Synthesis and electrochemical properties of bis(bipyridine)ruthenium(II) complexes bearing pyridinyl- and pyridinylidene ligands induced by cyclometalation of N′-methylated bipyridinium analogs

Article abstract of DOI:10.1016/j.jorganchem.2004.11.032

Ruthenium complexes with bipyridine-analogous quaternized (N,C) bidentate ligands [RuL(bpy)₂](PF₆)₂ (bpy = 2,2′-bipyridine, (1), L = L¹ = N′-methyl-2,4′- bipyridinium; (2), L = L² = N′-methyl-2,3′-bipyridinium) were synthesized and characterized. The structure of complex 2 was determined by the X-ray structure analysis. The ¹³C{¹H} NMR spectroscopic and cyclic voltammetric studies indicate that the coordination modes of these ligands are quite different, that is, the C-coordinated rings of (N,C)-ligands in 1 and 2 are linked to ruthenium(II) with a pyridinium manner and a pyridinylidene one, respectively. The ligand-localized redox potentials of 1 and 2 also revealed the substantial difference in the electron donating ability of both ligands.

Full text of DOI:10.1016/j.jorganchem.2004.11.032

Journal of Organometallic Chemistry 690 (2005) 1258–1264
www.elsevier.com/locate/jorganchem
Synthesis and electrochemical properties of
bis(bipyridine)ruthenium(II) complexes bearing pyridinyl- and
0
pyridinylidene ligands induced by cyclometalation of N -methylated
bipyridinium analogs
Take-aki Koizumi, Takashi Tomon, Koji Tanaka *
Institute for Molecular Science and CREST, Coordination Chemistry Laboratories, Japan Science and Technology Agency (JST),
5
–1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan
Received 6 September 2004; accepted 17 November 2004
Available online 22 December 2004
Abstract
0
6 2
) (bpy = 2,2 -bipyridine,
Ruthenium complexes with bipyridine-analogous quaternized (N,C) bidentate ligands [RuL(bpy) ](PF
2
1
1), L = L = N -methyl-2,4 -bipyridinium; (2), L = L = N -methyl-2,3 -bipyridinium) were synthesized and characterized. The
0
0
2
0
0
(
1
3
1
structure of complex 2 was determined by the X-ray structure analysis. The C{ H} NMR spectroscopic and cyclic voltammetric
studies indicate that the coordination modes of these ligands are quite different, that is, the C-coordinated rings of (N,C)-ligands in 1
and 2 are linked to ruthenium(II) with a pyridinium manner and a pyridinylidene one, respectively. The ligand-localized redox
potentials of 1 and 2 also revealed the substantial difference in the electron donating ability of both ligands.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Ruthenium; Crystal structures; Electrochemistry; Cyclometalated ligand; Pyridinylidene complex; Cyclic voltammetry
1
. Introduction
redox potentials of the complexes bearing (N,C) ligands
appear at potentials more negative than those of (N,N)
donors, because these (N,C) donors coordinate to metal
centers as anion ligands. Several Pd and Pt complexes
having quaternized (N,C) bidentate ligands derived
In recent years, ruthenium(II) complexes bearing
0
2
,2 -bipyridine analogous (N,C) bidentate ligands such
as 2-phenylpyridine (PhPy), 2-phenylquinoline (PhQn),
and so on, have been reported and their photo- and elec-
tro-chemical properties have been investigated from the
viewpoints of the comparison of analogous ruthe-
nium(II) polypyridyl complexes [1–14]. The Ru–C
bond-containing ruthenium complexes are thermally
stable, and show significant differences in both the
ground and excited state redox reactions compared to
those of Ru-polypyridyl analogs. The ligand-localized
0
0
from 2,2 - and 2,4 -bipyridine have been prepared [15–
17]. The ligand-based redox potentials of those com-
plexes with quaternized (N,C) ligands are similar or
more positive as compared with those of bpy complexes.
Despite a tremendous number of studies on ruthenium
complexes with (N,N) ligands so far, analogous com-
plexes having these quaternized (N,C) ligands have not
been synthesized. Furthermore, there has been no exam-
ple of transition metal complexes bearing quaternized
0
*
2,3 -bipyridine-derived (N,C) bidentate ligands. In this
paper, we report the synthesis, structure and electronic
Corresponding author. Tel.: +81564595580; fax: +81564595582.
E-mail address: ktanaka@ims.ac.jp (K. Tanaka).
0
022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.11.032

T. Koizumi et al. / Journal of Organometallic Chemistry 690 (2005) 1258–1264
1259
1
2.3. Preparation of [RuL (bpy) ](PF ) (1)
properties of cyclometalated ruthenium(II) complexes
with quaternized bipyridine-analogous (N,C) ligands.
2
6 2
1
[
RuCl (bpy) ] (100 mg, 0.206 mmol), [L H][PF ] (65
2 2 6
mg, 0.206 mmol) and triethylamine (2 mL) were dis-
solved in CH CH OH and refluxed for 3 h. The purple
2
. Experimental
3
2
solution turned immediately to crimson in color. The
solution was concentrated to ca. 1 mL, and poured into
aqueous NH PF solution. The generated reddish-
2
.1. Materials and physical measurements
4
6
0
0
N -methyl-2,4 -bipyridinium
1
hexafluorophosphate
(L H)(PF )) and N-methyl-2,2 -bipyridinium hexaflu-
brown precipitate was collected by filtration and dried
in vacuo. Recrystallization from an acetone–Et O mix-
ture afforded 1 as reddish-brown crystals (75 mg,
0
(
orophosphate ((L H)(PF )) were prepared by the anion
6
2
3
6
1
exchange reaction of corresponding iodide ((L H)I [15d]
2+
42%). ESI-MS: m/z 292 {M–2PF } . Anal. Calc. for
6
3
and (L H)I [17]) with NH PF in water. 2,3 -bipyridine
0
C H F N OP Ru (1 Æ acetone): C, 43.83; H, 3.46; N,
4
6
34 32 12
6
2
1
9.02. Found: C, 43.83; H, 3.60; N, 8.92. H NMR (ace-
was synthesized by the Stille coupling reaction of 2-
tri-(n-butyl)stannylpyridine with 3-bromopyridine, and
tone-d , 500 MHz); d 8.76 (d, 1H, J(H–H) = 9.0 Hz),
6
[
ature method. All other commercially available reagents
were used as purchased. H, C{ H}, and H– H
COSY NMR spectra were recorded on a JEOL GX-
Ru(bpy) Cl ] [18] were prepared according to the liter-
8.69 (d, 1H, J(H–H) = 8.0 Hz), 8.64 (m, 3H), 8.45 (d,
1H, J(H–H) = 6.5 Hz), 8.36 (d, 1H, J(H–H) = 7.0 Hz),
8.23 (d, 1H, J(H–H) = 5.5 Hz), 8.18 (dt, 1H, J(H–
H) = 8.0 and 1.0 Hz), 8.07–8.00 (m, 6H), 7.96 (d, 1H,
J(H–H) = 5.5 Hz), 7.92 (d, 1H, J(H–H) = 5.5 Hz), 7.89
(s, 1H), 7.85 (d, 1H, J(H–H) = 5.5 Hz), 7.61 (t 1H,
J(H–H) = 9.0 Hz), 7.45–7.40 (m, 4H), 7.37 (dt, 1H,
J(H–H) = 5.5 and 1.0 Hz), 4.13 (s, 3H, N–Me).
2
2
1
13
1
1
1
5
00 spectrometer. ESI-MS spectra were obtained on a
Shimadzu LCMS-2010 spectrometer. Electrochemical
measurements were performed with ALS/chi Electro-
chemical Analyzer 660A. A conventional three-electrode
configuration was used, with glassy carbon working
1
3
1
C{ H} NMR (acetone-d , 125.65 MHz); d 190.1
6
(
BAS PFCE carbon electrode) and platinum wire auxil-
+
(Ru–C), 161.9, 161.2, 156.5, 155.9, 155.8, 154.2, 154.1,
151.1, 149.9, 149.8, 148.3, 147.9, 136.8, 136.2, 136.1,
135.7, 135.2, 135.1, 126.9, 126.5, 126.4, 126.3, 126.2,
123.3, 123.1, 123.0, 123.0, 123.0, 119.1, 46.7 (N–Me).
iary electrode (BAS special order) and Ag|Ag reference
BAS RE-5). Cyclic Voltammogram were recorded at a
(
ꢀ
1
scan rate of 100 mV s . Elemental analyses were carried
out by the Molecular Scale Nano-Science Center of
IMS.
2
2.4. Preparation of [RuL (bpy) ](PF ) (2)
2
6 2
0
0
2
2
hexafluorophosphate ((L H)(PF ))
.2. Preparation of N -methyl-2,3 -bipyridinium
2
[RuCl (bpy) ] (100 mg, 0.206 mmol) and [L H][PF ]
2 2 6
(65.0 mg, 0.206 mmol) were dissolved in CH CH OH
3 2
6
and stirred at 80 °C for 10 min. A CH OH solution of
3
0
To a CHCl solution (20 mL) of 2,3 -bipyridine (500
3
AgPF (105 mg, 0.413 mmol) was added and the solu-
6
mg, 3.20 mmol) was added an excess amount of MeI (2
mL, 32.2 mmol, ca. 10 equiv) and the mixture was re-
fluxed. A yellow solid was precipitated after 10 min.
Refluxing was continued for 2 h, then the precipitated
powder was collected by filtration and dried in vacuo.
The resulting yellow powder was dissolved in water
tion was refluxed. The purple solution turned immedi-
ately to orange in color, and a off-white precipitate
(AgCl) appeared soon. After 1 h, the Ag salt was filtered
off, and the solution was concentrated to ca. 1 mL, and
poured into an aqueous NH PF solution. The gener-
4
6
ated orange-brown precipitate was collected by filtration
and dried in vacuo. Recrystallization from an MeCN–
Et O mixture afforded 2 as dark orange crystals (74
(30 mL) and addition of excess amount of NH PF to
4 6
the solution precipitated an off-white solid. The solid
2
2
+
was collected by filtration and dried in vacuo (670 mg,
+
0%). ESI-MS: m/z 171 {M–PF } . Anal. Calc. for
mg, 41%). ESI-MS: m/z 292 {M–2PF } . Anal. Calc.
6
7
C H F N P: C, 41.79; H, 3.51; N, 8.86. Found: C,
for C H F N OP Ru (2 Æ acetone): C, 43.83; H,
6
34 32 12
6
2
1
3.46; N, 9.02. Found: C, 43.47; H, 3.47; N, 9.03. H
1
1
11
6
2
1
1.69; H, 3.48; N, 8.83. H NMR (acetone-d , 500
4
NMR (acetone-d , 500 MHz); d 9.00 (s, 1H), 8.81 (d,
6
6
2
0
MHz); d 9.73 (s, 1H, H ), 9.29 (d, 1H, J(H–H) = 8.5
Hz, H ), 9.10 (d, 1H, J(H–H) = 6.0 Hz, H ), 8.81
1H, J(H–H) = 7.5 Hz), 8.71 (d, 1H, J(H–H) = 9.5 Hz),
8.69 (d, 1H, J(H–H) = 8.0 Hz), 8.44 (d, 2H, J(H–
H) = 8.5 Hz), 8.22 (t, 1H, J(H–H) = 8.0 Hz), 8.13 (t,
1H, J(H–H) = 6.0 Hz), 8.11 (t, 1H, J(H–H) = 7.5 Hz),
8.05 (t, 1H, J(H–H) = 7.5 Hz), 8.05 (d, 1H, J(H–
H) = 3.5 Hz), 8.04 (t, 1H, J(H–H) = 7.5 Hz), 8.02 (d,
1H, J(H–H) = 5.0 Hz), 8.01 (d, 1H, J (H–H) = 7.5
Hz), 7.98 (d, 1H, J(H–H) = 4.5 Hz), 7.92 (d, 1H, J(H–
H) = 5.5 Hz), 7.87 (d, 1H, J(H–H) = 5.5 Hz), 7.75 (d,
6
0
4
0
2
dd, 1H, J(H–H) = 5.0 and 2.0 Hz, H ), 8.34 (t, 1H,
(
J(H–H) = 7.5 Hz, H ), 8.24 (d, 1H, J(H–H) = 8.0 Hz,
5
0
5
H ), 8.07 (dt, 1H, J(H–H) = 7.5 and 2.0 Hz, H ), 7.58
4
3
dt, 1H, J(H–H) = 5.0 and 2.0 Hz, H ), 4.73 (s, 3H,
(
1
3
1
N–Me). C{ H} NMR (acetone-d , 125.65 MHz); d
6
1
1
50.9, 150.4, 145.5, 144.5, 142.6, 139.8, 138.5, 128.7,
25.7, 122.1, 49.4.

1260
T. Koizumi et al. / Journal of Organometallic Chemistry 690 (2005) 1258–1264
1
7
H, J(H–H) = 6.5 Hz), 7.65 (t, 1H, J(H–H) = 7.0 Hz),
.52 (t, 1H, J(H–H) = 7.0 Hz), 7.48 (t, 1H, J(H–
H) = 7.5 Hz), 7.36 (t, 1H, J(H–H) = 5.5 Hz), 7.34 (t,
1
4
1
1
1
1
1
H, J(H–H) = 7.5 Hz), 7.30 (d, 1H, J(H–H) = 7.0 Hz),
1
1
3
.18 (s, 3H, N–Me).
C{ H} NMR (acetone-d ,
6
25.65 MHz); d 232.1 (Ru–C), 161.2, 156.1, 155.8,
55.7, 153.3, 153.2, 150.3, 150.0, 149.9, 148.0, 147.1,
37.3, 136.4, 136.3, 136.2, 135.6, 134.5, 133.6, 132.4,
26.9, 126.7, 126.6, 126.5, 126.0, 124.8, 123.4, 123.1,
23.1, 123.0, 119.9, 45.7 (N–Me).
2
.5. Crystal structure determination
2
6
Fig. 1. ORTEP drawing of (L H)(PF ). Only one of the two molecules
Crystals for X-ray analyses were obtained as de-
scribed in the preparations. Suitable crystals were
mounted on glass fibers or sealed in thin-walled glass
constituting the asymmetric unit is depicted. Hydrogen atoms are
omitted for clarity.
2
capillaries. Data collection for [L H](PF ) and 2 were
6
performed at ꢀ100 °C on a Rigaku/MSC Mercury
1) MeI / CHCl3
+
N
N Me
CCD diffractometer with graphite monochromated Mo
˚
2) NH PF aq.
4 6
N
N
N
PF6-
Ka radiation (k = 0.7107 A). The structure was solved
1
by using the TEXSAN software package. Atomic scatter-
ing factors were obtained from the literature [19].
Refinements were performed anisotropically for all
non-hydrogen atoms by the full-matrix least-squares
method. Hydrogen atoms were placed at the calculated
positions and were included in the structure calculation
without further refinement of the parameters. The resid-
ual electron densities were of no chemical significance.
Crystal data and processing parameters are summarized
in Table 4.
(L H)(PF )
6
(1)
Me
N
1) MeI / CHCl3
N+
PF6-
2
) NH PF aq.
4 6
N
2
(
L H)(PF )
6
2
+
N+ Me
N
N
N
PF6-
N Ru N
N
(
PF6 )
Et N
2
3
N Me
3
. Results and discussion
The (N,C) ligand precursors, N -methyl-2,4 -
1
0
0
1
bipyridinium hexafluorophosphate ((L H)(PF )) and
2+
6
Me
N+
0
0
N -methyl-2,3 -bipyridinium
2
hexafluorophosphate
(L H)(PF )) were prepared by the reaction of corre-
N
N
PF -
N
N
N
6
(
N Ru N
6
N Ru N
Cl Cl
2 AgPF6
0
0
sponding 2,4 - or 2,3 -bipyridine with MeI, followed
by the anion exchange by using NH PF (Eq. (1)). Sin-
2
gle crystals of (L H)(PF ) suitable for X-ray diffraction
N
N
2
(PF6)2
4
6
Me
6
were grown from acetone–Et O.
2
2
The molecular structure of (L H)(PF ) is shown in
2
2
+
6
Me
N+
N
1
Fig. 1. The Ru(II) complex [RuL (bpy) ](PF ) (1) was
2
6 2
PF -
6
N N
N Ru N
N
N
Me
3
synthesized by the reaction of [Ru(bpy) Cl ] with
2
2
Et N
3
1
L H)(PF ) in ethanol in the presence of NEt under re-
(
(PF6)2
6
3
flux conditions (Scheme 1). The cyclometalation reac-
tion took place smoothly, and 1 was obtained in 42%
yield after recrystallization. Complex 2 was also pre-
pared by the reaction of [Ru(bpy) Cl ] with
+
2
2
2
(
L H)(PF ), similarly to complex 1. However, the prod-
6
N N
N Ru N
uct was mixtures of several species, and separation of 2
was not succeeded. Therefore, 2 was synthesized by the
N
N
(
PF6)
2
2
reaction of (L H)(PF ) with AgPF -treated [Ru-
6
6
4
(bpy) Cl ] in ethanol (41% yield). The ESI-MS spectra
2 2
of 1 and 2 showed the parent peak at m/z = 292. Inter-
Scheme 1.

T. Koizumi et al. / Journal of Organometallic Chemistry 690 (2005) 1258–1264
1261
at d 7.89 (singlet), 8.36 (doublet), and 8.45 (doublet) in
, and d 7.30 (doublet), 7.75 (doublet), and 9.00 (singlet)
in 2, respectively.
1
1
3
1
In C{ H} NMR, a remarkable difference between 1
and 2 was observed. Complex 1 exhibited a resonance at
d 190.1 which is assigned to the carbon which is bonding
to ruthenium directly. This chemical shift is similar to
those of the carbon directly coordinating to the Ru cen-
+
ter in the PhPy ligand of [Ru(bpy) (PhPy)] (d 193.1)
2
[
gand of [RuL(terpy)]
12d], and that in the quaternized (N,N,C) tridentate li-
2
+
00
0
(d 183.7, L = N -methyl-4 -
methylthio-2,2 :6 ,4 -terpyridine) [22], suggesting that
0
0
00
this C N ring has aromaticity and coordinates to the
5
Fig. 2. ORTEP drawing of the cationic part of 2. Hydrogen atoms are
omitted for larity.
Ru center as pyridinium. In contrast with 1, the reso-
nance of corresponding carbon in 2 was observed at d
232.1, shifting to lower field by ca. 40 ppm. This lowfield
shift indicates that the Ru–C bond in 2 contains a carbe-
0
estingly, when N-methyl-2,2 -bipyridinium hexafluoro-
3
phosphate ((L H)(PF )) was reacted with [RuCl (bpy) ],
6
2
2
nic character, that is, the C N ring forms a pyridinylid-
5
corresponding (N,C) complex 3 was not obtained but
[
Fig. 2 shows the molecular structure of 2 determined
2
Ru(bpy)3] (4) was only generated.
+
ene structure (Scheme 2). Such bidentate ligands
coordinating by a pyridinylidene fashion have not been
reported so far.
by X-ray diffraction study, and selected bond lengths
and angles are summarized in Table 1. The dication of
the complex is hexacoordinated and the structure is
Cyclic voltammetry data for the complexes 1, 2, and
reference complexes such as [Ru(bpy) ](PF ) (4), [Ru-
3
6 2
2
+
(bpy)
2
(PhPy)](PF
0
6
) (5), and [Ru(bpy)
2
(NPP)](PF
6
)
2
(6,
NPP = 4 -nitro-2-(2-pyridyl)phenyl) are given in Table
quite similar to those of [Ru(bpy) ] [20] and [Ru-
3
+
bpy) (PhPy)] [3b]. The Ru–C bond length of 2
˚
2.011(6) A) is shorter than those of Ru–N bonds
˚
2.058(4)–2.120(5) A) and other Ru–C distances in
(
(
(
2
2. Complex 1 showed one reversible Ru(III)/Ru(II) re-
+
dox couple at E1/2 = 0.51 V (vs Fc/Fc ) and two revers-
ible ligand-based redox processes at E1/2 = ꢀ1.49 and
ruthenium complexes involving cyclometallated bipyri-
˚
dine analogs (2.017(3)–2.133(5) A) [1b,11b,12b,14,21],
indicating that the Ru–C bond of 2 contains carbenic
character. Because of the trans influence, the Ru–N4
bond, which is located at trans position of Ru–C8 bond,
is longer than other Ru–N bonds.
ꢀ
1.88 V. Those redox potentials are much the same as
those of 6, suggesting that not only t orbital energy
2
g
of the central ruthenium atoms in 1 and 6 but also p*-
orbital levels of the quaternized (N,C) ligand and the
NPP one in those complexes are quite close with each
other. It is worthy of note that the Ru(III)/Ru(II) redox
potentials of 1 and 2 are situated at more negative than
that of 4 approximately by 450 mV, and at more positive
than that of 5 by 400 mV. The difference in the redox
potentials of the Ru(III)/Ru(II) couple between 4 and
The symmetry of these complexes are lower, hence,
every aromatic protons in these complexes are inequiva-
1
lent chemically and magnetically. In the H NMR spec-
tra, both complexes showed 23 resonances for two bpy
and the (N,C) ligands in the aromatic region, and one
singlet methyl signal of the N–Me group at d 4.13 (1)
and 4.18 (2), respectively. Resonances of the proton in
the quaternized moiety-containing ring were observed
5
apparently results from the strong electron donor abil-
ity of the C-coordinated phenyl ring compared with that
of N-coordinated pyridyl one. The order of the redox
potentials in Table 2, therefore, indicates that the elec-
tron donor ability of C-coordinated pyridinyl rings is
substantially weakened by quaternization but still is
stronger than that of N-coordinated pyridyl ring. The
first and the second ligand-localized redox potentials
in 1 and 2 are assigned to the reductions of the (N,C) li-
gand (ꢀ1.49 V (1) and ꢀ1.74 V (2)) and the bpy one
Table 1
˚
Selected bond distances (A) and angles (°) of 2
Ru1–N1
Ru1–N4
Ru1–N6
N2–C11
2.071(5)
2.120(5)
2.058(4)
1.50(1)
Ru1–N3
Ru1–N5
Ru1–C8
2.077(5)
2.064(6)
2.011(6)
N1–Ru1–N3
N1–Ru1–N5
N1–Ru1–C8
N3–Ru1–N5
N3–Ru1–C8
N4–Ru1–N6
N5–Ru1–N6
N6–Ru1–C8
84.7(2)
98.4(2)
79.6(2)
172.4(2)
96.4(2)
88.2(2)
78.7(2)
96.6(2)
N1–Ru1–N4
N1–Ru1–N6
N3-Ru1–N4
N3-Ru1–N6
N4–Ru1–N5
N4–Ru1–C8
N5–Ru1–C8
95.9(2)
175.2(2)
77.4(2)
98.6(2)
95.3(2)
172.7(2)
91.0(2)
Me
Me
+
N
N
N
N
+
[
Ru]
[Ru]
Scheme 2.

1262
T. Koizumi et al. / Journal of Organometallic Chemistry 690 (2005) 1258–1264
Table 2
Electrochemical data for ruthenium(II) complexes
Species
1/2
E V
n+ (n ꢀ 1)+
[Ru] /[Ru]
(n ꢀ 1)+
(n ꢀ 2)+
Ru(III)/Ru(II)
[Ru]
/[Ru]
Rest potential
1
2
+0.51
+0.59
+0.96
+0.10
+0.51
ꢀ1.49
ꢀ1.74
ꢀ1.59
ꢀ1.80
ꢀ1.50
ꢀ1.88
ꢀ1.92
ꢀ1.76
ꢀ2.09
ꢀ0.47
ꢀ0.45
ꢀ0.55
ꢀ0.31
[Ru(bpy)
[Ru(bpy)
[Ru(bpy)
3
2
2
(PF
(PhPy)](PF
(NPP)](PF
6 2
) (4)
6
) (5)
a
b
b
6
)
2
(6)
–
–
ꢀ1
4 4
Data taken from cyclic voltammetry at 50 mV s , in DMSO, with 0.1 M Me NBF as supporting electrolyte at room temperature. Potentials in V vs
+
Fc/Fc .
a
Reference [3b].
Not measured.
b
(
ꢀ1.88 V (1) and ꢀ1.92 V (2)), respectively. The redox
ligands lowers the energy level of the p* orbital. In the
present study, the bathochromic shift of the MLCT
band of 1 approximately by 40 nm compared with that
of 4 is ascribed to the r-donating pyridinium ligand. On
the other hand, The MLCT absorption maximum of 2 is
close to that of 4 (kmax = 451 nm). Based on the compar-
ison of the first ligand-localized reduction potentials be-
tween 1 and 2, the carbenic character of 2 increases the
electron density of the ligand probably due to the p-back
donation. So, we propose that the p-bond character of 2
potentials of the Ru(III)/Ru(II) couple, the first ligand-
centered process, and the second one of 2 appear at 80
mV more positive, 250 and 40 mV more negative,
respectively, compared with those of 1. Among the three
redox couples, the significant cathodic shift of the first
ligand-localized potential of 2 (DE1/2 = ꢀ250 mV) based
on that of 1 would be correlated with strong p back
donation from ruthenium(II) to the pyridinylidene li-
gand in 1, since such d–p interaction is not expected
for the Ru–C bond in 1.
Electronic spectra of 1 and 2, and of reference com-
plexes 4 and 5 in CH CN are shown in Fig. 3, and these
Table 3
UV–Vis spectral data for complexes in CH CN
3
3
data are summarized in Table 3. Complexes 1 and 2
show a strong absorption maximum at 490 nm (1) and
ꢀ1
ꢀ1
Species
kmax (nm) (e (L mol cm ))
1
2
4
5
490 (5016)
479 (sh)
431 (sh)
378 (sh)
344 (6368)
341 (12,890)
323 (sh)
4
52 nm (2), respectively, which are attributed to metal-
452 (13610)
423 (sh)
492 (7570)
379 (9618)
356 (sh)
404 (9487)
to-ligand charge transfer (MLCT). Metal–carbon bond
formation results in an increase of the r-donor charac-
ter which apparently destabilizes the metal t2g orbital.
As a result, introduction of metal–carbon bond shifts
the MLCT band maximum to longer wavelength [3].
The electron withdrawing group-substituted (N,C) li-
gand also causes a bathochromic shift of the MLCT
band, since introduction of p-acceptor substituents to
451 (15,000)
547 (8500)
368 (10,300)
Table 4
Crystal data and details of the structure refinement of 2 and
2
(
6
L H)(PF )
2
2 Æ MeCN
6
(L H)(PF )
Formula
C
33
29
H F
12
N
7
P
2
Ru
11 10 6 2
C H F N P
Molecular weight
Crystal system
Space group
914.64
Monoclinic
P2 /c (No. 14)
315.18
Orthorhombic
Pna2 (No. 33)
1
1
˚
a (A)
9.032(1)
32.565(4)
12.872(2)
99.242(2)
3737.1(9)
4
15.347(8)
20.16(1)
8.410(4)
˚
b (A)
˚
c (A)
b (°)
V (A )
˚
3
2602(2)
8
2.74
Z
ꢀ1
l (cm
F(000)
)
6.01
1832.00
1.626
8304
1272.00
1.609
3058
3168
362
ꢀ3
D
calc (g cm
)
No. unique reflns
No. reflns used
No. variables
8304
514
R
R
R
1
0.098
0.146
0.232
0.092
0.155
0.189
w
2
2
2
c
Fig. 3. UV–Vis absorption spectra of 1, 2, 4, and 5 in CH
solutions at room temperature.
3
CN
R
1
= RiF
o
| ꢀ |F
c
i/R|F
o
|
for I > 2.0r(I) data, Rw ¼ R½xðF o ꢀ F Þ =
2
2 1=2
2 1/2
RxðF Þ ꢁ . Weighting scheme [{R(F
o
)} ] .
o

T. Koizumi et al. / Journal of Organometallic Chemistry 690 (2005) 1258–1264
1263
causes the hypsochromic shift of the MLCT band com-
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,
(
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