A Stable Coordination Complex of Rh(IV) in an N,O-Donor Environment

We describe facial and meridional isomers of RhIII (pyalk) 3, as well as meridional RhIV (pyalk) 3+ pyalk =2- (2-pyridyl) -2-propanoate, the first coordination complex in an N, O-donor environment to show a clean, reversible RhIII/IV redox couple and to have a stable Rh (IV) form, which we characterize by EPR and UV–visible spectroscopy as well as X-ray crystallography. The unprecedented stability of the Rh (IV) species is ascribed to the exceptional donor strength of the ligands, their oxidation resistance, and the meridional coordination geometry.