Monoxide as a Building Block

A long-standing success in transition metal catalysis is the carbonylation reaction [66], in particular the synthesis of acetic acid [67]. Formally this is the insertion of CO into another bond, in particular into a carbon-halogen bond. After the oxidative addition to the transition metal (the breaking of the carbon-halogen bond), a reaction with a CO ligand takes place. This reaction is often called an insertion. Mechanistic studies have, however, shown that the actual reaction 

The reaction proceeds in MEK and cone. HC1 at 130°C. First, the alcohol is converted into the benzylic chloride. In this case a palladium catalyst 

In an attempt to replace the organohalides as starting materials, diazonium salts have been investigated as starting material. They, too, can react in an oxidative addition with the Pd° to form the first intermediate of the catalytic cycle. In a recent bench scale process for a herbicide in development (CGA 308956) a diazonium salt proved to be suitable. The product of the oxidative addition will 

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