Synthesis of 1,4-di(n-pyridyl)buta-1,3-diyne andformation of charge-transfer complexes. X-Ray structure of1,4-di(3-pyridyl)buta-1,3-diyne

摘要

J. Chem. Soc. Perkin Trans. 1 1997 709 Synthesis of 1,4-di(n-pyridyl)buta-1,3-diyne and formation of charge-transfer complexes. X-Ray structure of 1,4-di(3-pyridyl)buta-1,3-diyne J. Gonzalo Rodriacute;guez,*,a Rosa Martiacute;n-Villamil,a Felix H. Canob and Isabel Fonsecab a Departamento de Quiacute;mica Orgaacute;nica Universidad Autoacute;noma de Madrid Cantoblanco 28049-Madrid Spain b Departamento de Cristalografiacute;a C.S.I.C. Serrano 119 28006-Madrid Spain Ethynylpyridines have been satisfactorily prepared by two different routes (a) the Wittig reaction between chloromethylene(triphenyl)phosphine ylide and a pyridinecarbaldehyde followed by elimination of hydrogen chloride; (b) from the 2-methyl-4-(n-pyridyl)but-3-yn-2-ol intermediate by elimination of acetone. 1,4-Di(n-pyridyl)buta-1,3-diynes are obtained by oxidative dimerization in good yield.An X-ray structure of the 3-substituted dimer is reported. Mono- and di-methyl salts of the 3-substituted diyne have been obtained and the charge-transfer complexes with tetramethyl-p-phenylenediamine (TMPD) are formed. Introduction The use of molecular organic materials for conductor and nonlinear optics applications is an area of considerable recent activity. Interest in these materials is due to their inherent synthetic flexibility which permits the lsquo;designrsquo; of molecular properties. 1 Solid-state polymerization of 1,3-diynes to form crystalline conjugated polydiynes has attracted much attention.1,2 Some of the recent interest in poly-1,3-diynes is related to their large and fast nonlinear optical response making them good potential materials in ultrafast optical applications.3 Although the electronic and optical properties of poly-1,3-diynes are primarily dominated by the p-conjugated backbone the substituent groups markedly influence the topopolymerization behaviour of the 1,3-diynes and the physical and chemical properties of the crystalline conjugated poly-1,3-diynes.An aspect of the substituent effect that has received little attention is the influence of formally p-conjugated substituents on the electronic properties of poly-1,3-diynes because many of them are unreactive in the solid state,4ndash;6 although they may undergo liquid-crystalline polymerization to form polymers distinct from the solid-state polymers. However preliminary studies show that 4-amino-49-nitrodiphenyl-1,3-diyne is solid-state reactive.6 The discovery of a one-dimensional metallic state in the ionradical solid formed from the p-donor tetrathiafulvalene and the acceptor tetracyanoquinodimethane has stimulated interest in the structurendash;properties relationships of novel donors and acceptors.7 Metallic conductivity and superconductivity are the most important properties in these organic charge-transfer salts.Recently attention has also been directed to the novel magnetic and optical properties which they can display. Here we report the synthesis of the 1,4-di(n-pyridyl)buta-1,3- diynes 12 13 and 14 and the methylation of the 3-substituted derivative 13 to give molecules with acceptor characteristics which allow them to form charge-transfer complexes with donors. Results and discussion Synthesis of n-ethynylpyridines (a) By elimination of hydrogen chloride from the chlorovinyl derivatives.The starting acetylene derivatives 4ndash;6 were prepared in good yields from a mixture of the corresponding (E)- and (Z)-2-chlorovinylpyridines 1ndash;3 by dehydrochlorination with potassium tert-butoxide in tetrahydrofuran (THF) at different temperatures. In this elimination reaction we observed that the temperature had an influence on the yield and the reaction products. Furthermore the position of the vinyl group on the pyridine ring determined some of the necessary reaction conditions (Table 1 Scheme 1). The chlorovinyl derivatives were prepared by the Wittig reaction between chloromethylene(triphenyl)phosphine ylide 8 and Scheme 1 Reagents and conditions i Ph3P CHCl; ii ButO2K+ 25 8C (4ndash;6) or 70 8C (7a,b; 8) N C N CH=CHCl 1a,b 2-subst.Z and E 2a,b 3-subst. Z and E 3a,b 4-subst. Z and E i N CHO N CH=CHOBut ii 4 2-subst. 5 3-subst. 6 4-subst. ii CH 7a,b 2-subst. Z and E 8 4-subst. Table 1 Dehydrochlorination of 1ndash;3 with ButO2K+ in THF at different temperatures Chlorovinyl T/8C Elimination () Substitution () 1a 25 48 1a 70 50 E:Z = 1 1 1b 50 45 1b 70 40 E 2a + 2b 60 54 2a + 2b 70 25 3a + 3b 25 40 3a + 3b 70 20 710 J. Chem. Soc. Perkin Trans. 1 1997 the corresponding pyridinecarbaldehyde derivative in THF in good yield as a mixture of E:Z isomers (Scheme 1 Table 2). In the case of the 2-substituted derivative the main product is the Z isomer because the cis-1,2-oxaphosphetane precursor of this isomer is more stable. The ylide reacts on the face of the carbonyl group to give the oxaphosphetane intermediate with the dipolar moment of the CCl bond in the opposite direction to that of the NC dipole in the pyridine and this stereodisposition is the most stable.(b) From the n-halogenopyridines by insertion of the acetylene group catalysed by palladium. The low yield in the hydrogen chloride elimination step prompted us to carry out an alternative synthesis of the acetylene derivatives of pyridine using the coupling reaction between the bromopyridine and 2-methylbut- 3-yn-2-ol;9 the reaction is catalysed by palladium and the 2-methyl-4-(n-pyridyl)but-3-yn-2-ol derivatives 9ndash;11 were obtained in excellent yields. Finally the elimination of acetone gave the acetylene derivatives in moderate yield (Scheme 2 Table 3). Synthesis of 1,4-di(n-pyridyl)buta-1,3-diynes 12ndash;14 The title compounds were synthesized in good yield by oxidative dimerization 10 of the corresponding acetylene derivative with oxygen in pyridine in the presence of copper(I) iodide at 40 8C as solids which are stable to sunlight (Scheme 3).A single crystal of the 1,4-di(3-pyridyl)buta-1,3-diyne 13 was used for X-ray crystallographic analysis. The crystal was stable to Cu-Ka X-radiation and no topopolymerization to the monocrystalline poly-1,3-diyne was observed. Crystal structure analysis Compound 13 consists of a buta-1,3-diyne chain with 1,4- substitution at position 3 in both pyridine rings. Fig. 1 shows a view of the molecule with the atom numbering Scheme 2 Reagents and conditions i 2-methylbut-3-yn-2-ol Cl2Pd- (PPh3)2 Cu2I2 HNEt2; ii NaOH reflux N Br N C C C CH3 CH3 OH N C CH i ii 9 2-subst.10 3-subst. 11 4-subst. 4ndash;6 Scheme 3 Reagents Cu2CI2 O2 pyridine N C CH N C C C N C 4 2-subst. 5 3-subst. 6 4-subst. 12 2-subst. 13 3-subst. 14 4-subst. Table 2 Synthesis of 1ndash;3 via Wittig reaction Isomer Z () E () Yield () 1 84 16 77 2 50 50 90 3 50 50 84 scheme. A table of fractional atomic coordinates has been deposited as supplementary material,dagger; and in Table 4 are listed (a) the bond distances and (b) the bond angles. The molecule has a symmetry centre which coincides with a crystallographic one. The distances N(1)C(2) and N(1)C(6) of 1.338(3) and 1.325(3) Aring; respectively are similar to those found in pyridine. All distances and angles are within the expected values (Table 4). The pyridine ring is planar C(7) and C(8) deviating by 0.031(2) and 0.086(2) Aring; above this plane.Bond distances of the buta-1,3-diyne chain show normal values,11 with a C(7)C(8) triple bond distance of 1.199(3) Aring;. This chain is practically linear with a C(7)C(8)C(89) angle of 179.7(2)8. The crystal packs with the molecules in parallel columns (see Fig. 2) along the c-axis which defines the distance between the centroids of consecutive rings as being 3.87 Aring; forming with the c-axis an angle of 108. It can be seen in Fig. 2 that along the aaxis there are zones of neighbouring intermolecular rings and zones of intramolecular C CC C linear chains producing a so called lsquo;segregationrsquo; the overall least-squares planes through each molecule in the cell are parallel and within each column a stack is produced. Along the b-axis there are also chains of molecules in the so called lsquo;edge-to-edgersquo; mode with parallel molecules within a column but forming an angle of almost 908 between molecules of two neighbouring columns.In general in the reactive crystals of buta-1,3-diyne compounds the molecules are packed in a ladder-like fashion such that the ends of one triple-bond system approach an adjacent triple-bond system to a distance d 4 Aring; and the inclination angle formed with the translation axis is about 458.12 Charge-transfer complexes The p-electronic defect of the pyridine rings and the pextended conjugation to the diyne chain in 1,4-di(3-pyridyl)- buta-1,3-diyne 13 allowed it to take part in charge-transfer complexation with N,N,N9,N9-tetramethyl-p-phenylenediamine (TMPD) as donor. However the 1,4-di(n-pyridyl)buta-1,3- diyne derivative does not form charge-transfer complexes with Table 3 Yields of 9ndash;11 and 4ndash;6 Bromopyridine Alcohol () Acetylene () 2-subst.93 84 3-subst. 98 55 4-subst. 90 50 Table 4 Bond distances and angles for 13 (a) Bond distances (Aring;) N(1)C(2) 1.338(3) C(5)C(6) 1.394(3) N(1)C(6) 1.325(3) C(5)C(7) 1.431(3) C(2)C(3) 1.375(3) C(7)C(8) 1.199(3) C(3)C(4) 1.371(3) C(8)C(89) a 1.371(3) C(4)C(5) 1.392(3) (b) Bond angles (8) C(2)N(1)C(6) 117.3(2) C(4)C(5)C(6) 117.4(2) N(1)C(2)C(3) 123.1(2) C(6)C(5)C(7) 121.4(2) C(2)C(3)C(4) 119.2(2) N(1)C(6)C(5) 123.9(2) C(3)C(4)C(5) 119.0(2) C(5)C(7)C(8) 178.1(2) C(4)C(5)C(7) 121.2(2) C(7)C(8)C(89) a 179.7(2) a C(89) is related to C(8) by the symmetry operation (1 2 x 21 2 y 2 2 z). dagger; Supplementary material Tables of fractional atomic coordinates and thermal parameters and full bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC).See Instructions for Authors J. Chem. Soc. Perkin Trans. 1 1997 Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 207/78. J. Chem. Soc. Perkin Trans. 1 1997 711 some acceptors or donors so we carried out methylation of the pyridine rings to increase the acceptor character of these compounds (Scheme 4). The mono- and di-methylated salts of the meta diyne derivative were isolated pure and used to prepare charge-transfer complexes with the donor molecule TMPD. Thus slow evaporation of an equimolar mixture of the mono- or di-salt and TMPD in hot acetonitrile gave in both cases a metallic bright solid (black or green) (Fig.3). UV-Visible spectroscopy of the molecular complex of the monomethylated salt 15 and TMPD shows three chargetransfer bands at 543 565 and 615 nm. In the case of the molecular complex of the dimethylated salt 16 and TMPD the UV-visible spectrum also shows three charge-transfer bands at 594 617 and 642 nm. The IR spectra showed some differences between the complexes with TMPD and the free salts such that the intensity of the absorption for the C C conjugated bonds in the complexes is lower than that in the free salts. Experimental Mps were determined using a Reichert stage microscope and are uncorrected. IR Spectra were recorded using a Perkin-Elmer 681 spectrophotometer. NMR Spectra were recorded at 200 MHz using a Bruker WM-200-SY spectrometer; chemical shifts are given in d units using SiMe4 as internal reference; J values are given in Hz.UVndash;Visible spectra were recorded using a Perkin-Elmer Lambda 6 spectrophotometer. Mass spectra were recorded using a Hewlett-Packard SP85 spectrometer. Fig. 1 View of molecule 13 with the atom numbering scheme Scheme 4 Reagent MeI N C C N C C N C C N+Indash; C C CH3 ndash;I+N C C N+Indash; C C CH3 H3C 13 + 15 16 Preparation of ethynylpyridines by elimination of hydrogen chloride from the chlorovinyl derivatives 2-(2-Chlorovinyl)pyridine 1. To a suspension of chloromethyl- (triphenyl)phosphonium chloride (18.7 g 57 mmol) in dry THF (60 cm3) was slowly added a solution of butyllithium (1.6 M in hexane; 35.6 cm3 57 mmol) under argon at 210 8C. The solution acquired a red colour and after being stirred for 30 min was treated with pyridine-2-carbaldehyde (2 g 19 mmol).The mixture was stirred at room temperature for 10 h and then the solvent was removed to give a brown oil. Chromatography on silica gel with hexanendash;ethyl acetate afforded (Z)-2-(2-chlorovinyl) pyridine nmax(film)/cm21 3055 ( CH) 1620 (C C conj.) 1580 and 1560 (C C and C N) and 670 (Z); dH(200 MHz; CDCl3) 6.49 (1 H d J 8.3 CH CHCl) 6.86 (1 H d J 8.3 CH CHCl) 7.19 (1 H dd J 7.9 and 6.0 5-H) 7.70 (1 H t J 7.9 4-H) 8.02 (1 H d J 7.9 3-H) and 8.62 (1 H d J 6.0 6-H); m/z 141 (9) 139 (M+ 22) 104 (100) 84 (13) 78 (30) and 51 (27); and (E)-2-(2-chlorovinyl)pyridine nmax(film)/cm21 3070 ( CH) 1620 (C C conj.) 1580 and 1560 (C C and C N) and 970 (E); dH(200 MHz; CDCl3) 6.67 (1 H d J 13.3 CH CHCl) 7.20 (2 H m 3- and 5-H) 7.43 (1 H d J 13.3 CH CHCl) 7.63 (1 H m 4-H) and 8.53 (1 H br s 6-H); m/z 141 (9) 139 (M+ 27) 104 (100) 78 (25) and 51 (18).Fig. 2 Packing of the molecular crystal unit cells viewed down the baxis Fig. 3 N N CH3 CH3 H3C H3C N+Indash; C C C C N CH3 N N CH3 CH3 H3C H3C N+Indash; C C C C ndash;I+N CH3 H3C 712 J. Chem. Soc. Perkin Trans. 1 1997 3-(2-Chlorovinyl)pyridine 2. The same procedure was followed to prepare the 3-substituted derivative but with pyridine- 3-carbaldehyde. After purification by chromatography on silica gel the chlorovinyl derivative 2 was obtained as an oily mixture of E Z isomers (1 1) (2.38 g 90); nmax(film)/cm21 3050 ( CH) 1610 and 1605 (C C conj.) 1580 and 1560 (C C and C N) 970 (E) and 730 (Z); dH(200 MHz; CDCl3) 6.29 (1 H d J 8.2 CH CHCl Z) 6.69 (1 H d J 13.9 CH CHCl E) 6.74 (1 H d J 8.2 CH CHCl Z) 6.85 (1 H d J 13.9 CH CHCl E) 7.25 (1 H d J 8.0 5-H E) 7.32 (1 H dd J 8.0 and 5.4 5-H Z) 7.60 (1 H d J 8.0 4-H E) 8.13 (1 H d J 8.0 4-H Z) 8.49 (1 H br s 6-H E) 8.52 (1 H d J 5.4 6-H Z) 8.53 (1 H br s 2-H E) and 8.76 (1 H br s 2-H Z); m/z 141 (8) 139 (M+ 29) 104 (100) 86 (10) 77 (46) and 51 (64).4-(2-Chlorovinyl)pyridine 3. Following the same procedure we obtained the chlorovinyl derivative 3 from pyridine-4- carbaldehyde as an oily mixture of E Z isomers (1 1) (2.22 g 84); nmax(film)/cm21 3060 ( CH) 1610 (C C conj.) 1590 and 1540 (C C and C N) 960 (E) and 720 (Z); dH(200 MHz; CDCl3) 6.48 (1 H d J 8.2 CH CHCl Z) 6.60 (1 H d J 8.2 CH CHCl Z) 6.69 (1 H d J 13.8 CH CHCl E) 6.77 (1 H d J 13.8 CH CHCl E) 7.16 (2 H d J 4.8 3- and 5-H E) 7.52 (2 H d J 4.6 3- and 5-H Z) 8.56 (2 H d J 4.8 2- and 6-H E) and 8.62 (2 H d J 4.6 2- and 6-H Z); m/z 141 (8) 139 (M+ 29) 112 (29) 104 (38) 86 (84) 77 (36) 63 (16) and 51 (100).2-Ethynylpyridine 4. From the (Z)-2-(2-chlorovinyl)pyridine isomer 1a.mdash;To a solution of the (Z)-chlorovinyl derivative 1a (3 g 21 mmol) in dry THF (30 cm3) was slowly added potassium tert-butoxide (6 g 54 mmol) under argon at 0 8C. The mixture was stirred for 45 min at room temperature. Then the solution was poured onto icendash;water (150 cm3) and made alkaline (pH 8) with saturated aq. ammonium chloride. The mixture was extracted with dichloromethane; the extract was dried with magnesium sulfate and after filtration the solvent was removed to give a brown oil.Chromatography on silica gel with hexanendash; ethyl acetate (1 2) as eluent yielded the acetylene derivative 4 (1.04 g 48) as an orange oil bp 91ndash;92 8C/15 mmHg (lit.,9 85ndash; 86 8C/12 mmHg); nmax(film)/cm21 3260 ( CH) and 2114 (C C); dH(200 MHz; CDCl3) 3.25 (1 H s C CH) 7.21 (1 H dd J 7.7 and 5.1 5-H) 7.40 (1 H d J 7.7 3-H) 7.60 (1 H t J 7.7 4-H) and 8.54 (1 H d J 5.1 6-H); dC(200 MHz; CDCl3) 77.0 (PyC C) 82.5 (PyC C) 123.1 (C-5) 127.1 (C-3) 135.8 (C-4) 148.4 (C-2) and 149.5 (C-6); m/z 103 (M+ 100) 76 (46) and 50 (36). From the (E)-2-(2-chlorovinyl)pyridine isomer 1b.mdash;To a solution of the (E)-chlorovinyl derivative 1b (1 g 7.2 mmol) in dry THF (15 cm3) was slowly added potassium tert-butoxide (2 g 18 mmol) under argon at 0 8C. The mixture was stirred for 90 min at 50 8C.Then the solution was poured onto icendash;water (60 cm3) and made alkaline (pH 8) with saturated aq. ammonium chloride. The mixture was extracted with dichloromethane; the extract was dried with magnesium sulfate and after filtration the solvent was removed to give a brown oil. Chromatography on silica gel with hexanendash;ethyl acetate (1 2) as eluent yielded the acetylene derivative 4 (0.33 g 45) as an orange oil. 3-Ethynylpyridine 5. To a solution of the (Z,E)-chlorovinyl derivative 2 (3 g 21 mmol) in dry THF (30 cm3) was slowly added potassium tert-butoxide (6 g 54 mmol) under argon at 0 8C. The mixture was stirred for 60 min at 60 8C. Then the solution was allowed to cool and was poured onto icendash;water (150 cm3) and made alkaline (pH 8) with saturated aq. ammonium chloride. The mixture was extracted with dichloromethane; the extract was dried with magnesium sulfate and after filtration the solvent was removed to give a brown oil.Chromatography on silica gel with hexanendash;ethyl acetate (1 2) as eluent yielded the acetylene derivative 5 (1.17 g 54) as a yellow solid mp 35ndash;37 8C (lit.,13 39ndash;40 8C); nmax(film)/cm21 3280 ( CH) and 2120 (C C); dH(200 MHz; CDCl3) 3.30 (1 H s C CH) 7.25 (1 H ddd J 7.8 5.0 and 0.9 5-H) 7.70 (1 H dt J 7.8 and 2.0 4-H) 8.56 (1 H dd J 5.0 and 2.0 6-H) and 8.70 (1 H dd J 2.0 and 0.9 2-H); dC(200 MHz; CDCl3) 80.0 (PyC C) 80.6 (PyC C) 118.7 (C-3) 122.3 (C-5) 138.3 (C-4) 148.3 (C-6) and 151.9 (C-2); m/z 103 (M+ 100) 76 (38) and 50 (30). 4-Ethynylpyridine 6. Following the same procedure described to prepare 2-ethynylpyridine from the (Z)-chlorovinyl isomer 4-ethynylpyridine was obtained (40) as a solid from the 4-(chlorovinyl)isomer mp 63ndash;65 8C; nmax(film)/cm21 3270 ( CH) and 2100 (C C); dH(200 MHz; CDCl3) 3.40 (1 H s C CH) 7.35 (2 H d J 6.8 3- and 5-H) and 8.60 (2 H d J 6.8 2- and 6-H); dC(200 MHz; CDCl3) 80.6 (PyC C) 81.8 (PyC C) 129.9 (C-4) 125.7 (C-3 and -5) and 149.4 (C-2 and -6); m/z 103 (M+ 100) 76 (52) and 50 (41).Synthesis of ethynylpyridines by insertion of the acetylene group catalysed by palladium 2-Methyl-4-(2-pyridyl)but-3-yn-2-ol 9. Bis(triphenylphosphine) palladium(II) dichloride (220 mg 0.3 mmol) and copper( I) iodide (32 mg 0.2 mmol) were added successively to a solution of 2-bromopyridine (5 g 31.6 mmol) and 2-methylbut- 3-yn-2-ol (3.62 ml 37.3 mmol) in diethylamine (freshly distilled; 25 cm3) under argon at 0 8C.The mixture was stirred for 15 h at room temperature and then the diethylamine was removed under reduced pressure. The crude mixture was washed with water and extracted with dichloromethane; the extract was dried with magnesium sulfate and after filtration the solvent was removed to give a brown solid. Chromatography on silica gel with hexanendash;ethyl acetate as eluent yielded 2-methyl-4-(2- pyridyl)but-3-yn-2-ol 9 (4.76 g 93) as a yellow solid mp 60ndash; 62 8C (lit.,9 61ndash;63 8C); nmax(film)/cm21 3300 (OH) 2980 (CH) 2230 (C C) 1585 (C C conj.) 1380 and 1360 (CH3) 1170 (CO) 970 (Py) and 780 (PyH 2-subst.); dH(200 MHz; CDCl3) 1.70 (6 H s CH3 times; 2) 5.29 (1 H s OH) 7.20 (1 H dd J 6.7 and 5.0 5-H) 7.39 (1 H d J3,4 6.7 3-H) 7.62 (1 H td J4,3 = J4,5 6.7 and J4,6 0.8 4-H) and 8.59 (1 H br s 6-H); dC(200 MHz; CDCl3) 30.9 (CH3) 64.5 (COH) 80.6 (PyC C) 94.9 (PyC C) 122.5 (C-5) 126.7 (C-3) 136.0 (C-4) 142.6 (C-2) and 149.2 (C-6).2-Methyl-4-(3-pyridyl)but-3-yn-2-ol 10. Following the same procedure the 3-substituted derivative 10 was obtained (5 g 98) as a yellow solid from 3-bromopyridine mp 52ndash;54 8C; nmax(film)/cm21 3300 (OH) 2980 (CH) 2240 (C C) 1590 (C C conj.) 1380 and 1360 (CH3) 1170 (CO) 970 (Py) and 810 and 705 (PyH 3-subst.); dH(200 MHz; CDCl3) 1.58 (6 H s CH3 times; 2) 5.78 (1 H s OH) 7.15 (1 H dd J5,4 8.0 J5,6 6.4 5-H) 7.09 (1 H d J4,5 8.0 4-H) 8.38 (1 H s 6-H) and 8.60 (1 H s 2-H); dC(200 MHz; CDCl3) 31.1 (CH3) 64.3 (COH) 77.6 (PyC C) 98.6 (PyC C) 120.2 (C-3) 122.9 (C-5) 138.7 (C-4) 147.4 (C-6) and 151.3 (C-2).2-Methyl-4-(4-pyridyl)but-3-yn-2-ol 11. The preparation of the 4-substituted derivative 11 was carried out following the same procedure from 4-bromopyridine hydrochloride. Compound 11 was obtained (3.72 g 90) as a yellow solid mp 96ndash; 98 8C; nmax(film)/cm21 3350ndash;3040 (OH) 2980 (CH) 2230 (C C) 1600 (C C conj.) 1370 and 1360 (CH3) 1170 (CO) 970 (Py) and 840 (PyH 4-subst.); dH(200 MHz; CDCl3) 1.62 (6 H s CH3 times; 2) 3.10 (1 H s OH) 7.29 (2 H d J 8.1 3- and 5-H) and 8.59 (2 H s 2- and 6-H); dC(200 MHz; CDCl3) 31.0 (CH3) 64.5 (COH) 78.6 (PyC C) 100 (PyC C) 125.6 (C-3 and -5) and 148.8 (C-2 and -6). General procedure to prepare the ethynylpyridines from the 2-methyl-4-(n-pyridyl)but-3-yn-2-ols A solution of the alkynol (5 g 31 mmol) in dry toluene (30 cm3) was heated under reflux with pulverized sodium hydroxide (0.90 g) for 2 h.Then the solution was decanted and the solvent was evaporated under reduced pressure to give a brown solid. J. Chem. Soc. Perkin Trans. 1 1997 713 Chromatography on silica gel with hexanendash;ethyl acetate (1 2) yielded the ethynyl derivative 2-Ethynylpyridine (84) as an orange oil bp 90ndash;92 8C/15 mmHg; 3-ethynylpyridine (55) as a yellow solid mp 37ndash;39 8C and 4-ethynylpyridine (50) as a solid mp 63ndash;65 8C. Oxidative dimerization of ethynylpyridines. General procedure Oxygen was bubbled into a solution of copper(I) chloride (0.54 g 2.73 mmol) in pyridine (12 cm3) warmed to 40 8C after which the acetylene derivative (0.78 g 7.57 mmol) was added. The mixture was stirred for 3 h after which it was cooled and concentrated by removal of the pyridine by distillation.The crude mixture was washed with ammonium hydroxide until the blue colour disappeared after which it was extracted with dichloromethane. The extract was dried (MgSO4) filtered and evaporated to give a yellow solid chromatography of which on silica gel with hexanendash;ethyl acetate (1 2) as eluent yielded the diyne derivative. 3-Substituted product 13 (49) was a yellow solid mp 145ndash;146 8C; nmax(KBr)/cm21 1550 (C C conj.) 955 (Py) 800 and 700 (PyH 3-subst.); dH(200 MHz; CDCl3) 7.30 (2 H dd J 7.9 and 5.0 5-H) 7.82 (2 H dt J 7.9 and 1.7 4-H) 8.61 (2 H br s 6-H) and 8.78 (2 H br s 2-H); dC(200 MHz; CDCl3) 78.9 (C C) 118.5 (C-3) 122.7 (C-5) 139.1 (C-4) 149.2 (C-6) and 152.9 (C-2); m/z 204 (M+ 100) 177 (11) 151 (23) and 124 (8); lmax(CH2Cl2)/nm 229 (e/dm3 mol21 cm21 30 000) 244 (29 000) 292 (22 000) 319 (30 000) and 331 (26 000).4-Substituted product 14 (54) was a brown solid mp 198ndash; 201 8C; nmax(Nujol)/cm21 1580 (C C conj.) 980 (Py) and 810 (PyH 4-subst.); dH(200 MHz; CDCl3) 7.41 (4 H d J 7.2 3- and 5-H) and 8.67 (4 H br s 2- and 6-H); dC(200 MHz; CDCl3) 76.9 (PyC C) 79.9 (PyC C) 125.7 (C-3 and -5) 128.9 (C-4) and 149.6 (C-2 and -6); m/z 204 (M+ 100) 177 (13) 151 (14) and 124 (6). X-Ray crystallographic analysis of 1,4-di(3-pyridyl)buta-1,3- diyne 13 Yellow transparent plate-like crystals of 1,4-di(3-pyridyl)buta- 1,3-diyne 13 were grown by slow evaporation from an acetonitrile solution. A crystal of dimensions 0.29 times; 0.27 times; 0.18 mm3 was selected for X-ray diffraction analysis.Accurate cell dimensions were determined by least-squares analysis of setting angles of 40 reflections (15 2q 848) using graphite-monochromated Cu-Ka radiation (l = 1.5418 Aring;) automatically located and centred on a four-circle Philips PW1100 diffractometer. C14H8N2 M = 204.23 monoclinic a = 22.104(3) b = 6.017(1) c = 3.873(1) Aring; b = 91.48(1)8 V = 514.92(7) Aring;3 Z = 2 space group P21/n Dc = 1.317(3) g cm23 F(000) = 212 m = 6.253 cm21. Data collection. Two standard reflections were measured every 90 min to ascertain crystal stability; no significant variation was observed. The intensities were corrected for Lorentz and polarization effects. No corrections were made for absorption. For the intensity measurement reflections were surveyed in the range 2 q 658; from 975 independent reflections measured 778 were considered as observed satisfying the criterion I 2s(I) in the range h 227/27 k 0/8 l 0/5 and were used in the subsequent calculations.The structure was solved by direct methods using SIR92,14 and refined by anisotropic full-matrix least-squares.15 The H-atoms were located on a difference map and refined isotropically. After several cycles of mixed refinement (89 refined parameters) convergence was reached at R = 0.057 and Rw = 0.069 with a weighting scheme16 to prevent trends in middot;wD2FOgrave; vs. middot;verbar;Foverbar;Ograve; and middot;sinq/lOgrave;. The atomic scattering factors and the anomalous dispersion corrections were taken from the literature.17 Atomic coordinates bond distances and angles were calculated using the PARST program.18 1,4-Di(2-pyridyl)buta-1,3-diyne 12 To a suspension of copper(I) chloride (57 mg 0.58 mmol) and N,N,N9,N9-tetramethylethylenediamine (TMEDA) (0.11 cm3 0.75 mmol) in 1,2-dimethoxyethane (DME) (4 cm3) was added a solution of 2-ethynylpyridine 4 (0.3 g 2.9 mmol) in DME (1 cm3) previously heated for 10 min at 35 8C while oxygen was bubbled in.After 30 min the mixture changed in colour from green to brown and 15 min later the solvent was removed to give a brown solid chromatography of which on silica gel with hexanendash;ethyl acetate (2 3) as eluent yielded the diacetylene derivative 12 (150 mg 52) as a solid mp 120ndash; 122 8C (lit.,19 122ndash;123 8C); nmax(KBr)/cm21 1580 and 1560 (C C conj.) 990 (Py) 780 and 735 (PyH 2-subst.); dH(200 MHz CDCl3) 7.24 (2 H ddd J 7.6 4.8 and 1.1 5-H) 7.47 (2 H d J 7.7 3-H) 7.63 (2 H td J 7.7 and 1.7 4-H) and 8.55 (2 H d J 4.8 6-H); dC(200 MHz; CDCl3) 72.9 (PyC C) 80.7 (PyC C) 123.6 (C-5) 128.2 (C-3) 136.0 (C-4) 141.5 (C-2) and 150.2 (C-6); m/z 204 (M+ 100) 177 (14) 151 (14) 124 (5) 102 (6) and 78 (10); lmax(CH2Cl2)/nm 238 (e/dm3 mol21 cm21 23 600) 294 (18 400) 309 (24 000) and 330 (20 800).Methylation of the 1,4-di(3-pyridyl)buta-1,3-diyne 13 To a solution of the diyne derivative (100 mg 0.49 mmol) in ethanol (25 cm3) was added iodomethane (0.12 cm3 1.96 mmol). The mixture was stirred for 20 h at 50 8C. A yellow solid precipitated from the solution and was filtered off and identi- fied as the dimethylated derivative 16 (92 mg 38) mp 190 8C (decomp.). Then the mixture was allowed to cool and an orange solid precipitated out which was filtered off and identi- fied as the monomethylated derivative 15 (72 mg 42) mp 166 8C (decomp.).Dimethylated product 16 had nmax(KBr)/cm21 1620 and 1500 (C C and C N conj.) 1290 (NCH3) 1150 (Py+ndash;CH3) 810 and 665 (PyH 3-subst.); dH200 MHz; (CD3)2SO 4.37 (6 H s CH3 times; 2) 8.23 (2 H t 5-H) 8.91 (2 H d 4-H) 9.13 (2 H d 6-H) and 9.49 (2 H s 2-H); dC(200 MHz; CDCl3) 48.4 (CH3) 77.2 and 77.6 (PyC C) 120.1 (C-3) 127.7 (C-5) 146.4 (C-4) 147.9 (C-6) and 149.3 (C-2); m/z (FAB+) 234 (M+ 25) and 219 (52); lmax(CH2Cl2)/nm 237 (e/dm3 mol21 cm21 31 430) 290 (18 500) 308 (20 000) 330 (18 570) 345 (13 710) 354 (12 000) and 360 (11 430). Monomethylated product 15 had nmax(KBr)/cm21 1620 1580 and 1500 (C C and C N conj.) 1280 (NCH3) 1160 (Py+CH3) 830 800 700 and 675 (PyH 3-subst.); dH200 MHz; (CD3)2SO 4.31 (3 H s CH3) 7.50 (1 H m 5-H) 8.20 (2 H m 5-H in the methylated ring and 4-H) 8.70 (2 H m 2- and 6-H) 8.88 (1 H m 4-H in the methylated ring) 9.05 (1 H d 6-H in the methylated ring) and 9.42 (1 H br s 2-H in the methylated ring); dC(200 MHz; CDCl3) 48.4 (CH3) 77.2 and 77.6 (PyC C) 120.1 (C-3) 127.7 (C-5) 146.4 (C-4) 147.9 (C-6) and 149.3 (C-2); m/z (FAB+) 219 (M+ 100) and 205 (13); lmax(CH2Cl2)/nm 237 (e/dm3 mol21 cm21 40 250) 290 (17 750) 308 (22 500) 330 (24 000) and 345 (12 500).Charge-transfer complex of 1-(N-methylpyridinium-3-yl)-4-(3- pyridyl)buta-1,3-diyne iodide 15 with TMPD A hot solution of TMPD (24 mg 0.14 mmol) in acetonitrile (10 cm3) was added to a nearly boiling solution of the monomethylated buta-1,3-diyne derivative 15 (50 mg 0.14 mmol) in 100 cm3 of acetonitrile.The resulting dark violet solution was allowed to cool and then to evaporate slowly to yield a black solid with metallic lustre; nmax(Nujol)/cm21 1610 1580 and 1510 (C C and C N conj.) 1160 (Py+CH3) 950 (Py) 820 810 800 720 690 and 665 (PyH 3-subst.); lmax(CH2Cl2)/nm 238 309 330 350 543 565 and 615. Charge-transfer complex of 1,4-bis(N-methylpyridinium-3-yl)- buta-1,3-diyne diiodide 16 with TMPD The same procedure was followed to form the charge-transfer complex of the dimethylated buta-1,3-diyne derivative 16. 714 J. Chem. Soc. Perkin Trans. 1 1997 The complex was a green solid with a metallic lustre; nmax- (Nujol)/cm21 1620 and 1520 (C C and C N conj.) 1320 (NCH3) 1170 and 1150 (Py+CH3) 950 (Py) 815 720 and 665 (PyH 3-subst.); lmax(CH2Cl2)/nm 264 327 594 617 and 642.Acknowledgements We are indebted to the CAYCIT of Spain for financial support (project no. PB92-0142-C02-01). References 1 Polydiacetylenes ed. D. Bloor and R. R. Chance NATO ASI series E No. 102 Matinus Nijkoff Boston 1985; A. E. Stiegman E. Graham K. J. Perry R. Khundkard L. T. Cheng and J. W. Perry J. Am. Chem. Soc. 1991 113 1658 and references cited therein. 2 G. Wegner Z. Naturforsch. B Anorg. Chem. Org. Chem. 1969 24 824. 3 G. M. Carter Y. J. Chen M. F. Rubner D. J. Sandman M. K. Thakur and S. K. Tripathy in Nonlinear Optical Properties of Organic Molecules and Crystals ed. D. S. Chemla and J. Zyss Academic Press New York 1987 vol. 2 p. 85. 4 G. Wegner J. Polym. Sci. Part B Polym. Lett. 1971 9 133. 5 Y. Ozcayir J. Asrar and A. Blumstein Mol.Cryst. Liq. Cryst. 1984 110 1424. 6 G. H. Milburn A. R. Wernick J. Tsibouklis E. Bolton G. Thomson and A. Shand Polymer 1989 30 1004. 7 J. P. Ferraris D. O. Cowan V. Walatka and J. Perlstein J. Am. Chem. Soc. 1973 95 948. 8 G. Kouml;brig H. Trapp K. Flory and W. Drischel Chem. Ber. 1966 99 689. 9 D. E. Ames D. Bull and C. Takundwa Synth. Commun. 1981 364. 10 L. Brandsma Studies in Organic Chemistry Preparative Acetylenic Chemistry Elsevier Science Publishers B.V. Amsterdam 1988 vol. 34 p. 220. 11 J. G. Rodriacute;guez S. Ramos R. Martiacute;n-Villamil I. Fonseca and A. Albert J. Chem. Soc. Perkin Trans. 1 1996 541. 12 G. M. J. Schmidt Reactivity of the Photoexcited Organic Molecule Wiley New York 1967 p. 227. 13 S. D. Lrsquo;vova Y. P. Koslov and U. I. Gunar Zh. Obshch. Khim. 1977 47 1251. 14 A. Altomare G.Cascarano C. Giacovazzo and A. Guagliardi Dipartimento Geomineralogico University of Bari; M. Burla and G. Polidori Dipartimento Scienze della Terra University of Perugia; M. Camalli SIR92 Ist Strutt. Chimica CNR Monterrotondo Stazione Roma 1992. 15 J. M. Stewart F. A. Kundell and J. C. Badwin The XRAY80 System Computer Science Center University of Maryland College Park MD 1980. 16 M. Martinez-Ripoll and F. H. Cano PESOS A Computer Program for the Automatic Treatment of Weighting Schemes Instituto Rocasolano CSIC Madrid 1975. 17 International Tables for X-RAY Crystallography Kynoch Press Birmingham 1974 vol. 4. 18 M. Nardelli Comput. Chem. 1983 7 95. 19 U. Fritzsche and S. Hunig Tetrahedron Lett. 1972 4831. Paper 6/05468D Received 5th August 1996 Accepted 5th November 1996 J.Chem. Soc. Perkin Trans. 1 1997 709 Synthesis of 1,4-di(n-pyridyl)buta-1,3-diyne and formation of charge-transfer complexes. X-Ray structure of 1,4-di(3-pyridyl)buta-1,3-diyne J. Gonzalo Rodriacute;guez,*,a Rosa Martiacute;n-Villamil,a Felix H. Canob and Isabel Fonsecab a Departamento de Quiacute;mica Orgaacute;nica Universidad Autoacute;noma de Madrid Cantoblanco 28049-Madrid Spain b Departamento de Cristalografiacute;a C.S.I.C. Serrano 119 28006-Madrid Spain Ethynylpyridines have been satisfactorily prepared by two different routes (a) the Wittig reaction between chloromethylene(triphenyl)phosphine ylide and a pyridinecarbaldehyde followed by elimination of hydrogen chloride; (b) from the 2-methyl-4-(n-pyridyl)but-3-yn-2-ol intermediate by elimination of acetone. 1,4-Di(n-pyridyl)buta-1,3-diynes are obtained by oxidative dimerization in good yield.An X-ray structure of the 3-substituted dimer is reported. Mono- and di-methyl salts of the 3-substituted diyne have been obtained and the charge-transfer complexes with tetramethyl-p-phenylenediamine (TMPD) are formed. Introduction The use of molecular organic materials for conductor and nonlinear optics applications is an area of considerable recent activity. Interest in these materials is due to their inherent synthetic flexibility which permits the lsquo;designrsquo; of molecular properties. 1 Solid-state polymerization of 1,3-diynes to form crystalline conjugated polydiynes has attracted much attention.1,2 Some of the recent interest in poly-1,3-diynes is related to their large and fast nonlinear optical response making them good potential materials in ultrafast optical applications.3 Although the electronic and optical properties of poly-1,3-diynes are primarily dominated by the p-conjugated backbone the substituent groups markedly influence the topopolymerization behaviour of the 1,3-diynes and the physical and chemical properties of the crystalline conjugated poly-1,3-diynes.An aspect of the substituent effect that has received little attention is the influence of formally p-conjugated substituents on the electronic properties of poly-1,3-diynes because many of them are unreactive in the solid state,4ndash;6 although they may undergo liquid-crystalline polymerization to form polymers distinct from the solid-state polymers. However preliminary studies show that 4-amino-49-nitrodiphenyl-1,3-diyne is solid-state reactive.6 The discovery of a one-dimensional metallic state in the ionradical solid formed from the p-donor tetrathiafulvalene and the acceptor tetracyanoquinodimethane has stimulated interest in the structurendash;properties relationships of novel donors and acceptors.7 Metallic conductivity and superconductivity are the most important properties in these organic charge-transfer salts.Recently attention has also been directed to the novel magnetic and optical properties which they can display. Here we report the synthesis of the 1,4-di(n-pyridyl)buta-1,3- diynes 12 13 and 14 and the methylation of the 3-substituted derivative 13 to give molecules with acceptor characteristics which allow them to form charge-transfer complexes with donors. Results and discussion Synthesis of n-ethynylpyridines (a) By elimination of hydrogen chloride from the chlorovinyl derivatives.The starting acetylene derivatives 4ndash;6 were prepared in good yields from a mixture of the corresponding (E)- and (Z)-2-chlorovinylpyridines 1ndash;3 by dehydrochlorination with potassium tert-butoxide in tetrahydrofuran (THF) at different temperatures. In this elimination reaction we observed that the temperature had an influence on the yield and the reaction products. Furthermore the position of the vinyl group on the pyridine ring determined some of the necessary reaction conditions (Table 1 Scheme 1). The chlorovinyl derivatives were prepared by the Wittig reaction between chloromethylene(triphenyl)phosphine ylide 8 and Scheme 1 Reagents and conditions i Ph3P CHCl; ii ButO2K+ 25 8C (4ndash;6) or 70 8C (7a,b; 8) N C N CH=CHCl 1a,b 2-subst.Z and E 2a,b 3-subst. Z and E 3a,b 4-subst. Z and E i N CHO N CH=CHOBut ii 4 2-subst. 5 3-subst. 6 4-subst. ii CH 7a,b 2-subst. Z and E 8 4-subst. Table 1 Dehydrochlorination of 1ndash;3 with ButO2K+ in THF at different temperatures Chlorovinyl T/8C Elimination () Substitution () 1a 25 48 1a 70 50 E:Z = 1 1 1b 50 45 1b 70 40 E 2a + 2b 60 54 2a + 2b 70 25 3a + 3b 25 40 3a + 3b 70 20 710 J. Chem. Soc. Perkin Trans. 1 1997 the corresponding pyridinecarbaldehyde derivative in THF in good yield as a mixture of E:Z isomers (Scheme 1 Table 2). In the case of the 2-substituted derivative the main product is the Z isomer because the cis-1,2-oxaphosphetane precursor of this isomer is more stable. The ylide reacts on the face of the carbonyl group to give the oxaphosphetane intermediate with the dipolar moment of the CCl bond in the opposite direction to that of the NC dipole in the pyridine and this stereodisposition is the most stable.(b) From the n-halogenopyridines by insertion of the acetylene group catalysed by palladium. The low yield in the hydrogen chloride elimination step prompted us to carry out an alternative synthesis of the acetylene derivatives of pyridine using the coupling reaction between the bromopyridine and 2-methylbut- 3-yn-2-ol;9 the reaction is catalysed by palladium and the 2-methyl-4-(n-pyridyl)but-3-yn-2-ol derivatives 9ndash;11 were obtained in excellent yields. Finally the elimination of acetone gave the acetylene derivatives in moderate yield (Scheme 2 Table 3). Synthesis of 1,4-di(n-pyridyl)buta-1,3-diynes 12ndash;14 The title compounds were synthesized in good yield by oxidative dimerization 10 of the corresponding acetylene derivative with oxygen in pyridine in the presence of copper(I) iodide at 40 8C as solids which are stable to sunlight (Scheme 3).A single crystal of the 1,4-di(3-pyridyl)buta-1,3-diyne 13 was used for X-ray crystallographic analysis. The crystal was stable to Cu-Ka X-radiation and no topopolymerization to the monocrystalline poly-1,3-diyne was observed. Crystal structure analysis Compound 13 consists of a buta-1,3-diyne chain with 1,4- substitution at position 3 in both pyridine rings. Fig. 1 shows a view of the molecule with the atom numbering Scheme 2 Reagents and conditions i 2-methylbut-3-yn-2-ol Cl2Pd- (PPh3)2 Cu2I2 HNEt2; ii NaOH reflux N Br N C C C CH3 CH3 OH N C CH i ii 9 2-subst.10 3-subst. 11 4-subst. 4ndash;6 Scheme 3 Reagents Cu2CI2 O2 pyridine N C CH N C C C N C 4 2-subst. 5 3-subst. 6 4-subst. 12 2-subst. 13 3-subst. 14 4-subst. Table 2 Synthesis of 1ndash;3 via Wittig reaction Isomer Z () E () Yield () 1 84 16 77 2 50 50 90 3 50 50 84 scheme. A table of fractional atomic coordinates has been deposited as supplementary material,dagger; and in Table 4 are listed (a) the bond distances and (b) the bond angles. The molecule has a symmetry centre which coincides with a crystallographic one. The distances N(1)C(2) and N(1)C(6) of 1.338(3) and 1.325(3) Aring; respectively are similar to those found in pyridine. All distances and angles are within the expected values (Table 4). The pyridine ring is planar C(7) and C(8) deviating by 0.031(2) and 0.086(2) Aring; above this plane.Bond distances of the buta-1,3-diyne chain show normal values,11 with a C(7)C(8) triple bond distance of 1.199(3) Aring;. This chain is practically linear with a C(7)C(8)C(89) angle of 179.7(2)8. The crystal packs with the molecules in parallel columns (see Fig. 2) along the c-axis which defines the distance between the centroids of consecutive rings as being 3.87 Aring; forming with the c-axis an angle of 108. It can be seen in Fig. 2 that along the aaxis there are zones of neighbouring intermolecular rings and zones of intramolecular C CC C linear chains producing a so called lsquo;segregationrsquo; the overall least-squares planes through each molecule in the cell are parallel and within each column a stack is produced. Along the b-axis there are also chains of molecules in the so called lsquo;edge-to-edgersquo; mode with parallel molecules within a column but forming an angle of almost 908 between molecules of two neighbouring columns.In general in the reactive crystals of buta-1,3-diyne compounds the molecules are packed in a ladder-like fashion such that the ends of one triple-bond system approach an adjacent triple-bond system to a distance d 4 Aring; and the inclination angle formed with the translation axis is about 458.12 Charge-transfer complexes The p-electronic defect of the pyridine rings and the pextended conjugation to the diyne chain in 1,4-di(3-pyridyl)- buta-1,3-diyne 13 allowed it to take part in charge-transfer complexation with N,N,N9,N9-tetramethyl-p-phenylenediamine (TMPD) as donor. However the 1,4-di(n-pyridyl)buta-1,3- diyne derivative does not form charge-transfer complexes with Table 3 Yields of 9ndash;11 and 4ndash;6 Bromopyridine Alcohol () Acetylene () 2-subst.93 84 3-subst. 98 55 4-subst. 90 50 Table 4 Bond distances and angles for 13 (a) Bond distances (Aring;) N(1)C(2) 1.338(3) C(5)C(6) 1.394(3) N(1)C(6) 1.325(3) C(5)C(7) 1.431(3) C(2)C(3) 1.375(3) C(7)C(8) 1.199(3) C(3)C(4) 1.371(3) C(8)C(89) a 1.371(3) C(4)C(5) 1.392(3) (b) Bond angles (8) C(2)N(1)C(6) 117.3(2) C(4)C(5)C(6) 117.4(2) N(1)C(2)C(3) 123.1(2) C(6)C(5)C(7) 121.4(2) C(2)C(3)C(4) 119.2(2) N(1)C(6)C(5) 123.9(2) C(3)C(4)C(5) 119.0(2) C(5)C(7)C(8) 178.1(2) C(4)C(5)C(7) 121.2(2) C(7)C(8)C(89) a 179.7(2) a C(89) is related to C(8) by the symmetry operation (1 2 x 21 2 y 2 2 z). dagger; Supplementary material Tables of fractional atomic coordinates and thermal parameters and full bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC).See Instructions for Authors J. Chem. Soc. Perkin Trans. 1 1997 Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 207/78. J. Chem. Soc. Perkin Trans. 1 1997 711 some acceptors or donors so we carried out methylation of the pyridine rings to increase the acceptor character of these compounds (Scheme 4). The mono- and di-methylated salts of the meta diyne derivative were isolated pure and used to prepare charge-transfer complexes with the donor molecule TMPD. Thus slow evaporation of an equimolar mixture of the mono- or di-salt and TMPD in hot acetonitrile gave in both cases a metallic bright solid (black or green) (Fig.3). UV-Visible spectroscopy of the molecular complex of the monomethylated salt 15 and TMPD shows three chargetransfer bands at 543 565 and 615 nm. In the case of the molecular complex of the dimethylated salt 16 and TMPD the UV-visible spectrum also shows three charge-transfer bands at 594 617 and 642 nm. The IR spectra showed some differences between the complexes with TMPD and the free salts such that the intensity of the absorption for the C C conjugated bonds in the complexes is lower than that in the free salts. Experimental Mps were determined using a Reichert stage microscope and are uncorrected. IR Spectra were recorded using a Perkin-Elmer 681 spectrophotometer. NMR Spectra were recorded at 200 MHz using a Bruker WM-200-SY spectrometer; chemical shifts are given in d units using SiMe4 as internal reference; J values are given in Hz.UVndash;Visible spectra were recorded using a Perkin-Elmer Lambda 6 spectrophotometer. Mass spectra were recorded using a Hewlett-Packard SP85 spectrometer. Fig. 1 View of molecule 13 with the atom numbering scheme Scheme 4 Reagent MeI N C C N C C N C C N+Indash; C C CH3 ndash;I+N C C N+Indash; C C CH3 H3C 13 + 15 16 Preparation of ethynylpyridines by elimination of hydrogen chloride from the chlorovinyl derivatives 2-(2-Chlorovinyl)pyridine 1. To a suspension of chloromethyl- (triphenyl)phosphonium chloride (18.7 g 57 mmol) in dry THF (60 cm3) was slowly added a solution of butyllithium (1.6 M in hexane; 35.6 cm3 57 mmol) under argon at 210 8C. The solution acquired a red colour and after being stirred for 30 min was treated with pyridine-2-carbaldehyde (2 g 19 mmol).The mixture was stirred at room temperature for 10 h and then the solvent was removed to give a brown oil. Chromatography on silica gel with hexanendash;ethyl acetate afforded (Z)-2-(2-chlorovinyl) pyridine nmax(film)/cm21 3055 ( CH) 1620 (C C conj.) 1580 and 1560 (C C and C N) and 670 (Z); dH(200 MHz; CDCl3) 6.49 (1 H d J 8.3 CH CHCl) 6.86 (1 H d J 8.3 CH CHCl) 7.19 (1 H dd J 7.9 and 6.0 5-H) 7.70 (1 H t J 7.9 4-H) 8.02 (1 H d J 7.9 3-H) and 8.62 (1 H d J 6.0 6-H); m/z 141 (9) 139 (M+ 22) 104 (100) 84 (13) 78 (30) and 51 (27); and (E)-2-(2-chlorovinyl)pyridine nmax(film)/cm21 3070 ( CH) 1620 (C C conj.) 1580 and 1560 (C C and C N) and 970 (E); dH(200 MHz; CDCl3) 6.67 (1 H d J 13.3 CH CHCl) 7.20 (2 H m 3- and 5-H) 7.43 (1 H d J 13.3 CH CHCl) 7.63 (1 H m 4-H) and 8.53 (1 H br s 6-H); m/z 141 (9) 139 (M+ 27) 104 (100) 78 (25) and 51 (18).Fig. 2 Packing of the molecular crystal unit cells viewed down the baxis Fig. 3 N N CH3 CH3 H3C H3C N+Indash; C C C C N CH3 N N CH3 CH3 H3C H3C N+Indash; C C C C ndash;I+N CH3 H3C 712 J. Chem. Soc. Perkin Trans. 1 1997 3-(2-Chlorovinyl)pyridine 2. The same procedure was followed to prepare the 3-substituted derivative but with pyridine- 3-carbaldehyde. After purification by chromatography on silica gel the chlorovinyl derivative 2 was obtained as an oily mixture of E Z isomers (1 1) (2.38 g 90); nmax(film)/cm21 3050 ( CH) 1610 and 1605 (C C conj.) 1580 and 1560 (C C and C N) 970 (E) and 730 (Z); dH(200 MHz; CDCl3) 6.29 (1 H d J 8.2 CH CHCl Z) 6.69 (1 H d J 13.9 CH CHCl E) 6.74 (1 H d J 8.2 CH CHCl Z) 6.85 (1 H d J 13.9 CH CHCl E) 7.25 (1 H d J 8.0 5-H E) 7.32 (1 H dd J 8.0 and 5.4 5-H Z) 7.60 (1 H d J 8.0 4-H E) 8.13 (1 H d J 8.0 4-H Z) 8.49 (1 H br s 6-H E) 8.52 (1 H d J 5.4 6-H Z) 8.53 (1 H br s 2-H E) and 8.76 (1 H br s 2-H Z); m/z 141 (8) 139 (M+ 29) 104 (100) 86 (10) 77 (46) and 51 (64).4-(2-Chlorovinyl)pyridine 3. Following the same procedure we obtained the chlorovinyl derivative 3 from pyridine-4- carbaldehyde as an oily mixture of E Z isomers (1 1) (2.22 g 84); nmax(film)/cm21 3060 ( CH) 1610 (C C conj.) 1590 and 1540 (C C and C N) 960 (E) and 720 (Z); dH(200 MHz; CDCl3) 6.48 (1 H d J 8.2 CH CHCl Z) 6.60 (1 H d J 8.2 CH CHCl Z) 6.69 (1 H d J 13.8 CH CHCl E) 6.77 (1 H d J 13.8 CH CHCl E) 7.16 (2 H d J 4.8 3- and 5-H E) 7.52 (2 H d J 4.6 3- and 5-H Z) 8.56 (2 H d J 4.8 2- and 6-H E) and 8.62 (2 H d J 4.6 2- and 6-H Z); m/z 141 (8) 139 (M+ 29) 112 (29) 104 (38) 86 (84) 77 (36) 63 (16) and 51 (100).2-Ethynylpyridine 4. From the (Z)-2-(2-chlorovinyl)pyridine isomer 1a.mdash;To a solution of the (Z)-chlorovinyl derivative 1a (3 g 21 mmol) in dry THF (30 cm3) was slowly added potassium tert-butoxide (6 g 54 mmol) under argon at 0 8C. The mixture was stirred for 45 min at room temperature. Then the solution was poured onto icendash;water (150 cm3) and made alkaline (pH 8) with saturated aq. ammonium chloride. The mixture was extracted with dichloromethane; the extract was dried with magnesium sulfate and after filtration the solvent was removed to give a brown oil.Chromatography on silica gel with hexanendash; ethyl acetate (1 2) as eluent yielded the acetylene derivative 4 (1.04 g 48) as an orange oil bp 91ndash;92 8C/15 mmHg (lit.,9 85ndash; 86 8C/12 mmHg); nmax(film)/cm21 3260 ( CH) and 2114 (C C); dH(200 MHz; CDCl3) 3.25 (1 H s C CH) 7.21 (1 H dd J 7.7 and 5.1 5-H) 7.40 (1 H d J 7.7 3-H) 7.60 (1 H t J 7.7 4-H) and 8.54 (1 H d J 5.1 6-H); dC(200 MHz; CDCl3) 77.0 (PyC C) 82.5 (PyC C) 123.1 (C-5) 127.1 (C-3) 135.8 (C-4) 148.4 (C-2) and 149.5 (C-6); m/z 103 (M+ 100) 76 (46) and 50 (36). From the (E)-2-(2-chlorovinyl)pyridine isomer 1b.mdash;To a solution of the (E)-chlorovinyl derivative 1b (1 g 7.2 mmol) in dry THF (15 cm3) was slowly added potassium tert-butoxide (2 g 18 mmol) under argon at 0 8C. The mixture was stirred for 90 min at 50 8C.Then the solution was poured onto icendash;water (60 cm3) and made alkaline (pH 8) with saturated aq. ammonium chloride. The mixture was extracted with dichloromethane; the extract was dried with magnesium sulfate and after filtration the solvent was removed to give a brown oil. Chromatography on silica gel with hexanendash;ethyl acetate (1 2) as eluent yielded the acetylene derivative 4 (0.33 g 45) as an orange oil. 3-Ethynylpyridine 5. To a solution of the (Z,E)-chlorovinyl derivative 2 (3 g 21 mmol) in dry THF (30 cm3) was slowly added potassium tert-butoxide (6 g 54 mmol) under argon at 0 8C. The mixture was stirred for 60 min at 60 8C. Then the solution was allowed to cool and was poured onto icendash;water (150 cm3) and made alkaline (pH 8) with saturated aq. ammonium chloride.The mixture was extracted with dichloromethane; the extract was dried with magnesium sulfate and after filtration the solvent was removed to give a brown oil. Chromatography on silica gel with hexanendash;ethyl acetate (1 2) as eluent yielded the acetylene derivative 5 (1.17 g 54) as a yellow solid mp 35ndash;37 8C (lit.,13 39ndash;40 8C); nmax(film)/cm21 3280 ( CH) and 2120 (C C); dH(200 MHz; CDCl3) 3.30 (1 H s C CH) 7.25 (1 H ddd J 7.8 5.0 and 0.9 5-H) 7.70 (1 H dt J 7.8 and 2.0 4-H) 8.56 (1 H dd J 5.0 and 2.0 6-H) and 8.70 (1 H dd J 2.0 and 0.9 2-H); dC(200 MHz; CDCl3) 80.0 (PyC C) 80.6 (PyC C) 118.7 (C-3) 122.3 (C-5) 138.3 (C-4) 148.3 (C-6) and 151.9 (C-2); m/z 103 (M+ 100) 76 (38) and 50 (30). 4-Ethynylpyridine 6. Following the same procedure described to prepare 2-ethynylpyridine from the (Z)-chlorovinyl isomer 4-ethynylpyridine was obtained (40) as a solid from the 4-(chlorovinyl)isomer mp 63ndash;65 8C; nmax(film)/cm21 3270 ( CH) and 2100 (C C); dH(200 MHz; CDCl3) 3.40 (1 H s C CH) 7.35 (2 H d J 6.8 3- and 5-H) and 8.60 (2 H d J 6.8 2- and 6-H); dC(200 MHz; CDCl3) 80.6 (PyC C) 81.8 (PyC C) 129.9 (C-4) 125.7 (C-3 and -5) and 149.4 (C-2 and -6); m/z 103 (M+ 100) 76 (52) and 50 (41).Synthesis of ethynylpyridines by insertion of the acetylene group catalysed by palladium 2-Methyl-4-(2-pyridyl)but-3-yn-2-ol 9. Bis(triphenylphosphine) palladium(II) dichloride (220 mg 0.3 mmol) and copper( I) iodide (32 mg 0.2 mmol) were added successively to a solution of 2-bromopyridine (5 g 31.6 mmol) and 2-methylbut- 3-yn-2-ol (3.62 ml 37.3 mmol) in diethylamine (freshly distilled; 25 cm3) under argon at 0 8C.The mixture was stirred for 15 h at room temperature and then the diethylamine was removed under reduced pressure. The crude mixture was washed with water and extracted with dichloromethane; the extract was dried with magnesium sulfate and after filtration the solvent was removed to give a brown solid. Chromatography on silica gel with hexanendash;ethyl acetate as eluent yielded 2-methyl-4-(2- pyridyl)but-3-yn-2-ol 9 (4.76 g 93) as a yellow solid mp 60ndash; 62 8C (lit.,9 61ndash;63 8C); nmax(film)/cm21 3300 (OH) 2980 (CH) 2230 (C C) 1585 (C C conj.) 1380 and 1360 (CH3) 1170 (CO) 970 (Py) and 780 (PyH 2-subst.); dH(200 MHz; CDCl3) 1.70 (6 H s CH3 times; 2) 5.29 (1 H s OH) 7.20 (1 H dd J 6.7 and 5.0 5-H) 7.39 (1 H d J3,4 6.7 3-H) 7.62 (1 H td J4,3 = J4,5 6.7 and J4,6 0.8 4-H) and 8.59 (1 H br s 6-H); dC(200 MHz; CDCl3) 30.9 (CH3) 64.5 (COH) 80.6 (PyC C) 94.9 (PyC C) 122.5 (C-5) 126.7 (C-3) 136.0 (C-4) 142.6 (C-2) and 149.2 (C-6).2-Methyl-4-(3-pyridyl)but-3-yn-2-ol 10. Following the same procedure the 3-substituted derivative 10 was obtained (5 g 98) as a yellow solid from 3-bromopyridine mp 52ndash;54 8C; nmax(film)/cm21 3300 (OH) 2980 (CH) 2240 (C C) 1590 (C C conj.) 1380 and 1360 (CH3) 1170 (CO) 970 (Py) and 810 and 705 (PyH 3-subst.); dH(200 MHz; CDCl3) 1.58 (6 H s CH3 times; 2) 5.78 (1 H s OH) 7.15 (1 H dd J5,4 8.0 J5,6 6.4 5-H) 7.09 (1 H d J4,5 8.0 4-H) 8.38 (1 H s 6-H) and 8.60 (1 H s 2-H); dC(200 MHz; CDCl3) 31.1 (CH3) 64.3 (COH) 77.6 (PyC C) 98.6 (PyC C) 120.2 (C-3) 122.9 (C-5) 138.7 (C-4) 147.4 (C-6) and 151.3 (C-2).2-Methyl-4-(4-pyridyl)but-3-yn-2-ol 11. The preparation of the 4-substituted derivative 11 was carried out following the same procedure from 4-bromopyridine hydrochloride. Compound 11 was obtained (3.72 g 90) as a yellow solid mp 96ndash; 98 8C; nmax(film)/cm21 3350ndash;3040 (OH) 2980 (CH) 2230 (C C) 1600 (C C conj.) 1370 and 1360 (CH3) 1170 (CO) 970 (Py) and 840 (PyH 4-subst.); dH(200 MHz; CDCl3) 1.62 (6 H s CH3 times; 2) 3.10 (1 H s OH) 7.29 (2 H d J 8.1 3- and 5-H) and 8.59 (2 H s 2- and 6-H); dC(200 MHz; CDCl3) 31.0 (CH3) 64.5 (COH) 78.6 (PyC C) 100 (PyC C) 125.6 (C-3 and -5) and 148.8 (C-2 and -6). General procedure to prepare the ethynylpyridines from the 2-methyl-4-(n-pyridyl)but-3-yn-2-ols A solution of the alkynol (5 g 31 mmol) in dry toluene (30 cm3) was heated under reflux with pulverized sodium hydroxide (0.90 g) for 2 h.Then the solution was decanted and the solvent was evaporated under reduced pressure to give a brown solid. J. Chem. Soc. Perkin Trans. 1 1997 713 Chromatography on silica gel with hexanendash;ethyl acetate (1 2) yielded the ethynyl derivative 2-Ethynylpyridine (84) as an orange oil bp 90ndash;92 8C/15 mmHg; 3-ethynylpyridine (55) as a yellow solid mp 37ndash;39 8C and 4-ethynylpyridine (50) as a solid mp 63ndash;65 8C. Oxidative dimerization of ethynylpyridines. General procedure Oxygen was bubbled into a solution of copper(I) chloride (0.54 g 2.73 mmol) in pyridine (12 cm3) warmed to 40 8C after which the acetylene derivative (0.78 g 7.57 mmol) was added. The mixture was stirred for 3 h after which it was cooled and concentrated by removal of the pyridine by distillation.The crude mixture was washed with ammonium hydroxide until the blue colour disappeared after which it was extracted with dichloromethane. The extract was dried (MgSO4) filtered and evaporated to give a yellow solid chromatography of which on silica gel with hexanendash;ethyl acetate (1 2) as eluent yielded the diyne derivative. 3-Substituted product 13 (49) was a yellow solid mp 145ndash;146 8C; nmax(KBr)/cm21 1550 (C C conj.) 955 (Py) 800 and 700 (PyH 3-subst.); dH(200 MHz; CDCl3) 7.30 (2 H dd J 7.9 and 5.0 5-H) 7.82 (2 H dt J 7.9 and 1.7 4-H) 8.61 (2 H br s 6-H) and 8.78 (2 H br s 2-H); dC(200 MHz; CDCl3) 78.9 (C C) 118.5 (C-3) 122.7 (C-5) 139.1 (C-4) 149.2 (C-6) and 152.9 (C-2); m/z 204 (M+ 100) 177 (11) 151 (23) and 124 (8); lmax(CH2Cl2)/nm 229 (e/dm3 mol21 cm21 30 000) 244 (29 000) 292 (22 000) 319 (30 000) and 331 (26 000).4-Substituted product 14 (54) was a brown solid mp 198ndash; 201 8C; nmax(Nujol)/cm21 1580 (C C conj.) 980 (Py) and 810 (PyH 4-subst.); dH(200 MHz; CDCl3) 7.41 (4 H d J 7.2 3- and 5-H) and 8.67 (4 H br s 2- and 6-H); dC(200 MHz; CDCl3) 76.9 (PyC C) 79.9 (PyC C) 125.7 (C-3 and -5) 128.9 (C-4) and 149.6 (C-2 and -6); m/z 204 (M+ 100) 177 (13) 151 (14) and 124 (6). X-Ray crystallographic analysis of 1,4-di(3-pyridyl)buta-1,3- diyne 13 Yellow transparent plate-like crystals of 1,4-di(3-pyridyl)buta- 1,3-diyne 13 were grown by slow evaporation from an acetonitrile solution. A crystal of dimensions 0.29 times; 0.27 times; 0.18 mm3 was selected for X-ray diffraction analysis.Accurate cell dimensions were determined by least-squares analysis of setting angles of 40 reflections (15 2q 848) using graphite-monochromated Cu-Ka radiation (l = 1.5418 Aring;) automatically located and centred on a four-circle Philips PW1100 diffractometer. C14H8N2 M = 204.23 monoclinic a = 22.104(3) b = 6.017(1) c = 3.873(1) Aring; b = 91.48(1)8 V = 514.92(7) Aring;3 Z = 2 space group P21/n Dc = 1.317(3) g cm23 F(000) = 212 m = 6.253 cm21. Data collection. Two standard reflections were measured every 90 min to ascertain crystal stability; no significant variation was observed. The intensities were corrected for Lorentz and polarization effects. No corrections were made for absorption. For the intensity measurement reflections were surveyed in the range 2 q 658; from 975 independent reflections measured 778 were considered as observed satisfying the criterion I 2s(I) in the range h 227/27 k 0/8 l 0/5 and were used in the subsequent calculations.The structure was solved by direct methods using SIR92,14 and refined by anisotropic full-matrix least-squares.15 The H-atoms were located on a difference map and refined isotropically. After several cycles of mixed refinement (89 refined parameters) convergence was reached at R = 0.057 and Rw = 0.069 with a weighting scheme16 to prevent trends in middot;wD2FOgrave; vs. middot;verbar;Foverbar;Ograve; and middot;sinq/lOgrave;. The atomic scattering factors and the anomalous dispersion corrections were taken from the literature.17 Atomic coordinates bond distances and angles were calculated using the PARST program.18 1,4-Di(2-pyridyl)buta-1,3-diyne 12 To a suspension of copper(I) chloride (57 mg 0.58 mmol) and N,N,N9,N9-tetramethylethylenediamine (TMEDA) (0.11 cm3 0.75 mmol) in 1,2-dimethoxyethane (DME) (4 cm3) was added a solution of 2-ethynylpyridine 4 (0.3 g 2.9 mmol) in DME (1 cm3) previously heated for 10 min at 35 8C while oxygen was bubbled in.After 30 min the mixture changed in colour from green to brown and 15 min later the solvent was removed to give a brown solid chromatography of which on silica gel with hexanendash;ethyl acetate (2 3) as eluent yielded the diacetylene derivative 12 (150 mg 52) as a solid mp 120ndash; 122 8C (lit.,19 122ndash;123 8C); nmax(KBr)/cm21 1580 and 1560 (C C conj.) 990 (Py) 780 and 735 (PyH 2-subst.); dH(200 MHz CDCl3) 7.24 (2 H ddd J 7.6 4.8 and 1.1 5-H) 7.47 (2 H d J 7.7 3-H) 7.63 (2 H td J 7.7 and 1.7 4-H) and 8.55 (2 H d J 4.8 6-H); dC(200 MHz; CDCl3) 72.9 (PyC C) 80.7 (PyC C) 123.6 (C-5) 128.2 (C-3) 136.0 (C-4) 141.5 (C-2) and 150.2 (C-6); m/z 204 (M+ 100) 177 (14) 151 (14) 124 (5) 102 (6) and 78 (10); lmax(CH2Cl2)/nm 238 (e/dm3 mol21 cm21 23 600) 294 (18 400) 309 (24 000) and 330 (20 800).Methylation of the 1,4-di(3-pyridyl)buta-1,3-diyne 13 To a solution of the diyne derivative (100 mg 0.49 mmol) in ethanol (25 cm3) was added iodomethane (0.12 cm3 1.96 mmol). The mixture was stirred for 20 h at 50 8C. A yellow solid precipitated from the solution and was filtered off and identi- fied as the dimethylated derivative 16 (92 mg 38) mp 190 8C (decomp.). Then the mixture was allowed to cool and an orange solid precipitated out which was filtered off and identi- fied as the monomethylated derivative 15 (72 mg 42) mp 166 8C (decomp.).Dimethylated product 16 had nmax(KBr)/cm21 1620 and 1500 (C C and C N conj.) 1290 (NCH3) 1150 (Py+ndash;CH3) 810 and 665 (PyH 3-subst.); dH200 MHz; (CD3)2SO 4.37 (6 H s CH3 times; 2) 8.23 (2 H t 5-H) 8.91 (2 H d 4-H) 9.13 (2 H d 6-H) and 9.49 (2 H s 2-H); dC(200 MHz; CDCl3) 48.4 (CH3) 77.2 and 77.6 (PyC C) 120.1 (C-3) 127.7 (C-5) 146.4 (C-4) 147.9 (C-6) and 149.3 (C-2); m/z (FAB+) 234 (M+ 25) and 219 (52); lmax(CH2Cl2)/nm 237 (e/dm3 mol21 cm21 31 430) 290 (18 500) 308 (20 000) 330 (18 570) 345 (13 710) 354 (12 000) and 360 (11 430). Monomethylated product 15 had nmax(KBr)/cm21 1620 1580 and 1500 (C C and C N conj.) 1280 (NCH3) 1160 (Py+CH3) 830 800 700 and 675 (PyH 3-subst.); dH200 MHz; (CD3)2SO 4.31 (3 H s CH3) 7.50 (1 H m 5-H) 8.20 (2 H m 5-H in the methylated ring and 4-H) 8.70 (2 H m 2- and 6-H) 8.88 (1 H m 4-H in the methylated ring) 9.05 (1 H d 6-H in the methylated ring) and 9.42 (1 H br s 2-H in the methylated ring); dC(200 MHz; CDCl3) 48.4 (CH3) 77.2 and 77.6 (PyC C) 120.1 (C-3) 127.7 (C-5) 146.4 (C-4) 147.9 (C-6) and 149.3 (C-2); m/z (FAB+) 219 (M+ 100) and 205 (13); lmax(CH2Cl2)/nm 237 (e/dm3 mol21 cm21 40 250) 290 (17 750) 308 (22 500) 330 (24 000) and 345 (12 500).Charge-transfer complex of 1-(N-methylpyridinium-3-yl)-4-(3- pyridyl)buta-1,3-diyne iodide 15 with TMPD A hot solution of TMPD (24 mg 0.14 mmol) in acetonitrile (10 cm3) was added to a nearly boiling solution of the monomethylated buta-1,3-diyne derivative 15 (50 mg 0.14 mmol) in 100 cm3 of acetonitrile.The resulting dark violet solution was allowed to cool and then to evaporate slowly to yield a black solid with metallic lustre; nmax(Nujol)/cm21 1610 1580 and 1510 (C C and C N conj.) 1160 (Py+CH3) 950 (Py) 820 810 800 720 690 and 665 (PyH 3-subst.); lmax(CH2Cl2)/nm 238 309 330 350 543 565 and 615. Charge-transfer complex of 1,4-bis(N-methylpyridinium-3-yl)- buta-1,3-diyne diiodide 16 with TMPD The same procedure was followed to form the charge-transfer complex of the dimethylated buta-1,3-diyne derivative 16. 714 J. Chem. Soc. Perkin Trans. 1 1997 The complex was a green solid with a metallic lustre; nmax- (Nujol)/cm21 1620 and 1520 (C C and C N conj.) 1320 (NCH3) 1170 and 1150 (Py+CH3) 950 (Py) 815 720 and 665 (PyH 3-subst.); lmax(CH2Cl2)/nm 264 327 594 617 and 642.Acknowledgements We are indebted to the CAYCIT of Spain for financial support (project no. PB92-0142-C02-01). References 1 Polydiacetylenes ed. D. Bloor and R. R. Chance NATO ASI series E No. 102 Matinus Nijkoff Boston 1985; A. E. Stiegman E. Graham K. J. Perry R. Khundkard L. T. Cheng and J. W. Perry J. Am. Chem. Soc. 1991 113 1658 and references cited therein. 2 G. Wegner Z. Naturforsch. B Anorg. Chem. Org. Chem. 1969 24 824. 3 G. M. Carter Y. J. Chen M. F. Rubner D. J. Sandman M. K. Thakur and S. K. Tripathy in Nonlinear Optical Properties of Organic Molecules and Crystals ed. D. S. Chemla and J. Zyss Academic Press New York 1987 vol. 2 p. 85. 4 G. Wegner J. Polym. Sci. Part B Polym. Lett. 1971 9 133. 5 Y. Ozcayir J. Asrar and A.Blumstein Mol. Cryst. Liq. Cryst. 1984 110 1424. 6 G. H. Milburn A. R. Wernick J. Tsibouklis E. Bolton G. Thomson and A. Shand Polymer 1989 30 1004. 7 J. P. Ferraris D. O. Cowan V. Walatka and J. Perlstein J. Am. Chem. Soc. 1973 95 948. 8 G. Kouml;brig H. Trapp K. Flory and W. Drischel Chem. Ber. 1966 99 689. 9 D. E. Ames D. Bull and C. Takundwa Synth. Commun. 1981 364. 10 L. Brandsma Studies in Organic Chemistry Preparative Acetylenic Chemistry Elsevier Science Publishers B.V. Amsterdam 1988 vol. 34 p. 220. 11 J. G. Rodriacute;guez S. Ramos R. Martiacute;n-Villamil I. Fonseca and A. Albert J. Chem. Soc. Perkin Trans. 1 1996 541. 12 G. M. J. Schmidt Reactivity of the Photoexcited Organic Molecule Wiley New York 1967 p. 227. 13 S. D. Lrsquo;vova Y. P. Koslov and U. I. Gunar Zh. Obshch. Khim. 1977 47 1251.14 A. Altomare G. Cascarano C. Giacovazzo and A. Guagliardi Dipartimento Geomineralogico University of Bari; M. Burla and G. Polidori Dipartimento Scienze della Terra University of Perugia; M. Camalli SIR92 Ist Strutt. Chimica CNR Monterrotondo Stazione Roma 1992. 15 J. M. Stewart F. A. Kundell and J. C. Badwin The XRAY80 System Computer Science Center University of Maryland College Park MD 1980. 16 M. Martinez-Ripoll and F. H. Cano PESOS A Computer Program for the Automatic Treatment of Weighting Schemes Instituto Rocasolano CSIC Madrid 1975. 17 International Tables for X-RAY Crystallography Kynoch Press Birmingham 1974 vol. 4. 18 M. Nardelli Comput. Chem. 1983 7 95. 19 U. Fritzsche and S. Hunig Tetrahedron Lett. 1972 4831. Paper 6/05468D Received 5th August 1996 Accepted 5th November 1996 J.Chem. Soc. Perkin Trans. 1 1997 709 Synthesis of 1,4-di(n-pyridyl)buta-1,3-diyne and formation of charge-transfer complexes. X-Ray structure of 1,4-di(3-pyridyl)buta-1,3-diyne J. Gonzalo Rodriacute;guez,*,a Rosa Martiacute;n-Villamil,a Felix H. Canob and Isabel Fonsecab a Departamento de Quiacute;mica Orgaacute;nica Universidad Autoacute;noma de Madrid Cantoblanco 28049-Madrid Spain b Departamento de Cristalografiacute;a C.S.I.C. Serrano 119 28006-Madrid Spain Ethynylpyridines have been satisfactorily prepared by two different routes (a) the Wittig reaction between chloromethylene(triphenyl)phosphine ylide and a pyridinecarbaldehyde followed by elimination of hydrogen chloride; (b) from the 2-methyl-4-(n-pyridyl)but-3-yn-2-ol intermediate by elimination of acetone. 1,4-Di(n-pyridyl)buta-1,3-diynes are obtained by oxidative dimerization in good yield.An X-ray structure of the 3-substituted dimer is reported. Mono- and di-methyl salts of the 3-substituted diyne have been obtained and the charge-transfer complexes with tetramethyl-p-phenylenediamine (TMPD) are formed. Introduction The use of molecular organic materials for conductor and nonlinear optics applications is an area of considerable recent activity. Interest in these materials is due to their inherent synthetic flexibility which permits the lsquo;designrsquo; of molecular properties. 1 Solid-state polymerization of 1,3-diynes to form crystalline conjugated polydiynes has attracted much attention.1,2 Some of the recent interest in poly-1,3-diynes is related to their large and fast nonlinear optical response making them good potential materials in ultrafast optical applications.3 Although the electronic and optical properties of poly-1,3-diynes are primarily dominated by the p-conjugated backbone the substituent groups markedly influence the topopolymerization behaviour of the 1,3-diynes and the physical and chemical properties of the crystalline conjugated poly-1,3-diynes.An aspect of the substituent effect that has received little attention is the influence of formally p-conjugated substituents on the electronic properties of poly-1,3-diynes because many of them are unreactive in the solid state,4ndash;6 although they may undergo liquid-crystalline polymerization to form polymers distinct from the solid-state polymers. However preliminary studies show that 4-amino-49-nitrodiphenyl-1,3-diyne is solid-state reactive.6 The discovery of a one-dimensional metallic state in the ionradical solid formed from the p-donor tetrathiafulvalene and the acceptor tetracyanoquinodimethane has stimulated interest in the structurendash;properties relationships of novel donors and