•DFT calculations were carried out to study of the reaction mechanism.•The energy profile and optimized geometries of key intermediates are given.•The solvation effects play a significant role in determining the reaction mechanism.•The structural mimics we got can provides reference for the experiment.In this work, density functional theory (DFT) calculations were carried out to study the role of solvation effects on the reaction of diiron dithiolate complex with CO to form [Fe]-hydrogenase model complex. In the gas phase, the energy barrier of the first transition state TS1 species is ca. 6.1 kcal/mol higher than the second transition state TS2 species. However, when the solvation effects were included, the energy order was reversed, i.e., the energy barrier of TS1 falls ca. 1.2 kcal/mol lower than TS2, indicating that the insertion of the second CO to iron is the rate-determining step in the whole transformation process. The initial insertion of the CO plays an important role in increasing the reaction barrier of the binding of a second CO, which prevented the second step transformation. Thus, the solvation effects play a significant role in determining the reaction mechanism. In addition, the energy of PC species is lower than RC species, demonstrating that this transformation is a significantly exothermic process.

The reaction mechanism of Rh(III)-catalyzed cross-dehydrogenative aryl–aryl coupling between benzamides and haloarenes was investigated through detailed density functional theoretical (DFT) studies in terms of regioselectivity and deuterium kinetic isotope effects (KIEs). Three possible routes including one PivO–-assisted reaction route and two non-PivO–-assisted reaction routes have been studied. The calculated results refute the proposed mechanism (without PivO–-assisted process) in the experimental paper and demonstrate that the PivO–-assisted reaction mechanism is the most favored. Meanwhile, the calculation revealed that the PivO– anion plays a crucial role as a proton acceptor in the C–H bond activation, especially when the second C–H activation of haloarenearene proceeds via a SE3 mechanism. The SE3 mechanism is presented for the Rh(III)-catalyzed aryl–aryl reaction for the first time. Our mechanism is evaluated by the calculations of the para-/meta-regioselectivity and KIEs. And it is found that the second activation process is the rate-determining step of the whole catalytic cycle. All these calculated properties agree well with the experiment and Glorius’s proposal that the Rh(III)-catalyzed cross-dehydrogenative C–C coupling reaction proceeds by dual C–H activations. Our theoretical studies suggest that the Rh(III) complex catalyst strongly affects the mechanisms of the second C–H activation step and thus this work might provide insight into the design of new catalytic systems.

Oxidative C–H bond activation is a transformation of fundamental and practical interest, particularly if it can be carried out with high regio- and enantioselectivity. With nonheme iron oxygenases as inspiration (e.g., the Rieske oxygenases), a family of biomimetic nonheme iron complexes has been found to catalyze hydrocarbon oxidations by H2O2 via a postulated FeV(O)(OH) oxidant. Of particular interest is the Fe(S,S-PDP) catalyst discovered by White that, in the presence of acetic acid as an additive, performs selective C–H bond activation, even in complex organic molecules. The corresponding FeV(O)(OAc) species has been suggested as the key oxidant. We have carried out DFT studies to assess the viability of such an oxidant and discovered an alternative formulation. Theory reveals that the barrier for the formation of the putative FeV(O)(OAc) oxidant is too high for it to be feasible. Instead, a much lower barrier is found for the formation of a [(S,S-PDP)FeIII(κ2-peracetate)] species. In the course of C–H activation, this complex undergoes O–O bond homolysis to become a transient [(S,S-PDP)FeIV(O)(AcO·)] species that performs the efficient hydroxylation of alkanes. Thus, the acetic acid additive alters completely the nature of the high-valent oxidant, which remains disguised in the cyclic structure. This new mechanism can rationalize the many experimental observations associated with the oxidant formed in the presence of acetic acid, including the S = 1/2 EPR signal associated with the oxidant. These results further underscore the rich multioxidant scenario found in the mechanistic landscape for nonheme iron catalysts.Keywords: C−H activation; density functional calculations; nonheme iron; oxometal; O−O homolysis

The anaerobic metabolism of CCl4 by P450 enzymes was investigated using quantum chemical calculations. It was found that under anaerobic conditions, the substrate CCl4 might undergo one or two subsequent one-electron reductions to generate different reactive metabolites, trichloromethyl radical (˙CCl3) and dichlorocarbene (:CCl2) respectively. Meanwhile, it was the reduced ferrous haem complex rather than the unreduced ferric haem complex that could directly achieve such reductions. Based on the formation of the former reactive metabolite, a further one-electron reduction could take place with the assistance of a proton to yield the latter reactive species, i.e., a further reductive dechloridation of ˙CCl3 could take place via a novel SE3 mechanism. In addition, the ˙CCl3 species was capable of binding covalently to the meso-carbon atom of the prosthetic group, leading to the suicidal destruction of P450 enzymes. Whereas the :CCl2 species was involved in the CCl4-dependent reversible P450 inhibition as its hydrolysis product, CO, but was not significantly involved in the CCl4-dependent irreversible P450 destruction. It is obvious that the reductive metabolism of CCl4 to reactive intermediates by P450 enzymes is an essential prerequisite for its toxicity.