Reaction of AlR3 with [CPh3][B(C6F 5)4]: Facile degradation of [B(C6F 5)4]- by transient [AlR2] +

Article abstract of DOI:10.1021/om980400j

Trimethylaluminum reacts with [CPh₃][B(C₆F ₅)₄] at elevated temperatures to give a mixture of AlMe_3-x(C₆F₅)_x compounds, depending on the Al/B ratio. AlBuⁱ₃ reacts significantly faster under β-hydride abstraction. The Al-C₆F₅ species rapidly react with Cp₂ZrMe₂ or [Cp₂ZrMe] ⁺ under C₆F₅ transfer to give poorly active Cp₂ZrMe(C₆F₅); this reaction may have implications for the deactivation of Cp₂ZrMe₂/AlR ₃/[CPh₃][B(C₆F₅)₄] olefin polymerization catalysts.

Full text of DOI:10.1021/om980400j

5908
Organometallics 1998, 17, 5908-5912
Rea ction of AlR3 w ith [CP h 3][B(C6F 5)4]: F a cile
Degr a d a tion of [B(C6F 5)4]- by Tr a n sien t “[AlR2]+”
Manfred Bochmann* and Mark J . Sarsfield
School of Chemistry, University of Leeds, Leeds LS2 9J T, U.K.
Received May 19, 1998
Trimethylaluminum reacts with [CPh3][B(C6F5)4] at elevated temperatures to give a
mixture of AlMe3-x(C6F5)x compounds, depending on the Al/B ratio. AlBui3 reacts significantly
faster under â-hydride abstraction. The Al-C6F5 species rapidly react with Cp2ZrMe2 or
[Cp2ZrMe]+ under C6F5 transfer to give poorly active Cp2ZrMe(C6F5); this reaction may have
implications for the deactivation of Cp2ZrMe2/AlR3/[CPh3][B(C6F5)4] olefin polymerization
catalysts.
In tr od u ction
Two reasons attracted our interest in analogous
reactions of AlMe3. First, although the Cp2MR2/[CPh3]-
[B(C6F5)4]/AlR3 catalysts mentioned above2,3 show very
high initial activities, there is typically a significant
reduction of activity with time. Little is known about
the chemistry that underlies such catalyst deactivation
processes,6 and we speculated that a decay of the
pentafluorophenylborate anion, possibly with the par-
ticipation of AlR3, might be important. Second, while
there are numerous cationic aluminum alkyls [AlR2-
(L)2]+ stabilized by N- and O-ligands,7 with the excep-
As is now well established, highly active olefin po-
lymerization catalysts can be generated by reacting
metallocene dialkyls Cp2MR2 (M ) Ti, Zr, Hf) with
cation-generating agents, notably B(C6F5)3, [HNMe2Ph]-
[B(C6F5)4], or [CPh3][B(C6F5)4], to give complexes in
which the highly electrophilic active species [Cp2MR]+
is stabilized by weakly coordinating but chemically
very robust counteranions such as [MeB(C6F5)3]- and
[B(C6F5)4]-.1 Because of the high sensitivity of these
catalyst systems toward trace impurities the addition
of aluminum alkyls is usually beneficial. For example,
we have shown previously that the addition of 1 equiv
of AlMe3 stabilizes the 14-electron cation [Cp2ZrMe]+
by formation of a heterobinuclear complex, [Cp2Zr(µ-
Me)2AlMe2]+,2 and Chien et al. have developed highly
active catalysts based on mixtures of metallocene dichlo-
rides and [CPh3][B(C6F5)4] in the presence of an excess
of AlMe3 or AlEt3.3
8
tion of the metallocenes [AlCp2]+ and [AlCp*2]+
cationic [AlR2]+ species free of donor ligands are not
known, and we were intrigued by the possibility of
stabilizing such species with weakly coordinating anions
such as [B(C6F5)4]-.
Resu lts
A solution of [CPh3][B(C6F5)4] in toluene-d8 was
The success of these catalysts depends on the selective
reaction of B(C6F5)3 or [CPh3][B(C6F5)4] with the transi-
tion metal alkyl complex in preference to reaction with
the main group metal alkyl additive. This may seem at
first glance surprising since it is not obvious why
reactive electrophiles such as B(C6F5)3 or CPh3+ should
fail to react with a strong alkylating reagent such as
AlMe3. Indeed, we have shown earlier4 that the reaction
of B(C6F5)3 with Cp2AlMe to give [AlCp2]+[MeB(C6F5)3]-
is fast and quantitative even at low temperatures, and
J ordan et al.5 recently reported the facile methyl anion
abstraction from (benzamidinato)AlMe2 compounds to
give cationic aluminum methyl complexes.
treated with a 10-fold molar excess of AlMe3 and
(5) Coles, M. P.; J ordan, R. F. J . Am. Chem. Soc. 1997, 119, 8125.
Ihara, E.; Young, V. G.; J ordan, R. F. J . Am. Chem. Soc. 1998, 120,
8277. Radzewich, C. E.; Coles, M. P.; J ordan, R. F. J . Am. Chem. Soc.
1998, 120, 9384.
(6) For examples of reactions likely to be involved in catalyst
deactivation see: Kaminsky, W.; Sinn, H. Liebigs Ann. 1975, 424.
Kaminsky, W.; Vollmer, H. J . Liebigs Ann. 1975, 438. Kaminsky, W.;
Kopf, J .; Sinn, H.; Vollmer, H. J . Angew. Chem. 1976, 88, 688; Angew.
Chem., Int. Ed. Engl. 1976, 15, 629. Takahashi, T.; Kasai, K.; Suzuki,
N.; Nakajima, K.; Negishi, E. Organometallics 1994, 13, 3413. Shapiro,
P. J .; Cotter, W. D.; Schaefer, W. P.; Labinger, J . A.; Bercaw, J . E. J .
Am. Chem. Soc. 1994. 116, 4623. Bochmann, M.; Cuenca, T.; Hardy,
D. T. J . Organomet. Chem. 1994, 484, C10. Lancaster, S. J .; Robinson,
O. B.; Bochmann, M.; Coles, S. J .; Hursthouse, M. B. Organometallics
1995, 14, 2456. J ime´nez Pindado, G.; Thornton-Pett, M.; Bowkamp,
M.; Meetsma, A.; Hessen, B.; Bochmann, M. Angew. Chem., Int. Ed.
Engl. 1997, 36, 2358. J ime´nez Pindado, G.; Thornton-Pett, M.; Boch-
mann, M. J . Chem. Soc., Dalton Trans. 1997, 3115.
(7) Tobias, R. S. Organomet. Chem. Rev. 1966, 1, 93. Bott, S. B.;
Alvanipour, A.; Morley, S. D.; Atwood, D. A.; Means, C. M.; Coleman,
A. W.; Atwood, J . L. Angew. Chem., Int. Ed. Engl. 1987, 26, 485.
Engelhardt, L. M.; Kynast, U.; Raston, C. L.; White, A. H. Angew.
Chem., Int. Ed. Engl. 1987, 26, 681. Self, M. F.; Pennington, W. T.;
Laske, J . A.; Robinson, G. H. Organometallics 1991, 10, 36. Uhl, W.;
Wagner, J .; Fenske, D.; Baum, G. Z. Anorg. Allg. Chem. 1992, 612,
25. Atwood, D. A.; J ones, R. A.; Cowley, A. H.; Bott, S. G.; Atwood, J .
L. J . Organomet. Chem. 1992, 425, C1. Atwood, D. A.; J egier, J . Chem.
Commun. 1996, 1507.
(1) Reviews: Bochmann, M. J . Chem. Soc., Dalton Trans. 1996, 255.
Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth,
R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. Guram, A. S.;
J ordan, R. F. In Comprehensive Organometallic Chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Elsevier: Oxford, 1995;
Chapter 12.
(2) Bochmann, M.; Lancaster, S. J . Angew. Chem., Int. Ed. Engl.
1994, 33, 1634. Bochmann, M.; Lancaster, S. J . J . Organomet. Chem.
1995, 497, 55.
(3) Chien, J . C. W.; Xu, B. Makromol. Chem., Rapid Commun. 1993,
14, 109. Chien, J . C. W.; Tsai, W. M. Makromol. Chem., Macromol.
Symp. 1993, 66, 141. Chien, J . C. W.; Song, W.; Rausch, M. D. J . Polym.
Sci., Part A: Polym. Chem. 1994, 32, 2387.
(4) Dawson, D. M.; Bochmann, M. Angew. Chem. 1996, 108, 2371;
Angew. Chem., Int. Ed. Engl. 1996, 35, 2226.
(8) Dohmeier, C.; Schno¨ckel, H.; Robl, C.; Schneider, U.; Ahlrichs,
R. Angew. Chem., Int. Ed. Engl. 1993, 32, 1655.
10.1021/om980400j CCC: $15.00 © 1998 American Chemical Society
Publication on Web 12/03/1998

Reaction of AlR3 with [CPh3][B(C6F5)4]
Organometallics, Vol. 17, No. 26, 1998 5909
1
Sch em e 1
warmed to 60 °C. The reaction was monitored by H,
11B, and 19F NMR spectroscopy over 4.5 h. A slow
reaction takes place; formation of MeCPh3 is observed,
along with BMe3 [1H NMR (toluene-d8, 60 °C) δ 0.74;
11B NMR δ 86.8], and a new set of signals appears in
the 19F NMR spectrum, at δ -121.5 (o-F), -152.2
(p-F), and -160.8 (m-F), in addition to unreacted [CPh3]-
[B(C6F5)4]. In the presence of excess AlMe3 the reaction
is first-order in [CPh3+], with kobs ) 5 × 10-5 s-1 (at 60
°C). In the absence of AlMe3 toluene solutions of [CPh3]-
[B(C6F5)4] are stable under these conditions.
split into seven observable peaks (although additional
smaller methyl signals appear obscured by more intense
peaks), while three sets of C6F5 signals are observed in
the 19F NMR spectrum. None of the signals are attri-
butable to Al2Me6.11 Warming to -20 °C results in
broadening of all the signals in the 1H and 19F NMR
spectra, and at 20 °C the single methyl chemical shift
value observed is the averaged chemical shift of the
methyl groups of a number of isomers that are in rapid
equilibrium with each other (Scheme 1). Similarly, 1:2
mixtures of AlMe3 and Al(C6F5)3‚0.5toluene give pre-
dominantly [AlMe(C6F5)2]2. The pertinent NMR data of
the C6F5 species reported here are collected in Table 1.
Mixing Al(C6F5)3‚0.5toluene with AlMe3 in a ratio of
1:10 at room temperature in toluene on a preparative
scale, followed by removal of the solvent in vacuo with
mild heating, leads to the recovery of Al(C6F5)3‚
0.5toluene. Isolation of the initial product, AlMe2(C6F5),
was not possible due to the evidently very facile ligand
exchange and quantitative removal of excess AlMe3 even
under these mild conditions. In related recent work,
Roesky et al. reported the synthesis of AlMe2(C6F5) by
the reaction of AlMe2Cl with LiC6F5 as an uncharac-
terized intermediate which was converted to Al(C6F5)3
by heating to 180 °C in vacuo.12 Considering the facile
ligand exchange in this system (Scheme 1) we find that
such high temperatures are not required to shift the
equilibrium toward Al(C6F5)3.
This observation demonstrates that methyl abstrac-
+
tion from AlMe3 by CPh3 is very much less favorable
than with transition metal methyl complexes but occurs
slowly at elevated temperatures to give a transient
species “[AlMe2]+[B(C6F5)4]-”, which immediately de-
composes to B(C6F5)3 and AlMe2(C6F5). Evidently cat-
ions such as [AlMe2]+ (or possibly higher homologues,
e.g., [Al2Me5]+ or [Al3Me8]+, which might be envisaged
in the presence of excess AlMe3) are too electrophilic to
be stabilized even by [B(C6F5)4]- and immediately react
with abstraction of C6F5-. The difference in reactivity
between [AlMe2]+ and the thermally stable complexes
[AlCp2]+ and [(benzamidinate)AlMe]+ is most probably
due to the absence of any form of π-donor stabilization
in the dialkyl species.
Further ligand exchange between AlMe3-x(C6F5)x and
B(C6F5)3 can eventually lead to the formation of Al-
(C6F5)3 and BMe3, which in an open system escapes into
the gas phase, thereby shifting the equilibrium:
[CPh3][B(C6F5)4] + AlMe3 f Ph3CMe +
“[AlMe2]+[B(C6F5)4]-”
“[AlMe2]+[B(C6F5)4]-” f AlMe2(C6F5) + B(C6F5)3
AlMe2(C6F5) + B(C6F5)3 f AlMe(C6F5)2 +
The 19F NMR chemical shifts of all three aluminum
C6F5 species AlMe3-x(C6F5)x (x ) 1-3) are remarkably
similar, with changes in the δ value of para-F being
BMe(C6F5)2
AlMe(C6F5)2 + BMe(C6F5)2 f Al(C6F5)3 +
1
most indicative, though identification is possibly by H
BMe2(C6F5)
NMR. More pronounced changes are seen when the
exchange process is suppressed by adduct formation
with diethyl ether. The addition of excess Et2O to NMR
samples of AlMe2(C6F5) in toluene-d8 at 20 °C results
in the formation of AlMe2(C6F5)‚Et2O as the major
product, together with small amounts of AlMe(C6F5)2‚
Et2O and AlMe3‚Et2O. Likewise, addition of Et2O to
AlMe(C6F5)2 gives AlMe(C6F5)2‚Et2O as the major prod-
uct, with small amounts of AlMe2(C6F5)‚Et2O and
AlMe3‚Et2O also being detectable. The adducts were
characterized by 1H, 19F, and 13C{1H} NMR spectroscopy
(Table 1). Surprisingly, although Roesky et al.12 isolated
a crystalline THF adduct of Al(C6F5)3, the compound
appears not to form a complex with Et2O in toluene
solution, possibly for steric reasons.
BMe2(C6F5) + AlMe3 f AlMe2(C6F5) + BMe3
The reaction of B(C6F5)3 with AlMe3 in toluene to
afford Al(C6F5)3‚0.5toluene and BMe3 via a similar
sequence of ligand redistribution processes has recently
been described in a patent application by Biagini et al.
as a convenient synthetic method for Al(C6F5)3.9,10
Under the conditions of the NMR experiment in the
presence of an excess of AlMe3 the major product of the
reaction between [CPh3][B(C6F5)4] and AlMe3 is [AlMe2-
(C6F5)]2. The identity of this species was confirmed by
its independent preparation from a 2:1 mixture of AlMe3
and Al(C6F5)3‚0.5toluene. Treating 2 equiv of AlMe3 with
Al(C6F5)3‚0.5toluene at 20 °C in toluene-d8 in an NMR
tube causes an immediate shift of the methyl resonance
To test the suitability of the reaction of AlMe3 with
[CPh3][B(C6F5)4] as a synthetic route for Al(C6F5)3, a
10:1 mixture of the two reactants was heated at 65 °C
over 14 h. Triphenylethane was produced, and the color
of the solution changed from orange to pale yellow.
1
in the H NMR spectrum from δ -0.37 to -0.08 ppm.
Upon cooling the sample to -60 °C the methyl signal is
(9) Biagini, P.; Lugli, G.; Abis, L.; Andreussi, P. Eur. Patent Appl.
EP 0 694 548 A1, 1996 (Enichem Elastomeri S.r.l.).
(10) Ligand redistribution processes in the borate [BBun(C6F5)4-n
have been observed: Dioumaev, V. K.; Harrod, J . F. Organometallics
1997, 16, 2798.
-
]
(11) Williams, K. C.; Brown, T. L. J . Am. Chem. Soc. 1966, 88, 5460.
(12) Belgardt, T.; Storre, J .; Roesky, H. W.; Noltemeyer, M.; Schmidt,
H. G. Inorg. Chem. 1995, 34, 3821.

5910 Organometallics, Vol. 17, No. 26, 1998
Ta ble 1. 1H a n d 19F NMR Da ta of C6F 5 Com p ou n d s
Bochmann and Sarsfield
19F NMR (J FF, Hz)
compound
AlMe2(C6F5)a
AlMe(C6F5)2
Al(C6F5)3‚0.5toluene
1H NMR
o-F
p-F
m-Fb
-0.08 (Me)
0.04 (Me)
-122.5 (16.9)
-122.4 (16.9)
-122.7 (20.9)a
-121.9 (21)c
-122.5 (28.2)
-151.9 (br)
-151.4
-161.0
-161.0
-161.1a
-160.4c
-161.8
a
-151.3 (21.2)a
-149.6 (21)c
-155.1 (19.8)
a
AlMe2(C6F5)‚OEt2
-0.36 (Me)
0.69, 3.31 (Et2O)
-0.18 (Me)
0.88, 3.32 (Et2O)
-0.26 (µ-Me)
0.51 (Zr-Me)
6.44 (Cp)
a
AlMe(C6F5)2‚OEt2
-123.1 (28.2)
-124.0 (16.9)
-152.8 (19.8)
-155.2 (19.8)
-161.0
-162.6
c
Cp2ZrMe(µ-Me)Al(C6F5)3
Cp2ZrMe(C6F5) a
0.31 (Me)
-115.2 (25.4)
-156.7 (19.8)
-162.2
5.66 (Cp)
a
b
Toluene-d8, 20 °C. Multiplets or broadened signals. c CD2Cl2, -60 °C.
Sch em e 2
Sch em e 3
Removal of the solvent and drying for 4 h in vacuo
produced a light brown oily solid. The 19F NMR spec-
trum shows a major product in approximately 50% yield
with chemical shifts identical to an authentic sample
of Al(C6F5)3‚0.5toluene. However, the remaining 50% of
the signals were due to other C6F5 species which could
not be identified, and the reaction is evidently less clean
than the reaction of AlMe3 with B(C6F5)3.
In contrast to the rather slow reaction between AlMe3
and [CPh3][B(C6F5)4] which is initiated by alkyl abstrac-
different from Al(C6F5)3‚0.5toluene in CD2Cl2 at -60 °C
(cf. Table 1). Attempts to isolate this product resulted
only in the formation of a number of Cp complexes, one
of which is identified as Cp2ZrMe(C6F5). We conclude
that Al(C6F5)3 interacts with Cp2ZrMe2 in a way similar
to B(C6F5)314 to give initially zwitterionic methyl-bridged
complexes, but that redistribution of C6F5 ligands from
aluminum to zirconium proceeds much more readily
than in the case of B(C6F5)3 (Scheme 2), as observed for
example by Marks et al., who noted the slow decomposi-
tion of Cp′′2ZrMe(µ-Me)B(C6F5)3 to Cp′′2ZrMe(C6F5) by
Me/C6F5 exchange with a half-life of 10 h at room
temperature [Cp′′ ) C5H3(SiMe3)2].15
tion, the reaction of AlBui with [CPh3][B(C6F5)4] in-
3
volves hydride abstraction13 and isobutene elimination
(Scheme 2). This reaction proceeds very much faster:
at 20 °C a toluene solution of [CPh3][B(C6F5)4] discolors
immediately on addition of AlBui , and the 19F NMR
3
shows that all [B(C6F5)4]- has been consumed, with
formation of BBui , BBui (C6F5), and BBui(C6F5)2 (but
3
2
not, under these conditions, B(C6F5)3).
Im p lica tion s for th e Dea ctiva tion P r ocess of
Meta llocen e Ca ta lysts. The foregoing results show
that the reaction of aluminum alkyls with [CPh3]-
[B(C6F5)4] or B(C6F5)3 can lead to aluminum pentafluo-
rophenyl compounds, with borate degradation in the
presence of aluminum alkyls bearing â-hydrogens being
particularly facile. As pointed out in the Introduction,
catalyst deactivation processes are as yet little under-
stood, and the possible contribution of Al-C6F5 species
to catalyst deactivation was therefore of interest.
Treatment of Cp2ZrMe2 with an equimolar amount
of Al(C6F5)3‚0.5toluene in CD2Cl2 at -60 °C leads
immediately to the quantitative formation of Cp2ZrMe-
(µ-Me)Al(C6F5)3, according to 1H, 13C, and 19F NMR
At 20 °C a benzene-d6 solution of Cp2ZrMe2 reacts
immediately with Al(C6F5)3 in a 1:1 molar ratio with
formation of two major Cp compounds, one of which was
identified as Cp2ZrMe(C6F5), while the other could not
16
be assigned. The formation of Cp2Zr(C6F5)2 could not
be detected, even in the presence of an excess of
Al(C6F5)3. By contrast, the reaction of [Cp2Zr(µ-H)-
(C6F5)]2 with [CPh3][BBun(C6F5)4-n] has been reported
to proceed rapidly to give Cp2Zr(C6F5)2 and other
decomposition products.10 On a preparative scale Al-
(C6F5)3‚0.5toluene reacts with Cp2ZrMe2 in a 1:3 ratio
to give Cp2ZrMe(C6F5) in 54% yield. The same product
results from a 1:1 mixture of Cp2ZrMe2 and AlMe2(C6F5)
in toluene-d8 at 20 °C; the reaction is quantitative.
1
spectroscopy (Scheme 3). The H NMR spectrum shows
Cp, Zr-Me, and Zr-Me-Al resonances at δ 6.44, 0.51,
and -0.26 ppm, respectively. In the 13C{1H} spectrum
the Cp and Zr-Me signals are present at δ 113.9 and
40.5 ppm, the µ-Me signal is broad and centered at δ
7.9 ppm. Only one set of C6F5 signals in the 19F
spectrum are observed (Table 1) which are entirely
(14) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1991,
113, 3623. Deck, P. A.; Marks, T. J . J . Am. Chem. Soc. 1995, 117, 6128.
Siedle, A. R.; Newmark, R. A. J . Organomet. Chem. 1995, 497, 119.
(15) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1994,
116, 10015. Gomez, R.; Green, M. L. H.; Haggit, J . L. J . Chem. Soc.,
Dalton Trans. 1996, 939.
+
(13) For examples of â-H abstraction of main group alkyls by CPh3
see: J erkunica, J . M.; Traylor, T. G. J . Am. Chem. Soc. 1971, 93, 6278.
Hannon, J . S.: Traylor, T. G. J . Org. Chem. 1981, 46, 3645.
(16) Chaudhari, M. A.; Stone, F. G. A. J . Chem. Soc. A 1966, 838.

Reaction of AlR3 with [CPh3][B(C6F5)4]
Organometallics, Vol. 17, No. 26, 1998 5911
Syn th esis of Al(C6F 5)3‚0.5tolu en e. This compound was
prepared by modification of a literature procedure.9 CAU-
TION: Al(C6F5)3 has been reported to detonate on attempted
sublimation at elevated temperatures.21 A solution of B(C6F5)3
(3.55 g, 6.94 mmol) in toluene (20 mL) was added to a solution
of AlMe3 (0.50 g, 6.94 mmol) in toluene (40 mL) at room
temperature. A precipitate formed after 0.5 h, and the reaction
was left to stir for 16 h. The solid was isolated and dried under
vacuum for 3 h to give Al(C6F5)3‚0.5toluene as a white
microcrystalline solid (1.8 g). The filtrate was concentrated and
placed in the freezer overnight and provides another 1.5 g,
combined yield 3.3 g (5.74 mmol, 83%).
The above discussion shows that under certain cir-
cumstances, and particularly if AlBui /[CPh3][B(C6F5)4]
3
mixtures are used in catalyst preparation, the transfer
of C6F5 to zirconium may be facile. The deactivating
effect of C6F5 was assessed by reacting Cp2ZrMe(C6F5)
with [CPh3][B(C6F5)4] and B(C6F5)3, to give [{Cp2Zr-
(C6F5)}2(µ-Me)][B(C6F5)4] and Cp2Zr(C6F5)(µ-Me)B(C6F5)3,
respectively.17 Although at comparatively high zirco-
nium concentrations (1 mM) some ethylene polymeri-
zation was observed, the activities are very poor com-
pared to Cp2ZrMe2/activator mixtures. On the other
hand, if conditions that can give rise to “[AlR2]+” (such
as premixing CPh3+ with AlR3) are avoided, the system
Cp2ZrMe2/AlR3/[CPh3][B(C6F5)4] is thermally stable. For
example, heating equimolar mixtures of Cp2ZrMe2 and
[CPh3][B(C6F5)4] in toluene-d8 for 1 h at 60 °C, followed
by heating for a further 2 h in the presence of AlMe3
(Al/Zr ) 4), led to a darkening of the samples, but no
degradation of the [B(C6F5)4]- anion was observed by
19F NMR.
Rea ction of AlMe3 w ith [CP h 3][B(C6F 5)4]. For monitoring
the reaction by NMR, a solution of [CPh3][B(C6F5)4] (0.014 g,
15 µmol) in toluene-d8 (0.4 mL) was treated with a solution of
AlMe3 (0.6 mL, 0.11 M, 66 µmol) in toluene-d8 and immediately
placed in the spectrometer heated to 60 °C. The reaction was
monitored via 1H and 19F NMR over a period of 4.5 h. Signals
for AlMe2(C6F5) grew in and became the major species after
4.5 h. No other products were seen. The reaction is first-order
in triphenylmethyl salt, kobs ) 5 × 10-5 s-1
.
In a separate experiment, a toluene solution (5 mL) of [CPh3]-
[B(C6F5)4] (0.202 g, 0.22 mmol) was treated with a toluene
solution of AlMe3 (3 mL, 1.5 M, 4.50 mmol). The reagents were
heated at 65 °C for 14 h before the solvent was removed, and
the light brown oily residue was dried under vacuum for 4 h.
A sample of the crude product contained Al(C6F5)3 as the major
product in 50% yield by 19F NMR spectroscopy. NMR 19F
(toluene-d8) δ -122.7 (d, J ) 20.9 Hz, 6F, o-F), -151.3 (t, J )
21.2 Hz, 3F, p-F), -161.1 (m, 6F, m-F).
Con clu sion
Aluminum alkyl cocatalysts in MAO-free metallocene
systems are capable of reacting with the catalyst activa-
tors B(C6F5)3 and [CPh3][B(C6F5)4] at elevated temper-
atures with formation of AlMe3-x(C6F5)x compounds. The
degradation of [B(C6F5)4]- is initiated by a highly
electrophilic transient “[AlR2]+” species. The value of x
depends on the ratio of C6F5:Me ligands in the system.
Rea ction of AlBu i3 w ith [CP h 3][B(C6F 5)4]. An NMR tube
containing [CPh3][B(C6F5)4] (0.012 mmol) was reacted with a
solution of AlBui (0.070 mmol) in toluene-d8 at 20 °C. The
Aluminum alkyls carrying â-hydrogens such as AlBui
3
3
solution turned from orange to colorless immediately, and the
19F NMR spectrum contained no signals due to [B(C6F5)4]-.
Apart from the reaction products isobutene and triphenyl-
react with CPh3+ under hydride abstraction and alkene
elimination; this reaction leads to the rapid consumption
of [B(C6F5)4]- even at ambient temperatures. Al(C6F5)3
reacts with Cp2ZrMe2 to give the adduct Cp2ZrMe(µ-
Me)Al(C6F5)3 which is stable only at low temperatures
and on warming reacts under C6F5 transfer from
aluminum to zirconium. At room temperature and above
Cp2ZrMe2 reacts rapidly with AlMe3-x(C6F5)x to give
Cp2ZrMe(C6F5). The ethene polymerization activity of
Cp2ZrMe(C6F5)/B(C6F5)3, mixtures is about 3 orders of
magnitude lower that that of Cp2ZrMe2/B(C6F5)3, an
illustration of the deactivating consequence of C6F5
transfer reactions.
methane, signals were observed for AlBui (C6F5) [1H NMR δ
2
1.99 (m, 1H, CH), 0.97 (d, 6H, J ) 6.5 Hz, CH3), 0.28 (d, 2H,
J ) 7.2 Hz, CH2); 19F NMR δ -120.7 (m, 2F), -152.5 (t, 1F, J
) 19.8 Hz), -161.6 (m, 2F)], BBui(C6F5)2 [-130.9 (m, 2F),
-147.4 (t, 2F, J ) 21.2 Hz), -161.1 (m, 2F)], and BBui (C6F5)
2
[-134.3 (m, 2F), -153.3 (t, 1F, J ) 19.7 Hz), -161.8 (m, 2F)]
but not B(C6F5)3. The 11B and 1H NMR spectra show the
presence of BBui [1H NMR δ 1.56 (m, 1H, CH), 1.16 (d, 2H, J
3
) 7.0 Hz, CH2), 0.88 (d, 6H, J ) 6.5 Hz, CH3); 11B NMR δ
88.1].22
Rea ction of 2 Al(C6F 5)3‚0.5tolu en e w ith AlMe3. A solu-
tion of Al(C6F5)3‚0.5toluene (43 mg, 76 µmol) in toluene-d8 (0.5
mL) was treated with a solution of AlMe3 (0.1 mL, 0.38 M, 38
µmol) in toluene-d8 at 20 °C to form [AlMe(C6F5)2]2. The sample
was cooled to -60 °C, and three major and three minor methyl
signals could be seen in the 1H NMR spectrum at δ (rel int)
0.34 (1.2), 0.26 (8.9), 0.09 (7.2), -0.26 (10.0), -0.34 (4.5), -0.51
(3.8), and -0.57 (3.1). Three sets of peaks for C6F5 groups are
seen in the 19F NMR spectrum, at δ (rel int) -122.4 (40.0),
-122.7 (12.6), -123.1 (3.2) (o-F), -150.1 (1.6), -151.2 (20.0),
-152.4 (6.3) (p-F), and -160.1 (3.2), -160.4 (40.0), -160.9
(12.6) (m-F). At 20 °C [AlMe(C6F5)2]2 is characterized by the
following NMR parameters: 1H NMR (toluene-d8, 20 °C) δ 0.04
(s, br, Me); 13C{1H} NMR (toluene-d8, 20 °C) δ 150.0 (dm, J CF
) 236 Hz, o-CF), 142.3 (dm, J CF ) 254 Hz, p-CF), 137.2 (dm,
J CF ) 254 Hz, m-CF), -6.9 (Me); 19F NMR (toluene-d8, 20 °C)
δ -122.4 (d, J ) 16.9 Hz, 6F, o-F), -151.4 (s, br, 3F, p-F),
-161.0 (s, br, 6F, m-F).
Exp er im en ta l Section
All manipulations were carried out with the use of Schlenk,
vacuum-line, and glovebox techniques. Light petroleum (bp
40-60 °C), toluene, and diethyl ether were distilled under
nitrogen from sodium-potassium alloy. Deuterated solvents
were dried over Linde 4 Å molecular sieves and deoxygenated
via several freeze-thaw cycles. AlMe3 (97%, Aldrich) was used
as purchased. The compounds Cp2ZrMe2,18 B(C6F5)3,19 and
[CPh3][B(C6F5)4]20 were prepared by literature methods. The
1H, 13C, 11B, and 19F NMR spectra were recorded on a Bruker
DPX300 instrument. 1H and 13C NMR spectra were referenced
to residual solvent peaks relative to TMS; 11B and 19F spectra
were referenced externally to BF3‚Et2O and CFCl3, respec-
tively.
(17) A mixture of 50 µmol Cp2ZrMe(C6F5) and 50 µmol B(C6F5)3 in
F or m a tion of AlMe(C6F 5)2‚Et2O. An excess of diethyl
toluene (50 mL) at 50 °C under 1 bar ethene gave 0.2 g of PE after 1
ether was added to the above solution at 20 °C. 1H NMR
h, corresponding to a productivity of 4 kg PE (mol Zr)-1‚bar-1‚h-1
.
Although recrystallized Cp2ZrMe(C6F5) was used, the possibility of the
presence of traces of Cp2ZrMe2 cannot be entirely discounted.
(18) Samuel, E.; Rausch, M. D. J . Am. Chem. Soc. 1973, 95, 6263.
(19) Massey, A. G.; Park, A. J . J . Organomet. Chem. 1964, 2, 250.
(20) Bochmann, M.; Lancaster, S. J . J . Organomet. Chem. 1992, 434,
C1. Chien, J . C. W.; Rausch, M. D. J . Am. Chem. Soc. 1991, 113, 8570.
(21) Pohlmann, J . L. W.; Brinckmann, F. E. Z. Naturforsch. B 1965,
20b, 5. Chambers, R. D. Organomet. Chem. Rev. 1966, 1, 279.
(22) Davies, A. G.; Hare, D. G.; White, R. F. M. J . Chem. Soc. 1960,
1040. Mikhailov, B. M.; Kuimova, M. E. Bull. Acad. Sci. USSR, Div.
Chem. Sci. 1979, 288.

5912 Organometallics, Vol. 17, No. 26, 1998
Bochmann and Sarsfield
(toluene-d8, 20 °C): δ 3.32 (q, J ) 7.0 Hz, 4H, OCH2CH3), 0.88
Gen er ation of [{Cp2Zr (C6F5)}2(µ-Me)][B(C6F5)4]. A sample
of Cp2ZrMeC6F5 (16 mg, 0.045 mmol) in CD2Cl2 (0.3 mL) was
treated with [CPh3][B(C6F5)4] (0.024 mmol) in CD2Cl2 (0.3 mL)
at -78 °C and placed in the spectrometer at -50 °C. There
was a slow reaction to give [{Cp2Zr(C6F5)}2(µ-Me)][B(C6F5)4].
5
(t, J ) 7.0 Hz, 6H, OCH2CH3), -0.18 (t, J HF ) 1.2 Hz, 3H,
Me-Al). 13C{1H} (toluene-d8, 20 °C): δ 67.1 (OCH2CH3), 14.5
(OCH2CH3), -6.91 (s, br, Me-Al). 19F (toluene-d8, 20 °C): δ
-123.1 (d, J ) 28.2 Hz, 6 F, o-F), -152.8 (t, J ) 19.8 Hz, 3 F,
p-F), -161.0 (m, 6 F, m-F). Small amounts of AlMe2(C6F5)‚
Et2O (see below) and AlMe3‚Et2O are also present. AlMe3‚
Et2O: 1H (toluene-d8, 20 °C) δ -0.51 (s, 9H, Me-Al); 13C{1H}
(toluene-d8, 20 °C) δ -7.7 (s, br, Me-Al). The diethyl ether
signals quoted are a time-averaged value of all AlMe3-x(C6F5)x‚
Et2O species and free diethyl ether in equilibrium.
1
Complete conversion took 160 min at -30 °C. H NMR (CD2-
Cl2): δ 6.56 (s, 20H, Cp), -0.029 (bs, 3H, µ-Me). 13C{1H}
NMR: δ 115.0 (Cp), µ-Me not observed. 11B NMR: δ -14.5.
19F NMR (-80 °C): δ 113.1 (d, 2F, J ) 25.0 Hz, o-F of Zr-
C6F5), -119.3 (d, 2F, J ) 25.0 Hz, o-F of Zr-C6F5), -132.1
(m, 8F, o-F of B-C6F5), -152.2 (t, 2F, J ) 19.8 Hz, p-F of Zr-
C6F5), -158.3 (m, 2F, m-F of Zr-C6F5), -159.3 (m, 2F, m-F of
Zr-C6F5), -160.9 (m, 4F, p-F of B-C6F5), -164.9 (m, 8F, m-F
of B-C6F5).
Rea ction of Al(C6F 5)3‚0.5tolu en e w ith 2AlMe3. A solu-
tion of Al(C6F5)3‚0.5toluene (43 mg, 76 µmol) in toluene-d8 (0.2
mL) was treated with a solution of AlMe3 (0.4 mL, 0.38 M,
152 µmol) in toluene-d8 and placed in the spectrometer at 20
°C. The sample was cooled to -60 °C, and at least seven
separate methyl signals could be seen, which coalesce to one
singlet at 20 °C. [AlMe(C6F5)2]2: 1H NMR (toluene-d8, 20 °C)
δ -0.08 (s, br, 3H, Me); 13C{1H} NMR (toluene-d8, 20 °C) δ
150.1 (dm, J CF ) 249 Hz, o-C), 142.3 (dm, J CF ) 249 Hz, p-CF),
137.2 (dm, J CF ) 249 Hz, m-CF), -7.3 (Me); 19F NMR (toluene-
d8, 20 °C) δ -122.5 (d, J ) 16.9 Hz, 6F, o-F), -151.9 (s, br,
3F, p-F), -161.0 (s, br, 6F, m-F).
Rea ction of Al(C6F 5)3‚0.5tolu en e w ith Cp 2Zr Me2 a t 20
°C. A C6D6 solution of Cp2ZrMe2 (24 mg, 95 µmol) was treated
with Al(C6F5)3‚0.5toluene (18.5 mg, 32 µmol) in an NMR tube
at room temperature. An immediate reaction occurs providing
a quantitative conversion to Cp2ZrMe(C6F5).
In a preparative scale reaction two separate Schlenk tubes
were charged with Cp2ZrMe2 (0.641 g, 2.55 mmol) in one and
Al(C6F5)3‚0.5toluene (0.467 g, 0.85 mmol) in the other. Both
were dissolved in toluene (ca. 10 mL). The Al(C6F5)3 solution
was added to Cp2ZrMe2 at 20 °C. The reaction mixture was
stirred for 10 min before filtering and cooling to -78 °C over
48 h. A pale yellow precipitate was isolated, washed twice with
light petroleum, and dried in vacuo, to yield Cp2ZrMe(C6F5)
(0.55 g, 1.36 mmol, 54%). 1H NMR (C6D6, 20 °C): δ 5.66 (s,
10H, Cp), 0.31 (t, 5J HF ) 4.1 Hz, 3H, Me). 13C{1H} NMR (C6D6,
F or m a tion of AlMe2(C6F 5)‚Et2O. An excess of diethyl
1
ether was added to the above solution. H NMR (toluene-d8,
20 °C): δ 3.31 (q, J ) 7.0 Hz, 4 H, OCH2CH3), 0.69 (t, J ) 7.2
5
Hz, 6H, OCH2CH3), -0.36 (t, J HF ) 1.1 Hz, 6H, Me-Al). 13C-
{1H} (toluene-d8, 20 °C): δ 67.4 (OCH2CH3), 13.4 (OCH2CH3),
-8.1 (s, br, Me-Al). 19F (toluene-d8, 20 °C): δ -122.5 (d, J )
28.2 Hz, 6F, o-F), -155.1 (t, J ) 19.8 Hz, 3F, p-F), -161.8 (m,
6F, m-F). Small amounts of AlMe(C6F5)2‚Et2O and AlMe3‚Et2O
are also present.
20 °C): δ 13C{1H} NMR (CD2Cl2, -60 °C): δ 145.4 (dm, J CF
)
226 Hz, o-CF), 139.5 (dm, J CF ) 251 Hz, p-CF), 136.8 (dm, J CF
4
) 255 Hz, m-CF), 111.4 (Cp), 45.4 (t, J CF ) 6.0 Hz, Me). 19F
Gen er a tion of Cp 2Zr Me(µ-Me)Al(C6F 5)3. A solution of
Cp2ZrMe2 (12 mg, 48 µmol) in CD2Cl2 (0.6 mL) was treated
with Al(C6F5)3‚0.5toluene (29.4 mg, 51 µmol) in an NMR tube
at -78 °C and then placed in the spectrometer cooled to -60
°C. An immediate reaction occurs providing a quantitative
conversion to Cp2ZrMe(µ-Me)Al(C6F5)3. 1H NMR (CD2Cl2, -60
°C): δ 6.44 (s, 10H, Cp), 0.51 (s, 3H, Zr-Me), -0.26 (s, 3H,
NMR (C6D6, 20 °C): δ -115.2 (d, J ) 25.4 Hz, 6H, o-F), -156.7
(t, J ) 19.8 Hz, 3F, p-F), -162.2 (m, 6F, m-F). MS (EI): m/e
(%) 402 (2) (M+), 387 (80) [M+ - Me], 239 (85) [M+ - C6F5],
220 (100) [Cp2Zr].
Rea ction of AlMe2(C6F 5) w ith Cp 2Zr Me2. A sample of
AlMe2(C6F5) (228 µmol), prepared from Al(C6F5)3‚0.5toluene (43
mg, 76 µmol) and AlMe3 (0.4 mL, 0.38 M, 152 µmol) in toluene-
d8 as discussed above, was added to Cp2ZrMe2 (57 mg, 228
mmol) at 20 °C. An immediate reaction takes place with
quantitative conversion to Cp2ZrMe(C6F5) and AlMe3, identi-
fied by comparison with authentic samples.
Me-Al). 13C{1H} NMR (CD2Cl2, -60 °C): δ 149.8 (dm, J CF
)
234 Hz, o-CF), 141.0 (dm, J CF ) 249 Hz, p-CF), 136.7 (dm, J CF
) 226 Hz, m-CF), 113.9 (Cp), 40.5 (Zr-Me), 7.9 (br, Me-Al).
19F NMR (CD2Cl2, -60 °C): δ -124.0 (d, J ) 16.9 Hz, 6H,
o-F), -155.2 (t, J ) 19.8 Hz, 3F, p-F), -162.6 (m, 6F, m-F).
Gen er a tion of Cp 2Zr (C6F 5)(µ-Me)B(C6F 5)3. A sample of
Cp2ZrMeC6F5 (19 mg, 0.053 mmol) in CD2Cl2 (0.3 mL) was
treated with B(C6F5)3 (28.5 mg, 0.056 mmol) in CD2Cl2 (0.3
mL) at -78 °C and placed in the spectrometer at -50 °C.
Immediate formation of Cp2Zr(C6F5)(µ-Me)B(C6F5)3 was ob-
served. The Zr-C6F5 moiety shows hindered rotation at low
Th er m a l Sta bility of [Cp 2Zr Me][B(C6F 5)4]. In a control
experiment, 13 mg (14 µmol) of [CPh3][B(C6F5)4] and Cp2ZrMe2
(14 µmol) were mixed in an NMR tube at room temperature
in 0.5 mL of toluene-d8. The 19F NMR spectrum of the mixture
was monitored at 60 °C for 1 h; there was no indication of anion
degradation. Next, AlMe3 (66 µmol) was added and heating
was continued for another 2 h. No change in the signals for
[B(C6F5)4]- was observed.
1
temperature. H NMR (CD2Cl2): δ 0.56 (bs, 3H, B-Me), 6.60
(s, 10H, Cp). 13C{1H} NMR: δ 116.1 (Cp), 33.8 (B-Me). 11B
NMR: δ -11.1. 19F NMR (-80 °C): δ 112.6 (d, 1F, J ) 28.0
Hz, o-F of Zr-C6F5), -114.1 (d, 1F, J ) 28.0 Hz, o-F of Zr-
C6F5), -132.7 (d, 6F, J ) 22.5 Hz, o-F of B-C6F5), -152.3 (t,
1F, J ) 19.8 Hz, p-F of Zr-C6F5), -158.2 (t, 3F, J ) 21.2 Hz,
p-F of B-C6F5), -159.4 (m, 1F, m-F of Zr-C6F5), -160.0 (m,
1F, m-F of Zr-C6F5), -163.3 (m, 6F, m-F of B-C6F5).
Ack n ow led gm en t. This work was supported by BP
Chemicals Ltd., Sunbury. We thank Drs. P. Bre`s and
B. Dorer for helpful discussions.
OM980400J