Crystal Structure Study on Non-Coplanarly Organized Accumulating Aromatic Rings Molecules: Spatial Organization of C,C,N-Triaryl Substituted Imines ()
1. Introduction
Non-coplanarly accumulated aromatic-rings compounds, e.g., biphenyls and binaphthyls, have been demonstrated as unique building blocks in construction for many functional materials such as molecular catalysis and functional polymers [1-12]. Thus, minute spatial structural characterization of these compounds [13-16] has attracted attention of the chemists in the wide-range of organic molecular science and polymer materials fields. However, intraand inter-molecular interactions that afford various functions to such molecular units still remain ambiguous. As one of the protocols to estimate such interactions, the authors have been investigating synthesis and X-ray crystal structure analysis of congested spatial organization of aromatic rings accumulating molecules.
Recently, the authors have reported specific and characteristic electrophilic aromatic aroylation of naphthalene derivatives, i.e., two aroyl groups are regioselectively and effectively introduced at the 1,8-positions of the naphthalene ring accompanying with simultaneously proceeding retroaroylation behavior [17,18]. The 1-aroylated naphthalenes, which correspond to the intermediates in the diaroylation, are also obtained by choice of acidic mediator.
X-ray crystal structure study has revealed that the aroyl groups in these peri-aroylated naphthalene molecules are non-coplanarly attached to the naphthalene rings by giving crowded molecular organization [19-22]. In a natural consequence, the authors have planned to introduce additional aromatic ring planes to the core part of the aroylnaphthalene molecules for realization of more crowded inner spatial situation in accumulated aromatic-rings molecule. As one of the molecular transformation approaches to obtain such spatial organization, the authors designed conversion of ketonic carbonyl group on 1-aroylnaphthalene to imino moiety by the reaction with aniline derivative. Imination of 1-aroylated 2,7-dimethoxynaphthalene with aromatic amines scarcely proceeded with conventional additives except for TiCl4 and 1,4-diazabicyclo[2.2.2]octane (DABCO) mixture. In TiCl4—DABCO mediated imination, triaryl-substituted imine compounds were formed in moderate conversion with/without preceding methyl ether cleavage reaction of the starting compound (Scheme 1) [23]. The neighboring ketonic carbonyl group of peri-aroylated 2,7-dimethoxynaphthalene derivatives plausibly accelerates TiCl4- mediated scission of rather stable ether bonding.
In this article, the authors report and discuss the single molecular spatial organizations and the molecular packing characteristics of C,C,N-triarylated imine compounds by comparing with those of original ketone compounds: 1-aroyl-2,7-dimethoxynaphthalene and 1-aroyl-2-hydroxy- 7-methoxynaphthalene.
2. Experimental
All reagents were of commercial quality and were used as received. Solvents were dried and purified using standard techniques.
2.1. Measurements
1H NMR spectra were recorded on a JEOL JNM-AL300 spectrometer (300 MHz) and a JEOL ECX400 spectrometer (400 MHz). Chemical shifts are expressed in ppm relative to internal standard of Me4Si (δ 0.00). 13C NMR spectra were recorded on a JEOL JNM-AL300 spectrometer (75 MHz). Chemical shifts are expressed in ppm relative to internal standard of CDCl3 (δ 77.0). IR spectra were recorded on a JASCO FT/IR-4100 spectrometer. Elemental analyses were performed on a Yanaco CHN CORDER MT-5 analyzer. High-resolution FAB mass spectra were recorded on a JEOL MStation (MS700) ion trap mass spectrometer in positive ion mode.
2.2. Synthetic Procedure
Starting material 1 and triarylimines were prepared as follows.
2.2.1. Electrophilic Aromatic Substitution Aroylation of 2,7-Dimethoxynaphthalene by AlCl3
To a solution of 2,7-dimethoxynaphthalene (0.200 mmol68.2 mg) and 4-chlorobenzoyl chloride (0.220 mmol, 38.5 mg) in dichloromethane (0.5 mL), AlCl3 (0.220 mmol, 29.3 mg) was added by portions at 0˚C under nitrogen atmosphere. After the reaction mixture was stirred at r. t. for 3 h, it was poured into iced water (20 mL) and the mixture was extracted with CHCl3 (15 mL × 3). The combined extracts were washed with 2 M NaOH aq., sat. NaCl aq. and dried over anhydrous magnesium sulfate. The solvent was removed under reduced pressure to give powdery product. The crude product of 1-momoaroylnaphthalene 1 was purified by recrystallization (hexane, isolated yield 78%).
1-(4-Chlorobenzoyl)-2,7-dimethoxynaphthalene (1): Colourless needle (hexane), Mp 121.5˚C - 122˚C; IR (KBr): 1667, 1628, 1586, 1512 cm−1; 1H NMR δ (300 MHz, CDCl3): 7.87 (1H, d, J = 9.0 Hz), 7.78 (2H, d, J = 8.4 Hz), 7.72 (1H, d, J = 9.0 Hz), 7.39 (2H, d, J = 8.4 Hz), 7.16 (1H, d, J = 9.0 Hz), 7.02 (1H, dd, J = 2.4, 9.0 Hz), 6.78 (1H, d, J = 2.4 Hz), 3.79 (3H, s), 3.73 (3H, s) ppm; 13C NMR δ (75 MHz, CDCl3): 196.81, 158.96, 155.02, 139.71, 136.45, 132.94, 131.28, 130.87, 129.72, 128.86, 124.34, 121.06, 117.15, 110.05, 101.88, 56.239, 55.168 ppm; Calcd for C19H15O3Cl: C, 69.83%; H, 4.63%; Found: C, 69.61%; H, 4.74%.
2.2.2. TiCl4—DABCO Mediated Imination of 1-(4-Chlorobenzoyl)-2,7-dimethoxynaphthalene (1)
To a solution of 1-(4-chlorobenzoyl)-2,7-dimethoxynaphthalene (1, 0.200 mmol, 65.4 mg) in monochlorobenzene (1 mL), mixtures of aniline (0.220 mmol, 20.5 mg), TiCl4 (0.330 mmol, 62.4 mg), DABCO (1.320 mmol, 148 mg) and monochlorobenzene (1 mL) were added by portions at 90˚C under nitrogen atmosphere. After the reaction mixture was stirred at 125˚C for 1.5 h, the resulting solution was filtrated to remove the precipitate. The solvent was removed under reduced pressure to give crude material. The crude product was purified by silicagel column chromatography (Chloroform; isolated yield: imine 3, 10%; imine 4, 10%, 2-hydroxy compound 5, 8%).
Imine 3: Colourless block (CHCl3/hexane) Mp 174˚C - 175˚C, IR (KBr) 1625, 1502, 1238, 1029, 830 cm−1; 1H NMR δ (300 MHz, CDCl3): 7.72 (1H, d, J = 9.0 Hz), 7.66 (2H, d, J = 8.4 Hz), 7.60 (1H, d, J = 9.0 Hz), 7.29 (2H, d, J = 8.4 Hz), 7.25 (1H, d, J = 9.0 Hz), 7.02 (1H, d, J = 9.0 Hz), 6.92 (1H, dd, J = 9.0, 2.4 Hz), 6.74 (2H, d, J = 8.8 Hz), 6.68 (1H, d, J = 2.4 Hz), 6.53 (2H, d, J = 8.8