C(sp(3))-F reductive elimination from alkylgold(iii) fluoride complexes
1Department of Chemistry, University of California-Berkeley, Berkeley, CA, 94720, USA.
Chemical Science
|October 23, 2012
Summary
Gold complexes undergo rare C(sp(3))-F reductive elimination, a process influenced by the nature of the R group. This reaction pathway involves cationic gold intermediates and can compete with other elimination reactions.
Area of Science:
- Organometallic Chemistry
- Fluorination Chemistry
- Gold Catalysis
Background:
- Gold complexes are versatile catalysts in organic synthesis.
- Reductive elimination is a key step in many catalytic cycles.
- C(sp(3))-F bond formation via reductive elimination from gold is challenging and rarely observed.
Purpose of the Study:
- To investigate the mechanism of C(sp(3))-F reductive elimination from gold complexes.
- To explore factors influencing this reaction pathway.
- To characterize the intermediates involved in C(sp(3))-F reductive elimination.
Main Methods:
- Oxidation of gold(I) complexes with xenon difluoride (XeF(2)) to generate cis-F(2)Au(R)(IPr) intermediates.
- Kinetic studies to monitor reaction rates.
- Stereochemical analysis using chiral R groups.
- Density Functional Theory (DFT) calculations to model reaction pathways.
Main Results:
- Rare examples of C(sp(3))-F reductive elimination were observed from cis-F(2)Au(R)(IPr) intermediates.
- β-hydride elimination competed with C(sp(3))-F reductive elimination when R groups had β-hydrogens.
- Carbocation-like rearrangements preceded C(sp(3))-F reductive elimination for strained cyclic and acyclic R groups lacking β-hydrogens.
- DFT and experimental data suggest a mechanism involving transient cationic [(IPr)Au(F)(R)](+) intermediates.
Conclusions:
- C(sp(3))-F reductive elimination from gold complexes is feasible but sensitive to substrate structure.
- The reaction proceeds via cationic intermediates with significant Au-alkyl bond ionization.
- Understanding these pathways provides insights into gold-mediated fluorination reactions.
Related Concept Videos
02:25Elimination Reactions
A nucleophile can react with an alkyl halide to give the substitution product by displacing the halogen. Or it can function as a base to give the elimination product by deprotonation of the neighboring carbon to form an alkene. In an elimination reaction, the substrate loses two groups from adjacent carbons forming at least one π bond. The carbon attached to the halogen is called the α carbon, while the adjacent carbon is called the β carbon; hence, these reactions are called β elimination or...
01:16Amines to Alkenes: Hofmann Elimination
Alkenes can be obtained from amines via an E2 elimination. The amine is first converted into a good leaving group, such as a quaternary ammonium salt. This is accomplished by treating the amine with an excess of alkyl halide, which results in a halide salt. Next, the halide salt is transformed into a hydroxide salt that functions as a base to enable elimination.
Under thermal conditions, the hydroxide can abstract a proton from the β carbon; this generates an alkene with the simultaneous...
Under thermal conditions, the hydroxide can abstract a proton from the β carbon; this generates an alkene with the simultaneous...
01:38Preparation of Alcohols via Substitution Reactions
Overview
Alcohols can be synthesized from alkyl halides via nucleophilic substitution reactions. The highly polar carbon-halogen bond in the substrate makes halide a good leaving group. The hydroxide ion or water can act as a nucleophile to take the place of halide and form an alcohol. The substitution reactions occur via two different reaction pathways, SN1 or SN2, depending on the nature of carbon attached to the halide.
Primary alcohols are synthesized from primary alkyl halides, and the...
Alcohols can be synthesized from alkyl halides via nucleophilic substitution reactions. The highly polar carbon-halogen bond in the substrate makes halide a good leaving group. The hydroxide ion or water can act as a nucleophile to take the place of halide and form an alcohol. The substitution reactions occur via two different reaction pathways, SN1 or SN2, depending on the nature of carbon attached to the halide.
Primary alcohols are synthesized from primary alkyl halides, and the...
02:38Electrophilic Addition to Alkynes: Halogenation
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
01:15Acid Halides to Alcohols: Grignard Reaction
Organomagnesium halides, commonly known as Grignard reagents, convert acid halides to tertiary alcohols. The reaction requires two equivalents of the Grignard reagent and proceeds via a ketone intermediate.
Grignard reagents are a source of carbanions and function as nucleophiles. The mechanism begins with the nucleophilic attack by the carbanion at the carbonyl carbon of the acid halide to form a tetrahedral intermediate. Next, the carbonyl group is re-formed, and the halide ion departs,...
Grignard reagents are a source of carbanions and function as nucleophiles. The mechanism begins with the nucleophilic attack by the carbanion at the carbonyl carbon of the acid halide to form a tetrahedral intermediate. Next, the carbonyl group is re-formed, and the halide ion departs,...
01:26Radical Substitution: Hydrogenolysis of Alkyl Halides with Tributyltin Hydride
Radical substitution reactions can be used to remove functional groups from molecules. The hydrogenolysis of alkyl halides is one such reaction, where the weak Sn–H bond in tributyltin hydride reacts with alkyl halides to form alkanes. Here, the reagent Bu3SnH yields tributyltin halide as a byproduct.
The bonds formed in this reaction are stronger than the bonds broken, making it energetically favorable. The reaction follows a radical chain mechanism similar to radical halogenation reactions,...
The bonds formed in this reaction are stronger than the bonds broken, making it energetically favorable. The reaction follows a radical chain mechanism similar to radical halogenation reactions,...