Structure and C–C cross-coupling reactivity of iron(III) complexes of halogenated amine-bis(phenolate) ligands

The preparation of tetradentate amine-bis(phenol) proligands with dichloro and difluoro substituted phenol groups and their reaction with FeX3 (X = Cl or Br) is described. The compounds, 2-pyridylamino-N,N-bis(2-methylene-4,6-dichlorophenol), H2[L1]; 2-pyridylamino-N,N-bis(2-methylene-4,6-difluorophenol), H2[L2]; dimethylaminoethylamino-N,N-bis(2-methylene-4,6-dichlorophenol), H2[L3]; 2-tetrahydrofurfuryl-N,N-bis(2-methylene-4,6-dichlorophenol), H2[L4]; and methoxyethylamino-N,N-bis(2-methylene-4,6-dichlorophenol), H2[L5] were prepared in aqueous medium and obtained as white powders in good to excellent yield. Ten new iron(III) halide complexes supported by these tetradentate ligands are reported. Representative single crystal X-ray diffraction structures were obtained for H2[L1] and a water adduct of the iron(III) complex, aquachloro{2-pyridylamino-N,N-bis(2-methylene-4,6-dichlorophenolato)}iron(III), 2·H2O. The structure of the proligand H2[L1] shows intramolecular hydrogen bonding. In the solid-state structure, the iron complex exhibits intermolecular hydrogen bonding between the water ligand and the phenolate oxygen of a neighbouring complex. The anhydrous complexes were studied for catalytic activity towards C–C cross-coupling of Grignard reagent nucleophiles with alkyl halide electrophiles.

Graphical abstractThe synthesis of iron(III) complexes of chloro- and fluoro-functionalized amine-bis(phenolate) ligands, and their application for C–C cross-coupling of Grignard reagents with primary and secondary alkyl halides is described.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Halogenated amine-bis(phenol) ligands prepared “on-water”. ► New iron(III) complexes are prepared in high yield. ► Fe-catalyzed C–C cross-coupling of Grignard reagents and alkyl halides are studied.