A phenol-imidazole pro-ligand that can exist as a phenoxyl radical, alone and when complexed to copper(II) and zinc(II)

Laurent Benisvy, Alexander J. Blake, David Collison, E. Stephen Davies, C. David Garner, Eric J.L. McInnes, Jonathan McMaster, Gavin Whittaker, Claire Wilson

Research output: Contribution to journalArticlepeer-review

83 Scopus citations


A new N,O-bidentate, phenol-imidazole pro-ligand 2′-(4′, 6′-di-tert-butylhydroxyphenyl)-4,5-diphenyl imidazole (LH) has been designed, synthesised, and characterised. LH possesses no readily oxidisable position (other than the phenol) and involves o- and p-substituents on the phenol ring that prevent radical coupling reactions. LH undergoes a reversible one-electron oxidation to generate the corresponding [LH]̇+ radical cation that possesses phenoxyl radical character. The unusual reversibility of the [LH]/[LH]̇+ redox couple is attributed, at least in part, to a stabilisation of [LH]̇+ by intramolecular O-H ⋯N hydrogen bonding. The compounds [CuL2] (1) and [ZnL 2 (2) have been synthesised and characterised structurally, spectroscopically, and electrochemically. The crystal structures of 1·4DMF, 1·SMeOH, and 2·2.5MeCN·0.3CH 2Cl2 have been determined and each shown to possess an N2O2-coordination sphere, the geometry of which varies with the nature of the metal and the nature of the co-crystallised solvent. 1 and 2 each undergo two, reversible, ligand-based, one-electron oxidations, to form, firstly, [M(L)(L̇)]+ and secondly [M(L ̇)22+. The [M(L)(L̇)] + (M = Cu, Zn) cations have been generated by both electrochemical and chemical oxidation and their [ML2][BF4] salts isolated as air-stable, dark green, crystalline solids. The UV/vis, EPR, and magnetic characteristics of these compounds are consistent with each cation involving an MII (M = Cu or Zn) centre bound to a phenoxide (L-) and a phenoxyl radical (L̇). The structural information obtained by a determination of the crystal structures of [CuL2][BF 4]·2CH2Cl2 and [ZnL2][BF 4]·2CH2Cl2·0.75 pentane fully supports this interpretation. For each of these salts, there is a clear indication that the coordinated phenoxyl radical is involved in intramolecular π-π stacking interactions that parallel those in galactose oxidase.

Original languageEnglish
Pages (from-to)1975-1985
Number of pages11
JournalDalton Transactions
Issue number10
StatePublished - 21 May 2003
Externally publishedYes


Dive into the research topics of 'A phenol-imidazole pro-ligand that can exist as a phenoxyl radical, alone and when complexed to copper(II) and zinc(II)'. Together they form a unique fingerprint.

Cite this