ChemSusChem
10.1002/cssc.201601785
COMMUNICATION
1
Na
2
SO
4
, filtered and concentrated in vacuo to give the cinnamic acid
were analyzed by GCMS and H NMR spectroscopy, cinnamic
1
acid B was observed with a Z:E ratio of 98:2 (Figure S3).
Entries 6-11: Yields determined by H NMR spectroscopy with
isolated yield given in parentheses. Phneylacetylene was fully
product. The E/Z selectivity was determined by H NMR spectroscopy.
Calculation Methods All species involved in the reaction, including
reactants, products, minima, and transition states, were fully optimized by
1
d
converted to related products.
[15]
[16]
density functional theory using B3LYP
functional and DGDZVP
[
17]
basis set as built in Gaussian 09 package.
The convergence
In conclusion, our theoretical calculations indicated that it is
-
3
-3
thresholds are 10 a.u. on the gradient, 10 a.u. on the displacement,
kinetically
possible
to
obtain
cinnamic
acid,
the
/H
-
6
and 10 a.u. on the energy. The harmonic vibrational frequencies and
corresponding zero-point vibrational energies (ZPVE) are calculated at
the same level for all the optimized geometries, no imaginary mode for
minima and only one imaginary mode for transition states were confirmed.
The imaginary mode of each transition state was checked to correspond
to the right reaction coordinate. For each transition-state structure, we
calculated the intrinsic reaction coordinate (IRC) routes in both directions
toward the corresponding minima. All the energies reported in the
present study include the ZPVE and thermal correction. NBO analysis
was performed for the reactant and transition state (TS) for both Cu- and
hydrocarboxylation product, from phenylacetylene in a CO
2
2
system with NHC-supported Ag/Pd dual metal catalysts. The
reaction barriers in the single reaction steps for Cu or Ag-
catalyzed alkyne carboxylation and Pd-catalyzed alkyne
hydrogenation increase in the following order: Ag < Pd < Cu.
This indicates the reaction pathway selectivity in the following
order: Ag > Pd > Cu. The higher reaction barrier for NHC-
supported Cu-catalyzed carboxylation, as opposed to Ag-
catalyzed carboxylation, could be rationalized from the relative
stability of the metal acetylide complexes and different
coordinating ability of phenylacetylide to the metal center. The
reaction barriers for the Pd-catalyzed hydrogenation of
unsaturated intermediates and substrate were found to be
phenylpropiolic acid < phenylacetylene < cinnamic acid. Taken
together, these calculations provided an important clue to the
possibility of obtaining ,-unsaturated alkenoic acids from
[23]
Ag-catalyzed routes using NBO version 3.1.
Acknowledgements
2 2
terminal alkynes under a CO /H atmosphere with a Ag/Pd dual
catalyst system. These calculations have inspired and guided
experimental endeavor for successful development a poly-NHC
supported Ag/Pd catalyst for the carboxylation/hydrogenation
This work was supported by the Institute of Bioengineering and
Nanotechnology (Biomedical Research Council, Agency for
Science, Technology and Research (A*STAR), Singapore). The
authors thank A*STAR Computational Resource Centre for the
use of its high-performance computing facilities. We thank D.
Wu for assistance of data-collection in the early stage of this
work.
2 2
cascade reaction of terminal alkyne with CO /H . By tuning the
catalyst composition and reaction temperature, phenylacetylene
was selectively converted to cinnamic acid, hydrocinnamic acid
or phenyl propiolic acid in excellent yields.
Keywords: CO
2 2
utilization • H reduction • reductive
Experimental Section
carboxylation • Ag/Pd catalyst • terminal alkyne
Poly-NHC-Ag/Pd catalyst synthesis Poly-NHC materials and Poly-
[
1] (a) M. Aresta, Carbon dioxide as chemical feedstock, Willey-VCH,
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[
13b, 20]
NHC-Ag/Pd catalysts were synthesized based on literature.
P(NHC-Ag)0.5(NHC-Pd)0.5, AgNO (42.5 mg, 0.25 mmol) and Pd(OAc)
56 mg, 0.25 mmol) was added to a DMSO (10 ml) suspension of Poly-
For
3
2
2365; (d) M. Mori, Eur. J. Org. Chem. 2007, 2007, 4981; (e) A.
(
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1
imidazolium (250 mg, 0.5 mmol of imidazolium motif) in a reaction flask.
o
The reaction mixture was stirred at 70 C for 8 h. The solid product was
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filtered and dried to obtain a brown powder P(NHC-Ag)0.5(NHC-Pd)0.5
.
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The catalyst is directly used for reaction.
General procedure for hydrocarboxylation of phenylacetylene
Poly-(NHC)0.2(NHC-Ag)0.6(NHC-Pd)0.2 (5 mg), Cs
phenylacetylene (1 mmol) were added to DMF (4 mL) in a pressure
reactor (25 mL). The pressure reactor was flushed with CO (balloon).
The reactor was filled with CO up to 50 psi and then H up to 100 psi.
2
CO
3
(2 mmol),
[
[
2] (a) L. Zhang, Z. Hou, Chem. Sci. 2013, 4, 3395; (b) Q. Liu, L. P.
Wu, R. Jackstell and M. Beller, Nature Commun., 2015, 6, 5933;
2
(c) D. Yu, S. P. Teong and Y. Zhang, Coord. Chem. Rev., 2015,
2
2
293-294, 279.
The reaction mixture was stirred at 85 °C for 16 hours. After complete
consumption of the starting material, the reaction mixture was cooled to
room temperature added to an aqueous solution of potassium carbonate
solution (2 N, 5 mL) and stirred for 30 mins. Then the mixture was
extracted with dichloromethane (3 × 5 mL) and the aqueous layer was
acidified with concentrated HCl to pH = 1 and extracted with diethyl ether
3] Selected metal-catalyzed hydrocarboxylation reactions of alkynes
using CO or CO surrogates: (a) J. Hou, J. Xie, Q. Zhou, Angew.
Chem., Int. Ed. 2015, 54, 6302; (b) I.-T. Trotus, T. Zimmermann,
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Neumann, M. Beller, ChemCatChem 2009, 1, 28; (d) M.-C. Fu, R.
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[
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(b) S. Saito, S. Nakagawa, T. Koizumi, K. Hirayama, Y.
(3 × 5 mL). The combined organic layers were dried with anhydrous
Yamamoto, J. Org. Chem. 1999, 64, 3975; (c) M. Aoki, M.
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