CoTPPS cobalt

A number of metal porphyrins have been examined as electrocatalysts for H20 reduction to H2. Cobalt complexes of water soluble masri-tetrakis(7V-methylpyridinium-4-yl)porphyrin chloride, meso-tetrakis(4-pyridyl)porphyrin, and mam-tetrakis(A,A,A-trimethylamlinium-4-yl)porphyrin chloride have been shown to catalyze H2 production via controlled potential electrolysis at relatively low overpotential (—0.95 V vs. SCE at Hg pool in 0.1 M in fluoroacetic acid), with nearly 100% current efficiency.12 Since the electrode kinetics appeared to be dominated by porphyrin adsorption at the electrode surface, H2-evolution catalysts have been examined at Co-porphyrin films on electrode surfaces.13,14 These catalytic systems appeared to be limited by slow electron transfer or poor stability.13 However, CoTPP incorporated into a Nafion membrane coated on a Pt electrode shows high activity for H2 production, and the catalysis takes place at the theoretical potential of H+/H2.14... 

Diphenylphosphorylazide (DPPA) has also been shown to be an excellent nitrene source in aziridination reactions <06JOC6655>. The reaction of styrene and substituted styrenes with DPPA and tetraphenylporphyrin cobalt (CoTPP) provided the A-diphenylphosphinyl aziridines in moderate yields. 

Substituted cobalt porphyrins as catalysts in sulfuric acid. Further very active chelates for the reduction of oxygen in acids discovered in the early 70s were CoTPP by Sandstede and co-workers 9,13-15) and CoTAA and FeACC by Beck and co-workers 8 12>. Sandstede et al. determined the activities of their chelate catalysts by the suspension method briefly explained in Section 2.2.2.3. 

The influence of different organic skeletons with the same central atom is shown in Fig. 15. With cobalt as central atom, the activity decreases in the order TAA>TDAP>TMPP>Pc>TPAP>TPP. The last two of these classes of compounds are so inactive that their characteristic curves could not be shown in the same diagram (CoTPAP and CoTPP give potentials of 624 mV and 593 mV at 20 mA/g). 

It was reported that cobalt-tetraphenylporphyrin complex (CoTPP) coated on an electrode catalyzes electrocatalytic proton reduction,215 but the activity was not very high. We have found that metal porphyrins and metal phtahlocyanines when incorporated into a polymer membrane coated on an electrode show high activity in electrocatalytic proton reduction to produce H2.22,235 Some data are summarized in Table 19.2. It was shown that this catalyst is more active than a conventional platinum base electrode. 

The use of cobalt(II) tetraphenylporphyrin (CoTPP) as catalyst in the decomposition of unsaturated bicyclic endoperoxides represents the... 

Recently, three TPO models have been reported bis (salicylidene)ethylenediaminato cobalt(II) [Co(salen)] in MeOH (14), cobalt(II)tetraphenylporphyrin (CoTPP) (25) in DMF, and manganese phthalocyanine (Mn-Pc) in DMF (16). These models have been reported as having the TPO-mimic function of oxygenating skatole, a tryptophan analogue, to form 2-formamidoacetophenone (FA). However, one of the most critical problems for these models is the lack of structural similarity between the TPO active site (heme) and these models. The structure of these models is not similar to the heme in TPO with respect to the central metal and/or the ligand. Furthermore, Fe(salen) does not possess the TPO-mimic function (14). 

Cobalt m so-tetraphenylporphine (CoTPP. 1). I he cobalt salt is prepared as maroon crystals by reaction of TPP with Co(OAc), in CHCl HOAc. The salt is soluble in benzene, chloroform, and pyridine. ... 

Their best agent was the cobalt(lll) complex of 5,10-bis(4-methylpyridinium)-15,20-bis-(4-nitrophenyl)porphyrin, which had an SER of 1.22 at 50 pM towards CHO hypoxic cells. This complex was actually the most promising of over 50 studied. Using this CHO tumor cell line and identical XRT conditions (i.e. oxic and hypoxic lOOpM porphyrin concentration 16 Gy), O Hara et al. found that the cobalt(III) complexes, CoTPPS and COTMPyP, exhibited a weak sensitization effect (SER = 1.05-1.22, with or without serum-containing medium). These workers also concluded that the introduction of nitro and/or positively charged substituents on the porphyrin periphery serves to augment the net radiosensitization effect for these kinds of Co(lll) porphyrins [153,154]. Unfortunately, even when enhanced in this way, the net sensitization effect is small. 

Polymerization of MMA both thermally and pho-tochemically in the ordered media, cholesteryl oleyl carbonate and cholesteryl 2-ethylhexyl carbonate, were studied in the presence and absence of cobalt tetraphenylporphyrin. The percentage conversion and molecular weight were lowered in the presence of CoTPP for thermal polymerizations. In photopolymerizations, the percentage conversion was high and the molecular weights were low.129... 

Vitamin B12 is known for its ability to catalyze molecular rearrangements. A variety of cobalt chelates are logical models for vitamin B12, and their stoichiometric and catalytic activities in a variety of reactions,403 particularly olefin isomerizations, were studied intensively.404-411 Noncatalytic isomerization reactions based upon the synthesis of alkylcobalt chelates as model intermediates were favored. A variety of catalytic oxidations of substrates such as hydroquinone, azo compounds, phosphines, and olefins were also investigated.412-415 Copolymerization of a-methylstyrene and other monomers with oxygen in the presence of CoTPP led to alternating polyperoxides.416 418 Cobaloximes were found to catalyze... 

For molecular electrocatalysts otherwise, and especially transition metal macrocycles, the electrocatalytic activity is often modified by subtle structural and electronic factors spanning the entire mechanistic spectrum, that is, from strict four-electron reduction, as for the much publicized cofacial di-cobalt porphyrin, in which the distance between the Co centers was set at about 4 A [12], to strict two-electron reduction, as in the monomeric (single ring) Co(II) 4,4, 4",4" -tetrasulfophthalo-cyanine (CoTsPc) [20] and Co(II) 5,10,15,20-tetraphenyl porphyrin (CoTPP) [21]. Not surprisingly, nature has evolved highly specific enzymes for oxygen transport, oxygen reduction to water, superoxide dismutation and peroxide decomposition. 

Using a novel NMR shift reagent, for example cobalt(III)meso-tetraphenyl porphyrin (CoTPP), the conformation of (3) is found to be a mixture of many conformations. Theoretical and experimental results revealed ring current shift for (3) <90MRC343>. Electronic structure and conformational properties of the amide linkage were studied in lactams based on MNDO calculations and photoelectron spectroscopy <85Mi 9l8-oi>. 

Experiment 13-3 Electrocatalytic Proton Reduction to H2 Evolution by Cobalt Tetraphenylporphyrin 5 (CoTPP) Incorporated into a Naflon Membrane Coated on an Electrode (Section 13.2,3.2) [23(b)]. 

Imaoka and Yamamoto " reported that porphyrins possessing four ionic substituents of (mCTO-tetrakis(Af-methyl-4-pyridiniumyl)porphyrinatoRu(II) (RuTMPyP) and (me.y(9-tetrakis(4-sulfonatophenyl)porphyrinato)cobalt(II) (CoTPPS) associate spontaneously to form a dinuclear complex. Formation of CoTPPS-RuTMPyP was confirmed by UV-vis titration and TOF-mass spectra. The dinuclear complex exhibits an acceleration of intrinsic FT when it is present in a Nation film deposited on glassy carbon. The CoTPPS-RuTMPyP-Nation system catalyzes the four-electron reduction of O2 with an efficiency of 95%. 

The modified electrode with the attached CoTPP can reduce CO2 to CO whereas the electrode modified with adsorbed CoTPP cannot. The cyclic voltam-mogram of the modified porphyrin-amine-GC electrode in pH 6.8 phosphate buffer shows the appearance of the anodic hump after the electrode is polarized to potentials where the evolution of hydrogen takes place under N2 atmosphere see Figure 5.12. The ligand bonded to the glassy carbon does not show this hump, and then the authors associate it with the cobalt center. The hump would correspond to the oxidation of the formed hydride. Over the first-bonded porphyrin there are more than 100 layers of stacked porphyrins. Stacked Co(II)TPP could accept a hydrogen atom from CoTPP bonded GC to form HCo(II)TAPP. ... 

Figure 5.12. Cyclic voltammograms at 50 mV on CoTPP bonded GC in N2 and C02 atmospheres. Bridging compound is 4-aminopyridine. The solution was pH 6.8 phosphate buffer solution. Reprinted from Figure 5 H. Tanaka, A. Aramata, Aminopyridyl cation radical method for bridging between metal complex and glassy carbon Cobalt(II) tetraphenylporphyrin bonded on glassy carbon for enhancement of CO2 electroreduction. Journal of Electroanalytical Chemistry, 437 (1997) 29-35. Copyright 1997, with permission of Elsevier.

Aga et showed that CO2 can be catalytically electroreduced to form CO as the main product, on N4 cobalt complexes chemically bonded to GCE through -CONH-pyridine, with the N of the pyridine forming a coordinate bond with the Co center of the N4 complexes. Tanaka et al. employed aminopyridine as a bridge between the metal complex and the GCE, and the potential for the reduction of CO2 of -1.1 V was obtained . TheN4 complexes used as catalysts were CoNPc, CoTMPP, CoPc, vitamin B12, CoTPP, and CoDO (Figure 7.4a) and the modified electrode may be denoted as GC-py-Co. CoDO was however not able to reduce CO2. The mechanism for the reduction of CO2 by the rest of the N4 complexes was proposed as follows (Equation 7.11-7.14) ... 

Fig. 9 Influence of catalyst formal potential ( °) on log /ci for reaction of Co L with DBCH in a bicontinuous microemulsion (A) of DDAB/water/dodecane (21/39/40) and in dimethylformamide ( ) for dissolved catalysts vitamin B12, Co(salen), cobalt phthalocyaninetetrasulfonate (CoPCTS), cobalt tetraphenylporphyrin (CoTPP), and cobalt octaethylporphyrin (CoOEP). Points from reactions in the microemulsion (A) represent apparent k values for 0.4, 0.5,1.0, and 2.0 mM catalyst in order of decreasing log fci. (Adapted with permission from Ref [58], Copyright by American Chemical Society.)...

Mezour et al. successfully attached cobalt (II) 5,10,15,20-tetraphenyl-21 H, 23 h-porphine (CoTPP) onto gold and glassy carbon surfaces via its coordination with 4-aminothiophenol (ATP) self-assembled monolayers as depicted in the scheme of Fig. 26 [104]. The electrocatalytic activity of the resulting film, Au-ATP-CoTPP was investigated for oxygen reduction in H2SO4 (0.5 M) using SECM in the SG-TC mode. The tip was a Pt nanoelectrode with a diameter of 460 nm. The measurements were recorded at a constant distance of 6 pm which was achieved by means of shear force-based constant distance SECM [105]. 

The cobalt(II) porphyrin complex (CoTPP) has been found to be an efficient catalyst for the Wittig type olefination of acyl phosphonates (96) with ethyl diazoacetate (EDA) in the presence of triphenylphosphine (Seheme 32). ° In a one pot reaction under mild conditions, highly functionalized vinyl phosphonates (97) could be obtained in high yields (72-92%) and high E/Z selectivities (95/5-100/0), in relatively short reaction times. 

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