Multinuclear magnetic resonance (phosphorus-31, selenium-77, mercury-199) and electrochemical studies of nonlabile mercury(II) complexes with group 15/group 16 donor ligands

Multinuclear magnetic resonance (/sup 31/P, /sup 77/se, /sup 199/Hg) and electrochemical studies have been carried out on Hg(II) perchlorate complexes of pH/sub 2/PCH/sub 2/P(E)Ph/sub 2/ (E = S (dpmS), Se (dpmSe)) and Ph/sub 2/P(E)CH/sub 2/P(E)Ph/sub 2/ (E = S (dpmS/sub 2/), Se (dpmSe/sub 2/)) as well as the free ligands in dichloromethane, acetonitrile, and acetone with all results being independent of solvent. In all cases a single complex, (Hg(dpmE)/sub 2/)/sup 2+/ or (Hg(dpmE/sub 2/)/sub 2/)/sup 2+/, is formed, which is static at room temperature on the NMR time scale. Addition of excess ligand causes ligand exchange, but cooling slows the rate of ligand exchange, allowing observation of separate signals due to the mercury complex and free ligand. Coordination of selenium to mercury leads to a reduction of the phosphorus-selenium coupling constant relative to that in the free ligand, and mercury-selenium coupling is observed in some cases. Competitive exchange studies clearly show that mercury favors coordination to dpmE rather than dpmE/sub 2/. The electrochemical reduction of the complexes was studied at a mercury electrode. With the dpmE complexes, the processes are both chemically and electrochemically reversible, but in marked contrast, the dpmE/sub 2/ complexes exhibit chemical reversibility but electrochemical irreversibility, whichmore » is highly unusual for mercury complexes at a mercury electrode. This difference is explicable in terms of the preference of mercury for phosphorus rather than group 16 donor atoms. The reversible processes for the dpmE systems occur under conditions where both the mercury complex and the free ligand are present simultaneously at the electrode surface and mimic the NMR experiments where rapid exchange reactions occur. 32 refs., 5 figs., 4 tabs.« less