The N‐Methylpyrrolidone (NMP) Effect in Iron‐Catalyzed Cross‐Coupling with Simple Ferric Salts and MeMgBr. Issue 22 (8th May 2018)

• Record Type: Journal Article
• Authors: Muñoz, Salvador B.; Daifuku, Stephanie L.; Sears, Jeffrey D.; Baker, Tessa M.; Carpenter, Stephanie H.; Brennessel, William W.; Neidig, Michael L.
• Is Part Of: Angewandte Chemie international edition. Volume 57:Issue 22(2018)
• Page Start: 6496
• Page End: 6500
• Publication Date: 2018-05-08
• Subjects: cross-coupling -- iron -- MCD spectroscopy -- Mössbauer spectroscopy -- N-methylpyrrolidone; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201802087
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: The use of N ‐methylpyrrolidone (NMP) as a co‐solvent in ferric salt catalyzed cross‐coupling reactions is crucial for achieving the highly selective, preparative scale formation of cross‐coupled product in reactions utilizing alkyl Grignard reagents. Despite the critical importance of NMP, the molecular level effect of NMP on in situ formed and reactive iron species that enables effective catalysis remains undefined. Herein, we report the isolation and characterization of a novel trimethyliron(II) ferrate species, [Mg(NMP)6 ][FeMe3 ]2 (1 ), which forms as the major iron species in situ in reactions of Fe(acac)3 and MeMgBr under catalytically relevant conditions where NMP is employed as a co‐solvent. Importantly, combined GC analysis and 57 Fe Mössbauer spectroscopic studies identified 1 as a highly reactive iron species for the selective formation generating cross‐coupled product. These studies demonstrate that NMP does not directly interact with iron as a ligand in catalysis but, alternatively, interacts with the magnesium cations to preferentially stabilize the formation of 1 over [Fe8 Me12 ] − cluster generation, which occurs in the absence of NMP. Abstract : The N ‐methylpyrrolidone (NMP) effect promoting the highly selective formation of cross‐coupled products in reactions utilizing simple ferric salts and alkyl Grignard reagents is explored. A new three‐coordinate homoleptic iron‐alkyl complex, [Mg(NMP)6 ][FeMe3 ]2, is identified as the key in situ formed iron species in reactions with MeMgBr, and shown to be highly reactive for the selective generation of cross‐coupled product.