Reactions of substituted tetramethylcyclopentadienes with molybdenum hexacarbonyl

Article abstract of DOI:10.1016/j.ica.2013.01.010

The reactions of the substituted tetramethylcyclopentadienes [C ₅Me₄HR] [R = ethyl (1), n-propyl (2), i-propyl (3), cyclopentyl (4), cyclohexyl (5), 4-NMe₂Ph (6)] with Mo(CO) ₆ in refluxing xylene gave the corre

Full text of DOI:10.1016/j.ica.2013.01.010

Inorganica Chimica Acta 399 (2013) 126–130
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Reactions of substituted tetramethylcyclopentadienes with
molybdenum hexacarbonyl
Zhihong Ma a, Na Wang b, Kaiming Guo b, Xuezhong Zheng b, Jin Lin b,
⇑
a College of Basic Medicine, Hebei Medical University, Shijiazhuang 050017, China
b The College of Chemistry & Material Science, Hebei Normal University, Shijiazhuang 050024, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The reactions of the substituted tetramethylcyclopentadienes [C5Me4HR] [R = ethyl (1), n-propyl (2),
i-propyl (3), cyclopentyl (4), cyclohexyl (5), 4-NMe2Ph (6)] with Mo(CO)6 in refluxing xylene gave the cor-
Received 11 October 2012
Received in revised form 8 January 2013
Accepted 9 January 2013
responding dinuclear metal carbonyl complexes [
of [C5Me4H(4-NMe2Ph)] (6) with Mo(CO)6 afforded an unexpected product [(
Ph))MoO2]2( -O) (12). All the new complexes were fully characterized. The molecular structures of 7,
8, 11 and 12 have been determined by X-ray single crystal diffraction.
g
5-C5Me4R]2Mo2(CO)6 (7–11), while similar treatment
g
5-C5Me4(4-NMe2-
Available online 31 January 2013
l
Keywords:
Ó 2013 Elsevier B.V. All rights reserved.
Substituted tetramethylcyclopentadienyl
Structure
X-ray single crystal diffraction
Molybdenum carbonyl
1. Introduction
to use. 1H NMR spectra were recorded on a Bruker AV 500 instru-
ment, while IR spectra were recorded as KBr disks on a FT IR 8900
spectrometer. X-ray measurements were made on a Bruker Smart
The chemistry of metallocene metal complexes has been receiv-
ing much attention, one of considerable research is currently being
focused on the synthesis and study of metal–metal bonded transi-
tion metal complexes, owing to their important role in many cata-
lytic processes [1–4]. Cyclopentadienyls have been among the
most important ligands in organo-transition metal chemistry, as
they from a wide range of derivatives whose steric and electronic
properities can be easily tailored by varying the ring substituents.
These variations on the cyclopentadienyl unit not only open access
to construct new compounds, but also have great influence on the
metallocene catalytic activity [5–8]. To obtain a deeper insight into
the steric and electric effects of substituents on the molecular
structures and reactions of the corresponding biscyclopentadienyl
binuclear metal carbonyl complexes, we have prepared a series of
biscyclopentadienyl dimolybdenum complexes and determined
their structures.
APEX diffractometer with graphite monochromated Mo
Ka
(k = 0.071073 nm) radiation. Elemental analyses were performed
on a Vario EL III analyzer. The ligands [C5Me4HR] [R = ethyl (1),
n-propyl (2), i-propyl (3), cyclopentyl (4), cyclohexyl (5), 4-NMe2Ph
(6)] were prepared as described in the literature [9,10].
2.2. Synthesis of complex [g
5-C5Me4(CH2CH3)]2Mo2(CO)6 (7)
A solution of ligand C5Me4HCH2CH3 (1) (0.300 g, 2 mmol) and
Mo(CO)6 (0.528 g, 2 mmol) in 30 mL of xylene was refluxed for
12 h. After removal of solvent the residue was chromatographed
on an alumina column. Eluent with petroleum ether/CH2Cl2 gave
a dark-red band that afforded red crystals, yield: 0.373 g (56.6%),
m.p. 169 °C (dec.). Anal. Calc. for C28H34Mo2O6: C, 51.08; H, 5.20.
Found: C, 50.22; H, 5.13%. 1H NMR (500 MHz, CDCl3): d 1.75(s,
6H, CH3), 1.86(d, 12H, J = 4 Hz, C5Me4), 1.94(s, 4H, CH2), 3.00(d,
12H, C5Me4). IR (
m
CO, cmꢀ1): 1919(s), 1890(m), 1865(s).
2. Experimental
5-C5Me4(CH2CH2CH3)]2Mo2(CO)6 (8)
2.1. General considerations
2.3. Synthesis of complex [
g
All manipulations were performed at an argon/vacuum main-
fold using standard Schlenk techniques. Solvents were dried by
known procedures and used fresh distilled under nitrogen prior
Using a procedure similar to that described above, reaction of
ligand C5Me4HCH2CH2CH3 (2) with Mo(CO)6 in refluxing xylene
afforded complex 8 as red crystals in 57.8% yield. m.p.175 °C
(dec.). Anal. Calc. for C30H38Mo2O6: C, 52.49; H, 5.58. Found: C,
52.28; H, 5.66%. 1H NMR (CDCl3): d 2.26 (t, J = 8.0 Hz, 4H, C5Me4-
CH2), 1.92–1.98 (m, 24H, C5Me4), 1.34–1.50 (m, 4H, CH2), 0.91(t,
⇑
Corresponding author. Tel./fax: +86 311 80787431.
E-mail address: linjin64@126.com (J. Lin).
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.01.010

Z. Ma et al. / Inorganica Chimica Acta 399 (2013) 126–130
127
J = 7.5 Hz, 6H, CH3). IR (
1896(s).
m
CO, cmꢀ1): 1906(s), 1927(s), 1868(s),
The IR spectra of complexes 7–11 showed similar patterns and
characteristic absorption peaks for strong CO in the terminal v(CO)
region. The 1H NMR spectra of complex 7 showed two doublet
peaks for the four methyls protons while the 1H NMR spectra of
complexes 8–11 showed one multiple peak for the four methyls
protons, respectively.
However, when ligand [C5Me4HR] [R = 4-NMe2Ph (6)] reacted
with Mo(CO)6 under refluxing xylene for 12 h, the unexpected
dinuclear oxo-bridging complex 12 was obtained.
2.4. Synthesis of complex [g
5-C5Me4(CH(CH3)2)]2Mo2(CO)6 (9)
Using a procedure similar to that described above, reaction of
ligand C5Me4HCH(CH3)2 (3) with Mo(CO)6 in refluxing xylene
afforded complex 9 as red crystals in 30.4% yield. m.p. 121–
122 °C. Anal. Calc. for C30H38Mo2O6: C, 52.49; H, 5.58. Found: C,
52.60; H, 5.49%. 1H NMR (CDCl3): d 2.03–2.18 (m, 2H, CH), 1.93–
The IR of 12 showed three characteristic peaks at 910, 878 and
758 cmꢀ1, corresponding to the two terminal Mo@O stretching
modes and a bridging antisymmetric Mo–O–Mo stretching mode,
respectively. The 1H NMR spectrum of complex 12 showed one sin-
glet peak for the four methyls protons, two group doublet peaks for
the phenyl protons and one singlet peak for the N-methyls protons.
Complex 12 is an unexpected product and the structure is unu-
sual. Because our team has never observed similar reaction of
substituted tetramethylcyclopentadienes with metal carbonyl
complex, we are puzzled by this reaction. After consulting a large
number of literatures [11–13], since the mechanistic is uncon-
firmed, we suggest the following mechanistic pathway shown in
Scheme 2. when ligand 6 reacted with Mo(CO)6 under refluxing xy-
1.97 (m, 24H, C5Me4), 1.30 (d, J = 7.0 Hz, 12H, CH3). IR (mCO
,
cmꢀ1): 1927(s), 1863(s), 1830(s).
2.5. Synthesis of complex [g
5-C5Me4(CH(CH2)4)]2Mo2(CO)6 (10)
Using a procedure similar to that described above, reaction of
ligand C5Me4HCH(CH2)4 (4) with Mo(CO)6 in refluxing xylene
afforded complex 10 as red crystals in 43.1% yield. m.p. 182–
183 °C. Anal. Calc. for C34H42Mo2O6: C, 55.29; H, 5.73. Found: C,
55.41; H, 5.68%. 1H NMR (CDCl3): d 2.11–2.23 (m, 2H, C5Me4CH),
1.92–1.97 (m, 24H, C5Me4), 1.67–1.72 (m,16H, (CH2)4). IR (mCO
,
cmꢀ1): 1919(s), 1905(s), 1890(s).
lene for 12 h, the product
[g
5-C5Me4(4-NMe2Ph)]2Mo2(CO)4
(Mo„Mo) was firstly obtained, subsequent treatment of this dimer
2.6. Synthesis of complex [g
5-C5Me4(CH(CH2)5)]2Mo2(CO)6 (11)
with petroleum ether/CH2Cl2 as eluent exposed to the air, the reac-
tion was occur by oxidation of the carbonyl complex [
NMe2Ph)]2Mo2(CO)4 (Mo„Mo) with O2 in CH2Cl2, then carbonyl
loss to give a single oxygen bridged dimer [
5-C5Me4(4-NMe2-
Ph)MoO2]2( -O). This reaction illustrated that the Mo„Mo triple
g
5-C5Me4(4-
Using a procedure similar to that described above, reaction of
ligand C5Me4HCH(CH2)5 (5) with Mo(CO)6 in refluxing xylene
afforded complex 11 as red crystals in 84% yield. m.p. 158 °C
(dec.). Anal. Calc. for C36H46Mo2O6: C, 56.40; H, 6.05. Found: C,
56.29; H, 5.89. 1H NMR (CDCl3): d 2.39 (t, J = 11.5 Hz, 2H, CH),
g
l
bonded complex is not stable, very easy to react with O2 in the air.
1.84–2.14 (m, 24H, C5Me4), 1.20–1.54 (m, 20H, CH2). IR (mCO
,
3.2. Crystal structures
cmꢀ1): 1935(m), 1921(m), 1898(s), 1888(m), 1869(s), 1830(m).
The selected bond parameters for complexes 7, 8, 11 and 12 are
presented in Table 2 and their molecular structures are depicted in
Figs. 1–4.
2.7. Synthesis of complex [g l-O) (12)
5-C5Me4(4-NMe2Ph)MoO2]2(
The structures of complexes 7, 8, and 11 are shown in Figs. 1–3,
all the complexes consist of two (C5Me4R)Mo(CO)3 units, each of
the molybdenum atoms is coordinated with an
Using a procedure similar to that described above, reaction of
ligand [C5Me4H 4-NMe2Ph] (6) with Mo(CO)6 in refluxing xylene
afforded complex 12 as orange crystals in 60.2% yield. m.p.
165(dec.) °C. Anal. Calc. for C34H44Mo2N2O5: C, 54.26; H, 5.89.
Found: C, 53.96; H, 5.78%. 1H NMR (500 MHz, CDCl3): d 2.09(s,
24H, C5Me4), 2.97(s, 12H, N CH3), 6.72(d, 4H, J = 8 Hz, C6H4),
7.19(d, 4H, J = 8 Hz, C6H4). IR (Mo@O, Mo@O, Mo–O–Mo cmꢀ1):
910(s), 878(s), 758(s).
g
5-cyclopentadi-
enyl and three terminal CO ligands. All the complexes disposed
in the trans conformation and linked by a metal–metal bond, these
complexes lying on a crystallographic inversion. Two independent
but chemically equivalent molecules appear in the unit cell. The
fifth coordination position is occupied by a cyclopentadienyl ring
that is essentially planar. For complex 7, disorder on the location
of Mo has been shown in Fig. 1, the Mo1–Mo1i distance is
0.3272 nm, the Mo10–Mo10i distance is 0.2504 nm. The Mo1–CEN
distance is 0.2024 nm. The disorder share of Mo1 is 0.929 and
Mo10 is 0.071. For complex 11, the conformation of the cyclohexyl
ring has shown a very steady chair form. The structural parameters
2.8. Crystallographic studies
Single crystals of complexes 7, 8, 11 and 12 suitable for X-ray
diffraction were obtained from the slow evaporation of hexane-
dichloromethane solution. All X-ray crystallographic data were
collected on a Bruker Smart APEX diffractometer with graphite
of complexes 7, 8 and 11 are identical to those in [g
5-C5H4-
RMo(CO)3]2, Mo–Mo bond distances for the complexes 7, 8, and
11 are 0.3273, 0.3305 and 0.3291 nm, respectively, which are com-
parable to other metal–metal bond distances found in this kind of
monochromated Mo K
a (k = 0.71073 Å) radiation using the u/x
scan technique. The structures were solved by direct methods
and refined by full-matrix least-squares procedures based on F2
using the SHELXL-97 program system. The crystal data and summary
of X-ray data collection are presented in Table 1.
[g
5-C5H4RMo(CO)3]2
[R = Ph-Me,
(0.3283 nm);
R = Ph-Ome
(0.3307 nm) [14]; R = benzyl (0.3266 nm [15]; R = n-butyl
(0.3286 nm) [16]]. However, Mo–Mo bond distances for the com-
plexes 7, 8, and 11 are longer than that reported for trans-[g
5-C5H5-
i
3. Results and discussion
Mo(CO)3]2 [0.3235(1) nm] [17] and [(g
5-C5H4 Pr)Mo(CO)3]2
[0.3222(5) nm] [18], which indicate that the substituents of the
3.1. Synthesis of 7–12
cyclopentadienyl ring have steric hindrance.
The molecular structure for complex 12 is shown in Fig. 4. Com-
plex 12 is a pentaoxo dimer, and crystallizes in the monoclinic
space group P2(1)/c. Every molecule contains two molybdenum
atoms connected with a single oxygen bridge. The two cyclopenta-
dienyl planes are parallel. The complex is centrosymmetric with a
Treatment of the compounds [C5Me4HR] [R = ethyl (1), n-propyl
(2), i-propyl (3), cyclopentyl (4), cyclohexyl (5)] with Mo(CO)6 un-
der refluxing xylene for 12 h afforded the normal Mo–Mo single
bonded dinuclear complexes 7–11 (Scheme 1).

128
Z. Ma et al. / Inorganica Chimica Acta 399 (2013) 126–130
Table 1
Crystal data and structure refinement parameters for complexes 7, 8, 11 and 12.
Complex
7
8
11
12
Empirical formula
Formula weight
T (K)
C
28H34Mo2O6
C30H38Mo2O6
686.48
298(2)
C36H46Mo2O6
766.61
298(2)
C34H44Mo2N2O5
650.37
298(2)
658.43
298(2)
Crystal system
Space group
a (nm)
monoclinic
P2(1)/n
0.92417(14)
monoclinic
P2(1)/n
0.89270(17)
monoclinic
P2(1)/n
0.8954(5)
monoclinic
P2(1)/c
1.6454(3)
b (nm)
0.90929(14)
0.93258(18)
2.0743(11)
0.78203(16)
c (nm)
1.6505(3)
1.8089(4)
0.9166(5)
1.3233(3)
a
(°)
90
90
90
90
b (°)
97.646(2
90.593(2)
93.175(7)
109.344(3)
c
(°)
90
1.3746(4)
90
1.5058(5)
90
90
1.6066(6)
V (nm3)
1.6999(15)
Z
2
2
2
2
F(000)
668
1.591
700
1.514
788
1.498
772
1.556
Dcalc (g/cm3)
Crystal dimensions (mm)
h Range (°)
0.48 ꢁ 0.36 ꢁ 0.20
0.48 ꢁ 0.42 ꢁ 0.03
0.26 ꢁ 0.21 ꢁ 0.20
0.49 ꢁ 0.37 ꢁ 0.03
2.40–25.50
2.25–25.50
2.43–25.50
2.62–25.02
Reflection collected (Rint)
Independent reflections
Rint
6822 (0.0208)
2545
0.0208
7432
2802
0.0317
8376 (0.0482)
3151
0.0482
6515 (0.0329)
2835
0.0329
Parameterss
178
1.120
177
1.076
203
1.090
202
1.062
Goodness of fit (GOF) on F2
R1, wR2 [I > 2
R1, wR2 (all data)
CCDC deposition No.
r
(I)]
R1 = 0.0266, wR2 = 0.0651
R1 = 0.0314, wR2 = 0.0671
832372
R1 = 0.0306, wR2 = 0.0811
R1 = 0.0338, wR2 = 0.0852
883602
R1 = 0.0558, wR2 = 0.1170
R1 = 0.0736, wR2 = 0.1244
833999
R1 = 0.0383, wR2 = 0.0933
R1 = 0.0474, wR2 = 0.0983
834001
Complex 7: w = 1/[
Complex 8: w = 1/[
Complex 11: w = 1/[
Complex 12: w = 1/[
r
r
r
r
2(Fo2) + (0.0280 p)2 + 0.7464 p], where p = (Fo2 + 2Fc2)/3.
2(Fo2) + (0.0479 p)2 + 0.3556 p], where p = (Fo2 + 2Fc2)/3.
2(Fo2) + (0.0484 p)2 + 3.4886 p], where p = (Fo2 + 2Fc2)/3.
2(Fo2) + (0.0550 p)2 + 0.4486 p], where p = (Fo2 + 2Fc2)/3.
R
O(1)–Mo(1i) is first observed in our experiments, the liner
Mo(1)–O(1)–Mo(1i) bridge bond was attributed to -bonding after
the possible consequences of steric interactions were considered.
p
(CO)3
Mo(CO)6
R
In fact, a linear, centrosymmetric arrangement in a [(MoO2)2O] unit
R
Mo
(OC)3
Mo
was once previously observed in [(g l-O) [11]. In
5-C5Me5)MoO2]2(
xylene, reflux
complex 12, the bond distances of Mo(1)–O(1) and Mo(1i)–O(1)
are completely equal (0.18836 nm), the terminal Mo@O distances
(average 0.1706 nm) are much longer than [(g l-
5-C5Me5)MoO2]2(
Scheme 1. Synthesis of the complexes 7–11.
O) (average 0.167 nm)], the long bond distances of terminal Mo@O
bonds have been suggested to decrease O–O repulsion and result in
O–Mo–O angles larger than 90°. Further investigation of the reac-
tivity and stability of this complex is in progress.
Mo(1)–O(1)–Mo(1i) angle of 180°, the Mo(1)–O(1)–Mo(1i) is a
colinear bond at an oxygen atom, the linearity of the Mo(1)–
N
CO
Mo
CO
CO
Mo
CO
Mo(CO)6
N
xylene, reflux
N
N
O
O
O2
Mo
O
O
Mo
CH2Cl2
O
N
Scheme 2. Synthesis of the complex 12.

Z. Ma et al. / Inorganica Chimica Acta 399 (2013) 126–130
129
Table 2
Selected bond distances (nm) and angles (°) for complexes 7, 8, 11 and 12.
7
8
11
12
Mo(1)–Mo(1i)
0.3273
Mo–Mo(1i)
Mo(1)–C(1)
Mo(1)–C(2)
Mo(1)–C(3)
Mo(1)–C(4)
Mo(1)–C(5)
C(2)–Mo(1)–C(1)
C(2)–Mo(1)–C(3)
C(1)–Mo(1)–C(3)
C(2)–Mo(1)–C(4)
C(3)–Mo(1)–C(5)
C(1)–Mo(1)–Mo(1i)
0.3305
Mo–Mo(1i)
Mo(1)–C(1)
Mo(1)–C(2)
Mo(1)–C(3)
Mo(1)–C(4)
Mo(1)–C(5)
C(2)–Mo(1)–C(1)
C(2)–Mo(1)–C(3)
C(1)–Mo(1)–C(3)
C(2)–Mo(1)–C(4)
C(3)–Mo(1)–C(5)
C(1)–Mo(1)–C(16)
0.3291
Mo(1)–C(1)
Mo(1)–C(2)
Mo(1i)–O(1))
Mo(1)–O(1)
Mo(1)–O(2)
Mo(1)–O(3)
C(2)–Mo(1)–C(1)
C(2)–Mo(1)–C(3)
C(1)–Mo(1)–C(3)
C(2)–Mo(1)–C(4)
O(1)–Mo(1)–C(5)
Mo(1)–O(1)–Mo(1i)
0.2349(3)
0.2426(4)
Mo(1)–C(1)
0.2383(3)
0.2227(5)
0.1998(8)
0.2426(3)
0.2504(12)
18.5(4)
0.2378(2)
0.2313(2)
0.2321(3)
0.2380(3)
0.2425(3)
35.26(9)
35.88(10)
58.67(9)
58.77(9)
58.05(9)
111.31(6)
0.2313(5)
0.2385(5)
0.2409(5)
0.2381(5)
0.2313(5)
35.20(17)
34.53(18)
58.08(17)
58.16(18)
58.16(17)
139.8(2)
Mo(10)–C(1)
0.18836(5)
0.18836(5)
0.1708(3)
0.1704(3)
35.20(17)
33.17(12)
56.92(12)
55.80(12)
117.39(8)
180.0
Mo(10)–C(2)
Mo(1)–C(2)
Mo(10)–Mo(10i)
Mo(10)–C(3)–Mo(1)
Mo(1’)–C(1)–Mo(1)
C(5)–Mo(1)–C(1)
C(3)–Mo(1)–C(1)
O(1)–C(13)–Mo(1)
O(1)–C(13)–Mo(10)
18.4(4)
35.25(10)
57.86(9)
178.9(3)
177.7(3)
Fig. 1. The molecular structure of complex 7. Ellipsoids correspond to 30% probability. Hydrogen atoms are omitted for clarity.
Fig. 2. The molecular structure of complex 8. Ellipsoids correspond to 30% probability. Hydrogen atoms are omitted for clarity.

130
Z. Ma et al. / Inorganica Chimica Acta 399 (2013) 126–130
Fig. 3. The molecular structure of complex 11. Ellipsoids correspond to 30% probability. Hydrogen atoms are omitted for clarity.
Fig. 4. The molecular structure of complex 12. Ellipsoids correspond to 30% probability. Hydrogen atoms are omitted for clarity.
obtained free of charge from The Cambridge Crystallographic Data
4. Conclusions
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at http://dx.doi.org/10.1016/j.ica.2013.01.010.
In summary, six new metal carbonyl complexes have been syn-
thesized by the reactions of substituted tetramethylcyclopentadi-
enes with Mo(CO)6 in refluxing xylene, five of them are normal
product but one of them is unexpected product. The results re-
vealed the ligands coordinate to the molybdenum center by g5
model. Comparing the range of structures that have been deter-
mined for complexes of the type Cp⁄2Mo2(CO)6, we find that the
same overall structure with six terminal CO groups is presented
in all compounds. We also see that the Cp⁄ ligands are trans in
the dimeric structures in the solid state. The change of substituent
of cyclopentadienyl has some influence on the Mo–Mo bond
length. The Mo„Mo triple bonded complex was not stable, very
easy to react with O2 in the air.
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Appendix A. Supplementary material
CCDC 832372, 883602, 833999 and 834001 contain the supple-
mentary crystallographic data for 7, 8, 11 and 12. These data can be