technologies have matured and found widespread applications in organic synthesis. While there has been somewhat limited methodological research in this area in the intervening years, one particularly exciting new development is the diastereoselective ortho-metalations directed by chiral oxazolines. Sections 8.3.9.1-8.3.9.3 will discuss these new developments as well as new synthetic applications of these reactions. 

The synthesis of bis(rj8-cyclooctatetraene)uranium(IV) (uranocene)J from uranium tetrachloride and (cyclooctatetraene)dipotassium was first published in 1968.1 The method reported here is a modification of that procedure and is suitable for a large variety of cyclooctatefraene complexes.2-4 BisO 8-cyclo-octatetraene)uranium(IV) has also been prepared by the reaction of uranium tetrafluoride with (cyclooctatetraene)magnesium in the absence of solvent.5 Direct reaction of finely divided uranium metal with cyclooctatetraene vapors at 150° also gives some uranocene.5 However, both methods give low yields. 

The formation of the chromene caibamate 21 from resorcinol dicarbamate involves directed ortho metallation and an intramolecular 0- 0 carbamoyl transfer. Further manipulation utilising directed metallation and transition metal catalysed reactions allows the synthesis of plicadin, a naturally occurring coumestan <99AG(E)1435>. 

The standard approach to the synthesis of oxides in polycrystalline form is the direct reaction of a mixture of metal oxide starting materials at high temperature. The ratios of the starting materials will control the stoichiometry of the product provided the volatilities of the starting materials are relatively low. Syntheses of oxides containing volatile components are discussed in greater detail in the following sections. 

This chapter deals with the methods of synthesis, characterization, and growth mechanisms of well-defined uniform particles of metal sufides and selenides formed by direct reaction of metal ions with the chalcogenide ions, released from thioacetamide or selenourea in dilute solutions, or supplied continuously from outside in the form of a high concentration of sulfide ions. 

The first report of the preparation of organometallic compounds by direct reaction between metals atoms and organic ligands came in 1969 (727). Research into synthesis using metal atoms has expanded steadily since then and now seems likely to increase very rapidly as the necessary equipment becomes commercially available.1 The field has been reviewed in part before (55, 67, 78a, 84a, 129), but no comprehensive review of the organometallic aspects has yet been published. 

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