Short communication The first example of Cu(I) complex with 5-pyrazolyl-2-thioxotetrahydro-4H-imidazol-4-one: Synthesis and structural characterization Elena K. Beloglazkina ⁎, Nikolai I. Vorozhtsov, Lyudmila A. Sviridova, Oksana S. Grigorkevich, Diana D. Korablina, Anna A. Moiseeva, Nikolay V. Zyk, Alexander G. Majouga M.V. Lomonosov Moscow State University, Faculty of Chemistry, Leninskie gory, 1/3, Moscow 119991, Russia abstract article info Article history: Received 27 April 2016 Received in revised form 28 June 2016 Accepted 10 July 2016 Available online 14 July 2016 A new organic ligand 3-phenyl-5-((Z)-1,5-diphenyl-pyrazol-3-yl)methylene)-2-methylthio-4,5-dihydro- imidazol-4-one (L) has been synthesized by a two step reaction sequence starting from 3-phenyl-2- thiohydantoin and 3-formyl-pyrazoline. The complex of copper(I) with L 2 СuClO 4 composition was obtained by the reactions of this ligand with Сu(ClO 4 ) 2 ·6H 2 O; thus, the reduction of copper(II) took place during the complex formation. The crystal structure of synthesized complex has been determined by X-ray analysis. Copper atom has a distorted tetrahedral ligand environment and coordinated by four nitrogen atoms of two ligand moieties; per- chlorate ion does not participate in the coordination of the metal ion. This complex undergo reversible electro- chemical reduction at -0.32 V. © 2016 Published by Elsevier B.V. Keywords: Copper(I) complex Pyrazoles Pyrazolines 2-alkylthio-imidazol-4-ones Copper is an endogenous metal that is necessary for the normal cel- lular activity, it found in many enzymes (eukaryotic copper amine oxi- dase [1–3], NO-reductase [4–6], superoxide dismutase [7,8], etc.), therefore copper coordination compounds are assumed to be less toxic than platinum anticancer compounds. Bisthiosemicarbazone [9], phenantroline [10,11] and other [12] copper complexes show good cy- totoxicity against some cancer cell lines and some of them are currently in clinical trials [13,14]. Recently we have synthesized copper complexes with 2- thiohydantoin derivatives, namely (5Z)-(5-pyridylmethylene)-2- alkylthioimidazole-4-ones, possessing the cycotoxic activity against HEK-293 (transformed human embryonic kidney), SiHa (cervical can- cer) and MCF-7 (breast cancer) cell lines [18]. In further studies of 5- hetarylmethylene-substituted 2-thioxo-imidazole-4-ones and their S- alkylated derivatives [14–34] in this work we presented the novel type of 5-hetarylmethylene substituted 2-thio-imidazol-4-one ligand - 5-pyrazolylmethylene-2-alkylthio-imidazol-4-one, and its copper(I) complex. We have synthesized 3-phenyl-5-((Z)-1,5-diphenyl-pyrazol-3- yl)methylene)-2-methylthio-4,5-dihydro-imidazol-4-one 5 by a two steps reaction sequence shown in Scheme 1, starting from 3-phenyl- 2-thiohydantoin 1 and 3-formyl-pyrazoline 2. Condensation of thiohydantoin 1 with pyrazoline carbaldehyde 2 was performed in 2% KOH ethanolic solution, and then the resulting 5-pyrazolinemethylene- substituted thiohydantoin 3 was alkylated with methyl iodide in alkaline solution giving methyltio-imidazolone 4. The mild oxidation of com- pound 4 was carried out using lead tetraacetate; this reaction proceeded selectively, affecting only a pyrazoline ring and forming target ligand 5 with a good yield ([35]; see also Supplementary information). Compounds 3–5 were isolated as single geometric isomers, which were identified as the Z isomers basing on the chemical shifts of the vi- nylic protons in the 1H NMR spectra [23]. The preferential generation of Z isomers for these compounds may be the result of the formation of an intramolecular hydrogen bond between the pyrazoline nitrogen atom and the N-H fragment of the thiohydantoin cycle. The Z configurations of ligand 5 in its coordination compounds were also confirmed by X- ray diffraction data for complexes 6 (see below). A copper(I) complex of pyrazolylmethylene-imidazolone 5 was syn- thesized by direct reaction of ligand dissolved in CH 2 Cl 2 with copper(II) perchlorate (Scheme 2) [36]. The formed complex 6 (Scheme 2) was characterized by elemental analysis and X-ray diffraction data. The mo- lecular structure of coordination compound 6 is illustrated in Fig. 1; se- lected bond lengths and angles are given in the Figure caption. Crystallographic data and the full list of bond lengths and angles are given in the Supplementary information. Copper atom in the obtained complex is coordinated by four nitrogen atoms of pyrazole and thiohydantoin rings from two ligand moieties, forming a distorted tetra- hedral environment for metal ion; the Cu \\ N distances are 2.047– 2.083 Ǻ (Cu \\ N Imidazolone ) and 2.035–2.046 Ǻ (Cu \\ N Pyrazole ), which is Inorganic Chemistry Communications 71 (2016) 86–89 ⁎ Corresponding author. E-mail address: bel@org.chem.msu.ru (E.K. Beloglazkina). http://dx.doi.org/10.1016/j.inoche.2016.07.008 1387-7003/© 2016 Published by Elsevier B.V. Contents lists available at ScienceDirect Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche