Osmium and Cerium Porphyrins: Metalloporphyrins with Unnatural Metals as Models for Active Sites of Electron-Transfer Enzymes

Metal complexes with tetrapyrrole ligands: Part LXXVII. New osmium complexes of the 5,10,15,20-tetrakis-(4-carboxyphenyl) porphyrin

The synthesis and characterization of new alkali-soluble osmium tetraphenylporphyrinates, complexes of the 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin Os ( tH 4 cpp ) L 2 and Os ( tH 4 cpp ) LL ' (2a–j), is described. 2a–j are obtained from the corresponding new osmium porphyrinates Os ( tmecpp ) L 2 and Os ( tmecpp ) LL '(1a–k) by alkaline saponification and precipitation with hydrochloric acid. In fact, the osmium(II) porphyrinates 2c–f as well as 2i–j are oxidized to the osmium(III) porphyrinates Os ( tH 3 cpp ) L 2(3c–f) and Os ( tH 3 cpp ) LL '(3i–j) in the presence of air, as confirmed by UV-vis spectroscopy.

Direct electrochemistry and spectroelectrochemistry of osmium substituted horseradish peroxidase

In this contribution the substitution of the central protoporphyrin IX iron complex of horseradish peroxidase by the respective osmium porphyrin complex is described. The direct electrochemical reduction of the Os containing horseradish peroxidase (OsHRP) was achieved at ITO and modified glassy carbon electrodes and in combination with spectroscopy revealed the three redox couples Os(III)HRP/Os(IV)HRP, Os(IV)HRP/Os(V)HRP and Os(V)HRP/Os(VI)HRP. The midpoint potentials differ dependent on the electrode material used with E(1/2) (Os(III/IV)) of -0.4 V (ITO) and -0.25 V (GC), E(1/2) (Os(IV)/(V)) of -0.16 V (ITO) and +0.10 V (GC), and E(1/2) (Os(V/VI))of +0.18 V (ITO), respectively. Moreover, with immobilised OsHRP the direct electrocatalytic reduction of hydrogen peroxide and tert-butyl hydroperoxide was observed. In comparison to electrodes modified with native HRP the sensitivity of the OsHRP-electrode for tert-butyl hydroperoxide is higher.

Contributions to the chemistry of anionic water-soluble tetraarylporphyrins and their metal complexes

Recent contributions to the coordination chemistry of tetraanionic water-soluble tetraarylporphyrins, namely 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin, [1]4−, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin, [2]4−, and 5,10,15,20-tetrakis(4-hydroxidophosphorylmethylphenyl)porphyrin, [ H 43]4−, are reported. Problems with the isolation of sodium and potassium salts of [2]4− are discussed. The tetraphosphonoporphyrin H 8[3] is precipitated as a dihydrochloride H 8[3]·2 HCl , its metal complexes H 8[3-M] as such. The synthesis of salts containing Ce and Os complexes of [1]4−, Al , Ga , In , Ge , Sn , As , Sb , Mn , Mo , W , Re , Os , and Pt complexes of [2]4−, and Ni , Cu , Zn , Pt and Os complexes of [ H 43]4− as documented in publications and doctoral theses from the Darmstadt laboratory are reviewed. Some properties of the new complex salts are reported. The results of crystal structure determinations of the potassium salt of tetrakis(4-sulfonatophenyl)porphyrinatoplatinate(II), K 8[2-Pt]2·10 DMSO ·6 H 2O· C 7 H 8, and the mixed sodium-potassium salt of tetrakis(4-sulfonatophenyl)porphyrinatoaluminate, K 2 Na [ Al ( DMSO )2( tpps 4)]·8( DMSO )·2 H 2 O , are shown.

Synthesis, structure, spectroscopic properties, and electrochemistry of rare earth sandwich compounds with mixed 2,3-naphthalocyaninato and octaethylporphyrinato ligands

A series of 14 heteroleptic rare earth sandwich complexes [M(III)-(nc)(oep)] (M=Y, La-Lu except Ce and Pm; nc=2,3-naphthalocyaninate; oep = octaethylporphyrinate) have been prepared by a one-pot procedure from corresponding [M(acac)3] . nH2O (acac = acetylacetonate), metal-free porphyrin H2(oep), and naphthalonitrile the presence of 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) in n-octanol. The molecular structures of four of these complexes (M = Sm, Gd, Y, Lu) are isostructural, exhibiting a slightly distorted square antiprismatic geometry with two domed ligands. The interplanar distance decreases from 2.823 to 2.646 A along the series as a result of lanthanide contraction. The whole series of complexes have also been characterized spectroscopically. All the electronic absorptions, except the two B-bands due to nc and the oep rings, are metal-dependent, indicating that there are substantial pi-pi interactions. The hole or the unpaired electron in these double-deckers is delocalized over both macrocyclic ligands, as evidenced by the co-appearance of the IR marker bands for the nc*- (1315-1325 cm(-1)) and oep*- (1510-1531 cm(-1)) T radical ions. Three one-electron oxidation couples and up to three one-electron reduction couples have been revealed by electrochemical methods. All the potentials are linearly dependent on the size of the metal center. The changes in absorption spectra during the first electro-oxidation and reduction of the La(III), Eu(III), and Y(III) double-deckers have also been studied spectroelectrochemically. The spectral data recorded for [M(III)(nc)(oep)]-(M = Y, La-Lu except Ce and Pm) reduced chemically with hydrazine hydrate are in accord with those obtained by spectroelectrochemical methods. The first heteroleptic naphthalocyaninate-containing triple-deckers [M(III)2(nc)-(oep)2] (M = Nd, Eu) have also been prepared by a raise-by-one-story method by using [M(III)(nc)(oep)] (M = Nd, Eu), [M(acac)3] . nH2O (M = Nd, Eu), and H2(oep) as starting materials. The compounds adopt a symmetrical triple-decker structure with two outer oep rings and one inner nc ring, which has been confirmed by 'H NMR spectroscopy and X-ray structural determination of the Nd complex. Both compounds give a near-IR absorption at 1021 nm (for M=Nd) or 1101 nm (for M = Eu), which has rarely been observed for neutral (or hole-free) triple-decker complexes and can be ascribed to the lowest-energy Q'(0, 0) transition. Similarly to the double-decker analogues. these triple-decker complexes undergo a series of one-electron transfer processes with a relatively small potential gap (1.1 -1.2 V) between the first oxidation and the first reduction.