Influence of Electron-Withdrawing Substituents on the Electronic Structure of Oxidized Ni and Cu Salen Complexes.

Ni (Ni(SalCF3)) and Cu (Cu(SalCF3)) (SalCF3 = N,N'-Bis(3-tert-butyl-5-trifluoromethylsalicylidene)trans-1,2-cyclohexanediamine) complexes of an electron-poor salen ligand were prepd., and their 1-electron oxidized counterparts were studied using an array of spectroscopic and theor. methods. The electrochem. of both complexes exhibited quasi-reversible redox processes at higher potentials in comparison to the M(SalR) (R = tBu, OMe, NMe2) analogs, in line with the electron-withdrawing nature of the para-CF3 substituent. Chem. oxidn., monitored by UV-visible-near-IR (UV-visible-NIR) spectroscopy, afforded their corresponding 1-electron oxidized products. Ligand-based oxidn. was obsd. for [Ni(SalCF3)]+.bul., as evidenced by sharp NIR transitions in the UV-visible-NIR spectrum and a broad isotropic signal at g = 2.067 by soln. EPR spectroscopy. Such sharp NIR transitions obsd. for [Ni(SalCF3)]+.bul. are indicative of a delocalized electronic structure, which is in good agreement with electrochem. measurements and d. functional theory (DFT) calcns. The increased Lewis acidity of [Ni(SalCF3)]+.bul., evident from the EPR g-value and DFT calcns., was further quantified by the binding affinity of axial ligands to [Ni(SalCF3)]+.bul.. For [Cu(SalCF3)]+, an intense ligand-to-metal charge transfer band at 18,700 cm-1 in the UV-visible-NIR spectrum was obsd., which is diagnostic for the formation of a CuIII species. The CuIII character for [Cu(SalCF3)]+ is further confirmed by 19F NMR anal. Taken together, these results show that the electron-deficient salen ligand H2SalCF3 increases the Lewis acidity of the coordinating metal center. [on SciFinder(R)]

Références

Titre
Influence of Electron-Withdrawing Substituents on the Electronic Structure of Oxidized Ni and Cu Salen Complexes.
Type de publication
Article de revue
Année de publication
2015
Revue
Inorg. Chem.
Volume
54
Pagination
5970–5980
ISSN
0020-1669
Soumis le 12 avril 2018