Synthesis and spectroscopic characterisation of compounds with formula [{Fe2S2(CO)5}Ph2P(CH 2)nPPh2{Fe(CO)4}] and [{Fe2S2(CO)5}2Ph 2P(CH2)nPPh2] (n=3, 4 and 6)

Article abstract of DOI:10.1016/S0022-328X(99)00623-3

The work described herein concerns the synthesis and characterisation of compounds with formula [{Fe₂S₂(CO)₅}Ph₂P(CH ₂)_nPPh₂{Fe(CO)₄}] and [{Fe₂S₂(CO)₅}₂Ph ₂P(CH₂)_nPPh₂] (n=3, 4, 6). The iron bis-phosphine cluster compounds with formula [{Fe₃(CO)₁₁}₂Ph₂P(CH ₂)_nPPh₂] and [{Fe₃(CO)₁₁}Ph₂P(CH₂) _nPPh₂{Fe(CO)₄}] (n=3, 4, 6)] were reacted with stoichiometric amounts of cyclohexene episulfide [SC₆H₁₀] in toluene at 70°C for 30-60 min. Optimum yields of 42.1-78.2%, were obtained for {Fe₂S₂-Fe} type species when a 1:4 cluster-ligand mole ratio was used, while the {Fe₂S₂}₂ type species were prepared in yields of 30-38% when a 1:8 cluster-ligand mole ratio was used. The volume of reaction solvent was kept to a minimum. For the latter cluster compounds, three isomeric products were isolated from each reaction; a justification for their presence is offered. All of these reactions afford clusters with fewer iron atoms but with S atoms incorporated. In these reactions the Fe₃-unit is 'degraded' but at the same time the cluster is expanded from three atoms {Fe₃} to four {Fe₂S₂}.

Full text of DOI:10.1016/S0022-328X(99)00623-3

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 595 (2000) 191–198
Synthesis and spectroscopic characterisation of compounds with
formula [{Fe2S2(CO)5}Ph2P(CH2)nPPh2{Fe(CO)4}] and
[{Fe2S2(CO)5}2Ph2P(CH2)nPPh2] (n=3, 4 and 6)
Rosamund Hourihane a,*, Geraldine Gray a, Trevor Spalding b, Tony Deeney c
a Chemistry Department, Cork Institute of Technology, Rossa A6enue, Bishopstown, Cork, Ireland
b Chemistry Department, Uni6ersity College Cork, College Road, Cork, Ireland
c Physics Department, Uni6ersity College Cork, College Road, Cork, Ireland
Received 29 July 1999; received in revised form 28 September 1999
Abstract
The work described herein concerns the synthesis and characterisation of compounds with formula [{Fe2S2(CO)5}-
Ph2P(CH2)nPPh2{Fe(CO)4}] and [{Fe2S2(CO)5}2Ph2P(CH2)nPPh2] (n=3, 4, 6). The iron bis-phosphine cluster compounds with
formula [{Fe3(CO)11}2Ph2P(CH2)nPPh2] and [{Fe3(CO)11}Ph2P(CH2)nPPh2{Fe(CO)4}] (n=3, 4, 6)] were reacted with stoichiomet-
ric amounts of cyclohexene episulfide [SC6H10] in toluene at 70°C for 30–60 min. Optimum yields of 42.1–78.2%, were obtained
for {Fe2S2ꢀFe} type species when a 1:4 cluster–ligand mole ratio was used, while the {Fe2S2}2 type species were prepared in yields
of 30–38% when a 1:8 cluster–ligand mole ratio was used. The volume of reaction solvent was kept to a minimum. For the latter
cluster compounds, three isomeric products were isolated from each reaction; a justification for their presence is offered. All of
these reactions afford clusters with fewer iron atoms but with S atoms incorporated. In these reactions the Fe3-unit is ‘degraded’
but at the same time the cluster is expanded from three atoms {Fe3} to four {Fe2S2}. © 2000 Elsevier Science S.A. All rights
reserved.
Keywords: Iron; Diphosphine; Sulfur; Bridging ligand; Mo¨ssbauer; Isomer
(CH2)nPPh2{Fe(CO)4}] n=3 (1), n=4 (2) and n=6
(3), obtained from the reaction of the {Fe3ꢀFe}, clus-
ters with cyclohexene episulfide and (ii) compounds
with formula [{Fe2S2(CO)5}2Ph2P(CH2)nPPh2] n=3
(4–6), n=4 (7–9) and n=6 (10–12) formed from the
reaction of the {Fe3ꢀFe3} double clusters with cyclo-
1. Introduction
Iron and sulfur have an affinity for one another [1].
Quite often complexes are formed by the reactions
between metal carbonyls, or their derivatives, and ele-
mental sulfur [2]. However, iron also shows a tendency
hexene episulfide. The products were characterised us-
to abstract sulfur atoms from a wide variety of com-
ing IR and Mo¨ssbauer spectroscopies as well as C, H,
pounds including episulfides [3], disulfanes [4], or more
Fe, S analysis.
usually thiocyanate ion [5]. The cluster size can be
expanded [6–8] or expanded and degraded simulta-
neously [9,10] with the incorporation of sulfur into the
cluster unit The cluster compounds discussed here fol-
2. Experimental
low the trends described, however they also contain
phosphine ligands.
2.1. General
The results will be discussed in two sections as fol-
lows, (i) compounds with formula [{Fe2S2(CO)5}Ph2P-
All reactions were carried out under an inert atmo-
sphere. Subsequent work was carried out in air. All
purified products were stored in the refrigerator, or
under vacuum. Tetrahydrofuran (THF) was freshly dis-
* Corresponding author. Fax: +353-21-345-191.
E-mail address: rhourihane@cit.ie (R. Hourihane)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00623-3

192
R. Hourihane et al. / Journal of Organometallic Chemistry 595 (2000) 191–198
tilled from potassium diphenylketyl. Toluene was
freshly distilled from sodium diphenylketyl. Hexane
and dichloromethane were dried over P2O5 and distilled
prior to use. All other solvents were reagent grade and
used as received. Bisphosphine ligands and cyclohexene
episulfide were commercial products obtained from
Aldrich. Iron cluster compounds [{Fe3(CO)11}Ph2P-
(CH2)nPPh2{Fe(CO)4}] and [{Fe3(CO)11}2Ph2P(CH2)n-
PPh2] n=3–6, were prepared as described in the litera-
ture [11].
samples were prepared for Mo¨ssbauer experiments, by
wrapping (0.05–0.1 g) of the compound in paper,
which was then wrapped in adhesive tape, forming a
pouch and placed in the gamma ray beam. For small
samples (B0.03 g) the material was dissolved in the
least amount of dichloromethane needed to transfer the
compound to the prepared pouch. The solvent was
allowed to evaporate, before the sample was frozen in
liquid nitrogen. Recording times varied between 24 h
and 4 days.
IR spectra were recorded on Perkin–Elmer 682 or
Mattson Polaris FTIR 10410, spectrophotometers. So-
lution spectra were obtained in sodium chloride cells.
Relative intensities were designated as vs, very strong; s,
strong; m, medium; w, weak; vw, very weak; other
descriptions were sh, shoulder; shp, sharp; br, broad.
Mo¨ssbauer spectra of the iron-containing compounds
were recorded at liquid-nitrogen temperatures (80 K)
using a commercial constant acceleration drive unit and
transducer (Harwell Instruments) in conjunction with a
Canberra System 40 multichannel analyser as previ-
ously described [12]. The source was 57Co in Rh and
was of 20 mCi nominal strength. Data was processed
on a Vax 11/780 computer and all data were referred to
the spectrum of sodium nitroprusside as standard.
When sufficient quantities of material were available,
All C and H analyses were carried out on a PE 240
analyser. Sulfur content was determined by the oxygen
flask method. Iron content was determined by atomic
absorption spectroscopy using a Pye Unicam SP 191
atomic absorption spectrophotometer.
2.2. Standard reaction procedure for the reaction
between compounds [{Fe3(CO)11}Ph2P(CH2)nPPh2{Fe-
(CO)4}], and [{Fe3(CO)11}2Ph2P(CH2)nPPh2] (n=3–6)
with cyclohexene episulfide
Each of the title compounds was reacted with a
stoichiometric amount of cyclohexene episulfide in
toluene under an inert atmosphere at 65–70°C for
30–60 min. Specific reaction details are outlined in
Tables 1 and 2. The extent of the reaction was moni-
Table 1
Reaction of [{Fe3(CO)11}Ph2P(CH2)nPPh2{Fe(CO)4}] (A) with cyclohexene episulfide (B) a
n
Reagent A, g
(mmol)
Reagent B volume, ml
(mmol)
Solvent volume
(ml)
Time (min)
Product formula
g (% yield)
6
4
3
0.29 (0.263)
0.115 (0.11)
0.088 (0.082)
0.11 (0.98)
0.049 (0.43)
0.037 (0.3)
75
20
20
60
30
30
[{Fe2S2(CO)5}Ph2P(CH2)6
PPh2{Fe(CO)4}] (3)
[{Fe2S2(CO)5}PPh2(CH2)4
PPh2{Fe(CO)4}] (2)
[{Fe2S2(CO)5}Ph2P(CH2)3
PPh2{Fe(CO)4}] (1)
0.193 (78.2)
0.06 (60.3)
0.031 (42.1)
a Mole ratio, 1:4 A–B; reaction temperature, 70°C; reaction solvent, toluene.
Table 2
Reaction of [{Fe3(CO)11}2Ph2P(CH2)nPPh2] (A) with cyclohexene episulfide (B) a
n
6
4
3
Reagent A, g
(mmol)
Reagent B volume, ml
(mmol)
Solvent volume
(ml)
Time (min)
Product formula
g (% yield)
0.10 (0.071)
0.069 (0.05)
0.133 (0.097)
0.064 (0.57)
0.045 (0.40)
0.088 (0.77)
75
20
20
50
30
30
[{Fe2S2(CO)5}2Ph2P(CH2)6PPh2] (10)
[{Fe2S2(CO)5}2Ph2P(CH2)6PPh2] (11)
[{Fe2S2(CO)5}2Ph2P(CH2)6PPh2] (12)
[{Fe2S2(CO)5}2Ph2P(CH2)4PPh2] (7)
[{Fe2S2(CO)5}2Ph2P(CH2)4PPh2] (8)
[{Fe2S2(CO)5}2Ph2P(CH2)4PPh2] (9)
[{Fe2S2(CO)5}2Ph2P(CH2)3PPh2] (4)
[{Fe2S2(CO)5}2Ph2P(CH2)3PPh2] (5)
[{Fe2S2(CO)5}2Ph2P(CH2)3PPh2] (6)
0.026 (32.7)
0.025 (31.7)
0.029 (37.4)
0.017 (32.5)
0.016 (29.3)
0.006 (11.2)
0.034 (33.2)
0.03 (29.1)
0.016 (15.5)
a Mole ratio 1:8 A–B; reaction temperature, 70°C; reaction solvent, toluene.

R. Hourihane et al. / Journal of Organometallic Chemistry 595 (2000) 191–198
193
tored by thin-layer chromatography using silica gel 60
as the stationary phase and dichloromethane–hexane
as eluant. The reaction mixture was filtered and the
toluene removed under reduced pressure. The residue
was dissolved in dichloromethane and chromato-
graphed using preparative thin-layer chromatography,
with silica gel (PF254) on glass plates and a mixture of
3:2 dichloromethane–hexane as eluant.
by preparative thin-layer chromatography. The C, H,
and Fe analyses were consistent with the proposed
[{Fe2S2(CO)5}Ph2P(CH2)nPPh2{Fe(CO)4}] formulation.
Further support for the proposed structures comes
from the IR and Mo¨ssbauer spectra of the products
(Table 3).
3.1.2. Spectroscopic characterisation
2.2.1. Reaction of [{Fe3(CO)11}Ph2P(CH2)nPPh2-
{FeCO)4}] (n=3–6) with cyclohexene episulfide
3.1.2.1. IR spectra. A summary of the energies of band
maxima of the IR absorptions in the carbonyl region
for compounds 1–3 is given in Table 3, together with
related data for [Fe2S2(CO)6] [13], [{Fe(CO)4}2-
PhP(CH2)nPPh2] n=3, 4 [14], n=6 [15], and
[Fe2CoS2(CO)6(h5-C5H5)] [16]. From Table 3 it can be
seen that the absorptions in the spectra of compounds
1–3 are a ‘combination’ of those due to two distin-
guishable units, i.e. [Fe(CO)4] and [Fe2(CO)5]. However,
as both units have overlapping CO absorption band
maxima, unambiguous assignment of particular absorp-
tions to a specific individual unit is difficult.
For example, considering compound 3 (n=6), the
carbonyl absorptions occur at 2060 m, shp, 2040 shp,
2020 m, shp, 2005 m, shp, 1990 s, br, 1955w, br and
1920 vs, br cm−1. The absorptions at 2040, 1990, 1955
and 1920 cm−1 may be assigned to the [Fe(CO)4] unit.
However the absorptions at 2040 and 1990/5 cm−1 may
also arise from the [Fe(CO)3] fragment, Table 3.
The remaining absorptions at 2005, 2020 and 2060
cm−1 can be assigned to the [Fe2S2(CO)5] species which
may contain an [Fe(CO)3] unit by comparison with
values reported by Havlin and Knox for [Fe2S2(CO)6]
[13] and Cowie et al. for [Fe2CoS2(CO)6(h5-C5H5)] [16]
(Table 3, see also Table 4). Similar assignments can be
made for compounds 1 and 2.
The solvent was removed under reduced pressure
yielding a red–brown residue. Chromatographic sepa-
ration afforded one main product (red–brown) and
trace amounts of others. Only the main product was
extracted into dichloromethane. The dichloromethane
was removed under reduced pressure and the residue
was redissolved in hexane. The volume of hexane was
reduced to 10 ml and stored for 2–3 days at 0°C. A
microcrystalline red–brown solid was recovered and
was characterised by IR and Mo¨ssbauer spectroscopies,
as well as chemical analyses (Table 3, Section 3), as
[{Fe2S2(CO)5}Ph2P(CH2)nPPh2{Fe(CO)4}] (n=3–6).
2.2.2. Reaction of [{Fe3(CO)11}2Ph2P(CH2)nPPh2]
(n=3–6) with cyclohexene episulfide
The solvent was removed under reduced pressure
yielding a red–brown residue. Chromatographic sepa-
ration afforded three red–brown products. These were
extracted into dichloromethane. The solvent was re-
moved under reduced pressure and the residues were
redissolved in hexane. The volume of hexane was re-
duced to 5 ml in each case and was stored for up to 2
weeks at 0°C. Microcystalline red–brown solids were
recovered for all three compounds, which were charac-
terised by IR and Mo¨ssbauer spectroscopies, two of the
three compounds in each case were further character-
ised by chemical analyses (Table 4, Section 3), as
[{Fe2S2(CO)5}2Ph2P(CH2)nPPh2] (n=3–6).
3.1.2.2. Mo¨ssbauer spectra. Further support for the
[{Fe2S2(CO)5}Ph2P(CH2)nPPh2{Fe(CO)4}] (n=3, 4, 6)
formulation for compounds 1, 2 and 3 comes from the
3. Results and discussion
Mo¨ssbauer spectroscopic studies. The values (mm s−1
)
of isomer shift (l) and quadrupole splitting (Z), to-
gether with the line assignment, numbered 1–6 from
left to right, are given in Table 3. The Mo¨ssbauer
spectra of compounds 2 and 3 are illustrated in Fig. 1.
The Mo¨ssbauer parameters can be assigned to specific
units within each compound as follows. Taking as an
example compound 3, the pair of absorptions with
Z=2.44 mm s−1, is assigned to the Fe(CO)4 unit by
comparison with values of Z=2.44, 2.58 and 2.41 mm
s−1 for equivalent sites in [Fe(CO)4PPh3] [17,18],
[Fe(CO)4PMe2]2 [19] and [{Fe(CO)4}2Ph2P(CH2)6PPh2]
[15], respectively. Because of the similarity of the Z
values reported here to those in previous compounds,
where apical substitution of the [Fe(CO)4] unit was
3.1. Compounds with formula [{Fe2S2(CO)5}Ph2P-
(CH2)nPPh2{Fe(CO)4}] {n=3 (1), n=4 (2), n=6 (3)}
3.1.1. Syntheses
Compounds 1, 2 and 3 were the only products iso-
lated from the reaction between the appropriate dark
green compound [{Fe3(CO)11}Ph2P(CH2)nPPh2{Fe-
(CO)4}] (n=3, 4, 6), and stoichiometric amounts of
cyclohexene episulfide in toluene at 70°C for 30–60 min
(Scheme 1). Optimum yields of 1, 42.1%, 2, 60.3% and
3, 78.2%, were obtained when a 1:4 cluster–ligand mole
ratio was used and the volume of reaction solvent kept
to a minimum. In all cases the products were separated

194
R. Hourihane et al. / Journal of Organometallic Chemistry 595 (2000) 191–198
for the substituted and unsubstituted sites are made in
accordance with literature suggestions for compounds
with thiolate ligands [20,21]. The unsubstituted Fe(CO)3
site is assigned to the higher Z value while the substi-
tuted Fe(CO)2P site is assigned to the lower Z value.
The substituted atom shows a decrease in Z at-
tributable to a decrease in electron back donation of
justified, apical substitution is also proposed here. Now
considering the [Fe2S2(CO)5] species, it can be seen
from Table 2 that it is more difficult to assign Mo¨ss-
bauer parameters as compound 3 gives an unresolved
doublet for two possible sites. However, if either com-
pound 1 or 2 is considered, two resolved doublets are
discernible (Fig. 1). The assignments (l) and (Z) values
Table 3
Characteristics of substituted iron carbonyl compounds with [{Fe2S2(CO)5}Ph2P(CH2)nPPh2{Fe(CO)4}] formulation
Compound
Anal. Calc. (Found)
IR
Mo¨ssbauer
Site
g
C
H
Fe
17.84
wmax CO (cm−1
)

l
Z
Y
[{Fe2S2(CO)5}Ph2P(CH2)6PPh2{Fe(CO)4}] (3) a
49.91
3.44
2040 m, shp,
1955 m, br
1920 vs, br
2060 m, shp,
2020 m, shp,
2005 m, shp,
1990 s br
2040 s, shp,
1955 m, br,
1920 vs, br
2065 m, shp,
2020 m, shp
2010 m, shp,
1995 s, br
Fe(CO)t4P
1,6
2,5
0.20 2.44 0.20
0.32 0.60 0.35
(50.03)
(3.73)
(17.98)
Fe(CO)3S
Fe(CO)2PS
[{Fe2S2(CO)5}Ph2P(CH2)4PPh2{Fe(CO)4}] (2) a
48.82
3.10
18.41
(18.18)
Fe(CO)t4P
1,6
0.20 2.44 0.35
(48.00)
(3.07)
Fe(CO)3S
Fe(CO)2PS
2,5
3,4
0.35 0.85 0.60
0.45
[{Fe2S2(CO)5}Ph2P(CH2)3PPh2{Fe(CO)4}] (1) a
48.04
2.93
18.68
(18.91)
2040 s, shp,
1955 m, br,
1920 vs, br
2065 m
Fe(CO)t4P
1,6
0.19 2.39 0.35
(47.52)
(3.22)
Fe(CO)3S
Fe(CO)2PS
2,5
3,4
0.34 0.85 0.60
0.50
2020 m, shp,
1990 s, br
Fe(CO)t4P
0.19 2.41 0.25
a,c
[{Fe(CO)4}Ph2P(CH2)3]2
2040 vs, shp,
1992 vw, sh,
1955, s,
1920 vs, br
1992 vw, sh,
1955, s,
1929 vs, br
2040 vs, shp,
2010 vw,
1955 vw,
1960 s,
[{Fe(CO4)}2Ph2P(CH2)3PPh2] a,c
Fe(CO)4
0.19 2.46
1920 vs br
2083 s,
2042 s,
2005 m
2068 s,
[Fe2S2(CO)6] b
Fe(CO)3S
Fe(CO)3
0.29 0.59 0.45
[Fe2CoS2(CO)6(h5-C5H5)] d
2042 vs,
1993 vs
[Fe(CO)5] e
Fe(CO)t5
2.60
0.20 2.44
[Fe(CO)4PPh3] f
Fe(CO)t4P
a IR solvent CH2Cl2.
b IR solvent CCl4.
c Ref. [15].
d Ref. [16].
e Ref. [17].
f Ref. [18].
g
, line assignment; l, isomer shift; Z, quadrupole splitting; Y, peak-width at half-height.

R. Hourihane et al. / Journal of Organometallic Chemistry 595 (2000) 191–198
195
Table 4
Characteristics of substituted iron carbonyl compounds with proposed [{Fe2S2(CO)5}Ph2P(CH2)nPPh2] formulation
Compound
Anal. Calc. (Found)
IR
Mo¨ssbauer
Site
d
C
H
Fe
20.55
wmax CO (cm−1
)

l
Z
Y
[{Fe2S2(CO)5}2Ph2P(CH2)6PPh2] (10)
44.23
2.97
2063m, shp,
2038 w, shp,
2020 m, shp,
2010 m, shp
1990 s, br,
1970 sh,
Fe(CO)3S
Fe(CO)2SP
1,4
2,3
0.33
0.80
0.48
0.45
(44.65)
(3.47)
(20.50)
1920 w, br
2063 s, shp,
2040 vw, sh,
2020 vw,
[{Fe2S2(CO)5}2Ph2P(CH2)6PPh2] (11)
[{Fe2S2(CO)5}Ph2P(CH2)]2 (12)
44.23
(43.90)
2.97
(3.52)
20.55
(20.49)
Fe(CO)3S
1,4
2,3
0.33
0.33
0.31
0.33
0.36
0.35
0.80
0.50
0.50
0.55
0.60
0.60
0.60
0.55
Fe(CO)2SP
2010 w,
1990 vs, br
2063 s, shp,
2040 m, shp,
2025 s, shp,
2010 s, shp,
1990 vs, br
2070 m, shp,
2040 m, shp,
2025 m, shp,
2010 m, shp,
1995 vs, br
2065 s, shp,
2040 vw, sh,
2020 w, sh
2010 m, shp,
1995 vs, br
2065 m, shp,
2040 m,
Fe(CO)3S
1,4
2,3
0.88
0.63
Fe(CO)2SP
[{Fe2S2(CO)5}2Ph2P(CH2)4PPh2] (7)
[{Fe2S2(CO)5}2Ph2P(CH2)4PPh2] (8)
[{Fe2S2(CO)5}2Ph2P(CH2)2]2 (9)
[{Fe2S2(CO)5}2Ph2P(CH2)3PPh2] (4)
43.13
(42.16)
2.67
(2.60)
21.09
(21.10)
Fe(CO)3S
1,4
2,3
0.90
0.68
Fe(CO)2SP
43.13
(44.60)
2.67
(2.96)
21.09
(21.53)
Fe(CO)3S
1,4
2,3
0.90
0.68
Fe(CO)2SP
Fe(CO)3S
1,4
2,3
0.90
0.58
2025 m,
2010 m,
Fe(CO)2SP
1995 vs, br
2060 m, shp,
2040 w, shp,
2020 m, shp,
2005 m, shp,
1990 vs, br,
1960 sh,
42.60
(43.08)
2.59
(2.37)
21.37
(21.50)
Fe(CO)3S
0.63
Fe(CO)2SP
1920 w, br
2060 m, shp,
2040 vw, sh,
2020 vw, sh,
2005 m, shp,
1995 vs br
2065 m, shp,
2040 w, shp,
2020 m, shp,
2010 m, shp,
1990 s, br
[{Fe2S2(CO)5}2Ph2P(CH2)3PPh2] (5)
[{Fe2S2(CO)5}2Ph2P(CH2)3PPh2] (6)
42.60
(41.70)
2.59
(2.67)
21.37
(21.55)
Fe(CO)3S
1,4
2,3
0.35
0.85
0.45
0.68
0.60
0.45
Fe(CO)2SP
Fe(CO)3S
1,4
2,3
0.35
0.39
0.80
0.44
Fe(CO)2SP
[Fe2S2(CO)6] a,b
2083 s,
Fe(CO)3S
0.29
0.59
2042 s,
2005 m
2068 s,
2042 s,
[Fe2CoS2(CO)6(h5-C5H5)] a,b,c
1993 vs
a IR solvent CCl4.
b Ref. [13].
c Ref. [16]
d
, line assignment; l, isomer shift; Z, quadrupole splitting; Y, peak-width at half-height.

196
R. Hourihane et al. / Journal of Organometallic Chemistry 595 (2000) 191–198
the phosphine ligand compared with a CO ligand [20].
Interestingly, the Z value for the unsubstituted atom
(0.85 mm s−1) shows an increase, which may indicate a
slight change in geometry of the CO ligands at this iron
atom. de Beer et al. reported similarly for compounds
with thiolate ligands [21]. Similar assignments may be
made for compound 1.
The isomer shift values for the Fe(CO)t4P unit are
0.20 mm s−1 for 3 and 2 and 0.19 mm s−1 for 1, which
are very close to the value for this site in [Fe(CO)4PPh3]
[18], l=0.20 mm s−1 or in compound [{Fe(CO)4]2-
Ph2P(CH2)6PPh2] [15] l=0.19 mm s−1. The l value
assigned to each iron atom in the ‘Fe2’ unit in each of
the three compounds (1–3) are 0.34, 0.35 and 0.32 mm
s
−1, respectively. These show a marked increase from
that of the unsubstituted system Fe2S2(CO)6, l=0.29
mm s−1. An increase in isomer shift may be expected
with substitution of a CO by a phosphine ligand for the
reason discussed above [20].
3.2. Compounds with formula [{Fe2S2(CO)5]2Ph2P-
(CH2)nPPh2] {n=3 (4–6), n=4 (7–9), n=6 (10–12)}
3.2.1. Syntheses
The title compounds were isolated from the reaction
between the dark green compound [{Fe3(CO)11}2-
Ph2P(CH2)nPPh2] (n=3–6) and stoichiometric amounts
of cyclohexene episulfide in toluene at 70°C for 30–85
min. From each reaction three products were separated
Fig. 1. Mo¨ssbauer spectra of compounds with formula
[{Fe2S2(CO)5}Ph2P(CH2)nPPh2{Fe(CO)4}] (a) n=4 (2) and (b) n=6
(3).
by preparative thin-layer chromatography (Scheme 2,
for n=6, i.e. compounds 10–12). Generally optimum
yields of 30–38% were obtained when a 1:8 cluster–lig-
and mole ratio was used but in two cases, compounds
6 and 9, the isolated yields were 15.5 and 11.2%,
respectively. For the six compounds that were obtained
sufficiently pure, the C, H, and Fe analyses were consis-
tent
with
the
proposed
[{Fe2S2(CO)5}2Ph2P-
(CH2)nPPh2] formulation, Table 4. All nine compounds
were characterised by IR and Mo¨ssbauer spectro-
scopies. This data also supported the above formula-
tion.
3.2.2. Spectroscopic characterisation
3.2.2.1. IR spectra. A summary of the IR absorptions in
the carbonyl region for compounds 4–12 is given in
Table 4. From this table it can be seen that the posi-
tions of the carbonyl absorptions for each set of three
compounds (4–6, 7–9 and 10–12) are very similar.
Comparison of these values with those reported in the
Scheme 1. Proposed reaction scheme for the formation of compounds
with formulae {[Fe2S2(CO)5]Ph2P(CH2)nPPh2[Fe(CO)4]}.

R. Hourihane et al. / Journal of Organometallic Chemistry 595 (2000) 191–198
197
literature for compounds with [Fe2S2(CO)x] units shows
remarkable similarities. For example, compound 11,
n=6, with carbonyl absorptions, 2063 m, shp, 2040 w,
shp, 2020 w, 2010 w, 1990 vs, br cm−1, and
[Fe2CoS2(CO)6(h5-C5H5)] [16] with absorptions 2068,
2042 and 1995 cm−1 are very similar. Other
comparable values are provided by [Fe2PdS2(CO)6-
(m-PPh3)2] [22] with carbonyl absorptions 2050, 2008,
1971 cm−1, or the compounds already discussed
(Section 3.2.1, Table 3). However, it is impossible to
assign individual absorptions to particular sites.
3.2.2.2. Mo¨ssbauer spectra. The values (mm s−1) of
isomer shift (l) and quadrupole splitting (Z) for
compounds 4–12 are summarised in Table 4, together
with the line assignment numbered 1–4 from left to
right. The Mo¨ssbauer spectra of compounds 4 and 10
are illustrated in Fig. 2. From the table it can be seen
that all Fe(CO)3S sites of the Fe2S2(CO)5P unit are
assigned a quadrupole splitting value of 0.8590.05 mm
s
−1, while the Fe(CO)2PS sites have Z=0.5690.12
mm s−1. The only exception is compound 4, n=3,
which gave an unresolved doublet from which both
sites were assigned a value of Z 0.63 mm s−1. If these
values are compared with those in Table 3, it can be
seen that there is a remarkable similarity in the
quadrupole splitting values for the substituted and
unsubstituted iron sites within the Fe2S2(CO)5L moiety,
which endorses the proposed formulation for these
compounds.
Fig. 2. Mo¨ssbauer spectra of compounds with formula
[{Fe2S2(CO)5}2Ph2P(CH2)nPPh2] (a) n=6 (10) and n=3 (4).
The isomer shift value for all sites is 0.3990.05 mm
s
−1, which is very similar to that (l=0.3490.05) for
similar species in Table 1.
The peak-width at half-height values Y increase with
decreasing n, Y=0.50 mm s−1 (n=6) and 0.68 mm
s−1 (n=3).
4. Presence of isomers
The three compounds formed in each reaction were
found to have remarkably similar IR and Mo¨ssbauer
spectra. For each set of three compounds, it was found
that if any single purified material was allowed to stand
Scheme 2. Proposed reaction scheme for the formation of compounds
with formulae {[Fe2S2(CO)5]2Ph2P(CH2)nPPh2}.
Fig. 3. Geometrical representation of [Fe2S2(CO)6].

198
R. Hourihane et al. / Journal of Organometallic Chemistry 595 (2000) 191–198
Three isomers are predicted in theory and realised in
practice, in an experimental ratio of 1:1:1. It might not
have been expected that the isomers would be formed
in equal amounts for the reasons outlined above. How-
ever, the rate of formation of one isomer over another
as well as the thermodynamic stability of certain iso-
mers over others must also have an influence. Unfortu-
nately, because the isomers interconvert so rapidly in
solution, the isolation of crystals of a single isomer
could not be achieved.
Acknowledgements
We wish to thank Forbairt Ireland for financial
support for this research.
References
[1] H. Vahrenkamp, Angew. Chem. Int. Ed. Engl. 14 (1975) 322.
[2] R.S. Gall, C.T.W. Chu, L.F. Dahl, J. Am. Chem. Soc. 96 (1974)
4019.
[3] R.B. King, Inorg. Chem. 2 (1963) 326.
[4] R.J. Haines, J.A. de Beer, R. Greatrex, J. Organomet. Chem. 55
(1973) C30.
[5] J.M. Coleman, A. Wojacki, P.J. Pollick, L.F. Dahl, Inorg.
Chem. 6 (1967) 1236.
[6] W. Hieber, J. Gruber, Z. Anorg. Allg. Chem. 296 (1958) 91.
[7] F. Calderoni, F. Demartin, M. Carmela Iapalucci, F. Laschi, G.
Longoni, P. Zanello, Inorg. Chem. 35 (1996) 898.
[8] A.J. Edwards, A. Martin, M.J. Mays, D. Nazar, P.R. Raithby,
J.A. Solan, J. Chem. Soc. Dalton Trans. (1993) 355.
[9] N.S. Nametkin, B.I. Kolabkov, V.D. Tyurin, A.N. Muratov,
A.I. Nekaev, M. Mavlonov, A.Y. Sideridu, G.G. Aleksandrov,
A.V. Lebedev, M.T. Tashev, H.B. Dustov, J. Organomet. Chem.
276 (1984) 393.
Fig. 4. Possible combinations of two [Fe2S2(CO)6] units; (a) apical to
basal, (b) apical to apical and (c) basal to basal.
in dichloromethane solution for 30–60 min, mixtures of
all three compounds resulted. This clearly suggested the
presence of reactions leading to isomer formation or,
possibly, cluster-rearrangement. However, the latter
possibility was ruled out by the closely similar spectra
of the products and the chemical analyses.
[10] T. Mitsui, S. Inomata, H. Ogino, Inorg. Chem. 33 (1994) 4934.
[11] G. Ferguson, R. Hourihane, T.R. Spalding, Acta Crystallogr.
Sect. C 47 (1991) 544.
[12] W.E. Carroll, F.A. Deeney, F.J. Lalor, J. Organomet. Chem. 198
(1980) 189.
[13] R. Havlin, G.R. Knox, J. Organomet. Chem. 4 (1965) 247.
[14] P.A. Wegner, L.F. Evans, J. Haddock, Inorg. Chem. 4 (1975)
192.
From the examination of the structure of
[Fe2S2(CO)6], a number of possible isomers formed by
linking two such clusters through a diphosphine ligand
may be predicted. The crystal structure of [Fe2S2(CO)6]
was determined by Wei and Dahl, in 1965 [23] (Fig. 3).
Assuming that the probability of substitution of any of
the four ‘pseudo basal’ carbonyls C(2), (3), (5), (6) or
either of the two ‘pseudo apical’ carbonyls C(1), (4) by
a phosphine ligand will be the same, there are three
possible ways in which the ligand can link two
[Fe2S2(CO)x] units. These are via apical to apical, apical
to basal or basal to basal positions, (Fig. 4). It is
difficult to predict a theoretical ratio in which these
isomers might be formed without knowing how steric
and environmental factors effect CO substitution.
[15] R. Hourihane, Ph.D. Thesis, University College Cork, Ireland,
1992.
[16] M. Cowie, R.L. Dekock, T.R. Wagenmaker, D. Seyferth, R.S.
Henderson, M.K. Gallagher, Organometallics 8 (1989) 119.
[17] C.D. Pribula, T.L. Brown, E. Munck, J. Am. Chem. Soc. 96
(1974) 4149.
[18] W.E. Carroll, F.A. Deeney, J.A. Delaney, F.J. Lalor, J. Chem.
Soc. Dalton Trans. (1973) 718.
[19] T.G. Gibb, R. Greatrex, N.N. Greenwood, D.T. Thompson, J.
Chem. Soc. A (1967) 1663.
[20] R.V. Parish, The Organic Chemistry of Iron, vol. 1, Academic
Press, New York, 1978.
[21] J.A. de Beer, R.J. Haines, R. Greatrex, N.N. Greenwood, J.
Chem. Soc. A (1971) 3271.
[22] D. Seyferth, R.S. Henderson, L.C. Song, Organometallics 1
(1982) 125.
[23] C.H. Wei, L.F. Dahl, Inorg. Chem. 4 (1965) 1.