Porphyrin derivatives, reduction with

When Na-Hg is used as a reducing agent, care must be taken to insure that no undesired Hg is incorporated into the product e.g., reduction of [Co(Cl)np]BPh4 in THF with Na-Hg followed by BuOH gave the red-brown dimeric npCoHgHgConp in 65% yield , and the reaction of Hg with [NaMnfCOj] and tetraphenylporphy-rin-SnClj in THF gave a porphyrin derivative (II) with a Sn — Mn—Hg—Mn chain. ... 

The electrochemical process in substituted porphyrins can be more or less localized at the peripheral groups, as demonstrated with wero-pyridyporphyrins coordinated to one to four transition metal complexes [236]. A study involving porphyrin derivatives substituted with diones and tetraones demonstrated that these redox-active sites can function independently of the central macrocycle [237]. The reduction of the 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrin-2,3-diones, 2,3,-12,13-tetraones [L-(P-tetraone)M] and 2,3,7,8-tetraones [C-(P-tetraone)M], (where M is 2H, Cu ", Zn, Ni " and Pd " ) was investigated and the products characterized by ESR and thin-layer UV-Visible spectroelectrochemistry. In diones, the first two reduction processes occur at the peripheral units whereas in the... 

The complex with the reduced porphyrin derivative 5,10,15,20-tetramethylisobacteriochlorin, [Ni(TMiBC)] (688), has an -ruffled conformation and a bond length pattern indicative of a reduction of aromaticity, both of which are more pronounced than those found for the corresponding porphyrin and chlorin complexes.1786... 

Reduced porphyrin derivatives are not only involved in photosynthesis for example, a derivative of this type (isobacteriochlorin) is also concerned with the binding of soil nitrite and its reduction to ammonia. 

Sc(OEP)C>2CMe is 0.4 s, which is the longest for any porphyrin, while the fluorescent yield of 0.2 is very high. The radiative properties are explained in terms of covalent interactions between the metal and the ring as modified by the probable location of the metal ion above the porphyrin plane.24 Scandium OEP complexes are reduced to the a, y-dihydro derivatives on reduction with sodium anthracenide and methanol.25 The redox potentials of Sc(OEP)OH have been determined by cyclic voltammetry to be ligand oxidation in PrCN, 1.03 and 0.70 ligand reduction in DMSO, —1.54 (Ey2 values in V vs. SCE) no metal redox wave was observed.26... 

There are several porphyrin derivatives of gold(III) such as the tetraphenyl-porphyrinatogold(III) cation, [Au(TPP)]+ (95), which forms a square pyramidal complex [AuC TPP)] with chloride.620- 2 Reduction of the latter complex gives the phlorin derivative... 

Fig. 15.17. Current in milliamperes cm-2 for CO production from C02 using C02+ tetraphenyl porphyrins modified with various pyridyl derivatives. (Reprinted with permission from T. Atoguchi, A. Aramata, and M. Engo, C02 Reduction by Macrocyclic Transition Metal Complex-Modified Electrodes," in Proc. International Symposium on Chemical Fixation of Carbon Dioxide, p. 338, Fig. 5,1991.)...

Large metal ions such as thorium or uranium were also employed in order to combine a porphyrin, octaethylporphyrin (OEP), with a phthalocyanine (Pc) chromophore in face-to-face or double-decker orientation. and Th compounds could be electrogenerated in up to seven different oxidation states. The first two reductions occurred mainly on the Pc ring while the first two oxidations of the same heteroleptic compounds involved primarily orbitals of the porphyrin macrocycle. In contrast, the homoleptic (MP)2 and (MPc)2 derivatives undergo initial one-electron oxidations and reductions which are localized not at a single ring, but involve both macrocycles. ... 

The extremely air-sensitive purple tetraphenylporphyrin complex, CrTPP, has been isolated by reduction of CrCl(TPP) with Cr(acac)2 in toluene or THF. Magnetic studies confirm the presence of Cr with = 4.8 BM for the high-spin d configuration. The other possibility, viz, a Cr radical anion derived from porphyrin ring reduction, was ruled out by electrochemical and visible absorption studies. ... 

The kinetically best characterized system for which a bimolecular reductive elimination has been proposed is a neutral hydrido porphyrin derivative of Ru(III) [4]. Cyclic voltammetry and double potential step chronoamperometry afford data that are more consistent with a second order than with a first order decay for the 17-electron RuH(OEP)(L) (OEP = octaethylporphyrin L = THE, 1 -tert-bytyl-S-phenylimidazole) complexes in THF as solvent. The second order dependence of the rate constant and the independence on the parent 18-electron anion concentration exclude the proton transfer mechanism. The possibility of a disproportionation mechanism (which would afford the same second order dependence, see section 6.5.2), however, has not been considered, nor were studies in solvents other than THF carried out. In the light of the gathered information, the mechanism shown in Scheme 17 was proposed. 

The oxomolybdenuni(IV) porphyrin treated with trimethylsilylchloride produces the trans dichloro derivative Mo(OEP)Cl2 which gives Mo(OEP)(PhC=CPh) by reduction with LiAlH4 in the presence of diphenylacetylene. The dimer is then obtained by vacuum pyrolysis of this five coordinate complex. Molybdenum(II) dimers are also obtained by heating a mixture of MoCl2(CO)4 and H2(Por) in oxygen-free toluene (Eq. 26) where Por is OEP, its 5-formyl-, 5-amino-, and 5-isocyanato derivative, or 5,15-dimethyletiopor-phyrin II. 

The structural type of C. (2,3-dihydroporphyrins) is formally derived from that of porphyrin by reduction of a peripheral double bond in a pyrrole ring of the porphyrin skeleton. The name is based on that of chlorophyll which possesses the C. skeleton with a central magnesium(ll) ion. Other substances with the C. skeleton are, in addition to the chlorophylls and their degradation products, some bacterioch)orophylls, bo-nellin, chlorophyllone, cyclopheophorbide, factor I, heme d, and tunichlorin. 

A vast majority of the literature on Fe-nitroxyls or Fe-bound NO /FINO or complexes has been with porphyrin derivatives (28). These are commonly designated as FeNO systems even though the oxidation states are not defined when using EF notation. Earlier work relied on in situ spectroelectrochemical experiments to establish the formation of this otherwise elusive EF notation for Fe (26,28,42). In general, formation of these complexes is achieved by electrochemical or chemical reduction of an FeNO complex. However, more recent work (vide infra) has employed the reaction of NO(g) with Fe(I) complexes to generate FeNO f 43j. While examples of this EF notation are rare, significant advances have been made from 2011 to 2014 and their synthesis and properties are described below. 

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