10.1021/om500727t.s001 Jonathan M. Darmon Jonathan M. Darmon Renyuan Pony Yu Renyuan Pony Yu Scott P. Semproni Scott P. Semproni Zoë R. Turner Zoë R. Turner S. Chantal E. Stieber S. Chantal E. Stieber Serena DeBeer Serena DeBeer Paul J. Chirik Paul J. Chirik Electronic Structure Determination of Pyridine N‑Heterocyclic Carbene Iron Dinitrogen Complexes and Neutral Ligand Derivatives American Chemical Society 2015 Neutral Ligand DerivativesThe π acceptor base metal compounds Electronic Structure Determination spectroscopic iron dinitrogen example chelate Fe iPrCNC DFT NMR complex pyridine CNC 2015-12-17 05:07:19 Journal contribution https://acs.figshare.com/articles/journal_contribution/Electronic_Structure_Determination_of_Pyridine_N_Heterocyclic_Carbene_Iron_Dinitrogen_Complexes_and_Neutral_Ligand_Derivatives/2041740 The electronic structures of pyridine N-heterocyclic dicarbene (<sup>iPr</sup>CNC) iron complexes have been studied by a combination of spectroscopic and computational methods. The goal of these studies was to determine if this chelate engages in radical chemistry in reduced base metal compounds. The iron dinitrogen example (<sup>iPr</sup>CNC)­Fe­(N<sub>2</sub>)<sub>2</sub> and the related pyridine derivative (<sup>iPr</sup>CNC)­Fe­(DMAP)­(N<sub>2</sub>) were studied by NMR, Mössbauer, and X-ray absorption spectroscopy and are best described as redox non-innocent compounds with the <sup>iPr</sup>CNC chelate functioning as a classical π acceptor and the iron being viewed as a hybrid between low-spin Fe(0) and Fe­(II) oxidation states. This electronic description has been supported by spectroscopic data and DFT calculations. Addition of <i>N</i>,<i>N</i>-diallyl-<i>tert</i>-butylamine to (<sup>iPr</sup>CNC)­Fe­(N<sub>2</sub>)<sub>2</sub> yielded the corresponding iron diene complex. Elucidation of the electronic structure again revealed the CNC chelate acting as a π acceptor with no evidence for ligand-centered radicals. This ground state is in contrast with the case for the analogous bis­(imino)­pyridine iron complexes and may account for the lack of catalytic [2π + 2π] cycloaddition reactivity.