Hydrogenation/hydrolytic ring opening of 5-HMF by Cp-Iridium(III) half-sandwich complexes for bioketones synthesis

Article abstract of DOI:10.1021/cs501874v

A new method for one-step synthesis of ketones from biobased 5-hydroxymethylfurfural (5-HMF) and its derivatives is reported. Bipyridine coordinated Cp-Iridium(III) complexes (Cp, 1,2,3,4,5-pentamethylcyclopenta-1,3-diene) exhibit highly efficient catalytic performance for hydrogenation/hydrolytic ring opening of 5-HMF and derivatives to produce ketones. The catalytic mechanism is proposed to proceed via carbonyl hydrogenation, hydroxyl group promoted and directed hydrolytic furan ring opening, followed by hydrogenation of α,β-unsaturated carbonyl compound based on the experimental and independent events' statistical calculation results. (Chemical Equation Presented).

Full text of DOI:10.1021/cs501874v

Letter
pubs.acs.org/acscatalysis
Hydrogenation/Hydrolytic Ring Opening of 5‑HMF by Cp*-Iridium(III)
Half-Sandwich Complexes for Bioketones Synthesis
Zhanwei Xu, Peifang Yan, Wenjuan Xu, Xiumei Liu, Zhi Xia, Benjamin Chung, Songyan Jia,
and Z. Conrad Zhang*
Dalian National Lab for Clean Energy, State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of
Sciences, 457 Zhongshan Road, 116023 Dalian, China
S
* Supporting Information
ABSTRACT: A new method for one-step synthesis of ketones from
biobased 5-hydroxymethylfurfural (5-HMF) and its derivatives is reported.
Bipyridine coordinated Cp*-Iridium(III) complexes (Cp*, 1,2,3,4,5-
pentamethylcyclopenta-1,3-diene) exhibit highly efficient catalytic perform-
ance for hydrogenation/hydrolytic ring opening of 5-HMF and derivatives
to produce ketones. The catalytic mechanism is proposed to proceed via
carbonyl hydrogenation, hydroxyl group promoted and directed hydrolytic
furan ring opening, followed by hydrogenation of α,β-unsaturated carbonyl
compound based on the experimental and independent events’ statistical calculation results.
KEYWORDS: homogeneous catalysis, hydrogenation, iridium catalyst, 5-HMF, ketones
sustainable production of biobased chemicals of the
Afuture depends on the development of new technologies
with desired functional specificity in the transformation of
available bioresources. 5-Hydroxymethylfurfural (5-HMF), a
versatile platform feedstock, is available from selective
dehydration of fructose and isomerization/dehydration of
glucose.1−8 5-HMF is regarded as one of the most promising
building blocks to produce valuable chemicals and fuels.9
Starting with 5-HMF, numerous important chemicals have
become available. For example, 2,5-bis(hydroxymethyl)furan,
2,5-dimethylfuran, levulinic acid, alcohols, among others, have
been obtained by hydrogenation and/or hydrolysis of 5-HMF,
and these chemicals have been further converted to prepare
polymers, fuel additives, dyestuffs, and pharmaceutical com-
pounds.10−18 2,5-Furandicarboxylic acid, which can be obtained
by the oxidation of 5-HMF, is an alternative to terephthalic and
isophthalic acid for polymer production.19 Aldol condensation
of 5-HMF with acetone furnishes a precursor for biofuels.20−22
The above 5-HMF-derived chemicals are produced mainly
based on heterogeneous catalysts and processes. Homogeneous
catalysis is in principle anticipated to offer catalyst-specific
products and high selectivity under mild conditions, but only a
comparatively few are applied to the hydrogenation of 5-
HMF.23−27
another heterogeneous catalyst, that converted 5-HMF to
HHD (60% yield) with the aid of H3PO4.33 Generally,
heterogeneous catalysts in the synthesis of diketones from 5-
HMF proceeds in two steps, hydrogenation and acid-promoted
opening of furan ring. However, addition of excess acid
required for furan ring opening reaction may cause humin
formation.34−36 Moreover, the reported results were obtained
in long reaction time, high reaction pressure, and/or high
temperature, suggesting lower efficiency of the heterogeneous
catalysts.
Bipyridine coordinated Cp*Ir-complexes show excellent
catalytic performance for hydrogenation of ketones, esters,
acids, N-heterocycles, etc.37−40 We anticipate the Cp*Ir-
complexes to serve as bifunctional catalysts (Scheme 1), as
the Cp*Ir-complexes may catalyze the hydrogenation of 5-
Scheme 1. Strategy of This Work to Produce Bio-Diketone
from 5-HMF
Diketone derivatives have been used to prepare valuable
chemicals, such as alcohols, amines, cycloketones, pyrrolidine,
and so forth.28,29 Very recently, the direct conversion of 5-
HMF30,31 and its derivatives to produce biodiketone derivatives
1-hydroxyhexane-2,5-dione (HHD) by hydrogenation/hydro-
lytic ring opening reaction was reported on the basis of a Pd/C
heterogeneous catalyst system with CO2/H2O as the acid for
the ring opening of furan, resulted in 77% yield HHD from 5-
HMF.32 Ohyama et al. reported supported Au nanoparticles,
Received: November 25, 2014
Revised: December 21, 2014
Published: December 24, 2014
© 2014 American Chemical Society
788
DOI: 10.1021/cs501874v
ACS Catal. 2015, 5, 788−792

ACS Catalysis
Letter
HMF under H2, and in situ generated acid may facilitate the
furan ring opening reaction. To the best of our knowledge, the
catalytic hydrogenation/hydrolytic ring opening of 5-HMF into
diketones using Cp*Ir-complex as a homogeneous catalyst has
not been reported. In this study, we report on the efficient
synthesis of HHD and 2,5,8-nonanetrione by homogeneous
Cp*Ir-complexes catalyzed hydrogenation/hydrolytic ring
opening of 5-HMF and its derivatives in aqueous solution
under mild conditions. We further investigated this trans-
formation through quantitative isotope marked GC-MS results,
which led to a mechanism in this work based on the statistical
rationalization of the GC-MS results. This strategy represents a
significant advancement for understanding the homogeneous
Cp*Ir-complexes catalyzed hydrogenation/hydrolysis in aque-
ous solution.
11). The formation of HHD remains in high yield under 5 bar
of H2 (84.1%, entry 12). Compared with the reported
heterogeneous catalysis system,30−33 the homogeneous Cp*Ir-
complex exhibited superior catalytic performance in converting
5-HMF to HHD with higher yield under lower H2 pressure and
temperature.
To reveal the possible mechanism of Cp*Ir-complex-
catalyzed hydrogenation/hydrolytic ring opening of 5-HMF,
the time course of the conversion of 5-HMF to HHD was
followed as shown in Figure 1. As 5-HMF was consumed, the
The catalytic activities of Cp*Ir-complexes with different
bidentate ligands A−F were tested in the hydrogenation/
hydrolytic ring opening reaction of 5-HMF in a homogeneous
aqueous phase. As seen in Table 1, the reactions were first
a
Table 1. Optimization of Reaction Conditions
conversion
yield of DHMF
yield of HHD
b
b
b
entry
catalyst
(%)
(%)
(%)
1
A
B
A
B
C
D
E
F
89.0
90.6
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
8.2
8.1
<1
<1
<1
7.9
6.7
7.8
<1
<1
<1
<1
60.8
61.8
77.8
72.6
64.3
60.4
66.5
57.2
82.5
83.9
85.5
84.1
Figure 1. Time course of the conversion of 5-HMF to HHD. Reaction
conditions: 5-HMF (0.95 mmol), catalyst Cp*Ir-A (0.0025 mmol,
0.26 mol % to 5-HMF), and water (4.0 mL), under 7 bar of H2, at 120
°C.
2
3
4
5
6
7
8
9
c
c
yield of HHD was increased. However, DHMF maintained at
nearly 10% yield during the reaction and disappeared near the
end of the reaction. In addition, the selective hydrogenative ring
opening of DHMF was also studied (Table 2). Full conversion
d
A
A
A
A
e
10
11
12
d
d
,
,
f
f
,
,
g
a
Table 2. Reaction of Furans Catalyzed by Cp*Ir-A Catalyst
h
a
Reaction conditions: 5-HMF (0.95 mmol), catalyst (0.0025 mmol,
0.26 mol % to 5-HMF), and water (4.0 mL), under 20 bar of H2, at
b
110 °C, for 1.0 h. GC-MS yield, N,N-dimethylformamide was the
c
d
e
f
g
h
internal standard. 1.5 h. 120 °C. 130 °C. 2.0 h. 7 bar H2. 5 bar
b
b
entry
furans
yield of 2,5-HD (%)
yield of HHD (%)
H2.
1
2
3
2,5-DMF
5-MF
4.5
35.6
0
−
0
carried out at 110 °C under 20 bar of H2 by using 2,2′-
bipyridine coordinated Cp*Ir-A. After 1 h, 89.0% of 5-HMF
was converted to HHD in 60.8% yield and dihydroxy-
methylfuran (DHMF) in 8.2% yield (entry 1). A similar result
was observed when using phenanthroline coordinated Cp*Ir-B
(entry 2). To achieve full conversion of 5-HMF, longer reaction
time was required (1.5 h, entries 3 and 4), and the yield of
HHD was increased to 72.6−77.8%. When Cp*Ir-complexes
coordinated by [2,2′-bipyridin]-6-amine, 1,10-phenanthrolin-2-
amine, 2,2′-bipyrimidine, 4,4′-dimethoxy-2,2′-bipyridine (C−
F) were used as the catalysts, although full conversion of 5-
HMF was achieved after 1 h (entries 5−8), the yield of HHD
did not further increase compared with entry 3. Thus, Cp*Ir-A
was used as the catalyst for the subsequent optimization. When
the reaction was carried out at 120 °C, the yield of HHD was
increased to 82.5% (entry 9). The yield of HHD did not
increase any further at elevated temperature, 130 °C (entry 10).
The highest yield was obtained under 7 bar of H2 (85.8%, entry
DHMF
38.9
a
Reaction conditions: furans (0.5 mmol), catalyst (0.00125 mmol,
0.25 mol % to substrate), and water (2.0 mL), under 7 bar of H2, at
120 °C, for 0.5 h. GC-MS yield, N,N-dimethylformamide was the
internal standard.
b
of DHMF and 38% yield of HHD were observed. On the basis
of the results, we propose that 5-HMF is first hydrogenated to
produce highly reactive intermediate DHMF,30,31 followed by
hydrolytic ring opening of DHMF and a final hydrogenation to
form HHD.
We then studied the reaction of 2,5-dimethylfuran (2,5-
DMF) and 5-methylfufural (5-MF) by homogeneous Cp*Ir-A
catalyst (Table 2). Interestingly, the ring opening product of 5-
MF (35.6%, entry 2) is nearly 9 times of that from 2,5-DMF
(4.5%, entry 1). These results may be rationalized on the basis
that 5-MF is first hydrogenated to form (5-methylfuran-2-
789
DOI: 10.1021/cs501874v
ACS Catal. 2015, 5, 788−792

ACS Catalysis
Letter
Scheme 2. Plausible Mechanism for Ring Opening of 5-MF and DHMF
a
yl)methanol (5-MHF). Comparing with 2,5-DMF, the hydroxyl
group of 5-MHF may have accelerated the hydrolysis reaction.
The hydroxyl group of 5-MHF also controls H2O addition
direction (C2-addition product I was not detected by GC-MS,
Scheme 2), which led to (hexane-2,5-dione) 2,5-HD as the only
product. Although heterogeneous Ir catalysts were capable of
catalyzing ring opening of hydrocarbons,41 the reaction
substrates and conditions are very different from those studied
in this work with the homogeneous Ir complexes. On the basis
of our above results, we propose that31,32,42,43 hydroxymethyl
furans would generate intermediate G through Path A (two-
steps reaction: water added to double bond, followed by H- and
OH-elimination) or Path B (a hydroxymethyl group promoted
one-step hydrolysis process). α,β-Unsaturated carbonyl com-
pound H would be produced from hydrolysis of G, followed by
hydrogenation to form the final product J.
Table 3. Hydrogenation of K and the GC-MS Results
component of component of
equilibrium
Ir−H(D) (%)
equilibrium
H+(D)+ (%)
entry temperature (°C) pressure (bar) Ir−H Ir−D
H+
D+
1
2
3
4
5
100
100
100
80
5
88.8
86.9
87.8
91.6
74.1
11.2
13.1
12.1
8.4
2.9
2.7
2.8
2.8
3.3
97.1
97.3
97.2
97.2
96.7
10
15
10
10
120
25.9
a
Reaction conditions: substrate K (0.5 mmol), catalyst (0.00125
We also studied the fundamental mechanism of H2 activation
by the Cp*Ir-A complex in catalytic hydrogenation of carbon−
carbon double bond involved in Scheme 2 (step c). Compound
K was used as the analogue of α,β-unsaturated carbonyl
compound H. The hydrogenation of K catalyzed by Cp*Ir-A
was carried out in D2O, and the deuterated product L was
analyzed by GC-MS. Molecular ion M and fragment ion N
were used for the data analysis. The results shown in Table 3
were calculated on the basis of the deuteron incorporation in M
and N. (Details are shown in 3.1, Tables S1 and S2, Supporting
Information.) It is proposed that hydride/deuteride exchange
process happened during the reaction. It was obtained by GC-
MS analysis that the fraction of Ir-D is 11.2%, and the fraction
of Ir−H is 88.8% (entry 1). The fraction of Ir-D did not change
when H2 pressure was varied (entries 2 and 3). The fraction of
Ir-D was increased at higher temperature (entry 4) and vice
versa (entry 5). For proton/deuteron exchange process, it was
found that the fraction of D+ was maintained at 97%, and the
fraction of H+ was near 3%. These results supported the
expected high exchange rate between H+ and D2O generated
D+ in situ.
mmol, 0.25 mol % to K), and D2O (2.0 mL), for 0.5 h.
Scheme 3. Proposed Activation Mode of H2 by Cp*Ir-A
Complex in D2O
to generate IrIII−H and H+ intermediate, followed by H+
exchange with D2O to produce D+ (step 2), and IrIII−H
equilibrium with IrIII-D through an IrI intermediate (step 3).
To verify the pathway to generate intermediate G shown in
Scheme 2, the hydrogenation/hydrolysis ring opening of
DHMF catalyzed by Cp*Ir-A was also studied in D2O solution.
Statistical calculation based on independent events (Detailed
statistical calculations based on Path A are shown in Table S4
and Scheme S2; Detailed statistical calculations based on Path
B are shown in Table S3 and Scheme S1, Supporting
Information.) was used to estimate the composition of
deuterated fragment ion O (m/z = 101, 102, 103, 104). The
calculated values (ω) are summarized in Table 4. It became
On the basis of the above results and the literatures,44−46
a
plausible mechanism of H2 activation by Cp*Ir-A in D2O is
proposed as shown in Scheme 3. H2 was activated by Cp*Ir-A
790
DOI: 10.1021/cs501874v
ACS Catal. 2015, 5, 788−792

ACS Catalysis
Letter
a
Table 4. Statistical Calculation and Experimental Results
data resource
GC-MS
D1−N m/z = 100
D2−N m/z = 101
D3−N m/z = 102
D4−N m/z = 103
5.8%
70.1%
20.8%
2.7%
calcd (path A, Scheme 2)
calcd (path B, Scheme 2)
0.2%< ω <2.5%
4.7%
6.9%<ω <38.9%
70.7%
46.8%< ω <69.4%
24.5%
11.7%< ω <23.5%
0%
a
Reaction conditions: DHMF (0.5 mmol), catalyst (0.00125 mmol, 0.25 mol % to DHMF), and D2O (2.0 mL), under 10 bar of H2, at 120 °C, for
0.5 h.
evident that the calculated data based on path B and the
experimental data agree well. Thus, the calculated data support
that the formation of HHD from DHMF is mainly through
hydroxymethyl group promoted hydrolysis process (Path B,
Scheme 2).
ACKNOWLEDGMENTS
■
This research was supported by China Postdoctoral Science
Foundation (2013M540236), National Natural Science Foun-
dation of China (21306186), and the Chinese Government
“Thousand Talent” program funding.
Inspired by the above results, 4-(5-(hydroxymethyl)furan-2-
yl)but-3-en-2-one (HMFBE) was synthesized through con-
densation of 5-HMF with acetone. Cp*Ir-B was the most
effective catalyst for this reaction. Compared with the results of
5-HMF, the lower solubility of HMFBE in water may have
attributed to the decrease in catalytic reactivity, and nonane-
2,5,8-trione (2,5,8-NT) was obtained with 72% yield (Scheme
4).
REFERENCES
■
(1) Teong, S. P.; Yi, G.; Zhang, Y. Green Chem. 2014, 16, 2015−
2026.
(2) van Putten, R.-J.; van der Waal, J. C.; de Jong, E.; Rasrendra, C.
B.; Heeres, H. J.; de Vries, J. G. Chem. Rev. 2013, 113, 1499−1597.
(3) Zakrzewska, M. E.; Bogel-Łukasik, E.; Bogel-Łukasik, R. Chem.
Rev. 2011, 111, 397−417.
(4) Corma, A.; Iborra, S.; Velty, A. Chem. Rev. 2007, 107, 2411−
2502.
Scheme 4. Synthesis of 2,5,8-NT
(5) Jia, S.; Liu, K.; Xu, Z.; Yan, P.; Xu, W.; Liu, X.; Zhang, Z. C. Catal.
Today 2014, 234, 83−90.
(6) Zhao, H.; Holladay, J. E.; Brown, H.; Zhang, Z. C. Science 2007,
316, 1597−1600.
(7) Nikolla, E.; Roman
Catal. 2011, 1, 408−410.
(8) Roman-Leshkov, Y.; Chheda, J. N.; Dumesic, J. A. Science 2006,
́
-Leshkov, Y.; Moliner, M.; Davis, M. E. ACS
́
312, 1933−1937.
(9) Bozell, J. J.; Petersen, G. R. Green Chem. 2010, 12, 539−554.
(10) Nakagawa, Y.; Tamura, M.; Tomishige, K. ACS Catal. 2013, 3,
2655−2668.
In conclusion, we have demonstrated a highly efficient
homogeneous catalytic system for the hydrogenation/hydro-
lytic ring opening reaction of 5-HMF to produce biodiketones
HHD. High yield of HHD was achieved by using CP*Ir-A as
catalyst in water under mild conditions. This represents a
powerful addition to the suite of fundamental organic
transformations from biobased platform 5-HMF. The mecha-
nistic study based on the results of MS analysis and statistical
calculation not only allow us to rationalize our results but also
may broadly impact on the transformation of 5-HMF by
homogeneous catalysts. Further improvement of the catalyst
efficiency and developing a homogeneous catalytic process for
economic production of bioketones from 5-HMF are under-
way.
(11) Chen, J.; Lu, F.; Zhang, J.; Yu, W.; Wang, F.; Gao, J.; Xu, J.
ChemCatChem. 2013, 5, 2822−2826.
(12) Binder, J. B.; Raines, R. T. J. Am. Chem. Soc. 2009, 131, 1979−
1985.
(13) Roman-Leshkov, Y.; Barrett, C. J.; Liu, Z. Y.; Dumesic, J. A.
Nature 2007, 447, 982−985.
(14) Saha, B.; Bohn, C. M.; Abu-Omar, M. M. ChemSusChem 2014,
7, 3095−3101.
(15) Caretto, A.; Perosa, A. ACS Sustainable Chem. Eng. 2013, 1,
989−994.
́
(16) Chia, M.; Pagan-Torres, Y. J.; Hibbitts, D.; Tan, Q.; Pham, H.
N.; Datye, A. K.; Neurock, M.; Davis, R. J.; Dumesic, J. A. J. Am. Chem.
Soc. 2011, 133, 12675−12689.
́
(17) Buntara, T.; Noel, S.; Phua, P. H.; Melian-Cabrera, I.; de Vries,
ASSOCIATED CONTENT
J. G.; Heeres, H. J. Angew. Chem., Int. Ed. 2011, 50, 7083−7087.
(18) Zeng, C.; Seino, H.; Ren, J.; Hatanaka, K.; Yoshie, N.
Macromolecules 2013, 46, 1794−1802.
■
S
* Supporting Information
The following file is available free of charge on the ACS
(19) Gupta, N. K.; Nishimura, S.; Takagaki, A.; Ebitani, K. Green
Chem. 2011, 13, 824−827.
Publications website at DOI: 10.1021/cs501874v.
(20) Julis, J.; Holscher, M.; Leitner, W. Green Chem. 2010, 12, 1634−
̈
Full experimental details and calculation details (PDF)
1639.
(21) Sutton, A. D.; Waldie, F. D.; Wu, R.; Schlaf, M.; ‘Pete’ Silks, L.
A., III; Gordon, J. C. Nat. Chem. 2013, 5, 428−432.
(22) Pupovac, K.; Palkovits, R. ChemSusChem 2013, 6, 2103−2110.
(23) Thananatthanachon, T.; Rauchfuss, T. B. ChemSusChem 2010,
3, 1139−1141.
(24) Deuss, P. J.; Barta, K.; de Vries, J. G. Catal. Sci. Technol. 2014, 4,
1174−1196.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: zczhang@yahoo.com (Z.C.Z.).
Notes
The authors declare no competing financial interest.
791
DOI: 10.1021/cs501874v
ACS Catal. 2015, 5, 788−792

ACS Catalysis
Letter
(25) Pasini, T.; Solinas, G.; Zanotti, V.; Albonetti, S.; Cavani, F.;
Vaccari, A.; Mazzanti, A.; Ranieria, S.; Mazzoni, R. Dalton Trans. 2014,
43, 10224−10234.
(26) Grochowski, M. R.; Yang, W.; Sen, A. Chem.Eur. J. 2012, 18,
12363−12371.
(27) Xu, Z.; Yan, P.; Xu, W.; Jia, S.; Xia, Z.; Chung, B.; Zhang, Z.
Conrad RSC Adv. 2014, 4, 59083−59087.
(28) O’Reilly, E.; Iglesias, C.; Ghislieri, D.; Hopwood, J.; Galman, J.
L.; Lloyd, R. C.; Turner, N. J. Angew. Chem., Int. Ed. 2014, 53, 2447−
2450.
(29) Kotani, S.; Aoki, S.; Sugiura, M.; Ogasawara, M.; Nakajima, M.
Org. Lett. 2014, 16, 4802−4805.
(30) Schiavo, V.; Descotes, G.; Mentech, J. Bull. Soc. Chim. Fr. 1991,
128, 704−711.
(31) Luijkx, G. C. A.; Huck, N. P. M.; van Rantwijk, F.; Maat, L.; van
Bekkum, H. Heterocycles 2009, 77, 1037−1044.
(32) Liu, F.; Audemar, M.; De Oliveira Vigier, K.; Clacens, J.-M.; De
́ ̂
Campo, F.; Jerome, F. ChemSusChem 2014, 7, 2089−2093.
(33) Ohyama, J.; Kanao, R.; Esakia, A.; Suatsuma, A. Chem. Commun.
2014, 50, 5633−5636.
(34) Girisuta, B.; Janssen, L. P. B. M.; Heeres, H. J. Green Chem.
2006, 8, 701−709.
(35) Patil, S. K. R.; Heltzel, J.; Lund, C. R. F. Energy Fuels 2012, 26,
5281−5293.
(36) Patil, S. K. R.; Lund, C. R. F. Energy Fuels 2011, 25, 4745−4755.
(37) Brewster, T. P.; Miller, A. J. M.; Heinekey, D. M.; Goldberg, K.
I. J. Am. Chem. Soc. 2013, 135, 16022−16025.
(38) Fujita, K.; Tanaka, Y.; Kobayashi, M.; Yamaguchi, R. J. Am.
Chem. Soc. 2014, 136, 4829−4832.
(39) Deng, J.; Wang, Y.; Pan, T.; Xu, Q.; Guo, Q.-X.; Fu, Y.
ChemSusChem 2013, 6, 1163−1167.
(40) Liu, Z.; Deeth, R. J.; Butler, J. S.; Habtemariam, A.; Newton, M.
E.; Sadler, P. J. Angew. Chem., Int. Ed. 2013, 52, 4194−4197.
(41) For selected examples of ring opening of hydrocarbons
catalyzed by heterogeneous Ir catalysts: Baird, W. C. Jr.; Chen, J.
G.; McVicker, G. B. WO 2002008157, January 31, 2002.
́
(42) Alamillo, R.; Tucker, M.; Chia, M.; Pagan-Torres, Y.; Dumesic,
J. Green Chem. 2012, 14, 1413−1419.
(43) Horvat, J.; Klaic, B.; Metelko, B.; Sunjic, V. Tetrahedron Lett.
1985, 26, 2111−2114.
(44) Gabrielsson, A.; van Leeuwen, P.; Kaim, W. Chem. Commun.
2006, 4926−4927.
(45) Heiden, Z. M.; Rauchfuss, T. B. J. Am. Chem. Soc. 2006, 128,
13048−13049.
(46) Fukuzumi, S.; Kobayashi, T.; Suenobu, T. J. Am. Chem. Soc.
2010, 132, 1496−1497.
792
DOI: 10.1021/cs501874v
ACS Catal. 2015, 5, 788−792