Heptacoordinate dithiophosphate W(II) and Mo(II) complexes of diphosphines and iodide

Article abstract of DOI:10.1016/S0020-1693(01)00699-5

New complexes [MI(CO)₂(dppe){S₂P(OEt)₂}] (M=W, 1a; M=Mo, 1b), [MI(CO)₂(dppm){S₂P(OEt)₂}] (M=W, 2a; M=Mo, 2b) and [W(CO)(dppe){S₂P(OEt)₂}₂][O₂dppe] (3a), were synthesised from [MI₂(CO)₃(NCMe)₂] (M=Mo, W), after treatment with ammonium diethyldithiophosphate and phosphine under different conditions. The structure of the tungsten complexes was determined by single crystal X-ray diffraction. During the synthesis of 3a, oxidation of the phosphine took place and a molecule of oxidised phosphine occupies channels in the crystal. DFT/B3LYP calculations on models of 1a and 2a showed the capped octahedron structure, observed in most dicarbonyl complexes of this family, to be preferred by 1.4 and 2.6 kcalmol^-1 for the dppm and the dppe complexes, respectively. Strong steric repulsions can reverse this trend, as happens with the rigid dppm ligand. Complex 1a adopts a pentagonal bipyramidal geometry, which is often found in related monocarbonyl complexes.

Full text of DOI:10.1016/S0020-1693(01)00699-5

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Inorganica Chimica Acta 327 (2002) 169–178
Heptacoordinate dithiophosphate W(II) and Mo(II) complexes of
diphosphines and iodide
Huizhang Liu a, Maria Jose´ Calhorda a,b,*, Vitor Fe´lix c, Michael G.B. Drew d,
Lu´ıs F. Veiros e
a Instituto de Tecnologia Qu´ımica e Biolo´gica (ITQB), A6. da Repu´blica, EAN, Apt 127, 2781-901 Oeiras, Portugal
b Departamento de Qu´ımica e Bioqu´ımica, Faculdade de Cieˆncias da Uni6ersidade de Lisboa, 1749-016 Lisbon, Portugal
c Departamento de Qu´ımica, Uni6ersidade de A6eiro, 3810-193 A6eiro, Portugal
d Department of Chemistry, Uni6ersity of Reading, Whiteknights, Reading, RG6 6AD, UK
e Centro de Qu´ımica Estrutural, Complexo I, Instituto Superior Te´cnico, A6. Ro6isco Pais, 1, 1049-001 Lisbon, Portugal
Received 25 June 2001; accepted 29 August 2001
Dedicated to Professor K. Vrieze on the occasion of his retirement
Abstract
New complexes [MI(CO)2(dppe){S2P(OEt)2}] (M=W, 1a; M=Mo, 1b), [MI(CO)2(dppm){S2P(OEt)2}] (M=W, 2a; M=Mo,
2b) and [W(CO)(dppe){S2P(OEt)2}2][O2dppe] (3a), were synthesised from [MI2(CO)3(NCMe)2] (M=Mo, W), after treatment with
ammonium diethyldithiophosphate and phosphine under different conditions. The structure of the tungsten complexes was
determined by single crystal X-ray diffraction. During the synthesis of 3a, oxidation of the phosphine took place and a molecule
of oxidised phosphine occupies channels in the crystal. DFT/B3LYP calculations on models of 1a and 2a showed the capped
octahedron structure, observed in most dicarbonyl complexes of this family, to be preferred by 1.4 and 2.6 kcal mol−1 for the
dppm and the dppe complexes, respectively. Strong steric repulsions can reverse this trend, as happens with the rigid dppm ligand.
Complex 1a adopts a pentagonal bipyramidal geometry, which is often found in related monocarbonyl complexes. © 2002
Elsevier Science B.V. All rights reserved.
Keywords: Tungsten; Molybdenum; DFT calculations; Seven coordination; Crystal structures
unusual unsaturated 16 electron carbonyl derivatives
have also been described [4h]. The seven-coordinate
complexes exhibit the typical structures ranging from
the capped octahedron, capped trigonal prism and pen-
tagonal bipyramid, to the 4:3 geometry [4c], which have
been studied in detail, as well as their interconversion
pathways [7]. Following previous work [8], we describe
the synthesis and characterisation of new Mo(II) and
W(II) complexes containing carbonyl, iodide, phos-
phine and dithiophosphate. Some of the compounds
have been structurally characterised by single crystal
X-ray diffraction. Different structural arrangements are
observed in these two groups of compounds, depending
on the type of ligands in the coordination sphere of the
metal. A rationalisation of the preferences is given
based on DFT calculations [9] using the GAUSSIAN 98
program [10].
1. Introduction
The role of molybdenum in chemistry ranges from its
presence in metalloenzymes such as nitrogenase, where
it is involved in nitrogen fixation in association with
iron [1,2], to industrial processes, among which one of
the most relevant is hydrodesulfurisation [3]. A full
understanding of the mechanisms of these and other
reactions requires a good knowledge of molybdenum
chemistry. Molybdenum(II) derivatives have been
widely synthesised and characterised [4–6]. Most of the
organometallic complexes satisfy the 18 electron rule
and are heptacoordinate, although examples of more
* Corresponding author.
E-mail address: mjc@itqb.unl.pt (M.J. Calhorda).
0020-1693/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00699-5

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H. Liu et al. / Inorganica Chimica Acta 327 (2002) 169–178
2. Results and discussion
The two reactions described above were repeated
starting from the Mo complex [MoI2(CO)3(NCMe)2]
and allowing it to react with dppe or dppm, to afford,
respectively, [MoI(CO)2(dppe){S2P(OEt)2}] (1b) and
[MoI(CO)2(dppm){S2P(OEt)2}] (2b). The infrared spec-
tra of 1b also exhibited two wCꢀO stretching modes at
1943 and 1875 cm−1, while four peaks could be ob-
2.1. Chemical results
The complexes [MI2(CO)3(NCMe)2] (M=Mo, W) [4]
were treated with ammonium diethyldithiophosphate
(1:1), in dichloromethane. After separation of a solid
precipitate, phosphine (Ph2PCH2PPh2=dppm or
Ph2P(CH2)2PPh2=dppe) was added to the filtrate to
afford new complexes. The product from the reaction
of [WI2(CO)3(NCMe)2] with dppe (1a) exhibited two
wCꢀO stretching modes at 1933 and 1860 cm−1, assigned
to the symmetric and antisymmetric modes of two
1
served in the H NMR spectra in CD3CN. These peaks
were assigned to phenyl protons (l=7.59 ppm), CH2
from dppe (l=2.69–2.75 ppm), CH2 from OEt (l=
3.97–4.02 ppm) and CH3 from OEt (l=1.22–1.27
ppm) and integrated approximately as 20:4:4:6. The
structure of complex 1b therefore was considered to be
equivalent to that of the tungsten analogue. Similarly,
[MoI(CO)2(dppm){S2P(OEt)2}] (2b) exhibited two wCꢀO
stretching modes at 1934 and 1859 cm−1, as well as
four peaks in the 1H NMR spectrum, assigned to
phenyl protons (l=7.22–7.80 ppm), CH2 from dppm
(l=4.20–4.25 ppm), CH2 from OEt (l=3.77–3.99
ppm) and CH3 from OEt (l=1.28–1.38 ppm), inte-
grating as 20:2:4:6, comparable to the W analogue 2a.
[MoI2(CO)3(NCMe)2] [4] was treated with ammo-
nium diethyldithiophosphate, in dichloromethane. Af-
ter separation of a solid precipitate, dppe was added to
the filtrate and the final product allowed to precipitate
during a long period (2 weeks), in order to attempt to
form the tungsten analogue of the oxidation product
[Mo(O)(I)(dppe){S2P(OEt)2}] [8]. The single crystal X-
ray determination showed indeed that a new W com-
plex was present [W(CO)(dppe){S2P(OEt)2}2][O2dppe]
(3a), along with one molecule of dioxidised dppe. The
tungsten complex is the analogue of [Mo(CO)-
(dppe){S2P(OEt)2}2] (3b), previously described, but
formed after a relatively fast precipitation [8]. However,
while the oxidation took place on the metal for Mo, in
1
coordinated carbonyl groups. The H NMR spectrum
in CD3CN shows four groups of peaks, which can be
assigned to the phenyl protons of dppe (l=7.57 ppm),
the methylenic protons of dppe (l=2.70–2.76 ppm),
the methylenic protons of the ethyl group (l=3.96–
4.06 ppm) and the methylic protons of the ethyl group
(l=1.24–1.28 ppm), respectively, integrating approxi-
mately as 20:4:4:6, respectively. The structure of 1a
determined using single crystal X-ray diffraction was
found to be
a
heptacoordinate W(II) complex
[WI(CO)2(dppe){S2P(OEt)2}]. The same reaction was
carried out, using dppm as the phosphine. A similar
product, 2a, was obtained, which also exhibited two
wCꢀO stretching modes at 1930 and 1847 cm−1 and four
1H NMR peaks (multiplets) at l 7.55, 5.18–5.26, 4.10
and 1.27–1.32 ppm, for the phenyl and methylene
protons of dppm, and methylene and methyl protons of
the ethyl groups, respectively. The 31P NMR spectrum
in CD3CN showed two peaks at 101.1 and 52.3 ppm,
assigned to dppm and S2P(OEt)2, respectively. The
assignment of this complex as [WI(CO)2(dppm)-
{S2P(OEt)2}] was also confirmed by a single crystal
X-ray study.
1
the case of tungsten it occurs on the phosphine. The H
NMR spectrum of 3a in CD3CN exhibits peaks as-
signed to phenyl groups (l=7.34–7.64), methylenic
(l=3.89–3.92, Et; l=2.71, dppe) and methylic (l=
1.17–1.29), but a reliable integration is not possible.
One band at 1825 cm−1 could be assigned to the wCꢀO
stretching.
Table 1
,
Bond lengths (A) and angles (°) for complex [WI(CO)2(dppe)-
{S2P(OEt)2}] (1a)
Bond lengths
WꢁC(100)
WꢁS(11)
WꢁP(1)
WꢁI
1.951(12)
2.619(3)
2.513(4)
2.888(3)
WꢁC(200)
WꢁS(13)
WꢁP(4)
1.940(16)
2.599(4)
2.523(3)
2.2. Crystal structures
Bond angles
P(1)ꢁWꢁP(4)
C(100)ꢁWꢁP(1)
C(200)ꢁWꢁP(4)
C(200)ꢁWꢁS(13)
P(1)ꢁWꢁS(13)
C(200)ꢁWꢁS(11)
P(1)ꢁWꢁS(11)
S(13)ꢁWꢁS(11)
C(100)ꢁWꢁI
76.7(1)
80.7(4)
75.4(4)
124.2(3)
95.1(1)
73.8(4)
165.1(9)
74.9(1)
151.6(4)
78.6(1)
84.9(1)
C(100)ꢁMꢁC(200)
C(200)ꢁWꢁP(1)
C(100)ꢁWꢁP(4)
C(100)ꢁWꢁS(13)
P(4)ꢁWꢁS(13)
C(100)ꢁWꢁS(11)
P(4)ꢁWꢁS(11)
C(200)ꢁWꢁI
69.9(6)
121.1(4)
119.3(3)
76.9(4)
159.5(1)
107.1(4)
109.0(1)
138.3(4)
82.7(1)
The structures of complexes [WI(CO)2(dppe)-
{S2P(OEt)2}]
(1a),
[WI(CO)2(dppm){S2P(OEt)2}]·
0.25H2O (2a) and [W(CO)(dppe){S2P(OEt)2}2][O2dppe]
(3a) were determined by single crystal X-ray diffraction.
Bond distances and selected angles in the tungsten
coordination are given in Table 1 for complex 1a and in
Table 2 for complexes 2a and 3a. The three complexes
are all seven coordinate.
P(1)ꢁWꢁI
S(13)ꢁWꢁI
P(4)ꢁWꢁI
S(11)ꢁWꢁI
81.8(1)
An ORTEP diagram of the complex 1, presented in
Fig. 1, shows that two sulfurs from S2P(OEt)2, one

H. Liu et al. / Inorganica Chimica Acta 327 (2002) 169–178
171
Table 2
,
Bond lengths (A) and angles (°) for complexes [WI(CO)2(dppm){S2P(OEt)2}] (2a) and [W(CO)(dppe){S2P(OEt)2}2] (3a)
[WI(CO)2(dppm){S2P(OEt)2}] (2a)
Bond lengths
WꢁP(1)
WꢁC(100)
WꢁI
2.493(11)
1.92(4)
2.919(4)
WꢁP(3)
WꢁC(200)
2.562(10)
1.96(3)
WꢁS(11)
WꢁS(13)
2.605(11)
2.650(8)
Bond angles
P(1)ꢁWꢁP(3)
S(11)ꢁWꢁI
S(11)ꢁWꢁS(13)
C(200)ꢁWꢁP(3)
C(100)ꢁWꢁS(11)
P(1)ꢁWꢁS(11)
P(3)ꢁWꢁS(11)
64.4(3)
81.5(2)
75.5(3)
126.6(11)
102.7(10)
128.3(3)
159.9(3)
C(200)ꢁWꢁP(1)
C(200)ꢁWꢁS(11)
C(200)ꢁMꢁC(100)
C(200)ꢁWꢁI
C(100)ꢁWꢁI
P(1)ꢁWꢁI
71.7(12)
73.3(11)
76.2(11)
142.0(12)
82.3(10)
145.0(2)
92.7(3)
P(3)ꢁWꢁI
82.1(3)
171.2(11)
111.1(8)
104.4(12)
86.5(9)
C(100)ꢁWꢁS(13)
C(200)ꢁWꢁS(13)
C(100)ꢁWꢁP(1)
C(100)ꢁWꢁP(3)
P(1)ꢁWꢁS(13)
S(13)ꢁWꢁI
83.1(3)
88.9(2)
P(4)ꢁWꢁS(13)
[W(CO)(dppe){S2P(OEt)2}2] (3a)
Bond lengths
WꢁP(1)
WꢁS(11)
WꢁC(100)
2.481(4)
2.582(4)
1.892(12)
WꢁP(4)
WꢁS(21)
2.499(3)
2.609(4)
WꢁS(13)
WꢁS(23)
2.705(4)
2.608(4)
Bond angles
P(1)ꢁWꢁP(4)
75.9(1)
71.8(1)
169.8(4)
81.3(4)
83.5(4)
109.0(1)
140.6(1)
S(11)ꢁWꢁS(23)
P(1)ꢁWꢁS(21)
S(11)ꢁWꢁS(13)
C(100)ꢁWꢁP(4)
C(100)ꢁWꢁS(21)
P(1)ꢁWꢁS(23)
P(4)ꢁWꢁS(23)
74.0(1)
71.3(1)
75.9(1)
91.5(3)
104.4(3)
136.8(1)
144.8(1)
S(23)ꢁWꢁS(21)
S(21)ꢁWꢁS(13)
S(23)ꢁWꢁS(13)
C(100)ꢁWꢁS(11)
P(1)ꢁWꢁS(11)
P(4)ꢁWꢁS(13)
S(11)ꢁWꢁS(21)
73.8(1)
79.8(1)
88.9(1)
95.4(4)
147.4(1)
90.9(1)
139.7(1)
P(4)ꢁWꢁS(11)
C(100)ꢁWꢁS(13)
C(100)ꢁWꢁP(1)
C(100)ꢁWꢁS(23)
P(1)ꢁWꢁS(13)
P(4)ꢁWꢁS(21)
of the ligands around the metal leads to a coordination
sphere which can be described as a distorted bipyrami-
dal pentagon, although 2a is intermediate between that
geometry and the capped octahedron found in 1a.
Thus, in complex 2b the equatorial coordination
plane contains two phosphorus donors of a dppm
ligand, one iodine atom, one carbon atoms from a
iodine, two carbonyl groups and two phosphorus from
a dppe surround the metal centre in a distorted capped-
octahedral coordination environment with a carbonyl
C(200)ꢁO(200) in the capping position. The atoms
S(11), P(4) and C(100) defined the capped triangular
face, while the atoms S(13), P(1) and I define the
opposite uncapped face, leading to an angle
IꢁWꢁC(100) of 151.6(4)°. The two carbonyl groups are
bonded linearly to tungsten with WꢁCꢁO angles of
175.6(9) and 176.9 (10)°, respectively. This type of
geometric arrangement was found for related heptaco-
ordinate isomorphous complexes [M{S2P(OEt)2}2-
(CO)2(PPh3)] (M=W(II) 4a or Mo(II) 4b) and
[M(CO)2{S2P(OEt)2}2]2(m-dppe) (M=W(II) 5a or
Mo(II) 5b). However, in these complexes, the ligands
adopt a different disposition around the metal, with a
corner of the uncapped triangular face occupied by a
sulfur of the S2P(OEt)2 bidentate ligand rather than an
iodine. Furthermore, the remaining sulfur of this biden-
tate ligand substitutes on the equatorial plane a phos-
phorus of the dppe ligand. In spite of these structural
differences, the WꢁS, WꢁC and WꢁP distances in 1a
compare quite well with those found for 4a, 4b, 5a and
5b.
ORTEP diagrams of the complexes 2a and 3a together
with the labelling scheme adopted are presented in Figs.
2 and 3, respectively. In contrast with the former struc-
ture described, in these two complexes the disposition
Fig. 1. An ORTEP view of [WI(CO)2(dppe){S2P(OEt)2}] (1a) with
thermal ellipsoids drawn at 30% probability. The atom numbering
scheme of the phenyl and ethoxy groups is omitted for clarity.

172
H. Liu et al. / Inorganica Chimica Acta 327 (2002) 169–178
and 169.8(4)° in 3. In both cases the atoms that com-
pose the equatorial coordination plane display a signifi-
cant deviation from the mean least-squares plane
calculated with their atomic positions. These deviations
,
are in A: 0.437(10) [P(1)], 0.463(12) [S(11)], −0.716(14)
[C(200)], −0.138(7) [I] and −0.047(2) [P(3)] in 2a;
0.529(2) [S(21)], −0.437(2) [S(23)], 0.204(2) [S(11)],
−0.396(2) [P(1)] and 0.100(2) [P(4)] in 3a. However, the
cis angles subtended at the tungsten centre on the
equatorial coordination plane are close to the ideal
value of 72° for a perfect bipyramid. The largest shift of
this value is 10.1(3)° in 2a and only of 3.9(1)° in 3. In
both complexes the distortion of the coordination
sphere can be ascribed to the steric bulk of the
diphenylphosphine ligand, dppm in 2a or dppe in 3a.
Furthermore, and as would be expected, the PꢁWꢁP
angle of 64.4(3)° in 2a is smaller than that of 75.9(1)° in
3a, since dppm has a smaller bite angle than dppe. In
both complexes the MoꢁS axial distance is longer than
Fig. 2. An ORTEP view of [WI(CO)2(dppm){S2P(OEt)2}] (2a). Details
were given in Fig. 1.
,
the equatorial ones by approximately 0.10 A in 3a and
,
0.05 A in 2a. This is probably due to the fact that the
small bite angle of SꢁPꢁS of the S2P(OEt)2 ligand
prevents sulfur from achieving the ideal position of the
bipyramid. Indeed, the angle SaxꢁWꢁSeq is 75.9(1)° in 3a
and 75.5(3)° in 2a.
The X-ray structure of the molybdenum analogue of
3a, [Mo(CO)(dppe){S2P(OEt)2}2] (3b) has been reported
before [8]. Bond distances and angles are comparable in
the metal coordination sphere of both complexes. In the
crystal of 3a, an oxidised O2dppe molecule is located on
the crystallographic inversion centre adopting an anti
conformation with a PꢁCꢁCꢁP torsion angle of 180°.
,
The PꢁO distance of 1.26(3) A is consistent with a PꢂO
double bond [11].
The crystal structure of 1a and 2a consists of discrete
molecules
of
[WI(CO)2(dppe){S2P(OEt)2}]
and
[WI(CO)2(dppm){S2P(OEt)2}], respectively. The com-
plex 2a also contains crystallisation waters with an
occupancy factor of 0.25 in its crystal lattice. In both
cases, no additional relevant structural features are
apparent from their crystal packing diagrams.
In spite of the structural similarity between the struc-
tures of the complexes [M(CO)(dppe){S2P(OEt)2}2]
(M=W(II) in 3a and M=Mo(II) in 3b), they crys-
Fig. 3. An ORTEP view of [W(CO)(dppe){S2P(OEt)2}2] (3a). Details
were given in Fig. 1.
(
tallise in different centrosymmetric space groups (P1
for 3b and C2/c for 3a) yielding different packing
arrangements. In 3a the molecular assembly of the
[WI(CO)2(dppe){S2P(OEt)2}] molecules affords large
open channels running along the b crystallographic
axis. These channels accommodate the molecules of
O2dppe as shown in Fig. 4. No hydrogen bonds were
found involving [WI(CO)2(dppe){S2P(OEt)2}] and
O2dppe. Therefore, these molecules are aggregated in
the crystal only by van der Waals forces.
carbonyl group and one sulfur from a S2P(OEt)2 biden-
tate ligand. In complex 3a, three sulfurs of two
S2P(OEt)2 bidentate ligands and two phosphorus from
the dppe ligand determine the equatorial coordination
plane. In both complexes, the seven coordination is
completed with the remaining sulfur of the dithiolate
ligand and a carbonyl group in the axial positions,
leading to an angle S(13)ꢁWꢁC(100) of 171.2(11)° in 2a

H. Liu et al. / Inorganica Chimica Acta 327 (2002) 169–178
173
Scheme 1.
much simplified model based on monodentate ligands
containing P and S led to no consistent geometries. The
optimised geometry of [WI(CO)2(H2PCH2PH2)-
{S2P(OH)2}], a pentagonal bipyramid, is shown in Fig.
5a and compared with the X-ray structure (Fig. 5b).
There is a good agreement between the calculated
and experimental distances, the largest deviations being
found for the WꢁP bonds. A similar agreement is
observed for angles. For instance, the calculated
PꢁWꢁP angle of 66.4° is very similar to the experimen-
tal 64.1°. Fig. 5 emphasises the similarities between
both structures. The conformation of the WꢁPꢁCꢁPꢁW
cycle, however, differs considerably, the WꢁPꢁC−P
torsion angle varying from 23.6° in the experimental to
−10.6° in the calculated structure. The reason for this
difference can be assigned to the presence of the phenyl
groups which force a change in chain conformation
owing to their bulk. A similar, though less pronounced
effect, is observed in the ethyl groups of the sulfur
ligand. The possible existence of other isomers was
checked, considering that the capped face octahedron
was systematically observed in a family of related com-
pounds containing two carbonyl groups [8] and also in
the dppe analogue, 1a. In order to study this transfor-
mation, the carbonyl in the equatorial plane of the
bipyramid was constrained to move out of that plane
by 5° steps (Scheme 1), the geometry being fully opti-
mised for each point. The energy increases by 0.5, 1.6,
3.0, 4.5, 5.8 and 7.7 kcal mol−1, respectively, after each
Fig. 4. Crystal packing diagram of [W(CO)(dppe){S2P-
(OEt)2}2][O2dppe] (3a). View perpendicular to the [010] crystallo-
graphic plane, showing how the assembled complex species define the
channels, which accommodate O2dppe units. Molecules of complex
and O2dppe are represented in the CPK and ball and stick modes,
respectively.
2.3. Theoretical calculations
DFT calculations [9] were performed using the
B3LYP approach within GAUSSIAN 98 [10] on models
of complexes 2a and 1a where all the ethyl and phenyl
groups were replaced by hydrogen atoms, [WI(CO)2-
{H2P(CH2)nPH2}{S2P(OH)2}] with n=1 (dppm) or 2
(dppe). Complex 2a was chosen to start the study
because it carries the smaller bidentate phosphine
dppm, rather than dppe. Preliminary calculations on a
Fig. 5. The structure of model [WI(CO)2(H2PCH2PH2){S2P(OH)2}] (2a): (a) optimised structure from DFT calculations; (b) X-ray structure.
Hydrogen atoms omitted for clarity.

174
H. Liu et al. / Inorganica Chimica Acta 327 (2002) 169–178
Scheme 3.
Scheme 2.
lations on an isomer having the ligand arrangement of
2a resulted in a species with an energy higher by 2.6
kcal mol−1, shown in Scheme 3.
step, in a total amount of 23.1 kcal mol−1, when the
pentagonal bipyramid has become a capped octahedron
with a carbonyl as a capping ligand. This structure is
therefore not favoured on electronic grounds.
The previous results indicate that the capped octahe-
dron structure is slightly preferred in both cases, when
the bulky Ph and Et groups are not present. This
arrangement was found in analogous seven coordinate
complexes containing two carbonyls [8]. The energy
differences between the two isomers are very small,
namely 1.4 and 2.6 kcal mol−1 for the dppm and the
dppe complexes, respectively, and can easily be over-
come when steric repulsions introduced by the sub-
stituents are present. The four phenyl groups in the
rigid dppm phosphine seem to prevent this arrange-
ment, while dppe, with a longer carbon chain, is more
flexible and can adjust.
The pentagonal bipyramidal geometry found in
[WI(CO)2(dppm){S2P(OEt)2}] (2a) has been associated
with monocarbonyl derivatives. The other structurally
characterised complex of this work, [W(CO)(dppe)-
{S2P(OEt)2}2] (3a) also belongs to this group and ex-
hibits this geometry. It is interesting to notice how the
three bidentate ligands are arranged. Two of them
occupy four positions of the equatorial plane (as in 1a),
while the third, a dithiophosphate ligand, occupies the
fifth position of that plane as well as an axial one,
becoming trans to the carbonyl (as in 2a) and orthogo-
nal to the other bidentate ligands.
In the structure of 2a discussed above, the bidentate
ligands are orthogonal to each other, leading to a
carbonyl trans to a sulfur atom rather than to iodine.
On the other hand, complex 1a exhibits a different
structural arrangement because the two bidentate lig-
ands, namely the phosphine and the dithiophosphate lie
in the same plane (approximately), which is an equato-
rial plane of either a pentagonal bipyramid or a capped
octahedron (as observed). This alternative type of ar-
rangement was also checked for complex 2a and calcu-
lations on a suitable model led to an energy 1.4
kcal mol−1 lower (Scheme 2). Notice that this structure
is very similar to that observed in the dppe derivative
1a.
A model was also built for complex 1a and the
geometry optimisation led to a geometry similar to that
observed in the X-ray structure, which is shown in Fig.
6a and compared with the experimental one (Fig. 6b).
The calculated distances are a bit longer than the
experimental ones, but the agreement is relatively good.
The conformations of the R groups are, as expected,
not well reproduced by the hydrogen containing mod-
els, although the phosphine chain is very similar. Calcu-
Fig. 6. The structure of model [WI(CO)2{H2P(CH2)2PH2}{S2P(OH)2}] (1a): (a) optimised structure from DFT calculations; (b) X-ray structure.
Hydrogen atoms omitted for clarity.

H. Liu et al. / Inorganica Chimica Acta 327 (2002) 169–178
175
3. Conclusions
crystals of the product (0.135 g, yield 71%). One of the
crystals was suitable for a single crystal X-ray diffrac-
tion study.
New complexes [MI(CO)2(dppe){S2P(OEt)2}] (M=
W, 1a; M=Mo, 1b), [MI(CO)2(dppm){S2P(OEt)2}]
(M=W, 2a; M=Mo, 2b) and [W(CO)(dppe){S2-
P(OEt)2}2][O2dppe] (3a) were synthesised and the struc-
ture of the W complexes was determined by single
crystal X-ray diffraction. The capped octahedron ge-
ometry was found for 1a, while both 2a and 3a exhib-
ited a pentagonal bipyramidal arrangement. DFT/
B3LYP calculations performed on model complexes of
1a and 2a having Ph and Et groups replaced by hydro-
gen atoms showed similar stabilities for the two isomers
of each complex, the capped octahedron being slightly
favoured. The experimental observation of the pentago-
nal bipyramidal structure can be traced to the con-
straints imposed by the phosphine chelate chain, which
force the dppm derivative to adopt such geometry,
instead of the capped octahedron, usually preferred in
similar dicarbonyl complexes.
Anal. Calc.: C, 40.41; H, 3.58; S, 6.74. Found: C,
40.36; H, 3.73; S, 6.78%. IR (KBr, wCꢀO cm−1): 1933.1,
1
1860.3. H NMR (CD3CN, ppm): 7.57 (s, 20H, C6H5);
3.96–4.06 (m, 4H, OCH2CH3); 2.70–2.76 (m, 4H, CH2
from dppe); 1.24–1.28 (m, 6H, OCH2CH3).
4.3. Preparation of [WI(CO)2(dppm){S2P(OEt)2}] (2a)
[WI2(CO)3(NCMe)2] (0.1208 g, 0.2 mmol) was dis-
solved in CH2Cl2 (10 ml) and solid NH4[S2P(OEt)2]
(0.041 g, 0.2 mmol) was added with vigorous stirring.
The colour of the solution changed from dark-red to
red and a white precipitated formed gradually. The
reaction mixture was then filtered, solid dppm (0.077 g,
0.2 mmol) was added to the filtrate and the solution
was stirred for a further 30 min. Hexane (30 ml) was
added to the solution and the mixture was kept at 0 °C
for 3 days to afford red crystals of the product (0.110 g,
yield 59%). One of the crystals was suitable for a single
crystal X-ray diffraction study.
4. Experimental
Anal. Calc.: C, 39.74; H, 3.42; S, 6.84. Found: C,
39.14; H, 3.46; S, 6.60%. IR (KBr, wCꢀO cm−1): 1929.5,
4.1. Synthesis
1
1847.3. H NMR (CD3CN, ppm): 7.55 (s, 20H, C6H5);
5.18–5.26 (m, 2H, CH2 from dppm); 4.10 (s, 4H,
OCH2CH3); 1.27–1.32 (m, 6H, OCH2CH3). 31P, 101.1
(P from S2P(OEt)2); 52.3 (P from dppe).
Commercially available reagents and all solvents
were purchased from standard chemical suppliers. All
solvents were used without further purification except
acetonitrile (dried over CaH2), dichloromethane (dried
over CaH2) and THF, which was distilled over sodium/
benzophenone ketyl and used immediately. NH4[S2P-
(OEt)2] (Aldrich) was recrystallised from THF. The
complexes [MI2(CO)3(NCMe)3] (M=Mo, W) were syn-
thesised according to literature procedures [4a].
4.4. Preparation of [MoI(CO)2(dppe){S2P(OEt)2}] (1b)
[MoI2(CO)3(NCMe)2] (0.1032 g, 0.2 mmol) was dis-
solved in CH2Cl2 (10 ml) and solid NH4[S2P(OEt)2]
(0.041 g, 0.2 mmol) was added with vigorous stirring.
The colour of the solution changed from dark-red to
red–brown and a white precipitated formed gradually
in 30 min. The reaction mixture was then filtered and
solid dppe (0.080 g, 0.2 mmol) was added to the filtrate;
gas evolution occurred and the colour of the solution
changed to red quickly. The solution was stirred for a
further 30 min, hexane (20 ml) was added and the
mixture was kept at 0 °C for 3 days to afford red
crystals of 1b (0.14 g, yield 81%).
1H NMR spectra were recorded in a Bruker AMX-
300 (300 MHz) spectrometer in d3-CD3CN (l 1.93),
using TMS as internal reference and 31P shifts were
measured with respect to external 85% H3PO4. Elemen-
tal analyses were carried out at ITQB. The IR spectra
were recorded in a Unicam Mattson 7000 FTIR spec-
trometer. Samples were run as KBr pellets.
4.2. Preparation of [WI(CO)2(dppe){S2P(OEt)2}] (1a)
One of the crystals was suitable for a single crystal
X-ray diffraction study.
[WI2(CO)3(NCMe)2] (0.1208 g, 0.2 mmol) was dis-
solved in CH2Cl2 (10 ml) and solid NH4[S2P(OEt)2]
(0.041 g, 0.2 mmol) was added with vigorous stirring.
The colour of the solution changed from dark-red to
red and a white precipitate formed gradually in 30 min.
The reaction mixture was filtered, solid dppe (0.080 g,
0.2 mmol) was added to the filtrate and the colour of
solution quickly turned to orange. The solution was
stirred for a further 30 min and then concentrated to
about 5 ml. Hexane (20 ml) was added and the mixture
was cooled down (−20 °C) overnight to afford yellow
Anal. Calc.: C, 44.53; H, 3.94; S, 7.42. Found: C,
44.51; H, 4.14; S, 7.21%. IR (KBr, wCꢀO cm−1): 1943.4,
1
1874.9. H NMR (CD3CN, ppm): 7.59 (s, 20H, C6H5);
3.97–4.02 (m, 4H, OCH2CH3); 2.69–2.75 (m, 4H, CH2
from dppe); 1.22–1.27 (m, 6H, OCH2CH3).
4.5. Preparation of [MoI(CO)2(dppm){S2P(OEt)2}] (2b)
This dppm complex was prepared and crystallised in
a similar way as described for 2a. Red–brown crystals
were formed (0.09 g, yield 53%).

176
H. Liu et al. / Inorganica Chimica Acta 327 (2002) 169–178
Anal. Calc.: C, 43.86; H, 3.77; S, 7.55. Found: C,
3.92 (m, OCH2CH3), 2.71 (s, CH2CH2 from dppe),
1.17–1.29 (m, OCH2CH3).
42.57; H, 3.96; S, 7.49%. IR (KBr, wCꢀO cm−1): 1934.0,
1
1859.1. H NMR (CD3CN, ppm): 7.22–7.80 (m, 20H,
C6H5); 4.20–4.25 (m, 2H, CH2 from dppm); 3.77–3.99
(m, 4H, OCH2CH3); 1.28–1.38 (m, 6H, OCH2CH3).
4.7. Crystal structure determinations
The crystal data of the complexes 1a, 2a and 3a are
given in Table 3, together with refinement details. The
X-ray data for all three complexes were collected on a
MAR research plate system using graphite Mo Ka
radiation at Reading University. The crystals were posi-
tioned at 70 mm from the image plate. Ninety-five
frames were measured at 2° intervals using an adequate
counting time between 2 and 5 min. Data analysis was
carried out with the XDS program [12].
The structures were solved by direct methods with
the SHELXS program [13]. All non-hydrogen atoms were
refined with anisotropic thermal parameters. The hy-
drogen atoms were introduced in the refinement at the
geometric idealised positions giving isotropic thermal
parameters equal 1.2 times those of the carbon atom
they were attached. An empirical absorption correction
was applied to intensities of 1a, 2a and 3a using a
version of the DIFABS program modified for image plate
geometry [14]. Structures were then refined by full-ma-
trix least-squares on F2 until convergence with SHELXL
[15]. The three X-ray determinations showed positive
4.6. Preparation of
[W(CO)(dppe){S2P(OEt)2}2][O2dppe] (3a)
[WI2(CO)3(NCMe)2] (120.8 mg, 0.2 mmol) was dis-
solved in CH2Cl2 (10 ml) and solid NH4[S2P(OEt)2] (84
mg, 0.4 mmol) was added with vigorous stirring. The
colour of the solution changed from dark-red to orange
and a white precipitated formed gradually (30 min).
The reaction mixture was filtered, solid dppe (80 mg,
0.2 mmol) was added to the orange filtrate, the solution
was stirred for further 30 min, then concentrated to
about 3 ml. Hexane (30 ml) was added, the mixture was
kept at room temperature and dark-brown crystals
appeared after 2 weeks. The yield was 40 mg. One of
the crystals was suitable for a single crystal X-ray
diffraction analysis.
Anal. Calc.: C, 52.10; H, 4.95; S, 9.27. Found: C,
49.68; H, 4.09; S, 9.42%. IR (KBr, wCꢂO cm−1): 1825.
1H NMR (CD3CN, ppm): 7.34–7.64 (m, C6H5), 3.89–
Table 3
Crystal data and pertinent refinement details for complexes 1a, 2a and 3a
Compound
1a
2a
31H32.25IO4.25P3S2W
940.60
orthorhombic
Pbcn
3a
Empirical formula
Formula weight
Crystal system
Space group
C32H34IO4P3S2W
950.37
monoclinic
P21/n
C
C48H56O6P5S4W
1195.87
monoclinic
C2/c
Unit cell dimensions
,
a (A)
18.248(23)
10.988(14)
19.219(24)
12.147(15)
16.937(23)
37.297(38)
32.340(37)
11.113(14)
33.983(38)
,
b (A)
,
c (A)
h (°)
i (°)
113.34(1)
117.96(1)
k (°)
3
,
V (A )
Z
3538
4
1.784
7673
8
1.628
10788
8
1.473
Calculated density (Mg m−3
)
F(000)
1848
4.425
3650
4.081
4840
2.489
Absorption coefficient (mm−1
Theta range (°)
)
1.98 to 25.88
−205h520, 05k513,
−225l522
5751
2.00 to 25.56
05h514, −115k58,
−375l544
6399
1.36 to 26.09
−395h539, −135k513,
−405l540
Index ranges hkl
Reflections collected
31504
Unique reflections [Rint
]
4292 [0.0496]
4292/0/390
R1=0.0474, wR2=0.1298
R1=0.0707, wR2=0.1418
1.113
2796 [0.1117]
2796/30/386
R1=0.0901, wR2=0.2239
R1=0.1459, wR2=0.2515
1.078
10116 [0.1292]
10116/0/582
R1=0.0875, wR2=0.2216
R1=0.1246, wR2=0.2516
1.104
Data/restraints/parameters
Final R indices [I\2|(I)]
R indices (all data)
Goodness-of-fit on F2
Largest difference peak and hole
1.230 and −0.908
1.061 and −0.761
1.604 and −1.650
−3
,
(e A
)

H. Liu et al. / Inorganica Chimica Acta 327 (2002) 169–178
177
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5. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
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pounds 1a, 2b and 3a, respectively. Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (fax: +44-1223-336-033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
Acknowledgements
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grant. The University of Reading and EPSRC are
thanked for funds for the Image Plate system.
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