Carbonylation and other migratory insertion reactions

Cp2ZrCI2 SMe, Cp2Zr SiMe3-----Cp SiM03Cp2Zr SiMe3 Ph SIMe3 

CN Li-CH(Me) Cl Ph3Si LI-V7 Ll O Ph LjA-7 Ll O NC R1 uV ples of a-hetero-substituted or-ganolithiums used in migratory insertion reactions of organyizirconocene derivatives. 

---

The main steps in the catalytic MeOH carbonylation cyde which were proposed for the Co catalysed process [2] have served, with some modification perhaps in the carbonylation of MeOAc to AC2O, to the present day and are familiar as a classic example of a metal catalysed reaction. These steps are shown in Eigure 5.1. They are of course, (i) the oxidative addition of Mel to a metal center to form a metal methyl species, (ii) the migratory insertion reaction which generates a metal acyl from the metal methyl and coordinated CO and (iii) reductive elimination or other evolution of the metal acyl spedes to products. Broadly, as will be discussed in more detail later, the other ligands in the metal environment are CO and iodide. To balance the overall chemistry a molecule of CO must also enter the cycle. 

Negishi, E. L, de Meijere, A., Eds. Palladium-Catalyzed Carbonylation and Other Related Reactions Involving Migratory Insertion. In Handbook of Organopalladium Chemistry for Organic Synthesis-, Wiley-Interscience New York, 2002 Vol. 2, pp 2309-2714. 

Palladium-Catalyzed Carbonylation and Other Related Reactions Involving Migratory Insertion... 

Reaction 2.3.2.6 is a crucial step in CO-involving catalytic reactions such as carbonylation or hydroformylation. This reaction is called a migratory insertion reaction, as there is experimental evidence to show that the alkyl group migrates to CO. Finally, it should be noted that for aU insertion reactions, close proximity of the two ligands is a must. In other words, the alkene or CO must be cis and not trans to the bond in which they insert. 

The mechanisms of the two key migratory insertion steps are worth discussion. Hydrometallation occurs by initial n complex formation followed by addition of the metal to one end of the alkene and hydrogen to the other. Both of the possible regioisomers are formed. The carbonyl insertion reaction is another migration from the metal to the carbon atom of a CO ligand. 

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. 

The migratory aptitudes of the metal-boimd group R in carbonyl insertion reactions vary widely. The insertion of CO into some groups is thermod)mamically unfavorable, and the migratory aptitudes result from thermod)rnamic effects, rather than kinetic effects. In other cases, the insertions of CO into two different M-R bonds in the same complex or the insertion of CO into the M-R bonds in two different metal complexes are all favored thermodynamically, and the relative rates are controlled by kinetic effects. Examples of measurements of the relative rates for insertion in these two situations are described in this section. 

Addition of element-element compounds to alkynes has been reviewed.Other insertions of alkynes into palladium-hydride bonds have been identified in Drent s palladium-catalyzed alkoxycarbonylation of alkynes palladium(ii)-alkenyl complexes have been invoked to account for the observed H/D exchange when conducted in GH3OD and to identify the pathway (i.e., through migratory insertion into Pd-H and formation of acyl species by carbonylation) of the overall reaction. ... 

---