Reactivity of Pyridine Dipyrrolide Iron(II) Complexes with Organic Azides: C-H Amination and Iron Tetrazene Formation.

Abstract

Reaction of (MesPDPPh)Fe(thf) (H2MesPDPPh = 2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine) with organic azides has been studied. The identity of the azide substituent had a profound impact on the transformation type and nature of the observed products. Reaction with aromatic p-tolyl azide, N3Tol, resulted in exclusive formation of the corresponding iron tetrazene complex (MesPDPPh)Fe(N4Tol2). In contrast, the use of bulky 1-adamantyl azide led to clean intramolecular C-H amination of one of the benzylic C-H bonds of a mesityl substituent on the pyridine dipyrrolide, PDP, supporting ligand. The smaller aliphatic substituent in benzyl azide allowed for the isolation of two different compounds from distinct reaction pathways. One product is the result of double C-H amination of the PDP ligand via nitrene transfer, while the second one contains a dibenzyltetrazene and a benzaldimine ligand. All isolated complexes were characterized using a combination of X-ray crystallography, solid state magnetic susceptibility measurements, 1H NMR and 57Fe Mössbauer spectroscopy, and density functional theory (DFT), and their electronic structures were elucidated. Potential electronic structures for putative iron(IV) imido or iron(III) imidyl radical complexes were explored via DFT calculations.