Porphyrins, metal derivatives

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... 

Unsaturated heterocyclic ligands like pyrrols or porphyrins are formally derived from secondary organic amines and their metal derivatives are therefore amide complexes. The Ln-N bond lengths formed with simple monocyclic ligands... 

Not only has binding of imidazoles and pyridines to Fe protoporphyrin IX been studied, as discussed in Section 4.1.2, but also photodissociation of axial ligands such as pyridines, imidazoles, or piperidines from six-coordinate, low-spin Fe porphyrins, in which the porphyrin is derived from protoporphyrin IX, or proto- or deuteroporphyrin IX dimethyl ester, has been investigated in nonaqueous solvents using picosecond transient absorption spectroscopy (see Photochemistry of Transition Metal Complexes). It has been shown that photodissociation leads to the formation of five-coordinate complexes, that is, only one ligand appears to be released upon excitation of the six-coordinate complex. ... 

The general instability of the homoazaporphyrins has also limited attempts to prepare metalated derivatives. Specifically, efforts to prepare zinc(II) and copper(II) homoazaporphyrins from the metal-free homoazaporphyrin 4.6 resulted only in ring contraction to the corresponding we o-ethoxycarbonylamino-substituted metallo-porphyrins 4.9 or 4.10, respectively (Scheme 4.1.2). ... 

Heterometallic homo- and heteroleptic porphyrinate dimers with metal-thallium bonds have been described. These include (OEP)Rh Tl(OEP), (TPP)Rh Tl(OEP), (OEP)Rh-Tl(TPP), and (TPP)Rh-Tl(TPP). The ETV-visible spectroscopy confirms the presence of a strong tt-tt interaction between the macrocycles in each metal derivative. 

Several investigations of the redox properties of various free base hydroporphyrins and their metal derivatives have been reported. As is typical of many porphyrins and metalloporphyrins, these hydroporphyrins generally show two oxidations and one or more reductions. The reversibility of these redox reactions depends on the nature of the hydroporphyrin and its stereochemistry. For example, the cyclic voltammograms of ris-H2(OEC) and frans-H2(OEC) were superficially alike, although substantial differences existed in the stability of the cation radicals and dications of the cis and trans isomers [85]. The first oxidation of rrans-H2(OEC) was reversible whereas ds-H2(OEC) was not reversible. However, the notable features observed in the redox chemistry of hydroporphyrins is the shift of both oxidation and reduction potentials of hydroporphyrins towards more negative values compared to porphyrins, i.e., they are more easier to oxidise and difficult to reduce [78]. A significant trend was observed in the electrochemistry of free base octaethyl- [86, 87] and tetraphenyl [88,89] hydroporphyrins (Table 2). The porphyrin and chlorin of each series... 

Cu2+ and Ni2+ derivatives of STPPS results in metal centered reduction suggesting that the metal dx2 y2 orbital in both the metals are infact lower in energy than the eg(n ) orbitals of the porphyrin ring. The reverse is true for metal derivatives of normal porphyrins. The structures of CuSTPPCl and NiSTPPCl have revealed that the porphyrin plane is nonplanar and the thiophene ring is sharply bent out of the plane of the porphyrin. On the other hand, both CuTPP and NiTPP have a planar porphyrin core. Thus, this difference in the structures of the porphyrin core around the metal ion is probably responsible for the reversal of order of energy levels. 

When earlier transition metals are used in the cofacial DPX and DPD porphyrin motifs, oxidation reactions are promoted by a metal 0x0 intermediate. As for reductive catalysis, the oxidative catalytic reactions of the Pacman porphyrins are derived from PCET. The catalase reaction (H2O2 disproportionation to give 0.5 O2 and H2O) is exemplary of this PCET reactivity as the reaction includes both 0 0 bond making and bond-breaking catalysis coupled to proton transport. 

The effect of heavy atoms on the relative yields of fluorescence and phosphorescence has been investigated both by inserting Br and I substituents in the ring of deuterioporphyrin IX and its Zn derivative,340 and by adding ethyl iodide to the solution of a number of free base porphyrins.341 Other authors discuss the luminescence of protoporphyrin IX dimethylester after pulse radiolysis in benzene,848 and from monomeric and dimeric ethylenediamine-substituted protoporphyrin IX and some metal derivatives.343 Several reports consider the emission from porphyrins in Shpolskii matrices and other crystalline organic hosts.344-340... 

These ort/io-glucosylated porphyrin metal complexes have been shown to be active catalysts for aUcene epoxidation with certain asymmetric induction due to the presence of chiral sugar substituents in the vicinity of the metal center. However, as far as their medicinal apphcations are concerned, it was demonstrated that their deprotected, neutral derivatives exhibit neither toxicity nor phototoxicity against tumoral cells 1117]. A possible explanation for that considers a certain degree of globular structure for the molecules, which prevents suitable cell penetration. 

Thin films of porphyrin-metal polyamides have been prepared by the interfacial polymerization of tetrakis chloride derivatives with either aliphatic dianines or with tetrakis amino derivatives of the porphyrin-metal complexes. Films with thicknesses in the 0.0I-10 im range, display unique chemical asymmetry. Opposite surfaces show different concentrations of functional groups. When placed between identical semitransparent electrodes and irradiated with broad-band or pulsed laser light the films developed directional photopotential. Photopotentials of 25mV were seen. The directionality of the photopotentials is the result of electron transfer toward the acid surface of the asymmetric film. 

Scamporrino, E. and Vitalini, D., Main-Chain Porphyrin Polymers. 1. Synthesis and Characterization of Polyethers Containing Porphyrin Units and Their Metal Derivatives, Macromolecules, 25, 1625, 1992. 

---