Aggregation of star-shaped tris(tetrathiafulvalenylethynyl) benzene in solution and in the solid state Masashi Hasegawa, Jun-ichi Takano, Hideo Enozawa, Yoshiyuki Kuwatani and Masahiko Iyoda * Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan Received 22 February 2004; revised 22 March 2004; accepted 24 March 2004 Abstract—Neutral hexabutylthio-1,3,5-tris(tetrathiafulvalenylethynyl)benzene aggregates in CD 3 CN–CDCl 3 and CDCl 3 , whereas stronger stacking of the cationic counterparts in solution has been observed. In the solid state, X-ray analysis of hexamethylthio- 1,3,5-tris(tetrathiafulvalenylethynyl)-benzene shows a columnar structure, reflecting the threefold face-to-face stacking interaction of the TTF units. Ó 2004 Elsevier Ltd. All rights reserved. Tetrathiafulvalenes (TTFs) have attracted much interest due to their electron-donating ability, which have been used for the synthesis of new organic metals and superconductors, 1;2 and recently for supramolecular architectures. 3;4 The most remarkable property of TTF and its derivatives is their great facility for molecular association in the radical cation state as well as the one- dimensional column formation of the radical cations to give a conduction path in organic metals. In general, two or more neutral TTF molecules stack with SS interactions in the solid state to afford a dimeric or columnar structure (Fig. 1). 5 However, neutral TTF dissociates into monomers in solution through van der Waals interactions. The radical cation of TTF and neutral TTF form a mixed valence state (TTF) 2 Åþ , both in solution and in the solid state, and the mixed valence dimer is stabilized by a large exchange interaction. 6 The metallic conductivities of organic radical salts require a stacking structure of (TTF) n Åþ . 2a Two radical cations can also form the stable dimer (TTF Åþ ) 2 , which is sta- bilized by exchange and spin–spin interactions in solu- tion and in the solid state. 6 Although recent investigations have been carried out into the aggregation of large cyclic and helical molecules in solution and in the solid state for the construction of supramolecular wires and channels, 7;8 only a few of these studies reported on the self-assembly of star- shaped molecules such as tri-, tetra- and hexa(ethyn- yl)benzenes. 9 Our approach to anchoring the star mol- ecules in solution and in the solid state is to introduce TTF units as terminal substituents of poly(ethyn- yl)benzenes. Thus, the title compound 1 dimerizes in solution and in the solid state because three neutral TTF units or their cationic counterparts interact coopera- tively to form stacking structures (2 and 3). To investigate aggregation properties of 1, three alkylthio derivatives 1a–c have been synthesized (Scheme 1). The reaction of 1,3,5-triethynylbenzene (4) with 4,5-bis(methylthio)-4 0 -iodo-TTF (5a) 10 under the Sonogashira conditions afforded 1a in 75% yield. 11 For the synthesis of 1b,c, we employed a different combi- nation of the acetylene and iodide components. Thus, the Sonogashira coupling of ethynyl-TTF (6b or 6c) 12 with 1,3,5-triiodobenzene proceeded smoothly to pro- duce 1b or 1c in 89% or 92% yield. In a similar manner, the reaction of 6b with 1,3-diiodobenzene under the Sonogashira conditions afforded 7b in 63% yield. The tris–TTF derivative 1a is hardly soluble in C 6 D 6 and CDCl 3 , whereas 1b and 1c are moderately and highly soluble in C 6 D 6 and CDCl 3 , respectively. Interestingly, the 1 H NMR spectra of 1c in CDCl 3 – CD 3 CN (v/v ¼ 7:3) indicate either a concentration or a temperature dependence. At 20 °C, the chemical shift of the aromatic proton H a in 1c varied from d 7.513 to 7.470 as the concentration changed from 0.462 to Keywords: Aggregation; Tetrathiafulvalene; Face-to-face interaction; X-ray analysis. * Corresponding author. Tel.: +81-426-77-2547; fax: +81-426-77-2525; e-mail: iyoda-masahiko@c.metro-u.ac.jp 0040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2004.03.150 Tetrahedron Letters 45 (2004) 4109–4112 Tetrahedron Letters