Cyclopentadienyl Ring Of Ferrocene Research Articles

A theoretical study of ferrocene based on combined configuration interaction singles (CIS) and time-dependent density functional theory (TDDFT) approach

The state-of-the art density functional theory (DFT) is used to clearly resolve the two parallel cyclopentadienyl rings of ferrocene, which are either staggered (D5d symmetry) or eclipsed (D5h symmetry), in their ground-state conformation. Present result revealed that the eclipsed conformer with D5h point group represents the true minimum ground state structure of ferrocene. Natural population analysis is used to determine how atomic charge is distributed across different atoms of ferrocene D5h conformer and also the distribution of electrons in the core, valence, and Rydberg sub-shells. It is further investigated in potential energy scan that the rotation of the dihedral angle δ from 0° to 3π/5 will reproduce three times D5h or D5d conformers periodically as the period of 2π/5 due to the pentagonal structure of the CP ring. Further to examine optical spectra in the ultraviolet-visible (UV–vis) range, configuration interaction single (CIS) and time-dependent density functional theory (TDDFT) have conducted which help in locating the significant electronic shifts between different energy levels. Absorption spectra for high spin states were also generated in order to comprehend the characteristics of low-lying spin excitation. According to our estimates, the greatest absorption intensity is restricted to an energy range of 4–6 eV. Knowledge of ferrocene conformers will improve the research on other metallocenes and their derivatives, which have applications in biotechnology, nanotechnology, and solar technology.

Monomeric zinc ferrocene carboxylate [Zn(FcCOO)(3,5-dmp)2Cl] derived from 3,5-dimethylpyrazole: structural, optical, electrochemical and antimicrobial studies

Monomeric zinc ferrocene carboxylate [Zn(FcCOO)(3,5-dmp)2Cl] (1) has been synthesized from a reaction between the zinc chloride, sodium salt of ferrocene carboxylic acid (FcCOONa) and 3,5-dimethylpyrazole (3,5-dmp) at room temperature. Compound 1 was further characterized by elemental analysis, 1H NMR, FT-IR, absorption, emission spectroscopic techniques, and molecular structure was confirmed by single-crystal X-ray diffraction studies. The molecular structure of compound 1 crystallized in triclinic system with P1¯ space group and the central Zn2+ ion is in a distorted tetrahedral geometry with –FeN2OCl coordination environment. Compound 1 was further stabilized with the aid of inter and intramolecular hydrogen bonding and π–π interaction between cyclopentadienyl ring of ferrocene and aromatic heterocyclic five membered 3,5-dimethylpyrazole. Compound 1 exhibits broad emission band, indicating ligand-to-metal charger transfer (LMCT) or metal-to-ligand charger transfer (MLCT) nature. The electrochemical property of compound 1 revealed that one-electron anodic and cathodic peaks corresponding to the redox responsible of ferrocene/ferrocenium (FeII↔FeIII) moiety. Among the different strains of bacteria, the antibacterial activity of compound 1 showed comparatively a significant activity against gram negative bacterium Proteus vulgaris.

Ferrocene Derivatives Functionalized with Donor/Acceptor (Hetero)Aromatic Substituents: Tuning of Redox Properties

A series of functionalized ferrocene derivatives carrying electron-donor and electron-withdrawing (hetero)aromatic substituents has been designed as potential alternative electrolyte redox couples for dye-sensitized solar cells (DSSC). The compounds have been synthesized and fully characterized in their optical and electrochemical properties. A general synthetic approach that implies the use of a microwave assisted Suzuki coupling has been developed to access a significative number of compounds. The presence of different electron-rich and electron-poor substituents provided fine tuning of optical properties and energy levels. HOMO and LUMO energy values showed that the substitution of one or two cyclopentadienyl rings of ferrocene can be successfully exploited to increase the maximum attainable voltage from a standard DSSC device using TiO2 as a semiconductor, opening the way to highly efficient, non-toxic, and cheap redox shuttles to be employed in solar energy technologies.

Role of Electrostatics in Influencing the Pathway by Which the Excited State of [Ru(bpy)3]2+ Is Deactivated by Ferrocene Derivatives.

Excited states of tris(2,2'-bipyridine)ruthenium(II), [Ru(bpy)3]2+, can be deactivated by a wide range of ferrocene derivatives. The pathway by which deactivation takes place, either energy transfer (EnT) or electron transfer (ET), depends on several factors inherent to each specific donor-acceptor (D···A) system. In this work, we provide mechanistic insight into bimolecular quenching between [Ru(bpy)3]2+* and several ferrocene (Fc) derivatives in a variety of solvents. By introducing various functional groups onto the cyclopentadienyl ring of ferrocene, the chemical properties of the organometallic complexes were altered by tuning the oxidation potentials and charge of the iron complexes, and the manner in which the [Ru(bpy)3]2+ excited state is quenched by each ferrocene complex in solvents of various dielectric constants, including anhydrous acetonitrile (ACN), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and water (pH 10), was assessed. Through the use of transient absorption (TA) spectroscopy, the mechanism of [Ru(bpy)3]2+* quenching by each of five ferrocene derivatives (i.e., either EnT or ET) in the aforementioned solvents was evaluated. On the basis of these studies, electrostatic factors relating to the charge on the ferrocene moiety were found to influence the quenching pathway(s) for the [Ru(bpy)3]2+···Fc systems under interrogation. When the ferrocene moiety is positively charged, the [Ru(bpy)3]2+ excited state is quenched by EnT to Fc, while when the ferrocene moiety is neutral or negatively charged, the [Ru(bpy)3]2+ excited state is quenched via reductive ET.

3D in-situ hollow carbon fiber/carbon nanosheet/Fe3C@Fe3O4 by solventless one-step synthesis and its superior supercapacitor performance

Herein, 3D in-situ hollow carbon fiber/carbon nanosheet/Fe3C@Fe3O4 (h-CNF/CNS/Fe3C@Fe3O4) was constructed using ferrocene and oleic acid by a solventless one-step process that did not require additional filtering, neutralization, drying, or calcination steps. The iron-oleate chelating structure that self-assembled during annealing facilitated the fabrication of 3D in-situ h-CNF/CNS/Fe3C@Fe3O4 by undergoing graphitization at 600°C. This carbon shell of the 3D in-situ h-CNF/CNS/Fe3C@Fe3O4 was derived from the two cyclopentadienyl rings in ferrocene. This hybrid material made from economically cheap oleic acid exhibited superior supercapacitive behavior: high specific capacitance of 327Fg−1 at 5mVs−1 and 210Fg−1 at 10mVs−1, good rate capability of 60Fg−1 at 10Ag−1 (compared to 70Fg−1 at 1Ag−1 for pure Fe3O4), and superior retention of 108% after 6000 cycles at 100mVs−1. These superior supercapacitive properties were ascribed to the 3D graphitic h-CNF/CNS for enhancing electrical conductivity and the carbonaceous shell over Fe3C@Fe3O4 core for buffering the bulk expansion of iron-related particles.

Synthesis and nonlinear optical properties of novel chalcone analogues of ferrocenyl biaryl derivatives

A series of structurally novel organometallic compounds (3a–g) based on 1-biaryl-3-ferrocenylprop-2-en-1-one, were synthesized by the Suzuki-Miyaura cross-coupling reaction for applications as nonlinear optical (NLO) and liquid crystal (LC) materials. Notably, a single crystal of this class of compounds was obtained for the very first time, and it was found that the two phenyl rings of the chalconyl group were nearly coplanar to one of the cyclopentadienyl rings of ferrocene. Due to the high degree of conjugation, all the chalcone analogues of ferrocenyl biaryl derivatives displayed strong second harmonic generation (SHG) response (0.45–0.60 × 10−30 esu, 3–4 times greater that of potassium dideuterophosphate (KDP)). The density functional theory (DFT) was employed to calculate the main molecular orbital energies and compositions of 3d, based on its crystallographic structure. Compound 3d was found to exhibit excellent NLO properties due to its low Egap and superior charge transfer ability within the conjugated system. This work presents a new approach for the preparation of this class of ferrocenyl biaryl derivatives, which may have potential applications as NLO materials.

Molecular ring rotation in solid ferrocene revisited.

We report on quasielastic neutron spectroscopy experiments on ferrocene (bis(η(5)-cyclopentadienyl)iron) in its three different crystalline phases: the disordered monoclinic crystalline phase (T > 164 K), the metastable triclinic phase (T < 164 K), and the stable orthorhombic phase (T < 250 K). The cyclopentadienyl rings in ferrocene are known to undergo rotational reorientations for which the analysis of our large data set suggests partially a revision of the known picture of the dynamics and allows for an extension and completion of previous studies. In the monoclinic phase, guided by structural information, we propose a model for rotational jumps among non-equivalent sites in contrast to the established 5-fold jump rotation model. The new model takes the dynamical disorder into account and allows the cyclopentadienyl rings to reside in two different configurations which are found to be twisted by an angle of approximately 30°. In the triclinic phase, our analysis demands the use of a 2-ring model accounting for crystallographically independent sites with different barriers to rotation. For the orthorhombic phase of ferrocene, we confirm a significantly increased barrier of rotation using neutron backscattering spectroscopy. Our data analysis includes multiple scattering corrections and presents a novel approach of simultaneous analysis of different neutron scattering data by combining elastic and inelastic fixed window temperature scans with energy spectra, providing a very robust and reliable mean of extracting the individual activation energies of overlapping processes.

Linkage of α-cyclodextrin-terminated poly(dimethylsiloxanes) by inclusion of quasi bifunctional ferrocene

We report the noncovalent linkage of terminally substituted oligo(dimethylsiloxanes) bearing α-cyclodextrins (α-CD) as host end groups for the cyclopentadienyl rings of ferrocene. This double complexation of unsubstituted ferrocene leads to a supramolecuar formation of the siloxane strands. Structural characterization was performed by the use of 1H NMR and IR spectroscopy and by mass spectrometry. Electron microscopy studies and dynamic light scattering measurements show a significant decrease of the derivative size after the complexation with ferrocene. In addition, further evidence for the successful complexation of the end groups was verified by the shifts of the protons in the 1H NMR spectra and in the correlation signals of the 2D ROESY NMR spectra.

Redox Control of Rotary Motions in Ferrocene-Based Elemental Ball Bearings

Rotational motions of ferrocene-based carousels have been achieved by electron transfer centered on π-dimerizable 4,4'-bipyridinium substituents introduced on both cyclopentadienyl rings through covalent linkers of different size, geometry, and flexibility. Detailed spectroscopic, electrochemical, and theoretical analyses demonstrate that rigid and fully conjugated linkers allow the quantitative formation of intramolecular π-dimers resulting from optimized orbital overlaps within the HOMO of the electrochemically generated bis-radical species. The tetra-cationic "charge-repelled" conformers, the self-assembled π-dimers, and their electron triggered interconversions have been investigated by UV-vis, NMR, and ESR spectroscopy, electrochemistry, X-ray diffraction analysis, and theoretical calculations. These studies support the conclusion that the rotation of both cyclopentadienyl rings in ferrocene can be controlled electrochemically using noncovalent reversible interactions arising from π-radical coupling processes.

Binding properties of ferrocene–glutathione conjugates as inhibitors and sensors for glutathione S-transferases

The binding properties of two electroactive glutathione–ferrocene conjugates that consist in glutathione attached to one or both of the cyclopentadienyl rings of ferrocene (GSFc and GSFcSG), to Schistosoma japonica glutathione S-transferase (SjGST) were studied by spectroscopy fluorescence, isothermal titration calorimetry (ITC) and differential pulse voltammetry (DPV). Such ferrocene conjugates resulted to be competitive inhibitors of glutathione S-transferase with an increased binding affinity relative to the natural substrate glutathione (GSH). We found that the conjugate having two glutathione units (GSFcSG) exhibits an affinity for SjGST approximately two orders of magnitude higher than GSH. Furthermore, it shows negative cooperativity with the affinity for the second binding site two orders of magnitude lower than that for the first one. We propose that the reason for such negative cooperativity is steric since, i) the obtained thermodynamic parameters do not indicate profound conformational changes upon GSFcSG binding and ii) docking studies have shown that, when bound, part of the first bound ligand invades the second site due to its large size. In addition, voltammetric measurements show a strong decrease of the peak current upon binding of ferrocene–glutathione conjugates to SjGST and provide very similar K values than those obtained by ITC. Moreover, the sensing ability, expressed by the sensitivity parameter shows that GSFcSG is much more sensitive than GSFc, for the detection of SjGST.

Potential Applications of Ferrocene as a Structural Feature in Antioxidants

Comparing with the wide usage of ferrocene in novel materials, ferrocene was unusually applied to be a structural feature in designing drugs even though some researchers pointed out that ferrocene and its derivatives possessed potential pharmacological applications. This was due to that low polarity limited bioavailability of ferrocene in vivo. Since ferrocene was inert to the oxidation at atmosphere, it was deduced that synthetic derivatives of ferrocene may be a novel kind of antioxidant, in which other organic groups may enhance the bioavailability of ferrocene, or large conjugated system formed among ferrocenyl and other organic groups may increase the antioxidant effectiveness. Thus, synthetic derivatives of ferrocene were divided into nonconjugated and conjugated ones in this review. For nonconjugated ferrocenyl derivatives, carbon chain or simple group attached one or two cyclopentadienyl rings in ferrocene to form a novel molecule with ferrocenyl group. The aim of synthesis of nonconjugated ferrocenyl compounds was to increase the bioavailability of ferrocene in vivo. On the other hand, the conjugated ferrocenyl derivatives referred to introduce other group to form a conjugated system with the cyclopentadienyl ring in ferrocene. The large conjugated system was beneficial for the single electron to dispense among the whole molecule while forming radicals, and enhanced the antioxidant capacity of the whole molecule. This review summarized the potential usage of ferrocene in antioxidants.

Two types of protons in ferrocene

Two absorption bands of ferrocene, the in-plane bending C-H vibrations (βCH) at 1002 cm−1 and out-of-plane C-H vibration (γCH) at 816 cm−1, are accompanied with high-frequency satellites βCH (1055) and γCH (837 cm−1). In the spectrum of 1,1′-dideuteroferrocene, only the high-frequency bands suffer an isotopic shift, from 1055 to 859 cm−1, and from 837 to 668 cm−1. Only additional incorporation of deuterium into 1,1′-dideuteroferrocene results also in an isotopic shift of the basic bands: 1002 to 771 and 816 to 632 cm−1. Therefore, one of the five carbon atoms of cyclopentadienyl ring of ferrocene differs from the other in the static state. It is assumed that just this carbon atom is bonded with the iron atom by the σ-bond.

Bis((2-methoxymethyl)pyrrolidine)phosphine as effective chiral auxiliary for the stereoselective synthesis of chiral ferrocenyl diphosphines

The bis(2-methoxymethyl pyrrolidine)phosphine moiety is shown to be a very effective chiral auxiliary for the ortho- and diastereoselective lithiation of ferrocene, thereby allowing the highly selective attachment of various electrophiles to the cyclopentadienyl ring of ferrocene. The potential of the methodology is demonstrated by the synthesis of Kephos, a new family of ferrocenyl diphosphines and of OH-Taniaphos derivatives.

Ferrocene–Carbohydrate Conjugates as Electrochemical Probes for Molecular Recognition Studies

We report two methods that have allowed the attachment of glucose, mannose and lactose to one or both of the cyclopentadienyl rings of ferrocene. The resulting ferrocene-carbohydrate conjugates were synthesised by the reaction of thioglycosides with ferrocenemethanol and 1,1'-ferrocenedimethanol in acidic media. A second method based on the regiospecific copper(I)-catalysed cycloaddition of propargyl glycoside, azidomethyl and bis(azidomethyl)ferrocene as well as azidoethyl glycoside and ethynylferrocene was also used and led to the synthesis of 1,2,3-triazole-containing glycoconjugates. The electrochemical behaviour of the synthesised glycoconjugates was investigated. In addition, their binding interactions with beta-cyclodextrin were studied by means of NMR spectroscopy, isothermal titration calorimetry, and cyclic and differential pulse voltammetric experiments. These techniques allowed the determination of the thermodynamic parameters of the complexes, the stability constants for the complexes formed with both the neutral and the oxidised states of the ferrocenyl glycoconjugates, the mode of inclusion and the diffusion coefficients for both the glycoconjugates and the complexes.

Structural and property characterization of two new charge-transfer salts based on Keggin ions and ferrocene

Two new charge-transfer salts based on ferrocene and Keggin-type anions, [NBu 4] 6 [Fe(C 5H 5) 2][HAsMo 12O 40] 2 ( 1) and [NBu 4] 2[Fe(C 5H 5) 2] 2[HSiMo 12O 40]·2CH 3CN ( 2), were synthesized and their structures were determined by X-ray diffraction analysis. There are different stoichiometries (Keggin anion: ferrocene cation) in 1 and 2, namely, 2:1 and 1:2. There exist complex interactions between the polyanions, and the framework oxygens of anions and the cyclopentadienyl rings of ferrocene. One of two crystallographic asymmetric Keggin ions in 1 is surrounded by four parallel ferrocene cations with the closest distance of framework oxygens of anions and the cyclopentadienyl rings of ferrocene moiety of 3.16 Ǻ. Each anion in 2 is surrounded by six parallel ferrocene cations with the close distance of framework oxygens of anion and the cyclopentadienyl rings of ferrocene moiety from 3.197 to 3.401 Ǻ. The bond valence sum of Mo atoms in compounds 1 and 2 is in the range of 6.234–6.623 and much larger than 6, which suggests that there is more covalent ingredient between Mo–O in the change-transfer salts owing to the delocalization of one unpaired electron in the reduced Keggin ion. The UV–visible spectra, EPR and CV properties of the salts were also discussed.

A Concave‐Bound CpFe Complex of Sumanene as a Metal in a π Bowl

Dished up: The selective synthesis of a concave-bound iron complex was achieved by ligand exchange of a cyclopentadienyl ring of ferrocene with a fullerene-fragment π bowl, sumanene (see picture). The concave π surface serves as an η6 ligand.

A Joint Experimental and Theoretical Study of Cation−π Interactions: Multiple-Decker Sandwich Complexes of Ferrocene with Alkali Metal Ions (Li+, Na+, K+, Rb+, Cs+)

A systematic study of cation-pi interactions between alkali metal ions and the cyclopentadienyl ring of ferrocene is presented. The alkali metal (Li+, Na+, K+, Rb+, Cs+) salts of the ditopic mono(pyrazol-1-yl)borate ligand [1,1'-fc(BMe2pz)2]2- crystallize from dimethoxyethane as multiple-decker sandwich complexes with the M+ ions bound to the pi faces of the ferrocene cyclopentadienyl rings in an eta5 manner (fc = (C5H4)2Fe; pz = pyrazolyl). X-ray crystallography of the lithium complex reveals discrete trimetallic entities with each lithium ion being coordinated by only one cyclopentadienyl ring. The sodium salt forms polyanionic zigzag chains where each Na+ ion bridges the cyclopentadienyl rings of two ferrocene moieties. Linear columns [-CpR-Fe-CpR-M+-CpR-Fe-CpR-M+-](infinity) (R = [-BMe2pz]-) are established by the K+, Rb+, and Cs+ derivatives in the solid state. According to DFT calculations, the binding enthalpies of M+-eta5(ferrocene) model complexes are about 20% higher as compared to the corresponding M+-eta6(benzene) aggregates when M+ = Li+ or Na+. For K+ and Rb+, the degree of cation-pi interaction with both aromatics is about the same. The binding sequence along the M+-eta5(ferrocene) series follows a classical electrostatic trend with the smaller ions being more tightly bound.

Convenient methods for the synthesis of ferrocene-carbohydrate conjugates.

[structure: see text] We report two methods for the attachment of mono- and disaccharides to one or both of the cyclopentadienyl rings in ferrocene. The first strategy involves the reaction in acidic media of thioglycosides with ferrocenemethanol or 1,1'-ferrocenedimethanol. The second method consists of the regiospecific catalytic cycloaddition of propargyl glycoside and azidomethyl and bis(azidomethyl)ferrocene leading to the 1,2,3-triazole derivatives. The inverse strategy was also explored. The electrochemical behavior of the synthesized ferrocene-containing glycoconjugates was investigated.

Synthesis and characterization of meso-ferrocenylethynyl 5,15-diphenylporphyrins

A series of four meso-ferrocenylethynyl (5,15-diphenylporphyrinato)nickel(II) derivatives have been synthesized by Sonogashira coupling reactions. Three of these compounds contain the electron-withdrawing groups including –CHO, –CHC(CN) 2, and –CCC 6H 4NO 2 at the remaining meso position, with a view to preparing push–pull chromophores, in which ferrocene serves as the electron donor. All the new compounds have been characterized spectroscopically and the molecular structure of one of these porphyrins (compound 11) has also been determined. The studies show that although the ferrocenylethynyl group can extend the π system of the central porphyrin core, the cyclopentadienyl rings of ferrocene are almost orthogonal to the porphyrin ring. This hinders ferrocene serving as a good electron donor in these systems.

Synthesis of planar chiral ferrocenyl 1,3-diamines and 1,3-amino ethers.

The efficient syntheses of novel planar chiral 1,3-diamines and 1,3-amino ethers with an oxy or amino function directly bound to the cyclopentadienyl ring of ferrocene has been developed. The key reaction is the Cu2O promoted substitution of (pR)-N,N-diisopropyl-2-iodoferrocenecarboxamide with either phthalimide or AcOH to introduce nitrogen or oxygen functionality onto the cyclopentadienyl ring. The enantiomerically pure iodoferrocene derivative is available from the known enantioselective ortho-lithiation of N,N-diisopropylferrocenecarboxamide with n-BuLi-sparteine. In the course of these studies the synthesis of a novel C2 symmetric C-2 dimer of N,N-dimethyl-1-ferrocenylethylamine was characterised by single crystal X-ray diffraction.