Computational Insight into the Mechanism of Alkane Hydroxylation by Non-heme Fe(PyTACN) Iron Complexes. Effects of the Substrate and Solvent

Abstract

The reaction mechanisms for alkane oxidation processes catalyzed by non heme Fe V O complexes presented in literature vary from rebound stepwise to concerted highly asynchronous processes. The origin of these important differences is still not completely understood. Herein, in order to clarify this apparent inconsistency, the stereospecific hydroxylation of a series of alkanes (methane and substrates bearing primary, secondary, and tertiary C-H bonds) through a Fe V O species, iii) The HAT is the rate determining step for all analyzed cases; and iv)The barrier for the HAT decreases along methane  primary  secondary  tertiary carbon. The second part of the reaction mechanism corresponds to the rebound process. Therefore, the stereospecific hydroxylation of alkane C-H bonds by nonheme Fe V (O) species occurs through a rebound stepwise mechanism that resembles that taking place at heme analogues. Finally, our study also shows that to properly describe alkane hydroxylation processes mediated by Fe V O species, it is essential to consider the solvent effects during geometry optimizations. The use of gas-phase 3 geometries explains the variety of mechanisms for the hydroxylation of alkanes reported in the literature.

New Trends in Oxidative Functionalization of Carbon–Hydrogen Bonds: A Review

“…Radicals can be generated in the solvent cage, as in the so-called "oxygen rebound mechanism" [279][280][281][282] (21)/RCOOH system has been assumed to oxidize via a "crypto-radical" ("hydroperoxo-rebound") mechanism (Figure 19) [283]. …”

“…Radicals can be generated in the solvent cage, as in the so-called "oxygen rebound mechanism" [279][280][281][282] (21)/RCOOH system has been assumed to oxidize via a "crypto-radical" ("hydroperoxo-rebound") mechanism (Figure 19) [283]. m-Chloroperbenzoic acid in the presence of certain metal compounds efficiently oxidizes alkanes at low temperature with a very high degree of stereoselectivity (trans/cis << 1) [160,227,284,285].…”

Mono- and binuclear non-heme iron chemistry from a theoretical perspective

“…The accurate treatment of environment effects (including solvation) may also be of paramount importance, particularly when highly charged active species are investigated. [242] …”

Mechanistic insights into regioselective polymerization of 1,3-Dienes catalyzed by a bipyridine-ligated iron complex: A DFT study

“…In this basis set, 10 core electrons of Fe atom were replaced by ECP and the valence electrons were described by the 8s7p6d1f/6s5p3d1f basis set (MDF10). The B3LYP functional used in this study was widely adopted for calculation of iron complexes with redox‐active ligand, including prediction of electronic ground states of the complexes . Each optimized structure was analyzed by harmonic vibrational frequencies at the same level and characterized as a minimum or a transition state.…”