Reversible Redox Chemistry and Catalytic C(sp3)-H Amination Reactivity of a Paramagnetic Pd Complex Bearing a Redox-Active o-Aminophenol-Derived NNO Pincer Ligand

The synthesis, spectroelectrochemical characterization (ultraviolet-visible and nuclear magnetic resonance), solid state structures, and computational metric parameters of three isostructural PdCI(NNO) complexes 1 [PdCl(NNOISQ)], 2 {[PdCl(NNOAP)](-1)}, and 5 {[PdCl(NNOIBQ)](+)} (NNO = o-aminophenol-derived redox-active ligand with a pendant pyridine) with different NNO oxidation states are described. The reduced diamagnetic complex 2 readily reacts with halogenated solvents, including lattice solvent from crystalline pure material, as supported by spectroscopic data and density functional theory calculations. Thorough removal of chlorinated impurities allows for modest catalytic turnover in the conversion of 4-phenylbutyl azide into N-protected 2-phenylpyrrolidine, which is the first example of a palladium-catalyzed radical-type transformation facilitated by a redox-active ligand as well as the first C-H amination mediated by ligand-to-substrate single-electron transfer.