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

Abstract

Experimental mechanistic studies of iridium-catalyzed, enantioselective allylic substitution enabled by (phosphoramidite,olefin) ligands are reported. (η²-Allylic alcohol)iridium(I) and (η³-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 nucleophiles. 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.