Département de chimie moléculaire

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)]