Organometallic Compounds Substitution 1 Exchange Reactions

Metal-exchange reactions were also observed, as in the reaction of phenyl-chlorosilanes and phenyl-silylhydrides, when products in addition to the expected Siy 4 were formed195). This may be due to the formation of metal-silyl compounds during the reaction. It is known that organometallic compounds are easily formed with phenyl-substituted silane derivatives and with the Si—H bond. 

This reaction was clarified with hexenyl stearate (I) at 60°C during the reaction between zinc stearate and 4-chloro-2-hexene in tetrahydro-furan. During this reaction, zinc stearate reacts immediately with 2 mol of model compound, and kinetic laws do not suggest the presence of CIZnOCOR as an intermediate product in the substitution reaction. Nevertheless, such an organometallic compound was suggested by Frye and Horst (9) and also by Anderson and McKenzie (10) who assumed that such compounds accounted for the ligand exchange between cadmium chloride and barium carboxylate. 

Rearrangement and exchange reactions of main group organometallic compounds offer a rich variety of processes important both to the inorganic and organic chemist. These processes have provided examples of electrophilic substitution, electron transfer, and of concerted multi-centered processes, all of which are of both theoretical and practical importance. 

The spectrum of mechanisms of the electrophilic substitution at a saturated carbon atom is very broad [1,72-74]. The bimolecular Se2 exchange reactions in the series of organo-mercury compounds have been studied in the most detailed manner. For these reactions as well as for the Se2 reactions of other organometallic compounds, the derivatives of Li, Mg, B, Sn, Ge, a four-center transition state of XXIV type is assumed ... 

Several investigators have examined the possible correlation of these two activation parameters, particularly for series of similar reactions.134 136 Correlations have been attempted for reactions of transition metal coordination compounds, such as ligand substitution or isomerisation, or solvent exchange,135 137 and the issue has been addressed recently.138 However, correlations for these parameters for organometallic reactions have not yet been developed. 

A variety of arenes and heteroarenes react with alkenes in the presence of palladium(II) derivatives to produce alkenyl substitution products. Three methods are commonly employed for the in situ preparation of palladium derivatives (i) direct metallation of an arene or heteroarene with a Pd(II) salt (ii) exchange of the organic group from a main-group organometallic to a Pd(II) compound (iii) oxidative addition of an organic halide, an acetate, or triflate salt to Pd(0) or a Pd(0) complex. For catalytic reactions Cu(II) chloride or p-benzoquinone is usually used to reoxidize Pd(0) to Pd(II). 

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