Dinuclear complexes manganese

Martens, R. J. Swarthoff, T. (Unilever). Detergent Compositions Containing Dinuclear Manganese Complex as Bleach. Canadian Patent 2,083,661, 27 May, 1993. 

Apart from the catalytic properties of the Mn-porphyrin and Mn-phthalo-cyanine complexes, there is a rich catalytic chemistry of Mn with other ligands. This chemistry is largely bioinspired, and it involves mononuclear as well as bi- or oligonuclear complexes. For instance, in Photosystem II, a nonheme coordinated multinuclear Mn redox center oxidizes water the active center of catalase is a dinuclear manganese complex (75, 76). Models for these biological redox centers include ligands such as 2,2 -bipyridine (BPY), triaza- and tetraazacycloalkanes, and Schiff bases. Many Mn complexes are capable of heterolytically activating peroxides, with oxidations such as Mn(II) -> Mn(IV) or Mn(III) -> Mn(V). This chemistry opens some perspectives for alkene epoxidation. 

Telluroacetone coordinated to manganese was obtained from a tellurium-bridged dinuclear manganese complex and dimethyldiazomethane4. 

Beckmann K, Uchtenhagen H, Berggren G, et al. Formation of stoichiometrically lsO-labelled oxygen from the oxidation of lsO-enriched water mediated by a dinuclear manganese complex - a mass spectrometry and EPR study. Energy Environ Sci. 2008 1(6) 668-76. 

Dinuclear Manganese Complexes as Models for the Manganese Catalase. As discussed previously, the manganese catalase has a dinuclear active site that is thought to function by cycling redox states between Mn(II)2 and Mn(III)2. Although the [Mn(IV)(salpn)(/z2-0)]2 chemistry nicely explains the alternate catalase reactions of the OEC, this system is an inappropriate model for the Mn catalase because the redox cycle in that enzyme is lower and the core structure is believed to be dramatically different. In fact, a [Mn(III/IV)(/z2-0)]2 superoxidized state of the Mn catalase has been identified and shown to be inactive. 

The M 114.02 clusters were more active than the Mn30 clusters and the Mn clusters also catalyzed t-butyl hydroperoxide decomposition ( 1%) to acetone and methanol, which prevented reliable analysis of methane activation results. We could not compare the dinuclear manganese complexes to their tri and tetra analogues because of relative solubility differences however, we were able to do this with several iron di and tetra clusters and found that the Fe402 clusters were more active with the hydrocarbons studied. Therefore, higher nuclearity or a variety of ligands may provide the shape selectivity we seek fa ultimate methane activation with Mn and Fe clusters. 

Figure 16 Examples of core structures of dinuclear manganese complexes. Bridging oxo ligands are in bold.

Fig. 20. Schematic structure of dinuclear manganese complexes that can be formed with the ligand Mestacn ligand under different synthetic conditions 141).

Fig. 28. Schematic structure of the dinuclear manganese complex [Mn20(0Ac)2(tptn)] (6104)2.

Narita K (2004) Studies on catalytic activity for water oxidation induced by adsorption of di /i-0 dinuclear manganese complex onto heterogeneous matrixes. Master s thesis, Niigata University... 

Arafa WAA, Karkas MD, Lee B-L, et al. Dinuclear manganese complexes for water oxidation evaluation of electronic effects and catalytic activity. Rhys Chem Chem Phys. 2014 16 11950-11964. 

Sakiyama explored various dinuclear manganese complexes as catalase mimics derived from 2,6-bis N-[(2-dimethylamino)ethyl]iminomethyl-4-methylphenolate (2, Figure 10.1) and related ligands. Employing UV- ds and MS techniques both mono-and di-Mn -oxo intermediates could be detected [30]. Notably, the proposed mechanism (Scheme 10.2) is different from that reported for the manganese catalases and model compounds containing ligand 1 [30]. 

An enantiopure C3-symmetric trispyrrolidine-l,4,7-triazacyclononane ligand 24 was recently introduced (Figure 10.8) [75 dj. The tacn derivative was obtained by reduction of an L-proline derived cyclotripeptide and the corresponding dinuclear manganese complex was applied in the catalytic enantioselective epoxidation of vi-nylarenes with H2O2 as the oxidant. For the epoxidation of styrene, 3-nitrostyrene and 4-chlorostyrene, excellent conversions (up to 88%) and ee up to 30% were found [75 d]. 

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