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

Abstract

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 Fe^I 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 k_H/k_D: 15.5(3); PhCH₂D k_H/k_D: 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.