Tungsten-mediated synthesis of triazafluorenes Janusz Szklarzewicz a, * , Dariusz Matoga a , Magdalena Owcarz a , Wojciech Przybylski a , Daisuke Yoshioka b , Masahiro Mikuriya b a Faculty of Chemistry, Jagiellonian University, 30-060 Kraków, Ingardena 3, Poland b Kwansei Gakuin University, Gakuen 2-1, Sanda 669-1337, Japan article info Article history: Received 25 March 2009 Accepted 22 June 2009 Available online 27 June 2009 Keywords: Tungsten Cyano complexes Azafluorene Triazafluorene Picolinic aldehyde abstract Reaction of 2-pyridinecarboxaldehyde with aliphatic 1,2-diamines in aqueous/ethanolic solution medi- ated by [W(CN) 4 O 2 ] 4À affords the cationic disubstituted triazafluorenes in good yields. Single-crystal X-ray analysis of 4,9-bis(2-pyridyl)-4a,9a-dihydro-3H,9H-3,8a,9a-triazafluorenium hexafluorophosphate salt 1 reveals the formation of a novel heterocyclic tricycle, triaza analogue of fluorene. The identity and purity of the compounds have been verified with elemental analysis as well as IR, 1 H and 13 C NMR, UV– Vis, Raman and cyclic voltammetry measurements. Aliphatic 1,3- and 1,4-diamines as well as cycloali- phatic and aromatic ones are not reactive. The proposed pathway for the tungsten-mediated formation of triazafluorenes is discussed. Ó 2009 Elsevier B.V. All rights reserved. In our continuing quest to get a deeper insight in the versatile reactivity and properties of mixed-ligand cyanooxocomplexes of molybdenum(IV) and tungsten(IV) we have synthesized a series of such complexes with Schiff-base ligands, both symmetric and half-unit ones [1–6]. Mechanisms of the formation of such ligands on a molybdenum(IV) centre in mixed-solvent solutions have been discussed indicating the directing role of molybdenum in the syn- thesis of ligands [6–8]. The complexes with half-unit Schiff bases containing pendant amine groups were particularly interesting for us since they could further be used as building blocks for ex- tended systems. On the other hand, working with molybdenum and tungsten complexes, we have recently observed that several M(IV) cyano complexes participate in redox processes involving and influencing the reactivity of various ligands (O 2 , NO, nitriles, hydrazine) [9–14]. The propensity of these metals for both redox as well as template organic reactions prompted us to further study their reactivity towards potential Schiff-base components. In the present work we used 2-picolinic aldehyde and a series of diamines as Schiff-base precursors with a tungsten(IV) complex. Surprisingly, instead of a Schiff-base system, we obtained a triaza- fluorene derivative, formed in a one-pot reaction. Generally, het- erocyclic organic compounds with nitrogen atoms exhibit wide applications. For instance, compounds with five-membered rings such as antipyrine, imidazole, piramidon have been a base of numerous biologically and medically relevant products. Among them, azafluorene derivatives are reported to show antihistamine, neurotropic, antibacterial, antioxidant and pesticide activities [15]. Also, triazafluorene derivatives have recently been prepared and it has been found that they can act as insulin secretagogues [16]. High insulinotropic activities were found for a series of substituted 1,7,9-triazafluorene-6-carboxylic acids possessing two pyridine and one imidazole rings. Herein, we present a communication on the synthesis, X-ray crystal structure and physicochemical proper- ties of triaza analogues of fluorene. Of the particular importance in the current study is the novel synthetic method with the use of a transition metal complex as well as the crystallographic demon- stration of the structure of the product. To the best of our knowl- edge, such a synthetic study backed up by crystallographic analysis is not common for triazafluorenes. Reaction of 2-pyridinecarboxaldehyde with aliphatic 1,2-diami- noethane or 1,2-diaminopropane in the presence of K 3 Na[W(C- N) 4 O 2 ]Á6H 2 O results in the formation of intensely red-coloured solutions. The addition of NaPF 6 to it leads to the isolation of (C 20 H 16 N 5 )(PF 6 )(1) or (C 21 H 18 N 5 )(PF 6 )Á2H 2 O(2) as dark red crystals [17,18]. It has been found that in the absence of the tungsten com- plex, yellow Schiff bases, N,N 0 -ethylenebis(2-pyridinecarboxalde- hydeimine) or N,N 0 -1,2-propylenebis(2-pyridinecarboxaldehy- deimine) are exclusively formed. When KCN is used instead of the W(IV) cyano complex the formation of a-pyridoine is observed in both cases. Relatively high yields of the synthesis of 1 and 2 (58% or 77%, respectively; based on the aldehyde) indicate that the W(IV) complex acts as a catalyst. The calculated yields based on the tungsten complex are 230% and 310% for 1 and 2, respectively. The IR measurements of the solutions after the reactions are com- pleted (before products are isolated) show the lack of m(CN) bands. 1387-7003/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2009.06.024 * Corresponding author. Tel.: +48 12 6632231; fax: +48 12 6340515. E-mail address: szklarze@chemia.uj.edu.pl (J. Szklarzewicz). Inorganic Chemistry Communications 12 (2009) 819–822 Contents lists available at ScienceDirect Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche