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 ↓


CH activation


CH activation is a fascinating area of study within organometallic chemistry, a subdiscipline of chemistry that focuses on the interactions between organic molecules and metal atoms. CH activation refers to the process by which a carbon-hydrogen (CH) bond in an organic molecule is broken and a new bond with a metal is formed, making further chemical transformations possible.

Introduction

Traditionally, CH bonds are considered relatively inert, meaning they do not react easily under normal conditions. This is because CH bonds are quite strong and non-polar, providing stability to organic compounds. However, through CH activation, these typically inert bonds can become reactive, turning into functional groups more prone to chemical reactions.

CH activation plays a vital role in the creation of complex molecules, including pharmaceuticals, agrochemicals, and materials. It transforms readily available hydrocarbons into more valuable compounds by functionalizing them, enhancing their chemical and physical properties.

Mechanism of CH activation

The CH activation mechanism generally involves breaking the CH bond and forming a new bond between the carbon and the metal. This can occur via several different pathways:

  • Oxidative addition: Metal enters between carbon and hydrogen to form C-metal and H-metal bonds.
  • σ-bond metathesis: A four-center transition state is formed, in which the CH and ML bonds are broken and new CM and HL bonds are formed simultaneously.
  • Electrophilic activation: In some cases, an electrophilic metal center can activate a C-H bond by forming a transient carbocationic species.

Illustrative examples

Let's look at some of these mechanisms in more detail using examples:

Oxidative additives

Rh(I) + RH → [Rh(III)(R)(H)]

In this process, an electron-rich metal center such as rhodium (Rh) enters the C-H bond. The metal is oxidized as new C-Rh and H-Rh bonds are formed. This step usually requires transition metals known for their ability to change oxidation states such as palladium, platinum, and rhodium.

            
            
                
                
                
                
                R
                H
                RH

σ-bond metathesis

(C5Me5)2Lu-CH3 + RH → (C5Me5)2Lu-R + CH4

In σ-bond metathesis, commonly seen with rare-earth metals or early transition metals, a coordinated process occurs where the CH and MR bond partners switch. No oxidation state change is involved. Such mechanisms are particularly important for rare-earth metals, which do not readily undergo oxidative addition.

            
            
                
                
                
                
                R
                Heatwave
                CH₄

Factors affecting CH activation

Several factors can affect the efficiency and selectivity of CH activation, including:

  • Metal selection: Transition metals such as palladium, rhodium, and ruthenium have been widely studied for CH activation due to their ability to adopt different oxidation states and coordinate various ligands.
  • Ligands: Ligands attached to the metal center can dramatically affect the reactivity and selectivity of the reaction. Bulky ligands often provide steric hindrance that affects which C-H bonds are accessed and activated.
  • Steric and electronic properties of the substrate: The presence of electron-withdrawing or donating groups can affect the ease of CH activation. Primary CH bonds may behave differently from secondary or tertiary bonds due to steric effects.

Applications of CH activation

CH activation is becoming increasingly important in the development of new synthetic methods, with applications spanning many areas:

Synthesis of pharmaceuticals

One of its main applications is in drug synthesis. Many drug molecules have complex aromatic structures. CH activation allows selective functionalization of aromatic CH bonds, making it possible to manufacture drugs with high efficiency.

An example route might include the following:

Metal-catalyst + Ar-H (arene) → Ar-metal → Ar-X (functionalized arene)

Functionalization of polymers

Another exciting area is the functionalization of polymers. By selectively activating the C-H bonds in the polymer backbone, it is possible to modify the properties of the material, such as its strength, flexibility or transparency.

Organic synthesis

Beyond pharmaceuticals, CH activation is important in organic synthesis for the creation of complex natural products, materials, and fine chemicals. It plays a role in carbon-carbon and carbon-heteroatom bond formation.

Challenges and future directions

Although tremendous progress has been made in understanding and using CH activation, challenges still remain. A key challenge is controlling selectivity and achieving site-specific activation because CH bonds are common and often identical within a molecule.

Future research may focus on developing new catalysts that allow even greater selectivity and efficiency under weaker conditions and over a broader substrate scope. Attention is also being paid to sustainable and environmentally friendly processes, aimed at reducing waste and energy consumption.

Conclusion

CH activation represents a transformative approach in organometallic chemistry that has enormous potential to advance chemical synthesis. By activating normally inert CH bonds, this technique allows for the direct transformation of hydrocarbons, opening new avenues for the construction of complex, functional molecules.

Continued research in this area promises to open new dimensions in chemistry, particularly in the development of efficient, sustainable methods for building molecular complexity from simple, abundant starting materials. CH activation is not just a technological achievement in chemistry, but a stepping stone to future innovations in pharmaceuticals, materials science, and beyond.


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CH activation

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