Spectroscopic Capture and Reactivity of a Low‐Spin Cobalt(IV)‐Oxo Complex Stabilized by Binding Redox‐Inactive Metal Ions

Abstract

High-valent cobalt-oxo intermediates are proposed as reactive intermediates in a number of cobalt complex-mediated oxidation reactions. Herein we report the spectroscopic capture of low-spin (S = 1/2) Co(IV)-oxo species in the presence of redox-inactive metal ions, such as Sc3+, Ce3+, Y3+, and Zn2+ and investigation of their reactivity in C-H bond activation and sulfoxidation reactions. Theoretical calculations predict that the binding of Lewis-acidic metal ions to the cobalt-oxo core increases the electrophilicity of the oxygen atom, resulting in the redox tautomerism of a highly unstable [(TAML)CoIII-(O•)]2− species to a more stable [(TAML)CoIV-(O)(Mn+)] core. The present report supports the proposed role of the redox-inactive metal ions in facilitating formation of high-valent metal-oxo cores as a necessary step for oxygen evolution in chemistry and biology.

Photocatalytic oxidation of benzene to phenol using dioxygen as an oxygen source and water as an electron source in the presence of a cobalt catalyst

“…As reported previously, the NMR peaks assignable to the bpy and Cp* of 1 remained the same after the photocatalytic production of H 2 O 2 , indicating that 1 acted as a homogeneous catalyst during the reaction. 23 However, the catalytically active intermediates such as the Co( iv )-oxo species 29 have yet to be detected in the catalytic benzene hydroxylation with H 2 O 2 . There was no deuterium kinetic isotope effect (KIE) for benzene (Fig.…”

Characterization and Reactivity of a Terminal Nickel(III)–Oxygen Adduct

“…Ray/Nam and Tolman have recently made great strides in preparing the first examples of scandium(III)oxocobalt(IV) and hydroxocopper(III) species, respectively. [4] However, well-characterized high-valent terminal nickel-oxygen adducts remain elusive.…”

An Open‐Shell Spin Singlet Copper‐Nitrene Intermediate Binding Redox‐innocent Metal Ions: Influence of the Lewis Acidity of the Metal Ions on Spectroscopic and Reactivity Properties

“…Notably, a similar interaction between a high-valent manganese-oxo core and Ca 2+ ion is proposed to play a vital role during biological oxygen evolution in photosystem II. [22][23][24][25] The wider application of the strategy of utilizing redoxinnocent Lewis acids in trapping the short-lived intermediates responsible for the oxo-and nitrene-transfer reactions mediated by mid-to-late transition metals has also been demonstrated in the successful trapping of a low-spin (S = 1/2) [26] and an intermediate-spin (S = 3/2) [27] cobalt(IV)-oxo intermediates. The successful stabilization of a copper-nitrene core allowed us to carry out an extensive reactivity study on this important intermediate.…”