Dialkyl and methyl-alkyl zirconocenes: Synthesis and characterization of zirconocene-alkyls that model the polymeryl chain in alkene polymerizations

Article abstract of DOI:10.1021/om0601302

Zirconocene precatalysts with sterically bulky alkyl groups were designed as model systems for the propagating species in zirconocene-catalyzed alkene polymerization. Specialty alkyllithium reagents Li(CH₂CEt ₃) and Li(CH₂

Full text of DOI:10.1021/om0601302

3018
Organometallics 2007, 26, 3018-3030
Dialkyl and Methyl-Alkyl Zirconocenes: Synthesis and
Characterization of Zirconocene-Alkyls That Model the Polymeryl
Chain in Alkene Polymerizations
Sara B. Klamo,* Ola F. Wendt,‡ Larry M. Henling, Michael W. Day, and John E. Bercaw*
Arnold and Mabel Beckman Laboratories of Chemical Synthesis,
California Institute of Technology, Pasadena, California 91125
ReceiVed February 10, 2006
Zirconocene precatalysts with sterically bulky alkyl groups were designed as model systems for the
propagating species in zirconocene-catalyzed alkene polymerization. Specialty alkyllithium reagents Li-
(CH2CEt3) and Li(CH2CMe2CH2Ph) were prepared and utilized in the synthesis of dialkyl and methyl-
alkyl zirconocenes of the form CpCp*ZrR2, Cp2Zr(CH3)(R), and CpCp*Zr(CH3)(R) (Cp ) (η5-C5H5);
Cp* ) (η5-C5Me5); R ) CH2CMe3, CH2SiMe3, CH2CEt3, CH2CMe2CH2Ph). These new zirconocene
alkyls were isolated and fully characterized by NMR spectroscopy and in some cases by X-ray diffraction.
The molecular structures determined display the bent-sandwich coordination mode common for
zirconocenes. The steric influence of the alkyl group on the observed structural parameters is reflected
in slightly expanded C-Zr-C or C-Zr-Cl angles in the equatorial plane and long zirconium-alkyl
bond distances.
Scheme 1
Introduction
The propagating catalyst species in metallocene-catalyzed
alkene polymerization has been identified as a metallocenium-
polymeryl ion having a weakly coordinating anion.1 Tradition-
ally, propagating species are generated in situ starting from a
neutral metallocene precatalyst, generally a dichloride or dim-
ethyl species.2 The first step is reaction with an activator to
generate an ion-paired, cationic, 14-electron metal-alkyl initiator.
This initiating species then reacts with alkene in the initiation
step, followed by additional alkene insertions to form the
propagating species.
[CH3B(C6F5)3]- and unreacted [Cpx M-CH3]+[CH3B(C6F5)3]-
2
Our interest in developing models for the early propagating
species arose from a project examining fundamental aspects of
zirconocene-catalyzed alkene polymerization using kinetic and
mechanistic studies. Initial attempts focused on propagation
kinetics for propene polymerization and utilized anion-stabilized
methyl-zirconocenium and hafnocenium catalysts of the type
were present after consumption of all monomer (Scheme 1).3
Specifically, only 30-35% initiation was observed (1H NMR,
-70 °C, CD2Cl2) for [CpCp*Zr-CH3]+[CH3B(C6F5)3]- (Cp )
(η5-C5H5);Cp*)(η5-C5Me5))(A)afterpolymerizationof30equiv
of propene. Similarly, the ansa-zirconocene catalyst [iPrThpZr-
CH3]+[CH3B(C6F5)3]- (iPrThp ) [(1,2-SiMe2)2(η5-4-CHMe2-
C5H2)(η5-3,5-(CHMe2)2-C5H]) (B) showed less than 5% ini-
tiation after polymerization of 18 equiv of propene (1H NMR,
-50 °C, CD2Cl2). These observations may be attributed to a
kinetic situation where kp . ki (where kp and ki are the rate
constants for propagation and initiation). Similar slow initiation
versus propagation behavior has been reported for 1-hexene
polymerization by other metallocene4 and nonmetallocene5
group 4 [M-CH3]+ initiators.
[Cpx M(CH3)]+[CH3B(C6F5)3]- (Cpx ) (η5-C5RnH5-n); M ) Zr,
2
Hf). While this work suggested that propene propagation kinetics
could be directly examined at low temperatures using direct 1H
NMR monitoring, limitations associated with the use of methyl-
based initiators for these experiments were identified. In
particular, these [Cpx M-CH3]+ cations displayed poor initiation
2
behavior for propene polymerization, where only a small, but
continually increasing percentage of initiating complex was
converted to the propagating species under typical experimental
conditions. For example, when excess propene (18-30 equiv)
was added to catalyst solutions at low temperatures, incomplete
These findings prompted us to consider zirconocene initiators
bearing polymeryl-like alkyl groups, where ki may be on the
same order as kp. These compounds may model the propagating
species formed in propene polymerization, if the alkyl group
more closely resembles the polypropene polymeryl in both
Zr-C bond strength and steric influence on ion pairing. Well-
initiation occurred in all cases, as both [Cpx M-polymeryl]+-
2
* Corresponding authors. Current address: Chemical Sciences, The Dow
Chemical Company, 1776 Building, Midland, MI 48674. E-mail:
bercaw@caltech.edu.
‡ Current address: Department of Chemistry, Lund University, 221 00
Lund, Sweden.
(3) Wendt, O. F.; Bercaw, J. E. Unpublished results.
(4) Landis, C. R.; Rosaaen, K. A.; Sillars, D. R. J. Am. Chem. Soc. 2003,
125, 1710-1711.
(5) Mehrkhodavandi, P.; Bonitatebus, P. J.; Schrock, R. R. J. Am. Chem.
Soc. 2000, 122, 7841-7842.
(1) Jordan, R. F. AdV. Organomet. Chem. 1991, 32, 325-387.
(2) Brintzinger, H. H.; Fischer, D.; Mulhaupt, R.; Rieger, B.; Waymouth,
R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143-1170.
10.1021/om0601302 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 05/05/2007

Dialkyl and Methyl-Alkyl Zirconocenes
Organometallics, Vol. 26, No. 12, 2007 3019
defined initiators suitable for use in kinetic studies may be
produced directly from the activation step by reaction with an
appropriate zirconocene precatalyst. Therefore, the synthesis of
dialkyl and methyl-alkyl zirconocene precursors having more
sterically demanding polymeryl-like alkyl groups has been
undertaken.
Considerable efforts in both academic and industrial labora-
tories have produced a rich body of literature precedence for
the synthesis and activation of group 4 dimethyl metallocene
precatalysts.6 These efforts offer great diversity with respect to
choice of ancillary ligands and activating reagents, but are more
limited with respect to variations in alkyl groups. Examples
using zirconium and hafnium precatalysts of the form (Cp-
Rn)2MR′2 have generally been restricted to a small number of
bulky alkyl groups (R′ ) CH2CMe3 (Np), CH2SiMe3 (CH2-
TMS), CH(SiMe3)2, or CH2C6H5),1,2,7 and mixed methyl-alkyl
complexes Cp2M(CH3)(R′) are even fewer in number.
For eventual use in kinetic studies, the thermal stability of
the dialkyl zirconocene precatalysts, as well as the generated
zirconocene-alkyl cations, toward decomposition, especially via
â-hydride elimination,8,9 must also be considered. These reac-
tions are expected to be more facile for the active polymerization
catalysts. These cationic species display increased electrophi-
licity at the metal center, and accordingly, â-hydride elimination
has been identified as a major chain termination pathway for
propagating species in metallocene-catalyzed alkene polymer-
ization.2 In order to avoid complications arising from this type
of reactivity, we chose to investigate dialkyl and methyl-alkyl
zirconocenes with bulky alkyl groups having no â-hydrogens
as precursors to models of the propagating species. Decomposi-
tion pathways involving other â-elimination reactions may occur
for the cationic alkyl initiators generated from these zir-
conocenes. Studies by Horton,10 Marks,7 and our research
group11 have demonstrated that [(Cp-Rn)2Zr(CH2CMe3)]+-
[CH3B(C6F5)3]- compounds decompose to zirconocene-methyl
cations and isobutene via â-methyl elimination (eq 1).
tion-state structures.12 These findings suggested that the steric
environment might be tuned using both the influence of the
bulky alkyl group and the ancillary ligand framework to
potentially inhibit â-methyl elimination for the proposed alkyls
that model the propagating polymeryl group.
We report herein the syntheses and characterization of a series
of zirconocene precatalysts with sterically bulky alkyl groups.
The preparation of the mixed methyl-alkyl complexes proved
to be less than straightforward, and some more efficient synthetic
procedures have been devised that should prove useful in the
synthesis of other, related bulky alkyl zirconocene derivatives.
Results and Discussion
Synthesis of Mixed Cyclopentadienyl Ligand Dialkyl
Zirconocenes. The mixed cyclopentadienyl/pentamethylcyclo-
pentadienyl ligand dialkyl zirconocenes CpCp*ZrNp2 (1) and
CpCp*Zr(CH2TMS)2 (2) are precursors to catalyst initiators of
the form [CpCp*ZrR′]+[B(C6F5)4]- or [CpCp*Zr(R′)(NMe2Ph)]+-
[B(C6F5)4]- (R′ ) Np, CH2TMS), by activation of the precata-
lyst with [Ph3C]+[B(C6F5)4]- or [PhNMe2H]+[B(C6F5)4]-,
respectively.6 The dialkyl zirconocenes rather than the methyl-
alkyl zirconocenes were targeted for use with these activators
as multiple cationic species, such as mixtures of [Zr-CH3]+
and [Zr-Np]+, could potentially be generated upon protonative
activation of the methyl-alkyl zirconocenes. Although methyl
abstraction appears to be generally favored, other alkyls,
including neopentyl, are abstracted from nonmetallocene zir-
conium(IV) and hafnium(IV) dialkyl compounds using [Ph3C]+-
[B(C6F5)4]-.13-15
Horton has shown that the stability of zirconocene-neopentyl
cations toward decomposition via â-methyl elimination is
sensitive to the cyclopentadienyl ancillary ligands.10 While
[Cp*2ZrNp]+[CH3B(C6F5)3]- undergoes rapid decomposition at
temperatures as low as -80 °C, [Cp2ZrNp]+[CH3B(C6F5)3]- is
stable up to 0 °C. Therefore, the mixed ring cyclopentadienyl
ligation was chosen to provide an intermediate steric influence.
Additionally, it was thought that the Si-substituted alkyl group
might serve as a neopentyl analogue stable toward â-methyl
elimination, as silylene formation is unfavorable.7
Compounds 1 and 2 are prepared according to the methodol-
ogy reported by Lappert for the parent Cp2ZrR2 compounds.16
The reaction of 2 equiv of the appropriate lithium reagent with
CpCp*ZrCl2 proceeds cleanly in diethyl ether solvent to afford
1 or 2 as tan or off-white powders, respectively, in good yields
(eq 2).
For alkyl-zirconocenium ions, the rate of â-methyl elimina-
tion10 and the relative rates of â-hydride elimination versus
â-methyl elimination appear to be sensitive to the steric
influence of the cyclopentadienyl ancillary ligands.12 â-Hydride
elimination is the primary chain termination pathway for the
propagating catalyst produced in propene polymerization using
Cp2ZrCl2/methylaluminoxane (MAO) systems, while Cp*2ZrCl2/
MAO-derived catalyst chain terminates largely via â-methyl
elimination. In the latter case, the increased rate of â-methyl
compared to â-hydride elimination can be rationalized by
considering steric interactions between the Cp* ligand and the
â-substituents on the polymeryl chain in the respective transi-
Cooling a saturated pentane solution of 1 to -35 °C resulted
in the formation of pale yellow crystals that were suitable for
X-ray diffraction analysis. The molecular structure of 1 displays
a bent-sandwich coordination mode common among zir-
(6) Chen, E. Y. X.; Marks, T. J. Chem. ReV. 2000, 100, 1391-1434.
(7) Beswick, C. L.; Marks, T. J. J. Am. Chem. Soc. 2000, 122, 10358-
10370.
(8) Negishi, E.; Nguyen, T.; Maye, J. P.; Choueiri, D.; Suzuki, N.;
Takahashi, T. Chem. Lett. 1992, 2367-2370.
(13) Mehrkhodavandi, P.; Schrock, R. R. J. Am. Chem. Soc. 2001, 123,
10746-10747.
(9) Wendt, O. F.; Bercaw, J. E. Organometallics 2001, 20, 3891-3895.
(10) Horton, A. D. Organometallics 1996, 15, 2675-2677.
(11) Chirik, P. J.; Dalleska, N. F.; Henling, L. M.; Bercaw, J. E.
Organometallics 2005, 24, 2789-2794.
(14) Mehrkhodavandi, P.; Schrock, R. R.; Pryor, L. L. Organometallics
2003, 22, 4569-4583.
(15) Mehrkhodavandi, P. Ph.D. Thesis, Massachusetts Institute of
Technology, 2002.
(16) Collier, M. R.; Lappert, M. F.; Pearce, R. J. Chem. Soc., Dalton
Trans. 1973, 445-451.
(12) Resconi, L.; Piemontesi, F.; Franciscono, G.; Abis, L.; Fiorani, T.
J. Am. Chem. Soc. 1992, 114, 1025-1032.

3020 Organometallics, Vol. 26, No. 12, 2007
Klamo et al.
Figure 1. Structural drawing of (η5-C5H5)(η5-C5Me5)Zr(CH2-
CMe3)2 (1) with thermal ellipsoids at the 50% probability level.
Figure 2. Structural drawing of (η5-C5H5)(η5-C5Me5)Zr(CH2-
SiMe3)2 (2) with thermal ellipsoids at the 50% probability level.
Table 1. Selected Structural Parameters for
CpCp*Zr(CH2CMe3)2 (1) and CpCp*Zr(CH2SiMe3)2 (2)
Å; for C(21) Zr-R-H(A) ) 2.77 Å, Zr-R-H(B) ) 2.71 Å),
but even this contact is longer than could reasonably be
attributed to an agostic interaction. Moreover, the orientation
of R-H(B) does not appear correct for an interaction with
zirconium, as it lies 34.5° out of the C(21)-Zr-C(16) equatorial
plane, the location of the LUMO for the zirconocene moiety.
The absence of low-energy ν(C-H) expected for an R-agostic
structure in the IR spectrum of 1 also argues against a substantial
1
2
Distances (Å)
2.241(1)
2.260(1)
2.2651(14)
2.3524(14)
Zr-Ct(1)a
Zr-Ct(2)b
Zr-C(16)
Zr-C(21)
Zr-Ct(1)a
Zr-Ct(2)b
Zr-C(16)
Zr-C(20)
2.246(1)
2.247
2.2691(16)
2.3066(16)
Angles (deg)
1
Ct(1)-Zr-Ct(2)
C(16)-Zr-C(21)
129.1(1)
99.61(5)
Ct(1)-Zr-Ct(2)
C(16)-Zr-C(20)
131.1(1)
98.09(6)
interaction between Zr and R-H(16B). Further, the H and 13C
spectra of 1 at ambient temperature in benzene-d6 are not
indicative of a static R-agostic structure in solution, where two
doublets integrating to 2H are observed for the R-hydrogens
a Ct(1) is defined as the centroid of the ring made up of C(1)-C(5).
b Ct(2) is defined as the centroid of the ring made up of C(6)-C(10).
1
and JC-RH ) 109 Hz. The NMR equivalence of the two
neopentyl groups further signifies that their asymmetric orienta-
conocenes (Figure 1). The Zr-Cp and Zr-Cp* centroid
distances (2.241(1), 2.260(1) Å) and Cp centroid-Zr-Cp*
centroid angle (129.1(1)°) are similar to those found for Cp2-
ZrNp2 (2.25 Å; 128.3°).17 All of the hydrogen atoms were
located in the difference map and have been refined. Details of
the data collection and solution and refinement of the structure
can be found in Table 2.
tion observed in the crystal structure is not maintained in
1
solution, at least on the H NMR time scale.
The structure of compound 2 has also been established by
X-ray crystallography. This compound crystallized as colorless
blocks from pentane at -35 °C. The molecular structure of 2
(Figure 2), including orientation of the bulky alkyl groups, is
remarkably similar to 1. All hydrogens were located in the
difference map and have been refined. No ground-state agostic
interactions are observed, as the closest zirconium-R-hydrogen
and -γ-hydrogen distances found in 2 are 2.518(0) and 4.219-
(1) Å, respectively. Details of the data collection and solution
and refinement of the structure can be found in Table 2.
The neopentyl groups are oriented to direct the bulky tert-
butyl substituents away from each other and away from the Cp*
group in the solid-state structure. The tert-butyl group of C(21)
is directed toward the front, more open region of the zirconocene
wedge, while that of C(16) is pushed back into the wedge. Two
distinct bond lengths are found for Zr-C(σ) bonding to the
neopentyl groups (Zr-C(16) ) 2.2651(14), Zr-C(21) )
2.3524(14) Å). These short and long bond distances are within
The key structural parameters, including Zr-Cp centroid
distances and angles and Zr-CH2TMS bond lengths (Table 1),
are close to those found for Cp2Zr(CH2TMS)2 (2.24 Å; 128.3°;
2.278(4), 2.281(4) Å) respectively.17 While two unequal bond
distances are also found for Zr-CH2TMS σ bonding in 2, the
difference in bond lengths (0.0375 Å) is much smaller than that
observed for 1 (0.0873 Å). The Zr-C(21) bond in 1 (relative
to Zr-C(20) in 2) may be elongated to avoid a close contact
between the tert-butyl substituent of C(21) and C(16) (Figure
1). In 2 however, the longer C-Si bond length may alleviate
this interaction. Effectively, the trimethylsilylmethyl group is
larger than neopentyl, as the unit cell of 2 is larger by 200 Å3.
This might argue that the neopentyl group is smaller by 25 Å3.
the range typically observed for Cpx Zr-alkyl compounds
2
(2.251-2.388 Å).18,19 The molecular structure of 1 does not
indicate any ground-state γ-agostic interactions; the closest
zirconium-γ-hydrogen distance found is 3.82 Å. A close
contact is found between zirconium and R-hydrogen H(B),
located on C(16) (Zr-R-H(B) ) 2.38 Å, Zr-R-H(A) ) 2.58
(17) Jeffery, J.; Lappert, M. F.; Luongthi, N. T.; Webb, M.; Atwood, J.
L.; Hunter, W. E. J. Chem. Soc., Dalton Trans. 1981, 1593-1605.
(18) Atwood, J. L.; Hunter, W. E.; Hrncir, D. C.; Samuel, E.; Alt, H.;
Rausch, M. D. Inorg. Chem. 1975, 14, 1757-1762.
(19) Jeffery, J.; Lappert, M. F.; Luongthi, N. T.; Atwood, J. L.; Hunter,
W. E. J. Chem. Soc., Chem. Commun. 1978, 1081-1083.

Dialkyl and Methyl-Alkyl Zirconocenes
Organometallics, Vol. 26, No. 12, 2007 3021
Table 2. Crystal and Refinement Data for Complexes CpCp*Zr(CH2CMe3)2 (1), CpCp*Zr(CH2SiMe3)2 (2), CpCp*Zr(Np)(Cl)
(6), and Cp2Zr(CH3)(CH2CEt3) (22)
1
2
6
22
empirical formula
fw
C25H42Zr
433.81
C23H42Si2Zr
465.97
C20H31ClZr
398.12
C19H30Zr
349.65
T (K)
98(2)
98(2)
100(2)
98(2)
a, Å
b, Å
c, Å
9.7467(4)
25.9839(12)
10.2031(5)
9.9621(5)
26.8264(13)
10.4769(5)
8.9772(2)
13.5673(4)
17.2242(5)
101.6260(10)
104.3560(10)
100.4190(10)
1930.85(9)
4
17.658(3)
8.2098(13)
25.878(4)
R, deg
â, deg
116.6710(10)
116.3020(10)
109.532(2)
γ, deg
volume, Å3
Z
2309.07(18)
4
2510.0(2)
4
3535.7(10)
8
cryst syst
space group
d
monoclinic
P21/c
1.248
monoclinic
P21/n
1.233
triclinic
P1h
1.370
monoclinic
P2/c
1.314
calc, g/cm3
θ range, deg
1.57 to 28.37
0.482
none
1.52 to 28.36
0.539
none
1.58 to 46.45
0.704
none
1.71 to 28.52
0.613
none
µ, mm-1
abs corr
GOF
2.059
0.0247, 0.0475
2.088
0.0302, 0.0514
1.157
0.0390, 0.0748
1.217
0.0571, 0.0876
R1,a wR2b [I > 2σ(I)]
2
2
2
a R1 ) ∑|Fo| - |Fc|/∑|Fo|. b wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo )2]1/2
.
Precursors for Methyl-alkyl Zirconocene Compounds.
Methyl-alkyl zirconocene compounds of the form (Cp-Rn)2-
Zr(CH3)R′ potentially serve as precursors for [(Cp-Rn)2Zr-
(R′)]+[CH3B(C6F5)3]--type initiators formed via methide ab-
straction using the strongly Lewis acidic activator B(C6F5)3.6
Again, the mixed ring ancillary ligation was targeted for its
potential steric influence on initiator speciation. The steric
demand of the Cp* group should discourage formation of
bimetallic methyl-bridged monocations, such as [{(Cp-Rn)2-
Zr(R′)}2(µ-CH3)]+[A]- ([A]- ) [CH3B(C6F5)3]-, [B(C6F5)4]-),
which are often observed for zirconocene systems with open
coordination environments.6,20
white powder or pale yellow needles after purification from
toluene-petroleum ether at -35 °C.
Key starting materials for the formation of methyl-alkyl
complexes in zirconocene systems are (Cp-Rn)2Zr(CH3)Cl.
These compounds, however, are not cleanly obtained from the
reaction of (Cp-Rn)2ZrCl2 with 1 equiv of methyllithium.8
Conventional routes to obtain (Cp-Rn)2Zr(CH3)Cl compounds
from (Cp-Rn)2Zr(CH3)2 utilize HCl,11 [(CH3)3NH]+[Cl]-,21
[(CHMe2)2NH2]+[Cl]-,22 or PbCl2,23 as chlorinating reagents.
Reagents HCl, [(CHMe2)2NH2]+[Cl]-, and PbCl2 were tested
for the preparation of CpCp*Zr(CH3)Cl (3) from CpCp*Zr-
(CH3)2; however, in all cases 3 was contaminated with at least
5% CpCp*ZrCl2 as well as starting material. Separation of
mixtures of dialkyl zirconocenes and chloro-alkyl zirconocenes
is difficult due to their extreme solubility and similar physical
properties, as well as the limited number of compatible
purification methods available. Because we found that the purity
of 3 plays an important role in the successful isolation of pure
CpCp*Zr(CH3)R compounds, it was essential to devise a
procedure that affords very pure 3.
Synthesis of CpCp*Zr(CH3)(CH2TMS) and CpCp*Zr-
(CH3)(Np). The mixed ring zirconocene methyl-alkyl com-
pounds CpCp*Zr(CH3)(CH2TMS) (4) and CpCp*Zr(CH3)(Np)
(5) were prepared by the reaction of 3 with 1 equiv of the
appropriate lithium reagent. The synthesis of 4 proceeded
smoothly by this route in diethyl ether, and 4 was isolated as a
pale yellow oil in good yields (eq 4). Lyophilization or trituration
techniques, as well as a variety of solvent systems, failed in
attempts to obtain 4 as a powder or crystalline material. This
1
oil, as isolated, was judged to be >95% pure by H NMR
spectroscopy and suitable for use in further transformations.
A method was developed for the synthesis of clean samples
of 3 that is based on the ligand redistribution chemistry reported
by Jordan.24 A solution containing 0.5 M CpCp*ZrCl2 and 0.5
M CpCp*Zr(CH3)2 (C) in toluene-d8 was heated at 130 °C in a
J. Young NMR tube. After 10 days, 95% conversion to 3 was
observed by H NMR spectroscopy (eq 3). These conditions
were subsequently employed on preparative scale reactions and
afforded 3 contaminated with less than 3% CpCp*ZrCl2 as a
The reaction of 3 with neopentyllithium was more sensitive
to reaction conditions, including concentration, solvent, tem-
perature, and reaction time. Reactions following the above
methodology yielded 5 as a yellow oil (contaminated with other
zirconocene compounds including 1 and CpCp*Zr(CH3)2 (C))
that resists purification by recrystallization or precipitation.
Under the reaction conditions shown in eq 5 the product mixture
could be driven to 1, C, and 5 in a 1:1:3 ratio, respectively, as
1
(20) Bochmann, M.; Lancaster, S. J. Angew. Chem., Int. Ed. Engl. 1994,
33, 1634-1637.
(21) Zuckerman, R. L.; Krska, S. W.; Bergman, R. G. J. Am. Chem.
Soc. 2000, 122, 751-761.
(23) Wailes, P. C.; Weigold, H.; Bell, A. P. J. Organomet. Chem. 1972,
34, 155-164.
(24) Jordan, R. F. J. Organomet. Chem. 1985, 294, 321-326.
(22) Brandow, C. G.; Bercaw, J. E. Unpublished results.

3022 Organometallics, Vol. 26, No. 12, 2007
Klamo et al.
1
identified by comparison with the H NMR spectra of inde-
pendently synthesized compounds. This observation suggests
the alkylation of 3 with alkyllithium reagents may be reversible.
Reversible alkylation catalyzed by trace neopentyllithium would
provide a pathway for alkyl exchange, potentially explaining
the product mixture (Scheme 2). Alkyl exchange between group
4 centers via an intermolecular mechanism involving the
formation of bridging alkyl groups has been documented for
both metallocene24 and nonmetallocene compounds.25 While this
process is facile for methyl groups, which readily bridge metal
centers, it is likely slower for exchange of a bulky neopentyl
group between zirconocene centers having sterically demanding
ancillary ligation such as that in 5.
Scheme 2
Figure 3. Structural drawing of (η5-C5H5)(η5-C5Me5)Zr(CH2-
CMe3)Cl (6) showing the unique molecules found in the asymmetric
unit with thermal ellipsoids at the 50% probability level.
isotopically labeled versions of 5, such as CpCp*Zr(CD3)(Np)
or CpCp*Zr(13CH3)(Np), since a 15 mol % excess of CpCp*Zr-
(CH3)2 is used in the preparative scale synthesis of 3. As
monomethylation of CpCp*ZrCl2 is not possible with the lithium
reagent, we explored a route via the monoalkylated compound
CpCp*Zr(Np)(Cl) (6).
A successful set of reaction conditions were eventually
identified. Preparation in toluene along with careful control of
reaction temperature afforded a clean and reproducible meth-
odology (eq 6) and allowed isolation of 5 as an analytically
pure yellow powder after removal of lithium chloride by
filtration.
Compound 6 is prepared by reaction of CpCp*ZrCl2 with 1
equiv of neopentyllithium in toluene (eq 7).26 Although initially
6 is obtained as a sticky, bright yellow solid, it can be isolated
as a yellow powder after trituration with petroleum ether.
Alternate Routes for the Synthesis of CpCp*Zr(CH3)(Np).
A methodology to synthesize 5 utilizing successive monoalky-
lation reactions starting from CpCp*ZrCl2 is desirable, as it
would remove one step from the overall sequence and eliminate
the long reaction time required to prepare 3. Additionally, this
type of strategy would also be preferable in the preparation of
Yellow crystals of 6 were obtained by slow diffusion of
petroleum ether into diethyl ether solutions at -35 °C, and the
molecular structure was determined by X-ray diffraction (Figure
3). Overall, the structural parameters for 6, including Zr-Cl
(26) (a) Chirik, P. J.; Bercaw, J. E. Unpublished results. (b) For related
synthetic strategy utilizing Grignard reagents see: Song, F. Q.; et al.
Organometallics 2005, 24, 1315-1328.
(25) Mehrkhodavandi, P.; Schrock, R. R.; Bonitatebus, P. J. Organo-
metallics 2002, 21, 5785-5798.

Dialkyl and Methyl-Alkyl Zirconocenes
Organometallics, Vol. 26, No. 12, 2007 3023
Table 3. Selected Structural Parameters for 6 and 22
6
22
Distances (Å)
2.232
2.241
2.224
2.240
2.3258(12) Zr(1)-C(11A)
2.4503(3) Zr(1)-C(12A)
2.3287(12) Zr(2)-C(11B)
2.4432(3) Zr(2)-C(12B)
Zr(1)-Ct(1A)a
Zr(1)-Ct(2A)b
Zr(2)-Ct(1B)a
Zr(2)-Ct(2B)b
Zr(1)-C(16A)
Zr(1)-C1(1)
Zr(1)-Ct(1A)a
Zr(1)-Ct(2A)b
Zr(2)-Ct(1B)a
Zr(2)-Ct(2B)b
2.23
2.24
2.25
2.24
2.294(3)
2.248(3)
2.306(3)
2.252(3)
Zr(2)-C(16B)
Zr(2)-C1(2)
Design and Synthesis of Specialty Alkyllithium Reagents.
One strategy to stabilize the alkyl zirconocene cation formed
upon activation toward decomposition via â-methyl elimination
is to utilize a bulky alkyl group having no â-methyl groups.
Another approach is to design a catalyst where unfavorable steric
interactions between â-alkyl substituents and the cyclopenta-
dienyl framework in the transition structure for â-methyl
elimination inhibit this reaction. Therefore, syntheses of methyl-
alkyl zirconocenes of the type shown below were targeted.
Angles (deg)
Ct(1A)-Zr(1)-Ct(2A) 129.5
Ct(1B)-Zr(2)-Ct(2B) 129.8
Ct(1A)-Zr(1)-Ct(2A) 130.9
Ct(1B)-Zr(2)-Ct(2B) 130.9
C(16A)-Zr(1)-C1(1) 100.18(3) C(11A)-Zr(1)-C(12A) 94.54(12)
C(16B)-Zr(2)-C1(2) 99.91(3)
C(11B)-Zr(2)-C(12B) 95.07(12)
a Ct(1A) is defined as the centroid of the ring made up of C(1A)-C(5A);
Ct(1B) is defined as the centroid of the ring made up of C(1B)-C(5B).
b Ct(2A) is defined as the centroid of the ring made up of C(6A)-C(10A);
Ct(2B) is defined as the centroid of the ring made up of C(6B)-C(10B).
bond lengths, are comparable to those in CpCp*ZrCl2 (2.4421-
(9) Å).27 The observed zirconium-neopentyl carbon bond
distances (2.3258(12), 2.3287(12) Å for the two independent
molecules in the asymmetric unit) are on the long end of the
range typically found in alkyl zirconocenes and are roughly
intermediate of the range observed in 1 (Table 3).18,19 Evidence
for crowding in the equatorial plane of 6 is suggested by the
expanded C(16)-Zr-Cl angles (100.18(3)°, 99.91(3)°) as
compared with the Cl-Zr-Cl angle (97.78(5)°) found in
CpCp*ZrCl2. No special zirconium-hydrogen interactions are
evident in 6, as the closest Zr-H contact is 2.75 Å. Details of
the data collection and solution and refinement of the structure
can be found in Table 2.
Although catalysts derived from zirconocenes of type Cp-
(Cp-Rn)Zr(CH3)(CH2CEt3) might decompose via â-ethyl elimi-
nation, generally this reaction has not been observed in related
systems. Previously in our group, we noted that whereas {(η5-
C5Me4)2SiMe2}Sc{CH2CH(CH3)2} decomposes by fast, revers-
ible â-H and slower â-methyl elimination, the decomposition
of {(η5-C5Me4)2SiMe2}Sc{CH2CH(CH2CH3)2} proceeds with
no evidence for â-ethyl elimination.29 Resconi has also found
that chain transfer by â-ethyl elimination did not occur during
the polymerization of 1-butene by Cp*2MCl2/MAO (M ) Zr,
Hf) catalysts.12 Activated compounds based on Cp(Cp-Rn)Zr-
(CH3)(CH2CMe2CH2Ph) could decompose via â-methyl elimi-
nation; however this reaction may be inhibited for catalysts with
CpCp* ancillary ligation. Unfavorable steric interactions be-
tween the benzyl substituent of the alkyl and the cyclopenta-
dienyl ligands might sufficiently destabilize the transition state
for this reaction relative to that for [CpCp*Zr(Np)]+-
[CH3B(C6F5)3]-.
The synthetic methodology used to prepare 2,2-diethylbu-
tyllithium (Li(CH2CEt3)) (13) and 2,2-dimethyl-3-phenylpro-
pyllithium (Li(CH2CMe2CH2Ph)) (19) is shown in Scheme 3.
2,2-Diethylbutanol (10) was prepared conveniently in three steps
from commercially available 2-ethylbutric acid (7) using
standard procedures.30 A similar sequence gave 2,2-dimethyl-
3-phenylpropanol (16) from commercially available 2-methyl-
propionoic acid ethyl ester (14). Precedented reaction conditions
for the conversion of neopentyl-type alcohols (PPh3/Br2, CH3-
CN, heat) to alkylbromides failed for 10 and 16; low yields of
products were isolated for both substrates, 30% and 10%
respectively. The methane sulfonate esters 2,2-diethylbutyl
mesylate (11) and 2,2-dimethyl-3-phenylpropyl mesylate (17)
were prepared after the methodology for hindered primary
substrates of Servis.31 Compounds 11 and 17 were converted
to alkyl iodides 12 and 18 using conditions based on those
reported by Stevens for the preparation of (-)-9-iodocamphor
NMR scale reactions were used to explore methylation of 6
with several alkylating agents. Promising conditions were
observed with pre-dried, ether-free methyllithium, as 5 formed
cleanly in benzene-d6 after heating for 9 h at 80 °C (eq 8).
Reaction of 6 with (CH3)2Mg in benzene-d6 containing roughly
2 equiv of 1,4-dioxane at 80 °C also formed compound 5
cleanly, as assessed by 1H NMR spectroscopy. The addition of
dioxane to the reaction mixture appeared to minimize formation
of products arising from alkyl or halide exchange (possibly by
precipitation of magnesium halide salts) while increasing the
solubility of (CH3)2Mg. Reactions of 6 with (CH3)2Mg con-
ducted in the absence of dioxane (benzene-d6, 9 h, 80 °C)
resulted in multiple zirconocene species including 3 and C, along
with 5 and unreacted 6 after heating. Similarly, reaction of 6
with solid Li13CH3‚LiI (benzene-d6, 9 h, 80 °C) complex
afforded multiple zirconocene species, including 5 and unreacted
6, after heating. Li13CH3 and LiCD3 are commonly prepared or
purchased commercially as 1:1 complexes with lithium iodide,
and this additive appeared detrimental under these conditions.28
One of the new species is likely CpCp*Zr(Np)(I) on the basis
1
of the chemical shift of a new Cp resonance in the H NMR
spectrum as compared with that in CpCp*ZrI2. The reaction of
6 with CH3MgBr resulted in the formation of unreacted 6, 5,
and what appeared to be CpCp*ZrNpBr in a 2:1:2 ratio after 2
1
h at room temperature in diethyl ether, as determined by H
NMR spectroscopy. Thus, it appears that lithium or magnesium
methylating agents having halide present are not suited to clean
preparation of 5.
(29) Hajela, S. H.; Bercaw, J. E. Organometallics 1994, 13, 1147-1154.
(30) Vogel, A. I. Vogel’s Textbook of Practical Organic Chemistry, 5th
ed.; Longman: New York, 1989.
(31) Crossland, R. K.; Servis, K. L. J. Org. Chem. 1970, 35, 3195-
3196.
(27) Rogers, R. D.; Benning, M. M.; Kurihara, L. K.; Moriarty, K. J.;
Rausch, M. D. J. Organomet. Chem. 1985, 293, 51-60.
(28) Reynolds, K. A.; Ohagan, D.; Gani, D.; Robinson, J. A. J. Chem.
Soc., Perkin Trans. 1 1988, 3195-3207.

3024 Organometallics, Vol. 26, No. 12, 2007
Klamo et al.
Scheme 3
from (-)-9-bromocamphor.32 This transformation required forc-
ing conditions, again reflecting the steric inhibition of SN2
reactivity at the primary carbon center. The desired alkyllithium
reagents, 13 and 19, were synthesized from 12 and 18,
respectively, using the lithium-halogen exchange procedure
developed by Bailey33 and Negishi.34
complex crystallizes as a radial cluster and maintains this
preference under a variety of crystallization conditions.
The pale yellow blocks of 22 crystallized in the P2/c space
group having two independent molecules in the asymmetric unit,
differing in orientation of the bulky alkyl group (Figure 4). The
zirconium-Cp centroid and zirconium-methyl distances as well
as the Cp centroid-zirconium-Cp centroid and carbon-
zirconium-carbon angles found for 22 are in line with those
observed for Cp2Zr(CH3)(Np) (2.232, 2.2980(13) Å; 130.6°,
94.99°) (Table 3).11 The Zr-C(12) bond lengths (2.248(3) and
2.252(3) Å) in 22 are short in comparison to those found in 1
and 2 and to the range typically seen for zirconocenes having
bulky alkyl groups (2.251-2.388 Å).17-19 No close zirconium-
hydrogen contacts are found, as the nearest zirconium-hydrogen
distance found in 22 is 2.79 Å. Details of the data collection
and solution and refinement of the structure can be found in
Table 2.
Methyl-alkyl Zirconocene Synthesis Using Specialty Alkyl-
lithium Reagents. Syntheses of methyl-alkyl zirconocenes with
the specialty alkyl groups, CpCp*Zr(CH3)(CH2CEt3) (20),
CpCp*Zr(CH3)(CH2CMe2CH2Ph) (21), Cp2Zr(CH3)(CH2CEt3)
(22), and Cp2Zr(CH3)(CH2CMe2CH2Ph) (23), were explored
using the conditions shown in eqs 9 and 10. Reaction of 3 with
1 equiv of either 13 or 19 resulted in formation of 20 and 21,
respectively, along with additional zirconocene products as
1
determined by analysis of the isolated material by H NMR
spectroscopy. These additional compounds are likely CpCp*Zr-
(CH3)2 (C) and CpCp*ZrR2, possibly formed via the reversible
alkylation process postulated for alkyl exchange in 5. Unfor-
tunately, the oils containing 20 and 21 resisted purification by
crystallization or precipitation from pentane, even at tempera-
tures below -35 °C. This difficulty is attributed to the extreme
solubility of these compounds.
Conclusions
Synthesis and characterization of precatalysts that will likely
generate models for the propagating species in zirconocene-
catalyzed alkene polymerizations have been described. In this
regard, we have subsequently examined the activation of
CpCp*Zr(CH3)(Np) with B(C6F5)3 at low temperatures and
found that it does indeed initiate propene polymerization rapidly,
allowing for convenient studies of the kinetics. A full report of
those studies, along with that using CpCp*Zr(CH3)(CH2TMS),
is forthcoming.35 The intermediate steric demand of the mixed
ring CpCp* ancillary ligation allows preparation of dialkyl
zirconocenes with two bulky alkyl groups. A convenient general
starting material for preparation of CpCp*Zr(CH3)R′ is CpCp*Zr-
(CH3)Cl. Its preparation using ligand redistribution chemistry
minimizes product contamination by CpCp*ZrCl2. Synthesis on
the [CpCp*Zr] framework is often sensitive to the reaction
(32) Stevens, R. V.; Gaeta, F. C. A.; Lawrence, D. S. J. Am. Chem. Soc.
1983, 105, 7713-7719.
Compounds 22 and 23 are readily formed under these
conditions and are isolated in modest yields after crystallization
from pentane at -35 °C. While pale yellow X-ray quality
crystals of 22 were obtained, the brown pellets of 23 recovered
always showed extremely poor diffraction. This zirconocene
(33) Bailey, W. F.; Punzalan, E. R. J. Org. Chem. 1990, 55, 5404-
5406.
(34) Negishi, E.; Swanson, D. R.; Rousset, C. J. J. Org. Chem. 1990,
55, 5406-5409.
(35) Klamo, S. B.; Wendt, O. F.; Bercaw, J. E. Manuscript in preparation.

Dialkyl and Methyl-Alkyl Zirconocenes
Organometallics, Vol. 26, No. 12, 2007 3025
distilled from calcium hydride and stored in a Schlenk flask under
nitrogen. N-Methylpyrrolidinone was purchased anhydrous from
Aldrich in a Sure/Seal bottle. Benzene-d6 and toluene-d8 were
purchased from Cambridge Isotopes and vacuum distilled from
sodium benzophenone ketyl. Methylene chloride-d2 was purchased
from Cambridge Isotopes and vacuum distilled from calcium
hydride. CDCl3 was purchased from Cambridge Isotopes and stored
over molecular sieves. The syntheses of CpCp*ZrCl2, CpCp*Zr-
(CH3)2,39 Cp2Zr(CH3)Cl,40 LiNp,41 and LiCH2TMS42 were carried
out as previously reported. Li13CH3‚LiI28 and (CH3)2Mg43 were
prepared using standard procedures. NEt3 and HN(CHMe2)2 were
vacuum transferred from calcium hydride and stored in a Schlenk
flask under argon. Butyllithium was purchased from Aldrich and
stored under argon. Benzylbromide was purchased from Aldrich
and distilled before use. NaI was dried under vacuum for 6 h at 70
°C and stored under nitrogen in the drybox.
NMR spectra were recorded on Varian Mercury (300 MHz for
1H) and Varian UNITY Inova (500.13 MHz for 1H) spectrometers.
Chemical shifts are given in ppm downfield from TMS using
residual proton (C6D5H 7.16; CHCl3 7.26; C6D5CD2H 2.09; CDHCl2
5.32) or carbon (C6D6 128.39; CDCl3 77.23; CD2Cl2 54.00) signals
of the deuterated solvents. Elemental analyses were performed at
Midwest MicroLab LLC.
Synthesis of (η5-C5H5)(η5-C5Me5)Zr(CH2CMe3)2 (1)-
(CpCp*ZrNp2). In an inert atmosphere glovebox, a 50 mL round-
bottom flask equipped with a stir bar was charged with (η5-
C5H5)(η5-C5Me5)ZrCl2 (0.502 g, 1.38 mmol) and LiCH2CMe3
(0.239 g, 3.06 mmol) and attached to a small swivel frit assembly.
On the vacuum line, diethyl ether (25 mL) was vacuum transferred
onto the solids at -78 °C and the apparatus was backfilled with
Ar. The cooling bath was removed, and the reaction mixture was
allowed to warm to room temperature. Stirring for 36 h resulted in
a yellow-brown solution and an off-white precipitate. The solvent
was removed in vacuo, leaving a tan solid. Petroleum ether (25
mL) was added to the solids by vacuum transfer. The resulting
off-white precipitate was filtered away from the yellow-brown
filtrate and washed once with recycled solvent. Removal of all
volatiles and drying in vacuo yielded a tan powder. In the glovebox
the solid was dissolved in pentane and the solution concentrated to
8 mL. The solution was cooled to -35 °C to recrystallize the desired
product; pale yellow crystalline material suitable for X-ray diffrac-
tion was isolated and dried in vacuo. Yield: 0.398 g (66%). Anal.
Calcd. for C25H42Zr: C, 69.21; H, 9.76. Found: C, 68.97, 69.24;
Figure 4. Structural drawing of (η5-C5H5)2Zr(CH3)(CH2C(CH2-
CH3)3) (22) showing the unique molecules found in the asymmetric
unit with thermal ellipsoids at the 50% probability level.
conditions, resulting in side-product formation via facile salt-
mediated alkyl or halide exchange processes. This undesirable
reactivity can be minimized under optimized reaction conditions.
X-ray diffraction studies on CpCp*Zr(Np)2, CpCp*Zr(CH2-
TMS)2, CpCp*Zr(Np)(CI), and Cp2Zr(CH3)(CH2CEt3) indicate
minimal perturbation of the bent-sandwich coordination mode
in the molecular structures. In some cases however, the steric
bulk of the alkyl group is reflected in (a) a slightly contracted
Cp-Zr-Cp centroid angle, (b) an expanded carbon-Zr-
carbon(chloride) angle, and (c) zirconium-carbon bond lengths
on the long end of the range commonly observed in (Cp-Rn)2-
ZrR′2 and (Cp-Rn)2Zr(CH3)R′ compound types.
1
H, 9.64, 9.62. H NMR (500 MHz, C6D6): δ 5.94 (s, C5H5, 5H),
1.71 (s, C5(CH3)5, 15H), 1.18 (s, CH2C(CH3)3, 18H), 0.81 (d, CH2C-
(CH3)3, 2H, J ) 11.6 Hz), -0.47 (d, CH2C(CH3)3, 2H, J ) 11.6
Hz). 13C{1H} NMR (125 MHz, C6D6): δ 117.7 (C5(CH3)5), 109.7
(C5H5), 78.4 (Zr-CH2C(CH3)3), 37.1 (CH2C(CH3)3), 35.6 (CH2C-
(CH3)3), 12.5 (C5(CH3)5). 13C NMR (125 MHz, C6D6): δ 117.7 (s,
C5(CH3)5, 5C), 109.7 (d, C5H5, 5C, 1JCH ) 174.8 Hz), 78.4 (t, Zr-
1
CH2C(CH3)3, 2C, JCH ) 109.1 Hz), 37.1 (s, CH2C(CH3)3, 2C),
1
Experimental Section
35.6 (q, CH2C(CH3)3, 6C, JCH ) 123.3 Hz), 12.5 (q, C5(CH3)5,
1
5C, JCH ) 126.2 Hz).
General Considerations. All air- and moisture-sensitive com-
pounds were manipulated using standard high-vacuum line, Schlenk,
or cannula techniques, or in a drybox under a nitrogen atmosphere
as described previously.36 Argon gas was purified and dried by
passage through columns of MnO on vermiculite and activated 4
Å molecular sieves. Solvents for air- and moisture-sensitive
reactions were dried by the method of Grubbs37 and were stored
under vacuum over sodium benzophenone ketyl (diethyl ether,
pentane, tetrahydrofuran), titanocene38 (toluene, petroleum ether),
or calcium hydride (methylene chloride). 1,4-Dioxane was vacuum
Synthesis of (η5-C5H5)(η5-C5Me5)Zr(CH2SiMe3)2 (2) (CpCp*Zr-
(CH2TMS)2). In an inert atmosphere glovebox, a 50 mL round-
bottom flask equipped with a stir bar was charged with (η5-
C5H5)(η5-C5Me5)ZrCl2 (1.170 g, 3.23 mmol) and LiCH2SiMe3
(0.639 g, 6.78 mmol) and attached to a small swivel frit assembly.
(38) Marvich, R. H.; Brintzinger, H. H. J. Am. Chem. Soc. 1971, 93,
2046-2048.
(39) Wolczanski, P. T.; Bercaw, J. E. Organometallics 1982, 1, 793-
799.
(40) Surtees, J. R. Chem. Commun. 1965, 567.
(41) Schrock, R. R.; Fellmann, J. D. J. Am. Chem. Soc. 1978, 100, 3359-
3370.
(42) Tessier-Youngs, C.; Beachley, O. T., Jr. Inorg. Synth. 1986, 24,
95-97.
(43) Coates, G. E.; Heslop, J. A. J. Chem. Soc. A 1968, 514-518.
(36) Burger, B. J.; Bercaw, J. E. New DeVelopments in the Synthesis,
Manipulation, and Characterization of Organometallic Compounds; Ameri-
can Chemical Society: Washington, DC, 1987; Vol. 357.
(37) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518-1520.

3026 Organometallics, Vol. 26, No. 12, 2007
Klamo et al.
On the vacuum line, diethyl ether (30 mL) was vacuum transferred
onto the solids at -78 °C, and the apparatus was backfilled with
Ar. The reaction mixture was allowed to warm to room temperature
with stirring, and an off-white precipitate was observed. After
stirring for 12 h, the solvent was removed in vacuo, leaving a
colorless, oily paste. Pentane (35 mL) was added to the mixture
by vacuum transfer. The resulting off-white precipitate was filtered
away from the colorless filtrate and washed two times with recycled
solvent. Removal of all volatiles and drying in vacuo yielded an
off-white powder. In the glovebox the solid was dissolved in
pentane and the solution concentrated to 8 mL. The solution was
cooled to -35 °C to recrystallize the desired product; colorless
crystalline material suitable for X-ray diffraction was isolated and
dried in vacuo. Yield: 1.051 g (70%). Anal. Calcd. for C23H42Si2-
with (η5-C5H5)(η5-C5Me5)Zr(CH3)Cl (0.866 g, 2.53 mmol) and
LiCH2SiMe3 (0.240 g, 2.54 mmol) and attached to a small swivel
frit assembly. On the vacuum line, diethyl ether (25 mL) was
vacuum transferred onto the solids at -78 °C and the apparatus
was backfilled with Ar. The reaction mixture was allowed to warm
to room temperature over 12 h with stirring. At this time a colorless
solution with a white precipitate was observed. The solvent was
removed, and resultant paste was dried in vacuo. Pentane (20 mL)
was added to the mixture by vacuum transfer. The resulting white
precipitate was filtered away from the colorless filtrate and washed
twice with recycled solvent. Removal of all volatiles and drying in
vacuo resulted in a pale yellow oil. Repeated attempts to solidify
the product by trituration with pentane or lyophilization with
benzene failed. Yield: 0.865 g (87%). 1H NMR (300 MHz,
C6D6): δ 5.79 (s, C5H5, 5H), 1.68 (s, C5(CH3)5, 15H), 0.21 (s, CH2-
Si(CH3)3, 9H), -0.29 (s, CH3, 3H) -0.31 (d, CH2Si(CH3)3, 1H, J
) 9.5 Hz), -0.38 (d, CH2Si(CH3)3, 1H, J ) 9.5 Hz). 13C{1H} NMR
(75 MHz, C6D6): δ 117.9 (C5(CH3)5), 111.4 (C5H5), 44.9 (Zr-CH2-
Si(CH3)3), 34.0 (Zr-CH3), 12.4 (C5(CH3)5), 4.3 (CH2Si(CH3)3).
Reaction of (η5-C5H5)(η5-C5Me5)Zr(CH3)Cl and LiCH2CMe3
Leading to Multiple Dialkyl Zirconocene Products. In an inert
atmosphere glovebox, a 50 mL round-bottom flask equipped with
a stir bar was charged with (η5-C5H5)(η5-C5Me5)Zr(CH3)Cl (0.500
g, 1.46 mmol) and LiCH2CMe3 (0.126 g, 1.60 mmol) and attached
to a small swivel frit assembly. On the vacuum line, diethyl ether
(30 mL) was vacuum transferred onto the solids at -78 °C and the
apparatus was backfilled with Ar. The cooling bath was removed,
and the reaction mixture was stirred for 48 h at room temperature.
At this time a bright yellow solution with a white precipitate was
observed. The solvent was removed in vacuo, leaving an oily
residue. Pentane (15 mL) was added to the mixture by vacuum
transfer. The resulting white precipitate was filtered away from the
yellow filtrate and washed with recycled solvent. Removal of all
volatiles and drying in vacuo resulted in a yellow-brown oil.
Characterization of the crude oil by 1H NMR indicated three
compounds in the product mixture. (η5-C5H5)(η5-C5Me5)Zr(CH3)2,
(η5-C5H5)(η5-C5Me5)Zr(CH3)(Np), and (η5-C5H5)(η5-C5Me5)Zr(Np)2
were present in a 16:66:18 ratio, respectively.
1
Zr: C, 59.28; H, 9.08. Found: C, 59.45, 59.37; H, 9.20, 8.95. H
NMR (500 MHz, C6D6): δ 5.89 (s, C5H5, 5H), 1.70 (s, C5(CH3)5,
15H), 0.21 (s, CH2Si(CH3)3, 18H), -0.25 (d, CH2Si(CH3)3, 2H, J
) 10.7 Hz), -0.54 (d, CH2Si(CH3)3, 2H, J ) 10.9 Hz). 13C{1H}
NMR (125 MHz, C6D6): δ 118.2 (C5(CH3)5), 110.8 (C5H5), 46.0
(Zr-CH2Si(CH3)3), 12.4 (C5(CH3)5), 4.10 (CH2Si(CH3)3).
NMR Scale Synthesis of (η5-C5H5)(η5-C5Me5)Zr(CH3)Cl (3)
(CpCp*Zr(CH3)Cl). In an inert atmosphere glovebox, (η5-C5H5)(η5-
C5Me5)ZrCl2 (45 mg, 0.12 mmol) was weighed into a small vial.
To this was added 0.25 mL of a 0.5 M solution of (η5-C5H5)(η5-
C5Me5)Zr(CH3)2 (40 mg, 0.12 mmol) in toluene-d8. The contents
of the vial were transferred via pipet to a J. Young NMR tube, and
the vial was rinsed with an additional 0.45 mL of solvent. The
reaction was heated in an oil bath regulated at 130 °C, and the
1
reaction progress was monitored by H NMR spectroscopy. The
solution was pale yellow and a solid crystallized out upon cooling
the sample to room temperature to acquire 1H NMR data. After 10
days of heating at this temperature, clean formation of 3 was
1
observed in 95% yield (by H NMR).
Synthesis of (η5-C5H5)(η5-C5Me5)Zr(CH3)Cl (3) (CpCp*Zr-
(CH3)(CI)). In an inert atmosphere glovebox, a thick walled glass
vessel equipped with a stir bar was charged with (η5-C5H5)(η5-C5-
Me5)ZrCl2 (2.001 g, 5.52 mmol) and (η5-C5H5)(η5-C5Me5)Zr(CH3)2
(2.048 g, 6.37 mmol). Toluene (24 mL, vacuum transferred from
titanocene) was added, giving a mixture consisting of a yellow
solution and remaining solid (η5-C5H5)(η5-C5Me5)ZrCl2. The vessel
was sealed with an 8 mm Kontes needle valve, and the mixture
was stirred in the box to break up the solid. In the hood, the reaction
was heated with stirring in an oil bath regulated at 130 °C for 11.64
days. At this temperature a homogeneous solution was observed.
The reaction was removed from the oil bath and cooled to room
temperature, resulting in a green solution and an off-white
precipitate. In the glovebox, a small heterogeneous sample was dried
in vacuo for analysis by 1H NMR spectroscopy and confirmed clean
conversion to product (<5% (η5-C5H5)(η5-C5Me5)ZrCl2). At this
point toluene was added, and the reaction mixture was transferred
to a flask and was concentrated and dried in vacuo. The resulting
solid was stirred in petroleum ether (100 mL) and filtered. The
precipitate was isolated and was purified by precipitation from a
concentrated toluene-petroleum ether solution at -35 °C. Removal
of all volatiles gave 0.340 g of an off-white solid identical (by 1H
NMR spectroscopy) to that obtained using the literature procedure.
An additional 2.953 g of product was obtained by concentration of
the combined organic filtrates and several repetitions of the
purification procedure. Yield: 3.293 g (87%). Anal. Calcd. for
C16H23ClZr: C, 56.19; H, 6.78. Found: C, 56.49, 56.29; H, 6.72,
Synthesis of (η5-C5H5)(η5-C5Me5)Zr(CH3)(CH2CMe3) (5)
(CpCp*Zr(CH3)(Np)). In an inert atmosphere glovebox, a 100 mL
round-bottom flask equipped with a stir bar was charged with (η5-
C5H5)(η5-C5Me5)Zr(CH3)Cl (0.592 g, 1.73 mmol) and LiCH2CMe3
(0.136 g, 1.74 mmol) and attached to a small swivel frit assembly.
On the vacuum line, toluene (70 mL) was vacuum transferred onto
the solids at -78 °C and the apparatus was backfilled with Ar.
The reaction mixture was stirred for 9 h at -78 °C, then allowed
to warm to room temperature over 14 h with stirring. At this time
a yellow-green solution was observed. The solvent was removed
in vacuo, leaving an oily paste. Pentane (25 mL) was added to the
mixture by vacuum transfer. The resulting white precipitate was
filtered away from the yellow filtrate and washed with recycled
solvent. Removal of all volatiles and drying in vacuo resulted in a
yellow oil. In the glovebox this oil was dissolved in petroleum ether
(20 mL) and filtered via pipet through Celite directly into a 50 mL
Kjeldahl flask equipped with a stir bar. The flask was attached to
a needle valve, and on the vacuum line the volatiles were removed.
Pentane (15 mL) was added by vacuum transfer to dissolve the oil
and was removed slowly in vacuo with rapid stirring. Further
trituration with pentane (generally 3 cycles) gave a yellow powder,
which was dried in vacuo. Yield: 0.550 g (84%). Anal. Calcd. for
C21H34Zr: C, 66.78; H, 9.07. Found: C, 66.52, 66.76; H, 8.97,
1
6.82. H NMR (300 MHz, C6D6): δ 5.79 (s, C5H5, 5H), 1.71 (s,
C5(CH3)5, 15H), 0.22 (s, CH3, 3H). 13C{1H} NMR (75 MHz,
C6D6): δ 120.5 (C5(CH3)5), 113.6 (C5H5), 35.3 (Zr-CH3), 12.2
(C5(CH3)5).
1
9.01. H NMR (300 MHz, C6D6): δ 5.86 (s, C5H5, 5H), 1.67 (s,
C5(CH3)5, 15H), 1.13 (s, CH2C(CH3)3, 9H), 0.45 (d, CH2C(CH3)3,
1H, J ) 12.6 Hz), -0.18 (d, CH2C(CH3)3, 1H, J ) 12.6 Hz), -0.27
(s, CH3, 3H). 13C{1H} NMR (75 MHz, C6D6): δ 117.9 (C5(CH3)5),
111.3 (C5H5), 70.9 (Zr-CH2C(CH3)3), 36.5 (Zr-CH3), 36.3
(CH2C(CH3)3), 36.0 (CH2C(CH3)3), 12.3 (C5(CH3)5).
Synthesis of (η5-C5H5)(η5-C5Me5)Zr(CH3)(CH2SiMe3) (4)
(CpCp*Zr(CH3)(CH2TMS)). In an inert atmosphere glovebox, a
50 mL round-bottom flask equipped with a stir bar was charged

Dialkyl and Methyl-Alkyl Zirconocenes
Organometallics, Vol. 26, No. 12, 2007 3027
Synthesis of (η5-C5H5)(η5-C5Me5)Zr(CH2CMe3)Cl (6)
(CpCp*Zr(Np)Cl). In an inert atmosphere glovebox, a 50 mL
round-bottom flask equipped with a stir bar was charged with (η5-
C5H5)(η5-C5Me5)ZrCl2 (0.385 g, 1.06 mmol) and LiCH2CMe3
(0.088 g, 1.13 mmol) and attached to a small swivel frit assembly.
On the vacuum line, toluene (25 mL) was vacuum transferred onto
the solids at -78 °C and the apparatus was backfilled with Ar.
The cooling bath was removed, and the reaction mixture was
allowed to warm to room temperature. Stirring for 5 h resulted in
a bright yellow solution and a white precipitate. The reaction was
filtered, and the precipitate was washed twice with recycled solvent.
The solvent was removed in vacuo, leaving a bright yellow oil that
began to solidify. Petroleum ether (10 mL) was added to the isolated
material by vacuum transfer followed by stirring at room temper-
ature. Removal of all volatiles and drying in vacuo yielded a bright
yellow powder. The product may be crystallized by slow diffusion
of petroleum ether into a diethyl ether solution cooled to -35 °C;
yellow crystalline fragments suitable for X-ray diffraction were
obtained via this method. Yield: 0.303 g (72%). Anal. Calcd. for
C20H31ClZr: C, 60.33; H, 7.85. Found: C, 60.10, 60.41; H, 7.73,
C5H5)(η5-C5Me5)Zr(CH2CMe3)Br (6-Br), and 5 were observed in
roughly a 2:2:1 ratio respectively.
Alternate Methods for the Synthesis of (η5-C5H5)(η5-C5Me5)-
Zr(CH2CMe3)(CH3) (5): Reaction of (η5-C5H5)(η5-C5Me5)Zr-
(Cl)(CH2CMe3) with Mg(CH3)2. In an inert atmosphere glovebox,
a J. Young NMR tube was charged with (η5-C5H5)(η5-C5Me5)Zr(CH2-
CMe3)Cl (13 mg, 0.03 mmol) and Mg(CH3)2 (1.4 mg, 0.02 mmol).
Benzene-d6 (0.82 mL) was added, giving a yellow solution. The
reaction mixture was heated at 80 °C and was allowed to proceed
for 9 h, over which time the solution became more yellow-green
1
in color and a precipitate was observed. The H NMR spectrum
indicated a 60:35:5:1 mixture of compounds 6, 5, 3, and (η5-
C5H5)(η5-C5Me5)Zr(CH3)2 respectively.
Alternate Methods for the Synthesis of (η5-C5H5)(η5-C5Me5)-
Zr(CH3)(CH2CMe3) (5): Reaction of (η5-C5H5)(η5-C5Me5)Zr-
(CH2CMe3)Cl with Mg(CH3)2-1,4-Dioxane. In an inert atmos-
phere glovebox, a J. Young NMR tube was charged with (η5-
C5H5)(η5-C5Me5)Zr(CH2CMe3)Cl (10 mg, 0.02 mmol), Mg(CH3)2
(1.5 mg, 0.02 mmol), and 1,4-dioxane (5 µL, 0.06 mmol). The
addition of benzene-d6 (0.83 mL) gave a yellow solution. The
reaction mixture was heated at 80 °C, and the reaction was allowed
to proceed for 9.5 h, over which time the solution became more
yellow-green in color and a precipitate was observed. Analysis of
the reaction mixture by 1H NMR spectroscopy indicated clean
formation of compound 5.
1
7.87. H NMR (300 MHz, C6D6): δ 5.94 (s, C5H5, 5H), 1.69 (s,
C5(CH3)5, 15H), 1.26 (s, CH2C(CH3)3, 9H), 1.21 (d, CH2C(CH3)3,
1H, J ) 13.2 Hz), 0.16 (d, CH2C(CH3)3, 1H, J ) 13.2 Hz). 13C-
{1H} NMR (75 MHz, C6D6): δ 121.0 (C5(CH3)5), 113.3 (C5H5),
68.9 (Zr-CH2C(CH3)3), 36.5 (CH2C(CH3)3), 35.5 (CH2C(CH3)3),
12.4 (C5(CH3)5).
2-Ethylbutyric Acid Methyl Ester (8). A 500 mL round-bottom
flask was charged with 2-ethylbutyric acid (7) (92.4 g, 795 mmol)
and methanol (275 mL, 6760 mmol). Concentrated H2SO4 (23 mL)
was added, and a reflux condenser was attached. The mixture was
heated to reflux for 24 h. Methanol was distilled off on a water
bath. The residue was diluted with water (500 mL), and the layers
were separated. Organics remaining in the aqueous layer were
extracted with diethyl ether. The combined organic phases were
washed with saturated NaHCO3, water, and dried over MgSO4. The
solvent was removed under reduced pressure. The product was
distilled (137 °C, 1 atm) to produce a clear liquid. Yield: 51.65 g
Alternate Methods for the Synthesis of (η5-C5H5)(η5-C5Me5)-
Zr(CH3)(CH2CMe3) (5): Reaction of (η5-C5H5)(η5-C5Me5)Zr-
(CH2CMe3)Cl with LiCH3. In an inert atmosphere glovebox, a J.
Young NMR tube was charged with (η5-C5H5)(η5-C5Me5)Zr(CH2-
CMe3)Cl (12 mg, 0.03 mmol) and dry, ether-free solid LiCH3 (1.5
mg, 0.07 mmol). Benzene-d6 (0.78 mL) was added to give a yellow
solution; LiCH3 was not soluble in C6D6 at room temperature. The
reaction was heated at 80 °C and monitored by 1H NMR
spectroscopy. After 4 h of heating, the 1H NMR spectrum indicated
a 30:70 mixture of 6 and 5, respectively. The reaction was complete
(by 1H NMR) after an additional 5 h of heating at this temperature
to yield 5 cleanly as the only product.
1
(50%). H NMR (300 MHz, CDCl3): δ 3.67 (s, OCH3, 3H), 2.21
(m, CH(CH2CH3)2, 1H), 1.56 (m, CH(CH2CH3)2, 4H), 0.88 (t, CH-
(CH2CH3)2, 6H, J ) 7.5 Hz). 13C{1H} NMR (75 MHz, CDCl3): δ
176.89, 51.61, 49.19, 25.45, 12.24. DEPT (75 MHz, CDCl3): δ
176.89 (quaternary C), 49.18 (CH), 25.43 (CH2), 51.58, 12.23
(CH3).
Alternate Methods for the Synthesis of (η5-C5H5)(η5-C5Me5)-
Zr(CH3)(CH2CMe3) (5): Reaction of (η5-C5H5)(η5-C5Me5)Zr-
(CH2CMe3)Cl with Li13CH3‚LiI. In an inert atmosphere glovebox,
a J. Young NMR tube was charged with (η5-C5H5)(η5-C5Me5)Zr(CH2-
CMe3)Cl (12.8 mg, 0.03 mmol) and dry, ether-free solid Li13CH3‚
LiI (7.0 mg, 0.04 mmol). Benzene-d6 (0.81 mL) was added to give
a yellow solution; Li13CH3‚LiI was not soluble in C6D6 at room
temperature. The reaction mixture was heated for 9 h in an oil bath
regulated at 80 °C. At this time the sample was cooled to room
temperature and a yellow-green solution with a white precipitate
2,2-Diethylbutyric Acid Methyl Ester (9). A 1 L Schlenk flask
with addition funnel was purged with argon and charged with HN-
(CHMe2)2 (47.4 mL, 338 mmol). THF (250 mL) was added via
cannula and the solution cooled to 0 °C. Butyllithium (211 mL,
338 mmol) was transferred to the addition funnel by cannula and
was added to the reaction mixture over 40 min with stirring. The
reaction mixture was then cooled to -30 °C, and 8 (40.0 g, 307
mmol) was added slowly by syringe. The yellow solution was stirred
for 30 min at this temperature. Ethyl iodide (27.3 mL, 338 mmol)
was added at -78 °C. The mixture was stirred at this temperature
for 5 h and then at room temperature overnight. The reaction
mixture was added to a separatory funnel with diethyl ether and
water, and the phases were separated. The aqueous layer was
extracted with additional diethyl ether. The combined organic layers
were washed with saturated NaCl and dried over MgSO4. The
solvent was removed under reduced pressure. The resulting yellow
liquid was distilled under full vacuum (30-31 °C, ∼1 mmHg),
and a clear liquid was collected in two fractions. Yield: 39.3 g
1
was observed. Analysis by H NMR spectroscopy indicated three
compounds were present. Compounds 6, (η5-C5H5)(η5-C5Me5)Zr(CH2-
CMe3)I (6-I), and 5 were observed in roughly a 7:1:12 ratio,
respectively.
Alternate Methods for the Synthesis of (η5-C5H5)(η5-C5Me5)-
Zr(CH3)(CH2CMe3) (5): Reaction of (η5-C5H5)(η5-C5Me5)Zr-
(CH2CMe3)Cl with CH3MgBr. In an inert atmosphere glovebox,
(η5-C5H5)(η5-C5Me5)Zr(CH2CMe3)Cl (31 mg, 0.08 mmol) was
dissolved in diethyl ether (5 mL) and cooled to -35 °C. A 3.17 M
ethereal solution of CH3MgBr (0.04 mL, 0.12 mmol) was diluted
in diethyl ether (2 mL) and cooled to -35 °C. The chilled solution
of CH3MgBr was added dropwise to the bright yellow solution of
(η5-C5H5)(η5-C5Me5)Zr(CH2CMe3)Cl. The reaction mixture was
stirred for 2 h, over which time it became a darker yellow color.
1,4-Dioxane (2 mL) was added and a white solid precipitated from
the yellow solution. The reaction mixture was filtered, and removal
of all volatiles followed by drying in vacuo yielded a yellow, oily
residue. Analysis of the isolated material by 1H NMR spectroscopy
revealed three compounds were present. Compounds 6, (η5-
1
(81%). H NMR (300 MHz, CDCl3): δ 3.66 (s, OCH3, 3H), 1.57
(q, C(CH2CH3)3, 6H, J ) 7.5 Hz), 0.75 (t, C(CH2CH3)3, 9H, J )
7.3 Hz). 13C{1H} NMR (75 MHz, CDCl3): δ 177.90, 51.66, 50.32,
26.40, 8.71. DEPT (75 MHz, CDCl3): δ 177.90, 50.32 (quaternary
C), 26.40 (CH2), 51.67, 8.71 (CH3).
2,2-Diethylbutanol (10). In the glovebox, a 3 L three-neck flask
was charged with LiAlH4 (7.19 g, 190 mmol). Outside the glovebox,

3028 Organometallics, Vol. 26, No. 12, 2007
Klamo et al.
an addition funnel was attached under a flow of argon. All joints
were sealed with Teflon tape and all adaptors secured with wire
and rubber bands. The flask was cooled in an ice-NaCl bath, and
diethyl ether (750 mL) was added through the addition funnel by
cannula. Compound 9 (30.0 g, 190 mmol) was poured into the
addition funnel and dissolved in diethyl ether against a strong flow
of argon. This solution was added dropwise over 1 h and the
temperature maintained at 0 °C. Stirring continued overnight. The
reaction was quenched using Fieser conditions: water (8 mL), 15%
NaOH (8 g of solution), water (24 mL). The liquids were removed
from the sludgy, white precipitate with additional diethyl ether. The
phases were separated, and the aqueous layer was washed three
times with diethyl ether. The combined organic layer was dried
over MgSO4 and the solvent removed under reduced pressure. The
resulting cloudy liquid was distilled from CaSO4 under reduced
pressure (80-82 °C, 20 mmHg), producing a white liquid. Yield:
22.0 g (89%). 1H NMR (300 MHz, CDCl3): δ 3.34 (d, CH2C(CH2-
CH3)3, 2H, J ) 3.9 Hz), 1.30 (br, OH, 1H), 1.22 (q, CH2C(CH2-
CH3)3, 6H, J ) 7.5 Hz), 0.77 (t, CH2C(CH2CH3)3, 9H, J ) 7.6
Hz). 13C{1H} NMR (75 MHz, CDCl3): δ 65.99, 39.79, 25.26, 7.73.
DEPT (75 MHz, CDCl3): δ 39.79 (quaternary C), 65.96, 25.25
(CH2), 7.72 (CH3).
tert-butyllithium (0.56 mL, 0.95 mmol) was added dropwise using
an Ar-flushed syringe. During the addition, formation of a white
precipitate was observed. The reaction mixture was stirred at -78
°C for 40 min. The dry ice-acetone bath was removed, and the
reaction mixture was allowed to warm to room temperature with
stirring for 30 min, after which time a colorless solution was
observed. The septum was replaced with a Kontes needle valve,
and the solvent was removed. Drying in vacuo yielded a glassy,
white solid. In the glovebox the reaction flask was attached to a
small swivel frit assembly. On the vacuum line, pentane (12 mL)
was vacuum transferred onto the glassy solid at -78 °C. Warming
to room temperature and stirring to break up the solids resulted in
a colorless solution with a white precipitate. This solution was
filtered and the precipitate washed one time with recycled solvent.
The solvent was removed to yield a pale yellow, almost colorless,
1
oil, which was dried in vacuo. Yield: 0.045 g (88%). H NMR
(300 MHz, C6D6): δ 1.34 (br q, CH2C(CH2CH3)3 6H, J ) 7.2 Hz),
0.90 (t, CH2C(CH2CH3)3, 9H, J ) 7.5 Hz), -0.71 (br s, CH2C(CH2-
CH3)3, 2H).
2,2-Dimethyl-3-phenylpropionoic Acid Ethyl Ester (15). A 1
L Schlenk flask with addition funnel was purged with argon and
charged with HN(iPr)2 (66.4 mL, 473 mmol). THF (300 mL) was
added via cannula and the solution cooled to 0 °C. Butyllithium
(296 mL, 474 mmol) was transferred to the addition funnel by
cannula and was added to the reaction mixture over 40 min with
stirring. The reaction mixture was then cooled to -30 °C, and
2-methylpropionoic acid ethyl ester (14) (50.0 g, 430 mmol) was
added slowly by syringe. The yellow solution was stirred for 30
min at this temperature. Benzyl bromide (56.3 mL, 473 mmol) was
added at -78 °C. The mixture was stirred at this temperature for
5 h and then at room temperature overnight. The reaction mixture
was added to a separatory funnel with diethyl ether and water, and
the phases were separated. The aqueous layer was extracted with
additional diethyl ether. The combined organic layers were washed
with saturated NaCl and dried over MgSO4. The solvent was
removed under reduced pressure. The resulting yellow liquid was
distilled under full vacuum (55-57 °C, ∼1 mmHg), yielding a faint-
ly yellow liquid. Yield: 74.8 g (84%). 1H NMR (300 MHz,
CDCl3): δ 7.23 (m, m- and p-PhH, 3H), 7.11 (dd, o-PhH, 2H, J )
1.65, 7.65 Hz), 4.11 (q, OCH2CH3, 2H, J ) 7.2 Hz), 2.85 (s,
C(CH3)2CH2Ph, 2H), 1.23 (t, OCH2CH3, 3H, J ) 7.2 Hz), 1.17 (s,
C(CH3)2CH2Ph, 6H). 13C{1H} NMR (75 MHz, CDCl3): δ 177.54,
138.13, 130.33, 128.09, 126.54, 60.65, 46.59, 43.79, 25.30, 14.53.
DEPT (75 MHz, CDCl3): δ 177.54, 138.13, 43.79 (quaternary C),
130.32, 128.10, 126.56 (CH), 60.69, 46.58 (CH2), 25.30, 14.57
(CH3).
(2,2-Diethyl)butyl Mesylate (11). A 250 mL round-bottom flask
was charged with 10 (7.07 g, 54.3 mmol) and purged with argon.
CH2Cl2 (125 mL) was added via cannula. NEt3 (11.4 mL, 81.7
mmol) was added by syringe, and the mixture was cooled to 0 °C.
CH3SO2Cl (4.8 mL, 62.0 mmol) was added dropwise. The solution
became pale yellow and a precipitate formed. Stirring continued at
this temperature for 1 h. For workup, additional CH2Cl2 was added
and organics were washed with ice water (250 mL), chilled 10%
HCl (250 mL), saturated NaHCO3, and saturated NaCl. After drying
over Na2SO4 the solvent was removed under reduced pressure to
yield a thick, yellow liquid that was >95% pure by NMR. Yield:
1
11.3 g (quantitative). H NMR (300 MHz, CDCl3): δ 3.95 (s,
CH2C(CH2CH3)3, 2H), 2.30 (s, CH3, 3H), 1.30 (q, CH2C(CH2CH3)3,
6H, J ) 7.5 Hz), 0.81 (t, CH2C(CH2CH3)3, 9H, J ) 7.5 Hz).
13C{1H} NMR (75 MHz, CDCl3): δ 72.71, 39.13, 37.35, 25.34,
7.58. DEPT (75 MHz, CDCl3): δ 39.13 (quaternary C), 72.69,
25.32 (CH2), 37.35, 7.59 (CH3).
2,2-Diethyl-1-iodobutane (12). A 50 mL flask with condenser
was charged with 11 (2.91 g, 13.9 mmol) and anhydrous NaI (10.45
g, 69.7 mmol) and was purged with argon. N-Methylpyrrolidinone
(30 mL) was added via syringe. The reaction mixture was heated
to 140 °C for 4 h under argon. The reaction mixture was cooled,
and water and pentane were added. The phases were separated,
and the aqueous layer was extracted with pentane. The combined
organic phases (400 mL) were washed with saturated Na2S2O3,
twice with saturated CuSO4, and water. After drying over MgSO4,
the pentane was removed under reduced pressure. The yellow liquid
was purified by column chromatography on silica with hexanes.
The product was a clear liquid that was homogeneous by TLC.
2,2-Dimethyl-3-phenylpropanol (16). In the glovebox, a 3 L
three-neck flask was charged with LiAlH4 (10.41 g, 274 mmol).
Outside the glovebox, an addition funnel was attached under a flow
of argon. All joints were sealed with Teflon tape and all adaptors
secured with wire and rubber bands. The flask was cooled in an
ice-NaCl bath, and diethyl ether (850 mL) was added through the
addition funnel by cannula. Compound 15 (50.0 g, 242 mmol) was
poured into the addition funnel and dissolved in diethyl ether against
a strong flow of argon. This solution was added dropwise over 1
h and the temperature maintained at 0 °C. Stirring continued
overnight. The reaction was quenched using Fieser conditions:
water (11 mL), 15% NaOH (11 g of solution), water (33 mL). The
liquids were removed from the sludgy, white precipitate with
additional diethyl ether. The phases were separated, and the aqueous
layer was washed three times with diethyl ether. The combined
organic layer was dried over MgSO4 and the solvent removed under
reduced pressure. The resulting cloudy liquid was distilled from
CaSO4 under full vacuum (68-72 °C, ∼0.2 mmHg), producing a
white liquid that later solidified to a hard white solid. Yield: 35.20
g (88%). 1H NMR (300 MHz, CDCl3): δ 7.26 (m, m- and p-PhH,
3H), 7.17 (dd, o-PhH, 2H, J ) 1.5, 7.35 Hz), 3.32 (d, CH2C(CH3)2-
1
Yield: 2.40 g (72%). H NMR (300 MHz, CDCl3): δ 3.12 (s,
CH2C(CH2CH3)3, 2H), 1.30 (q, CH2C(CH2CH3)3, 6H, J ) 7.8 Hz),
0.76 (t, CH2C(CH2CH3)3, 9H, J ) 7.35 Hz). 13C{1H} NMR (75
MHz, CDCl3): δ 38.04, 27.38, 20.25, 8.15. DEPT (75 MHz,
CDCl3): δ 38.04 (quaternary C), 27.38, 20.25 (CH2), 8.14 (CH3).
Synthesis of LiCH2C(CH2CH3)3 (13) (LiCH2CEt3). 2,2-Di-
ethyl-1-iodobutane (0.102 g, 0.43 mmol) was weighed into a 25
mL round-bottom flask equipped with a 180° needle valve and was
degassed with two freeze-pump-thaw cycles at 77 K on the high-
vacuum line. Pentane and then diethyl ether were added by vacuum
transfer at -78 °C in a 3:2 ratio, respectively, to give a total solvent
volume of 12 mL. (Note: this reaction also worked effectively in
3:1 pentane-diethyl ether solvent.) The apparatus was backfilled
with Ar and stirred briefly at room temperature. The Kontes needle
valve was replaced with a septum using a positive Ar counterflow.
The solution was then cooled to -78 °C, and a 1.7 M solution of

Dialkyl and Methyl-Alkyl Zirconocenes
Organometallics, Vol. 26, No. 12, 2007 3029
CH2Ph, 2H, J ) 5.4 Hz), 2.58 (s, CH2C(CH3)2CH2Ph, 2H), 1.54
(t, OH, 1H, J ) 5.4 Hz), 0.89 (s, CH2C(CH3)2CH2Ph, 6H). 13C{1H}
NMR (75 MHz, CDCl3): δ 138.95, 130.68, 128.03, 126.13, 71.41,
44.97, 36.77, 24.35. DEPT (75 MHz, CDCl3): δ 138.95, 36.77
(quaternary C), 130.68, 128.02, 126.12 (CH), 71.40, 44.98 (CH2),
24.51 (CH3).
precipitate washed three times with recycled solvent. The solvent
was removed, yielding a yellow oil, which was dried in vacuo.
(Note: this compound was generally isolated as a diethyl etherate.)
1
Yield: 0.185 g (90%). H NMR (300 MHz, C6D6): δ 7.05-7.25
(m (partially obscured by C6D6), C6H5, 5H), 2.55 (s, CH2C-
(CH3)2CH2Ph, 2H), 1.07 (s, CH2C(CH3)2CH2Ph, 6H), -1.01 (br s,
CH2C(CH3)2CH2Ph, 2H).
(2,2-Dimethyl-3-phenyl)propyl Mesylate (17). A 250 mL
round-bottom flask was charged with 16 (5.82 g, 35.4 mmol) and
purged with argon. CH2Cl2 (110 mL) was added via cannula. NEt3
(7.6 mL, 54.5 mmol) was added by syringe, and the mixture was
cooled to 0 °C. CH3SO2Cl (3.2 mL, 41.3 mmol) was added
dropwise. The solution became pale yellow and a precipitate
formed. The reaction mixture stirred at this temperature for 1 h.
For workup, additional CH2Cl2 was added and the organics were
washed with ice water (250 mL), chilled 10% HCl (250 mL),
saturated NaHCO3, and saturated NaCl. After drying over Na2SO4
the solvent was removed under reduced pressure to yield a yellow
liquid that was >95% pure by NMR. Yield: 8.50 g (quantitative).
1H NMR (300 MHz, CDCl3): δ 7.28 (m, m- and p-PhH, 3H), 7.14
(dd, o-PhH, 2H, J ) 2.1, 7.35 Hz), 3.87 (s, CH2C(CH3)2CH2Ph,
2H), 3.02 (s, CH3, 3H), 2.62 (s, CH2C(CH3)2CH2Ph, 2H), 0.98 (s,
CH2C(CH3)2CH2Ph, 6H). 13C{1H} NMR (75 MHz, CDCl3): δ
137.47, 130.66, 128.26, 126.61, 77.05, 44.81, 37.47, 35.67, 24.39.
DEPT (75 MHz, CDCl3): δ 137.47, 35.67 (quaternary C), 130.65,
128.25, 126.60 (CH), 77.05, 44.79 (CH2), 37.46, 24.39 (CH3).
Synthesis of (η5-C5H5)(η5-C5Me5)Zr(CH3)(CH2C(CH2CH3)3)
(20) (CpCp*Zr(CH3)(CH2CEt3)). In an inert atmosphere glovebox,
(η5-C5H5)(η5-C5Me5)Zr(CH3)Cl (0.129 g, 0.38 mmol) was added
to the 25 mL round-bottom flask equipped with a stir bar containing
LiCH2CEt3 (0.045 g, 0.38 mmol) and attached to a small swivel
frit assembly. On the vacuum line, diethyl ether (12 mL) was
vacuum transferred onto the reaction mixture at -78 °C. The
apparatus was backfilled with Ar, and the yellow solution was
allowed to warm to room temperature over 14 h with stirring. A
yellow solution with a white precipitate was observed. The solvent
was removed, and the oily residue was dried in vacuo. Pentane
(10 mL) was added to the oil by vacuum transfer, and the reaction
mixture was stirred briefly at room temperature to break up the
solids. The resulting white precipitate was filtered away from the
yellow filtrate and washed once with recycled solvent. Removal
of all volatiles and drying in vacuo resulted in a yellow-brown oil
(0.130 g) that was 59% product 20 as judged by 1H NMR
spectroscopy. Repeated attempts to purify this material by crystal-
lization or precipitation from concentrated pentane solutions at -35
°C failed. 1H NMR (500 MHz, C6D6): δ 5.89 (s, C5H5, 5H), 1.69
(s, C5(CH3)5, 15H), 1.43 (m, CH2C(CH2CH3)3, 3H, J ) 7.8 Hz),
1.35 (m, CH2C(CH2CH3)3, 3H, J ) 7.8 Hz), 0.83 (t, CH2C-
(CH2CH3)3, 9H, J ) 7.4 Hz), -0.13 (d, CH2C(CH2CH3)3, 1H, J )
13.4 Hz), -0.16 (d, CH2C(CH2CH3)3, 1H, J ) 13.4 Hz), -0.28 (s,
CH3, 3H).
2-Methyl-2-benzyl-1-iodopropane (18). A 50 mL flask with
condenser was charged with 17 (1.86 g, 7.67 mmol) and anhydrous
NaI (5.75 g, 38.4 mmol) and was purged with argon. N-Methylpyr-
rolidinone (16 mL) was added via syringe. The reaction mixture
was heated to 140 °C for 7 h under argon. The reaction mixture
was cooled, and water and pentane were added. The phases were
separated and the aqueous layer was extracted with pentane. The
combined organic phases (250 mL) were washed with saturated
Na2S2O3, twice with saturated CuSO4, and water. After drying over
MgSO4, the pentane was removed under reduced pressure. The
yellow liquid was purified by column chromatography on silica
with hexanes, and the product was a clear liquid that was
homogeneous by TLC. Yield: 1.77 g (84%). 1H NMR (300 MHz,
CDCl3): δ 7.25 (br m, o-, m-, and p-PhH, 5H), 3.13 (s,
CH2C(CH3)2CH2Ph, 2H), 2.65 (s, CH2C(CH3)2CH2Ph, 2H), 1.04
(s, CH2C(CH3)2CH2Ph, 6H). 13C{1H} NMR (75 MHz, CDCl3): δ
138.36, 130.46, 128.15, 126.50, 46.63, 35.08, 27.44, 24.53. DEPT
(75 MHz, CDCl3): δ 138.46, 35.08 (quaternary C), 130.45, 128.14,
126.49 (CH), 46.62, 24.67 (CH2), 27.44 (CH3).
Synthesis of (η5-C5H5)(η5-C5Me5)Zr(CH3)(CH2CMe2CH2Ph)
(21) (CpCp*Zr(CH3)(CH2CMe2CH2Ph)). In an inert atmosphere
glovebox, (η5-C5H5)(η5-C5Me5)Zr(CH3)Cl (0.410 g, 1.19 mmol) was
added to the 25 mL round-bottom flask equipped with a stir bar
containing LiCH2CMe2CH2Ph (0.185 g, 1.19 mmol) and attached
to a small swivel frit assembly. On the vacuum line, diethyl ether
(18 mL) was vacuum transferred onto the reaction mixture at -78
°C. The apparatus was backfilled with Ar, and the reaction mixture
was allowed to warm to room temperature. After stirring for 36 h
a yellow-brown solution with an off-white precipitate was observed.
The solvent was removed, and the oily residue was dried for 1 h in
vacuo. Pentane (15 mL) was added to the oil by vacuum transfer,
and the reaction mixture was stirred briefly at room temperature to
break up the solids. The resulting white precipitate was filtered
away from the dark brown filtrate and washed once with recycled
solvent. Removal of all volatiles and drying in vacuo for 1.5 h at
50 °C resulted in a dark brown oil (0.396 g) that was 71% product
21 as judged by 1H NMR spectroscopy. Repeated attempts to purify
this material by crystallization or precipitation from concentrated
Synthesis of Li(CH2C(CH3)2CH2Ph) (19) (LiCH2CMe2CH2Ph).
2-Methyl-2-benzyl-1-iodopropane (0.365 g, 1.33 mmol) was weighed
into a 25 mL round-bottom flask equipped with a 180° needle valve
and was degassed with two freeze-pump-thaw cycles at 77 K on
the high-vacuum line. Pentane and then diethyl ether were added
by vacuum transfer at -78 °C in a 3:1 ratio, respectively, to give
a total solvent volume of 12 mL. The apparatus was backfilled
with Ar and stirred briefly at room temperature. The Kontes needle
valve was replaced by a septum using a positive Ar counterflow.
The solution was then cooled to -78 °C, and a 1.7 M solution of
tert-butyllithium (1.80 mL, 2.92 mmol) was added dropwise using
an Ar-flushed syringe. A white precipitate was observed im-
mediately following the addition. The reaction mixture was stirred
at -78 °C for 35 min. The dry ice-acetone bath was removed,
and the reaction mixture was allowed to warm to room temperature
with stirring for 45 min, during which time the solution turned
yellow. The septum was replaced with a Kontes needle valve, the
solvent was removed, and the oily residue was dried in vacuo. In
the glovebox the reaction flask was attached to a small swivel frit
assembly. On the vacuum line, pentane (12 mL) was vacuum
transferred onto the oil at -78 °C. Warming to room temperature
and stirring to break up the solids resulted in a yellow solution
with a white precipitate. This solution was filtered and the
1
pentane solutions at -35 °C have failed. H NMR (300 MHz,
C6D6): δ 7.15-7.25 (m (partially obscured by C6D6), C6H5, 5H),
5.82 (s, C5H5, 5H), 2.58 (d, CH2C(CH3)2CH2Ph, 1H, J ) 12.6 Hz),
2.54 (d, CH2C(CH3)2CH2Ph, 1H, J ) 12.1 Hz), 1.64 (s, C5(CH3)5,
15H), 1.15 (s, CH2C(CH3)2CH2Ph, 3H), 0.92 (s, CH2C(CH3)2CH2-
Ph, 3H), 0.44 (d, CH2C(CH3)2CH2Ph, 1H, J ) 12.0 Hz), -0.27 (s,
CH3, 3H), -0.33 (d, CH2C(CH3)2CH2Ph, 1H, J ) 12.7 Hz).
Synthesis of (η5-C5H5)2Zr(CH3)(CH2C(CH2CH3)3) (22) (Cp2Zr-
(CH3)(CH2CEt3)). 2,2-Diethyl-1-iodobutane (0.274 g, 1.14 mmol)
was weighed into a 25 mL round-bottom flask equipped with a
180 ° needle valve and was degassed at 77 K on the high-vacuum
line. Pentane (8 to 10 mL) and then diethyl ether (2 to 4 mL) were
added by vacuum transfer at -78 °C. The apparatus was backfilled
with Ar and stirred briefly at room temperature. The Kontes needle
valve was replaced by a septum using a positive Ar counterflow.
The solution was then cooled to -78 °C, and a 1.7 M solution of

3030 Organometallics, Vol. 26, No. 12, 2007
Klamo et al.
tert-butyllithium (1.50 mL, 2.51 mmol) was added dropwise using
an Ar-flushed syringe. A white precipitate was observed in the
colorless solution before the addition was completed. The reaction
mixture was stirred at -78 °C for 30 min. The dry ice-acetone
bath was removed and the reaction mixture stirred at room
temperature for 30 min. The septum was replaced with a Kontes
needle valve, and the solvent was removed. Drying in vacuo yielded
a glassy, white solid. In an inert atmosphere glovebox, (η5-C5H5)2-
Zr(CH3)Cl (0.310 g, 1.14 mmol) was added to the flask containing
this solid, which was then attached to a small swivel frit assembly.
On the vacuum line, diethyl ether (13 mL) was vacuum transferred
onto the solids at -78 °C and the apparatus was backfilled with
Ar. The reaction mixture was allowed to warm to room temperature
over 20 h with stirring. At this time a brown-green solution with a
white precipitate was observed. The solvent was removed, and the
resulting yellow-brown oil was dried at 30 °C in vacuo. Pentane
(10 mL) was vacuum transferred onto the oil at -78 °C. Stirring
at room temperature gave a yellow-brown solution with an off-
white precipitate. Filtration followed by removal of solvent yielded
a yellow-brown oil, which was dried at 30 °C in vacuo. In the
glovebox this oil was dissolved in pentane, giving a yellow solution,
which was filtered via pipet through Celite and concentrated to
less than 10 mL. The solution was cooled to -35 °C to recrystallize
the desired product; pale yellow crystalline material suitable for
X-ray diffraction was isolated and dried in vacuo. Yield: 0.128 g
(32%). Anal. Calcd. for C19H30Zr: C, 65.26; H, 8.65. Found: C,
64.50, 64.39; H, 8.65, 8.42. 1H NMR (500 MHz, C6D6): δ 5.78 (s,
C5H5, 10H), 1.29 (q, CH2C(CH2CH3)3, 6H, J ) 7.4 Hz), 0.80 (t,
CH2C(CH2CH3)3, 9H, J ) 7.4 Hz), 0.15 (s, CH2C(CH2CH3)3, 2H),
-0.015 (s, CH3, 3H). 13C{1H} NMR (125 MHz, C6D6): δ 110.3
(C5H5), 76.8 (Zr-CH2C(CH2CH3)3), 46.5 (CH2C(CH2CH3)3), 33.0
(CH2C(CH2CH3)3), 25.9 (Zr-CH3), 9.3 (CH2C(CH2CH3)3).
solution with an off-white precipitate. Filtration followed by removal
of solvent yielded a brown oil, which was dried at 30 °C in vacuo.
In the glovebox this oil was dissolved in pentane, giving a yellow-
brown solution, which was filtered via pipet through Celite and
concentrated to less than 10 mL. The solution was cooled to -35
°C to recrystallize the desired product as brown pellets, which were
isolated and dried in vacuo. Yield: 0.208 g (33%). Anal. Calcd.
for C22H28Zr: C, 68.87; H, 7.35. Found: C, 68.56, 68.62; H, 7.26,
7.28. 1H NMR (300 MHz, C6D6): δ 7.16-7.25 (m (partially
obscured by C6D6), C6H5, 5H), 5.73 (s, C5H5, 10H), 2.49 (s, CH2C-
(CH3)2CH2Ph, 2H), 0.98 (s, CH2C(CH3)2CH2Ph, 6H), 0.45 (s,
CH2C(CH3)2CH2Ph, 2H), -0.043 (s, CH3, 3H). 1H NMR (500 MHz,
C7D8): δ 7.10-7.20 (m (partially obscured by C7D8), C6H5, 5H),
5.73 (s, C5H5, 10H), 2.43 (s, CH2C(CH3)2CH2Ph, 2H), 0.94 (s,
CH2C(CH3)2CH2Ph, 6H), 0.41 (s, CH2C(CH3)2CH2Ph, 2H), -0.12
(s, CH3, 3H). 1H NMR (500 MHz, C7D8, 193 K): δ 7.15-7.25 (m
(partially obscured by C7D8), C6H5, 5H), 5.63 (s, C5H5, 10H), 2.49
(s, CH2C(CH3)2CH2Ph, 2H), 1.00 (s, CH2C(CH3)2CH2Ph, 6H), 0.40
1
(s, CH2C(CH3)2CH2Ph, 2H), 0.024 (s, CH3, 3H). H NMR (500
MHz, CD2Cl2): δ 7.24 (t, m-C6H5, 2H, J ) 7.0 Hz), 7.17 (t, p-C6H5,
1H, J ) 7.3 Hz), 7.08 (d, o-C6H5, 2H, J ) 7.25 Hz), 6.08 (s, C5H5,
10H), 2.40 (s, CH2C(CH3)2CH2Ph, 2H), 0.89 (s, CH2C(CH3)2CH2-
Ph, 6H), 0.37 (s, CH2C(CH3)2CH2Ph, 2H), -0.31 (s, CH3, 3H).
13C{1H} NMR (125 MHz, CD2Cl2): δ 141.2 (i-C6H5), 131.2 (m-
C6H5), 127.8 (o-C6H5), 126.0 (p-C6H5), 110.6 (C5H5), 75.6 (Zr-
CH2C(CH3)2CH2Ph), 55.0 (CH2C(CH3)2CH2Ph), 41.4 (CH2C(CH3)2-
CH2Ph), 31.8 (CH2C(CH3)2CH2Ph), 27.6 (Zr-CH3). DEPT (75 MHz,
CD2Cl2): δ 141.2, 41.4 (quaternary C), 131.2, 127.8, 126.0, 110.6
(CH), 75.6, 55.0 (CH2), 31.8, 27.6 (CH3).
X-ray Crystal Data: General Procedure. Crystals grown from
pentane (1, 2, and 22) at -35 °C were isolated and dried in vacuo,
then transferred to a microscope slide coated with Paratone N oil.
Crystals grown from Et2O-petroleum ether (6) at -35 °C were
removed quickly from a scintillation vial to a microscope slide
coated with Paratone N oil. Samples were selected and mounted
on a glass fiber with Paratone N oil. Data collection was carried
out on a Bruker Smart 1000 CCD diffractometer. The structures
were solved by direct (1, 2, 6) or Patterson methods (22)
(SHELXTL-97, Sheldrick, 1990) in conjunction with standard
difference Fourier techniques. All non-hydrogen atoms were refined
anisotropically. Some details regarding refined data and cell
parameters are available in Table 2. Selected bond distances and
angles are supplied in Tables 1 and 3.
Synthesis of (η5-C5H5)2Zr(CH3)(CH2C(CH3)2CH2Ph) (23)
(Cp2Zr(CH3)(CH2CMe2CH2Ph)). 2-Methyl-2-benzyl-1-iodopro-
pane (0.448 g, 1.63 mmol) was weighed into a 25 mL round-bottom
flask equipped with a 180° needle valve and was degassed at 77 K
on the high-vacuum line. Pentane (8 to 10 mL) and then diethyl
ether (2 to 4 mL) were added by vacuum transfer at -78 °C. The
apparatus was backfilled with Ar and stirred briefly at room
temperature. The Kontes needle valve was replaced by a septum
using a positive Ar counterflow. The solution was then cooled to
-78 °C, and a 1.7 M solution of tert-butyllithium (2.15 mL, 3.60
mmol) was added dropwise using an Ar-flushed syringe. A white
precipitate was observed in the colorless solution before the addition
was completed. The reaction mixture was stirred at -78 °C for 30
min. The dry ice-acetone bath was removed and the reaction
mixture stirred at room temperature for 30 min. The septum was
replaced with a Kontes needle valve, and the solvent was removed.
Drying in vacuo yielded a bright yellow, oily residue. In an inert
atmosphere glovebox, (η5-C5H5)2Zr(CH3)Cl (0.445 g, 1.14 mmol)
was added to the flask containing this solid, and it was attached to
a small swivel frit assembly. On the vacuum line, diethyl ether (13
mL) was vacuum transferred onto the solids at -78 °C, and the
apparatus was backfilled with Ar. The reaction mixture was allowed
to warm to room temperature over 19 h with stirring. At this time
a yellow-brown solution with a white precipitate was observed.
The solvent was removed, and the resulting brown oil was dried at
45 °C in vacuo. Pentane (10 mL) was vacuum transferred onto the
oil at -78 °C. Stirring at room temperature gave a yellow-brown
Acknowledgment. This work has been supported by US-
DOE Office of Basic Energy Sciences (Grant No. DE-FG03-
85ER13431), Exxon Chemicals America, and the National
Science Foundation (Grant No. CHE-0131180). We wish to
thank Professor Thomas Livinghouse for useful suggestions in
the synthesis of the specialty alkyl lithiums, David Kurtz for
preparation of organic precursors, and Paul Elowe for assistance
with X-ray crystallographic figures.
Supporting Information Available: Tables of bond lengths,
angles, and anisotropic displacement parameters for 1, 2, 6, and
22. X-ray crystallographic data (CIF). This material is available
free of charge via the Internet at http://pubs.acs.org.
OM0601302