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.