Porphyrin cobaltous

According to [96], electrochemical methods, especially the application of cyclic voltammetry, could be a powerful tool to find suitable catalysts for NO removal from combustion products. Investigation of electrocatalytic properties of vitamin B12 toward oxidation and reduction of nitric oxide was reported in [97]. The catalytic activity of meso-tetraphenyl-porphyrin cobalt for nitric oxide oxidation in methanolic solution and in Nafion film was reported in [98]. 

Cobalt porphyrins have been some of the most studied catalysts for oxygen reduction, due in part to their strong interaction with molecular oxygen and the ease with which they catalyze the reduction at low potentials. Anson and coworkers [97] performed a study of the simplest of cobalt porphyrins, cobalt porphine, in the hope of gaining a baseline for the observed reactions of other porphyrins. Instead, they observed a very different process from most other monomeric cobalt porphyrins. 

The porphyrin-cobalt complex gives rise to the cation radical with charge spin localization at the nitrogen atom of the porphyrin ring. The cation radical thus formed acquires enhanced reactivity and can add tolane (Kochi 1986), Scheme 1-52. The main point... 

Advantages of electrocatalytic reactions in textile applications example - electrocatalytic oxidation of sodium dithionite at a phthalocyanine and porphyrin cobalt(ll)-modified gold electrode... 

In this chapter, it will be shown that the detection of sodium dithionite on bare gold electrodes can be improved by electrocatalysis using a cobalt(II)tetrasulphonated phthalocyanine, sodium salt (CoTSPc) or a 5,10,15,20-tetrakis-(4-sulphonatophenyl)porphyrin cobalt(II), tetrasodium salt (CoTSPor) as catalyst. The selection of these catalysts was based on... 

Zhang s group developed highly active chiral (porphyrin)cobalt(II) complexes 327b-d, which catalyzed the cyclopropanation reactions of styrenes [356-358] and even of ot,(3-unsaturated esters or nitriles [358, 359] by diazoacetates. Nitrodi-azoacetates [360] or sulfonyldiazomethane [361] also proved to be useful in asymmetric cyclopropanation reactions of styrenes, acrylic derivatives, and in some cases even simple olefins with good to high de and moderate to excellent ee (highlight [362]). 

Chiral binaphthyl-bridged mevo-tetrakis(2-aminophenyl)porphyrin]cobalt or polymer-supported chiral (salen)Co complexes also catalyzed the cyclopropanation of styrenes albeit so far with lower diastereo- and enantioselectivities [363, 364],... 

Zhang and coworkers reported recently that (porphyrin)cobalt(II) complexes are suitable for intramolecular amination of C-H bonds. Initially, ort/io-substituted arylsulfonyl azides 333a were subjected to 2 mol% of Co(TPP) 326a. Benzosultams 334a were formed in 87-99% yield (Fig. 80) [370]. When substrates... 

Fig. 80 (Porphyrin)cobalt-catalyzed intramolecular C-H amination reactions...

Styrenes, enolates, and dienoates 337 can be nitrosated using (tetraphenyl-porphyrin)cobalt(II) 326a as the catalyst (entry 17). Under these conditions oximes 345 were isolated in 31-94% yield. The mechanistic details of this reaction remain to be elucidated [397]. 

Porphyrin cobalt complexes, too, activate 02. The confacial diporphyrin (17-F-IV) is unusual since it does not bind 02 in the [PConConP] state but gives remarkably strong 02 adducts on oxidation to [PCouComP]+ and [PCoinComP]2+.26... 

Epoxidation of Alkenes Catalyzed by Porphyrin Cobalt Complexes... 

The porphyrin cobalt complex in radical polymerization of methylmethacrylate catalyzes the chain transfer to the monomer without affecting the polymerization rate. The phthalocyanine cobalt complex catalyzes the chain termination. 

The PANl/porphyrin nanocomposites have been fabricated using the similar approach [110,111]. To extend the functionalities of the nanocomposites, metalloporphyrin has also been used as template to synthesize CP/ cobalt porphyrin nanocomposites through electrochemical polymerization. Similar to porphyrin, cobalt porphyrin can also form J-aggregates, and many rod-like structures have been observed after dispersing their aqueous solution onto freshly cleaved mica. An electrochemical polymerization forming PPy was templated by J-aggregates of cobalt porphyrin to form PPy/cobalt porphyrin nanocomposites in the presence of cobalt porphyrin in the pyrrole solution [112]. Ihe diameter of the as-synthesized PPy/cobalt porphyrin composite nanorods was aroimd 50 nm when the cobalt porphyrin solution was ultrosonicated for at least three hours before the electropolymerization of pyrrole on the electrode surface. In the presence of cobalt porphyrin, the composite nanorods exhibited excellent elec-trocatalytic activity. 

The metal cobalt(ll) is usually chelated. This can be cobalt porphyrin, cobalt phthalocyanin, or cobalt oxime, as well as others. The polymer molecules that form have, as stated earlier, terminal double bonds and can be illustrated as follows. 

Pioneering works on functional molecules incorporating conducting polymers firstly demonstrated them as modified electrodes, on which redox molecules such as ruthenium tetraoxide [1] for photo-oxidation of water, mesotetrakis (4-sulphonatophenyl)porphyrin cobalt [2] and iron phthalocyanine [3] for redox catalysis, were incorporated chemically or electrochemically in polypyrrole conducting polymer. They suggested that functionalized conducting polymers should show the native function of a functional molecule while maintaining the native conductivity without a big decrease. 

Another cobalt porphyrin, cobalt[5,15-(/7-anfinophenyl)-10,20-(pentafluo-rophenyl)porphyrin], CoAPFP, was covalently linked to GO and the resnlting hybrid underwent electrocatalytic electrons oxygen reduction [95]. 

Figures A schematic representation of supramolecular polymer formation via porphyrin/cobalt coordination (adapted from U. Michelsen and C.A. Hunter. Angew. Chem. Int. Ed. 39 764-767, 2000.).

Collman s group has also examined oxygen binding to picket fence porphyrin-cobalt complexes of m so-tetra-(a,a,a,a"0-pivalamidophenyl) por-phyrinato-cobalt(II)"l"methylimidazole and 1,2-dimethylimidazole (246). 

The equilibrium constant for the addition of NCS ion to tetrakis-(3-iV-methyl-pyridyl)porphinecobalt(iii) is less (by a factor of ca. 2) than for addition to the less basic 4-A -methylpyridyl isomer, and the difference is reflected in a larger rate of dissociation of the Co—SCN bond in the case of the 3-7/-methylpyridyl complex. Two further studies of porphyrin-cobalt(iii) complexes have appeared. For the aquation of [Co(a,/S,y,6-tetra-4-A -methylpyridylporphine)(X)(H20)] + (X= NCS, Cl, Br, I, or py) a linear free-energy relationship holds between the rate... 

Almost at the same time Nyokong et al. [125] used a similar method to covalently bind Ni(II)-2 to carboxylic acid functionalized SWCNT. More recently, Nyokong et al. [126] have reported a method of functionalization of SWCNTs, with amine groups using a previously developed diazonium approach. This makes it possible the direct attachment of the Zn(II)-10 by an amide bond to the CNT as illustrated in Fig. 4. Kim and Jeon [129] have reported on the immobilization of a cobalt porphyrin (cobalt tetrakis(o-aminophenyl)porphyrin) of several carbon nanomaterials via the diazonum strategy, but in this case, the diazotation was performed on the macrocycle, by the diazotation of aromatic amine groups of the porphyrin. 

The authors have also reported on the comparison between the electrocatalytic activity of electropolymerized films of cobalt porphyrins and phthalocyanines (cobalt tetrakis(p-hydroxyphenyl)porphyrin cobalt tetrakis(o-aminophenyl)porphyrin and Co(II)-2), with emphasis on the effect of the film thickness on the electro-oxidation of 2-mercaptoethanol [52]. It was shown that, despite the porphyrins modified electrodes exhibit electrocatalytic activity, their activity strongly depends on the film thickness with a decrease of activity as the thickness increases, in contrast to the phthalocyanine-based electrodes. This difference in behavior was attributed to lower electronic conductivity of electropolymerized porphyrin films relative to phthalocyanine-based ones, and to the potential implication of the less reactive Co(III) form of the deposited porphyrin complexes. 

The dechlorination of chlorinated alkenes could also be performed by porphyrin cobalt complex such as 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin cobalt ((TCPP)-Co). This cobalt complex, structurally similar to vitamin B12, was found to have superior aqueous-phase dechlorination activity on chlorinated ethylenes relative to vitamin Bi2. Based on fully detailed parameters dependence, the authors suggest the catalytic cycle below.This methodology has been used to synthesize C-labeled air-DCE from TCE (Scheme 33). ... 

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