Synthesis and non-linear properties of disubstituted diphenylacetylene and related compounds Koichi Kondo,*a Takumi Fujitanib and Noriaki Ohnishib aDepartment of Chemistry, Faculty of Science and Engineering, Ritsumeikan University, Kusatsu, Shiga 525, Japan bDepartment of Applied Fine Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565, Japan A variety of disubstituted diphenylacetylenes and related compounds have been synthesized by a modified Horner–Emmons reaction, and their second harmonic generation (SHG) has been evaluated by the Kurtz powder method.The diphenylacetylenes with weak electron-donating and -withdrawing groups are found to be efficient for SHG, as well as having the lowest cut-off wavelength. In recent decades, much attention has been focused on non- (5, 7, 9 and 13) were prepared from various aldehydes (Scheme 2).linear materials from both theoretical and practical points of Diphenylbutadiyne 7 is considered to be a potentially useful view. In particular, second harmonic generation (SHG) based compound for third harmonic generation (THG) since some on organic compounds is interesting because of the large nonpoly( diacetylene)s synthesized from butadiynes have been linear susceptibilities produced by intramolecular charge transfound to exhibit large THG properties.10 Moreover, the ter- fer (ICT) in p-conjugated systems, which is substantially minal acetylene 9 is attractive as a potential monomer for different from inorganic materials.1 Most SHG active organic polymerization by W, Ta11 and/or Rh catalysts12 into a poly- compounds are based on p-nitroaniline derivatives, despite the (phenylacetylene) system with similar properties.recent discovery of non-linear rigid ICT acetylene frameworks.2 The SHG intensity of compounds 3, 5, 7, 9 and 13 relative Disubstituted diphenylacetylene derivatives, however, have not to urea was determined by the Kurtz powder method.13 The been studied in terms of their non-linear properties, except for results are summarized in Table 1 (for 3) and Table 2 (for 5, 7, a few examples such as 1-(4-methoxyphenyl)-2-(4-nitrophe- 9 and 13).Table 1 shows only the SHG active phenylacetylenes nyl)acetylene3,4 and 1-(4-bromophenyl)- and 1-(4-iodophenyl)- out of more than seventy compounds prepared via the reported 2-(4-nitrophenyl)acetylene,5 due to the tedious preparation method.The fact that a number of diphenylacetylenes are based on the oxidative coupling of cuprous arylacetylides with SHG active indicates that they tend to adopt the non-centro- aryl iodides. Although this classical oxidative method has symmetric crystal packing essential for SHG, a suggestion that now been superseded by the recently developed Pd-catalysed is supported by X-ray crystallographic analysis of these mol- coupling of ethynylbenzene derivatives with iodo- or bromoecules. 14 The large number of chloro-substituted compounds substituted aromatic compounds, the latter is limited to pthat exhibit SHG also indicates that weak dipole polarization conjugated systems.6 may favour non-centrosymmetric crystal packing, which can While searching for another preparation of diphenylacetyrely on a ICT structure linked to the cut-off wavelength as lenes, we realised that a modified Horner–Emmons reaction shown in the weak dipole–dipole interaction of SHG active 3- has previously proved useful for triple bond formation and methyl-4-nitropyridine N-oxide.15 The cut-off wavelength of has afforded a variety of pyridylphenylacetylenes.7 the chloro-substituted compounds 3 was as low as that of Here we describe the synthesis of 4,4¾-disubstituted diphenyl- stilbene derivatives.16 In general, compounds 3 with weak acetylenes and related compounds based on a modified electron-withdrawing and -donating groups such as Cl and Horner–Emmons reaction, together with their SHG properties.Results and Discussion Zimmer et al. reported that phosphonate carbanions couple with aryl aldehydes under mild basic conditions to give chlorostilbenes or diphenylacetylenes.8 This method, however, has not been used widely because of the sensitive reaction conditions required for the preparation of the starting hydroxy phosphonate, which is thermally liable and prone to rearrangement to the phosphate.9 Therefore the temperature control, as well as choice of solvent, was examined.Diphenyl phosphite was allowed to react with the appropriate 4-substituted benzaldehydes in THF for a few hours below 25°C to afford diphenyl hydroxy(aryl)methylphosphonates 1, which were converted to the chloro compounds 2 by treatment with POCl3–PhNEt2 for 1 h at 90°C.Thus, further 4-substituted benzaldehydes and 2 were subsequently treated with 2 equiv. of ButOK in THF for 3 h at room temperature to afford the 4,4¾-disubstituted diphenylacetylenes 3 X CHO X OH P O OPh OPh X Cl P O OPh OPh X Y 1 POCl3 PhNEt2 CHO Y (PhO)2P(O)H 2 ButOK 2 3 Scheme 1 (Scheme 1). Based on this reaction, the related compounds J. Mater. Chem., 1997, 7(3), 429–433 429NO2 NO2 S S X Cl P O OPh OPh Y X S S CHO CHO Y CHO CHO H CH(OEt)2 OHC 2 X = Cl, Br, CN, NO2, MeO 4 O2N CH(OEt)2 4 ButOK 6 X 8 10 H 2 ButOK O2N CHO 5 7 12 13 O2N 2 ButOK 2 ButOK (X = NO2) H+ 9 OMe 11 2 (X = OMe) 2 ButOK (X = NO2) Scheme 2 MeO exhibit a hypsochromic shift in the cut-off wavelength 65 times as active as urea.However, when recrystallized from ethanol, as in our study, they are only twice as active as urea.(337 nm) that arises from the weak ICT structure needed for SHG, as compared with the bathochromic shift for compounds Such solvent effects may be due to crystal polymorphism related to crystal packing, which can vary when different with strong electron-withdrawing and -donating groups (590 nm for nitro and dimethylamino substitutents) (Table 3).solvents are used during crystallization. Further studies involving X-ray crystallography are currently in progress. No significant effect of the chain length of the substituted alkoxy groups on SHG was found. Additional triple bond conjugation was not significantly effective for SHG, as shown Experimental for the nitro- and methoxy-substituted compounds 3 (X= NO2, Y=MeO): 7 (X=MeO, Y=NO2) and 13, in which SHG THF was distilled over sodium and LiAlH4. 4- Alkoxybenzaldehydes were obtained by the reaction of active 3 shows a decrease in the cut-off wavelength, while SHG inactive butadiyne 7 is much more highly conjugated than the 4-hydroxybenzaldehyde with the relevant alkyl bromide [Me(CH2)nBr; n=4–11] in DMF in the presence of sodium extended p-conjugated diphenylacetylene type compound 13 (Tables 1 and 2).SHG active 5 is of interest because of its hydride at 50°C for 24 h. 6,6-Diformyl-1,4-dithiafulvene 4,18 4-ethynylbenzaldehyde 819 and 4-(diethoxymethyl)benzal- triangular structure, which is similar to SHG active L-type methanediamine derivatives.17 dehyde 1020 were prepared by literature methods. 4-Substituted 3-phenyprop-2-ynal 6 was obtained by the formylation of 4- Sample manipulation affects SHG significantly. For example, 1-(4-methylthio- and 1-(4-methoxy-phenyl)-2-(4-nitrophe- substituted ethynylbenzene,21 which was derived from 4-substituted trimethylsilylethynylbenzene6a or 4-aryl-2-methylbut-3- nyl)acetylene which were chromatographed on silica gel2 and recrystallized from methylcyclohexane,3 respectively, are 50 to yn-2-ol.22 430 J.Mater. Chem., 1997, 7(3), 429–433Table 1 Relative SHG powder efficiency of 3 Table 3 Cut-off wavelength for varied substitution in compound 3 3 3 cut-off cut-off X Y SHGa wavelength/nm X Y wavelength/nm NO2 F 418 NO2 SMe 2.7 462 NO2 OMe 2.0 425 NO2 OMe 425 NO2 NEt2 590 CN OC5H11 7.5 373 CN OC6H13 0.1 375 CN F 350 CN OMe 374 CN OC7H15 4.0 375 CN F 0.1 350 CN NEt2 474 Br F 324 CN Br 0.1 406 CN NMe2 0.1 457 Br OMe 347 Br NEt2 433 CN NEt2 0.1 474 Cl SMe 0.1 360 Cl F 320 Cl OMe 337 Cl OMe 0.1 337 Cl OEt 0.1 343 Cl NEt2 427 Cl OPr 0.1 332 Cl OBu 0.1 346 Cl OC5H11 0.1 337 Cut-off wavelength Cl OC6H13 2.8 350 Cl OC7H15 0.1 348 The cut-off wavelength was determined from 95% of the Cl OC8H17 0.8 347 transmittance, which was measured for a 1 mM MeCN solution Cl OC10H25 0.9 342 of the compounds.Cl OC12H25 0.5 383 Cl F 0.1 320 Diphenyl hydroxy(4-nitrophenyl )methylphosphonate 1 Cl NMe2 4.7 433 Cl NEt2 0.1 427 (X=NO2) Br OMe 1.4 347 To a solution of 4-nitrobenzaldehyde (12 g, 80 mmol) in dry Br OC6H13 0.1 352 Br OC7H15 0.1 351 THF (30 cm3) was added dropwise a solution of diphenyl Br OC8H17 0.1 428 phosphite (18.7 g, 80 mmol) in dry THF (20 cm3) over 30 min, Br NEt2 0.1 433 and the reaction was stirred for 3 h at room temperature.After evaporation of the solvent, the residue was recrystallized from aRelative to urea. ethanol to give the product (65%), mp 125 °C; dH[(CD3)2SO] 4.65 (1H, s, OH), 5.38 (1H, d, CH, JHP12†), 6.90–7.41 (10H, Table 2 Relative SHG powder efficiency of extended p-conjugated m, aromatic H), 7.68 (2H, d, aromatic H), 8.18 (2H, d, aromatic systems H); nmax(KBr)/cm-1 3280s (OH), 1520s and 1330s (NO2 ), 1250m (PNO), 1060m, 1020m and 960m (P–O) (Found: C, cut-off 59.15; H, 4.17; N, 3.60.C19H16NO6P requires C, 59.22; H, 4.19; wavelength/ extended p-conjugated system SHGa nm N, 3.64%). Diphenyl chloro(4-nitrophenyl )methylphosphonate 2 (X=NO2) 1 (X=NO2 ) (9.3 g, 24.1 mmol) was treated with 25 cm3 of 0.1 520 POCl3 in the presence of N,N-diethylaniline (2 cm3) for 1 h at 90°C.After evaporation of the solvent and addition of ice– water, the reaction was extracted with CH2Cl2, and the extracts were washed with aqueous sodium hydrogen carbonate and 5.0 483 dried over MgSO4. The solvent was evaporated in vacuo and the residue recrystallized from ethanol to give the product (84%), mp 121 °C; dH[(CO3)2SO] 5.64 (1H, d, CH, JHP 15), 1.0 475 7.20–7.65 (10H, m, aromatic H), 8.08 (2H, d, aromatic H), 8.52 (2H, d, aromatic H); nmax(KBr)/cm-1 1520s and 1350s 1.5 467 (NO2), 1270m (PNO), 1070m, 1020m and 960m (P–O) (Found: C, 56.71; H, 3.68; N, 3.37.C19H15NO5PCl requires C, 56.52; H, 3.74; N, 3.47%). 0 485 Diphenyl chloro(4-methoxyphenyl )methylphosphonate 2 0 456 (X=MeO) Yield 27%, mp 117°C; dH[(CD3)2SO] 3.85 (3H, s, CH3 ), 5.20 0 470 (1H, d, CH, JHP 14), 6.80–7.65 (14H, m, aromatic H) (Found: C, 61.35; H, 4.96. C20H18O4PCl requires C, 61.78; H, 4.63%). aRelative to urea. Diphenyl chloro(4-cyanophenyl )methylphosphonate 2 (X=CN) Second harmonic generation measurements The samples were ground with a mortar and pestle, meshed Yield 68%, mp 125°C; dH[(CD3 )2SO] 5.23 (1H, d, CH, JHP 15), 6.80–7.30 (10H, m, aromatic H), 7.65 (4H, m, aromatic to 75 to 100 mm and fixed on a glass slide by tape.The slide was irradiated by a Nd-YAG laser (l=1064 nm, pulse width H) (Found: C, 62.26; H, 3.92; N, 3.68. C20H15NO3PCl requires C, 62.59; H, 3.94; N, 3.65%). 350 ps, power density 5 GWcm-2, spot size 0.8 mm) and the intensity of SHG light (532 nm) was monitored by a photodiode and compared with the SHG intensity of urea.† J values given in Hz. J. Mater. Chem., 1997, 7(3), 429–433 431Diphenyl chloro(4-chlorophenyl )methylphosphonate 2 (X=Cl ) 1.32 (6H, t, CH3), 3.75 (4H, q, CH2 ), 5.50 (1H, s, CH), 7.60 (2H, d, aromatic H), 8.15 (2H, d, aromatic H).The acetal (3 g, Yield 56% mp 91°C; dH[(CD3)2SO] 5.17 (1H, d, CH, JHP 14), 12 mmol) was hydrolysed with 0.5 M sulfuric acid (50 cm3) at 6.90–7.50 (14H, m, aromatic H) (Found: C, 57.94; H, 3.67. 110°C for 40 min, and the reaction was extracted with CH2Cl2 C19H15O3PCl2 requires C, 58.04; H, 3.85%). to give 3-(4-nitrophenyl)prop-2-ynal in 54% yield, mp 95°C; dH(CDCl3) 7.78 (2H, d, aromatic H), 8.30 (2H, d, aromatic Diphenyl bromo(4-bromophenyl)methylphosphonate 2 (X=Br) H), 9.50 (1H, s, CH); nmax(KBr)/cm-1 2260m (COC), 1620s (CNO) (Found: C, 61.50; H, 3.05; N, 7.87.C9H5NO3 requires Yield 29%, mp 107 °C; dH[(CD3)2SO] 5.17 (1H, d, CH, JHP C, 61.71; H, 2.88; N, 8.00%). 14), 6.50–7.30 (10H, m, aromatic H), 7.48 (4H, s) (Found: C, 51.84; H, 3.40.C19H15O3PClBr requires C, 52.14; H, 3.45%). 1-(4-Ethynylphenyl)-2-(4-nitrophenyl )acetylene 9 (X=NO2 ) 1-(4-Methoxyphenyl )-2-(4-nitrophenyl )acetylene 3 Compound 2 (X=NO2) (2.01 g, 4.9 mmol) and 4-ethynylben- (X=NO2, Y=MeO) zaldehyde 8 (0.65 g, 4.9 mmol) were treated with ButOK (1.20 g, 10.7 mmol) in THF (30 cm3) for 3 h at room tempera- Compound 2 (X=NO2) (1.25 g, 3.07 mmol) and 4-methoxy- ture.After evaporation of the solvent, the residue was extracted benzaldehyde (0.60 g, 4.0 mmol) in THF (30 cm3) were treated with CH2Cl2, and the solution dried over MgSO4. The solvent with ButOK (1.0 g, 8.9 mmol) for 3 h at room temperature. was removed and the residue recrystallized from ethanol to After evaporation of the solvent, water (20 cm3) was added to give the product in 44% yield, mp 211 °C; dH(CDCl3 ) 3.23 the residue, the aqueous mixture was extracted with CH2Cl2, (1H, s, CH), 7.52 (2H, d, aromatic H), 7.70 (2H, d, aromatic and the organic fractions were dried over MgSO4 .The solvent H), 8.13 (2H, d, aromatic H), 8.28 (2H, d, aromatic H); was removed in vacuo and the residue was recrystallized nmax(KBr)/cm-1 3240m (C–H), 2200m (COC), 1500s and from ethanol to give the product in 58% yield, mp 115 °C; 1335s (NO2) (Found: C, 77.62; H, 3.60; N, 5.58.C16H9NO2 dH(CDCl3 ) 3.90 (3H, s, CH3), 7.09–8.24 (8H, m, aromatic H); requires C, 77.72; H, 3.67; N, 5.67%). nmax(KBr)/cm-1 2210m (COC), 1510s and 1335s (NO2) (Found: C, 71.06; H, 4.39; N, 5.50. C15H11NO3 requires C, 1-(4-Cyanophenyl)-2-( 4-ethynylphenyl )acetylene 9 (X=CN) 71.14; H, 4.38; N, 5.53%).Mp 207 °C; dH(CDCl3) 3.10 (1H, s, CH), 7.38 (4H, m, aromatic 1-(4-Cyanophenyl )-2-(4-pentyloxyphenyl ) acetylene 3 H), 7.52 (4H, m, aromatic H); nmax(KBr)/cm-1 3225m (C–H), (X=CN, Y=C5H11O) 2220m (CON), 2200 (COC) (Found: C, 89.63; H, 3.80; N, 6.05. C17H9N requires C, 89.84; H, 3.99; N, 6.16%). Yield 34%, mp 83°C; dH(CDCl3 ) 0.63–2.65, (8H, m, CH2), 3.65 (3H, t, CH3), 6.54–7.25 (8H, m, aromatic H); 6,6-Bis[ 2-(4-nitrophenyl ) ethynyl]-1,4-dithiafulvene 5 nmax(KBr)/cm-1 2940s, 2910s and 2840s (C–H), 2210m (CON), 2200m (COC) (Found: C, 82.64; H, 6.63; N, 4.57.C20H19NO Compound 2 (X=NO2 ) (1.61 g, 4 mmol) and 6,6-diformyl-1,4- requires C, 83.01; H, 6.62; N, 4.84%). dithiafulvene (0.30 g, 1.7 mmol) were treated with ButOK (1.0 g, 9.2 mmol) in THF (50 cm2) for 4 h at room temperature. After evaporation of the solvent, the residue was extracted 1-(4-Chlorophenyl )-2-(4-dimethylaminophenyl )acetylene 3 with CH2Cl2 and the solution dried over MgSO4.The solvent (X=Cl, Y=NMe2 ) was removed and residue recrystallized from ethanol to give Yield 32%, mp 150 °C; dH(CDCl3) 2.03 (6H, d, CH3) 6.55–7.43 the product in 15% yield, mp 115 °C; dH(CDCl3 ) 7.15–8.25 (8H, m, aromatic H); nmax(KBr)/cm-1 2890s, 2850s and 2800s (8H, m, aromatic H); nmax(KBr)/cm-1 2200m (COC), 1510s (C–H), 2200m (COC) (Found: C, 75.10; H, 5.37; N, 5.17. and 1330s (NO2) (Found: C, 58.52; H, 2.85; N, 6.52.C16H14NCl requires C, 75.14; H, 5.52; N, 5.48%). C20H12N2O4S2 requires C, 58.81; H, 2.96; N, 6.86%). 1-(4-Bromophenyl )-2-(4-methoxyphenyl ) acetylene 3 1-(4-Methoxyphenylethynyl )-4-(4-nitrophenylethynyl )benzene (X=Br, Y=MeO) 13 Yield 26%, mp 155 °C; dH(CDCl3) 3.86 (3H, s, CH3 ) 6.36–7.50 Compound 2 (X=NO2) (2.01 g, 5.01 mmol) and compound (8H, m, aromatic H); nmax(KBr)/cm-1 2970m, 2930m and 10 (1.0 g, 4.81 mmol) were treated with ButOK (1.2 g, 2840m (C–H), 2200m (COC) (Found: C, 62.48; H, 3.77. 10.7 mmol) in THF (30 cm3) for 3 h at room temperature. C15H11OBr requires C, 62.74; H, 3.86%). After evaporation of the solvent the residue was stirred with 1 M hydrochloric acid (50 cm3) for 30 min, then the reaction 3-(4-Nitrophenyl )prop-2-ynal 6 (Y=NO2 ) was extracted with CH2Cl2, and the organic fractions dried over MgSO4 .The solvent was removed under reduced pressure, 4-Bromonitrobenzene (50 g, 247 mmol) and 2-methylbut-3-yn- and the residue recrystallized from ethanol to give 1-(4- 2-ol (25 g, 297 mmol) were refluxed for 2 h in triethylamine formylphenyl)-2-(4-nitrophenyl)acetylene 12 (X=NO2) in (500 cm3).The solvent was evaporated under reduced pressure 60% yield. Compound 12 (X=NO2) (0.15 g, 1 mmol) and and the residue was recrystallized from benzene to give 4-(4- compound 2 (X=MeO) (0.39 g, 1 mmol) were similarly treated nitrophenyl)-2-methylbut-3-yn-2-ol in 79% yield, mp 102 °C; with ButOK (0.23 g, 2.02 mmol) to give the final product in dH(CDCl3 ) 1.62 (6H, s, CH3 ), 2.17 (1H, s, OH), 7.50 (2H, d, 20% yield, mp 193 °C; dH(CDCl3) 6.75–7.50 (8H, m, aromatic aromatic H), 8.13 (2H, d, aromatic H).The alcohol (15 g, H), 7.55 (2H, d, aromatic H), 8.10 (2H, d, aromatic H); 73 mmol) and ButOK (2 g, 17.8 mmol) were refluxed for 50 min nmax(KBr)/cm-1 2200m (COC), 1505s and 1335s (NO2) in ButOH (50 cm3), the solvent was evaporated under reduced (Found: C, 78.05; H, 4.18; N, 3.85.C23H15NO3 requires C, pressure and the residue was recrystallized from ethanol 78.17; H, 4.28; N, 3.96%). to give 1-ethynyl-4-nitrobenzene in 67% yield, which can also be prepared from 1-bromo-4-nitrobenzene and tri- 1-(4-Methoxyphenyl)-4-(4-nitrophenyl )buta-1,3-diyne 7 methylsilylacetylene.6a Thus, 1-ethynyl-4-nitrobenzene (1.48 g, (X=MeO, Y=NO2 ) 10.0 mmol) and triethyl orthoformate (30 cm3) were heated in the presence of zinc iodide (0.14 g, 0.4 mmol) at 140 °C for 2 h 3-(4-Nitrophenyl)prop-2-ynal (0.175 g, 1 mmol) and comto remove ethanol by distillation.The residue was distilled pound 2 (X=MeO) (0.388 g, 1 mmol) were treated with ButOK under reduced pressure to give 3-(4-nitrophenyl)prop-2-ynal (0.25 g, 2.2 mmol) in THF (30 cm3) for 4 h at room temperature. After evaporation of the solvent, the residue was dissolved diethyl acetal (bp 150 °C at 1 torr) in 60% yield; dH(CDCl3) 432 J.Mater. Chem., 1997, 7(3), 429–4337 K. Kondo, N. Ohnishi, K. Takemoto, H. Yoshida and K. Yoshida, in CH2Cl2 and dried over MgSO4. The solvent was removed J. Org. Chem., 1992, 57, 1622. in vacuo and the residue was recrystallized from benzene to 8 H. Zimmer, P. J. Berez, PO. J. Maltenieks and M. W. Moor, J. Am. give the title compound in 20% yield, mp 244 °C; dH(CDCl3) Chem.Soc., 1965, 87, 2777. 3.98 (3H, s, CH3), 6.89 (2H, d, aromatic H), 7.57 (2H, d, 9 A. N. Pudovik and I. V. Konovalova, Synthesis, 1979, 81. aromatic H), 7.75 (2H, d, aromatic H), 8.33 (2H, d, aromatic 10 B. I. Greene, J. Orenstein, R. R. Millard and L. R. Williams, Chem. Phys. L ett., 1987, 139, 381. H); nmax(KBr)/cm-1 2200m (COC), 1510s and 1335s (NO2) 11 T.Msuda, N. Sasaki and T. Higashimura, Macromolecules, 1975, (Found: C, 73.30; H, 3.98; N, 4.80. 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