Katarzyna Grubel - Structural and Spectroscopic Characterization of Iron(II), Cobalt(II), and Nickel(II) Ortho-Dihalophenolate Complexes: Insights into Metal-Halogen Secondary Bonding

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  Machonkin, T. E.; Boshart, M. D.; Schofield, J. A.; Rodriguez, M.   M.; Grubel, K.; Rokhsana, D.; Brennessel, W. W.; Holland, P. L.   Inorganic Chemistry 2014, 53,   9837-9848.


  Metal complexes incorporating the   tris(3,5-diphenylpyrazolyl)borate ligand (TpPh2) and   ortho-dihalophenolates were synthesized and   characterized in order to explore metal–halogen secondary bonding   in biorelevant model complexes. The complexes TpPh2ML   were synthesized and structurally characterized, where M was   Fe(II), Co(II), or Ni(II) and L was either 2,6-dichloro- or   2,6-dibromophenolate. All six complexes exhibited metal–halogen   secondary bonds in the solid state, with distances ranging from   2.56 Å for the TpPh2Ni(2,6-dichlorophenolate) complex   to 2.88 Å for the TpPh2Fe(2,6-dibromophenolate)   complex. Variable temperature NMR spectra of the   TpPh2Co(2,6-dichlorophenolate) and   TpPh2Ni(2,6-dichlorophenolate) complexes showed that   rotation of the phenolate, which requires loss of the secondary   bond, has an activation barrier of ∼30 and ∼37 kJ/mol,   respectively. Density functional theory calculations support the   presence of a barrier for disruption of the metal–halogen   interaction during rotation of the phenolate. On the other hand,   calculations using the spectroscopically calibrated angular   overlap method suggest essentially no contribution of the halogen   to the ligand-field splitting. Overall, these results provide the   first quantitative measure of the strength of a metal–halogen   secondary bond and demonstrate that it is a weak noncovalent   interaction comparable in strength to a hydrogen bond. These   results provide insight into the origin of the specificity of the   enzyme 2,6-dichlorohydroquinone 1,2-dioxygenase (PcpA), which is   specific for ortho-dihalohydroquinone substrates and   phenol inhibitors.

  Address (URL): http://pubs.acs.org/doi/full/10.1021/ic501424e