New syntheses of ansa-metallocenes or unbridged substituted metallocenes by the respective reductive dimerization of fulvenes with Group 4 metal divalent halides or with Group 4 metal dichloride dihydrides

Article abstract of DOI:10.1016/j.poly.2005.03.020

Two unprecedented syntheses of Group 4 metallocenes from 6-substituted fulvenes have been discovered and developed into high-yielding processes. In the first route the di-n-butylmetal dichlorides of Ti, Zr and Hf are generated in toluene suspensions of LiCl at -78°C from the metal tetrachlorides and 2 equiv. of n-butyllithium. Bringing the Bun2MCl2 to 25°C and then heating at reflux for several hours gave complete conversion to slurries of MCl₂ (M = Ti, Zr, Hf). Heating such slurries of MCl₂ with 2 equiv. of 6-substituted or 6,6-disubstituted fulvenes gave high yields of ansa-metallocenes or substituted ethylene-bis(cyclopentadienyl)metallocene dichlorides (fulvenes: 6,6-dimethyl-, 6-phenyl-, 6-(1-naphthyl)-, 6-(9-anthryl)-). For 6-substituted fulvenes, both racemic- and meso-1,2-disubstituted ethylene-ansa-metallocene dichlorides are expected to form, but with M = Zr (or Ti), the actual racemic- to meso-ansa-metallocene dichloride ratios observed were: phenyl, 50:50; 1-naphthyl, 83:17; 9-anthryl, 100:0. Apparently for steric reasons 6,6-diphenylfulvene underwent no ansa-metallocene dichloride formation with ZrCl₂ but rather produced bis(diphenylmethyl(cyclopentadienyl))zirconium dichloride. The second route to novel metallocenes involves generating Bun2MCl2 at -78°C in toluene slurry, as in the foregoing method, but then adding 2 equiv. of the 6-substituted or 6,6-disubstituted fulvene immediately thereafter at -78°C. Except with Bun2TiCl2, warming the reaction mixture to 25°C and then further heating at 65°C cause a smooth bis-hydrometallation by transfer to occur, giving good to very good yields of bis(substituted cyclopentadienyl)metal dichlorides (M = Zn, Hf). The instability of Bun2TiCl2, even at -78°C, rapidly led to a mixture of TiCl₂ and Bun2TiCl2and hence to a mixture of ansa-titanocene dichlorides and unbridged, bis(substituted cyclopentadienyl) titanocene dichlorides. With a detailed study of the attainment and the stereochemistry of the formation of ansa-bridged complexes or metallocenes with acetophenone, benzylideneaniline and 6-arylfulvenes, a mechanistic model is developed involving either a three-membered metallocycle formed from MCl ₂ or an open-face sandwich complex of the fulvene and MCl₂. Such intermediates offer a rational steric explanation for the observed stereochemistry of ansa-bridge C-C bond formation. Finally, in comparative polymerizations of ethylene by such metallocenes, cocatalyzed by MAO, the superior catalytic activity of ansa-metallocenes in the order, Ti > Zr > Hf and of ansa-metallocenes over unbridged substituted metallocenes is attributed to the hyperconjugative stabilization afforded by the ansa σ C-C bond to the metallocenium cation at the active olefin-polymerization site.

Full text of DOI:10.1016/j.poly.2005.03.020

Polyhedron 24 (2005) 1325–1339
www.elsevier.com/locate/poly
New syntheses of ansa-metallocenes or unbridged
substituted metallocenes by the respective reductive dimerization
of fulvenes with Group 4 metal divalent halides or with Group 4
q
metal dichloride dihydrides
*
John J. Eisch , Fredrick A. Owuor, Xian Shi
Department of Chemistry, State University of New York at Binghamton, P.O. Box 6000, Binghamton, NY 13902-6000, USA
Received 10 March 2005; accepted 29 March 2005
Available online 27 June 2005
Abstract
Two unprecedented syntheses of Group 4 metallocenes from 6-substituted fulvenes have been discovered and developed into high-
yielding processes. In the first route the di-n-butylmetal dichlorides of Ti, Zr and Hf are generated in toluene suspensions of LiCl at
ꢀ78 ꢀC from the metal tetrachlorides and 2 equiv. of n-butyllithium. Bringing the Bun MCl2 to 25 ꢀC and then heating at reflux for several
2
hours gave complete conversion to slurries of MCl2 (M = Ti, Zr, Hf). Heating such slurries of MCl2 with 2 equiv. of 6-substituted or
6,6-disubstituted fulvenes gave high yields of ansa-metallocenes or substituted ethylene-bis(cyclopentadienyl)metallocene dichlorides
(fulvenes: 6,6-dimethyl-, 6-phenyl-, 6-(1-naphthyl)-, 6-(9-anthryl)-). For 6-substituted fulvenes, both racemic- and meso-1,2-disubstituted
ethylene-ansa-metallocenedichloridesareexpectedtoform, butwithM = Zr(orTi),theactualracemic-tomeso-ansa-metallocenedichlo-
ride ratiosobservedwere:phenyl, 50:50;1-naphthyl, 83:17;9-anthryl,100:0. Apparentlyfor stericreasons 6,6-diphenylfulveneunderwent
no ansa-metallocene dichloride formation with ZrCl2 but rather produced bis(diphenylmethyl(cyclopentadienyl))zirconium dichloride.
The second route to novel metallocenes involves generating Bun MCl2 at ꢀ78 ꢀC in toluene slurry, as in the foregoing method,
2
but then adding 2 equiv. of the 6-substituted or 6,6-disubstituted fulvene immediately thereafter at ꢀ78 ꢀC. Except with Bun TiCl2,
2
warming the reaction mixture to 25 ꢀC and then further heating at 65ꢀC cause a smooth bis-hydrometallation by transfer to occur,
giving good to very good yields of bis(substituted cyclopentadienyl)metal dichlorides (M = Zn, Hf). The instability of Bun TiCl2,
2
even at ꢀ78 ꢀC, rapidly led to a mixture of TiCl2 and Bun TiCl2and hence to a mixture of ansa-titanocene dichlorides and unbridged,
2
bis(substituted cyclopentadienyl)titanocene dichlorides.
With a detailed study of the attainment and the stereochemistry of the formation of ansa-bridged complexes or metallocenes with
acetophenone, benzylideneaniline and 6-arylfulvenes, a mechanistic model is developed involving either a three-membered metallo-
cycle formed from MCl2 or an ‘‘open-face sandwich’’ complex of the fulvene and MCl2. Such intermediates offer a rational steric
explanation for the observed stereochemistry of ansa-bridge C–C bond formation.
Finally, in comparative polymerizations of ethylene by such metallocenes, cocatalyzed by MAO, the superior catalytic activity of
ansa-metallocenes in the order, Ti > Zr > Hf and of ansa-metallocenes over unbridged substituted metallocenes is attributed to the
hyperconjugative stabilization afforded by the ansa r C–C bond to the metallocenium cation at the active olefin-polymerization site.
ꢁ 2005 Elsevier Ltd. All rights reserved.
Keywords: Group 4 metals; Metallocenes; Fulvenes; Reductive dimerization; Hydrometallation
q
Organic Chemistry of Subvalent Transition Metal Complexes, 34. Part 33: J.J. Eisch, A.A. Adeosun, S. Dutta, P.O. Fregene, Eur. J. Org. Chem.
(2005), in press.
*
Corresponding author. Tel.: +1 607 777 4261; fax: +1 607 777 4865.
E-mail address: jjeisch@binghamton.edu (J.J. Eisch).
0277-5387/$ - see front matter ꢁ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.03.020

1326
J.J. Eisch et al. / Polyhedron 24 (2005) 1325–1339
n
1. Introduction
˚
2 Bu Li, 78 C
n
MCl4
2 Bu 2 MCl2
THF solution
1
M = Ti, Zr, Hf
or
Over the last decade we have been interested in
applying the diverse chemical reactions of subvalent
transition metal salts to the methodology of organic
synthesis [1–4]. Our attention was especially drawn
to the salts of Group 4 metals by the reports of the
novel reductive dimerization of carbonyl derivatives
to olefins by subvalent titanium reductants of unspec-
ified oxidation state and composition (Eq. (1)).
PhMe slurry
ð2Þ
˚
˚
25 C to 65 C
MCl2
− 2 Bu
2
in THF : bis-THF solvate
in PhMe : slurry with LiCl
By the use of such reagents as 2 of well-defined va-
lence and stoichiometry, considerable control could be
exerted on both the extent and stereochemistry of the
reductive coupling of ketones [2]. Acetophenone (3),
for example, reacts with 2 equiv. of TiCl2 in refluxing
THF to give upon hydrolysis 83% of the racemic-2,3-di-
phenyl-2,3-butanediol (7) only, while with 4 equiv. of
TiCl2 the ketone gives 88% of olefin 8 as a 92:8 mixture
of E and Z isomers. The exclusive formation of racemic
7 is consistent with the likely intermediacy of the three-
membered ring 4 and the sterically controlled transition
state 5 for the insertion of the second ketonic unit to
form 6 (Scheme 1) [3,4].
R
R
R'
R
Ti (?)
2
C
O
C
C
ð1Þ
− Ti(?)O
R'
R'
E – isomer chiefly
Such reports have issued independently from three dif-
ferent research groups where each utilized an empirical
combination of a Ti(III) or Ti(IV) salt with a main-
group metal or metal hydride [5–7]. This transforma-
tion, which has come to be termed the McMurry
coupling after one of its discoverers, has found many
valuable applications in organic synthesis [8–10]. But
the use of such empirical reductants either in mechanis-
tic studies of the McMurry coupling itself or in the
synthesis of transition metal organometallics has up
to now proved to be impractical. Hence, the recent dis-
covery of a convenient, low-temperature route to the
Group 4 dichlorides, MCl2, as bis-THF solvates in
THF, or as slurries with LiCl in toluene, has proved
crucial for a systematic study of reductive dimeriza-
tions [2–4]. In a process termed alkylative reduction
the MCl4 is dialkylated with n-butyllithium at
ꢀ78 ꢀC to form intermediate 1; warming 1 to 25 ꢀC
and above causes the reductive elimination of butyl
groups (as butane and butene) and the high-yielding
production of 2 (Eq. (2)).
Accordingly, the stereoselective reductive coupling of
carbonyl derivatives by TiCl2 depicted in Scheme 1 and
the analogous reductive coupling subsequently observed
with imines, such as N-benzylideneaniline (9), as medi-
ated by TiCl2 or ZrCl2 (Scheme 2), have provided excel-
lent model systems with which to assess steric effects in
forming C–C bonds in such ansa-bridged systems, such
as 6 and 10 and 11 (where the bridging O–CH2–
CH2–O and NPh–CHPh–CHPh–NPh linkages can be
envisaged as providing a ‘‘handle’’ (L. ansa) on the
metal center). In all three systems these intermediate
metallocycles can readily be hydrolyzed and the ratio
of the resulting racemic:meso glycols (7) or diamines
[(PhCH–NHPh)2 from 10 and 11] can be determined
1
by H NMR spectroscopy. Alternatively, the ratio of
the metallocycles 10 and 11 can be estimated directly
1
from their H NMR spectra.
O
C
3
O
Me
Ph
Ph
Ph
TiCl2
2 equiv.
∆, THF
TiCl2
4 equiv.
∆, THF
C
C
C
TiCl2
Me
Me
Me
Ph
8
4
(E:Z =92:8)
3
O
Ph
Ph
Me
Me
Ph
Ph
Me
OH
H3O+
C
O
O
C
C
TiCl2
O
C
Me
Me
Ph
TiCl2
C
Me
Ph
C
OH
5
6
7
Scheme 1.

J.J. Eisch et al. / Polyhedron 24 (2005) 1325–1339
1327
Ph
H
Ph
Ph
H
Ph
in toluene of 16, 17 and 18 admixed with LiCl by-prod-
uct were prepared according to Eq. (2) and allowed to
react with 2 equiv. of fulvene 15 at reflux. Although
the fulvene was largely consumed and the ansa-metalloc-
enes 19–21 formed in good to high yield, moderate to
fair yields of unbridged substituted metallocenes (25–
27) were also obtained. The source of the unbridged
metallocenes 25–27 as side-products was traced to the
presence of undecomposed Bu2MCl2 (22–24) in the
MCl2 formed in toluene at 25 ꢀC . Clearly Bu2MCl2 per-
formed a bis-hydrometallation by transfer of two moles
of fulvene 15 [13].
C
C
N
N
C
C
N
N
Ph
H
MCl2
C
N
2
MCl2
Ph
MCl2
Ph
+
H
Ph
H
Ph
M = Ti, Zr
9
Ph
10
11
0%
20%
M = Ti 100%
M = Zr 80%
Scheme 2.
Because of the foregoing success with the efficient and
stereoselective reductive dimerizations of both ketones
and imines with Group 4 metal dichlorides, we were in-
spired to attempt a similar dimerization of 6-substituted
fulvenes (12) with the hope of producing thereby novel
ansa-metallocenes having some stereochemical prefer-
ence for the substituents on the ansa-bridge (ratio of
13:14) (Eq. (3)) [11,12]. Were such a dimerization to suc-
ceed, it would represent a radical departure from estab-
lished routes to bridged or ansa-metallocenes and offer a
new approach to stereochemical isomers of such systems
as 13 and 14 [12].
2.2. Preparation of tetramethylethylene-
bis(cyclopentadienyl)metal dichlorides 19, 20 and 21
In light of this insight complete conversion of any
Bu2MCl2 remaining in the toluene suspension to MCl2
could be assured by heating the reagent at reflux for sev-
eral hours. Then the reaction of such purified MCl2 gave
yields of over 90% for ansa-metallocenes 19–21, as well
as pure product by Soxhlet extraction or flash column
chromatography in 80–85% yield.
R'
R
R'
R
R
MCl2
?
2
MCl2
MCl2
+
2.3. Preparation of bis(isopropylcyclopentadienyl)metal
dichlorides 25, 26 and 27
R
R'
R'
R
R'
12
R, R' = H, alkyl,aryl
13 racemic
14 meso
The discovery of the interesting bis-hydrozirconation
by Bu2MCl2 leading to unbridged metallocenes 25–27
prompted us to attempt to maximize this course of reac-
ð3Þ
tion by generating the individual Bun MCl2 at ꢀ78 ꢀC in
2
2. Results
toluene (Eq. (1)) and immediately thereupon adding the
2 equiv. of 6,6-dimethylfulvene. The resulting reaction
was warmed to 25 ꢀC and then heated at 65 ꢀC for several
hours. This procedure was most effective in producing
75–85% yields of bis(isopropylcyclopentadienyl)-zirco-
nium dichloride (26) and bis(isopropylcyclopentadie-
nyl)hafnium dichloride (27), which products were
shown to be free of the corresponding ansa-derivatives
(20 and 21, respectively) by NMR criteria [13].
However, in the reaction of TiCl4 with n-butyllithium
in toluene at ꢀ78 ꢀC, minutes after admixing the re-
agents the solution turned black, which signaled forma-
tion of TiCl2. Even though the fulvene 15 was then
2.1. Initial attempts with 6,6-dimethylfulvene (15) and
Group 4 metal dihalides
The reactions of 6,6-dimethylfulvene (15) with the
Group 4 metal dichlorides, TiCl2 (16), ZrCl2 (17) or
HfCl2 (18), were initially examined in THF, a solvent
in which such salts are readily prepared at room temper-
ature according to Eq. (2) (e.g., TiCl2 Æ 2THF) [11].
Although ansa-metallocene formation (19–21) was ob-
served in refluxing THF, such reductive dimerization
was slow (Scheme 3). Accordingly, individual slurries
Me
Me
H
Me
Me
C
Me2C
n
Bu 2MCl2
MCl2
MCl2
MCl2
2
PhMe
Me
Me
PhMe, ∆
Me2C
H
15
25 : M = Ti
22 : M = Ti
23 : M = Zr
24 : M = Hf
16 : M = Ti
17 : M = Zr
18 : M = Hf
19 : M = Ti
20 : M = Zr
21 : M = Hf
26 : M = Zr
27 : M = Hf
Scheme 3.

1328
J.J. Eisch et al. / Polyhedron 24 (2005) 1325–1339
added at ꢀ78 ꢀC, subsequent warming of the mixture
to 25 ꢀC and then to 65 ꢀC led to an inseparable mixture
of bis(isopropylcyclopentadienyl)titanium dichloride
(25) and tetramethylethylene-bis(cyclopentadienyl)tita-
nium dichloride (19), formed in approximately equal
amounts.
resulting from the coupling of two units of 6-(1-naph-
thyl)fulvene by ZrCl2. By plotting such data this 1,2-
di(1-naphthyl)ethylene-bis(cyclopentadienyl)zirconium
dichloride has been shown unambiguously to be the
racemic-isomer (29a) and that furthermore two chlorine
atoms are also bonded to the zirconium center. This
structural evidence confirms the assignment made in
Section 4.7.4. of the ratio of racemic-(29a) to meso-
(29b) isomers formed by integration of the methine H
2.4. ansa-Zirconocenes from 6-substituted fulvenes and
zirconium dichloride
1
singlets at 6.28 and 6.20 ppm in the H NMR spectrum
of the isomeric mixture.
In order to investigate steric effects on the stereo-
chemistry of ansa-bridge formation a trio of 6-arylful-
venes (28–30), where Ar = phenyl, 1-naphthyl or
9-anthryl, was subjected to reductive coupling by pure
To substantiate the presence of the MCl2 group
in these metallocenes, two representative metallo-
cenes, tetramethylethylene-bis(cyclopentadienyl)titanium
dichloride (19) and tetramethylethylene-bis(cyclopenta-
dienyl)zirconium dichloride (20), were subjected to mass
spectrometry by the electrospray technique with NaI.
Both 19 and 20 yielded mass spectra having prominent
peaks for parent ions containing 35Cl2, 35Cl37Cl and
37Cl2 mass contributions, respectively, in the expected
intensity ratios. Therefore, based on the XRD of 29a
and the MS data for 19 and 20, we can be confident that
all these metallocenes resulting from the interaction of 2
equiv. of a fulvene with 1 equiv. of either MCl2 or
ZrCl2 (free of Bun ZrCl2, cf. supra). In each reaction
2
ansa-bridge formation occurred in satisfactory yield
but with different ratios of racemic- and meso-isomers
(Scheme 4). A random ratio of racemic:meso-isomers
was obtained with Ar equals phenyl (28a:28b = 50:50),
a
great preference with Ar equals 1-naphthyl
(29a:29b = 83:17) and an exclusive formation of race-
mic-isomer (30a) with Ar = 9-anthryl.
In order to learn whether the covalent radii of Ti (132
pm) and Zr (145 pm) would have any effect on the race-
mic–meso-isomer ratio of ansa-bridged product, the
reductive dimerization of 6-phenylfulvene (28) was also
performed with pure TiCl2. In this case, ansa-derivative
formation also occurred efficiently in 75% yield but
again the ratio of racemic- and meso-isomers obtained
was 50:50 (analogous to 28a and 28b, with Zr replaced
by Ti).
Bun MCl2 contain the atomic grouping of MCl2 (details
2
in Sections 4.3, 4.6.1 and 4.7.1).
Further structural specification for the individual
metallocenes is completely corroborated by NMR
spectroscopic data (cf. Section 4.3): (1) the individual
1H NMR spectrum has the proper integral ratio of pro-
tons, with each proton having the expected chemical shift
and proton–proton coupling; and (2) the individual 13C
NMR spectrum of the pure metallocene or isomeric mix-
ture displays exactly the proper number of singlets with
the expected chemical shifts; moreover, the 13C NMR
spectrum in a DEPT experiment shows the expected
number of quaternary C and methine C (C–H) centers.
On the basis of the foregoing array of instrumental
analyses we judge that the structures assigned to these
novel metallocenes are dependably correct.
2.5. Structure assignments of the resulting ansa-
metallocenes and the unbridged substituted metallocenes
The ultimate structure determination usually is
achieved by an XRD analysis of a single crystal of a
substance. Although not yet achieved with any of the
present metallocenes, partly refined electron-diffraction
data however were obtained on the major isomer
Ar
Ar
H
Ar
H
H
ZrCl2
2
ZrCl2
ZrCl2
+
H
Ar
Ar
H
meso (%)
racemic (%)
28 : Ar =
28a : 50
29a : 83
30a : 100
28b : 50
29b : 17
29 : Ar =
30b :
0
30 : Ar =
Scheme 4.

J.J. Eisch et al. / Polyhedron 24 (2005) 1325–1339
1329
2.6. Attempted synthesis of tetraphenylethylene-
bis(cyclopentadienyl)zirconium dichloride (32) and the
generalized hydrozirconation of fulvenes
dissociation of 32 into stabilized biradical 33. Eventual
H-atom abstraction by 33 from toluene would result in
product 34.
Since 6,6-dimethylfulvene (15) undergoes efficient
reductive dimerization to ansa-derivatives 19, 20 and
21 with the respective metal dichloride, we were curious
to determine whether 6,6-diphenylfulvene (31) would re-
act similarly (Scheme 5). To an organic chemist, ansa-
product 32 would have a structure closely similar to
the unknown hexaphenylethane, Ph3C–CPh3, which if
fleetingly formed would be expected rapidly to dissociate
into stable trityl radicals [14]. When reductive coupling
of 31 with ZrCl2 was attempted, no ansa-derivative
was isolable.
3. Discussion
3.1. Mechanism of the reductive dimerization of the model
system, benzylideneaniline (9), with Group 4 metal
dichlorides
In considering the reactivity of TiCl2 (16), ZrCl2 (17)
or HfCl2 (18) toward a carbonyl (Scheme 1), an imine
(Scheme 2) or a fulvene substrate (Eq. (3)), it is impor-
tant to realize that the monomeric MCl2 unit delivered
must first be detached from a highly associated aggre-
gate [MCl2]x. For unsolvated MCl2 generated in toluene
such an aggregate could resemble the layer lattice of
TiCl2, for example, where infinite layers of Ti atoms
are sandwiched between two layers of Cl atoms. But
the MCl2 formed in Eq. (2) clearly can exist in much
smaller, oligomeric aggregates. In THF solution the
complex TiCl2 Æ 2THF (35) has been shown to form
[2]. Although the degree of association of such a com-
plex is not known, its ready solution in toluene would
not be consistent with a polymeric aggregate. Further-
more, such a solution of TiCl2 is diamagnetic and does
not show an EPR signal even at low temperatures.
Fortunately, information on the state of aggregation
of titanium(II) salts has been obtained from a study of
the properties of titanium(II) isopropoxide (36b), which
can be prepared analogous to TiCl2 (Eq. (2)), by treating
Ti(OPri)4 with 2 equiv. of n-butyllithium. Even when
prepared in THF, complex 36b can be completely freed
of THF in vacuo and redissolved in toluene. Such solu-
tions of 36b exhibit a strong EPR signal indicative of a
biradical and hence the presence of two unpaired elec-
trons. The strength of the signal coupling is best in ac-
cord with the unpaired electrons being on titanium
centers located 1,3 to each other (36b), rather than on
vicinal or the same Ti center(s) (Eq. (5)) [16,17]. The
bulky nature of the isopropoxy ligands may strain the
three-membered ring (36a) and favor the biradical 36b.
With much smaller chloro ligands the diamagnetic ring
in 35a should be much less strained. There would likely
be sufficient room about each Ti atom in 35a to accom-
modate two THF units and thereby permit octahedral
coordination.
Instead, substituted zirconocene 34 was obtained in
25% yield. Because a number of 6-substituted fulvenes,
such as 28, 29, 30 and 31, undergo satisfactory hydrozirc-
onation with Bun ZrCl (Eq. (4)), an authentic sample of
2
34, prepared in an unambiguous manner, was available
for spectral comparison and positive identification of
product 34 resulting from the attempted synthesis of 32.
H
R
C
C
n
R
Bu ZrCl2
2
R'
ZrCl2
2
R'
H
R
R'
28 : R = Ph; R' = H
28c
29c
30c
29 : R = 1-Naphthyl; R' = H
30 : R = 9-Anthryl; R' = H
31 : R = Ph; R' = Ph
31c = 34
ð4Þ
Accordingly, it is reasonable to conclude that the
F-strain [15] imposed on the ansa-C–C bond of 32 by
the near eclipsing of neighboring phenyl groups causes
H
C
Ph2
n
Ph
Ph
Bu 2 ZrCl2
ZrCl2
2
H
C
31
Ph2
34
ZrCl2
−
Ph CH2 Ph CH3
Ph
Ph
Ph
C
C
Ph
?
L2
Ti
ZrCl2
ZrCl2
Ph
Ph
L2Ti
TiL2
Ph
Ph
Ti
L2
Ti
Ti
L2
L2
ð5Þ
32
33
35b : L =Cl
35a : L =Cl
i
i
36a : L = OPr
36b : L = OPr
Scheme 5.

1330
J.J. Eisch et al. / Polyhedron 24 (2005) 1325–1339
The process of forming a three-membered ring or epi-
H
C
D
Ph
H
Ph
H
D2O
C
N
Ph
C
N Ph
Ph
metallated product, like 4 for carbonyl substrates or 38
for imines such as 9, could be viewed as in Scheme 6. At-
tack of 35 (or 36) on 9 would lead to biradical 37, which
would close the most rapidly to 38 by intramolecular
radical displacement [18]. The presence of 38 in such
reductive coupling was corroborated by work-up of
the reaction mixture with D2O and finding the N-phe-
nylbenzylamine dideuterated (39).
The observed stereochemistry of reductive coupling
can be readily understood by postulating the insertion
of a second 9 into the C–Ti bond of 38 via transition
state 40 where the phenyl groups would minimize steric
repulsion by forming the racemic dimer 41 [19]. With
little modification the less stereoselective coupling of
9 by ZrCl2 (racemic:meso = 80:20) can follow from
the longer C–M bond in the Zr intermediate analogous
to 38. The larger covalent radius of Zr over Ti, 145 versus
132 pm, would mean that the two carbon centers would
be farther apart in the transition state (similar to 40)
and thus not as sensitive to the steric effects of the
phenyl groups.
N
D
Ph
− (TiL2)2
Ti
L2
L2Ti Ti TiL2
L2
39
38
37
9
or 36
35
Ph
N
Ph
H
C
N
Ph
Ph
Ph
Ph
H
H
9
N
H
C
C
C
Ti
TiCl2
H
N
Ph
C
N
Ph
Ph
40
Ph
41
Scheme 6.
Bun ZrCl2 in toluene. We are forced to conclude there-
2
fore that epimetallated zirconium intermediate 44 has
been formed from 23 by the process of the transfer-
epimetallation of 9 (Scheme 7).1 The generation of the
racemic- and meso-metallocycles (45 and 46) would en-
sue as with the titanium analog (38 ! 41, Scheme 6).
Transfer-epititanation of a wide variety of unsaturated
substrates by Bun TiCl2 (22) has been amply demon-
The only remaining puzzling observation is that made
in the attempted transfer-hydrozirconation of 9 by
2
strated to be an important process in the functionaliza-
tion of alkenes and alkynes [20,21], in the Kulinkovich
cyclopropanol synthesis [22] and in olefin polymeriza-
tion [23,24].
Bun ZrCl2 (23).1 From our experience with other sub-
2
strates in hydrozirconation [13], the expected major
product should have been N-phenylbenzylamine (43),
formed via 42. Although 43 was in fact obtained in
49% yield, yet comparable amounts (51%) of an 80:20
mixture of racemic- and meso-1,2-dianilinoethanes (47
and 48) were also formed, products expected to arise
from the reductive coupling of 9 by ZrCl2 (cf. supra).
However, at the temperature of reaction, 25 ꢀC, ZrCl2
had not yet formed from the decomposition of
3.2. Transfer-hydrometallation of fulvenes and the
synthesis of unbridged substituted
bis(cyclopentadienyl)metal dichlorides
3.2.1. Chemical and physical properties of fulvenes (12)
Fulvenes (12) are colored nonaromatic hydrocarbons
possessing a dipole moment and a high degree of
chemical reactivity by virtue of their uneven p-electron
1
The generalized reactions discussed in this section, ‘‘transfer-
hydrometallation’’ and ‘‘transfer-epimetallation’’, as well as their
metal-specific counterparts, ‘‘transfer-epititanation, transfer-epizirco-
nation, transfer-hydrotitanation and transfer-hydrozirconation, are
reactions that have been studied and established in previous publica-
tions of our research group. Transfer-hydrozirconation as described in
[13] refers to the transfer of zirconium dichloride dihydride from di-n-
butylzirconium dichloride to an unsaturated substrate C = E (car-
bonyl, imine or fulvene) with release of 1-butene:
H
C
H
C
Ph
H
n
1. Bu 2 ZrCl2 (23)
Ph 2. H2O
Ph
Ph
Ph
C
N
PhCH2NHPh
+
43
9
Ph
N
N
H
H
H2O
racemic - (47)
and
meso - (48)
23
(PhCH2NPh)2ZrCl2
− 1-butene
42
diamines
n
2( H
C E ) 2 ZrCl2 CH CH CH CH2
+
3 2
2
C
E+ Bu 2ZrCl2
H2O
H
C
H
C
Analogously, transfer-epizirconation as described in [20] and [21] refers
to the transfer of zirconium dichloride from di-n-butylzirconium
dichloride to C = E (carbonyl, imine or fulvene) with release of two bu-
tyl radicals (or as butane and 1-butene):
Ph
Ph
23
9
C
N
Ph
Ph
Ph
Ph
− 2 Bu
H
Zr
N
N
Cl2
Zr
Cl2
44
racemic - (45)
and
meso - (46)
n
E + Bu 2ZrCl2
C
E + 2CH3CH2CH2CH2
C
metallocycles
Zr
Cl2
Scheme 7.

J.J. Eisch et al. / Polyhedron 24 (2005) 1325–1339
1331
3.3. Reductive coupling of fulvenes by union with
biradicals
R'
C
−
H
C
R
R'
R
R'
R
R"
R
R'
+
C
C
+
−
Li+
Li+
Li AlH4
R"Li
−
−
Analogous to the mechanistic insight gained from the
reductive dimerization of ketones or of benzylideneani-
line by Group 4 metal(II) dichlorides (Schemes 1 and
2), we propose the analogous biradical ‘‘open-face sand-
wich’’ 56 (Scheme 10), which could be formed via radi-
cal-anion 55 by SET from biradical MCl2(››).
Interaction of 56a with a second fulvene 12 would surely
be sensitive to steric factors during the formation of the
ansa-C–C bond. But if the rate of formation of the final
ansa-complexes 13 and 14 is determined by the complex-
ation of biradical 56a with a second fulvene 12 to form
56b, then the subsequent C–C bonding would be fast
and steric hindrance would have only an attenuated ef-
fect on the ansa-racemic- and meso-isomeric ratio.
Whether R = phenyl and R0 = H or whether M = Ti or
Zr in 56b would then have no large steric effect. Only
when R = 1-naphthyl or 9-anthryl and R0 = H would a
steric effect become unavoidable. This effect may have
nothing to do with steric bias in the relatively rapid
ansa-C–C bond formation but rather in the rate of com-
plexation of 56a with the prochiral p-electron cloud sur-
face of the second fulvene.
49
12
50
12a
Scheme 8.
distribution (12a and its resonance structures). Espe-
cially for our present purposes, the long-known addition
reactions of fulvenes with organolithium reagents (RLi)
[25] and with LiAlH4 [26] are especially relevant
(Scheme 8). In the formation of adducts 49 and 50 the
regioselectivity is driven by the aromatic stabilization at-
tained with the formation of the cyclopentadienyl anion.
3.2.2. Transfer-hydrometallation of fulvenes
Whether the elimination of 1-butene from Bun MCl2
(22–24) precedes the interaction of Bun MCl2 with the
fulvene to produce H2MCl2 (step a) or accompanies such
an interaction with the fulvene (step b) cannot be
decided at present (Scheme 9). Either path produces
the ‘‘open-face sandwich’’ (51). p-Complexation of 51
with a second 12, so that the RR0HC-groups on the ring
are anti to each other, would yield the final metallocenes
(52–54) with minimal steric hindrance.
2
2
3.4. Comparative polymerization of ethylene by ansa-
metallocene and unbridged metallocene procatalysts with
MAO cocatalysis
n
A complete survey of all the ansa- and unbridged cat-
alysts synthesizable from fulvenes has not yet been
made. However, the preliminary results obtained thus
far and presented in Table 1 permit us to propose three
valuable trends in reactivity: first, ansa-metallocenes are
much more active polymerization catalysts than their
unbridged counterparts: for Ti, consider runs 1, 2 and
3; for Zr, compare runs 4, 5 and 6 as well as runs 7
and 9; second, the normal order of polymerization activ-
ity for unbridged metallocenes, Zr > Ti > Hf, is changed
Bu 2MCl2
H
R'
R
12
12
22 24
C
n
step b Cl
Cl
Bu
M
−
H
12
Cl
Cl
C
R'
MCl2
step a
−
R
51
H
C
H
MCl2
R'
R
n
Bu
52 − 54
Scheme 9.
MCl2 (
)
−
e− from MCl2 (
− MCl2+
)
− MCl2+
(
)
R
R
C
R
C
C
R'
R'
R'
(
)
12
55
56a
12
slow
R
C
R'
fast
MCl2
13
+ 14
R
C
R'
56b
Scheme 10.

1332
J.J. Eisch et al. / Polyhedron 24 (2005) 1325–1339
Table 1
Comparative polymerization of ethylene with metallocene procatalysts and MAO cocatalysts
Run Metallocene
Polymerization activitya
(g PE/g M h atm)
1
2
3
Tetramethylethylene-bis(cyclopentadienyl)titanium dichloride (19)
Titanocene dichloride
2640
1100
3170
racemic- and meso-1,2-Diphenylethylene-bis(cyclopentadienyl)titanium dichloride, 1:1 mixture
(titanium analogue of 28a and 28b)
4
5
racemic- and meso-1,2-(Diphenylethylene-bis(cyclopenta-dienyl)zirconium dichloride (28a and 28b), 1:1 mixture
Bis(benzylcylcopentadienyl)zirconium dichloride (28c)
360
242
62
6
Bis[(diphenylmethyl)cyclopentadienyl)]zirconium dichloride (34)
Bis[(1-naphthylmethyl)cyclopentadienyl)]zirconium dichloride (29c)
1,2-Di-[(1-naphthylethylene)-cyclopentadienyl]titanium dichloride (titanium analogue of 29a)
1,2-Di-[(1-naphthylethylene)-cyclopentadienyl]zirconium dichloride (83:17 mixture of 29a and 29b)
Bis(isopropylcyclopentadienyl)hafnium dichloride
7
126
313
52
8
9
10
a
182
All runs were conducted in toluene at ambient temperature with uncontrolled exotherm employing 0.2–1.0 mmol of metallocene and 50 equiv. of
MAO. Comparisons of polymerization activity are reported per grams of metal in the catalyst and are measured for polymerizations proceeding
under a constant pressure of ethylene, under the spontaneous exotherm of polymerization and in a reaction mixture turning rapidly from homo-
geneous to heterogeneous. Therefore, this empirical measure of activity, widely used in industry, cannot be expected to rank polymerization rates of
catalysts in an absolute and accurate series. But as employed here, such measurements can readily distinguish among catalysts of high activity,
intermediate activity and low activity. Finally, it should be noted that the accurate measurement of initial polymerization rates (the only reliable
measure of intrinsic catalyst activity) is a most difficult procedure to carry out in a reproducible and reliable manner (cf. Fischer, D. ‘‘Untersuch-
ungen zur Propenpolymerisation an Homogenen Zirconocen/Methylaluminoxan Ziegler-Natta Katalysatoren’’, Doctoral Dissertation, Albert-
Ludwig University, Freiburg (Breisgau), Germany, 1992.
for ansa-metallocenes, where Ti > Zr > Hf; and third,
unbridged substituted zirconocenes have depressed
activities, as the steric size of the cyclopentadienyl ring
substituent increases: note runs 5, 6 and 7.
C
C
Me
Me
+
Cl
Cl
C
+
σ
Ti
R
Zr
Ti
R
Zr
The usual reason for the lesser polymerization activ-
ity of unbridged titanocenes over analogous zirconoc-
enes is the lower kinetic stability of the titanocenium
cation 57, which has been proposed as the active poly-
merization site [27]. The greater reactivity for ansa-tita-
nocenes over ansa-zirconocenes or ansa-hafnocenes,
therefore, may arise from the greater stabilization of cat-
ion 58. A source of such stabilization of the titanium
cation in 58 could be the r-bond hyperconjugation pro-
vided to the backside of the empty sp3-hybridized orbital
of the cationic Ti center (58).2 Since such stabilization
would be more important in ansa-titanocenes than in
ansa-zirconocenes (better orbital-energy match and
shorter distance between the metal center and the r-elec-
trons of the C–C bond), ansa-titanocenes should show a
larger increase in polymerization activity than ansa-
zirconocenes.
Me
Me
C
57
58
59a
59b
Finally, the reduced polymerization activity of
bis(substituted cyclopentadienyl)zirconium dichlorides
(with substituents of PhCh2-, Ph2CH- and 1-naphthylm-
ethyl (runs 5, 6 and 7)) can be attributed to the favoring
of those conformers where the substituents project out
of the wider gap between the tilted rings (59a and
59b). Such substituents thereby impede the interaction
of such zirconocenes with the MAO cocatalyst and the
approach of the ethylene to the zirconocenium cation
in the active site.
4. Experimental
4.1. Starting reagents and solvents
2
Such r-bond hyperconjugation is widely recognized as stabilizing
carbenion ions b to silicon as in R3Si–CH2–CH2+ (W. Hanstein, H.J.
Berwin, T.G. Trayler, J. Am. Chem. Soc. 92 (1970) 829) and in
promoting the facile ring-opening of the cyclopropyl carbenium ion to
the allyl cation (S.F. Cristol, R.M. Segueira, C.H. DePuy, J. Am.
Chem. Soc. 87 (1965) 4007). Since the ansa-C–C bond is closer to the
titanium cation, r-bond hyperconjugation is more likely to be the
operative effect than some inductive release of electron density from
the ansa-carbon centers to the titanium centers but operative through
the p-bonding of the rings.
Cyclopentadiene was freshly cracked from commer-
cially available dicyclopentadiene and distilled under
an atmosphere of dry argon directly before use.
6,6-Dimethylfulvene, 6,6-diphenylfulvene, 1-naphtha-
ldehyde, 9-anthraldehyde, benzylideneaniline, tita-
nium(IV), zirconium(IV) and hafnium(IV) chlorides
and n-butyllithium in hexane were obtained from

J.J. Eisch et al. / Polyhedron 24 (2005) 1325–1339
1333
commercial sources in at least 98% purity and were used
directly. All solvents employed with organometallic re-
agents or anhydrous metal salts were dried and distilled
from a sodium metal–benzophenone ketyl mixture prior
to use [28].
awe, UK) equipped with an orthogonal electrospray
source (Z spray) operated in a positive ion mode. The
samples were prepared in a solution containing acidified
methanol and sodium iodide as an internal mass
standard.
4.2. General procedures
4.4. Preparation of Group 4 metal dichlorides
All procedures involving the purification of reaction
solvents, the individual preparation of Group 4 metal
dialkylmetal dichlorides, Group 4 metal dichlorides
and their subsequent reactions leading to metallocenes
and their purification were conducted under an atmo-
sphere of anhydrous, oxygen-free argon. The drying
and deoxygenation of argon were carried out by means
of a purification apparatus previously described [28].
Nonhydrolytic workup of certain reactions to recover
the organic ligand was achieved with 3 N aqueous HCl.
4.4.1. Titanium dichloride (16)
The preparation of titanium dichloride in THF and
its isolation as the LiCl-free and analytically supported
complex, TiCl2 Æ 2THF (35), has been described else-
where [2]. The complex 35 was analyzed after removal
of the THF in vacuo and found to have retained two
moles of solvated THF per Ti unit. However, the sol-
vate-free titanium dichloride (16), prepared in hydro-
carbon slurry with LiCl, has proved more effective in
the following reductive dimerizations of fulvenes. A
colorless solution of TiCl4 (5.5 mL, 5.5 mmol) in
20 mL of THF was prepared at ꢀ78 ꢀC to avoid cleav-
age of the THF. Then 6.9 mL of n-butyllithium 1.6 M
in hexane (11 mmol) was added dropwise at ꢀ78 ꢀC
causing the formation of a red-brown solution. The
dark red solution was brought to RT, stirred for
12 h and then heated at reflux for 3 h. After solvent
removal in vacuo the dark residue was diluted with
30 mL of toluene to give a black solution of 16 (5.5
mmol) with suspended LiCl.
4.3. Instrumentation and analysis
After purification the reaction products were rou-
1
tinely subjected to IR and H and 13C NMR spectro-
scopic and, in some cases, mass spectrometric analysis.
Since such data served to corroborate the structures as-
signed to the metallocenes satisfactorily, elemental anal-
yses were considered unnecessary. The IR spectra were
recorded with a Perkin–Elmer instrument (model 457)
and samples were measured under argon either as min-
eral oil mulls or as KBr films. The NMR spectra (1H
and 13C) were recorded under argon with a Bruker spec-
trometer (model EM-360) and tetramethylsilane (Me4Si)
was used as the internal standard. The chemical shifts
reported are expressed on the d scale in parts per million
(ppm) from the Me4Si reference signal. No data on JHH
4.4.2. Zirconium dichloride (17)
Zirconium dichloride can likewise be prepared in
THF and isolated as the LiCl-free and analytically pure
complex, ZrCl2 Æ 2THF (17). Again, here the complex 17
in toluene slurried with LiCl has proved more effective in
ansa-metallocene preparations. Thus a clear solution of
ZrCl4 (0.20 g, 0.86 mmol), prepared in 20 mL of THF at
ꢀ78 ꢀC, was treated with 1.1 mL of 1.6 M n-butylli-
thium in hexane (1.72 mmol). The dark red solution
was brought to RT, stirred for 12 h and then heated
at reflux for 3 h. After solvent removal in vacuo the
black residue was treated with 20 mL of toluene to give
a black solution of 17 (0.86 mmol) with suspended LiCl.
In a similar manner a suspension of ZrCl2 (5.89
mmol) and LiCl in hexane alone was prepared from
5.89 mmol of ZrCl4 and 11.8 mmol of n-butyllithium
in a total of 40 mL of hexane.
1
coupling constants exhibited in the H NMR spectra
have been included because such values are in all cases
in the expected range and unexceptional. However, it
is worth noting that DEPT measurements in the 13C
NMR spectra reported here were able to distinguish
quaternary carbon centers (C) from methine–carbon
(C–H) centers. The latter but not the former carbon sig-
nals underwent resonance with inversion of signal. The
number of quaternary C signals and methine–carbon
signals observed fit the assigned structure in every case.
The gas chromatographic analyses were carried out
with a Hewlett–Packard instrument (model 5880) pro-
vided with a 2-m OV-101 packed column or with a Hew-
lett–Packard instrument (model 4890) having a 30 m
SE-30 capillary column. Melting points were determined
on a Thomas-Hoover Unimelt capillary melting point
apparatus and are uncorrected.
4.4.3. Hafnium dichloride (18)
Hafnium dichloride (18) prepared in THF appears to
form the solvate, HfCl2 Æ 2THF, as well but the solvate is
not stable upon removal of the THF in vacuo. Thus a
clear solution of HfCl4 (3.73 g, 11.6 mmol) in 80 mL
of THF at ꢀ78 ꢀC was treated with 15 mL of 1.6 M
n-butyllithium (23.2 mmol). The pale yellow solution
was then stirred for 12 h at RT and then heated at reflux
for 5 h. The dark brown solution was freed of solvent in
The mass spectral measurements were performed at
the Mass Spectrometry & Proteomics Facility at the
Ohio State University and employed a Micromass
ESI-Tofe mass spectrometer (Micromass, Wythensh-

1334
J.J. Eisch et al. / Polyhedron 24 (2005) 1325–1339
vacuo and the residue of HfCl2 (18) and LiCl was sus-
pended in 60 mL of toluene.
1H NMR (CDCl3): 8.5 (s, 1H), 8.16–8.13 (m, 2H),
8.06–8.01 (m, 2H), 7.94 (s, 1H), 7.51–7.44 (m, 4H),
6.65–6.60 (m, 2H), 6.52–6.49 (m, 1H), 5.89 (d, 1H).
13C NMR (CDCl3): 150.3, 134.5, 134.3, 132.4, 131.2,
130.6, 130.1, 128.5, 127.7, 126.3, 125.8, 125.4, 125.3,
122.5.
4.5. Synthesis of fulvenes
4.5.1. 6-Phenylfulvene (28)
To a solution of freshly distilled benzaldehyde (dis-
tilled under argon, 0.40 mL, 4.0 mmol) and freshly
cracked cyclopentadiene (0.82 mL, 10 mmol) in 4.0
mL of methanol was added 0.5 mL of pyrrolidine.
After 15-min stirring a 0.4 mL-portion of acetic acid
was added and the solution stirred for a further 15
min. A mixture of ether and water was added and
the organic layer separated and dried over solid
MgSO4. Ether removal from the organic layer left pure
6-phenylfulvene (28), 584 mg (89%) of dark orange
crystals, mp. 33–34 ꢀC. The reaction could be run on
a 20-fold scale with little decrease in yield. Anal. Calc.
for C12H10: C, 93.46; H, 6.54. Found: C, 93.65; H,
6.49%.
4.6. ansa-Metallocene dichlorides of titanium
4.6.1. From 6,6-dimethylfulvene (15)
To a black solution of 10.0 mmol of TiCl2 Æ 2THF
(16) in 30 mL of toluene (cf. Section 4.4.1) were added
20.0 mmol (2.41 mL) of 6,6-dimethylfulvene (15) and
the resulting mixture heated at reflux for 6 h. There-
upon, the suspension was filtered and the black solid
was washed twice with chloroform. The filtrate was
freed of volatiles in vacuo to give red-brown 19, spec-
trally quite pure, consistently in >90% yield in duplicate
runs. Alternatively, the solvent was removed in vacuo,
and the solid residue transferred under argon to
the thimble of a Soxhlet extraction apparatus. Extrac-
tion with hexane over 20 h gave a hexane solution
of 1,1,2,2-tetramethylethylene-bis(cyclopentadienyl)tita-
nium dichloride (19). By solvent removal, washing with
cold pentane and vacuum-drying, product 19 was iso-
lated as a reddish brown solid (2.81 g, 85%). Further
purification could be achieved by flash column chroma-
tography with a gradient of hexane–chloroform, starting
from pure hexane and ranging to pure chloroform. This
metallocene is oxygen- and moisture-sensitive, turning
1H NMR (CDCl3): 7.59–9.56 (m, 2H), 7.42–7.30 (m,
3H), 7.20 (s, 1H), 6.71–6.64 (m, 2H), 6.52–6.49 (m, 1H),
6.33–6.31 (m, 1H). 13C NMR (CDCl3): 145.3, 138.2,
136.8, 136.4, 130.8, 130.7, 129.0, 128.6, 127.2, 120.3.
4.5.2. 6-(1-Naphthyl)fulvene (29)
To a solution of 1-naphthaldehyde (9.1 g, 58.2 mmol)
in 50 mL of methanol was added the fresh cyclopentadi-
ene (12.0 mL, 0.146 mol). After 15-min stirring 7.30 mL
of pyrrolidine was introduced, causing the mixture to
turn orange during 4 h-stirring at RT. Addition of 5.3
mL of acetic acid, further stirring for 20 min and dilu-
tion of the reaction mixture with water and ether yielded
a biphasic system. The organic layer was separated,
dried over MgSO4 and freed of solvent to provide the
crude 29. Its purification by flash column chromatogra-
phy on silica gel with a hexane–ethyl acetate eluent gave
orange crystals of 29 (9.93 g, 84%), m.p. 52–54 ꢀC.
Anal. Calc. for C16H12: C, 93.71; H, 6.29. Found: C,
93.84; H, 6.18%.
1
yellowish green in moist air. H NMR (CDCL3): 6.90
(t, 4H), 6.25 (t, 4H), 1.45 (s, 12H). 13C NMR (CDCl3):
145.5, 128.5, 112.5, 45.5, 28.0. MS (electrospray in ESI
with N2 gas; capillary voltage 3000 V, source tempera-
ture 110 ꢀC, cone voltage 55 V) prominent parent ion
+ Na peaks (intensity) at 297 (10), 299 (5), 301 (1),
corresponding to the theoretical masses and intensi-
ties of C12H1235Cl2TiNa, C12C1235Cl37ClTiNa and
C12C1237Cl2TiNa, respectively.
1H NMR (CDCl3): 8.11 (d, 1H), 7.90 (t, 3H), 7.76 (d,
1H), 7.53 (t, 3H), 6.69 (d, 2H), 6.56 (s, 1H), 6.50 (s, 1H).
13C NMR (CDCl3): 147.1, 135.7, 134.9, 133.8, 133.4,
132.0, 131.8, 130.0, 129.4, 128.6, 126.6, 126.2, 126.1,
125.4, 124.4, 121.5.
4.6.2. From 6-phenylfulvene (28)
In a similar manner, a solution of 6-phenylfulvene
(28, 1.54 g, 10.0 mmol) and a solution slurry of
TiCl2 Æ 2THF (16, 5.0 mmol) with the suspended LiCl
in 50 mL of toluene were heated at reflux for 6 h.
The reaction suspension was filtered and the black filter
cake washed twice with chloroform. Removing vola-
tiles from the filtrate gave >90% of a spectrally pure
1:1 mixture of meso- and racemic-isomers. Alterna-
tively, analogous Soxhlet extraction and subsequent
workup provided 85% of a brown-red 1:1 mixture
of the meso-ansa- and the racemic-ansa-isomers of
1,2-diphenylethylene-bis(cyclopentadienyl)titanium di-
chloride. The conclusion that both isomers are present
in such product is drawn from the 13C NMR spectrum,
4.5.3. 6-(9-Anthryl)fulvene (30)
In a procedure analogous to the foregoing, a solution
of 9-anthraldehyde (15.0 g, 82.8 mmol) and cyclopent-
adiene (15.0 mL, 0.182 mol) in 75 mL of methanol
was treated with 9.1 mL of pyrrolidine and worked up
with water and ether. The crude 30 was purified by flash
column chromatography to give orange crystals of 30
(12.6 g, 68%), m.p. 100–101 ꢀC.
Anal. Calc. for C20H14: C, 94.45; H, 5.55. Found: C,
94.22; H, 5.60%.
which displays 18 sp2-carbon and
2
sp3-carbon

J.J. Eisch et al. / Polyhedron 24 (2005) 1325–1339
1335
(methine carbon) signals. The 1H NMR signals also
come in signal packets of 10:4:4:1:1, consistent with
the presence of both meso- and racemic-isomers. The
equal intensity of the methine singlets at 4.85 and
4.35 ppm confirm the presence of a 1:1 mixture. The
signal at 4.35 ppm is assigned to the racemic-isomer,
since its methine H should be shielded by the p-cloud
of the adjacent phenyl group. The meso- and racemic-
isomers could be separated by flash column chroma-
authentic sample of 34 for confirming the structure of
this reaction product. 1H NMR (CDCl3): 7.28–7.09
(m, 20H), 6.05 (t, 4H), 5.78 (t, 4H), 5.64 (s, 2H). 13C
NMR (CDCl3): 143.4, 136.3, 129.0, 128.4, 126.7,
116.0, 115.2, 51.5.
4.7.3. From 6-phenylfulvene (28)
A suspension of ZrCl2 (17, 10.0 mmol) and LiCl in
30 mL of toluene was heated at reflux with 6-phenylful-
vene (3.08 g, 20 mmol) for 8 h. Work-up by filtration
gave >90% of essentially pure 28a and 28b. Alterna-
tively, nonhydrolytic workup and Soxhlet extraction
gave 3.53 g (75%) of a colorless 1:1 mixture of the
meso-ansa-(28b) and racemic-ansa-(28a) isomers of 1,2-
diphenylethylene-bis(cyclopentadienyl)zirconium dich-
loride. Spectral evidence for such a composition of these
isomers and the assignment of the methine H at 4.28
ppm to the racemic-isomer follow the arguments given
tography with
a
hexane–chloroform gradient. 1H
NMR (CDCl3): 7.16–6.80 (m, 10H), 5.88–5.85 (m,
4H), 5.77–5.76 (m, 4H), 4.85 (s, 1H), 4.35 (s, 1H).
13C NMR (CDCl3): 140.8, 139.2, 137.4, 136.9, 134.0,
130.6, 129.3, 129.1, 128.8, 128.5, 127.8, 127.5, 126.9,
126.9, 117.7, 116.7, 113.2, 109.4, 53.9, 51.1.
The greater thermal lability and reactivity of the
other ansa-metallocenes made their isolation more diffi-
cult, so a more extensive study of ansa-metallocenes was
undertaken with zirconium analogues.
1
in Section 4.6.2. for the titanium analogue. H NMR
(CDCl3): 7.16–6.90 (m, 20H), 5.90 (t, 4H), 5.85–5.70
(m, 4H), 4.91 (s, 1H), 4.28 (s, 1H). 13C NMR (CDCl3):
141.6, 139.8, 135.6, 129.5, 129.0, 128.7, 127.8, 127.6,
127.0, 113.5, 113.3, 110.7, 106.1, 54.4, 51.3.
4.7. ansa-Metallocene dichlorides of zirconium
4.7.1. From 6,6-dimethylfulvene (15)
A solution of 6,6-dimethylfulvene (15, 1.20 mL, 10
mmol) in 60 mL of toluene was combined with a solution
slurry of ZrCl2 (17, 5.0 mmol, cf. Section 4.4.2.) and LiCl
in 50 mL of toluene and the mixture stirred at reflux for
8 h. Filtration of the reaction mixture and washing of
the filtered cake twice with chloroform gave an extract,
from which volatiles were removed in vacuo. The off-
white 20 was spectrally pure and isolated in >90% yield.
Alternatively, nonhydrolytic workup and Soxhlet extrac-
tion provided 1.31 g of colorless tetramethylene-
bis(cyclopentadienyl)zirconium dichloride (20) in 70%
yield. 1H NMR (CDCl3): 6.70 (t, 4H), 6.20 (t, 4H), 1.45
(s, 12H). 13C NMR (CDCl3): 143.5, 123.3, 108.8, 45.2,
28.4. MS (electrospray in ESI with N2 gas; capillary volt-
age 3000 V, source temperature 110 ꢀC, cone voltage 55 V)
the three most prominent parent ion + Na peaks (inten-
sity) at 339 (1.5), 341 (1.5) and 343 (1.0), corresponding
to the theoretical intensities of C12C1235Cl2ZrNa,
C12C1235Cl37ClZrNa and C12C1237Cl2ZrNa, respectively.
4.7.4. From 6-(1-naphthyl)fulvene (29)
In a similar procedure, a solution of 6-(1-naphthyl)ful-
vene (29, 352 mg, 1.72 mmol) in 30 mL of toluene was
heated at reflux with ZrCl2 (17, 0.86 mmol) for 4 h. The
reaction mixture was filtered and the filter cake washed
repeatedly with toluene. The solvent was removed from
the combined filtrate and washings in vacuo to give
369 mg (75%) of off-white meso-ansa-(29b) and racemic-
ansa-(29a) isomers. The spectral evidence for the presence
of both meso- and racemic-isomers is: (1) the presence of
30 sp2-C signals; and (2) the presence of 2 sp3-C signals
and of 2 1H methine singlets. The ratio of the meso:race-
mic-isomers can be obtained by integrating the 1H
methine singlets at 6.20 and 6.28 ppm and obtaining a ra-
tio of 6.20:6.28 signals of 17:83. Noting that the racemic
methine H should be more shielded (Section 4.6.2), we
can conclude that the racemic-ansa-isomer (29a) is the
major isomer. Upon recrystallization of mixture 29a
and 29b from a toluene–hexane pair a colorless product
was recovered; its 1H NMR spectrum now lacked the sin-
glet at 6.20 ppm and its 13C NMR spectrum had no signal
at 45.5. Hence, the recrystallized product consisted of
essentially the racemic-ansa-isomer. Crystal samples sub-
mitted thus far to Professor A.L. Rheingold (then of the
University of Delaware and now of the University of Cal-
ifornia at San Diego) for single-crystal X-ray determina-
tion have led to the unambiguous determination that
this isomer has the racemic structure (29a). However, bet-
ter crystals will be required, in order to refine the data to
attain R < 10%.
4.7.2. From 6,6-diphenylfulvene (31), (attempted)
Heating a suspension of ZrCl2 (17, 9.5 mmol) and
LiCl with a solution of 6,6-diphenylfulvene (31, 2.20 g,
9.5 mmol) in 60 mL of toluene for 18 h gave upon usual
nonhydrolytic workup an off-white, air- and moisture-
sensitive solid in about 25% yield that proved to be
bis(diphenylmethyl(cyclopentadienyl))zirconium dichlo-
ride (34), rather than the expected ansa-metallocene
32. The presence of a singlet signal for the methine
hydrogen at 5.64 ppm provided decisive evidence
against the presence of 32. Moreover, the straightfor-
ward hydrozirconative coupling of 31 by dibutylzirco-
nium dichloride (23) (Section 4.9.5) provided an
1H NMR (CDCl3): 8.56 (d, 4H), 7.99 (d, 2H), 7.79–
7.66 (m, 6H), 7.52–7.18 (m, 8H), 6.85 (m, 4H), 6.52

1336
J.J. Eisch et al. / Polyhedron 24 (2005) 1325–1339
(m, 4H), 6.44 (s, 2H), 6.20–6.28 (2s, total of 2H). 13C
NMR (CDCl3): 136.58, 136.12, 134.94, 134.57, 133.87,
131.63, 129.21, 129.13, 128.98, 128.17, 128.05, 127.86,
127.51, 127.21, 126.40, 125.72, 125.64, 125.55, 125.50,
125.25, 124.46, 1223.13, 123.02, 122.16, 121.52, 120.00,
113.43, 113.24, 110.28, 106.66, 48.30, 45.46.
ethylfulvene and warming to RT and finally 65 ꢀC led
to the formation of a mixture of tetramethylethylene-
bis(cyclopentadienyl)titanium dichloride (19) (NMR
spectral data in Section 4.6.1) and bis(isopropylcyclo-
pentadienyl)titanium dichloride (25), readily identifiable
by a 12H doublet at 1.45 and a 2H septet at 3.25 ppm.
4.7.5. From 6-(9-anthryl)fulvene (30)
4.9.2. Hydrozirconation of 6,6-dimethylfulvene (15)
To a white suspension of ZiCl4 (2.12 g, 9.1 mmol) in
50 mL of toluene at ꢀ78 ꢀC were slowly added 2 equiv.
of n-butyllithium (18.2 mmol, 11.4 mL of 1.6 M), where-
upon the solution turned light brown as it was warmed
to RT. After 6 h 6,6-dimethylfulvene (15, 1.97 g, 18.6
mmol) was added and the reaction continued for 1 h
at RT and 6 h at 65 ꢀC. Filtration of the cooled reaction
mixture and removal of volatiles in vacuo gave the light-
brown bis(isopropylcyclopentadienyl)zirconium dichlo-
ride (26) consistently in >90% yield. Extraction with
hexane in a Soxhlet apparatus over 1 h gave colorless
A solution of 6-(9anthryl)fulvene (30, 2.23 g, 8.8
mmol) in 30 mL of toluene was stirred with a suspension
of ZrCl2 (14.4 mol) and LiCl in 20 mL of toluene at RT
for 12 h and then at reflux for 6 h. The cooled reaction
mixture was filtered and the filtrate cake washed thrice
with 20-mL portions of toluene. The combined filtrate
and washings were freed of solvent in vacuo to give
1.92
g
(65%) of light brown racemic-1,2-(di-9-
anthryl)ethylene-bis(cyclopentadienyl)zirconium dichlo-
ride (30a). Recrystallization from a toluene–hexane gave
colorless, air- and moisture-sensitive 30a. 1H NMR
(CDCl3): 7.95 (d, 2H), 7.74 (d, 4H), 7.65 (d, 2H),
7.44–7.15 (m, 10H), 6.81 (m, 4H), 6.47 (m, 2H), 6.40
(s, 2H), 6.16 (s, 2H). 13C NMR (CDCl3): 137.8, 136.1,
134.6, 133.9, 131.7, 129.2, 129.0, 128.2, 128.1, 127.6,
126.4, 125.9, 125.6, 125.3, 124.5, 123.1 spectrum (6.16)
and in the 13C spectrum (48.4) are consonant with only
one ansa-isomer. Steric control decisively supports the
racemic structure (30a) for that single isomer.
1
26 in 75% yield. H NMR (CDCl3): 6.60 (t, 4H), 6.45
(t, 4H), 3.25 (septet, 2H), 1.45 (d, 12H). 13C NMR
(CDCl3): 142.0, 114.6, 112.0, 28.3, 23.2.
4.9.3. Hydrozirconation of 6-phenylfulvene (28)
A mixture of 6-phenylfulvene (28, 860 mg, 5.6 mmol)
and di-n-butylzirconium dichloride (23, 2.8 mmol, cf. Sec-
tion 4.9.2) in 40 mL of toluene was allowed to react at RT
for 1 h and at reflux for 2 h. Solvent removal in vacuo and
the solid washed well with pentane to remove any residual
28. The residue was slurried again with toluene and the
LiCl filtered off. The filtrate was freed of volatiles in vacuo
to give 282 mg (95%) of light brown bis(benzylcyclopenta-
dienyl)zirconium dichloride (28c). Further purification by
4.8. ansa-Metallocene dichlorides of hafnium
4.8.1. From 6,6-dimethylfulvene (15)
A mixture of 6,6-dimethylfulvene (15, 1.00 mL, 8.7
mmol) and a suspension of HfCl2 (11.6 mmol) and LiCl
in 60 mL of toluene was heated at reflux for 12 h. The
cooled reaction mixture was freed of solvent in vacuo
and the residue subjected to Soxhlet extraction with
10% chloroform in hexane to yield 1.83 g (90%) of col-
orless, air- and moisture-sensitive tetramethylene-
bis(cyclopentadienyl)hafnium dichloride (21). H NMR
(CDCl3): 6.57 (t, 4H), 6.02 (t, 4H), 1.46 (s, 12H). 13C
NMR (CDCl3): 141.6, 121.7, 106.7, 44.7, 28.5.
1
Soxhlet extraction gave 75% of colorless 28c. H NMR
(C6D6): 715–6.99 (m, 10H), 5.89 (t, 4H), 5.69 (t, 4H),
3.98 (s, 4H). 13C NMR (CDCl3): 140.71, 133.81, 129.59,
129.16, 127.03, 117.51, 112.96, 36.07.
1
4.9.4. Hydrozirconation of 6-(1-naphthyl)fulvene (29)
A mixture of 6-(1-naphthyl)fulvene (29, 1.9 g, 9.2
mmol) and Bun ZrCl2 (23, 4.6 mmol) in 40 mL of tolu-
2
ene was allowed to react for 1 h at RT and 3 h at 65 ꢀC.
The cooled mixture was filtered to remove the LiCl. The
filtrate was freed of solvent in vacuo and the residue was
extracted with methylene chloride in a Soxhlet appara-
tus. In this way a 55% yield of almost colorless bis(1-
naphthylmethyl(cyclopentadienyl))zirconium dichloride
4.9. Hydrometallations of fulvenes
4.9.1. Hydrotitanation of 6,6-dimethylfulvene (15),
(attempted)
Attempts to generate di-n-butyltitanium dichloride
(22) at ꢀ78 ꢀC just before adding 6,6-dimethylfulvene
(15) to such a reagent failed because of the instability
of 22 even at such low temperatures. Thus to a solution
of TiCl4 (4.0 mL, 4.0 mmol) in 30 mL of toluene at
ꢀ78 ꢀC were slowly added 2 equiv. of n-butyllithium
(5.0 mL of 1.6 M in hexane, 8.0 mmol). During 30 min
the progression of a colorless reaction mixture to yellow
to green to brown and then to black signaled decompo-
sition of 22 to TiCl2 (16). Addition of 2 equiv. of 6,6-dim-
1
(29c) was obtained. H NMR (CDCl3): 8.05 (m, 3H),
7.88 (m, 4H), 7.76 (m, 3H), 7.44 (m, 4H), 6.21 (m,
4H), 6.16 (m, 4H), 4.52 (s, 4H). 13C NMR (CDCl3):
142.5, 136.0, 133.9, 128.8, 127.4, 127.0, 126.1, 125.9,
125.7, 124.7, 124.0, 117.5, 112.4, 47.7.
4.9.5. Hydrozirconation of 6,6-diphenylfulvene (31)
A mixture of 6,6-diphenylfulvene (31, 202 g, 8.84
mmol) and Bun ZrCl2 (23, 4.42 mmol) in 40 mL of
2

J.J. Eisch et al. / Polyhedron 24 (2005) 1325–1339
1337
toluene was allowed to react for 1 h at RT and 3 h at
4.10.3. Analogous polymerization with
65 ꢀC. The cooled reaction mixture was freed of sol-
vent in vacuo and the residue extracted with methy-
lene chloride in a Soxhlet apparatus. The filtrate was
freed of volatiles to give a light brown residue of
bis(diphenylmethyl(cyclopentadienyl))zirconium dichlo-
ride (31c) (65% yield). Washing with pentane gave an
off-white sample of 31c, whose 1H and 13C NMR
spectra were identical with the product obtained in
Section 4.7.2.
bis(isopropylcyclopentadienyl)hafnium dichloride (27)
A parallel polymerization of ethylene using 1.02
mmol of 27 and 50 equiv. of MAO for 30 min gave a
PA = 182 g PE/g Hf h atm.
4.10.4. Analogous polymerization with
bis(benzylcyclopentadienyl)zirconium dichloride (28c)
With 0.85 mmol of 28c and 50 equiv. of MAO for 15
min of ethylene purge, a PA of 242 g PE/g Zr h atm was
obtained.
4.9.6. Hydrohafniation of 6,6-dimethylfulvene (15)
A mixture of 6,6-dimethylfulvene (15, 1.7 mL, 14.2
4.10.5. Analogous polymerization with bis(diphenyl-
methyl(cyclopentadienyl))zirconium dichloride (31c)
With 0.18 mmol of 31c and 50 equiv. of MAO for 10 min
ofethylene purge, a PA of 62 g PE/g Zr h atmwas obtained.
mmol) and Bun HfCl2 (24, 7.1 mmol, made analogous
2
to Bun ZrCl2 from HfCl4 and 2 equiv. of n-butyllithium)
2
in 40 mL of toluene was allowed to react for at RT for
1 h and at 65–70 ꢀC for 4 h. The toluene was removed
from the reaction mixture and the residue extracted with
hexane in a Soxhlet apparatus. The hexane yielded 2.44
4.10.6. Analogous polymerization with bis(1-naphthyl-
methyl(cyclopentadienyl))zirconium dichloride (29c)
With 0.79 mmol of 29c and 50 equiv. of MAO for 15
min of ethylene purge, a PA of 126 g PE/g Zr h atm was
obtained.
g
(73%) of red-brown bis(isopropylcyclopentadie-
nyl)hafnium dichloride (27). 1H NMR (CDCl3): 6.30
(t, 3H), 6.12 (t, 4H), 3.14 (septet, 2H), 1.14 (d, 12H).
13C NMR (CDCl3): 141.3, 113.1, 110.7, 27.0, 22.6.
4.10.7. Analogous polymerization with 1:1 racemic- and
meso-1,2-diphenylethylene-bis(cyclopentadienyl)
titanium dichloride
4.10. Comparative polymerizations of ethylene with
metallocene catalysts
With 0.45 mmol of this metallocene and 50 equiv. of
MAO for 10 min of ethylene purge, a PA of 3170
g PE/g Zr h atm was obtained.
4.10.1. Typical polymerization run for
tetramethylethylene-bis(cyclopentadienyl)titanium
dichloride (19)
Polymerizations were conducted in 250 mL resin-
coated glass pressure (Fisher-Porter) bottle provided
with magnetic stirring and equipped with a metal head
(polymer coated on the inside) bearing a pressure
gauge, an outlet for gas and reagents by syringe,
and a stopcock for evacuation. The metallocene pro-
catalysts, tetramethylethylene-bis(cyclopentadienyl)tita-
nium dichloride (19, 0.560 mmol), in 100 mL of
predried and deoxygenated toluene was treated with
28 mmol of MAO in toluene (Al:Ti = 50:1) and the
bottle purged with anhydrous ethylene to initiate the
polymerization. Under an ethylene overpressure of
40 psi the polymerizations are allowed to proceed
for 10 min. Usual quench with aqueous HCl and fil-
tration with a methanol-wash allow the polyethylene
to be isolated. In this case the polymerization activity
(PA) in grams of polyethylene (PE) per gram of Ti,
per atmosphere was calculated as 2640. Such polyeth-
ylene generally melted over 135 ꢀC.
4.10.8. Analogous polymerization with racemic- and
meso-1,2-di(1-naphthyl)ethylene-bis(cyclopentadienyl)-
titanium dichloride
With 0.20 mmol of this catalyst and 50 equiv. of MAO
for 10 min of ethylene purge, a PA of 313 g PE/g Zr h atm
was obtained.
4.10.9. Analogous polymerization with 1:1 racemic- and
meso-1,2-diphenylethylene-bis(cyclopentadienyl)-
zirconium dichloride (28a and 28b)
With 0.75 mmol of this catalyst and 50 equiv. of MAO
for 10 min of ethylene purge, a PA of 360 g PE/g Zr h atm
was obtained.
4.10.10. Analogous polymerization with 83:17 mixture of
racemic- and meso-1,2-di(1-naphthyl)ethylene-
bis(cyclopentadienyl)zirconium dichloride (29a and 29b)
With 0.22 mmol of this mixture and 50 equiv. of MAO
for 15 min of ethylene purge, a PA of 52 g PE/g Zr h atm
was obtained.
4.10.2. Analogous polymerization with
bis(cyclopentadienyl)titanium dichloride
An analogous polymerization of ethylene using 0.53
mmol of titanocene dichloride and 28 mmol (50
equiv.) of MAO for 10 min gave a PA = 1100
g PE/g Ti h atm.
4.11. Reductive dimerizations of N-benzylideneaniline (9)
4.11.1. With titanium dichloride
To 15 mmol of TiCl2 (16) in 40 mL of toluene (free of
Bun TiCl2, Eq. (2)) but containing the LiCl by-product
2

1338
J.J. Eisch et al. / Polyhedron 24 (2005) 1325–1339
was added 5.40 g (30 mmol) of N-benzylideneaniline (9)
at 25 ꢀC. The mixture was heated at reflux for 2 h to
form a dark khaki-colored suspension. Hydrolysis with
1 N aqueous HCl and separation of the organic layer,
which was dried over MgSO4 and freed of solvent in va-
cuo, provided 5.10 g (94% recovery) of products, which
by 1H NMR spectroscopy and comparison with spectral
data of authentic samples to consist of 15% of N-phe-
nylbenzylamine (39, but without D atoms) and 85% of
racemic-1,2-dianilino-1,2-diphenylethane. After ex-
change with D2O, the racemic-isomer showed a sharp
C–H peak at 4.6 ppm. The corresponding CH peak
for the meso-isomer at 5.0 ppm was absent [29].
When an identical reaction run was worked up with
DCl in D2O, the N-phenylbenzylamine (39) was mono-
deuteriated in the methylene group (1H NMR peak at
4.29 and the N–H peak at 3.97 ppm was absent), the
changes of which are consistent with the structure,
Ph–CHD–ND–Ph (39).
mers 10 and 11, calculated to be a 70% yield and present
in a 80:20 ratio. This product could be recrystallized
1
from a toluene–hexane pair. H NMR (THF-d8) of 10
and 11: 7.60–7.00 (m), 6.93–6.88 (m), 6.56–6.46 (m),
4.90 (s, meso-CH), 4.55 (s, racemic-CH); 13C NMR
(THF-d8): 65.3 (racemic-CH), 63.3 (meso-CH).
4.11.5. Polymerization with the mixture of racemic- and
meso-1,1-dichloro-2,3,4,5-tetraphenyl-2,5-diazazircona-
cyclopentanes (10 and 11 with M = Zr)
Analogous to the foregoing polymerizations a mix-
ture of 10 and 11 (160 mg, 0.29 mmol) in 100 mL of tol-
uene was treated with 28 mmol (50 equiv.) of MAO was
treated with ethylene at 40 psi for 15 min. Usual work-up
gave 9.45 g of polyethylene for a PA = 129 PE/g Zr h atm.
Acknowledgments
The authors hereby thank the US National Science
Foundation and Akzo Corporate Research America for
supporting the initiation of this research, the Solvay Cor-
poration of Brussels, Belgium for its continuation and the
Boulder Scientific Company of Mead, Colorado for
bringing this project to ultimate fruition. Former group
members, Drs. Adetenu A. Adeosun, John N. Gitua
and Peter O. Otieno have contributed valuable orienting
experiments to the research approach herein described.
4.11.2. With zirconium dichloride (17)
Similar to the foregoing, a mixture of N-benzylide-
neaniline (9) (6.00 g, 33 mmol) and freshly prepared
ZrCl2 (17, 16.3 mmol) free of Bun ZrCl2 but containing
2
LiCl was heated to reflux for 4 h. Hydrolytic work-up
gave a 90% conversion to a mixture of N-phenylbenzyl-
amine (20%) and an 80:20 mixture of racemic-1,2-dianil-
inoethane and meso-1,2-dianilinoethane (85%). The
proportion of racemic to meso-isomers was determined
by integration of C–H proton peaks at 4.6 and 5.0 ppm.
References
4.11.3. With di-n-butylzirconium dichloride (23)
N-Benzylideneaniline (9, 2.1 g, 11.4 mmol) and a slur-
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2
mixed at 25 ꢀC to form a dark brown suspension in an
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(51%).
Although the N-phenylbenzylaniline could have resulted
either from transfer-hydrozirconation or epizirconation,
formation of the racemic- and meso-1,2-dianilinoethanes
require epizirconation, either directly by ZrCl2 or by
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[9] J.E. McMurry, Acc. Chem. Res. 16 (1983) 405.
[10] Reductive coupling on a broad spectrum of carbonyl and
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¨
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¨
4.11.4. With zirconium dichloride (17) and the isolation
of the mixture of racemic- and meso-1,1-dichloro-2,3,4,5-
tetraphenyl-2,5-diazaazirconacyclopentanes (10 and 11
with M = Zr)
¨
¨
Mynott, Tetrahedron 51 (1995) 8875;
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(e) J. Gao, M.-Y. Hu, J.-X. Chen, S. Yuan, W.-X. Chen,
Tetrahedron Lett. (1993) 1617;
The experiment described in Section 4.11.2 but in-
stead of a hydrolytic work-up the reaction mixture was
cooled to RT and filtered to remove the LiCl. The filtrate
was freed of toluene in vacuo and the dark tan washed
repeatedly to give a mixture of racemic- and meso-iso-
(f) D.-Q. Shi, J.-X. Chen, W.-Y. Chai, W.-X. Chen, T.-Y. Kao,
Tetrahedron Lett. (1993) 2963;
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Kao, Synthesis (1993) 87;

J.J. Eisch et al. / Polyhedron 24 (2005) 1325–1339
1339
(h) R. Dams, M. Malinowski, I. Westdop, H. Geise, J. Org.
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¨
H H
R'"
N
C
I
Repulsions between R−R'and R−R" in T.S.
[11] J.J. Eisch, X. Shi, F.A. Owuor, Oganometallics 17 (1998) 5219:
the preliminary communication of the synthesis of ansa-metalloc-
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R"
R'
R
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[12] For previously known methods of metallocene synthesis, the
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.
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preparation).
(a) R.B. King, in: J.J. Eisch, R.B. King (Eds.), Organometallic
Syntheses , vol. 2, Academic Press, New York, 1966 , p. 64;
(b) K.M. Kane, P.J. Shapiro, A. Vij, R. Cubbon, A.L. Rheingold,
Organometallics 16 (1997) 4567;
[18] In the ring formation of cyclic amines from the reaction, Br–
(CH2)n–NH2 ! (CH2)nNH Æ HBr, the rate of closure to the
aziridine (n = 2) is faster by 100-fold than the closure to the
azetidine (n = 3): G. Salomon, Helv. Chim. Acta 19 (1936)
743.
(c) N.J. Long, Metallocenes – An introduction to sandwich
complexes, Blackwell Science, Oxford, 1998, 285 pp.
[13] J.J. Eisch, F.A. Owuor, X. Shi, Organometallics 18 (1999) 1583:
the preliminary communication of the synthesis of Group 4
bis(substituted-cyclopentadienyl)metal dichlorides by the transfer-
hydrometallation of fulvenes.
[19] Related to the proposed reactions of 38 or its zirconocene
analogue with imine 9 are the interesting insertion reactions of
zirconaziridines, Cp2Zr-g2-[N(R1)CH(R2)](THF) with carbodii-
mides: J.A. Tunge, C.J. Czerwinski, D.A. Gately, J.R. Norton,
Organometallics 20 (2001) 254.
[14] Since Moses Gombergꢀs discovery of the trityl radical it was
believed that the reassociation of trityl radicals would form
hexaphenylethane, until NMR measurements revealed that the
dimer actually has the structure shown in a (telltale sp3 C–H in 1H
NMR spectrum) H. Lankamp, W.T. Nauta, C. MacLean,
Tetrahedron Lett. (1968) 249,
[20] J.J. Eisch, J.N. Gitua, Organometallics 22 (2003) 24.
[21] J.J. Eisch, J.N. Gitua, Organometallics 22 (2003) 4172.
[22] J.J. Eisch, A.A. Adeosun, J.N. Gitua, Eur. J. Org. Chem. (2003)
4721.
[23] J.J. Eisch, J.N. Gitua, P.O. Otieno, A.A. Adeosun, Macromol.
Symp. 213 (2004) 187.
H
Ph
Ph
C
[24] J.J. Eisch, P.O. Otieno, Eur. J. Org. Chem. (2004) 3269.
[25] K. Ziegler, W. Schaefer, Liebigs Ann. Chem. 511 (1934) 101.
[26] K. Ziegler, H.G. Gellert, H. Martin, K. Nagel, J. Schneider,
Liebigs Ann. Chem. 589 (1954) 91.
Ph3C
a
[15] In organic chemistry Front or F-Strain can refer to the retardation
.
[27] J.J. Eisch, A.M. Piotrowski, S.K. Brownstein, E.J. Gabe, F.L.
Lee, J. Am. Chem. Soc. 107 (1985) 7219.
of the quaternization of tertiary amines by alkyl iodides in SN2
reactions, where the steric hindrance between substituents in such
backside-attack raises the energy of the transition state (below).
Also in equilibria of Lewis acid–Lewis base complexation, such as
[28] J.J. Eisch, in: J.J. Eisch, R.B. King (Eds.), Organometallic
Syntheses, vol. 2, Academic Press, New York, 1981, p. 1.
[29] J.J. Eisch, D. Drew, C.J. Peterson, J. Org. Chem. 31 (1966)
453.
0
in R3 N ꢀ BR3 adduct formation, greater F-strain between the R
and R0 groups promotes complex dissociation. Cf. M.S. Newman