Direct Olefination of Alcohols with Sulfones by Using Heterogeneous Platinum Catalysts

Article abstract of DOI:10.1002/chem.201505109

Carbon-supported Pt nanoparticles (Pt/C) were found to be effective heterogeneous catalysts for the direct Julia olefination of alcohols in the presence of sulfones and KOtBu under oxidant-free conditions. Primary alcohols, including aryl, aliphatic, allyl, and heterocyclic alcohols, underwent olefination with dimethyl sulfone and aryl alkyl sulfones to give terminal and internal olefins, respectively. Secondary alcohols underwent methylenation with dimethyl sulfone. Under 2.5 bar H_2, the same reaction system was effective for the transformation of alcohol OH groups to alkyl groups. Structural and mechanistic studies of the terminal olefination system suggested that Pt⁰ sites on the Pt metal particles are responsible for the rate-limiting dehydrogenation of alcohols and that KOtBu may deprotonate the sulfone reagent. The Pt/C catalyst was reusable after the olefination, and this method showed a higher turnover number (TON) and a wider substrate scope than previously reported methods, which demonstrates the high catalytic efficiency of the present method. Olefination of alcohols: The first heterogeneous catalytic terminal and internal olefination of primary alcohols and methylenation of secondary alcohols with sulfones, a reusable carbon-supported Pt catalyst, and KOtBu is reported (see scheme).

Full text of DOI:10.1002/chem.201505109

DOI: 10.1002/chem.201505109
Full Paper
&
Heterogeneous Catalysis
Direct Olefination of Alcohols with Sulfones by Using
Heterogeneous Platinum Catalysts
S. M. A. Hakim Siddiki,[a] Abeda Sultana Touchy,[b] Kenichi Kon,[b] and Ken-ichi Shimizu*[a, b]
Abstract: Carbon-supported Pt nanoparticles (Pt/C) were
found to be effective heterogeneous catalysts for the direct
Julia olefination of alcohols in the presence of sulfones and
KOtBu under oxidant-free conditions. Primary alcohols, in-
cluding aryl, aliphatic, allyl, and heterocyclic alcohols, under-
went olefination with dimethyl sulfone and aryl alkyl sul-
fones to give terminal and internal olefins, respectively. Sec-
ondary alcohols underwent methylenation with dimethyl
sulfone. Under 2.5 bar H2, the same reaction system was ef-
fective for the transformation of alcohol OH groups to alkyl
groups. Structural and mechanistic studies of the terminal
olefination system suggested that Pt0 sites on the Pt metal
particles are responsible for the rate-limiting dehydrogena-
tion of alcohols and that KOtBu may deprotonate the sul-
fone reagent. The Pt/C catalyst was reusable after the olefi-
nation, and this method showed a higher turnover number
(TON) and a wider substrate scope than previously reported
methods, which demonstrates the high catalytic efficiency of
the present method.
Introduction
with phenyl methyl sulfone in the presence of NaH
(2.5 equiv).[11] Although the Julia olefination of alcohols is po-
tentially attractive, the reported methods are only applicable
to activated (benzyl, naphthyl) primary alcohols and are not ef-
fective for the olefination of primary aliphatic and secondary
alcohols.[9,11] The only example of a catalytic Julia olefination of
primary alcohols[9] suffers from a low turnover number (TON)
and difficulties in catalyst/product separation and reuse of the
homogeneous Ru catalyst. As a part of our continuing interest
in the heterogeneous catalysis for bond formation reactions
that are driven by the acceptorless dehydrogenation of alco-
hols,[12] we report herein a heterogeneous catalytic system for
the direct olefination of various primary and secondary alco-
hols with sulfones by using catalytic Pt nanoparticles loaded
on carbon (Pt/C). To our knowledge, this is the first general
heterogeneous Julia olefination of primary and secondary alco-
hols that includes aliphatic, aryl, and allyl alcohols.
Olefins are important structural moieties in chemicals and syn-
thetic intermediates; consequently, olefination is one of the
most important steps in both small-scale organic synthesis and
the production of chemicals in industry.[1] Among various olefi-
nation protocols, the most convenient method is the olefina-
tion of carbonyl compounds with stabilized carbanions, such
as Wittig reaction,[2] Horner–Wittig reaction,[3] Horner–Wads-
worth–Emmons reaction,[4] Peterson reaction,[5] and Julia olefi-
nation.[6] The olefination of alcohols is well established owing
to the availability of a wide variety of substrates, and conven-
tional methods use a two-step procedure: stoichiometric oxi-
dation of the alcohol to give a carbonyl compound followed
by olefination.[7] To improve the atom efficiency of the olefina-
tion of alcohols, a few studies have reported the catalytic aero-
bic[8a–e] and oxidant-free[8f,g] oxidation of alcohols to carbonyl
compounds followed by their Wittig-type olefination. Very re-
cently, Milstein and co-workers[9] reported the first example of
the direct Julia olefination of aryl alcohols with sulfones Results and Discussion
through the acceptorless dehydrogenation of alcohols by
using pincer PNP ruthenium complexes.[10] Kang et al. have re-
Characterization of Pt/C
ported the direct Julia olefination of aryl alcohols (10 equiv)
Figure 1 shows the temperature-programmed H2-reduction
(H2-TPR) profile of an unreduced catalyst precursor, carbon-
loaded platinum oxide (PtOx/C). The H2-TPR profile shows an
H2 consumption peak below 2008C, which is assignable to the
reduction of PtOx to metallic Pt. Figures 2A and B show the X-
ray absorption near-edge structure (XANES) and the extended
X-ray absorption fine structure (EXAFS) spectra, respectively, of
the catalyst precursor PtOx/C, the reduced catalyst Pt/C at
3008C, and a reference compound (Pt foil). Table 1 lists the dis-
tances and coordination numbers for PtÀO and PtÀPt shells,
which are estimated by the curve-fitting analysis of EXAFS. The
[a] Dr. S. M. A. H. Siddiki, Prof. K.-i. Shimizu
Elements Strategy Initiative for Catalysts and Batteries
Kyoto University, Katsura, Kyoto 615-8520 (Japan)
[b] Dr. A. S. Touchy, Dr. K. Kon, Prof. K.-i. Shimizu
Institute for Catalysis, Hokkaido University
N-21, W-10, Sapporo 001-0021 (Japan)
Fax: (+81)11-706-9163
E-mail: kshimizu@cat.hokudai.ac.jp
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201505109.
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Figure 3. Typical TEM image and Pt particle size distribution of Pt/C.
Figure 1. H2-TPR profile of the precatalyst PtOx/C (unreduced precursor of
Pt/C).
Optimization of catalysts and reaction conditions
We carried out a catalyst screening by using a series of sup-
ported Pt catalysts that had been pre-reduced in H2 at 3008C
and contained 0.01 mmol (1 mol%) of Pt. These were tested in
a model olefination reaction of benzyl alcohol (1.5 mmol) with
dimethyl sulfone (1 mmol) and KOtBu (1.1 mmol) in refluxing
toluene (1.5 mL) under N2 for 10 h. Table 2 shows the conver-
sion of dimethyl sulfone and the yield of styrene based on the
sulfone with different catalysts. The reaction in the absence of
the transition-metal catalyst (entry 1) or in the presence of
platinum oxides loaded on carbon (PtOx/C, entry 2) resulted in
no yield of styrene, which indicates that neither KOtBu nor
platinum oxides can catalyze the olefination reaction. The Pt/C
catalyst, which was generated from the reduction of PtOx/C at
Figure 2. Pt L3-edge A) XANES spectra and B) EXAFS Fourier transforms of
PtOx/C, Pt/C, and Pt foil.
Table 1. Curve-fitting analysis of Pt L3-edge EXAFS of Pt/C.
Table 2. Catalyst screening for the olefination of benzyl alcohol to sty-
rene.
Sample
Shell
N[a]
R [Š][b]
s [Š][c]
Rf [%][d]
PtOx/C
Pt/C
Pt foil
O
Pt
Pt
2.7
9.9
(12)[e]
2.00
2.75
(2.76)[e]
0.104
0.073
–
1.6
1.1
–
[a] Coordination numbers. [b] Bond length. [c] Debye–Waller factor. [d] Re-
sidual factor. [e] Crystallographic data.
Catalyst
Conv. [%]
GC yield [%][a]
1
–
–
–
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
PtOX/C
Pt/C
14
100
76
100
95
100
73
64
66
64
61
56
45
41
74
73
67
58
41
27
26
20
44
–
88
65
84
81
84
60
53
48
47
47
46
31
29
63
61
59
48
31
19
17
16
35
Pt/C-air[b]
Pt/CKB
Pt/CVX
Pt/CSA
Pt/Al2O3
Pt/CeO2
Pt/MgO
Pt/ZrO2
Pt/Nb2O5
Pt/TiO2
Pt/SiO2
Pt/HBEA
Rh/C
XANES spectrum of PtOx/C shows a large white line peak,
which is characteristic of platinum oxides, and the EXAFS spec-
trum consists of a PtÀO contribution (2.7 PtÀO bonds at
2.00 Š). The latter indicates that the Pt species in PtOx/C is
platinum oxide, which is consistent with the XANES results.
The XANES spectrum of the reduced catalyst Pt/C is nearly
identical to that of Pt foil, which is indicative of the metallic
electronic state of Pt being present in the Pt/C catalyst. The
EXAFS of the Pt/C catalyst consists of 9.9 PtÀPt bonds with
a length of 2.75 Š, which is close to the PtÀPt distance of bulk
Pt metal (2.76 Š). The PtÀPt coordination number (9.9), which
is lower than that of bulk Pt (12), is characteristic of small
metal nanoparticles. Figure 3 shows a representative TEM
image and the Pt particle size distribution histogram of Pt/C;
the average diameter of Pt particles was 4.4Æ1.1 nm. In sum-
mary, the unreduced precursor PtOx/C consists of carbon-sup-
ported platinum oxides, whereas the reduced catalyst Pt/C is
made up of Pt metal nanoparticles, which are 4.4 nm in diame-
ter, loaded on carbon.
Ir/C
Ru/C
Pd/C
Re/C
Cu/C
Ni/C
Co/C
Pt(acac)2
[a] Yield of styrene is based on sulfone. [b] Pre-reduced Pt/C catalyst was
exposed to air at room temperature for 0.5 h.
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3008C, gave 88% yield of styrene (entry 3). Exposure of the re-
duced Pt/C catalyst to air at room temperature for 30 min re-
sulted in a lower yield of 65% (entry 4), which could be due to
the air oxidation of the surface Pt0 atoms. Hence, thereafter
the metal-loaded catalysts were prepared by H2 reduction
(3008C, entries 3–23) of the oxide precursor, and the olefina-
tion reactions were carried out without exposing the catalyst
to air. The Pt/C catalyst prepared by using different carbon ma-
terials (Kishida chemical, entry 3; Ketjenblack EC-600 JD,
entry 5; Vulcan-XC72, entry 6) and a commercial Pt catalyst
from Sigma-Aldrich (Pt/CSA, entry 7) showed similar yields of
styrene (81–88%), which indicates that the activity does not
markedly depend on the type of carbon or the catalyst prepa-
ration method. When the pre-reduced commercial Pt/CSA was
exposed to air, the yield was 63% (not shown). Hereafter, the
Pt/C catalyst with the highest yield (entry 3) was used as the
standard Pt/C catalyst.
Table 3. Optimization of the reaction conditions for olefination of benzyl
alcohol to styrene.
Alcohol Sulfone Base (x)
[mmol] [mmol]
Solvent
Atmosphere GC yield
[%]
1
2
3
4
5
6
7
8
9
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.25
1.5
2.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
–
toluene
toluene
toluene
toluene
N2
N2
N2
N2
N2
N2
N2
N2
N2
N2
N2
N2
N2
N2
–
KOtBu (0.5)
KOtBu (1.0)
KOtBu (1.1)
28
53
68
61
47
59[a]
47[a]
35[a]
29
75
88
82
54
57
65
11
KOtBu (1.25) toluene
KOtBu (2.0)
KOtBu (1.1)
KOtBu (1.1)
KOtBu (1.1)
KOtBu (1.1)
KOtBu (1.1)
KOtBu (1.1)
KOtBu (1.1)
KOtBu (1.1)
KOtBu (1.1)
KOtBu (1.1)
K2CO3 (1.1)
Cs2CO3 (1.1) toluene
NaOH (1.1)
KOH (1.1)
NaOCH3 (1.1) toluene
Et3N (1.1)
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
n-octane
10 0.5
11 1.25
12 1.5
13 2.0
14 1.5
15 1.5
16 1.5
17 1.5
18 1.5
19 1.5
20 1.5
21 1.5
22 1.5
23 1.5
24 1.5
25 1.5
26 1.5
As listed in entries 8–15, the metal-oxide-supported Pt cata-
lysts showed lower yields of styrene (29–60%) than the Pt/C
catalysts. Next, we tested a series of 5 wt% transition-metal-
loaded carbon catalysts (entries 16–23); the yield of styrene
changed in the order of Pt>Rh>Ir>Ru>Pd>Re>Cu>Ni>
Co. Platinum(II) acetylacetonate as a homogeneous PtII catalyst
(entry 24) gave only 35% yield of styrene. In summary, the
Pt/C catalyst (entry 3) was found to be the most effective cata-
lyst for the model olefination of benzyl alcohol with dimethyl
sulfone in the presence of KOtBu.
n-nonane N2
mesitylene N2
toluene
N2
N2
N2
N2
N2
N2
N2
O2
29
45
59
34
–
toluene
toluene
toluene
toluene
toluene
toluene
toluene
DBU (1.1)
2
KOtBu (1.1)
KOtBu (1.1)
KOtBu (1.1)
86
88
60[c]
Next, we optimized the reaction conditions for the Pt/C-cata-
lyzed model olefination reaction (Table 3). Initially, we studied
the effect of the amount of KOtBu for the reaction of benzyl al-
cohol (1 mmol) with dimethyl sulfone (1 mmol). Styrene was
not obtained in the absence of KOtBu (entry 1), which indicat-
ed that the base was indispensible for the success of the reac-
tion. The yield increased with the amount of KOtBu up to
1.1 mmol (entries 2–4), above which it decreased (entries 5,6).
In the presence of the optimal amount of KOtBu (1.1 mmol),
we carried out the reaction with different amounts of dimethyl
sulfone (1.0–2.0 mmol, entries 4,7–9), and we found that
1 mmol of dimethyl sulfone (entry 4) gave the highest yield of
styrene based on benzyl alcohol. The reactions of dimethyl sul-
fone (1.0 mmol) with different amounts of benzyl alcohol (0.5–
2.0 mmol, entries 4,10–13) showed that 1.5 mmol of benzyl al-
cohol (entry 12) resulted in the highest yield of styrene based
on dimethyl sulfone. Comparison of the reactions in various
solvents under reflux showed that toluene (entry 12) gave
a higher yield than n-octane, n-nonane, and mesitylene (en-
tries 14–16). Notably, the GC analysis of the reaction mixture
after the reaction in toluene (entry 12) showed no peaks that
were due to hydrogenation products of toluene (such as meth-
ylcyclohexane), which indicates that toluene does not act as
a hydrogen acceptor in this system. The reaction with various
basic additives (entries 12,17–23) showed that KOtBu (entry 12)
was more effective than weak bases, such as K2CO3 and Cs2CO3
(entry 17,18), and strong nucleophilic bases, such as NaOH and
KOH (entry 19,20). Organic bases, such as triethylamine and
1,8-diazabicyclo[5.4.0]undec-7-en (entry 22,23), gave 0 and 2%
yield of styrene, respectively. The reactions under different at-
N2 flow[b]
H2
[a] Yield of styrene is based on benzyl alcohol. [b] N2 flow rate was
20 cm3 minÀ1. [c] Ethylbenzene (0.25 mmol) was observed.
mospheres are compared in entries 12 and 24–26. The reaction
under 1 atm O2 gave a similar yield of styrene compared to
the reaction in N2 (86%, entry 24 vs. 12), which suggests that
O2 does not act as a hydrogen acceptor in this system. The re-
action under 1 atm of flowing N2 gave the same yield as that
of the closed system under N2 (88%, entry 25 vs. 12). This im-
plies that removal of the H2 gas that is produced by the reac-
tion does not improve the yield of styrene, which is possibly
due to the low pressure of H2 produced in the standard closed
system under N2. The reaction under 1 atm H2 (entry 26) gave
60% yield of styrene with 25% yield of ethyl benzene as a hy-
drogenated product.
Figure 4 shows the concentration/time plot of the reactive
components under the standard conditions. It was found that
the reaction time of 10 h was sufficient to obtain the highest
yield of styrene (88%) based on dimethyl sulfone. The byprod-
ucts that were observed by GC analysis after 10 h were identi-
fied as a-methylstyrene (0.02 mmol) and diphenyl butene
(0.03 mmol), but ethyl benzene was not observed. A further in-
crease in the reaction time resulted in the gradual hydrogena-
tion of styrene to give ethylbenzene (results not shown). In
conclusion, the optimized conditions for the Pt-catalyzed olefi-
nation are as follows: dimethyl sulfone (1.0 mmol), benzyl alco-
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Figure 5. Catalyst reuse for the olefination of benzyl alcohol by dimethyl sul-
fone with Pt/C for 10 h. Conditions: see Table 3, entry 12.
!
*
Figure 4. Amount of ( ) benzyl alcohol, (+) dimethyl sulfone, ( ) styrene,
~
!
*
) benzaldehyde, ( ) a-methylstyrene, and ( ) ethylbenzene versus reac-
(
tion time. Conditions: benzyl (1.5 mmol) alcohol, dimethyl sulfone (1 mmol),
Pt/C (1 mol%), KOtBu (1.1 mmol).
Next, we studied the substrate scope of this catalytic olefina-
tion method. Initially, we tested the terminal olefination of pri-
mary alcohols with dimethyl sulfone (Table 4). As the previous
catalytic method for this reaction was effective only for aryl al-
cohol substrate,[9] we tested the olefination of various primary
alcohols, which included aryl, aliphatic, and heterocyclic alco-
hols. Benzyl alcohols with different electron-donating and
-withdrawing para substituents (methyl, methoxy, tert-butyl,
fluoro, chloro, CF3À, phenyl) were successfully methylated to
give the corresponding vinylbenzene derivatives in good to
high isolated yields (77–94%, entries 1–8) based on the sul-
fone. Disubstituted benzyl alcohol, 3,4-dimethoxybenzyl alco-
hol (entry 9), was successfully transformed to 1,2-dimethoxy-4-
vinylbenzene in 91% yield. Naphthyl alcohols (1- and 2-naph-
thylmethanol) were converted to give the corresponding vinyl
naphthalene products in high yields (entries 11 and 10, respec-
tively). Heteroaromatic alcohols with furanyl, thienyl, pyridinyl,
and benzo[1,3]dioxonyl groups were also tolerated, and the
corresponding olefins were obtained in 78, 75, 84, and 89%
yield, respectively (entries 12–15). Aliphatic (entries 16,17) and
allylic primary alcohols (entries 18,19) also underwent the olefi-
nation to give the corresponding vinyl and conjugated allyl de-
rivatives in moderate to good yields. This is the first direct cat-
alytic method for the terminal Julia olefination of a wide range
of primary alcohols (aryl, aliphatic, allyl, and heterocyclic alco-
hols).
hol (1.5 equiv), KOtBu (1.1 equiv), and Pt/C (1 mol%) in toluene
under N2 heated at reflux for 10 h.
To further support that the present reaction is an acceptor-
less dehydrogenative reaction, we analyzed the gas-phase
products by mass spectrometry in the early stage of the reac-
tion. The results, which are depicted in Equation (1), show that
the amount of benzyl alcohol that is converted (0.42 mmol) is
close to the amount of H2 that is produced in the gas phase
(0.40 mmol) as well as the total amount of the liquid-phase
products (0.41 mmol), which can be produced by the dehydro-
genation of benzyl alcohol. This confirms that the reaction is
an acceptorless dehydrogenative reaction.
As shown in Table 5, the method was also effective for the
direct olefination of secondary alcohols, including benzylic and
aliphatic derivatives. 1-Phenyl-ethanol with methyl and meth-
oxy substituents at the p-position, 1-naphthyl-ethanol, cyclo-
propyl-phenyl-methanol, diphenyl-methanol, and 2-octanol
were converted to the corresponding 2,2-disubstituted alkenes
with good to high yields (68–94%, entries 1–7). This is the first
direct method for the transformation of OH groups into meth-
ylidene groups by Julia olefination.
Pt/C-catalyzed direct olefination of alcohols with sulfones
Under the optimized reaction conditions, we studied the cata-
lytic properties of the Pt/C-catalyzed olefination method.
Figure 5 shows the results of the catalyst recycle tests for the
standard reaction. After each cycle, acetone (3 mL) was added
to the mixture and the catalyst was separated by centrifuga-
tion, washing with water (3 mL) and acetone (6 mL), drying at
1008C for 3 h, and H2 reduction at 3008C for 0.5 h. The fresh
reaction mixture with KOtBu (1.1 mmol) was then added to the
reactor with the recovered Pt/C catalyst. The recovered catalyst
was reused four times without a marked loss of the yield. After
the first cycle, ICP-AES analysis of the reaction mixture after
the removal of the Pt/C catalyst showed that the content of Pt
in the solution was below the detection limit (10 ppb). These
results demonstrate that Pt/C is a reusable heterogeneous cat-
alyst under this reaction protocol.
Next we studied the internal olefination of primary alcohols
with phenyl ethyl sulfone (Table 6, entries 1–12) and phenyl
benzyl sulfone (entries 13–30) under the standard reaction
conditions. Benzyl alcohol, p-substituted benzyl alcohols with
methyl, methoxy, tert-butyl, chloro, and phenyl groups, 3,4-
methoxybenzyl alcohol, and 2-naphthyl alcohol were trans-
formed into the corresponding propenyl benzene derivatives
in 71–83% yields (entries 1–8). The internal olefination of het-
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Table 4. Pt/C-catalyzed terminal olefination of primary alcohols.
Alcohol
Olefin
t [h]
Yield [%][a]
88[b]
Alcohol
Olefin
t [h]
Yield [%][a]
1
10
11
15
94
2
3
10
12
86
82
12
13
12
12
78[b]
75[b]
4
12
79
14
12
84
5
6
7
8
10
10
8
81[b]
79[b]
77[b]
94
15
16
17
18
12
15
15
15
89
56[b]
74[b]
69[b]
12
9
15
15
91
96
19
15
79[c]
10
1
[a] Yields of isolated products based on sulfone. [b] GC yield. [c] E/Z=94:6 (determined by H NMR analysis).
eroaromatic alcohols with phenyl ethyl sulfone gave the corre-
sponding 2-propenyl-derivatives in high yields (78–81%, en-
tries 9–11). Cinnamyl alcohol was converted into penta-1,3-
dienyl-benzene and isolated in 83% yield and an E/Z ratio of
82:18 (entry 12). The reaction of n-octanol with phenyl ethyl
sulfone gave 17% yield of the corresponding olefin (result not
shown).
(entry 29). Overall, the results in Table 6 demonstrate that this
is a general internal olefination method for primary alcohols
with sulfones, which includes the first example of the internal
olefination of aliphatic alcohols.
Finally, we studied the TON of the present system for gram-
scale reactions by using 10.0 mmol of dimethyl sulfone,
15.0 mmol of alcohol, 11.0 mmol of KOtBu, and 0.02 mol% of
Pt/C catalyst in 10 mL of toluene for 90 h. The reactions with
benzyl alcohol, 4-biphenylmethanol, and diphenylmethanol
gave 79, 76, and 85% yields of the corresponding olefin based
on the sulfone [Eq. (2)–(4) ], and the TONs of these reactions
were 3950, 3800, and 4520, respectively. These TON values are
more than 150 times higher than that of the previously report-
ed catalyst (TON of 25) for the olefination of benzyl alcohol
with dimethyl sulfone.[9]
The reaction of various primary alcohols with benzyl phenyl
sulfone (entries 13–30) also resulted in the highly E-selective
formation of styryl derivatives. Benzyl alcohols were selectively
converted to give the corresponding E-stilbenes with high iso-
lated yields (83–93%, entries 13–20). Naphthyl alcohols (en-
tries 21,22) and heteroaromatic alcohols with furanyl, thienyl,
pyridinyl, and benzo[1,3]dioxonyl groups (entries 23–26) were
also converted to the corresponding styryl derivatives in good
to high yields (84–94%). The internal olefination of cinnamyl
alcohol gave trans,trans-1,4-diphenyl-1,3-butadiene in 92%
yield with high stereoselectivity. The olefination of aliphatic al-
cohols with benzyl phenyl sulfone was also successful (en-
tries 28–30). For most of the reactions in Table 6 (entries 1–28),
we have reported E/Z ratios in a range of 86:14 to 99:1, which
indicates that the present internal olefination method is highly
E selective. Exceptionally, the reaction of n-octanol resulted in
the highly Z-selective formation of the styryl derivative
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Table 5. Pt/C-catalyzed methylenation of secondary alcohols.
Alcohol
Olefin
t [h]
Yield [%][a]
78
1
2
10
10
12
81
80
Figure 6. Kinetic isotopic effect (KIE) in the olefination of benzyl alcohol
(1.5 mmol) with dimethyl sulfone (1 mmol), Pt/C (1 mol%), and KOtBu
(1.1 mmol) in refluxing toluene. The KIE (kH/kD) estimated from the zero-
order rate constants (the slope of the lines) are shown.
3
4
5
15
15
84
88
6
7
15
15
77[b]
68[b]
Figure 7. Formation rate of styrene as a function of the concentration of
A) benzyl alcohol (0.30 to 1.11m), B) dimethyl sulfone (0.58 to 1.11m), and
C) KOtBu (0.30 to 1.11m). Conditions: benzyl alcohol (1.0m), dimethyl sulfone
(0.66m), and KOtBu (0.73m).
[a] Yield of isolated products. [b] GC yields.
Figure 7 shows the effects of the initial concentration of
benzyl alcohol (A), dimethyl sulfone (B), and KOtBu (C) on the
formation rates of styrene. The double logarithmic plots all
show linear relationships, and the slope of the line corresponds
to the reaction order (n). The rate increased with the concen-
tration of benzyl alcohol and KOtBu, and the reaction orders
were +1.2 and +1.5, respectively. Conversely, a negative slope
(n=À0.6) was observed when the concentration of dimethyl
sulfone was increased. These results suggest that the alcohol
and KOtBu are involved in kinetically important steps, which is
consistent with the KIE result, whereas dimethyl sulfone is not
involved in a rate-limiting step. Scheme 1 shows a possible re-
action pathway for the Pt-catalyzed olefination method. The
Pt/C catalyst is responsible for the dehydrogenation of the al-
cohol to afford an aldehyde, which is the rate-limiting step.
The reaction order with respect to KOtBu is +1.5 (Figure 7),
which indicates that KOtBu is involved in a kinetically impor-
tant step. In accordance with the mechanism proposed in the
literature for the acceptorless dehydrogenation of alcohols,[10]
the base may deprotonate alcohols and facilitate their dehy-
drogenation. By considering the previously reported results
that a strong base can deprotonate a sulfone to give a sulfone
salt[13] combined with our observation that the weak bases
(such as K2CO3) give lower yields of styrene than KOtBu
(Table 3), we propose that KOtBu deprotonates the sulfone to
give a sulfone salt. The aldehyde on the catalyst reacts with
the sulfone salt to yield the olefin possibly via a b-hydroxy sul-
fone intermediate.
Kinetic study
Regarding the mechanism of this reaction, Milstein et al.[9] re-
ported that the Julia olefination of benzaldehyde and dimethyl
sulfone with a homogeneous catalyst gave a much lower yield
of styrene than the reaction of benzyl alcohol and dimethyl
sulfone. They speculated that a metal-coordinated aldehyde
rather than a free aldehyde was an intermediate in the reac-
tion, which then reacted with the sulfone species to yield a b-
hydroxy sulfone intermediate.[9] Our test reactions also suggest
that “free” benzaldehyde is not an intermediate in the produc-
tion of styrene; the Pt/C-catalyzed reaction of benzaldehyde
(1.0 mmol) and dimethyl sulfone (1.0 mmol) with of KOtBu
(1.1 mmol) in toluene (1.5 mL) under standard conditions gave
0.13 mmol of styrene. However, as an a-CÀH/a-CÀD kinetic iso-
topic effect (KIE) was observed for the reaction of dimethyl sul-
fone and benzyl alcohol (or a-deutero benzyl alcohol), we can
infer that the dehydrogenation of the benzyl alcohol is in-
volved in the kinetically important steps of the catalytic Julia
olefination (Figure 6). Furthermore, the moderate kH/kD value
of 2.2 indicates that the dissociation of the a-CÀH bond of
benzyl alcohol is a moderately slow step.
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Table 6. Pt/C-catalyzed internal olefination of primary alcohols.
Alcohol
Olefin
t [h] Yield [%][a] E/Z[c]
Alcohol
Olefin
t [h] Yield [%][a] E/Z[c]
1
12
73[b]
92:8
16
24
88
99:1
2
3
12
15
78
82
90:10 17
20
20
84
83
99:1
99:1
91:9
95:5
18
19
4
15
76
24
91
99:1
5
6
12
15
72[b]
81
90:10 20
86:14 21
24
24
83
92
99:1
99:1
7
15
71[b]
96:4
22
24
94
99:1
8
9
15
12
81
75
84:16 23
24
24
90
86
99:1
98:2
91:9
97:3
96:4
24
25
26
10
12
78
24
84
97:3
11
12
13
14
12
15
20
20
81
83
92
93
24
24
28
28
91
92
84
79
98:2
99:1
92:8
18:82
82:18 27
99:1
99:1
99:1
28
29
30
15
24
89
28
63[b]
–
1
[a] Yield of isolated E/Z mixture of products based on sulfone. [b] GC yields. [c] E/Z ratio determined by H NMR analysis.
reported a tandem oxidation/Wittig olefination of alcohols fol-
lowed by hydrogenation of the C=C bond under pressured
H2.[14b] Williams et al.[14b] developed the borrowing-hydrogen-
type CÀC bond formation by dehydrogenation/Wittig olefina-
tion of alcohols followed by hydrogenation of the C=C bond
of the olefins by borrowed hydrogen. Milstein et al. developed
the direct conversion of a hydroxyl group into a methyl group
by a Julia-type olefination of alcohols with dimethyl sulfone
followed by hydrogenation of the C=C bond of the olefin
under pressured H2.[9] Knowing that our heterogeneous catalyt-
ic system is effective for the Julia-type olefination of alcohols
and the Pt/C catalyst can generally hydrogenate olefins to give
Scheme 1. A proposed pathway for the Pt-catalyzed olefination of benzyl al-
cohol with dimethyl sulfone.
One-pot synthesis of CÀC bond formation by olefination
Only a few studies have reported the direct catalytic conver-
sion of alcohol hydroxyl groups into alkyl groups. Lebel et al.
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4) wide substrate scope, which includes primary and secondary
alcohols with aryl, alkyl, allyl, or heterocyclic substituents.
Table 7. Pt/C-catalyzed direct conversion of alcohol hydroxyl groups into
alkyl groups.
Experimental Section
General
Alcohol
Sulfone
Alkane
Yield [%][a]
73
Commercially available organic and inorganic compounds (from
Tokyo Chemical Industry, Wako Pure Chemical Industries, Kishida
Chemical, or Mitsuwa Chemicals) were used without further purifi-
cation. Benzyl-a,a-d2 alcohol (BzCD2OH) with 99.5 atom% D was
purchased from Aldrich. The GC (Shimadzu GC-14B) and GCMS
(Shimadzu GCMS-QP2010) analyses were carried out with Ultra
ALLOY capillary column UA+-1 (Frontier Laboratories Ltd.) by using
1
2
81
79
3
4
1
nitrogen or He as the carrier gas. H and 13C NMR spectra were re-
corded at ambient temperature on a JEOL-ECX 600 spectrometer
operating at 600.17 and 150.92 MHz, respectively, with tetramethyl-
silane as an internal standard.
76
5
77
72
66
80
Catalyst preparation
The standard carbon support (296 m2 gÀ1, Kishida Chemical) and
other carbon materials (CKB =Ketjenblack EC-600 JD, Lion,
1310 m2 gÀ1; CVX =carbon black, Vulcan XC72, 210 m2 gÀ1) were
commercially supplied. g-Al2O3 was prepared by calcination of g-
AlOOH (Catapal B Alumina purchased from Sasol) at 9008C for 3 h.
CeO2 (JRC-CEO3, 81 m2 gÀ1), MgO (JRC-MGO-3), TiO2 (JRC-TIO-4),
and H+-type BEA zeolite (HBEA, SiO2/Al2O3 =25Æ5, JRC-Z-HB25)
were supplied by Catalysis Society of Japan. ZrO2 was prepared by
hydrolysis of zirconium oxynitrate 2-hydrate by an aqueous NH4OH
solution, followed by filtration, washing with distilled water, drying
at 1008C for 12 h, and calcination at 5008C for 3 h. Nb2O5 was pre-
pared by calcination of Nb2O5·nH2O (supplied by CBMM) at 5008C
for 3 h. SiO2 (Q-10, 300 m2 gÀ1) was supplied from Fuji Silysia Chem-
ical Ltd.
6
7
8[b]
[a] GC yields based on sulfone. [b] 36h.
alkanes under pressured H2, we tried the direct alkylation of al-
cohols by using our standard olefination conditions under
pressured H2 (Table 7). We carried out the Pt/C-catalyzed reac-
tion of benzyl alcohol (1.5 mmol), dimethyl sulfone (1 mmol)
and KOtBu (1.1 mmol) in toluene under H2 (2.5 bar) heating at
reflux for 24 h. GC and GC-MS analyses of the mixture showed
73% yield of ethylbenzene, 2% yield of 1-isopropyl-benzene,
and 17% yield of ethylcyclohexane. Under the same condi-
tions, hydroxyl groups of substituted benzyl alcohols, 2-naph-
thylmethanol, and nicotinyl alcohol were also converted to
methyl groups with good yields of the products (76–81%, en-
tries 2–6). The method was also effective for the conversion of
alcohol hydroxyl groups into ethyl and benzyl moieties: the re-
actions of benzyl alcohol with phenyl ethyl sulfone and phenyl
benzyl sulfone under H2 gave propylbenzene and 1,2-diphenyl-
ethane in 66 and 80% yield, respectively (entries 7,8).
The precursor of Pt/C was prepared by an impregnation method. A
mixture of carbon and an aqueous HNO3 solution of Pt(NH3)2(NO3)2
was concentrated at 508C followed by drying at 908C for 12 h.
Before each catalytic experiment, the Pt/C catalyst with Pt loading
of 5 wt% was prepared by pre-reduction of the precursor in
a pyrex tube under a flow of H2 (20 cm3 minÀ1) at 3008C for 0.5 h.
Other supported Pt catalysts with Pt loading of 5 wt% were also
prepared by the same method. M/C (M=Rh, Ir, Ru, Pd, Re, Cu, Ni,
Co) catalysts with metal loading of 5 wt% were prepared by the
similar manner as for Pt/C by using an aqueous HNO3 solution of
Rh(NO3)3 or Pd(NH3)2(NO3)2 or an aqueous solution of metal nitrates
(for Ni, Cu, Co), IrCl3·nH2O, RuCl3, or NH4ReO4. A commercial Pt-
loaded carbon catalyst (Pt/CSA, Pt=5 wt%) was purchased from
Sigma–Aldrich.
Conclusion
Characterization
Temperature-programmed reduction under H2 (H2-TPR) was carried
out with BELCAT (MicrotracBEL). Unreduced precursor of PtOx/C
(20 mg) was mounted in a quartz tube, and the sample was
heated with a temperature ramp-rate of 108C minÀ1 in a flow of
5% H2/Ar (20 cm3 minÀ1). The effluent gas was passed through
a trap containing 4Š MS to remove water, then through the ther-
mal conductivity detector. The amount of H2 consumed during the
experiment was detected by a thermal conductivity detector.
We have developed the first heterogeneous and reusable cata-
lytic method for the terminal and internal olefination of pri-
mary alcohols and methylenation of secondary alcohols by
using sulfone reagents, catalytic carbon-supported Pt nanopar-
ticles, and KOtBu under N2. Additionally, the alcohol hydroxyl
groups can be selectively converted into alkyl groups by hy-
drogenation of the C=C bond under 2.5 bar H2. Compared
with a previous catalytic method for the Julia olefination of al-
cohols, our method has the following advantages: 1) easy cata-
lyst/product separation, 2) catalyst reusability, 3) high TON, and
The number of surface metal atoms in the Pt/C catalyst, reduced
under H2 at 3008C for 0.5 h, was estimated from the CO uptake of
the samples at room temperature by using the pulse-adsorption of
Chem. Eur. J. 2016, 22, 6111 – 6119
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CO in a flow of He by BELCAT (MicrotracBEL). The average Pt parti-
cle size was calculated from the CO uptake, which was based on
the assumption that CO was adsorbed on the surface of spherical
Pt particles at CO/(surface Pt atom)=1:1 stoichiometry. Transmis-
sion electron microscopy (TEM) measurements were carried out by
using a JEOL JEM-2100F TEM operated at 200 kV. X-ray diffraction
(XRD) patterns of the powdered catalysts were recorded with
a Rigaku MiniFlex II/AP diffractometer with CuKa radiation.
Keywords: alcohols · heterogeneous catalysis · olefination ·
platinum · sulfones
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Typical procedure of catalytic reactions
Pt/C (39 mg, 1 mol% with respect to the sulfone), pre-reduced
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1
The products were identified by H and 13C NMR spectroscopy and
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Acknowledgements
This work was supported by JSPS KAKENHI (Grant No.
26289299), a MEXT program “Elements Strategy Initiative to
Form Core Research Center” and a Grant-in-Aid for Scientific
Research on Innovative Areas “Nano Informatics” (25106010)
from JSPS.
Received: December 21, 2015
Revised: February 1, 2016
Published online on March 1, 2016
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