Electron Transfer Studies on Conjugated Ferrocenyl-Containing Oligomers

Ferrocenyl-triazole complexes and their use in heavy metal cation sensing

Complexes tris((1-ferrocenyl-1H-1,2,3-triazol-4-yl)methyl)amine (3), bis((1-ferrocenyl-1H-1,2,3-triazol-4-yl)methyl)amine (6), bis((1-ferrocenyl-1H-1,2,3-triazol-4-yl)methyl)ether (7), and 1-ferrocenyl-1H-1,2,3-triazol-4-yl)methanamine (9) were synthesized using the copper-catalyzed click reaction. Complexes 3, 6, 7, and 9 were characterized using NMR (1H and 13{1H}) and IR spectroscopy, elemental analysis, and mass spectrometry. Structures of 3, 7, and 9 in the solid state were determined using single-crystal X-ray diffraction. It was found that the triazole rings were planar and slightly twisted with respect to the cyclopentadienyl groups attached to them. Chains and 3D network structures were observed due to the presence of π⋯π and C-H⋯N interactions between the cyclopentadienyl and triazole ligands. A reversible redox behavior of the Fc groups between 239 and 257 mV with multicycle stability was characteristic for all the compounds, revealing that the electrochemically generated species Fc+ remained soluble in dichloromethane. Electrochemical sensor tests demonstrated the applicability of all the complexes to enhance the quantification sensing behavior of the screen-printed carbon electrode (SPCE) toward Cd2+, Pb2+, and Cu2+ ions.

Rearrangement of Diferrocenyl 3,4-Thiophene Dicarboxylate

Treatment of 3,4-(ClC(O))2-cC4H2S (1) with [FcCH2OLi] (2-Li) (Fc = Fe(η5-C5H5)(η5-C5H4)) in a 1:2 ratio gave 3,4-(FcCH2OC(O))2-cC4H2S (3). Compound 3 decomposes in solution during crystallization to produce FcCH2OH (2) along with 3,4-thiophenedicarboxylic anhydride (4). The cyclic voltammogram of 3 exhibits a reversible ferrocene-related redox couple (E1/2 = 108 mV, vs. Cp2Fe/Cp2Fe+) using [NnBu4] [B(C6F5)4] as the supporting electrolyte. DFT calculations reveal that the energy values of the LUMO orbitals of 3 (3,4-thiophene core) show 1 eV higher energies than that one of 2,5-(FcCH2OC(O))2-cC4H2S (5), both compounds’ HOMO orbitals are close to each other. Compound 4 was characterized by single X-ray structure analysis. It forms a band-type structure based on intermolecular O1···S1 interactions being parallel to (110) and (1–10) in the solid state, while electrostatic C···O interactions between the C=O functionalities of adjacent molecules connect both 3D-networks. Hirshfeld surface analysis was used to gain more insight into the intermolecular interactions in 4, the enrichment ratios (E) suggest that O···H, S···S, and O···C are the most favored intermolecular interactions, as shown by E values above 1.20. The relevance of the weak O···H, O···O, and O···C contacts in stabilizing the molecular structure of 4 was highlighted by the interaction energies between molecular pairs.

(Electrochemical) Properties and Computational Investigations of Ferrocenyl-substituted Fe3(μ3-PFc)2(CO)9 and Co4(μ4-PFc)2(CO)9 Clusters and Their Reduced Species

The formation of ferrocenyl-functionalized iron and cobalt carbonyl clusters is reported, based on a reaction of FcPCl₂ (3) (Fc = Fe(η⁵-C₅H₅)(η⁵-C₅H₄)) with Fe₂(CO)₉ and Co₂(CO)₈, respectively. Therein, nido-Fe₃(CO)₉(μ₃-PFc)₂ (4) and nido-Co₄(CO)₁₀(μ₃-PFc)₂ (5) clusters were obtained as the first diferrocenyl-substituted carbonyl clusters with a symmetrical cluster core. Cluster 4 shows two reversible one-electron processes within the anodic region, based on Fc/Fc⁺ redox events, as well as two processes in the cathodic region. In situ IR and electron paramagnetic resonance (EPR) measurements of all electronic states confirmed an Fc-based oxidation and a core-based reduction. On the basis of the results of a single-crystal X-ray analysis of structures of 4 and 5, computational studies of the highest occupied molecular orbital-lowest unoccupied molecular orbital energies, the spin density, quantum theory of atom-in-molecule delocalization indices, and the atomic charges were performed to explain the experimental results. The latter revealed a reorganization of the cluster core upon reduction and the existence of weak P···P interactions in 4 and 5. Ferrocenyl-related redox processes, occurring reversibly in case of 4, were absent for 5, due to a different distribution of the HOMO energies. EPR measurements furthermore confirmed the core-based radical anion and the formation of a decomposition product at potentials lower than [M]^2- (M = Fe, Co).

Anodic electrochemistry of mono- and dinuclear aminophenylferrocene and diphenylaminoferrocene complexes

Two related three-membered series of nonlinear aminophenylferrocene and diphenylaminoferrocene complexes were prepared and characterized by 1H and 13C NMR spectroscopy. The first series consists of 4-(diphenylamino)phenylferrocene (TPA-Fc, 1a), its dimethoxy-substituted tetraphenylphenylenediamine derivative (M2TPPD-Fc, 1c), and the triphenylamine-bridged bis(ferrocenyl) complex (Fc-TPA-Fc, 1b). The second series involves bis(4-methoxyphenyl)aminoferrocene (M2DPA-Fc, 1d), 4-methoxyphenylaminoferrocene (MPA-Fc) with N-phenyl-appended terminal TPA (1e), and the corresponding bis(MPA-Fc) complex with bridging TPA (1f). The structure of complex 1d was further confirmed by single crystal X-ray diffraction. Combined investigations, based on anodic voltammetry, UV-vis-NIR spectroelectrochemistry and density functional theory (DFT) calculations, were conducted to illustrate the influence of the integration of multiple redox-active components on the sequential oxidation of these complexes. The first anodic steps in 1a-1f are localized preferentially on the ferrocenyl units, followed by oxidation of the TPA or TPPD moieties (absent in 1d). Irreversible oxidation of the ferrocene-appended strong donor DPA/MPA units in 1d-1f terminates the anodic series. The one-electron oxidation of the triphenylamine-bridged diferrocenyl (1b) and bis(phenylaminoferrocenyl) (1f) complexes triggers their facile redox disproportionation to dicationic bis(ferrocenium) products.