Spectroscopic study of [Fe2O2(5-Et3-TPA)2]3+: Nature of the Fe2O2 diamond core and its possible relevance to high-valent binuclear non-heme enzyme intermediates

Journal of the American Chemical Society

Volumn 125, Issue 24, 2003, Pages 7344-7356

  Skulan, Andrew J ^a   Hanson, Melissa A ^a   Hsu, Hua Fen ^b   Que Jr , Lawrence ^b   Solomon, Edward I ^a  

^a STANFORD UNIVERSITY   (United States)

^b University of Minnesota   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

CHEMICAL BONDS; ELECTRONIC STRUCTURE; ENZYME KINETICS; LOW TEMPERATURE EFFECTS; PROBABILITY DENSITY FUNCTION; RAMAN SPECTROSCOPY;

METAL-BASED ORBITALS;

IRON COMPOUNDS;

HEME; IRON COMPLEX; METHYLAMINE; OXYGEN; TRIS(5 ETHYL 2 PYRIDYLMETHYL)AMINE; UNCLASSIFIED DRUG; ENZYME; FE(2)O(2) TRIS(5 ETHYL 2 PYRIDYLMETHYL)AMINE; FE(2)O(2)-TRIS(5-ETHYL-2-PYRIDYLMETHYL)AMINE; FERRIC ION; FERRIC OXIDE; PYRIDINE DERIVATIVE; TRIS(2 PYRIDYLMETHYL)AMINE; TRIS(2-PYRIDYLMETHYL)AMINE;

ARTICLE; CALCULATION; CALIBRATION; CHEMICAL STRUCTURE; CIRCULAR DICHROISM; COMPLEX FORMATION; ELECTROCHEMICAL ANALYSIS; GEOMETRY; HYDROGEN BOND; MAGNETISM; POLARIZATION; RAMAN SPECTROMETRY; SPECTROSCOPY; STRUCTURE ANALYSIS; TEMPERATURE DEPENDENCE; CHEMISTRY; CONFORMATION; TEMPERATURE; THERMODYNAMICS; ULTRAVIOLET SPECTROPHOTOMETRY;

CIRCULAR DICHROISM; ENZYMES; FERRIC COMPOUNDS; HEME; MOLECULAR CONFORMATION; PYRIDINES; SPECTROPHOTOMETRY, ULTRAVIOLET; SPECTRUM ANALYSIS, RAMAN; TEMPERATURE; THERMODYNAMICS;

EID: 0037773627     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja021137n     Document Type: Article

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71. 2 core. Single point enthalpy of formation values was calculated for a variety of orientations using a 3.2 Å α-C-bridging oxo distance to gauge the effect of the steric bulk upon substrate approach. This distance is greater than the 2.55 Å (Basch, H.; Musaev, D. G.; Mogi, K.; Morokuma, K. J. Phys. Chem. B 2001, 105, 4770-4770. Musaev, D. G.; Basch, H.; Morokuma, K. J. Am. Chem. Soc. 2002, 124, 4135-4148.) → 2.70 Å (Siegbahn, P. E. M. Inorg. Chem. 1999, 38, 2880-2889.) α-C-bridging oxo distance proposed for the transition state of the putative hydrogen atom abstraction step in MMO, but using r(α-C-O) = 2.6 Å led to ligand-substrate approaches of less than the combined van der Waals radii. Thus, the longer distance was used to identify steric barriers.
72. 2 core. Single point enthalpy of formation values was calculated for a variety of orientations using a 3.2 Å α-C-bridging oxo distance to gauge the effect of the steric bulk upon substrate approach. This distance is greater than the 2.55 Å (Basch, H.; Musaev, D. G.; Mogi, K.; Morokuma, K. J. Phys. Chem. B 2001, 105, 4770-4770. Musaev, D. G.; Basch, H.; Morokuma, K. J. Am. Chem. Soc. 2002, 124, 4135-4148.) → 2.70 Å (Siegbahn, P. E. M. Inorg. Chem. 1999, 38, 2880-2889.) α-C-bridging oxo distance proposed for the transition state of the putative hydrogen atom abstraction step in MMO, but using r(α-C-O) = 2.6 Å led to ligand-substrate approaches of less than the combined van der Waals radii. Thus, the longer distance was used to identify steric barriers.
73. 2 core. Single point enthalpy of formation values was calculated for a variety of orientations using a 3.2 Å α-C-bridging oxo distance to gauge the effect of the steric bulk upon substrate approach. This distance is greater than the 2.55 Å (Basch, H.; Musaev, D. G.; Mogi, K.; Morokuma, K. J. Phys. Chem. B 2001, 105, 4770-4770. Musaev, D. G.; Basch, H.; Morokuma, K. J. Am. Chem. Soc. 2002, 124, 4135-4148.) → 2.70 Å (Siegbahn, P. E. M. Inorg. Chem. 1999, 38, 2880-2889.) α-C-bridging oxo distance proposed for the transition state of the putative hydrogen atom abstraction step in MMO, but using r(α-C-O) = 2.6 Å led to ligand-substrate approaches of less than the combined van der Waals radii. Thus, the longer distance was used to identify steric barriers.
74. 2 core.
75. This corresponds to 8/2σ bonds and 3/2π bonds distributed over the four Fe-O bonds for the low-spin complex, and a net 5/2σ and 6/2π for the high-spin analogue.
76. Both the high-spin and low-spin states can be accessed in mononuclear peroxo-Fe(III)-TPA complexes by varying the position of alkyl substitutents on the TPA ligand, resulting in small changes in the Fe-N(TPA) bond lengths. (Zang, Y.; Kim, J.; Dong, Y. H.; Wilkinson, E. C.; Appelman, E. H.; Que, L. J. Am. Chem. Soc. 1997, 119, 4197-4205.) The bonding in such complexes is dominated by the iron-peroxo interaction. (Lehnert, N.; Ho, R. Y. N.; Que, L.; Solomon, E. I. J. Am. Chem. Soc. 2001, 123, 8271-8290. Lehnert, N.; Ho, R. Y. N.; Que, L.; Solomon, E. I. J. Am. Chem. Soc. 2001, 123, 12802-12816.) This indicates that small changes in the substituted TPA ligand can change the spin state without changing the dominant contributors to the electronic structure of the complex.
77. Both the high-spin and low-spin states can be accessed in mononuclear peroxo-Fe(III)-TPA complexes by varying the position of alkyl substitutents on the TPA ligand, resulting in small changes in the Fe-N(TPA) bond lengths. (Zang, Y.; Kim, J.; Dong, Y. H.; Wilkinson, E. C.; Appelman, E. H.; Que, L. J. Am. Chem. Soc. 1997, 119, 4197-4205.) The bonding in such complexes is dominated by the iron-peroxo interaction. (Lehnert, N.; Ho, R. Y. N.; Que, L.; Solomon, E. I. J. Am. Chem. Soc. 2001, 123, 8271-8290. Lehnert, N.; Ho, R. Y. N.; Que, L.; Solomon, E. I. J. Am. Chem. Soc. 2001, 123, 12802-12816.) This indicates that small changes in the substituted TPA ligand can change the spin state without changing the dominant contributors to the electronic structure of the complex.
78. Both the high-spin and low-spin states can be accessed in mononuclear peroxo-Fe(III)-TPA complexes by varying the position of alkyl substitutents on the TPA ligand, resulting in small changes in the Fe-N(TPA) bond lengths. (Zang, Y.; Kim, J.; Dong, Y. H.; Wilkinson, E. C.; Appelman, E. H.; Que, L. J. Am. Chem. Soc. 1997, 119, 4197-4205.) The bonding in such complexes is dominated by the iron-peroxo interaction. (Lehnert, N.; Ho, R. Y. N.; Que, L.; Solomon, E. I. J. Am. Chem. Soc. 2001, 123, 8271-8290. Lehnert, N.; Ho, R. Y. N.; Que, L.; Solomon, E. I. J. Am. Chem. Soc. 2001, 123, 12802-12816.) This indicates that small changes in the substituted TPA ligand can change the spin state without changing the dominant contributors to the electronic structure of the complex.
79. Glerup, J.; Goodson, P. A.; Hazell, A.; Hazell, R.; Hodgson, D. J.; McKenzie, C. J.; Michelsen, K.; Rychlewska, U.; Toftlund, H. Inorg. Chem. 1994, 33, 4105-4111.
80. Exchange between two SOMOs with orbital overlap produces an AF contribution to J, exchange between a SOMO and an unoccupied molecular orbital results in a ferromagnetic contribution to J, and that pairs of unoccupied orbitals do not contribute to exchange. (Goodenough, J. B. Phys. Rev. 1955, 79, 564. Kanamori, J. J. Phys. Chem. Solids 1959, 10, 87.) These contributions are summed over the 25 orbital pathways (5 × 5 combinations of d-orbitals) to generate the observed ground-state spin ladder.
81. Exchange between two SOMOs with orbital overlap produces an AF contribution to J, exchange between a SOMO and an unoccupied molecular orbital results in a ferromagnetic contribution to J, and that pairs of unoccupied orbitals do not contribute to exchange. (Goodenough, J. B. Phys. Rev. 1955, 79, 564. Kanamori, J. J. Phys. Chem. Solids 1959, 10, 87.) These contributions are summed over the 25 orbital pathways (5 × 5 combinations of d-orbitals) to generate the observed ground-state spin ladder.
82. -1 in the valence-delocalized S = 3/2 calculation.
83. 2* electron.
84. Brunold, T. C.; Gamelin, D. R.; Solomon, E. I. J. Am. Chem. Soc. 2000, 122, 8511-8523.
85. Siegbahn, P. E. M. Inorg. Chem. 1999, 38, 2880-2889.