The Effect of beta-Hydrogen Atoms on Iron Speciation in Cross-Couplings with Simple Iron Salts and Alkyl Grignard Reagents

摘要

The effects of beta-hydrogen-containing alkyl Grignard reagents in simple ferric salt cross-couplings have been elucidated. The reaction of FeCl3 with EtMgBr in THF leads to the formation of the cluster species [Fe8Et12](2-), a rare example of a structurally characterized metal complex with bridging ethyl ligands. Analogous reactions in the presence of NMP, a key additive for effective cross-coupling with simple ferric salts and beta-hydrogen-containing alkyl nucleophiles, result in the formation of [FeEt3](-). Reactivity studies demonstrate the effectiveness of [FeEt3](-) in rapidly and selectively forming the cross-coupled product upon reaction with electrophiles. The identification of iron-ate species with EtMgBr analogous to those previously observed with MeMgBr is a critical insight, indicating that analogous iron species can be operative in catalysis for these two classes of alkyl nucleophiles.