Lead-207 NMR, mass spectrometric, and electrochemical studies on labile lead(II) dithiocarbamate complexes: formation of mixed mercury-lead complexes at a mercury electrode in dichloromethane solution

Abstract

{sup 207}Pb NMR spectra have been observed in dichloromethane for series of Pb(RR{prime}dtc){sub 2} compounds (RR{prime}dtc = dialkylthiocarbamate). The resonances are rather broad, and molecular weight determinations show that this is caused by polymerization reactions. Ligand exchange between different Pb(RR{prime}dtc){sub 2} compounds is fast on the NMR time scale, and the complexes are therefore labile. The labile nature of the Pb(RR{prime}dtc){sub 2} systems in the solid state is confirmed by mass spectrometric measurements on mixtures of different complexes. Electrochemical reduction of Pb(RR{prime}dtc){sub 2} in dichloromethane (0.1 M Bu{sub 4} NClO{sub 4}) at mercury electrodes takes place in a single reversible two-electron step to give lead amalgam and free (RR{prime}dtc){sup {minus}}, the reversibility of this process further confirming the lability of the complexes. At platinum electrodes, initially an irreversible reduction occurs to generate elemental lead and (RR{prime}dtc){sup {minus}}. However, long-term behavior at platinum electrodes is complicated by the gradual coating of the electrode with elemental lead, thereby generating a lead electrode at which reversible responses are observed. Electrochemical oxidation processes at mercury electrodes are best described in terms of oxidation of the electrode in the presence of Pb(RR{prime}dtc){sub 2}. The electrochemistry in solution and the nature of the isolated products inmore » the solid state indicate that when mercury and lead are competing for dithiocarbamate in a ligand deficient situation, then mercury is the successful element. 13 refs., 5 figs., 4 tabs.« less