Bis(2,6-dinitroaryl)platinum(II) Complexes. Cis/Trans Isomerization<sup>†</sup>

The complexes <i>cis</i>-[Pt(κ<sup>2</sup>-Aryl)(κ<sup>1</sup>-Aryl)L] (κ<sup>2</sup>-Aryl = κ<sup>2</sup>-(<i>C</i>,<i>O</i>)-C<sub>6</sub>(NO<sub>2</sub>)<sub>2</sub>-2,6-(OMe)<sub>3,</sub> κ<sup>1</sup>-Aryl = κ<sup>1</sup>(<i>C</i>)-C<sub>6</sub>(NO<sub>2</sub>)<sub>2</sub>-2,6-(OMe)<sub>3</sub>, L = <i>S</i>-dmso (<b>2</b><b><i>cis</i></b>), XyNC (<b>4</b><b><i>cis</i></b>; Xy = 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>4</sub>), CO (<b>5</b><b><i>cis</i></b>), PPh<sub>3</sub> (<b>7</b><b><i>cis</i></b>)) have been obtained by reacting at room temperature <i>cis</i>-[Pt(κ<sup>2</sup>-Aryl)(κ<sup>1</sup>-Aryl)(OH<sub>2</sub>)] (<b>1</b><b><i>cis</i></b>) with dimethyl sulfoxide (dmso; 1:1 or excess), XyNC (1:1), or CO (excess) or <i>cis</i>-(Me<sub>4</sub>N)[Pt(κ<sup>2</sup>-Aryl)(κ<sup>1</sup>-Aryl)Cl] with PPh<sub>3</sub> (1:1), respectively. The room-temperature reaction of <b>1</b><b><i>cis</i></b> with XyNC (1:2), of <b>5</b><b><i>cis</i></b> with PPh<sub>3</sub> (1:1), or of <i>cis</i>-(Me<sub>4</sub>N)[Pt(κ<sup>2</sup>-Aryl)(κ<sup>1</sup>-Aryl)Cl] with PPh<sub>3</sub> (1:2) gives <i>cis</i>-[Pt(κ<sup>1</sup>-Aryl)<sub>2</sub>LL‘] (L = L‘ = XyNC (<b>3</b><b><i>cis</i></b>), PPh<sub>3</sub> (<b>8</b><b><i>cis</i></b>); L = CO, L‘ = PPh<sub>3</sub> (<b>6</b><b><i>cis</i></b>)). Complexes <b>3</b><b><i>cis</i></b>, <b>4</b><b><i>cis</i></b>, and <b>5</b><b><i>cis</i></b> isomerize on heating in solution or in the solid state to give <b>3</b><b><i>trans</i></b>, <b>4</b><b><i>trans</i></b>, and <b>5</b><b><i>trans</i></b>, respectively, while <b>6</b><b><i>cis</i></b> and <b>8</b><b><i>cis</i></b> decompose to give <b>7</b><b><i>cis</i></b> instead of their trans isomers; these, however, can be prepared by reacting <b>5</b><b><i>trans</i></b> or <b>6</b><b><i>trans</i></b> with PPh<sub>3</sub> in molar ratios of 1:1 or 1:2, respectively. When they are heated, <b>6</b><b><i>trans</i></b> and <b>8</b><b><i>trans</i></b> also descompose to <b>7</b><b><i>cis</i></b>, while <b>2</b><b><i>cis</i></b> and <i>cis</i>-[Pt(κ<sup>2</sup>-Aryl)(κ<sup>1</sup>-Aryl)L] (L = H<sub>2</sub>O (<b>1</b><b><i>cis</i></b>), PhCN, tht) decompose to a mixture of unidentified products (<b>1</b><b><i>cis</i></b>) or are recovered unchanged. These results, and others reported in the literature, on the stability of <i>cis</i>- and <i>trans</i>-diaryl complexes of platinum or palladium can be explained as the result of two competing factors, transphobia and the steric requirements of the ligands. The X-ray crystal structures of <b>2</b><b><i>cis</i></b>,<b> 3</b><b><i>cis</i></b>,<b> 3</b><b><i>trans</i></b>, <b>4</b><b><i>trans</i></b>·CHCl<sub>3</sub>, <b>5</b><b><i>cis</i></b>·CH<sub>2</sub>Cl<sub>2</sub>, <b>5</b><b><i>cis</i></b>·0.5hexane, <b>6</b><b><i>cis</i></b>,<b> 6</b><b><i>trans</i></b>·CHCl<sub>3</sub>, <b>7</b><b><i>cis</i></b>·Me<sub>2</sub>CO, and <b>8</b><b><i>trans</i></b>·0.5CHCl<sub>3</sub> have been determined.