Synthesis and Study of the Structure of Palladium(II) Acyclic Diaminocarbene Complexes Containing a 1,2,4-Oxadiazole Moi
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hesis and Study of the Structure of Palladium(II) Acyclic Diaminocarbene Complexes Containing a 1,2,4-Oxadiazole Moiety S. V. Baikova,*, Yu. A. Trukhanovab, M. V. Tarasenkoc, and M. A. Kinzhalova a St. Petersburg State University, St. Petersburg, 199034 Russia St. Petersburg State University of Chemistry and Pharmacy, St. Petersburg, 197376 Russia c M.V. Dorogov Center for Transfer of Pharmaceutical Technologies, K.D. Ushinskii Yaroslavl State Pedagogical University, Yaroslavl, 150000 Russia *e-mail: [email protected] b
Received August 19, 2020; revised August 19, 2020; accepted August 24, 2020
Abstract—The reaction of anilines containing a 1,2,4-oxadiazole moiety with the bis(xylylisocyanide) Pd(II) complex leads to the formation of acyclic diaminocarbene complexes. The oxadiazole ring is not involved in the reaction. Composition and structure of the obtained complexes have been confirmed by means of mass spectrometry, NMR spectroscopy, and single-crystal X-ray diffraction analysis. Keywords: acyclic diaminocarbene palladium complexes, oxadiazoles, isocyanide ligands, π–π-stacking
DOI: 10.1134/S1070363220100126 Investigation of the N-nucleophiles interaction with isocyanides coordinated to transition metals (Pd, Pt, Au) is the priority field of research in inorganic and coordination chemistry [1–6]. Its topicality is due to great practical importance of acyclic diaminocarbenes complexes formed in this reaction. For example, acyclic diaminocarbene complexes of Pd(II) are efficient catalysts for cross-coupling reactions (Suzuki [7–15], Sonogashira [9, 16–22], Hiyama [23, 24], and Heck [25]) and their characteristics are comparable with these of the most popular N-heterocyclic carbenes-based catalysts (NHC) [2, 26]. In addition to synthetic application, similar complexes have been recently investigated as antibacterial agents [27], anti-cancer agents [28–30], and as building blocks for the synthesis of supramolecular ensembles via crystal engineering methods [31, 32]. The reaction of N-nucleophiles with isocyanide complexes has been described for compounds with a single nucleophilic site (for example, amines) [33, 34] as well as for polynucleophiles (phenylenediamines, aminopyridine, aminothiazoles, and iminoindalinones) [35–40]. Considering the first case, a nucleophile is generally added to a single isocyanide ligand which is transformed into the diaminocarbene, while other ligands and the metal center remain intact. In the case of di- and
polynucleophiles, other ligands can also be involved, affording diverse chelate carbene complexes. Anilines with 1,2,4-oxadiazole substituent are among potential polynicleophiles. The interest to these compounds is due to huge demand for derivatives of 1,2,4-oxadiazole in medicinal chemistry [41–50]. Moreover, 1,2,4-oxadiazoles have been used as organic ligands for metal-complex drug design [51–53]. In particular, series of Au(I) and Ag(I) complexes with carbene ligands bearing the 1,2,4-oxadiazole cycle, possessing anti-tumor properties have been described [54]. In vie
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