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ChemComm
† Electronic Supplementary Information (ESI) available: [Experimental
details and characterization data]. See DOI: 10.1039/b000000x/
the G0-PdNP catalyst, the cross-coupling with phenylboronic
acid is quantitative with bromobenzene: TON = 0.99 x 106; TOF
= 1.65 x 104 h-1, and the yield is 63% for 1,4-bromoanisole (TON
= 0.63 x 106; TOF = 1.05 x 104 h-1).
DOI: 10.1039/C3CC45132A
65 at 28°C even with a very small quantity of Pd (PdNPs stabilized by G0-27
TEG), down to 3 x 10-5 mol %, i.e. 0.3 ppm Pd in 80% yield (TON = 2.7
x 106; TOF = 2.8 x 104 h-1.
5
The results of the Suzuki-Miyaura reactions of bromoarenes are
gathered in Table 1. In conclusion, for bromoarenes, the TONs
are very impressive at 80°C, sometimes even larger than 106.
Concerning the G1-PdNP catalyst, reactions under the same
conditions as in Table 1, (80°C, 2.5 days) between bromoarenes
10 and phenylboronic acid using 1 ppm Pd give yields of 20% with
bromobenzene, 27% with bromoanisole and 39% with 1,4-
bromonitrobenzene. The catalytic efficiency of G1-PdNPs is
lower than that of the G0-PdNPs, which is taken into account by
the fact that PdNPs prepared in G1-81 TEG 2 are larger than that
15 in G0-27 TEG 1. This also is in accord with the leaching
mechanism.4c With chloroarenes, the results with G0 are less
impressive than with the other halogenoarenes, because high
temperatures (> 100°C) are required to activate chloroarenes
under these conditions, and at such temperatures these PdNPs
1
2
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Conclusions
In conclusion, the TEGylated click dendrimer assemblies
represent a new type of nanoreactors for PdNPs that provide
25 stability and catalytic activity during several months without the
strain of inert atmosphere. The TEG termini of the dendrimer
tethers are responsible for this high degree of intradendritic PdNP
stabilization, because they interact interdendritically to form large
assemblies. The intradendritic PdNPs are loosely liganded by the
30 1,2,3-triazoles, which present an excellent compromise between
stabilization and lability for an optimized catalytic activity. The
catalytic activity of these PdNPs is exceptionally high with
bromoarenes, reaching TONs that are equal to or larger than 106
never reached with PdNPs stabilized with ferrocene6c or
35 sulfonated6d dendrimers’ termini, which enhances the role of the
TEG termini (see S.I. table S4). The catalyst 1-PdNPs is the most
active for the Suzuki-Miyaura reaction in aqueous solvent, in
terms of TONs for bromoarenes,4-6 (see S.I. table S3) with
90
95
100
105
110
115
120
125
130
5
longstanding catalytic activity on
multi-gram scales of
40 substrates. We suggest that the reasons for this exceptional
catalytic activity of the dendritic nanorector 1 are (i) the loose
intradendritic stabilization of PdNPs by the triazole ligands
combined with the inter-dendritic assembly provided by the TEG
termini better protects the PdNPs than a single dendrimer, (ii) the
45 leaching mechanism4c generates very active Pd atoms in solution
that are less easily quenched by the mother PdNPs because of the
protection by the nanoreactor, and (iii) the leaching is easier for
small PdNPs (1.4 ± 0.7 nm, truncated bipyramid, high proportion
of reactive Pd atoms on the edges and summits) than for larger
50 ones. As a consequence, extremely high TONs are reached,
because the catalytic activity is retained at extremely high
substrate/catalyst ratios. Finally, these water-soluble dendrimers
are very stable and easy to recover8 whenever needed when they
are used in substantial quantity, and they can indefinitely be re-
55 used.
6
Notes and references
a ISM, UMR CNRS 5255, Univ. Bordeaux, 351 Cours de la Libération,
7
8
V. Percec, C. Mitchell, W.-D. Cho, S. Uchida, M. Glodde, G.
Ungar, X. Zeng, Y. Liu and V. S. K. Balagurusamy, J. Am. Chem.
Soc., 2004, 126, 6078.
A. K. Diallo, E. Boisselier, L. Liang, J. Ruiz, D. Astruc, Chem. Eur.
J. 2010, 16, 11832.
33405 Talence Cedex, France
b LCC, CNRS, 205 Route de Narbonne, 31077 Toulouse Cedex, France.
60 cICMCB, UPR CNRS N°9048, 87 avenue, Pey-Berland, 33608 Pessac
Cedex, France.
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