Redox-active Ferrocenyl Research Articles

α,ω-Diferrocenyl Cumulene Molecular Wires. Synthesis, Spectroscopy, Structure, and Electrochemistry

Cumulene sp-carbon molecular wires C2 [Fc(Ph)CC(Ph)Fc] up to C7 [Fc(Ph)CCCCCCC(Ph)Fc] endcapped by two electroactive ferrocenyl groups are presented in this report. Synthetically, ferrocenyl cumulenes can be built-up by a modular strategy using C1 synthon ferrocenyl(phenyl)ketone as starting material with various acetylenic/propargylic/homopropargylic C2−C5 reagents, taking into account and exploiting the efficient stabilization of an electron-deficient carbenium center by an adjacent ferrocenyl moiety. With increasing cumulene chain length the reactivity of cumulenes increases considerably, indicating steric protection as the main requirement for bulk stability. Even cumulenes C2, C4, and C6 are conjugated “molecular wires” effecting electronic communication between the terminal ferrocenyl substituents, whereas odd cumulenes C3, C5, and C7 are nonconjugated and electronically decoupled due to their orthogonal terminal π-systems. Electrochemically, separate redox waves can be detected up to a C6 cumulene spacer, but the electronic communication between the endcapping redox-active ferrocenyl substituents decreases with increasing cumulene length.

Ferrocene-bridged Pd–NCN pincer complexes

The meta-diaminoaryl ferrocene Fe[η 5-C 5H 4(NCNH)] 2 [NCNH=1-C 6H 3(CH 2NMe 2) 2-3,5] ( 3) can be synthesised by the reaction of Fe[η 5-C 5H 4(ZnCl)] 2 ( 1) with I–C 6H 3(CH 2NMe 2) 2-3,5 ( 2) in a 1:2 molar ratio in the presence of catalytic amounts of [Pd(PPh 3) 2]. The two meta-dimaminoaryl NCNH pincer units in 3 can be used to assemble multimetallic complexes. Thus, 3 produces on reaction with tBuLi and (Me 2S) 2PdCl 2 trimetallic Fe[η 5-C 5H 4(NCN–4-PdCl)] 2 {NCN=1-C 6H 2(CH 2NMe 2) 2-3,5} ( 6) along with heterobimetallic Fe[η 5-C 5H 4(NCNH)][η 5-C 5H 4(NCN–4-PdCl)] ( 5). Complex 6 contains two bis- ortho-chelated pincer NCN–PdCl units, whereas 5 possesses one bis- ortho-chelated NCN pincer entity and one non-metallated NCNH moiety. Complex 6 is the first example in organometallic chemistry in which two bis- ortho-chelated diaminoaryl palladium units are bridged via the respective para C-atoms spanned by a redox-active ferrocenyl building block.

Self-assembled nanostructures of redox-functionalized terpyridines monitored by optical second-harmonic generation

Adsorption and self-organization of ferrocenyl-functionalized terpyridines on gold substrates were investigated in situ by optical second-harmonic generation (SHG). Film growth of these organometallic compounds could be detected in the submonolayer regime. The SHG data have been compared to the results of ellipsometric measurements and show that monolayer films are formed. Film growth is followed by self-assembly of ordered redox-active ferrocenyl nanostructures.

Multimetallic Complex Composed of Redox-Active Bridging Quinonediimine Ligand

Abstract A π-conjugated quinonediimine ligand possessing two terminal redox-active ferrocenyl groups, N,N′-bis{(4′-ferrocenylcarboxamide)phenyl}-1,4-benzoquinonediimine (Lox), was synthesized. The quinonediimine ligand Lox was reduced to Lred composed of the phenylenediamine moiety on treatment with hydrazine hydrate. The reaction of Lox with the palladium(II) complex 1 bearing the N,N′-bis(2-phenylethyl)-2,6-pyridinedicarboxamide ligand afforded the multimetallic complex 2. Variable temperature 1H NMR studies of 2 indicated the existence of syn and anti isomers, in which the anti isomer is enthalpically more favorable than the syn isomer in CD2Cl2 by 0.9 kcal mol−1, but entropically less favorable by 2.6 cal mol−1 K−1 from the van’t Hoff plot. The redox function of the quinonediimine moiety is modulated by complexation with 1. The complex 2 showed three separate redox waves, which are assignable to the successive one-electron reduction of the quinonediimine moiety and oxidation of the two terminal ferrocenyl groups. Chemical reduction of 2 in CH2Cl2 with [Co(Cp)2] resulted in the appearance of ESR signals with weak 105Pd coupling centered around g = 2.004. The unpaired electron appears to locate mostly on the quinonediimine moiety with some delocalization onto the palladium center.

Effect of Electrolyte Concentration on Interfacial and Bulk Solution Properties of Ferrocenyl Surfactants with Anionic Headgroups

We report the effect of electrolyte concentration on the surface and bulk solution properties of a redox-active ferrocenyl surfactant, Fc(CH2)11SO3-Na+, where Fc is ferrocene. Electrochemical oxidation of the electrically neutral Fc moiety to the ferrocenium cation reversibly transforms the anionic surfactant (Fc(CH2)11SO3-) into a zwitterionic species (Fc+(CH2)11SO3-). Whereas the effect of an increase in electrolyte concentration on the surface activity of Fc(CH2)11SO3- and Fc+(CH2)11SO3- is similar to that for classical anionic (surface tension decreases) and zwitterionic surfactants (surface tension invariant), respectively, the bulk solution behavior is not. We measured oxidation of Fc(CH2)11SO3- to Fc+(CH2)11SO3- to lead to the spontaneous transformation of either monomers or globular micelles into vesicle-like assemblies (Rg/Rh = 1.0 ± 0.3) with hydrodynamic diameters of 90 ± 10 nm in 1 mM Li2SO4. We observed the addition of salt to Fc+(CH2)11SO3- to lead to a modest decrease in the size of the ves...

Electrochemical Rectification Using Mixed Monolayers of Redox-Active Ferrocenyl Dendrimers and n-Alkanethiols

A strategy for constructing a dendrimer-based electrochemical current rectifier that permits current flow in only one direction is described. This approach is based on the insulating properties of n-alkanethiol self-assembled monolayers and the ability of redox-active ferrocenyl dendrimers to mediate electron transfer. The dendrimer-based rectifying layer is prepared by direct adsorption of second-, third-, or fourth-generation ferrocene-functionalized poly(propylene imine) dendrimers onto Au surfaces, followed by adsorption of n-hexadecanethiol. Reflection infrared spectroscopy, ellipsometry, and electrochemical measurements are used to characterize the resulting two-component monolayers. The surface coverage of ferrocenyl dendrimers in the two-component monolayers is estimated to be about 50% of maximum coverage. Cyclic voltammetry in electrolyte solutions containing the redox-active probes Fe(CN)64-, Fe(bpy)32+, and Co(bpy)32+ reveals that the ferrocenyl dendrimer/n-alkanethiol-modified electrodes exhibit excellent barrier properties that prevent direct oxidation/reduction of the solution-phase redox molecules. Electrochemical current rectification occurs via mediated electron transfer across the surface-confined ferrocenyl dendrimers.

Allylferrocenylselenide and the synthesis of the first seleno-substituted allenylidene complex: synthesis, spectroscopy, electrochemistry and the effect of electron transfer from the ferrocenylselenyl subunit

Allylferrocenylselenide ( 2) is prepared from diferrocenyldiselenide ( 1Se) which was characterized along with its sulfur analog 1S by X-ray structure analysis. In the crystal lattice the packing is determined by ‘point-to-face’ CH⋯π interactions with close contacts between the CH π donors and cyclopentadienyl rings as the π acceptors. Compound 2 is then used in the trapping of the primary butatrienylidene intermediate trans-[ClRu(dppm) 2CCCCH 2] +. The isolated product, trans-[Cl(dppm) 2RuCCC(SeFc)(C 4H 7)] + ( 3) (Fc=ferrocenyl), represents the first seleno-substituted allenylidene complex to be reported to date. Compound 3 is formed in a sequence involving regioselective addition of the selenium nucleophile to C γ followed by hetero-Cope-rearrangement of the allyl vinyl substituted SeR 3 + cation. Its spectroscopic properties place 3 at an intermediate position between sulfur and arene substituted all-carbon allenylidene complexes of the same metal fragment. The selenoallenylidene complex 3 contains a redox active ferrocenyl substituent attached to the heteroatom giving rise to reversible electrochemistry. ESR spectroscopy proves that electron transfer occurs from this site and its effect on the spectroscopic properties of 3 is probed by combining electrochemistry and IR or UV–vis/NIR spectroscopy by in situ techniques. In contrast, the reversible reduction primarily involves the allenylidene ligand as ascertained by ESR spectroscopy. In situ spectro-electrochemical techniques reveal how the reduction affects the bonding within the unsaturated ligand.

Tetrapyrrole derivatives substituted with ferrocenylethynyl moieties. synthesis and electrochemical studies.

Up to eight redox-active ferrocenyl units have been incorporated, through the unsaturated ethynyl linkers, on the periphery of a series of cyclic tetrapyrrole derivatives including zinc(II) phthalocyanine and 2,3-naphthalocyanine, and nickel(II) meso-diphenylporphyrin. The synthesis of the former two macrocycles 4 and 7 involves the Sonogashira coupling reaction of ferrocenylethyne with 4,5-dichlorophthalonitrile (1) or 6,7-dibromonaphthalonitrile (5), respectively, followed by a base-promoted cyclization. The meso-bis(ferrocenylethynyl)porphyrin 11 has been prepared from the dibromo analogue 10 also by a palladium-catalyzed coupling reaction. These novel macrocyclic compounds have been spectroscopically and electrochemically characterized. As revealed by cyclic voltammetry, the ferrocenyl moieties appear to be electrochemically independent in these complexes and there is no significant electronic coupling among the iron(II) centers.

N,N‘-Diferrocenyl-N-heterocyclic Carbenes and Their Derivatives

In continuation of our work on Wanzlick/Arduengo carbenes containing redox-active ferrocenyl substituents we report on the synthesis of N,N‘-diferrocenyl imidazol(in)ium salts as precursors of imidazol(in)-2-ylidenes. The necessary starting material for this chemistry is aminoferrocene, which was prepared by an improved and large-scale synthesis by the sequence solid lithioferrocene, iodoferrocene, N-ferrocenylphthalimide, aminoferrocene. The preparation of N,N‘-diferrocenyl heterocycles involves condensation of aminoferrocene with glyoxal to afford N,N‘-diferrocenyldiazabutadiene [Fc-DAB], reduction, condensation with formaldehyde, and oxidation with trityl salts to yield N,N‘-diferrocenylimidazol(in)ium salts. In situ deprotonation and trapping with electrophiles yielded the expected metal complexes and derivatives in some cases [Ag+ or S8], but attempted reaction with other transition metals [e.g., Pd(II)] failed to give the corresponding complexes, due to (i) steric hindrance by the two N-ferrocenyl substituents, (ii) reduced acidity of the imidazol(in)ium precursors, and (iii) inaccessibility of the free carbenes. Spectroscopic [IR, Raman, UV−vis, MS, NMR (1H, 13C, 109Ag)], structural [X-ray], and electrochemical [CV] properties are reported and compared to those of other N-heterocyclic carbene derivatives.

Synthesis of conjugated polyphenylacetylenes with redox active ferrocenyl end-groups

Metathesis polymerization has been employed for the synthesis of polyphenylacetylene (PPA) containing redox-active ferrocene groups at both ends. Two reversible one electron oxidation waves were detected in CV. The ΔE values decreased with increase in chain length of the polymer, indicating that the metal-metal interaction decreases by increasing the chain length.

Cyclic siloxanes and silsesquioxanes as cores and frameworks for the construction of ferrocenyl dendrimers and polymers

Starting from 1,3,5,7-tetramethylcyclotetrasiloxane as core, novel ferrocenyl silicon-containing dendrimers have been constructed up to the third generation, which contains 16 peripheral ferrocene moieties. As precursors of these ferrocenyl dendritic molecules, Si— Cl- and Si— allyl-terminated cyclotetrasiloxane-based dendrimers were also built step by step, by the repetition of hydrosilylation and alkenylation reactions as growing steps. The dendritic structures have been confirmed by 1 H, 13 C and 29 Si NMR, infrared spectroscopy, elemental analysis, mass spectrometry and vapor-pressure osmometry. Solution electrochemical studies showed that all the ferrocenyl redox centers attached to the dendritic surface behave as independent, electronically isolated units, so that the dendrimers exchange all the electrons simultaneously at the same potential. We also describe the application of the first redox-active ferrocenyl polymer containing an octakis(dimethylsiloxy)octasilsesquioxane framework, as a mediator in the electrocatalytic oxidation of ascorbic acid. Copyright # 1999 John Wiley & Sons, Ltd.

Surface Coordination Chemistry of YBa2Cu3O7-δ

The surface coordination chemistry of the cuprate superconductor, YBa2Cu3O7-δ has been extensively surveyed using cyclic voltammetry in conjunction with a series of redox-active ferrocenyl containing adsorbate molecules. Evidence supporting the adsorption of molecules with primary alkylamine, secondary alkylamine, tertiary alkylamine, arylamine, thiol, disulfide, and selenol functionalities is reported. Cyclic voltammetry, atomic force microscopy, scanning electron microscopy, X-ray powder diffraction and resistivity vs temperature measurements were utilized to evaluate the influence of the modification conditions on the bulk and surface properties of the high-Tc superconductor. The spontaneous adsorption of redox-active alkylamines, arylamines, and thiols onto the surfaces of cuprate materials has been shown to produce stable and robust monolayer films with no apparent damage to the bulk properties of the underlying superconductors. Of the molecules studied thus far, primary alkylamines have been determined to be the optimum adsorbates based upon surface coverage values and monolayer durability. Tertiary alkylamines form monolayers on YBa2Cu3O7-δ with an electrochemical persistence comparable to primary alkylamine monolayers, suggesting that hydrogen binding with the surface is not necessary for adsorption. We propose that amines act as Lewis bases and bind to Lewis acidic Cu surface site(s) in YBa2Cu3O7-δ to form stable coordination bond(s).

Diferrocenyl diselenides: excellent thiol peroxidase-like antioxidants

Synthesis, structure and thiol peroxidase-like antioxidant activity of several diaryl diselenides having intramolecularly coordinating amino groups are described; the diselenides having both tertiary amino groups and redox-active ferrocenyl units show excellent peroxidase activity.

Oxidation-State-Dependent Reactivity and Catalytic Properties of a Rh(I) Complex Formed from a Redox-Switchable Hemilabile Ligand

The synthesis and characterization of a phosphinoalkylarene, redox-switchable hemilabile ligand (RHL), (η5-C5H5)Fe(η5-C5H4C6H4OCH2CH2PPh2) (1), are reported. This ligand, which incorporates a redox-active ferrocenyl group, exhibits oxidation-state-dependent bonding properties and, hence, affords electrochemical control over the electronic and steric environments of bound transition metal centers. Two equivalents of 1 complex to Rh(I) to yield a bis(phosphine), η6-arene complex [(η1:η6-(η5-C5H5)Fe(η5-C5H4C6H4OCH2CH2PPh2))(η1-(η5-C5H5)Fe(η5-C5H4C6H4OCH2CH2PPh2))Rh]+BF4- (2). Single-crystal X-ray diffraction studies of 2·1.25CH2Cl2, as well as solution spectroscopic data of 2, are consistent with this formulated piano-stool geometry. Foremost, the properties of 2 as a function of bound RHL state-of-charge are extensively investigated. Interestingly, 2D 1H NMR exchange spectroscopy (EXSY) studies demonstrate significantly faster intramolecular η6-arene, free arene exchange rates only upon oxidation of the lig...

Metallosupramolecular cluster assemblies based on donor–acceptor type structural frameworks. Syntheses, crystal structures and spectroscopic properties of novel triosmium alkylidyne carbonyl clusters bearing remote ferrocenyl units as electron donors

Two pyridyl ligands containing redox-active ferrocenyl groups [Fe(η5-C5H5)(η-5C5H4C6H4R)][R = C5H4N I or NCH(C5H4N)II] have been prepared using a palladium-catalysed aromatic cross-coupling reaction. Treatment of the cluster [Os3(µ-H)3(CO)9(µ3-CCl)] with one equivalent of 1,8-diazabicyclo[5.4.0] undec-7-ene in the presence of a ten-fold excess of the ferrocenyl ligands I and II produces the compounds [Os3(µ-H)2(CO)9(µ3-CNC5H4R′)][R′= C6H4(η5-C5H4)Fe(η5-C5H5)1, R′= CHNC6H4(η5-C5H4)Fe(η5-C5H5)2] respectively in good yields. Both compounds 1 and 2 exhibit donor-π-acceptor structural frameworks and show considerable negative solvatochromism in their UV/VIS spectra. Unlike 1 and 2 which possess extended donor-π-acceptor nature, the ferrocenyl-phosphine cluster derivative [Os3(µ-H)2(CO)9{µ3-CPPh2(η5-C5H4)Fe(η5-C5H4PPh2)}]3 has also been synthesised in moderate yield by the same synthetic route using 1,1′-bis(diphenylphosphino)ferrocene as the nucleophile. The new clusters 1–3 have all been fully characterised by both spectroscopic and crystallographic methods. Conceptually, the classification of 1–3 as supermolecules is straightforward, since molecular subunits with well defined intrinsic properties can be easily identified, thus affording a new type of covalently linked donor–acceptor system. Both structural features and spectroscopic data for compounds 1–3 are fully consistent with a zwitterionic formulation for these supramolecular species. These results suggest that a strong interaction exists between the ferrocenyl moiety and the Os3C core in their ground states.

Ferrocenyl ligands—II. In search of redox-active ferrocenyl ligands. The preparation and characterization of two schiff's base derivatives of 1,1′-

With the aim of producing redox-active ferrocenyl ligands, the synthesis and characterization of two arylhydrazones, phenyl ( 1) and pyridyl ( 2)

Selective Labeling, Cross-Linking, and Cleavage of Proteins with Transition-Metal Complexes

Abstract Because the substitution reactions of transition-metal complexes can be controlled precisely by the choice of the metal and the ligands, and because these complexes have various spectroscopic and electrochemical properties, they are well-suited for many applications in biochemical and biophysical laboratories. Complex [Pt(trpy)Cl)+ reacts, under mild conditions and noninvasively, with the exposed side chains of His, Cys, and even Arg residues in proteins. The derivatives can be separated chromatographically. The Pt(trpy)2+ tags are stable. They are easily detected and quantitated owing to the strong UV-vis bands, whose positions and relative intensities depend on the identity and the environment of the tagged residue. The selectivity of Pt(II) chloro complexes as labeling reagents can be controlled by purposeful changes of the other three ancillary ligands. Treatment of Cys residues with (η5-C5H5)Fe(η5-C5H4HgCl)results in attachment of the redox-active ferrocenyl tag to the protein. Proteins can ...