Citation: Fomenko, I.S.; Koshcheeva, O.S.; Kuznetsova, N.I.; Larina, T.V.; Gongola, M.I.; Afewerki, M.; Abramov, P.A.; Novikov, A.S.; Gushchin, A.L. Novel Copper(II) Complexes with BIAN Ligands: Synthesis, Structure and Catalytic Properties of the Oxidation of Isopropylbenzene. Catalysts 2023, 13, 849. https://doi.org/10.3390/ catal13050849 Academic Editors: Victorio Cadierno and Raffaella Mancuso Received: 18 April 2023 Revised: 4 May 2023 Accepted: 4 May 2023 Published: 8 May 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). catalysts Article Novel Copper(II) Complexes with BIAN Ligands: Synthesis, Structure and Catalytic Properties of the Oxidation of Isopropylbenzene Iakov S. Fomenko 1 , Olga S. Koshcheeva 1 , Nina I. Kuznetsova 2 , Tatyana V. Larina 2 , Marko I. Gongola 3 , Medhanie Afewerki 3 , Pavel A. Abramov 1 , Alexander S. Novikov 4,5 and Artem L. Gushchin 1, * 1 Nikolaev Institute of Inorganic Chemistry, Siberian Branch of Russian Academy of Sciences, 3 Acad. Lavrentiev Ave., Novosibirsk 630090, Russia; fom1-93@mail.ru (I.S.F.); koshchee@niic.nsc.ru (O.S.K.); abramov@niic.nsc.ru (P.A.A.) 2 Federal Research Center Boreskov Institute of Catalysis, 5 Acad. Lavrentiev Ave., Novosibirsk 630090, Russia; kuznina@catalysis.nsk.su (N.I.K.); larina@catalysis.ru (T.V.L.) 3 Novosibirsk State University, 1 Pirogova Str., Novosibirsk 630090, Russia; m.gongola@g.nsu.ru (M.I.G.); medahaben@gmail.com (M.A.) 4 Saint Petersburg State University, Universitetskaya Nab. 7/9, Saint Petersburg 199034, Russia; a.s.novikov@spbu.ru 5 Peoples’ Friendship University of Russia (RUDN University), Miklukho-Maklaya Street 6, Moscow 117198, Russia * Correspondence: gushchin@niic.nsc.ru Abstract: Two new isomeric complexes [CuBr 2 (R-bian)] (R = 4-Me-Ph (1), 2-Me-Ph (2)) were ob- tained by reacting copper(II) bromide with 1,2-bis[(2-methylphenyl)imino]acenaphthene ligands and characterized. The crystal structure of 2 was determined by X-ray diffraction analysis. The copper atom has a distorted square-planar environment; the ω angle between the CuN 2 and CuBr 2 planes is 37.004 ◦ . The calculated ω parameters for optimized structures 1 and 2 were 76.002 ◦ and 43.949 ◦ , indicating significant deviations from the ideal tetrahedral and square-plane geometries, respectively. Molecules 2 form dimers due to non-covalent Cu···Br contacts, which were analyzed by DFT calculations. The complexes were also characterized by cyclic voltammetry and UV-Vis spectroscopy. A quasi-reversible Cu(II)/Cu(I) redox event with E 1/2 potentials of 0.81 and 0.66 V (vs. SHE) was found for 1 and 2, respectively. The electronic absorption spectra showed the presence of Cu(I) species as a result of the partial reduction of the complexes in the acetonitrile solution. Both complexes were tested as homogenous catalysts for the oxidation of isopropylbenzene (IPB) in acetonitrile at low temperatures. Differences in the mechanism of the catalytic reaction and the composition of the reaction products depending on the oxidizing ability of the catalyst were revealed. Keywords: copper complexes; BIAN ligands; redox-active ligands; oxidation; isopropylbenzene 1. Introduction Bis(imino)-acenaphthenes (BIANs) belong to the class of α-diimines, which combine 1,4-diazabutadiene and naphthalene fragments [1–3]. Due to this combination, BIANs have strong σ-donor and π-acceptor properties, providing stabilization of both high and low oxi- dation states of the metal upon coordination. BIANs form complexes with almost all main group elements [4–8] and transition metals [9–20]. The key feature of BIANs is their pro- nounced redox activity [21–25], and this property is widely exploited by scientists to imple- ment various catalytic transformations [1]. Historically, the first BIAN-based catalysts were Brookhart’s catalysts for the polymerization of olefins [9,26]. The various stereoelectronic properties of BIAN ligands, including their oxidation states, allowed for the modulation of catalyst properties, polyethylene branching, and polymer microstructure [27–29]. Catalysts 2023, 13, 849. https://doi.org/10.3390/catal13050849 https://www.mdpi.com/journal/catalysts