Deprotonation of the Transition Metal Hydride (η⁵-C₅Me₅)(PMe₃)IrH₂. Synthesis and Chemistry of the Strongly Basic Lithium Iridate (η⁵-C₅Me₅)(PMe₃)Ir(H)(Li)

Treatment of (η⁵-C₅Me₅)(PMe₃)IrH₂ (1) with tert-butyllithium gives (η⁵-C₅Me₅)(PMe₃)Ir(H)(Li) (2) as a bright yellow solid. NMR evidence indicates that the lithium iridate 2 is aggregated in benzene, is converted to a single symmetrical species in THF, and is present as a dimer in DME. Treatment of 2 with 3,3-dimethylbutane trifluoromethanesulfonate-1,2-syn-d₂ (3-syn-d₂) gave the alkylated hydridoiridium complex 4a-anti-d₂, which was converted to the corresponding chloride Cp*(PMe₃)Ir(CHDCHDCMe₃)(Cl) (4c-anti-d₂) by treatment with CCl₄. 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_N2 displacement and not an outer-sphere electron-transfer reaction. Protonation studies carried out on iridate 2 with organic acids of varying pK_a allowed us to estimate that the pK_a of the dihydride 1 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 pK_a has been quantitatively estimated. Treatment of 2 with main group electrophiles allowed the preparation of several other hydridoiridium derivatives, including Cp*(PMe₃)Ir(SnPh₃)(H) (5a), Cp*(PMe₃)Ir(SnMe₃)(H) (5b), and Cp*(PMe₃)Ir(BR₂)(H) (6a, R = F; 6b, R = Ph). Reaction of 2 with acid chlorides and anhydrides leads to acyl hydrides Cp*(PMe₃)Ir(COR)(H), and fluorocarbons also react, giving products such as Cp*(PMe₃)Ir(C₆F₅)(H) in the case of hexafluorobenzene as the electrophile.