Synthesis and reactivity of a mononuclear non-haem cobalt(IV)-oxo complex

Abstract

Terminal cobalt(IV)–oxo (CoIV–O) species have been implicated as key intermediates in various cobalt-mediated oxidation reactions. Herein we report the photocatalytic generation of a mononuclear non-haem [(13-TMC)CoIV(O)]2+ (2) by irradiating [CoII(13-TMC)(CF3SO3)]+ (1) in the presence of [RuII(bpy)3]2+, Na2S2O8, and water as an oxygen source. The intermediate 2 was also obtained by reacting 1 with an artificial oxidant (that is, iodosylbenzene) and characterized by various spectroscopic techniques. In particular, the resonance Raman spectrum of 2 reveals a diatomic Co–O vibration band at 770 cm−1, which provides the conclusive evidence for the presence of a terminal Co–O bond. In reactivity studies, 2 was shown to be a competent oxidant in an intermetal oxygen atom transfer, C–H bond activation and olefin epoxidation reactions. The present results lend strong credence to the intermediacy of CoIV–O species in cobalt-catalysed oxidation of organic substrates as well as in the catalytic oxidation of water that evolves molecular oxygen.

Tuning the Electronic Properties of Prussian Blue Analogues for Efficient Water Oxidation Electrocatalysis: Experimental and Computational Studies

“…Interestingly,t he reactive Co IV centerh as ah igh degree of radicalc haracter distributed over the CoÀOb ond. Such electronic structure fingerprints of high-valent Co moieties were recently shown to be related to reactivity, [43] where an apparent Co IV =oxo species having am ixed electronic structure of the oxyl/oxo type was reported. In that work, one of us (Y.D.)…”

“…In that work, one of us (Y.D.) showed that, similarly to the case reported here, the oxowall [43] was indeed not broken,a nd the local quartet spin arrangement, delocalized alongt he CoÀOb ond, showed substantial radicalc haracter on oxygen.O verall, am ore appropriate electronic structure assignment for the in situ generated, catalytically competent, OÀOb ond-formings pecies is am ixed Co-oxo/oxyl. CN stretching frequencies (n(CN)) and molecular orbitals were investigated to elucidate the molecular basis for the catalytic activity ( Table 2).…”

Water Oxidation Electrocatalysis with a Cobalt‐Borate‐Based Hybrid System under Neutral Conditions

“…[58] Moreovert he bond order of around 1.6 indicates that the oxowall [58] wasindeed not broken,but there is as ubstantial radical character on the oxygen. The electrons in the bonding and antibonding set of orbitals 50, 53 and 51, 54 contribute to al arge radicalc haractero n oxygen, that is, approximatelyo ne electron.…”

“…Hence, formal assignmentso fC o IV (O)o rC o III -(OC)f or the Co center are incom- Overall, these give ab ond order of (5.57-2.41)/2 = 1.58, suggesting as ignificant double bond character,y et still far from af ormal Co=oxo nature.R ecently,asimilar electronic structure fingerprint and its relation to reactivity for Co-oxo/oxyls ystemsw as demonstrated. [58] Moreovert he bond order of around 1.6 indicates that the oxowall [58] wasindeed not broken,but there is as ubstantial radical character on the oxygen. Hence, it can be surmised that high valenta nd reactive Co moieties share this mixed Co-oxo/oxyl feature, and we are in the process of generalizing this theoretically to an umber of catalytically active Co-oxo/oxylsystems.…”

From Enzymes to Functional Materials—Towards Activation of Small Molecules

“…[183] Likewise, monometallic and bimetallic Fe-, Ni-, Cu-, Co-, and Mn-cyclam complexes allow for OÀOb ond activation and formationo fh igh-valent metal-oxo species. [186][187][188][189][190] Among these complexes, the Co IV -oxo complexes in particular were shown to facilitate CÀHb ond activation, epoxidation of olefins, and oxygen transfer-reactions. [186]…”