Mixtures of Configurationally Stable and Fluxional Atropisomeric Monodentate P Ligands in Asymmetric Rh-Catalyzed Olefin Hydrogenation

✍ Scribed by Manfred T. Reetz; Xiaoguang Li

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 268 KB
• Volume: 44
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/anie.200462612

✦ Synopsis

Several years ago it was reported that monodentate phosphites, [1] phosphonites, [2] and phosphoramidites [3] derived from 2,2'-dihydroxy-1,1'-binaphthyl (BINOL) are efficient ligands in various Rh-catalyzed asymmetric olefin-hydrogenation reactions (90-99 % ee). These observations were surprising, because it had been accepted that chelating bidentate P ligands are generally necessary for high levels of enantioselectivity, probably due to restricted rotation in the Rh complexes. Examples of other types of monodentate P ligands are also known. [4] Preliminary mechanistic results show that two monodentate phosphites (or phosphonites) are bonded to Rh in the transition state of hydrogenation [5] when the precatalyst is [Rh(cod)(1) 2 ]BF 4 (cod = cycloocta-1,5diene). Based on these results we subsequently demonstrated that the use of a mixture of two different monodentate P ligands constitutes a new and efficient approach to combinatorial asymmetric transition-metal catalysis. [6] Once a library

[*] Prof.