Metals reactions with alkyl halides

Phosphines may be obtained by reaction with Grignard reagents (6.45), phosphites from reactions with alcohols (6.296,6.310) and phosphonic and phosphinic halides from reactions with metal alkyls (6.142,6.153) or other organic compounds (6.145-6.148,6.151,6.153). 

Organocadmium compounds can be prepared from Grignard reagents or organo-lithium compounds by reaction with Cd(II) salts.180 They can also be prepared directly from alkyl, benzyl, and aryl halides by reaction with highly reactive cadmium metal generated by reduction of Cd(II) salts.181... 

The polarity of carbon-halogen bond of alkyl halides is responsible for their nucleophilic substitution, elimination and their reaction with metal atoms to form organometallic compounds. Nucleophilic substitution reactions are categorised into and on the basis of their kinetic properties. Chirality has a profound role in understanding the reaction mechanisms of Sj l and Sj 2 reactions. Sj 2 reactions of chiral all l halides are characterised by the inversion of configuration while Sj l reactions are characterised by racemisation. 

In this context it is interesting to note that benzonitrile, Ph—C=N, trimerizes to a triazine on a Raney nickel surface. It was assumed that Jt-bonded nitriles were involved in the reaction mechanism.10 This reaction resembles the well-known template synthesis of phthalocyanine complexes from phthalodinitrile. Formation of linear polymers [—C(R)—N—] occurs on heating aryl or alkyl cyanides with metal halides.11... 

The structurally novel bicyclic oxazinone was prepared based on D-glucopyranose. The lithium enolates of these compounds undergo highly diastereoselective alkylation reactions with reactive alkyl halides, in modest yields. Use of the phosphazene P4 base enhanced the yields of these processes, suggesting that metal enolate aggregation is at least partly... 

Nucleophilic aromatic substitution often requires metal catalysis, as described above. In contrast, alkyl halides undergo reactions with phosphines directly. Nevertheless, metal-catalyzed cross-couplings of these reactive electrophiles have been developed by activation of the nucleophile. 

Oxidative-addition reactions of alkyl halides also occur with metal ions such as thallium(I). In this case, the HOMO is an s orbital on the metal of a symmetry. The concerted mechanism is now impossible and only a two-step reaction can occur. The same is true for reactions of metals in the free state, such as zinc or magnesium, with alkyl halides. Note that free radicals may be formed, instead of ions, in all cases discussed. Free radical reactions are usually allowed by symmetry. 

The alkyl nucleophiles used in the reactions shown in Eq. (5.26) and Figure 5.12 are all prepared from primary alkyl halides. Similar reactions with secondary alkylzinc reagents are more difficult, not only because of the increased steric hindrance but also because of the possibility for a secondary metal-alkyl species to undergo isomerization. For the coupling of propargyUc electrophiles specifically. 

The preparation of alkyllithiums and alkylmagnesium bromides from the alkyl halides by reaction with the metals occurs with loss of stereochemical integrity at the site of the reaction. Stereoisomeric halides give rise to organometallics of identical... 

Oxidative addition with cleavage of H—H, C—H, and Si—H bonds requires a co-ordinatively unsaturated metal species such as four-co-ordinate / -complexes. Thus, although nucleophilic anions such as [Mn(CO)5] react readily with alkyl halides, the reaction with HSiPhg is photoinduced." Irradiation gives [Mn(CO)4]", which can then undergo oxidative addition leading to cis [MnH(SiPhs)(CO)4]-. 

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