The Formation, Structure, and Reactions of Binuclear Complexes of Cobalt

Reactivities and Electronic Structures of μ-1,2-Peroxo and μ-1,2-Superoxo CoIIICoIII Complexes: Electrophilic Reactivity and O2 Release Induced by Oxidation

“…This is closely related to 0.71 V vs Fc + /Fc in [(tpa){Co III (μ-1,2-O 2 )(μ-OH)Co III }(tpa)] 3+ that was assigned to a metal-centered oxidation leading to a {Co III (μ-1,2-peroxo)Co IV } species 76 rather than to the established ligand-centered oxidation leading to a {Co III (μ-1,2-superoxo)Co III } complex. 27,32,36,40,49 We have studied this oxidation and the electronic structure of the oxidized species in more detail to re-examine the nature of this oxidation.…”

“…These {Co III (μ - 1,2-peroxo)­Co III } complexes can be reversibly oxidized, and Alfred Werner initially assigned this to a metal-centered oxidation resulting in a {Co IV (μ - 1,2-peroxo)­Co III } species . Based on structural and spectroscopic characterization, this oxidation was later reassigned to be ligand-centered leading to a {Co III (μ - 1,2-superoxo)­Co III } species . The assignment as a superoxo species is supported by the following evidence: the O–O bond lengths decrease from 1.46–1.49 to 1.33–1.35 Å upon oxidation, − reflected in an increase in the corresponding ν­(O–O) vibrational frequency from 790–930 to 1075–1195 cm –1 . ,, Furthermore, EPR spectra reveal a S = 1/2 signal with a 15-line isotropic hyperfine splitting pattern that was attributed to the S = 1/2 centers interacting nearly equivalently with the two 59 Co nuclei ( I = 7/2) with A iso ≈ 25–40 MHz. − Finally, electronic absorption spectra exhibit a strong π* σ → d­(σ*) LMCT around 26,000–33,000 cm –1 and a weak low-energy d­(π) → π* π MLCT around 14,000–15,000 cm –1 . − …”

“…Dinuclear μ - 1,2-peroxo Co III Co III complexes are accessible by the reaction of Co II with molecular O 2 using nitrogen-based ligands under basic conditions ,, and were reported to catalyze ORR , and to exhibit even electrophilic HAT reactivity, the latter being induced by a ligand constraint . The first assignment to a {Co III (μ - 1,2-peroxo)­Co III } core structure was made by Alfred Werner .…”

“…31 Based on structural and spectroscopic characterization, this oxidation was later reassigned to be ligand-centered leading to a {Co III (μ-1,2-superoxo)Co III } species. 27 The assignment as a superoxo species is supported by the following evidence: the O−O bond lengths decrease from 1.46−1.49 to 1.33−1.35 Å upon oxidation, 32−39 26,40 Furthermore, EPR spectra reveal a S = 1/2 signal with a 15-line isotropic hyperfine splitting pattern that was attributed to the S = 1/2 centers interacting nearly equivalently with the two 59 Co nuclei (I = 7/2) with A iso ≈ 25−40 MHz. 41−48 Finally, electronic absorption spectra exhibit a strong π* σ → d(σ*) LMCT around 26,000−33,000 cm −1 and a weak low-energy d(π) → π* π MLCT around 14,000− 15,000 cm −1 .…”

Facile Transformations of a Binuclear Cp*Co(II) Diamidonaphthalene Complex to Mixed-Valent Co(II)Co(III), Co(III)(μ-H)Co(III), and Co(III)(μ-OH)Co(III) Derivatives

“…Binuclear cobalt complexes have attracted considerable interest in the exploration of base-metal-mediated bond activation and catalysis. − The prime examples are binuclear cobalt carbonyl compounds such as Co 2 (CO) 8 and its derivatives, , which catalyze the hydroformylation of alkenes, and the hydrosilylation of alkynes, , or serve as key coupling reagents in organic synthesis . Compared to their mononuclear counterparts, the dicobalt systems usually have more tunable electronic parameters − and are more flexible concerning electronic variations. , Recent research into cobalt-catalyzed H 2 evolution and H 2 O oxidation − shows that bimetallic synergism is significant in the performance of multielectron redox transformations.…”