Computational Exploration of Chiral Iron Porphyrin-Catalyzed Asymmetric Hydroxylation of Ethylbenzene Where Stereoselectivity Arises from π–π Stacking Interaction

Abstract

The mechanism and origins of stereoselectivity of chiral iron porphyrin-catalyzed asymmetric hydroxylation of ethylbenzene were explored with density functional theory. The hydrogen atom abstraction is the rate- and stereoselectivity-determining step. In good agreement with experimental results, the formation of the (R)-1-phenylethanol product is found to be the most favorable pathway. The transition state of hydrogen atom abstraction which leads to the (S)-1-phenylethanol product is unfavorable by 1.7 kcal/mol compared to the corresponding transition state which leads to the (R)-1-phenylethanol product. Enantioselectivity arises from an attractive π–π stacking interaction between the phenyl group of ethylbenzene substrate and the naphthyl group of the porphyrin ligand.

Molecular Dynamics of Iron Porphyrin-Catalyzed C–H Hydroxylation of Ethylbenzene

“…The detailed description of the mechanism of iron porphyrin-catalyzed asymmetric hydroxylation of ethylbenzene was presented in our previous paper. 26 Here, we explored the key HAA/OR steps starting from the high valent iron-oxo species at the level of (U)B3LYP/6-31G*−LANL2DZ with Gaussian 16. Figure 1 shows the computed free energy diagram of ethylbenzene oxidation by the iron-oxo species in the gas phase.…”

Computational Exploration of Dirhodium Complex-Catalyzed Selective Intermolecular Amination of Tertiary vs. Benzylic C−H Bonds

“…The distortion/interaction model has been widely used to understand the origins of reactivities and selectivities [ 50 , 51 , 52 , 53 , 54 , 55 ]. This model links activation energy with the distortion energy required for the geometrical deformation of reactants achieving their transition-state geometry, as well as with the interaction energy generated by the interactions between the two distorted reactants in the transition state structure [ 56 , 57 ]. Figure 9 shows the distortion/interaction model of the tertiary C–H bond amination.…”

Comparative oxidative ability of mononuclear and dinuclear high-valent iron–oxo species towards the activation of methane: does the axial/bridge atom modulate the reactivity?

“…71,135 In heme models, due to the presence of a flat equatorial ligand, the substrate can approach the oxo group in a π-fashion without any substantial substrate-catalyst strain, which is usually present in non-heme models. Furthermore, we have observed C-H⋯π non-covalent interactions [136][137][138][139][140][141][142] between the substrate and the porphyrin ring (2.60 to 3.40 Å) anchoring the substrate in the vicinity of all four species. This isosurface demonstrates that the π-face of the porphyrin ring and the edge of the methyl group engage in an attractive interaction 143 (see Fig.…”

“…144 For these reasons, for all catalysts modelled, a preferential π-pathway is noted. 43,45,140,145 For all complexes, the π(FevO) orbitals are high in energy to be the source of electrons. 146 This forces the axial HO − ligand to participate in the π orbitals of the HO-FevO moiety (see Fig.…”