Synthesis, characterization, and laser flash photolysis reactivity of a carbonmonoxy heme complex

Article abstract of DOI:10.1021/ic026307b

We present here the synthesis, characterization, and flash photolysis study of [(F₈TPP)Fe^II(CO)(THF)] (1) {F₈TPP = tetrakis(2,6-difluorophenyl)porphyrinate(2-)}. Complex 1 crystallizes from THF/heptane solvent system as a tris-THF solvate, [(F₈TPP)Fe ^II(CO)(THF)]·3THF (1·3THF), with ferrous ion in the porphyrin plane (C₆₁H₅₂F₈FeN₄O ₅; a = 11.7908(2) A, b = 20.4453(2) A, c = 39.9423(3), α = 90°, β = 90°, γ = 90°; orthorhombic, orthorhombic, P2₁2₁2₁, Z = 8; Fe-N ₄(av) = 2.00 A; N-Fe-N (all) = 90.0°). This complex (as 1·THF) has also been characterized by ¹H NMR {six-coordinate, low-spin heme; CD₃CN, RT, δ 8.82 (s, pyrrole-H, 8H), 7.89 (s, para-phenyl-H, 8H), 7.46 (s, meta-phenyl-H, 4H), 3.58 (s, THF, 8H), 1.73 (s, THF, 8H)}, ²H NMR (pyrrole-deuterated analogue) [(F ₈TPP-d₈)Fe^II(CO)-(THF)] {THF, RT, δ 8.78 ppm (s, pyrrole-D)}, ¹³C NMR (on ¹³CO-enriched adduct) {THF-d₈, RT, δ 206.5 ppm; CD₂Cl₂, RT, δ 206.1 ppm}, UV-vis {THF, RT, λ_max, 411 (Soret), 525 nm}, and IR {293 K, solution, v_CO 1979 cm^-1 (THF), 1976 cm^-1 (acetone), 1982 cm^-1 (CH₃CN)} spectroscopies. In order to more fully understand the intricacies of solvent-ligand binding (as compared to CO rebinding to the photolyzed heme), we have also synthesized the bis-THF adduct [(F₈TPP)Fe ^II(THF)₂]. Complex 2 also crystallizes from THF/heptane solvent system as a bis-THF solvate, [(F₈TPP)Fe ^II(THF)₂]·2THF (2·2THF), with ferrous iron in the porphyrin plane (C₆₀H₅₂F₈FeN ₄O₄; a = 21.3216(3) A, b = 12.1191(2) A, c = 21.0125(2) A, α = 90°, β = 105.3658(5)°, γ = 90°; monoclinic, C2/c, Z = 4; Fe-N₄(av) = 2.07 A; N-Fe-N (all) = 90.0°). Further characterization of 2 includes UV-vis {THF, λ _max, 421 (Soret), 542 nm} and ¹H NMR {six-coordinate, high spin heme; THF-d₈, RT, δ 56.7 (s, pyrrole-H, 8H), 8.38 (s, para-phenyl-H, 8H), 7.15 (s, meta- phenyl-H, 4H)} spectroscopies. Flash photolysis studies employing 1 were able to resolve the CO rebinding kinetics in both THF and cyclohexane solvents. In CO saturated THF {[CO] ～ 5 mM} and at [1] ?5 μM, the conversion of [(F₈TPP)Fe ^II(THF)₂] (produced after photolytic displacement of CO) to [(F₈-TPP)Fe^II(CO)(THF)] was monoexponential, with k_obs = 1.6 (±0.2) × 10⁴ s^-1. Reduction in [CO] by vigorous Ar purging gave k_obs ? 10 ³ S^-1 in cyclohexane. The study presented in this report lays the foundation for applying fast-time scale studies based on CO flash photolysis to the more complicated heterobimetallic heme/Cu systems.

Full text of DOI:10.1021/ic026307b

Inorg. Chem. 2003, 42, 5211−5218
Synthesis, Characterization, and Laser Flash Photolysis Reactivity of a
Carbonmonoxy Heme Complex
David W. Thompson,† Ryan M. Kretzer,† Estelle L. Lebeau,† Donald V. Scaltrito,† Reza A. Ghiladi,†
,†
,†
Kin-Chung Lam,‡ Arnold L. Rheingold,‡ Kenneth D. Karlin,* and Gerald J. Meyer*
Department of Chemistry, The Johns Hopkins UniVersity, Charles and 34th Streets,
Baltimore, Maryland 21218, and Crystallography Laboratory, Department of Chemistry,
UniVersity of Delaware, Newark, Delaware 19716
Received December 26, 2002
II
We present here the synthesis, characterization, and flash photolysis study of [(F TPP)Fe (CO)(THF)] (1) {F TPP
8
8
) tetrakis(2,6-difluorophenyl)porphyrinate(2−)}. Complex 1 crystallizes from THF/heptane solvent system as a
II
tris-THF solvate, [(F TPP)Fe (CO)(THF)]‚3THF (1‚3THF), with ferrous ion in the porphyrin plane (C H F FeN O ;
8
61 52
8
4 5
a ) 11.7908(2) Å, b ) 20.4453(2) Å, c ) 39.9423(3), R ) 90°, â ) 90°, γ ) 90°; orthorhombic, P212121, Z )
8; Fe−N (av) ) 2.00 Å; N−Fe−N (all) ) 90.0°). This complex (as 1‚THF) has also been characterized by 1H NMR
4
{six-coordinate, low-spin heme; CD CN, RT, δ 8.82 (s, pyrrole-H, 8H), 7.89 (s, para-phenyl-H, 8H), 7.46 (s, meta-
3
II
phenyl-H, 4H), 3.58 (s, THF, 8H), 1.73 (s, THF, 8H)}, 2H NMR (pyrrole-deuterated analogue) [(F TPP-d8)Fe (CO)-
8
(THF)] {THF, RT, δ 8.78 ppm (s, pyrrole-D)}, 13C NMR (on 13CO-enriched adduct) {THF-d8, RT, δ 206.5 ppm;
CD Cl2, RT, δ 206.1 ppm}, UV−vis {THF, RT, λmax, 411 (Soret), 525 nm}, and IR {293 K, solution, νCO 1979
2
cm-1 (THF), 1976 cm-1 (acetone), 1982 cm-1 (CH CN)} spectroscopies. In order to more fully understand the
3
intricacies of solvent−ligand binding (as compared to CO rebinding to the photolyzed heme), we have also synthesized
II
the bis-THF adduct [(F TPP)Fe (THF)2]. Complex 2 also crystallizes from THF/heptane solvent system as a bis-
8
II
THF solvate, [(F TPP)Fe (THF)2]‚2THF (2‚2THF), with ferrous iron in the porphyrin plane (C H F FeN O ; a )
8
60 52
8
4 4
21.3216(3) Å, b ) 12.1191(2) Å, c ) 21.0125(2) Å, R ) 90°, â ) 105.3658(5)°, γ ) 90°; monoclinic, C2/c, Z
) 4; Fe−N (av) ) 2.07 Å; N−Fe−N (all) ) 90.0°). Further characterization of 2 includes UV−vis {THF, λmax, 421
4
(Soret), 542 nm} and 1H NMR {six-coordinate, high spin heme; THF-d8, RT, δ 56.7 (s, pyrrole-H, 8H), 8.38 (s,
para-phenyl-H, 8H), 7.15 (s, meta-phenyl-H, 4H)} spectroscopies. Flash photolysis studies employing 1 were able
to resolve the CO rebinding kinetics in both THF and cyclohexane solvents. In CO saturated THF {[CO] ∼ 5 mM}
II
and at [1] = 5 µM, the conversion of [(F TPP)Fe (THF)2] (produced after photolytic displacement of CO) to [(F -
8
8
TPP)Fe (CO)(THF)] was monoexponential, with kobs ) 1.6 (±0.2) × 104 s-1. Reduction in [CO] by vigorous Ar
purging gave kobs = 103 s-1 in cyclohexane. The study presented in this report lays the foundation for applying
fast-time scale studies based on CO flash photolysis to the more complicated heterobimetallic heme/Cu systems.
II
Introduction
use of carbonmonoxy heme complexes in the study of
transient oxygenation after photolytic displacement of the
CO ligand.15 The near ubiquitous use of the carbon monoxide
ligand in flash photolysis studies of heme proteins and
In studies of heme proteins including cytochrome c oxidase
(CcO), carbon monoxide has often been exploited to serve
as a surrogate for the physiological reactant dioxygen
(O2).1-12 Such investigations have been extended to CO-
adduct formation of model heme systems,13,14 including the
(1) Varotsis, C.; Zhang, Y.; Appelman, E. H.; Babcock, G. T. Proc. Natl.
Acad. Sci. U.S.A. 1993, 90, 237-241.
(2) Ferguson-Miller, S.; Babcock, G. T. Chem. ReV. 1996, 96, 2889-
* To whom correspondence should be addressed. E-mail: karlin@jhu.edu
(K.D.K.); meyer@jhu.edu (G.J.M.).
2907.
(3) Einarsdottir, O.; Dyer, R. L.; Lemon, D. D.; Killough, P. M.; Hubig,
S. M.; Atherton, S. J.; Lopez-Garriga, J. J.; Palmer, G.; Woodruff,
W. H. Biochemistry 1993, 32, 12013-12024.
† The Johns Hopkins University.
‡ The University of Delaware.
10.1021/ic026307b CCC: $25.00 © 2003 American Chemical Society
Published on Web 07/19/2003
Inorganic Chemistry, Vol. 42, No. 17, 2003 5211

Thompson et al.
model complexes is due to several factors, including its
ability to form stable adducts which are resistant to redox
changes, its use as a competitive inhibitor of O2-reduction
in both proteins and model complexes, its high quantum yield
for photodissociation, and its characteristic intense infrared
absorption.
a copper complex used in heme-copper synthetic analogues
has been investigated previously,34 the need for studying the
CO chemistry of the tetraarylporphryinate (F8TPP)FeII {F8-
TPP ) tetrakis(2,6-difluorophenyl)porphyrinate(2-), see
diagram, where ArF ) 2,6-difluorophenyl}14 is also required.
Fast-time scale investigations employing CO flash pho-
tolysis have been fruitful for probing the reactivity and
dynamics of dioxygen binding and reduction occurring in
the heme-copper binuclear active site of CcO,3,16-25 and we
wish to extend such studies to our synthetic heme-copper
model systems.26-33 However, in light of the likely difficulty
in interpreting data from heterobimetallic heme-copper
systems, the elucidation of CO binding and photolysis
relating to the individual metal components is essential.
While carbon monoxide photodissociation and rebinding in
Thus, we describe here the synthesis, structural characteriza-
tion, and laser flash photolysis study of the heme-CO adduct
[(F8TPP)FeII(CO)(THF)] (1) {see diagram}. Furthermore,
given the need for understanding ligand binding processes
and solvent coordination influences upon reactivity in the
ferrous-heme model complex, we have also synthesized the
bis-solvento complex, [(F8TPP)FeII(THF)2] (2), and its physi-
cal and structural characterization is presented here as well.
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36, 554-565.
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Experimental Section
Materials and Methods. All reagents and solvents were
purchased from commercial sources and were of reagent quality
unless otherwise stated. Chromatographic grade alumina (80-200
mesh) was purchased from EM Science. Air-sensitive compounds
were handled under argon atmosphere using standard Schlenk
techniques, or in an MBraun Labmaster 130 inert atmosphere (<1
ppm O2, <1 ppm H2O) glovebox filled with nitrogen. Solvents were
distilled over drying agents under argon prior to use: acetonitrile
(CH3CN), propionitrile (CH3CH2CN), methylene chloride (CH2-
Cl2), methanol, and heptane from calcium hydride; tetrahydrofuran,
diethyl ether, and toluene from sodium/benzophenone; and acetone
from Drierite (97% CaSO4, 3% CoCl2). Deoxygenation of these
solvents was achieved by bubbling with argon for 30 min, followed
by 3 freeze/pump/thaw cycles prior to introduction into the
glovebox. NMR solvents were distilled as described and deoxy-
genated through 5 freeze/pump/thaw cycles. Addition of carbon
monoxide (Matheson Gas Products) for UV-vis, infrared (IR), and
1H-, 2H-, and 13C-nuclear magnetic resonance (NMR) spectroscopic
studies was effected by direct bubbling through an R & D
Separations oxygen/moisture trap model OT3-4 into the sample
solution via a syringe needle. 13CO was purchased in 100 mL
breakseals from ICON Services, Inc., Marion, NY. Elemental
analyses were performed by Desert Analytics, Tucson, AZ.
Synthesis. (F8TPP)FeII and its pyrrole-deuterated analogue (F8-
TPP-d8)FeII were synthesized according to published procedures.30,35
[(F8TPP)FeII(CO)(THF)]‚THF (1‚THF). In the glovebox, to a
100 mL Schlenk flask fitted with a rubber septum was addded a
100 mg sample of (F8TPP)FeII dissolved in 10 mL of THF. On the
benchtop, the solution was sparged for ∼3 min with CO via syringe
needle, followed by layering with ∼50 mL CO-saturated heptane.
After 6 days, lustrous, red crystals suitable for X-ray diffraction
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41, 2282-2291.
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K. D. Inorg. Chem. 2003, 42, 3016-3025.
(15) Momenteau, M.; Reed, C. A. Chem. ReV. 1994, 94, 659-698.
(16) Babcock, G. T. Proc. Natl. Acad. Sci., U.S.A. 1999, 96, 12971-12973.
(17) Kitagawa, T.; Ogura, T. Prog. Inorg. Chem. 1997, 45, 431-479.
(18) Szundi, I.; Liao, G.-L.; Einarsdottir, O. Biochemistry 2001, 40, 2332-
2339.
(19) Han, S.; Takahashi, S.; Rousseau, D. L. J. Biol. Chem. 2000, 275,
1910-1919.
(20) Giuffre, A.; Forte, E.; Antonini, G.; D’Itri, E.; Brunori, M.; Soulimane,
T.; Buse, G. Biochemistry 1999, 38, 1057-1065.
(21) Woodruff, W. H. J. Bioenerg. Biomembr. 1993, 25, 177-188.
(22) Koutsoupakis, K.; Stavrakis, S.; Pinakoulaki, E.; Soulimane, T.;
Varotsis, C. J. Biol. Chem. 2002, 277, 32860-32866.
(23) Fiamingo, F. G.; Altschult, R. A.; Moh, P. P.; Alben, J. O. J. Biol.
Chem. 1982, 257, 1639-1650.
(24) Alben, J. O.; Moh, P. P.; Fiamingo, F. G.; Altschult, R. A. Proc. Natl.
Acad. Sci., U.S.A. 1981, 78, 234-237.
(25) Park, S.; Pan, L.-P.; Chan, S. I.; Alben, J. O. Biophys. J. 1996, 71,
1036-1047.
(26) Ghiladi, R. A.; Ju, T. D.; Lee, D.-H.; Moe¨nne-Loccoz, P.; Kaderli,
S.; Neuhold, Y.-M.; Zuberbu¨hler, A. D.; Woods, A. S.; Cotter, R. J.;
Karlin, K. D. J. Am. Chem. Soc. 1999, 121, 9885-9886.
(27) Ghiladi, R. A.; Hatwell, K. R.; Karlin, K. D.; Huang, H.-w.; Moe¨nne-
Loccoz, P.; Krebs, C.; Huynh, B. J.; Marzilli, L. A.; Cotter, R. J.;
Kaderli, S.; Zuberbu¨hler, A. D. J. Am. Chem. Soc. 2001, 123, 6183-
6184.
(28) Ghiladi, R. A.; Karlin, K. D. Inorg. Chem. 2002, 41, 2400-2407.
(29) Ju, T. D.; Ghiladi, R. A.; Lee, D.-H.; van Strijdonck, G. P. F.; Woods,
A. S.; Cotter, R. J.; Young, J. V. G.; Karlin, K. D. Inorg. Chem. 1999,
38, 2244-2245.
(30) Kopf, M.-A.; Neuhold, Y.-M.; Zuberbu¨hler, A. D.; Karlin, K. D. Inorg.
Chem. 1999, 38, 3093-3102.
(31) Kopf, M.-A.; Karlin, K. D. Inorg. Chem. 1999, 38, 4922-4923.
(32) Kopf, M.-A.; Karlin, K. D. In Biomimetic Oxidations; Meunier, B.,
Ed.; Imperial College Press: London, 2000; Chapter 7, pp 309-362.
(33) Kim, E.; Helton, M. E.; Wasser, I. M.; Karlin, K. D.; Lu, S.; Huang,
H.-w.; Moe¨nne-Loccoz, P.; Incarvito, C. D.; Rheingold, A. L.;
Honecker, M.; Kaderli, S.; Zuberbu¨hler, A. D. Proc. Natl. Acad. Sci.
U.S.A. 2003, 100 (7), 3623-3628.
(34) Scaltrito, D. V.; Fry, H. C.; Showalter, B. M.; Thompson, D. W.;
Liang, H.-C.; Zhang, C. X.; Kretzer, R. M.; Kim, E.-i.; Toscano, J.
P.; Karlin, K. D.; Meyer, G. J. Inorg. Chem. 2001, 40, 4514-4515.
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2001, 40, 5754-5767.
5212 Inorganic Chemistry, Vol. 42, No. 17, 2003

Carbonmonoxy Heme Complex
Table 1. Crystal Data and Structure Refinement for
[(F8TPP)FeII(CO)(THF)]‚3THF (1‚3THF) and
[(F8TPP)FeII(THF)2]‚2THF (2‚2THF)
were obtained; crystallographic analysis later revealed a formulation
of [(F8TPP)FeII(CO)(THF)]‚3THF (1‚3THF) for these crystals. A
purple powder, 1‚THF, was obtained by rapid addition of an excess
of heptane to the THF solution (5:1; v/v, both CO saturated)
containing (F8TPP)FeII followed by gravity filtration under an inert
atmosphere. The isolated solid was kept under a CO atmosphere
to prevent loss of the carbonyl ligand. Analysis of the noncrystalline
[(F8TPP)FeII
(CO)-(THF)]‚3THF
(1‚3THF)
[(F8TPP)FeII
(THF)2]‚2THF
(2‚2THF)
formula
fw
C61H52F8FeN4O5
1128.92
C60H52FeN4O4
1100.91
C2/c
1
material follows. UV-vis (THF; λmax, nm): 411 nm, 525 nm. H
space group
a, Å
b, Å
P212121
NMR (CD3CN): δ 8.82 (s, pyrrole-H, 8H), 7.89 (s, para-phenyl-
H, 8H), 7.46 (s, meta-phenyl-H, 4H), 3.58 (s, THF, 8H), 1.73 (s,
THF, 8H). Anal. Calcd for [(F8TPP)FeII(CO)(THF)]‚1THF, C53H36F8-
FeN4O3: C, 63.41; H, 3.66; N, 5.69. Found: C, 63.91; H, 3.38; N,
6.03.
11.7908(2)
20.4453(2)
39.9423(3)
21.3216(3)
12.1191(2)
21.0125(2)
105.3658(5)
5235.51(9)
4
dark blue plate
1.397
3.69
c, Å
â, deg
V, Å3
9628.7(2)
8
Z
[(F8TPP)FeII(THF)2]‚THF (2‚THF). The bis-tetrahydrofuran
analogue of (F8TPP)FeII was prepared by dissolution of 54 mg of
(F8TPP)FeII in 10 mL deoxygenated THF in a glovebox. The THF/
porphyrin solution was layered with an equal volume of heptane.
After 3 days, dark purple/blue crystals suitable for X-ray diffraction
were obtained; crystallographic analysis later revealed a formulation
of [(F8TPP)FeII(THF)2]‚2THF (2‚2THF) for this crystalline mate-
rial. A noncrystalline purple solid of 2‚THF was obtained by rapid
addition of an excess (5:1, v/v) of heptane to the THF solution
containing (F8TPP)FeII, followed by gravity filtration under an inert
atmosphere. Analysis of the powder material follows. UV-vis
(THF; λmax, nm): 421 nm, 542 nm. 1H NMR (THF-d8): δ 56.7 (s,
pyrrole-H, 8H), 8.38 (s, para-phenyl-H, 8H), 7.15 (s, meta-phenyl-
H, 4H). Anal. Calcd for [(F8TPP)FeII(THF)2]‚THF, C56H44F8-
FeN4O3: C, 65.37; H, 4.28; N, 5.45. Found: C, 64.72; H, 4.10; N,
5.35.
cryst color, habit
D(calcd), g cm3
µ(Mo KR), cm-1
temp, K
diffractometer
radiation
deep red plate
1.558
4.05
203(2)
173(2)
Siemens P4/CCD
Mo KR
(λ ) 0.71073 Å)
8.98
Siemens P4/CCD
Mo KR
(λ ) 0.71073 Å)
6.66
R(F), %
R(wF2),a %
23.56
19.38
2
2
a Quantity minimized ) R(wF2) ) ∑[w(Fo2 - Fc )2]/∑[(wFo )2]1/2; R )
∑∆/∑(Fo), ∆ ) |(Fo - Fc)|.
refined by full-matrix least-squares procedures. The asymmetric
unit of 1 contains two independent, but chemically equivalent, iron
complexes. Platon/Squeeze37 was applied to 1 to resolve three THF
molecules (120 electrons) per complex. Within the 2018.9 Å3 void
space occupied by solvent molecules per unit cell, a total of 985
electrons were found. In this treatment of solvent, the contribution
of the solvent molecule is treated collectively and is not refined as
individual atoms. The R factor for 1 was significantly reduced when
refined as 87/13 racemic mixture. All phenyl rings of 1 were fixed
as rigid planar groups. The asymmetric unit of 2 contains half of
an Fe complex which lies on an inversion center and two halves of
THF molecules, one of which is equally distorted over two
positions. All non-hydrogen atoms in both structures were refined
with anisotropic displacement coefficients. All hydrogen atoms,
except those bonded with the distorted THF molecule for 2, were
treated as idealized contributions.
Infrared Spectroscopy. IR spectra were obtained at room
temperature using a Mattson Galaxy 4030 series FT-IR spectro-
photometer. IR samples were prepared in a drybox by dissolving
5-10 mg of (F8TPP)FeII in ∼1 mL of solvent in a glass vial, which
was subsequently sealed with a rubber septum prior to removal to
the benchtop. After an IR spectrum was taken using a SPECAC
solution cell of the (F8TPP)FeII as a control, the stock solution in
the vial was bubbled with CO for 5-10 s. An IR spectrum was
then taken of the carbonylated species in order to observe the
specific ν(CO)Fe.
Laser Flash Photolysis Studies. Transient absorbance measure-
ments were performed on a previously described apparatus.36
Excitation was carried out using the 532 or 417 nm laser pulses,
ca. 8 nm and 1-30 mJ cm-2, from a Nd:YAG (Continuum Surelite
II or III) laser (with a H2-filled Raman shifter for 417 nm excitation).
The sample was protected from the probe light using a fast shutter
and appropriate UV and heat absorbing glass and solution filter
combinations. In general, kinetic traces represent the average of
10-160 laser shots, typically 40. Samples were prepared in the
inert atmosphere of a glovebox, and cuvettes were stoppered with
a rubber septum, which was pierced with a noncoring needle for
CO bubbling.
All software and sources of the scattering factors are contained
in the SHELXTL (version 5.10) program library (G. Sheldrick,
Siemens XRD, Madison, WI).
Results and Discussion
Synthesis. The carbonmonoxy-THF complex [(F8TPP)-
FeII(CO)(THF)]‚3THF (1‚3THF) was prepared by dissolving
a pure sample of (F8TPP)FeII in deaerated THF, followed
by carbonylation via direct bubbling of CO for several
minutes. Crystalline material suitable for X-ray diffraction
study with the structurally deduced formula 1‚3THF was
obtained by slow precipitation from a CO-saturated THF/
heptane cosolvent system. This six-coordinate, low-spin (vide
infra) FeII complex has been characterized: X-ray crystal-
lography and IR spectroscopy are presented here, while UV-
vis and 1,2H/13C NMR discussions (including Experimental
Methods) are given in the Supporting Information. Elemental
analysis on the noncrystalline material obtained from rapid
precipitation of the heme-CO adduct confirms the loss of
two molecules of THF (solvent) when compared to the
Crystallographic Studies. Crystal, data collection, and refine-
ment parameters are given in Table 1. The systematic absences in
the diffraction data for 1 were uniquely consistent for the orthor-
hombic space group P212121, and the data for 2 were consistent
with the space groups C2/c and Cc. E-statistics, as well as the
presence of an inversion center of 2, suggested the centrosymmetric
option, which yielded chemically reasonable and computationally
stable results of refinement. The structures were solved using direct
methods, completed by subsequent difference Fourier syntheses and
(36) Kelly, C. A.; Thompson, D. W.; Farzad, F.; Meyer, G. J. Langmuir
1999, 15, 731.
(37) Spek, A. L. Acta Crystallogr., Sect. A 1990, 46, C34.
Inorganic Chemistry, Vol. 42, No. 17, 2003 5213

Thompson et al.
Figure 1. ORTEP (30% ellipsoids) diagram of [(F8TPP)FeII(CO)(THF)]‚
3THF (1‚3THF). Hydrogen atoms and two molecules of THF (solvent,
nonbinding) are omitted for clarity.
Figure 2. ORTEP (30% ellipsoids) diagram of [(F8TPP)FeII(THF)2]‚2THF
(2‚2THF). Hydrogen atoms and two molecules of THF (solvent, nonbind-
ing) are omitted for clarity.
crystalline product, for a formulation of [(F8TPP)FeII(CO)-
1
(THF)]‚1THF (1‚THF); this result is supported by the H
Table 2. Selected Distances (Å) and Angles (deg) for
[(F8TPP)FeII(CO)(THF)]‚3THF (1‚3THF)
NMR solution study in CD3CN which shows only 2 THF
molecules present in the noncrystalline material. Complex
1 dissolves in CH2Cl2 and THF and is sparingly soluble in
toluene and benzene. In CH3CN and CH3CH2CN, the THF
axial base is likely replaced by the nitrile solvent, but the
CO ligand remains bound to the iron site for extended periods
as evidenced by solution infrared studies (see following
paragraphs).
Intramolecular Distances (Å)
O(2)-C(61)
Fe(1)-O(1)
Fe(1)-N(2)
Fe(1)-N(4)
1.141(7)
2.121(4)
2.022(5)
1.979(5)
Fe(1)-C(61)
Fe(1)-N(1)
Fe(1)-N(3)
1.755(6)
1.978(5)
2.021(4)
Intramolecular Angles (deg)
O(2)-C(61)-Fe(1)
C(61)-Fe(1)-N(1)
C(61)-Fe(1)-N(3)
N(1)-Fe(1)-O(1)
N(3)-Fe(1)-O(1)
N(1)-Fe(1)-N(2)
N(1)-Fe(1)-N(4)
N(4)-Fe(1)-N(2)
176.1(5)
93.0(2)
89.9(2)
89.57(19)
87.58(19)
90.23(19)
89.8(2)
C(61)-Fe(1)-O(1)
175.0(2)
95.8(2)
89.7(2)
88.48(19)
86.03(18)
177.1(2)
89.4(2)
C(61)-Fe(1)-N(2)
C(61)-Fe(1)-N(4)
N(2)-Fe(1)-O(1)
N(4)-Fe(1)-O(1)
N(1)-Fe(1)-N(3)
N(3)-Fe(1)-N(2)
N(4)-Fe(1)-N(3)
Since we were investigating ligand and solvent coordina-
tion influences upon the properties of (F8TPP)FeII, we also
synthesized the bis-tetrahydrofuran analogue [(F8TPP)FeII-
(THF)2] (2) to compare iron-ligand (axial) and iron-
porphyrin structural parameters. The axial THF ligand was
chosen because it is a weak-field, weakly coordinating ligand.
Dissolution of (F8TPP)FeII in deoxygenated THF under an
inert atmosphere gave a deep purple-red solution, which
yielded dark purple crystals upon layering with deaerated
heptane; X-ray diffraction study of the crystalline material
yielded the structurally deduced formulation of [(F8TPP)-
FeII(THF)2]‚2THF (2‚2 THF). A noncrystalline purple solid
was obtained by rapid addition of an excess (5:1, v/v) of
heptane to the THF solution; elemental analysis revealed a
formulation of [(F8TPP)FeII(THF)2]‚1THF (2‚1 THF), a loss
of one THF solvent molecule compared to the crystalline
material. As with complex 1, the bis-THF adduct 2 dissolves
in CH2Cl2 and THF and is sparingly soluble in toluene and
benzene. However, in CH3CN and CH3CH2CN, both axial
THF ligands are lost, and a five-coordinate, high-spin species
with a nitrile axial ligand is generated.
X-ray Crystal Structure Determination of [(F8TPP)-
FeII(CO)(THF)]‚3THF (1‚3THF) and [(F8TPP)FeII(THF)2]‚
2THF (2‚2THF). Details of the data collection and refine-
ment parameters for 1‚3THF and 2‚2THF are provided in
Table 1 and the Supporting Information. Figures 1 and 2
show the ORTEP diagrams (30% ellipsoids) of 1‚3 THF
and 2‚2 THF, respectively, and a summary of selected bond
distances and angles is provided in Tables 2 and 3. The
crystal structures of 1 and 2 both indicate six-coordinate FeII
centers with ligation to the four-coordinate porphyrin and
two axial ligands in each case. In 1, CO and a solvent THF
molecule provide axial ligation, while two THF molecules
174.5(2)
90.31(18)
Table 3. Selected Distances (Å) and Angles (deg) for
[(F8TPP)FeII(THF)2]‚2THF (2‚2THF)
Intramolecular Distances (Å)
Fe(1)-O(1)
Fe(1)-N(2)
2.314(3)
2.074(3)
Fe(1)-N(1)
2.061(3)
Intramolecular Angles (deg)
O(1A)-Fe(1)-O(1) 180.0 N(1)-Fe(1)-O(1)
89.57(10) N(2)-Fe(1)-O(1)
90.43(10)
88.79(10)
N(1A)-Fe(1)-O(1)
N(2A)-Fe(1)-O(1)
N(1)-Fe(1)-N(2)
91.20(10) N(1)-Fe(1)-N(1A) 179.997(1)
89.87(11) N(1)-Fe(1)-N(2A) 90.13(11)
serve as ligands for the axial sites in 2. In 1, the Fe atom is
pulled out of the porphyrin plane slightly toward the tightly
bound CO ligand. In 2, the two axial THF ligands are related
by a center of inversion with a linear angle between axial
ligands (180.0°) and a near centering of the Fe atom in the
porphyrin plane. Neither complex 1 or 2 shows any
significant ruffling of the porphyrin from planarity.
The average Fe-Nporphyrin distances are 2.00 Å in 1 and
2.07 Å in 2. These values are consistent with other Fe-
Nporphyrin bond lengths for low- and high-spin (respectively)
ferrous species (Table 4).38,39 Comparable core expansion
of the hexacoordinate, high-spin [(TPP)FeII(THF)2] species
is observed with an average Fe-Nporphyrin distance of 2.06
Å. All of the diamagnetic, low-spin complexes have an
(38) Reed, C. A.; Mashiko, T.; Scheidt, W. R.; Spartalian, K.; Lang, G. J.
Am. Chem. Soc. 1980, 102, 2302-2306.
(39) Scheidt, W. R.; Reed, C. A. Chem. ReV. 1981, 81, 543-555.
5214 Inorganic Chemistry, Vol. 42, No. 17, 2003

Carbonmonoxy Heme Complex
Table 4. Comparative Data for FeII Heme Model Compounds
Fe-CCO
,
C-O,
Å
OCO-CCO-Fe,
CCO-Fe-Oax or
CCO-Fe-Nax, deg
av. Fe-Nporph
,
Fe-Oax or
Fe-Nax, Å
ν
CO (solvent),
cm-1
compd
Å
deg
Å
[(F8TPP)FeII(THF)2]a
2.07
2.06
2.314(3)
2.351(3)
2.127(3)
2.014(5)
2.001(6)
2.121(4)
2.10
2.127(4)
2.043(6)
2.041(5)
[(TPP)FeII(THF)2]38
[(TPP)FeII(Pip)2]54
2.004(4)
1.997(4)
1.958(6)
2.00
2.02(3)
1.98
[(TPP)FeII(1-MeIm)2]55
[(THFPP)FeII(py)2]56
[(F8TPP)FeII(THF)(CO)]a
[(TPP)FeII(CO)(py)]57
[(deut)FeII(THF)(CO)]42
[(C2-Cap)FeII(CO)(1-MeIm)]58
[(C2-Cap)FeII(CO)(1-MeIm)]58
1.755(6)
1.77(2)
1.706(5)
1.742(7)
1.748(7)
1.141(7)
1.12(2)
1.144(5)
1.161(8)
1.158(8)
176.1(5)
179(2)
178.3(14)
172.9(6)
175.9(6)
175.0(2)
177.5(8)
177.4(9)
174.7(3)
177.8(3)
1979 (THF)
1980
1955 (KBr)
2002 (Nujol)
2002 (Nujol)
1.990(7)
1.988(13)
a This work. Abbreviations used: TPP ) meso-tetraphenylporphyrin; Pip ) piperidine; 1-MeIm ) N-methylimidazole; THFPP ) 5,10,15,20-
tetrakis(heptafluoropropyl)porphyrin; py ) pyridine; deut ) deuteroporphyrin; C2-Cap ) 5,10,15,20-[pyromellitoyl(tetrakis(o-oxyethoxyphenyl))]porphyrin.
average Fe-Nporphyrin distance between 1.96 and 2.02 Å. The
Although 1 is more densely packed than [(deut)FeII(CO)-
(THF)], crystallographic packing forces are not completely
responsible for the differences in geometry as evidenced by
the large differences in the CO stretching frequency in
solution (see IR discussion). The bending and tilting of 1 is
more consistent with the angles observed for sterically
blocked, capped porphyrins (Table 4). The geometry of 1
represents one of the largest tilt and bend combinations
observed for an unblocked heme model complex.
IR Spectroscopy. Solution cell IR spectra of 1 reveal a
single CO stretch in the typical region for six-coordinate,
low-spin Fe(II)-porphyrin complexes (Table 4), with νCO
) 1979 cm-1 in THF, 1976 cm-1 in acetone, and 1982 cm-1
in acetonitrile. Although the vibrational frequencies of the
Fe-CO unit are generally thought of as useful indicators of
the trans ligand interactions with the iron heme, the CO
stretch does not correlate well with the base strength of the
solvent in this case. Other complexes believed to have strong
axial ligation also fall in the region between 1980 and 2000
cm-1.
For comparison, the complex [(deut)FeII(CO)(THF)] pro-
duced a particularly low energy CO stretch at 1955 cm-1 in
KBr and 1962 cm-1 in THF.42 The difference in the CO
stretching frequency between 1 and [(deut)FeII(CO)(THF)]
is significant. The most likely explanation is the nature of
the difference in the porphyrins, leading to variations in
Fe-C bond lengths; [(deut)FeII(CO)(THF)] has a stronger
Fe-C bond (Table 4), leading to a weaker C-O bond (and
lower ν(CO)).43 Another influence may be the larger devia-
tion from linearity of the Fe-CO group with 1, giving rise
to poorer overlap between the Fe dπ and CO π* orbitals.
Electron-withdrawing fluorines in F8-TPP in 1 also lead to
less CO back-bonding.
increase in average bond length for a high-spin ferrous
2
2
species is consistent with the population of the 3dx -y orbital
in both complex 1 and [(TPP)FeII(THF)2].40
The Fe-OTHF distance in the heme-CO adduct 1 is 2.121-
(4) Å but is elongated by ∼0.19 Å in 2. The shorter bond in
1 and in [(deut)FeII(CO)(THF)] compared to other low-spin
six-coordinate hemes (without a CO ligand) (Tables 3 and
4) is expected because of the trans effect of CO. The
especially long 2.314(3) Å Fe-OTHF distance in 2 is
2
consistent with the population of the 3dz orbital as required
by the high-spin ground state of this complex. The relatively
long Fe-OTHF bond distance in all of these examples is
consistent with the assignment of THF as a weak-field,
weakly binding ligand. By contrast, the bond length between
FeII and strongly coordinating axial ligands is shorter by
∼0.2-0.3 Å, as in the bis-piperdine, 1-methylimidazole, and
pyridine complexes (Table 4), when compared to the bis-
THF systems. The carbonyl CO bond distance of 1.141(7)
Å in 1 is consistent with that of other FeII-CO porphyrin
complexes (Table 4). The tight binding of the carbonyl is
indicated by the short Fe-C(CO) bond distance of 1.755(6)
Å, which is also in the expected range for low-spin carbonyl
heme complexes.
The Fe-CO unit prefers a linear geometry in order to
maximixe the Fe dπ f CO π* back-bonding.41 Two angles
which are significant with respect to defining linearity of
the CO are given as θ, the deviation of the Fe-C bond from
perpendicularity relative to the porphrin plane, and φ, the
angle of the CO bond relative to the Fe-C bond (see
diagram). In 1, θ is 5°, and φ is 3.9°. The combination of
Axial Ligand Substitution Kinetics. Rapid visible spec-
tral changes are observed when [(F8TPP)FeII(THF)2] in THF
is anaerobically treated with CO, Figure 3. The spectral
changes are assigned to the reaction given in eq 1.
The kinetics for the reaction of [(F8TPP)FeII(THF)2] (2)
with CO were on a time scale amenable for study by
nanosecond time-resolved absorption “flash and trap” tech-
these two angles leads to a 0.33 Å deviation from perpen-
dicularity of the O atom. For comparison, θ is 2.6° and φ is
1.7° in [(deut)FeII(CO)(THF)], leading to only a 0.16 Å
displacement of the O atom from the perpendicular position.
(40) Scheidt, W. R. Acc. Chem. Res. 1977, 10, 339-345.
(41) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 5th ed.;
John Wiley: New York, 1988.
(42) Scheidt, W. R.; Haller, K. J.; Fons, M.; Mashiko, T.; Reed, C. A.
Biochemistry 1981, 20, 3653-3657.
(43) We thank a reviewer for pointing out this explanation.
Inorganic Chemistry, Vol. 42, No. 17, 2003 5215

Thompson et al.
Figure 4. Absorption difference spectra obtained after pulsed 532 nm
light excitation of in carbon monoxide saturated THF. The spectra were
recorded at the following delay times: 0 µs (9), 20 µs (b), 50 µs (1), 100
µs ([), and 240 µs (×). The inset shows an absorption transient acquired
at 415 nm with a superimposed fit to a first-order kinetic model.
Figure 3. Ground state absorption spectra of [(F8TPP)FeII(CO)(THF)] (1)
(9) and [(F8TPP)FeII(THF)2] (2) (b) in neat THF. The inset represents the
calculated absorption difference spectra as found by Abs[(F8TPP)FeII(THF)2]
- Abs[(F8TPP)FeII(CO)(THF)].
[(F8TPP)FeII(THF)2] + CO T
[(F8TPP)FeII(CO)(THF)] + THF (1)
niques similar to those used in previous reports.15,44-46
Described in the following paragraphs are the results of
kinetic studies on the reaction given in eq 1, in both THF
and cyclohexane media followed by a proposed mechanistic
model.
Absorption difference spectra measured after pulsed laser
excitation of [(F8TPP)FeII(CO)(THF)] (1) (∼10-5 M) in CO-
saturated THF ([CO] ∼ 5 mM) are shown in Figure 4. We
note that either 417 or 532 nm laser excitation yielded
identical absorption difference spectra. The spectrum shows
a sharp bleach, i.e., negative absorption change, at 415 nm
and a positive absorption band at 430 nm. The spectral
features are consistent with CO loss and the immediate
appearance of [(F8TPP)FeII(THF)2] (2). In support of this
assignment, the calculated absorption difference spectrum,
determined by subtracting the ground state spectrum of [(F8-
TPP)FeII(THF)2] (2) from that of [(F8TPP)FeII(CO)(THF)]
(1) (inset Figure 3) shows a similar profile to that of
transiently observed absorption difference spectrum.
The CO photodissociation and the trapping by THF are
rapid and occur within the instrument response function, <10
ns. The absorption spectral changes observed for the conver-
sion of [(F8TPP)FeII(THF)2] (2) to [(F8TPP)FeII(CO)(THF)]
(1) in neat THF under 1 atm of CO were monoexponential
and returned cleanly to ground state products with a rate
constant, kobs ) 1.6 (( 0.2) × 104 s-1. Ground state
absorbance measurements taken before and after pulsed laser
experiments gave no evidence of sample decomposition.
Reduction of the CO concentration by vigorous Ar purging
reduced kobs to ∼103 s-1.
Figure 5. The observed rate constant for eq 1 as a function of [CO]/
[THF] in cyclohexane. The inset shows a double reciprocal plot of the same
data.
studied in cyclohexane as a function of THF concentration.
Cyclohexane was chosen because it is noncoordinating, does
not π-stack with porphyrins, and should not significantly alter
the kinetic rate constant for THF binding. Transient signals
were monitored at 427 and 410 nm in cyclohexane over a
THF concentration range 1 mM to 1 M. The observed rate
constants determined by analysis of the time dependent
absorption changes at 410 and 427 nm were found to
decrease with increasing [THF] ([CO] ∼ 5 mM) and finally
became independent of [THF] when [THF] > 0.30 M, Figure
5.
Mechanistic Model for Ligand Substitution Reactions.
Scheme 1 summarizes the proposed mechanism for CO
photodissociation and rebinding. Note that we have adopted
the notation of Stynes, where the trans ligand is indicated
as a superscript and the leaving (-) or entering (+) groups
as a subscript.45,46
To gain additional insight into the kinetic processes that
occur after laser excitation, CO recombination kinetics were
Pulsed laser excitation into either the Soret or R band of
[(F8TPP)FeII(CO)(THF)] (1) produces a photodissociative
excited state, [(F8TPP)FeII(CO)(THF)]*. Previous studies of
[(heme)FeII(His)(CO)], where His is histidine, have estab-
(44) Traylor, T. G. Acc. Chem. Res. 1981, 14, 102-113.
(45) Thompson, D. W.; Stynes, D. V. Inorg. Chem. 1991, 30, 636-640.
(46) Thompson, D. W.; Stynes, D. V. Inorg. Chem. 1990, 29, 3815-3822.
5216 Inorganic Chemistry, Vol. 42, No. 17, 2003

Carbonmonoxy Heme Complex
Scheme 1
equilibrium appears to exists between the mono- and bis-
THF compounds.52 Therefore, the species present on nano-
second and longer time scales are the mono- and bis-THF
adducts and the carbonyl compound shown in the box on
the right-hand side of Scheme 1. The equilibrium constants
for CO and THF binding in a related heme (deuteroheme)
have been determined to be 5 × 104 M-1 and 5.2 M-1,
respectively.53
There is an overwhelming body of evidence in support of
a dissociative (D) mechanism for CO coordination to a six-
coordinate heme.15,44-46 For a reaction proceeding through
a D mechanism, kobs is not an elementary rate constant and
is given by eq 2.
THF
-THF +CO
k
kTHF [CO] + k-THCFO k+THTFHF[THF]
kobs
)
(2)
THF
+CO
THF
k
[CO] + k
[THF]
+THF
The kinetic terms in eq 2 are defined in Scheme 1.15,44-46
In THF solution, where [THF] . [CO] and k-CO is small,
the reaction proceeds to completion, and eq 2 simplifies to
kobs ) kf[CO]
(3)
where
THF
-THF +CO
k
kTHF
kf )
(4)
THF
+THF
k
[THF]
With kobs ) 1.6 ((0.2) × 104 s-1 and [CO] ∼ 5 × 10-3
M, kf is calculated to be 3.2 × 106 M-1 s-1. The forward
rate constants for eq 1 depend on the lability of THF and
the relative rate parameters kT+HCFO/k+THTFHF. The [(F8TPP)FeII-
(THF)2] complex is high spin, and the rate constants for axial
ligand substitution are expected to be large. This point will
be elaborated upon in the following paragraphs.
Reaction 1 was also studied in cyclohexane with added
THF to fully establish the dissociative mechanism and to
provide a kinetic rate constant for THF dissociation. The
observed rate constant displays a linear dependence on [CO]/
[THF] under conditions where the [CO]/[THF] ratio ap-
proaches zero. Equations 3 and 4 can be rearranged to give
eq 5.
lished that both the His and CO ligands are photodissociated
in the excited state on a 300 fs time scale to yield a four-
coordinate “bare” heme.47 Similar dynamics are assumed to
occur in this work since THF is a weaker ligand for Fe(II)
when compared to histidine. We note that stronger-field
ligands, such as isocyanides, are apparently retained after
photolysis.48,49 Upon ligand dissociation, the excited heme
relaxes nonradiatively in ∼40 ps to yield the four-coordinate
heme.47
Mechanistically, the bare four-coordinate heme present
after photolysis and excited state relaxation can react with
either CO or THF. Geminate recombination of hemes and
the photodissociated ligands occurs on a time scale too fast
to be measured by our apparatus.50 If geminate CO rebinding
occurs, no spectral changes would be observed. Ford and
Traylor have shown that most ligands react with unsaturated
hemes with diffusion controlled rates while CO differs
significantly with activation control in low viscosity sol-
vents.51 The data reported here in neat THF are consistent
with rapid trapping to form [(F8TPP)FeII(THF)2] within 10
ns. At low THF concentrations in cyclohexane, a rapid
THF
+THF
k
[THF]
[CO]
1
THF
1
-1
kobs
)
+
(5)
THF
THF
(
)(
)(
)
(
)
k-THF k+CO
k-THF
Plots of the kinetic data to eq 5 (inset in Figure 5) were
found to be linear with a slope 1.5 × 10-5 s and an intercept
(52) We note that Reed et al. (ref 38) suggest that the structurally
characterized complex [(TPP)FeII(THF)2] is most likely five-coordinate
in THF solution.
(53) Rougee, M.; Brault, D. Biochemistry 1975, 14, 4100-4106.
(54) Radonovich, L. J.; Bloom, A.; Hoard, J. L. J. Am. Chem. Soc. 1972,
94, 2073-2078.
(55) Jameson, G. B.; Molinaro, F. S.; Ibers, J. A.; Collman, J. P.; Brauman,
J. I.; Rose, E. J.; Suslick, K. S. J. Am. Chem. Soc. 1980, 102, 3224-
3237.
(56) Moore, K. T.; Fletcher, J. T.; Therien, M. J. J. Am. Chem. Soc. 1999,
121, 5196-5209.
(57) Peng, S.-M.; Ibers, J. A. J. Am. Chem. Soc. 1976, 98, 8032-8036.
(58) Kim, K.; Ibers, J. A. J. Am. Chem. Soc. 1991, 113, 6077-6081.
(47) Huang, Y.; Marden, M. C.; Lambry, J.-C.; Fontaine-Aupart, M.-P.;
Pansu, R.; Martin, J.-L.; Poyart, C. J. Am. Chem. Soc. 1991, 113,
9141-9144.
(48) Dixon, D. W.; Kirmaier, C.; Holten, D. J. Am. Chem. Soc. 1985, 107,
808-813.
(49) Taube, D.; Traylor, T. G.; Magde, D.; Walda, K.; Luo, J. J. Am. Chem.
Soc. 1992, 114, 9182-9188.
(50) Traylor, T. G.; Magde, D.; Luo, J.; Walda, K. N.; Bandyopadhyay,
D.; Wu, G. Z.; Sharma, V. S. J. Am. Chem. Soc. 1992, 114, 9011-
9017.
(51) Traylor, T. G.; Luo, J.; Simon, J. A.; Ford, P. C. J. Am. Chem. Soc.
1992, 114, 4340-4345.
Inorganic Chemistry, Vol. 42, No. 17, 2003 5217

Thompson et al.
1.8 × 10-6 s. From these data, the limiting off rate of THF
use of weak-field ligands in nominally noncoordinating
solvents (cyclohexane) allows for the study of four-coordinate
hemes (upon photolysis) and may be potentially useful as
probes to mimic active sites in a number of iron-containing
enzymes. Furthermore, the results presented here lay the
foundation for similar studies involving the more complicated
carbonyl adducts of heterobimetallic complexes as models
for the active site of cytochrome c oxidase, and such studies
are now in progress.
THF
-THF
was determined to be k
) 5.6 × 105 s-1 and kT+HCFO/kTHF
+THF
) 0.12. The saturation kinetics observed at higher THF
concentrations are fully consistent with a D mechanism
whereby THF dissociation from [(F8TPP)FeII(THF)2] to
generate the five-coordinate transient intermediate, [(F8TPP)-
FeII(THF)], is the rate determining step for CO rebinding.
The saturation kinetics also provide compelling evidence that
a six-coordinate THF complex is obtainable in solution. A
comparison with the literature data reveals that [(F8TPP)-
FeII(THF)2] has some of most labile axial ligands known for
heme porphryins.15,44-46
Acknowledgment. This research was supported by the
National Institutes of Health (Grants GM28962 and GM60353
to K.D.K.), the National Science Foundation (NSF) (Grant
CHE-9708222 to G.J.M.), and an NSF environmental
research grant (CRAEMS, K.D.K. and G.J.M.). R.M.K. also
acknowledges a Howard Hughes Summer Fellowship through
the Johns Hopkins University.
Conclusions
We have synthesized and structurally characterized both
the heme-CO adduct [(F8TPP)FeII(THF)(CO)] (1) and the
bis-THF adduct [(F8TPP)FeII(THF)2] (2). Both complexes
were shown to be six-coordinate in the solid state. We also
present evidence that 2 is a six-coordinate high-spin ferrous
heme in solution. Complex 1 proved amenable to study by
fast-time scale UV-vis spectroscopy as initiated by flash
photolysis, and we have provided a reasonable mechanism
which describes the kinetics of CO-dissociation (photolytic)
and rebinding in the weakly coordinating THF solvent. The
Supporting Information Available: X-ray structure informa-
tion (CIF files) for [(F8TPP)FeII(CO)(THF)]‚3THF (1‚3THF) and
[(F8TPP)FeII(THF)2]‚2THF (2‚2THF), UV-vis and 1,2H/13C NMR
discussions (including Experimental Methods), and 13C and 2H
NMR spectra for 1‚3THF. This material is available free of charge
via the Internet at http://pubs.acs.org.
IC026307B
5218 Inorganic Chemistry, Vol. 42, No. 17, 2003