Chapter23_LectureSlides
Chapter 23: Introduction to Organometallic Compounds
Overview
Focus on Organometallic Compounds from David Klein's text.
Importance of electronegativity in understanding organometallic chemistry.
23.1 Properties of Organometallic Compounds
Introduction
Organometallic compounds have been discussed previously, highlighting their importance in organic synthesis.
Carbon is more electronegative than the metal it bonds with, influencing reactivity.
Reactivity
Reactivity differences are primarily based on electronegativity differences among involved elements.
Examples of Organometallic Compounds
Example compounds include but not limited to: organomagnesium and organolithium.
Special focus is on predicting products from reactions, such as the Michael reaction.
23.2 Organolithiums & Organomagnesiums
Introduction
Organolithium and organomagnesium compounds exhibit a high degree of ionic character and reactivity.
Formation
Organolithium compounds are derived from alkyl halides, typically using solvates like hexane.
Grignard Reagents
Synthesis and reactions of organomagnesium (Grignard) reagents:
Grignard reagents react vigorously with protic substances, acting as strong bases.
Often utilized in various organic synthesis reactions.
Mechanism of Formation
Free radical mechanisms govern the formation of organolithium and organomagnesium compounds, typically utilizing diethyl ether or THF as a solvent.
23.3 Lithium Dialkyl Cuprates (Gilman Reagents)
Introduction
Gilman reagents are formed by the reaction of an organolithium compound with a cuprous halide.
These reagents can be alkyl, vinyl, or aryl in nature.
Reaction Characteristics
Gilman reagents can undergo coupling reactions with alkyl halides, demonstrating stereospecificity and compatibility with various functional groups.
The Corey-Posner/Whitesides-House reaction showcased as a key coupling reaction.
Reactions with Acid Halides
Gilman reagents can also react with acid halides effectively.
Reactions with Alpha, Beta-Unsaturated Ketones
Detail mechanisms and reactions with functional groups like alpha, beta-unsaturated ketones.
23.4 Simmons-Smith Reaction and Carbenoids
Introduction
Organozinc compounds form under conditions similar to Grignard reagents, showing less polarity and ionic character.
Cyclopropanation via Simmons-Smith Reaction
The ICH2ZnI compound acts as a carbenoid in cyclopropanation reactions, demonstrating stereospecificity.
Examples of compounds used within the Simmons-Smith reaction are detailed.
Other Cyclopropanation Methods
Carbenes are highlighted for their dual roles as electrophiles and nucleophiles in alternative cyclopropanation reactions.
23.5 Stille Coupling
Introduction
The importance of Pd catalysts in facilitating synthetic organic chemistry reactions.
Mechanism
Stille coupling involves the transition through three key steps: oxidative addition, transmetallation, and reductive elimination.
Other aspects include acceptable electrophiles and leaving groups for successful reactions.
Advantages
Stille coupling allows high selectivity and utility, particularly for complex organic syntheses.
Applications
Multiple examples highlight the reaction's versatility, including application in β-carotene synthesis.
23.6 Suzuki Coupling
Overview
Suzuki coupling methodology is similar to Stille but employs organoboranes, showcasing a broader substrate tolerance.
Base requirements and structural considerations are discussed.
Limitations and Advantages
Comparison between Suzuki and Stille reveals advantages like ease of byproduct removal and lower toxicity of organoboron intermediates.
23.7 Negishi Coupling
Introduction
The Negishi coupling reaction offers a versatile method for C–C bond formation using organozinc, organoaluminum, or organometallic compounds.
Mechanism
Detailed discussion of the mechanistic steps and the factors influencing reactivity.
Final Applications
Highlight integral syntheses, including β-carotene synthesis demonstrating Negishi coupling's significance.
23.8 The Heck Reaction
Characteristics
The Heck reaction is an essential method for creating C–C bonds by substituting vinylic H with R groups, demonstrating a range of functional compatibility.
Mechanism
Elaboration on the mechanistic pathway, emphasizing the need for a base during catalytic processes.
23.9 Alkene Metathesis
Overview
Explanation of alkene metathesis, mechanisms, catalysts, and possible products.
Discusses the significance of ring-closing and ring-opening metathesis under various functional group conditions.
Review of Reactions
Summary of key reactions, highlighting preparations and coupling processes.