Metallkomplexe mit Tetrapyrrol‐Liganden, II¹⁾ Metallchelate des α.γ‐Dimethyl‐α.γ‐dihydro‐octaäthylporphins durch reduzierende Methylierung von Octaäthylporphinato‐zink

Abstract

(1 and Niz@ ions, respectively, in the same solvent. 9 is dehydrogenated by molecular oxygen in glacial acetic acid to yield g,y-dimethyl-octaethylporphin (0DM)Hz 10, which is further characterized by preparation of the metal chelates (0DM)Cu 11 b and (0DM)Ni l l c . The constitution of the products is proved by mass spectra (table l), IHresonance spectra (tables 2 and 3) and electronic spectra. The new tetrapyrrole pigments are compared with the known porphins as well as the meso unsubstituted a,y-dihydroporphins and the influence OF the central metal on the course of the reductive methylation is discussed. 912 (1969).

Molecular Engineering of Free‐Base Porphyrins as Ligands—The N−H⋅⋅⋅X Binding Motif in Tetrapyrroles

“…Formal two-, four-, or six-electron oxidation of these nonaromatic macrocycles leads to calix[4]phyrins,which bear analogy to both porphyrins and calix[4]pyrroles by containing amixture of sp 2 -a nd sp 3 -hybridized meso-like positions.T he partial interruptions in the conjugation introduce anumber of unique structural features since the sp 3 -carbon atoms perturb the p-system and significantly modify the molecular shape and flexibility.Likewise,far-range electronic induction effects still exist so that functional groups may be used for fine-tuning of conformational and chemical properties. [80] Early examples of rational calixphyrin syntheses include acid-catalyzed cyclization reactions between ketones and pyrrolic precursors followed by partial oxidation (Figure 9B) [81] and Buchlersr eductive methylation to yield metalloporphodimethenes [82] or substitution reactions. [83] Thep roducts are usually distorted and feature structural cavities and accessible inner nitrogen atoms ( Figure 9C), which may aid the binding of substrates.…”

Structure of the Krasnovskii Photoreduction Product of Chlorophyll a

“…The chemical shift values for both the methine and methylene protons fall in the ranges characteristic for di-and tetrapyrrolic compounds in which an aromatic macrocycle is lacking. The chemical shift value of 7.42 ppm assigned to the a-methine proton corresponds satisfactorily to the methine resonances in zinc porphodimethenes obtained by reductive methylation of zinc porphyrins [7.05 for a,,ydimethyl-a,'y-dihydro-octaethyl-porphyrin-zinc in C62H6 (10), (10) and photochemical (11)(12)(13) reduction of metalloporphyrins and phlorins (14). Reductive methylation of various octaethylporphyrin metal complexes yields a,'y-dihydro-a,'y-dimethyl porphyrins (10).…”

“…The chemical shift value of 7.42 ppm assigned to the a-methine proton corresponds satisfactorily to the methine resonances in zinc porphodimethenes obtained by reductive methylation of zinc porphyrins [7.05 for a,,ydimethyl-a,'y-dihydro-octaethyl-porphyrin-zinc in C62H6 (10), (10) and photochemical (11)(12)(13) reduction of metalloporphyrins and phlorins (14). Reductive methylation of various octaethylporphyrin metal complexes yields a,'y-dihydro-a,'y-dimethyl porphyrins (10). Recently, one of the isomers obtained by Krasnovskii reduction of zinc-a,'y-dimethyloctamethylporphyrin was isolated and characterized by 1HMR as the a,'y-dihydroproduct (11).…”

Synthesis and Stereochemistry of Hydroporphyrins

“…With CH 3 I as methylation reagent, and subsequent oxidation, the a,y-methylated OEP 29a was obtained from the dianion of 29 30 OEP in 607o yield, thus confirming a high electron density of the dianion at opposite methine positions. 53 The uv-vis spectra of the dimethylporphyrins 29 show considerable bathochromic shifts (as compared to the educt porphyrins), which are characteristic for oligopyrrole pigments that are twisted due to steric hindrance (Brunings-Corwin effect 17 - ; for a critical study see ref. 55).…”