Grignard reactions metal insertion reaction

Metal insertion reactions of alkyl halides produce organometal-lic derivatives such as Grignard reagents, which are synthetically useful sources of carbanions and change the reactive character of the carbon atom of the alkyl halide. 

Aryl and alkenyl halides undergo reactions with metals such as Zn, Mg, and Li to give products where the C-X bond is replaced with a C-metal bond. The best-known metal insertion reaction is the Grignard reaction, which uses Mg. Lithiation requires two equivalents of Li, because each Li supplies only one electron, but the Grignard and zinc insertion reactions require only one equivalent. The rate of insertion is strongly dependent on X, with I > Br 5S> Cl, corresponding to the strength of the C-X bonds. 

Contents Comparison of synthetic reactions by transition metal complexes with those by Grignard reagents. -Formation of a-bond involving transition metals. -Reactivities of a-bonds involving transition metals. -Insertion reactions. - Liberation of organic compounds from the a-bonded complexes. - Cyclization reactions, and related reactions. - Concluding remarks. 

In Grignard reactions, Mg(0) metal reacts with organic halides of. sp carbons (alkyl halides) more easily than halides of sp carbons (aryl and alkenyl halides). On the other hand. Pd(0) complexes react more easily with halides of carbons. In other words, alkenyl and aryl halides undergo facile oxidative additions to Pd(0) to form complexes 1 which have a Pd—C tr-bond as an initial step. Then mainly two transformations of these intermediate complexes are possible insertion and transmetallation. Unsaturated compounds such as alkenes. conjugated dienes, alkynes, and CO insert into the Pd—C bond. The final step of the reactions is reductive elimination or elimination of /J-hydro-gen. At the same time, the Pd(0) catalytic species is regenerated to start a new catalytic cycle. The transmetallation takes place with organometallic compounds of Li, Mg, Zn, B, Al, Sn, Si, Hg, etc., and the reaction terminates by reductive elimination. 

The classical Reformatsky reaction consists of the treatment of an a-halo ester 1 with zinc metal and subsequent reaction with an aldehyde or ketone 3. Nowadays the name is used generally for reactions that involve insertion of a metal into a carbon-halogen bond and subsequent reaction with an electrophile. Formally the Reformatsky reaction is similar to the Grignard reaction. 

The number of insertion reactions known to occur is very large. However, they can be considered to fall into a much smaller number of reaction types that arise as a result of the types of bonds between the metal and other ligand at the reactive site. The following equations illustrate these reaction types. One very simple insertion reaction is the formation of a Grignard reagent in which magnesium is inserted between R and X,... 

Bacteria, antimicrobials against, 12, 456 Baeyer-Villiger oxidation, via tin amides, 9, 370 Barbier-Grignard-type reactions, and sonochemical metal insertions, 1, 315 Barbier-type reactions allenyl and propargyl tins, 9, 358 with allylic tins, 9, 357 with antimony(III) compounds, 9, 426 with bismuth(III) compounds, 9, 433 with cerium reagents, 10, 409 with indium compounds, 9, 685... 

Organolithium compounds may be made by a similar oxidative insertion reaction from lithium metal and alkyl halides. Each inserting reaction requires two atoms of lithium and generates one equivalent of lithium halide salt. As with Grignard formation, there is really very little limit on the types of organolithium that can be made this way. 

Metallated alkenes such as alkenyllithium or Grignard species undergo addition reactions with various electrophiles. Reaction with primary alkyl bromides or iodides is possible. Wurtz self-coupled products can be avoided if the alkenyllithium species is generated by tin-lithium exchange, or by insertion of lithium metal into... 

The free dithiocarboxylic acids can be isolated, but their salts are preferred. In some cases their metal complexes can be prepared directly by insertion of carbon disulfide into metal-carbon bonds. Thus, the reaction of Grignard reagents, RMgX, with CS2, followed by acid treatment gives the dithiocarboxylic acids RCSSH and metal complexes in good yields.311... 

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