Synthesis of binuclear ligands possessing two discrete multidentate N-heterocyclic podand coordination sites and their bimetallic nickel(II) complexes

Article abstract of DOI:10.1246/cl.2001.1328

Binuclear ligands possessing two discrete multidentate N-heterocyclic podand coordination sites connected by a flexible propylene spacer and a rigid m-xylene spacer were synthesized. Treatment of the binuclear ligands with Ni(OAc)₂ afforded the

Full text of DOI:10.1246/cl.2001.1328

1328
Chemistry Letters 2001
Synthesis of Binuclear Ligands Possessing Two Discrete Multidentate
N-Heterocyclic Podand Coordination Sites and Their Bimetallic Nickel(II) Complexes
Toshiyuki Moriuchi, Isao Nakayama, Kouichirou Nishimura, Masahito Nishiyama,
Eiko Mochizuki, Yasushi Kai, and Toshikazu Hirao*
Department of Applied Chemistry, Faculty of Engineering, Osaka University, Yamada-oka, Suita, Osaka 565-0871
(Received September 12, 2001; CL-010901)
Binuclear ligands possessing two discrete multidentate N-
chelidamic acid according to the path shown in Scheme 1,
instead of using 4-chloro-2,6-pyridinedicarbonyl dichloride as a
starting compound. Chelidamic acid was converted into the
methyl ester 1, two molecules of which were linked by treatment
with 1,3-dibromopropane or 1,3-bis(bromomethyl)benzene in the
presence of potassium carbonate to give 2 in good yields.
Amidation of 2 with 2-(2-aminoethyl)pyridine afforded the
desired binuclear ligands 3 in moderate yields (3a, 64%; 3b, 68%
based on 2). The thus-obtained binuclear ligands 3 were fully
characterized by spectral data and elemental analyses.6 Only one
set of well-resolved signals for protons of podand coordination
heterocyclic podand coordination sites connected by a flexible
propylene spacer and a rigid m-xylene spacer were synthesized.
Treatment of the binuclear ligands with Ni(OAc)2 afforded the
bimetallic nickel(II) complexes with two discrete nickel cen-
ters. The single-crystal X-ray structure determination of the
bimetallic nickel(II) complex with a propylene spacer revealed
a little distorted square planar geometry at each nickel center.
Amido-N ligands, which possess σ-donor properties of the
deprotonated nitrogen, are known to afford stable complexes
with transition metals.1 We have demonstrated that the efficient
catalytic systems for oxygenation reaction with molecular oxy-
gen are achieved by utilization of transition metal complexes
with the multidentate N-heterocyclic podand ligands composed
of 2,6-pyridinedicarboxamide unit.2 An intramolecular axial
coordination of the podand N-heterocyclic moiety by virtue of
the flexibility of the podand moieties appears to participate in
forming an efficient catalytic system. Flexible podand ligands
are considered to confer to complexes possessing various metal
geometry under different modes of coordination.3 On the other
hand, two metal centers in close proximity cooperatively activate
oxygen in oxygenases like tyrosinase and methane monooxyge-
nase.4 A bimetallic system is considered to be important from
the viewpoints of biomimetic models and synthetic catalysts.5
We herein report the synthesis of binuclear ligands possessing
two discrete multidentate N-heterocyclic podand coordination
sites and characterization of the bimetallic nickel(II) complexes.
Binuclear ligands 3 composed of a flexible propylene spacer
and a rigid m-xylene spacer were prepared conveniently from
1
moieties was observed in H NMR, indicating that both podand
coordination moieties adopt the symmetrical conformation.
A synthetically useful catalytic epoxidation of olefins by
nickel(II) complexes in the presence of aldehydes under molec-
ular oxygen has been investigated extensively.7 In this context,
we embarked upon the preparation of the bimetallic nickel(II)
complex with the binuclear ligand 3 although complexation
with five- or six-coordinated transition metal is possible.
Complexation of 3a and 3b with Ni(OAc)2 led to the selective
formation of the bimetallic nickel(II) complexes 4a and 4b,
respectively.8 The single-crystal X-ray structure determination
of 4a revealed that the nickel center is coordinated by four nitro-
gens of the deprotonated amide moieties, central pyridine, and
one of the podand pyridines as shown in Figure 1.9 A little dis-
torted square planar geometry was observed at each nickel cen-
ter substituted with two amide nitrogens of 3a (N(2)-Ni(1)-N(3),
164.0°; N(7)–Ni(2)–N(8), 163.8°). The two deprotonated amido
moieties and central pyridine ring are coplanar to form two five-
membered chelate rings with extended conjugation, resulting in
the significant deviation from 90° of the bond angles involving
Copyright © 2001 The Chemical Society of Japan

Chemistry Letters 2001
1329
the chelation (N(1)–Ni(1)–N(2), 82.6°; N(1)–Ni(1)–N(3), 83.2°;
N(6)–Ni(2)–N(7), 82.6°; N(6)–Ni(2)–N(8), 82.8°). The lengths
of two nickel-amide nitrogen bonds are different, probably due
to the formation of six-membered chelate ring with one of the
podand pyridine moiety (Ni(1)–N(2), 1.97 Å; Ni(1)–N(3), 1.90
Å; Ni(2)–N(7), 1.95 Å; Ni(2)–N(8), 1.90 Å).
Thanks are due to the Analytical Center, Faculty of
Engineering, Osaka University, for the use of the NMR and MS
instruments.
References and Notes
1
a) H. Sigel and R. B. Martin, Chem. Rev., 82, 385 (1982). b) T. J.
Collins, Acc. Chem. Res., 27, 279 (1994).
2
a) T. Hirao, T. Moriuchi, S. Mikami, I. Ikeda, and Y. Ohshiro,
Tetrahedron Lett., 34, 1031 (1993). b) T. Moriuchi, T. Hirao, Y.
Ohshiro, and I. Ikeda, Chem. Lett., 1994, 915. c) T. Moriuchi,
T.Hirao, T. Ishikawa, Y. Ohshiro, and I. Ikeda, J. Mol. Catal. A:
Chemical, 95, L1 (1995). d) T. Hirao, T. Moriuchi, T. Ishikawa, K.
Nishimura, S. Mikami, Y. Ohshiro, and I. Ikeda, J. Mol. Catal. A:
Chemical, 113, 117 (1996).
3
a) F. A. Chavez, M. M. Olmstead, and P. K. Mascharak, Inorg.
Chem., 35, 1410 (1996). b) F. A. Chavez, M. M. Olmstead, and P.
K. Mascharak, Inorg. Chem., 36, 6323 (1997). c) A. L. Vance, N.
W. Alcock, J. A. Heppert, and D. H. Busch, Inorg. Chem., 37, 6912
(1998).
4
5
a) J. Reedijk, “Bioinorganic Catalysis,” Dekker, New York (1993).
b) I. Bertini, H. B. Gray, S. J. Lippard, and J. S. Valentine,
“Bioinorganic Chemistry,” University Science Books, Mill Valley
(1994).
For reviews on this subject, see: a) N. Kitajima and Y. Moro-oka,
Chem. Rev., 94, 737 (1994). b) L. Que, Jr. and Y. Dong, Acc. Chem.
Res., 29, 190 (1996). c) E. K. van den Beuken and B. L. Feringa,
Tetrahedron, 54, 12985 (1998) and references therein. d) P.
Molenveld, J. F. J. Engbersen, and D. N. Reinhoudt, Chem. Soc.
Rev., 29, 75 (2000).
1
6
3a: mp 107–108 °C (uncorrected); IR (KBr): 3337, 1673 cm– 1; H
NMR (600 MHz, CD3OD): δ 8.45 (ddd, 4H, J = 5.0, 1.8, 0.7 Hz),
7.74 (s, 4H), 7.73 (td, 4H, J = 7.7, 1.8 Hz), 7.34 (ddd, 4H, J = 7.7,
1.2, 0.7 Hz), 7.26 (ddd, 4H, J = 7.7, 5.0, 1.2 Hz), 4.39 (t, 4H, J = 6.0
Hz), 3.77 (t, 8H, J = 7.2 Hz), 3.11 (t, 8H, J = 7.2 Hz), 2.38 (t, 2H, J
= 6.0 Hz); FABMS m/z 823 (M++1); Anal. Calcd for
C45H46N10O6·CH2Cl2: C, 60.86; H, 5.33; N, 15.43%. Found: C,
60.92; H, 5.70; N, 15.62%. 3b: mp 81–82 °C (uncorrected); IR
(KBr): 3335, 1675 cm– 1 1H NMR (400 MHz, CD3OD): δ 8.45
;
(ddd, 4H, J = 5.1, 1.8, 0.7 Hz), 7.78 (s, 4H), 7.73 (td, 4H, J = 7.7,
1.8 Hz), 7.59 (br s, 1H), 7.44–7.48 (m, 3H), 7.34 (ddd, 4H, J = 7.7,
1.1, 0.7 Hz), 7.26 (ddd, 4H, J = 7.7, 5.1, 1.1 Hz), 5.31 (s, 4H), 3.77
(t, 8H, J = 7.3 Hz), 3.11 (t, 8H, J = 7.2 Hz); FABMS m/z 885
(M++1); Anal. Calcd for C50H48N10O6·CH2Cl2: C, 63.29; H, 5.00;
N, 14.47%. Found: C, 63.26; H, 5.18; N, 14.51%.
7
a) T. Yamada, T. Takai, O. Rhode, and T. Mukaiyama, Chem. Lett.,
1991, 1. b) R. Irie, Y. Ito, and T. Katsuki, Tetrahedron Lett., 32,
6891 (1991). c) T. Mukaiyama and T. Yamada, Bull. Chem. Soc.
Jpn., 68, 17 (1995). d) W. Nam, H. J. Kim, S. H. Kim, R. Y. N. Ho,
and J. S. Valentine, Inorg. Chem., 35, 1045 (1996). e) B. B.
Wentzel, P. A. Gosling, M. C. Feiters, and R. J. M. Nolte, J. Chem.
Soc., Dalton Trans., 1998, 2241.
The catalysis of bimetallic nickel(II) complexes 4 was
examined in the catalytic epoxidation reaction of trans-1-
phenylprop-1-ene. Treatment of trans-1-phenylprop-1-ene with
a catalytic amount of 4 in the presence of pivalaldehyde under
molecular oxygen led to the selective formation of the corre-
sponding trans-epoxide in a moderate yield (4a: 60%, 4b:
76%).10 The bimetallic nickel(II) complex 4b exhibited a higher
catalytic activity than the mononuclear nickel(II) complex 5
(53%). The reason still remains obscure why the more enhanced
epoxidation reaction was observed with 4b. The two metal cen-
ters of 4b, which are orientated by a rigid m-xylene spacer, are
supposed to operate cooperatively in the epoxidation reaction;
one metal center of 4b binds to the substrate or two metal cen-
ters activate molecular oxygen.
In conclusion, the binuclear ligands composed of two dis-
crete multidentate N-heterocyclic podand coordination sites
were synthesized. The thus-obtained binuclear ligands were
found to form the bimetallic nickel(II) complexes 4 with two
discrete nickel centers. The bimetallic nickel(II) complex 4b
exhibited the enhanced catalytic activity in the epoxidation reac-
tion of trans-1-phenylprop-1-ene probably due to bimetallic
catalysis. Further investigation on the catalytic reaction includ-
ing mechanistic study is now in progress.
8
9
4a: mp 253–254 °C (decomp.); IR (KBr): 1600 cm– 1; FABMS m/z
937 (M++1); Anal. Calcd for C45H42N10O6Ni2·2MeOH: C, 56.43; H,
5.04; N, 14.00%. Found: C, 56.77; H, 5.17; N, 13.97%. 4b: mp
208–209 °C (decomp.); IR (KBr): 1597 cm–1; FABMS m/z 999
(M++1); Anal. Calcd for C50H44N10O6Ni2·MeOH: C, 59.45; H, 4.70;
N, 13.59%. Found: C, 59.68; H, 4.49; N, 13.50%.
Crystal data for 4a: C45H42N10O6Ni2·CH3OH, M = 968.33, triclinic,
–
space group P1 (No. 2), a = 16.781(3) Å, b = 16.741(2) Å, c =
10.5593(8) Å, α = 101.264(7)°, β = 101.38(1)°, γ = 109.23(2)°, V =
2635.0(8) Å3, Z = 2, Dcalcd = 1.220 g cm–3, R = 0.114, Rw = 0.311.
Crystallographic data (excluding structure factors) for the structure
in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication number
CCDC-165879 for 4a. Copies of the data can be obtained, free of
charge, on application to CCDC, 12 Union Road, Cambridge CB2
1EZ, U.K. [fax: +44(0)-1223-336033 or e-mail:
deposit@ccdc.cam.ac.uk].
10 To a solution of 4 (0.01 mmol) or 5 (0.02 mmol) in 1,2-
dichloroethane (1 mL) was added trans-1-phenylprop-1-ene (52
µL, 0.40 mmol) and pivalaldehyde (87 µL, 0.80 mmol), and then
the resulting mixture was stirred at 20 °C for 12 h under an atmos-
pheric pressure of oxygen. The formation of the trans-epoxide was
detected by 1H NMR and GLC.