Sterically Crowded Palladium(II) Complexes
Organometallics, Vol. 26, No. 27, 2007 6747
4-Me-C6H4), 6.88 (s, 1H, mim H4/H5), 6.73 (s, 3H, mim H4/H5),
5.36 (d, J ) 12, 1H, CH), 4.74 (d, J ) 12, 1H, CH), 3.49 (s, 3H,
mim NMe), 3.12 (s, 3H, mim NMe), 2.77 (s, 3H, COMe), 2.25 (s,
6H, 4-Me-C6H4). 13C{1H} NMR (CD2Cl2, -40 °C): δ 217.4
(C(O)Me), 173.5 (PdCO), 144.8, 143.7, 138.4, 138.3, 135.0, 134.6,
129.7, 129.6, 127.8, 127.5, 127.3, 126.5, 122.3, 122.1, 61.4 (CH),
41.5 (COMe), 39.8 (CH), 34.6 (mim NMe), 33.6, (mim NMe), 20.7.
IR (CD2Cl2, cm-1): 2123 (VCO), 1736 (Vacyl).
Me). 13C{1H} NMR (CD2Cl2, -60 °C): δ 217.4 (C(O)Me), 172.5
(PdCO), 156.8, 154.4, 149.5, 147.1, 143.3, 142.4, 136.9, 136.8,
136.7, 136.4, 135.7, 135.6, 135.1, 132.0, 130.9, 129.0, 127.6, 126.6,
126.5, 124.5, 124.2, 51.7 (CH), 49.5 (CH), 40.3 (COMe), 21.2,
20.6, 20.4, 20.3, 18.4, 18.3. IR (CD2Cl2, cm-1): 2127 (VCO), 1750
(Vacyl).
Generation of [{((2,4-Me2-C6H3)2HC)HC(3-Me-quin)2}-
Pd{C(dO)Me}(CO)][B(C6F5)4] (7q). A valved NMR tube contain-
ing a CD2Cl2 (0.7 mL) solution of {((2,4-Me2-C6H3)2HC)HC(3-
Mequin)2}PdMe2 (5 mg, 8 µmol) and [H(Et2O)2][B(C6F5)4] (6 mg,
8 µmol) was cooled to -196 °C, exposed to CO (5 atm), sealed,
warmed to -78 °C, and then briefly warmed to 23 °C and
vigorously shaken. The tube was kept at -78 °C and transferred
to a precooled (-40 °C) NMR probe, and NMR spectra were
recorded. NMR spectra showed that 7q had formed quantitatively.
1H NMR (CD2Cl2, -40 °C): δ 8.65 (d, J ) 9, 1H, quin H8/H8′),
8.39 (d, J ) 9, 1H), 8.35 (s, 1H, quin H4/H4′), 8.07 (s, 1H, quin
H4/H4′), 7.85 (m, 4H), 7.65 (m, 2H), 7.26 (m, 2H), 7.12 (d, J )
10, 1H, CH), 7.02 (d, J ) 8, 1H), 6.92 (m, 2H), 6.68 (s, 1H), 6.16
(d, J ) 11, 1H, CH), 2.93 (s, 3H, quin 3/3′-Me), 2.22 (s, 3H, 4/4′-
Me of 2,4-Me2-C6H3), 2.15 (s, 3H, C(dO)Me), 2.12 (s, 3H, 4/4′-
Me of 2,4-Me2-C6H3), 1.89 (s, 3H, quin 3/3′-Me), 1.70 (s, 3H, 2/2′-
Me of 2,4-Me2-C6H3), 1.43 (s, 3H, 2/2′-Me of 2,4-Me2-C6H3). The
1H NMR assignments were confirmed by a NOESY experiment.
13C{1H} NMR (CD2Cl2, -40 °C): δ 211.5 (C(O)Me), 172.7
(PdCO), 161.1, 158.8, 145.3, 144.6, 142.4, 141.2, 137.5, 137.3,
136.7, 136.0, 135.0, 133.2, 132.6, 132.5, 132.2, 131.8, 131.4, 129.3,
129.0, 128.8, 128.5, 128.3, 128.1, 127.7, 127.0, 126.9, 126.5, 54.9
(CH), 52.8 (CH), 39.4 (COMe), 22.0, 20.6, 20.5, 20.3, 19.1, 18.9.
IR (CD2Cl2, cm-1): 2126 (VCO).
Generation of [{((4-Me-C6H4)3C)HC(mim)2}Pd{C(dO)-
Me}(CO)][B(C6F5)4] (7j). This compound was generated quanti-
tatively from 2j, [HNMe2Ph][B(C6F5)4], and CO using the procedure
1
for 7i. H NMR (CD2Cl2, -40 °C): δ 7.08 (d, J ) 8, 6H, 4-Me-
C6H4), 6.89 (s, 1H, mim H4/H5), 6.85 (s, 1H, mim H4/H5), 6.81
(s, 1H, mim H4/H5), 6.78 (s, 1H, mim H4/H5), 6.53 (br s, 6H,
4-Me-C6H4), 5.70 (s, 1H, CH), 3.24 (s, 3H, mim NMe), 3.01 (s,
3H, mim NMe), 2.45 (s, 3H, COMe), 2.33 (s, 9H, 4-Me-C6H4).
13C{1H} NMR (CD2Cl2, -40 °C): δ 219.9 (C(O)Me), 172.7
(PdCO), 144.1 (mim C2/C2′), 141.7 (mim C2/C2′), 138.2, 137.3,
131.8, 128.4, 127.7, 126.0, 124.0, 122.7, 65.8, 44.7 (CH), 41.7
(COMe), 36.1 (mim NMe), 34.2, (mim NMe), 20.5. IR (CD2Cl2,
cm-1): 2119 (VCO), 1728 (Vacyl).
Generation of [{((4-Me-C6H4)2HC)HC(3-Me-py)2}Pd{C-
(dO)Me}(CO)][B(C6F5)4] (7m). A valved NMR tube containing
a CD2Cl2 (0.7 mL) solution of 3m (16 mg, 30 µmol) and
[Li(Et2O)2.8][B(C6F5)4] (27 mg, 30 µmol) was cooled to -196 °C
and exposed to CO (5 atm). The tube was sealed, warmed to -78
°C, and briefly warmed to 23 °C and vigorously shaken. A slurry
of a fine white solid in a colorless supernatant was obtained. The
tube was kept at -78 °C and transferred to a precooled (-40 °C)
NMR probe, and NMR spectra were recorded. NMR spectra showed
that 7m had formed quantitatively. 1H NMR (CD2Cl2, -40 °C): δ
8.33 (d, J ) 5, 1H, py H6/H6′), 8.25 (d, J ) 5, 1H, py H6/H6′),
7.71 (d, J ) 8, 1H, py H4/H4′), 7.55 (d, J ) 8, 1H, py H4/H4′),
7.29 (m, 1H, py H5/H5′), 7.21 (d, J ) 8, 2H, 4-Me-C6H4), 7.18
(m, 1H, py H5/H5′), 7.04 (m, 4H, 4-Me-C6H4), 6.99 (d, J ) 8, 2H,
4-Me-C6H4), 6.93 (d, J ) 12, 1H, CH), 5.66 (d, J ) 12, 1H, CH),
2.83 (s, 3H, C(dO)Me), 2.48 (s, 3H, Me), 2.23 (s, 3H, Me), 2.20
(s, 3H, Me), 2.19 (s, 3H, Me). 13C{1H} NMR (CD2Cl2, -40 °C):
δ 216.7 (C(O)Me), 172.8 (PdCO), 155.8, 154.9, 149.5, 148.7, 147.6,
146.8, 143.3, 142.4, 137.7, 137.6, 136.8, 136.5, 136.3, 136.2, 129.6,
129.4, 127.7, 127.5, 124.3, 124.2, 58.8 (CH), 50.4 (CH), 41.7
(COMe), 20.7, 20.5, 19.7. IR (CD2Cl2, cm-1): 2127 (VCO), 1742
(Vacyl).
Generation
of
[{((4-Me-C6H4)2HC)HC(mim)2}PdMe-
(H2CdCH2)][B(C6F5)4] (8i). A solution of 5i in CD2Cl2 in a valved
NMR tube was generated as described above and cooled to -196
°C, and ethylene (ca. 4 equiv) was added by vacuum transfer. The
tube was warmed to -78 °C and transferred to a precooled (-60
°C) NMR probe. NMR spectra established that 8i had formed (100%
versus NMe2Ph). At -60 °C, exchange of bound and free ethylene
1
is slow on the NMR time scale. H NMR (CD2Cl2, -60 °C): δ
7.12 (d, J ) 8, 2H, 4-Me-C6H4), 7.08 (d, J ) 8, 4H, 4-Me-C6H4),
7.04 (d, J ) 8, 2H, 4-Me-C6H4), 6.94 (s, 1H, mim H4/H5), 6.74
(s, 1H, mim H4/H5), 6.70 (s, 1H, mim H4/H5), 6.68 (s, 1H, mim
H4/H5), 5.33 (d, J ) 11, 1H, CH), 4.95 (m, 4H, H2CdCH2,
AA′XX′), 4.71 (d, J ) 11, 1H, CH), 3.33 (s, 3H, mim NMe), 3.29
(s, 3H, mim NMe), 2.21 (s, 3H, 4-Me-C6H4), 2.20 (s, 3H, 4-Me-
C6H4), 0.76 (s, 3H, PdMe). 13C{1H} NMR (CD2Cl2, -60 °C): δ
144.4 (mim C2/C2′), 143.1 (mim C2/C2′), 137.9, 137.8, 135.0,
134.9, 129.4, 129.3, 127.2, 127.1, 125.4, 123.9, 122.0, 121.3, 86.7
(H2CdCH2), 61.5 (CH),39.8 (CH), 33.9 (mim NMe), 33.8 (mim
NMe), 20.6, 6.9 (PdMe).
Generation of [{((2,4-Me2-C6H3)2HC)HC(5-Me-py)2}Pd{C-
(dO)Me}(CO)][B(C6F5)4] (7n). This compound was generated
quantitatively from 3n, [Li(Et2O)2.8][B(C6F5)4], and CO using the
1
procedure for 7m. H NMR (CD2Cl2, -60 °C): δ 8.22 (s, 1H, py
H6/H6′), 8.05 (s, 1H, py H6/H6′), 7.76 (s, 2H), 7.44 (d, J ) 8,
1H), 7.40 (d, J ) 7.9, 1H), 7.20 (d, J ) 8, 1H), 6.95 (d, J ) 8,
1H), 6.92 (d, J ) 8, 1H), 6.89 (s, 1H), 6.74 (d, J ) 8, 1H), 6.69 (s,
1H), 6.50 (d, J ) 12, 1H, CH), 5.02 (d, J ) 12, 1H, CH), 2.51 (s,
3H, C(dO)Me), 2.30 (s, 3H, Me), 2.26 (s, 3H, Me), 2.25 (s, 3H,
Me), 2.14 (s, 3H, Me), 2.13 (s, 3H, Me), 1.88 (s, 3H, Me). 13C{1H}
NMR (CD2Cl2, -60 °C): δ 216.9 (C(O)Me), 172.7 (PdCO), 153.4,
152.8, 150.8, 148.8, 141.8, 141.1, 136.5, 136.4, 135.7, 135.5, 135.4,
135.1, 134.7, 134.6, 131.7, 130.7, 129.7, 128.0, 1127.5, 127.4,
127.0, 126.4, 61.3 (CH), 47.8 (CH), 50.0 (COMe), 20.6, 20.4, 20.3,
19.3, 17.9, 17.7. IR (CD2Cl2, cm-1): 2127 (VCO), 1749 (Vacyl).
Generation of [{((4-Me-C6H4)3C)HC(mim)2}PdMe(H2C
dCH2)][B(C6F5)4] (8j). This species was generated quantitatively
from 5j and ethylene (ca. 4 equiv) using the procedure for 8i and
characterized by NMR at -40 °C. At -40 °C, exchange of bound
and free ethylene is slow on the NMR time scale. 1H NMR (CD2Cl2,
-40 °C): δ 7.01 (d, J ) 8, 6H, 4-Me-C6H4), 6.88 (s, 2H, mim
H4/H5), 6.84 (s, 1H, mim H4/H5), 6.60 (s, 1H, mim H4/H5), 6.49
(d, J ) 8, 6H, 4-Me-C6H4), 5.76 (s, 1H, CH), 4.33 (m, 4H,
H2CdCH2, AA′XX′), 3.23 (s, 3H, mim NMe), 3.10 (s, 3H, mim
NMe), 2.30 (s, 9H, 4-Me-C6H4), 0.14 (s, 3H, PdMe). 13C{1H} NMR
(CD2Cl2, -40 °C): δ 143.1 (mim C2/C2′), 142.2 (mim C2/C2′),
137.8, 137.7, 131.4, 128.2, 125.8, 123.5, 123.3, 122.7, 85.8
(H2CdCH2), 67.5, 44.5 (CH), 33.6 (mim NMe), 34.7 (mim NMe),
20.5, 6.5 (PdMe).
Generation of [{((2,4-Me2-C6H3)2HC)HC(3-Me-py)2}Pd{C-
(dO)Me}(CO)][B(C6F5)4] (7o). This compound was generated
quantitatively from 3o, [Li(Et2O)2.8][B(C6F5)4], and CO using the
1
procedure for 7m. H NMR (CD2Cl2, -60 °C): δ 8.33 (d, J ) 5,
1H, py H6/H6′), 8.12 (d, J ) 5, 1H, py H6/H6′), 7.83 (d, J ) 8,
1H), 7.57 (d, J ) 8, 1H), 7.27 (m, 2H), 7.14 (d, J ) 8, 1H), 6.95
(d, J ) 8, 1H), 6.92 (s, 1H), 6.80 (m, 4H), 5.54 (d, J ) 11, 1H,
CH), 2.72 (s, 3H, C(dO)Me), 2.28 (s, 3H, Me), 2.26 (s, 3H, Me),
2.18 (s, 3H, Me), 2.13 (s, 3H, Me), 1.65 (s, 3H, Me), 1.58 (s, 3H,
Generation of [{((4-Me-C6H4)2HC)HC(5-Me-py)2}PdMe-
(H2CdCH2)][B(C6F5)4] (8l). A valved NMR tube containing a
CD2Cl2 (0.7 mL) solution of 3l (11 mg, 20 µmol) and
[Li(Et2O)2.8][B(C6F5)4] (18 mg, 0.020 µmol) was cooled to -196