Catalyst deactivation reactions: The role of tertiary amines revisited

Article abstract of DOI:10.1021/om1007693

Decamethylzirconocene cation [Cp*₂ZrMe]⁺ (2) decomposes in bromobenzene-d₅ solution to generate σ-aryl species [Cp*₂Zr(2-C₆H₄Br-κBr,C)] [B(C₆F₅)₄] (3). This σ-bond metathesis reaction is catalyzed by tertiary amines via a two-step mechanism, in which the amine acts as a proton relay. In benzene-d₆ compound 2 decomposes via C-H bond activation of one of the Cp* ligands to generate tucked-in compound [Cp*{?⁵:?¹-C₅Me ₄(CH₂)}Zr]⁺ (4). In the presence of Et ₃N, no formation of tucked-in compound 4 is observed, but instead an overall double C-H bond activation and C-N bond cleavage of the tertiary amine is observed, resulting in [Cp*₂Zr{C(Me)NEt-κC,N}] ⁺ (6). A mechanism is proposed that nominates [Cp* ₂ZrNEt₂]⁺ as an intermediate, the result of a C-H bond activation of Et₃N, followed by ?-amide elimination. Attempted synthesis of this species by treatment of Cp* ₂Zr(NEt₂)Me with [Ph₃C][B(C₆F ₅)₄] results, again, in formation of compound [6] ⁺. The presence of Et₃N also has an effect on the stability of THF adduct [Cp*₂ZrMe(THF)]⁺ as the amine performs a nucleophilic THF ring-opening to generate [Cp* ₂ZrMe{O(CH₂)₄NEt₃}]⁺ (7). The results show that amine coproducts, often generated in the synthesis of cationic transition-metal complexes, are not necessarily innocent.

Full text of DOI:10.1021/om1007693

92 Organometallics 2011, 30, 92–99
DOI: 10.1021/om1007693
Catalyst Deactivation Reactions: The Role of Tertiary Amines Revisited
Elena Novarino,†,‡ Itzel Guerrero Rios,†,‡ Siebe van der Veer,† Auke Meetsma,†
Bart Hessen,† and Marco W. Bouwkamp*,†
†Molecular Inorganic Chemistry, Stratingh Institute for Chemistry, University of Groningen,
Nijenborgh 4, 9747 AG Groningen, The Netherlands, and ‡Dutch Polymer Institute,
PO Box 902, 5600 AX Eindhoven, The Netherlands
Received August 8, 2010
Decamethylzirconocene cation [Cp*2ZrMe]þ (2) decomposes in bromobenzene-d5 solution to
generate σ-aryl species [Cp*2Zr(2-C6H4Br-κBr,C)][B(C6F5)4] (3). This σ-bond metathesis reaction is
catalyzed by tertiary amines via a two-step mechanism, in which the amine acts as a proton relay. In
benzene-d6 compound 2 decomposes via C-H bond activation of one of the Cp* ligands to generate
tucked-in compound [Cp*{η5:η1-C5Me4(CH2)}Zr]þ (4). In the presence of Et3N, no formation of
tucked-in compound 4 is observed, but instead an overall double C-H bond activation and C-N
bond cleavage of the tertiary amine is observed, resulting in [Cp*2Zr{C(Me)NEt-κC,N}]þ (6). A
mechanism is proposed that nominates [Cp*2ZrNEt2]þ as an intermediate, the result of a C-H bond
activation of Et3N, followed by β-amide elimination. Attempted synthesis of this species by treatment
of Cp*2Zr(NEt2)Me with [Ph3C][B(C6F5)4] results, again, in formation of compound [6]þ. The
presence of Et3N also has an effect on the stability of THF adduct [Cp*2ZrMe(THF)]þ as the amine
performs a nucleophilic THF ring-opening to generate [Cp*2ZrMe{O(CH2)4NEt3}]þ (7). The results
show that amine coproducts, often generated in the synthesis of cationic transition-metal complexes,
are not necessarily innocent.
Introduction
the frequently applied Brønsted acidic reagents of the type
[R3NH][BAr4] (R = alkyl, aryl; Ar = Ph, C6F5), one equiv-
alent of a tertiary amine is generated during the activation
process. In general, these amine coproducts are con-
sidered innocent, although it is known that these substrates
can bind to the metal center, forming a dormant site,5 and a
number of examples are known in which N,N-dimethyl-
aniline can undergo C-H bond activation reactions at the
methyl6 or the 2-position.7
In general, the active species in olefin polymerization
catalysis using early transition-metal complexes is a cationic
metal alkyl.1 There are a number of methods to prepare these
types of species,2 including the treatment of transition-metal
halides with methylaluminoxane3 and the reaction of the
corresponding metal alkyl precursors with Lewis or
Brønsted acidic borane or borate reagents.4 In the case of
One of the most commonly observed deactivation routes
for these Lewis-acidic catalysts for olefin polymerization,
not including hydrolysis or oxidation by incorrect handling
of these typically highly oxophilic metal complexes, involves
*To whom correspondence should be addressed. E-mail:
M.W.Bouwkamp@rug.nl.
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pubs.acs.org/Organometallics
Published on Web 12/14/2010
2010 American Chemical Society

Article
Organometallics, Vol. 30, No. 1, 2011 93
Figure 2. C-H bond activation of the Cp* ligand to generate
[4(THF-dn)][BAr4] (Ar = Ph, n = 0; Ar = C6F5, n = 8).
Counterions of intermediates and [4] and [4(THF-dn)] have been
omitted for clarity.
Figure 1. C-H bond activation of the bromobenzene to generate
[3][B(C6F5)4]. Counterions for compounds [2(PhBr)][B(C6F5)4]
and [3][B(C6F5)4] have been omitted for clarity.
C-H bond activation reactions. Among these are cyclo-
metalation reactions of reactive C-H bonds of ancillary
ligands,5e,7c,8 solvents,9 alkyltris(pentafluorophenyl)borate
anions,10 and R-olefin substrates.11 Here we report that
Brønsted basic coproducts of frequently used activators for
olefin polymerization catalysts can have a significant impact
on these C-H bond activation processes.
co-workers using chlorobenzene as a solvent,9a we observed C-H
activation of the solvent to generate [Cp*2Zr(2-C6H4Br-κBr,C)]-
[B(C6F5)4] ([3][B(C6F5)4], Figure 1). What was unexpected,
though, was the fact that this reaction is catalyzed by tertiary
amines. A computational study revealed a new two-step mecha-
nism, in which the amine acts as a proton relay (Figure 1). After
initial coordination of the halobenzene solvent to the metal
center,13 the bromobenzene ligand is deprotonated by the amine
base to generate the neutral σ-aryl species Cp*2Zr(2-C6H4Br)Me
and ammonium salt [R3NH][B(C6F5)4]. In a subsequent step,
the ammonium reagent thus generated reacts with the Zr-Me
bond to afford the observed ion pair [3][B(C6F5)4]. These results
have been supported by a kinetic study, which reveals that, for
R3N = PhNMe2, the rate of the reaction can be separated into a
noncatalyzed reaction and a catalyzed reaction, following the
rate depicted in eq 1. Furthermore, there is a qualitative correla-
tion between basicity of the amine and the rate of the C-H bond
activation reaction.
Results and Discussion
C-H Activation of Halobenzene Solvents. Recently we
communicated the deactivation of the decamethylzirconocene
cation [Cp*2ZrMe]þ (2) in bromobenzene solution.12 As ex-
pected, on the basis of the results obtained by Jordan and
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X.; Parvez, M. J. Am. Chem. Soc. 2000, 122, 5499.
rate ¼ - ð2:69ð8Þ ꢀ 10 - 6 þ 5:52ð7Þ ꢀ 10 - 5 ½PhNMe2ꢁÞ ½2ꢁ ð1Þ
C-H Activation of the Pentamethylcyclopentadienyl Ligand.
In the absence of halogenated arene solvents, C-H activation
of the pentamethylcyclopentadienyl ligand was observed. Treat-
ment of decamethylzirconocene dimethyl with [PhNMe2H]-
[B(C6F5)4] in benzene-d6 resulted in the overnight formation of
an insoluble red oil, identified as [Cp*{η5:η1-C5Me4(CH2)}Zr]-
[B(C6F5)4] by its reaction with THF-d8, which afforded
the corresponding THF-d8 adduct ([4(THF-d8)][B(C6F5)4],
Figure 2). The formation of these types of tucked-in complexes
of group 4 metals is a known phenomenon,14 although this is, to
(11) (a) Horton, A. D. Organometallics 1996, 15, 2675. (b) Vatamanu,
M.; Stojcevic, G.; Baird, M. C. J. Am. Chem. Soc. 2008, 130, 454.
(12) Guerrero Rios, I.; Novarino, E.; Van der Veer, S.; Hessen, B.;
Bouwkamp, M. W. J. Am. Chem. Soc. 2009, 131, 16658.
(13) (a) Bochmann, M.; Jaggar, A. J.; Nicholls, J. C. Angew. Chem.,
Int. Ed. Engl. 1990, 29, 780. (b) Plenio, H. Chem. Rev. 1997, 97, 3363.
(c) Bouwkamp, M. W.; De Wolf, J.; Del Hierro Morales, I.; Gercama, J.;
Meetsma, A.; Troyanov, S. I.; Hessen, B.; Teuben, J. H. J. Am. Chem. Soc.
2002, 124, 12956. (d) Bouwkamp, M. W.; Budzelaar, P. H. M.; Gercama,
J.; Del Hierro Morales, I.; De Wolf, J.; Meetsma, A.; Troyanov, S. I.; Teuben,
J. H.; Hessen, B. J. Am. Chem. Soc. 2005, 127, 14310. (e) Basuli, F.;
Aneetha, H.; Huffman, J. C.; Mindiola, D. J. J. Am. Chem. Soc. 2005, 127,
17992.
(14) (a) Bercaw, J. E.; Marvich, R. H.; Bell, L. G.; Brintzinger, H. H.
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Organometallics 1987, 6, 232. (e) Pool, J. A.; Bradley, C. A.; Chirik, P. J.
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Lobkovsky, E.; Chirik, P. J. Organometallics 2006, 25, 1092.

94 Organometallics, Vol. 30, No. 1, 2011
Novarino et al.
˚
Table 1. Selected Bond Distances (A) and Angles (deg)
of [4(THF)]
Zr1-Cp*a
2.2055
2.1507
Zr1-Fv*
Zr1-O1
Zr1-C120
2.224(2)
2.366(4)
1.457(5)
1.412(5)
1.446(5)
1.427(5)
1.421(5)
1.448(5)
141.59
C115-C120
C111-C112
C111-C115
C112-C113
C113-C114
C114-C115
Cp*-Zr1-Fv*
Fv*-C115-C120
C120-Zr1-O1
144.3
105.76(10)
a Cp* is defined as the centroid of C11-C15; Fv* is defined as the
centroid of C111-C115.
Figure 3. ORTEP representation of [4(THF)] at the 30% prob-
ability level. Hydrogen atoms and [BPh4] counterion are omitted
for clarity.
C-H Activation of Triethylamine. Preparation of the
decamethylzirconocene cation in benzene-d6 using [Et3NH]-
[B(C6F5)4] as a reagent again shows unexpected reactiv-
ity. Treatment of Cp*2ZrMe2 with [Et3NH][B(C6F5)4] in
benzene-d6 resulted in the formation of a red, oily precipitate,
and gas evolution was observed. Recrystallization of the
material from THF/cyclohexane resulted in yellow crystals,
which were characterized by a single-crystal X-ray diffrac-
tion study as the imino-acyl species [Cp*2Zr{C(Me)NEt-κC,N}-
(THF)][B(C6F5)4] ([6(THF)][B(C6F5)4], Figure 4), resulting
from an overall double C-H bond activation and C-N bond
cleavage.17 Refinement was frustrated by disorder in one of the
Cp* ligands. From the solution, it was clear that the position of
one of the Cp* ligands was highly disordered. A disorder model
with two alternative positions of the Cp* ligand with bond
restraints was used in the final refinement. The sof of the major
fraction of the component of the disorder model refined to a
value of 0.555(7). An ORTEP representation of the major
fraction of the compound is depicted in Figure 6 (see Table 2
for pertinent bond distances and angles). The zirconocene cation
adopts the usual bent-metallocene structure, with a Cp*-Zr-
Cp* bent angle of 137.65°. Both the iminoacyl ligand and
the THF solvent molecule are located in the plane bisect-
ing the metallocene framework. The iminoacyl ligand is
bound to the metal center in the N-inside fashion, which is
common for these types of ligands.18,19 Both the Zr-N
the best of our knowledge, the first time it has been identified as
a catalyst decomposition reaction in olefin polymerization
catalysis. During the reaction gas evolution was observed,
and a Toepler pump experiment revealed that 2 equiv of gas
was generated per zirconium (identified by GC analysis as
methane). The 1H NMR spectrum of a dark purple solution of
the compound in THF-d8 reveals two characteristic doublets at
2.45 and 2.13 ppm (JHH = 6.9 Hz) for the methylene group, as
well as five singlets for the remaining methyl groups: four for
the methyl ligands of the tetramethylfulvene ligand and one
with an intensity corresponding to 15 protons for the Cp*
ligand. The compound can be prepared independently by
treatment of Cp*(η3:η4-C5Me3(CH2)2}Zr15 with [PhNMe2H]-
[BAr4] (Ar = Ph, C6F5) in THF or THF-d8 solution (Figure 2).
In the case of [4(THF)][BPh4], we were able to crystallize
the product from THF/cyclohexane, affording single crystals
that were suitable for X-ray analysis. The structure of cation
[4(THF)] is shown in Figure 3 (see Table 1 for selected bond
distances and angles). The geometry of the compound is
similar to that of other tetramethylfulvene complexes of zirco-
nium with comparable bond distances and angles.14d,16 As
observed for complexes of this type, the Zr-Fv* distance
˚
(2.1507 A) is shorter compared to the Zr-Cp* distance
þ
˚
˚
(2.2055 A); the Zr-CH2 distance in [4(THF)] is 2.366(4) A.
As is typical for these types of complexes, the centroids
of the Cp* and the Fv* ligands, the metal center, and the
THF-oxygen atom are virtually coplanar (sum of the angles
around the metal center is 356.34°).
˚
and Zr-C bond distances (2.259(5) and 2.207(6) A, re-
spectively) are similar to other molecules of this type, and
19
˚
the C-N bond distance of 1.258(8) A is in the range
expected for a C-N double bond. Both the carbon and
the nitrogen atom of the iminoacyl fragment are planar
(sum of the angles is 360.0(9)° and 359.8(8)°).
As expected, Cp*-methyl C-H bond activation was also
observed when the zirconocene methyl cation was generated
using Cp*2ZrMe2 and [Ph3C][B(C6F5)4]. When monitoring both
this reaction and the one where [PhNMe2H][B(C6F5)4] was used
to generate [Cp*2ZrMe]þ, there is no clear indication, unlike the
aforementioned bromobenzene solvent C-H bond activation
reaction, that this reaction is catalyzed by tertiary amines. In both
activation routes a small amount (∼10%) of a side-product was
observed. The nature of this species, which shows a resonance,
1
The H NMR spectrum of cation [6(THF)]þ reveals a
singlet at 1.83 ppm for two Cp* ligands, a quartet (3.76 ppm,
2H) and a triplet (1.18 ppm, 3H) for the ethyl moiety, and
a singlet (2.63 ppm, 3H) for the iminoacyl-methyl group;
13C NMR spectroscopy reveals a resonance at 246.3 ppm,
1
(17) For a review on iminoacyl complexes see: Durfee, L. D.;
Rothwell, I. P. Chem. Rev. 1988, 88, 1059.
(18) Tatsumi, K.; Nakamura, A.; Hofmann, P.; Stauffert, P.; Hofmann,
presumably for a Cp* ligand, at δ 1.40 ppm in the H NMR
spectrum (4:1 benzene-d6/THF-d8 mixture), remains unknown.
R. J. Am. Chem. Soc. 1985, 107, 4440.
(19) (a) Bochmann, M. B.; Wilson, L. M.; Hursthouse, M. B.; Short,
R. L. Organometallics 1987, 6, 2556. (b) Erker, G.; Korek, U.; Petersen, J. L.
J. Organomet. Chem. 1988, 355, 121. (c) Lubben, T. V.; Ploessl, K.; Norton,
J. R.; Miller, M. M.; Anderson, O. P. Organometallics 1992, 11, 122.
(d) Barriola, A. M.; Cano, A. M.; Cuenca, T.; Fernandez, F. J.; Gomez-Sal,
P.; Manzanero, A.; Royo, P. J. Organomet. Chem. 1997, 542, 247. (e) Spies,
P.; Kehr, G.; Kehr, S.; Frohlich, R.; Erker, G. Organometallics 2007, 26,
5612.
(15) Pattiasina, J. W.; Hissink, C. E.; De Boer, J. L.; Meetsma, A.;
Teuben, J. H. J. Am. Chem. Soc. 1985, 107, 7758.
(16) (a) Pellny, P.-M.; Kirchbauer, F. G.; Burlakov, V. V.; Baumann,
W.; Spannenberg, A.; Rosenthal, U. Chem.;Eur. J. 2000, 6, 8. (b) Kraft,
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ꢁ
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Article
Organometallics, Vol. 30, No. 1, 2011 95
Figure 4. Double C-H and C-N bond activation of Et3N to generate [6][B(C6F5)4]. Included is a schematic overview of the proposed
mechanism. Counterions have been omitted for clarity.
indicative of an η2-bound iminoacyl ligand in solution.20,19a,19c
˚
Table 2. Selected Bond Distances (A) and Angles (deg)
of [6(THF)]
The iminoacyl compound is further characterized by a νCN
stretch at 1642 cm-1 in the IR spectrum.20a,b,d
Zr1-Cp*1a
Zr1-Cp*2ab
Zr1-N1
2.277
2.290
Intrigued by this overall double C-H bond activation
reaction and C-N bond cleavage, we were interested in the
mechanism of the formation of cation [6]þ. Generation of
[Cp*2ZrMe][B(C6F5)4] using both Lewis and Brønsted acidic
borate activators and subsequent addition of one equivalent
of triethylamine gave similar results, indicating that the
formation of [6][B(C6F5)4] is the result of the activation
of triethylamine by the decamethylzirconocene methyl cat-
ion. Depending on the activator, two ([Ph3C][B(C6F5)4]) or
three ([Et3NH][B(C6F5)4]) equivalents of gas per zirconium
were generated.21 GC analysis of the gas reveals a mixture
of methane, ethane, and propane, and perhaps molecular
hydrogen (we were not able to identify H2 by GC analysis). A
meticulous Toepler pump experiment revealed that approxi-
mately one ([Ph3C][B(C6F5)4]) or two ([Et3NH][B(C6F5)4])
2.259(5)
2.337(4)
2.207(6)
1.258(8)
1.456(8)
1.513(9)
134.85
82.45(15)
32.68(19)
115.11(17)
Zr1-O1
Zr1-C125
N1-C125
N1-C127
C125-C126
Cp*1-Zr1-Cp*2a
N1-Zr1-O1
N1-Zr1-C125
O1-Zr1-C125
a Cp*1 is defined as the centroid of C11-C15. b Cp*2a is defined as
the centroid of C111a-C115a.
equivalents of a mixture of methane and dihydrogen and one
equivalent of a mixture of ethane and propane were formed.22
On the basis of these results, we propose the mechanism as
depicted in Figure 4. Although the mechanism for the formation
of [6][B(C6F5)4] is described, the same mechanism can be applied
to the reactions where other activators are used and where the
triethylamine is added separately. Dimethyl precursor Cp*2ZrMe2
(20) (a) Lappert, M. F.; Luong-Thi, N. T.; Milne, C. R. C.
J. Organomet. Chem. 1979, 174, C35. (b) Campion, B. K.; Falk, J.; Tilley,
T. D. J. Am. Chem. Soc. 1987, 109, 2049. (c) Beshouri, S. M.; Chebi, D. E.;
Fanwick, P. E.; Rothwell, I. P. Organometallics 1990, 9, 2375. (d) Guo, Z.;
Swenson, D. C.; Guram, A. S.; Jordan, R. F. Organometallics 1994, 13, 766.
(e) Temme, B.; Erker, G. J. Organomet. Chem. 1995, 488, 177.
(21) These amounts are relative to the amount of the iminoacyl
species formed.
(22) We were unable to distinguish between propane and propylene
using GC analysis, though based on the stoichiometry of the reaction we
propose that in this reaction propane is generated.

96 Organometallics, Vol. 30, No. 1, 2011
Novarino et al.
is converted to the corresponding methyl cation, [Cp*2ZrMe]þ,
followed by C-H bond activation of the concurrently formed
triethylamine. The four-membered aza-zirconacyclobutane
intermediate thus generated can undergo a β-diethylamide
elimination reaction to generate zirconium-amide cation,
[Cp*2ZrNEt2][B(C6F5)4], and one equivalent of ethylene.23
The amide cation is then converted into the hydride cation
[Cp*2ZrH][B(C6F5)4],24 via a β-hydride elimination,5h,25
which reacts with the N-(ethylidene)ethylamine formed in
the β-hydride elimination to generate the observed iminoacyl
species. The ethylene formed in the β-diethylamide elimina-
tion reaction can either be hydrogenated by the [Cp*2ZrH]þ
to form ethane or alternatively generate propane by insertion
into the Zr-Me bond of the initially formed [Cp*2ZrMe]
cation followed by hydrogenolysis of the Zr-C bond of the
resulting cation [Cp*2ZrPr]þ.
Figure 5. Formation of [6(THF-d8)][B(C6F5)4] from Cp*2Zr-
(NEt2)Me (anion of [6(THF-d8)][B(C6F5)4] omitted for clarity).
To further investigate the viability of this mechanism,
we aimed at the independent synthesis of [Cp*2ZrNEt2]-
[B(C6F5)4] to assess its stability. As a precursor to this
species, we prepared the methyl diethylamide compound
Cp*2Zr(Me)NEt2. The preparation of Cp*2Zr(Me)NEt2
from Cp*2Zr(Me)Cl and LiNMe2 resulted in low isolated
1
yields. When following the reaction by H NMR spectros-
copy, the formation of Cp*2ZrMe2 was observed. A control
experiment in which Cp*2Zr(Me)NEt2 was treated with
Cp*2Zr(Me)Cl in THF-d8 did not show any reactivity,
indicating that its formation does not originate from a
disproportionation reaction of the product with the starting
material. We therefore propose that there is competition
between transmetalation of LiNEt2 with the chloride ligand
and the methyl ligand of Cp*2Zr(Me)Cl.26 This will generate,
in addition to Cp*2Zr(Me)NEt2 and LiCl, Cp*2Zr(Cl)NEt2
and MeLi, the latter of which can react with Cp*2Zr(Me)Cl
to generate Cp*2ZrMe2.
We therefore used a different approach to the synthesis of
Cp*2Zr(Me)NEt2 in which in situ generated [Cp*2ZrMe(THF)]-
[BPh4] was treated with LiNEt2.27 Also in this case, the
isolated yield is rather low, although NMR spectroscopic
studies reveal that on an NMR tube scale this reaction is
virtually quantitative. Subsequent treatment of Cp*2Zr(Me)-
NEt2 with [Ph3C][B(C6F5)4] in benzene-d6 or bromobenzene-d5
did not result in the formation of the corresponding amide
cation, [Cp*2ZrNEt2]þ. Instead this reaction afforded, upon
dissolution in THF-d8, iminoacyl compound [6(THF-d8)]-
[B(C6F5)4] (Figure 5). Unfortunately the reaction is not clean,
precluding the performance of a Toepler pump experiment to
determine the amount of gas that is produced. One of the
secondary products can be identified as Ph3CH. Although small
amounts of this coproduct have been observed in previous
experiments as well (<5%), in this case a significant amount
of Ph3CH is formed (6:Ph3CH ≈ 1:2 in benzene-d6 and 1:3 in
bromobenzene-d5). We have observed this species only when
Figure 6. ORTEP representation of [6(THF)] at the 30% prob-
ability level. Hydrogen atoms and counterion are omitted for
clarity.
[Ph3C][B(C6F5)4] is used in combination with amines or transition-
metal amides. In a control experiment [Ph3C][B(C6F5)4] was
treated with Et3N in C6D5Br. Also in this case the formation of
Ph3CH was observed, showing that these two reagents are not
compatible, even in the absence of transition-metal complexes.
This is an important observation for the field of cationic transition-
metal complexes, as it suggests that trityl reagents may not
always be compatible with amine functionalities in ligands or
with transition-metal amides. Despite these observations, we are
able to conclude that [Cp*2ZrNEt2]þ is a likely intermediate in
the formation of the iminoacyl species in the Et3N-mediated
deactivation of [Cp*2ZrMe]þ.
A similar deactivation of a zirconocene diethylamide
cation has been reported by Erker and co-workers, in which
they prepare the thermally labile zirconocene diethylamide
cation, [Cp2ZrNEt2][MeB(C6F5)3].20e In benzene-d6 the
compound decomposes to generate a similar iminoacyl
species, [Cp2Zr{C(Me)NEt-κC,N}][HB(C6F5)3]. Although
the authors propose a mechanism in which methane is liberated
from the initially formed diethylamido ion pair, [Cp2ZrNEt2]-
[MeB(C6F5)3], to generate Cp2Zr(η2-EtNCHMe), methane,
and B(C6F5)3, we think that a similar mechanism to the one
proposed here is more likely. In that case the diethylamide
cation undergoes a β-H elimination reaction to form a
cationic hydride intermediate and N-(ethylidene)ethylamine.
This compound can undergo isomerization in which the
hydride ligand is exchanged for the methyl group that is
attached to boron, to account for the observed product with
the [HB(C6F5)3] anion, before reacting with the imine to
generate the observed product. Addition of the Lewis acidic
borane reagent, B(C6F5)3, to compound 1 in benzene-d6 in
the presence of Et3N results again in formation of cation [6].
It is interesting to note, though, that a mixture of the imino-
acyl cation with both the [MeB(C6F5)3] and [HB(C6F5)3]
(23) (a) Al-Najjar, I. M.; Green, M. J. Chem. Soc., Dalton Trans.
1979, 1651. (b) Steinborn, T.; Sedlak, U.; Taube, R. Z. Anorg. Allg. Chem.
1982, 492, 103. (c) Steinborn, D. Angew. Chem., Int. Ed. Engl. 1992,
31, 401.
(24) Yang, X. M.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1994,
116, 10015. Yang, X. M.; Stern, C. L.; Marks, T. J. Angew. Chem., Int. Ed.
Engl. 1992, 31, 1375.
(25) Mayer, J. M.; Curtis, C. J.; Bercaw, J. E. J. Am. Chem. Soc. 1983,
105, 2651.
(26) Otten, E.; Meetsma, A.; Hessen, B. J. Am. Chem. Soc. 2007, 129,
10100.
(27) Evans, W. J.; Perotti, J. M.; Ziller, J. W. J. Am. Chem. Soc. 2005,
127, 3894.

Article
Organometallics, Vol. 30, No. 1, 2011 97
Figure 7. Formation of [7][B(C6F5)4] (anions of [2(THF)][B(C6F5)4] and [7)][B(C6F5)4] are omitted for clarity).
Et3N, resulting in ring-opening of the THF ligand to form
anion was observed in a close to 1:1 ratio. We propose that
the formation of the species with the [HB(C6F5)3] anion is
the result of a similar isomerization reaction of [Cp*2ZrH]-
[MeB(C6F5)3] as proposed for the parent zirconocene,
to form [Cp*2ZrMe][HB(C6F5)3], which can react with
N-(ethylidene)ethylamine to generate the observed product.
Ring-Opening of THF. One method to stabilize highly
reactive transition-metal cations is the complexation of a
Lewis base such as THF.28 Treatment of Cp*2ZrMe2 with
either [Ph3C][B(C6F5)4] or [R3NH][B(C6F5)4] (R3NH =
PhNMe2H, Et3NH) in THF indeed results in formation of
the corresponding THF adduct of the decamethylzircono-
cene methyl cation, [Cp*2ZrMe(THF)]þ ([2(THF)], Figure 7).
In the absence of Et3N, these complexes are stable at room
temperature in THF-d8 solution. On the other hand, in the case
that Et3N is present in the reaction mixture, either by treatment
of Cp*2ZrMe2 with [Et3NH][B(C6F5)4] or by addition of Et3N
to a solution of [Cp*2ZrMe(THF)][B(C6F5)4] in THF-d8 solu-
tion, ring-opening of the THF solvent molecule to generate
[Cp*2ZrMe{O(CD2)4NEt3}][B(C6F5)4] ([7-d8][B(C6F5)4]) is
observed. When repeating the reaction in THF, the nondeuter-
ated isotopologue was obtained. The 1H NMR spectrum of the
compound is characterized by four methylene resonances at 4.06,
3.13, 1.54, and 1.44 ppm for the butylene moiety. An analogous
THF ring-opening by nucleophilic attack of the trimethylamine
on a THF adduct of zirconocene methyl cation was reported
previously by Jordan et al.29
[Cp*2ZrMe{O(CH2)4NEt3}]þ. These results show that amine
coproducts, generated upon activation of transition-metal
alkyl complexes with ammonium borate reagents, can have a
significant impact on the stability of the corresponding cationic
complexes.
Experimental Section
General Considerations. All manipulations of air- and moisture-
sensitive compounds were performed under a nitrogen atmo-
sphere using standard Schlenk and vacuum line techniques or
in an MBraun glovebox. Reagents were purchased from com-
mercial providers and used without further purification, unless
stated otherwise. THF and pentane were dried by percolation
under nitrogen atmosphere over columns of alumina, molecular
sieves, and supported copper oxygen scavenger (BASF R3-11);
benzene-dn (n = 0, 6) and THF-d8 were dried over Na/K alloy;
bromobenzene-dn (n = 0, 5) were dried over CaH2. All solvents
were distilled under reduced pressure. PhNMe2 and Et3N were
dried over molecular sieves. Cp*2ZrMe2,30 Cp*{η5:η1:η1-C5Me3-
(CH2)2}Zr,15 [PhNMe2H][BPh4],31 [Et3NH][B(C6F5)4],32
33
and B(C6F5)3 were prepared following literature procedures.
NMR spectra were recorded on Varian Inova 500, Varian Gemini
VXR 400, Varian VXR 300, and Varian Gemini 200 instruments.
1H chemical shifts are referenced to residual protons in deuterated
solvents and are reported relative to tetramethylsilane. GC analyses
were performed on a HP 5890 instrument with a PORAPAK
column (2 m length, 0.25 mm i.d.). GC/MS analyses of the reaction
products were performed on a HP 5973 mass-selective detector
attached to a HP 6890 gas chromatograph equipped with a flame
ionization detector and a HP-5MS capillary column (30 m length,
0.25 mm i.d., 0.25 μm film thickness).
Conclusions
Decamethylzirconocene compound [Cp*2ZrMe]þ decom-
poses via C-H bond activation processes. The stability of
this species is highly dependent on the presence and nature of
tertiary amines in the reaction mixture. In bromobenzene
solution, the corresponding bromobenzene adduct [Cp*2ZrMe-
(BrC6H5)]þ undergoes C-H bond activation of the solvent
to generate σ-aryl species [Cp*2Zr(2-C6H4Br-κBr,C)][B(C6F5)4].
Results show that this σ-bond metathesis reaction is accelerated
in the presence of tertiary amines, and DFT calculations have
revealed a new mechanism for this process, in which the amine
acts as a proton relay. In benzene solution, no solvent C-H
bond activation has been observed. Instead, when [Cp*2ZrMe]þ
is generated using [Ph3C][B(C6F5)4] or [PhNMe2H][B(C6F5)4],
Cp*-methyl activation was observed, resulting in the formation
of tucked-in compound [Cp*{η5:η1-C5Me4(CH2)}Zr(THF)]þ.
In the presence of Et3N, an overall double C-H bond activation
and C-N bond cleavage of the amine is observed, to afford
[Cp*2Zr{C(Me)NEt-κC,N}(THF)]þ. Also in THF solution, the
corresponding THF adduct [Cp*2ZrMe(THF)]þ reacts with
[Cp*{η5:η1-C5Me4(CH2)}Zr(THF)][BPh4]. THF (1 mL) was
added to a mixture of Cp*{η5:η1:η1-C5Me3(CH2)2}Zr (58.8 mg,
0.163 mmol) and [PhNMe2H][BPh4] (72.1 mg, 0.163 mmol).
After 5 min cyclohexane (3 mL) was cautiously layered on top of
the resulting dark purple solution, which, after overnight diffu-
sion of the cyclohexane solvent into the THF solution, resulted
in the formation of purple crystals. Decanting of the super-
natant and washing with pentane (3 mL) afforded 98.3 mg
(0.131 mmol, 80%) of the title compound after evaporation
1
of the residual pentane. H NMR (400 MHz, THF-d8): δ 7.24
(br, 8H, o-Ph), 6.82 (t, 7.3 Hz, 8H, m-Ph), 6.68 (t, 7.3 Hz, 4H,
p-Ph), 2.45 (d, 6.9 Hz, 1H, CH2), 2.13 (d, 6.9 Hz, 1H, CH2), 2.00
(s, 3H, Me), 1.96 (s, 15H, Cp*), 1.94 (s, 3H, Me), 1.40 (s, 3H,
Me), 1.37 (s, 3H, Me) ppm. 13C{1H} NMR (125.5 MHz, THF-d8):
δ 165.4 (BPh4-ipso), 137.3 (BPh4), 131.4 (C5Me4CH2), 129.3
(C5Me4CH2), 127.4 (C5Me4CH2), 126.6 (C5Me4CH2), 125.9
(BPh4), 124.6 (C5Me4CH2), 124.3 (BPh4), 122.1 (Cp*), 74.4
(30) Stehling, U. M.; Stein, K. M.; Kesti, M. R.; Waymouth, R. M.
Macromolecules 1998, 31, 2019.
(31) Eshuis, J. J. W.; Tan, Y. Y.; Meetsma, A.; Teuben, J. H.;
Renkema, J.; Evens, G. G. Organometallics 1992, 11, 362.
(32) Wang, Q; Quyom, Q. W. R.; Gillis, D. J.; Tudoret, M.-J.;
Hunter, D. J. B. K.; Baird, M. C. Organometallics 1996, 15, 693.
(33) Tjaden, A. B.; Swenson, D. C.; Jordan, R. F.; Peterson, J. L.
Organometallics 1995, 14, 371.
(28) (a) Jordan, R. F.; Dasher, W. E.; Echols, S. F. J. Am. Chem. Soc.
1986, 108, 1718. (b) Jordan, R. F.; Bajgur, C. S.; Willet, R.; Scott, B. J. Am.
Chem. Soc. 1986, 108, 7410.
(29) Borkowsky, S. L.; Jordan, R. F.; Hinch, G. D. Organometallics
1991, 10, 1268.

98 Organometallics, Vol. 30, No. 1, 2011
Novarino et al.
(C5Me4CH2), 12.5 (C5Me4CH2), 11.7 (Cp*), 11.4 (C5Me4CH2),
11.1 (C5Me4CH2), 11.0 (C5Me4CH2) ppm. Anal. Calcd for
C48H47BOZr: C 76.66, H 7.64. Found: C 76.61, H 7.72.
Generation of [Cp*{η5:η1-C5Me4(CH2)}Zr(THF-d8)][B(C6F5)4]
Starting from Cp*(η5:η1:η1-C5Me3(CH2)2}Zr and [PhNMe2H]-
[B(C6F5)4]. In an NMR tube, THF-d8 (0.4 mL) was added to a
mixture of Cp*(η5:η1:η1-C5Me3(CH2)2}Zr (14 mg, 0.040 mmol) and
[PhNMe2H][B(C6F5)4] (32 mg, 0.040 mmol). An immediate color
change to purple was observed. 1H NMR spectroscopy revealed the
quantitative formation of the title compound, [Cp*{η5:η1-C5Me4-
(CH2)}Zr(THF-d8)][B(C6F5)4].
second batch of gas (0.021 mmol), which was identified by GC
analysis as ethane. 1H NMR spectroscopy revealed the formation of
the title compound (76% based on integration).
Generation of [Cp*2Zr{C(Me)NEt-K2C,N}(THF-d8)][B(C6F5)4]
Starting from Cp*2ZrMe2, [Ph3C][B(C6F5)4], and Et3N. A Toepler
pump experiment analogous to the one described above for the
generation of [Cp*2Zr{C(Me)NEt-κ2C,N}(THF-d8)][B(C6F5)4]
starting from Cp*2ZrMe2 and [Et3NH][B(C6F5)4] was performed
using Cp*2ZrMe2 (11.8 mg, 0.030 mmol), [Ph3C][B(C6F5)4] (27.7mg,
0.030 mmol), and NEt3 (133 mmHg, 0.0042 mL, 0.030 mmol). This
resulted in the observation of 0.027 mmol of methane and hydrogen
Generation of [Cp*{η5:η1-C5Me4(CH2)}Zr(THF-d8)][B(C6F5)4]
Starting from Cp*2ZrMe2 and [PhNMe2H][B(C6F5)4]. An NMR
tube was charged with Cp*2ZrMe2 (7.9 mg, 0.020 mmol) and
[PhNMe2H][B(C6F5)4] (16.1 mg, 0.0201 mmol) and connected to
a vacuum line. Benzene-d6 (0.5 mL) was condensed into the tube in
vacuo at -196 °C. The tube was warmed to RT, resulting in the
precipitation of a red oil and gas evolution. After 35 h the gas was
collected via a series of freeze-pump-thaw cycles into a calibrated
volume using a Toepler pump. A total amount of 0.037 mmol of gas
was obtained. The 1H NMR spectrum of the residue after addition
of THF-d8 revealed the formation of the title compound (87% based
on integration). The reaction was followed over time by preparing
solutions of Cp*2ZrMe2 (7.9 mg, 0.020 mmol) and [PhNMe2H]-
[B(C6F5)4] (16.1 mg, 0.0201 mmol) in benzene-d6 (0.4 mL). After
different time intervals (0.5, 1, 2, 3, 17, 24, and 48 h) THF-d8
(0.1 mL) was added to dissolve the species present. These experi-
ments show that after 3 h no more [Cp*2ZrMe(THF)][B(C6F5)4] is
present and that the main species observed is the title compound.
Generation of [Cp*{η5:η1-C5Me4(CH2)}Zr][B(C6F5)4] Start-
ing from Cp*2ZrMe2 and [Ph3C][B(C6F5)4]. The reaction of
Cp*2ZrMe2 with [Ph3C][B(C6F5)4] was followed over time by
preparing solutions of Cp*2ZrMe2 (7.9 mg, 0.020 mmol) and
[Ph3C][B(C6F5)4] (18.5 mg, 0.0201 mmol) in benzene-d6
(0.4 mL). After different time intervals (0.5, 1, 2, 3, 17, 24, and
48 h) THF-d8 (0.1 mL) was added to dissolve the species present.
These experiments show that after 3 h no more [Cp*2ZrMe-
(THF)][B(C6F5)4] is present and that the main species observed
is the tucked-in species.
and 0.026 mmol of ethane and propane. H NMR spectroscopy
revealed the formation of the title compound (81% based on
integration).
1
Generation of [Cp*2Zr{C(Me)NEt-K2C,N}(THF-d8)][XB(C6F5)3]
(X = H, Me) Starting from Cp*2ZrMe2, B(C6F5)3, and Et3N. A
Toepler pump experiment analogous to the one described above for
the generation of [Cp*2Zr{C(Me)NEt-κ2C,N}(THF-d8)][B(C6F5)4]
starting from Cp*2ZrMe2 and [Et3NH][B(C6F5)4] was performed
using Cp*2ZrMe2 (11.8 mg, 0.030 mmol), B(C6F5)3 (0.0153 mg,
0.0299 mmol), and NEt3 (133 mmHg, 0.0042 mL, 0.030 mmol).
This resulted in the observation of 0.027 mmol of methane and
0.024 mmol of ethane. 1H NMR spectroscopy revealed the forma-
tion of the title compound (80% based on integration).
Cp*2Zr(Me)Cl. To a toluene solution (20 mL) of Cp*2ZrMe2
(450 mg, 1.14 mmol) was added an equimolar amount of
[PhNMe2H]Cl (179.0 mg, 1.14 mmol). The reaction was stirred
for 1.5 h at room temperature. Removal of LiCl by filtration
followed by evaporation of solvent and volatiles resulted in
a white powder. Recrystallization from toluene at -30 °C
afforded off-white crystals in 75% yield (472.6 mg, 1.14 mmol).
NMR spectroscopy revealed formation of the title compound.34
Synthesis of Cp*2Zr(Me)NEt2 from Cp*2Zr(Me)Cl and LiNEt2.
To a THF solution (25 mL) of Cp*2ZrMeCl (0.2143 g, 0.522 mmol)
was added LiNEt2 (83.6 mg, 1.05 mmol). The reaction mixture was
stirred overnight at room temperature, resulting in a yellow solution.
Solvent and volatiles were removed under reduced pressure. The
residue was extracted with 15 mL of toluene. Recrystallization from
toluene at -30 °C afforded yellow crystals of the title compound in
1
[Cp*2Zr{C(Me)NEt-K2C,N}(THF)][B(C6F5)4]. Benzene (1 mL)
was added to a mixture of Cp*2ZrMe2 (40.0 mg, 0.102 mmol) and
[Et3NH][B(C6F5)4] (73.0 mg, 0.102 mmol). Immediately a red oily
precipitate was formed. After 20 h at room temperature, the volatiles
were removed at reduced pressure. The resulting yellow solid was
recyrstallized by slow diffusion of cyclohexane (3 mL) into a THF
solution (1 mL) of the compound. Yellow crystals thus obtained
were isolated by decanting the supernatant and drying in vacuo. This
afforded 67 mg (0.067 mmol, 67%) of the title compound. 1H NMR
(500 MHz, THF-d8): δ 3.79 (q, 7.3 Hz, 2H, NCH2CH3), 2.63 (s, 3H,
Me), 1.83 (s, 30H, Cp*), 1.20 (t, 7.3 Hz, NCH2CH3) ppm. 13C{1H}
NMR (125 MHz, THF-d8): δ 150.2 (d, 240 Hz, o-CF), 138.4 (d, 240
Hz, p-CF), 136.4 (d, 241 Hz, m-CF), 125.5 (br, Cipso), 120.5 (Cp*),
44.8 (NCH2CH3), 19.8 (CMe), 15.4 (NCH2CH3), 11.8 (Cp*) ppm.
19F NMR (375 MHz, THF-d8): δ -131.2 (br, 8F, o-F), -163.8
(t, 20 Hz, 4F, p-F), -166.9 (t, 20 Hz, 8F, m-F) ppm. Anal. Calcd
for C52H46BF20NOZr: C 52.80, H 3.92, N 1.18. Found: C 52.94, H
3.42, N 1.12.
25% yield (58.3 mg, 0.137 mmol). H NMR (200 MHz, C6D6):
δ2.98 (q, 6.8 Hz, 4H, NCH2CH3),1.86(s,30H,Cp*),0.92(t,6.8Hz,
6H, NCH2CH3), -0.07 (s, 3H, ZrMe) ppm. 13C{1H}(125 MHz,
C6D6): δ 118.06 (Cp*), 44.58 (NCH2), 31.90 (ZrMe), 15.03
(NCH2CH3), 12.29 (Cp*). Anal. Calcd for C25H43NZr: C 66.94,
H 9.66, N 3.12. Found: C 67.23, H 9.60, N 2.89. The compound
has been further characterized by X-ray analysis (see Supporting
Information).
Cp*2Zr(Me)NEt2 from [Cp*2ZrMe(THF)][BPh4] and LiNEt2.
Cp*2ZrMe2 (98.2 mg, 0.25 mmol) and [PhNMe2H][BPh4] (116.2 mg,
0.26 mmol) were dissolved in THF (5 mL). Upon stirring, the
mixture immediately turned bright yellow. After 0.5 h LiNEt2
(21.7 mg, 0.275 mmol) was added, and the mixture was stirred
overnight, during which the solution turned red. All volatiles were
removed in vacuo, after which the tacky yellow solid was suspended
in pentane. The product was extracted from the Li[BPh4] residue,
and the volatiles were removed. Recrystallization from toluene
yielded the title compound (30.5 mg, 0.068 mmol, 27%).
Generation of [Cp*2Zr{C(Me)NEt-K2C,N}(THF-d8)][B(C6F5)4]
Starting from Cp*2Zr(Me)NEt2 and [Ph3C][B(C6F5)4]. In benzene-d6:
An NMR tube was loaded with Cp*2Zr(NEt2)Me (9.9 mg,
0.022 mmol), [Ph3C][B(C6F5)4] (20.0 mg, 0.0217 mmol), and benzene-
d6 (0.4 mL). The yellow solution was stirred overnight, after which a
brown oil had precipitated. All volatiles were removed and THF-d8
was added to dissolve all solids. Two major products could be
identified by 1H NMR spectroscopy: [Cp*2Zr{C(Me)NEt-κ2C,N}-
(THF-d8)][B(C6F5)4] and Ph3CH, 1:2 ratio. In bromobenzene-d5: In
an NMR tube Cp*2Zr(NEt2)Me (2.5 mg, 0.0056 mmol) and
Generation of [Cp*2Zr{C(Me)NEt-K2C,N}(THF-d8)][B(C6F5)4]
Starting from Cp*2ZrMe2 and [Et3NH][B(C6F5)4]. An NMR tube
was charged with Cp*2ZrMe2 (11.8 mg, 0.030 mmol) and [Et3NH]-
[B(C6F5)4] (23.5 mg, 0.030 mmol) and connected to a vacuum line.
Benzene (0.5 mL) was condensed into the tube in vacuo at -196 °C.
The tube was warmed to RT, resulting in the precipitation of a red
oil and gas evolution. After 24 h the gas was collected into a
calibrated volume using a Toepler pump via a series of freeze-
pump-thaw cycles using liquid nitrogen to freeze the sample. A
total amount of 0.051 mmol of gas was obtained. The gas was
identified by GC analysis as methane. The reaction mixture was
subjected to another series of freeze-pump-thaw cycles, using an
EtOH/N2 bath at -85 °C to freeze the sample, which resulted in a
(34) Chirik, P. J.; Dalleska, N. F.; Henling, L. M.; Bercaw, J. E.
Organometallics 2005, 24, 2789.

Article
Organometallics, Vol. 30, No. 1, 2011 99
[Ph3C][B(C6F5)4] (5.0 mg, 0.0054 mmol) were dissolved in bromo-
benzene-d5 (0.4 mL). After 2.5 h the reaction mixture showed, after
addition of THF-d8 to solubilize the reaction mixture, a 1:3 mixture
of [Cp*2Zr{C(Me)NEt-κ2C,N}(THF-d8)][B(C6F5)4] and Ph3CH,
as well as a mixture of unidentified species.
(31 mg, 0.040 mmol) in THF-d8 (0.5 mL). Initially formation
of [Cp*2ZrMe(THF)][B(C6F5)4] was observed. After 14 days at
1
RT, the H NMR spectrum of the reaction mixture showed a
1:10 mixture of [Cp*2ZrMe(THF)][B(C6F5)4] and [Cp*2ZrMe-
{O(CD2)4NEt3}][B(C6F5)4].
[Cp*2ZrMe{O(CH2)4NEt3}][B(C6F5)4]. A 10 mL THF solu-
tion of [Cp*2ZrMe(THF)][B(C6F5)4] (113 mg, 0.100 mmol) was
treated with Et3N (0.014 mL, 0.10 mmol). The reaction mixture
was stirred at room temperature for 15 days. Solvent and
volatiles were removed under reduced pressure, leaving a pale
yellow foam. The solid was washed with pentane and dried
under vacuum. The 1H NMR spectrum shows formation of
a mixture of the title compound and the starting material.
1H NMR (400 MHz, THF-d8): δ 4.06 (t, 6.2 Hz, 2H, OCH2),
3.29 (q, 7.2 Hz, 6H, NCH2), 3.13 (m, 2H, NCH2), 1.86 (s, 30H,
Cp*), 1.54 (m, 2H, CH2), 1.44 (m, 2H, CH2), 1.29 (t, 6.3 Hz, 9H,
NCH2CH3, 9H), -0.49 (s, 3H, ZrMe) ppm. 13C{1H} NMR
(75 MHz, THF-d8): δ 118.1 (Cp*), 71.5 (OCH2), 68.8 (NCH2),
53.6 (NCH2), 31.0 (ZrMe), 26.5 (CH2), 19.6 (CH2), 11.5 (Cp*),
7.6 (NCH2CH3) ppm.
Generation of [Cp*2ZrMe{O(CD2)4NEt3}][B(C6F5)4] from
[Cp*2ZrMe(THF)][B(C6F5)4] and Et3N. A THF-d8 solution of
[Cp*2ZrMe(THF)][B(C6F5)4] (generated in situ by reaction of
Cp*2ZrMe2 with one equivalent of trityl borate) was contacted
with one equivalent of Et3N (40 μmol, 5.5 μL). After 14 days at room
temperature a 1:10 mixture of [Cp*2ZrMe(THF)][B(C6F5)4] and
[Cp*2ZrMe{O(CD2)4NEt3}][B(C6F5)4] was obtained.
Acknowledgment. This work is part of the research
program of the Dutch Polymer Institute, projects #639
and #332. M.W.B. acknowledges The Netherlands Orga-
nization for Scientific Research for a VENI grant.
Supporting Information Available: Crystallographic informa-
tion files of compounds [4(THF)][BPh4], [6(THF)][B(C6F5)4],
and Cp*2Zr(Me)NEt2. This material is available free of charge
via the Internet at http://pubs.acs.org.
Generation of [Cp*2ZrMe{O(CD2)4NEt3}][B(C6F5)4] from
Cp*2ZrMe2 and [Et3NH][B(C6F5)4]. Cp*2ZrMe2 (14 mg, 0.040 mmol)
was treated with one equivalent of [Et3NH][B(C6F5)4]