Metalloporphyrins complexes

Bis(cyclopentadienyl) complexes are central to the organometallic chemistry of the early transition metals and feature in applications such as alkene polymerization chemistry. Parallels can be drawn between a porphyrin ligand and two cyclopentadienyl ligands, in that they both contribute a 2— formal charge and exert a considerable steric influence on other ligands in the same molecule. Several of the metalloporphyrin complexes discussed below have bis(cyclopentadienyl) counterparts, and authors in some ca.ses have drawn quite detailed comparisons, although these discussions will not be repeated here. 

In a number of model studies it has been demonstrated that synthetic porphyrin complexes are able to be oxidized to oxo-metalloporphyrin complexes which will, in turn, oxidize organic substrates of the type mentioned previously. Thus, in an early investigation it was shown that a synthetic Fe(m) porphyrin will catalyze oxygenation of hydrocarbons using iodosylbenzene as the reduced-oxygen source (Groves, Nemo Myers, 1979). Following this report, a number of related cytochrome... 

Por )=0 intermediates. Many metalloporphyrin complexes are bleached by peroxides, but the germanium porphyrins remain intact even in the presence of excess alkylhydroperoxide. This suggests that high oxidation state intermediates... 

A new trend in the field of oxidations catalyzed by metalloporphyrin complexes is the use of these biomimetic catalysts on various supports ion-exchange resins, silica, alumina, zeolites or clays. Efficient supported metalloporphyrin catalysts have been developed for the oxidation of peroxidase-substrates, the epoxidation of olefins or the hydroxylation of alkanes. 

Scheme I. Structures of sulfonated robust metalloporphyrin complexes. The axial ligand of these water-soluble metalloporphyrins depend on the pH value, at acidic pH an hydroxo ligand occupies the axial position whereas it is a water molecule at basic pH values.

The metalloporphyrin complexes and their derivatives have been studied from the standpoint of model compounds of hemoglobin. The polymer-metalloporphyrin complexes are also formed by the reaction in Scheme 8, and a few qualitative investigations have been made with poly(L-lysine)9,10, poly(L-histidine)11, and poly(vinylimidazole)12 as the polymer ligand. Blauer9 has studied the complex formation of heme with poly(L-lysine) and has discussed the effects of the molecular weight and secondary structure of poly(L-lysine) on complex formation. 

At room temperature these polymer-Co(II)porphyrin complex, except CoMb, were irreversibly oxidized to the Co(HI) complexes. Oxidation of the Fe(II)-por-phyrin complexes proceeds more rapidly than that of the Co(II)porphyrin complexes. The next section deals with attempts to make polymer ligands act as inhibitors to the irreversible oxidation of metalloporphyrin complexes. 

We also synthesized polymer-metalloporphyrin complexes in which both the porphyrin ring and a nitrogenous axial ligand were fixed on a polymer chain by covalent bonds, as represented in 46 and 47l0S ESR and visible measurements indicated that the Co(II)- and Fe(II)porphyrin complexes of 46 and 47 were reversibly oxygenated in toluene or dimethylformamide. These results confirmed that the metalloporphyrin complex attached on a polymer at low concentration behaves virtually as in a solution at infinite dilution. 

The redox potentials of many metalloporphyrin complexes are sensitive to the nature of the electrolyte in which they are measured. This is because one or both axial positions are coordinated by either solvent or anionic ligands. Such dependencies of E° values have been extensively studied by Kadish and coworkers 29 notably good correlation between E° data and Donor/Acceptor Number properties of solvents have been observed. 

The second and third steps involve successive additions of the pyrazine and non-surfactant water soluble metalloporphyrin complexes to the template submerged in the aqueous phase (Steps 2 and 3, respectively). The two-layered assembly is then removed from the water through a protective monolayer of stearic acid to prevent disruption of the film structure (Step 4). If instead of removing the assembly in Step 4, Steps 2 and 3 were successively repeated, multi-layered assemblies having the essential features described in Figure 1 might be realized. 

Discussions to this point rely on the hypothesis that the ligands of oxo(salen)manganese(V) complexes have planar structures by analogy to metalloporphyrin complexes and Mn(III)-salen complexes 11 and 12, the structures of which were determined by the X-ray crystallographic analysis [29a,47]. However, the assumption that the ligand of the oxo-Mn-salen species is planar failed to give a satisfactory explanation for the following stereochemistry observed in the recent study. Trans-cis selectivity in the epoxidation of 1-alkylindenes usually improves as the steric bulk of the catalyst increases. However, the epoxidation of 1-methylindene with the smallest... 

Metalloporphyrin complexes serve as catalysts for aziridination in the presence of PhI=NTs [73], Che et al. have reported the chiral version of metalloporphyrin-catalyzed aziridination (Scheme 6B.36) [81], The reaction of styrene derivatives with a D4-manganese(III) porphyrin complex 34 proceeds with fairly good enantioselectivity, up to 68% ee. This reaction is proposed to proceed through a Mn(IV)-PhINTs adduct 35 on the basis of EPR analysis. 

DiMarco G, Lanza M. Optical solid state oxygen sensors using metalloporphyrin complexes immobilized in suitable polymeric matrices. Sens Actuators 2000 B63 42-8. 

In 1988, Schiffrin s group [4] claimed that the use of lutetium biphthalocyanine (LuPc2) complex more hydrophobic than Fc enabled observation and investigation of a true , or heterogeneous, ET across the 0/W interface. A series of subsequent papers reported ET systems by other hydrophobic metal complexes including tin diphthalo-cyanine [5], iron and ruthenium metalloporphyrin complexes with pyridine [6] and Fc derivatives [7]. These experimental studies then stimulated theoretical studies on the ET kinetics [8-12]. 

A question that is central to the chemistry of metalloporphyrin complexes concerns the energy of the metal-based ionizations and their relationship with respect to the porphyrin-based n ionizations. One example that... 

The organic materials extracted from a number of domestic tar sands contain various amounts of vanadium and nickel, sometimes in substantial quantities. Metalloporphyrin complexes of these two metals have been detected in some outcrop and shallow core samples. If these porphyrins are indigenous petroporphyrins, it is evident that these compounds can survive weathering processes. 

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