SYNTHESIS AND CHARACTERIZATION OF A SOLUBLE HEMIHEXAPHYRAZINE DERIVATIVE Текст научной статьи по специальности «Химические науки»

Porphyrazines Порфиразины

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Paper Статья

DOI: 10.6060/mhc234968i

Synthesis and Characterization of a Soluble Hemihexaphyrazine Derivative

Yana E. Kibireva,a'b Mikhail K. Islyaikin,a'b@ M. Salomé Rodríguez-Morgade,c and Tomás Torresa'c

aResearch Institute of Macroheterocycles, IRLoN, Ivanovo State University of Chemistry and Technology, 153000 Ivanovo, Russia

bG.A. Krestov Institute of Solution Chemistry of the Russian Academy of Sciences, 153045 Ivanovo, Russia cDepartment of Organic Chemistry, Universidad Autónoma de Madrid, 28049 Madrid, Spain @Corresponding author E-mail: [email protected]

Dedicated to the member of Russian Academy of Sciences, Professor Asian Tsivadze on the occasion

of his Anniversary

The symmetrically substituted hexakis(n-hexyl)hemihexaphyrazine was synthesized by condensation of 3,6-bis(n-hexyl)phthalonitrile and 2,5-diamino-1,3,4-thiadiazole in the presence of sodium pentanolate. The macrocycle was characterized by MALDI-TOF mass spectrometry, as well as IR, 1H and 13C NMR, UV-Vis absorption and fluorescence spectroscopies.

Keywords: Expanded azaporphyrin, hemihexaphyrazine, 1,3,4-thiadiazole, hexaphyrin.

Синтез и характеристика растворимого производного гемигексафиразина

Я. E. Кибирева,a'b M. K. ИсляйкинЛ13® M. С. Родригес — Моргаде^ T. Торрес^

aМеждународная научно-исследовательская лаборатория наноматериалов, НИИ химии макрогетероциклов, Ивановский государственный химико-технологический университет, 153000 Иваново, Россия ьИнститут химии растворов им. Г.А. Крестова Российской академии наук, 153045 Иваново, Россия сКафедра органической химии, Мадридский автономный университет, 28049 Мадрид, Испания @E-mail: [email protected]

Симметрично-замещенный гексакис(н-гексил)гемигексафиразин был синтезирован конденсацией 3,6-бис(н-гексил)фталонитрила и 2,5-диамино-1,3,4-тиадиазола в присутствии пентанолята натрия, взятых в сте-хиометрическом соотношении (1:1:0.5), в пентаноле. Целевое соединение было охарактеризовано с помощью масс-спектрометрии MALDI-TOF, данных ИК- и ЯМР-спектроскопии 1H и 13C, а также спектров поглощения и флуоресценции.

Ключевые слова: Азапорфирин с увеличенной координационной полостью, гемигексафиразин, 1,3,4-тиадиазол, гексафирин.

Introduction

Expanded porphyrinoids display modified ^-systems that alter the porphyrin aromatic character.[1-4] This translates into unusual optical, electrochemical and photophysi-cal properties that render them promising building blocks

for the construction of new molecular materials at different technological fields.[5] In addition, their large, polydentate central cavities provide interesting coordination abilities, such as anion binding, or multimetallic complexation, which are virtually inaccessible within the corresponding tetramers.[6-8] Contrasting with the great assortment of ex-

panded porphyrins reported to date, examples of the corresponding expanded meso-aza-analogues are still very scarce. One prototypical example of the latter is constituted by the family of the hemihexaphyrazines, a kind of hexamer consisting of an expanded hemiporphyrazine that has been developed in our group.[9,10]

Hemihexaphyrazines are highly symmetrical macro-heterocyclic compounds of ABABAB-type, made up of three alternated thiadiazole and pyrrole subunits interconnected by nitrogen atoms (see Scheme 2).[11] The macrocy-clic backbone consists of a planar structure, displaying a 30 tc-electron electronic circuit, wherein the thiadiazole sulfur atoms point outside the macrocycle and the inner cavity contains 15 nitrogen atoms. The development of soluble, symmetric derivatives that are obtained as single regioiso-mers, is desirable from the preparative point of view, especially for many applications that involve the use large amounts of compounds. Alkyl substitution at the 3- and 6-positions of the isoindole fragments promotes self-organization of certain macrocycles, such as phthalocya-nines, leading to molecular materials of interest for recording and storing information.[12] Inspired by these examples, we have developed in this work a soluble, processable hem-ihexaphyrazine derivative, hexafunctionalized at the isoindole 3,6-positions by linear hexyl chains.

Experimental

MALDI-TOF spectra were recorded with a Bruker Reflex III. NMR spectra were recorded with a Bruker AC-300 and Bruker DRX-500 instruments. UV-vis spectra were recorded with a Hewlett-Packard 8453 instrument at the Interdepartmental Investigation Service (SIdl) of Universidad Autónoma de Madrid.

IR spectra were registered on an Avatar 360 FT-IR instrument. The study was carried out using the resources of the Center for collective use of scientific equipment of ISUCT.

The fluorescence quantum yield (Of) was determined on FluoTime 300 (LDH-P-C-450) using an integration sphere. Time-resolved fluorescence measurements were carried out by means of a high performance fluorescence lifetime and a steady state spectrometer FluoTime 300 (PicoQuant, Germany) with a laser 450 nm, LDH-P-C-450 (PicoQuant, Germany) as an excitation source. The fluorescence decay curves were measured, and the fluorescence lifetimes were obtained by deconvolution of the decay curves using the EasyTau 2 software package (PicoQuant, Germany). This work was carried out with the help of the center of the scientific equipment collective use «The upper Volga region center of physico-chemical research».

Hexylzinc iodide. A suspension of zinc dust (7.5 g, 0.15 mol) was stirred and decanted twice in a 2% solution of HCl (20 mL) for 2 min. The resulting dust was sequentially stirred and decanted in water (3 x 20 mL) and ethanol (2 x 20 mL). The solid was washed with diethyl ether (20 mL). Finally, the activated zinc was dried under vacuum, purged with argon, flame dried under vacuum and again purged with argon. Under an argon atmosphere, 1,2-dibromoethane (0.35 mL, 0.80 g, 0.004 mol) was added via syringe to the freshly prepared activated zinc dust under stirring in anhydrous THF (20 mL), and the mixture was subsequently re-fluxed for ca. 20 min. After cooling to room temperature, trime-thylsilyl chloride (0.50 mL, 0.45 g, 0.004 mol) was added, the mixture was refluxed once more and allowed to cool. Hexyl iodide (3.5 mL, 5 g, 0.024 mol) was added via syringe and the mixture was stirred for 16 h at 40 °C. The mixture was cooled to rt and the excess zinc was allowed to settle. The resultant grey solution was transferred to a Schlenk tube via cannula, and the remaining zinc powder was washed with THF (4 mL) and transferred to the Schlenk tube, to afford the title compound (24 mL, 0.90 M solution).

3,6-Bis(n-hexyl)phthalonitrile (2). In a flame-dried flask, bis(triphenylphosphine)nickel(II) dichloride (0.46 g, 0.70 mmol), triphenylphosphine (0.36 g, 1.35 mmol) and anhydrous THF (15 mL) were placed under argon. Addition of n-butyllithium (0.54 mL, 1.35 mmol, 2.5 M in hexanes) to the stirred mixture produced a blood red slurry. 3,6-Bis(trifluoromethanesulfonyloxy)phthalonitrile (2.90 g, 6.84 mmol) and KBr (2.45 g, 20.6mmol) were added under argon and the resultant brown solution was cooled to -78 °C. Freshly prepared hexylzinc iodide (24 mL, 21.6 mmol, 0.90 M solution in THF) was added dropwise over a period of 1 h via cannula, the reaction mixture was allowed to warm to rt and stirred for a further 16 h. The reaction was quenched by careful addition of 10% HCl (25 mL) and the mixture was extracted with ethyl acetate (3 x 25 mL). The combined organic extracts were successively washed with 10% HCl (25 mL), 5% NaOH (50 mL) and brine (50 mL). The solution was dried (MgSO4) and the solvent was evaporated at reduced pressure. The resultant solid was purified by column chromatography on silica gel using 5% EtOAc in hexane (v:v) as eluent. 3,6-Bis(n-hexyl)phthalonitrile was isolated as white solid (1.09 g, 54%). Rf = 0.34 (5% EtOAc in hexane). 'H NMR (CDCl3, 300 MHz) 8h ppm: 7.46 (s, 2H, Harom), 2.87-2.82 (t, 4H, -CH2-), 1.70-1.60 (m, 4H, -CH2-), 1.29 (m, 12H, -CH2-), 0.89 (t, 6H, -CH3). 13C NMR (CDCl3, 300 MHz) 8c ppm: 146.30 (C3 and Ca), 133.58 (C4 and C5), 115.66 (C1 and C2), 115.25 (CN), 34.49 (C4'), 31.52 (C2'), 30.75 (C3'), 28.89 (C1'), 22.56 (C5'), 14.08 (Cd'). IR (KBr) Vmax cm-1: 3414, 3064, 2925, 2854, 2228, 1618, 1559, 1464, 1382, 1280, 1230, 1173, 1114, 899, 850, 790, 759, 723, 647, 492, 463.

1,4,13,16,25,28-Hexakis[n-hexyl]-5,36:12,17:24,29-triimino-7,10:19,22:31,34-trithio-[f,p,z]-tribenzo-1,2,4,9,11,12,14,19,21,22, 24,29-dodecazacyclotriaconta-2,4,6,8,10,12,14,16,18,20,22,24,26,28, 30-pentadecaene (4). 3,6-Bis(n-hexyl)phthalonitrile (50 mg, 0.17 mmol) and 2,5-diamino-1,3,4-thiadiazole (20 mg, 0.17 mmol) were refluxed under argon in dry pentanol (4 mL) until the solution became homogeneous. Sodium (2 mg, 0.08 mmol) was added, and the reaction mixture was refluxed for 24 h under argon. Afterward, the pentanol was rotary evaporated, the residue was dissolved in THF (30 mL) and filtered through Celite. The solvent was evaporated and the residue was washed with methanol, ethyl acetate and hexane. Yield: 14 mg (21%). MS (MALDI-TOF, dithranol): 1186.6 [M+H]+, 1208.6 [M+Na]+, 1224.6 [M+K]+. >H NMR (CDCl3, 300 MHz) 8h ppm: 12.12 (s, 3H, NH), 7.14 (s, 6H, Harom), 2.87 (s, 12H, -CH2-), 1.61 (s, 12H, -CH2-), 1.39 (s, 36H, -CH2-), 0.96 (s, 18H, -CH3). 13C NMR (CDCl3, 75.5 MHz) 8c ppm: 169.75, 153.48, 141.14, 133.76, 130.88, 31.92, 30.80, 30.47, 29.83, 22.94, 14.33. UV-Vis (CHCb) ¿max nm (log e): 280 (4.53), 400 (4.74), 420 (4.72), 465 (4.19), 505 (3.93). IR (KBr) Vmax cm-1: 3211 (Vn-h), 2955, 2924, 2853 (Vcsp3-h), 1623 (Vc=c), 1457, 1426, 1379 (8csp3-H), 1254, 1191 (vcsp3-csp3), 1118, 1063, 833, 729 (8csp3-Csp3), 697 (Vc-s).

Results and Discussion

3,6-B/'s(n-hexyl)phthalonitrile 2 was synthesized by reaction of the corresponding of 3,6-b/'s(triflate)phthalonitrile 1 and freshly prepared hexylzinc iodide (Scheme 1) following the methods described in literature.[13,14]

The preparation of hexakis(n-hexyl)hemihexaphyrazine 4 (Scheme 2) was carried out in 21 % yield by condensation of phthalonitrile 2 with 2,5-diamino-1,3,4-thiadiazole 3[15] in stoichiometric 1:1 ratio, in the presence of sodium pentano-late in dry pentanol.

The characterization of macrocycle 4 was performed by 1H and 13C NMR, IR and UV-Vis spectroscopies, as well as MS. The MS spectrum (Figure 1) of 4 displays a peak at m/z = 1186.6 corresponding to the molecular ion [M + H]+, accompanied by peaks at m/z = 1208.6 and m/z = 1224.6, assigned to [M + Na]+ and [M + K]+, respectively.

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Scheme 1. Synthesis of 3,6-6«(«-hexyl)phthalonitrile 2. a: Py, CHzCh, -78 °C to rt, 24 h, Ar; b: NiCl2(PPh3)2, PPh3, BuLi, KBr; c: -78 °C.

Scheme 2. Synthesis of hexakis(«-hexyl)hemihexaphyrazine 4. i: C5HiiONa, C5H11OH, reflux, argon, 24 h.

Figure 1. MS spectrum (MALDI-TOF) of compound 4. Insets: isotopic distributions of the main peak at 1186.6 Da (above); calculated isotopic pattern for [M+H]+ (below).

1H NMR spectrum of hemihexaphyrazine 4 (Figure 2), reveals the aliphatic signals of the hexyl groups as four multiplets between 2.88-0.95 ppm, in addition to a singlet at 7.17 ppm corresponding to the benzene rings. A broad signal at 12.17 ppm characterizes the isoindolic NH protons, as a diagnostic of the non-aromatic character of 4.

The 13C NMR spectrum of 4 is shown in Figure 3. A signal at 169.75 ppm can be assigned to the 1,3,4-thiadiazole fragments, while four signals at 153.48, 141.14, 133.76 and 130.88 ppm account for the isoindole subunits.

The IR spectrum of 4 (Figure 4) shows a peak at 3211 cm-1 corresponding to vibrations of the N-H bonds of the isoindole moiety.

Macrocycle 4 displays the typical optical attributes of

other hemihexaphyrazines.[9,10,16-19] Thus, a UV-Vis spectrum (Figure 5) that is dominated by two intense absorptions at 400 and 420 nm is obtained, in addition to weaker bands at 465 and 505 nm, the latter (log £ = 3.93) corresponding to the 0-*0 energy gaps.

Light excitation in the range between 400 and 500 nm produces a broad fluorescence spectrum that maximizes at 580 nm, accompanied by weaker shoulders at 541 and 625 nm, which does not mirror image the absorption pattern (Figure 5). The fluorescence quantum yield (Of) of 4, calculated using an integration sphere, was of 7 %. Actual pulsed light-source and sample response show the gradual decay of fluorescence intensity with time. A single-exponential fit gives a lifetime of 2 ns for the excited state of 4 (Figure 6).

Figure 2. 'H NMR spectrum of compound 4 in CDCI3.

Figure 3. 13C NMR of compound 4 in CDCl3.

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M. K. Islyaikin et al.

Figure 4. IR spectrum (KBr) of 4.

Figure 5. UV-Vis absorption (blue line) (C = 1.8-10"5 mol/l)

and fluorescence (red line) (C = 4.7-10-6 mol/l) spectra in chloroform.

Figure 6. The intensity decay of the fluorescence of 4 (where red curve - LUDOX decay).

Conclusions

A soluble hemihexaphyrazine hexasubstituted with hexyl chains was prepared by a reaction of 3,6-bis(n-hexyl)phthalonitrile and 2,5-diamino-1,3,4-thiadiazole. The product was characterized by MS, 1H and 13C NMR, IR, UV-Vis and fluorescence spectroscopies. Acknowledgements. This research was partially supported by grant of the Ministry of Science and Higher Education of the Russian Federation [No. 075-15-2021-579]. The study was carried out using the resources of the Center for Shared Use of

Scientific Equipment of the ISUCT (N. 075-15-2021-671).

The authors thank for the financial support from the RF

Presidential scholarship to study abroad.

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Received 16.02.2023 Accepted 17.03.2023