Search

The reduction mechanism of the pesticide vinclozoline (3-(3,5-dichlorophenyl)-5-methyl-5-vinyl-1,3-oxazolidine-2,4-dione) was studied in nonaqueous solvents in the confined environment of a cyclodextrin (CD) cavity. The effect of the cavity dimensions on the mechanism of the redox process was evaluated using glucose as a reference and using three cyclodextrin molecules of different cavity sizes, namely, αCD, βCD, and γCD. In the absence of CD the main reduction product of vinclozoline in the first reduction step is dichloroaniline. An addition of glucose leads to a quantitative change of mechanism with 10 products in total. Addition of CD, however, leads exclusively to dechlorination of the phenyl ring. The degree of dechlorination depends strongly on the choice of cyclodextrin molecule. The importance of the complex formation equilibria in the change of the mechanism is supported by a series of semiempirical AM1 quantum-mechanical calculations. Very good correlation (correlation coefficient 0.995) was obtained between the complex stabilization energy of the inclusion complex and the degree of pesticide dechlorination. Additionally, we were able to show that the complexes are stabilized by the formation of intermolecular hydrogen bonds between the host and guest species. CD molecules do not simply act as proton donors in a nonaqueous environment, but also protect parts of the molecule included within the cavity and steer the degradation process toward fewer products.

Electrochemical reduction of cyclobutadienecyclopentadienylcobalt derivatives, C4R4−Co−C5(HgY)5 [R = C6H5−, Y = −SMe (3), −SCOMe (4), −SCH2CH2SCH3 (5), −SCH2CH2SCOCH3 (6); R = p-EtOCOC6H4−, Y = −SEt (7), −SCOMe (8), −SCH2CH2SCH3 (9), −SCH2CH2SCOCH3 (10)], and the parent C4R4−Co−C5H5 [R = C6H5− (11) and R = p-EtOCOC6H4− (12)] has been examined. Reversible one-electron “metal-centered” reduction of 11 (−2.24 V vs Ag/AgCl) yields a stable radical anion. In 12, it takes place at −1.70 V. In 3−10, similar metal-centered reduction occurs irreversibly, accompanied by an adsorption pre-wave at −0.7 to −1.15 V. We propose that the radical anion loses a −HgSX substituent soon after it is formed. Electrochemical cleavage of the substituents occurs before the metal-centered reduction in 4 and 8 and afterward in the others. The cleaved thiolate fragments yield an anodic peak. In all compounds with ester groups, ester reduction is observed at −2.1 to −2.5 V.

The electrochemical behavior of dimetallic [Ni2Cp2](RC&tbd1;CR‘) (Cp = π-cyclopentadienyl; R = R‘ = Ph; COOMe; R = H, R‘ = Ph; R= Me, R‘ = Ph; R = Ph, R‘ = −C&tbd1;CPh) and tetrametallic M2M2‘(PhC&tbd1;CC&tbd1;CPh) (M2 = M2‘ = Ni2Cp2; M2 = Ni2Cp2, M2‘ = Co2(CO)6) derivatives has been investigated. All dinickel compounds undergo an electrochemically and chemically reversible 1e (metal-centered) reduction followed by further ligand-based reductions. The tetrametallic complex [Ni2Cp2]2(PhC&tbd1;CC&tbd1;CPh) shows two fully reversible 1e (metal-centered) reductions, indicating a strong electronic communication between the two redox units (ΔE° = 670 mV). The mixed-metal [Ni2Cp2][Co2(CO)6](PhC&tbd1;CC&tbd1;CPh) derivative exhibits a 1e (Co2-centered) reduction at first, followed by a further 1e (Ni2-centered) reduction; such an electrochemical scenario is complicated by a fast decomposition following the first reduction, which produces some amount of [Ni2Cp2](PhC&tbd1;CC&tbd1;CPh) compound, having a dangling (uncoordinated) triple bond.

The behavior of nonaqueous solutions of 1,3,5-tris[12-[[3-(ethylthio)propyl]dimethylsilyl]-1,12-dicarba-closo-dodecaboran-1-yl]benzene (2) and four simpler related compounds on a mercury electrode was studied by cyclic voltammetry and ac impedance measurements. It was established that 2 is attached to mercury in two different ways depending on the applied potential, while the interaction of the other compounds with the electrode is less pronounced. At relatively negative potentials 2 is weakly adsorbed at the electrode. At positive potentials a strongly adsorbing mercury ion complex of 2 is produced and forms a compact surface layer. The influence of the supporting electrolyte and the solvent has been examined.