A novel heterobimetallic complex composed of the imide-bridged [3]ferrocenophane and the tridentate palladium(II) complex

Article abstract of DOI:10.1016/S0022-328X(99)00748-2

The imide-bridged [3]ferrocenophane, 2-pyridyl-1,1′-ferrocenedicarboximide, served as a monodentate ligand to form the corresponding heterobimetallic complex 4 with the palladium(II) complex bearing the tridentate podand ligand, through displacement of the ancillary acetonitrile. The X-ray crystal-structure determination revealed that the pyridyl nitrogen of the ferrocenophane coordinates to the palladium center with distortion of the ferrocenophane moiety, which lies below the coordination plane of palladium. Such a structure is considered to be present even in solution, resulting in four nonequivalent broad signals of Cp protons in the ¹H-NMR spectrum, due to the electronic environment effect of the coordination plane of palladium. A π-π stacking interaction was observed between the benzene ring of the podand moieties and the pyridine ring of the neighboring molecule in the crystal packing of 4.

Full text of DOI:10.1016/S0022-328X(99)00748-2

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 599 (2000) 135–142
A novel heterobimetallic complex composed of the imide-bridged
[
3]ferrocenophane and the tridentate palladium(II) complex
Toshiyuki Moriuchi, Seiji Bandoh, Yoko Miyaji, Toshikazu Hirao *
Department of Applied Chemistry, Faculty of Engineering, Osaka Uni6ersity, Yamada-oka, Suita, Osaka 565-0871, Japan
Received 18 October 1999; received in revised form 22 November 1999; accepted 3 December 1999
Abstract
The imide-bridged [3]ferrocenophane, 2-pyridyl-1,1%-ferrocenedicarboximide, served as a monodentate ligand to form the
corresponding heterobimetallic complex 4 with the palladium(II) complex bearing the tridentate podand ligand, through
displacement of the ancillary acetonitrile. The X-ray crystal-structure determination revealed that the pyridyl nitrogen of the
ferrocenophane coordinates to the palladium center with distortion of the ferrocenophane moiety, which lies below the
coordination plane of palladium. Such a structure is considered to be present even in solution, resulting in four nonequivalent
1
broad signals of Cp protons in the H-NMR spectrum, due to the electronic environment effect of the coordination plane of
palladium. A p–p stacking interaction was observed between the benzene ring of the podand moieties and the pyridine ring of
the neighboring molecule in the crystal packing of 4. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structure; [3]Ferrocenophane; Heterobimetallic complex; Tridentate podand ligand
1
. Introduction
complexation behavior of 1. Palladium(II) complexes
bearing a tridentate podand ligand are envisaged to
provide one metal binding site and flexible second-
sphere and/or sterically demanding interaction sites
based on the podand moieties. The complexation of the
imide-bridged [3]ferrocenophane (1) with the tridentate
palladium(II) complex was investigated in this report.
Ferrocenophanes have attracted much attention due
to both their physical properties based on the distortion
of two cyclopentadienyl (Cp) rings and their potential
utilization as redox-active receptors [1]. Complexation
with [n]ferrocenophane ligands, in which two Cp rings
are bridged intramolecularly by one chain, is expected
to induce structural and electronic environmental
changes of the ferrocenophane moiety through restric-
tion of the fluxional process of Cp rings. Hetero-
bimetallic complexes composed of [n]ferrocenophane
ligands and transition metals are of interest in this
context [2]. In a previous paper [3], 2-aminopyridine
was demonstrated to react with 1,1%-ferrocenedicar-
boxylic acid chloride to give the novel imide-bridged
2. Results and discussion
Amido-N ligands, which have s-donor properties of
the deprotonated nitrogen, are well known to afford
stable complexes with transition metals. In this respect,
the tridentate podand ligand, N,N%-bis(2-phenylethyl)-
2,6-pyridinedicarboxamide (2) [4], is considered to serve
as an excellent tridentate ligand possessing s-donor
[
3]ferrocenophane (1) bearing the pendant 2-pyridyl
moiety, in which two Cp rings are staggered and tilted
6.4° with respect to each other. The coordination of
properties.
N(pyridine) hydrogen bonds (N(2)···N(1), 2.688 A
N(3)···N(1), 2.644 A) and NH(amide)···O(water) hydro-
gen bonds (N(2)···O(3), 3.053 A; N(3)···O(3), 3.025 A
Two
intramolecular
NH(amide)···
1
,
;
the pendant 2-pyridyl moiety of 1 to a metal center is
considered to orient the ferrocenophane moiety toward
the metal center, which prompted us to investigate the
,
,
,
)
were observed in the crystal structure of 2 (Fig. 1 and
Table 1). Treatment of the podand ligand 2 with
Pd(OAc) in acetonitrile led to the formation of the
*
Corresponding author. Fax: +81-6-68797415.
2
E-mail address: hirao@ap.chem.eng.osaka-u.ac.jp (T. Hirao)
corresponding palladium(II) complex 3. The absence of
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00748-2

136
T. Moriuchi et al. / Journal of Organometallic Chemistry 599 (2000) 135–142
Fig. 1. ORTEP view of the X-ray crystal structure of 2 (40% probability ellipsoids).
1
the amide protons in H-NMR confirmed that the
podand ligand 2 coordinates in a deprotonated form.
The X-ray crystal structure of 3 indicates a sligthly
distorted square-planar geometry at palladium substi-
tuted with two amide nitrogens of 2 (N(2)ꢀPdꢀN(3),
an interchangeable coordination site of 3. The ancillary
acetonitrile was displaced by the reaction of 1 with 3 to
give the 1:1 palladium complex 4 in 90% yield (Scheme
1). The structure of the isolated complex 4 was eluci-
1
dated by H-NMR (Fig. 3). Interestingly, Cp protons
1
61.4°) as shown in Fig. 2. The two deprotonated amido
moieties and the pyridine ring are coplanar to form the
five-membered chelate rings with extended conjugation
appeared as four nonequivalent broad signals at 4.92,
4.75, 4.54, and 4.44 ppm, three of which were observed
at higher field as compared with those of 1 at room
1
1
[
5]. The C(1)ꢀC(11)ꢀN(2) and C(5)ꢀC(21)ꢀN(3) angles
temperature. Combined H– H COSY and NOE exper-
iments conducted at 223 K established that four signals
of Cp protons all belong to the same Cp. From these
results, magnetically nonequivalent Cp protons of 4 are
probably explained by the electronic environment effect
of the coordination plane of palladium with extended
conjugation composed of the two deprotonated amido
moieties and the pyridine ring. The uncomplexed
[3]ferrocenophane (1) exhibited only two Cp signals that
persisted from 298 to 193 K, demonstrating the very low
energy barrier in the torsional twist of the Cp rings of
1. If fluxional processes of Cp rings were frozen
in the five-membered chelate rings decreased slightly
upon complexation (2: C(1)ꢀC(11)ꢀN(2), 114.8°;
C(5)ꢀC(21)ꢀN(3), 114.3°; 3: C(1)ꢀC(11)ꢀN(2), 113.3°;
C(5)ꢀC(21)ꢀN(3), 112.6°). The open coordination site is
occupied by the ancillary acetonitrile with a PdꢀN(4)
distance of 2.014 A and N(1)ꢀPdꢀN(4) angle of 179.5°,
,
suggesting a utility of 3 as a metalloreceptor through
metal coordination [6]. Selected bond distances and
bond angles are listed in Table 2.
The coordination behavior of the imide-bridged
3]ferrocenophane ligand (1) was investigated by use of
[
Scheme 1.

T. Moriuchi et al. / Journal of Organometallic Chemistry 599 (2000) 135–142
137
Fig. 2. ORTEP view of the X-ray crystal structure of 3 (40% probability ellipsoids).
Table 1
Crystallographic data for 2–4
at a lower temperature, eight Cp signals would be
expected in the case of 4. On lowering the temperature
from 298 to 193 K, however, four Cp resonances were
sharpened to four multiplets, indicating that torsional
twist of the Cp rings of 4 is neither static even at 193 K
and the rotation of C(43)ꢀN(5) bond might be frozen.
On the other hand, the upfield shift of the pyridyl
proton on C(47) atom was detected throughout the
temperature-lowering process. The swing of the pyridyl
moiety about the palladium center is suggested to be
frozen at the lower temperature to locate the pyridyl
proton on C(47) atom above the coordination plane of
palladium. Notably, the signals attributable to the
methylene protons on C(12) and C(13) exhibited
nonequivalent resonances in the region 3.74–3.68,
2.74–2.66, and 2.15–2.07 ppm at room temperature,
although those of 3 are magnetically equivalent and in
the expected form of a triplet. These results indicate
that the free rotation of the podand moieties of 3 is
restrained by the coordination of the sterically hindered
[3]ferrocenophane (1).
2
ff3
4
Formula
C23H23N O ·H O C25H24N O Pd C40H33N O -
3 2 2 4 2 5 4
FePd·CHCl3
929.36
Molecular
weight
Crystal system Monoclinic
391.47
518.89
Monoclinic
Triclinic
(
P1 (no. 2)
Space group
P2 /c (no. 14)
P2 /n (no. 14)
1
1
a (A
,
)
)
)
9.478(2)
11.134(1)
19.743(2)
9.406(3)
19.849(4)
12.220(2)
22.482(4)
13.420(3)
9.331(2)
111.02(2)
114.02(1)
108.04(2)
2028(1)
2
b (A
,
c (A
,
h (°)
i (°)
k (°)
95.16(1)
92.51(2)
V (A
,
3)
2075.1(4)
4
1.253
2279.2(8)
4
1.512
Z
Dcalc.
1.521
(
g cm−3)
v (Mo–K )
0.84
8.44
10.45
a
−
1
(
cm
T (°C)
u (Mo–Ka)
)
23
0.71069
23
0.71069
23
0.71069
(
A
,
)
a
R
0.058
0.029
0.045
0.037
0.056
0.069
Further structural information of 4 was obtained by
the single-crystal X-ray structure determination (Fig.
4). The important bond distances and bond angles of 4
are summarized in Tables 2 and 3. The pyridyl nitrogen
b
Rw
a
R=ꢀ(ꢁF ꢁ−ꢁF ꢁ)/ꢀꢁF ꢁ.
o
c
o
2
b
2 1/2
R =[ꢀ w(ꢁF ꢁ−ꢁF ꢁ) /ꢀ wꢁF ꢁ ]
.
w
o
c
o

/
599
(
2
0
0
0
)
135
142
Fig. 3. 1H-NMR spectra of 4 in CD Cl at (a) 298 K; (b) 243 K.
2
2

T. Moriuchi et al. / Journal of Organometallic Chemistry 599 (2000) 135–142
139
Fig. 4. ORTEP view of the X-ray crystal structure of 4 (40% probability ellipsoids). (a) Top view; (b) side view. Hydrogen atoms are omitted for
clarity.

140
T. Moriuchi et al. / Journal of Organometallic Chemistry 599 (2000) 135–142
Table 2
Table 3
Selected bond distances (A
,
) and angles (°) for 2–4
Selected bond distances (A) and angles (°) for 4
,
2
3
4
Bond distances
FeꢀC(31)
FeꢀC(32)
FeꢀC(33)
FeꢀC(34)
FeꢀC(35)
FeꢀC(36)
FeꢀC(37)
FeꢀC(38)
FeꢀC(39)
1.965(9)
2.048(9)
2.09(1)
FeꢀC(40)
2.042(9)
1.47(1)
1.50(1)
1.198(10)
1.207(10)
1.41(1)
1.44(1)
1.42(1)
5.24
Bond distances
PdꢀN(1)
PdꢀN(2)
PdꢀN(3)
C(31)ꢀC(42)
C(36)ꢀC(41)
C(41)ꢀO(4)
C(42)ꢀO(3)
C(41)ꢀN(5)
C(42)ꢀN(5)
C(43)ꢀN(5)
FeꢀPd
–
–
–
–
1.924(3)
2.023(3)
2.024(3)
2.014(3)
1.479(6)
1.514(6)
1.246(5)
1.240(4)
1.341(5)
1.338(5)
1.922(7)
2.013(7)
2.037(7)
2.061(7)
1.50(1)
2.06(1)
2.006(10)
1.957(9)
2.006(9)
2.08(1)
PdꢀN(4)
C(1)ꢀC(11)
C(5)ꢀC(21)
C(11)ꢀO(1)
C(21)ꢀO(2)
C(11)ꢀN(2)
C(21)ꢀN(3)
1.515(4)
1.498(3)
1.228(3)
1.226(3)
1.321(4)
1.326(3)
1.49(1)
1.233(10)
1.249(9)
1.35(1)
2.08(1)
Bond angles
C(31)ꢀC(42)ꢀN(5) 117.8(9)
C(31)ꢀC(42)ꢀO(3) 123.6(9)
O(3)ꢀC(42)ꢀN(5) 118.5(9)
C(36)ꢀC(41)ꢀN(5) 117.1(8)
C(36)ꢀC(41)ꢀO(4) 122.6(8)
O(4)ꢀC(41)ꢀN(5) 120.3(9)
C(41)ꢀN(5)ꢀC(42)
C(41)ꢀN(5)ꢀC(43)
C(42)ꢀN(5)ꢀC(43)
C(43)ꢀN(4)ꢀPd
125.7(7)
117.6(7)
115.3(7)
125.8(6)
115.5(6)
1.35(1)
Bond angles
N(1)ꢀPdꢀN(2)
N(1)ꢀPdꢀN(3)
N(1)ꢀPdꢀN(4)
N(2)ꢀPdꢀN(3)
N(2)ꢀPdꢀN(4)
N(3)ꢀPdꢀN(4)
C(11)ꢀN(2)ꢀPd
C(21)ꢀN(3)ꢀPd
C(1)ꢀC(11)ꢀN(2)
C(5)ꢀC(21)ꢀN(3)
N(1)ꢀC(1)ꢀC(11)
N(1)ꢀC(5)ꢀC(21)
–
–
–
–
80.8(1)
80.6(1)
179.5(1)
161.4(1)
98.7(1)
81.0(3)
80.4(3)
175.4(3)
161.4(3)
98.2(3)
C(47)ꢀN(4)ꢀPd
–
–
–
–
99.9(1)
100.4(3)
114.8(6)
114.5(6)
112.8(8)
113.0(8)
113.3(8)
113.4(8)
114.0(3)
115.2(3)
113.3(4)
112.6(4)
114.4(4)
113.2(4)
Table 4
Selected strucural parameters
114.8(3)
114.3(3)
116.5(3)
116.6(3)
of 1, which was slightly deviated from the square-planar
coordination plane (N(1)ꢀPdꢀN(4), 175.4°), coordinated
to the palladium center at the interchangeable coordina-
tion site of 3. The dihedral angle between the least-
square planes of the pyridine ring of
1
and
PdꢀN(1)ꢀN(2)ꢀN(3) was found to be 75.7°. It is note-
worthy that the coordination of the pyridyl nitrogen
locates the ferrocenophane moiety below the coordina-
tion plane of palladium, being consistent with the spec-
troscopically nonequivalent Cp protons of
H-NMR.
4 in
1
The staggered orientation of two Cp rings (33.3°) was
slightly released although the dihedral angle (16.2°)
between the least-squares planes of two Cp rings was
not affected so much by complexation with 1 (35.5 and
molecule in the crystal packing of 4 (Fig. 5). The
distance between the benzene and pyridine rings was ca.
,
3.6 A, suggesting a p–p stacking interaction. The dihe-
16.4°, respectively). The structural parameters of 4 are
summarized in Table 4. There are two distinct b-angles,
defined as the angle between the plane of the Cp ring
and C(ipso)ꢀCO(bridging) bond: 32.7° for C(31)ꢀ
C(32)ꢀC(33)ꢀC(34)ꢀC(35) and C(31)ꢀC(42)O(3) and
dral angle between the least-square planes of the ben-
zene and pyridine rings was 5.73°, which is reasonable
for a face-to-face interaction.
The electrochemical properties of 4 were studied by
cyclic voltammetry. A reversible oxidation wave of the
4
9.5° for C(36)ꢀC(37)ꢀC(38)ꢀC(39)ꢀC(40) and C(36)ꢀ
+
C(41)O(4). The location of the ferrocenophane moiety
below the coordination plane of palladium is likely to
require the rotation of C(31)ꢀC(42)O(3) bond possibly
due to the steric or electronic interaction, which leads to
the rotation of the opposite C(36)ꢀC(41)ꢀO(4) bond
giving the above-mentioned dihedral angle between two
Cp rings.
FcꢁFc couple was observed at E1 value of 1.03 V
/2
+
versus AgꢁAg . The ferrocenophane complex 4 showed
a cathodic shift of 10 mV in comparison with the
uncomplexed ferrocenophane 1 (E1/2=1.04 V), indicat-
ing a cathodic perturbation of the ferrocenophane redox
couple via the complexation. This result is consistent
with the above-mentioned upfield shift of Cp protons
based on the location of the ferrocenophane moiety
below the coordination plane of palladium.
Notably, the benzene ring of the podand moieties
almost faces the pyridine ring of the neighboring

T. Moriuchi et al. / Journal of Organometallic Chemistry 599 (2000) 135–142
141
3.1. Syntheses
3.1.1. Palladium complex 3
A mixture of 2 (18.7 mg, 0.05 mmol) and Pd(OAc)2
11.2 mg, 0.05 mmol) in acetonitrile (5.0 ml) was stirred
(
under argon at room temperature (r.t.) for 2 h. After
evaporation of the solvent, the palladium complex 3
was isolated in 96% yield (24.9 mg) as yellow crystals
by recrystallization from acetonitrile. M.p. 165–167°C
−
1 1
(
(
uncorrected). IR (KBr): 1590 (CꢁO) cm . H-NMR
400 MHz, CD CN, 298 K): l 8.01 (t, 1H, J=7.7 Hz,
3
Py), 7.56 (d, 2H, J=7.7 Hz, Py), 7.33–7.19 (m, 10H,
Ph), 3.40 (t, 4H, J=7.3 Hz, CH ), 2.78 (t, 4H, J=7.3
2
13
Hz, CH2). C-NMR (100 MHz, CD CN, 298 K): l
3
1
70.8 (CꢁO), 153.9 (Py), 142.4 (Py), 141.7 (Ph), 130.0
(
Ph), 129.2 (Ph), 126.8 (Ph), 124.9 (Py), 49.1 (CH ),
2
+
3
7.7 (CH ). MS (FAB): m/z: 478 ([MꢀCH CN] +1).
2
3
Anal. Calc. for C H N O Pd: C, 57.87; H, 4.66; N,
25
24
4
2
1
0.80 Found: C, 57.83; H, 4.75; N, 10.76%.
3.1.2. Ferrocenophane complex 4
A mixture of the imide-bridged [3]ferrocenophane (1)
16.6 mg, 0.05 mmol) and the palladium complex 3
25.9 mg, 0.05 mmol) in dichloromethane (2.0 ml) was
(
(
Fig. 5. Molecular packing of 4.
stirred under argon at r.t. for 1 h. The reaction mixture
was filtered and concentrated. The ferrocenophane
complex 4 was isolated in 90% yield (36.4 mg) as
orange crystals by recrystallization from chloroform–
hexane. M.p. 184–187°C (dec.). IR (KBr) 1707 (CꢁO),
In conclusion, the imide-bridged [3]ferrocenophane
1) forms the heterobimetallic complex with the triden-
−
1
1
(
1679 (CꢁO), 1583 (CꢁO) cm . H-NMR (400 MHz,
tate palladium(II) complex composed of the two depro-
tonated amido moieties and the pyridine ring through
the coordination of the pendant 2-pyridyl moiety of the
imide linkage. The coordination of the pendant 2-
pyridyl moiety of 1 to the palladium center locates the
ferrocenophane moiety below the coordination plane of
palladium with extended conjugation to influence the
structural and electronic environmental changes of the
ferrocenophane moiety.
CD Cl , 298 K): l 8.04 (td, 1H, J=7.9, 1.8 Hz, Py),
2
2
8.00 (t, 1H, J=7.8 Hz, Py), 7.63 (t, 2H, J=7.8 Hz,
Py), 7.60 (ddd, 1H, J=7.9, 1.1, 0.5 Hz, Py), 7.45 (ddd,
1H, J=5.4, 1.8, 0.5 Hz, Py), 7.29–7.20 (m, 7H, Ph and
Py), 7.02–6.99 (m, 4H, Ph), 4.92 (br s, 2H, Cp), 4.75
(br s, 2H, Cp), 4.54 (br s, 2H, Cp), 4.44 (br s, 2H, Cp),
3
2
2
.74–3.68 (m, 2H, CH ), 2.74–2.66 (m, 4H, CH ),
.15–2.07 (m, 2H, CH2). C-NMR (150 MHz, CDCl3,
2
2
13
98 K): l 170.6 (CꢁO), 170.5 (CꢁO), 154.1 (Py), 152.8
(
Py), 151.9 (Py), 141.3 (Ph), 140.6 (Py), 140.4 (Py),
1
(
7
29.4 (Ph), 128.3 (Ph), 127.5 (Py), 125.8 (Ph), 124.7
Py), 124.2 (Py), 75.9 (Cp), 75.9 (ipso Cp), 75.7 (Cp),
3.3 (Cp), 73.1 (Cp), 48.4 (CH ), 35.9 (CH ). MS
3. Experimental
2
2
+
(
FAB): m/z: 810 [M +1]. Anal. Calc. for
All reagents and solvents were purchased from com-
C H N O FePd·H O: C, 58.02; H, 4.26; N, 8.46.
40
33
5
4
2
mercial sources and were further purified by the stan-
dard methods, if necessary. Melting points were
determined on a Yanagimoto micromelting point ap-
paratus and were uncorrected. Infrared spectra were
obtained with a Perkin–Elmer model 1605 FT-IR. H-
NMR spectra were recorded on a JEOL JNM-GSX-
Found: C, 58.42; H, 4.11; N, 8.54%.
3.2. Electrochemical experiments
1
The cyclic voltammetry measurements were per-
formed on a BAS CV-50W voltammetry analyzer in
deaerated dichloromethane containing 0.1 M
4
00 (400 MHz) spectrometer with tetramethylsilane as
1
3
n
an internal standard. C-NMR spectra were recorded
on a JEOL JNM-GSX-400 (100 MHz) spectrometer
and a Varian Unity Inova 600 (150 MHz) spectrometer.
Mass spectra were run on a JEOL JMS-DX303HF
mass spectrometer.
Bu NClO as a supporting electrolyte at 25°C with a
4 4
three-electrode system consisting of a highly polished
glassy carbon working electrode (BAS), a platinum
auxiliary electrode (BAS), and an AgꢁAgCl reference
−
1
electrode (BAS) with scan rate 100 mV s . Potentials

142
T. Moriuchi et al. / Journal of Organometallic Chemistry 599 (2000) 135–142
are reported versus aqueous AgꢁAgCl and are not cor-
rected for the junction potential. For a 1.0 mM dichloro-
methane solution of ferrocene as an internal standard,
the E1/2 value was 0.51 with 0.13 V peak separation.
and MS instruments. Partial financial support by a
Grant-in-Aid for Scientific Research on Priority Areas
from the Ministry of Education, Science, and Culture,
Japan and a Research Aid of Inoue Foundation for Sci-
ence are also acknowledged.
3.3. X-ray structure analysis
The measurement was made on a Rigaku AFC5R dif-
References
fractometer with graphite-monochromated Mo–K ra-
a
diation and a rotating anode generator. The data were
collected at a temperature of 2391°C using the ꢀ−2q
scan technique to a maximum 2q value of 55.1°. The
structure of 2 was solved by direct methods and ex-
panded using Fourier techniques. The structures of 3
and 4 were solved by heavy-atom Patterson methods and
expanded using Fourier techniques. The non-hydrogen
atoms were refined anisotropically. The H atoms in-
volved in hydrogen bonding were located in electron
density maps. The remainder of the H atoms were placed
in idealized positions and allowed to ride with the C
atoms to which each was bonded. Crystallographic de-
tails are given in Table 1.
[
1] (a) T. Saji, Chem. Lett. (1986) 275. (b) U.T. Mueller-Westerhoff,
Angew. Chem. Int. Ed. Engl. 25 (1986) 702. (c) T. Saji, J.
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