Modulation of multimetal complexation behavior of tetraoxime ligand by covalent transformation of olefinic functionalities

Article abstract of DOI:10.1021/ic9019926

A new multimetal complexation system that can change its complexation behavior by C-C bond formation has been developed. The acyclic tetraoxime ligand H₄L¹ having two terminal allyl groups was synthesized. The olefin metathesis of H₄L¹ selectively produced trans-H₄L² while the reaction of [L¹Zn ₂Ca] exclusively afforded cis-H₄L². The saturated analogue H₄L³ was synthesized by hydrogenation. The complexation of the ligands H₄L (L=L¹, trans-L ², cis-L², L³) with zinc(II) acetate (3 equiv) yielded the trinuclear complexes [LZn₃] with a similar trinuclear core bridged by acetato ligands. Whereas the formation process of [L ¹Zn₃] having an acyclic ligand was highly cooperative, the macrocyclic analogues [LZn₃] (L = trans-L², cis-L ²,. L³) were formed in a stepwise fashion via the intermediate 2:3 complex [(HL)₂Zn₃]. The trinuclear complexes [LZn₃] (L = L¹, trans-L², cis-L ², L³) can recognize alkaline earth metal ions via site-selective metal exchange. The acyclic [L¹Zn₃] selectively recognizes Ca²⁺, while the cyclic [trans-L ²Zn₃] showed a Ba²⁺ selectivity. The metal exchange of [LZn₃] (L = L¹, cis-L², cis-L ², L³) with La³⁺ efficiently occurred to give [LZn₂La], but the irans-olefin linker of the [trans-L ²Zn₂La] significantly deforms the structure in such a way that one of the salicylaldoxime moieties does not participate in the coordination. Consequently, the chemical transformation of the olefinic moiety significantly affects the multimetal complexation behavior of the tetraoxime ligands.

Full text of DOI:10.1021/ic9019926

Inorg. Chem. 2010, 49, 2141–2152 2141
DOI: 10.1021/ic9019926
Modulation of Multimetal Complexation Behavior of Tetraoxime Ligand by Covalent
Transformation of Olefinic Functionalities
Shigehisa Akine, Satoko Kagiyama, and Tatsuya Nabeshima*
Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan
Received October 7, 2009
A new multimetal complexation system that can change its complexation behavior by C-C bond formation has been
developed. The acyclic tetraoxime ligand H4L1 having two terminal allyl groups was synthesized. The olefin metathesis of
H4L1 selectively produced trans-H4L2 while the reaction of [L1Zn2Ca] exclusively afforded cis-H4L2. The saturated
analogue H4L3 was synthesized by hydrogenation. The complexation of the ligands H4L (L=L1, trans-L2, cis-L2, L3) with
zinc(II) acetate (3 equiv) yielded the trinuclear complexes [LZn3] with a similar trinuclear core bridged by acetato ligands.
Whereas the formation process of [L1Zn3] having an acyclic ligand was highly cooperative, the macrocyclic analogues
[LZn3] (L = trans-L2, cis-L2, L3) were formed in a stepwise fashion via the intermediate 2:3 complex [(HL)2Zn3]. The
trinuclear complexes [LZn3] (L = L1, trans-L2, cis-L2, L3) can recognize alkaline earth metal ions via site-selective metal
exchange. The acyclic [L1Zn3] selectively recognizes Ca2þ, while the cyclic [trans-L2Zn3] showed a Ba2þ selectivity. The
metal exchange of [LZn3] (L = L1, trans-L2, cis-L2, L3) with La3þ efficiently occurred to give [LZn2La], but the trans-olefin
linkerofthe [trans-L2Zn2La] significantly deforms the structure in sucha way thatone ofthe salicylaldoxime moieties does
not participate in the coordination. Consequently, the chemical transformation of the olefinic moiety significantly affects
the multimetal complexation behavior of the tetraoxime ligands.
Introduction
and photodimerization,4 have been used for the conversion
to regulate the metal complexation ability. These methods
are useful as a tool for the interconversion because cova-
lent and coordination bonds can be formed under mild
conditions.
We have designed a system that uses ruthenium-catalyzed
olefin metathesis5 to convert acyclic ligands to cyclic struc-
tures. Nowadays, the synthesis of various supramolecular
systems utilizes the olefin metathesis as a tool for cycliza-
tion.6-8 Olefinmetathesisof two terminalolefins produces an
internal olefin with a cis or trans configuration under mild
conditions, and the internal olefins are easily converted to the
saturated analogue by hydrogenation. Consequently, we can
obtain three kinds of cyclic host molecules (cis and trans
olefin, and the saturated analogue) by ring-closing olefin
metathesis from a host molecule bearing terminal olefin
moieties at both ends. In this strategy, it is important to
Macrocyclic ligands play an important role in the selective
strong binding with metal ions in coordination chemistry.
The difference between the acyclic and cyclic ligands during
the coordination behavior mainly arises from the preorgani-
zation of the coordinating atoms for the metal ions
(macrocyclic effect).1 In general, the cyclic derivatives show
a stronger binding ability than the acyclic ones, and the
higher selectivity is achieved using the cyclic framework.
Highly selective metal coordination in crown ether chemistry
is mainly based on this principle.
Therefore, conversion from an acyclic structure to cyclic
ones is expected to significantly change the metal com-
plexation ability. To date, several cyclization methods,
such as metal coordination,2 disulfide bond formation,3
*To whom correspondence should be addressed. E-mail: nabesima@
chem.tsukuba.ac.jp. Fax: þ81-29-853-4507. Phone: þ81-29-853-4507.
(1) Cabbiness, D. K.; Margerum, D. W. J. Am. Chem. Soc. 1969, 91,
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Inorg. Chem. 1993, 32, 1407–1416.
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Commun. 1983, 1409–1411. (b) Shinkai, S.; Inuzuka, K.; Miyazaki, O.; Manabe,
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r
2010 American Chemical Society
Published on Web 02/04/2010
pubs.acs.org/IC

2142 Inorganic Chemistry, Vol. 49, No. 5, 2010
Akine et al.
Scheme 1. Olefin Metathesis and Hydrogenation for the Structural Conversion to Regulate the Multimetal Complexation Behavior
develop a method to selectively obtain the cis or trans isomer
of the olefinic macrocycle. We have preliminarily reported
that an oligometallic template strategy is effective for obtain-
ing the two isomers of a tetraoxime ligand for multimetal
complexation.9 The parent tetraoxime ligand with methoxy
groups instead of olefinic moieties is converted to the tri-
nuclear metallohost via cooperative complexation, exhibiting
a cation recognition ability through the metal exchange
process.10 In this study, we investigated the complexation
ability and selectivity during the transmetalation-based ion
recognition of three kinds of macrocyclic molecules, olefins
(trans and cis) and saturated analogues, which are obtained
from the acyclic tetraoxime ligand H4L1 via the olefin
metathesis (Scheme 1).
(400 and 100 MHz) spectrometer. Mass spectra (ESI-TOF,
positive mode) were recorded on an Applied Biosystems QStar
Pulsar i spectrometer. Absorption spectra were recorded on a
JASCO Ubest V560 spectrometer.
Materials. 2,3-Dihydroxybenzene-1,4-dicarbaldehyde (3),10e
3-allyloxy-2-hydroxybenzaldehyde (1),11 and 1,2-bis(aminooxy)-
ethane12 were prepared according to the literature. Benzyl-
idenebis(tricyclohexylphosphine)dichlororuthenium (Grubbs I)
and benzylidene[1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinyl-
idene]dichloro(tricyclohexylphosphine)ruthenium (Grubbs II)
were purchased from Aldrich.
Synthesis of 3-Allyloxy-2-hydroxybenzaldehyde O-(2-(amino-
oxy)ethyl) Oxime (2). A solution of 3-allyloxy-2-hydroxy-
benzaldehyde (1, 843 mg, 4.73 mmol) in ethanol (30 mL) was
added dropwise to a stirred solution of 1,2-bis(aminooxy)ethane
(962 mg, 10.4 mmol) in ethanol (15 mL) at 60 °C, and the
resulting solution was stirred for further 1 h at the same
temperature. After removal of the solvent, the residue was
subjected to column chromatography on silica gel (eluent,
hexane/ethyl acetate, 1:1) to yield the oxime 2 (950 mg, 80%)
as colorless crystals; mp 70-71 °C, 1H NMR (400 MHz, CDCl3)
δ 3.95-3.98 (m, 2H), 4.35-4.38 (m, 2H), 4.64 (dt, J=5.4, 1.4 Hz,
2H), 5.29 (dq, J=10.4, 1.4 Hz, 1H), 5.42 (dq, J=17.2, 1.4 Hz,
1H), 5.51 (brs, 2H), 6.10 (ddt, J = 17.2, 10.4, 5.4 Hz, 1H),
6.80-6.85 (m, 2H), 6.91-6.95 (m, 1H), 8.23 (s, 1H), 9.82 (s, 1H).
13C NMR (100 MHz, CDCl3) δ 70.17 (CH2), 72.71 (CH2), 73.70
(CH2), 115.79 (CH), 116.86 (C), 117.95 (CH2), 119.33 (CH),
122.76 (CH), 133.29 (CH), 147.04 (C), 147.59 (C), 151.43 (CH).
Anal. Calcd for C12H16N2O4: C, 57.13; H, 6.39; N, 11.10.
Found: C, 57.24; H, 6.44; N, 10.95.
Synthesis of Tetraoxime Ligand H4L1. A solution of 2,3-
dihydroxybenzene-1,4-dicarbaldehyde (3, 368 mg, 2.21 mmol)
in ethanol (40 mL) was added slowly to a solution of oxime 2
(1.17 g, 4.64 mmol) in ethanol (35 mL) at 60 °C, and the solution
was stirred for 1 h at the same temperature. After the solution
was allowed to stand overnight at room temperature, precipi-
tates were collected on a suction filter to afford H4L1 (1.17 g,
83%) as colorless crystals; mp 122-125 °C. 1H NMR (400 MHz,
CDCl3) δ 4.47-4.52 (m, 8H), 4.63 (dt, J=5.4, 1.5 Hz, 4H), 5.29
(dq, J=10.4, 1.5 Hz, 2H), 5.42 (dq, J=17.2, 1.5 Hz, 2H), 6.09
(ddt, J=17.2, 10.4, 5.4 Hz, 2H), 6.76 (s, 2H), 6.79-6.86 (m, 4H),
6.92 (dd, J=7.2, 2.2 Hz, 2H), 8.23 (s, 2H), 8.26 (s, 2H), 9.59 (s,
2H), 9.68 (s, 2H). 13C NMR (100 MHz, CDCl3) δ 70.21 (CH2),
73.03 (CH2), 73.20 (CH2), 116.01 (CH), 116.75 (C), 117.61 (C),
117.90 (CH2), 119.36 (CH), 120.75 (CH), 122.90 (CH), 133.29
(CH), 145.78 (C), 147.01 (C), 147.62 (C), 151.33 (CH), 151.88
(CH). Anal. Calcd for C32H34N4O10: C, 60.56; H, 5.40; N, 8.83.
Found: C, 60.37; H, 5.42; N, 8.73.
Experimental Section
General Procedures. All experiments were carried out in air
unless otherwise noted. Dichloromethane and tetrahydrofuran
(THF) were distilled under argon atmosphere from calcium
hydride and sodium benzophenone ketyl, respectively, prior to
use. Commercial chloroform, methanol, and ethanol were used
without purification. All chemicals were of reagent grade and
used as received. Column chromatography was performed with
Kanto Chemical silica gel 60N (spherical, neutral). Gel permea-
tion chromatography (GPC) was performed by an LC-908W
equipped with JAI gel 1H þ 2H columns (Japan Analytical
Industry) with chloroform as eluent. Melting points were deter-
mined on a Yanaco melting point apparatus and not corrected.
1H and 13C NMR spectra were recorded on a Bruker ARX400
(7) For ring-closing metathesis using a template, see: (a) Clark, T. D.;
Ghadiri, M. R. J. Am. Chem. Soc. 1995, 117, 12364–12365. (b) Ng, P. L.;
Lambert, J. N. Synlett 1999, 1749–1750. (c) Cardullo, F.; Calama, M. C.;
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Snellink-Ruel, B. H. M.; Weidmann, J.-L.; Bielejewska, A.; Fokkens, R.;
Nibbering, N. M. M.; Timmerman, P.; Reinhoudt, D. N. Chem. Commun.
2000, 367–368. (d) Chuchuryukin, A. V.; Dijkstra, H. P.; Suijkerbuijk, B. M. J.
M.; Klein Gebbink, R. J. M.; van Klink, G. P. M.; Mills, A. M.; Spek, A. L.; van
Koten, G. Angew. Chem., Int. Ed. 2003, 42, 228–230. (e) Yang, X.; Gong, B.
Angew. Chem., Int. Ed. 2005, 44, 1352–1356. (f) Kaucher, M. S.; Harrell,
W. A., Jr.; Davis, J. T. J. Am. Chem. Soc. 2006, 128, 38–39. (g) Nawara, A. J.;
Shima, T.; Hampel, F.; Gladysz, J. A. J. Am. Chem. Soc. 2006, 128, 4962–4963.
(h) Hiraoka, S.; Yamauchi, Y.; Arakane, R.; Shionoya, M. J. Am. Chem. Soc.
2009, 131, 11646–11647.
(8) For ring-closing metathesis from a helical structure, see: Blackwell, H.
E.; Sadowsky, J. D.; Howard, R. J.; Sampson, J. N.; Chao, J. A.; Steinmetz,
W. E.; O’Leary, D. J.; Grubbs, R. H. J. Org. Chem. 2001, 66, 5291–5302.
(9) Akine, S.; Kagiyama, S.; Nabeshima, T. Inorg. Chem. 2007, 46, 9525–
9527.
(10) (a) Akine, S.; Taniguchi, T.; Nabeshima, T. Angew. Chem., Int. Ed.
2002, 41, 4670–4673. (b) Akine, S.; Taniguchi, T.; Saiki, T.; Nabeshima, T.
J. Am. Chem. Soc. 2005, 127, 540–541. (c) Akine, S.; Matsumoto, T.; Taniguchi,
T.; Nabeshima, T. Inorg. Chem. 2005, 44, 3270–3274. (d) Akine, S.; Taniguchi,
T.; Nabeshima, T. Tetrahedron Lett. 2006, 47, 8419–8422. (e) Akine, S.;
Taniguchi, T.; Nabeshima, T. J. Am. Chem. Soc. 2006, 128, 15765–15774.
ꢀ
(11) Kilenyi, S. N.; Mahaux, J.-M.; van Durme, E. J. Org. Chem. 1991, 56,
2591–2594.
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Article
Synthesis of trans-H4L2. Under nitrogen atmosphere, a solu-
Inorganic Chemistry, Vol. 49, No. 5, 2010 2143
[(trans-L2)Zn3(OAc)2(MeOH)]. Yield 91% (method A),
yellow crystals. Anal. Calcd for C35H36N4O15Zn3 CHCl3: C,
tion of Grubbs I (16.9 mg, 0.0205 mmol) in dichloromethane
(20 mL) was added to a solution of H4L1 (130.5 mg, 0.206 mmol)
in dichloromethane (150 mL). The solution was stirred for 46 h
at room temperature keeping the flask in the dark. After the
removal of the solvent, the residue was recrystallized from
chloroform/methanol to give trans-H4L2 (84.8 mg, 68%) as
colorless crystals, mp 207-209 °C. 1H NMR (400 MHz, CDCl3)
δ 4.45-4.47 (m, 4H), 4.50-4.52 (m, 4H), 4.61-4.62 (m, 4H),
6.10-6.12 (m, 2H), 6.79 (t, J=7.6 Hz, 2H), 6.80 (s, 2H), 6.83 (dd,
J=7.6, 2.1 Hz, 2H), 6.91 (dd, J=7.6, 2.1 Hz, 2H), 8.19 (s, 2H),
8.27 (s, 2H), 9.56 (s, 2H), 9.94 (s, 2H). 13C NMR (100 MHz,
CDCl3) δ 69.37 (CH2), 72.37 (CH2), 74.99 (CH2), 116.80 (CH),
116.97 (C), 117.73 (C), 119.19 (CH), 121.24 (CH), 123.24 (CH),
128.31 (CH), 145.69 (C), 146.93 (C), 148.06 (C), 150.95 (CH),
152.90 (CH), ESI-MS m/z 629.2 for [M þ Na]þ. Anal. Calcd for
C30H30N4O10: C, 59.40; H, 4.99; N, 9.24. Found: C, 59.23; H,
5.03; N, 9.16.
3
40.48; H, 3.49; N, 5.24. Found: C, 40.56; H, 3.68; N, 5.38.
[(cis-L2)Zn3(OAc)2(MeOH)]. Yield 77% (method A, dichloro-
methane was used instead of chloroform), yellow crystals. Anal.
Calcd for C35H36N4O15Zn3 0.5CH2Cl2: C, 43.01; H, 3.76; N, 5.65.
3
Found: C, 42.68; H, 3.85; N, 5.69.
[L3Zn3(OAc)2(MeOH)]. Yield 80% (method A), yellow cry-
stals. Anal. Calcd for C35H38N4O15Zn3 0.5CHCl3: C, 42.19; H,
3.84; N, 5.54. Found: C, 41.80; H, 3.93; N, 5.65.
3
Procedure for the Synthesis of [(HL)2Zn3(MeOH)2(H2O)]
(L=trans-L2, L3). A solution of H4L (0.0067 mmol) in dichloro-
methane (33 mL) was mixed with a solution of zinc(II) acetate
dihydrate (0.010 mmol) in methanol (33 mL). After the mixture
was allowed to stand at room temperature, the precipitates were
collected.
[(trans-HL2)2Zn3(MeOH)2(H2O)]. Yield 86%, yellow cry-
stals. Anal. Calcd for C62H64N8O23Zn3 CH2Cl2: C, 48.18; H,
3
Synthesis of cis-H4L2. Under nitrogen atmosphere, a solution
of Grubbs II (25.5 mg, 0.030 mmol) in THF (15 mL) was added
to a solution of [L1Zn2Ca(OAc)2] (137.9 mg, 0.15 mmol) in THF
(15 mL). The solution was refluxed for 9 h keeping the flask in
the dark. After the removal of the solvent, the residue was
treated with chloroform (36 mL) and hydrochloric acid (1 M,
36 mL), and the mixture was stirred for 1 h at room temperature.
The organic layer was separated, and the aqueous layer was
extracted with chloroform. The combined organic layer was
dried over anhydrous magnesium sulfate and concentrated to
dryness. The residue was recrystallized from chloroform/metha-
nol to give cis-H4L2 (58.4 mg, 64%) as colorless crystals, mp
180-182 °C; 1H NMR (400 MHz, CDCl3) δ 4.46-4.48 (m, 4H),
4.51-4.52 (m, 4H), 4.73 (d, J=2.8 Hz, 4H), 5.97 (t, J=2.8 Hz,
2H), 6.61 (s, 2H), 6.70 (t, J=7.8 Hz, 2H), 6.76 (dd, J=7.8, 1.4
Hz, 2H), 6.80 (dd, J=7.8, 1.4 Hz, 2H), 8.16 (s, 2H), 8.17 (s, 2H),
9.51 (s, 2H), 9.98 (s, 2H). 13C NMR (100 MHz, CDCl3) δ 66.01
(CH2), 73.72 (CH2), 75.99 (CH2), 115.12 (CH), 116.59 (C),
117.45 (C), 119.10 (CH), 120.89 (CH), 122.83 (CH), 127.84
(CH), 145.28 (C), 146.68 (C), 147.20 (C), 151.61 (CH), 152.30
(CH). ESI-MS m/z 629.2 for [M þ Na]þ. Anal. Calcd for
4.24; N, 7.14. Found: C, 48.63; H, 4.17; N, 7.35.
[(HL3)2Zn3(MeOH)2(H2O)]. Yield 73%, yellow crystals.
Anal. Calcd for C62H68N8O23Zn3 0.5CH2Cl2: C, 49.00; H,
4.54; N, 7.31. Found: C, 48.90; H, 4.55 N, 7.38.
3
Procedure for the Synthesis of Heterotrinuclear Complexes. A
solution of H4L (L=L1, trans-L2, cis-L2, L3) in chloroform was
mixed with a solution of zinc(II) acetate dihydrate (2 equiv) and
metal salt (Ca(OAc)2 H2O, Ba(OAc)2, La(OAc)3 1.5H2O) in
3
3
aqueous methanol. The product was precipitated from the
reaction mixture (method A) or obtained by recrystallization
from chloroform/methanol/ether after removal of the solvent
(method B).
[L1Zn2Ca(OAc)2]. Yield 80% (method B), orange crystals;
Anal. Calcd for C36H36CaN4O14Zn2 0.5H2O: C, 46.57; H, 4.02;
3
N, 6.03. Found: C, 46.49; H, 3.99; N, 5.79.
[(cis-L2)Zn2Ca(OAc)2]. Dichloromethane was used instead of
chloroform. Yield 86% (method A), yellow crystals. Anal.
Calcd for C34H32CaN4O14Zn2: C, 45.81; H, 3.62; N, 6.28.
Found: C, 45.92; H, 3.74; N, 6.13.
[L3Zn2Ca(OAc)2]. Yield 86% (method A), yellow crystals.
C30H30N4O10 0.5H2O: C, 58.53; H, 5.08; N, 9.10. Found: C,
Anal. Calcd for C34H34CaN4O14Zn2 0.4CHCl3: C, 43.90; H,
3
3
58.57; H, 4.99; N, 8.89.
3.68; N, 5.95. Found: C, 43.96; H, 3.82; N, 5.81.
Synthesis of H4L3. Pd/C (10%, 20.2 mg) was added to a
solution of trans-H4L2 (86.3 mg, 0.14 mmol) in dichloro-
methane/ethanol (1:1, 40 mL), and the mixture was stirred for
30 min at room temperature under 1 atm hydrogen atmosphere.
After the catalyst was filtered off and washed with ethanol, the
filtrate was concentrated to 1/3 of the original volume. The
precipitates were collected to give H4L3 (51.7 mg, 60%) as
colorless crystals; mp 196-198 °C. 1H NMR (400 MHz, CDCl3)
δ 2.02-2.05 (m, 4H), 4.07-4.10 (m, 4H), 4.45-4.47 (m, 4H),
4.50-4.52 (m, 4H), 6.73 (s, 2H), 6.74 (t, J=7.6 Hz, 2H), 6.78 (dd,
J=7.6, 2.0 Hz, 2H), 6.87 (dd, J=7.6, 2.0 Hz, 2H), 8.18 (s, 2H),
8.22 (s, 2H), 9.58 (s, 2H), 9.87 (s, 2H). 13C NMR (100 MHz,
CDCl3) δ 26.12 (CH2), 68.76 (CH2), 72.83 (CH2), 75.39 (CH2),
115.22 (CH), 116.68 (C), 117.65 (C), 119.14 (CH), 121.10 (CH),
122.47 (CH), 145.58 (C), 147.30 (C), 147.47 (C), 151.23 (CH),
152.65 (CH). ESI-MS m/z 609.2 for [M þ H]þ. Anal. Calcd for
C30H32N4O10: C, 59.21; H, 5.30; N, 9.21. Found: C, 59.20; H,
5.39; N, 9.01.
[L1Zn2Ba(OAc)2]. Yield 86% (method B), orange crystals.
Anal. Calcd for C36H36BaN4O14Zn2 H2O: C, 41.78; H, 3.70; N,
5.41. Found: C, 41.39; H, 3.76; N, 5.00.
3
[(trans-L2)Zn2Ba(OAc)2]. Yield 48% (method A), yellow
crystals. Anal. Calcd for C34H32BaN4O14Zn2 0.5CHCl3: C,
3
39.52; H, 3.12; N, 5.34. Found: C, 39.53; H, 3.46; N, 5.19.
[(cis-L2)Zn2Ba(OAc)2]. Dichloromethane was used instead of
chloroform. Yield 78% (method A), yellow crystals. Anal.
Calcd for C34H32BaN4O14Zn2 H2O: C, 40.56; H, 3.40; N,
5.56. Found: C, 40.53; H, 3.47; N, 5.40.
3
[L3Zn2Ba(OAc)2]. Yield 9% (method A), yellow crystals.
Anal. Calcd for C34H34BaN4O14Zn2 2CHCl3: C, 35.17; H,
2.95; N, 4.56. Found: C, 35.57; H, 2.98; N, 4.38.
3
[L1Zn2La(OAc)3]. Yield 88% (method B), orange crystals.
Anal. Calcd for C38H39LaN4O16Zn2 0.5CHCl3: C, 40.67; H,
3
3.50; N, 4.93. Found: C, 40.62; H, 3.79; N, 4.68.
[(trans-HL2)Zn2La(OAc)4]. Yield 74% (method B), orange
crystals. Anal. Calcd for C38H39LaN4O18Zn2: C, 41.14; H, 3.54;
N, 5.05. Found: C, 41.52; H, 3.82; N, 5.52.
Procedure for the Synthesis of [LZn3(OAc)2(MeOH)n] (L=
L1, trans-L2, cis-L2, L3; n=1 or 2). A solution of H4L in chloro-
form was mixed with a solution of zinc(II) acetate dihydrate
(3.0 equiv) in methanol. The product was precipitated from the
reaction mixture (method A) or obtained by recrystallization
from chloroform/methanol/ether after removal of the solvent
(method B).
[(cis-L2)Zn2La(OAc)3]. Yield 78% (method B), orange crys-
tals. Anal. Calcd for C36H35LaN4O16Zn2 2H2O: C, 39.84; H,
3
3.62; N, 5.16. Found: C, 39.95; H, 3.61; N, 4.97.
[L3Zn2La(OAc)3]. Yield 73% (method B), orange crystals.
Anal. Calcd for C36H37LaN4O16Zn2 1.5CHCl3 0.5H2O: C,
3
3
[L1Zn3(OAc)2(MeOH)2]. Yield 73% (method B), yellow
36.34; H, 3.21; N, 4.52. Found: C, 36.07; H, 3.17; N, 4.33.
General Procedure of Product Analysis of Ring-Closing Meta-
thesis. A mixture of substrate (H4L1, [L1Zn3], or [L1Zn2M])
crystals. Anal. Calcd for C38H44N4O16Zn3 0.5CHCl3: C,
3
43.27; H, 4.20; N, 5.24. Found: C, 43.47; H, 4.10; N, 5.57.

2144 Inorganic Chemistry, Vol. 49, No. 5, 2010
Akine et al.
Table 1. Crystallographic Data
[L1Zn3(OAc)2(MeOH)2]
[(trans-L2)Zn3(OAc)2(MeOH)]
3
3
trans-H4L2
cis-H4L2
CHCl3 0.5MeOH
0.7CHCl3 0.5H2O
3
3
formula
C30H30N4O10
triclinic
P1
C30H30N4O10
triclinic
P1
C39.5H47Cl3N4O16.5Zn3
triclinic
C35.7H37.7Cl2.1N4O15.5Zn3
monoclinic
P21/n
crystal system
space group
P1
˚
a/A
˚
b/A
˚
c/A
8.4656(13)
20.596(3)
32.583(5)
92.955(2)
90.244(2)
96.276(2)
5639.2(15)
8
9.6197(9)
11.0878(10)
14.2308(13)
81.4800(10)
85.2880(10)
73.5460(10)
1438.4(2)
2
13.350(6)
14.073(4)
14.187(4)
83.293(12)
68.602(15)
70.833(14)
2344.0(14)
2
10.564(3)
23.317(5)
16.731(5)
R/deg
β/deg
γ/deg
99.821(11)
3
˚
V/A
4060.8(17)
4
Z
T/K
90
100
120
120
D
calcd/g cm-3
1.429
1.401
1.621
1.703
0.0406
0.1018
R1a (I > 2σ(I))
wR2a (all data)
0.0629
0.0387
0.0504
0.1562
0.0958
0.1551
[(cis-L2)Zn3(OAc)2(MeOH)]
[L3Zn3(OAc)2(MeOH)]
CHCl3
[(trans-HL2)2Zn3(MeOH)2(H2O)]
[(HL3)2Zn3(MeOH)2(H2O)]
3
3
3
3
0.5CH2Cl2
6CH2Cl2
2.5CH2Cl2 0.5H2O
3
formula
C35.5H37ClN4O15Zn3
monoclinic
P21/n
C36H39Cl3N4O15Zn3
monoclinic
P21/n
C68H76Cl12N8O23Zn3
triclinic
P1
C64.5H74Cl5N8O23.5Zn3
triclinic
P1
crystal system
space group
˚
a/A
˚
b/A
˚
c/A
10.523(2)
10.630(3)
16.165(6)
17.405(5)
17.591(5)
97.886(12)
110.375(13)
112.294(13)
4081(2)
13.817(5)
15.178(6)
18.739(6)
70.992(13)
79.984(12)
85.528(15)
3658(2)
23.149(5)
23.876(5)
16.859(5)
16.861(4)
R/deg
β/deg
γ/deg
102.788(12)
105.783(11)
3
˚
V/A
4004.8(17)
4
4118.1(18)
4
Z
2
2
T/K
120
120
120
120
D
calcd/g cm-3
1.644
0.0727
0.2063
1.726
0.0484
0.1422
1.623
1.553
R1a (I > 2σ(I))
wR2a (all data)
0.0992
0.0722
0.2553
0.1675
[L1Zn2Ca(OAc)2] 0.5CHCl3
[(cis-L2)Zn2Ca(OAc)2]
[L3Zn2Ca(OAc)2]
3
0.5MeOH
3
3
3
1.5CH2Cl2
2CHCl3
formula
C37H38.5CaCl1.5N4O14.5Zn2
C35.5H35CaCl3N4O14Zn2
triclinic
C36H36CaCl6N4O14Zn2
triclinic
crystal system
space group
triclinic
P1
P1
P1
˚
a/A
˚
b/A
˚
c/A
13.791(3)
15.788(4)
20.439(4)
84.018(10)
81.632(10)
73.877(11)
4220.1(17)
4
11.826(6)
12.942(5)
14.995(7)
63.850(13)
71.662(18)
82.025(17)
1955.6(15)
2
13.129(5)
13.629(5)
14.925(8)
76.252(15)
66.462(15)
62.042(12)
2158.4(16)
2
R/deg
β/deg
γ/deg
3
˚
V/A
Z
T/K
120
120
120
Dcalcd/g cm-3
R1a (I > 2σ(I))
wR2a (all data)
1.566
1.730
1.742
0.0638
0.0523
0.0567
0.1839
0.1335
0.1530
[L1Zn2Ba(OAc)2]
[(trans-L2)Zn2Ba(OAc)2]
[(cis-L2)Zn2Ba(OAc)2]
[L3Zn2Ba(OAc)2]
3
0.7CHCl3 0.6MeOH
3
3
3
1.5CHCl3 0.5Et2O
0.5MeOH
2CHCl3
3
3
formula
C37.3H39.1BaCl2.1N4O14.6Zn2
C37.5H38.5BaCl4.5N4O14.5Zn2
C34.5H34BaN4O14.5Zn2
triclinic
C36H36BaCl6N4O14Zn2
triclinic
crystal system
space group
triclinic
P1
triclinic
P1
P1
P1
˚
a/A
˚
b/A
˚
c/A
14.446(4)
15.882(3)
20.178(6)
88.392(9)
79.764(11)
69.993(8)
4278.1(18)
4
12.580(6)
13.505(5)
15.324(7)
79.997(14)
70.491(17)
65.950(16)
2238.7(17)
2
10.5880(6)
13.0232(7)
15.2344(8)
103.5402(16)
107.7635(15)
102.6695(17)
1846.52(17)
2
12.715(5)
13.474(6)
15.258(8)
79.705(18)
69.719(17)
65.578(14)
2230.6(17)
2
R/deg
β/deg
γ/deg
3
˚
V/A
Z
T/K
120
120
120
120
D
calcd/g cm-3
1.738
1.787
1.807
1.831
R1a (I > 2σ(I))
wR2a (all data)
0.0354
0.0402
0.0398
0.0350
0.0953
0.1021
0.1105
0.0879

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2145
Table 1. Continued
[L1Zn2La(OAc)3]
CHCl3
[(trans-HL2)Zn2La-
[(cis-L2)Zn2La(OAc)3(MeOH)0.75
]
[L3Zn2La(OAc)3(MeOH)0.5
1.5CHCl3
]
3
3
3
(OAc)4(H2O)]
1.5MeOH
formula
C39H40Cl3LaN4O16Zn2
triclinic
C38H41LaN4O19Zn2
triclinic
P1
C38.25H44LaN4O18.25Zn2
triclinic
C38H40.5Cl4.5LaN4O16.5Zn2
crystal system
space group
triclinic
P1
P1
P1
˚
a/A
˚
b/A
˚
c/A
12.836(5)
13.302(5)
14.564(5)
115.026(14)
94.160(17)
93.458(17)
2236.0(14)
2
14.002(4)
18.183(6)
18.530(5)
69.979(11)
86.008(10)
73.150(12)
4240(2)
4
12.515(5)
13.342(6)
13.551(6)
109.182(17)
94.939(17)
91.653(16)
2125.3(16)
2
12.504(5)
13.294(6)
15.402(5)
88.589(15)
80.960(13)
65.885(15)
2305.6(15)
2
R/deg
β/deg
γ/deg
3
˚
V/A
Z
T/K
120
120
120
120
Dcalcd/g cm-3
R1a (I > 2σ(I))
wR2a (all data)
1.778
1.766
1.752
1.795
0.0468
0.0535
0.0341
0.0619
0.1408
0.1500
0.0868
0.1591
P
P
P
P
a R1 = ||Fo| - |Fc||/ |Fo|; wR2 = [ w(Fo2 - Fc2)2/ w(Fo2)2]1/2
.
Scheme 2. Synthesis of Ligand H4L1 and Its Metal Complexes
(0.020 mmol), catalyst (Grubbs I or II), and solvent was stirred
in the dark under argon atmosphere under the conditions A (in
dichloromethane, 1 mM, RT, 30 h) or B (in THF, 5 mM, reflux,
9 h). The solvent was then removed under reduced pressure.
When metal complex was used as the substrate, chloroform and
1 M hydrochloric acid were added to the mixture, which was
stirred for 1 h at room temperature, and then the organic layer
was separated, dried over anhydrous magnesium sulfate, and
concentrated to dryness. The mixture was analyzed by 1H NMR
(CDCl3) and GPC.
Characterization of Byproducts 4 and 5. 4: 1H NMR (400
MHz, CDCl3) δ 4.47-4.52 (m, 8H), 4.63 (d, J=5.3 Hz, 2H),
5.29 (dd, J=10.6, 1.4 Hz, 1H), 5.42 (dd, J=17.2, 1.4 Hz, 1H),
5.61 (brs, 1H), 6.10 (ddt, J=17.2, 10.6, 5.3 Hz, 1H), 6.74 (dd,
J=7.8, 1.5 Hz, 1H), 6.77 (s, 2H), 6.80-6.85 (m, 3H), 6.92 (dd,
J=6.9, 2.7 Hz, 1H), 6.96 (dd, J=7.8, 1.5 Hz, 1H), 8.22 (s, 1H),
8.23 (s, 1H), 8.24 (s, 1H), 8.26 (s, 1H), 9.61 (s, 1H), 9.70 (s, 1H),
9.73 (s, 1H), 9.92 (s, 1H). 5: 1H NMR (400 MHz, CDCl3)
δ 4.50-4.52 (m, 8H), 5.61 (brs, 2H), 6.74 (dd, J = 7.9,
1.1 Hz, 2H), 6.78 (s, 2H), 6.82 (t, J=7.9 Hz, 2H), 6.96 (dd,
J=7.9, 1.1 Hz, 2H), 8.22 (s, 2H), 8.23 (s, 2H), 9.66 (s, 2H),
9.92 (s, 2H).
1H NMR Titration (Ligand-Zinc(II)). Sample solutions con-
taining ligand (1.0 mM for H4L1; 0.5 mM for trans-H4L2, cis-
H4L2, H4L3) and varying amount of zinc(II) acetate dihydrate
(0 to 5 equiv) in CDCl3/CD3OD (1:1, 0.6 mL) were prepared.
1H NMR spectrum (400 MHz) of each sample was recorded
at 298 K.
1H NMR Titration (Ligand-Zinc(II)-Guest Cation). Sample
solutions containing ligand (H4L1, trans-H4L2, cis-H4L2, H4L3;
0.5 mM), zinc(II) acetate dihydrate (1.5 mM), and guest cation
(La(NO3)3 or M(OAc)2 (M = Mg, Ca, Ba); 0 to 3 equiv) in
CDCl3/CD3OD (1:1, 0.6 mL) were prepared. 1H NMR spectra
(400 MHz) were recorded at 298 K.
repeated reflections. The structures were solved by direct methods
(SIR97)13 or Patterson methods (DIRDIF 99)14 and refined by full-
matrix least-squares on F2 using SHELXL 97.15 The crystallo-
graphic data are summarized in Table 1.
X-ray Crystallographic Analysis. Intensity data were collected
on a Rigaku R-AXIS Rapid or a Bruker SMART APEX II
diffractometer with Mo KR radiation (λ=0.71069 A). The data
were corrected for Lorentz and polarization factors, and for absor-
ption by semiempirical methods based on symmetry-equivalent and
˚
Results and Discussion
Synthesis of Ligand H4L1 and Its Metal Complexes. The
diallyl ligand H4L1 was synthesized by a procedure ana-
logous to that for the corresponding methoxy derivative
(Scheme 2)10 as described in the preliminary communica-
tion.9 The reaction of 3-allyloxy-2-hydroxybenzaldehyde
(1)11 with excess 1,2-bis(aminooxy)ethane12 afforded the
(13) SIR97, program for crystal structure solution: Altomare, A.; Burla,
M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo, C.; Guagliardi, A.;
Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 1999, 32,
115–119.
(14) Beurskens, P. T.; Beurskens, G.; de Gelder, R.; Garcia-Granda, S.;
Gould, R. O.; Israel, R.; Smits, J. M. M. The DIRDIF-99 Program system;
Crystallography Laboratory, University of Nijmegen: Nijmegen, The Netherlands,
1999.
(15) Sheldrick, G. M. SHELXL 97, Program for crystal structure refine-
€
€
ment; University of Gottingen: Gottingen, Germany, 1997.

2146 Inorganic Chemistry, Vol. 49, No. 5, 2010
Akine et al.
Figure 1. X-ray crystal structures of the trinuclear complexes (a) [L1Zn3(OAc)2(MeOH)2], (b) [L1Zn2Ca(OAc)2], (c) [L1Zn2Ba(OAc)2], and (d)
[L1Zn2La(OAc)3] with thermal ellipsoids drawn at 50% probability level. Hydrogen atoms, disordered atoms, and solvent molecules are omitted for
clarity. One of the crystallographically independent molecules is shown for [L1Zn2Ca(OAc)2] and [L1Zn2Ba(OAc)2].
Table 2. Geometrical Features of the Metal Complexes of Diallyl Ligand H4L1
oxime 2 in 80% yield. The target H4L1 ligand was obtained
in 83% yield by the reaction of 2 with 2,3-dihydroxyben-
zene-1,4-dicarbaldehyde (3)10e in ethanol.
˚
distance (A)
winding angle
a
b
c
complex
[L1Zn3]
dCC
dOO
dMO
θ (deg)d
The corresponding metal complexes were prepared by
the reaction with the appropriate metal salts according to
the reported procedure.9 The complexation of H4L1 with
3 equiv of zinc(II) acetate produced the homotrinuclear
complex [L1Zn3] in 73% yield. Heterotrinuclear com-
plexes [L1Zn2Ca], [L1Zn2Ba], and [L1Zn2La] were ob-
tained by the reaction of H4L1 with 2 equiv of zinc(II)
acetate and 1 equiv of the central metal source, Ca(OAc)2,
Ba(OAc)2, and La(OAc)3, respectively, in 80-88%
yields.
g
-
12.312
10.121 (3.749)g
[L1Zn2Ca] (A)e 3.933, 4.160 f 3.150
(B)e 3.754, 3.626 f 3.093
2.496
2.469
2.747
2.761
2.583
314.8
319.7
293.8
290.5
315.8
[L1Zn2Ba] (A)e 5.771, 4.924 f 4.360
(B)e 5.067, 5.431f 4.443
[L1Zn2La]
3.903
3.361
a Defined as the distance between the two allylic carbon atoms.
b Defined as the distance between the two allyloxy oxygen atoms.
c Defined as the average of the six M-O distances d1-d6. d Defined as
the sum of the five O-M-O angles θ1-θ5. e A and B denote the
crystallographically independent molecules. f The allyl groups are dis-
ordered over two positions. g Non helical, S-shaped conformation in
which some oxygen atoms do not coordinate to M.
Structure of Metal Complexes. The structures of the
complexes were determined by X-ray crystallography.
The structures of [L1Zn3], [L1Zn2Ca], and [L1Zn2La] were
already reported in the preliminary communication,9 and
we here report the structure of [L1Zn2Ba] to investigate
the effect of the ionic radius of the central metal ions.
The homotrinuclear complex [L1Zn3] adopts an
S-shaped conformation in which the two terminal allyl
groups point in opposite directions (Figure 1a). The
˚
distance between the two allylic carbons (dCC) is 12.3 A
(Table 2). Neither the allyloxy (O2 and O10) nor phenoxo
groups (O1 and O9) coordinate to Zn2 in the central O6
site. The coordination geometry of the central zinc (Zn2)
is a distorted octahedral, two from the catechol moiety of
ligand L4-, two from μ-acetato, and two from methanol
molecules. Such a structural feature is in striking contrast
to the conformation of the methoxy analogue,10a,e in
which two methoxy groups are close to each other (the
those of the lanthanum and calcium complexes (θ =
315-320°) because of the longer Ba-O distances (average
˚
˚
˚
Ba-O distances, 2.75 A; Ca-O, 2.48 A; La-O, 2.58 A).
Conversion to the Three Kinds of Cyclic Ligands. Ring-
closing metathesis of the diallyl ligand H4L1 and its metal
complexes was carried out to obtain the corresponding
macrocyclic compounds (Scheme 3), some of which are
reported in the preliminary communication.9 Treatment
of the free ligand H4L1 in dichloromethane (1 mM) with
Grubbs I catalyst afforded the corresponding monomeric
macrocycle H4L2 in addition to a small amount of
oligomeric products. The crude product contained the
cis and trans isomers of H4L2 (Table 3, entry 1) in a 7:93
ratio. The major product, that is, the trans isomer, can be
easily isolated in 68% yield by recrystallization of
the crude product. The X-ray crystallographic analysis
of the major isomer unambiguously determined the trans
configuration of the olefinic moiety, as well as the mon-
omeric macrocyclic structure (Figure 2a). In the crystal
˚
C-C distance between the methoxy groups is 3.724 A).
Thus, the molecular shape of the [L1Zn3] complex is
sensitive to the slight difference in the terminal alkyl
group.16
For the heterotrinuclear complexes, all four phenoxo
oxygen donors and allyloxy groups coordinate to the central
metal cation (Ca, Ba, La) at the central O6 site
(Figure 1b-d). The coordination makes the acyclic ligand
L1 wrap around the central metal cation in a C-shaped
helical fashion. The distances between the two terminal
˚
allylic carbons are much less shorter (dCC = 3.2-5.8 A)
compared to that of [L1Zn3]. The winding angle of
[L1Zn2Ba] (θ = 290-294°) is considerably smaller than
(16) Akine, S.; Taniguchi, T.; Nabeshima, T. Inorg. Chem. 2008, 47, 3255–
3264.

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2147
Scheme 3. Ring-Closing Metathesis of H4L1 and Its Metal Complexes
Table 3. Ring-Closing Metathesis of H4L1 and Its Metal Complexesa
yield (%)
entry
substrate
catalyst mol %
conditionsb
H4L2
cis/transc
4
5
H4L1 recovery
1
2
3
4
5
6
7
H4L1
I, 5
II, 10
I, 10
II, 10
II, 10
II, 10
II, 10
A
A
B
B
B
B
B
94d [68, trans]
7:93
6:94
0
0
0
0
0
4
0
0
5
0
7
H4L1
89d
13
[L1Zn3]
[L1Zn3]
[L1Zn2Ca]
[L1Zn2Ba]
[L1Zn2La]
25:75
32:68
100:0
24:76
100:0
19
12
4
0
58
63
16
16
17
26
58
77 [64, cis]
73
5
a Yields were determined from 1H NMR spectra of the crude reaction mixture. Isolated yields after recrystallization are given in brackets.
b A: In dichloromethane, 1 mM, RT, 30 h. B: In THF, 5 mM, reflux, 9 h, followed by demetalation with 1 M HCl. c Cis/trans ratios of macrocycle H4L2.
d The product contains a small amount of oligomeric compounds.
Scheme 4. Synthesis of Saturated Ligand H4L3
hydrochloric acid. It is noteworthy that the cis/trans ratio
of the cyclic product H4L2 significantly changed in the
case of the zinc(II) complex (32:68).
The reaction of [L1Zn2Ca] mainly gave the cis cyclic
Figure 2. Crystal structures of (a) trans-H4L2 (one of the crystallogra-
product (entry 5). Pure cis-H4L2 was isolated in 64% yield
phically independent molecules is shown) and (b) cis-H4L2 with thermal
after recrystallization of the crude product (Figure 2b).
ellipsoids drawn at 50% probability level.
The selectivity dramatically changed in the case of
[L1Zn2Ba] (entry 6); the trans isomer was the major
structure, there are O-H N hydrogen bonds in the
product (cis/trans = 24:76). The reaction of [L1Zn2La]
afforded only the cis-H4L2 as a cyclic product in lower
yield (entry 7). Instead, the deallylated products 4 and 5
were formed (Scheme 3). Consequently, the metal ions M
in the substrates [L1Zn2M] significantly affect the yield
and cis/trans selectivity of the ring closing metathesis.17
As a result, cis-H4L2 was very efficiently obtained
from [L1Zn2Ca] after demetalation, and trans-H4L2 was
obtained from the free ligand H4L1. Pure samples of the
3 3 3
salicylaldoxime moieties with the O-N distances ranging
from 2.59 to 2.71 A. These hydrogen bonds are probably
˚
responsible for the relatively high yield of the monomeric
32-membered macrocycle without using a template metal,
because the intramolecular hydrogen bonds significantly
reduce the conformational flexibility during the cycliza-
tion reaction. Use of Grubbs II instead of Grubbs I did
not significantly change the product ratio (entry 2).
In contrast, the metathesis reaction of [L1Zn3] with
Grubbs I did not efficiently proceed (entry 3). The reac-
tion with Grubbs II gave the cyclic product H4L2 in
a better yield (entry 4) after demetalation with dilute
(17) (a) Marsella, M. J.; Maynard, H. D.; Grubbs, R. H. Angew. Chem.,
€
Int. Ed. Engl. 1997, 36, 1101–1103. (b) Konig, B.; Horn, C. Synlett 1996, 1013–
1014.

2148 Inorganic Chemistry, Vol. 49, No. 5, 2010
Akine et al.
Figure 3. 1H NMR spectra of H4L ((a) L = L1; (b) L = trans-L2; (c) L = cis-L2; (d) L = L3) in the presence of 1.5 equiv of zinc(II) acetate (400 MHz,
CDCl3/CD3OD, 1:1, 0.5 mM). Filled circles, open circles, and open squares denote H4L, [LZn3], and [(HL)2Zn3], respectively. The oxime protons, aromatic
protons of catecholato moiety, and olefinic protons are marked in the spectra.
cis and trans isomers for the complexation study (see
below) were prepared by these methods. The saturated
ligand H4L3 was prepared by the hydrogenation of trans-
H4L2 using the Pd/C catalyst (Scheme 4).
revealed that the intermediate was the 2:3 complex
[(HL)2Zn3] (L=trans-L2, L3) (Figure 4d, e). These com-
plexes consist of two molecules of the triply deprotonated
ligand (HL)3- and three zinc(II) ions. Two [(HL)Zn] units
are held together by the third zinc(II) ion via the coordi-
nation of the catecholato moiety of each [(HL)Zn] unit. In
the [(HL)Zn] unit, the two N2O2 coordination moieties
(salamo moieties, hereafter) are in a nonequivalent en-
vironment; one of the two salamo moieties is metalated
while the other is vacant.
Complexation with Zinc(II). We have previously re-
ported that the methoxy substituted ligand forms a tri-
nuclear complex with zinc(II) and that the complexation
process is highly cooperative.10 The allyloxy substituted
derivative, H4L1, formed a similar homotrinuclear com-
plex [L1Zn3] in a highly cooperative fashion as observed
for those of the methoxy derivative. When 1.5 equiv of
zinc(II) ion was added, half of the ligand H4L1 was
converted into the trinuclear complex [L1Zn3], and the
other half remained unchanged (Figure 3a).
This unsymmetrical feature is also evident in solution.
The H NMR spectra of the intermediates exhibit four
1
singlets with equal intensities for the oxime protons
(8.0-8.6 ppm). In addition, a pair of doublets was
observed for the aromatic protons of the central cate-
cholato moiety (Figure 3b-d; signals marked by open
squares at 6.4-7.2 ppm). These spectral patterns are
consistent with the crystal structures, in which the two
salamo moieties are in nonequivalent environments.
The formation of the 2:3 complex was also confirmed
by the peak at m/z 1403.1 for [(trans-HL2)2Zn3 þ H]þ in
the ESI-MS measurements.
Consequently, the complexation of the cyclic ligands
H4L (L = trans-L2, cis-L2, L3) with zinc(II) acetate
gave the trinuclear complex [LZn3] in a non-cooperative,
stepwise fashion via the intermediate 2:3 complex
[(HL)2Zn3], whereas the formation of the acyclic ana-
logue [L1Zn3] was cooperative. The conversion of H4L1
into cyclic ligands significantly changes the formation
process of the trinuclear complexes [(HL)2Zn3] and
[LZn3] (Scheme 5).
The trinuclear complexes [LZn3] (L=trans-L2, cis-L2, L3)
were almost quantitatively formed upon the addition of
3 equiv of zinc(II) acetate. The structures of these trinuclear
complexes were determined by X-ray crystallography
(Figure 4a-c). In these complexes, the zinc(II) trinuclear
core is bridged by acetato ligands as observed in the
methoxy analogue.10a,e
However, when less than 3 equiv of zinc(II) acetate was
1
added, the H NMR spectra of the cyclic ligands H4L
(L=trans-L2, cis-L2, L3) showed signals other than those
of H4L and [LZn3]. These signals are assignable to an
intermediate species during the formation process of the
trinuclear complex [LZn3]. The mole fraction of the inter-
mediate species was at the maximum when 1.5 equiv of
zinc(II) acetate was added (Figure 3b-d). This indicates
that the intermediate complex has a 2:3 (ligand/metal)
stoichiometry. The maximum mole fractions of the inter-
mediate complexes were 53% (trans-L2; Figure 3b), 17%
(cis-L2; Figure 3c), and 76% (L3; Figure 3d).
Selectivity in Guest Ion Recognition via the Metal Ex-
change of Zinc(II) Trinuclear Complexes. We have pre-
viously reported that the zinc(II) homotrinuclear
complex having methyl groups instead of the olefinic
moieties can recognize guest ions by the site-selective
From a solution of trans-H4L2 or H4L3 containing 1.5
equiv of zinc(II) acetate, yellow crystals of the intermedi-
ate complexes were isolated. The crystallographic study

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2149
Figure 4. X-ray structures of (a) [(trans-L2)Zn3(OAc)2(MeOH)], (b) [(cis-L2)Zn3(OAc)2(MeOH)], (c) [L3Zn3(OAc)2(MeOH)], (d) [(trans-HL2)2Zn3-
(MeOH)2(H2O)], and (e) [(HL3)2Zn3(MeOH)2(H2O)] with thermal ellipsoids drawn at 50% (a, b, c) or 30% (d, e) probability level. Hydrogen atoms,
disordered atoms, and solvent molecules are omitted for clarity.
Scheme 5. Complexation of Acyclic Ligand (H4L1) and Cyclic Ligands (trans-H4L2, cis-H4L2, H4L3) with Zinc(II) Acetate
metal exchange.10 The metal exchange efficiently proceeds
upon the addition of rare earth metals and Ca2þ. The guest
ion recognition behavior of the trinuclear complexes [LZn3]
(L=L1, trans-L2, cis-L2, L3) is studied to clarify the ring
effects and the structural effects of the linking moiety
between the salamo moieties (Scheme 6, Table 4).

2150 Inorganic Chemistry, Vol. 49, No. 5, 2010
Akine et al.
Asexpected, fourcomplexes[LZn3] (L=L1, trans-L2, cis-
L2, L3) showed a different selectivity in the recognition of
alkaline earth metal ions. The acyclic derivative [L1Zn3]
showed Ca2þ selectivity, as observed for the methoxy
derivative.10b,e Although the crystal structures of [L1Zn3]
and the methoxy derivative were significantly different
from each other, the structural fluxionality in solution
probably leads to the similar complexation behavior. On
the contrary, [(trans-L2)Zn3] binds Ba2þ much stronger
than Ca2þ or Mg2þ. Thus, the Ca2þ/Ba2þ selectivity is
reversed from 13 to 1/300 by the conversion of the acyclic
L1 to the trans-L2. This probably results from the restricted
conformation of the cyclic ligand trans-H4L2 compared to
the corresponding acyclic derivative H4L1. The longer
trans-olefin linkage fixes the two ether oxygen atoms
further apart from each other. This makes the cavity large
When La3þ was used as a guest, the metal exchange of
the central Zn2þ with La3þ quantitatively proceeded
regardless of the ligand structure (L1, trans-L2, cis-L2,
L3). This is probably because the binding of the phenoxo
moieties to La3þ via an electrostatic interaction is stron-
ger than that to the divalent cations (Ca2þ and Ba2þ). The
stabilization must be high enough to replace the Zn2þ in
the central cavity, even though La3þ does not always fit
well into the central O6 cavity.
Crystal Structures of Metallohost-Guest Complexes.
X-ray crystallographic analysis was carried out to inves-
tigate the structure in relation to the stability of the
metallohost-guest complexes. In the crystal structure
of [(cis-L2)Zn2Ca(OAc)2], all the six oxygen donor atoms
of the recognition site coordinate to Ca2þ (Figure 5a). The
distance between the two allyloxy oxygen atoms (dOO) is
enough to surround larger cations such as Ba2þ
.
2.8 A (Table 5), which is slightly shorter than that of the
˚
˚
The shorter cis-olefin linkage has a different effect on
the metal exchange equilibrium. As expected, the metal
exchange of [(cis-L2)Zn3] with Ca2þ very efficiently took
place. The [(cis-L2)Zn3] can also recognize Ba2þ despite
its larger ionic radius than the cavity size. In this case, the
guest sits at a position displaced from the center of the
cavity keeping suitable O-Ba distances from the oxygen
donor atoms. The equilibrium constants of [(cis-L2)Zn3]
with Ca2þ and Ba2þ are higher than that of the acyclic
derivative [L1Zn3]. On the other hand, the metal exchange
of [(cis-L2)Zn3] with Mg2þ was less efficient than that of
[L1Zn3]. This is presumably attributed to the conforma-
tional constraint of the macrocycle that prevents all of the
six oxygen donor atoms from coordinating to the small
Mg2þ. Consequently, the Ca2þ/Mg2þ or Ba2þ/Mg2þ
selectivity significantly increased after the conversion of
L1 to cis-L2.
acyclic analogue [L1Zn2Ca(OAc)2] (dOO = 3.1 A). This
structural resemblance indicates that the cis-olefin linkage
does not produce a significant strain in the Zn2Ca trinuclear
moiety. This is the reason why the metal exchange of [(cis-
L2)Zn3] by calcium ion efficiently occurred. The structural
resemblance also accounts for the high efficiency of the
ring-closure and excellent cis/trans selectivity of [L1Zn2Ca],
because the olefin metathesis giving the cis olefin is expected
to proceed without any large structural deformations. The
saturated analogue [L3Zn2Ca(OAc)2] adopted a simi-
˚
lar structure with dOO = 2.9 A (Figure 5b), in which
the tetramethylene moiety adopted a gauche conformation
to make a cavity size suitable for Ca2þ. Crystals of [(trans-
L2)Zn2Ca(OAc)2] were not obtained probably because of
the low efficiency of the metal exchange (equilibrium
constant K=0.20).
In the case of barium complexes, single crystals of
[LZn2Ba(OAc)2] were obtained for all the three cyclic
ligands (L=trans-L2, cis-L2, L3). These three complexes
have a similar structure in which the six oxygen donor
atoms coordinated to the barium ion in the central O6 site
The saturated analogue [L3Zn3] exhibited a binding
behavior similar to that of [(cis-L2)Zn3]. This result is
rationalized by the flexible tetramethylene linker that would
change its conformation suitable for the guest recognition.
Scheme 6. Ion Recognition by Trinuclear Complexes Based on Metal Exchange
Table 4. Equilibrium Constants K for Metal Exchange of [LZn3] by Guest Ionsa
guest M
trinuclear complex
La(NO3)3
Mg(OAc)2
Ca(OAc)2
Ba(OAc)2
[L1Zn3]
>1000 [100%]b
>1000 [100%]b
>1000 [98%]b
>1000 [100%]b
1.2(2) [50%]
0.19(1) [27%]
0.011(2) [8%]
0.015(3) [9%]
100 [91%]b
0.20(2) [30%]
>1000 [100%]b
400 [95%]b
7(2) [70%]
60 [89%]b
[(trans-L2)Zn3]
[(cis-L2)Zn3]
[L3Zn3]
>1000 [100%]b
600 [96%]b
a The equilibrium constants were determined by non-linear least-squares analysis. Standard deviation is given in parentheses. The mole fraction of
[LZn2M] upon the addition of guest M (1 equiv) is given in brackets. b The equilibrium constants were roughly estimated by the above-mentioned mole
fractions.

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2151
Figure 5. Crystal structure of trinuclear complexes (a) [(cis-L2)Zn2Ca(OAc)2], (b) [L3Zn2Ca(OAc)2], (c) [(trans-L2)Zn2Ba(OAc)2], (d) [(cis-L2)Zn2Ba-
(OAc)2], (e) [L3Zn2Ba(OAc)2], (f) [(trans-HL2)Zn2La(OAc)4], (g) [(cis-L2)Zn2La(OAc)3], and (h) [L3Zn2La(OAc)3] with thermal ellipsoids drawn at 50%
probability level. Hydrogen atoms, disordered atoms, and solvent molecules are omitted for clarity.
(Figure 5c-e). The distances dOO of these complexes are
for the high Ba2þ/Ca2þ selectivity of the metal exchange
of [(trans-L2)Zn3]. In contrast, the distance dOO of
˚
in the range of 3.7-4.4 A, which are longer than those of
[(cis-L2)Zn2Ca(OAc)2] and [L3Zn2Ca(OAc)2] (around
2
[(cis-L )Zn2Ba(OAc)2] was shorter (3.7 A). In the
˚
2
2.8 A). In particular, the cavity size of the trans-L is
case of the saturated analogue [L3Zn2Ba(OAc)2], the
˚
˚
suitable for the inclusion of a barium ion. The distance
distance (dOO = 4.1 A) is nearly the same as that of
2
dOO of [(trans-L )Zn2Ba(OAc)2] (4.3 A) is nearly the same
[(trans-L2)Zn2Ba(OAc)2] (dOO = 4.3 A). The conforma-
˚
˚
1
as that of the acyclic analogue [L Zn2Ba(OAc)2] (4.4 A),
˚
tion of the tetramethylene moiety is all-anti. This is well
which does not have a constraint because of a cyclic
skeleton. This indicates that the [(trans-L2)Zn2] moiety
can accommodate a barium ion without any signi-
ficant strain. The larger cavity of trans-L2 accounts
contrasted with the gauche conformation in [L3Zn2Ca-
˚
(OAc)2] with a shorter dOO (2.8 A). As a result, the metal
exchange of [L3Zn3] by Ca2þ or Ba2þ highly efficiently
takes place in an induced-fit fashion, because the [L3Zn2]

2152 Inorganic Chemistry, Vol. 49, No. 5, 2010
Akine et al.
Table 5. Geometrical Parameters of Metallohost-Guest Complexes [LZn2M]
coordination. As a result, the La3þ does not fit into
the central O6 site. This is mainly attributed to the
conformational constraint of the trans-olefin moiety,
which prohibits coordination of all the oxygen atoms.
(L = L1, cis-L2, trans-L2, L3; M = Ca2þ, Ba2þ, La3þ
)
˚
distance (A)
winding angle
a
b
complex
dOO
dMO
θ (deg)c
[L1Zn2Ca(OAc)2]
(A)d 3.150
2.496 314.8
2.469 319.7
2.477 316.1
2.473 319.0
2.747 293.8
2.761 290.5
2.812 286.9
2.765 296.4
2.783 291.1
Conclusion
(B)d 3.093
2.787
The new acyclic tetraoxime ligand, H4L1, having two
terminal allyl groups was designed and synthesized. The
terminal allyl groups were introduced so that the olefin
metathesis can convert H4L1 into the cyclic derivatives,
trans-H4L2, cis-H4L2, and then the saturated analogue,
H4L3, by hydrogenation. The cyclic trans-H4L2 ligand was
selectively obtained via the olefin metathesis of H4L1, while
the reaction of [L1Zn2Ca] exclusively afforded cis-H4L2. The
complexation of the H4L ligands (L=L1, trans-L2, cis-L2,
L3) with zinc(II) acetate (3 equiv) yielded the trinuclear
complexes [LZn3]. The trinuclear complex of the acyclic
ligand ([L1Zn3]) was formed in a highly cooperative fashion.
On the other hand, macrocyclic ligands (L=trans-L2, cis-L2,
L3) first gave the intermediate 2:3 complex [(HL)2Zn3] and
then the trinuclear complexes [LZn3]. Spectroscopic investi-
gation showed that the trinuclear complexes [LZn3] (L=L1,
trans-L2, cis-L2, L3) can recognize alkaline earth metal ions
via the site-selective metal exchange. The acyclic [L1Zn3] and
cyclic [(trans-L2)Zn3] showed the opposite Ca2þ/Ba2þ selec-
tivity. The metal exchange of [LZn3] with La3þ quantitatively
took place to give [LZn2La], but the number of coordinating
oxygen atoms in the crystal of [(trans-HL2)Zn2La(OAc)4]
was different from those in other complexes. Consequently,
the complexation behavior of the tetraoxime ligands signifi-
cantly changes by linking of the terminal olefinic moieties of
H4L1 and the linking structure (trans-, cis-olefin, and satu-
rated). The transformation using olefin metathesis is useful to
modulate the complexation behavior of multidentate ligands,
because the olefin metathesis and hydrogenation take place
under mild conditions. The transformation would also be
useful for fine-tuning of thechemical or physical properties of
the oligometallic core, such as the catalytic activity or redox
and magnetic properties.
[(cis-L2)Zn2Ca(OAc)2]
[L3Zn2Ca(OAc)2]
[L1Zn2Ba(OAc)2]
2.860
(A)d 4.360
(B)d 4.443
4.267
[(trans-L2)Zn2Ba(OAc)2]
[(cis-L2)Zn2Ba(OAc)2]
[L3Zn2Ba(OAc)2]
3.700
4.136
3.361
[L1Zn2La(OAc)3]
2.583 315.8
[(trans-HL2)Zn2La(OAc)4] (A)d 4.853, 5.083 3.679e
-
-
e
(B)d 4.871
2.837
3.173
3.641e
e
[(cis-L2)Zn2La(OAc)3]
2.534 318.3
2.559 320.3
[L3Zn2La(OAc)3]
a Defined as the distance between the two ArOCH2- oxygen atoms.
b Defined as the average of the six M-O distances d1-d6. c Defined as the
sum of the five O-M-O angles θ1-θ5. d A and B denote crystal-
lographically independent molecules. e Some oxygen atoms do not
coordinate to M.
moiety changes its conformation and dOO according to
the size of the guest.
Zinc-lanthanum heterotrinuclear complexes were also
prepared from the three macrocyclic ligands H4L (L =
trans-L2, cis-L2, L3; Figure 5f-h). Among them, cis-H4L2
and H4L3 formed trinuclear complexes [LZn2La(OAc)3]
(L = cis-L2, L3) with a structure analogous to the
[LZn2Ca(OAc)2]. However, trans-H4L2 produced a dif-
ferent type of complex upon the reaction with zinc(II)
acetate and lanthanum(III) acetate. The obtained com-
plex was [(trans-HL2)Zn2La(OAc)4], in which one of
the salicylaldoxime moieties does not participate in the
Acknowledgment. We thank Dr. Kenji Yoza (Bruker
AXS KK) for the X-ray data collection of trans-H4L2 and
cis-H4L2. This work was supported by Grants-in-Aid for
Scientific Research from the Ministry of Education,
Culture, Sports, Science and Technology, Japan.
Supporting Information Available: X-ray crystallographic
data in CIF format. This material is available free of charge
via the Internet at http://pubs.acs.org.