Abstract
The mono- and dinuclear oxidovanadium(v) complexes [VVO(L1)(Cl)] (1) and [L1VVO(μ2-O)VO(L1)] (2) of ONNO donor amine-bis(phenolate) ligand (H2L1) were readily synthesized by the reaction between H2L1 and VCl3.(THF)3 or VO(acac)2 in MeOH or MeCN, respectively, and then characterized through mass spectroscopy, 1H-NMR and FTIR techniques. Both the complexes possess distorted octahedral geometry around each V centre. Upon the addition of 1 equivalent or more acid to a MeCN solution of complex 1, it immediately turned into the protonated form, which might be in equilibrium as: [L1ClVVOH]+ ↔ [L1ClVV-OH]+ (in the case of [L1ClVVOH]+ oxo-O is just protonated, whereas in [L1ClVV-OH]+ it is a hydroxo species), with the shift in λmax from 610 nm to 765 nm. Similar was the case for complex 2. The complexes 1 and 2 could efficiently catalyze the oxidative bromination of salicylaldehyde in the presence of H2O2 to produce 5-bromo salicylaldehyde as the major product with TONs of 405 and 450, respectively, in the mixed solvent system (H2O:MeOH:THF = 4:3:2, v/v). The kinetic analysis of the bromide oxidation reaction indicated a first-order mechanism in the protonated peroxidovanadium complex and a bromide ion and limiting first-order mechanism on [H+]. The evaluated kBr and kH values were 5.78 ± 0.20 and 11.01 ± 0.50 M-1 s-1 for complex 1 and 6.21 ± 0.13 and 20.14 ± 0.72 M-1 s-1 for complex 2, respectively. The kinetic and thermodynamic acidities of the protonated oxido species of complexes 1 and 2 were pKa = 2.55 (2.35) and 2.16 (2.19), respectively, which were far more acidic than those reported by Pecoraro et al. for peroxido-protonation instead of oxido protonation. On the basis of the chemistry observed for these model compounds, a mechanism of halide oxidation and a detailed catalytic cycle are proposed for the vanadium haloperoxidase enzyme and these were substantiated by detailed DFT calculations.
| Original language | English |
|---|---|
| Pages (from-to) | 2799-2809 |
| Number of pages | 11 |
| Journal | Dalton Transactions |
| Volume | 47 |
| Issue number | 8 |
| DOIs | |
| Publication status | Published - 2018 Jan 1 |
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All Science Journal Classification (ASJC) codes
- Inorganic Chemistry
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Mono- and dinuclear oxidovanadium(v) complexes of an amine-bis(phenolate) ligand with bromo-peroxidase activities : Synthesis, characterization, catalytic, kinetic and computational studies. / Debnath, Mainak; Dolai, Malay; Pal, Kaberi; Bhunya, Sourav; Paul, Ankan; Lee, Hon Man; Ali, Mahammad.
In: Dalton Transactions, Vol. 47, No. 8, 01.01.2018, p. 2799-2809.Research output: Contribution to journal › Article
TY - JOUR
T1 - Mono- and dinuclear oxidovanadium(v) complexes of an amine-bis(phenolate) ligand with bromo-peroxidase activities
T2 - Synthesis, characterization, catalytic, kinetic and computational studies
AU - Debnath, Mainak
AU - Dolai, Malay
AU - Pal, Kaberi
AU - Bhunya, Sourav
AU - Paul, Ankan
AU - Lee, Hon Man
AU - Ali, Mahammad
PY - 2018/1/1
Y1 - 2018/1/1
N2 - The mono- and dinuclear oxidovanadium(v) complexes [VVO(L1)(Cl)] (1) and [L1VVO(μ2-O)VO(L1)] (2) of ONNO donor amine-bis(phenolate) ligand (H2L1) were readily synthesized by the reaction between H2L1 and VCl3.(THF)3 or VO(acac)2 in MeOH or MeCN, respectively, and then characterized through mass spectroscopy, 1H-NMR and FTIR techniques. Both the complexes possess distorted octahedral geometry around each V centre. Upon the addition of 1 equivalent or more acid to a MeCN solution of complex 1, it immediately turned into the protonated form, which might be in equilibrium as: [L1ClVVOH]+ ↔ [L1ClVV-OH]+ (in the case of [L1ClVVOH]+ oxo-O is just protonated, whereas in [L1ClVV-OH]+ it is a hydroxo species), with the shift in λmax from 610 nm to 765 nm. Similar was the case for complex 2. The complexes 1 and 2 could efficiently catalyze the oxidative bromination of salicylaldehyde in the presence of H2O2 to produce 5-bromo salicylaldehyde as the major product with TONs of 405 and 450, respectively, in the mixed solvent system (H2O:MeOH:THF = 4:3:2, v/v). The kinetic analysis of the bromide oxidation reaction indicated a first-order mechanism in the protonated peroxidovanadium complex and a bromide ion and limiting first-order mechanism on [H+]. The evaluated kBr and kH values were 5.78 ± 0.20 and 11.01 ± 0.50 M-1 s-1 for complex 1 and 6.21 ± 0.13 and 20.14 ± 0.72 M-1 s-1 for complex 2, respectively. The kinetic and thermodynamic acidities of the protonated oxido species of complexes 1 and 2 were pKa = 2.55 (2.35) and 2.16 (2.19), respectively, which were far more acidic than those reported by Pecoraro et al. for peroxido-protonation instead of oxido protonation. On the basis of the chemistry observed for these model compounds, a mechanism of halide oxidation and a detailed catalytic cycle are proposed for the vanadium haloperoxidase enzyme and these were substantiated by detailed DFT calculations.
AB - The mono- and dinuclear oxidovanadium(v) complexes [VVO(L1)(Cl)] (1) and [L1VVO(μ2-O)VO(L1)] (2) of ONNO donor amine-bis(phenolate) ligand (H2L1) were readily synthesized by the reaction between H2L1 and VCl3.(THF)3 or VO(acac)2 in MeOH or MeCN, respectively, and then characterized through mass spectroscopy, 1H-NMR and FTIR techniques. Both the complexes possess distorted octahedral geometry around each V centre. Upon the addition of 1 equivalent or more acid to a MeCN solution of complex 1, it immediately turned into the protonated form, which might be in equilibrium as: [L1ClVVOH]+ ↔ [L1ClVV-OH]+ (in the case of [L1ClVVOH]+ oxo-O is just protonated, whereas in [L1ClVV-OH]+ it is a hydroxo species), with the shift in λmax from 610 nm to 765 nm. Similar was the case for complex 2. The complexes 1 and 2 could efficiently catalyze the oxidative bromination of salicylaldehyde in the presence of H2O2 to produce 5-bromo salicylaldehyde as the major product with TONs of 405 and 450, respectively, in the mixed solvent system (H2O:MeOH:THF = 4:3:2, v/v). The kinetic analysis of the bromide oxidation reaction indicated a first-order mechanism in the protonated peroxidovanadium complex and a bromide ion and limiting first-order mechanism on [H+]. The evaluated kBr and kH values were 5.78 ± 0.20 and 11.01 ± 0.50 M-1 s-1 for complex 1 and 6.21 ± 0.13 and 20.14 ± 0.72 M-1 s-1 for complex 2, respectively. The kinetic and thermodynamic acidities of the protonated oxido species of complexes 1 and 2 were pKa = 2.55 (2.35) and 2.16 (2.19), respectively, which were far more acidic than those reported by Pecoraro et al. for peroxido-protonation instead of oxido protonation. On the basis of the chemistry observed for these model compounds, a mechanism of halide oxidation and a detailed catalytic cycle are proposed for the vanadium haloperoxidase enzyme and these were substantiated by detailed DFT calculations.
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U2 - 10.1039/c7dt04718e
DO - 10.1039/c7dt04718e
M3 - Article
AN - SCOPUS:85042386131
VL - 47
SP - 2799
EP - 2809
JO - Dalton Transactions
JF - Dalton Transactions
SN - 1477-9226
IS - 8
ER -