Synthesis and properties of novel components for organic metals dihydrotellurophene derivatives Eva H. Mørkved,*a Gerardo Faccin,b Davide Manfrotto,b Helge Kjøsen,a James Y. Becker,c Lev Shapiro,c Arkady Ellern,c Joel Bernsteinc and Vladimir Khodorkovsky*c aDepartment of Organic Chemistry Norwegian University of Science and T echnology 7034 T rondheim Norway bDepartment of Chemistry University of Padova 35131 Padova Italy cDepartment of Chemistry Ben-Gurion University of the Negev Beer-Sheva 84120 Israel Two series of dihydrotellurophenes have been synthesized derivatives of 4,6-dihydro-1H,3,H-telluropheno[3,4-c]tellurophene (1) and derivatives of 1,3,6,8-tetrahydrobenzo[1,2-c;3,4-c¾]ditellurophene (2). X-Ray structure determinations confirm the tetraiodo structures of 1a and 2a. The tetraiodo derivatives are reduced by sodium borohydride to the corresponding dihydrotellurophenes 1b and 2b which undergo the characteristic divalent tellurium reaction with iodomethane to form telluronium methiodides.Both dihydrotellurophenes 1b and 2b are moderate electron donors and react with 7,7,8,8-tetracyanoqiunodimethane TCNQ aording blue semiconductive solids. The present study was initiated with the purpose of exploring a vicinal bis(bromomethyl) compound reacts with tellurium and a large excess of sodium iodide in 2-methoxyethanol to various aspects of dihydrotellurophene chemistry and in particular the potential of dihydrotellurophenes to form give a derivative of 2,2-diiodo-1,3-dihydrotellurophene. Compounds 1a and 2a were separated from unreacted tellurium conducting charge-transfer (CT) complexes with electron acceptors.A comprehensive survey of tellurium heterocycles with cold dimethyl sulfoxide (DMSO). Undissolved tellurium was filtered o and water was added to the DMSO filtrates has appeared recently,1 and some derivatives of dihydrotellurophene have been reported to form CT complexes with electron to precipitate pure 1a and 2a which were obtained as stable yellow or orange amorphous solids in fair to good yields acceptors.2,3 Methyl benzo and quinoxalino derivatives of 2,5- dihydrotellurophene form low conducting CT complexes with (60–80%). The identity of compound 1a was verified by 1H and 13C NMR mass and IR spectroscopy and microanalysis. 7,7,8,8-tetracyanoquinodimethane (TCNQ) or chloranil but the electronic structures of these complexes are not well Compound 2a was identified by spectroscopic means only.A reported synthesis5 of an [1,2-c;4,5-c¾] isomer of 2a understood. where the isomer was obtained as a yellow solid in comparable yields to 2a has been reinvestigated recently.6 The crude Results and Discussion [1,2-c;4,5-c¾] isomer precipitated as a yellow–orange solid and recrystallization from dimethylformamide (DMF) aorded The procedure reported by Ziolo and Gu� nther4 was used to prepare 4,6-dihydro-1H,3,H-telluropheno[3,4-c]tellurophene pure isomer as orange–red crystals in low yield (10–14%). However most of the crude product (80–90%) was recovered 1a and 2,2,7,7-tetraiodo-1,3,6,8-tetrahydrobenzo[1,2-c; 3,4- c’]ditellurophene 2a as outlined in Scheme 1. By this method as a yellow amorphous precipitate which was not further identified.Having this contradiction in mind we attempted to grow single crystals for X-ray crystal structure determinations of both 1a and 2a. Both compounds form shiny orange crystals from DMSO. Compound 2a forms a powdery precipitate at first but after several days the powder is replaced with crystals. The crystals of 1a are hygroscopic and convert into an amporphous solid in a few weeks. The X-ray diraction study of 2a shows that all three rings are almost planar within 0.0119 A ° (Fig. 1). The iodine atoms Scheme 1 Reagents i NaI MeOCH2CH2OH; ii NaBH4 EtOH; iii Fig. 1 Molecular structure of 2a showing 50% probability ellipsoids MeI MeNO2 J. Mater. Chem. 1997 7(9) 1697–1700 1697 are found on either side of and in a plane almost perpendicular the dark but somewhat unstable to light in good agreement with observations on dihydrobenzo[c]tellurophene.7 The to this ring system.The IMTeMI angles are 174–1760 and the TeMI bond lengths are in the range of 2.889(1)–2.940(1) A ° . structure of 2b was verified by 1H and 13C NMR spectroscopy and microanalysis. Compound 1b decomposes visibly in air In the five-membered rings the lengths of the saturated TeMC bonds are 2.120(4)–2.149(4) A ° and the CMTeMC angles are and light in less than 1 h. A high resolution mass spectrum was not obtained for this compound. However the 1H and 85.7(2)0. The most interesting feature of the 2a structure is the molecular packing. Firstly there is a distinct intermolecular 13C NMR spectra are in good agreement with the spectra reported for other dihydrotellurophene derivatives.8 interaction between an iodine atom of one molecule and the Reactions of dihydrotellurophenes with methyl iodide are Te atom of the next molecule.The Te,I intermolecular generally found to give the corresponding methyltelluronium contacts are 3.79–3.93 A ° which is significantly shorter than iodides.1 The precipitate from a reaction of 1b with methyl the sum of the van der Waals radii of the corresponding atoms iodide is slightly soluble in DMSO but the solution deposited (Te=2.06 I=2.06 A ° ). Secondly there is an interaction between some dark-grey solid apparently due to decomposition of the the Te atoms and the solvent the polar molecules of DMSO product. The 1H NMR spectrum of this product also supports are orientated in a crystal to form a Te,O contact of this observation since the strong singlet at d 2.15 (CH3) is 2.82–2.91 A ° (the van der Waals radius of oxygen is equal to mixed with several others of low intensity.In addition several 1.52 A ° ). Both kinds of intermolecular interaction complete the doublets at d 3.2–3.3 (CH2) are partly covered by the signal coordination of the Te atom to form a distorted octahedral from the residual H2O in the DMSO. Microanalysis shows a coordination (Fig. 2). somewhat higher content of tellurium and a correspondingly The geometrical parameters of 1a are very similar to those lower content of iodine than would be in good agreement with of 2a (Fig. 3). The iodine atoms are situated on either side of structure 1c. The analysis is consistent with loss of hydrogen the planar (within 0.009 A ° ) bicyclic ring system the IMTeMI iodide from one quarter of the tellurium moieties of 1c; in angle is 176.92(5)0 the TeMI bond lengths are other words one quarter of the methyldihydrotelluronium 2.735(2)–2.786(2) A ° and the CMTeMC angle is 86.2(4)0.The iodide rings have apparently been oxidized to T e–methyl- packing diagram of 1a exhibits the same type of intermolecular hydrotellurophene rings. interactions as for 2a i.e. the coordination number of Te is 6 The cyclic voltammetry measurements of 1b and 2b showed in a distorted octahedron. However the arrangement of molonly poorly resolved irreversible oxidation peaks at ca. ecules in the crystal is quite dierent. Whereas the ‘herringbone’ 1.3–1.5 V (vs. standard calomel electrode SCE on a glassy type structure is observed for 2a the layers of molecules in 1a carbon electrode).Reactions of 1b and 2b with TCNQ aorded are separated by layers of solvent molecues and the Te,I dark-blue microcrystalline powders. Conductivity of the shortened contacts (3.54 A ° ) are intralayer ones (Fig. 4). 1b–TCNQ complex is 1.3–2.5×10-5 and the conductivity of Diiododihydrotellurophenes 1a and 2a were reduced with 2b–TCNQ is ca. 5×10-7 S cm-1 (measured on pressed pellets sodium borohydride in ethanol to give the dihydrotellurofour probe measurements). Microanalysis of 2b–TCNQ indi- phenes 1b and 2b. Compound 2b is fairly stable when kept in cates a 151 adduct. The IR spectra of the present TCNQ complexes confirm the presence of TCNQ radical anions. Li–TCNQ a known radical anion salt of TCNQ has CN absorptions at 2202 and 2186 cm-1; the corresponding absorptions of the complexes a at 2218 2186 2211 and 2186 cm-1 (neutral TCNQ absorbs at 2224 cm-1).Other characteristic absorptions of Li–TCNQ at 1575 1508 1361 1349 and 1182 cm-1 are found at approximately the same wavenumbers for the 2b–TCNQ complex also. Conclusions The facile formation of the stable tetraiodo tellurophenotellurophene derivative 1a is demonstrated and its structure proved by X-ray diraction measurements. A reductive elimination of the four iodines on 1a gives compound 1b which is unstable to air and light and was therefore characterised by spectroscopic means only. Microanalysis of the adduct from 1b and methyl iodide indicates a 151 mixture of 1c and (1c–HI). Compound 2a was prepared in good yields and its structure has been proved by X-ray structure determination.Compound 2a was reduced to Fig. 2 Projection of the crystal structure of 2a in the bc plane the dihydrobenzotellurophene derivative 2b characterised by 1H and 13C NMR spectroscopy and C H microanalysis. Cyclic voltammetry indicates that both 1b and 2b are electron donors of moderate strength and they undergo irreversible oxidation. Both compounds react with TCNQ with the formation of semiconducting complexes. The IR spectra of both confirm the presence of TCNQ anion radicals. Compounds 1 and 2 merit further investigation and the continuation of our studies will be reported in due course. Experimental General Mass spectra were obtained on an AEI MS-902 spectrometer Fig. 3 Molecular structure of 1a showing 50% probability ellipsoids at 70 eV electron energy.IR spectra were obtained on a Nicolet 1698 J. Mater. Chem. 1997 7(9) 1697–1700 Fig. 4 Projection of the crystal structure of 1a in the bc plane 20-SXC FTIR spectrometer. 1H and 13C NMR spectra were 2a) was added tellurium (6 mmol) and sodium iodide (36 mmol). The suspension was stirred vigorously under reflux recorded on a JEOL EX400 NMR spectrometer at 399.65 and 100.40 MHz respectively and with tetramethylsilane (TMS) for 1 h. The bright orange precipitate was filtered o together with unreacted tellurium and washed with acetone to remove as internal standard. UV–VIS spectra were obtained on a Perkin-Elmer 500 UV–VIS spectrophotometer. Melting points iodine and sodium iodide. Water was added to the methoxyethanol filtrate and some additional orange precipitate was were obtained on a Bu� chi 530 apparatus and are uncorrected.Merck Kieselgel 60F 254 was used for TLC and Merck silica filtered o. The combined precipitate was dissolved in a minimal amount of DMSO at ambient temperature tellurium 63–200 mm was used for column chromatography. Microanalyses were performed by the Analytische was removed by filtration and water was added to the filtrate Laboratorien Lindlar Germany. whereupon compound 1a or 2a precipitated and was filtered The X-ray diraction measurements of 2a were carried out o and dried at ambient temperature at 1 Torr for 15 h. using a Syntex P-1 diractometer (Mo-Ka radiation graphite Compound 1a 1.51 g (59%) was a yellow amorphous solid monochromator h/2h scan 2h52 °). Crystal data monoclinic mp 200–210 °C (charring I2 evolved); MS [m/z (% rel.int.)] C10H10I4Te2·2DMSO 20 °C a=12.786(3) b=14.116(3) c= 384 (2.1) 382 (1.5) 338 (5.4) 336 (6.9) 332 (6) 128 (59.5) 15.266(3) A ° ; b=112.72(3) ° V=2601.0(9) A ° 3 Z=4 space 127 (32.2) 79 (100); u/cm-1 (KBr) 1618 (CNC) 1376 1133 group P21/c 5661 independent reflections. The structure was 1039 817 706 590; dH[(CD3)2SO] 3.95 (CH2 s); dc[(CD3)2SO] interpreted by direct methods and refined anisotropically using 45.85 126.29 (Found C 9.03; H 1.17; I 56.95; Te 32.30. Calc. SHELX93 to WR2=0.0689 GOF=1.05. The H-atoms were for C6H8I4Te2 C 8.55; H 0.96; I 60.22; Te 30.27%). placed in calculated positions and included in the calculations Compound 2a 1.3 g (51%) was a yellow–orange powder with fixed positional and isotropic thermal parameters. mp 240 °C (charring iodine evolved); MS [m/z (% rel.int.)] The X-ray diraction measurements of 1a were carried out 389 (2.3) 388 (1.6) 386 (2.1) 384 (7.2) 260 (13) 258 (26.4) using a Syntex P-1 diractometer (Mo-K a radiation graphite 256 (21.6) 254 (67.8) 128 (70) 127 (57.4) 45 (100); dH monochromator h/2h scan 2h60 °). Because of the very weak [(CD3)2SO] 4.68 (4H s) 4.82 (4H s) 7.28 (2H s); u/cm-1 diracting capacity of 1a the crystals were tested for the (KBr) 2923 2874 1688 1453 1354 1092 832. possibility of low temperature measurements. However all Preparation of a crystalline sample of 1a. Compound 1a attempts to reach low temperature resulted in the destruction (100 mg) was mixed with DMSO (1 ml) and the mixture was of the samples due to transformation into a microcrystalline state. Measurements were therefore carried out at ambient filtered through glass wool.The yellow solution was left in a temperature. Crystal data monoclinic C6H8I4Te2·2DMSO stoppered vial for ca. four weeks. Crystals separated slowly 20 °C a=12.336(3) b=11.008(3) c=8.660(2) A ° ; b= from the solution. 102.22(2) ° V=1149.3(5) A ° 3 Z=4 space group P21/c; 3493 Crop 1. Some of the crystals were collected with a spatula and independent reflections. The semiempirical y-scan absorption washed with diethyl ether. These crystals had decomposed in correction was used. The structure was interpreted by direct air after ca. two weeks. methods and refined anisotropically using SHELX93 toWR2= Crop 2. This was used for X-ray analysis. 0.1973 [(R1=0.087 for 1838 reflections with F>4s(F)] 100 Preparation of a crystalline sample of 2a.Compound 2a refined parameters; GOF=1.05. The H-atoms were placed in (60 mg) was mixed with DMSO (1 ml) and the lemon coloured calculated positions and included in the calculations with fixed suspension was filtered (gravity) through glass wool. The positional and isotropic thermal parameters. The poorly yellow–orange filtrate became cloudy and after 12 h a pale diracting sample and the disorder of the solvent moecules yellow fluy precipitate appeared. After one week some orange lead to a comparatively high R-factor. crystals had formed but some of the yellow powdery precipitate 1,4-Dibromo-2,3-bis(bromomethyl)but-2-ene mp 159– was present as well. After 10 d all of the yellow precipitate had 160 °C (recrystallized twice from ethyl acetate) was prepared9 been replaced with shiny orange crystals.Some of the crystals from 2,3-dimethylbutane; lit.9 mp 158–159 °C. 1,2,3,4-Tetrakis were collected with a spatula washed with diethyl ether and (bromomethyl)benzene mp 116–118 °C (ethanol) was presubjected to X-ray analysis. pared10 from 1,2,3,4-tetramethylbenzene; lit.10 mp 124–126 °C. Preparation of 4,6-dihydro-1H,3H-telluro- Preparation of 2,2,5,5-tetraiodo-4,6-dihydro-1H,3Hpheno[ 3,4-c]tellurophene 1b and 1,3,6,8-tetrahydro- telluropheno[3,4-c]tellurophene 1a and 2,2,7,7-tetraiodo- 1,3,6,8-tetrahydrobenzo[1,2-c;3,4-c¾]ditellurophene 2a benzo[1,2-c;3,4-c¾]ditellurophene 2b. General procedure. A suspension of sodium borohydride General procedure. To a solution of the bromomethyl compound (3 mmol) in 2-methoxyethanol (8 ml for 1a 25 ml for (0.64 g 16 mmol) in ethanol (35 ml ) was added dropwise J.Mater. Chem. 1997 7(9) 1697–1700 1699 during 10 min to a stirred suspension of 1a or 2a (2 mmol) in Compound 1b+TCNQ; dark-blue powder/microcrystals. u/cm-1 (KBr) 2218 (w) 2186 1657 1592(s) 1377 (s) 1262 (s) ethanol (25 ml ) kept at 0 °C. A grey precipitate formed upon 1106 1014 637. addition of the reducing agent. The reaction mixture was Compound 2b+TCNQ; dark blue powder/microcrystals. protected from light and stirred at 0 °C for 1 h after complete u/cm-1 (KBr) 2950 (w) 2211 (sh) 2185 (s) 2120 (sh) 1658 addition. Water (60 ml ) was added and the suspension was (sh) 1595 1566 (sh) 1502 1475 1443 1366 1344 1244 1189 extracted with benzene (3×40 ml) and dichloromethane (Found C 47.08; H 3.44; N 7.67. Calc. for C22H14N4Te2 C (3×40 ml) for 1b or chloroform (3×15 ml) for 2b.The organic 44.82; H 2.39; N 9.50; Te 43.28%). extracts were filtered and evaporated to dryness atmbient Li–TCNQ (reference). u/cm-1 (KBr) 2202 2186 1575 1508 temperature. 1361 1349 1182. Compound 1b 0.36 g (54%) mp 155–160 °C (black sintering) 180 °C (gas evol.) MS [m/z (% rel. int.)] 340 (26 M Preparation of 2,5-diiodo-2,5-dimethyl-4,6-dihydro-1H,3H- 130Te,130Te) 338 (50.5,M 130Te,128Te) 336 (50.7,M,128Te,128Te) telluropheno[3,4-c]tellurophene 1c 335 (13.6) 334 (35.6 M 128Te,126Te) 332 (20 M 126Te,126Te) 254 (22.3) 130 (12.0) 128 (10.5) 126 (6.6) 79 (100); u/cm-1 Iodomethane (0.34 g 2.4 mmol) was added to a solution of 1b (KBr) 1437 1270 1120 1070 (s) 777 (s) 629 (s) 587; (0.034g 0.1 mmol) in benzene (10 ml ) at ambient temperature. dH[(CD3)2SO] 3.74 (CH2 s); dc[(CD3)2SO] 3.33 125.99.The precipitate was filtered o washed with diethyl ether and Compound 2b 1.79 g was a yellow–grey powder air dried; 1c 0.06 g (70%) grey amorphous solid mp 160 °C mp>300 °C (discoloured 170 °C). The work-up procedure for (sintering black). u/cm-1 (KBr) 3411 2902 1391(v.s) 1130 this compound was modified since a substantial part of 2b 1069 871 631; dH[(CD3)2SO] 2.15 (CH3 s) 3.2–3.3 (CH2 was undissolved after the first chloroform extraction and H2O m) [Found C 16.65; H 2.18; I 33.35; Te 47.10. Calc. for settled as a yellow powder at the bottom of the separation 0.5 (C8H14I2Te2+C8H13ITe2) C 17.54; H 2.48; I 33.41; Te funnel. This solid was taken out through the bottom of the 46.58%]. funnel and dried and was found to be spectroscopically identical to the rest of 2b obtained from the chloroform E.H.M.thanks the Norwegian University of Science and extracts; MS [m/z (% rel. int.)] 390 (9.0 M 130Te,130Te) 388 Technology Trondheim Norway for support and a sabbatical (16.8 M 128Te,130Te) 386 (19.4 M 128Te,128Te) 384 (11.9 M leave of absence. G.F. and D.M. thank the ERASMUS 128Te,126Te) 382 (6.7 M 126Te,126Te) 258 (4.9) 256 (2.5) 130 Interuniversity Cooperation Programme for the award of (100) 129 (17.1) 128 (14.7) 115 (17.3); u/cm-1 (KBr) 2919 student exchange grants. 2873 1468 1353 1090 1028 838; dH[(CD3)2SO] 4.47 (8H s) 6.98 (2H s); dH(CDCl3) 4.53 (4H s) 4.59 (4H s) 6.95 (2H s); References dc [(CD3)2SO] 8.10 125.94 (Found C 28.02; H 2.37. Calc. for 1 Chemistry of Heterocyclic Compounds ed. E. C. Taylor Vol. 53 C10H10Te2 C 31.17; H 2.62; Te 66.21%).M. R. Detty and M. B. O’Regan T ellurium Containing Heterocycles Wiley New York 1994. 2 K. Y. Abid and W. R. McWhinnie J. Organomet. Chem. 1987 Reactions of 1b and 2b with TCNQ 330 337. 3 H. B. Singh W. R. McWhinnie R. F. Ziolo and C. H. W. Jones General procedure. The dihydrotellurophenes 1b or 2b J. Chem. Soc. Dalton T rans. 1984 1267. (0.05 mmol) and TCNQ (0.05 mmol) were dissolved separately 4 R. F. Ziolo and W. H. H. Gu� nther J. Organomet. Chem. 1978 in minimum amounts of warm acetonitrile. The two solutions 146 245. were mixed heated under reflux for 1 h and then filtered to 5 H. B. Singh P. K. Khanna and S. K. Kumar J. Organomet. Chem. remove small amounts of undissolved material. The reaction 1988 338 1. mixture from 1b darkened almost immediately whereas the 6 H.A. Al-Shirayda Heteroatom Chem. 1993 4 537. 7 E. Cuthbertson and D. D. MacNicol T etrahedron L ett. 1975 one from 2b became gradually darker over several hours. The 1893. solutions were transferred to open beakers and were left for 8 J. Bergman and L. Engman J. Am. Chem. Soc. 1981 103 2715. slow evaporation at ambient temperature and finally at ca. 9 H. Stetter and E. Tresper Chem. Ber. 1971 104 71. 50 °C. Some red–brown material settled on the upper part of 10 J. T. Stapler and J. Bornstein J. Heterocycl. Chem. 1973 983. the walls of the beakers whereas dark-blue–black crystals that eventually formed at the bottom of the beakers were collected. Paper 7/00975E; Received 11th February 1997 1700 J. Mater. Chem. 1997 7(9) 1697–17