Re-catalyzed deoxydehydration of polyols to olefins using indoline reductants

Article abstract of DOI:10.1016/j.poly.2018.11.061

A rhenium (CH₃ReO₃, MTO) catalyzed deoxydehyradration (DODH) of glycols to alkenes has been achieved using hydroaromatic compounds as H-transfer reductants. Of the hydroaromatics examined, indoline was the most efficient and proved to be better potential hydrogen donor. The yield of the products is moderate to excellent and the reaction is very clean with the only indole, the oxidized byproduct of indoline detected.[Figure presented]

Full text of DOI:10.1016/j.poly.2018.11.061

Polyhedron 160 (2019) 268–271
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Re-catalyzed deoxydehydration of polyols to olefins using indoline
reductants
⇑
Alana Jefferson, Radhey S. Srivastava
Department of Chemistry, University of Louisiana at Lafayette, LA 70504, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
A rhenium (CH3ReO3, MTO) catalyzed deoxydehyradration (DODH) of glycols to alkenes has been
achieved using hydroaromatic compounds as H-transfer reductants. Of the hydroaromatics examined,
indoline was the most efficient and proved to be better potential hydrogen donor. The yield of the prod-
ucts is moderate to excellent and the reaction is very clean with the only indole, the oxidized byproduct
of indoline detected.
Received 4 September 2018
Accepted 30 November 2018
Available online 15 December 2018
Keywords:
Deoxydehydration (DODH)
Oxorhenium
Polyol
Alkene
Indoline
OH
MTO 10 mol%
HO
+
°
Toluene, 19 0 C
R
R
+
N
H
N
H
1-Butanol
Ó 2018 Elsevier Ltd. All rights reserved.
1. Introduction
The Re-catalyzed DODH reaction of vicinal diols has received
increasing attention within the past few years probably because
MTO (CH3ReO3) is air and water resistant [5]. Oxo-Re catalyzed
conversion of diols and epoxides to alkenes was reported by the
Abu-Omar group using molecular hydrogen as a reductant [6].
Bergman et al. has employed sacrificial alcohols as a reductant in
the presence of Re2(CO)10 [7] Nicholas et al. [8] has applied sulfite
as a reducing agent in the presence of various oxorhenium cata-
lysts. The oxo-rhenium catalyzed deoxygenation of epoxides was
achieved by Fernandes et al. without a reducing agent [9]. Abu-
Omar and Toste’s groups independently described rhenium cat-
alyzed DODH and transfer hydrogenation of biomass-derived glyc-
erol, polyols, and sugar alcohols [10,11]. Moreover, Schlaf and
Bullock have applied organometallic ruthenium catalysts for the
deoxygenation of alcohols [12]. We have also exploited catalysts,
[Cp*Ru(CO)2]2 for deoxygenation, hydrodeoxygenation and cis-
RuCl2(R2SO)4 for hydrogenolysis of diols and epoxides using hydro-
gen as a reductant to produce alkanes, alcohols and hydrocracking
products [13].
Declining petroleum resources has made carbohydrates an
attractive target for value-added chemicals and renewable energy
resources [1]. The conversion of biomass commonly requires the
removal of oxygen atoms from the highly oxygenated nature of
biomass, which is a critical step to increase the energy content
and allow their use as an energy source. Depletion of fossil fuel
stocks of energy and their fluctuating costs is a powerful driving
force for the discovery and development of proficient methods
for the conversion of abundantly available renewable biomass
resources to value-added chemicals and fuels. Lately, deoxygena-
tion by reductive processes such as catalytic dehydration,
hydrogenolysis, hydrodeoxygenation and deoxydehyadration
(DODH) has been well received [2]. In fact, much attention has
been focused on DODH (Scheme 1), which effects vicinal OH
removal with the formation of olefins [3]. Selective production of
value-added chemicals and energy source can be achieved by the
deoxygenation of biomass substrate [4]. It produces valuable
unsaturated products which are widely used in academia and
industry as intermediates and end-products.
Earlier studies have focused on the development of a catalyst
and reductant for the DODH reactions of polyols and epoxides.
Among the catalysts, oxo-rhenium compounds such as MeReO3,
NH4ReO4, Cp*ReO3 in combination with various reductants such
as triphenyl phosphine [14], molecular hydrogen [6], sulfite [8],
⇑
Corresponding author. Fax: +1 337 482 5676.
E-mail address: rss1805@louisiana.edu (R.S. Srivastava).
https://doi.org/10.1016/j.poly.2018.11.061
0277-5387/Ó 2018 Elsevier Ltd. All rights reserved.

A. Jefferson, R.S. Srivastava / Polyhedron 160 (2019) 268–271
269
2.2. Representative procedure for DODH reactions
OH
R'
R
LMOx
OH
R
Red
+
1-Phenyl-2-ethanediol (0.32 mmol, 44 mg), MTO (0.032 mmol,
8 mg), indoline (0.36 mmol, 34 L), toluene (1 mL), and dodecane
(5 L) were added to a thick-walled Ace glass tube reactor. The
+
H2O
Red-O
+
l
R'
l
reactor was placed in a heating mantle bath at 190 °C for 2.5 h
while stirring magnetically. After cooling to room temperature,
the reaction mixture was filtered and analyzed by GC–MS. For
NMR of Diprophylline (7-(2,3-Dihydroxypropyl)-3,7-dihydro-1,3-
dimethyl-1H-purine-2,6-dione), mucic acid (tetrahydroxyadipic
Scheme 1. General Deoxydehydration reaction of glycols.
and Lewis acids (Zn, Fe, Mn, C) [15] have been extensively
explored. In addition to oxorhenium compounds, oxo-molybde-
num and oxovanadium compounds have also been utilized as
DODH catalysts in combination with phosphines and sulfites as
reductants. Moreover, sacrificial alcohols as potential H-transfer
reductants have also received much attention [7,11,16–18].
In the search for a better hydrogen transfer reductant for metal-
catalyzed DODH reactions, we initiated a project for the develop-
ment of new DODH reaction procedures. The new DODH system
acid), and inositol, a 100
lL aliquot of reaction mixture was with-
drawn. To this mixture CDCl3 and 2
lL DMSO as internal standard
for NMR analysis was added. The product was identified and quan-
tified by 1H NMR spectroscopy and by comparison with an authen-
tic sample.
2.3. Isolation
must have
a practical reductant, which would generate H2
MeReO3 (28 mg, 0.1 mmol), (R,R)-(+)-hydrobenzoin (214 mg,
in situ. Hydroaromatics H-transfer reagents have been used as liq-
uid organic hydrogen carriers for hydrogenation reactions and for
hydrogen storage [19]. Various hydroaromatics, are abundantly
found in fossil resources. The catalytic activity of redox-active solid
metal oxides has been explored for the dehydrogenation of alkyl
aromatics [20]. This indicates the potential use of these reductants
in homogeneous oxo-metal-catalyzed reactions. Nonetheless, very
few hydroaromatics are known for their reactivity with soluble
oxo-metal species [21]. Hydroaromatics are visualized as hydrogen
carriers and could carry hydrogen safely to the reaction mixture.
Sacrificial alcohols including 1-butanol have been used as reduc-
tants in the biomass reduction. We report here the MTO catalyzed
DODH reactions with a small amount of indoline as reductant and
in the absence of 1-butanol (acts as a reducing agent) compared to
earlier reports [22], where two reductants, indoline and 1-butanol
were used. We revisited the chemistry of MeReO3 and developed a
modified process that requires a small amount (3.0 Â 10À4 mol)
one reductant (indoline) compared to earlier reports. In addition,
four different examples (1, 2, 3, 9, 10, Table 1), a comparative study
of solvent/catalyst and various catalyst loading compared to ref 22
were studied.
1 mmol), indoline (119 lL), and anhydrous toluene (5 mL) were
added to a thick-walled Ace glass reactor tube. The reactor was
placed in a heating mantle bath in the range of 190 °C for 24 h
while stirring magnetically. The reaction mixture was cooled and
filtered over silica gel. Solvents were removed using a rotary evap-
orator under reduced pressure. The product was separated by col-
umn chromatography using ethyl acetate/hexane eluent (1: 2.5).
Product yield was 121 mg, 67%.
3. Result and discussion
To test the viability of a dihydroaromatic compound as a reduc-
tant for the DODH of glycols, an exploratory reaction was carried
out with styrene diol, indoline and MTO (10 mol %) in anhydrous
toluene, which produced styrene quantitatively in 2.5 h at 190 °C.
We began the survey with several Re-catalysts, polar and nonpolar
solvents at various temperatures. Among the four-rhenium cata-
lysts examined, MTO was for superior than the others, which pro-
duces
a quantitative yield of alkene. NH4ReO4, Re2O7, and
Re2(CO)10 also exhibited modest activity and good selectivity to
styrene (Table 1, entries 1–4). Catalyst loading is one of the crucial
steps in the catalytic cycle. Consequently, to know the efficacy of
MTO, we examined MTO loading (10 mol%, 5 mol% and 2.5 mol%)
and found that 10 mol% yielded better result of alkene (Table 1,
run 4,11,12). The addition of 4 Å molecular sieve did not improve
product yield. The coordinating solvent such as THF and acetoni-
trile also produced significantly lower yield of styrene, probably
due to the coordination of solvent to Re (Table 1). Our next step
was to screen the effect of temperature and we found that 190 °C
was the optimum temperature for the model substrate for opti-
mum yield of alkene. We performed the reaction to test the effi-
2. Experimental
2.1. General information
All reactants were purchased commercially and used without
further purification. All solvents were ACS grade and were used
directly. GC–MS analyses were obtained on an Agilent instrument
using a Stabilwax capillary column.
cacy
of
hydroaromatic
reductants
such
as
1,2,3,4-
Table 1
Optimization.
tetrahydronaphthalene (tetralin) and indoline under identical
reaction conditions. The results demonstrated that indoline proved
to be a better hydrogen transfer reagent than 1,2,3,4-tetrahydron-
aphthalene for DODH of the model substrates. In addition to the
excellent yield of olefin produced by indoline, its co-product is
indole, which is easily detected by GC. The olefin to indole ratio
were found to be close to 1:1.
The results of the conversion of various diols to olefins are
shown in Table 2. The olefin formation in the DODH reaction is
regioselective since no other isomers were detected. The DODH
reaction of styrene diol at 150 °C and 170 °C produced 48% and
58% styrene respectively in 24 h. However, the similar reaction at
190 °C produced a quantitative yield of styrene in 2.5 h (Table 2,
entry 1). A long chain glycol, 1,2-tetradecanediol at optimized
Entry Catalyst
Solvent
Styrene (%) Time (h)
1
2
3
4
5
6
7
8
NH4ReO4
Re2O7
Re2(CO)10
Toluene
Toluene
Toluene
67
29, 49
9
24
2.5, 10
5
MeReO3 (MTO) 10 mol% Toluene
99
17
55
9
2.5
2.5
2.5
2.5
2.5
2.5
24
MTO, 10 mol%
MTO, 10 mol%
MTO, 10 mol%
MTO, 10 mol%
MTO, 10 mol%
MTO, 10 mol%
MTO 5 mol%
Benzene
THF
Acetonitrile
Dichloroethane 34
9
Indoline
Isopropanol
Toluene
33
7
10
11
12
67
35
2.5
2.5
MTO 2.5 mol%
Toluene

270
A. Jefferson, R.S. Srivastava / Polyhedron 160 (2019) 268–271
Table 2
Re-Catalyzed DoDH with indoline as reductant.
OH
MTO 10 mol%
Toluene, 19 00C
HO
+
R
R
+
N
H
N
H
T(0C)
150
Yield (%)a, b
entry
1
Alkene
Time (h)
Glycol
OH
24
24
48
OH
58
170
190
99 (72)d
2.5
C12H25
C12H25
2
3
OH
190
190
24
63
9
OH
OH
24
OH
OH
73
O
190
190
5
OH
O
O
4
5
OH
26, 48
O
5, 22
C18H37
OH
OH
OH
C18H37
O
O
H3C
N
6
H3C
N
70
N
N
190
24
N
N
O
N
CH3
O
N
CH3
OH
OH
7
HOOC
COOH
36c, e
190
190
COOBu-n
48
70
n-BuOOC
OH
OH
O
OH
58 (41)d
O
OEt
OEt
8
EtO
EtO
O
HO
O
Ph
Ph
OH
OH
HO
Ph
9
80 (67)d
20
190
190
24
24
Ph
OH
OH
HO
10
OH
HO
OH
aConversion and yield determined by gas chromatography (GC), with dodecane as the internal standard.
bIsolated yields are given in parentheses.
cYield determined by 1H NMR.
d1H and 13C NMR of isolated products are given in supplementary materials.
e0.2 M-butenol-1 was added in the reaction.
conditions produced 63% alkene after 24 h (Table 2, entry 2). We
found that aromatic diols are more reactive than the aliphatic diols.
Furthermore, a cyclic glycol, cis-1,2-cyclohexanediol, was very
sluggish under these conditions and produced only 9% cyclohex-
ene. However, no reaction with trans- cyclohexanediol was
detected. This observation implies a syn diol elimination, consis-
tent with a concerted fragmentation of the presumed Re-glycolate
intermediate. We also examined functional group tolerance of the
substrate. Thus, 3-phenoxy-1, 2-propanediol having an ether link-
age produced an alkene with a 73% yield in 5 h (Table 2 entry 4).
The batyl alcohol (1-O-Octadecyl-rac-glycerol) that has an ester
linkage was slow and produced 26% after 5 h and 48% in 22 h
(Table 2, entry 5). Diprophylline (7-(2,3-Dihydroxypropyl)-3,7-
dihydro-1,3-dimethyl-1H-purine-2,6-dione) produced good yield
(70%) of N-allyl purine [23]. N-Allyl heterocycles, such as N-allyl
purine (Table 2, entry 6) have wide-ranging biological activity such
as drug-induced sleep modulators and spontaneous activity, [24]
as selective binders to the A2 adenosine receptor [25] and as anti-
cancer and antiviral agents [26]. The polyhydroxy carboxylic acids,
mucic acid (Table 2, entry 7) provided an esterified alkene product,

A. Jefferson, R.S. Srivastava / Polyhedron 160 (2019) 268–271
271
Supplementary data. Supplementary data
H
N
Supplementary data to this article can be found online at 10.
1016/j.poly.2018.11.061.
OH
R
HO
+
H2O
H2O
N
H
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Conflicts of interest
There are no conflicts of interest to declare.
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We are thankful for the financial support of the Louisiana Board
of Regents [LEQSF (2013-16)-RD-B-06].