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COMMUNICATION
Journal Name
9
0.5 mol% 7d
K2CO3 (2 equiv.)
Br
Beilstein J. Org. Chem., 2012, 8, 1637. DOI: 10.1039/C7CC02487H
+
10 A. Chartoire, A. Boreux, A. R. Martin and S. P. Nolan, RSC
Adv., 2013, 3, 3840.
EtOH (2 mL)
R
16 h, 80 o
C
R
11 F. Izquierdo, A. Chartoire and S. P. Nolan, ACS Catal., 2013, 3,
2190.
12 G. Bastug and S. P. Nolan, J. Org. Chem., 2013, 78, 9303.
13 S. Meiries, G. Le Duc, A. Chartoire, A. Collado, K. Speck, K. S.
Athukorala Arachige, A. M. Z. Slawin and S. P. Nolan, Chem.
Eur. J., 2013, 19, 17358.
14 T. Terashima, S. Inomata, K. Ogata and S. I. Fukuzawa, Eur. J.
Inorg. Chem., 2012, 1387.
85%
MeO
92%
76%
H2N
Scheme 4. Selected Mizoroki-Heck reactions (with isolated yields) performed with the
palladate 7d.
15 B. R. Dible, R. E. Cowley and P. L. Holland, Organometallics,
2011, 30, 5123.
16 S. Roy and H. Plenio, Adv. Synth. Catal., 2010, 352, 1014.
17 E. L. Kolychev, A. F. Asachenko, P. B. Dzhevakov, A. Bush, V.
V. Shuntikov, V. N. Khrustalev and M. S. Nechaev, Dalton
Trans., 2013, 42, 6859.
18 P. R. Melvin, A. Nova, D. Balcells, W. Dai, N. Hazari, D. P.
Hruszkewycz, H. P. Shah and M. T. Tudge, ACS Catal., 2015,
5, 3680.
19 A. Chartoire, M. Lesieur, L. Falivene, A. M. Z. Slawin, L.
Cavallo, C. S. J. Cazin and S. P. Nolan, Chem. Eur. J., 2012, 18,
4517.
20 L. Wu, E. Drinkel, F. Gaggia, S. Capolicchio, A. Linden, L.
Falivene, L. Cavallo and R. Dorta, Chem. Eur. J., 2011, 17,
12886.
21 N. Marion, O. Navarro, J. Mei, E. D. Stevens, N. M. Scott, and
S. P. Nolan, J. Am. Chem. Soc. 2006, 128, 4101-4111.
22 V. Jurcik, T. E. Schmid, Q. Dumont, A. M. Z. Slawin and C. S. J.
Cazin, Dalton Trans., 2012, 41, 12619.
23 R. M. Drost, T. Bouwens, N. P. Van Leest, B. De Bruin and C. J.
Elsevier, ACS Catal., 2014, 4, 1349.
24 M. S. Viciu, O. Navarro, R. F. Germaneau, R. A. Kelly III, W.
Sommer, N. Marion, E. D. Stevens, L. Cavallo and S. P. Nolan,
Organometallics, 2004, 23, 1629.
25 A. Chartoire, C. Claver, M. Corpet, J. Krinsky, J. Mayen, D. J.
Nelson, S. P. Nolan, I. Peñafiel, R. Woodward and R. E.
Meadows, Org. Proc. Res. Devel., 2016, 20, 551–557.
26 C. M. Kelly, D. Kwon, M. J. Ferguson, S. M. Bischoff, O. L.
Sydora, D. H. Ess, M. Stradiotto and L. Turculet, Angew.
Chem. Int. Ed., 2015, 54, 14498.
27 N. Marion, E. C. Ecarnot, O. Navarro, D. Amoroso, A. Bell and
S. P. Nolan, J. Org. Chem., 2006, 71, 3816.
28 A. R. Martin, Y. Makida, S. Meiries, A. M. Z. Slawin and S. P.
Nolan, Organometallics, 2013, 32, 6265.
29 A. Collado, A. Gómez-Suárez, A. R. Martin, A. M. Z. Slawin
and S. P. Nolan, Chem. Commun., 2013, 49, 5541.
30 R. Visbal, A. Laguna and M. C. Gimeno, Chem. Commun.,
2013, 49, 5642.
31 O. Santoro, A. Collado, A. M. Z. Slawin, S. P. Nolan and C. S. J.
Cazin, Chem. Commun., 2013, 49, 10483.
32 R. Savka and H. Plenio, Dalton Trans., 2015, 44, 891.
33 G. Peh, E. A. B. Kantchev, Y. Er and J. Y. Ying, Chem. Eur. J.,
2010, 16, 4010.
34 G. Peh, E. A. B. Kantchev, C. Zhang and J. Y. Ying, Org. Biomol.
Chem., 2009, 7, 2110.
In summary, while investigating the involvement of palladate
species as intermediates in the synthesis of well-defined Pd-NHC
complexes using a weak base approach, a simple and efficient
procedure to access an important class of palladium-NHC cross-
coupling pre-catalysts, [Pd(NHC)(ƞ3-R-allyl)Cl], was developed. All
that is necessary to form the neutral Pd-NHC complexes is a mild
inorganic base and an inexpensive solvent. The reactions are easy
to carry out and can be performed in air. The reaction proceeds via
the formation of an imidazolium palladate and the rate of the
formation of the latter is principally affected by the steric bulk of
the NHC used. The simplicity and efficiency of this protocol ensures
reliable scale-up of previously developed pre-catalysts and will most
likely facilitate the development of new congeners of this
frequently used class of cross-coupling precursors.
Conclusions
Finally, these palladate salts have proven to be as efficient as the
well-defined palladium-NHC complexes in the Suzuki-Miyaura and
in the Mizoroki-Heck reactions, when they were activated in situ
prior to the addition of the coupling partners. Ease of access, high
stability to air, and use in catalysis make these salts valuable and
practical pre-catalysts. The synthetic protocol involving the “ate”
intermediates continues to evolve but may prove to be quite a
general one using other palladium precursors. We feel the simple
“ate” protocol has potential to be extended to other transition
metals. On-going work is aimed at testing this hypothesis across the
Periodic Table.
Notes and references
1
2
N. Marion and S. P. Nolan, Acc. Chem. Res., 2008, 41, 1440.
E. A. B. Kantchev, C. J. O’Brien and M. G. Organ, Angew.
Chem. Int. Ed., 2007, 46, 2768.
3
4
5
Science of Synthesis: N-Heterocyclic Carbenes in Catalytic
Organic Synthesis, vol 1 & 2(Eds. S. P. Nolan, C. S. J. Cazin)
Thieme, Stuttgart, 2016.
A. Chartoire and S. P. Nolan, New Trends in Cross-Coupling:
Theory and Applications, (Ed. T. J. Colacot), RSC, Cambridge,
2014, ch. 4, pp. 139-227.
M. Hoyos, D. Guest and O. Navarro, N-Heterocycle Carbenes:
Effective Tools for Organometallic Synthesis,(Ed. S. P. Nolan),
Wiley-VCH, New York, 2014, ch. 4, pp. 85-110.
6
7
M. S. Viciu, R. F. Germaneau, O. Navarro-Fernandez, E. D.
Stevens and S. P. Nolan, Organometallics, 2002, 21, 5470.
C. J. O’Brien, E. A. B. Kantchev, C. Valente, N. Hadei, G. A.
Chass, A. Lough, A. C. Hopkinson, M. G. Organ, Chem. Eur. J.,
2006, 12, 4743.
a) N. C. Bruno, M. T. Tudge and S. L. Buchwald, Chem. Sci.,
2013, 4, 916; b) A. J. DeAngelis, P. G. Gildner, R. Chow and T.
J. Colacot, J. Org. Chem., 2015, 80, 6794; c) P. M. MacQueen,
A. J. Chisholm, B. K. V. Hargreaves and M. Stradiotto, Chem.
Eur. J., 2015, 21, 11006.
35 Similarities between this and protocols developed by Organ
and Ying for Pd-NHC complexes are of note. We suspect a
palladate may be involved as intermediates in these.
36 [Pd(NHC)(ƞ3-cin)Cl] (NHC = IPr, SIPr, IPr*) are commercially
available from SigmaAldrich, Strem and Umicore.
37 D. Hruszewycz, D. Balcells, L. M. Guard, N. Hazari and M.
Tilset, J. Am. Chem. Soc., 2014, 136, 7300.
38 CCDC 1439389 (7a) and 1439390 (7c) contain the
crystallographic data for this paper and can be obtained via
8
4 | J. Name., 2012, 00, 1-3
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