Synergistic effects in Fe nanoparticles doped with ppm levels of (Pd + Ni). A new catalyst for sustainable nitro group reductions

Article abstract of DOI:10.1039/c7gc02991h

A remarkable synergistic effect has been uncovered between ppm levels of Pd and Ni embedded within iron nanoparticles that leads to mild and selective catalytic reductions of nitro-containing aromatics and heteroaromatics in water at room temperature. NaBH₄ serves as the source of inexpensive hydride. Broad substrate scope is documented, along with several other features including: low catalyst loading, low residual metal in the products, and recycling of the catalyst and reaction medium, highlight the green nature of this new technology.

Full text of DOI:10.1039/c7gc02991h

Green Chemistry
View Article Online
View Journal
COMMUNICATION
Synergistic effects in Fe nanoparticles doped with
ppm levels of (Pd + Ni). A new catalyst for
sustainable nitro group reductions†
Cite this: DOI: 10.1039/c7gc02991h
Received 3rd October 2017,
Accepted 27th November 2017
Haobo Pang,a Fabrice Gallou, b Hyuntae Sohn,c Jeffrey Camacho-Bunquin,c
DOI: 10.1039/c7gc02991h
a
Massimiliano Delferro c and Bruce H. Lipshutz
*
rsc.li/greenchem
A remarkable synergistic effect has been uncovered between ppm water at room temperature when ppm levels of both Pd and Ni
levels of Pd and Ni embedded within iron nanoparticles that leads are embedded within iron nanoparticles.
to mild and selective catalytic reductions of nitro-containing aro-
Selective reduction of nitro groups represents an essential
matics and heteroaromatics in water at room temperature. NaBH4 methodology, given the importance of this functional group
serves as the source of inexpensive hydride. Broad substrate scope within intermediates for fine chemicals, agrochemicals, phar-
is documented, along with several other features including: low maceuticals, dyes, and polymers.5 In general, reductions of
catalyst loading, low residual metal in the products, and recycling nitroarenes tend to be either metal-free or metal-based.6 The
of the catalyst and reaction medium, highlight the green nature of latter category tends to rely on precious metals such as Pd,7
this new technology.
Au,8 Ru,9 Pt10 and In,11 or non-noble metals such as Co,12
Ni,13 Mo,14 Zn,15 Ti16 and Fe.17 Although hydrogenation has
been the most widely used approach, issues such as the need
for high pressure equipment, flammable hydrogen gas, and
relatively high loadings of expensive metals that oftentimes
Introduction
Bimetallic catalysis is a blossoming area of synthetic organic can localize as residual metal in the product remain.
chemistry, potentially offering tremendous opportunities that Environmental concerns stemming in large measure
augment traditional metal-catalyzed processes.1 As recently from organic waste that is mainly attributed to organic sol-
reviewed by Pye and Mankad,2 both mixed metal and multi- vents18 can add to the unattractiveness of such traditional
valent, single metal catalysts have led to exciting C–C and C–X approaches.
couplings, while selected oxidations using related species have
In previous work from our group,19 it was found that com-
also been highlighted this year as well by Parmeggiani, mercial sources of FeCl3 augmented with only 80 parts per
Matassini, and Cardona.3 Missing from these discussions are million (ppm) Pd, upon processing into nanoparticles (NPs),
applications of synergistic effects to multiple metal-catalyzed could be used to catalyze the reduction of nitroarenes at room
processes in general, and to nitro group reductions, in particu- temperature. Only two weight percent of our designer surfac-
lar. Development of a highly efficient new technology that not tant TPGS-750-M in water was needed to generate nanomi-
only takes advantage of two transition metals working in celles that serve as the reaction medium, with NaBH4 as the
harmony towards a common synthetic goal, but also adheres stoichiometric source of hydride. Due to the extremely low pal-
to many of the 12 Principles of Green Chemistry4 would be of ladium loading, we endeavoured to further enhance the
special merit. In this report we describe a newly discovered activity of this catalyst (Fe/ppm Pd NPs), especially with highly
synergistic relationship between two group 10 metals. That is, functionalized substrates. Therefore, a far more reactive and
very clean reduction of aromatic and heteroaromatic nitro functional group tolerant catalyst was sought that would mini-
groups to the corresponding primary amines takes place in mize reaction times, of particular interest to reactions run at
scale.
aDepartment of Chemistry and Biochemistry, University of California, Santa Barbara,
California 93106, USA. E-mail: lipshutz@chem.ucsb.edu
bNovartis Pharma AG, Basel, Switzerland
cChemical Sciences and Engineering Division, Argonne National Laboratory, Lemont,
Results and discussion
IL 60439, USA
Our initial study began with replacement of the Pd present in
the NPs with varying amounts of Ni salts, with best results
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
c7gc02991h
This journal is © The Royal Society of Chemistry 2017
Green Chem.

View Article Online
Communication
Green Chemistry
Table 2 Comparison between Fe/ppm Pd + Ni NPs and NPs of Fe/ppm
Pd (without Ni)
obtained using Ni(NO3)2·6H2O (Fig. 1). Reagent optimization
studies revealed a dependence on two key variables in addition
to the nickel(II) source: (1) the equivalents of MeMgCl used to
form the NPs, and (2) the amount of NaBH4 used for catalyst
activation (see the ESI, Tables S1 to S5†). Using 4-chloronitro-
benzene as a model substrate, reaction with Fe/ppm Ni NPs
was surprisingly slower (12 h) than the corresponding reaction
using Fe/ppm Pd NPs (2 h; Table 1). Remarkably, preparing
the same NPs containing both 80 ppm Pd, 1600 ppm Ni and
2 mol% Fe led to complete conversion in 15 minutes.
Additional examples, as illustrated in Table 2, attest to this
same trend. Fe NPs prepared from pure FeCl3 in the absence
of both Pd and Ni led to a very slow reaction (19% product
after 14 h).
Fe/ppm Pd + Nia
Fe/ppm Pd
Time
Substrate
Time
Yieldb
Yieldb
96%
30 min
98%
88%
98%
90 min
2 h
12 h
2 h
72%
94%
30 min
Following reduction with MeMgCl, the mixture was
quenched with pentanes containing traces of water, and then
triturated by additional pentanes to afford khaki-colored Fe/
ppm Pd + Ni NPs (Fig. 1). The nanoparticles could be used
directly upon activation with NaBH4 (Fig. 2), or isolated and
stored in solid form, without loss of activity, for several
months at room temperature and without protection from air.
Should these NPs turn from yellow-brown to orange upon
exposure to air over time, there is no loss in activity since the
NaBH4 in the pot quickly converts them back to their active
form. This process could be further streamlined by taking
advantage of the recently disclosed co-solvent effect,20 in these
cases using 10% THF. As revealed by each of the five additional
30 min
2 h
99%
88%
2 h
8 h
98%
90%
a Ni source: Ni(NO3)2·6H2O, MeMgCl: 1.27 equiv. b Isolated yield.
Fig. 1 Generation and appearance of iron nanoparticles continuing
ppm levels of Pd and Ni.
Fig. 2 Generation (A) and appearance, after exposure to NaBH4; (B) of
iron nanoparticles containing ppm levels of Pd and Ni.
Table 1 Comparison of rates of reduction by NPs in water
examples illustrated in Table 2, the rates of reduction could be
increased significantly.
Analyses of the active NPs by transmission electron
microscopy (TEM), using a copper grid, in 2 wt% TPGS-750-M
aqueous solutions show spherical particles (Fig. 3). As seen
previously,21 these metal NPs are associated with existing
nanomicelles in aqueous solution due to the presence of (M)
PEG within the surfactant. Energy Dispersive X-Ray (EDX) data
(Fig. 4) for the same nanoparticles indicate that the ratio of Fe/
Ni is 12.3, which is close to the theoretical ratio of 11.9 (see
the detailed calculation in ESI 5b†). The presence of palladium
at these low levels, as expected,19 was not observed.
Nanoparticles (NPs)
Yield (%)
Time
Fe/ppm Pd NPs
90
79
96
2 h
12 h
15 min
Fe/ppm Ni NPsa
Fe/ppm Pd + Ni NPsb
a Ni(NO3)2·6H2O as Ni source, 1600 ppm Ni. b Ni(NO3)2·6H2O as Ni
source; 1600 ppm Ni, 80 ppm Pd.
To assess the scope of this technology, an expansive study
was undertaken examining several types of nitroarenes and
-heteroarenes. Under standard conditions (i.e.,
2 wt%
Green Chem.
This journal is © The Royal Society of Chemistry 2017

View Article Online
Green Chemistry
Communication
13, 19, 22, 24) were found to also lead to clean overall primary
amine formation. Lowering the global concentration from 0.5
to 0.25, or even 0.10 M also occasionally was beneficial (see 11,
14, 15, 16, 22, 24, 25, 26, 27, 28). Typically, NaBH4 was used to
generate the Pd–H species, although on occasion, KBH4 led to
a more effective reduction, as noted previously by Gallou and
co-workers.22
Given the increasing number of key synthetic transform-
ations that can now be run under mild conditions in aqueous
media using micellar technology,23 sequences can be planned
that take advantage of the commonality of this reaction
medium. As examples that include nitro group reductions,
product 27 could be formed via this NP-mediated reduction,
after which it is then converted to its Cbz derivative 28. Final
cyclization via a Fischer indole synthesis to 29 proceeded in
good overall yield (Scheme 1).
Fig. 3 Catalyst characterization by cryo-TEM of Fe/ppm Pd + Ni NPs in
aqueous TPGS-750-M after adding NaBH4.
An alternative, representative 1-pot sequence, illustrated
Scheme 2, converts 4-chloronitorbenzene initially to its aniline
derivative. Subsequent SNAr addition leads to adduct 30, and
then a Suzuki–Miyaura coupling affords biaryl 31, all done in
water between rt and 45 °C in high overall yield.
As is characteristic of designer surfactant technology in
water, “in flask” recycling of an aqueous reaction mixture is
straight forward.18 Thus, following reduction of a nitroaro-
matic (Scheme 3), extraction of the resulting substituted
aniline upon addition of minimal amounts of a single organic
solvent (e.g., MTBE) afforded the desired product, subject to
purification. The E Factor24 associated with this process based
on solvent usage as a measure of “greenness” is <4, which is
quite low and reflects the limited solvent needed to remove the
product from the reaction mixture. As THF remains partly in
the aqueous phase, no additional co-solvent is needed with
Fig. 4 EDX for Fe/ppm Pd + Ni NPs in the presence of NaBH4.
TPGS-750-M/H2O, NaBH4 (3 equiv.), 10% THF co-solvent at each recycle. Addition of fresh NPs, however, was required to
room temperature), most reactions took place quite smoothly ensure full conversion after an extractive workup. Yields for
and in excellent yields (Table 3). Products containing substitu- each of the four recycles studied remained high.
ents on the aromatic/hetroaromatic ring, including fluoro-(10),
Another important aspect of this protocol concerns the
chloro-(1, 4), bromo-(2, 7, 10, 14), trifluoromethyl-(12, 17, 18), amounts of residual metal to be expected in the product from
chlorodifluoromethoxy-(23), were formed without incident. reductions of nitroarenes. Established guidelines for allowable
Reduction in the presence of other functionality, such as ester, levels of transition metal impurities vary as a function of levels
amide, sulfonyl-, thio-, hydrazinyl-, as well as C–C double of toxicity.25 Residual Fe is considered relatively innocuous
bonds, likewise, occurred smoothly. Heterocycles including pyri- (limit: 1300 ppm), while limits for both Ni (25 ppm) and
dine, isoxazole, quinoline, piperazine, piperidine, morpholine especially Pd (10 ppm) are far more rigorous.19 Metal impuri-
were all tolerated, strongly suggesting potential applications to ties that exceed these levels require additional time, effort, and
targets in the pharmaceutical and agrochemical arenas. By con- cost to have them removed or at least, reduced to allowable
trast, reactions run under identical conditions but in pure THF levels.
were extremely slow, with 4-chloronitrobenzene affording the
targeted product to the extent of only 27% after 16 hours.
Analyses were conducted on several products resulting
from Fe/ppm Pd + Ni NP-catalyzed nitro group reductions by
Several of the examples studied (Table 3) presented special inductively coupled plasma mass spectrometry (ICP-MS).
challenges due to the nature of nitro compounds that can be Results (see ESI†) showed residual palladium to be below
highly crystalline, and/or flocculent solids and therefore, slow 10 ppm, while residual nickel was below 1 ppm. Residual iron
to gain entry to the inner micellar cores. Practical issues, such was also measured and found to be below 5 ppm, implying in
an adherence to the stir bar, or formation of insoluble gums, the composite that release of any metal from these NPs is
were readily solved by the presence of varying amounts of a co- minimal.
solvent. While THF was the first co-solvent to be chosen (see
The role played by the added Ni in enhancing reactivity of
products 14, 18, 20, 25, 27), varying percentage of other water- the in situ-formed palladium hydride can be initially ascer-
miscible co-solvents such as MeOH (see 16) and DMSO (see tained via XAS experiments on the activated catalysts, Fe/ppm
This journal is © The Royal Society of Chemistry 2017
Green Chem.

View Article Online
Communication
Green Chemistry
Table 3 Representative reductions of nitroarenesa,b
a Reaction conditions: Nitro compound (0.5 mmol), Fe nanoparticles (6 mg, 2% Fe, 80 ppm Pd, 1600 ppm Ni), NaBH4 (1.5 mmol), 2 wt%
TPGS-750-M/H2O (1 mL), THF (0.1 mL). b Isolated yield. c Nitro compound (0.125 mmol), Fe nanoparticles (3 mg), NaBH4 (0.375 mmol), 2 wt%
TPGS-750-M/H2O (1 mL), THF (0.1 mL). d DMSO (0.25 mL). e Nitro compound (0.125 mmol), Fe nanoparticles (3 mg), NaBH4 (0.375 mmol),
2 wt% TPGS-750-M/H2O (1 mL), THF (0.3 mL). f Nitro compound (0.25 mmol), Fe nanoparticles (3 mg), NaBH4 (0.75 mmol), TPGS-750-M/H2O
(1 mL), THF (0.1 mL). g Nitro compound (0.25 mmol), Fe nanoparticles (3 mg), NaBH4 (0.75 mmol), TPGS-750-M/H2O (1 mL), CH3OH (0.25 mL).
h Nitro compound (0.5 mmol), Fe nanoparticles (12 mg), NaBH4 (3 mmol), 2 wt% TPGS-750-M/H2O (1 mL), DCM (0.1 mL). i THF (0.25 mL). j Nitro
compound (0.5 mmol), Fe nanoparticles (12 mg), KBH4 (3 mmol), 2 wt% TPGS-750-M/H2O (1 mL), THF (0.25 mL). k Nitro compound
(0.125 mmol), Fe nanoparticles (1.5 mg), KBH4 (0.375 mmol), 2 wt% TPGS-750-M/H2O (1 mL), DMSO (0.25 mL). l Nitro compound (0.125 mmol),
Fe nanoparticles (2.5 mg), KBH4 (0.75 mmol), 2 wt% TPGS-750-M/H2O 1 mL, DMSO 0.25 mL. m Nitro compound (0.25 mmol), Fe nanoparticles
(2.5 mg), KBH4 (0.75 mmol), 2 wt% TPGS-750-M/H2O (1 mL), THF (0.25 mL). n Nitro compound (0.25 mmol), Fe nanoparticles (3 mg), NaBH4
(0.75 mmol), 2 wt% TPGS-750-M/H2O (1 mL), DCM (0.3 mL). o Nitro compound (0.125 mmol), Fe nanoparticles (1.5 mg), KBH4 (0.75 mmol),
2 wt% TPGS-750-M/H2O (1 mL), THF (0.25 mL).
Pd and Fe/ppm Pd + Ni. On the basis of EXAFS data, a higher tion-corrected HAADF STEM would be needed to establish Pd
shell scattering feature attributed to Pd–Pd interactions and site isolation in the presence of Ni, and these experiments are
the presence of Pd oligomers was observed for the Fe/ppm Pd presently under consideration. That a base metal such as
system. Such a feature was not observed in the presence of Ni nickel can be used to enhance the reactivity of a precious
(see ESI†), indicating that Ni dilutes the palladium content on metal within a nanoparticle catalyst, leading to greater activity
the surface of these NPs, leading to increased Pd dispersity notwithstanding the ppm levels involved, is an exciting discov-
and thereby, increasing the reactivity of the isolated palladium ery that may have a considerable number of applications to
atoms.26 More definitive imaging techniques such as aberra- other types of precious metal catalysis.
Green Chem.
This journal is © The Royal Society of Chemistry 2017

View Article Online
Green Chemistry
Communication
Acknowledgements
Financial support provided by Novartis and the NSF (SusChEM
1566212) is warmly acknowledged with thanks. Work at
Argonne National Laboratory is supported by the U.S.
Department of Energy (DOE), Office of Basic Energy Sciences,
Division of Chemical Sciences, Biosciences and Geosciences
under Contract DE-AC02-06CH11357. Use of the Advanced
Photon Source at Argonne National Laboratory is supported by
the U.S. Department of Energy, Office of Science, and Office of
Basic Energy Sciences, under Contract DE-AC02-06CH11357.
MRCAT operations are supported by the Department of Energy
and the MRCAT member institutions.
Scheme 1 1-Pot nitro group reduction followed by amine protection
and Fischer indole synthesis.
Notes and references
1 (a) S. De, J. Zhang, R. Luque and N. Yan, Energy Environ.
Sci., 2016, 9, 3314–3347; (b) M. Delferro and T. J. Marks,
Chem. Rev., 2011, 111, 2450–2485.
2 D. R. Pye and N. P. Mankad, Chem. Sci., 2017, 8, 1705–
1718.
3 C. Parmeggiani, C. Matassini and F. Cardona, Green Chem.,
2017, 19, 2030.
Scheme 2 1-Pot, 3-step sequence involving NO2 group reduction
/SNAr/Suzuki–Miyaura coupling, in water.
4 (a) P. T. Anastas and J. C. Warner, Green Chemistry: Theory
and Practice, Oxford University Press, 1998; (b) P. Anastas
and N. Eghbali, Chem. Soc. Rev., 2010, 39, 301.
5 (a) A. M. Birch, S. Groombridge, R. Law, A. G. Leach,
C. D. Mee and C. Schramm, J. Med. Chem., 2012, 55,
3923; (b) R. S. Downing, P. J. Kunkeler and H. van
Bekkum,
Catal.
Today,
1997,
37,
121–136;
(c) H.-U. Blaser, H. Steiner and M. Studer, ChemCatChem,
2009, 1, 210.
6 M. Orlandi, D. Brenna, R. Harms, S. Jost and M. Benaglia,
Org. Process Res. Dev., 2016, DOI: 10.1021/acs.oprd.6b00205.
7 (a) M. M. Dell’Anna, S. Intini, G. Romanazzi, A. Rizzuti,
C. Leonelli, F. Piccinni and P. Mastrorilli, J. Mol. Catal. A:
Chem., 2014, 395, 307; (b) A. Chinnappan and H. Kim, RSC
Adv., 2013, 3, 3399; (c) O. Verho, K. P. J. Gustafson,
A. Nagendiran, C.-W. Tai and J.-E. Bäckvall, ChemCatChem,
2014, 6, 3153.
Scheme 3 Studies on recycling and determination of E factor.
Conclusion
8 L. He, L.-C. Wang, H. Sun, J. Ni, Y. Cao, H.-Y. He and
K.-N. Fan, Angew. Chem., Int. Ed., 2009, 48, 9538.
9 S. G. Oh, V. Mishra, J. K. Cho, B.-J. Kim, H. S. Kim,
Y.-W. Suh, H. Lee, H. S. Park and Y. J. Kim, Catal.
Commun., 2014, 43, 79.
10 (a) E. H. Boymans, P. T. Witte and D. Vogt, Catal. Sci.
Technol., 2015, 5, 176; (b) H. Wei, X. Liu, A. Wang,
L. Zhang, B. Qiao, X. Yang, Y. Huang, S. Miao, J. Liu and
T. Zhang, Nat. Commun., 2014, 5, 5634; (c) B. Zhang,
H. Asakura, J. Zhang, J. Zhang, S. De and N. Yan, Angew.
Chem., Int. Ed., 2016, 55, 8319–8323.
In summary, a new catalyst useful for nitro group reductions
in water has been uncovered that contains ppm levels of both
Pd and Ni that work in harmony to afford greater reactivity
than that observed using related catalysts based on either indi-
vidual metal. The process is safe, takes place in water under
mild conditions, and allows for facile in-flask product isolation
as well as recycling of the entire aqueous reaction mixture.
Very low levels of residual metals are found in the isolated pro-
ducts, further enhancing the attractiveness of this environ-
mentally responsible technology.
11 N. Sakai, S. Asama, T. Konakahara and Y. Ogiwara,
Synthesis, 2015, 47, 3179.
12 (a) F. A. Westerhaus, R. V. Jagadeesh, G. Wienhöfer,
M.-M. Pohl, J. Radnik, A.-E. Surkus, J. Rabeah, K. Junge,
Conflicts of interest
The authors declare no conflicts of interest.
This journal is © The Royal Society of Chemistry 2017
Green Chem.

View Article Online
Communication
Green Chemistry
H. Junge, M. Nielsen, A. Brückner and M. Beller, Nat. 20 C. M. Gabriel, N. R. Lee, F. Bigorne, P. Klumphu,
Chem., 2013, 5, 537; (b) R. K. Rai, A. Mahata,
S. Mukhopadhyay, S. Gupta, P.-Z. Li, K. T. Nguyen, Y. Zhao,
M. Parmentier, F. Gallou and B. H. Lipshutz, Org. Lett.,
2017, 19, 194.
B. Pathak and S. K. Singh, Inorg. Chem., 2014, 53, 2904; 21 E. D. Slack, C. M. Gabriel and B. H. Lipshutz, Angew.
(c) R. V. Jagadeesh, D. Banerjee, P. B. Arockiam, H. Junge, Chem., Int. Ed., 2014, 53, 14051.
K. Junge, M.-M. Pohl, J. Radnik, A. Bruckner and M. Beller, 22 (a) C. M. Gabriel, M. Parmentier, C. Riegert, M. Lanz,
Green Chem., 2015, 17, 898.
S. Handa, B. H. Lipshutz and F. Gallou, Org. Process Res.
Dev., 2017, 21, 247; (b) See also M. Orlandi, D. Brenna,
R. Harms, S. Jost and M. Benaglia, Org. Process Res. Dev.,
2016, DOI: 10.1021/acs.oprd.6b00205.
13 (a) R. J. Kalbasi, A. A. Nourbakhsh and F. Babaknezhad,
Catal. Commun., 2011, 12, 955; (b) O. Mazaheri and
R. J. Kalbasi, RSC Adv., 2015, 5, 34398; (c) A. Chinnappan
and H. Kim, RSC Adv., 2013, 3, 3399.
14 E. Pedrajas, I. Sorribes, A. L. Gushchin, Y. A. Laricheva,
K. Junge, M. Beller and R. Llusar, ChemCatChem, 2017, 9,
1128.
15 S. M. Kelly and B. H. Lipshutz, Org. Lett., 2014, 16, 98.
16 M. L. Di Gioia, A. Leggio, I. F. Guarino, V. Leotta, E. Romio
and A. Liguori, Tetrahedron Lett., 2015, 56, 5341.
23 (a) B. H. Lipshutz and S. Ghorai, Green Chem., 2014, 16,
3660–3679; (b) B. H. Lipshutz, Johnson Matthey Technol.
Rev., 2017, 61, 196.
24 (a) R. A. Sheldon, I. W. C. E. Arends and U. Hanefeld,
Green Chemistry and Catalysis, Wiley-VCH, Weinheim,
2007, pp. 1–47; (b) R. A. Sheldon, Green Chem., 2007, 9,
1273.
17 (a) A. J. MacNair, M.-M. Tran, J. E. Nelson, G. U. Sloan, 25 Committee For Medicinal Products For Human Use
A. Ironmonger and S. P. Thomas, Org. Biomol. Chem., 2014,
12, 5082; (b) R. V. Jagadeesh, G. Wienhofer,
F. A. Westerhaus, A.-E. Surkus, M.-M. Pohl, H. Junge,
(CHMP), Guideline On The Specification Limits For Residues
Of Metal Catalysts Or Metal Reagents, European Medicines
Agency, London, 2008.
K. Junge and M. Beller, Chem. Commun., 2011, 47, 10972; 26 (a) J. Qu, X. Zhou, F. Xu, X.-Q. Gong and S. C. E. Tsang,
(c) K. Junge, B. Wendt, N. Shaikh and M. Beller, Chem.
Commun., 2010, 46, 1769.
18 B. H. Lipshutz, N. A. Isley, J. C. Fennewald and E. D. Slack,
Angew. Chem., Int. Ed., 2013, 52, 10911.
19 J. Feng, S. Handa, F. Gallou and B. H. Lipshutz, Angew.
Chem., Int. Ed., 2016, 55, 8979.
J. Phys. Chem. C, 2014, 118, 24452; (b) G. Liu, L. Zeng,
Z.-J. Zhao, H. Tian, T. Wu and J. Gong, ACS Catal., 2016, 6,
2158; (c) L. Shi, G.-M. Deng, W.-C. Li, S. Miao, Q.-N. Wang,
W.-P. Zhang and A.-H. Lu, Angew. Chem., Int. Ed., 2015, 54,
13994; (d) B. Qiao, A. Wang, X. Yang, L. F. Allard, Z. Jiang,
Y. Cui, J. Liu, J. Li and T. Zhang, Nat. Chem., 2011, 3, 634.
Green Chem.
This journal is © The Royal Society of Chemistry 2017