Cobalt(II) complexes of the quadridentate macrocycle 2,12-dimethyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),2,11,13,15-pentaene

Long, Kenneth M.; Busch, Daryle H.

doi:10.1021/ic50085a015

Cited by 49 publications

(23 citation statements)

References 1 publication

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“…S6-S8, ESI †). These results are consistent with a square planar geometry for the Co I state, [Co I (CR)] + , and a penta-or hexacoordinate Co II state, 51 [Co II (CR)Cl(X) x ] n+ (X = Cl or CH 3 CN, x = 0 or 1, n = 0 or 1) for the chloro complex (Fig. 3) and [Co II (CR)(CH 3 CN) x ] 2+ (x = 1 or 2) for the aqua derivative (Fig.…”

Section: Electrochemicalsupporting

confidence: 84%

“…S4, ESI †). 51 The absorption spectrum of the green solution of Co I , which has been obtained for the first time, exhibits two intense transitions at 325 nm and 432 nm (e B 8000 and 6000 M À1 cm À1 , respectively), and a less intense visible transition at 680 nm (e B 2000 M À1 cm À1 ) associated with a shoulder at 810 nm. 52 EPR spectra recorded at 100 K confirms the oxidation states of the cobalt species, with the presence of an EPR signal for the one-electron reduced solution typical of a low-spin d 7 Co II center, 51,53 while the diamagnetic Co III and Co I solutions are EPR silent (Fig.…”

Section: Electrochemicalmentioning

confidence: 91%

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Efficient photocatalytic hydrogen production in water using a cobalt(iii) tetraaza-macrocyclic catalyst: electrochemical generation of the low-valent Co(i) species and its reactivity toward proton reduction

Varma

Castillo

Stoll

et al. 2013

Phys. Chem. Chem. Phys.

114

171

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A very efficient homogeneous system for visible-light driven hydrogen production in water is reported. This comprises the [Co(CR)Cl2](+) cobalt(III) tetraaza-macrocyclic complex (Cat1) as a noble metal-free catalyst, [Ru(bpy)3]Cl2 as a photosensitizer and ascorbate/ascorbic acid as a sacrificial electron donor and buffer. This system gives up to 1000 turnovers at pH 4.0 versus the catalyst with a relatively low photosensitizer/catalyst ratio (10/1) and a high concentration of catalyst (1 × 10(−4) M), thus producing a significant amount of H2 (12.3 mL for 5 mL of solution). It also exhibits long-term stability (more than 20 hours). The efficiency of Cat1 has been compared under the same experimental conditions to those of three other H2-evolving catalysts, which are known to operate in water, [Co{(DO)(DOH)pn}Br2] (Cat2), [Co(dmbpy)3]Cl2 (Cat3) and [Rh(dmbpy)2Cl2]Cl (Cat4). These comparative studies show that Cat4, although based on a noble metal, is about four times less active, while Cat2 and Cat3 produce more than one hundred times less hydrogen than Cat1. The low-valent CoI form of Cat1 has been successfully electrogenerated in CH3CN. Its high stability can be related to the high catalytic performance of the Cat1 system. We have also shown that in acidic aqueous solution (photocatalytic conditions) reduction at a slightly more negative potential than the Co(II)/Co(I) couple is needed to ensure efficient catalysis; this reduction is performed by the photogenerated [Ru(II)(bpy)2(bpy(˙−))](+) species.

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Section: Electrochemicalsupporting

confidence: 84%

Section: Electrochemicalmentioning

confidence: 91%

Efficient photocatalytic hydrogen production in water using a cobalt(iii) tetraaza-macrocyclic catalyst: electrochemical generation of the low-valent Co(i) species and its reactivity toward proton reduction

Varma

Castillo

Stoll

et al. 2013

Phys. Chem. Chem. Phys.

114

171

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“…In this study we used ascorbic acid/sodium ascorbate mixtures (H 2 Asc/NaHAsc 51 suggesting that the ascorbate ion is coordinating the Co(II) metal site. For instance, comparison of the XANES spectra reveals a 0.4 eV energy shift and a change in the spectral features between the two Co(II) species (Fig.…”

Section: ·3-interaction Of Co(ii) Species With Ascorbate Electron Donormentioning

confidence: 99%

Tracking the Structural and Electronic Configurations of a Cobalt Proton Reduction Catalyst in Water

Moonshiram¹,

Gimbert‐Suriñach

Guda

et al. 2016

J. Am. Chem. Soc.

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Time resolved X-ray absorption spectroscopy (X-TAS) has been used to study the light induced hydrogen evolution reaction catalyzed by a highly stable tetradentate macrocyclic cobalt complex with the formula [LCo III Cl 2 ] + (L = macrocyclic ligand), [Ru(bpy) 3 ] 2+ photosensitizer and an equimolar mixture of sodium ascorbate/ascorbic acid electron donor in pure water. XANES and EXAFS analysis of a binary mixture of the octahedral Co(III) pre-catalyst and [Ru(bpy) 3 ] 2+ after illumination, revealed in-situ formation of a Co(II) intermediate with significantly distorted geometry and electron transfer kinetics of 51 ns. On the other hand, X-TAS experiments of the complete photocatalytic system in the presence of the electron donor showed the formation of a square planar Co(I) intermediate species within a few nanoseconds followed by its decay in the microsecond timescales. The Co(I) structural assignment is supported by calculations based on density functional theory (DFT). At longer reaction times, we observe the formation of the initial Co(III) species concomitant to the decay of Co(I), thus closing the catalytic cycle. The experimental Xray absorption spectra of the molecular species formed along the catalytic cycle are modeled using a combination of molecular orbital DFT calculations (DFT-MO) and Finite Difference Method (FDM). These findings allowed us to unequivocally assign the full mechanistic pathway followed by the catalyst as well as to determine the rate limiting step of the process, which consists in the protonation of the Co(I). This study provides a complete kinetics scheme for the hydrogen evolution reaction by a cobalt catalyst, revealing unique information for the development of better catalysts for the reductive side of hydrogen fuel cells.

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“…Deoxygenated solutions were prepared under argon using either an Omni-Lab glovebox (Vacuum Atmospheres) operating at <0. 3 Long and Busch, 14 as adapted by Lacy et al 15 Briefly, CoBr 2 (1.35 g, 6.17 mmol) and 2,6-diacetylpyridine (1.00 g, 6.13 mmol) were dissolved in 20 mL of deoxygenated ethanol at room temperature under argon, followed by the addition of 0.5 mL of water, and then, over the course of several min, degassed 3,3′-diaminodipropylamine (0.857 mL, 6.13 mmol) was added dropwise. The initial blue−green color of the CoBr 2 and 2,6-diacetylpyridine mixture gradually turned to dark red upon addition of the amine.…”

Section: ■ Introductionmentioning

confidence: 99%

A Cobalt Schiff-Base Complex as a Putative Therapeutic for Azide Poisoning

Praekunatham

Garrett

Bae

et al. 2019

Chem. Res. Toxicol.

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There is presently no antidote available to treat azide poisoning. Here, the Schiff-base compound Co(II)-2, 12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]heptadeca-1(17)2,11,13,15-pentaenyl dibromide (Co(II)N 4 [11.3.1]) is investigated to determine if it has the capability to antagonize azide toxicity through a decorporation mechanism. The stopped-flow kinetics of azide binding to Co(II)N 4 [11.3.1] in the absence of oxygen exhibited three experimentally observable phases: I (fast); II (intermediate); and III (slow). The intermediate phase II accounted for ∼70% of the overall absorbance changes, representing the major process observed, with second-order rate constants of 29 (±4) M −1 s −1 at 25 °C and 70 (±10) M −1 s −1 at 37 °C. The data demonstrated pH independence of the reaction around neutrality, suggesting the unprotonated azide anion to be the attacking species. The binding of azide to Co(II)N 4 [11.3.1] appears to have a complicated mechanism leading to less than ideal antidotal capability; nonetheless, this cobalt complex does protect against azide intoxication. Administration of Co(II)N 4 [11.3.1] at 5 min post sodium azide injection (ip) to mice resulted in a substantial decrease of righting-recovery times, 12 (±4) min, compared to controls, 40 (±8) min. In addition, only two out of seven mice "knocked down" when the antidote was administered compared to the controls given toxicant only (100% knockdown).

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Cobalt(II) complexes of the quadridentate macrocycle 2,12-dimethyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),2,11,13,15-pentaene

Cited by 49 publications

References 1 publication

Efficient photocatalytic hydrogen production in water using a cobalt(iii) tetraaza-macrocyclic catalyst: electrochemical generation of the low-valent Co(i) species and its reactivity toward proton reduction

Efficient photocatalytic hydrogen production in water using a cobalt(iii) tetraaza-macrocyclic catalyst: electrochemical generation of the low-valent Co(i) species and its reactivity toward proton reduction

Tracking the Structural and Electronic Configurations of a Cobalt Proton Reduction Catalyst in Water

A Cobalt Schiff-Base Complex as a Putative Therapeutic for Azide Poisoning

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