Iron Complexes Supported by a Rigid Macrocyclic PNPN Ligand

Seesaw ligands enforce a coordination geometry of the two coligands being in a cis configuration in an octahedral environment. While nitrogen-based weak field seesaw ligands are often employed, strong field ligands with mixed nitrogen and phosphine donors are rarely encountered. Herein we report the synthesis of iron(II) dihalide complexes 1 supported by a rigid seesaw PNPN ligand, yielding C2v-symmetric compounds. Halide abstraction resulted in formation of 5-fold coordinated cationic complexes 2. Uptake of π-acidic ligands gave cationic complex 3. Dicationic complex 4, containing two acetonitrile monodentate ligands, was prepared from Fe(OTf)2. The structure of 1 and 3 was studied in solid-state and in solution, including 15N NMR spectroscopy. Furthermore, the application as catalysts in sp2-sp3 Kumada cross-coupling was demonstrated, showing high reactivity with a catalyst loading of 1 mol% in 1 h reaction time at room temperature.