Ferrocene Ring Research Articles

Side-Chain Type Ferrocene Macrocycles.

A class of side-chain type ferrocene macrocycles with a radially conjugated system is introduced in this study. The stereo configurations of these ferrocene rings were determined through single-crystal X-ray diffraction analysis. Notably, in the solid state, the ferrocene rings exhibit a distinctive herringbone stacking pattern imposed by a ferrocene-to-ring host-guest interaction. Through UV-vis absorption spectroscopy, electrochemical measurements, and theoretical calculations, valuable insights into the electronic properties of these rings were obtained. In addition, the single crystal of macrocycle A 2 B demonstrates a second-order nonlinear optical response. As a class of organometallic nanorings, this work holds great potential for further exploration in the fields of organometallic chemistry, molecular electronics, and host-guest chemistry.

Synthesis, crystal structure and Hirshfeld surface analysis of 1-ferrocenylundecane-1,11-diol.

The racemic title compound, [Fe(C5H5)(C16H27O2)], comprises an α,ω-diol-substituted undecyl chain with a ferrocenyl substituent at at one terminus. The alkane chain is inclined to the substituted ring of the ferrocene grouping by 84.22 (13)°. The ferrocene rings are almost eclipsed and parallel. The crystal structure features O-H⋯O and C-H⋯O hydrogen bonds and C-H⋯π contacts that stack the mol-ecules along the c-axis direction. A Hirshfeld surface analysis reveals that H⋯H inter-actions (83.2%) dominate the surface contacts.

Oxidation-promoted synthesis of ferrocenyl planar chiral rhodium(iii) complexes for C–H functionalization catalysis

The chemical oxidation of rhodium(i) complexes [Rh(L)(COD)][BF4], where L is a ferrocenyl phosphine/N-heterocyclic carbene ligand, with 2 equiv. of a triaryl-aminium salt [(4-BrC6H4)3N][BF4] in acetonitrile gave planar chiral, air-stable [Rh(L–H)(MeCN)3][BF4]2 complexes where the ferrocene (C5H4CH2ImR or C5H4CH2BImCH2Mes) ring has been C–H activated at the position 2 in good to excellent yields. An important reactivity difference between our complexes and the ubiquitous [Cp*Rh(MeCN)3]X2 complex has been observed in the Grignard-type arylation of 4-nitrobenzaldehyde.

Naked Eye and Colorimetric Detection of Cyanide with a 1,3‐Diethyl‐2‐thiobarbituric Acid Substituted Ferrocene Chemosensor

AbstractA 1,3‐diethyl‐2‐thiobarbituric‐acid‐substituted ferrocene (FET) has been evaluated for its cyanide sensing ability by UV‐visible absorption spectroscopy and other characterization methods. FET provides a ratiometric colorimetric chemosensor for the CN− anion detection in 1 : 1 DMSO/H2O (v/v) solution. The addition of CN− results in an immediate color change from dark blue to pale orange that is visible to the naked eye. Mechanism studies and molecular modelling with TD‐DFT calculations demonstrate that nucleophilic addition of CN− to an electrophilic sp2‐hybridized carbon atom blocks charge transfer from the ferrocene ring complex to the thiobarbituric acid moiety. The FET sensor exhibits excellent selectivity for CN− and a limit of detection of 0.2 μM.

Supramolecular architectures in the salt trimethoprimium ferrocene-1-carboxylate and the cocrystal 4-amino-5-chloro-2,6-dimethylpyrimidine-ferrocene-1-carboxylic acid (1/1).

In the salt trimethoprimium ferrocenecarboxylate [systematic name: 2,4-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidin-1-ium ferrocene-1-carboxylate], (C14H19N4O3)[Fe(C5H5)(C6H4O2)], (I), of the antibacterial compound trimethoprim, the carboxylate group interacts with the protonated aminopyrimidine group of trimethoprim via two N-H...O hydrogen bonds, generating a robust R22(8) ring motif (heterosynthon). However, in the cocrystal 4-amino-5-chloro-2,6-dimethylpyrimidine-ferrocene-1-carboxylic acid (1/1), [Fe(C5H5)(C6H5O2)]·C6H8ClN3, (II), the carboxyl-aminopyrimidine interaction [R22(8) motif] is absent. The carboxyl group interacts with the pyrimidine ring via a single O-H...N hydrogen bond. The pyrimidine rings, however, form base pairs via a pair of N-H...N hydrogen bonds, generating an R22(8) supramolecular homosynthon. In salt (I), the unsubstituted cyclopentadienyl ring is disordered over two positions, with a refined site-occupation ratio of 0.573 (10):0.427 (10). In this study, the two five-membered cyclopentadienyl (Cp) rings of ferrocene are in a staggered conformation, as is evident from the C...Cg...Cg...C pseudo-torsion angles, which are in the range 36.13-37.53° for (I) and 22.58-23.46° for (II). Regarding the Cp ring of the minor component in salt (I), the geometry of the ferrocene ring is in an eclipsed conformation, as is evident from the C...Cg...Cg...C pseudo-torsion angles, which are in the range 79.26-80.94°. Both crystal structures are further stabilized by weak π-π interactions.

Cyclopalladation of ferrocene tertiary amines: Experimental, theoretical, and reactive studies toward Suzuki-Miyaura cross-coupling reaction

The ferrocene tertiary amines of general formula [(η5C5H5)Fe(η5C5H4)CH2N(CH3)CH2C(R)CHC6H5, RH (3a) and RCH3 (3b)] were conveniently prepared from the corresponding ferrocenylimines [(η5C5H5)Fe(η5C5H4)CH2NCHC(R)CHC6H5, RH (1a) and RCH3 (1b)] in two steps. Metalation of 3a, 3b with Li2PdCl4 and CH3COONa, followed by treatment with PPh3, gave the ortho palladium (II) complexes Pd{[(η5C5H5)Fe(η5C5H3)CH2N(CH3)CH2CHCHC6H5]}ClPPh3 (5a) and Pd{[(η5C5H5)Fe(η5C5H3)CH2N(CH3)CH2C(CH3)CHC6H5]}ClPPh3 (5b), respectively. However, Palladation of ferrocenylimines 1a and 1b afforded the heteroannular palladium (II) complexes. This protocol proved that the isomerism around the CN moiety might indicate that the palladium entered into the lower ferrocene ring, giving the heteroannular palladium (II) complexes. Additionally, theoretical studies indicated that the CH bond in the substituted ferrocene ring for the ligands 3a and 3b was prior to metalation. As for the catalyst, the palladacycles showed high efficiency in Suzuki-Miyaura cross-coupling reaction using low catalyst loading 0.1 mol%.

Presenting a ferrocene Ferris wheel

By fusing ferrocene molecules together, a research team has prepared new iron-based macrocycles that resemble a Ferris wheel. Ferrocene linear chains and macrocycles have been made before, but they contained spacer groups separating the metallocene units, which don’t allow much interaction between the iron atoms. Michael S. Inkpen, Nicholas J. Long, and Tim Albrecht of Imperial College London and their colleagues have now made examples in which five to nine ferrocene units are fused by direct cyclopentadienyl C–C linkages. These redox-active ferrous/ferric nanorings have substantial charge delocalization and are more stable than previous ferrocene-based macromolecules, with the six-membered version representing an organometallic analog of benzene (Nat. Chem. 2016, DOI: 10.1038/nchem.2553). The researchers made the ferrocene rings via copper-mediated Ullmann coupling reactions of dilute solutions of iodinated ferrocene or linear ferrocene oligomers. The internal cavity of the molecules provides opportuniti...

Density functional theory investigations on binding and spectral features of complexes of ferrocenyl derivatives with cucurbit [7]uril

Host–guest interactions between ferrocene (Fc) and its derivatives containing electron donating and electron withdrawing substituents viz., 2-ferrocenyl benzoxazole (FcOz) or 2-ferrocenyl benzothiazole (FcTz) and cucurbit [7]uril (CB[7]) host have been analyzed employing density functional theory incorporating various exchange correlation functionals. Electronic structures of these complexes reveal the encapsulation of ferrocene ring within the CB[7] container with the benzoxazole or benzothiazole substituent interacting with host portals via C=O⋯H interactions. Further the M06-2X based calculations show stronger host–guest binding compared to those predicted from wB97x, PBE0 and B3LYP functionals. The contributions of electrostatic and other dispersive interactions toward such binding have been assessed. The 1H NMR chemical shifts from the gauge independent atomic orbital (GIAO) theory using different functionals demonstrated that subtle changes in δH signals of cyclopentadienyl protons and those encapsulated in the CB[7] cavity in water are better reproduced by the wB97x functional. Calculated infrared spectra revealed that the complexation is accompanied by frequency shift of the C–N stretching in benzoxazole or benzothiazole ring, and the characteristic methine and carbonyl vibrations of CB[7]. The direction of such frequency shifts has been explained from the natural bond orbital analyses and ‘Quantum Theory of Atoms in Molecules’ approach. Time dependent density functional theory calculations further demonstrated that substitution on the cyclopentadienyl ring brings a bathochromic shift of the ~200nm band in the electronic spectra for the unsubstituted Fc-CB[7] complex. Furthermore, FcOz@CB[7] or FcTz@CB[7] complexes exhibit low energy absorption band at ~480nm in its electronic spectra as a result of intramolecular charge transfer from 3d orbitals of Fe to π* orbitals of benzothiazole or benzoxazole, unlike that in the Fc@CB[7] complex.

Unusual metal-ligand charge transfer in ferrocene functionalized μ3-O iron carboxylates observed with Mössbauer spectroscopy

Temperature dependent Mössbauer studies of two ferrocenecarboxylate functionalized {Fe3O} complexes in solid state are reported. It was found that conjugation of ferrocene ring orbitals with the π orbitals of the adjacent carboxylic group promotes a shift of electron density from the ferrocene FeII ion to the cyclopentadienide rings with π-orbital character giving rise to a new type of mixed-valence compound.

Synthesis and Conformational Study of Bioconjugates Derived from 1‐Acetyl‐1′‐aminoferrocene and α‐Amino Acids

Abstract1,1′‐Disubstituted ferrocene conjugates present useful and efficient bioorganometallic constraint design to reduce the conformational flexibility of small peptides. In this study we present the first systematic conformational analysis of nonsymmetric ferrocene peptidomimetics (Boc‐AA‐NH‐Fn‐COMe; Boc = tert‐butoxycarbonyl; AA = Gly, L‐Ala, L‐Val; Fn = 1,1′‐ferrocenylene) and their monosubstituted analogues (Boc‐AA‐NH‐Fc; Fc = ferrocenyl; AA = Gly, L‐Ala, L‐Val). The spectroscopic data (IR, NMR and CD) were corroborated by DFT calculations and indicated the engagement of the NH group closest to the ferrocene unit in intrachain hydrogen bonds. This medium‐strength bond is not disrupted by the introduction of a hydrogen‐bonding acceptor on the other ferrocene ring, but rather is accompanied by an additional interchain hydrogen bond, which causes the restricted rotation of ferrocene rings and gives rise to a chiral arrangement of the ferrocene core in a P helical manner.

Ferrocenyl-amidinium compound as building block for aqueous proton-coupled electron transfer studies

A water-soluble amidinium-appended ferrocene moiety is characterized in which the amidinium functionality is fused directly to the ferrocene ring (Fcam1). This species is designed to form a building block for aqueous proton-coupled electron transfer in which proton transfer occurs to the bulk and electron transfer occurs to a chemical oxidant. pH-Dependent absorption spectroscopy and electrochemistry show that the electrochemical potential is directly linked to the protonation state of the amidinium. A thermodynamic square scheme is constructed for Fcam1. The square scheme serves as motivation and provides direction for incorporating this species into a covalently-bound system for the study of proton-coupled electron transfer.

1,1′-Bis-(n-benzotriazolyl) ferrocenecarboxamide: Precursor for synthesis of 1,1′-bis-ferrocenoyl esters and thioesters

A microwave assisted synthesis methodology has been presented for the preparation of the bisferrocenoyl esters and thioesters. 1,1′-bis-ferrocenedicarboxylic acid was derivatized using direct 1H-benzotriazole/SOCl2 methodology to prepare 1,1′-bis-(N-benzotriazolyl) ferrocenecarboxamide, 1, as a convenient tool for the functionalization of ferrocene ring. The starting material, 1, was reacted with alcohols and thiols in mild conditions to prepare bisferrocenoyl esters and thioesters in high purity and in moderate yields. The solid state structure of 2b has also been determined by X-ray crystallography. H-bond interactions and plane geometries between ring systems have been discussed.

Synthesis of planar chiral ferrocenyl cyclopentadienyl chelate ligand precursors

Two families of planar chiral ferrocenyl cyclopentadienyl chelate ligands for use in ansa-half sandwich metallocene complexes of catalytically active transition metals are described. The first family was derived in 4–5 steps from an enzymatic resolution of 1-iodo-2-(methylalcohol)ferrocene and possesses a cyclopentadiene derivative [Cp(H)=1-indenyl, 2-indenyl or Ph4Cp(H)] directly attached to the ferrocene ring with an adjacent vicinal tether CH2Z donor group (Z=OH, OMe, NHMe, NMe2 or PPh2). The second family was derived from a chiral auxiliary approach and has the donor group (Z=PPh2 or NMe2) attached directly to the ferrocene ring with an adjacent tether vicinal CH2Cp(H) group [Cp(H)=Cp(H), fluorenyl, 1-indenyl, Me4Cp(H) or Ph4Cp(H)].

3-(Ferrocen-1-ylcarbonyl)-1-methyl-4-(4-methylphenyl)spiro[pyrrolidine-2,11′-indeno[1,2-b]quinoxaline

In the title compound, [Fe(C5H5)(C32H26N3O)], the pyrrolidine ring adopts a twist conformation. The indeno–quinoxaline ring system [86.44 (5)°], the methyl­phenyl ring [86.06 (7)°] and the ferrocene rings [82.00 (7) and 83.95 (9)°] are almost perpendicular to the pyrrolidine ring. The two cyclopentadienyl rings adopt an eclipsed conformation. The crystal structure features C—H⋯N inter­actions.

Synthesis, cytotoxicity and antimalarial activity of ferrocenyl amides of 4-aminoquinolines

Series of 4-aminoquinolines bearing an amino side chain linked to the ferrocene moiety through an amide bond were synthesized and evaluated for their antimalarial activity against both chloroquine-sensitive (D10, CQ-S) and chloroquine-resistant (Dd2, CQ-R) strains of Plasmodium falciparum. They were also tested for cytotoxicity against Chinese Hamster Ovarian (CHO) cells. Amide 12 featuring propyl side chain linked to the ferrocene ring was the most active of all tested compounds. With an IC50 value of 0.08 microg/mL, this amide showed 1.5-fold higher activity than chloroquine diphosphate (IC50 = 0.12 microg/mL) against the resistant strain, with a selectivity index of 550 indicating its high selectivity towards the parasite. Derivatives which were equipotent against both strains also showed up to ten-fold increase in activity compared to primaquine.

N-ferrocenoyl benzotriazole: A convenient tool for the synthesis of ferrocenoyl esters

A new synthesis methodology has been presented for the preparation of the ferrocenoyl esters. Ferrocene carboxylic acid was derivatized using direct 1 H-benzotriazole/SOCl 2 methodology to prepare N-ferrocenoyl benzotriazole as a convenient tool for the functionalization of ferrocene ring. N-ferrocenoyl benzotriazole was reacted with alcohols in mild conditions to prepare ferrocenoyl esters in high purity and in good yield. The solid state structure of benzyl-1-ferrocenoate, 2f, has also been determined by X-ray crystallography. In the crystal structure, intermolecular C–H···O hydrogen bonds link the molecules into a two-dimensional network. The π···π contacts between the cyclopentadiene rings and cyclopentadiene and phenyl rings, [centroid–centroid distances = 3.296(1) and 3.750(1) Å] may further stabilize the structure. Two weak C–H···π interactions are also found.

Synthesis and structure of heteroannular cyclopalladated chiral ferrocenylimines: theoretical interpretation of the cyclopalladated complexes based on density functional calculations

The reaction of novel chiral ferrocenylimines (η5-C5H5)Fe(η5-C5H4)–CH(CH3)–NCH–2-R (R = furyl (3) and pyridyl (6)) with Li2PdCl4 and anhydrous CH3COONa in dry MeOH produced heteroannular cyclopalladated {Pd[(η5-C5H4)Fe(η5-C5H4)–CH(CH3)–NCH–2-R](μ-Cl)}2 (R = furyl) (4) and Pd(N∧N) [(η5-C5H5)Fe(η5-C5H4)–CH(CH3)–NCH–2-R]PdCl2 (R = pyridyl) (7) complexes, respectively. The Pd(μ-Cl)2Pd bridge was cleaved by triphenylphosphine to give monomeric derivative 5. The structures of the monomeric and dimeric palladium complexes were confirmed by elemental analyses, IR, 1D and 2D NMR spectra, and X-ray diffraction. All the results led to the conclusion that the palladium atom is bound to the unsubstituted ferrocenyl moiety in compounds 4 and 5, while for compound 7, the palladium atom is coordinated by two nitrogen atoms. The 1H NMR spectra showed that cyclopalladated complex 4 may exist as two diastereoisomers, with a new axial chirality being induced by the rotation of the two ferrocene rings. To explain these experimental results, detailed DFT computational studies have been carried out.

Microwave assisted synthesis of ferrocene amides

A new microwave assisted synthesis methodology has been presented for the preparation of the ferrocene amides. Ferrocene carboxylic acid was derivatised using direct 1 H-Benzotriazole/SOCl 2 methodolgy to prepare N-ferrocenoyl benzotriazole as a new starting material for the functionalization of ferrocene ring. N-ferrocenoyl benzotriazole was reacted with mono- and di-amines under microwave irradiation to prepare ferrocene mono- and di-amides in high purity and in good yield.

4-[(E)-2-Ferrocenylethenyl]-1,8-naphthalic anhydride

In the structure of the title compound, [Fe(C5H5)(C19H11O3)], the plane of the substituted ferrocene ring is tilted by 14.17 (6)° with respect to the mean plane through the naphthalene ring system. In the crystal structure, centrosymmetric dimers are formed through π–π inter­actions [centroid–centroid distance = 3.624 (2) Å] between the substituted ferrocene ring and the three fused rings of the naphthalic anhydride unit. Pairs of dimers are held together by further naphthalene–naphthalene π–π interactions [distance between parallel mean planes 3.45 (3) Å]. Each dimer inter­acts with four neighbouring dimers in a herringbone fashion through C—H⋯π inter­actions, so forming a two-dimensional sheet-like structure.

Synthesis of Ferrocene-containing Polyacetylenes by Click Chemistry

Ferrocene-containing polyacetylenes are synthesized in good yields by Cu-catalyzed click reactions of azido moieties of poly[(6-chloro-1-phenyl-1-hexyne)-co-(6-azido-1-phenyl-1-hexyne)] and poly{1-[(4-azidohexyloxy)phenyl]-2-phenylacetylene} with ethynylferrocene. All the organometallic polymers are completely soluble in common organic solvents such as chloroform, THF and toluene. Spectroscopic analyses reveal that all the azido functional groups have cyclized with ethynylferrocene. With the incorporation of ferrocene rings into the polyacetylene structure, the resulting polymers show enhanced thermal stability and redox activity.