Nickel porphyrins, metalation

Similar results are observed in the conjugative addition of CH-acidic methylene compounds with the metal derivatives of 2-nitro-5,10,15.20-tetraphenylporphyrin (6). The nickel porphyrin 6 (M = Ni) yields with an excess of dimethyl malonate the cyclopropane derivative 7 whereas the copper porphyrin 6 (M — Cu) forms with two equivalents of malononitrile the bisadduct 8.111... 

One-electron oxidation of the vinylidene complex transforms it from an Fe=C axially symmetric Fe(ll) carbene to an Fe(lll) complex where the vinylidene carbon bridges between iron and a pyrrole nitrogen. Cobalt and nickel porphyrin carbene complexes adopt this latter structure, with the carbene fragment formally inserted into the metal-nitrogen bond. The difference between the two types of metalloporphyrin carbene, and the conversion of one type to the other by oxidation in the case of iron, has been considered in a theoretical study. The comparison is especially interesting for the iron(ll) and cobalt(lll) carbene complexes Fe(Por)CR2 and Co(Por)(CR2) which both contain metal centers yet adopt... 

Extensive work has been carried out on microsensors built from electropolymerized nickel porphyrin films.328,329 Films of Prussian blue (Fe4[Fe(CN)6]3) 345 metal-salen complexes (M = Co, Fe, Cu, Mn)346 or the ferrocene-containing Nin-tetraaza[14] annulene (24),347 also exhibit interesting activity for NO electrooxidation and sensing. 

Intrinsic reactivity patterns of the different porphyrins are reflected in their metal deposition profiles, which serve as fingerprints marking the reaction sequence. Vanadium profiles (Fig. 25) from pure VO-etiopor-phyrin in oil demetallation experiments are steeper with less deposit in the pellets center than the nickel profiles (Fig. 26) from the analogous experiment with pure nickel porphyrin. Pure compound intrinsic reactivity data revealed that vanadium was more reactive than nickel at most temperatures of interest. However, a reduction in VO-porphyrin diffusion by stronger adsorption interactions would also contribute to a steepening of the metal deposition profiles. Metal profiles have not been examined from demetallating model oils containing both Ni- and VO-porphyrins. 

The V and Ni images show that the left particle has been in the unit for a long time while the right particle is very new. In the older particle, the vanadium distribution is nearly homogeneous while the new particle shows vanadium diffusing from the external surface. This observation shows that vanadyl as well as nickel porphyrins must crack on the external catalyst skin. Vanadium migration then occurs after the metal deposit is on the catalyst surface. The Ni distribution confirms the age of the pair, but also reveals that edge enhancement persists on very old particles. This confirms that the deposited nickel has very little or no mobility in the FCC unit. 

Both low and high oxidation states of nickel porphyrins are easily accessible in many nonaqueous solvents and the exact site of electron transfer (metal vs ring) upon reduction or oxidation has been the topic of numerous studies [7]. Bocian and coworkers [325], as well as Connich and Macor [326], showed that a Ni(II) porphyrin tt-cation radical can be converted to a Ni(III) porphyrin in binding solvents such as Py, THF or MeCN. The type of Ni(II) porphyrin tt-cation radical, that is, aiu or a2u, wiU depend on the type of porphyrin macrocycle anda Ni(II) jr-cation... 

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