Mononitrosyl tris(thiolate) iron complex [Fe(NO)(SPh)3] - and dinitrosyl iron complex [(EtS)2Fe(NO) 2]-: Formation pathway of dinitrosyl iron complexes (DNICs) from nitrosylation of biomimetic rubredoxin [Fe(SR)4] 2-/1- (R = Ph, Et)

Article abstract of DOI:10.1021/ic061439g

Nitrosylation of the biomimetic reduced- and oxidized-form rubredoxin [Fe(SR)₄]^2-/1- (R = Ph, Et) in a 1:1 stoichiometry led to the formation of the extremely air- and light-sensitive mononitrosyl tris(thiolate) iron complexes (MNICs) [Fe(NO)(SR)₃]^- along with byproducts [SR]^- or (RS)₂. Transformation of [Fe(NO)(SR)₃]^- into dinitrosyl iron complexes (DNICs) [(RS)₂Fe(NO)₂]^- and Roussin's red ester [Fe₂(μ-SR)₂(NO)₄] occurs rapidly under addition of 1 equiv of NO_(g) and [NO]⁺, respectively. Obviously, the mononitrosyl tris(thiolate) complex [Fe(NO)(SR)₃] ^- acts as an intermediate when the biomimetic oxidized- and reduced-form rubredoxin [Fe(SR)₄]^2-/1- exposed to NO _(g) were modified to form dinitrosyl iron complexes [(RS) ₂Fe(NO)₂]^-. Presumably, NO binding to the electron-deficient [Fe^III(SR)₄]^- and [Fe ^III(NO)(SR)₃]^- complexes triggers reductive elimination of dialkyl/diphenyl disulfide, while binding of NO radical to the reduced-form [Fe^II(SR)₄]^2- induces the thiolate-ligand elimination. Protonation of [Fe(NO)(SEt)₃] ^- yielding [Fe(NO)(SPh)₃]^- by adding 3 equiv of thiophenol and transformation of [Fe(NO)(SPh)₃]^- to [Fe(NO)(SEt)₃]^- in the presence of 3 equiv of [SEt] ^-, respectively, demonstrated that complexes [Fe(NO)(SPh) ₃]^- and [Fe(NO)(SEt)₃]^- are chemically interconvertible. Mononitrosyl tris(thiolate) iron complex[Fe(NO)(SPh)₃]^- and dinitrosyl iron complex [(EtS)₂Fe(NO)₂]^- were isolated and characterized by X-ray diffraction. The mean NO bond distances of 1.181(7) A (or 1.151(7) A) in complex [(EtS)₂Fe(NO) ₂]^- are nearly at the upper end of the 1.178(3)-1.160(6) A for the anionic {Fe(NO)₂}⁹ DNICs, while the mean FeN(O) distances of 1.674(6) A (or 1.679(6) A) exactly fall in the range of 1.695(3)-1.661(4) A for the anionic {Fe(NO)₂} ⁹ DNICs.

Full text of DOI:10.1021/ic061439g

Inorg. Chem. 2006, 45, 8799−8806
-
Mononitrosyl Tris(Thiolate) Iron Complex [Fe(NO)(SPh)3] and Dinitrosyl
-
Iron Complex [(EtS)2Fe(NO)2] : Formation Pathway of Dinitrosyl Iron
Complexes (DNICs) from Nitrosylation of Biomimetic Rubredoxin
-/1-
[Fe(SR)4]2
(R ) Ph, Et)
Tsai-Te Lu, Show-Jen Chiou, Chun-Yu Chen, and Wen-Feng Liaw*
Department of Chemistry, National Tsing Hua UniVersity, Hsinchu 30013, Taiwan
Received August 1, 2006
-/1-
Nitrosylation of the biomimetic reduced- and oxidized-form rubredoxin [Fe(SR)4]2
(R ) Ph, Et) in a 1:1
stoichiometry led to the formation of the extremely air- and light-sensitive mononitrosyl tris(thiolate) iron complexes
(MNICs) [Fe(NO)(SR)3]- along with byproducts [SR]- or (RS)2. Transformation of [Fe(NO)(SR)3]- into dinitrosyl
iron complexes (DNICs) [(RS)2Fe(NO)2]- and Roussin’s red ester [Fe2(
µ
-SR)2(NO)4] occurs rapidly under addition
of 1 equiv of NO(g) and [NO]+, respectively. Obviously, the mononitrosyl tris(thiolate) complex [Fe(NO)(SR)3]- acts
as an intermediate when the biomimetic oxidized- and reduced-form rubredoxin [Fe(SR)4]2
exposed to NO(g)
-/1-
were modified to form dinitrosyl iron complexes [(RS)2Fe(NO)2]-. Presumably, NO binding to the electron-deficient
[FeIII(SR)4]- and [FeIII(NO)(SR)3]- complexes triggers reductive elimination of dialkyl/diphenyl disulfide, while binding
of NO radical to the reduced-form [FeII(SR)4]2- induces the thiolate-ligand elimination. Protonation of [Fe(NO)(SEt)3]-
yielding [Fe(NO)(SPh)3]- by adding 3 equiv of thiophenol and transformation of [Fe(NO)(SPh)3]- to [Fe(NO)(SEt)3]-
in the presence of 3 equiv of [SEt]-, respectively, demonstrated that complexes [Fe(NO)(SPh)3]- and [Fe(NO)(SEt)3]-
are chemically interconvertible. Mononitrosyl tris(thiolate) iron complex [Fe(NO)(SPh)3]- and dinitrosyl iron complex
[(EtS)2Fe(NO)2]- were isolated and characterized by X-ray diffraction. The mean NO bond distances of 1.181(7)
Å (or 1.191(7) Å) in complex [(EtS)2Fe(NO)2]- are nearly at the upper end of the 1.178(3)
−1.160(6) Å for the
9
anionic
{
Fe(NO)2
}
DNICs, while the mean FeN(O) distances of 1.674(6) Å (or 1.679(6) Å) exactly fall in the range
9
of 1.695(3)
−1.661(4) Å for the anionic {Fe(NO)2} DNICs.
Introduction
Extensive EPR studies have identified nitrosyl non-heme iron
complexes as products from the interaction of NO with
several iron-sulfur and other iron-containing proteins.1-5
Coordination of NO with [Fe-S] clusters is thought to result
in impairment of metabolic functions.6 It is also proposed
Dinitrosyl iron complexes (DNICs) have been suggested
as intermediates of iron-catalyzed degradation and formation
of S-nitrosothiols (RSNO) and as one of two possible forms
for storage and transport of NO in biological systems.1
(2) (a) Badorff, C.; Fichtlscherer, B.; Muelsch, A.; Zeiher, A. M.;
Dimmeler, S. Nitric Oxide 2002, 6, 305-312. (b) Mulsch, A.;
Mordvintcev, P. I.; Vanin, A. F.; Busse, R. FEBS Lett. 1991, 294,
252-256.
(3) (a) Cruz-Ramos, H.; Crack, J.; Wu, G,; Hughes, M. N.; Scott, C.;
Thomson, A. J.; Green, J.; Poole, R. K. EMBO J. 2002, 21, 3235-
3244. (b) Sellers, V. M.; Johnson, M. K.; Dailey, H. A. Biochemistry
1996, 35, 2699-2704. (c) Schmidt, H. H. H. W FEBS Lett. 1992,
307, 102-107.
(4) Cesareo, E.; Parker, L. J.; Pedersen, J. Z.; Nuccetelli, M.; Mazzetti,
A. P.; Pastore, A.; Federici, G.; Caccuri, A. M.; Ricci, G.; Adams, J.
J.; Parker, M. W.; Bello, M. L. J. Biol. Chem. 2005, 280, 42172-
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* To whom correspondence should be addressed. E-mail: wfliaw@
mx.nthu.edu.tw.
(1) (a) Stamler, J. S. Cell 1994, 78, 931-936. (b) Stamler, J. S.; Singel,
D. J.; Loscalzo, J. Science 1992, 258, 1898-1902. (c) Ford, P. C.;
Lorkovic, I. M. Chem. ReV. 2002, 102, 993-1017. (d) Butler, A. R.;
Megson, I. L. Chem. ReV. 2002 102, 1155-1166. (e) Ueno, T.; Susuki,
Y.; Fujii, S.; Vanin, A. F.; Yoshimura, T. Biochem. Pharmacol. 2002,
63, 485-493. (f) Frederik. A. C.; Wiegant, I. Y.; Malyshev, I. Y.;
Kleschyov, A. L.; van Faassen, E.; Vanin, A. F. FEBS Lett 1999, 455,
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Chem. ReV. 2002, 102, 1019-1065. (h) McCleverty, J. A. Chem. ReV.
2004, 104, 403-418. (i) Hayton, T. W.; Legzdins, P.; Sharp, W. B.
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10.1021/ic061439g CCC: $33.50
Published on Web 09/01/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 21, 2006 8799

Lu et al.
that the interplay between NO (or some NO-derived mol-
ecules) and [Fe-S] clusters at critical catalytic sites is crucial
in the response to environmental signals within cells.6 In
addition, nitrite was demonstrated as a highly effective
species in inducing posttranslational modifications normally
associated with NO, such as heme nitrosylation and S-
nitrosation, in a variety of mammalian tissues.7 Examples
of nitric oxide coordination to iron and the spectroscopic
signals of dinitrosyl iron complexes are of much interest,
particularly in light of role(s) in sulfur-rich protein uptake
and degradation.1-7 Recently, EPR and UV-vis absorption
studies demonstrated that mammalian ferrochelatase is
strongly inhibited by nitric oxide via degradation of the
[2Fe-2S] clusters to form cysteinyl-coordinated monomeric
iron-dinitrosyl complex.8 In addition, activation of SoxR
protein, a redox-sensitive transcription activator, in Escheri-
chia coli on exposure to macrophage-generated NO was
suggested to occur through nitrosylation of the [2Fe-2S]
clusters to form protein-bound dinitrosyl-iron dithiol ad-
ducts.9 In particular, Ding and co-workers showed that when
E. coli cells are exposed to nitric oxide, the ferredoxin [2Fe-
2S] clusters are modified to form protein-bound dinitrosyl
iron complexes. In the repair of the nitric oxide-modified
ferredoxin [2Fe-2S] cluster, the dinitrosyl iron complexes
can be directly transformed back to the ferredoxin [2Fe-
2S] cluster by cysteine desulfurase (IscS) and L-cysteine in
vitro with no need for the addition of iron or any other protein
components.10
Here the electronic structure/state of M(NO)2 unit of DNICs
is generally designated as {M(NO)2}n (M ) transition metal).
This formalism {M(NO)2}n invokes the Enemark-Feltham
notation which stresses the well-known covalence and
delocalization in the electronically amorphous M(NO)2 unit.14
In model compounds, a study with synthetic models
proposed that [2Fe-2S], as well as [4Fe-4S], clusters
reacting with NO, respectively, yield DNICs which can give
rise to the EPR g ) 2.03 signal.1d Very recently, Lippard
and co-workers reported that reaction of [Fe(StBu)4]2- and
NO(g) inCH3CN-THFledtotheformationof[Fe(NO)(StBu)3]-,15a
and the electronic structure of [Fe(NO)(StBu)3]- was char-
acterized as [FeIII(NO-)(StBu)3]-.15 The mononitrosyl iron
tris(thiolate) complex (MNIC) [Fe(NO)(StBu)3]- was sub-
sequently converted into [(StBu)2Fe(NO)2]- under limited
NO(g).15a We have shown that nitrosylation of the [2Fe-2S]
cluster [S5Fe(µ-S)2FeS5]2- yielding [S5Fe(NO)2]-, and the
reversible transformation of complex [S5Fe(NO)2]- to the
[S5Fe(µ-S)2FeS5]2- by photolysis in the presence of the NO-
acceptor reagent [(C4H8O)Fe(S,S-C6H4)2]- are consistent
with reports of in vitro the degradation of ferredoxin [2Fe-
2S] clusters to DNICs and the repair of nitric oxide-modified
[2Fe-2S] ferredoxin by cysteine desulfurase and L-cysteine.12b
In particular, the detailed spectroscopic analysis (EPR and
IR νNO spectra) may provide a superior level of insight on
discrimination of the anionic {Fe(NO)2}9 DNICs, neutral
{Fe(NO)2}9 DNIC, and Roussin’s red ester.12a We also
demonstrated that the NO-releasing ability of the anionic {Fe-
(NO)2}9 [(RS)2Fe(NO)2]- is finely tuned by the coordinated
thiolate ligands.12c The objective of this study was to
delineate the formation pathway of the anionic {Fe(NO)2}9
DNICs [(RS)2Fe(NO)2]- from nitrosylation of the biomimetic
oxidized- and reduced-form rubredoxin [Fe(SR)4]2-/1- (R )
Ph, Et)16 and to elucidate the reactivity of the mononitrosyl
tris(thiolate) complexes [Fe(NO)(SR)3]-, an intermediate for
the conversion of [Fe(SR)4]2-/1- into DNICs in the presence
of NO(g). In addition, the anionic {Fe(NO)}7 [Fe(NO)(SPh)3]-
containing monodentate phenylthiolates and the anioinic {Fe-
(NO)2}9 [(EtS)2Fe(NO)2]- containing monodentate ethylthio-
lates coordinated to the {Fe(NO)2} unit were isolated and
characterized by X-ray diffraction.
As has been known, characterization of both protein-bound
and low-molecular-weight DNICs in vitro has been made
possible via their distinctive EPR signals at g ) 2.03.1-10
To our knowledge, also known in inorganic chemistry is the
precedence for small-molecule DNICs in four oxidation
levels of the {Fe(NO)2} unit, including the EPR-active (i)
anionic {Fe(NO)2},9 (ii) neutral {Fe(NO)2},9 and (iii) cationic
{Fe(NO)2}9 DNICs coordinated by [SR]- and N-containing
ligands, as well as (iv) the EPR-silent, neutral {Fe(NO)2}10
DNICscoordinatedbyCO,PPh3,andN-containingligands.11-13
(6) Drapier, J. C. Methods 1997, 11, 319-329.
(7) Bryan, N. S.; Fernandez, B. O.; Bauer, S. M.; Garcia-Saura, M. F.;
Milsom, A. B.; Rassaf, T.; Maloney, R. E.; Bharti, A.; Rodriguez, J.;
Feelisch, M. Nat. Chem. Biol. 2005, 1, 290-297.
(8) Dailey, H. A.; Dailey, T. A.; Wu, C.-K.; Medlock, A. E.; Rose, J. P.;
Wang, K.-F. Cell. Mol. Life Sci. 2000, 57, 1909-1926.
(9) Ding, H.; Demple, B. Proc. Natl. Acad. Sci. U.S.A. 2000, 97, 5146-
5150.
(10) (a) Yang, W.; Rogers, P. A.; Ding, H. J. Biol. Chem. 2002, 277,
12868-12873. (b) Rogers, P. A.; Ding, H. J. Biol. Chem. 2001, 276,
30980-30986.
(11) (a) Chiang, C.-Y.; Miller, M. L.; Reibenspies, J. H.; Darensbourg, M.
Y. J. Am. Chem. Soc. 2004, 126, 10867-10874. (b) Baltusis, L. M.;
Karlin, K. D.; Rabinowitz, H. N.; Dewan, J. C.; Lippard, S. J. Inorg.
Chem. 1980, 19, 2627-2632.
Results and Discussion
Nitrosylation of [Fe(SPh)4]2-/1-. Upon addition of 1 equiv
of NO(g) into the CH3CN solution of the biomimetic reduced-
form rubredoxin [FeII(SPh)4]2-,16 a pronounced color change
from red-brown to purple occurs at 0 °C. The IR, UV-vis,
and single-crystal X-ray diffraction studies confirmed the
formation of the mononitrosyl tris(phenylthiolate) complex
[Fe(NO)(SPh)3]- (1) (yield 78%) accompanied by byproduct
(12) (a) Tsai, M.-L.; Liaw, W.-F. Inorg. Chem. 2006, 45, ASAP. (b) Tsai,
M.-L.; Chen, C.-C.; Hsu, I.-J.; Ke, S.-C.; Hsieh, C.-H.; Chiang, K.-A.;
Lee, G.-H.; Wang, Y.; Liaw, W.-F. Inorg. Chem. 2004, 43, 5159-
5167. (c) Tsai, F.-T.; Chiou, S.-J.; Tsai, M.-C.; Tsai, M.-L.; Huang,
H.-W.; Chiang, M.-H.; Liaw, W.-F. Inorg. Chem. 2005, 44, 5872-
5881. (d) Chen, T.-N.; Lo, F.-C.; Tsai, M.-L.; Shih, K.-N.; Chiang,
M.-H.; Lee, G.-H.; Liaw, W.-F. Inorg. Chimi. Acta 2006, 359, 2525-
2533. (e) Hung, M.-C.; Tsai, M.-C.; Liaw, W.-F. Inorg. Chem. 2006,
45, 6041-6047. (f) Butler, A. R.; Glidewell, C.; Li, M.-H. AdV. Inorg.
Chem. 1988, 32, 335-393.
(14) Enemark, J. H.; Feltham, R. D.Coord. Chem. ReV. 1974, 13, 339-
406.
(15) (a) Harrop, T. C.; Song, D. T.; Lippard, S. J. J. Am. Chem. Soc. 2006,
128, 3528-3529. (b) Jaworska, M.; Stasicka, Z. J. Organomet. Chem.
2004, 689, 1702-1713.
(16) (a) Rao, P. V.; Holm, R. H. Chem. ReV. 2004, 104, 527-559. (b)
Arulsamy, N.; Bohle, D. S.; Butt, J. A.; Irvine, G. J.; Jordan, P. A.;
Sagan, E. J. Am. Chem. Soc. 1999, 121, 7115-7123.
(13) Reginato, N.; McCrory, C. T. C.; Pervitsky, D.; Li, L. J. Am. Chem.
Soc. 1999, 121, 10217-10218.
8800 Inorganic Chemistry, Vol. 45, No. 21, 2006

[Fe(NO)(SPh)3]- and [(EtS)2Fe(NO)2]-
Scheme 1
Table 1. Selected Infrared and UV-vis Data for the MNICs and
DNICs
complex
IR (cm-1
)
UV (nm)
ref
MNICs
1
4
1731a
1697a
1703a
500a
this work
this work
15a
459a
[Et4N][Fe(StBu)3(NO)]-
370, 475a
DNICs
2
5
1693, 1737a 479, 798a
1674, 1715a 436, 802a
this work
this work
[PPN][(S(CH2)3S)Fe(NO)2] 1671, 1712a 430, 578, 807a 12e
[Et4N][(StBu)2Fe(NO)2]-
(H+bme-daco)Fe(NO)2
[(C9H21N2S2)Fe(NO)2]
1690, 1739b N/A
1696, 1740a N/A
1695, 1740c N/A
15a
11a
11b
a THF. b CH3CN. c KBr.
1
[PPN][SPh] identified by IR (KBr) and H NMR (Scheme
1a). Instead of phenylthiolate-ligand displacement observed
in the reaction of [FeII(SPh)4]2- and NO(g), reaction of NO(g)
with the oxidized-form [FeIII(SPh)4]- in a 1:1 stoichiometry
in CH3CN also led to the formation of complex 1 but
accompanied by byproduct (PhS)2 characterized by IR (KBr)
Figure 1. Infrared νNO absorbance changes for the reaction of complex 1
with NO(g) in a 1:1 stoichiometry in CH3CN at ambient temperature. Curve
(- -) corresponds to complex 1, and curve (s) corresponds to the formation
of complex 2.
1
and H NMR (Scheme 1b). Obviously, NO radical binding
toanelectron-deficientiron(III)centerofcomplex[FeIII(SPh)4]-
triggers reductive elimination of the coordinated phenylthio-
late ligand to yield complex 1 and diphenyl disulfide, in
contrast to the phenylthiolate-ligand elimination observed in
the nitrosylation of complex [FeII(SPh)4]2- containing the
relative electron-rich iron(II) center.
to purple was observed. The reaction mixture led to the
isolation of the extremely air- and light-sensitive complex
1, accompanied by byproduct (PhS)2 identified by IR and
1H NMR. Interestingly, reaction of [FeII(SPh)4]2- and [PPN]-
[NO2], the NO-derived molecule, also led to the formation
of complex 1 in CH2Cl2.
Complex 1 is extremely air- and light-sensitive in solution
and solid states. The EPR spectrum (g values at 3.76 and
2.012 in CH2Cl2-toluene (1:1 volume ratio) frozen solution
at 4 K, Supporting Information Figure S1)12f,15 and the
magnetic measurement (the temperature-dependent effective
magnetic moment µeff decreases from 3.83 µB at 300 K to
3.66 µB at 50 K, Supporting Information Figure S2) of
complex 1 are consistent with the Fe(III)-NO- electronic
configuration in a tetrahedral ligand field, as characterized
by Lippard and co-workers in complex [Fe(NO)(StBu)3]-.15
The infrared spectrum of complex 1 shows one broad
stretching band (1726 (KBr), 1732 cm-1 (THF)) in the υNO
region, which shifts to 1697 cm-1 (THF) upon isotopic
substitution with 15NO. The higher-energy υNO band of
complex 1 shifted by 22 cm-1 from that of complex
[Fe(NO)(StBu)3]- (νNO 1704 cm-1 (KBr)) is consistent with
the weaker electron-donating character of [PhS]- ligand,
compared to [StBu]- (Table 1).15 In addition, the formation
of complex 1 was also displayed by reaction of [FeII(SPh)4]2-
and [NO][BF4]. When a CH3CN solution of complex
[FeII(SPh)4]2- was treated with 1 equiv of [NO][BF4], an
immediate change in color of the solution from red-brown
When 1 equiv of NO(g) (or [(Ph)3CSNO]) was added to
the THF solution of complex 1 at ambient temperature, a
rapid reaction occurred to afford the well-known dinitrosyl
iron complex [(PhS)2Fe(NO)2]- (2) accompanied by the
liberation of diphenyl disulfide identified by IR (KBr) and
1H NMR (Scheme 1c). The shift of the νNO stretching
frequencies from 1734 (complex 1) to 1745, 1698 cm-1 (CH3-
CN) confirmed the formation of complex 2 (Figure 1). The
conversion of complexes 1 to 2 was also monitored by UV-
vis spectrometry; the intense band at 500 nm disappeared,
accompanied by the simultaneous formation of two absorp-
tion bands at 479 and 798 nm (complex 2) (Figure 2). As
observed in the nitrosylation of the [FeIII(SPh)4]- complex,
the reaction mechanism, NO binding to the electron-deficient
iron(III) center of complex 1 triggering the reductive
elimination of the coordinated phenylthiolate ligand to yield
complex 2, was proposed. Instead of the formation of
complex 2, treatment of complex 1 with 1 equiv of [NO]-
[BF4] in THF solution at ambient temperature led to the
Inorganic Chemistry, Vol. 45, No. 21, 2006 8801

Lu et al.
stability to light. Presumably, the more electron-donating
functionality of the coordinated ethylthiolates in complex 4
is responsible for the stabilization of the [Fe(III)-NO-]
state.15
Consistent with the stronger electron-donating thiolates
[R′S]- promoting thiolate-ligand exchange of complex
[(RS)2Fe(NO)2]- to produce the stable [(R′S)2Fe(NO)2]-
observed in the previous study,12c quantitative transformation
of complex 1 to complex 4 was displayed and monitored by
IR νNO spectra. The shift of the NO stretching frequency
from 1734 cm-1 to the lower frequency 1704 cm-1 confirmed
the formation of complex 4 (yield 90%) when CH3CN
solution of complex 1 was reacted with 3 equiv of [SEt]-
(Scheme 1f). Complex 4 does not react with [SPh]- via
thiolate-ligand exchange to form complex 1. Conversion of
complex 4 to complex 1 was expected to be driven by
protonation (PhSH) of complex 4; reaction of complex 4 and
3 equiv of thiophenol in THF led to the isolation of complex
1. Presumably, protonation (electrophilic reaction of PhSH)
of complex 4 by thiophenol occurs only at the more
accessible, electron-rich sulfur site to form complex 1 (yield
95%) at ambient temperature (Scheme 1f). Obviously,
mononitrosyl tris(phenylthiolate) complex 1 containing the
coordinated phenylthiolate ligands and complex 4 containing
the coordinated ethylthiolate ligands are chemically inter-
convertible.
Isolation of the Stable [(EtS)2Fe(NO)2]- (5) with Ethyl-
thiolates Coordinated to a {Fe(NO)2}9 Motif. Of impor-
tance is that the conversion of complex 4 to the stable
[(EtS)2Fe(NO)2]- (5) was displayed when 1 equiv of NO(g)
was added to the THF solution of complex 4 at ambient
temperature (Scheme 1g), the color of the solution changed
from red to reddish-brown, where the IR υNO stretching
frequency at 1697 cm-1 (THF) disappeared with the forma-
tion of two stretching frequencies at 1715 and 1674 cm-1
(THF). The dark red-brown complex 5 was isolated in 90%
yield after the reaction solution was separated from (SEt)2
and recrystallized with hexane. Consistent with the charac-
teristic g value of DNICs,9-15 complex 5 exhibits an isotropic
EPR spectrum with signal at g ) 2.028 at 298 K (Supporting
Information Figure S3).12f Magnetic susceptibility data of a
powdered sample of complex 5 was collected in the
temperature range of 2-300 K in a 0.5 T applied field. The
effective magnetic moment (µeff) decreases from 2.8 at 300
K to 1.77 at 8 K (Supporting Information Figure S4). As
observed in the previous study,12c the temperature-dependent
magnetic moment in complex 5 may be contributed from
the antiferromagnetic interactions between the Fe+ (d7, S )
3/2) center and two •NO (S ) 1/2) radicals, and the dynamic
resonance hybrid of {Fe+(•NO)2}9 and {Fe-(+NO)2}9 by
temperature. The IR spectra for DNICs 2 and 5 had the same
pattern but differed in position (1737, 1693 cm-1 for complex
2 vs 1715, 1674 cm-1 for complex 5). The surprisingly stable
complex 5 is the first example of the anionic {Fe(NO)2}9
DNICs [(RS)2Fe(NO)2]- containing monodentate alkylthio-
lates coordinated to the {Fe(NO)2}9 motif isolated and
characterized by single-crystal X-ray diffraction.11 This
complex represents an important starting point to understand
Figure 2. Conversion of complex 1 to complex 2 monitored by UV-vis
spectrometry under addition of 1 equiv of NO(g) to complex 1 in THF at
ambient temperature. The absorption band at 500 nm (- -) disappeared
followed by the simultaneous formation of two absorption bands at 479
and 798 nm (s).
Scheme 2
formation of [Fe2(µ-SPh)2(NO)4] (3) (yield 95%),17 and the
byproduct (PhS)2 identified by IR (KBr) and 1H NMR. The
formation of complex 3 under [NO]+ oxidation of complex
1 may be accounted for by the following reaction sequence;
the [NO]+ oxidant has available only the ability of oxidizing
the coordinated phenylthiolate of complex 1 to produce a
thiyl radical ([PhS]•) (subsequently coupled to yield (PhS)2)
and NO radical, followed by the rapid binding of a generated
NO radical leading to the buildup of unstable, neutral {Fe-
(NO)2}8 [(PhS)2Fe(NO)2] (A) species (Scheme 2). This
highly reactive, neutral {Fe(NO)2}8 species A is then driven
by the formation of complex 3 via an intramolecular
reductive elimination of diphenyl disulfide (Scheme 2).
Nitrosylation of [FeIII(SEt)4]-. To further corroborate the
formation mechanism of DNICs from nitrosylation of
[Fe(SR)4]2-/1- and investigate the stability/reactivity of the
anionic {Fe(NO)}7 MNICs [Fe(NO)(SR)3]- and {Fe(NO)2}9
DNICs [(RS)2Fe(NO)2]-, the reaction of the biomimetic
oxidized-form rubredoxin [FeIII(SEt)4]- was investigated. As
shown in Scheme 1e, when complex [FeIII(SEt)4]- was
treated with 1 equiv of NO(g) in CH3CN at 0 °C, a rapid
reaction ensues over the course of 1 min to give the stable,
purple complex [Fe(NO)(SEt)3]- (4) (yield 74%) after
1
removal of (SEt)2 identified by IR (KBr) and H NMR. In
comparison with complex 1 dominated by one intense
absorption band at 500 nm (THF), the electronic spectrum
of complex 4 coordinated by the more electron-donating
ethylthiolates displays a blue-shift to 459 nm (Table 1). In
contrast to complex 1, which is unstable in THF solution,
the ligand-modified analogue complex 4 displays more
(17) Rauchfuss, T. B.; Weatherill, T. D. Inorg. Chem. 1982, 21, 827-
830.
8802 Inorganic Chemistry, Vol. 45, No. 21, 2006

[Fe(NO)(SPh)3]- and [(EtS)2Fe(NO)2]-
Table 2. Selected Bond Length (Å) and Angle (deg) for Complex 1
and [Fe(StBu)3((NO)]- 15a
complex
Fe-N
1
[Fe(StBu)3(NO)]-
1.682
2.272
1.169
108.7
109.2
116.5
103.9
108.4
109.5
164.6
1.171
2.274
1.168
103.2
109.2
113.2
105.4
109.9
116.1
174.2
Fe-S (average)
N-O
N-Fe-S
N-Fe-S
N-Fe-S
S-Fe-S
S-Fe-S
S-Fe-S
Fe-N-O
are consistent with the distorted tetrahedral coordination
environment about Fe(1) of complex 1. It is noticed that the
NO bond length of 1.169(6) Å in complex 1 is longer than
that of 1.1677(19) Å in complex [Fe(NO)(StBu)3]-, and the
Fe(1)N(1) bond length of 1.682(5) Å in complex 1 is shorter
than that of 1.7110(14) Å in complex [Fe(NO)(StBu)3]-
(Table 2).15a Interestingly, the Fe-N-O bond angle of 164.6-
(5)° in complex 1 is distinct from that of 174.18(13)° in
complex [Fe(NO)(StBu)3]-.15a The changes in Fe-N-O
bond angle from the bent form (164.6(5)° for complex 1) to
the less-bent form (170.3(6)°/172.9(6)° for complex 5) are,
presumably, caused by electronic perturbation from the {Fe-
(NO)}7 complex 1 to the {Fe(NO)2}9 complex 5. The X-ray
crystal structure of complex 5 consists of two crystallo-
graphically independent molecules (Figure 4). The geometry
of iron center of complex 5 is best described as a distorted
tetrahedral with N(3)-Fe(1)-N(4), N(4)-Fe(1)-S(1), and
S(1)-Fe(1)-S(2) bond angles of 121.5(3)°, 99.8(2)°, and
106.72(8)°, respectively. The mean NO bond distances of
1.191(7) (1.194(6) and 1.188(7) Å) and 1.181(7) Å (1.180-
(7) and 1.182(7) Å) in complex 5, comparable to the average
NO bond distance of 1.186(7) Å observed in [(H+bme-daco)-
Fe(NO)2] (Table 3),11a are nearly at the upper end of the
1.178(3)-1.160(6) Å for the anionic {Fe(NO)2}9 DNICs,
while the mean FeN(O) distances of 1.674(6) Å (or 1.679-
(6) Å) in complex 5 exactly fall in the range of 1.695(3)-
1.661(4) Å for the anionic {Fe(NO)2}9 DNICs.12
Figure 3. ORTEP drawing and labeling scheme of [Fe(NO)(SPh)3]- with
thermal ellipsoids drawn at 50% probability. Selected bond distances (Å)
and angles (deg): Fe(1)-N(1) 1.682(5); Fe(1)-S(3) 2.2670(14); Fe(1)-
S(1) 2.2696(12); Fe(1)-S(2) 2.2780(13); O(1)-N(1) 1.169(6); N(1)-Fe-
(1)-S(3) 108.69(18); N(1)-Fe(1)-S(1) 109.19(18); S(3)-Fe(1)-S(1)
103.87(5); N(1)-Fe(1)-S(2) 116.52(16); S(3)-Fe(1)-S(2) 108.35(5);
S(1)-Fe(1)-S(2) 109.47(5).
Figure 4. ORTEP drawing and labeling scheme of [(EtS)2Fe(NO)2]- with
thermal ellipsoids drawn at 50% probability. Selected bond distances (Å)
and angles (deg): Fe(1)-N(3) 1.673(6); Fe(1)-N(4) 1.674(6); Fe(1)-S(1)
2.2659(19); Fe(1)-S(2) 2.283(2); Fe(2)-N(5) 1.679(6); Fe(2)-N(6) 1.678-
(6); Fe(2)-S(3) 2.269(2); Fe(2)-S(4) 2.273(2); O(1)-N(3) 1.194(6); O(2)-
N(4) 1.188(7); O(3)-N(5) 1.180(7); O(4)-N(6) 1.182(7); N(3)-Fe(1)-
N(4) 121.5(3); N(3)-Fe(1)-S(1) 108.6(2); N(4)-Fe(1)-S(1) 99.8(2);
N(3)-Fe(1)-S(2) 107.7(2); N(4)-Fe(1)-S(2) 111.4(2); S(1)-Fe(1)-S(2)
106.72(8); N(5)-Fe(2)-N(6) 123.1(3); N(5)-Fe(2)-S(3) 109.9(2); N(6)-
Fe(2)-S(3) 107.0(2); N(5)-Fe(2)-S(4) 99.3(2); N(6)-Fe(2)-S(4) 108.66-
(19); S(3)-Fe(2)-S(4) 107.91(8).
Conclusion and Comments. Studies on nitrosylation of
the biomimetic reduced- and oxidized-form rubredoxin
[Fe(SR)4]2-/1- (R ) Ph, Et) and the reactivity/transformation
between mononitrosyl tris(thiolate) iron complexes [Fe(NO)-
(SR)3]- and dinitrosyl iron complexes [(RS)2Fe(NO)2]- have
resulted in the following results.
(1) Nitrosylation of complexes [Fe(SR)4]2-/1- (R ) Ph,
Et) in a 1:1 stoichiometry led to the formation of the
extremely air- and light-sensitive mononitrosyl tris(thiolate)
iron complexes [Fe(NO)(SR)3]- along with byproducts [SR]-
or (RS)2. The facile transformations of MNICs [Fe(NO)(SR)3]-
into DNICs [(RS)2Fe(NO)2]- and [Fe2(µ-SR)2(NO)4] under
1 equiv of NO(g) and [NO]+, respectively, were also
demonstrated. Obviously, the mononitrosyl tris(thiolate)
complex [Fe(NO)(SR)3]- serves as an intermediate during
the nitrosylation of the biomimetic oxidized- and reduced-
form rubredoxin [Fe(SR)4]2-/1- to form [(RS)2Fe(NO)2]-.
the factors that are responsible for the stability and reactivity
of the anionic {Fe(NO)2}9 alkylthiolate-containing DNICs.
Transformation of complex 5 to complex 2 was displayed
when reaction of complex 5 and 2 equiv of thiophenol in
THF. Consistent with the facile conversion of complex 1 to
complex 4 under reaction of complex 1 and 3 equiv of
[SEt]-, the coordinated [SPh]- ligands of complex 2 were
replaced by the stronger electron-donating ethylthiolate
[SEt]- to yield complex 5 when reacting complex 2 with 3
equiv of [SEt]- (or more) in CH3CN at ambient temperature
(Scheme 1h′). Conversion of complex 2 into complex 5 was
observed only in the presence of 3 equiv (or more) of [SEt]-
and complex 2 in CH3CN at ambient temperature.
Structures. Figures 3 and 4 display the thermal ellipsoid
plot of the anionic complexes 1 and 5, respectively, and
selected bond distances and angles are given in the figure
captions. The N(1)-Fe(1)-S(3), N(1)-Fe(1)-S(1), S(3)-
Fe(1)-S(2), and S(1)-Fe(1)-S(2) bond angles of 108.69-
(18)°, 109.19(18)°, 108.35(5)°, and 109.47(5)°, respectively,
(2) Reductive elimination of dialkyl/diphenyl disulfides
occurs when NO binds to the electron-deficient Fe(III) [FeIII-
Inorganic Chemistry, Vol. 45, No. 21, 2006 8803

Lu et al.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for Complex 5, [(C9H21N2S2)Fe(NO)2],11b [(H+Bme-daco)Fe(NO)2],11a and
[(S(CH2)3S)Fe(NO)2]- 12e
complex
5
(C9H21N2S2)Fe(NO)2
(H+bme-daco)Fe(NO)2
[(S(CH2)3S)Fe(NO)2]-
Fe-N
1.676
2.273
1.186
122.3
99.6
107.8
108.6
110.7
106.9
172.1
1.680
2.270
1.160
118.1
103.5
103.8
111.5
118.8
109.2
169.8
1.669
2.278
1.186
117.5
103.4
103.6
110.0
111.7
111.1
171.5
1.676
2.258
1.178
118.6
107.6
107.9
108.5
111.7
100.9
170.1
Fe-S
N-O
N-Fe-N
N-Fe-S
N-Fe-S
N-Fe-S
N-Fe-S
S-Fe-S
Fe-N-O
(iv) transformation of the neutral {Fe(NO)2}9 [(RS)(L′)Fe-
(NO)2] (L′ ) N-containing ligand) to the anionic {Fe(NO)2}9
[(RS)2Fe(NO)2]- by ligand replacement,12a (v) the direct
nitrosylation of the biomimetic [2Fe-2S] cluster in the
presence of S-trapping agent,12b and (vi) the direct nitrosy-
lation of the biomimetic reduced- and oxidized-form rubre-
doxin[Fe(SR)4]2-/1- viaintermediateMNIC[Fe(NO)(SR)3]-,15a
as shown in this study (Scheme 3).
Scheme 3
These results may also predict/decipher that the most
straightforward and facile pathway of the formation of the
anionic {Fe(NO)2}9 DNICs [(RS)2Fe(NO)2]- is the direct
nitrosylation of [Fem(SR)n]x- clusters (e.g., [Fe(SR)4]2-/1- and
[(RS)2Fe(µ-S)2Fe(SR)2]2-), i.e., the direct nitrosylation of
[1Fe-0S]/[2Fe-2S] iron-sulfur proteins in biology. Presum-
ably, the formation of DNICs via combination of Fe2+ ion,
S-cysteine and NO, as suggested by biochemists,1-2,18 may
occur through the original formation of the [Fem(SR)n]x-
clusters followed by nitrosylation as observed in this study.
For the synthetic methodology, the isolation of complex
5 shows that the synthetic pathway may play a key role in
synthesizing the stable DNICs [(RS)2Fe(NO)2]- containing
alkylthiolates coordinated to {Fe(NO)2}9 motif.11,12
(SR)4]-/[FeIII(NO)(SR)3]- complexes, while binding of NO
radical to the reduced-form [FeII(SR)4]2- induces the thiolate-
ligand ([SR]-) elimination.
(3) Complex 1 containing phenylthiolates coordinated to
{Fe(NO)}7 motif and complex 5 containing ethylthiolates
coordinated to {Fe(NO)2}9 motif were isolated and charac-
terized by X-ray diffraction. The mean Fe-N(O) distances
of 1.674(6) Å (or 1.679(6) Å) in complex 5 exactly fall in
the range of 1.695(3)-1.661(4) Å for the anionic {Fe(NO)2}9
DNICs.12e
(4) In addition to the combination reaction of iron salts,
NO and ligands [RS]- yielding a EPR-detectable, four-
coordinated DNICs,18 six synthetic routes leading to the
formation of the anionic {Fe(NO)2}9 [(RS)2Fe(NO)2]- were
demonstrated (Scheme 3): (i) the facile transformation of
the neutral {Fe(NO)2}10 [(L)2Fe(NO)2] (L ) N-containing
neutral ligands) to the anionic {Fe(NO)2}9 [(RS)2Fe(NO)2]-
via the cationic {Fe(NO)2}9 [(L)2Fe(NO)2]+ followed by
addition of 2 equiv of thiolates,12e (ii) reaction of the anionic
{Fe(NO)2}9 [(R′S)2Fe(NO)2]- and PhSH/[RS]-/(RS)2 yield-
ing the stable anionic {Fe(NO)2}9 [(RS)2Fe(NO)2]- by
protonation, ligand-exchange reaction and S-S bond activa-
tion, respectively,12 (iii) conversion of Roussin’s red ester
into the anionic [(RS)2Fe(NO)2]- triggered by the nucleo-
philic thiolates inducing the cleavage of bridging thiolates,12
Experimental Section
Manipulations, reactions, and transfers were conducted under
nitrogen according to Schlenk techniques or in a glovebox (argon
gas). Solvents were distilled under nitrogen from appropriate drying
agents (diethyl ether from CaH2; acetonitrile from CaH2/P2O5;
methylene chloride from CaH2; methanol from Mg/I2; hexane and
tetrahydrofuran (THF) from sodium benzophenone) and stored in
dried, N2-filled flasks over 4 Å molecular sieves. Nitrogen was
purged through these solvents before use. Solvent was transferred
to the reaction vessel via stainless cannula under positive pressure
of N2. The reagents thiophenol, sodium nitrite, nitrosonium tet-
rafluroborate ([NO][BF4]), iron trichloride, ethanethiol (Aldrich),
bis(triphenylphosphoranylidene)ammonium chloride ([PPN][Cl])
(Fluka) were used as received. The NO(g) (SanFu, 10% NO + 90%
N2) was passed through an Ascarite II column to remove higher
nitrogen oxides before use.19 Compounds [PPN]2[FeII(SPh)4],16a
[PPN][FeIII(SPh)4],16a [PPN][FeIII(SEt)4],16a and S-nitrosothiol
([(Ph)3CSNO])16b were synthesized by published procedures.
Infrared spectra of the νNO stretching frequencies were recorded
on a PerkinElmer model spectrum One B spectrometer with sealed
solution cells (0.1 mm, KBr windows). UV-vis spectra were
(18) McDonald, C. C.; Phillips, W.; Mower, H. F. J. Am. Chem. Soc. 1965,
87, 3319-3326.
(19) Works, C. F.; Jocher, C. J.; Bart, G. D.; Bu, X.; Ford, P. C. Inorg.
Chem. 2002, 41, 3728-3739.
8804 Inorganic Chemistry, Vol. 45, No. 21, 2006

[Fe(NO)(SPh)3]- and [(EtS)2Fe(NO)2]-
recorded on a Jasco V-570 spectrometer. Analyses of carbon,
hydrogen, and nitrogen were obtained with a CHN analyzer
(Heraeus).
formation of the known [PPN][(PhS)2Fe(NO)2] (2).12c Hexane was
added to precipitate complex 2 (yield 0.063 g, 72%) characterized
by IR (νNO 1737, 1693 cm-1 (THF)) and UV-vis (479, 798 nm
(THF)), and byproduct (PhS)2 soluble in THF/hexane solution was
Reaction of [PPN]2[FeII(SPh)4] and NO(g). Method A. Under
N2 atmosphere, to a CH3CN solution (3 mL) of [PPN]2[Fe(SPh)4]
(0.16 g, 0.1 mmol) was added NO(g) (24 mL (10% NO + 90%
N2), 0.1 mmol) via a gastight syringe at 0 °C. The reaction solution
was stirred and monitored by FTIR immediately. The IR υNO
spectrum shows a strong stretching band at 1734 cm-1 (CH3CN).
The solution was then dried under vacuum, and the crude solid
was redissolved in THF/diethyl ether (1:1 volume ratio). The
mixture solution was filtered to remove the insoluble [PPN][SPh]
1
isolated and identified by IR (KBr) and H NMR.
Reaction of [PPN][Fe(SPh)3(NO)] (1) and [NO][BF4]. A CH3-
CN solution (7 mL) of [NO][BF4] (0.058 g, 0.5 mmol) was added
drop by drop to a CH3CN solution (5 mL) of complex 1 (0.476 g,
0.5 mmol) via cannula under positive N2 pressure. The solution
was stirred for 10 min at ambient temperature. The IR νNO spectrum
displays three stretching bands at 1757 s, 1784 s, 1815 w cm-1
(CH3CN) assigned to the formation of the known [Fe2(µ-SPh)2-
(NO)4] (3).17 The solution mixture was dried under vacuum and
then redissolved in THF (10 mL). The solution mixture was filtered
to remove the insoluble [PPN][BF4]. The filtrate was concentrated
under vacuum, and then hexane was added to precipitate the red-
brown complex 3 (yield 0.214 g, 95%). The byproduct (PhS)2
existing in the THF/hexane solution was then isolated and identified
1
characterized by IR (KBr) and H NMR. Addition of hexane to
the filtrate (THF/diethyl ether solution) led to the precipitation of
dark purple solid [PPN][Fe(SPh)3(NO)] (1) (yield 0.74 g, 78%).
Hexane was added slowly to the layer above the THF solution of
complex 1. The flask was tightly sealed and kept in the refrigerator
at 10 °C for 4 days. The dark purple crystals suitable for X-ray
diffraction analysis were isolated.
1
by IR (KBr) and H NMR.
Method B. A CH3CN solution (7 mL) of [NO][BF4] (0.058 g,
0.5 mmol) was added in a dropwise manner to a CH3CN solution
of [PPN]2[Fe(SPh)4] (0.79 g, 0.5 mmol) at 0 °C under N2
atmosphere. The reaction solution was stirred for 10 min. The IR
νNO spectrum shows a strong absorption band at 1734 cm-1. The
solution mixture was then dried under vacuum. The crude solid
was redissolved in THF and then filtered to remove the insoluble
[PPN][BF4]. Hexane was then added to precipitate the dark purple
solid [PPN][Fe(SPh)3(NO)] (1) (yield 0.4 g, 84%), and the
byproduct (PhS)2 soluble in THF/hexane solution was isolated and
Preparation of [PPN][Fe(SEt)3(NO)] (4). Complex [PPN][Fe-
(SEt)3(NO)] (4) was prepared in the same manner as described in
the synthesis of complex 1. To a CH3CN solution (3 mL) of [PPN]-
[FeIII(SEt)4] (0.168 g, 0.2 mmol) was added NO(g) (48 mL (10%
NO + 90% N2), 0.2 mmol) via a gastight syringe at 0 °C. The
solution was stirred under anaerobic condition at room temperature
for 10 min and monitored by IR. The IR νNO spectrum shows a
strong absorption at 1704 cm-1 (CH3CN). The solution was dried
under vacuum, and the crude solid was redissolved in THF. Hexane
was then added to precipitate complex 4 (yield 0.12 g, 74%). IR
1
identified by IR (KBr) and H NMR.
ν
NO: 1697 cm-1 (THF), 1704 cm-1 (CH3CN). Absorption spectrum
(THF) [λmax, nm (ꢀ, M-1 cm-1)]: 459(2733).
Method C (Reaction of [PPN]2[FeII(SPh)4] and [PPN][NO2]).
Complexes [PPN]2[Fe(SPh)4] (0.314 g, 0.2 mmol) and [PPN][NO2]
(0.117 g, 0.2 mmol) loaded in a 10-mL tube were dissolved in CH2-
Cl2 (7 mL). The solution was stirred for 10 min at ambient
temperature under N2 atmosphere. The IR νNO spectrum shows a
strong absorption band at 1737 cm-1. Hexane was added to
precipitate the dark purple solid, and the dark purple solid was dried
after solvent was removed. The crude solid was then redissolved
in THF. The mixture solution was filtered to remove the insoluble
solid, and hexane was added to lead to the precipitation of [PPN]-
[Fe(SPh)3(NO)] (1) (yield 0.076 g, 40%). IR νNO: 1732 (THF),
1734 (CH3CN), 1737 cm-1 (CH2Cl2). IR ν15NO: 1697 cm-1 (THF).
Absorption spectrum (THF) [λmax, nm (ꢀ, M-1 cm-1)]: 500 (1951).
Anal. Calcd for C54H45N2OP2S3Fe: C, 68.13; H, 4.76; N, 2.94.
Found: C, 68.65; H, 5.18; N, 2.92.
Transformation of [PPN][Fe(SPh)3(NO)] (1) into [PPN][Fe-
(SEt)3(NO)] (4). Complexes 1 (0.095 g, 0.1 mmol) and [PPN][SEt]
(0.18 g, 0.3 mmol) were dissolved in THF (5 mL) under N2
atmosphere. The solution mixture was stirred for 10 min at ambient
temperature. IR νNO spectrum displaying a strong stretching band
at 1697 cm-1 (THF) shows the formation of complex 4. Diethyl
ether (5 mL) was added to the mixture solution, and then the mixture
solution was filtered to remove the insoluble [PPN][SPh]. Hexane
was added to the filtrate to precipitate the red-brown complex 4
(yield 0.073 g, 90%) characterized by IR and UV-vis.
Conversion of [PPN][Fe(SEt)3(NO)] (4) into [PPN][Fe(SPh)3-
(NO)] (1). A THF solution (3 mL) of [PPN][Fe(SEt)3(NO)] (0.081
g, 0.1 mmol) was added to thiophenol (HSPh, 31 µL) by
microsyringe under N2 atmosphere. The reaction solution was stirred
for 10 min at ambient temperature. The IR νNO spectrum showing
a strong stretching band at 1732 cm-1 shifted from 1697 cm-1
(THF) confirmed the formation of complex 1. Hexane was then
added to precipitate the dark purple complex 1 (yield 0.09 g, 95%)
characterized by IR and UV-vis.
Reaction of [PPN][Fe(SEt)3(NO)] (4) and NO(g). To a THF
solution (3 mL) of complex 4 (0.081 g, 0.1 mmol) was added NO(g)
(24 mL (10% NO + 90% N2), 0.1 mmol) via a gastight syringe at
0 °C. The reaction solution was stirred for 10 min at ambient
temperature and monitored by IR. The IR νNO spectrum displays
two bands at 1715 and 1674 cm-1 (THF). Hexane was slowly added
to precipitate the red-brown solid characterized as 5 (yield 0.054
g, 69%). Hexane was added slowly to layer above the THF solution
of complex 5. The flask was tightly sealed and kept in the
refrigerator at 10 °C for 4 days. Dark red-brown crystals suitable
for X-ray diffraction analysis were obtained. IR νNO: 1715, 1674
cm-1 (THF), 1722, 1680 cm-1 (CH3CN). Absorption spectrum
(THF) [λmax, nm (ꢀ, M-1 cm-1)]: 436(2839), 802(430). Anal. Calcd
Reaction of [PPN][FeIII(SPh)4] and NO(g). To a CH3CN solution
(5 mL) of [PPN][Fe(SPh)4] (0.21 g, 0.2 mmol) was added NO(g)
(48 mL (10% NO + 90% N2), 0.2 mmol) via a gastight syringe at
0 °C, followed by stirring another 5 min at ambient temperature
under N2 atmosphere. The IR νNO spectrum shows a strong
absorption band at 1734 cm-1 (CH3CN) assigned to the formation
of complex 1. Solvent was then removed under vacuum. The crude
solid was redissolved in THF and recrystallized in THF/hexane.
The byproduct (PhS)2 soluble in THF/hexane solution was then
isolated and identified by IR and 1H NMR. The dark purple crystals
were collected, washed with diethyl ether, and dried to afford
complex 1 (yield 0.064 g, 34%) characterized by IR and UV-vis.
Reaction of [PPN][Fe(SPh)3(NO)] (1) and NO(g). To a THF
solution (3 mL) of complex 1 (0.095 g, 0.1 mmol) was added NO(g)
(24 mL (10% NO + 90% N2), 0.1 mmol) via a gastight syringe.
The solution was stirred under anaerobic condition for 10 min at
ambient temperature. The IR νNO spectrum shows two strong
stretching bands at 1737 and 1693 cm-1 (THF), assigned to the
Inorganic Chemistry, Vol. 45, No. 21, 2006 8805

Lu et al.
for C40H40N3O2P2S2Fe: C, 61.86; H, 5.19; N, 5.41. Found: C,
62.57; H, 5.29; N, 5.13.
under 0.5 (or 1) T external magnetic field in the temperature range
of 2-300 K. The magnetic susceptibility data was corrected with
Transformation of [PPN][(SPh)2Fe(NO)2] (2) into [PPN]-
[(SEt)2Fe(NO)2] (5). Complexes 2 (0.087 g, 0.1 mmol) and [PPN]-
[SEt] (0.18 g, 0.3 mmol) were dissolved in CH3CN (5 mL) under
N2 atmosphere. The solution mixture was stirred for 10 min at
ambient temperature. The IR νNO spectrum displaying two strong
stretching bands at 1722 and 1680 cm-1 (CH3CN) shows the
formation of complex 5. Diethyl ether (5 mL) was added to the
mixture solution, and then the mixture solution was filtered to
remove the insoluble [PPN][SPh] and the excess [PPN][SEt].
Hexane was added to the filtrate to precipitate the red-brown
complex 5 (yield 0.066 g, 90%) characterized by IR and UV-vis.
Reaction of [PPN][Fe(SPh)3(NO)] (1) and S-Nitrosothiol
([(Ph)3CSNO]). A CH2Cl2 solution (3 mL) of [(Ph)3CSNO] (0.031
g, 0.1 mmol) was added to a CH2Cl2 (3 mL) solution of complex
1 (0.095 g, 0.1 mmol) via cannula under positive N2 pressure. The
reaction solution was stirred for 2 h at ambient temperature and
monitored by FTIR. The IR νNO spectrum shows two strong
stretching bands at 1737 and 1693 cm-1 assigned to the formation
of the known complex 2. Addition of hexane led to precipitation
of complex 2 (yield 0.077 g, 93%) characterized by IR and UV-
vis.
EPR Measurements. EPR measurements were performed at
X-band using a Bruker EMX spectrometer equipped with a Bruker
TE102 cavity. The microwave frequency was measured with a
Hewlett-Packard 5246L electronic counter. X-band EPR spectra
of complex 1 frozen in CH2Cl2/tolune were obtained with a
microwave power of 1.006 mW, frequency at 9.631 GHz, and
modulation amplitude of 2.0 G at 100 kHz, and spectra of complex
5 in THF were obtained with a microwave power of 19.971 mW,
frequency at 9.604 GHz, and modulation amplitude of 1.6 G at
100 kHz.
temperature independent paramagnetism (TIP, 2 × 10-4 cm3 mol-1
)
and ligands’ diamagnetism by the tabulated Pascal’s constants.
Crystallography. Crystallographic data and structure refinements
parameters of complexes 1 and 5 are summarized in the Supporting
Information. The crystals chosen for X-ray diffraction studies
measured 0.32 × 0.21 × 0.20 mm3 for complex 1, and 0.45 ×
0.35 × 0.15 mm3 for complex 5, respectively. Each crystal was
mounted on a glass fiber and quickly coated in epoxy resin. Unit-
cell parameters were obtained by least-squares refinement. Dif-
fraction measurements for complexes 1 and 5 were carried out on
a SMART Apex CCD diffractometer with graphite-monochromated
Mo KR radiation (λ ) 0.7107 Å) and between 1.41° and 27.50°
for complex 1, between 1.42° and 27.50° for complex 5. Least-
squares refinement of the positional and anisotropic thermal
parameters of all non-hydrogen atoms and fixed hydrogen atoms
was based on F2. A SADABS20 absorption correction was made.
The SHELXTL21 structure refinement program was employed.
Acknowledgment. We gratefully acknowledge financial
support from the National Science Council of Taiwan.
Authors thank Miss Chun-Yu Chen (Department of Chem-
istry, National Tsing Hua University) for single-crystal X-ray
structure determinations.
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determinations of [PPN][Fe(NO)-
(SPh)3] and [PPN][(EtS)2Fe(NO)2]. This material is available free
of charge via the Internet at http://pubs.acs.org.
IC061439G
(20) Sheldrick, G. M. SADABS, Siemens Area Detector Absorption Cor-
rection Program; University of Go¨ttingen: Go¨ttingen, Germany, 1996.
(21) Sheldrick, G. M. SHELXTL, Program for Crystal Structure Determi-
nation; Siemens Analytical X-ray Instruments Inc.: Madison, WI,
1994.
Magnetic Measurements. The magnetic data were recorded on
a SQUID magnetometer (MPMS5 Quantum Design Company)
8806 Inorganic Chemistry, Vol. 45, No. 21, 2006