Metallaborane Heteroatom Incorporation Reactions:  Enyne Insertion into <i>arachno</i>-[(CO)(PMe<sub>3</sub>)<sub>2</sub>HIrB<sub>8</sub>H<sub>12</sub>]

<i>arachno</i>-[(CO)(PMe<sub>3</sub>)<sub>2</sub>HIrB<sub>8</sub>H<sub>12</sub>] (<b>1</b>) reacts with HC⋮C−C(CH<sub>3</sub>)CH<sub>2</sub> in xylene at 138 °C to afford [7-{C(CH<sub>3</sub>)CH<sub>2</sub>}-9,9,9-(CO)(PMe<sub>3</sub>)<sub>2</sub>-<i>nido</i>-9,7,8-IrC<sub>2</sub>B<sub>8</sub>H<sub>10</sub>] (<b>2</b>; 10%) together with traces of [5,5,5-(CO)(PMe<sub>3</sub>)<sub>2</sub>-μ-6,7-{CHC(CH<sub>3</sub>)CH<sub>2</sub>}-<i>nido</i>-5,6-IrCB<sub>8</sub>H<sub>11</sub>] (<b>3</b>, <1%). Compound <b>2 </b>is a conventional <i>nido</i> 11-vertex metallacarborane with the {C<sub>2</sub>Ir} three-atom string in the open face of the cluster, whereas compound <b>3</b> is based on a <i>nido</i> 10-vertex {5,6-IrCB<sub>8</sub>} skeleton with C(2) of the original butyne bridging adjacent B(7) and C(6) cluster open-face positions. Compounds <b>2</b> and <b>3</b> are characterized by <sup>1</sup>H, <sup>31</sup>P, and <sup>11</sup>B NMR spectroscopy and by single-crystal X-ray diffraction analysis.