Ruthenium and rhenium complexes with silyl-substituted bipyridyl ligands

Article abstract of DOI:10.1016/S0022-328X(00)00429-0

The preparation of 5,5′-bis(trimethylsilyl)- (1a) and 5,5′-bis(pentamethyldisilanyl)-2,2′-bipyridines (1b) by dehalogenative coupling of the corresponding 2-bromo-5-silylpyridines is described. Silyl substitution causes broad and red shifted π → π* and σ → π* UV-vis absorption bands; electrochemical reduction is facilitated. With these ligands, a series of ruthenium complexes [Ru(bpy)₂(L)](PF₆)₂ (3a, L = 1a; 3b, L = 1b) and [RuL₃](PF₆)₂ (4a, L = 1a; 4b, L = 1b), as well as rhenium compounds Re (L)(CO)₃Cl (5a, L = 1a; 5b, L = 1b) (bpy = 2,2′-bipyridine) were synthesized. These complexes give rise to red-shifted metal-to-lig-and charge-transfer absorptions in the region of 460-480 nm for the ruthenium complexes and around 400 nm for the rhenium complexes. While the oxidation potentials of ruthenium complexes 3a, 3b, 4a, and 4b are almost the same as that of [Ru(bpy)₃](PF₆)₂, reduction of the ruthenium and rhenium complexes occurs at more positive potentials than that of [Ru(bpy)₃](PF₆)₂ and Re(bpy)(CO)₃Cl. Band maxima of the metal-to-ligand charge-transfer emission of the ruthenium and the rhenium complexes were observed at 620 and 610 nm, respectively. The results indicate that the LUMO levels of 2,2′-bipyridine and its metal complexes are lowered by electron-accepting effects of trimethylsilyl and pentamethyldisilanyl substituents, while the HOMO level of bpy is elevated by pentamethyldisilanyl substitution due to the effective σ-π conjugation between an Si-Si bonding orbital and a bpy π orbital.

Full text of DOI:10.1016/S0022-328X(00)00429-0

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 612 (2000) 117–124
Ruthenium and rhenium complexes with silyl-substituted bipyridyl
ligands
Andreas F. Stange a, Satoshi Tokura b, Mitsuo Kira a,b,
*
a Department of Chemistry, Graduate School of Science, Tohoku Uni6ersity, Aoba-ku, Sendai 980-8578, Japan
b Photodynamics Research Center, The Institute of Physical and Chemical Research, 19-1399, Koeji, Nagamachi, Aoba-ku,
Sendai 980-0868, Japan
Received 15 March 2000; received in revised form 8 May 2000; accepted 19 May 2000
Abstract
The preparation of 5,5%-bis(trimethylsilyl)- (1a) and 5,5%-bis(pentamethyldisilanyl)-2,2%-bipyridines (1b) by dehalogenative
coupling of the corresponding 2-bromo-5-silylpyridines is described. Silyl substitution causes broad and red shifted p“p* and
s“p* UV–vis absorption bands; electrochemical reduction is facilitated. With these ligands, a series of ruthenium complexes
[Ru(bpy)2(L)](PF6)2 (3a, L=1a; 3b, L=1b) and [RuL3](PF6)2 (4a, L=1a; 4b, L=1b), as well as rhenium compounds Re
(L)(CO)3Cl (5a, L=1a; 5b, L=1b) (bpy=2,2%-bipyridine) were synthesized. These complexes give rise to red-shifted metal-to-lig-
and charge-transfer absorptions in the region of 460–480 nm for the ruthenium complexes and around 400 nm for the rhenium
complexes. While the oxidation potentials of ruthenium complexes 3a, 3b, 4a, and 4b are almost the same as that of
[Ru(bpy)3](PF6)2, reduction of the ruthenium and rhenium complexes occurs at more positive potentials than that of
[Ru(bpy)3](PF6)2 and Re(bpy)(CO)3Cl. Band maxima of the metal-to-ligand charge-transfer emission of the ruthenium and the
rhenium complexes were observed at 620 and 610 nm, respectively. The results indicate that the LUMO levels of 2,2%-bipyridine
and its metal complexes are lowered by electron-accepting effects of trimethylsilyl and pentamethyldisilanyl substituents, while the
HOMO level of bpy is elevated by pentamethyldisilanyl substitution due to the effective s–p conjugation between an SiꢀSi
bonding orbital and a bpy p orbital. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Ruthenium complexes; Rhenium complexes; Silyl substituted bipyridyl ligands
1. Introduction
upon excitation of the MLCT band. For more detailed
understanding of these phenomena extensive investiga-
tions of well-defined mononuclear model compounds
are necessary.
2,2%-Bipyridine derivatives are the most widely used
chelates for metal binding. Systematic variations of
substituents have served as important tools for the
understanding of physical properties of metal com-
plexes [1]. Among metal bipyridine complexes research
was focussed on ruthenium and to a lesser extent on
rhenium complexes, because of their potential use in
light harvesting systems and as photocatalysts [1].
Functionalization and linkage of bipyridine ligands
were used to tune the photochemical properties of the
complexes and to create supramolecular systems [2].
Recently we reported the optoelectronic properties of
Very recently the synthesis of macrocyclic ligands
bearing two 2,2%-bypyridine units interconnected at 4-
and 4%-position by two ꢀ(CH2)Si(CH3)2(CH2)ꢀ or
ꢀ(CH2)2Si(C6H5)2(CH2)2ꢀ spacers was reported [4]. Due
to the presence of fragile benzylic positions, a ruthe-
nium complex could only be prepared with the latter
ligand [4b]. However, neither simple silyl substituted
bipyridines nor their metal complexes have been re-
ported so far. We here present the synthesis and prop-
erties of 5,5%-bis(trimethylsilyl)- (1a) and 5,5%-bis(penta-
methyldisilanyl)-2,2%-bipyridines (1b) as well as their
ruthenium(II) and rhenium(I) complexes. The influence
of silyl substitution on the spectroscopic and electro-
chemical properties of 2,2%-bipyridine and its metal
complexes will be discussed.
polymers bearing alternating silicon
bipyridyl p units in the backbone [3]. Ruthenium com-
plexes of these polymers showed photoconductivity
s and 2,2%-
* Corresponding author. Fax: +81-22-2176589.
E-mail address: mkira@si.chem.tohoku.ac.jp (M. Kira).
0022-328X/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00429-0

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A.F. Stange et al. / Journal of Organometallic Chemistry 612 (2000) 117–124
2. Results and discussion
2.1. Synthesis and properties of
5,5%-disilyl-2,2%-bipyridyls 1a and 1b
Our approach to silyl substituted 2,2%-bipyridines re-
lies upon the nickel(0) coupling of 2-halopyridines [5–
9], as shown in Scheme 1. Lithiation of 2,5-dibromo
pyridine at −90°C followed by treatment with tri-
methylchlorosilane and pentamethylchlorodisilane gave
2-bromo-5-trimethylsilyl- (2a) and 2-bromo-5-penta-
methyldisilanylpyridines (2b), respectively, with high re-
gioselectivity in good yields [10]. Bromosilylpyridines 2a
and 2b were coupled to the corresponding bipyridyl
derivatives to give 1a and 1b in 35% and 55% yields,
respectively. Bipyridines 1a and 1b show very good
solubility in organic solvents like ether, toluene, and
chloroform, but they hardly dissolve in solvents with
higher polarity such as acetone, acetonitrile, and alco-
hols. These new ligands exhibited the expected NMR
spectroscopic properties.
Fig. 1. UV–vis spectra of free bipyridines in CH2Cl2.
reversible reduction wave, whereas the reduction of 1b
remains irreversible even at scan rates of 1 V s−1. In
both cases peak potentials were found to be shifted to
more positive potentials compared to unsubstituted
2,2%-bipyridine. Facilitated electrochemical reduction in-
dicates the lower LUMO energy levels of 1a and 1b in
the same extent.
UV–vis spectral and electrochemical data of 1a and
1b are summarized in Table 1; the UV–vis spectra are
shown in Fig. 1. Compared to parent 2,2%-bipyridine,
both 1a and 1b exhibit more intense and red shifted
p–p* absorption bands at around 300 nm. The major
reason for the red shift of both 1a and 1b would be
ascribed to lowering the LUMO energy level due to the
electron-accepting effect of silyl substituents [11]. The
more pronounced red-shift in the electronic spectrum of
1b than that of 1a is suggestive of the higher HOMO
level of 1b due to the effective hyperconjugation be-
tween the SiꢀSi s orbital and the heteroaromatic p
HOMO. The above explanation is supported by the
electrochemical data in THF. Bipyridyl 1a exhibits a
2.2. Synthesis of metal complexes with 1a and 1b as
ligands
Two different types of ruthenium complexes with
silyl-substituted bipyridyl ligands were synthesized; het-
eroleptic complexes [Ru(bpy)2(L)](PF6)2 (3a, L=1a; 3b,
L=1b) and [RuL3](PF6)2 (4a, L=1a; 4b, L=1b). The
ruthenium complexes were obtained as red brown solids
by refluxing the appropriate metal precursors
[Ru(bpy)2Cl2](H2O)2 [12] and Ru(dmso)4Cl2 [13]
(dmso=dimethylsulfoxide) in the presence of 1a and
1b and subsequent precipitation with hexafluorophos-
Scheme 1.
Table 1
Spectroscopic a and electrochemical data b of free bipyridines
Bpy
Me3SibpySiMe3 (1a)
Me5Si2bpySi2Me5 (1b)
umax (nm c) (m (l mol−1cm−1))
283 (14 000)
244 (9500)
237 (11 000)
−2.80
294 (22 400)
253 (14 700)
246 (14 100)
−2.63
303 (25 700)
256 (11 000)
Ered
−2.63 (pc)
a In CH2Cl2.
b From cyclic voltammetry at 100 mV s−1 in THF–Bu4NPF6 (0.1 M). Potentials in V versus ferrocene/ferrocenium. (pc); cathodic peak potential
for irreversible reduction.
c
92 (nm).

A.F. Stange et al. / Journal of Organometallic Chemistry 612 (2000) 117–124
119
1
phate salts. In the course of the experiments we realized
that the disilanyl group of metal coordinated 1b was
very sensitive towards acidic conditions. In contrast to
4a, precipitation of 4b with NH4PF6 led to significant
decomposition of the coordinated ligand probably by
electrophilic desilylation of the heterocycle [14]. Due to
the lower solubility of 1b in polar solvents longer
reaction times or higher temperatures were necessary
for the synthesis of 3b and 4b. Rhenium complexes
Re(L)(CO)3Cl (5a, L=1a; 5b, L=1b) were prepared
by refluxing Re(CO)5Cl in toluene in the presence of the
ligands [15]. Slow cooling of the reaction mixtures
afforded yellow crystalline substances. All metal com-
plexes of 1a and 1b have a greater solubility in organic
solvents in comparison with the parent bipyridine
compounds.
bipyridine ligands (Fig. 2). For this reason, H- as well
as 13C-NMR spectra of 3a and 3b exhibited somewhat
more complicated patterns. Moreover, resonances of
the methyl protons of the dimethylsilyl unit in spectra
of 3b showed diastereotopic splitting due to the chiral-
1
ity of the metal center. All H-NMR resonances for 3a
and 3b could be assigned by comparing with the corre-
sponding resonances for analogous homoleptic
compounds.
The general effects of the Re complexation to 1a and
1b on the proton resonances are somewhat downfield
shifts of singlets due to 6- and 6%-and 4- and 4%-protons,
and up-field shift of 3- and 3%-protons [17]. The H-
NMR spectrum of 5b also exhibited two signals for the
nonequivalent methyl groups of the dimethylsilyl
1
group; one methyl group is cis and the other one trans
to Cl atom.
2.3. Spectroscopic studies of the metal complexes
The carbonyl stretching frequencies of the rhenium
complexes are given in Table 2. Three intense w(CO)
modes were observed confirming the facial structure of
the complexes [15]. The band with the highest fre-
quency is assigned to wsym(CO) of the carbonyl group
cis to the Cl atom [18]. Electron withdrawing sub-
stituents on the bipyridine ligand shift the frequency
energy to higher values [17], indicating that the disilanyl
substituent is more electron donating than trimethylsilyl
and methyl groups.
In Table 3 UV–vis data for the metal complexes are
summarized. For the ruthenium compounds two basic
types of transitions were observed (Fig. 3). These are
MLCT transitions in the regions of 250 and 450 nm,
the latter causing the intense red color of the sub-
1H-NMR spectra of complexes 4a and 4b revealed
clear separation of the three aromatic proton reso-
nances. Hydrogen atoms at 6- and 6%-positions of the
silylated bipyridines exhibited the expected shift from
8.7 to 7.6 ppm upon ruthenium coordination. Coordi-
nation of a bidentate ligand like 2,2%-bipyridine to the
six-coordinated ruthenium center gives rise to two
enantiomeric forms, L and D [16]. Substitution of one
bipyridine of (bpy)3Ru2+ to 1a or 1b causes different
chemical surroundings for the equatorial and axial pyr-
idine rings of the remaining two unsubstituted
Table 2
Carbonyl stretching frequencies of Re complexes a
w (cm−1
)
Reference
Re(1a)(CO)3Cl
Re(1b)(CO)3Cl
Re(MebpyMe)(CO)3
2017; 1910; 1892
2010; 1916; 1871
2018; 1932; 1909; 1878
This work
This work
[17]
Cl b
a KBr pellets.
Fig. 2. Schematic representation of axial (ax) and equatorial (eq)
pyridine rings as well as diastereotopic methyl groups in complex 3b.
b MebpyMe=4,4%-dimethyl-2,2%-bipyridine.

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A.F. Stange et al. / Journal of Organometallic Chemistry 612 (2000) 117–124
Table 3
Table 4
Spectroscopic data of metal complexes a
Electrochemical data a of metal complexes b
Solvent umax (nm) (m (l mol−1 cm−1))
Solvent
Eox
Ered
[Ru(bpy)3]2+
CH3CN 451 (13 000); 287 (70 500); 244
(23 000)
CH3CN 461 (12 800); 288 (83 400); 246
(32 800)
CH3CN 458 (12 100); 288 (72 600); 246
(28 100)
CH3CN 481 (12 000); 294 (96 500); 252
(34 500)
CH3CN 471 (11 000); 307 (76 500); 264
(34 500)
CH2Cl2 387 (2900); 294 (16 000); 239
(17 000)
CH2Cl2 393 (2900); 324 (13 000, sh); 302
(20 500); 246 (18 000)
CH2Cl2 388 (2900, sh); 327 (20 000); 257
(18 500)
[Ru(bpy)3]2+
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
DMA c
DMA
0.90
−1.72; −1.92; −2.17
[Ru(bpy)2(1a)]2+
[Ru(bpy)2(1b)]2+
[Ru(1a)3]2+
0.92 (pa) −1.68; −1.90; −2.16
0.88 −1.70; −1.92; −2.16
0.92 (pa) −1.64; −1.88; −2.15
[Ru(bpy)2(1a)]2+
[Ru(bpy)2(1b)]2+
[Ru(1a)3]2+
[Ru(1b)3]2+
Re(bpy)(CO)3Cl
Re(1a)(CO)3Cl
Re(1b)(CO)3Cl
0.93
−1.61; −1.83; −2.10
−1.77; −2.42 (pc)
−1.68; −2.32 (pc)
−1.69; −2.33 (pc)
DMA
[Ru(1b)3]2+
a From cyclic voltammetry at 100 mV s−1 in a solution containing
0.1 M Bu4NPF6. Potentials in V versus ferrocene/ferrocenium. (pa):
Anodic peak potential for irreversible oxidation. (pc): Cathodic peak
potential for irreversible reduction.
Re(bpy)(CO)3Cl
Re(1a)(CO)3Cl
Re(1b)(CO)3Cl
b Ru complexes: Hexafluorophosphate salts.
c DMA: N,N-dimethylacetamide.
a All Ru complexes are hexafluorophosphate salts.
stances. Other intense bands at 300 nm are assigned as
intra ligand p–p* transitions [1]. The MLCT absorp-
tion maximum shifts to longer wavelengths with higher
substitution by 1a and 1b; e.g. the absorption maximum
of [Ru(bpy)3](PF6)2[2] at 452 nm shifts to 461 and 480
nm by replacement of one and three bipyridine ligands
by 1a, respectively. This behavior can be explained in
terms of the electron withdrawing effect of the silyl
substituents which lowers the LUMO energy of the
electron-accepting bipyridine ligand [19]. The accepting
ability of trimethylsilyl group is suggested to be slightly
larger than that of pentamethyldisilanyl group by com-
paring the maxima between the Ru complexes with 1a
and 1b as the ligands. The intra-ligand p–p* transitions
of the Ru complexes with 1a and 1b as ligands were
found to be broadened and shifted to lower energies.
Rhenium complexes 5a and 5b also exhibited the
MLCT transitions at 400 and 320 nm and the intra-lig-
and p–p* transitions at higher energy. The spectral
changes of the Re complexes upon introducing the silyl
groups on bipyridine ligand are similar to those found
in the Ru complexes: a slightly red-shifted MLCT band
and a broader p–p* transition due to s-donation of the
silyl groups were observed (Fig. 4).
Fig. 3. UV–vis spectra of homoleptic ruthenium complexes
[Ru(L)3](PF6)2 in CH3CN.
2.4. Electrochemistry of the metal complexes
Table 4 shows redox potentials of ruthenium com-
plexes in acetonitrile and rhenium complexes in N,N-
dimethylacetamide (DMA). Ruthenium complexes
exhibit three well-resolved reduction waves. Each re-
duction process involves a ‘spatially isolated’ p* ligand
orbital in the Ru2+ field [1a]. Reduction of 4a at
−1.64 and of 4b at −1.61 V compared to reduction of
[Ru(bpy)3](PF6)2 at −1.72 V is consistent with the
lower energy p* orbitals of 1a and 1b compared to bpy,
as derived from the trends in the electronic spectra. It
is interesting to note that among complexes
Fig. 4. UV–vis spectra of rhenium complexes Re(L)(CO)3Cl in
CH2Cl2.

A.F. Stange et al. / Journal of Organometallic Chemistry 612 (2000) 117–124
121
[Ru(bpy)3](PF6)2, 3a, and 3b only the first reduction
potential differs, whereas the second and the third
reductions occurs at the same potential within the
experimental error. This observation is rationalized by
the first reduction occurring on the silyl substituted
ligands 1a and 1b in 3a and 3b, respectively, while the
second and third reduction on the unsubstituted
bipyridines, supporting the ‘isolation’ of the p* ligand
orbitals.
Since the oxidation potentials of the Ru complexes,
which were assigned to oxidation of the ruthenium(II)
center [1a], [19], did not change significantly, the silyl-
substituents do not seem to affect the metal d orbital
energy. While oxidation of 3a and 4a was reversible, the
oxidation of the corresponding Ru complexes with 1b
was irreversible due to adsorption processes.
Oxidation of both 5a and 5b could not be achieved in
DMA, but they exhibited one reversible reduction wave
followed by an irreversible one. The first one was
assigned to the reduction of the bipyridyl ligand and the
second irreversible one was accompanied by chloride ion
formation [20]. Again, reduction of 5a and 5b occurs at
more positive potentials than that of Re(bpy)(CO)3Cl; 5a
and 5b at −1.68 and −1.69 V, respectively, while
Re(bpy)(CO)3Cl at −1.77 V.
silyl-substituted bipyridyl ligands were found to be
shifted around 10 nm to longer wavelengths than that of
[Ru(bpy)3](PF6)2; a similar silyl-substituent effect was
observed for rhenium complexes, while the shift was
smaller. At 77 K ruthenium emission maxima shifted to
higher energy, confirming this transition as MLCT in
character [1].
3. Concluding remarks
Very recently, metal complexes of polymers containing
alternating 2,2%-bipyridine and carbon[21] or silicon[3]
based spacers have been reported as systems with photo-
conducting properties. Mechanistically, electrons will be
injected into the polymer backbone through excitation of
the MLCT transition of the [Ru(bpy)2]2+ complexes of
the polymers and then transported away through intra-
chain migration. The efficiency of this process depends
both on charge transportation and direction of the
charge injection. Mabrouk and Wrighton have shown
that electron releasing and withdrawing substituents on
2,2%-bipyridine have influenced on the localization of the
exited electrons [22]. Generally, for mixed-ligand com-
plexes, the exited electrons are localized on the more
easily reduced ligand. Accordingly, the exited electrons
will be localized on the unsubstituted bipyridyl ligands
in the lowest exited state for [Ru(Me2bpy)(bpy)2]2+
(Me2bpy=4,4%-dimethylbipyridyl), but on the silyl-sub-
stituted bipyridyls for 4a or 4b. Considering
[Ru(Me2bpy)(bpy)2]2+ as a model unit for a ruthenium
containing polymer with a carbon spacer, the advantage
of polymers with a silicon spacer becomes evident:
electron transportation in the latter polymer should be
more efficient, because the exited electron will be initially
directed on the bipyridine which is part of the polymer
backbone.
2.5. Luminescence
Both ruthenium and rhenium complexes with
bipyridyl ligands exhibit typical luminescence at around
600 nm originated from a MLCT exited state. The
luminescence band maxima of the examined complexes
are summarized in Table 5. Luminescence at room
temperature was observed in acetonitrile for ruthenium
complexes and in dichloromethane for rhenium com-
pounds. Emission maxima of ruthenium complexes with
Table 5
Luminescence a of metal complexes b
4. Experimental
Complex
Solvent
CH3CN
T (K)
umax (em) (nm)
4.1. General methods
[Ru(bpy)3]2+
[Ru(bpy)2(1a)]2+
[Ru(bpy)2(1b)]2+
[Ru(1a)3]2+
293
610
580
621
588
617
584
623
596
622
595
607
615
612
EtOH–MeOH c 77
Reactions were carried out under dry argon atmo-
sphere using standard Schlenk techniques. Diethyl ether,
THF, toluene, and hexane were freshly distilled from
sodium. Bis(triphenylphosphine)nickel(II) bromide [23],
bis(2,2%-bipyridine)ruthenium(II) chloride [12], and
CH3CN
EtOH–MeOH
CH3CN
EtOH–MeOH
CH3CN
EtOH–MeOH
CH3CN
293
77
293
77
293
77
293
77
293
293
293
tetrakis(dimethylsulfoxide)ruthenium(II)
chloride[13]
[Ru(1b)3]2+
were prepared according to the methods in literature.
Other chemicals were commercially available and used
as received.
EtOH–MeOH
Re(bpy)(CO)3Cl
Re(1a)(CO)3Cl
Re(1b)(CO)3Cl
DMA d
DMA
DMA
1H- (300 MHz), 13C- (75.4 MHz), and 29Si- (59.6 MHz)
NMR spectra were measured on a Bruker AC300P
a After irradiation of the MLCT band.
NMR spectrometer. H- and 13C-NMR chemical shifts
1
b All Ru complexes are hexafluorophosphate salts.
c A 4:1 mixture.
are referenced to residual solvent peaks. 29Si-NMR
chemical shifts are relative to Me4Si. Electronic
d DMA: N,N-dimethylacetamide.

122
A.F. Stange et al. / Journal of Organometallic Chemistry 612 (2000) 117–124
spectra were recorded on a Milton Roy SP-3000 spec-
trometer. Fluorescence spectra were recorded on a
Hitachi 850 fluorescence spectrophotometer. Infrared
spectra were recorded on a Shimadzu FTIR-8600PC
spectrometer. Cyclic voltammetric experiments were
performed with a HA-501 potentiostat and an HB-104
function generator from Hokuto Denko in dry acetoni-
trile or N,N-dimethylacetamide containing 0.1 M
Bu4NPF6 using a three-electrode configuration (glassy-
carbon electrode, Pt counter electrode, Ag/AgCl refer-
ence). The ferrocene/ferrocenium couple served as
internal reference.
aqueous ammonia. Separation of organic layer, extrac-
tion of the aqueous layer with diethyl ether, removal of
the solvent from the combined organic layer under
reduced pressure, and recrystallization from methanol
1
gave 1a (1.59 g, 25%). H-NMR (CDCl3) l 0.31 (s, 18
3
4
H, Si(CH3)3), 7.90 (dd, 2 H, J=8.0 Hz, J=2.0 Hz,
3
4,4%-H), 8.33 (d, 2H, J=7.5 Hz, 3,3%-H), 8.74 (d, 2 H,
4J=1.3 Hz, 6,6%-H). 13C-NMR (CDCl3) l −1.0
(Si(CH3)3), 120.5, 135.6, 142.4, 153.7, 156.6. 29Si-NMR
(CDCl3) l −3.81. Anal. Calc. for C16H24N2Si2: C,
63.94; H, 8.05; N, 9.32. Found: C, 63.86; H, 7.88; N,
9.31%.
Compound 1b was prepared by the same procedure:
colorless crystals: m.p. 142°C; 52% yield. 1H-NMR
(CDCl3) l 0.06 (s, 18 H, Si(CH3)3), 0.37 (s, 12 H,
4.2. 2-Bromo-5-trimethylsilylpyridine (2a) and
2-bromo-5-pentamethyldisilanylpyridine (2b)
3
4
Si(CH3)2), 7.83 (dd, 2H, J=7.8, J=1.7 Hz, 4,4%-H),
3
5
A hexane solution of n-butyllithium (1.6 M, 34.0 ml)
was added slowly to a solution of 2,5-dibromopyridine
(13.0 g, 54.9 mmol) in diethyl ether (150 ml) at −90°C.
After stirring for 1 h at −90°C, trimethylchlorosilane
(5.96 g, 54.9 mmol) in ether (10 ml) were added via a
cannula. Stirring was continued for another hour, then
the solution was allowed to warm up to 0°C followed
by hydrolysis with water (100 ml) and then separated.
The aqueous layer was extracted with diethyl ether
(four times, 40 ml) and the solvent of the combined
organic layer was removed under reduced pressure.
Final kugelrohr distillation (115°C, 10 mm Hg) gave 2a
8.31 (dd, 2 H, J=7.7, J=1.0 Hz, 3,3%-H), 8.67 (m, 2
H, 6,6%-H). 13C-NMR (CDCl3) l −4.1, −2.1, 120.5,
135.3, 142.7, 153.9, 156.2. 29Si-NMR (CDCl3) l −22.1,
−19.0. Anal. Calc. for C20H36N2Si4: C, 57.63; H, 8.70;
N, 6.72. Found: C, 57.17; H, 8.57; N, 6.75%.
4.4. Bis(2,2%-bipyridine)(5,5%-trimethylsilyl-
2,2%-bipyridine)ruthenium(II) hexafluorophosphate (3a)
A
mixture of 1a (114 mg, 0.37 mmol) and
Ru(bpy)2Cl2 (157 mg, 0.30 mmol) were refluxed for 12
h in ethanol (40 ml). Addition of a solution of NH4PF6
(2.0 g) in water (10 ml), evaporation of ethanol and
addition of water lead to precipitation of red 3a (250
mg, 83%). 1H-NMR (CD3CN) l 0.09 (s, 18 H,
Si(CH3)3), 7.39 (dq, 4 H, 3J=7.3 Hz, 4J=1.1 Hz,
bpy-5,5%-H), 7.50 (s, 2 H, Sibpy-6,6%-H), 7.74 (d, 2 H,
1
(11.5 g, 91%) as a colorless liquid. H-NMR (CDCl3) l
3
0.23 (s, 9 H, Si(CH3)3); 7.38 (d, 1 H, J=7.7 Hz, 3-H);
3
4
7.56 (dd, 1 H, J=7.9 Hz, J=2.1 Hz, 4-H); 8.34 (d, 1
H, 4J=1.9 Hz, 6-H); 13C-NMR (CDCl3) l −1.5
(Si(CH3)3), 127.5, 134.0, 143.2, 143.2, 154.1. 29Si-NMR
(CDCl3) l −3.4. Anal. Calc. for C8H12BrNSi: C, 41.74;
H, 5.25; N 6.09. Found: C, 42.11; H, 5.27; N, 6.16%.
Compound 2b was prepared by the same procedure:
colorless liquid. B.p. 130°C (4 mm Hg); yield, 61%.
1H-NMR (CDCl3) l 0.06 (s, 9 H, Si(CH3)3), 0.34 (s, 6
3
3J=5.4 Hz, bpy-6-H), 7.81 (d, 2 H, J=5.5 Hz, bpy-
3
4
6%-H), 8.07 (dq, 4 H, J=7.9 Hz, J=1.2 Hz, bpy-4,4%-
H), 8.12 (dd,
2
H, 3J=8.0 Hz, 4J=1.3 Hz,
Sibpy-4,4%-H), 8.42 (d, 2 H, 8.0 Hz, Sibpy-3,3%-H), 8.51
(t, 4 H, 3J=7.6 Hz, bpy-3,3%-H). 13C-NMR (CD3CN) l
−3.3 (Si(CH3)3), 122.9, 123.8, 124.0, 127.1, 127.3,
137.4, 137.5, 140.7, 142.2, 151.5, 151.7, 153.7, 156.6,
156.8, 156.9. 29Si-NMR (CD3CN) l −2.3. Anal. Calc.
for C36H40F12N6P2RuSi2: C, 43.07; H, 4.02; N, 8.37.
Found: C, 43.51; H, 4.24; N, 8.37%.
3
H, Si(CH3)2), 7.43 (d, 1 H, J=7.8 Hz, 3-H), 7.54 (dd,
1 H, 3J=7.8 Hz, 4J=2.1 Hz, 4-H), 8.33 (d, 1 H,
4J=1.9 Hz, 6-H). 13C-NMR (CDCl3) l -4.3, −2.5,
127.6, 133.9, 142.9, 143.6, 154.4. 29Si-NMR (CDCl3) l
−21.8, −19.2.
4.3. 5,5%-Di-(trimethylsilyl)-2,2%-bipyridine (1a) and
5,5%-di-(pentamethyldisilanyl)-2,2%-bipyridine (1b)
4.5. Bis(2,2%-bipyridine)(5,5%-pentamethyldisilanyl-2,2%-
bipyridine)ruthenium(II) hexafluorophosphate (3b)
Bis(triphenylphosphine)nickel(II) bromide (3.10 g,
4.15 mmol), freshly activated zinc (6.00 g, 91.8 mmol),
and tetraethylammonium iodide (3.00 g, 1.17 mmol)
were placed in a 100 ml two-necked flask equipped with
a condenser and dried under vacuum at 70°C for 2 h.
THF (5 ml) was injected by a syringe, and the brown
slurry was stirred for 30 min at 50°C. After adding a
solution of 2a (9.55 g, 41.5 mmol) in THF (15 ml) and
refluxing for 3 h, the mixture was poured into diluted
Ru(bpy)2Cl2 (60.5 mg, 0.116 mmol), 1b (48.5 mg,
0.116 mmol), and ethanol (10 ml) were placed in a
small flask and refluxed for 24 h. The product was
precipitated by addition of saturated aqueous KPF6 (10
ml) and water (10 ml). Filtration, washing with water,
and drying in vacuum gave 3b (74 mg, 57%) as a red
powder. 1H-NMR (CD3CN) l −0.17 (s, 18 H,
Si(CH3)3), 0.13 (s, 6 H, Si(CH3)), 0.16 (s, 6 H, Si(CH%),
3

A.F. Stange et al. / Journal of Organometallic Chemistry 612 (2000) 117–124
123
7.38–7.44 (m, 6 H, bpy−5,5%-H, Sibpy-6,6%-H), 7.74 (d,
temperature rhombic yellow crystals were formed. Fil-
tration and washing with hexane gave 5a (30 mg, 50%).
1H-NMR (CDCl3) l 0.38 (s, 18 H, Si(CH3)3), 8.10 (m,
4 H, bpy-3,3%,4,4%-H), 8.99 (s, 2 H, bpy-6,6%-H). 13C-
NMR (CDCl3) l −1.28 (Si(CH3)3), 122.32, 141.49,
144.17, 155.97, 156.71, 197.68 (CO). 29Si-NMR
(CDCl3) l −1.99. Anal. Calc. for C19H24ClN2O3ReSi2:
C, 37.64; H, 3.99; N, 4.62. Found: C, 37.35; H, 4.10; N,
4.62%. 5b was prepared by the same procedure: yellow
3
3
2 H, J=5.4 Hz, bpy-6-H), 7.81 (d, 2 H, J=5.5 Hz,
bpy-6-H%), 8.02–8.11 (m, 6 H, bpy, Sibpy-4,4%-H), 8.40
(d, 2 H, 3J=8.0 Hz, Sibpy-3,3%-H), 8.51 (t, 4 H,
3J=8.0 Hz, bpy-3,3%-H). 13C-NMR (CD3CN) l −6.29
(br, Si(CH3)2), −3.80 (Si(CH3)3), 122.94 (Sibpy),
123.92 (bpy), 124.06 (bpy%), 127.32 (bpy), 127.37 (bpy%),
137.54 (bpy), 137.67 (bpy%), 140.96 (Sibpy), 142.29
(Sibpy), 151.37 (bpy), 151.70 (bpy%), 153.54 (Sibpy),
156.34 (bpy), 156.47 (bpy%), 156,77 (Sibpy). 29Si-NMR
1
powder; 36% yield; H-NMR (CDCl3) l 0.12 (s, 18 H,
(CD3CN)
l
−20.1, −18.5. Anal. Calc. for
Si(CH3)3), 0.42 (s, 6 H, Si(CH3)(CH3)%), 0.43 (s, 6 H,
3
4
C40H52F12N6P2RuSi2(H2O): C, 42.21; H, 4.78; N, 7.38.
Found: C, 41.70; H, 4.74; N, 7.33%.
Si(CH3)(CH3)%), 8.00 (dd, 2 H, J=7.9 Hz, J=1.3 Hz,
bpy-4,4%-H), 8.08 (d, 2 H, 3J=7.9 Hz, bpy-3,3%-H), 8.94
(s, 2 H, bpy-6,6%-H). 13C-NMR (CDCl3) l −4.25
(Si(CH3)(CH3)%), −4.11 (Si(CH3)(CH3)%), −2.11
(Si(CH3)3), 122.14, 141.58, 144.10, 155.59, 156.94,
197.75 (CO). 29Si-NMR (CDCl3) l −20.09. −18.59.
Anal. Calc. for C23H36ClN2O3ReSi4: C, 38.23; H, 5.02;
N, 3.88. Found: C, 38.73; H, 5.15; N, 3.79%.
4.6. Tris(5,5%-trimethylsilyl-2,2%-bipyridine)ruthenium(II)
hexafluorophosphate (4a)
A mixture of Ru(dmso)4Cl2 (60 mg, 0.12 mmol) and
1a (112 mg, 0.37 mmol) in ethanol (20 ml) were refluxed
for 15 h. Slow addition of a solution of NH4PF6 (2.0 g)
in water (10 ml) and then water (5 ml) gave red
1
Acknowledgements
microcrystalline 4a (75 mg, 47%). H-NMR (CD3CN) l
0.12 (s, 54 H, Si(CH3)3), 7.58 (s, 6 H, bpy-6,6%-H), 8.20
3
4
This work was supported by the Ministry of Educa-
tion, Science, Sports, and Culture of Japan (grant-in-
aid for Scientific Research (A) No. 08404042 (M.K.).
We are also grateful to the European Union for an EU
Science & Technology Fellowship (STF 11 to A.F.S.).
(dd, 6 H, J=8.0, J=1.4 Hz, bpy-4,4%-H), 8.48 (d, 6
H, 3J=7.8 Hz, bpy-3,3%-H). 13C-NMR (CD3CN) l
−3.1 (Si(CH3)3), 123.5, 140.7, 142.2, 153.2, 157.3.
29Si-NMR (CD3CN)
l
−2.2. Anal. Calc. for
C60H108F12N6P2RuSi12: C, 43.90; H, 6.63; N, 5.12.
Found: C, 43.70; H, 6.69; N, 5.01%.
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