Two efficient ligand-assisted systems of two different ionic Schiff base ligands for palladium chloride catalyzed in Suz
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Ó Indian Academy of Sciences Sadhana(0123456789().,-volV)FT3](0123456 789().,-volV)
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Two efficient ligand-assisted systems of two different ionic Schiff base ligands for palladium chloride catalyzed in Suzuki-Miyaura reaction FARZANEH NEHZAT and GHOLAMHOSSEIN GRIVANI* School of Chemistry, Damghan University, Damghan 36715-364, Iran E-mail: [email protected] MS received 15 July 2019; revised 30 September 2019; accepted 1 October 2019
Abstract. The bis- methyl imidazolium chloride-salophen Schiff base ligand as cationic Schiff base ligand (L1) was synthesized by the reaction of methyl imidazoliumsalicylaldehyde chloride (S1) and phenylendiamine. The phenylendiamine was also reacted by monosodium 5-sulfonatosalycilaldehyde (S2) to give the bis-sodium sulfonate-salophen Schiff base ligand (L2) as the anionic ligand. These two ligands were characterized by the 1H-NMR, 13C-NMR, IR, UV–visible and mass spectroscopy, as well as elemental analysis. The ligand assisted PdCl2 catalyst was investigated in the Suzuki-Miyaura reaction by using the L1 and L2 as cationic and anionic Schiff base ligands and different reaction conditions such as temperature, solvent and mol% of PdCl2 were optimized. The results revealed that the anionic ligand assistance had a better activity for the catalytic system of PdCl2 in Suzuki-Miyaura reaction. Keywords. Schiff base ligands; ligand assisted system; Suzuki-Miyaura reaction.
1. Introduction In organic chemistry, one of the most important and useful conversion is the construction of the carboncarbon bonds. In 1979, Miyaura, Yamada and Suzuki1 published a coupling reaction between boronic acid and an organo-halide catalyzed by a palladium complex. The importance of this coupling is obvious in different areas, from the synthesis of natural product to industrial material.2 Although there are many research groups that have introduced many systems for this synthesis by different catalysis in water, there are many drawbacks in their procedure such as evaluated temperature, the addition of tetra butyl ammonium bromide (TBAB) as phase transfer catalyst and complicated work-up procedure.3–12 In general, activation of aryl chloride needs hard reaction conditions and high amount of palladium as a catalyst. The development of benign methods for the synthesis of the Suzuki-Miyaura reaction that use the small amount of catalyst is a subject of continuous interest for synthetic chemists.13–22 Especially, for the catalyst which is precious and exhaustive as palladium. There are some reports that have introduced ligand-free Suzuki*For correspondence
Miyaura reactions catalyzed by simple palladium salts such as [Pd(OAc)2], [Pd(dba)2], and PdCl2. There are some drawbacks in their systems, for example, they are inappropriate for low-cost systems and in competition with the ligand assisted-systems, their selectivity is less. For many years, phosphine-based ligands were the superior ligands for Suzuki-Miyaura reaction, because by changing the attached groups to the phosphorus atom, the properties
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