Synthesis and Spectroscopy of μ-Oxo (O2-)-Bridged Heme/Non-heme Diiron Complexes: Models for the Active Site of Nitric Oxide Reductase

Ian M. Wasser, Constantinus F. Martens, Claudio N. Verani, Eva Rentschler, Hong Wei Huang, Pierre Moěnne-Loccoz, Lev N. Zakharov, Arnold L. Rheingold, Kenneth D. Karlin

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46 Scopus citations


In this paper, we describe the synthesis and study of a series of heme/non-heme Fe-O-Fe′ complexes supported by a porphyrin and the tripodal nitrogen ligand TMPA [TMPA = tris(2-pyridylmethyl)amine]. The complete synthesis of [(6L)Fe-O-Fe(X)]+ (1) (X = OMe- or Cl-, 69:31 ratio), where 6L is the dianion of 5-(o-O-[(N,N-bis(2-pyridylmethyl)-2-(6-methoxyl)pyridinemethanamine)phenyl]-10, 15,20-tris(2,6-difluorophenyl)porphine, is reported. The crystal structure for 1-PF6 reveals an intramolecular heme/non-heme diferric complex bridged by an Fe-O-Fe′ moiety; ∠(Fe-O-Fe′) = 166.7(3)°, and d(Fe⋯Fe′) = 3.556 Å, Crystal data for C70H 57ClF12Fe2N8O3P (1·PF6): triclinic, P1, a = 13.185(3) Å, b = 14,590 (3) Å, c = 16.885(4) Å, α = 104.219(4)°, β = 91.572(4)°, γ = 107.907(4)°, V = 2977.3(11) Å3, Z = 2, T = 150(2) K. Complex 1 (where X = Cl-) is further characterized by UV-vis (λmax = 328, 416 (Soret), 569 nm), 1H NMR (δ 27-24 [TMPA-CH2-], 16.1 [pyrrole-H], 15.2-10.5 [PY-3H, PY-5H], 7.9-7.2 [m- and p-phenyl-H], 6.9-5.8 [PY-4H] ppm), resonance Raman (νas(Fe-O-Fe′) 844 cm-1), and Mössbauer (δFe = 0.47, 0.41 mm/s; ΔEA = 1.59, 0.55 mm/s; 80 K) spectroscopies, MALDI-TOF mass spectrometry (m/z 1202), and SQUID susceptometry (J = - 114,82 cm-1, S = 0). We have also synthesized a series of 3-, 4-, and 5-methyl-substituted as well as selectively deuterated TMPA(Fe′) complexes and condensed these with the hydroxo complex (F8)FeOH or (F8-d8)FeOH to yield "untethered" Fe-O-Fe′ analogues. Along with selective deuteration of the methylene hydrogens in TMPA, complete 1H NMR spectroscopic assignments for 1 have been accomplished. The magnetic properties of several of the untethered complexes and a comparison to those of 1 are also presented. Complex 1 and related species represent good structural and spectroscopic models for the heme/non-heme diiron active site in the enzyme nitric oxide reductase.

Original languageEnglish (US)
Pages (from-to)651-662
Number of pages12
JournalInorganic Chemistry
Issue number2
StatePublished - Jan 26 2004

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry


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