Synthesis of Mixed-Metal (Ru−Rh) Bimetallacarboranes via <i>exo</i>-<i>nido</i>- and <i>closo</i>-Ruthenacarboranes. Molecular Structures of (η<sup>4</sup>-C<sub>8</sub>H<sub>12</sub>)Rh(μ-H)Ru(PPh<sub>3</sub>)<sub>2</sub>(η<sup>5</sup>-C<sub>2</sub>B<sub>9</sub>H<sub>11</sub>) and (CO)(PPh<sub>3</sub>)Rh(μ-H)Ru(PPh<sub>3</sub>)<sub>2</sub>(η<sup>5</sup>-C<sub>2</sub>B<sub>9</sub>H<sub>11</sub>) and Their Anionic <i>closo</i>-Ruthenacarborane Precursors

The reaction of <i>exo</i>-<i>nido</i>-5,6,10-[Cl(PPh<sub>3</sub>)<sub>2</sub>Ru]-5,6,10-(μ-H)<sub>3</sub>-10-H-7,8-C<sub>2</sub>B<sub>9</sub>H<sub>8</sub>) (<b>1</b>) with [(η<sup>4</sup>-diene)RhCl]<sub>2</sub> in EtOH or with [(CO)<sub>2</sub>RhCl]<sub>2</sub> in MeOH in the presence of KOH produced novel mixed-metal bimetallacarboranes (η<sup>4</sup>-diene)Rh(μ-H)Ru(PPh<sub>3</sub>)<sub>2</sub>(η<sup>5</sup>-C<sub>2</sub>B<sub>9</sub>H<sub>11</sub>) (<b>4</b>, diene = COD; <b>5</b>, diene = NBD) or (CO)(PPh<sub>3</sub>)Rh(μ-H)Ru(PPh<sub>3</sub>)<sub>2</sub>(η<sup>5</sup>-C<sub>2</sub>B<sub>9</sub>H<sub>11</sub>) (<b>10</b>) along with a small amount of the mononuclear complexes <i>closo</i>-(CO)<sub>2</sub>(PPh<sub>3</sub>)Ru(η<sup>5</sup>-C<sub>2</sub>B<sub>9</sub>H<sub>11</sub>) and <i>closo</i>-(CO)(PPh<sub>3</sub>)<sub>2</sub>Ru(η<sup>5</sup>-C<sub>2</sub>B<sub>9</sub>H<sub>11</sub>), respectively. Complexes <b>4</b> and <b>10</b> were characterized by single-crystal X-ray diffraction studies which revealed the existence of two types of bridging bonds Ru−H−Rh and B−H···Rh in these species. The bridging hydrogen atoms are asymmetrically disposed within these linkages. Several separate experiments have been carried out for the synthesis of the anionic complex [<i>closo</i>-3,3-(PPh<sub>3</sub>)<sub>2</sub>-3-H-3,1,2-RuC<sub>2</sub>B<sub>9</sub>H<sub>11</sub>]<sup>-</sup>, which is proposed to be the key intermediate in the reaction of <b>1</b> with [(η<sup>4</sup>-diene)RhCl]<sub>2</sub>. The reaction of (PPh<sub>3</sub>)<sub>3</sub>RuHCl with [7,8-C<sub>2</sub>B<sub>9</sub>H<sub>12</sub>][Me<sub>3</sub>NH] under reflux in THF in the presence of Et<sub>4</sub>NCl yielded [<i>closo</i>-3,3-(PPh<sub>3</sub>)<sub>2</sub>-3-Cl-3,1,2-RuC<sub>2</sub>B<sub>9</sub>H<sub>11</sub>][Et<sub>4</sub>N] (<b>7</b>), which after reduction by LiAlH<sub>4</sub> in THF afforded [<i>closo</i>-3,3-(PPh<sub>3</sub>)<sub>2</sub>-3-H-3,1,2-RuC<sub>2</sub>B<sub>9</sub>H<sub>11</sub>][Et<sub>4</sub>N] (<b>8</b>) in poor yield. Alternatively, treatment of (PPh<sub>3</sub>)<sub>3</sub>RuHCl with Tl<sub>2</sub>[7,8-C<sub>2</sub>B<sub>9</sub>H<sub>11</sub>] in THF at ambient temperature led to <b>8</b> in 84% yield. The anionic complex <b>8</b> and the known neutral <i>closo</i>-3,3-(PPh<sub>3</sub>)<sub>2</sub>-3-Cl-3-H-3,1,2-RuC<sub>2</sub>B<sub>9</sub>H<sub>11</sub> (<b>6</b>) have been substituted for <b>1</b> in the synthesis of <b>4</b> under the same conditions. Structures of both anionic <i>closo</i>-ruthenacarboranes <b>7</b> and <b>8</b> have been confirmed by single-crystal X-ray diffraction studies. The NMR data [<sup>1</sup>H, <sup>13</sup>C{<sup>1</sup>H}, <sup>31</sup>P{<sup>1</sup>H}, and <sup>11</sup>B] for the new mononuclear and binuclear ruthenacarborane complexes are discussed in detail.