Search

A simple treatment of the fundamentals of solution-phase voltammetry is followed by six examples of porphyrinoids highlighting how structural changes of the redox species influence formal reduction potentials. Electronic communication among different molecular groups is demonstrated, and it is shown how the correct solvent and supporting electrolyte choice may result in observing 17 of a possible 18 redox processes in a cadmium triple-decker phthalocyanine. The difference between outer- and inner-sphere electron transfer processes is used to introduce adsorption effects of redox species on electrodes. This forms the bases of electrocatalysis, and a short theoretical introduction to electrocatalysis is presented. The reader is then eased into electrocatalysis concepts through a discussion of electrocatalyzed alcohol oxidation and sulfite sensors with adsorbed porphyrin polymers. Covalent binding or adsorption to the electrode or solution-phase electrocatalysts are demonstrated. Electrocatalysis in fuel production or energy storage systems concludes this chapter. CO2 reduction by an Fe0 porphyrin, an octaalkoxylated Co phthalocyanine, which aggregates less, and covalent– and metal–organic framework complexes of Co porphyrinoids, are considered. Hydrogen evolution by Ni porphyrins, oxygen reduction to either H2O or H2O2, and H2O oxidation to O2 utilizing carefully chosen porphyrinoids are other reactions that are discussed.

The synthesis, electrochemistry and oxidative addition kinetics are presented for a new [Rh(β-diketonato)(CO)(PPh3)] complex (2), of rhodium metal complexed with a β-diketonato ligand, β-L1 = (CH3COC(C10H21OC6H4COO)COCH3)−, containing a long and sterically large chain (Rα = C10H21OC6H4COO) substituted at the α position. This rhodium triphenylphosphine complex (2), [Rh(β-L1)(CO)(PPh3)], was subsequently converted from a rhodium(I) to a rhodium(III) complex, by chemical and electrochemical oxidation. The kinetics of the chemical conversion from RhI to RhIII, which was obtained by the oxidative addition reaction [Rh(β-L1)(CO)(PPh3)] + CH3I, demonstrated that the reaction occurs in two reaction steps, with a RhIII-alkyl species as the main reaction product. The sterically large and long chain (Rα = C10H21OC6H4COO) at the α-position of the β-diketonato ligand, did not at all affect either the second order reaction rate constant (k1) of the first oxidative addition step of the [Rh(β-L1)(CO)PPh3] + CH3I reaction, nor the value of the oxidation potential (Epa) of the electrochemical oxidation of [RhI(β-L1)(CO)PPh3] to a RhIII-species. This was proven via a literature study, by comparing the k1 and Epa values from this study with the respective rate constants (k1) and oxidation potentials (Epa) of a wide variety of related [Rh(β-diketonato)(CO)(PPh3)] complexes without such a Rα substituent at the α position.

Three different classes of ferrocenyl-containing β-keto compounds Fc-CO-CH2-CO-R were synthesised to obtain two β-diketones with R = CH3, 3, and R = Fc (ferrocenyl = FeII(C5H5)(C5H4)), 4, a β-ketoester, 5, with R = OEt and a β-ketoamide, 6, with R = NH2. The β-diketones exhibited keto ⇌ enol tautomerization with the enol form Fc-CO-CH=C(OH)-R as the dominant isomer. Both the β-ketoester and β-ketoamide primarily existed in the keto form. FTIR and 1H NMR measurements could distinguish between keto and enol isomers. Dilute CHCl3 solutions of 3 and 4 exhibited FTIR ѵC=O keto vibrations between 1627 and 1712 cm−1 and ѵC=O enol vibrations between 1590 and 1660 cm−1. X-ray photoelectron spectroscopic (XPS) measurements showed keto isomer Fe 2p3/2 photoelectron lines at smaller binding energies than enol isomers. Significantly lower calculated molecular energies of the keto form of the β-ketoester 5 and β-ketoamide 6 utilising the Gaussian09 suite of programs at the B3LYP (uB3LYP for open-shell species), confirmed that 5 and 6 almost exclusively exists in the keto conformation. Cyclic voltammetry also distinguished between keto and enol isomers, and it was found that the electrochemical reversible ferrocenyl formal oxidation potential, E°ꞌ, of keto isomers of compounds can be estimated with the equation E°ꞌketo = 170.99χR–57.57 where χR is the group electronegativities of R in FcCOCH2COR. This result complements earlier research that enables calculation of the ferrocenyl formal oxidation potentials of enol isomers of β-diketones. Computational studies further showed that the HOMO orbitals of 3–6 is exclusively on the Fe centre and computed Mulliken spin densities on the dxy orbital of the oxidised iron species approached 1 e−.

The data presented in this paper are related to the research article entitled "Electrochemical behaviour of chloro- and hydroxy-subphthalocyanines" [1]. This paper presents detailed oxidation and reduction potential data, obtained from cyclic voltammograms of three subphthalocyanines (SubPcs), in both dichloromethane (DCM) and dichloroethane (DCE) as solvent. The first SubPc is the unsubstituted boron-subphthalocyanine, (ClB)SubPc(H)12, as reference SubPc, the second SubPc is (ClB)SubPc(F)12, containing an electron-poor macro-cycle and (HOB)SubPc(C12H25)6(H)6, containing an electron-rich macro-cycle. The oxidation and reduction potential of (ClB)SubPc(F)12 in DCM is ca. 0.5 V more positive than that of the reference ClBSubPc(H)12, while oxidation and reduction potential of (HOB)SubPc(C12H25)6(H)6 in DCM is ca. 0.45 V more negative than that of the reference (ClB)SubPc(H)12.

The data presented in this paper is related to the research article entitled “Synthesis, Spectroscopy, Electrochemistry and DFT of Electron-Rich Ferrocenylsubphthalocyanines” [1] where electrochemical redox data and cyclic voltammograms at only a scan rate of 0.10 V s−1 of four ferrocenylsubphthalocyanine dyads Fc(CH2)nCO2BSubPc(H)12 (n = 0, 1 or 3) and FcCO(CH2)2CO2BSubPc(H)12, are presented. This data article provides extensive electrochemical redox data and cyclic voltammograms at various scan rates from 0.05 up to 5.00 V s−1 to illustrate the effect of the different scan rates on the electrochemical behaviour of the four ferrocenylsubphthalocyanine dyads.

A novel subphthalocyanine (HO)BSubPc(C12H25)6(H)6, 3, with a hydroxy group in the axial position and alkyl ligands (C12H25) on the non-peripheral positions as well as two other subphthalocyanines, ClBSubPc(H)12, 2, and ClBSubPc(F)12, 1, have been synthesized and characterized. The redox properties of subphthalocyanines 1–3 was investigated using cyclic voltammetry (CV), both in dichloromethane (at 25 °C) and dichloroethane (at 60 °C) as solvent and compared to previous studies. The electrochemical experimental conditions used made it possible for the first time to experimentally observe electrochemically quasi reversible oxidation for subphthalocyanines. It was found that the novel subphthalocyanine 3 exhibits the lowest macrocycle-based oxidation potential reported for SubPcs till date. The results obtained were further validated by DFT calculations on subphthalocyanines 1–3 as well as related subphthalocyanines from literature. Linear relationships between the redox potentials (oxidation and reduction vs Fc+/Fc) of these subphthalocyanines and various solvent phase B3LYP calculated energies were obtained.

National Research Foundation, South Africa, (DIB, Grant number 76226; JCS, Grant number 81829), and by the Spanish MICINN and CAM (IF, Grants CTQ2010-20714-CO2-01/BQU, Consolider-Ingenio 2010, CSD2007-00006, S2009/PPQ-1634).

The series [(CO)5W═C(XR)Fc] (1, XR = OEt; 3, XR = NHBu) as well as [(CO)5W═C(XR)–Fc′–(XR)C═W(CO)5] (2, XR = OEt; 4, XR = NHBu) of mono- and biscarbene tungsten(0) complexes with Fc = FeII(C5H5)(C5H4) for monosubstituted derivatives and Fc′ = FeII(C5H4)2 for disubstituted derivatives were synthesized and characterized spectroscopically. The oxidized ferrocenium complex [1+]·PF6 was also synthesized and characterized. Electrochemical and computational studies were mutually consistent in confirming the sequence of redox events for the carbene derivatives 1–4 as first a carbene double-bond reduction to a radical anion, –W–C•, at peak cathodic potentials less than −2 V, then a ferrocenyl group oxidation in the range 0.206 0.540 V vs FcH/FcH+ in CH2Cl2/[(nBu4)N][PF6]. This is in contrast with the sequence of oxidation events in ferrocenylcarbene complexes of chromium, where Cr(0) is first oxidized in a one-elec...

A series of ten ferrocenyl, furyl, and thienyl mono- and biscarbene chromium(0) complexes were synthesized and characterized spectroscopically and electrochemically. The single crystal structure of the biscarbene complex [(CO)5Cr═C(OEt)-Fu'-(OEt)C═Cr(CO)5] (4a) was determined: C20H12Cr2O13; triclinic; P1; a = 6.2838(5), b = 12.6526(9), c = 29.1888(19) Å, α = 89.575(2), β = 88.030(2), γ = 87.423(2)°; Z = 4. Results from an electrochemical study in CH2Cl2 were mutually consistent with a computational study in showing that the carbene double bond of 1-6 is reduced to an anion radical, (-)Cr-C• at formal reduction potentials-1.7 V vs FcH/FcH(+). The Cr centers are oxidized in two successive one electron transfer steps to Cr(II) via the Cr(I) intermediate. Only Cr(I) oxidation is electrochemically irreversible. Dicationic Cr(II) species formed upon two consecutive one-electron oxidation processes are characterized by a peculiar bonding situation as they are stabilized by genuine CH···Cr agostic interactions. With respect to aryl substituents, carbene redox processes occurred at the lowest potentials for ferrocene derivatives followed by furan complexes. Redox process in the thiophene derivatives occurred at the highest potentials. This result is mutually consistent with a (13)C NMR study that showed the Cr═C functionality of furyl complexes were more shielded than thienyl complexes. The NHBu carbene substituent resulted in carbene complexes showing redox processes at substantially lower redox potentials than carbenes having OEt substituents.

A series of ferrocenyl and thienyl mono- and biscarbene chromium(0) complexes 1-6 were synthesised. The complexes were characterised both spectroscopically and electrochemically, and the single crystal X-ray structure of 3 was determined. Electrochemical measurements in CH2Cl2 revealed that the carbene double bond of 1-6 is reduced to an anion radical, (-)Cr-C˙ at formal reduction potentials-1.7 V vs. FcH/FcH(+). A computational study on 1, 3 and 4 (B3LYP/def2-SVP level) is consistent with electrochemical results in showing that electrochemically generated chromium(I) species may be further electrochemically irreversibly oxidised to chromium(II) at Epa0.95 V. The reactivity towards follow-up chemical reactions of the anodically produced Cr(II) species is much higher than the reactivity of the cathodically produced radical anions as the latter was still observably reoxidised to the parent Cr=C species at fast scan rates. The ferrocenyl group is oxidised electrochemically reversibly to ferrocenium at larger potentials than the electrochemically reversible oxidation of the Cr(0) centre to Cr(I). That all redox centres in 1-6 are involved in one-electron transfer steps was confirmed by comparing the ferrocenyl voltammetric wave with those of the other redox centres in linear sweep voltammetric experiments. The ferrocenyl group was electrochemically shown to stabilise the Cr=C centre almost as much as the NHBu, and much more than the ethoxy and thienyl groups.