Planar Chiral Rhodium Complexes of 1,4‐Benzoquinones.

Diene rhodium complexes are important catalysts in modern organic synthesis. Herein, we report a new approach to such complexes with the uncommon planar chirality. The synthesis is achieved by face‐selective coordination of the prochiral 2,5‐disubstituted‐1,4‐benzoquinones (R2‐Q) with rhodium precursors containing the chiral auxiliary ligand S‐salicyl‐oxazoline (S‐Salox). Such coordination leads to the formation of (R,R‐R2‐Q)Rh(S‐Salox) complexes in high yields and with exceptional diastereoselectivity (d. r.>20 : 1). Subsequent replacement of the auxiliary ligand provides various benzoquinone rhodium complexes with retention of the planar chirality. Combined theoretical and experimental studies show that due to their electron‐withdrawing nature benzoquinones bind metals stronger than the related 1,4‐cyclohexadiene, but weaker than other common diene ligands, such as cyclooctadiene. [ABSTRACT FROM AUTHOR]