Synthesis and properties of azole-substituted ferrocenes Tomoyuki Mochida a,b, * , Hirotaka Shimizu a , Shinya Suzuki a , Takahiro Akasaka a a Department of Chemistry, Faculty of Science, Toho University, Miyama, Funabashi, Chiba 274-8510, Japan b Research Center for Materials with Integrated Properties, c/o Faculty of Science, Toho University, Japan Received 3 April 2006; received in revised form 1 August 2006; accepted 11 August 2006 Available online 22 August 2006 Abstract 4-Ferrocenyltriazole, 4-(4-ferrocenylphenyl)triazole, 4-ferrocenyltetrazole, and 4-(4-ferrocenylphenyl)tetrazole have been prepared. Redox potentials and decomposition temperatures were evaluated and all the compounds were crystallographically characterized; in most cases, weak intermolecular CHN hydrogen bonds (HN dist. = 2.3–2.5 A ˚ ) were formed between the azole moieties. Two poly- morphs were found for 4-ferrocenyltetrazole, formed with either CHN or p–p interactions. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Ferrocene; Tetrazole; Triazole; Crystal structures; Hydrogen bond; Redox potentials 1. Introduction Organometallic supramolecular assemblies have attracted special attention in recent decades [1,2]; heteroa- ryl-substituted ferrocene ligands provide a useful approach towards their synthesis. For this purpose, we have designed a variety of ligands, which are shown in Chart 1 [3,4]. These versatile ligands give topologically diverse assembled structures when combined with various metal salts; the modes of assembly depend on the number and position of the ligands’ nitrogen coordination sites. To extend the study, we designed the azole-substituted ferrocenes shown in Chart 2. Azole substituents provide versatile ligating sites so have the potential to form a vari- ety of metal complexes [5]. Their chemistry has been the subject of intense development with applications in medi- cine, biology, agriculture, and other fields [6]. We report here the preparation and properties of 4-ferrocenyl-4H- [1,2,4]triazole (FcTr), 4-(4-ferrocenylphenyl)-4H-[1,2,4]tri- azole (FcPhTr), 4-ferrocenyl-1H-tetrazole (FcTe), and 4- (4-ferrocenylphenyl)-1H-tetrazole (FcPhTe). These mole- cules are expected to be useful for the development of multi-functional metal assemblies such as spin-crossover complexes [7]. As a related example, 5-ferrocenyl-2H-tetra- zole [8] is known, which is a C-substituted tetrazole having an NH proton. Tetrazoles and their metal salts are known as explosives [9,10], so we used thermogravimetric analysis to evaluate the thermal decomposition behavior of our molecules. To date, only a few crystal structures of N-aryl triazoles and tetrazoles have been reported; therefore, our compounds were fully characterized crystallographically, and the importance of weak CHN hydrogen bonds to their crys- tal architectures was revealed. Weak intermolecular inter- actions in organic crystals are of interest from the viewpoint of organic crystal engineering [11,12]. 2. Results and discussion 2.1. Preparation The azole-substituted ferrocenes could be prepared by methods analogous to those used for the preparation of N-aryl triazoles, but the yield was generally lower. In par- ticular, the yield of the ferrocenyl derivatives (FcTr and 0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2006.08.020 * Corresponding author. Address: Department of Chemistry, Faculty of Science, Toho University, Miyama, Funabashi, Chiba 274-8510, Japan. Fax: +81 47 472 4406. E-mail address: mochida@chem.sci.toho-u.ac.jp (T. Mochida). www.elsevier.com/locate/jorganchem Journal of Organometallic Chemistry 691 (2006) 4882–4889