Seven-coordinate complexes of molybdenum(II) containing a trichlorogermyl ligand: X-ray crystal structure of a novel [Mo(GeCl3)2(CO)2(NCEt)3]

Article abstract of DOI:10.1016/S0022-328X(99)00213-2

The oxidative-addition of GeCl₄ to [Mo(CO)₄(NCMe)₂] in CH₂Cl₂ provides a high-yield and fast route to the trichlorogermyl complex [MoCl(GeCl₃)(CO)₃(NCMe)₂] (1). Beside 1, other compounds containing a Mo-Ge bond are formed, as was shown by IR and NMR investigation of the reaction mixture. These compounds react further with an excess of propionitrile giving among others, a novel, crystallographically characterized [Mo(GeCl₃)₂(CO)₂(NCEt)₃] (3). Compound 3 is the first structurally characterized molybdenum(II) carbonyl complex, containing two trichlorogermyl ligands. Reaction of 1 or 3 with an alkyne (PhCCPh, PhCCMe, PhCCH) affords compounds in which CO and/or nitrile ligands were replaced by alkyne ligands. The alkyne molybdenum(II) complexes formed were characterized structurally by IR and NMR spectroscopy. However, the reaction of 1 with phenylacetylene (PA) leads to the catalytic coupling of alkyne molecules and the formation of cyclotrimers and polymers. The possible mechanisms for the formation of molybdenum(II) complexes and their role in the catalytic process are discussed.

Full text of DOI:10.1016/S0022-328X(99)00213-2

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 585 (1999) 215–224
Seven-coordinate complexes of molybdenum(II) containing a
trichlorogermyl ligand: X-ray crystal structure of a novel
[Mo(GeCl3)2(CO)2(NCEt)3]
*
Teresa Szyman´ska-Buzar *, Tadeusz Glowiak, Izabela Czelus´niak
*
*
Faculty of Chemistry, Uni6ersity of Wroclaw, 14 F. Joliot-Curie, 50-383 Wroclaw, Poland
Received 7 December 1998; received in revised form 30 March 1999
Abstract
The oxidative–addition of GeCl4 to [Mo(CO)4(NCMe)2] in CH2Cl2 provides a high-yield and fast route to the trichlorogermyl
complex [MoCl(GeCl3)(CO)3(NCMe)2] (1). Beside 1, other compounds containing a Mo–Ge bond are formed, as was shown by
IR and NMR investigation of the reaction mixture. These compounds react further with an excess of propionitrile giving among
others, a novel, crystallographically characterized [Mo(GeCl3)2(CO)2(NCEt)3] (3). Compound 3 is the first structurally character-
ized molybdenum(II) carbonyl complex, containing two trichlorogermyl ligands. Reaction of 1 or 3 with an alkyne (PhCꢀCPh,
PhCꢀCMe, PhCꢀCH) affords compounds in which CO and/or nitrile ligands were replaced by alkyne ligands. The alkyne
molybdenum(II) complexes formed were characterized structurally by IR and NMR spectroscopy. However, the reaction of 1 with
phenylacetylene (PA) leads to the catalytic coupling of alkyne molecules and the formation of cyclotrimers and polymers. The
possible mechanisms for the formation of molybdenum(II) complexes and their role in the catalytic process are discussed. © 1999
Elsevier Science S.A. All rights reserved.
Keywords: Molybdenum(II); Germanium; Crystal structure; Seven-coordinate; Heterobimetallic complexes; Nitrile complexes; Alkyne complexes;
Cyclotrimerization
W–Ge [8] and Mo–Sn bond [9]. However, the chem-
istry of analogous heterobimetallic Mo–Ge complexes
has been developed very weakly. Baker and Kendrick
briefly mentioned the formation of [MCl(GeCl3)-
(CO)3(NCMe)2], M=W, Mo, by the reaction of
[M(CO)3(NCMe)3] with GeCl4 in acetonitrile, but they
could not obtain those compounds in a pure state [10].
Therefore, we decided to repeat the synthesis and to
verify the nature of the Mo–Ge compound formed in
the oxidative–addition reaction of molybdenum(0)
compound and germanium tetrachloride. However, we
found that the compound with Mo–Ge bond is more
conveniently obtained in high yield by using CH2Cl2
instead of acetonitrile, as the solvent for the reaction of
[Mo(CO)4(NCMe)2] with GeCl4. Here, we describe the
improved synthesis of [MoCl(GeCl3)(CO)3(NCMe)2] (1)
and the first characterization of the bis(trichlorogermyl)
complex [Mo(GeCl3)2(CO)2(NCEt)3] (3). A novel com-
pound 3 was isolated in crystalline form and its struc-
ture established by X-ray crystallography. The intent of
1. Introduction
The synthesis and reactivity of Group 6 metal, seven-
coordinate complexes is an area of considerable interest
at present [1]. Recent reports include the use of such
complexes for alkene metathesis and ring-opening
metathesis polymerization applications [2–4], and for
alkyne polymerization [2,5]. In recent years we have
been investigating the chemistry of the seven-coordinate
compounds of tungsten(II) and molybdenum(II) [2,5–
9]. Such compounds can be formed easily in an oxida-
tive–addition reaction of d6 Group 6 metal complexes
and Group 14 element tetrahalides. In this way we have
synthesized and structurally characterized by X-ray,
several seven-coordinate chlorocarbonyl complexes of
tungsten(II) and molybdenum(II) with a W–Sn [5–7],
* Corresponding author. Fax: +48-71-222348.
E-mail address: tsz@chem.uni.wroc.pl (T. Szyman´ska-Buzar)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00213-2

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T. Szyman´ska-Buzar et al. / Journal of Organometallic Chemistry 585 (1999) 215–224
this work was to obtain molybdenum(II) complexes
with loosely bound, labile nitrile ligands in the hope
that this will lead to active homogeneous catalysts. To
determine whether 1 is a convenient precursor for the
alkyne polymerization catalyst, we studied the substitu-
tion of the labile acetonitrile and CO ligands by alky-
nes.
C, 16.95; H, 1.47; N, 5.95%. The remaining compounds
(Scheme 1) were not separated and were detected only
by IR and NMR spectroscopy in the reaction mixture
(Table 1).
2.2.2. [MoCl(GeCl3)(CO)3(NCEt)2] (2)
Compound 1 was dissolved in propionitrile and the
solution was stirred for 60 min. Filtration followed by
removal of the solvent in vacuo, gave a residue which
was recrystallized from CH2Cl2–heptane giving a bis(-
nitrile) complex 2 contaminated with a small amount of
dicarbonyl compound as was shown by IR spectra
(Table 1).
2. Experimental
2.1. General data
All operations were carried out in an inert atmo-
sphere using standard Schlenk techniques. All solvents
and liquid reagents were dried and distilled over CaH2.
Solution IR spectra were obtained using KBr or NaCl
plates while solid samples were recorded using KBr
pellets on an FT-IR model-400 Nicolet instrument.
Far-IR spectra were recorded (500–50 cm−1) with a
2.2.3. [Mo(GeCl3)2(CO)2(NCEt)3] (3)
The mixture of Mo–Ge compounds obtained in the
reaction of [Mo(CO)4(NCMe)2] and GeCl4 was dis-
solved in propionitrile. The removal of the solvent in
vacuo, gave a residue which was recrystallized from
CH2Cl2–heptane giving the large golden yellow crystals
in a reddish brown oily precipitate which was extracted
to toluene. Insoluble in toluene, the crystalline com-
pound was identified as clear compound 3. Anal. Calc.
for C11H15Cl6GeMoN3O2: C, 19.57; H, 2.24; N, 6.22.
Found: C, 19.48; H, 2.30; N, 6.12%.
Bru¨cker IFSv instrument in Nujol mull on
a
polyethylene film. NMR spectra were obtained using a
Bruker AMX-300 spectrometer. The analysis of the
catalytic reaction products was performed on
a
Hewlett–Packard 5890 GC–MS system and by 1H-
NMR and IR spectroscopy.
2.3. Crystal and refinement data for compound 3
2.2. Synthesis
Crystal data and relevant refinement details are col-
lected in Table 2. A golden yellow crystal approxi-
mately 0.15×0.15×0.20 mm was removed from the
flask and rapidly coated with a light hydrocarbon oil to
protect it from the atmosphere. Data collection was
performed on a KM4 s-axis computer controlled [12]
four-circle diffractometer operating in the ꢀ–2q scan
mode with graphite-monochromated Mo–Ka radiation
2.2.1. [MoCl(GeCl3)(CO)3(NCMe)2] (1)
Dissolution of [Mo(CO)4(NCMe)2] [11] (2.2 g, 7.7
mmol) in CH2Cl2 (30 cm3) was followed by addition of
an equimolar quantity of GeCl4 (0.9 cm3, 7.7 mmol) by
means of a syringe. The mixture was stirred for 30 min,
during which time the yellow solution gradually
changed to a golden brown color, while the w(CO)
frequency of [Mo(CO)4(NCMe)2] disappeared. After
this reaction time IR spectroscopy confirmed the reac-
tion to be complete. Evaporation of the solvent led to
the isolation of a mixture of molybdenum(II) complexes
as a golden brown powder. The crude product was
washed with heptane (3×10 cm3) to remove Mo(CO)6
and a compound with two w(CO) bands at 2078 vw and
1949 vs cm−1, characteristic of a [Mo(CO)5] unit. The
residue was redissolved in CH2Cl2 (50 cm3), heptane (10
cm3) was layered on top and it was stored in the freezer
for several days affording a precipitate identified by
analysis and by IR and NMR spectra as
,
(u=0.71073 A) at 293 K. The accurate cell dimensions
and the crystal orientation matrix were determined by a
least-squares refinement of the setting angles of 90
carefully centered reflections in the range 20.6B2qB
40.2°. A total of 5163 unique reflections were measured,
of which 4539 (230 variables) with [I]2|(I)] in the
range 6–57° were used to solve and refine the structure
(
in the monoclinic space group P1.
The hydrogen atoms were placed in the geometrically
calculated positions with the isotropic temperature fac-
tors taken as 1.2 and 1.5 Ueq of the neighboring heavier
atoms for CH2 and CH3, respectively. Several cycles of
refinement of the coordinates and anisotropic thermal
parameters for non-hydrogen atoms (parameters of the
H atoms were fixed) reduced the R1 to 0.0615 and wR2
[MoCl(GeCl3)(CO)3(NCMe)]2.
Anal.
Calc.
for
C10H6Cl8Ge2Mo2N2O6: C, 13.79; H, 0.69; N, 3.22.
Found: C, 14.21; H, 0.89; N, 3.08%. Recrystallization
of this compound from acetonitrile gives the chlorine
bridge cleaved mononuclear compound 1, contami-
nated with a small amount of dicarbonyl compound as
was shown by the IR spectra (Table 1). Anal. Calc. for
C7H6Cl4GeMoN2O3: C, 17.65; H, 1.27; N, 5.88. Found:
to 0.1703. The maximum and minimum residual densi-
−3
,
ties in the difference map were 1.93 and −1.262 e A
respectively. Goodness-of-fit was 1.118.
,
The structure was solved by heavy-atom methods
with the SHELXS-86 program [13] and refined by a
full-matrix least-squares method, using the SHELXL pro-

T. Szyman´ska-Buzar et al. / Journal of Organometallic Chemistry 585 (1999) 215–224
217
gram [14]. Neutral atomic scattering factors were taken
from the SHELXL-93 program [14].
2.4. Reactions with alkynes
2.4.1. Reaction of 1 with diphenylacetylene (DPA)
To a solution of 1 (0.5 g, 1.1 mmol) in 20 cm3 of
CH2Cl2 was added PhCꢀCPh (0.4 g, 2.2 mmol) in
CH2Cl2 (5 cm3). The mixture was stirred and the
progress of the reaction was monitored by the disap-
pearance of w(CO) bands due to 1. At the beginning of
the reaction (2–4 h) several new w(CO) bands appear
and increase (2100, 2073, 1984 and 1951 cm−1). The
band at 2100 cm−1 next decays after a prolonged
reaction time. At least one week was allowed for the
reaction to go to completion. The solution was filtered
off and the solvent removed in vacuo. The residue was
washed several times with heptane and toluene to
remove a compound with two w(CO) bands at 2073 vw
and 1951 vs cm−1 characteristic of a [Mo(CO)5] unit.
The product was identified by IR and NMR studies
(Table 3) as a mixture of DPA compounds. The major
product [MoCl2(NCMe)2(PhCꢀCPh)2] was detected due
to two signals of acetylenic carbons in 13C-NMR spec-
tra at l 191.34 and 186.77. In CH2Cl2 solution this
compound dimerizes with
a loss of acetonitrile
molecule to yield the less soluble [Mo(m-
Cl)Cl(NCMe)(PhCꢀCPh)2]2. This process is reversible
in the presence of an excess of acetonitrile. The alkyne
compound with w(CO) band at 1984 cm−1 can be
formulated as [MoCl2(CO)(GeCl2)(NCMe)(PhCꢀCPh)]
(Scheme 2). The resulting compounds were not sepa-
rated but characterized by IR and NMR spectroscopy
(see Table 3) in the reaction mixture.
Recrystallization of the mixture of the above DPA
compounds from propionitrile leads to the formation
of a better soluble [MoCl2(NCEt)2(PhCꢀCPh)2] and
less soluble [MoCl2(CO)(GeCl2)(NCEt)(PhCꢀCPh)]
(Table 3).
2.4.2. Reaction of 3 with DPA
The alkyne (0.07 g, 0.4 mmol) was added to a
solution of complex 3 (0.14 g, 0.2 mmol) in CH2Cl2 (20
cm3) at room temperature (r.t.). The mixture was
stirred and the progress of the reaction was monitored
by the disappearance of w(CO) bands due to 3. From
the beginning of the reaction the new w(CO) band at
2013 cm−1 appears and increases. At least 1 week was
allowed for reaction to go to completion. The solution
was filtered and reduced to a greenish yellow residue.
Washing with heptane removed an yellow oil and
unreacted DPA from the desired product remained as a
light green solid. The IR spectrum of reaction product
was characterized by a strong w(CO) band at 2003, a
weak one at 1908 and a very weak one at 2092 cm−1
.

218
T. Szyman´ska-Buzar et al. / Journal of Organometallic Chemistry 585 (1999) 215–224
Scheme 1.
The product was identified by IR and NMR (Table
3) as a mixture of compounds with two and one
alkyne ligand in the coordination sphere of molybde-
num(II): [MoCl2(NCEt)2(PhCꢀCPh)2] and [MoCl2-
(CO)(GeCl2)2(PhCꢀCPh)].
from light orange to dark orange. The progress of the
reaction was monitored by the disappearance of
w(CO) bands of 1. At the beginning of the reaction a
new w(CO) band appears and increases at 2098 cm−1
which next decays after a prolonged reaction time.
Stirring for 21 h, followed by the filtration and evap-
oration of the solvent under low pressure gave an
orange solid. The crude product was washed out with
heptane to remove a compound with two w(CO)
bands at 2072 vw and 1949 vs cm−1, characteristic of
2.4.3. Reaction of 1 with 1-phenylprop-1-yne
(PhCꢀCMe)
The alkyne (0.5 cm3, 4 mmol) was added to a solu-
tion of complex 1 (0.53 g, 1.1 mmol) in a CH2Cl2/
CH3CN mixture (15/1 cm3) at r.t. The progress of the
reaction was monitored by the disappearance of
w(CO) bands of 1. At the beginning of the reaction
several new w(CO) bands appear and increase. The
band at 2087 cm−1 next decays after a prolonged
reaction time. Stirring for four days followed by the
filtration and evaporation of the solvent under low
pressure gave a green solid. The crude product was
washed out with heptane and toluene to remove a
compound with two w(CO) bands at 2072 vw and
1949 vs cm−1, characteristic of a [Mo(CO)5] unit and
organic compounds. The product was identified by IR
and NMR studies (Table 3) as a mixture of com-
pounds. The major product with a w(CO) band at
1977 cm−1 and two signals of acetylenic carbons in
13C-NMR spectra at l 224.28 and 222.91 can be for-
mulated as [MoCl2(CO)(GeCl2)(NCMe)(PhCꢀCMe)].
The second alkyne compound [MoCl2(NCMe)2-
(PhCꢀCMe)2] was identified due to two signals of
acetylenic carbons in 13C-NMR spectra at l 194.98
and 178.51. In CH2Cl2 solution the last compound
dimerizes with the loss of an acetonitrile molecule to
Table 2
Crystal data and details of refinement for [Mo(GeCl3)2(CO)2(NCEt)3]
(3)
Chemical formula
Molecular weight
Crystal system
C11H15Cl6Ge2MoN3O2
675.08
Triclinic
(
Space group
Unit cell dimensions
P1
,
a (A)
8.568(2)
11.591(2)
12.498(2
98.27(3)
93.28(3)
101.02(3)
1201.0(4)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
V (A )
3
,
Z
Reflections determining lattice
T (K)
90
293(2)
Crystal size (mm)
0.15×0.15×0.20
1.867
Dcalc (g cm−3
)
,
u (Mo–Ka) (A)
v (Mo–Ka) (cm−1
F(000)
71073
36.78
652
)
yield
the
less
soluble
[Mo(m-Cl)Cl(NCMe)-
Method of collection
2q Range (°)
Index ranges
ꢀ/2q scan
6B2qB57
−115h511, 155k515,
05l516
5163
4539/230
0.0615, 0.1703
1.118
(PhCꢀCMe)2]2. The organic products based on GC–
MS characterization were mainly cyclotrimers 1,2,4-
trimethyltriphenylbenzene
and
1,3,5-trimethyltri-
No. of unique data
No. of data with [I52|(I)]
Residuals R1, wR2
Goodness-of-fit
phenylbenzene in the ratio 4:1.
2.4.4. Reaction of 1 with phenylacetylene (PA)
The addition of four equivalents of PA (0.22 cm3,
2.1 mmol) to a stirred CH2Cl2 solution (10 cm3) of 1
(0.25 g, 0.5 mmol) at r.t. resulted in a color change
Extinction coefficient
0.0070(18)
1.930/−1.262
−3
,
Final (Dz)(e A
)

T. Szyman´ska-Buzar et al. / Journal of Organometallic Chemistry 585 (1999) 215–224
219
Table 3
Selected IR and NMR data for molybdenum(II) alkyne complexes
Complex
IR (w, cm−1
)
1H-NMR (l, ppm) b
13C-NMR (l, ppm) b
w(CO)
w(CN) a
d
[MoCl2(CO)(NCMe)(PhCꢀCPh)2]
[MoCl2(CO)(GeCl2)(NCMe)(PhCꢀCPh)]
2100 c
1981 a
–
–
–
2325 w,
2297 vw
2.06 (s, 1 CH3CN)
227.33 (s, 1 CO), 224.36 (s, 1 PhCꢀCPh),
222.83, (s, 1 PhCꢀCPh), 137.42 (s, 1 Ci–Ph),
137.17, (Ci–Ph),126.63 (s, 1 CH3CN), 4.04
(s, 1 CH3CN)
[MoCl2(NCMe)2(PhCꢀCPh)2]
–
2319 w,
2289 vw
2.35 (s, 2 CH3CN)
191.34 (s, 2 PhCꢀCPh), 186.77 (s, 2 PhCꢀ
CPh), 136.22 (s, 2 Ci–Ph), 135.17, (s, 2 Ci–Ph),
126.64 (s, 2 CH3CN), 4.75 (s, 2 CH3CN)
–
193.24 (s, 2 PhCꢀCPh), 188.47 (s, 2 PhCꢀ
CPh), 138.11 (s, 2 Ci–Ph), 136.71, (s, 2 Ci–Ph),
132.85 (s, 2 CH3CH2CN), 14.32 (s, 2 CH3-
CH2CN), 10.13 (s, 2 CH3CH2CN) e
231.94 (s, 1 CO), 226.13 (s, 1 PhCꢀCPh),
224.51 (s, 1 PhCꢀCPh), 136.31 (s, 1 Ci–Ph),
136.02, (s, 1 Ci–Ph) e
[MoCl2(CO)(GeCl2)(NCEt)(PhCꢀCPh)]
[MoCl2(NCEt)2(PhCꢀCPh)2]
1977 a
–
–
2293 w
2.47 (q, 2 CH3CH2CN),
1.26 (t, 2 CH3CH2CN) e
[MoCl2(CO)(GeCl2)2(PhCꢀCPh)]
2003 a
–
–
[MoCl2(CO)(NCMe)(PhCꢀCMe)2]
[MoCl2(CO)(GeCl2)(NCMe)(PhCꢀCMe)]
2087 c
1972 a
–
–
3.27 (s, 1 PhCꢀCMe), 2.31 226.69 (s, 1 CO), 224.28 (s, 1 PhCꢀCme),
(s, CH3CN)
222.91 (s, 1 PhCꢀCMe), 137.20 (s, 1 Ci–
Ph),127.73, (s, 1 CH3CN), 18.77 (s, 2 PhCꢀ
CMe), 4.05 (s, 1 CH3CN)
[MoCl2(NCMe)2(PhCꢀCMe)2]
–
2325 w,
2397 vw
3.27 (s, 2 PhCꢀCMe), 2.31 194.98 (s, 2 PhCꢀCMe), 178.51 (s, 2
(s, 2 CH3CN)
PhCꢀCMe), 135.98 (s, 2 Ci–Ph),126.41 (s, 2
CH3CN), 18.40 (s, 2 PhCꢀCMe), 4.75 (s, 2
CH3CN)
–
–
[MoCl2(CO)(NCMe)(PhCꢀCH)2]
[MoCl2(NCMe)2(PhCꢀCH)2] and other
2096 c
–
–
–
2325 w,
2397 vw
11.24, 11.09, 10.85, 10.68
(PhCꢀCH), 2.53 (CH3CN)
a Spectra recorded in KBr disc.
b Spectra recorded in CDCl3.
c Spectra recorded in CH2Cl2.
d Not observable.
e Spectra recorded in CD2Cl2.
a [Mo(CO)5] unit and of PA oligomerization prod-
ucts. The heptane extract contained organic products
identified by GC–MS as 1,2,4-triphenylbenzene
(68.8%), 1,3,5-triphenylbenzene (29.9%), diphenylbuta-
diene (0.8%) and 1H-indene-1-(phenylmethylene)
(0.5%). The residue was dried in vacuo to give a
brownish yellow mixture of compounds with four sig-
nals in the 1H-NMR spectrum characteristic for PA
coordinated to molybdenum in the region of l 11–
10. As was shown by elemental analysis there are
compounds with two alkynes in the coordination
sphere of molybdenum, probably [MoCl2(NCMe)2-
(PhCꢀCH)2], [Mo(m-Cl)Cl)(NCMe)(PhCꢀCH)2]2 and
[Mo2(m-Cl)3Cl(NCMe)(PhCꢀCH)4].
of CH2Cl2 (5 cm3), ortho-xylene (the internal chro-
matographic standard), PA (1 mol dm−3), and a
molybdenum complex 1 (PA/Mo 100 or PA/Mo 50)
was stirred at r.t. under nitrogen for 24 h. The slow
disappearance of PA was confirmed by GC (45% af-
ter 24 h). The polyphenylacetylene (PPA) was precipi-
tated in methanol (20 cm3) as a dark orange powder.
The polymerization yield (%), defined by comparing
the polymer weight to the weight of the PA used, was
no greater than 17%. The polymer was analyzed by
1H-NMR, IR spectroscopy and gel-permeation chro-
matography. Molecular weights of the PPA were
measured using CHCl3 solutions, a refractive index
monitor and a Plgel 10 m MIXED-B column. The
values recorded are the weight of polystyrene that
would exhibit the chromatograms observed. Molecu-
lar weights of the PPA achieved the value, 1×104.
1H-NMR spectra of the polymers were recorded in a
CDCl3 solution at 300 MHz. The stereostructure of
the polymer was elucidated to be 58% cis-transoidal,
using the 1H-NMR data by the following equation
Anal. Calc. for C34H27Cl4Mo2N: C, 52.14; H, 3.47;
N, 1.79. Found: C, 51.17; H, 3.67; N, 1.48%.
2.5. Catalytic con6ersion of PA
In a typical experiment, the mixture was composed

220
T. Szyman´ska-Buzar et al. / Journal of Organometallic Chemistry 585 (1999) 215–224
according to Ref. [15],% cis=A5.85×104/At×16.66,
where A denotes the integrated absorption area of the
signal at l=5.85 ppm and At=the total integral of the
NMR spectrum.
trile (Scheme 1). The formation of compounds with two
GeCl3 groups coordinated to the molybdenum center
was also observed (Scheme 1). These compounds can be
formed in
a
disproportionation reaction giving
The filtrate obtained after the precipitation of the
polymers was evaporated to dryness and the CH2Cl2
solution of the residue was investigated by GC–MS.
Analysis showed mainly 1,2,4-triphenylbenzene and
1,3,5-triphenylbenzene in an average ratio of 3:1. The
PA dimers, 1H-indene-1-(phenylmethylene), different
isomers of diphenylbutadiene were formed in low yield
(below 2%). The yield of oligomerization, calculated as
the difference between the conversion and yield of
polymerization reaction, was about 28% after 24 h
reaction time.
[MoCl2(CO)5−n(NCR)n], where n=2 or 3. Such a
course of the reaction may well be a consequence of
lower thermal stability of the [MoCl2(CO)5−n(NCR)n]
by-product in comparison to [Mo(GeCl3)2(CO)5−n
(NCR)n] as a result of the p-acceptor character of the
GeCl3 ligand [16] in relation to the p-donor character of
the chloride ligand. Subsequently, as earlier studies of
molybdenum(II) nitrile compounds suggest [17,18],
compounds of the type [MoCl2(CO)5−n(NCR)n] upon
further reaction with the nitrile undergo disproportion-
ation to compounds of molybdenum(0) and MoCl3
solvated by nitrile. In this case Mo(CO)6 and
[Mo(CO)5(NCMe)] were identified as side products.
3. Results and discussion
3.2. Spectral studies of Mo–Ge compounds
3.1. Synthesis of Mo–Ge compounds
The IR spectra of [MoCl(GeCl3)(CO)3(NCR)2] (R=
Me and Et) compounds in KBr show a common profile
which includes three bands in the CO region, with only
small changes in frequencies within the nitrile series
(Table 1). They are similar to that for the analogous
molybdenum–tin complex obtained for the first time by
Baker and Bury [9,19] and are in excellent agreement
with the data reported for tungsten compounds of the
type [WCl(MCl3)(CO)3(NCMe)2], M=Sn [7], Ge [8].
The germyl ligand can be identified by far-IR spectra
Following our report [8] of the synthesis, molecular
structure and reactivity of the unusual bimetallic tung-
sten–germanium
compounds
[(CO)4W(m-Cl)3W-
(GeCl3)(CO)3] and [WCl(GeCl3)(CO)3(NCR)2], R=
Me, Et, Bu, Ph, it has recently been found that the
oxidative–addition reaction of [Mo(CO)4(NCMe)2]
with
[MoCl(GeCl3)(CO)3(NCMe)2] (1). The first time com-
pound was obtained in the reaction of
GeCl4
leads
to
an
analogous
1
[Mo(CO)3(NCMe)3] and GeCl4 in acetonitrile [10].
However, we found that compound 1 is more conve-
niently obtained in high yield by using CH2Cl2 instead
of acetonitrile as solvent for the reaction of
[Mo(CO)4(NCMe)2] with GeCl4. Besides 1, other com-
pounds containing Mo–Ge bonds are formed (Scheme
1). They include seven-coordinate mononuclear and
dinuclear compounds with varying numbers (1–3) of
CO and nitrile ligands (Scheme 1). They are less soluble
in CH2Cl2 or CHCl3, but the dimers can be restored to
readily soluble monomers by recrystallization from ni-
due to the w(GeCl) band at ca. 380 cm−1
.
The 13C-NMR spectrum of compound 1 in CDCl3 at
293 K consists of one sharp resonance at l 219.34 ppm.
Very similar single resonances were observed for three
equivalent carbonyl groups of other compounds of the
type [MCl(M%Cl3)(CO)3(NCMe)2] (l 211.9 for W–Sn
[7], 214.8 for W–Ge [8] and 219.39 for the Mo–Sn [9]
1
compound). The single resonance in the H-NMR spec-
trum clearly indicates that all bis(nitrile) compounds
contain two equivalent nitrile ligands (Table 1).
Scheme 2.

T. Szyman´ska-Buzar et al. / Journal of Organometallic Chemistry 585 (1999) 215–224
221
The complex [MoCl(GeCl3)(CO)3(NCMe)2] (1) syn-
thesized by Baker and Kendrick showed three carbonyl
bands at w(CO) 2040 (s), 1953 (s), 1877 (m) cm−1 but
six resonances in the carbonyl region (l 231.53–202.92)
of the 13C-NMR spectrum [10]. This is in contrast to
the results for [WCl(SnCl3)(CO)3(NCMe)2] [7],
[WCl(GeCl3)(CO)3(NCMe)2] [8] and [MoCl(SnCl3)-
(CO)3(NCMe)2] [9] which showed analogous distorted
capped octahedron geometry and similar IR spectrum
containing three carbonyl bands, but only one carbonyl
resonance of three equivalent CO groups. Besides the
w(CO) frequency at 1877 cm−1, it is characteristic for
dicarbonyl rather than tricarbonyl species (Table 1).
However, compound 3 and other compounds con-
taining two GeCl3 groups coordinated to molybdenum,
have different spectral data (Table 1). First of all there
is a downfield shift of the carbon resonance of CO
groups to l ca. 230 in 13C-NMR spectra. This shift is
consistent with the lowering of electron density on
molybdenum due to the higher electron-withdrawing
character of two trichlorogermyl ligands. Thus the
molybdenum atom in 3 is effectively more oxidized
than in 1. The IR spectrum of 3 shows two w(CO)
bands at 1961 s and 1897 vs cm−1, which is in the
region, and intensely characteristic of other seven-coor-
dinate bis(carbonyl) nitrile compounds [1,9]. The spec-
troscopic data obtained for 3 are analogous to those
presented by [Mo(SnCl3)2(CO)2(NCEt)3] [9].
6
Fig. 1. Molecular structure of [Mo(GeCl3)2(CO)2(NCEt)3] (3).
The molybdenum–germanium bond is short, at 2.534
,
A (average), compared to the sum of the relevant
,
covalent radii of 2.83 A [27,28]. In view of the estab-
lished p-acceptor properties of the GeCl3 group [16] it
clearly indicates that the Mo–Ge bond does possess
some double-bond character. Similar Mo–Ge distances
had been observed for [CpMo(CO)2(PMe3)(GeCl2H]
(2.531(2) [20]) and [CpMo(CO)2(PMe3)(GeCl3] (2.505(7)
[20]) but longer for the triphenylgermyl complexes
3.3. Structure of [Mo(GeCl3)2(CO)2(NCEt)3] (3)
,
(2.658(2) [21] and 2.604(2) A [22]).
Although the structures of numerous complexes con-
taining a molybdenum–germanium bond have been
determined crystallographically [20–22], no bis(tri-
chlorogermyl) complexes have thus far been studied.
The structure of compound 3, is shown in Fig. 1 with
the atom-numbering scheme. Table 2 gives a summary
of the crystal data and refinement obtained for 3. The
principal interatomic bond distances and angles are
presented in Table 4.
The geometry of the coordination sphere of molybde-
num atom in 3 approximates that of the 4:3 ‘piano
stool’ structure identified in several molybdenum(II)
complexes ([Mo(CNPh)7]2+ [23], [Mo2Cl3(CO)4-
{P(OMe)3}4]+ [24] and [Mo-Br(CO)3(1,4,7-triazacy-
clononane)]+ [25]). In the description of 3 the tetrago-
nal base is defined by two carbon atoms,
The germanium atom is four-coordinate with a ge-
ometry that is best described as a distorted tetrahedral
with Cl–Ge–Cl angles in the range 99.7(1)–101.2(1)
and Cl–Ge–Mo angles in the range 113.7(8)–121.9(8)°,
so the tetrahedral geometry is distorted by the greater
repulsions associated with the molybdenum atom.
An X-ray study of complex 3 showed that the GeCl3
ligands occupy a position mutually trans with the Ge–
Mo–Ge angle of 124.6(3)°. The 4:3 ‘piano stool’ ge-
ometry similar to that for 3, with two mutually trans
trichlorostannyl ligands, and three mutually cis nitrile
ligands, was observed previously for analogous
[Mo(SnCl3)2(CO)2(NCEt)3] [9]. However, the Mo–N
distances are longer (av. 2.197 vs. 2.179) and Mo–C
distances are shorter (av. 1.968 vs. 1.984) in 3 than in
the bis(trichlorostannyl) compound [9].
,
Mo–C=1.968 A (average) and two germanium atoms,
,
Mo–Ge=2.534 A (average). In the trigonal base there
3.4. Reactions of molybdenum(II) compounds with alky-
nes
are three nitrogen atoms with a mean Mo–N bond
,
length of 2.186(5), 2.193(5) and 2.212(5) A and cis
N–Mo–N bond angles 79.8(2), 79.9(2) and 79.3(2)°.
The angle between tetragonal and trigonal base is 2.6
(1)° confirming the 4:3 geometry [26]. One nitrogen
atom (N(21)) of the trigonal base and one carbon atom
(C(1)) of the tetragonal base almost overlap (Fig. 2).
The complexes obtained in the reaction of 1 and
alkynes (Scheme 2) are listed in Table 3 along with their
IR and NMR spectroscopic data.
When the reaction of 1 with two molecular equiva-
lents of DPA at r.t. in CH2Cl2 was monitored by IR, at

222
T. Szyman´ska-Buzar et al. / Journal of Organometallic Chemistry 585 (1999) 215–224
the beginning, decay of w(CO) bands due to 1 was
accompanied by appearance and growth of several
w(CO) bands at 2100, 2073, 1984 and 1950 cm−1. But
after a prolonged reaction time (24 h), a new w(CO)
band at 2100 cm−1 of the alkyne complex decays.
Based on the IR data the initial complex can be de-
scribed as [MoCl2(CO)(NCMe)(PhCꢀCPh)2] with the
structure close to the one obtained and characterized
crystallographically by Baker et al. in the reaction of
[WI2(CO)3(NCMe)2] and RCꢀCR (R=Me, Ph) [29,30].
The loss of the CO group leads to formation of chlo-
ride-bridged dimer [Mo(m-Cl)Cl(NCMe)(PhCꢀCPh)2]2
(Scheme 2). The IR and NMR spectral data for the
reaction product indicate that it is a mixture of com-
pounds with and without CO in the coordination
sphere of the molybdenum. The mononuclear com-
pound [MoCl2(NCMe)2(PhCꢀCPh)2], with two mutu-
ally cis alkyne ligands, which are magnetically
equivalent and give two signals of acetylenic carbons in
13C-NMR spectra at l 191.34 and 186.77, was identified
as the main product. In CH2Cl2 solution this compound
dimerizes with a loss of acetonitrile molecule to yield
less soluble chloride-bridged complexes. This process is
reversible in the presence of an excess of acetonitrile
(Scheme 2). Thus, nitrile effects the nucleophilic cleav-
age of an Mo(m-Cl)2Mo bridge. The alkyne compound
with a w(CO) band at 1984 cm−1 was characterized
Fig. 2. Projection of the coordination sphere of Mo on the trigonal
base illustrating the 4:3 geometry of 3. Lines joining the atoms to
define the planes. The angle between tetragonal and trigonal base is
2.6(1)°.
only in the reaction mixture by IR and NMR spec-
troscopy
and
can
be
formulated
as
[MoCl2(CO)(GeCl2)(NCMe)(PhCꢀCPh)]. The spectral
characteristic of the latter compound is very similar to
the [MoCl(GeCl3)(CO)(NCMe)(PPh3)(PhCꢀCPh)] ob-
served by Baker et al. in the reaction of
[MoCl(GeCl3)(CO)2(NCMe)2(PPh3)] with DPA [31] and
to the other monoalkyne compounds of molybdenum
of the type [MoBr2(CO)(PR3)2(RCꢀCR%)] observed by
Table 4
,
Selected bond lengths (A) and bond angles (°) for
[Mo(GeCl3)2(CO)2(NCEt)3] (3)
1
Templeton et al. [32–34]. The acetylenic H- and 13C-
NMR chemical shift values observed here (Table 2) are
comparable to literature values for other four-electron
donor alkyne ligands in mono(alkyne) compounds [32–
34]. The reaction of 1 with alkynes in dichloromethane
solution containing acetonitrile leads to the formation
of higher yield of mono(alkyne) than bis(alkyne)
compound.
Mo(1)–Ge(1)
Mo(1)–Ge(2)
Mo(1)–C(1)
Mo(1)–C(2)
Mo(1)–N(3)
Mo(1)–N(2)
Mo(1)–N(1)
Ge(1)–Cl(1)
2.529(1) Ge(1)–Cl(3)
2.539(1) Ge(1)–Cl(2)
1.962(7) Ge(2)–Cl(4)
1.974(6) Ge(2)–Cl(6)
2.186(5) Ge(2)–Cl(5)
2.193(5) N(1)–C(11)
2.212(5) N(2)–C(21)
2.172(2) N(3)–C(31)
2.179(2)
2.180(2)
2.175(2)
2.179(2)
2.181(2)
1.126(8)
1.121(8)
1.118(9)
Spectral studies revealed that in the reaction of 1
with PhCꢀCH (PA) the precursor complex 1 is liable to
lose CO and acetonitrile, but at the beginning, one CO
and acetonitrile ligand still remains in the coordination
sphere of the molybdenum. The IR spectrum of this
product showed one w(CO) band at 2095 cm−1. How-
ever, the isolated compound does not contain carbonyl
ligand and after recrystallization from acetonitrile, was
identified as [MoCl2(NCMe)2(PhCꢀCH)2] contaminated
with dinuclear species. The hydrogen resonance due to
phenylacetylene coordinated to molybdenum was ob-
served at l 11.09, 11.24, 10.85 and 10.68.
As was mentioned above we were unable to prepare
the alkyne complexes containing trichlorogermyl lig-
and, because the hydrolysis of GeCl3 occurred and
GeCl2 coordinated to molybdenum(II), [MoCl2-
(CO)(GeCl2)(NCMe)(PhCꢀCPh)] or molybdenum(0),
C(1)–Mo(1)–C(2)
106.0(2)
N(1)–Mo(1)–Ge(2)
Ge(1)–Mo(1)–Ge(2) 124.6(3)
97.6(1)
C(1)–Mo(1)–N(3) 127.2(2)
C(2)–Mo(1)–N(3) 100.5(2)
C(1)–Mo(1)–N(2) 141.9(2)
C(2)–Mo(1)–N(2)
N(3)–Mo(1)–N(2)
C(1)–Mo(1)–N(1)
C(2)–Mo(1)–N(1) 171.3(2)
N(3)–Mo(1)–N(1)
N(2)–Mo(1)–N(1)
C(1)–Mo(1)–Ge(1) 68.7(2)
C(2)–Mo(1)–Ge(1) 74.4(2)
N(3)–Mo(1)–Ge(1) 75.9(1)
N(2)–Mo(1)–Ge(1) 149.4(1)
N(1)–Mo(1)–Ge(1) 114.0(1)
C(1)–Mo(1)–Ge(2) 73.8(2)
C(2)–Mo(1)–Ge(2) 78.6(2)
N(3)–Mo(1)–Ge(2) 157.3(2)
N(2)–Mo(1)–Ge(2) 77.5(1)
Cl(1)–Ge(1)–Cl(3)
Cl(1)–Ge(1)–Cl(2)
Cl(3)–Ge(1)–Cl(2)
Cl(1)–Ge(1)–Mo(1) 117.4(8)
Cl(3)–Ge(1)–Mo(1) 118.1(7)
Cl(2)–Ge(1)–Mo(1) 117.3(7)
Cl(4)–Ge(2)–Cl(6)
Cl(4)–Ge(2)–Cl(5)
Cl(6)–Ge(2)–Cl(5)
Cl(4)–Ge(2)–Mo(1) 116.0(7)
Cl(6)–Ge(2)–Mo(1) 121.9(8)
Cl(5)–Ge(2)–Mo(1) 113.7(8)
C(11)–N(1)–Mo(1) 175.6(5)
C(21)–N(2)–Mo(1) 176.7(5)
C(31)–N(3)–Mo(1) 177.0(6)
99.7(1)
99.8(1)
101.2(1)
92.2(2)
79.8(2)
80.2(2)
79.9(2)
79.3(2)
100.5(1)
100.5(1)
101.2(1)
O(1)–C(1)–Mo(1)
O(2)–C(2)–Mo(1)
174.4(6)
177.4(6)

T. Szyman´ska-Buzar et al. / Journal of Organometallic Chemistry 585 (1999) 215–224
223
[Mo(CO)5GeCl2], identified by IR and NMR spec-
troscopy, resulted. The latter compound which is ex-
tremely air-sensitive, readily soluble even in
cyclohexane and other hydrocarbons, gives character-
istic (for the pentacarbonyl unit) w(CO) bands at 2072
w and 1950 vs cm−1 in the IR spectrum and two
carbon resonances at l 213.26 (1 CO) and 205.94 (4
CO) in the intensity ratio 1:4, in the 13C-NMR spec-
trum. These data are in a good agreement with the
spectral data for compounds of the type,
[Mo(CO)5(GeX2)] [16,35].
initial coordination of two alkynes to the metal, rear-
rangement to a metallacyclopentadiene, insertion of a
coordinated alkyne into a Mo–C s-bond leading to
metalacycloheptatriene and reductive elimination of
cyclotrimers with release of the coordinatively unsatu-
rated metal fragment. The formation of linear conju-
gated polyenic polymers involves oxidative coupling
and formation of a series of metallacyclic species. The
metallacycle formed with four molecules of alkyne
can then rearrange to an alkylidene ligand initiating
the increase of the polymer chain, as was observed by
Yeh et al. [36,37] (Scheme 3).
Our experimental results suggest that the catalytic
cycle (Scheme 3) which has long been suggested
([36,37] and Refs. cited therein) is operating in our
system. The following points have been proven: (i) in
the reactions of 1 with alkyne a cis-bis(alkyne) com-
plex is a detectable species, (ii) decomposition of the
catalytic system with methanol gives phenylacetylene
dimers (1H-indene-1-(phenylmethylene) and DPBD),
(iii) the departure of the cyclotrimer from the coordi-
nation sphere of molybdenum recovers alkyne com-
plex and (iv) PPA has a regular cis-transoidal (58%)
structure.
3.5. Catalytic reactions
Conversion of PA occurs very smoothly at r.t. in
CH2Cl2 containing compound 1 (45% after 24 h).
Treatment of the reaction mixture with a large
amount of methanol produced quantitatively PPA as
a fine dark orange powder which has a number-aver-
age molecular weight (Mw) from 4 to 10×103, deter-
mined by GPC. The resulting PPA was completely
soluble, enabling us to investigate its molecular struc-
1
ture by spectroscopy. We used H-NMR spectroscopy
to determine the stereostructure of the PPA according
to Simionescu and Percec’s method [12]. The 1H-
NMR spectra of PPA in CDCl3 displayed a sharp
singlet due to the vinylic protons at l 5.85 ppm in
addition to a set of multiplets at 6.60–7.00 ppm
which has been correlated to the cis-transoidal (58%)
structure of PPA [15]. The IR spectrum of PPA is
The reactivity of 1 towards acetylenes is compared
with that of the related [WCl(GeCl3)(CO)3(NCMe)2]
[8]. In contrast with its tungsten analogue, reaction of
the molybdenum complex 1 with terminal acetylenes
yielded the cyclotrimers in greater yield. The tungsten
complex is more selective towards polymer formation.
characterized by a low intensity band at 740 cm−1
.
However, the catalytic coupling of alkynes in the
presence of 1 yields at least two types of products in
the approximate ratio 2:1, namely polymers with con-
jugated polyenic structures and cyclic oligomers, espe-
cially the aromatic cyclotrimers 1,2,4- and
1,3,5-triphenylbenzene (TPB). Minor amounts of
other oligomers arise, mainly linear diphenylbutadi-
enes (DPBD), which contain, for example, hydrogen
derived from the solvent and also a dimer of PA
detected by MS as 1H-indene-1-(phenylmethylene).
A plausible mechanism for the formation of cy-
clotrimers from PA shown in Scheme 3 involves the
4. Conclusions
The generation of the Mo–Ge species was achieved
in a straightforward manner that demonstrates that
oxidative–addition is a viable reaction to generate
metal–metal bonds in organometallic compounds.
A compound with two trichlorogermyl ligands is
unusual, and [Mo(GeCl3)2(CO)2(NCEt)3] (3) is the
first structurally characterized example of such a com-
pound.
Scheme 3.

224
T. Szyman´ska-Buzar et al. / Journal of Organometallic Chemistry 585 (1999) 215–224
[11] G.R. Dobson, M.F. Amr El Sayed, I.W. Stolz, R.K. Sheline,
Alkyne complexes can indeed be readily formed in
Inorg. Chem. 1 (1961) 526.
[12] KUMA KM4 Software, User’s Guide, Version 3.1, Kuma Diffrac-
the reaction of the seven-coordinate molybdenum(II)
complexes. The resulting air-unstable compounds are
all characterized mainly by IR, 1H- and 13C-NMR
spectroscopy in the reaction mixture.
The Mo–Ge compound appears as a very good
catalyst in polymerization and cyclooligomerization of
alkynes. The catalytic coupling of alkynes in the pres-
ence of Mo–Ge compounds yields at least two types of
product, namely polymers with conjugated polyenic
structures and cyclic oligomers, especially the aromatic
cyclotrimers.
*
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