Synthesis, electrochemistry and structural characterization of luminescent rhenium(I) monoynyl complexes and their homo- and hetero-metallic binuclear complexes

Article abstract of DOI:10.1016/S0022-328X(03)00010-X

A series of luminescent rhenium(I) monoynyl complexes, [Re(N-N)(CO)₃(C≡C-R)] (N-N = bpy, ^tBu₂bpy; R = C₆H₅, C₆H₄-Cl-4, C₆H₄-OCH₃-4, C₆H₄-C₈H₁₇-4, C₆H₄-C₆H₅, C₈H₁₇, C₄H₃S, C₄H₂S-C₄H₃S, C₅H₄N), together with their homo- and heterometallic binuclear complexes, {Re(N-N)(CO)₃(C≡C-C₅H₄N)[M]} (N-N = bpy, ^tBu₂bpy; [M] = [Re{(CF₃)₂-bpy}(CO)₃]ClO₄, [Re(NO₂-phen)(CO)₃]ClO₄, W(CO)₅) have been synthesized and their electrochemical and photoluminescence behaviors determined. The structural characterization and electronic structures of selected complexes have also been studied. The luminescence origin of the rhenium(I) alkynyl complexes has been assigned as derived states of a [dπ(Re) → π*(N-N)] metal-to-ligand charge transfer (MLCT) origin mixed with a [π(C≡CR)→π*(N-N)] ligand-to-ligand charge transfer (LLCT) character. The assignments are further supported by extended Hu?ckel molecular orbital (EHMO) calculations, which show that the LUMO mainly consists of π*(N-N) character while the HOMO is dominated by the antibonding character of the Re-C≡CR moiety resulted from the overlap of the dπ(Re) and π(C≡CR) orbitals.

Full text of DOI:10.1016/S0022-328X(03)00010-X

Journal of Organometallic Chemistry 670 (2003) 205ꢁ220
/
www.elsevier.com/locate/jorganchem
Synthesis, electrochemistry and structural characterization of
luminescent rhenium(I) monoynyl complexes and their homo- and
hetero-metallic binuclear complexes
Vivian Wing-Wah Yam *, Keith Man-Chung Wong, Samuel Hung-Fai Chong,
Victor Chor-Yue Lau, Sally Chan-Fung Lam, Lingjun Zhang, Kung-Kai Cheung
(HKU-CAS Joint Laboratory on New Materials), Department of Chemistry, (Center for Carbon-Rich Molecular and Nano-scale Metal-Based
Materials Research), The University of Hong Kong, Pokulam Road, Hong Kong, P.R. China
Received 15 November 2002; received in revised form 4 January 2003; accepted 4 January 2003
Abstract
A series of luminescent rhenium(I) monoynyl complexes, [Re(Nꢀ
4, C6H4ꢀOCH3-4, C6H4ꢀC8H17-4, C6H4ꢀC6H5, C8H17, C4H3S, C4H2Sꢀ
metallic binuclear complexes, {Re(NꢀN)(CO)3(CꢁCꢀC5H4N)[M]} (Nꢀ
/
N)(CO)3(Cꢁ
C4H3S, C5H4N), together with their homo- and hetero-
Nꢀ [Re{(CF3)2-bpy}(CO)3]ClO4,
bpy, tBu2bpy; [M]ꢀ
/
Cꢀ
/
R)] (Nꢀ
/
Nꢀ
/
bpy, tBu2bpy; Rꢀ
/
C6H5, C6H4ꢀ
/
Cl-
/
/
/
/
/
/
/
/
/
/
[Re(NO2-phen)(CO)3]ClO4, W(CO)5) have been synthesized and their electrochemical and photoluminescence behaviors
determined. The structural characterization and electronic structures of selected complexes have also been studied. The luminescence
origin of the rhenium(I) alkynyl complexes has been assigned as derived states of a [dp(Re)0
transfer (MLCT) origin mixed with a [p(CꢁCR)0p*(NꢀN)] ligand-to-ligand charge transfer (LLCT) character. The assignments
are further supported by extended Huckel molecular orbital (EHMO) calculations, which show that the LUMO mainly consists of
/
p*(Nꢀ/N)] metal-to-ligand charge
/
/
/
¨
p*(Nꢀ
of the dp(Re) and p(Cꢁ
# 2003 Elsevier Science B.V. All rights reserved.
/
N) character while the HOMO is dominated by the antibonding character of the Reꢀ
/
Cꢁ
/
CR moiety resulted from the overlap
/
CR) orbitals.
Keywords: Rhenium(I); Alkynyl; Metallo-ligand; Electrochemistry; Luminescence; Metal-to-ligand charge transfer (MLCT) transition
1. Introduction
focused on the luminescence behavior of this class of
compounds [3ꢁ10]. As a continuing research effort on
the luminescence studies of d8 and d10 transition-metal
alkynyl complexes [11ꢁ
16], the d6 metal polypyridine
complexes with intriguing metal-to-ligand-charge-trans-
fer (MLCT) excited states have aroused our interests
and we have recently explored on the luminescence
studies of rhenium(I) alkynyl complexes. Incorporation
of the alkynyl framework into the luminescent rhe-
nium(I) diimine system has been achieved and reported
by us and the effects on the luminescence behavior upon
extension of the sp carbon chain and coordination of d10
metal centers onto the alkynyl ligand have also been
explored [17].
/
In recent years, there has been a rapidly growing
interest in the design and synthesis of organometallic
complexes containing carbon-rich, rigid and p-conju-
gated chains due to their potential use as precursors for
the syntheses of organometallic polymers [1] and p-
conjugated bi- or multi-metallic systems. This class of
complexes also exhibit significantly altered physical
properties compared with their conjugated organic
oligomers and polymers [2]. The preparations of one-
dimensional organometallic polymers have also been
reported [1,2]. Despite the growing interests and studies
in metal alkynyl systems, relatively less attention was
/
Since we have developed a rather general synthetic
route for the preparation of luminescent rhenium(I)
alkynyl diimine complexes, the incorporation of func-
tionalized alkynyl groups into these complexes may
* Corresponding author. Tel.: ꢂ
1586.
E-mail address: wwyam@hku.hk (V.W.-W. Yam).
/
852-2589-2153; fax: ꢂ852-2857-
/
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00010-X

206
V.W.-W. Yam et al. / Journal of Organometallic Chemistry 670 (2003) 205ꢁ220
/
represent an interesting area of research. In this regard,
we have identified two major areas. One involves the use
of thiophene and bithiophene moieties as the functional
unit since oligo- and polythiophenes are currently
attracting a great deal of attention due to the fact that
the properties of one-dimensional organometallic poly-
mers can be fine-tuned by variation of the fragments of
the chain [18]. Another area involves the incorporation
of coordinating ligands such as pyridine to the alkynyl
unit since this would open up new avenues for the
construction of homo- and hetero-binuclear complexes
by making use of the rhenium(I) alkynyl complex as the
building block. In view of these, a series of rhenium(I)
monoynyl complexes containing different diimine li-
gands and alkynyl groups including thiophene, bithio-
2. Experimental
2.1. Materials
Rhenium pentacarbonyl chloride [Re(CO)5Cl] and
tungsten hexacarbonyl [W(CO)6] were obtained from
Strem Chemicals, Inc. 2,2?-Bipyridine (bpy), 4,4?-di-
methyl-2,2?-bipyridine(Me2bpy), silver trifluorometha-
nesulfonate (AgOTf), copper(I) chloride (CuCl), 4-n-
octylphenylacetylene, 4-methoxyphenylacetylene and 1-
decyne were obtained from Aldrich Chemical Co.
Triethylamine, phenylacetylene and 1-chloro-4-phenyla-
cetylene were purchased from Lancaster Synthesis Ltd.
4,4?-Di-tert-butyl-2,2?-bipyridine [19] (tBu2bpy) and
5,5?-bis(trifluoromethyl)-2,2?-bipyridine [20] {(CF3)2-
bpy}, 2-ethynylthiophene [21] (HCꢁ
yl-2,2?-bithiophene [22] (HCꢁCC4H2Sꢀ
CH) were prepared accord-
/
CC4H3S), 5-ethyn-
phene and pyridyl substituents [Re(Nꢀ
R)] (NꢀNꢀbpy, RꢀC6H5, 1; C6H4ꢀ
C8H17-4, 3; C4H3S, 4; C4H2ꢀC4H3S, 5; Nꢀ
Nꢀt
Bu2bpy, RꢀC6H4ꢀOCH3-4, 6; C6H4ꢀC6H5-4, 7;
C8H17, 8; C4H3S, 9; C4H2ꢀC4H3S, 10; C5H4N, 11) as
well as their related homo- and hetero-binuclear com-
plexes N)(CO)3(CꢁCꢀC5H4N)[M]} (Nꢀ
{Re(Nꢀ
Nꢀt
Bu2bpy, [M]ꢀ[Re{(CF3)2-bpy}(CO)3])ClO4, 12;
[Re(NO2-phen)(CO)3]ClO4, 13; [W(CO)5], 14; NꢀNꢀ
bpy, [M]ꢀ[W(CO)5], 15) have been synthesized
/
N)(CO)3(Cꢁ
/
Cꢀ
/
/
/C4H3S) and 4-
/
/
/
/
Cl-4, 2; C6H4ꢀ
/
ethynylpyridine [23] (pyCꢁ
/
/
/
ing to the literature procedures. [Re(tBu2bpy)(CO)3Cl]
[24], [Re(bpy)(CO)3Cl] [24], [Re{(CF3)2-bpy}(CO)3-
(MeCN)]OTf [25], [Re(NO2-phen)(CO)3(MeCN)]OTf
/
/
/
/
/
[25] and W(CO)5(pyCꢁ
slight modification of the reported procedure.
/
CH) [26] were synthesized by
/
/
/
/
/
/
Pyridine was obtained from BDH Chemical Co. Ltd.
and was pre-dried over KOH and distilled under an
inert atmosphere of nitrogen before use. THF was
distilled over sodium benzophenone ketyl before use.
CH2Cl2 and MeCN were purified and distilled using
standard procedures before use. All other reagents were
of analytical grade and were used as received.
/
/
/
(Scheme 1). Their photophysical and electrochemical
properties have been studied. X-ray crystal structure
determinations of 1, 10 and 11 and EHMO study of 10
have also been performed.
Scheme 1.

V.W.-W. Yam et al. / Journal of Organometallic Chemistry 670 (2003) 205ꢁ
/220
207
2.2. Physical measurements and instrumentation
UVꢁvis spectra were obtained on a HewlettꢁPackard
8452A diode array spectrophotometer. IR spectra as
nitrogen, followed by stirring at room temperature (r.t.)
for 24 h. Water was then added to destroy the unreacted
/
/
RCꢁ
/
CLi. The product was extracted with a THFꢁEt2O
/
mixture, dried over anhydrous magnesium sulfate, and
then filtered. The filtrate was reduced in volume and
purified by column chromatography on silica gel using
Nujol mulls on a Bio-Rad FTS-7 Fourier-transform
infrared spectrophotometer (4000ꢁ
400 cmꢃ1), and
/
steady-state excitation and emission spectra on a Spex
Fluorolog 111 spectrofluorometer equipped with a
Hamamatsu R-928 photomultiplier tube. Low-tempera-
ture (77 K) spectra were recorded by using an optical
CH2Cl2ꢁ
/
n-hexane (1:1, v/v) as eluent. Subsequent
recrystallization from an acetoneꢁ
gave the desired product.
/n-hexane mixture
1
Dewar sample holder. H-NMR spectra were recorded
2.3.2. Method B
on a 270 MHz JEOL JNM-GSX270 or a 300 MHz
Bruker DPX300 fourier-transform NMR spectrometer.
Chemical shifts (d ppm) were reported relative to
tetramethylsilane (Me4Si). Positive ion FAB mass spec-
tra were collected on a Finnigan MAT95 mass spectro-
meter. Elemental analyses of the new complexes were
performed by the Butterworth Laboratories Ltd or on a
Carlo Erba 1106 elemental analyzer at the Institute of
Chemistry, Chinese Academy of Sciences.
A
reaction mixture of [Re(CO)3(Nꢀ
Bu2bpy, bpy) (0.54 mmol), AgOTf (0.60 mmol),
CR (0.76 mmol) and THF (100
/
N)Cl] (Nꢀ
/
Nꢀt
Et3N (0.60 mmol), HCꢁ
/
/
ml) was allowed to reflux under an inert atmosphere of
nitrogen in the dark for 24 h. After cooling to r.t., the
dark brown suspension was filtered and the orangeꢁred
/
filtrate was reduced in volume under reduced pressure.
The residue was then purified by column chromatogra-
phy on silica gel using CH2Cl2 as eluent. Subsequent
Emission lifetime measurements were performed
using a conventional laser system. The excitation source
was the 355-nm output (third harmonic) of a Spectra-
Physics Quanta-Ray Q-switched GCR-150 pulsed Nd-
YAG laser (10 Hz). Luminescence decay signals were
recorded on a Tektronix model TDS-620A (500 MHz,
2GS/s) digital oscilloscope, and analyzed using a pro-
gram for exponential fits. All solutions for photophysi-
cal studies were prepared under vacuum in a 10-cm3
round-bottom flask equipped with a side-arm 1-cm
fluorescence cuvette and sealed from the atmosphere
by a Bibby Rotaflo HP6 Teflon stopper. Solutions were
recrystallization from acetoneꢁ
sired product.
/
Et2O afforded the de-
2.4. Synthesis of [Re(bpy)(CO)3(Cꢁ
/
Cꢀ
/
C6H5)] (1)
This was synthesized according to method B in which
HCꢁ
CC6H5 was used. Yield: 85 mg, 30%. 1H-NMR
/
(300 MHz, acetone-d6, 298 K, relative to Me4Si): d 6.80
(d, 2H, aryl H meta to ethynyl group), 6.96 (m, 3H, aryl
H ortho and para to ethynyl group), 7.74 (t, 2H, 4- and
4?-pyridyl H’s), 8.30 (t, 2H, 5- and 5?-pyridyl H’s), 8.70
(d, 2H, 3- and 3?-pyridyl H’s), 9.12 (d, 2H, 6- and 6?-
rigorously degassed with no fewer than four freezeꢁ
/
pyridyl H’s). IR (Nujol mull, cmꢃ1): 2083 n(Cꢁ
/
C);
O). Positive FABMS: ion clusters
at m/z 529 [M]ꢂ, 500 [MꢃCO]ꢂ. Elemental analyses,
Found: C, 47.40; H, 2.31; N, 5.28. Calc. for
[Re(bpy)(CO)3(CꢁCꢀC6H5)]: C, 47.78; H, 2.46; N,
5.31%.
pumpꢁthaw cycles.
/
Cyclic voltammetric measurements were performed
by using a CH Instrument Inc. model CHI 620 Electro-
analytical Analyzer, interfaced to a personal computer.
2008, 1904, 1885 n(Cꢁ
/
/
The ferroceniumꢁferrocene couple was used as the
/
/
/
internal standard in the electrochemical measurements
in MeCN (0.1 M nBu4NPF6). The working electrode
was a glassy carbon (Atomergic Chemetals V25) elec-
trode, with Ag/AgNO3 (0.1 M in MeCN) as the
reference electrode and a platinum foil acting as the
counter electrode. Treatment of the electrode surfaces
was as reported previously [27].
2.5. Synthesis of [Re(CO)3(bpy)(Cꢁ
(2)
/
Cꢀ
/
C6H4ꢀ/Cl-4)]
This was synthesized by method B in which HCꢁ
/
Cꢀ
/
C6H4ꢀ
/
Cl-4 was used. Yield: 91 mg, 30%. 1H-NMR (300
2.3. Syntheses
MHz, acetone-d6, 298 K, relative to Me4Si): d 6.78 (d,
2H, aryl H meta to ethynyl group), 7.00 (m, 2H, aryl H
ortho to ethynyl group), 7.74 (t, 2H, 4- and 4?-pyridyl
H’s), 8.30 (t, 2H, 5- and 5?-pyridyl H’s), 8.70 (d, 2H, 3-
and 3?-pyridyl H’s), 9.12 (d, 2H, 6- and 6?-pyridyl H’s).
The rhenium(I) diimine monoynyl complexes were
synthesized by either of the two methods.
2.3.1. Method A
A solution of [Re(CO)3(tBu2bpy)Cl] (0.174 mmol) in
IR (Nujol mull (cmꢃ1)): 2092 n(Cꢁ
n(Cꢁ
[M]ꢂ, 534 [Mꢃ
44.54; H, 1.86; N, 4.65. Calc. for [Re(bpy)(CO)3(Cꢁ
C6H4ꢀCl-4)]: C, 44.86; H, 2.14; N, 4.98%.
/
C); 2005, 1901, 1876
O). Positive FABMS: ion clusters at m/z 562
CO]ꢂ. Elemental analyses, Found: C,
Cꢀ
/
THF (10 ml) was treated at ꢃ
RCꢁCLi (0.575 mmol) in THF (10 ml), prepared in situ
from RCꢁ
CH and nBuLi, under an inert atmosphere of
/
40 8C with a solution of
/
/
/
/
/
/

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V.W.-W. Yam et al. / Journal of Organometallic Chemistry 670 (2003) 205ꢁ220
/
2.6. Synthesis of [Re(bpy)(CO)3(Cꢁ
/
Cꢀ
/
C6H4ꢀ/C8H17-
N, 4.55. Calc. for [Re(bpy)(CO)3(Cꢁ
/
Cꢀ
/
C4H2Sꢀ
/
4)] (3)
C4H3S)]: C, 45.01; H, 4.62; N, 4.54%.
This was synthesized by method B in which HCꢁ
C6H4ꢀ
C8H17-4 was used. Yield: 104 mg, 30%. 1H-NMR
(300 MHz, acetone-d6, 298 K, relative to Me4Si): d 0.84
(t, 3H, ꢀCH3ꢀ), 1.24 (m, 10H, ꢀCH2ꢀ), 1.46 (m, 2H, ꢀ
CH2ꢀ), 2.42 (t, 2H, ꢀCH2ꢀ), 6.70 (d, 2H, aryl H meta to
/
Cꢀ
/
2.9. Synthesis of [Re(tBu2bpy)(CO)3(Cꢁ
OCH3-4)] (6)
/
Cꢀ
/
C6H4ꢀ
/
/
/
/
/
/
/
This was synthesized according to method A in which
4-methoxyphenylacetylene was used. Yield: 55 mg, 47%.
1H-NMR (270 MHz, acetone-d6, 298 K, relative to
/
/
/
ethynyl group), 6.82 (m, 2H, aryl H ortho to ethynyl
group), 7.74 (t, 2H, 4- and 4?-pyridyl H’s), 8.30 (t, 2H, 5-
and 5?-pyridyl H’s), 8.70 (d, 2H, 3- and 3?-pyridyl H’s),
9.12 (d, 2H, 6- and 6?-pyridyl H’s). IR (Nujol mull
Me4Si): d 1.4 (s, 18H, tBu), 3.65 (3H, s, ꢀ
6.54, 6.58 (4H, 2d, phenyl H), 7.77ꢁ
5?-pyridyl H’s), 8.70ꢁ8.71 (2H, d, 3- and 3?-pyridyl H’s),
8.98ꢁ9.00 (2H, dd, 6- and 6?-pyridyl H’s). IR (Nujol
mull (cmꢃ1)): 2085 n(Cꢁ
C); 1996, 1901, 1878 n(CꢁO).
Positive FABMS: ion clusters at m/z 670 [M]ꢂ, 539
[MꢃCꢁCꢀC6H4ꢀ
OCH3-4]ꢂ.
/OCH3 group),
/
7.76 (2H, dd, 5- and
/
(cmꢃ1)): 2083 n(Cꢁ
/
C); 2005, 1916, 1890 n(Cꢁ
Positive FABMS: ion clusters at m/z 640 [M]ꢂ, 612
[Mꢃ
CO]ꢂ. Elemental analyses, Found: C, 54.34; H,
4.41; N, 4.28. Calc. for [Re(bpy)(CO)3(CꢁCꢀC6H4ꢀ
C8H17-4)]: C, 54.44; H, 4.54; N, 4.38%.
/
O).
/
/
/
/
/
/
/
/
/
/
/
2.10. Synthesis of [Re(tBu2bpy)(CO)3(Cꢁ
C6H5-4)] (7)
/
Cꢀ
/
C6H4ꢀ
/
2.7. Synthesis of [Re(bpy)(CO)3(Cꢁ
/
Cꢀ
/
C4H3S)] (4)
This was synthesized according to method B in which
HCꢁCꢀC4H3S was used. It was purified by column
chromatography on silica gel using CH2Cl2ꢁpetroleum
ether (boiling point (b.p.) 40ꢁ60 8C) (4:1 v/v) as eluent.
n-hexane
This was synthesized according to method A in which
ethynylbiphenyl was used to give orange crystals of 7.
/
/
/
Yield: 57 mg, 46%. 1H-NMR (270 MHz, acetone-d6, 298
t
/
K, relative to Me4Si): d 1.4 (s, 18H, Bu), 6.86ꢁ
/7.56
Subsequent recrystallization from CH2Cl2ꢁ
/
(9H, m, biphenyl H), 7.77ꢁ
pyridyl H’s), 8.70ꢁ8.71 (2H, d, 3- and 3?-pyridyl H’s),
8.98ꢁ9.00 (2H, dd, 6- and 6?-pyridyl H’s). IR (Nujol
mull (cmꢃ1)): 2094 n(Cꢁ
C); 2015, 1912, 1898 n(CꢁO).
Positive FABMS: ion clusters at m/z: 747 [M]ꢂ, 539
[MꢃCꢁCꢀC6H4ꢀ
C6H5-4]ꢂ.
/
7.76 (2H, dd, 5- and 5?-
gave orange crystals of 4. Yield: 63 mg, 55%. 1H-
NMR (300 MHz, acetone-d6, 298 K, relative to Me4Si),
/
/
6.70 (dd, 1H, Jꢀ
2H, Jꢀ6.1 Hz, 4- and 4?-pyridyl H’s), 8.20 (t, 2H, Jꢀ
7.8 Hz, 5- and 5?-pyridyl H’s), 8.60 (d, 2H, Jꢀ8.1 Hz, 3-
and 3?-pyridyl H’s), 9.10 (d, 2H, Jꢀ5.2 Hz, 6- and 6?-
pyridyl H’s). IR (Nujol mull on KBr disc, n (cmꢃ1)):
2080 n(CꢁC); 2006, 1912, 1888 n(CꢁO). Positive
FABMS: ion clusters at m/z 534 [M]ꢂ, 460 [Mꢃ
(Cꢁ
Cꢀ
C4H3S)]ꢂ. Elemental analyses Found: C, 42.00; H,
2.01; N, 4.76. Calc. for [Re(bpy)(CO)3(CꢁCꢀC4H3S)]×1/
2H2O: C, 42.06; H, 1.78; N, 4.68%.
/
1.2 and 5.2 Hz, 5-thiophene H), 7.70 (t,
/
/
/
/
/
/
/
/
/
/
2.11. Synthesis of [Re(tBu2bpy)(CO)3(Cꢁ
(8)
/
Cꢀ
/
C8H17)]
/
/
/
/
/
This was synthesized according to method A in which
1-decyne was used to give orange crystals of 8. Yield: 53
mg, 45%. 1H-NMR (270 MHz, acetone-d6, 298 K,
/
/
/
relative to Me4Si): d 0.9 (3H, t, ꢀ
m, ꢀCH2ꢀ
), 1.4 (18H, s, tBu), 1.75 (2H, t, ꢀ
7.78ꢁ7.80 (2H, dd, 5- and 5?-pyridyl H’s), 8.79ꢁ
(2H, d, 3- and 3?-pyridyl H’s), 8.98ꢁ9.00 (2H, d, 6- and
6?-pyridyl H’s). IR (Nujol mull (cmꢃ1)): 2012 n(Cꢁ
C);
2001, 1909, 1874 n(CꢁO). Positive FABMS: ion clusters
at m/z 678 [M]ꢂ, 539 [Mꢃ C8H17]ꢂ.
CꢁCꢀ
/
Me), 1.0ꢁ
/
1.4 (12H,
Cꢀ),
8.81
2.8. Synthesis of [Re(bpy)(CO)3(Cꢁ
/
Cꢀ
/
C4H2Sꢀ
/
/
/
/
CH2Cꢁ
/
/
C4H3S)] (5)
/
/
/
The procedure was similar to that of 4, except HCꢁ
CꢀC4H2SꢀC4H3S was used instead. Yield: 40 mg, 30%.
1H-NMR (300 MHz, acetone-d6, 298 K, relative to
Me4Si): d 6.20 (d, 1H, Jꢀ3.7 Hz, 4-bithiophene H),
6.70 (d, 1H, Jꢀ3.7 Hz, 3-bithiophene H), 6.80 (dd, 1H,
Jꢀ
1.1 and 3.6 Hz, 3?-bithiophene H), 7.10 (dd, 1H, Jꢀ
and 5.1 Hz, 5?-bithiophene H), 7.70 (t, 2H, Jꢀ
and 4?-pyridyl H’s), 8.20 (t, 2H, Jꢀ7.8 Hz, 5- and 5?-
pyridyl H’s), 8.60 (d, 2H, Jꢀ8.1 Hz, 3- and 3?-pyridyl
H’s), 9.10 (d, 2H, Jꢀ5.2 Hz, 6- and 6?-pyridyl H’s). IR
(Nujol mull on KBr disc, n (cmꢃ1)): 2100 n(Cꢁ
C); 2014,
1915, 1890 n(CꢁO). Positive FABMS: ion clusters at m/
z 616 [M]ꢂ, 588 [MꢃCO]ꢂ, 427 [Mꢃ
(CꢁCꢀC4H2Sꢀ
C4H3S)]ꢂ. Elemental analyses Found: C, 44.81; H, 4.71;
/
/
/
/
/
/
/
/
/
/
2.12. Synthesis of [Re(tBu2bpy)(CO)3(Cꢁ
(9)
/
Cꢀ/C4H3S)]
/
3.6 and 5.1 Hz, 4?-bithiophene H), 6.90 (dd, 1H, Jꢀ
/
/
1.1
/
6.1 Hz, 4-
The procedure was similar to that of 4, except
[Re(tBu2bpy)(CO)3Cl] was used as a precursor. Yield:
/
1
65 mg, 59%. H-NMR (300 MHz, acetone-d6, 298 K,
/
t
relative to Me4Si): d 1.40 (s, 18H, Bu), 6.30 (dd, 1H,
/
/
Jꢀ
and 5.2 Hz, 4-thiophene H), 6.70 (dd, 1H, Jꢀ
5.2 Hz, 5-thiophene H), 7.70 (dd, 2H, Jꢀ1.8 and 5.8
Hz, 5- and 5?-pyridyl H’s), 8.60 (d, 2H, Jꢀ1.8 Hz, 3-
/
1.2 and 3.5 Hz, 3-thiophene H), 6.50 (dd, 1H, Jꢀ
/3.5
/
/1.2 and
/
/
/
/
/
/
/

V.W.-W. Yam et al. / Journal of Organometallic Chemistry 670 (2003) 205ꢁ
/220
209
and 3?-pyridyl H’s), 8.90 (d, 2H, Jꢀ
pyridyl H’s). IR (Nujol mull on KBr disc, n (cmꢃ1)):
2078 n(CꢁC); 2006, 1908, 1883 n(CꢁO). Positive
FABMS: ion clusters at m/z 646 [M]ꢂ, 618 [Mꢃ
CO]ꢂ, 539 [Mꢃ C4H3S)]ꢂ. Elemental analyses
(CꢁCꢀ
Found: C, 50.15; H, 4.18; N, 4.33. Calc. for
[Re(tBu2bpy)(CO)3(Cꢁ
CꢀC4H3S)]: C, 50.33; H, 4.19;
N, 4.36%.
/
5.8 Hz, 6- and 6?-
mixture was heated to reflux under an inert atmosphere
of nitrogen for 12 h to give a bright yellow solution.
After evaporation of the solution to dryness, the yellow
solid mass was redissolved in minimum amount of
methanol, and a saturated methanolic solution of
LiClO4 was added to precipitate the product as its
perchlorate salt. The solid was further recrystallized by
slow diffusion of Et2O vapor into a MeCN solution in
the dark to give yellow crystals of 12. Yield: 118 mg,
/
/
/
/
/
/
/
/
2.13. Synthesis of [Re(tBu2bpy)(CO)3(Cꢁ
C4H3S)] (10)
/
Cꢀ
/
C4H2Sꢀ
/
70%. 1H-NMR (300 MHz, acetone-d6, 298 K, relative to
t
Me4Si): d 1.4 (18H, s, Bu), 6.62ꢁ
/
6.65 (2H, dd, pyridyl
t
H meta to N), 7.75ꢁ
8.14ꢁ8.17 (2H, dd, pyridyl H ortho to N), 8.71ꢁ
(2H, d, 3,3?-H of tBu2bpy), 8.85ꢁ
8.88 (2H, 2d, 4,4?-H of
(CF3)2-bpy), 8.95ꢁ
8.97 (2H, d, 6,6?-H of tBu2bpy),
9.09ꢁ9.12 (2H, d, 3,3?-H of (CF3)2-bpy), 9.77 (2H, s,
6,6?-H of (CF3)2-bpy). IR (Nujol mull (cmꢃ1)): 2105
n(CꢁC); 2035, 1999, 1937, 1929, 1908, 1898 n(CꢁO).
Positive FABMS: ion clusters at m/z 1203 [M]ꢂ, 563
[Mꢃ Cꢀ
Re(tBu2bpy)(CO)3(Cꢁ C5H4N)]ꢂ, 539 [Mꢃ
Re{(CF3)2-bpy}(CO)3(CꢁCꢀ
C5H4N)]ꢂ.
/
7.77 (2H, dd, 5,5?-H of Bu2bpy),
The procedure was similar to that of 5, except
[Re(tBu2bpy)(CO)3Cl] was used as a precursor. Yield:
/
/8.72
/
1
50 mg, 40%. H-NMR (300 MHz, acetone-d6, 298 K,
/
relative to Me4Si): d 1.40 (s, 18H, tBu), 6.30 (d, 1H, Jꢀ
/
/
3.7 Hz, 4-bithiophene H), 6.70 (d, 1H, Jꢀ3.7 Hz, 3-
/
bithiophene H), 6.80 (dd, 1H, Jꢀ
bithiophene H), 6.90 (dd, 1H, Jꢀ
bithiophene H), 7.20 (dd, 1H, Jꢀ
bithiophene H), 7.70 (dd, 2H, Jꢀ
5?-pyridyl H’s), 8.60 (d, 2H, Jꢀ1.8 Hz, 3- and 3?-pyridyl
H’s), 8.90 (d, 2H, Jꢀ5.8 Hz, 6- and 6?-pyridyl H’s). IR
(Nujol mull on KBr disc, n (cmꢃ1)): 2096 n(Cꢁ
C); 2010,
1910, 1888 n(CꢁO). Positive FABMS: ion clusters at m/
z 728 [M]ꢂ, 700 [MꢃCO]ꢂ, 539 [Mꢃ
(CꢁCꢀC4H2Sꢀ
C4H3S)]ꢂ. Elemental analyses Found: C, 49.01; H, 3.89;
N, 3.63. Calc. for [Re(tBu2bpy)(CO)3(Cꢁ
CꢀC4H2Sꢀ
C4H3S)]×1/2CH2Cl2: C, 48.79; H, 3.87; N, 3.54%.
/
3.6 and 5.1 Hz, 4?-
1.1 and 3.6 Hz, 3?-
1.1 and 5.1 Hz, 5?-
/
/
/
/
/
/
/
/
/1.8 and 5.8 Hz, 5- and
/
/
/
/
2.16. Synthesis of [Re(tBu2bpy)(CO)3(Cꢁ
C5H4N)Re(NO2-phen)(CO)3]ClO4 (13)
/
Cꢀ
/
/
/
/
/
/
/
/
The synthesis was similar to 12, except [Re(NO2-
phen)(CO)3(MeCN)]OTf was used instead of
[Re{(CF3)2-bpy}(CO)3(MeCN)]OTf. Yield 94 mg,
/
/
/
1
/
60%. H-NMR (300 MHz, acetone-d6, 298 K, relative
to Me4Si): d 1.4 (18H, s, tBu), 6.52ꢁ
/
6.55 (2H, d, pyridyl
7.72 (2H, d, pyridyl N ortho to N),
8.01 (2H, d, 5,5?-H of tBu2bpy), 8.40ꢁ
8.48 (2H, m,
3,8-H of NO2-phen), 8.66ꢁ8.67 (2H, d, 3,3?-H of
tBu2bpy), 8.89ꢁ8.91 (2H, dd, 6,6?-H of tBu2bpy),
9.27ꢁ9.31 (2H, sꢂd, ‘s’ for the 6-H and ‘d’ for the 4-
H of NO2-phen), 9.42ꢁ9.45 (1H, d, 7-H of NO2-phen),
9.93ꢁ9.98 (2H, td, 2,9-H of NO2-phen). IR (Nujol mull
(cmꢃ1)): 2100 n(Cꢁ
C); 2010, 1998, 1942, 1928, 1917,
1909 n(CꢁO). Positive FABMS: ion clusters at m/z 1135
[M]ꢂ, 539 [Mꢃ C5H4N)]ꢂ.
Re(NO2-phen)(CO)3(CꢁCꢀ
2.14. Synthesis of [Re(tBu2bpy)(CO)3(Cꢁ
C5H4N)] (11)
/
Cꢀ
/
H meta to N), 7.70ꢁ
/
8.09ꢁ
/
/
/
This was synthesized according to method A in which
4-ethynylpyridine was used. It was purified by column
chromatography on silica gel using Et2O as eluent.
Subsequent recrystallization by slow evaporation of an
acetone solution of the complex gave orange crystals of
11. Yield: 45 mg, 40%. 1H-NMR (270 MHz, acetone-d6,
298 K, relative to Me4Si): d 1.4 (18H, s, tBu), 6.70 (2H,
/
/
/
/
/
/
/
/
/
/
broad, pyridyl H meta to N), 7.77ꢁ
5?-pyridyl H’s), 8.19 (2H, broad, pyridyl H ortho to N),
8.73ꢁ8.74 (2H, d, 3- and 3?-pyridyl H’s), 9.00ꢁ9.02 (2H,
dd, 6- and 6?-pyridyl H’s). IR (Nujol mull (cmꢃ1)): 2096
n(CꢁC); 2003, 1917, 1892 n(CꢁO). Positive FABMS:
ion clusters at m/z 641 [M]ꢂ, 539 [Mꢃ C5H4N]ꢂ.
CꢁCꢀ
/7.79 (2H, dd, 5- and
2.17. Synthesis of [Re(tBu2bpy)(CO)3(Cꢁ
C5H4N)W(CO)5] (14)
/
Cꢀ
/
/
/
/
/
A mixture of [Re(tBu2bpy)(CO)3Cl] (100 mg, 0.17
mmol), Et3N (52 mg, 0.51 mmol), AgOTf (48 mg, 0.19
/
/
/
mmol) and W(CO)5(NC5H4Cꢁ/CH) (111 mg, 0.26
2.15. Synthesis of [Re(tBu2bpy)(CO)3(Cꢁ
C5H4N)Re{(CF3)2-bpy}(CO)3]ClO4 (12)
/
Cꢀ
/
mmol) in THF (70 ml) was allowed to reflux under an
inert atmosphere of nitrogen in the dark for 24 h. After
cooling to r.t., the dark brown suspension was filtered
and the orange filtrate was reduced in volume under
reduced pressure. The residue was then purified by
The complex was prepared by a method similar to
that of other related rhenium(I) tricarbonyl diimine
pyridine systems [25]. [Re{(CF3)2-bpy}(CO)3(MeC-
N)]OTf (100 mg, 0.13 mmol) was dissolved in THF,
column chromatography on silica gel using Et2Oꢁ
petroleum ether (b.p. 40ꢁ60 8C) (1:1 v/v) as eluent.
Subsequent recrystallization from CH2Cl2ꢁn-hexane
gave orange crystals of 14. Yield: 30 mg, 18%. 1H-
/
/
and one equivalent of [Re(tBu2bpy)(CO)3(Cꢁ
C5H4N)] (83 mg, 0.13 mmol) was added to it and the
/
Cꢀ
/
/

210
V.W.-W. Yam et al. / Journal of Organometallic Chemistry 670 (2003) 205ꢁ220
/
NMR (300 MHz, acetone-d6, 298 K, relative to Me4Si):
the complexes were purified by column chromatography
on silica gel using CH2Cl2ꢁn-hexane as eluent in both
methods.
t
d 1.40 (s, 18H, Bu), 6.50 (d, 2H, Jꢀ
meta to N), 7.60 (d, 2H, Jꢀ6.0 Hz, pyridyl H ortho to
N), 7.70 (dd, 2H, Jꢀ1.8 and 5.8 Hz, 5- and 5?-pyridyl
H’s), 8.60 (d, 2H, Jꢀ1.8 Hz, 3- and 3?-pyridyl H’s), 8.90
(d, 2H, Jꢀ5.8 Hz, 6- and 6?-pyridyl H’s). IR (Nujol
mull on KBr disc, n (cmꢃ1)): 2107 n(Cꢁ
C); 2072, 2000,
1979, 1952, 1933, 1900, 1883, 1860 n(CꢁO). Positive
FABMS: ion clusters at m/z 965 [M]ꢂ, 909 [Mꢃ
2CO]ꢂ, 539 [Mꢃ C)]ꢂ. Elemental
[W(CO)5(NC5H4Cꢁ
analyses Found: C, 41.01; H, 2.90; N, 4.35. Calc. for
[Re(tBu2bpy)(CO)3(Cꢁ
CꢀC5H4N)W(CO)5]: C, 40.83;
H, 3.04; N, 4.17%.
/
6.0 Hz, pyridyl H
/
/
/
The synthesis of homo-metallic binuclear complexes
12 and 13 has been achieved by utilization of the
‘metalloligand’ approach through the use of the starting
/
/
precursor complex, [Re(tBu2bpy)(CO)3(Cꢁ
/
Cꢀ/C5H4N)]
/
/
(11), in which the uncoordinated pyridyl nitrogen could
serve as the coordination site for a second rhenium
metal center. Typical for the preparation of the related
cationic luminescent rhenium(I) complexes, [Re-
(diimine)(CO)3(C5H4N)]ꢂ, complexes 12 and 13 were
obtained by the reaction of 11 with [Re({CF3}2-
bpy)(CO)3(MeCN)]ClO4 and [Re(NO2-phen)(CO)3-
(MeCN)]ClO4, respectively, in THF under reflux con-
/
/
/
/
/
2.18. Synthesis of [Re(bpy)(CO)3(Cꢁ
/
Cꢀ
/
C5H4N)W(CO)5] (15)
dition. In the preparation of mixed-metal rheniumꢁ
/
tungsten complexes 14 and 15, [W(CO)5(C5H4NꢀCꢁ
/
/
The procedure was similar to that described for the
preparation of 14, except [Re(bpy)(CO)3Cl] (79 mg, 0.17
mmol) was used in place of [Re(tBu2bpy)(CO)3Cl] to
give orange crystals of 15. Yield: 28 mg, 14%. 1H-NMR
(300 MHz, acetone-d6, 298 K, relative to Me4Si): d 6.50
CH)], which serve as the ‘metalloligand’, was then
reacted with the corresponding [Re(tBu2bpy)(CO)3Cl]
and [Re(bpy)(CO)3Cl] under the reaction conditions as
described in Section 2.3.2.
(d, 2H, Jꢀ
Jꢀ6.0 Hz, pyridyl H ortho to N), 7.70 (t, 2H, Jꢀ
Hz, 4- and 4?-pyridyl H’s), 8.20 (t, 2H, Jꢀ7.8 Hz, 5-
and 5?-pyridyl H’s), 8.70 (d, 2H, Jꢀ8.1 Hz, 3- and 3?-
pyridyl H’s), 9.10 (d, 2H, Jꢀ5.0 Hz, 6- and 6?-pyridyl
H’s). IR (Nujol mull on KBr disc, n (cmꢃ1)): 2110 n(Cꢁ
C); 2065, 2000, 1986, 1958, 1922, 1890, 1883, 1866 n(Cꢁ
O). Positive FABMS: ion clusters at m/z 852 [M]ꢂ, 824
[Mꢃ [W(CO)5(NC5H4Cꢁ
2CO]ꢂ, 427 [Mꢃ C)]]ꢂ. Ele-
mental analyses Found: C, 35.21; H, 1.41; N, 3.19. Calc.
for [Re(bpy)(CO)3(CꢁCꢀC5H4N)W(CO)5]: C, 35.27; H,
1.60; N, 2.99%.
/
6.0 Hz, pyridyl H meta to N), 7.60 (d, 2H,
/
/
6.3
/
3.2. Structural characterization
/
/
The perspective drawings of 1, 10 and 11 are depicted
/
in Figs. 1ꢁ3. The crystallographic data are given in
/
/
Table 1, while their selected bond lenghts and bond
angles are collected in Table 2. In general, the coordina-
tion geometries of the complexes are distorted octahe-
dral with three carbonyl ligands arranged in a facial
fashion. As commonly observed in other Re(I) tricar-
/
/
/
/
/
bonyl diimine systems [17], the Nꢀ
/
Reꢀ/N bond angles [1,
74.4(2)8; 10, 73.6(2)8; 11, 73.5(2) and 74.1(2)8] are found
to be less than 908 as required by the bite distance
exerted by the steric demand of the chelating bipyridine
3. Results and discussion
ligand. The Reꢀ
[1, 176.4(6)8; 10, 175.2(8)8; 11, 177.3(7) and 178.2(7)8] as
expected for the sp hydridization of CꢁC bond in the
alkynyl moiety. The CꢁC bond lengths [1, 1.199(9) A;
/
Cꢀ
/
C units show a linear arrangement
3.1. Syntheses
/
The synthesis of luminescent rhenium(I)ꢁ
type alkynyl complexes, [Re(tBu2bpy)(CO)3(Cꢁ
was firstly reported by employing the reaction of
CR) (Rꢀalkyl, aryl group) with
/
bipyridyl
˚
/
/CR)],
˚
˚
10, 1.20(1) A; 11, 1.196(10) and 1.195(10) A] are typical
of terminal s-bonded metalꢀalkynyl bonds. [17] In
complex 10, the CꢀS bond lengths are 1.69(1)ꢁ
1.756(10) A, similar to those commonly found in
thiophene systems.[28] The CꢀC bond distances of the
thiophene ring linked directly to the ethynyl unit vary
/
alkynyllithium (LiCꢁ
/
/
[Re(tBu2bpy)(CO)3Cl] in diethyl ether (method A)
[17a,17b,17c]. Despite the fact that a series of target
complexes with various alkynyl groups have been
prepared, this method only applies to the use of starting
precursor complexes, such as [Re(tBu2bpy)(CO)3Cl],
which are soluble in diethyl ether. No desired products
could be obtained under similar reaction conditions for
the synthesis of the related unsubstituted 2,2?-bipyridyl
analogues. An alternative method was developed to
/
/
˚
/
˚
from 1.32(1) to 1.40(1) A, which are slightly shorter than
˚
the distance of 1.44(1) to 1.47(2) A of the second
thiophene ring. The two thiophene rings display a trans
arrangement in order to minimize the steric repulsion
between the lone pairs on each of the sulfur atoms.
This has also been commonly observed in free bithio-
phene ligands and organometallic bithiophene com-
plexes [28].
prepare the related analogues [Re(bpy)(CO)3(Cꢁ
by refluxing the suspension of [Re(bpy)(CO)3Cl],
AgOTf, HCꢁCR and Et3N in THF (method B). All
/CR)]
/

V.W.-W. Yam et al. / Journal of Organometallic Chemistry 670 (2003) 205ꢁ
/220
211
Fig. 1. The perspective drawing of 1 with atomic numbering scheme. Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are shown at
the 50% probability level.
3.3. Electrochemistry
for their first oxidation wave than the chloro counter-
part, [Re(bpy)(CO)3Cl] (ꢂ1.38 V vs. SCE) [25c] is
/
Similar to other rhenium(I) diimine complexes [25,29],
both reduction and oxidation couples have been ob-
served in the cyclic voltammongrams upon reductive
consistent with the better s-donating ability of the
alkynyl than the chloro group, which would render the
rhenium(I) metal center more electron rich, and hence
increases its ease of oxidation. The bithiophene-sub-
and oxidative scan, respectively, in complexes 1ꢁ
Their electrochemical data are summarized in Table 3.
For the mononuclear complexes 1ꢁ11, one quasi-
reversible reduction couple has been observed at ca. ꢃ
1.43 to ꢃ1.60 V versus SCE, and is tentatively assigned
as ligand-centered reduction of the bipyridyl ligand. The
/15.
stituted complexes, [Re(Nꢀ
C4H3S)] (5 and 10) (ca. ꢂ0.82 V) show a less positive
potential than the corresponding monothiophene-sub-
stituted complexes, [Re(NꢀN)(CO)3(CꢁCꢀC4H3S)] (4
and 9) (ca. ꢂ0.92 V); consistent with the higher p-
electron-donating ability of CꢁCꢀC4H2SꢀC4H3S than
that of CꢁCꢀC4H3S, rendering the rhenium(I) center
/
N)(CO)3(Cꢁ
/
Cꢀ
/
C4H2Sꢀ
/
/
/
/
/
/
/
/
/
t
reduction potential for complexes 6ꢁ
ligand occurs at ca. ꢃ1.50 to ꢃ1.60 V, which is found
to be more negative than that for 1ꢁ5 with bpy ligand
which occurs at ca. ꢃ1.43 to ꢃ1.48 V. This is in line
/11 with Bu2bpy
/
/
/
/
/
/
/
/
more electron-rich and hence increases its ease of
/
/
oxidation. In addition to the first oxidation wave at
with the attachment of the electron-donating tert-butyl
substituents on the bipyridine ligand, which would
render the bipyridine ligand more electron-rich and
poorer p-accepting, thus decreases its ease of reduction.
ca. ꢂ
complexes with 2-ethynyl-2,2?-bithiophene ligand, 5 and
10, show two irreversible oxidation waves at ca. ꢂ1.15
and ꢂ1.35 V versus SCE while the rhenium(I) com-
plexes containing 2-ethynylthiophene ligand, 4 and 9,
show only one irreversible oxidation wave in the range
/
0.80 to ꢂ
/
0.90 V versus SCE, the rhenium(I)
/
/
The first oxidation waves of 1ꢁ
to ꢂ1.07 V, are tentatively assigned as Re(I)/Re(II)
oxidation. The observation that the complexes
[Re(bpy)(CO)3(CꢁCR)] show a less positive potential
/
11, which occur at ꢂ
/
0.82
/
of ꢂ
/
1.24 to ꢂ1.30 V versus SCE. Fig. 4 depicts the
/
/
cyclic voltammograms showing the reduction and oxi-

212
V.W.-W. Yam et al. / Journal of Organometallic Chemistry 670 (2003) 205ꢁ220
/
matched well with that observed in their counterparts
[Re{(CF3)2-bpy}(CO)3(C5H4N)]ClO4 and [Re(NO2-
phen)(CO)3(C5H4N)]ClO4. On the other hand, the first
three quasi-reversible reduction couples in complex 12,
which occurred at ꢃ
SCE are believed to originate from the [Re{(CF3)2-
)] unit, as their values are
/
0.73, ꢃ
/
0.88 and ꢃ
/
1.18 V versus
bpy}(CO)3(NC5H4Cꢁ
/
Cꢀ
/
comparable to that of [Re{(CF3)2-bpy}(CO)3-
(C5H4N)]ClO4. The fourth quasi-reversible reduction
couple at ꢃ
ligand-centered reduction, as similar reduction is ob-
served in the analogous complex 11 at ꢃ1.55 V. Upon
scanning to more negative potential, two additional
irreversible reduction waves are observed at ꢃ1.97 and
2.20 V. No attempts have been made to assign these
/
1.53 V versus SCE is believed to be tBu2bpy
/
/
ꢃ
/
two waves which occur at such negative potentials, as
decomposition might have occurred as reflected by the
disappearance of the anodic peaks of the waves at
ꢃ
/
0.73, ꢃ
Similarly, for complex 13, the quasi-reversible reduction
couples at ꢃ0.58 and ꢃ1.16 V are assigned as reduction
of the [Re(NO2-phen)(CO)3(NC5H4CꢁCꢀ)] unit while
1.52 V is assigned as Bu2bpy ligand-
/
0.88 and ꢃ
/
1.18 V after scanning to ꢃ
/
2.40 V.
/
/
/
/
t
the wave at ꢃ
/
centered reduction.
For the heterodinuclear 4-ethynylpyridine bridged
Fig. 2. The perspective drawing of 10 with atomic numbering scheme.
Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are
shown at the 50% probability level.
complexes,
(14 and 15), the cyclic voltammograms display two
[Re(Nꢀ
/
N)(CO)3(Cꢁ
/
Cꢀ/C5H4N)W(CO)5]
irreversible oxidation waves at ca. ꢂ
/
1.09 to ꢂ
/
1.34 V
and a quasi-reversible reduction couple at ca. ꢃ
/
1.40 to
dation of 4. These oxidation waves are assigned as
thiophene-based oxidations. Similar observations were
reported in other organometallic oligothienylacetylide
complexes [28b].
For the homo-metallic binnclear complexes 12 and 13,
far more complicated cyclic voltammograms are ob-
tained. For complex 12, two quasi-reversible oxidation
ꢃ
/
1.48 V versus SCE. The first oxidation wave which
occurs at ca. ꢂ1.10 V versus SCE has tentatively been
assigned as a Re(I)/Re(II) oxidation, while the second
oxidation wave which occurs at ca. ꢂ1.30 V versus SCE
/
/
is tentatively assigned as a tungsten-centered oxidation,
commonly observed in the electrochemical studies of
other related tungsten-containing complexes [30]. The
quasi-reversible reduction couple is tentatively assigned
as a bipyridyl ligand-centered reduction. The observa-
couples at ꢂ
/
1.19 and ꢂ1.85 V versus SCE are observed.
/
With reference to other related alkynyl complexes as
well as its mono-rhenium counterparts 11 and
[Re{(CF3)2-bpy}(CO)3(C5H4N)]ClO4, the first oxida-
tion couple is tentatively assigned as a Re(I)/Re(II)
oxidation of the rhenium center that is coordinated to
tBu2bpy and the alkynyl ligand [29]. The slightly more
tion that [Re(tBu2bpy)(CO)3(Cꢁ
(14) (ꢃ1.48 V vs. SCE) show a more negative reduction
potential than that of the corresponding analogue,
C5H4N)W(CO)5] (15) (ꢃ1.40 V
/
Cꢀ/C5H4N)W(CO)5]
/
[Re(bpy)(CO)3(Cꢁ
/
Cꢀ
/
/
vs. SCE) is similarly attributed to the poorer p-accepting
ability of the Bu2bpy ligand.
positive potentials of ꢂ
than ꢂ1.07 V in 11 can be rationalized by the
coordination of positively charged [Re{(CF3)2-
/
1.19 V in 12 and ꢂ1.23 V in 13
/
t
/
a
3.4. Electronic absorption and emission spectroscopies
bpy}(CO)3] and [Re(NO2-phen)(CO)3] unit, respectively,
to the pyridine ends in 12 and 13, which would result in
a reduced ease of oxidation, both from the reduced
donating ability of the 4-ethynylpyridine ligand upon
coordination of a second Re(I) center as well as the
increased positive charge on the complex. The second
In general, the electronic absorption spectra of
rhenium(I) diimine alkynyl complexes show intense
high-energy absorption bands at ca. 256ꢁ338 nm and
/
low-energy absorption bands at ca. 400 nm with
extinction coefficients of the order of 103 dm3 molꢃ1
cmꢃ1. The photophysical data for 1ꢁ
15 together with
two related complexes are shown in Table 4. The high-
/
oxidation couple at ca. ꢂ
13 are tentatively assigned as the Re(I)/Re(II) oxidation
of the respective [Re{(CF3)2-bpy}(CO)3(NC5H4CꢁCꢀ)]
and [Re(NO2-phen)(CO)3(NC5H4CꢁCꢀ)] unit as they
/
1.85 V in 12 and ꢂ1.80 V in
/
/
/
energy absorption bands, which are also found in the
free bpyꢁt
Bu2bpy and alkynyl ligands, are assigned as
/
/
/

V.W.-W. Yam et al. / Journal of Organometallic Chemistry 670 (2003) 205ꢁ
/220
213
Fig. 3. The perspective drawing of 11 with atomic numbering scheme. Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are shown
at the 40% probability level.
p0
ligands while the low-energy absorption bands are
tentatively assigned as the dp(Re)0p*(diimine) metal-
to-ligand charge transfer (MLCT) transition, probably
/
p* transitions of bpyꢁt
/
Bu2bpy and the alkynyl
conjugation of the oligothienyl ligand is supportive of
such an assignment. The trend is also supported by
similar observations in the related ruthenium oligothie-
nylacetylide complexes [28b]. As there is a red shift in
/
mixed with some p(Cꢁ
charge transfer (LLCT) character. This MLCT absorp-
tion band is at lower energy than that observed in the
/
C)0
/
p*(diimine) ligand-to-ligand
the pꢁ
thiophene units in the oligothienyl ligands, the MLCT
absorption band at ca. 410ꢁ420 nm is suggested to be
masked by the intense pꢁp* transition energies in the
bithiophene-substituted complexes, [Re(NꢀN)(CO)3(Cꢁ
CꢀC4H2SꢀC4H3S)] (5 and 10). The higher MLCT
absorption energies in 9 than that of 4 is consistent
with the higher p* orbital energies of tBu2bpy as a result
of its poorer p-accepting abilities derived from the
presence of the more electron-rich tert-butyl substituent
on the bipyridine ligand.
/
p* transition energy upon an increase in the
/
related precursor complex [Re(Nꢀ
/N)(CO)3Cl]. It is
/
suggested that the dp(Re) orbital in the alkynyl complex
is higher-lying in energy as a result of the stronger s-
donating ability of the alkynyl ligand than the chloro
/
/
/
/
counterpart. The 338ꢁ
in the oligothienyl substituted alkynyl complexes
[Re(NꢀN)(CO)3(CꢁCꢀC4H3S)] and [Re(NꢀN)(CO)3-
(CꢁCꢀC4H2SꢀC4H3S)] (4, 5, 9 and 10), are ascribed
to the thiophene-based p0p* transitions of the CꢁCꢀ
C4H3S and CꢁCꢀC4H2SꢀC4H3S moieties. These bands
/
372 nm bands which are present
/
/
/
/
/
/
/
/
/
/
For the 4-ethynylpyridine bridged homo-metallic bi-
nuclear complexes 12 and 13 and the hetero- binuclear
complexes 14 and 15, a strong absorption band at ca.
350 and 370 nm, respectively, is observed, with extinc-
/
/
/
are absent in the electronic absorption spectra of
oligothienyl ligand-free analogues and the extinction
coefficients of these thiophene-based p0
/
p* transitions
tion coefficients in the order of 104 dm3molꢃ1 cmꢃ1
,
are in the range expected for such transitions [17,24,25].
Fig. 5 depicts the electronic absorption spectra of 4 and
5 in THF solution at room temperature. The red shift in
absorption energies from ca. 340 nm in the monothio-
phene complexes to ca. 370 nm in the bithiophene
counterparts with an increase in the extent of p-
which are much larger than that of the mononuclear
counterparts. It is suggested that the absorption band in
complexes 12ꢁ15 might possess some charge-transfer
/
character between the two metal centers, involving a
charge transfer from the donor [Re(tBu2bpy)(CO)3] or
[Re(bpy)(CO)3] unit to the acceptor [Re{(CF3)2-

214
V.W.-W. Yam et al. / Journal of Organometallic Chemistry 670 (2003) 205ꢁ220
/
solution. The origin of the emission has been ascribed to
3
a MLCT dp(Re)0
/
p*(Nꢀ/N) excited state, similar to
that of the other luminescent rhenium(I) diimine systems
reported [17,24,25]. In accordance with the trend in
MLCT absorption energies, the lower emission energy
in the rhenium(I) alkynyl complexes compared with
their chloro analogues is ascribed to the better s-donor
ability of the alkynyl moiety which would render the
rhenium center more electron rich and hence lower the
MLCT emission energy. For the complexes with the
same diimine ligand, a dependence of the emission
energy on the nature of the alkynyl ligands has been
observed. The shift in the emission energy correlates well
with the s- and p-donating ability of the alkynyl ligand,
with emission energies in the order: 5ꢀ
and 10ꢀ9ꢀ8ꢀ7ꢀ6:11 in the solid state. Fig. 6
shows the solid-state emission spectra of 1ꢁ4 at room
/
4ꢀ
/
2ꢀ
/
1ꢀ3
/
/
/
/
/
/
/
temperature. The monothiophene-substituted com-
plexes, 4 and 9, are found to emit at higher energies
than their bithiophene-substituted counterparts, 5 and
10. The observation of a red shift in emission energy
upon increasing the number of thiophene units is
consistent with the better p-electron-donating ability of
Cꢁ
/
Cꢀ
/
C4H2Sꢀ
/
C4H3S than Cꢁ
/
Cꢀ
/
C4H3S, which renders
the Re dp orbital more electron-rich, and raises the Re
t
dp orbital energy. Complexes 9 and 10 with Bu2bpy
ligand show higher emission energies than their respec-
tive analogues 4 and 5 with bpy ligand, again consistent
with the presence of electron-releasing tert-butyl groups
on the tBu2bpy ligand, which renders the p* orbital
t
energy of Bu2bpy higher-lying than bpy.
For the 4-ethynylpyridine-bridged donorꢁacceptor
/
dirhenium(I) complexes 12 and 13, relatively weak
emissions are observed in fluid solution. It is envisaged
that with this class of donorꢁacceptor system, once the
/
Fig. 4. Cyclic voltammogram showing (a) the oxidation and (b)
molecule is excited, its excited state energy would be
transferred from the donor portion of the molecule,
[Re(tBu2bpy)(CO)3] to its acceptor side, [Re{(CF3)2-
bpy}(CO)3] and [Re(NO2-phen)(CO)3]. However, in
view of their weakly emissive behavior and the close
resemblance of the emission energies of both the donor
and acceptor parts of the complexes as reflected from
the emission data of their mononuclear precursors, no
attempts have been made to assign the emission
unambiguously. The hetero-metallic complex 14, on
the other hand, is found to emit at a higher emission
energy than that of its mononuclear counterpart, 11
both in acetone and in the solid state at 298 K. This is
consistent with the decrease in the p-electron-donating
ability of the 4-ethynylpyridine ligand upon coordina-
tion of the electron-withdrawing W(CO)5 moiety, which
resulted in the lowering of Re dp orbital energy and
hence an increase in the MLCT emission energy. The
higher MLCT emission energy in 14 than 15 is again
consistent with the higher p* orbital energy of the
tBu2bpy ligand than bpy.
reduction of [Re(CO)3(bpy)(Cꢁ
/
CꢀC4H3S)] (4) in acetonitrile (0.1
/
mol dmꢃ3 n Bu4NPF6).
bpy}(CO)3], [Re(NO2-phen)(CO)3] or [W(CO)5] moiety.
By comparing complexes 12ꢁ14 with their mononuclear
counterpart 11, the bridged complexes 12ꢁ14 are found
/
/
to absorb at higher energies than 11. This could be
rationalized by the fact that the 4-ethynylpyridine ligand
upon coordinating to two metal centers would be less
electron rich and hence rendered the Re dp orbitals
lower-lying in energy, leading to a larger MLCT
transition energy. An alternative rationale for the
increased MLCT absorption energy is that the elec-
tron-donating ability of the 4-ethynylpyridine is lowered
as the electron-withdrawing substituent, [Re{(CF3)2-
bpy}(CO)3], [Re(NO2-phen)(CO)3] or W(CO)5, is at-
tached to the 4-ethynylpyridine. This would also lead to
the increase in the MLCT transition energy.
Upon excitation at l ꢀ
diimine alkynyl complexes exhibit
orangeꢁred emission in the solid state and in fluid
/
350 nm, the rhenium(I)
a
long-lived
/

V.W.-W. Yam et al. / Journal of Organometallic Chemistry 670 (2003) 205ꢁ
/220
215
Table 1
Crystallographic data for complexes 1, 10 and 11
Complex
1
10
11
Empirical formula
Formula weight
Temperature (K)
[ReC21H13N2O3]×
556.59
301
/
1/2[(CH3)2CO] [(ReC31H29N2O3S2)×
/CH2Cl2]
[ReO3N2C28H28
640.75
301
]
812.84
301
˚
Wavelength (A)
0.71073
Orthorhombic
Pbcn (No. 60)
18.104(3)
11.266(1)
20.429(2)
90
0.71073
Monoclinic
P21/n (No.14)
10.695(2)
12.217(2)
26.198(3)
90
0.71073
Monoclinic
P21/n (No.14)
20.405(5)
12.186(3)
23.312(4)
90
Crystal system
Space group
˚
a (A)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
V (A )
Z
Dcalc (g cmꢃ3
90
90
96.26(2)
90
112.85(1)
90
3
˚
4166(1)
8
1.774
3402.6(9)
2
1.587
5352(2)
8
1.590
)
m(Moꢁ
F(000)
Crystal size (mm)
/
Ka) (cmꢃ1
)
58.63
2144
38.86
1608
45.74
2528
0.35ꢄ
2umax
h: 0ꢁ
/
0.20ꢄ
48
20; k: 0ꢁ
/
0.15
0.35ꢄ
2umax
h: 0ꢁ
/
0.10ꢄ
50.9
12; k: 0ꢁ
/
0.07
0.20ꢄ
2umax
31 to 31 h: 0ꢁ
/
0.10ꢄ
45
21; k: 0ꢁ
/
0.35
Collection range (8)
Index ranges
ꢀ
/
ꢀ
/
ꢀ
/
/
/
12; l: ꢃ
/
23 to 0
/
/
13; l: ꢃ
/
/
/
13; l: ꢃ22 to 22
/
Independent reflections
Reflections used in refinement
Number of parameters
R
3690
2345
263
5855
4461
379
7389
4924
631
a
b
c
0.027
0.032
1.61
0.052
0.072
2.22
0.027
0.030
1.14
wR
Goodness-of-fit on F2
˚
Largest difference peak and hole (e A
ꢃ3
)
ꢂ
/
0.83, ꢃ
/0.50
ꢂ
/
0.72, ꢃ
/
2.02
ꢂ
/
0.44, ꢃ0.45
/
a
wꢀ
/
4F2o/s2(Fo2), where s2(F2o)ꢀ
4F2o/s2(Fo2), where s2(F2o)ꢀ
4F2o/s2(Fo2), where s2(F2o)ꢀ
/
[s2(I)ꢂ
/
(0.015F2o)2] with I ꢀ
/
3s(I).
3s(I).
3s(I).
b
c
wꢀ
/
/
[s2(I)ꢂ(0.035F2o)2] with I ꢀ
[s2(I)ꢀ(0.017F2o)2] with I ꢀ
/
/
wꢀ
/
/
/
/
3.5. Molecular orbital calculation
plexes, have been synthesized and some of them have
been structurally characterized. Low-energy absorption
Molecular orbital studies using extended Huckel
¨
bands at ca. 400 nm, attributable to the dp(Re)0
N) MLCT transition probably with some mixing of a
some p(CꢁC)0p*(NꢀN) LLCT character, have been
observed in the electronic absorption spectra. All of the
complexes display intense orangeꢁred emission at ca.
350 nm, assigned as
/
p*(Nꢀ
/
molecular orbital (EHMO) theory on a selected rhe-
nium(I) diimine alkynyl complex 10 have been per-
formed. The calculated molecular orbital energies,
/
/
/
percentage composition and the HOMOꢁ
/
LUMO en-
/
ergy gap are shown in Table 5. Fig. 7 shows the CACAO
plots of the HOMO and LUMO. EHMO study shows
that the LUMO mainly consists of p*(tBu2bpy) char-
acter while the HOMO is mainly dominated by the
600 nm upon excitation at l ꢀ
/
3MLCT emissions. Semi-empirical EHMO and electro-
chemical studies provide further support for the spectral
assignments.
antibonding character of the Reꢀ
moiety resulted from the overlap of the dp(Re) and
p(CꢁCꢀC4H2SꢀC4H3S) orbitals, which is supportive of
a mixed dp(Re)0 CꢀC4H2Sꢀ
p*(tBu2bpy) MLCT/p(Cꢁ
p*(tBu2bpy) LLCT character for the electro-
/
Cꢁ
/
Cꢀ
/
C4H2Sꢀ
/
C4H3S
/
/
/
5. Supplementary material
/
/
/
/
C4H3S)0
nic transition.
/
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Center, CCDC nos. 200101ꢁ200103 for complexes
/
1, 10 and 11, respectively. Copies of these data may be
obtained free of charge from The Director, CCDC, 12
4. Conclusions
Union Road, Cambridge CB2 1EZ, UK (Fax: ꢂ44-
/
A number of luminescent mononuclear rhenium(I)
alkynyl complexes, together with some binuclear com-
1223-336033 or e-mail: deposit@ccdc.cam.ac.uk or
www: http://www.ccdc.cam.ac.uk.

216
V.W.-W. Yam et al. / Journal of Organometallic Chemistry 670 (2003) 205ꢁ220
/
Table 2
˚
Selected bond lengths (A) and bond angles (8) for 1, 10 and 11
Compound 1
Bond length
Re(1)ꢀ
Re(1)ꢀ
Re(1)ꢀ
C(4)ꢀ
/
N(1)
C(1)
C(3)
2.181(5)
1.955(8)
1.904(9)
1.199(9)
Re(1)ꢀ
Re(1)ꢀ
Re(1)ꢀ
/
N(2)
C(2)
C(4)
2.182(6)
1.918(8)
2.151(7)
/
/
/
/
/
C(5)
Bond angles
N(1)ꢀRe(1)ꢀ
C(1)ꢀRe(1)ꢀC(4)
C(4)ꢀC(5)ꢀC(6)
/
/
C(2)
173.1(3)
176.3(3)
176.3(7)
N(2)ꢀ
Re(1)ꢀ
N(1)ꢀRe(1)ꢀ
/
Re(1)ꢀ
/
C(3)
173.4(3)
176.4(6)
74.4(2)
/
/
/
C(4)ꢀC(5)
/
/
/
/
/
N(2)
Compound 10
Re(1)ꢀ
Re(1)ꢀ
Re(1)ꢀ
C(4)ꢀ
/
N(1)
C(1)
C(3)
2.177(7)
1.955(9)
1.914(9)
1.20(1)
Re(1)ꢀ
Re(1)ꢀ
Re(1)ꢀ
C(8)ꢀ
/
N(2)
C(2)
C(4)
2.188(6)
1.917(10)
2.144(8)
1.38(1)
/
/
/
/
/
C(5)
/
C(9)
N(1)ꢀ
C(1)ꢀRe(1)ꢀ
C(4)ꢀC(5)ꢀ
/
Re(1)ꢀ
/
C(2)
167.9(3)
179.2(3)
175.7(10)
N(2)ꢀ
Re(1)ꢀ
N(1)ꢀRe(1)ꢀ
/
Re(1)ꢀ
/
C(3)
172.3(3)
175.2(8)
73.6(2)
/
/
C(4)
/
C(4)ꢀ
/
C(5)
/
/C(6)
/
/
N(2)
Compound 11
Re(1)ꢀ
Re(1)ꢀ
Re(1)ꢀ
C(4)ꢀ
Re(1)ꢀ
Re(2)ꢀ
Re(2)ꢀ
/
N(1)
C(1)
C(3)
2.175(5)
1.948(9)
1.891(9)
1.196(10)
2.179(6)
1.913(9)
2.126(8)
Re(1)ꢀ
Re(1)ꢀ
Re(1)ꢀ
Re(1)ꢀ
Re(2)ꢀ
Re(2)ꢀ
C(32)ꢀ
/
N(2)
C(2)
2.184(6)
1.914(9)
2.121(8)
2.178(6)
1.957(9)
1.903(9)
1.195(10)
/
/
/
/
C(4)
/
C(5)
/
N(4)
C(29)
C(31)
/
N(5)
/
/
C(30)
C(32)
/
/
/
C(33)
N(1)ꢀ
C(1)ꢀRe(1)ꢀ
N(1)ꢀRe(1)ꢀ
N(5)ꢀRe(2)ꢀ
Re(2)ꢀ
/
Re(1)ꢀ
/
C(2)
170.1(3)
177.5(3)
73.5(2)
N(2)ꢀRe(1)ꢀ
Re(1)ꢀC(4)ꢀC(5)
N(4)ꢀRe(2)ꢀC(30)
C(29)ꢀRe(2)ꢀC(32)
N(4)ꢀRe(2)ꢀN(5)
/
/
C(3)
169.7(3)
177.3(7)
171.9(3)
178.5(3)
74.1(2)
/
/
C(4)
/
/
/
/
N(2)
/
/
/
/
C(31)
C(33)
169.8(3)
178.2(7)
/
/
/
C(32)ꢀ
/
/
/
Table 3
Electrochemical data for 1ꢁ
a
/
15 and the related complexes in acetonitrile (0.1 mol dmꢃ3 n BuNPF6) at 298 K
b
Oxidation Epa (V) vs. SCE
c
Complex
Reduction E1/2 (V) vs. SCE (DEp (mV))
1
ꢂ
/
0.99, ꢂ
1.02, ꢂ
0.94, ꢂ
0.92, ꢂ
0.82, ꢂ1.14, ꢂ
0.88, ꢂ1.33, ꢂ
0.97, ꢂ1.40, ꢂ
0.97, ꢂ1.75
0.91, ꢂ1.30, ꢂ
0.82, ꢂ1.16, ꢂ
1.07, ꢂ1.25, ꢂ1.74
1.19, ꢂ
1.23, ꢂ
1.09, ꢂ
1.09, ꢂ
/
1.78
1.78
1.78
ꢃ
/
1.47 (70)
1.45 (80)
1.46 (70)
1.43(71)
1.48(84)
1.60 (70)
1.54 (60)
1.60 (58)
1.51 (75)
1.50 (75)
1.55 (69)
2
ꢂ
/
/
ꢃ
/
3
ꢂ
/
/
ꢃ
/
4
ꢂ
/
/
1.24, ꢂ
/
1.79
ꢃ
/
5
ꢂ
/
/
/1.34, ꢂ
/
1.82
ꢃ
/
6
ꢂ
/
/
/1.76
ꢃ
/
7
ꢂ
/
/
/1.90
ꢃ
/
8
ꢂ
/
/
ꢃ
/
9
10
ꢂ
/
/
/1.76
ꢃ
/
ꢂ
/
/
/1.36, ꢂ
/1.79
ꢃ
/
11
12
ꢂ
/
/
/
ꢃ
/
d
ꢂ
/
/
1.85
1.80
1.34
1.32
ꢃ
/
0.73 (88), ꢃ
/
0.88 (80), ꢃ
/
1.18 (67), ꢃ
/
1.53 (75), ꢃ
/
1.97 d, ꢃ
2.40
/
2.20
d
13
14
ꢂ
/
/
ꢃ
/
0.58 (71), ꢃ1.16 (79), ꢃ
/
/
1.52 (86), ꢃ
/
1.76 d, ꢃ
/
2.19 d, ꢃ
/
ꢂ
/
/
ꢃ
/
1.48 (84)
15
[Re{(CF3)2-bpy}(CO)3(C5H4N)]ClO4
ꢂ
/
/
ꢃ
/
1.40 (79)
e
ꢂ
/
1.84
ꢃ
/
0.69 (63), ꢃ
/0.91 (168), ꢃ
/
1.19 (117), ꢃ
/
1.20 (101)
d
1.73 d, ꢃ
/
1.85
e
[Re(NO2-phen)(CO)3(C5H4N)]ClO4
ꢂ
/
1.80
ꢃ
/
0.56 (64), ꢃ1.01 (163), ꢃ
/
/
1.60,ꢃ
/
Working electrode: glassy carbon; DEp of Fcꢂ/Fc ranges from 61 to 64 mV; scan rate: 100 mV sꢃ1
.
a
b
c
Epa, anodic peak potential.
Epa ꢂ Epc
E1/2
ꢀ
/
; where Epa and Epc are anodic and cathodic peak potentials, respectively. DEpꢀ
/
jEpa Epcj.
ꢃ
/
2
Cathodic peak potential for irreversible wave.
Ref. [31].
d
e

V.W.-W. Yam et al. / Journal of Organometallic Chemistry 670 (2003) 205ꢁ
/220
217
Table 4
Photophysical spectral data for 1ꢁ15
/
Complex
Medium (T (K)) Absorption labs (nm) (o (dm3 molꢃ1 cmꢃ1))
Emission lem (nm) (to (ms))
1
Solid (298)
Solid (77)
585 (0.19)
570
CH2Cl2 (298)
Solid (298)
Solid (77)
286 (37 250), 298sh (30 160), 326sh (10 430), 420 (3240) 654 (B0.01)
/
2
3
4
580 (0.20)
565
CH2Cl2 (298)
Solid (298)
Solid (77)
284 (39 880), 298sh (35 380), 324sh (13 330), 420 (2710) 650 (B0.01)
/
597 (0.27)
588
CH2Cl2 (298)
Solid (298)
Solid (77)
278 (36 120), 298sh (29 200), 328sh (9570), 424 (2430)
246 (27 220), 296 (35 920), 338sh (11 570), 420 (3110)
668 (B
/
0.01)
573 (B
/
0.1)
a
580 (10.35, 1.77)
640 (B0.1)
575 (6.99, 0.61)
560 (B0.1)
548 (0.52)
649 (B0.1)
THF (298)
/
b
a
Glass (77)
5
Solid (298)
Solid (77)
THF (298)
/
246 (29 740), 300 (23 030), 370 (30 480), 390sh (24 320)
338sh (6620), 420 (2290)
/
b
a
Glass (77)
520 (3.51, 0.39)
600 (0.15)
585
6
7
Solid (298)
Solid (77)
THF (298)
Solid (298)
Solid (77)
THF (298)
Me2CO
720 (B0.1)
/
590 (0.27)
572
310 (36 680), 338 (25 850), 406 (2780)
396sh (2860)
680 (B
/
0.1)
680 (B
/
0.1)
8
9
Solid (298)
Solid (77)
THF (298)
Solid (298)
Solid (77)
THF (298)
580 (0.13)
570
256 (17 965), 292 (19 225), 336sh (2510), 424 (2540)
242 (31 010), 294 (40 790), 338sh (11 400), 412 (3180)
690 (B/0.1)
585 (B/0.1)
a
a
a
a
570 (0.91, 0.10)
625 (B0.1)
551 (7.16, 0.88)
550 (B0.1)
530 (0.84, 0.12)
640 (B0.1)
/
b
Glass (77)
10
11
Solid (298)
Solid (77)
THF (298)
/
242 (48 140), 298 (33 540), 372 (43 250), 390sh (35 020)
/
b
Glass (77)
Solid (298)
Solid (77)
520 (3.14, 0.19)
600 (0.23)
580
Me2CO (298)
CH2Cl2
384 (3620)
364 (43 000)
670 (B
Not measured
/
0.1)
12
13
14
Me2CO (298)
CH2Cl2 (298)
Me2CO (298)
Solid (298)
Solid (77)
352 (41 000)
272 (12 235), 296sh (8810), 362 (7070)
352 (22 300)
650 (B
670 (B
640 (B
555 (B
/
0.1)
0.1)
0.1)
0.1)
/
/
/
a
545 (3.14, 0.27)
THF (298)
Me2CO (298)
252 (64 040), 296 (48 570), 362 (38 450), 390sh (25 060)
358 (25 640), 380sh (20 430)
610 (B
/
0.1)
615 (B
/
0.1)
b
a
a
a
Glass (77)
527 (5.94, 1.57)
564 (B0.1)
552 (2.60, 0.19)
620 (B0.1)
526 (5.66, 0.80)
680 (B0.1)
630 (1.20)
15
Solid (298)
Solid (77)
THF (298)
/
244 (58 900), 298 (42 770), 372 (39 560), 394sh (26 710)
/
b
Glass (77)
c
[Re{(CF3)2-bpy}(CO)3(C5H4N)]ClO4
c
[Re(NO2-phen)(CO)3(C5H4N)]ClO4
Me2CO (298)
Me2CO (298)
382 (3030)
360sh (4550)
/
a
Double exponential decay.
b
EtOHꢁ/MeOH (4:1 v/v).
c
Ref. [31].

218
V.W.-W. Yam et al. / Journal of Organometallic Chemistry 670 (2003) 205ꢁ220
/
Fig. 6. Solid-state emission spectra of 1 (*
/
), 2 (---), 3 (×
/
×
/
×
/
) and 4 (ꢁ
/
×
/
ꢁ/
) at 298 K.
Fig. 7. CACAO plots of (a) HOMO and (b) LUMO of 10.
Table 5
Calculated molecular orbital energies and transition energies
Number
Level (eV)
Composition (%)
Re CꢁCC4H2Sꢀ
HOMOꢁLUMO energy gap DEgap (eV)
/
/
/
C4H3S
3CO t Bu2bpy
a
103
102
ꢃ
/
8.876
16
68
1
14
77
13
1.964
(1000101)
ꢃ
/
8.956
1
a
/
a
101 (LUMO)
100 (HOMO)
ꢃ
/
9.447
2
a
94
a
ꢃ
/
11.411
12.282
12.374
1
8
94
3
a
99
98
ꢃ
/
76
11
ꢃ/
15 65
8
a
Percentage composition of less than 0.5%.
Acknowledgements
Croucher Senior Research Fellowship from the Crou-
cher Foundation. The work described in this paper has
been supported by a CERG Grant from the Research
Grants Council of Hong Kong Special Administrative
Region, China (Project No. HKU 7123/00P). K.M.-
V.W.-W.Y. acknowledges support from The Univer-
sity of Hong Kong Foundation for Educational Devel-
opment and Research Limited, and the receipt of a

V.W.-W. Yam et al. / Journal of Organometallic Chemistry 670 (2003) 205ꢁ
/220
219
[11] (a) V.W.W. Yam, K.M.C. Wong, N. Zhu, J. Am. Chem. Soc. 124
(2002) 6506;
C.W. acknowledges the receipt of a University Post-
doctoral Fellowship from The University of Hong
Kong; S.C.-F. Lam and S.H.-F. Chong the receipt the
postgraduate studentships administered by The Univer-
sity of Hong Kong.
(b) V.W.W. Yam, R.P.L. Tang, K.M.C. Wong, K.K. Cheung,
Organometallics 20 (2001) 4476;
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Phillips, K.L. Yu, R.W.K. Wong, H. Yan, Q.J. Meng, Organo-
metallics 17 (1998) 2590;
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