Probing the Origins of Puzzling Reactivity in Fe/Mn–Oxo/Hydroxo Species toward C–H Bonds: A DFT and Ab Initio Perspective

Abstract

Activation of C−H bonds using an earth-abundant metal catalyst is one of the top challenges of chemistry, where highvalent Mn/Fe−oxo(hydroxo) biomimic species play an important role. There are several open questions related to the comparative oxidative abilities of these species, and a unifying concept that could accommodate various factors influencing reactivity is lacking. To shed light on these open questions, here, we have used a combination of density functional theory (DFT) (B3LYP-D3/def2-TZVP) and ab initio (CASSCF/NEVPT2) calculations to study a series of highvalent metal−oxo species [M n+ H 3 buea(O/OH)] (M = Mn and Fe, n = II to V; H 3 buea = tris[(N′-tert-butylureaylato)-N-ethylene)]aminato towards the activation of dihydroanthracene (DHA). The H-bonding network in the ligand architecture influences the ground state−excited state gap and brings several excited states of the same spin multiplicity closer in energy, which triggers reactivity via one of those excited states, reducing the kinetic barriers for the C−H bond activation and rationalizing several puzzling reactivity trends observed in various high-valent Mn/Fe−oxo(hydroxo) species.

The interplay of covalency, cooperativity, and coupling strength in governing C–H bond activation in Ni2E2 (E = O, S, Se, Te) complexes

“…S48–S52 and S53–S56‡ for EVP). 103 After the hydrogen atom abstraction, the formation of radical intermediate ( Int1 ) is exothermic for 1 and endothermic for the rest (−96.6, 39.9, 40.6 and 67.1 kJ mol −1 , for 1–4 , respectively) with S T = 0 ground state arising from antiferromagnetic for all with the exception of 3 (here S T = 2). In all cases, the corresponding exchange coupled excited state was found to lie close within an energy margin of 1.3–6.6 kJ mol −1 , with the triplet states lying much higher in energy (38–71 kJ mol −1 ).…”

How do quantum chemical descriptors shape hydrogen atom abstraction reactivity in cupric-superoxo species? A combined DFT and machine learning perspective

“…Importantly, none of these parameters requires transition state geometries (see Tables S28 and 29‡), or the estimation of kinetic barriers, which is not only a challenging task but, given the open-shell nature of the reaction, often involves multiple spin states and spin coupling that may lead to the possibility of even missing the lowest energy transition state. 86,87 Furthermore, a robust ML model based on simple quantities adapted here can help to pave the way forward for larger screening and more robust prediction.…”

Unravelling the Mechanism of CO2 Activation: Insights Into Metal‐Metal Cooperativity and Spin‐Orbit Coupling with {3d–4f} Catalysts

“…Apart from the given mechanistic consideration from DFT calculations, it is apparent that the nature of the Ln(III) ions also influences the catalytic reactivity. As Dy(III) and Er(III) ions are strongly anisotropic, a single reference method [26] such as DFT cannot be employed. To circumvent this problem, we have employed the geometry from the DFT calculations and performed CASSCF/RASSI‐SO calculations on all the species in the potential energy surface to elucidate the role of spin‐orbit coupled states and how the geometry around the Ln(III) alters the related SO states and influence the overall reaction.…”