Table of contents |
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Introduction |
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Formation of Organometallic Reagents |
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Common Organometallic Reagents |
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Mechanism for the Addition to Carbonyls |
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Organometallic Reagents as Bases |
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Solved Examples |
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The alkali metals (Li, Na, K etc.) and the alkaline earth metals (Mg and Ca, together with Zn) are good reducing agents, the former being stronger than the latter. These same metals reduce the carbon-halogen bonds of alkyl halides. The halogen is converted to a halide anion, and the carbon bonds to the metal which has characteristics similar to a carbanion (R:-).
Because organometallic reagents react as their corresponding carbanion, they are excellent nucleophiles. The basic reaction involves the nucleophilic attack of the carbanionic carbon in the organometallic reagent with the electrophilic carbon in the carbonyl to form alcohols.
Both Grignard and Organolithium Reagents will perform these reactions.
Addition to ketones gives 3° alcohols
Addition to carbon dioxide (CO2) forms a carboxylic acid
Going from Reactants to Products Simplified
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Grignard and Organolithium Reagents
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The mechanism for a Grignard agent is shown; the mechanism for an organometallic reagent is the same.
As discussed above, Grignard and organolithium reagents are powerful bases. Because of this they cannot be used as nucleophiles on compounds which contain acidic hydrogens. If they are used they will act as a base and deprotonate the acidic hydrogen rather than act as a nucleophile and attack the carbonyl. A partial list of functional groups which cannot be used are: alcohols, amides, 1o amines, 2o amines, carboxylic acids, and terminal alkynes.
Example 1: Please write the product of the following reactions.Ans:
Example 2: Please indicate the starting material required to produce the product.
Ans:
Example 3: Please give a detailed mechanism and the final product of this reaction.
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Example 4: Please show two sets of reactants which could be used to synthesize the following molecule using a Grignard reaction.
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1. What are organometallic reagents? | ![]() |
2. How are organometallic reagents formed? | ![]() |
3. What are some common organometallic reagents? | ![]() |
4. How do organometallic reagents add to carbonyl compounds? | ![]() |
5. Can organometallic reagents act as bases? | ![]() |