1
52 Organometallics, Vol. 23, No. 1, 2004
Notes
t
+
-
-
species [(Me4C5)SiMe2N Bu]TiMe rPBA (PBA ) tris-
2,2′,2′′-nonafluorobiphenyl)fluoroaluminate), at δ 61.99
µs. The multiplicities and coupling constants were derived from
analysis of gated decoupled spectra. Operating conditions for
(
1
1
3
H NMR measurements: spectral width 5 kHz; spectrum
and 60.50 ppm. Thus, in contrast to the Cp2TiCl2/MAO
and Cp2TiMe2/MAO systems, in the “constrained-
geometry” titanium catalysts heterobinuclear species of
the type [LTi(µ-Me)2AlMe2] were not found, and only
zwitterion-like” species were detected. A similar be-
accumulation frequency 0.5-0.2 Hz; number of transients 32-
6
4, ca. 30° pulse at 2 µs. 1H peaks were assigned to the
respective carbon signals by double-resonance techniques. For
+
1
13
calculations of H and C chemical shifts, the resonances of
the CH group of the toluene solvent were taken as 2.09 and
1.40 ppm, respectively. The sample temperature measure-
“
3
havior was recently reported for the titanium half-
sandwich system Cp*TiCl3/MAO, where “zwitterion-
2
ment uncertainty and temperature reproducibility were less
than (1 °C.
P r ep a r a tion of MAO a n d Al Me Sa m p les. Solid MAO
2 6
was prepared from commercial MAO (Witco) by removal of the
solvent in vacuo at 20 °C. The solid product obtained (poly-
meric MAO with total Al content 40 wt % and Al as residual
+
-
like” intermediates Cp*TiMe2 rMe-Al tMAO strongly
dominate in solution at Al:Ti ) 300 while there was no
evidence for expected adducts of the types [Cp*Ti(Me)-
µ-Me)2AlMe2] and [Cp*Ti{(µ-Me)2AlMe2}2]+ (Cp* )
+
(
1
4
C5Me5). It is possible that in the more open half-
sandwich and constrained-geometry complexes a closer
AlMe
13CH
drich) by sequential treatments with Al metal at 80 °C and
Na metal in C12 26 at 100 °C. For this goal, a dried glass
ampule was filled with argon and charged with 0.126 g (4.7
3
ca. 5 wt %) was used for the preparation of the samples.
13
3
2 6 3
-labeled Al Me was prepared from 99% CH I (Al-
-
approach of [Me-MAO] is favored, to give “zwitterion-
like” species upon activation by MAO, while for the more
restricted coordination gap aperture of metallocenes
heterobinuclear ion pairs of type III are preferable.
H
13
13
mmol) of Al metal powder, 1.0 g (7 mmol) of CH
3
I (99% C),
and I (used as catalyst). The ampule was evacuated and
2
Con clu sion s
sealed off at the vacuum line. The reaction mixture was kept
at 80 °C for 10 h. The resulting suspension was mixed under
vacuum with Na metal (0.170 g) suspended in dodecane. The
The activation of Cp2TiX2 with MAO leads to the
formation of several intermediates, II-IV (X ) Cl, Me).
At Al:Ti ratios approaching real polymerization condi-
tions (100-300:1), complexes III and IV are the major
species in solution. The heterobinuclear cationic com-
1
3
mixture was stirred at 100 °C for 5 h. The product, CH3-
labeled Al Me
(99% 13C), was distilled in vacuo from the
reaction mixture.
2
6
1
3
CH
3
-enriched MAO was prepared by ligand exchange of
99% 13CH -labeled Al Me (70 mol % of total Me groups) and
+
-
pound [L2Ti(µ-Me)2AlMe2] [MeMAO] (III) predomi-
nates in solution under the higher MAO:Ti ratios typical
of polymerization conditions and is the most probable
precursor of the active polymerizing species. In contrast,
heterobinuclear species were found to be below the
3
2
6
solid MAO (30 mol % of total Me groups) in toluene solution.
In a typical experiment, 0.12 g of polymeric MAO powder (total
Al content 1.8 mmol) was dissolved in 5 mL of toluene, and
1
3
∼
0.3 mL (∼ 2 mmol of Al) of CH
3 2 6
-labeled Al Me was added
to the solution. The reaction mixture was stirred for 24 h at
5 °C, and the liquid fraction Al
under vacuum to give a sample of C-enriched MAO (65-70%
2
C) with the desired Al Me6 content (polymeric MAO with
detection limit in the “constrained geometry” system
(Me4C5)SiMe2N Bu]TiX2/MAO, most probably due to
13
2
2
Me
6
(70% C) was removed
t
[
13
1
3
steric reasons.
total Al content of 40 wt % and Al as residual AlMe
%
3
ca. 5 wt
). The 13C-enriched MAO prepared either was used for sam-
Exp er im en ta l Section
ple preparation directly or was used afterward as a ca. 1:1
mixture with nonlabeled MAO.
Methylaluminoxane (MAO) was purchased from Witco
GmbH (Bergkamen, Germany) as a toluene solution (total Al
content 1.8 M, Al as AlMe 0.5 M). Toluene was dried over
3
P r ep a r a tion of Cp
2
TiMe
2
a n d Cp
2
TiMeCl + Cp
TiMeCl and Cp
2
TiMe
TiMe
2
Mixtu r e. Cp TiMe and a mixture of Cp
2
2
2
2
2
molecular sieves (4 Å) and purified by refluxing over sodium
metal and distilling under dry nitrogen. Solvents were distilled
over sodium or sodium-benzophenone under nitrogen and
degassed in vacuo. All operations were carried out under dry
nitrogen (99.999%) by standard Schlenk techniques. Solids and
(
ca. 1:1) were prepared by stirring appropriate amounts of
LiMe (1.6 M ether solution) with a suspension of Cp TiCl in
toluene at 0 °C for 3 h. After removal of LiCl, the resulting
yellow solution was collected, volatiles were removed in vacuo,
and the residue was dissolved in toluene. H and C chemical
shifts are presented in Table 1.
2
2
1
13
toluene were transferred and stored in a glovebox. Cp
2
TiCl
2
1
5
was used as purchased; [Ph
3
C][B(C
6
F
5
)
4
]
and [(Me
4
C
5
13
)SiMe
2
-
) + 13C-MAO (+[P h
TiCl , MAO, and
Sa m p les of Cp
B(C ]). The appropriate amounts of Cp
Ph C][B(C ] were weighed into NMR tubes in a glovebox
2
TiCl
2
(Cp
2
TiMe
2
3
C]-
+
16
1
1
N Bu]TiCl
2
were prepared as described. H and C{ H}
[
[
6
F
5
)
4
2
2
NMR spectra were recorded at 300.130 and 75.473 MHz,
respectively, on a Bruker Avance-300 MHz NMR spectrometer.
3
6 5 4
F )
and the tubes closed with septum stoppers. Further addition
of toluene and AlMe (if necessary) was performed outside the
glovebox with gastight microsyringes in the flow of nitrogen
upon appropriate cooling.
1
3
Typical operating conditions for C NMR measurements were
as follows: spectral width 20 kHz; spectrum accumulation
frequency 0.2-0.1 Hz; 100-10 000 transients, 45° pulse at 5
3
(
13) Chen, Y.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1997,
19, 2582.
14) Bryliakov, K. P.; Semikolenova, N. V.; Zakharov, V. A.; Talsi,
Ack n ow led gm en t. This work was supported by the
European Commission, INTAS grant 00-841. The au-
thors thank Dr. D. E. Babushkin and Dr. N. V. Semi-
1
(
E. P. J . Organomet. Chem. 2003, 683, 23-28.
(
C1.
(
15) Bochmann, M.; Lancaster, S. J . J . Organomet. Chem. 1992, 434,
1
3
kolenova for the synthesis of Al( CH3)3 and fruitful
1
3
16) Stevens, J . C.; Timmers, F. J .; Wilson, D. R.; Schmidt, G. F.;
methodology of C-enriched MAO.
Nickias, P. N.; Rosen, R. K.; Knight, G. W.; Lai, S.-y. Eur. Pat. Appl.
416815A2, 1991.
0
OM034026L
Bryliakov, Konstantin P.
