Synthesis and characterization of a stable copper (I) calix[4]dicyano-diimidazole complex Sebastien Noel a , Hui Ren a , Tao Tu b , Erwann Jeanneau a , Caroline Félix a , Florent Perret a , Francis Vocanson c , Christophe Bucher d , Guy Royal d , Isabelle Bonnamour a,⇑ , Ulrich Darbost a,⇑ a Université de Lyon, Lyon, Université Lyon 1, Villeurbanne, CNRS, UMR5246, Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, CSAp, 43 Boulevard du 11 Novembre 1918, F-69622 Villeurbanne, France b Department of Chemistry, Fudan University, 220 Handan Road, 200433 Shanghai, China c Université de Lyon, Université de Saint-Etienne, CNRS UMR 5516, Laboratoire Hubert Curien, France, F-42000, Saint-Etienne, France d Département de Chimie Moléculaire, Laboratoire de Chimie Inorganique Rédox, (DCM-CIRE-UMR CNRS/UJF 5250), Université Joseph Fourier, BP-53, 38041 Grenoble Cedex 9, France article info Article history: Received 24 May 2012 Revised 5 June 2012 Accepted 11 June 2012 Available online 19 June 2012 Keywords: Calixarene Copper(I) X-ray structure Synthesis abstract A new calix[4]dicyano-diimidazole ligand was prepared in two steps from a de-tert-butylated calix[4]ar- ene. The corresponding Cu (I) complex was found to be remarkably stable. The X-ray structure of the lat- ter revealed a mixture of both monomeric–mononuclear and dimeric–dinuclear complexes. Detailed investigations on this copper complex, involving NMR (VT and DOSY), Infra-red, and MS analyses, dem- onstrated that the dimeric–dinuclear complexe does not exist in solution. Despite the presence of two cyano binding groups on the calixarene platform, every attempts to isolate a stable Cu(II) complex failed. Ó 2012 Elsevier Ltd. All rights reserved. One of the greatest challenges in molecular electronics may be to design dynamic molecular objects that could be controlled and manipulated by an electrical stimulus. 1 This field opens great per- spectives for the development of highly performing devices. 2 Par- ticularly, this domain of research can bring solutions for the storage of numerical data, since storing bites on molecules could lead to new high density storage materials. 3 Our research focuses on the elaboration of redox molecular switches 4 based on calixarenes. 5 We have recently reported an example of a coordinating architecture based on a flexible calix[4]- arene allowing the stabilization of a copper ion in two different oxidation states (see Scheme 1, structure 1). 6 In order to modify the kinetics of the Cu(II)/Cu(I) switching process, both oxyquino- line binding fragments in 1 have been replaced by two flexible cy- ano alkyl chains. The targeted calix[4]dicyano-diimidazole 4 was synthesized according to an efficient two step sequence starting from the de-tert-butylated calix[4]arene 2 (Scheme 1). Following a literature procedure, 7 the regioselective dialkylation of 2 with an excess of 4-bromobutyronitrile in the presence of K 2 CO 3 affor- ded the dicyanocalixarene 3 in 69% yield. Alkylation of the two remaining hydroxy positions using 2- chloromethyl-N-methylimidazole with NaH in THF led to the tar- geted ligand calix[4]dicyano-diimidazole 4 in 51% yield. This ligand was thus synthesized in two steps with a 35% overall yield, and fully characterized by 1 H, 13 C NMR, IR, mp, HR-MS, and by X-Ray diffraction analyses (see Supplementary data). Scheme 1 displays the synthesis of the novel calixarene 4, prepared through an effi- cient two step procedure, starting from the known de-tert- butylated calix[4]arene precursor 2. In order to check the ability of the ligand 4 to stabilize a Cu(I), a stoichiometric mixture of 4 and CuPF 6 (CH 3 CN) 4 in chloroform under aerobic condition was prepared. After an overnight stirring, a white precipitate was formed and collected by filtration, corresponding to 85% wt of the introduced solids. Single crystals were obtained by slow diffusion of diethylether in acetonitrile. Regarding the previous results, 6,8 a mononuclear Cu(I) pinched species, namely [4ÁCu(I)]PF 6 , was expected. Surprisingly, two different arrangements were obtained in the same crystal. The first structure corresponds to the expected mononuclear structure [4ÁCu(I)]PF 6 with the Cu ion strongly pinched between the two imidazoles (Cu–N imi bonds (1.85(9) and 1.85(7) Å) and stabilized by an oxygen atom of the calixarene (d(Cu–O calix ) = 2.63(4) Å) (see Fig. 1). The second species corresponds to a dimeric complex [[4ÁCu(I)]PF 6 ] 2 wherein the Cu ion, still pinched between two imidazole units (d(Cu–N imi ) = 1.89(4) Å), is further bound to a nitrile ligand from a second calixarene 0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tetlet.2012.06.065 ⇑ Corresponding authors. Tel.: +33 426 234 405 (U.D.), +33 426 234 405 (I.B.). E-mail addresses: isabelle.bonnamour@univ-lyon1.fr (I. Bonnamour), ulrich. darbost@univ-lyon1.fr (U. Darbost). Tetrahedron Letters 53 (2012) 4648–4650 Contents lists available at SciVerse ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet