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

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.