16-Membered pentaaza bis(macrocyclic) nickel(II) complexes containing aromatic nitrogen–nitrogen linkers, {[Ni([16]aneN5)]2R}(ClO4)4: Synthesis, characterization and catalytic oxidation of cyclohexene with molecular oxygen

New square-planar bis(macrocyclic)dinickel(II) complexes containing phenylene bridges between 16-membered pentaaza macrocyclic subunits have been synthesized via in situ one pot template condensation reaction of aromatic nitrogen–nitrogen linker (R = 1,4-phenylenediamine; benzidine; 4,4′-diaminodiphenylmethan; 4,4′-diaminodiphenylether; 4,4′-diaminodiphenylsulfon), formaldehyde, bis(1,3-diaminopropane) nickel(II) perchlorate and 1,3-dibromopropane in a 1:4:2:2 molar ratio results in the formation of new series of binuclear nickel(II) complexes; 1-phenyl- (1); 1,1′-phenyl- (2); 1,1′-diphenylmethan- (3); 1,1′-diphenylether- (4); 1,1′-diphenylsulfon- (5) bis(1,3,7,11,15-pentaazacyclohexadecane) nickel(II)), {[Ni([16]aneN5)]2R}(ClO4)4′′. The formation of the macrocyclic framework and the mode of bonding of the complexes have been confirmed by data obtained from elemental analyses, FAB, UV–vis, FT-IR, 1H NMR, electronic spectral studies, conductivity and magnetic susceptibility measurements. These complexes have been found to be effective catalysts for the selective oxidation of cyclohexene to 2-cyclohexene-1-one and 2-cyclohexene-2-ol with molecular oxygen as the oxidant.

Graphical abstractNew square-planar bis(macrocyclic)dinickel(II) complexes containing phenylene bridges between 16-membered pentaaza macrocyclic subunits have been synthesized via in situ one pot template condensation reaction of aromatic nitrogen–nitrogen linker (R = 1,4-phenylenediamine; benzidine; 4,4′-diaminodiphenylmethan; 4,4′-diaminodiphenylether; 4,4′-diaminodiphenylsulfon), formaldehyde, bis(1,3-diaminopropane) nickel(II) perchlorate and 1,3-dibromopropane in a 1:4:2:2 molar ratio results in the formation of new series of binuclear nickel(II) complexes. These complexes have been found to be effective catalysts for the selective oxidation of cyclohexene to 2-cyclohexene-1-one and 2-cyclohexene-2-ol with molecular oxygen as the oxidant. Figure optionsDownload full-size imageDownload as PowerPoint slide