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Electronic Structure Determination of Pyridine N‑Heterocyclic Carbene Iron Dinitrogen Complexes and Neutral Ligand Derivatives
journal contribution
posted on 2015-12-17, 05:07 authored by Jonathan
M. Darmon, Renyuan Pony Yu, Scott P. Semproni, Zoë R. Turner, S. Chantal E. Stieber, Serena DeBeer, Paul J. ChirikThe electronic structures of pyridine
N-heterocyclic dicarbene
(iPrCNC) 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 (iPrCNC)Fe(N2)2 and the related pyridine derivative (iPrCNC)Fe(DMAP)(N2) were studied by NMR, Mössbauer,
and X-ray absorption spectroscopy and are best described as redox
non-innocent compounds with the iPrCNC 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 N,N-diallyl-tert-butylamine to (iPrCNC)Fe(N2)2 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.