Effects of 2,6-Dichlorophenyl Substituents on the Coordination Chemistry of Pyridine Dipyrrolide Iron Complexes

A series of iron complexes featuring the pyridine dipyrrolide (PDP) pincer ligand [(PDPPh)-P-Cl2Ph](2-), obtained via deprotonation of 2,6-bis(5-(2,6-dichlorophenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine, (H2PDPPh)-P-Cl2Ph, is reported and structurally and spectroscopically characterized. While the bis-pyridine adduct ((PDPPh)-P-Cl2Ph)Fe(py)(2) exhibits nearly identical features as previously reported ((PDPPh)-P-Mes)Fe(py)(2) ((H2PDPPh)-P-Mes=2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine), the diethyl ether and tetrahydrofuran adducts ((PDPPh)-P-Cl2Ph)Fe(OEt2) and ((PDPPh)-P-Cl2Ph)Fe(thf) show additional weak Fe-Cl interactions that impact the overall coordination geometries and result in strong deviations from planar coordination environments. The reaction of ((PDPPh)-P-Cl2Ph)Fe(thf) with 1-adamantyl azide provided the isolable iron imido complex ((PDPPh)-P-Cl2Ph)Fe(N(1)Ad), highlighting the improved stability of [(PDPPh)-P-Cl2Ph](2-) towards intramolecular nitrene group transfer from the high-valent iron-imido unit. The electronic structure of ((PDPPh)-P-Cl2Ph)Fe(N(1)Ad) was investigated by density functional theory (DFT) and complete active space self-consistent field (CASSCF) calculations. These computational studies suggest energetically close-lying diamagnetic and paramagnetic states and help to conceptualize the unusual magnetic properties of the complex observed by variable-temperature H-1 NMR spectroscopy.

Automated summary

A series of iron complexes featuring the pyridine dipyrrolide (PDP) pincer ligand were synthesized and characterized structurally and spectroscopically. Some complexes exhibited nearly identical features as previously reported, while others showed additional weak Fe-Cl interactions and strong deviations from planar coordination geometries. Computational studies on the electronic structure of a specific complex revealed energetically close-lying diamagnetic and paramagnetic states, helping to explain the unusual magnetic properties observed.