E. Tyrrell et al. / Journal of Organometallic Chemistry 696 (2011) 3465e3472
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4.2.2. 1-(Trimethoxysilyl)propyl-3-mesitylimidazolium bromide
(1b)
was accomplished by trituration with anhydrous diethyl ether
(3 ꢁ 20 mL), yielding the title compound 6b as a yellow solid
(0.530 g, 47%, as a mixture of trans-syn- and trans-anti-rotamers).
1H NMR (400 MHz, CHCl3): 6.95e7.00 (m, 3H, Ar-H), 6.91e6.93 (m,
1H, Ar-H imid.), 6.81e6.86 (m, 2H, Ar-H), 6.69e6.72 (m, 1H, Ar-H),
6.62e6.66 (m, 1H, Ar-H), 4.54e4.70 (m, 2H, alkyl-CH2, syn-isomer),
4.11e4.26 (m, 2H, alkyl-CH2, anti-isomer), 3.56e3.60 (s, 18H, OCH3),
2.41e2.48 (s, 3H, p-CH3, syn-isomer), 2.34e2.38 (s, 3H, p-CH3, anti-
isomer), 2.15e2.30 (m, 8H, alkyl-CH2, syn-isomer and o-CH3, syn-
isomer overlapping), 1.85e1.94 (m, 8H, alkyl-CH2, anti-isomer and
o-CH3, anti-isomer overlapping), 0.79e0.95 (m, 2H, alkyl-CH2, syn-
isomer), 0.45e0.53 (m, 2H, alkyl-CH2, anti-isomer). 13C NMR
(100 MHz, CHCl3): 170.9, 170.5, 138.4, 137.5, 137.4, 136.9, 136.8,
136.5, 136.2, 136.0, 135.7, 135.6, 128.88, 128.83, 128.79, 128.75,
122.65, 122.55, 122.4, 122.25, 121.0, 120.9, 120.85, 120.75, 53.28,
53.1, 53.03, 52.87, 50.7, 24.45, 24.3, 24.1, 24.0, 21.35, 21.08, 19.65,
19.23, 19.13, 19.0, 18.95, 18.88, 18.7, 18.55, 6.44, 6.39, 6.1, 6.07. Note:
duplication of all signals observed as a result of syn- and anti-
isomerism. MS (EI): m/z 835 (Mþ ꢂ Cl). HRMS (EI): calculated for
C36H56O6N4Si2Pd; 870.2161, found: 870.2161.
This was synthesised as described for 1a using N-mesitylimi-
dazole (0.930 g, 5 mmol). Trituration in diethyl ether (3 ꢁ 50 mL)
provided the title compound as an off-white solid (MP: 120e123 ꢀC,
1.846 g, 86%). 1H NMR (400 MHz, CHCl3): 10.05e10.09 (s, 1H, Ar-H),
7.88e7.91 (m, 1H, Ar-H), 7.19e7.21 (m, 1H, Ar-H), 6.82e6.85 (s, 2H,
Ar-H), 4.50e4.56 (t, J ¼ 6.96 Hz, 2H, alkyl-CH2), 3.38e3.42 (s, 9H,
OeCH3), 2.16e2.19 (s, 3H, eCH3), 1.88e1.99 (m, 8H, alkyl-CH2 and
Ar-CH3 overlapping), 0.48e0.55 (t, J ¼ 8.06 Hz, 2H, alkyl-CH2). 13
C
NMR (100 MHz, CHCl3): 141.1, 137.6, 134.1, 130.7, 129.8, 123.6, 123.5,
51.9, 50.7, 24.3, 21.1, 17.6, 5.6. MS (ES): 349 m/z (Mþ ꢂ Br). HRMS
(EI): calculated for C18H29O3N2Si; 349.1942, found: 349.1939.
4.2.3. 1-(Trimethoxysilyl)propyl-3-(20,60-diisopropylphenyl)
imidazolium bromide (1c)
N-(2,6-diisopropylphenyl)imidazole (764 mg, 3.2 mmol) in
acetonitrile (20 mL) was added to a dry, round-bottomed flask
under an atmosphere of nitrogen. 3-(bromopropyl)trimethox-
ysilane (684 mg, 3.2 mmol) was added and the mixture heated to
100 ꢀC for 7 h. After cooling to room temperature, the solvent was
removed in vacuo and the crude product (now solid) was triturated
in diethyl ether (3 ꢁ 50 mL) to yield the title compound 1c as an off-
white solid (MP: 116e118 ꢀC, 1.17 g, 76%). 1H NMR (400 MHz,
CHCl3): 10.30e10.36 (s, 1H, Ar-H), 7.91e7.94 (s, 1H, Ar-H), 7.47e7.55
(m, 1H, Ar-H), 7.25e7.30 (m, 2H, Ar-H), 7.19e7.22 (m, 1H, Ar-H),
4.74e4.81 (t, J ¼ 6.96 Hz, 2H, alkyl-CH2), 3.52e3.57 (s, 9H,
OeCH3), 2.19e2.30 (septet, J ¼ 6.96 Hz, 2H, alkyl-CH), 2.04e2.14
(quintet, J ¼ 8.06 Hz, 2H, alkyl-CH2), 0.63e0.69 (t, J ¼ 8.06 Hz, 2H,
alkyl-CH2). 13C NMR (100 MHz, CHCl3): 145.4, 138.4, 132.0, 130.2,
124.8, 124.2, 123.2, 52.1, 50.8, 28.8, 24.5, 24.2, 5.6. MS (ES): 391 m/z
(Mþ ꢂ Br). HRMS (EI): calculated for C19H35O3N2Si; 391.2411, found:
391.2401.
4.2.6. Bis-1-(trimethoxysilyl)-3-benzylimidazol-2-ylidene
palladium dichloride (5a)
As
described
using
1-(trimethoxysilyl)propyl-3-
benzylimidazolium bromide 1a (0.399g, 1 mmol) was used as the
imidazolium salt (adjusting the quantities of the other reagents
according to this stoichiometry). The title compound was obtained
as a bright yellow solid (0.205 g, 56%). 1H NMR (400 MHz, CHCl3):
7.15e7.50 (m, 14H, Ar-H), 5.49e5.82 (m, 4H, benzyl-CH2, syn- and
anti-isomers), 4.32e4.49 (m, 4H, alkyl-CH2, syn- and anti-isomers),
3.39e3.55 (m, 18H, eOCH3, several overlapping signals), 2.02e2.35
(m, 4H, alkyl-CH2, syn- and anti-isomers), 0.63e0.89 (m, 4H, alkyl-
CH2, syn- and anti-isomers). 13C NMR (100 MHz, CHCl3):Not
reported due to overlapping signals originating from syn- and anti-
isomers. HRMS (EI): calculated for C32H48O6N4Si2Pd; 814.1535,
found: 814.1537.
4.2.4. 1-(Trimethoxysilyl)propyl-3-(20,60-diisopropylphenyl)
imidazolium iodide (1d)
The procedure was carried out as described for 1c using N-(2,6-
diisopropylphenyl)imidazole (764 mg, 3.2 mmol) and 3-
iodopropyltrimethoxysilane (3.2 mmol). The title compound 1d
was isolated as an orange oil (1.38 g, 96%). 1H NMR (400 MHz,
CHCl3): 9.87e9.91 (s, 1H, Ar-H), 8.01e8.05 (s, 1H, Ar-H), 7.43e7.51
(m, 1H, Ar-H), 7.20e7.27 (m, 3H, Ar-H), 4.64e4.71 (t, J ¼ 6.96 Hz, 2H,
alkyl-CH2), 3.46e3.54 (s, 9H, OeCH3), 2.14e2.26 (septet, J ¼ 6.77 Hz,
2H, alkyl-CH), 1.99e2.09 (quintet, J ¼ 8.06 Hz, 2H, alkyl-CH2),
1.05e1.17 (dd, J ¼ 6.77 Hz, 12H, eCH3), 0.57e0.65 (t, J ¼ 8.06 Hz, 2H,
alkyl-CH2). 13C NMR (100 MHz, CHCl3): 145.1, 137.0, 131.7, 129.7,
124.4, 124.3, 123.6, 51.8, 50.6, 28.4, 24.3, 24.2, 24.0, 5.2. MS (ES):
391 m/z (Mþ ꢂ I).
4.2.7. Bis-1-(trimethoxysilyl)-3-(20,60-diisopropylphenyl)imidazol-
2-ylidene palladium dichloride (5c)
As described using 1-(trimethoxysilyl)propyl-3-(20,60-diisopro-
pylphenyl) imidazolium bromide (0.235 g, 0.5 mmol) was used as
the imidazolium salt (adjusting the quantities of the other reagents
according to this stoichiometry). The title compound was obtained
as a dull-yellow solid (0.112 g, 47%). 1H NMR (400 MHz, CHCl3):
7.26e7.36 (m, 6H, Ar-H), 6.89e7.08 (m, 2H, Ar-H), 6.65e6.81 (m, 2H,
Ar-H), 4.67e4.89 (m, 2H, alkyl-CH2, syn-isomer), 4.05e4.39 (m, 2H,
alkyl-CH2, anti-isomer), 3.43e3.63 (m, 18H, eOCH3), 2.80e3.01 (m,
2H, alkyl-CH2, syn-isomer), 2.52e2.73 (m, 2H, alkyl-CH2, anti-
isomer), 2.20e2.38 (m, 2H, alkyl-CH, syn-isomer), 1.73e1.84 (m,
2H, alkyl-CH, syn-isomer), 0.75e1.41 (m, 28H, alkyleCH3 and alkyl-
CH2). 13C NMR (100 MHz, CHCl3) Not reported due to overlapping
signals originating from syn- and anti-isomers. HRMS (EI): calcu-
lated for C42H68O6N4Si2Pd; 954.3089, found: 954.3090.
4.2.5. Bis-1-(trimethoxysilyl)-3-mesitylimidazol-2-ylidene
palladium dichloride (5b)
1-(Trimethoxysilyl)propyl-3-mesitylimidazolium bromide 1b
(1.287 g, 3 mmol) was added to a dry, light-protected Schlenk tube
under a nitrogen atmosphere. To this was added silver (I) oxide
(0.348 g, 1.5 mmol) and anhydrous chloroform (7.5 mL) and the
resulting mixture was stirred at room temperature overnight. The
mixture was carefully removed under continuous nitrogen flow, by
pipette and filtered through celite directly into another dry, light-
protected Schlenk tube under nitrogen (an extra 2.5 mL of anhy-
drous chloroform was used to dissolve any product remaining in
the original vessel). The white precipitate was discarded. Bis-
(benzonitrile)palladium (II) dichloride (0.504 g, 1.3 mmol) was
added gradually and the mixture was stirred overnight. The
mixture (bright-yellow) was again filtered through celite and the
solvent removed in vacuo to yield the crude product. Purification
4.2.8. General procedure for immobilisation of imidazolium salts
1aec
Under nitrogen, a dry round-bottomed flask was charged with
imidazolium salt (1 mmol), anhydrous toluene (60 mL) and silica
gel (1.00 g, pre-dried). The mixture was fitted with a DeaneStark
trap and refluxed for 24 h. After cooling to room temperature, the
mixture was filtered and washed with anhydrous dichoromethane
(3 ꢁ 50 mL). The resulting white solid was dried in vacuo at 60 ꢀC
over phosphorous pentoxide (24 h) to yield the modified support
material (>95% by weight). 1H NMR analysis of the dichloro-
methane washings showed no trace of the imidazolium salt starting