Organometallics
Article
DFT grid. Here, we used the finer m5 grid throughout. Pictures of
molecular orbitals and geometries were made with the TmoleX
graphical user interface. Orbital pictures were constructed using
isovalues of 0.05.
300 MHz): δ 9.86 (1H, t, J = 1.7 Hz), 8.13 (1H, t, J = 1.7 Hz), 7.97
(1H, t, J = 1.7 Hz), 7.54−7.37 (5H, m), 7.15 (2H, s), 5.59 (2H, s),
3.33 (3H, s), 2.33 (3H, s), 2.01 (6H, s). 13C NMR (d6-DMSO, 75
MHz): δ 140.2, 137.8, 135.0, 134.1, 131.4, 129.2, 129.0, 128.7, 128.2,
124.2, 123.2, 52.0, 20.5, 16.9. HRMS (EI) calculated for C19H20N2 m/z
276.1626 (M). Found 276.1625.
All the transmetalation reactions were performed under argon using
standard Schlenk techniques. DCM was distilled over CaH2. All the
other solvents were obtained as HPLC quality and used as received.
1H and 13C NMR spectra were recorded at room temperature (except
the reaction kinetics experiments) using a Varian Mercury 300 or
Varian Inova 500 machine. 1H and 13C spectra were referenced to the
solvent signals (in CDCl3, 7.26 and 77.16 ppm, respectively; in d6-
DMSO, 2.50 and 39.52 ppm, respectively). High-resolution mass
spectra (EI) were obtained on MS JEOL JMS-700 and HR-ESI MS
with Bruker MicroTOF instruments.
Compounds 1 and 4 were synthesized and characterized according
to the literature as well as 5 and 6.18c,23,19c,37 Trimethylphenylimida-
zole and PhICl2 were prepared as reported.38,39 Me2SAuCl was
prepared by directly mixing Me2S and HAuCl4 in methanol and
collected by filtration.
4.2. X-ray Data of B. Crystals suitable for X-ray diffraction of B
were grown from dichloroethane solution. Crystal structure determi-
nations was performed on a Nonius KappaCCD diffractometer at
123(2) K using Mo Kα radiation (λ = 0.71073 Å). Direct methods
were used for structure solution (SHELXS-97),36 refinement was
carried out using SHELXL-97 (full-matrix least-squares on F2), and
hydrogen atoms were refined using a riding model. A semiempirical
absorption correction was applied.
4.3.2. General Procedure for Au(III) Complexes A−C. All the steps
in this procedure were done using dry solvents under argon, protecting
as much as possible the reaction mixtures from light. Filtration of the
intermediate complexes was done under air. The corresponding
imidazole salt (0.27 mmol) and Ag2O (0.18 mmol) were stirred in
DCM (7 mL) at rt for 16 h. The reaction mixture was then filtrated
through a short pad of Celite to remove the unreacted Ag2O, and the
solvents were evaporated. The resulting silver complex was allowed to
react with (Me2S)AuCl (0.27 mmol) in DCM (7 mL) for 24 h.
Filtration of the reaction mixture through Celite, followed by
evaporation in vacuo, afforded the corresponding Au(I) complex
that was immediately dissolved in 17 mL of DCM. After addition via
cannula at 0 °C of a DCM (10 mL) solution of PhICl2 (0.32 mmol),
the resulting reaction mixture was allowed to stir overnight at rt. After
evaporation, the pure product was precipitated from a small amount of
DCM with hexane. Product was collected by filtration and dried in
vacuo.
Trichloro[1-(2-pyridinylmethyl)-3-(2,4,6-trimethylphenyl)-2H-imi-
dazol-2-ylidene]gold (A):13 Pale yellow solid, yield 84%, mp 183−186
1
°C. H NMR (CDCl3, 500 MHz): δ 8.66 (1H, d, J = 4.3 Hz), 7.84
(1H, td, J = 7.7, 1.3 Hz), 7.72−7.66 (2H, m), 7.38 (1H, dd, J = 7.7, 4.3
Hz), 7.10 (1H, d, J = 1.7 Hz), 6.98 (2H, s), 5.69 (2H, s), 2.34 (3H, s),
2.13 (6H, s). 13C NMR (CDCl3, 126 MHz): δ 152.4, 150.0, 143.8,
141.2, 138.4, 135.5, 132.4, 130.0, 125.3, 124.7, 124.6, 124.6, 56.1, 21.3,
18.6. Anal. Calcd for C18H19AuCl3N3: C, 37.23; H, 3.30; N, 7.24.
Found: C, 37.46; H, 3.52; N, 6.81.
Data for B: yellow crystals, C21H25AuClN3O−C2H4Cl4, Mr
=
737.71, crystal size = 0.08 × 0.16 × 0.24 mm, monoclinic, space group
P21/c (No. 14), a = 16.1402(16) Å, b = 9.678(1) Å, c = 17.512(1) Å, β
= 97.745(5)°, V = 2710.6(3) Å3, Z = 4, ρ = 1.808 Mg/m−3, μ(Mo Kα)
= 5.942 mm−1, T = 123(2) K, F(000) = 1440, 2θmax = 55°, 32 271
reflections, of which 6199 were independent (Rint = 0.046), 304
parameters, R1 = 0.029 (for I > 2σ(I)), wR2 = 0.057 (all data), S =
1.06, largest diff. peak/hole = 1.208/−0.718 e Å−3.21
Trichloro[1-((4-methoxy-3,5-dimethyl-)2-pyridylmethyl)-3-(2,4,6-
trimethylphenyl)-2H-imidazol-2-ylidene]gold (B): Pale yellow solid,
1
yield 77%, mp 197−200 °C. H NMR (CDCl3, 500 MHz): δ 8.29
4.3. Synthesis and Characterization. Trimethylphenylimida-
zole. Yellowish solid, yield 70%. 1H NMR (CDCl3, 300 MHz): δ 7.43
(1H, t, J = 1.1 Hz), 7.23 (1H, t, J = 1.1 Hz), 6.96 (2H, d, J = 0.6 Hz),
6.88 (1H, t, J = 1.1 Hz), 2.34 (3H, s), 1.98 (6H, s). 13C NMR (CDCl3,
75 MHz): δ 139.0, 137.6, 134.6, 133.5, 129.7, 129.1, 120.2, 21.1, 17.4.
4.3.1. General Procedure for the Synthesis of Imidazole Salts A/
B-L.20 The hydrochloride salt of the correponding 2-chloromethyl
pyridine precursor (2.8 mmol) was dissolved in toluene (5 mL) and
neutralized with a K2CO3 saturated aqueous solution. After extraction,
the organic phase was subsequently poured onto a flask with
trimethyphenylimidazole (2.6 mmol). The mixture was stirred at
110 °C for 3 days. Filtration of the resulting precipate and further
washing with toluene afforded the corresponding pure imidazole salt
A/B-L.
(1H, s), 7.74 (1H, s, broad), 7.09 (1H, s), 6.97 (2H, s), 5.71 (2H, s),
3.89 (3H, s), 2.53 (3H, s), 2.33 (3H, s), 2.32 (3H, s), 2.13 (6H, s). 13C
NMR (CDCl3, 126 MHz): δ 165.8, 149.7, 149.6, 143.3, 141.1, 135.6,
132.6, 130.0, 127.7, 126.9, 125.4, 124.7, 60.6, 53.3, 21.3, 18.6, 13.7,
11.8. HRMS (ESI) calculated for C21H25AuCl2N3O m/z 602.1035
(M)+. Found 602.1027. Anal. Calcd for C21H25AuCl3N3O: C, 39.49;
H, 3.94; N, 6.58. Found C, 38.64; H, 3.96; N, 6.21.
Trichloro[1-(2-benzyl)-3-(2,4,6-trimethylphenyl)-2H-imidazol-2-
1
ylidene]gold (C): Pale yellow solid, yield 81%, mp 245−249 °C. H
NMR (CDCl3, 500 MHz): δ 7.46 (5H, s, broad), 7.15 (1H, d, J = 1.9
Hz), 7.08 (1H, d, J = 1.9 Hz), 7.00 (2H, s), 5.61 (2H, s), 2.35 (3H, s),
2.17 (6H, s). 13C NMR (CDCl3, 126 MHz): δ 143.8, 141.2, 135.5,
132.8, 132.4, 130.1, 129.8, 129.8, 129.2, 125.7, 123.2, 55.4, 21.3, 18.7,
HRMS (ESI) calculated for C21H23AuCl2N3 m/z 584.0929 (M +
MeCN)+. Found 584.0930. Anal. Calcd for C19H20AuCl3N2: C, 39.37;
H, 3.48; N, 4.83. Found: C, 38.59; H, 3.47; N, 4.71.
1-(2,4,6-Trimethylphenyl)-3-(2-pyridylmethyl)imidazolium Chlor-
ide (A-L):20 White solid, yield 74%, mp 231−235 °C. H NMR (d6-
1
DMSO, 300 MHz): δ 9.85 (1H, t, J = 1.7 Hz), 8.57−8.51 (1H, m),
8.15 (1H, t, J = 1.7 Hz), 7.99 (1H, t, J = 1.7 Hz), 7.91 (1H, td, J = 7.7,
1.7 Hz), 7.57 (1H, d, J = 7.7 Hz), 7.44−7.38 (1H, m), 7.15 (2H, s),
5.77 (2H, s), 2.33 (3H, s), 2.05 (6H, s). 13C NMR (d6-DMSO, 75
MHz): δ 153.4, 149.5, 140.2, 138.7, 137.5, 134.3, 131.2, 129.2, 123.9,
123.7, 123.6, 122.3, 53.1, 20.6, 16.9. HRMS (EI) calculated for
C18H19N3 m/z 277.1579 (M). Found 277.1592.
4.4. Catalytic Studies. All conversions and yields were determined
according to the relative integration of the 1H NMR respective signals
using 1,3,5-trimethoxybenzene as an internal standard. Reactions were
done under an aerobic atmosphere. In phenol synthesis, the total
concentration was 0.2 and 0.1 M during the indole cyclization.
4.4.1. Phenol Synthesis. A 0.40 mL portion of a base solution of 1
(0.333 mmol/mL, including internal standard 0.0446 mmol/mL) was
placed in a test tube. A 0.20 mL aliquot of the catalyst base solution
(A/B/C 1.72 μmol/mL, 0.25 mol %) was added, and the tube was
sealed. The tube, including stirrer, was placed into an oil bath at the
1-(2,4,6-Trimethylphenyl)-3-((4-methoxy-3,5-dimethyl-)2-
pyridylmethyl)imidazolium Chloride (B-L): White solid, yield 75%,
mp 208−209 °C. 1H NMR (d6-DMSO, 300 MHz): δ 9.62 (1H, t, J =
1.7 Hz), 8.13 (1H, s), 8.03 (1H, t, J = 1.7 Hz), 7.95 (1H, t, J = 1.7 Hz),
7.16 (2H, s), 5.73 (2H, s), 3.76 (3H, s), 2.34 (3H, s), 2.29 (3H, s),
2.21 (3H, s), 2.08 (6H, s). 13C NMR (d6-DMSO, 75 MHz): δ 163.6,
151.3, 148.8, 140.2, 139.1, 134.3, 131.2, 129.2, 125.8, 124.4, 123.6,
123.3, 60.0, 51.2, 20.6, 16.8, 12.8, 10.1. HRMS (EI) calculated for
C21H25N3O m/z 335.1998 (M). Found 335.2003.
1
corresponding temperature. The H NMR spectrum was measured
directly from the reaction solution after the proposed time when
CDCl3 was used as solvent.
2-(5-Methyl)furylmethyl Propargyl Ether (1): H NMR (CDCl3,
1
500 MHz): δ 6.24 (1H, d, J = 3.0 Hz), 5.92 (1H, dd, J = 3.0, 1.0 Hz),
4.49 (2H, s), 4.16 (2H, d, J = 2.4 Hz), 2.45 (1H, t, J = 2.4 Hz); 2.29
(3H, d, J = 1.0 Hz). 13C NMR (CDCl3, 126 MHz): δ 153.1, 149.0,
111.3, 106.4, 79.6, 74.8, 63.3, 56.7, 13.7.
1-(2,4,6-Trimethylphenyl)-(2-benzyl)imidazolium Chloride (C-L):
Prepared as A/B-L from benzyl chloride and trimethylphenylimida-
1
zole. White solid, yield 53%, mp 216−218 °C. H NMR (d6-DMSO,
I
dx.doi.org/10.1021/om3003027 | Organometallics XXXX, XXX, XXX−XXX