General Synthesis of Di-μ-oxo Dimanganese Complexes as Functional Models for the Oxygen Evolving Complex of Photosystem II
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posted on 2005-10-17, 00:00 authored by Hongyu Chen, Ranitendranath Tagore, Siddhartha Das, Christopher Incarvito, J. W. Faller, Robert H. Crabtree, Gary W. BrudvigA series of complexes with the formula [Mn<sup>III/IV</sup><sub>2</sub>(μ-O)<sub>2</sub>(L)<sub>2</sub>(X)<sub>2</sub>]<sup>3+</sup> have been prepared in situ from Mn<sup>II</sup>LCl<sub>2</sub> precursors
by a general preparative method (L = terpy, Cl-terpy, Br-terpy, Ph-terpy, tolyl-terpy, mesityl-terpy, <i>t</i> Bu<sub>3</sub>-terpy,
EtO-terpy, py-phen, dpya, Me<sub>2</sub>N-terpy, or HO-terpy, and X = a labile ligand such as water, chloride, or sulfate).
The parent complex, where L = terpy and X = water, is a functional model for the oxygen-evolving complex of
photosystem II (Limburg, et al. <i>J. Am. Chem. Soc.</i> <b>2001</b>, <i>123</i>, 423−430). Crystals of Mn<sup>II</sup>(dpya)Cl<sub>2</sub>, Mn<sup>II</sup>(Ph-terpy)Cl<sub>2</sub>, Mn<sup>II</sup>(mesityl-terpy)Cl<sub>2</sub>, and an organic-soluble di-μ-oxo di-aqua dimanganese complex, [Mn<sup>III/IV</sup><sub>2</sub>(μ-O)<sub>2</sub>(mesityl-terpy)<sub>2</sub>(OH<sub>2</sub>)<sub>2</sub>](NO<sub>3</sub>)<sub>3</sub>, were obtained and characterized by X-ray crystallography. Solutions of the in situ-formed
di-μ-oxo dimanganese complexes were characterized by electrospray mass spectrometry, EPR spectroscopy, and
UV−visible spectroscopy, and the rates of catalytic oxygen-evolving activity were assayed. The use of Mn<sup>II</sup>LCl<sub>2</sub>
precursors leads to higher product purity of the Mn dimers while achieving the 1:1 ligand to Mn stoichiometry
appropriate for catalytic activity assay. These methods can be used to screen the catalytic activity of other di-μ-oxo
dimanganese complexes generated by using a ligand library.
