Elektrokromik uygulamalara yönelik tiyofen içeren rutenyum komplekslerinin sentezi
Synthesis of ruthenium complexes containing thiophene derivatives for electrochromic applications
Yazar: HAJAR SULTANOVA
Danışman: DOÇ. DR. BARIŞ YÜCEL
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Kimya Ana Bilim Dalı / Kimya Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: Kimya = Chemistry

Özet:
Bu çalışmada rutenyum kompleksine konjuge olmayan gruplarla bağlanmış tiyofen türevleri (ProDOT, EDOT, SNS) içeren elektroaktif monomerler üretilmiştir. Bu malzemelerin polimerleştirilmesi sonucu elde edilecek metal içeren konjuge polimerlerin elektrokromik özelliğe sahip olmaları beklenmektedir. Elektrokromik malzemeler uygun elektrik akımının etkisiyle yükseltgenerek ya da indirgenerek farklı redoks aşamalarında farklı renkler gösterebilen malzemelerdir. İlk zamanlarda inorganik oksitler [tungsten trioksit (WO3), iridyum dioksit (IrO2)] elektrokromik malzemeler olarak ilgi görmesine karşın son yıllarda araştırmalar mekanik özellikleri ve işlenebilirlikleri açısından rakiplerini geride bırakan organik moleküller üzerine yoğunlaşmıştır. Metal içeren konjuge polimerler iki elektroaktif malzemenin (metal kompleksi ve iletken organik yapı) özelliklerini kendinde birleştiren yeni nesil hibrit malzemelerdir.
Monomerlerin üretilmesi için öncelikle gereken ligandlar (a-i) sentezlendi. Ligand a, b ve c bipiridil grupu, polimerleşebilir tiyofen türevi (sırasıyla ProDOT, EDOT ve SNS) ve de bu grupları birbirine bağlamakla beraber konjuge olmayan yapısı nedeniyle aralarındaki elektonik etkileşime engel olan eter köprüsü içermektedir. Bu ligandların literatürde sıkça kullanılan ve farklı koşullarda gerçekleştirilebilen "click" reaksiyonlarından amaca uygun olanı seçilerek üretilmiştir. Katalizator olarak Cu ve Cu(CH3CN4)4PF6 kullanılan asetonitril içerisinde üç gün devam eden reaksiyon sonucu ligand a, b ve c sırasıyla %73, %54 ve %51 gibi verimlerle başarıyla sentezlenmiştir.
Ligand d, e ve f yapıları ligand a, b ve c'ye benzemekle beraber diğer tüm ligandlardan farklı olarak yapısında bir değil iki benzer tiyofen türevi içerir ki, bu durumun polimerleşmeyi kolaylaştıracağı öngörülmektedir. Ligandlar iki eşdeğer tiyofen türevi ile bir eşdeğer bipiridil türevi arasında Cu ve Cu(CH3CN4)4PF6  katalizatorlüğünde gerçekleşen "click" reaksiyonu sonucu %55, %45 ve %58 verimle elde edilmiştir.
Ligand g, h ve i tasarımında metal atomu ve polimer temel zinciri arasındaki mesafenin kısaltılması ve bu durumun malzemenin   elektronik özelliklerine etkisinin anlaşılması amacıyla eter zinciri tamamen aradan kaldırılmıştır. Bahsi geçen ligandların sentezi için literatür taraması sonucu CuSO4.5H2O ve sodyum askorbat eşliğinde THF/H2O karışımı içerisinde gerçekleşen "click" reaksiyonu tercih edilmiş ve ligandlar %71, %70 ve %60 verimlerle elde edilmiştir.
Monomerlerin (A-I) üretilmesi amacıyla ligandların (a-i) satın alınan Ru(bpy)2Cl2.2H2O kompleksi ile etanol ve su karışımı içerisinde 100 oC sıcaklıkta reaksiyonu gerçekleştirilmiştir. İnce tabaka kromotografisiyle takip edilen reaksiyonlar ortalama 4 saat sonra başlangıç maddelerin tükendiği anlaşılarak sonlandırılmış ve ürünün NH4PF6 yardımıyla çöktürülmesi sonucu monomerler (A-I) elde edilmiştir.

Abstract:
In recent years, electrochromic materials have been studied intensively because of an increasing demand in the production of smart glasses or electrocromic windows. A substance  which changes its color reversible  upon application of an appropriate potential via oxidation and reduction processes is called an electrochromic material. There are different chemical classes of electrochromic molecules ranging from metal oxides and metal complexes to viologens, organic conducting polymers and metallopolymers. In last few decades organic materials are gaining more importance as they can be functionalized easily and have  good stability.
Metallopolymers are one of the main classes of conducting materials which incorporate electronic proporties of metal complexes and organic molecules. In this type of polymers, transition metals such as Ru, Ir, Os and Fe are used as a metal atom and thiophene, pyrrole, aniline are usually prefered as an organic part of the molecule. 
In this work, we prepared nine monomers consisting of  a ruthenium complex, a polymerizable thiophene derivative (ProDOT, EDOT and SNS) and a nonconjugated  spacer group(ether or alkyl group). The electropolymerization of these monomers and the characterization of produced polymer films have been performed by Prof. Dr Pınar Çamurlu and her research group at Akdeniz University.  All metallopolymers obtained by electropolymerization of ruthenium complexes were proven to be  multichromic (substance exibiting more than two color after the application of potencial) materials. Since the obtained polymer structures and their electrochromic properties, and electrochemical characterization are not included in the scope of this thesis, thus the results are not reported here.
In order to achieve monomers (A-I), we stared with the synthesis of appropriate ligands (a-i). All of the ligands were produced via commonly used click chemistry. Ligand a, b and c contain a bipyridyl group, one polymerizable thiophene derivative (respectively  ProDOT, EDOT and SNS) and a nonconjugated spacer group (ether). Appropriate click reaction condition was chosen for this synthesis. Cu and Cu(CH3CN4)4PF6 were used as catalysts and  acetonitrile used  as a solvent. After stirring the reaction three days at room temperature ligand a, b and c were isolated in  %73, %54 ve %51 yields, respectively by a column chromatograph on silica gel.
Structures of ligand d, e and f are  similar to those of ligand a, b and c. However these ligands (d, e and f) incorporate two polymerizable thiophene units. We thought that increasing number of thiophene units (ProDOT, EDOT or SNS)  make polymerization process easier. These ligands (d, e and f) were synthesized by click reactions includingCu and Cu(CH3CN4)4PF6 catalysts in acetonitrile at room temperature. Under these conditions, the reaction between two equivalents of  azide substituted thiophene derivative  (ProDOT-N3,   EDOT-N3,   SNS-N3)   and   one   equivalent of   propargyl

bipyridines  gave desired ligands d, e and f. Products were purified by a column chromotography and obtained in %55, %45 and  %58 yields,respectively.
In the design of ligand g, h and i, ether spacers are completely removed and the distance between metal atom and the conjugated chain become shorter in the resulting polymer structures. It is important to analyze the effect of the length of nonconjugated spacer on optical and electronical properties of metallopolymer. Synthesis of these ligands were also performed by  "click" reaction between 2-ethynylpyridine and azide substituted thiophene derivatives (ProDOT-N3, EDOT-N3 or SNS-N3) in the presence  of CuSO4.5H2O and sodium ascorbate. All reaction were stirred in THF/H2O solvent system at room temperature and monitored by TLC. After the completion of reactions, ligand (g, h and i) were isolated by a column chromotography in  %71, %70 and %60 yields, respectively.
Starting materials (except 2-ethynylpyridine) which are used for  the synthesis of the  ligands (a-i) were prepared according to literature procedures. ProDOT-N3 which is the reactant in the synthesis of ligand a, d and g was produced from dimethoxytiophene in three steps. In the first step, the reaction of 3,4-dimethoxythiophene with trimethylolethane  in toluene in the presence of catalytic amount p-TSA produced  hydroxymethyl substituted ProDOT derivative  in 75% yield. In the second step, the product was mesylated in CH2Cl2 at room temperature in a mixture of MsCl and Et3N. After four hours, the resulting mixture was evaporated and the residue, without purification, was dissolved in DMF and NaN3 was added in order to achive desired reactant ProDOT-N3 for the click reaction.
EDOT-N3  is the starting material of  the ligands b, e and h  and synthesized in two steps by following literature procedures. In the first step, the reaction of 3,4-dimethoxythiophene in toluene with chloro-1,2-propanediol in the presence of catalytic amount of  p-TSA produced a chloromethyl substituted EDOT compound. The obtained product was transformed into EDOT-N3 in 95% yield using the same reaction conditions described above for the production of ProDOT-N3.

SNS-N3 which was needed to produce the ligands c, f and i was obtained in  three high yield steps. In the first step of the synthesis, the hydroxyethyl substituted SNS derivative  was obtained by the reaction known as Paal-Knorr condensation between the thiophenyl substituted 1,4-butenedione and ethanolamine in the presence of p-TSA. The reaction between the obtained SNS alcohol derivative with TsCl in the mixture of DMAP and Et3N produced the tosylated SNS  derivative  in 90% yield. In the last step, the SNS derivative (SNS-N3) bearing the desired azide group was successfully synthesized in a quantitative yield by the reaction of SNS-OTs obtained in the second step  with NaN3 in DMF.
The other starting material, the propargyl bipyridine derivative, required for the synthesis of ligand a, b and c were synthesized starting from purchased 4,4'-dimethyl-2,2'-bipyridine. In the first step, one of the methyl groups of 4,4'-dimethyl-2,2'-bipyridine was oxidized to the aldehyde by SeO2, and then the obtained aldehyde functionality was reduced to alcohol in the presence of NaBH4 in a high yield (95%). The propargyl bipyridine derivative was produced in %75 yield by the reaction  between  hydroxymethyl substituted bipyridine with NaH and following addition of propargyl bromide. 

Bispropargyl bipyridine derivative was needed to produce ligand d, e and f and it was synthesized in four steps. In the first step, 4,4-dimethyl-2,2-bipyridine was oxidized to the dicarboxylic acid derivative by using K2Cr2O7. In the second step, the dicarboxylic acid was converted to the 4,4'-diethylester-2,2-bipyridine derivative in  the presence of H2SO4 in 86% yield in three days. After then, in the third step,  the diester product was  reduced to dialcohol derivative with NaBH4 by refluxing the reaction mixture in ethanol for 24 h. The desired  compound bispropargyl bipyridine derivative was obtained in high yield (84%) by the reaction of dialkol with NaH and following addition of propargyl bromide into the resulting solution in DMF at room temperature.
After preparing the ligands, we started to synthesize monomer ruthenium complexes (A-I).  Although, various ruthenium complexes can be found in the literature, there are no standard reaction conditions in the applied methods. In this study, the desired monomer ruthenium complexes (A-I) were obained by the reaction of  commercially available  Ru(bpy)2Cl2.2H2O with the corresponding ligand (a-i). A mixture of equal amount of  water and ethanol was preferred as a solvent system and PF6- (NH4PF6) as a counter ion. The reactions were stirred  at 100 oC and monitored by TLC. After about 3-4 hour (when the ligands were not observed by TLC) the reactions were cooled and aqueous solution of  NH4PF6 was added in order to precipitate the product. Orange solid monomers were filtered and washed with water and ethanol and purified by a column chromotography.
All  monomers and ligands synthesized in this study were charecterized by hydrogen and carbon NMR spectroscopies and high resolution mass spectroscopy.