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Asymmetric Rhodium(I)-Catalyzed C–C Activations with Zwitterionic Bis-phospholane Ligands

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journal contribution
posted on 10.02.2014, 00:00 by Evelyne Parker, Nicolai Cramer
The development of unconventional ligand scaffolds is an important aspect to alter reaction pathways of transition-metal-catalyzed reactions. The nature of the counterion of cationic metal complexes plays an important role in the catalyst reactivity. We herein report a chiral anionic bidentate bis-phosphine ligand based on the popular phospholane scaffold. Subsequently, zwitterionic rhodium­(I) complexes with no external counterion were synthesized, and their potential was evaluated in asymmetric carbon–carbon bond activation of cyclobutanones. This type of rhodium complex allows for a significantly lower reaction temperature than analogous cationic rhodium complexes and enables, for the first time, asymmetric transformations with up to 93.5:6.5 enantiomeric ratio.