CoTPPS

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. 

Barlow DE, Scudiero L, Hipps KW (2004) An STM study of the structure and orbital mediated tunneling spectra of CoPc and CoTPP on Au(lll) mixed composition films. Langmuir 20 4413 1421... 

The rate of Sc -promoted photoinduced electron transfer from Ceo to CI4Q determined from the decay rate of the absorbance due to Ceo at 740 nm (inset of Fig. 11) obeys pseudo-first-order kinetics and the pseudo-first-order rate constant increases linearly with increasing the p-chloranil concentration [CI4Q] [135]. From the slope of the linear correlation, the second-order rate constant of electron transfer ( et) in Scheme 15 was obtained. The A et value increases linearly with increasing the Sc + concentration. This indicates that CUQ produced in the photoinduced electron transfer forms a 1 1 complex with Sc + (Scheme 15) [78]. When CI4Q is replaced by p-benzoquinone (Q), the value for electron transfer from Ceo to Q increases with an increase in [Sc " ] to exhibit a first-order dependence on [Sc ] at low concentrations, changing to a second-order dependence at high concentrations, as shown in Fig. 13 (open circles) [135]. Such a mixture of first-order and second-order dependence on [Sc ] was also observed in electron transfer from CoTPP (TPP = tetraphenylporphyrin dianion) to Q... 

Figure 13 Plots of fcet versus [Sc ] for electron transfer from Ceo to Q (open circles) and from CoTPP (1.0 x 10 M) to Q (1.0 X 10 M) (closed circles) in the presence of Sc " in deaerated PhCN at 298 K. (From Ref. 135.)...

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). 

The oxygen activity of various Co—N4 complexes in sulfuric acid can be considerably improved by subjecting the carbon/chelate sample to thermal pretreatment in an atmosphere of a protective gas 7>. Such an effect is also reported by other authors for CoTMPP 22>. Figure 21 shows the influence of pretreatment on CoTMPP, pCoPc, and CoTAA. The given loadings (in mA/g catalyst) are all related to chelate plus carbon. The activity of CoTPP and CoTPAP is so low that,... 

Shi and Zhang studied dioxygen binding to a variety of transitional metal macrocycles and reported an 02 binding energy to the CoP and CoTPP of -10.8 and -9.9 kcal mol, respectively (202). Only the end-on structure was found to be stable. 

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... 

The CoTPP-catalyzed decomposition of endoperoxides as 89 leads to divinylepoxides as 90 which can be converted through a 3,3-sigmatropic rearrangement to dihydrooxepine derivatives as 91 (Sch. 54) [33a], The result appears interesting due to the discovery of the oxepine nucleus in a number of biologically active natural products. 

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. ... 

CoTPP also cleaves dioxetanes such as 2 to dii arbonyl compounds. ... 

Rearrangement of 1,4-endoperoxides.1 CoTPP catalyzes the rearrangement of 1,4-endoperoxides to syn-1,2 3,4-diepoxides at -78°. Neither meso-tetraphenylporphine nor zinc meso-tetraphenylporphine catalyzes this rearrangement. N,N,N, N -Tetramethyl-ethylenediamine catalyzes the reaction, but only very slowly. The yields from the catalyzed reaction are much higher than those obtained by thermolysis. 

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. 

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