Iron(II) Complexes Featuring a Redox‐Active Dihydrazonopyrrole Ligand

Abstract

Nature uses control of the secondary coordination sphereto facilitate an astounding variety of transformations.Similarly, synthetic chemists have found metal-ligand cooperativity to be a powerful strategy for designing complexes that can mediate challenging reactivity. In particular, this strategy has been used to facilitate two electron reactions with first row transition metals thatmore typically engage in one electron redox processes. While NNN pincer ligands feature prominently in this area, examples which can potentially engage in both proton and electron transfer are less common. Dihydrazonopyrrole (DHP) ligands have been isolated in a variety of redox and protonation states when complexed to Ni. However, the redox-state of this ligand scaffold is less obvious whencomplexed to metal centers with more accessible redox couples. Here, we synthesize a new series of Fe-DHP complexes in two distinct oxidation states. Detailed characterization supports that the redox chemistryin this set is still primarily ligand based. Finally, thesecomplexes exist as 5-coordinate species with an open coordination site offering the possibility of enhanced reactivity.File list (3) download file view on ChemRxiv Manuscript.pdf (1.66 MiB) download file view on ChemRxiv TOC.tif (647.29 KiB) download file view on ChemRxiv SI.pdf (909.39 KiB)

Direct Aerobic Generation of a Ferric Hydroperoxo Intermediate Via a Preorganized Secondary Coordination Sphere

“…This presence of a low energy absorbance was previously seen with isolated tBu/Ph,-Tol DHP ligand radicals on Ni and Fe centers, further supporting the assignment of 3 with a ligand based radical on tBu,Tol DHP-H • (Scheme 2). 53,69,85 Evolution of 3 Upon Warming. As mentioned above, upon being warmed, 3 reacts further to form a new complex, 4, by UV−visible spectroscopy (Figure 1).…”

“…This presence of a low energy absorbance was previously seen with isolated t Bu/Ph,Tol DHP ligand radicals on Ni and Fe centers, further supporting the assignment of 3 with a ligand based radical on t Bu,Tol DHP-H • (Scheme ). ,, …”

Noninnocent Behavior of a (3-Imino)indol-2-yl Ligand in Metal Complexes

“…Accordingly, the electron paramagnetic resonance (EPR) spectrum of 2 measured in THF at 10 K exhibits rhombic signals with a g eff matrix of [5.52, 2.47, 1.67] that are typical of S = 3/2 systems. 27 DFT calculations at the B3LYP level also suggest an S = 3/2 ground spin state for 2, which is lower in energy than those of the S = 5/2 and S = 1/2 states by 10.6 and 14.1 kcal/mol, respectively. The optimized structure at the S = 3/2 state shows a gross resemblance to the molecular structure established by the X-ray diffraction study (Table 1), and the major difference is found in the C−N and C−C distances of the chelating rings, since those in the two chelating rings in the X-ray structure are comparable with each other and those in the optimized structure show and apparent difference.…”

“…Solution susceptibility measurements, however, indicated a solution magnetic moment of 4.1(1) μ B for 2 , pointing to an S = 3/2 ground spin state. Accordingly, the electron paramagnetic resonance (EPR) spectrum of 2 measured in THF at 10 K exhibits rhombic signals with a g eff matrix of [5.52, 2.47, 1.67] that are typical of S = 3/2 systems …”