Arene C-H Bond Activation
Exp er im en ta l Section
Organometallics, Vol. 22, No. 19, 2003 3889
in CH2Cl2 (3-4 mL); the resulting solution was filtered
through Celite and concentrated in vacuo, affording 3a as a
red solid (0.199 g, 63%). 1H NMR (300 MHz, CD2Cl2): δ -0.269
(s, 6H, Pd-CH3), 1.35 (s, 36H, C(CH3)3), 2.06 (s, 6H, NdC-
Gen er a l Con sid er a tion s. All moisture-sensitive com-
pounds were manipulated using standard vacuum line, Schlenk,
4
4
or cannula techniques or in
a drybox under a nitrogen
CH3), 6.73 (d, J H-H ) 1.8 Hz, 4H, o-Ar-H), 7.28 (t, J H-H
)
1.8 Hz, 2H, p-Ar-H). 13C{1H} NMR (300 MHz, CD2Cl2): δ
-5.189 (Pd-CH3), 20.16 (NdC-CH3), 31.73 (C(CH3)3), 35.50
(C(CH3)3), 115.76 (o-Ar-C), 119.64 (p-Ar-C), 147.34, 151.92
(Ar-C), 169.84 (NdC-CH3). Anal. Calcd for C34H54N2Pd
(Found): C, 68.38 (68.23/68.10); H, 9.11 (8.90/8.72); N, 4.69
(4.60/4.73).
atmosphere. Argon and dinitrogen gases were purified by
passage over columns of MnO on vermiculite and activated
molecular sieves. Trifluoroethanol was purchased from either
Aldrich or Lancaster, purified, and dried over a mixture of
CaSO4/NaHCO3, then either vacuum distilled or distilled
under argon and stored over activated molecular sieves under
vacuum. Trifluoroethanol-d3 was purchased from Aldrich or
Cambridge Isotopes, stored over activated molecular sieves and
a small amount of NaHCO3 under vacuum, and then vacuum
distilled. The solvent was syringed into oven-dried screw-cap
NMR tubes fitted with septa for kinetic studies. Benzene and
benzene-d6 were vacuum distilled from sodium benzophenone
ketyl shortly before kinetic runs and stored over activated
molecular sieves. Diethyl ether, THF, and CH2Cl2 were puri-
fied over an activated alumina column. 1,4-Bis(3,5-di-tert-butyl-
(CF
)
2
3
{
Ar DABMe}P d Me2 (3b). A Schlenk flask was charged
with [(COD)PdMe2] (0.122 g, 0.500 mmol) and
) ArDABMe
(CF
3
2
(0.257 g, 0.500 mmol). The flask was cooled to 0 °C, and Et2O
(10 mL) was transferred via cannula onto the solids. A bright
red precipitate formed from a clear solution, and the resulting
red suspension was stirred for 1 h at 0 °C and warmed to room
temperature. The red solid was filtered, washed with cold Et2O
and pentane, and dried in vacuo, affording 3b as a red powder
1
(0.185 g, 58%). H NMR (300 MHz, CD2Cl2): δ -0.217 (s, 6H,
phenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene (tBu ArDABMe),10a
2
Pd-CH3), 2.11 (s, 6H, NdC-CH3), 7.45 (br s, 4H, o-Ar-H),
7.84 (br s, 2H, p-Ar-H). 13C{1H} NMR (300 MHz, acetone-
1,4-bis(3,5-ditrifluoromethylphenyl)-2,3-dimethyl-1,4-diaza-
1,3-butadiene {(CF ) ArDABMe},10b [(COD)PdMe2],14 [(pyridazine)-
3
2
3
d6): δ -4.72 (Pd-CH3), 20.59 (NdC-CH3), 119.50 (m, J C-F
tBu
(CF
3
PdMe2]n,13
(
ArDABMe)PdMe2 (3a ),11
{
) ArDABMe}PdMe2
2
2
) 3.8 Hz, p-Ar-C), 122.30 (m, 3J C-F ) 3.8 Hz, o-Ar-C), 124.10
(3b),11 [(tBu ArDABMe)Pd(H2O)2][BF4]2 (4a ),22 [(tBu ArDABMe)Pd-
2
2
1
2
(q, J C-F ) 273 Hz, CF3), 132.15 (q, J C-F ) 273 Hz, m-Ar-
C-CF3), 149.80 (Ar-C), 173.96 (NdC-CH3). Anal. Calcd for
(OH)]2[BF4]2 (5a ),22 [(PhCN)2PdCl2],28 and (tBu ArDABMe)PdCl2
2
(6a )21 were synthesized according to literature procedures. All
other solvents and reagents were used as received without
further purification.
C
22H18F12N2Pd (Found): C, 40.98 (41.18/41.13); H, 2.81 (2.91/
2.92); N, 4.34 (4.24/4.27).
[(tBu Ar DABMe)P d (H2O)2][BF 4]2 (4a ). (tBu ArDABMe)PdCl2
(6a , 0.250 g, 0.392 mmol ) was slurried in 1:1 THF/CH2Cl2
solution (15 mL). AgBF4 (0.156 g, 0.803 mmol) was dissolved
in dry THF (1 mL) and added to the reaction flask dropwise.
An off-white precipitate formed immediately in a yellow
solution. After 3 h, the solution was filtered through Celite
and the filtrate was removed in vacuo to afford 4a as a yellow
2
2
NMR spectra were recorded on a Varian CCE 600 (1H,
599.662 MHz), a Varian INOVA 500 (1H, 499.852 MHz), or a
Varian Mercury 300 (1H, 299.8 MHz, 13C, 75.4626 MHz)
spectrometer. Elemental analyses were performed at Midwest
MicroLab LLC.
The quantification of 5a /b was accomplished by 1H NMR
integration against the residual solvent peak (CF3CHDOD) as
an internal standard. The biphenyl quantification was ac-
complished by GC-MS.
1
solid (0.225 g, 74%). H NMR (300 MHz, TFE-d3): δ 1.37 (s,
4
36H, C(CH3)3), 2.27 (s, 6H, NdC-CH3), 7.23 (d, J H-H ) 1.6
4
Hz, 4H, o-Ar-H), 7.77 (t, J H-H ) 1.6 Hz, 2H, p-Ar-H), O-H
resonances not found due to exchange with CF3CD2OD. 13C-
{1H} NMR (300 MHz, TFE-d3): δ 21.34 (NdC-CH3), 31.99
(C(CH3)3), 37.01 (C(CH3)3), 118.42 (o-Ar-C), 127.17 (p-Ar-C),
143.91, 156.55 (Ar-C), 187.66 (NdC-CH3). Anal. Calcd for
Bitolyl products, which are not commercially available, were
synthesized by the Suzuki coupling methodology developed by
Fu.29 Bis(trifluoromethyl)biphenyl products were synthesized
by oxidation of the aryl Grignard reagent by TiCl4.30
Syn th esis a n d Ch a r a cter iza tion of Meth yl Aqu o Ca t-
ion s (2a /b). The aquo complexes were prepared in situ by
procedures described by Tilset and co-workers.10b Complexes
2a /b could not be isolated as pure solids, but are stable in TFE
solution for >12 h. For the kinetic studies, cations 2a /b are
generated in situ (vide infra), and the chemical shifts reported
below are for solutions in TFE-d3 in the absence of substrate.
C
32H52N2O2F8B2Pd (Found): C, 49.48 (49.18/49.17); H, 6.75
(6.68/6.73); N, 3.61 (3.59/3.55).
[{(CF Ar DABMe}P d (H2O)2][BF 4]2 (4b). 1H NMR (600 MHz,
TFE-d3): δ 2.19 (s, 6H, NdC-CH3), 8.12 (br s, 4H, o-Ar-H),
8.18 (br s, 2H, p-Ar-H), O-H resonances not found due to
exchange with CF3CD2OD.
)
3
2
[(t Bu Ar DABMe)P d (OH )]2[BF 4]2 (5a ). This compound was
2
[(tBu Ar DABMe)P d (CH3)(H2O)][BF 4] (2a ). 1H NMR (300
2
synthesized in the same manner as 4a , but is present in the
solid isolated after a 1 h reaction time. This complex was not
isolated cleanly from 4a and other related products (see
Results and Discussion section), but can be isolated cleanly
MHz, TFE-d3): δ 0.492 (s, 3H, Pd-CH3), 1.34, 1.36 (s, 18H,
4
C(CH3)3), 2.12, 2.19 (s, 3H, NdC-CH3), 6.77, 6.93 (d, J H-H
)
1.6 Hz, 2H, o-Ar-H), 7.49, 7.55 (t, 1H, p-Ar-H).
)
[{(CF Ar DABMe}P d (CH3)(H2O)][BF 4] (2b). 1H NMR (600
MHz, TFE-d3): δ 0.511 (s, 3H, Pd-CH3), 2.20, 2.28 (s, 3H, Nd
C-CH3), 7.50, 7.58 (br s, 2H, o-Ar-H), 7.94, 7.95 (br s, 1H,
p-Ar-H).
1
3
2
from the reaction of 2a with C6H6 (under 1 atm O2). H NMR
(300 MHz, TFE-d3): δ 1.24 (s, 72H, C(CH3)3), 2.09 (s, 12H,
4
NdC-CH3), 6.87 (d, J H-H ) 1.6 Hz, 8H, o-Ar-H), 7.52 (t,
4J H-H ) 1.6 Hz, 4H, p-Ar-H), O-H resonances not found due
1
tBu
Ar DABMe)P d Me2 (3a ). A Schlenk flask was charged
2
to exchange with CF3CD2OD. H NMR (300 MHz, CD2Cl2): δ
(
-3.51 (s, 2H, OH), 1.19 (s, 72H, C(CH3)3), 2.06 (s, 12H, Nd
with [(pyridazine)PdMe2]n (0.115 g, 0.530 mmol) and
4
4
tBu
ArDABMe (0.256 g, 0.556 mmol). The flask was cooled to 0
2
C-CH3), 6.93 (d, J H-H ) 1.6 Hz, 8H, o-Ar-H), 7.34 (t, J H-H
) 1.6 Hz, 4H, p-Ar-H).
°C, and Et2O (15 mL) was transferred via cannula onto the
solids. A dark red precipitate forms from the suspension of
starting materials almost immediately upon solvent addition.
The mixture was stirred for 2 h at 0 °C, warmed to room
temperature, and filtered. The crude product was dissolved
)
[{(CF Ar DABMe}P d (OH)]2[BF 4]2 (5b). 1H NMR (600 MHz,
TFE-d3): δ 1.99 (s, 12H, NdC-CH3), 7.61 (br s, 8H, o-Ar-H),
8.01 (br s, 4H, p-Ar-H), O-H resonances not found due to
3
2
exchange with CF3CD2OD.
tBu
2
2
(
Ar DABMe)P d Cl2 (6a ). tBu ArDABMe (0.520 g, 1.13 mmol)
(28) Kharasch, M. S.; Seyler, R. C.; Mayo, F. R. J . Am. Chem. Soc.
1938, 60, 882-884.
was dissolved in CH2Cl2 (10 mL) and added to a solution of
[(PhCN)2PdCl2] (0.433 g, 1.13 mmol) in CH2Cl2 (10 mL). An
orange precipitate formed immediately. The reaction was
stirred for 1-2 h. The precipitate was filtered, washed with
CH3OH and Et2O, and dried in vacuo to afford 6a as an orange
(29) Littke, A. F.; Dai, C.; Fu., G. C. J . Am. Chem. Soc. 2000, 122,
4020-4028.
(30) Inoue, A.; Kitagawa, K.; Shinokubo, H.; Oshima, K. Tetrahedron
2000, 56, 9601-9605.