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 (eta(5)-C5Me5)(PMe3)IrH2 (1) with tert-butyllithium gives (eta(5)-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-d(2) (3-syn-d(2)) gave the alkylated hydridoiridium complex 4a-anti-d(2), which was converted to the corresponding chloride Cp*(PMe3)Ir(CHDCHDCMe3)(Cl) (4c-anti-d(2)) 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(N)2 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(BRr)(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.