Organometallics
Article
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Other nuclei were referenced to an external standard: H3PO4 (31P),
H2PtCl6·6H2O in 30% v/v D2O/1 M HCl (195Pt), all at 0 ppm.
Infrared spectra were recorded on a Thermo Scientific Nicolet 6700
series spectrometer. GC-MS analyses were performed on an HP
Model 6890N chromatograph equipped with a 30 m × 25 mm × 0.40
μm HP5-1 column and equipped with an HP 5973 mass-selective EI
detector. High-resolution mass spectra (HRMS) were obtained at the
California Institute of Technology Mass Spectral Facility.
Minor isomer (Z)-2,3-diisopropoxybut-2-ene: H NMR (500 MHz,
CD2Cl2) δ 4.15 (m, 2H), 1.67 (s, 6H), 1.12 (d, J = 6.0 Hz, 12H); 13
C
NMR (126 MHz, CD2Cl2) δ 135.47, 79.51, 22.91, 12.52. (E/Z)-2,3-
diisopropoxybut-2-ene: HRMS (EI) m/z calcd for C10H20O2 [M]+
172.1463, found 172.1493.
General Procedure for Reaction of Bis(carbene)platinum(II)
Complexes with Pyridine. In a J. Young NMR tube was added
0.040 g (0.10 mmol) of bis(carbene) 3 as a solution in THF-d8, and
8.5 μL (0.11 mmol) of pyridine was added via microsyringe. The
NMR tube was sealed and heated in an oil bath at 55 °C for 2 h,
during which time the reaction mixture changed from colorless to a
dichroic green/red solution. The reaction mixture was filtered through
Celite, and solvent was removed from the filtrate, resulting in isolation
of a dark green oil. Despite repeated attempts to purify the product,
analytically pure material could not be obtained.
Synthesis of Compounds. Coupling of (CO)5Cr{C(OMe)(p-
MeOC6H4)} with Pt(PPh3)4. To a J. Young NMR tube was added a
solution of 32.1 mg (0.094 mmol) of Cr(carbene) 1 and 7.4 mg
(0.0059 mmol) of Pt(PPh3)4 in THF-d8. Conversion to 13% of
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dimerization product 2 (by H NMR integration) took place over 9
days; the formation of a Pt mirror was observed to form on the NMR
tube over time. Subsequent heating in a 50 °C oil bath for 16 h did not
result in any further conversion of 1 to 2. 2 has been reported in the
literature,19 but we were unable to find suitable spectral data for the
compound; therefore, we synthesized 2 independently by reacting 18.5
mg (0.054 mmol) of Cr(carbene) 1 with 10 mol % of Pd2dba3 in
dichloromethane-d2. During stirring for 48 h at ambient temperature
the solution changed from bright red to dark brown with visible Pd
black precipitation. The solvent was removed from the reaction
mixture, and the resulting dark brown residue was dissolved in diethyl
ether and filtered through a plug of silica gel. Removal of solvent from
the filtrate gave 2 as a pale yellow powder. Yield: 74% . Data for (E/
Z)-1,2-dimethoxy-1,2-bis(4-methoxyphenyl)ethane (2) are as follows.
1H NMR (300 MHz, THF-d8): δ 7.64 (d, J = 8.3 Hz, 2H, ArH), 7.06
(d, J = 8.3 Hz, 2H, ArH), 6.91 (d, J = 8.4 Hz, 2H, ArH), 6.70 (d, J =
8.2 Hz, 2H, ArH), 3.80 (s, 3H, OCH3), 3.71 (s, 3H, OCH3), 3.51 (s,
3H, OCH3), 3.28 (s, 3H, OCH3). 13C NMR (126 MHz, THF-d8): δ
160.16, 160.10, 145.29, 143.57, 131.65, 130.29, 128.63, 127.70, 114.14,
114.11, 58.24, 55.40, 55.30. HRMS (FAB): m/z calcd for C18H20O4
[M]+ 300.1362, found 300.1359.
Cl2Pt{C(OMe)(Me)}2 (3). Complex 3 was prepared by a modified
literature procedure. A 2.00 g amount (3.86 mmol) of hexachlor-
oplatinic acid was dissolved in 12 mL of dry MeOH, and 5.3 mL (23.4
mmol) of bis(trimethylsilyl)acetylene was added via syringe. The
orange solution was stirred at 49 °C; after 3 h, the solution turned
yellow and white solids formed. Approximately two-thirds of the
solvent was removed in vacuo, and the white solid was filtered and
washed three times with 3 mL portions of MeOH. In some
preparations a yellow solid was obtained, which could be further
purified by dissolving in dichloromethane and filtering through a glass
frit; removal of solvent from the filtrate resulted in a white powder.
The identity of the compound was confirmed by comparison with the
reported spectroscopic data.
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Cl(py)Pt(COMe){C(OMe)(Me)} (8). Dark green oil. Yield: 93%. H
NMR (300 MHz, THF-d8): δ 8.88 (m, 2H, o-CH), 7.91 (t, J = 7.7, 1H,
4
p-CH), 7.49 (t, J = 7.0, 2H, m-CH), 5.04 (s, 3H, JPt,H = 7.9 Hz,
OCH3), 2.69 (s, 3H, 3JPt,H = 22.3 Hz, CCH3), 1.89 (s, 3H, 3JPt,H = 21.7
Hz, COCH3). 13C NMR (126 MHz, THF-d8): δ 283.0 (s, 1JPt,C = 1428
1
3
Hz, PtC), 212.8 (s, JPt,C = 1130 Hz, Pt−COMe), 152.9 (s, JPt,C
=
16 Hz, o-CH), 139.7 (s, p-CH), 126.1 (s, 4JPt,C = 24 Hz, m-CH), 70.47
3
2
(s, JPt,C = 116 Hz, OCH3), 44.68 (s, JPt,C = 355 Hz, COCH3), 42.52
(s, 2JPt,C = 170 Hz, CCH3). 195Pt NMR (107 MHz, CD2Cl2): δ −2431.
IR (THF): νCO 1639 cm−1. This compound is air and moisture
sensitive, and despite repeated attempts the molecular ion peak
calculated for C10H14ClNO2Pt [M + H]+ 410.0361 could not be
detected. The ion fragment [M − Me] was detected in the sample of
8. HRMS (FAB): m/z calcd for C9H11ClNO2Pt [M − Me] 396.0116,
found 396.0113.
Br(py)Pt(COMe){C(OMe)(Me)} (9). This compound was obtained
similarly as a yellow oil. Yield: 98%. H NMR (300 MHz, THF-d8): δ
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8.90 (m, 2H, o-CH), 7.90 (m, 1H, p-CH), 7.48 (dd, J = 7.1, 5.8, 2H,
m-CH), 5.01 (s, 3H, 4JPt,H = 7.4 Hz, OCH3), 2.74 (s, 3H, 3JPt,H = 22.7
Hz, CCH3), 1.90 (s, 3H, JPt,H = 22.0 Hz, COCH3). 13C NMR (126
3
MHz, THF-d8): δ 282.9 (s, 1JPt,C = 1408 Hz, PtC), 212.7 (s, 1JPt,C
=
1138 Hz, Pt−COMe), 153.2 (s, 3JPt,C = 17 Hz, o-CH), 139.5 (s, p-CH),
4
3
126.0 (s, JPt,C = 24 Hz, m-CH), 70.36 (s, JPt,C = 116 Hz, OCH3),
2
2
43.53 (s, JPt,C = 370 Hz, COCH3), 42.39 (s, JPt,C = 169 Hz, CCH3).
IR (THF): νCO 1642 cm−1. HRMS (FAB): m/z calcd for
C10H15BrNO2Pt [M + H]+ 454.9914, found 455.9917.
Cl(py)Pt(COMe){C(OiPr)(Me)} (10). The reaction of 5 with pyridine
was slower than those of 3 and 4; the sealed J. Young NMR tube
containing the reaction mixture was heated for 21 h at 55 °C, and
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similar workup gave 10 as an orange oil. Yield: 98%. H NMR (300
MHz, THF-d8): δ 8.87 (m, 2H, o-CH), 7.90 (m, 1H, p-CH), 7.47
(ddd, J = 7.7, 5.0, 1.5 Hz, 2H, m-CH), 7.00 (sp, 1H, OCH), 2.67 (s,
General Procedure for Reduction of Bis(carbene)platinum(II)
Complexes. In a J. Young NMR tube was added 20.2 mg (0.053
mmol) of bis(carbene) 3 in dichloromethane-d2, followed by 19.9 mg
(0.11 mmol) of CoCp2 in dichloromethane-d2, resulting in an
immediate color change of the solution from nearly colorless to
dark brown and the formation of a Pt mirror on the NMR tube. (E/
3
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3H, JPt,H = 23.0 Hz, CCH3), 1.91 (s, 3H, JPt,H = 20.3 Hz, COCH3),
1.59 (d, J = 6.3 Hz, 6H, CH(CH3)2). 13C NMR (126 MHz, THF-d8):
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δ 276.9 (s, JPt,C = 1421 Hz, PtC), 213.5 (s, JPt,C = 1125 Hz, Pt−
3
COMe), 153.0 (s, JPt,C = 17 Hz, o-CH), 139.6 (s, p-CH), 126.1 (s,
4JPt,C = 25 Hz, m-CH), 91.58 (s, 3JPt,C = 107 Hz, OCH), 44.46 (s, 2JPt,C
1
2
Z)-2,3-dimethoxybut-2-ene (6) was the only product observed by H
= 351 Hz, COCH3), 42.72 (s, JPt,C = 164 Hz, CCH3), 21.94
(CH(CH3)2). IR (THF): νCO 1638 cm−1. HRMS (FAB): m/z calcd
for C12H18NO2ClPt [M + H]+ 438.0674; found 438.0649.
NMR spectroscopy. 6 was isolated by vacuum transfer to a clean J.
Young tube. Yield: 64%. Data for 6 (product ratio 1/2.36) are as
follows. Major isomer (E)-2,3-dimethoxybut-2-ene: 1H NMR (300
MHz, CD2Cl2) δ 3.43, 1.77; 13C NMR (75 MHz, CD2Cl2) δ 140.9,
56.79, 10.81. Minor isomer (Z)-2,3-dimethoxybut-2-ene: 1H NMR
(300 MHz, CD2Cl2) δ 3.50, 1.71; 13C NMR (75 MHz, CD2Cl2) δ
137.1, 57.12, 13.95. (E/Z)-2,3-dimethoxybut-2-ene: GC−MS m/z (%
relative intensity, ion) 116 (43, M), 101 (73, M − Me), 73 (62), 43
(100).
The analogous reaction of 4 with CoCp2 gave 6 in 49% yield. In the
analogous reaction of 5, attempts to isolate 7 by vacuum transfer
resulted in decomposition to unidentified products. 7 was therefore
characterized in the presence of [CoCp2]Cl in the crude reaction
mixture; side products in the reaction could not be identified. Yield:
41%. Major isomer (E)-2,3-diisopropoxybut-2-ene: 1H NMR (500
MHz, CD2Cl2) δ 3.96 (m, 2H), 1.72 (s, 6H), 1.11 (d, J = 6.1 Hz,
12H); 13C NMR (126 MHz, CD2Cl2) δ 138.80, 69.45, 22.51, 12.52.
[Cl2Pt(COMe){C(OMe)(Me)}]nBu4NCl (11). To a J. Young NMR
tube was added 30.0 mg (0.078 mmol) of 3 in dichloromethane-d2.
Addition of 21.8 mg (0.078 mmol) of nBu4NCl as a solution in
dichloromethane-d2 to the NMR tube resulted in an immediate color
change of the solution from nearly colorless to bright yellow. 11 was
the only product observed to form by 1H NMR spectroscopy.
Removal of solvent from the reaction mixture followed by trituration
with pentane resulted in isolation of a pale yellow powder. Yellow
crystals of 11 were obtained by carefully layering pentane onto a
concentrated THF solution of 11 at ambient temperature. Yield: 87%
1
4
(44.5 mg). H NMR (300 MHz, CD2Cl2): δ 4.89 (s, 3H, JPt,H = 8.7
3
Hz, OCH3), 3.23 (m, 8H, NCH2CH2CH2CH3), 2.44 (s, 3H, JPt,H
=
23.2 Hz, CCH3), 2.23 (s, 3H, 3JPt,H = 14.3 Hz, COCH3), 1.65 (m, 8H,
NCH2CH2CH2CH3), 1.45 (m, 8H, NCH2CH2CH2CH3), 1.01 (t, J =
7.3 Hz, 12H, NCH2CH2CH2CH3). 13C NMR (75 MHz, CD2Cl2) δ
6656
dx.doi.org/10.1021/om300733h | Organometallics 2012, 31, 6652−6657