Porphyrins free base analogs

In addition to forming complexes with divalent cations, the porphycenes act as ligands for certain trivalent metal cations. In many cases this chemistry parallels that seen in the porphyrin series. For instance, the (x-oxo-diiron(lll)porphycenates 3.72 and 3.73 were prepared from the corresponding free-base porphycene 3.20 or 3.23 using a procedure analogous to that used to prepare the corresponding p-oxo-diiron(III)porphyrinates. Thus, the reaction of 3.20 or 3.23 with Fe(acac)3 in... 

Each of the new homoporphyrin derivatives prepared by this alternative approach was demonstrated to form a stable nickel(II) complex when treated with Ni(OAc)2 (e.g., 4.46-4.50). Further, the free-base homoporphyrin 4.41 was shown to form the stable complexes 4.51-4.53 when treated with the appropriate divalent metal salt (M = Cu, Zn, Co, X = OAc). ° Additionally, in analogy to the porphyrins, treatment of the free-base homoporphyrin 4.41 with FeCl2 was found to give, after workup, the iron(III) complex 4.54 (Scheme 4.1.19) it presumably results from normal, porphyrin-like autoxidation at the metal. ... 

One of the first reported Ceo-based donor-acceptor systems is also the H2P-C60 and the analog ZnP-Cso dyad (20), in which H2P denotes the metal-free base tetraphenyl porphyrin and ZnP is the corresponding zinc tetraphenylporphyrin... 

The photophysical properties of a Ceo-linked phytochlorin (31) [344, 373], a porphyrin analog, are quite different from those of conventional Cgo-linked porphyrins. The phytochlorin-Cfio exciplex is formed in both toluene and benzonitrile via either the singlet excited states of the phytochlorin or the Ceo- The exciplex relaxes directly to the ground state in toluene, whereas it undergoes a conversion to the charge-separated state, followed by the decay to the ground state in benzonitrile. A similar proposal for the exciplex formation has been forwarded by the report on a free-base porphyrin Ceo dyad [374, 375]. 

One of the first reported self-assembled monolayers of porphyrins is cobalt(II)-porphyrins 5 and 6 and the analog free-base porphyrins 7 and 8, in which the number and location of the thiol-containing tails are varied systematically [300, 314]. 

Deoxomesopyropheophorbide-a and 7,8-Dihydro-DPEP. Sedimentary bitumen at or near a level of maturity such that free-base porphyrins are present or dominant also yield tetrapyrroles with electronic spectra characteristic of deoxomesopyropheophorbide-a (DOMPP-a). DOMPP-a is isolated, in the greatest amounts, from the non-polar chromatographic fractions, has an HCL of ca. 5-7 and, thus, are decarboxylated (7-R-7-despropio R=-H,-CH3,-CH2CH3) analogs. As such, an alternate semi-systematic name would be 7,8-dihydro DPEP. 

The thermal behavior of an analogous series of octakis(alkoxyethyl)porphyrins was also investigated for comparison ((22) M = 2H, Zn, Cu, Pd, Cd, n = 4, 6, 8, 10), and in order to decrease the viscosity, which was still high in the octaester systems. Thus, while only the free-base derivative with octyl chains was mesomorphic (Cr 84 Col 891), all the metal complexes were mesomorphic (Figure 28), the mesophase decreasing in stability as the chains were elongated. " In all cases, the fluid mesophase was identified by optical microscopy as columnar. 

The electrochemical behavior of water-soluble yS-pyrrole brominated porphyrins is more complex than that of their water insoluble analogs. The metal-centered redox reactions of (TMPyP)Mn and (TMPyPBrg)Mn are reversible while the majority of porphyrin ring-centered redox reactions of the free-base, Cu, and Mn derivatives of TMPyPBrs are irreversible The metal-centered oxidation of (TMPyPBr8)Mn is anodically shifted by 420 mV compared to 1/2 for the corresponding reaction of (TMPyP)Mn (Table 9.2). The metal-centered... 

One or two Al(III) cationic porphyrin(s) is (are) connected with a peripheral mono- or di-phenolic free base, and their photophysical properties are compared with previously described tin(IV), germanium(IV), and phosphorous(V) oxophilic porphyrins. Two processes can occur in these nonelectronically coupled species, the first being observed upon excitation of the aluminum porphyrin. When excited at 550 nm, the Al(II) species fluorescence is quenched by the free base component mostly by energy transfer, but concomitantly by electron transfer in polar media. The second process occurs upon excitation of the free base species, and consists in a poorly efficient (low <2h2%) electron transfer from the free base to the Al(ni) species. The same process is quite efficient in the case of P(V), Sn(IV), and Ge(IV) analogs with respective 0H2 values of 93, 82, and 69%. ... 

Photoinduced ET in SAMs of porphyrin-linked Ceo systems shows that the maximum of the photo current using free-base porphyrin Qo moieties is five times larger than in an analogous free-base porphyrin SAM system without Ceo. In the former system and in a Ceo-terminated oligothiophene mentioned... 

As expected, dendrimers containing 2,4, 8, 16, 32, and 64 free-base and zinc(II) porphyrins appended on the surface (Fig. 20d) exhibit an electrochemical behavior completely different from that described for porphyrin-cored analogs, as demonstrated by Crossley et al. [128]. They show reversible behavior and redox potentials almost independent of dendrimer generation. Multiple it-cation and a-anion radicals as well as dications and dianions were formed as expected for oxidation and... 

Similarly, Giraudeau and coworkers showed that exhaustive electrooxidation of zinc(ll) P-octaethylporphyrin (ZnOEP) in the presence of an excess of pyridine at a potential leading to the formation of the porphyrin radical cation, actually +0.70 V/SCE, allows the formation of the mono-substituted zinc mcjo-pyridinium-P-octaethylporphyrin (ZnOEP(py) with a yield of 71 % [113]. Yet again, the analogous free base H20EP(py) porphyrin had previously been obtained by Smith and coworkers using thaUium(lll) nitrate as chemical oxidant with a much lower yield (45 %) [104]. 

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