A new versatile binuclear seven-coordinate complex of molybdenum(II), [(μ-Cl)2{Mo(μ-Cl)(SnCl3)(CO)3}2]2-

Article abstract of DOI:10.1016/j.jorganchem.2009.09.006

The two new seven-coordinate anionic complexes of molybdenum(II), binuclear [(μ-Cl)₂{Mo(μ-Cl)(SnCl₃)(CO)₃}₂]^2- and mononuclear [MoCl₃(GeCl₃)(CO)₃]^2-, have b

Full text of DOI:10.1016/j.jorganchem.2009.09.006

Journal of Organometallic Chemistry 694 (2009) 4196–4203
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Journal of Organometallic Chemistry
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A new versatile binuclear seven-coordinate complex of molybdenum(II),
[(l-Cl)2{Mo(l
-Cl)(SnCl3)(CO)3}2]2ꢀ
*
´
Magdalena Zyder, Andrzej Kochel, Teresa Szymanska-Buzar
Faculty of Chemistry, University of Wrocław, ul. F. Joliot-Curie 14, 50-383 Wrocław, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 March 2009
Received in revised form 3 September 2009
Accepted 4 September 2009
Available online 10 September 2009
The two new seven-coordinate anionic complexes of molybdenum(II), binuclear [(l-Cl)2{Mo(l-
Cl)(SnCl3)(CO)3}2]2ꢀ and mononuclear [MoCl3(GeCl3)(CO)3]2ꢀ, have been synthesized and characterized
by single-crystal X-ray diffraction studies. The binuclear complex exhibits a unique mode of reactivity
towards norbornene. In a strictly anhydrous atmosphere the binuclear complex effectively initiates the
ring-opening metathesis polymerization reaction of norbornene, but in the presence of water norbornene
is efficiently transformed to the binorbornyl ether (C7H11)2O.
Keywords:
Molybdenum(II)
Ó 2009 Elsevier B.V. All rights reserved.
Stannyl ligand
Germyl ligand
Heterobimetallic complexes
Ring opening metathesis polymerization
Etherification catalyst
1. Introduction
to a concurrent reaction which under special condition can give a
high yield of 2,20-binorbornylidene (bi-nbe) [6]. However, the yield
The activation of the M–Cl
r
-bond of tin or germanium tetra-
of bi-nbe is greatly influenced by the presence of water, and under
non-strictly anhydrous conditions the formation of an nbe:HCl
(1:1) adduct (C7H11Cl, Mr = 130.61) and an nbe:H2O (2:1) adduct
(C14H22O, Mr = 206.32) have previously been detected by GC–MS.
Although the 1:1 adduct of nbe and HCl was easily identified by
NMR spectroscopy as exo-2-chloronorbornane, the nature of the
bi-nbe-H2O adduct has remained unresolved even if we initially
used the name 3-hydroxyl-2,20-binobornyl for the latter undesir-
able side product [4,6]. Therefore it seemed interesting to explain
the nature of the bi-nbe-H2O adduct formed in reaction of nbe ini-
tiated by binuclear complexes of tungsten(II) and also of molybde-
num(II) containing chloride bridges. To that end we looked for new
binuclear complexes of molybdenum(II), similar to the previously
chlorides due to oxidative addition to electron-rich molybde-
num(0) or tungsten(0) carbonyl complexes has previously been
shown to be a valuable route to Mo(II) and W(II) seven-coordinate
complexes [1–3]. Oxidative decarbonylation of low-oxidation-state
tungsten and molybdenum carbonyl complexes such as [M(CO)4L2]
(L = nitrogen or phosphorous donor ligands) with SnCl4 or GeCl4
gave complexes of the type [MCl(M0Cl3)(CO)3L2] (M0 = Sn, Ge) [1–
3]. However, we have recently shown that during the oxidative
addition reaction of the tungsten(0) compound [W(CO)4(pip)2]
(pip = piperidine, C5H10NH) with Lewis acids such as tin or germa-
nium tetrachlorides, the piperidine ligands are removed from the
coordination sphere of tungsten, and seven-coordinate anionic
complexes, dinuclear [(
l
-Cl)3{W(SnCl3)(CO)3}2]ꢀ and mononuclear
described complex [(l-Cl)3{Mo2(SnCl3)(CO)7] [9].
[WCl3(GeCl3)(CO)3]2ꢀ, are formed [4,5].
In these studies, using the molybdenum(0) complex [Mo(CO)4-
In our previous investigations, we have shown that seven-coor-
dinate complexes of molybdenum(II) and tungsten(II) readily react
with norbornene (nbe) and vinylnorbornene to initiate the ring-
opening metathesis polymerization (ROMP) reaction in dichloro-
methane solution at room temperature [3–8]. In the case of a binu-
clear initiator, the yield of the ROMP reaction of nbe declines due
(pip)2] [10,11] as a precursor, we synthesized a new binuclear
complex of molybdenum(II), [(C3H5)pip]2[(l-Cl)2{Mo(l-Cl)(SnCl3)-
(CO)3}2] (1), and a mononuclear complex, [Hpip]2[MoCl3(GeCl3)-
(CO)3}2] (2), and described their crystal and molecular structures.
The chemical properties of complexes 1 and 2 were investigated
by IR and NMR spectroscopy and their catalytic activity was
checked in reaction with norbornene. The properties of the
new binuclear compound 1 were compared with those of the
photochemically synthesized
l-trichloro-bridged dimer of molyb-
* Corresponding author. Tel.: +48 71 375 7221; fax: +48 71 328 2348.
E-mail address: tsz@wchuwr.chem.uni.wroc.pl (T. Szyman´ ska-Buzar).
denum(II), the complex [( -Cl)3{Mo2(SnCl3)(CO)7] (3) [9].
l
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.09.006

M. Zyder et al. / Journal of Organometallic Chemistry 694 (2009) 4196–4203
4197
2.2. X-ray crystal structure of compound 1
2. Results and discussion
The unit cell of complex 1 is built up from dimeric molybdenum
-Cl)2{Mo(
-Cl)(SnCl3)(CO)3}2]2ꢀ and N-allylpiperidinium
2.1. Synthesis and spectroscopic identification of complex 1
anions [(
l
l
cations [(C3H5)pip]+. Crystal data and structure refinement param-
eters for this compound are given in Table 1. An ORTEP diagram,
including the crystallographic labeling scheme of the binuclear an-
ion in complex 1, is shown in Fig. 1. Selected bond distances and
key bond angles are given in Table 2.
Synthesis of compound 1 was achieved by reaction of [Mo-
(CO)4(pip)2] [10,11] with an excess of SnCl4 (1:7–10) in dichloro-
methane solution at room temperature. After keeping the
reaction mixture in a refrigerator overnight, orange crystals were
precipitated, which were determined through analysis by single-
crystal X-ray diffraction studies to be the ionic compound 1
(Scheme 1). The IR spectrum of 1 in a KBr pellet exhibited
The basic structural units of the anion of compound 1 are two
seven-coordinate molybdenum atoms linked by two chlorine
atoms occupying a bridging position between the two molybde-
num atoms. The resultant geometry at each molybdenum atom is
approximately a capped octahedron with the tin atom occupying
the unique capping position above the center of the trigonal face
defined by the chlorine atom and two carbonyl ligands with the
m
(C„O) stretching modes at 2019 (m), 1947–1944 (m,sh), and
1933 (vs) cmꢀ1. Three
m
(C„O) bands in the IR spectrum of 1 sug-
gest a C3v local symmetry of the Mo(CO)3 carbonyl moiety. The
ꢀ
presence of an SnCl3 moiety was confirmed by the IR spectrum
in Nujol mull, which revealed
m
(Sn–Cl) stretching modes at
350 cmꢀ1
.
The 119Sn chemical shift for the trichlorostannyl
ꢀ
SnCl3 ligand in 1 was observed at d = 65 in CD2Cl2 solution, i.e.
in a region very close to d = 74 detected here for the binuclear com-
plex 3 [9]. What was very surprising and not seen before was the
formation of the N-allylpiperidinium cation [(C3H5)pip]+ in the
above reaction. However, it was proved by X-ray diffraction studies
in solid state and by 1H and 13C NMR measurements in solution
(see Section 3). Additional evidence was obtained by ESI-MS anal-
ysis, where the signal of the cation C8H16N+, with M+ = 126.1, was
detected. The question arises how the latter cation is formed, when
the only probable source of this cation is the piperidine ligand. The
proposed mechanism for the formation of [(C3H5)pip]+ involves the
splitting of the N–C and C–C bonds in one of the piperidine ligands
due to synergic interactions with the molybdenum atom and the
tin atom of the Lewis acid SnCl4, leading to the creation of an allyl
ligand. This process can be compared to the ring-opening polymer-
ization of cyclic ethers such as tetrahydrofurane [12] or 1,3,5-triox-
ane [13] or ring-opening of 2-phenylazetidines [14]. The formation
of an intermediate allyl ligand of the molybdenum complex was
detected by NMR spectroscopy analysis of the crude reaction mix-
ture. The 1H NMR spectrum shows three signals for the allyl group
from three sets of protons, central (Hc), syn (Hs), and anti (Ha) at d
Table 1
Crystal data and structure refinement parameters for compounds 1 and 2.
1
2
Empirical formula
Formula weight
Crystal size (mm)
Crystal system
Space group
Unit cell dimensions
a (Å)
C22H32Cl10Mo2N2O6Sn2 C19H38Cl9GeMoN3O3
1204.30
0.10 ꢁ 0.08 ꢁ 0.05
Monoclinic
P21/c
844.10
0.10 ꢁ 0.06 ꢁ 0.05
Monoclinic
P21/c
9.363(2)
15.357(3)
13.758(3)
100.75(2)
1943.5(7)
2
11.219(5)
33.354(6)
9.897(4)
115.17(5)
3352(2)
b (Å)
c (Å)
b (°)
V (Å3)
Z
4
Dcalcd (g/cm3)
Diffractometer
Radiation
2.058
1.673
Kuma KM4CCD
Mo K ( = 0.71073 Å)
100(2)
2.625
1160
Kuma KM4CCD
Mo K ( = 0.71073 Å)
100(2)
2.015
1696
15 854/335
ꢀ18 6 h 6 18;
ꢀ43 6 k 6 55;
ꢀ16 6 h 6 16
58 667/15 854
Temperature (K)
l
(mmꢀ1
)
F(0 0 0)
Number of data/parameters 8747/200
Index ranges
ꢀ15 6 h 6 15;
3
3
ꢀ25 6 k 6 19;
3.90 (tt, JH–H = 10 and 6.8 Hz, Hc), 3.61 (d, JH–H = 6.8 Hz, Hs), and
22 6 l 6 18
3
1.12 (d, JH–H = 10 Hz, Ha) with an integral intensity ratio of
Number of reflections
collected/unique
Data collected, h minimum/
maximum (°)
Rint
S
31 195/8747
1:2:2. In the 13C NMR spectrum, two signals, at d = 74.4 (CHc)
and 58.0 (2CH2), can be assigned to the allyl ligand. The NMR char-
acteristics of this allyl ligand are very similar to those of other allyl
ligands in molybdenum(II) complexes [15–19]. The latter allyl li-
gand can take part in the creation of the [(C3H5)pip]+ cation, i.e.
the formation of an N–C bond between the nitrogen atom of the
piperidine ligand and the carbon atom of the allyl ligand. This reac-
tion may occur at the molybdenum atom in a similar way as the
formation of a C–C bond recently observed by Legzdins et al. dur-
ing the reaction of an allyl complex of tungsten with cyclic amines
[20].
2.65/36.87
2.72/36.94
0.0619
0.921
0.0402/0.0504
0.0485
1.019
0.0378/0.0663
Final residuals: R1, wR2
(I > 2
Tmin, Tmax
max Dqmin (e Åꢀ3
r(I))
0.678, 0.930
1.147/ꢀ0.800
0.810, 0.980
0.889/ꢀ0.702
D
q
/
)
Complex 1, like other binuclear complexes of molybdenum(II)
and tungsten(II), is highly reactive, and its reactivity toward nor-
bornene is described below (Section 2.5).
O(2)
C(2) O(1)
C(1)
Cl(5)i
Mo(1)
Mo(1)i
O(3)
C(3)
Cl(2)
Cl(5)
[Mo(CO)4(pip)2] + ECl4 (E = Sn, Ge)
CH2Cl2
Cl(3)
Sn(1)
Cl(4)
Cl(1)
[(C3H5)pip]2[(µ-Cl)2{Mo(µ-Cl)(SnCl3)(CO)3}2] (1)
[MoCl (GeCl )(CO) ] (2)
[Hpip]2
Fig. 1. The molecular structure and the atom numbering scheme of an anion of 1.
Atomic displacement ellipsoids are shown at the 50% probability level. Symmetry
transformation used to generate equivalent atoms: i (ꢀx ꢀ 1, ꢀy + 1, ꢀz ꢀ 1).
3
3
3
Scheme 1.

4198
M. Zyder et al. / Journal of Organometallic Chemistry 694 (2009) 4196–4203
(vs), 1919 (vs) cmꢀ1. The presence of the GeCl3 moiety was con-
firmed by the IR spectrum in Nujol mull, which revealed (Ge–
ꢀ
Table 2
Selected bond lengths (Å) and angles (°) for anion of 1.
m
Cl) stretching modes at 363 cmꢀ1. Crystals of 2 were extremely
insoluble, which prevented their use as a solution and purification
by recrystallization. NMR studies of 2 in CD2Cl2 solution were
unsuccessful, the main obstacle being its very poor solubility in a
non-coordinating solvent, but in a coordinating solvent such as
CD3CN, the rearrangement of compound 2 was observed.
The precise mechanism for the formation of compound 2 re-
mains uncertain, although it is clear that the complex [Mo(CO)4-
(pip)2] reacts differently with SnCl4 and GeCl4. As can be seen in
Scheme 1, the piperidine ligands were lost, and what had been
the piperidine ligand had now become a piperidinium cation:
[(C3H5)pip]+ in 1 and [Hpip]+ in 2. The origin of the Hpip+ cation
is not clear, although generation of HCl under the reaction condi-
tions is the most likely.
Atoms
Distance
Atoms
Angle
Mo(1)–C(1)
Mo(1)–C(2)
Mo(1)–C(3)
Mo(1)–Cl(2)
Mo(1)–Cl(5)i
Mo(1)–Cl(5)
Mo(1)–Cl(4)
Mo(1)–Sn(1)
Sn(1)–Cl(4)
Sn(1)–Cl(3)
Sn(1)–Cl(1)
Sn(1)–Cl(2)
C(1)–O(1)
1.974(3)
1.991(3)
1.976(3)
2.503(3)
2.527(1)
2.552(1)
2.565(1)
2.689(1)
2.815(1)
2.330(1)
2.340(1)
2.384(1)
1.153(3)
1.144(3)
1.154(3)
C(2)–Mo(1)–C(1)
C(3)–Mo(1)–C(2)
C(1)–Mo(1)–C(3)
C(2)–Mo(1)–Cl(5)i
C(1)–Mo(1)–Cl(5)i
C(3)–Mo(1)–Cl(5)i
C(1)–Mo(1)–Cl(5)
C(3)–Mo(1)–Cl(5)
C(2)–Mo(1)–Cl(5)
Cl(5)–Mo(1)–Cl(5)i
C(1)–Mo(1)–Cl(4)
C(3)–Mo(1)–Cl(4)
C(2)–Mo(1)–Cl(4)
C(1)–Mo(1)–Sn(1)
C(3)–Mo(1)–Sn(1)
C(2)–Mo(1)–Sn(1)
Cl(5)i–Mo(1)–Sn(1)
Cl(5)–Mo(1)–Sn(1)
Cl(4)–Mo(1)–Sn(1)
Mo(1)i–Cl(5)–Mo(1)
Mo(1)–Sn(1)–Cl(4)
Mo(1)–Cl(4)–Sn(1)
76.22(11)
76.30(11)
104.95(11)
88.34(8)
157.17(8)
87.19(8)
84.67(8)
164.33(8)
94.48(8)
79.80(3)
110.89(8)
105.32(8)
171.56(8)
70.01(8)
70.16(8)
123.05(8)
132.80(2)
125.3(1)
64.75(2)
100.20(3)
55.49(1)
59.76(2)
C(2)–O(2)
C(3)–O(3)
Complex 2 appeared totally non-reactive toward nbe. The start-
ing material remained unchanged when complex 2 and nbe were
stirred in CH2Cl2 solution for 24 h.
2.4. X-ray crystal structure of compound 2
Symmetry transformation used to generate equivalent atoms:
ꢀzꢀ1).
i
(ꢀxꢀ1, ꢀy+1,
The unit cell of complex 2 is built up from a molybdenum anion
[MoCl3(GeCl3)(CO)3}2]2ꢀ, a chloride anion Clꢀ, a piperidinium cat-
ion [Hpip]+, and a dichloromethane molecule. Crystal data and
structure refinement parameters for this mixture of compounds
are given in Table 1. An ORTEP diagram, including the crystallo-
graphic labeling scheme, for the anion of compound 2 is shown
in Fig. 2. Selected bond distances and key bond angles are given
in Table 3.
The geometry of the seven-coordinate molybdenum atom in the
anion of complex 2 is very similar to the capped octahedral struc-
ture in each half of the dimeric anion of complex 1. The small dif-
ferences that are observed result from the fact that in 2 all ligands
Cl(4)–Mo(1)–Sn(1) angle of 64.75(2)° and the C–Mo(1)–Sn(1) an-
gles of 70.01(8)° and 70.16(8)°. The average angle between the
three atoms occupying the capped face is 107.05°, while that be-
tween the three carbonyl carbons occupying the uncapped face is
much smaller (85.82°). The angles between the carbonyl and the
chloride ligands (C–Mo(1)–Cl), 164.33(8)° and 157.17(8)°, indicate
approximately trans positions of these ligands. The two indepen-
dent (l-Cl)Mo(l-Cl)(SnCl3)(CO)3 moieties are joined centrosym-
metrically by two bridging chlorine atoms, which are present in
an edge-shared bioctahedron arrangement with an average bridg-
are terminal, while in 1 three chlorine atoms are shared as
l-Cl
bridges. The unique capping position above the center of the trigo-
nal face defined by the chlorine atom and two carbonyl ligands
with the Cl(1)–Mo–Ge angle of 70.21(2)° and the C–Mo–Ge angles
of 69.19(6)° and 68.16(5)° is occupied by the germanium atom. The
average angle between the three atoms: Cl(1), C(3) and C(1), occu-
pying the capped face is 108.07°, while that between three car-
bonyl carbons occupying the uncapped face is much smaller
(89.40°). The lengths of the Mo–Cl(1) bond of 2.567(2) Å is slightly
longer than the two other Mo–Cl bond distances of 2.509(1) and
2.511(1) Å found for chlorine atoms occupying the uncapped face.
The angles between the carbonyl and the chloride ligands (C–Mo–
ing l-Cl–Mo distance of 2.54 Å and a Cl–Mo–Cl angle of 79.80(3)°.
The length of the Mo–Sn bond of 2.689(1) Å is close to the Mo–Sn
bond distance of 2.707(1) Å found in the previously reported di-
meric compound 3 [9].
The tin atom is five-coordinate in 1 with a geometry that is best
described as distorted trigonal bipyramid. The tin-to-bridging-
chlorine distance is 2.815(1) Å, considerably longer than the tin-
to-nonbridging-chlorine distances (av. 2.35 Å). Similar Mo–Cl–Sn
bridges had been found before in mononuclear seven-coordinate
molybdenum(II)
complexes
[Mo(
l-Cl)(SnCl3)(CO)2(
g
4-C7H8)-
(NCMe)] (Sn–Cl of 2.897(2) Å) [21] and [Mo(l-Cl)(SnCl3)(CO)3(N-
CEt)2] (Sn–Cl of 2.730(1) Å) [9], but it was the first time that such
a bridge had been detected in a binuclear complex like 1.
In the allyl moiety bonded to the nitrogen atom of the piperid-
inum cation, one of the C–C bond distances is shorter, at
1.314(5) Å, while the other is longer, at 1.481(4) Å. This clearly
indicates the terminal position of the double C@C bond and the for-
mulation of [(C3H5)pip]+ as the N-(2-propenyl)piperidinum cation
in 1. This was proved by NMR data obtained in solution (see Sec-
tion 3).
O(3)
Cl(4)
Cl(5)
C(3)
Cl(2)
O(2)
Mo(1)
Cl(1)
Ge(1)
C(2)
2.3. Synthesis and identification of compound 2
The reaction of the yellow complex [Mo(CO)4(pip)2] with an ex-
cess of GeCl4 (1:7) in dichloromethane solution at room tempera-
ture for 2 h gave a new compound that precipitated during
overnight refrigeration to give greenish-yellow crystals that ap-
peared to be the ionic complex 2, as indicated by single-crystal
X-ray diffraction studies (Scheme 1). The IR spectrum of 2 in a
C(1)
Cl(6)
Cl(3)
O(1)
Fig. 2. The molecular structure and the atom numbering scheme of an anion of 2.
KBr pellet exhibited
m
(C„O) stretching modes at 2026 (m), 1923
Atomic displacement ellipsoids are shown at the 50% probability level.

M. Zyder et al. / Journal of Organometallic Chemistry 694 (2009) 4196–4203
4199
Table 3
100.14(3)–119.31(3)°. However, the Mo–Ge–Cl bond angles
(117.65° av.) are much larger than the Cl–Ge–Cl angles (100.16°
av.).
Selected bond lengths (Å) and angles (°) for anion of 2.
Atoms
Distance
Atoms
Angle
Mo(1)–C(1)
Mo(1)–C(2)
Mo(1)–C(3)
Mo(1)–Cl(2)
Mo(1)–Cl(3)
Mo(1)–Cl(1)
Mo(1)–Ge(1)
Ge(1)–Cl(4)
Ge(1)–Cl(6)
Ge(1)–Cl(5)
C(1)–O(1)
1.987(2)
1.981(3)
1.985(2)
2.509(1)
2.511(1)
2.567(2)
2.528(1)
2.170(1)
2.183(1)
2.183(1)
1.148(2)
1.136(3)
1.142(2)
C(2)–Mo(1)–C(1)
C(3)–Mo(1)–C(2)
C(1)–Mo(1)–C(3)
C(2)–Mo(1)–Cl(2)
C(3)–Mo(1)–Cl(2)
C(1)–Mo(1)–Cl(2)
C(2)–Mo(1)–Cl(3)
C(3)–Mo(1)–Cl(3)
C(1)–Mo(1)–Cl(3)
Cl(2)–Mo(1)–Cl(3)
C(2)–Mo(1)–Ge(1)
C(3)–Mo(1)–Ge(1)
C(1)–Mo(1)–Ge(1)
Cl(2)–Mo(1)–Ge(1)
Cl(3)–Mo(1)–Ge(1)
C(2)–Mo(1)–Cl(1)
C(3)–Mo(1)–Cl(1)
C(1)–Mo(1)–Cl(1)
Cl(2)–Mo(1)–Cl(1)
Cl(3)–Mo(1)–Cl(1)
Ge(1)–Mo(1)–Cl(1)
75.33(9)
74.93(9)
110.18(8)
92.42(7)
81.30(6)
159.70(5)
93.21(7)
159.47(6)
82.04(6)
82.57(2)
113.91(6)
69.19(6)
68.16(5)
132.12(2)
131.34(3)
175.87(6)
106.91(7)
107.12(7)
84.27(4)
83.93(2)
70.21(2)
2.5. Reactions of norbornene initiated by binuclear complexes 1 and 3
In reaction of nbe initiated by 1 at room temperature in toluene
solution and at strictly anhydrous conditions, a ROMP polymer
(poly-1,3-cyclopentylenevinylene, poly-nbe) was isolated in 89%
yield by mass (Scheme 2). However, when a 1:1 mixture of nbe
and water reacted in CH2Cl2 solution in the presence of complex
1, the major product detected by GC-MS was an adduct containing
two molecules of nbe and H2O (bi-nbe-H2O) (ca. 82% by GC–MS in
a mixture containing 15% of bi-nbe and 3% of nbe-H2O adduct), but
poly-nbe was formed only in 4% yield by mass. A similar reaction
course was observed in the presence of the binuclear complex 3
in CH2Cl2 solution containing a 1:1 mixture of nbe and H2O
(Scheme 3). Although poly-nbe was isolated in 23% yield by mass,
the remaining nbe was transformed mainly to the bi-nbe-H2O ad-
duct (90% of liquid products). Under similar conditions (CH2Cl2
solution, room temperature) but without the addition of water,
complex 3 gave 31% yield of poly-nbe, but the major product de-
tected by GC–MS was bi-nbe (45%). The content of the reaction
products was confirmed by 1H NMR spectra, after revealing the
nature of the bi-nbe-H2O adduct, which NMR analysis surprisingly
identified as binorbornyl ether (C7H11)2O, (nba)2O (see below). An
identical binorbornyl ether was obtained in separate experiments
in which nbe reacted with exo-norborneol, or exo-norborneol
alone, was subjected to etherification (dehydration) in CH2Cl2 solu-
tion in the presence of a catalytic amount of complex 1 (Scheme 3).
Assignment of the proton and carbon signals of (nba)2O was
C(2)–O(2)
C(3)–O(3)
Cl), of 175.87(6)°, 159.70(5)°, and 159.47(6)° (165.0° av.), indicate
approximately trans positions of these ligands. The lengths of the
Mo–Ge bond of 2.528(1) Å is almost identical as the Mo–Ge bond
distance of 2.529(1) and 2.539(1) Å found in the seven-coordinate
compound [Mo(GeCl3)2(CO)2(NCEt)3] [22], but distinctly shorter
than the 2.631(1) Å found in the compound [MoCl(GeCl3)-
(CO)3(g
4-C7H8)] [23].
The germanium atom in the GeCl3 anion is nearly tetrahedral
with an average bond angle of 108.87°, varying in the range
ꢀ
done by combining the NMR data from 1H–1H COSY and 1H–13
C
n
89%
poly-nbe
1
toluene
O
1
OH
n
CH2Cl2 +H2O
3%
4%
79%
14%
OH
1
poly-nbe
bi-nbe
bi-nbe-H2O
CH2Cl2
O
43%
(nba)2O
Scheme 2.
O
n
3
4%
31%
20%
45%
3
bi-nbe-H2O
poly-nbe
bi--nbe
(nbe)3
CH2Cl2
3
CH2Cl2
+H2O
n
OH
O
3
3%
23%
2%
69%
3%
poly-nbe
bi-nbe
bi-nbe-H2O
(nbe)3
Scheme 3.

4200
M. Zyder et al. / Journal of Organometallic Chemistry 694 (2009) 4196–4203
24.83 ppm (Fig. 3). This spectrum suggests the presence of a diaste-
S
reometric compound (1:1 mixture of two diastereoisomers, rac and
mezo), which can be expected due to two chiral centers in a mole-
cule of (C7H11)2O. Two signals of equal intensity, at d 80.02 and
79.51, assigned to the chiral methine carbons HC-2, are at a higher
separation, while the separation of signals in each successive pair
decreases with the decrease in chemical shift. The 1H NMR spec-
trum shows poorly resolved multiplets due to methine protons at
C-2 and C-1, at d 3.35 and 2.23, respectively. These signals, after
careful analysis of 600, 500, and 300 MHz spectra appear rather
as two multiplet signals. Similar analysis of other proton signals re-
veals that most of them are very close double signals. Although
their assignment to relevant carbons was done without difficulty
by 1H–13C HMQC correlations, the coupling constants could not
be measured accurately.
6
7
(a)
O
1
2
6
5
4
5
3
7
3
4
1
2
The mechanism for the formation of the binorbornyl ether
(nba)2O can involve the intermediacy of a molybdanorbornylidene
species which under anhydrous conditions initiates the ROMP
reaction of nbe [26]. The coupling of two norbornylidene ligands
leads to the formation of bi-nbe. This compound is formed as a
mixture of four stereoisomers identified by NMR spectroscopy
due to four proton signals at d 2.79, 2.76, 2.58, and 2.54 ppm, char-
acteristic of the methine protons HC-1 [4,6,27], and was observed
here in all experiments, even at a 1:1 molar ratio of nbe:H2O
(Fig. 3). In the presence of water, the norbornylidene ligand can
be transformed to norborneol, which was detected in small
amounts in our experiments as nbe-H2O adduct by GC–MS method
(Scheme 2 and 3). Such formation of alcohol in reaction of a car-
bene ligand had been observed before [28–32]. In a similar way
as with water, the carbene ligand interacts with alcohol [33–34].
Thus, the addition of the H–O bond of norborneol to the carbon
atom of molybdanorbornylidene species and the formation of
C–O and C–H bonds is one of the method of the formation of
(nba)2O (Scheme 4). It is important to note that in this route, for
each equivalent of water present, two equivalents of norbornene
are consumed, since the initially formed norborneol can react with
another equivalent of norbornene to give (nba)2O. Another route
that can be considered is the elimination of water from two mole-
cules of previously formed norborneol. To determine the role of
norborneol during the reaction, we also studied the reaction of a
1:1 mixture of nbe and norborneol and norborneol alone in the
presence of 1 in dichloromethane solution. We were struck by
the high yield of ether formation, which reached 43% after 24 h
at room temperature for the 1:1 nbe/norborneol mixture and
77% for norborneol alone.
h
h
h
75.0
42.0
22.0
80.0
37.0
32.0
27.0
(ppm)
3,7
(b)
4
h
7,5
6
2
6,3
h
5
1
*
*
*
*
1.6
0.7
3.4
3.1
2.8
2.5
2.2
(ppm)
1.9
1.3
1.0
Fig. 3. NMR spectra of the binorbornyl ether: (a) 13C{1H} NMR spectrum (126 MHz,
CDCl3, 298 K) and (b) 1H NMR spectrum (500 MHz, CDCl3, 293 K). The solvent signal
is labeled as S. Asterisks denote the bi-nbe resonances, and h denotes n-heptane
resonances.
Both the chloro-bridged binuclear complexes 1 and 3 react sim-
ilarly with nbe and under slightly different reaction conditions can
be used as catalysts for the synthesis of poly-nbe, bi-nbe, and
(nba)2O. Similar reactivity of the binuclear compounds 1 and 3 re-
sults from the similar mechanism of interaction of both com-
pounds with olefin, i.e. the splitting of chloride bridges by olefin
and the formation of a mononuclear coordinatively unsaturated
HMQC correlations and DEPT experiments. The analysis of these
spectra was aided considerably by the prior assignment of exo-
and endo-norborneol [24–25]. The 125 MHz 13C{1H} NMR spec-
trum of a chloroform solution of the resulting binorbornyl ether
exhibited six pairs of equal-intensity carbon signals in the
range of 80–28 ppm and one higher-intensity carbon signal at
OH
[Mo]
[Mo] +
H2O
OH
O
H
H
1
[Mo]
CH2Cl2
O
[Mo]
[Mo] +
O
H
Scheme 4.

M. Zyder et al. / Journal of Organometallic Chemistry 694 (2009) 4196–4203
4201
molybdenum species that is able to activate an olefin molecule. It
3.2. Reaction of [Mo(CO)4(pip)2] with SnCl4 and the formation of
compound 1
is worth pointing out that the detection of bi-nbe provides direct
evidence for molybdenum(II)-promoted transformation of olefin
to a molybdaalkylidene ligand, which is able to initiate the ROMP
reaction or disproportionate giving a new olefin as the alkyl-
idene-alkylidene coupling product. In the presence of HCl or H2O,
the molybdanorbornylidene species decomposes to give 2-chloro-
norbornane or norborneol, respectively.
Although the dehydration of alcohols to ethers has been re-
cently observed in the presence of transition metal catalysts [35–
42] the formation of ether in one-pot synthesis from olefin is very
scarce [43–44]. The reaction catalyzed by 1 not only proceeds un-
der very mild conditions but is selective as well.
A slurry of [Mo(CO)4(pip)2] (0.045 g, 0.12 mmol) in dichloro-
methane (15 cm3) was treated with an excess of SnCl4 (0.1 cm3,
0.85 mmol), added by means of a syringe. A color change from light
yellow to deep orange and complete dissolution of the piperidine
compound were observed when the solution was stirred under
ambient conditions for 2 h. The solvent was evaporated in vacuum
to give an orange residue, which was washed several times with n-
heptane and dried under vacuum to give 0.086 g of an orange
powder. The cation of compound 1, [C8H16N]+ (M+ = 126.1), and
anions [Mo2Sn2Cl8C4O4]ꢀ (Mꢀ = 823.0), and [Mo2Sn2Cl8C3O3]ꢀ
(Mꢀ = 794.9), were detected by ESI-MS. The sample, very poorly
soluble in halogenated hydrocarbons, was investigated by NMR
and IR spectroscopy. Single orange crystals of compound 1 were
deposited from the dichloromethane solution by keeping the crude
reaction mixture at 273 K. X-ray confirmed that they contained io-
2.6. Conclusions
The studies reported in this paper were conducted in order to
investigate the reactivity of molybdenum(II) complexes towards
nbe and water. To that end two new seven-coordinate complexes
of molybdenum(II) were synthesized. The binuclear complex of
molybdenum(II) reacts readily with nbe and under the reaction
conditions can be used as an efficient initiator for the ring-opening
metathesis polymerization reaction, dimerization, which gives bi-
nbe, and etherification, which leads to the formation of binorbor-
nyl ether. The mononuclear complex of molybdenum(II), synthe-
sized in reaction between [Mo(CO)4(pip)2] and GeCl4 appeared
totally non-reactive toward nbe.
nic compounds: [(C3H5)pip]2[(
IR (KBr disc):
(CO) 2019 (s), 1947–1944 (m,sh), 1933 (vs) cmꢀ1
IR (Nujol mull):
(Sn–Cl) 350 cmꢀ1 1H NMR (500 MHz, CD2Cl2,
253 K): d = 6.11 (s, 1H, NH), 5.85 (ddt, JH–H = 16.8, 10.0, 7.3 Hz,
l-Cl)2{Mo(l-Cl)(SnCl3)(CO)3}2] (1).
m
.
m
.
3
3
1H, CbH-allyl), 5.67 (d, JH–H = 10.0 Hz, 1H, C H2-allyl), 5.60 (d,
c
3JH–H = 16.8 Hz, 1H, C H2-allyl), 3.70 (m, 2H, C H2-allyl), 3.35 (s,
c
a
4H, C H2-pip), 1.85 (s, 4H, CbH2-pip), 1.67 (s, 2H, C H2-pip).
a
c
13C{1H} NMR (126 MHz, CD2Cl2, 253 K): d = 223.2 (CO), 129.6 (1C,
CbH-allyl), 124.2 (1C, C H2-allyl), 54.7 (1C, C H2-allyl), 47.5 (2C,
c
a
C H2-pip), 23.1 (2C, CbH2-pip), 21.7 (1C, C H2-pip). 119Sn{1H}
a
c
In conclusion, we report a very simple and efficient method of
preparing a versatile binuclear anionic molybdenum(II) complex
1, and the discovery of a molybdenum catalytic system for one-
pot synthesis of binorbornyl ether from nbe and water. This is a
rare example of etherification using a group 6 metal complex as
catalyst.
NMR (186.5 MHz, CD2Cl2, 298 K): d = 65.
3.3. Reaction of [Mo(CO)4(pip)2] with GeCl4 and the formation of
compound 2
A sample of GeCl4 (0.1 cm3, 0.86 mmol) was added by means of
a syringe to a stirred suspension of [Mo(CO)4(pip)2] (0.045 g,
0.12 mmol) in dichloromethane (15 cm3). A color change from light
yellow to greenish-yellow and complete dissolution of the piperi-
dine compound were observed when the solution was stirred un-
der ambient conditions for 2 h. The solvent was evaporated in
vacuum to give a greenish-yellow residue, which was washed sev-
eral times with n-heptane and dried under vacuum to give 0.030 g
of a greenish-yellow powder.
3. Experimental
3.1. General data
The synthesis and manipulation of all chemicals were carried
out under an atmosphere of nitrogen using standard Schlenk tech-
niques. Solvents and liquid reagents were pre-dried with CaH2
and vacuum transferred into small storage flasks prior to use.
Mo(CO)6 and exo-norborneol (Aldrich) were used as received. IR
spectra were measured with a Nicolet-400 FT-IR and a Bruker
IF-S66 instrument. 1H, 13C, two-dimensional 1H–1H COSY and
1H–13C HMQC, and DEPT NMR spectra were recorded with Bruker
600, 500, and 300 MHz instruments. All chemical shifts are refer-
enced to residual solvent protons for 1H NMR (d 7.24 CDCl3, 5.32
CD2Cl2, 1.98 CD3CN) and to the chemical shift of the solvent for
13C NMR (77.0 CDCl3; 54.0 CD2Cl2, 118.0 CD3CN). The 119Sn chem-
ical shifts are referenced to an external standard, Ph3SnCl
(d = ꢀ44.7 ppm [45]). Analyses of the catalytic reaction products
were performed on a Hewlett-Packard GC–MS system. The orga-
nometallic compounds were analyzed on MicroOTOF-Q Bruker
using the ESI method. Mo(CO)6, norbornene and exo-norborneol
were used as received. [Mo(CO)4(pip)2] [10,11] was synthesized
in photochemical reaction of Mo(CO)6 with piperidine in n-hep-
tane. During this reaction the molybdenum complex containing
piperidine ligands was settled as a light yellow powder. The com-
plex 3 was synthesized in photochemical reaction of Mo(CO)6
with SnCl4 in n-heptane according the familiar method [9], and
its 119Sn{1H} NMR (186.5 MHz, CD2Cl2, 298 K) spectrum showed
a signal at d = 74. The photolysis source was an HBO 200 W
high-pressure Hg lamp.
(Anal. Calc. for C13H24Cl6GeMoN2O3: C, 24.29; H, 3.79; N, 4.39.
Found: C, 25.34; H, 4.04; N, 4.19%). Single greenish-yellow crystals
of compound 2 were deposited from the dichloromethane solution
by keeping the crude reaction mixture at 273 K. X-ray confirmed
that they contained ionic compounds: [Hpip]2[MoCl3(GeCl3)(CO)3]
(2).
IR (KBr disc):
m
(CO) 2026 (m), 1923 (vs), 1919 (vs) cmꢀ1. IR (Nu-
1H NMR (500 MHz, CD3CN, 298 K):
jol mull):
m
(Ge–Cl) 363 cmꢀ1
.
d = 7.39 (s, 2H, NH2), 3.01 (s, 4H, CH2), 1.94 (s, 4H, CH2), 1.77 (s,
2H, CH2). 13C{1H} NMR (126 MHz, CD3CN, 298 K): d = 229.3
(2CO), 217.2 (1CO).
3.4. X-ray crystallography
The crystal data collection and refinement details for complexes
1 and 2 are summarized in Table 1. X-ray crystal structure analyses
were performed using data collected at 100 K on a KM4-CCD dif-
fractometer and graphite-monochromated Mo Ka radiation gener-
ated from a Diffraction X-ray tube operated at 50 kV and 35 mA.
The images were indexed, integrated, and scaled using the KUMA
data reduction package [46]. The structure was solved by the heavy
atom method using SHELXS97 [47] and refined by the full-matrix
least-squares method on all F2 data [48]. Non-H atoms were in-
cluded in the refinement, with anisotropic displacement parame-

4202
M. Zyder et al. / Journal of Organometallic Chemistry 694 (2009) 4196–4203
ters, and H atoms were included from the geometry of the mole-
cules and were not refined. The intensities were corrected for
absorption [46]; min/max absorption coefficients: 0.678/0.930 for
1 and 0.810/0.980 for 2.
4. Supplementary material
CCDC 719774 and 719773 contain the supplementary
crystallographic data for 1 and 2. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
3.5. General procedure for reaction of nbe in the presence of complexes
1 and 3
Acknowledgments
In a round-bottomed flask equipped with a magnetic stirrer,
complex 1 or 3 was weighed (ca. 0.03 mmol). Next, the solvent
(10 cm3 CH2Cl2 or toluene) and the reagents: nbe, H2O, or norbor-
neol (ca. 1.5 mmol), were added through the septum to a solution
of the molybdenum complex, and the reaction mixture was stirred
at room temperature for 24 h. After that time the solvent was re-
moved in vacuum at room temperature and the residue was ex-
tracted with n-heptane and analyzed by GC–MS. The solid that
was not dissolved in n-heptane was treated with CHCl3 (5 cm3)
and its solution with methanol (10 cm3). The precipitate (polymer)
was then separated from the solution, dried under vacuum, and
weighed.
This work was generously supported by the Polish Ministry of
Science and Higher Education (Grant No. N204 288 534). Dr. M.
Kowalska and S. Baczynski for the measurement of NMR spectra
´
and M. Hojniak for GC–MS analyses.
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m = 2953 (vs), 2869 (s), 1474 (w), 1450 (m), 1438 (w),
1346 (m), 1315 (w), 1308 (w), 1289 (vw), 1221 (vw), 1175 (m),
1149 (m), 1115 (m), 1092 (s), 1040 (m), 1027 (s), 985 (w), 923
(vw), 883 (vw), 840 (w), 803 (m), 763 (vw), 665 (m). 1H NMR
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2
(d, JH–H = 4.7 Hz, 1H, CH-1), 2.18 (s, 1H, CH-4), 1.50 (dd, JH–H
=
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1.43 (dd, JH–H = 11 Hz, JH–H = 11 Hz, 1H, CH2-6), 1.37 (dd, JH–H
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=
3
2
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11 Hz, JH–H = 11 Hz, 1H, CH2-5), 1.31 (dd, JH–H = 11 Hz, JH–H
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