Monosubstituted thermotropic ferrocenomesogens: an overview 1976–1999

Research in the late 1940s in academic institutions, most notably the University of Hull in the UK, led to the development of liquid crystal display technology in the 1970s, which has subsequently had a large impact throughout the world. The liquid crystal technology is based on simple organic molecules. Since the late 1980s, some liquid crystal scientists have turned their attention to investigating the effect of introducing a metal atom into the systems. This review focuses on the major developments in the field of ferrocenyl‐containing liquid crystals in which the organometallic group is situated in a terminal position with respect to the core of the molecule. Metallomesogens with terminal metal atoms are not very common, since it can be deduced from the theory of organic liquid crystals that bulky terminal groups would not be conducive to the stabilization of liquid crystal phases. Nevertheless, a terminal ferrocenyl group can stabilize a nematic liquid crystal phase and examples of this will be discussed in this review. Copyright © 2001 John Wiley & Sons Ltd.     

The electrochemistry of some ferrocene derivatives: redox potential and substituent effects

Fifteen ferrocene derivatives I–IX (four of which have been prepared for the first time: II, IIIf, V and VIII) have been prepared by Friedel–Crafts acetylation, Claisen condensation, Michael reaction, and ring closure by hydrazine hydrate. The anodic behaviour of these compounds has been studied by cyclic voltammetry at a platinum electrode in an aprotic solvent. All these substituted ferrocenes exhibit a reversible one‐electron oxidation reduction centred at each iron centre, and the effect of substituents on the half‐wave oxidation potential is discussed in terms of their electronic properties. Linear correlations have been observed between these potentials and the Hammett σ_x constant for the substituents. Cyclic voltammetry has been carried out for ferrocene derivatives IIIa, V and IX. Copyright © 2003 John Wiley & Sons, Ltd.     

High Pressure Mössbauer Spectroscopic Studies of Molecular Solids. The Importance of ‘Free’ Space in Molecular Lattices

The behaviour of a number of different molecular solids (both neutral and charged) to applied pressure is discussed. It is shown that the geometry of the molecules, the presence of and number of charges, and the ability of the molecules to alter their shape are all important in the response of their respective lattices to applied pressure. The presence of ‘free’ space in the lattices at room pressure is shown to be a major factor that needs to be taken into account in order to understand their behaviour. This revised version was published online in August 2006 with corrections to the Cover Date.     

Organometallic compounds with biologically active molecules: in vitro antibacterial and antifungal activity of some 1,1′‐(dicarbohydrazono) ferrocenes and their cobalt(II), copper(II), nickel(II) and zinc(II) complexes

Some 1,1′‐(dicarbohydrazono) ferrocenes have been prepared by condensing 1,1′‐diacetylferrocene with either 2‐furoic hydrazide, 2‐thiophenecarboxylic hydrazide or 2‐salicylic hydrazide. All the ligands synthesized were characterized by IR and NMR spectroscopy and elemental analysis data (carbon, hydrogen, nitrogen) and then were used as ligands to react with cobalt(II), copper(II), nickel(II) and zinc(II) metals as chlorides to afford metal complexes having the general formula M(L)Cl₂. IR and electronic spectral data, magnetic moment and elemental analyses were used in the structural investigation of the metal complexes synthesized. The ligands synthesized and their metal(II) complexes have been screened for their in vitro antibacterial activity against Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa, Salmonella typhi, Shigella dysenteriae, Bacillus cereus, Corynebacterium diphtheriae, Staphylococcus aureus and Streptococcus pyogenes bacterial strains and for in vitro antifungal activity against Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani and Candida glabrata. The results of these studies show the metal complexes to be more antibacterial and antifungal than the uncomplexed ligands. However, the potency of all the ligands synthesized and their metal complexes was lower than that of the standard drugs. Copyright © 2005 John Wiley & Sons, Ltd.     

Cyclic and linear poly(ferrocenylene alkylene)s synthesized from addition‐condensation polymerization of ferrocene with aldehydes

Oligo‐ and poly(ferrocenylene alkylene)s, [Fe(C₅H_5‐x)(C₅H_5‐y)CHR]_n (x = y = 1 or x = 2, y = 0; R = alkyl, aryl), were synthesized by Lewis acid‐promoted addition‐condensation polymerization of ferrocene with aldehydes. The reaction of alkyl aldehydes, such as n‐hept‐CHO, EtCHO and nBuCHO, with ferrocene yields a mixture of the cyclic and linear poly(ferrocenylene alkylene)s, while aryl aldehyde, such as C₆F₅CHO, CF₃C₆H₄‐4‐CHO and MeC₆H₄‐4‐CHO, forms the linear polymers exclusively. The linear polymer has terminal ? Fe(C₅H₄)(C₅H₅) and ? CH₂Aryl groups, which are characterized by high resolution mass spectroscopy. Results of addition‐condensation polymerization of ferrocenemethanol catalyzed by BF₃ indicate that the propagating polymer of the above addition‐condensation polymerization contains terminal 1‐hydroxyalkyl‐ferrocenylene group, ? Fe(C₅H₄)[C₅H₄{CH(OH)R}]. The trimer prepared from ferrocene and paraformaldehyde dimethylacetal contains 1,1′‐, 1,2‐, and 1,3‐ferrocenylene units, suggesting that the polymers obtained from alkyl and aryl aldehydes are also composed of these structural units. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3627–3635     

Proton Pump for O2 Reduction Catalyzed by 5,10,15,20‐Tetraphenylporphyrinatocobalt(II)

Oxygen reduction : A polarized water|1,2‐dichloroethane (DCE) interface acts as a proton pump for the [Co(tpp)] (TPP=5,10,15,20‐tetraphenylporphyrinato) catalyzed O₂ reduction by ferrocene (Fc) compounds to produce H₂O₂ (see figure; IT=ion transfer, ET=electron transfer). This system favours the collection of H₂O₂ by extraction immediately after its formation in DCE to the adjacent water phase.

     

Dendritic Molecular Electrochromic Batteries Based on Redox‐Robust Metallocenes

In this Concept article, we summarize and discuss recent reports on dendritic molecular electrochromic batteries. Giant dendrimers containing 3ⁿ⁺² terminal tethers (n=generation number) and terminated by first‐raw late‐transition‐metal metallocenes, permethyl metallocenes and other sandwich complexes were shown to be redox robust. Indeed, they can be oxidized and reduced without decomposition and exist under two stable oxidation states (Fe^III/II, Co^III/II). Thus, a pre‐determined number of electrons (up to 14 000) per dendrimer can be exchanged. Cyclic voltammetry showed a remarkable complete reversibility even up to 14 000 Fe and Co termini in metallodendrimers, indicating fast electron hoping among the redox sites and between dendrimers on a carbon surface covered by arylcarboxylate groups. The dendrimer sizes were measured by dynamic light scattering in solution and by AFM (subsequent to flattening in the condensed state also indicating that these metallodendrimers aggregate to form discrete nanoparticles of dendrimers, as atoms do). The metallodendrimer size varies considerably between the two redox forms due to tether extension of the cationic dendrimers upon oxidation, and a breathing mechanism was shown by atomic and electric force microscopy (AFM and EFM). When the redox potential is very negative, the reduced form is an electron‐reservoir system that can deliver a large number of electrons per dendrimer to various reducible substrates. These systems are thus potential dendritic molecular batteries with two different colors for the two redox forms (electrochromic behavior).     

Synthesis and chemical oxidation of 3-ferrocenylpyrrole and ferrocenyl-substituted triazoles: Iron versus ligand based oxidation

Copper catalyzed [3+2] cycloaddition reactions between ethynylferrocene and benzylazides yields 1-benzyl-4-ferrocenyl-1,2,3-triazoles (2–5). Reaction between phenylacetylene and azidoferrocene yields 1-ferrocenyl-4-phenyl-1,2,3-triazole (6). Anodic electrochemistry of 2–6 suggests reversible oxidation at potentials more positive than ferrocene. Chemical oxidation of 2 and 3-ferrocenylpyrrole (1) with dichlorodicyanoquinone (DDQ) yields the salts [2⁺] [DDQ⁻] and [1⁺] [DDQ⁻], respectively. ⁵⁷Fe Mössbauer spectroscopy reveals the presence of low-spin Fe^II in [1⁺][DDQ⁻] while Fe^II is oxidized to low-spin Fe^III in [2⁺][DDQ⁻]. Magnetization measurements indicate that [1⁺][DDQ⁻] is paramagnetic and cannot be viewed as a simple neutral charge transfer complex reminiscent of the mixed stack diamagnetic [ferrocene]⁰[TCNE]⁰.