Efficient Hydrogenation of Biomass Oxoacids to Lactones by Using NHC–Iridium Coordination Polymers as Solid Molecular Catalysts

Article abstract of DOI:10.1002/asia.201601537

A series of NHC–iridium coordination polymers have proven to be robust, efficient and recyclable solid molecular catalysts toward the hydrogenation of biomass levulinic acid (LA) to γ-valerolactone. Along with quantitative yields attained at 0.01 mol % catalyst loading under 50 atm of H₂, the solid molecular catalyst was readily recovered and reused for 12 runs without obvious loss of the selectivity and activity. Remarkably, up to 1.2×10⁵ TON, an unprecedented value could be achieved in this important transformation. In addition, a number of LA homologues, analogues and derivatives were well tolerated to deliver various intriguing and functional lactones in good to excellent yields, which further confirmed the feasibility of the solid molecular catalysts.

Full text of DOI:10.1002/asia.201601537

CHEMISTRY
AN ASIAN JOURNAL
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Accepted Article
Title: Highly Efficient Hydrogenation of Biomass Oxoacids to Lactones
by Using NHC-Iridium Coordination Polymers as Solid Molecular
Catalysts
Authors: Tao Tu, Yaoqi Liu, Zheming Sun, and Changyu Huang
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Highly Efficient Hydrogenation of Biomass Oxoacids to Lactones
by Using NHC-Iridium Coordination Polymers as Solid Molecular
Catalysts
Yaoqi Liu,[a] Zheming Sun,[a] Changyu Huang[a] and Tao Tu*[a, b]
Abstract: A series of NHC-iridium coordination polymers have been
demonstrated as robust, efficient and recyclable solid molecular
catalysts toward hydrogenation of biomass LA to GVL. Along with
quantitative yield attained at 0.01 mol% catalyst loading under 50
atm H2 atmosphere, the solid molecular catalyst was readily
recovered and reused for 12 runs without obvious loss of the
selectivity and activity. Remarkably, up to 1.2×105 TON, an
unprecedented value could be achieved in this important
reported homogenous catalysts derived from noble metal
(mainly Ru and Ir) precursors and sensitive phosphine ligands
usually exhibit high catalytic activity and selectivity (Scheme 1).
To the best of our knowledge, up to 7.1 × 104 TON could be
obtained with the homogenous phosphine iridium pincer
complex develope by Zhou and coworkers.[22] However, this air
sensitive system requires the strict absence of water, especially,
the catalyst is hard to be recovered. Despite all these advances,
from a practical perspective, it is quite important and necessary
to process large volume LA continuously, therefore, the
development of robust and recyclable catalysts based on the
highly active homogenous complexes may be considered as a
suitable option for this crucial and sustainable transformation
under mild reaction conditions.
transformation. In addition,
a number of LA’s homologues,
analogues and derivatives were well tolerated to deliver various
intriguing and functional lactones in good to excellent yields, which
further confirmed the feasibility of the solid molecular catalysts.
Introduction
Along with the continuous consumption of fossil resources,
demands for alternatives from lignocellulosic biomass to biofuels
and other valuable chemicals are dramatically increasing in
recent years.[1] Therefore, tremendous efforts have been
devoted to search diverse biomass-derived platform molecules
and develop suitable methodologies in this field.[2–6] In this
context, γ-valerolactone (GVL) is regarded as one of the most
attractive candidates to produce various value-added chemicals,
biofuels, environmental benign solvents as well as functional
additives for foods and fuels.[7–10] Currently, selective
transformations of suitable and inexpensive biomass for the
sustainable production of GVL are under intensive
investigation.[11] Among them, the hydrogenation of biomass
levulinic acid (LA) and its derivatives followed by cyclization
constitute one of the most attractive and effective approaches to
access GVL. Until now, a plenty of heterogeneous[12–18] and
homogenous[19–25] catalysts have been developed and
investigated. In general, heterogeneous catalysts offer several
prominent advantages including easy separation and possible
reusability of the catalysts.[13,14] However, due to their low
activities, high reaction temperatures and H2 pressures are
required to achieve satisfactory outcomes. In contrast, most
Scheme 1. Hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL).
As “mimics” of phosphine ligands, N-heterocyclic carbenes
(NHCs) represent one of robust and environment-benign
ligands,[26,27] which exhibit good activity in a wide range of
transition metal catalyzed reactions.[28,29] However, to the best of
our knowledge, there is no report on NHC-based transition metal
complexes catalyzed hydrogenation of LA to GVL. In addition,
by using “self-supporting” strategy,[30–34] a number of NHC-based
coordination polymers could be readily accessed from
conformationally rigid bis-imidazolium salts and corresponding
metal precursors,[35] which may allow us to investigate their
applicability and reusability as solid catalysts. Recently, we
reported a series of robust NHC-Ir coordination polymers, which
function as highly efficient solid molecular catalysts in the
selective oxidative dehydrogenation of glycerol to potassium
lactate under relatively mild reaction conditions even at ppm
catalyst loadings.[36] Therefore, we subsequently sought to
explore their catalytic efficiency in the hydrogenation reactions.
Following our recent works on the synthesis organometallic
assemblies and exploring their potentials in catalysis, sensors,
[a]
[b]
Y. Liu, Z. Sun, C. Huang, Prof. T. Tu
Department of Chemistry
Fudan University
220 Handan Road, Shanghai, 200433 (China)
E-mail: taotu@fudan.edu.cn
Prof. T. Tu
State Key Laboratory of Organometallic Chemistry
Shanghai Institute of Organic Chemistry
Chinese Academy of Sciences, Shanghai, 200032 (China)
Supporting Information and the ORCID identification number(s) for
the author(s) of this article can be found under
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10.1002/asia.201601537
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and material sciences,[37–41] herein, we demonstrated the NHC-Ir
coordination polymers could function as solid molecular
catalysts and exhibit extremely high activity and selectivity in the
hydrogenation of LA to GVL by using H2 as hydrogen source
under mild reaction conditions. Remarkably, the solid molecular
catalysts could be reused 12 times without obvious loss of
activity and selectivity, and up to 1.2×105 turnover numbers
(TONs) could be achieved.
outcomes were observed (Table 1, entry 3). Aprotic solvents
including DMF, THF, Toluene and DCE are not favorable in this
transformation, only trace mount of GVL could be detected,
which highlights the strong solvent effects in the system (Table
S1, entries 5–12). Subsequently, other inorganic bases including
LiOH, NaOH, K3PO4 and t-BuOK were also tested. No better
outcomes were found. Furthermore, organic bases including
DBU, Et3N and pyridine all resulted in unsatisfactory yields
(Table 1, entries 4, 5 and Table S1, entries 13–19). Decreasing
the reaction time, temperature or the pressure of H2, all leds to
inferior results (Table 1, entries 6, 7 and Table S1, entries 20–
21).
Results and Discussion
Synthesis and Characterization of NHC-Ir Coordination
Polymers: According to our previous protocols, a series of
robust NHC-Ir(I) coordination polymers 1a–d (Scheme 2) were
readily fabricated in excellent yields from conformationally rigid
bis-benzimidazolium salts and iridium precursors via self-
Table 1. Optimization of reaction conditions.[a]
assembly
process
in
the
presence
of
lithium
bis(trimethylsilyl)amid (LiHMDS) as a base.[36] IR analysis, solid
NMR, energy dispersive X-ray (EDX) and X-ray photoelectron
spectroscopy (XPS) analysis all indicated the obtained solids
were consistent with its elemental composition and state as
expected. Scanning electron microscopy (SEM), transmission
electron microscopy (TEM), and powder X-ray diffraction
(PXRD) confirmed their amorphous nature as our previous
studies (See the Supporting Information, Figures S1–S23).
Entry
[Cat.]
Solvent
Base
Time
(h)
T
Yield
(%)
(oC)
1
2
3
4
5
6
7
8
1a
1a
1a
1a
1a
1a
1a
1c
1a
1b
1d
2
i-PrOH
MeOH
EtOH
KOH
KOH
KOH
NaOH
t-BuOK
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
4
4
4
4
4
1
4
4
4
4
4
4
24
72
72
100
100
100
100
100
100
80
100
100
100
100
100
100
100
120
>99
34
90
88
8
65
42
48
97
81
90
31
>99
85
60
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
9[b]
10[b]
11[b]
12[b]
13[c]
14[d]
15[e]
1a
1a
1a
[a] Reactions were carried out with LA (10 mmol), catalyst (0.05 mol%), base
(1.0 equiv.), H2 (50 atm) in the selected solvent (5 mL), the yield was
determined by 1H NMR with mesitylene as an internal standard. [b] With 0.025
mol% catalyst. [c] With 0.01 mol% catalyst. [d] With 0.001 mol% catalyst. [e]
With 0.0005 mol% catalyst.
Scheme 2. NHC-Ir coordination polymers 1 and molecular complex 2.
Investigation of Catalytic Activity of NHC-Ir Complex and
Coordination Polymers in the Hydrogenation of LA to GVL:
With these fully characterized solid coordination polymers in
hands, the initial investigation of their catalytic activity in the
reduction of LA was carried out with different hydrogen sources.
In general, there are two different hydrogen sources applied in
the hydrogenation of LA. One is hydrogen gas and the other is
formic acid. When formic acid was used along with Et3N, 84%
With the optimized reaction conditions in hand, the catalytic
activity of other solid catalysts 1b–d was then evaluated (Table
1, entries 8-11). Pleasantly, at 0.05 mol% catalyst loading, solids
1b and 1d also revealed high activity, whereas, solid 1c was
less efficient (Table 1, entry 8 and Table S1, entries 24–26). In
the case of solid 1a, even at 0.025 mol% catalyst loading, 97%
yield of GVL was still obtained within 4 h (entry 9), whilst, low
outcomes were found with 1b and 1d (entries 10 and 11).
However, when a homogeneous analogou of 1a, NHC-Ir
complex 2, was applied instead under identical reaction
conditions, only 31% yield was observed (Table 1, entry 12),
which may arouse by the possible inactive dinuclear iridium
species formation during the reaction[42] and further highlight the
advantage of solid catalysts.
o
yield of GVL could be achieved with 1 mol% solid 1a at 100 C
with relatively long reaction time (72 h, See the Supporting
Information, Table S1). Whilst, when the reaction was carried
out under the 50 atm H2 atmosphere, the reaction processed
very efficiently (Table 1). In the presences of 0.05 mol% solid 1a,
LA can selectively and completely convert to GVL in i-PrOH with
o
KOH as base at 100 C within 4 h (Table 1, entry 1), indicating
In order to further evaluate the catalytic efficiency of solid 1a,
a series of experiments at low catalyst loading with extended
reaction time was carried out. Pleasingly, even at the catalyst
loading of 0.01 mol%, reaction can proceed smoothly, producing
GVL in quantitative yield with 1×104 TON within 24 h under the
the NHC-Ir coordination polymer catalytic efficiency. However,
when MeOH was applied, only a 34% yield of GVL was obtained,
possibly due to its low boiling point (Table 1, entry 2). When
other alcohols were involved, similar but slightly inferior
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10.1002/asia.201601537
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optimized reaction conditions (Table 1, entry 13). Further
decreasing catalyst loading to 0.001 mol%, still 85% yield was
obtained within 72 h (8.5×104 TON, Table 1, entry 14).
Remarkably, up to 1.2×105 TON could be attained simply
decreasing the catalyst loading to 0.0005 mol% and elevating
In order to get the catalytic nature of solid 1a during the
reaction and recycling, the filtration after each run was analyzed
by inductively coupled plasma-atomic emission spectroscopy
(ICP-AES) for possible iridium leaching. In attention, the orignal
Ir content in the polymer 1a is 31.2%, detected by ICP-AES,
which is accordance with the theoretical value (30.9%) of
(C12H12BF4IrN4O2•DMF)n. Delightedly, only trace amount of
iridium could be detected in the filtrates, which may also explain
the decreasing of yields after the 10th run. Pleasingly, no metal
nanoparticle or cluster was formed, indicating the solid polymer
act as the true catalyst in this transformation. Moreover,
investigated by SEM, TEM and EDS mapping, the morphology
and distribution of recovered solid 1a after the 13th run were
relatively similar with the newly prepared one (Figure 2, a–c vs.
d–f), which may highlight the catalyst 1a preserves the structural
features and functions as a robust solid molecular catalyst.
However, the IR spectra of the recovered solids 1a are
somewhat different from that of the freshly prepared one. The
absorption bands of CO ligand in the solid 1a around 1984 and
2047 cm−1 do not exist anymore (See the Supporting Information,
Figure S65), which may suggest that CO ligands are relatively
labile to the iridium center of solid 1a, and gradually dissociate
from the metal during reaction and leave more vacant sites for
substrates activation.
o
reaction temperature to 120 C (Table 1, entry 15), which is the
highest TON achieved so far for this crucial transformation.
Figure 1. Recycling and reuse of the solid NHC-Ir catalyst 1a in the
hydrogenation of LA to GVL (the reactions were carried out in 20 mmol scale
with 0.1 mol% solid 1a under the optimized reaction conditions for 4 h and the
average yields of two parallel recycling sequences were provided).
The Recyclability of NHC-Ir Solid Catalyst: In light of the
insolubility of solid 1a in all selected organic solvents, the
catalyst is readily recovered quantitatively by simple
centrifugation and decantation after the reaction completion. To
our delight, the product obtained by aforementioned process is
pure enough for NMR analysis. Especially, the recovered solids
1a after washing with i-PrOH can be directly reused as the
catalyst in the second run without additional activation steps, just
simply charging LA, base and solvent, without obvious
decreasing in the selectivity and yield of GVL. Due to its high
catalytic efficiency, the solid catalyst 1a could be reused up to
13 times, even in the 12th runs, 88% yield of GVL could be still
obtained (Figure 1).
Table 2. Hydrogenation of various levulinic acid homologues, analogues and
derivatives.[a]
[a] Reactions were carried out with oxoacids (5 mmol), catalyst (0.1
mol%), KOH (2.0 equiv.), H2 (50 bar) in i-PrOH (5 mL) at 100 oC for 4 h,
isolated yield. [b] LA derivatives (1 mmol), catalyst (1 mol%). [c] i-PrOH
(20 mL). [d] 24 h. [e] Yield was calculated by 1H NMR spectroscopy with
mesitylene as an internal standard.
Substrate Scope: In light of high efficiency of solid
molecular catalyst 1a in the reduction of LA to GVL, we
sought to further investigate it feasibility to catalyze the
reduction of various substituted LAs, LA derivatives or even
analogues to access a number of functional lactones (Table
2).[43,44] When the ketone terminal of LA was substituted by
aromatic rings, all substrates with different electronic and
steric properties are well tolerated (6–9); up to 95% isolated
Figure 2. a–c): SEM, TEM, EDS images of the freshly prepared NHC-Ir
coordination polymer 1a; d–f): corresponding images of the recovered solid 1a
after the 13th run.
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residual proton signal of the deuterated solvent (CHCl3 at δ 7.26 ppm,
DMSO at δ 2.50 ppm); coupling constants are expressed in hertz (Hz).
13C NMR spectra were referenced to the carbon signal of CDCl3 (77.0
ppm) or DMSO (39.4 ppm). The following abbreviations are used to
describe NMR signals: s = singlet, d = doublet, t = triplet, m = mulitplet,
dd = doublet of doublets, q = quartet. IR spectra were recorded on
AVATAR FT-IR 360 instrument. Powder XRD studies were performed on
a Bruker AXS D8. SEM experiments were carried out on a Nova
NanoSem 450 microscope operated at 20 kV. TEM experiments were
carried out on a JEOL JEM-2010 transmission electron microscope.
yield could be obtained in the presence of 0.1 mol% solid
1a. Whilst substrate containing -OMe substitute, only a
moderate yield could be produced even with increased
catalyst loading to 1 mol% (6c), whereas, its methyl
analogue resulted in 95% yield of 6b at 0.1 mol% catalyst
loading. Notably, halides are well compatible and delivery
the corresponding halides containing lactones (7) in good
yields, which may also provid an opportunity for their further
transformation.[45–48] In the heterocyclic case, when
substrate containing thiophene with strong coordination
ability was involved, 51% yield of bi-heterocycle 9 was still
obtained by simply extending reaction time to 24 h.
Delightedly, the protocol could be also applied in the
reduction of LA ester, up to >99% yield was obtained under
the optimized reaction conditions. Furthermore, in the
presence of 0.1 mol% solid 1a, the LA homologues, oxoacid
with longer space between two carbonyl groups, also
produce the corresponding lactones in good yields (10). In
consideration of the importance of phthalates in
pharmaceuticals and nature products,[49–51] we also test its
catalytic activity of solid 1a in the reduction of
General protocol to synthesize solid NHC-Ir coordination polymer: A
Schlenk tube was charged with 1,3,5,7-tetramethyl-benzodiimidazolium,
diiodide or ditetrafluoroborate[36] (0.5 mmol) and the iridium precursor
(0.5 mmol). The mixture was dissolved in DMF (1 mL) under N2 at room
temperature, LiHMDS (1 mmol) solution in THF was then added in
dropwise. The resulting mixture was stirred under N2 at 80 oC for 12 h.
The dark brown solids were isolated after filtration and washed with
deionized water for three times. The polymer solids were then dried over
under vacuum to deliver the desired NHC-Ir coordination polymer.
NHC-Ir coordination polymer (1a): dark-brown solid, 93% yield. IR (KBr
pellet) ν 418.22, 424.01, 599.84, 1084.05, 1257.84, 1383.96, 465.51,
1629.09, 1984.76, 2045.68, 2273.14, 3443.20 cm-1; Elemental analysis
(%) Calcd. for (C12H12BF4IrN4O2•DMF)n: C, 32.81; H, 3.40; N, 11.25;
found: C, 31.35; H, 3.60; N, 11.94; Solid state 13C-NMR(150 MHz): δ =
231.95, 171.53, 132.86, 92.53, 34.19.
benzoannelated LA analogues. With
loading, good isolated yields for
1
mol% catalyst
corresponding
benzoannelated products 11 and 12 could be obtained,
which further indicated the catalytic efficiency of the solid
molecular catalyst 1a.
NHC-Ir coordination polymer (1b): dark-brown solid, 97% yield. IR (KBr
pellet) ν 668.94, 830.13, 1108.12, 1347.58, 1458.87, 1559.86, 1617.67,
1654.08, 1684.89, 1932.80, 2023.33, 2239.64, 3421.95 cm-1; Elemental
analysis (%) Calcd. for (C12H12BF4IrN4O2•1.5 DMF•4 H2O)n: C, 28.82; H,
4.25; N, 9.99; found: C, 29.39; H, 4.42; N, 9.67.
Conclusions
NHC-Ir coordination polymer (1c): dark-brown solid, 99% yield. IR (KBr
pellet) ν 455.20, 763.95, 1023.98, 1273.33, 1383.97, 1523.04, 1571.54,
1629.33, 2932.07, 3432.38 cm-1; Elemental analysis (%) Calcd. for
(C20H26BF4IrN4)n: C, 39.94; H, 4.36; N, 9.31; found: C, 39.68; H, 4.65; N,
9.55.
In summary, a series of NHC-iridium coordination polymers have
been demonstrated as robust, efficient and recyclable solid
molecular catalysts in the selective hydrogenation of biomass LA
to GVL by using H2 as hydrogen source. Along with quantitative
yield could be attained at catalyst loading as low as 0.01 mol%
under relatively mild reaction conditions, the solid catalyst was
readily recovered and reused for 12 runs without obvious loss of
the selectivity and activity. In addition, the solid molecular
catalyst shows better catalytic activity than its homogenous
counterpart under the identical reaction condtions, clearly
indicating the advantage of the solid molecular catalysts.
Remarkably, the highest 1.2×105 TON in this crucil
transformation could be achieved in this study. Furthermore, the
protocol is fully compitible with other LA homologues, analogues
and derivatives and produces a variety of intriguing and
functional lactones in good to excellent yields, highlighting the
solid molecular catalyst efficiency.
NHC-Ir coordination polymer (1d): dark-brown solid, 95% yield. IR (KBr
pellet) ν 763.93, 1000.21, 1023.75, 1083.79, 1356.68, 1383.97, 1425.38,
1437.69, 1449.00, 1458.54, 1466.11, 1523.03, 1571.52, 1629.31,
1636.52, 1653.94, 2830.75, 2879.73, 2932.08, 2956.61, 2983.15,
3432.45, 3629.71 cm-1; Elemental analysis (%) Calcd. for
(C23H33IIrN5O•DMF)n: C, 38.65; H, 4.65; N, 9.80; found: C, 38.21; H,
4.50; N, 9.59.
Catalytic procedure of hydrogenation of LA to GVL with NHC-Ir
coordination polymer：A stainless autoclave equipped with a magnetic
stirring bar was charged with LA (10 mmol), NHC-Ir coordination polymer
(0.05 mol%), KOH (85% purity) (660 mg, 10 mmol) and isopropanol (5
mL). The autoclave was tightened and flushed with hydrogen three times
and was finally charged with hydrogen to 50 atm. The reaction mixture
was stirred under hydrogen pressure at 100 oC for 4 h. The autoclave
was then cooled to room temperature and the pressure was released.
After pH regulation and additional 1 h stirring at room temperature,
mesitylene (120 mg, 1 mmol) was added to the reaction mixture as an
internal standard for 1H NMR analysis to determine the yield.
Experimental Section
General: All commercial reagents were used as purchased without
further purification, unless otherwise noted. Hydrogen gas (99.99%) was
purchased from Dumaoai. CDCl3 was purchased from Cambridge
Isotope Laboratories. 1H, 13C and 19F NMR spectra were recorded on
Jeol ECA-400 and Bruker 400 DRX spectrometers. The chemical shifts
(δ) for 1H NMR are given in parts per million (ppm) referenced to the
Operation procedure for the solid catalyst 1a recovery: A stainless
autoclave equipped with a magnetic stirring bar was charged with LA (2.3
g, 20 mmol), solid catalyst 1a (11 mg, 0.1 mol%), KOH (85% purity) (1.3
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g, 20 mmol) and isopropanol (5 mL). After the hydrogenation by the
aforementioned general operation procedure and the pressure was
released, the solid catalysts were readily recovered after centrifugation
and decantation. The recovered catalysts 1a was washed with
isopropanol (5 mL × 3), the recovered solid catalysts were reused directly
in the next run without additional activation steps, just simply recharging
LA, KOH and i-PrOH in the autoclave.
2H), 2.74 (t, J = 4.0 Hz, 2H), 2.66 (s, 3H), 2.41 (s, 3H); 13C NMR (100
MHz, CDCl3, 298 K) δ = 193.67, 179.04, 147.79, 135.26, 134.74, 125.70,
35.89, 27.95, 15.98, 14.87.
General procedure of hydrogenation of various LA’s homologues,
analogues and derivatives: A stainless autoclave equipped with a
magnetic stirring bar was charged with the substrate 3 (5 mmol), solid
catalyst 1a (2.7 mg, 0.1 mol%), KOH (85% purity) (660 mg, 10 mmol)
and isopropanol (5 mL). The autoclave was tightened and flushed with
hydrogen three times and was finally charged with hydrogen to 50 atm.
General synthetic procedure of substrates 3：Succinic anhydride (3 g,
30 mmol) was treated with aryl derivatives (60 mmol) in the presence of
anhydrous aluminium chloride (8 g, 60 mmol). The reaction mixture was
stirred for 6 h. The desired product was purified by dissolving in 5 %
sodium hydroxide solution and filtered. Dilute hydrochloric acid was
added to mother liquor to precipitate the product. The solid was obtained
after filtration. After washing with cold water, drying and recrystallization,
the desired compounds 3 could be delivered.
o
The reaction mixture was stirred under hydrogen at 100 C for 4 h. After
the reaction completion, the autoclave was cooled to room temperature
and the pressure was then released. After pH regulation and additional 1
h stirring at room temperature, the reaction mixture was purified by silica
gel column chromatography to affording desired product.
γ-Phenyl-γ-butyrolactone (6a): colourless oil, 98% yield. 1H NMR (400
MHz, CDCl3, 298 K) δ = 7.42 - 7.33 (m, 5H without additional activation
procedure, just simply charging LA, KOH and i-PrOH,), 5.52 (t, J = 5.2 Hz,
1H), 2.68 - 2.64 (m, 3H), 2.24 - 2.17 (m, 1H); 13C NMR (100 MHz, CDCl3,
298 K) δ = 176.88, 139.24, 128.62, 128.30, 125.17, 81.14, 30.80, 28.82.
3-Benzoylpropanoic acid (3a): white solid, 77% yield. 1H NMR (400 MHz,
CDCl3, 298 K) δ = 8.00 (d, J = 8.0 Hz, 2H), 7.59 (t, J = 8.0 Hz, 1H), 7.48
(t, J = 8.0 Hz, 2H), 3.34 (t, J = 6.0 Hz, 2H), 2.83 (t, J = 6.0 Hz, 2H); 13C
NMR (100 MHz, CDCl3, 298 K) δ = 197.83, 179.01, 136.26, 133.25,
128.56, 127.96, 33.06, 27.99.
γ-(4-Methylphenyl)-γ-butyrolactone (6b): white solid, 95% yield. 1H NMR
(400 MHz, CDCl3, 298 K) δ = 7.20 (dd, J = 12.0, 8.0 Hz, 4H), 5.49 (dd, J
= 8.0, 4.0 Hz, 1H), 2.68 - 2.62 (m, 3H), 2.37 (s, 1H), 2.21 - 2.18 (m, 1H);
13C NMR (100 MHz, CDCl3, 298 K) δ = 177.03, 138.29, 136.33, 129.38,
125.37, 81.35, 30.92, 29.04, 21.12.
3-(4-Methylbenzoyl)propanoic acid (3b): white solid, 64% yield. 1H NMR
(400 MHz, CDCl3, 298 K) δ = 7.89 (d, J = 8.0 Hz, 2H), 7.27 (d, J = 8.0 Hz,
2H), 3.30 (t, J = 6.0 Hz, 2H), 2.81 (t, J = 6.0 Hz, 2H), 2.42 (s, 1H); 13C
NMR (100 MHz, CDCl3, 298 K) δ = 197.56, 178.72, 144.06, 133.82,
129.21, 128.01, 32.96, 28.02, 21.52.
γ-(4-Methoxyphenyl)-γ-butyrolactone (6c): white solid, 67% yield. 1H
NMR (400 MHz, CDCl3, 298 K) δ = 7.27 (d, J = 8.0 Hz, 2H), 6.92 (d, J =
8.0 Hz, 2H), 5.48 (dd, J = 8.0, 4.0 Hz, 1H), 3.82 (s, 3H), 2.69 - 2.61 (m,
3H), 2.23 - 2.18 (m, 1H); 13C NMR (100 MHz, CDCl3, 298 K) δ = 176.96,
159.66, 131.07, 126.93, 114.01, 81.30, 55.23, 30.77, 29.14.
3-(4-Methoxybenzoyl)propanoic acid (3c): white solid, 35% yield. 1H
NMR (400 MHz, CDCl3, 298 K) δ = 7.96 (d, J = 8.0 Hz, 2H), 6.93 (d, J =
8.0 Hz, 2H), 3.87 (s, 1H), 3.27 (t, J = 6.0 Hz, 2H), 2.80 (t, J = 6.0 Hz, 2H);
13C NMR (100 MHz, DMSO-D6, 298 K) δ = 197.27, 174.35, 163.52,
130.55, 129.81, 114.28, 55.92, 33.09, 28.33.
γ-(4-Bromophenyl)-γ-butyrolactone (7a): white solid, 82% yield. 1H NMR
(400 MHz, CDCl3, 298 K) δ = 7.53 (d, J = 8.0 Hz, 2H), 7.22 (d, J = 8.0 Hz,
2H), 5.47 (dd, J = 8.0, 4.0 Hz, 1H), 2.69 - 2.63 (m, 3H), 2.19 - 2.12 (m,
1H); 13C NMR (100 MHz, CDCl3, 298 K) δ = 176.49, 138.36, 131.82,
126.91, 122.28, 80.37, 30.81, 28.77.
3-(4-Bromobenzoyl)propanoic acid (3d): white solid, 26% yield. 1H NMR
(400 MHz, CDCl3, 298 K) δ = 7.85 (d, J = 8.0 Hz, 2H), 7.62 (d, J = 8.0 Hz,
2H), 3.28 (t, J = 4.8 Hz, 2H), 2.82 (t, J = 4.8 Hz, 2H); 13C NMR (100 MHz,
CDCl3, 298 K) δ = 196.82, 178.21, 135.08, 131.97, 129.55, 128.54, 33.09,
27.86.
γ-(4-Chlorophenyl)-γ-butyrolactone (7b): yellow solid, 93% yield. 1H NMR
(400 MHz, CDCl3, 298 K) δ = 7.37 (d, J = 8.0 Hz, 2H), 7.27 (d, J = 8.0 Hz,
2H), 5.48 (dd, J = 8.0, 4.0 Hz, 1H), 2.68 - 2.64 (m, 3H), 2.19 - 2.13 (m,
1H); 13C NMR (100 MHz, CDCl3, 298 K) δ = 176.51, 137.80, 134.12,
128.93, 126.62, 80.36, 30.81, 28.78.
3-(4-Chlorobenzoyl)propanoic acid (3e): white solid, 38% yield. 1H NMR
(400 MHz, CDCl3, 298 K) δ = 7.93 (d, J = 8.0 Hz, 2H), 7.45 (d, J = 8.0 Hz,
2H), 3.29 (t, J = 4.8 Hz, 2H), 2.82 (t, J = 4.8 Hz, 2H); 13C NMR (100 MHz,
CDCl3, 298 K) δ = 196.63, 178.85, 139.73, 134.62, 129.40, 126.91, 33.04,
27.92.
γ-(4-Fluorophenyl)-γ-butyrolactone (7c): colourless oil, 90% yield. 1H
NMR (400 MHz, CDCl3, 298 K) δ = 7.32 (dd, J = 8.4, 5.2 Hz, 2H), 7.08 (t,
J = 8.4 Hz, 2H), 5.49 (dd, J = 8.0, 4.0 Hz, 1H), 2.69 - 2.64 (m, 3H), 2.20 -
2.17 (m, 1H); 19F NMR (CDCl3, 376 MHz, 298 K): δ = -113.31; 13C NMR
(100 MHz, CDCl3, 298 K) δ = 176.68, 163.75, 161.29, 135.01, 134.98,
127.19, 127.11, 115.68, 115.46, 80.60, 30.86, 28.90.
3-(4-Fluorobenzoyl)propanoic acid (3f): white solid, 39% yield. 1H NMR
(400 MHz, CDCl3, 298 K) δ = 8.01 (dd, J = 8.0, 4.0 Hz, 2H), 7.15 (t, J =
8.0 Hz, 2H), 3.29 (t, J = 4.8 Hz, 2H), 2.82 (t, J = 4.8 Hz, 2H); 19F NMR
(CDCl3, 376 MHz, 298 K): δ = -104.74; 13C NMR (100 MHz, CDCl3, 298
K) δ = 196.28, 178.90, 167.07, 164.54, 132.76, 132.73, 130.68, 130.59,
115.79, 115.58, 32.97, 27.95.
γ-(2-Naphthyl)-γ-butyrolactone (8): white solid, 92% yield. 1H NMR (400
MHz, CDCl3, 298 K) δ = 7.90 - 7.82 (m, 4H), 7.53 - 7.51 (m, 2H), 7.43 -
7.40 (m, 1H), 5.70 (t, J = 7.6 Hz, 1H), 2.73 - 2.69 (m, 3H), 2.34 - 2.27 (m,
1H); 13C NMR (100 MHz, CDCl3, 298 K) δ = 176.90, 136.58, 133.02,
132.91, 128.68, 127,91, 127.61, 126.47, 126.32, 124.17, 122.76, 81.18,
30.71, 28.78.
3-(2-Naphthoyl)propanoic acid (3g): yellow solid, 14% yield. 1H NMR
(400 MHz, CDCl3, 298 K) δ = 8.52 (s, 1H), 8.05 (dd, J = 8.6, 1.8 Hz, 1H),
7.98 (d, J = 8.2 Hz, 1H), 7.92 - 7.88 (m, 2H), 7.64 - 7.55 (m, 2H), 3.48 (t,
J = 6.6 Hz, 2H), 2.89 (t, J = 6.6 Hz, 2H); 13C NMR (100 MHz, DMSO-D6,
298 K) δ = 198.51, 174.01, 135.10, 133.76, 132.24, 129.81, 129.65,
128.66, 128.33, 127.69, 126.96, 123.49, 33.21, 28.04.
5-(2,5-Dimethyl-3-thienyl)dihydro-2(3H)-furanone (9): white solid, 51%
yield. 1H NMR (400 MHz, CDCl3, 298 K) δ = 6.59 (s, 1H), 5.48 (dd, J =
8.4, 6.4 Hz, 1H), 2.67 - 2.63 (m, 2H), 2.54 - 2.50 (m, 2H), 2.73 (s, 3H),
2,5-Dimethyl-γ-oxo-3-thiophenebutanoic acid (3h): white solid, 40% yield.
1H NMR (400 MHz, CDCl3, 298 K) δ = 7.03 (s, 1H), 3.12 (t, J = 4.0 Hz,
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2.27 (s, 3H), 2.25 - 2.20 (m, 1H); 13C NMR (100 MHz, CDCl3, 298 K) δ =
176.85, 136.70, 134.34, 134.29, 123.13, 76.46, 29.55, 29.20, 14.99,
12.73.
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Entry for the Table of Contents (Please choose one layout)
NHC-Iridium polymers function as
robust, efficient and recyclable solid
Yaoqi Liu, Zheming Sun,
Changyu Huang, Tao Tu*
molecular
catalyst
in
the
Page No. – Page No.
hydrogenation of LA to GVL, which
was readily recovered and reused for
12 runs. Besides up to 1.2×105 TON
could be achieved, the protocol is
readily to extend to other LA’s
Highly Efficient
Hydrogenation of Biomass
Oxoacids to Lactones by
Using NHC-Iridium
Coordination Polymers as
Solid Molecular Catalysts
homologues,
analogues
and
derivatives producing
a
variety of
intriguing functional lactones.
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