F  and OH  induced monodeprotonation of a lacunar cationic dibenzotetraaza[14]annulene: experimental evidence of tautomerism in a monoanionic macrocycle Lukasz Dudek, Jarosław Grolik, Alicja Kaz ´ mierska, Edward Szneler, Andrzej Eilmes, Katarzyna Stadnicka, Julita Eilmes ⇑ Department of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland article info Article history: Received 11 February 2011 Revised 4 April 2011 Accepted 3 May 2011 Available online 11 May 2011 Keywords: Dibenzotetraaza[14]annulene Deprotonation Macrocyclic monoanion Tautomerism abstract A search for selective receptors of anions resulted in a new lacunar cationic derivative of dibenzotetra- aza[14]annulene (DBTAA) being synthesized and its crystal structure determined. UV–vis, fluorescence and preliminary 1 H NMR studies of anion binding abilities revealed that under the influence of F  and OH  , deprotonation of the macrocycle takes place leading to a zwitterionic species containing a monoan- ionic DBTAA core and a positively charged quaternized amine nitrogen. The tautomerism of the remain- ing single NH hydrogen is discussed on the basis of 1 H NMR experiments and DFT calculations. Ó 2011 Elsevier Ltd. All rights reserved. Dibenzotetraaza[14]annulenes (DBTAAs) belong to the class of tetraaza macrocycles of bioinorganic relevance, known and appreci- ated for their synthetic accessibility, rich chemistry and similarity to porphyrins. 1 Although the DBTAA macrocycle has been studied for more than 40 years and many derivatives have been reported, little is known about the anion binding behavior of DBTAA-based recep- tors. With the aim of designing DBTAA-based selective anion recep- tors we recently synthesized a new cationic lacunar derivative 3 (Scheme 1). Compound 3 was synthesized in two steps starting from bis(2-hydroxybenzoyl)-5,14-dihydrodibenzo[b,i][1,4,8,11]tet- raazacyclotetradecine (1). O,O 0 -Bis-alkylation using 1,4-dibromobu- tane gave 2 which, on reaction with dimethylamine, produced 3. The identity of product 3 was confirmed by single crystal X-ray crystal- lography (Fig. 1 and Supplementary data). In the course of preliminary evaluation of the anion binding abilities of the ligand 3 using UV–vis spectroscopy we observed that, in contrast to anions such as Br  , Cl  , NO 3  and HSO 4  , which only influenced the spectra marginally, addition of F  and OH  in- duced distinct changes in band positions and intensities (Fig. 2). Moreover, simultaneous fluorescence emission appeared at 576 nm, with the excitation wavelength at 380 nm ( Fig. 3). Also, simple visual observation revealed orange to red color changes and an orange luminescence on addition of tetrabutylammonium fluoride (TBAF) or hydroxide (TBAOH) to the solution of 3. It should be mentioned here that a related case and similar observations have been described previously. 3 To elucidate the nature of the interactions with F  , UV–vis titra- tion of 3 with a DMSO solution of TBAF was performed (Fig. 4). A 0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2011.05.008 ⇑ Corresponding author. Tel.: +48 12 632294; fax: +48 12 6340515. E-mail address: jeilmes@chemia.uj.edu.pl (J. Eilmes). NH N N HN O O O O N NH N N HN O O O O Br Br NH N N HN O O OH OH PF 6 1 2 3 = [LH 2 ] + PF 6 - DMF, RT K 2 CO 3 Br Br H N DMF/toluene, 60 °C NH 4 PF 6 1. 2. MeOH , , Scheme 1. Synthesis of 3. Tetrahedron Letters 52 (2011) 3597–3601 Contents lists available at ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet