Synthesis and reactivity of Mo-Sn compounds: X-ray crystal structure of a novel [Mo(SnCl3)2(CO)2(NCEt)3]

Article abstract of DOI:10.1016/S0022-328X(98)00982-6

[Mo(CO)₄(NCMe)₂] reacts with SnCl₄ in CH₂Cl₂ to produce a mixture of compounds which can be regarded as the results of oxidative addition with the elimination of CO and the formation of a Mo-Sn bond. The compound [MoCl(SnCl₃)(CO)₃(NCMe)₂] 1 is the main product but others containing Mo-Sn bond compounds can be formed also in variable amounts, as was shown by IR and NMR investigation of the reaction mixture. The structure of a novel [Mo(SnCl₃)₂(CO)₂(NCEt)₃] 4 was established by X-ray crystallography. This is the first structurally characterized molybdenum(II) carbonyl complex containing two anionic SnCl₃ ligands and the very rare example of the 4:3 piano stool seven-coordinate geometry. In the reaction of 1 with alkynes, complexes were isolated in which CO and/or acetonitrile 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 leads to the catalytic coupling of alkyne molecules and the formation of cycloligomers 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(98)00982-6

Journal of Organometallic Chemistry 575 (1999) 98–107
Synthesis and reactivity of Mo–Sn compounds: X-ray crystal structure
of a novel [Mo(SnCl3)2(CO)2(NCEt)3]
*
Teresa Szyman´ska-Buzar *, Tadeusz Glowiak
*
*
Faculty of Chemistry, Uni6ersity of Wroclaw, 14 F. Joliot-Curie, 50-383 Wroclaw, Poland
Received 7 August 1998
Abstract
[Mo(CO)4(NCMe)2] reacts with SnCl4 in CH2Cl2 to produce a mixture of compounds which can be regarded as the results of
oxidative addition with the elimination of CO and the formation of a Mo–Sn bond. The compound [MoCl(SnCl3)(CO)3(NCMe)2]
1 is the main product but others containing Mo–Sn bond compounds can be formed also in variable amounts, as was shown by
IR and NMR investigation of the reaction mixture. The structure of a novel [Mo(SnCl3)2(CO)2(NCEt)3] 4 was established by
X-ray crystallography. This is the first structurally characterized molybdenum(II) carbonyl complex containing two anionic SnCl3
ligands and the very rare example of the 4:3 piano stool seven-coordinate geometry. In the reaction of 1 with alkynes, complexes
were isolated in which CO and/or acetonitrile 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 leads to
the catalytic coupling of alkyne molecules and the formation of cycloligomers 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); Tin; Crystal structure; Seven-coordinate; Heterobimetallic complexes; Nitrile complexes; Alkyne
complexes; Cyclooligomerization of alkynes
It has been long known that compounds
[Mo(CO)4L2], L=N-, P-donor ligands, react with
1. Introduction
RnSnCl4−n to form the seven-coordinate compounds
In recent years work in this laboratory involving
with Mo–Sn bond [4–9]. Among them bis(nitrile) com-
Group 6 metal carbonyls has largely focused on the
pounds are especially interesting as useful starting ma-
catalytic activity of compounds with d4 electronic
terials in which the labile nitrile groups can be easily
configuration in reaction of alkenes and alkynes [1–3].
replaced by other ligands [9–17]
Such compounds can be formed easily in oxidative-ad-
In 1989 Baker and Bury reported the synthesis of
[MoCl(SnCl3)(CO)3(NCMe)2] 1 in the reaction of
[Mo(CO)3(NCMe)3] and SnCl4 in acetonitrile [9]. The
complex 1 was characterized by elemental analysis, IR
dition reactions of d6 Group 6 metal complexes and
Group 14 metal halides. Particularly heterobimetallic
complexes with Mo–Sn or W–Sn bonds are intriguing
because of the possibility that on reaction with alkene
or alkyne the unsaturated carbon–carbon bond may be
activated.
and NMR spectroscopy and showed three carbonyl
bands at w(CO) 2026 (s), 1939 (s), 1912 (s) cm−1 but 12
resonances in the carbonyl region l 227.84–201.97 ppm
of 13C-NMR spectrum [9]. This is in contrast to the
results for [WCl(SnCl3)(CO)3(NCMe)2] [18] and
[WCl(GeCl3)(CO)3(NCMe)2] [19] which showed similar
IR spectrum containing three carbonyl bands, but only
* Corresponding
author.
Fax:
+48-71-222348;
e-mail:
tsz@chem.uni.wroc.pl.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)00982-6

*
T. Szyman´ska-Buzar, T. Glowiak / Journal of Organometallic Chemistry 575 (1999) 98–107
99
Scheme 1.
one carbonyl resonance of three equivalent CO
2.2. Synthesis
groups; at l 211.9 ppm [18] for W–Sn and at l 214.8
ppm [19] for the W–Ge compound. The possibility of
forming several different isomers of 1 was particularly
intriguing to us, so we decided to repeat the synthesis
of 1 and to verify the nature of the Mo–Sn com-
pounds formed in the oxidative-addition reaction of
molybenum(0) and tin tetrahalide. An X-ray diffrac-
tion study of one of these products was desirable to
confirm the existence of different seven-coordinate
molybdenum compounds containing the Mo–Sn
bond.
2.2.1. [MoCl(SnCl3)(CO)3(NCMe)2] 1
To [Mo(CO)4(NCMe)2] [20] (2.0 g, 6.9 mmol) dis-
solved in CH2Cl2 (50 cm3) with continuous stirring
under a stream of nitrogen, a stoichiometric amount
of SnCl4 (0.8 cm3, 6.9 mmol) was added by means of
a syringe. The mixture was stirred for 1 h, during
which time the yellow solution gradually changed to
a redish–orange colour, while the w(CO) frequency of
[Mo(CO)4(NCMe)2] disappeared. After this reaction
time IR spectroscopy confirmed the reaction to be
complete. Volatiles were removed in vacuo to yield an
orange solid. The crude product was washed with
heptane (3×10 cm3) to remove Mo(CO)6 and a com-
pound with characteristic for [Mo(CO)5] unit w(CO)
bands at 2072 vw and 1949 vs cm−1. The residue was
treated with CH2Cl2 (50 cm3). The solution was sepa-
rated from less soluble orange powder by filtration
and heptane was added (10 cm3). Overnight cooling
in a refrigerator afforded orange crystals. They were
washed with heptane and dried under vacuum. By
analysis and by their IR and NMR spectra were
identified as pure 1 (2.88 g, 80%). Less soluble in
It was also interesting to compare structural, spec-
troscopic and catalytic properties investigated by us
earlier [WCl(SnCl3)(CO)3(NCMe)2] with
compound of molybdenum.
a similar
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 us-
ing KBr pellets on an FT-IR Model-400 Nicolet in-
strument. Far-IR spectra were recorded (500–50
cm−1) with a Bru¨cker IFSv instrument in nujol mull
on a polyethylene film. NMR spectra were run using
a Bruker AMX-300 spectrometer. The analysis of the
CH2Cl2 residue was identified as
a mixture of
mononuclear and dinuclear compounds of the type:
[MoCl(SnCl3)(CO)2(NCMe)3], [Mo(m-Cl)(SnCl3)(CO)3-
(NCMe)]2, [Mo(m-Cl)(SnCl3)(CO)2(NCMe)2]2 [Mo(Sn-
Cl3)2(CO)3(NCMe)2], and [Mo(SnCl3)2(CO)2(NCMe)3].
The dimers react with acetonitrile to give the bridge
cleaved mononuclear compounds (Scheme 1).
Satisfactory analysis has been obtained only for com-
pound 1. Anal. found: C, 16.04; H, 1.26; N, 5.20.
C7H6Cl4MoN2O3Sn calc.: C, 16.09; H, 1.16; N, 5.36.
Remaining compounds were not separated and detected
catalytic reaction products was performed on
a
Hewlett-Packard GC-MS system and by 1H-NMR
and IR spectroscopy.

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T. Szyman´ska-Buzar, T. Glowiak / Journal of Organometallic Chemistry 575 (1999) 98–107
100
only by IR and NMR spectroscopy in the reaction
mixture (Table 1).
2.3.3. Reaction of 1 with phenylacetylene (PA)
The addition of four equivalents of PA (0.16 cm3, 1.52
mmol) to a stirred CH2Cl2 solution (15 cm3) of 1 (0.2 g,
0.38 mmol) at room temperature resulted in a color
change from light orange to dark orange. The progress
of the reaction was monitored by disappearance of w(CO)
bands of 1. Stirring for 2 h followed by the filtration and
evaporation of the solvent under low pressure gave an
orange solid, which was washed out with a small portion
of heptane and dried in vacuo to give a brownish–yellow
mixture of compounds containing mainly [MoCl2-
2.2.2. [MoCl(SnCl3)(CO)3(NCR)2], 2 (R=C2H5); 3
(R=C6H5)
1 was dissolved in an appropriate nitrile 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 pure bis(ni-
trile) complex 2 and 3. For 2 anal. found: C, 19.65; H,
1.89; N, 4.50. C9H10Cl4MoN2O3Sn calc.: C, 19.63; H,
1.83; N, 5.09. For 3 anal. found: C, 30.09; H, 1.99; N,
4.34. C17H10Cl4MoN2O3Sn calc.: C, 31.57; H, 1.56; N,
4.33.
1
(NCMe)2(PhCꢀCH)2], as was shown by H- and 13C-
NMR spectra. (Table 2). In CH2Cl2 solution this com-
pound dimerizes but crystallization of the mixture from
MeCN restores a better soluble in the CH2Cl2 mononu-
clear compound. The heptane extract contained organic
products: 1,2,4-triphenylbenzene (66.2%), 1,3,5-tri-
phenylbenzene (31.1%), diphenylbutadiene (0.9%) and
1H-indene-1-(phenylmethylene) (1.8%).
2.2.3. [Mo(SnCl3)2(CO)2(NCEt)3] 4
The insoluble in the CH2Cl2 mixture of Mo–Sn
compounds separated from 1 (Section 2.2.1) was dis-
solved in propionitrile. The removal of the solvent in
vacuo, gave a residue which was recrystallized from
CH2Cl2–heptane giving the large redish–orange crystals,
which could be separated easily by hand as 4. Anal.
found: C, 17.58; H, 2.18; N, 5.09. C11H15Cl6MoN3O2Sn2
calc.: C, 17.22; H, 1.97; N, 5.48. The residue contained
several other propinitrile compounds (see Table 1) and
presumably molybdenum chlorides, which could not be
separated.
2.3.4. Reaction of 1 with PA in an NMR tube
To the NMR tube containing the solution of 1 (0.05
g, 0.09 mmol) in CD2Cl2 (0.7 cm3) two equivalents of PA
(0.02 cm3, 0.19 mmol) were added by means of a
microlitre syringe and a sample was periodically analyzed
1
by H-NMR spectroscopy at room temperature. Com-
plete transformation of 1 detected by the decay of the
signal at l 2.46 due to protons of coordinated CH3CN,
occurred within 24 h. At the same time new signals of
free and coordinated NCMe appeared at l 1.97 and 2.20
ppm, respectively. The signal of free PA, (ꢀCH) at l 3.13
ppm had decayed but three signals appeared and in-
creased in the region characteristic for PA coordinated
to molybdenum at l 11.15, 10.97 and 10.88 ppm. After
a prolonged reaction time, the intensity of the latter three
signals decreased but several new signals appeared in the
region l 11.3–10.8 ppm The hydrogen signals of organic
reaction products were observed in the region l 5–8 ppm.
The organic products based on GC-MS characterization
were 1,2,4-triphenylbenzene (64.9%), 1,3,5-triphenylben-
zene (32.4%), diphenylbutadiene (2.3%) and 1H-indene-
1-(phenylmethylene) (0.4%).
2.3. Reactions with alkynes
2.3.1. Reaction of 1 with diphenylacetylene (DPA)
To a solution of 1 (0.6 g, 1.1 mmol) in 15 cm3 of
CH2Cl2 was added PhCꢀCPh (0.41 g, 2.2 mmol) in
CH2Cl2 (5 cm3). The mixture was stirred and the progress
of the reaction was monitored by the disappearance of
w(CO) bands due to 1. At the begining of the reaction
(2–4 h), one new w(CO) band appears and increases at
about 2100 cm−1 which next decays after prolonged
reaction time. The solution was filtered to remove an
insoluble white solid containing SnCl2. Evaporation of
the solvent followed by washing with heptane produced
a compounds identified by IR and NMR studies (Table
2) as [MoCl2(NCMe)2(PhCꢀCPh)2]. In dichloromethane
this compound very easily releases acetonitrile and
dimerizes to give an insoluble in CH2Cl2 and CHCl3 most
probably [Mo(m-Cl)Cl(NCMe)(PhCꢀCPh)2]2. Crystal-
lization of the above greenish–yellow solid from acetoni-
trile restores the mononuclear bis(acetonitrile)
compound.
2.3.5. Reaction of 3 with PA
The PA (0.11 cm3, 1 mmol) was added to a solution
of 3 (0.16 g, 0.25 mmol) in CH2Cl2 (15 cm3). The progress
of the reaction was monitored by the disappearance of
w(CO) bands of 1. Stirring for 2 h followed by the
evaporation of the solvent under low pressure gave an
orange solid, which was washed out with a small portion
of heptane and dried in vacuo to give a brownish–yellow
2.3.2. Reaction of 2 with DPA
1
The alkyne (0.16 g, 0.9 mmol) was added to a solution
of complex 2 (0.25 g, 0.45 mmol) in CH2Cl2 (15 cm3) at
room temperature. The procedure was the same as in
Section 2.3.1. The resulting compound was characterized
by IR and NMR spectroscopy (see Table 2).
mixture of compounds with signals in H-NMR spec-
trum characteristic for PA coordinated to tungsten
probably in the mixture of compounds such as
[MoCl2(NCPh)2(PhCꢀCH)2] (l 10.86 ppm) and
[MoCl(m-Cl)(NCPh)(PhCꢀCH)2]2 (l 11.23 and 11.06

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101

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T. Szyman´ska-Buzar, T. Glowiak / Journal of Organometallic Chemistry 575 (1999) 98–107
102

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T. Szyman´ska-Buzar, T. Glowiak / Journal of Organometallic Chemistry 575 (1999) 98–107
103
ppm). The heptane extract contained organic prod-
ucts: 1,2,4-triphenylbenzene (81.2%), 1,3,5-triphenyl-
benzene (18.3%), diphenylbutadiene (0.5%).
of oligomerization calculated as the difference be-
tween the conversion (%) and yield of polymerization
reaction was about 24% after 24 h reaction time.
2.3.6. Reaction of 1 with 1-phenylprop-1-yne
(PhCꢀCMe)
2.5. Crystal and refinement data for compound 4
The alkyne (0.3 cm3, 2.4 mmol) was added to a
solution of complex 1 (0.27 g, 0.5 mmol) in CH2Cl2
(15 cm3) at room temperature. The procedure was the
same as for the PA reaction. The spectral data for
alkyne compound are shown in Table 2. The organic
products based on GC-MS characterization were
mainly cyclotrimers 1,2,4-trimethyltriphenylbenzene
and 1,3,5-trimethyltriphenylbenzene in the ratio 8/1.
Crystal data and relevant refinement details are col-
lected in Table 3. A redish–orange crystal ca. 0.12×
0.12×0.15 mm was removed from the flask and
rapidly coated with a light hydrocarbon oil to protect
it from the atmosphere. Data collection was per-
formed on a KM4 s-axis computer-controlled [22]
four-circle diffractometer operating in the ꢀ−2q scan
mode with graphite-monochromated Mo–Ka radia-
˚
tion (u=0.71069 A) at 293 K. The accurate cell di-
2.4. Procedures for testing catalytic acti6ity
mensions and the crystal orientation matrix were
determined by a least-squares refinement of the set-
ting angles of 50 carefully centred reflections in the
range 20B2qB40o. A total of 4199 unique reflec-
tions were measured, of which 2484 (229 variables)
with I]2|(I) in the range 5–50o were used to solve
and refine the structure in the monoclinic space group
P21/n. Absorption corrections following the DIFABS
[23] were applied to the data: minimum 0.7968 and
maximum 1.094.
Catalytic reactions of alkynes were carried out in a
reaction mixture composed of CH2Cl2, ortho-xylene
(the internal chromatographic standard), phenyl-
acetylene (PA) (1 M), and a molybdenum complex
(PA/Mo 100 or PA/Mo 50). The conversion of PA
monitored by chromatography after 24 h reached the
higher value 46%. Small amounts of the acetonitrile
added to the reaction mixture protect the catalyst
against deactivation. For the analysis of PA reaction
products, reactions were continued for 24 h and then
methanol was added. The polymer was collected,
washed with methanol, dried and weighed. The poly-
merization yield (%) defined by comparing the poly-
mer weight to the weight of the PA used was no
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 neighbouring
Table 3
Crystal data and details of refinement for [Mo(SnCl3)2(CO)2(NCEt)3]
4
1
greater than 22%. The polymer was analyzed by H-
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 from 5000
to 6000. 1H-NMR spectra of the polymers were
recorded in a CDCl3 solution at 300 MHz. The mi-
crostructural details of the polymers were calculated
from the 1H-NMR integrals (%cis=A5.85×104/At×
16.66, where A5.85 is the area of the signal at l=5.85
ppm and At is the total integral of the NMR spec-
trum [21]). The chemical shift of the ꢁCH groups
(5.85 ppm) and its intensity showed that the polymer
appeared to possess both cis and trans linkages, with
about 75% cis form.
Chemical formula
Molecular weight
Crystal system
C11H15Cl6MoN3O2Sn2
767.28
Monoclinic
P21/n
Space group
Unit cell dimensions
˚
a (A)
8.791(2)
25.682(5)
11.622(2)
103.32(3)
2553.3(9)
4
˚
b (A)
˚
c (A)
i (°)
V (A )
3
˚
Z
Reflections determining lattice 50
T (K)
293(2)
0.12×0.12×0.15
1.996
0.71069
30.62
1448
ꢀ/2q scan
5B2qB50
Crystal size (mm)
Dcalc. (g cm−3
u(Mo–Ka) (A)
v(Mo–Ka) (cm−1
F(000)
)
˚
)
Method of collection
2q Range (°)
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 3/1.The PA
dimers, 1H-indene-1-(phenylmethylene) and diphenyl-
butadiene were formed in low yield, below 2%. Yield
Index ranges
No. of unique data
No. of data with I52|(I)
Correction factors (min, max) 0.7968, 1.0940
Residuals R1, wR2
Goodness-of-fit
Final (Dz) (e A )
–105h510, 05k530, 05l513
4199
2484
0.0362, 0.0778
0.923
0.525/−0.625
3
˚

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T. Szyman´ska-Buzar, T. Glowiak / Journal of Organometallic Chemistry 575 (1999) 98–107
104
heavier atoms for CH2 and CH3, respectively. Several
cycles of refinement of the coordinates and anisotropic
thermal parameters for non-hydrogen atoms (parame-
ters of the H atoms were fixed) reduced the R1 to
0.0362 and wR2 to 0.0778. The maximum and minimum
residual densities in the difference map were 0.525 and
2320 cm−1) in comparison to w(CO) bands in IR
spectrum of the reaction product mixture with the
increase of Sn/Mo molar ratio. Simultaneously, the
intensity of weak w(CO) band at about 2100 cm−1
characteristic for metal (II) halocarbonyl dimers formed
in oxidation of Group 6 metal carbonyls, M(CO)6,
M=W, Mo, with such oxidants as Cl2, Br2 [28–30],
CCl4 [3], SnCl4 [31] and GeCl4 [19], increases. The yield
of dimer formed as the result of CO loss (Scheme 1)
depends mainly on solvent. The dichloromethane as
solvent favours especially the CO loss. The insoluble in
CH2Cl2 or CHCl3 dimers can be restore to soluble
monomers by recrystallization from nitrile (Scheme 1).
The formation of compounds with two SnCl3 groups
coordinated to molybdenum centre was observed also
(Scheme 1). These compounds can be formed in dispro-
portionation reaction giving [MoCl2(CO)5−nLn] and
next MoCl2 solvated by nitrile. Such a course of the
reaction may well be a consequence of lower thermal
stability of [MoCl2(CO)5−nLn] by-product in compari-
son to [Mo(SnCl3)2(CO)5−nLn] as a result of the p-ac-
ceptor character of the SnCl3 ligand [32] in relation to
the p-donor character of the chloride ligand.
−0.625 e A−3, respectively. Goodness-of-fit was 0.923.
˚
The structure was given a weighting scheme in the form
w=1/[|2(F2o)+(0.0380P)2+0.0000P], where P=
(F2o+2F2c)/3.
The structure was solved by heavy-atom methods
with the SHELXS-86 program [24] and refined by a
full-matrix least-squares method, using the SHELXL pro-
gram [25]. Neutral atomic scattering factors were taken
from the SHELXL-93 program [25].
2.6. Supplementary material a6ailable
Atomic coordinates, thermal parameters, and bond
lengths and angles were deposited at the Cambridge
Crystallographic Data Centre (CCDC) and are avail-
able on request.
3. Results and discussion
3.2. Spectroscopic studies of Mo–Sn compounds
3.1. Synthesis of Mo–Sn compounds
The IR spectra of [MoCl(SnCl3)(CO)3(NCR)2] com-
pounds (R=Me, Et and Ph) in KBr show a common
profile which includes three bands in the CO region
(Table 1) and are similar to that for the analogous
molybdenum–tin complex obtained first time by Baker
and Bury, (w(CO) 2026s, 1939s and 1912vs cm−1[9])
and are in excellent agreement with the data reported
A number of seven-coordinated compounds contain-
ing molybdenum–tin bonds have been prepared by
reaction of molybdenum(0)-substituted carbonyls and
tin tetrahalides or organometallic halides, RnSnCl4−n
R=Me, Bu, Ph [4–9,26]. The first time bis(nitrile)
compound was obtained in the reaction of
,
1
for
comparable
compounds
of
the
type
[Mo(CO)3(NCMe)3] and SnCl4 in acetonitrile [9]. How-
ever, we found that compound 1 is more conveniently
obtained in high yields by using CH2Cl2 instead of
acetonitrile as solvent for the reaction of
[Mo(CO)4(NCMe)2] with SnCl4.
[WCl(MCl3)(CO)3(NCMe)2], M=Sn [18], Ge [19].
The 1H-NMR spectrum of bis(nitrile) compounds
show single resonance consistent with two identical
nitrile groups. The room-temperature 13C-NMR spectra
show one carbonyl resonance of the three equivalent
CO group at l ꢁ220 ppm in keeping with the symme-
try of these compounds in the solid state analogous to
tungsten compounds [18].
Treatment of a slurry of [Mo(CO)4(NCMe)2] in
CH2Cl2 with an equimolar amount of SnCl4 gives the
oxidative-addition product compound 1 in good yield
(80%). Besides 1, others containing Mo–Sn bond com-
pounds are formed (Scheme 1). They include seven-co-
ordinated monomeric and dimeric compounds with a
varying number (from 3 to 2) of CO and nitrile ligands.
We found, that the equilibrium between mononuclear
and dinuclear species was dependent upon the molar
ratio of Mo and Sn compounds used in the oxidative-
addition reaction (Scheme 1). The higher Sn/Mo molar
ratio favour the formation of dinuclear compounds is
probably due to removing the nitrile ligands from the
coordination sphere of Mo by the stronger Lewis acid,
SnCl4. In this interaction the very well known complex
[SnCl4(NCMe)2] [27] can be formed. We observed the
decrease of the intensity of w(CN) bands (2290 and
However, compounds containing two SnCl3 groups
coordinated to molybdenum have different spectral
data (Table 1). First of all there are down-field shifts of
carbon resonance of two equivalents of the CO group
to ꢁ230 ppm in the 13C-NMR spectra.
3.3. Reactions of molybdenum(II) compounds with
alkynes
The complexes obtained in reaction of 1 and alkynes
(Scheme 2) are listed in Table 2 along with certain of
their IR and NMR spectral properties. As was men-
tioned in Section 2.3 we were unable to prepare the
alkyne complexes containing Mo–Sn bonds, because

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105
Scheme 2.
the hydrolysis of SnCl3 occurred and a white precipitate
of SnCl2 together with [Mo(CO)5SnCl2] resulted. The
latter, good solubility compound was identified due to
the characteristics for pentacarbonyl unit w(CO) bands
at 2072 w and 1949 vs cm−1 in IR spectrum and two
carbon resonances at l 211.60 (1CO) and l 205.12
(4CO) in intensity ratio 1/4, in 13C-NMR spectrum.
These data are in a good agreement with the spectral
data for compounds of that type [Mo(CO)5(SnX2)] [32].
When the reaction of 1 with two molecular equiva-
lents of diphenylacetylene at room temperature in
CH2Cl2 was monitored by IR, at the beginning, decay
of w(CO) bands due to 1 was accompanied by appear-
ance of one w(CO) band at 2100 cm−1. But after
prolonged reaction time (24 h), new w(CO) band of
alkyne complex decays. Based on the IR data the initial
ever, the isolated product does not contain carbonyl
ligand and after recrystallization from acetonitrile was
identified as [MoCl2(NCMe)2(PhCꢀCH)2]. The 13C-
NMR spectrum of this compound showed acetylenic
carbon signals at l 182.19 (ꢀCPh) and 169.58 (ꢀCH).
The hydrogen resonance due to phenylacetylene coordi-
nated to molybdenum was observed at l 10.88 ppm
(ꢀCH) and acetonitrile at l 2.20 ppm.
1
The acetylenic H- and 13C-NMR chemical shift val-
ues observed here (Table 2) are comparable to literature
values for other three-electron-donor alkyne ligands
[33–35].
3.4. Catalytic acti6ity of 1
Polymerization of PA occurs very smoothly at room
temperature in CH2Cl2 containing the compound 1.
Treatment of the reaction mixture with a large amount
of methanol produced quantitatively poly(phenyl-
acetylene) (PPA) as a fine dark-orange powder which
has a number-average molecular weight (Mw) from 5 to
6×103, determined by GPC. All the polymers pro-
duced were soluble in CH2Cl2, CHCl3 and toluene. IR
complex
can
be
described
as
[MoCl2(CO)(NCMe)(PhCꢀCPh)2] with the structure
close to the one obtained and characterized crystallo-
graphically by Baker et al. in the reaction of
[WI2(CO)3(NCMe)2] and RCꢀCR (R=Me, Ph) [33,34].
The loss of the CO group leads to formation of chlo-
ride-bridged dimer [W(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 but without CO in coordination sphere of the
1
and H-NMR spectroscopy was used to establish the
stereochemistry in PPA [21]. The IR spectrum of PPA
is characterized by a low intensity band at 740 cm−1
.
1
molybdenum.
The
mononuclear
compound
The H-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 l 6.60–7.00 ppm
which has been correlated to the cis-transoidal (75%)
structure of PPA [21].
[MoCl2(NCMe)2(PhCꢀCPh)2], with two mutually cis
alkyne ligands, which are magnetically equivalent and
give two signals of acetylenic carbons in 13C-NMR
spectra at l 191.23 and 186.65 ppm, 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.
Spectral studies revealed that in the reaction of 1
with PhCꢀCH (PA) the precursor complex 1 is liable to
loose 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-
However, the catalytic coupling of alkynes in the
presence of 1 yields at least two types of products in the
approximately ratio 1/1, namely polymers with conju-
gated 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 diphenylbutadienes
(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 reasonable mechanism for the formation of cy-
clotrimers from PA involves the initial coordination of

*
106
T. Szyman´ska-Buzar, T. Glowiak / Journal of Organometallic Chemistry 575 (1999) 98–107
Scheme 3.
two alkynes to the metal, rearrangement to a metallacy-
clopentadiene, insertion of third alkyne into the Mo–C
bond and reductive cyclization to the cyclotrimers
(Scheme 3). The formation of linear conjugated
polyenic polymers involves oxidative coupling and for-
mation of a series of metallacyclic species. The metalla-
cycle 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]
(Scheme 3).
Our results provide direct information only as re-
gards the first step. In the reactions of 1 with alkynes
that we investigated, the molybdenum complexes that
could be isolated usually contained a cis arrangement
of the two alkyne ligands.
14,26,37,38], no bis(trichlorotin) complexes have thus
far been studied.
The structure of compound 4, is shown in Fig. 1 with
the atom-numbering scheme. Table 3 gives a summary
of the crystal data and refinement obtained for 4. The
principal interatomic bond distances and angles are
presented in Table 4.
The geometry of the coordination sphere of molybde-
num atom in 4 approximates that of the 4:3 piano stool
structure identified in several molybdenum(II) com-
plexes ([Mo(CNPh)7]2+ [39], [Mo2Cl3(CO)4{P(O-
Me)3-}4]+ [40] and [MoBr(CO)3(1,4,7-triazacyclonon-
ane)]+[41]. In this description the tetragonal base is
˚
defined by two carbon atoms, Mo–C=1.981 A (aver-
˚
age) and two tin atoms, Mo–Sn=2.693 A (average). In
The compound 1 has shown similar catalytic activity
to that investigated by us earlier in the W–Sn com-
pound [18]. However, yield of oligomerization products
in case of molybdenum catalyst is much greater.
Table 4
˚
Bond lengths (A) and bond angles (°) for [Mo(SnCl3)2(CO)2(NCEt)3]
4
˚
Bond lengths (A)
Mo–C(1%)
Mo–C(2%)
Mo–N(1)
Mo–N(2)
Mo–N(3)
Mo–Sn(1)
Mo–Sn(2)
Sn(1)–Cl(1)
1.984(9)
1.978(8)
2.179(6)
2.201(6)
2.158(7)
2.6864(9)
2.6989(9)
2.334(2)
Sn(1)–Cl(2)
Sn(1)–Cl(3)
Sn(2)–Cl(4)
Sn(2)–Cl(5)
Sn(2)–Cl(6)
N(1)–C(1)
N(2)–C(4)
N(3)–C(7)
2.334(2)
2.339(2)
2.342(3)
2.342(3)
2.313(3)
1.135(8)
1.106(9)
1.150(9)
3.5. Structure of [Mo(SnCl3)2(CO)2(NCEt)3] 4
Although the structures of numerous seven-coordi-
nate complexes containing molybdenum–tin bonds
have been determined crystallographically [12–
Bond angles (°)
C(1%)–Mo–C(2%) 105.0(3)
C(1%)–Mo–N(1) 130.1(3)
N(2)–Mo–Sn(2)
Sn(1)–Mo–Sn(2)
Cl(1)–Sn(1)–Cl(3)
Cl(1)–Sn(1)–Cl(2)
Cl(2)–Sn(1)–Cl(3)
Cl(2)–Sn(1)–Mo
Cl(1)–Sn(1)–Mo
Cl(3)–Sn(1)–Mo
Cl(4)–Sn(2)–Cl(5)
Cl(4)–Sn(2)–Cl(6)
Cl(5)–Sn(2)–Cl(6)
Cl(4)–Sn(2)–Mo
Cl(5)–Sn(2)–Mo
Cl(6)–Sn(2)–Mo
C(1)–N(1)–Mo
C(4)–N(2)–Mo
C(7)–N(3)–Mo
O(1)–C(1%)–Mo
O(2)–C(2%)–Mo
94.3(2)
129.10(3)
98.95(11)
98.37(9)
98.61(11)
119.85(7)
118.65(7)
118.11(7)
98.26(13)
98.61(12)
99.0(2)
112.74(7)
115.20(6)
128.06(11)
173.4(6)
177.0(7)
177.7(5)
172.9(8)
178.4(6)
C(1%)–Mo–N(2)
C(1%)–Mo–N(3) 142.4(3)
C(2%)–Mo–N(1) 99.5(2)
C(2%)–Mo–N(2) 169.7(3)
81.3(3)
C(2%)–Mo–N(3)
N(1)–Mo–N(2)
N(1)–Mo–N(3)
N(2)–Mo–N(3)
C(1%)–Mo–Sn(1)
C(2%)–Mo–Sn(1)
N(1)–Mo–Sn(1)
89.3(3)
81.9(2)
79.3(2)
80.9(2)
69.3(2)
77.5(2)
74.8(2)
N(1)–Mo–Sn(2) 154.4(2)
N(2)–Mo–Sn(1) 112.6(2)
N(3)–Mo–Sn(1) 148.3(2)
N(3)–Mo–Sn(2)
C(1%)–Mo–Sn(2)
C(2%)–Mo–Sn(2)
75.1(2)
73.6(2)
80.0(2)
Fig. 1. Molecular structure of [Mo(SnCl3)2(CO)2(NCEt)3] 4.

*
T. Szyman´ska-Buzar, T. Glowiak / Journal of Organometallic Chemistry 575 (1999) 98–107
107
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*
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˚
79.3(2)°. The angle between tetragonal and trigonal
base is 4.6(2)° confirming the 4:3 geometry [42]. One
atom (N(2)) of the trigonal base and one atom (C(1%))
of the tetragonal base almost overlap (Fig. 2).
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˚
The Mo–Sn distance of 2.699(1) and 2.686(1) A is
comparable with those noted for other Mo–Sn com-
pounds, e.g. for [MoCl(SnCl3)(CO)3(C4H10S2)](CH2Cl2)
˚
2.688(2)
A
[26], [MoCl(MeSnCl2)(CO)3(C10H8N2)]
+
˚
˚
2.753(3) A [37], [Mo(SnCl3)(CO)4(dppe)] 2.729(4) A
[38], [MoCl(SnBuCl2)(CO)2{P(OMe)3}3] 2.774(1)
˚
A
[12,13]
and
[Mo(SnBuCl2){S2P(OEt)2}(CO)2{P-
˚
(OMe)3}2] 2.709(7) A [14]. The Mo–Sn bond is short
compared to the sum of the relevant covalent radii of
*
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˚
3.00 A [43,44]. In view of the established p-acceptor
(1995) 207.
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.
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Financial support from the Polish State Committee
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