Strong Electronic Effects on Enantioselectivity in Rhodium‐Catalyzed Hydroborations with Novel Pyrazole‐Containing Ferrocenyl Ligands

Abstract

The highest enantioselectivity yet for a hydroboration (98% ee) was achieved with the ferrocenyl ligand 1, R1 = R3 = Me, R2 = H, Ar = 4CF3C6H4, in the Rh-catalyzed reaction of styrene with catecholborane. The influence of the substituents on both the pyrazolyl and phosphano fragments was studied, and the observations tentatively interpreted in terms of the varying electronic asymmetry they engender at the metal center.