Observation of non-chelated bis(pentamethylcyclopentadienyl)zirconium-alkyl-alkene complexes is thwarted by competitive arene or amine coordination or by β-hydride elimination

Article abstract of DOI:10.1016/S0022-328X(01)01217-7

The reaction of Cp*₂Zr(CH₃)₂ (1) with [(C₆H₅)₃C][B(C₆F₅ )₄] in CD₂Cl₂ at -78 °C proceeds with the unexpected formation of [Cp*₂Zr(CH₃)η-C₆H₅ C(C₆H₅)₂CH₃][B(C₆ F₅)₄] (2). Evidence for the coordination of one of the phenyl rings to zirconium comes from ¹H- and ¹³C-NMR chemical shifts and from nOe experiments showing spin saturation transfer from the Cp* methyl protons to the protons of the bound phenyl ring. No chemical exchange between the bound and free phenyl rings is observed up to 0 °C, where decomposition to intractable products occurs. Attempts to disfavor coordination of the arene ring by employing a more sterically protective isobutyl substituent in Cp*₂Zr(CH₃)CH₂CH(CH₃) ₂ (7) led to rapid, quantitative β-hydride elimination producing isobutylene and [Cp*₂Zr(H)η-C₆H₅C(C₆H ₅)₂CH₃]B(C₆F₅) ₄ (8) even at temperatures as low as -135 °C. Addition of propylene to cold solutions of the trityl-coordinated complexes resulted in very rapid formation of polypropylene. This polymerization resulted in no observable changes in the NMR spectra of the zirconium complexes in solution, implying a very rapid rate of propagation following a much slower first monomer insertion.

Full text of DOI:10.1016/S0022-328X(01)01217-7

Journal of Organometallic Chemistry 642 (2002) 120–130
www.elsevier.com/locate/jorganchem
Observation of non-chelated
bis(pentamethylcyclopentadienyl)zirconium-alkyl–alkene complexes
is thwarted by competitive arene or amine coordination or by
b-hydride elimination
Charles P. Casey *, Donald W. Carpenetti II *
Department of Chemistry, Uni6ersity of Wisconsin—Madison, Madison, WI 53706, USA
Received 18 June 2001; received in revised form 28 August 2001; accepted 28 August 2001
Abstract
The reaction of Cp*2 Zr(CH3)2 (1) with [(C6H5)3C][B(C6F5)4] in CD2Cl2 at −78 °C proceeds with the unexpected formation of
[Cp2*Zr(CH3)h-C6H5C(C6H5)2CH3][B(C6F5)4] (2). Evidence for the coordination of one of the phenyl rings to zirconium comes
1
from H- and 13C-NMR chemical shifts and from nOe experiments showing spin saturation transfer from the Cp* methyl protons
to the protons of the bound phenyl ring. No chemical exchange between the bound and free phenyl rings is observed up to 0 °C,
where decomposition to intractable products occurs. Attempts to disfavor coordination of the arene ring by employing a more
sterically protective isobutyl substituent in Cp*Zr(CH3)CH2CH(CH3)2 (7) led to rapid, quantitative b-hydride elimination
2
producing isobutylene and [Cp*Zr(H)h-C6H5C(C6H5)2CH3][B(C6F5)4] (8) even at temperatures as low as −135 °C. Addition of
2
propylene to cold solutions of the trityl-coordinated complexes resulted in very rapid formation of polypropylene. This
polymerization resulted in no observable changes in the NMR spectra of the zirconium complexes in solution, implying a very
rapid rate of propagation following a much slower first monomer insertion. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Metallocene; Zirconium cation; b-Hydride elimination; Arene complex
1. Introduction
peratures, we have been able to observe propene
coordination to an yttrium alkyl complex; this was the
first observation of a non-chelated metallocene-alkyl–
alkene complex, a key proposed intermediate in metal-
locene catalyzed alkene polymerization [5,6] (Scheme
1). Also, by taking advantage of increased steric
hindrance after one insertion of propene into
Cp2*YCH2CH2CH(CH3)2, we have been able to arrest
the polymerization and observe the product of a single
insertion. This has allowed us to measure the kinetic
parameters associated with the first monomer addition
to a growing polymer chain [5].
The ability of trityl cation, (C6H5)3C+, to act as a
powerful alkide-abstracting agent makes it a highly
effective co-catalyst for the activation of metallocene
and related metal–alkyl complexes. When combined
with non-coordinating anions such as B(C6F5)4− [1] or
Al(C6F5)4− [2], trityl activated metallocenes can be
highly efficient alkene polymerization catalysts [3]. Am-
monium salts possessing an acidic proton can also be
highly effective co-catalysts when used to protonate the
ZrꢀC bond of an appropriate zirconium alkyl complex
[4].
Erker’s group has also observed the first alkene
insertion into a growing polymer chain (Scheme 2). In
Erker’s system, internal ion-pairing and p-coordination
Efforts in our group have focused on studying yt-
trocene polymerization catalysts. At extremely low tem-
* Corresponding authors. Present address: Delphi Automotive Sys-
tems, P.O. Box 580970, Tulsa, OK 74158-0970 (D.W. Carpenetti II).
E-mail
addresses:
casey@chem.wisc.edu
(C.P.
Casey),
donald.w.carpenetti@delphiauto.com (D.W. Carpenetti, II).
Scheme 1.
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01217-7

C.P. Casey, D.W. Carpenetti, II / Journal of Organometallic Chemistry 642 (2002) 120–130
121
2. Results
2.1. Arene complexation pre6ents obser6ation of
propene complexation
Our first attempt to generate a cationic zirconium
complex capable of binding propene involved methyl
abstraction from Cp2*Zr(CH3)2 (1) with trityl cation.
The reaction of 1 with one equivalent of [(C6H5)3C]-
[B(C6F5)4] in CD2Cl2 at −78 °C led to formation of an
orange solution containing [Cp*2 Zr(CH3)h-C6H5C-
(C6H5)2CH3][B(C6F5)4] (2) (Scheme 3). Evaporation of
CD2Cl2 from a solution of 2 at −78 °C gave a viscous
oil that resisted all attempts at crystallization. Conse-
Scheme 2.
Scheme 3.
1
quently, 2 was identified as an arene complex by H-
and 13C-NMR spectroscopy at −78 °C.
1
The H-NMR of 2 exhibits two sets of resonances in
of a CꢁC to the zirconium center after the first insertion
allowed observation of the dormant post-insertion cata-
lyst state [7].
Examples of zirconium–benzyl complexes that insert
only one equivalent of an alkene due to stabilization of
the mono-insertion product by an interaction between
the metal and the phenyl ring have been reported by
Pellecchia [8] and Horton [9].
Here we report attempts to extend our studies of
non-chelated yttrium-alkyl–alkene complexes to their
more catalytically relevant zirconium analogs. We
sought a system which would allow observation of a
cationic zirconium–propene complex at low tempera-
tures and possibly also allow observation of the first
insertion of propene into the growing alkyl chain.
the phenyl region. The 2:1 ratio of the peak intensities
indicates that one of the phenyl rings experiences a
different chemical environment than its two neighbors
(Fig. 1). The hydrogen resonances for the unique
phenyl ring at l 7.67 (ortho), 7.87 (meta) and 8.25
(para) ppm are all shifted to significantly higher fre-
quency. The para hydrogen is shifted +1.03 ppm, the
meta hydrogens +0.60 ppm and the ortho hydrogens
+0.59 ppm compared to the resonances of the other
two phenyl rings. The high frequency shifts of the
resonances of the unique phenyl ring are reminiscent of
our observations for alkene coordination to a d0 metal
center [10], and are consistent with phenyl coordination
to a cationic zirconium(IV) center. This interaction
Fig. 1. Phenyl region of 1H-NMR spectrum of 2 showing 2:1 ratio of resonances corresponding to free and bound phenyl groups.

122
C.P. Casey, D.W. Carpenetti, II / Journal of Organometallic Chemistry 642 (2002) 120–130
involves no metal–ligand back-bonding, but significant
electron donation from the arene to the metal.
tially unchanged up to 0 °C where decomposition to
intractable products occurred rapidly. Spin saturation
transfer experiments at −20 °C showed no exchange
between the free and bound phenyl rings. Also, addi-
tion of toluene-d8 to a solution of 2 resulted in no
observable displacement of the bound phenyl ring.
Baird made similar observations indicative of tight
arene binding in 3 and similar compounds [11].
Comparison of the 1H-NMR chemical shifts of 2
with those of other arenes coordinated to cationic
zirconium centers provided further support for coordi-
nation of one trityl phenyl ring. Baird reported that the
1H-NMR resonances of the bound toluene in
[Cp(CH3)2Zr(h6-toluene)][CH3B(C6F5)3] (3) were shifted
to higher frequency (l 7.78, 7.38 and 7.04) compared
with uncomplexed toluene (l 7.09, 7.00 and 6.98) [11].
In light of the steric bulk of the pentamethylcy-
clopentadienyl ligands, we questioned whether more
than two arene carbons could interact with zirconium
simultaneously. To distinguish between symmetric
structures with h3 or h5 binding of the phenyl ring and
rapidly fluxional asymmetric h2 or h4 structures, we
attempted to freeze out fluxional behavior at low tem-
perature. Static h2- or h4-coordination would result in
an asymmetric bound arene with different ortho and
meta hydrogens. The mixture of CDCl2F and CDClF2
provides a very low viscosity solvent suitable for use
1
Horton and de With reported that the H-NMR reso-
nances of the bound phenyl ring of {[Si(CH3)2(t-
BuN)2]Zr[h1,h6-C(CH3)ꢁC(CH3)CH2C6H5]}{B(C6F5)4}
(4) appeared at higher frequency (l 8.16, 8.12 and 7.88)
than those of the phenyl ring after displacement from
zirconium by THF (l 7.05 and 7.25) [9,12].
1
down to −150 °C [13]. The region of the H-NMR
spectrum corresponding to the bound phenyl peaks of 2
in CDCl2F–CDClF2 at −135 °C is shown in Fig. 2.
Although the resolution of the spectrum is much lower
than those taken at −78 °C in CD2Cl2, it is apparent
that the bound phenyl ring is still symmetric as evi-
denced by the 1:2:2 ratio of the peak intensities. The
ortho and meta positions on either side of the bound
phenyl ring still experience identical magnetic environ-
ments on the NMR time scale. This indicates that if the
The 13C-NMR spectrum of 2 also supports coordina-
tion of one of the trityl phenyl rings to zirconium. The
para carbon of the bound phenyl at l 143.5 is shifted
16.7 ppm to higher frequency than the para carbon of
the unbound phenyl. The meta carbon of the bound
phenyl at l 142.9 is shifted 13.5 ppm to higher fre-
quency than the meta carbon of the free phenyl. Signifi-
cantly, the more crowded ortho carbon is shifted only
1.9 ppm to higher frequency in the coordinated ring.
Because three of the phenyl carbons exhibit significant
shifts to higher frequency, and two others exhibit minor
shifts, we believe that at least three and possibly five of
these carbons experience interaction with the cationic
zirconium center. This is consistent with either a sym-
metric structure with h3 or h5 binding of the phenyl
ring or with rapidly fluxional asymmetric h2 or h4
binding.
As observed in related compounds [9,12], addition of
THF to a solution of 2 leads to displacement of the
bound arene and formation of a 1:1 THF adduct. The
1H- and 13C-NMR spectra show only one set of arene
resonances with shifts corresponding to those observed
for an independently synthesized sample of
(C6H5)3CCH3. Further support for the coordination of
one phenyl group in 2 came from observation of a
2–3% nOe enhancement of the hydrogen resonances
assigned to the bound arene from through space satura-
tion transfer from the Cp* methyl groups. No nOe
enhancement of arene resonances was observed after
addition of THF which displaces the bound arene.
No evidence for dissociation of the bound phenyl
group from trityl complex 2 was observed up to its
decomposition temperature. The observed resonances
for the free and bound phenyl rings remained essen-
1
high frequency shifts of the five phenyl positions in H-
and 13C-NMR are the result of rapid sampling of
different h2-coordination modes of the bound phenyl
ring, then the rate of that interchange is too fast to be
frozen out.
In light of the ability of THF to displace the bound
phenyl ring from the metal center of 2, we sought to
determine if addition of an alkene monomer such as
propene might also displace the bound arene and allow
the observation of a zirconium–propene complex.
Small amounts of propene (ca. two equivalents) were
condensed into NMR tubes containing 2 in CD2Cl2 or
CDCl2F–CDClF2 at −196 °C, the tubes were then
placed in the pre-cooled probe of the NMR spectrome-
ter and allowed to thaw at −90 and −135 °C, respec-
tively. The samples were briefly ejected, shaken, and
placed back into the cooled spectrometer probe. In
both cases, no resonances corresponding to propene
were observed: instead, alkyl resonances corresponding
to atactic polypropylene (l 0.9–1.5) were seen. In addi-
tion, a small amount of solid (polypropylene?) was
observed. The only zirconium species observed was 2,
which showed no change in peak integrations relative
to an internal standard. This suggests that the initial
propene insertion (initiation) is followed by much faster
subsequent insertions (propagation) which consume all
of the propene but only a vanishingly small amount of
catalyst.

C.P. Casey, D.W. Carpenetti, II / Journal of Organometallic Chemistry 642 (2002) 120–130
123
Fig. 2. Bound phenyl region of the 1H-NMR spectrum of 2 in CDCl2F–CDClF2 at −135 °C.
Scheme 4.
2.2. Amine complexation pre6ents obser6ation of
propene complexation
block coordination of arenes and amines by employing
more sterically demanding isobutylzirconium
a
precatalyst.
Our second attempt at generating a cationic zirco-
nium complex capable of binding propene involved
protonolysis of 1. We had previously synthesized
cationic zirconium-alkyl–alkene chelates by protona-
tion of 3-allyl-zirconacyclobutanes with [HNCH3-
(C6H5)2][B(C6F5)4] and found that the conjugate base
NMePh2 did not displace the chelated alkene from
zirconium (Scheme 4) [10].
Addition of excess isobutylmagnesium chloride to
Cp*ZrCl2 led to the formation of Cp*Zr(Cl)CH2-
2
2
CH(CH3)2 (6) in excellent yield. Apparently, the com-
bined steric bulk of the isobutyl substituent and the
Cp* rings prevents reaction with a second equivalent of
isobutylmagnesium chloride. Subsequent addition of
methyl magnesium bromide led to formation of
Cp*Zr(CH3)[CH2CH(CH3)2] (7) (Scheme 6).
2
The reaction of 1 with [HNCH3(C6H5)2][B(C6F5)4] in
CD2Cl2 at −78 °C led to formation of a brown–or-
The reaction of 7 with the methide abstracting agent
[(C6H5)3C][B(C6F5)4] in CD2Cl2 at −78 °C was carried
out in an attempt to generate the cationic isobutylzirco-
ange solution containing [Cp*Zr(CH3)NCH3(C6H5)2]-
2
1
nium complex Cp*ZrCH2CH(CH3)+2 . While methyl ab-
[B(C6F5)4] (5) and methane (Scheme 5). The H-NMR
2
chemical shift of the NCH3 group at l 4.03 is indicative
of coordination to zirconium; the chemical shift of the
NCH3 group of the free amine is l 3.18 [10].
straction occurred, the desired intermediate apparently
Complex 5 was also formed in CDCl2F–CDClF2
solution. Both the CD2Cl2 and the CDCl2F–CDClF2
solutions of 5 rapidly polymerized propene at low
temperatures. Again, no apparent change in the
1
amount of zirconium complex 5 was observed by H-
Scheme 5.
and 13C-NMR.
2.3. i-Hydride elimination pre6ents obser6ation of
isobutylzirconium complexes
In a third attempt to generate a cationic zirconium
complex capable of binding propene, we sought to
Scheme 6.

124
C.P. Casey, D.W. Carpenetti, II / Journal of Organometallic Chemistry 642 (2002) 120–130
nium-alkyl–propene complex. In all cases, propene was
completely consumed before the first NMR spectrum
could be recorded and only polypropylene and undi-
minished 8 or 9 were observed. As expected, the
isobutylene produced by b-hydride elimination was not
incorporated into the polymer. These results suggests
that the initial addition of zirconium hydride to
propene (initiation) is followed by much faster subse-
quent insertions of propene (propagation) which con-
sume all of the propene but only a vanishingly small
amount of the hydride catalyst.
Scheme 7.
underwent immediate b-hydride elimination and an or-
ange solution containing [Cp*Zr(H)h-C6H5C(C6H5)2-
2
CH3][B(C6F5)4] (8) and isobutylene was formed
(Scheme 7) [14]. Similar zirconium alkyls have been
shown to undergo facile b-hydride or b-methyl elimina-
tion [15,16]. The assignment of the ZrꢀH resonance of
8 was verified by nOe experiments showing excitation
transfer from the Cp* hydrogens to the one proton
singlet at l 5.57 which is therefore assigned to the
hydride. This zirconium hydride chemical shift is simi-
lar to those of cationic zirconium hydrides reported by
Marks [17]. Experiments attempting to detect nOe be-
tween isobutylene and Cp* ligands were all negative,
indicating that isobutylene does not interact with the
metal center.
3. Discussion
For yttrium complexes, we were able to observe d0
metal-alkyl–alkene complexes for both chelates and
non-chelates; but for zirconium, so far, we have been
able to observe only chelated d0 metal-alkyl–alkene
complexes. Why is zirconium so different? A major
difference is the mode of generating 14-electron zirco-
nium cations capable of coordinating an alkene. Methyl
The reaction of 7 with [(C6H5)3C][B(C6F5)4] was at-
tempted in CDCl2F–CDClF2 at −135 °C to deter-
mine if the b-hydride elimination could be avoided at
lower temperatures. However, even at −135 °C, rapid
formation of 8 and isobutylene occurred. We were
therefore unable to determine whether the isobutyl
group prevented arene coordination and were unable to
study the kinetics of the b-hydride elimination.
abstraction from
1
with trityl cation generates
triphenylethane which complexes strongly with zirco-
nium to give arene complex 2. Similarly, protonation of
1 with [HNCH3(C6H5)2][B(C6F5)4] gave the amine com-
plex 5. While the arene and amine functionalities of
NCH3(C6H5)2 do not compete with intramolecular co-
ordination of a chelated alkene to zirconium, they
effectively compete with intermolecular coordination of
propene. We were able to make cationic zirconium-al-
kyl–alkene chelates in the presence of [CH3B(C6F5)3]
anion; this anion did not compete with the tethered
alkene for coordination to zirconium. Marks has re-
In a second attempt to generate the desired cationic
isobutylzirconium intermediate Cp*ZrCH2CH(CH3)+2 ,
2
the reaction of 7 with [HNCH3(C6H5)2][B(C6F5)4] was
investigated. In CD2Cl2 at −78 °C or in CDCl2F–
CDClF2 at −135 °C, the reaction proceeded with
rapid and quantitative formation of [Cp*Zr(H)NCH3-
ported that the tight ion pair [Cp*Zr(CH3)][CH3B-
2
2
(C6H5)2][B(C6F5)4] (9), isobutylene, and methane
(Scheme 8). Apparently protonolysis of the methyl
group occurs, but rapid b-hydride elimination and
amine coordination ensues. The assignment of the hy-
dride was supported by nOe experiments, in this case
from the N-methyl group to the resonance at l 3.28
assigned to the hydride. Once again, experiments at-
tempting to detect nOe between isobutylene and Cp*
ligands were negative, indicating that isobutylene does
not interact with the metal center.
(C6F5)3] was generated from 1 and B(C6H5)3 and that
this ion pair rapidly polymerizes propene [18]. No
evidence for propene complexation was obtained. Ei-
ther propene does not thermodynamically compete with
[CH3B(C6F5)3] anion for complexation to zirconium or
insertion of propene occurs more rapidly than propene
substitution for the anion. In the case of yttrium, we
were able to generate yttrium alkyls in the absence of
arenes, amines, and [CH3B(C6F5)3] anion; without com-
petition from these complexing agents, propene coordi-
nation was observed [5].
The reactions of solutions of the cationic zirconium
hydrides 8 and 9 with propene were monitored at low
temperature in an effort to detect formation of a zirco-
Can we imagine an observable [Cp*Zr(CH3)-
2
(propene)]+ complex with any anion? Not yet! Such a
Scheme 8.

C.P. Casey, D.W. Carpenetti, II / Journal of Organometallic Chemistry 642 (2002) 120–130
125
complex will require a much less tightly bound anion
than [CH3B(C6F5)3]; the B(C6F5)4 anion is a possibility,
but a new way of generating the ion pair will be
externally to CFCl3. Spectrometer temperatures were
measured after 15 min equilibration, using
a
a
methanol standard containing 0.03% HCl [20] or a
thermocouple. CD2Cl2 (Cambridge Isotopes) was dried
over P2O5 and then distilled from CaH2. Tetrahydro-
furan and pentane were dried over sodium and then
distilled. Isobutylmagnesium chloride and methylmag-
nesium bromide were obtained from Aldrich and used
as received. Propene was purchased from Aldrich and
required. Observation of [Cp*Zr(CH3)(propene)]+ will
2
also require that the anion be kinetically displaced by
propene at a rate faster than methyl migration to
coordinated propene.
In the case of arene complex 2 and amine complex 5,
contact with propene led to polypropylene with no
perceptible decrease in the amount of polymerization
catalysts 2 or 5. It is likely that the initial more crowded
b-alkyl substituted alkyl zirconium insertion products
are more reactive towards propene than the starting
methyl zirconium complex. Similar results have been
seen by Marks [18] and by Landis [19]. These observa-
tions suggest that the more crowded alkyl zirconium
complexes might have a more easily displaced anion
and might allow observation of a zirconium-alkyl–
propene complex.
used as received or dried over Na–K alloy. Cp*ZrCl2
2
was purchased from Strem. [(C6H5)3C][B(C6F5)4] was
supplied by Dow Chemical Company. [HNCH3-
(C6H5)2][B(C6F5)4] [10,21], Cp*Zr(CH3)2 [22], and
2
CCl2FD–CClF2D [13] were prepared by known proce-
dures.
4.2. Preparation of
[Cp*Zr(CH3)p-C6H5C(C6H5)2CH3][B(C6F5)4] (2)
2
We attempted to generate the more sterically de-
manding isobutylzirconium precatalyst. [Cp*2 ZrCH2-
CH(CH3)2][B(C6F5)4] either by methyl abstraction from
7 with [(C6H5)3C][B(C6F5)4] or by protonation of 7 with
[HNCH3(C6H5)2][B(C6F5)4]. In both cases, while the
initial cleavage of the methyl zirconium bond was seen,
the presumed isobutyl zirconium intermediate appar-
ently underwent immediate b-hydride elimination to
give cationic zirconium hydride complexes of the amine
or arene.
CD2Cl2 (0.5 ml) was condensed into a resealable
NMR tube containing Cp*2 Zr(CH3)2 (0.020 g, 3.9×
10−5 mol) and [(C6H5)3C][B(C6F5)4] (0.036 g, 3.9×
10−5 mol) at −78 °C. The tube was shaken briefly at
−78 °C to give an orange solution of 2. 1H-NMR
(−78 °C, 500 MHz, CD2Cl2) l 0.24 (s, ZrCH3), 1.98
(s, Cp*CH3), 2.14 (s, (C6H5)3CCH3), 7.08 (d, J=7 Hz,
4H, o-C6H5), 7.22 (t, J=7 Hz, 2H, p-C6H5), 7.27 (t,
J=7Hz, 4H, m-C6H5), 7.67 (d, J=7 Hz, 2H, o-h-
C6H5), 7.87 (t, J=7 Hz, 2H, m-h-C6H5), 8.25 (t, J=7
Hz, 1H, p-h-C6H5). 13C-NMR (gated decoupled,
−78 °C, 126 MHz, CD2Cl2) l 11.6 (q, J=126 Hz,
Cp*CH3), 30.1 (q, J=126 Hz, (C6H5)3CCH3), 52.3 (s,
(C6H5)3CCH3), 56.1 (q, J=118 Hz, ZrCH3), 123.6 (br
s, ipso-BC), 125.7 (br s, C5Me5), 126.0 (dt, J=160, 7
Hz, p-C6H5), 127.9 (dd, J=156, 7 Hz, o-C6H5), 128.6
(dt, J=156, 7 Hz, m-C6H5), 130.5 (dd, J=167, 8 Hz,
o-h-C6H5), 136.1 (d, JCF=242 Hz, C6F5), 138.0 (d,
Can we imagine an observable [Cp*ZrR(propene)]+
2
complex with any crowded alkyl group? Possibly, but
the R group must be resistant to b-hydride elimination.
One possibility would be the neopentyl group
CH2CMe3, but b-alkyl elimination is likely to be a
major problem encountered in related systems [16a,b].
[Cp2*Zr(CH2Ph)(propene)]+ is a possibility since b-alkyl
elimination is impossible, but p-benzyl formation is a
serious concern. [Cp*Zr(CH2SiMe3)(propene)]+ should
JCF=241 Hz, C6F5), 139.6 (d, J=8 Hz, ipso-h-C6H5),
2
be resistant to b-alkyl elimination since it would result
in an unstable CꢁSi product and offers perhaps the best
hope for success.
142.9 (dt, J=165, 6 Hz, m-h-C6H5), 143.5 (dt, J=164,
7 Hz, p-h-C6H5), 147.8 (d, JCF=242 Hz, C6F5), 149.0
(s, ipso-C6H5). 19F-NMR (416.5 MHz, CD2Cl2, line
broadened, −78 °C) l −135.9 (s, 8F, C6F5), −166.2
(s, 4F, C6F5), −170.2 (s, 8F, C6F5).
4. Experimental
A 2:1 mixture of CDCl2F and CDClF2 (0.5 ml) was
condensed into resealable NMR tube containing
4.1. General procedure
Cp*Zr(CH3)2 (0.020 g, 3.9×10−5 mol) and
2
[(C6H5)3C][B(C6F5)4] (0.036 g, 3.9×10−5 mol) at
−196 °C. The tube was inserted directly into the
NMR probe pre-cooled to −135 °C. After allowing
the tube to equilibrate at −135 °C, it was briefly
ejected, shaken, and reinserted into the probe. Upon
shaking, the solution immediately took on the orange
All reactions were carried out in an inert atmosphere
glovebox or using standard high-vacuum line tech-
niques. All NMR experiments were carried out in 1.9
ml medium-walled resealable NMR tubes that were
flamed-dried under vacuum prior to use. 1H-NMR
spectra were obtained using a Varian Unity500 spec-
trometer. 13C- and 19F-NMR spectra were obtained on
a Varian Unity500 spectrometer operating at 126 and
416.5 MHz, respectively. 19F spectra were referenced
1
color of the solute, 2. H-NMR (−135 °C, 500 MHz,
CDCl2F–CDClF2) l 0.27 (s, ZrCH3), 1.96 (s, Cp*CH3),
2.21 (s, (C6H5)3CCH3), 7.14 (br, 4H, o-C6H5), 7.25 (br,
2H, p-C6H5), 7.29 (br, 4H, m-C6H5), 7.81 (br, 2H,

126
C.P. Casey, D.W. Carpenetti, II / Journal of Organometallic Chemistry 642 (2002) 120–130
o-h-C6H5), 7.97 (br, 2H, m-h-C6H5), 8.35 (br, 1H,
p-h-C6H5). 13C-NMR (gated decoupled, −135 °C, 126
MHz, CDCl2F–CDClF2) l 11.9 (q, J=126 Hz,
Cp*CH3), 30.9 (q, J=126 Hz, (C6H5)3CCH3), 50.8 (s,
(C6H5)3CCH3), 57.6 (q, J=118 Hz, ZrCH3), 123 (br s,
ipso-BC), 125.7 (br s, C5Me5), 126.0 (d, J=160 Hz,
p-C6H5), 127.9 (d, J=156 Hz, o-C6H5), 128.6 (d, J=
156 Hz, m-C6H5), 130.5 (d, J=167 Hz, o-h-C6H5),
136.1 (d, JCF=242 Hz, C6F5), 138.0 (d, JCF=241 Hz,
C6F5), 139.6 (s, ipso-h-C6H5), 142.9 (d, J=165 Hz,
m-h-C6H5), 143.5 (d, J=164 Hz, p-h-C6H5), 147.8 (d,
2 at −196 °C. The tube was inserted directly into the
NMR probe pre-cooled to −135 °C. After allowing
the tube to equilibrate at −135 °C, it was briefly
ejected, shaken, and reinserted into the probe. Reso-
nances corresponding to polypropylene were observed.
No resonances for propene were present. Catalyst
peaks and their respective integrations versus an inter-
nal standard of bis(trimethylsilyl)methane were un-
changed within experimental error.
4.5. Preparation of
J
CF=242 Hz, C6F5), 149.0 (s, ipso-C6H5). 19F-NMR
[Cp*Zr(CH3)NCH3(C6H5)2][B(C6F5)4] (5)
2
(416.5 MHz, CDCl2F–CDClF2, line broadened,
−135 °C) l −134.8 (s, 8F, C6F5), −167.2 (s, 4F,
C6F5), −169.1 (s, 8F, C6F5).
CD2Cl2 (0.5 ml) was condensed into a resealable
NMR tube containing Cp*2 Zr(CH3)2 (0.020 g, 3.9×
10−5 mol) and [HNCH3(C6H5)2][B(C6F5)4] (0.040 g,
4.6×10−5 mol) at −78 °C. The tube was shaken
briefly at −78 °C to give a brown–orange solution of
4.3. Reaction of 2 with THF
A small amount of THF was condensed into a
resealable NMR tube containing 2. Upon shaking at
−78 °C, the solution changed from orange to yellow.
1H-NMR (−78 °C, 500 MHz, CD2Cl2) l 0.27 (s,
ZrCH3), 1.77 (br m, free b-THF), 1.82 (br m, 4H,
bound b-THF), 1.89 (s, Cp*CH3), 2.13 (s,
(C6H5)3CCH3), 3.51(br m, 2H, bound a-THF), 3.63 (br
m, free a-THF), 3.77 (br m, 2H, bound a-THF), 7.04
(d, J=7 Hz, o-C6H5), 7.17 (t, J=7 Hz, p-C6H5), 7.23
(t, J=7Hz, m-C6H5). 13C-NMR (gated decoupled,
−78 °C, 126 MHz, CD2Cl2) l 12.1 (q, J=125 Hz,
Cp*CH3), 25.8 (t, J=135 Hz, bound b-THF), 26.4 (t,
J=133 Hz, free b-THF), 27.3 (t, J=135 Hz, bound
b-THF), 30.8 (q, J=129 Hz, (C6H5)3CCH3), 50.7 (q,
J=118 Hz, ZrCH3), 53.0 (s, (C6H5)3CCH3), 68.6 (t,
J=155 Hz, free a-THF), 73.2 (t, J=150 Hz, bound
a-THF), 77.5 (t, J=155 Hz, bound a-THF), 124.0 (br
s, ipso-BC), 124.4 (br s, C5Me5), 126.8 (dt, J=156, 7
Hz, p-C6H5), 128.6 (dd, J=156, 7 Hz, o-C6H5), 129.4
(dt, J=156, 7 Hz, m-C6H5), 136.9 (d, JCF=242 Hz,
5
and methane. 1H-NMR (−78 °C, 500 MHz,
CD2Cl2) l −0.38 (s, 4H, CH4), 0.24 (s. 3H, ZrCH3),
1.98 (s, 30H, Cp*CH3), 4.03 (s, 3H, ZrNCH3), 7.40 (d,
J=7 Hz, 4H, o-C6H5), 7.66 (t, J=7 Hz, 2H, p-C6H5),
7.67 (t, J=7 Hz, 4H, m-C6H5). Additional evidence
supporting the assignments came from 1D nOe spec-
troscopy, where through space spin transfer was ob-
served between the N-methyl group and the Cp*
methyl groups. 13C-NMR (gated decoupled, −78 °C,
126 MHz, CD2Cl2) l −3.0 (pentet, J=126 Hz, CH4),
12.7 (q, J=126 Hz, Cp*CH3), 41.1 (q, J=127 Hz,
NCH3), 56.1 (q, J=118 Hz, ZrCH3), 123.6 (br s,
ipso-BC), 124.5 (br s, C5Me5), 130.0 (dd, J=156, 7 Hz,
o-C6H5), 132.0 (dt, J=156, 7 Hz, m-C6H5), 132.6 (dt,
J=160, 7 Hz, p-C6H5), 136.1 (d, JCF=242 Hz, C6F5),
138.0 (d, JCF=241 Hz, C6F5), 145.9 (s, ipso-C6H5),
147.8 (d, JCF=242 Hz, C6F5). 19F-NMR (416.5 MHz,
CD2Cl2, line broadened, −78 °C) l −135.9 (s, 8F,
C6F5), −166.2 (s, 4F, C6F5), −170.2 (s, 8F, C6F5).
A 2:1 mixture of CDCl2F and CDClF2 (0.5 ml) was
condensed into resealable NMR tube containing
C6F5), 138.8 (d, JCF=241 Hz, C6F5), 148.6 (d, JCF
=
242 Hz, C6F5), 149.7 (s, ipso-C6H5). 19F-NMR (416.5
MHz, CD2Cl2, line broadened, −78 °C) l −136.3 (s,
8F, C6F5), −167.1 (s, 4F, C6F5), −170.5 (s, 8F, C6F5).
Cp*Zr(CH3)2 (0.020 g, 3.9×10−5 mol) and [HNCH3-
2
(C6H5)2][B(C6F5)4] (0.040 g, 4.6×10−5 mol) at
−196 °C. The tube was inserted directly into the
NMR probe pre-cooled to −135 °C. After allowing
the tube to equilibrate at −135 °C, it was briefly
ejected, shaken, and reinserted into the probe. Upon
shaking the solution immediately took on the orange–
4.4. Reaction of 2 with propene
Two equivalents of propene were condensed into an
NMR tube containing a CD2Cl2 solution of 2 at
−78 °C. The sample was shaken briefly and inserted
directly into the probe of the pre-cooled NMR spec-
trometer. Resonances corresponding to polypropylene
were observed. No resonances for propene were
present. Catalyst peaks and their respective integrations
versus an internal standard of tetramethylsilane were
unchanged within experimental error.
1
brown color of the solute 5. H-NMR (−135 °C, 500
MHz, CDCl2F–CDClF2) l −0.4 (br s, 4H, CH4), 0.2
(br s. 3H, ZrCH3), 2.0 (br s, 30H, Cp*CH3), 4.1 (s, 3H,
ZrNCH3), 7.3 (br, 4H, o-C6H5), 7.7 (br m, 6H, p-C6H5
and m-C6H5). 13C-NMR (gated decoupled, −135 °C,
126 MHz, CDCl2F–CDClF2) l −3.2 (pentet, J=123
Hz, CH4), 13.3 (q, J=125 Hz, Cp*CH3), 42.7 (q,
J=129 Hz, NCH3), 56.5 (q, J=121 Hz, ZrCH3), 123.4
(br s, ipso-BC), 124.9 (br s, C5Me5), 130.7 (d, J=156
Hz, o-C6H5), 131.9 (d, J=156 Hz, m-C6H5), 132.6 (d,
Two equivalents of propene were condensed into an
NMR tube containing a CDCl2F–CDClF2 solution of

C.P. Casey, D.W. Carpenetti, II / Journal of Organometallic Chemistry 642 (2002) 120–130
127
J=160 Hz, p-C6H5), 136.4 (d, JCF=242 Hz, C6F5),
138.8 (d, JCF=241 Hz, C6F5), 145.7 (s, ipso-C6H5),
147.3 (d, JCF=242 Hz, C6F5). 19F-NMR (416.5 MHz,
CDCl2F–CDClF2, line broadened, −135 °C) l −
134.9 (s, 8F, C6F5), −167.4 (s, 4F, C6F5), −169.3 (s,
8F, C6F5).
THF (40 ml) in a 100 ml Schlenk flask. CH3MgBr (1.1
ml of a 3.0 M solution in THF, 3.30 mmol) was added
via syringe under N2 flush at −78 °C. The reaction
mixture was warmed slowly to r.t. and stirred
overnight. The THF was evaporated under reduced
pressure and the resulting material was triturated with
pentane and filtered. Evaporation of pentane from the
1
4.6. Reaction of 5 with propene
filtrate afforded 7 (0.79 g, 75%). H-NMR (24 °C, 500
MHz, CD2Cl2) l −0.83 (s, 3H, ZrCH3), −0.33 (d,
J=6.2 Hz, ZrCH2), 0.61 (d, J=6.2 Hz, CH(CH3)2),
1.89 (s, Cp*CH3), 3.98 (apparent sextet, J=6.2 Hz,
ZrCH2CH(CH3)2). 13C-NMR (gated decoupled, 24 °C,
126 MHz, CD2Cl2) l 11.90 (q, J=125 Hz, Cp*CH3),
29.0 (q, J=127 Hz, CH(CH3)2), 30.0 (d, J=132 Hz,
CH(CH3)2), 41.2 (q, J=117 Hz, ZrCH3), 64.5 (t, J=
112 Hz, ZrCH2), 118.1 (s, C5Me5). MS (MALDI–TOF)
Calc. (Found) for C24H39ClZr 454.25 (454.3).
Two equivalents of propene were condensed into an
NMR tube containing a CD2Cl2 solution of 5 at
−78 °C. The sample was shaken briefly and inserted
directly into the probe of the pre-cooled NMR spec-
trometer. Resonances corresponding to polypropylene
were observed. No resonances for propene were
present. Catalyst peaks and their respective integrations
versus an internal standard of tetramethylsilane were
unchanged within experimental error.
Two equivalents of propene were condensed into an
NMR tube containing a CDCl2F–CDClF2 solution of
5 at −196 °C. The tube was inserted directly into the
NMR probe pre-cooled to −135 °C. After allowing
the tube to equilibrate at −135 °C it was briefly
ejected, shaken, and reinserted into the probe. Reso-
nances corresponding to polypropylene were observed.
No resonances for propene were present. Catalyst
peaks and their respective integrations versus an inter-
nal standard of bis(trimethylsilyl)methane were un-
changed within experimental error.
4.9. Reaction of 7 with [(C6H5)3C][B(C6F5)4]
CD2Cl2 (0.5 ml) was condensed into a resealable
NMR tube containing 7 (0.020 g, 4.6×10−5 mol) and
[(C6H5)3C][B(C6F5)4] (0.042 g, 4.6×10−5 mol) at −78
°C. The tube was shaken briefly at −78 °C to give a
yellow–orange solution of [Cp*2 Zr(H)h-C6H5C-
(C6H5)2CH3][B(C6F5)4] (8) and isobutylene. 1H-NMR
(−78 °C, 500 MHz, CD2Cl2) l 1.88 (s, CH2ꢁC(CH3)2),
1.97 (s, Cp*CH3), 2.05 (s, C6H5CCH3), 4.55 (br s,
CH2ꢁC(CH3)2), 5.57 (s, ZrH), 7.08 (d, J=7 Hz, 4H,
o-C6H5), 7.20 (t, J=7 Hz, 2H, p-C6H5), 7.26 (t, J=7
Hz, 4H, m-C6H5), 7.65 (d, J=7 Hz, 2H, o-h-C6H5),
7.85 (t, J=7 Hz, 2H, m-h-C6H5), 8.24 (t, J=7 Hz, 1H,
p-h-C6H5). Additional evidence supporting the assign-
ment of the zirconium hydride resonance came from 1D
nOe spectroscopy, where through space spin transfer
was observed between the zirconium hydride and the
Cp* methyl groups and between the zirconium hydride
and the protons of the bound phenyl ring. 13C-NMR
(gated decoupled, −78 °C, 126 MHz, CD2Cl2) l 12.4
(q, J=126 Hz, Cp*CH3), 30.1 (q, J=126 Hz,
(C6H5)3CCH3), 30.8 (q, J=129 Hz, CH2ꢁC(CH3)2),
52.3 (s, (C6H5)3CCH3), 111.1 (t, J=155 Hz, CH2=
C(CH3)2), 123.6 (br s, ipso-BC), 126.4 (br s, Cp*-ring
C), 126.0 (dt, J=160, 7 Hz, p-C6H5), 127.9 (dd, J=
156, 7 Hz, o-C6H5), 128.6 (dt, J=156, 7 Hz, m-C6H5),
130.5 (dd, J=167, 8 Hz, o-h-C6H5), 136.1 (d, JCF=242
Hz, C6F5), 138.0 (d, JCF=241 Hz, C6F5), 139.6 (d,
J=8 Hz, ipso-h-C6H5), 142.4 (s, CH2ꢁC(CH3)2), 143.7
(dt, J=165, 6 Hz, m-h-C6H5), 144.2 (dt, J=164, 7 Hz,
p-h-C6H5), 147.8 (d, JCF=242 Hz, C6F5), 149.0 (s,
ipso-C6H5). 19F-NMR (416.5 MHz, CD2Cl2, line broad-
ened, −78 °C) l −135.9 (s, 8F, C6F5), −166.2 (s, 4F,
C6F5), −170.2 (s, 8F, C6F5).
4.7. Cp*Zr(Cl)CH2CH(CH3)2 (6)
2
Cp*ZrCl2 (1.00 g, 2.31 mmol) was slurried in 40 ml
2
of THF in a 100 ml Schlenk flask. The solution was
cooled to −78 °C and isobutylmagnesium chloride
(3.0 ml of a 2.0 M solution in THF, 6 mmol, 2.6
equivalents) was added via syringe under N2 flush. The
solution was allowed to warm slowly to room tempera-
ture (r.t.) and was stirred overnight (ca. 16 h). THF was
evaporated under reduced pressure. The resulting solid
material was slurried in pentane and filtered to give 6
(0.85 g, 81%) as a light orange powder. 1H-NMR
(24 °C, 500 MHz, CD2Cl2) l 0.26 (d, J=5.9 Hz,
ZrCH2), 0.80 (d, J=6.3 Hz, CH(CH3)2), 1.80 (apparent
quintet of triplets; smallest lines of expected septet not
resolved; J=6.3, 5.9 Hz, CH2CH(CH3)2), 1.94 (s,
Cp*CH3). 13C-NMR (gated decoupled, 24 °C, 126
MHz, CD2Cl2) l 12.24 (q, J=125 Hz, Cp*CH3), 28.7
(q, J=123 Hz, CH(CH3)2), 30.7 (d, J=126 Hz,
CH(CH3)2), 65.5 (t, J=117 Hz, ZrCH2), 121.2 (s,
C5Me5). MS (MALDI–TOF) Calc. (Found) for
C24H42Zr 433.84 (433.9).
4.8. Preparation of Cp*Zr(CH3)CH2CH(CH3)2 (7)
CDCl2F–CDClF2 (0.5 ml) was condensed into a
resealable NMR tube containing 7 (0.020 g, 4.6×10−5
mol) and [(C6H5)3C][B(C6F5)4] (0.042 g, 4.6×10−5
2
Compound 6 (1.00 g, 2.20 mmol) was dissolved in

128
C.P. Casey, D.W. Carpenetti, II / Journal of Organometallic Chemistry 642 (2002) 120–130
mol) at −196 °C. The tube was inserted directly into
the NMR probe pre-cooled to −135 °C. After allow-
ing the tube to equilibrate at −135 °C it was briefly
ejected, shaken, and reinserted into the probe. Upon
shaking, the solution immediately took on the yellow–
orange color of the solute mixture 8 and isobutylene.
1H-NMR (−135 °C, 500 MHz, CDCl2F–CDClF2) l
1.87 (s, CH2ꢁC(CH3)2), 1.94 (s, Cp*CH3), 2.08 (s,
C6H5CCH3), 4.5 (br s, CH2ꢁC(CH3)2), 5.6 (s, ZrH),
7.18 (br, 4H, o-C6H5), 7.29 (br, 2H, p-C6H5), 7.35 (br,
4H, m-C6H5), 7.75 (br, 2H, o-h-C6H5), 7.94 (br, 2H,
m-h-C6H5), 8.31 (br, 1H, p-h-C6H5). Additional evi-
dence supporting the assignment of the zirconium hy-
dride resonance came from 1D nOe spectroscopy,
where through space spin transfer was observed be-
tween the zirconium hydride and the Cp* methyl
groups and between the zirconium hydride and the
protons of the bound phenyl ring. 13C-NMR (gated
decoupled, −135 °C, 126 MHz, CDCl2F–CDClF2) l
12.2 (q, J=126 Hz, Cp*CH3), 30.4 (q, J=126 Hz,
(C6H5)3CCH3), 31.2 (q, J=129 Hz, CH2ꢁC(CH3)2),
53.3 (s, (C6H5)3CCH3), 111.1 (t, J=155 Hz,
CH2ꢁC(CH3)2), 123.6 (br s, ipso-BC), 126.4 (br s,
C5Me5), 126.5 (d, J=160 Hz, p-C6H5), 128.5 (d, J=
156 Hz, o-C6H5), 128.6 (d, J=156 Hz, m-C6H5), 130.5
(d, J=167 Hz, o-h-C6H5), 136.1 (d, JCF=242 Hz,
C6F5), 138.0 (d, JCF=241 Hz, C6F5), 139.6 (s, ipso-h-
C6H5), 142.4 (s, CH2ꢁC(CH3)2), 144.3 (d, J=165 Hz,
m-h-C6H5), 145.0 (d, J=164 Hz, p-h-C6H5), 147.8 (d,
4.11. Reaction of 7 with [HNCH3(C6H5)2][B(C6F5)4]
CD2Cl2 (0.5 ml) was condensed into a resealable
NMR tube containing 7 (0.020 g, 4.6×10−5 mol) and
[HNCH3(C6H5)2][B(C6F5)4] (0.040 g, 4.6×10−5 mol) at
−78 °C. The tube was shaken briefly at −78 °C to
give a brown–orange solution of [Cp*Zr(H)NCH3-
2
1
(C6H5)2][B(C6F5)4] (9), isobutylene, and methane. H-
NMR (−78 °C, 500 MHz, CD2Cl2) l −0.38 (s, CH4),
1.90 (s, CH2ꢁC(CH3)2), 1.98 (s, Cp*CH3), 3.28 (s, ZrH),
4.03 (s, ZrNCH3), 4.67 (br s, CH2ꢁC(CH3)2), 7.40 (d,
J=7 Hz, o-C6H5), 7.66 (t, J=7 Hz, p-C6H5), 7.67 (t,
J=7 Hz, m-C6H5). Additional evidence supporting the
assignment of the zirconium hydride resonance came
from 1D nOe spectroscopy, where through space spin
transfer was observed between the zirconium hydride
and the Cp* methyl groups and between the zirconium
hydride and the protons on the methyl group of the
bound amine. 13C-NMR (gated decoupled, −78 °C,
126 MHz, CD2Cl2) l −3.0 (pentet, J=126 Hz, CH4),
12.7 (q, J=126 Hz, Cp*CH3), 25.2 (q, J=130 Hz,
CH2ꢁC(CH3)2), 41.1 (q, J=127 Hz, NCH3), 111.2 (t,
J=155 Hz, CH2ꢁC(CH3)2), 123.6 (br s, ipso-BC), 124.5
(br s, C5Me5), 130.0 (dd, J=156, 7 Hz, o-C6H5), 132.0
(dt, J=156, 7 Hz, m-C6H5), 132.6 (dt, J=160, 7 Hz,
p-C6H5), 136.1 (d, JCF=242 Hz, C6F5), 138.0 (d, JCF
=
241 Hz, C6F5), 143.9 (CH2ꢁC(CH3)2), 145.9 (s, ipso-
C6H5), 147.8 (d, JCF=242 Hz, C6F5). 19F-NMR (416.5
MHz, CD2Cl2, line broadened, −78 °C) l −135.9 (s,
8F, C6F5), −166.2 (s, 4F, C6F5), −170.2 (s, 8F, C6F5).
CDCl2F–CDClF2 (0.5 ml) was condensed into a
resealable NMR tube containing 7 (0.020 g, 4.6×10−5
mol) and [(C6H5)3C][B(C6F5)4] (0.042 g, 4.6×10−5
mol) at −196 °C. The tube was inserted directly into
the NMR probe pre-cooled to −135 °C. After allow-
ing the tube to equilibrate at −135 °C it was briefly
ejected, shaken, and reinserted into the probe. Upon
shaking, the solution immediately took on the yellow–
orange color of the solute mixture 9, isobutylene and
methane. 1H-NMR (−135 °C, 500 MHz, CDCl2F–
CDClF2) l −0.40 (s, CH4), 1.92 (s, CH2ꢁC(CH3)2),
1.99 (s, Cp*CH3), 3.34 (s, ZrH), 4.11 (s, ZrNCH3), 4.67
(br s, CH2ꢁC(CH3)2), 7.40 (br, o-C6H5), 7.66 (br, p-
C6H5), 7.67 (br, m-C6H5). Additional evidence support-
ing the assignment of the zirconium hydride resonance
came from 1D nOe spectroscopy, where through space
spin transfer was observed between the zirconium hy-
dride and the Cp* methyl groups and between the
zirconium hydride and the protons on the methyl group
of the bound amine. 13C-NMR (gated decoupled,
−135 °C, 126 MHz, CDCl2F–CDClF2) l −3.2 (pen-
tet, J=126 Hz, CH4), 12.9 (q, J=126 Hz, Cp*CH3),
26.0 (q, J=130 Hz, CH2ꢁC(CH3)2), 41.1 (q, J=127
Hz, NCH3), 111.7 (t, J=155 Hz, CH2ꢁC(CH3)2), 124
(br s, ipso-BC), 124.8 (br s, C5Me5), 130.0 (d, J=156
Hz, o-C6H5), 132.0 (d, J=156 Hz, m-C6H5), 132.6 (d,
J
CF=242 Hz, C6F5), 149.0 (s, ipso-C6H5). 19F-NMR
(416.5 MHz, CDCl2F–CDClF2, line broadened,
−135 °C) l −136.2 (s, 8F, C6F5), −166.8 (s, 4F,
C6F5), −170.5 (s, 8F, C6F5).
4.10. Reaction of 8 with propene
Two equivalents of propene were condensed into an
NMR tube containing a CD2Cl2 solution of 8 at −
78 °C. The sample was shaken briefly and inserted
directly into the probe of the pre-cooled NMR spec-
trometer. Resonances corresponding to polypropylene
were observed. No resonances for propene were
present. Catalyst peaks and their respective integrations
versus an internal standard of tetramethylsilane were
unchanged within experimental error.
Two equivalents of propene were condensed into an
NMR tube containing a CDCl2F–CDClF2 solution of
8 at −196 °C. The tube was inserted directly into the
NMR probe pre-cooled to −135 °C. After allowing
the tube to equilibrate at −135 °C, it was briefly
ejected, shaken, and reinserted into the probe. Reso-
nances corresponding to polypropylene were observed.
No resonances for propene were present. Catalyst
peaks and their respective integrations versus an inter-
nal standard of bis(trimethylsilyl)methane were un-
changed within experimental error.

C.P. Casey, D.W. Carpenetti, II / Journal of Organometallic Chemistry 642 (2002) 120–130
129
(h) A.K. Rappe´, W.M. Skiff, C.J. Casewit, Chem. Rev. 100
(2000) 1435.
[4] (a) G.G. Hlatky, D.J. Upton, H.W. Turner, PCT Int. Appl. WO
91/09882, 1991;
J=160 Hz, p-C6H5), 136.1 (d, JCF=242 Hz, C6F5),
138.0 (d, JCF=241 Hz, C6F5), 143.9 (CH2ꢁC(CH3)2),
145.9 (s, ipso-C6H5), 147.8 (d, JCF=242 Hz, C6F5).
19F-NMR (416.5 MHz, CD2Cl2, line broadened,
−78 °C) l −135.8 (s, 8F, C6F5), −166.1 (s, 4F,
C6F5), −170.1 (s, 8F, C6F5).
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[6] For more information on the proposed mechanisms for metal-
locene-catalyzed alkene polymerization see: (a) P. Cossee, J.
Catal. 3 (1964) 80;
4.12. Reaction of 9 with propene
Two equivalents of propene were condensed into an
NMR tube containing a CD2Cl2 solution of mixture 9,
isobutylene, and methane at −78 °C. The sample was
shaken briefly and inserted directly into the probe of
the pre-cooled NMR spectrometer. Resonances corre-
sponding to polypropylene were observed. No reso-
nances for propene were present. Catalyst peaks and
their respective integrations versus an internal standard
of tetramethylsilane were unchanged within experimen-
tal error.
Two equivalents of propene were condensed into an
NMR tube containing a CDCl2F–CDClF2 solution of
mixture 9, isobutylene, and methane at −196 °C. The
tube was inserted directly into the NMR probe pre-
cooled to −135 °C. After allowing the tube to equili-
brate at −135 °C, it was briefly ejected, shaken, and
reinserted into the probe. Resonances corresponding to
polypropylene were observed. No resonances for
propene were present. Catalyst peaks and their respec-
tive integrations versus an internal standard of
bis(trimethylsilyl)methane were unchanged within ex-
perimental error.
(b) E.J. Arlman, P. Cossee, J. Catal. 3 (1964) 99;
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(1994) C9.
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121 (1999) 9483;
(b) C.P. Casey, D.W. Carpenetti, Organometallics 19 (2000)
3970;
(c) C.P. Casey, D.W. Carpenetti, H. Sakurai, Organometallics 20
(2001) 4262.
[11] D.J. Gillis, R. Quyoum, M.-J. Tudoret, Q. Wang, D. Jeremic,
A.W. Roszak, M.C. Baird, Organometallics 15 (1996) 3600.
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R.M. Gauvin, J.A. Osborn, J. Kress, Organometallics 19 (2000)
2944;
Acknowledgements
(b) L.H. Doerrer, M.L.H. Green, D. Ha˜ußinger, J.
Saßmannshausen, J. Chem. Soc. Dalton Trans. (1999) 2111;
(c) M.G. Thorn, Z.C. Etheridge, P.E. Fanwick, I.P. Rothwell,
Organometallics 17 (1998) 3636;
(d) Y.-X. Chen, T.J. Marks, Organometallics 16 (1997) 3649;
(e) A.D. Horton, J. de With, J. Chem. Soc. Chem. Commun.
1(1996) 1375;
We thank the National Science Foundation for finan-
cial support (CHE-9972183) and the purchase of NMR
spectrometers (CHE-9629688), Dow Chemical Com-
pany for donation of [(C6H5)3C][B(C6F5)4], and Dr
Charles Fry and Dr Jon Tunge for helpful discussions.
(f) A.D. Horton, J. de With, A.J. van der Linden, H. van de Weg,
Organometallics 15 (1996) 2672;
(g) A. van der Linden, C.J. Schaverien, N. Meijboom, C. Ganter,
A.G. Orpen, J. Am. Chem. Soc. 117 (1995) 3008;
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M.B. Hursthouse, Organometallics 14 (1995) 2456;
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(1993) 1160;
(k) C. Pellecchia, A. Immirzi, A. Grassi, A. Zambelli,
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