Abstract
Aliphatic C-H bonds are inert by nature. Therefore, synthetic chemists have shown sustained interest in reactions involving their functionalization, as this provides a means of activating and enhancing their reactivity. The biomimicry of heme-iron complexes led to the development of non-heme iron complexes.
Chemists have been especially interested in alkane oxidation to alcohol under mild conditions. This provides a way for the proper use of light alkanes such as methane, which can be used to produce alcohol and other important chemical products. This is because light alkanes are extremely difficult to functionalize. Therefore, they have been underutilized as feedstock within the chemical industry. In addition, this utilization of methane, a greenhouse gas, as a substrate has significant environmental health implications for mankind. By mimicking iron oxygenase enzymes, which carry out this chemical transformation under mild conditions in biological systems with great selectivity, chemists have developed several heme and non-heme iron (II) catalysts for this functionalization of alkanes, but there is still a need to improve their activity to make this process scalable.
In this work, computational modelling techniques in conjunction with Quantitative Structure-Activity Relationship (QSAR) methods were used to develop and evaluate a new generation of non-heme Fe(II) triflate complexes as catalysts for the selective oxidation of the C–H bond in methane. Crystal structure data of several non-heme iron (II) complexes were extracted from the Cambridge Crystallographic Structure Database (CCSD). Thereafter, their activation energies for the Hydrogen Atom Transfer (HAT) step of the methane oxidation reaction mechanism were evaluated using Density functional theory (DFT) methods. The next stage involved the identification of suitable 2D and 3D structural descriptors for the activity of these non-heme iron(II) catalysts at an atomistic level from the DFT calculation results. These were used to develop a QSAR model, which elucidated their structure-activity relationship. By applying the developed QSAR models of their reactivity, we proposed and evaluated modified structures as a new generation of non–heme iron(II) catalysts for methane oxidation.
Keywords: Alkane oxidation, non-heme iron (II) complexes, QSAR, DFT, Biomimicry.