Taç eterli bir salisilaldimin schiff bazı sentezi ve Co II, Cu II, Ni II ve UO2 VI ile komplekslerinin incelenmesi

Abstract

ÖZET Bu çalışmada, 1, 2-dihidroksibenzen'den başlanarak benzo[15-crown-5] ve 4'-hidroksibenzo[15-crown-5] literatürde verilen metodlarla elde edilmiştir. 4'-Hidroksibenzo[15-crown-5] ve hekzametilentetramin, trifluoroasetik asit içinde refluks edilerek 4 ' -hidroksi-5 ' -f ormilbenzo[ 15-crown-5] sentezlenmiştir. Bu bileşiğin etilendiamin ile alkolde kondensasyonundan 1, 2-bis ( 4 ' -hidroks ibenzo[ 15-crown-5 ] -5 ' -iminil ) etan ligandı elde edilmiştir. Hem salisilaldimin hem de taç eter grupları ihtiva eden bu ligandm Co(II), Cu(II), Ni(II) ve U02(VI) metallerinin asetatları ile uygun solventlerde muamelesinden, tekabül eden kompleksler hazırlanmıştır. Ligandm önce NaN03 ve ardından metal asetatlarla muamelesinden, hem geçiş metali hem de Na+ ihtiva eden kompleksler izole edilmiştir. Kobalt kompleksinin DMSO'daki çözeltisinin kuru hava ile muamelesinden u-perokso-dikobalt kompleksi elde edilmiştir. Komplekslerin Calvin-Bjerrum pH-titrasyon tekniğinden elde edilen verileri kullanarak Irving-Rossotti metoduna göre yapılan hesaplamalardan stabilite sabitlerinin LCu>LU02>LNi>LCo sırasında olduğu bulunmuştur. Ligand ve komplekslerin yapıları elementel analiz, nmr, ir, uv spektrumlarından alman verilere göre aydınlatılmaya çalışılmıştır. viii

SUMMARY SYNTHESIS AND CHARACTERIZATION OF CROWN-ETHER SUBSTITUTED SALICYLALDIMINE SCHIFF'S BASE LIGAND AND ITS COMPLEXES WITH COBALT(II), COPPER(II), NICKEL(II), AND ORANYL(VI). Recently, crown ether groups have been extensively employed to construct new compounds with extraordinary properties; ion channels formed by the superposition of the crown ether macrocycles in the tetra-crown ether substituted phthalocyanines or the agglomerization of the phthalocyanine units induced by the alkali metal cations are two outstanding examples. Schiff'e base bis (crown ether) ligand containing recognition sites, for alkali and transition metal guest cations had been also reported. In the course of our investigations on the complexes of the crown ether-substituted ligands; y_ic_-dioximes were found to give complexes soluble in common organic solvents. The octahedral Co (II) complex of 4', 5'-bis(salicylideneimino)benzo[15-crown-5] was capable of binding molecular oxygen. The first crown ether containing phthalocyanines were also reported as a part of our researches on MN4-core containing co- ordination compounds. Hydroxyformylbenzocrown ethers are thought to be interesting starting materials because of the utility of the reactive groups on the aromatic ring. In this paper, we describe the synthesis and characterization of 4'-hydroxy-5'-formylbenzo[15-crown-5], the Schiff's base derived from this aldehyde and 1,2-diaminoethane and its complexes with various transition metal ions. Furthermore we examined the formation constants of the complexes by potentiometric method. iH and i3C nmr spectra were measured on a Bruker 200 MHz spectrometer. I.r. spectra were obtained on a Perkin-Elmer 598 spectrophotometer in KBr pellets. U.v. -visible spectra were recorded on a Carry-14 spectrophotometer. The magnetic susceptibilities were measured with a magnetic balance of the Gouy type at room temperature and the balance was calibrated with CuS04.5H20 and HgCo(NCS)4. A pH-meter (Orion 701A), with a glass-calomel electrode assembly, was used to determine the change in hydrogen ion concentration of the solution due to complexation. The route for the synthesis of 4 '-hydroxy s' -formylbenzo[15-crown-5] (SA) is given in the Scheme in the experimental section. The first step is the synthesis of 4'-hydroxybenzo[15-crown-5]. Hydrolysis of the diazonium salt of 4'-aminobenzo[15-crown-5] in aqueous acid or in the presence of copper catalyst afforded mixtures too complex to isolate the desired product. ixBaeyer-Villiger oxidation of 4'-acetylbenzo- [15-crown-5] followed by alkaline hydrolysis was proved to be a convenient route to 4 ' -hydroxybenzo [15-crown-5]. Similar problems were encountered also for the introduction of formyl group. Even though electrophilic substitution in general seemed to be promising for the synthesis of substituted benzo[15-crown-5], the reactions, especially those carried out under the catalysis of metal salts, resulted with the deactivation of the metal salts or complex reaction products owing to the formation of crown ether complexes. Formylation by Smith modification of Duff reaction was found to be most promising because no inorganic reagent was required in the reaction. Consequently, formylation of 4 ' -hydroxybenzo- [15-crown-5] was accomplished with hexamethylene- tetramine and trif luoroacetic acid. The condensation of SA with 1,2-diaminoethane gave 1, 2-bis ( 4 ' -hydroxybenzo [ 15-crown-5 ] -5 ' - iminy 1 ) ethane (LH2) as an N202-donor with two crown ether moieties. In the 1H nmr spectra of SA and LH2, the OH protons appaer as singlets at 10.78 and 13.45 ppm, respectively, which disappear by deuterium exchange; aldehyde and azomethine protons are observed at 9.95 and 8.12 ppm. There is almost no chemical shift difference between the etheral protons of SA and LH2. !3C nmr shifts also confirm the structure given. The protonated benzene carbon (C6) with ortho -C=N and -0-CH2 substituents appear at 116.83 ppm while the other protonated carbon (C3) with ortho -OH and -0-CH2 substituents come out at 101.73 ppm. iH-coupled spectra give a doublet for each of these carbons. The formation of azomethine bond causes a shift from 193.90 ppm in SA to 165.25 ppm in LH2 for C7. The 0-H stretching absorptions of SA and LH2 did not appear as isolated bands in the i.r. spectra because of the hydrogen bridges formed with 0 atom of aldehyde or N atom of azomethine groups. These bridges were observable as weak broad absorptions between 2800-2900 cm-i, but they were screened in SA and LH2 by the. strong C-H stretches of crown ethers. Reaction of LH2 with the acetates of cobalt(II), copper (II), nickel (II), and uranyl(VI) gives products with metal :ligand ratios of 1:1 (Fig. 2). The insertion of alkali metal ion into the crown ether can be accomplished by refluxing LH2 with the alkali metal salt (e.g. NaN03) before the addition of transition metal ion. iH and 13C nmr spectra of diamagnetic Ni(II) and U02(VI) complexes are similar to those of LH2. One obvious difference is the disappearence of OH protons after complex formation. The infrared spectra of the complexes show most ligand absorptions at the same frequencies except for the C=N stretches which are shifted slightly (~15 cm-i) to the lower energy after the complex. formation. Similar shifts have been reported for the N,N' -coordinatedYJus.-dioxime complexes of various transition metal ions. Lattice water absorptions are readily observed as broad bands around 3420 cm-i in the ligand and its complexes2i. Characteristic 0=U=0 stretching vibrations are observed at 890 cm-1 for the uranyl complexes. When sodium ion is inserted into the crown ether group in the case of the transition metal complexes of LH2, the stretching vibrations of the counter ion (i.e. 1380 cm-i for N03-) are the most significant differences. N, N ' -ethyienebis ( salicy lideneiminato ) eobalt{ II) (CoSalen) complexes have been investigated extensively as chelates that can take up and release molecular oxygen reversibly since the synthesis of the complex by Pfeiffer et.al. in 1933. Even though LCo is a close representative of the parent compound, CoSalen, with the addition of two crown ether units, we could not isolate any crystalline form of this compound which bound oxygen reversibly in the solid state. The Co(II) oxygen carriers reported in the literature as oxygen-bridged dimeric species all exhibit little or no paramagnetism. (LCo) is paramagnetic (n=2.43 B.M.), but the oxygen adduct of (LCo) obtained from its solution in DMSO is diamagnetic. Elemental analysis results indicate a n-peroxo-complex with two solvent molecules: (DMSO) (LCo)02 (LCo) (DMSO) The role of the solvent molecule undoubtedly is to stabilize the Co-oxygen bond by enabling octahedral coordination around the metal to be achieved upon oxygenation in solution. The 0-0 stretching vibration of the u-peroxo-complex cannot be seen due to the centrosymmetric structure of the molecule. When dissolved in chloroform in order to obtain iH nmr spectra, the diamagnetic compound quickly decomposes into paramagnetic species as reported by Floriani and Calderazzo. Even though DMF was also recommended as a suitable solvent for oxygenation in solution, an octahedral complex with two solvent molecules [LCo (DMF) 2] was the only product isolated under similar conditions. In contrast to the expectations the result of crown ether substitution on the Cosalen does not enhance the molecular oxygen binding property of the new molecule, even though ether groups will increase the electron density of the nucleus. The steric effect should be taken into account since crown ether groups diminish the planar structure of Cosalen. Consequently, no oxygen binding property is observed for LCo.2NaN03. 4H2O. The electronic spectra of the transition metal complexes in ethanol are very similar to the spectrum of LH2 except for the high intensity charge transfer absorptions around 400 nm. Only in the case of LCu.2NaN03.4H20 a weak broad absorption around 550 nm (e=l60 dm3 mol-i cm-i) which can be assigned to a d-d transition is observed. xiAs expected for a d8 configuration in square-planar field, the Ni*1 complexes are diamagnetic as the uranyl complexes are. The effective magnetic susceptibilities of LCu and LCu.2NaN03.4H20 closely follow the spin-only formula (n=1.80 and 1.83 B.M. respectively) while those of LCo (n=2.43 B.M.) and LCo.2NaN03. 4H20 (u=2.40 B.M.) are higher than the calculated values for d? structure but in concordance with the values reported for Col* in square planar complexes. An important feature of the complexes of LH2 is their^ solubility in common organic solvents as well as in water. This property prevents us to measure the alkali picrate extracting capability of crown ethers from water to organic solvents (e.g. chloroform). The solubility of metal complexes, on the other hand, enabled us to investigate the stability of the complexes in water. For this purpose, the Calvin-Bjerrum pH-titration technique, as used by Banerjee and Dey, has be,en applied to determine the stepwise pçotonation constants of LH2 and the stepwise formation constants of the complexes. The following six mixtures were prepared to use Calvin-Bjerrum pH-titration technique: Mixture A: 10 ml of KC1 (1 M) and 5 ml of HC1 (0.1 N) Mixture B: Mixture A and 25 ml of LH2 (0.007 M) Mixture C-F: Mixture B and 10 ml of metal solution (0.01M), separately Double distilled water was added in each mixture to make the volume 100 ml in each case. Excess ligand was used to fulfil the maximum coordination number of the metal. KC1 was added to maintain an ionic strength of 0.1 M KC1. The mixtures were then titrated with progressive addition of NaOH solution (0.1 N), in 0.2 ml increments. The corresponding change in the pH of the solution was observed and recorded. All the experiments were carried out at a constant room temperature of 25 °C. Six titration curves were obtained by plotting pH against the volume of NaOH solution added. The protonation constants correspond to the following equilibria: L2- + H*. Kax -LH- LH` + H*55=^=*LH2 LH2+Hr. Kaz ^lh; XiiThe formation constants are defined as following: LH2+M2*` 1 MLHM]* + H* [LHM]*^==*[LM] + H* The values of titration curves are used to calculate the stepwise protonation constants and stepwise formation constants T)y successive approximation and interpolation at half -ft- values according to Irving and Rossotti. The results obtained by these two methods quite closely follow each other. Evaluation of the stepwise protonation constanst shows that the first three protonations are pretty close, but the fourth one occurs at pH»3. The order of the over-all formation constants» (02=Ki.K2) of the complexes is as follows: LCu>LU02>IjNİ>LCo. The tendency of complex formation in all four metal ions is high enough to prevent the precipitation of metal-hydroxides upto pH»12. LCo and LNi are stable only pH>6 and they will dissociate into protonated species at lower pH values. xiii