Nowadays the C-H/O-H/N-H bond activations are the important applications in biological and industrial process. High-valent first row transition metal complexes are serving an astonishing paradigm for the highly efficient and selective C-H/O-H/N-H bond activation reactions and providing several catalytic transformation reactions such as dehydrogenation, halogenation, hydroxylation, amination, olefin epoxidation etc. These are very applicable in in the pharmaceutical industries as well in synthetic laboratories. These are also a platform for understanding the relevant enzymatic reactions.
There are general issue persist in metal mediated catalytic reactions today are; (1) what is the nature of species involved in the catalytic reactions? (2) What is the exact mechanism of the catalytic transformations? (3) What are the specific reasons for the selectivity and the efficiency of a particular catalyst? (4) How can be tune ligands design? And ultimately (5) Can a model complex be made which could mimic all the functions and efficiency of the enzyme? (5) How spectroscopic parameters (such as IR, Raman, UV-Vis, EPR, Mossbauer) can help to fine tune electronic structures?
Being a computational chemist, our aim to understand the reaction mechanism of C-H/O-H/N-H bond activation reactions involving various spin states of biomimetic model complexes and the extension of that knowledge to the design and prediction of the selective catalysts of practical use. Computationally, one can alter the relative population of the various spin states upon varying the substituents through their electronic and steric grounds if we know the relative energies between various spin states. It is very important to predict reliably how the electronic changes in the catalyst affect the relative rates of similar reactions. Further, understanding of the nature of the catalytic site, its structure and chemical bonding is essential for studying the reaction mechanisms. Experimentally controlling the relative height of activation energy barriers in order to tune their catalytic selectivity is a very difficult task but with the help of computation where tuning can be easily achieved as the exact mechanism is established, one can easily overcome this challenge. Additionally this study will also provide some clues and also offer a way to understand the important biological process occurring in the nature with high-valent metal-oxo/peroxo/superoxo intermediates and it can also help to experimentalists to design new catalysts on cheap cost. So our ultimate goal is to reach "new generation catalysts".
We generally employ Gaussian09, ORCA, Aomix suite to calculate the nature of transition state, mechanism of reaction, rate limiting step, energetics of the reaction,structure and bonding, spectroscopic properties to corroborate experimental observations and make predictions towards novel approach of chemical reactions.
Our group have investigated a detailed mechanistic study on the ortho-hydroxylation of aromatic compounds by non-heme iron complexes and our calculations show that the transient Fe(V)=O species prefers an electrophilic attack on the benzene ring rather than the usual aromatic C-H activation step. Apart from mechanistic part, we have also highlighted the importance of ligand design in this chemistry and suggested that this concept can be used to enhance the reactivity and efficiency of the oxidants by increasing the electrophilicity of the ferryl oxygen atoms.
Here we focussed on comparative oxidative abilities of metal superoxo species towards C-H bond activation reaction and also compared the reactivity with corressponding metal-oxo species. We have also established a correlation between C-H bond reactivity and magnetic exchange with metal-superoxo species for the first time. Our findings suggest that the magnetic-exchange plays a crucial role in C-H bond activation.
Basicity of ligand is playing a crucial role in C-H bond actiation and differentiated the reactivity. Here we also unfold the mechanism of proton-transfer followed by electron transfer, electron-transfer followed by proton transfer and concerted proton-coupled electron transfer mechanism.
Our computational analysis reveals that the Fe(IV)=NTs species are expected to be more reactive than the corresponding Fe(IV)=O intermediates and the possibility of having an S=3 state for the Fe(IV)=NTs offers room for further enhancement of reactivity.