Tetranuclear copper(ii)–Schiff-base complexes as active catalysts for oxidation of cyclohexane and toluene

Abstract

Three new Cu(ii) complexes, [Cu(4)(O)(L(n))(2)(CH(3)COO)(4)] where HL(1) = 4-methyl-2,6-bis(2-fluoroethyliminomethyl) phenol for complex , HL(2) = 4-methyl-2,6-bis(2-chloroethyliminomethyl) phenol for complex .0.25CH(3)CN and HL(3) = 4-methyl-2,6-bis(2-bromoethyliminomethyl) phenol for complex have been synthesized and characterized by elemental analysis, FTIR, UV-vis spectroscopy, and electrospray ionization mass spectroscopy. The structure of complex .0.25CH(3)CN has also been confirmed by single crystal X-ray diffraction analysis. These complexes have been found to be active catalysts for the oxidation of cyclohexane and toluene in the presence of hydrogen peroxide as the oxidant under mild conditions. Cyclohexane is oxidized to yield cyclohexanol and cyclohexanone, whereas toluene is oxidized to benzyl alcohol and benzaldehyde.

An azo-azomethine ligand and its copper(II) complex: Synthesis, X-ray crystal structure, spectral, thermal, electrochemical and photoluminescence properties

“…In the last few decades many copper complexes have been reported [13,14]. The growing interest on the coordination compounds of copper with various N-donor ligands, comes mainly from their capability of combining characteristic structural flexibility [13,14], mimicking of protein active sites [15][16][17], ease of preparation [18,19], and stabilization of both oxidation states of the metal usual in biological systems [20,21].…”

Syntheses, spectral characterization, thermal properties and DNA cleavage studies of a series of Co(II), Ni(II) and Cu(II) polypyridine complexes with some new schiff-bases derived from 2-chloroethylamine

“…These bands were absent in all the complexes, indicating deprotonation on coordination of the Schiff base ligands to metal ion. In addition, the bands at 1346-1350 cm -1 attributed to the phenolic C-O stretching vibrations of the free ligands were blue-shifted to 1341-1431 cm -1 upon complexation suggesting the involvement of the phenolic oxygen atom in the coordination [18][19][20]. The imine (C=N) functional group of the free ligands was observed as strong bands between 1670-1643 cm -1…”

“…Three absorption bands were observed in the electronic spectra of the free Schiff base ligands L 1 , L 2 and L 3 in the 264-430 nm, 264-435 nm and 261-434 nm range respectively were assigned to π-π* and n-π* transitions. The bands observed at 350 nm, 316 nm and 349 nm were assigned to the π-π* transitions of the azomethine, which were shifted to 411-437 nm range in the electronic spectra of complexes indicating the azomethine nitrogen was involved in coordination [20,21]. The bands observed at 264 nm were assigned to the π-π* transitions of the phenol [25].…”

“…These bands were assigned to 3 transitions which corresponds to octahedral geometry [28,29]. The weak absorption bands in the spectra of complexes were contribution from spin allowed metal to ligand charge transfer, MLCT [20]. Table 2.…”

Mono- and tetra-nuclear copper complexes bearing bis(imino)phenoxide derived ligands: catalytic evaluation for benzene oxidation and ROP of ε-caprolactone

“…[1] In the field of lactone polymerization, the 25 coordination/insertion mechanism has drawn analogies with biological systems and in-particular the mechanism of hydrolysis of some metalloenzymes, where one of the metal present can coordinate water thereby lowering its pKa ( whilst Chaudhuriet al have extended such studies to related ONONO-type ligation and have examined the magnetic susceptibility of the resulting Cu 2 and Cu 4 complexes. [7] More recently bis(imino)phenoxy N 2 O type ligation has been utilized to isolate complexes that can act as catalysts for the oxidation of 50 cyclohexane and toluene, [8] and in catecholase-like activity. [9] We also note that Pandey et al have, by employingβ-ketoaminato ligands, isolated both mono and tetranuclear copper complexes, the formation of which was dictated by the use of anhydrous conditions or not.…”