Synthesis and Structure of Pyrazole-Containing Ferrocenyl Ligands for Asymmetric Catalysis

A series of new chiral ferrocenyl chelating ligands containing a tertiary phosphine and a pyrazole moiety (3) have been obtained in moderate to good yields from the reaction of the corresponding phosphinoferrocenyl amine derivatives 1a—k with the 1H-pyrazoles 2a—w in acetic acid at temperatures between 70 and 90 °C. For unsymmetrically substituted pyrazoles a remarkable site selectivity is observed, leading in most cases to only one regioisomer. Six compounds have been characterized by X-ray diffraction and were found to display very similar conformational features.