Synthesis and characterization of novel ferrocene-containing pyridylamine ligands and their ruthenium(II) complexes: Electronic communication through hydrogen-bonded amide linkage

Article abstract of DOI:10.1021/ic7016038

Tris(2-pyridylmethyl)amine (TPA) derivatives with one or two ferrocenoylamide moieties at the 6-position of one or two pyridine rings of TPA were synthesized. The compounds, N-(6-ferrocenoylamide-2-pyridylmethyl)-N,N- bis(2-pyridylmethyl)amine (Fc-TPA; L1) and N,N-bis(6-ferrocenoylamide-2- pyridylmethyl)-N-(2-pyridylmethyl)amine (Fc₂-TPA; L2), were characterized by spectroscopic methods, cyclic voltammetry, and X-ray crystallography. Their Ru(II) complexes were also prepared and characterized by spectroscopic methods, cyclic voltammetry, and X-ray crystallography. [RuCl(L1)(DMSO)]PF₆ (1) that contains S-bound dimethyl sulfoxide (DMSO) as a ligand and an uncoordinated ferrocenoylamide moiety exhibited two redox waves at 0.23 and 0.77 V (vs ferrocene/ferrocenium ion as 0 V), due to Fc/Fc⁺ and Ru(II)/Ru(III) redox couples, respectively. [RuCl(L2)]PF₆ (2) that contains both coordinated and uncoordinated amide moieties showed two redox waves that were observed at 0.27 V (two electrons) and 0.46 V (one electron), assignable to Ru(II)/Ru(III) redox couples overlapped with the uncoordinated Fc/Fc⁺ redox couple and the coordinated Fc/Fc⁺, respectively. In contrast to 2, an acetonitrile complex, [Ru(L2)(CH₃CN)](PF₆)₂ (3), exhibited three redox couples at 0.26 and 0.37 V for two kinds of Fc/Fc⁺ couples, and 0.83 V for the Ru(II)/Ru(III) couple (vs ferrocene/ferrocenium ion as 0 V). In this complex, the redox potentials of the coordinated and the uncoordinated Fc-amide moieties were discriminated in the range of 0.11 V. Chemical two-electron oxidation of 1 gave [Ru^IIICl(L1 ⁺)(DMSO)]³⁺ to generate a ferromagnetically coupled triplet state (S = 1) with J = 13.7 cm^-1 (H = -JS₁S ₂) which was estimated by its variable-temperature electron spin resonance (ESR) spectra in CH₃CN. The electron spins at the Ru(III) center and the Fe(III) center are ferromagnetically coupled via an amide linkage. In the case of 2, its two-electron oxidation gave the same ESR spectrum, which indicates formation of a similar triplet state. Such electronic communication may occur via the amide linkage forming the intramolecular hydrogen bonding.

Full text of DOI:10.1021/ic7016038

Inorg. Chem. 2008, 47, 886−895
Synthesis and Characterization of Novel Ferrocene-Containing
Pyridylamine Ligands and Their Ruthenium(II) Complexes:
Electronic Communication through Hydrogen-Bonded Amide Linkage
Takahiko Kojima,*,† Daisuke Noguchi,‡ Tomoko Nakayama,‡ Yuji Inagaki,‡,# Yoshihito Shiota,§
Kazunari Yoshizawa,§ Kei Ohkubo,† and Shunichi Fukuzumi†
Department of Material and Life Science, Graduate School of Engineering, Osaka UniVersity and
SORST (JST), Yamada-oka, Suita, Osaka 565-0871, and Department of Chemistry, Faculty of
Sciences, and Institute for Materials Chemistry and Engineering, Kyushu UniVersity, Hakozaki,
Higashi-Ku, Fukuoka 812-8581, Japan
Received August 11, 2007
Tris(2-pyridylmethyl)amine (TPA) derivatives with one or two ferrocenoylamide moieties at the 6-position of one or
two pyridine rings of TPA were synthesized. The compounds, N-(6-ferrocenoylamide-2-pyridylmethyl)-N,N-bis(2-
pyridylmethyl)amine (Fc−TPA; L1) and N,N-bis(6-ferrocenoylamide-2-pyridylmethyl)-N-(2-pyridylmethyl)amine (Fc −
2
TPA; L2), were characterized by spectroscopic methods, cyclic voltammetry, and X-ray crystallography. Their Ru(II)
complexes were also prepared and characterized by spectroscopic methods, cyclic voltammetry, and X-ray
crystallography. [RuCl(L1)(DMSO)]PF
uncoordinated ferrocenoylamide moiety exhibited two redox waves at 0.23 and 0.77 V (vs ferrocene/ferrocenium
ion as 0 V), due to Fc/Fc+ and Ru(II)/Ru(III) redox couples, respectively. [RuCl(L2)]PF
(2) that contains both
6
(1) that contains S-bound dimethyl sulfoxide (DMSO) as a ligand and an
6
coordinated and uncoordinated amide moieties showed two redox waves that were observed at 0.27 V (two electrons)
+
and 0.46 V (one electron), assignable to Ru(II)/Ru(III) redox couples overlapped with the uncoordinated Fc/Fc
+
redox couple and the coordinated Fc/Fc , respectively. In contrast to 2, an acetonitrile complex, [Ru(L2)(CH
3
CN)]-
6 2
)
(3), exhibited three redox couples at 0.26 and 0.37 V for two kinds of Fc/Fc+ couples, and 0.83 V for the
(
PF
Ru(II)/Ru(III) couple (vs ferrocene/ferrocenium ion as 0 V). In this complex, the redox potentials of the coordinated
and the uncoordinated Fc amide moieties were discriminated in the range of 0.11 V. Chemical two-electron oxidation
−
III
+
3+
13.7 cm-
1
of 1 gave [Ru Cl(L1 )(DMSO)] to generate a ferromagnetically coupled triplet state (S
) 1) with J )
(H
) −JS ) which was estimated by its variable-temperature electron spin resonance (ESR) spectra in CH
1
S
2
3
CN.
The electron spins at the Ru(III) center and the Fe(III) center are ferromagnetically coupled via an amide linkage.
In the case of 2, its two-electron oxidation gave the same ESR spectrum, which indicates formation of a similar
triplet state. Such electronic communication may occur via the amide linkage forming the intramolecular hydrogen
bonding.
1
2
Introduction
molecules and molecular assemblies. They have also been
applied to regulation of reactivity of a Rh(I) catalyst toward
Redox-active ligands including metallocene moieties have
been developed to construct redox-responsive functional
3
different directions (hydrogenation and hydrosilylation) and
to control of reactivity of carbonyl ligands as reported by
4
Wrighton and co-workers. On the other hand, Mirkin and
co-workers have reported on alteration of structures of metal
complexes based on the redox behavior of metallocene
moieties of their ligands (hemilabile ligands) to control the
donicity of coordinated atoms.
Among those, metallocenoylamide-containing supramol-
ecules have been developed toward molecular recognition.
*
To whom correspondence should be addressed. E-mail: kojima@
chem.eng.osaka-u.ac.jp.
†
Department of Material and Life Science, Osaka University and SORST
(
JST).
‡
§
#
Department of Chemistry, Faculty of Science, Kyushu University.
Institute for Materials Chemistry and Engineering, Kyushu University.
Present address: Department of Applied Quantum Physics, Graduate
5
School of Engineering, Kyushu University, 744 Motooka, Fukuoka 819-
395, Japan.
0
886 Inorganic Chemistry, Vol. 47, No. 3, 2008
10.1021/ic7016038 CCC: $40.75
© 2008 American Chemical Society
Published on Web 01/09/2008

Ru Complexes with Ferrocene-Containing Pyridylamine Ligands
Beer, Tucker and their co-workers have reported that redox
processes of the metallocene moiety could control binding
constants of anionic guest molecules by changing the acidity
of metallocene-connected amide N-H groups. Ferrocene-
containing ruthenium complexes have also been reported to
for Ru(II) complexes. In this Article, we describe the
synthesis and characterization of new TPA ligands with
ferrocenoylamide moiety and their Ru(II) complexes in terms
of their structures and redox behavior, including formation
and observation of triplet states derived from chemical
oxidations of bimetallic and trimetallic Ru(II)-ferrocene
systems.
6
exhibit not only multiple redox processes but also photoin-
7
duced intramolecular charge separation. Thus, metallo-
cenoylamide-containing ligands can be utilized to construct
redox-responsive multifunctional molecular devices.
Experimental Section
Metal complexes bearing metallocene-containing ligands
have been reported to exhibit multistep redox processes and
have been investigated mainly to focus on mixed-valence
states of those complexes.8,9 Dowling et al. have first reported
on the observation of intervalence-transfer transitions in near-
3
Materials and Instrumentation. Acetonitrile (CH CN) and
triethylamine (NEt ) were distilled over CaH . CH Cl was washed
3
2
2
2
with concentrated H
a silica gel column, and finally distilled over CaH
2
SO
4
, followed by water, then passed through
. Methanol was
2
refluxed and dried over Mg and then distilled prior to use. Diethyl
ether was distilled from sodium benzophenone ketyl solution. All
NMR measurements were performed on JEOL GX-400 and EX-
IR regions for ruthenium(II) complexes with ferrocene-
containing nitrile ligands.10 However, intramolecular mag-
2
70 spectrometers. UV-vis absorption spectra were measured in
netic interaction between the ferrocenium moiety involving
CH CN on a Jasco Ubest 55 UV-vis spectrophotometer at room
3
1
a low-spin Fe(III) (S ) /
2
) and a metal ion with unpaired
temperature. Infrared (IR) spectra were recorded by the Nujol
electron(s) has yet to be investigated. It is important to
demonstrate the intramolecular magnetic interactions as a
fundamental aspect of transition metal complexes with
ferrocene moieties to extend their further applicability as
redox-active and redox-switchable functional molecules.
We have previously reported on the synthesis, character-
ization, and functionality of ruthenium(II) complexes with
-1
method in the range of 4000-400 cm on a Jasco IR model 800
infrared spectrophotometer. Fast atom bombardment mass spectra
FAB-MS) were measured on a JMS-SX/SX102A tandem mass
(
spectrometer. Electrospray ionization mass spectra (ESI-MS) were
measured on a Perkin-Elmer Sciex API 300 mass spectrometer.
All elemental analysis data were obtained at the Service Center of
the Elemental Analysis of Organic Compounds, Department of
Chemistry, Kyushu University.
11
bisamide-TPA ligands (TPA ) tris(2-pyridylmethyl)amine).
Hydrochloric salts of N-(6-amino-2-pyridylmethyl)-N,N-bis(2-
pyridylmethyl)amine (amino-TPA) and N,N-bis(6-amino-2-pyridyl-
methyl)-N-(2-pyridylmethyl)amine (diamino-TPA) were prepared
as described previously.1 Ferrocenecarboxylic acid (FcCOOH),
oxalyl chloride, and N,N-dimethyaminopyridine (DMAP) were
In order to add redox-responsive property to those Ru(II)
complexes, we introduced ferrocenoylamide moieties to TPA
1b
(
1) (a) Beer, P. D.; Gale, P. A.; Chen, G. Z. Coord. Chem. ReV. 1999,
1
85-186, 3-36. (b) Beer, P. D.; Gale, P. A.; Chen, G. Z. J. Chem.
Soc., Dalton Trans. 1999, 1897-1909. (c) Inouye, M.; Takase, M.
Angew. Chem., Int. Ed. 2001, 40, 1746-1748.
purchased from Wako Pure Chemicals. [RuCl
synthesized in accordance with a reported procedure.
Synthesis of Chlorocarbonyl Ferrocene (FcCOCl).13,14 Oxalyl
chloride (16.3 mL, 0.19 mol) in CH Cl was added dropwise to a
suspension of ferrocenecarboxylic acid (6.55 g, 28.35 mmol) in
dry CH Cl at 0 °C. The mixture was stirred overnight at room
2 4
(DMSO) ] was
12
(
2) (a) Castro, R.; Cuadrado, I.; Alonso, B.; Casado, C. M.; Mor a´ n, M.;
Kaifer, A. E. J. Am. Chem. Soc. 1997, 119, 5760-5761. (b) Astruc,
D. Acc. Chem. Res. 2000, 33, 287-298.
2
2
(
(
(
3) Lorkovic, I. M.; Duff, R. R., Jr.; Wrighten, M. S. J. Am. Chem. Soc.
1
995, 117, 3617-3618.
4) Lorkovi c´ , I. M.; Wrighton, M. S.; Davis, W. M. J. Am. Chem. Soc.
994, 116, 6220-6228.
2
2
1
temperature and then was dried under reduced pressure. The residue
was extracted with hexane, and the extract was dried to give
FcCOCl as a red solid (6.31 g, 89% yield). IR spectrum (Nujol):
5) (a) Singlewald, E. T.; Mirkin, C. A.; Stern, C. L. Angew. Chem., Int.
Ed. Engl. 1995, 34, 1624-1627. (b) Allgeier, A. M.; Stone, C. S.;
Mirkin, C. A.; Liable-Sands, L. M.; Yap, G. P. A.; Rheingold, A. L.
J. Am. Chem. Soc. 1997, 119, 550-559. (c) Allgeier, A. M.; Mirkin,
C. A. Angew. Chem., Int. Ed. 1998, 37, 895-908. See also: (d) Miller,
T. M.; Ahmed, K. J.; Wrighton, M. S. Inorg. Chem. 1989, 28, 2347-
-
1
ν
max/cm (CO); 1765.
Synthesis of N-(6-Ferrocenoylamide-2-pyridylmethyl)-N,N-
bis(2-pyridylmethyl)amine (Fc-TPA; L1). To a degassed solution
containing amino-TPA (0.838 g, 2.74 mmol) and NEt (4.2 mL,
was added a solution of FcCOCl (0.745
(30 mL) dropwise, followed by the addition
2355.
(
6) (a) Szemes, F.; Hesek, D.; Chen, Z.; Dent, S. W.; Drew, M. G. B.;
Goulden, A. J.; Graydon, A. R.; Grieve, A.; Mortimer, R. J.; Wear,
T.; Weightman, J. S.; Beer, P. D. Inorg. Chem. 1996, 35, 5868-5879.
3
30 mmol) in dry CH
g, 3 mmol) in CH Cl
2
Cl
2
2
2
(
b) Beer, P. D. Acc. Chem. Res. 1998, 31, 71-80. (c) Carr, J. D.;
of DMAP (4-N,N-dimethylaminopyridine) (1.0 g, 8.2 mmol) at
room temperature. The mixture was stirred for 11 h at room
Coles, S. J.; Hursthouse, M. B.; Light, M. E.; Tucker, J. H. R.;
Westwood, J. Angew. Chem., Int. Ed. 2000, 39, 3296-3299. (d) Beer,
P. D.; Hayes, E. J. Coord. Chem. ReV. 2003, 240, 167-189.
temperature under N
aqueous solution, the mixture was extracted by CH
2
. After being basified by saturated NaHCO
Cl and the
3
(
7) Siemeling, U.; Von der Br u¨ ggen, J.; Vorfeld, U.; Neumann, B.;
Stammler, A.; Stammeler, H.-G.; Brockhinke, A.; Plessow, R.;
Zanwllo, P.; Laschi, F.; Fabrizi de Biani, F.; Fontani, M.; Steenken,
S.; Stapper, M.; Gurzadyan, G. Chem.sEur. J. 2003, 9, 2819-2833.
8) Sixt, T.; Fiedler, J.; Kaim, W. Inorg. Chem. Commun. 2000, 3, 80-
2
2
(11) (a) Kojima, T.; Hayashi, K.; Matsuda, Y. Chem. Lett. 2000, 1008-
1009. (b) Kojima, T.; Hayashi, K.; Matsuda, Y. Inorg. Chem. 2004,
43, 6793-6804. (c) Kojima, T.; Miyazaki, S.; Hayashi, K.; Shimazaki,
Y.; Tani, F.; Naruta, Y.; Matsuda, Y. Chem.sEur. J. 2004, 10, 6402-
6410. For others, see: (d) Jitsukawa, K.; Oka, Y.; Yamaguchi, S.;
Masuda, H. Inorg. Chem. 2004, 43, 8119-8129.
(12) James, B. R.; Ochiai, E.; Rempel, G. I. Inorg. Nucl. Chem. Lett. 1971,
7, 781-784.
(13) Carr, J. D.; Coles, S. J.; Hassan, W. W.; Hursthouse, M. B.; Malik,
K. M. A.; Tucker, J. H. R. J. Chem. Soc., Dalton Trans. 1999, 57-
62.
(
(
82.
9) (a) Liu, T.-Y.; Chem, Y. J.; Tai, C.-C.; Kwan, K. S. Inorg. Chem.
1
999, 38, 674-679. (b) Chen, Y. J.; Kao, C.-H.; Lin, S. L.; Tai, C.-
C.; Kwan, K. S. Inorg. Chem. 2000, 39, 189-194. (c) Zhu, Y.; Clot,
O.; Wolf, M. O.; Yap, G. P. A. J. Am. Chem. Soc. 1998, 120, 1812-
1
821. (d) Li, Z.; Beatty, A. M.; Fehler, T. P. Inorg. Chem. 2003, 42,
707-5714. (e) Colbert, M. C. B.; Lewis, J.; Long, N. J.; Raithby, P.
5
R.; White, A. J. P.; Williams, D. J. J. Chem. Soc., Dalton Trans. 1997,
9
9-104.
10) Dowling, N.; Henry, P. M.; Lewis, N. A.; Taube, H. Inorg. Chem.
981, 20, 2345-2348.
(
(14) Knobloch, F. W.; Rauscher, W. H. J. Polym. Sci. 1961, 54, 651-
1
656.
Inorganic Chemistry, Vol. 47, No. 3, 2008 887

Kojima et al.
extract was dried on anhydrous Na
was concentrated to a small volume and then eluted on an alumina
column with ethyl acetate/hexane (2/1 v/v). A fraction (R ) 0.4)
was collected, and the solvents were removed under reduced
pressure to give an orange powder of L1 (0.32 g, 22% yield). Anal.
2
CO
3
. After filtration, the filtrate
Table 1. Crystallographic Data for L1 and 1
L1
1
f
formula
fw
C29H27FeN5O
517.41
C31H33N5O2ClSFeRuPF6
877.03
cryst syst
space group
A, Å
B, Å
c, Å
monoclinic
P21/n (No. 14)
14.3218(10)
11.1188(7)
15.7468(10)
100.953(4)
2461.9(3)
4
1.396
6.45
-160 ( 1
5545
monoclinic
P21/c (No. 14)
12.8071(7)
12.2123(5)
21.5373(12)
98.431(3)
3332.1(3)
4
Calcd for C29
H
27
N
5
2
OFe‚1/3H O: C, 66.55; H, 5.33; N, 13.38.
1
Found: C, 66.71; H, 5.41; N, 13.22. H NMR (acetone-d
6
, δ): 8.77
br-s, 1H, NH), 8.38 (d, 2H, 5 Hz, py-H6), 8.02 (d, 1H, 8 Hz, py-
Fc)-H3), 7.6 (pseudo-t, 3H, py-H4 and py(Fc)-H4), 7.55 (2H, d, 8
(
(
â, deg
V, Å3
Hz, py-H3), 7.31 (d, 1H, 8 Hz, py(Fc)-H5), 7.10 (td, 2H, py-H5, 7
and 1 Hz), 4.95 (pseudo-t, 2H, 2 Hz, H2 and H5 of substituted
Cp), 4.34 (pseudo-t, 2H, 2 Hz, H3 and H4 of substituted Cp), 4.12
Z
Dcalc, g/cm3
µ(Mo KR), cm
T, °C
1.748
11.52
-140 ( 1
7576
575
0.079
0.203
0.073
-
1
(
Cp, 5H, s), 3.74 (s, 4H, CH
2
), 3.65 (s, 2H, CH
2
). IR spectrum (in
-
1
KBr pellet): ν/cm ; 1662 (CdO). Absorption maximum (λmax
,
no. of observns
no. of variables
-
1
-1
nm) in CH
Synthesis of N,N-Bis(6-ferrocenoylamide-2-pyridylmethyl)-
N-(pyridylmethyl)amine (Fc -TPA; L2). Diamino-TPA‚3HCl
was neutralized by an aqueous NaHCO solution, extracted by CH
Cl , and dried on Na CO . To a degassed solution of diamino-TPA
0.911 g, 2.84 mmol) and triethylamine (4.1 mL, 29.6 mmol) in
CH Cl (200 mL) was added FcCOCl (6.31 g, 25.29 mmol) in CH
Cl (90 mL) dropwise over a period of 30 min under N at 0 °C.
3
CN: 440 (ꢀ ) 865 M cm ).
434
0.052
0.156
0.049
a
R
b
Rw
2
R1 (I > 2σ(I))
GOF
c
3
2
-
1.17
1.37
2
2
3
a
R ) ∑(Fo - Fc )/∑Fo . Rw ) [∑(w(Fo - Fc ) )/∑w(Fo2)2]1/2. R1
∑|Fo| - |Fc|/∑|Fo|.
2
2
2
b
2
2 2
c
(
)
2
2
2
-
in KBr pellet): νmax/cm-1; 1680 (CdO), 1067 (SdO). Absorption
2
2
(
After the mixture was stirred for 1 h at 0 °C, DMAP (1.14 g, 9.32
mmol) was added, and the mixture turned red-purple. This was
dried under reduced pressure after stirring for 7 h at room
-1
-1
maxima (λmax, nm) in CH CN: 282 (ꢀ ) 22 800 M cm ), 350
3
-1
-1
(
ꢀ ) 12 700 M cm ).
Preparation of [RuCl(L2)]PF
L2 (100 mg, 0.134 mmol) in MeOH (15 mL) was added [RuCl
DMSO) ] (78 mg, 0.161 mmol) under N . The mixture was
refluxed for 34 h and turned red during the reaction. KPF (45 mg,
.242 mmol) in MeOH was added to the solution under N . The
6
(2). To a degassed solution of
temperature. To the residue, a saturated NaHCO
(
3
aqueous solution
60 mL) was added, and the mixture was extracted with CH Cl (3
100 mL). The combined extracts were dried on anhydrous
CO , filtered, and the solvent was removed under reduced
2
-
2
2
(
4
2
×
6
Na
2
3
0
2
pressure. The crude product was purified by column chromatog-
raphy on activated alumina (2:1 ethyl acetate/hexane) to give pure
L2 as an orange solid. The yield was 36% (0.753 g). Anal. Calcd
mixture was concentrated under reduced pressure (one-third
volume), and a red precipitate emerged. The precipitate was filtered
and washed with a small volume of EtOH and Et
The yield was 41% (56 mg). Anal. Calcd for C40
ClRu‚4H O: C, 43.76; H, 4.04; N, 7.65. Found: C, 43.61; H, 3.60;
N, 7.42. 1H NMR (CD
CN, δ (ppm)): 9.46 (s, 1H, NH of
coordinated amide), 9.25 (s, 1H, NH of uncoordinated amide), 8.60
d, 1H, 5 Hz, ax-py-H6), 8.44 (d, 1H, 8 Hz, py-H3), 7.76 (t, 1H, 8
Hz, py-H4), 7.62 (t, 1H, 8 Hz, py(Fc)-H4), 7.52 (t, 2H, 8 Hz, py-
Fc)-H4′), 7.05-7.17 (m, py- and py(Fc)-H3 and H5), 5.28 (AXd,
2
O, and then dried.
for C40
1.36; H, 4.90; N, 10.40. FAB-MS: m/z ) 745.1 (M + H) . H
NMR (CDCl , δ (ppm)): 8.48 (d, 1H, 4.0 Hz, py-H6), 8.36 (s,
H, NH), 8.04 (d, 2H, 8 Hz, py(Fc)-H3), 7.73 (t, 2H, 8 Hz, py-
Fc)-H4), 7.72 (t, 1H, 8 Hz, py-H4), 7.65 (d, 1H, 8 Hz, py-H3),
H
36
6 2
N O Fe
2
‚2H
2
O: C, 61.55; H, 5.17; N, 10.77. Found: C,
H
36
N
6
O
2
Fe PF
2
6
-
+
1
6
2
3
3
1
(
(
7
4
.36 (d, 2H, 8 Hz, py(Fc)-H5), 7.19 (t, 1H, 6 Hz, py-H5), 4.88 (t,
H, 2 Hz, H2 and H5 of substituted Cp), 4.45 (t, 4H, 2 Hz, H3 and
(
H4 of substituted Cp), 4.22 (s, 10H,Cp), 3.89 (s, 2H, CH2 of py),
2
2H, 14 Hz, CH ), 4.99 and 4.63 (pseudo-t, 4H, H2- and H5-Cp),
3
.80 (s, 4H, CH2 of py(Fc)). IR spectrum (in KBr pellet): νmax
/
4.88 (AXd, 2H, 15 Hz, CH
2
), 4.76 (AXd, 2H, 15 Hz, CH ), 4.26
2
-1
cm (CO); 1653. Absorption maximum (λmax, nm) in CH
3
CN: 445
and 4.37 (pseudo-t, 4H, H3- and H4-Cp), 4.11 and 4.27 (s, 10H,
-
1
-1
(ꢀ ) 1060 M cm ).
+
Cp). FAB-MS: m/z ) 881.1 (M ). IR spectrum (in KBr pellet):
-
1
Preparation of [RuCl(L1)(DMSO)]PF
L1 (100 mg, 0.193 mmol) in ethanol (20 mL), [RuCl
6
(1). To a solution of
(DMSO)
97 mg, 0.200 mmol) was added in portions with vigorous stirring
under N . The mixture was refluxed for 6 h, and NH PF (49 mg,
.300 mmol) was added as a solid after cooling. The solution was
ν
max/cm (CO); 1627 (coordinated amide), 1674 (uncoordinated
2
4
]
amide). Absorption maxima (λmax, nm) in CH CN: 345 (ꢀ ) 16 900
3
-
1
-1
-1
-1
(
M
cm ), 442 (ꢀ ) 12 700 M cm ).
Preparation of [Ru(L2)(CH CN)](PF
0.165 mmol) was added to a red solution of 2 (130 mg, 0.127 mmol)
in CH CN (25 mL). The mixture was refluxed for 4 h and turned
2
4
6
3
6 2 3
) (3). AgNO (28 mg,
0
concentrated to a small volume (one-fifth volume) to obtain an
orange powder, which was washed with ethanol and diethyl ether,
then dried in vacuo (137 mg, 78% yield). Anal. Calcd for
3
orange, and AgCl emerged during the reaction. After filtration with
a Celite pad, the filtrate was dried under reduced pressure. The
residue was dissolved in a small volume of acetone (10 mL) and
C
31
H
33
N
5
O
2
ClSFeRuPF
Found: C, 40.57; H, 3.69; N, 7.83. H NMR (CD
br-s, 1H, NH), 9.60 (d, 6 Hz, 1H, ax-py-H6), 8.82 (d, 6 Hz, 1H,
6
‚2H
2
O: C, 40.78; H, 4.08; N, 7.67.
1
3
CN, δ): 10.72
4 6
filtered. To the filtrate were added EtOH (20 mL) and NH PF (40
(
mg, 0.245 mmol) in EtOH (20 mL), and then the solution was
1
eq-py-H6), 8.33 (d, 8 Hz, 1H, ax-py-H3), 7.76 (t, 8 Hz, 1H, eq-
py-H4), 7.75 (t, 8 Hz, 1H, eq-py(Fc)-H4), 7.68 (t, 8 Hz, 1H, ax-
py-H4), 7.42 (d, 8 Hz, 1H, eq-py(Fc)-H5), 7.34 (t, 1H, 6 Hz, ax-
py-H5), 7.30 (t, 1H, ex-py-H5), 7.18 (d, 1H, 8 Hz, eq-py(Fc)-H3),
concentrated under reduced pressure (to /10 volume) and a brown
precipitate formed. The precipitate was filtered and washed with a
small volume of EtOH and Et
2
O, and then dried. The yield was
1
51% (76 mg). H NMR (CD
3
CN, δ (ppm)): 9.38 (s, 1H, NH of
7
(
(
.12 (d, 1H, 7 Hz, eq-py-H3), 5.71 (AXd, 2H, 15 Hz, CH
pseudo-s, 1H, H5′ of Cp), 5.28 (pseudo-s, 1H, H2′ of Cp), 5.25
AXd, 2H, 15 Hz, CH ), 4.65 (AXd, 2H, 15 Hz, CH ). 4.63 (AXd,
H, 15 Hz, CH ), 4.56 (pseudo-t, 2H, 2 Hz, H3 and H5 of
substituted Cp), 4.51 (s, 2H, CH ), 4.24 (s, 5H, Cp). IR spectrum
2
), 5.41
coordinated Fc-amide), 9.06 (s, 1H, NH of free Fc-amide), 8.50
(d, 1H, 6 Hz, py-H6), 8.46 (d, 1H, 8 Hz, py-H3), 7.85 (t, 1H, 8
Hz, py-H4), 7.75 (t, 1H, 8 Hz, py(Fc)-H4), 7.67 (t, 1H, 8 Hz, py-
2
2
2
2
(Fc)-H4′), 4.3-5.1 (m, Cp and CH
2
of pyr and substituted-py), 4.23
of CH CN). FAB-MS:
2
and 4.11 (s, 10H, Cp), 2.38 (s, 3H, CH
3
3
888 Inorganic Chemistry, Vol. 47, No. 3, 2008

Ru Complexes with Ferrocene-Containing Pyridylamine Ligands
Scheme 1. Schematic Description for Structures of the Ligands and the Complexes Discussed in This Articlea
a
Fc stands for the Fe(cyclopentadienyl)2 group.
m/z ) 885.8 (M - H) . IR spectrum (Nujol method): νmax/cm-1
1
+
;
The values for the mass attenuation coefficients are those of Creagh
and Hubbell.18 Crystallographic data for L1 and 1 are summarized
in Table 1.
626 and 1682 (CO), 2274 (CtN). Absorption maxima (λmax, nm)
in CH CN: 286, 364 (sh).
3
Cyclic Voltammetry. All cyclic voltammograms were recorded
on an HECS 312B dc pulse polarograph (Fuso Electrochemical
System) attached to an HECS 321B potential sweep unit of the
same manufacture. Glassy carbon was employed as a working
electrode. A platinum coil was used as a counter electrode, and a
X-ray Crystallography on L1 and 1. All measurements were
made on a Rigaku Mercury CCD area detector with graphite-
monochromated Mo KR (λ ) 0.7107 Å) radiation.
A single crystal of L1 was obtained by recrystallization from
ethyl acetate. The orange platelet crystal having approximate
silver/silver nitrate (Ag/AgNO
electrode. All measurements were carried out in dry CH
containing 0.1 M [(n-Bu) N]ClO as a supporting electrolyte under
at ambient temperatures. The redox potentials were determined
relative to the ferrocene/ferrocenium redox couple as a reference
0 V).
Electron Spin Resonance Measurements. Variable-temperature
3
) electrode served as a reference
3
dimensions of 0.10 × 0.10 × 0.05 mm was mounted on a glass
3
CN
fiber. The data were collected at a temperature of -160 ( 1 °C to
the maximum 2θ value of 55.0°. The structure was solved by direct
methods and expanded using Fourier techniques. The non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were refined
isotropically. The final cycle of full-matrix least-squares refinement
4
4
N
2
(
2
on F was based on 5455 observed reflections and 434 variable
electron spin resonance (ESR) measurements were performed using
a JEOL X-band spectrometer (JES-RE1XE) with a quartz ESR tube
parameters. The maximum and minimum peaks on the final
difference Fourier map corresponded to 0.46 and -0.47 e/Å3,
respectively. All calculations were performed using the Crystal-
Structure software package except for refinement, which was
performed using SHELXL-97.15
(
1.2 mm i.d.). The solution was transferred to an ESR tube under
argon. The ESR spectra of the triplet states of oxidized species of
and 2 were measured in frozen CH CN at 123 K after two- or
three-electron-transfer oxidation of the complexes with [Ru(bpy) ]-
1
3
3
A single crystal of 1 suitable for X-ray analysis was obtained
by recrystallization of the crude product from MeOH. The single
crystal was mounted on a glass capillary with silicon grease. The
data were collected at a temperature of -140 ( 1 °C to the
maximum 2θ value of 55.0°. A total of 1240 oscillation images
were collected. The structure was solved by direct methods and
expanded using Fourier techniques. The non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were refined isotropically.
(PF ) (bpy ) 2,2′-bipyridine) at room temperature. The g values
6
3
were calibrated using a Mn2 marker.
+
ESR measurements down to 2.6 K were performed using a JEOL
ES-SCKA X-band spectrometer equipped with an Oxford continu-
ous flow cryostat (ESR910). Through the measurements, the
temperature was controlled by helium flow and heater controllers
(Oxford VC30 and ITC503). The magnetic field and applied
frequency were monitored by a gauss meter (LakeShore450) and a
microwave counter (ADVANTEST TR5212), which allowed us to
determine the precise g values.
2
The final cycle of full-matrix least-squares refinement on F was
made based on 7576 observed reflections and 575 variable
parameters. Neutral atom scattering factors were taken from Cromer
Density Functional Theory Calculations. Density functional
and Waber.16 Anomalous dispersion effects were included in Fcalc
;
III
+
3+
theory (DFT) calculations on [Ru Cl(Fc -TPA)(DMSO)] were
carried out on a workstation. Structure optimization was made using
the values for ∆f ′ and ∆f ′′ were those of Creagh and McAuley.17
1
9
the Los Alamos ECP with double-ú basis for the Ru and Fe ions.
The D95 basis set,20 a standard double-ú basis, was applied for
(15) Sheldrick, G. M. SHELX97, Programs for Crystal Structure Refine-
ment. University of G o¨ ttingen, Germany, 1997.
other atoms.
(16) Cromer, D. T.; Waber, J. T. International Tables for X-ray Crystal-
lography; Kynoch Press: Birmingham, England, 1974; Vol. IV, Table
2
.2 A.
(18) Creagh, D. C.; Hubbell, J. H. International Tables for Crystallography;
Wilson, A. J. C., Ed.; Kluwer Academic Publishers: Boston, MA,
1992; Vol. C, Table 4.2.4.3, pp 200-206.
(
17) International Tables for X-ray Crystallography; Kluwer Academic
Publishers: Boston, MA, 1992; Vol. C.
Inorganic Chemistry, Vol. 47, No. 3, 2008 889

Kojima et al.
Table 2. Selected Bond Lengths (angstroms) and Angles (deg) for L1
Fe1-C1
Fe1-C3
Fe1-C5
Fe1-C7
Fe1-C9
O1-C11
N5-C12
2.039(3)
2.041(3)
2.031(3)
2.046(3)
2.049(2)
1.230(2)
1.396(3)
Fe1-C2
2.052(3)
2.034(3)
2.040(3)
2.052(2)
2.033(2)
1.377(3)
1.473(3)
122.8(2)
Fe1-C4
Fe1-C6
Fe1-C8
Fe1-C10
N5-C11
C10-C11
O1-C11-N5
121.1(2)
O1-C11-C10
N4-C12-N5
112.8(2)
Table 3. Selected Bond Lengths (angstroms) and Angles (deg) for 1
Figure 1. ORTEP drawing of L1 with 50% probability thermal ellipsoids.
Hydrogen atoms are omitted for clarity except that attached to the N5.
Ru1-Cl1
Ru1-N1
Ru1-N3
Fe1-Cp
O1-C11
N5-C12
S1-O2
2.434(1)
2. 084(4)
2.108(4)
2.027 (av)
1.222(7)
1.372(7)
1.477(4)
Ru1-S1
2.253(1)
2.131(4)
2.078(4)
2.030 (av)
1.400(7)
1.475(8)
Ru1-N2
Ru1-N4
Fe1-Cp(CO)
N5-C11
C10-C11
S1-Ru1-Cl1
N1-Ru1-N2
N1-Ru1-N4
N2-Ru1-N4
N2-C12-N5
N5-C11-O1
O1-C11-C10
87.58(5)
79.7(2)
82.2(1)
161.9(2)
115.4(4)
122.3(5)
122.0(5)
N1-Ru1-Cl1
N1-Ru1-N3
N3-Ru1-S1
Ru1-S1-O2
C11-N5-C12
N5-C11-C10
171.8(1)
81.9(2)
177.7(1)
120.7(2)
125.8(4)
115.8(5)
HCl, which is derived from the condensation of FcCOCl with
the precursors, resulting in adsorption on an activated
alumina.
Ru(II) complexes, [RuCl(L1)(DMSO)]PF
(L2)]PF (2), were prepared by the reaction of [RuCl
DMSO) ] with L1 and L2, respectively, in MeOH by
refluxing under N . The complexes should be treated under
until KPF is added; otherwise, the product was con-
6
(1) and [RuCl-
Figure 2. ORTEP drawing of the cationic moiety of 1 with 50%
probability thermal ellipsoids. Hydrogen atoms are omitted for clarity.
2
-
6
(
4
2
N
2
6
Results and Discussion
taminated by unknown species. An acetonitrile complex, [Ru-
Synthesis. In order to synthesize L1 and L2, the neutral-
ization of the precursors, the HCl salts of amino-TPA and
diamino-TPA, is indispensable prior to the amide formation
with FcCOCl. Neutralized amino- and diamino-TPA should
(L2)(CH CN)](PF ) (3), was synthesized from the reaction
3
6 2
of 1 with AgNO in CH CN by refluxing. The reaction to
3
3
+
remove the chloride ligand with Ag hardly occurred at room
temperature. A schematic description of the complexes is
given in Scheme 1.
be dried using Na
2
CO
3
3
after extraction with CHCl to prepare
L1 and L2, respectively. When MgSO
drying agent, no amide formation reaction occurred. In this
case, the signal assigned to the H5 of ferrocene-linked
4
was employed as a
Crystal Structure of L1. An ORTEP drawing of the
compound is shown in Figure 1 with 50% probability thermal
ellipsoids. Selected bond lengths are given in Table 2. The
bond lengths of Fe-C(Cp) bonds are in the range of 2.031-
(3)-2.052(3) Å. In the crystal, an intermolecular hydrogen
bond was found for N2‚‚‚N5′ (3.041 Å, N2-H1′-N5′ )
160.5°). Intermolecular π-π interactions were also recog-
nized for N2‚‚‚C6 (3.285 Å), C5‚‚‚C14 (3.563 Å), and
C4‚‚‚C22 (3.618 Å) (Supporting Information). The dihedral
angle between the amide plane and the Cp ring connected
to the amide moiety was 7.4°, and that between the amide
plane and the pyridine plane was 18.1°. This suggests that
the Cp ring π-system strongly conjugates with the amide
and pyridine moieties.
pyridine showed a downfield shift, probably due to proto-
1
nation by acidic MgSO
spectrum.
4
as observed in the H NMR
The ligands, L1 and L2, were synthesized by the reactions
of FcCOCl with amino-TPA and diamino-TPA in dry CH
Cl under N , respectively. For the synthesis of the ligands,
NEt was used as a base and DMAP was also required as an
2
-
2
2
3
activating agent of the acid chloride to complete the reaction.
In this process, it is required to add an excess mount of
DMAP, probably due to both the poor nucleophilicity of the
6-amino group of the pyridine and the poor electrophilicity
of the carbonyl group attached to the negatively charged
cyclopentadienyl (Cp) ring. The residues treated with a
Crystal Structure of 1. A single crystal of 1 was obtained
by recrystallization from MeOH. An ORTEP drawing is
depicted in Figure 2 and selected bond lengths (angstroms)
and angles (deg) are listed in Table 3. The Ru(II) center is
surrounded by L1 in a tetradentate fashion, chloride, and
the S-bound dimethyl sulfoxide (DMSO) ligand, and the
geometry is similar to that of [RuCl(1-Naph-TPA)(DMSO)]-
saturated NaHCO
3
aqueous solution were extracted with
CHCl . Without this process, the ligands are protonated by
3
(
19) (a) Dunning, T. H.; Hay, P. J. In Modern Theoretical Chemistry;
Schaefer, H. F., III., Ed.; Plenum: New York, 1976; Vol. 3, p 1. (b)
Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270.
(20) See ref 19b.
6
PF (4) (1-Naph-TPA ) N-(6-(1-naphthoyl)amide-2-pyridyl-
890 Inorganic Chemistry, Vol. 47, No. 3, 2008

Ru Complexes with Ferrocene-Containing Pyridylamine Ligands
ferrocenoylamide-pyridylmethyl arms, and that at 3.89 ppm
was assigned to the methylene groups for the pyridylmethyl
arm. A singlet at 4.22 ppm was assigned to the Cp ligands
of the Fc moieties, a pseudotriplet at 4.45 ppm was assigned
to H3 and H4 of Cp′ of the Fc moieties, and that at 4.88
ppm was assigned to H2 and H5 of the Cp′ ligands. A broad
singlet at 8.36 ppm was assigned to the NH protons of the
amide moieties, and the signal intensity decreased upon
2
addition of D O. A doublet at 8.48 ppm was assigned to the
H6 proton of the pyridine moiety without the ferrocenoyla-
mide moiety.
-1
The IR spectrum showed a peak at 1653 cm , which was
assigned to amide CO vibration. The UV-vis spectrum in
Figure 3. Dihedral angles of the ferrocenoylamidepyridine moiety in 1.
Values written in red are those for two-electron oxidized species of 1
obtained by DFT calculations.
CH
3
CN showed bands assigned to a π-π* transition of
pyridine at 285 nm and assigned to a d-d transition of Fe-
2
1
methyl)-N,N-bis(2-pyridylmethyl)amine). The longest Ru-N
bond length was observed at Ru1-N2 (2.131(4) Å), which
is involved in the ferrocenoylamide-linked pyridine. This is
probably due to the spherical requirement for the intramo-
lecular hydrogen bonding between the amide N-H and the
chloride ligand as mentioned below. In complex 1, the
separation between the Ru(II) center and the Fe(II) center
was determined to be 6.656 Å.
-
1
-1
(
II) in the Fc moieties at 445 nm (ꢀ ) 1060 M cm ).
B. Complex 1. In the H NMR spectrum of 1 in CD CN,
3
1
two singlets are assigned to the methyl groups of the S-bound
DMSO ligand at 2.85 and 3.03 ppm. This suggests that the
DMSO ligand is not allowed to rotate freely and that the
two methyl groups are distinguished to be diastereotopic in
a chiral coordination environment as observed in 4.21
A broad singlet due to the amide hydrogen, which
In complex 1, an intramolecular hydrogen bond was found
between N5 and Cl1 (3.183(4) Å) with ∠ N5-H1-Cl1 )
2
diminished upon addition of D O, was observed at 10.72
68.6°, which was longer than that (3.135(3) Å)21 observed
ppm and exhibited a large downfield shift (∆δ ) 1.95 ppm)
derived from hydrogen bonding with the chloride ligand. In
the IR spectrum of 1 (in KBr pellet), a peak assigned to ν-
1
in 4. This is probably due to the reduced acidity of the N-H
group in 1 arising from conjugation with negatively charged
Cp ring. No significant intermolecular interaction was
recognized in the crystal.
The dihedral angles around the amide moiety are described
in Figure 3. The amide plane is almost coplanar with the Cp
ring and the pyridine ring connected to the Fc moiety,
exhibiting the dihedral angles of 13.7° and 22.8°, respec-
tively.
-
1
(
N-H) was observed at 3166 cm , which was a higher value
-
1 21
than that observed for 4 (3122 cm ). This is consistent
with the atomic distances between N(amide) and Cl (3.183-
4) Å for 1 and 3.135(3) Å for 4), indicating that the
-
2
1
(
hydrogen bonding in 1 is weaker than that in 4.
1
In the H NMR spectrum of 1, signals assigned to the
methylene moieties of the ligand were observed four AX
doublets with a large geminal coupling constant (JAX ) 15
Hz) at 5.71, 5.25, 4.65, and 4.63 ppm and a pseudosinglet
at 4.51 ppm. This also indicates that 1 possesses a chiral
environment in terms of the stereogenic tertiary amino
1
Spectroscopic Properties. A. L1 and L2. The H NMR
spectrum of L1 was measured in acetone-d , and peak
6
1
1
assignments were made by peak integrations and H- H
COSY (correlation spectroscopy). A singlet at 3.65 ppm (2H)
was assigned to the methylene protons of the ferrocenoyla-
mide-pyridylmethyl arms, and that at 3.74 ppm (4H) was
ascribed to the methylene groups for the pyridylmethyl arm.
A singlet at 4.12 ppm is due to the Cp ligands of the Fc
moieties, a pseudotriplet at 4.34 ppm was assigned to H3
and H4 of the substituted Cp ligands (Cp′) of the Fc moieties,
and that at 4.95 ppm was assigned to H2 and H5 of the Cp′
ligands. In the range from 7 to 8.5 ppm, signals due to
pyridine protons were observed and assigned as described
in the Experimental Section. At 8.77 ppm, a broad singlet
was detected and assigned to the amide N-H based on its
2
1
nitrogen. As for the Fc moiety, the nonsubstituted Cp ring
protons exhibited a singlet at 4.24 ppm. Signals due to H2
and H5 of the Cp′ ring exhibited different chemical shifts
of 5.28 and 5.41 ppm, respectively; however, they showed
the same chemical shift (4.95 ppm) under noncoordinating
situation. This suggests that the substituted Cp is not allowed
to rotate freely because of the steric congestion by chelation
of the ligand.
C. Complex 2. The H NMR spectrum of 2 in CD
1
3
CN
showed three sets of peaks assigned to the methylene protons
as follows: an AB quartet at 4.22 and 4.40 ppm (JAB
)
1
2 Hz), another AB quartet at 4.57 and 4.91 ppm (JAB ) 14
disappearance upon addition of D
2
O.
Hz), and two AX doublets at 4.64 and 5.28 ppm (JAX
)
The IR spectrum in a KBr pellet showed a peak at 1662
-1
14 Hz).
cm , which was assigned to amide CO vibration. The UV-
vis spectrum in CH CN showed a d-d transition band of
Fe(II) in the Fc moiety at 440 nm (ꢀ ) 865 M cm ).
In the H NMR spectrum of L2 in CDCl
.80 ppm was assigned to the methylene protons for the
Two sets of peaks of the ferrocene moieties were observed.
Singlet peaks at 4.11 and 4.27 ppm were assigned to protons
of the Cp rings of the Fc groups, which linked to the
uncoordinated and the coordinated amide moieties, respec-
tively. Two pseudotriplets at 4.26 and 4.70 ppm were
assigned to resonances due to the H3 and H4 and the H2
3
-
1
-1
1
3
, a singlet at
3
(
21) Kojima, T.; Matsuda, Y. Chem. Lett. 2005, 34, 258-259.
Inorganic Chemistry, Vol. 47, No. 3, 2008 891

Kojima et al.
cm , assignable to ν(CN) for the coordinated CH CN. This
suggests that a CH CN molecule binds to the Ru center in
an η -N fashion. This result is consistent with other [Ru-
(L)(CH CN)](PF (L ) (1-Naph) -TPA, (2-Naph) -TPA,
isob -TPA, in which a CH CN molecule is also suggested
to bind to the Ru center in an η -N fashion.
-
1
and H5 of the Cp′ ring of the uncoordinated Fc moiety,
respectively. The other two pseudotriplets at 4.37 and 4.99
ppm were assigned to the resonances for the H3 and H4 and
that of the H2 and H5 of the Cp′ of the coordinated Fc
moiety, respectively. The discrimination between the two Fc
moieties in L2 also indicates that the one of amide CdO is
bound to the ruthenium center to hold an asymmetric
3
3
1
3
6
)
2
2
2
2
3
1
22
Redox Behavior of L1, L2, and Their Ruthenium(II)
Complexes. Cyclic voltammetry (CV) of L1, L2, and their
3
structure in CH CN. A singlet at 9.22 ppm was assigned to
the NH in the uncoordinated amide, and a singlet at 9.47
ppm was assigned to the NH in the coordinated amide, based
on the decrease of their peak intensities upon adding D O.
2
3
Ru(II) complexes were performed in CH CN at room
temperature in the presence of 0.1 M TBAP as an electrolyte.
Redox potentials were determined relative to the ferrocene/
ferrocenium ion couple as 0 V.
The FAB-MS spectrum of 2 showed a peak cluster
+
assigned to {[RuCl(L2)]} at 881.1, and its isotopic pattern
The cyclic voltammogram of L1 showed one reversible
redox wave at E1/2 ) 0.21 V. As for L2, one reversible redox
agrees with the computer simulation. The IR spectrum of 2
-
1
+
(
Nujol) showed a peak at 1622 cm , assigned to CO
wave due to the Fc/Fc couple was observed at E1 ) 0.23
/2
vibration of the amide linkage, in which the oxygen binds
V and ∆E () Epa - E ) was 0.11 V at 100 mV/s. These
pc
-
1
to the Ru center, and that at 1674 cm was assigned to CO
vibration for the uncoordinated counterpart, on the basis of
comparison with those of uncoordinated L1 and L2. Its UV-
values are comparable to that (0.24 V) of [{(6-methyl-2-
pyridyl)amino}carbonyl]ferrocene reported by Carr et al.13
The CV of complex 1 exhibited two redox waves at 0.23
V (∆E ) 86 mV) and 0.77 V (∆E ) 159 mV) at the scan
rate of 100 mV/s as shown in Figure 4. Based on the redox
vis spectrum in CH CN showed a band due to a π-π*
3
transition of pyridine at 285 nm and a ligand-to-metal charge-
-
transfer (LMCT) band from Cl to the Ru center at 442 nm.
+
23
potentials of L1, [RuCl(TPA)(DMSO)] (0.61 V), and
Those values are consistent with those of structurally
+
23
[RuCl(5-Me
3
-TPA)(DMSO)] (0.52 V), we assigned the
characterized Ru(II)-TPA complexes with two amide groups
+
first redox process to the Fc/Fc couple of the coordinated
L1 and the second one to the Ru /Ru couple. The peak
at the same positions as in L2.11b
II
III
1
D. Complex 3. The H NMR spectrum of 3 in CD
3
CN
current for the latter process was changed in accordance with
II
III
showed a singlet at 2.38 ppm, which was assigned to the
signal due to the CH of the coordinated CH CN. Two kinds
the scan rates, suggesting the second Ru /Ru couple should
II
3
3
be quasi-reversible. The higher redox potential for the Ru /
III
of peaks ascribed to the ferrocene moieties were also
observed. A singlet at 4.11 ppm was assigned to the protons
of Cp of Fc connected to the uncoordinated amide moiety.
A singlet at 4.23 ppm was assigned to the protons of Cp of
Fc connected to the coordinated amide linkage. These
indicate that the one of the amide CdO moieties is still bound
to the ruthenium center to hold the asymmetric structure as
in complex 2. A singlet at 9.06 ppm was assigned to the
resonance due to the NH of the uncoordinated amide, and a
broad singlet at 9.38 ppm was assigned to that of the NH of
the coordinated amide, judging from their disappearance
Ru couple results from the π-back-bonding from the
ruthenium center to the S-bound DMSO ligand.23
Concerning the chloride complex 2, two reversible redox
couples at 0.27 and 0.46 V were observed at 20 mV/s as
shown in Figure 5. The peak current of the first redox couple
was twice as large as that of the following redox wave and
assigned to the overlap of two redox waves due to the
+
II
III
uncoordinated Fc/Fc and the Ru /Ru with small separa-
tion. The second redox couple at 0.46 V was assigned to
+
the coordinated Fc/Fc process, based on those values of
RuCl(isob -TPA)]PF (0.27 V for Ru /Ru ) and L2. At
2 6
II
III 24
[
upon addition of D
2
O.
the scan rate of 20 mV/s in the sweep range from -0.4 to
0.7 V, the reversibility of the redox couples mentioned above
was intact. Therefore, no significant structural change occurs
upon the one-electron oxidation of the coordinated ferro-
cenoylamide moieties for this complex. These results suggest
that the coordination of amide oxygen is strengthened by
virtue of chelation and the intramolecular hydrogen bonding
and it is hard to dissociate from the Ru(II) center to maintain
the structure.
The ESI-MS spectrum of 3 showed a peak cluster assigned
+
+
to {[Ru(L2)(CH
pattern was consistent with computer simulation. The UV-
vis spectrum of 3 in CH CN showed a band due to a π f
3
CN)] - H } at 885.8, and its isotopic
3
π* transition of pyridine rings at 285 nm, a metal-to-ligand
charge-transfer (MLCT) band from Ru to pyridine at 371
-
nm. The lack of an LMCT band from Cl to Ru at 442 nm
-
observed for 2 to indicates that the Cl ligand is substituted
by CH
3
CN.22
3
In the CV of the acetonitrile complex 3 in CH CN, three
The IR spectrum of 3 (Nujol) showed a peak at 1626 cm-1
assigned to the CO vibration for the coordinated amide
moiety and at 1682 cm-1 assigned to CO vibration due to
the uncoordinated amide moiety, which were similar to those
of 2. In addition, a very weak peak was observed at 2274
redox couples were observed at 0.26 V (∆E ) 0.07 V),
p
0.37 V (∆E ) 0.08 V), and 0.83 V (∆E ) 0.14 V) at 20
p
p
mV/s within the sweep range (from -0.25 to 1.2 V) as shown
in Figure 6. In analogy with 2, the first and second redox
couples were reversible and assigned to the uncoordinated
(
22) Kojima, T.; Hayashi, K.; Shiota, Y.; Tachi, Y.; Naruta, Y.; Suzuki,
(23) Kojima, T.; Amano, T.; Ishii, Y.; Ohba, M.; Okaue, Y.; Matsuda, Y.
Inorg. Chem. 1998, 37, 4076-4085.
(24) See ref 11b.
T.; Uezu, K.; Yoshizawa, K. Bull. Chem. Soc. Jpn. 2005, 78, 2152-
2158.
892 Inorganic Chemistry, Vol. 47, No. 3, 2008

Ru Complexes with Ferrocene-Containing Pyridylamine Ligands
the change of the electron density at the ruthenium center.
-
Both loss of the anionic Cl ligand and binding of CH
3
CN
with π-acceptor character lower the electron density at the
Ru center to exert a stronger electron-withdrawing effect on
the coordinated Fc moiety. This effect raises its redox
potential to separate it from that of the uncoordinated
+
counterpart. The two Fc/Fc redox couples are intact in the
change of scan rate from 20 to 1000 mV/s. This indicates
that the structure is maintained upon the one-electron
oxidation of the coordinated ferrocenoylamide moiety.
Variable-Temperature ESR Measurements. In order to
clarify the oxidation processes in the Ru-Fc complexes, we
Figure 4. Cyclic voltammogram of 1 in CH3CN in the presence of TBAP
examined chemical oxidations of those complexes by [Ru-
(0.1 M) at room temperature. The potential was given relative to that of
3+
(
bpy)
3
]
and measured the ESR spectra of the oxidized
CN.
ferrocene/ferrocenium ion as 0 V.
species in CH
3
-
3
Two-electron oxidation of 1 (2.0 × 10 M) with two
3+
-3
III
equiv of [Ru(bpy)
3
]
(4.0 × 10 M) in CH
3
CN gave [Ru -
+
3+
Cl(L1 )(DMSO)] , and its variable-temperature ESR spec-
trum is shown in Figure 7a. As can be seen in the spectrum,
a signal assigned to that derived from a forbidden transition
in a triplet state was observed at g ) 4.28 (∆m ) 2) and a
s
signal due to the transition of ∆m
This spectrum is different from that of Fc , for which the g
s
) 1 is at g ) 2.0038.
+
values have been reported to be g
|
) 4.36 and g
⊥
) 1.30 in
25
acetone at 20 K. The one-electron oxidation of L1 by [Ru-
3
+
(
bpy)
2.0186 and a weak signal at g ) 4.22 in CH
see the Supporting Information), which was different from
3
]
gave spectra exhibiting an intense signal at g )
Figure 5. Cyclic voltammogram of 2 in CH3CN (0.1 M TBAP) at room
temperature: scan rate, 20 mV/s. The potential was described relative to
that of ferrocene/ferrocenium ion as 0 V.
3
CN at 2.6 K
(
that observed for the two-electron oxidized species of 1. The
peak intensity of the signal at g ) 4.28 increased in
accordance with lowering temperature down to 2.6 K,
III
+
3+
indicating that the ground state of [Ru Cl(L1 )(DMSO)]
should be a triplet state (S ) 1). The temperature-dependent
change of the intensity of the signal at g ) 4.28 (∆m ) 2),
obtained by double integration, allowed us to estimate a
s
-
1
ferromagnetic coupling constant to be J ) 13.7 cm (H )
JS ) based on curve-fitting of the data (Figure 7b) with
the Bleaney-Bowers equation (Supporting Information).
-
1 2
S
26,27
-
1 28
This value is smaller than that (J ) 15 cm ) observed in
a bis-µ-hydroxo dinuclear Fe(II)Fe(III) complex and that (J
-
1 29
)
75 cm ) for a Cu(II)-radical complex; however, it is
-1
larger than that (J ) 1.04 cm ) for an oxalato-bridged two-
dimensional coordination polymer, (tetrabutylammonium)-
II
III
30
[
Mn Ru (oxalato)
In order to gain structural insights into the triplet state,
we applied DFT calculations to optimize the structure of the
3
].
(
(
25) Prins, B.; Reinders, F. J. J. Am. Chem. Soc. 1969, 91, 4929-4931.
26) Bleaney, B.; Bowers, K. D. Proc. R. Soc. London, Ser. A 1952, 214,
4
51-465. The Bleaney-Bowers equation was used to estimate the J
-1
value: IT ∝ (3 + exp(-J/kT)) , where H ) -JS1S2. The procedure
Figure 6. Cyclic voltammograms of [Ru(L2)(CH3CN)](PF6)2 (3) in CH3-
CN (0.1 M TBAP) at room temperature: (a) scan rate, 1000 mV/s; (b)
scan rate, 20 mV/s. The potential was described relative to that of ferrocene/
ferrocenium ion as 0 V.
for the IT-T plot is described in Supporting Information.
(27) (a) Elsner, O.; Ruiz-Molina, D.; Vidal-Gancedo, J.; Rovira, C.;
Veciana, J. Chem. Commun. 1999, 579-580. (b) Kobayashi, K.; Ohtsu,
H.; Wada, T.; Kato, T.; Tanaka, K. J. Am. Chem. Soc. 2003, 125,
6
729-6739.
(
28) Stubna, A.; Jo, D.-H.; Costas, M.; Brenessel, W. W.; Andres, H.;
+
+
Fc/Fc and the coordinated Fc/Fc , respectively; however,
Bominaar, E. L.; M u¨ nck, E.; Que, L., Jr. Inorg. Chem. 2004, 43, 3067-
3
29) Luneau, D.; Rey, P. Coord. Chem. ReV. 2005, 249, 2591-2611.
30) Larionova, J.; Mombelli, B.; Sanchiz, J.; Kahn, O. Inorg. Chem. 1998,
37, 679-684.
079.
the third redox couple was irreversible on the basis of the
(
(
+
∆
E
p
. In this complex, the two Fc/Fc redox potentials can
be discriminated. The coordinated Fc is directly affected by
Inorganic Chemistry, Vol. 47, No. 3, 2008 893

Kojima et al.
Figure 10. ESR spectrum of two-electron oxidized species of 2
-
4
(
(
measured in frozen CH3CN at -150 °C): 2 (3.3 × 10 M) and [Ru-
-4
bpy)3](PF6)3 (6.6 × 10 M).
is about 1 Å longer than that of the original singlet state
6.656 Å for the distance between Ru(II) and Fe(II) in 1) as
(
shown in Figure 3. The dihedral angles changed, and larger
distortion was predicted between the amide plane and the
Cp plane. These structural change can be derived from the
electrostatic repulsion between more positively charged metal
centers (Ru(III) and Fe(III)) than those in 1. The spin density
at each metal center obtained by DFT calculations is shown
in Figure 8. The calculated values (+0.925 for Ru(III) and
+
1.397 for Fe(III)) suggest that the unpaired electrons are
mainly localized at the metal centers. The magnetic interac-
tion between Ru(III) and Fe(III) may occur through bonds
rather than through space. As shown in Figure 9, the
magnetization can be induced alternatively and the spins of
two unpaired electrons on both metal centers can com-
municate to form the triplet state. The hydrogen bonding
may play an important role to fix the structure of the
ferrocenoylamide moiety.
We also examined the two- and three-electron oxidations
3
+
Figure 7. (a) Temperature-dependent ESR spectral change for the two-
of 2 with [Ru(bpy)
3
]
3
in CH CN, and ESR measurements
-
3
electron oxidized form of 1 (2.0 × 10 M) in CH3CN in the temperature
range from 2.6 to 140 K. (b) Temperature dependence of IT of the two-
electron oxidized form of 1. The closed circles represent the experimental
data, and the dotted line is the curve-fit of the data to the Bleaney-Bowers
equation.
were undertaken at -150 °C. In the case of the two-electron
oxidation, the ESR spectrum of the reaction product ([Ru -
Cl(L2 )] ) exhibited signals at g ) 2.01 (∆m
III
+
3+
s
) 1) and g
)
4.11 (∆m ) 2) as shown in Figure 10. This spectrum
s
indicates that both the ruthenium and iron centers are
oxidized to form a triplet state as observed in 1. The
uncoordinated ferrocene moiety in 2 may be first oxidized
3
1
as indicated by the CV (vide supra).
In Scheme 2, we summarize the redox behavior of the
ruthenium complexes 1-3. Complex 1 exhibited two revers-
ible redox couples; the first one at 0.23 V is due to that of
the ferrocene moiety, and the second one at 0.77 V is for
the ruthenium center. Complex 2 exhibited an ill-resolved
two-electron redox couple for concomitant oxidation of Ru-
(II) center and the uncoordinated ferrocene moiety at 0.27
V, followed by the oxidation of the coordinated ferrocene
part at 0.46 V. Complex 3 exhibited stepwise three redox
couples for the uncoordinated Fc arm at 0.26 V followed by
the coordinated Fc arm at 0.37 V and the ruthenium center
at 0.83 V.
Figure 8. Optimized structure of the triplet state of two-electron oxidized
1
. All hydrogen atoms are omitted for clarity. Values in parentheses are
the spin density at each metal center.
Summary
We have synthesized and characterized novel ferrocene-
containing pyridylamine ligands and their Ru(II) complexes.
The two ferrocene-containing TPA ligands, L1 and L2, were
characterized by spectroscopic methods, electrochemical
measurements, and X-ray crystallography. The crystal struc-
Figure 9. Schematic description of superexchange interaction to cause
ferromagnetic coupling between Ru(III) and Fe(III) centers.
S ) 1 state. An optimized structure is given in Figure 8. In
the optimized structure, the separation between the Ru(III)
center and the Fe(III) center is estimated to be 7.523 Å, which
III
(
31) The product of the three-electron oxidation ([Ru Cl(L22+)]4+
)
exhibited weak ESR signals due to the residual signal of the two-
electron oxidized species at -150 °C.
894 Inorganic Chemistry, Vol. 47, No. 3, 2008

Ru Complexes with Ferrocene-Containing Pyridylamine Ligands
Scheme 2. Summary of Redox Behavior of 1-3a
a
1
AN represents the η -N acetonitrile ligand.
ture of the Ru(II) complex of L1, complex 1, was determined
to reveal that the uncoordinated ferrocenoylamide arm
strongly linked to the chloride ligand via intramolecular
hydrogen bonding. This complex exhibited two-step redox
The ferrocene-containing multidentate pyridylamine ligands
described here will provide new multiredox systems to
exhibit the intramolecular 4d-3d ferromagnetic coupling
between Ru(III) and Fe(III) centers. To our knowledge, this
is the first observation of intramolecular ferromagnetic
coupling in the transition metal complexes involving the
ferrocenium moiety.
+
processes ascribed to the Fc/Fc and Ru(II)/Ru(III) couples.
The Ru(II) complexes with L2, 2, and 3, were also prepared
and characterized by spectroscopic and electrochemical
methods. On the basis of the spectroscopic data, those
Acknowledgment. This work was supported in part by
a Grant-in-Aid (No. 165500567) from The Ministry of
Education, Culture, Sports, Science and Technology of Japan.
We thank Professor Hiroshi Kitagawa (Kyushu University)
for his kind support and helpful discussion. We appreciate
Dr. Yuichi Shimazaki (Institute for Materials Chemistry and
Engineering, Kyushu University) for his help in X-ray
crystallography. We also thank Professor Teruo Shinmyozu
(Institute for Materials Chemistry and Engineering, Kyushu
University) for his kind accommodation to use their NMR
spectrometer.
5
complexes have the amide-coordinating η -L2 with intramo-
lecular hydrogen bonding between the coordinated amide
oxygen and the uncoordinated amide N-H group, as
observed for other related bisamide-TPA complexes. The
redox behavior of the complexes is revealed to show
+
unresolved two Fc/Fc redox couples prior to that of the
Ru(II)/Ru(III) couple in the chloride complex, and the Fc/
+
Fc redox couples could be discriminated in the acetonitrile
complex.
+
]3 in CH
In the two-electron oxidation of 1 by [Ru(bpy)
3
3
-
CN, the formation of the triplet (S ) 1) species was observed.
Variable-temperature ESR spectroscopy allowed us to esti-
mate the intramolecular ferromagnetic coupling constant
Supporting Information Available: Crystallographic data for
L1 and 1 (CIF format), crystal packing of L1, variable-temperature
+
ESR of Fc -TPA in a frozen CH
3
CN solution, and a procedure to
III
+
3+
III
1
III
1
-1
estimate the peak intensity of [Ru Cl(Fc -TPA)(DMSO)] .
between Ru (S ) /
2 2
) and Fe (S ) / ) to be 13.7 cm .
This material is available free of charge via the Internet at
http://pubs.acs.org.
As for complex 2, two-electron oxidation took place at the
Ru(II) center and the uncoordinated ferrocenoylamide moiety
to give a triplet state, similar to that of 1.
IC7016038
Inorganic Chemistry, Vol. 47, No. 3, 2008 895