Syntheses of the terpyridine-bipyridine linked binary ligands and structural and redox properties of their cobalt complexes

Article abstract of DOI:10.1021/ic900932j

New binary ligands consisting of 2,2′:6′,2″-terpyridine and 2,2′-bipyridine were synthesized through the linkage of various lengths of the polymethylene chain (1a-1d; n=3-6, where n is the number of CH₂ units). Their Co(II) complexes, 2a-2d (Cl

Full text of DOI:10.1021/ic900932j

Inorg. Chem. 2009, 48, 8593–8602 8593
DOI: 10.1021/ic900932j
Syntheses of the Terpyridine-Bipyridine Linked Binary Ligands and Structural
and Redox Properties of Their Cobalt Complexes
Hiroki Kon and Toshi Nagata*
Research Center for Molecular Scale Nanoscience, Institute for Molecular Science, 5-1 Higashiyama, Myodaiji,
Okazaki 444-8787, Japan
Received May 14, 2009
New binary ligands consisting of 2,20:60,200-terpyridine and 2,20-bipyridine were synthesized through the linkage of
various lengths of the polymethylene chain (1a-1d; n=3-6, where n is the number of CH2 units). Their Co(II)
complexes, 2a-2d (Cl complexes) and 2a0-2d0 (H2O complexes), were synthesized. They exclusively formed
mononuclear complexes, which could be oxidized to Co(III) complexes in aqueous solutions after prolonged exposure
to the air. The single crystals of 2b and Co(III) complex 2c00 were obtained, and their crystal structures were
determined. Cyclic voltammograms of the Co(II) complexes showed the redox processes of the terpyridine, Co(II)/
Co(I), and Co(III)/Co(II). The redox waves of Co(II)/Co(I) in 2a and 2a0 were slightly different from those of other
complexes because of the short polymethylene chain.
Introduction
and to form “mixed-ligand” complexes.2 In these complexes,
the terpyridine ligands tune the various properties of the
complexes. The auxiliary ligands are often bidentate, so that
one of the octahedral coordination sites can be vacant and
utilized for catalytic reactions.
These mixed-ligand terpyridine complexes are synthesized
with various 4d and 5d metal ions such as ruthenium,
rhodium, osmium, and iridium.2 As for the 3d metal ions,
the mixed-ligand complexes should be more difficult to
isolate, because of the high tendency of ligand substitution
of 3d metals in comparison with that of the 4d and 5d metals.
Nevertheless, the mixed-ligand complexes of 3d metals
should be worth investigating, because they are likely to
present interesting characteristics hitherto unknown.
Polypyridyl ligands, such as 2,20:60,200-terpyridine (trpy),
2,20-bipyridine (bpy), and 1,10-phenanthroline (phen), are
intriguing ligands for constructing various photo- and redox-
active complexes.1 Among these, terpyridine derivatives are
particularly unique from the viewpoint of structural coordi-
nation chemistry. Because of their planar nature, the terpyr-
idine derivatives function almost exclusively as meridional
tridentate ligands, and the structural changes are restricted
when the oxidation state of the center changes. On the basis
of these characteristics, one effective use of terpyridine
ligands is to combine them with other “auxiliary” ligands
In order to synthesize the stable mixed-ligand complexes
with the substitution labile 3d metals, a certain artifice is
necessary in the ligand part. The most common approach
is to use small-ring (five- or six-membered) chelates involving
the metal ions; this approach generally gives metal complexes
with substantial chemical stability and conformational
rigidity.3 However, although these characteristics are useful
for physical applications such as electron transport or lumi-
nescence, they are less attractive when catalytic chemistry is
concerned, where conformational flexibility often plays an
important role. An alternative approach is to connect the
terpyridine and auxiliary ligands by polymethylene linkers.
In such “binary” ligands, the two different ligands are
*To whom correspondence should be addressed. E-mail: toshi-n@ims.ac.jp.
(1) (a) Schubert, U. S.; Hofmeier, H.; Newkome, G. R. Modern Terpyr-
idine Chemistry; Wiley-VCH: New York, 2006. (b) Flamigni, L.; Barigellentti, F.;
Armaroli, N.; Collin, J.-P.; Dixon, I. M.; Sauvage, J.-P.; Williams, J. A. G. Coord.
Chem. Rev. 1999, 190-192, 671–682. (c) Baranoff, E.; Collin, J.-P.; Flamigni,
L.; Sauvage, J.-P. Chem. Soc. Rev. 2004, 33, 147–155. (d) Sakai, K.; Ozawa, H.
Coord. Chem. Rev. 2007, 251, 2753–2766. (e) Herrero, C.; Lassalle-Kaiser, B.;
Leibl, W.; Rutherford, A. W.; Aukauloo, A. Coord. Chem. Rev. 2008, 252, 456–
468. (f) Wonters, K. L.; Tacconi, N. R.; Konduri, R.; Lezna, R. O.; MacDonnell, F.
M. Photosynth. Res. 2006, 87, 41–55. (g) Swiegers, G. F.; Malefetse, T. J. Chem.
Rev. 2000, 100, 3483–3538. (h) Huynh, M. H. V.; Meyer, T. J. Chem. Rev. 2007,
107, 5004–5064.
(2) (a) Kon, H.; Tsuge, K.; Imamura, T.; Sasaki, Y.; Ishizaka, S.;
Kitamura, N. Inorg. Chem. 2006, 45, 6875–6883. (b) Gagliardo, M.; Perelaer,
J.; Hartl, F.; van Klink, G. P. M.; van Koten, G. Eur. J. Inorg. Chem. 2007, 2111–
2120. (c) Ronco, S. E.; Thompson, D. W.; Gahan, S. L.; Petersen, J. C. Inorg.
Chem. 1998, 37, 2020–2027. (d) Yoshikawa, N.; Matsumura-Inoue, T.; Kanehisa,
N.; Kai, Y.; Takashima, H.; Tsukahara, K. Anal. Sci. 2004, 20, 1639–1644. (e)
Pruchnik, F. P.; Robert, F.; Jeannin, Y.; Jeannin, S. Inorg. Chem. 1996, 35, 4261–
4263. (f) Hyslop, A. G.; Orphanide, M.; Javed, U.; Megehee, E. G. Inorg. Chim.
Acta 2003, 355, 272–279. (g) Aragazzi, R.; Bertolasi, E.; Chiorboli, C.; Bignozzi,
C. A.; Itokazu, M. K.; Iha, N. Y. M. Inorg. Chem. 2001, 40, 6885–6891.
(3) (a) Comba, P.; Kerscher, M.; Lawrance, G. A.; Martin, B.; Wadepohl,
H.; Wunderlich, S. Angew. Chem., Int. Ed. 2008, 47, 4740–4743. (b)
McCleverty, J. A.; Meyer, T. J. Comprehensive Coordination Chemistry II;
Elsevier: New York, 2004; Volume 6.
r
2009 American Chemical Society
Published on Web 08/13/2009
pubs.acs.org/IC

8594 Inorganic Chemistry, Vol. 48, No. 17, 2009
Scheme 1. Synthetic Routes for 1a-1d
Kon and Nagata
arranged closely so that the construction of mixed-ligand
complexes is made easy and, at the same time, the connection
is flexible enough for the complex to acclimate to the change
of the chemical environments.
Among the 3d metals, we are currently interested in cobalt
complexes. There are very few examples of mixed-ligand
cobalt complexes containing terpyridines,4 so that binary
ligands should be effective. In our previous work, we synthe-
sized the terpyridine-catechol-Co(III) complexes and
discussed their structural and redox properties.5 However,
we would also like to work with Co(II) and Co(I) complexes,
because Co(II) and Co(I) complexes exhibit various interest-
ing chemistries, such as hydrogen production, the formation
of metal-carbon bonds, reversible O2 adsorption, and so
on.6 On the other hand, the mixed-ligand Co(II) (and Co(I))
complexes pose a greater challenge than the Co(III) com-
plexes, because these ions are more labile toward ligand
substitution than Co(III).
In this paper, we wish to report the syntheses of new
terpyridine-based binary ligands, 1a-1d, and their Co(II)
complexes, 2a-2d and 2a0-2d0. We use bipyridine as the
auxiliary ligand, which is more suitable for Co(II) systems
than catechol. Because the bipyridine and terpyridine are
used, the ligands act as the penta-dentate ligands, and one
coordination site will be vacant. As we will see later, the
ligand exchange at this site is crucial for the redox properties
of the complexes. The crystal structures and redox properties
of these complexes are also reported.
(4) (a) Zhu, T.; Jackson, W. G. Wuji Huaque Xuebao 2000, 16, 485–491.
(b) Ramprasad, D.; Gilicinski, A. G.; Markley, T. J.; Pez, G. P. Inorg. Chem. 1994,
33, 2841–2847.
Results and Discussion
(5) Nagata, T.; Tanaka, K. Inorg. Chem. 2000, 39, 3515–3521.
Ligand Design. The binary ligands 1a-1d (Scheme 1)
consist of the terpyridine and bipyridine units linked by
polymethylene linkers of various lengths, which enables
the change in the distance between the terpyridine and
bipyridine units. The 1,2-phenylene group at the 40 posi-
tion of terpyridine acts as a fulcrum for the polymethylene
linker and allows the conformational variation of the
ꢀ
(6) (a) Colon, C. M.; Guadalupe, A. R. Electroanalysis 1998, 10, 621–627.
(b) Kellett, R. M.; Spiro, T. G. Inorg. Chem. 1985, 24, 2373–2377. (c) Koelle, U.;
Paul, S. Inorg. Chem. 1986, 25, 2689–2694. (d) Collman, J. P.; Brauman, J. I.;
Doxsee, K. M.; Halbert, T. R.; Hayes, S. E.; Suslick, K. S. J. Am. Chem. Soc.
1978, 100, 2761–2766. (e) Uruma, K.; Tsuge, K.; Sasaki, Y.; Imamura, T. Chem.
Lett. 2005, 34, 474–475. (f) Suzuki, M.; Kanatomi, H.; Murase, I. Bull. Chem.
Soc. Jpn. 1984, 57, 36–42. (g) Samsel, E. G.; Kochi, J. K. Inorg. Chem. 1986, 25,
ꢀ
2450–2457. (h) Saveant, J.-M. Chem. Rev. 2008, 108, 2348–2378.

Article
Inorganic Chemistry, Vol. 48, No. 17, 2009 8595
Scheme 2. Syntheses of Co(II) Complexes 2a-2d and 2a0-2d0
linker via the rotation along the phenylene-terpyridine
bond.7 The carboxylic ester group on the phenylene ring
is intended for a connection of yet another functional
group with additional capability (such as photoactivity).
As a side effect, we later found that this group was
also useful in restricting the conformation of the poly-
methylene linker.
The compounds 1a-1d are designed with synthetic
versatility in mind. The precursors of 1a-1d are
11a-11d, which have a tert-butoxycarbonyl (Boc) pro-
tected amino group at the end of the polymethylene
linker, and the ester-protected carboxylic acid at the
phenylene group. Consequently, various derivatives of
11a-11d can be easily made by well-established synthetic
methods of amino acids.8
Ligand Syntheses. The synthetic route of the binary
ligands, 1a-1d, is shown in Scheme 1. The key step is the
introduction of the diprotected phenyl group at the
40 position of terpyridine by the Suzuki-Miyaura cou-
pling of 5 and 6.9 In our first attempt, we followed the
procedure that we used in our previous work5 (Pd(OAc)2/
P(o-tol)3/Na2CO3/toluene/H2O/MeOH); however, only
a trace amount of 7 was obtained together with un-
changed 5 and the hydrolyzed product 4. After optimiza-
tion of the reaction conditions, the best results were
obtained when Pd(PPh3)4/S-Phos10 and KF/Na2CO3
were used as the catalyst and the base, respectively. Under
these conditions, product 7 was obtained very effectively
and reproducibly.
metal-based oxidants should be avoided if possible, be-
cause the formation of terpyridine-metal complexes
might complicate the workup process. The reagents of
choice were I2 and KOH,11,12 with careful control of the
reaction temperature (see the Experimental Section).
The syntheses of the binary ligands were completed by
the deprotection of t-butoxycarbonyl group and the
condensation with 2,20-bipyridine-4-carboxylic acid
(13). The binary ligands 1a-1d were purified by column
chromatography and recrystallization and obtained as
analytically pure, crystalline solids.
Syntheses of the Co(II) Complexes. The cobalt(II) com-
plexes, 2a-2d and 2a0-2d0, were prepared from 1a-1d
by treatment with CoCl2 6H2O and Co(NO3)2 6H2O,
3
3
respectively (Scheme 2). The compounds 2a-2d were
chloro complexes, whereas 2a0-2d0 were aqua complexes.
These complexes were mononuclear complexes with
1:1 (metal/ligand) stoichiometry; neither the multinuclear
complexes nor complexes with multiple ligands (like
bis-terpyridine) were produced, as proven by the electro-
spray ionization (ESI)-mass spectrometry (vide infra).
Recrystallization of 2b was performed by the diffusion
of CH3CN/MeOH over several weeks, and single crystals
of [Co(1b)Cl](PF6) 2CH3OH (2b 2CH3OH) were ob-
3
3
tained. On the other hand, when recrystallization of 2c
was performed through the slow evaporation of a
CH3CN/H2O mixed solvent over a few months, the
obtained crystals were the Co(III) complexes, [Co(1c)-
OH](PF6)2 H2O (2c00 H2O), as proven by the X-ray
3
3
Another step worth mentioning is the conversion of the
formyl group to the carboxylic ester group (i.e., 10 to 11).
It was necessary that this reaction proceeded without the
deprotection of the Boc group. In addition, the use of
crystallographic analysis and ESI-mass spectrometry
(vide infra). We assume that the oxidation took place
during the prolonged exposure to the air. In fact, when a
basic solution of 2c0 in EtOH/H2O was exposed to O2 for
1 day, the same Co(III) complex 2c00 was generated.
Structures of the Co Complexes. The crystal structures
of 2b and 2c00 are shown in Figures 1 and 2. Details of the
crystallographic parameters and the structure refine-
ments are listed in Table 1, and the selected bond dis-
tances and angles are given in Table 2.
(7) Bonnet, S.; Collin, J.-P.; Sauvage, J.-P. Inorg. Chem. 2007, 46, 10520–
10533.
(8) There are reports of artificial “amino acids” containing metal-terpyr-
idine complexes: (a) Ohr, K.; McLaughlin, R. L.; Williams, M. E. Inorg.
Chem. 2007, 46, 965–974. (b) Heinze, K.; Hempel, K. Chem.;Eur. J. 2009, 15,
1346–1358.
(9) (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457–2483. (b) Wolfe,
J. P.; Singer, R. A.; Yang, B. H.; Buchwald, S. L. J. Am. Chem. Soc. 1999, 121,
9550–9561. (c) Grosshenny, V.; Romero, F. M.; Ziessel, R. J. Org. Chem. 1997,
62, 1491–1500. (d) Goodall, W.; Wild, K.; Arm, K. J.; Williams, J. A. G. J. Chem.
Soc., Perkin Trans. 2 2002, 1669–1681.
These two compounds were mononuclear Co com-
plexes with six-coordinate octahedral geometry. It is
notable that, in both structures, the Co center binds two
(10) (a) Walker, S. D.; Barder, T. E.; Martinelli, J. R.; Buchwald, S. L.
Angew. Chem., Int. Ed. 2004, 43, 1871–1876. (b) Ishikawa, S.; Manabe, K.
Chem. Lett. 2006, 35, 164–165.
(11) Inch, T. D.; Ley, R. V.; Rich, P. J. Chem. Soc. C 1968, 1693–1699.
(12) Yamada, S.; Morizono, D.; Yamamoto, K. Tetrahedon Lett. 1992,
33, 4329–4332.

8596 Inorganic Chemistry, Vol. 48, No. 17, 2009
Kon and Nagata
Table 1. Crystallographic Data for 2b 2CH3OH and 2c00 H2O
3
3
2b 2CH3OH
3
2c00 H2O
3
formula
Mw
C40H40N6O6CoClPF6 C39H37N6O6CoP2F12
940.14
-100
1034.62
-100
triclinic
P1
temp/°C
crystal system
space group
monoclinic
P21/n
˚
a/A
18.270(14)
8.975(7)
24.559(19)
90
95.662(13)
90
4007(5)
4
6.913
12.100(5)
13.696(6)
14.426(6)
111.920(5)
90.574(4)
108.828(2)
2075.8(15)
2
˚
b/A
˚
c/A
R/deg
β/ deg
γ/ deg
3
˚
V/A
Z
μ/cm-1
6.005
1.655
14219
dcalcd/g cm-3
1.558
no. obsd reflns (I > 2σ(I)) 22158
no. unique reflns (Rint
no. params
GOF
)
8426 (0.037)
581
1.037
0.0647, 0.1505
8943 (0.018)
628
1.199
R1, wR2
0.0580, 0.1405
˚
Table 2. Selected Bond Distances (A) and Angles (deg) for 2b 2CH3OH and
3
2c00 H2O
3
2b 2CH3OH
3
2c00 H2O
3
bond distances
Co1-Cl1
Co1-N1
Co1-N2
Co1-N3
Co1-N4
Co1-N5
2.4318(5)
Co1-O5
Co1-N1
Co1-N2
Co1-N3
Co1-N4
Co1-N5
1.9023(14)
1.9491(17)
1.8563(19)
1.9502(19)
1.938(2)
2.1832(14)
2.0763(15)
2.1875(14)
2.1095(17)
2.1499(14)
Figure 1. ORTEP drawing of the complex cation of 2b: (a) overall view
and (b) side view from the Co-N4 axis.
1.9626(17)
bond angles
Cl1-Co1-N1
Cl1-Co1-N2
Cl1-Co1-N3
Cl1-Co1-N4
Cl1-Co1-N5
N1-Co1-N2
N1-Co1-N3
N1-Co1-N4
N1-Co1-N5
N2-Co1-N3
N2-Co1-N4
N2-Co1-N5
N3-Co1-N4
N3-Co1-N5
N4-Co1-N5
93.76(3)
93.04(4)
93.08(3)
94.76(4)
170.52(4)
75.44(5)
150.10(5)
101.71(6)
90.18(5)
75.15(5)
171.87(5)
96.30(5)
106.68(6)
87.75(5)
75.98(6)
O5-Co1-N1
O5-Co1-N2
O5-Co1-N3
O5-Co1-N4
O5-Co1-N5
N1-Co1-N2
N1-Co1-N3
N1-Co1-N4
N1-Co1-N5
N2-Co1-N3
N2-Co1-N4
N2-Co1-N5
N3-Co1-N4
N3-Co1-N5
N4-Co1-N5
91.02(7)
91.69(7)
88.16(7)
90.39(7)
172.58(7)
82.36(7)
164.54(8)
97.24(8)
91.40(7)
82.26(8)
177.89(7)
95.58(7)
98.21(8)
91.36(7)
82.33(8)
different polypyridyl ligands (terpyridine and bipyridine).
Although such structures are commonly observed in 4d
and 5d metals,13 they are less common in 3d metals. In
fact, only two such complexes are known for cobalt.4b
Obviously, this demonstrates the advantage of the binary
ligands.
(13) (a) Hecker, C. R.; Fanwick, P. E.; McMillin, D. R. Inorg. Chem.
1991, 30, 659–666. (b) Stagni, S.; Palazzi, A.; Zacchini, S.; Ballarin, B.; Bruno,
C.; Marcaccio, M.; Paolucci, F.; Monari, M.; Carano, M.; Bard, A. J. Inorg.
Chem. 2006, 45, 695–709. (c) Rasmussen, S. C.; Ronco, S. E.; Mlsna, D. A.;
Billadeau, M. A.; Pennington, W. T.; Kolis, J. W.; Petersen, J. D. Inorg. Chem.
1995, 34, 821–829. (d) Demadis, K. D.; Neyhart, G. A.; Kober, E. M.; White, P.
S.; Meyer, T. J. Inorg. Chem. 1999, 38, 5948–5959. (e) Coia, G. M.; White, P. S.;
Meyer, T. J.; Wink, D. A.; Keefer, L. K.; Davis, W. M. J. Am. Chem. Soc. 1994,
::
116, 3649–3650. (f) Seok, W. K.; Lee, H. N.; Kim, M. Y.; Klapotke, T. M.; Dong,
Y.; Yun, H. J. Organomet. Chem. 2002, 654, 170–175. (g) Kim, M. Y.; Seok, W.
K.; Dong, Y.; Yun, H. Inorg. Chim. Acta 2001, 319, 194–198.
Figure 2. ORTEP drawing of the complex cation of 2c00: (a) overall view
and (b) side view from the Co-N4 axis.

Article
Inorganic Chemistry, Vol. 48, No. 17, 2009 8597
˚
The average bond length of Co-N in 2b was 2.14 A,
whereas in 2c00, the average bond length of N-Co
was 1.93 A. This difference strongly suggests that the
˚
valence of cobalt is different, namely, Co(II) in 2b and
Co(III) in 2c00. Indeed, the individual bond lengths and
angles of CoII(trpy) and CoII(bpy) moieties in 2b were
consistent with those of previously reported complexes,
respectively.14 Similarly, the bond lengths and angles of
2c00 were consistent with those of CoIII(trpy) or CoIII-
(bpy).14b,14c,15 The bond length of Co-Cl (2.4318 A)
˚
is also consistent with other Co(II) complexes (2.37-
2.46 A).14d,16 On the other hand, the Co-O bond length
˚
00
˚
in 2c is 1.9023(14) A, which is close to the distance of
17
˚
Co(III)-OH (1.89-1.90 A)
rather than that of
18
˚
Co(III)-OH2 (1.93-1.95 A). This indicates that the
sixth ligand coordinating to the Co ion is not aqua but
hydroxo. The formulation of Co(III)-OH requires that
the complex cation has a þ2 charge, which is consistent
with the observed crystallographic unit cell, including two
PF6- anions per complex cation.
Figure 3. Partial structures of (a) 2b and (b) 2c00, showing the deforma-
tion of the 40-phenylene ring from the terpyridine plane.
ESI-Mass Spectra. The ESI-mass spectra of these com-
plexes measured in CH3CN showed the characteristic
dependence on the “sixth” ligand (see the Supporting
Information, Figure S1). The spectrum of 2a shows only
one major peak at m/z=716, and the isotope patterns are
consistent with the theoretical patterns calculated for 2a
([CoII(1a)Cl]þ). In addition, other fragment peaks at m/z=
340.5, 358, and 361 are the divalention peaks, and the mass
numbers and the isotope patterns are consistent with
Apart from the differences of the Co-N distances, the
overall structures of Co(trpy)(bpy) moieties are very similar
for 2band 2c00. However, there arecharacteristic differences
in the structures of the linker part, which are attributed to
the different lengths of the polymethylene chains. First, the
plane of the amide bond (-NHCO-) in 2b is tilted in the
opposite direction from the 40-phenylene ring, but in 2c00
they are in the same direction (Figures 1b and 2b). This is
because the distance between the two termini of the poly-
[CoII(1a)]2þ, [CoII(1a)Cl]2þ, and [CoII(1a)(CH3CN)]2þ
,
˚
methylene chain (N6-O2) is shorter in 2b (5.156 A, four
respectively. The mass numbers and peak patterns of 2a0
are also consistent with its theoretical patterns. The main
divalent ion peak at m/z=340.5 is [CoII(1a)]2þ, and other
fragment peaks at m/z = 361 and 826 are [CoII(1a)-
(CH3CN)]2þ and [CoII(1a)(PF6)]þ, respectively. The dif-
ference in the major peak can be reasonably explained
since the neutral H2O ligand in 2a0 is more easily detached
from the complex than the anionic chloro ligand in 2a.
Importantly, the ESI-mass spectra of all these complexes
showed only one major peak corresponding to the mono-
nuclear complex; that is, the dinuclear or higher multi-
nuclear complexes were not produced.
00
˚
methylenes) than in 2c (5.428 A, five methylenes).
Second, the para-carbon atom of the 40-phenylene ring
was bent out of the terpyridine plane, and the displace-
ment was larger in 2c00 than that in 2b (Figure 3). The out-
of-plane distances of the C29 atom from the central
˚
pyridyl ring of the terpyridine were 0.1724 A and
00
˚
0.5030 A in 2b and 2c , respectively. Such a difference is
caused by the C5 chain in 2c00 requiring more space than
the C4 chain in 2b. These facts indicate that a small
difference in the length of the polymethylene chain of
only one carbon can result in significant modification of
the structures of these complexes.
The Co(III) complex, [CoIII(1c)(OH)](PF6)2 (2c00), was
confirmed with ESI-mass spectrometry. The transition of
ESI-mass spectra from 2c0 to 2c00 is shown in Figure 4.
Figure 4a-c represent the spectrum of 2c0, the spectrum
after theexposure of2c0 to O2 gasfor12 h, and the spectrum
of 2c00, respectively.19 In Figure 4a, the major peak at m/z=
354.5 corresponds to the fragment peak of [CoII(1c)]2þ
and the peak at m/z=854 to [CoII(1c)(PF6)]þ. Figure 4b
shows the peaks at m/z=354.5, 363, 770, and 787, which
are assigned to the fragments [CoII(1c)]2þ, [CoIII(1c)-
(OH)]2þ, [CoII(1c)(NO3)]þ, and [CoIII(1c)(OH)(NO3)]þ,
respectively. Finally, the spectrum of Figure 4c shows the
peaks derived from 2c00 at m/z= 363 and 871, which are
assigned to [CoIII(1c)(OH)]2þ and [CoIII(1c)(OH)(PF6)]þ,
respectively.
~
(14) (a) Gaspar, A. B.; Munoz, M. C.; Niel, V.; Real, J. A. Inorg. Chem.
2001, 40, 9–10. (b) Indumathy, R.; Radhika, S.; Kanthimathi, M.; Weyhermuller,
T.; Nair, B. U. J. Inorg. Biochem. 2007, 101, 434–443. (c) Yu, Z.; Nabei, A.;
Izumi, T.; Okubo, T.; Kuroda, T. Acta Crystallogr., Sect. C 2008, 64, m209–
m212. (d) Jouaiti, A.; Jullien, V.; Hosseini, M. W.; Planeix, J.-P.; Cian, A. Chem.
Commum. 2001, 1114–1115. (e) Szalda, D. J.; Creutz, C.; Mahajan, D.; Sutin, N.
Inorg. Chem. 1983, 22, 2372–2379. (f) Papadopoulos, C. D.; Hatzidimitriou, A.
Z.; Voutsas, G. P.; Lalia-Kantouri, M. Polyhedron 2007, 26, 1077–1086. (g)
Deng, R. M. K.; Bilton, C.; Dillon, K. B.; Howard, J. A. K. Acta Crystallogr.,
Sect. C 2000, 56, 142–145.
(15) (a) Jitsukawa, K.; Hata, T.; Yamamoto, T.; Kano, K.; Masuda, H.;
Einaga, H. Chem. Lett. 1994, 1169–1172. (b) Matthews, C. J.; Elsegood, M. R.;
Bernardinelli, G.; Clegg, W.; Williams, A. F. Dalton Trans. 2004, 492–497.
ꢀ
(16) (a) Hayami, S.; Hashiguchi, K.; Juhasz, G.; Ohba, M.; Okawa, H.;
Maeda, Y.; Kato, K.; Osaka, K.; Takata, M.; Inoue, K. Inorg. Chem. 2004,
::
€
43, 4124–4126. (b) Desroches, C.; Ohrstrom, L. Acta. Crystallogr., Sect. C
::
€
All of these results show the exclusive formation of the
1:1 (metal/ligand) complexes. This is ascribed to an
2007, 63, m190–m192. (c) Larsson, K.; Ohrstrom, L. Inorg. Chim. Acta 2004,
357, 657–664.
(17) (a) Poth, T.; Paulus, H.; Elias, H.; Eldik, R.; Grohmann, A. Eur. J.
Inorg. Chem. 1999, 643–650. (b) Kucharski, E. S.; Skelton, B. W.; White, A. H.
Aust. J. Chem. 1978, 31, 47–51.
(19) Figure 4a and c show the spectra of 2c0 and 2c00, which were isolated
Co(II) and Co(III) complexes as PF6 salts, respectively. The spectrum of
(18) (a) Failes, T. W. Acta. Crystallogr., Sect. E 2004, 60, m781–m782. (b)
Bombieri, G.; Polo, A.; Benetollo, F.; Tobe, M. L.; Humanes, M.; Chatterjee, C.
Acta Crystallogr., Sect. C 1987, 43, 1866–1869.
Figure 4b was measured by the reaction mixture of Co(NO3)2 6H2O and 1c
3
in EtOH/H2O directly.

8598 Inorganic Chemistry, Vol. 48, No. 17, 2009
Kon and Nagata
Figure 5. Cyclic voltammograms for (a) 2a-2d and (b) 2a0-2d0.
larger internal freedom has a stronger tendency to form
the 2:2 or higher complexes in preference to the 1:1
complex. The methoxycarbonyl group in 1a causes
restriction on the conformation of the polymethylene
linker in comparison with 14a, which is beneficial for the
formation of the 1:1 complex. This kind of “remote”
control is a novel concept for designing metal complexes
and will be useful in constructing complicated metal-
containing systems.
Figure 4. ESI-mass spectra of (a) 2c0, (b) after the exposure of 2c0 to O2
gas for 12 h, and (c) 2c00.
entropy effect, because the formation of the 1:1 complex
generally causes a smaller loss of entropy than the for-
mation of 2:2 or higher complexes. This entropy effect
may be offset by the loss of enthalpy when the poly-
methylene chain is too short and the formation of a
mononuclear complex causes large intramolecular strain.
However, in the case 1a-1d, such offsets by the enthalpy
term should be small, given the observation of only the
mononuclear complexes.
On the other hand, we encountered an interesting
observation when we examined the variant binary ligand
14a, which lacks the methoxycarbonyl group adjacent to
the polymethyleneoxy group. When 14a was allowed to
Cyclic Voltammograms. The cyclic voltammograms
(CVs) of 2a-2d and 2a0-2d0 are shown in Figure 5, and
the redox potentials are listed in Table 3.
For 2a, only one reversible wave at -1.72 V and
irreversible and quasi-reversible waves around -1.4 V
and -0.2 V were observed. The reversible wave was
assigned to the redox process of terpyridine, and the
others were assigned to the redox couples Co(II)/Co(I)
and Co(III)/Co(II). These potentials were consistent with
those of analogous compounds, such as [Co(trpy)2]2þ and
[Co(bpy)3]2þ in previous literature reports.14f,22 The CVs
of 2b-2d showed very similar waves as 2a, except that the
waves at -1.3 V were quasi-reversible in 2b-2d and was
distinctly irreversible in 2a. These differences are ascribed
to the different response to the change of the oxidation
state of the Co center, which is caused by the differences
of the length of the polymethylene linker. Before the
reduction of the complexes, the coordination geometry
of the Co(II) center is six-coordinate octahedral.23 On the
other hand, the coordination geometry of Co(I) com-
plexes is generally four-coordinate tetrahedral or five-
coordinate bipyramidal.3b Accordingly, after the reduc-
tion of Co(II) to Co(I), the coordination geometry was
generally expected to change. The Co(II) mononuclear
react with CoCl2 6H2O, a 2:2 complex, 15a ([(Co(14a)-
3
Cl)2](PF6)4), was obtained (the chemical structures of
14a and 15a and the preliminary crystal structure of
15a are shown in the Supporting Information).20 Further-
more, the fragment peaks derived from the 2:2 complex
were observed in the ESI-mass spectrum.21 This striking
difference between 1a and 14a is likely to be caused by
the degree of internal freedom of the metal-free ligand.
When the ligand has a large internal freedom (like poly-
methylene linkers in 1a-1d and 14a), the formation of the
1:1 complex will cause a significant loss of entropy due to
the restriction of the internal movement, and the loss will
be much larger for the 1:1 complex than the higher
complexes. Therefore, it is possible that the ligand with
~
(22) (a) Arana, C.; Yan, S.; Keshavarz-K, M.; Potts, K.; Abruna, H. D.
Inorg. Chem. 1992, 31, 3680–3682. (b) Yoshida, T.; Iida, T.; Shirasagi, T.; Lin, R.
J.; Kaneko, M. J. Electroanal. Chem. 1993, 344, 355–362. (c) Ruminski, R. R.;
(20) Although the high-quality crystals could not be obtained, the crystal
structure of 15a was observed as the dinuclear complex. See Figure S2 and
Tables S1 and S2 in the Supporting Information.
ꢀ
Petersen, J. D. Inorg. Chim. Acta 1985, 97, 129–134. (d) Plonska, M. E.; Dubis,
e
A.; Winkler, K. J. Electroanal. Chem. 2002, 526, 77–84.
(21) Among the observed signals, the following peaks were attributed to
(23) The rþesting potentials were ca. -0.3 V (vs Fc/Fcþ, 2a-2d) and -0.2
fragments derived from [(Co(14a)Cl2)]: 328.5, [(Co(14a)Cl)2]4þ
;
438,
V (vs Fc/Fc , 2a0-2d0), and the oxidation waves of Co(III)/Co(II) were
observed at the first sweep to the positive potential. These facts indicate that
the valence of Co is divalent.
[(Co(14a)Cl)2]3þ; 735.5, [(Co(14a)(CH3CN))2Cl(PF6)]2þ; 753, [(Co(14a)-
(CH3CN))2(PF6)]2þ. See Figure S3 (Supporting Information).

Article
Inorganic Chemistry, Vol. 48, No. 17, 2009 8599
Table 3. Redox Potentials of the Complexes. (V vs. Fc/Fcþ)
trpy0/-
CoII/I
CoIII/II
E1/2
Epc
Epa
Epc
Epa
(ΔEp)
(ΔEp)
(ΔEp)
2a
2b
2c
-1.72
(0.07)
-1.74
(0.07)
-1.74
(0.07)
-1.74
(0.07)
-1.72
(0.07)
-1.73
(0.07)
-1.74
(0.07)
-1.74
(0.07)
-1.46
-1.45
-1.45
-1.43
-1.30
-1.27
-1.24
-1.21
-1.35, -1.18
-1.27
-0.28
-0.29
-0.29
-0.28
-0.19
-0.21
-0.23
-0.25
-0.08
-0.09
-0.04
0.00
(0.20)
(0.20)
(0.25)
(0.28)
(0.63)
(0.71)
(0.81)
(0.96)
(0.18)
(0.21)
(0.23)
-1.24
2d
2a0
2b0
2c0
2d0
-1.20
-1.23, -1.11
-1.20
0.44
0.50
(0.07)
(0.08)
(0.09)
-1.16
0.58
-1.12
0.71
complex 2a was not suitable for the structural change
following the reduction, whereas 2b-2d were more adap-
tive for the structural change because of the longer methy-
lene chain. This argument is consistent with the observation
that the redox wave of 2a around -1.4 V was irreversible,
whereas the corresponding waves of 2b-2d were quasi-
reversible. On the other hand, the voltammograms re-
mained almost unchanged after several cycles, suggesting
that these complexes were chemically invariable during the
redox processes. The peak-to-peak separations (ΔEp) for
the Co(II)/Co(I) couples (except for 2a) and the Co(III)/
Co(II) couples become larger with longer polymethylene
chains. The larger ΔEp corresponds to slower electron
transfer, which is likely to be caused by the large structural
change of the longer polymethylene chain.
The CVs of 2a0-2d0 show similar trends to those of
2a-2d. The notable difference was that the redox potentials
for the Co(II)/Co(I) and Co(III)/Co(II) couples were
slightly shifted to the positive, reflecting the difference in
the ligand, chloro or aqua. In the CV of 2a0, the redox wave
at -1.2 V was irreversible, as with 2a. This is also attributed
to the short length of the polymethylene chain. The ΔEp’s
for the Co(III)/Co(II) couples of 2a0-2d0 are much larger
than those of 2a-2d. Such differences can be explained by
assuming that the oxidation of the Co(II)-OH2 complex is
accompanied by deprotonation to give the Co(III)-OH
complex. This interpretation is also consistent with the ob-
servation of the Co(III)-OH complex described above. The
voltammograms of 2a0-2d0 were also invariant after several
cycles, suggesting that the proton-coupled redox process
(Co(III)-OH/Co(II)-OH2) is chemically reversible.
In summary, we synthesized binary ligands consisting
of terpyridine and bipyridine groups linked with poly-
methylene chains. These ligands exclusively formed
1:1 complexes with Co(II) ion, and the redox properties
were consistent with the linker lengths. These character-
istics will be useful for constructing complicated, multi-
molecular systems containing metal complexes.
prepared according to literature procedures: 40-((trifluorome-
thanesulfonyl)oxy)-2,20:60,200-terpyridine (6),24 t-butoxycarbony-
laminopropyl bromide (9a),25 t-butoxycarbonylaminoalkyl me-
sylate (9b-9d),26 and 2,20-bipyridine-4-carboxylic acid (13).27
1H NMR spectra were measured at room temperature with a
JEOL LA400 spectrometer. ESI-mass spectra were recorded on
a Waters Micromass LCT.
Ligand Syntheses. 2-(Methoxymethoxy)benzaldehyde (3). A
solution of salicylaldehyde (17.5 g, 0.14 mol) in N,N-dimethyl-
formamide (DMF; 20 mL) was added dropwise to a suspension
of NaH (6.4 g, 0.16 mol) in dry tetrahydrofuran (THF; 20 mL) at
0 °C with stirring. After 30 min, a solution of chloromethyl
methyl ether (18.3 mL, 0.16 mmol) in dry THF (40 mL) was
added dropwise to the solution kept at 0 °C with stirring. After
2 h, hexane was added, and the mixture was washed with H2O
and then washed thrice with NaOH (aq., 20%). The organic
phase was separated, dried over Na2SO4, evaporated, and dried
in a vacuum. Yield: 22.6 g (0.136 mol, 98%). 1H NMR (CDCl3):
δ 10.48 (s, 1H, -CHO), 7.81 (dd, 1H, 3JH,H=7.6 Hz, 4JH,H
=
1.6 Hz, 6-Ar), 7.50 (dt, 1H, 3JH,H=7.6 Hz, 4JH,H=2.0 Hz, 4-Ar),
7.19 (d, 1H, 3JH,H=8.4 Hz, 3-Ar), 7.05 (t, 1H, 3JH,H=7.2 Hz,
5-Ar), 5.28 (s, 2H, -OCH2O-), 3.49 (s, 3H, -OCH3).
2-(2-Methoxymethoxyphenyl)-5,5-dimethyl-1,3-dioxane (4).
A mixture of 3 (6.73 g, 40.4 mmol), 2,2-dimethyl-1,3-propane-
diol (6.73 g, 64.6 mmol), and p-toluenesulfonic acid monohy-
drate (407.1 mg, 2.14 mmol) in CH2Cl2 was stirred for 30 min
at room temperature. The resulting solution was washed
with saturated NaHCO3 (aq.), dried over Na2SO4, and evapo-
rated. The pale yellow oil was dried in a vacuum. Yield: 9.37 g
(37.2 mmol, 92%). 1H NMR (CDCl3): δ 7.65 (dd, 1H, 3JH,H
=
8.0 Hz, JH,H = 1.6 Hz, 6-Ar), 7.26 (dt, 1H, JH,H = 8.0 Hz,
4
3
3
3JH,H=1.6 Hz, 4-Ar), 7.06 (d, 1H, JH,H=7.2 Hz, 3-Ar), 7.03
3
(t, 1H, JH,H=7.2 Hz, 5-Ar), 5.77 (s, 1H, acetal-CH), 5.18 (s,
2H, -OCH2O-), 3.70 (ABquartet, 4H, 4JH,H=11.2 Hz, acetal-
CH2), 3.47 (s, 3H, -OCH3), 1.31 (s, 3H, acetal-Me), 0.77 (s, 3H,
acetal-Me).
3-(4,4-Dimethyl-2,6-dioxacyclohexyl)-2-methoxymethoxyphe-
nylboronic Acid (5). A 1.6 M hexane solution of n-BuLi (33 mL,
52.8 mmol) was added dropwise to the solution of 4 (9.17 g,
36.4 mmol) in dry THF (80 mL) at 0 °C under N2. After 3 h of
(24) Potts, K. T.; Konwar, D. J. Org. Chem. 1991, 56, 4815–4816.
(25) Gothard, C. M.; Rao, N. A.; Nowick, J. S. J. Am. Chem. Soc. 2007,
129, 7272–7273.
Experimental Section
(26) Kim, T. W.; Park, J.; Hong, J.-I. J. Chem. Soc., Perkin Trans. 2 2002,
923–927.
(27) Panetta, C. A.; Kumpaty, H. J.; Heimer, N. E.; Leavy, M. C.;
Hussey, C. L. J. Org. Chem. 1999, 64, 1015–1021.
General. Reagents were purchased from Wako, Nacalai,
and Aldrich. All reagents were used without further purifica-
tion unless otherwise noted. The following compounds were

8600 Inorganic Chemistry, Vol. 48, No. 17, 2009
Kon and Nagata
stirring at 0 °C, triisopropyl borate (16 mL, 69.3 mmol) was
added at once to the mixture and stirred for 2 h. The solution of
NH4Cl (9 g, 168 mmol) in H2O (90 mL) was added to the
resulting solution, and the mixture was stirred for 12 h at room
temperature. The organic phase was separated, and the aqueous
phase was extracted with ethyl acetate. The organic solutions
were combined and dried over Na2SO4. Evaporating the solvent
gave pale yellow oil, and hexane was added to this oil with
stirring. The resulting mixture was left to stand in a freezer
overnight. The white crystals were collected by filtration and
washed with hexane. This compound should be kept in a freezer
because it slowly decomposes at room temperature. Yield: 6.16 g
CH2Cl2 and NaHSO3 (aq.) were added, and the separated
organic phase was further washed with NaHSO3 (aq.) and
H2O. The organic phase was dried over Na2SO4, evaporated,
and dried in a vacuum. The purification was performed by
chromatography on an alumina column with CH2Cl2/hexane.
Yield: 561.8 mg (1.04 mmol, 69%). Anal. Found: C, 68.80; H,
5.80; N, 10.28%. Calcd for C31H32N4O5: C, 68.87; H, 5.97; N,
10.36%. 1H NMR (CDCl3): δ 8.72 (s, 2H, trpy-30-H, trpy-50-H),
8.71 (d, 2H, 3JH,H=5.2 Hz, trpy-6-H, trpy-600-H), 8.67 (d, 2H,
3
3JH,H = 8.0 Hz, trpy-3-H, trpy-300-H), 7.89 (dt, 2H, JH,H
=
4
7.6 Hz, JH,H = 1.6 Hz, trpy-4-H, trpy-400-H), 7.86 (dd, 1H,
4
3
3JH,H =8.0 Hz, JH,H =1.6 Hz, 4-Ar), 7.73 (dd, 1H, JH,H
=
1
4
3
(20.8 mmol, 57%). H NMR (CDCl3): δ 7.81 (m, 2H, 4-Ar,
7.6 Hz, JH,H = 1.6 Hz, 6-Ar), 7.35 (dt, 2H, JH,H = 8.0 Hz,
4JH,H=1.2 Hz, trpy-5-H, trpy-500-H), 7.29 (t, 1H, 3JH,H=7.6 Hz,
5-Ar), 5.42 (br, 1H, -NHCO-), 3.96 (s, 3H, COOMe), 3.75 (t,
2H, 3JH,H=5.6 Hz, -OCH2CH2-), 3.18 (q, 2H, 3JH,H=6.4 Hz,
-CH2CH2NH-), 1.71 (m, 2H, -OCH2CH2CH2-), 1.32 (s, 9H,
Boc-Bu). [Note: Although the literature suggested the reaction
at 50 °C,11 the reaction hardly proceeded at this temperature in
our case. At 0 °C, the reaction proceeded smoothly.12 However,
if the temperature rose to room temperature before workup, the
hydrolysis reaction of the ester group took place. The failure of
the reaction at 50 °C is probably due to the instability of the
active species derived from I2 and KOH. Furthermore, it was
necessary to remove residual I2 as much as possible, so that the
reaction mixture was washed with NaHSO3 (aq.); otherwise,
unidentified byproducts were formed.]
6-Ar), 7.24 (t, 1H, 3JH,H=7.6 Hz, 5-Ar), 6.01 (s, 2H, -B(OH)2),
5.61 (s, 1H, acetal-CH), 5.09 (s, 2H, -OCH2O-), 3.70
(ABquartet, 4H, JH,H = 11.2 Hz, acetal-CH2), 3.51 (s, 3H,
4
-OCH3), 1.32 (s, 3H, acetal-Me), 0.79 (s, 3H, acetal-Me).
40-(3-(4,4-Dimethyl-2,6-dioxacyclohexyl)-2-methoxymethoxy-
phenyl)-2,20:60,200- terpyridine (7). Compounds 5 (1.57 g, 5.30
mmol), 6 (1.57 g, 4.12 mmol), Pd(PPh3)4 (62.8 mg, 0.054 mmol),
2-dicyclohexylphosphino-20,60-dimethoxybiphenyl (S-phos,10
195.2 mg, 0.48 mmol), KF (1.8 g, 31 mmol), and Na2CO3
(3.2 g, 30 mmol) were suspended in toluene/H2O (30 mL/
5 mL). The mixture was purged with N2 gas and heated at
120 °C for 12 h under N2. After the reaction mixture was allowed
to cool to room temperature, CH2Cl2 and water were added, and
the organic phase was separated and dried over Na2SO4. The
organic solution was concentrated to remove CH2Cl2, and then
hexane was added to the remaining solution and left to stand
overnight. The orange-pink crystals were collected by filtration.
Yield: 1.86 g (3.86 mmol, 93%). Anal. Found: C, 71.75; H, 6.05;
N, 8.61%. Calcd for C29H29N3O4: C, 72.03; H, 6.04; N, 8.69%.
1H NMR (CDCl3): δ 8.71 (d, 2H, 3JH,H=4.4 Hz, trpy-6-H, trpy-
2-(4-(tert-Butoxycarbonylamino)butoxy)-3-methoxycarbonyl-
phenyl-2,20:60,200-terpyridine (11b). This compound was synthe-
sized by a similar procedure using 8 (590.9 mg, 1.67 mmol), 9b
(700.0 mg, 2.78 mmol), K2CO3 (1.1 g, 7.97 mmol), and KI
(488.0 mg, 2.94 mmol) in DMF (30 mL), then KOH (493.0 mg,
8.80 mmol) and I2 (544.4 mg, 4.29 mmol) in MeOH (20 mL).
Yield: 600.0 mg (1.08 mmol, 65%). Anal. Found: C, 69.42; H,
6.24; N, 9.98%. Calcd for C32H34N4O5: C, 69.30; H, 6.18; N,
10.10%. 1H NMR (CDCl3): δ 8.72 (d, 2H, 3JH,H=4.0 Hz, trpy-
3
600-H), 8.69 (s, 2H, trpy-30,50-H), 8.66 (d, 2H, JH,H =8.0 Hz,
3
4
trpy-3-H, trpy-300-H), 7.87 (dt, 2H, JH,H = 7.6 Hz, JH,H
=
3
2.0 Hz, trpy-5-H, trpy-500-H), 7.81 (dd, 1H, JH,H = 7.8 Hz,
3JH,H=1.6 Hz, 4-Ar), 7.56 (dd, 1H, 3JH,H=7.6 Hz, 6-Ar), 7.34
6-H, trpy-600-H), 8.71 (s, 2H, trpy-30-H, trpy-50-H), 8.67 (d, 2H,
3
3
3
(dt, 2H, JH,H=7.6 Hz, JH,H=1.2 Hz, trpy-4-H, trpy-400-H),
3JH,H = 7.6 Hz, trpy-3-H, trpy-300-H), 7.88 (dt, 2H, JH,H
=
7.32 (t, 1H, 3JH,H=7.6 Hz, 5-Ar), 5.89 (s, 1H, acetal-CH), 4.74
7.8 Hz, JH,H = 1.6 Hz, trpy-4-H, trpy-400-H), 7.86 (dd, 1H,
4
4
4
3
(s, 2H, -OCH2O-), 3.75 (ABquartet, 4H, JH,H = 11.2 Hz,
acetal-CH2), 3.19 (s, 3H, -OCH3), 1.37 (s, 3H, acetal-Me), 0.82
(s, 3H, acetal-Me).
3JH,H =8.0 Hz, JH,H =1.6 Hz, 4-Ar), 7.71 (dd, 1H, JH,H
=
4
3
7.6 Hz, JH,H = 2.0 Hz, 6-Ar), 7.35 (dt, 2H, JH,H = 8.0 Hz,
4JH,H=1.6 Hz, trpy-5-H, trpy-500-H), 7.28 (t, 1H, 3JH,H=7.6 Hz,
5-Ar), 4.43 (br, 1H, -NHCO-), 3.94 (s, 3H, COOMe), 3.67 (t,
2H, 3JH,H=6.0 Hz, -OCH2CH2-), 2.88 (q, 2H, 3JH,H=6.4 Hz,
-CH2CH2NH-), 1.52 (m, 2H, -OCH2CH2CH2-), 1.38 (sþm,
11H, -OCH2CH2CH2-, Boc-Bu).
40-(3-Formyl-2-hydroxyphenyl)-2,20:60,200-terpyridine (8). Com-
pound 7 (483.6 mg, 1.00 mmol) and BF3 Et2O (1.5 mL,
3
12 mmol) were dissolved in MeOH (20 mL), and the mixture
was heated at 65 °C. After 3 h, the solution was neutralized by
saturated NaHCO3 (aq.), evaporated to remove MeOH, and
filtered. Yield: 361.3 mg (1.02 mmol, 102%). 1H NMR (DMSO-
2-(5-(tert-Butoxycarbonylamino)pentyloxy)-3-methoxycarbo-
nylphenyl-2,20:60,200-terpyridine (11c). This compound was
prepared similarly to 11a using 8 (209.6 mg, 0.59 mmol), 9c
(257.3 mg, 0.91 mmol), K2CO3 (437.7 g, 3.17 mmol), and KI
(236.8 mg, 1.43 mmol) in DMF (8 mL), then KOH (205.9 mg,
3.65 mmol) and I2 (232.7 mg, 1.83 mmol) in MeOH (10 mL).
Yield: 216.1 mg (0.38 mmol, 64%). Anal. Found: C, 69.68; H,
6.39; N, 9.88%. Calcd for C33H36N4O5: C, 69.70; H, 6.38; N,
9.85%. 1H NMR (CDCl3): δ 8.71 (s, 2H, trpy-30-H, trpy-50-H),
d6): δ 11.61 (br, 1H, -OH), 10.16 (s, 1H, -CHO), 8.92 (d, 2H,
=
3
3JH,H = 8.0 Hz, trpy-6-H, trpy-600-H), 8.86 (d, 2H, JH,H
4.4 Hz, trpy-3-H, trpy-300-H), 8.80 (s, 2H, trpy-30, 50-H), 8.35
3
3
(dt, 2H, JH,H=7.6 Hz, JH,H=1.2 Hz, trpy-5-H, trpy-500-H),
7.99 (two overlapping doublets, 2H, 3JH,H=7.6 Hz, 4-Ar, 6-Ar),
3
7.78 (t, 2H, JH,H=6.4 Hz, trpy-4-H, trpy-400-H), 7.31 (t, 1H,
3JH,H=7.6 Hz, 5-Ar).
8.70 (d, 2H, 3JH,H=6.0 Hz, trpy-6-H, trpy-600-H), 8.68 (d, 2H,
2-(3-(tert-Butoxycarbonylamino)propyloxy)-3-methoxycar-
bonylphenyl-2,20:60,200- terpyridine (11a). Compound 8 (530.7
mg, 1.50 mmol), 9a (520.9 mg, 2.19 mmol), K2CO3 (940.2 mg,
7.03 mmol), and KI (519.4 mg, 3.13 mmol) were suspended in
DMF (10 mL), and the solution was stirred for 12 h at 50 °C
under N2. Saturated NaCl (aq.) and CH2Cl2 were added to the
reaction mixture, and the organic phase was separated. The
organic solution was washed twice with H2O and dried over
Na2SO4. Evaporating the solvent gave 10a as orange oil. Sub-
sequently, the orange oil (10a) was dissolved in MeOH (20 mL)
and cooled to 0 °C. KOH (365.2 mg, 6.52 mmol) was added to
the solution and stirred for 5 min; then, I2 (419.0 mg, 3.30 mmol)
was added and stirred for 6 h at 0 °C. Aqueous KHSO4 was
added to the reaction mixture to neutralize it. To the mixture
3
3JH,H = 8.0 Hz, trpy-3-H, trpy-300-H), 7.89 (dt, 2H, JH,H
=
4
8.0 Hz, JH,H = 2.0 Hz, trpy-4-H, trpy-400-H), 7.86 (dd, 1H,
4
3
3JH,H =7.6 Hz, JH,H =1.6 Hz, 4-Ar), 7.70 (dd, 1H, JH,H
=
4
3
7.6 Hz, JH,H = 2.0 Hz, 6-Ar), 7.35 (dt, 2H, JH,H = 6.0 Hz,
4JH,H=1.2 Hz, trpy-5-H, trpy-500-H), 7.28 (t, 1H, 3JH,H=7.6 Hz,
5-Ar), 4.41 (br, 1H, -NHCO-), 3.94 (s, 3H, COOMe), 3.65 (t,
2H, JH,H=5.6 Hz, -OCH2CH2-), 2.76 (m, 2H, -CH2CH2-
NH-), 1.51 (m, 2H, -OCH2CH2CH2-), 1.41 (s, 9H, Boc-Bu),
3
1.16 (m, 4H, -CH2CH2CH2CH2NH-).
2-(6-(tert-Butoxycarbonylamino)hexyloxy)-3-methoxycarbon-
ylphenyl-2,20:60,200-terpyridine (11d). This compound was
prepared similarly to 11a using 8 (202.9 mg, 0.58 mmol), 9d
(262.5 mg, 0.89 mmol), K2CO3 (427.9 g, 3.10 mmol), and KI

Article
Inorganic Chemistry, Vol. 48, No. 17, 2009 8601
(206.1 mg, 1.24 mmol) in DMF (8 mL), then KOH (198.6 mg,
3.55 mmol) and I2 (209.8 mg, 1.65 mmol) in MeOH (10 mL).
Yield: 217.7 mg (0.37 mmol, 65%). Anal. Found: C, 69.91; H,
6.62; N, 9.69%. Calcd for C34H38N4O5: C, 70.08; H, 6.57; N,
9.62%. 1H NMR (CDCl3): δ 8.72 (s, 2H, trpy-30-H, trpy-50-H),
2-(5-(2,20-Bipyridin-4-ylcarbonylamino)pentyloxy)-3-methox-
ycarbonylphenyl-2,20:60,200-terpyridine (1c). This compound
was synthesized by a procedure similar to that of 1a, using 11c
(169.6 mg, 0.30 mmol) and trifluoroacetic acid (8 mL), and then
DMAP (79.2 mg, 0.65 mmol), HOBt (85.6 mg, 0.63 mmol),
8.70 (d, 2H, 3JH,H=6.0 Hz, trpy-6-H, trpy-600-H), 8.68 (d, 2H,
EDC HCl (159.0 mg, 0.68 mmol), 13 (59.8 mg, 0.30 mmol), and
3
3
3JH,H = 8.0 Hz, trpy-3-H, trpy-300-H), 7.89 (dt, 2H, JH,H
=
CH2Cl2 (10 mL). Yield: 165.9 mg (0.26 mmol, 85%). Anal.
Found: C, 71.92; H, 5.34; N, 12.86%. Calcd for C39H34N6O4: C,
4
7.6 Hz, JH,H = 1.6 Hz, trpy-4-H, trpy-400-H), 7.86 (dd, 1H,
4
3
1
3JH,H =8.8 Hz, JH,H =2.0 Hz, 4-Ar), 7.70 (dd, 1H, JH,H
=
71.98; H, 5.27; N, 12.92%. H NMR (CDCl3): δ 9.02 (d, 1H,
4
3
7.6 Hz, JH,H = 2.0 Hz, 6-Ar), 7.35 (dt, 2H, JH,H = 7.6 Hz,
4JH,H=1.2 Hz, trpy-5-H, trpy-500-H), 7.27 (t, 1H, 3JH,H=7.6 Hz,
5-Ar), 4.40 (br, 1H, -NHCO-), 3.94 (s, 3H, COOMe), 3.65 (t,
4JH,H=2.0 Hz, bpy-6-H), 8.72 (d, 1H, 3JH,H=4.8 Hz, bpy-60-H),
8.69 (s, 2H, trpy-30-H, trpy-50-H), 8.68 (d, 2H, 3JH,H=4.8 Hz,
3
trpy-6-H, trpy-600-H), 8.63 (d, 2H, JH,H = 7.6 Hz, trpy-3-H,
3
2H, JH,H=6.4 Hz, -OCH2CH2-), 2.83 (m, 2H, -CH2CH2-
trpy-300-H), 8.47 (d, 1H, 3JH,H=8.8 Hz, bpy-30-H,), 8.45 (d, 1H,
NH-), 1.49 (m, 2H, -OCH2CH2CH2-), 1.43 (s, 9H, Boc-Bu),
1.07 (m, 6H, -CH2CH2CH2CH2CH2NH-).
3JH,H=9.2 Hz, bpy-3-H), 8.13 (dd, 1H, 3JH,H=8.0 Hz, 4JH,H
=
2.4 Hz, bpy-4-H), 7.81-7.90 (m, 4H, 4-Ar, bpy-40-H, trpy-4-H,
trpy-400-H), 7.69 (dd, 1H, 3JH,H=7.6 Hz, 3JH,H=2.0 Hz, 6-Ar),
7.37 (t, 1H, bpy-50-H), 7.26-7.34 (m, 3H, trpy-5-H, trpy-500-H,
5-Ar), 6.40 (br, 1H, -NHCO-), 3.92 (s, 3H, -COOMe), 3.70 (t,
2H, 3JH,H=6.0 Hz, -OCH2CH2-), 3.12 (q, 2H, 3JH,H=5.6 Hz,
-CH2CH2NH-), 1.56 (m, 2H, -OCH2CH2CH2-), 1.30-1.32
(m, 4H, -OCH2CH2CH2CH2CH2-).
2-(3-(2,20-Bipyridin-4-ylcarbonylamino)propyloxy)-3-methox-
ycarbonylphenyl-2,20:60,200-terpyridine (1a). A solution of 11a
(420.6 mg, 0.78 mmol) in trifluoroacetic acid (10 mL) was stirred
for 2 h at room temperature. The solution was neutralized
by saturated NaHCO3 (aq.). The white solids deposited, which
were collected by filtration to obtain deprotected product 12a.
Subsequently, 12a, 4-dimethylaminopyridine (DMAP; 207.7 mg,
1.70 mmol), 1-hydroxybenzotriazole (HOBt; 228.5 mg,
1.69 mmol), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide
2-(6-(2,20-Bipyridin-4-ylcarbonylamino)hexyloxy)-3-methoxy-
carbonylphenyl-2,20:60,200-terpyridine (1d). This compound was
synthesized by a procedure similar to that of 1a, using 11d
(190.2 mg, 0.33 mmol) and trifluoroacetic acid (8 mL), and then
DMAP (80.3 mg, 0.66 mmol), HOBt (87.1 mg, 0.65 mmol),
hydrochloride (EDC HCl; 298.0 mg, 1.56 mmol), and 13
3
(152.8 mg, 0.76 mmol) were dissolved in CH2Cl2 (15 mL),
and the mixture was stirred for 14 h at room temperature.
The reaction mixture was washed with water, and then with
saturated NaHCO3 (aq.). The separated organic phase was
dried over Na2SO4 and evaporated to give pale yellow oil. The
purification was performed by chromatography on an alumina
column and recrystallization from CH2Cl2/hexane. Yield:
356.5 mg (0.57 mmol, 74%). Anal. Found: C, 71.13; H, 4.84;
N, 13.44%. Calcd for C37H30N6O4: C, 71.37; H, 4.86; N,
EDC HCl (125.0 mg, 0.65 mmol), 13 (62.1 mg, 0.31 mmol), and
CH2Cl2 (10 mL). Yield: 154.1 mg (0.23 mmol, 71%). Anal.
Found: C, 72.16; H, 5.59; N, 12.42%. Calcd for C40H36N6O4: C,
3
1
72.27; H, 5.46; N, 12.64%. H NMR (CDCl3): δ 9.04 (d, 1H,
4JH,H =2.0 Hz, bpy-6-H), 8.68-8.72 (m, 3H, bpy-60-H, trpy-
6-H, trpy-600-H), 8.69 (s, 2H, trpy-30-H, trpy-50-H), 8.64 (d, 2H,
=
3
3JH,H = 7.6 Hz, trpy-3-H, trpy-300-H), 8.46 (d, 1H, JH,H
8.0 Hz, bpy-30-H,), 8.45 (d, 1H, 3JH,H=8.0 Hz, bpy-3-H), 8.19
(dd, 1H, 3JH,H=8.0 Hz, 4JH,H=2.4 Hz, bpy-4-H), 7.82-7.87 (m,
4
13.50%. 1H NMR (CDCl3): δ 9.13 (d, 1H, JH,H = 2.4 Hz,
bpy-6-H), 8.79 (s, 2H, trpy-30-H, trpy-50-H), 8.69 (d, 1H, 3JH,H
=
4H, 4-Ar, bpy-40-H, trpy-4-H, trpy-400-H), 7.66 (dd, 1H, 3JH,H
=
4.4 Hz, bpy-60-H), 8.66 (d, 2H, 3JH,H=8.0 Hz, trpy-6-H, trpy-600-
H), 8.63 (d, 2H, 3JH,H=4.8 Hz, trpy-3-H, trpy-300-H), 8.42 (d,
1H, 3JH,H=8.8 Hz, bpy-30-H,), 8.40 (d, 1H, 3JH,H=8.4 Hz, bpy-
7.6 Hz, 3JH,H=1.6 Hz, 6-Ar), 7.23-7.37 (m, 4H, bpy-50-, trpy-
5-H, trpy-500-H, 5-Ar), 6.44 (br, 1H, -NHCO-), 3.94 (s, 3H,
-COOMe), 3.68 (t, 2H, 3JH,H=5.6 Hz, -OCH2CH2-), 3.21 (q,
3
4
3
3-H), 8.23 (dd, 1H, JH,H=8.4 Hz, JH,H=2.4 Hz, bpy-4-H),
7.94 (dd, 1H, 3JH,H=8.0 Hz, 4JH,H=1.6 Hz, 4-Ar), 7.79-7.88
(m, 5H, trpy-4-H, trpy-400-H, bpy-40-H, bpy-50-H, 6-Ar),
7.31-7.35 (m, 4H, trpy-5-H, trpy-500-H, 5-Ar, -NHCO-),
2H, JH,H =6.0 Hz, -CH2CH2NH-), 1.52 (m, 2H, -OCH2-
CH2CH2-), 1.08-1.26 (m, 6H, -OCH2CH2CH2CH2CH2-).
Syntheses of Co(II) Complexes. [CoCl(1a)](PF6) (2a). The
ligand 1a (50.6 mg, 0.081 mmol) and LiCl (11.8 mg, 0.28 mmol)
were suspended in EtOH (10 mL), and the solution was heated
3
3.95 (s, 3H, -COOMe), 3.84 (t, 2H, JH,H=5.6 Hz, -OCH2-
CH2-), 3.68 (q, 2H, 3JH,H=6.0 Hz, -CH2CH2NH-), 1.83 (m,
2H, -OCH2CH2CH2-).
at 80 °C to dissolve 1a. A solution of CoCl2 6H2O (19.3 mg,
3
0.081 mmol) in EtOH (5 mL) was added to the hot EtOH
solution, and the mixture was refluxed for 2 h. The reaction
mixture was cooled; NH4PF6 was added to the solution and
left to stand overnight. The pale brown powder was collected
by filtration and dried at 100 °C in a vacuum. Yield: 67.4 mg
(0.078 mmol, 96%). Anal. Found: C, 49.48; H, 3.75; N, 9.26%.
2-(4-(2,20-Bipyridin-4-ylcarbonylamino)butoxy)-3-methoxycar-
bonylphenyl-2,20:60,200-terpyridine (1b). This compound was
synthesized by a procedure similar to that of 1a, using 11b
(183.8 mg, 0.33 mmol) and trifluoroacetic acid (8 mL), and then
DMAP (78.3 mg, 0.64 mmol), HOBt (79.6 mg, 0.59 mmol),
EDC HCl (115.2 mg, 0.60 mmol), 13 (64.1 mg, 0.32 mmol), and
3
Calcd for C37H30N6O4ClCoF6P 2H2O: C, 49.49; H, 3.82; N,
3
CH2Cl2 (10 mL). Yield: 143.8 mg (0.23 mmol, 68%). Anal.
Found: C, 71.45; H, 5.20; N, 13.16%. Calcd for C34H38N4O5: C,
9.36%.
[Co(1a)H2O](PF6)2 (2a0). The ligand 1a (47.1 mg, 0.076 mmol)
was suspended in EtOH (10 mL), and the solution was heated
1
71.68; H, 5.07; N, 13.20%. H NMR (CDCl3): δ 8.96 (d, 1H,
=
4JH,H=2.0 Hz, bpy-6-H), 8.71 (dd, 1H, 3JH,H=4.8 Hz, 4JH,H
at 80 °C. The aqueous solution (5 mL) of Co(NO3)2 6H2O
3
0.8 Hz, bpy-60-H), 8.70 (s, 2H, trpy-30-H, trpy-50-H), 8.65 (dd,
(21.6 mg, 0.074 mmol) was added to the hot EtOH solution, and
the mixture was refluxed for 2 h. The reaction mixture was
cooled; NH4PF6 was added to the solution and left to stand
overnight. The micro brown crystals were collected by filtration
and dried at 100 °C in a vacuum. Yield: 56.1 mg (0.057 mmol,
77%). Anal. Found: C, 44.38; H, 3.14; N, 8.34%. Calcd for
2H, 3JH,H=4.8 Hz, 4JH,H=1.2 Hz, trpy-6-H, trpy-600-H), 8.62
3
(d, 2H, JH,H = 8.0 Hz, trpy-3-H, trpy-300-H), 8.46 (dd, 1H,
3JH,H=8.0 Hz, 4JH,H=0.8 Hz, bpy-30-H,), 8.41 (d, 1H, 3JH,H
=
8.0 Hz, bpy-3-H), 8.08 (dd, 1H, 3JH,H=8.4 Hz, 4JH,H=2.4 Hz,
bpy-4-H), 7.90 (dd, 1H, 3JH,H=8.0 Hz, 4JH,H=1.6 Hz, 4-Ar),
7.85 (dt, 1H, 3JH,H=8.0 Hz, 4JH,H=1.6 Hz, bpy-40-H), 7.83 (dt,
2H, 3JH,H=8.0 Hz, 4JH,H=2.0 Hz, trpy-4-H, trpy-400-H), 7.72
(dd, 1H, 3JH,H=7.6 Hz, 3JH,H=2.0 Hz, 6-Ar), 7.36 (t, 1H, bpy-
50-H), 7.27-7.32 (m, 3H, trpy-5-H, trpy-500-H, 5-Ar), 6.56 (br,
C37H32N6O5CoF12P2 H2O: C, 44.11; H, 3.40; N, 8.34%.
3
[CoCl(1b)](PF6) (2b). This complex was synthesized by the
same procedure as for 2a by using 1b (45.7 mg, 0.072 mmol),
LiCl (12.7 mg, 0.30 mmol), and CoCl2 6H2O (17.3 mg,
3
1H, -NHCO-), 3.93 (s, 3H, -COOMe), 3.75 (t, 2H, 3JH,H
5.6 Hz, -OCH2CH2-), 3.25 (q, 2H, JH,H = 6.0 Hz, -CH2-
CH2NH-), 1.55-1.68 (m, 4H, -OCH2CH2CH2CH2-).
=
0.073 mmol). Yield: 62.8 mg (0.071 mmol, 99%). Anal. Found:
C, 51.05; H, 4.28; N, 9.12%. Calcd for C38H32N6O4ClCoF6P
2CH3OH: C, 51.10; H, 4.29; N, 8.94%.
3
3

8602 Inorganic Chemistry, Vol. 48, No. 17, 2009
Kon and Nagata
[Co(1b)H2O](PF6)2 (2b0). This complex was synthesized by
the same procedure as for 2a0 by using 1b (42.7 mg, 0.067 mmol)
and Co(NO3)2 6H2O (19.9 mg, 0.068 mmol). Yield: 46.2 mg
were a platinum disk and a platinum wire, respectively.
The sample solutions (ca. 0.001 M) in 0.1 M n-Bu4NClO4/
DMF were deoxygenated with a stream of nitrogen gas. All
values of redox potentials are reported in reference to Fc/Fcþ
(Fc=ferrocene); in practice, a Ag/Agþ electrode was used as a
reference (-0.15 V vs Fc/Fcþ).
3
(0.046 mmol, 69%). Found: C, 44.23; H, 3.33; N, 8.09%. Calcd
for C38H34N6O5CoF12P2 1.5H2O: C, 44.29; H, 3.62; N, 8.15%.
3
[CoCl(1c)](PF6) (2c). This complex was synthesized by the
same procedure as for 2a by using 1c (42.4 mg, 0.065 mmol),
LiCl (9.3 mg, 0.22 mmol), and CoCl2 6H2O (15.5 mg, 0.065
X-Ray Diffraction Studies. Suitable single crystals of 2b were
obtained from the diffusion of CH3CN/MeOH, and those
of 2c00 were obtained from the slow evaporation of a solution of
2c0 in a CH3CN/H2O mixed solvent, respectively. The measure-
ments were performed at -100 °C. Data collection was made on a
Mercury CCD area detector coupled with a Rigaku/MSC dif-
fractometer with graphite monochromated Mo KR radiation (λ=
3
mmol). Yield: 52.8 mg (0.059 mmol, 91%). Found: C, 51.03; H,
3.84; N, 9.27%. Calcd for C39H34N6O4ClCoF6P 1.5H2O: C,
3
51.08; H, 4.06; N, 9.16%.
[Co(1c)H2O](PF6)2 (2c0). This complex was synthesized by
the same procedure as for 2a0 by using 1c (48.4 mg, 0.075 mmol)
and Co(NO3)2 6H2O (22.0 mg, 0.076 mmol). Yield: 55.2 mg
28
˚
0.71070 A) by use of the CrystalClear software. All of the
3
calculations were carried out on the CrystalStructure software.29
The structures were solved by direct methods and expanded by
Fourier anddifference Fourier techniques. The crystalscontained
methanol or water molecules as crystal solvents. Details of crystal
parametersandstructurerefinementare given inTable1. Selected
bond lengths and angles are shown in Table 2.
(0.054 mmol, 73%). Found: C, 45.11; H, 3.56; N, 7.99%. Calcd
for C39H36N6O5CoF12P2 H2O: C, 45.23; H, 3.70; N, 8.12%.
3
[CoCl(1d)](PF6) (2d). This complex was synthesized by the
same procedure as for 2a by using 1d (35.6 mg, 0.054 mmol),
LiCl (7.6 mg, 0.18 mmol), and CoCl2 6H2O (14.3 mg,
3
0.060 mmol). Yield: 43.9 mg (0.049 mmol, 90%). Anal. Found:
C, 52.10; H, 4.02; N, 9.14%. Calcd for C40H36N6O4Cl-
CoF6P H2O: C, 52.10; H, 4.15; N, 9.11%.
Acknowledgment. The authors thank Prof. Koji Tanaka
(IMS) for his permission to use the X-ray diffractometer and the
ESI-mass spectrometer, Dr. Takashi Fukushima for his helpful
advice, Mr. Seiji Makita for performing elemental analysis, and
the Instrument Center of IMS for use of the NMR spectrometer.
This work was supported by IMS and a Grant-in-aid for
Scientific Research (C) (No. 19550173) from the Japan Society
for Promotion of Science (JSPS).
3
[Co(1b)H2O](PF6)2 (2d0). This complex was synthesized by
the same procedure as for 2a0 by using 1d (34.1 mg, 0.051 mmol)
and Co(NO3)2 6H2O (15.4 mg, 0.053 mmol). Yield: 38.6 mg
3
(0.037 mmol, 74%). Anal. Found: C, 45.80; H, 3.66; N, 7.99%.
Calcd for C40H38N6O5CoF12P2 H2O: C, 45.77; H, 3.84; N,
8.01%.
3
Electrochemical Methods. Cyclic voltammograms were mea-
sured with an ALS/CHI Model 660 voltammetric analyzer
at a scan rate of 100 mV/s. The working and counter electrodes
Supporting Information Available: Crystallographic data for
1b and 1c00 in CIF format; the ESI-mass spectra of 2a, 2a0, and
15a; and the preliminary X-ray structure of 15a. This material is
available free of charge via the Internet at http://pubs.acs.org.
(28) CrystalClear; Rigaku Corp.: Tokyo, 1999.
(29) CrystalStructure, ver. 3.8.2; Rigaku Corp.: Tokyo, 2007.