Alkyne Hydroarylations with Dicarbene Palladium Catalysts
and the arene (if liquid) were then added and the resulting solution
was stirred at 25 °C for 5 min. Finally the alkyne (13.2 mmol) was
added and the reaction mixture was stirred at 25 °C for the time
indicated in the tables. Portions of the solution (0.2 mL) were
drawn off from the reaction mixture and analysed by H NMR or
GC–MS. The same conditions were used for the tests reported in
nature of these ligands, this is further confirmation that the
combination of a strongly coordinating and electron-donat-
ing ligand, together with the presence of positive charge on
the metal, may yield complexes that in spite of the nature
of the ligand exhibit excellent performance as electrophilic
catalysts.[21]
1
Table 6, however, without the use of a catalyst and silver salt.
Work currently in progress aims at expanding the scope
of the reaction to different classes of aromatic systems, at
finding novel applications for electrophilic metal carbene
complexes as well as at developing still less-impacting reac-
tion media.
Determination of Conversion Curves Reported in Figure 7: Penta-
methylbenzene (13.2 mmol), the palladium(II) complex (1.32 µmol)
and AgBF4 (2.64 µmol) were placed in a 100 mL round-bottomed
flask previously evacuated and filled with argon. HBF4 (13.2 mmol
or 1.32 mmol) and 1,2-dichloroethane (the quantity necessary to
reach a total volume of 6.3 mL) were then added and the resulting
solution was stirred at 25 °C for 5 min. Finally, ethyl propiolate
(13.2 mmol) was added and the reaction mixture was stirred at
25 °C. Portions of the solution (0.2 mL) were drawn off from the
Experimental Section
General Remarks: All manipulations were carried out using stan-
dard Schlenk techniques under argon or dinitrogen. The reagents
were purchased by Aldrich as high-purity products and generally
used as received. Complexes 1,[13b] 3,[22] 4,[23] 5,[24] 6,[25] 7[26] and
8,[27] were prepared according to literature procedures. All solvents
were used as received as technical grade solvents. NMR spectra
were recorded with a Bruker Avance 300 spectrometer (300.1 MHz
1
reaction mixture and analysed by H NMR or GC–MS.
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1
for H and 75.5 for 13C). Chemical shifts (δ) are reported in units
of ppm relative to the residual solvent signals. Elemental analyses
were carried out by the microanalytical laboratory of our depart-
ment with a Fisons EA 1108 CHNS-O apparatus.
Synthesis of (1,1Ј-Dimethyl-3,3Ј-methylenedibenzimidazolin-2,2Ј-
ylidene)palladium(II) Bis(trifluoroacetate) (2): A suspension of com-
plex 1 (0.20 g, 0.25 mmol) and AgTFA (0.11 g, 0.50 mmol) in ace-
tonitrile (15 mL) was heated at 60 °C for 4 h and then filtered
through Celite to remove silver salts. The solvent was removed un-
der vacuum and the off-white residue was washed with diethyl ether
(2ϫ5 mL), filtered and dried under vacuum (132 mg, yield 76%).
C21H16F6N4O4Pd·0.5AgBr (702.7): calcd. C 35.90, H 2.30, N 7.97;
1
found C 35.63, H 1.79, N 7.88. H NMR ([D6]DMSO, 25 °C): δ =
4.02 (s, 3 H, CH3), 6.75 and 7.40 (2 d, 1 H, CH2), 7.40–7.60 (m, 4
H, Ar), 7.76 (d, 1 H, CH=CH), 8.25 (d, 1 H, CH=CH) ppm.
13C{1H} NMR ([D6]DMSO, 25 °C): δ = 34.0 (CH3), 57.1 (CH2),
111.3, 111.9, 124.5, 124.6, 132.3, 133.7 (CAr) ppm. Signals arising
from carbene carbon atoms and CF3COO groups were not de-
tected.
General Procedures for the Catalytic Tests
Tests Reported in Tables 1, 2, and 3. Determination of Conversion
Curves Reported in Figures 2, 3, and 4: The arene (13.2 mmol, if
solid), the palladium(II) complex (1.32 or 6.6 µmol for the tests
reported in Table 2) and silver trifluoroacetate (2.64 or 13.2 µmol
for the tests reported in Table 2) were placed in a 100 mL round-
bottomed flask previously evacuated and filled with argon. Tri-
fluoroacetic acid (4 mL), 1,2-dichloroethane (1 mL) and the arene
(if liquid) were then added and the resulting solution was stirred at
25 °C for 5 min. Finally the alkyne (13.2 mmol) was added and the
reaction mixture was stirred at 25 °C for the time indicated in the
tables. Portions of the solution (0.2 mL) were drawn off from the
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1
reaction mixture and analysed by H NMR or GC–MS.
Tests Reported in Tables 4 and 5. Determination of the Conversion
Curves Reported in Figure 5: The arene (13.2 mmol, if solid), the
palladium(II) complex (1.32 µmol) and the silver salt (2.64 µmol,
AgTFA when HTFA was used, AgOTf for HOTf, AgBF4 for
HBF4) were placed in a 100 mL round-bottomed flask previously
evacuated and filled with argon. The acid (13.2 mmol), 1,2-dichlor-
oethane (the quantity necessary to reach a total volume of 6.3 mL)
Eur. J. Org. Chem. 2009, 3189–3198
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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