Effect of intramolecular π-π and CH-π interactions between ligands on structure, electrochemical and spectroscopic properties of fac-[Re(bpy)(CO)3(PR3)]+ (bpy = 2,2′-bipyridine; PR3 = trialkyl or triarylphosphines)

Article abstract of DOI:10.1039/b407947g

Intramolecular π-π and CH-π interactions between the bpy and PR, ligands fac-[Re(bpy)(CO)₃(PR₃)]⁺ affect their structure, and electrochemical and spectroscopic properties. Intramolecular CH-π interaction was observed between the alkyl groups on the phosphine ligand (R = Bu, Et) and the bpy ligand, and intramolecular π-π and CH-π interactions were both observed between the aryl group(s) on the phosphorus ligand (R = p-MeOPh, p-MePh, Ph, p-FPh, OPh) and the bpy ligand, while no such interactions were found in the trialkylphosphite complexes (R = O′Pr, OEt, OMe). The intramolecular interactions distort the pyridine rings of the bpy ligand as long as 3.7 × 10^-2 A in crystals. Molecular orbital calculations of the bpy ligand suggest that this distortion decreases the energy gap between its and * orbitals. An absorption band attributed to the π-π*(bpy) transition of the distorted rhenium complexes, measured in a K Br pellet, was red-shifted by 1-5 nm compared to the complexes without the distorted bpy ligand. Even in solution, similar red shifts of the π-π*(bpy) absorption were observed. The redox potential E_1/2(bpy/bpy^-) of the complexes with the trialkylphosphine and triarylphosphine ligand are shifted positively by 110-120 m V and 60-80 m V respectively, compared with those derived from the electron-attracting property of the phosphorus ligand. In contrast with these properties, three v_CO IR bands, which are sensitive to the electron density on the central rhenium because of π-back bonding, were shifted to higher energy, and a Re(I/II)-based oxidation wave was observed at a more positive potential according to the electron-attracting property of the phosphorus ligand.

Full text of DOI:10.1039/b407947g

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F U L L P A P E R
Effect of intramolecular p–p and CH–p interactions between ligands
on structure, electrochemical and spectroscopic properties of
fac-[Re(bpy)(CO)3(PR3)]+ (bpy = 2,2ꢀ-bipyridine; PR3 = trialkyl or
triarylphosphines)†
Hideaki Tsubaki,a Shigeki Tohyama,b Kazuhide Koike,c Hideki Saitohb and Osamu Ishitani*a
a Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of
TechnologyCREST, Japan Science and Technology Agency, Okayama 2-12-1, Meguro-ku,
Tokyo 152-8551, Japan
b Graduate School of Science and Engineering, and Molecular Analysis and Life Science Center,
Saitama University, Shimo-Okubo 255, Sakura-ku, Saitama 338-8570, Japan
c National Institute of Advanced Industrial Science and Technology, Onogawa 16-1, Tsukuba
305-8569, Japan
Received 26th May 2004, Accepted 18th November 2004
First published as an Advance Article on the web 6th December 2004
Intramolecular p–p and CH–p interactions between the bpy and PR3 ligands of fac-[Re(bpy)(CO)3(PR3)]+ affect their
structure, and electrochemical and spectroscopic properties. Intramolecular CH–p interaction was observed between
n
the alkyl groups on the phosphine ligand (R = Bu, Et) and the bpy ligand, and intramolecular p–p and CH–p
interactions were both observed between the aryl group(s) on the phosphorus ligand (R = p-MeOPh, p-MePh, Ph,
p-FPh, OPh) and the bpy ligand, while no such interactions were found in the trialkylphosphite complexes (R = OiPr,
OEt, OMe). The intramolecular interactions distort the pyridine rings of the bpy ligand as long as 3.7 × 10−2 A in
˚
crystals. Molecular orbital calculations of the bpy ligand suggest that this distortion decreases the energy gap
between its p and p* orbitals. An absorption band attributed to the p–p*(bpy) transition of the distorted rhenium
complexes, measured in a KBr pellet, was red-shifted by 1–5 nm compared to the complexes without the distorted
bpy ligand. Even in solution, similar red shifts of the p–p*(bpy) absorption were observed. The redox potential
E
1/2(bpy/bpy•−) of the complexes with the trialkylphosphine and triarylphosphine ligand are shifted positively by
110–120 mV and 60–80 mV respectively, compared with those derived from the electron-attracting property of the
phosphorus ligand. In contrast with these properties, three mCO IR bands, which are sensitive to the electron density
on the central rhenium because of p-back bonding, were shifted to higher energy, and a Re(I/II)-based oxidation wave
was observed at a more positive potential according to the electron-attracting property of the phosphorus ligand.
The present study aims to clarify how large interligand weak
interactions affect the molecular structure, redox properties, and
absorption spectra of transition metal complexes in crystal and
Introduction
p–p and CH–p interactions are important noncovalent forces
that contribute to self-assembly and molecular recognition
in solution. Accordingly, we synthesized the series of rhenium(I)
processes in various chemical and biological systems.1–8 In
complexes fac-[Re(bpy)(CO)3(PR3)]+ (1+–10+ in Scheme 1 and
coordination chemistry, these weak interactions are important
Table 1); the phosphorus ligand (PR3) is located in the cis
in determining the conformations,9–12 the selectivities of the
position relative to the 2,2ꢀ-bipyridine ligand (bpy) and the R
reactions,13–15 and the crystal structures16–19 of metal complexes.
group(s) should be closely located to the bpy ligand not only
in crystal but also in solution. The complexes are classified
into three types according to the substituent groups on the
For example, cis–trans isomerization,9 the enantioselective
Diels–Alder reaction,13–15 and photochemical ligand substitu-
tion reaction20 of metal complexes are all successfully controlled
phosphorus ligand: R = alkyl groups which are expected to
using the interligand p–p and/or CH–p interactions. It has
recently been reported that the photophysical properties of tran-
sition metal complexes are affected by intramolecular p–p and
make intramolecular CH–p interaction with the bpy ligand; or
R = phenyl and its derivatives which are expected to make
intramolecular p–p interaction with the bpy ligand; or R =
alkoxy and phenoxy groups with the alkyl and phenyl groups
located further from the bpy ligand because of the presence of
the oxygen atom, and the interligand “weak” interactions might
be weaker.
CH–p interactions.21–27 For instance, Barigelletti et al. suggested
that the excited-state lifetime of a ruthenium(II) polypyridine
complex is prolonged by intramolecular p–p interaction between
a terpyridine ligand and a phenyl group bonded to another
ligand.21 Such interligand interactions might be used to control
various properties of metal complexes. However, no systematic
studies of the effects of these interactions on electrochemical
and photophysical properties of metal complexes have yet been
performed.
Scheme 1
† Electronic supplementary information (ESI) available: Colour ver-
sion of Fig. 5. ORTEP drawings of 2+–4+, 7+, and 9+, list of mCO
frequencies for 1+–10+ measured in acetonitrile solution and complete
The photochemical, photophysical, and electrochemical
properties of fac-[Re(bpy)(CO)3(L)]+ have been widely studied
as a result of their excellent emitting abilities28–30 and photo-
chemical and electrochemical catalyses.31–34 However, to our
1H-NMR data, and plot of Epox–E1/2 versus the MLCT absorption
red
maximum measured in an MeCN solution at room temperature. See
http://www.rsc.org/suppdata/dt/b4/b407947g/
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
D a l t o n T r a n s . , 2 0 0 5 , 3 8 5 – 3 9 5
3 8 5
©

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Table 1 Phosphorus ligands of the fac-[Re(bpy)(CO)3(PR3)]+ and their
(Ag+CF3SO3−) was refluxed under a nitrogen atmosphere for
5 h in darkness. After removal of precipitated AgCl by filtration,
257 mg (0.73 mmol) tris(4-methoxyphenyl)phosphine (P(p-
MeOPh)3) was added to the filtrate. The solution was refluxed
overnight under a nitrogen atmosphere in darkness and then
evaporated under reduced pressure. The resulting yellow solid
was recrystallized from CH2Cl2–ether to give the CF3SO3− salts
of 3+. To 2 mL of methanolic solution of these salts was added
properties
Cone angle/◦
R
va
5.25
Tolman’s valueb
Stahl’s valuec
137
1+
2+
3+
4+
5+
6+
7+
8+
9+
10+
nBu
Et
p-MeOPh
p-MePh
Ph
132
132
145
145
145
145
130
109
107
128
6.30
10.5
11.5
13.2
15.7
19.0
21.6
24.1
30.2
−
dropwise a concentrated NH4+PF6 methanolic solution. The
precipitated PF6 salt of 3+ was collected by filtration, washed
−
with water, and dried in vacuo. Elemental analysis data was
p-FPh
−
obtained using the CF3SO3 salt of 3+. Yield: 69% (Found: C,
OiPr
OEt
OMe
OPh
134
128
45.58; H, 3.11; N, 3.02. C35H29N2O9F3PReS requires C, 45.31; H,
3.15; N, 3.02%). 1H-NMR (300 MHz, CD3COCD3): d 8.92 (2H,
dd, J = 5.5, 0.8 Hz, bpy-6,6ꢀ), 8.55 (2H, dd, J = 8.1, 1.4 Hz,
bpy-3,3ꢀ), 8.29 (2H, ddd, J = 8.1, 7.6, 0.8 Hz, bpy-4,4ꢀ), 7.65
(2H, ddd, J = 7.6, 5.5, 1.4 Hz, bpy-5,5ꢀ), 7.2–7.1 (6H, m, Ph-m),
7.0–6.8 (6H, m, Ph-o), 3.82 (9H, s, CH3O).
a v Represents the net electron-attracting ability of a phosphorus
compound.42a b From ref. 42b c From ref. 49
fac-[Re(bpy)(CO)3{P(p-MePh)3}]+PF6 (4+PF6−), and fac-
−
knowledge, there have been only a few reports concerning
interligand weak interactions in rhenium complexes,24,35 and
detailed understanding is still lacking.
[Re(bpy)(CO)3{P(p-FPh)3}]+PF6− (6+PF6−). The PF6− salts of
4+ and 6+ were synthesized in a similar manner to that of 3+
using tris(4-methylphenyl)phosphine (P(p-MePh)3) and tris(4-
fluorophenyl)phosphine (P(p-FPh)3), respectively, instead of
P(p-MeOPh)3. All elemental analysis data were obtained using
Experimental
Physical methods
−
the CF3SO3 salts of the complexes.
Data for 4+. Yield: 78% (Found: C, 47.41; H, 3.23; N, 3.18.
C35H29N2O6F3PReS requires C, 47.78; H, 3.32; N, 3.18%). H-
IR spectra were recorded with a JEOL JIR-6500 FTIR spec-
trophotometer at 1 cm−1 resolution. UV/vis spectra were
recorded using an Hitachi-330 spectrophotometer ( 0.2 nm
wavelength accuracy; 0.1 nm reproducibility). Pellets for solid-
state UV/vis absorption measurement were prepared from a
mixture of 1 mg of a complex and 100 mg of KBr and were
dried in vacuo at 100 ◦C for one day prior to use. Air was used as
reference for this measurement, and the counter anion was the
same as is used in X-ray crystallography. Emission spectra were
recorded at 25 ◦C with a JASCO FP-6600 spectrofluorometer
with correction for the detector sensitivity determined using
correction data supplied by JASCO. Proton-NMR spectra were
measured in an acetone-d6 solution at a sample concentration
of 20 mM using a Bruker AC300P (300 MHz) system. Residual
protons of acetone-d6 were used as an internal standard for
the measurements. Cyclic voltammograms of the complexes
were measured in acetonitrile solution containing tetra-n-
butylammonium tetrafluoroborate (0.1 M) as supporting elec-
trolyte using an ALS/CHI CHI620 electrochemical analyzer
with a glassy-carbon disk working electrode (3 mm diameter),
an Ag/AgNO3 (0.1 M) reference electrode, and a Pt counter
electrode. The supporting electrolyte was dried in vacuo at 100 ◦C
for one day prior to use.
1
NMR (300 MHz, CD3COCD3): d 8.89 (2H, dd, J = 5.6, 0.7 Hz,
bpy-6,6ꢀ), 8.53 (2H, dd, J = 8.1, 1.4 Hz, bpy-3,3ꢀ), 8.27 (2H,
ddd, J = 8.1, 7.6, 0.7 Hz, bpy-4,4ꢀ), 7.62 (2H, ddd, J = 7.6,
5.6, 1.4 Hz, bpy-5,5ꢀ), 7.25–7.05 (12H, m, Ph-o, m), 2.33 (9H, s,
CH3–Ph).
Data for 6+. Yield: 46% (Found: C, 42.70; H, 2.21; N, 3.05.
1
C35H29N2O9F3PReS requires C, 43.10; H, 2.26; N, 3.14%). H-
NMR (300 MHz, CD3COCD3): d 8.95 (2H, dd, J = 5.5, 0.7 Hz,
bpy-6,6ꢀ), 8.60 (2H, dd, J = 7.1, 0.8 Hz, bpy-3,3ꢀ), 8.31 (2H, td,
J = 7.1, 0.7 Hz, bpy-4,4ꢀ), 7.68 (2H, ddd, J = 7.1, 5.5, 0.8 Hz,
bpy-5,5ꢀ), 7.40–7.25 (6H, m, Ph-m), 7.25–7.15 (6H, m, Ph-o).
Crystal structure determination
The single crystals of the PF6 salts of 1+, 2+, 5+, 7+, 8+, and
−
10+, and the CF3SO3 salts of 3+, 4+, and 9+, were obtained by
−
slow diffusion of diethyl ether into a dichloromethane solution
containing the complex. No single crystal of 6+ adequate for
X-ray crystallography could be obtained. All diffraction data
were collected at room temperature on a Mac Science MXC18K
four-circle diffractometer using graphite-monochromated Mo-
˚
Ka (k = 0.71073 A) radiation. The unit cell dimensions
were determined from 22 reflections in the ranges measured.
Diffraction intensity data were collected using a 2h–h scan over
all the 2h range. Three standard reflections were measured at
intervals of 100 reflections. The intensity data were corrected
for Lorentz and polarization effects. All crystal structures were
Materials
Reagents and solvents were purchased from Kanto Chemi-
cal Co., Junsei Chemical Co., Tokyo Kasei Co., Wako Pure
Chemical Industries and Aldrich Chemical Company, and
were used without further purification unless otherwise noted.
Acetonitrile was dried three times over P2O5 and then distilled
from CaH2 prior to use. Acetone was distilled from Molecular
Sieves 4A. Tetra-n-butylammonium tetrafluoroborate was triply
recrystallized from ethyl acetate/benzene.
38a
determined by the direct method using the Sir92 program, and
the structures were refined versus F2 by full-matrix least-square
38b
procedures using the SHELXL-97 program. Atomic and
anomalous scattering factors were taken from the literature.
39a
No secondary extinction corrections were applied. Absorption
correction was applied for 2+ and 7+ using the w scan method. All
crystals have only a single crystallographically distinct rhenium
cation in the asymmetric unit. In the least-square refinements,
all atoms other than hydrogen were refined with anisotropic
displacement parameters; all hydrogen atoms were assigned
by calculation at ideal positions, and refined using a riding
model with an isotropic thermal parameter 1.2 times that of
the attached carbon atom (1.5 times for methyl hydrogens).
Table 2 gives crystal parameters and details of data collection
and refinement.
Synthetic procedures
The PF6 salts of fac-[Re(bpy)(CO)3(PR3)]+, where R = Bu
(1+), Et (2+), Ph (5+), OiPr (7+), OEt (8+), OMe (9+), and OPh
(10+) were synthesized according to the previously reported
methods.36,37
−
n
fac-[Re(bpy)(CO)3{P(p-MeOPh)3}]+PF6 (3+PF6−). An ace-
−
tone solution containing 64 mg (0.14 mmol) fac-Re(bpy)(CO)3Cl
and 40 mg (0.16 mmol) silver trifluoromethanesulfonate
3 8 6
D a l t o n T r a n s . , 2 0 0 5 , 3 8 5 – 3 9 5

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Molecular orbital calculation
Our MOPAC (parameters: PM3) calculation was performed
39b
with a CAChe working system on an Apple Power Macintosh
G3 computer. Coordinates of the bpy ligands obtained by the
X-ray crystallographic analyses were used in calculating the
orbitals of a 2,2ꢀ-bipyridine molecule.
Results
Infrared spectra
All complexes have three intense IR bands in the mCO region
which are similar in intensity. This is typical of the facial
form of tricarbonyl rhenium bipyridine complexes with CS
symmetry.40,41 Fig. 1 illustrates the linear relationship between
the mCO frequencies and Tolman’s v value,42 which indicates the
electron-attracting ability of the phosphorus ligand. It clearly
shows that a stronger electron-attracting PR3 ligand reduces the
electron densities of the dp orbitals of the central rhenium, which
in turn causes weaker p-back donation from the central rhenium
to the carbonyl ligands.
Fig. 1 Plots of mCO frequencies versus the v value of the phosphorus
ligand.
Proton-NMR
1
All complexes showed four H-NMR signals, due to the bpy
protons in an acetone-d6 solution, between 25 ◦C to −90 ◦C. This
indicates that the two pyridine rings of the bpy ligand are
equivalent on the NMR time scale. The chemical shifts for the
bpy protons in the complexes measured at 25 ◦C are summarized
in Table 3.
Redox potentials
The cyclic voltammogram of 4+ measured in an acetonitrile
solution is shown in Fig. 2 as an example. In the cathodic
scan, one reversible and one irreversible wave were observed
Table 3 1H-NMR Chemical shifts for bpy-protons in 1+–10+ measured
in acetone-d6 at 25 ◦Ca
d/ppm
H3,3ꢀ
H4,4ꢀ
H5,5ꢀ
H6,6ꢀ
1+
2+
3+
4+
5+
6+
7+
8+
9+
10+
8.89
8.86
8.55
8.53
8.60
8.60
8.85
8.83
8.83
8.76
8.50
8.47
8.29
8.27
8.26
8.31
8.45
8.45
8.45
8.40
7.95
7.93
7.65
7.62
7.61
7.68
7.93
7.90
7.89
7.77
9.35
9.33
8.92
8.89
8.89
8.95
9.23
9.22
9.23
9.01
−
a All complexes were PF6 salts.
D a l t o n T r a n s . , 2 0 0 5 , 3 8 5 – 3 9 5
3 8 7

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UV/vis absorption and emission spectra
Fig. 3 shows the UV/vis absorption spectra of 4+ in an acetoni-
trile solution, a dichloromethane solution, and a KBr pellet. The
intense and relatively sharp absorption band around 320 nm,
which was almost identical in all media, is attributed to the p–p*
transition localized on the bpy ligand. A broad absorption band
was also observed around 350 nm in acetonitrile solution, which
shifted by 20 nm to longer wavelength in dichloromethane. This
is typical of metal-to-bpy charge-transfer (MLCT) absorption
of rhenium bipyridine complexes.30,44–46,48
Fig. 2 Cyclic voltammograms of 4+ (0.5 mM) measured in a MeCN
solution containing n-Bu4NBF4 (0.1 M) using a glassy carbon working
electrode, a Pt counter electrode, and a Ag/AgNO3 (0.1 M) reference
electrode. The scan rate was 200 mV s−1
.
at −1.57 V and −2.01 V, respectively. In the anodic scan, one
irreversible wave was observed at 1.5 V. Similar voltammograms
were observed for the other complexes. The redox potentials
are summarized in Table 4.43 The reversible redox wave is
attributable to reduction of the bpy ligand (bpy/bpy•−), and
the irreversible waves to rhenium-based reduction (Re0/ReI)
and oxidation (ReI/ReII) respectively, based on similarity to
30,31c,44–47
analogous rhenium complexes.
Fig. 3 UV/vis absorption spectra (— line in MeCN; -·- line in CH2Cl2;
. . . in KBr) of 4+ measured at room temperature.
Table 4 Electrochemical data for 1+–10+a
The complex 4+ emits strongly at room temperature. The
emission was unstructured and a broad band, with a maximum
at 540 nm, and was efficiently quenched by O2. We have reported
previously that fac-[Re(bpy)(CO)3(PR3)]+ type complexes in-
cluding 8+ emit from their lowest 3MLCT excited state.37 Since
the emission properties of 4+ are very similar to these, the
emissive state of 4+ should also be 3MLCT. The other complexes
showed similar UV/vis absorption and emission spectra, and the
data are summarized in Table 5.
Fig. 4a plots the maximum of the p–p*(bpy) absorption
wavelength, measured in a KBr pellet against the v value.
Although no clear correlation is observed, the complexes divide
into two groups: one contains the trialkyl- and triarylphosphine
complexes (1+–6+), and the other contains the trialkyl- and
triphenylphosphite complexes (7+–10+) for which the p–p*(bpy)
absorption maxima were observed at 319–322 and 317–318 nm,
respectively. The p–p*(bpy) absorption of 6+ and 7+ were
different by 2 nm, for example, but their phosphorus ligands have
similar v values. Since ligand-centered absorption is affected
little by the electronic properties of the other ligands, the “red-
shifted” p–p*(bpy) absorption for 1+–6+, which have the trialkyl-
or triarylphosphine ligand, implies the existence of a direct inter-
action between the PR3 and bpy ligands. Interestingly, a similar
redb
E1/2
Epred/Vc
Epox/Vd
V vs. Ag/AgNO3
1+
2+
3+
4+
5+
6+
7+
8+
9+
10+
−1.55 (63)
−1.54 (69)
−1.57 (67)
−1.57 (64)
−1.56 (68)
−1.53 (70)
−1.59 (63)
−1.59 (63)
−1.56 (64)
−1.54 (60)
−2.11
−2.11
−2.03
−2.01
−1.98
−1.92
−2.09
−2.10
−2.04
−1.94
1.49
1.51
1.50
1.50
1.55
1.58
1.57
1.56
1.60
e
-
a All complexes were PF6− salts (0.5 mM). Cyclic voltammograms of 1+–
10+ were taken in MeCN solutions containing n-Bu4NBF4 (0.1 M) as a
supporting electrolyte at a 200 mV s−1 scan rate using a glassy carbon
working electrode, a Pt counter electrode, and a Ag/AgNO3 (0.1 M)
reference electrode.43 b Redox potential for the reversible process, that
was measured by a scan reversed after the first reduction peak. Values
in parentheses are the peak-to-peak separation in mV. Experimental
errors were 0.01V. c Peak potential for irreversible reduction. d Peak
ox
potential for irreversible oxidation. e We were unable to determine Ep
for 10+ because we observed a catalytic wave upon oxidation of 10+.
Table 5 Photophysical data for 1+–10+ in MeCN solution and in a KBr pelleta
Absorption kmax (e)/nm (M−1 cm−1
)
MLCT in MeCN
p–p*(bpy) in MeCN
p–p*(bpy) in KBr
E
em/nmb
1+
2+
3+
4+
5+
6+
7+
8+
9+
10+
354 (3500)
352 (4200)
346 (3400)
343 (3500)
341 (3100)
340 (3600)
330 sh
330 sh
325 sh
320 sh
317.7 (1.1)
317.6 (1.4)
319.1 (1.2)
320.3 (1.3)
319.4 (1.0)
319.0 (1.4)
315.7 (1.6)
315.3 (1.2)
315.5 (1.5)
317.0 (1.5)
319
319
319c
322c
321
320
318
317
318c
318
561d
561d
547
544
540d
537
543d
542d
543d
522
a All complexes were PF6 salts unless otherwise stated. b Emission maximum in an acetonitrile solution at room temperature. c CF3SO3 Salts were
used. d From reference 37.
−
−
3 8 8
D a l t o n T r a n s . , 2 0 0 5 , 3 8 5 – 3 9 5

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Fig. 4 Plots of the p–p*(bpy) absorption maximum of the rhenium
complex versus the v value, (a) in a KBr pellet (b) in a MeCN solution.
behavior was observed for the p–p*(bpy) absorption measured
in acetonitrile solution (Fig. 4b). The average differences were
1.8 nm between 1+, 2+ and 7+–10+ and 3.6 nm between 3+–6+
and 7+–10+ (the reproducibility of the spectrometer was 0.1 nm
and these differences of the absorption maxima are large enough
to be distinguished).
A good linear relation is observed between the MLCT
absorption maximum observed in acetonitrile solution and
ox
Ep − E1/2red (see Fig. 6S in ESI†). This is expected since MLCT
transition energy should depend on both the energy levels of the
dp orbital of the central rhenium and on those of the p* orbital
of the bpy ligand.
Crystal structure
X-Ray crystallographic analyses were performed successfully
for all complexes except for 6+, for which no adequate single
crystal could be obtained. All complexes have facial structures
in agreement with their spectroscopic data. Fig. 5 shows ORTEP
drawings of 1+PF6−, 5+PF6−, 8+PF6−, and 10+PF6− as examples,
and selected bond distances and angles are listed in Table 6. The
Re–P bond distances vary with PR3 ligand, such that Re–P =
+
+
+
+
˚
˚
2.49–2.50 A for 1 and 2 , 2.50–2.52 A for 3 –5 , and 2.41–
+
+
˚
2.44 A for 7 –10 . The strength of the Re–P p-back bonding is
mainly responsible for these differences, and the cone angles of
42b,49
the PR3 ligands (Table 1)
possibly contribute a weak effect,
including the shorter Re–P length in 1+ and 2+ than in 3+–5+. The
Re–N bond lengths are similar for all the complexes except for
2+. The bond distances of Re–C(3) in 7+–10+ are slightly longer
than in 1+–5+ probably because the stronger p-back donation
to the phosphorus ligand in the trans position to the carbonyl
ligand weakens the Re–C(3) bond.
Intramolecular interactions between the bpy and PR3 ligands
The ORTEP drawing of 1+PF6 is shown in Fig. 5a, in which
−
atoms interacting with each other are shown in light grey and are
connected by dotted lines. This shows the intramolecular CH–
p interaction between the hydrogen atoms in the two n-butyl
groups of the tri-n-butylphosphine ligand and the bpy ligand:
the n-butyl groups are closely located along the N(1)–C(4) and
D a l t o n T r a n s . , 2 0 0 5 , 3 8 5 – 3 9 5
3 8 9

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Fig. 5 ORTEP drawings (50% probability thermal ellipsoids) of (a) 1+PF6−, (b) 5+PF6−, (c) 8+PF6−, and (d) 10+PF6−. Atoms interacting with each
other are shown in light grey and are connected by dotted lines. Counter anions were omitted for clarity. For treatment of the hydrogens, see the
Experimental section.
3 9 0
D a l t o n T r a n s . , 2 0 0 5 , 3 8 5 – 3 9 5

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˚
Table 7 Interatomic contacts (A) between the PR3 and bpy ligands in
1+–5+ and 7+–10+
˚
Distances/A
1+
2+
3+
C(4)–H(15A) 2.89, C(13)–H(19A) 2.69
C(4)–H(15A) 2.46
N(1)–C(14) 3.259(7), N(1)–C(19) 3.153(7), C(4)–C(19) 3.270(8)
C(6)–C(18) 3.517(9), C(8)–C(14) 3.352(7), C(9)–C(15) 3.473(8),
C(13)–H(25) 2.62
N(1)–C(14) 3.271(9), C(4)–C(19) 3.208(13), N(2)–C(25)
3.193(9) C(13)–C(25) 3.242(10), N(2)–H(25) 2.71, C(9)–H(25)
2.65 C(10)–H(25) 2.89
N(1)–C(14) 3.268(15), C(4)–C(19) 3.178(21), N(2)–C(25)
3.218(16), C(13)–C(25) 3.216(18), C(9)–H(25) 2.77
—
4+
5+
7+
8+
—
9+
C(4)–H(14A) 2.94
C(8)–C(15) 3.320(14), C(9)–C(15) 3.384(14)
Fig. 6 Packing diagram of 10+PF6−. One phenyl group in the triph-
enylphosphite ligand is interposed between the bpy ligand in the same
complex and the phenyl ring in the close neighboring complex as shown
by dotted lines.
10+
N(2)–C(13) bonds of the bpy ligand. Table 7 summarizes the
interatomic contacts between the PR3 and bpy ligands. Similar
intramolecular CH–p interactions were observed in the crystal
of 2+PF6
.
−
Fig. 5b shows the ORTEP drawing of 5+PF6−. In this case,
intramolecular p–p interaction was observed between one of
the three phenyl groups on the triphenylphosphine ligand and
the bpy ligand. The distance between the centers of the p-
˚
stacked rings is 3.62 A, and the angle between the rings
◦
˚
is 19.4 . These are typical distances (3.3–3.8 A) and angles
(< 40◦) for p-stacked aromatic rings.51 The short distances
˚
between the atoms of the two rings are 3.218(16) A for N(2)–
C(25) and 3.208(13) A for C(4)–C(19), which are shorter by 0.10
˚
˚
and 0.33 A respectively than the sums of the corresponding van
der Waals radii50 as shown in Table 7. Intramolecular CH–p
interaction was also observed between one of the other phenyl
groups on the triphenylphosphine ligand and the bpy ligand;
˚
C(9)–H(25) bond length is 2.77 A and the angle between the
rings is 44.8◦. Similar interactions were also observed in the
crystals of 3+CF3SO3 and 4+CF3SO3−. The distances between
−
˚
the centroids of the pyridine ring and the aryl group are 3.65 A
˚
and 3.70 A, and the corresponding angles between the rings are
14.0◦ and 22.7◦. Although CH–p interaction was also observed
in 3+ and 4+ (Table 7), the relative configurations of the phenyl
ring and the pyridine ring are rather different with plane–plane
angles of 84.6◦ and 40.2◦ respectively.
Fig. 7 Lateral view of the pyridine rings of the bpy ligand in 1+–5+
and 7+–10+, which are doubly extended in a direction perpendicular to
the p-planes. The pyridine rings are viewed in the direction along the
C5–C6–C7 and C10–C11–C12 planes, respectively.
Fig. 5c shows the ORTEP drawing of 8+PF6−. No intramolec-
ular p–p or CH–p interactions were observed in 7+ and 8+
between the alkoxy groups on the trialkylphosphite ligand and
the bpy ligand. In the case of 9+, the distance between H(14A)
on the trimethylphosphite ligand and C(4) on the bpy ligand
direction perpendicular to the p-plane is magnified twofold.
Interestingly, the pyridine rings in 1+–5+ in which intramolecular
p–p and/or CH–p interactions were observed between the bpy
and PR3 ligands are considerably distorted, whereas those in 7+–
9+ with no such interaction, and 10+ in which P(OPh)3 interacts
weakly with the bpy ligand are almost flat. In particular, the
N(1), N(2), C(4), C(8), C(9), and C(13) atoms which directly
interact with the PR3 ligands in 1+–5+ are strongly distorted;
their deviations from the best least-squares planes of the pyridine
˚
(2.942 A) is close to the sum of the van der Waals radii of the
aromatic carbon and hydrogen atoms.50
The ORTEP drawing of 10+PF6− (Fig. 5d) shows that a phenyl
group of the triphenylphosphite ligand is located close to the bpy
˚
ligand, with a centroid–centroid distance of 3.71 A. However, the
closest distance between the atoms in the two rings is 3.320(14)
+
+
˚
˚
A for C(8)–C(15), about 0.1 A longer than in 3 –5 . This phenyl
group is interposed by the bpy ligand in the same complex
and a phenyl ring of the triphenylphosphite ligand in a close-
neighboring complex as shown in Fig. 6. The packing effect
should enforce the short distance among these rings. In fact the
P(1)–Re–N(1) angle (96.7◦) in 10+ was significantly wider than
in the other complexes with no packing effect (86.1◦–90.5◦). No
intramolecular CH–p interaction was observed in the crystal of
10+.
+
+
rings are up to 3.7 × 10−2 A, whereas those in 7 –10 are less
˚
+
+
than 1.6 × 10−2 A (Table 8). The distortions observed in 1 –5
˚
were 2–3 times larger than their standard deviations while those
observed in 7+–10+ were approximately within their standard
deviations. Furthermore, the value of R(d2/r2) (where r is the
standard deviation of each atom), which represents the proba-
bility with which each pyridine ring takes a non-plane struc-
ture, are 21.0–56.5 for 1+–5+ and 8.1–11.8 for 7+–10+. The
intermolecular packing effect does not seem to be the reason
for the distortion of the pyridine rings, however, because the
R(d2/r2) values are not affected by the presence or absence of the
intermolecular interaction. Typically, in 4+ with a relatively large
distortion of the pyridine rings, no intermolecular interaction
Distortion of the pyridine rings
Fig. 7 illustrates two pyridine rings in the bpy ligand of
the complexes viewed in the lateral direction along with the
respective C(5)–C(6)–C(7) and C(10)–C(11)–C(12) planes; the
D a l t o n T r a n s . , 2 0 0 5 , 3 8 5 – 3 9 5
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a
Table 8 Deviations (× 10−3 A) of the atoms in the pyridine rings of the bpy ligand from their best least-squares planes
˚
1+
2+
3+
4+
5+
7+
8+
9+
10+
N(1)
C(4)
C(5)
C(6)
C(7)
C(8)
N(2)
C(9)
C(10)
C(11)
C(12)
C(13)
−17.0(6.8)
1.2(8.0)
1.6(10.2)
5.1(3.7)
21.5(5.8)
−16.5(7.2)
4.8(8.8)
1.6(9.8)
3.5(8.8)
−15.0(6.6)
15.3(5.4)
−15.6(5.8)
2.4(6.8)
10.8(7.7)
−10.7(7.1)
−2.3(6.0)
12.2(8.2)
−2.1(9.0)
2.2(10.9)
3.2(7.0)
1.1(7.4)
5.4(5.7)
−3.4(9.9)
11.7(6.1)
−4.8(12.0)
15.0(14.9)
−21.9(14.5)
18.7(14.1)
−8.6(12.7)
5.6(9.7)
−26.9(10.3)
20.7(12.1)
4.9(15.6)
−1.7(4.5)
−3.2(5.4)
4.6(5.5)
−2.6(7.2)
−5.0(7.9)
9.8(7.6)
−6.8(6.5)
−0.7(5.6)
7.9(5.5)
−2.0(5.6)
−2.0(7.0)
0.1(7.9)
−4.1(10.0) −10.2(7.7)
20.0(9.0)
−25.9(9.3)
10.5(8.6)
11.2(7.2)
−30.0(7.5)
27.4(8.2)
−6.5(9.2)
−11.0(10.1)
7.8(9.9)
−8.3(7.4)
11.3(6.8)
−7.3(6.1)
0.1(6.2)
−3.4(6.6)
0.7(7.6)
7.3(8.7)
−12.9(9.4)
10.5(9.1)
−2.3(7.3)
3.4(13.3)
11.5(10.9)
4.6(11.2)
−0.7(9.5)
10.1(10.1)
−8.2(8.5)
−2.7(6.5)
−1.8(6.3)
−4.2(6.8)
6.3(8.5)
−11.3(12.0)
20.1(10.8)
−21.1(9.6)
−25.9(8.2)
−11.4(9.8)
37.1(10.8)
−25.6(11.1)
−11.5(9.7)
37.2(8.2)
−1.2(4.8)
−3.7(4.0)
−25.2(3.7)
15.0(4.4)
4.7(5.3)
−11.9(12.5)
16.5(8.2)
−11.7(9.1)
−5.9(9.2)
−9.6(10.6)
14.6(10.9)
−3.8(10.0)
−14.6(5.7)
−2.6(9.4)
−3.3(8.4)
5.5(7.2)
−25.9(15.3)
4.6(5.2)
5.7(7.6)
−9.6(6.5)
12.2(8.7)
21.5(11.4)
15.5(4.3)
a Standard deviations are shown in parentheses. Positive values imply deviations from the best least-squares planes toward the C(3)O(3) ligand, and
negative values imply deviations toward the PR3 ligand. Deviations larger than 1.2 × 10−2 (A) are shown in bold. Atoms close to the PR3 ligands are
˚
written in Italic. b dave denotes the average deviation for all the atoms.
was observed between the carbon atoms on the bpy ligand and
the counter anions or other complexes. On the other hand,
the pyridine rings in 8+ were not distorted even though one
force because of the lower electron density on the pyridine rings,
causing the distortion of the pyridine rings. This will be discussed
in more detail below.
−
PF6 counter anion was located close to the p-plane of the bpy
The UV/vis absorption spectra of the rhenium complexes
measured in KBr pellets seem to be affected by the intramolecu-
lar interaction. The bpy-localized (p–p*(bpy)) absorption were
319–322 nm for 1+–6+ with intramolecular interaction, but
317–318 nm for 7+–10+ without the interaction (Fig. 4a).
The differences between the two groups were relatively small
(1 nm–5 nm) but are large enough to be distinguished in view
of the reproducibility of the spectrometer, namely 0.1 nm.
It is noteworthy that the p–p*(bpy) absorption maximum of
Re(bpy)(CO)3Cl measured in KBr is 318 nm that is almost
identical to those of 7+–10+ even though the electronic properties
of Cl− are very different from the phosphorus ligands. In fact,
through-bond electronic perturbation on the bpy ligand by
the phosphorus ligand via the central rhenium ion, which is
quantitatively indicated by the v value of the phosphorus ligand,
does not affect the p–p*(bpy) absorption (see Fig. 4).52
Two possible causes of the difference in p–p*(bpy) absorption
are suggested by the structural data of 1+–5+ and 7+–10+; one
is the non-planarity of the pyridine ring in 1+–5+, and the
other is the dihedral angle between two pyridine rings in 1+–
5+. To estimate the effects of these structural distortions of the
bpy ligand, we made molecular orbital calculations using the
MOPAC PM3 method. Fig. 8 is plot of the calculated HOMO–
LUMO energy-gap DEcalc vs. (a) average deviation of the atoms in
the bpy ligand from their best least-squares plane (dave ) obtained
by X-ray crystallography, and (b) the dihedral angle between
the pyridine rings, respectively. The distortion from planarity of
the pyridine ring itself has a significant effect on DEcalc; an
increase in dave induces higher DEcalc, of which the maximum
difference reached 409 meV. The effect of the dihedral angle
between the pyridine rings on DEcalc is much smaller between
0◦ and 8◦,53 which is the maximum angle observed for the
complexes 3+ and 10+; the increase of DEcalc is less than
10 meV. We therefore conclude that the dihedral angle between
the pyridine rings has a negligible effect in these cases.
ligand. Disorder also does not seem to be the reason for the
distortion because we defined the distortion as a function of
standard deviation, which is generally proportional to thermal
ellipsoids. These results suggest that the intramolecular p–p and
CH–p interactions between the bpy and PR3 ligands cause the
distortion of the pyridine rings of the bpy ligand.
The dihedral angle between the two pyridine rings of the bpy
ligand also seems to be affected by the intramolecular p–p and
CH–p interacti◦ons. The observed dihedral angles are 5.5◦ for 1+,
5.8◦ for 2+, 8.1 for 3+, 4.6◦◦ for 4+, 7.9◦ for 5+, 3.8◦ for 7+, 0.2◦
for 8+, 3.8◦ for 9+, and 8.2 for 10+. The larger dihedral angles
for 3+–5+ are at least partially due to the intramolecular p–p
interaction, since the pyridine rings engaged in intramolecular
p–p interaction were pulled up to the aryl group of the PR3
ligand. In contrast, the phenyl group in 10+ pushed down
the pyridine ring. As discussed above, this phenyl group was
interposed between the pyridine ring of the same complex and
a phenyl group of another complex. These results suggest that
the intramolecular interaction in 10+ is different from the p–p
interaction in 3+–5+. The alkyl groups of the trialkylphosphine
ligand pushed down the pyridine rings in 1+ and 2+.
Discussion
Solid state properties
The rhenium complexes synthesized in this study can be classi-
fied into three groups on the basis of their X-ray crystallographic
data: 1+ and 2+ display CH–p interaction between the trialkyl
substituent on the phosphorus ligand and the bpy ligand; 3+–
5+ (probably 6+ is included in this group) have p–p and CH–p
interactions between the aryl substituent on the phosphorus
ligand and the bpy ligand; 7+–10+ have no or only very weak
interaction between the phosphorus and bpy ligands.
The through-space interaction between the aryl or alkyl
group(s) on the phosphorus ligand and the bpy ligand causes
distortion of the pyridine rings of the bpy ligand, as shown in
Fig. 7. Deviations of the atoms from the best least-squares plane
Fig. 9 shows the relation between DEcalc and the p–p*(bpy)
energies derived from the absorption maxima of the rhenium
complexes. They are reasonably correlated except for 2+, sug-
gesting that the non-planarity of the pyridine ring in 1+–5+ is
one of the reasons for the difference in p–p*(bpy) absorption
from 7+–10+.54 Electronic perturbations of the CH–p and p–
p interactions are further causes of this difference, probably
causing the deviation in Fig. 9. The difference in electronic
perturbation between the CH–p and p–p interactions will be
discussed in a later section.
+
+
of the pyridine ring are as long as 3.7 × 10−2 A for 1 –5 with
˚
+
+
the interligand interactions but less than 1.6 × 10−2 A for 7 –10
˚
with weak or no interaction. Decrease of the electron density in
the bonding p orbital on the bpy ligand as a result of the CH–p
interaction should be largely responsible for the distortion of the
pyridine rings on 1+ and 2+. With the p–p interaction, partial
charge transfer from the p-electrons on the aryl group to the
antibonding p* orbital on the pyridine ring may be a driving
Two important questions now arise, (1) are the intramolecular
CH–p and p–p interactions maintained in fluid solution? If so,
3 9 2
D a l t o n T r a n s . , 2 0 0 5 , 3 8 5 – 3 9 5

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Fig. 8 Plots of the calculated HOMO–LUMO energy-gap (DEcalc) vs.
(a) average deviation of the atoms in the bpy ligand from the best
least-squares plane of the pyridine rings (dave ), and (b) dihedral angle
between two pyridine rings in 2,2ꢀ-bipyridine.
Fig. 10 Plots of (a) Epox versus v, (b) E1/2red versus v, and (c) E1/2red versus
Ecalc
.
on the electron density on the central rhenium ion, that is,
the phosphorus ligand affects the electron accepting ability
of the bpy ligand only through the P–Re–N(bpy) bond, then
only a single relation, similar to Fig. 10a, would be observed
between E1/2red and v. But there is a difference in E1/2red of 60 mV
between 6+ and 7+, even though these have similar v values. The
red
differences in the observed E1/2 from the values obtained by
extrapolation of the linear E1/2red vs. v relation for the complexes
with the trialkyl- and triphenylphosphite ligand (7+–10+) are
110–120 mV for the trialkylphosphine complexes (1+ and 2+),
and 60–80 mV for the triarylphosphine complexes (3+–6+); in the
same series of complexes, the E1/2red were “normally” dependent
on the v values (Fig. 10b). This result implies that there is a
perturbation on the electron affinity of the bpy ligand by the PR3
ligand even in solution, beyond the P–Re–N(bpy) through-bond
interaction, i.e., the through-space p–p and CH–p interactions
similar to those in the crystals.
Fig. 9 Plot of calculated HOMO–LUMO energy-gap (DEcalc) vs. the
p–p*(bpy) energy obtained from the UV/vis absorption spectrum of
the rhenium complex in a KBr pellet.
(2) how do these “weak” interactions affect the properties of the
complexes in solution?
Electrochemical and spectroscopic properties in solution
Fig. 10a shows the relation between the oxidation potential
(Epox) and the v value of the PR3 ligand in which the complex
with higher v value has more positive Epox. In spite of the
irreversibility, the peak potentials are expected to reflect the
electron density on the central rhenium. This relation clearly
shows that the electron densities of the dp orbitals of the
central rhenium decrease with a stronger electron-attracting
phosphorus ligand. This is consistent with the observed infrared
spectra of the complexes (see Results section).
The p–p*(bpy) absorption maxima of the complexes mea-
sured in acetonitrile solution correlate well with those measured
in a KBr pellet, which were affected by the intramolecular p–p
and CH–p interactions as described above (Fig. 11). This also
supports that similar intramolecular interactions between the
ligands are dynamically maintained in solution as in crystal.
Proton-NMR spectra of the complexes measured in ace-
tonitrile solution show that the PR3 ligand can rotate around
the Re–P bond on the time scale of the NMR measurements,
at least above −90 ◦C, since only four kinds of bpy-protons
were observed for all of the complexes. The finer detail of
their chemical shifts in Table 3 provides some information on
the relative conformation between the ligands, however, Vos
Plots of the reduction potentials (E1/2red) versus the v value fall
onto three lines having distinct slopes and intercepts (Fig. 10b),
i.e., for the trialkylphosphine complexes (1+ and 2+), for the
triarylphosphine complexes (3+–6+), and for the trialkyl- and
triphenylphosphite complexes (7+–10+). If E1/2red depended only
D a l t o n T r a n s . , 2 0 0 5 , 3 8 5 – 3 9 5
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in the p–p*(bpy) absorption in the crystal. MOPAC calculations
indicate that the distortion of the pyridine rings decrease its
LUMO energy and increase the HOMO energy. Spectral data
and electrochemical results for the complexes suggest that the
intramolecular interactions are maintained even in solution.
As a result of the p–p and CH–p interactions, the bpy-based
reduction potentials of the complexes are shifted positively
by 60–120 mV. Similar red-shifts in the p–p*(bpy) absorption
due to these interactions were also observed in solution. In
contrast, the Re(I/II)-based oxidation potentials and the mCO
bands of the complexes are predominantly controlled by the
electronic properties of the phosphorus ligands; these “weak”
interactions do not strongly affect the electron densities of the
central rhenium.
Fig. 11 Correlation between the p–p*(bpy) absorption maxima of the
complexes measured in an MeCN solution and those measured in a KBr
pellet.
CCDC reference numbers 239864–239872 for 1+–5+ and 7+–
10+.
See http://www.rsc.org/suppdata/dt/b4/b407947g/ for cry-
stallographic data in CIF or other electronic format.
and co-workers55 have reported that, in proton-NMR spectra
of some ruthenium(II) bpy complexes with p–p interaction
between the bpy ligands and a phenyl ring bonded to another
ligand, aromatic proton resonances are upfield-shifted because
of shielding effects of the ring currents. A similar shielding
effect of the aryl group(s) on the triarylphosphine ligand is
apparent on the bpy-protons in 3+–6+ (Dd = −0.14 to −0.34 ppm
compared with 7+–9+), but is much weaker in 10+ (Dd =
−0.05 to −0.22 ppm compared with 7+–9+). This indicates that
conformations in which the bpy ligand and the aryl group(s)
on the triarylphosphine ligand are located close to each other
in parallel fashion are more favorable in 3+–6+ than in 10+,
suggesting that the intramolecular interactions are dynamically
maintained in solution. One of two phenoxy groups over the
bpy ligand can bend away from the bpy ligand as a result of the
flexibility of the P–O–C bonds of the triphenylphosphite ligand
in 10+, as in the crystal structure (see Fig. 5d). Since the redox
character and the p–p*(bpy) absorption of 10+ in solution are
similar to the group of the complexes with the trialkylphosphite
ligand 7+–9+, as shown in Figs. 10b and 4b, the weak p–p
interaction observed in the crystal of 10+PF6− probably becomes
weaker in solution or disappears entirely. This p–p interaction in
the crystal of 10+ is supported by the packing effect with another
complex (see Results section), which is lost in solution.
Acknowledgements
The authors would like to thank Dr Koichi Nozaki (Osaka
Univ.) for his valuable comments. We also thank Dr Hisao
Hori (AIST) for giving some rhenium complexes. The work is
partially supported by a Grant-in-Aid for Scientific Research
(No.14350451) from the Ministry of Education, Culture, Sports,
Science, and Technology, Japan and Japan Science and Technol-
ogy Agency (CREST).
References
1 M. Nishio, M. Hirota and Y. Umezawa, The CH/p Interaction:
Evidence, Nature, and Consequences, Wiley-VCH, Weinheim, 1998.
2 J.-M. Lehn, Supramolecular Chemistry: Concepts and Perspectives,
Wiley-VCH, Weinheim, 1995.
3 J.-M. Lehn, Angew. Chem., Int. Ed. Engl., 1990, 29, 1304–1319.
4 G. R. Desiraju, Angew. Chem., Int. Ed. Engl., 1995, 34, 2311–2327.
5 P. R. Ashton, J. Huff, S. Menzer, I. W. Parsons, J. A. Preece, J. F.
Stoddart, M. S. Tolley, A. J. P. White and D. J. Williams, Eur. J. Chem.,
1996, 2, 31–44.
6 D. Philp and J. F. Stoddart, Angew. Chem., Int. Ed. Engl., 1996, 35,
1155–1196.
7 C. A. Hunter, K. R. Lawson, J. Perkins and C. J. Urch, J. Chem. Soc.,
Perkin Trans. 2, 2001, 651–669.
8 E. A. Meyer, R. K. Castellano and F. Diederich, Angew. Chem., Int.
Ed. Engl., 2003, 42, 1210–1250.
The chemical shifts of H6,6
in 1+ and 2+ with the tri-
ꢀ
alkylphosphine ligand were observed in magnetic fields lower
by ∼0.13 ppm than in 7+–9+. This strongly suggests that the
CH–p interaction between the alkyl group(s) and the bpy ligand
is also maintained in solution and affects the electron density
9 L. Hirsivaara, M. Haukka and J. Pursiainen, Eur. J. Inorg. Chem.,
2001, 2255–2262.
of H6,6 which is bound to the closest bpy-carbon to the alkyl
ꢀ
10 (a) K. Yamanari, T. Nozaki, A. Fuyuhiro and S. Kaizaki, Chem.
Lett., 1996, 35–36; (b) K. Yamanari, T. Nozaki, A. Fuyuhiro, Y.
Kushi and S. Kaizaki, J. Chem. Soc., Dalton Trans., 1996, 2851–2856.
11 M. Mizutani, S. Tomosue, H. Kinoshita, K. Jitsukawa, H. Masuda
and H. Einaga, Bull. Chem. Soc. Jpn., 1999, 72, 981–988.
12 O. Yamauchi and A. Odani, J. Am. Chem. Soc., 1985, 107, 5938–5945.
13 R. W. Quan, Z. Li and E. N. Jacobsen, J. Am. Chem. Soc., 1996, 118,
8156–8157.
groups in the phosphine ligand. The CH–p interaction generally
has a charge-transfer character from p orbital of aromatic ring
to r* orbital of C–H bond,1 and the electron density on the bpy
ligand should fall.
On the other hand, the p–p interaction may have a charge
transfer character from the aryl group on the phosphine ligand
to the bpy ligand because of lower charge density on the bpy
ligand. In addition, perturbations between the p orbitals and
between the p* orbitals of the aryl group and the bpy ligand
probably give effects on the energy levels of the p and p* orbitals
of the bpy ligand. This difference in the charge-transfer character
between the CH–p and p–p interactions explains the difference
in the bpy-based redox potentials between 1+–2+ and 3+–6+;
the observed redox potentials of 1+–2+ were about 60 mV more
positive than those of 3+–6+.
14 (a) S. Otto, G. Boccaletti and J. B. F. N. Engberts, J. Am. Chem. Soc.,
1998, 120, 4238–4239; (b) S. Otto and J. B. F. N. Engberts, J. Am.
Chem. Soc., 1999, 121, 6798–6806.
15 M. Yamakawa, I. Yamada and R. Noyori, Angew. Chem., Int. Ed.
Engl., 2001, 40, 2818–2821.
16 D. Braga, F. Grepioni and G. R. Desiraju, Chem. Rev., 1998, 98,
1375–1405.
17 D. Gut, A. Rudi, J. Kopilov, I. Goldberg and M. Kol, J. Am. Chem.
Soc., 2002, 124, 5449–5456.
18 H. Suezawa, T. Yoshida, Y. Umezawa, S. Tsuboyama and M. Nishio,
Eur. J. Inorg. Chem., 2002, 3148–3155.
19 G. A. Bogdanovic, A. Spasojevic-de Bire and S. D. Zaric, Eur. J. Inorg.
Chem., 2002, 1599–1602.
20 F. Wu, E. Riesgo, A. Pavalova, R. A. Kipp, R. H. Schmehl and R. P.
Thummel, Inorg. Chem., 1999, 38, 5620–5628.
21 (a) F. Barigelletti, B. Ventura, J.-P. Collin, R. Kayhanian, P. Gavina
and J.-P. Sauvage, Eur. J. Inorg. Chem., 2000, 113–119; (b) J.-P. Collin,
R. Kayhanian, J.-P. Sauvage, G. Calogero, F. Barigelletti, A. De Cian
and J. Fisher, J. Chem. Soc., Chem Commun., 1997, 775–776.
Conclusions
In crystals of the salts with fac-[Re(bpy)(CO)3(PR3)]+ (R = alkyl
and aryl groups), intramolecular p–p and/or CH–p interactions
exist between the bpy and PR3 ligands attached to the central
rhenium in cis positions relative to each other. These interactions
distort the pyridine rings in the bpy ligand and cause a red-shift
3 9 4
D a l t o n T r a n s . , 2 0 0 5 , 3 8 5 – 3 9 5

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22 (a) D. Hesek, G. A. Hembury, M. G. B. Drew, S. Taniguchi and Y.
Inoue, J. Am. Chem. Soc., 2000, 122, 10236–10237; (b) D. Hesek,
G. A. Hembury, M. G. B. Drew, V. V. Borovkov and Y. Inoue, J. Am.
Chem. Soc., 2001, 123, 12232–12237.
23 E. C. Riesgo, Y.-Z. Hu, F. Bouvier, R. P. Thummel, D. V. Scaltrito
and G. J. Meyer, Inorg. Chem., 2001, 40, 3413–3422.
24 (a) G. A. Reitz, W. J. Dressick, J. N. Demas and B. A. DeGraff, J. Am.
Chem. Soc., 1986, 108, 5344–5345; (b) G. A. Reitz, J. N. Demas, B. A.
DeGraff and E. M. Stephens, J. Am. Chem. Soc., 1988, 110, 5051–
5059; (c) L. Sacksteder, M. Lee, J. N. Demas and B. A. DeGraff,
J. Am. Chem. Soc., 1993, 115, 8230–8238.
25 (a) K.-H. Wong, K.-K. Cheung, M. C.-W. Chan and C.-M. Che,
Organometallics, 1998, 17, 3505–3511; (b) S.-W. Lai, T.-C. Cheung,
M. C. W. Chan, K.-K. Cheung, S.-M. Peng and C.-M. Che, Inorg.
Chem., 2000, 39, 255–262; (c) W. Lu, M. C. W. Chan, K.-K. Cheung
and C.-M. Che, Organometallics, 2001, 20, 2477–2486.
26 M. T. Miller, P. K. Gantzel and T. B. Karpishin, Inorg. Chem., 1998,
37, 2285–2290.
37 K. Koike, N. Okoshi, H. Hori, K. Takeuchi, O. Ishitani, H. Tsubaki,
I. P. Clark, M. W. George, F. P. A. Johnson and J. J. Turner, J. Am.
Chem. Soc., 2002, 124, 11448–11455.
38 (a) A. C. G. Altomare, C. Ciacovazzo, A. Guagliardi, M. C. Burla,
G. Polidori and M. Camalli, J. Appl. Crystallogr, 1994, 27, 435;
(b) G. M. Sheldrick, SHELXL97, University of Go¨ttingen, Germany,
1997.
39 (a) CAChe, version 4.1.1, Oxford Molecular Ltd; (b) International
Tables for X-ray Crystallography, ed. J. A. Ibers and W. C. Hamilton,
Kynoch Press, Birmingham, 1974, vol. 4.
40 P. J. Giordano and M. S. Wrighton, J. Am. Chem. Soc., 1979, 101,
2888–2897.
41 D. M. Dattelbaun, K. M. Omberg, J. R. Schoonover, R. L. Martin
and T. J. Meyer, Inorg. Chem., 2002, 41, 6071–6079.
42 (a) T. Bartik, T. Himmler, H. G. Schulte and K. Seevogel,
J. Organomet. Chem., 1984, 272, 29–41; (b) C. A. Tolman, Chem.
Rev., 1977, 77, 313–348.
43 The data reported here differs slightly from the values reported
previously (ref. 36). We believe that repeated experiments with
improved accuracy of the apparatus improve the accuracy of the
data.
27 L. B. Picraux, B. T. Weldon and J. K. McCusker, Inorg. Chem., 2003,
42, 273–282.
28 (a) D. J. Stufkens, Comments Inorg. Chem., 1992, 13, 359–385; (b) D. J.
Stufkens and A. Vlcek, Jr., Coord. Chem. Rev., 1998, 177, 127–179.
29 K. Kalyanasundaram, J. Chem. Soc., Faraday Trans. 2, 1986, 82,
2401–2415.
44 G. Tapolsky, R. Duesing and T. J. Meyer, Inorg. Chem., 1990, 29,
2285–2297.
45 L. Sacksteder, A. P. Zipp, E. A. Brown, J. Streich, J. N. Demas and
B. A. DeGraff, Inorg. Chem., 1990, 29, 4335–4340.
46 R. Lin, Y. Fu, C. P. Brock and T. F. Guarr, Inorg. Chem., 1992, 31,
4346–4353.
47 W.-M. Xue, M. C.-W. Chan, Z.-M. Su, K.-K. Cheung, S.-T. Liu and
C.-M. Che, Organometallics, 1998, 17, 1622–1630.
48 M. S. Wrighton and D. L. Morse, J. Am. Chem. Soc., 1974, 96,
998–1003.
30 L. A. Worl, R. Duesing, P. Chen, L. Della Ciana and T. J. Meyer,
J. Chem. Soc., Dalton Trans., 1991, 849–858.
31 (a) H. Hori, F. P. A. Johnson, K. Koike, O. Ishitani and T. Ibusuki,
J. Photochem. Photobiol., A: Chem., 1996, 96, 171–174; (b) K. Koike,
H. Hori, M. Ishizuka, J. R. Westwell, K. Takeuchi, T. Ibusuki, K.
Enjouji, H. Konno, K. Sakamoto and O. Ishitani, Organometallics,
1997, 16, 5724–5729; (c) H. Hori, F. P. A. Johnson, K. Koike, K.
Takeuchi, T. Ibusuki and O. Ishitani, J. Chem. Soc., Dalton Trans.,
1997, 1019–1023; (d) H. Hori, J. Ishihara, K. Koike, K. Takeuchi, T.
Ibusuki and O. Ishitani, J. Photochem. Photobiol., A: Chem., 1999,
120, 119–124.
32 (a) J. Hawecker, J.-M. Lehn and R. Ziessel, J. Chem. Soc., Chem
Commun., 1987, 536–538; (b) J. Hawecker, J.-M. Lehn and R. Ziessel,
J. Chem. Soc., Chem Commun., 1984, 328–330; (c) J. Hawecker, J.-M.
Lehn and R. Ziessel, Helv. Chim. Acta, 1986, 69, 1990–2012.
33 (a) C. Kutal, M. A. Weber, G. Ferraudi and D. Geiger,
Organometallics, 1985, 4, 2161–2166; (b) C. Kutal, A. J. Corbin and
G. Ferraudi, Organometallics, 1987, 6, 553–557.
49 L. Stahl and R. D. Ernst, J. Am. Chem. Soc., 1987, 109, 5673–
5680.
50 A. Bondi, J. Phys. Chem., 1964, 68, 441.
51 C. Janiak, J. Chem. Soc., Dalton Trans., 2000, 3885–3896.
52 The good linear relation between these three mCO bands of the
complexes and the c values (see Fig. 1) strongly suggests that
the electron density of the central rhenium is “normally” affected
by the phosphorus ligand, i.e., via the Re–P bond. See Results
section.
53 In this calculation, only the dihedral angle was changed while the
two pyridine rings were assumed to be planar.
34 B. P. Sullivan, C. M. Bolinger, D. Conrad, W. J. Vining and T. J.
Meyer, J. Chem. Soc., Chem Commun., 1985, 1414–1416.
35 V. W.-W. Yam, K. M.-C. Wong and K.-K. Chueng, Organometallics,
1997, 16, 1729–1734.
36 H. Hori, K. Koike, M. Ishizuka, K. Takeuchi, T. Ibusuki and O.
Ishitani, J. Organomet. Chem., 1997, 530, 169–176.
54 Comparison of the absolute values between both axes has no
meaning, because DEcalc was calculated for a non-coordinated “free”
bpy molecule but the coordination of the bpy ligand obtained by
X-ray crystallography was used.
55 J. A. Bolger, G. Ferguson, J. P. James, C. Long, P. McArdle and J. G.
Vos, J. Chem. Soc., Dalton Trans., 1993, 1577–1583.
D a l t o n T r a n s . , 2 0 0 5 , 3 8 5 – 3 9 5
3 9 5