Organoborane-Modified Silica Supports
Organometallics, Vol. 21, No. 8, 2002 1725
collected using φ frames. From a total of 22 592 absorption-
corrected reflections measured [2θ(max) ) 54.2°], 17 266 were
unique (Rint ) 0.025) with 14 106 considered observed [I > 2σ-
(I)]. The structure was solved by direct methods and refined
by full-matrix, least-squares methods based on F2 (SHELXTL-
IRIX). Two cyclopentane rings were found to be conformation-
ally disordered, which could be modeled by including atoms
C4A/C4B and C13A/C13B in the refinement with 50:50 and
80:20 site occupancies, respectively. Final R(F) and wR(F2)
were 0.0418 and 0.0975 with maximum residuals of 0.51 and
-0.50 e Å3. Selected crystallographic and refinement data
appear in Table 1, and selected bond lengths and angles in
Table 2. Full details of the structure are included in the
Supporting Information.
the 1H NMR spectrum of the second solution were recorded.
On the basis of integration of signals due to compound 3 and
Cp2ZrMe2 with respect to the tetrafluoro-p-xylene standard,
the volume of each required to give a 1:1 stoichiometry was
calculated.
To 350 µL of a solution of compound 3 in an NMR tube was
added ∼64 µL of the solution of Cp2ZrMe2 at -80 °C. The tube
was quickly shaken to mix the contents and then transferred
to a probe maintained at -80 °C. 19F and 1H NMR spectra
were recorded while the temperature was increased in ca. 10°
increments. Representative 19F NMR spectra are shown in
Figure 2.
19F a n d 1H NMR R ea ct ion b et w een Cp 2Zr Me2 a n d
MeB(C6F 5)2. A similar procedure was employed as that
described above using about 0.1 mmol of each compound, and
the ion-pair 4 was generated at ca. -40 °C before being
transferred into the NMR probe maintained at -30 °C.
Syn th esis of Com p ou n d 5. Compound 3 (342 mg, 0.179
mmol) was dissolved in 3 mL of toluene, and the solution cooled
to -15 °C. Then, Cp2ZrMe2 (90.0 mg, 0.356 mmol) was
dissolved in 1 mL of toluene, and this solution was also cooled
to -15 °C. The latter solution (500 µL, 1.0 equiv) was slowly
added to the solution of compound 3 via syringe. The yellow
solution was stirred for 20 min at -15 °C, the cooling bath
was removed, and on warming to room temperature the
solution was stirred for an additional 20 min. The solution
decolorized upon warming. An additional 100 µL (0.2 equiv)
of the Cp2ZrMe2 solution was added at room temperature, and
stirring was continued for 30 min.
1
Variable-temperature 19F and H NMR spectroscopic data are
provided in the Supporting Information. Ion-pair 4: 1H NMR
(200 MHz, 55:45 v/v of toluene-d8/bromobenzene-d5, -30 °C)
δ 5.78 (s, 10 H, Cp) 0.35 (s, 3H, ZrMe) superimposed on 0.30
(v br s, 6H BMe2); at higher T (e.g., 0 °C) the signals due to
both Zr-Me and B-Me groups are coincident and exchange-
broadened; 19F NMR (188 MHz, 55:45 v/v of toluene-d8/
bromobenzene-d5, -30 °C) δ -134.2 (dd, o-F), -160.95 (t, p-F)
-164.55 (m, m-F). On warming the solution to room temper-
ature, decomposition of 4 occurred to provide Me2B(C6F5) and
Cp2ZrMe(C6F5). For spectroscopic data see ref 4 and Support-
ing Information.
The volume was reduced by half under vacuum, and the
solution was transferred into a glovebox. The solution was
chromatographed on purified Bio Beads SX-2 (10.525 g of dry
beads swollen in dry toluene, column bed volume ∼40 mL)
eluting with toluene. Five fractions were collected in the
following amounts: 10, 5, 10, 10, and 50 mL, and 19F NMR
spectra were recorded of each fraction. The third fraction
contained the desired compound, while the fourth contained
a mixture of this compound and MeB(C6F5)2. The latter fraction
was concentrated and then rechromatographed to provide
additional material. Fractions containing only compound 5
were combined and concentrated in vacuo to provide an oil. A
white solid was obtained after freeze-drying a benzene solution
of this oil (140 mg, 54% yield). Compound 5: 1H NMR (200
MHz, toluene-d8) δ 1.19 (br m, 7H), 1.67 (br, m 28 H) 1.91 (br
m, 28 H), 6.02 (s, 10 H); the latter signal appears as two closely
spaced singlets (5 H each) in mixed toluene-d8/bromobenze-d5
solution at lower temperatures; 19F NMR (188 MHz, toluene-
d8) δ -131.71 (m, o-F), -149.27 (tt, J ) 20.8, 5.3 Hz p-F),
-161.86 (m, m-F); 11B NMR (64.2 MHz, toluene-d8) δ 32.9 (br);
29Si{1H} NMR (39.7 MHz, 0.02 M Cr(acac)3 toluene-d8) δ
-64.39 (1 Si), -64.87 (2 Si), -65.21(1 Si), -65.56 (1 Si), -66.62
(2 Si). Anal. Calcd for C57H73BF10O12Si7Zr: C, 47.59; H 5.11;
F, 13.21. Found: C, 51.15; H, 5.24; F, 14.58.
19F a n d 1H NMR Rea ction betw een Com p ou n d 3 a n d
MeAl(BHT)2. A solution of MeAl(BHT)2 in benzene-d6 (27 mg.
0.062 mmol in 1.0 mL) was prepared at room temperature,
and about 0.5 mL of this solution was used to dissolve
compound 3 (20 mg, 0.010 mmol). 19F and 1H NMR spectra
were recorded periodically every few minutes, but no reaction
was evident after ) 1 h and 24 h at 25 °C. The concentrations
of MAD and 3 employed here are about 50× and 167× higher,
respectively, than those employed in the following polymeri-
zation experiments.
P olym er iza t ion E xp er im en t s. Detailed polymerization
procedures and methods for polymer characterization are
described in the literature.25 In the first experiment sum-
marized in the text, 10.0 mL of a solution of Cp2ZrMe2 (2.5
mM in toluene) was added to a solution of compound 3 (3.0
mM) in 10.0 mL of toluene in a glovebox, and the resulting
solution was transferred to a sample bomb, which was then
attached to a polymerization reactor containng 480 mL of
toluene, presaturated with ethylene at 75 psi at 30 °C, 1000
rpm, and containing 272 mg (0.625 mmol) of MeAl(BHT)2 as
a scrubbing agent. The contents of the sample vessel were
introduced into the reactor (after a total period of about 15
min at room temperature) by slightly overpressurizing the
vessel with dry nitrogen while stirring at 1000 rpm. In this
case, ethylene uptake was minimal (as measured by a cali-
brated mass flow meter), and only trace quantities of PE were
obtained (i.e., <100 mg) after 60 min.
The second experiment involved prior addition of a solution
of compound 3 to the reactor in the same manner, followed by
the addition of a solution of Cp2ZrMe2 shortly thereafter. In
this case, after a brief induction period of <5 min duration,
rapid uptake of ethylene was observed and steady consumption
of ethylene at a rate of 0.21 ( 0.02 mmol s-1 was observed for
a total period of 35 min. The reactor was quenched by the
addition of a small quantity of MeOH and then vented. A total
of 10.5 g of PE was recovered by filtration, washing with
MeOH, and then drying in vacuo.
Subsequent work has revealed that this compound is
unstable in solid form and in concentrated solution. The nature
of the decomposition process is as yet unclear but may be
responsible for the unsatisfactory analysis obtained. A solid
sample stored in a glovebox for a period exceeding 6 months
at room temperature was found not to contain detectable C6F5
groups (!), while oily samples noticeably decompose after
several days at room temperature to form a complex mixture.
This compound is reasonably stable (∼1 week) when stored
at -30 °C under N2 or in dilute solution at room temperature.
19F a n d 1H NMR Rea ction betw een Com p ou n d 3 a n d
Cp 2Zr Me2. A stock solution containing 47.7 mg of 2,3,5,6-
tetrafluoro-p-xylene dissolved in 1500 µL of solvent (55:45 v/v
of toluene-d8/bromobenzene-d5) was prepared. Using this solu-
tion, a 600 µL solution containing 134.6 mg (0.070 mmol) of
compound 3 and a 500 µL solution containing 80.1 mg (0.317
mmol) of Cp2ZrMe2 were prepared. Small aliquots were
removed, and the 19F NMR spectrum of the first solution and
(25) Bravakis, A. M.; Bailey, L. E.; Pigeon, M.; Collins, S. Macro-
molecules 1998, 31, 1000, and references therein.
Metcalfe, Robert A.
