High-Spin Iron Imido Complexes Competent for C–H Bond Amination

Reduction of previously reported
(ArL)­FeCl with potassium
graphite furnished a low-spin (S = 1/2) iron complex
(ArL)Fe which features an intramolecular η6-arene interaction and can be utilized as an FeI synthon
(ArL = 5-mesityl-1,9-(2,4,6-Ph3C6H2)­dipyrrin). Treatment of (ArL)Fe with adamantyl
azide or mesityl azide led to the formation of the high-spin (S = 5/2), three-coordinate imidos (ArL)­Fe­(NAd)
and (ArL)­Fe­(NMes), respectively, as determined by EPR,
zero-field 57Fe Mössbauer, magnetometry, and single
crystal X-ray diffraction. The high-spin iron imidos are reactive
with a variety of substrates: (ArL)­Fe­(NAd) reacts with
azide yielding a ferrous tetrazido (ArL)­Fe­(κ2-N4Ad2), undergoes intermolecular nitrene
transfer to phosphine, abstracts H atoms from weak C–H bonds
(1,4-cyclohexadiene, 2,4,6-tBu3C6H2OH) to afford ferrous
amido product (ArL)­Fe­(NHAd), and can mediate intermolecular
C–H amination of toluene [PhCH3/PhCD3 kH/kD: 15.5(3);
PhCH2D kH/kD: 11(1)]. The C–H bond functionalization reactivity
is rationalized from a two-step mechanism wherein each step occurs
via maximal energy and orbital overlap between the imido fragment
and the C–H bond containing substrate.