ja310022p_si_002.cif (41.72 kB)
Oxygen Atom Transfer and Oxidative Water Incorporation in Cuboidal Mn3MOn Complexes Based on Synthetic, Isotopic Labeling, and Computational Studies
dataset
posted on 2013-01-23, 00:00 authored by Jacob
S. Kanady, Jose L. Mendoza-Cortes, Emily
Y. Tsui, Robert J. Nielsen, William A. Goddard, Theodor AgapieThe oxygen-evolving complex (OEC) of photosystem II contains
a
Mn4CaOn catalytic site, in
which reactivity of bridging oxidos is fundamental to OEC function.
We synthesized structurally relevant cuboidal Mn3MOn complexes (M = Mn, Ca, Sc; n = 3,4) to enable
mechanistic studies of reactivity and incorporation of μ3-oxido moieties. We found that MnIV3CaO4 and MnIV3ScO4 were
unreactive toward trimethylphosphine (PMe3). In contrast,
our MnIII2MnIV2O4 cubane reacts with this phosphine within minutes to generate a novel
MnIII4O3 partial cubane plus Me3PO. We used quantum mechanics to investigate the reaction
paths for oxygen atom transfer to phosphine from MnIII2MnIV2O4 and MnIV3CaO4. We found that the most favorable reaction
path leads to partial detachment of the CH3COO– ligand, which is energetically feasible only when Mn(III) is present.
Experimentally, the lability of metal-bound acetates is greatest for
MnIII2MnIV2O4. These results indicate that even with a strong oxygen atom acceptor,
such as PMe3, the oxygen atom transfer chemistry from Mn3MO4 cubanes is controlled by ligand lability, with
the MnIV3CaO4 OEC model being unreactive.
The oxidative oxide incorporation into the partial cubane, MnIII4O3, was observed experimentally upon
treatment with water, base, and oxidizing equivalents. 18O-labeling experiments provided mechanistic insight into the position
of incorporation in the partial cubane structure, consistent with
mechanisms involving migration of oxide moieties within the cluster
but not consistent with selective incorporation at the site available
in the starting species. These results support recent proposals for
the mechanism of the OEC, involving oxido migration between distinct
positions within the cluster.
History
Usage metrics
Categories
Keywords
novel MnIII 4OMnIII 2MnIV cubaneoxygen atom transfer chemistryoxygen atom transferMnIV 3CaO OEC modelcuboidal Mn 3MOn complexesoxidative oxide incorporationMnIV 3CaOOxygen Atom TransferMn 3MO cubanesOxidative Water IncorporationoxidoCuboidal Mn 3MOn Complexes3POCH 3COO ligandoxygen atom acceptorMnIII 2MnIV
Licence
Exports
RefWorks
BibTeX
Ref. manager
Endnote
DataCite
NLM
DC