Zr(IV)-Fe(III), -Ga(III), and -Sn(IV) binary metal complexes as synergistic and reusable esterification catalysts

Article abstract of DOI:10.1002/adsc.200505083

Synergism in catalytic activity with the combined use of Hf(O-i-Pr) ₄ or Zr(O-i-Pr)₄ and Fe(O-i-Pr)₃ for direct esterification and a very simple method for their extraction with ionic liquids for their recovery and reuse are described. This Zr(IV)-Fe(III) complex is an environmentally benign catalyst due to its high turnover number, extremely mild Lewis acidity, low toxicity, reusability, and commercial availability at low cost.

Full text of DOI:10.1002/adsc.200505083

COMMUNICATIONS
ꢀ
ꢀ
ꢀ
Zr(IV) Fe(III), Ga(III), and Sn(IV) Binary Metal Complexes
as Synergistic and Reusable Esterification Catalysts
a
a
a
a,
Atsushi Sato, Yuka Nakamura, Toshikatsu Maki, Kazuaki Ishihara, *
b,
Hisashi Yamamoto *
Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan
a
Fax: (þ81)-52-789-3222, e-mail: ishihara@cc.nagoya-u.ac.jp
b
Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue, Chicago, IL 60637, USA
Fax: (þ1)-773-703-0805, e-mail: yamamoto@uchicago.edu
Received: February 9, 2005; Accepted: April 29, 2005
Table 1. Synergistic effect of the combined use of Zr(OH)x
Abstract: Synergism in catalytic activity with the
combined use of Hf(O-i-Pr)4 or Zr(O-i-Pr)4 and
[a]
(
OAc) and additives on the direct esterification of 1 with 2.
y
Fe(O-i-Pr) for direct esterification and a very simple
Additive
Yield [%]
of 3
Additive
Yield [%]
of 3
3
[
b]
[b]
method for their extraction with ionic liquids for
their recovery and reuse are described. This Zr(IV)
[c]
[d]
–
44 (50)
77
82
Sn(O-i-Pr)4
Fe(O-i-Pr)3
89
89
ꢀ
Fe(III) complex is an environmentally benign cata-
Al(O-i-Pr)3
Ga(O-i-Pr)3
lyst due to its high turnover number, extremely mild
Lewis acidity, low toxicity, reusability, and commer-
cial availability at low cost.
[a]
A solution of 1 (5 mmol) and 2 (5 mmol) in heptane
(
2.5 mL) was heated in the presence of Zr(OH) (OAc)y
x
(
0.1 mmol) and additive (0.1 mmol) at 1208C (bath tem-
Keywords: dehydration; esterification; esters; green
chemistry; ionic liquids; recyclingcatalyst
perature) without the removal of water for 12 h.
Determined by H-NMR spectral analysis of crude pro-
[b]
1
ducts.
No additive was used.
[
[
c]
d]
4
mol % of Zr(OH) (OAc) was used.
x y
Recently, we found that HfCl ·2 THFand ZrCl ·2 THF
4
4
are highly effective catalysts for direct esterification us- combination with Al(III), Ga(III), Sn(IV), and Fe(III)
ingequimolar amounts of carboxylic acids and alco-
hols. This is one of the ideal methods for preparinges-
salts. These binary metal ion complexes were much
more active than those of previously reported catalysts,
[1]
ters and polyesters not only because it gives a higher HfCl ·2 THF, ZrCl ·2 THF, Zr(OH) (OAc) , Zr(O-i-
4
4
x
y
[
5]
atom efficiency but also because it gives a lower E-fac- Pr) , ZrOCl ·8 H O, etc.
4
2
2
[
2]
tor, defined as the mass ratio of waste to desired prod-
Next, we investigated in detail the synergistic effects
However, these metal(IV) chlorides are mois- of the combined use of Zr(O-i-Pr) and Fe(O-i-Pr) for
[
3–5]
uct.
4
3
ture-sensitive, and gradually decompose to inactive the esterification of 1 with 2 because of their low toxici-
[
7]
metal oxychlorides and hazardous hydrogen chloride ty and commercial availability at low cost. Zr(O-i-Pr) ,
by hydrolysis.
4
[1c,6]
We report here synergism in catalytic commercially available at higher purity, was chosen in
activity with the combined use of Hf(O-i-Pr) or Zr(O- place of Zr(OH) (OAc) . The esterification was con-
4
x
y
i-Pr) and Fe(O-i-Pr) for direct esterification and a ducted in heptane at azeotropic reflux with the removal
4
3
very simple method for their extraction with ionic liq- of water usinga Dean–Stark apparatus. The yield of 3
uids for their recovery and reuse. This Zr(IV)ꢀFe(III) over the course of the reaction is plotted (A in Figure 1).
complex is an environmentally benign catalyst due to As expected, Fe(III) (x marks) was much less active than
its high turnover number, extremely mild Lewis acidity, Zr(IV) (white circles), but in combination (black cir-
low toxicity, reusability, and commercial availability at cles) they showed synergistic activity. Similar experi-
low cost.
ments were conducted for Hf(O-i-Pr) ꢀFe(O-i-Pr)
4
3
We initially investigated the effects of metal alkoxides and Ti(O-i-Pr) ꢀFe(O-i-Pr) because Hf(IV) and
4
3
[
1,3,5f]
(
2 mol %), which synergistically promote the model es- Ti(IV) are also known to be good catalysts.
The es-
terification reaction of 4-phenylbutyric acid (1) with cy- terification of 1 with benzyl alcohol (4), which is more
clododecanol (2) to give the corresponding ester 3 in the reactive than 2, was chosen to reduce the reaction
[
6]
presence of Zr(OH) (OAc) (xþy¼4, 2 mol %). As time. As shown in B in Figure 1, the addition of Fe(III)
x
y
shown in Table 1, a synergistic effect was observed in (black circles) synergistically increased the catalytic ac-
Adv. Synth. Catal. 2005, 347, 1337–1340
DOI: 10.1002/adsc.200505083
ꢀ 2005 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim
1337

COMMUNICATIONS
Atsushi Sato et al.
Figure 2. The relationship between the molar ratio of Zr(IV)
and Fe(III). A solution of 1 (5 mmol) and 2 (5 mmol) in hep-
tane (2.5 mL) was heated at 1208C (bath temperature) with
the removal of water for 2 h in the presence of Zr(O-i-Pr)4
(
10 mol %) and Fe(O-i-Pr) (x mol %).
3
[
10]
[10]
in [EMIM][BF4] and [BMIM][PF ], but was still ac-
6
[
10]
[10]
tive in [EMIM][OTf] and [BMIM][NTf2] (6). The
amounts of Zr(IV) and Fe(III) species in the ionic liquid
layer after esterification were estimated by ICP (induc-
tively coupled plasma) emission spectroscopic analysis
Figure 1. Synergistic effect of the combined use of two differ-
ent metal species on the esterification rate. A solution of 1
(
Table 2). When esterification was carried out using
(
(
5 mmol) and 2 (5 mmol) or 4 (5 mmol) in heptane
2.5 mL) was heated at 1208C (bath temperature) with the re-
Zr(O-i-Pr) alone, Zr(IV) species remained in the hep-
tane layer (entry 1). However, when 1 equiv. of Fe(O-
i-Pr) was added per Zr(IV), Zr(IV) species was easily
transferred to a layer of 6 together with Fe(III) (entry
4
moval of water in the presence of Zr(O-i-Pr) , Hf(O-i-Pr) ,
4
4
3
Ti(O-i-Pr) , or Fe(O-i-Pr) .
4
3
2). Three mL of 6 were required to extract Zr(IV)
tivity of Hf(IV) (white circles), with the combined use of (0.025 mmol) and Fe(III) (0.025 mmol) in quantitative
Zr(IV) and Fe(III). On the other hand, the addition of yields (entry 3). However, the use of a large amount of
Fe(III) (black crosses) slightly inhibited the catalytic ac- ionic liquid seriously diminished the esterification rate.
tivity of Ti(IV) (white triangles). These experimental re- Fortunately, based on the further screeningof ionic liq-
[
10]
sults indicate that the catalytic activities of Hf(IV) and uids, we found that [BPY][NTf2] (7) was 6 times more
Zr(IV) for esterification are essentially different from effective than 6: Zr(IV) (0.05 mmol) and Fe(III)
[8]
that of Ti(IV).
(0.05 mmol) were almost completely extracted with
Next, we explored the recovery and reuse of the 1 mL of 7 (entry 4).
Zr(IV) catalyst by biphasic extraction. Ionic liquids
The generality and scope of the direct esterification
are very attractive as solvents for the extraction of inor- catalyzed by a Zr(IV)ꢀFe(III) complex was examined
[
9]
ganic species because of their high polarity. To explore (Table 3). Non-polar hydrocarbon was suitable as a sol-
the catalytic activity of Zr(IV)ꢀFe(III) species in ionic vent, and the reaction temperature was controlled by the
liquids, the esterification of 1 with 4 was conducted in boilingpoint of the chosen solvent. Most of the aliphatic
the presence of Zr(O-i-Pr) and/or Fe(O-i-Pr) in a bi- and aromatic carboxylic acids and primary and secon-
4
3
phasic system of heptane and ionic liquid. Their catalytic dary alcohols, includingsterically hindered and acid-
activities were influenced by the counter anion in the sensitive ones, were suitable as substrates, and their es-
ionic liquid. Surprisingly, Zr(O-i-Pr) was almost inert terification proceeded cleanly to give the desired esters
4
[a]
Table 2. Extraction of Zr(IV) and Fe(III) species from the esterification mixture with ionic liquids.
Entry
Catalysts [mol%]
Zr(IV)
Ionic liquid [mL]
Time [h]
Recovery [% yield]
Fe(III)
Zr(IV)
Fe(III)
1
2
3
4
1
1
0.5
1
–
1
0.5
1
6, 1
6, 1
6, 3
7, 1
8
8
12
8
4
75
92
–
78
>99
>99
>91
[
a]
A solution of 1 (5 mmol) and 4 (5 mmol) in heptane (2.5 mL) and ionic liquid was heated in the presence of Zr(O-i-Pr)4
1 mol %) and/or Fe(O-i-Pr) (1 mol %) at azeotropic reflux with removal of water (bath temperature, 1158C) for 8 h.
(
3
After the reaction was complete, hexane (2 mL) was added to clearly separate a hydrocarbon layer and an ionic layer.
1338
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Zr(IV)ꢀFe(III), ꢀGa(III), and ꢀSn(IV) Binary Metal Complexes
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[a]
Table 3. Reusable Zr(IV)–M(n)-catalyzed direct esterification.
1
2
[b]
Entry
R CO HþR OH
Additive M(O-i-Pr)n
Solvent, Time [h]
Yield [%] (Trial Number)
2
[
[
[
[
[
[
c]
c]
c]
e]
c]
f]
[d]
1
2
3
4
5
6
1þ4
1þ4
1þ4
1þ4
1þ2
1þ
Fe(III)
Sn(IV)
Ga(III)
Fe(III)
Fe(III)
Fe(III)
Heptane, 8
Heptane, 8
Heptane, 8
Octane, 12
Octane, 12
Heptane, 15
99 (15)
[d]
96 (3)
[d]
98 (3)
[d]
99 (2)
[d]
>99 (3)
>99
[
f]
7
1þ
Fe(III)
Heptane, 19
>99
[
[
f]
f]
[
8
9
1
1
1þPhOH
Fe(III)
Sn(IV)
Ga(III)
Fe(III)
o-Xylene, 20
o-Xylene, 20
o-Xylene, 20
Heptane, 23
53
89
94
1þPhOH
f]
f]
0
1
1þPhOH
[
1þNCCH CH OH
>99
2
2
[
f]
12
13
14
þ2
Fe(III)
Fe(III)
Fe(III)
Heptane, 23
Heptane, 18
Heptane, 17
91
98
99
[
[
f]
f]
PhOCH CO Hþ2
2
2
þ4
[
f]
15
þ4
Fe(III)
Octane, 6
>99
[
[
[
[
f]
f]
c]
f]
[g]
1
1
1
1
6
7
8
9
1-AdCO H þ4
Fe(III)
Fe(III)
Fe(III)
Fe(III)
Heptane, 20
Heptane, 50
Toluene, 7
>99
93
97 (3)
99
2
[g]
1-AdCO H þcC H OH
2
6
11
[d]
PhCO Hþ4
2
PhCO HþcC H OH
Toluene, 45
2
6
11
[
a]
Unless otherwise noted, a solution of carboxylic acid (5 mmol) and alcohol (5 mmol) in hydrocarbon (2.5 mL) and/or 7
(
1 mL) was heated in the presence of Zr(O-i-Pr) (1 mol %)–M(O-i-Pr) (1 mol %) at azeotropic reflux with the removal
4
n
of water.
Trial number for reuse of catalysts.
Compound 7 (1 mL) was added in the reaction mixture to recover and reuse catalysts.
An average yield in each recycled run is shown.
Amounts: 1 (100 mmol), 4 (100 mmol), Zr(O-i-Pr) (0.1 mol %), Fe(O-i-Pr) (0.1 mol %), octane (10 mL), 7 (2 mL).
[
[
[
[
[
[
b]
c]
d]
e]
f]
4
3
Compound 7 was not added.
g]
1
-AdCO H¼1-adamantylcarboxylic acid.
2
in high yields. Zr(IV)ꢀFe(III) catalyst was repeatedly vent consistingof heptane and 7 more than 15 times
recycled as a solution of 7 without isolation. For exam- without any loss of activity (entry 1). In a similar man-
ple, Zr(IV)ꢀFe(III) catalyst (1 mol %) could be reused ner, Zr(IV)–Sn(IV) and Zr(IV)–Ga(III) complexes
for the esterification reaction of 1 with 4 in abiphasic sol- were also reusable (entries 2 and 3). Whilethe esterifica-
Adv. Synth. Catal. 2005, 347, 1337–1340
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Atsushi Sato et al.
tion of phenol was disturbed by the addition of Fe(O-i- Acknowledgements
Pr) (entry 8), other additives such as Sn(IV) and
3
Thiswork was su pported by SORST, Japan Science and Tech-
nology Corporation (JST), the Tokuyama Science Foundation,
and the Iwatani Naoji Foundation.
Ga(III) could be used in place of Fe(III) (entries 9 and
0). The applicability of the present protocol to a
1
large-scale process (100 mmol scale, 0.1 mol % of
Zr(IV)ꢀFe(III) catalyst) is demonstrated in entry 4.
In summary, Fe(III), Ga(III), or Sn(IV) is required as
a co-catalyst of Zr(IV) or Hf(IV) not only to accelerate
the reaction rate but also to extract Zr(IV) or Hf(IV)
with ionic liquid 7 quantitatively. Although the role of
Fe(III), Ga(III), or Sn(IV) is not still clear, stable salt
complexes between 7 and the 1 to 1 molar ratio mixture
of binary metal ion species may be generated in situ. Fur-
ther studies on the mechanism of the esterification reac-
tion catalyzed by binary metal ion species are in progress
in our laboratory.
References and Notes
[
1] a) K. Ishihara, S. Ohara, H. Yamamoto, Science 2000,
90, 1140; b) K. Ishihara, M. Nakayama, S. Ohara, H. Ya-
2
mamoto, Synlett 2001, 1117; c) K. Ishihara, M. Nakaya-
ma, S. Ohara, H. Yamamoto, Tetrahedron 2002, 58, 8179.
2] R. A. Sheldon, C. R. Acad. Sci. Paris, S e´ rie IIc, Chimie/
Chemistry 2000, 3, 541.
[
[
[
3] J. Otera, Esterification, Wiley-VCH, Weinheim, 2003.
4] For esterification of carboxylic acids with equimolar
amounts of alcohols, see: a) K. Wakasugi, T. Misakai,
K. Yamada, Y. Tanabe, Tetrahedron Lett. 2000, 41,
5249; b) K. Manabe, S. Iimura, X.-M. Sun, S. Kobayashi,
Experimental Section
[1,3,5f]
J. Am. Chem. Soc. 2002, 124, 11971; see also refs.
[
5] For reusable esterification catalysts, see: a) J. Xiang, S.
Toyoshima, A. Orita, J. Otera, Angew. Chem. Int. Ed.
N-Butylpyridinium Trifluoromethanesulfonimide
[
11]
(
7)
2
001, 40, 3670; b) J. Xiang, A. Orita, J. Otera, Adv. Synth.
Catal. 2002, 344, 84; c) K. Ishihara, A. Hasegawa, H. Ya-
mamoto, Angew. Chem. Int. Ed. 2001, 40, 4077; d) K. Ish-
ihara, A. Hasegawa, H. Yamamoto, Synlett 2002, 1296;
e) K. Ishihara, A. Hasegawa, H. Yamamoto, Synlett
2002, 1299; f) M. Nakayama, A. Sato, K. Ishihara, H. Ya-
mamoto, Adv. Synth. Catal. 2004, 346, 1275.
An equimolar of N-butylpyridinium bromide (21.6 g,
1
1
00 mmol) and lithium trifluoromethanesulfonimide (28.7 g,
00 mmol) in H O (175 mL) was heated at 708C for 12 h.
2
The resultingmixture was extracted with 100 mL of CH Cl ,
2
2
and concentrated. The crude oil was washed with a linear
EtOAc gradient in hexane and purified by column chromatog-
raphy on neutral active aluminium oxide usingEtOAc, and
dried under 0.04 torr to give 7 (d: 1.46) in quantitative yield.
IR (neat): n¼3095, 2969, 2880, 1636, 1490, 1351, 1192, 1141,
[6] Zr(OH) (OAc) , which is halide-free and commercially
x
y
available, is a good catalyst, as well as ZrCl ·2 THF
4
[5f]
and HfCl ·2 THF.
4
ꢀ
1
1
1
3
1
1
057, 789, 770, 740, 685 cm
;
H
NMR (DMSO-d ,
–1
6
[7] LD50 [ZrCl oral, rat] ¼1688 mgkg ; lethal intake of
4
00 MHz): d¼9.08 (d, J¼6.3 Hz, 2H), 8.61 (t, J¼8.1 Hz,
H), 8.16 (dd, J¼6.9, 7.2 Hz, 2H), 4.60 (t, J¼7.5 Hz, 2H),
.91 (tt, J¼7.5, 7.8 Hz, 2H), 1.28 (tq, J¼7.2, 7.8 Hz, 2H), 0.92
Fe(II or III)¼7–35 g, see: J. Emsley, The Elements; 3rd
edn., Clarendon, Oxford, 1998.
[
[
8] It is known that Hf(IV) and Zr(IV) do not catalyze
transesterification, while Ti(IV) catalyzes transesterifica-
(
t, J¼7.5 Hz, 3H); anal. calcd. for C H N F O S : C 31.73,
1
0
14
2
6
4 2
H 3.39, N 6.73%; found: C 31.74, H 3.44, N 6.80%.
[1]
tion.
9] a) J. Dupont, R. F. de Souza, P. A. Z. Suarez, Chem. Rev.
002, 102, 3667; b) C. Hilgers, P. Wasserscheid, in: Ionic
2
Typical Procedure for Direct Esterification Catalyzed
Liquidsin Synthe si s , (Eds.: P. Wasserscheid, T. Welton),
Wiley-VCH, Weinheim, 2003, p. 21.
by Zr(IV)ꢀFe(III) Complex and Catalyst Recycling
using 7
[
10] [EMIM][BF4]: ethylmethylimidazolium tetrafluorobo-
rate; [BMIM][PF ]: butylmethylimidazolium hexafluoro-
phosphate; [EMIM][OTf]: ethylmethylimidazolium tri-
A 20-mL, single-necked, round-bottomed flask equipped with
a Teflon-coated magnetic stirring bar and a Dean–Stark appa-
ratus surmounted by a reflux condenser was charged with car-
boxylic acid (5 mmol) and alcohol (5 mmol) as substrates and
Zr(O-i-Pr) (16.3 mg, 0.05 mmol) and Fe(O-i-Pr) (11.7 mg,
6
fluoromethanesulfonate; [BMIM][NTf
imidazolium trifluoromethanesulfonimide
]: butylmethyl-
(6);
2
[BPY][NTf ]: butylpyridinium trifluoromethanesulfon-
4
3
2
0.05 mmol) as catalysts in 7 (1 mL) and hydrocarbon
imide (7).
(
2.5 mL). The mixture was brought to reflux with the removal
[11] a) P. J. Dyson, G. Laurenczy, C. A. Ohlin, J. Vallance, T.
Welton, Chem. Commun. 2003, 2418; b) C. Hardacre,
J. D. Holbrey, S. P. Katdare, K. R. Seddon, Green
Chem. 2002, 4, 143.
of water. After the reaction was complete, the resultingmix-
ture was cooled to ambient temperature and a colorless hydro-
carbon layer was separated from a brown ionic liquid layer by
simple extraction with hexane-Et O. The desired ester was iso-
2
lated from a hydrocarbon layer by column chromatography on
silica gel. On the other hand, the Zr(IV)–Fe(III) catalyst that
remained in 7 was used directly in the next reaction without fur-
ther purification.
1340
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asc.wiley-vch.de
Adv. Synth. Catal. 2005, 347, 1337–1340