Manganese complexes catechol

The density functional calculations of the electronic, and molecular structures of manganese complexes of catechol and pinacolborane were investigated at the DFT B3LYP and BP86 levels to understand the structures, bonding, and energetics of the interactions and were found to be in excellent correlation with the experimental values <2007JOM1997>. 

Mn(III). Structurally characterized higher valent manganese complexes with phenoxide-type ligation are limited to Mn(III) and Mn(IV) Schiff base complexes (128-135), Mn(III) and Mn(IV) catecholates (136-139), Mn(III) and Mn(IV) salicylates (140-142), and Mn(III) bi-phenoxides (143). However, of these ligands, only biphenoxide is similar electronically to tyrosine Mn(III) complexes of these ligands, in general, lack the intense phenoxide - metal charge transfer band centered at 435 nm. 

The aromatic dihydroxylated ligands (represented by catechol, 2,3-dihydroxybenzoate, and 4,5-dihydroxynapthalene 2,7-disulfonate) stabilize the 3+ and 2+ oxidation states of manganese in alkaline media. The data for salicylate indicate that it forms a less stable Mn(III) complex than the dihydroxy ligands. Formation of the 4+ complex is precluded because the ligands are more easily oxidized than are the Mn(III) complexes. 

The oxalate [Mn(C204)3], like the catecholate [Mn(cat)3] compounds, can be readily oxidized to Mn state. Otherwise, oxalate can form polymers and the combination of phosphate and oxalate in fomting hybrid framework materials has been also explored. Several hydroxycarboxylates exist as monomers or polymers and the first mononuclear manganese citrate complex, (NH4)4[Mn(C6H507)2], has been recently isolated and crystallographically characterized. ... 

In special circumstances the metal and a ligand can compete for the spin in a paramagnetic complex. As this alternative involves oxidation-state changes, it is referred to as valence tautomerization or redox isomerization [78]. Such behavior is observed for o-semiquinone complexes of cobalt and manganese [78] recently, a copper(I)-semiquinone-copper(II)-catecholate equilibrium system (7) of biochemical interest has been analyzed by temperature-dependent ESR [79]. 

The number of trinuclear manganese (II) complexes with bridging carboxylates is limited and most possess the linear [Mn3(/u,-carboxylate)6] core as in [Mn3(02CMe)6(bipy)2] and there is only one example of a hydroxocentered complex [(py)s(Mn3(/U,2-02CMe)3(/X3-0H) (catechol)] (Type I). Several mixed-valence or Mn Mn Mn carboxylato... 

Manganese(IV) complexes, 102-109 alkyls, 103 bipyridyl, 103 bipyridyl oxides, 106 carbon ligands, 102 catechol, 106 chlorides, 108 cyanides, 83,102 dialkyidithiocarbamates, 106 dithiolates, 106 dithiolenes, 107 fluorides, 107 halides, 107 hydroxides, 104 iodates, 105... 

Further oxidation to the (iv)/(iv) complex is also observed. The latter ion, [MnaOa(phen)4] +, is reduced by a variety of substrates including OH, Cl", and catechols. Addition of one equivalent of OH or Cl yields [Mn202(phen)J + while excess of these reagents induces breakdown of the //-dioxo-bridge. Reaction with catechols results in the formation of quinones and manganese(ii) complexes [equation (1)]. 

The catecholate functionality of CTC should make it a more effective metal binder than is CTV, although there are few known examples. A discrete trinuclear chelate complex of deprotonated CTC with Pt(II) has been reported. The manganese hydroxide-linked MeLa tetrahedra of the type discussed in Section 4.1.2 link into a complicated 3D coordination polymer through bridging oxides and sandwich-type interactions to additional Cs + cations that occur between (MnOH)6L4 tetrahedra. ... 

In order to generate more structurally relevant biomimetics for dinuclear metallohydrolases much effort has been devoted to the synthesis of asymmetric ligands. These ligands are considered to be more suitable models for the asymmetric coordination environment found in enzymatic systems. Nordlander et al. proposed that asymmetric complexes are not only more appropriate functional models for the active site of phosphoesterase enzymes, but also that they exhibit enhanced catalytic rates compared with their symmetric counterparts [1-3]. A selection of ligands used to generate purple acid phosphatase [1, 4, 5, 6-10], phosphoesterase [11], urease [12, 13], catechol oxidase [14] and manganese catalase biomimetics [15, 16] is displayed in Fig. 7.1. 

Considerable effort has been expended in studies of the interaction of metal ions with catechols with a view to understanding oxygenase activity. In aprotic media, the electrochemical properties of substituted catechols have been examined. Reactions of 3,5-di-tert-butyl-o-quinone with manganese(II) result in stable tris-Mn(IV) or bis-Mn(III) complexes of the corresponding catecholate dianion, Bu C , depending on whether the initial ratio of reactants is 1 3 or 1 2. This flexible redox chemistry may be important for redox catalysis. The O2 oxidation of the iron-catechol complex [Fe(salen)(Bu2CH)] has also been examined in aprotic media. 

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