Synthesis and X-ray crystal structure of a vinylogue of tetramethyltetraselenafulvalene Martin R. Bryce,* Antony Chesney, Shimon Yoshida, Adrian J. Moore, Andrei S. Batsanov and Judith A. K. Howard Department of Chemistry, University of Durham, Durham, UK DH1 3L E Efficient syntheses of 2,2¾-ethanediylidenebis(4,5-dimethyl-2H-1,3-diselenole) 14 and the 1,3-dithiole analogue 16 are described. Cyclic voltammetry establishes that they are efficient p-electron donors. The molecular structures of 14 and 16 have been determined by single crystal X-ray analysis: the crystals are isomorphous and the molecules form planar layers parallel to the crystallographic (10 2) plane.The study of molecular conductors1 has progressed rapidly which is a charge-density wave localisation inherent to one dimensional conducting systems.5 since the discovery that the charge-transfer complex of the pelectron donor tetrathiafulvalene (TTF) 1 and the p-electron The incorporation of conjugated alkene linking groups between the two 1,3-dithiole rings of TTF has been widely explored as a structural modification to the p-donor unit.6,7 The rationale behind the design of TTF derivatives with extended conjugation is twofold: (i) the oxidised states responsible for conduction in charge-transfer complexes and radical cation salts should be stabilised by decreased intramolecular Coulombic repulsion, and (ii) increased spacial extension of the p-framework should lead to increased dimensionality. There is now clear evidence from detailed solution electrochemical studies on several 2,2¾-ethanediylidenebis(1,3-dithiole) derivatives, e.g.the parent system 4a,6a,b that the second oxidation potential is significantly lower than that of TTF 1. The vinylogue 5 of BEDT-TTF 3 was recently synthesised independently and concurrently by three research groups.6c–e Although,to date, donor 5 has not yielded any superconducting salts, a recent report that donor 6a, which comprises a closelyrelated vinylogous TTF framework, affords a superconducting Au(CN)2 salt6h has added a new impetus to studies on these systems,and a 1,3-diselenole analogue 6b has been synthesised.8 Here we describe the synthesis of compound 14, which is the first reported vinylogue of TMTSF 2, along with the X-ray crystal structure and solution electrochemical properties of this new p-electron donor.The synthesis, X-ray crystal structure and electrochemistry of the tetramethyldiselenadithiafulvalene analogue 16 are also reported for the first time. acceptor tetracyano-p-quinodimethane (TCNQ) exhibited met- Results and Discussion allic conductivity.2 Salts of the related p-donor molecule tetramethyltetraselenafulvalene (TMTSF) 2 provided the first Synthesis family of organic superconductors3 and the synthesis of new multi-chalcogen p-electron donors has remained at the fore- The synthesis of 14 is presented in Scheme 1.The key step in assembling the vinylogous TMTSF skeleton is the Wittig front of research, with a few systems, notably bis(ethylenedithio)- tetrathiafulvalene (BEDT-TTF) 3, providing radical cation reaction of aldehyde 13 with the phosphorus ylide derived from reagent 12, for which the starting material was the known salts which are organic superconductors with Tc values as high as ca. 12 K.4 The complex TTF–TCNQ, is considered to be a selone 7.9 Methylation of 7 using methyl trifluoromethanesulfonate yielded the 1,3-diselenolium cation salt 8 which, upon one-dimensional metal, whereas salts of TMTSF 2 and BEDTTTF 3 are characterised by an increase in dimensionality reduction with sodium cyanoborohydride, yielded the unstable selenoether 9.Conversion of compound 9 into the 1,3-diselenol- of their transport properties, arising from close interstack chalcogen···chalcogen interactions. This effect is known to ium cation 10 was achieved by treatment with tetrafluoroboric acid in diethyl ether.Salt 10 was isolated as a very hygroscopic, stabilise the metallic state by suppressing the Peierls distortion, 381 J. Mater. Chem., 1997, 7(3), 381–385382 Scheme 2 Reagents and conditions: i, BuLi, THF, -78 °C, 0.25 h; ii, 13, THF, -78�20 °C, 12 h Fig. 1 Molecular structure of 16; symmetrically related atoms are primed Table 1 Bond lengths from the crystal structures of 14 and 16 bond lengths/A° 14(X=Se) 16(X=Se/S) Scheme 1 Reagents and conditions: i, CF3SO3Me, CH2Cl2, 20°C, 2 h; ii, NaCNBH3, THF, 20 °C, 0.25 h; iii, HBF4, Et2O, 0 °C, 0.5 h; iv, C(1)–X(1) 1.897(3) 1.847(3) PPh3, MeCN, 20 °C, 12 h; v, PBu3, MeCN, 20°C, 0.5 h; vi, Et3N, C(1)–X(2) 1.895(3) 1.848(3) MeCN, 20 °C, 0.25 h; vii, glyoxal (aq), 20 °C, 3 h; viii, KOBut, MeCN, C(1)–C(4) 1.353(4) 1.348(5) 20 °C, then immediately compound 13, 20°C, 0.66 h X(1)–C(3) 1.906(3) 1.865(3) X(2)–C(2) 1.908(3) 1.870(3) C(2)–C(3) 1.342(4) 1.344(5) unstable solid, which was used immediately in the next step.C(4)–C(4¾) 1.437(5) 1.440(7) The overall yield for the three-step sequence 7�10 was typically 70–75%. Cation salt 10, upon reaction with triphenylphosphine or tributylphosphine, yielded the unstable Table 2 Crystal data for 14 and 16 salts 11 and 12, respectively: the former could be isolated as a pink solid, but the latter decomposed rapidly and could not 16 14 be isolated.Therefore, compound 12 was used immediately formula C12H14S2Se2 C12H14Se4 after preparation. Deprotonation of 11 with triethylamine at M 380.3 474.1 0°C gave a transient ylide which was intercepted in situ with a/A° 6.411(1) 6.483(1) aqueous glyoxal to furnish the desired vinylogous aldehyde 13 b/A° 6.837(1) 6.873(1) (70% yield) as a pale yellow solid which could be conveniently c/A° 8.337(1) 8.378(1) stored under an inert atmosphere at 0°C for up to four weeks.a(°) 70.35(1) 70.48(1) The ylide from triphenylphosphine reagent 11 was not suffic- b(°) 81.76(1) 81.67(1) c(°) 82.47(1) 82.44(1) iently activated to react with the conjugated aldehyde group setting reflns 478 512 of 13, so we used the more reactive tributylphosphine analogue h range(°) 10–30 10–30 12, drawing on our experience of 1,3-dithiole Wittig chemis- V /A° 3 339.25(8) 346.75(8) try.10 Thus, sequential addition of potassium tert-butoxide and Dx/g cm-3 1.86 2.27 aldehyde 13 to salt 12 yielded the target compound 14 as an m(Mo-Ka)/cm-1 57.3 105.5 air-stable, bright yellow crystalline solid in 70% yield.crystal size/mm 0.4×0.1×0.06 0.4×0.22×0.14 min./max. transmission 0.338/0.736 0.077/0.325 Similarly, the tetramethyldiselenadithiafulvalene analogue 16 data total 2833 3106 was obtained (78% yield) by deprotonation of 1,3-dithiole data unique 1808 1841 reagent 15 using butyllithium, following the known pro- Rinta 0.080, 0.040 0.122, 0.033 cedure,11 followed by addition of aldehyde 13 (Scheme 2).data observed, |F|>4s(F) 1615 1694 R(F, obs. data) 0.039 0.028 X-Ray molecular structures of 14 and 16 wR(F2, all data) 0.100 0.073 goodness-of-fit 1.23 1.15 The molecular structures of compounds 14 and 16 have been Dr max, min/e A° -3 0.73, -0.67 0.45, -1.16 determined by single crystal X-ray analysis.Crystals of 14 and 16 are isomorphous. Both molecules (Fig. 1, Tables 1 and 2) aBefore and after the absorption correction.J . Mate r . Chem., 1997, 7(3), 381–385 383 Table 3 Cyclic voltammetric data for new vinylogous systems 14 and possess a crystallographic inversion centre and adopt small 16, with selected compounds for comparison.Data are versus Ag/AgCl, chair-like distortions, the dithiole/diselenole rings folding by unless otherwise stated 7.8 (14) and 7.0° (16) along the S(Se)···S(Se) vectors. In 16 the Ci molecular symmetry is spurious, due to disorder, which Compound E11/2/V E21/2/V DE/V makes the S and Se atoms indistinguishable.This observation 1 TTF 0.34 0.71 0.37 has precedent in other mixed sulfur/selenium tetrachalcogeno- TSFa,b 0.48 0.76 0.28 fulvalene derivatives.12 The C(1)NC(4) and C(4)–C(4¾) bond 4ac 0.20 0.36 0.16 distances are similar to thos other planar systems of this 4bc 0.26 0.40 0.14 kind6d,f and indicate a small degree of p-delocalisation (ca. 4cc 0.32 0.47 0.14 10%).13 TMTTFa,c 0.25 0.61 0.36 Molecules in the crystals are arranged in planar layers 2 TMTSFd 0.44 0.72 0.28 4dc 0.19 0.34 0.15 parallel to the crystallographic (10 2) plane (Fig. 2). Molecules 16 0.29 0.44 0.15 within a layer, related via the b translation, form intermolecular 14 0.36 0.50 0.14 chalcogen···chalcogen contacts of 3.87 (in 14) and 3.90 A° (in 16). The latter (effectively, Se···S) distance is slightly longer aTSF=tetraselenafulvalene; TMTTF=tetramethyltetrathiafulvalene.than the sum of the van der Waals radii of selenium (2.0 A° )13 bRef. 16. cRef. 6(b). dRef. 17. Data taken from ref. 16, reported using and sulfur (1.8 A° ),14 while the former (Se···Se) contact is shorter Et4NClO4 in MeCN versus SCE. than the double radius of selenium. It is noteworthy that the substitution of Se for S causes no appreciable expansion of the structure along the y axis [b=6.837(1) A° in 16 vs. 6.873(1) A° in 14, while the difference between the S and Se radii should the following general trends in the redox properties. With have contributed 0.2 A° per unit cell translation]. The effect increasing conjugative length there is (i) a lowering of both can be attributed to the higher atomic polarisability of Se redox potentials (especially E21/2) due to the increased electron compared to S (3.77×10-24 and 2.90×10-24 cm3, respect- delocalisation and (ii) a smaller difference (DE) between E11/2 ively15), which makes the electron shell of the former easier to and E21/2 (tending to zero as the conjugation length increases), deform to maximise the packing density elsewhere, but is also indicative of increased stabilisation of the dicationic state as a favourable for stronger intermolecular interactions.The result of increased charge separation (and thus reduced on-site interplanar separations between the layers are ca. 3.68 (14) Coulombic repulsion). For the series 4d,6b 16 and 14 it is and 3.64 A° (16), with only partial overlap between the noteworthy that the oxidation becomes harder by sequentially molecules.substituting selenium atoms for sulfur whilst DE is essentially unaffected by selenium replacement. These observations are Solution electrochemistry attributable to a decrease in p-orbital interaction between the carbon framework and the heteroatom as a result of increasing The solution redox properties of donors 14 and 16 have been heteroatom size.16 studied by cyclic voltammetry and the results are collated in Table 3, along with selected model compounds for comparison.The new extended compounds are very efficient p-electron Conclusions donors; they display the expected two reversible, one-electron In summary, we have achieved the first synthesis of a vinylogue redox couples.These data are entirely consistent with previous of TMTSF 2, namely 2,2¾-ethanediylidenebis(4,5-dimethyl-2H- work with vinylogous TTF systems,6 which has established 1,3-diselenole) 14. The 1,3-dithiole analogue 16 is also reported. These new compounds are very efficient p-electron donors, and X-ray structural analysis of 14 and 16 reveals that the molecules are arranged in planar layers.This combination of structural and electrochemical properties makes compounds 14 and 16 promising candidates for the formation of conducting or superconducting radical ion salts. Experimental General details Details of equipment and procedures are the same as those reported recently.18 Solvents and reagents employed were standard reagent grade and were used as received unless otherwise stated.All anhydrous solvents were obtained by standard techniques and acid-free CH2Cl2 was prepared by either washing with dilute sodium hydrogen carbonate or filtration through basic alumina, followed by distillation prior to use. Cyclic voltammetric experiments were performed using 10-5 M donor and 0.1 M Bu4NClO4 in dry MeCN under argon Fig. 2 Crystal packing of 14, showing short intermolecular Se···Se versus Ag/AgCl, Pt working and counter electrodes, 20°C, contacts (<4 A°). Symmetrically related atoms are primed; H atoms are omitted. recorded on a BAS 50W electrochemical analyser.384 4,5-Dimethyl-2-methylseleno-1,3-diselenolium (4,5-Dimethyl-2H-1,3-diselenol-2-yl )tributylphosphonium trifluoromethanesulfonate 8 Tetrafluoroborate salt 10 (65 mg, 0.198 mmol) was dissolved To a stirred solution of 4,5-dimethyl-2H-1,3-diselenole-2-selone in dry MeCN (20 cm3) under argon at 20°C and treated with 79 (300 mg, 0.98 mmol) in dry CH2Cl2 (25 cm3) was added freshly distilled tributylphosphine (0.07 cm3, 0.26 mmol).The methyl trifluoromethanesulfonate (0.14 cm3, 1.22 mmol). The orange solution immediately decolorised and was left to stir resultant mixture was stirred under an argon atmosphere for for 0.5 h whereupon it was used directly in the preparation 2 h at 20°C whereupon the volume of the mixture was reduced of 14.to ca. 5 cm3 in vacuo. Addition of anhydrous diethyl ether precipited a solid, which was filtered, washed with diethyl ether 2-(4,5-Dimethyl-2H-1,3-diselenol-2-ylidene)ethanal 13 and dried to give 8 (400 mg, 87%) as an unstable pale yellow To a solution of reagent 11 (260 mg, 0.53 mmol) in MeCN solid, mp 120–121 °C (Calc.for C7H9F3O3SSe3: C, 17.87; H, (20 cm3) was added triethylamine (0.11 cm3, 0.8 mmol) and 1.91. Found: C, 19.19; H, 2.37%); dH (CDCl3) 3.17 (3H, s), 2.67 the mixture was stirred for 15 min at 20°C, whereupon glyoxal (6H, s).(1.0 cm3 of a 40% aqueous solution, excess) was added and the solution stirred at room temperature for 3 h. The mixture 4,5-Dimethyl-2-methylseleno-2H-1,3-diselenole 9 was diluted with water (50 cm3), extracted with CH2Cl2 To a solution of salt 8 (400 mg, 0.86 mmol) in anhydrous THF (2×50 cm3), the organic portions were combined and dried (30 cm3) under argon at 20°C was added sodium cyanoborohy- (MgSO4), and the solvent removed in vacuo.The residue was dride (1 M in THF, 1.07 mol, 1.07 cm3) dropwise over 2 min. purified by column chromatography on neutral alumina, The yellow solution rapidly turned light orange and was initially with CH2Cl2–hexane as eluent (152 v/v) followed by maintained at 20°C for 15 min. At this point, the THF was CH2Cl2, to afford 13 (100 mg, 70%) as a pale yellow solid, mp removed in vacuo and the residue taken up in a mixture of 65–67°C; m/z (80Se, DCI) 269 (MH+, 100%) (HRMS: Calc.diethyl ether (50 cm3) and water (50 cm3). The aqueous phase for C7H8OSe2, 267.8906. Found, 267.9071); dH(CDCl3) 9.46 was separated and washed with diethyl ether (2×50 cm3), the (1H, d, J 1.8), 7.20 (1H, d, J 1.8), 2.17 (3H, s), 2.13 (3H, s); dC organic layers were combined and dried (MgSO4). Removal (CDCl3 ) 182.7, 161.5, 133.0, 126.5, 114.0, 15.7, 15.6; of the solvent in vacuo afforded compound 9 (257 mg, 93%) nmax(KBr)/cm-1 1605 (CNO). as a bright yellow solid (mp 61–63 °C) which was essentially pure by 1H NMR spectroscopy. Correct elemental analysis 2,2¾-Ethanediylidenebis(4,5-dimethyl-2H-1,3-diselenole) 14 could not be obtained due to the rapid decomposition of 9 during handling (with the liberation of methyl selenol) (Calc.To a stirred solution of phosphonium salt 12 in anhydrous for C6H10Se3 : C, 22.59; H, 3.16. Found: C, 24.15; H, 3.00%); MeCN, as prepared above, at 20°C was added potassium tertm/ z (DCI, 80Se) 322 (M+, 5%), 226 (M+-MeSeH, 100); butoxide (22 mg, 0.198 mmol) followed by the immediate dH(CDCl3) 5.9 (1H, s), 2.2 (3H, s), 1.95 (6H, s).addition of an MeCN solution of aldehyde 13 (58 mg, 0.216 mmol). The mixture turned deep orange on addition of 4,5-Dimethyl-1,3-diselenolium tetrafluoroborate 10 the butoxide and then bright yellow with the formation of a white precipitate on addition of the aldehyde. The mixture was To an ice-cooled solution of 9 (240 mg, 0.75 mmol) in anhy- stirred for 40 min and then the solvent was evaporated in drous diethyl ether (20 cm3) was added dropwise over 5 min vacuo to afford a brown residue which was flushed through a tetrafluoroboric acid (0.82 mmol, 0.14 cm3 of a 54% complex column containing a short plug of neutral alumina using acid- in diethyl ether).After 0.5 h, the pink solid which had precipi- free CH2Cl2–hexane mixture (151 v/v) as the eluent, to yield tated was rapidly filtered and washed with dry diethyl ether yellow crystals contaminated with a small amount of an (50 cm3) to afford 10 (217 mg, 89%) as an extremely hygro- unidentified orange oil.After washing this product with diethyl scopic, salmon-pink solid which was used directly in sub- ether, compound 14 (80 mg, 85%) was isolated as bright yellow sequent reactions.crystals, mp 244–245 °C (from CS2) (Calc. for C12H14Se45C, 30.37; H, 2.95. Found: C, 30.22; H, 2.91%); m/z (80Se, DCI) (4,5-Dimethyl-2H-1,3-diselenol-2-yl )triphenylphosphonium 477(M+, 100%); dH(CDCl3 ) 5.95 (2H, s), 1.95 (12H, s); tetrafluoroborate 11 nmax(KBr)/cm-1 1647, 1519, 792; lmax(MeCN)/nm (e) 371 Tetrafluoroborate salt 10 (250 mg, 0.77 mmol) was dissolved (1.9×104).A crystal of 14 suitable for X-ray analysis was in dry MeCN (30 cm3) under argon at 20°C and treated with grown by slow evaporation of a CS2 solution. triphenylphosphine (220 mg, 0.85 mmol). The resultant solution was stirred under argon for 12 h, by which time the 2-[2-(4,5-Dimethyl-2H-1,3-diselenol-2-ylidene)ethylidene]-4,5- solution had turned deep red.The volume of the mixture was dimethyl-2H-1,3-dithiole 16 reduced in vacuo to ca. 2 cm3 before ice-cold anhydrous diethyl To a stirred solution of compound 1511 (35 mg, 0.15 mmol) in ether (50 cm3) was added. The resultant solution was stirred dry THF (20 cm3) under argon at -78 °C was added BuLi at room temperature for 15 min, whereupon an off-white solid (0.1 cm3 of a 1.6 M solution in hexane, 0.16 mmol) and the precipitated.The diethyl ether was decanted off and the solid solution stirred for 15 min. Compound 13 (35 mg, 0.13 mmol) washed rapidly with ice-cold anhydrous diethyl ether in dry THF (5 cm3) was then added and stirring continued at (2×20 cm3). The solid was dried under high vacuum to afford -78°C for 1 h and the reaction mixture was allowed to reach 11 (260 mg, 70%) as a hygroscopic pink solid, mp 46–50 °C; dH(CDCl3) 7.8–7.6 (15H, m), 6.85 (1H, d, J 4.7†), 2.0 (6H, s). 20°C (ca. 15 h). The solvent was evaporated, water (10 cm3) was added and the residue was extracted with CH2Cl2 (acidfree, 3×25 cm3). The combined extracts were washed with † J values given in Hz.J .Mate r . Chem., 1997, 7(3), 381–385 385 Chem. Soc., 1981, 103, 2440; (b) K. Bechgaard and D. Je�rome, Sci. water (2×10 cm3) and dried (MgSO4), and the solvent was Am., 1982, 247, 50. evaporated. Column chromatography of the residue on neutral 4 (a) A. M. Kini, U. Geiser, H. H. Wang, K. D. Carlson, alumina eluting with hexane–toluene (251 v/v) afforded com- J. M. Williams, W.K. Kwok, K. G. Vandervoot, J. E. Thompson, pound 16 (39 mg, 78%) as a yellow solid, mp 242–243 °C D. L. Stupka, D. Jung and M-H. Whangbo, Inorg.Chem., 1990, 29, (from CS2 ) (Calc. for C12H14S2Se2 : C, 37.90; H, 3.71. Found: 2555; (b) J. M. Williams, J. R. Ferraro, R. J. Thorn, K. D. Carlson, U. Geiser, H. H. Wang, A. M. Kini and M-H. Whangbo, Organic C, 38.13 H, 3.98%); m/z (80Se, DCI) 382 (M+, 100%); Superconductors (including Fullerenes), Prentice Hall, New Jersey, dH[CS2–(CD3)2CO] 6.12 (1H, d, J 10.5), 5.55 (1H, d, J 10.5), 1992. 1.95 (3H, s), 1.94 (3H, s), 1.90 (3H, s), 1.89 (3H, s); 5 S. Roth, One-Dimensional Metals, VCH, Weinheim, 1995. nmax(KBr)/cm-1 1630, 1501; lmax(MeCN)/nm (e) 393 6 (a) Z. Yoshida, T. Kawasi, H. Awaji, I. Sugimoto, T. Sugimoto and (1.8×104).A crystal suitable for X-ray analysis was grown by S. Yoneda, T etrahedron L ett., 1983, 24, 3469; (b) T. Sugimoto, H. Awaji, I. Sugimoto, Y. Misaki, T. Kawase, S. Yoneda and slow evaporation of a CS2–hexane solution. Z. Yoshida, Chem. Mater., 1989, 1, 535; (c) V. Yu Khodorkovskii, L. N. Veselova and O. Ya. Neiland, Khim. Geterotsikl. Soedin., 1990, 130 (Chem. Abstr., 1990, 113, 22868); (d) A.J. Moore, M. R. X-Ray crystallography Bryce, D. J. Ando and M. B. Hursthouse, J. Chem. Soc., Chem. Commun., 1991, 320; (e) T. K. Hansen, M. V. Lakshimikantham, Single-crystal diffraction experiments were carried out at T= M. P. Cava, R. M. Metzger and J. Becher, J. Org. Chem., 1991, 56, 150 K on a Siemens 3-circle diffractometer with a CCD area 2720; (f ) M.R. Bryce, M. A. Coffin and W. Clegg, J. Org. Chem., detector, using graphite monochromated Mo-Ka radiation 1992, 57, 1696;(g)M.Salle�,M.Jubault, A. Gorgues, K. Boubekeur, (l=0.71073 A° ). The yellow plate-like crystals of 14 and 16 M. Fourmigue�, P. Batail and E. Canadell, Chem. Mater., 1993, 5, were isomorphous, in triclinic space group P1� (No. 2), Z=1. 1196; (h) Y. Misaki, N.Higuchi, H. Fujiwara, T. Yamabe, T. Mori, H. Mori and S. Tanaka, Angew. Chem., Int. Ed. Engl., 1995, 34, A hemisphere of data with 2h 61° were collected in an v 1222; (i ) Y. Misaki, T. Ohta, N. Higuchi, H. Fujiwara, T. Yamabe, scan mode (0.3° steps) and corrected for absorption using the T. Mori, H. Mori and S. Tanaka, J. Mater. Chem., 1995, 5, 1571; Gaussian integration technique for the real crystal shape (8 ( j) D.Lorcy, R. Carlier, A. Robert, A. Tallec, P. Le Magueres and and 6 faces indexed, respectively). The structures were solved L. Ouahab, J. Org. Chem., 1995, 60, 1443; (k) M. R. Bryce, by direct methods and refined by full-matrix least-squares A. J. Moore, B. K. Tanner, R. Whitehead, W. Clegg, F. Gerson, A. Lamprecht and S. Pfenninger, Chem.Mater., 1996, 8, 1182.(non-H atoms with anisotropic displacement parameters; the 7 For reviews on vinylogous TTF donors see: (a) Z. Yoshida and disordered Se/S atoms in 16 were refined at common sites with T. Sugimoto, Angew. Chem., Int. Ed. Engl., 1988, 27, 1573; 0.5/0.5 occupancies; all H atoms refined in isotropic approxi- (b) M. R. Bryce, J. Mater. Chem., 1995, 5, 1481. mation; 101 variables) against F2 of all data, using SHELXTL 8 Y.Misaki, H. Fujiwara, T. Yamabe, T. Mori, H. Mori and software.19 Crystal data and experimental details are listed S. Tanaka, Chem. Commun., 1996, 363. 9 K. Bechgaard, D. O. Cowan, A. N. Bloch and L. Henriksen, J. Org. in Table 2. Chem., 1975, 40, 746. Atomic coordinates, thermal parameters, and bond lengths 10 A. J. Moore and M.R. Bryce, unpublished observations. See also and angles have been deposited at the Cambridge references 6(a) and 6(b) in which tributylphosphine is used exclus- Crystallographic Data Centre (CCDC). See Information for ively in similar reactions. Authors, J. Mater. Chem., 1997, Issue 1. Any request to the 11 K. Akiba, K. Ishikawa and N. Inamoto, Bull. Chem. Soc. Jpn., 1978, 51, 2674; A.J. Moore and M. R. Bryce, J. Chem. Soc., Perkin CCDC for this material should quote the full literature citation T rans. 1, 1991, 157. and the reference number 11451/24. 12 (a) A. Mhanni, L. Ouahab, D. Grandjean, J. Amouroux and J. M. Fabre, Acta Crystallogr., Sect. C, 1991, 47, 1980; (b) S. Triki, L. Quahab, D. Grandjean, J. Amouroux and J. M. Fabre, Acta We thank EPSRC for funding this work.Crystallogr., Sect. C, 1991, 47, 1941. 13 L. Pauling, T he Nature of the Chemical Bond, 3rd edn., Cornell University Press, Ithaca, 1960. 14 G. Filippini and A. Gavezzotti, Acta Crystallogr., Sect. B, 1993, References 49, 868. 1 (a) J. R. Ferraro and J. M. Williams, Introduction to Synthetic 15 T. Miller and B. Bedeson, Adv. Atom. Mol. Phys., 1977, 13, 1. Electrical Conductors, Academic Press, London, 1987; 16 E. M. Engler, F. B. Kaufman, D. C. Green, C. E. Klots and R. N. (b) M. R. Bryce, Chem. Soc. Rev., 1991, 20, 355; (c) A. E. Underhill, Compton, J. Am. Chem. Soc., 1975, 97, 2921. 17 E. M. Engler, V. V. Patel, J. R. Anderson, R. R. Schumaker and J. Mater. Chem., 1992, 2, 1; (d) J. Mater. Chem., Special Issue on A. A. Fukushima, J. Am. Chem. Soc., 1978, 100, 3769. Molecular Conductors, 1995, 5, 1469. 18 General details: M.R. Bryce, A. Chesney, A. K. Lay, A. S.Batsanov 2 (a) J. P. Ferraris, D. Cowan, V. Walatka anPerlstein, J. Am. and J. A. K. Howard, J. Chem. Soc., Perkin T rans. 1, 1996, 2451. Chem. Soc., 1973, 95, 948; (b) L. B. Coleman, M. J. Cohen, 19 G. M Sheldrick, SHELXTL, ver. 5/VMS, Siemens Analytical X- D. J. Sandman, F. G. Yamagishi, A. F. Garito and A. J. Heeger, Ray Instruments Inc., Madison, Wisconsin, USA, 1995. Solid State Commun., 1973, 12, 1125. 3 (a) K. Bechgaard, K. Carneiro, F. B. Rasmussen, M. Olsen, G. Rindorf, C. S. Jacobsen, H. J. Pedersen and J. C. Scott, J. Am. Paper 6/06834K; Received 7th October, 1996