Russian Chemical Bulletin, International Edition, Vol. 69, No. 4, pp. 683—690, April, 2020 683 Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 0683—0690, April, 2020. 1066-5285/20/6904-0683 © 2020 Springer Science+Business Media LLC Nickel(II) N-heterocyclic carbene complexes as efcient catalysts for the Suzuki—Miyaura reaction* S. B. Soliev, A. V. Astakhov, D. V. Pasyukov, and V. M. Chernyshev M. I. Platov South-Russian State Polytechnic University (NPI), 132 ul. Prosveshcheniya, 346428 Novocherkassk, Russian Federation. E-mail: chern13@yandex.ru Catalytic activity of nickel(II) and palladium(II) N-heterocyclic carbene (NHC) complexes derived from imidazole, benzimidazole, and 1,2,4-triazole was comparatively evaluated in the cross-coupling reactions of aryl halides with arylboronic acids. Readily available nickel bis-NHC complexes (NHC) 2 NiX 2 (X = Cl, Br, or I) exhibited the activity comparable to that of the structurally related palladium complexes and, consequently, can be applied as efcient catalysts for the Suzuki—Miyaura reaction. Key words: nickel, palladium, N-heterocyclic carbenes, catalysis, Suzuki—Miyaura reaction. After forty years since the publication of first results, 1,2 the Suzuki—Miyaura reaction has become not only an important and powerful tool for the academic research used to form the carbon—carbon bonds 3—6 but also found application in industry for the manufacturing of drugs, pesticides, and functional materials. 7,8 The most studied and widely used catalysts for this reaction are palladium and its complexes with various ligands; 3—6,9—11 however, over recent years a considerable attention was paid to more available nickel compounds. 3,12—15 Nickel N-heterocyclic carbene (Ni/NHC) complexes are considered as promis- ing catalysts. 16—20 However, the catalytic activity of nickel mono-NHC complexes, viz. compounds 1 (Fig. 1), and Ni pincer complexes 3,12—20 in the Suzuki—Miyaura reac- tions have been mainly explored. Although some nickel pincer complexes show a relatively high catalytic activity even at the catalyst loadings of ~0.1—1 mol.%. 21—27 The synthesis of such complexes is often a multi-step process and the corresponding ligands are hardly available. Nickel bis-NHC complexes 2 of the general formula (NHC) 2 NiX 2 (X = Cl, Br, or I) (Fig. 1) is of special inter- est as the catalysts. Complexes 2 can be synthesized in one step by heating nickel salts with readily available azolium salts (the NHC proligands). 28—30 However, despite the availability of nickel bis-NHC complexes 2, their catalytic activity in the Suzuki—Miyaura reactions is still insuf- ciently explored. To the best of our knowledge, there are only two publications on the cross-couplings of aryl halides with arylboronic acids catalyzed by (NHC) 2 NiX 2 com- plexes. 31,32 Louie and co-workers 31 have shown only the * Based on the materials of the International Conference "Catalysis and Organic Synthesis" (ICCOS-2019) (September 15—20, 2019, Moscow, Russia). Compounds 2 and 3b,c R X 2a,d,g Me I 2b,f Bn Br 2c, 3b Mes Cl 2e,h, 3c Bu Br 2i Bn Cl Fig. 1. Ni/NHC and Pd/NHC complexes used in the present work as the catalysts for the Suzuki—Miyaura reaction.