472
R. Metelková et al. / Electrochimica Acta 82 (2012) 470–477
946, 886, 848, 811, 755,678 cm−1. Anal. Calcd for C12H9CrNO6: C,
45.73; H, 2.88; N, 4.44. Found: C, 45.70; H, 3.27; N, 4.19.
Ground state electronic structure calculations have been done
by density-functional theory (DFT) method using Gaussian 09
[13] program package. B3LYP hybrid functional [14,15] was used
together with 6-311g(d) polarized triple- basis sets [16,17] for H,
C, N, O, S and Cr atoms.
Geometry of all the complexes was optimized without any sym-
metry constrains, vibrational analysis was used for characterization
of stationary points. For proper minima no imaginary frequen-
cies were found. MO analysis was done at optimized structures
using the same level of theory. MO plots were generated by the
GaussView software.
furyl)carbene]chromium(0)
(IIb)
It was prepared in a different way according to the reported
procedure [18].
2.3.4. Pentacarbonyl[(N,N-dimethylamino)(2-
thienyl)carbene]chromium(0)
(IIIa)
Mixture of hexane–dichloromethane (2:1) was used for the elu-
tion. Yellow crystals, yield 65%, M.p. >87 ◦C (decomp.). 1H NMR
(300 MHz, CDCl3): ı 3.22 (s, 1H, CH3), 4.00 (s, 1H, CH3), 6.53 (m, 1H,
CH), 6.98 (m, 1H, CH), 7.29 (m, 1H, CH). 13C NMR (75 MHz, CDCl3):
ı 46.6, 51.4, 118.2, 123.9, 127.0, 152.9, 216.8, 223.7, 270.2. IR: 2056,
1973, 1937, 1879, 1810, 1794, 1542, 1511, 1435, 1401, 1234, 1160,
2.3. Synthesis of aminocarbene complexes
2.3.1. General
2.3.1.1. Chemicals for carbene complexes. All experiments were
carried out under argon. Tetrahydrofuran was distilled from
benzophenone ketyl under argon prior to use. Chromium
hexacarbonyl and Me3SiCl were purchased from Aldrich
and were used without purification. Silica and alumina were
the corresponding acylchloride with excess of N,N-dimethylamine
in diethylether. N,N-dimethylthiophene-2-carboxamide [19],
1103, 1077, 1041, 1019, 935, 851, 825, 793, 741, 693, 669, cm−1
.
Anal. Calcd for C12H9CrNO5S: C, 43.51; H, 2.74; N, 4.23. Found: C,
2.3.5. Pentacarbonyl[(N,N-dimethylamino)(3-
thienyl)carbene]chromium(0)
(IIIb)
Mixture of hexane–dichloromethane (4:1) was used for the elu-
tion. Yellow crystals, yield 48%, M.p. 70–73 ◦C. 1H NMR (300 MHz,
CDCl3): ı 3.10 (s, 3H, CH3), 3.96 (s, 3H, CH3), 6.66 (m, 2H, CH), 7.37
(br s, 1H, CH). 13C NMR (75 MHz, CDCl3): ı 46.0, 51.0, 112.6, 121.8,
126.7, 153.3, 217.1, 223.7, 272.4. IR: 3742, 3121, 2951, 2871, 2053,
1975, 1939, 1917, 1848, 1544, 1514, 1451, 1401, 1357, 1233, 1211,
N,N-dimethylthiophene-3-carboxamide
[19],
2-bromo-1-
methylpyrrole[20], 3-bromo-1-methylpyrrole[20] were prepared
according to the reported procedures. Melting points were deter-
mined on a Kofler block and are uncorrected. 1H and 13C NMR
spectra were recorded on a Varian Gemini 300 spectrometer (1H
at 300 MHz, 13C at 75.4) in CDCl3.
1176, 1118, 1083, 1025, 955, 870, 845, 785, 753, 695, 678, 663 cm−1
.
Anal. Calcd for C12H9CrNO5S: C, 43.51; H, 2.74; N, 4.23. Found: C,
42.98; H, 2.92; N, 4.19.
2.3.1.2. General procedure for the preparation of chromium aminocar-
bene complexes. The solution of sodium naphthalenide prepared
from sodium (0.170 g, 7.4 mmol), naphthalene (0.947 g, 7.4 mmol)
in THF (5 mL) was slowly added under argon atmosphere to the
stirred suspension of Cr(CO)6 (0.63 g, 2.9 mmol) in THF (10 mL) at
−78 ◦C. The mixture was allowed to warm to 0 ◦C and kept at this
temperature until all solid carbonyl dissolved (0.5 h). After cool-
ing to −78 ◦C a solution of the corresponding amide (2.0 mmol) in
THF (5 mL) was added through a double-ended needle. The mix-
ture was stirred at −78 ◦C for 30 min and then 30 min at 0 ◦C. After
cooling to −78 ◦C, Me3SiCl (0.73 mL; 5.7 mmol) was added via a
syringe. The solution was stirred at −78 ◦C for 30 min, then the
cooling bath was removed, the mixture was allowed to warm to
0 ◦C and neutral alumina (8 g) was added. The solvent was removed
under reduced pressure on a rotatory evaporator (bath temperature
<30 ◦C) and the residue was dried under high vacuum to remove all
the THF. Then the sample was transferred on the top of a column
filled with 50 g of silica. Naphthalene was eluted with pure hex-
ane and further elution with a hexane–CH2Cl2 mixture gave the
product
2.3.6. Pentacarbonyl[(N,N-dimethylamino)(1-methyl-2-
pyrrolyl)carbene]chromium(0)
(IVa)
To the solution of 2-bromo-1-methylpyrrole (1.87 g, 11.7 mmol)
in THF (60 mL) n-BuLi (7.30 mL, 11.7 mmol, 1.6 M solution in hex-
ane) and TMEDA (1.70 mL, 11.7 mmol) in THF (60 mL) were added
at −78 ◦C. The resulting mixture was stirred 30 min at −78 ◦C and
then was allowed to warm to 0 ◦C. To such prepared solution
of 1-methyl-2-pyrrolyllithium chromium hexacarbonyl (3.08 g,
14.0 mmol) was added and the resultant mixture was stirred 12 h
at room temperature. The solvents were then evaporated in vacuo
at 0 ◦C. The residue was dissolved in CH2Cl2 (50 mL), cooled to
−30 ◦C followed by dropwise addition of acetyl bromide (0.87 mL,
11.7 mmol). The mixture was then stirred 30 min at −10 ◦C and
after recooling to −40 ◦C dimethylamine (20.0 mL, 20.0 mmol of
1 M solution in Et2O) was added. The mixture was stirred for
1 h without cooling, and neutral alumina (5 g) was added. Sol-
vents were removed under reduced pressure, and the residue
was dried under high vacuum. Column chromatography (silica
gel, hexane–dichloromethane, 2:1) afforded the title carbene com-
plex. Yellow crystals, yield 46%, M.p. >85 ◦C (decomp.). 1H NMR
(300 MHz, CDCl3): ı 3.04 (s, 3H, CH3), 3.33 (s, 3H, CH3), 3.99 (s, 3H,
CH3), 5.85 (m, 1H, CH), 6.15 (m, 1H, CH), 6.52 (m, 1H, CH). 13C NMR
(75 MHz, CDCl3): ı 33.6, 46.1, 50.5, 102.7, 108.7, 120.4, 142.9, 216.8,
224.0, 272.8. IR: 2945, 2052, 1973, 1889, 1536, 1517, 1469, 1442,
1397, 1350, 1297, 1230, 1176, 1120, 1085, 1053, 1024, 1006, 900,
832, 776, 702, 660, 646, 604, 591, 559, 455 cm−1. Anal. Calcd for
C13H12CrN2O5: C, 47.57; H, 3.68; N, 8.53. Found: C, 47.21; H, 3.65;
N, 8.48.
2.3.2. Pentacarbonyl[(N,N-dimethylamino)(2-
furyl)carbene]chromium(0)
(IIa)
Mixture of hexane–dichloromethane (2:1) was used for the elu-
tion. Yellow crystals, yield 41%, M.p. 60–63 ◦C. 1H NMR (300 MHz,
CDCl3): ı 3.32 (s, 3H, CH3), 3.97 (s, 3H, CH3), 6.33 (m, 1H, CH), 6.48
(m, 1H, CH), 7.50 (m, 1H, CH). 13C NMR (75 MHz, CDCl3): ı 48.1,
51.5, 107.8, 111.4, 142.3, 158.7, 217.0, 223.8, 260.5. IR: 3162, 3141,
2993, 2951, 2925, 2854, 2054, 1976, 1944, 1863, 1786, 1551, 1524,
1457, 1400, 1381, 1223, 1247, 1204, 1163, 1118, 1087, 1033, 1027,