Reductive elimination of alkyl halides

Oxidative Addition and Reductive Elimination of Alkyl Halides... 

This reaction is part of the mechanism for reductive eliminations of alkyl halides from Pt(IV). As noted in Chapter 8 (reductive elimination), this reaction occurs by initial dissociation of iodide to generate a cationic Pt(IV) methyl complex and subsequent attack of iodide on the platinum(IV) methyl group to generate methyl iodide (Equation 11.13). The reductive elimination of methyl aryl ethers, methyl acetate, and methyl trifluoroacetate... 

The reversibility argument also applies to reductive elimination of alkyl halides for which an Sn2 pathway (Fig. 6.2) applies for the oxidative addition direction. Iodide attacks the coordinated methyl trans to the open site and nucleophili-cally displaces the Pt complex, which is a good leaving group. The reactive 5-coordinate intermediate, which can even be isolated in some cases, can also undergo concerted reductive elimination of ethane if the concentration is low. ... 

The preparation of [Ni(PMe3)4]+ by the addition of PMe3 to [NiXMe-(PMe3)2] (X = halide) (215) is particularly noteworthy in suggesting that the reductive elimination of alkyl or aryl halides from Ni(II) phosphine complexes via 17-electron intermediates may be important in catalytic cycles... 

Reductive elimination to form carbon-heteroatom bonds from acyl complexes occurs more readily than it does from alkyl or aryl complexes. This fast rate is consistent with the trends noted previously—namely, reductive elimination is faster from complexes containing groups that are sp hybridized, that are electrophilic, and that can coordinate to the metal center during tiie reductive elimination. Reductive elimination of acid halides has been proposed as a step in the Monsanto acetic acid process, and experimental evidence has been obtained for this type of reductive elinunation from acetylrhodium halide complexes generated in solution (Equation 8.66). - A closely related incorporation of KZO into add halides catalyzed by Wilkinson s catalyst provides further evidence for reversible addition and elimination of add halides involving Rh(I) and Rh(III), respectively. ... 

As we have seen, oxidative addition is the inverse of reductive elimination and vice versa. In principle, each reaction is reversible, but in practice the reactions tend to go in the oxidative or reductive direction only. The position of equilibrium in any particular case is governed by the overall thermodynamics this in turn depends on the relative stabilities of the two oxidation states and the balance of the A—B versus the M—A and M—B bond strengths. Alkyl hydride complexes commonly eliminate alkane, but only rarely do alkanes oxidatively add to a metal. Conversely, alkyl halides commonly add to metal complexes, but the adducts rarely reductively eliminate the alkyl halide. Third-row elements, which tend to have stronger metal-ligand bonds, tend to give more stable adducts. Occasionally, an equilibrium is established in which both the forward and back reactions are observed. 

Although in this chapter we shall be restricting coverage to reactions of transition-metal complexes, the phenomenon of oxidative addition is not confined to this type of compound. Such reactions are also well established for non-transition metals—a recently reported example concerns the oxidative addition of methyl bromide to indium(i) bromide to give InBr2Me— and for non-metals, as in the reaction of phosphorus trichloride with chlorine, to cite a very familiar example. Likewise, reductive eliminations are known and studied outside the area of transition-metal complexes. One example has been mentioned in Chapter 1 of Part II of this volume, namely the elimination of alkyl halides from the thallium(iii) compounds TlRXa. ... 

Reaction No. 5 (Table 11) is part of a synthetically useful method for the alkylation of aromatic compounds. At first the aromatic carboxylic acid is reductively alkylated by way of a Birch reduction in the presence of alkyl halides, this is then followed by an eliminative decarboxylation. In reaction No. 9 decarboxylation occurs probably by oxidation at the nitrogen to the radical cation that undergoes decarboxylation (see... 

Alkenes are obtained by the transformation of various functional groups, e.g. dehydration of alcohols (see Section 5.4.3), dehalogenation of alkyl halides (see Section 5.4.5) and dehalogenation or reduction of alkyl dihalides (see Section 5.4.5). These reactions are known as elimination reactions. An elimination reaction results when a proton and a leaving group are removed from adjacent carbon atoms, giving rise to a tt bond between the two carbon atoms. 

Carbonylation of alkyl halides is rare. As an exception, AcOH is produced commercially by the Monsanto process from MeOH and CO using Rh as a catalyst in the presence of HI. In this process (Scheme 3.10), Mel is generated in situ from MeOH and HI and undergoes oxidative addition. Insertion of CO generates an acetylrhodium intermediate, and nucleophilic attack of water produces AcOH, regenerating the Rh catalyst and HI (or reductive elimination to give acetyl iodide and hydrolysis). 

A. Oxidative Addition of Alkyl Halides or Related Reagents and Reductive Elimination... 

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