New pentadentate carboxylate-derivatized sulfur ligands affording water soluble iron complexes with [Fe(NS4)] cores that bind small molecules (CO, NO, PMe3) as co-ligands

Article abstract of DOI:10.1002/ejic.200300519

In the search for polydentate sulfur ligands that are able to form water-soluble iron complexes which can bind nitrogenase relevant molecules, the new pentadentate ligands pyCO₂MeS₄-H₂ [2,6-bis[2-mercapto-3-(methoxycarbonyl)phenylthio]dimethylpyridine] (1) and pyCO₂HS₄-H₂ [2,6-bis(2-mercapto-3- carboxyphenylthio)dimethylpyridine] (2) having NS₄ donor atom sets and terminal thiolate donors have been synthesized. The starting material was CO₂MeS₂-H₂ (2,3-dimercapto benzoic acid methyl ester) which was alkylated with 2,6-bis[(tosyloxy)methyl]pyridine. The problem of specifically achieving regioselective monoalkylation of this 1,2-benzene-dithiol derivative was solved by carrying out the alkylation of CO₂MeS₂-H₂ at -78 °C in the presence of stoichiometric amounts of a base. Saponification of 1 afforded the carboxylic acid derivative. Coordination of pyCO₂MeS₄^2- to Fe^II in the presence of co-ligands (L = CO, PMe₃) yielded the complexes [Fe(L)(pyCO₂MeS₄)] where L = CO (5) or PMe₃ (4). Upon treatment with NOBF₄, complex 5 afforded [Fe(NO)(pyCO₂MeS₄)]BF₄ (7) which could be subsequently converted to the isolable 19 valence electron species [Fe(NO)(pyCO₂MeS₄)] (8) upon reduction with N ₂H₄. In the absence of potential co-ligands, coordination of pyCO₂MeS₄^2- to Fe^II afforded the dinuclear complex [Fe(pyCO₂MeS₄)]₂ (6) whilst coordination to Ni^II gave [Ni(pyCO₂MeS₄)] _x (3). Solubility of these complexes in water could be achieved by replacing the CO₂Me groups with CO₂H substituents. The ligand pyCO₂HS₄^2- afforded the iron complexes [Fe(L)(pyCO₂HS₄)] [L = CO (10) and PMe₃ (12)] and [Fe(NO)(pyCO₂HS₄)]BF₄ (11). Both 10 and 12 could be reversibly deprotonated to give the corresponding water-soluble salts (NMe₄)₂[Fe(L)(pyCO₂S₄)] with L = CO {(NMe₄)₂ [9]} and PMe₃ {(NMe₄) ₂ [13]}. The complexes were characterized by elemental analysis, spectroscopic methods and X-ray structural determinations. The molecular structure of [Fe(PMe₃)(pyCO₂HS₄)] (12) was found to exhibit inter- and intramolecular O-H...O and O-H...S hydrogen bonds which serve as models for proton transfer steps from external sources to the active sites of metal sulfur enzymes. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejic.200300519

FULL PAPER
New Pentadentate Carboxylate-Derivatized Sulfur Ligands Affording Water
Soluble Iron Complexes with [Fe(NS4)] Cores that Bind Small Molecules (CO,
NO, PMe3) as Co-Ligands[‡]
Dieter Sellmann,[†][a] Kai P. Peters,*[a] and Frank W. Heinemann[a]
Keywords: Iron / Nickel / S ligands / P ligands / Water solubility
In the search for polydentate sulfur ligands that are able to
electron species [Fe(NO)(pyCO2MeS4)] (8) upon reduction
form water-soluble iron complexes which can bind nitro- with N2H4. In the absence of potential co-ligands, coordina-
genase relevant molecules, the new pentadentate ligands
tion of pyCO2MeS4 to FeII afforded the dinuclear complex
2−
pyCO2MeS4−H2 [2,6-bis[2-mercapto-3-(methoxycarbonyl)- [Fe(pyCO2MeS4)]2 (6) whilst coordination to NiII gave
phenylthio]dimethylpyridine] (1) and pyCO2HS4−H2 [2,6-
bis(2-mercapto-3-carboxyphenylthio)dimethylpyridine] (2)
having NS4 donor atom sets and terminal thiolate donors
have been synthesized. The starting material was
CO2MeS2−H2 (2,3-dimercapto benzoic acid methyl ester)
which was alkylated with 2,6-bis[(tosyloxy)methyl]pyridine.
The problem of specifically achieving regioselective mono-
alkylation of this 1,2-benzene-dithiol derivative was solved
by carrying out the alkylation of CO2MeS2−H2 at −78 °C in
the presence of stoichiometric amounts of a base. Saponifica-
[Ni(pyCO2MeS4)]x (3). Solubility of these complexes in water
could be achieved by replacing the CO2Me groups with
CO2H substituents. The ligand pyCO2HS42− afforded the iron
complexes [Fe(L)(pyCO2HS4)] [L = CO (10) and PMe3 (12)]
and [Fe(NO)(pyCO2HS4)]BF4 (11). Both 10 and 12 could be
reversibly deprotonated to give the corresponding water-sol-
uble salts (NMe4)2[Fe(L)(pyCO2S4)] with L = CO {(NMe4)2
[9]} and PMe3 {(NMe4)2 [13]}. The complexes were character-
ized by elemental analysis, spectroscopic methods and X-ray
structural determinations. The molecular structure of [Fe(P-
tion of 1 afforded the carboxylic acid derivative. Coordina- Me3)(pyCO2HS4)] (12) was found to exhibit inter- and intra-
tion of pyCO2MeS42− to FeII in the presence of co-ligands (L =
CO, PMe3) yielded the complexes [Fe(L)(pyCO2MeS4)]
where L = CO (5) or PMe3 (4). Upon treatment with NOBF4,
complex 5 afforded [Fe(NO)(pyCO2MeS4)]BF4 (7) which
molecular O−H···O and O−H···S hydrogen bonds which serve
as models for proton transfer steps from external sources to
the active sites of metal sulfur enzymes.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
could be subsequently converted to the isolable 19 valence Germany, 2004)
Introduction
Iron atoms in sulfur dominated coordination spheres
constitute the active sites of numerous metal enzymes.[1] In
the search for low-molecular weight complexes which are
capable of modeling characteristic features of the active
sites of FeMo, FeV or FeFe nitrogenases such as the sulfur
environment of the iron centers, binding of small molecules,
and redox-activity, we have recently discovered the
[Fe(pyS4)] fragment (see Figure 1).[2]
Figure 1. Schematic structure of [Fe(pyS4)] and [Fe(NHS4)] frag-
ments
This fragment binds small molecules, e.g. CO, N2H2,
N2H4, NH3.[3] The resultant complexes are redox-active and
are formed diastereoselectively, always exhibiting the thiol-
ate and thioether donors in trans positions. In contrast with
[‡]
Transition Metal Complexes with Sulfur Ligands, 159. Part 158:
D. Sellmann, A. Hille, F. W. Heinemann, M. Moll, A. Rösler,
J. Sutter, G. Brehm, B. A. Hess, M. Reiher, S. Schneider, Inorg.
Chim. Acta 2003, 348, 194-198.
related [Fe(L)(NHS4)][4] complexes of the pentadentate li-
2Ϫ
gand NHS4
[ϭ dianion of 2,2Ј-bis(2-mercapto-phenyl-
[†]
Deceased.
[a]
thio)diethylamine] which may contain low- or high-spin
FeII depending on the σ or σ-π character of the ligand L,
all 18 valence electron [Fe(L)(pyS4)] complexes are diamag-
netic. This was demonstrated, for example, by [Fe(CO)-
Institut für Anorganische Chemie der Universität Erlangen-
Nürnberg,
Egerlandstraße 1, 91058 Erlangen, Germany
Fax: (internat.) ϩ49-9131-852-7367
E-mail: peters@anorganik.chemie.uni-erlangen.de
Eur. J. Inorg. Chem. 2004, 581Ϫ590
DOI: 10.1002/ejic.200300519
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
581

D. Sellmann, K. P. Peters, F. W. Heinemann
FULL PAPER
(pyS4)] and [Fe(N2H4)(pyS4)] which are both diamagnetic.[3]
After a number of laborious experiments, it was finally
[Fe(L)(pyS4)] complexes are, however, usually soluble only found that alkylation of CO2MeS2ϪH2 in the presence of
in non-aqueous solvents thus preventing any investigations one equivalent of NMe4OH at Ϫ78 °C afforded the target
in water which is clearly the important solvent in biological molecule 1 as the major product. Even then however, a
systems. In order to resolve this problem and to obtain purification step via the nickel complex [Ni(pyCO2MeS4)]x
water-soluble complexes, we attempted to introduce car- was necessary. Acidic hydrolysis of [Ni(pyCO2MeS4)]x af-
2Ϫ
boxylic acid substituents into the pyS4 ligand. This re- forded 1 as its HCl salt in isomeric purity after recrystalliza-
quired new ligands, the design and synthesis of which are tion. Saponification of the ester functions of 1 gave the acid
reported here together with some related iron and nickel derivative pyCO2HS4ϪH2 (2) (Scheme 1).
complexes.
Results and Discussion
Ligand Synthesis
Figure 2 summarizes starting materials, notations and the
target ligands 1 and 2.
Scheme 1. Synthesis of the target ligands 1 and 2: (i) 1) ϩ2
Figure 2. Starting materials, notations and the target ligands 1
NMe4OH, Ϫ78 °C, THF/MeOH, 15 h; 2) HClaq., CH2Cl2; 3) ϩ2
and 2
LiOMe, ϩ Ni(OAc)2·4H2O, MeOH; 4) HClaq., CH2Cl2. (ii) 1) ϩ10
NaOHaq., THF, 72 h; 2) HClaq., CH2Cl2
The
notations
CO2MeS2ϪH2,
pyCO2MeS4ϪH2,
pyCO2HS4ϪH2, etc. have been used throughout in order to
facilitate legibility and designation of the degrees of pro-
tonation/deprotonation of the individual ligands.
The starting material for the pentadentate target ligand
1 was CO2MeS2ϪH2, and the major problem was to con-
nect two of these molecules with 2,6-bis[(tosyloxy)methyl]-
pyridine such that only one of the two SH functions in
CO2MeS2ϪH2 would be regioselectively alkylated.
All attempts to achieve a regioselective mono-alkylation
using [FeII(CO)2] or [NiII] complex fragments as templates
remained unsuccessful, although such template reactions
have afforded very good results in previous preparations of
related ligands.[5] Analogous attempts with the acid deriva-
tive CO2HS2ϪH2 also failed, as did direct alkylations of
CO2MeS2ϪH2 under ambient conditions in the absence of
templates. In all cases an inseparable mixture of the three
regioisomers 1, 1a, and 1b was obtained (Figure 3).
Neither 1H nor 13C NMR spectroscopy enabled us to
unambiguous distinguish the target ligand 1 from its sym-
metrical regioisomer 1b. This was possible only by an X-ray
structural determination (vide infra).
Syntheses of Iron and Nickel Complexes
2Ϫ
Straightforward coordination of the anion pyCO2MeS4
to FeII and NiII afforded a series of complexes which are
shown in Scheme 2.
.
Reaction of 1.HCl with Ni(OAc)2 4H2O in the presence
of three equivalents of LiOMe (for deprotonation of the
pyridinium NH and thiol SH functions) afforded yellow-
brown [Ni(pyCO2MeS4)]x (3) which is presumably dinuclear
like the analogous [Ni(pyS4)]2.[2] Complex 3 is moderately
soluble in DMF and DMSO but only sparingly soluble in
all other common solvents. Analogous reactions of 1.HCl
.
with FeCl2 4H2O in the presence of PMe3 or CO gave red
[Fe(PMe3)(pyCO2MeS4)] (4) and red [Fe(CO)(py-
CO2MeS4)] (5), respectively, with 5 showing a ν(CO) band
at 1952 cmϪ1 in KBr. In the absence of potential co-ligands,
dinuclear violet-red [Fe(pyCO2MeS4)]2 (6) was formed in-
stead. Complex 6 is almost insoluble in all common sol-
vents although THF suspensions of 6 react with gaseous
CO to give 5 indicating that 6 partially dissociates into co-
ordinatively unsaturated [Fe(pyCO2MeS4)] monomers.
Treatment of the carbonyl complex [Fe(CO)(pyCO2MeS4)]
Figure 3. Isomers of pyCO2MeS4ϪH2 (1)
582
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Water Soluble Iron Complexes that Bind Small Molecules (CO, NO, PMe3)
FULL PAPER
Scheme 3. Synthesis of acidic [Fe(L)(pyCO2HS4)] complexes and
corresponding salts with [Fe(L)(pyCO2S4)]2Ϫ anions: (i) ϩ FeCl2·
4H2O, ϩ exc. PMe3, MeOH; (ii) ϩ4 LiOMe, ϩ FeCl2·4H2O, ϩ exc.
CO, MeOH; (iii) ϩ2 HCl, H2O (iv) ϩ NOBF4, CH2Cl2
Scheme 2. Fe and Ni complexes with [M(pyCO2MeS4)] fragments:
(i) ϩ3 LiOMe, ϩ Ni(OAc)2·4H2O, MeOH; (ii) ϩ3 LiOMe, ϩ
FeCl2·4H2O, MeOH; (iii) ϩ3 LiOMe, ϩ FeCl2·4H2O, ϩ exc. CO,
MeOH; (iv) ϩ exc. CO, THF; (v) ϩ NOBF4, CH2Cl2; (vi) ϩ2
NOBF4, CH2Cl2; (vii) ϩ exc. H2N4, MeOH; (viii) ϩ3 LiOMe, ϩ
FeCl2·4H2O, ϩ exc. PMe3, MeOH
(10). Complex 10 could be reversibly deprotonated with
NMe4OH
to
give
(NMe4)2[Fe(CO)(pyCO2S4)]
{(NMe4)2[9]} and treatment of 10 with NOBF4 afforded the
corresponding nitrosyl complex [Fe(NO)(pyCO2HS4)](BF4)
(11) (ν(NO): 1900 cmϪ1 in KBr). Complex 11 could not be
isolated in an analytically pure form but its identity was
established from a combination of NMR and IR spec-
troscopy. Surprisingly, the PMe3 complex [Fe(PMe3)(py-
CO2HS4)] (12) formed directly from neutral pyCO2HS4ϪH2
(5) with NOBF4 led to CO substitution and formation of
the brown 18 valence electron nitrosyl derivative [Fe(NO)-
(pyCO2MeS4)]BF4 (7) having a ν(NO) band at 1881 cmϪ1
.
Complex 7 also formed when dinuclear 6 was treated with
an excess of NOBF4. Reduction of 7 with hydrazine gave
the neutral red-brown [Fe(NO)(pyCO2MeS4)] (8) having a
ν(NO) band at 1617 cmϪ1
.
.
and FeCl2 4H2O in the presence of an excess of PMe3. The
Preparation of complexes with the acid derivative
excess PMe3 presumably acts as base giving PMe3Hϩ cat-
ions which result in the appropriate proton concentration
needed for formation of neutral 12. Deprotonation of 12
with NMe4OH gave the salt (NMe4)2[Fe(PMe3)(pyCO2S4)]
{(NMe4)2[13]}.
pyCO2HS4ϪH2 (2) or its fully deprotonated anion
4Ϫ
pyCO2S4
were generally achieved in the same way
(Scheme 3). The resultant complexes enabled studies of the
reversible deprotonations and the electronic influence of
carboxylic acid vs. carboxylate functions. It proved difficult
to obtain analytically pure samples of salts containing
[Fe(pyCO2S4)]2Ϫ anions. Recrystallization attempts of these
salts always afforded powders and, in fact, single crystals
X-ray Structural Determinations
X-ray structural determinations were indispensable for
suitable for an X-ray diffraction study could not be ob- confirming the regioselectivity of the alkylation reactions
tained. (vide supra). Figure 4 shows the molecular structures
Reaction of pyCO2HS4ϪH2 (2) with four equivalents of of pyCO2MeS4ϪH2·HCl (1·HCl), [Fe(CO)(pyCO2MeS4)]
.
LiOMe and subsequent treatment with FeCl2 4H2O and CO (5), [Fe(pyCO2MeS4)]2·H2O·THF (6·H2O·THF) and
afforded Li2[Fe(pyCO2S4)] (Li2[9]). This compound ten- [Fe(PMe3)(pyCO2HS4)]·0.25MeOH
(12·0.25MeOH).
aciously retained varying amounts of LiCl, H2O, and Table 1 lists selected distances and angles.
MeOH. Its identity, however, was confirmed by IR and
The ligand 1.HCl exhibits C2 symmetry in the solid state.
NMR spectroscopy and by its reaction with aqueous HCl The carboxylic acid methyl ester substituents are located in
which afforded the neutral complex [Fe(CO)(pyCO2HS4)] positions ortho to the thiol functions. The ClϪ counterion
Eur. J. Inorg. Chem. 2004, 581Ϫ590
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D. Sellmann, K. P. Peters, F. W. Heinemann
FULL PAPER
Figure 4. Molecular structures of pyCO2MeS4ϪH2·HCl (1·HCl), [Fe(CO)(pyCO2MeS4)] (5), [Fe(pyCO2MeS4)]2·H2O·THF (6·H2O·THF)
and [Fe(PMe3)(pyCO2HS4)]·0.25MeOH (12·0.25MeOH) (50% probability ellipsoids, C-bonded H atoms and solvent molecules omitted)
imposed inversion center and contains both enantiomers of
the chiral [Fe(pyCO2MeS4)] fragment. 5 crystallizes in the
chiral space group P21 and contains only one enantiomer.
Distances and angles show no anomalies and lie in the
range observed for the parent complex [Fe(CO)(pyS4)].[2]
The FeϪN(pyridine) distances range from 197. 8(3) to
201.2(6) pm in 6 and 7 respectively. FeϪS(thioether) dis-
tances (ഠ221 pm) are always shorter than FeϪS(thiolate)
distances (ഠ228 pm) within the [FeNS4] cores. The FeϪS
distances to the bridging thiolate donors in dinuclear 6 are
distinctly longer (ഠ234 pm) indicating the tendency of 6 to
Table 1. Selected distances (pm) and angles (deg) of [Fe(CO)(py-
CO2MeS4)] (5), [Fe(pyCO2MeS4)]2·H2O·THF (6·H2O·THF) and
[Fe(PMe3)(pyCO2HS4)]·0.25MeOH (12·0.25MeOH)
Complex
5
6
12
Fe1ϪN1
Fe1ϪS1
Fe1ϪS2
Fe1ϪS3
Fe1ϪS4
Fe1ϪL
N1ϪFe1ϪS3
N1ϪFe1ϪS4
S1ϪFe1ϪS4
S2ϪFe1ϪS4
S2ϪFe1ϪS1
S3ϪFe1ϪS4
S2ϪFe1ϪS3
201.0(2)
230.79(6)
220.05(6)
221.80(6)
228.41(6)
174.1(2)
84.83(5)
90.12(6)
174.19(2)
85.35(2)
89.75(2)
90.05(2)
169.86(2)
197.8(3)
227.7(1)
222.1(1)
220.9(1)
228.7(1)
234.8(1)
86.29(9)
88.03(9)
176.12(4)
93.84(4)
88.61(4)
89.51(4)
170.40(4)
200.4(3)
229.5(1)
220.9(1)
220.4(1)
227.7(1)
223.4(1)
85.02(8)
89.84(7) dissociate into mononuclear [Fe(pyCO2MeS4)] fragments.
176.53(4)
88.95(3)
89.03(3)
88.89(3)
The structure of [Fe(PMe3)(pyCO2HS4)] (12) deserves
special interest because the crystal lattice contains chains of
[Fe(PMe3)(pyCO2HS4)] molecules which are connected by
intermolecular OϪH···O hydrogen bonds. Each [Fe(PMe3)-
(pyCO2HS4)] molecule exhibits an additional intramolecu-
lar OϪH···S(thiolate) hydrogen bond. Figure 5 shows part
170.05(4)
forms a hydrogen bond to the protonated pyridine N atom.
The metal centers of all the complexes are six-coordinate
and exhibit pseudo octahedral geometries. The thiolate and
thioether donors always adopt trans positions to each other
with the pyridine N donors in apical positions such that
square pyramidal [MNS4] cores result. This indicates that
the rigid bis-methylene-pyridine bridge connecting the 1,2-
benzene-dithiol fragments exerts a stereochemical directing
influence. The sixth positions of the pseudo-octahedral me-
tal centers are occupied either by the co-ligand L (CO,
PMe3) or a thiolate donor of another [MNS4] core. Di-
Figure 5. Intra- and intermolecular hydrogen bonds of [Fe(PMe3)-
nuclear [Fe(pyCO2MeS4)]2 possesses a crystallographically (pyCO2HS4)] (12)
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Water Soluble Iron Complexes that Bind Small Molecules (CO, NO, PMe3)
FULL PAPER
of the crystal lattice consisting of chains that each contain
only homochiral molecules.
1H NMR spectroscopy proved to be particularly suitable
for quickly checking the purity and symmetry of the ligands
The presence of intermolecular hydrogen bonds can be and complexes. The 1H and 13C NMR spectra show typical
inferred from the distances d(O22ϪH22) ϭ 82 pm, signals for pyS4 cores corroborating the two-fold symmetry
d(H22···O11B) ϭ 193 pm, d(O22···O11b) ϭ 274.1(4) pm for all compounds. Like [Fe(PR3)(pyS4)] (R ϭ PMe3,
and the angle [O22ϪH22···O11B] ϭ 170.8°. The intramol- PnPr3), the PMe3 complexes 4, 12, and (NMe4)2[13] show
1
ecular OϪH···S hydrogen bonds are indicated by the dis- sharp H NMR signals only in the presence of an excess of
tances d(O12ϪH12) ϭ 82 pm, d(H12···S1) ϭ 211 pm, PMe3. This has been previously explained by suggesting the
d(O12···S1) ϭ 289.0(3) pm and the angle [O12ϪH12···S1] ϭ occurrence of a reversible dissociation of the phosphane li-
159.4°. In particular, the d(H12···S1) distance is consider- gands in solution.[3]
ably shorter than the sum of van der Waals radii of sulfur
and hydrogen (rH ϭ 100 pm, rS ϭ 180 pm)[7] and suggests
a strong S···H interaction. Such a strong S···H interaction Electronic Influence of Benzene Ring Substituents
is also indicated by an IR band in 12 at 2612 cmϪ1 (in
CO2R (R ϭ alkyl, H) substituents are generally con-
sidered to withdraw electron density from benzene rings by
inductive or mesomeric effects. It was therefore of interest
to examine whether such an electron-withdrawing effect of
the CO2R substituents would reach beyond the thioether
and thiolate donors and be detectable at the metal centers
of the homologous complexes. This question was probed by
examining the ν(CO) frequencies of the iron complexes
listed in Table 2.
KBr). This band can be assigned to a ν(OH) vibration
strongly lowered in energy by hydrogen-bonding or alterna-
tively to a ν(SH) vibration indicating protonation of the
thiolate donor. The two types of hydrogen bonds in which
the carboxylic acid groups are involved make these groups
vibrationally inequivalent such that two different ν(CO)-
bands can be observed in the IR (KBr) spectrum of
COOH
12 at 1701 and 1668 cmϪ1
.
Inter- and intramolecular hydrogen bonds like those ob-
served in 12 are of interest because they can serve as models
for the transport of protons in metal sulfur enzyme pro-
teins. Protons from an external source first bind to car-
boxylic acid/carboxylate side chains of the protein, migrate
from there to Brønsted-basic sulfur sites and, if needed in
an [Hϩ/eϪ] coupled enzyme reaction, to a substrate mol-
ecule coordinated to a metal center.
Table 2. ν(CO) Frequencies of iron carbonyl complexes with
[Fe(pyS4)] cores [cmϪ1
]
Complex
In KBr In solution
[Fe(CO)(pyS4)]
1963
1955[2]
1952
1962
1974 (THF)[9]
Ϫ
1974 (THF)
1963 (DMF)
1973 (MeOH)
1973 (MeOH)
1969 (THF)[9]
[Fe(CO)(pyS4)]·MeOH
[Fe(CO)(pyCO2MeS4)]
[Fe(CO)(pyCO2HS4)]
General Properties and Spectroscopic Characterization of
Complexes
Li2[Fe(CO)(pyCO2S4)]·H2O·3MeOH·LiCl 1969
(NMe4)2[Fe(CO)(pyCO2S4)]·2H2O
1949
1969
[Fe(CO)(pybuS4)
A major goal of this work was to achieve water solubility
of specific complexes by the rational design of ligands. This
objective was successfully accomplished with lithium and
ammonium salts of the anions [Fe(CO)(pyCO2S4)]2Ϫ (9)
Table 2 demonstrates that all CO complexes show very
and [Fe(PMe3)(pyCO2S4)]2Ϫ (13). The salts Li2[9], similar or almost identical ν(CO) frequencies in solution
(NMe4)2[9], and (NMe4)2[13] are soluble in H2O and water- indicating that different benzene ring substituents have
like solvents such as MeOH. All the other complexes are practically no influence upon the electron density at the
sparingly soluble or insoluble in H2O or MeOH. The low iron centers. In the solid state (KBr), the ν(CO) frequencies,
solubility of neutral [Fe(CO)(pyCO2HS4)] (5) or [Fe(PMe3)- although lying in the same range, show larger differences.
(pyCO2HS4)] (12) in H2O corresponds to the insolubility in As evidenced by both [Fe(CO)(pyS4)][9] and [Fe(CO)(pyS4)]
water of higher aliphatic or aromatic carboxylic acids.
· MeOH,[2] however, the presence of a lattice MeOH mol-
All complexes were characterized by elemental analysis ecule can cause a wavenumber shift of 8 cmϪ1. Conversely,
and common spectroscopic methods. The IR (KBr) spectra [Fe(CO)(pyCO2HS4)] and [Fe(CO)(pybuS4)][9] show practi-
of the CO complexes exhibit characteristic ν(CO) bands in cally identical ν(CO) frequencies in KBr, although two elec-
the region 1970Ϫ1949 cmϪ1 and those of the 18 VE nitrosyl tron-withdrawing CO2H substituents have been replaced by
complexes [Fe(NO)(pyCO2RS4)](BF4) [R ϭ Me (7), R ϭ H four electron donating tertiary butyl substituents. In con-
(11)] display ν(NO) bands at 1881 and 1900 cmϪ1. The clusion, the results indicate that the benzene ring substitu-
ν(NO) band of the neutral 19 valence electron species ap- ents have no significant influence upon the electron density
pears at 1617 cmϪ1, indicating that the unpaired electron at the metal center but, rather, the ν(CO) shifts observed
occupies an antibonding orbital. As shown by DFT calcu- are due to solvation or crystal packing effects. This con-
lations for the related parent complex [Fe(NO)(pyS4)], this clusion is supported by cyclic voltammetry (CV) studies.
molecular orbital is antibonding with respect to all The isoelectronic iron carbonyl complexes [Fe(CO)-
FeϪligand interactions and has a large contribution from a (pyS4)],[9] [Fe(CO)(pyCO2MeS4)], and [Fe(CO)(pyCO2HS4)]
π* type NO orbital.[8]
each show a reversible redox wave in the anodic region.
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585

D. Sellmann, K. P. Peters, F. W. Heinemann
FULL PAPER
Table 3 lists the redox potentials of the three complexes in of enzymes when small molecules binding to these centers
either CH2Cl2 or DMF.
are reduced by coupled [Hϩ/eϪ] transfer steps.
Table 3. Redox potentials of carbonyl complexes with [Fe(pyS4)]
cores [mV]
Experimental Section
Complex
CH2Cl2
DMF
General Methods: Unless noted otherwise, all procedures were car-
ried out under nitrogen using standard Schlenk techniques at room
temperature with stirring. Solvents were dried and distilled before
use. As far as possible, reactions were monitored by IR or NMR
spectroscopy. Spectra were recorded on the following instruments:
IR (KBr discs or CaF2 cuvettes, solvent bands were compensated):
PerkinϪElmer 16PC FTIR. NMR: Jeol-JNM-GX 270, JNM-EX
270 and JNM-LA 400 with the residual signals of the deuterated
solvent used as an internal reference. Spectra were recorded at
25 °C. Mass spectra: JEOL MSTATION 700 spectrometer. El-
emental analysis: Carlo Erba EA 1106 or 1108 analyzer. Magnetic
susceptibility: Johnson Matthey susceptibility balance. Cyclic vol-
tammetry was performed with a Radiometer Copenhagen IMT 102
electrochemical interface using a three-electrode cell with a glassy
carbon (Radiometer Copenhagen EDI) working electrode and Pt
reference and counter electrodes. Solutions were 10Ϫ3 ; NBu4[PF6]
(10Ϫ1 ) was used as the supporting electrolyte. Potentials were
referenced to the normal hydrogen electrode (NHE) using Fc/Fcϩ
[Fe(CO)(pyS4)]
[Fe(CO)(pyCO2MeS4)]
[Fe(CO)(pyCO2HS4)]
460
514
Ϫ
468
539
490
The potentials (Table 3) indicate that CO2R substituents
render complexes with [Fe(pyS4)] cores more difficult to ox-
idize. Conversely, when changing from CO2Me to CO2H,
the trend in redox potentials is reversed. In addition the
overall shifts of the redox potentials in the range of 22Ϫ71
mV (in DMF) are small. Taking into account also the fact
that redox potentials in solution are sensitive towards the
nature of the solvent and solvation effects (cf. the values in
CH2Cl2 and DMF), it can safely be assumed that the ν(CO)
frequencies listed in Table 2 indeed confirm that CO2R sub-
stituents do not have a significant influence upon the elec-
tron density at the metal centers or [Fe(L)(NS4)] cores.
ϩ
as an internal standard (EFc/Fc ϭ 0.4 V vs. NHE).[11] ‘‘S2’’-H2
(1,2-benzene-dithiol),[12] CO2MeS2ϪH2 (2,3-dimercapto benzoic
acid methyl ester),[13] and 2,6-bis[(tosyloxy)methyl]pyridine[14] were
prepared as described in the literature.
Concluding Discussion
Two new pentadentate ligands containing NS4 donor pyCO2MeS4؊H2 (1):
A yellow solution of CO2MeS2ϪH2
(17.38 mmol, 3.48 g) and NMe4OH (17.38 mmol, 7.36 mL of a 25%
solution in MeOH) in THF (100 mL) was combined with a solu-
tion of 2,6-bis[(tosyloxy)methyl]pyridine (3.89 g, 8.69 mmol) in
THF (130 mL) at Ϫ78 °C. After 2 h at Ϫ78 °C and 15 h at room
temperature the resultant white precipitate was separated by fil-
tration and washed with THF (35 mL). The combined filtrates were
evaporated and the remaining residue was dissolved in CH2Cl2
(100 mL). Concentrated hydrochloric acid (20 mL) was added and
the resultant mixture was stirred vigorously for 5 min. The CH2Cl2
phase was separated from the aqueous phase, washed with water
atom sets and terminal thiolate donors have been synthe-
sized and coordinated to FeII and NiII centers affording a
series of new iron and nickel complexes. The general prob-
lem of achieving a regioselective and specific mono-alky-
lation of the nearly equivalent thiol functions in the 1,2-
benzenedithiol derivative CO2MeS2ϪH2 could be solved by
carrying out the alkylation at low temperature in the pres-
ence of limited amounts of
CO2MeS2ϪH2) affording
a
base (1 NMe4OH:1
the target ligand
pyCO2MeS4ϪH2 (1). Saponification of pyCO2MeS4ϪH2 (5 ϫ 25 mL) until a pH of 7 was attained, dried over Na2SO4 and
the solvents evaporated. The resultant almost colorless solid foam
was suspended in MeOH (75 mL), and LiOMe (17.33 mmol,
17.33 mL of a 1  solution in MeOH) was added. The resultant
(1) gave the acid derivative pyCO2HS4ϪH2 (2) that enabled
synthesis of [Fe(L)(pyCO2HS4)] complexes (L ϭ CO,
PMe3). These complexes become water-soluble upon depro-
tonation of the CO2H substituents and form salts of the
type (cation)2[Fe(L)(pyCO2S4)] which had been the primary
goal of this work.
Spectroscopic, electrochemical and X-ray structural re-
sults indicate that introducing CO2Me or CO2H substitu-
ents into the benzene rings of [Fe(L)(pyS4)] complexes does
solution was filtered and combined with
a solution of
.
Ni(OAc)2 4H2O (2.16 g, 8.68 mmol) in MeOH (40 mL). The yel-
low-brown precipitate thus obtained was separated by filtration
after 1 h, washed with MeOH (30 mL), dried in vacuo and sus-
pended in CH2Cl2 (120 mL). Concentrated hydrochloric acid
(30 mL) was added and the mixture was stirred vigorously for
20 min. The CH2Cl2 phase was separated from the acidic green
not change the electron density at the Fe centers signifi- aqueous phase, dried over Na2SO4 and the solvents evaporated.
The resultant yellow solid foam was recrystallized from CH2Cl2/n-
hexane to give green-yellow crystals. Yield: 2.33 g
cantly. This is important for further investigations since
achieving water solubility of the [Fe(L)(pyS4)] complexes
was the major goal but without changing the coordination
properties of the iron centers that bind a considerable num-
ber of small molecules relevant to nitrogenase.
The X-ray structure of [Fe(PMe3)(pyCO2HS4)] (12)
further revealed that such complexes can form inter- and
intramolecular OϪH···O and OϪH···S(thiolate) bonds.
These hydrogen bonds may serve as models for the trans-
pyCO2MeS4ϪH2·HCl (1·HCl) (61%).1H NMR (CDCl3,
269.60 MHz): δ ϭ 18.2 (br., 2 H, NH), 7.97 (vdd, 2 H, C6H3), 7.80
(vt, 1 H, Hγ, pyridine), 7.59 (vdd, 2 H, C6H3), 7.17 (vd, 2 H, Hβ,
pyridine), 7.06 (vt, 2 H, C6H3), 6.58 (s, 2 H, SH), 4.65 (s, 4 H,
CH2), 3.87 (s, 6 H, CO2CH3) ppm. 13C{1H} NMR (CDCl3,
67.83 MHz): δ ϭ 167.3 (CO2CH3), 154.2, 143.6, 139.4, 132.4,
132.3, 131.7, 127.2, 124.3 [C(aryl)], 52.6 (CO2CH3), 36.3 (CH2)
ppm. IR (KBr): ν˜ ϭ 2486 (br. m, NϪH ϩ SϪH), 1714 cmϪ1 (s,
port of protons from external sources to the metal centers CϭO). MS (FDϩ, CH2Cl2): m/z ϭ 504 [pyCO2MeS4ϪH3]ϩ.
586
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Eur. J. Inorg. Chem. 2004, 581Ϫ590

Water Soluble Iron Complexes that Bind Small Molecules (CO, NO, PMe3)
FULL PAPER
C23H22ClNO4S4 (540.14): calcd. C 51.14, H 4.11, N 2.59, S 23.75;
found C 51.36, H 4.10, N 2.61, S 23.62.
0.42 mmol) and LiOMe (1.25 mmol, 1.25 mL of a 1  solution in
MeOH) in THF (15 mL) under an atmosphere of CO. The mixture
was kept under CO gas for a further 2 h. The resultant red precipi-
tate was separated by filtration, washed with MeOH (10 mL) and
Et2O (10 mL) and dried in vacuo. Recrystallization from CH2Cl2/
Et2O afforded fine red needles. Yield: 0.174 g [Fe(CO)(py-
CO2MeS4)] (5) (71%).1H NMR (CDCl3, 269.60 MHz): δ ϭ 7.67
(m, 4 H, C6H3), 7.32 (vt, 1 H, Hγ, pyridine), 7.11 (vd, 2 H, Hβ,
pyridine), 6.91 (vt, 2 H, C6H3), 5.12 (d, 2 H, CHH), 4.48 (d, 2
H, CHH), 3.84 (s, 6 H, CO2CH3) ppm. 13C{1H} NMR (CDCl3,
67.70 MHz): δ ϭ 214.7 (CO), 167.5 (CO2CH3), 160.2, 157.3, 136.7,
135.6, 135.3, 132.2, 132.1, 121.6, 121.2 [C(aryl)], 56.6 (CH2), 51.9
(CO2CH3) ppm. IR (KBr): ν˜ ϭ 1967 (sh, CO), 1952 (s, CO),
1718 (s, CϭO) cmϪ1. IR (THF): ν˜ ϭ 1974 (s, CO) cmϪ1. MS
pyCO2HS4؊H2 (2): A suspension of 1·HCl (1.00 g, 1.85 mmol) and
NaOH (18.5 mmol, 18.5 mL of a 1  solution in H2O) in THF
(20 mL) was stirred vigorously for 24 h, reduced to one half of its
volume, stirred again for 48 h and then filtered. Concentrated hy-
drochloric acid (18.5 mmol, 18.5 mL) was added to the pale yellow
filtrate. The resultant pale yellow precipitate was separated by fil-
tration, washed with H2O (60 mL) and dried in vacuo. Yield:
0.815 g pyCO2HS4ϪH2 (2) (93%). 1H NMR ([D8]1,4-dioxane,
269.72 MHz): δ ϭ 11.73 (br., 2 H, CO2H), 7.95 (vdd, 2 H, C6H3),
7.54 (vdd, 2 H, C6H3), 7.50 (vt, 1 H, Hγ, pyridine), 7.13 (br., 2 H,
SH), 7.07 (vd, 2 H, Hβ, pyridine), 7.00 (vt, 2 H, C6H3), 4.23 (s, 4
H, CH2) ppm. 13C{1H} NMR ([D8]1,4-dioxane, 67.83 MHz): δ ϭ
169.2 (COOH), 157.8, 143.4, 138.3, 137.6, 135.5, 132.1, 127.6,
124.3, 122.5 [C(aryl)], 40.6 (CH2) ppm. IR (KBr): ν˜ ϭ 2960 (br. m,
OϪH), 2490 (m, SϪH), 1685 cmϪ1 (s, CϭO). MS (FDϩ; 1,4-
dioxane): m/z ϭ 476 [pyCO2HS4ϪH2]ϩ. C21H17NO4S4 (475.63):
calcd. C 53.03, H 3.60, N 2.94, S 26.97; found C 52.98, H 3.47, N
3.01, S 26.85.
(FDϩ, CH2Cl2): m/z
ϭ
585 [Fe(CO)(pyCO2MeS4)]ϩ, 557
[Fe(pyCO2MeS4)]ϩ. C24 H19FeNO5S4 (585.52): calcd. C 49.23, H
3.27, N 2.39, S 21.91; found C 49.46, H 3.21, N 2.37, S 21.66.
[Fe(pyCO2MeS4)]2 (6):
A solution of FeCl2·4H2O (0.320 g,
1.61 mmol) in MeOH (55 mL) was added dropwise to a solution
of 1·HCl (0.950 g, 1.76 mmol), LiOMe (5.28 mmol, 5.28 mL of a 1
 solution in MeOH) and a small amount of NaBH4 in THF
(50 mL) over the course of 3 h. The violet microcrystalline solid
which formed was separated by filtration after 45 min, washed with
THF (40 mL), MeOH (25 mL) and again with THF (15 mL) and
dried in vacuo. Yield: 0.925 g [Fe(pyCO2MeS4)]2·H2O·THF
(6·H2O·THF) (87%). IR (KBr): ν˜ ϭ 1711 (s, CO) cmϪ1. MS (FDϩ,
DMF): m/z ϭ 557 [Fe(pyCO2MeS4)]ϩ. Magnetic susceptibility
(296 K): µeff ϭ 0 µB. C50H48Fe2N2O10S8 (1205.16): calcd. C 49.83,
H 4.01, N 2.32, S 21.29; found C 49.59, H 3.85, N 2.34, S 21.37.
[Ni(pyCO2MeS4)]x (3): To
a suspension of 1·HCl (0.400 g,
0.74 mmol) in MeOH (30 mL) and THF (10 mL) was added Li-
OMe (2.22 mmol, 2.22 mL of a 1  solution in MeOH). The result-
ant yellow solution was filtered, and a solution of Ni(OAc)2·4 H2O
(0.160 g, 0.64 mmol) in MeOH (12 mL) was added dropwise. The
yellow-brown precipitate which formed was separated by filtration,
washed with MeOH and dried in vacuo. Yield: 0.288 g [Ni(pyCO2-
MeS4)]x (3) (80%). IR (KBr): ν˜ ϭ 1721 cmϪ1 (s, CϭO). MS (FD,
DMF): m/z ϭ 559 [Ni(pyCO2MeS4)]ϩ. C23H19NNiO4S4 (560.36):
calcd. C 49.30, H 3.42, N 2.50, S 22.89; found C 49.39, H 3.42, N
2.29, S 22.64.
[Fe(NO)(pyCO2MeS4)]BF4 (7)
(a) from 6: NOBF4 (0.023 g, 0.20 mmol) and 6·H2O·THF (0.119 g,
0.10 mmol) were suspended in CH2Cl2 (15 mL) for 2.5 h. The re-
sultant brown precipitate was separated using a centrifuge, washed
with CH2Cl2 (5 mL), and recrystallized from acetone. Yield: 0.070 g
[Fe(NO)(pyCO2MeS4)]BF4·0.5 acetone (7·0.5 acetone) (50%).
[Fe(PMe3)(pyCO2MeS4)] (4): A solution of FeCl2·4 H2O (0.073 g,
0.37 mmol) in MeOH (8 mL) was added to a solution of 1·HCl
(0.199 g, 0.37 mmol), LiOMe (1.1 mmol, 1.1 mL of a 1  solution
in MeOH) and PMe3 (0.073 mL, 0.74 mmol) in MeOH (25 mL).
After 2 h the resultant red precipitate was separated by filtration,
washed with MeOH (15 mL) and Et2O (15 mL), and dried in va-
cuo. Yield: 0.170 g [Fe(PMe3)(pyCO2MeS4)] (9) (73%). 1H NMR
(CD2Cl2, exc. PMe3, 399.65 MHz): δ ϭ 7.65 (vdd, 2 H, C6H3), 7.31
(vdd, 2 H, C6H3), 7.05 vt, 1 H, Hγ, pyridine), 6.92 (vd, 2 H, Hβ,
pyridine), 6.71 (vt, 2 H, C6H3), 4.70 (d, 2 H, CHH), 4.35 (d, 2 H,
CHH), 3.63 (s, 6 H, CO2CH3), 0.96 [d, 2J (P, H) ϭ 9 Hz, 9 H,
P(CH3)3], 0.87 [s, exc. P(CH3)3] ppm. 13C{1H} NMR (CD2Cl2, exc.
PMe3, 100.40 MHz): δ ϭ 168.5 (CO2CH3), 159.4, 138.3, 135.3,
133.1, 132.9, 120.3, 120.1 [C(aryl)], 57.6 (d, CH2), 51.9 (CO2CH3),
16.6 [exc. P(CH3)3], 16.3 [P(CH3)3] ppm. 31P{1H} NMR (CD2Cl2,
exc. PMe3, 161.70 MHz): δ ϭ 22.1 [P(CH3)3], Ϫ61.3 [exc. P(CH3)3]
C24.5H22BF4FeN2O5.5S4 (703.37): calcd. C 41.84, H 3.15, N 3.98, S
18.23; found C 41.95, H 2.93, N 3.96, S 18.18.
(b) from 5: Solid NOBF4 (0.020 g, 0.17 mmol) was added to a solu-
tion of 5 (0.100 g, 0.17 mmol) in CH2Cl2 (40 mL). The resultant
brown precipitate was separated by filtration after 18 h, washed
with CH2Cl2 (15 mL) and dried in vacuo. Yield: 0.110 g
[Fe(NO)(pyCO2MeS4)]BF4·0.25CH2Cl2 (7) (93%). 1H NMR
(CD3CN, 269.73 MHz): δ ϭ 7.97 (m, 4 H, C6H3), 7.72 (vt, 1 H,
Hγ, pyridine), 7.42 (vd, 2 H, Hβ, pyridine), 7.39 (vt, 2 H, C6H3),
5.49 (d, 2 H, CHH), 4.95 (d, 2 H, CHH), 3.84 (s, 6 H, CO2CH3)
ppm. 13C{1H} NMR (CD3CN,, 67.83 MHz): δ ϭ 166.8 (CO-
OCH3), 159.0, 154.1, 140.6, 137.1, 134.9, 133.7, 132.0, 127.2, 125.6
[C(aryl)], 56.2 (CH2), 53.0 (CO2CH3) ppm. IR (KBr): ν˜ ϭ 1881
(s, NO), 1712 (s, CϭO) cmϪ1. MS (FDϩ, CH3CN): m/z ϭ 557
[Fe(pyCO2MeS4)]ϩ. C23.25H19.5BCl0.5F4FeN2O5S4 (695.56): calcd.
C 40.15, H 2.82, N 4.03, S 18.44; found C 40.45, H 2.77, N 3.83,
S 18.44.
ppm. IR (KBr): ν˜ ϭ 1718 (s, CϭO), 948 (m, PϪCϪH) cmϪ1
.
C26H28FeNO4PS4 (633.60): calcd. C 49.29, H 4.45, N 2.21, S 20.24;
found C 49.10, H 4.67, N 2.21, S 19.99.
[Fe(CO)(pyCO2MeS4)] (5)
(a) from 6: A suspension of 6·H2O·THF (0.070 g, 0.06 mmol) in
THF (20 mL) was saturated with CO gas for 3 h and kept under a
CO atmosphere for a further 24 h. The resultant red solution was
filtered and reduced to one third of its volume. After addition of
MeOH (5 mL) the red precipitate which formed was separated by
filtration, washed with MeOH (5 mL) and dried in vacuo. Yield:
0.060 g [Fe(CO)(pyCO2MeS4)] (5) (82%).
[Fe(NO)(pyCO2MeS4)] (8): Hydrazine (0.02 mL, 0.66 mmol) was
added to a brown solution of 7·0.25CH2Cl2 (0.050 g, 0.07 mmol)
in MeOH (15 mL). A red-brown precipitate formed which was
separated using a centrifuge after 15 h, washed with MeOH
(10 mL) and dried in vacuo. Yield: 0.025 g [Fe(NO)(pyCO2MeS4)]
(8) (61%). IR (KBr): ν˜ ϭ 1720 (s, CϭO), 1617 (s, NO) cmϪ1. MS
(FDϩ, DMF): m/z ϭ 557 [Fe(pyCO2MeS4)]ϩ. C23H19FeN2O5S4
(587.53): calcd. C 47.02, H 3.26, N 4.77, S 21.83; found C 47.09,
(b) from 1: A solution of FeCl2·4H2O (0.083 g, 0.42 mmol) in
MeOH (15 mL) was added to a solution of 1·HCl (0.225 g, H 3.29, N 4.50, S 21.47.
Eur. J. Inorg. Chem. 2004, 581Ϫ590
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587

D. Sellmann, K. P. Peters, F. W. Heinemann
FULL PAPER
Li2[Fe(CO)(pyCO2S4)] {Li2[9]}:
A
solution of
2
(0.336 g,
1382 (s, CO22Ϫ) cmϪ1. C31H45FeN3O9S4 (771.83): calcd. C 48.24,
H 5.88, N 5.44, S 16.62; found C 48.09, H 6.13, N 5.64, S 16.59.
0.71 mmol) and LiOMe (2.84 mmol, 2.84 mL of a 1  solution in
MeOH) in MeOH (20 mL) was combined with a solution of
FeCl2·4H2O (0.141 g, 0.71 mmol) in MeOH (10 mL). The resultant
dark red solution was saturated with CO gas for 1.5 h and filtered
after addition of THF (15 mL). The solvent was then removed in
vacuo. The so formed light red residue was suspended in THF
(50 mL) for 2 h, separated by filtration, washed with THF (30 mL)
and dried in vacuo. Yield: 0.497 g Li2[Fe(CO)(pyCO2HS4)]·
LiCl·H2O·3MeOH (Li2[9]·LiCl·H2O·3MeOH) (96%). 1H NMR
(D2O,): δ ϭ 7.63 (vd, 2 H, C6H3), 7.31 (vt, 1 H, Hγ, pyridine), 7.14
(vd, 2 H, Hβ, pyridine), 6.95 (m, 4 H, C6H3), 4.92 (vd, 2 H, CHH),
4.61 (vd, 2 H, CHH) ppm. 13C{1H} NMR (D2O, 100.40 MHz):
δ ϭ 217.0 (CO), 178.1 (CO22Ϫ), 158.0, 149.7, 142.5, 137.4, 135.7,
[Fe(PMe3)(pyCO2HS4)] (12): A solution of FeCl2·4H2O (0.090 g,
0.46 mmol) in MeOH (5 mL) was added dropwise to a yellow solu-
tion of 2 (0.217 g, 0.46 mmol) and PMe3 (0.365 mL, 3.65 mmol)
in MeOH (10 mL). The resultant red precipitate was separated by
filtration after 30 min, washed with MeOH (10 mL) and dried in
1
vacuo. Yield: 0.200 g [Fe(PMe3)(pyCO2HS4)] (12) (72%). H NMR
([D6]DMSO, 399.65 MHz, exc. PMe3): δ ϭ 12.47 (s, 2 H, COOH),
7.94 (vd, 2 H, C6H3), 7.34 (m, 5 H, C6H3 ϩ Hγ, pyridine ϩ Hβ,
pyridine), 6.89 (vt, 2 H, C6H3), 4.78 (d, 2 H, CHH), 4.66 (d, 2 H,
CHH), 1.05 [d, 2J (P, H) ϭ 8 Hz, 9 H, P(CH3)3], 0.99 [s, exc.
P(CH3)3] ppm. 13C{1H} NMR ([D6]DMSO, 100.40 MHz, exc.
PMe3): δ ϭ 168.7 (COOH), 159.8, 158.80, 137.1, 134.9, 133.5,
133.2, 129.7, 120.3, 120.1 [C(aryl)], 56.3 (CH2), 16.0 [exc. P(CH3)3],
15.7 [P(CH3)3] ppm. 31P{1H} NMR ([D6]DMSO, 161.70 MHz, exc.
PMe3): δ ϭ 24.1 [P(CH3)3], Ϫ61.8 [exc. P(CH3)3] ppm. IR (KBr):
ν˜ ϭ 2966 (m, OϪH), 2612 (w, SϪH/OϪH), 1701, 1668 (s, CO),
133.0, 127.9, 124.2, 122.7 [C(aryl)], 56.2 (CH2) ppm. IR (KBr): ν˜ ϭ
1969 (s, CO), 1586 (s, CO22Ϫ), 1392 (s, CO2
) .
cmϪ1
2Ϫ
C25H27ClFeLi3NO9S4 (725.85): calcd. C 41.37, H 3.75, N 1.93, S
17.67; found C 41.45, H 3.58, N 1.88, S 17.31.
949 (m, PϪCϪH) cmϪ1
. ϭ 529
MS (FDϩ, DMSO): m/z
[Fe(CO)(pyCO2HS4)] (10): Hydrochloric acid (1.92 mmol, 7 mL of
a 1% solution in H2O) was added dropwise to a solution of
Li2[9]·LiCl·H2O·3MeOH (0.347 g, 0.48 mmol) in H2O (25 mL).
The resultant light red precipitate was separated using a centrifuge,
washed with H2O (30 mL) and MeOH (40 mL) and dried in vacuo.
Yield: 0.255 g [Fe(CO)(pyCO2HS4)] (10) (95%). 1H NMR
([D6]DMSO, 269.73 MHz): δ ϭ 12.67 (br., 2 H, COOH), 7.90 (vd,
2 H, C6H3), 7.61 (vt, 1 H, Hγ, pyridine), 7.44 (m, 4 H, Hβ, pyridine
ϩ C6H3), 6.98 (vt, 2 H, C6H3), 4.90 (s, 4 H, CH2) ppm. 13C{1H}
NMR ([D6]DMSO, 67.83 MHz): δ ϭ 216.8 (CO), 168.1 (COOH),
156.9, 156.7, 136.4, 135.7, 134.9, 133.3, 130.5, 121.7 [C(aryl)], 55.7
(CH2) ppm. IR (KBr): ν˜ ϭ 2974 (m, OϪH), 1962 (s, CO), 1681 (s,
CϭO) cmϪ1. MS (FDϩ, DMSO): m/z ϭ 529 [Fe(pyCO2HS4)]ϩ.
C22H15FeNO5S4 (557.48): calcd. C 47.40, H 2.71, N 2.51, S 23.01;
found C 47.68, H 2.59, N 2.58, S 23.21.
[Fe(pyCO2HS4)]ϩ. C24H24FeNO4PS4 (605. 54): calcd. C 47.60, H
4.00, N 2.31, S 21.18; found C 47.35, H 4.28, N 2.33, S 20.93.
(NMe4)2[Fe(PMe3)(pyCO2S4)]
{(NMe4)2[13]}:
NMe4OH
(0.19 mmol, 0.076 mL of a 25% solution in MeOH) was combined
with a suspension of 12 (0.099 g, 0.18 mmol) in MeOH (15 mL)
giving a red solution that was filtered after 10 min. The filtrate was
evaporated in vacuo and the resultant dark red residue was dried in
vacuo for 15 h. Yield: 0.062 g (NMe4)2[Fe(PMe3)(pyCO2S4)]·H2O
{(NMe4)2[13]·H2O} (88%). 1H NMR (CD3OD, 269.72 MHz, exc.
PMe3): δ ϭ 7.63 (vd, 2 H, C6H3), 7.13 (m, 5 H, Hγ, pyridine ϩ Hβ,
pyridine), 6.93 (vd, 2 H, C6H3), 6.79 (vt, 2 H, C6H3), 4.82 (br., 2
2
H, CHH), 4.56 (br., 2 H, CHH), 1.05 [d, J (P, H) ϭ 9 Hz, 9 H,
P(CH3)3], 1.00 [exc. P(CH3)3] ppm. 13C{1H} NMR (CD3OD,
67.83 MHz, exc. PMe3): δ ϭ 179.0 (CO2), 161.2, 156.9, 144.7,
136.8, 133.8, 131.9, 126.2, 121.2, 120.7 [C(aryl)], 57.4 (CH2), 56.1
[N(CH3)4ϩ], 17.0 [d, P(CH3)3], 16.4 [exc. P(CH3)3] ppm. 31P{1H}
NMR (CD3OD, 161.79 MHz, exc. PMe3): δ ϭ 22.3 [P(CH3)3],
Ϫ61.7 [exc. P(CH3)3] ppm. C32H48FeN3O5PS4 (769.84): calcd. C
49.93, H 6.28, N 5.46, S 16.61; found C 49.92, H 6.55, N 5.31,
S 16.73.
[Fe(NO)(pyCO2HS4)]BF4 (11): NOBF4 (0.045 g, 0.39 mmol) and 10
(0.215 g, 0.39 mmol) were suspended in CH2Cl2 (40 mL) for 3 days.
The resultant brown precipitate was separated by filtration, washed
with CH2Cl2 (20 mL), dried partially in vacuo and dissolved in
MeCN (10 mL). The resultant brown solution was filtered and the
solvents evaporated. The brown residue thus formed was dried in
vacuo for 60 h. Yield: 0.185 g [Fe(NO)(pyCO2HS4)]BF4 (11) (73%).
1H NMR (CD3CN, 269.72 MHz): δ ϭ 7.98 (vd, 4 H, C6H3), 7.70
(vt, 1 H, Hγ, pyridine), 7.38 (m, 4 H, Hβ, pyridine ϩ C6H3), 5.48
(d, 2 H, CHH), 4.93 (d, 2 H, CHH) ppm. 13C{1H} NMR (CD3CN,
67.75 MHz): δ ϭ 158.2, 153.8, 139.8, 136.5, 134.5, 133.1, 131.7,
130.8, 126.4, 124.8 [C(aryl)], 55.2 (CH2) ppm. IR (KBr): ν˜ ϭ 2959
(br., OϪH), 1900 (s, NO), 1711 (s, CϭO) cmϪ1. MS (FDϩ, DMF):
m/z ϭ 529 [Fe(pyCO2HS4)]ϩ. C21H15BF4FeN2O5S4 (646.25): calcd.
C 39.03, H 2.34, N 4.33; found C 37.94, 2.52 H, N 3.91.
X-ray Structural Determinations of pyCO2MeS4؊H2·HCl (1·HCl),
[Fe(CO)(pyCO2MeS4)]
(6·H2O·THF) and
(5),
[Fe(pyCO2MeS4)]2·H2O·THF
MeOH
[Fe(PMe3)(pyCO2HS4)]·0.25
(12·0.25MeOH): Green-yellow single crystals of 1·HCl were grown
by layering a solution of the ligand (0.560 g, 1.04 mmol) in CH2Cl2
(40 mL) with n-hexane (70 mL) over one week. Red plates of
6·H2O·THF were obtained by layering a solution of FeCl2·4H2O
(0.021 g, 0.11 mmol) in H2O (20 mL) successively with a solution
of 1·HCl (0.058 g, 0.11 mmol) in THF (20 mL), a layer of THF
(8 mL), a layer of MeOH (20 mL) and 0.32 mL of a 1  solution
of LiOMe in MeOH. Orange prisms of 5 formed within one week
from a saturated CH2Cl2 solution which had been layered with the
same amount of MeOH. Red blocks of 12·0.25MeOH were ob-
tained by layering a solution of 1a·HCl (0.080 g, 0.17) in THF
(5 mL) with a solution of FeCl2·4H2O (0.033 g, 0.17 mmol) and
PMe3 (0.1 mL, 0.1 mmol) in MeOH (3 mL).
(NMe4)2[Fe(CO)(pyCO2S4)] {(NMe4)2[9]}: NMe4OH (0.36 mmol,
0.15 mL of a 25% solution in MeOH) was combined with a suspen-
sion of 10 (0.099 g, 0.18 mmol) in MeOH (15 mL) giving
a red solution that was filtered and the solvents evaporated.
The resultant red residue was dried in vacuo for 15 h. Yield
0.118 g (NMe4)2[Fe(CO)(pyCO2S4)]·2H2O·MeOH [(NMe4)2[9]·2
H2O·MeOH) (85%). 1H NMR (D2O, 269.72 MHz): δ ϭ 7.61 (vdd,
2 H, C6H3), 7.33 (vt, 1 H, Hγ, pyridine), 7.15 (vd, 2 H, Hβ, pyri-
Suitable single crystals were embedded either in protective per-
dine), 6.92 (m, 4 H, C6H3), 4.88 (d, 2 H, CHH), 4.61 (d, 2 H, fluoro polyalkyl ether oil or sealed in a glass capillary under N2.
CHH), 2.96 [s, 24 H, N(CH3)4ϩ] ppm. 13C{1H} NMR (D2O, Intensity data were collected using graphite monochromated Mo-
67.83 MHz): δ ϭ 217.6 (CO), 178.7 (CO2), 158.5, 150.2, 143.0,
137.9, 136.3, 133.6, 128.4, 124.8, 123.2 [C(aryl)], 57.1 (CH2), 56.7
Kα radiation (λ ϭ 71.073 pm) on a NoniusϪKappaCCD dif-
fractometer (6, 5) or Siemens P4 diffractometer (1·HCl,
a
[N(CH3)4ϩ] ppm. IR (KBr): ν˜ ϭ 1949 (s, CO), 1580 (s, CO22Ϫ), 12·0.25MeOH). Intensity data have been corrected for absorption
588
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 581Ϫ590

Water Soluble Iron Complexes that Bind Small Molecules (CO, NO, PMe3)
FULL PAPER
Table 4. Crystallographic data for pyCO2MeS4ϪH2·HCl (1·HCl), [Fe(CO)(pyCO2MeS4)] (5), [Fe(pyCO2MeS4)]2·H2O·THF (6·H2O·THF)
and [Fe(PMe3)(pyCO2HS4)]·0.25MeOH (12·0.25MeOH)
Compound
1·HCl
5
6·H2O·THF
12·0.25MeOH
Formula
C23H22ClNO4S4
540.11
0.45ϫ0.38ϫ0.25
2240
C24H19FeNO5S4
585.49
0.40ϫ0.25ϫ0.14
600
C50H48Fe2N2O10S8
1205.08
0.50ϫ0.30ϫ0.10
622
C24.25H25FeNO4.25PS4
613.51
0.60ϫ0.35ϫ0.20
633
Mr [g molϪ1
]
Crystal size [mm]
F(000)
Crystal system
Space group
a [pm]
b [pm]
c [pm]
orthorhombic
Fdd2
3868.1(4)
1015.8(1)
1234.0(1)
90
90
90
4.8487(8)
8
1.480
monoclinic
P21
809.65(2)
1468.12(4)
1014.06(3)
90
100.614(2)
90
1.18475(6)
2
1.641
1.028
100(2)
4.06Ϫ28.00
12127
triclinic
P1
triclinic
P1
¯
¯
972.42(6)
1076.16(6)
1460.90(9)
91.415(5)
107.943(6)
115.724(4)
1.2877(2)
1
1.554
0.948
100(2)
3.44Ϫ26.37
21722
757.9(1)
1247.4(1)
1429.6(1)
87.76(1)
79.64(1)
86.67(1)
1.3267(2)
2
1.536
0.977
200(2)
2.22Ϫ27.00
7099
α [°]
β [°]
γ [°]
V [nm3]
Z
ρcalcd. [g cmϪ3
]
µ [mmϪ1
T [K]
]
0.534
294(2)
2.11Ϫ25.99
2494
θ range [°]
Measured refl.
Unique refl.
Rint.
Observed refl.
2377
0.0342
1440
5145
0.0334
4881
5247
0.0573
4101
5780
0.0325
4348
σ criterion
Refl. parameters
R1 [I Ͼ 2σ(I)]
I Ͼ 2σ(I)
154
0.0583
0.1512
0.759/0.816
0.1(2)
I Ͼ 2σ(I)
373
0.0260
0.0584
0.770/0.900
0.00(1)
I Ͼ 2σ(I)
364
0.0450
0.1224
0.747/1.000
Ϫ
I Ͼ 2σ(I)
362
0.0455
0.1165
0.380/0.430
Ϫ
wR2 (all data)
Absorption correction Tmin/Tmax
Absolute structure parameters[18]
effects using either Psi-scans (1·HCl, 12·0.25MeOH), multiple scans
of equivalent reflections (SADABS,[15] 6·H2O·THF) or a numerical
Gaussian integration (5). The structures were solved by direct
methods, and full-matrix least-squares refinements were carried out
on F2 (SHELXTL NT 5.10[16] for 5, 12 or SHELXTL NT 6.12[17]
for 1, 6). All non hydrogen atoms were refined anisotropically. Li-
gand 1 crystallizes as an HCl adduct and the complexes 6 and 12
crystallize with solvent molecules (6·H2O·THF, 12·0.25MeOH).
The MeOH solvate molecule in 12·0.25MeOH is disordered on a
crystallographic inversion center, as is the THF molecule in
6·H2O·THF, with two alternative sites for the O atom of the THF
molecule. No hydrogen atoms have been taken into account for the
structural model of the disordered MeOH of 12·0.25MeOH and
the solvent water of 6·H2O·THF. The PMe3 group in 12 is dis-
ordered with two different sites having occupancies of 62(1)% and
38(1)%, respectively. The hydrogen atoms in 1·HCl, 6·H2O·THF
and 12·0.25MeOH were geometrically positioned with isotropic
displacement parameters fixed at 1.2 or 1.5 times the U(eq) of the
corresponding carbon atom. The positions of the hydrogen atoms
in 5 were taken from a difference Fourier synthesis. Their positional
parameters were refined with a fixed common isotropic displace-
ment parameter. Table 4 summarizes selected crystallographic
data.[19]
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D. Sellmann, K. P. Peters, F. W. Heinemann
FULL PAPER
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Received July 29, 2003
Early View Article
Published Online December 12, 2003
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 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 581Ϫ590