Electronic Structure Description of a Doubly Oxidized Bimetallic Cobalt Complex with Proradical Ligands

Clarke, Ryan M.; Hazin, Khatera; Thompson, John R.; Savard, Didier; Prosser, Kathleen E.; Storr, Tim

doi:10.1021/acs.inorgchem.5b02231

Cited by 31 publications

(21 citation statements)

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“…The electronic structure of the compound was investigated by the Evans method, which yielded a magnetic susceptibility of 4.34 μ B , suggesting an S = 3/2 d 7 cobalt, as expected for a tetrahedral geometry. Previously reported square planar cobalt(II) salen complexes exhibit magnetic susceptibilities near 1.7 μ B , indicative of low-spin, S = 1/2 d 7 cobalt. ,− This unusual geometry is likely due to ferrocene’s torsional flexibility relative to common salen ligand backbones …”

Section: Results and Discussionmentioning

confidence: 99%

Redox-Switchable Hydroelementation of a Cobalt Complex Supported by a Ferrocene-Based Ligand

Shepard

Diaconescu

2016

Organometallics

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ABSTRACT:The first crystallographically characterized tetrahedral cobalt salen (salen = N,N'-ethylenesalicylimine) complex was synthesized by using a 1,1'-ferrocene derivative, salfen (salfen = 1,1′-di(2,4-di-tert-butyl-6-salicylimine)ferrocene). The complex undergoes two oxidation events at low potentials, which were assigned as iron and ligand centered by comparison to the corresponding zinc complex. The cobalt complex was found to catalyze the hydroalkoxylation of styrenes, similarly to related square planar cobalt salen complexes, likely due to its fluxional behavior in alcoholic solvents. Furthermore, the one electron oxidized species was found to be inactive toward hydroalkoxylation. Thus, the hydroalkoxylation reactivity could be turned on/off in situ by redox chemistry.

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Section: Results and Discussionmentioning

confidence: 99%

Redox-Switchable Hydroelementation of a Cobalt Complex Supported by a Ferrocene-Based Ligand

Shepard

Diaconescu

2016

Organometallics

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“…The interaction between the redox centers in 2 – 6 in electrolyte III is thus stronger than in the bis‐Co(salen) complex discussed by Clarke et al. earlier, [37] where peak splitting was not observed in DCM+0.1 M NBu 4 ClO 4 .…”

Section: Resultsmentioning

confidence: 62%

“…The differences in behavior of the complexes in MeCN vs. DCM based electrolytes could further be affected by a change in the electronic structure of the oxidized forms of the Co centers. The solvent dependent distribution of the spin density between the central metal atom and the ligand [37,39] could modify the equilibrium species or resonance structure contributions [36] . However, the electrochemical data do not provide additional evidence to solve this question.…”

Section: Discussionmentioning

confidence: 99%

“…In general other factors (temperature, nature of the solvent and the metal ion or substituents) may define the electronic structure of the one‐electron oxidation product as well [35] . In some cases, spin density resides both on the high‐spin Co(III) center and in the (phenoxyl type) ligand [36–39] . Nevertheless, we will refer to the redox reactions leading to these oxidized forms as “metal centered” in the following.…”

Section: Introductionmentioning

confidence: 99%

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Interactions Between Two Cobalt Salen Centers Bridged by Non‐Conjugated Linkers**

Speiser

Zitzer

2021

ChemElectroChem

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Tetra‐tert‐butyl‐Co(salen), an amido‐substituted derivative and a series of bis(salen) complexes of cobalt(II) with the two metal centers bridged by flexible, non‐conjugated bis‐amido linkers are investigated by cyclic voltammetry, chronoamperometry, and differential pulse voltammetry in four electrolytes (acetonitrile or dichloromethane, conventional or weakly coordinating anion). Cyclic voltammograms are analyzed by simulation based on E or EE mechanisms. The compounds are characterized by formal potentials E0 , diffusion coefficients D and number of electrons transferred, n. Differences in the E0 values for the subsequent two one‐electron transfer steps are used as indicators for the interaction between the metal centers in the bis(salen) complexes. The effects of solvent and supporting electrolyte are consistent with the assumption of electrostatic through‐space interactions and coordination to the Co centers. In the dinuclear complexes step‐wise electron transfers according to normal potential ordering makes these compounds “pretenders” in Winter's terms (R.F. Winter, Organometallics 2014, 33, 4517–4536).

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“…It has been found out that ligand centred oxidation and radical formation are important events in the catalytic cycle. Hence in the literature there are reports of cobalt(II) as well as cobalt(III) phenoxyl radical complexes . Herein we report a facile synthesis and characterization of novel cobalt(II) radical complex [Co(L)(L + )]NO 3 and molecular structure of the complex was determined by X‐ray crystallography.…”

Section: Figurementioning

confidence: 98%

Non‐Innocent Property of Tridentate Ligand in Novel Cobalt Complex : Crystal Structure and Evidences for Cobalt(II) Phenoxyl Radical Complex Formation

et al. 2016

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A phenoxyl radical complex [Co II (L)(L + )]NO 3 (where LH = (E)-2,4di-tert-butyl-6-((2-phenyl-2-(pyridin-2-yl)hydrazono)methyl)phenol and H = dissociable proton) was synthesized at room temperature in aerobic condition and was characterized. Crystal structure, UV-Vis-NIR and 1 H-NMR spectra, magnetic properties and electrochemical studies authenticated the presence of Co (II) phenoxyl radical complex.Generation of phenoxyl radical complexes and their reactivity studies are significantly important in the context of structural and functional modelling of galactose oxidase enzyme and are important areas in chemical research. [1, 2] Although phenoxyl radical complex of copper exhibit vital role in the oxidation chemistry of galactose by the native enzyme, phenoxyl radical complexes of cobalt gained considerable current interest because of their essential roles in the catalytic cycle performed by Jacobsen catalyst. [3][4][5][6] Cobalt complexes derived from salen type ligand exhibit crucial role in epoxide formation and CO 2 / polymerization reactions. [5,6] It has been found out that ligand centred oxidation and radical formation are important events in the catalytic cycle. Hence in the literature there are reports of cobalt(II) as well as cobalt(III) phenoxyl radical complexes. [2][3][4][5][6][7] Herein we report a facile synthesis and characterization of novel cobalt(II) radical complex [Co(L)(L + )]NO 3 and molecular structure of the complex was determined by X-ray crystallography.Recently, Fujii and co-workers reported Co(salen)(X) complex with the 40 % character of Co II (salen * + )(X) and 60 % character of Co III (salen)(X). [4] Thomas and co-workers have shown similar kind of cobalt(II) salen complex and one electron oxidized complex was found to have 70 % electron density over the cobalt ion and remaining 30 % electron density spreading over the ligand. [8] In another report by the same group, phenolato donor was replaced by the anilido donor and the resultant complex was found to have 75 % contribution of metal ion in SOMO. [6] Hence, to the best of our knowledge there is no report of phenoxyl radical complex of cobalt(II) in the literature in a ligand system other than salen and salen type ligands. We would like to mention here that Benisvy and co-workers synthesized octahedral cobalt(II) complex bearing imidazole-phenolato moiety and oxidation of this complex afforded a cobalt (II) phenoxyl radical complex; [12] however no crystal structure was described in this report. We have been working with a tridentate ligand [9] LH (shown in Figure 1) and in present study, deprotonated ligand having NNO donors was treated with cobalt(II) nitrate to afford a green colored complex. The resultant cobalt complex provided several interesting properties which are described below.Presence of phenolato function in the ligand frame and synthesis of complex [Co II (L)(L + )]NO 3 , one could simply expect the formation of a diamagnetic Co(III) complex with formula [Co III L 2 ]NO 3 however we have solved the molecular str...

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Electronic Structure Description of a Doubly Oxidized Bimetallic Cobalt Complex with Proradical Ligands

Cited by 31 publications

References 164 publications

Redox-Switchable Hydroelementation of a Cobalt Complex Supported by a Ferrocene-Based Ligand

Redox-Switchable Hydroelementation of a Cobalt Complex Supported by a Ferrocene-Based Ligand

Interactions Between Two Cobalt Salen Centers Bridged by Non‐Conjugated Linkers**

Non‐Innocent Property of Tridentate Ligand in Novel Cobalt Complex : Crystal Structure and Evidences for Cobalt(II) Phenoxyl Radical Complex Formation

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