Extensive Redox Non-Innocence in Iron Bipyridine-Diimine Complexes: a Combined Spectroscopic and Computational Study.
Ontology highlight
ABSTRACT:
SUBMITTER: Thenarukandiyil R
PROVIDER: S-EPMC8653161 | biostudies-literature |
REPOSITORIES: biostudies-literature
Similar Datasets
Project description:Three new dinitrosyl iron complexes LFe(NO)(2) (L = 2,2'-bipyridine (bipy) (1), 2,2',2''-terpyridine (terpy) (2) and 1,10-phenathroline (phen) (3)) were synthesized by the reaction of Fe(NO)(2)(CO)(2) with corresponding ligands in tetrahydrofuran. Complexes 1-3 were studied using IR, UV-vis, MS, NMR, and electrochemical techniques. Complexes 1 and 2 were also characterized using single crystal X-ray diffraction analysis. IR spectra of complexes 1-3 display two strong characteristic NO stretching frequencies (nu(NO)) in the region reflecting donor properties of the ligands. Cyclic voltammetry studies show two quasi-reversible one-electron reductions for all complexes. Electrochemical investigations using different concentrations show that an irreversible one-electron reduction at -1.85 V for complex 2 and -1.80 V for complex 3 are from solvated species. Single-crystal X-ray structural analysis reveals that complex 1 crystallizes in the triclinic P1 space group and the asymmetric unit consists of one Fe(NO)(2)(bipy) molecule with the two NO groups located on two sides of Fe(bipy) plane. Complex 2 crystallizes in monoclinic P21/n space group, and the asymmetric unit contains one Fe(NO)(2)(terpy) molecule, in which the NO groups are located on two sides of the plane consisted of Fe and two coordinated pyridyl rings, but almost parallel to the uncoordinated pyridyl ring. The crystal packings of both complexes 1 and 2 show intermolecular H-bonding and strong pi-pi stacking interactions.
| S-EPMC2760620 | biostudies-literature
Project description:Two sets of FeIII/II dithione complexes [FeII( i Pr2Dt0)3][PF6]2 ([1][PF6]2), [FeII(Me2Dt0)3][PF6]2 ([2][PF6]2), and [FeIII( i Pr2Dt0)3][PF6]3 ([3][PF6]3), [FeIII(Me2Dt0)3][PF6]3 ([4][PF6]3), and compound [FeIII( i Pr2Dt0)3][FeCl4][PF]2 ([3][FeCl4][PF6]2) were synthesized from N,N'-diisopropyl piperazine-2,3-dithione ( i Pr2Dt0) and N,N'-dimethyl piperazine-2,3-dithione (Me2Dt0) ligands. Complexes [1][PF6]2-[4][PF6]3 have been characterized by NMR, IR, and UV-visible spectroscopies, and by electrochemistry. The molecular structures of [2][PF6]2 and [3][FeCl4][PF6]2 have been determined by X-ray crystallography. Complexes [2][PF6]2 and [3][FeCl4][PF6]2 both crystallized in the monoclinic space group P21/n. Both complexes exhibit distorted octahedral geometry and the three coordinated ligands in each complex exhibit different dithione folding. Complexes [1][PF6]2-[4][PF6]3 exhibit a single FeIII/II based couple and three quasi-reversible ligand-based redox couples. The electronic spectra of [1][PF6]2-[4][PF6]3 show intense MLCT bands that indicate strong mixing between metal and ligand orbitals. DFT calculations were used to provide a framework for understanding the electronic origin of their redox chemistry and spectroscopic features.
| S-EPMC9057267 | biostudies-literature
Project description:In Fe- and Mn-dependent superoxide dismutases (SODs), second-sphere residues have been implicated in precisely tuning the metal ion reduction potential to maximize catalytic activity (Vance, C. K.; Miller, A.-F. J. Am. Chem. Soc. 1998, 120, 461-467). In the present study, spectroscopic and computational methods were used to characterize three distinct Fe-bound SOD species that possess different second-coordination spheres and, consequently, Fe(3+/2+)reduction potentials that vary by approximately 1 V, namely, FeSOD, Fe-substituted MnSOD (Fe(Mn)SOD), and the Q69E FeSOD mutant. Despite having markedly different metal ion reduction potentials, FeSOD, Fe(Mn)SOD, and Q69E FeSOD exhibit virtually identical electronic absorption, circular dichroism, and magnetic circular dichroism (MCD) spectra in both their oxidized and reduced states. Likewise, variable-temperature, variable-field MCD data obtained for the oxidized and reduced species do not reveal any significant electronic, and thus geometric, variations within the Fe ligand environment. To gain insight into the mechanism of metal ion redox tuning, complete enzyme models for the oxidized and reduced states of all three Fe-bound SOD species were generated using combined quantum mechanics/molecular mechanics (QM/MM) geometry optimizations. Consistent with our spectroscopic data, density functional theory computations performed on the corresponding active-site models predict that the three SOD species share similar active-site electronic structures in both their oxidized and reduced states. By using the QM/MM-optimized active-site models in conjunction with the conductor-like screening model to calculate the proton-coupled Fe(3+/2+) reduction potentials, we found that different hydrogen-bonding interactions with the conserved second-sphere Gln (changed to Glu in Q69E FeSOD) greatly perturb the p K of the Fe-bound solvent ligand and, thus, drastically affect the proton-coupled metal ion reduction potential.
| S-EPMC6468990 | biostudies-literature
Project description:The synthesis, characterization, and catalytic activity of pyridine(diimine) iron piperylene and isoprene complexes are described. These diene complexes are competent precatalysts for (i) the selective cross-[2+2]-cycloaddition of butadiene or (E)-piperylene with ethylene and α-olefins and (ii) the 1,4-hydrovinylation of isoprene with ethylene. In the former case, kinetic analysis implicates the diamagnetic η4-piperylene complex as the resting state prior to rate-determining oxidative cyclization. Variable temperature 1H NMR and EXSY experiments established that diene exchange from the diamagnetic, 18e- complexes occurs rapidly in solution at ambient temperature through a dissociative mechanism. The solid-state structure of (Me(Et)PDI)Fe(η4-piperylene) (Me(Et)PDI = 2,6-(2,6-Me2-C6H3N═CEt)2C5H3N), was determined by single-crystal X-ray diffraction and confirmed the s-trans coordination of the monosubstituted 1,3-diene. Possible relationships between ligand-controlled diene coordination geometry, metallacycle denticity, and chemoselectivity of iron-mediated cycloaddition reactions are discussed.
| S-EPMC7236768 | biostudies-literature
Project description:The reaction of the redox active 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-BIAN) and iron(II) iodide in acetonitrile led to a new complex [(dpp-BIAN)FeIII2] (1). Molecular structure of 1 was determined by the single crystal X-ray diffraction analysis. The spin state of the iron cation in complex 1 at room temperature and the magnetic behavior of 1 in the temperature range of 2-300 K were studied using Mossbauer spectroscopy and magnetic susceptibility measurements, respectively. The neutral character of dpp-BIAN in 1 was confirmed by IR and UV spectroscopy. The electrochemistry of 1 was studied in solution and solid state using cyclic voltammetry. The generation of the radical anion form of the dpp-BIAN ligand upon reduction of 1 in a CH2Cl2 solution was monitored by EPR spectroscopy.
| S-EPMC8158106 | biostudies-literature
Project description:A new bimetallic platform comprising a six-coordinate Fe(ONO)2 unit bound to an (ONO)M (M = Fe, Zn) has been discovered ((ONOcat)H3 = bis(3,5-di-tert-butyl-2-phenol)amine). Reaction of Fe(ONO)2 with either (ONOcat)Fe(py)3 or with (ONOq)FeCl2 under reducing conditions led to the formation of the bimetallic complex Fe2(ONO)3, which includes unique five- and six-coordinate iron centers. Similarly, the reaction of Fe(ONO)2 with the new synthon (ONOsq˙)Zn(py)2 led to the formation of the heterobimetallic complex FeZn(ONO)3, with a six-coordinate iron center and a five-coordinate zinc center. Both bimetallic complexes were characterized by single-crystal X-ray diffraction studies, solid-state magnetic measurements, and multiple spectroscopic techniques. The magnetic data for FeZn(ONO)3 are consistent with a ground state S = 3/2 spin system, generated from a high-spin iron(ii) center that is antiferromagnetically coupled to a single (ONOsq˙)2- radical ligand. In the case of Fe2(ONO)3, the magnetic data revealed a ground state S = 7/2 spin system arising from the interactions of one high-spin iron(ii) center, one high-spin iron(iii) center, and two (ONOsq˙)2- radical ligands.
| S-EPMC5530940 | biostudies-literature
Project description:Nonheme iron halogenases are unique enzymes in nature that selectively activate an aliphatic C-H bond of a substrate to convert it into C-X (X = Cl/Br, but not F/I). It is proposed that they generate an FeIII(OH)(X) intermediate in their catalytic cycle. The analogous FeIII(OH) intermediate in nonheme iron hydroxylases transfers OH• to give alcohol product, whereas the halogenases transfer X• to the carbon radical substrate. There remains significant debate regarding what factors control their remarkable selectivity of the halogenases. The reactivity of the complexes FeIII(BNPAPh2O)(OH)(X) (X = Cl, Br) with a secondary carbon radical (R•) is described. It is found that X• transfer occurs with a secondary carbon radical, as opposed to OH• transfer with tertiary radicals. Comprehensive computational studies involving density functional theory were carried out to examine the possible origins of this selectivity. The calculations reproduce the experimental findings, which indicate that halogen transfer is not observed for the tertiary radicals because of a nonproductive equilibrium that results from the endergonic nature of these reactions, despite a potentially lower reaction barrier for the halogenation pathway. In contrast, halogen transfer is favored for secondary carbon radicals, for which the halogenated product complex is thermodynamically more stable than the reactant complex. These results are rationalized by considering the relative strengths of the C-X bonds that are formed for tertiary versus secondary carbon centers. The computational analysis also shows that the reaction barrier for halogen transfer is significantly dependent on secondary coordination sphere effects, including steric and H-bonding interactions.
| S-EPMC9228086 | biostudies-literature
Project description:We report on a systematical reactivity study of β-diketiminate zinc complexes with redox-active 2,2'-bipyridine (bpy). The reaction of LZnI (L = HC[C(Me)N(2,6-iPr2C6H3)]2) with NaB(C6F5)4 in the presence of bpy yielded [LZn(bpy)][B(C6F5)4] (1), with bpy serving as a neutral ligand, whereas reduction reactions of LZnI with 1 or 2 equiv of KC8 in the presence of bpy gave the radical complex LZn(bpy) (2) and [2.2.2-Cryptand-K][LZn(bpy)] (3), in which bpy either acts as a π-radical anion or a diamagnetic dianion, respectively. The paramagnetic nature of 2 was confirmed via solution magnetic susceptibility measurements, and UV-vis spectroscopy shows that 2 exhibits absorption bands typical for bpy radical species. The EPR spectra of 2 and its deuterated analog 2-d 8 demonstrate that the spin density is localized to the bpy ligand. Density functional theoretical calculations and natural bond orbital analysis were employed to elucidate the electronic structure of complexes 1-3 and accurately reproduced the structural experimental data. It is shown that reduction of the bpy moiety results in a decrease in the β-diketiminate co-ligand bite angle and elongation of the Zn-N(β-diketiminate) bonds, which act cooperatively and in synergy with the bpy ligand by decreasing Zn-N(bpy) bond lengths to stabilize the energy of the LUMO.
| S-EPMC8296587 | biostudies-literature
Project description:Nature uses control of the secondary coordination sphere to facilitate an astounding variety of transformations. Similarly, synthetic chemists have found metal-ligand cooperativity to be a powerful strategy for designing complexes that can mediate challenging reactivity. In particular, this strategy has been used to facilitate two electron reactions with first row transition metals that more typically engage in one electron redox processes. While NNN pincer ligands feature prominently in this area, examples which can potentially engage in both proton and electron transfer are less common. Dihydrazonopyrrole (DHP) ligands have been isolated in a variety of redox and protonation states when complexed to Ni. However, the redox-state of this ligand scaffold is less obvious when complexed to metal centers with more accessible redox couples. Here, we synthesize a new series of Fe-DHP complexes in two distinct oxidation states. Detailed characterization supports that the redox-chemistry in this set is still primarily ligand based. Finally, these complexes exist as 5-coordinate species with an open coordination site offering the possibility of enhanced reactivity.
| S-EPMC9435867 | biostudies-literature
Project description:The known iron(II) complex [Fe(II)(LN3S)(OTf)] (1) was used as starting material to prepare the new biomimetic (N4S(thiolate)) iron(II) complexes [Fe(II)(LN3S)(py)](OTf) (2) and [Fe(II)(LN3S)(DMAP)](OTf) (3), where LN3S is a tetradentate bis(imino)pyridine (BIP) derivative with a covalently tethered phenylthiolate donor. These complexes were characterized by X-ray crystallography, ultraviolet-visible (UV-vis) spectroscopic analysis, (1)H nuclear magnetic resonance (NMR), and Mössbauer spectroscopy, as well as electrochemistry. A nickel(II) analogue, [Ni(II)(LN3S)](BF4) (5), was also synthesized and characterized by structural and spectroscopic methods. Cyclic voltammetric studies showed 1-3 and 5 undergo a single reduction process with E(1/2) between -0.9 V to -1.2 V versus Fc(+)/Fc. Treatment of 3 with 0.5% Na/Hg amalgam gave the monoreduced complex [Fe(LN3S)(DMAP)](0) (4), which was characterized by X-ray crystallography, UV-vis spectroscopic analysis, electron paramagnetic resonance (EPR) spectroscopy (g = [2.155, 2.057, 2.038]), and Mössbauer (? = 0.33 mm s(-1); ?E(Q) = 2.04 mm s(-1)) spectroscopy. Computational methods (DFT) were employed to model complexes 3-5. The combined experimental and computational studies show that 1-3 are 5-coordinate, high-spin (S = 2) Fe(II) complexes, whereas 4 is best described as a 5-coordinate, intermediate-spin (S = 1) Fe(II) complex antiferromagnetically coupled to a ligand radical. This unique electronic configuration leads to an overall doublet spin (S(total) = 1/2) ground state. Complexes 2 and 3 are shown to react with O2 to give S-oxygenated products, as previously reported for 1. In contrast, the monoreduced 4 appears to react with O2 to give a mixture of sulfur oxygenates and iron oxygenates. The nickel(II) complex 5 does not react with O2, and even when the monoreduced nickel complex is produced, it appears to undergo only outer-sphere oxidation with O2.
| S-EPMC3827697 | biostudies-other