Synthesis and structural characterization of a dinuclear palladium(II) complex with N,N′N″N?-tetrakis(2-p-toluenesulfonamidoethyl) cyclam

Article abstract of DOI:10.1246/bcsj.81.1454

Dinuclear palladium(II) complex with 1,4,8,1l-tetrakis(2-p- toluenesulfonarnidoethyl)-1,4,8,11-tetraazacyclotetra-decane (H ₄tstaec), [Pd₂(tstaec)], was synthesized and characterized by elemental analysis and IR and UV-vis spectros-c

Full text of DOI:10.1246/bcsj.81.1454

1454 Bull. Chem. Soc. Jpn. Vol. 81, No. 11, 1454–1460 (2008)
Ó 2008 The Chemical Society of Japan
Synthesis and Structural Characterization
of a Dinuclear Palladium(II) Complex with
N,N0,N00,N000-Tetrakis(2-p-toluenesulfonamidoethyl)cyclam
ꢀ
Shusaku Wada, Takanori Kotera, and Masahiro Mikuriya
Department of Chemistry and Open Research Center for Coordination Molecule-based Devices,
School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337
Received January 29, 2008; E-mail: junpei@kwansei.ac.jp
Dinuclear palladium(II) complex with 1,4,8,11-tetrakis(2-p-toluenesulfonamidoethyl)-1,4,8,11-tetraazacyclotetra-
decane (H4tstaec), [Pd2(tstaec)], was synthesized and characterized by elemental analysis and IR and UV–vis spectros-
copies. The crystal structures of H4tstaec and [Pd2(tstaec)] were determined by single-crystal X-ray diffraction method.
In the former ligand, the cyclam ring moiety takes a trans IV conformation with the tosyl arms pointing away from each
other, whereas each palladium atom is bound by two nitrogen atoms of the cyclam moiety and two nitrogen atoms of
˚
the tosyl arms with Pd Pd distance of 5.617(1) A intervening the trans IV cyclam ring in the latter complex. DFT
calculations were performed based on these crystal structures.
ꢁꢁꢁ
Macrocyclic polyamines with functional pendant arms and
TsHN
TsHN
NHTs
NHTs
H2N
H2N
NH2
NH2
their metal complexes have attracted much attention over
two decades, because they have been widely studied in various
fields ranging from molecular recognition of anions or cations
to potential applications in diagnostic and nuclear medicine.1,2
It is known that some additional donor groups of the pendant
arms improve the thermodynamic and the kinetic stability of
the metal complexes and this property is essential for in vivo
applications.2 Beside these, metal complexes of such macro-
cyclic ligands show interesting structural features depending
on the functionalized side arms.1 Previously, we and others
reported on metal complexes with a fully N-substituted cyclam
ligand by aminoethyl groups (cyclam = 1,4,8,11-tetraaza-
cyclotetradecane), 1,4,8,11-tetrakis(2-aminoethyl)-1,4,8,11-
tetraazacyclotetradecane (abbreviated as taec).3 Interestingly,
this ligand does not form mononuclear metal species which
are common in metal complexes of macrocyclic ligands, but
invariably gives dinuclear metal complexes with coordination
of the nitrogen atoms of the 2-aminoethyl groups and the
cyclam ring. Two types of dinuclear structures, the chair form
of the taec ligand in [M2(taec)]X4 (M ¼ CrII, NiII, and CuII;
X ¼ ClO4ꢂ, BF4ꢂ, and Brꢂ) and the boat form of the ligand
in anion-bridged complexes of [M2X(taec)]Y3 (M ¼ CoII,
NiII, CuII, ZnII, and CdII; X ¼ Fꢂ, Clꢂ, Brꢂ, Iꢂ, OHꢂ, and
CO32ꢂ; Y ¼ ClO4ꢂ, PF6ꢂ, CF3SO3ꢂ, B(C6H5)4ꢂ, and Clꢂ)
have been found for metal complexes with taec. This can be
ascribed to the high coordination ability of the primary amine
nitrogen atoms of the pendant groups compared with those
of the tertiary amine nitrogen atoms of the cyclam moiety. If
all of the primary amines of the pendant arms are tosylated,
the possibility of using the coordination of the macrocyclic
ring to a metal ion arises as a way of forming a mononuclear
species with the poor ꢀ-donor ability of the secondary amine
of the TsNH groups.4 In this study, we examined coordination
properties of tetratosylated taec derivative, 1,4,8,11-tetrakis(2-
N
N
N
N
N
N
N
N
taec
H4tstaec
O
S
O
Ts =
Chart 1.
CH3
p-toluenesulfonamidoethyl)-1,4,8,11-tetraazacyclotetradecane
(H4tstaec). Transition-metal complexes with N-tosylated
ligands are scarce,4 although the tosylated amino groups are
used as anion or cation recognition parts.5,6 The tetra-N-tosy-
lation could hamper their coordinating ability; the characteri-
zation and properties of this ligand and its metal complexes
have not been described, although tosylated taec is the precur-
sor compound of taec. We report here, the synthesis and
structural characterization of dinuclear palladium(II) complex
with an N-tosylated macrocyclic ligand, H4tstaec, together
with the crystal structure of the free ligand, as well as a study
of the electronic structures by density functional theory (DFT)
calculations (Chart 1).
Experimental
Synthesis. Unless otherwise specified, all reagents were pur-
chased commercially and used without further purification.
H4tstaec. The macrocyclic ligand, H4tstaec, was synthesized
according to a method described in the literature3b and obtained
as white powder. The product was recrystallized from hot DMF
to give colorless crystals. Anal. Found: C, 55.69; H, 7.05; N,
11.56%. Calcd for C46H68N8O8S4 (H4tstaec): C, 55.84; H, 6.93;
Published on the web November 12, 2008; doi:10.1246/bcsj.81.1454

S. Wada et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 11 (2008) 1455
Table 1. Crystal Data and Data Collection Details
H4tstaec
[Pd2(tstaec)] 2CH3CN
ꢁ
Formula
FW
C46H68N8O8S4
989.32
C50H70N10O8Pd2S4
1280.20
Crystal system
Space group
Monoclinic
P21=n
Monoclinic
P21=c
˚
a/A
9.454(2)
13.546(2)
19.693(3)
90.205(3)
2522.0(7)
2
14.484(2)
21.335(3)
8.947(1)
92.861(3)
2761.1(7)
2
˚
b/A
˚
c/A
ꢅ/ꢃ
3
˚
V/A
Z
Dc/g cmꢂ3
Dm/g cmꢂ3
1.30
1.29
1.54
1.57
Crystal size/mm3
ꢆ(Mo Kꢄ)/mmꢂ1
2ꢇ range/ꢃ
0:25 ꢄ 0:20 ꢄ 0:10
0.247
1.82–28.43
15195
0:35 ꢄ 0:30 ꢄ 0:15
0.864
1.41–28.63
16980
No. of reflections
No. of unique reflections
with I > 2ꢀðIÞ
5778
0.0469, 0.1157
0.903
6425
0.0419, 0.1069
0.953
R1, wR2 [I > 2ꢀðIÞ]a)
Goodness-of-fit on F2
2
2
1=2
2
2
2
a) R1 ¼ ꢀjjFoj ꢂ jFcjj=ꢀjFoj; wR2 ¼ ½ꢀwðFo ꢂ Fc Þ =ꢀwðFo Þ ꢅ
.
N, 11.33%. IR (KBr, cmꢂ1): ꢁ(NH) 3259, ꢁas(SO2) 1328, ꢁs(SO2)
1164. 1H NMR (DMSO-d6, T ¼ 298 K): ꢂ 0.43 (4H, quintet,
J ¼ 6:1 Hz), 1.25 (8H, t, J ¼ 4:5 Hz), 1.37 (8H, s), 1.51 (8H, t,
J ¼ 6:1 Hz), 1.53 (12H, s), 1.93 (8H, t, J ¼ 4:5 Hz), 6.54 (8H,
d, J ¼ 8:1 Hz), 6.59 (4H, s), 6.82 (8H, d, J ¼ 8:1 Hz).
age.7 Crystallographic data have been deposited with Cambridge
Crystallographic Data Centre: Deposit numbers CCDC-657151
and 657152. Copies of the data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from
the Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge, CB2 1EZ, UK; Fax: +44 1223 336033; e-mail:
deposit@ccdc.cam.ac.uk).
[Pd (tstaec)] CH CN.
H4tstaec (40 mg, 0.04 mmol) was
ꢀ
2
3
dissolved in DMF (10 mL) at 60 ꢃC. To this solution was added
CH3CN solution (2 mL) of palladium(II) acetate (18 mg, 0.08
mmol), and the mixture was heated at 60 ꢃC for 10 min. On to
the resulting yellow solution was layered acetonitrile (18 mL),
and allowed to stand at room temperature to give orange crystals.
Yield, 18.5 mg (38%). Anal. Found: C, 46.26; H, 5.60; N, 10.59%.
Calcd for C48H67N9O8Pd2S4: C, 46.52; H, 5.45; N, 10.17%. IR
(KBr, cmꢂ1): ꢁas(SO2) 1261, ꢁs(SO2) 1130. UV–vis: ꢃmax ("/
Computational Methods. Density functional theory (DFT)
calculations were performed for H4tstaec and [Pd2(tstaec)]. The
geometric parameters were given from X-ray diffraction analysis
and the calculations were carried out by using Gaussian 03 (revi-
sion C.02) program.8 The geometries were optimized at the hybrid
ꢀ
B3LYP level of DFT using the standard 3-21G basis set for hy-
drogen, carbon, oxygen, nitrogen, and sulfur, and the LANL2DZ
basis set for palladium. Excited-state energies and oscillator
strengths were computed within the time-dependent density
functional theory (TD-DFT) framework as implemented in the
Gaussian 03 program.
M
ꢂ1 cmꢂ1, measured in DMF) 410 nm (858). 1H NMR (DMSO-
d6, T ¼ 353 K): ꢂ 1.75 (12H, s), 1.86 (4H, m), 2.08 (8H, m),
2.42 (8H, m), 2.68 (8H, m), 2.98 (8H, m), 6.57 (8H, d, J ¼
7:9 Hz), 7.22 (8H, d, J ¼ 7:9 Hz).
Measurements. Elemental analyses were conducted using
a Thermo Finnigan FLASH EA 1112 series CHNS-O Analyzer.
Infrared spectra were measured with a JASCO MFT-2000
FT-IR Spectrometer in the 4000–600 cmꢂ1 region. The electronic
spectra were measured with a Shimadzu UV–vis–NIR Recording
Spectrophotometer Model UV-3100. 1H NMR spectra were
recorded on a LA 400 spectrometer operating at 400.1 MHz
Results and Discussion
Macrocyclic Ligand, H4tstaec.
The tosylated ligand,
H4tstaec, was prepared from a reaction of 1,4,8,11-tetraazacy-
clotetradecane with four equivalents of N-(p-toluenesulfo-
nyl)aziridine in acetonitrile. The IR spectrum of H4tstaec ex-
hibits strong absorptions at 1328 and 1164 cmꢂ1 due to S–O
stretching vibrations in addition to a ꢁ(N–H) stretching band
at 3259 cmꢂ1. Attempts to recrystallize from DMF gave color-
less crystals suitable for single-crystal X-ray diffraction study.
The crystal structure of H4tstaec is shown in Figure 1. The
asymmetric unit contains one-half of the H4tstaec molecule,
the macrocycle being centered on a crystallographic inversion
center (Table 2). According to the stereochemical description
of the cyclam ring introduced by Bosnich et al.,9 the relative
orientation of the four nitrogen substituents can be ascribed
to a trans IV configuration where two aminoethyl groups
1
for H. Chemical shifts were referenced to the residual peaks of
DMSO-d6 (ꢂ 2.49).
X-ray Crystallography.
A preliminary examination was
made and data were collected on a Bruker CCD X-ray diffractom-
eter (SMART APEX) using graphite-monochromated Mo Kꢄ
radiation at 20 ꢃC. Crystal data and details concerning data collec-
tion are given in Table 1. The structure was solved by direct meth-
ods, and refined by full-matrix least-squares methods. The hydro-
gen atoms were inserted at their calculated positions and fixed
there. All of the calculations were carried out on a Pentium IV
Windows 2000 computer utilizing the SHELXTL software pack-

1456 Bull. Chem. Soc. Jpn. Vol. 81, No. 11 (2008)
Dinuclear Palladium(II) Complex
O1
O2
S1
C3
C6
C4
N3
C5
C8
N1
C2
C9
N2
C15
C16
C7
C13
C1
C10
C12
C11
C14
C19
C18
N4
O4
O3
C17
C23
C20
S2
C21
C22
Figure 1. ORTEP drawing of the structure of H4tstaec
showing the 25% probability thermal ellipsoids and atom
labeling scheme. Hydrogen atoms are omitted for clarity.
ꢃ
˚
Table 2. Selected Bond Distances (A) and Angles ( ) for
H4tstaeca)
a
c
N1–C2
N1–C1
N1–C6
N2–C4
N2–C5
N2–C15
N3–C7
N4–C16
1.463(3)
1.469(3)
1.472(2)
1.463(2)
1.452(3)
1.460(3)
1.463(2)
1.461(3)
S1–O1
S1–O2
S1–N3
S1–C8
S2–O3
S2–O4
S2–N4
S2–C17
1.424(2)
1.426(2)
1.615(2)
1.764(2)
1.430(2)
1.430(2)
1.597(2)
1.756(2)
b
Figure 2. Crystal packing of tstaec.
C14
C11
C10
C12
C13
O1–S1–O2
O1–S1–N3
O2–S1–N3
O1–S1–C8
O2–S1–C8
N3–S1–C8
O3–S2–O4
O3–S2–N4
O4–S2–N4
O3–S2–C17
O4–S2–C17
N4–S2–C17
C2–N1–C1
C2–N1–C6
C1–N1–C6
C5–N2–C15
119.8(1)
106.6(1)
107.5(1)
108.8(1)
107.3(1)
106.1(1)
119.4(1)
107.1(1)
106.8(1)
108.1(1)
107.0(1)
108.1(1)
112.7(2)
113.3(2)
110.6(2)
113.5(2)
C5–N2–C4
C15–N2–C4
C7–N3–S1
C16–N4–S2
N1–C1–C50
N1–C2–C3
C2–C3–C4
N2–C4–C3
N2–C5–C10
N1–C6–C7
N3–C7–C6
C13–C8–S1
C9–C8–S1
N2–C15–C16
N4–C16–C15
111.1(2)
110.4(2)
118.3(1)
122.2(1)
114.4(2)
112.4(2)
112.8(2)
115.0(2)
114.2(2)
115.1(2)
111.0(2)
120.0(2)
120.2(2)
110.3(2)
107.5(2)
C9
C8
O3
O1
C21
C22
C18
S1
C23
C20
O2
O4
S2
C17
C19
N3
N4
C1
N2’
C7
C2
C3
Pd1
N1
C6
C4
C16
C15
N1’
Pd1’
N4’
N2
C5
N3’
a) Prime refers to the equivalent position (ꢂx þ 1, ꢂy þ 1,
ꢂz).
Figure 3. ORTEP drawing of the structure of [Pd2-
(tstaec)] 2CH3CN showing the 25% probability thermal
ellipsoids and atom labeling scheme. Hydrogen atoms
are omitted for clarity.
ꢁ
separated by two methylene carbon atoms and the other two
aminoethyl groups are oriented on opposite sides of the macro-
cyclic ring. Tosyl arms point away from each other in order to
avoid their steric hindrance. As shown in Figure 2, this extend-
ed structure is hydrogen-bonded through the tosylated amino
equivalent of palladium(II) acetate in DMF. Layering of
acetonitrile to the DMF solution provided orange crystals of
[Pd2(tstaec)] 2CH3CN. The 1H NMR spectra measured in
ꢁ
groups in the crystal, the closest contact being N3 O4
˚
DMSO for the H4tstaec ligand and the PdII complex confirms
the ligand coordination in solution when we consider the dif-
ference between the spectral features in the range observed
for the signals, in addition to the disappearance of the NH
signal of the NHTs groups upon the complex formation. The
ꢁꢁꢁ
(x ꢂ 1=2, ꢂy þ 1=2, z ꢂ 1=2) of 3.030(2) A.
Attempts were made to react the H4tstaec ligand with a
variety of transition-metal salts including CoCl2 6H2O,
NiCl2 4H2O, and Cu(ClO4)2 6H2O. Unfortunately no charac-
terizable products could be isolated except for the starting
materials in the case of simple 1:1 reaction, presumably due
to the weak coordinating ability of the tosylated nitrogen atom
with this sterically hindered system. However, we successfully
isolated a metal complex when H4tstaec was treated with two
ꢁ
ꢁ
ꢁ
crystal structure of [Pd2(tstaec)] 2CH3CN was determined
by X-ray structure analysis.
ꢁ
A
perspective view of
[Pd2(tstaec)] is shown in Figure 3. Selected bond distances
and angles are listed in Table 3. The dinuclear [Pd2(tstaec)]
molecule possesses an inversion center. Each palladium atom

S. Wada et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 11 (2008) 1457
ꢃ
˚
Table 3. Selected Bond Distances (A) and Angles ( ) for
[Pd2(tstaec)] 2CH3CNa)
ꢁ
Pd1–N1
Pd1–N2
Pd1–N3
Pd1–N4
C1–N20
N1–C6
N1–C4
N1–C3
2.066(3)
2.047(3)
2.042(3)
2.034(3)
1.463(5)
1.452(6)
1.499(5)
1.599(6)
S1–N3
N2–C10
N2–C5
N2–C15
N3–C7
S2–N4
N4–C16
1.580(3)
1.463(5)
1.494(5)
1.497(5)
1.486(5)
1.589(3)
1.465(5)
N1–Pd1–N2
N1–Pd1–N3
N1–Pd1–N4
N2–Pd1–N3
N2–Pd1–N4
N3–Pd1–N4
C6–N1–C4
C6–N1–C3
C4–N1–C3
C6–N1–Pd1
C4–N1–Pd1
C3–N1–Pd1
C2–C1–N20
O1–S1–O2
O1–S1–N3
O2–S1–N3
N3–S1–C8
C10–N2–C5
C10–N2–C15
C5–N2–C15
86.0(1)
83.2(1)
163.2(1)
162.5(1)
82.1(1)
C10–N2–Pd1
C5–N2–Pd1
C15–N2–Pd1
C7–N3–S1
C7–N3–Pd1
S1–N3–Pd1
O3–S2–O4
O3–S2–N4
O4–S2–N4
N4–S2–C17
C2–C3–N1
C16–N4–S2
C16–N4–Pd1
S2–N4–Pd1
C5–C4–N1
C4–C5–N2
N1–C6–C7
N3–C7–C6
C16–C15–N2
N4–C16–C15
121.6(3)
106.7(2)
98.7(2)
b
115.8(3)
102.5(2)
125.9(2)
118.0(2)
109.6(2)
109.6(2)
108.2(2)
113.7(3)
115.5(3)
110.5(2)
131.2(2)
113.3(3)
113.3(3)
111.2(4)
108.8(3)
111.2(4)
109.0(3)
a
c
Figure 4. Crystal packing of [Pd2(tstaec)] 2CH3CN.
ꢁ
103.9(1)
111.9(4)
109.3(4)
110.8(3)
109.8(3)
100.1(2)
114.6(2)
118.9(4)
116.9(2)
108.8(2)
112.3(2)
106.6(2)
111.3(3)
107.5(3)
110.1(3)
0.18
230
281
259
266
0.12
330
236
443
415
0.06
330
416
487
500
0
200
250
300
350
400
450
550
600
Wavelength / nm
Figure 5. Diffused reflectance spectra of [Pd2(tstaec)]
ꢁ
a) Prime refers to the equivalent position (ꢂx þ 1, ꢂy þ 1,
ꢂz þ 2).
CH3CN with the TD-DFT calculated transition energies
as absorption wavelengths in nm and oscillator strengths
indicated by vertical lines for comparison.
is coordinated to the two tertiary amino nitrogen atoms
of the macrocycle and the two amido nitrogen atoms of the
[2-(salicylideneamino)ethyl]-1,4,8,11-tetraazacyclotetradecane
and its substituted derivatives.12 In these complexes, two
0
˚
tosylaminoethyl arms. The Pd1 Pd1 distance is 5.617(1) A.
ꢁꢁꢁ
Although the coordination geometry around each palladium
atom is square planar, the palladium atom deviates from the
metal atoms are well separated with a long Mn Mn distance
˚
of 9.675(4)–10.097(3) A because of the non-coordination of
ꢁꢁꢁ
˚
basal plane of N1, N2, N3, and N4 by 0.264 A, presumably
reflecting that the palladium(II) is too large to fit within the
N4-donor square plane. The Pd–N bond lengths range from
the cyclam-ring nitrogen atoms. Although the cyclam ring
takes a similar trans IV configuration to H4tstaec, the crystal
structure of [Pd2(tstaec)] 2CH3CN is different from that of
H4tstaec. The coordination to the palladium atoms encountered
in [Pd2(tstaec)] also affects the spatial extension of the pendant
ꢁ
˚
2.034(3) to 2.066(3) A and are typical of such Pd–N bond
lengths in other related complexes.10 The Pd1–N1 and Pd1–
˚
N2 bond lengths of 2.066(3) and 2.047(3) A, respectively,
˚
are slightly longer than those of Pd1–N3 2.042(3) A and
˚
Pd1–N4 2.034(3) A, presumably as a consequence of different
˚
˚
arms, giving a cavity with 3.7 A ꢄ 5.0 A in the crystal, in
which acetonitrile molecules are housed (Figure 4).
The diffuse reflectance spectrum of [Pd2(tstaec)] CH3CN
ꢁ
donor properties of the alkylated cyclam nitrogen and the de-
protonated amido nitrogen atoms. It is known that the amido
nitrogen atom binds to metal ion more strongly than the amino
nitrogen atom.11 It turns out that the cyclam skeleton keeps a
trans IV configuration upon coordination of the tosylated ami-
no groups to the two palladium atoms. This structure is com-
parable to the case of [M2(taec)]X4 complexes in chair form,
in which the two metal atoms are bound by the nitrogen atoms
is shown in Figure 5. The spectrum is characterized by an
intense band at 230 nm with some shoulders around 266 and
330 nm which may be charge-transfer transitions in origin,
and broad absorptions around 415 and 443 nm, which can be
associated with d–d transitions. This spectral feature is con-
sistent with square-planar palladium(II) ion surrounded by N4
donor atoms.13
The coordination of the tosyl groups could be caused by
deprotonation of the tosylamide groups. We therefore decided
to compare the electronic structure of H4tstaec (as the proto-
nated form) and [Pd2(tstaec)] (as the deprotonated form) by
DFT methods. DFT calculations were performed on optimized
structures of the ligand and the palladium complex using
of the cyclam ring and the pendant arms with a metal–metal
3b,3e
˚
separation of 5.267(2)–5.565(1) A.
However, the cyclam
ring takes a trans III configuration in the taec complexes. A
trans IV configuration can be found in related dinuclear metal
complexes with the cyclam-based ligands, 1,4,8,11-tetrakis-

1458 Bull. Chem. Soc. Jpn. Vol. 81, No. 11 (2008)
Dinuclear Palladium(II) Complex
H4tstaec
[Pd2(tstaec)]
1
1
0
Ar (π*)
0
Ar(π*)
LUMO
-1
-1
-2
-3
-4
-5
-6
-7
-8
-9
dx2-y 2
LUMO
-2
-3
-4
-5
HOMO
HOMO
Ncyclam (2p)
dxy (+Narm(2p))
Narm(2p)
-6
-7
-8
-9
Narm (2p)
dz2
Ar(π)
dxz, dyz
Narm (2p)(+Ar(π))
Ar(π)
O(2p)
Narm (2p)
O (2p)
N(2p)(+dyz
)
dxy(+Narm(2p))
dxy(+N(2p))
Ncyclam(2p)
O(2p)
Ar (π)
Figure 6. MO energy diagrams for H4tstaec (left) and [Pd2(tstaec)] (right).
Figure 7. Calculated isosurface of HOMO (bottom) and
LUMO (top) for H4tstaec.
Figure 8. Calculated isosurface of HOMO (bottom) and
LUMO (top) for [Pd2(tstaec)].
the coordinates obtained from the crystallographic data. The
MO energy diagrams for H4tstaec and [Pd2(tstaec)] are shown
in Figure 6. The molecular orbital surfaces generated by
Gaussian 03 for H4tstaec show that the HOMO is indeed
dominated by the 2p orbital of the nitrogen atoms of the cy-
atoms directs in the alternating opposite direction, it is not hard
to understand why the coordination of these cyclam-ring-nitro-
gen atoms is difficult to achieve in this ligand. The HOMO
and LUMO diagrams for [Pd2(tstaec)] are shown in Figure 8.
The HOMO is a metal dxy orbital mixed with the nitrogen 2p
orbitals of the deprotonated tosylamido groups. The LUMO
is essentially metal-based empty dx2ꢂy2 orbital with some
clam ring. The LUMO is almost entirely made up of aromatic
ꢈ
ꢀ
LUMO diagrams for H4tstaec are shown in Figure 7.). Since
each lobe of the 2p orbital of the four cyclam-ring-nitrogen
orbitals of the tosyl pendant groups (The HOMO and

S. Wada et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 11 (2008) 1459
K. P. Wainwright, Coord. Chem. Rev. 1997, 166, 35. d) S. F.
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Coord. Chem. Rev. 2001, 216–217, 287.
contribution from the deprotonated tosylamido-nitrogen and
cyclam-ring-nitrogen donors. As depicted in Figure 6, a rela-
tively low lying cyclam-ring-nitrogen 2p orbital (HOMOꢂ17,
Ncyclam(2p)) compared with the HOMO of H4tstaec can be
observed in [Pd2(tstaec)]. Presumably, the 2p orbital is
stabilized by its coordination to the metal ion. To gain insight
into the electronic transitions responsible for the observed
UV–vis spectra of [Pd2(tstaec)], TD-DFT calculations were
performed using the Gaussian program suite. The transitions
calculated at 487 and 416 nm may be compared to the exper-
imental bands at about 443 and 415 nm (Figure 5). These
bands are mainly d–d transitions composed of the HOMO
2
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x2ꢂy2
(Pd(dxy)) ! LUMO (Pd(d
)) and the HOMOꢂ1 (N(2p)
with participation of the palladium d orbital) ! LUMO, re-
spectively. The calculated transition at 330 nm can be ascribed
to the experimental bands at 330 nm. This transition is mixed
in character, with d–d (HOMOꢂ5 (Pd(dxz)), HOMOꢂ6
(Pd(dyz)) ! LUMO), and LMCT (HOMOꢂ3 (aromatic ꢈ of
the tosyl group) ! LUMO). The transitions with larger oscil-
lator strengths at 281 and 259 nm may be assigned to the ex-
perimental shoulder bands at 266 nm. They can be described
as charge-transfer transitions having the HOMO ! LUMO+1
3
a) I. Murase, M. Mikuriya, H. Sonoda, S. Kida, J. Chem.
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K. P. Wainwright, P. A. Duckworth, J. Chem. Soc., Dalton Trans.
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ꢀ
ꢀ
(aromatic ꢈ ) and the HOMO ! LUMO+3 (aromatic ꢈ ).
The calculated transition at 236 nm consists mainly of LMCT
(the HOMOꢂ10(O) ! LUMO). This may be responsible for
the strong absorption at 230 nm in the experimental spectra.
As a whole, the calculated values have a general resemblance
to the experimental spectra.
In the present study we report the results of an investigation
on an N-tosylated macrocyclic ligand with some metal ions.
We could isolate only the palladium complex. The X-ray struc-
ture determination of the palladium complex shows that the
tstaec ligand is octadentate and is coordinated to two palla-
dium(II) ions similarly to the taec ligand, giving two planar
N4 donor atoms. It is to be noted that the deprotonated amido-
nitrogen atoms bind more strongly to palladium(II) than do
the tertiary amines, while alkylation of a secondary amine
generally results in a reduction of its metal ion affinity due
to steric factors. This fact suggests that the deprotonated form
of the present ligand has a binding ability to metal ions.
Among Pd2þ, Cu2þ, Ni2þ, and Co2þ ions, the highest tendency
to promote amide deprotonation was observed for palladi-
um(II) ion.14 This trend may be one of the reasons why only
the palladium(II) species was isolated in the present system.
We are now making an effort to synthesize metal complexes
other than the palladium complex, although it seems to be
difficult to isolate such species.
´
a) A. Sousa, M. R. Bermejo, M. Fondo, A. Garcıa-Deibe-
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5
a) T. N. Lambert, B. D. Smith, Coord. Chem. Rev. 2003,
240, 129. b) A. P. Davis, J.-B. Joos, Coord. Chem. Rev. 2003,
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6 S. Elshani, S. Chun, B. Amiri-Eliasi, R. A. Bartsch, Chem.
Commun. 2005, 279.
7 G. M. Scheldrick, SHELXTL Crystallographic Software
Package, Version 5.1, Bruker AXS, Inc., Madison, WI, 1998.
8
M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven,
K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi,
V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A.
Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R.
Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O.
Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,
J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski,
P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J.
Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels,
M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K.
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S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko,
We thank Prof. Makoto Handa and Dr. Takahisa Ikeue of
Shimane University for the NMR experiments reported here.
This present work was partially supported by the ‘‘Open
Research Center’’ Project for Private Universities: matching
fund subsidy and Grants-in-Aid for Scientific Research No.
19550074 from the Ministry of Education, Culture, Sports,
Science and Technology.
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