An efficient Nozaki-Hiyama allenylation promoted by the acid derived MIL-101 MOF

Article abstract of DOI:10.1039/C8RA09600G

A concise synthesis of the sulfonic acid-containing MIL-101 MOF catalyst was reported using commercially available materials. A series of characterization of as-synthesized MIL-101-SO₃H including SEM, XRD, FTIR, BET and TGA was also demonstrated. Using MIL-101-SO₃H as a catalyst, an efficient Nozaki-Hiyama allenylation reaction was achieved to generate various polyfunctionalized α-allenic alcohols in high yield and good selectivity. Taking advantage of the high acidity of the MIL-101-SO₃H MOF structure, such transformations were also achieved under mild reaction conditions and short reaction times. Based on our observed evidence during this study, a mechanism was proposed involving a substrate activation/γ-nucleophilic addition reaction sequence. In addition, the MIL-101-SO₃H catalyst can be recycled ten times during the Nozaki-Hiyama allenylation reaction without compromising the yield and selectivity.

Full text of DOI:10.1039/C8RA09600G

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An efficient Nozaki–Hiyama allenylation promoted
by the acid derived MIL-101 MOF†
Cite this: RSC Adv., 2019, 9, 7479
a
*
Yi Luan,
Zonghui Cai,a Xiujuan Li,a Daniele Ramella,b Zongcheng Miaoc
d
*
and Wenyu Wang
A concise synthesis of the sulfonic acid-containing MIL-101 MOF catalyst was reported using commercially
available materials. A series of characterization of as-synthesized MIL-101-SO3H including SEM, XRD, FTIR,
BET and TGA was also demonstrated. Using MIL-101-SO3H as a catalyst, an efficient Nozaki–Hiyama
allenylation reaction was achieved to generate various polyfunctionalized a-allenic alcohols in high yield
and good selectivity. Taking advantage of the high acidity of the MIL-101-SO3H MOF structure, such
transformations were also achieved under mild reaction conditions and short reaction times. Based on
our observed evidence during this study, a mechanism was proposed involving a substrate activation/g-
nucleophilic addition reaction sequence. In addition, the MIL-101-SO3H catalyst can be recycled ten
times during the Nozaki–Hiyama allenylation reaction without compromising the yield and selectivity.
Received 22nd November 2018
Accepted 9th February 2019
DOI: 10.1039/c8ra09600g
rsc.li/rsc-advances
structure, they have been used as the efficient solid catalysts for
several catalytic transformations.10 Among all the reported
Introduction
examples, a stable and recyclable MOF structure bearing
sulfonic acid functionality can serve as a low pKa catalytic
material,11 and we eventually choose to use a chemically stable
and previously described MIL-101-SO3H MOF in our catalytic
reaction development study.12 Due to its chemical and physical
stabilities, MIL-101-SO3H has been utilized as an efficient
catalyst for several organic reactions.13
Herein, we reported a highly efficient Nozaki–Hiyama alle-
nylation reaction catalyzed by MIL-101-SO3H MOF using prop-
argyl boronates, which provided rapid access to the a-allenic
alcohol products. This newly synthesized MIL-101-SO3H catalyst
bearing aromatic sulfonic acid groups was obtained using
commercially available monosodium 2-sulfoterephthalate. A
broad scope of propargyl boronates and aldehydes were tested
to be tolerable under the optimal reaction conditions with high
catalytic reactivities. Furthermore, the as-synthesized MIL-101-
SO3H catalyst can be readily ltered and separated from the
allenylation reaction mixture. Recycling the MIL-101-SO3H up
to ten times doesn't compromise yield or selectivity of the
benzaldehyde allenylation.
Allenes have proven to be versatile and useful intermediates or
synthons1 for synthesis of drug-like molecules or natural
products due to the existence of two orthogonal p-bonds.2
Recently, a-allenic alcohols have drawn much attention because
they can be easily transformed to dihydrofurans3 and cyclo-
propanes,4 and iodination of the allene could provide subse-
quent access to vinyl epoxides,5 syn-1,2-diols6 and syn-1,2-amino
alcohols7 in high diastereoselectivities. Synthesis of a-allenic
alcohols has been achieved through allenylation of carbonyls
with allenyl metal or propargyl metal species.2l However,
controlling the formation of allenols over homopropargyl
alcohols is challenging due to the facile isomerization between
the allenyl metal and the corresponding propargyl metal
species, especially given the fact that propargyl alcohols are
generally thermodynamically favored over the allenols.
Recently, metal–organic frameworks (MOFs) have emerged
as a new class of solid catalysts,8 by virtue of their highly tail-
orable nature, porous structure and large surface area.9 Incor-
poration of Brønsted acidity into MOFs materials have also been
developed and due to their well-dened porous acidic micro
aSchool of Materials Science and Engineering, University of Science and Technology
Beijing, 30 Xueyuan Road, Haidian District, Beijing 100083, P. R. China. E-mail:
yiluan@ustb.edu.cn
Results and discussion
bDepartment of Chemistry, Temple University-Beury Hall, 1901, N. 13th Street,
MIL-101-SO3H can be readily synthesized and puried accord-
ing to the reported hydrothermal methods as a crystalline
powder.14 It is isostructural to MIL-101 (Fig. 1), and thus has the
same pore structures. The SEM images of MIL-101-SO3H
showed (Fig. 1) the rectangular crystals of MIL-101-SO3H are
evenly distributed with a size of 200 nm.
Philadelphia, PA 19122, USA
cKey Laboratory of Organic Polymer Photoelectric Materials, School of Science, Xijing
University, Xi'an, 710123, China
dBroad Institute, 415 Main Street, Cambridge, Massachusetts 02142, USA
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c8ra09600g
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Fig. 1 The detailed structure of MIL-101-SO3H and its SEM image.
Subsequently, powder X-ray diffraction (PXRD) measure-
ments were conducted (Fig. 2) and showed good agreement with
literature values.15 In addition, the obtained XRD data of MIL-
101-SO3H demonstrated high similarity to the XRD patterns of
the MIL-101, which also indicated our successful preparation of
the MIL-101-SO3H MOF.
Fig. 3 N2 adsorption–desorption isotherm of MIL-101-SO3H.
necessary for the reaction to occur. Subsequently, HCl showed
modest yield at 1 mol% catalytic loading and the reaction was
slow due to the low catalyst loading and undesired a-addition
byproduct 4a (Table 1, entry 3) was also observed. p-TsOH
provided satisfying yield and selectivity at 1 mol% catalyst
loading, despite the fact it is not recyclable and being corrosive
to several equipments (Table 1, entry 4). As expected, MIL-101
bearing no acidic functional group provided only traces of
product at 23 ꢀC in CH2Cl2 solvent (Table 1, entry 5). We expect
metal–organic framework material bearing –SO3H can provide
the high reaction efficiency and recyclable nature at the same
time. Our previously reported UiO-66-RSO3H indeed provided
an increase for the yield.17 However, alkyl sulfonic acid func-
tional group inside the UiO-66-RSO3H catalyst was not acidic
enough to provide the quantitative conversion (Table 1, entry 6).
In contrast, 1 mol% MIL-101-SO3H showed almost quantitative
conversion and over 99% selectivity for the allenylation 1a.17
The greatly enhanced acidity could efficiently allow the rear-
rangement of boronate for g-nucleophilic addition to aldehyde
to provide the desired a-allenic alcohol 2a in excellent yield
(Table 1, entry 7). Toluene gave almost comparable yield for the
allenylation reaction (Table 1, entry 8). Polar nonprotic/protic
solvents, such as THF and ethanol, gave decent yield of the
The specic surface areas of the products were then analyzed
by N2 adsorption–desorption measurements at 77 K. As shown
in Fig. 3, the trace of the MIL-101-SO3H showed a type-I
isotherm. N2 gas sorption isotherms reveal a Brunauer–
Emmett–Teller (BET) surface area of 1243 m2 gÀ1
.
Additionally, the thermal structural stabilities of MIL-101-
SO3H were examined by thermal gravimetric analysis (TGA). A
weight loss at about 300 ꢀC was observed during the TGA
measurement,16 which indicated high thermal stability of the
acid derived MIL-101-SO3H sample, which should provide reli-
able stability during the catalytic reaction temperature range
(Fig. 4).
With the MOF catalyst in hand, we started our catalytic
Nozaki–Hiyama allenylation reaction studies. Several reaction
factors such as nature of the catalyst and solvent, were tested in
order to reveal the optimal reaction condition (Table 1). First,
a control experiment was performed to study the background
rate of the allenylation reaction of propargyl boronate 1a. As
expected, no conversion was observed for propargyl boronate 1a
in the absence of catalyst or using biphenol as the catalyst
(Table 1, entries 1–2) suggesting that a low pKa acid is indeed
Fig. 2 Powder XRD patterns of (a) MIL-101 and (b) MIL-101-SO3H.
7480 | RSC Adv., 2019, 9, 7479–7484
Fig. 4 TGA of MIL-101-SO3H.
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Table 1 Reaction condition optimization for allenylation reactiona
Table 2 Nucleophile (boronate) variations for allenylation reactiona
Entry
1
Boronate
Product
Yield
99%
Entry
Catalyst
Solvent
Yield of 3a
Selectivity
1
2
3
4
5
6
7
8
—
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
PhCH3
THF
<5%
<5%
53%
91%
<5%
77%
99%
98%
68%
44%
23%
N.A.
N.A.
71%
99%
N.A.
96%
99%
99%
99%
99%
99%
Biphenol
HCl
p-TsOH
MIL-101
UiO-66-RSO3H
MIL-101-SO3H
MIL-101-SO3H
MIL-101-SO3H
MIL-101-SO3H
MIL-101-SO3H
2
3
98%
95%
9
10
11
EtOH
DMF
4
97%
a
Reaction condition: 1 mol% catalyst, TIPS propargyl boronate 1a and
benzaldehyde 2a were stirred in the solvent (0.2 M) for 1 h at room
temperature.
a
Reaction condition: 1 mol% MIL-101-SO3H, propargyl boronate 1 and
benzaldehyde 2a were stirred in CH2Cl2 for 1 h at room temperature.
a,b-unsaturated aldehyde 2k was also tested and only the
desired addition product was observed in 95% yield, although
boronates are known to undergo 1,4-addition into enones. More
challenging aliphatic aldehydes (2l–2n, 2p) also provide
desired allenylation product with diminished yields (Table 1,
entries 9–10). Mildly basic solvent, DMF was not suitable for the
acidic heterogeneous MIL-101-SO3H promoted allenylation
reaction (Table 1, entry 11). Further solvent evaluation indicated
that dichloromethane is the optimal reaction solvent for further
allenylation reaction studies (Table 1, entries 7–11). Optimiza-
tion of catalyst structure demonstrated that MIL-101-SO3H can
efficiently catalyze the allenylation reaction using propargyl
boronates and aldehyde as the starting material.
Table 3 Electrophile (aldehyde) variations for allenylation reactiona
With an optimal catalyst and reaction condition identied,
the scope of propargyl boronate reaction partners were next
investigated. Simple TIPS-protected boronate 1a and benzalde-
hyde 2a resulted in quantitative formation of 3a without any
undesired propargyl a-addition byproduct (Table 2, entry 1).
Phenyl substituted propargyl boronate 1b also tolerated this
chemistry, which gave allenic alcohol 3b in 95% yield. The 1,1-
disubstituted vinyl moiety on 1c is known to undergo proton-
ation to generate a stabilized tertiary carbocation which
potentially provide us a diminished yield of the desired alle-
nylation product. Gratifyingly, the complex vinylpropargyl
borate 1c also gave desired 3c in excellent yield (Table 2, entry 3)
under identical reaction condition, which illustrated the
versatility of MIL-101-SO3H as a catalyst in this reaction.
Consistently, acid labile substrate 1d also provided desired
product 3d in great yield without losing TBS group (Table 2,
entry 4).
We next examined MIL-101-SO3H catalyst in allenylation of
a wide variety of aldehydes (Table 3). Electronic rich and de-
cient benzaldehydes as well as polyaromatic benzaldehyde (2e–
2h) were all shown to be tolerant for such transformation, as
well as a heterocyclic aldehyde such as furfurals (2i and 2j). The
a
Reaction condition: 1 mol% MIL-101-SO3H, propargyl boronate 1 and
benzaldehyde 2a were stirred in CH2Cl2 for 1 h time at room
temperature.
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excellent yields and selectivity. Furthermore, alkene aldehydes
(2k, 2o) were shown to be well tolerant in our catalytic system to
provide corresponding allenic alcohols in more than 95%
yields.
A detailed reaction mechanism has been proposed. First, the
Brønsted acidic site on MIL-101-SO3H catalyst would activate
the aldehyde substrate by protonation, and simultaneously, the
generated sulfonate anion on the backbone of the MOF catalyst
could further activate the boronate species to form intermediate
A (Scheme 1). Therefore, by using our heterogeneous catalyst
MIL-101-SO3H formation of the key zwitterionic intermediate A
could introduce a better reactant approximation for the ideal
reactivity to occur whereas using traditional acid, such as HCl,
would bring less control of the desired reactivity which lead to
formation of the undesired propargyl alcohols (cf. Table 1). The
well-dened porous structure of the catalyst will facilitate this
double activation of both reactant and trigger the desired g-
nucleophilic addition from boronate to the aldehyde.
Fig. 5 MIL-101-SO3H catalyst recycling test for the allenylation of 1a.
S2†), which also suggested the high chemical stability of the
MIL-101-SO3H catalyst.
However, if such double activation did not work properly, the
undesried a-nucleophilic addition could also happen to give the
propargyl byproduct. Subsequently, the catalyst could be
regenerated by hydrolysis of borate intermediate B.
Experimental
Additionally, we tested recyclability of the acidic MIL-101-
SO3H catalyst and showed that it can be recycled up to ten times
without compromising the yield and selectivity of the allenyla-
tion reaction of aldehyde 1a. The recyclability of the MIL-101-
SO3H catalyst was evaluated using TIPS-propargyl boronate 1a
in 2 mL of CH2Cl2 at room temperature. As for MIL-101-SO3H,
the yield of desired 3a remained 98% aer usage of the same
recycled catalyst with 10 batches of fresh reagent (Fig. 5).
A hot ltration test was also performed for the MIL-101-SO3H
catalyzed allenylation reaction. Aer 20 minutes of reaction, the
solid MIL-101-SO3H catalyst was ltered off and at this point,
the allenylation of aldehyde 1a did not further proceed, which
further suggested no acid leaching into the reaction solution
(Fig. 6). Meanwhile SEM images and X-ray powder diffraction
spectrum of the MIL-101-SO3H catalyst were also recorded aer
ten allenylation reaction cycles. These data were found to be
identical to those of the freshly prepared catalyst (Fig. S1 and
Synthetic procedures
General procedure for synthesis of MIL-101-SO3H. MIL-101
and MIL-101-SO3H were prepared according to the
literature.14,18
General procedure for synthesis of propargyl boronates.
Modied from the procedure by Brown et al.19 (triisopropylsilyl)
acetylene (5 g, 27.5 mmol) was added to a solution of LDA (26.3
mmol) in dry THF (60 mL) previously cooled to 78 ꢀC under
argon and allowed to stir for 1 h. 2-(Iodomethyl)-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane (6.7 g, 25 mmol) was then
added in one portion. Aer an additional 30 min of stirring, the
reaction allowed to warm to room temperature and was le
overnight without stirring. The reaction was then cooled to 0 ꢀC
and 2 M anhydrous HCl in diethyl ether (13.75 mL, 27.5 mmol)
was added carefully dropwise with vigorous stirring. The
Scheme 1 Proposed reaction mechanism.
7482 | RSC Adv., 2019, 9, 7479–7484
Fig. 6 MIL-101-SO3H catalyst hot filtration test.
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precipitate was then ltered off and the solvent removed. The Research Plan in Shaanxi Province of China (No. 2018JQ5028,
resulting residue was extracted with pentane (100 mL for 3 No. 2017JM5134 and No. 2018JM5047) and the Science
ꢀ
times) and the extracts combined and cooled to À78 C over- Research Foundation of Xijing University (Grant No. XJ16T02)
night. The pentane solution was warmed to room temperature for nancial support.
and then decanted into an oven-dried 500 mL ask and solvent
then removed.
Notes and references
General procedure for synthesis of a-allenic alcohols. A
10 mL round-bottom ask was charged with stir bar under open
air. To the ask was added MIL-101-SO3H (0.005 mmol based on
–SO3H group) and propargyl boronate 1a (177 mg, 0.55 mmol)
then dissolved in CH2Cl2 (2 mL). The mixture was stirred at
room temperature for 5 minutes. Then benzaldehyde 2a (51 mL,
0.5 mmol) was added and stirred for 1 h. The organic layer was
separated and the aqueous layer extracted with hexanes and the
product puried by ash silica gel chromatography (1–5%
acetone in hexanes or 100% DCM) to afford 3a as a colorless oil.
Reusability of the MIL-101-SO3H catalyst. For the recycla-
bility test of the MIL-101-SO3H catalyst, the catalytic reactions
were performed under the same optimized conditions in
dichloromethane for 1 h using the recovered MIL-101-SO3H
catalyst. A leaching study of the MIL-101-SO3H catalyst was
conducted; the mother liquor was ltered and the supernatant
was re-evaluated using fresh starting material under optimized
catalytic conditions.
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Conclusions
In conclusion, a heterogeneous MIL-101-SO3H catalyst bearing
an aromatic sulfonic acid group was synthesized and applied to
allenylation reaction of aldehydes for the efficient synthesis a-
allenic alcohols. Simple reaction setup using mild reaction
conditions and low catalyst loadings are hallmarks of this MOF
promoted allenylation methodology. The MIL-101-SO3H
promoted reaction was found to be general for aldehydes and
the ability to vary the alkyne substitution on the boronate,
which makes this methodology a powerful tool for the genera-
tion of a wide range of a-allenic alcohol products. The structural
morphology and properties of MIL-101-SO3H were fully char-
acterized by SEM, XRD, TGA, FTIR and BET. The newly devel-
oped MIL-101-SO3H showed higher reaction efficiency and
selectivity in the allenylation reaction at 1 mol% catalyst load-
ings in comparison with several other catalyst systems. The high
chemical stability of the MIL-101-SO3H catalyst was due to its
strong covalent bond, and did not suffer from leaching. Further
studies involving new synthetic applications of the MIL-101-
SO3H catalyst are currently in progress and will be reported in
the due course.
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This work is supported by Beijing Natural Science Foundation
(No. 2172037) and National Natural Science Foundation of
China (No. 51673157). We also thank the Natural Science Basic
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