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The N ‐Methylpyrrolidone (NMP) Effect in Iron‐Catalyzed Cross‐Coupling with Simple Ferric Salts and MeMgBr
Author(s) -
Muñoz Salvador B.,
Daifuku Stephanie L.,
Sears Jeffrey D.,
Baker Tessa M.,
Carpenter Stephanie H.,
Brennessel William W.,
Neidig Michael L.
Publication year - 2018
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201802087
Subject(s) - chemistry , catalysis , reagent , ferric , alkyl , coupling reaction , ligand (biochemistry) , solvent , salt (chemistry) , in situ , combinatorial chemistry , magnesium , inorganic chemistry , organic chemistry , biochemistry , receptor
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 ][FeMe 3 ] 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 [Fe 8 Me 12 ] − cluster generation, which occurs in the absence of NMP.