Synthesis and X-ray crystal structures of three new nickel(II) complexes of benzoylhydrazones: Catalytic applications in the synthesis of 2-arylbenzoxazoles

• Published in: Inorganica Chimica Acta Vol. 500; p. 119222
• Main Authors: Layek, Samaresh, Agrahari, Bhumika, Kumar, Akash, Dege, Necmi, Pathak, Devendra D.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 24.01.2020; Elsevier Science Ltd
• Subjects: 2-Arylbenzoxazole; Aldehydes; Aminophenol; Aromatic compounds; Catalysts; Chemical analysis; Chemical synthesis; Coordination compounds; Crystal structure; Homogeneous catalysis; Imines; Infrared analysis; Ligands; Mass spectrometry; Nickel; Nickel(II) complex; Nitrogen; NMR spectroscopy; ONO pincer-type; Single crystals; ONO pincer-type; 2-Arylbenzoxazole; Nickel(II) complex; Homogeneous catalysis; Crystal structure
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2019.119222

[Display omitted] •Synthesis of three new pincer type nickel(II) complexes of benzoylhydrazone.•Characterization by Elemental analysis, FT-IR, 1H, 13C, 31P NMR and mass spectrometry.•Structure of all complexes confirmed by single crystal X-ray studies.•Efficient catalysts for synthesis of a series of 2-arylbenzoxazoles with good TON/TOF. Three new complexes of nickel(II), having general formula [Ni(L1)(PPh3)] (1), [Ni(L1)(4-picoline)] (2), and [Ni(L2)(4-picoline)] (3) were synthesized by the reaction of Ni(OAc)2·4H2O with corresponding benzolyhydrazine-derived Schiff base ligands i.e. [4-(diethylamino)-2-hydroxybenzylidene]-benzohydrazonic acid (H2L1) or [2-(hydroxynaphthalen-1-yl)methylene]-benzohydrazonic acid (H2L2) and PPh3/4-picoline as co-ligand in 1:1:1 ratio in methanol. All the three complexes were air-stable, isolated as reddish brown solids and characterized by Elemental analysis, FT-IR, 1H, 13C{1H}, 31P{1H} NMR spectroscopy and mass spectrometry. The structures of all three complexes were determined by single crystal X-ray diffraction studies which revealed the distorted square planar geometry of the complexes. In these complexes, three coordination sites were occupied by ONO pincer type Schiff base ligand and the fourth site was blocked by phosphorus (P) or nitrogen (N) atom of the co-ligand. The catalytic potential of all three complexes was explored in the synthesis of a series of 2-arylbenzoxazoles from aldehydes and 2-aminophenol, using low catalyst loading (0.5 mol%). Complex 1 was found to be the best catalyst among three complexes, for the synthesis of a series of 2-aryl benzoxazoles. The ease of synthesis, air-stability and robustness of the catalyst, and good TONs are some of the key characteristics of the described catalytic system.