Cobalt metallo

It is not necessary to start with the protonated Fe(II) complex to isolate these substituted products, however. Reaction of a slurry of the unsubstituted Fe(III) complex with anhydrous HC1 in diethyl sulfide produced a mixture of substitution products, including the species shown in Eq. (12). Although no evidence has been found for a protonated cobalt metallo-carborane analog, boron-substituted complexes of cobalt (III) may also be obtained by reaction of the (1,2-C2B9Hn)2Co- ion with R2S and HC1 52). 

The spacer units in 3.60 are assembled from polyphosphazenes that bear p-bromophc-noxy side groups via a lithiation reaction, and treatment with a diorganochlorophosphine to give 3.62. The chemistry is summarized in reaction sequence (45).107 Polymer 3.62 coordinates to a variety of metallo species,108 including osmium cluster compounds and cobalt carbonyl hydroformylation catalysts. When used as a polymeric hydroformylation catalyst, this latter species proved how stable the polyphosphazene backbone is under the drastic conditions often needed for these types of reactions. The weakest bonds in the molecule proved to be those between the phosphine phosphorus atoms and the aromatic spacer groups. 

Cobalt complexes of dendritic phthalocyanines (Fig. 6.37) showed a 20% lower catalytic activity (TON 339 min-1 for G2 dendrons) as catalysts for the oxidation of 2-mercaptoethanol than non-dendritic phthalocyanines [56]. By way of compensation, however, the dendritic catalysts proved to be more stable than non-dendritic ones, which is probably attributable to enclosure of the metallo-phthalocyanine core unit by the dendrons. This also prevents molecular aggregation of the phthalocyanines in polar solvents and thin films. 

Starting with l,l/-methylene-di(2-naphtol) 13 and 5-nitro-phthalonitrile 12, bis-phthalonitrile 14 was prepared. To obtain metal-free ball-type Pc 15, a suspension of 14 in dry amyl alcohol and lithium metal was heated in a sealed tube at 170°C for 8 h, Fig. 4. The metallo Pcs with zinc 16 and cobalt 17 were synthesized by heating a... 

Figure 1 An example of the way metallo-enzymes are under controlled formation through both controlled uptake (rejection) of a metal ion and controlled synthesis of all the proteins connected to its metabolism and functions. The example is that of iron. Iron is taken up via a molecular carrier by bacteria but by a carrier protein, transferrin, in higher organisms. Pumps transfer either free iron or transferrin into the cell where Fe + ions are reduced to Fe + ions. The Fe + ions form heme, aided by cobalamin (cobalt 2 controls) and a zinc enzyme for a-laevulinic acid (ALA) synthesis. Heme or free iron then goes into several metallo-enzymes. Free Fe + also forms a metallo-protein transcription factor, which sees to it that synthesis of all iron carriers, storage systems, metallo-proteins, and metallo-enzymes are in fixed amounts (homeostasis). There are also iron metallo-enzymes for protection including Fe SOD (superoxide dismutase). Adenosine triphosphate (ATP) and H+ gradients supply energy for all processes. See References 1 -3.

Cobalt seems to produce similar effects to those of Ni and Cr. Most authors agree that secondary harmful reactions are not directly generated by the presence of ions, but by their still scarcely known metabolites. The degree of oxidation and the formation of metallo-organic complexes may play an essential role, in particular for Cr, the primary ionic form of which after liberation is the trivalent ion. Its active toxic, allergenic and carcinogenic form, however, is the hex-avalent ion (Bartolozzi and Black 1985). 

A second important focus of our work is the development of suitable analytical methods for the solid state and in solution. The physical characterization of metallo-supramolecular systems has mainly relied on crystal structure determination. Studies have also been performed on surface layers 40-42). The classical analytical methods (like FAB mass spectrometry) or most polymer methods (like light scattering, vapor pressure osmometry or membrane osmometry) can not be used. In solution, ESI mass spectrometry (43-45) and NMR (27,46) have been succesfully applied. We have explored whether MALDI-TOF mass spectrometry in the solid state (Schubert, U. S. Lehn, J.-M. Weidl, C. H. Spickermann, J. Goix, L. Rader, J. Mullen, K., unpublished data.) and sedimentation equilibrium analysis in the analytical ultracentrifuge for solutions may be employed. Grid-like cobalt coordination arrays ([2 X 2] Co(n)-Grid) were used as model systems in the analytical ultracentrifuge (47). 

Amouri has reported the anion-directed synthesis of a series of coordi-natively unsaturated metallo-cages with general formula [Co2(L )4(RCN)2C (BF4)](BF4)3 (R = Me, Ft, Ph) [35]. The X-ray crystal structures of some of these assemblies (see Fig. 7 for an example) have revealed the presence of an encapsulated BF4 anion which interacts with the coordinatively unsaturated cobalt(ll) centres. Interestingly when analogous reactions were performed in the presence of other anions (such as Cl and NO3) different metal-organic assemblies were formed [36]. 

The final steps involve methylation at meso-carbons C-5 and C-15, to give precorrin-Sx followed by a [l,5]-sigmatropic shift of the methyl group from C-11 to C-12, decarboxylation of the acetic acid group at C-12, to give hydrogenobyrinic acid, and insertion of cobalt to give the completed metallo-corrin macrocycle, cobyrinic acid. 

Similar studies using differently functionalized pyrene and iron or cobalt porphyrins were proposed to obtain integrated SWCNT nanohybrids [128] and, very interestingly, the use of multi-walled CNTs (MWCNTs) produced remarkable results as well [129, 130]. Complexes of MWCNTs and pyrene were obtained and combined with metallo-porphyrins, giving rise to charge separated species upon photoexcitation. MWCNTs are easier to process and their electrOTiic structure is more suitable to achieve charge transfer and transport due to the presence of concentric internal graphitic layers. 

METALLO ENZYMES AND METALLO COENZYMES — covers the preparation, analysis, and biochemical effects of enzymes and co-enzymes that contain metals such as cobalt, copper, iron, zinc, and molybdenum. Also included are items dealing with metallo proteins, metal-containing vitamins, and mechanisms by which metals are bound to various enzymes. 

An unsymmetrical L-proline-functionalized metallo-organic triangle incorporating cobalt(II) acts as a size-, diastereo-, and enantio-selective catalyst for aldols the reactions have been followed by MS, NMR, UV-vis, and CD spectroscopy. ... 

Incorporation of metallo-phthalocyanines and metallo-porphyrins into PIM networks helps to allow access to the catalytic metal centers. It was shown that such network-PIMs demonstrate effective heterogeneous catalysis in reactions such as the oxidation of hydroquinone. Desulfurization of salt water has been shown to be catalyzed by a cobalt phthalocyanine network-PIM. Suzuki carbon-carbon coupling reactions can be catalyzed effectively by a hexaazatrinaphthylene-based Pd-loaded PIM network. 

Nitrile hydratases (EC 4.2.1.84) are metallo-enzymes that catalyze the hydration of nitriles to their corresponding amides. From a structural viewpoint, nitrile hydratases consist of two non-identical subunits (a and P), with similar molecular masses of approximately 23kDa. Nitrile hydratases exist as ap dimers or 0i2 2 tetramers, with each ap dimer binding a single metal atom. The amino acid sequence of each subunit is unrelated, with the structural genes normally adjacent to each other on the same operon [49]. Nitrile hydratases are classified into two groups on the basis of their catalytic metal ion center a nonheme iron atom [50] or a noncorrinoid cobalt atom [51]. 

Parts of this Chapter have been reprinted with permission from (L.J. Daumann et al.. Synthesis, Magnetic Properties, and Phosphoesterase Activity of Dinuclear Cobalt(II) Complexes. Inorganic Chemistry 2013 52(4), 2029-2043). Copyright (2013) American Chemical Society and in L.J. Daumann et al., Dinuclear Cobalt(II) Complexes as Metallo-f-lactamase Mimics. Eur. J. Inorg. Chem. 2013, 17, 3082-3089. 

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