Transition metal complexes are one of the most important type of catalyst and have been used in various reaction types. The transition metal catalytic system generally contains three crucial components, which are metal type, ligand type and additives. The metal and ligand determine the structure of the catalyst, and additives usually participate in the process of catalyst regeneration. The transition metal catalyst can affect the chemical selectivity, regioselectivity and stereoselectivity of the reaction, thereby significantly affecting the mechanism of the catalytic reaction. Different types of ligands and a certain type of transition metal can form a metal complex with a specific structure under specific conditions. When the metal complex can change the reaction during the kinetic process, it becomes a catalyst for this reaction. The acceleration of the process of industrial development requires people to understand the reaction mechanism of different reactions catalyzed by transition metals at the molecular level, which leads to the application of computational quantum chemistry. Researchers have a better grasp of the specific mechanism of the reaction, so as to predict and guide the experiment through the study of mechanism of the transition metal catalytic reaction.
Figure 1. Proposed mechanism for the transition-metal-catalyzed anhydride-mediated decarbonylation. (Manuel, A.; et al. 2016)
Advantages of Transition Metal Catalytic Reaction
- Mild reaction conditions.
- Rapid and high selectivity.
The Process of Studying the Reaction Mechanism
- Determine the structure of the metal complex
Determining the structure of the metal complex is an important step in the study of the reaction mechanism, which directly determines whether the reaction mechanism obtained on this basis is reasonable. The basic principle for finding the existence form of metal complexes is: the principle of lowest energy.
- Determine the breaking mode of C-H bond
The breaking mode of the C-H bond depends on the structure of the complex. There are mainly three C-H bond breaking modes: cooperative metalization-deprotonation mechanism, exogenous alkali-assisted deprotonation mechanism, and σ-metathesis mechanism.
1. Cooperative metalization-deprotonation mechanism
In a catalytic system where a coordinated metalization-deprotonation mechanism occurs, there will be a ligand with at least two coordination sites, one of which coordinates with the metal, and the other assists in the removal of hydrogen atoms.
2. Exogenous alkali-assisted deprotonation mechanism
In a catalytic system where an exogenous base-assisted deprotonation mechanism occurs, there is often the existence of Brontes base (in order to accept protons). During the auxiliary cleavage of C-H bond, the exogenous base does not coordinate to the transition metal, and there is only one proton acceptor site assisting in the removal of hydrogen atoms.
3. σ-metathesis mechanism
In the σ-metathesis mechanism, a typical four-membered ring transition state is formed in which hydrogen directly attacks the atoms in the ligand that bond with the metal.
Alfa Chemistry is committed to providing calculation of the transition metal catalytic reaction mechanism. Our fast and high-quality services include the following:
- Density functional theory (DFT)
DFT is widely used to calculate and analyze the reaction path of transition metal catalytic reaction at the molecular level.
1. We use the classic B3LYP and M06 density functional method and the basic group layer calculation model system to study its mechanism.
2. Our teams deduce the most likely reaction paths for different catalytic reaction by comparing the energy requirements of various possible reaction paths, analyzing the structure and electronic properties of key intermediates and transition states in the reaction process.
3. We also study the intrinsic correlation between the electronic effect of the ligand and the selectivity of the reaction illustrates.
- First-principles theory
1. Combining first-principles calculation methods and thermodynamic knowledge, Alfa Chemistry has established a series of thermodynamic models based on first-principles calculations.
2. We construct the relationship between the d-band electron filling degree of the catalytically active central atom in the transition metal oxide catalyst and the catalytic activity of the catalyst for oxygen reduction based on the first-principles calculations.
3. Our teams systematically study the catalytic process of oxygen reduction on the surface of different crystal phases, and the electronic density of states distribution of the plate model involved.
- Ab initio calculation
1. We use the ab initio calculation methods involving the activation of small molecules and the redox reaction of metals, to design a novel catalyst with more function.
2. Our experts can study the ligands and catalytic systems according to the properties of transition metals.
Advantages of Our Services
- Explore in detail how metal complexes formed by transition metals and ligands affect the bond breaking/bonding process of the reaction.
- We can provide crucial information of structure and relative energy of key intermediates and transition states, studying the influence of the electronic effects and stereo effects in these key intermediates and transition states on the entire catalytic reaction process.
- We can plot the potential energy surface under different bond-breaking modes and find the lowest energy barrier for different paths, assisting in determining the transition metal catalytic reaction mechanism.
- Our scientist have proposed a new catalytic activity indicator suitable for transition metal oxide oxygen reduction catalysts is proposed, helping to design a new transition metal catalyst for specific reaction systems.
Alfa Chemistry provides transition metal catalytic reaction mechanism calculation services. Our scientists use a variety of quantum chemical calculation methods to study several important organic reactions catalyzed by a variety of transition metal complexes, and investigate the detailed elementary reaction mechanism at the molecular level, which provides a powerful support for the development of new organic reactions and the design of new catalysts. If you have any questions, please feel free to contact us.
- Boehr, D. D.; et al. Engineered control of enzyme structural dynamics and function. Protein Science, 2018, 27(4).
- Manuel, A.; et al. Mechanism of Pd-Catalyzed Decarbonylation of Biomass-Derived Hydrocinnamic Acid to Styrene following Activation as an Anhydride. Inorganic Chemistry, 2016.