Carbon monoxide migratory insertion reactions

Organometallic Compounds. Mononuclear carbon monoxide complexes of palladium are relatively uncommon because of palladium s high labihty, tendency to be reduced, and competing migratory insertion reactions in the presence of a Pd—C bond (201). A variety of multinuclear compounds... 

Organometallic Compounds. Mononuclear carbon monoxide complexes of palladium are relatively uncommon because of palladium s high lability, tendency to be reduced, and competing migratory insertion reactions in the presence of a Pd—C bond (201). A variety of multinuclear compounds are known (202), including [Pd2Cl4(CO)2] [75991-68-3], [Pd3(P(C6H5)3)3(CO)3] [36642-60-1], and [Pd7(P(CH3)3)7(p3-CO)3(p2-CO)4] [83632-51-3]. 

It is often found that the migratory insertion reaction is strongly solvent dependent. In addition, electron acceptors bring about great rate enhancements. As will be described in this section, the mechanism for this rate enhancement appears to proceed via initial attack of the electron acceptor on the oxygen of the carbon monoxide ligand involved in the insertion process. 

VI.2 Migratory Insertion Reactions of Alkyl-, Aryl-, Alkenyl-, and Alkynylpalladium Derivatives Involving Carbon Monoxide and Related Derivatives... 

Another route to enantiomcrically pure iron-acyl complexes depends on a resolution of diastereomeric substituted iron-alkyl complexes16,17. Reaction of enantiomerically pure chloromethyl menthyl ether (6) with the anion of 5 provides the menthyloxymethyl complex 7. Photolysis of 7 in the presence of triphenylphosphane induces migratory insertion of carbon monoxide to provide a racemic mixture of the diastereomeric phosphane-substituted menthyloxymethyl complexes (-)-(/ )-8 and ( + )-( )-8 which are resolved by fractional crystallization. Treatment of either diastereomer (—)-(/J)-8 or ( I )-(.V)-8 with gaseous hydrogen chloride (see also Houben-Weyl, Vol 13/9a, p437) affords the enantiomeric chloromethyl complexes (-)-(R)-9 or (+ )-(S)-9 without epimerization of the iron center. 

A catalyst used for the u-regioselective hydroformylation of internal olefins has to combine a set of properties, which include high olefin isomerization activity, see reaction b in Scheme 1 outlined for 4-octene. Thus the olefin migratory insertion step into the rhodium hydride bond must be highly reversible, a feature which is undesired in the hydroformylation of 1-alkenes. Additionally, p-hydride elimination should be favoured over migratory insertion of carbon monoxide of the secondary alkyl rhodium, otherwise Ao-aldehydes are formed (reactions a, c). Then, the fast regioselective terminal hydroformylation of the 1-olefin present in a low equilibrium concentration only, will lead to enhanced formation of n-aldehyde (reaction d) as result of a dynamic kinetic control. 

The mechanism of this three-component coupling reaction is probably analogous to the aforementioned insertion of acyl chlorides (above). One can imagine assembling an intermediate acylpalladium species either by oxidative addition to an acyl chloride or, in this case, by oxidative addition to the aromatic iodide followed by migratory insertion into carbon monoxide. Once formed, the acylpalladium intermediate can insert into the SCB to furnish a 7-(chlorosilyl)propyl ketone, which cyclizes in the presence of the amine to afford cyclic enol ethers. 

Different types of migratory insertions are exemplified by reactions 10, 11, and 12 in the Table II. An evaluation scheme is given in Matrix 6. In the present study we consider this reaction according to its general mechanism, shown in Eq. (6), where L is a neutral ligand (olefin, carbon monoxide, carbene, etc.) which becomes X (anionic c-donor ligand). X is also an anionic a-donor ligand. 

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