Redox Noninnocence of the Bridge in Copper(II) Salophen and Bis(oxamato) Complexes.

Two square-planar copper(II) complexes of 1,2-bis(2-hydroxy-3,5-di-tert-butylbenzimino)-4,5-bis(dimethylamino)benzene (1) and N-[4,5-bis(dimethylamino)-2-(oxalylamino)benzene]oxamate (22-) were prepd. The crystal structures of the proligands H2L1 (3) and Et2H2L2 (4), as well as the corresponding complexes, are reported. The proligands each display a one-electron-oxidn. wave, which is assigned to oxidn. of the bis(dimethylamino)benzene moiety into a $π$ radical. Complexes 1 and 22- exhibit reversible one-electron-oxidn. waves in their cyclic voltammograms (E1/21 = 0.14 and E1/22 = 0.31 V for 1 and E1/21 = -0.47 V vs. Fc+/Fc for 22-). The first process corresponds to oxidn. of the bis(dimethylamino)benzene central ring into a $π$ radical, while the second process for 1 is ascribed to oxidn. of the $π$ radical into an $\alpha$-diimino quinone. The one-electron-oxidized species 1+ and 2- exhibit intense visible-near-IR absorptions, which are diagnostic of $π$ radicals. They display a triplet signal in their ESR spectra, which stem from magnetic coupling between the ligand-radical spin and the copper(II) spin. The zero-field-splitting parameters are larger for 2- than 1+ because of greater delocalization of the spin d. onto the coordinated amidato N atoms. D. functional theory calcns. support a $π$-radical nature of the one-electron-oxidized complexes, as well as S = 1 ground spin states. The electrogenerated 12+ comprises a closed-shell diimino quinone ligand coordinated to a copper(II) metal center. Both 1 and 2 catalyze the aerobic oxidn. of benzyl alc., albeit with different yields. [on SciFinder(R)]


Soumis le 12 avril 2018