PHD
  1. Inorganic chemistry  1.1. Coordination chemistry  1.1.1. Ligand field theory  1.1.2. Crystal field theory  1.1.3. Molecular Orbital Theory for Coordination Compounds  1.1.4. Stability of Coordination Compounds  1.1.5. Electronic spectra of coordination compounds  1.1.6. Isomerism in Coordination Compounds  1.1.7. Kinetics and mechanism of coordination reactions  1.2. Organometallic Chemistry  1.2.1. Metal Carbonyls  1.2.2. Metal alkyl and aryl  1.2.3. Fischer and Schrock carbonaceans  1.2.4. Oxidative Addition and Reductive Elimination  1.2.5. Metal Hydrides  1.2.6. Catalysis by organometallic compounds  1.2.7. Metallocenes and Sandwich Complexes  1.2.8. CH activation  1.3. Solid state chemistry  1.3.1. Crystal structures and lattices  1.3.2. Band theory and electrical properties  1.3.3. Defects in the crystal  1.3.4. Synthesis of solid state materials  1.3.5. Magnetic and optical properties of solids  1.3.6. Superconductivity  1.3.7. Solid state ionics  1.4. Bio-inorganic chemistry  1.4.1. Metalloproteins and enzymes  1.4.2. Metal ion transport and storage  1.4.3. The role of metals in medicine  1.4.4. Bioinspired catalysis  1.4.5. Metal–DNA interactions  1.4.6. Metal Complexes in Medical Science  1.5. Lanthanides and Actinides  1.5.1. Electronic configuration and oxidation states in lanthanides and actinides  1.5.2. Spectral and Magnetic Properties in Lanthanides and Actinides  1.5.3. Separation and Extraction of Lanthanides and Actinides  1.5.4. Coordination chemistry of f-block elements  1.6. Main Group Chemistry  1.6.1. Chemistry of boron compounds  1.6.2. Chemistry of Silicon and Germanium Compounds  1.6.3. Chemistry of Phosphorus and Sulfur Compounds  1.6.4. Organosilicon chemistry  1.6.5. Noble Gas Chemistry
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition and substitution reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic Reactions  2.1.7. Photochemical reactions  2.2. Stereoscopic  2.2.1. Chirality and optical activity  2.2.2. Structural analysis  2.2.3. Stereoelectronic effects  2.2.4. Asymmetric synthesis  2.2.5. Dynamic Stereochemistry  2.3. Organometallic Chemistry in Organic Synthesis  2.3.1. Organolithium and organomagnesium reagents  2.3.2. Transition metal catalyzed coupling reactions  2.3.3. Palladium-catalyzed reactions  2.3.4. Olefin Metathesis  2.3.5. Gold and silver catalysis  2.4. Natural products chemistry  2.4.1. Alkaloids and terpenoids  2.4.2. Steroids and Flavonoids  2.4.3. Total synthesis of natural products  2.4.4. Biosynthesis of natural products  2.5. Supramolecular Chemistry  2.5.1. Host-Guest Chemistry  2.5.2. Self-assembly and molecular recognition  2.5.3. Supramolecular Catalysis  2.5.4. Molecular Machines
  3. Physical Chemistry  3.1. Thermodynamics  3.1.1. Laws of Thermodynamics  3.1.2. Chemical Potential and Equilibrium  3.1.3. Statistical thermodynamics  3.1.4. Non-equilibrium thermodynamics  3.2. Quantum Chemistry  3.2.1. Schrödinger equation and its applications  3.2.2. Molecular orbital theory  3.2.3. Density functional theory  3.2.4. Post-Hartree–Fock methods  3.3. Chemical kinetics  3.3.1. Reaction rate theory  3.3.2. Mechanism and rate laws  3.3.3. Catalysis and enzyme kinetics  3.3.4. Reaction dynamics  3.4. Spectroscopy and molecular structure  3.4.1. Infrared Spectroscopy  3.4.2. UV-visible spectroscopy  3.4.3. Nuclear Magnetic Resonance Spectroscopy  3.4.4. Mass Spectrometry  3.4.5. Raman Spectroscopy  3.5. Surface and Colloid Chemistry  3.5.1. Absorption and Catalysis  3.5.2. Surfactants and micelles  3.5.3. Colloidal Stability  3.5.4. Nanomaterials and Interfaces
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.1.4. Ion Chromatography  4.2. Electroanalytical techniques  4.2.1. Voltammetry and Polarography  4.2.2. Conductometry and potentiometry  4.2.3. Colometry  4.3. Spectroscopic Methods  4.3.1. Atomic absorption spectroscopy  4.3.2. Fluorescence Spectroscopy  4.3.3. X-ray diffraction  4.3.4. Electron paramagnetic resonance spectroscopy  4.4. Chemometrics  4.4.1. Data processing and statistical methods  4.4.2. Multidisciplinary analysis  4.4.3. Machine Learning in Analytical Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.2. Quantum chemistry methods  5.3. Computational drug design  5.4. Machine Learning in Chemistry  5.5. Ab initio molecular dynamics
  6. Biophysics and Medicinal Chemistry  6.1. Drug discovery and design  6.2. Enzyme kinetics and inhibition  6.3. Chemical biology approach  6.4. Protein-ligand interactions  6.5. Bioorthogonal chemistry
  7. Materials chemistry  7.1. Polymer chemistry  7.1.1. Polymerization mechanism  7.1.2. Functional Polymers  7.1.3. Biodegradable Polymer  7.1.4. Conducting and semiconducting polymers  7.2. Nano Chemistry  7.2.1. Nanoparticles and nanostructures  7.2.2. Carbon-based nanomaterials  7.2.3. Quantum dots  7.3. Energy and Environmental Chemistry  7.3.1. Battery and Fuel Cell Chemistry  7.3.2. Green chemistry and sustainable materials  7.3.3. Photocatalysis

PHD → Inorganic chemistry → Organometallic Chemistry ↓


Fischer and Schrock carbonaceans


In the fascinating world of organometallic chemistry, one of the areas of intense interest is the study and applications of carbenes. Carbenes are a class of highly reactive molecules that contain a divalent carbon atom (C) with two unshared valence electrons. This makes them highly versatile in chemical reactions. It is important to understand their nature and types, and among the different types of carbenes, Fischer and Schrock carbenes are of vital importance. These two types of carbenes differ mainly in their electronic structure and the type of their bonding with metals.

Introduction to carbenes

Carbenes are neutral molecules consisting of a carbon atom with two non-bonded electrons and are generally represented as :CR 2, where R can be any substituent group (e.g. hydrogen, alkyl, etc.). The nature of these electrons gives rise to a singlet or triplet state depending on their spin properties.

Singlet and triplet carbenes

Singlet carbenes: In singlet carbenes, two electrons are paired, making this state diamagnetic. Carbenes in this state are often formed through stabilization with lone pair interactions, and their shape is bent. An example is:

C : R 2

Triplet carbenes: In triplet carbenes, these two electrons are unpaired, resulting in a paramagnetic state. These carbenes usually exhibit linear geometry. Simple examples include:

C : R 2

Introduction to Fischer carbenes

Fischer carbenes are characterized by a neutral or electron-withdrawing substituent bonded to the carbene carbon atom. This type of carbene is named after Ernst Otto Fischer, Nobel Prize winner in Chemistry. Fischer carbenes are usually singlet carbenes and are often formed from transition metals via metal-carbon bonding, particularly in low oxidation states.

Chemical structure of Fischer carbene

The general formula of a Fischer carbene is as follows:

LM=C(R)

where L is usually a π-acceptor ligand such as a carbon monoxide group, M represents the metal, and R is an aryl or alkyl group.

An example of a Fischer carbene structure with a metal is:

O || -M=C(R)

Synthesis of Fischer carbenes

Fischer carbenes are typically synthesized by the reaction of a metal carbonyl complex with a nucleophile. This often involves the use of a base to deprotonate a transition metal hydride or related species, followed by reaction with a carbonyl compound.

An example of the reaction mechanism for the synthesis of a Fischer carbene is shown below:

M(CO) 5 + R -> Base -> [M(CO) 4 (C=R)]

Introduction to Schrock carbenes

Schrock carbenes are a well-known type of carbenes, named after Richard Schrock, who made important contributions to the chemistry of these species. Unlike Fischer carbenes, Schrock carbenes are characterized by having electron-donating substituents that are more basic. These carbenes are often associated with early transition metals, which generally have higher oxidation states.

Chemical structure of Schrock carbene

The general structure of a Schrock carbene can be represented as:

LM=C(R)

In this structure, L represents the ligand surrounding the metal, M represents the metal, and R is usually a silyl or alkyl group.

An example of a Schrock carbene structure is:

R \ M=C / L

Synthesis of Schrock carbene

Schrock carbenes are typically produced by treating a metal complex with an appropriate alkylidene transfer reagent. They require the formation of a high oxidation state intermediate that is typically stabilized by strong π-donor ligands, such as alkylamines or alkoxides.

The mechanism for the synthesis of Schrock carbene is as follows:

[M] + Alkylidene transfer reagent -> Schrock Carbene complex

Comparison between Fischer and Schrock carbenes

Fischer and Schrock carbenes differ considerably in their electronic properties, metallization type, and reactivity. Here are some of the main differences:

Electronic structures and reactivity

  • Fischer carbene:
    • It is usually obtained from late transition metals in low oxidation states.
    • Stabilized by π-acceptor ligand.
    • Formed with aryl or alkyl substituents.
    • They exhibit electrophilic character due to the electron-withdrawing nature of the ligand.
    • Favor the formation of more stable products through controlled reactions.
  • Schrock carbenes:
    • Derived from early transition metals in high oxidation states.
    • Stabilized by σ-donor ligand.
    • Formed with alkyl- or silyl-substituents.
    • They show nucleophilic properties due to the donor character of the substituent.
    • Often participate in catalytic cycles such as olefin metathesis.

Application

Both Fischer and Schrock carbenes find wide applications in modern organic synthesis and industrial chemical processes.

Fischer carbenes in synthesis

Fischer carbenes perform well in cyclopropanation reactions, carbon–hydrogen activation, and facilitating selectivity in asymmetric synthesis due to their electrophilic nature.

Schrock carbene in catalysts

Schrock carbenes are important in olefin metathesis reactions, which are used in polymerization processes and in the petrochemical industry to produce specialty chemicals.

Conclusion

Fischer and Schrock carbenes represent the fundamental types of carbenes in organometallic chemistry. Their differences in structure and behavior highlight the range of behavior that carbenes can exhibit and their potential in industrial, synthetic, and catalytic applications. Understanding and manipulating these molecules allows chemists to perform complex reactions and synthesize new materials, underscoring the important role of carbenes in modern chemistry.


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Fischer and Schrock carbonaceans

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