The Nature of the Chemical Bonds of High-Valent Transition–Metal Oxo (M=O) and Peroxo (MOO) Compounds: A Historical Perspective of the Metal Oxyl–Radical Character by the Classical to Quantum Computations

Abstract

This review article describes a historical perspective of elucidation of the nature of the chemical bonds of the high-valent transition metal oxo (M=O) and peroxo (M-O-O) compounds in chemistry and biology. The basic concepts and theoretical backgrounds of the broken-symmetry (BS) method are revisited to explain orbital symmetry conservation and orbital symmetry breaking for the theoretical characterization of four different mechanisms of chemical reactions. Beyond BS methods using the natural orbitals (UNO) of the BS solutions, such as UNO CI (CC), are also revisited for the elucidation of the scope and applicability of the BS methods. Several chemical indices have been derived as the conceptual bridges between the BS and beyond BS methods. The BS molecular orbital models have been employed to explain the metal oxyl-radical character of the M=O and M-O-O bonds, which respond to their radical reactivity. The isolobal and isospin analogy between carbonyl oxide R2C-O-O and metal peroxide LFe-O-O has been applied to understand and explain the chameleonic chemical reactivity of these compounds. The isolobal and isospin analogy among Fe=O, O=O, and O have also provided the triplet atomic oxygen (3O) model for non-heme Fe(IV)=O species with strong radical reactivity. The chameleonic reactivity of the compounds I (Cpd I) and II (Cpd II) is also explained by this analogy. The early proposals obtained by these theoretical models have been examined based on recent computational results by hybrid DFT (UHDFT), DLPNO CCSD(T0), CASPT2, and UNO CI (CC) methods and quantum computing (QC).

Synthesis of aminoalcohols from substituted alkenes via tungstenooxaziridine catalysis

“…Based on the observed chemoselectivity and high stereoselectivity, we anticipated a potentially fast tungstenooxaziridine addition across the alkene with formation of short-lived biradical species through homolytic cleavage of the N – O bond in the transition state. 21 Experiments with deuterated substrates showed that 2j1- d and 2p1- d reacted to provide 3j1- d and 3p1- d without any deuterium scrambling, thus both experiments confirming that a highly concerted syn -addition is likely to be the predominant pathway. We also wanted to address if 3 formed through hydrolysis of aziridine 5 under the reaction conditions, and we found that 5 j does not provide 3j under the reaction conditions.…”

C–H bond activation by high-valent iron/cobalt–oxo complexes: a quantum chemical modeling approach

“…Also, the higher reactivity of cobalt–oxo species may be due to the population of the anti-bonding π* orbitals on the M–O moiety which results in a relatively weak Co–O bond than the Fe–O bond. 59 b ,60 The second order perturbation analysis from the NBO basis of the metal–oxygen (M–O) bond indicated that species 1 has a higher stabilization energy (65.7 kcal mol −1 ) than species 2 (48 kcal mol −1 ). Here, we found that species 2 has weaker bonding between the metal and oxygen compared to species 1 .…”