Toward a Square Grid Polymer:  Electrochemistry of Tentacled Tetragonal Star Connectors, C<INF>4</INF>R<INF>4</INF>−Co−C<INF>5</INF>(HgY)<INF>5</INF>, on Mercury

Electrochemical reduction of cyclobutadienecyclopentadienylcobalt derivatives, C<INF>4</INF>R<INF>4</INF>−Co−C<INF>5</INF>(HgY)<INF>5</INF> [R = C<INF>6</INF>H<INF>5</INF>−, Y = −SMe (<BO>3</BO>), −SCOMe (<BO>4</BO>), −SCH<INF>2</INF>CH<INF>2</INF>SCH<INF>3</INF> (<BO>5</BO>), −SCH<INF>2</INF>CH<INF>2</INF>SCOCH<INF>3</INF> (<BO>6</BO>); R = p-EtOCOC<INF>6</INF>H<INF>4</INF>−, Y = −SEt (<BO>7</BO>), −SCOMe (<BO>8</BO>), −SCH<INF>2</INF>CH<INF>2</INF>SCH<INF>3</INF> (<BO>9</BO>), −SCH<INF>2</INF>CH<INF>2</INF>SCOCH<INF>3</INF> (<BO>10</BO>)], and the parent C<INF>4</INF>R<INF>4</INF>−Co−C<INF>5</INF>H<INF>5</INF> [R = C<INF>6</INF>H<INF>5</INF>− (<BO>11</BO>) and R = p-EtOCOC<INF>6</INF>H<INF>4</INF>− (<BO>12</BO>)] has been examined. Reversible one-electron “metal-centered” reduction of <BO>11</BO> (−2.24 V vs Ag/AgCl) yields a stable radical anion. In <BO>12</BO>, it takes place at −1.70 V. In <BO>3</BO>−<BO>10</BO>, 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 <BO>4</BO> and <BO>8</BO> 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.