Synthesis and characterization of sterically expanded ansa- η1-fluorenyl-amido complexes

Article abstract of DOI:10.1016/j.poly.2005.03.011

The octamethyloctahydrodibenzofluorenyl (Oct) ligand has been incorporated into twelve ansa-Oct-amido complexes having the general structures Me ₂Si(η¹-C₂₉H₃₆) (η¹-N-^tBu)MX₂ ? L or Me ₂Si(η⁵-C₂₉H₃₆) (η¹-N-^tBu)MX₂ (M = Zr or Hf): 2 (X = Cl, L = Et₂O); 3 (X = Br, L = Et₂O); 4 (X = Me, L = Et ₂O); 5 (X = Me, L = THF); 6 (X = CH₂Ph); and 7 (X = CH₂SiMe₃). The solid-state structures have been determined for seven of these complexes by X-ray crystallography, revealing η⁵-C₂₉H₃₆ coordination for the ether-free, pseudotetrahedral species 6-Zr, 6-Hf, and 7-Zr, but η¹-C ₂₉H₃₆ coordination for the ether-bound, trigonal bipyramidal species 2-Zr, 3-Zr, 3-Hf, and 5-Zr. The unusual η¹- C₂₉H₃₆ coordination was assigned because only one metal-carbon bond in each structure was in the range of 2.281-2.330 A?; a second metal-carbon distance was found between 2.731 and 2.847 A?; the remaining metal-carbon distances were found between 3.130 and 4.029 A?. An increase in the hapticity of these and other Oct- and fluorenyl-containing compounds was correlated to a convergence in the carbon-carbon bond lengths within the relevant five-membered rings.

Full text of DOI:10.1016/j.poly.2005.03.011

Polyhedron 24 (2005) 1314–1324
www.elsevier.com/locate/poly
Synthesis and characterization of sterically expanded
ansa-g1-fluorenyl-amido complexes
*
Levi J. Irwin, Joseph H. Reibenspies, Stephen A. Miller
Department of Chemistry, Texas A&M University, College Station, TX 77843-3255, United States
Received 17 January 2005; accepted 8 March 2005
Available online 25 April 2005
Abstract
The octamethyloctahydrodibenzofluorenyl (Oct) ligand has been incorporated into twelve ansa-Oct-amido complexes having the
general structures Me2Si(g1-C29H36)(g1-N-tBu)MX2 Æ L or Me2Si(g5-C29H36)(g1-N-tBu)MX2 (M = Zr or Hf): 2 (X = Cl, L = Et2O);
3 (X = Br, L = Et2O); 4 (X = Me, L = Et2O); 5 (X = Me, L = THF); 6 (X = CH2Ph); and 7 (X = CH2SiMe3). The solid-state structures
have been determined for seven of these complexes by X-ray crystallography, revealing g5-C29H36 coordination for the ether-free,
pseudotetrahedral species 6-Zr, 6-Hf, and 7-Zr, but g1-C29H36 coordination for the ether-bound, trigonal bipyramidal species 2-
Zr, 3-Zr, 3-Hf, and 5-Zr. The unusual g1-C29H36 coordination was assigned because only one metal–carbon bond in each structure
˚
˚
was in the range of 2.281–2.330 A; a second metal–carbon distance was found between 2.731 and 2.847 A; the remaining metal–carbon
˚
distances were found between 3.130 and 4.029 A. An increase in the hapticity of these and other Oct- and fluorenyl-containing com-
pounds was correlated to a convergence in the carbon–carbon bond lengths within the relevant five-membered rings.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: Constrained geometry catalyst; Olefin polymerization; Linear low density polyethylene; Hapticity; Ansa; Fluorenyl
1. Introduction
Si(g5-C5Me4)(g1-N-tBu)TiCl2 (1) [7–10], which relies
on a silicon-linked tetramethylcyclopentadienyl-amido
ligand [11,12].
The world demand for linear low density polyethyl-
ene (LLDPE) grew from 12 billion kg in 2000 to 18
billion kg in 2004 – an annualized growth rate of
about 10% [1]. Despite the numerous advantages asso-
ciated with single-site catalyst technology [2–5], only
about 5% of the current demand of LLDPE is met
with such discrete, organometallic catalysts. Nonethe-
less, this is a rapidly growing percentage that has
spawned considerable research in the area of ansa-
cyclopentadienyl-amido complexes, commonly known
as ‘‘constrained geometry catalysts’’ (CGCs) [6].
Fig. 1 depicts the prototypical titanium CGC, Me2-
Synthetic modification of 1 has led to indenyl- [13–17]
and fluorenyl-containing [18–24] variants, some of
which exhibit enhanced polymerization activity or
increased a-olefin incorporation rates. All structural
characterizations of existing group IV cyclopentadie-
nyl-, indenyl-, and fluorenyl-amido complexes reveal
the expected hapticities: g1 to nitrogen and g5 to the
carbon-based ligand. Very recently, we reported the sole
exception to this rule and found that inclusion of a
sterically expanded fluorenyl ligand, octamethyl-
octahydrodibenzofluorenyl (Oct) [25], resulted in g1
ligation to the Oct moiety; see Me2Si(g1-C29H36)(g1-
N-tBu)ZrCl2 Æ OEt2 (2-Zr) in Fig. 2 [26]. Herein, we
report the synthesis and structural characterization of
several additional ansa-Oct-amido complexes that
*
Corresponding author. Tel.: +1 979 845 2543; fax: +1 979 845 9452.
E-mail address: samiller@mail.chem.tamu.edu (S.A. Miller).
0277-5387/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.03.011

L.J. Irwin et al. / Polyhedron 24 (2005) 1314–1324
1315
2. Results and discussion
2.1. Synthesis of Zr and Hf complexes
The synthesis of zirconium and hafnium Oct-amido
complexes (Scheme 1) parallels that of Okuda for the
synthesis of zirconium fluorenyl-amido complexes [18].
Octamethyloctahydrodibenzofluorene [27] is deproto-
nated with n-butyllithium [25,28] and transferred into
a hexane solution containing excess dimethyldichlorosi-
lane. Subsequent reaction with Me3CNHLi, followed by
double deprotonation with n-butyllithium and combina-
tion with ZrCl4 or HfCl4 provides 2-Zr or 2-Hf. Interest-
ingly, these five steps can be performed in two flasks
(OctLi must be added to excess SiMe2Cl2), without iso-
lation of the intermediates or their separation from salts,
to yield 17 g of 2-Zr as yellow microcrystals in 31.6%
overall yield. The dibromide 3-Zr was obtained from
ZrBr4. Additionally, we have shown that 3-Zr and
3-Hf can be synthesized from the dichlorides 2-Zr and
2-Hf via direct halide exchange with an excess of LiBr
in diethyl ether.
2-Zr and 2-Hf are readily derivatized with alkylating
agents. The use of methyllithium with diethyl ether as
solvent provides diethyl ether adducts 4-Zr and 4-Hf,
whereas with methylmagnesium chloride in the presence
of tetrahydrofuran, THF adducts 5-Zr and 5-Hf are ob-
tained. The use of larger alkylating agents does not af-
ford ethereal adducts. The dibenzyl species 6-Zr and
6-Hf are made from benzyl potassium and the bis(tri-
methylsilylmethyl) species 7-Zr and 7-Hf are made from
trimethylsilylmethyllithium.
Fig. 1. The titanium ansa-tetramethylcyclopentadienyl-amido precat-
alyst 1, upon activation with methylaluminoxane (MAO), readily
copolymerizes ethylene and a-olefins to form linear low density
polyethylene (LLDPE).
Fig. 2. The first CGC with g1 ligation to the carbon-based five-
membered ring [26]. X-ray structure of 2-Zr with thermal ellipsoids
drawn at 50% probability and hydrogen atoms omitted.
contain the g1-Oct motif. These structures are compared
to alkylated derivates with normal g5-Oct binding in the
context of quantifying and understanding this variable
hapticity, which may be related to the unusual prefer-
ence toward a-olefins over ethylene that 2-Zr/MAO
can exhibit.
Scheme 1. Synthetic route to zirconium and hafnium ansa-Oct-amido complexes 2–7.

1316
L.J. Irwin et al. / Polyhedron 24 (2005) 1314–1324
2.2. X-ray crystallography of Zr and Hf complexes
ligand (Oct) and a di-substituted fluorenyl ligand.
3-Zr and 3-Hf are isomorphic, and only 5-Zr cocrys-
tallizes with solvent, packing one diethyl ether
molecule into the cleft of each Oct ligand. In this case,
note the selectivity of the metal to bind THF
despite the use of diethyl ether as the crystallization
solvent.
Crystals suitable for X-ray crystallography were ob-
tained for complexes 3-Zr, 3-Hf, and 5-Zr by cooling
saturated diethyl ether solutions. Crystals of 6-Zr and
6-Hf were grown by vapor diffusion of diethyl ether into
saturated dichloromethane solutions, while crystals of
7-Zr were obtained by cooling a saturated pentane solu-
tion. Fig. 3 depicts the structural results of the X-ray
crystallography.
It is readily apparent that ethereal solvents remain
bound to the metal in 3-Zr, 3-Hf, and 5-Zr, resulting
in a trigonal bipyramid with oxygen and nitrogen in
the apical positions. This trigonal bipyramid structure
is unprecedented for fluorenyl-amido complexes; even
the remarkably similar Me2Si(g5-2,7-tBu2-C13H6)(g1-
N-tBu)ZrCl2 [29,30] and Me2Si(g5-3,6-tBu2-C13H6)
(g1-N-tBu)ZrCl2 [23,31] adopt the g5, pseudotetrahe-
dral geometry. Apparently there is an important
difference between a 2,3,6,7-tetra-substituted fluorenyl
6-Zr, 6-Hf, and 7-Zr, which bear the larger benzyl or
trimethylsilylmethyl groups, crystallize as ether-free spe-
cies with a pseudotetrahedral coordination sphere and
g5 ligation to Oct. 6-Zr and 6-Hf are isomorphic and
each of these structures contains one benzyl group that
2
˚
is arguably g . The M–CH2Ph bond length is 2.295 A
˚
for 6-Zr (2.299 A for 6-Hf) and the M–(Cipso) distance
˚
˚
is 2.793 A for 6-Zr (2.871 A for 6-Hf). The structure
of 7-Zr is quite similar to that published for the parent
fluorenyl-containing compound, Me2Si(g5-C13H8)(g1-
N-tBu)Zr(CH2SiMe3)2 [18].
Table 1 lists selected bond lengths and angles for 2-Zr
[26], 3-Zr, 3-Hf, 5-Zr, 6-Zr, 6-Hf, and 7-Zr. In the g1
Fig. 3. X-ray structures of 3-Zr, 3-Hf, 5-Zr, 6-Zr, 6-Hf, and 7-Zr with thermal ellipsoids drawn at 50% probability and hydrogen atoms omitted.

L.J. Irwin et al. / Polyhedron 24 (2005) 1314–1324
1317
Table 1
Selected bond lengths (A) and angles (ꢁ)
˚
Complex
M–C(1)
M–N
M–X(1)
M–X(2)
M–O
cent-C(1)–Sia
Si–N–M
X–M–X
N–M–O
2-Zr (Cl2 Æ Et2O)
3-Zr (Br2 Æ Et2O)
3-Hf (Br2 Æ Et2O)
5-Zr (Me2 Æ THF)
6-Zr ((CH2Ph)2)
6-Hf ((CH2Ph)2)
7-Zr ((CH2SiMe3)2)
a
2.299(7)
2.300(8)
2.281(8)
2.330(5)
2.397(2)
2.373(1)
2.390(2)
2.013(5)
2.019(6)
2.022(7)
2.068(4)
2.052(2)
2.087(8)
2.0648(18)
2.4155(19)
2.5427(13)
2.5112(14)
2.240(6)
2.3918(18)
2.5387(13)
2.4974(15)
2.274(5)
2.330(5)
2.322(6)
2.297(6)
2.280(4)
203.67
202.78
204.90
197.86
156.80
155.80
156.46
99.1(2)
99.0(3)
98.8(3)
99.3(2)
103.47(9)
99.9(4)
102.85(9)
112.92(7)
112.31(5)
111.93(5)
111.8(2)
169.87(19)
169.6(2)
167.1(3)
167.05(16)
2.295(2)
2.299(9)
2.249(2)
2.316(2)
2.305(11)
2.265(2)
116.20(9)
111.6(4)
107.30(8)
cent is defined as the centroid of the five-membered ring of the Oct ligand.
trigonal bipyramidal structures, the metal–C(1) bond
˚
2.3. Hapticity analysis of Zr and Hf complexes by X-ray
crystallography
lengths are consistently shorter (2.281–2.330 A) than
the corresponding bond lengths in the g5 pseudotetrahe-
dral structures (2.373–2.397 A). The shortening of the
While g5-fluorenyl ligands are the most common [36–
40], a number of g3-fluorenyl examples have also been
documented [41–46]. In contrast, g1-fluorenyl ligands
are quite rare. The first definitive examples were found
with octahedral mid-transition metal species such as
Mn(g1-C13H9)(CO)3(P(n-Bu)3)2 [47], Mn(g1-C13H9)
(CO)3(PEt3)2 [48], and Re(g1-C13H9)(CO)5 [49,50]. La-
ter, examples were found with early transition metal
species such as pseudotetrahedral (g5-C5H4Me)2Zr(g1-
C13H9)Cl, (g5-C5H5)2Zr(g1-C13H9)2 [51], and pseudotri-
gonal bipyramidal Me2C(g5-C5H4)(g1-C13H8)TaMe3
[52].
˚
remaining M–C bond upon g5 to g1 ring-slip is typical
for cyclopentadienyl [32] and indenyl ligands [33]. In
ansa-metallocenes and cyclopentadienyl-amido com-
plexes, the C5centroid–C(1)–Si angle is always less than
180ꢁ; examples are rac-Me2Si(g5-C9H6)2ZrCl2 (163.7ꢁ)
[34] and Me2Si(g5-C5Me4)(g1-N-tBu)TiCl2 (152.3ꢁ)
[35]. For the g5 complexes in Table 1, this angle is
ꢀ156ꢁ, a typical value. Strikingly, the C5centroid–C(1)–
Si angles for the g1 complexes are considerably larger
than 180ꢁ and range from 197.9ꢁ to 204.9ꢁ. Thus, the sil-
icon atom and the metal are on opposite sides of the Oct
ligand. This results in the most sterically open class of
CGCs reported.
The assignment of hapticity can sometimes be arbi-
trary [53], but the metrical parameters cataloged in
Fig. 4. Structures of 2-Zr, 3-Zr, 3-Hf, 5-Zr, 6-Zr, 6-Hf, and 7-Zr with the Oct ligand truncated to the five-membered ring. Bond lengths and
˚
interatomic distances (A) correspond to the metal–Oct interaction, moving clockwise from the C(1) carbon.

1318
L.J. Irwin et al. / Polyhedron 24 (2005) 1314–1324
Fig. 4 largely support the conclusion that 2-Zr, 3-Zr,
3-Hf, and 5-Zr are g1, while 6-Zr, 6-Hf, and 7-Zr are
g5. Assignments from the literature place the threshold
for zirconium–carbon bonding between 2.65 and
˚
2.81 A [41,54]. For example, the two ‘‘non-bonded’’ car-
bons in (g5-C13H9)(g3-C13H9)ZrCl2 are 2.801 and
˚
2.807 A from the metal while the remaining eight
˚
‘‘bonded’’ carbons are between 2.395 and 2.645 A away
˚
d is 0.114 A for
octamethyloctahydrodibenzofluorene and is predicted to decrease with
increasing hapticity.
Fig. 5. The bond length difference parameter
[42]. In Re(g1-C13H9)(CO)5 the bonded carbon is
˚
2.307 A from rhenium while the four unequivocally
˚
non-bonded carbons are between 3.193 and 4.149 A
from the metal [50]. In structures 2-Zr, 3-Zr, 3-Hf,
and 5-Zr, the bonded carbon is between 2.281 and
˚
2.330 A from the metal. Each structure has one metal–
carbon interatomic distance between 2.731 and
˚
2.847 A, which is at the upper limit of the bonding
range. The remaining three distances for each structure
become more similar as an g5, aromatic cyclopentadie-
nide core is approached.
1
˚
The largest value of d (0.095 A) is found for Re(g -
C13H9)(CO)5, an electronically (18eÀ) and coordin-
atively (octahedral) saturated compound that cannot
increase its g1 hapticity with the fluorenyl ligand.
Although (g5-C5H4Me)2Zr(g1-C13H9)Cl and Me2C(g5-
C5H4)(g1-C13H8)TaMe3 are not electronically saturated,
sterics probably dissuade a greater hapticity, resulting in
a high d value (0.081 for both). The next three species
are 3-Hf, 3-Zr, and 5-Zr, which have d values of
˚
are at least 3.130 A, considerably beyond normal zirco-
nium–carbon or hafnium–carbon bond lengths.
An alternative method for assessing hapticity is by
measurement of the carbon–carbon bond lengths of
the five-membered ring. In octamethyloctahydro-
dibenzofluorene, long bonds are found connecting the
3
˚
˚
sp carbon to the aromatic rings (1.515 A) and short
bonds are found as part of the aromatic rings
0.069, 0.066, and 0.047 A, respectively, which still indi-
cate significant carbon–carbon bond length differences.
This last value is also found for a complex reported as
g3, Mo(g3-C13H9)(g3-C3H5)3. The remaining twelve
compounds, including 6-Zr, 7-Zr, and 6-Hf, have d val-
˚
(1.401 A) [26]. The parameter d can be defined as the dif-
ference between these bond lengths – or average differ-
ence for non-symmetrical species – as defined in Fig.
5. Table 2 lists carbon–carbon bond lengths and the cal-
culated parameter d for a variety of fluorenyl- and Oct-
containing compounds. The entries are listed in order of
decreasing d, which corresponds to increasing hapticity
since the carbon–carbon bond lengths are predicted to
5
˚
ues of 0.030 A or less and are predicted to be g . Three
anomalies exist in this range: (g5-C13H9)(g3-
C13H9)ZrCl2 (d = 0.025), which is reported as g3; 2-Zr
(d = 0.021), which is reported as g1; and fluor-
enylLi(Et2O)2 (d = À0.018), which is reported as g2. It
Table 2
˚
Carbon–carbon bond lengths of the fluorenyl or Oct five-membered ring along with the bond length difference parameter d = (a + e À b À d)/2 in A
Compound
a
b
c
d
e
d
References
OctH (C29H38)
Fluorene (C13H10
1.515(2)
1.504(2)
1.506
1.401(2)
1.397(2)
1.405
1.471(2)
1.472(3)
1.451
1.401(2)
1.397(2)
1.417
1.515(2)
1.504(2)
1.505
0.114
0.107
0.095
0.081
0.081
0.069
0.066
0.047
0.047
0.030
0.029
0.027
0.026
0.025
0.021
0.018
0.011
0.008
0.005
0.000
[26]
[55]
)
Re(g1-C13H9)(CO)5
[50]
[51]
(g5-C5H4Me)2Zr(g1-C13H9)Cl
Me2C(g5-C5H4)(g1-C13H8)TaMe3
3-Hf (Br2 Æ Et2O)
1.505(5)
1.502(4)
1.485(10)
1.474(11)
1.459(8)
1.476(3)
1.46(1)
1.415(5)
1.417(5)
1.410(10)
1.439(10)
1.428(7)
1.407(3)
1.43(1)
1.461(5)
1.448(4)
1.479(11)
1.449(11)
1.445(8)
1.465(4)
1.46(1)
1.405(5)
1.417(4)
1.409(10)
1.383(11)
1.417(8)
1.433(3)
1.42(1)
1.477(5)
1.493(4)
1.472(12)
1.479(12)
1.480(7)
1.458(3)
1.45(1)
[52]
this work
this work
this work
[43]
3-Zr (Br2 Æ Et2O)
5-Zr (Me2 Æ THF)
Mo(g3-C13H9)(g3-C3H5)3
Me2Si(g5-3,6-tBu2-C13H6)(g1-N-tBu)ZrCl2
6-Zr ((CH2Ph)2)
[23]
1.455(3)
1.453(3)
1.454(14)
1.50
1.426(3)
1.426(3)
1.416(12)
1.41
1.447(3)
1.454(3)
1.447(14)
1.47
1.430(3)
1.421(3)
1.445(14)
1.43
1.459(3)
1.448(3)
1.459(13)
1.39
this work
this work
this work
[42]
7-Zr ((CH2SiMe3)2)
6-Hf ((CH2Ph)2)
(g5-C13H9)(g3-C13H9)ZrCl2
2-Zr (Cl2 Æ Et2O)
1.468(9)
1.450(4)
1.449(5)
1.457(6)
1.44
1.431(8)
1.426(4)
1.431(5)
1.430(6)
1.42
1.434(8)
1.442(4)
1.434(5)
1.443(6)
1.44
1.437(9)
1.431(4)
1.440(5)
1.458(6)
1.44
1.441(9)
1.442(4)
1.443(5)
1.447(6)
1.43
[26]
[18]
Me2Si(g5-C13H8)(g1-N-tBu)Zr(CH2SiMe3)2
Me2C(g5-C5H4)(g5-C29H36)ZrCl2
Ph2C(g5-C5H4)(g5-C29H36)ZrCl2
(g5-C13H9)(g3-C13H9)ZrCl2
Me2C(g5-C5H4)(g5-C13H8)ZrCl2
FluorenylLi(Et2O)2
[56]
[25]
[42]
[57]
1.45(1)
1.424(4)
1.44(1)
1.443(4)
1.43(1)
1.434(4)
1.44(1)
1.443(5)
1.43(1)
1.426(5)
À0.018
[40]

L.J. Irwin et al. / Polyhedron 24 (2005) 1314–1324
1319
Table 3
Selected 1H NMR and 13C NMR chemical shifts (ppm) for Oct–Zr species: aromatic C–H in the 1 and 4 positions; M–C(1); and aromatic C (in C6D6
except 7-Zr, recorded in CDCl3)
Compound
H
H
C(1)
C
C
C
C
C
C
References
OctH (C29H38
)
7.46
8.01
8.01
7.93
7.82
8.15
7.92
7.94
8.03
7.98
8.24
8.27
8.23
8.15
8.16
8.17
8.02
8.03
36.5
71.9
72.0
70.8
86.3
73.9
71.1
96.5
93.0
117.5
121.5
122.0
120.6
117.4
120.1
120.1
117.6
117.0
123.3
123.2
124.0
122.7
118.5
122.0
122.5
119.1
121.2
140.3
125.3
126.0
123.7
133.6
122.7
123.2
135.8
134.6
141.4
134.8
134.6
135.0
137.6
134.1
133.9
138.7
139.6
143.4
143.6
this work
[26]
2-Zr (Cl2
3-Zr (Br2
•
Et2O)
Et2O)
145.6
146.0
142.6
139.7
145.7
142.7
139.7
141.4
148.9
148.8
146.7
141.9
147.0
146.1
143.0
142.8
•
this work
this work
this work
this work
this work
this work
this work
4-Zr (Me2
5-Zr (Me2
•
Et2O)
THF)
•
6-Zr ((CH2Ph)2)
7-Zr ((CH2SiMe3)2)
Me2Si(η1-C29H36)(η1-N-tBu)ZrCl 2
Me2Si(η1-C29H36)(η1-N-tBu)ZrBr 2
•
THF
NCMe
•
should be noted that d is an indirect measure of haptic-
ity. It only measures carbon–carbon bond length distor-
tions that occur in response to a metalꢀs location and
bonding. Thus, d and hapticity are reasonably correla-
tive, but the exceptions remind us that hapticity is best
determined by measuring metal–carbon interatomic
distances.
fected ethereal binding in the solid-state when the
remaining ligands were small (X = Cl, Br, or Me).
Ether-free species were observed when larger ligands
(X = benzyl or trimethylsilylmethyl) were present.
X-ray crystallography established that an unusual trigo-
nal bipyramidal g1-Oct structure accompanied ethereal
binding (n = 1, m = 1), while the ether-free species
adopted the anticipated pseudotetrahedral g5-Oct struc-
ture (n = 5, m = 0). The hapticity assignments were
made largely by analyzing the relevant metal–carbon
distances, but a correlation between hapticity and con-
verging carbon–carbon bond lengths of the five-mem-
bered ring was also identified.
2.4. Hapticity analysis of Zr complexes in solution by
NMR
1
The solution H NMR spectra of the diethyl ether
complexes (2-Zr, 2-Hf, 3-Zr, 3-Hf, 4-Zr, and 4-Hf) show
sharp resonances for the ethereal protons, a trait usually
attributed to unbound ether species. Thus suggests solu-
tion species with g5-Oct ligation. The THF adducts, how-
ever, provide somewhat broad resonances for the ethereal
protons, indicating that THF coordination and low Oct
hapticity are maintained in solution. Careful inspection
4. Experimental
4.1. General remarks
1
of the H and 13C NMR chemical shifts of compounds
All air sensitive procedures were carried out under a
purified atmosphere of nitrogen in a glove box equipped
with a À35 ꢁC freezer, or by using standard Schlenk line
techniques. Solvents were dried and distilled under
nitrogen into Straus flasks and stored until needed.
Diethyl ether and tetrahydrofuran were distilled from
sodium/benzophenone; n-heptane and dichloromethane
were distilled from calcium hydride; and toluene was
distilled from elemental sodium.
The commercially available reagents n-butyllithium
(Acros, 2.5 M in hexanes or Alfa Aesar, 2.87 M in hex-
anes), LiCH2SiMe3 (Aldrich, 1.0 M in pentane), MeLi
(Aldrich, 1.6 M in diethyl ether), MeMgCl (Aldrich,
3.0 M in tetrahydrofuran), zirconium tetrachloride
(Strem, 99.5+%), hafnium tetrachloride (Strem,
99.9+%), zirconium tetrabromide (Strem, 98%), and
lithium bromide (Aldrich, 99.995+%) were used as re-
ceived, unless otherwise noted. Both KCH2Ph [58] and
the ligand Me3CNHSiMe2(C29H37) [26] were prepared
according to literature procedures.
2-Zr through 7-Zr indeed reveals unusual chemical shifts
for only the THF adduct 5-Zr (Table 3). The aromatic C–
H protons in the 1 and 4 positions of the Oct moiety are
the most upfield of this group at 7.82 and 8.15 ppm. The
M–C(1) carbon is the most downfield (86.3 ppm) and, of
the aromatic carbons, two have comparatively high
chemical shifts (133.6 and 137.6 ppm) and four have
comparatively low chemical shifts (117.4, 118.5, 139.7
and 141.9 ppm). These unusual chemical shifts for 5-Zr
are mirrored in Me2Si(g1-C29H36)(g1-N-tBu)ZrCl2 Æ
THF and Me2Si(g1-C29H36)(g1-N-tBu)ZrBr2 Æ NCMe
(see Table 3), suggesting that each of these also maintains
g1-Oct ligation in solution.
3. Conclusions
A series of sterically expanded ansa-fluorenyl-amido
zirconium and hafnium complexes with the general for-
mula Me2Si(gn-C29H36)(g1-N-tBu)MX2 Æ Lm was syn-
thesized and characterized. Incorporation of the
octamethyloctahydrodibenzofluorenyl (Oct) ligand ef-
All NMR chemical shifts are given in ppm and were
a
Mercury-300BB spectrometer (1H,
recorded on
299.91 MHz; 13C {1H}, 75.41 MHz) using the residual

1320
L.J. Irwin et al. / Polyhedron 24 (2005) 1314–1324
3
0.86 (s, 6H, (CH3)2Si), 1.11 (t, JHH = 7.0 Hz, 6H,
protonated solvent peak as an internal standard
(CDCl3: 1H, 7.27 ppm; 13C, 77.0 ppm. C6D6: 1H, 7.15 ppm;
13C, 128.0 ppm).
ether–CH3), 1.27, 1.34, 1.39, 1.41 (s, 24H, Oct–CH3),
1.31 (s, 9H, –C(CH3)3), 1.61 (m, 8H, Oct–CH2), 3.26
3
(q, JHH = 7.0 Hz, 4H, ether–CH2), 8.01, 8.27 (s, 4H,
4.2. Syntheses
Oct–CH1). 13C {1H} NMR (C6D6): d 5.8, 15.5, 32.1,
32.7, 33.0, 34.98, 35.0, 35.3, 35.4, 56.9, 65.9, 72.0,
122.0, 124.0, 126.0, 134.6, 146.0, 148.8.
4.2.1. Synthesis of Me2Si(g1-C29H36)(g1-N-tBu)ZrCl2 Æ
OEt2 (2-Zr)
In the glove box Me3CNHSiMe2(C29H37) (3.00 g,
6.26 mmol) was charged into a 100 ml pear-shaped
round bottom and then attached to a 3 cm swivel frit.
The frit was then evacuated and diethyl ether (50 ml)
was vacuum transferred in. Next, n-butyllithium
(5.51 ml, 13.77 mmol, 2.5 M in hexanes) was syringed
in. The orange slurry was stirred for 20 h and then the
diethyl ether was removed under vacuum. ZrCl4
(1.46 g, 6.26 mmol) was added in the glove box and
diethyl ether (40 ml) was vacuum transferred in on the
line. After slowly warming to room temperature and
stirring the light brown slurry for 48 h, the LiCl was fil-
tered off and the cake was extracted until colorless. The
slurry was concentrated to about 10 ml and the precipi-
tated solid was collected by filtration. The cake was
washed once to remove a brown oil and then evacuated
until dry. This yielded 1.42 g (31.8%) of product as a
neon yellow solid. Large rod-shaped crystals can be
grown by cooling a saturated diethyl ether solution to
À35 ꢁC. 1H NMR (C6D6): d 0.86 (s, 6H, (CH3)2Si),
4.2.4. Synthesis of Me2Si(g1-C29H36)(g1-N-tBu)HfBr2 Æ
OEt2 (3-Hf)
In the glove box, 2-Hf (0.13 g, 0.16 mmol) was
charged into a 100 ml pear-shaped round bottom flask
followed by the addition of anhydrous LiBr (4.90 g,
56.42 mmol). Next, the flask was attached to a 3 cm swi-
vel frit and brought out to the line where diethyl ether
(60 ml) was vacuum transferred in. The slurry was then
stirred for 2 days after which time the solvent was re-
moved under vacuum and pentane (30 ml) was vacuum
transferred in. All insoluble material was removed via fil-
tration and the cake was extracted until colorless. Con-
centration of the filtrate to 5 ml followed by filtration
yielded 0.07 g (69.0%) of 3-Hf as an orange-yellow pow-
der. Large rod-shaped crystals can be grown by cooling a
saturated diethyl ether solution to À35 ꢁC. X-ray crystal-
lography suggested that complete salt metathesis of the
Hf–Cl bonds had been achieved. This was further sup-
1
ported by H NMR via a characteristic shift of the aro-
matic Oct–CH1 protons from 8.22 ppm (2-Hf) to
8.26 ppm (3-Hf). A similar shift is observed between
2-Zr and 3-Zr. 1H NMR (C6D6): d 0.89 (s, 6H, (CH3)2Si),
1.03 (t, 3JHH = 6.0 Hz, 6H, ether–CH3), 1.28, 1.31, 1.35,
1.36 (s, 24H, Oct–CH3), 1.32 (s, 9H, –C(CH3)3), 1.63
3
1.10 (t, JHH = 7.0 Hz, 6H, ether–CH3), 1.26 (s, 9H,
–C(CH3)3), 1.28, 1.35, 1.38, 1.39 (s, 24H, Oct–CH3),
3
1.62 (m, 8H, Oct–CH2), 3.25 (q, JHH = 7.0 Hz, 4H,
ether–CH2), 8.01, 8.24 (s, 4H, Oct–CH1). 13C {1H}
NMR (C6D6): d 5.9, 15.5, 32.3, 32.6, 32.8, 32.9, 33.4,
34.95, 35.02, 35.3, 35.4, 56.4, 66.0, 71.9, 121.5, 123.2,
125.3, 134.8, 145.6, 148.9. Elemental analysis: Anal.
Calc.: C, 62.44; H, 8.13; N, 1.87; Cl, 9.45. Found: C,
61.40; H, 8.24; N, 1.81; Cl, 9.45%.
3
(m, 8H, Oct–CH2), 3.19 (q, JHH = 6.0 Hz, 4H, ether–
CH2), 8.00, 8.26 (s, 4H, Oct–CH1).
4.2.5. Synthesis of Me2Si(g1-C29H36)(g1-N-tBu)
ZrMe2 Æ OEt2 (4-Zr)
In the glove box 2-Zr (0.50 g, 0.67 mmol) was
charged into a 100 ml pear-shaped round bottom flask,
which was then attached to a 3 cm swivel frit. The frit
was evacuated on the vacuum line and diethyl ether
(50 ml) was then vacuum transferred in. Next, a LiBr-
free diethyl ether solution of CH3Li (0.83 ml,
1.33 mmol, 1.6 M in diethyl ether) was slowly syringed
into the yellow solution while vigorously stirring. The
solution began to bleach and acquire a very pale fluores-
cent yellow color. (Note: Extended exposure to excess
CH3Li leads to a dark brown/black solution and com-
plete decomposition of the product in a matter of
hours.) After 2 h the precipitated LiCl was removed
via filtration and extracted until colorless. Concentra-
tion of the filtrate to 10 ml and collection of the precip-
itated product on the frit led to 0.42 g (89.0%) of
product as a pale yellow solid. 1H NMR (C6D6): d
À0.59 (s, 6H, Zr(CH3)2), 0.89 (s, 6H, (CH3)2Si), 1.10
4.2.2. Synthesis of Me2Si(g1-C29H36)(g1-N-tBu)HfCl2 Æ
OEt2 (2-Hf)
2-Hf was prepared in a manner analogous to 2-Zr ex-
cept that HfCl4 (3.34 g, 10.43 mmol) was utilized yield-
1
ing 3.30 g (39.5%) of 2-Hf as a yellow solid. H NMR
3
(C6D6): d 0.84 (s, 6H, (CH3)2Si), 0.99 (t, JHH = 6.0 Hz,
6H, ether–CH3), 1.31, 1.34, 1.39, 1.42 (s, 24H, Oct–
CH3), 1.37 (s, 9H, –C(CH3)3), 1.65 (app. s, 8H, Oct–
3
CH2), 3.19 (q, JHH = 6.0 Hz, 4H, ether–CH2), 7.99,
8.22 (s, 4H, Oct–CH1).
4.2.3. Synthesis of Me2Si(g1-C29H36)(g1-N-tBu)ZrBr2 Æ
OEt2 (3-Zr)
3-Zr was prepared in a manner analogous to 2-Zr ex-
cept that ZrBr4 (2.57 g, 6.26 mmol) was utilized yielding
1.30 g (24.8%) of 3-Zr as a bright yellow powder. Large
rod-shaped crystals can be grown by cooling a saturated
1
3
diethyl ether solution to À35 ꢁC. H NMR (C6D6): d
(t, JHH = 7.0 Hz, 6H, ether–CH3), 1.32, 1.37 (s, 24H,

L.J. Irwin et al. / Polyhedron 24 (2005) 1314–1324
1321
Oct–CH3), 1.33 (s, 9H, –C(CH3)3), 1.64 (m, 8H, Oct–
3
CH2), 3.24 (q, JHH = 7.0 Hz, 4H, ether–CH2), 7.93,
34.9, 35.4, 35.5, 36.2, 36.4, 51.4, 66.2, 71.6, 117.5,
118.8, 126.6, 133.8, 137.9, 142.0.
8.23 (s, 4H, Oct–CH1). 13C {1H} NMR (C6D6): d 6.6,
15.5, 32.6, 32.8, 32.9, 33.2, 34.5, 34.8, 35.2, 35.55,
35.57, 39.4, 55.0, 65.9, 70.8, 120.6, 122.7, 123.7, 135.0,
142.6, 146.7.
4.2.9. Synthesis of Me2Si(g5-C29H36)(g1-N-tBu)Zr
(CH2Ph)2 (6-Zr)
In the glove box, 2-Zr (4.00 g, 5.33 mmol) was
charged into a 100 ml pear-shaped round bottom flask
followed by the addition of KCH2Ph (1.39 g,
10.66 mmol). The flask was then attached to a 3 cm swi-
vel frit and brought out onto the line where diethyl ether
(60 ml) was vacuum transferred in. The contents were al-
lowed to slowly warm to room temperature and then stir
for 2 h before the salt was removed by filtration and
the cake extracted until colorless. Concentration of the
slurry to 20 ml, followed by filtration, led to the desired
product as a yellow solid (3.21 g, 76.5%). Large block-
like crystals were grown by the vapor diffusion of diethyl
ether into dichloromethane saturated with 6-Zr. 1H
4.2.6. Synthesis of Me2Si(g1-C29H36)(g1-N-tBu)
HfMe2 Æ OEt2 (4-Hf)
4-Hf was prepared in a manner analogous to 4-Zr ex-
cept that 2-Hf (0.40 g, 0.49 mmol) was utilized yielding
0.23 g (60.5%) of 4-Hf as a pale yellow powder. 1H
NMR (C6D6): d À0.16 (s, 6H, Hf(CH3)2), 0.84 (s, 6H,
3
(CH3)2Si), 1.02 (t, JHH = 6.0 Hz, 6H, ether–CH3),
1.34, 1.35, 1.36, 1.38 (s, 24H, Oct–CH3), 1.37 (s, 9H,
–C(CH3)3), 1.66 (app. s, 8H, Oct–CH2), 3.17 (q,
3JHH = 6.0 Hz, 4H, ether–CH2), 7.84, 8.21 (s, 4H, Oct–
CH1).
2
NMR (C6D6): d À0.48, 0.86 (d, JHH = 10.5 Hz, 4H,
4.2.7. Synthesis of Me2Si(g1-C29H36)(g1-N-tBu)
ZrMe2 Æ THF (5-Zr)
Zr–CH2), 0.99 (s, 9H, –C(CH3)3), 1.01 (s, 6H, (CH3)2Si),
1.34, 1.38, 1.39, 1.42 (s, 24H, Oct–CH3), 1.62 (m, 8H,
Oct–CH2), 6.69 (m, 4H, Zr–CH2C6H5), 6.89 (m, 2H,
Zr–CH2C6H5), 7.16 (m, 4H, Zr–CH2C6H5), 8.15, 8.16
(s, 4H, Oct–CH1). 13C {1H} NMR (CDCl3): d 6.2,
32.4, 32.6, 32.8, 33.0, 33.5, 34.8, 35.06, 35.08, 35.09,
56.9, 61.3, 73.1, 119.8, 121.2, 122.2, 123.1, 127.5,
128.8, 133.4, 143.5, 145.5, 146.8. 13C {1H} NMR
(C6D6): d 6.4, 32.57, 32.6, 33.06, 33.1, 33.6, 34.9, 35.2,
35.26, 35.3, 57.2, 61.9, 73.9, 120.1, 122.0, 122.7, 123.6,
128.3, 129.3, 134.1, 143.7, 145.7, 147.0
In the glove box, 2-Zr (5.00 g, 6.67 mmol) was
charged into a 100 ml pear-shaped round bottom flask.
The flask was then attached to a 3 cm swivel frit and
diethyl ether (80 ml) was vacuum transferred in on the
line. Next, while the flask was still cold, MeMgCl
(4.44 ml, 13.33 mmol, 3.0 M in THF) was slowly added
via syringe. A large quantity of white precipitate imme-
diately formed. The contents of the flask were stirred for
2 h before the precipitated salt was removed by filtra-
tion. The cake was extracted until the eluent was color-
less. The solvent was then removed under vacuum and
the frit was brought into the box where the off-white
product was recrystallized by cooling a saturated diethyl
ether solution to À35 ꢁC, yielding 2.98 g (63.0%) of
product as nearly white crystals which were suitable
4.2.10. Synthesis of Me2Si(g5-C29H36)(g1-N-tBu)Hf
(CH2Ph)2 (6-Hf)
6-Hf was prepared in a manner analogous to 6-Zr ex-
cept that 2-Hf (1.50 g, 1.87 mmol) was utilized yielding
0.42 g (25.8%) of 6-Hf as a yellow-orange solid. Large
block-like crystals were grown by the vapor diffusion
of diethyl ether into dichlormethane saturated with
6-Hf. 1H NMR (C6D6): d À0.30, 0.66 (d, 2JHH = 7.2 Hz,
4H, Hf–CH2), 0.95 (s, 6H, (CH3)2Si), 1.01 (s, 9H,
–C(CH3)3), 1.33, 1.34, 1.35, 1.36 (s, 24H, Oct–CH3),
1.57 (m, 8H, Oct–CH2), 6.65 (m, 4H, Hf–CH2C6H5),
6.82 (m, 2H, Hf–CH2C6H5), 7.12 (m, 4H, Hf–
CH2C6H5), 8.04, 8.26 (s, 4H, Oct–CH1). 13C {1H}
NMR (CDCl3): d 6.2, 32.5, 32.6, 33.0, 33.6, 33.7, 34.9,
35.0, 35.08, 35.1, 55.9, 70.4, 71.4, 120.0, 121.1, 122.4,
122.7, 127.5, 128.0, 134.1, 143.5, 146.5, 147.4.
1
for X-ray diffraction. H NMR (C6D6): d 0.02 (s, 6H,
Zr(CH3)2), 0.77 (s, 6H, (CH3)2Si), 1.14 (br, 4H, THF–
CH2), 1.34, 1.37, 1.40, 1.43 (s, 24H, Oct–CH3), 1.52 (s,
9H, –C(CH3)3), 1.69 (m, 8H, Oct–CH2), 2.81 (br, 4H,
THF–CH2), 7.82, 8.15 (s, 4H, Oct–CH1). 13C {1H}
NMR (C6D6): d 3.9, 15.5, 32.6, 32.7, 32.9, 33.3, 34.5,
34.8, 35.0, 35.9, 36.0, 39.7, 57.2, 65.8, 86.3, 117.4,
118.5, 133.6, 137.6, 139.7, 141.9.
4.2.8. Synthesis of Me2Si(g1-C29H36)(g1-N-tBu)
HfMe2 Æ THF (5-Hf)
5-Hf was prepared in a manner analogous to 5-Zr ex-
cept that 2-Hf (0.43 g, 0.54 mmol) was utilized yielding
0.43 g of 5-Hf as an off-white solid (>95% yield, some
persistent THF). 1H NMR (C6D6): d 0.29 (s, 6H,
Hf(CH3)2), 0.70 (s, 6H, (CH3)2Si), 1.01 (br, 4H, THF–
CH2), 1.33, 1.40, 1.45, 1.48 (s, 24H, Oct–CH3), 1.67 (s,
9H, –C(CH3)3), 1.73 (m, 8H, Oct–CH2), 2.41 (br, 4H,
THF–CH2), 7.67, 8.13 (s, 4H, Oct–CH1). 13C {1H}
NMR (C6D6): d 3.8, 15.9, 25.8, 33.0, 33.03, 33.3, 33.7,
4.2.11. Synthesis of Me2Si(g5-C29H36)(g1-N-tBu)Zr
(CH2SiMe3)2 (7-Zr)
In the glove box, 2-Zr (0.50 g, 0.67 mmol) was
charged into a 100 ml pear-shaped round bottom flask.
The flask was then attached to a 3 cm swivel frit and
brought out to the vacuum line where pentane (50 ml)
was vacuum transferred in. Next, LiCH2SiMe3
(1.40 ml, 1.40 mmol, 1.0 M in pentane) was slowly

1322
L.J. Irwin et al. / Polyhedron 24 (2005) 1314–1324
Table 4
Crystallographic data summary
Compound
3-Zr (Br2 Æ Et2O)
3-Hf (Br2 Æ Et2O)
5-Zr (Me2 Æ THF) 6-Zr ((CH2Ph)2)
6-Hf ((CH2Ph)2)
7-Zr ((CH2SiMe3)2)
Empirical formula
Formula weight
Temperature (K)
C
39H61Br2NOSiZr C39H61Br2NOSiHf C45H75NO2SiZr
C49H65NSiZr
787.33
110(2)
C49H65NSiHf
874.60
110(2)
C43H73NSi3Zr
779.53
110(2)
839.02
110(2)
926.29
110(2)
781.36
110(2)
1.54184
monoclinic
P21/c
˚
Wavelength (A)
1.54184
monoclinic
Cc
0.71073
monoclinic
Cc
0.71073
monoclinic
P21/n
1.54184
monoclinic
P1/n
0.71073
monoclinic
P21
Crystal system
Space group
˚
a (A)
24.122(3)
11.7263(11)
15.0453(16)
90
24.094(10)
11.765(5)
15.069(7)
90
12.564(7)
25.347(8)
14.555(6)
90
14.6594(14)
16.0990(15)
18.1773(17)
90
14.630(3)
16.103(3)
18.162(4)
90
12.980(4)
20.326(5)
17.152(5)
90
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
109.000(6)
90
108.847(7)
90
107.60(3)
90
95.952(2)
90
95.410(9)
90
93.840(4)
90
3
˚
Volume (A )
4023.9(7)
4
1.385
4042(3)
4
1.522
4418(3)
8
1.175
4271.9(7)
4
1.224
4259.6(14)
4
1.364
4515(2)
5
1.147
Z
Dcalc (g cmÀ3
)
l (mmÀ1
)
5.059
4.616
2.548
0.319
5.033
0.351
Crystal size (mm3)
Reflections
0.50 · 0.01 · 0.01
22767
5158
0.22 · 0.21 · 0.08
15407
6476
0.10 · 0.05 · 0.05 0.42 · 0.39 · 0.27 0.20 · 0.20 · 0.05 0.60 · 0.40 · 0.20
41117
6237
48123
9745
31312
6016
42757
19672
Independent
reflections
Data/restraints/
parameters
5158/314/445
6476/17/434
6237/1/461
9745/0/491
6016/349/470
19672/1/866
GOF (F2)
1.005
0.0489
1.078
0.0381
1.037
0.0592
1.215
0.0540
1.020
0.0595
1.066
0.0310
R1 [I > 2r(I)]
wR2 [I > 2r(I)]
R1 (all data)
wR2 (all data)
Largest differential
0.1192
0.0620
0.0990
0.0409
0.1262
0.1078
0.1312
0.0645
0.1148
0.1594
0.0790
0.0325
0.1257
0.676, À0.0943
0.1009
1.792, À1.381
0.1425
0.819, À1.428
0.1498
2.320, À0.655
0.1381
1.634, À1.517
0.0800
0.713, À0.356
À3
˚
peak, hole (e A
)
syringed into the still cold solution in the flask. The con-
tents were allowed to stir for 1 h before the LiCl was re-
moved by filtration and the salt was extracted until
colorless. The solvent was removed under vacuum yield-
ing a yellow foam. This was brought into the box where
5 ml of pentane was added causing the precipitation of a
neon yellow powder. The solvent was decanted and the
powder collected and dried under vacuum yielding
0.35 g (67.0%) of 7-Zr. Pentane (5 ml) was then satu-
rated with 7-Zr and stored in a À35 ꢁC freezer for one
month, resulting in the formation of large block-like
CH2), À0.11 (s, 18H, –Si(CH3)3), 0.89 (s, 6H, (CH3)2Si),
1.33, 1.35, 1.46, 1.49 (s, 24H, Oct–CH3), 1.37 (s, 9H,
–C(CH3)3), 1.79 (app. s, 8H, Oct–CH2), 7.72, 8.02 (s,
4H, Oct–CH1).
4.3. Crystallographic studies
Crystals were mounted at room temperature in min-
eral oil, and affixed to a glass fiber. X-ray crystallo-
graphic data were obtained using a Bruker SMART
1000 three-circle diffractometer operating at 50 kV and
crystals. 1H NMR (C6D6):
d
À1.32, À0.77 (d,
40 mA, Mo Ka (k = 0.71073 A) with a graphite mono-
˚
2JHH = 12.3 Hz, 4H, Zr–CH2), 0.17 (s, 18H, –Si(CH3)3),
0.89 (s, 6H, (CH3)2Si), 1.31 (s, 9H, –C(CH3)3), 1.39,
1.41, 1.41, 1.49 (s, 24H, Oct–CH3), 1.68 (m, 8H, Oct–
CH2), 7.92, 8.17 (s, 4H, Oct–CH1). 13C {1H} NMR
(CDCl3): d 3.3, 6.3, 32.2, 32.9, 33.1, 33.3, 34.3, 34.9,
35.08, 35.1, 35.3, 55.0, 55.9, 71.1, 120.1, 122.5, 123.2,
133.9, 142.7, 146.1.
chromator and a CCD-PXL-KAF2 detector or a Bruker
GADPS instrument operating at 40 kV and 40 mA, Cu
˚
Ka (k = 1.54578 A) with a graphite monochromator
and a CCD-PXL-KAF2 detector. Details of the crystal-
lographic data collection and refinement are summa-
rized in Table 4. The molecular structures were solved
by direct methods and were refined employing the
SHELXS-97 [59] and SHELXL-97 programs [60].
4.2.12. Synthesis of Me2Si(g5-C29H36)(g1-N-tBu)Hf
(CH2SiMe3)2 (7-Hf)
7-Hf was prepared in a manner analogous to 7-Zr ex-
cept that 2-Hf (0.40 g, 0.49 mmol) was utilized yielding
5. Supplementary material
1
0.24 g (54.5%) of 7-Hf as a yellow powder. H NMR
Crystallographic data for 3-Zr (CCDC 260056), 3-Hf
(CCDC 260057), 5-Zr (CCDC 260058), 6-Zr (CCDC
2
(CDCl3): d À2.09, À1.38 (d, JHH = 12.0 Hz, 4H, Hf–

L.J. Irwin et al. / Polyhedron 24 (2005) 1314–1324
[25] S.A. Miller, J.E. Bercaw, Organometallics 23 (2004) 1777.
1323
260055), 6-Hf (CCDC 260059), and 7-Zr (CCDC
260060) have been deposited with the Cambridge Crys-
tallographic Data Centre. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/
cif, or by emailing data_request@ccdc.cam.ac.uk, or
by contacting The Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge CB2 1EZ, UK;
fax: +44 1223 336033.
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Acknowledgements
This research is supported by grants from The Robert
A. Welch Foundation (No. A-1537) and the Texas Ad-
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