Study of Intermediates in lridium-(Phosphoramidite,Olefin)-Catalyzed Enantioselective Allylic Substitution

摘要

Experimental mechanistic studies of iridi-um-catalyzed, enantioselective allylic substitution enabled by (phosphoramidite,olefin) ligands are reported, (η~2-Allylic alcohol)iridium(I) and (η~3-allyl)iridium(III) complexes were synthesized and characterized by NMR spectroscopy as well as X-ray crystallography. The substrate complexes are catalytically and kinetically competent to be intermediates in allylic substitutions of branched, racemic allylic alcohols with various nucleo-philes. In addition, we have identified an off-cycle pathway involving reversible binding of molecular oxygen to iridium, which contributes to the air tolerance of the catalyst system.