Stereoselective synthesis of an ansa-zirconocene in a spirane scaffold

Article abstract of DOI:10.1016/j.jorganchem.2005.08.049

Methodology is described for the preparation of a rigid C ₂-bridged zirconocene catalyst system where the C₂-bridge is embedded in a spirane scaffold. The ligand was prepared from 3,4-dihydro-2H-fluoren-1(9H)-one. Initially, the oxo

Full text of DOI:10.1016/j.jorganchem.2005.08.049

Journal of Organometallic Chemistry 691 (2006) 356–360
www.elsevier.com/locate/jorganchem
Stereoselective synthesis of an ansa-zirconocene in a spirane scaffold
*
Geir Langli, Christian Rømming, Kjell Undheim
Department of Chemistry, University of Oslo, P.O. Box 1033, N-0315 Oslo, Norway
Received 8 July 2005; received in revised form 25 August 2005; accepted 25 August 2005
Available online 27 October 2005
Abstract
Methodology is described for the preparation of a rigid C2-bridged zirconocene catalyst system where the C2-bridge is embedded in a
spirane scaffold. The ligand was prepared from 3,4-dihydro-2H-fluoren-1(9H)-one. Initially, the oxo group was converted into a spiro-
cyclobutanone function. Further conversion to a fulvene was followed by regio- and stereoselective saturation to provide the ligand
cis-2-(cyclopentadienyl)-10,20,30,40-tetrahydro-9H-spiro[cyclobutane-1,10-fluorene]. The ligand was dilithiated and reacted with zirconium
tetrachloride to provide the corresponding (g5-cyclopentadienyl)-spiro[cyclobutane-1,10-(g5-fluorenyl)]zirconium dichloride complex.
The structure of the zirconocene dichloride has been established by crystal X-ray analysis.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Zirconocene C2-spirane-bridges; Spirane scaffold; Rigid ansa-zirconozene; Stereoselective ligand synthesis; Dilithiation and zirconation
1. Introduction
unit whereas the second cyclopentadienyl unit is part of a
tetrahydrofluorene system where the C-1 carbon is also
the spiro carbon in the scaffold. From models it appears
that the bite angle in the spirane and the free C2-bridges
would not be greatly different.
The bridging unit between the two g5-coordinated aro-
matic ligands in ansa-zirconocene dichloride complexes lar-
gely controls the bite angle between the cyclopentadienyl
units and have a profound influence on the catalytic prop-
erties of these complexes [1–3]. The substitution patterns of
the commonly studied C1-, Si1- and C2-bridges also affect
the bite angle and hence the reactivity as catalyst for poly-
merisation, and consequently the polymer microstructures.
We aim to prepare highly rigidified metallocenes. The rota-
tional flexibility of C1-bridged metallocenes has been
greatly reduced by incorporation of the C1-bridge carbon
as the C-4 carbon in 4-cyclopentadienyl-4,5,6,7-tetrahydro-
indenyl derived zirconium derivatives [4,5]. Our interest for
C2-bridged ansa-zirconocenes [1,2,6] has been directed to-
wards methods for the preparation of rigid C2-bridges in
a zirconocene catalyst system where the C2-unit constitutes
a part of a spirane scaffold. Methods for the stereoselective
preparation of sandwiched bisaryls bridged by spiranes
have been reported [7,8]. In the targeted zirconocene A in
Fig. 1, one of the spirane substituents is a cyclopentadienyl
2. Results and discussion
The synthesis of the targeted ligand 5 is outlined in
Scheme 1. The substrate was the 1-fluorenone (1) [9]. An
initial attempt to form an adduct between the ketone 1
and lithiated cyclopropyl phenyl sulfide failed [10]. The for-
mer acted as a base with abstraction of an acidic indene
proton in preference to nucleophilic addition to the oxo
group as indicated by the dark red coloration of the reac-
tion medium. We therefore turned to less basic organome-
tallic species. An organometallic derivative of cerium
trichloride was appropriate [11]. The metallated species
was available by quenching lithiated cyclopropyl phenyl
sulfide with cerium trichloride. Adduct formation pro-
1
ceeded in the cold to provide the alcohol adduct 2. H
NMR spectra of the crude product showed full conversion.
Part of the material was lost on chromatographic purifica-
tion, probably because of ready elimination of water, the
isolated yield being 66%. By analogy to the rearrangements
*
Corresponding author. Tel.: +47 22855521; fax: +47 22855507.
E-mail address: kjell.undheim@kjemi.uio.no (K. Undheim).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.08.049

G. Langli et al. / Journal of Organometallic Chemistry 691 (2006) 356–360
357
generation of the cis-isomer 5. Regioselectivity in the sat-
uration was provided by metal hydride reactions. Initially,
simple metal hydride reagents had provided mixtures of
stereoisomers. For steric reasons, a bulky metal hydride
reagent was required. The requirement was met by the
use of lithium triethylborohydride which cleanly provided
the cis-isomers 5 in high yield. The stereoselectivity is due
to addition of the metal hydride reactant to the less
shielded side of the cyclobutyl fulvene double bond. The
cyclobutadienyl substituent is thereby forced into the
H
Zr
Cl
Cl
1
A
Fig. 1. C2-bridged zirconocene with the C2-bridge embedded in a rigid
spirane scaffold.
reported by Trost [12], the cyclopropyl phenyl sulfide 2
could be rearranged by acid catalysis under the influence
of aqueous fluoroboric acid in benzene to furnish the
cyclobutanone 3 in 57% yield. In the subsequent step, the
ketone was to be converted into a fulvene derivative 4. In
general, several methods are available for fulvene forma-
tion [13]. In this work the ketone 3 was reacted with cyclo-
pentadiene in the presence of pyrrolidine as a base to
provide the fulvene 4.
1
cis-configuration. H NMR showed the crude product to
consist mainly of two endocyclic double bond isomers
in the cyclopentadiene unit. The product was chemolabile
in that only about 30% was recovered after a flash chro-
matographic operation on silica gel. The crude ligand
product was therefore used in the subsequent metallation
work.
For the zirconocene formation, the ligand 5 was lithi-
ated and subsequently treated with ZrCl4 (Scheme 2).
Addition of one molar equivalent of n-BuLi to a solution
of the ligand in diethyl ether gave a clear solution. Addition
of a second molar equivalent of n-Buli led to precipitation of
a tan dilithiated powder which was isolated by filtration
and was washed with pentane. The dilithiated product
was added to toluene without any further characterisation
and treated with solid ZrCl4 which had been purified by
sublimation. The zirconocene 7 was isolated in 25% yield.
The modest yield was not significantly improved by the
use of the ZrCl4(THF)2 complex for the zirconation. In
In the final step, a stereoselective reduction of the ful-
vene double bond was required. Only in the cis-configura-
tion, as in structure 5, can the zirconium metal become
coordinated or attached to the fluorenyl and cyclopenta-
dienyl moieties in a sandwiched zirconocene structure.
The cis-configuration, however, leads to a significant
repulsive interaction with the larger part of the fluorene
component, and is thermodynamically the less favourable
structure of the two geometrical isomers. The sterical
shielding of the two faces of the fulvene unit in the spi-
rane 4 differs significantly. Stereoselective saturation of
the fulvene exocyclic double bond was required for the
O
SPh
SPh
HO
O
35% HBF4(aq)
CeCl2
PhH
70 oC, 14 h
THF
-78 oC
1
3 57%
2 66%
Pyrrolidine
MeOH
0 oC, 18 h.
LiBEt3H
THF
0-20 oC, 1.5 h
4 48%
5 >95%, de>90%
Scheme 1.
Li+
Zr
Cl
n-BuLi
ZrCl4
Cl
Et2O
0-20 oC, 24 h
PhMe
20 oC, 20 h.
Li+
7 25 %
5
6 90%
Scheme 2.

358
G. Langli et al. / Journal of Organometallic Chemistry 691 (2006) 356–360
part, the modest yield may be explained by the face selec-
tivity during the zirconation. A sandwich complex requires
an intramolecular reaction where the zirconium reactant
becomes attached to the inner face of the fluorene ring.
When ZrCl4 becomes attached to the other outer face of
the ring, intermolecular products are likely to be formed.
The zirconocene was extremely sensitive to oxygen. Solu-
tions turned dark green, and only small amounts of impure
7 could be isolated from such solutions.
The zirconocene structure 7 has been established by a
single-crystal X-ray analysis and is shown by the ORTEP
plots of the crystal in Fig. 2. Crystals suitable for X-ray
analysis were obtained by slow evaporation of a toluene
solution of the zirconocene 7 at room temperature. The
crystal unit consisted of two crystallographically indepen-
dent molecules of compound 7. Using other solvents like
CH2Cl2 and Et2O led to decomposition with dark green
coloration. The toluene solution also turned slightly green
after a few days, even though it was standing in a glovebox.
The target molecule in this project was to be a conform-
ationally highly constrained C2-ansa-zirconocene. A com-
parison of the X-ray data will show that the selected
torsion angles and the bond distances are similar to the
corresponding torsion angles and bond distances in the
simple ethylene-bridged C2-symmetric rac-ethylenebis-
(1-indenyl)]ZrCl2 [14], and the homologue rac-[ethylen-
bis(4,7-dimethyl-1-indenyl)]ZrCl2 [15].
The properties of the zirconocene complex as a propene
polymerisation precatalyst was briefly studied with MAO
in toluene under a propene pressure of 1.1 bar at 30 ꢁC.
The product was atactic PP. Activity of the zirconocene
was calculated to be 0.47 · 106 g PP/mol[Zr] [C ] h. The
*
*
3
1
molecular weight was estimated by H NMR end-group
analysis [16], Mw = 600 g/mol.
3. Conclusion
Methodology for the synthesis of a C2-bridged zircono-
cene, (g5-cyclopentadienyl)spiro[cyclobutane-1,10-(g5-flu-
orenyl)]zirconium dichloride, is described. The C2-bridge
in the ligand is embedded in a rigid spirane scaffold confer-
ring rigidity onto the organometallic complex. As a poly-
merisation precatalyst, the complex provided atactic PP.
4. Experimental section
The 1H NMR spectra were recorded at 500 MHz with a
Bruker DPX 500 instrument, at 300 MHz with a Bruker
DPX 300 instrument, or at 200 MHz with a Bruker DPX
200 instrument. The 13C NMR spectra were recorded at
1
125, 75 or 50 MHz using the same instruments. H and
13C spectra were referenced to residual protons in the sol-
vent. Mass spectra were recorded at 70 eV ionizing voltage
and are presented as m/z (% rel. int.). Elemental analyses
were performed by Ilse Beetz Mikroanalytisches Laborato-
rium, Kronach, Germany. All organometallic reactions
were run under an argon atmosphere using Schlenk and
glovebox techniques. THF, Et2O and toluene were distilled
from sodium/benzophenone and CH2Cl2 from CaH2.
CeCl3 was bought as the heptahydrate and dried according
to the literature [17].
Fig. 2. ORTEP plot of the two crystallographically independent molecules
of compound 7. Ellipsoids are shown at 50% probability. Selected angles (ꢁ)
˚
and bond lengths (A) in the molecules: X(1A)–Zr(1)–X(1B) = 125.7, Cl(1)–
Zr(1)–Cl(2) = 98.5, Zr(1)–Cl(1) = 2.423, Zr(1)–Cl(2) = 2.420, Zr(1)–
X(1A) = 2.200,
Zr(1)–X(1B) = 2.243;
X(3A)–Zr(31)–X(3B) = 125.8,
Cl(31)–Zr(31)–Cl(32) = 98.8, Zr(31)–Cl(31) = 2.432, Zr(31)–Cl(32) =
2.424, Zr(31)–X(3A) = 2.199, Zr(31)–X(3B) = 2.241. Estimated standard
˚
deviations are 0.1ꢁ in angles and 0.001 A in bond lengths.

G. Langli et al. / Journal of Organometallic Chemistry 691 (2006) 356–360
359
4.1. X-ray crystallographic analysis for zirconocene (7)
1-ol (2) (628 mg, 1.9 mmol) in dry benzene (25 mL) and the
mixture heated at 70 ꢁC for 10 h. Dichloromethane
(100 mL) was added to the cold reaction mixture and the
solution extracted with saturated aqueous NaHCO3
(30 mL), and water (10 mL), the organic solution dried
(MgSO4), evaporated and the residual material subjected
to flash chromatography on silica gel using EtOAc:hexane
1:20; yield 243 mg (57%) of a light yellow oil which solidi-
fied on storage in the refrigerator. (Anal. Calc. for
C16H16O: C, 85.68; H, 7.19. Found: C, 85.59; H, 7.20%).
1H NMR (300 MHz, CDCl3): d 1.8–2.1 (m, 5H), 2.2–2.4
(m, 1H), 2.5 (m, 2H), 3.0–3.4 (m, 4H), 7.1–7.4 (m, 4H).
13C NMR (75 MHz): d 19.9, 22.1, 25.3, 32.2, 36.8, 43.1,
66.8, 118.4, 123.5, 124.6, 126.3, 137.7, 138.8, 142.4, 144.9,
213.0. MS(EI): 224 (M+, 3%), 196 (91), 182 (100), 16
(81), 152 (22), 141 (20), 115 (11), 82 (5).
X-ray data were collected on a Siemens SMART CCD
diffractometer [18] using graphite monochromated Mo
˚
Ka radiation (k = 0.71073 A). Data collection method: x-
scan, range 0.6ꢁ, crystal to detector distance 5 cm. Data
reduction and cell determination were carried out with
the SAINT and XPREP programs [18]. Absorption correc-
tions were applied by the use of the SADABS program [19]. The
structures were determined and refined using the SHELXTL
program package [20]. The non-hydrogen atoms were
refined with anisotropic thermal parameters; hydrogen
atoms were located from difference Fourier maps and refined
with isotropic thermal parameters. X-ray structural data for
zirconocene 7 have been deposited at the Cambridge Crystal-
lographic Data Centre, deposition number CCDC 266324.
Crystal data for C21H20Cl2Zr (7) M = 434.49, triclinic,
P1, a = 11.123(1) A, b = 12.807(1) A, c = 12.930(1) A,
4.4. 2-(Cyclopenta-2,4-dienylidene)-10,20,30,40-tetrahydro-
9H-spiro[cyclobutane-1,10-fluorene] (4)
ꢀ
˚
˚
˚
a = 101.62(1)ꢁ, b = 99.13(1)ꢁ, c = 90.09(1)ꢁ, V = 1780.1
3
(2) A , Z = 4, Dx = 1.621 Mg mꢀ3, l = 0.917 mmꢀ1, T =
˚
150(2) K, measured 36,306 reflections in 2h range 3.2–
80.6ꢁ, Rint = 0.0148. 593 parameters refined against
19,480 F2, R = 0.030 for I0 > 2r(I0) and 0.046 for all data.
Pyrrolidine (6.7 mL, 80 mmol) was added dropwise to a
solution of 10,20,30,40-tetrahydro-9H-spiro[cyclobutane-
1,10-fluoren]-2-one (3) (4.5 g, 20 mmol) and cyclopentadiene
(8.1 mL, 100 mmol) in methanol (60 mL) and dichloro-
methane (10 mL) at 0 ꢁC and the mixture stirred at this
temperature for 18 h. The reaction mixture was poured
into ice-cold 0.5 M HCl (100 mL), the resultant mixture ex-
tracted with hexane (3 · 100 mL), the hexane extracts dried
(MgSO4), the solution evaporated and the residual material
subjected to flash chromatography on silica gel using
EtOAc:hexane 1:40; yield 2.6 g (48%) of a dark yellow
oil. (Anal. Calc. for C21H20: C, 92.60; H: 7.40. Found: C,
4.2. 1,2,3,4-Tetrahydro-9H-1-[1-(phenylthio)cyclopropyl]
fluoren-1-ol (2)
n-BuLi (1.6 M in hexane, 4.40 mL, 7.0 mmol) was added
to a solution of cyclopropyl phenyl sulfide [10] (1.05 g,
7.05 mmol) in THF (10 mL) at 0 ꢁC, the mixture stirred at
this temperature for 30 min, the temperature lowered to
ꢀ78 ꢁC and the solution cannulated into a solution of anhy-
drous CeCl3 (2.08 g, 8.23 mmol) in THF (20 mL) at ꢀ78 ꢁC.
The resultant mixture was stirred at ꢀ78 ꢁC for 3 h. A solu-
tion of 3,4-dihydro-2H-fluoren-1(9H)-one (1) (865 mg,
4.7 mmol) in THF (5 mL) was added dropwise, and the
reaction mixture allowed to reach room temperature over-
night. Water (50 mL) was added, the mixture extracted with
diethyl ether (3 · 100 mL), the ether extracts dried
(MgSO4), the solution evaporated to dryness and the resid-
ual material subjected to flash chromatography on silica gel
using EtOAc:hexane 1:10; yield 1.04 g (66%) of a light yel-
low oil. (Anal. Calc. for C22H22OS: C, 79.00; H, 6.63.
Found: C, 78.54; H, 6.59%). HRMS(EI): M 334.1359. Anal.
Calc. for C22H22OS: 334.1391. 1H NMR (300 MHz,
CDCl3): d 1.1–1.2 (m, 2H), 1.4–1.6 (m, 2H), 1.9–2.1 (m,
4H), 2.4–2.5 (m, 2H), 3.2–3.5 (m, 2H), 7.2–7.4 (m, 9H).
13C NMR (75 MHz, CDCl3): d 11.5, 13.8, 19.2, 22.3, 33.3,
35.1, 36.6, 72.1, 118.7, 123.6, 125.0, 126.0, 126.03, 128.3,
130.2, 136.2, 141.2, 142.5, 143.1, 144.5. MS(EI): 334 (M+,
3%), 316 (4), 185 (100), 165 (7), 150 (50), 128 (9), 55 (5).
1
92.49; H, 7.58%). H NMR (CD2Cl2, 300 MHz): d 1.8–
2.4 (m, 5H), 2.6 (m, 1H), 2.7 (m, 2H), 3.2–3.4 (m, 2H),
3.5 (s, 2H), 6.23 (dt, J = 1.7, 5.2 Hz, 1H), 6.48 (m, 1H),
6.55 (dt, J = 1.8, 5.1 Hz, 1H), 6.61 (d, 1H), 7.33 (m, 1H),
7.46 (m, 2H), 7.55 (d, J = 7.3 Hz, 1H). 13C NMR (CD2Cl2,
75 MHz): d 20.5, 23.0, 27.9, 31.6, 37.6, 37.7, 51.9, 118.9,
120.4, 121.0, 124.1, 125.0, 126.8, 130.6, 131.3, 137.6,
139.7, 143.5, 144.5, 145.9, 166.5. MS(EI): 272 (M+,
100%), 257 (15), 243 (49), 228 (16), 182 (14), 165 (16),
115 (9), 91 (5).
4.5. cis-2-(Cyclopentadienyl)-10,20,30,40-tetrahydro-9H-
spiro[cyclobutane-1,10-fluorene] (5)
One molar LiBEt3H in THF (2.8 mL) was added
dropwise to 2-(cyclopenta-2,4-dienylidene)-10,20,30,40-
tetrahydro-9H-spiro[cyclobutane-1,10-fluorene] (4) (500 mg,
1.8 mmol) in THF (10 mL) at 0 ꢁC. The mixture stirred at
room temperature for 1.5 h and poured into ice/water
(100 mL) and dichloromethane (100 mL), the two layers
separated, the water phase extracted with dichloromethane
(2 · 50 mL), the combined organic solutions washed with
water (3 · 10 mL), dried (MgSO4) and the residual material
subjected to flash chromatography on silica gel using CH2-
Cl2:hexane 1:40; yield 151 mg (30%) of a colourless oil
4.3. 10,20,30,40-Tetrahydro-9H-spiro[cyclobutane-1,10-
fluoren]-2-one (3)
Aqueous 35% HBF4 (1.3 mL) was added to a solution of
1,2,3,4-tetrahydro-9H-1-[1-(phenylthio)cyclopropyl]fluoren-

360
G. Langli et al. / Journal of Organometallic Chemistry 691 (2006) 356–360
consisting of a 1:1 mixture of two double bond isomers.
HRMS(EI): 274.1723. Anal. Calc. for C21H22:
1H), 6.59 (q, J = 2.0, 3.3 Hz, 1H), 6.73 (q,J = 1.6,
3.2 Hz, 1H), 7.08–7.11 (m, 1H), 7.17–7.21 (m, 1H), 7.37
(dd, J = 0.5, 5.1 Hz, 1H, 7.47 (dd, J = 0.5, 5.1 Hz, 1H).
13C NMR (CD2Cl2, 75 MHz): d 19.5, 20.1, 23.9, 30.6,
38.5, 49.1, 50.8, 95.7, 108.2, 113.5, 118.6, 120.0, 123.2,
123.5, 125.1, 126.1, 126.4, 126.5, 132.7, 138.2, 142.1.
MS(EI): 432 (M+, 95%), 396 (20), 341 (47), 303 (22), 251
(68), 182 (56), 165 (70), 152 (31), 91 (25).
M
274.1721. 1H NMR (CD2Cl2, 300 MHz): d 1.9–3.6 (m,
15H), 6.1 (m, 1H), 6.3 (m, 1.5H), 6.4 (m, 0.5H), 7.1–7.4
(m, 4H). 13C NMR (CD2Cl2, 75 MHz): d 20.3, 20.5, 21.6,
22.0, 23.02, 23.03, 32.1, 32.3, 38.7, 38.9, 40.0, 40.1, 41.3,
43.4, 46.0, 46.7, 47.4, 48.8, 118.17, 118.24, 123.5, 123.6,
124.1, 124.2, 125.8, 126.2, 126.3, 126.4, 131.6, 132.3,
133.8, 134.6, 137.0, 137.2, 143.6, 143.8, 145.88, 145.90,
145.99, 146.0, 149.3, 151.9. MS(EI): 274 (M+, 8%), 195
(12), 182 (100), 167 (17), 153 (7), 141 (9), 91 (7). MS(CI,
CH4): 275 (M+, 63%), 211 (17), 195 (15), 183 (100), 93
(75), 79 (8), 49 (9).
References
[1] L. Resconi, L. Cavallo, A. Fait, F. Piemontesi, Chem. Rev. 100
(2000) 1253–1345.
[2] H.G. Alt, Chem. Rev. 100 (2000) 1205–1221.
[3] P. Schertl, H.G. Alt, J. Organomet. Chem. 545–546 (1997) 553–557.
[4] C. Psiorz, G. Erker, R. Fro¨lich, M. Grehl, Chem. Ber. 128 (1995)
357–364.
[5] G. Erker, C. Psiorz, R. Fro¨lich, Z. Naturforsch b 50 (1995) 469–
475.
4.6. 2-(g5-Cyclopentadienyl)-10,20,30,40-tetrahydro-
spiro[cyclobutane-1, 10-(g5-fluorenyl)]zirconium dichloride
(7)
[6] E.J. Thomas, J.C.W. Chien, M.D. Rausch, Macromolecules 33
(2000) 1546–1552.
[7] M. Rolandsgard, S. Baldawi, D. Sirbu, V. Bjørnstad, C. Rømming,
K. Undheim, Tetrahedron 61 (2005) 4129–4140.
[8] M.L. Falck-Pedersen, C. Rømming, K. Undheim, Tetrahedron 55
(1999) 8525–8538.
[9] F.H. Howell, D.A.H. Taylor, J. Chem. Soc. (1957) 3011–3015.
[10] K. Tanaka, H. Uneme, S. Matsui, A. Kaji, Bull. Chem. Soc. Jpn. 55
(1982) 2965–2972.
[11] T. Imamato, Pure Appl. Chem. 62 (1990) 747–752.
[12] (a) B.M. Trost, Acc. Chem. Res. 7 (1974) 85–92;
(b) B.M. Trost, D.E. Keeley, H.C. Arndt, M.J. Bogdanowicz, J. Am.
Chem. Soc. 99 (1977) 3088–3100.
[13] K.J. Stone, R.D. Little, J. Org. Chem. 49 (1984) 1849–1853.
[14] F. Piemontesi, I. Camurati, L. Resconi, D. Balboni, A. Sironi, M. Moret,
R. Zeigler, N. Piccolrovazzi, Organometallics 14 (1995) 1256–1266.
[15] L. Resconi, F. Piemontesi, I. Camurati, D. Balboni, A. Sironi, M. Moret,
H. Rychlicki, R. Zeigler, Organometallics 15 (1996) 5046–5059.
[16] (a) J.A. Ewen, J. Am. Chem. Soc. 106 (1984) 6355–6364;
(b) G. Moscardi, L. Resconi, Organometallics 20 (2001) 1918–1931;
(c) C.J. Schaverien, R. Ernst, P. Schut, T. DallÕOcco, Organometallics
20 (2001) 3436–3452.
[17] N. Takeda, T. Imamoto, Org. Synth. 76 (1999) 228–238.
[18] SMART and SAINT. Area-Detector Control and Integration Software
Version 5.054. Bruker Analytical X-ray Instruments Inc., Madison,
WI, USA, 1998.
[19] G.M. Sheldrick, SADABS Version 2.01. Program for Empirical
Correction of Area Detector Data, University of Go¨ttingen, Ger-
many, 2000.
[20] G.M. Sheldrick, SHELXTL, Structure Determination Programs Version
5.10, Bruker Analytical X-ray Instruments Inc., Madison, WI, USA,
1997.
1.6 M n-BuLi in hexane (4.2 mL, 6.8 mmol) was
added to a solution of cis-2-(cyclopentadienyl)-10,20,30,40-
tetrahydro-9H-spiro[cyclobutane-1,10-fluorene] (5) (890 mg,
3.25 mmol) in diethyl ether (40 mL) under argon at 0ꢁ.
The reaction mixture was allowed to reach ambient tem-
perature overnight. A tan coloured precipitate was formed.
Filtration, washing with pentane and drying under high
vacuum gave 836 mg (90%) of the dilithiated ligand. The
product was suspended in toluene (30 mL), the temperature
lowered to 0 ꢁC and solid zirconium tetrachloride was
added in one portion. The reaction mixture was allowed
to reach room temperature overnight. The solution was
then filtered through a glass sinter, and the resultant clear
dark yellow solution was concentrated to approximately
3 mL. Pentane (40 mL) was added and a light yellow pre-
cipitate was formed. The precipitate was filtered, washed
with pentane (15 mL) and dried under high vacuum; yield:
317 mg (25%) of a light yellow solid. Slow evaporation of a
toluene solution yielded crystals suitable for X-ray analysis.
(Anal. Calc. for C21H20Cl2Zr: C, 58.05; H, 4.64. Found: C,
58.27; H, 5.03%). HRMS(EI): M 431.9997. Anal. Calc. for
C21H20Cl2Zr: 431.9989. 1H NMR (CD2Cl2, 300 MHz):
1.50–1.56 (m, 1H), 1.93–1.96 (m, 2H), 2.01–2.09 (m, 2H),
2.36–2.39 (m, 2H), 2.57–2.62 (m, 1H), 2.72–2.77 (m, 1H),
3.17 (dt, J = 2.0, 9.5 Hz, 1H), 3.75 (t, J = 5.2 Hz, 1H),
6.01 (q, J = 1.5, 3.1 Hz, 1H), 6.18 (q, J = 1.9, 3.3 Hz,