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Tetrahedron 70 (2014) 805e809

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Tetrahedron

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Synthesis and characterization of 6,6000-bis(anthracen-9-yl)-2,20;60,200;600,2000-quaterpyridine

Monika Wa1esa-Chorab, Maciej Kubicki, Violetta Patroniak *

Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61614 Pozna�n, Poland

a r t i c l e i n f o

Article history:Received 22 October 2013Received in revised form 30 November 2013Accepted 16 December 2013Available online 21 December 2013

Keywords:N-donor ligandStille-type couplingSuzukieMiyaura couplingAnthracene derivative

* Corresponding author. Tel.: þ48 61 829 1483; faaddresses: vpat@gazeta.pl, violapat@amu.edu.pl (V. P

0040-4020/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.tet.2013.12.045

a b s t r a c t

New bianthracene-quaterpyridine ligand 6,600 0-bis(anthracen-9-yl)-2,20;60,200;600 ,200 0-quaterpyridine L hasbeen obtained in a multistep synthesis using SuzukieMiyaura and Stille-type coupling reactions. Thedianthracene ligand L has four nitrogen-donor atoms and can form different supramolecular architec-tures with transition metal ions. Ligand L and intermediate compounds have been characterized byspectroscopic methods and elemental analyses. 2-(Anthracen-9-yl)-6-bromopyridine and 6-(anthracen-9-yl)-60-bromo-2,20-bipyridine have been also characterized by X-ray crystallography.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Anthracene derivatives have been considered worthy of at-tention in recent years mainly due to their emission of bluelight.1e3 Such compounds show high luminescence quantumyield and long excited state lifetime4 and are regarded as goodcandidates for construction organic light-emitting diodes(OLEDs).5,6 Luminescence properties of anthracene derivativesdepend on many factors, such as conformation and crystalpacking of molecules, solvent polarity and pH.7e10 For dia-nthracene derivatives of di(hydroxyphenyl)pyrimidine strongluminescence was found when the molecule had helical confor-mation while U-shape conformation led to quenching of lumi-nescence via photo-induced electron transfer process (PET).8 Itwas observed that luminescence properties of Zn(II) complexeswith anthracene-based ligand depend on the solid-state struc-ture: for the same molecular composition but different crystalpacking these compounds emit light at two different wave-lengths. For crystals with CH/p interactions between anthracenemoieties the emission is shifted from blue to green light incomparison with molecules without such interactions.9 Similarred-shift of emission maxima was also observed for cadmium(II)complexes in solution, with increasing polarity of solvent.10

Compounds containing anthracene groups have also been foundto be good fluorescent sensors for different anions11 or metal

x: þ48 61 829 1555; e-mailatroniak).

All rights reserved.

ions,12e14 for example an anthraceneeoxyquinoline dyad is a se-lective fluorescent indicator for Hg(II),12 tripodal anthracene-based ligand is a selective sensor for Zn(II) ions13 and amino-acids functionalized by anthracene moiety are selective chemo-sensors for Fe(III) ions.14

In view of successful synthesis of different supramolecular ar-chitectures of dimethylquaterpyridine ligands15e20 we attemptedto prepare new N4-donor ligand L (Fig. 1) containing two bulkyanthracene moieties.

The ligand L has been obtained bymultiple SuzukieMiyaura andStille-type coupling reactions and characterized by spectroscopicmethods. We also report crystal structures of two intermediates, 2-(anthracen-9-yl)-6-bromopyridine and 6-(anthracen-9-yl)-60-bromo-2,20-bipyridine.

Fig. 1. The dianthracene-quaterpyridine ligand L.

M. Wałesa-Chorab et al. / Tetrahedron 70 (2014) 805e809806

2. Results and discussion

Quaterpyridine ligands are good complexing agents for transi-tion metal ions. Our previous research on dimethylquaterpyridineligand revealed that it can form many types of supramoleculararchitectures (Scheme 1).15e20

Scheme 1. Self-assembly of dimethylquaterpyridine ligand.

Reactions with Ag(I)15 and Cu(I)15,16 cations, which prefertetrahedral coordination geometry, lead to formation of dinuclearhelical complexes, while octahedral metal ions form mono-nuclear complexes.15,17 Organometallic complex of Pt(IV) hasbeen obtained by reaction of ligand with platinum(II) chloride

Scheme 2. The synthesis of dianthr

and has been found as highly selective catalyst precursor in thehydrosilylation of styrene and terminal alkynes.18 Very in-teresting is also linear structure of (m-Cl)-tetranuclear cobaltcomplex containing two [Eu(NO3)5]2� anions formed by self-assembly of quaterpyridine ligand with mixture of cobalt(II)chloride and europium(III) nitrate.19 Reactions of N4-ligand withlanthanide(III) trifluoromethanesulfonate and perchlorate resul-ted in the formation of organic salts.20

The ligand L has been obtained in multistep SuzukieMiyauraand Stille-type coupling reaction as outlined in Scheme 2.

2-(Anthracen-9-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane Awas obtained in 64% yield via Pd(II)-catalyzed reaction of 9-bromoanthracene with 4,4,5,5-tetramethyl-1,3,2-dioxaborolane.21

When reaction was performed in the light decomposition ofproduct and/or substrate and subsequent formation of anthraqui-none22 was observed (Scheme 3) in 18% yield, in the darkness nodecomposition of product and/or substrate was observed and theyield of A was 77%.

For this reason all reactions were performed with protectionfrom light. Decomposition of A to anthraquinone occurred alsoduring attempts to obtain the single crystal of A. Its structure wasreported long time ago.23e25

The SuzukieMiyaura cross-coupling reaction of A with 2,6-dibromopyridine in the presence of Pd(0) catalyst results in theformation of 2-(anthracen-9-yl)-6-bromopyridine B in 67% yield asa yellow crystalline compound, which has been characterized byspectroscopic methods and X-ray crystallography (Fig. 2).

2-(Anthracen-9-yl)-6-bromopyridine B via catalytic reactionwith hexamethylditin was converted into trimethylstannylderivative C, which was used in Stille-type coupling reaction

acene-quaterpyridine ligand L.

Fig. 2. Perspective view of the molecule B; ellipsoids are drawn at 50% probabilitylevel, hydrogen atoms are shown as spheres of arbitrary radii.

Scheme 3. Decomposition resulting from the photolysis of anthracene derivatives.

M. Wałesa-Chorab et al. / Tetrahedron 70 (2014) 805e809 807

with 2,6-dibromopyridine. 6-(Anthracen-9-yl)-60-bromo-2,20-bipyridine D was obtained as a white solid in 65% yield. The crystalstructure of D (Fig. 3) was determined by X-ray diffraction method.

Fig. 3. Perspective view of the molecule D; ellipsoids are drawn at 70% probabilitylevel, hydrogen atoms are shown as spheres of arbitrary radii.

In both B and D the anthracyl fragments are planar (max de-viations from the least-squares planes are smaller than 0.08�A), andthe other aromatic fragments are almost perpendicular to theseplanes. The dihedral angles between the appropriate planes arebetween 67� and 80�. In the crystal structures of B and D there aredirectional CeH/Br and CeH/p contacts (shorter in D than in B).In D two pyridine rings are in trans disposition, with NeCeCeNtorsion angle of 170.23(13)� and, in contrast to 6-bromo-60-methyl-2,20-bipyridine reported earlier,26 the two rings are twisted sig-nificantly, by 11.09(9)�.

In the next step of the synthesis 6-(anthracen-9-yl)-60-bromo-2,20-bipyridine D was converted into stannyl derivative E viacatalytic reaction with hexamethylditin. The Stille-type couplingreaction of E with D gave ligand L with 68% yield as a white solid

insoluble in most organic solvents. Ligand Lwas found to be solublein hot nitromethane during complexation reactions with differenttransition metal ions.

3. Conclusion

The new dianthracene-quaterpyridine ligand L has beenobtained in multistep synthesis using SuzukieMiyaura and Stille-type coupling reactions. Ligand L contains four nitrogen-donoratoms and can be a good coordination agent for transition metalions. At the same time, it is expected to have luminescence withmaximum corresponding to blue light. By complexation reactionof L with luminescent metal ions, e.g., zinc(II), cadmium(II) orsilver(I) emission maxima of ligand can be shifted to longerwavelength and such compounds can emit blue-green or greenlight, what is very interesting for construction organic light-emitting diodes (OLED).

4. Experimental section

4.1. General

Compound A was obtained according to literature.21 NMRspectra was run on a Varian Gemini 300 MHz spectrometer andwere calibrated against the residual protonated solvent signals(CDCl3, d 7.24) and shifts are given in parts per million. ESI massspectra for acetonitrile solutions w10�4 M were measured usinga Waters Micromass ZQ spectrometer. FAB mass spectra were runon Bruker 320MS/450GC spectrometer. Microanalyses were ob-tained using a Vario EL III CHN element analyzer. IR spectra wereobtained with a Bruker FTIR IFS 66/s spectrometer and peak posi-tions are reported in cm�1.

4.2. 2-(Anthracen-9-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (A)

To a solution of 9-bromoanthracene (4.00 g, 15.6 mmol) in40 ml of distilled toluene triethylamine (6.4 ml, 46.0 mmol),pinacolborane (3.5 ml, 24.0 mmol) and dichlorobis(-triphenylphosphine)palladium(II) (0.54 g, 0.8 mmol) were added.The solution was refluxed for 24 h under argon atmosphere thensolvent was evaporated and residue was dissolved in dichloro-methane. The solution was washed with water and organic layerwas dried over MgSO4. The crude product was purified by col-umn chromatography on SiO2 using hexane as eluant. After re-crystallization form hexane 2-(anthracen-9-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane A was obtained as a colorlesscrystals. Yield: 64% (3.02 g) and 77% (3.64 g) when reaction wasperformed with protection from light [Found: C, 78.95; H, 6.94.C20H21BO2 requires C, 78.97; H, 6.96%]; nmax (KBr) n(CeH)ar 3050,nas(CH3) 2976, ns(CH3) 2930, n(CeC) 1679, n(C]C) 1558, 1487,n(BeAr) 1421, 1139, n(BeO) 1372, 1314, r(CeH) 1242, 977, 896,g(CeH) 846, 791, 738, 673, 524, 485 cm�1. dH (CDCl3, 300 MHz)8.50 (d, 2H, J¼8.0 Hz), 8.48 (s, 1H), 8.02 (m, 2H), 7.50 (m, 4H), 1.60(s, 12H). dC (CDCl3, 300 MHz) 136.0, 131.2, 129.6, 128.9, 128.4,125.9, 125.5, 125.0, 84.5, 25.3. m/z 304.1 (Mþ, 100%).

4.3. 2-(Anthracen-9-yl)-6-bromopyridine (B)

To a solution of A (2.00 g, 6.6 mmol) in toluene (100 ml) 2,6-dibromopyridine (1.17 g, 4.9 mmol), tetrakis(triphenylphosphine)palladium(0) (0.38 g, 0.32 mmol) and aqueous 1 M solution ofK2CO3 (13.2 ml, 2 equiv) were added. The mixture was heated at100 �C for 24 h with protection form light, then toluene wasevaporated and the residue was taken up in dichloromethane(100 ml) and washed with water (3�60 ml). The organic layer was

Table 1Crystal data and structural refinement parameters for compound B and D

Compound B D

Formula C19H12BrN C24H15BrN2

Formula weight 334.21 411.29Crystal system Triclinic monoclinicSpace group P-1 P21/ca (�A) 8.541(2) 11.312(2)b (�A) 9.657(2) 9.752(2)c (�A) 9.881(2) 16.697(3)

67.19(3) 90b (�) 73.50(2) 97.72(2)

86.04(2) 90V (�A3) 1825.2(6) 719.5(3)Z 2 4dx (g cm�3) 1.54 1.50F(000) 336 832m (mm�1) 2.85 2.26Q range (

�) 2.90e26.00 2.93e28.23

hkl range �10�h�10 �14�h�14�11�k�11 �12�k�12�12�l�12 �21�l�22

Reflections:Collected 12,927 18,602Unique (Rint) 2830 (0.028) 4084 (0.019)With I>2s(I) 2210 3711

WeightingA 0.0603 0.0268B 0.5177 1.2258

R(F) [I>2s(I)] 0.045 0.023wR(F2) [I>2s(I)] 0.113 0.055R(F) [all data] 0.061 0.027wR(F2) [all data] 0.121 0.057Goodness of fit 1.05 1.04Max/min Dr (e �A�3) 1.25/�0.32 0.34/�0.33

M. Wałesa-Chorab et al. / Tetrahedron 70 (2014) 805e809808

dried over anhydrous MgSO4 and solvent was evaporated. 2-(Anthracen-9-yl)-6-bromopyridine B was purified by columnchromatography (SiO2 CH2Cl2/hexane 2:8) and obtained as a yellowsolid. Yield: 67% (1.47 g) [Found: C, 68.25; H, 3.61; N, 4.20.C19H12BrN requires C, 68.28; H, 3.62; N, 4.19%]; nmax (KBr) n(CeH)ar3102, 3040, n(C]C) 1578, 1544, 1484, n(C]N) 1442, 1406, 1354,1261, r(CeH) 1202, 1160, 1120, 985, 888, g(CeH) 848, 796, 729, 634,554, 426 cm�1. dH (CDCl3, 300 MHz) 8.55 (s, 1H), 8.05 (d, 2H,J¼7.8 Hz), 7.77 (t, 1H, J¼7.6 Hz), 7.66 (dd,1H, J¼8.0, 0.9 Hz), 7.59 (dd,2H, J¼8.8, 1.0 Hz), 7.51e7.37 (m, 5H). dC (CDCl3, 300 MHz) 159.3,142.2, 138.5, 133.2, 131.2, 129.9, 128.5, 128.1, 126.8, 126.1, 125.8,125.6, 125.1 ppm. m/z 334.0 (Mþ, 100%).

4.4. 2-(Anthracen-9-yl)-6-(trimethylstannyl)pyridine (C)

To a solution of 2-(anthracen-9-yl)-6-bromopyridine B (1.03 g,3.08 mmol) in distilled toluene (15 ml) hexamethylditin (1.01 g,3.08 mmol) and tetrakis(triphenylphosphine)palladium(0) (0.18 g,0.15 mmol) were added. The mixture was refluxed under an argonatmosphere for 2 h with protection from light. Then solvent wasevaporated in vacuo and residue was used without further purifi-cation in next step of synthesis.

4.5. 6-(Anthracen-9-yl)-60-bromo-2,20-bipyridine (D)

To a solution of 2-(anthracen-9-yl)-6-(trimethylstannyl)pyri-dine C (1.29 g, 3.08 mmol) in 30 ml of distilled toluene 2,6-dibromopyridine (0.88 g, 3.71 mmol), tetrakis(triphenylphosphine)palladium(0) (0.18 g, 0.15 mmol) were added. Themixture was protected from light and refluxed for 24 h under anargon atmosphere. After that solvent was evaporated and residuewas purified by column chromatography (SiO2, CH2Cl2/hexane 1:1).6-(Anthracen-9-yl)-60-bromo-2,20-bipyridine was obtained asa white solid. Yield: 65% (0.82 g) [Found: C, 70.07; H, 3.69; N, 6.80.C24H15BrN2 requires C, 70.09; H, 3.68; N, 6.81%]; nmax (KBr)n(CeH)ar 3082, 3060, 3045 n(C]C) 1572, 1545, n(C]N) 1440, 1420,1357, r(CeH) 1202, 1153, 1126, 1072, 984, 955, 879, g(CeH) 842,786, 730, 703, 622, 553, 525, 422 cm�1. dH (CDCl3, 300 MHz):d¼8.49 (dd, J¼8.1, 1.0 Hz, 1H), 8.27 (dd, J¼7.6, 0.9 Hz, 1H), 7.96 (dd,J¼15.9, 8.1 Hz, 1H), 7.57 (dd, J¼8.8, 0.9 Hz, 1H), 7.45 (ddd, J¼7.7, 4.4,3.4 Hz,1H), 7.41e7.34 (m, 2H), 7.29 (ddd, J¼8.7, 6.5, 1.3 Hz,1H) ppm.dC (CDCl3, 300 MHz): d¼157.7, 159.4, 154.8, 141.5, 139.2, 137.3, 135.0,131.4, 130.0, 128.5, 128.0, 127.6, 127.4, 126.0, 125.9, 125.1, 120.3,120.0 ppm. m/z 451 (40) [LþK]þ, 433 (80) [LþNa]þ, 411 (100%)[LþH]þ.

4.6. 6-(Anthracen-9-yl)-60-(trimethylstannyl)-2,20-bipyridine(E)

To a solution of 6-(anthracen-9-yl)-60-bromo-2,20-bipyridine D(0.37 g, 0.90 mmol) in distilled toluene (10 ml) hexamethylditin(0.30 g, 0.91 mmol) and tetrakis(triphenylphosphine)palladium(0)(0.06 g, 0.05mmol) were added. Themixturewas refluxed under anargon atmosphere for 2 h with protection from light. Then solventwas evaporated in vacuo and residue was used without furtherpurification in next step of synthesis.

4.7. 6,600 0-Bis(anthracen-9-yl)-2,20;60,200;600,200 0-quaterpyridine(L)

To a solution of 6-(anthracen-9-yl)-60-(trimethylstannyl)-2,20-bipyridine E (0.44 g, 0.89 mmol) in 20 ml of distilled toluene 6-(anthracen-9-yl)-60-bromo-2,20-bipyridine D (0.37 g, 0.90 mmol),tetrakis(triphenylphosphine)palladium(0) (0.05 g, 0.04 mmol)were added. The mixture was protected from light and refluxed for24 h under an argon atmosphere. Precipitated white solid was

filtered off, washed with dichloromethane and dried. Yield: 68%(0.40 g) [Found: C, 86.97; H, 4.53; N, 8.44. C48H30N4 requires C,86.98; H, 4.56; N, 8.45%]; nmax (KBr) n(CeH)ar 3083, 3050, 3028,3005 n(C]C) 1589, 1563, 1521, 1459 n(C]N) 1446,1435, 1415, 1362,1306, r(CeH) 1205, 1163, 1144, 1111, 1087, 1066, 1018, 990, 955, 886,g(CeH) 840, 827, 797, 745, 734, 694, 631, 620, 604, 553, 517, 465,421 cm�1. m/z 662.3 (Mþ, 100%).

4.8. Single crystal structure determination

X-ray diffraction data were collected at 100 (1) K (D) or at roomtemperature (B) by the u-scan technique on Agilent Technologiesfour-circle Xcalibur diffractometer (Eos detector) with graphite-monochromatized MoKa radiation (l¼0.71073 �A). The data werecorrected for Lorentz-polarization and absorption effects.27 Accu-rate unit-cell parameters were determined by a least-squares fit of3374 (B) and 7921 (D) reflections of highest intensity, chosen fromthe whole experiment. The structures were solved with SIR9228

and refined with the full-matrix least-squares procedure on F2 bySHELXL-2013.29 All non-hydrogen atoms were refined anisotropi-cally, hydrogen atoms in D were found in difference Fourier mapsand isotropically refined, while in B was placed in the calculatedpositions, and refined as ‘riding model’ with the isotropic dis-placement parameters set at 1.2 times the Ueq value for appropriatenon-hydrogen atom. Relevant crystal data are listed in Table 1, to-gether with refinement details.

Crystallographic data (excluding structure factors) for thestructural analysis has been deposited with the Cambridge Crys-tallographic Data Centre, Nos. CCDC-959725 (B), and CCDC-959724(D). Copies of this informationmay be obtained free of charge from:The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK. Fax:

M. Wałesa-Chorab et al. / Tetrahedron 70 (2014) 805e809 809

þ44(1223)336 033, e-mail: deposit@ccdc.cam.ac.uk, or www:www.ccdc.cam.ac.uk.

Acknowledgements

Financial support received from the Polish Ministry of HigherEducation and Science (Project Iuventus Plus no. IP2011 058871) isgratefully acknowledged.

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