A DFT-Elucidated Comparison of the Solution-Phase and SAM Electrochemical Properties of Short-Chain Mercaptoalkylferrocenes: Synthetic and Spectroscopic Aspects, and the Structure of Fc-CH2CH2-S-S-CH2CH2-Fc

A General Strategy for Increasing the Air Stability of Phosphines Including Primary Phosphines

A general approach for increasing the air-stability of various primary phosphines in the absence of kinetic stabilization is presented that contrasts with previous interpretations, which were limited to specific phosphines. This contribution shows the synthesis of a series of air-stable primary phosphines Fc(CH2 )n PH2 , where n=0,1,2,3; and Fc=ferrocenyl, and their corresponding isolable primary phosphine oxides. It was demonstrated that the ferrocene moiety exerts an antioxidant effect on the primary phosphine group, which is intermolecular, solvent dependent and increases with the electron density on the ferrocene moiety. Furthermore, we demonstrated that the presence of ferrocene in solution also inhibits the oxidation of other secondary and tertiary phosphines in air. Together our findings suggest that quenching of singlet oxygen is the actual reason for the antioxidant effect; this was experimentally confirmed by using other established singlet oxygen quenchers, thus demonstrating a key role of singlet oxygen in the aerobic oxidation of phosphines.

Ferrocene-Bearing Dodecylphthalocyanines: Synthesis, Spectroscopic and Electrochemical Behavior

Ferrocenylbutoxy-bearing dodecylated phthalocyanines, MPc(C₁₂H₂₅)_x(OC₄H₈Fc)_y with M = 2H (compound series 6 and 8) or Zn (compound series 5, 7 and 9), x ≤ 8 and y ≤ 4, were synthesized through either metal-free statistical condensation between 3,6-bis(dodecyl)phthalonitrile, 2, and 4- (1), or 3-(4'-ferrocenylbutoxy)phthalonitrile, 4, or a zinc template statistical condensation between 4,5-bis(dodecyl)phthalonitrile, 3, and 1 in the presence of anhydrous zinc acetate, or by zinc insertion into metal-free phthalocyanines. Compounds were designed to have eight nonperipheral dodecyl substituents, six nonperipheral dodecyl, either one peripheral or one nonperipheral 4'-ferrocenylbutoxy substituent, four nonperipheral dodecyl and two peripheral 4'-ferrocenylbutoxy substituents, or four peripheral 4'-ferrocenylbutoxy substituents. The compound having six peripheral dodecyl and one peripheral 4'-ferrocenylbutoxy substituents was also synthesized. Metal-free and zinc complex Q-band maximum absorption wavelengths increased nonlinearly from 704 to 725 nm for the Q_y-band of metal-free compounds, or from 676 to 699 nm for the Q-band of zinc complexes in moving from all peripheral-substituted to all non-peripheral-substituted complexes. A rare case of accidental Q-band degeneracy where only one electronic Q-band is observed for asymmetrical zinc complexes NOT having D_4h symmetry, compounds 5, 7b-e, and 9b, is also described. X-ray photoelectron spectroscopy (XPS) differentiated between four types of phthalocyanine nitrogen atoms; binding energies were ca. 399.8 (N-H), 398.1 (N_meso), 397.8 (N_core), and 398.7 eV (N-Zn), respectively. An electrochemical study of these compounds revealed up to five different redox processes in dichloromethane but only three in tetrahydrofuran (THF). The first ring-based oxidation of both metal-free compounds 6a-e and zinc phthalocyanines 7a-e exhibited a near-linear increase in peak anodic potentials, E_pa, with the systematic replacement of two nonperipheral dodecyl substituents with one peripheral 4'-ferrocenylbutoxy group. When four 4'-ferrocenylbutoxy groups were substituted on the phthalocyanine macrocycle, aggregation of the first oxidized species was observed. Zinc insertion into metal-free phthalocyanines lowered formal redox potentials. An electrochemical scheme consistent with electrochemical results is provided.

Melnikov M, Zyk NV, Skvortsov DA, Lopatukhina EV, Vaneev AN, Gorelkin PV, Erofeev AS, Majouga AG, Beloglazkina EK. New Fe–Cu bimetallic coordination compounds based on ω-ferrocene carboxylic acids and 2-thioimidazol-4-ones: structural, mechanistic and biological studies

Synthesis, characterization and in vitro cytotoxic investigation of a series of new ferrocene-containing derivatives based on ω-ferrocene carboxylic acids and 2-alkylthioimidazolin-4-ones and their copper complexes have been reported.

Synthesis, Spectroscopy, Electrochemistry and DFT of Electron-Rich Ferrocenylsubphthalocyanines

A series of novel ferrocenylsubphthalocyanine dyads Y-BSubPc(H)₁₂ with ferrocenyl-carboxylic acids Y-H = (FcCH₂CO₂-H), (Fc(CH₂)₃CO₂-H) or (FcCO(CH₂)₂CO₂-H) in the axial position were synthesized from the parent Cl-BSubPc(H)₁₂ via an activated triflate-SubPc intermediate. UV/Vis data revealed that the axial ferrocenyl-containing ligand did not influence the Q-band maxima compared to Cl-BSubPc(H)₁₂. A combined electrochemical and density functional theory (DFT) study showed that Fe group of the ferrocenyl-containing axial ligand is involved in the first reversible oxidation process, followed by a second oxidation localized on the macrocycle of the subphthalocyanine. Both observed reductions were ring-based. It was found that the novel Fc(CH₂)₃CO₂BSubPc(H)₁₂ exhibited the lowest first macrocycle-based reduction potential (-1.871 V vs. Fc/Fc⁺) reported for SubPcs till date. The oxidation and reduction values of Fc(CH₂)_nCO₂BSubPc(H)₁₂ (n = 0-3), FcCO(CH₂)₂CO₂BSubPc(H)₁₂, and Cl-BSubPc(H)₁₂ illustrated the electronic influence of the carboxyl group, the different alkyl chains and the ferrocenyl group in the axial ligand on the ring-based oxidation and reduction values of the SubPcs.

Can Electrochemical Measurements Be Used To Predict X-ray Photoelectron Spectroscopic Data? The Case of Ferrocenyl-β-Diketonato Complexes of Manganese(III)

In order to better understand intramolecular communication between molecular fragments, a series of ferrocene-functionalized β-diketonato manganese(III) complexes, [Mn(FcCOCHCOR)₃] with R = CF₃, 1, CH₃, 2, Ph = C₆H₅, 3, and Fc = Fe^II(η⁵-C₅H₄)(η⁵-C₅H₅), 4, the mixed ligand β-diketonato complex [Mn(FcCOCHCOFc)₂(FcCOCHCOCH₃)], 5, as well as the acac complex [Mn(CH₃COCHCOCH₃)₃], 6, were subjected to an electrochemical and X-ray photoelectron spectroscopy (XPS) study. The ferrocenyl (Fe^II) and Mn^III redox potentials, E°', and photoelectron lines were sufficiently resolved in each complex to demonstrate a linear correlation between E°' and group electronegativities of ligand R groups, χ_R, or Σχ_R, as well as with binding energies of both the Fe 2p_3/2 and Mn 2p_3/2 photoelectron lines. These relationships are consistent with effective communication between molecular fragments of 1-5. From these relationships, prediction of Mn and Fe core electron binding energies in [Mn(R¹COCHCOR²)₃] complexes from known manganese and/or ferrocenyl redox potentials are, therefore, now possible. Ligand infrared carbonyl stretching frequencies were successfully related to binding energy as a measure of the energy required for inner-sphere reorganization. In particular it became possible to explain why, upon electrochemical oxidation or photoionization, the ferrocenyl Fe^II inner-shell of 1-5 needs more energy in complexes with ligands bearing electron-withdrawing (CF₃) groups than in ligands bearing electron-donating groups such as ferrocenyl. The XPS determined entity I_ratio (the ratio between the intensities of the satellite and main metal 2p_3/2 photoelectron lines) is an indication not only of the amount of charge transferred, but also of the degree of inner-sphere reorganization. Just as for binding energy, the quantity I_ratio was also found to be related to the energy requirements for the inner-sphere reorganization depicted by the vibrational frequency, v_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.