| 1. |
|
|
| 2. |
- Das, Biswanath, et al.
(författare)
-
A di‑iron(III) μ-oxido complex as catalyst precursor in the oxidation of alkanes and alkenes
- 2022
-
Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 0162-0134. ; 231
-
Tidskriftsartikel (refereegranskat)abstract
- The oxido-bridged diiron(III) complex [Fe2(μ-O)(μ-OAc)(DPEAMP)2](OCH3) (1), based on a new unsymmetrical ligand with an N4O donor set, viz. [2-((bis(pyridin-2-ylmethyl)amino)methyl)-6-((ethylamino)methyl)-4-methylphenol (HDPEAMP)], has been prepared and characterized by spectroscopic methods and X-ray crystallography. The crystal structure of the complex reveals that each Fe(III) ion is coordinated by three nitrogen and three oxygen donors, two of which are the bridging oxido and acetate ligands. Employing H2O2 as a terminal oxidant, 1 is capable of oxidizing a number of alkanes and alkenes with high activity. The catalytic oxidation of 1,2-dimethylcyclohexane results in excellent retention of configuration. Monitoring of the reaction of 1 with H2O2 and acetic acid in the absence of substrate, using low-temperature UV–Vis spectroscopy, suggests the in situ formation of a transient Fe(III)2-peroxido species. While the selectivity and nature of oxidation products implicate a high-valent iron-oxido complex as a key intermediate, the low alcohol/ketone ratios suggest a simultaneous radical-based process.
|
|
| 3. |
- Das, Biswanath, et al.
(författare)
-
A Heterobimetallic FeIIIMnII Complex of an Unsymmetrical Dinucleating Ligand : A Structural and Functional Model Complex for the Active Site of Purple Acid Phosphatase of Sweet Potato
- 2014
-
Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; 2014:13, s. 2204-2212
-
Tidskriftsartikel (refereegranskat)abstract
- The heterodinuclear mixed-valence complex [FeMn(ICIMP)(OAc)(2)Cl] (1) {H2ICIMP = 2-(N-carboxylmethyl)-[N-(N-methylimidazolyl-2-methyl)aminomethyl]-[6-(N-isopropylmethyl)-[N-(N-methylimidazolyl-2-methyl)]aminomethyl-4-methylphenol], an unsymmetrical N4O2 donor ligand} has been synthesized and fully characterized by several spectroscopic techniques as well as by X-ray crystallography. The crystal structure of the complex reveals that both metal centers in 1 are six-coordinate with the chloride ion occupying the sixth coordination site of the Mn-II ion. The phenoxide moiety of the ICIMP ligand and both acetate ligands bridge the two metal ions of the complex. Mossbauer spectroscopy shows that the iron ion in 1 is high-spin Fe-III. Two quasi-reversible redox reactions for the complex, attributed to the (FeMnII)-Mn-III/(FeMnII)-Mn-II (at -0.67 V versus Fc/Fc(+)) and (FeMnII)-Mn-III/(FeMnIII)-Mn-III (at 0.84 V), were observed by means of cyclic voltammetry. Complex 1, with an Fe-III-Mn-II distance of 3.58 angstrom, may serve as a model for the mixed-valence oxidation state of purple acid phosphatase from sweet potato. The capability of the complex to effect organophosphate hydrolysis (phosphatase activity) has been investigated at different pH levels (5.5-11) by using bis(2,4-dinitrophenyl)phosphate (BDNPP) as the substrate. Density functional theory calculations indicate that the substrate coordinates to the Mn-II ion. In the transition state, a hydroxide ion that bridges the two metal ions becomes terminally coordinated to the Fe-III ion and acts as a nucleophile, attacking the phosphorus center of BDNPP with the concomitant dissociation of the leaving group.
|
|
| 4. |
- Das, Biswanath, et al.
(författare)
-
Catalytic Oxidation of Alkanes and Alkenes by H2O2 with a mu-Oxido Diiron(III) Complex as Catalyst/Catalyst Precursor
- 2015
-
Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1099-0682 .- 1434-1948. ; :21, s. 3590-3601
-
Tidskriftsartikel (refereegranskat)abstract
- A new mu-oxo diiron(III) complex of the lithium salt of the pyridine-based unsymmetrical ligand 3-[(3-{[bis(pyridin-2-ylmethyl)amino]methyl}-2-hydroxy-5-methylbenzyl)(pyridin2-ylmethyl)amino] propanoate (LiDPCPMPP), [Fe-2(mu-O)(LiDPCPMPP)(2)](ClO4)(2), has been synthesized and characterized. The ability of the complex to catalyze oxidation of several alkanes and alkenes has been investigated by using CH3COOH/H2O2 (1:1) as an oxidative system. Moderate activity in cyclohexane oxidation (TOF = 33 h(-1)) and good activity in cyclohexene oxidation (TOF = 72 h(-1)) were detected. Partial retention of configuration (RC = 53%) in cis- and trans-1,2-dimethylcyclohexane oxidation, moderate 3 degrees/2 degrees selectivity (4.1) in adamantane oxidation, and the observation of a relatively high kinetic isotope effect for cyclohexane oxidation (KIE = 3.27) suggest partial metal-based oxidation, probably in tandem with free-radical oxidation. Low-temperature UV/Vis spectroscopy and mass spectrometric studies in the rapid positive detection mode indicate the formation of a transient peroxido species, [Fe-2(O)(O-2)-(LiDPCPMPP)(2)](2+), which might be an intermediate in the metal-based component of the oxidation process.
|
|
| 5. |
- Das, Biswanath, et al.
(författare)
-
Di- and tetrairon(III) μ-oxido complexes of an N3S-donor ligand : Catalyst precursors for alkene oxidations
- 2019
-
Ingår i: Frontiers in Chemistry. - : Frontiers Media SA. - 2296-2646. ; 7:MAR
-
Tidskriftsartikel (refereegranskat)abstract
- The new di- and tetranuclear Fe(III) μ-oxido complexes [Fe 4 (μ-O) 4 (PTEBIA) 4 ](CF 3 SO 3 ) 4 (CH 3 CN) 2 ] (1a), [Fe 2 (μ-O)Cl 2 (PTEBIA) 2 ](CF 3 SO 3 ) 2 (1b), and [Fe 2 (μ-O)(HCOO) 2 (PTEBIA) 2 ](ClO 4 ) 2 (MeOH) (2) were prepared from the sulfur-containing ligand (2-((2,4-dimethylphenyl)thio)-N,N-bis ((1-methyl-benzimidazol-2-yl)methyl)ethanamine (PTEBIA). The tetrairon complex 1a features four μ-oxido bridges, while in dinuclear 1b, the sulfur moiety of the ligand occupies one of the six coordination sites of each Fe(III) ion with a long Fe-S distance of 2.814(6) Å. In 2, two Fe(III) centers are bridged by one oxido and two formate units, the latter likely formed by methanol oxidation. Complexes 1a and 1b show broad sulfur-to-iron charge transfer bands around 400-430 nm at room temperature, consistent with mononuclear structures featuring Fe-S interactions. In contrast, acetonitrile solutions of 2 display a sulfur-to-iron charge transfer band only at low temperature (228 K) upon addition of H 2 O 2 /CH 3 COOH, with an absorption maximum at 410 nm. Homogeneous oxidative catalytic activity was observed for 1a and 1b using H 2 O 2 as oxidant, but with low product selectivity. High valent iron-oxo intermediates could not be detected by UV-vis spectroscopy or ESI mass spectrometry. Rather, evidence suggest preferential ligand oxidation, in line with the relatively low selectivity and catalytic activity observed in the reactions.
|
|
| 6. |
- Das, Biswanath, et al.
(författare)
-
Water oxidation catalyzed by molecular di- and nonanuclear Fe complexes: importance of a proper ligand framework
- 2016
-
Ingår i: Dalton Transactions. - : ROYAL SOC CHEMISTRY. - 1477-9226 .- 1477-9234. ; 45:34, s. 13289-13293
-
Tidskriftsartikel (refereegranskat)abstract
- The synthesis of two molecular iron complexes, a dinuclear iron(III,III) complex and a nonanuclear iron complex, based on the di-nucleating ligand 2,2-(2-hydroxy-5-methyl-1,3-phenylene)bis(1H-benzo[d]imidazole-4-carboxylic acid) is described. The two iron complexes were found to drive the oxidation of water by the one-electron oxidant [Ru(bpy)(3)](3+).
|
|
| 7. |
- Fuchs, Michael G G, et al.
(författare)
-
A five-coordinate [2Fe-2S] cluster.
- 2010
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 49:13, s. 5853-5858
-
Tidskriftsartikel (refereegranskat)abstract
- A unique [2Fe-2S] cluster (1) with genuinely five-coordinate ferric ions has been synthesized and investigated both structurally and spectroscopically. The crystal structure of 1 as well as (1)H NMR data reveal that 2,6-bis(imidazol-2-yl)pyridine binds to the [2Fe-2S] core as a tridentate capping ligand. DFT calculations showing spin density on all coordinating atoms support this finding. Cluster 1 has also been characterized by Mössbauer and UV/vis spectroscopy, mass spectrometry, cyclic voltammetry, and magnetic susceptibility measurements. Significant spectroscopic properties that make 1 distinct from conventional [2Fe-2S] clusters include a rather small quadrupole splitting of 0.43 mm/s.
|
|
| 8. |
- Jarenmark, Martin, et al.
(författare)
-
Synthesis, characterization, and reactivity studies of heterodinuclear complexes modeling active sites in purple Acid phospatases.
- 2011
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 50:9, s. 3866-3887
-
Tidskriftsartikel (refereegranskat)abstract
- To model the heterodinuclear active sites in plant purple acid phosphatases, a mononuclear synthon, [Fe(III)(H(2)IPCPMP)(Cl(2))][PF(6)] (1), has been generated in situ from the ligand 2-(N-isopropyl-N-((2-pyridyl)methyl)aminomethyl)-6-(N-(carboxylmethyl)-N-((2-pyridyl)methyl)amino methyl)-4-methylphenol (IPCPMP) and used to synthesize heterodinuclear complexes of the formulas [Fe(III)M(II)(IPCPMP)(OAc)(2)(CH(3)OH)][PF(6)] (M = Zn (2), Co (3), Ni (4), Mn (5)), [Fe(III)Zn(II)(IPCPMP)(mpdp)][PF(6)] (6) (mpdp = meta-phenylene-dipropionate), and [Fe(III)Cu(II)(IPCPMP) (OAc)}(2)(μ-O)][PF(6)] (7). Complexes 2-4, 6, and 7 have been crystallographically characterized. The structure of 6 is a solid state coordination polymer with heterodinuclear monomeric units, and 7 is a tetranuclear complex consisting of two heterodinuclear phenolate-bridged Fe(III)Cu(II) units bridged through a μ-oxido group between the two Fe(III) ions. Mössbauer spectra confirm the presence of high spin Fe(III) in an octahedral environment for 1, 3, and 5 while 2 and 4 display relaxation effects. Magnetic susceptibility measurements indicate weak antiferromagnetic coupling for 3, 4, and 5 and confirm the assignment of the metal centers in 2-5 as high spin Fe(III)-M(II) (M = Zn, Co (high spin), Ni (high spin), Mn (high spin)). Complexes 2-5 are intact in acetonitrile solution as indicated by IR spectroscopy (for 2-4) and electrospray ionization mass spectrometry (ESI-MS) but partly dissociate to hydroxide species and a mononuclear complex in water/acetonitrile solutions. UV-vis spectroscopy reveal pH-dependent behavior, and species that form upon increasing the pH have been assigned to μ-hydroxido-bridged Fe(III)M(II) complexes for 2-5 although 2 and 3 is further transformed into what is propsed to be a μ-oxido-bridged tetranuclear complex similar to 7. Complexes 2-5 enhance phosphodiester cleavage of 2-hydroxy-propyl-p-nitrophenyl phosphate (HPNP) and bis(2,4-dinitrophenyl)phosphate (BDNPP), but the reactivities are different for different complexes and generally show strong pH dependence.
|
|
| 9. |
- Li, Yong, et al.
(författare)
-
Non-heme FeIV=O complexes supported by four new pentadentate ligands : reactivity towards H- and O-atom transfer processes
- 2023
-
Ingår i: Inorganic Chemistry. - 1520-510X. ; 62:45, s. 18338-18356
-
Tidskriftsartikel (refereegranskat)abstract
- Four new pentadentate N5-donor ligands, [N-(1-methyl-2-imidazolyl)methyl-N-(2-pyridyl)-methyl-N-(bis-2-pyridylmethyl)-amine] (L1), [N-bis(1-methyl-2-imidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L2), (N-(isoquinolin-3-ylmethyl)-1,1-di(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine (L3) and N,N-bis(isoquinolin-3-ylmethyl)-1,1-di(pyridin-2-yl)methanamine (L4), have been synthesized based on the N4Py ligand framework, where one or two pyridyl arms of the N4Py parent are replaced by (N-methyl)imidazolyl or N-(isoquinolin-3-ylmethyl) moieties. Using these four pentadentate ligands, the mononuclear complexes [FeII(CH3CN)(L1)]2+ (1a), [FeII(CH3CN)(L2)]2+ (2a), [FeII(CH3CN)(L3)]2+ (3a) and [FeII(CH3CN)(L4)]2+ (4a) have been synthesized and characterized. The half-wave potentials (E1/2) of the complexes become more positive in the order: 2a < 1a < 4a 3a [Fe(N4Py)(CH3CN)]2+. The order of oxidation potentials correlates well with the Fe-Namine distances observed by crystallography, which are 2a 1a 4a 3a [Fe(N4Py)(CH3CN)]2+. The corresponding ferryl complexes [FeIV(O)(L1)]2+ (1b), [FeIV(O)(L2)]2+ (2b), [FeIV(O)(L3)]2+ (3b), and [FeIV(O)(L4)]2+ (4b) could be prepared by reaction of the ferrous complexes with isopropyl 2-iodoxybenzoate (IBX ester) in acetonitrile. The greenish complexes 3b and 4b could also be isolated in the solid state by reaction of the ferrous complexes in CH3CN with ceric ammonium nitrate in water. Mössbauer spectroscopy and magnetic measurements (SQUID) show that the four complexes 1b, 2b, 3b and 4b are low-spin (S = 1) FeIV=O complexes. UV/Vis spectra of the four FeIV=O complexes in acetonitrile show typical long wavelength absorptions around 700 nm, which are expected for FeIV=O complexes with N4Py-type ligands. The wavelengths of these absorptions decrease in the following order: 721 nm (2b) > 706 nm (1b) > 696 nm (4b) > 695 nm (3b) = 695 nm ([FeIV(O) (N4Py)]2+), indicating that the replacement of pyridyl arms with (N-methyl) imidazolyl moieties makes L1 and L2 exert weaker ligand fields than the parent N4Py ligand, while the ligand field strengths of L3 and L4 are similar to the N4Py parent despite the replacement of pyridyl arms with N-(isoquinolin-3-ylmethyl) moieties. Consequently, complexes 1b and 2b tend to be less stable than the parent [FeIV(O)(N4Py)]2+ complex: the half-life sequence at room temperature is 1.67 h (2b) < 16 h (1b) < 45 h (4b) < 63 h (3b) ≈ 60 h ([FeIV(O)(N4Py)]2+). Compared to the parent complex, 1b and 2b exhibit enhanced reactivity in both oxidation of thioanisole by oxygen atom transfer (OAT) reaction and oxygenation of C-H bonds of aromatic and aliphatic substrates, presumed to occur via an oxygen rebound process. Furthermore, second-order rate constants for hydrogen atom transfer (HAT) reactions affected by the ferryl complexes can be directly related to the C-H bond dissociation energies of a range of substrates that have been studied. Using either IBX ester or H2O2 as oxidant, all four new FeII complexes display good performance in catalytic reactions involving both HAT and OAT reactions.
|
|
| 10. |
- Mitra, Mainak, et al.
(författare)
-
Nonheme Fe(IV) Oxo Complexes of Two New Pentadentate Ligands and Their Hydrogen-Atom and Oxygen-Atom Transfer Reactions
- 2015
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 54:15, s. 7152-7164
-
Tidskriftsartikel (refereegranskat)abstract
- Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) framework have been synthesized, viz. [N-(1-methyl-2-benzimidazolyl)methyl-N-(2-pyridyl)methyl-N-(bis-2-pyridyl methyl)amine] (L1) and [N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L2), where one or two pyridyl arms of N4Py have been replaced by corresponding (N-methyl)benzimidazolyl-containing arms. The complexes [FeII(CH3CN)(L)]2+ (L = L1 (1); L2 (2)) were synthesized, and reaction of these ferrous complexes with iodosylbenzene led to the formation of the ferryl complexes [FeIV(O)(L)]2+ (L = L1 (3); L2 (4)), which were characterized by UV–vis spectroscopy, high resolution mass spectrometry, and Mössbauer spectroscopy. Complexes 3 and 4 are relatively stable with half-lives at room temperature of 40 h (L = L1) and 2.5 h (L = L2). The redox potentials of 1 and 2, as well as the visible spectra of 3 and 4, indicate that the ligand field weakens as ligand pyridyl substituents are progressively substituted by (N-methyl)benzimidazolyl moieties. The reactivities of 3 and 4 in hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions show that both complexes exhibit enhanced reactivities when compared to the analogous N4Py complex ([FeIV(O)(N4Py)]2+), and that the normalized HAT rates increase by approximately 1 order of magnitude for each replacement of a pyridyl moiety; i.e., [FeIV(O)(L2)]2+ exhibits the highest rates. The second-order HAT rate constants can be directly related to the substrate C–H bond dissociation energies. Computational modeling of the HAT reactions indicates that the reaction proceeds via a high spin transition state.
|
|
