Counter-ligand and solvent dependent oxygen-metal nteractions of hemilabile coordinating hydroxy groups in chiral diphosphine rhodium(I) hydrogenation catalysts

摘要

In cationic Rh[(R,R)-1,4-bis(diphenylphosphino)butane-2,3-diol] complexes the interaction of the hemilabile coordinating hydroxy groups with the metal is strongly dependent upon the nature of the counter-ligand and the solvent. As a result of the 'arm-off, arm-on' mechanism the conformation of the chirality inducing backbone is changed. Spectroscopic and catalytic investigations demonstrate that the #eta#~3-coordination mode of the tetradentate ligand is reponsible for the deceleration of the asymmetric hydrogenation. By the assistance of the second HO-group the Rh-O interaction can be suspended.