Synthesis of new octakis(benzylthio)tetraazaporphyrin complexes with bivalent transition metal ions and an investigation of their spectral, redox and catalytic properties

Abstract

Transition metals in the þ2 oxidation state form complexes with octakis(benzylthio)tetraazaporphyrin [M{TAP(SBn) 8 }] (M ¼ Mn 2þ , Co 2þ , Ni 2þ , Cu 2þ , Zn 2þ and 2H þ ; Bn ¼ ACH 2 Ph; TAP ¼ tetraazaporphyrin) and were prepared via demetallation of the template-synthesized complex [Mg{TAP(SBn) 8 }] in ClCH 2 COOH, followed by insertion of the metal ions in a PhCl-DMF mixture. All compounds were characterized by u.v-vis, 1 H-n.m.r., e.s.r. and mass spectra, microanalyses and magnetic susceptibility data. PM3 geometry optimization showed near coplanar arrangement of five phenyl rings vis-a`-vis the TAP ring plane, while the remaining three phenyl rings lie bent over it. The Mn 2þ , Co 2þ and Cu 2þ complexes exhibited reversible one electron oxidation waves, that were observed at E 1/2 À0.33, À0.29 and 0.58 V versus Ag/AgCl respectively. They all exhibited an irreversible reduction wave at E p À1.1 V versus Ag/AgCl followed by appearance of an irreversible oxidation wave at E p 1.1-1.2 V versus Ag/AgCl. This has been interpreted in terms of reductive dissociation, leading to removal of the benzyl substituents, and subsequent oxidation of thiolate products. The Mn 2þ , Co 2þ and Cu 2þ complexes exhibited metal ion-based e.s.r. signals. The [Co{TAP(SBn) 8 }] complex in a homogeneous DMF solution was found to catalyze electroreduction/oxidation of nitrite ions. In the presence of a 1/5 molar quantity of the complex [Co{TAP(SBn) 8 }], the nitrite reduction peak was observed to be shifted by 0.1 V towards the positive potential side and the peak current rose by a factor of 1.33. Similarly a sharp rise in the anodic current, corresponding to oxidation of nitrite ions, was observed in the presence of the complex.

Synthesis, spectroscopic and electrochemical investigations of supramolecular nickel(II)tetraazaporphyrin complexes

“…The pentanuclear complexes generally exhibited good voltammograms, with multiple oxidation waves, as compared with corresponding dinuclear complexes. Since nickel(II) porphyrin exhibits an irreversible oxidation at E p = 1.2 V vs SCE in DMF [57], considering the relative peak currents and in analogy with our earlier studies, the lower oxidation wave at E 1/2 = 0.39 V could be assigned to the Ru II /Ru III process, while the other two waves at E 1/2 = 0.68 and 0.91 V could be attributed to the two successive oxidations of the [Ni(OBTTAP)] [28,[58][59][60][61]. The Ru II /Ru III process at E 1/2 = 0.38 V as compared to that observed in the [(bpy) 2 Ru-{S 2 Bn 2 C 2 (CN) 2 ] 2+ (E 1/2 = 1.04 V), is very much easier.…”

“…Q and Soret bands (Table 1). In complex 1 the Q band was observed at 627 nm and the Soret band at 320 nm [28]. The latter band is nearly three times more intense than the former one.…”

Synthesis, Structure and Catalytic Properties of Two Complexes: ((Butylthio)8porphyrazinato)cobalt(II), Co(PzS8) and ((Butyloxyl) (Butylthio)7porphyrazinato)cobalt(II), Co(PzOS7)

“…At the same time, the substrates with electron‐withdrawing groups such as ‐NO 2 (entry 3) and ‐Br (entry 4) needed longer reaction time than those with electron‐donating groups such as ‐CH 3 , ‐OCH 3 (entry 6 and 2) to obtain satisfied yields. In particular Benzil, which were used as building blocks for the synthesis of pharmaceuticals, photo initiators and precursors of porphyrins, are also obtained from benzoin in high yield after 3 h. It indicated that the position of substituentof benzyl alcohols has little effect on the oxidation, but higher electron density and conjugation effect on α‐carbon with hydroxyl group is favorable to this reaction.…”

“…Porphyrinic macrocycles have aroused renewed research interest for its potential for creating structure diversity since the inherent synthesis ease of diverse peripheral substituents . Recently, metal phthalocyanine (Pc) is proved to be comparable efficient in producing energy‐rich oxygen in photo‐ and thermo‐catalytic oxidation and receives massive attention .…”

EPR and semi-empirical studies as tools to assign the geometric structures of FeIII isomer models for transferrins

“…This method has been successfully used in cases involving transition metal complexes. [30][31][32] The spin state of the Fe III isomers was stated as high-spin, ground state 6 S, according to the EPR data. The calculations were carried out on a 2.6 GHz Athlon PC, with 1 GB RAM and 40 Gb HD, under the Windows 2000 operational system.…”