Disubstituted Ferrocene Research Articles

Synthesis and crystal structures of disubstituted ferrocenes carrying bromo and N-heteroaryl substituents

Noncovalent interactions in crystal packing play significant roles in the formation of extended network structures. Thus, this study aims to investigate the influence of noncovalent bonds, particularly halogen bonds, on the crystal packing of ferrocene derivatives. For this purpose, disubstituted ferrocene derivatives carrying both bromo and N-heteroaryl substituents, 1‑bromo-1ʹ-(Het)ferrocene [Het = 5-pyrimidyl (1), 2-pyridyl (2), and 4-pyridyl (3)] and 1‑bromo-2-(Het)ferrocene [Het = 5-pyrimidyl (4) and 4-pyridyl (6)], were synthesized. Here, we discuss a comparison of their molecular and crystal structures, with those of a related compound, 1‑bromo-2-(2-pyridyl)ferrocene (5). Although the crystal packings of 1–5 are classified into quasi-one-dimensional chain structures, their intermolecular interactions are different. Compounds 1–3 exhibit Br⋅⋅⋅cyclopentadienyl halogen bonds to form extended structures. In contrast, 4 shows the π–π stacking interactions between the pyrimidine rings of adjacent molecules, and 5 exhibits the Br⋅⋅⋅N halogen bonds between adjacent molecules. The crystal structures contained chiral molecules of opposing handedness.

NIR-absorbing TCBD and cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD bridged derivatives of 1,1′-bis(N,N-dimethylaniline)-substituted ferrocene

Symmetrical and unsymmetrical donor-acceptor (D–A) based chromophores were designed and synthesized by the Pd–catalyzed Sonogashira cross–coupling reaction of 1,1′-diiodoferrocene with (4-N,N-dimethylaminophenyl)ethyne followed by [2+2] cycloaddition-retroelectrocyclization reaction with tetracyanoethylene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ). Ferrocene was used as a central donor unit and 4-(N,N-dimethylamino)phenyl group as the end-capping donor. Herein, we report the cycloaddition-retrocyclization reaction of TCNE/TCNQ groups on the disubstituted ferrocene containing more than one triple bond to get disubstituted tetracyanobutadiene (TCBD) and cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD products. The effect of the conjugation length and different π–acceptor linkers were investigated by photophysical, redox and computational studies. The redox study reveals multiple oxidation waves corresponding to donor moieties (ferrocene and 4-(N,N-dimethylamino)phenyl group) and reduction waves corresponding to acceptor units (TCBD / cyclohexa-2,5- diene-1,4-diylidene-expanded TCBD). The thermogravimetric analysis data shows that the compounds exhibit high thermal stability. The computational studies reveal HOMO-LUMO gaps consistent with the experimentally obtained data.

Mechanochemical synthesis and antiproliferative activity of novel ferrocene quinoline/quinolone hybrids

The synthesis of novel 1,1′‐disubstituted ferrocene conjugates appended with N‐1 and O‐4 alkylated quinolone and quinoline was reported. The target compounds were synthesized employing a liquid‐assisted grinding (LAG) mechanochemical method in copper‐catalyzed azide‐alkyne cycloaddition (CuAAC) to obtain ferrocene−quinoline/quinolone hybrids (5a–5d, 6a–6d, 7a, 7b, 8a, and 8b) in higher yields and shorter reaction time compared to a conventional method, thus proving superiority of mechanochemistry versus conventional synthesis. Bis‐quinoline and bis‐quinolone ferrocene derivatives were evaluated for their antiproliferative effects on five selected tumor and two non‐tumor cell lines. Bis‐6‐methylquinolone–ferrocene conjugate 8b showed the best antiproliferative effect on T‐cell lymphoma (HuT78) cells (IC50 = 14.8 μM) and no cytotoxicity on both non‐tumor MDCK1 and BJ cells. Results obtained after mitochondrial membrane potential (∆Ψm) measurement using flow cytometry showed that compound 8b caused accumulation of HuT78 cells in subG0/G1 phase, disturbance of mitochondrial membrane potential, and apoptosis. The structure of the quinolone and ferrocene hybrid 8b can be further optimized to obtain candidates with better inhibitory effects on HuT78 cells.

Separation of planar chiral ferrocenes by capillary electrokinetic chromatography and liquid chromatography

Capillary electrokinetic chromatography (CEKC) and liquid chromatography (LC) methods were explored for the enantiomeric separation of six unsymmetrically disubstituted ferrocene derivatives. In normal-phase mode liquid chromatography, the use of n-heptane, ethanol or isopropanol with 1% n-butylamine as mobile phase on six polysaccharide-based columns, allowed to fully separate the enantiomers of three compounds out of the six (i.e 7-chloro-N-(2-((dimethylamino)methyl)ferrocenyl)quinolin-4-amine (ferroquine) (compound 1), 1-[(1S)-(1-Aminoethyl)]-2-(diphenylphosphino)ferrocene (compound 5) and 1-[(1R)-1-(Dicyclohexylphosphino)ethyl]-2-(diphenylphosphino)ferrocene (compound 6). Among the columns used, the Lux i-Cellulose-5 was the most effective. In capillary electrokinetic chromatography, a phosphate buffer of 25 mM concentration and pH equal to 2.5 was chosen as background electrolyte, leading to cationic ferrocene derivatives. The addition of neutral cyclodextrins was undertaken first and native β- or γ-cyclodextrins were found to resolve the enantiomers of two derivatives. Then, 15 mM of anionic cyclodextrins were added to the background electrolyte. The use of SBE-β-CD, S-β-CD or S-γ-CD have allowed the separation of the enantiomers for most of the ferrocene derivatives studied with high resolution values in short migration time. For instance, for 1-(R)-2-(Diphenylphosphino)ethyldi-tert-butylphosphine ferrocene (compound 2), the migration times were less than 2 minutes and the resolution value was equal to 3.52 in short-end mode with 15 mM S-β-CD, at 25 kV and 25°C. Finally, a dual cyclodextrins system was tested using 15 mM of S-β-CD plus 15 mM HP-γ-CD in the phosphate buffer. This system allowed the improved separation of two ferrocene derivatives with an unusual resolution value equal to 41.5 in long-end mode. Overall, CEKC showed better enantioseparating power of the six chiral ferrocenes studied than liquid chromatography.

Synthesis and crystal structure of [(Sp )-(2-phenyl-ferrocen-yl)meth-yl]tri-methyl-ammonium iodide di-chloro-methane monosolvate.

As a follow-up to our research on the chemistry of disubstituted ferrocene derivatives, the synthesis and the structure of the title compound, [Fe(C5H5)(C15H19N)]I·CH2Cl2, is described. The cation mol-ecule is built up from a ferrocene disubstituted by a tri-methyl-ammonium methyl group and a phenyl ring. The asymmetric unit contains the iodide to equilibrate the charge and a disordered di-chloro-methane solvate. The disordered model results from a roughly statistical exchange (0.6/0.4) between one Cl and one H. The packing of the structure is stabilized by weak C-H⋯X (X = I, Cl), C-H⋯π(Cp) and C-Cl⋯π(phen-yl) inter-actions, building a three-dimensional network. The cation has planar chirality with Sp (Fc) absolute configuration. The structure of the title compound is compared with related disubstituted (tri-meth-ylammonio)-methyl ferrocenes.

Synthesis and crystallographic studies of 2-(di-phenyl-phosphino-thio-yl)-2-(3-oxobut-1-en-yl)ferrocene.

As a follow-up to our research on the chemistry of disubstituted ferrocene derivatives, the synthesis and the structure of the title compound, 2-(di-phenyl-phosphino-thio-yl)-2-(3-oxobut-1-en-yl)ferrocene, [Fe(C5H5)(C21H18OPS)], are described. The mol-ecule is built up from a ferrocene unit disubstituted by an S-protected di-phenyl-phosphine group and by a methyl-vinyl-ketone chain. The crystal structure features weak C-H⋯O and C-H⋯S inter-actions, which build a two-dimensional network. This structure is compared to that of the related disubstituted di-phenyl-phosphino ferrocene.

On the N‐Arylation of Acetamide Using 2‐, 3‐ and 1’‐Substituted Iodoferrocenes**

AbstractVarious 2‐, 3‐ and 1’‐substituted iodoferrocenes were reacted with acetamide in the presence of copper(I) iodide (1 equiv), N,N’‐dimethylethylenediamine (1 equiv), tripotassium phosphate (2 equiv) in dioxane at 90 °C for 14 h, and allowed a large range of original 1,2‐, 1,3‐ and 1,1’‐disubstituted ferrocenes to be obtained. The results were compared as a function of the substituent and its position on the ring. DFT calculations revealed higher activation barrier for the oxidative addition in the ferrocene series when compared with classical planar aromatics. Structure‐property relationships were applied to rationalize the reactivity of the different iodoferrocenes.

Benchmarking DFT Calculations of 1H and 13C Chemical Shifts in Monosubstituted Ferrocenes

AbstractDifferent density functional theory (DFT) approaches were tested for the computation of 1H and 13C nuclear magnetic resonance (NMR) chemical shifts in monosubstituted ferrocenes. The results were evaluated against experimental values. Generally, the conductor‐like polarizable continuum model and cc‐pVTZ basis set are recommended. The geometries providing the best accuracies are B3LYP‐optimized for 1H and M06‐L‐optimized for 13C. Functional rankings at these geometries are: TPSSh > M06‐L > CAM‐B3LYP > B3LYP > PBE0 > M06 (the first one is the most accurate) for 1H NMR computations and M06 > M06‐L > PBE0 > TPSSh > B3LYP > CAM‐B3LYP for 13C. The most accurate functionals have root‐mean‐square deviations of 0.08 ppm (1H, TPSSh) and 3.97 ppm (13C, M06) and showed similar accuracy for a set of disubstituted ferrocenes and decamethylferrocene. The utilization of Jensen's pcSseg‐2 basis set improves the results for 1H but worsens the results for 13C. The linear scaling is generally not recommended. The errors can be minimized using an appropriate method for a given nucleus, so the DFT‐assisted signal assignment is possible for substituted ferrocenes.

Novel π‐Extended Quinazoline‐Ferrocene Conjugates: Synthesis, Structure, and Redox Behavior

Novel ferrocene conjugates of tricyclic quinazoline derivatives are prepared by condensation of active C‐6 methylene groups of mackinazolinones with ferrocenecarbaldehyde. Following this route the conjugated parent alkaloid as well as derivatives with nitro, amino, and alkanoylamino groups at C‐2 were attached at the ferrocene moiety, thereby significantly extending the delocalized π system. In addition, the parent compound was subjected to the reaction with ferrocene‐1,1'‐dicarbaldehyde, giving rise to the symmetrical and unsymmetrical double condensation products – 1,1'‐disubstituted ferrocene derivatives, which bear two alkaloid substituents. Some of the compounds obtained were subjected to X‐ray crystallographic analyses. The influence of the substituents at C‐2 through the extended conjugated π system on the iron atom is reflected by results of cyclovoltammetric measurements.

Synthesis, crystal structures and electrochemical properties of ferrocenyl imidazole derivatives

Six ferrocenyl imidazole derivatives substituted with -Cl, -NO2 and -CH3 on the 2-position of the 1H-imidazole ring have been synthesized. Of the six compounds, the di-substituted ferrocenes, i.e. compounds 4 (1,1′-ferrocenylmethyl(2-chloroimidazole)), 5 (1,1′-ferrocenyl(2-nitroimidazole)), and 6 (1,1′-ferrocenylmethyl(2-methylimidazole)) are reported for the first time. The structure-property relationships of compounds 4, 5 and 6 were investigated by means of UV-visible, FTIR, 1H-NMR, 13C-NMR spectroscopy and electrochemical studies. UV-visible analysis in acetonitrile showed that the π -π* band of compounds 2 (1-ferrocenylmethyl(2-nitroimidazole)) and 5 appeared at longer wavelength compared to 1 (1-ferrocenylmethyl(2-chloroimidazole)), 3 (1-ferrocenylmethyl(2-methylimidazole)), 4 and 6. This phenomenon is due to the different electronics around the imidazole moieties. In cyclic voltammetry analysis, all compounds exhibited a quasi-reversible redox wave for the ferrocenyl and imidazole moieties. Density functional theoretical (DFT) calculations with the B3LYP/6-311+G(d) basis set were performed on compounds 1–6, and the calculated HUMO-LUMO band gap energies correlated with those obtained from electrochemical and spectroscopic data. The X-ray crystallographic analysis highlighted the effect of electron-withdrawing and electron-donating substituents on the conformation of the cyclopentadienyl rings attached to the ferrocenyl moiety.

Chirality Induction in Bioorganometallic Conjugates

Considerable attention has been given to the research field of bioorganometallic chemistry, which is a hybrid chemistry field between biology and organometallic chemistry. The introduction of biomolecules, which have hydrogen bonding sites and chiral centers, into organometallic compounds is a promising strategy to construct chirality-organized bioorganometallic conjugates. This feature paper sketches an outline of induction of helical chirality into bioorganometallic conjugates by the control of a torsional twist of the organometallic moiety. Topics covered included control of the helical chirality of 1,n′-disubstituted ferrocene moieties in ferrocene-dipeptide conjugates, and the chirality induction of the Au(I)–Au(I) axis in the dinuclear organogold(I)-uracil conjugates.

Synthesis and Light-Induced Actuation of Photo-Labile 2-Pyridyl-1,2,3-Triazole Ru(bis-bipyridyl) Appended Ferrocene Rotors.

To realise useful control over molecular motion in the future an extensive toolbox of both actionable molecules and stimuli-responsive units must be developed. Previously, our laboratory has reported 1,1′-disubstituted ferrocene (Fc) rotor units which assume a contracted/π-stacked conformation until complexation of cationic metal ions causes rotation about the Ferrocene (Fc) molecular ‘ball-bearing’. Herein, we explore the potential of using the photochemical ejection of [Ru(2,2′-bipyridyl)2]2+ units as a stimulus for the rotational contraction of new ferrocene rotor units. Fc rotors with both ‘regular’ and ‘inverse’ 2-pyridyl-1,2,3-triazole binding pockets and their corresponding [Ru(2,2′-bipyridyl)2]2+ complexes were synthesised. The rotors and complexes were characterised using nuclear magnetic resonance (NMR) and ultraviolet (UV)-visible spectroscopies, Electro-Spray Ionisation Mass Spectrometry (ESI–MS), and electrochemistry. The 1,1′-disubstituted Fc ligands were shown to π-stack both in solution and solid state. Density Functional Theory (DFT) calculations (CAM-B3LYP/6-31G(d)) support the notion that complexation to [Ru(2,2′-bipyridyl)2]2+ caused a rotation from the syn- to the anti-conformation. Upon photo-irradiation with UV light (254 nm), photo-ejection of the [Ru(2,2′-bipyridyl)2(CH3CN)2]2+ units in acetonitrile was observed. The re-complexation of the [Ru(2,2′-bipyridyl)2]2+ units could be achieved using acetone as the reaction solvent. However, the process was exceedingly slowly. Additionally, the Fc ligands slowly decomposed when exposed to UV irradiation meaning that only one extension and contraction cycle could be completed.

Metallosupramolecular Architectures Formed with Ferrocene-Linked Bis-Bidentate Ligands: Synthesis, Structures, and Electrochemical Studies.

The self-assembly of ligands of different geometries with metal ions gives rise to metallosupramolecular architectures of differing structural types. The rotational flexibility of ferrocene allows for conformational diversity, and, as such, self-assembly processes with 1,1'-disubstituted ferrocene ligands could lead to a variety of interesting architectures. Herein, we report a small family of three bis-bidentate 1,1'-disubstituted ferrocene ligands, functionalized with either 2,2'-bipyridine or 2-pyridyl-1,2,3-triazole chelating units. The self-assembly of these ligands with the (usually) four-coordinate, diamagnetic metal ions Cu(I), Ag(I), and Pd(II) was examined using a range of techniques including 1H and DOSY NMR spectroscopies, high-resolution electrospray ionization mass spectrometry, X-ray crystallography, and density functional theory calculations. Additionally, the electrochemical properties of these redox-active metallosupramolecular assemblies were examined using cyclic voltammetry and differential pulse voltammetry. The copper(I) complexes of the 1,1'-disubstituted ferrocene ligands were found to be coordination polymers, while the silver(I) and palladium(II) complexes formed discrete [1 + 1] or [2 + 2] metallomacrocyclic architectures.

Crystal structure of {[1'-(di-phenyl-phosphino)ferrocen-yl]meth-yl}di-methyl-ammonium chloride monohydrate.

Individual ions and the solvating water mol-ecule constituting the structure of the title compound, [Fe(C8H13N)(C17H14P)]Cl·H2O, assemble into dimeric units located around crystallographic inversion centers via N-H⋯Cl and O-H⋯Cl hydrogen bonds. These discrete fragments are further inter-connected into chains by C-H⋯O inter-actions. The disubstituted ferrocene core in the {[1'-(di-phenyl-phosphino)ferrocen-yl]meth-yl}di-methyl-ammonium cation has an approximate synclinal eclipsed conformation and is tilted by 3.40 (11)°.

Deltoid versus Rhomboid: Controlling the Shape of Bis-ferrocene Macrocycles by the Bulkiness of the Substituents

Precise structural control of heteroannularly disubstituted ferrocene (Fc) structures is very challenging as the high rotational mobility of the Fc unit allows a large conformational diversity. Herein we present the syntheses, characterization, and electrochemical investigation of two complementary bis-ferrocene macrocycles, built up via Sonogashira cross coupling and intramolecular ring-closing reaction. While the X-ray structure of 1,2-ethynylbenzene bridged bis-ferrocene complex 1 shows a deltoidal conformation, a stretched oriented rhomboidal bis-ferrocene metallacycle 2 is formed when the peripheral benzene rings are decorated with bulky tert-butylsulfanyl groups. VT-NMR spectroscopy is used to assign the rotation of the embedded Fc units in rhomboid 2. Moreover, cyclic voltammetry (CV) of deltoid 1 and rhomboid 2 indicate that electronic communication between both ferrocenyl groups can be neglected, while the electrostatic through space coupling is significant.

Oligomeric ferrocene rings.

Cyclic oligomers comprising strongly interacting redox-active monomer units represent an unknown, yet highly desirable class of nanoscale materials. Here we describe the synthesis and properties of the first family of molecules belonging to this compound category-differently sized rings comprising only 1,1'-disubstituted ferrocene units (cyclo[n], n = 5-7, 9). Due to the close proximity and connectivity of centres (covalent Cp-Cp linkages; Cp = cyclopentadienyl) solution voltammograms exhibit well-resolved, separated 1e(-) waves. Theoretical interrogations into correlations based on ring size and charge state are facilitated using values of the equilibrium potentials of these transitions, as well as their relative spacing. As the interaction free energies between the redox centres scale linearly with overall ring charge and in conjunction with fast intramolecular electron transfer (∼10(7) s(-1)), these molecules can be considered as uniformly charged nanorings (diameter ∼1-2 nm).

N]Ferrocenophanes (n = 2, 3) with Nitrogen and Phosphorus in Bridging Positions.

The in situ prepared dilithio derivative of the known species 1-bromo-1'-(trimethylsilylamino)ferrocene (1) reacted with tBuPCl2 to form the first example of a [2]ferrocenophane ([2]FCP) bridged by nitrogen and phosphorus (2). Sulfurization of 2 followed by column chromatography on silica gel gave the expected [2]FCP with a tBu(S)PN(SiMe3) bridging moiety (3a) and its desilylated counterpart with a tBu(S)PNH bridging moiety (3b). The molecular structure of 3b was determined by single-crystal X-ray analysis (α = 18.40(11)°). Using a common synthetic methodology, two new 1-amino-1'-bromoferrocene derivatives were prepared, one species with a PhCH2 (6a) and another with a tBuCH2 group (6b) on nitrogen. Dilithiation of 6a followed by addition of tBuPCl2 gave a mixture of three constitutional isomers: the targeted [2]FCP (7a), the 1,1'-disubstituted ferrocene derivative (tBuPH)(PhCH═N)fc (8a), and the [3]FCP bridged by a (NH)(CHPh)PtBu moiety (9a). NMR spectroscopy revealed that 8a is the precursor for 9a. The salt-metathesis reaction of the dilithio derivative of 6b with tBuPCl2 exclusively gave the 1,1'-disubstituted ferrocene derivative (tBuPH)(tBuCH═N)fc (8b), which does not isomerize to the respective [3]FCP. DFT calculations at the M06/6-311+G(d,p) level were used to better rationalize these unexpected results.

Tricyclic Quinazoline Alkaloids Conjugated to Ferrocene: Synthesis, Structure, and Redox Behavior of Ferrocenylmethylene‐Substituted 7H‐Deoxyvasicinones

AbstractThe first organometallic derivatives of tricyclic quinazoline derivatives are prepared by condensation of the active C‐3 methylene group of 7H‐deoxyvasicinones with ferrocenecarbaldehyde. By following this route the conjugated parent alkaloid and derivatives with nitro, amino, as well as some alkanoylamino groups at C‐7 were attached at the ferrocene moiety, thereby significantly extending the π system. In addition, the parent compound was subjected to the reaction by treatment with ferrocene‐1,1′‐dicarbaldehyde, giving rise to the double condensation product, which is only the second case of a 1,1′‐disubstituted ferrocene derivative with two alkaloid substituents. A number of the compounds obtained were subjected to X‐ray crystallographic analyses. In all cases, the substituents adopt a coplanar conformation with the ferrocene cyclopentadienyl ligands. The influence of the substituents at C‐7 through the extended conjugated π system on the iron atom is reflected by results of cyclic voltammetric measurements as well as by DFT calculations.

Crystal structure of 1,1'-bis-(2-meth-oxy-carbonyl-2-methyl-prop-yl)ferrocene.

The Fe atom in the title ferrocene derivative, [Fe(C11H15O2)2], is situated on an inversion centre. As a result of the point-group symmetry -1 of the mol­ecule, the ferrocene moiety adopts a staggered conformation. The average Fe—C(Cp) bond length (Cp is cyclo­penta­dien­yl) is 2.045 (4) Å, in agreement with that of other disubstituted ferrocenes. The Fe—C bond length involving the substituted C atom is slightly longer [2.0521 (17) Å] than the remaining Fe—C bond lengths caused by the inductive effect of the methyl­ene group on the Cp ring. Apart from van der Waals forces, no significant inter­molecular inter­actions are observed in the crystal packing.

Synthesis, chemical reactivity and electrochemical behaviour of mono- and difluoro metallocenes

We report the synthesis of mono- and 1,1′-difluoro-substituted metallocenes (ferrocene, ruthenocene) and of asymmetrical 1,1′-disubstituted ferrocenes with one substituent being fluorine. Lithiation of metallocenes and subsequent addition of the fluorinating agent NFSI gave the fluorinated metallocenes after optimization of the experimental conditions. All new compounds were comprehensively characterized and the cyclic voltammograms of fluoro- and 1,1′-difluoroferrocene were recorded and compared to other mono- and dihalogenated ferrocenes. Half-wave potentials of +106 mV and +220 mV vs. FcH0/+ were obtained for monofluorinated species and difluorinated ferrocene, respectively. Both values are remarkably low compared to the other halogenated ferrocenes (Cl, Br, and I). Finally, 1-bromo-1'-fluoro-ferrocene turns out to be an ideal starting material for further fluoro-substituted ferrocene derivatives.