Synthesis and Characterization of Organic Materials with Conveniently

Earlier syntheses of 1,3,5-tris(1-naphthyl)benzene (1) provided materials that were poorly ... The Journal of Organic Chemistry 0 (proofing), ... Kenn...
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J. Phys. Chem. 1996, 100, 1081-1090

1081

Synthesis and Characterization of Organic Materials with Conveniently Accessible Supercooled Liquid and Glassy Phases: Isomeric 1,3,5-Tris(naphthyl)benzenes Craig M. Whitaker and Robert J. McMahon* Department of Chemistry, UniVersity of Wisconsin, Madison, Wisconsin 53706-1396 ReceiVed: October 4, 1995X

1,3,5-Tris(1-naphthyl)benzene (1), 1,3-bis(1-naphthyl)-5-(2-naphthyl)benzene (2), and 1-(1-naphthyl)-3,5bis(2-naphthyl)benzene (3) easily supercool and form glasses on cooling from the melt. We synthesized 1, 2, and 3 using Suzuki’s conditions to effect the cross-coupling reactions of 1,3,5-tribromobenzene with 1-naphthylboronic acid and/or 2-naphthylboronic acid. Variable-temperature 13C NMR studies of 1 establish a barrier of ca. 12 kcal/mol for rotation about the aryl-aryl bond; this value displays good agreement with the barrier of 13 kcal/mol computed using molecular mechanics calculations (MM2). This relatively low rotational barrier is inconsistent with the previously held notion that 1,3,5-tris(1-naphthyl)benzene (1) exists as a mixture of noninterconverting rotational isomers (atropisomers) in solution at room temperature. Variabletemperature 13C NMR studies of 2 establish barriers of ca. 12 kcal/mol for rotation about the 1-naphthylaryl bond and 131 ppm correspond to quaternary carbons.23 Semiempirical

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Figure 3. Proton-decoupled 13C NMR spectra of 1 in tetrahydrofuran at various temperatures.

calculations of 13C NMR chemical shifts for 1a and 2a indicate the ipso carbons on the central benzene ring should display the largest chemical shift.24 Each compound containing a 2-naphthyl substituent displays fewer 13C resonances than would be expected from the symmetry of the molecule. This occurs because of fortuitous overlap of 13C-H resonances associated with the 2-naphthyl ring, as clearly illustrated by the 13C NMR spectrum of 4 (Figure 1). Molecular mechanics calculations indicate that two lowenergy conformational isomers of 1 are nearly isoenergetic: for 1a, ∆Hf° ) +39.1 kcal/mol and for 1b, ∆Hf° ) +39.0 kcal/ mol. Two distinct internal rotations are possible in conforma-

tional isomers of 1 (Scheme 5). In 1a, rotation about any of the three equivalent aryl-1-naphthyl bonds produces 1b. In 1b, rotation about the unique aryl-1-naphthyl bond produces 1a, while rotation about either of the symmetry-equivalent aryl1-naphthyl bonds produces a degenerate conformation of 1b. We computed the rotational barriers for these processes by performing a series of energy-minimization calculations; the dihedral angle between one 1-naphthyl ring and the central benzene ring was fixed (15° increments from 0° to 360°) while all other variables were free to optimize. The transition state for the rotation converting 1a to 1b occurs at a dihedral angle of 0° (1-naphthyl ring and benzene ring coplanar) with an energy

Synthesis and Characterization of Organic Materials ca. 13 kcal/mol higher than that of conformation 1a (Figure 2). Similarly, the transition state for the rotation interconverting degenerate conformations of 1b occurs at a dihedral angle of 0° (1-naphthyl ring and benzene ring coplanar) with an energy ca. 13 kcal/mol higher than that of conformation 1b.25 The calculations provide no evidence for “geared” rotation of the 1-naphthyl rings. In both 1a and 1b, the forced rotation of one 1-naphthyl ring does not lead to the correlated rotation of another 1-naphthyl ring. Given the modest rotational barriers, the naphthyl rings in 1 will rotate rapidly in solution at room temperature; 1a and 1b do not exist as separable atropisomers under these conditions. Variable temperature 13C NMR studies of 1 unequivocally establish that the aryl-naphthyl bonds undergo rapid rotation on the NMR timescale in solution at room temperature. Spectra of 1 taken in the temperature range 193-253 K reveal the dynamic processes associated with rotation about the arylnaphthyl bonds (Figure 3). In the limit of rapid rotation (T > 253 K), 1 possesses average C3V symmetry and therefore displays only 12 resonances in the decoupled 13C NMR spectrum. At 193 K, two dynamic processes have been frozen out: the rotation about the aryl-naphthyl bond that interconverts conformations 1a and 1b and the rotation about the arylnaphthyl bond that interconverts degenerate conformations of 1b (Scheme 5). This is evident by considering the behavior of the lowest-field resonance at 140.8 ppm; this resonance corresponds to the ipso carbons of the central benzene ring. At 253 K, the ipso carbons appear as a single resonance because of fast aryl-naphthyl rotation. At 193 K, the ipso carbons appear as three resonances: one resonance originates from conformation 1a and two resonances originate from conformation 1b. Note that this observation requires that the rotation interconverting degenerate conformations of 1b must be frozen out at 193 K. If this were not the case, conformation 1b would display a single resonance for the ipso carbons because of dynamic averaging of the degenerate conformations. The ipso carbon resonances of the central benzene ring in 1 decoalesce between 243 and 233 K (Figure 3). We did not attempt to resolve the two distinct dynamic processes. Using an estimated coalescence temperature of 238 K, we obtain a barrier to rotation for the 1-naphthyl substituents in 1 of 12.0 ( 0.4 kcal/mol.26,27 We probed the conformational behavior of 2 in a manner similar to that described for 1. Our detailed analysis reveals a complex manifold of conformational stereodynamics (Scheme 6). Molecular mechanics calculations of 2 provided three energy-minimized conformations of nearly equal energy: 2a, ∆Hf° ) +37.5 kcal/mol; 2b, ∆Hf° ) +37.3 kcal/mol; 2c, ∆Hf° ) +37.3 kcal/mol. As before, we computed the rotational barriers for the various internal rotations in 2 by performing a series of energy-minimization calculations (see above). In 2a, rotation about an aryl-1-naphthyl bond produces conformer 2b (computed barrier of 14 kcal/mol),28 while rotation about the aryl-2-naphthyl bond produces conformer 2c (computed barrier of 2 kcal/mol) (Figure 4). In 2b, rotation about one aryl1-naphthyl bond produces conformer 2a (computed barrier of 14 kcal/mol), rotation about the other aryl-1-naphthyl bond produces conformer 2c (computed barrier of 14 kcal/mol), and rotation about the aryl-2-naphthyl bond produces a degenerate conformation of 2b (computed barrier of 2 kcal/mol).29 In 2c, rotation about an aryl-1-naphthyl bond produces conformer 2b (computed barrier of 14 kcal/mol), while rotation about the aryl-2-naphthyl bond produces conformer 2a (computed barrier of 2 kcal/mol).28 The calculations provide no evidence for “geared” rotation of any of the naphthyl rings in 2. Given the modest rotational barriers, the naphthyl rings in 2 will rotate

J. Phys. Chem., Vol. 100, No. 3, 1996 1085

Figure 4. Computed potential energy diagram for rotation about the aryl-1-naphthyl bond (b) and for rotation about the aryl-2-naphthyl bond (3) in 2a.

freely in solution at room temperature; 2a, 2b, and 2c do not exist as separable atropisomers under these conditions. Variable temperature 13C NMR studies of 2 unequivocally establish that both the aryl-1-naphthyl bond and the aryl2-naphthyl bond undergo rapid rotation on the NMR timescale in solution at room temperature. Spectra of 2 taken in the temperature range 193-263 K reveal the dynamic processes associated with rotation about the aryl-naphthyl bonds (Figure 5). In the limit of rapid rotation (T > 263 K), 2 possesses average Cs symmetry and should display 24 resonances in the decoupled 13C NMR spectrum. We are able to resolve 23 resonances (Vide supra). At 193 K, the dynamic process associated with rotation about the aryl-1-naphthyl bond has been frozen out; the dynamic process associated with rotation about the aryl-2-naphthyl bond has not. This is evident by considering the behavior of the two lowest-field resonances near 141 ppm; these resonances correspond to the ipso carbons of the central benzene ring. At 263 K, the ipso carbons appear as two resonances because of fast aryl-naphthyl rotation. The more intense resonance at 141.4 ppm corresponds to the two ipso carbons attached to a 1-naphthyl substituent, and the less intense resonance at 141.0 ppm corresponds to the single ipso carbon attached to a 2-naphthyl substituent. At 193 K, the ipso carbons appear as four resonances; two resonances originate from the dynamic average of conformations 2a and 2c, and two resonances originate from conformation 2b. Rotation about the aryl-2-naphthyl bond remains rapid at 193 K since the ipso carbons appear as four resonances and not six and since the resonances associated with the 2-naphthyl substituent do not decoalesce.30 We obtain a barrier to rotation for the 1-naphthyl substituents in 2 of 12.0 ( 0.4 kcal/mol based on an estimated coalescence temperature of 218 K.26,27 Similarly, we obtain an upper limit for the barrier to rotation for the 2-naphthyl substituent in 2 of ca. 9 kcal/mol based on an upper limit for the coalescence temperature of 193 K. Differential Scanning Calorimetry Differential scanning calorimetry (DSC) studies of 1-4 reveal dramatically different physical properties within this isomeric series of compounds. On the initial heating cycle, crystalline samples of 1-4 melt (Tm ) 182, 194, 147, and 238 °C, respectively) (Table 1 and Figure 6). Both 1 and 2 display phase

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Figure 5. Proton-decoupled 13C NMR spectra of 2 in tetrahydrofuran at various temperatures.

transitions prior to melting; this behavior suggests the presence of polymorphic forms of 1 and 2 in the solid state. Upon cooling, compounds 1-3 form glasses (Tg values given in Table 1 and Figure 7); consequently, these materials do not melt during subsequent heating cycles.31 In contrast, compound 4 crystallizes upon cooling and remelts during subsequent heating cycles.2d We find two comparisons particularly interesting. First, 3 exhibits both the lowest melting point and the lowest glass transition temperature among the three glass-formers. The solid, liquid, and glassy states are all accessible within an unusually

narrow temperature range. This material shows promise for further studies of bulk and molecular properties associated with the glass transition. Second, 3 and 4 differ minimally in molecular structure but differ significantly in bulk properties. Again, this observation invites further detailed investigation. Analysis Our 1H and 13C NMR data unequivocally establish the structures of 1-4 in solution. Molecular mechanics calculations

Synthesis and Characterization of Organic Materials

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Figure 7. DSC traces obtained on heating glassy samples of tris(naphthyl)benzene isomers 1-3 (heating rate ) 20 °C/min).

TABLE 1: Melting (Tm) and Glass Transition (Tg) Temperatures for Tris(naphthyl)benzenes 1-4

Figure 6. DSC traces obtained on heating crystalline samples of tris(naphthyl)benzene isomers 1-4 (heating rate ) 20 °C/min).

compound

Tma, °C

Tmb, °C

Tgc, °C (midpoint)

Tgc, °C (onset)

1 2 3 4

180-182 193-194 148-150 238-241

182 194 147 238

81 77 67 e

78 75 65 e

Tg/Tmd 0.771 0.745 0.805

a Melting point determined using capillary melting point apparatus. Melting point determined using DSC. c Glass transition temperature determined using DSC. d Ratio of absolute temperatures (K) using Tg (onset). e Crystallizes on cooling from the melt. b

and NMR studies of 1 and 2 demonstrate that rapid rotation about the aryl-naphthyl bonds occurs in solution at room temperature. In the absence of further experimental data, one cannot draw conclusions about the conformations of 1 or 2 in the solid state. Numerous conformations of 1 and 2 are accessible in solution during the crystallization process; the solid state structures could be composed of any or all of these conformations. Given the large number of possible conformers in solution, the resulting solid-state structure could be very sensitive to the experimental conditions involved in the crystallization process. Polymorphism is likely. To our knowledge, X-ray diffraction studies of 1, cited in early papers by Magill et al.,2 were never published. The Cambridge Crystal Database does not contain structures for 1-4. We obtained 1H and 13C NMR spectra of a sample of 1 prepared by Magill. On the basis of a comparison to the spectra of our authentic samples of 1 and 2, we conclude that the structure of Magill’s sample is 2, not 1. In their initial description of the synthesis of 1, Clapp and Morton specifically commented on the difficulties they encountered in purifying 1

if the starting material, 1-acetylnaphthalene, contained the isomeric 2-acetylnaphthalene as a contaminant.10 This observation suggests the possible origin of 2 in Magill’s sample. Impure starting materials produced a mixture containing 1 and 2. Multiple recrystallizations2c eventually enriched the mixture in the higher-melting component, 2, because the higher-melting component typically crystallizes preferentially. Moreover, our experience indicates that 1 and 2 would not be separable by ordinary TLC or column chromatography. Thus, the origin of the structural misassignment becomes apparent. The misassignment would have been very difficult to detect with the analytical methods available at the time the material was originally synthesized.32 The failure of recent NMR investigations9,33 to detect this error is more surprising. Given the erroneous premise that 1 exists as a separable mixture of atropisomers,2 the 13C NMR spectrum of 2 (averaged to Cs symmetry) could be misinterpreted in terms of atropisomer 1b (static Cs symmetry).

1088 J. Phys. Chem., Vol. 100, No. 3, 1996 Given the complicating factors of isomeric purity and polymorphism, we are reluctant to utilize literature melting points as either a criterion of structure or a criterion of purity for our materials. We note, however, that the melting point we obtained in our laboratories for a purified sample of Magill’s material (192 °C) shows good agreement with our authentic sample of 2 (193-194 °C) and does not show good agreement with our authentic sample of 1 (180-182 °C). The differences in glass transition temperatures (Tg) for 2 reported by Magill (69 °C) and by us (75 or 77 °C) arise from two sources: differences in the methods used to derive Tg from the experimental data and differences in the heating rates of the samples.34 Summary We synthesized 1-3 using Suzuki cross-coupling reactions. Molecular mechanics calculations and variable temperature 13C NMR spectroscopy establish a barrier for aryl-1-naphthyl bond rotation of ca. 12 kcal/mol in 1 and ca. 12 kcal/mol in 2. Molecular mechanics calculations provide a barrier for the aryl2-naphthyl bond rotation of ca. 2 kcal/mol in 2; this process remains rapid on the NMR timescale at 193 K. Neither 1 nor 2 exists as a separable mixture of atropisomers in solution at room temperature. The glassy state is more easily accessible for 3 than for 1 or 2. The lower melting point and glass transition temperature of 3 make it an ideal candidate for viscosity and viscoelasticity studies. Given the structural misassignment of Magill’s sample, as well as the misconceptions about the barriers to internal rotation in 1 and 2, it seems prudent to recommend a re-evaluation of the earlier physical studies of this material. In particular, conclusions drawn from recent molecular dynamics studies should be reconsidered in light of possible contributions from intramolecular processes. Experimental Section General Methods. 1H and 13C NMR spectra were obtained with a Bruker AC-300 spectrometer in the indicated solvents. Variable temperature 13C NMR spectra were obtained with a Bruker AM-360 spectrometer in THF. Chemical shifts (δ) are reported as ppm downfield from an internal standard, tetramethylsilane. Mass spectra were recorded on a Kratos MS80RFA instrument employing electron-impact ionization (ca. 50 eV). Infrared spectra were recorded on a Nicolet Model 740 FT-IR spectrometer (mercury cadmium telluride detector). Ultraviolet/visible spectra were recorded on a Hitachi U-3210 spectrophotometer. Melting points were measured using a Thomas Hoover capillary melting point apparatus and are uncorrected. TLC was carried out using E. Merck silica gel (60F-254) plates. All glassware were flame-dried and purged with nitrogen prior to use. All reactions were run under a nitrogen atmosphere with stirring. CH2Cl2 was dried over and distilled from CaH2 immediately prior to use. THF was dried over KOH, predistilled from CaH2, then distilled from Na/ benzophenone immediately prior to use. 1-Bromonaphthalene (5), 2-bromonaphthalene, 1,3,5-tribromobenzene (8), 2-acetylnaphthalene, n-BuLi, triethyl orthoformate, trimethylborate, and Pd(PPh3)4 were purchased from Aldrich and used without further purification. Differential Scanning Calorimetry. DSC studies were performed using a Perkin-Elmer DSC7 instrument at a heating rate of 20 °C/min. Melting points (Tm) were determined by extrapolating the onset of melting (see Figure 6). Glass transition temperatures (Tg) were determined using two different conventions: obtaining the midpoint along the curve between

Whitaker and McMahon the two tangents to the base lines; extrapolating the onset of the glass transition (see Figure 7). 1-Naphthylboronic Acid (6). 1-Naphthylboronic acid was synthesized in a manner analogous to literature procedures.19 A solution of 5 (11 g, d ) 1.489 g/mL, 53 mmol) in THF (20 mL) was cooled to -78 °C. n-BuLi (2.5 M in hexanes, 21 mL, 53 mmol) was added dropwise over 5 min. After 30 min, B(OMe)3 (16 mL, d ) 0.915 g/mL, 140 mmol) was added. The mixture was stirred at -78 °C for 20 min and then at room temperature for 10 min. The reaction was quenched with water (50 mL) and 10% aqueous HCl (100 mL). The layers were separated, and the aqueous layer was extracted 3 times with Et2O. The organic layers were combined, washed once with saturated aqueous NaCl, dried over MgSO4, and evaporated to yield an off-white solid. The solid was added to 10% aqueous NaOH, and the unreacted starting material was removed by vacuum filtration. The filtrate was acidified with 10% aqueous HCl, and the aqueous solution was extracted 3 times with Et2O. The organic layers were combined, dried over MgSO4, and evaporated to yield a white solid. The solid was washed with benzene to yield 6 (3.3 g, 36%) as a white powder: mp, 203207 °C (lit.19b 202 °C); 1H NMR (CDCl3) δ, 8.37 (d, 1 H), 7.93 (dd, 2 H), 7.71 (d, 1 H), 7.47 (m, 3 H), 6.42 (s (br), 2 H); mass spectrum calcd (found) for C10H9BO2, 172.0711 (172.0706); mass spectrum m/z (relative intensity), 172 (M+, 100), 154 (56), 128 (51), 81 (12), 73 (18), 69 (26). 1,3-Dibromo-5-(1-naphthyl)benzene (9). Pd(PPh3)4 (0.25 g, 0.2 mmol) and 2 M aqueous Na2CO3 (6.4 mL, 13 mmol) were added to a solution of 6 (1.1 g, 6.4 mmol) and 8 (2.2 g, 6.9 mmol) in toluene (10 mL) and EtOH (2 mL). The reaction mixture was purged with nitrogen for 20 min. After refluxing for 20 h, the solution was cooled to room temperature and quenched with water and benzene (100 mL) was added. The organic layer was separated, washed with saturated aqueous NaCl, dried over MgSO4, and evaporated to give a greenishbrown oil. The oil was purified by column chromatography (SiO2/hexane:CH2Cl2 (10:1)) to give 9 (1.4 g, 62%) as a white powder: mp 125-127 °C; 1H NMR (CDCl3) δ, 7.92 (t, 2 H), 7.80 (d, 1 H), 7.74 (s, 1 H), 7.55 (m, 5 H), 7.38 (d, 1 H); mass spectrum calcd (found) for C16H10Br2 363.9126 (363.9115), 361.9146 (361.9125); 359.9166; (359.9165); mass spectrum m/z (relative intensity), 364, 362, 360 (M+, 27, 63, 29), 202 (100), 101 (45), 73 (12). 1-Bromo-3,5-bis(1-naphthyl)benzene (10). Pd(PPh3)4 (0.24 g, 0.2 mmol) and 2 M aqueous Na2CO3 (6 mL, 12 mmol) were added to a solution of 6 (1.0 g, 7 mmol) and 8 (1.0 g, 3 mmol) in toluene (10 mL) and EtOH (2 mL). The reaction mixture was purged with nitrogen for 20 min. After refluxing for 20 h, the solution was cooled to room temperature. The reaction was quenched with water (200 mL) and then extracted with benzene (100 mL). The organic layer was washed with saturated aqueous NaCl, dried over MgSO4, and evaporated to give a brown oil. The oil was purified by column chromatography (SiO2/hexane:CH2Cl2 (8:1)) followed by radial TLC (Chromatotron; SiO2/hexane:CH2Cl2 (8:1)) to give 10 (0.4 g, 40%) as a white powder: mp, 131-135 °C; 1H NMR (CDCl3) δ, 8.01 (d, 2 H), 7.90 (m, 4 H), 7.34 (d, 2 H), 7.59 (t, 1 H), 7.51 (m, 8 H); mass spectrum calcd (found) for C26H17Br, 410.0489 (410.0515), 408.0509 (408.0502); mass spectrum m/z (relative intensity), 410, 408 (M+, 100, 98), 329 (55), 313 (15), 164 (20). 1,3,5-Tris(1-naphthyl)benzene (1). A solution of Ba(OH)2 (5.0 g, 16 mmol), 8 (0.6 g, 2 mmol), and 6 (1.4 g, 8 mmol) in DME (20 mL), EtOH (20 mL), and water (25 mL) was purged with nitrogen for 20 min. Pd(PPh3)4 (0.3 g, 0.3 mmol) was added, and the reaction mixture was refluxed for 72 h. After

Synthesis and Characterization of Organic Materials cooling to room temperature, the reaction was quenched with water (50 mL) and CH2Cl2 (100 mL) was added. The organic layer was washed with saturated aqueous NaCl, dried over MgSO4, and evaporated to yield an oil. The oil was purified via two flash column chromatography runs (SiO2/benzene followed by SiO2/hexane:benzene (9:1)). Recrystallization from hexane provided 1 (0.25 g, 30%) as white crystals: mp, 180182 °C (lit. 190.5-191 °C,10 195-196 °C11); 1H NMR (CDCl3) δ, 8.21 (m, 3 H), 7.91 (m, 6 H), 7.76 (s, 3 H), 7.53 (m, 12 H); 13C {1H} NMR (CDCl ) δ, 140.8, 139.8, 133.9, 131.6, 130.7, 3 128.4, 127.9, 127.3, 126.2, 126.0, 125.8, 125.4; mass spectrum calcd (found) for C36H24, 456.1872 (456.1887); mass spectrum m/z (relative intensity), 456 (M+, 100), 327 (10), 256 (7), 129 (10). 2-Naphthylboronic Acid (11). 2-Naphthylboronic acid was synthesized in a manner analogous to 1-naphthylboronic acid. A solution of 2-bromonaphthalene (5.0 g, d ) 1.489 g/mL, 25 mmol) in THF (20 mL) was cooled to -78 °C. n-BuLi (2.5 M in hexanes, 10 mL, 25 mmol) was added dropwise over 5 min. After 30 min, B(OMe)3 (6 mL, d ) 0.915 g/mL, 63 mmol) was added. The mixture was stirred at -78 °C for 20 min and then stirred at room temperature for 10 min. The reaction was quenched with water (50 mL) and 10% aqueous HCl (100 mL). The layers were separated, and the aqueous layer was washed 3 times with Et2O. The organic layers were combined, washed once with saturated aqueous NaCl, dried over MgSO4, and evaporated to yield a tan solid. The solid was added to 10% aqueous NaOH, and unreacted starting material was removed via vacuum filtration. The filtrate was acidified with 10% aqueous HCl, and the aqueous solution was extracted 3 times with Et2O. The organic layers were combined, dried over MgSO4, and evaporated to yield a white solid. The solid was washed with benzene to yield 11 (2.0 g, 48%) as a white powder: mp, 267-270 °C (lit.19b 266 °C); 1H NMR (Me2COd6) δ, 8.45 (s, 1 H), 7.93 (m, 4 H), 7.52 (m, 2 H), 7.32 (s (br), 2 H); mass spectrum calcd (found) for C10H9BO2, 172.0711 (172.0697); mass spectrum m/z (relative intensity), 172 (M+, 30), 154 (18), 128 (100), 81 (10), 73 (13). 1,3-Dibromo-5-(2-naphthyl)benzene (12). Pd(PPh3)4 (0.4 g, 0.03 mmol) and Ba(OH)2 (5 g, 16 mmol) were added to a solution of 11 (1.4 g, 7.9 mmol) and 7 (2.8 g, 8.7 mmol) in DME (18 mL) and EtOH (2 mL). The reaction mixture was purged with nitrogen for 20 min. After refluxing 16 h, the solution was cooled to room temperature and benzene (100 mL) was added. The organic layer was washed with saturated aqueous NaCl, dried over MgSO4, and evaporated to give an oil. The oil was purified by column chromatography (SiO2/ hexane) to give 12 (1.9 g, 66%) as a white solid: mp, 138140 °C; 1H NMR (CDCl3) δ, 8.05 (s, 1 H), 7.87 (m, 5 H), 7.73 (d, 1 H), 7.50 (m, 3 H); mass spectrum calcd (found) for C16H10Br2, 363.9126 (363.9203), 361.9146 (361.9173), 359.9166 (359.9377); mass spectrum m/z (relative intensity), 364, 362, 360 (M+, 19, 38, 22), 254 (100), 202 (32). 1,3-Bis(1-naphthyl)-5-(2-naphthyl)benzene (2). Compounds 10 (0.4 g, 1 mmol) and 11 (0.2 g, 1 mmol) and 2 M aqueous Na2CO3 (1 mL, 2 mmol) were added to a solution of toluene (6 mL) and EtOH (1 mL). The mixture was purged with nitrogen for 20 min, and then Pd(PPh3)4 (0.05 g, 0.04 mmol) was added. After refluxing 24 h, the solution was cooled to room temperature and quenched with water (50 mL) and CH2Cl2 (200 mL). The aqueous layer was extracted with CH2Cl2 (100 mL). The organic layers were combined, dried over MgSO4, and evaporated to yield a yellow oil. The oil was purified via flash column chromatography (SiO2/hexane:CH2Cl2 (8:1)) followed by radial TLC (Chromatotron; SiO2/hexane:

J. Phys. Chem., Vol. 100, No. 3, 1996 1089 CH2Cl2 (10:1)). Recrystallization from hexane provided 2 (0.3 g, 70%) as a white powder: mp, 193-194 °C; 1H NMR (CDCl3) δ, 8.15 (m, 3 H), 7.93 (m, 10 H), 7.69 (t, 1 H), 7.53 (m, 10 H); 13C {1H} NMR (CDCl ) δ, 141.4, 141.0, 139.9, 138.0, 133.9, 3 133.7, 132.7, 131.7, 130.7, 128.6, 128.4, 128.2, 128.0, 127.9, 127.6, 127.2, 126.4, 126.3, 126.1, 126.0, 125.9, 125.6, 125.4; mass spectrum calcd (found) for C36H24, 456.1872 (456.1877); mass spectrum m/z (relative intensity), 456 (M+, 100), 328 (13), 129 (17), 97 (10), 83 (19), 73 (42). 1-(1-Naphthyl)-3,5-bis(2-naphthyl)benzene (3). Compounds 9 (0.7 g, 1.9 mmol) and 11 (0.8 g, 4.7 mmol) and 2 M aqueous Na2CO3 (4 mL, 7.5 mmol) were added to a solution of toluene (20 mL) and EtOH (4 mL). The mixture was purged with nitrogen for 20 min, and then Pd(PPh3)4 (0.18 g, 0.2 mmol) was added. After refluxing 20 h, the solution was cooled to room temperature. The reaction was quenched with water (100 mL), and CH2Cl2 (100 mL) was added. The aqueous layer was extracted with CH2Cl2 (100 mL). The organic layers were combined, dried over MgSO4, and evaporated to yield an orangeyellow oil. The oil was purified via flash column chromatography (SiO2/hexane:CH2Cl2 (9:1)) and then recrystallization from hexane:CHCl3 (10:1), providing 3 (0.7 g, 84%) as a white powder: mp, 148-150 °C; 1H NMR (CDCl3) δ, 8.15 (m, 4 H), 7.92 (m, 13 H), 7.57 (m, 7 H); 13C {1H} NMR (CDCl3) δ, 142.0, 141.8, 140.0, 138.2, 133.9, 133.7, 132.8, 131.7, 130.7, 128.6, 128.4, 128.2, 128.1, 127.9, 127.7, 127.1, 126.4, 126.3, 126.1, 125.9, 125.6, 125.4; mass spectrum calcd (found) for C36H24, 456.1872 (456.1877); mass spectrum m/z (relative intensity), 456 (M+, 100), 328 (9), 326 (10), 97 (7), 83 (10), 71 (9). 1,3,5-Tris(2-naphthyl)benzene (4). The synthesis of 4 followed a literature procedure.11 Dry HCl gas was bubbled through a solution of 2-acetylnaphthalene (2.0 g, 12 mmol) and triethyl orthoformate (2.5 g, 17 mmol) in 10 mL absolute EtOH for 1 h. A yellow precipitate was collected via vacuum filtration and washed with hot methanol (50 mL). The yellow solid was dissolved in toluene with decolorizing charcoal, and the mixture was heated for 10 min. The charcoal was removed by vacuum filtration. The filtrate was isolated and the solvent removed by evaporation to give a dark residue. The residue was purified by column chromatography (2 times; SiO2/hexane:CH2Cl2 (10: 1)) followed by radial TLC (Chromatotron; SiO2/hexane:CH2Cl2 (10:1)). Two recrystallizations from hexane:CH2Cl2 (10: 1) provided 4 (0.3 g, 6%) as an off-white powder: mp, 238241 °C (lit. 234-235 °C,10 241-242 °C11); 1H NMR (CDCl3) δ, 8.23 (s, 3 H), 8.08 (s, 3 H), 7.95 (m, 12 H), 7.54 (m, 6 H); 13C {1H} NMR (CDCl ) δ, 142.4, 138.4, 133.7, 132.8, 128.6, 3 128.3, 127.7, 126.4, 126.1, 125.7; mass spectrum calcd (found) for C36H24, 456.1872 (456.1865); mass spectrum m/z (relative intensity), 456 (M+, 100), 331 (11), 330 (36), 326 (11), 228 (17). Acknowledgment. We thank Forrest R. Blackburn and Professor Mark D. Ediger for stimulating our interest in this problem and Professor J. H. Magill for generously providing a sample of his material. We acknowledge the National Science Foundation for support through the Presidential Young Investigator Program (CHE-8957529). We gratefully acknowledge matching funding from the 3M Corporation. We thank Marco A. Medina for help with the variable temperature NMR studies and Forrest R. Blackburn, Marcos Bassani, and Professor John H. Perepezko for help with the differential scanning calorimetry experiments. R.J.M. is a Fellow of the Alfred P. Sloan Foundation.

1090 J. Phys. Chem., Vol. 100, No. 3, 1996 References and Notes (1) For reviews and leading references, see the following. (a) Angell, C. A. Science 1995, 267, 1924-1935. (b) Stillinger, F. H. Science 1995, 267, 1935-1945. (c) Proceedings of the Second International Discussion Meeting on Relaxations in Complex Systems. J. Non-Cryst. Solids 1994, 172-174. (d) Dynamics of Disordered Materials: Proceedings of the ILL Workshop. Springer Proc. Phys. 1989, 37. (2) (a) Magill, J. H.; Ubbelohde, A. R. Trans. Faraday Soc. 1958, 54, 1811-1821. (b) Magill, J. H.; Plazek, D. J. Nature 1966, 209, 70-71. (c) Plazek, D. J.; Magill, J. H. J. Chem. Phys. 1966, 45, 3038-3049. (d) Magill, J. H.; Plazek, D. J. J. Chem. Phys. 1967, 46, 3757-3769. (e) Magill, J. H. J. Chem. Phys. 1967, 47, 2802-2807. (f) Plazek, D. J.; Magill, J. H. J. Chem. Phys. 1968, 49, 3678-3682. (3) Grest, G. S.; Cohen, M. H. Phys. ReV. B 1980, 21, 4113-4117. (4) Taborck, P.; Kleinmann, R. N.; Bishop, D. J. Phys. ReV. B 1986, 34, 1835-1840. (5) Ehlich, D.; Sillescu, H. Macromolecules 1990, 23, 1600-1610. (6) (a) Zhu, X. R.; Wang, C. H. J. Chem. Phys. 1986, 84, 6086-6090. (b) Ma, R.-J.; He, T.-J.; Wang, C. H. J. Chem. Phys. 1988, 88, 14971500. (7) (a) Fujara, F.; Petry, W. Europhys. Lett. 1987, 4, 921-927. (b) Bartsch, E.; Debus, O.; Fujara, F.; Kiebel, M.; Petry, W.; Sillescu, H.; Magill, J. H. Physica B 1992, 180/181, 808-810. (8) (a) Ro¨ssler, E. Phys. ReV. Lett. 1990, 65, 1595-1598. (b) Ro¨ssler, E. J. Chem. Phys. 1990, 92, 3725-3735. (9) Zemke, K.; Schmidt-Rohr, K.; Magill, J. H.; Sillescu, H.; Spiess, H. W. Mol. Phys. 1993, 80, 1317-1330. (10) Clapp, D. B.; Morton, A. A. J. Am. Chem. Soc. 1936, 58, 2172. (11) Wirth, H. O.; Kern, W.; Schmitz, E. Makromol. Chem. 1963, 68, 69-99. (12) Plater, M. J. Synlett. 1993, 405-406. (13) (a) Reddelien, G. Liebigs Ann. Chem. 1912, 388, 165-199. (b) Vorla¨nder, D.; Fischer, E.; Wille, H. Chem. Ber. 1929, 62, 2836-2844. (c) Bernhauer, K.; Mu¨ller, P.; Neiser, F. J. Prakt. Chem. 1936, 145, 301-308. (14) A general review of aryl-aryl coupling reactions: Sainsbury, M. Tetrahedron 1980, 36, 3327-3359. (15) (a) Stille, J. K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508-524. (b) Mitchell, T. N. Synthesis 1992, 803-815. (16) (a) Semmelhack, M. F.; Helquist, P.; Jones, L. D.; Keller, L.; Mendelson, L.; Ryono, L. S.; Smith, J. G.; Stauffer, R. D. J. Am. Chem. Soc. 1981, 103, 6460-6471. (b) Fonta, P. E. Synthesis 1974, 9-21. (c) Fonta, P. E. Chem. ReV. 1964, 64, 613-632. (17) (a) Miyaura, N.; Yanagi, T.; Suzuki, A. Synth. Commun. 1981, 11, 513-519. (b) Suzuki, A. Pure Appl. Chem. 1994, 66, 213-222. (c) Martin, A. R.; Yang, Y. Acta Chem. Scand. 1993, 47, 221-230. (d) Gronowitz, S.; Lawitz, K. Chem. Scr. 1983, 22, 265-266. (e) Gronowitz, S.; Bobosik, V.; Lawitz, K. Chem. Scr. 1984, 23, 120-122. (18) (a) Katz, H. E. J. Org. Chem. 1987, 52, 3932-3934. (b) Miller, T. M.; Neenan, T. X. Chem. Mater. 1990, 2, 346-349. (c) Gronowitz, S.; Peters, D. Heterocycles 1990, 30, 645-653. (d) Shabana˜, R.; Galal, A.; Mark, H. B.; Zimmer, H.; Gronowitz, S.; Ho¨rnfeldt, A.-B. Phosphorus, Sulfur Silicon Relat. Elem. 1990, 48, 239-244. (e) Unrau, C. M.; Campbell, M. G.; Snieckus, V. Tetrahedron Lett. 1992, 33, 2773-2776. (f) Fisher, E.; Hess, H.; Lorenz, T.; Musso, H.; Rossnagel, I. Chem. Ber. 1991, 124, 783-789. (19) (a) Yabroff, D. L.; Branch, G. E. K.; Bettman, B. J. Am. Chem. Soc. 1934, 56, 1850-1855. (b) Koenig, W.; Scharrnbeck, W. J. Prakt. Chem. 1930, 236, 153-170. (c) Toressel, K. In Progress in Boron Chemistry; Steinberg, H., McCloskey, A. L., Eds.; Pergamon: Oxford, 1964; Vol. 1, p 374. (d) Manabe, K.; Okamura, K.; Date, T.; Koga, K. J. Org. Chem. 1993, 58, 6692-6700.

Whitaker and McMahon (20) House, H. O.; Campbell, W. J.; Gall, M. J. Org. Chem. 1970, 35, 1815-1819. (21) (a) Tsuzuki, S.; Tanabe, K.; Nagawa, Y.; Nakanishi, A. J. Mol. Struct. 1990, 216, 279-295. (b) Cosmo, R.; Sternhell, S. Aust. J. Chem. 1987, 40, 1107-1126. (c) Handal, J.; White, J. G.; Frank, R. W.; Yuh, Y. H.; Allinger, N. L. J. Am. Chem. Soc. 1977, 99, 3345-3349. (d) Carter, R. E.; Liljetors, T. Tetrahedron 1976, 32, 2915-2922. (e) Cough, R. L.; Roberts, J. D. J. Am. Chem. Soc. 1976, 98, 1018-1020. (22) (a) MacroModel, Version 3.5a; Department of Chemistry, Columbia University: New York, April 1992. (b) Mohamadi, F.; Richards, N. G. J.; Guida, W. C.; Liskamp, R.; Lipton, M.; Caufield, C.; Chang, G.; Hendrickson, T.; Still, W. C. J. Comput. Chem. 1990, 11, 440-467. (23) Derome, A. E. In Modern NMR Techniques for Chemistry Research; Baldwin, J. E., Magnus, P. D., Eds.; Pergamon: Oxford, 1987; p 143. (24) Chemical shifts computed from the AM1-optimized geometries using the VAMP program: Rauhut, G.; Alex, A.; Chandrasekhar, J.; Steinke, T.; Clark, T. VAMP; Universita¨t Erlangen-Nu¨rnberg: Germany, 1993. See also Rauhut, G.; Clark, T.; Steinke, T. J. Am. Chem. Soc. 1993, 115, 91749181. (25) In principle, the symmetry-equivalent 1-naphthyl groups in 1b can rotate in either of two nonequivalent directions: toward the syn 1-naphthyl group or toward the anti 1-naphthyl group. The computed barriers for these processes, 13 kcal/mol, are indistinguishable within the accuracy of our calculations. (26) (a) Binsch, G. Dynamic NMR Spectroscopy; Jackman, L. M., Cotton, F. A., Eds.; Academic Press: New York, 1975; p 45. (b) Gutowsky, H. S.; Holm, C. H. J. Chem. Phys. 1956, 25, 1228-1234. (27) By monitoring the coalescence behavior of four different 13C NMR resonances in 1 and 2, we obtained four separate values for the aryl1-naphthyl rotational barriers. In each case, these four values were averaged to give the quoted barrier of 12.0 kcal/mol. The individual values all lie within the range 12.0 ( 0.4 kcal/mol. (28) In principle, the symmetry equivalent 1-naphthyl groups in 2a and 2c can rotate in either of two nonequivalent directions: toward the other 1-naphthyl group or toward the 2-naphthyl group. The computed barriers for these processes, 14 kcal/mol, are indistinguishable within the accuracy of our calculations. (29) In principle, the 1-naphthyl groups in 2b can rotate in either of two nonequivalent directions: toward the other 1-naphthyl group or toward the 2-naphthyl group. The computed barriers for these processes, 14 kcal/ mol, are indistinguishable within the accuracy of our calculations. Similarly, the 2-naphthyl group in 2b can rotate in either of two nonequivalent directions: toward the syn 1-naphthyl group or toward the anti 1-naphthyl group. The computed barriers for these processes, 2 kcal/mol, are indistinguishable within the accuracy of our calculations. (30) The limited solubility of tris(naphthyl)benzenes 1 and 2 in THF at temperatures below 193 K precluded NMR studies at lower temperatures. (31) We note that Grest and Cohen previously described the dependence of the glass transition in 1 on heating and cooling rates.3 (32) The UV/vis and IR spectra of the tris(naphthyl)benzenes 1 and 2 are nearly identical. Low-field 1H NMR spectroscopy would not have been diagnostic. (33) See unpublished data cited in refs 7 and 8. (34) Magill and co-workers determined Tg ) 69 °C using dilatometry and DSC. Dilatometry experiments with a cooling rate of 1 °C/min gave Tg ) 69 °C,2a,c but it is well known that the Tg for this material depends on heating and cooling rates.2c,3 In DSC experiments, Magill determined Tg from the onset of heat flow,2e whereas we determined Tg from the midpoint along the curve between the two tangents to the base lines or from the extrapolated onset of the glass transition (see Figure 7).

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