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