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In recent years, a number of high-valent iron intermediates have been identified as reactive species in iron-containing metalloproteins. Inspired by the interest in these highly reactive species, chemists have synthesized Fe(iv) and Fe(v) model complexes with terminal oxo or nitrido groups, as well as a rare example of an Fe(vi)-nitrido species. In all these cases, X-ray absorption spectroscopy has played a key role in the identification and characterization of these species, with both the energy and intensity of the pre-edge features providing spectroscopic signatures for both the oxidation state and the local site geometry. Here we build on a time-dependent DFT methodology for the prediction of Fe K- pre-edge features, previously applied to ferrous and ferric complexes, and extend it to a range of Fe(iv), Fe(v) and Fe(vi) complexes. The contributions of oxidation state, coordination environment and spin state to the spectral features are discussed. These methods are then extended to calculate the spectra of the heme active site of P450 Compound II and the non-heme active site of TauD. The potential for using these methods in a predictive manner is highlighted. [ABSTRACT FROM AUTHOR]

Dimetallic compounds I(P-P)M(S2C6H2S2)M(P-P)] (M=Ni, Pd; P-P=chelating bis(phosphine), 3a-3f) are prepared from OCS2C6H2S2CO or nBu2SnS2C6H2S2SnnBu2, which are protected forms of 1,2,4,5-benzenetetrathiolate. Selective monodeprotections of OCS2C6H2S2CO or nBu2SnS2C6H2S2SnnBu2 lead to [(P-P)Ni(S2C6- H2S2CO)] or [(P-P)Ni(S2C6H2S2SnnBu2)]; the former is used to prepare trimetallic compounds [(dcpe)Ni(S2C6H2S2)M(S2C6H2S2)Ni(dcpe)] (M = Ni (6a) or Pt (6b); dcpe = 1 ,2-bis(dicyclohexylphosphino)ethane). Compounds 3a-3f are redox active and display two oxidation processes, of which the first is generally reversible. Dinickel compound [(dcpe)Ni(S2C6H2S2)Ni(dcpe)] (3d) reveals two reversible oxidation waves with ΔE½=0.66 V, corresponding to κC of 1.6 x 1011 for the mixed valence species. Electrochemical behavior is unstable to repeated scanning in the presence of [Bu4N][PF6] electrolyte but indefinitely stable with Na[BArF24] (BArF24 = tetrakis(3, 5-bis(frifluoromethyl)phenyl)borate), suggesting that the radical cation generated by oxidation is vulnerable to reaction with PF6-. Chemical oxidation of 3d with [Cp2Fe][BArF24] leads Information of [3d][BArF24]. Structural identification of [3d][BArF24] reveals appreciable shortening and lengthening of C-S and C-C bond distances, respectively, within the tetrathioarene fragment compared to charge neutral 3d, indicating this to be the redox active moiety. Attempted oxidation of [(dppb)Ni(S2C6H2S2)Ni(dppb)] (3c) (dppb = 1 ,2-bis(diphenylphosphino)benzene) with AgBArF24 produces [[(dppb)Ni(S2C6H2S2)Ni(dppb)]2(μ-Ag2)][BArF24]2, [4c][BArF24]2, in which no redox chemistry has occurred. Crystal structures of bis(disulfide)-linked compounds [(P-P)Ni(S2C6H2(u-S2)2C6H2S2)Ni(P-P)] are reported. Near IR spectroscopy upon cationic [3d]+ and neutral 6a reveals multiple intense absorptions in the 95O-14OO nm region. Time-dependent density functional theory (DFT) calculations on a 6a model compound indicate that these absorptions are transitions between ligand-based π-type orbitals that have significant contributions from the sulfur p orbitals. [ABSTRACT FROM AUTHOR]