Reaction of pentacarbonyl(η2-bis(trimethylsilyl)ethyne) tungsten(0) with tricyclohexylphosphine: X-ray structure of pentacarbonyltricyclohexylphosphinetungsten(0)

Article abstract of DOI:10.1016/j.jorganchem.2003.08.032

The pentacarbonyl(?²-bis(trimethylsilyl)ethyne)tungsten(0), W(CO)₅(?²-btmse), reacts with tricyclohexylphosphine, PCy₃, to yield two stable endproducts which could be isolated and fully characterized by using the single crystal X-ray diffractometry and the MS, IR, and NMR spectroscopy: W(CO)₅(PCy₃) and trans-W(CO) ₄(PCy₃)₂. The former complex is the alkyne substitution product, while the latter one is formed from the conversion of its labile cis -isomer, which is generated by further reaction of the CO substitution product, cis-W(CO)₄ (?²-btmse)(PCy₃), with a second PCy₃ molecule. The intermediate cis-W(CO)₄(?²-btmse) (PCy₃) complex could not be detected even in the solution. The cis-W(CO)₄(PCy₃)₂ complex was observable, however, found to be instable and rapidly isomerizes to trans-W(CO)₄(PCy₃)₂. The crystal and molecular structure of W(CO)₅(PCy₃) was determined and compared with those of trans-W(CO)₄(PCy₃) ₂. The coordination sphere around the W atom is a slightly distorted octahedron, involving five carbonyls and one phosphine. The W-C distances have values between 1.986(6) and 2.042(6) ?. The W-P distance is 2.5794(12) ?. Maximum deviation from an ideal octahedral coordination angle is observed to be 95.68(17)°. All three cyclohexyl rings are in chair configuration.

Full text of DOI:10.1016/j.jorganchem.2003.08.032

Journal of Organometallic Chemistry 688 (2003) 68Á74
/
www.elsevier.com/locate/jorganchem
Reaction of pentacarbonyl(h2-bis(trimethylsilyl)ethyne)tungsten(0)
with tricyclohexylphosphine: X-ray structure of
pentacarbonyltricyclohexylphosphinetungsten(0)
a
a,
Oktay Demircan , Saim Ozkar *, Dincer Ulku b,1, Leyla Tatar Yildirim b
¨
¨
¸
¨
a Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey
b Department of Engineering Physics, Hacettepe University, Beytepe, 06532 Ankara, Turkey
Received 17 June 2003; received in revised form 16 August 2003; accepted 27 August 2003
Abstract
The pentacarbonyl(?2-bis(trimethylsilyl)ethyne)tungsten(0), W(CO)5(?2-btmse), reacts with tricyclohexylphosphine, PCy3, to yield
two stable endproducts which could be isolated and fully characterized by using the single crystal X-ray diffractometry and the MS,
IR, and NMR spectroscopy: W(CO)5(PCy3) and trans-W(CO)4(PCy3)2. The former complex is the alkyne substitution product,
while the latter one is formed from the conversion of its labile cis-isomer, which is generated by further reaction of the CO
substitution product, cis-W(CO)4(?2-btmse)(PCy3), with a second PCy3 molecule. The intermediate cis-W(CO)4(?2-btmse)(PCy3)
complex could not be detected even in the solution. The cis-W(CO)4(PCy3)2 complex was observable, however, found to be instable
and rapidly isomerizes to trans-W(CO)4(PCy3)2. The crystal and molecular structure of W(CO)5(PCy3) was determined and
compared with those of trans-W(CO)4(PCy3)2. The coordination sphere around the W atom is a slightly distorted octahedron,
˚
involving five carbonyls and one phosphine. The W-C distances have values between 1.986(6) and 2.042(6) A. The W-P distance is
˚
2.5794(12) A. Maximum deviation from an ideal octahedral coordination angle is observed to be 95.68(17)8. All three cyclohexyl
rings are in chair configuration.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Carbonyl; Tungsten; bis(Trimethylsilyl)ethyne; Tricyclohexylphosphine; X-ray diffraction; Crystal structure; Molecular structure; MS,
IR and NMR data
1. Introduction
inaccessible. Since the complexes of tricyclohexylpho-
sphine have gained interest due to the agostic CÁH0
/
/
M
The UV photolysis of W(CO)6 in alkane solution with
bis(trimethylsilyl)ethyne (btmse) yields W(CO)5(h2-
btmse) which is stable enough to be isolated as yellow
crystals from the hydrocarbon solution and survives in
solution even in the absence of btmse at room tempera-
ture [1]. However, it is labile towards ligand substitution
at room temperature, giving alkyne and/or carbonyl
substitution depending on the incoming ligand [2]. Thus,
it can be used as starting material for the preparation of
some metal-carbonyl derivatives, which are otherwise
interaction of a cyclohexyl hydrogen [3] we decided to
study the reaction of W(CO)5(h2-btmse) with tricyclo-
hexylphosphine at ambient temperature. A CO substitu-
tion accompanied by an alkyne detachment might
generate an 16-elecron W(CO)4(PCy3) complex with an
agostic CÁ
/
H0
/
W interaction of a cyclohexyl hydrogen.
The 16-elctron complexes of the type trans-
M(CO)3(PCy3)2 are known for all of the Group 6
metals, chromium [4], molybdenum, and tungsten [5].
These complexes are in fact 18-electron species due to an
agostic CÁ
/
H0
/
M interaction of a cyclohexyl hydrogen,
which has been shown to be weak enough to allow
replacement by Lewis bases [6]. M(CO)5(PCy3) and
M(CO)4(PCy3)2 complexes have been known for a
long time [7]. Here we report on the reaction of
W(CO)5(h2-btmse) with tricyclohexylphosphine, the
* Corresponding author. Tel.: ꢀ
210-1280.
E-mail address: sozkar@metu.edu.tr (S. Ozkar).
/
90-312-210-3212; fax: ꢀ90-312-
/
¨
1
¨
D. Ulku and L.T. Y ld r m were responsible for the X-ray crystal-
ı
ı ı
¨
structure analysis.
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2003.08.032

O. Demircan et al. / Journal of Organometallic Chemistry 688 (2003) 68Á
/74
69
isolation and characterization of possible substitution
products: W(CO)5(PCy3), trans-W(CO)4(PCy3)2, and
cis-W(CO)4(PCy3)2. This is the first example of reac-
tions involving both the CO and alkyne substitution in
an alkyne complex. In the presence of tricyclohexylpho-
sphine, W(CO)5(h2-btmse) undergoes both the CO and
alkyne substitution at room temperature. This substitu-
tion indicates the labilization of CO groups cis to the
alkyne ligand. It is exactly this unique ability of
W(CO)5(h2-btmse) to give both the alkyne and CO
substitution (from the position cis to the alkyne ligand),
which enable us to observe, for the first time, the
formation of cis-W(CO)4(PCy3)2. The latter complex is
a kinetic product and rapidly converted to the thermo-
dynamically more stable trans-W(CO)4(PCy3)2. All the
complexes have also been prepared for verification by
using the known procedure.
mmol) was completely dissolved in 20 ml n-hexane at
room temperature (r.t.). This solution was transferred
into another Schlenk tube containing an n-hexane
solution of 0.25 g (0.50 mmol) W(CO)5(h2-btmse) under
stirring at r.t. The solution was stirred at r.t. The
reaction was followed by recording the IR spectra of
the samples taken from the solution. When the reaction
was completed, the solution was left for one night over
dry-ice for crystallization. The crystals separated from
the mother liquor contains two compounds as deter-
mined by IR spectra: W(CO)5(PCy3) and trans-
W(CO)4(PCy3)2. These two complexes were separated
on a silica gel column (20 cm long, 3 cm diameter).
W(CO)5(PCy3) was first eluded with n-hexane and then
crystallized from the same solution as pale yellow
needle-like crystals. trans-W(CO)4(PCy3)2 was eluded
as the second fraction with a 1:3 mixture of dichlor-
omethane and n-hexane, and then crystallized from n-
hexane as colorless needle like crystals. W(CO)5(PCy3):
2. Experimental
MS: m/z 604 [Mꢀ]; IR (n-hexane) n(CO)ꢁ
1968 (vw), 1938 (s), 1933 (vs), 1929 (s) cmꢂ1 13C-NMR
(d-chloroform) dꢁ199.31 ppm (COtrans, d, Jꢁ20.2
Hz), 198.80 ppm (COcis, d, Jꢁ6.7 Hz), 37.09 (C1, d,
/
2065 (w),
.
2.1. General remarks
/
/
/
All of reactions and manipulations were carried out
either in vacuum or under a dry and oxygen free
nitrogen atmosphere. Solvents were distilled after re-
fluxing over metallic sodium or phosphorous pentoxide
18.1 Hz), 30.48 (C3 and C5, s), 27.94 (C2, C6, d, 10.6
Hz), and 26.61 (C4, s) ppm; 31P-NMR (d-chloroform)
dꢁ
constant is 232 Hz); H-NMR (d-chloroform) dꢁ
1.67, 1.36, 1.22 ppm. trans-W(CO)4(PCy3)2: MS: m/z
856 [Mꢀ]; IR (n-hexane) ?(CO)ꢁ1865 (vs) cmꢂ1 13C-
NMR (d-chloroform) dꢁ207.27 ppm (CO, t, Jꢁ12.3
/
33.41 ppm (183W satellites, 183WÁ31
/
P coupling
1
/1.85,
for 3Á4 days and stored under nitrogen until used.
/
Analytical grade and deuterated solvents, tricyclohex-
ylphosphine, piperidine (pip), and hexacarbonyltung-
sten(0) were purchased from Aldrich Chemical Co. Ltd.,
Dorset, UK, and bis(trimethylsilyl)ethyne (btmse) was
purchased from Fluka (Buchs, Switzerland), and used as
received. The thermal reactions and other treatments of
organometallic compounds such as purification and
crystallisation were followed by taking IR spectra
/
;
/
/
Hz), 36.69 (C1, t, 9.8 Hz), 28.68 (C3 and C5, s), 26.82
(C2 and C6, t, 4.9 Hz), and 25.57 (C4, s) ppm; 31P-NMR
(d-chloroform) dꢁ
183WÁ31
chloroform) dꢁ
/
32.18 ppm
(
183W satellites,
1
/
P coupling constant is 256 Hz); H-NMR (d-
/
2.02, 1.91, 1.79, 1.64, 1.45, 1.21 ppm.
from solutions on a PerkinÁ
/
Elmer 16 PC FT-IR
spectrometer. NMR spectra were recorded on a Bruker
2.3. X-ray diffraction structure analyses
1
Avance DPX 400 (400.1 MHz for H; 161.3 MHz for
X-ray diffraction data were collected at r.t. with
31P; and 100.6 MHz for 13C). TMS was used as internal
graphite-monochromated MoÁ
/
Ka radiation on an En-
1
reference for H- and 13C-NMR chemical shifts. H2SO4
rafÁNonius CAD4 diffractometer [10] operating in v Á
/
/
(85%, in a glass capillary) was used as reference for 31P-
NMR chemical shifts. Mass spectra were taken on a
Finnigan MAT 8400.
2u scan mode. The cell parameters were determined
from a least-squares refinement of 15 centred reflections
in the range of 10.095
/
u 511.298. Cell refinement was
/
Photochemical reactions were carried out in an
carried out using CAD-4 EXPRESS. During data collec-
tion, three standard reflections were periodically mea-
sured every 120 min, showed no significant intensity
variation. Absorption correction (c-scan) was applied
immersion-well apparatus[8] (solidex glass, l ꢀ280
/
nm) by using a Hanau TQ 150 high pressure mercury
lamp, which was cooled by circulating water or cold
methanol. W(CO)5(h2-btmse) [1] and cis-W(CO)4(pip)2
[9] were prepared according to the literature procedures.
(Tmax
ꢁ/0.243, Tmin
ꢁ0.175). Data reduction was car-
/
ried out using SHELXL-97 [11]. The structure was solved
by direct methods using the program SHELXS-97 [11] in
the WINGX package [12]. A full-matrix least-squares
2.2. Reaction of W(CO)5(h2-btmse) with
tricyclohexylphosphine
refinement on F2 converged at Rꢁ
0.03. For all non-
/
hydrogen atoms anisotropic displacement parameters
were refined. Hydrogen atoms of the C6 and C12 were
taken from a difference map, while the other hydrogen
In a Schlenk tube, a certain amount of tricyclohex-
ylphosphine (P(c-C6H11)3, PCy3; 0.14Á
/
0.70 g, 0.50Á2.5
/

70
O. Demircan et al. / Journal of Organometallic Chemistry 688 (2003) 68Á74
/
atoms were placed geometrically. A riding model was
used with Uiso(H)ꢁ1.2 Ueq(C). A negative residual
electron density of ꢂ1.502 is observed at a distance of
/
/
˚
0.80 A from W atom. All three cyclohexyl rings are in
chair form. In one of the rings which is composed of the
C18ÁC23 atoms, the parapositioned C20 and C23 atoms
/
show disorder evidenced by the larger displacement
parameter values. An attempt to model the disorder
indicated that it is an orientation disorder of the two
components with a 40 to 60% ratio.
A chemical diagram of W(CO)5(PCy3) (2) is given in
Scheme 1. The ORTEP drawing [13] of the molecule is
shown in Fig. 2. Crystal and experimental data are given
in Table 1, selected bond lengths and angles are given in
Table 2.
3. Results and discussion
To a solution of W(CO)5(h2-btmse) (1) in n-hexane
was added the n-hexane solution of tricyclohexylpho-
sphine, PCy3, in various amount (one to five equiva-
lents) at room temperature. The solution was stirred at
room temperature under argon atmosphere. The reac-
tion was followed by monitoring the IR spectrum of the
samples taken from the reaction solution. Some IR
spectra taken during the reaction of 1 with two
equivalents of PCy3 in n-hexane at room temperature
are depicted in Fig. 1 as an illustrating example. The IR
spectrum of the solution just before the addition of PCy3
shows five n(CO) bands at 2080 s, 1988 vw, 1960 s, 1953
Fig. 2. ORTEP [13] drawing of the title molecule with the atom
numbering scheme. Displacement ellipsoids are drawn at the 30%
probability level and H atoms are shown as small circles with arbitrary
radii.
Table 1
Crystal and experimental X-ray data for the W(CO)5P(c-C6H11 3
complex 2
)
Empirical formula
Formula weight (g molꢂ1
Crystal color
C23H33O5PW
604.30
)
Colorless/prismatic
295(2)
0.71073
Temperature (K)
˚
Wavelength (A)
s, 1938 s cmꢂ1 and one n(Cꢀ
/
C) band at 1906 w cmꢂ1 in
Crystal system
Space group [no.]
Unit cell dimensions
Monoclinic
P21/n [no.14]
the carbonyl stretching region (Fig. 1a). In the course of
reaction these absorption features decrease gradually
and new absorption bands grow in concomitantly. After
two hours reaction the spectrum looks very rich in
absorption bands for the CO stretching region. How-
ever, all the species present in the solution can be
identified by comparing the spectrum with those of the
corresponding substances in pure or almost pure state
˚
a (A)
11.7210(12)
12.7055(14)
17.688(3)
90
˚
b (A)
˚
c (A)
a (8)
b (8)
108.270(10)
90
g (8)
3
V (A )
˚
2501.3(5)
4
1.605
(Fig. 1a,dÁf). The absorption bands at 2065, 1938, 1933
/
Z
and 1929 cmꢂ1 are readily assigned to W(CO)5(PCy3),
the FTIR spectrum of which is given in Fig. 1d. The
Dcalc (Mg mꢂ3
)
m (mmꢂ1
)
4.711
Crystal size (mm3)
0.4ꢃ
2.43Á
135
225
/
0.4ꢃ
26.3
h 5
l 5
/
0.3
u Range (8)
Index ranges
/
ꢂ
ꢂ/
/
/
/
14, 05
/
k 5/15,
/
/
0
Reflections collected/unique
Absorption correction
Refinement method
5221/5069 [Rint
Psi-scan
ꢁ
/
0.0422]
Full-matrix least-squares refine-
ment on F2
5069/2/279
1.03
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I ꢀ
R indices (all data)
Largest difference peak and hole 1.124 and ꢂ
/
2s(I)]
R1ꢁ
/
0.0329, wR2ꢁ
0.0519, wR2ꢁ
1.502
/
0.0847
0.0921
R1ꢁ
/
/
/
ꢂ3
˚
(e A
)
Scheme 1.

O. Demircan et al. / Journal of Organometallic Chemistry 688 (2003) 68Á
/74
71
Table 2
Selected bond lengths (A) and bond angles (8) of the W(CO)5P(c-
C6H11 3 complex 2 (esd’s are given parentheses)
are attributed to the cis-W(CO)4(PCy3)2 complex
(Fig. 1f).
˚
)
As the reaction further proceeds the absorption bands
of the cis-W(CO)4(PCy3)2 complex starts to decrease
gradually and disappears completely after 12 h at room
temperature, while the absorption bands for
W(CO)5(PCy3) and trans-W(CO)4(PCy3)2 are increas-
ing. After the reaction completed, the latter two com-
plexes W(CO)5(PCy3) and trans-W(CO)4(PCy3)2 could
be isolated from the reaction solution by column
chromatography and crystallization. On a silica-gel
column (20 cm length, 3 cm diameter), W(CO)5(PCy3)
was eluded with n-hexane and then trans-
W(CO)4(PCy3)2 with a 1:3 mixture of dichloromethane
and n-hexane.
Pentacarbonyltricyclohexylphosphinetungsten(0),
W(CO)5(PCy3), 2 was also prepared by adding P(c-
C6H11)3 to W(CO)5(THF), generated photochemically
from the hexacarbonyltungsten(0) in tetrahydrofurane
(THF) [14], for the purpose of comparison. Both
samples of the complex give exactly the same spectral
feature. The complex could be obtained in the form of
needle like crystals by crystallizing from the n-hexan
solution of the first eluent after the chromatography of
Bond lengths
WÁ
WÁ
WÁ
WÁ
WÁ
/
C3
C4
C5
C1
C2
1.986(6)
2.032(6)
2.037(6)
2.041(6)
2.042(6)
WÁ
/
P
2.5794(12)
1.848(6)
1.862(5)
1.865(5)
/
PÁ
PÁ
PÁ
/
C18
/
/
C6
/
/
C12
/
Bond angles
C3Á
C3Á
C4Á
C3Á
C4Á
C5Á
C3Á
C4Á
C5Á
C1Á
C3Á
/
WÁ
WÁ
WÁ
WÁ
WÁ
WÁ
WÁ
WÁ
WÁ
WÁ
WÁ
/
C4
C5
C5
C1
C1
C1
C2
C2
C2
C2
P
89.6(3)
85.5(3)
89.6(2)
89.8(3)
178.2(2)
88.6(2)
87.0(2)
92.3(2)
172.2(2)
89.3(2)
178.8(2)
C4Á
C5Á
C1Á
C2Á
C18Á
C18Á
C6ÁPÁ
C18ÁPÁ
C6ÁPÁ
C12ÁPÁ
/
WÁ
WÁ
WÁ
WÁ
PÁ
PÁ
/
P
P
P
P
90.65(18)
95.68(17)
89.97(16)
91.81(16)
107.8(3)
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
C6
/
/
/
/
C12
104.0(3)
/
/
/
/C12
102.7(2)
/
/
/
/
W
114.42(18)
111.31(15)
115.65(16)
/
/
/
/W
/
/
/
/
W
/
/
strong absorption band at 1865 cmꢂ1 is attributed to
the trans-W(CO)4(PCy3)2 complex (Fig. 1e). The four
absorption bands at 2006, 1900, 1880, and 1870 cmꢂ1
Fig. 1. IR spectra in the CO stretching region recorded during the reaction of W(CO)5(h2-btmse) (1) with two equivalents of PCy3 in n-hexane at
complex 2 in n-
hexane, (e) of the trans-W(CO)4(PCy3)2 complex 5 in n-hexane, (f) of the cis-W(CO)4(PCy3)2 complex 4 in n-hexane (small amount of trans-
room temperature: (a) before reaction, just of W(CO)5(h2-btmse) (1), (b) after 2 h, a(c) after 12 h, (d) of the W(CO)5P(c-C6H11 3
)
W(CO)4(PCy3)2 present).

72
O. Demircan et al. / Journal of Organometallic Chemistry 688 (2003) 68Á74
/
the products mixture of the reaction with W(CO)5(h2-
btmse).
Inspection of the X-ray structural data in Table 2
reveals some important findings. In essence, the metal
atom has a pseudooctahedral arrangement of six
P(c-C6H11)3: 37.09 (d, J(13CÁ31
/
P)ꢁ18.1 Hz), 30.48 (s),
/
27.94 (d, J(13CÁ31
/
P)ꢁ10.6 Hz), and 26.61 (s) ppm.
/
In the 31P-NMR spectrum of W(CO)5(PCy3), one
observes a signal at 33.43 ppm, accompanied by the
183W satellites (the 183WÁ31
P coupling constant is 232
Hz, similar to the values observed for the W(CO)5(PR3)
/
ligands, one phosphine and five carbonyls. The metalÁ
/
carbon bond distance for CO in trans-position to the
complexes [19]).
˚
1.986(6) A] is noticeably
The second fraction eluded with a 1:3 mixture of
dichloromethane and n-hexane on the silica-gel column
of the solution obtained from the reaction of
W(CO)5(h2-btmse) with P(c-C6H11)3 contains trans-
W(CO)4(PCy3)2. This latter complex could be crystal-
lized from the n-hexane solution and characterized by
using the IR, MS and NMR spectroscopy.
phosphine ligand [WÁ
shorter than those for the four equatorial CO ligands,
which are almost equivalent [WÁC4ꢁ2.032(6), WÁ
C5ꢁ2.037(6), WÁC1ꢁ2.041(6), and WÁC2ꢁ2.042(6)
A]. The small differences observed in the WÁCO bond
/
C3ꢁ
/
/
/
/
/
/
/
/
/
˚
/
distances for the carbonyl groups cis to the phosphine
ligand seemingly originate from crystal packing effects
The molecular structure of trans-W(CO)4(PCy3)2 has
already been reported in a recent paper [20]. It is
[15]. The difference in WÁ
cis- and trans-carbonyls in the complex 2 is in accord
with the notion of an enhanced tungsten (dp)0carbonyl
(p*) back-donation arising from the fact that the p-
accepting ability of phosphine is less than that of carbon
monoxide.
/
CO bond distances between
noteworthy to compare the WÁ
/
P and WÁCO bond
/
/
distances and bond angles in these two complexes,
W(CO)5(PCy3) (2) and trans-W(CO)4(PCy3)2 (5). The
˚
P bond distance of 2.5794(12) A,
complex 2 has a WÁ
/
Concerning the PÁ
deviation is observed only in the C5Á
95.68(17)8, from the regular 908. This may be attributed
to the steric interaction between the carbonyl ligand and
/
WÁ
/
CO bond angles, a noticeable
which is slightly longer than those in the complex 5 [WÁ
/
˚
/
WÁP angle,
/
Pꢁ
[WÁ
compare well with the metalÁ
equatorial CO ligands in 2 [WÁ
2.037(6), WÁC1ꢁ2.041(6), and WÁ
All of them are slightly longer than the metalÁ
bond distance for CO trans to the phosphine ligand in
/
2.525(3), 2.506(3) A]. The WÁ
Cꢁ2.129(13), 2.064(13), 2.018(14), and 1.99(2) A]
carbon bonds for the four
C4ꢁ2.032(6), WÁC5ꢁ
C2ꢁ2.042(6) A].
carbon
/
C bond distances in 5
˚
/
/
/
one cyclohexyl group of P(cÁ
toward this CO. All the other PÁ
more or less close to the values expected for a regular
octahedral geometry [C1ÁWÁPꢁ89.97(16), C2ÁWÁ
Pꢁ91.81(16), C3ÁWÁPꢁ178.8(2), and C4ÁWÁPꢁ
90.65(18)8].
/
C6H11)3, which is oriented
/
/
/
/
˚
/
WÁCO bond angles are
/
/
/
/
/
/
/
/
/
/
/
˚
/
/
/
/
/
/
/
W(CO)5P(c-C6H11)3 [WÁ
/
C3ꢁ1.986(6) A]. The trans-
/
W(CO)4(PCy3)2 complex shows more distortion from
the regular octahedral geometry than W(CO)5(PCy3), as
The IR spectrum of W(CO)5(PCy3) exhibits four
prominent absorption bands at 2065, 1938, 1933 and
1929 cmꢂ1 in the CO stretching vibrational region,
along with a weak feature at 1968 cmꢂ1. The five-band
n(CO) pattern indicates that the C4v symmetry of
W(CO)5 skeleton, commonly observed for M(CO)5L
complexes [n(CO) modes: 2A1, E (IR active) and A2 (IR
inactive)] [16], is reduced to C2v symmetry by the bulky
phosphine ligand: the degeneracy of the very intense E
seen from the PÁ
/
WÁP bond angle of 170.93(8)8, for
/
example.
The appearance of one single strong n(CO) band at
1865 cmꢂ1 in the IR spectrum is indicative of a square-
planar structure of the W(CO)4 skeleton in trans-
W(CO)4(PCy3)2, which implies that in the presumed
octahedral coordination geometry the phosphine ligands
are in mutual trans-positions.
The 13C-NMR spectrum of trans-W(CO)4(PCy3)2
shows one signal at 207.27 ppm, which is split to a
mode is lifted (0
/
B1, B2) and the A2 becomes IR active
(0B1), albeit with intrinsically low intensity, such that
/
the assignments of bands in Fig. 1d is straightforward.
A1: 2065, A1: 1968, B1: 1938, B2: 1933 and A1: 1929
triplet due to the 13CÁ31
appearance of only one signal for the four equatorial
CO groups indicates that the molecule is fluxional with
/
P coupling (Jꢁ12.3 Hz). The
/
cmꢂ1
.
The 13C-NMR spectrum of W(CO)5(PCy3) shows two
doublets for the carbonyl groups at 199.31 (Jꢁ20.2 Hz)
and 198.8 ppm (Jꢁ6.7 Hz) in approximately 1:4
respect to rotation about the metalÁ
axis. In the 13CÁ{1H}-NMR spectrum, the complex 5
shows four signals for the cyclohexyl carbons of P(c-
C6H11)3: 36.69 (t, J(13CÁ31
P)ꢁ9.8 Hz), 28.68 (s), 26.82
/
phosphine bond
/
/
/
intensity ratio [17]. The appearance of only one signal
for the four equatorial CO groups indicates that the
molecule is fluxional with respect to rotation about the
/
/
(t, J(13CÁ31
/
P)ꢁ4.9 Hz), and 25.57 (s) ppm.
/
The 31P-NMR spectrum of trans-W(CO)4(PCy3)2
exhibits one signal at 32.18 ppm, accompanied by the
metalÁ
/
phosphine bond axis. The 13CÁ31
/
P coupling is
stronger for trans CO than for cis CO groups as
183W satellites (the 183WÁ31
/
P coupling constant is 256
Hz, similar to the values observed for the trans-
W(CO)4(PR3)2 complexes [21]. The larger 183WÁ31
coupling constant in trans-W(CO)4(PCy3)2 than that in
observed in the W(CO)5PR3 complexes [18]. In the
13CÁ
C6H11)3 shows four signals for the cyclohexyl carbons of
/
{1H}-NMR spectrum, the complex W(CO)5P(c-
/
P

O. Demircan et al. / Journal of Organometallic Chemistry 688 (2003) 68Á
/74
73
W(CO)5(PCy3) is consistent with the stronger (shorter)
WÁP bond in the former than that in the latter complex.
W(CO)5(PCy3) (2). The other five-coordinate, 16-elec-
tron intermediate cis-W(CO)4(h2-btmse) may be at-
tacked by of P(c-C6H11)3 forming the complex 3, cis-
W(CO)4(h2-btmse)(PCy3). The latter complex 3 is not
stable because of the presence of bulky trimetylsilyl and
cyclohexyl groups close to each other. The labile alkyne
ligand in 3 is easily replaced by another PCy3 molecule
forming the complex 4 cis-W(CO)4(PCy3)2. This com-
plex 4 is the kinetic product, however, is thermodyna-
/
In the reaction of W(CO)5(h2-btmse) with of P(c-
C6H11)3 at room temperature, four n(CO) bands at
2006, 1900, 1880 and 1870 cmꢂ1 grow in first, then start
to decrease and finally disappear at the end of the
reaction. In a separate experiment, the reaction was
ceased by cooling the solution down when these four
bands have maximum intensity for the purpose of
isolation of the species giving rise these absorption
features in the IR spectra. By recrystallization from n-
hexane solution we could get a sample which gave the
IR spectrum in Fig. 1f, which shows, in addition to the
four strong absorption bands of this species, a n(CO)
band at 1865 cmꢂ1 for trans-W(CO)4(PCy3)2. On
standing the sample at room temperature, these four
absorption bands lose intensity while the band at 1865
cmꢂ1 grows in concomitantly, indicating that the
species giving rise the four absorption bands is con-
verted to trans-W(CO)4(PCy3)2. Thus, this species is
concluded to be the cis-W(CO)4(PCy3)2 complex, which
is thermodynamically not stable and rapidly converted
to the trans isomer.
mically
not
stable
because
of
the
bulky
tricyclohexylphosphine ligand. The large cone angle of
1708 for the tricyclohexylphosphine [22] may account
for the difficulty in the preparation of the complex 4 cis-
W(CO)4(PCy3)2 as reported previously [23]. The instable
complex 4 cis-W(CO)4(PCy3)2 is converted to the
thermodynamically
W(CO)4(PCy3)2.
stable
isomer
5
trans-
A recent paper [24] has interestingly reported the
preparation of the analogous molybdenum complex,
cis-Mo(CO)4(PCy3)2, from cis-tetracarbonylbis(piperi-
dine) molybdenum(0) following the procedure of Dar-
ensbourg and Kump [9]. In a similar experiment with
cis-tetracarbonylbis(piperidine)tungsten(0), the cis-
W(CO)4(PCy3)2 complex was generated as an inter-
mediate which rapidly isomerized to the stable trans-
product as followed by IR spectroscopy.
Although the reaction of W(CO)5(h2-btmse) with PF3
yields isolable CO substitution products [1], the complex
3, cis-W(CO)4(h2-btmse)(PCy3) could not be detected in
the solution by IR spectroscopy. Neither it could be
obtained from the reaction of the photochemically
generated cis-W(CO)4)(PCy3)(THF) with of P(c-
C6H11)3, a procedure used for the preparation of cis-
W(CO)4(h2-alkene)(PR3) complexes [25]. The instability
of cis-W(CO)4(h2-alkyne)(PCy3) may be arising from
the mutual steric and/or electronic effects of two bulky
ligands.
The mechanism in Scheme 2 can be proposed for the
reaction of the complex W(CO)5(h2-btmse) (1) with
PCy3 at room temperature. It has already been shown
that W(CO)5(h2-btmse) can undergo both the alkyne
and CO dissociations, resulting in the reversible forma-
tion of the five-coordinate, 16-electron intermediates,
W(CO)5 and cis-W(CO)4(h2-btmse), which can be
attacked by any potential ligands [1]. In the presence
of tricyclohexylphosphine, the five-coordinate, 16-elec-
tron intermediate W(CO)5 forms the stable complex
The reaction of W(CO)5(h2-btmse) with of P(c-
C6H11)3 was carried out with various initial proportion
of tricyclohexylphosphine to the alkyne complex. It was
found that the reaction of W(CO)5(h2-btmse) with of
P(c-C6H11)3 in different ligand to complex ratio between
1 and 5 yields always the same products, W(CO)5(PCy3)
and trans-W(CO)4(PCy3)2, however, in varying relative
amount. Increasing the ligand to complex ratio causes
the relative amount of the alkyne substitution product
W(CO)5(PCy3) to decrease while the relative amount of
trans-W(CO)4(PCy3)2 increases. This can be rationalised
by considering the reaction mechanism given in Scheme
1.
4. Supplementary material
Scheme 2. The reaction of pentacarbonyl(h2-bis(trimethylsilyl)ethi-
ne)tungsten(0), W(CO)5(h2-btmse), with tricyclohexylphosphine,
PCy3.
Crystallographic data (excluding structure factors) for
the structural analysis have been deposited with the

74
O. Demircan et al. / Journal of Organometallic Chemistry 688 (2003) 68Á74
/
(d) F.G. Moers, J.G.A. Reuvers, Recl. Trav. Chim. Pays-Bas 93
(1974) 246.
[8] F.-W. Grevels, J.G.A. Reuvers, J. Takats, Inorg. Synth. 24 (1986)
Cambridge Crystallographic Data Centre, CCDC no.
212613. Copies of this information may be obtained free
of charge from The Director, CCDC, 12 Union Road,
176Á
[9] D.J. Darensbourg, R.L. Kump, Inorg. Chem. 17 (1978) 2680.
[10] EnrafÁNonius, CAD-4 EXPRESS Software, Version 1.1. EnrafÁ
Nonius, Delft, Netherlands, 1993.
/180.
Cambridge CB2 1EZ, UK (Fax: ꢀ44-1223-336033; e-
/
/
/
mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
[11] G.M. Sheldrick, SHELXS-97 and SHELXL-97, Program for Crystal
Structure Solution and Refinement, University of Gottingen,
Germany, 1997.
[12] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.
[13] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[14] W. Strohmeier, Angew. Chem. Int. Ed. Engl. 3 (1964) 730.
[15] Such a distortion caused by crystal packing is not seldom. Even
Acknowledgements
Partial support of this work by Turkish Academy of
Sciences is gratefully acknowledged.
W(CO)6, where all six carbonyls are chemically equivalent, shows
˚
a variation of 2.020Á
/
2.055 A in the WÁ
/
C bond distances and of
˚
1.14Á
Heinemann, H. Schmidt, K. Peters, D. Thiery, Z. Kristallogr.
198 (1992) 123Á124.
/1.16 A in the CÁ
/O bond distances [2]. See also: F.
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