304
Published on the web February 20, 2010
Size Control of Catalytic Reaction Space by Intercalation of Alkylcarboxylate Anions
into Ni-Zn Mixed Basic Salt Interlayer: Application for Knoevenagel Reaction in Water
Takayoshi Hara, Jun Kurihara, Nobuyuki Ichikuni, and Shogo Shimazu*
Graduate School of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522
(Received January 5, 2010; CL-100012; E-mail: shimazu@faculty.chiba-u.jp)
Table 1. Knoevenagel condensation under various conditionsa
The interlayer space of layered Ni-Zn mixed basic salt
CN
CO2Et
(NiZn) can be controlled precisely by the intercalation of various
carboxylate anions with long alkyl chains via simple anion
exchange. Expansion of interlayer space in the anion-exchanged
NiZn depends on the alkyl chain lengths of pillar molecules. The
NiZn catalyst
solvent
50 °C, 1 h
O
+
+ H2O
CN
CO2Et
1
2
3
C. S.
/nmb
Convn Yield
/%c /%c
18 18
29 24
49 42
69 69
>99 98 (93)e
>99 98
¹
butyrate anion-exchanged NiZn (C3H7COO /NiZn) catalyst
Entry Catalyst
Solvent
promoted effectively various base-catalyzed Knoevenagel re-
¹
¹
1
2
3
4
5
HCOO /NiZn
0.45 toluene
CH3COO /NiZn 0.85 toluene
C2H5COO /NiZn 0.95 toluene
C3H7COO /NiZn 1.06 toluene
actions in water with remarkably high yield. This C3H7COO /
¹
NiZn catalyst was reusable without any loss of catalytic activity
or selectivity.
¹
¹
¹
C3H7COO /NiZn 1.06 H2O
¹
It is well known that Knoevenagel condensation of alde-
hydes with active methylene compounds in organic solvent is a
useful tool for the stereoselective synthesis of ¡,¢-unsaturated
carbonyls or nitriles with E-geometry.1 Although alkali metal
hydroxides, alkoxides, amines, or ammonia are conventionally
applied for these reactions in organic solvent, they are harmful
and furthermore bring about large amounts of wastes after
neutralization.2 To achieve green organic transformation, it is
necessary to establish a catalyst design for high-performance
recyclable solid base catalysts, which work even in water
solvent.
Hydroxy double salts (HDSs) and layered double hydrox-
ides (LDHs) have received considerable interest as anion-
exchangeable layered compounds due to their potential appli-
cations as catalyst supports.3 The Ni-Zn mixed basic salt
(NiZn), considered a HDSs, has a typical chemical composition
of Ni1¹xZn2x(CH3COO)2x(OH)2¢nH2O (0.15 < x < 0.25).4 We
have recently reported a novel strategy for catalyst design via
anion exchange by use of NiZn as a catalyst support. For
example, the introduction of anionic Pd hydroxide species into
the NiZn interlayer can generate monomeric [Pd(OH)4]2¹
species stabilized by strong electrostatic interaction with Zn(II)
cation, which acts as efficient heterogeneous catalyst for aerobic
alcohol oxidation in air.5 In this sort of catalysts, the active
species are metal complexes but not host supports. Considering
the use of NiZn itself as a catalyst, the size control of interlayer
space is a key issue to create an effective catalytic reaction field.6
Herein, we will report the synthesis of novel nanostructured
NiZn by the intercalation of various carboxylate anions with
long alkyl chains as a pillar molecule. The interlayer space of
NiZn can be controlled precisely by changing alkyl chain length
of pillars. In this paper, the Knoevenagel reaction in water
catalyzed by synthesized NiZn is also presented.
6d C3H7COO /NiZn 1.06 H2O
¹
7
8
9
C3H7COO /NiZn 1.06 n-hexane >99 97
¹
C3H7COO /NiZn 1.06 DMF
C3H7COO /NiZn 1.06 1,2-DCE
87 87
86 86
82 81
74 73
33 30
39 39
36 34
¹
¹
10 C3H7COO /NiZn 1.06 CH3OH
11 C3H7COO /NiZn 1.06 CH3CN
12 C5H11COO /NiZn 1.49 toluene
13 C7H15COO /NiZn 1.74 toluene
¹
¹
¹
¹
14 C9H19COO /NiZn 2.11 toluene
aEthyl cyanoacetate (1.5 mmol), benzaldehyde (1 mmol), NiZn
catalyst (0.1 g), solvent (5 mL), 50 °C, 1 h. bClearance space
was calculated by XRD pattern. C.S = d001 ¹ thickness of
layer (0.46 nm). cDetermined by GC using an internal standard.
dReuse experiment. eThe value in a parenthesis was an isolated
yield.
ly. The anion exchange in the NiZn interlayer was achieved
by a simple anion-exchange process in water. Treatment of
CH3COO /NiZn with various sodium alkyl carboxylates
¹
yielded the anion-exchanged NiZn catalysts (X/NiZn, X was
exchanged alkylcarboxylate anion) as a green powder.8 In the
¹
case of HCOO /NiZn catalyst, the d001 peak shifted to a large
angle from that of CH3COO /NiZn catalyst, and the calculated
C. S. (clearance space = basal spacing (d001) ¹ thickness of
layer (0.46 nm)) was 0.45 nm. On the contrary, the C. S.
increased with increasing alkyl chain length: the C9H19COO
anion extended the NiZn interlayer up to 2.11 nm. The C. S.
calculated from XRD is proportional to the length of alkyl
groups (slope: 0.17 nm/CH2). It can be said that the C. S. as a
catalytic reaction field can be controlled precisely by simple
intercalation with alkylcarboxylate anions. To explore the
catalytic abilities of various anion-exchanged NiZn, the
Knoevenagel reaction between ethyl cyanoacetate (1) and
benzaldehyde (2) was carried out. The results and the C. S. of
the X/NiZn catalysts is also shown in Table 1.9
¹
¹
The acetate-intercalated Ni-Zn mixed basic salt
¹
(CH3COO /NiZn), was synthesized by a previously reported
procedure.7 Based on characterization by XRF, and TG-DTA,
¹
the chemical formula and anion-exchange capacity of
The parent CH3COO /NiZn did not catalyze this conden-
sation efficiently, yielding only 24% of (2E)-2-cyano-3-phenyl-
2-propenoic acid ethyl ester (3) after 1 h (Entry 2). In the case of
¹
CH3COO /NiZn were found to be Ni0.78Zn0.44(OAc)0.44
-
(OH)2¢0.86H2O (Ni/Zn = 1.77) and 2.93 mmol g¹1, respective-
Chem. Lett. 2010, 39, 304-305
© 2010 The Chemical Society of Japan
Hara, Takayoshi
