Deprotonation of the Transition Metal Hydride (η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(PMe<sub>3</sub>)IrH<sub>2</sub>. Synthesis and Chemistry of the Strongly Basic Lithium Iridate (η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(PMe<sub>3</sub>)Ir(H)(Li)

Treatment of (η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(PMe<sub>3</sub>)IrH<sub>2</sub> (<b>1</b>) with <i>tert</i>-butyllithium gives (η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(PMe<sub>3</sub>)Ir(H)(Li) (<b>2</b>) as a bright yellow solid. NMR evidence indicates that the lithium iridate <b>2</b> is aggregated in benzene, is converted to a single symmetrical species in THF, and is present as a dimer in DME. Treatment of <b>2</b> with 3,3-dimethylbutane trifluoromethanesulfonate-1,2-<i>syn-d</i><sub>2</sub> (<b>3-</b><b><i>syn-d</i></b><b><sub>2</sub></b>) gave the alkylated hydridoiridium complex <b>4a-</b><b><i>anti-d</i></b><b><sub>2</sub></b>, which was converted to the corresponding chloride Cp*(PMe<sub>3</sub>)Ir(CHDCHDCMe<sub>3</sub>)(Cl) (<b>4c-</b><b><i>anti-d</i></b><b><sub>2</sub></b>) by treatment with CCl<sub>4</sub>. Analysis of this material by NMR spectroscopy showed that it was contaminated with ≤15% syn isomer. The alkylation therefore proceeds with predominant inversion of configuration at carbon, indicating that the major pathway is an S<sub>N</sub>2 displacement and not an outer-sphere electron-transfer reaction. Protonation studies carried out on iridate <b>2</b> with organic acids of varying p<i>K</i><sub>a</sub> allowed us to estimate that the p<i>K</i><sub>a</sub> of the dihydride <b>1</b> falls in the range 38−41, making it less acidic than DMSO and more acidic than toluene. This represents the least acidic transition metal hydride whose p<i>K</i><sub>a</sub> has been quantitatively estimated. Treatment of <b>2</b> with main group electrophiles allowed the preparation of several other hydridoiridium derivatives, including Cp*(PMe<sub>3</sub>)Ir(SnPh<sub>3</sub>)(H) (<b>5a</b>), Cp*(PMe<sub>3</sub>)Ir(SnMe<sub>3</sub>)(H) (<b>5b</b>), and Cp*(PMe<sub>3</sub>)Ir(BR<sub>2</sub>)(H) (<b>6a</b>, R = F; <b>6b</b>, R = Ph). Reaction of <b>2</b> with acid chlorides and anhydrides leads to acyl hydrides Cp*(PMe<sub>3</sub>)Ir(COR)(H), and fluorocarbons also react, giving products such as Cp*(PMe<sub>3</sub>)Ir(C<sub>6</sub>F<sub>5</sub>)(H) in the case of hexafluorobenzene as the electrophile.