Enantioselective assembly structures of copper(II) complexes with the 1:1 condensation products of DL-phenylalanine and either 2- or 5-methyl-4- formylimidazole

Article abstract of DOI:10.1246/cl.2006.792

Copper(II) complexes with the 1:1 condensation products of DL-phenylalanine and either 2- or 5-methyl-4-formylimidazole, [CuCl(HL^2-Me)] (1) and [CuCl(HL^5-Me)]·MeOH (2), were prepared, and their assembly structures were determined. Bo

Full text of DOI:10.1246/cl.2006.792

792
Chemistry Letters Vol.35, No.7 (2006)
Enantioselective Assembly Structures of Copper(II) Complexes with the 1:1 Condensation
Products of DL-Phenylalanine and Either 2- or 5-Methyl-4-formylimidazole
Tomotaka Iihoshi, Shinya Imatomi, Takefumi Hamamatsu, Ryoko Kitashima, and Naohide Matsumotoꢀ
Department of Chemistry, Faculty of Science, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555
(Received April 18, 2006; CL-060466; E-mail: naohide@aster.sci.kumamoto-u.ac.jp)
Copper(II) complexes with the 1:1 condensation products of
DL-phenylalanine and either 2- or 5-methyl-4-formylimidazole,
[CuCl(HL2-Me)] (1) and [CuCl(HL5-Me)] MeOH (2), were pre-
.
pared, and their assembly structures were determined. Both
complexes assumed two-dimensional (2D) assembly structures
due to a helical chain structure constructed by the intermolecular
imidazole–carboxylate hydrogen bond and interchain Cuꢀ–Cl
coordination bond. 2 crystallized in acentrosymmetric space
group C2221 showing a spontaneous resolution, while 1 crystal-
lized in centrosymmetric space group P21=a.
Figure 1. Molecular structure of [CuCl(HL2-Me)] (1) with the
atom numbering scheme. Thermal ellipsoids are drawn with
the 50% probability level.
The fields of crystal engineering and supramolecular chem-
istry have attracted much attention in which a self-assembly
process plays an important role and a number of synthetic strat-
egies have been proposed.1 The self-assembly process involving
a metal ion is especially attractive and useful for the purpose of
the constructing a variety of molecular architectures and func-
tional materials.2 Chirality has been one of the most important
subjects because asymmetric synthesis and optical resolution
are not only important in chemistry but also practically impor-
tant in pharmacology and industry. Numerous studies have been
devoted to elucidating the detailed mechanism of enantioselec-
tivity.
We have studied metal complexes with multidentate Schiff-
base ligands involving the imidazole group that can function as a
self-complementary building block for the assembly reaction.3
Depending on the ligand framework and metal ion, a variety
of assembly structures, such as the cyclic-oligomer, zigzag-
chain polymer, and 2D network structures, have been generated.
In this study, we studied the enatioselective self-assembly struc-
tures of the CuII complexes with the tridentate Schiff-base
ligands of the 1:1 condensation products of DL-phenylalanine
and either 2- or 5-methyl-4-formylimidazole, [CuCl(HL2-Me)]
Figure 2. Hetero-chiral 2D network structure of [CuCl-
(HL2-Me)] constructed by intrachain imidazole–carboxylate hy-
˚
drogen bond of N(2)ꢁꢁꢁO(1) = 2.810(2) A and the interchain
ꢀ
ꢀ
˚
Cu –Cl coordination bond of Cu –Cl = 2.8936(7) A. Two com-
plex species of the adjacent chains are related by an inversion
center and are bridged by two Clꢂ ions with Cu–Cl =
ꢀ
˚
˚
2.2326(6) A and Cu –Cl = 2.8936(7) A to give a di-ꢀ-chloro
binuclear structure.
(1) and [CuCl(HL5-Me)] MeOH (2). Here, we report enantiose-
.
lective assembly 2D structures depending on the substituent
and spontaneous resolution of 2.
ordinated to the CuII ion. As a result of the repeating hydrogen
bonds, the complex produces a helical chain structure running
along the b axis, where within a helical chain the adjacent two
CuII complexes are related by a twofold screw axis and have
the same chirality. The crystal consists of the helical chains,
where the adjacent two helical chains with opposite chiralities
are linked by the interchain Cuꢀ–Cl weak coordination bond
The tridentate ligands, HL2-Me and HL5-Me, were prepared
by mixing DL-phenylalanine and either 2- or 5-methyl-4-formyl-
imidazole in 1:1 molar ratio in methanol. To the ligand solution
.
was added a methanol solution of CuCl2 2H2O, and the resulting
solution was allowed to stand for several hours to produce the
CuII complex.4 The complexes 1 and 2 were obtained as plate-
like and needle crystals, respectively.
ꢀ
˚
with Cu –Cl = 2.8936(7) A to produce a hetero-chiral 2D net-
work structure, as being seen in Figure 2.
Although the complex 2 was prepared from the reaction of
The complex 1 crystallized in the monoclinic centrosym-
metric space group P21=a (No. 14).5 The molecular structure
with the atom numbering scheme is shown in Figure 1. As shown
in Figure 2, the imidazole group of a CuII complex is hydrogen-
bonded to the carboxylate oxygen atom O(1) of the adjacent CuII
complex with the hydrogen-bond distance of N(2)ꢁꢁꢁO(1) =
.
CuCl2 2H2O and the ligand involving DL-phenylalanine, a piece
of the crystals crystallized in acentrosymmetric space group
C2221 (No. 20), demonstrating that a spontaneous resolution oc-
curs.5 The Flack parameter calculated indicates that the crystal
consists of D-phenylalanine moiety. Figure 3 shows the molecu-
˚
2.810(2) A. It should be noted that the oxygen atom O(1) is co-
Copyright Ó 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.7 (2006)
793
This work was supported by a Grant-in-Aid for Science Re-
search (No. 16205010) from the Ministry of Education, Culture,
Sports, Science and Technology, Japan.
References and Notes
1
a) J.-M. Lehn, Supramolecular Chemistry, VCH, Weinheim,
Germany, 1995. b) Transition Metals in Supramolecular
Chemistry, ed. by L. Fabbrizzi, A. Poggi, ASI Kluwer Aca-
demic Publisheres, Dordrecht, The Netherlands, 1994. c)
P. J. Stang, B. Olenyuk, Angew. Chem., Int. Ed. Engl. 1996,
35, 732. d) J. J. Jacques, A. Collet, S. H. Wilen, Enantiomers,
Racemates and Resolutions, Kringer, Malabar, FL, 1991.
a) N. Ohata, H. Masuda, O. Yamauchi, Angew. Chem., Int.
Ed. Engl. 1996, 35, 531. b) T. Konno, T. Yoshimura, G.
Masuyama, M. Hirotsu, Bull. Chem. Soc. Jpn. 2002, 75,
2185. c) L. Casella, M. Gullotti, G. Pallaza, M. Buga, Inorg.
Chem. 1991, 30, 221.
a) I. Katsuki, Y. Motoda, Y. Sunatsuki, N. Matsumoto, T.
Nakashima, M. Kojima, J. Am. Chem. Soc. 2002, 124, 629.
b) N. Matsumoto, Y. Motoda, T. Matsuo, T. Nakashima, N.
Re, F. Dahan, J.-P. Tuchagues, Inorg. Chem. 1999, 38, 1165.
c) Y. Shii, Y. Motoda, T. Matsuo, F. Kai, T. Nakashima,
J.-P. Tuchagues, N. Matsumoto, Inorg. Chem. 1999, 38,
3513. d) M. Mimura, T. Matsuo, T. Nakashima, N. Matsumoto,
Inorg. Chem. 1998, 37, 3553. e) Y. Sunatsuki, Y. Motoda,
N. Matsumoto, Coord. Chem. Rev. 2002, 226, 199.
2
3
Figure 3. Molecular structure of [CuCl(HL5-Me)] MeOH (2)
with the atom numbering scheme. Thermal ellipsoids are drawn
with the 50% probability level.
.
4
The tridentate ligands HL2-Me and HL5-Me were prepared by the
1:1 condensation reactions of DL-phenylalanine and either 2- or
5-methyl-4-formylimidazole, respectively, in a mixture of
methanol and water on a hot plate for 30 min. The ligand solu-
tions were used for the syntheses of the CuII complexes with-
out the isolation of the ligands. To a solution of the ligand
Figure 4. Homo-chiral 2D network structure of [CuCl-
(HL5-Me)] constructed by intrachain imidazole–carboxylate hy-
.
˚
(0.5 mmol) was added a solution of CuCl2 2H2O (0.5 mmol).
drogen bond of N(2)ꢁꢁꢁO(1) = 2.903(5) A and the interchain
Cuꢀ–Cl coordination bond. Two complex species of the adjacent
The mixture was warmed and stirred for 10 min and then fil-
tered. The filtrate was kept to stand for overnight, during which
time crystals precipitated. They were collected by suction fil-
tration, washed with methanol and dried. Yield 34%. [CuCl-
(HL2-Me)]: blue plate crystals, Anal. Calcd for C14H14N3O2-
ClCu: C, 47.33; H, 3.97; N, 11.83%. Found: C, 47.10; H,
4.16; N, 11.60%. IR(KBr): ꢁC=O, 1670 cmꢂ1, ꢁC=N(imine),
1624 cmꢂ1. [CuCl(HL5-Me)]: blue needle crystals and efflores-
cence, Yield 22%. Anal. Calcd for C14H14N3O2ClCu: C,
47.33; H, 3.97; N, 11.83%. Found: C, 47.35; H, 4.17; N,
chains are bridged by two Clꢂ ions with Cu–Cl = 2.244(2) A
˚
ꢀ
˚
and Cu –Cl = 2.737(2) A.
lar structure with the atom numbering scheme. Figure 4 shows
the 2D network structure, in which the imidazole group of a
CuII complex is hydrogen-bonded to the carboxylate oxygen
atom O(1) of the adjacent CuII complex with the hydrogen-bond
˚
distance of N(2)ꢁꢁꢁO(1) = 2.903(5) A. As a result of the repeat-
ing hydrogen bonds, the complex species with the same chirality
produce a helical chain structure. In the crystal, the adjacent
chains with the same chirality (D-form) are lꢀinked by the weak
11.72%. IR(KBr): ꢁC=O, 1665 cmꢂ1, ꢁC=N(imine), 1638 cmꢂ1
.
5
The X-ray diffraction data were collected using a Rigaku R-
Axis Rapid diffractometer at 296 K and the structures were
solved by CrystalStructure software package. Hydrogen atoms
were fixed at the calculated positions and refined using a riding
model. X-ray crystallographic data [CuCl(HL2-Me): formula =
C14H14N3O2ClCu, fw 355.28, monoclinic, space group P21=a
ꢀ
˚
interchain Cu –Cl coordination bond of Cu –Cl = 2.737(2) A
to produce a homo-chiral 2D network structure. It should be not-
ed that the interchain Cuꢀ–Cl distance of 2 is shorter than that of
ꢀ
˚
1 (Cu –Cl = 2.8936(7) A).
In summary, the two CuII complexes with the tridentate
ligands involving imidazole and chiral amino acid moieties, 1
and 2, were prepared. Each complex functions as a chiral self-
complementary building block to produce an assembly helical
chain structure due to the intrachain imidazole–carboxylate hy-
drogen bond. The same chirality is preserved at least within a
helical chain. The adjacent chains are linked by the weak inter-
chain Cuꢀ–Cl coordination bond. Homo- or hetero-chiral inter-
chain discrimination depends on the steric effect of the substitu-
ent at the imidazole moiety. Homochiral interchain interaction
due to the shorter Cuꢀ–Cl distance is preferable for 2 and the
spontaneous resolution occurs.
˚
(No. 14), a ¼ 6:843ð3Þ, b ¼ 16:727ð7Þ, c ¼ 12:671ð5Þ A, ꢂ ¼
90:13ð2Þꢃ, V ¼ 1450ð1Þ A , T ¼ 296 K, Z ¼ 4, Dcalcd
¼
3
˚
1:627 g cmꢂ1, ꢀ(Mo Kꢃ) = 16.90 cmꢂ1, total of independent
reflections 3275, R ¼ 0:028, Rw ¼ 0:074. X-ray crystallo-
graphic data [CuCl(HL5-Me)] CH3OH: formula = C15H18-
.
N3O3ClCu, fw 3587.32, orthorhombic, space group C2221
˚
(No. 20), a ¼ 7:254ð3Þ, b ¼ 17:409ð5Þ, c ¼ 26:921ð9Þ A,
V ¼ 3399ð2Þ A , T ¼ 296 K, Z ¼ 8, Dcalcd ¼ 1:513 g cmꢂ1
,
3
˚
ꢀ(Mo Kꢃ) = 14.58 cmꢂ1, total of independent reflections
3901, R ¼ 0:056, Rw ¼ 0:141. Flack parameter for D-form =
0.028. Crystallographic data in CIF format has been deposited
at the deposition Nos. 299424 and 604561 of CCDC.
Published on the web (Advance View) June 17, 2006; doi:10.1246/cl.2006.792