Porphyrins deprotonation

It is noteworthy to mention that employment of silver(i) trifluoroacetate in place of silver(i) acetate, as in the case of A-confused porphyrin, did not give the desired products. This has been attributed to the better basicity of the acetate anion than the trifluoroacetate, which aided the deprotonation of the three interior GH/NH protons at the carbaporphyrin ligand. Besides, it has been noticed that an excessive amount of silver acetate was required for the synthesis. The mechanism of the silver insertion reaction for this type of ligands was proposed, according to what Bruckner had proposed for the synthesis of silver(m) w -triarylcorroles.218,236 The reaction was suggested to occur via a disproportionation reaction, with the supportive observation of silver deposit formation after the reaction.237... 

The precursor model of FAB applies well to ionic analytes and samples that are easily converted to ionic species within the liquid matrix, e.g., by protonation or deprotonation or due to cationization. Those preformed ions would simply have to be desorbed into the gas phase (Fig. 9.6). The promoting effect of decreasing pH (added acid) on [M+H] ion yield of porphyrins and other analytes supports the precursor ion model. [55,56] The relative intensities of [Mh-H] ions in FAB spectra of aliphatic amine mixtures also do not depend on the partial pressure of the amines in the gas phase, but are sensitive on the acidity of the matrix. [57] Furthermore, incomplete desolvation of preformed ions nicely explains the observation of matrix (Ma) adducts such as [M+Ma+H] ions. The precursor model bears some similarities to ion evaporation in field desorption (Chap. 8.5.1). 

Ni(II) by strong oxidants, such as OH, Br and (SCN), produced by pulse radiolysis and flash photolysis. Rate constants are 10 M" s for oxidation by OH and Brf and = 10 M s for (SCN)f Ref. 259. The most popular means of production in both aqueous and nonaqueous solution is electrolytic, jjjg ligands which stabilize Ni(III) are cyanide, deprotonated peptides, amines and aminocarboxylates, a-diimines and tetraaza macrocycles, including porphyrins. Low spin d Ni(III) resembles low spin Co(II). The kinetics of the following types of reactions have been studied ... 

Fig. 12. Proposed mechanism for the HO-1-catalyzed conversion of Fe a-meso-hydroxyheme (shown deprotonated) to Fe verdoheme. In an equally good variant of this mechanism, the oxygen molecule binds to the Fe" before it binds to the carbon of the porphyrin to give the same peroxo-bridged intermediate.

A number of bis(arylamido)- and bis(diarylamido)ruthenium(IV) porphyrin complexes have been reported. In general, these complexes can be prepared by the reduction of [Ru(0)2(por)] with corresponding aromatic amines or by the oxidative deprotonation of [Ru (por)(ArNH2)2], as shown in Scheme 18. 

The porphyrin macrocycle is an ampholyte with two pyrrolenine (=N—) nitrogen atoms capable of accepting protons, and two NH groups capable of deprotonation. The most useful scheme for assigning pK values is due to Phillips (60MI30700) in this the metal-free porphyrin is abbreviated PH2, the dianion P2 and the dication PH42+ ... 

Neutral nickel(II) complexes with a number of deprotonated porphyrins have been prepared in most cases by the direct reaction of a nickel salt, usually Ni(ac)2-4H20, with the preformed diacid macrocycle, using media such as DMF, MeC02H or PhCl at refluxing temperature. Recently, the template synthesis of the complex with tetraalkylporphyrins has been reported (Scheme 61).2883 On the other hand the condensation reaction of 1,3,4,7-tetraalkylisoindole and nickel acetate tetrahydrate gives the [Ni(omtbp)] complex (omtbp = octamethyltetrabenzoporphyrinate dianion), 2884... 

Nickel(II) complexes have also been reported with reduced porphyrins, usually referred to as chlorins and corrins. Some nickel(II) complexes with chlorins (406)2883 have been obtained as by-products in the template synthesis of tetraalkylporphyrins. The main difference between [Ni(tmc)] and [Ni(tmp)] (tmc = deprotonated tetramethylchlorin, tmp = deprotonated tetra-methylporphyrin Table 110) is the lack of symmetry in the former complex with respect to the latter. The synthesis and reactivity properties of a number of corrin-nickel(II) complexes have been reported, mostly by Johnson and co-workers.2910-2915 Scheme 62 is a typical example of oxidative cyclization in the presence of a nickel salt.2914... 

Corroles are stronger acids and weaker bases than porphyrins.239 They are deprotonated in dilute alkali to form aromatic anions. In acidic media, the first protonation occurs on the pyrrole nitrogen, but the second proton adds to the meso carbon causing loss of the aromaticity (Scheme 72). 

An interesting new bridged complex, [Ru(TDBOHPP) L a L] (type H) in which the bridge L a L is 4,4 -azopyridine, has been studied in the search for molecular switches [217]. Protonation of the polymer induces partial oxidation of the Ru(II) to Ru(III) at the expense of the azo groups which are reduced to hydrazo species. Along with the formation of the Ru(II)-Ru(III) mixed valence compound a NIR intervalence band is switched on . The chemistry of these complexes is further complicated by the phenolic hydroxy groups in the porphyrin ligand which can also be deprotonated and oxidized. 

A chromophore such as the quinone, ruthenium complex, C(,o. or viologen is covalently introduced at the terminal of the heme-propionate side chain(s) (94-97). For example, Hamachi et al. (98) appended Ru2+(bpy)3 (bpy = 2,2 -bipyridine) at one of the terminals of the heme-propionate (Fig. 26) and monitored the photoinduced electron transfer from the photoexcited ruthenium complex to the heme-iron in the protein. The reduction of the heme-iron was monitored by the formation of oxyferrous species under aerobic conditions, while the Ru(III) complex was reductively quenched by EDTA as a sacrificial reagent. In addition, when [Co(NH3)5Cl]2+ was added to the system instead of EDTA, the photoexcited ruthenium complex was oxidatively quenched by the cobalt complex, and then one electron is abstracted from the heme-iron(III) to reduce the ruthenium complex (99). As a result, the oxoferryl species was detected due to the deprotonation of the hydroxyiron(III)-porphyrin cation radical species. An extension of this work was the assembly of the Ru2+(bpy)3 complex with a catenane moiety including the cyclic bis(viologen)(100). In the supramolecular system, vectorial electron transfer was achieved with a long-lived charge separation species (f > 2 ms). 

Complexation of macrocyclic ligands to lanthanide cations has been studied extensively [207,208], One main reason for the current interest in those macro-cyclic complexes are their intrinsic paramagnetic and luminescent properties. There is also the steadily increasing number of tailor-made macrocyclic ligands [209], This section will focus on complexes which contain macrocycles as discrete counterions and in particular on the coordination chemistry of phthalocyanine (Pc) and porphyrin (Por) ligands. Schiff base ligands which display another source of amine functionalities are usually not deprotonated under the prevailing reaction conditions [210]. 

The isolation of the first stable oxo-terf-butylimido complexes of ru-thenium(VI) and osmium(VI) porphyrins by oxidative deprotonation of [M(porp)CBuNH2)2] has been reported (289). These complexes are diamagnetic and have been characterized by NMR and IR spectroscopy. The [RuVI(porp)(0)(N Bu)] complex rapidly reacts with PPh3 in solution to give 0=PPh3, Ph3P=N Bu, and [Ru(porp)(PPh3)2]. 

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