Shilov reaction

As both nucleophiles, Z and Y , can participate in a reductive elimination reaction, a mixture of reaction products, R-Z and R-Y, forms. Such behavior is observed in the Shilov reaction (Fig. 2). Formation of a mixture of methanol and methyl chloride is considered in Shilov chemistry as a result of occurrence of two concurrent S 2 processes with water and chloride anion as competing nucleophiles [18, 19]. The rate of the formation of chloromethane in aqueous solutions of [MePt Clsl in this reaction was shown to be first order in chloride ion concentration. 

The Shilov reaction is an example of an Si 2 - t3q>e C(sp )-X reductive elimination reaction where several nucleophiles compete for the same electrophilic high-valent metal complex [18,19]. A detailed analysis of C(sp )-0 reductive elimination from symmetric (dpms)Pt Me(OH)2, 9, in aqueous solutions shows that this reaction also follows a complex mechanism characterized by the involvement of several competing nucleophilic Pt hydroxo and methoxo complexes (Fig. 10) [30]. 

That finding implies it should be possible to replace Pt(IV) with any suitable oxidant and thus escape the requirement for stoichiometric consumption of Pt in the original Shilov reaction however, there are two severe constraints on what counts as suitable . Oxidation of RPt(II) must be fast enough to compete with protonolysis, but the oxidant must not be so powerful as to also oxidize inorganic Pt(II), which is needed to carry out the C-H activation step. The rapidity of the oxidation step with [Pt Cle] appears quite remarkable while the absolute rate cannot be measured, the relative rate of oxidation to protonolysis can be estimated from the amounts of the corresponding products obtained when [(CH3)Pt Cl3] is generated transiently from nucleophilic attack of CP at a methyl of [(CH3)2Pt CLt] in an aqueous... 

FIGURE 12.11 (a) The proposed mechanism of the Shilov reaction b) Periana s related methane oxidation. 

Dyashkovskii and Shilov [Kinetics and Catalysis, 4 (808), 1963] have studied the kinetics of the reaction between ethyl lithium and ethyl iodide in decalin solution. 

A.E. Shilov and G.R Shul pin Activation and Catalytic Reactions of Saturated... 

NA Shilov. About Reactions of Cooxidation. Moscow Tipografiya Mamontova, 1905 [in Russian]. 

AE Shilov, GB Shulpin. Activation and Catalytic Reactions of Saturated Hydrocarbons in the Presence of Metal Complexes. Dordrecht Kluwer Academic, 2000. 

This cycle, often referred to as the Shilov-cycle converts methane into methanol and chloromethane in homogeneous aqueous solution at mild temperatures of 100-120 °C (11). However, while Pt(II) (added to the reaction as PtCl ) serves as the catalyst, the system also requires Pt(IV) (in the form of PtCle-) as a stoichiometric oxidant. Clearly, this system impressively demonstrates functionalization of methane under mild homogeneous conditions, but is impractical due to the high cost of the stoichiometric oxidant used. A recent development by Catalytica Advanced Technology Inc., often referred to as the Catalytica system used platinum(II) complexes as catalysts to convert methane into methyl-bisulfate (12). The stoichiometric oxidant in this case is S03, dissolved in concentrated H2S04 solvent. This cycle is depicted in Scheme 3. 

An electrochemical explanation of the basic reaction was suggested by P rumkin 17), while Shilov et al. 22, 23) claimed surface oxides of definite structure to be the only cause of either acidic or basic reaction. Shilov formulated the acidic surface oxides as carboxylic acid anhydrides bound to the edges of the carbon layers. 

Shilov AE, Shul pin GB (2000) Activation and catalytic reactions of saturated hydrocarbons. Kluwer, Dordrecht... 

The most important contributions to studies of these reactions came from the groups of Schrauzer147 and Shilov 148 there has been a long controversy about the mechanism. 

A. E. Shilov, Metal Complexes in Biomimetic Chemical Reactions, CRC Press, Boca Raton, FL, 1997. 

The Shilov method, discussed in Section 10.4.1, has been accomplished as a catalytic process.327 Aqueous platinum chlorides can be used as catalysts for the homogeneous catalytic chlorination of methane. The reaction is carried out at 100-125°C with chlorine to yield methyl chloride that is partially hydrolyzed to... 

Polar Cycloadditions R. R. Schmidt, Angew. Chem., Int. Ed. Engl., 1973, 12, 212-224. Addition Reactions with Intramolecular Cyclisation V. I. Staninets and E. A. Shilov, Russ. Chem. Rev. (Engl. Transl.), 1971, 40, 272-283. 

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