Carbon-bridged tri(cyclopentadiene): Synthesis and coordination with ytterbium

Article abstract of DOI:10.1002/cjoc.201400598

Reaction of a mixture of 1,1-bis(cyclopentadienyl)cyclohexane and pentamethylenefulvene with metallic sodium in THF led to a mixture of cyclohexylidene-bridged bis(cyclopentadienyl) sodium and two-cyclohexylidenebridged tri(cyclopentadienyl) sodium. Reaction of the salt solutions with anhydrous YbCl₃ in THF afforded a ytterbium complex mixed-ligated by bridged bis(cyclopentadienide) and bridged tri(cyclopentadienide).

Full text of DOI:10.1002/cjoc.201400598

COMMUNICATION
DOI: 10.1002/cjoc.201400598
Carbon-bridged Tri(cyclopentadiene): Synthesis and
Coordination with Ytterbium
Lin Sha, Li Li, and Fugen Yuan*
School of Chemistry and Biochemistry, Suzhou University of Science and Technology,
Suzhou, Jiangsu 215009, China
Reaction of a mixture of 1,1-bis(cyclopentadienyl)cyclohexane and pentamethylenefulvene with metallic so-
dium in THF led to a mixture of cyclohexylidene-bridged bis(cyclopentadienyl) sodium and two-cyclohexylidene-
bridged tri(cyclopentadienyl) sodium. Reaction of the salt solutions with anhydrous YbCl3 in THF afforded a
ytterbium complex mixed-ligated by bridged bis(cyclopentadienide) and bridged tri(cyclopentadienide).
Keywords cylcopentadienyl, ytterbium, lanthanide, fulvene
Introduction
0.256 mol) was added to a suspension of NaOH powder
(26.5 g) in THF (60 mL). The mixture was stirred for 2
h. Cyclohexanone (11.08 mL, 0.119 mol) in THF (10
mL) was added dropwise and the mixture was stirred for
3 h. The resulting mixture was hydrolyzed, acidified and
extracted by petroleum ether. The organic layer was
dried by anhydrous MgSO4. The liquid in low boiling
point was removed in vacuo, and the residue was a sort
of yellow oil (15.02 g). It was dissolved in about 25 mL
of THF, and metallic sodium (3.60 g, 0.156 mol) was
added in. The mixture was stirred at room temperature
for 1 d and at 45 ℃ for another 2 d. After being cen-
trifugalized, a clear reddish solution was obtained. This
was a mixture of cyclohexylidene-bridged bis(cyclo-
pentadienyl) sodium and two-cyclohexylidene-bridged
tri(cyclopentadienyl) sodium. About 2 mL of salt solu-
tion was drawn out for analysis. After being hydrolyzed
and extracted by hexane, the sample was detected by
GC-MS. The front peak in GC was assigned to penta-
methylenefulvene, i.e. (C5H4)C(CH2)5. MS m/z (%): 146
(M＋, 100), 131 (M＋−CH3, 37.2), 117 (M＋−C2H5, 79.4),
105 (27.4), 91 (42.2), 78 (42.2), 65 ([C5H5]＋, 9.5), 51
(7.8). The second peak was in accordance with 1,1-bis-
(cyclopentadienyl)cyclohexane, i.e. (C5H5)C(CH2)5-
(C5H5). MS m/z (%): 212 (M＋, 100), 197 (M＋−CH3,
11.0), 183 (M＋−C2H5, 17.0), 169 (M＋−C3H7, 64.9), 155
(M＋−C4H9, 61.5), 141 (M＋−C5H11, 54.1), 128 (M＋
−C6H12, 43.8), 115 (M＋−C7H13, 41.5), 91 (40.3), 77
(20.3). The last peak was consistent with a tri(cyclo-
pentadiene) linked by two cyclohexylidene bridges, i.e.
(C5H5)C(CH2)5(C5H4)C(CH2)5(C5H5). MS m/z (%): 358
(M＋, 100), 293 (M＋−C5H5, 68.7), 211 (M＋−C5H5−
C(CH2)5, 40.6), 147 (M＋−C5H5−C(CH2)5−C5H4, 82.0),
91 (38.7), 79 (37.2).
Cyclopentadienyl group (Cp−) is a traditional ligand
in organolanthanide chemistry. Effort to prepare or-
ganolanthanide complexes with σ-bond such as
Cp2LnCH3, especially for light lanthanide elements (La
through Nd, with large ionic radii), has developed
−
multi-substituted Cp (bulky, such as C5Me5 ), Cp with
side chains (such as MeOCH2CH2Cp−) and linked
bis(cyclopentadienyl) ligand (such as Me2C(Cp−)2).[1-4]
They have played a leading role in constructing ther-
mally stable organolanthanide complexes. Ligand of
linked tri(cyclopentadiene) has been unknown.
Recently we were interested in ansa-lanthanocene
complexes, as the ansa-bridge was reported to have
multiple functions such as increasing the electrophilicity
of the metal and increasing the access of substrates to
the equatorial wedge of the complex.[5-9] Cyclo-
hexylidene-bridged
bis(cyclopentadienyl)
ligand,
−
(CH2)5C(C5H4 )2, is what we selected. This ligand has
been used in constructing ansa-transition metal com-
plexes,[10-12] showing unique catalytic property for eth-
ylene polymerization.[12,13] But it has not been intro-
duced into lanthanide area. Our initial purpose is to
synthesize lanthanide complexes with this ligand to lay
the foundation to investigate their catalytic property. As
a result, unprecedented two-cyclohexylidene-bridged
tri(cyclopentadiene) was obtained out of expectation.
Also, its ytterbium complex was isolated and structur-
ally characterized.
Experimental
Synthesis process
The freshly distilled cyclopentadiene (21.2 mL,
*
E-mail: yuanfugensuzhou@163.com; Tel.: 0086-0512-65613020; Fax: 0086-0512-68418935
Received September 8, 2014; accepted October 4, 2014; published online XXXX, 2014.
Chin. J. Chem. 2014, XX, 1—3
© 2014 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1

Sha, Li & Yuan
COMMUNICATION
Synthesis of {(CH2)5C(η5-C5H4)2Yb}2(η5-C5H4)C-
(CH2)5(μ-η1:η1-C5H4)C(CH2)5(η5-C5H4) (1)
A flask was charged with anhydrous YbCl3 (0.548 g,
1.96 mmol), and about 25 mL of THF was condensed in.
The THF solution of cyclohexylidene-bridged bis-
(cyclopentadienyl) sodium and two-cyclohexylidene-
bridged tri(cyclopentadienyl) sodium (relative molar
ratio 4∶1) (3.7 mL, 1.611 mol•L−1 of alkali, 5.96 mmol
of alkali) was added in by a syringe. After being stirred
for 24 h at room temperature, the reaction mixture was
centrifugalized. A dark-green solution was obtained,
and then evaporated off to dryness under vacuum. The
residue was dissolved in DME, and small amount of
hexane was added. Finally the solution was kept at −20
℃. Dark-green crystals of 1•DME (0.410 g, 0.338
mmol, 34.5% based on Yb) were produced. m.p.
150−151 ℃ (dec); IR (KBr) ν: 2932 (s), 2857 (s), 2375
(m), 1620 (s), 1399 (m), 1077 (s), 897 (w), 620 (s) cm−1.
Anal. calcd for C63H78O2Yb2: C 62.37, H 6.43, Yb
28.55; found C 61.76, H 6.28, Yb 28.35.
Figure 1 The MS spectra and possible splitting route for car-
bon-bridged tri(cyclopentadiene). MS m/z (%): 358 (M＋, 100),
293 (M＋ −C5H5, 68.7), 211 (M＋ −C5H5−C(CH2)5, 40.6), 147
(M＋−C5H5−C(CH2)5−C5H4, 82.0), 91 (38.7), 79 (37.2).
Scheme 1 Synthesis route to complex 1
O
Results and Discussion
(1) NaOH/THF
(2) H2O
Na/THF
-H2
+
+
According to the purpose to prepare ansa-lanthanide
complexes, the first work we did was to prepare spiro-
methylene bis(cyclopentadiene), (CH2)5C(C5H5)2. The
synthesis was carried out in reference to the previous
literature[12] by reaction of cyclohexanone and
cyclopentadiene (freshly distilled) in NaOH-THF. A
sort of yellow oil was obtained as product. According to
the spectra from GC-MS, the product was a mixture of
1,1-bis(cyclopentadienyl)cyclohexane and pentameth-
ylenefulvene. Suppose small amount of fulvene did not
affect the deprotonation of 1,1-bis(cyclopeantadienyl)-
cyclohexane, direct reaction of the yellow mixture and
metallic sodium in THF was made. This reaction pro-
ceeded firstly at room temperature for 1 d, and then at
45 ℃ for 2 d, as the reaction was rather slow according
to the emergence of gas bubbles. After work up, a salt
solution was obtained. Sample solution was drawn out,
hydrolyzed and analyzed by GC-MS. It is astonishing
that a new peak, compared with those for former yellow
oil, appeared in the GC spectra, and its MS spectra well
match the fracture of two-cyclohexylidene-bridged
tri(cyclopentadiene) step by step (Figure 1). Notably the
synthesis is well reproducible. Hence the salt solution
should be a mixture of cyclohexylidene-bridged bis-
(cyclopentadienyl) sodium and two-cyclohexylidene-
bridged tri(cyclopentadienyl) sodium. We supposed that
the carbon-bridged tri(cyclopentadiene) may come from
the reaction of bridged bis(cyclopentadienyl) sodium
and pentamethylenefulvene. In general, the molar ratio
of linked bis(cyclopentadiene) and linked tri(cyclo-
pentadiene) was (4−5)∶1. The reaction process is out-
lined in Scheme 1.
Na+
Na+
-
-
YbCl3/THF
-NaCl
+
Na+
Na+
Yb
Yb
afforded dark-green crystals of {(CH2)5C(η5-C5H4)2-
Yb}2(η5-C5H4)C(CH2)5(μ-η1:η1-C5H4)C(CH2)5(η5-C5H4)
(1), characterized by elemental analyses, IR and X-ray
crystallography.[14] The molecular structure of 1 is
shown in Figure 2. It is obvious that the cyclohexy-
lidene-bridged bis(cyclopentadienyl) ligand coordinates
＋
with a Yb3 ion in a sandwich fashion. In this dinuclear
＋
complex, two Yb3 ions were linked by a dianionic
tri(cyclopentadienyl) group with two cyclohexylidene-
bridges. The middle cyclopentadiene in bridged tri-
(cyclopentadiene) was not deprotoned. The neutral
＋
cyclopentadiene interacts with two Yb3 ions via two
Yb－C(29) interactions in two opposite directions. The
distance of Yb－C(29) (2.716 Å) is a little smaller than
＋
the sum of ionic radius of Yb3 (10 coordinate, 1.10 Å)
and the Van der Waals radius of carbon (1.71 Å), and a
little greater than the bond distances of Yb－C(Cp) (av.
Reaction of the salt solution with anhydrous YbCl3
in THF afforded a dark-green solution. Crystallization
of the product in DME-hexane solvents at −20 ℃
2.620 Å).
＋
The three η5-cyclopentadienyl ligands around a Yb3
ion are approximately equivalent in the coordination.
2
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© 2014 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2014, XX, 1—3

Carbon-bridged Tri(cyclopentadiene): Synthesis and Coordination with Ytterbium
＋
The Yb3 coordination is solvent-free, maybe due to
the steric saturation around the ion. The α angle of
C(7)－C(1)－C(12) is 99.5(12)°. This angle is smaller
than the corresponding angles in Me2C-bridged lan-
thanocenes of rac-(CH3)2C(C5H3-3-Si(CH3)3)2Yb(μ2-
plexes with such ligand is currently in progress.
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(102.0(8)°),[16]
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[14] Crystal data for 1•DME: C63H78O2Yb2, Mr＝1213.33, trigonal, P 321,
a＝21.8200(10) Å, b＝21.8200(10) Å, c＝14.4936(16) Å, α＝
90.00°, β＝90.00°, γ＝120.00°, V＝5976.1(8) Å3, Z＝3, F(000)＝
1833, μ(Mo Kα)＝2.361 cm−1, Dcalcd＝1.011 g•cm−3. Data collec-
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meter (Mo Kα radiation, λ＝0.71073 Å, graphite monochromator, φ
and ω scans). A total of 61550 reflections were collected and 9195
were independent, of which 6309 were observed with I＞2σ(I). The
structure was solved by direct method with SHELXS-97 program
and refined with SHELXL-97 by full-matrix least squares tech-
niques on F2. Notably, one hydrogen atom in the central cyclopenta-
diene, which was obviously reasonable in chemistry, did not take
part in the final refinement. The final cycle of full-matrix least
squares refinement on F2 converged to R1＝0.0677 and wR2＝
0.1871. Crystallographic data for the structural analysis have been
deposited at the Cambridge Crystallographic Data Center with
CCDC No. 1006861.
Figure 2 ORTEP drawing of complex 1. Selected bond dis-
tances (Å) and angles (°): Yb(1)－Cen(1) 2.412, Yb(1)－Cen(2)
2.347, Yb(1)－Cen(3) 2.322, Yb(1)－C(29) 2.716 and C(7)－C(1)
－C(12) 99.5(12), C(23)－C(17)－C(28) 104.1(10), Cen(1)－
Yb(1)－Cen(2) 108.5, Cen(1)－Yb(1)－Cen(3) 122.6, Cen(2)－
Yb(1)－Cen(3) 118.6, dihedral angle between planes of C(7)－
C(11) and C(12)－C(16), 80.06. Cen(1), Cen(2) and Cen(3) rep-
resent the centroids of C(7)－C(11), C(12)－C(16) and C(23)－
C(27), respectively.
Conclusions
We have found a route to prepare new compound of
two-cyclohexylidene-bridged tri(cyclopentadiene), and
presented a ytterbium complex with this ligand. The
study on coordination and property of lanthanide com-
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(Cheng, F.)
Chin. J. Chem. 2014, XX, 1—3
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