Homogeneous CO hydrogenation and transfer hydrogenation catalyzed by ruthenium(II) complexes containing optically active Ph2PCH(Ph)CH(Me)NH2 and 1,2-C5H8(PPh2)2 ligands

Combination of (1S,2S)-cyclopentanediylbis(diphenylphosphine) with [Ru(η4-C8H12){η3-(CH2)2CMe}2] afforded the chelate complex [Ru{η3-(CH2)2CMe}2{(1S,2S)-C5H8(PPh2)2}] (1), which gave (OC-6-13)-[RuCl2{(1S,2S)-C5H8(PPh2)2}{(1S,2S)-Ph2PCH(Ph)CH(Me)NH2}] (2) upon reaction with methanolic HCl in acetone, followed by the addition of the β-aminophosphine in DMF. The (P ∩ N)2-chelated complexes (OC-6-13)-[RuCl2{(1S,2S)-Ph2PCH(Ph)CH(Me)NH2}2] (3) and (OC-6-13)-[RuCl2{(1R,2S)-Ph2PCH(Ph)CH(Me)NH2}2] (4) resulted from RuCl3 · 3H2O and the P,N ligands under reducing conditions. The crystal structures of 3 and 4 were determined by single-crystal X-ray diffraction. Following activation by KOBu-t in isopropanol, compounds 2–4 catalyzed the enantioselective transfer hydrogenation of acetophenone with i-PrOH as the hydrogen source as well as the direct hydrogenation of the ketone by H2 in low to moderate e.e. (up to 67%).

Both (P ∩ N)2- and P ∩ P/P ∩ N-coordinated RuII complexes with optically active Ph2PCH(Ph)CH(Me)NH2 and 1,2-trans-C5H8(PPh2)2 ligands are (pre)catalysts for the enantioselective transfer hydrogenation of acetophenone with i-PrOH as the hydrogen source as well as for the direct hydrogenation of the ketone by H2 under pressure.Figure optionsDownload as PowerPoint slide