dried (Na2SO4), evaporated to dryness, and analysed by 1H NMR
spectroscopy.
very high THT concentrations (1006 excess vs Pd) substrate
conversion decreases to 68%. This indicates that the catalyst
system is not significantly poisoned by sulfur-containing
impurities.
1 A. J. Arduengo, Acc. Chem. Res., 1999, 32, 913; D. Bourissou,
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2 H. M. J. Wang and I. J. B. Lin, Organometallics, 1998, 17, 972;
A. R. Chianese, X. Li, M. C. Janzen, J. W. Faller and R. H. Crabtree,
Organometallics, 2003, 22, 1663; J. C. Garrison and W. J. Youngs,
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3 P. J. Fraser, W. R. Roper and F. G. A. Stone, J. Chem. Soc., Dalton
Trans., 1974, 102; M. F. J. Lappert, J. Organomet. Chem., 1975, 100,
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6 H. Lebel, M. K. Janes, A. B. Charette and S. P. Nolan, J. Am. Chem.
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7 S. Sole´, H. Gornitzka, W. W. Schoeller, D. Bourissou and G. Bertrand,
Science, 2001, 292, 1901; V. Lavallo, Y. Canac, A. DeHope,
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8 A. R. Chianese, B. M. Zeglis and R. H. Crabtree, Chem. Commun.,
2004, 2176.
In conclusion, oxidative addition of iodo-functionalised imida-
zolium salts to zero-valent palladium precursors provides a mild
and rational access to N-heterocyclic carbene complexes that are
non-classically bound via C(4). In some cases, this methodology is
complementary to direct metallation and may be useful for ligand
systems that are thermally unstable. The applied synthetic protocol
allows the installation of various chelating donor groups via
regioselective N-functionalisation in order to tune the properties of
the coordinated metal centre. The catalytic activity of the
corresponding C(4)-bound carbene palladium complex 2 is
comparable to classical C(2)-bound carbene complexes and
presumably originates from Pd–carbene bond breaking and
colloidal Pd0 formation. Currently, we are exploiting the scope
and limitations of this oxidative addition protocol for the synthesis
of various non-classical carbene complexes with other late
transition metals.
M.A. gratefully acknowledges an Alfred Werner Assistant
Professorship. We thank the Swiss National Science Foundation
for financial support (grant 200021–107802).
9 M. Albrecht and G. van Koten, Angew. Chem., Int. Ed., 2001, 40, 3750.
10 D. Bacciu, K. J. Cavell, I. A. Fallis and L. Ooi, Angew. Chem., Int. Ed.,
2005, 44, 5282.
Notes and references
11 H. Pauly and E. Arauner, J. Prakt. Chem., 1928, 118, 33; K. J. Brunings,
J. Am. Chem. Soc., 1947, 69, 205; H. B. Bensuan and M. S. R. Naidu,
Biochemistry, 1967, 6, 12.
12 D. S. McGuinness, K. J. Cavell, B. F. Yates, B. W. Skelton and
A. H. White, J. Am. Chem. Soc., 2001, 123, 8317; S. Gru¨ndemann,
M. Albrecht, A. Kovacevic, J. W. Faller and R. H. Crabtree, J. Chem.
Soc., Dalton Trans., 2002, 2163; N. D. Clement, K. J. Cavell, C. Jones
and C. J. Elsevier, Angew. Chem., Int. Ed., 2004, 43, 1277.
13 A. A. Tulloch, S. Winston, A. A. Danopoulos, G. Eastham and
M. B. Hursthouse, Dalton Trans., 2003, 699.
14 S. Gru¨ndemann, M. Albrecht, J. A. Loch, J. W. Faller and
R. H. Crabtree, Organometallics, 2001, 20, 5485.
15 J. P. Collmann, L. S. Hegedus, J. R. Norton and R. G. Finke, Principles
and Applications of Organotransition Metal Chemistry, University
Science Books, Mill Valley (CA), 1987.
{ Synthesis of 2: Solid [Pd(dba)2] (141 mg, 0.25 mmol) was added to a
suspension of imidazolium salt 1 (100 mg, 0.25 mmol) in dry CH2Cl2 at
0 uC. The mixture was allowed to warm to room temperature and was
filtered after 24 h through celite. The filter residue was extracted with
copious amounts of MeNO2 (8 mL total) and precipitated with Et2O. This
gave 2 (72 mg, 54%) as a yellow powder. Crystals suitable for X-ray
diffraction were grown by slow DMSO–Et2O liquid–liquid diffusion.
Anal. found (calcd) for C12H15BrIN3Pd (514.50): C 28.12 (28.01), H 2.43
(2.94), N 8.11 (8.17); 1H NMR (500 MHz, DMSO-d6, 298 K): d 9.25 (br s,
1H, H2imi), 8.97 (s, 1H, H5imi), 8.14 (br s, 1H, H6py), 7.79 (m, 1H, Hpy), 7.61
3
(m, 1H, Hpy), 7.15 (m, 1H, Hpy), 5.58 (s, 2H, NCH2), 4.51 (sept, JHH
=
6.4 Hz, 1H, CHMe2), 1.39 (d, 3JHH = 6.4 Hz, 6H, CCH3); 13C{1H} NMR
(125 MHz, DMSO-d6, 298 K): d 154 (br, Cpy), 151.86 (Cpy), 139.96 (Cpy),
132.16 (C2imi), 124.98 (Cpy), 124.69 (Cpy), 124 (br, Cimi), 54.30 (NCH2),
51.16 (CHMe2), 22.24 (CCH3), C–Pd not observed.
16 J. A. Loch, M. Albrecht, E. Peris, J. Mata, J. W. Faller and
R. H. Crabtree, Organometallics, 2002, 21, 700; N. Tsoureas,
A. A. Danopoulos, A. A. D. Tulloch and M. E. Light,
Organometallics, 2003, 22, 4750.
17 J. A. Widegren and R. G. Finke, J. Mol. Catal. A: Chem., 2003, 198,
317; J. G. de Vries, Dalton Trans., 2006, 421.
18 D. R. Anton and R. H. Crabtree, Organometallics, 1983, 2, 855.
19 Formation of Pd0 from classically bound carbene complexes has been
studied theoretically: see D. C. Graham, K. J. Cavell and B. F. Yates,
Dalton Trans., 2006, 1768. For an experimental study on the
decomposition of analogous Pd(diphosphine) complexes, see:
M. Tromp, J. R. A. Sietsma, J. A. van Bokhoven, G. P. F. van
Strijdonck, R. J. van Haaren, A. M. M. van der Eerden, P. W. N. M.
van Leeuwen and D. C. Koningsberger, Chem. Commun., 2003, 128.
20 M. Heckenroth, A. Neels, H. Stoeckli-Evans and M. Albrecht, Inorg.
Chim. Acta, 2006, 359, 1929; C. Tubaro, A. Biffis, C. Gonzato, M. Zecca
and M. Basato, J. Mol. Catal. A: Chem., 2006, 248, 93.
{ Crystal data for 2: Empirical formula [C12H15BrIN3Pd 6 C2H6OS], M
592.61, orange block, monoclinic, space group P21/n (no. 14), a =
˚
10.6134(9), b = 14.8459(16), c = 12.0432(10) A, b = 91.267(10)u, V =
3
23
˚
˚
1897.1(3) A , Z = 4, Dc = 2.075 g cm , MoKa radiation, l = 0.71073 A,
T = 173(2) K, 11103 reflections measured, 3656 unique (Rint = 0.0573).
Final GooF = 0.912, R1 = 0.0418, wR2 = 0.1133, R indices based on 2369
reflections with I . 2s(I) (refinement on F2), 204 parameters, 0 restraints.
Lp and absorption corrections applied, m = 4.826 mm21. CCDC 615954.
For crystallographic data in CIF or other electronic format see DOI:
10.1039/b611212a.
§ General Heck Procedure: Unless stated otherwise, aryl halide (1 mmol),
NaOAc (1.1 mmol), styrene (1.5 mmol), diethylene glycol dibutyl ether
(0.25 mmol, 1H NMR standard) and eventual additives were suspended in
dimethylacetamide (DMA, 4.5 mL). The mixture was preheated to 140 uC
for 10 min, then the catalyst solution (10 mM in DMA, 0.5 mL, 5 mmol
corresponding to 0.5 mol%) was added. At the times indicated, a sample
was withdrawn and extracted with hexane and H2O. The organic layer was
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