Synthesis of 18pi annulenic fluorofullerenes from tertiary carbanions: size matters!

A range of tertiary carbanions XCH(CO2Et)2 of differing sizes have been reacted with C60F18 to assess the steric effect of X on the position of nucleophilic substitution. For X = CO2Et, NO2, P(O)(OMe)2, SO2CH2Ph, the all trans annulenes (trannulenes) were obtained as a result of extended S(N)2' (i.e. S(N)2') substitution; in the case of the phosphorus compound, with reduced amounts of base (DBU) dephosphonylation of one or more P(O)(OMe)2 groups by hydrogen occurred. Trannulene formation did not occur for X = F, CN due to the smaller size of the nucleophile, and in the latter case substitution was shown to take place by an S(N)2' mechanism, resulting in the addend being adjacent to a fluorine addend. Trannulenes (X = CO2Et, Br, Cl) exhibited reversible one-electron reductions at potentials (-0.02 to -0.09 V) significantly more positive than for [60]fullerene. Trannulene (X = NO2) exhibited an irreversible one-electron reduction (0.08 V); the irreversibility may be associated with fluorine loss. Conformational isomerism at temperatures below 298 K was observed for all trannulene derivatives as a result of eclipsing addend-addend interactions. Minimum energy conformations with a rotational energy barrier of 12-15 kcal mol(-1) were observed when these interactions are calculated using molecular mechanics.     

A computational study on mixed-ligand N2P3 donor-set iron(II) and ruthenium(II) classical and non-classical hydrides

Iron and ruthenium classical and non-classical hydrides of the type [MH(N–N)P₃]⁺ and [M(η²-H₂)(N–N)P₃]²⁺ {M = Fe, Ru; N–N = 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen); P = phosphites} were reported in 2004 together with an evaluation of the pseudo-aqueous pK_a values of the η²-H₂ complexes. The non-classical hydrides, even if doubly charged, showed a relatively low acidity, their pK_a values ranging between −5.4 and −4.3. Moreover, ruthenium(II) derivatives showed to be more acidic than the corresponding iron(II) complexes. Information about the structural and electronic proprieties of complexes of this type, which allowed to better understand the role of both the metal centres and the ancillary ligands in the acidity of the co-ordinated hydrogen molecule, was obtained on the basis of DFT B3LYP calculations.     

PVC chlorination using fluorine as initiator

The chlorination of PVC has been studied in a fluidized bed reactor, initiating the reaction with elementary fluorine. The reaction has been carried out at temperatures between 20° and 60° for various concentrations of chlorine and fluorine. The rate of reaction is given by the equation:

(1)$\text{x=}\text{k[}\text{Cl}{}_2\text{]}{}^{\mathrm{0·5}}\text{[}\text{F}{}_2\text{]t}\text{1+k[}\text{Cl}{}_2\text{]}{}^{\mathrm{0·5}}\text{[}\text{F}{}_2\text{]t}$

, temperature is given by

$\text{log}\text{k=}\text{3500}\text{4·57}\text{1}\text{T}\text{+0·707}$

.Equation (1) is satisfied also by data obtained from a small scale plant reactor. A reaction mechanism is proposed.     

Metastable (1 × 2) and (1 × 3) reconstructions of Pd(110)

By adsorption and subsequent reduction of oxygen on Pd(110), metastable (1 × 2) and (1 × 3) reconstructed surfaces have been produced. Oxygen was not present after the reduction but a small amount of residual hydrogen (< 0.15 monolayers) remained. However this is not the origin of the reconstruction as adsorption of this amount of hydrogen on the clean surface did not cause reconstruction. The structures were stable up to ˜ 370 K, and at higher temperatures they reverted to (1 × 1). These results are compared with Rh(110) where similar reconstructions have been found.     

Synchotron radiation photoemission study of adsorbate-induced 3d core level shifts of Pd(110)

The surface core level shifts of Pd(110) and oxygen and CO covered Pd(110) have been measured using synchrotron radiation. The results are consistent with values predicted using a Born-Haber cycle, confirming the usefulness of this approach. The largest shift occurs for the CO covered surface, indicating that initial state charge transfer does not dominate the shifts.     

Cyclic voltammetry and bulk electronic properties of soluble carbon nanotubes

The bulk electronic properties of pyrrolidine-functionalized nanotubes are obtained from cyclic voltammetry measurements and discussed in the light of quantum chemical calculations. The functionalization is found to preserve the metallic character and to hardly affect the average density of electronic states.     

A light-harvesting fluorinated fullerene donor-acceptor ensemble; long-lived charge separation

In a first example of a trannulene-based donor-acceptor dyad visible light photoexcitation generates a long-lived (870 ns) charge-separated state.     

Modulation of the reduction potentials of fullerene derivatives

The cyclic voltammetric (CV) study of a series of novel bisfulleropyrrolidines (3) and bisfulleropyrrolidinium ions (4) is reported. The eight possible stereoisomers of each series were systematically investigated under strictly aprotic conditions that allowed the observation of up to four and five subsequent reversible reductions in 3 and 4, respectively. Because of the stabilizing effect of positive charges, a significant enhancement of the electronegative properties was observed in 4. In fact, 4-trans-2 and 4-trans-1 result among the strongest reversible electron-accepting C(60) oligoadducts. Furthermore, the study evidenced that, in both 3 and 4, the CV pattern, and in particular the potential separation between the second and third reductions, changes significantly with the addition pattern. A sequential pi-electron model that simulates the effect of subsequent reductions of C(60) bis-adducts gives a good correlation (r > 0.96) with the cyclic voltammetry data when the molecules are divided in two sets dependent on the location of the addends in the same or in opposite hemispheres.     

Auger lineshape analysis as a tool to study surface reactions: kinetics of the dissociation of NO on Rh(110)

We present a new method for following the kinetics of the dissociation of chemisorbed molecules, by Auger electron spectroscopy (AES) in the pulse counting mode. By following the time evolution of the Auger lineshape, it is possible to quantify the relative weight of the dissociated and undissociated chemisorbed species as a function of time. As an example, we have applied the method to the case of NO chemisorbed on rhodium (110). The high signal to noise ratio which can be obtained by AES in the pulse counting mode makes it possible to measure the kinetics with good accuracy, without affecting the reaction.