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Borane-assisted hydride addition and dihydrogen reductive elimination at iridium: a gateway to Ir(-i)/Ir(i) redox
Hajime Kameo1, Younosuke Kawahara1, Yoshihiro Shimoyama2
1Department of Chemistry, Graduate School of Science, Osaka Metropolitan University Sugimoto-cho, Sumiyoshi-ku Osaka 558-8585 Japan h.kameo@omu.ac.jp.
Abstract:
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, T 1 measurements, IR (ν CO), XPS (Ir 4f7/2), and DFT analyses support a d 8 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.
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