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Stereoselective Catalysis Achieved through in Situ Desymmetrization of an Achiral Iron Catalyst Precursor
Cesar M Manna1, Aman Kaur1, Lauren M Yablon1
1Eugene F. Merkert Chemistry Center, Department of Chemistry, Boston College , 2609 Beacon Street, Chestnut Hill, Massachusetts 02467, United States.
Abstract:
Stereoselective catalysis is described that proceeds with catalyst control but without the need to synthesize preformed chiral catalysts or ligands. Iron-based catalysts were discovered to effect the stereoselective polymerization of lactides starting from a single achiral precursor and the proper choice of an achiral silanol additive. Spectroscopic analysis of the polymer revealed that the stereoselectivity originates from an enantiomorphic site rather than a chain end stereocontrol mechanism. Iron intermediates that are stereogenic at iron are proposed to form in situ as a result of desymmetrization that occurs from a change in the metal coordination number. The proposed mechanism is supported by a combination of spectroscopic measurements, model complexes, kinetic measurements, and DFT calculations.
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