Substituted salen and baen tetradentate Schiff-base ligands. Synthesis, characterization, and electrochemistry of cobalt(III) complexes

Averill, Donald F.; Broman, Robert F.

doi:10.1021/ic50190a018

Cited by 72 publications

(25 citation statements)

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“…The electrochemical reduction o f Co(III) Schiffbase chelates in the form of the perchlorates in pyridine has been reported by Averill and Broman [9] and -after in situ electrolytic generation from the Co(II) complex without isolation of the Co(III) species -by Hanzlik et al [23], In the pre sent study, through the com parison of the oxida tion of 1 and the reduction of the Co(III)(salen)+ cation, however, the unim portance of the associa tion of the cation with the anion (here C1") be comes obvious.…”

Section: Cyclic Voltammetrymentioning

confidence: 84%

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Electrochemistry of Oxygenation Catalysts, Part 2⁺ Improved Synthesis, Crystal Structure, and Electrochemical Properties of N,N′-Bis(salicylidene)ethylenediaminatocobalt(III) Chloride

Eichhorn

Rieker

Speiser

et al. 1993

Zeitschrift Für Naturforschung B

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Oxygenation Catalyst, Cobalt Schiff-Base Complex, Crystal Structure, Electrochemistry N,N'-Bis(salicylidene)ethylenediaminatocobalt(III) hydroxide is treated with chloroform in methanol to yield the corresponding chloride in pure, crystalline form. Results of the crystal structure determination compare well with those in earlier reports of dimeric [Co(salen)Cl]2 units and incorporated CHC13 molecules. Electrochemical experiments in D M F and pyridine show that the chloride fully dissociates in these donor solvents. Thus, the quasireversible oneelectron reduction to Co(salen) is observed in cyclic voltammograms.

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Section: Cyclic Voltammetrymentioning

confidence: 84%

“…Due to the less basic properties of the chlo ride ion as com pared to O H ', 3 may be a better candidate to study the reduction reaction in ( 1). An alternative approach to the synthesis of hexacoordinated Co(III) Schiff-base perchlorates by air oxidation was also given [9].…”

Section: Introductionmentioning

confidence: 99%

Electrochemistry of Oxygenation Catalysts, Part 2⁺ Improved Synthesis, Crystal Structure, and Electrochemical Properties of N,N′-Bis(salicylidene)ethylenediaminatocobalt(III) Chloride

Eichhorn

Rieker

Speiser

et al. 1993

Zeitschrift Für Naturforschung B

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“…The procedure for preparation and structural identification of the salophen complex of cobalt(III) perchlorate was similar to the method described elsewhere [25]. The structures of these complexes are shown in Scheme 1.…”

Section: Methodsmentioning

confidence: 99%

Voltammetric Determination of Methimazole Using a Carbon Paste Electrode Modified with a Schiff Base Complex of Cobalt

Shahrokhian

Ghalkhani

2008

Electroanalysis

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The electrochemical behavior of methimazole, as an antithyroid agent, is investigated on the surface of a carbon-paste electrode modified with a newly synthesized Schiff base complex of cobalt. The prepared modified electrode showed an efficient catalytic role in the electrochemical oxidation of methimazole, leading to remarkable decrease in oxidation overpotential and enhancement of the kinetics of the electrode reaction. The mechanism of the electrocatalytic process on the surface of the modified electrode is analyzed by obtaining the cyclic voltammograms in various potential sweep rates and pHs of the buffer solutions. The differential pulse voltammetry is applied as a very sensitive analytical method for the determination of sub-micromolar amounts of methimazole. A linear dynamic range of 1 Â 10 À6 to 1 Â 10 À4 M with a detection limit of 5 Â 10 À7 M is resulted for methimazole. The modified electrode is successfully applied for the accurate determination of methimazole in pharmaceutical and clinical preparations. The linear range in calibration curves remains constant in addition to tablet preparations of methimazole and also in spiking to the synthetic human serum samples. In comparison to calibration curves in background buffer solution, the slope of the curves showed a variation less than 3% in determinations in background solutions of tablet and human synthetic serum samples. These results showed high efficiency of the Voltammetric procedure for accurate determination of methimazole in drug and clinical preparations. The modified electrode can be prepared very easy and renewed in its surface by simple polishing. The reproducibility of the electrode response, based on ten measurements during two month, was 3.2% for the slope of the calibration curve.

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“…In this way, one can begin to address the question of substrate generality, which is so important in asymmetric catalysis today. [18,19] To demonstrate proof of principle for cassette-ISES, we employed a focused chiral salen array (Figure 1) that crosses chiral space variation in the constituent 1,2-diamines with considerable steric [20] and electronic variation in the "salicylaldehyde partners" (including the benzoylacetaldehyde (baen) precursor [21] ). Figure 2 illustrates the "four coordinate" structure-enantioselectivity relationship (SER) data that one obtains from such a cassette-ISES protocol.…”

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confidence: 99%

“Cassette” In Situ Enzymatic Screening Identifies Complementary Chiral Scaffolds for Hydrolytic Kinetic Resolution Across a Range of Epoxides

Dey¹,

Powell²,

Hu³

et al. 2007

Angew Chem Int Ed

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For combinatorial catalysis, [1,2] rapid and information-rich screening methods are very useful. Toward this end, we describe herein a new "cassette" in situ enzymatic screening (ISES) approach that allows the experimentalist to obtain a parallel readout on substrate specificity, as well as a sense and magnitude of enantioselectivity.[3] In its first iteration, cassette-ISES is used to "cherry pick" only those catalysts in the array that show high ISES ee-value readouts across both test substrates. Two such catalysts are then investigated further, yielding promising results.In our ISES approach, typically the reaction product [4] or by-product [5] diffuses from an organic layer into an aqueous layer containing the "reporting enzyme". [6][7][8][9] There, an enzyme-catalyzed reaction leads to a spectroscopic signal that is monitored in real time. The approach complements other emerging screens by using chiroptical techniques, [10] liquid crystalline arrays, [11] IR thermography, [12] mass, [13] NMR, [14] IR [15] and fluorescence spectroscopy.[16] The technique is sensitive (i.e. 10 nmol of product gives rise to DA 340 % 0.12 for a dehydrogenase reporting enzyme in a 500 mL aqueous volume), allowing one to get information on catalyst performance at relatively early conversions/short reaction times. Catalysts may be screened in parallel in a standard spectrophotometer with a multicell changer without the need to draw aliquots or work up the reaction. Moreover, the need to install a chromophore (adding steps and potentially altering substrate reactivity) is obviated.Herein, we describe a new pair of reporting enzymes (Scheme 1) that are capable of differentiating the 1,2-hexanediol antipodes (Lactobacillus kefir alcohol dehydrogenase (LKADH): highly S selective k S /k R % 20, and horseliver alcohol dehydrogenase (HLADH): modestly S selective k S /k R % 2.2). This allows one to obtain simultaneous enantioselectivity readouts on two distinct substrates for the Co IIIsalen-mediated (salen = (salicylidene)ethylenediamine) hydrolytic kinetic resolution (HKR) of epoxides, [17] presenting both "short" (propylene oxide; R = Me) [4] and long (hexene oxide: R = Bu) R groups. In this way, one can begin to address the question of substrate generality, which is so important in asymmetric catalysis today. [18,19] To demonstrate proof of principle for cassette-ISES, we employed a focused chiral salen array (Figure 1) that crosses chiral space variation in the constituent 1,2-diamines with considerable steric [20] and electronic variation in the "salicylaldehyde partners" (including the benzoylacetaldehyde (baen) precursor [21] ). Figure 2 illustrates the "four coordinate" structure-enantioselectivity relationship (SER) data that one obtains from such a cassette-ISES protocol. The x and y axes represent the two structural variables in the salen array. The directionality and length of the z vector provide the Scheme 1. A suitable pair of "reporting enzymes" for 1,2-hexanediol permits a cassette-ISES evaluation of HKR catalyst candidat...

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Substituted salen and baen tetradentate Schiff-base ligands. Synthesis, characterization, and electrochemistry of cobalt(III) complexes

Cited by 72 publications

References 29 publications

Electrochemistry of Oxygenation Catalysts, Part 2⁺ Improved Synthesis, Crystal Structure, and Electrochemical Properties of N,N′-Bis(salicylidene)ethylenediaminatocobalt(III) Chloride

Electrochemistry of Oxygenation Catalysts, Part 2⁺ Improved Synthesis, Crystal Structure, and Electrochemical Properties of N,N′-Bis(salicylidene)ethylenediaminatocobalt(III) Chloride

Voltammetric Determination of Methimazole Using a Carbon Paste Electrode Modified with a Schiff Base Complex of Cobalt

“Cassette” In Situ Enzymatic Screening Identifies Complementary Chiral Scaffolds for Hydrolytic Kinetic Resolution Across a Range of Epoxides

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Substituted salen and baen tetradentate Schiff-base ligands. Synthesis, characterization, and electrochemistry of cobalt(III) complexes

Cited by 72 publications

References 29 publications

Electrochemistry of Oxygenation Catalysts, Part 2+ Improved Synthesis, Crystal Structure, and Electrochemical Properties of N,N′-Bis(salicylidene)ethylenediaminatocobalt(III) Chloride

Electrochemistry of Oxygenation Catalysts, Part 2+ Improved Synthesis, Crystal Structure, and Electrochemical Properties of N,N′-Bis(salicylidene)ethylenediaminatocobalt(III) Chloride

Voltammetric Determination of Methimazole Using a Carbon Paste Electrode Modified with a Schiff Base Complex of Cobalt

“Cassette” In Situ Enzymatic Screening Identifies Complementary Chiral Scaffolds for Hydrolytic Kinetic Resolution Across a Range of Epoxides

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Electrochemistry of Oxygenation Catalysts, Part 2⁺ Improved Synthesis, Crystal Structure, and Electrochemical Properties of N,N′-Bis(salicylidene)ethylenediaminatocobalt(III) Chloride

Electrochemistry of Oxygenation Catalysts, Part 2⁺ Improved Synthesis, Crystal Structure, and Electrochemical Properties of N,N′-Bis(salicylidene)ethylenediaminatocobalt(III) Chloride