promoted the reaction less effectively (85% at 1 h). This result
suggests that hydrophobic grid cavities of 1 bind the substrate very
efficiently to promote the rapid reaction.
Table 1 Reaction of imines with Me
3
SiCN catalyzed by 1
Reaction
1
R CHNNR2
Yield (%)a
time/h
3 2 2
Interestingly, Cd(NO ) ·4H O (suspension) poorly promoted the
reaction under the same conditions. The difference in the catalytic
PhCHNNPh (2a)
1
1
1.5
1
14
2
1.5
1
97
98
99
96
98
86
96
70
8
activity is explained by comparing the crystal structures of 1 and
m-CH
o-CH
p-CH –C H CHNNPh
3 6 4
–C H CHNNPh
9
Cd(NO
3
)
2
·4H
2
O. In 1, the Cd(II) atom has hexacoordinate
3 6 4
–C H CHNNPh
environment with pyridyl groups at the equatorial positions and two
water molecules at the apical positions [Fig. 3(a)] and nitrate ions
3
6 4
p-CF
c-C
-C10
PhCHNNCH
3
–C
11CHNNPh
CHNNPh
Ph
6
H
4
CHNNPh (2b)
exist in the grid. Meanwhile, the Cd(II) atom in Cd(NO
3
)
2
·4H
2
O has
6
H
H
1
7
an octacoordinate environment with four water molecules at the
equatorial positions and two nitrate ions at the apical positions [Fig.
2
a
3(b)]. As a result, the Cd(II) center of 1 is more cationic than that of
Trimethylsilyl was hydrized during the workup and the products were
isolated as corresponding aminonitriles. Isolated yields are given. 1- C10
1-naphthyl.
H
7
Cd(NO ·4H O and the Lewis acidity increases.
3
)
2
2
=
The imine addition was compared with aldehyde addition to
obtain some mechanistic insight. We found that the cyanosilylation
of 2a was much faster than that of benzaldehyde: the latter required
higher temperature (30 °C) and prolonged reaction time (24 h) to
obtain the adduct in 77% yield. A competition experiment sharply
contrasted the difference in the reactivity of these substrates: when
a 1:1 mixture of 2a and benzaldehyde was treated with 3 at 0 °C for
catalytic active metal centers in network complexes, particularly in
porous complexes, provides a new strategy for designing solid
catalyst at molecular level.
24 h, only 4a was formed and benzaldehyde remained unchanged.
The higher reactivity of an imine over an aldehyde does not agree
with the general understanding that a nucleophile preferentially
attacks a more polar CNO group rather than a less polar CNN group
under strong Lewis acidic conditions. In fact, 4a adds aldehydes
Notes and references
1
(a) M. Fujita, Y. J. Kwon, S. Washizu and K. Ogura, J. Am. Chem. Soc.,
994, 116, 1151; (b) O. M. Yaghi, M. O’Keeffe, N. F. Ockwig, H. K.
1
Kae, M. Eddaoudi and J. Kim, Nature, 2003, 423, 705.
(a) K. Kasai, M. Aoyagi and M. Fujita, J. Am. Chem. Soc, 2000, 122,
2140; (b) J. Luo, M. Hong, R. Wang, R. Cao, L. Han, D. Yuan, Z. Lin
and Y. Zhou, Inorg. Chem., 2003, 42, 4486.
selectively in solution in the presence of SnCl
acid).10 In the literature, the imine-selective addition of Me
takes place only if the reaction is mediated by a lanthanoid Lewis
acid such as Yb(OTf) (catalytic amount) because the metal is
4
(a strong Lewis
2
3
SiCN
3 (a) F. Robinson and M. J. Zawarotko, J. Chem. Soc., Chem. Commun.,
3
1995, 2413; (b) O. M. Yaghi and H. Li, J. Am. Chem. Soc., 1996, 118,
295; (c) B. F. Hoskins and R. Robson, J. Am. Chem. Soc., 1990, 112,
1546.
selectively coordinated by the more electron-donating imino
nitrogen. Thus, we conclude that the present heterogeneous
reaction should involve the selective activation of imino nitrogen
by the weak Lewis acidic Cd(II) center.
4
(a) M. Kondo, T. Yoshitomi, K. Seki, H. Matsuzaka and S. Kitagawa,
Angew. Chem., Int. Ed. Engl., 1997, 36, 1725; (b) H. Li, M. Eddaoudi,
T. L. Groy and O. M. Yaghi, J. Am. Chem. Soc., 1998, 120, 8571; (c) M.
Kondo, T. Okubo, A. Asami, S.-I. Noro, T. Yoshitomi, S. Kitagawa, T.
Ishii, H. Matsuzaka and K. Seki, Angew. Chem., Int. Ed. Engl., 1999, 38,
140.
The present reaction is applicable to a variety of imine substrates
(Table 1). Taking the advantage of the heterogeneous catalysis, the
products are in most cases isolated quantitatively only by filtrating
the catalyst. The reaction proceeds in 1–2 h at 0 °C except for the
reaction of 2b where the substrate is electron deficient. In this case,
5 (a) K. Biradha and M. Fujita, Angew. Chem., Int. Ed. Engl., 2002, 41,
392; (b) K. Biradha, Y. Hongo and M. Fujita, Angew. Chem., Int. Ed.
3
3
the electron-withdrawing CF group weakens the Cd coordination
Engl., 2002, 41, 3395; (c) K. Uemura, S. Kitagawa, M. Kondo, K. Fukui,
R. Kitaura, H.-C. Chang and T. Mizutani, Chem. Eur. J., 2002, 8, 3587;
of imino nitrogen in consistent with our proposed mechanism.
In summary, we found the heterogeneous catalysis of infinite
grid complex 1 for cyanosilylation of imines. The incorporation of
(
1
d) M. P. Suh, J. W. Ko and H. J. Choi, J. Am. Chem. Soc., 2002, 124,
0976.
(a) O. R. Evans, H. L. Ngo and W. Lin, J. Am. Chem. Soc., 2001, 123,
0395; (b) J. S. Seo, D. Whang, H. Lee, S. I. Jun, J. Oh, Y. J. Jeon and
6
1
K. Kim, Nature, 2000, 404, 982; (c) B. Gomez-Lor, E. Gutiérrez-
Puebla, M. Iglesias, M. A. Monge, C. Ruiz-Valero and N. Snejko, Inorg.
Chem., 2002, 41, 2429; (d) T. Dewa, T. Siki and Y. Aoyama, J. Am.
Chem. Soc, 2001, 123, 502.
7
8
Catalysis of a hydrogen-bonded network: K. Endo, T. Ezuhara, M.
Koyanagi, H. Masuda and Y. Aoyama, J. Am. Chem. Soc., 1997, 119,
4
117.
M. Aoyagi, K. Biradha and M. Fujita, Bull. Chem. Soc. Jpn., 2000, 73,
Fig. 3 Environment around Cd(II) ion in crystal structures of the square grid
1369.
complex 1 and Cd(NO
View around the Cd(II) ion of Cd(NO
blue, C = grey).
3
)
2
·4H
2
O (a) View around the Cd(II) ion of 1. (b)
9 B. Matkovic and B. Ribar, Croat. Chem. Acta, 1963, 35, 147.
10 S. Kobayashi and S. Nagayama, J. Am. Chem. Soc., 1997, 119,
10049.
3 2
)
·4H O (Cd = purple, O = red, N
2
=
C h e m . C o m m u n . , 2 0 0 4 , 1 5 8 6 – 1 5 8 7
1587