In the 1970s, Kochi proposed the use of simple iron salts and Grignard reagents for iron-catalyzed cross-coupling reactions. However, there is limited mechanistic understanding of these systems. Many proposals exist, suggesting a myriad of potential oxidation states for the catalytically relevant species. Furthermore, some studies suggest that β-hydrogen plays a key role in the reaction mechanism. This led to the proposal that Grignard reagents without β-hydrogens (like MeMgBr and PhMgBr) will have a reaction mechanism completely different than systems using Grignard reagents with a β-hydrogens (like EtMgBr). Previous work in the group has provided significant evidence for catalytically relevant iron species by crystallizing Fe8Me12- from FeCl3 and MeMgBr. Characterization of the Fe8Me12- crystal via EPR and MCD studies is consistent with S = 1/2 species Kochi originally reported. Despite the advances in understanding iron-catalyzed cross-coupling using simple iron salts and MeMgBr, there is limited evidence of intermediate species when aryl Grignard reagents are used. Current efforts are being placed on isolating and crystallographically characterizing intermediate iron species formed in-situ from simple iron salts and aryl Grignard reagents. Preliminary EPR and Mössbauer spectroscopy suggest intermediates formed in the presence of aryl Grignard reagents are different than intermediates formed in the presence of MeMgBr.

Mechanistic insight and structure determination of in-situ species in iron-catalyzed cross-coupling with aryl nucleophiles

254th National Meeting (2017)

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