Oxygen Atom Transfer and
Oxidative Water Incorporation
in Cuboidal Mn<sub>3</sub>MO<sub><i>n</i></sub> Complexes
Based on Synthetic, Isotopic Labeling, and Computational Studies
Jacob
S. Kanady
Jose L. Mendoza-Cortes
Emily
Y. Tsui
Robert J. Nielsen
William A. Goddard
Theodor Agapie
10.1021/ja310022p.s002
https://acs.figshare.com/articles/dataset/Oxygen_Atom_Transfer_and_Oxidative_Water_Incorporation_in_Cuboidal_Mn_sub_3_sub_MO_sub_i_n_i_sub_Complexes_Based_on_Synthetic_Isotopic_Labeling_and_Computational_Studies/2449828
The oxygen-evolving complex (OEC) of photosystem II contains
a
Mn<sub>4</sub>CaO<sub><i>n</i></sub> catalytic site, in
which reactivity of bridging oxidos is fundamental to OEC function.
We synthesized structurally relevant cuboidal Mn<sub>3</sub>MO<sub>n</sub> complexes (M = Mn, Ca, Sc; <i>n</i> = 3,4) to enable
mechanistic studies of reactivity and incorporation of μ<sub>3</sub>-oxido moieties. We found that Mn<sup>IV</sup><sub>3</sub>CaO<sub>4</sub> and Mn<sup>IV</sup><sub>3</sub>ScO<sub>4</sub> were
unreactive toward trimethylphosphine (PMe<sub>3</sub>). In contrast,
our Mn<sup>III</sup><sub>2</sub>Mn<sup>IV</sup><sub>2</sub>O<sub>4</sub> cubane reacts with this phosphine within minutes to generate a novel
Mn<sup>III</sup><sub>4</sub>O<sub>3</sub> partial cubane plus Me<sub>3</sub>PO. We used quantum mechanics to investigate the reaction
paths for oxygen atom transfer to phosphine from Mn<sup>III</sup><sub>2</sub>Mn<sup>IV</sup><sub>2</sub>O<sub>4</sub> and Mn<sup>IV</sup><sub>3</sub>CaO<sub>4</sub>. We found that the most favorable reaction
path leads to partial detachment of the CH<sub>3</sub>COO<sup>–</sup> ligand, which is energetically feasible only when Mn(III) is present.
Experimentally, the lability of metal-bound acetates is greatest for
Mn<sup>III</sup><sub>2</sub>Mn<sup>IV</sup><sub>2</sub>O<sub>4</sub>. These results indicate that even with a strong oxygen atom acceptor,
such as PMe<sub>3</sub>, the oxygen atom transfer chemistry from Mn<sub>3</sub>MO<sub>4</sub> cubanes is controlled by ligand lability, with
the Mn<sup>IV</sup><sub>3</sub>CaO<sub>4</sub> OEC model being unreactive.
The oxidative oxide incorporation into the partial cubane, Mn<sup>III</sup><sub>4</sub>O<sub>3</sub>, was observed experimentally upon
treatment with water, base, and oxidizing equivalents. <sup>18</sup>O-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.
2013-01-23 00:00:00
novel MnIII 4O
MnIII 2MnIV cubane
oxygen atom transfer chemistry
oxygen atom transfer
MnIV 3CaO OEC model
cuboidal Mn 3MOn complexes
oxidative oxide incorporation
MnIV 3CaO
Oxygen Atom Transfer
Mn 3MO cubanes
Oxidative Water Incorporation
oxido
Cuboidal Mn 3MOn Complexes
3PO
CH 3COO ligand
oxygen atom acceptor
MnIII 2MnIV