Publication Type Journal Article
Title Diastereomeric dinickel(II) complexes with non-innocent bis(octaazamacrocyclic) ligands: isomerization, spectroelectrochemistry, DFT calculations and use in catalytic oxidation of cyclohexane
Authors Anatolie Dobrov Denisa Darvasiova Michal Zalibera Lukas Bucinsky Ingrid Jelemenska Peter Rapta Sergiu Shova Dan Dumitrescu Marta A. Andrade L.M.D.R.S. Martins Armando J.L. Pombeiro Vladimir B. Arion
Groups Chem4Env CCC
Journal DALTON TRANSACTIONS
Year 2022
Month
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Volume 51
Number 13
Pages 5151-5167
Abstract Diastereomeric dinickel(II) complexes with bis-octaazamacrocyclic 15-membered ligands [Ni(L1-3-L1-3)Ni] (4-6) have been prepared by oxidative dehydrogenation of nickel(II) complexes NiL1-3 (1-3) derived from 1,2- and 1,3-diketones and S-methylisothiocarbohydrazide. The compounds were characterized by elemental analysis, ESI mass spectrometry, and IR, UV-vis, H-1 NMR, and C-13 NMR spectroscopy. Single crystal X-ray diffraction (SC-XRD) confirmed the isolation of the anti and syn isomers of bis-octaazamacrocyclic dinickel(II) complexes 4a and 4s, the syn-configuration of 5s and the anti-configuration of the dinickel(II) complex 6a. Dimerization of prochiral nickel(ii) complexes 1-3 generates two chiral centers at the bridging carbon atoms. The anti-complexes were isolated as meso-isomers (4a and 6a) and the syn-compounds as racemic mixtures of R,R/S,S-enantiomers (4s and 5s). The syn-anti isomerization (epimerization) of the isolated complexes in chloroform was disclosed. The isomerization kinetics of 5a was monitored at five different temperatures ranging from 20 degrees C to 50 degrees C by H-1 NMR spectroscopy indicating the clean conversion of 5a into 5s. The activation barrier determined from the temperature dependence of the rate constants via the Eyring equation was found to be Delta H-double dagger = 114 +/- 1 kJ mol(-1) with activation entropy Delta S-double dagger = 13 +/- 3 J K-1 mol(-1). The complexes contain two low-spin nickel(ii) ions in a square-planar coordination environment. The electrochemical behavior of 4a, 4s, 5s and 6a and the electronic structure of the oxidized species were studied by UV-vis-NIR-spectroelectrochemistry (SEC) and DFT calculations indicating the redox non-innocent behavior of the complexes. The dinickel(ii) complexes 4a, 4s, 5s and 6a/6s were investigated as catalysts for microwave-assisted solvent-free oxidation of cyclohexane by tert-butyl hydroperoxide to produce a mixture of cyclohexanone and cyclohexanol (KA oil). The best value for KA oil yield (16\%) was obtained with a mixture of 6a/6s after 2 h of microwave irradiation at 100 degrees C.
DOI http://dx.doi.org/10.1039/d2dt00154c
ISBN
Publisher
Book Title
ISSN 1477-9226
EISSN 1477-9234
Conference Name
Bibtex ID WOS:000766798700001
Observations
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