Electron paramagnetic resonance (EPR) studies at 295 K of the radical anion of buckminsterfullerene (C60 •-) generated electrochemically by bulk-controlled potential electrolysis of neutral C60 in mixed toluene−acetonitrile solvents (5−20% v/v acetonitrile with 0.1−0.2 M n-Hex4NPF6 or n-Bu4NPF6 as the supporting electrolyte) have shown that at least three different forms of C60 •- exist in solution. The radical anions have different g values and can thus be detected by EPR spectroscopy in the form of single line signals with different line widths. The familiar species with the broad line width signal (ΔH pp = 6 mT) was present in a high percentage (ca. >95%) along with two species with narrow line width (ΔH pp = 0.16 and 0.07 mT) signals that were present between 1 and 5% of the total concentration of C60 •-. The concentrations of the species with narrow line width EPR signals increased with increasing time so that over a 20-h period their EPR signal intensity approximately doubled. The purity of the toluene was found to be very important in determining the number of species detected with sharp EPR signals. Although two species were always detected with sharp EPR signals, when lower purity toluene (<99%) was used, the number of species with narrow line width signals increased to >2. The increase in the sharp EPR signals with increasing time is not inconsistent with a slow reaction between C60 •- and low levels of impurities in the solvent to form lower symmetry paramagnetic species, the narrow line width signals being very similar to those reported for substituted fullerene radicals. EPR and cyclic voltammetry experiments were conducted on C60 in the presence of several complexing agents, cyclotriveratrylene (CTV), the symmetrical tris-allyl substituted analogue of CTV [CTV(allyl)3], and p-benzyl-calix[5]arene. The intensity of the narrow and broad line width EPR signals decreased when C60 •- was electrochemically generated in the presence of the complexing agents, indicating that the host−guest π−π interactions were sufficiently strong to alter the EPR signals of C60 •-. Cyclic voltammetry experiments performed on C60 in the presence of the complexing agents showed that the first four reduction processes of C60 split into two new processes upon complexation, with the time allowed for the host−guest reaction being critical in determining the voltammetric behavior.

No abstract

The polyoxometalate, α-[S2Mo18O62]4- is reduced by phosphines in the mixed-solvent medium CH3CN/H2O (95/5 v/v). Monitoring of reaction pathways by voltammetric and NMR (17O, 31P) techniques shows that the identity of the final products is determined by the basicity of the phosphine. Thus reaction with aryl- (Ph3P, Ph2PCH2PPh2, and Ph2PCH2CH2PPh2) and alkyl- (Et3P and nBu3P) phosphines leads to two- and one-electron reduced polyoxometalate products, respectively, for example:  [S2Mo18O62]4- + Ph3P + H2O → [HS2Mo18O62]5- + Ph3PO + H+; 2[S2Mo18O62]4- + 3nBu3P + H2O → 2[S2Mo18O62]5- + nBu3PO + 2nBu3PH+. For each reaction, the primary electron-transfer step is believed to be [S2Mo18O62]4- + R3P → [S2Mo18O62]5- + R3P•+with R3P•+ then reacting with water to generate R3PO and protons. If R3P is relatively basic (R = nBu, Et), a 1:2 mixture of R3PO and R3PH+ is formed due to the protonation of R3P. However, if R3P (R = Ph) is a weak base, H+ preferentially initiates the following disproportionation reaction:  2[S2Mo18O62]5- + H+ ⇄ [HS2Mo18O62]5- + [S2Mo18O62]4-. Reactions in the presence of light lead to significant photocatalysis. A quantitative photoelectrochemical channel electrode study demonstrates that oxidation of Ph3P by [S2Mo18O62]4- is accelerated substantially by irradiation in the 300−400 nm wavelength range, where absorption bands of both [S2Mo18O62]4- and [S2Mo18O62]5- are present.

Oxidative electrochemical properties in dichloromethane have been examined for compounds of the types cis- or trans-[Re(CO)2(P−P)2]+ and trans-Re(CO)(P−P)2X (P−P = diphosphine ligand, X = Cl, Br) which exhibit a range of charge and ligand types. In all cases 17e Re(II) species are formed, although the oxidation potentials vary over a reasonably wide range. The Re(II) compounds have been characterized by spectroelectrochemical (IR) and electrospray mass spectrometry (ESMS) studies. The stabilities of the Re(II) species are dependent upon charge and ligand types. The trans configuration is strongly preferred in the Re(II) state, so when the starting material is cis, there is rapid isomerization following electron transfer. The major form of reactivity detected is facile reduction of the trans-[Re(CO)2(P−P)2]2+ species. The particularly high stability of trans-[Re(CO)(dpe)2X]+ (dpe = Ph2P(CH2)2PPh2) allows solid-state studies to be undertaken for the trans-[Re(CO)(dpe)2X]+/0 couple when the compounds are mechanically attached to a graphite electrode immersed in water (electrolyte).