2,3-Dimethoxy-5,12-tetracenequinone

The molecule of the title compound, C20H14O4, is approximately planar [maximum deviation 0.168 (2) Å]. The two methoxy groups are slightly twisted relative to the plane of the 5,12-tetracenequinone system, with twist angles of 3.3 (3) and 5.6 (2)°. All O atoms are involved in intermolecular C—H⋯O interactions and the molecules are arranged into slipped face-to-face stacks along the b axis via π–π interactions with an interplanar distance of 3.407 (2) Å.

The molecule of the title compound, C 20 H 14 O 4 , is approximately planar [maximum deviation 0.168 (2) Å ]. The two methoxy groups are slightly twisted relative to the plane of the 5,12-tetracenequinone system, with twist angles of 3.3 (3) and 5.6 (2) . All O atoms are involved in intermolecular C-HÁ Á ÁO interactions and the molecules are arranged into slipped face-to-face stacks along the b axis viainteractions with an interplanar distance of 3.407 (2) Å .

Comment
Although the title compound (I) was already synthesized (Reichwagen et al., 2005), the X-ray structre was not reported.
We prepared 2,3-dimethoxytetracene from 8,9-dimethoxy-5,12-tetracenequinone (McOmie & Perry, 1973), and attemped to perform the X-ray analysis of crystals made by recrystallization from a hot DMF solution under air and light. The analysis revealed that the molecule was not as expected 2,3-dimethoxytetracene but the title compound. Quinones have a weak dipole moment along the molecular long axis and are expected to take a antiparallel arrangement with respect to one another. The latter propensity may lead to the formation of face-to-face π-overlap along the stacking direction (Kitamura et al., 2008).
In the crystal structure, the molecules are linked through intermolecular C-H···O hydrogen bonds between the methoxy groups as well as between the tetracene groups (Table 1, Fig. 2). Interestingly, along the stacking direction, not antiparallel but just slipped π-π stacking can be found. The interplanar distance is 3.407 (2) Å. The dipole moment of (I) was calculated by MO calculations (B3LYP/6-31G*), which afforded an estimation of 0.01 debye. Thus, (I) is a non-polar molecule. Therefore, it seems reasonably to conclude that the electrostatic property can determine either an antiparallel or a non-antiparallel arrangement.
To a suspension of LiAlH 4 (224 mg, 5.9 mmol) in dry THF (15 ml), 8,9-dimethoxy-5,12-tetracenequinone (479 mg, 1.5 mmol) was added under nitrogen. The mixture was refluxed for 30 min, cooled to room temperature, and 6M HCl (7 ml) was added under cooling with ice. The residue was filtered, and washed with water, MeOH, and Et 2 O. After drying, a yellow solid was isolated. The solid was added into a suspension of LiAlH 4 (235 mg, 6.2 mmol) in dry THF (15 ml). The mixture was again refluxed for 30 min, cooled to room temperature, and 6M HCl (7 ml) was added under cooling with ice. The product was filtered, and washed with water, MeOH, and Et 2 O. After drying, 2,3-dimethoxytetracene was obtained (287 mg, 66%) as a yellow solid. Heating the tetracene in DMF under air and light, and then cooling the solution to room temperature resulted in deposition of brown crystals suitable for X-ray analysis.
supplementary materials sup-2 Refinement All H atoms were positioned geometrically and refined using a riding model approximation with C-H = 0.94Å and U iso (H) = 1.2U eq (C) for aromatic C-H, and C-H = 0.97Å and U iso (H) = 1.5U eq (C) for CH 3 . Fig. 1. The molecular structure of the title compound showing 50% probability displacement ellipsoids for non-H atoms. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.