Porphyrin complex stability

Iron(II) alkyl anions fFe(Por)R (R = Me, t-Bu) do not insert CO directly, but do upon one-electron oxidation to Fe(Por)R to give the acyl species Fe(Por)C(0)R, which can in turn be reduced to the iron(II) acyl Fe(Por)C(0)R]. This process competes with homolysis of Fe(Por)R, and the resulting iron(II) porphyrin is stabilized by formation of the carbonyl complex Fe(Por)(CO). Benzyl and phenyl iron(III) complexes do not insert CO, with the former undergoing decomposition and the latter forming a six-coordinate adduct, [Fe(Por)(Ph)(CO) upon reduction to iron(ll). The failure of Fe(Por)Ph to insert CO was attributed to the stronger Fe—C bond in the aryl complexes. The electrochemistry of the iron(lll) acyl complexes Fe(Por)C(0)R was investigated as part of this study, and showed two reversible reductions (to Fe(ll) and Fe(l) acyl complexes, formally) and one irreversible oxidation process."" ... 

The chemical reactivity of the organoruthenium and -osmium porphyrin complexes varies considerably, with some complexes (M(Por)R2, M(Por)R and Os(OEP)(NO)R) at least moderately air stable, while most are light sensitive and Stability is improved by handling them in the dark. Chemical transformations directly involving the methyl group have been observed for Ru(TTP) NO)Me, which inserts SO2 to form Ru(TTP)(N0) 0S(0)Me and Ru(OEP)Me which undergoes H- atom abstraction reactions with the radical trap TEMPO in benzene solution to yield Ru(OEP)(CO)(TEMPO). Isotope labeling studies indicate that the carbonyl carbon atom is derived from the methyl carbon atom. "" Reaction of... 

In terms of relative Co—C bond energies, those in the trihalomethyl complexes Co(OEP)CX3 are observed to be qualitatively weaker than in Co-alkyl porphyrin complexes. The high thermal stability of the cobalt porphyrin stannyl complexes was interpreted as an indication that, surprisingly, the Co—Sn bond is stronger than the Co—C bond in Co(Por)(alkyl) complexes. " ... 

M = Eu(III), Y(III), Lu(III)] 8-16%. These protonated compounds were isolated as the sole product, in contrast to the similar reactions with TBPPH2, where the non-protonated analogues Lnnl(Pc)(TBPP) (TBPP, 5,10,15,20-tetrakis[(4- ert-butyl)phenyl]-porphyrin) were obtained instead [106]. These results clearly show that the inversion of a pyrrole ring in N-confused porphyrins can stabilize the protonated complexes. 

B. T. Holland, C. Walkup, and A. Stein, Encapsulation, stabilization and catalytic properties of flexible metal porphyrin complexes in MCM-41 with minimal electronic perturbation by the... 

Porphyrins, 21 14, 36, 135 -based manganese complexes, 46 400-402 as cobalt complex ligants, 44 284-290 compared to phthalocyanines, 7 75 complexes, 19 144, 145, 147 complex stability, 42 135-137 degeneracy lifting, 36 206 metalloporphyrins, DNA cleavage and, 45 271-283... 

The ferrous complex of octaethyl porphyrin in SDS micelles has been characterized as four coordinated (S = 1) ferrous heme species and is similar to that observed for the ferrous protoheme complex in CTAB. It is noted that ferrous complexes of natural porphyrins cannot be stabilized in aqueous SDS micelles, and much larger aqueous micelles like CTAB were needed to stabilize various ferrous protohemes. This indicates that the environment around the octaethyl porphyrin complex in aqueous SDS is more hydrophobic than that of the analogous natural heme species, suggesting that the OEP moiety is embedded much deeper inside the micellar hydrophobic cavity than the protoporphyrin analogue. 

Nitrogen-bearing cyclophanes like 351 [16] and 352 [17] bind larger organic anions in water due to superposition of the hydrophobic effect and electrostatic attraction. The phenanthridinium hosts like 351 have been found to form the most stable nucleotide complexes known so far. On the other hand, free tetrapyrrolic porphyrins do not bind anions since their cavity is too small to take advantage of the convergent N-H dipoles for the complex stabilization [18]. However, expanded diprotonated porphyrins like sapphyrin 353 were shown to form stable complexes with phosphate [19a] and halide [19b] anions. 

Porphyrin (8) and phthalocyanine complexes stabilize a square planar structure, probably as a result of extensive electron delocalization. Square planar complexes often give paramagnetic bis adducts with a Irans octahedral geometry. 

Alkali metals form porphyrin complexes of the type M2(Por) when their alkoxides are heated with porphyrin in dry pyridine, but are readily hydrolyzed.17 The transmetallation experiments indicate the stability of M2(Por) in the order K < Na < Li (Using radioactive sodium. Na2(TPP) is shown to undergo rapid metal exchange with Nal in pyridine (equation 2). 

Parallel to the work on in situ three-component catalysts, a nature-inspired in situ catalyst based on iron porphyrin complexes, was developed, since high stability of the... 

Due to poor chemistry and the stability of the porphyrin complexes containing the precious metals Ag, Au, Pd, and Pt, most papers dealing with these complexes are devoted to physical measurements, especially optical or photophysical investigations [23]. 

It has been suggested [95] that the synthesis of structured porphyrins with controllable steric ambience is a strategic direction in the reproduction of enzyme protein cavities, which control the selectivity and stability of biochemical reactions such as cytochrome P-450. Such an approach to the synthesis of biomimics has considerable potential, especially in their application on mineral matrices silicon dioxide, alumina and zeolites. Data exist on the synthesis of a biomimic [96] with a complex porphyrin complex (5-pentafluorophenyl-10,15,20-tri(2,6-dichlorophenyl)porphyrin (FeMPFDCPP)) covalently linked to aminopropyl silicon dioxide, which is applied in oxidation of ds-cyclooctene, cyclohexene, cyclohexane and adamantane with participation of iodosylbenzene dissolved in dichloromethane. 

Usually, high oxidation states of metals are stabilized most effectively when in combination with the most electronegative atoms, fluorine and oxygen. Rather surprisingly, no FeIV or higher oxidation state compounds with fluorine are known. Indeed rather few stable or well-defined higher oxidation state iron compounds are known. Despite this, there can be no doubt about the importance of such compounds. We have already encountered the FeIV and Fev states in reactive intermediates in the reactions of several metalloproteins and of several synthetic porphyrin complexes. 

---