Stable Iridium(IV) Complexes of an Oxidation-Resistant Pyridine-Alkoxide Ligand: Highly Divergent Redox Properties Depending on the Isomeric Form Adopted

The preparation of
the facial and meridional isomers of [Ir­(pyalk)3] (pyalk = 2-(2-pyridyl)­isopropanoate),
as model complexes for a powerful water oxidation catalyst, is reported.
The strongly donating N3O3 ligand set is very
oxidation-resistant, yet promotes facile metal-centered oxidation
to form stable Ir­(IV) compounds. The IrIII/IV reduction
potentials of the two isomers differ by 340 mV despite the identical
ligand set. A ligand field rationalization is advanced and supported
by DFT calculations.