Reaction of Fe(CO)2(η2-CS2){P(OR)3} 2 with phosphines: Desulphurization versus substitution. Crystal structures of Fe(CO)2(CS){P(OPh)3}2 and Fe(CO)3{P(OPh)3}2

Article abstract of DOI:10.1016/S0022-328X(98)00575-0

The reaction of Fe(CO)₂(η²-CS₂){P(OPh)₃} ₂ 1 with two equivalents of PBu₃ in a minimum volume of a polar solvent such as acetonitrile or dimethylsulfoxide afforded the thiocarbonyl derivative Fe(CO)₂(CS){P(OPh)₃}_} 2 in ca. 80% yield whereas reaction in solvents such as dichloromethane or benzene afforded the substitution products Fe(CO)₂(η²-CS₂){P(OPh) ₃}(PBu₃) and Fe(CO)₂(η²-CS₂)(PBu₃) ₂. Although desulphurization of Fe(CO)₂(η²-CS₂){P(OR)₃} ₂ by PBu₃ in polar solvents is not a general route to Fe(CO)₂(CS){P(OR)₃}₂ for all R, the new compound Fe(CO)₂(CS){P(OEt)₃}₂ has been obtained and characterised spectroscopically. The crystal structures of 2 and Fe(CO)₃{P(OPh)₃}₂ were determined and are very similar. Both compounds are trigonal bipyramidal about the Fe atom with trans apical phosphite ligands and a trigonal planar arrangement of CO/CS groups. The CS ligand in 2 was found to be disordered over two sites with occupancies 0.63 and 0.37.

Full text of DOI:10.1016/S0022-328X(98)00575-0

Journal of Organometallic Chemistry 563 (1998) 201–207
Reaction of Fe(CO)2(p2-CS2){P(OR)3}2 with phosphines:
desulphurization versus substitution. Crystal structures of
Fe(CO)2(CS){P(OPh)3}2 and Fe(CO)3{P(OPh)3}2
M. Barrow a, N.L. Cromhout a, D. Cunningham b, A.R. Manning a,*, P. McArdle b, J. Renze c
a Department of Chemistry, Uni6ersity College Dublin, Belfield, Dublin 4, Ireland
b Department of Chemistry, Uni6ersity College Galway, Galway, Ireland
c Department of Chemistry, Uni6ersity of Wu¨rtzburg, Wu¨rtzburg, Germany
Received 25 February 1998
Abstract
The reaction of Fe(CO)2(p2-CS2){P(OPh)3}2 1 with two equivalents of PBu3 in a minimum volume of a polar solvent such as
acetonitrile or dimethylsulfoxide afforded the thiocarbonyl derivative Fe(CO)2(CS){P(OPh)3}2 2 in ca. 80% yield whereas reaction
in solvents such as dichloromethane or benzene afforded the substitution products Fe(CO)2(p2-CS2){P(OPh)3}(PBu3) and
Fe(CO)2(p2-CS2)(PBu3)2. Although desulphurization of Fe(CO)2(p2-CS2){P(OR)3}2 by PBu3 in polar solvents is not a general
route to Fe(CO)2(CS){P(OR)3}2 for all R, the new compound Fe(CO)2(CS){P(OEt)3}2 has been obtained and characterised
spectroscopically. The crystal structures of 2 and Fe(CO)3{P(OPh)3}2 were determined and are very similar. Both compounds are
trigonal bipyramidal about the Fe atom with trans apical phosphite ligands and a trigonal planar arrangement of CO/CS groups.
The CS ligand in 2 was found to be disordered over two sites with occupancies 0.63 and 0.37. © 1998 Elsevier Science S.A. All
rights reserved.
Keywords: Thiocarbonyl complex; Desulphurization; Carbonyl complexes
1. Introduction
complexes requires prior formation of the S-alkylated
cations [Fe(CO)2(p2-CS2Me)(PR3)2]+ and, for PR3=
PMe3 or P(Me2Ph), reduction with Na/Hg [4]; for
PR3=PPh3 treatment of the cation with excess phos-
phine in polar solvents affords the required thiocar-
bonyl compound [5]. However, in the case where
L=P(OPh)3 the thiocarbonyl complex is directly acces-
sible from Fe(CO)2(p2-CS2){P(OPh)3}2, 1, and we have
previously reported the preparation of Fe(CO)2
(CS){P(OPh)3}2, 2, by reaction of 1 with PBu3 in CCl4,
although in only 10–15% yield [6]. We now report a
method for the facile and high yield synthesis of
Fe(CO)2(CS){P(OPh)3}2 and investigate the generality
of the preparative procedure. A redetermination of the
crystal structure of 2 is also presented and we further
report the crystal and molecular structure of the related
iron complex Fe(CO)3{P(OPh)3}2, 3.
The desulphurization of co-ordinated carbon
disulfide by phosphines (Eq. 1) is a convenient route to
thiocarbonyl metal complexes [1].
However, this method has proven to be very sensitive
to the nature of both the metal and the ancillary
ligands. Thus, the readily accessible complexes
Fe(CO)2(p2-CS2)(L)2 {L=PR3 or P(OR)3} [2] are inert
towards desulphurization by added phosphine when
L=PR3 [3]. Instead, preparation of Fe(CO)2(CS)(PR3)2
* Corresponding author. Fax: +353 1 7062127.
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00575-0

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M. Barrow et al. / Journal of Organometallic Chemistry 563 (1998) 201–207
2. Experimental
2.1. General methods
115°C. Anal. Found: C, 60.0; H, 3.84; S, 4.20%.
C39H30FeO8P2S requires: C, 60.3; H, 3.89; S, 4.12%. IR
(cm−1) wCO 1995, 1936 (CH2Cl2), 1989, 1929, (KBr), wCS
1266 (KBr). 1H-NMR l 7.23 (m, Ph). 13C-NMR l
315.8 (t, JCP=54, CS), 207.6 (t, JCP=34, CO), 151.0
(d, JCP=3.4, i-Ph), 129.6 (s, o-Ph), 125.1 (s, p-Ph),
122.0 (s, m-Ph). 31P-NMR l 171.8 (s). m/z (EI) 720
(Mꢀ2CO); 410 {ꢀP(OPh)3}; 366 (ꢀCS).
All reactions were performed under N2 using solvents
predried by standard procedures. Phosphines and phos-
phites were purchased from Aldrich and used without
further purification. Compound 1 was prepared accord-
ing to the modified literature procedure [7] given below.
Complexes Fe(CO)2(CS2)(L)2 where L=PPh(OMe)2,
P(OEt)3 or 1/2[(PPh3){P(OMe)3}] were prepared from 1
by ligand exchange in CH2Cl2 solution [7].
Fe(CO)3{P(OPh)3}2 was prepared according to the liter-
ature method [8]. IR spectra were recorded on a Perkin-
Elmer 1710FT spectrometer. NMR spectra were
obtained in CDCl3 solution on a Jeol JNM-GX270
2.3.2. Method B
The above reaction was repeated using one equiva-
lent of PBu3 to afford a 74% yield of 2 after 90 min
reaction time.
2.3.3. Method C
The reaction of Method A was repeated using a
suspension of 1 (0.750 g) in 20 cm3 of acetonitrile. The
starting material was consumed after 1 h and a 56%
yield of 2 was isolated.
FT-NMR spectrometer. H (270 MHz) and 13C (67.8
1
MHz) chemical shifts are reported downfield from te-
tramethylsilane as internal standard; 31P (109.3 MHz)
spectra are referenced to 85% phosphoric acid with
downfield shifts reported as positive. All coupling con-
stants are in Hertz. Mass spectra were recorded on a
VG Analytical 7070 mass spectrometer. Elemental
analyses were performed in the Microanalytical Labo-
ratory, University College Dublin.
2.3.4. Influence of added phosphine
An attempt was made to convert 1 into 2 by the
action of two equivalents of PMe3 and PPh3, respec-
tively, on 1 as in Method A. PMe3 was used as a 1 M
solution in THF and afforded a 51% yield of 2 after 90
min reaction time. PPh3 afforded a mixture of 1,
2.2. Synthesis of Fe(CO)2(CS2){P(OPh)3}2 1
Fe(CO)2(CS2){P(OPh)3}(PPh3)
and
Fe(CO)2(CS2)
(PPh3)2 which were identified by their IR spectra [7].
No trace of the thiocarbonyl complex was observed and
isolation of the products was not attempted.
A mixture of finely ground Fe2(CO)9 (1.00 g, 2.75
mmol) and triphenylphosphite (2.87 cm3, 11.0 mmol) in
CS2 (40 cm3) was heated at gentle reflux for ca. 30 min
and then allowed to stir at room temperature (r.t.) for
1 h. The resulting dark brown solution was filtered to
remove unreacted Fe2(CO)9. EtOH (15 cm3) was added
to the filtrate, the CS2 was removed under reduced
pressure without heating and the resulting precipitate
was isolated by filtration and washed with EtOH then
2.3.5. Influence of the sol6ent
The reaction of Method A was performed in DMSO
(10 cm3). After 1 h the mixture was extracted with
CH2Cl2 and H2O. Drying and concentration of the
organic layer afforded an orange residue which was
crystallised from hexane/toluene to afford 2 in 80%
yield.
Treatment of 1 with PBu3 in pyridine gave a solution
from which a 65% yield of 2 was isolated after 1 h
reaction time. In methanol, 1 gave a suspension and
less than 2% yield of 2 after 5 h stirring at r.t. with
added PBu3. A 45% yield of 2 was obtained on reaction
of 1 in acetone solution.
diethyl
ether
to
afford
analytically
pure
Fe(CO)2(CS2){P(OPh)3}2 in 50% yield based on reacted
Fe2(CO)9. M.p. 96–100°C dec. Anal. Found: C, 57.5;
H, 3.68; S, 8.24%. C39H30FeO8P2S2 requires: C, 57.95;
H, 3.74; S, 7.93%. IR (cm−1) wCO 2024, 1963, wCS 1160
1
(NCMe). H-NMR l 7.50 (m, Ph). 31P-NMR l 141.2
(s).
Reaction in CH2Cl2 afforded a near quantitative
yield of Fe(CO)2(CS2)(PBu3)2 and no trace of the thio-
carbonyl derivative.
2.3. Synthesis of Fe(CO)2(CS){P(OPh)3}2 2
2.3.1. Method A
Tri-n-butylphosphine (0.46 cm3, 1.86 mmol) was
added to a suspension of Fe(CO)2(CS2){P(OPh)3}2
(0.750 g, 0.93 mmol) in acetonitrile (10 cm3). The
mixture was stirred at r.t. for 1 h to afford an orange–
brown solution. The solvent was removed under re-
duced pressure and the residue was redissolved in a
minimum of toluene. Hexane was added to precipitate
Fe(CO)2(CS){P(OPh)3}2 (0.606 g, 84% yield). M.p.
2.4. Synthesis of Fe(CO)2(CS){P(OEt)3}2 4
Tri-n-butylphosphine (0.40 cm3, 1.62 mmol) was
added to a solution of Fe(CO)2(CS2){P(OEt)3}2 (0.420
g, 0.81 mmol) in acetonitrile (6 cm3) and the mixture
stirred at room temperature for 4 days. The solvent was
removed under reduced pressure and the residue chro-

M. Barrow et al. / Journal of Organometallic Chemistry 563 (1998) 201–207
203
matographed on silica TLC plates using CH2Cl2/40–60
petroleum ether as eluent. Three bands were developed
and identified as the starting material (20% recovered),
Fe(CO)2(CS){P(OEt)3}2 (ca. 15%) and Fe(CO)2(CS2)
(PBu3)2 (ca. 40%). The latter two compounds could
only be partially separated.
the phosphine [7]. This ligand exchange reaction is
maximally suppressed in acetonitrile or dimethylsulfox-
ide to favour desulphurization and formation of the
thiocarbonyl compound Fe(CO)2(CS){P(OPh)3}2, 2.
We investigated the reaction in a range of solvents and
found that, in general, increasing solvent polarity led to
an increase in reaction rate and product yield. The
results parallel those described by Dixneuf and co-
workers for the desulphurization of [Fe(CO)2
(PPh3)2(CS2Me)][I] by PBu3: the thiocarbonyl complex
Fe(CO)2(CS)(PPh3)2, 5, was obtained in 80% yield after
12 h stirring in DMSO whereas only 45% yield was
obtained after 72 h in CH2Cl2 or CHCl3 [5].
Spectroscopic data for 4: IR (cm−1) wCO 1978, 1915
1
(CH2Cl2), 1973, 1908 (KBr), wCS 1246 (KBr). H-NMR
l 4.17 (m, 2H, CH2), 1.37 (t, 3H, JHH=7, CH3).
13C-NMR l 318.0 (t, JPC=50, CS), 209.9 (t, JPC=33,
CO), 61.9 (s, CH2), 16.2 (s, CH3).
2.5. X-Ray data collection and structure refinement
The extent of ligand substitution versus CS forma-
tion in the Fe(CO)2(p2-CS2){P(OPh)3}2 system was also
found to depend on the concentration of the reactants:
optimum yields (84%) of 2 were obtained when the
X-ray quality single crystals of 2 were grown from a
toluene/hexane solution; single crystals of 3 were grown
slowly from a CDCl3/hexane mixture. X-ray data were
collected on an Enraf Nonius CAD4 diffractometer
with graphite monochromatised Mo–Kh radiation (u=
Table 1
˚
Summary of crystal data and details of the data collection and
refinement for 2 and 3
0.7093 A) at 293(2) K. The structures were solved by
direct methods, SHELXS-86 [9], and refined by full-ma-
trix least squares using SHELXL-97 [10] for 2 and
SHELXL-93 [11] for 3. Data were corrected for
Lorentz and polarisation effects but not for absorption.
Hydrogen atoms were included in calculated positions
with thermal parameters 30% larger than the atoms to
which they were attached. Calculations were performed
on a Pentium PC (for 2) or a Silicon Graphics R4000
(3) computer. Details of the X-ray data collection and
structure refinement are summarised in Table 1 and
selected bond lengths and angles are given in Table 2.
Supplementary material comprises a complete list of
bond lengths and bond angles, atom positions, thermal
parameters, and observed and calculated structure
factors.
Complex
2
3
Empirical formula
Molecular weight (g mol−1
Colour, habit
C39H30FeO8P2S C39H30FeO9P2
776.48
Orange, block
)
760.42
Pale yellow,
block
0.20×0.35
×0.40
Triclinic
P1
9.832(2)
10.975(3)
17.131(3)
96.68(2)
92.99(2)
99.76(2)
1804.5(7)
2
Crystal size (mm)
0.21×0.32
×0.40
Triclinic
P1
9.897(3)
11.012(2)
17.218(4)
97.82(2)
92.56(2)
99.90(2)
1826.9(8)
2
Crystal system
Space group
˚
a (A)
˚
b (A)
˚
c (A)
h (°)
i (°)
k (°)
3
˚
Volume (A )
Z
Dcalc. (g cm−3
F(000)
)
1.412
800
0.61
1.399
784
0.56
3. Results and discussion
v (mm−1
)
q range for data collection
hkl range
2 to 25
2 to 25
Two reaction pathways are possible on treatment of
Fe(CO)2(p2-CS2)(L)2 {L=PR3 or P(OR)3} with added
phosphine PR%3 viz. ligand substitution (Scheme 1a) or
desulphurization of CS2 to CS (Scheme 1b).
0–11, −13–12, 0–12, −13–13,
−20–20
7007
6395
0.028
5010
6395/9/469
0.964
R1=0.0544
wR2=0.1589
R1=0.0651
wR2=0.1698
−21–21
7701
7080
0.052
5345
Reflections collected
Unique reflections
Rint
Reflections with I\2|(I)
Data/restraints/parameters
Goodness-of-fitb
The type of reaction favoured is determined in the
first instance by the co-ordinated ligand L. Thus, when
L=PR3 substitution products are obtained exclusively
and access to the thiocarbonyl compounds is only
possible via the S-alkylated cations as described previ-
ously by Dixneuf and co-workers [4,5]. However, when
L=P(OR)3 both reaction pathways (a) and (b) operate
and we find that the ratio of substitution to S-abstrac-
tion is then determined by the reaction medium and the
concentration of the reactants.
7080/0/460
1.091
Final R indices [I\2|(I)]
R1=0.0447
wR2=0.1400
R1=0.0576
wR2=0.1503
0.48, –0.46
R indices (all data)a
Density range in final D-map 0.72, –0.45
−3
˚
(e A
)
a R indices; R1=[SꢀFoꢁ–ꢁFcꢀ]/SꢁFoꢁ (based on F), wR2=[S{w(ꢁF2o–
1
F2cꢁ)2/Sw(F2o)2}]2 (based on F2), w=1/[(|F2o)+(0.1303*P)2+0.42*P]
In solvents such as benzene, CH2Cl2 and CHCl3,
Fe(CO)2(p2-CS2){P(OPh)3}2, 1, reacts with PBu3 to
substitute first one and then both phosphite ligands for
for 2, w=1/[(|F2o)+(0.1038*P)2] for 3.
1
b Goodness-of-fit=[Sw(Fo2 –Fc2)2/(Nobs-Nparameters)]2.

204
M. Barrow et al. / Journal of Organometallic Chemistry 563 (1998) 201–207
Table 2
˚
Selected bond lengths (A) and angles (°) for 2 and 3
2
3
˚
Bond lengths (A)
Fe(1)–P(1)
Fe(1)–P(2)
Fe(1)–C(1)
Fe(2)–C(2)
Fe(1)–C(3)
P(1)–O(3)
P(1)–O(4)
P(1)–O(5)
P(2)–O(6)
P(2)–O(7)
P(2)–O(8)
S(1)–C(3)
2.1462(8)
2.1528(9)
1.793(4)
Fe(1)–P(1)
Fe(1)–P(2)
Fe(1)–C(1)
Fe(1)–C(2)
Fe(1)–C(3)
P(1)–O(4)
P(1)–O(5)
P(1)–O(6)
P(2)–O(7)
P(2)–O(8)
P(2)–O(9)
2.1408(8)
2.1421(8)
1.759(3)
1.778(3)
1.778(3)
1.608(2)
1.595(2)
1.599(2)
1.614(2)
1.604(2)
1.601(2)
Scheme
2.
Proposed
mechanism
of
reaction
of
Fe(CO)2(CS2){P(OPh)3}2 with phosphines.
1.7803(11)a
1.7724(10)a
1.597(2)
trile, the required thiocarbonyl product is easily isolated
from the ligand exchange co-products viz.
Fe(CO)2(CS2){P(OPh)3}(PBu3)
(PBu3)2, by precipitation from hexane in which solvent
the latter species are extremely soluble.
1.610(2)
1.595(2)
1.607(2)
1.611(2)
and
Fe(CO)2(CS2)
1.600(2)
1.5443(10)a
1.5459(11)a
1.157(4)
In an experiment in which the volume of acetonitrile
was doubled the IR spectra of the reaction mixture
showed an increase in ligand substitution products at
the expense of thiocarbonyl formation and the isolated
yield of 2 was reduced to 56%. In the presence of only
one equivalent of PBu3 the desulphurization reaction
was both slower and lower-yielding: a 74% yield of 2
was obtained after 90 min stirring at room temperature.
The above results agree with the postulate that the
ligand exchange reaction occurs via a dissociative path-
way [7]. The competing desulphurization reaction, how-
ever, appears to be bimolecular; this is consistent with
the mechanism proposed by Fenster and Butler [12]
which involves attack of free phosphine at the co-ordi-
nated sulphur atom of the CS2 ligand (Scheme 2).
The reaction of 1 with the phosphines PMe3 and
PPh3 was also investigated. The former reagent was
used as a 1 M solution in THF and under these
conditions afforded a 51% yield of the thiocarbonyl on
stirring with 1 in acetonitrile for 90 min. Reaction with
PPh3, however, afforded an equilibrium mixture of
S(11)–C(2)
O(1)–C(1)
O(2)–C(2)
O(1)–C(1)
O(2)–C(2)
O(3)–C(3)
O(4)–C(16)
O(5)–C(10)
O(6)–C(4)
O(7)–C(22)
O(8)–C(28)
O(9)–C(34)
1.146(3)
1.150(3)
1.148(3)
1.399(3)
1.410(3)
1.413(3)
1.400(3)
1.412(3)
1.394(3)
1.1734(11)a
O(3)–C(4)
O(4)–C(10)
O(5)–C(16)
O(6)–C(22)
O(7)–C(28)
O(8)–C(34)
1.404(4)
1.399(3)
1.410(3)
1.406(4)
1.389(4)
1.393(5)
Bond angles (°)
P(1)–Fe(1)–P(2) 177.27(3)
Fe(1)–P(1)–O(3) 120.18(8)
Fe(1)–P(1)–O(4) 118.61(8)
Fe(1)–P(1)–O(5) 113.51(8)
Fe(1)–P(2)–O(6) 118.93(9)
Fe(1)–P(2)–O(7) 120.05(9)
Fe(1)–P(2)–O(8) 119.27(10)
Fe(1)–C(1)–O(1) 178.3(3)
P(1)–Fe(1)–P(2)
Fe(1)–P(1)–O(4)
Fe(1)–P(1)–O(5)
Fe(1)–P(1)–O(6)
Fe(1)–P(2)–O(7)
Fe(1)–P(2)–O(8)
Fe(1)–P(2)–O(9)
Fe(1)–C(1)–O(1)
Fe(1)–C(2)–O(2)
Fe(1)–C(3)–O(3)
177.21(3)
118.85(7)
120.28(6)
113.13(6)
119.80(7)
119.61(8)
119.26(7)
177.6(2)
179.0(2)
179.0(3)
a The thiocarbonyl is disordered with one of the carbonyl groups.
Fe(CO)2(CS2)(L1)2,
Fe(CO)2(CS2)(L1)(L2)
and
Fe(CO)2(CS2)(L2)2 where L1=PPh3 and L2=P(OPh)3.
The same behaviour is observed on addition of PPh3 to
chloroform solutions of 1 [7]. The results suggest that
only the more basic trialkyl phosphines are effective in
the desulphurization of 1.
reaction was carried out in a minimum of acetonitrile
(nominal concentration ca. 0.1 M) and in the presence
of two equivalents of PBu3. Under these conditions the
starting material is consumed within 1 h as evidenced
by IR spectroscopy and, after removal of the acetoni-
The synthetic utility of the desulphurization proce-
dure described here appears to be effectively limited to
the triphenylphosphite complex 1. Thus, the bis(phos-
phonite) compound Fe(CO)2(CS2){PPh(OMe)2}2 failed
to react with PBu3 in acetonitrile even on prolonged
stirring (4 days) at room temperature. On heating to
30°C rapid ligand substitution occurred to afford
Fe(CO)2(CS2){PPh(OMe)2}(PBu3) and Fe(CO)2(CS2)
(PBu3)2 which were identified spectroscopically [7]. The
mixed phosphine/phosphite complex Fe(CO)2(CS2)
(PPh3){P(OMe)3} underwent only slow ligand substitu-
tion to afford ca. 40% of the bis-substituted complex
Fe(CO)2(CS2)(PBu3)2 after 1 week.
However, the thiocarbonyl complex Fe(CO)2(CS)
{P(OEt)3}2, 4, was successfully prepared, although in
Scheme 1. Reaction pathways for Fe(CO)2(p2-CS2)(L)2 and PR3% .

M. Barrow et al. / Journal of Organometallic Chemistry 563 (1998) 201–207
205
only ca. 15% yield, on extended reaction of
Fe(CO)2(CS2){P(OEt)3}2 with PBu3 in acetonitrile.
Compound 4 is difficult to separate from the co-product
Fe(CO)2(CS2)(PBu3)2 which has a very similar solubility
and Rf value in the solvent mixtures investigated and an
analytically pure sample was not obtained. However, 4
was unambiguously identified from the spectroscopic
data. The IR spectrum exhibits a strong absorption at
1246 cm−1 which may be compared with wCS frequen-
cies of 1266 and 1235 cm−1 in the IR spectra of
compounds 2 and 5 [5], respectively. The low-field
resonance at l 318.0 in the 13C-NMR spectrum of 4 is
also consistent with a thiocarbonyl 13C nucleus: corre-
sponding chemical shift values are l 315.8 for 2 and
324.3 for 5.
3.1. Crystal and molecular structure of
Fe(CO)2(CS){P(OPh)3}2
An ORTEX [13] diagram of compound 2 is shown in
Fig. 1 and selected bond lengths and angles are pre-
sented in Table 2. The co-ordination about the iron
atom is trigonal bipyramidal with the two phosphite
ligands occupying trans apical sites [P–Fe–P bond
angle 177.27(3)°] and the CO and CS ligands in the
equatorial plane of the molecule [C–Fe–C bond angles
sum to 359.92(3)°]. We have previously reported the
structure of 2 [6] and the CS group was found to be
disordered; the present structural determination was
undertaken in order to model this disorder properly.
Thus, we find the CS ligand to be disordered over two
sites involving C(2) and C(3). A model in which the CꢁS
˚
bond length was restrained to be 1.550 A in both sites
was refined to give a refined site occupancy of 0.63 for
the major site and 0.37 for the minor site occupancy.
The precision of the present structural determination is
better by a factor of ca. 3 in the S.D.’s than the structure
of 2 reported in the original communication [6].
Fig. 2. Three views of 2 with the atoms drawn as their van der Waal’s
spheres: (a) view down the non-disordered O–C–Fe axis, (b) view
down the S–C–Fe minor site and (c) view down the major S–C–Fe
site.
Three views down the O/S–C–Fe axes of 2 with the
atoms as their van der Waal’s spheres are presented in
Fig. 2 as PLUTON [14] diagrams. It is evident that four
phenyl groups of the phosphite ligands closely surround
the non-disordered CO ligand (Fig. 2a) whereas four
phenyl groups adopt a more open arrangement around
the minor CS site (Fig. 2b). Only three Ph groups are
associated with the major CS site (Fig. 2c).
Fig. 1. ORTEX diagram of the molecular structure of
Fe(CO)2(CS){P(OPh)3}2 2.

206
M. Barrow et al. / Journal of Organometallic Chemistry 563 (1998) 201–207
Table 3
The compound
2
and its phosphine analogue
˚
Selected bond lengths (A) and angles (°) for the compounds
Fe(CO)3(L)2 (L=P(OPh)3 3, P(OMe)3 6, PPh3 7) and 7·Et2O
Fe(CO)2(CS)(PPh3)2, 5, reported by Dixneuf and co-
workers in 1986 [5] are the only structurally character-
ised examples of zerovalent iron thiocarbonyl
complexes. The latter compound crystallises with two
independent molecules, A and B, in the unit cell and
there is no disorder of the CS ligand. The C–S bond
3
6a
7
7·Et2O
Fe–P
Fe–C
2.1408(8)
2.1421(8)
1.759(3)
1.778(3)
1.778(3)
2.155(1)
2.2144(9)
2.2201(9)
1.765(4)
1.770(4)
1.776(4)
2.207(3)
2.225(3)
1.755(8)
1.779(8)
1.783(7)
172.54(8)
116.9(3)
117.1(3)
125.9(3)
1.760(5)
1.764(7)
˚
lengths were determined as 1.550(7) and 1.563(8) A in
molecules A and B, respectively. An average value of
˚
1.768 A was reported for the corresponding Fe–CS
P–Fe–P
C–Fe–C 117.07(13)
120.04(12)
177.21(3)
178.5(1)
119.8(2)
120.6(2)
172.56(4)
118.08(17)
118.34(17)
123.56(17)
bond lengths.
The thiocarbonyl derivative 2 is closely related to the
tricarbonyl iron compound Fe(CO)3{P(OPh)3}2 3. Al-
though this latter complex has been known since 1958
[15] its structure has not been reported; a single crystal
122.65(12)
a
Molecule lies on a 2-fold axis.
X-ray diffraction analysis of
undertaken.
3
was therefore
consequent reduced back-donation into the Fe–P
bonds in 2. The (non-disordered) Fe–CO bond length
˚
[1.793(4) A] in 2 is also slightly longer, and the C–O
3.2. Crystal and molecular structure of
Fe(CO)3{P(OPh)3}2
˚
bond length [1.157(4) A] slightly shorter, than the cor-
responding distances in 3 [range of Fe–CO is 1.759(3)–
˚
˚
1.778(3) A; range of C–O is 1.146(3)–1.150(3) A]
although these differences are not statistically
significant.
An ORTEX [13] diagram of 3 is shown in Fig. 3 and
selected bond lengths and angles are given in Table 2.
The complex is trigonal bipyramidal about the Fe atom
with the phosphite ligands occupying mutually trans
apical sites [P–Fe–P bond angle 177.21(3)°] and a
meridional arrangement of CO groups [C–Fe–C bond
angles sum to 359.96(2)°]. Comparison of the structural
parameters of molecules 2 and 3 shows that replace-
ment of CO by CS increases the Fe–P bond distances
The conformations of the molecules 2 and 3 are
essentially identical. In particular we note the presence
in both structures of an Fe–P–O bond angle [Fe–
P(1)–O(5)=113.51(8)° in
2 and Fe–P(1)–O(6)=
113.13(6)° in 3] some 6° smaller than the remaining
P(1)–O bond angles (Table 2). A related distortion has
previously been described by Ginderow in the structure
of Fe(CO)3{P(OMe)3}2, 6, in which one of the Fe–P–O
bond angles at 113.27(7)° is 5.8° smaller than the
average [119.02(7)°] of the remaining two [16]. This
asymmetry of the phosphite ligands is manifested in the
IR spectra of both compounds 3 and 6 i.e. a splitting of
the otherwise degenerate E wCO band and the appear-
ance of the IR-forbidden A1 band [17].
˚
[average Fe–P=2.141(1) A in 3; average Fe–P=
˚
2.150(1) A in 2], an effect which may be correlated with
the greater y-acidity of the CS ligand versus CO [1] and
The structure of the phosphine analogue of 3 viz.
Fe(CO)3(PPh3)2, 7, has recently been reported by two
independent groups [18,19] (the latter structure is that
of the etherate 7·Et2O). A comparison of selected
structural data of these molecules is presented in Table
3 together with data for the bis(phosphite) complex 6.
Two structural features of the phosphine complex 7
and its etherate 7·Et2O are notable: the significant
deviation from linearity of the P–Fe–P bond angle and
the distortion of the Fe(CO)3 unit from trigonal planar
geometry as evidenced by the C–Fe–C bond angles,
two of which are nearly equivalent [118.08(17) and
118.34(17)° in 7] while the third [123.56(17)°] is substan-
tially larger. Glaser has recently attributed similar fea-
tures in the compound Fe(CO)3(PPh2Me)2 to packing
effects allowing for optimisation of intermolecular
phenyl-phenyl interactions [20]. Comparable molecular
distortions are not observed in the structures of the
Fig. 3. ORTEX diagram of the molecular structure of
Fe(CO)3{P(OPh)3}2 3.

M. Barrow et al. / Journal of Organometallic Chemistry 563 (1998) 201–207
207
Acknowledgements
We thank the Erasmus Student Exchange Programme
for funding for J. Renze.
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Fig. 4. Hydrogen bonding interactions in Fe(CO)3{P(OPh)3}2 3.
complexes 3 and 6 which contain the less sterically
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1758.
Analysis of the intra- and intermolecular interactions
in 3 using PLATON [22] reveals an intermolecular H…O
i
˚
contact of 2.73 A involving C(7)–H(7)…O(8) (i=x−1,
y−1, z) and two weaker C–H…y (arene) interactions
with H(23)…C(30)ii and H(24)…C(24)ii (ii=x−1, y, z)
˚
˚
which are 2.92 A and 2.91 A, respectively. These inter-
actions are depicted for 3 in Fig. 4. The related inter-
i
˚
molecular interactions in 2 are H(19)…O(6) 2.72 A,
[21] C.A. Tolman, Chem. Rev. 77 (1977) 313.
[22] A.L. Spek, PLATON, Molecular Geometry Program, May 1997
version, University of Utrecht, The Netherlands.
(i=1+x, 1+y, z), H(32)…C(25)ii 2.92
A
and
˚
ii
˚
H(33)…C(24) 2.93 A, (ii=1+x, y, z).
.