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Benisvy L, Bill E, Blake AJ, et al. Phenoxyl radicals: H-bonded and coordinated to Cu(II) and Zn(II). Dalton Trans. 2005;(1):258-67doi: 10.1039/b513221p.
Benisvy, L., Bill, E., Blake, A. J., Collison, D., Davies, E. S., Garner, C. D., McArdle, G., McInnes, E. J., McMaster, J., Ross, S. H., & Wilson, C. (2006). Phenoxyl radicals: H-bonded and coordinated to Cu(II) and Zn(II). Dalton transactions (Cambridge, England : 2003), (1), 258-67. https://doi.org/10.1039/b513221p
Benisvy, Laurent, et al. "Phenoxyl radicals: H-bonded and coordinated to Cu(II) and Zn(II)." Dalton transactions (Cambridge, England : 2003) vol. ,1 (2006): 258-67. doi: https://doi.org/10.1039/b513221p
Benisvy L, Bill E, Blake AJ, Collison D, Davies ES, Garner CD, McArdle G, McInnes EJ, McMaster J, Ross SH, Wilson C. Phenoxyl radicals: H-bonded and coordinated to Cu(II) and Zn(II). Dalton Trans. 2006 Jan 07;(1):258-67. doi: 10.1039/b513221p. Epub 2005 Nov 09. PMID: 16357984.
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Dalton Trans. 2006 Jan 07;(1):258-67. doi: 10.1039/b513221p. Epub 2005 Nov 09.

Phenoxyl radicals: H-bonded and coordinated to Cu(II) and Zn(II).

Dalton transactions (Cambridge, England : 2003)

Laurent Benisvy, Eckhard Bill, Alexander J Blake, David Collison, E Stephen Davies, C David Garner, Graeme McArdle, Eric J L McInnes, Jonathan McMaster, Stephanie H K Ross, Claire Wilson

Affiliations

  1. School of Chemistry, The University of Nottingham, University Park, Nottingham, UK NG7 2RD.

PMID: 16357984 DOI: 10.1039/b513221p

Abstract

Two pro-ligands ((R)LH) comprised of an o,p-di-tert-butyl-substituted phenol covalently bonded to a benzimidazole ((Bz)LH) or a 4,5-di-p-methoxyphenyl substituted imidazole ((PhOMe)LH), have been structurally characterised. Each possesses an intramolecular O-H[dot dot dot]N hydrogen bond between the phenolic O-H group and an imidazole nitrogen atom and (1)H NMR studies show that this bond is retained in solution. Each (R)LH undergoes an electrochemically reversible, one-electron, oxidation to form the [(R)LH] (+) radical cation that is considered to be stabilised by an intramolecular O...H-N hydrogen bond. The (R)LH pro-ligands react with M(BF(4))(2).H(2)O (M = Cu or Zn) in the presence of Et(3)N to form the corresponding [M((R)L)(2)] compound. [Cu((Bz)L)(2)] (), [Cu((PhOMe)L)(2)] (), [Zn((Bz)L)(2)] and [Zn((PhOMe)L)(2)] have been isolated and the structures of .4MeCN, .2MeOH, .2MeCN and .2MeCN determined by X-ray crystallography. In each compound the metal possesses an N(2)O(2)-coordination sphere: in .4MeCN and .2MeOH the {CuN(2)O(2)} centre has a distorted square planar geometry; in .2MeCN and .2MeCN the {ZnN(2)O(2)} centre has a distorted tetrahedral geometry. The X-band EPR spectra of both and , in CH(2)Cl(2)-DMF (9 : 1) solution at 77 K, are consistent with the presence of a Cu(ii) complex having the structure identified by X-ray crystallography. Electrochemical studies have shown that each undergo two, one-electron, oxidations; the potentials of these processes and the UV/vis and EPR properties of the products indicate that each oxidation is ligand-based. The first oxidation produces [M(II)((R)L)((R)L )](+), comprising a M(ii) centre bound to a phenoxide ((R)L) and a phenoxyl radical ((R)L ) ligand; these cations have been generated electrochemically and, for R = PhOMe, chemically by oxidation with Ag[BF(4)]. The second oxidation produces [M(II)((R)L )(2)](2+). The information obtained from these investigations shows that a suitable pro-ligand design allows a relatively inert phenoxyl radical to be generated, stabilised by either a hydrogen bond, as in [(R)LH] (+) (R = Bz or PhOMe), or by coordination to a metal, as in [M(II)((R)L)((R)L )](+) (M = Cu or Zn; R = Bz or PhOMe). Coordination to a metal is more effective than hydrogen bonding in stabilising a phenoxyl radical and Cu(ii) is slightly more effective than Zn(II) in this respect.

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