Benzyl- or p-cyanobenzyl-substituted NHC-silver complexes
for 24 h. The volatile components were removed, and the crude
product was re-dissolved in dichloromethane. The solid, presum-
ably KI, was filtered and discarded, and the volatile components
were removed in vacuo to yield a yellow crystalline solid (1.32 g,
8.72 mmol, 97.0% yield) (5b).
1H NMR (δ ppm CDCl3, 400 MHz): 7.36 (s, 1H, NCHN), 3.61 (s, 3H,
N-CH3). 13CNMR(δ ppmCDCl3, 100 MHz, protondecoupled):134.6
(NCN), 125.5, 113.7 (CCl), 32.5 (N-CH3). IR absorptions (KBr, cm−1):
3437 (m), 3099 (s), 2953 (w), 1663 (w), 1521 (s), 1494 (s), 1463 (w),
1362 (m), 1262 (s), 1209 (m), 1126 (s), 988 (s), 835 (m), 721 (m), 666
(s), 623 (m), 540 (m). UV–vis (CH3OH, nm): λ 225 (ε 4371), λ 275 (ε
933). MS (m/z, QMS-MS/MS): 150.92 [M+]. Microanalysis calculated
for C4H4N2Cl2 (150.99): calcd–C, 31.81%; H, 2.67%; N, 18.55%; Cl,
46.95%; found–C, 31.37%; H, 2.59%; N, 18.05%; Cl, 46.40%.
Synthesis of (1-methyl-3-benzylimidazole-2-ylidene) silver(I) acetate
(8a)
1-Methyl-3-benzylimidazolium bromide (0.253 g, 1.00 mmol) was
dissolved in dichloromethane (40 ml), silver acetate (0.333 g,
2.00 mmol) was added, and the mixture was refluxed for 2 d.
The precipitate, presumably AgBr, was filtered and a clear solution
was obtained. The volatile components were removed in vacuo
to produce an off-white sticky solid. The solid was washed with
pentane and dried under reduced pressure to yield (0.080 g,
0.235 mmol, 23.6% yield) 8a.
1H NMR (δ ppm CDCl3, 400 MHz): 7.42–7.24 (m, 5H, CHBenzyl),
6.97 (d, J = 1.7 Hz, 1H, CHImid), 6.92 (d, J = 1.7 Hz, 1H, CHImid),
5.27 (s, 2H, CH2), 3.85 (s, 3H, N-CH3), 2.07 (s, 3H, COCH3). 13C NMR
(δ ppm CDCl3, 125 MHz, proton decoupled): 179.9 (NCN), 177.9
(C O), 135.5, 129.0, 128.5, 127.9, 122.5, 121.0 (CBenzyl + CImid), 55.7
(CH2), 38.8 (N-CH3), 22.5 (COCH3). IR absorption (KBr, cm−1): 3382
(w), 3135 (w), 3096 (w), 1579 (s), 1406 (s), 1158 (s), 1082 (w), 1018
(m), 919 (m), 819 (w), 721 (s), 646 (m), 621 (w), 463 (w). UV–vis
(CH3OH, nm): λ 219 (ε 4075), λ 230 (ε 3008), λ 269 (ε 1878). MS
(m/z, QMS-MS/MS): 280.10 [M+-O2CCH3]. Microanalysis calculated
for C13H15N2O2Ag (339.14): calcd–C, 46.04%; H, 4.45%; N, 8.26%;
Ag, 31.80%; found–C, 45.86%; H, 5.01%; N, 8.31%; Ag, 30.39%.
Synthesis of 4,5-dichloro-1-methyl-3-benzylimidazolium bromide
(7b)
Benzyl bromide (2.37 ml, 20.0 mmol) was added in one portion
to a stirred suspension of 4,5-dichloro-1-methylimidazole (1.50 g,
10.0 mmol) in 40 ml of toluene. The mixture was stirred for 48 h
at room temperature. Afterwards the solvent was removed under
reduced pressure. The resulting yellow residue was saturated with
diethyl ether to get a light yellow precipitate, which was filtered,
washed with diethyl ether and finally dried in vacuo in order to
give compound 7b (2.05 g, 6.36 mmol, 63.7% yield).
Synthesis of (4,5-dichloro-1-methyl-3-benzylimidazole-2-ylidene)
silver(I) acetate (8b)
1H NMR (δ ppm CDCl3, 400 MHz): 11.29 (s, 1H, NCHN), 7.56 (d,
J = 6.2 Hz, 2H, CHBenzyl), 7.47–7.34 (m, 3H, CHBenzyl), 5.64 (s, 2H,
CH2), 4.08 (s, 3H, N-CH3). 13C NMR (δ ppm CDCl3, 100 MHz, proton
decoupled): 138.0 (NCN), 131.6, 129.6, 129.4, 128.9 (CBenzyl), 119.9,
118.9 (CCl), 52.6 (CH2), 35.6 (N-CH3). IR absorptions (KBr, cm−1):
3410 (s), 3363 (s), 3121 (w), 3068 (m), 2918 (m), 2865 (w), 1629 (w),
1583 (m), 1560 (m), 1455 (s), 1346 (w), 1261 (w), 1160 (s), 1096 (w),
1029 (w), 801 (w), 732 (m), 703 (m), 621 (w). UV–vis (CH3OH, nm):
λ 228 (ε 4894), λ 274 (ε 2665). MS (m/z, QMS-MS/MS): 242.13 [M+-
Br]. Microanalysis calculated for C11H11N2Cl2Br (322.03): calcd–C,
41.02%; H, 3.44%; N, 8.69; Br, 24.81%; Cl, 22.01%; found–C, 41.78%;
H, 3.43%; N, 8.57%; Br, 24.37%; Cl, 21.79%.
4,5-Dichloro-1-methyl-3-benzylimidazolium bromide (0.253 g,
1.00 mmol) was dissolved in CH2Cl2 (40 ml) and silver acetate
(0.333 g, 2.00 mmol) was added. The mixture was stirred at room
temperature for 1 day. The yellow precipitate of AgBr was filtered
and a clear solution was obtained. The volatile components were
removed in vacuo to produce an off-white sticky solid. The solid
was washed with diethyl ether and dried under reduced pressure
to yield (0.150 g, 0.367 mmol, 36.8% yield) 8b as a white solid.
1H NMR (δ ppm CDCl3, 400 MHz): 7.47–7.01 (m, 5H, CHBenzyl),
5.25 (s, 2H, CH2), 3.76 (s, 3H, N-CH3), 1.99 (s, 3H, COCH3). 13C NMR
(δ ppm CDCl3, 100 MHz, proton decoupled): 180.1 (NCN), 179.0
(C O), 134.1, 129.0, 128.7, 127.7, 118.2, 117.4 (CCl + CBenzyl), 54.5
(CH2), 38.0 (N-CH3), 22.6 (COCH3). IR absorptions (KBr, cm−1): 3443
(s), 3064 (w), 1575 (s), 1405 (m), 1338 (w), 1261 (w), 1130 (w), 1097
(w), 1022 (w), 800 (w), 746 (w), 704 (m), 468 (w). UV–vis (CH3OH,
nm): λ 216 (ε 13 422), λ 241 (ε 8362), λ 280 (ε 4414). MS (m/z,
QMS-MS/MS): 348.22 [M+-O2CCH3]. Microanalysis calculated for
C13H13N2O2Cl2Ag (408.03): calcd–C, 38.26%; H, 3.21%; N, 6.86%;
Cl, 17.37%; Ag, 26.43%; found–C, 37.85%; H, 3.13%; N, 6.66%; Cl,
17.25%; Ag, 26.21%.
Synthesis of 1-methyl-3-benzylbenzimidazolium bromide (7c)
Benzyl bromide (2.37 ml, 20.0 mmol) was added in one portion to
a stirred suspension of 1-methylbenzimidazole (1.32 g, 10.0 mmol)
in 40 ml of toluene. The mixture was stirred for 4 days at room
temperature. Afterwards the solvent was removed under reduced
pressure. The resultant residue was washed four times with diethyl
ether and dried in vacuo to yield (2.75 g, 9.06 mmol, 90.7% yield) a
colourless solid 7c.
1H NMR (δ ppm CDCl3, 400 MHz): 11.38 (s, 1H, NCHN), 7.76 (d,
J = 8.2 Hz, 1H, CHBenzimid), 7.66–7.53 (m, 5H, CHBenzyl), 7.38–7.30
(m, 3H, CHBenzimid), 5.89 (s, 2H, CH2), 4.29 (s, 3H, N-CH3). 13C NMR (δ
ppmCDCl3,100 MHz,protondecoupled):142.0,131.7,131.1,129.9,
Synthesis of (1-methyl-3-benzylbenzimidazole-2-ylidene) silver(I)
acetate (8c)
1-Methyl-3-benzylbenzimidazolium bromide (0.322 g, 1.00 mmol)
was dissolved in dichloromethane (50 ml) and silver acetate
(0.333 g, 2.00 mmol) was added. The mixture was stirred at room
temperature for 1 day. The yellow precipitate, presumably AgBr,
was filtered and discarded. The volume of the reaction mixture
was reduced under pressure to 5 ml. Pentane (200 ml) was added
and the fine white precipitate was filtered out, washed with diethyl
etheranddriedinvacuotoyieldawhitesolid(0.260 g, 0.668 mmol,
66.8% yield) 8c.
128.3, 128.1, 127.3, 126.2, 124.2, 112.7, 112.0 (NCN + CBenzimid
+
CBenzyl), 50.3 (CH2), 33.0 (CH3). IR absorptions (KBr, cm−1): 3410 (s),
3131 (w), 3065 (m), 2965 (w), 1562 (s), 1490 (w), 1458 (m), 1424
(w), 1384 (m), 1348 (w), 1277 (w), 1195 (m), 1094 (w), 1018 (w),
874 (w), 757 (s), 713 (m), 659 (w). UV–vis (CH3OH, nm): λ 222 (ε
7831), λ 250 (ε 6382), λ 269 (ε 6270). MS (m/z, QMS-MS/MS): 223.41
[M+-Br-H2O]. Microanalysis calculated for C15H17N2BrO (321.21):
calcd–C, 56.09%; H, 5.33%; N, 8.72%; Br, 24.88%; found–C, 56.31%;
H, 5.08%; N, 8.98%; Br, 24.15%.
1H NMR (δ ppm CDCl3, 400 MHz): 7.59–7.09 (m, 9H, CHBenzimid
CHBenzyl), 5.61 (s, 2H, CH2), 4.08 (s, 3H, N-CH3), 2.11 (s, 3H, COCH3).
13C NMR (δ ppm CDCl3, 125 MHz, proton decoupled): 180.0 (NCN),
+
c
Appl. Organometal. Chem. 2010, 24, 781–793
Copyright ꢀ 2010 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc