Organometallic compounds of lithium and Grignard reagents
Organometallic Chemistry Reaction
Hello! Everyone today we have to discuss the Formation of Carbon-carbon single bonds using Organometallic catalysts like Organolithium Reagents, Organomagnesium Reagents, Organising reagents, Organometallic of boron, tin, and silicon, etc. They all contain the main group Chemistry.
|organometallic reagents reaction
We have to use Gilman reagents which are Organocopper reagents and similar types of another reagent are Grignard reagent which is Organomagnesium reagents. In the Organometallic catalyst’s studies, more effective reagents are organocobalt reagents, organopalladium reagents.
Today we going to briefly discuss Organolithium reagents(R-Li).
In Organolithium compounds containing a carbon lithium bond, we can write as R-Li, where R may be an alkyl group. clearly, this type of organometallic compound is called the alkyl-lithium reagents. Organolithium reagents are very much useful in organic synthesis, which is acts as a base or as a nucleophile. They react with a very large amount of electrophiles. The reaction occurs via proton abstraction or nucleophilic attacks on more electron-deficient centers like carbonyl group present compounds.
|Electronegativity difference that causes the nucleophilic attack
The polarity of a covalent bond between carbon and lithium metal, Which is mostly the difference between the electronegativity. The more electronegativity a carbon atom comparatively. The greater difference between the attraction for the bonding electrons and the bond becomes more polarized. In case bond complete polarization and covalent bonds going to exist. That is replaced by electrostatic attraction of opposite ionic charge.
|M.O diagram for the Carbon lithium bond
How to make organolithium reagents
We can prepare organolithium reagents, Simply mixed with alkyl halides ( R-Br, R-I ) and lithium metal. In case use of a small amount of Diethyl Ether as a solvent.
Each reaction required two equivalent of lithium metal and the formation of one equivalent of lithium halide solutions.
We will see e.g that secondary alkyl lithiums, aryl lithium, and vinyl lithiums. That is the formation of Grignard reagents. Lithium they are an oxidation state transformed from Li(0) to Li(I) during the reaction and there is no halide attached to the Li. Instead, a second Li metal has to be used to make the lithium halide.
Also, Li(I) is much more stable than Li(0) that causes the reaction to occur irreversible process. When ether solvents are often used, there is less need for extra coordination and hydrocarbon solvents such as pentane or hexane, THF, TMEDA, are also good.
How to make Grignard reagents
Grignard reagents are making a reaction of alkyl halides(RX) with magnesium metal(Mg) in ether solvents to the formation of alkyl magnesium halide(RMgX).
|Organolithium and Organomagnesium reagents oxidation state.
The idea of alkyl halides, use of chlorides, bromides, and iodides without any functional group, and formation of Grignard reagents. we are drawing the scheme of the reaction, now we will see the overall reaction mechanism. The overall reaction about we can conclude that is an insertion of magnesium into the new Carbon hydrogen bond.
And there change in the oxidation state of the metal, from Mg(0) to Mg(2). Similar to organolithium reaction, this type of reaction is called oxidative addition Reaction.
|Making Grignard reagents
This is the generalisation of the reaction process, for such another metal e.g Mg, Li, Zn, and Cu.
Similarly, we can use Diethyl ether, DME, and THF as a solvent.
Commercially available organolithium reagents and Grignard reagent
Organic chemists are working on this organometallic catalysis for organic synthesis. The several examples of organometallic compounds are Methyllithium (Me-Li), n- butyllithium ( n-BuLi), sec-butyl lithium (sec-BuLi), phenyl lithium (Ph-Li), etc. All are examples of organolithium reagents.
Similarly, the example Grignard reagents are methylmagnesium Chloride, bromide, iodide (MeMgX), Ethylmagnesium bromide, allyl magnesium chloride, and bromide, phenyl magnesium chloride, and bromide (PhMgX and PhMgX), etc. They all are important organolithium and Grignard reagents.