| Summary: | Heterobimetallic derivatives of a bis(carborane), [μ<sub>7,8</sub>-(1′,3′−3′-Cl-3′-PPh<sub>3</sub>-<i>closo</i>-3′,1′,2′-RhC<sub>2</sub>B<sub>9</sub>H<sub>10</sub>)-2-(<i>p</i>-cymene)-<i>closo</i>-2,1,8-RuC<sub>2</sub>B<sub>9</sub>H<sub>10</sub>] (<b>1</b>) and [μ<sub>7,8</sub>-(1′,3′−3′-Cl-3′-PPh<sub>3</sub>-<i>closo</i>-3′,1′,2′-RhC<sub>2</sub>B<sub>9</sub>H<sub>10</sub>)-2-Cp-<i>closo</i>-2,1,8-CoC<sub>2</sub>B<sub>9</sub>H<sub>10</sub>] (<b>2</b>) have been synthesised and characterised, including crystallographic studies. A minor co-product during the synthesis of compound <b>2</b> is the new species [8-{8′-2′-H-2′,2′-(PPh<sub>3</sub>)<sub>2</sub>-<i>closo</i>-2′,1′,8′-RhC<sub>2</sub>B<sub>9</sub>H<sub>10</sub>}-2-Cp-<i>closo</i>-2,1,8-CoC<sub>2</sub>B<sub>9</sub>H<sub>10</sub>] (<b>3</b>), isolated as a mixture of diastereoisomers. Although, in principle, compounds <b>1</b> and <b>2</b> could also exist as two diastereoisomers, only one (the same in both cases) is formed. It is suggested that the preferred exopolyhedral ligand orientation in the rhodacarboranes in the non-observed diastereoisomers would lead to unacceptable steric crowding between the PPh<sub>3</sub> ligand and either the <i>p</i>-cymene (compound <b>1</b>) or Cp (compound <b>2</b>) ligand of the ruthenacarborane or cobaltacarborane, respectively.
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