Intramolecularly hydrogen-bonded versus copper(II) coordinated mono- and bis-phenoxyl radicals.
Ligands bearing two salicylidene imine moieties substituted in ortho and para positions by tert-butyl groups have been electrochemically oxidized into mono- and bis-phenoxyl radicals. The process involves an intramolecular proton coupled to electron transfer and affords a radical in which the oxygen atom is hydrogen-bonded to a protonated ammonium or iminium group. A weak intramolecular dipolar interaction exists between the two phenoxyl moieties in the bis-radical species. The copper(II) complexes of these ligands have been characterized and electrochemically oxidized. The mono-phenoxyl radical species are X-band EPR silent. The bis-phenoxyl radical species exhibits a (S= 3/2) ground state: it arises from a ferromagnetic exchange coupling between the two spins of the radicals and that of the copper(II) when the spacer is rigid enough; a flexible spacer such as ethylidene induces decomplexation of at least one phenoxyl group. Metal coordination is more efficient than hydrogen-bonding to enhance the chemical stability of the mono-phenoxyl radicals.
Thomas
Fabrice
F
Laboratoire de Chimie Biomimetique, LEDSS, UMR CNRS 5616, ICMG FR CNRS 2607, Universite J. Fourier, BP 53, 38041 Grenoble cedex 9, France. Fabrice.Thomas@ujf-grenoble.fr
Jarjayes
Olivier
O
Duboc
Carole
C
Philouze
Christian
C
Saint-Aman
Eric
E
Pierre
Jean-Louis
JL
D040761:Biomimetic Materials / Q000737:chemistry; D002413:Cations, Divalent; D003300:Copper / Q000737:chemistry*; D004563:Electrochemistry; D005609:Free Radicals / Q000737:chemistry; D006860:Hydrogen Bonding; D007097:Imines / Q000737:chemistry; D008024:Ligands; D009942:Organometallic Compounds / Q000737:chemistry; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry*; D012459:Salicylates / Q000737:chemistry
D002413:Cations, Divalent; D005609:Free Radicals; D007097:Imines; D008024:Ligands; D009942:Organometallic Compounds; D010636:Phenols; D012459:Salicylates; C042329:phenoxy radical; D003300:Copper