Ta(V)-Based Metallocene and Non-Metallocene Complexes
Organometallics, Vol. 21, No. 5, 2002 835
of 3. The combined mother liquors were concentrated and
cooled again to -40 °C, producing a third crop of 3 (0.15 g).
The total yield is 0.58 g (20.2%).
Anal. Calcd for C49H19Al2F30Ta: C, 41.67; H, 1.36. Found: C,
41.99; H, 1.47.
Rea ction of Cp 2Ta Me3 w ith 1 Equ iv of Al(C6F 5)3. In a
small vial, Cp2TaMe3 and Al(C6F5)3‚0.5(toluene) were mixed
in 0.7 mL of bromobenzene-d5 in a 1:1 ratio (0.01 mmol scale),
and the mixture was loaded into a J . Young NMR tube in a
glovebox. The mixture was allowed to react at room temper-
ature for 10 min before the NMR spectra were recorded. A
clear solution was obtained immediately after mixing, and the
NMR spectra indicated the clean formation of the correspond-
ing cationic species Cp2TaMe2+CH3Al(C6F5)3-. 1H NMR (C6D5-
Br, 23 °C): δ 5.79 (s, 10H, C5H5), 0.38 (s, br, 3H, Al-CH3),
0.21 (s, br, 6H, Ta-CH3). 19F NMR (C6D5Br, 23 °C): δ -120.96
(dd, 6F, o-F), -158.02 (t, 3F, p-F), -163.09 (m, 6F, m-F). The
same reaction in benzene-d6 or toluene-d8 produced initially
a yellow suspension which gradually turned to oily precipitates
at the bottom of the NMR tube. NMR spectra of the solution
phase showed a mixture of species, including the unreacted
Cp2TaMe3. The 1H and 19F NMR chemical shifts are very
sensitive to the concentration and temperature, and the
spectra are difficult to reproduce.
Complex 3 (0.188 g, 0.25 mmol) was suspended in 15 mL of
diethyl ether and cooled to -40 °C. MeMgBr (0.425 mL, 3.0
M in Et2O, 1.27 mmol) was added via syringe, and large
precipitates formed during the addition. The mixture was
stirred at room temperature for 45 min after the addition, and
the solvent of the resulting yellow suspension was removed
under reduced pressure to leave a solid residue. The residue
was extracted with hexanes (15 mL) and filtered through
Celite to produce a yellow solution which was filtered again
through Celite. The filtrate was cooled to -40 °C in a freezer
inside the box, and no crystals were obtained. The solvent was
then removed and the residue was dried in vacuo to afford
the crude product as a yellow solid. Further purification was
made by redissolving the solid in hexane, filtering through
Celite, and drying in vacuo to produce the desired product 4
in quantitative yield. Anal. Calcd for C30H49N2Ta: C, 58.24;
H, 7.98; N, 4.53. Found: C, 57.59; H, 7.64; N, 4.23.
Alternatively, 4 can be prepared in better than 70% overall
yield based on the diamine ligand from a one-pot approach by
mixing the neutral diamine ligand with TaCl5 at -30 °C and
stirring at room temperature for another 2 h, followed by an
addition of 5 equiv of MeMgBr.
Rea ction of Cp 2Ta Me3 a n d B(C6F 5)3. In a glovebox, Cp2-
TaMe3 and B(C6F5)3 were mixed in 0.7 mL of benzene-d6 in a
1:1 ratio (0.02 mmol scale), and the solution was loaded into
a J . Young NMR tube. The mixture was allowed to react at
room temperature for 15 min before the NMR spectra were
recorded. The initially formed light yellow suspension turned
gradually to yellow oily precipitates at the bottom of the tube.
NMR spectra of the solution phase indicated formation of a
1
Spectroscopic data for 4 are as follows. H NMR (C6D6, 23
°C): δ 7.18-7.11 (m, 6H, Ar), 3.61-3.50 (m, 8H, -CHMe2,
-NCH2CH2), 2.15 (m, 2H, -NCH2CH2), 1.37 (d, J ) 6.9 Hz,
12H, -CHMe2), 1.25 (d, J ) 6.9 Hz, 12 H, -CHMe2), 1.02 (s,
-
mixture of two products, Cp2TaMe2+CH3B(C6F5)3 and Cp2-
1
9H, Ta-CH3). H NMR (C6D6, 80 °C): δ 3.65 (t, 4H, -NCH2-
TaMe2+[(C6F5)3B-CH3-B(C6F5)3]-, in a ca. 1:2 ratio, along
with unreacted Cp2TaMe3. However, this ratio became ca. 2:1
after this phase stood in the NMR tube at room temperature
CH2), 3.57 (sept, 4H, -CHMe2).1H NMR (C6D5Br, 23 °C): δ
7.34 (m, 6H, Ar), 3.89 (t, J ) 5.7 Hz, 4H, -NCH2CH2), 3.70
(sept, J ) 6.9 Hz, 4H, -CHMe2), 2.66 (m, 2H, -NCH2CH2),
1.53 (d, J ) 6.6 Hz, 12H, -CHMe2), 1.45 (d, J ) 6.6 Hz, 12H,
-CHMe2), 1.04 (s, 9H, Ta-CH3). 13C NMR (C6D6, 23 °C): δ
144.87, 127.40, 126.82, 124.56 (Ar), 65.55 (-NCH2CH2), 55.94
(Ta-CH3), 28.34, 27.02, 25.99, 24.72 (-CHMe2, -CHMe2,
-NCH2CH2).
1
for 1 h. H NMR (C6D6, 23 °C): δ 5.05 (s, br, 10H, C5H5), 1.33
(s, br, 3H, B-CH3-B), 0.95 (s, br, 3H, B-CH3), -0.40 (br, Ta-
3
CH3). 19F NMR (C6D6, 23 °C): δ -131.99 (d, J F-F ) 21.2 Hz,
3
12F, o-F, binuclear anion), -132.30 (d, J F-F ) 21.2 Hz, 6F,
o-F, mononuclear anion), -163.98 (t, 3J F-F ) 21.4 Hz, 6F, p-F,
3
binuclear anion), -164.05 (t, J F-F ) 21.4 Hz, 3F, p-F,
Rea ction of Cp 2Ta Me3 w ith 2 Equ iv of Al(C6F 5)3 a n d
Isola tion of Cp 2Ta Me2+[(C6F 5)3Al-CH3-Al(C6F 5)3]- (5).
NMR-scale reactions were carried out in J . Young NMR tubes,
the samples being loaded into the NMR tubes in a glovebox
after mixing Cp2TaMe3 (0.02 mmol) and Al(C6F5)3‚0.5(toluene)
(11.4 mg, 0.04 mmol) in 0.7 mL of C6D6. The mixture was
allowed to react at room temperature for 10 min before the
NMR spectra were recorded. The solution became cloudy
immediately, and colorless crystals started to precipitate onto
the wall of NMR tubes. NMR spectra of the solution phase
indicated formation of the clean product 5. 1H NMR (C6D6, 23
mononuclear anion), -166.57 (t, 12F, m-F, binuclear anion),
-166.64 (t, 6F, p-F, mononuclear anion). The 1:2 Cp2TaMe3/
B(C6F5)3 reaction produced a yellow oil containing the same
mixture of species in the solution phase but with substantially
sharper peaks for the Cp and Ta-CH3 resonances. A substan-
tial amount of the unreacted B(C6F5)3 was also present in the
solution.
The reactions were repeated in bromobenzene-d5 (0.01 mmol
scale) to afford clear solutions. NMR spectra of the 1:1 ratio
-
.
1H
reaction indicated formation of Cp2TaMe2+CH3B(C6F5)3
NMR (C6D5Br, 23 °C): δ 5.78 (s, 10H, C5H5), 1.29 (s, br, 3H,
B-CH3), 0.21 (s, 6H, Ta-CH3). 19F NMR (C6D5Br, 23 °C): δ
-131.95 (d, 3J F-F ) 21.2 Hz, 6F, o-F), -163.50 (t, 3J F-F ) 21.0,
3F, p-F), -166.12 (m, 6F, m-F). NMR spectra of the 1:2
reaction showed formation of the same product, along with
unreacted B(C6F5)3 and a small amount of MeB(C6F5)2.
Rea ction of Cp 2Ta Me3 a n d P h 3C+[B(C6F 5)4]-. In a small
vial, Cp2TaMe3 and Ph3C+[B(C6F5)4]- were mixed in 0.7 mL
of bromobenzene-d5 in a 1:1 ratio (0.01 mmol scale) and the
mixture was loaded into a J . Young NMR tube in a glovebox.
The mixture was allowed to react at room temperature for 10
min before the NMR spectra were recorded. A clear yellow
solution was obtained immediately after the mixing. NMR
spectra indicated the clean formation of the corresponding
cationic species Cp2TaMe2+[B(C6F5)4]- and 1 equiv of Ph3CCH3.
1H NMR (C6D5Br, 23 °C): δ 5.78 (s, 10H, C5H5), 2.24 (s, 3H,
Ph3CCH3), 0.21 (s, 6H, Ta-CH3). 19F NMR (C6D5Br, 23 °C): δ
°C): δ 4.96 (s, 10H, C5H5), 1.77 (s, br, Al-CH3-Al), -0.40 (s,
3
6H, Ta-CH3). 19F NMR (C6D6, 23 °C): δ -122.66 (d, J F-F
)
18.3 Hz, 12F, o-F), -154.58 (s, br, 6F, p-F), -162.35 (m, 12F,
m-F). The crystals collected were redissolved in bromobenzene-
d5, and the NMR spectra indicated a species identical with
that in the solution (vide infra).
This reaction was repeated in bromobenzene-d5 (0.01 mmol
scale) to afford a clear solution. NMR spectra indicated
1
formation of the clean product 5. H NMR (C6D5Br, 23 °C): δ
5.78 (s, 10H, C5H5), 2.21 (s, br, 3H, Al-CH3-Al), 0.23 (s, 6H,
3
Ta-CH3). 19F NMR (C6D5Br, 23 °C): δ -122.83 (d, J F-F
)
18.3 Hz, 12F, o-F), -154.39 (s, br, 6F, p-F), -162.19 (t,
3J F-F ) 18.1 Hz, 12F, m-F). 13C NMR (C6D5Br, 23 °C): δ 112.10
1
1
(C5H5, J CH ) 175.5 Hz), 57.05 (Ta-CH3, J CH ) 125.3 Hz).
The preparative isolation of the complex was carried out in
the glovebox by mixing Cp2TaMe3 (0.018 g, 0.05 mmol) and
Al(C6F5)3‚0.5(toluene) (0.057 g, 0.1 mmol) in 10 mL of toluene
and stirring at room temperature for 5 min. The solvent was
removed under reduced pressure, and the residue was washed
with 2 mL of hexane and dried in vacuo, affording 0.067 g of
the clean product as a white crystalline solid. Yield: 94.9%.
3
-131.62 (s, br, 6F, o-F), -161.40 (t, J F-F ) 21.0, 3F, p-F),
-165.35 (s, br, 6F, m-F). The 1:2 reaction produced the same
product, even after heating at 100 °C.
Rea ction of [Ar N(CH2)3NAr ]Ta Me3 (4) a n d B(C6F 5)3. In
a small vial, [ArN(CH2)3NAr]TaMe3 and B(C6F5)3 were mixed