Manganese binuclear

The nitrogen atom in ri -pyrrolylmanganesetricarbonyl forms a donor-acceptor bond with transition metals. Complexes in which the pyrrolyl ring behaves as a tt ligand for the manganese atom and n-donor for the other metal were synthesized 12 (M = Mn, Re) [78JOM(157)431]. The binuclear heterobimetallic complexes... 

The synthesis as well as spectral and electrochemical properties of a series of unsymmetrical bis(phenoxo)-bridged macrocyclic binuclear manganese(III) complexes based on (178), incorporating dissimilar coordination sites, have been reported." The bis(phenoxo)-bridged complexes yielded two reduction waves in the region 0.00V to —1.60V assigned to the process Mn2 —> Mn Mn Mn2 ]. In the positive region (0.00 V to +1.00 V), two oxidation couples were... 

Catalases catalyze the conversion of hydrogen peroxide to dioxygen and water. Two families of catalases are known, one having a heme cofactor and the second a structurally distinct family, found in thermophilic and lactic acid bacteria. The manganese enzymes contain a binuclear active site and the functional form of the enzyme cycles between the (Mn )2 and the (Mn )2 oxidation states. When isolated, the enzyme is in a mixture of oxidation states including the Mn /Mn superoxidized state and this form of the enzyme has been extensively studied using XAS, UV-visible, EPR, and ESEEM spectroscopies. Multifrequency EPR and microwave polarization studies of the (Mn )2 catalytically active enzyme from L. plantarum have also been reported. ... 

The spectroscopic and kinetic data from this reaction indicated the existence of a long sought catalytic reaction topology, bimetallic catalytic binuclear elimination. The kinetic data provided a linear-bilinear form in organometallics [95]. One term represented the classic unicyclic rhodium catalyzed hydroformylation and the other represented the attack of manganese hydride carbonyl on an acyl rhodium tetracarbonyl species. A representation of the interconnected topology is shown in Figure 4.12. 

Stewart s conclusion underscores the need for short-wavelength, low-temperature studies, if very high accuracy electrostatic properties are to be evaluated by Fourier summation. But, as pointed out by Hansen (1993), the convergence can be improved if the spherical atoms subtracted out are modified by the k values obtained with the multipole model. Failure to do this causes pronounced oscillations in the deformation density near the nuclei. For the binuclear manganese complex ( -dioxo)Mn(III)Mn(IV)(2,2 -bipyridyl)4, convergence of the electrostatic potential at the Mn nucleus is reached at 0.7 A" as checked by the inclusion of higher-order data (Frost-Jensen et al. 1995). 

The structure of the active component, manganese pyrophosphate, has been reported in the literature (24). It is layer like with planes of octahedrally coordinated Hn ions being separated by planes of pyrophosphate anions (P20y ). Examination of models of this compound gave calculated Hn-Hn thru space distances of 3.26 and 3.45 angstroms, a metal-metal distance close to that found for binuclear dibridged peroxo- and superoxo- complexes of cobalt ( ). 

Tab. 4 Nonaqueous electrochemical data for binuclear manganese complexes... 

A second structural motif in binuclear manganese chemistry is the triply bridged structure in which one /x-oxo unit has been replaced by two bridging carboxy-lates (8 in Sect. 16.1.4). The remaining coordination sites on each metal are commonly occupied by a tridentate tripod or a macrocyclic ligand such as HB(pz)3 ... 

This process is catalyzed by a variety of catalase enzymes, the most common being the heme catalases, which accomplish the two-electron chemistry of Eq. (12) at a mononuclear heme center. Here, both the iron and its surrounding porphyrin ligand participate to the extent of one electron each in the redox process. Manganese catalases contain a binuclear Mn center and cycle between Mn2(II,II) and Mn2(III,III) oxidation states while carrying out the disproportionation of H2O2. The enzyme can... 

Binuclear Iron, Manganese and Copper Centers in Biology—Synthetic Analogue Approach (Mukherjee, 1997)... 

Metal salts and complexes have also often been used as redox catalysts for the indirect electrochemical oxidation of alcohols. Particularly, the transformation of benzylic alcohols to benzaldehydes has been studies. For this purpose oxoruthe-nium(IV) and oxoruthenium(V) complexes have been applied as redox catalysts. In a similar way, certain benzyl ethers can be cleaved to yield benzaldehydes and the corresponding alcohols using a di-oxo-bridged binuclear manganese complex Electrogenerated 02(804)3 was used to generated 1-naphthaldehyde from 1-naphthylmethanol... 

Other than (CO)4Fe(CHO) and derivatives thereof (22-25), only a few of the formyl complexes in Table I show significant stability at room temperature. Of these, the binuclear rhenium formyl cis-(CO)5ReRe(CO)4(CHO) [19, Eq. (5)] has received the greatest attention (37. 38. 42. 47). The manganese and mixed manganese/rhenium homologs (12, 18) can be similarly prepared, but are less stable (35. 38, 47). 

Binuclear manganese complexes (55) have been obtained from their mononuclear analogs, either by heating in an inert atmosphere, or by treating them with Mn(OEt2)(CO)2(i C5H5) (74) ... 

The first six entries in this section of Table X (entries 93-98) relate to attempted insertion reactions of fluoroalkenes or fluoroalkynes into Si-Mn or Si-Fe bonds. Even in the successful cases, yields are generally low, and in some instances (e.g., entry 94) MesSiF is lost from the insertion product to leave a fluoroalkenyl manganese carbonyl. In the case of the iron hydrido compound in entry 98, there is formal loss of hydrogen to give the binuclear derivative [CljSiFelCO). ... 

The synthesis of pentacarbonyl rhenium(I) halides, Re(CO)5X, succeeded from simple and complex rhenium halides below 200 atm of CO at 200° C. The compounds are extraordinarily stable and form easily, often quantitatively, from carbon monoxide and rhenium metal in the presence of other heavy metal halides or halogen sources such as CC14. Later we prepared the corresponding carbonyl halides of manganese (67) and technetium (68) from their respective carbonyls. It was found that the corresponding binuclear tetracarbonyl halides [M(CO)4X]2 (M = Mn, Re) could be made by heating the mononuclear M(CO)5X complexes (15, 69), as well as by other methods. 

Magnuson A, Liebisch P, Hogblom J, et al. Bridging-type changes facilitate successive oxidation steps at about IV in two binuclear manganese complexes - implications for photosynthetic water-oxidation. J Inorg Biochem 2006 100 1234-3. 

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