z Catalysis Preparation, Characterization and First Application of Graphene Oxide-Metformin-Nickel for the Suzuki Cross- Coupling Reaction Farveh Raoufi,* [a] Majid Monajjemi, [a] Hossein Aghaei, [a] Karim Zare, [a] and Mehrorang Ghaedi [b] In this project, in the first step, the graphene oxide-metformin- nickel catalyst has been prepared and then the Ni(II) was reduced to Ni(0) by hydrazine hydrate and Ni(0) nanoparticle coordinated to metformin-GO was achieved. After full charac- terization of catalyst structure by different analyses like fourier- transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-Ray analysis (EDX), X-Ray diffraction analysis (XRD), thermal gravimetric analysis (TGA), and coupled plasma/atomic emission spectroscopy (ICP), as well as confirm the successful synthesis of catalyst, the activity of catalyst has been examined in the Suzuki–Miyaura cross-coupling reaction. Introduction Carbon has various allotropes which are structurally different but composed the same element. Famous and oldest forms of carbon are diamond and graphite. Though recently, some other important allotropes of carbon were discovered such as fullerene, nanotubes and graphene. [1] Graphene and graphite are just different in number of layers and if separate the graphite layers, graphene is formed in a single layer structure. [2] Due to the structure with one atom thick layer, graphene is classified in nanomaterials with diverse applications. [3] Also, graphene can convert to graphene oxide (GO) by oxidation reaction and some functional groups like carboxyl, hydroxyl and epoxide are created on its basal plane and edges which are proper for immobilization of organic and inorganic ligands to catalyze organic reactions. [4] Recently, undoubtedly, one of the most important chal- lenge for organic chemists is the formation of carbon-carbon bond between two different starting materials. The cross- coupling reactions are kind of organic reactions in which two fragments are reacted together using of metal catalysts and created of new covalent bond in product. [5] In 2010, Heck, Suzuki and Negishi were awarded Nobel prize in chemistry for presentation of palladium as a transition metal catalyst in cross-coupling reactions. [6] Suzuki–Miyaura reaction is the most popular cross-coupling reaction which leads to synthesis of worthwhile biaryl organic compounds. [7] However, in the past decade, most of chemists carried out the Suzuki–Miyaura cross- coupling reactions with the use of palladium as a transition metal catalysts. These days, the researchers are attracted to develop other transition metal-based catalysts like iron, [8] copper, [9] cobalt [10] and nickel [11] which are cost effective and nontoxic than palladium. [12] The first use of nickel as a transition metal catalyst goes back to 1997 which Miyaura and co-workers reported the cross- coupling reaction of inert aryl chlorides with various boronic acids. [13] They reduced nickel chloride complex NiCl 2 (dppf) (dppf = 1,10-bis(diphenylphosphino)ferrocene) to Ni(0) and used in synthesis of different biaryl derivatives. Yield of the reactions was better when they carried out the reaction in presence of Ni(0). Three years later (2000), Inada and Miyaura studied the application of NiCl 2 /PPh 3 complex in the reaction of tolylboronic acids with arene chlorides. Their procedure was more efficient and cheaper than previous study. [14] Also, in this year, Lipshutz and co-workers prepared nickel(0) supported on charcoal (Ni/C) and investigated its activity in Suzuki–Miyaura cross-coupling reaction. [15] One the most advantages of their study was the easy separation of catalyst due to the heterogeneity of their catalyst. In 2006, Hu and co-workers directly formed C  C bond via Suzuki–Miyaura reaction in mild condition and presence of Ni(cod) 2 (cod = 1,5-cyclooctadiene) with the aid of ferrocenylmethylphosphine at room temperature. [16] Tobisu and co-workers developed Suzuki– Miyaura reaction of various aryl fluorides with different aryl boronic esters in presence of Ni complexes. [17] This protocol has been carried out with metal fluoride like ZrF 4 and TiF 4 as a co- catalyst. Recently, for the first time, the application of Ni(II) complex catalyst has been reported by Shi and coworkers for the synthesis of biaryl compounds via nitrogen-carbon amide bond activation. [18] The Ni complex could catalyze the gen- eration of aryl electrophiles from aryl amides and then easy formation of product. Although, most of above protocols have many advantages, but the most disadvantage of the mentioned methods is the use of non-environmentally friendly conditions and failure to [a] Dr. F. Raoufi, Prof. M. Monajjemi, Prof. H. Aghaei, Prof. K. Zare Department of Chemistry, Science and Research Branch, Islamic Azad University, Tehran, P.O. Box 14515–755, Tehran, Iran E-mail: fraoufi@yahoo.com [b] Prof. M. Ghaedi Department of Chemistry, Yasouj University, Yasouj 75918-74831, Iran Supporting information for this article is available on the WWW under https://doi.org/10.1002/slct.201903749 Full Papers DOI: 10.1002/slct.201903749 211 ChemistrySelect 2020, 5,211–217 © 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim