Formation of a cobalt(III)-phenoxyl radical complex by acetic acid promoted aerobic oxidation of a Co(II)salen complex.
The activation of N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diamino Co(II), [Co(II)(1)], by the addition of acetic acid under aerobic conditions has been investigated by a range of spectroscopic techniques including continuous-wave EPR, HYSCORE, pulsed ENDOR, and resonance Raman. These measurements have revealed for the first time the formation of a coordinated cobalt(III)-bound phenoxyl radical labeled [Co(III)(1(*))(OAc)(n)](OAc)(m) (n = m = 1 or n = 2, m = 0). This cobalt(III)-bound phenoxyl radical is characterized by the following spin Hamiltonian parameters: g(x) = 2.0060, g(y) = 2.0031, g(z) = 1.9943, A(x) = 17 MHz, A(y) = 55 MHz, and A(z) = 14 MHz. Although the radical contains coordinated acetate(s), the experiments unambiguously proved that the phenoxyl radical is situated on ligand (1) as opposed to a phenoxyl radical ligated to cobalt in the axial position. Density functional theory computations on different models corroborate the stability of such a phenoxyl radical species and suggest the ligation of one or two acetate molecules to the complex. A mechanism is proposed, which accounts for the formation of this unusual and extremely robust phenoxyl radical, never previously observed for [Co(1)].
Vinck
Evi
E
Department of Physics, University of Antwerp, B-2610 Antwerp, Belgium.
Murphy
Damien M
DM
Fallis
Ian A
IA
Strevens
Robert R
RR
Van Doorslaer
Sabine
S
D000085:Acetates / Q000737:chemistry*; D000388:Air; D002384:Catalysis; D003035:Cobalt / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D004852:Epoxy Compounds / Q000737:chemistry; D005029:Ethylenediamines / Q000737:chemistry*; D006868:Hydrolysis; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry*; D011789:Quantum Theory; D013059:Spectrum Analysis, Raman; D013237:Stereoisomerism
D000085:Acetates; D004852:Epoxy Compounds; D005029:Ethylenediamines; D009942:Organometallic Compounds; D010636:Phenols; C042329:phenoxy radical; D003035:Cobalt; C011452:disalicylaldehyde ethylenediamine