Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 26, Issue 58, Pages 13311-13316Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.202002811
Keywords
asymmetric hydrogenation; iridium catalysis; ketones; ligand development; N-heterocyclic carbene
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Funding
- Swedish Research Council (VR)
- Stiftelsen Olle Engkvist Byggmastare
- Swedish Energy Agency
- SYNFLOW (FP7)
- Knut and Alice Wallenberg foundation [KAW 2016:0072, 2018:0066]
- Chulabhorn Graduate Institute, Chulabhorn Royal Academy, Thailand
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Novel bidentate N-heterocyclic carbene-phosphine iridium complexes have been synthesized and evaluated in the hydrogenation of ketones. Reported catalytic systems require base additives and, if excluded, need elevated temperature or high pressure of hydrogen gas to achieve satisfactory reactivity. The developed catalysts showed extremely high reactivity and good enantioselectivity under base-free and mild conditions. In the presence of 1 mol % catalyst under 1 bar hydrogen pressure at room temperature, hydrogenation was complete in 30 minutes giving up to 96 % ee. Again, this high reactivity was achieved in additive-free conditions. Mechanistic experiments demonstrated that balloon pressure of hydrogen was sufficient to form the activate species by reducing and eliminating the 1,5-cyclooctadiene ligand. The pre-activated catalyst was able to hydrogenate acetophenone with 89 % conversion in 5 min.
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