Polymer‐anchored mononuclear and binuclear Cu II Schiff‐base complexes: Impact of heterogenization on liquid phase catalytic oxidation of a series of alkenes

• Published in: Applied organometallic chemistry 2019-09, Vol.33 (9)
• Main Authors: Maurya, Abhishek, Kesharwani, Neha, Kachhap, Payal, Mishra, Vivek Kumar, Chaudhary, Nikita, Haldar, Chanchal
• Format: Article
• Language: English
• ISSN: 0268-2605; 1099-0739
• DOI: 10.1002/aoc.5094

Liquid phase catalytic oxidation of a number of alkenes, for example, cyclohexene, cis ‐cyclooctene, styrene, 1‐methyl cyclohexene and 1‐hexene, was performed using polymer‐anchored copper (II) complexes PS‐[Cu (sal‐sch)Cl] ( 5 ), PS‐[Cu (sal‐tch)Cl] ( 6 ), PS‐[CH 2 {Cu (sal‐sch)Cl} 2 ] ( 7 ) and PS‐[CH 2 {Cu (sal‐tch)Cl} 2 ] ( 8 ). Neat complexes [Cu (sal‐sch)Cl] ( 1 ), [Cu (sal‐tch)Cl] ( 2 ), [CH 2 {Cu (sal‐sch)Cl} 2 ] ( 3 ) and [CH 2 {Cu (sal‐tch)Cl} 2 ] ( 4 ) were isolated by reacting CuCl 2 ·2H 2 O with [Hsal‐sch] ( I ), [Hsal‐tch] ( II ), [H 2 bissal‐sch] ( III ) and [H 2 bissal‐tch] ( IV ), respectively, in refluxing methanol. Complexes 1–4 have been covalently anchored in Merrifield resin through the amine nitrogen of the semicarbazide or thiosemicarbazide moiety. A number of analytical, spectroscopic and thermal techniques, such as CHNS analysis, Fourier transform‐infrared, UV–Vis, PMR, 13 C‐NMR, electron paramagnetic resonance, scanning electron microscopy, energy‐dispersive X‐ray analysis, thermogravimetric analysis, atomic force microscopy, atomic absorption spectroscopy, and electrospray ionization‐mass spectrometry, were used to analyze and establish the molecular structure of the ligands ( I )–( IV ) and complexes ( 1 )–( 8 ) in solid state as well as in solution state. Grafted complexes 5 – 8 were employed as active catalysts for the oxidation of a series of alkenes in the presence of hydrogen peroxide. Copper hydroperoxo species ([Cu III (sal‐sch)‐O‐O‐H]), which is believed to be the active intermediate, generated during the catalytic oxidation of alkenes, are identified. It was found that supported catalysts are very economical, green and efficient in contrast to their neat complexes as well as most of the recently reported heterogeneous catalysts.