Solution Structure and Behavior of Benzophenone-based Achiral Bisphosphine Ligands in Noyori-Type Ru(II)-Catalysts

✍ Scribed by Qing Jing; Christian A. Sandoval; Yoshiki Yamaguchi; Koichi Kato; Kui-Ling Ding

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 136 KB
• Volume: 25
• Category: Article
• ISSN: 0256-7660
• DOI: 10.1002/cjoc.200790217

✦ Synopsis

Abstract

We herein report on solution structural studies of Ru^II^ catalysts (3a, 9) composed of achiral bisphosphine ligands (4, 8) and the enantiopure 1,2‐diphenylethylenediamine (DPEN). Complete chiral induction from enantiopure (R,R)‐DPEN to achiral bisphosphine ligand 3a was observed in solution, with the complex adopting a single, stable and non‐fluxional (even at 70 °C) configuration. The coordination of the CO moiety in 4 to the cationic Ru^II^ center is considered to be of key importance in providing the higher thermodynamic and kinetic rotation barrier for the flexible bisphosphine ligand in the complex. The obtained enantioselectivity (91% enantiomeric excess) and sense of chiral induction in the hydrogenation of acetophenone were found to be solely dependent on the chirality of the 1,2‐diamine. Consistent with the hydrogenation product, the (R,R)‐DPEN induces a M‐conformation (right‐handed) chirality for flexible phosphine ligand 4 in the complex, resulting in a λ,λ‐configuration about the Ru^II^ center.