Protonation-Enhanced Lewis Acidity of Iridium Complexes Containing Noninnocent Amidophenolates

The effect of protonation of metal complexes of noninnocent ligands is investigated. The anilidophenolate complexes Cp*Ir(t)BA(tBu) (1) and Cp*Ir(t)BA(F)Ph (2) were examined [H(2)(t)BA(tBu) = 2-tert-butylamino-4,6-di-tert-butylphenol, H(2)(t)BA(F)Ph = 2-(2-trifluoromethyl) amino-4,6-di-tert-butylphenol]. Protonation of 1 with HBF4 gave the anilinophenolate [1H](+). Crystallographic characterization of this complex revealed an elongatated Ir-N bond, but the Ir-III center remains pentacoordinate. The anilinophenolate hydride 1H(H) was prepared by treatment of [1H](+) with boron hydride reagents and with formic acid. X-ray crystallography confirmed the structure and revealed that the hydride and ammonium hydrons occupy sites on opposite sides of the IrONC6 ring. Complex 2 is protonated only by strong acids, and the resulting derivative is unstable in the absence of ligands such as CO and PMe3. Crystallographic characterization of [2(PMe3)](+) revealed that protonation occurs at O not N. The carbonylation of [2H](+) reveals the intermediacy of kinetic adducts, which are proposed to be the anilino tautomer.