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Preparation, Structure, and Amphoteric Redox Properties of p-Phenylenediamine-Type Dyes Fused with a Chalcogenadiazole Unit Takanori Suzuki* and Takashi Tsuji Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan
Tsuneyuki Okubo, Akihisa Okada, Yoshiaki Obana, Takanori Fukushima, and Tsutomu Miyashi Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Aramaki, Sendai 980-8578, Japan
Yoshiro Yamashita Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Yokohama 226-8502, Japan
[email protected] Received August 9, 2001
4,7-Bis(dialkylamino)benzo[c][1,2,5]chalcogenadiazoles are a novel class of organic dyes that undergo reversible two-stage one-electron oxidation as well as one-electron reduction. They exhibit absorption maxima in the long-wavelength region, which are assigned as intramolecular charge transfer bands from the phenylenediamine moiety to the electron-accepting heterocycle. Their redox properties as well as molecular and crystal structures are affected by the alkyl substituents on the amino nitrogen and/or by the chalcogen atom (O, S, Se) in the heterocycle. Recently, much attention has been focused on organic redox systems due to their special properties such as their conducting behavior and ferromagnetism.1 We designed the title molecules, 4,7-bis(dialkylamino)benzo[c][1,2,5]chalcogenadiazoles (1-3(a,b)), as novel Wurster-type electron donors,2 which show several interesting features by annelation of an electron-withdrawing chalcogenadiazole ring:3 (1) in addition to their strong donating properties inherent to the tetramethyl-p-phenylenediamine (TMPD)4a or 1,4-bis(1-pyrrolidinyl)benzene (BPB)4b skeleton, they also undergo one-electron reduction within an easily accessible potential window; (2) they exhibit strong absorptions in the visible region by intramolecular charge transfer (CT) from the phenylenediamine moiety to the heterocycle; and (3) their packing arrangement in crystal form may be affected by electrostatic interaction through short contacts between heteroatoms, which has been shown to be favorable for giving conducting organic solids.5 We report here the preparation and properties of 1-3(a,b), along with the effects of the chalcogen atom * Corresponding author. Fax: +81-11-706-4924. (1) Bryce, M. R. Adv. Mater. 1999, 11, 11. (2) Deuchert, K.; Hu¨nig, S. Angew. Chem., Int. Ed Engl. 1978, 17, 875. (3) Sherman, E. O.; Lambert, S. M.; Pilgram, K. J. Heterocycl. Chem. 1977, 11, 763. (4) (a) Nelsen, S. F.; Tran, H. Q.; Nagy, M. A. J. Am. Chem. Soc. 1998, 120, 298. Roth, H. D. Tetrahedron 1986, 42, 6097. (b) Leonard, N. J.; Sauers, R. R. J. Org. Chem. 1956, 21, 1187. (5) Suzuki, T.; Kabuto, C.; Yamashita, Y.; Mukai, T.; Miyashi, T.; Saito, G. Bull. Chem. Soc. Jpn. 1988, 61, 483. Iwasaki, K.; Ugawa, A.; Kawamoto, A.; Yamashita, Y.; Yakushi, K.; Suzuki, T.; Miyashi, T. Bull. Chem. Soc. Jpn. 1992, 65, 3350. Yamashita, Y.; Tanaka, S.; Imaeda, K.; Inokuchi, H.; Sano, M. J. Org. Chem. 1992, 57, 5517. Ono, K.; Tanaka, S.; Imaeda, K.; Yamashita, Y. Chem. Commun. 1994, 899.
(X ) O, S, Se) on their amphoteric redox properties and crystal structures. The effects of alkyl substituents on amino nitrogens (Namino) are also discussed by comparing two series of compounds with dimethylamino (a) and pyrrolidinyl groups (b).
Results and Discussion Preparation. 4,7-Bis(dimethylamino)benzo[c][1,2,5]oxadiazole (1a) was prepared in 67% yield by N-methylation6 of the corresponding free diamine 1c with HCHONaBH4. 4,7-Bis(1-pyrrolidinyl) derivative 1b was also obtained from 1c in 19% yield by treating the trifluoroacetylated compound 1d with 1,4-dibromobutane/KOH7 (Scheme 1). Similarly, the thiadiazole derivatives 2a and 2b were prepared from 2c in respective yields of 94 and 59%. The diamine 2c is also a new compound and was obtained in 65% yield by reacting 4-aminobenzothiadiazole (4c) with p-N2+-C6H4-SO3- followed by reduction of the azo dye with Na2S2O4 (Scheme 2). (6) Giumanini, A. G.; Chiaveri, G.; Musiani, M. M.; Rossi, P. Synthesis 1980, 743. (7) Johnstone, R. A. W.; Payling, D. W.; Thomas, C. J. Chem. Soc. C 1969, 2223.
10.1021/jo010808h CCC: $20.00 © 2001 American Chemical Society Published on Web 11/30/2001
Bis(dialkylamino)benzochalcogenadiazole
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Scheme 1
Figure 1. Bond lengths (R) of 2a and 2e determined by X-ray analyses at -150 °C (upper) and π-bond orders (p) (lower) calculated using the following equations: R/Å ) 1.514 0.188p for C-C; R/Å ) 1.443 - 0.167p for C-N.11 Estimated standard deviations for bond lengths are 0.003-0.005 Å for 2a and 0.002-0.004 Å for 2e.
Scheme 3 Scheme 2
Reductive ring opening8 of the thiadiazole ring in 2a and 2b by LiAlH4 gave air-sensitive tetramines 5a and 5b, respectively, from which the selenadiazole derivatives 3a and 3b were prepared by treatment with SeO2 in yields of 45 and 34% in two steps (Scheme 1). Unsymmetrically alkylated diamine 2ab which has both dimethylamino and pyrrolidinyl groups was also prepared in a stepwise manner as shown in Scheme 2. All of the bis(dialkylamino)benzochalcogenadiazoles (1-3(a,b)) could be isolated as light- and air-stable crystalline materials with a deep red to violet color. Molecular Structures. To determine the precise geometries of the newly prepared electron donors, singlecrystal X-ray structural analyses were carried out at -150 °C for the thiadiazole derivatives 2a and 2b. The crystallographic study was also conducted on 2e,9 which does not have any amino groups. Inspection of the bond distances in 2e shows that the benzothiadiazole skeleton exhibits pronounced bond alternation (Figure 1) as previously suggested by NMR spectroscopy.12 Comparisons of π-bond orders13 with dimethylamino derivative 2a clearly show that the degree of bond alternation in the sixmembered ring is larger in 2a than in the parent (8) Mataka, S.; Takahashi, K.; Imura, T.; Tashiro, M. J. Heterocycl. Chem. 1982, 19, 1481. (9) While X-ray structure of 2e has been reported previously,10 it was reanalyzed here to obtain precise bond distances with a sufficient accuracy (esd < 0.004 Å). (10) Luzzati, V. Acta Crystallogr. 1951, 4, 193. (11) Ha¨felinger, G. Chem. Ber. 1970, 103, 2902. (12) Brown, N. M.; Bladon, P. Spectrochim. Acta 1968, 24A, 1869.
heterocycle 2e. This result may be accounted for by the reduced contribution of the delocalized form (D in Scheme 3) due to the introduction of strong electron-donating groups15 and may indicate an only small contribution of the polarized structure (P) in the ground state of 2a. This seems to also be true for pyrrolidinyl derivative 2b, although detailed comparisons are inappropriate due to the relatively large errors (0.01 Å) for the bond distances in 2b. A marked difference between 2a and 2b is found in the geometry around Namino. In both cases, one of the two alkyl carbons on Namino is located nearly in the same plane as benzothiadiazole. However, the other alkyl carbon close to the inimo nitrogen deviates from this plane; the deviation is much greater in dimethylamino derivative 2a (1.25 and 1.29 Å) than in pyrrolidinyl derivative 2b (0.80 and 0.91 Å). Such differences may be due to the greater steric requirements of the methyl compared to the methylene in the pyrrolidinyl group. On the other (13) π-Bond orders were calculated by using the established relationship, where the parameters were defined to fit hetero-π-systems containing carbon-nitrogen bonds.11 The equations shown in the caption of Figure 1 were successfully used to analyze the geometrical features of thiadiazine and selenadiazine derivatives.14 (14) Gieren, A.; Lamm, V.; Haddon, R. C.; Kaplan, M. L. J. Am. Chem. Soc. 1979, 101, 7277; J. Am. Chem. Soc. 1980, 102, 5070. (15) In the X-ray analyses on p-phenylenediamines, the C1sC2 bond (d12) and its equivalents were longer than the standard of CArsCAr, whereas the C2sC3 bond and its equivalents (d23) tended to be shortened. For example, d1 in tetrakis(2-pyridylmethyl)-p-phenylenediamine are 1.403(2) and 1.402(2) Å, and much longer than d2 [1.380(2) Å].16 In the case of tetraisopropyl-p-phenylenediamine, crystallographic studies were conducted at 150 K on the two rotational isomers around the NaminosCAr bond; the dihedral angle between the Namino lone pair and the benzene π system is 28 and 74° in monoclinic and triclinic modifications, respectively. The larger interaction between the Namino lone pair and the π-system in the former induces a significant difference between d12 and d23 (d12, 1.400, 1.402, 1.403, 1.404 Å; d23, 1.387, 1.388 Å), whereas d12 and d23 are nearly equal in the latter modification (d12, 1.398, 1.395 Å; d23, 1.392 Å)17 (esd of bond length 0.001-0.005 Å). (16) Buchen, T.; Hazell, A.; Jessen, L.; McKenzie, C. J.; Nielsen, L. P.; Pederson, J. Z.; Schollmeyer, D. J. Chem. Soc., Dalton Trans. 1997, 2697. (17) Bock, H.; Go¨bel, I.; Na¨ther, C.; Havlas, Z.; Gavezzotti, A.; Filippini, G. Angew. Chem., Int. Ed. Engl. 1993, 32, 1755.
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Suzuki et al.
Figure 2. Angular geometry around amino nitrogens of 2a (a) and 2b (b). Estimated standard deviations for bond angles are 0.1-0.3° for 2a and 0.4-0.7° for 2b.
Figure 3. UV-vis spectra of 2a and 2b measured in MeCN.
Table 1. Oxidation (Eox) and Reduction Potentials (Ered.)a and the Lowest-Energy Absorption Maxima (λmax) for 1-3 and Related Compounds in MeCN compd
E1ox/V
Y ) NM2 1a (X ) O) +0.24 2a (X ) S) +0.19 3a (X ) Se) +0.15 TMPD +0.10 Y ) 1-pyrrolidinyl 1b (X ) O) +0.09 2b (X ) S) -0.02 3b (X ) Se) -0.05 BPB -0.02 Y)H 1e (X ) O) >+2.3 2e (X ) S) >+2.3 3e (X ) Se) +2.15d a
E2ox/V
E1red./V
Esum/Vb λmax/nm
+0.68 -1.73c +0.58 -1.72c +0.47 -1.57c +0.67 3σΙ and 173 parameters. Estimated standard deviations are 0.007-0.01 Å for bond lengths and 0.4-0.7° for bond angles. Crystal data for 2e. C6H4N2S, M 136.17, colorless cube, 0.4 × 0.4 × 0.4 mm (sublimation), orthorhombic Pna21, a ) 12.572(8) Å, b ) 12.132(8) Å, c ) 3.803(2) Å, V ) 580.1(6) Å3, F (Z ) 4) ) 1.559 g cm-1. A total of 743 unique data (2θmax ) 55.0°) were measured at T ) 123 K by a Rigaku Mercury CCD (27) Zincke, T.; Schwarz, P. Liebigs Ann. Chem. 1899, 307, 28. (28) Khaletskii, A. M.; Pesin, V. G. Z. Obs. Khim. 1950, 20, 1914 [cf. Chem. Abstr. 1952, 46, 106f]. (29) Bird, C. W.; Cheeseman, G. W. H.; Sarsfield, A. A. J. Chem. Soc. 1963, 4767.
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apparatus (Mo KR radiation, λ ) 0.710 69 Å). Absorption correction was applied (µ ) 4.43 cm-1). The structure was solved by the direct method (SIR92) and refined by the fullmatrix least-squares method on F with anisotropic temperature factors for non-hydrogen atoms. Hydrogen atoms were picked up from the D-map and fixed at these positions. The final R and Rw values are 0.029 and 0.042 for 712 reflections with I > 3σΙ and 83 parameters. Estimated standard deviations are 0.002-0.004 Å for bond lengths and 0.1-0.2° for bond angles. Crystal data for 3a. C10H14N4Se, M 269.21, violet cube, 0.35 × 0.30 × 0.20 mm (n-hexane), monoclinic Cc, a ) 19.764(2) Å, b ) 13.557(1) Å, c ) 9.584(1) Å, β ) 112.155(8)°, V ) 2378.2(4) Å3, F (Z ) 8, two crystallographically independent molecules) ) 1.504 g cm-1. A total of 2803 unique data (2θmax ) 55°) were measured at T ) 295 K by a Rigaku AFC-7R fourcircle diffractometer with ω-2θ scan mode (Mo KR radiation, λ ) 0.710 69 Å). Absorption correction was applied (µ ) 31.33 cm-1). The structure was solved by the Patterson method and refined by the full-matrix least-squares method on F with anisotropic temperature factors for non-hydrogen atoms. Hydrogen atoms were located at the calculated positions. The
Suzuki et al. final R and Rw values are 0.028 and 0.027 for 2422 reflections with I > 3σΙ and 269 parameters. Estimated standard deviations are 0.004-0.01 Å for bond lengths and 0.2-1.0° for bond angles.
Acknowledgment. This work was supported by the Ministry of Education, Science and Culture, Japan (Grants 10146101 and 13440184). Financial support from the Izumi Science and Technology Foundation and a Research Grant from the Iwatani Naoji Foundation are gratefully acknowledged. We thank Prof. Tamotsu Inabe (Hokkaido University) for use of the X-ray structure analysis system. Supporting Information Available: ORTEP drawings (Figures S1-S4) and structural data for the X-ray analyses (positional and thermal parameters, bond distances and angles) of 2a, 2b, 2e, and 3a. This material is available free of charge via the Internet at http://pubs.acs.org. JO010808H
