Carbonylation is one of the most important reactions leading to C-C bond formation. Direct synthesis of carbonyl compounds with CO gives rise to carboxylic acids and their derivatives, such as esters, amides, lactones, lactams etc. The process can be represented by the simple reactions of Scheme . In general, carbonylation proceeds via activation of a C-H or a C-X bond in the olefins and halides or alcohols, respectively, followed by COinsertion into the metal-carbon bond. In order to form the final product there is a need for a nucleophile, Reaction of an R-X compound leads to production of equivalent amounts. | Chapter 5 Carbonylation Introduction Carbonylation is one of the most important reactions leading to C-C bond formation. Direct synthesis of carbonyl compounds with CO gives rise to carboxylic acids and their derivatives such as esters amides lactones lactams etc. The process can be represented by the simple reactions of Scheme . Scheme In general carbonylation proceeds via activation of a C-H or a C-X bond in the olefins and halides or alcohols respectively followed by COinsertion into the metal-carbon bond. In order to form the final product there is a need for a nucleophile Nu . Reaction of an R-X compound leads to production of equivalent amounts of X the accumulation of which can be a serious problem in case of halides. In many cases the catalyst is based on palladium but cobalt nickel rhodium and ruthenium complexes are also widely used. One of the most common nucleophiles in these reactions is OUT which can be logically supplied by H2O or aqueous base solutions. By this 191 192 Chapter 5 aqueous organometallic catalysis gets a special flavour since water now is not only a solvent but one of the reactants. Aside chemistry this means that the amount of water in such systems may vary from stoichiometric quantities usually homogeneously dissolved in the organic solvent or in the substrate of the reaction to larger volumes in form of a separate aqueous phase. Although both kinds of reaction media are aqueous in the following we shall mostly quote examples of the second variant. In such aqueous organic biphasic systems the catalyst can be dissolved in the organic or in the aqueous phase and we shall include both methods into our description since water is essential in both cases. This is also a field of chemistry where biphasic and phase transfer-assisted organometallic catalysis 11-12 are very close and sometimes may even overlap. One reason for this closeness is in that inorganic bases are often used in aqueous solutions. Of them OH is so strongly .
