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 (2(2-)) were prepared. The crystal structures of the proligands H2L(1) and Et2H2L(2), as well as the corresponding complexes, are reported. The proligands each display a one-electron-oxidation wave, which is assigned to oxidation of the bis(dimethylamino)benzene moiety into a π radical. Complexes 1 and 2(2-) exhibit reversible one-electron-oxidation waves in their cyclic voltammograms (E1/2(1) = 0.14 and E1/2(2) = 0.31 V for 1 and E1/2(1) = -0.47 V vs Fc(+)/Fc for 2(2-)). The first process corresponds to oxidation of the bis(dimethylamino)benzene central ring into a π radical, while the second process for 1 is ascribed to oxidation of the π radical into an α-diiminoquinone. 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 electron paramagnetic resonance 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 density onto the coordinated amidato N atoms. Density functional theory calculations support a π-radical nature of the one-electron-oxidized complexes, as well as S = 1 ground spin states. The electrogenerated 1(2+) comprises a closed-shell diiminoquinone ligand coordinated to a copper(II) metal center. Both 1 and 2 catalyze the aerobic oxidation of benzyl alcohol, albeit with different yields.
Department of Chemistry and Biochemistry, Concordia University , Montreal, Quebec H4B 1R6, Canada.
David
D
de Bellefeuille
Laboratoire de Spectrochimie Infrarouge et Raman, Université des Sciences et Technologies de Lille, UMR CNRS 8516 , 59655 Villeneuve d'Ascq Cedex, France.
Maylis
M
Orio
Laboratoire National des Champs Magnétiques Intenses, CNRS , 25 rue des Martyrs, 38042 Grenoble, France.
Anne-Laure
AL
Barra
Institut de Chimie Moléculaire et des Matériaux d'Orsay, UMR CNRS 8182, Université Paris-Sud XI , 91405 Orsay, France.|Service de Bioénergétique, Biologie Structurale et Mécanismes (SB2SM), CEA, iBiTec-S; Biochimie Biophysique et Biologie Structurale (B3S), I2BC, UMR 9198, 91191 Gif-sur-Yvette, France.
Ally
A
Aukauloo
Institut de Chimie Moléculaire et des Matériaux d'Orsay, UMR CNRS 8182, Université Paris-Sud XI , 91405 Orsay, France.|Sorbonne Universités, UPMC Université Paris 06, UMR CNRS 8232, Institut Parisien de Chimie Moléculaire, France.
Yves
Y
Journaux
Equipe CIRE, Département de Chimie Moléculaire, UMR CNRS 5250, Université Grenoble-Alpes , 38041 Grenoble Cedex 9, France.
Christian
C
Philouze
Department of Chemistry and Biochemistry, Concordia University , Montreal, Quebec H4B 1R6, Canada.
Xavier
X
Ottenwaelder
Equipe CIRE, Département de Chimie Moléculaire, UMR CNRS 5250, Université Grenoble-Alpes , 38041 Grenoble Cedex 9, France.
Fabrice
F
Thomas
D019905:Benzyl Alcohol / Q000737:chemistry; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D015394:Molecular Structure; D010072:Oxamic Acid / Q000031:analogs & derivatives / Q000737:chemistry; D010084:Oxidation-Reduction; D012459:Salicylates / Q000737:chemistry
D056831:Coordination Complexes; D012459:Salicylates; C090416:salophen; D003300:Copper; D019905:Benzyl Alcohol; D010072:Oxamic Acid