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 ^tBA ^tBu (1) and Cp*Ir ^tBA ^FPh (2) were examined [H ₂ ^tBA ^tBu = 2-tert-butylamino-4,6-di-tert- butylphenol, H ₂ ^tBA ^FPh = 2-(2-trifluoromethyl) amino-4,6-di-tert-butylphenol]. Protonation of 1 with HBF ₄ 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 IrONC ₆ ring. Complex 2 is protonated only by strong acids, and the resulting derivative is unstable in the absence of ligands such as CO and PMe ₃. Crystallographic characterization of [2(PMe ₃)] ⁺ 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.