Synthesis and catalytic reactivity in Friedel–Crafts acylations of monobridged bis(cyclopentadienyl)molybdenum(I) carbonyl complexes

Article abstract of DOI:10.1016/j.poly.2018.03.021

When the monobridged biscyclopentadienes (C₅H₅)R(C₅H₅) [R = C(CH₃)₂ (1), Si(CH₃)₂ (2), C(CH₂)₅ (3)] reacted with Mo(CO)₆ in refluxing xylene, the corresponding complexes [(η⁵-C₅H₄)₂R][Mo(CO)₃]₂ [R = C(CH₃)₂ (4), Si(CH₃)₂ (5), C(CH₂)₅ (6)] were obtained. These complexes were separated by chromatography and characterized by elemental analysis, IR, and ¹H NMR spectroscopy. The molecular structures of 4 and 5 were determined by X-ray diffraction analysis. Friedel–Crafts acylation reactions of anisole derivatives with aromatic or aliphatic acyl chlorides catalyzed by complexes 4–6 showed that all of these monobridged bis(cyclopentadienyl)molybdenum carbonyl complexes have catalytic activity.

Full text of DOI:10.1016/j.poly.2018.03.021

Polyhedron 147 (2018) 75–79
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and catalytic reactivity in Friedel–Crafts acylations of
monobridged bis(cyclopentadienyl)molybdenum(I) carbonyl complexes
a
a
Xin Long Yan a,1, Ning Zhang a,1, Zhi Qiang Hao a,1, Zhi Hong Ma b, , Zhan Gang Han , Xue Zhong Zheng ,
⇑
Jin Lin a,
⇑
a National Demonstration Center for Experimental Chemistry Education, The College of Chemistry & Material Science, Hebei Normal University, Shijiazhuang 050024, China
b School of Pharmacy, Hebei Medical University, Shijiazhuang 050017, China
a r t i c l e i n f o
a b s t r a c t
Article history:
When the monobridged biscyclopentadienes (C5H5)R(C5H5) [R = C(CH3)2 (1), Si(CH3)2 (2), C(CH2)5 (3)]
reacted with Mo(CO)6 in refluxing xylene, the corresponding complexes [(g
5-C5H4)2R][Mo(CO)3]2 [R = C
Received 22 January 2018
Accepted 21 March 2018
Available online 29 March 2018
(CH3)2 (4), Si(CH3)2 (5), C(CH2)5 (6)] were obtained. These complexes were separated by chromatography
and characterized by elemental analysis, IR, and 1H NMR spectroscopy. The molecular structures of 4 and
5 were determined by X-ray diffraction analysis. Friedel–Crafts acylation reactions of anisole derivatives
with aromatic or aliphatic acyl chlorides catalyzed by complexes 4–6 showed that all of these mono-
bridged bis(cyclopentadienyl)molybdenum carbonyl complexes have catalytic activity.
Ó 2018 Elsevier Ltd. All rights reserved.
Keywords:
Synthesis
Monobridged biscyclopentadiene
Friedel–Crafts acylation reaction
Molybdenum carbonyl complex
Catalysis
1. Introduction
catalytic reactivities of three monobridged bis(cyclopentadienyl)-
molybdenum carbonyl complexes.
Since the discovery of ferrocene over 60 years ago, considerable
attention has been focused on the synthesis and chemical behavior
of its derivatives, owing to its high stability and numerous
applications within catalysis and material science [1–7]. Some
key metal–metal bonded systems are dinuclear complexes in
which two cyclopentadienyl ligands are linked by a bridge. This
type of bridged bis(cyclopentadienyl) dinuclear metal complexes
in which two reactive metal centers are held in close proximity
could potentially exhibit cooperative electronic and chemical
effects that may promote distinctive chemical reactivity and cat-
alytic properties [8–15]. Molybdenum carbonyl complexes are
known to catalyze FC acylation reactions [16–18]. Our group has
reported catalytic reactivity of molybdenum carbonyl complexes
in Friedel–Crafts reaction of aromatic compounds [19,20]. We have
also investigated the reactions a series of monobridged biscy-
clopentadiene ligands with Re2(CO)10 and researched the catalytic
activity of these monobridged bis(cyclopentadienyl)rhenium
carbonyl complexes on Friedel–Crafts reactions [21]. To obtain a
deeper insight into the structures and reactivities of this species,
in this paper we will further report the synthesis, structures and
2. Results and discussion
2.1. Preparation of the complexes
Complexes [(g
5-C5H4)2R][Mo(CO)3]2 [R = C(CH3)2 (4), Si(CH3)2
(5), C(CH2)5 (6)] were prepared from the reaction of ligand precur-
sors (C5H5)R(C5H5) [R = C(CH3)2 (1), Si(CH3)2 (2), C(CH2)5 (3)] with
Mo(CO)6 according to Scheme 1. IR spectra of 4–6 showed similar
patterns and exhibited strong terminal CO absorptions at 1863–
2010 cmÀ1. 1H NMR spectra of 4–6 were similar and showed a mul-
tiplet peak for the cyclopentadienyl protons at 5.23–5.64 ppm. In
1C NMR spectra of 4–6, peaks at 103.5–122.9 cmÀ1 revealed the
presence of cyclopentadienyl groups, strong absorptions at
229.5–234.4 cmÀ1 were attributed to stretching of C@O groups.
2.2. X-ray studies
The molecular structures of 4 and 5 were determined by single
crystal X-ray diffraction analyses. Selected bond parameters for
these complexes are summarized in Table 1. The molecular struc-
tures of 4 and 5 are provided in Figs. 1 and 2, respectively.
Single-crystal X-ray diffraction analysis showed that 4 is a
monobridged bis(cyclopentadienyl)molybdenum carbonyl com-
plex (Fig. 1), which belongs to a monoclinic crystal system. In the
⇑
Corresponding authors.
E-mail addresses: mazhihong-1973@163.com (Z.H. Ma), linjin64@126.com
(J. Lin).
1
These authors contributed equally to this work.
https://doi.org/10.1016/j.poly.2018.03.021
0277-5387/Ó 2018 Elsevier Ltd. All rights reserved.

76
X.L. Yan et al. / Polyhedron 147 (2018) 75–79
Scheme 1. Synthesis of 4–6. R = C(CH3)2, (4), Si(CH3)2 (5), C(CH2)5 (6).
Table 1
Selected bond distances (Å) and angles (°) for 4 and 5.
4
5
Bond distances
Mo(1)–C(1)
Mo(2)–C(12)
Mo(3)–C(20)
Mo(4)–C(31)
C(6)–O(1)
C(7)–O(2)
C(8)–O(3)
C(1)–C(2)
Mo(1)–Mo(2)
Mo(4)–Mo(3)
Mo(1)–Cp(centroid)
Mo(2)–Cp(centroid)
Mo(3)–Cp(centroid)
Mo(4)–Cp(centroid)
2.418(2)
2.324(2)
2.418(2)
2.340(2)
1.145(3)
1.154(3)
1.141(3)
1.429(3)
3.1629(4)
3.1524(4)
2.0184
Mo(1)–C(1)
Mo(1)–C(2)
Mo(1)–C(3)
Mo(1)–C(4)
Mo(1)–C(5)
Si(1)–C(1)
Si(1)–C(6)
C(7)–O(1)
C(8)–O(2)
C(9)–O(3)
2.355(3)
2.361(3)
2.361(3)
2.337(3)
2.347(3)
1.877(3)
1.859(3)
1.151(3)
1.149(4)
1.153(3)
Fig. 2. The molecular structure of complex 5. Ellipsoids correspond to 30%
probability. Hydrogen atoms are omitted for clarity.
Mo(1)–Mo(1i)
Mo(1)–Cp(centroid)
3.2052(5)
2.0203
2.0061
2.0163
2.0084
Bond angles
attributed to the flexibility of the singly bridged biscyclopentadi-
enyl ligands which allows the CO groups to reduce steric repul-
sions that force the metal atoms away from each other. Although
there are two independent molecules in the unit cell, the 1H
NMR spectrum of 4 shows the existence of only one. This indicates
that they may exist as one form in solution; however, a rapid flux-
ional process cannot be excluded [24,25]. Complex 5 is a singly sil-
icon bridged biscyclopentadienyl dimolybdenum complex as
shown in Fig. 2. 5 has a symmetric structure, the molecule consists
C(12)–C(9)–C(1)
C(31)–C(28)–C(20)
C(2)–Mo(1)–C(1)
C(16)–Mo(2)–C(15)
C(22)–Mo(3)–C(23)
C(22)–Mo(3)–C(23)
111.05(18)
111.44(17)
34.83(7)
34.67(8)
35.66(9)
35.66(9)
C(1i)–Si(1)–C(1)
C(6)–Si(1)–C(6i)
C(1)–Mo(1)–C(2)
C(8)–Mo(1)–C(7)
C(8)–Mo(1)–C(9)
Si(1)–C(1)–Mo(1)
110.67(15)
112.7(2)
35.61(9)
75.88(11)
77.50(13)
123.50(12)
unit cell there are two crystallographically independent molecules,
that are 4A and 4B, which have the same structure basically, just
small differences in some bond lengths and angles. Both of the
of two [(
bridge, with each of two Mo(CO)3 units coordinated to the
cyclopentadienyl ring in an
5 mode. The Mo–Mo distance of com-
plex 5 is 3.2052(5) Å, shorter than that in trans-[CpMo(CO)3]2
[3.235(1) Å] [22], but much longer than that in (CH2)[(
5-C5H4)
g
5-C5H4)Mo(CO)3] moieties linked by a single Si(CH3)2
two molecules consist of two [(g
5-C5H4)Mo(CO)3] moieties linked
g
by the single carbon bridge, with each of two Mo(CO)3 units coor-
dinated to the cyclopentadienyl ring in an g5 mode. The Mo-Mo
distances are 3.1629(4) Å (4A) and 3.1524(4) Å (4B), both shorter
than that in trans-[CpMo(CO)3]2 [3.235(1) Å] [22], and show a
moderate compression on the Mo-Mo bond imposed by the single
carbon bridged ligand, close to that in singly C(CH2)5 bridged com-
g
Mo(CO)3]2 [3.1406 Å] [26]. The Mo-CEN (CEN means centroid of
the cyclopentadienyl ring) distances are 2.0184 Å, 2.0061 Å,
2.0163 Å, and 2.0084 Å for 4, and 2.0203 Å for 5, which are presum-
ably attributed to the electron withdrawing effect of bridging
Si(Me)2 is larger when compared to the bridging C(Me)2.
plex C(CH2)5[(g
5-C5H4)Mo(CO)3]2 [3.1708 Å] [23]. This may be
Fig. 1. The molecular structure of complex 4. Two crystallographically independent molecules in the unit cell are shown as 4A (left) and 4B (right). Ellipsoids correspond to
30% probability. Hydrogen atoms are omitted for clarity.

X.L. Yan et al. / Polyhedron 147 (2018) 75–79
77
2.3. Catalysis studies
To develop an optimal catalytic system, we investigated 4 as a
precatalyst for the Friedel–Crafts acylation reaction of anisole with
cinnamoyl chloride (Scheme 2 and Table 2). A solution of anisole
(2 mmol) and cinnamoyl chloride (6 mmol) in 1,2-dichloroethane
(3.5 mL) was heated in the presence of the precatalyst and differ-
ent amounts of o-chloranil under an argon atmosphere. Using
refluxing 1,2-dichloroethane, the main para products was
obtained. The isolated yield reached 66.7% with higher para selec-
tivity when the reaction time was 24 h and the ratio of 4 to o-chlo-
ranil was 1:4 (Table 2, entry 6). Upon increasing the proportion of
oxidant, the isolated yield has not improved (Table 2, entries 16
and 18). With an extended reaction time, the yield has not
improved also. The experiment was carried out under the absence
of 4 or o-chloranil (Table 2, entries 9 and 10), the results showed
that no products were obtained, which suggested that elec-
trophilic-substitution mechanism was involved in the complex 4/
o-chloranil catalytic system.
In order to test the capability of Friedel–Crafts acylation reac-
tions (Scheme 3) catalyzed by these monobridged bis(cyclopenta-
dienyl)molybdenum carbonyl complex, influencing factors such
as the reaction time, yield, economic considerations etc., the fol-
lowing experimental conditions were chosen for further work:
1,2-dichloroethane as solvent; a molar ratio of aromatic substrates
and acylation reagents of 1:3; the molar ratio of catalyst to oxidant
was 1:4; reaction time 24 h; temperature 80 °C. Three aromatic
substrates were chosen under the optimized conditions and six
acylation reagents were employed, as shown in Table 3. Complex
4 proved to be capable of catalyzing Friedel–Crafts acylation reac-
tions. The yields% were found to vary with the different reactions
as indicated in Table 3. The structure and characterization of cat-
alytic products were presented in the Supporting Information.
Among six acylation reagents, benzoyl chloride could be used as
acylation reagent in these reactions and the corresponding acyl
products were obtained with high selectivity for the para-products
Scheme 3. Complex 4 catalyzed Friedel–Crafts acylation reactions.
in all cases, this reason may be due to the fact that benzoyl acylium
ion is relatively stable. The order of increasing reactivity was found
to be: 2-bromoanisole < anisole < 2-methylanisole, the results
showed that the reaction was favored by the presence of elec-
tron-donating groups in the aromatic substrate. It is consistent
with the characteristics of the aromatic electrophilic substitution
reaction [27]. Further studies will be needed to elucidate the mech-
anism of these catalytic reactions.
With the above catalytic studies of 4, 5 and 6 with o-chloranil
were further investigated under the optimal experimental condi-
tions, the results are shown in Table 4. Both complexes 5 and 6
proved to be capable of catalyzing Friedel–Crafts acylation reac-
tions also; moreover, the catalytic yields had only a small change
with the different catalysts used. The results showed that the cat-
alytic behavior was not obviously affected by the different ligand
bridges.
3. Conclusions
The reactions of monobridged biscyclopentadiene ligands
(C5H5)R(C5H5) [R = C(CH3)2 (1), Si(CH3)2 (2), C(CH2)5 (3)] with Mo
(CO)6 in refluxing xylene result in the formation of monobridged
bis(cyclopentadienyl) dimolybdenum carbonyl complexes. A new
Friedel–Crafts acylation catalyst is reported in this study, consist-
ing of various monobridged bis(cyclopentadienyl) dimolybdenum
carbonyl complexes and an organic oxidant, namely o-chloranil.
Compared with traditional catalysts, the present catalyst system
has a significant practical advantage: both of the catalyst precur-
sors [(g
5-C5H4)2R][Mo(CO)3]2 and o-chloranil are stable, easy to-
handle solids and they do not exhibit acidity unless mixing in an
aromatic solvent. Therefore, directly employing a harmful strong
acid reagent can be avoided. Besides, the catalyst system could
Scheme 2. Complex 4 catalyzed Friedel–Crafts acylation reaction of anisole with
cinnamoyl chloride.
Table 2
Optimization of Friedel–Crafts acylation of anisole using 4.
Entry
4 [mol%]
o-Chloranil [mol%]
Temp. [°C]
t [h]
Isolated yielda [%]
1
2
3
4
5
6
7
8
2.5
10
60
12
24
12
24
12
24
12
24
24
24
12
24
12
24
12
24
12
24
28.6
40.2
30.3
43.7
35.9
66.7
32.1
50.3
0
2.5
2.5
2.5
10
10
10
70
80
90
80
9
0
2.5
2.5
10
0
5
10
11
12
13
14
15
16
17
18
0
25.4
29.3
30.4
40.0
33.2
49.8
33.4
49.8
2.5
2.5
2.5
7.5
12.5
15
a
Isolated yield was determined by column chromatography.

78
X.L. Yan et al. / Polyhedron 147 (2018) 75–79
Table 3
Complex 4 catalyzed reactions of aromatic substrates with different acylation reagents.
Entry
Substrate
Reagent
Isolated yielda [%]
Product
1
2
3
4
5
6
7
8
MeCOCl
PhCOCl
71.3
92.0
48.4
66.7
60.0
40.2
44.2
97.0
63.0
65.7
66.7
45.9
10.9
68.7
38.1
27.0
31.0
4.2
7a
7b
7c
7d
7e
7f
8a
8b
8c
8d
8e
8f
9a
9b
9c
9d
9e
9f
PhCH2COCl
PhCH@CHCOCl
c-C6H11COCl
n-C5H11COCl
MeCOCl
PhCOCl
9
PhCH2COCl
PhCH@CHCOCl
c-C6H11COCl
n-C5H11COCl
MeCOCl
10
11
12
13
14
15
16
17
18
PhCOCl
PhCH2COCl
PhCH@CHCOCl
c-C6H11COCl
n-C5H11COCl
a
Isolated yield was determined by column chromatography.
Table 4
The catalytic data for 5 and 6.
Entry
Substrate
Reagent
Comp.5/o-chloranil
Comp.6/o-chloranil
Product
Yield [%]
Yield [%]
1
2
3
4
5
6
7
8
MeCOCl
PhCOCl
73.8
94.8
49.6
68.4
62.3
42.2
47.1
98.5
63.7
66.9
68.7
46.3
12.1
69.4
40.1
28.3
32.3
5.3
70.2
89.9
45.3
38.6
55.3
63.4
42.8
95.6
62.7
63.4
65.2
42.1
8.7
7a
7b
7c
7d
7e
7f
8a
8b
8c
8d
8e
8f
9a
9b
9c
9d
9e
9f
PhCH2COCl
PhCH@CHCOCl
c-C6H11COCl
n-C5H11COCl
MeCOCl
PhCOCl
9
PhCH2COCl
PhCH@CHCOCl
c-C6H11COCl
n-C5H11COCl
MeCOCl
10
11
12
13
14
15
16
17
18
PhCOCl
62.1
33.8
26.1
29.9
3.7
PhCH2COCl
PhCH@CHCOCl
c-C6H11COCl
n-C5H11COCl
Reagents and conditions: Substrate (2 mmol), reagent (6 mmol), complex (2.5 mol%), o-chloranil (10.0 mol%), solvent 3.5 mL, 84 °C, 24 h.
be recovered and reused for further cycles. To elucidate the reac-
tion mechanism and expand the synthetic utility of these catalysts,
further studies are ongoing.
of solvent the residue was placed on an alumina column. Elution
with petroleum ether/CH2Cl2 (10:1) developed a red band, which
was collected and after concentration, afforded [(g
5-C5H4)2(CMe2)]
[Mo(CO)3]2 (4) as a brown crystals, yield: 0.192 g (24.1%). M.P:
216–218 °C; Anal. Calc. for C19H14Mo2O6: C, 43.04; H, 2.66. Found
(%): C, 43.22; H, 2.67; 1H NMR (500 MHz, CDCl3): d 1.52 (s, 6H,
CH3), 5.23–5.29 (m, 8H, C5H4); 13C NMR (125 MHz, CDCl3): d
31.2, 36.3, 86.7, 122.9, 234.3; IR (KBr, cmÀ1): 1866(s), 1878(s),
1896(s), 1909(s), 1916(s), 1946(s), 1964(s), 2002(s).
4. Experimental
4.1. General considerations
Schlenk and vacuum line techniques were employed for all
manipulations. All solvents were distilled from appropriate drying
agents under an argon atmosphere prior to use. 1H and 13C NMR
spectra were recorded on a Bruker AV 500/400 instrument in
CDCl3, while IR spectra were recorded as KBr disks on an FT IR
8900 spectrometer. Agilent 6820 gas chromatograms were
recorded for analysis of samples. Mass-spectrometric measure-
ments were performed on a DSQ(Ⅱ) gas chromatograph-mass
spectrometer.
4.3. Synthesis of [(g
5-C5H4)2(Si(CH3)2)][Mo(CO)3]2 (5)
Using a procedure similar to that described above, 2 was
reacted with Mo(CO)6 in refluxing xylene for 12 h. After chro-
matography with petroleum ether/ethyl acetate (30:1), [(g5
-
C5H4)2(Si(CH3)2)][Mo(CO)3]2 (5) was obtained (0.521 g, 63.6%
yield) as brown crystals. M.P: 230 °C; Anal. Calc. for
C
18H14Mo2O6Si: C, 39.58; H, 2.58. Found (%): C, 39.73; H, 2.59; 1H
4.2. Synthesis of [(
g
5-C5H4)2(CMe2)][Mo(CO)3]2 (4)
NMR (500 MHz, CDCl3): d 0.46 (s, 6H, CH3), 5.04 (s, 2H, C5H4),
5.52–5.64 (m, 6H, C5H4); 13C NMR (125 MHz, CDCl3): d 91.2, 91.7,
92.7, 99.3, 103.5, 223.7, 229.5, 234.2; IR (KBr, cmÀ1): 1867(m),
1891(m), 1906(m), 1935(m), 2003(m).
A solution of 1 (0.258 g, 1.50 mmol) and Mo(CO)6 (0.792 g,
3 mmol) in xylene (30 mL) was refluxed for 10 h. After removal

X.L. Yan et al. / Polyhedron 147 (2018) 75–79
79
Table 5
(0.098 g, 0.4 mmol) were mixed with 1,2-dichloroethane (3.5 mL)
in a 25 mL round-bottom flask at room temperature with magnetic
stirring. The solution was immediately darkened. After the mixture
had been stirred for 40 min at room temperature, aromatic com-
pounds and acylation reagents were added by syringe. The reaction
mixture was heated at 80 °C in an oil bath for 24 h. After cooling to
room temperature, the solvent was removed by rotary evaporation,
and the residue was purified by Al2O3 column chromatography,
eluting with petroleum ether developed colorless liquid that
afforded the corresponding white solid product. The catalyst was
recovered and washed with petroleum ether, then reused for
further cycles. The course of the reaction was monitored using an
Agilent 6820 gas chromatograph.
Crystal data and structure refinement parameters for 4 and 5.
Complex
4
5
Empirical formula
Formula weight
T (K)
C
19H14Mo2O6
C18H14Mo2O6Si
546.26
298(2)
0.71073
monoclinic
C2/c
13.3955(11)
10.2663(9)
15.4684(13)
90
112.228(3)
90
1969.2(3)
4
1.843
1.365
530.18
273(2)
k (Ǻ)
0.71073
monoclinic
P2(1)/c
14.3143(16)
9.4538(10)
28.240(3)
90
98.556(3)
90
3779.0(7)
8
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V(Å3)
Z
Acknowledgements
Dcalc (g cmÀ3
)
1.864
1.360
2080
l
(mmÀ1
)
This work was financially supported by the National Natural
Science Foundation of China (No. 21372061), the Hebei Natural
Science Foundation of China (No. B2017205006), and the Key
Research Fund of Hebei Normal University (No. L2017Z02).
F (000)
Crystal size (mm)
1072
6.34 Â 0.96 Â
0.40 Â 0.35 Â
0.35
0.22
h range (°)
Reflections collected / unique
R(int)
Completeness to h
Absorption correction
Maximum and minimum
transmission
Refinement method
Data/restraints/parameters
Goodness of fit on F2
2.20–28.37
54838/9247
0.0261
2.58–25.01
4768/1727
0.0172
Appendix A. Supplementary data
99.6%
99.8%
semi-empirical from equivalents
0.6476 and
0.0422
0.7533/0.6112
CCDC 1585595 and 1576325 contains the supplementary crys-
tallographic data for 4 and 5. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at https://doi.org/10.
1016/j.poly.2018.03.021.
full-matrix least-squares on F2
9247/0/491
1.043
0.0256, 0.0570
0.0380, 0.0612
0.605
1727/0/125
1.126
0.0188, 0.0437
0.0250, 0.0478
0.562
R1, wR2 [I > 2
r
(I)]
R1, wR2 (all data)
Maximum peak/(e ǺÀ3
)
)
Minimum peak/(e ǺÀ3
À0.622
À0.309
CCDC
1585595
1576325
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Using a procedure similar to that described above, 3 was
reacted with Mo(CO)6 in refluxing xylene for 12 h. After chro-
matography with petroleum ether/ethyl acetate (15:1), [(g5
-
C5H4)2(C(CH2)5)][Mo(CO)3]2 (6) was obtained (0.255 g, 26.2% yield)
as red crystals. M.P: 230 °C; Anal. Calc. for C22H18Mo2O6: C, 46.34;
H, 3.18. Found: C, 46.29; H, 3.14. 1H NMR (400 MHz, CDCl3): d
5.59–4.98 (m, 8H, C5H4), 1.97–1.76 (m, 4H, C6H10), 1.55–1.39 (m,
6H, C6H10); 13C NMR (100 MHz, CDCl3): d 22.8, 25.3, 38.9, 39.8,
121.6, 234.4; IR (KBr, cmÀ1): 1863(s), 1878(s), 1894(s), 1918(s),
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4.5. Crystallographic studies
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Suitable crystals of 4 and 5 for X-ray diffraction were obtained
from the slow evaporation of a hexane/CH2Cl2 solution. Crystallo-
graphic data collections were performed on a Bruker Smart APEX
or Bruker D8 venture diffractometer with graphite monochro-
mated Mo K
a (k = 0.71073 Å) radiation using the u/x scan tech-
nique. Semi-empirical absorption corrections were applied for 4
and 5. The structures were solved using the SHELXL-97 program
[28] by full-matrix least-squares procedures on F2 values. Hydro-
gen atoms were fixed at calculated positions and refined using a
riding mode. The crystal data and summary of X-ray data collection
are summarized in Table 5.
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Under an argon atmosphere, the monobridged bis(cyclopenta-
dienyl)molybdenum carbonyl complex (0.1 mmol) and o-chloranil