Borane-assisted hydride addition and dihydrogen reductive elimination at iridium: a gateway to Ir(– i )/Ir( i ) redox catalysis

The σ-electron accepting character of the Z-type borane ligand enables hydride addition to the neutral Ir(i) carbonyl hydride complex 1 upon reaction with potassium alkoxide, concomitantly affording a ketone and an anionic Ir(i) complex 2 bearing two terminal hydride ligands. Single-crystal X-ray diffraction, T1 measurements, IR (νCO), XPS (Ir 4f7/2), and DFT analyses support a d8 Ir(i) assignment for 2. Thermolysis of 2 triggers H2 reductive elimination to give the structurally characterized tetrahedral Ir(–i) carbonyl complex 3 and exposure of 3 to H2 cleanly regenerates 2, substantiating a reversible Ir(–i)/Ir(i) oxidative addition/reductive elimination process. This process is amenable to catalysis, as illustrated by the dehydrogenation of a secondary alcohol, highlighting the potential of Lewis-acidic Z-type ligands to access unconventional low-valent redox chemistry at iridium.