Synthesis of Bis(hydroxylmethylfurfuryl)amine Monomers from 5-Hydroxymethylfurfural

Article abstract of DOI:10.1002/cssc.201600122

We report the synthesis of bis(hydroxylmethylfurfuryl)amine (BHMFA) from 5-hydroxymethylfurfural (5-HMF) by reacting 5-HMF with primary amines in the presence of homogeneous Ru^II catalysts having sterically strained ligands. BHMFA is a group of furan-based monomers that offer great potential to form functional biopolymers with tunable properties. A range of primary amines, such as aliphatic and benzyl amines, are readily converted with 5-HMF to form the corresponding BHMFA in good yields. The reaction proceeds through reductive amination of 5-HMF with primary amine to form secondary amine, followed by reductive amination of 5-HMF with in situ generated secondary amine to produce BHMFA.

Full text of DOI:10.1002/cssc.201600122

DOI: 10.1002/cssc.201600122
Communications
Synthesis of Bis(hydroxylmethylfurfuryl)amine Monomers
from 5-Hydroxymethylfurfural
Zhanwei Xu, Peifang Yan, Kairui Liu, Lu Wan, Wenjuan Xu, Huixiang Li, Xiumei Liu, and
Z. Conrad Zhang*[a]
We report the synthesis of bis(hydroxylmethylfurfuryl)amine
(BHMFA) from 5-hydroxymethylfurfural (5-HMF) by reacting
5-HMF with primary amines in the presence of homogeneous
RuII catalysts having sterically strained ligands. BHMFA is
a group of furan-based monomers that offer great potential to
form functional biopolymers with tunable properties. A range
of primary amines, such as aliphatic and benzyl amines, are
readily converted with 5-HMF to form the corresponding
BHMFA in good yields. The reaction proceeds through reduc-
tive amination of 5-HMF with primary amine to form secondary
amine, followed by reductive amination of 5-HMF with in situ
Figure 1. Furan-based monomers from 5-HMF.
generated secondary amine to produce BHMFA.
Lignocellulosic biomass is the most abundant and renewable
feedstock in nature. 5-Hydroxymethylfurfural (5-HMF), a versa-
tile platform feedstock, is available from fructose, glucose, su-
crose, starch, inulin, as well as cellulose.[1] 5-HMF is regarded as
one of the most promising building blocks to produce valua-
ble chemicals and fuels. Starting with 5-HMF, numerous impor-
tant chemicals have become available.[2] For example,
2,5-dimethylfuran,[3] an important hydrogenation product from
5-HMF, was considered a suitable replacement for ethanol in
gasoline–ethanol blends. Levulinic acid obtained from 5-HMF
can be further converted to prepare fuel additives, dyestuffs,
and pharmaceutical compounds.[4] The hydrogenative/hydro-
lytic product 1-hydroxyhexane-2,5-dione may serve as a new
feedstock.[5] Aldol condensation of 5-HMF with acetone fur-
nishes a precursor for biofuels.[6]
with high CO2 adsorption capacity;[13] and 2,5-furandimethanol,
an hydrogenation product of 5-HMF, was used to synthesize
polyesters.[14] Some of the furan-based polymers were further
converted by thermo reversible Diels–Alder (D-A) reactions
with maleimide. These functional polymers may offer various
interesting properties, such as recyclability, shape memory,
soft–hard conversion, and healing ability. Although both the
synthesis of 2,5-disubstituted furans and polymerization have
been well developed so far, there are few studies regarding
the synthesis of aminated furan-based monomers from 5-HMF.
In this paper, we report the synthesis of bis(hydroxylmethyl-
furfuryl)amines (BHMFAs) directly from 5-HMF (Figure 1). We
anticipate BHMFAs to be a new group of inspiring furan-based
monomers owing to some important features of BHMFAs:
1) they can be easily prepared from 5-HMF; 2) compared with
2,5-disubstituted furans, a large number of BHMFAs can be
synthesized by varying the kinds of substituents; and 3) the
properties of BHMFAs can be modified by different substitu-
ents, which make it possible to synthesize biopolymers, such
as polyester and polyurethane, with self-healing ability and
malleability.
The recent rapid development of 5-HMF also offers numer-
ous opportunities for the synthesis and exploration of new
furan-based monomers and polymers (Figure 1). For example,
5-HMF can be converted to various 2,5-disubstituted furans, in-
cluding 2,5-furandicarboxylicacid,[7] 2,5-furandicarbaldehyde,[8]
2,5-furandimethanol,[9] and 2,5-furandiamine.[10] These mono-
mers show a high potential in step-growth and chain-growth
polymerizations.[11] More specifically, 2,5-furandicarboxylic acid
is an alternative to terephthalic and isophthalic acid;[12]
2,5-furandicarbaldehyde is a monomer to produce polyimines
The realm of BHMFAs has been the subject of very few in-
vestigations, beginning with Dunlop’s pioneering work
30 years ago, which described the synthesis of bis(hydroxylme-
thylfurfuryl)butylamine[15] and bis(hydroxylmethylfurfuryl)me-
thylamine[16] by Mannich-type reaction of furfuryl alcohol,
amine, and formaldehyde. Although the products yields were
not given in the patents, the yields of BHMFA are expected to
be low as furfuryl alcohol is unstable in strong acidic solution
and a complex procedure was adopted in the synthesis. Since
1980, using 5-HMF as a starting material to form BHMFAs has
been rarely studied, and very few structures are reported so
far.[17] Zhu and co-authors reported a one-pot reaction of
[a] Dr. Z. Xu, P. Yan, K. Liu, L. Wan, Dr. W. Xu, H. Li, Dr. X. Liu, Prof. Z. C. 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)
E-mail: zczhang@yahoo.com
Supporting Information for this article can be found under:
http://dx.doi.org/10.1002/cssc.201600122.
ChemSusChem 2016, 9, 1255 – 1258
1255
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communications
5-HMF and tryptamine with excess, costly Na(CN)BH3 as a hy-
drogen source, which generated copious amounts of waste or
toxic NaCN under humid conditions.[17]
decreased sharply at 1008C (entry 7). Under optimized condi-
tions, subsequent synthesis of furan-based BHMFA monomers
from 5-HMF and various amines was performed with
Ru(DMP)2Cl2 as the catalyst in EtOH at 110 8C under a H2 atmos-
phere (20 bar=2 MPa).
Ru-catalyzed reductive amination is a powerful method to
synthesize functional secondary and tertiary amines from alde-
hyde.[18] However, preparation of tertiary amines directly from
aldehyde and primary amines has limited studies. Recently, we
reported the Ru-catalyzed reductive amination of 5-HMF with
different amines.[19] Hydroxylmethylfurfurylamines were ob-
tained from a broad scope of primary and secondary amines.
We hypothesized that BHMFAs could be synthesized from
5-HMF and primary amines by Ru-catalyzed direct reductive
amination. To obtain BHMFAs as the major product, we applied
an excess of 5-HMF, increased temperature, higher H2 pressure,
and more Ru catalyst (Table 1).
The synthesis of furan-based monomers from 5-HMF and pri-
mary amines was performed under optimized conditions, and
the results are shown in Figure 2. The reactions of aliphatic
straight-chain amines such as ethyl, n-butyl, and n-dodecyl
amine smoothly proceeded to generate the corresponding
Table 1. Optimization of reaction conditions.[a]
Entry
Catalyst
T [8C]
Yield [%][b]
1
2
3
4
5
6
7
Ru(Bipy)2Cl2
110
110
110
110
110
120
100
71.3
85.4
23.1
90.3
0
Ru(Dmbp)2Cl2
Ru(Phen)2Cl2
Ru(DMP)2Cl2
RuHCl(CO)(PPh3)3
Ru(DMP)2Cl2
Ru(DMP)2Cl2
84.9
69.6
[a] Reaction conditions: Ru catalyst (1.0 mol% to amine), n-heptylamine
(115.2 mg, 1.0 mmol), EtOH (2.0 mL), and 5-HMF (290.0 mg, 2.3 equiv. to
n-heptylamine), under H2 (20 bar=2 MPa) for 12 h. [b] GC–MS yield.
Figure 2. Synthesis of furan-based monomers from 5-HMF. Reaction condi-
tions: Ru(DMP)2Cl2 (1.0 mol% to amine), amine (1.0 mmol), EtOH (2.0 mL),
and 5-HMF (290.0 mg, 2.3 equiv. to amine), under H2 (20 bar=2 MPa) for
12 h. Isolated yield is given in the figure.
Our initial studies began with the reaction of 5-HMF with
n-heptylamine as a model reaction for proof-of-concept inves-
tigation, followed by further optimization of the reaction con-
ditions (Table 1). Easily prepared and air-stable RuII com-
plexes,[20] including RuII(Bipy)2Cl2 (Bipy=2,2’-bipyridine),
RuII(Dmbp)2Cl2
(Dmbp=6,6’-dimethyl-2,2’-bipyridine),
(Phen=1,10-phenanthroline),
products 1b, 1c, and 1g in good yields (56.8%, 79.6%, and
82.6%, respectively). An aqueous solution of ethylamine
(65 wt%) was used. The lower yield of 1b is a result of the in-
fluence of additional water, as water could suppress imine/
iminium-ion formation. We also studied the reactivity of meth-
ylamine (25 wt%). Trace amounts of the corresponding prod-
uct 1a was observed from GC–MS analysis. As a more dilute
aqueous solution of methylamine (25 wt%) was used, more
water was introduced into the solution compared with ethyla-
mine (65 wt%), suggesting that the reactivity of methylamine
is lower than that of ethylamine. To increase the yield of 1a,
methylamine hydrochloride was used as a starting material.[22]
The yield of 1a was increased to 70.5% as the reaction was
carried out in the absence of water. iso-Butylamine gave the
product 1d in 75.1% yield, whereas no product was obtained
using tert-butylamine.[22] The sterically hindered tert-butyl
group hindered the coordination of the corresponding imine
with the Ru catalyst. Phenylethylamine gave the corresponding
RuII(Phen)2Cl2
RuII(DMP)2Cl2
and
(DMP=2,9-dimethyl-1,10-phenanthroline),
RuII(H)(Cl)(CO)(PPh3)3 were tested for the reaction in ethanol
(EtOH) solution (entries 1–5). Bidentate ligands seem to play an
important role to control reaction selectivity. The RuII catalysts
coordinated by sterically hindered ligands, such as Dmbp and
DMP, exhibited good catalytic activity (entries 2 and 4 with
yields of 85.4% and 90.3%, respectively), whereas Bipy- or
Phen-based catalysts resulted in poor product yields (entries 1
and 3 with yields of 71.3% and 23.1%, respectively). It is likely
that the Ru catalysts coordinated with sterically hindered li-
gands prefer cis-coordination mode,[21] which may be favorable
for H2 activation. The electron-donating methyl group may
also enhance the hydrogenative ability of RuII complexes. In-
creasing temperature for the Ru(DMP)2Cl2 catalyst in EtOH
from 110 8C (entry 4) to 1208C was not found to further im-
prove the product yield (entry 6). However, the product yield
ChemSusChem 2016, 9, 1255 – 1258
www.chemsuschem.org
1256
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communications
tertiary amine 1h in 88.3% yield. The reactivity of benzyl
amines was also studied. Good product yields of 79.7% and
87.4% were obtained when benzyl amine bore a bromo (1j) or
a methoxy group (1k), respectively. However, when the phenyl
ring is linked with a hydroxyl group, no desired product was
detected. Coordination of the phenol group to the catalyst
likely suppressed the reaction.
To test the practicability of this method, a gram-scale syn-
thesis of 1 f was studied. 1 f could be obtained in 84% yield
when 5-HMF (5.8 g) and n-heptylamine (2.3 g) were used.[22]
We performed X-ray photoelectron spectroscopy (XPS) analysis
of the catalyst residue after performing the hydrogenation.[22]
No reduction of the RuII complex to Ru0 metal was observed.
We studied the reaction of 5-HMF with n-heptylamine in the
presence of Ru(DMP)2Cl2 (0.5 mol%). The isolated yield of prod-
uct was 43% at 24 h, and the turnover number (TON) was 86.
Further work to improve the Ru catalyst for higher TON and
turnover frequency (TOF) is in progress.
Scheme 3. Proposed Ru-catalyzed hydrogenation pathway.
form intermediate a. The reaction of a with H2 forms b. As the
hydride atom and the imine group are on the ortho-position,
b generates c through the intramolecular hydrogenation path-
way. The reaction of c with acid produces amine and releases
the Ru catalyst. Stericly strained amines (tert-butylamine) may
influence the coordination chemistry of the corresponding
imine–Ru complex, which may further lower the hydrogena-
tion reactivity.
To investigate the reaction pathway, the hydrogenation of
imine 2 was studied (Scheme 1), and 95% of secondary amine
3 was obtained. Amine 3 reacted with 5-HMF to produce terti-
ary amine 1i with 90% yield. These results support our pro-
posed mechanism (Scheme 2) that the synthesis of BHMFA
from 5-HMF and primary amines proceeds through imine 4
formation, followed by hydrogenation of imine 4. The in situ
generated secondary amine 5 may further react with 5-HMF to
form iminium ion intermediate 7 through intermediate 6.[23]
The final hydrogenation of 7 may form furan-based BHMFA.
The mechanism of Ru-catalyzed hydrogenation is proposed
as shown in Scheme 3. Ru(DMP)2Cl2 with a trans-coordination
mode is not a favored structure, as the hydride atom and the
imine group are on the para-position. Ru(DMP)2Cl2 with steri-
cally hindered DMP ligand prefers cis-coordination mode.[21]
cis-Ru(DMP)2Cl2 may undergo ligand exchange with imine to
In summary, a simple and efficient procedure to synthesize
BHMFAs by direct hydrogenation of biomass-derived 5-HMF
and primary amines was developed. Sterically unstrained ali-
phatic at a-C position and benzyl amines showed good reac-
tivity and yield to form new furan-based diols. This represents
an important addition to the suite of furan-based monomers
from bio-based platform 5-HMF. Further improving of the cata-
lyst efficiency and a homogeneous catalytic process for eco-
nomic production of BHMFAs from 5-HMF, as well as produc-
tion of bio-polymers from BHMFAs, are underway.
Experimental Section
Synthesis of BHMFA: To a solution of 5-HMF (290.0 mg, 2.3 mmol)
in EtOH (2.0 mL) at room temperature was added Ru catalyst
(1.0 mol% to amine) and amine (1.0 mmol). The high pressure re-
actor (10 mL) was purged with H2 (20 bar=2 MPa) three times, and
was heated to the set temperature for 12 h until completion of the
reaction. After removing the solvent, the crude residue was puri-
fied on a silica gel column to afford the product.
Acknowledgements
Scheme 1. Reaction pathway studied.
This research was supported by China Postdoctoral Science Foun-
dation (2013M540236), the CAS/SAFEA International Partnership
Program for Creative Research Teams, and the Chinese Govern-
ment “Thousand Talent” program funding.
Keywords: biomass · green chemistry · polymers · renewable
resources · ruthenium
[1] a) S. P. Teong, G. Yi, Y. Zhang, Green Chem. 2014, 16, 2015; b) R. A. Shel-
don, Green Chem. 2014, 16, 950; c) R.-J. van Putten, J. C. van der Waal,
E. de Jong, C. B. Rasrendra, H. J. Heeres, J. G. de Vries, Chem. Rev. 2013,
113, 1499; d) M. E. Zakrzewska, E. Bogel-Łukasik, R. Bogel-Łukasik, Chem.
Scheme 2. Proposed mechanism.
ChemSusChem 2016, 9, 1255 – 1258
www.chemsuschem.org
1257
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communications
Rev. 2011, 111, 397; e) J. J. Bozell, G. R. Petersen, Green Chem. 2010, 12,
539; f) A. Corma, S. Iborra, A. Velty, Chem. Rev. 2007, 107, 2411.
[2] a) S. Zhu, J. Wang, W. Fan, Catal. Sci. Technol. 2015, 5, 3845; b) D. (D. J.)
Liu, E. Y.-X. Chen, Green Chem. 2014, 16, 964; c) Y. Nakagawa, M.
Tamura, K. Tomishige, ACS Catal. 2013, 3, 2655; d) T. Buntara, S. Noel,
P. H. Phua, I. Meliµn-Cabrera, J. G. de Vries, H. J. Heeres, Angew. Chem.
Int. Ed. 2011, 50, 7083; Angew. Chem. 2011, 123, 7221.
Scandola, R. A. Gross, Macromolecules 2013, 46, 796; d) L. Wu, R. Min-
cheva, Y. Xu, J. Raquez, P. Dubois, Biomacromolecules 2012, 13, 2973;
e) J. Ma, Y. Pang, M. Wang, J. Xu, H. Ma, X. Nie, J. Mater. Chem. 2012, 22,
3457; f) M. Jiang, Q. Zhang, C. Ye, G. Zhou, J. Polym. Sci. Part A 2012, 50,
1026; g) M. Gomes, A. Gandini, A. J. D. Silvestre, B. Reis, J. Polym. Sci.
Part A 2011, 49, 3759; h) A. Gandini, A. J. D. Silvestre, C. P. Neto, A. F.
Sousa, M. Gomes, J. Polym. Sci. Part A 2009, 47, 295.
[3] a) B. Saha, M. M. Abu-Omar, ChemSusChem 2015, 8, 1133; b) Y. Qian, L.
Zhu, Y. Wang, X. Lu, Renewable Sustainable Energy Rev. 2015, 41, 633;
c) L. Hu, L. Lin, S. Liu, Ind. Eng. Chem. Res. 2014, 53, 9969.
[13] a) T. Xiang, X. Liu, P. Yi, M. Guo, Y. Chen, C. Wesdemiotis, J. Xu, Y. Pang,
Polym. Int. 2013, 62, 1517; b) J. Ma, M. Wang, Z. Du, C. Chen, J. Gao, J.
Xu, Polym. Chem. 2012, 3, 2346.
[4] a) A. DØmolis, N. Essayem, F. Rataboul, ACS Sustainable Chem. Eng. 2014,
2, 1338; b) A. Caretto, A. Perosa, ACS Sustainable Chem. Eng. 2013, 1,
989; c) J. Zhang, S. Wu, B. Li, H. Zhang, ChemCatChem 2012, 4, 1230;
d) W. R. H. Wright, R. Palkovits, ChemSusChem 2012, 5, 1657; e) X.-L. Du,
L. He, S. Zhao, Y.-M. Liu, Y. Cao, H.-Y. He, K.-N. Fan, Angew. Chem. Int. Ed.
2011, 50, 7815; Angew. Chem. 2011, 123, 7961.
[5] a) Z. Xu, P. Yan, W. Xu, X. Liu, Z. Xia, B. Chung, S. Jia, Z. Conrad Zhang,
ACS Catal. 2015, 5, 788; b) F. Liu, M. Audemar, K. De Oliveira Vigier, J.-M.
Clacens, F. De Campo, F. JØrôme, ChemSusChem 2014, 7, 2089; c) F. Liu,
M. Audemar, K. De Oliveira Vigier, J.-M. Clacens, F. De Campo, F. JØrôme,
Green Chem. 2014, 16, 4110; d) J. Ohyama, R. Kanao, A. Esakia, A. Suat-
suma, Chem. Commun. 2014, 50, 5633.
[6] a) A. D. Sutton, F. D. Waldie, R. Wu, M. Schlaf, L. A. ‘Pete’ Silks, III, J. C.
Gordon, Nat. Chem. 2013, 5, 428; b) K. Pupovac, R. Palkovits, ChemSu-
sChem 2013, 6, 2103; c) J. Julis, M. Hçlscher, W. Leitner, Green Chem.
2010, 12, 1634.
[7] a) H. G. Cha, K.-S. Choi, Nat. Chem. 2015, 7, 328; b) J. Zhang, J. Li, Y.
Tang, L. Lin, M. Long, Carbohydr. Polym. 2015, 130, 420; c) W. P. Dijkman,
D. E. Groothuis, M. W. Fraaije, Angew. Chem. Int. Ed. 2014, 53, 6515;
Angew. Chem. 2014, 126, 6633.
[14] a) Y. Jiang, A. J. J. Woortman, G. O. R. Alberda van Ekenstein, D. M. Pet-
´
rovic, K. Loos, Biomacromolecules 2014, 15, 2482; b) P. Gopalakrishnan,
S. Narayan-Sarathy, T. Ghosh, K. Mahajan, M. N. Belgacem, J. Polym. Res.
2014, 21, 340; c) T. Ikezaki, R. Matsuoka, K. Hatanaka, N. Yoshie, J. Polym.
Sci. Part A 2014, 52, 216; d) C. Zeng, H. Seino, J. Ren, K. Hatanaka, N.
Yoshie, Polymer 2013, 54, 5351; e) C. Zeng, H. Seino, J. Ren, K. Hatanaka,
N. Yoshie, Macromolecules 2013, 46, 1794.
[15] A. P. Dunlop, US 4219485, 1980.
[16] A. P. Dunlop, US 4219486, 1980.
[17] D. Zhu, J. Zuo, S. Qu, W. Duan, G. Wang, C. Tan, P. He, F. Ji, C. Sun, X.
Yao, WO 2011127833, 2011.
[18] a) K. Beydoun, G. Ghattas, K. Thenert, J. Klankermayer, W. Leitner,
Angew. Chem. Int. Ed. 2014, 53, 11010; Angew. Chem. 2014, 126, 11190;
b) S. Zhu, X. Lu, Y. Luo, W. Zhang, H. Jiang, M. Yan, W. Zeng, Org. Lett.
2013, 15, 1440; c) M. Vaquero, A. Suµrez, S. Vargas, G. Bottari, E. lvarez,
A. Pizzano, Chem. Eur. J. 2012, 18, 15586; d) F. Chen, Z. Ding, J. Qin, T.
Wang, Y. He, Q.-H. Fan, Org. Lett. 2011, 13, 4348; e) C. P. Casey, G. A.
Bikzhanova, I. A. Guzei, J. Am. Chem. Soc. 2006, 128, 2286.
[19] Z. Xu, P. Yan, W. Xu, S. Jia, Z. Xia, B. Chung, Z. Conrad Zhang, RSC Adv.
2014, 4, 59083.
[8] a) N. Mittal, G. M. Nisola, J. G. Seo, S.-P. Lee, W.-J. Chung, J. Mol. Catal. A
2015, 106, 404; b) J. Artz, S. Mallmann, R. Palkovits, ChemSusChem
2015, 8, 672; c) C. A. Antonyraj, B. Kim, Y. Kim, S. Shin, K.-Y. Lee, I. Kim,
J. K. Cho, Catal. Commun. 2014, 57, 64.
[9] a) G. Bottari, A. J. Kumalaputri, K. K. Krawczyk, B. L. Feringa, H. J. Heeres,
K. Barta, ChemSusChem 2015, 8, 1323; b) T. Pasini, A. Lolli, S. Albonetti,
F. Cavani, M. Mella, J. Catal. 2014, 317, 206; c) A. J. Kumalaputri, G. Bot-
tari, P. M. Erne, H. J. Heeres, K. Barta, ChemSusChem 2014, 7, 2266; d) X.
Kong, Y. Zhu, H. Zheng, F. Dong, Y. Zhu, Y.-W. Li, RSC Adv. 2014, 4,
60467.
[20] a) S. Thota, M. Imran, M. Udugula, S. S. Karki, N. Kanjarla, R. Yerra, J. Bal-
zarini, E. De Clercq, J. Coord. Chem. 2012, 65, 823; b) Sk. Jasimuddin,
D. G. Thakurata, Transition Met. Chem. 2009, 34, 937; c) J. E. Collins,
J. J. S. Lamba, J. C. Love, J. E. McAlvin, C. Ng, B. P. Peters, X. Wu, C. L.
Fraser, Inorg. Chem. 1999, 38, 2020; d) A. S. Goldstein, R. H. Beer, R. S.
Drago, J. Am. Chem. Soc. 1994, 116, 2424.
[21] J. P. Collin, J. P. Sauvage, Inorg. Chem. 1986, 25, 135.
[22] See SI for more information.
[23] a) H. Guan, M. Iimura, M. P. Magee, J. R. Norton, G. Zhu, J. Am. Chem.
Soc. 2005, 127, 7805; b) M. P. Magee, J. R. Norton, J. Am. Chem. Soc.
2001, 123, 1778; c) M. J. Earle, R. A. Fairhurst, H. Heaney, G. Papageor-
giou, R. F. Wilkins, Tetrahedron Lett. 1990, 31, 4229.
[10] F. H. Isikgor, C. Remzi Becer, Polym. Chem. 2015, 6, 4497.
[11] E. Gubbels, L. Jasinska-Walc, C. E. Koning, J. Polym. Sci. Part A 2013, 51,
890.
[12] a) S. Rajendran, R. Raghunathan, I. Hevus, R. Krishnan, A. Ugrinov, M. P.
Sibi, D. C. Webster, J. Sivaguru, Angew. Chem. Int. Ed. 2015, 54, 1159;
Angew. Chem. 2015, 127, 1175; b) C. H. R. M. Wilsens, J. M. G. A. Verho-
even, B. A. J. Noordover, M. R. Hansen, D. Auhl, S. Rastogi, Macromole-
cules 2014, 47, 3306; c) J. Zhu, J. Cai, W. Xie, P.-H. Chen, M. Gazzano, M.
Received: January 29, 2016
Revised: February 29, 2016
Published online on May 6, 2016
ChemSusChem 2016, 9, 1255 – 1258
www.chemsuschem.org
1258
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim