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Stereoselective Catalysis Achieved through in Situ Desymmetrization of an Achiral Iron Catalyst Precursor

Author:
Manna, Cesar M., Kaur, Aman, Yablon, Lauren M., Haeffner, Fredrik, Li, Bo, Byers, Jeffery A.
Source:
Journal of the American Chemical Society 2015 v.137 no.45 pp. 14232-14235
ISSN:
1520-5126
Subject:
catalysts, catalytic activity, iron, ligands, models, polymerization, polymers, spectral analysis, stereochemistry
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.
Agid:
5416629