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[60]Fullerene-containing liquid-crystalline dendrimers were synthesized from the first to the fourth generation by applying the 1,3-dipolar cycloaddition reaction from a mesomorphic dendritic-type aldehyde derivative, sarcosine (N-methylglycine) or glycine and C60. The cyanobiphenyl unit was used as a liquid-crystalline promoter. With the exception of the first-generation fullerene dendrimer, which was found to be nonmesomorphic, all fullerene-based dendrimers gave rise to a smectic A phase. The liquid-crystalline fullerenes led to two different supramolecular organizations within the smectic layers:  for the second-generation dendrimers, the molecules are oriented in a head-to-tail fashion within the layers; for each molecule the cyanobiphenyl units point in the same direction. For the dendrimers of third and fourth generations, the dendritic core extends laterally, parallel to the layer planes; the mesogenic units are oriented above and below the dendritic core. For the aldehyde precursors, only one organization inside the layers was obtained, similar to the one observed for the third and fourth fullerene-based dendrimers. Cyclic voltametry investigations displayed several one-electron and multielectron reduction processes; no significant interaction in the ground state between the fullerene and the dendrimer was noticed. The title compounds showed the typical electrochemical stability of fulleropyrrolidines.

The electronic properties of the family of pyridyl− and pyrimidyl− ferrocenyl complexes [Fe(η⁵-C5H4-4-C5H4N)(η⁵-C5H5)] (1), [Fe(η⁵-C5H4-4-C5H4N)2] (2), [Fe(η⁵-C5H4-4-C5H4N)(η⁵-C5H4-5-C4H3N2)] (3), [Fe(η⁵-C5H4-5-C4H3N2)2] (4), [Fe(η⁵-C5H4−C6H4-4-C5H4N)(η⁵-C5H4-5-C5H4N)] (5), and [Fe(η⁵-C5H4−C6H4-4-C5H4N)2] (6), prepared by Suzuki coupling starting from ferrocenyl diboronic acid, have been investigated by electrochemical, spectroscopic, and quantum-chemical methods. All complexes display photo- and electrochemical stability and strong electronic interactions in the ground state between the ferrocenyl moiety and pyridine/pyrimidine rings. The efficient modulation of the potentials of ferrocenyl-based oxidation is shown to be strongly dependent on the nature of the hetero ring. These features, together with their high chelating ability, are potentially useful in the preparation of redox-active complexes of complexes such as mixed-metal metallamacrocycles.

ESR studies carried out during the reaction of ferrocenoylsilanes with Grignard reagents at low temperature led to the detection of the radical anions of the former compounds. Cyclic voltammetric experiments indicate that the observed radical anions are likely to originate through an inner‐sphere electron transfer process. Different radical species were observed upon annealing, originating from destruction of the ferrocenyl moiety. Paramagnetic species were also detected on reacting ferrocenoylsilanes with LiAlH4. Copyright © 2004 John Wiley & Sons, Ltd.

The study of the electrochemical behavior (CV) of 9-anthrylmethylcyclopentadienyl (AnCH2C5H4) derivatives of rhodium(I) and iridium(I) of formula [M(η⁵-AnCH2C5H4)L2] (M = Rh or Ir; L = η²-C2H4, η¹-CO, η²-C8H14, PPh3; L2 = η⁴-C8H12), 1−8, in strictly aprotic conditions, allows a satisfactory interpretation of the observed electrode processes and gives information about the location of the redox sites along with the thermodynamic characterization of the corresponding redox processes. These data show that the occurrence of an intramolecular charge-transfer process between the photoexcited 9-anthryl group and the cyclopentadienylmetal unit is a possible route for the observed anthracenic fluorescence quenching in the compounds 1−8. Moreover, a study was carried out on the redox behavior of these complexes under chemical activation. The one-electron oxidation of compounds 1−8 by thallium(III) trifluoroacetate leads to the formation of the corresponding cation radicals, whose highly resolved X-band EPR spectra were fully interpreted by computer simulation as well as by semiempirical and DFT calculations of spin density distribution.

The redox properties of cis-[Ru(dcbpyH2)2(NCS)2] ([Ru(dcbpyH2)2(NCS)2]; dcbpyH2 = 2,2‘-bipyridine- 4,4‘-dicarboxylic acid) have been investigated in various solvents by combining electrochemical techniques (cyclic voltammetry (CV) and spectroelectrochemistry), mass spectrometry, digital simulation techniques, and semiempirical quantum chemical calculations. The electrochemical study has shown that while in polar solvents such as acetonitrile and ethanol the complex undergoes, following oxidation, the rapid loss of SCN ligands, forming the corresponding solvato complexes. In the less polar solvent tetrahydrofuran, a reversible oxidative CV behavior is observed at relatively low scan rates. On the basis of the CV and spectroelectrochemical studies and supported by quantum chemical calculations, a complex parallel ECE mechanism is proposed, comprising the loss of the SCN ligands in their pristine (anionic) form, which is initiated by the metal-centered oxidation process.

9,10-Bis(cyclopentadienylmethyl)anthracene (1) is obtained by reacting 9,10-bis(bromomethyl)anthracene with cyclopentadienylsodium and transformed into its dithallium(I) derivative 3 on reaction with thallium ethoxide. The reaction of 3 with the chloro derivatives of rhodium(I) of formula [RhClL2]2 (L = η²-C2H4 or CO; L2 = η⁴-C7H8) leads to the corresponding bimetallic complexes [L2Rh{C5H4CH2(9,10-anthrylene)CH2C5H4}RhL2], 4 (L = η²-C2H4), 5 (L = CO), and 6 (L2 = η⁴-C7H8), in 13, 22, and 55% yields, respectively. All complexes have been characterized by elemental analysis, particle beam mass spectrometry, ¹H NMR, and FT-IR. The UV−vis spectra (280−800 nm) of 4−6 are indicative of the existence of strong electronic interactions among the anthrylic chromophore and the two cyclopentadienylRhL2 moieties. When excited at ca. 370 nm, 1 becomes an efficient light-emitting molecule, while 4−6 are poorly luminescent compounds. The fluorescence spectra of all the complexes present the vibrational structure typical of the anthrylic fluorophore but have low intensity:  6, 3, and 15% of the one observed for 9-methylanthracene, taken as the reference compound, respectively for 4, 5, and 6. The study of the electrochemical behavior of 4−6 in strictly aprotic conditions allows a satisfactory interpretation of the observed electrode processes and furnishes information about the location of the redox sites along with the thermodynamic characterization of the corresponding redox processes. These data show that the occurrence of an intramolecular charge-transfer process between the photoexcited 9,10-anthrylenic moiety and the cyclopentadienylRhL2 unit is a possible route for the observed quenching of emission in the compounds 4−6. The one-electron oxidation of compounds 4−6 by thallium(III) trifluoroacetate in a 1:1 dichloromethane/1,1,1,3,3,3-hexafluoropropan-2-ol mixture leads to the formation of the corresponding radical cations [L2Rh{C5H4CH2(9,10-anthrylene)CH2C5H4}RhL2]⁺. Two of them, i.e., 4⁺ (L = η²-C2H4) and 5⁺ (L = CO), give rise to highly resolved EPR spectra which allow one to describe such species as average-valence [Rh^+1/2, Rh^+1/2] complexes. DFT calculations of spin density distribution confirm the EPR results and allow a further insight into the structure of 4⁺ and 5⁺ complexes.

The electrochemical behavior of the family of mononuclear Re(I) complexes, [Re^I(CO)3LX]ⁿ⁺, with L = 2,2‘-bipyridine (bpy), 1,10-phenanthroline (phen) and X = Cl, CN (n = 0); ACN (n = 1) and that of the metal−metal-bonded dimeric complexes [(L)(CO)3Re−Re(CO)3(L)] (L = bpy, phen) has been studied in various aprotic solvents using cyclic voltammetry (CV), chronoamperometry, and spectroelectrochemistry. The wide cathodic potential window investigated has permitted the observation of the largest number of redox processes so far obtained for these species. A detailed description of the kinetics of both oxidation and reduction processes of such species is given. The electrochemistry of the complexes [Re(CO)3(L)CN] (L = bpy, phen) is reported here for the first time. The electrochemical behavior of the monomeric species is greatly influenced by the nature of the monodentate ligand X. The concentration dependence of the cyclic voltammetric reductive behavior has evidenced the occurrence of bimolecular homogeneous processes. Such processes include homogeneous electron transfers and the competitive formation of metal−metal or μ-Cl bridged dimeric species. The influence of the solvent and that due to the presence or absence of Cl^- ions in solution is discussed. Digital simulation of the cyclic voltammetric curves is extensively used both for confirming the reaction mechanisms and for the evaluation of the relevant thermodynamic (E1/2) and kinetic parameters. Linear correlation between spectroscopic and electrochemical data for the whole family of monomeric and dimeric complexes has been found.

The electrochemical behavior of the species [Co(η⁵-C5H5)(η³-2-MeC3H4)I] and [Co(η⁵-C5H5)(η³-2-MeC3H4)(ACN)]⁺ in ACN solutions, at 25 °C, is described. The kinetic analysis of the cyclic voltammetry curves indicates that the introduction of one electron in the former complex is concerted with the dissociation of the Co−I bond. The ensuing radical undergoes fast solvation to yield the solvato complex [Co(η⁵-C5H5)(η³-2-MeC3H4)(ACN)]^•, which then acts as an efficient electron donor toward the starting material with the formation of [Co(η⁵-C5H5)(η³-2-MeC3H4)(ACN)]⁺; finally, the cation is electroreduced at the working potentials to conclude an overall autocatalytic sequence. The solvato complex [Co(η⁵-C5H5)(η³-2-MeC3H4)(ACN)]^•, formed as a product of the above reduction process, can be reversibly reduced to the corresponding anion at more negative potentials. Confirmation of the above mechanism and of the fact that the solvato complex can act as a solution electron donor toward the starting material was obtained by studying the electrochemical behavior of the solvato complex itself and through calculations aimed to better define the dissociative electron-transfer process to [Co(η⁵-C5H5)(η³-2-MeC3H4)I]. The dissociation of the metal−halide bond in the neutral complex [Co(η⁵-C5H5)(η³-2-MeC3H4)I], with the formation of [Co(η⁵-C5H5)(η³-2-MeC3H4)(ACN)]⁺, was also found to occur spontaneously, in the bulk, through the observation of a progressive change of the cyclic voltammetric pattern. Support for the occurrence of the reaction between the starting complex and the solvent was confirmed by conductivity and spectroscopic measurements, which allowed the rate constant for the homogeneous solvolysis to be determined.