Scandium and ytterbium tris(perfiuorobutanesulfonyl)methide complexes: Extremely efficient Lewis acid catalysts

Article abstract of DOI:10.1055/s-1999-2994

Lanthanide tris(perfluorobutanesulfonyl)methides, scandium and ytterbium complexes in particular, were synthesized and shown to be water-tolerant and extremely efficient Lewis acid catalysts for the Friedel-Crafts acylation, Diels-Alder reaction, and Meer

Full text of DOI:10.1055/s-1999-2994

1990
LETTER
Scandium and Ytterbium Tris(perfluorobutanesulfonyl)methide Complexes:
Extremely Efficient Lewis Acid Catalysts
Joji Nishikido,a Fumihiko Yamamoto,a Hitoshi Nakajima,a Yutaka Mikami,b Yousuke Matsumoto,b Koichi Mikamib*
aThe Noguchi Institute, Itabashi-ku, Tokyo 173-0003, Japan
bDepartment of Chemical Technology, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8552, Japan
Fax +81-3-5734-2776; E-mail: kmikami@o.cc.titech.ac.jp
Received 7 October 1999
First of all, the syntheses of the lanthanide(III) tris(perflu-
Abstract: Lanthanide tris(perfluorobutanesulfonyl)methides, scan-
orobutanesulfonyl)methide complexes are worth men-
dium and ytterbium complexes in particular, were synthesized and
tioning (Scheme 1). Based on our precedent report on the
shown to be water-tolerant and extremely efficient Lewis acid cata-
higher catalytic activities of lanthanide(III) bis(perfluo-
robutanesulfonyl)amide complexes5a compared to bis(tri-
fluoromethanesulfonyl)amide complexes, we focused our
attention on the syntheses of the lanthanide(III) tris(per-
fluorobutanesulfonyl)methide complexes. According to
Seppelt’s original paper7 on the preparation of tris(trifluo-
romethanesulfonyl)methane, HC(SO2CF3)3, tris(perfluo-
robutanesulfonyl)methane, HC(SO2C4F9)3 was prepared
through modification by using hydrogen fluoride-free and
anhydrous perfluorobutanesulfonyl fluoride and the slow
addition into a vigorously stirred solution of methylmag-
nesium chloride in tetrahydrofuran.8 Acidic work up with
sulfuric acid followed by the treatment with cesium car-
bonate gave the cesium salt of tris(perfluorobutanesulfo-
nyl)methane, CsC(SO2C4F9)3 as a white solid. Upon
protonation of CsC(SO2C4F9)3 with 100% sulfuric acid
and vacuum-sublimation at 75 °C / 3 mmHg, to remove
volatile materials, and then at 110 °C / 2 mmHg, a white
crystalline HC(SO2C4F9)3 was obtained in 25% yield (lit.8
19% yield).
lysts for the Friedel-Crafts acylation, Diels-Alder reaction, and
Meerwein-Ponndorf-Verley reduction.
Key words: tris(perfluorobutanesulfonyl)methide, scandium, ytter-
bium, lanthanides, Lewis acid catalysis
Recently, a wide variety of Lewis acid complexes have
been developed to realize unique reactivities and selectiv-
ities in reactions promoted therewith, and some of them
have been applied in industrial processes.1 However, the
Lewis acid complexes have often been used in more than
a stoichiometric amount. Therefore, it is desirable to de-
crease the amount of the Lewis acid complexes by devel-
oping an efficient catalyst and catalytic processes
therewith. Amongst, the Friedel-Crafts reactions, which
are one of the most important carbon-carbon bond form-
ing processes in organic synthesis, are generally carried
out by using Lewis acid complexes such as aluminum
trichloride.2 However, the Friedel-Crafts acylation reac-
tion generally requires at least a stoichiometric amount of
Lewis acid due to the complexation with the aromatic ke-
tone product. In this respect, lanthanide(III) triflates have
been reported as the catalysts of choice.3,4 Furthermore,
lanthanide(III) bis(perfluoroalkanesulfonyl)amide com-
plexes have been found to be more active catalysts.5 Quite
recently, the syntheses and catalytic use of ytterbium and
scandium tris(trifluoromethanesulfonyl)methides were
reported for aromatic nitration.6 We herein report the syn-
theses of lanthanide(III) tris(perfluorobutanesulfonyl)me-
thide complexes and the remarkably high catalytic
activities of the scandium and ytterbium complexes in car-
bon-carbon bond forming reactions such as the Friedel-
Crafts acylation and Diels-Alder reaction.
The lanthanide tris(perfluorobutanesulfonyl)methide
complexes were synthesized in water using lan-
thanide(III) carbonates, acetates, or oxides. The ytterbi-
um(III) tris(perfluorobutanesulfonyl)methide complex
was prepared by mixing HC(SO2C4F9)3 (6 mmol) with a
slightly excess amount of ytterbium(III) carbonate hy-
drate at room temperature for 3 hours and then at 70 °C for
2 hours in water. After filtration, evaporation and then
drying at 90 °C / 0.01 mmHg for 6 hours, ytterbium(III)
tris(perfluorobutanesulfonyl)methide complex was ob-
tained as a hygroscopic white powder in 98% yield (5.42
g): Yb[C(SO2C4F9)3]3 Anal.: Yb 6.2%, C 16.7%; Calcd.:
Yb 6.3%, C 17.0%; 19F NMR (dioxane-d8) d -126.1, -
121.2, -107.3, -81.4 ppm. Likewise, the scandium(III)
tris(perfluorobutanesulfonyl)methide complex was pre-
pared by mixing HC(SO2C4F9)3 (6 mmol) with a slightly
excess amount of scandium(III) acetate hydrate at room
temperature for 3 hours and then at 70 °C for 3 hours in
water. After filtration, evaporation and then drying at
90 °C / 0.01 mmHg for 6 hours, scandium(III) tris(perflu-
orobutanesulfonyl)methide complex was obtained as a
hygroscopic white powder in 99% yield (5.21 g):
Sc[C(SO2C4F9)3]3 Anal.:1.6%, 17.4%; Calcd.: Sc 1.7%, C
H2SO4
3 C4F9SO2F + 4 CH3MgCl
(C4F9SO2)3CMgCl
H2SO4
1/2 Cs2CO3
(C4F9SO2)3CH
(C4F9SO2)3CCs
1/6 Yb2(CO3)3
or 1/3Sc(OAc)3
(C4F9SO2)3CH
[(C4F9SO2)3C]3M
M = Sc or Yb
Scheme 1
Synlett 1999, No. 12, 1990–1992 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Extremely Efficient Lewis Acid Catalysts
1991
17.8%; 19F NMR (dioxane-d8) d -126.4, -121.7, -107.8, -
81.6 ppm.
cat. (1.5 or 5 mol%)
+
CH2Cl2 2 ml, 25°C
Then, the catalytic activities of the scandium and ytterbi-
um complexes were examined in carbon-carbon bond
forming reactions such as the Friedel-Crafts acylation and
Diels-Alder reaction. The Friedel-Crafts acylation reac-
tions of anisole (1 mmol) with acetic anhydride (2 mmol)
were carried out in the presence of a catalytic amount (5
mol%) of the lanthanide complexes in benzotrifluoride (2
ml) at 50 °C for 1-3 hours. Depending critically on the
kind of the anionic ligands employed, the aromatic ketone
product was obtained in low-to-good chemical yields as
calculated by GC analysis using n-decane as an internal
standard (Scheme 2, Table 1). Scandium tris(perfluorobu-
tanesulfonyl)methide complex provides slightly higher
chemical yield than that obtained by the ytterbium cata-
lyst. In addition, the tris(perfluorobutanesulfonyl)methide
complex affords comparable or even higher chemical
yield than that obtained by the bis(perfluorobutane-
sulfonyl)amide complex. Thus, the order of the
catalytic activities are as follows: Sc[C(SO2C4F9)3]3 ≥
Yb[C(SO2C4F9)3]3 ≥ Yb[N(SO2C4F9)2]3 > Sc(OSO2CF3)3
> Yb(OSO2CF3)3.
O
O
1 mmol
1.5 mmol
Scheme 3
Table 2 Diels-Alder reactions
%Yield a)
Time
ScOTf(5 mol%)
ScC4me(1.5 mol%)
10min
1h
79%
95%
88%
95%
5h
20h
97%
a)
Calculated by GC analysis using n-nonane as an
internal standard.
ScOTf: Sc(OSO2CF3)3
,
ScC4me: Sc[C(SO2C4F9)3]3
Finally, the Meerwein-Ponndorf-Verley reductions10 of
benzaldehyde (1 mmol) with 2-propanol (6 ml) were ex-
amined in the presence of a catalytic amount (10 mol%)
of lanthanide complexes at 50 °C for 1-3 hours. The ben-
zylalcohol product was obtained in low-to-good yield as
calculated by GC analysis using n-nonane as an internal
standard (Scheme 4, Table 3). Ytterbium methide com-
plexes provide higher chemical yields than those obtained
by the ytterbium amide and triflate catalysts. Benzyl iso-
propyl ether was also obtained as a by-product
(Yb[C(SO2C4F9)3]3:10%, Yb[N(SO2C4F9)2]3:9%).
Ac
cat. (5 mol%)
+
Ac2O
benzotrifluoride 2 ml
50°C
OMe
OMe
2 mmol
1 mmol
Scheme 2
Table 1 Friedel-Crafts Acylation reactions
cat. (10 mol%)
%Yield a)
CH2OH
CHO
YbOTf
ScOTf
YbC4am
Time
YbC4me
91%
ScC4me
2-propanol 6 ml
50°C
39%
48%
75%
87%
89%
93%
5%
1h
3h
1 mmol
12%
Scheme 4
a) Calculated by GC analysis using n-decane as an internal standard.
YbOTf: Yb (OSO2CF3)3
,
ScOTf: Sc(OSO2CF3)3
YbC4am: Yb[N(SO2C4F9)2]3
ScC4me: Sc[C(SO2C4F9)3]3
YbC4me: Yb[C(SO2C4F9)3]3
Table 3 Meerwein-Ponndorf-Verley Reductions
%Yield a)
Time
AlCl3
trace
Al(OPr-i)3
YbOTf
YbC4am
52%
YbC4me
85%(97%)b)
The Diels-Alder reactions9 of 2,3-dimethylbutadiene (1
mmol) with methyl vinyl ketone (1.5 mmol) were carried
out in the presence of a catalytic amount (1.5 to 5 mol%)
of scandium complexes in dichloromethane (2 ml) at
25 °C. Acetylcyclohexene was obtained in moderate-to-
good chemical yield as calculated by GC analysis using n-
nonane as an internal standard (Scheme 3, Table 2). Scan-
dium methide complex affords the higher chemical yield
than that obtained by scandium triflate complex.
1%
3%
1h
3h
trace
a)
Calculated by GC analysis using n-nonane as an internal standard.
b) The value in parenthesis refers to the conversion of the starting
benzaldehyde.
YbOTf: Yb(OSO2CF3)3
YbC4am: Yb[N(SO2C4F9)2]3
YbC4me: Yb[C(SO2C4F9)3 ]3
In summary, we have disclosed herein that lanthanide
tris(perfluorobutanesulfonyl)methide complexes such as
the scandium and ytterbium complexes are synthesized
and shown to be extremely efficient Lewis acid catalysts
Synlett 1999, No. 12, 1990–1992 ISSN 0936-5214 © Thieme Stuttgart · New York

1992
J. Nishikido et al.
LETTER
Inanaga, J.; Sugimoto, Y.; Hanamoto, T. New. J. Chem. 1995,
19, 707.
for the Friedel-Crafts acylation, Diels-Alder reaction, and
Meerwein-Ponndorf-Verley reduction.
(5) (a) Yb[N(SO2C4F9)2]3: Nishikido, J.; Nakajima, H.; Saeki, T.;
Ishii, A.; Mikami, K. Synlett 1998, 1347. (b) Al-, Ti-,
Yb[N(SO2CF3)2]3: Mikami, K.; Kotera, O.; Motoyama, Y.;
Sakaguchi, H.; Maruta, M. Synlett 1996, 171. Also see: X-ray
analysis of [Mg(H2O)6].N(SO2CF3)2: Haase, A.; Klare, Ch.
Bert, P.; Bruckmann, J.; Kruger, C.; Tsay, Y.-H.; Aubke, F.
Acknowledgement
K. M. is grateful to Prof. K. Seppelt of Freie Universitat Berlin and
Dr. W. M. Lamanna of 3M Fluorochemical Technology Center for
their useful discussion on the preparation of tris(trifluoromethane-
sulfonyl)methane, HC(SO2CF3)3 and tris(perfluorobutanesulfo-
nyl)methane, HC(SO2C4F9)3 at the 15th International Symposium
on Fluorine Chemistry in Vancouver, Canada on August 1997.
.
Inorg. Chem. 1996, 35, 1920. Sc[N(SO2CF3)2]3 1.5CH3CO2H:
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Ghosez, L. Synlett 1995, 565. Li-, Mg-, Zn-,
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Article Identifier:
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Synlett 1999, No. 12, 1990–1992 ISSN 0936-5214 © Thieme Stuttgart · New York