Vanadium-salen and -salan complexes: Characterization and application in oxygen-transfer reactions

Vanadium-salen and -salan complexes: Characterization and application in oxygen-transfer reactions

Salen complexes are a versatile and standard system in oxidation catalysis. Their reduced derivatives, called salan, share their versatility but are still widely unexplored. We report the synthesis of a group of new vanadium-salen and -salan complexes, their characterization and application in the o...

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Bibliographic Details
Published in:Pure and applied chemistry Vol. 81; no. 7; pp. 1279 - 1296
Main Authors: Adão, Pedro, Maurya, Mannar R., Kumar, Umesh, Avecilla, Fernando, Henriques, Rui T., Kusnetsov, Maxim L., Costa Pessoa, João, Correia, Isabel
Format: Journal Article
Language:English
Published: Berlin De Gruyter 30-06-2009
Walter de Gruyter GmbH
Subjects:
Catalysis
Coordination compounds
Crystals
Cumene
Cyclohexene
Diamines
Dichroism
Electron paramagnetic resonance
Fourier transforms
Hydrogen peroxide
Imines
Ligands
Magnetic properties
NMR
Nuclear magnetic resonance
Organic chemistry
Oxidation
Oxygen transfer
oxygen-transfer reactions
salan
salen
Single crystals
Vanadium
vanadium complexes
X-ray diffraction
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Summary:Salen complexes are a versatile and standard system in oxidation catalysis. Their reduced derivatives, called salan, share their versatility but are still widely unexplored. We report the synthesis of a group of new vanadium-salen and -salan complexes, their characterization and application in the oxidation of simple organic molecules with H . The ligands are derived from pyridoxal and chiral diamines (1,2-diaminocyclohexane and 1,2-diphenylethylenediamine) and were easily obtained in high yields. The V complexes were prepared and characterized in the solid state (Fourier transform infrared, FTIR, and magnetic properties) and in solution by spectroscopic techniques: UV–vis, circular dichroism (CD), electron paramagnetic resonance (EPR), and V NMR, which provide information on the coordination geometry. Single crystals suitable for X-ray diffraction studies were obtained from solutions containing the V -pyr( -chan) complex: [V O{pyr( -chen)}] (μ-O) ·2(CH NCHO, where the ligand is the “half” Schiff base formed by pyridoxal and 1 ,2 -diaminocyclohexane. The dinuclear species shows a OV (μ-O) O unit with tridentate ligands and two μ-oxo bridges. The V complexes of the salan-type ligands oxidize in organic solvents to a V species, and the process was studied by spectroscopic techniques. The complexes were tested as catalysts in the oxidation of styrene, cyclohexene, and cumene with H as oxidant. Overall, the V-salan complexes show higher activity than the parent V-salen complexes and are an alternative ligand system for oxidation catalysis.
ISSN:0033-4545
1365-3075
DOI:10.1351/PAC-CON-08-09-07