Synthesis, characterization and structures of zirconocene complexes of sterically demanding pentaphenylcyclopentadienyl and tetraphenyl-m-tolyl cyclopentadienyl ligands

Article abstract of DOI:10.1016/S0022-328X(03)00637-5

The synthesis, characterization and catalytic activity of zirconium complexes containing bulky pentaarylcyclopentadienyl ligands are reported. The monocyclopentadienyl 12-electron complex, trichloropentaphenylcyclopentadienylzirconium(IV), C₅Ph₅ZrCl₃ (I), has an unusual monomeric structure in the solid state and has short Zr-ligand distances suggesting that the complex has significant Lewis acidity. The phenyl rings adopt a propeller arrangement in the solid state; VT ¹H-NMR measurements of the analogous trichloro(tetraphenyl- m -tolylcyclopentadienyl)zirconium(IV) (II) indicate that there is rapid rotational motion of the phenyl rings. The Lewis acidity of this complex is manifested in its ability to catalyze the [4+2] cycloadditions of acrolein and methyl acrylate to cyclopentadiene. The sandwich complex, C₅Ph₅ CpZrCl₂ (III), has more typical Zr-ligand distances, but has a more parallel arrangement of the two cyclopentadienyl rings and does not display the reactivity shown by I and II.

Full text of DOI:10.1016/S0022-328X(03)00637-5

Journal of Organometallic Chemistry 682 (2003) 8ꢀ13
/
www.elsevier.com/locate/jorganchem
Synthesis, characterization and structures of zirconocene complexes
of sterically demanding pentaphenylcyclopentadienyl and
tetraphenyl-m-tolyl cyclopentadienyl ligands
Deborah L. Greene a, Alex Chau a, Marisa Monreal a, Carmen Mendez a, Iris Cruz a,
Tambi Wenj a, Wayne Tikkanen a,*, Brian Schick b, Katherine Kantardjieff b
a Department of Chemistry and Biochemistry, California State University, 5151 State University Drive, Los Angeles, CA 90032, USA
b Department of Chemistry and Biochemistry, California State University, State University Drive, Fullerton, CA 92634, USA
Received 15 May 2003; received in revised form 7 July 2003; accepted 8 July 2003
Abstract
The synthesis, characterization and catalytic activity of zirconium complexes containing bulky pentaarylcyclopentadienyl ligands
are reported. The monocyclopentadienyl 12-electron complex, trichloropentaphenylcyclopentadienylzirconium(IV), C5Ph5ZrCl3 (I),
has an unusual monomeric structure in the solid state and has short Zrꢀligand distances suggesting that the complex has significant
/
1
Lewis acidity. The phenyl rings adopt a propeller arrangement in the solid state; VT H-NMR measurements of the analogous
trichloro(tetraphenyl-m-tolylcyclopentadienyl)zirconium(IV) (II) indicate that there is rapid rotational motion of the phenyl rings.
The Lewis acidity of this complex is manifested in its ability to catalyze the [4ꢁ
/
2] cycloadditions of acrolein and methyl acrylate to
cyclopentadiene. The sandwich complex, C5Ph5CpZrCl2 (III), has more typical Zrꢀ/ligand distances, but has a more parallel
arrangement of the two cyclopentadienyl rings and does not display the reactivity shown by I and II.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Zirconocene; Pentaphenylcyclopentadienyl; X-ray structure; Monocyclopentadienyl; Lewis
1. Introduction
nium(IV) (II) and prochiral C5Ph5CpZrCl2 (III), are
reported. The syntheses and structures of I and III, a 1H
VT-NMR study of II and results of the study of [4ꢁ2]
The development of catalysts for promoting stereo-
selective organic transformations is an important goal
[1]. One method that has enjoyed considerable success is
the development of asymmetric catalysts for the desired
/
cycloaddition reactivity of I and II are reported.
transformations [2ꢀ
developing chiral half sandwich or piano stool Lewis
acid complexes to promote CÃC bond formation
reactions like [4ꢁ2] cycloaddition among other reac-
tions. Half sandwich complexes offer great potential as
chiral catalysts as recently summarized [12]. In this
paper, the synthesis and characterization of complexes
containing the pentaphenylcyclopentadienide ligand
(C5Ph5) with zirconium(IV), C5Ph5ZrCl3 (I), an analo-
gue, m-tolyltetraphenylcyclopentadienyltrichlorozirco-
/
11]. Our work is directed towards
2. Results and discussion
/
We have previously reported the preparation and
characterization of two complexes of zirconium with
C5Ph5 [13]. Our routes to the piano stool complex, I,
(Fig. 1) and the bent sandwich complex, III, (Fig. 2) are
shown below along with their ORTEP diagrams.
Complex I, C5(C6H5)5ZrCl3, is obtained by refluxing
a mixture of lithium pentaphenylcyclopentadienide and
zirconium tetrachloride in toluene for 2 days. Removal
of the solvent and extraction of the solids with refluxing
xylenes gives I in 88.4% yield. The pale yellow solid I
often crystallizes from the xylenes upon cooling. The
structure shows that the phenyl rings in I adopt a
/
* Corresponding author. Tel.: ꢁ
6490.
E-mail address: wayne@calstatela.edu (W. Tikkanen).
/
1-32-3343-2372; fax: ꢁ1-32-3343-
/
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00637-5

D.L. Greene et al. / Journal of Organometallic Chemistry 682 (2003) 8ꢀ
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9
Fig. 1. Synthesis and structure of I.
propellor arrangement to reduce steric contacts. The 1H-
NMR of I (C6D6) shows a complex multiplet centered at
d 7.05 for the phenyl protons. The 13C-NMR show one
resonance for the ortho and meta carbons, suggesting
that there is a process that renders these atoms
equivalent on the NMR time scale or that they have
coincidental chemical shifts. Chirality due to static left
or right handed propeller orientations of the phenyl
groups would lead to diastereomers upon substitution of
chiral ligands for the chloride ligands of I. If the phenyl
rings had facile rotation about the ipso-carbon-cyclo-
pentadienyl carbon-bond, then interconversion between
right-handed and left-handed propellers would be rapid.
In order to investigate the dynamic behavior of this
five bladed propeller we prepared trichloro-(meta-tolyl-
tetraphenylcyclopentadienyl)zirconium(IV) (II) through
methods similar to those used to synthesize I. This
modification installs a spectroscopic flag, the methyl
group (a singlet at d 2.08 and increases the solubility of
II over that of I. The meta-tolyl group is expected to
have similar steric bulk to a phenyl group since the
methyl group is relatively remote and should not cause
significant changes in the rotational barrier, compared
to an ortho substitution. The 1H-NMR spectra obtained
rotation of the rings, perhaps through mechanisms
analogous to that proposed for the ring rotations in
tri-aryl boranes [14] and more recently for polyphenyl-
cyclopentadienes [15].
Metathesis of I with lithiumcyclopentadienide in
dichloromethane for 24 h gives a pale yellow suspension.
Removal of the solvent and extraction of the residue
with dichloromethane gives the pale yellowꢀ
product CpC5Ph5ZrCl2 (III) in 95.1% yield. Analytically
pure yellowꢀgreen crystalline material is obtained by
/
green
/
Soxhlet extraction of the crude with refluxing xylenes
resulting in a final yield of 77%. Complex III is sparingly
soluble in toluene and benzene and more soluble in
polar organic solvents such as chloroform and dichlor-
omethane. In the 1H-NMR (CD2Cl2), a singlet is
observed for the C5H5 at d 6.60, and the phenyl ring
protons are observed as multiplets centered at d 6.98
and 7.09 ppm. The 13C{1H}-NMR is also consistent
with the given formulation.
The structure of C5Ph5ZrCl3 (Fig. 1, Tables 1 and 2) is
unusual for two reasons. It is a monomeric piano stool,
not undergoing the oligomerization observed in the solid
state in other Cp?ZrCl3 complexes [16] and has short
Zrꢀligand bond distances. The monomeric structure is
/
in CD2Cl2 at ambient temperature and ꢂ
virtually identical, confirming the presence of a facile
/
90 8C were
likely due to the steric demands of the C5Ph5 ligand;
changes in geometry have been observed upon substitu-
Fig. 2. Synthesis and structure of III.

10
D.L. Greene et al. / Journal of Organometallic Chemistry 682 (2003) 8ꢀ13
/
Table 1
Summary of structural parameters for I and III with comparison values
˚
Cp(cnt) (A)
˚
Cl (A)
Compound
(cnt)Zr(cnt) (8)
ZrÃ
/
ClÃ
/
ZrÃ
/
Cl (8)
ZrÃ
/
Reference
C5Ph5ZrCl3
(CpZrCl3)n (pseudo-octahedral)
C5Ph5CpZrCl2
n/a
n/a
2.222
2.196
101.2
n/a
96.9
2.34
2.419 (non-bridging)
2.42
This work
[18]
This work
132.9
2.211 (Cp)
2.302 (C5Ph5)
2.193
(CH2)3(h5-C5H4)2ZrCl2
(h5-C5H4-CH3)2ZrCl2
Me2Si(h5-C5H4)2ZrCl2
((SiMe3)3C5H2)2ZrCl2
129.5
128.9
125.4
135.41
96.92
2.441
2.442
2.435
2.429
[27]
[19]
[19]
[20]
2.197
2.246
97.98
96.2
‘pocket’ by about 5 pm. The centroidꢀ
angle of 132.98 is larger than that of (MeÃ
/
Zrꢀ
/
centroid
Table 2
X-ray collection data for I and III
/Cp)2ZrCl2
(128.98) [19] but not as open as the 135.48 in hexa-
kis(trimethylsilyl)zirconocene dichloride [20]. The dis-
tances to the chloride ligands (242 pm) are somewhat
smaller than those for zirconocene dichloride (244.3 pm)
Compound
I
III
Empirical formula
Formula weight
C
35H25Cl3Zr
C40H30Cl2Zr
672.76
643.12
0.4ꢃ
Pna21
Crystal size (mm) 0.4ꢃ
Space group
Cell constants
/
/0.1
0.50ꢃ
P21/c
/
0.59ꢃ0.50
/
[19] as is the Cl1Ã
/
ZrÃCl2 angle of (96.698) when
/
compared to that of other zirconocene dichlorides
(988). The structural similarities between the C5Ph5
complex and the severely hindered hexakis(trimethylsi-
lyl)zirconocenedichloride [20] complexes reflect like
steric effects; however, the lack of a second bulky ligand
in III should result in greater reactivity by allowing
attack from the side of the less bulky Cp ligand.
˚
a (A)
16.680(3)
12.4266(6)
14.0366(7)
17.7939(9)
92.9590(10)
3099.6(3)
4
˚
b (A)
10.1308(15)
17.835(3)
n/a
˚
c (A)
b (8)
3
˚
V (A )
3013.8(8)
4
Z
Diffractometer
used
Radiation
SMART CCD area de- SMART CCD area de-
tector
Mo
As 12-electron complexes, I and II are expected to
display Lewis acidity as observed in other such low-
tector
Mo
R1 (3422F ꢀ
R1 (7153 all)
wR2
/
4sF ) 0.0387
0.1284
0.0499
0.0579
0.1335
0.1130
0.1593
electron count complexes [11,21ꢀ/24]. Both complexes I
and II accelerate the [4ꢁ2] cyclization reaction of
/
acrolein and methyl acrylate with cyclopentadiene and
also change the selectivity towards endo and exo isomers
compared to the control reactions. A wide variety of
conditions (different temperatures, orders of addition,
rate of addition and diene:dienophile ratio) were ex-
plored to optimize yields of the different isomers and to
gain some insight to the mechanism of the reaction. The
selectivity and yields reported below represent a mini-
mum of three runs each.
tion of a C5Ph5 ligand for a Cp ligand [17]. Also,
complex I is formally a 12-electron complex; the electron
deficiency is reflected in the shorter metalꢀ
dienide and metalꢀchloride bonds. The C5Ph5 centroid
and the chloride ligands in I are about 8 pm closer to the
Zr atom than in the 16-electron complex III. Compar-
/
cyclopenta-
/
For the reactive dienophile, acrolein, the catalyzed
reaction proceeds to completion in about an hour and
ison of Zrꢀ
finds that the ZrÃ
even though the ZrÃ
shorter in I [18]. These differences may reflect either
donor strength or steric differences between the two
cyclopentadienyl ligands.
/
ligand distances with oligomeric CpZrCl3
CpꢁPRO centroid is 2.6 pm longer
Cl (unbridged) distance is 8.0 pm
/
the control proceeds to ꢀ95% conversion at room
/
/
temperature. The endo:exo ratio for the uncatalyzed
reaction of acrolein and cyclopentadiene at 294 K is
about 4.390.02. At loadings of 1.0 mol.% I or II,
/
endo:exo ratios of about 2.0 were obtained when
cyclopentadiene is added to a solution containing the
The X-ray crystal structural data for III (Fig. 2,
Tables 1 and 2) shows a systematic variation of the ZrÃ
/
catalyst and acrolein (I; 2.059
Reaction at ꢂ85 8C for 25 h with 1.0 mol.% loading
of II gives endo:exo ratios of 2.4390.47 with 62%
conversion and the uncatalyzed control has an endo:exo
ratio of 3.3690.23 with only 13% conversion.
/
0.05: II; 2.0990.08).
/
C distances; the average ZrÃ
/
C distance to the penta-
/
phenylcyclopentadienyl ligand (260.4 pm) are all longer
than that to the cyclopentadienyl group (251.2 pm). The
/
ZrÃ
than the ZrÃ
tion, the distances to each ring show significant varia-
tion, with those ZrÃC distances above the ‘pocket’ (C1,
C2 and C3)being longer than those away from the
/Cp(cnt) distance (221.1 pm) is about 9 pm shorter
/
/
C5Ph5(cnt) distance (230.2 pm). In addi-
Methyl acrylate cycloaddition shows different selec-
tivity. At room temperature, the control reaction runs
nearly to completion in 2 h, with an endo:exo ratio
/

D.L. Greene et al. / Journal of Organometallic Chemistry 682 (2003) 8ꢀ
/13
11
4.159
/
0.03. However, the presence of I or II increases
3.3. C5(C6H5)5ZrCl3 (I)
the endo:exo ratio. Best results in our hands came from
adding cyclopentadiene to a solution containing the
dienophile and catalyst. At 1.0 mol.% II, endo:exo ratios
Pentaphenylcyclopentadienyltrichlorozirconium (I)
was prepared by refluxing 3.462 g of lithium pentaphe-
nylcyclopentadienide with 2.651 g of zirconium tetra-
of 17.71.9
10.5990.87 for I. The selectivities decrease with lower
catalyst loading. Optimal conditions appear to be at
lower temperature; at ꢂ15 8C and 1 mol.% II, endo:exo
ratios of 24.791.1 were obtained with complete con-
sumption of methyl acrylate in 18 h. Catalyst I gave
endo:exo ratio of 22.090.4 with 88.2% conversion and
the uncatalyzed reaction mixture had an endo:exo ratio
of 4.8590.13 with only 15% consumption of methyl
acrylate at ꢂ15 8C after 18 h. The endo:exo ratio
/0.06 were obtained, with lower ratios of
/
chloride for ꢁ24 h in 50 ml dry xylene. The solvent was
/
removed in vacuo and the reddish brown solid was then
extracted with 50 ml of dry xylene for 24 h in a Soxhlet
type extractor. The solvent was removed in vacuo to
give a yellow solid and the remaining residue extracted
for an additional 24 h. The total product obtained from
two successive extractions was 4.35 g with an 88.4%
yield. Analytically pure crystalline material may be
/
/
/
/
1
/
obtained by slow cooling of the xylenes solution. H-
obtained with II is higher than that reported for a
cationic zirconocene catalyst reported by Hong et al.,
which had endo:exo ratios of 22 at even lower tempera-
tures with lower conversion [6].
Current efforts are directed at understanding the root
of the different selectivity observed for the two dieno-
philes by computational methods as well as investigating
the versatility of these achiral precursors. We are
investigating the coordination chemistry of I and II
with the methacrolein and methyl acrylate by NMR
methods and pursuing the synthesis of chiral derivatives
of I and II by the substitution of chloride ligands with
chiral alkoxides.
NMR (CDCl3): overlapping multiplets centered at d
7.2. 13C{1H}-NMR (CDCl3, 75 MHz): C5(C6H5), d
128.0; C5(C6H5), ipso-C, d 133.8; o-C d 131.7; m-C, d
132.0; p-C,
d
65.25(65.36); H, 4.10(3.92)%.
127.8. Anal. Found (Calc.): C,
3.4. X-ray structure of I
The sample crystallized as yellow hexagonal plates
from a slowly cooled, hot xylenes solution. One plate of
ca. 0.4ꢃ
with graphite monochromated Moꢀ
uꢄ28.288 by a Bruker SMART CCD area detector
/
0.4ꢃ/0.1 mm was sampled by X-ray diffraction
/
Ka radiation up to
/
mounted on a three-circle goniostat. The diffraction
pattern of the crystal was consistent with a Pna21
orthorhombic space group with cell dimensions of aꢄ
/
3. Experimental
˚
16.680(3), bꢄ
/
10.1308(15), and cꢄ17.835(3) A. 31 756
/
observations were measured and averaged with their
symmetry-related reflections to form 7153 unique reflec-
tions. Of the unique reflections, 3422 reflections had an
3.1. General considerations
Most of the compounds described were air sensitive
and were prepared with use of either Schlenk or high-
vacuum techniques. Solid compounds were manipulated
in a Vacuum Atmospheres Corp. (VAC) HE-43 Dri-Lab
with an HE-63P Pedatrol pressure regulator and HE-
393 Dri Train. The inert gas used in the glovebox and
Schlenk and vacuum lines was either nitrogen or argon,
which was further purified by passage through activated
intensity I ꢀ/2sI. Rint
ꢄ0.0982. The structure was
/
solved by Patterson methods and subsequently refined
to convergence with the SHELXTL software package. All
non-hydrogen atoms were refined anisotropically, and
hydrogen atoms were isotropically refined from initial
ideal positions. The final agreement statistic of 3422
structure factor amplitudes having F ꢀ
/
4sF were R1ꢄ
/
3.87% based on F, and wR2ꢄ4.99% based on I.
/
˚
Chemalog R3-11 catalyst and activated 4 A molecular
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic
Data Center, CCDC No. 132703.
sieves. Solvents were all reagent grade or better and were
further purified by standard techniques [25]. Pentaphe-
nylcyclopentadiene and the lithium salt were prepared as
previously described [26] with minor modifications.
3.5. ((m-CH3Ã/C6H4)(C6H5)4C5)OH
3.2. Physical measurements
Under an atmosphere of nitrogen, 10.0 g tetraphe-
nylcyclopentadienone is dissolved with stirring in 150 ml
of freshly distilled toluene. Next, m-tolylmagnesium
chloride (3.0 M in ether) is added dropwise until the
purple solution turns golden yellow (17.3 ml of the
1H- and 13C-NMR spectra were obtained with Bruker
AM-400 or AM-300 spectrometers. Proton NMR spec-
tra were referenced by either the residual proton
resonance or internal tetramethylsilane. Elemental ana-
lyses were performed by Schwarzkopf Microanalytical
Laboratories, Woodside, NY.
Grignard added over 1ꢀ2 min). The solution is then
/
placed over an ice bath and quenched dropwise using
100 ml H2SO4 (1 M degassed with N2). The organic

12
D.L. Greene et al. / Journal of Organometallic Chemistry 682 (2003) 8ꢀ13
/
layer is separated, washed three times with 75 ml H2O,
and dried over MgSO4. Next, the toluene is removed in
vacuo providing a tan/brown residue. The residue is
placed over a sintered glass filter and washed several
times with heptane to provide a golden yellow solid.
Recrystallization from heptanes provided the analytical
CH3Ã
/
C6H4)(C6H5)4C5)H with n-butyllithium) is placed
along with 1.00 g zirconium(IV) tetrachloride in 40 ml of
dry toluene. The purple suspension is left to reflux 48 h.
The toluene is then removed under vacuum and the
residue transferred to a continuous extraction appara-
tus. The dark tan solids are continuously extracted for
24 h with toluene. The product crystallizes from the
extraction liquors to provide 2.06 g yellow to tan
granular crystals (73% yield). 1H-NMR (CDCl3): d
2.07 (s, CH3, 3H); d 6.8, 7.12 (m, Ph, 24H).13C{1H}-
sample as yellow nodules 88% yield m.p. 167ꢀ170 8C.
/
The residue provided before recrystalization was of
sufficient quality to be used, as is, for further synthesis
(m.p. 160ꢀ
165). 1H-NMR (CDCl3): d 2.27 (s, CH3, 3H);
/
d 2.44 (s, OH, 1H); d 7.02 (m, Ph); d 7.10 (m, Ph). d
7.23 (s(br), Ph). 13C{1H}-NMR (CDCl3): d 21.73 CH3;
d 90.16 C-1: d 147.93, 142.37, 137.86, 135.11, 133.90,
130.39, 129.91, 129.54, 128.35, 127.85, 127.70, 127.28,
127.01, 126.93, 125.84, 125.72, 122.09 Ph and sp2
cyclopentadiene carbons. Anal. Found (Calc.): C,
90.72(90.65); H, 5.92(6.04)%.
NMR (CDCl3): ((m-CH3Ã
/
C6H4)(C6H5)4C5)ZrCl3 d
21.3 CH3; d 137.23: 133.7, 132.7, 132.0, 131.72,
131.69, 131.41, 129.06, 128.70, 127.98, 127.73, 127.67,
127.55, Ph and C5 Anal. Found (Calc.): C, 65.79(65.87);
H, 4.14(4.62); Cl, 16.18(16.05)%.
3.8. CpC5Ph5ZrCl2 (III)
3.6. ((m-CH3Ã/C6H4)(C6H5)4C5)H
Cyclopentadienyl(pentaphenylcylopentadienyl)di-
chlorozirconium III, was prepared by stirring 4.120 g of
A 4.78 g sample of ((m-CH3Ã
/
C6H4)(C6H5)4C5)OH is
pentaphenylcyclopentadienyltrichlorozirconium
and
dissolved in 100 ml glacial acetic acid with heating. An
aliquot of 5.0 ml conc. HCl is added and the solution
refluxed for 1 h. Next, 2.72 g Zn powder is added along
with 20 ml more glacial acetic acid. The mixture is left to
reflux. After 24 h the reaction mixture is gravity filtered
hot and to the filtrate is added 300 ml of water. The
precipitate is collected on a Buchner funnel and washed
with ample water providing a pale yellow powder.
Recrystallization from dry toluene provided the analy-
0.451 g of lithium cyclopentadienide in 30 ml of dry
dichloromethane for 24 h at room temperature. Re-
moval of the solvent in vacuo gave a yellow brown solid.
The solid was then Soxhlet extracted with 60 ml of dry
dichloromethane to yield 4.021 g of II as a pale yellow
powder in a 95.1% yield. Analytically pure crystalline
material may be obtained by slow cooling of a hot
1
xylenes solution of II. H-NMR (CDCl3): C5H5, d 6.55
d
7.10 (m),d 6.94. 13C{1H}-NMR
(s); C5(C6H5)5
tical sample in (yellow faceted crystals m.p. 207ꢀ
with 95% yield. The powder provided before recrystalli-
zation was of sufficient quality to be used, as is, for
/
210 8C)
(CDCl3): C5H5, d 118.6; C5(C6H5), ipso-C d 133.5; m-
C d 132.0; p-C d 127.5; o-C d 127.3; C5(C6H5) d 129.9.
Anal. Found (Calc.): C, 71.40(71.41); H, 4.49(4.49)%.
further synthesis (m.p. 189ꢀ199 8C).
/
The synthetic procedure results in a statistical mixture
of the three isomers, 1:2:2 of 1-m-tolyltetraphenylcyclo-
pentadiene, 2-m-tolyltetraphenylcyclopentadiene and 3-
m-tolyltetraphenylcyclopentadiene, respectively. 1H-
NMR (CDCl3): d 2.08, 2.15, 2.23 (s; CH3; 3H, 2:2:1
intensities, respectively): d 5.05, 5.09 (s; Cp ring CH; 1
H, 1:4 intensities, respectively): d 6.8 (m; Ph); d 7.0 (m;
Ph); d 7.2 (m, Ph) (total Ph; 24H). 13C{1H}-NMR
(CDCl3): d 21.48 (1C); 21.35 (2C); 21.29 (2C) CH3; d
62.56 C-1: d 146.67, 146.44, 146.21, 144.13, 144.01,
143.88, 143.84, 138.20, 138.16, 137.81, 137.24, 136.91,
136.23, 136.19, 135.98, 135.83, 135.62, 130.78, 130.09,
129.78, 129.51, 129.18, 129.03, 128.99, 128.93, 128.52,
128.50, 128.43, 128.32, 127.82, 1237.78, 127.64, 127.49,
127.39, 127.14, 127.09, 126.62, 126.47, 126.54, 126.12,
125.49, Ph and C5. Anal. Found (Calc.): C, 93.87(93.41);
H, 6.13(6.00)%.
3.9. X-ray structure of III
The sample crystallized as dark green violet prisms
from a slowly cooled hot xylenes solution. One prism of
ca. 0.5ꢃ
with graphite monochromated Moꢀ
uꢄ28.288 by a Bruker SMART CCD area detector
/
0.5ꢃ/0.5 mm was sampled by X-ray diffraction
/
Ka radiation up to
/
mounted on a three-circle goniostat. The diffraction
pattern of the crystal was consistent with a P21/c
monoclinic space group with cell dimensions of aꢄ
/
˚
14.0366(7), and cꢄ17.7939(9) A, and
12.4266(6), bꢄ
/
/
with bꢄ92.9590(10)8. 30 932 observations were mea-
/
sured and averaged with their symmetry-related reflec-
tions to form 7076 unique reflections. Of the unique
reflections, 4562 reflections had an intensity I ꢀ
Rint 0.1192 before correction factors were refined for
absorption and decay, and Rint 0.0456 after correc-
/4sI.
ꢄ
/
ꢄ
/
tion. The structure was solved by Patterson methods
and subsequently refined to convergence with the
SHELXTL software package. All non-hydrogen atoms
were refined anisotropically, and hydrogen atoms were
isotropically refined from initial ideal positions. The
3.7. ((m-CH3Ã
/
C6H4)(C6H5)4C5)ZrCl3 (II)
Under an atmosphere of nitrogen, 2.00 g of the
lithium dienide (prepared by deprotonation of ((m-

D.L. Greene et al. / Journal of Organometallic Chemistry 682 (2003) 8ꢀ
/13
13
final agreement statistics of 4562 structure factor
amplitudes having F ꢀ4sF were R1ꢄ5.79% based on
F, and wR2ꢄ13.35% based on I. Crystallographic data
Chemical Society and to the National Institutes of
Health MARC Program Grant T34 GM 08228 (MB)
for support of this research.
/
/
/
for the structural analysis has been deposited with the
Cambridge Crystallographic Data Center, CCDC No.
132704.
References
4. Cycloaddition studies
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Schlenk flask, evacuated and filled with N2. The solid
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/
85 8C) were performed by
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mꢃ
/
0.53 mmꢃ1.5 mm column and thermal conductiv-
/
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¨
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The purchase of the Bruker AM-400 NMR Spectro-
meter was supported in part by PHS grant RR-08101
from the NIH-MBRS program, NSF Grant DMB-
8503839 and grants from the W.M. Keck Foundation
and the Camille and Henry Dreyfus Foundation.
Acknowledgment is made to the donors of the Petro-
leum Research Fund, administered by the American
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