ja5b12741_si_001.pdf (3.02 MB)
Photoinitiated Reactivity of a Thiolate-Ligated, Spin-Crossover Nonheme {FeNO}7 Complex with Dioxygen
journal contribution
posted on 2016-02-26, 00:00 authored by Alison
C. McQuilken, Hirotoshi Matsumura, Maximilian Dürr, Alex M. Confer, John P. Sheckelton, Maxime A. Siegler, Tyrel M. McQueen, Ivana Ivanović-Burmazović, Pierre Moënne-Loccoz, David P. GoldbergThe nonheme iron
complex, [Fe(NO)(N3PyS)]BF4, is a rare
example of an {FeNO}7 species that exhibits spin-crossover
behavior. The comparison of X-ray crystallographic studies at low
and high temperatures and variable-temperature magnetic susceptibility
measurements show that a low-spin S = 1/2 ground
state is populated at 0–150 K, while both low-spin S = 1/2 and high-spin S = 3/2 states are populated at T >
150
K. These results explain the observation of two N–O vibrational
modes at 1737 and 1649 cm–1 in CD3CN
for [Fe(NO)(N3PyS)]BF4 at room temperature. This
{FeNO}7 complex reacts with dioxygen upon photoirradiation
with visible light in acetonitrile to generate a thiolate-ligated,
nonheme iron(III)-nitro complex, [FeIII(NO2)(N3PyS)]+, which was characterized by EPR, FTIR, UV–vis, and
CSI-MS. Isotope labeling studies, coupled with FTIR and CSI-MS, show
that one O atom from O2 is incorporated in the FeIII–NO2 product. The O2 reactivity of [Fe(NO)(N3PyS)]BF4 in methanol is dramatically different from CH3CN, leading exclusively to sulfur-based oxidation, as opposed to
NO· oxidation. A mechanism is proposed for the NO· oxidation
reaction that involves formation of both FeIII-superoxo
and FeIII-peroxynitrite intermediates and takes into account
the experimental observations. The stability of the FeIII-nitrite complex is limited, and decay of [FeIII(NO2)(N3PyS)]+ leads to {FeNO}7 species
and sulfur oxygenated products. This work demonstrates that a single
mononuclear, thiolate-ligated nonheme {FeNO}7 complex can
exhibit reactivity related to both nitric oxide dioxygenase (NOD)
and nitrite reductase (NiR) activity. The presence of the thiolate
donor is critical to both pathways, and mechanistic insights into
these biologically relevant processes are presented.