2244
Inorg. Chem. 1999, 38, 2244-2245
Dioxygen Reactivity of Fully Reduced [LFeII‚‚‚CuI]+ Complexes Utilizing Tethered
Tetraarylporphyrinates: Active Site Models for Heme-Copper Oxidases
Telvin D. Ju,† Reza A. Ghiladi,† Dong-Heon Lee,† Gino P. F. van Strijdonck,† Amina S. Woods,‡ Robert J. Cotter,‡
Victor G. Young Jr.,§ and Kenneth D. Karlin*,†
Department of Chemistry, The Johns Hopkins University, Charles and 34th Streets, Baltimore, Maryland 21218, Department of
Pharmacology and Molecular Sciences, The Johns Hopkins School of Medicine, Baltimore, Maryland 21205, and Department of Chemistry,
The University of Minnesota, Minneapolis, Minnesota 55455
ReceiVed January 6, 1999
In aerobic organisms, the heme a3-CuB binuclear active center
in heme-copper oxidases is responsible for O2 binding, O-O
reductive cleavage, and protonation to give H2O.1 The enzyme
couples this 4e-/4H+ O2 reduction to the translocation of protons,
creating the membrane potential used to drive ATP synthesis.
There is considerable interest in developing structural, spectro-
scopic, and functional active site models,2-4 but only a few
discrete heterobinuclear FeII‚‚‚CuI species have been well char-
acterized and employed for critical O2-reactivity studies.3,5-8
We wish to study systems where the (porphyrinate)FeII/LCuI/
O2 chemistry (L ) copper ligand) may be controlled (but also
systematically varied), in situations where intramolecular reactions
are favored. Here, we report such chemistry with heterobinucle-
ating ligands, the constitutional isomers 6L and 5L, where a
tetradentate TMPA9 ligating moiety is covalently attached to the
periphery of a porphryin, through either the 6-position (6L) or
Scheme 1
6
5
the 5-position (5L) of one pyridine arm (Scheme 1). L and L
take advantage by employing a Cu ligand with an established
(TMPA)CuI/O2 chemistry with known kinetics, thermodynamics,
structures, and spectroscopy.10 In addition to the description of
† The Johns Hopkins University.
‡ The Johns Hopkins School of Medicine.
§ The University of Minnesota.
(1) (a) Ferguson-Miller, S.; Babcock, G. T. Chem. ReV. 1996, 96, 2889-
2907. (b) Ostermeier, C.; Harrenga, A.; Ermler, U.; Michel, H. Proc.
Natl. Acad. Sci. U.S.A. 1997, 94, 10547-10553. (c) Yoshikawa, S.;
Shinzawa-Itoh, K.; Nakashima, R.; Yaono, R.; Yamashita, E.; Inoue,
N.; Yao, M.; Jei-Fei, M.; Libeu, C. P.; Mizushima, T.; Yamaguchi, H.;
Tomizaki, T.; Tsukihara, T. Science 1998, 280, 1723-1729.
(2) (a) Kitajima, N. AdV. Inorg. Chem. 1992, 39, 1-77. (b) Holm, R. H.
Pure Appl. Chem. 1995, 67, 217-224. (c) Karlin, K. D.; Lee, D.-H.;
Obias, H. V.; Humphreys, K. J. Pure Appl. Chem. 1998, 70, 855-862.
(3) Collman, J. P. Inorg. Chem. 1997, 36, 5145-5155.
(4) (a) Obias, H. V.; van Strijdonck, G. P. F.; Lee, D.-H.; Ralle, M.;
Blackburn, N. J.; Karlin, K. D. J. Am. Chem. Soc. 1998, 120, 9696-
9697. (b) Kopf, M.-A.; Karlin, K. D. In Biomimetic Oxidations; Meunier,
B., Ed.; Imperial College Press: London, 1999; Chapter 7, in press. (c)
Nanthakumar, A.; Fox, S.; Karlin, K. D. J. Chem. Soc., Chem. Commun.
1995, 499-501.
(5) Berry, K. J.; Gunter, M. J.; Murray, K. S. In Oxygen and Life; The Royal
Society of Chemistry: London, U.K., 1980; Vol. Special Publication
No. 39; pp 170-179.
(6) Collman, J. P.; Rapta, M.; Bro¨ring, M.; Raptova, L.; Schwenninger, R.;
Boitrel, B.; Fu, L.; L’Her, M. J. Am. Chem. Soc. 1999, 121, 1387-
1388 and references cited therein.
(7) Monzani, E.; Casella, L.; Gullotti, M.; Panigada, N.; Franceschi, F.;
Papaefthymiou, V. J. Mol. Catal. A: Chem. 1997, 117, 199-204.
(8) Sasaki, T.; Nakamura, N.; Naruta, Y. Chem. Lett. 1998, 351-352.
(9) Abbreviations used: TMPA, tris(2-pyridylmethyl)amine; F8-TPP, tetrakis-
(2,6-difluorophenyl)porphyrinate; MALDI-TOF-MS, matrix-assisted laser
desorption ionization time-of-flight mass spectrometry; BArF, tetrakis-
(3,5-bis(trifluoromethyl)phenyl)borate; THF, tetrahydrofuran; EXAFS,
extended X-ray absorption fine structure.
(10) (a) Tyekla´r, Z.; Jacobson, R. R.; Wei, N.; Murthy, N. N.; Zubieta, J.;
Karlin, K. D. J. Am. Chem. Soc. 1993, 115, 2677-2689. (b) Karlin, K.
D.; Kaderli, S.; Zuberbu¨hler, A. D. Acc. Chem. Res. 1997, 30, 139-
147. (c) Karlin, K. D.; Zuberbu¨hler, A. D. In Bioinorganic Catalysis:
Second Edition, ReVised and Expanded; Reedijk, J., Bouwman, E., Eds.;
Marcel Dekker: New York, 1999; pp 469-534.
new FeII (with “empty tether”) and FeII‚‚‚CuI complexes with 6L
5
and L, we report biomimetic reactions where µ-oxo FeIII-O-
CuII cores are generated directly from O2 reduction;11 a crystal
6
structure of the L oxygenation product is described.
The complexes described herein (Scheme 1) are characterized
by multinuclear NMR12 and UV-visible spectroscopies, and
supported by MALDI-TOF mass spectrometry on isolated solids.13
6
Metalation begins with addition of excess FeCl2 to either the L
5
or L ligands, followed by air oxidation. This procedure yields
(11) (a) With separate mononuclear reduced heme and copper(I) complexes,
we have previously11b,c described details of the reaction of (F8-TPP)FeII
plus [(TMPA)CuI(RCN)]+ with O2, which produces the µ-oxo complex
[(F8-TPP)FeIII-O-CuII(TMPA)]+ (5). Isotope labeling showed that the
oxo atom in 5 is derived from O2, and the reaction stoichiometry
(unpublished results) is Fe:Cu:O2 ) 2:2:1. (b) Karlin, K. D.; Nantha-
kumar, A.; Fox, S.; Murthy, N. N.; Ravi, N.; Huynh, B. H.; Orosz, R.
D.; Day, E. P. J. Am. Chem. Soc. 1994, 116, 4753-4763. (c)
Nanthakumar, A.; Nasir, M. S.; Karlin, K. D.; Ravi, N.; Huynh, B. H.
J. Am. Chem. Soc. 1992, 114, 6564-6566.
(12) 1H NMR spectra, particularly pyrrole resonances, are useful as a criterion
for compound purity, since most of the compounds (including impurities)
possess paramagnetically shifted and distinctive (i.e., highly sensitive
to spin and oxidation states) resonances.
(13) See Supporting Information.
10.1021/ic9900511 CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/24/1999