4th EucheMs chemistry congress

wednesday, 29-Aug 2012 | thursday, 30-Aug 2012
s696
chem. Listy 106, s587–s1425 (2012)
inorganic Chemistry plus Young inorganic chemistry day
New trends in organometallic chemistry – iV
o - 3 2 0
PALLAdiuM(ii) CoMPLexeS with SMALL
n-heteroCyCLiC CArBene LiGAndS AS hiGhLy
ACtive CAtALyStS for the SuzuKi-MiyAurA
reACtion
A. trzeCiAK 1 , M. SzuLMAnowiCz 1 , A. GnieweK 1
1 University of Wroclaw, Faculty of Chemistry, Wroclaw, Poland
Palladium complexes, bearing bulky N-heterocyclic carbene
ligands (NHC), found many applications in catalytic reactions
and, in particular, in the Suzuki-Miyaura cross-coupling. In
contrast, much less is known about reactivity of carbene palladium
complexes bearing small substituents at N-atoms of imidazole
ring. Consequently, we synthesized two groups of palladium(II)
complexes, namely monomeric, of the type Pd(NHC) X and
2 2
dimeric of [PdX (NHC)] composition with the aim to apply them
2 2
in the Suzuki-Miyaura reaction. Moreover, mechanistic studies
were undertaken in order to recognize structural transformations
of palladium complexes under reaction conditions. All new
complexes were characterized by spectroscopic and X-ray
methods and, in particular, for Pd(bmim-y) Br , (bmim-y = 1-
2 2
-methyl-3-butylimidazol-2-ylidene) both isomers, cis and trans,
were obtained. All of the complexes studied exhibited very high
activity in Suzuki-Miyaura cross-coupling in ethylene glycol,
achieving TONs of up to 760000. High activity was also noted
when NaBPh was used instead of PhB(OH) . ESI-MS studies of
4 2
the reaction mixtures allowed to identify dimeric forms of the type
+ Pd (NHC) X and trimeric intermediates of the composition
2 4 3
Pd (NHC) Ph 3 4 + , most probably participating in the catalytic cycle.
Further studies, performed with TEM method, confirmed the
presence of Pd(0) nanoparticles in the reaction mixture.
Interestingly, the size of nanoparticles decreased during
Suzuki-Miyaura reaction indicating on their solubilization with
formation of soluble palladium species. Consequently, we
proposed a homogeneous pathway of the reaction with the
participation of palladium species bearing imidazolium cations or
N-heterocyclic carbenes as key intermediates.
Keywords: palladium; carbene ligands; cross-coupling;
homogeneous catalysis; ligands effects;
Young inorganic chemistry day – i
4 th EucheMs chemistry congress
o - 4 4 4
BASe-ASSiSted MetAL-CAtALyzed C-h Bond
funCtionALizAtionS
L. ACKerMAnn 1
1 University of Goettingen, Institute for Organic and
Biomolecular Chemistry, Goettingen, Germany
Direct C–H bond functionalizations of (hetero)arenes are
highly attractive tools for an overall streamlining of synthetic
chemistry, since these methods avoid the preparation and use of
prefunctionalized starting materials. [1] Recently, we introduced
carboxylates as efficient cocatalysts for site-selective direct
arylations and alkylations employing inexpensive ruthenium
complexes, [2] which were found to display complementary
selectivities as compared to palladium(0)- or copper(I) catalysts. [3]
Detailed mechanistic insight into the C–H bond ruthenation step
set the stage for the development of ruthenium-catalyzed twofold
C–H bond functionalizations, as well as step-economical
oxidative annulations of alkynes. [4] These oxidative C–H bond
functionalizations could be performed in an aerobic fashion under
ambient air, [5] and provided step-economical access to various
important bioactive heterocycles. [4]
references:
1. a) L. Ackerman, R. Vicente, A. Kapdi, Angew. Chem. Int.
Ed. 2009, 48, 9792.
b) L. Ackermann, Modern Arylation Methods,
Wiley-VCH, Weinheim, 2009.
c) D. Alberico, M. E. Scott, M. Lautens, Chem. Rev. 2007,
107, 174.
2. a) L. Ackermann, P. Novák, R. Vicente, N. Hofmann,
Angew. Chem. Int. Ed. 2009, 48, 6045.
b) L. Ackermann, R. Vicente, A. Althammer, Org. Lett.
2008, 10, 2299. Reviews:
c) L. Ackermann, Chem. Commun. 2010, 46, 4866. (d) L.
Ackermann, Chem. Rev. 2011, 111, 1315.
e) L. Ackermann, A. Althammer, R. Born, Angew. Chem.
Int. Ed. 2006, 45, 2619.
f) L. Ackermann, R. Born, P. Álvarez-Bercedo, Angew.
Chem. Int. Ed. 2007, 46, 6364.
3. a) L. Ackermann, A. Althammer Angew. Chem. Int. Ed.
2007, 46, 1627.
b) L. Ackermann, A. Althammer, S. Fenner, Angew. Chem.
Int. Ed. 2009, 48, 201.
4. a) L. Ackermann, A. V. Lygin, N. Hofmann, Angew. Chem.
Int. Ed. 2011, 50, 6503.
b) L. Ackermann, J. Pospech, Org. Lett. 2011, 13, 4153.
5. L. Ackermann, L. Wang, A. V. Lygin, Chem. Sci. 2012, 3,
177.
Keywords: C-H activation; Ruthenium; Carboxylate ligands;
Green chemistry; Homogeneous catalysis;
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc