Angewandte
Chemie
diethylphenyl)imidazol-2-ylidene}] complex generated in situ
is a suitable catalyst for the selective semihydrogenation of
aryl-substituted alkynes to Z alkenes. The procedure for the
formation of palladium(0)–NHC catalysts in situ starting from
Chemtracts 2003, 16, 205; c) K. J. Cavell, D. S. McGuinness,
Coord. Chem. Rev. 2004, 248, 671.
2] For selected examples, see: a) H. M. Lee, D. C. Smith, Jr., Z. He,
E. D. Stevens, C. S. Yi, S. P. Nolan, Organometallics 2001, 20,
[
794; b) J. R. Miecznikowski, R. H. Crabtree, Organometallics
[
Pd(ma)(nbd)] is very efficient. This procedure may also
2001, 20, 629; c) L. D. Vꢁzquez-Serrano, B. T. Owens, J. M.
prove effective for the generation of catalysts for various
Buriak, Chem. Commun. 2003, 2518.
other catalytic reactions such as CÀC couplings, telomeriza-
[3] D. S. McGuinness, K. J. Cavell, B. W. Skelton, A. H. White,
Organometallics 1999, 18, 1596.
4] P. L. Arnold, F. G. N. Cloke, T. Geldbach, P. B. Hitchcock,
tions, and additions of elemental hydrogen to unsaturated
compounds. Further studies aimed at the elucidation of the
reaction mechanism of the palladium–NHC-catalyzed semi-
hydrogenation are in progress.
[
[
[
Organometallics 1999, 18, 3228.
5] N. D. Clement, K. J. Cavell, C. Jones, C. J. Elsevier, Angew.
Chem. 2004, 116, 1297; Angew. Chem. Int. Ed. 2004, 43, 1277.
6] For homogeneous palladium(0)-catalyzed hydrogenations of
alkynes, see: a) E. W. Stern, P. K. Maples, J. Catal. 1972, 27,
120; b) B. M. Trost, R. Braslau, Tetrahedron Lett. 1989, 30, 4657;
c) K. Tani, N. Ono, S. Okamoto, F. Sato, J. Chem. Soc. Chem.
Commun. 1993, 386; d) M. W. van Laren, C. J. Elsevier, Angew.
Chem. 1999, 111, 3926; Angew. Chem. Int. Ed. 1999, 38, 3715;
e) M. W. van Laren, M.A. Duin, C. Klerk, M. Naglia, D.
Rogolino, P. Pelagatti, A. Bacchi, C. Pelizzi, C. J. Elsevier,
Organometallics, 2002, 21, 1546.
[7] a) E. Markꢂ, S. Stꢃrin, O. Buisine, G. Mignani, P. Branlard, B.
Tinant, J.-P. Declercq, Science 2002, 298, 204; b) J. W. Sprengers,
M. J. Mars, M. A. Duin, K. J. Cavell, C. J. Elsevier, J. Organomet.
Chem. 2003, 679, 149; c) I. E. Markꢂ, S. Stꢃrin, O. Buisine, G.
Berthon, G. Michaud, B. Tinant, J.-P. Declercq, Adv. Synth.
Catal. 2004, 346, 1429.
Experimental Section
All experiments were carried out using standard Schlenk-line
techniques under an atmosphere of dry nitrogen. Solvents were
dried according to standard procedures and distilled prior to use.
2
d: The compound was prepared in an analogous manner to that
[
11]
1
described in the literature:
(9.54 g, 25.9 mmol, 51%). H NMR
3
(300.1 MHz, [D ]DMSO, 208C): d = 1.11 (t, J(H,H) = 7.4 Hz, 12H,
6
3
CH ), 2.40 (m, 8H, CH ), 7.44 (d, J(H,H) = 8.0 Hz, 4H, m-CH), 7.60
3
3
2
4,5
(t, J(H,H) = 8.0 Hz, 2H, p-CH), 8.47 (s, 2H, im-H ), 10.06 ppm (s,
2
13
1
2
H, im-H ); C NMR (75.5 MHz, [D ]DMSO, 208C): d = 15.8 (CH ),
6
3
4
,5
4.5 (CH ), 126.4 (im-H ), 128.2 (m-CH), 132.1(p-CH), 132.5 (ipso-
2
2
C), 139.5 (im-CH ), 141.0 ppm (o-C).
4
: 1,3-Dimesitylimidazolium chloride (172 mg, 0.51 mmol) and
tBuOK (0.77 mL of 1m solution in THF, 0.77 mmol) were dissolved in
THF (8 mL), and the solution was stirred for 30 min at 208C.
[8] A. M. Kluwer, C. J. Elsevier, M. Buhl, M. Lutz, A. L. Spek,
Angew. Chem. 2003, 115, 3625; Angew. Chem. Int. Ed. 2003, 42,
3501.
[
Pd(ma)(nbd)] (150 mg, 0.51 mmol) was added, and the dark purple
mixture was stirred at 208C for 30 min. Maleic anhydride (50.0 mg,
.51 mmol) was then added. The dark red solution was stirred for 2 h
[9] a) R. Jackstell, M. Gꢂmez Andreu, A. Frisch, K. Selvakumar, A.
Zapf, H. Klein, A. Spannenberg, D. Rꢄttger, O. Briel, R. Karch,
M. Beller, Angew. Chem. 2002, 114, 1028; Angew. Chem. Int. Ed.
2002, 41, 986; b) K. Selvakumar, A. Zapf, A. Spannenberg, M.
Beller, Chem. Eur. J. 2002, 8, 3901; c) R. Jackstell, S. Harkal, H.
Jiao, A. Spannenberg, C. Borgmann, D. Rꢄttger, F. Nierlich, M.
Elliot, S. Niven, K. J. Cavell, O. Navarro, M. S. Viciu, S. P. Nolan,
M. Beller, Chem. Eur. J. 2004, 10, 3891; d) N. D. Clement, K. J.
Cavell, unpublished results.
0
at 208C and filtered over celite, and the solvent was evaporated. The
solid compound was washed with ether (4 ꢀ 10 mL) and dried in vacuo
1
to give
a
red powder (157 mg, 0.26 mmol, 51%). H NMR
(
499.8 MHz, CD Cl , À508C): d = 1.72 (s, 6H, CH ), 2.28 (s, 6H,
2
2
3
3
CH ), 2.31 (s, 6H, CH ), 3.53 (d, J(H,H) = 4.6 Hz, 2H, CH=CH), 4.13
3
3
3
(
d, J(H,H) = 4.6 Hz, 2H, CH=CH), 6,89 (s, 2H, (Ar)CH), 7.07 (s, 2H,
(
4
,5
13
Ar)CH), 7.32 ppm (s, 2H, im-H ); C NMR (125.7 MHz, CD Cl ,
2
2
À408C): d = 17.4 (CH ), 18.2 (CH ), 18.4 (CH ), 64.7 (CH=CH), 68.2
[10] J. W. Sprengers, M. J. Agerbeek, C. J. Elsevier, H. Kooijman,
A. L. Spek, Organometallics 2004, 23, 3117.
[11] L. Delaude, M. Szypa, A. Demonceau, A. F. Noels, Adv. Synth.
Catal. 2002, 344, 749.
3
3
3
4
,5
(
(
CH=CH), 124.8 (im-H ), 129.3 (m-CH), 129.7 (m-CH), 134.5
(Ar)C), 135.0 ((Ar)C), 135.4 ((Ar)C), 139.6 ((Ar)C), 167.6 (C=O),
2
1
1
67.9 (C=O), 193.1 ppm (im-CH ); IR (KBr): n˜ = 1816 (C=O),
761 cm (C=O).
À1
Typical procedure for catalytic hydrogenation (in situ experi-
ment): THF (30 mL), imidazolium chloride (0.05 mmol), [Pd(ma)-
nbd)] (0.05 mmol), and tBuOK (0.20 mmol) were introduced into a
(
two-necked Schlenk tube, equipped with a septum and a stirring bar.
After stirring for 1 h, the solution was filtered over Celite to remove
traces of palladium black. Then the appropriate alkyne (5.0 mmol)
was added through a syringe, and hydrogen gas (1 bar) was bubbled
slowly through the solution by using a gas tube. Samples were
removed periodically for GC analysis. The crude reaction mixtures
1
were also analyzed by H NMR spectroscopy for comparison.
Received: December 14, 2004
Published online: February 23, 2005
Keywords: alkynes · hydrogenation · N-heterocyclic carbenes ·
.
palladium
[
1] a) W. A. Herrmann, Angew. Chem. 2002, 114, 1342; Angew.
Chem. Int. Ed. 2002, 41, 1290; b) B. S. Yong, S. P. Nolan,
Angew. Chem. Int. Ed. 2005, 44, 2026 –2029
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2029