Palladium(II) complexes with diaminomaleonitrile-based Schiff-base ligands: Synthesis, characterization and application as Suzuki–Miyaura coupling catalysts Zeinab Beigi a , Ali Hossein Kianfar a,⇑ , Gholamhossein Mohammadnezhad a , Helmar Görls b , Winfried Plass b a Department of Chemistry, Isfahan University of Technology, Isfahan 84156-8311, Iran b Institute of Inorganic and Analytical Chemistry, Chair of Inorganic Chemistry II, Friedrich Schiller University Jena, Humboldtstr. 8, Jena 07743, Germany article info Article history: Received 5 April 2017 Accepted 8 June 2017 Available online 15 June 2017 Keywords: Schiff base Palladium complexes X-ray crystallography Suzuki–Miyaura Homo-coupling abstract The characterization of synthesized Schiff base ligands (L 1 –L 5 ); (where L 1 = N-salicyliden- 2,3-diamino- cis-2-butenedinitrile, L 2 = 3- methoxy-N-salicyliden-2,3-diamino-cis-2-butenedinitrile, L 3 = 5-bromo-N- salicyliden-2,3-diamino-cis-2-butenedinitrile, L 4 = 5-nitro-N-salicyliden-2,3-diamino-cis-2-butenedini- trile, and L 5 = 5-methoxy-N-salicyliden-2,3-diamino-cis-2-butenedinitrile) and their palladium com- plexes [PdL(PPh 3 )] (L 1 –L 5 ) were carried out by FT-IR, UV–vis, 1 H NMR, 13 C NMR and elemental analysis. The coordination geometry of [PdL 3 (PPh 3 )] was determined by single crystal X-ray crystallogra- phy. In this structure the palladium center was in a partially distorted NNOP square planar coordination environment. The catalytic potential of the synthesized complexes was evaluated in Suzuki–Miyaura cross-coupling reaction by choosing different arylhalides and phenylboronic acid. The results showed that arylhalides with electron withdrawing substituents were more appropriate in this reaction. In all cases, the desired product of cross coupling Suzuki reaction was the major product. It is also worth to mention that the product of homo-coupling reaction was also observed as a minor product. In this regards, a blank reaction with just phenylboronic acid was performed and the results showed the occur- rence of the homo-coupling product in a good yield. Ó 2017 Published by Elsevier Ltd. 1. Introduction Palladium as an important noble metal with common oxidation states of +II and +IV, has exclusive properties. It was applied in many electronics, ceramic capacitors and LCD displays [1–2]. Also, it has a key role in the technologies used in the fuel cells [3–4]. Its catalytic application in the organic synthesis was interested during the twentieth century [5–8]. In this regards, the coupling reactions in the presence of a palladium-containing catalyst, have arguably become one of the most utilized tools for the construction of C–C bonds [9–11]. Especially, the cross-coupling of the organic halides with aryl boronic acids, which is catalyzed by palladium, is one of the considerable procedure for the formation of C–C bonds. [12– 14]. Suzuki reaction is taken into consideration due to its high importance in various fields including pharmaceutical, polymer and etc. [15–18]. Its superiority over the other coupling reactions is due to the mild reaction conditions, non-toxic nature of the pro- cess and stereoselectivity [19]. Soluble palladium(II) complexes with a diversity of ligands, such as phosphines [20], oxime pallada- cycles [21], imidazole-phenolates [22], Schiff bases [23] and N- heterocyclic carbines [24] have been utilized as efficient catalysts in Suzuki reaction. Schiff base compounds have the versatile cat- alytic application for a wide range of organic reactions [25–26]. The synthesis and catalytic activity of complexes bearing Schiff base ligands have been widely reported [27]. Also, there is a large interest to employ nitrogen containing Schiff base of palladium(II) for Suzuki–Miyaura coupling reactions [28]. They can be used as the active and selective catalyst for hydrogenation, hydrosilylation, and Suzuki/Heck C–C bond coupling reactions [29]. Herein, [L 1 –L 5 ] ligands and [PdL(PPh 3 )] complexes (where L 1 = N-salicyliden-2,3-diamino-cis-2-butenedinitrile, L 2 = 3-meth- oxy-N-salicyliden-2,3-diamino-cis-2-butenedinitrile, L 3 = 5-bromo- N-salicyliden-2,3-diamino-cis-2-butenedinitrile, L 4 = 5-nitro-N- salicyliden-2,3-diamino-cis-2-butenedinitrile, L 5 = 5-methoxy-N- salicyliden-2,3-diamino-cis-2-butenedinitrile) were synthesized with the aim of highlighting the influence of substitutions on the catalytic properties. The complexes were systemati- cally characterized by various analytical and spectroscopic tech- niques. The geometry of [PdL 3 (PPh 3 )] was determined by X-ray http://dx.doi.org/10.1016/j.poly.2017.06.009 0277-5387/Ó 2017 Published by Elsevier Ltd. ⇑ Corresponding author. Fax: +98 31 33912350. E-mail addresses: akianfar@cc.iut.ac.ir, asarvestani@yahoo.com (A.H. Kianfar). Polyhedron 134 (2017) 65–72 Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly