Synthesis, structure, and redox properties of the sulfido bridged tetranuclear cluster complex [(Ph3P)2N][Fe3(CO)9{μ 3-SFeCp(CO)2}]

Article abstract of DOI:10.1016/S0020-1693(98)00390-9

Reaction of [CpFe(CO)₂THF]BF₄ with [(Ph₃P)₂N]₂[Fe₃(CO) ₉(μ₃-S)] (1) produces the new cluster [(Ph₃P)₂N][Fe₃(CO)₉{μ ₃-SFeCp(CO)₂}] (2), which consists of a Fe₃(CO)₉S fragment coordinated to the iron atom of CpFe(CO)₂. Compound 2 was characterized by ¹H and ¹³C NMR, mass spectroscopy, elemental analysis, cyclic voltammetry, and single crystal X-ray structure determination. Compound 2 undergoes a quasi reversible oxidation at 0.19 V versus Ag AgCl. Chemical oxidation of 2 by tropylium produces the known cluster Fe₃(CO)₉(μ₃-S)₂. Thermolysis of 2 yields the known compounds [CpFe(CO)₂]₂, [(Ph₃P)₂N]₂[Fe₃(CO) ₉(μ₃-S)], and [(Ph₃P)₂N]₂[Fe₅(CO) ₁₄(μ₃-S)₂] (3), which were identified by IR and mass spectrometry.

Full text of DOI:10.1016/S0020-1693(98)00390-9

Inorganica Chimica Acta 286 (1999) 142–148
Synthesis, structure, and redox properties of the sulfido bridged
tetranuclear cluster complex [(Ph3P)2N][Fe3(CO)9{m3-SFeCp(CO)2}]
Hee-Joo Jeon, Nicholas Prokopuk, Charlotte Stern, Duward F. Shriver *
Department of Chemistry, Northwestern Uni6ersity, E6anston, IL 60208, USA
Received 14 May 1998; accepted 27 October 1998
Abstract
Reaction of [CpFe(CO)2THF]BF4 with [(Ph3P)2N]2[Fe3(CO)9(m3-S)] (1) produces the new cluster [(Ph3P)2N][Fe3(CO)9{m3-
SFeCp(CO)2}] (2), which consists of a Fe3(CO)9S fragment coordinated to the iron atom of CpFe(CO)2. Compound 2 was
1
characterized by H and 13C NMR, mass spectroscopy, elemental analysis, cyclic voltammetry, and single crystal X-ray structure
determination. Compound 2 undergoes a quasi reversible oxidation at 0.19 V versus Ag ꢀ AgCl. Chemical oxidation of 2 by
tropylium produces the known cluster Fe3(CO)9(m3-S)2. Thermolysis of 2 yields the known compounds [CpFe(CO)2]2,
[(Ph3P)2N]2[Fe3(CO)9(m3-S)], and [(Ph3P)2N]2[Fe5(CO)14(m3-S)2] (3), which were identified by IR and mass spectrometry. © 1999
Elsevier Science S.A. All rights reserved.
Keywords: Crystal structures; Electrochemistry; Iron complexes; Sulfido complexes; Cluster complexes
1. Introduction
Sulfido ligands capping metal triangles in a m3 coordi-
nation mode are known to have a lone pair of electrons
capable of coordinating transition metal complexes and
these can serve as building blocks to higher nuclearity
clusters [3,9,16,23]. Tetrahedral m4-sulfido ligands have
been generated by the coordination of the sulfur atom
of a [M3(CO)9(m3-S)]2− to transition metal Lewis acids,
Scheme 1. Alternatively, the transition metal can add to
the M–S–M face of clusters to generate a m4-butterfly
structure [8,11,24]. A tetrahedral m4-sulfido ligand geo-
metry A is postulated as an intermediate to the butterfly
structure B. Conversion from structure A to struc-
Iron–sulfur compounds are of interest to chemists in
a variety of fields due to their structural and chemical
diversity. Sulfur ligands bind to iron clusters in a
number of coordination modes including m, m3, m4, m5,
and m6 [1–17]. Both the chemical and electrochemical
properties of these clusters are sensitive to the binding
mode of the sulfur. Cubane type clusters, {Fe4S4},
undergo multiple electron-transfer steps while keeping
the {Fe4S4} framework intact [18,19]. However, under a
CO atmosphere, the cubane clusters are much less
stable and are likely to undergo a structural rearrange-
ment upon oxidation or reduction, resulting in iron–
iron and iron–sulfur bond formation or rupture [20].
For example, the reduction of the cubane cluster
[Fe4S4(SPh)4]2− under CO produces the dinuclear com-
plex [Fe2S2(CO)6]2− [21]. By contrast, the chemical
reduction of [Fe4S4(SPh)4]2− with butyl lithium under a
CO atmosphere yields the triangular cluster
[Fe3(CO)9(m3-S)]2− and reoxidation of this cluster by
electrochemical
or
chemical
means
produces
[Fe5(CO)14(m3-S)2]2− which has a bow-tie structure [22].
* Corresponding author. Tel.: +1-847-4915655; fax: +1-847-
4917713; e-mail: shriver@chem.nwu.edu.
Scheme 1.
0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(98)00390-9

H.-J. Jeon et al. / Inorganica Chimica Acta 286 (1999) 142–148
143
ture B has been achieved with thermolysis reactions of
the tetrahedral sulfido cluster [(Ph3P)2N][Fe3(CO)9{m3-
SRe(CO)5}] which produces the butterfly cluster
[(Ph3P)2N][Fe3Re(CO)12(m4-S)] [24]. In this paper we
report the synthesis, structure and redox properties of
[(Ph3P)2N]2[Fe3(CO)9{m3-SFeCp(CO)2}].
evaporated and the residue was extracted with two 10
ml portions of THF. The THF extractions were com-
bined and diethyl ether (20 ml) was added to the THF
solution precipitating [(Ph3P)2N][BF4] as a white pow-
der. The solids were filtered and the filtrate was concen-
trated to 10 ml. Pentane was added dropwise to the
concentrated solution and the resulting dark precipitate
was isolated by vacuum filtration and washed twice
with 10 ml portions of pentane. The solid was identified
as the new compound, [(Ph3P)2N][Fe3(CO)9{m3-SFe-
Cp(CO)2}] (2). Total yield: 197 mg (86%) Anal. Calc.
for C52H35NO11P2SFe4: C, 53.52; Fe, 19.10; H, 3.02; N,
1.20; P, 5.30; S, 2.74. Found: C, 52.24; Fe, 19.57; H,
2.88; N, 0.50; P, 5.78; S, 3.15%. 1H NMR (CDCl3,
20°C): l 5.357 (Cp). 13C NMR (CDCl3, 20°C): l 219.6
(9CO), 211.5 (2CO). IR (CH2Cl2, wCO): 1900 (w), 1928
2. Experimental
2.1. General procedures
All manipulations were carried out under an atmo-
sphere of purified nitrogen with standard Schlenk and
syringe techniques. The solvents methylene chloride,
acetonitrile, ether, pentane, and toluene were dried over
P2O5, CaH2, Na–benzophenon, 4 A molecular sieves,
(m), 1954 (vs), 2009 (s), 2047 (w) cm−1
.
˚
and CaH2, respectively, and distilled prior to use. Both
[(Ph3P)2N]2[Fe3(CO)9S] and [CpFe(CO)2THF][BF4]
were prepared by literature methods [22,25]. 13C-en-
riched [(Ph3P)2N]2[Fe3(CO)9S] (ca. 30% 13C) was pre-
pared by the method of Schauer et al. [24]. [Bu4N]BF4
(Aldrich) was recrystallized from methanol and diethyl
ether. Thin-layer chromatography (TLC) plates (2.5
mm silica gel on glass with 254 nm fluorescent indica-
tor) from Aldrich were used as received.
Solution infrared data were recorded on a Bomem
MB-100 FTIR spectrometer set at 2 cm−1 resolution
using a 0.1 mm path length CaF2 cell. 1H and 13C
NMR spectra were recorded on a Varian XLA-400
spectrometer at 400 and 100 MHz, respectively. Elec-
trochemical measurements were obtained with a Bioan-
alytical Systems 100B electrochemical analyzer. A Pt
disk working electrode and a Pt-foil counter electrode
were employed. Cyclic voltammograms were obtained
in a single compartment cell and potentials were mea-
sured against a Ag ꢀ AgCl reference electrode. For refer-
ence, cyclic voltammograms on a methylene chloride
solution of ferrocene in 0.1 M [Bu4N][BF4] exhibit a
reversible oxidation couple at 0.40 V. Electron impact
(EI) and fast-atom-bombardment (FAB) mass spectra
were obtained by Dr D.L. Hung of the Analytical
Services Laboratory of Northwestern University on a
VG 70/250 SE spectrometer. Elemental analysis was
performed by Oneida Research Service, Whiteboro,
NY.
2.3. Thermolysis of [(Ph3P)2N][Fe3(CO)9-
{v3-SFeCp(CO)2}]
A sample of 2 (0.065 mmol) was dissolved in toluene
in a Schlenk flask equipped with a water cooled con-
denser and a mineral oil bubbler. The solution was
heated to reflux for 8 min and allowed to cool to room
temperature under a slow N2 purge. During reflux the
color changed from black to light brown and a black
oil formed. The solution was separated from the oil by
filtration through a medium porosity glass frit. IR and
mass spectrometry revealed the presence of
[CpFe(CO)2]2 along with trace amounts of [(Ph3P)2N]2-
[Fe3(CO)9(m3-S)]. Both compounds were previously re-
ported [22,26]. The oil was extracted with THF, and
concentration of the dark THF extract produced a red
solid precipitate which was identified by IR and mass
spectrometry as [(Ph3P)2N]2[Fe3(CO)9(m3-S)]. The major
component remaining in the green THF solution was
identified by IR and FAB-MS as [(Ph3P)2N]2-
[Fe5(CO)14(m3-S)2], along with a small amount of
[(Ph3P)2N]2[Fe3(CO)9(m3-S)] [22].
2.4. Chemical oxidation of [(Ph3P)2N]-
[Fe3(CO)9{v3-SFeCp(CO)2}]
A sample of [(Ph3P)2N][Fe3(CO)9{m3-SFeCp(CO)2}]
(0.09 mmol) was dissolved in 8 ml CH3CN and cooled
to −78°C. One equivalent of C7H7BF4 (27 mg in 5 ml
CH3CN) was added dropwise to the cluster solution.
The solution was slowly warmed to room temperature
and allowed to stir overnight in a Schlenk flask con-
nected to a bubbler with a slow nitrogen flow. It was
then evaporated to dryness under vacuum. The residue
was extracted with pentane and subjected to TLC, with
pentane as eluant. The first band contained the known
2.2. Synthesis of [(Ph3P)2N][Fe3(CO)9{v3-SFeCp(CO)2}]
A 30 ml Schlenk flask was charged with 0.30 g (0.20
mmol) [(Ph3P)2N]2[Fe3(CO)9S] (1) and 0.07 g (0.21
mmol) [CpFe(CO)2THF][BF4] and cooled to −78°C.
Methylene chloride (12 ml) was added to the flask and
the solution was allowed to warm to room temperature.
After stirring for 30 min at room temperature the color
of the solution changed to black. The solvent was then

144
H.-J. Jeon et al. / Inorganica Chimica Acta 286 (1999) 142–148
Table 1
compound Fe3(CO)9(m3-S)2 as determined by IR and EI
mass spectrometry. A second yellow–green band was
not identified, however, no evidence for CP was de-
tected in the IR spectrum of this compound. Extraction
of the residue with diethyl ether removed Fe2(CO)6(m-
S)2, which was identified by IR spectroscopy [27]. The
remaining pentane and ether insoluble residue con-
tained other unidentified iron carbonyl species.
Crystal data for [(Ph3P)2N][Fe3(CO)9{m3-FeCp(CO)2}]
Empirical formula
Molecular weight
Crystal size (mm)
Crystal system
Fe4O11SP2NC52H35
1167.24
0.43×0.34×0.33
monoclinic
P21/n (no. 14)
17.328(2)
17.270(4)
17.392(4)
107.03(2)
4976(1)
Space group
˚
a (A)
˚
b (A)
˚
c (A)
˚
i (A)
3
˚
V (A )
2.5. X-ray crystal structure of
[(Ph3P)2N][Fe3(CO)9{v3-SFeCp(CO)2}]
Z
4
Dcalc. (g cm−3
)
1.558
13.10
−120.0
0.051
v(Mo Ka) (cm−1
T (°C)
)
Crystals of [(Ph3P)2N][Fe3(CO)9{m3-SFeCp(CO)2}]
were grown by slow diffusion of ether into a THF–
toluene of the cluster. A dark, opaque, prismatic crystal
of approximate dimensions 0.43×0.34×0.33 mm was
mounted on a glass fiber with Paratone-N (Exxon) and
transferred to an Enraf–Nonius CAD4 diffractometer.
Data were collected with graphite-monochromated Mo
Ka radiation at −120°C. Least-squares refinement of
the primitive monoclinic cell was obtained from three
carefully centered reflections. The space group was
determined to be P21/n (no. 14) by the systematic
absences of h0l (h+1"2n) and 0k0 (k"2n). The data
were collected using the ꢀ–q scan technique to a
maximum 2q value of 47.9°. Of the 8410 reflections
collected, 8142 were unique (Rint=0.024) and 5219
observed (I\3.00|(I)). The intensities of three repre-
sentative reflections were measured every 90 min of
X-ray exposure, and no appreciable decay was ob-
served. An analytical absorption correction was applied
with resulting transmission factors from 0.53 to 0.70.
The data were corrected for Lorentz and polarization
effects. A summary of the crystallographic data is given
in Table 1.
R(F)a
Rw(F)b
0.045
a R(F)=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ.
b Rw(F)=[Sw(ꢀFoꢀ−ꢀFcꢀ)2/SwFo2]1/2
.
[CpFe(CO)2THF]BF4 and [(Ph3P)2N]2[Fe3(CO)9(m3-S)]
(1). Single crystal X-ray diffraction reveals that the
structure of 2 consists of a Fe3(CO)9(m3-S) moiety coor-
dinated to the iron atom of CpFe(CO)2 through the
sulfido ligand. A diagram of the cluster anion is shown
in Fig. 1. The crystallographic data are given in Table
1, positional parameters in Table 2, and selected bond
lengths and angles in Table 3. The sulfur atom adopts
a m4 pseudo tetrahedral geometry coordinating the four
iron atoms. Ligation of the sulfur atom to the metal
centers is reminiscent of [Os3(CO)9(m3-S){m3-SW(CO)5}]
which is generated by the photolysis of W(CO)6 in the
presence of [Os3(CO)9(m3-S)2] [9]. Bond angles between
the Fe atoms of the iron triangle of 2 and the iron atom
The structure was solved by direct methods
(SHELXS86) with TEXSAN crystallographic software
(Molecular Structure). Neutral atom scattering factors
[28] and anomalous dispersion effects [29] were taken
from the literature. The non-hydrogen atoms except for
C10 were refined isotropically. Thermal parameters of
C12, C16, and the most intense peaks in the final
difference map (1.32 and −0.97 e A−3) indicate that
˚
there may be disorder in the C5H5 ring and carbonyl
ligand of C10, so C10 was refined isotropically. Hydro-
gen atoms were included in idealized positions but not
refined. The final cycle of full-matrix least-squares refin-
ement converged with an R value of 0.051 (Rw=0.045).
3. Results and discussion
The cluster [(Ph3P)2N][Fe3(CO)9{m3-SFeCp(CO)2}]
(2) is prepared in good yield (86%) from
Fig. 1. Diagram of the anion of [(Ph3P)2N][Fe3(CO)9{m3-SFeCp-
(CO)2}]. Thermal ellipsoids are at 50% probability.

H.-J. Jeon et al. / Inorganica Chimica Acta 286 (1999) 142–148
145
Table 2
Table 2 (continued)
Positional parameters and ieq values for [(Ph3P)2N][Fe3(CO)9{m3-
SFeCp(CO)2}]
a
Atom
x
y
z
ieq
a
Atom
x
y
z
ieq
C(43)
C(44)
C(45)
C(46)
C(47)
C(48)
C(49)
C(50)
C(51)
C(52)
−0.0978(4)
−0.0888(4)
−0.0838(4)
−0.0871(4)
−0.0103(4)
−0.0091(4)
0.0589(6)
0.1265(5)
0.1271(4)
0.0583(4)
−0.1303(4)
−0.1095(4)
−0.0327(4)
0.0238(4)
0.0627(4)
0.0044(4)
−0.0094(5)
0.0353(5)
0.0935(5)
0.1166(5)
0.0433(4)
0.0246(4)
0.0797(4)
0.3121(4)
0.3675(5)
0.4297(5)
0.4377(5)
0.3850(5)
0.3215(4)
3.7(2)
3.0(2)
2.8(2)
2.6(2)
2.4(2)
4.0(2)
5.0(2)
4.4(2)
3.8(2)
2.9(2)
Fe(1)
Fe(2)
Fe(3)
Fe(4)
S
P(1)
P(2)
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
O(9)
O(10)
O(11)
N
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
0.29164(5)
0.40123(6)
0.44141(5)
0.31706(6)
0.35862(9)
0.15605(5)
0.11941(6)
0.20175(5)
0.33584(6)
0.23252(9)
0.24256(10)
0.07842(10)
0.2662(3)
0.13068(5)
0.26634(6)
0. 15698(5)
0.28021(6)
0.22368(10)
0.1740(1)
0.2261(1)
0.0018(3)
0.1687(3)
0.0392(3)
0.3791(3)
0.2113(3)
0.3900(3)
0.0878(3)
0.2416(3)
0.0175(3)
0.4426(4)
0.2970(4)
0.1848(3)
0.0521(4)
0.1556(4)
0.0766(4)
0.3316(4)
0.2320(4)
0.3406(4)
0.1152(4)
0.2096(4)
0.0721(4)
0.3772(6)
0.2897(5)
0.156(1)
0.2215(8)
0.2985(5)
0.3058(6)
0.2172(8)
0.1286(3)
0.1207(4)
0.0891(5)
0.0671(4)
0.0752(4)
0.1056(4)
0.2648(3)
0.3066(4)
0.3777(4)
0.4081(4)
0.3671(5)
0.2957(4)
0.1096(4)
0.1088(4)
0.0587(4)
0.0092(5)
0.0096(5)
0.0595(5)
0.2601(4)
0.3345(4)
0.3597(5)
0.3106(6)
0.2367(5)
0.2115(5)
0.1541(4)
0.1713(4)
2.03(2)
2.52(2)
2.20(2)
3.13(3)
2.16(4)
2.09(4)
2.22(4)
3.6(1)
3.2(1)
3.6(1)
5.2(2)
5.0(2)
4.8(2)
3.9(1)
5.0(2)
3.9(1)
9.1(2)
6.1(2)
2.6(1)
2.5(2)
2.1(2)
2.4(2)
3.2(2)
3.4(2)
3.1(2)
2.4(2)
3.2(2)
2.6(2)
6.1(2)
4.4(2)
16.0(7)
8.4(4)
4.7(2)
5.4(3)
10.5(4)
2.0(2)
3.4(2)
4.6(2)
4.2(2)
4.2(2)
3.6(2)
1.9(1)
2.5(2)
3.3(2)
4.4(2)
4.2(2)
3.1(2)
2.4(2)
2.7(2)
3.2(2)
4.1(2)
4.4(2)
3.7(2)
2.4(2)
3.1(2)
3.9(2)
4.8(2)
5.0(2)
3.8(2)
2.3(2)
3.3(2)
−0.12881(10)
−0.0971(1)
0.2217(3)
0.1077(4)
0.1411(3)
0.2993(3)
0.3118(3)
0.4243(3)
0.5531(3)
0.4933(3)
0.6058(3)
0.4162(3)
0.1237(3)
0.0147(3)
0.0786(3)
a ieq=8/3y2(U11(aa*)2+U22(bb*)2+U33(cc*)2+2U12aa*bb*
cos k+2U13aa*cc* cos i+2U23bb*cc* cos h).
−0.0371(3)
0.1507(3)
0.0637(3)
0.2530(3)
0.3046(3)
0.2894(4)
0.2590(3)
0.1587(3)
0.2213(4)
0.1361(3)
0.0695(4)
0.0943(4)
0.0252(5)
0.1372(4)
0.1175(4)
0.2331(4)
0.2643(4)
0.3166(6)
0.2870(4)
0.3932(6)
0.4107(5)
0.4417(4)
0.4483 (4)
0.4190(6)
0.3013(4)
0.2721(4)
0.3191(5)
0.3938(5)
0.4223(4)
0.3766(4)
0.2915(4)
0.3336(4)
0.3707(4)
0.3655(5)
0.3233(5)
0.2857(4)
0.2421(4)
0.3037(4)
0.3003(4)
0.2383(5)
0.1770(4)
0.1801(4)
0.0651(4)
0.0946(4)
0.0902(4)
0.0558(4)
0.0260(5)
0.0310(4)
0.0040(4)
−0.0745(4)
of the CpFe(CO)2 unit range from 130 to 140° indicat-
ing that the CpFe(CO)2 unit is slightly skewed toward
one side of the Fe3 triangle. This tilt may relieve stress
caused by the bulky Cp ligand. By contrast the
HRu3(CO)9[m3-SMn(CO)3(NCCH3)2], has a m4 pseudo
tetrahedral sulfido ligand bridging the Ru3 triangle and
the Mn(CO)3(NCCH3)2 unit, with Ru–S–Mn bond
angles ranging from 134 to 137° [23].
0.4166(4)
0.1732(3)
−0.0900(3)
0.2503(4)
0.2024(4)
0.2986(4)
0.3439(4)
0.4163(4)
0.4937(4)
0.4717(4)
0.5392(4)
0.4245(4)
0.3786(5)
0.2303(5)
0.274(1)
0.3730(8)
0.3772(5)
0.2990(5)
0.2526(6)
The Fe3(CO)9(m3-S) unit of 2 is slightly altered from
the starting material 1. The Fe–Fe bonds of 2 are
C(7)
C(8)
C(9)
˚
˚
2.621–2.636 A longer than those of 1: 2.574–2.595 A.
Coordination of the sulfido ligand to the Lewis acid
[CpFe(CO)2]+ should result in a net decrease in elec-
tron density on the Fe3 triangle, and the increase in the
Fe–Fe bond length is consistent with a depopulation of
the predominately Fe–Fe bonding HOMO of the
Fe3(CO)9 fragment as predicted by molecular orbital
calculations on capped Fe3(CO)9 clusters [30]. Shifts in
the w(CO) region of the infrared spectra of 1, 2, and
[CpFe(CO)2THF]+ are consistent with a shift in elec-
tron density from the cluster unit to the CpFe(CO)2
fragment of 2. The IR spectrum of the w(CO) region of
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
C(32)
C(33)
C(34)
C(35)
C(36)
C(37)
C(38)
C(39)
C(40)
C(41)
C(42)
−0.0681(4)
0.0035(4)
0.0520(5)
0.0294(5)
−0.0410(5)
−0.0903(4)
−0.1282(3)
−0.0604(4)
−0.0587(4)
−0.1236(5)
−0.1910(5)
−0.1934(4)
−0.2313(4)
−0.2837(4)
−0.3626(4)
−0.3894(4)
−0.3374(4)
−0.2589(4)
−0.1841(4)
−0.1845(4)
−0.2529(5)
−0.3205(5)
−0.3224(4)
−0.2538(4)
−0.0960(3)
−0.1023(4)
Table 3
˚
Selected bond angles (A) and angles (°) for [(Ph3P)2N][Fe3(CO)9{m3-
SFeCp(CO)2}]
Fe(1)–Fe(2)
Fe(2)–Fe(3)
Fe(2)–S
2.636(1)
2.627(1)
2.142(2)
2.255(2)
1.758(6)
1.766(7)
1.766(8)
1.759(8)
1.744(10)
2.30(2)
Fe(1)–Fe(3)
Fe(1)–S
Fe(3)–S
2.621(1)
2.147(2)
2.159(2)
1.755(7)
1.788(7)
1.778(8)
1.773(7)
1.783(8)
1.774(8)
2.059(9)
2.037(7)
Fe(4)–S
Fe(1)–C(1)
Fe(1)–C(3)
Fe(2)–C(5)
Fe(3)–C(7)
Fe(3)–C(9)
Fe(4)–C(11)
Fe(4)–C(13)
Fe(4)–C(15)
Fe(1)–C(2)
Fe(2)–C(4)
Fe(2)–C(6)
Fe(3)–C(8)
Fe(4)–C(10)
Fe(4)–C(12)
Fe(4)–C(14)
Fe(4)–C(16)
2.082(7)
1.979(9)
Fe(2)–Fe(1)–Fe(3)
Fe(1)–Fe(3)–Fe(2)
Fe(2)–S–Fe(4)
59.95(3)
60.30(3)
133.80(8)
Fe(1)–Fe(2)–Fe(3)
Fe(1)–S–Fe(4)
Fe(3)–S–Fe(4)
59.75(3)
130.10(8)
140.94(8)

146
H.-J. Jeon et al. / Inorganica Chimica Acta 286 (1999) 142–148
2. The shorter Fe–S bonds of 2 are attributed to an
increased p-acid character of the sulfido ligand upon
coordination of the CpFe(CO)2 unit. Compound 2 was
also characterized by mass, 13C and 1H NMR spec-
troscopy, and elemental analysis. The MS-FAB− spec-
trum of 2 (calc. m/z 629) gives a molecular ion peak at
m/z 452 corresponding to [Fe3(CO)9S]−. No peak is
observed at m/z 629 indicating that the CpFe(CO)2 unit
is easily lost. 13C NMR spectroscopy of 2 prepared
from 13C-enriched 1 and unenriched [CpFe(CO)2THF]-
BF4 reveals two peaks at l 219.6 and 211.5 in the
carbonyl region with a temperature-independent inten-
sity ratio of 9:2. These peaks are assigned to the nine
carbonyl ligands of the Fe3(CO)9S unit (l 219.6) and
the two of the CpFe(CO)2 fragment (l 211.5). The 9:2
ratio indicates that scrambling of CO occurred between
[CpFe(CO)2THF]BF4 and [(Ph3P)2N]2[Fe3(CO)9(m3-S)]
Fig. 2. Infrared spectra of (A) [(Ph3P)2N]2[Fe3(CO)9(m3-S)], (B)
[CpFe(CO)THF]BF4, and (C) [(Ph3P)2N][Fe3(CO)9{m3-SFeCp(CO)2}]
in CH2Cl2.
1
upon combination. A single peak is observed in the H
NMR spectrum of 2 at l 5.357 corresponding to the
protons of the Cp ring.
2 resembles a combination of the IR spectra of 1 shifted
to higher energy and [CpFe(CO)2THF]+ shifted to
lower energy, Fig. 2. Relative to the starting material,
the Fe–Fe bonds in 2 are elongated and the bonds
between the sulfur atom and the metal atoms of the Fe3
triangle are shortened. Iron–sulfur bond lengths of 1
Thermolysis reactions of 2 in toluene were carried
out in an attempt to generate a m4-sulfido cluster in a
butterfly geometry, instead the known compounds
[CpFe(CO)2]2, [(Ph3P)2N]2[Fe3(CO)9(m3-S)] (1), and
[(Ph3P)2N]2[Fe5(CO)14(m3-S)2] (3) were produced. Com-
pound 3 was first synthesized by chemical or electro-
chemical oxidation of 1 [22]. Similarly, a redox process
between the [CpFe(CO)2]+ and [Fe3(CO)9(m3-S)]2−
fragments of 2 may result in 3 and the reduced iron
species [CpFe(CO)2]2. In effect, the [CpFe(CO)2]+ unit
acts as a chemical oxidant toward 1. Cyclic voltamme-
try on 1 reveals a one-electron oxidation at −0.22 V
versus Ag ꢀ AgCl in 0.1 M [Bu4N]BF4 in CH2Cl2, Fig.
3A. Upon oxidation 1 is converted to 3 and the subse-
quent redox waves at 0.08, and 0.44 V correspond to
the electrochemical oxidation of 3. The assignments of
these waves to the oxidation of 3 have been verified by
Longoni and coworkers [22]. A chemically irreversible
reduction is observed in the cyclic voltammogram of
[CpFe(CO)2THF]BF4 at Ec −0.21 V, Fig. 3B. Reduc-
tion of [CpFe(CO)2THF]+ is followed by dimerization
of the CpFe(CO)2 to [CpFe(CO)2]2. Reoxidation of
[CpFe(CO)2]2 occurs at Ea 0.76 V, Fig. 3B. From the
reduction potential of [CpFe(CO)2THF]+ and the oxi-
dation potential of 1, a redox reaction between the two
is predicted to be thermodynamically favorable.
˚
˚
range from 2.184 to 2.198 A versus 2.142 to 2.159 A for
Cyclic voltammograms of 2, 0.1 M [Bu4N]BF4 in
CH2Cl2, reveal an oxidation wave at 0.19 V, which
represents an anodic shift from 1 by 0.41 V, Fig. 3C.
Presumably this oxidation process corresponds to re-
moval of an electron from the Fe3(CO)9(m3-S) compo-
nent of 2. At fast sweep rates, in excess of 1 V s−1, the
oxidation wave is chemically reversible with Ia/Ic value
of 0.92. Slow sweep rates or extension to higher poten-
tials results in a poorly developed return wave for the
first oxidation at 0.19 V. The absence of oxidation
Fig. 3. Cyclic voltammogram of (A) [(Ph3P)2N]2[Fe3(CO)9(m3-S)], (B)
[CpFe(CO)THF]BF4, and (C) [(Ph3P)2N][Fe3(CO)9{m3-SFeCp(CO)2}]
obtained in 0.1 M [Bu4N]BF4 CH2Cl2 with a Pt disk working and Pt
foil counter electrodes. Scan rates: —, 0.1 V s−1; ---, 1.0 V s−1
.

H.-J. Jeon et al. / Inorganica Chimica Acta 286 (1999) 142–148
147
waves at 0.44 V corresponding to compound 3 indicates
that the oxidative decomposition of 2 is significantly
different from 1. Apparently, coordination of the
[CpFe(CO)2]+ unit to the sulfur ligand of [Fe3(CO)9-
(m3-S)]2− prevents the formation of 3 upon oxidation.
No features in the cyclic voltammogram of 2 can be
assigned to the reduction of the CpFe(CO)2 unit. The
increased electron density on [CpFe(CO)2]+ upon inter-
action with [Fe3(CO)9(m3-S)]2− is expected to shift the
reduction potentials more negative compared to the
free cation [CpFe(CO)2THF]+. However, no reduction
waves are observed within the electrochemical window,
down to −1.5 V. Schauer and coworkers report a
chemically and electrochemically quasi-reversible oxida-
tion couple for Fe3(CO)9[m3-PFe(CO)2Cp]2, which con-
sist of a Fe3(CO)9 triangle capped by two m3-phosphido
ligands coordinating to two CpFe(CO)2 groups [31].
This oxidation process is assigned to the opening and
closing of the Fe3 triangle [32]. Upon extensive oxida-
tion of Fe3(CO)9[m3-PFe(CO)2Cp]2, a reduction wave
appears at −0.4 V. This new wave most likely corre-
sponds to the reduction of either a decomposition
product of the oxidized cluster or a dissociated
[CpFe(CO)2]+ unit. As in the present case, no redox
couples are assigned to the reduction of the
by C7H7+ which indicate the possible incorporating of
CpFe(CO)2 into charged species and the 13C NMR data
which indicate scrambling between the carbonyl ligands
of the CpFe(CO)2 moiety and the Fe3S fragment. Fur-
ther evidence for strong Fe3S–Fe interaction is the
absence of
a redox couple associated with the
CpFe(CO)2 fragment in the cyclic voltammogram of 2.
If the CpFe(CO)2 were linked to the Fe3S unit by a
simple donor–acceptor bond with no gross restructur-
ing of the molecular orbitals, the reduction of the
CpFe(CO)2 moiety of 2 would be expected to occur at
negative potentials. These experiments demonstrate the
importance of the sulfur ligand and its ligation in
determining the chemical and electrochemical proper-
ties of metal clusters.
5. Supplementary material
Tables of positional parameters, thermal parameters,
bond distances, and bond angles are available from the
authors on request. Crystallographic data have been
deposited with the Cambridge Crystallographic Data
Centre as supplementary material publication no.
CCDC-103521.
[CpFe(CO)2]+
Fe3(CO)9(m3-P)2 cluster.
fragment
coordinated
to
the
Chemical oxidation of 2 by tropylium produces the
known bicapped disulfido cluster Fe3(CO)9(m3-S)2 which
contains an open Fe3 triangle [33] and the dinuclear
complex Fe2(CO)6(m-S)2. Other iron carbonyl species
produced in the oxidation reaction were not identified.
Interestingly, there was no sign of Fe3(CO)9(m3-S)2 in
the voltammetry experiments where 2 is electrochemi-
cally oxidized. The cluster Fe3(CO)9(m3-S)2 undergoes
two one-electron reductions at −0.43 and −1.38 V
versus Ag ꢀ AgCl which were reported previously [34].
Infrared spectroscopy on reaction mixtures of 2 with
tropylium in closed reaction vessels indicate that
Fe3(CO)9(m3-S)2 is formed, however a large portion of
unreacted compound 2 remains after 24 h. When the
reaction vessel was fitted with a nitrogen bubbler, 2 is
entirely consumed after one day. Presumably, loss of
CO accompanies the oxidation process. Since no Cp
containing compounds were detected in the ether or
pentane extracts of the solid residue from the reaction
mixture, any intact CpFe(CO)2 fragments have likely
been incorporated into charged complexes.
Acknowledgements
We gratefully appreciate the support of the National
Science Foundation, award no. CHE-9417250.
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