Ligand Contributions to the Electronic Structures of the Oxidized Cobalt(II) salen Complexes.

Square planar Co(II) complexes of salen ligands N,N'-bis(3-tert-butyl-5R-salicylidene)-1,2-cyclohexanediamine, where R = OMe (1) and tert-Bu (2), were prepd. 1 And 2 were electrochem. reversibly oxidized into cations [1-H2O]+ and [2-H2O]+ in CH2Cl2. The chem. generated [1-H2O](SbF6)·0.68 H2O·0.82CH2Cl2 and [2-H2O](SbF6)·0.3H2O·0.85CH2Cl2 were characterized by x-ray diffraction and NIR spectroscopy. Both complexes are paramagnetic species contg. a square pyramidal Co ion coordinated at the apical position by an exogenous H2O mol. They exhibit remarkable NIR bands at 1220 (7370 M-1 cm-1) and 1060 nm (5560 M-1 cm-1), resp., assigned to a CT transition. DFT calcns. and magnetic measurements confirm the paramagnetic (S = 1) ground spin state of the cations. More than 70{%} of the total spin d. in [1-H2O]+ and [2-H2O]+ is localized on the metal, the remaining spin d. being distributed over the arom. rings (30{%} phenoxyl character). In the presence of N-methylimidazole (IM), 1 and 2 are irreversibly oxidized by air into the genuine octahedral Co(III) bis(phenolate) complexes [1-IM2]+ and [2-IM2]+, the former being structurally characterized. Neither [1-IM2]+ nor [2-IM2]+ exhibits a NIR feature in its electronic spectrum. 1 And 2 were electrochem. two-electron oxidized into [1]2+ and [2]2+. The cations were identified as Co(III)-phenoxyl species by their characteristic absorption band at ∼400 nm in the UV-visible spectrum. Coordination of the phenoxyl radical to the Co(III) metal ion is evidenced by the EPR signal centered at g = 2.00. [on SciFinder(R)]


Soumis le 12 avril 2018