A manganese oxido complex bearing facially coordinating trispyridyl ligands - is coordination geometry crucial for water oxidation catalysis?

作者：Berends Hans Martin; Manke Anne Marie; Naether Christian; Tuczek Felix^*; Kurz Philipp

来源：Dalton Transactions, 2012, 41(20): 6215-6224.

DOI：10.1039/c2dt30129f

In this work the synthesis of the novel manganese complex [Mn-2(III,III)(tpdm)(2)(mu-O)(mu-OAc)(2)](2+) (1) is reported, containing two manganese centres ligated to the unusual, facially coordinating, all-pyridine ligand tpdm (tris(2-pyridyl)methane). The geometric and electronic properties of complex 1 were characterised by X-ray crystallography, vibrational (IR and Raman) and optical spectroscopy (UV/Vis and MCD). Cyclic voltammograms of 1 showed a quasi-reversible oxidation event at 950 mV and an irreversible reduction wave at -250 mV vs. Ag/Ag+. The redox behaviour of the compound was investigated in detail by UV/Vis- and X-band EPR-spectroelectrochemistry. Both electrochemical (+1200 mV) and chemical (tBuOOH) oxidations transform 1 into the singly oxidized di-mu-oxido species [Mn-2(III,IV)(tpdm)(2)(mu-O)(2)(mu-OAc)](2+). Further electrochemical oxidation at the same potential results in the removal of a second electron to obtain a Mn-2(IV,IV)-species. The ability of compound 1 to evolve O-2 was studied using different reaction agents. While reactions with both hydrogen peroxide and peroxomonosulfate yield O-2, homogeneous water-oxidation using Ce-IV was not observed. Nevertheless, the oxidation reactions of 1 are very interesting model processes for oxidation state (S-state) transitions of the natural manganese water-oxidation catalyst in photosynthesis. However, despite its favourable coordination geometry and multielectron redox chemistry, complex 1 fails to be a catalytically active model for natural water-oxidation.

• 出版日期2012