Reductive Cyclization Products Of

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Reductive Cyclization Products of 1,2-bis(2-nitrophenoxy)ethanes. X-ray Structures of

10-membered Azoxycrown Ether Stereoisomers and theSodium Iodide Complex of a 20-membered Azoazoxycrown

E. Luboch,* V. Ch. Kravtsovy and A. Konitz

Department of Chemistry, Technical University of Gdan ˜ sk, 80-952 Gdan ˜ sk, Poland

Received 23 October 2000

Abstract—Reductive cyclization of 1,2bis(2-nitrophenoxy)ethanes is described; macrocyclization observes a template effect. Themajor products are 10-membered azoxycrown ethers. Isomers of 10-membered azo- and azoxycrowns have been prepared, purified,and characterized. The structures of Z -E -1,2-azoxy-3,4,9,10-bis(4-phenylbenzo)-5,8-dioxacyclodecane have been solved by X-raycrystallographic analyses. 20-Membered crown ethers have been isolated as side products. The structure of a 20-membered azoa-zoxycrown ether has been obtained by X-ray methods as its NaI complex. # 2001 Elsevier Science Ltd. All rights reserved.

Introduction

Owing to the reversible Z À!ÀE isomerization of azocompounds, they are used as the photo- or redox-active

components of films deposited on solid substrates.1

Likeazo compounds, azoxy derivatives also can undergoZ À!ÀE isomerization. Analogously to azobenzenesazoxybenzenes with cis aryl groups isomerize easily totrans compounds. In the last case, the reverse reactionwas not observed. Only several cis azoxybenzenes pre-pared by selective synthesis are characterized.2 Largerring azoxy compounds (like open-chained) exist in Z (trans) form. For steric reasons, small cyclic aliphatic3

and aromatic4 azoxy compounds exist predominantly inthe E (cis) form. It is expected that cyclic azoxy com-pounds of intermediate size may adopt either config-uration depending on steric strain. Such compoundscould potentially be applied for similar purposes like

azocompounds.

We have previously reported the syntheses of 13- and lar-ger-membered azo- and azoxycrown ethers by reductive

(stannite) macrocyclization of the respective dinitropodands.5À7 The ratio of azocrown and azoxycrownethers produced depends on the structure of the startingpodand and on the template effect.6,7 The formation of

dimers was also observed.8

An alternate route to azox-ycrown ethers is oxidation of the respective azocrownethers.7À9

Numerous reported azo- and azoxycrown ethers haveutility as ion carriers for ion-selective membrane elec-trodes. The membranes, when doped with 13-memberedazocrown ethers, are highly sodium selective,6,10

whereas the 16-membered analogues induce potassiumselectivity.7 We have previously described solid-statestructures of several azo- and azoxycrown ethers, and of various metal ion complexes.5,7À9,11À14 Uncomplexedazocrowns were found to exist in both Z (cis) and E (trans) forms.7,9,13,15 The previously prepared 13-mem-

bered and larger azoxycrown ethers and their com-plexes8,12,16 were all found to exist as Z -N¼N(O)-isomers in the solid state. 1H NMR spectroscopy con-firmed this stereochemistry in solution; Z À!ÀE iso-merization was not observed in solutions of 13-, 16- and26-membered azoxycrowns.

We now report the results of reductive cyclization reac-tions involving bis(2-nitrophenoxy)ethane and its di-n-octyl and di-phenyl derivatives. The products are illu-strated in Scheme 1.

1472-7862/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.P I I : S 1 4 7 2 - 7 8 6 2 ( 0 1 ) 0 0 0 09 - 0

Journal of Supramolecular Chemistry 1 (2001) 101–110

Keywords: Azocrown ethers; Azoxycrown ethers; Synthesis; Stereo-isomers; Spectroscopic characteristics; Complex; X-ray crystal struc-tures.*Corresponding author.yOn leave from the Institute of Applied Physics, Moldovian Academyof Sciences, Kishinev, Moldova.



Experimental

All materials and solvents used for syntheses were of analytical reagent grade. Silica gel 60 (FLUKA) wasused for column separations. TLC experiments were

performed on Silica gel 60 F254 (aluminium sheets,Merck). Preparative TLC glass plates covered withSilica gel 60 F254 (Merck) were used in some cases forfinal separation and purification of crown ethers.

1H NMR spectra (CDCl3) were carried out with Varianinstruments. UV–vis spectra were recorded in CH3CN(Merck) on a UNICAM UV300 apparatus. The identityof macrocyclic compounds was established by HRMStaken on an AMD-604 apparatus. The mp (C) areuncorrected.

General synthesis of podands

A mixture of 2-nitrophenol (or its 4-n-octyl7,17 or 4-phenylderivative7,18) (16 mmol), 1,2-dibromoethane (0.78 mL;9 mmol), 4 mL DMF and anhydrous K2CO3 (2.22 g;16 mmol) was heated for 6 h at 140 C. The mixture wasdiluted with water and the precipitate was collected.

1,2-Bis(2-nitrophenoxy)ethane (1). Yield 59%, mp 165– 167 C. 1H NMR (200 MHz, d [ppm]): 4.55 (4H, s,CH2); 7.09 (2H, dt, J =8.1, 1 Hz, ArH); 7.25 (2H, dd,J =8, 1 Hz, ArH); 7.59 (2H, dt, J =8, 1.8 Hz, ArH); 7.84(2H, dd, J =8, 1.6 Hz, ArH). IR (nujol, cmÀ1) 1588,1520, 1480, 1280, 1248, 1152, 1088, 1052, 936, 848, 768,732, 672. This compound is identical with an authentic

sample.

19

1,2-Bis(2-nitro-4-n-octylphenoxy)ethane (2). Yield 64%,mp 54–55 C. 1H NMR (200MHz, d [ppm]): 0.88 (6H, t,J =6.5 Hz, CH3); 1.20–1.40 (20H, m, CH2); 1.50–1.70(4H, m, ArCH2CH2); 2.60 (4H, t, J =7.6 Hz, ArCH2);4.49 (4H, s, OCH2); 7.14 (2H, d, J =8.5 Hz, ArH); 7.37

(2H, dd, J =8.5, 2.2 Hz, ArH); 7.64 (2H, d, J =2.2 Hz,ArH). IR (nujol, cmÀ1) 1616, 1536, 1340, 1268, 1152,1088, 1036, 816, 720. MS (EI): m/z=528. HRMS: forC30H43O5N2 (MÀOH) found 511.31567; calcd511.31720.

1,2-Bis(2-nitro-4-phenylphenoxy)ethane (3). Yield 79%,mp 245–247 C. 1H NMR (200 MHz, d [ppm]): 4.62(4H, s, CH2); 7.34 (2H, d, J =8.7 Hz, ArH); 7.38–7.62(10H, m, ArH); 7.82 (2H, dd, J =8.7, 2.4 Hz, ArH); 8.08(2H, d, J =2.3 Hz, ArH). IR (nujol, cmÀ1) 1616, 1536,1490, 1264, 1060, 880, 768, 730, 688, 608. HRMS (EI):for C26H20O6N2 found 456.13310; calcd 456.13214.

General syntheses of crown ethers from podand 1

Water (40 mL) was added to a stirred mixture of podand 1 (4.5 g; 15 mmol), stannous chloride dihydrate(15 g), acetone (45 mL) and NaOH (19.5 g). The mixturewas vigorously stirred and boiled gently for 2 h, cooled,diluted with water (50 mL) and extracted several timeswith chloroform. The organic extracts were combined,washed with water and the solvent was removed underreduced pressure. The residue was diluted with tolueneand the solvent was evaporated again. The mixture waschromatographed (methylene chloride) to obtain cyclicproducts. The second chromatography was performed

in polarity gradient [begin: hexane/CH2Cl2 (1:1); end:

Scheme 1.

102 E. Luboch et al. / Journal of Supramolecular Chemistry 1 (2001) 101–110



CH2Cl2]. The first fraction contains 10-membered azo-crown ether 7 (0.18 g), the second fraction contains Z (trans) isomer of 10-membered azoxycrown ether 4(1.1 g);and the thirdfraction contains E (cis) isomer of 10-membered azoxycrown ether 4 (0.13 g). The final orange-red fraction eluted with methylene chloride contains 20-membered crown ethers. The last crown ethers were sepa-rated and purified by preparative TLC using sodium chlo-

ride impregnated silica gel (cf. ref 6). Azocompound 8(0.22 g), azoazoxycompound 9 (0.67 g) and two diazox-ycompounds 10a and 10b (0.15 g) were obtained.

In an analogous synthesis, NaOH was replaced byKOH, LiOH, or by LiOH and KOH 1:1 (mol/mol)mixture. Yields are recorded in Table 1.

Azocrown 7, isomer E . Oil was crystallized at low tem-perature. The crystals were washed with methanol; mp45–46 C. TLC: R f (CH2Cl2) 0.65. 1H NMR (200 MHz,d [ppm]): 4.46 (4H, s, CH2); 7.15–7.39 (6H, m, ArH);7.72 (2H, dd, J =1.8, 7.7 Hz, ArH). IR (film, cmÀ1)3072, 2928, 1600, 1570, 1472, 1450, 1392, 1310, 1268,

1212, 1152, 1104, 1044, 948, 864, 768, 596, 560, 480.UV–vis, lmax 238 nm (Emax=9060); lmax 312 nm(Emax=21400) and lmax 454 nm (Emax=260).

Azocrown 7, isomer Z . This was crystallized from hep-tane; mp 114–115 C. TLC: R f (CH2Cl2) 0.20. 1H NMR(500 MHz, d [ppm]): 3.89 (2H, broad, CH2); 4.40 (2H,broad, CH2); 6.65 (2H, d, J =7.3 Hz, ArH); 6.89–6.97(4H, m, ArH); 7.03–7.08 (2H, m, ArH); 1H NMR atÀ60C (500 MHz, d [ppm]): 3.86–3.92 (4H, m, CH2);4.46–4.52 (4H, m, CH2); 6.67 (2H, dd, J =8, 1.2 Hz,ArH); 6.93–6.98 (4H, m, ArH); 7.07–7.12 (2H, m, ArH).IR (film, cmÀ1): 3064, 2980, 2928, 2880, 1584, 1520,

1470, 1444, 1280, 1224, 1152, 1104, 1056, 944, 896, 816,768, 736, 496. UV–vis, l 210 nm (s) (Emax=20,200); lmax

247 nm (Emax=7900) and lmax 409 nm (Emax=590).

Compound 7. HRMS (EI), for C14H12O2N2 found240.08845, calcd 240.08988.

Azoxycrown 4, isomer Z (cf. ref 20) Oil crystallizing atlow temperature; mp 74–75 C. TLC R f (CH2Cl2) 0.53.1H NMR (200 MHz, d [ppm]): 4.31–4.41 (4H, m, CH2);7.17–7.38 (5H, m, ArH); 7.46 (1H, dt, J =7.7, 1.8 Hz,ArH); 7.84 (1H, dd, J =8.1, 1.9 Hz, ArH); 7.96 (1H, dd,J =7.6, 2 Hz, ArH). IR (film, cmÀ1): 3072, 2928, 1600,1480, 1450, 1328, 1300, 1264, 1232, 1136, 1088, 1040,

932, 884, 760, 588. UV, l 240 nm (s) (Emax=8410); lmax

308 nm (Emax=5090).

Azoxycrown 4, isomer E (cf. ref 20) This was crystal-lized from 2-propanol; mp 138–139 C. TLC: R f

(CH2Cl2) 0.12. 1H NMR (500 MHz, d [ppm]): 3.92–3.98(1H, m, CHaHb); 4.03–4.09 (1H, m, CHaHb); 4.54–4.64(2H, m, CH2); 6.91 (2H, dt, J =7.8, 1.5 Hz, ArH); 6.94– 6.99 (2H, m, ArH); 7.01 (1H, dd, J =8.3, 1 Hz, ArH);7.08 (1H, dt, J =7.8, 1.5 Hz,); 7.15 (1H, dd, J =7.8,1.5 Hz, ArH); 7.24 (1H, dt, J =7.8, 1.5 Hz, ArH). IR(nujol, cmÀ1): 1600, 1280, 1232, 1088, 1056, 896, 832,768, 730, 688. UV, lmax 239 nm (Emax=13400); lmax 309

nm (Emax=1480).


Diazocrown 8. This was crystallized from methanol/methylene chloride (5:1); mp 190–191 C (lit. 113.5– 114.5 C21). 1H NMR (500 MHz, d [ppm]): 4.62 (8H, s,CH2); 6.77 (4H, dt, J =8,1 Hz, ArH); 6.98 (4H, dd,J =7.8, 1.4 Hz, ArH); 7.06 (4H, dd, J =8.3, 0.9 Hz,ArH); 7.33 (4H, dt, J =7.8, 1.5 Hz, ArH). IR (nujol,cmÀ1): 1584, 1280, 1248, 1112, 944, 752. HRMS (EI),

for C28H24O4N4 found 480.18450, calcd 480.17975.

Azoxyazocrown 9. This was crystallized from methanol/methylene chloride (5:1) mp 187–188. 1H NMR(500 MHz, d [ppm]): 4.40–4.53 (8H, m, CH2); 6.94–7.10(8H, m, ArH); 7.24–7.42 (6H, m, ArH); 7.53 (1H, dd,J =8, 1.7 Hz, ArH); 7.99 (1H, dd, J =8, 1.7Hz, ArH).IR (nujol, cmÀ1): 1584, 1280, 1244, 1168, 1068, 932, 752.HRMS (EI), for C28H24O5N4 found 496.17329, calcd496.17468.

Oxidation of azoxyazocrown 9 to diazoxycrown ethers10

20-Membered azoxyazocrown ether 9 (100 mg) wastreated with 4 mL of acetic acid and 2 mL of 30%hydrogen peroxide. The mixture was heated at 100 Cfor 1 h. The solvents were evaporated, to the residuewater was added and the product was extracted withmethylene chloride. Column chromatographic separa-tion gave 60mg (59%) of a mixture of 10a and 10b.Both products were separated on preparative TLCplates (CH2Cl2). The upper (R f 0.63, methylene chlo-ride/acetone 20:1) compound 10a melts at 200–201 C,the lower (R f 0.58, the solvent as above) compound 10bmelts at 217–218 C. The ratio of the upper to the lowercompound is %2:3.

Diazoxycrown 10a. 1H NMR (200 MHz, d [ppm]): 4.42(4H, s, CH2); 4.39 (4H, s, CH2); 6.96–7.14 (8H, m,ArH); 7.30–7.45 (4H, m, ArH); 7.65 (2H, dd, J =8,1.5 Hz, ArH); 8.17 (2H, dd, J =8, 1.6 Hz, ArH). IR(nujol, cmÀ1): 1592, 1328, 1280, 1244, 1088, 944, 750.HRMS (EI), for C28H24O6N4 found 512.16386, calcd512.16956.

Diazoxycrown 10b. 1H NMR (200 MHz, d [ppm]): 4.30– 4.40 (4H, m, CH2); 4.40–4.50 (4H, m, CH2); 6.96–7.13(8H, m, ArH); 7.24–7.45 (4H, m, ArH); 7.65 (2H, dd,J =8, 1.6 Hz, ArH); 8.11 (2H, dd, J =8, 1.6Hz, ArH).

IR (nujol, cm

À1

): 1588, 1280, 1240, 1070, 924, 740.

Table 1. Template effect in reductive macrocyclization reaction

% Yield for specified cation

Compound Na+ K+ Li+ Li++K+

7 5 2 12 84 32 20 20 248 3 <0.5 <0.5 29 9 <0.5 1 2

10 2 <0.5 <0.5 <0.5Total 51 $23 $34 $36

E. Luboch et al. / Journal of Supramolecular Chemistry 1 (2001) 101–110 103



HRMS (EI), for C28H24O6N4 found 512.16765, calcd512.16956.

The 20-membered diazoxy compounds isolated from thereduction products are identical with oxidationproducts of 9.

Synthesis of crown ether 5 from podand 2. The reduction

was performed as above with stannous chloride in thepresence of NaOH. Reaction time was 4 h. Immediatelyafter the reaction was completed an oily Z isomer of 10-membered azoxycrown ether 5 and approximately 10times less of isomer E melting at 94–95 C (frommethanol) were isolated by column chromatography.The oily Z compound converts slowly to give crystallineisomer E . The overall yield of the azoxycrown ethers 5was 38%. TLC; R f (CH2Cl2) isomer Z 0.95; isomer E 0.38. The other products were not isolated.

Azoxycrown 5, isomer Z . 1H NMR (200 MHz, d [ppm]):0.73–0.87 (6H, m, CH3); 1.10–1.25 (20H, m, CH2); 1.42– 1.67 (4H, m, ArCH2CH2); 2.48–2.64 (4H, m, ArCH2);

4.13–4.28 (4H, m, OCH2); 7.0–7.21 (4H, m, ArH); 7.54(1H, d, J =2.1 Hz, ArH); 7.66 (1H, d, J =1 Hz, ArH).IR (film, cmÀ1): 2928, 2856, 1504, 1470, 1295, 1264,1136, 1040, 884, 832. UV, lmax 306nm (Emax=5160).

Azoxycrown 5, isomer E . 1H NMR (200 MHz, d [ppm]):0.89 (6H, t, J =6.6 Hz, CH3); 1.10–1.50 (24H, m, CH2);2.43 (4H, t, J =7.6 Hz, ArCH2); 3.81–4.03 (2H, m,OCH2); 4.44–4.60 (2H, m, OCH2); 6.66 (1H, d,J =1.6 Hz, ArH); 6.78 (1H, d, J =8.1 Hz, ArH); 6.84(1H, dd, J =8.3, 1.8 Hz, ArH); 6.86 (1H, d, J =8.3 Hz,ArH); 6.92 (1H, d, J =1.8 Hz, ArH); 6.99 (1H, dd,J =8.2, 2 Hz, ArH). IR (film, cmÀ1): 2928, 2848, 1504,

1456, 1344, 1264, 1132, 1088, 1056, 1024, 900, 832, 736.UV–VIS, l 221nm (s) (Emax=15,800); l 241 nm (s)(Emax=9180).


Synthesis of crown ether 6 from podand 3. The reductionrequires 6 h reaction time. Yield of the azoxycrownether 6 was 11%. Immediately after the reaction wascompleted, chromatographic separation afforded isomerZ as a main macrocyclic product; mp 135–136 C(CH2Cl2/MeOH). A solution of both isomers in meth-ylene chloride/hexane deposites crystals of isomer E , mp

175–178 C. TLC: R f (CH2Cl2) 0.93 for isomer Z ; 0.30for isomer E .

Azoxycrown 6, isomer Z . 1H NMR (500 MHz, d [ppm]):4.40–4.44 (2H, m, CH2); 4.44–4.48 (2H, m, CH2); 7.30(1H, d, J =8.8 Hz, ArH); 7.36 (1H, d, J =8.3 Hz, ArH);7.38–7.44 (2H, m, ArH); 7.46–7.52 (4H, m, ArH); 7.57(1H, dd, J =8.8, 2.4 Hz, ArH); 7.63–7.67 (4H, m, ArH);7.71 (1H, dd, J =8.3, 2.5 Hz, ArH); 8.10 (1H, d,J =2.5 Hz, ArH); 8.23 (1H, d, J =2.4 Hz, ArH). IR(film, cmÀ1): 3056, 3024, 2928, 1600, 1484, 1300, 1264,1228, 1184, 1060, 1024, 944, 884, 848, 760, 704, 608.UV, lmax 204 nm (Emax=72600); lmax 254 nm

(Emax=48,600).

Azoxycrown 6, isomer E . 1H NMR (500 MHz, d [ppm]):3.98–4.05 (1H, m, CHaHb); 4.09–4.14 (1H, m, CHaHb);4.61–4.69 (2H, m, CH2); 7.00 (1H, d, J =8.3 Hz, ArH);7.08 (1H, d, J =8.8 Hz, ArH); 7.16 (1H, d, J =2.4 Hz,ArH); 7.28 (1H, dd, J =8.3, 2.4 Hz, ArH); 7.31–7.38(10H, m, ArH); 7.40 (1H, d, J =2 Hz, ArH); 7.44 (1H,dd, J=8.3, 2 Hz, ArH). IR (nujol, cmÀ1): 1600, 1280,1232, 1088, 1056, 896, 832, 768, 730, 688. UV, lmax

199 nm (Emax=105,000); lmax 250 nm (Emax=62,800).


Preparation of single crystals of NaI complex of 20-membered azoazoxycrown ether 9 (complex 11). A mix-ture of crown ether 9 (1 mmol) and sodium iodide(2 mmol) was dissolved in methanol and then the sol-vent was evaporated in vacuo. The residue partiallydissolves in acetone on heating; the filtered solutiondeposites crystals upon cooling. The complex liberatesacetone at 130–140 C and decomposes at >200 C.

Membrane electrodes and potentiometric measurements

The preparation of membrane for ion-selective electro-des was described earlier in detail.6 Composition of membranes are: ionophore 3 mg, potassium tetrakis( p-chlorophenyl)borate 0.5 mg, poly(vinyl chloride) 50 mgand o-nitrophenyl octyl ether 0.1 mL. The electrodeselectivities were measured by separate solutionsmethod (SSM).22

X-ray crystal structure determinations

X-Ray studies of Z and E isomers of 1,2-azoxy-3,4,9,10-

bis(4-phenylbenzo)-5,8-dioxacyclodecane (compound 6).Crystals of both isomers of compound 6 have similarpale yellow color but belong to different crystal systemsand essentially differ in habit. The crystals of triclinicisomer Z are block like, whereas well defined crystals of monoclinic isomer E have a shape of very thin longplates.

X-Ray diffraction measurement for both isomers wereperformed at 293 K on KUMA diffractometer, emploinggraphite-monochromated MoK

a-radiation. Lattice con-stants and orientation matrices were refined by least-squares fits of 25 reflections in y-range 5.3–11.3 for Z -iso-mer and 27 reflections iny-range 7.1–11.2 for E . Intensity

data were collected up to y=25.05 for Z and 20.84 for E using o-2y scan mode. There were not ‘observed’ reflec-tions beyond this limit. Three standard reflections, mea-sured every 100 reflections collected, show decay of 21.2%for the crystal of E -isomer during data collection. Analysisof data collection showed that the crystal began to destroyonly in the last stage of experiment. The decay influencedonly about 6% of data with I >2s(I ). Three standardreflections measured after every 200 reflections for Z -iso-mer show no decay during data collection. Crystals of bothisomers diffracted weakly and only 985 (30%) for Z and1155 (30%) reflections for E could be labeled as ‘observed’(I >2s(I )) among 3267 and 3860 measured independent

reflections for 6Z

and 6E

, respectively.




Table 3. Selected bond lenghts (A ˚ ) and valence and torsion angles () for isomers Z and E of compound 6

Compound 6 Isomer Z Isomer E

Molecule a Molecule b

O(1)–C(10) 1.371 (11) 1.390 (7) 1.372 (7)O(1)–C(2) 1.434 (12) 1.440 (9) 1.448 (9)C(2)–C(3) 1.491 (14) 1.446 (11) 1.482 (9)C(3)–O(4) 1.498 (11) 1.432 (9) 1.459 (9)

O(4)–C(5) 1.391 (10) 1.411 (7) 1.381 (6)C(5)–C(6) 1.332 (12) 1.390* 1.390*C(6)–N(7) 1.469 (11) 1.426 (10) 1.472 (9)N(7)–O(7) 1.234 (9) 1.212 (10)y 1.250 (8)N(7)–N(8) 1.298 (10) 1.238 (11) 1.257 (9)N(8)–O(8) — 1.195 (11)y – N(8)–C(9) 1.381 (11) 1.420 (11) 1.455 (9)C(9)—C(10) 1.418 (11) 1.390* 1.390*C(10)–O(1)–C(2) 118.1 (7), 114.8 (9) 118.8 (8) 117.4 (7), 113.0 (8)O(1)–C(2)–C(3) 109.3 (8) 112.1 (9) 107.2 (8)C(2)—C(3)–O(4) 115.2 (7) 113.4 (10) 114.3 (6)C(3)–O(4)–C(5) 124.0 (9) 115.5 (7) 114.9 (6)O(4)—C(5)–C(6) 123.1 (8) 118.9 (6) 121.2 (6)C(5)—C(6)-N(7) 119.8 (7) 117.9 (6) 114.2 (8)C(6)—N(7)–O(7) 110.9 (7) 122.4 (12)y 126.3 (8)C(6)—N(7)—N(8) 129.1 (7) 122.4 (10) 119.4 (9)O(7)–N(7)–N(8) — 114.7 (12)y –

N(7)–N(8)–O(8) 119.8 (8) 114.7 (16)y

111.3 (8)N(7)–N(8)–C(9) — 119.5 (10) – O(8)–N(8)–C(9) 109.7 (8) 125.5 (15)y 121.1 (6)N(8)–C(9)–C(10) 122.1 (8) 121.6 (7) 118.0 (6)O(1)—C(10)–C(9) 118.2 (6)O(1)—C(2)—C(3)—O(4) À117 (1) 48 (1) 52 (1)C(2)—C(3)—O(4)—C(5) 138 (1) À134 (1) À139 (1)C(3)—O(4)—C(5)—C(6) À92 (1) 123 (1) 132 (1)O(4)—C(5)—C(6)—n(7) 8 (1) 6 (1) À1 (1)C(5)—C(6)—N(7)—N(8) 31 (1) À80 (1) À71 (1)C(6)—N(7)—N(8)—C(9) À173 (1) À6 (2) À8 (1)N(7)—N(8)—C(9)—C(10) 172 (1) 106 (1) 111 (1)N(8)—C(9)—C(10)—O(1) 4 (1) 0 (1) À5 (1)C(9)—C(10)—O(1)—C(2) À64 (1) À120 (1) À118 (1)C(10)—O(1)—C(2)—C(3) 108 (1) 51 (1) 43 (1)

*Assumed value.y

Disordered azoxy group in molecule a of isomer E.

Table 2. Crystallographic characteristics for Z and E isomers of 10-membered azoxycrown ethers 6 and of NaI complex of 9, acetone solvate

(complex 11)

Characteristic Isomer 6Z Isomer 6E Complex 11

Molecular formula C26H20N2O3 C26H20N2O3 C34H36IN4NaO7

Molecular weight 408.44 408.44 762.56Wavelenght (A ˚ ) 0.71073 0.71073 0.71073Crystal system Triclinic Monoclinic MonoclinicSpace group P1

-P21/c P21/n

a (A ˚

) 7.999(6) 14.643(2) 13.287(7)b (A ˚ ) 11.141(7) 13.492(2) 11.863(5)c (A ˚ ) 12.320(9) 21.992(3) 22.703(9) () 105.93(5) 90 90 () 101.53(6) 108.02(1) 95.70(5) () 93.60(5) 90 90V (A ˚ 3) 1026.4(13) 4131.7(10) 3561(3)Z 2 8 4Density (calcd) (g/cm3) 1.322 1.313 1.422Absorption coeff. (mmÀ1) 0.087 0.087 0.962F(000) 428 1712 1552Crystal size (mm) 0.1Â0.4Â0.6 0.05Â0.4Â1.0 0.15Â0.1Â0.1y range for data collection () 1.76–25.05 1.46–20.81 1.80–23.25Index ranges À9 < h < 8 À11 < h < 14 0 < h < 14

0 < k < 12 0 < k < 13 0 < k < 13À13 < l < 14 À21 < l < 20 À25 < l < 24

Reflections collected 3588 4045 5192

Independent reflections 3267 [R(int)=0.0887] 3860 [R(int)=0.0760] 5026 [R(int)=0.0571]Final R indices R1=0.0827 R1=0.0753 R1=0.0728wR2=0.2233 wR2=0.1851 wR2=0.1678

Largest diff. peak and hole (eA ˚ À3) 0.139 and À0.300 0.368 and À0.276 0.856 and À1.044




The structures were solved by direct method and refinedby full matrix least squares in anisotropic approach.Hydrogen atoms were placed in calculated positionsand were refined as constrained to bonding atoms in a‘ride’ mode. The individual isotropic temperaturefactors were applied for them. To improve the data/parameters ratio for E -isomer the aromatic residueswere refined as regular hexagon moieties (C–C=1.39

A ˚ ). All calculations were performed using SHELXS-86and SHELXL-93 programs.23 Crystallographic dataare summarized in Table 2. Selected interatomicdistances, valence and torsion angles are given inTable 3.

X-Ray studies of acetone solvate of NaI complex of crown ether 9 (complex 11). Orange colored prismaticmonocrystals were obtained directly from preparation.The data were collected at 293 K on KUMA-diffractionKM-4 diffractometer. The lattice constants were refined

by least squares fits of 32 reflections in y range9.1–14.8. Intensity data were collected using o-o/2yscan mode. The crystal diffracted poor, and only 1245(25%) reflections for 11 could be labeled as ‘observed’(I >2s(I )) among 5026 measured independent reflec-tions. The structure was solved by direct methodand refined by full matrix least squares method inanisotropic approach using SHELX-9724 programs.

To decrease the number of refined parameters andimprove the data/parameter ratio the aromatic residueswere refined as a regular hexagon of ideal geometry (C– C=1.39 A ˚ ). Positions of hydrogen atoms of methylgroups were found from refining ideal -CH3 moietyduring rotation around corresponding single bonds,with U(H) equal 1.5 Ueqv. of the attached atoms. Thepositions of remaining hydrogens were calculated fromgeometrical considerations and were refined as con-strained to bonding atoms in a ‘ride’ mode withU(H)=1.2 Ueqv.

Table 4. Selected bond distances (A ˚ ), valence and torsion angles () for complex 11

Atoms Distance Atoms Distance

Na–O(1) 2.614(11) Na–N(7) 2.731(17)Na–O(4) 2.655(12) Na–N(17) 2.650(18)Na–O(11) 2.657(11) Na–O(1a) 2.333(14)Na–O(14)

2.568(12) Na–O(1b) 2.356(14)O(1)–C(20) 1.337(13) C(10)–O(11) 1.372(11)O(1)–C(2) 1.458(18) O(11)–C(12) 1.482(15)C(2)–C(3) 1.48(2) C(12)–C(13) 1.491(19)C(3)–O(4) 1.431(17) C(13)–O(14) 1.476(16)O(4)–C(5) 1.370(13) O(14)–C(15) 1.360(12)C(6)–N(7) 1.490(17) C(16)–N(17) 1.446(18)N(7)–N(8) 1.193(19) N(17)–N(18) 1.212(18)N(8)–O(8) 1.23(2) N(18)–O(18) 1.21(2)N(8)–C(9) 1.429(19) N(18)–C(19) 1.426(19)

Atoms Angle Atoms Angle

O(1)–Na–O(4) 64.9(4) O(11)–Na–O(14) 64.4(3)O(4)–Na–N(7) 58.4(4) O(14)–Na–N(17) 58.9(4)N(7)–Na–O(11) 62.7(4) O(1)–Na–N(17) 62.9(4)

O(1)–C(2)–C(3)–O(4) À69.0(15) O(11)–C(12)–C(13)–O(14) À67.4(15)C(2)–C(3)–O(4)–C(5) À177.8(12) C(12)–C(13)–O(14)–C(15) À175.4(11)C(3)–O(4)–C(5)–C(6) À177.5(10) C(13)–O(14)–C(15)–C(16) 174.8(10)O(4)–C(5)–C(6)–N(7) 9.7(12) O(14)–C(15)–C(16)–N(17) 5.4(10)C(5)–C(6)–N(7)–N(8) À156.2(13) C(15)–C(16)–N(17)–N(18) À147.3(11)C(6)–N(7)–N(8)–C(9) 177.0(11) C(16)–N(17)–N(18)–C(19) À177.6(10)N(7)–N(8)–C(9)–C(10) 48.8(18) N(17)–N(18)–C(19)–C(20) 39.0(17)N(8)–C(9)–C(10)–O(11) À3.6(14) N(18)–C(19)–C(20)–O(1) À2.3(13)C(9)–C(10)–O(11)–C(12) 165.2(9) C(19)–C(20)–O(1)–C(2) 158.7(10)C(10)–O(11)–C(12)–C(13) À173.7(11) C(20)–O(1)–C(2)–C(3) À174.6(12)

Table 5. Hydrogen bonds and short intermolecular interactions for complex 11*

D—HÁ Á ÁA d (D-H) (A ˚ ) d (H. . .A) (A ˚ ) d (D. . .A) (A ˚ ) Angle (D-HÁ Á ÁA) ()

C(31)—HÁ Á ÁI(1)#1 0.93 3.16 3.933(10) 142.0C(28)—HÁ Á ÁI(1)#2 0.93 3.17 3.988(8) 147.2C(34)—HÁ Á ÁI(1)#3 0.93 3.32 4.052(12) 137.4C(3b)—HÁ Á ÁI(1)#4 0.96 3.12 4.059(19) 165.5C(26)—HÁ Á ÁI(1) 0.93 3.34 4.075(10) 137.1

*Symmetry transformations used to generate equivalent atoms: #1 x+1/2,À y+3/2, z+1/2; #2Àx+3/2, y+1/2, Àz+1/2; #3 x, y+1, z; #4Àx+1,À y+1, Àz+1.




Crystallographic data are summarized in Table 2.Selected interatomic distances, valence and torsionangles are given in Table 4.

Results and Discussion

bis(2-Nitrophenoxy)ethane 1 and its n-octyl 2 andphenyl derivative 3 were reduced to produce 10-mem-bered azoxycrown ethers as the major macrocyclic pro-ducts. The Z and E isomers of these compounds were

separated by column and/or preparative thin layerchromatographic methods and identified. The Z (trans)isomer predominates in the reaction mixture. In a solidstate the Z and E isomers of 10-membered azoxycrownethers are stable. In solution, at room temperature, bothisomers show comparable stability under equilibrium(TLC and 1H NMR); however, the spontaneous Z À!ÀE isomerization proceeds relatively slow. This is in contrastto larger-ring azoxycrown ethers, which exist essentiallyin the Z form in both the free and complexed states, andto small ring azoxy compounds existing in E form.

Studies of photoisomerization of azoxycrown ethers of

intermediate size is under progress.

We have found that the E isomers crystallize readilyfrom solution. Their melting points are higher thanthose of the Z isomers. Pure, crystalline Z isomers wereobtained by rapid crystallization (seeding) from con-centrated solutions or from oil at low temperature of freshly chromatographically isolated compounds.

The geometry of each 10-membered azoxycrown etherisomer was established by X-ray studies in the solid stateand by 1H NMR and UV spectroscopy in solution. It is

Figure 1. 1H NMR spectra (CDCl3) of isomers of compound 4 (top: E (cis); bottom: Z (trans)).

Figure 2. UV absorption spectra of isomers of compound 4..




apparent from the 1H NMR spectra shown in Figure 1that aromatic proton signals (ortho to the azoxy groups)differ significantly. These protons are strongly shieldedfor E -isomers because conjugation is hindered due tononcoplanarity of the azoxy and benzene units. Forexample, chemical shifts for the ortho protons of E -4 are7.24 and 7.15 ppm, whereas the corresponding shifts are7.96 and 7.84ppm for Z -4. The oxyethylene CH2CH2

protons are also diagnostic: they are almost equivalentfor Z -isomers but clearly differentiated for E -isomers(4.31–4.41ppm for Z -4 and 3.92–4.64 ppm for E -4).

The UV spectra (Fig. 2) show characteristic lmax at239nm for E -4 and lmax at 308 nm for Z -4. The longwavelength band for E -4 is very weak (cf. spectra of azoxybenzene [2]).

The 10-membered azocrown ethers also are formed inthe above described reaction, although with significantlylower yield. In this case also isomers of compound 7were isolated and characterized by NMR, UV–VIS andX-ray studies [25].

20-Membered ring structures were isolated from thesereactions mixtures in addition to the 10-membered ring

products (see Scheme 1). The yields were dependent onreduction conditions and on the alkali metal ion presentduring the reaction (Table 1). Compound 9, the major20-membered ring product, was characterized by X-raymethods as its NaI complex. The overall yield of mac-rocyclic products formed during reductive cyclization of 1,2-bis(2-nitrophenoxy)ethane amounts up to 50%.

In contrast to results obtained with 13- and 16-mem-bered azo- and azoxycrown ethers, the 10-memberedazo- and azoxycrown ethers are poor ion-carriers inmembrane electrodes. Membranes doped with 20-mem-bered azocrown ether 8 were responsive to sodium andpotassium ions, but the K/Na selectivity was low. Theorder of cation preferences was: Ag+)Pb2+>

H+>K+%Cs+>Rb+>Na+>Cu2+>NH4

+>Zn2+

>Ca2+> Sr2+>Ba2+>Ni2+>Co2+>Li+>Mg2+.The high silver-ion selectivity is typical of many azo-and azoxycrown ethers [6]. Unexpected is relatively highPb2+ selectivity.

Structure description of isomer Z of compound 6. Thedisplacement ellipsoid plot with the atom numberingscheme of isomer Z in the projection on the best plane isshown in Figure 3.

The core of the 10-membered azoxy macrocycle withtrans oriented aromatic residues is roughly planar. Thedihedral angles between the azoxy group and the meanplanes of benzene residues on N(7) and N(8) equal28.7(9) and 10.9(12), respectively. Biphenyl moietiesare non-planar. Dihedral angles between phenylene andphenyl residues equal 29.4(4) and 38.3(3) for the

Figure 3. Displacement ellipsoid plot for compound 6 Z with atomnumbering scheme.

Figure 4. General view and atom numbering scheme for compound 6

E (molecule a). Only one position of disordered O atom is shown. Figure 5. Fragment of packing in the structure of compound 6E

.




fragment adjacent to N(7) and N(8), respectively.

The characteristic geometric features of azoxy groupcorrespond to those found for the similar com-

pounds.8,12 Conformation of oxyethylene chain isdescribed by the following set of torsional angles-sc, ac,-ac, ac and-ac starting from C(10)–O(1) bond.

Structure description of isomer E of compound 6. The X-ray structure analysis show that there are two crystal-lographically independent molecules (a and b) in asym-metric part of unit cell. They are essentially non-planarand take boat shape. Figure 4 shows the numberingscheme and displacement ellipsoid drawing for moleculea. Aromatic residues are in cis-position with respect toazoxy groups. It was found that the oxygen atom of theazoxy group in molecule a is statistically disordered

between two nitrogen atoms with different probability:it equals 0.67 and 0.33 for position on N(7a) and N(8a),respectively. In molecule a, the azoxy group formsdihedral angles 82.3(5) and 74.0(8) with the proximalaromatic residues on N(7) and N(8), while they are77.6(4) and 53.5(4) for molecule b, respectively. Dihe-dral angles between phenylene and phenyl residues inbiphenyl moieties connected to N(7) and N(8) formolecule a equal 38.5(3) and 32.7(2), respectively; theanalogous angles equal 11.5(4) and 39.5(4) for mole-cule b. Both independent molecules have the same con-formation of oxyethylene chain, which could be describedby the following successive set of torsional angles:-ac, sc,sc,-ac and ac starting from C(10)–O(1) bond.

Molecules a related by symmetry center are united in adimer due to CH. . .O hydrogen bonds between C(14a)and O(7a) atoms (Fig. 5). Parameters of the hydrogenbonds for the form with higher probability of oxygenlocation on N(7a) are C(14a). . .O(7a)=3.318(12),H. . .O 2.39 and angle C—H. . .O equal 174.2, andC(15a). . .O(8a)=3.29(2), H. . .O 2.38 and angle C– H. . .O equal 166.6 for the second position of oxygenatom. Although shapes of these molecules are verysimilar they play a different role in formation of thecrystal structure. The mutual arrangement of thebiphenyl moieties and 10-membered macrocycle are

such that molecule a and b form a pseudo-cavity. Figure

5 shows formation of centrosymmetric dimer by mole-cules a and inclusion of molecule b in the pseudo-cavity of molecule a.

Structure description of complex 11. The structure withthe atomic numbering scheme is given in Figure 6. X-Ray analysis showed that oxygen atom of the azoxy-group in the crystal is statistically distributed over two

positions: on N(8) and N(18) with equal probability.The 20-membered macrocyclic molecule consists of azoxy and azo groups joining aromatic moieties intrans-position. The aromatic moieties adopt alternatingpositions around macroring resulting in its essentiallynon-planar saddle-like conformation. The dihedralangles A/B/C/D/A between the neighboring aromaticmoieties equal 73.5(5), 84.4(4), 76.1(4) and 85.6(5),respectively. Sodium atom coordinated to four oxygenand two nitrogen atoms of the macrocycle lies close(0.167(7) A ˚ displacement) to the mean plane of theseheteroatoms. The Na–O and Na–N distances are longerthan those observed for sodium complexes of the related13- and 16-membered macrocycles;13,14 they correspond

or are shorter than the Na–O distances in sodium com-plexes of 18-membered crown ether (1:1 stoichiometry),where sodium fits the cavity.26 The transanular dis-tances O(1)Á Á ÁO(11)=5.18(1), O(4)Á Á ÁO(14)=5.05(1)and N(7)Á Á ÁN(17)=5.34(2) A ˚ reveal that the 20-mem-bered macrocyclic cavity of 11 is complementary to thesodium size and well suited for its binding. Two acetonemolecules complete sodium coordination number to 8.

The sequence of the torsion angles around macrocycleindicates its C 2 non-crystallographic symmetry. In thepolyether chains C–C and C–O bonds adopt usual cis-and anti - conformation. The organic ligand completely

encapsulates sodium cation and separates it well fromthe iodide counter ion. Iodine in the structure formsrelatively short contacts with macrocycle; it could beinterpreted as C–HÁ Á ÁI hydrogen bonds (Table 5).

Conclusion

10-Membered dibenzoazoxycrown ethers were obtainedby reduction of dinitropodands. It was found that thesecompounds exist in two forms Z and E of comparablestability in solutions. Thus, they present a good modelfor studies of this type of isomerization. Both forms areeasily distinguishable by chromatography, and by1H NMR and UV spectra. Properties of these isomersrelate to those of azocompounds applied in opticalmemory devices.1 Electrochemistry and photochemistryof these systems is under progress.

Both isomers of 10-membered azoxycrown ethers wereobtained in crystalline state and their X-ray structureswere established.

Other products of the reduction of podands were alsoisolated and characterized, namely the isomers of 10-membered azocrown ethers and 20-membered crownethers. The structure of a main dimeric 20-membered

azoazoxycrown product, formed during the reaction

Figure 6. Sodium iodide complex of compound 9..




in the presence of sodium ions, has been obtained byX-ray methods as its NaI complex.

Acknowledgements

Financial support from the Technical University of Gdansk (DS Grant No. 014169/003) is gratefully

acknowledged. The authors thank Professor J. B az.e-

jowski (University of Gdan ˜ sk) and Professor W. Woj-nowski (Technical University of Gdansk) for use of their KUMA diffractometers. The authors thank also E.Wagner-Wysiecka for UV–VIS measurements, andProf. J.F. Biernat for discussion.

References

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