Tetrabenzoporfirin sentezi için yeni taç eter türevleri

Abstract

Ftalosiyaninlere çok benzeyen bir yapıda olmalarına rağmen tetrabenzoporfirinler (TBP) üzerlerinde aynı yoğunlukta araştırma yapılmamıştır. Bu çalışmada/ gurubumuzda daha önce gerçekleştirilen ve ilgi çekici sonuçlar veren taç eter sübstitüe ftalosiyaninlere benzer tetrabenzoporfirinlerin sentezinde kullanılacak başlangıç maddelerinin hazırlanması amaçlanmıştır. Bilinen tetrabenzoporfirin sentez yöntemleri içerisinde, taç eterli türevlerinin hazırlanmasına en uygun başlangıç maddeleri ftalik anhidrid ve 2-asetilbenzoik asid olarak tesbit edilmiştir. 2-Asetilbenzoik asidin taç eterli türevini hazırlamak için benzo-15-crown-5'in asetillenmesi ile 4'-asetil-benzo-15-crown-5 elde edilmiş, bunun nitrolanması ile de 4'-Asetil-5'-nitro- benzo-15-crown-5 ele geçmiştir. Bu maddenin indirgenmesi ile oluşan aminin diazolanması ve Sandmeyer yöntemine göre CuCN ile reaksiyonundan 4'-Asetil-5'-siyano-benzo-15- crown-5'e geçilmiştir. Asidik şartlarda hidroliz sonucu 4'-Asetil- (benzo-15-crown-5) -5'-karboksilik asid elde edilmiştir. Taç eter sübstitüe ftalonitrilin alkali ortamda hidrolizi ve asetik anhidrid ile reaksiyonundan (15-crown-5) sübstitüe ftalik anhidride ulaşılmıştır. Her iki başlangıç maddesi ile Zn(II) ve Cu(I) iyonlarının template etkisinden yararlanarak tetrabenzoporfirin türevi elde edilmeye çalışılmış fakat yapılan ilk denemelerde istenilen renk dönüşümleri gözlenemediginden herhangibir ürün izole edilememiştir. Elde edilen yeni maddelerin yapıları, elementel analiz, I.R., NMR ve kütle spektrumu ile aydınlatılmıştır.

In addition to their wide use as dyes and pigments due to their intense colours, phthalocyanines and their structurally, similar analogs porphyrins, tetraazaporphyrins and tetrabenzoporphyrins are also extensively studied for their biological significance, catalytic and electrical properties. Phthalocyanine çC*o Tetrabenzoporphyrine N H H y N Tetraazaporphyrine Porphyrine Tetrabenzoporphine and its metal complexes, as structural analogs of porphine, are convenient objects for use in the modeling of important biological processes: photosynthesis, the fixation and transfer of oxygen, enzymic reactions. However, despite the ever- increasing interest in these compounds, their extensive investigation is made difficult by their poor accessibility. VI Metalloporphyrins/ which include such important natural complexes as chlorophyll, haem of the blood, and others, represent a vast and unique group of inter complex compounds. The central metal atom displaces two hydrogen ions from the porphyrin ligand and practically finds itself in a symmetrical electrostatic field of four nitrogen atoms with which it may form four equivalent, or almost equivalent, coordinate donor-acceptor bonds. The specific features of metalloporphyrins as intercomplex compounds are due not only to the polydentate (tetradentate) nature of the ligand but also to its rigidity. The latter is determined by the planar structure of the large ring of the porphyrin molecule, by the unique conjugation in it which is due to the strong % -electron interaction over the entire large ring (the so- called macroring), and by the particularly favourable structure of the coordination centre, consisting of four nitrogen atoms, on account of which most metal ions easily enter this space, coming into close contact with the nitrogen atoms. Because of its high rigidity the porphyrin ligand imposes specific requirements on the geometric parameters of the metal ion, whereby they form two clearly defined groups of stable or labile complexes. Characteristically, the metal ion that has entered into coordination with a porphyrin is in fact a partner of the conjugated porphyrin system and may either stabilize or destabilize it. Owing to this direct contact with the atoms of the conjugated system, it influences all, even the most remote parts, of the large molecule and alters the oxidation-reduction, acid-base, electron- optical, and all other properties of the porphyrin. In this connection it is of particular interest for a coordination chemist to use metalloporphyrins in examining the effect of the nature of the metal involved, the type of chemical bonding, and its strength on the major properties of porphyrins. A spesific feature of metalloporphyrins is their insolubility in water and solubility in organic solvents in cases where no significant solvation centres are present among the functional substituents of the ligand. This is the reason why most studies of porphyrins and metalloporphyrins have been conducted in non-aqueous media. vn The spesific features and great diversity of porphyrin, particularly metal loporphyr ins, are the factors responsible for their importance and wide distribution in nature, their extensive use in various physical, physicochemical, quantum-chemical, biological studies, as well as in the production of dyes, semiconductors, and catalysts. The structral diversity of porphyrins and metal loporphyr ins opens up enormous possibilities for studying the effect of functional substituents and central atoms on the properties of porphyrins. Such studies will make it possible in the future to provide an answer to the question why Nature has chosen, as the basic component of the photosynthetic and respiratory molecular system, porphyrins with a particular combination of functional substituents such as can be found chlorophyllic acids and protoporphyrin. Finally, an important and unique feature of porphyrins and their metal derivatives is their electronic absorption and emission spectra. The diversity of the latter, corresponding to the great variety of porphyrins, the typical arrangement of spectral bands, the sensitivity to certain effects on the molecule, and their complexity, make them not only a most reliable means for identifying porphyrins but also a rich source of information on the structure of porphyrins, the type of their coordinations, the interaction between substituents and ionizing media, and the intramolecular energies. Since the early work of Pedersen on crown ethers, intensive research on macrocyclic chemistry has been grown and resulted with new branching of the field such as "supramolecular chemistry" or "host-guest chemistry". Also another important step has been the combination of hard and soft donor sites in the same molecule such as crown ether substitued vic-dioximes or phthalocyanines which have been introduced for the first time by Bekaroğlu and coworkers. The aim of the present work is to extend this approach to tetrabenzoporphyrins by preparing their crown ether substituted derivatives. Since crown ether units need to be attached before the cyclomerization to tetrabenzoporphyrine, new substituted crown ethers are required. vm TBPH2 _. _ _ Among the relatively few possibilities, crown ether substituted phthalic anhydride and o-acetyl benzoic acid appear to be the most appropriate condidates. The first one has been prepared by alkaline hydrolysis of 4', 5'- dicyanobenzo-15-crown-5 and then subsequent treatment with acetic anhvride. O^J C o cr-\ 0 0^1 !3CC COOH C-CH- II 0 Phtalic anhydride o-acetyl benzoic acid The synthesis of 4'-Acetyl- (benzo-15-crown-5) -5'- carboxylic acid has been accomplished by starting with 4' -acetyl derivative which is obtained from benzo-15- crown-5 by Friedel Crafts acetylation using polyphosphoric acid as catalyst. This compoud has been nitrated with concentrated nitric acid to introduce the N-contening group in o-position. Reduction of nitro- group to amino has been carried out by tin. Diazotization of amino group and then treatment with CuCN K as in the case of well known Sandmeyer reaction gives the 4'-acetyl-5'-cyanobenzo-15-crown-5. Hydrolysis of cyano- group in alkaline medium gives the desired compound. Although convert these starting materials into tetrabenzoporphyrine or analogous compounds with 1-3 bridging (=N-) groups in the presence of metal ions such as Cu(I) or Zn(II), no intense colour changes indicating the formation of these conjugated systems were observed. The main reason for this failure is the difficulty in maintaining temperature control at high temperatures (350°-400°C) necessary for the cyclotetramerization reaction. The new compounds isolated during this work have been analysed with various spectral techniques such as İR, İH NMR, 13c NMR and Mass Spectra to verify their structures. When the IR spectra of the crown ether derivatives are compared, C=0 stretching vibration of 4'-acetyl derivative comes out at 1665 cirri. After nitration in ortho-position this band shifts to 1690 cm-l and the NO2 vibration appears at 1520cirrl as a strong band. After reduction of nitro group to amine, C=0 band shifts to 1660 cm~l and the stretching vibration of nitro group disappears; simultaneously bending and stretching vibrations of primary amino group appear at 1620 and 3400 cm~l, respectively. The characteristic absorption of nitrile group is at 2210 cirri in the 4'-acetyl-5'-cyano derivative. After hydrolysis of CsN to carboxylic acid, an intense band at 1740 cirri comes out and there is a broad absorption between 3100-2500 cirri which is characteristic for H-bridged carboxylic acid dimers. In the İH NMR spectra, we may follow the changes occuring şn the substitution pattern of aromatic groups. In 4'-acetylbenzo-15-crown-5, aromatic protons show two doublets and one singlet. After nitration in ortho- position, there are only two singlets at 7.59 and 6.73 ppm. When the amino-group is converted into nitrile by Sand-meyer reaction, the singlets for aromatic protons are shifted to 7.39 and 7.15 ppm. After hydrolysis of nitrile into carboxylic acid, the singlets for aromatic protons are again shifted further away from each other (i.e. 6.85 and 7.49 ppm). The deuterium exchangeable carboxylic acid proton comes out at 10 ppm as expected. In the 13c NMR spectrum if 4'-acetyl-5'-cyanobenzo-15- crown-5, protonated aromatic carbons come out at 109.97 and 108.61 ppm, while the acetyl carbon appears at 154.06 ppm. The mass spectrum of the same compound gives M+ and (M+l)+ peaks at 335 and 336, (M-CN)+ at 310 and (M-C0CH3)+ at 293 ppm.