Contribution of the <i>n</i><i>ido</i>-[7,8-C<sub>2</sub>B<sub>9</sub>H<sub>10</sub>]<sup>-</sup> Anion to the Chemical Stability, Basicity, and <sup>31</sup>P NMR Chemical Shift in <i>n</i><i>ido-o-</i>Carboranylmonophosphines

The icosahedral dicarboranes and their decapitated anion, 1-R‘-1,2-C<sub>2</sub>B<sub>10</sub>H<sub>10</sub> (<i>closo</i>) and [7-R‘-7,8-C<sub>2</sub>B<sub>9</sub>H<sub>10</sub>]<sup>-</sup> (<i>nido</i>), exert a distict influence at the α position of substituents attached to the cage carbon atom. The <i>closo</i> fragment is electron-withdrawing while the <i>nido </i>anion is electron-releasing. These effects are studied by <sup>31</sup>P NMR, phosphorus oxidation, and phosphorus protonation in [7-PR<sub>2</sub>-8-R‘-7,8-C<sub>2</sub>B<sub>9</sub>H<sub>10</sub>]<sup>-</sup> species. The <sup>31</sup>P NMR chemical shift dependence is related to the R alkyl or aryl nature of [7-PR<sub>2</sub>-8-R‘-7,8-C<sub>2</sub>B<sub>9</sub>H<sub>10</sub>]<sup>-</sup>. No direct relationship to the nature of the R substituent on the <i>nido</i>-carboranylmonphosphine toward oxidation has been found. The basicity of the <i>nido</i>-alkylcarboranylmonophosphines is the highest while the lowest corresponds to the <i>nido</i>-arylcarboranylmonophosphines. Interpretation can be carried out qualitatively by considering the electronic properties of the cluster and the nature of the R groups. The influence of R‘ is less relevant. Confirmation of the molecular structure of the oxidated and protonated <i>nido</i>-carboranylmonophosphine compounds was obtained by X-ray diffraction analysis of [NBu<sub>4</sub>][7-P(O)Ph<sub>2</sub>-8-Ph-7,8-C<sub>2</sub>B<sub>9</sub>H<sub>10</sub>] and [7-PH(<sup>i</sup>Pr)<sub>2</sub>-8-Me-7,8-C<sub>2</sub>B<sub>9</sub>H<sub>10</sub>].