Migratory deinsertion reaction

As shown in equation 7.59, OA of the aldehyde yields the cis-hydridoacylrhodium complex, 39. Heating results in ligand dissociation to give 40, which undergoes migratory deinsertion (to be discussed in Chapter 8) to produce 41. Isomerization of 41 to a d.v-hydridoalkyl complex presumably occurs before final the final RE step to yield the C-H elimination product. These reactions have applications in catalytic industrial process known as olefin hydroformylation (Section 9-2). Equation 7.60 illustrates straightforward RE to form a new C-H bond. 

This reaction profile, also called carbonylation, governs the reactivity of Pd-carbonyl complexes. Anionic M[Pd(CO)l3], for instance, catalyzes the reductive carbonylation of esters.f On the other hand, Pd(CO)(PPh3)3 was reported to catalyze the carboxymethy-lation of organic halides and the cyclocarbonylation of cinnamyl halides.f " However, the Pd-CO complexes are most often generated in situ from preformed alkyl -palladium complexes and CO under stoichiometric or catalytic conditions, for example, in the copolymerization of alkenes and CO. Decarbonylation reactions also involve the intermediacy of Pd-CO complexes. In this case, migratory deinsertion (Sect, n.3.1), that is, the microscopic reversal of the migratory insertion, takes place. 

Migratory insertion and its microscopic reversal, that is, migratory deinsertion, are two of the 20 or so fundamental processes discussed in Sect. 1.2 in which Pd participates. In principle, they should be observed with a wide variety of substrates. In reality, however, the current scope of these processes observable with organopalladiums is almost totally limited to those that involve CO and related compounds, such as isonitriles. Conse-qnently, the migratory insertion-deinsertion chemistry of organopalladium compounds at present is essentially synonymous with their carbonylation-decarbonylation reactions. 

Aldehydes undergo a decarbonylation reaction by action of a transition metal complex [17]. For example, benzaldehyde was decarbonylated with Wilkinson complex to furnish benzene along with a rhodium carbonyl complex 47 (Scheme 7.14) [17e,f]. Oxidative addition of the aldehydic C-H bond to rhodium, migratory deinsertion of CO, and reductive elimination operate in sequence for the decarbonylation reaction. Decanal was also decarbonylated to furnish a mixture of nonane and nonene, which were produced via the alkylpalladium intermediate 48 (Scheme 7.15) [17d]. 

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