Synthesis, photophysics, and electrochemistry of luminescent binuclear rhenium(I) complexes containing μ-bridging thiolates. X-ray crystal structure of [{Re(bpy)(CO)3}2(μ-SC6H4-CH 3-P)]OTf

Article abstract of DOI:10.1021/om960797w

A series of binuclear Re(I) thiolato complexes [{Re(L-L)(CO)₃}₂(μ-SC₆H ₄-X-P)]OTf[L-L = phen, X = CH₃ (1), OCH₃ (2), C(CH₃)₃ (3), Cl (4), F (5); L-L = bpy, X = CH₃ (6); L-L = 5,5′-Me₂-bpy, X = CH₃ (7)] have been synthesized and their photophysical and electrochemical properties studied. The X-ray crystal structure of 6 has also been determined. The complexes have been shown to exhibit long-lived luminescence both in the solid state and in fluid solutions at room temperature. The emission has been assigned as being derived from a ³MLCT origin.

Full text of DOI:10.1021/om960797w

Organometallics 1997, 16, 1729-1734
1729
Syn th esis, P h otop h ysics, a n d Electr och em istr y of
Lu m in escen t Bin u clea r Rh en iu m (I) Com p lexes
Con ta in in g µ-Br id gin g Th iola tes. X-r a y Cr ysta l
Str u ctu r e of [{Re(bp y)(CO)3}2(µ-SC6H4-CH3-p)]OTf
Vivian Wing-Wah Yam,* Keith Man-Chung Wong, and Kung-Kai Cheung
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong
Received September 17, 1996X
A series of binuclear Re(I) thiolato complexes [{Re(L-L)(CO)3}2(µ-SC6H4-X-p)]OTf [L-L
) phen, X ) CH3 (1), OCH3 (2), C(CH3)3 (3), Cl (4), F (5); L-L ) bpy, X ) CH3 (6); L-L )
5,5′-Me2-bpy, X ) CH3 (7)] have been synthesized and their photophysical and electrochemical
properties studied. The X-ray crystal structure of 6 has also been determined. The complexes
have been shown to exhibit long-lived luminescence both in the solid state and in fluid
solutions at room temperature. The emission has been assigned as being derived from a
3MLCT origin.
In tr od u ction
Besides, the well-documented MLCT excited state chem-
istry of rhenium(I) R,R′-diimine complexes,1-5 together
with our recent interest in the photophysical studies of
polynuclear metal-chalcogen systems,8 has attracted
our attention to the synthesis of luminescent complexes
of rhenium(I) thiolates. Thiolate ligands are also well-
known to have different bonding modes, capable of
forming polynuclear complexes with various transition
metal ions.9 To the best of our knowledge, there have
been no reports on the photophysical studies of rhe-
nium(I)-thiolato complexes despite a number of rhe-
nium thiolate systems, limited to those of structural
studies, being known.10 Moreover, despite numerous
studies on supramolecular chemistry employing bridg-
ing diimine ligands,1b,3a,4c,11 attempts to utilize the
ability of the thiolate ligand to bridge various metal
centers in the design of supramolecular systems were
not known. Therefore, it is our aim to employ thiolate
ligands in the synthesis and design of polynuclear
luminescent rhenium(I) tricarbonyl R,R′-diimine com-
plexes and to fine tune their excited state behavior
through the systematic variation of the thiolate ligand.
In this work, we report the synthesis, photophysics, and
electrochemistry of a series of luminescent binuclear
rhenium(I) complexes containing µ-bridging thiolato
Rhenium(I) tricarbonyl R,R′-diimine systems have
been extensively studied for their rich photoluminescent
properties and their ability to effect electrocatalytic
reduction of carbon dioxide. Numerous reports on the
photophysical and photochemical studies have appeared
as a result of the sensitivity of their luminescent
behavior to changes in the nature of the environment
as well as their stability to photodecomposition.1-5 The
electrocatalytic reduction of carbon dioxide employing
such a system has also been widely studied by bulk
electrolysis, cyclic voltammetry, and IR spectroelectro-
chemical investigations.6
Recently, there has been a growing interest in the
studies of rhenium-sulfur complexes owing to their
possible involvement in hydrodesulfurization catalysis.7
X Abstract published in Advance ACS Abstracts, March 15, 1997.
(1) See, for example: (a) Horva´th, O.; Stevenson, K. L. Charge
Transfer Photochemistry of Coordination Compounds; VCH: New York,
1993. (b) Balzani, V.; Scandola, F. Supramolecular Photochemistry;
Ellis Horwood: Chichester, U.K., 1991.
(2) See, for example: (a) Wrighton, M. S.; Morse, D. L. J . Am. Chem.
Soc. 1974, 96, 998. (b) Wrighton, M. S. J . Am. Chem. Soc. 1974, 74,
4801. (c) Fredericks, S. M.; Luong, J . C.; Wrighton, M. S. J . Am. Chem.
Soc. 1979, 101, 7415.
(3) See, for example: (a) Wallendael, S. V.; Shaver, R. J .; Rillema,
D. P.; Yoblinski, B. J .; Stathis, M.; Guarr, T. F. Inorg. Chem. 1990,
29, 1761. (b) Sacksteder, L. A.; Zipp, A. P.; Brown, E. A.; Streich, J .;
Demas, J . N.; DeGraff, B. A. Inorg. Chem. 1990, 29, 4335. (c)
Sacksteder, L. A.; Lee, M.; Demas, J . N.; DeGraff, B. A. J . Am. Chem.
Soc. 1993, 115, 8230. (d) Wallace, L.; Woods, C.; Rillema, D. P. Inorg.
Chem. 1995, 34, 2875. (e) Stufkens, D. J . Comments Inorg. Chem. 1992,
13, 359. (f) Sullivan, B. P. J . Phys. Chem. 1989, 93, 24. (g) Lees, A. J .
Chem. Rev. 1987, 87, 711.
(4) See, for example: (a) Caspar, J . V.; Meyer, T. J . J . Phys. Chem.
1983, 87, 952. (b) Tapolsky, G. T.; Duesing, R.; Meyer, T. J . J . Phys.
Chem. 1989, 93, 3885. (c) Tapolsky, G. T.; Duesing, R.; Meyer, T. J .
Inorg. Chem. 1990, 29, 2285.
(7) See, for example: (a) Pecoraro, T. A.; Chianelli, R. R. J . Catal.
1981, 67, 430. (b) Ledoux, M. J .; Michaux, O.; Agostini, G.; Panissod,
P. J . Catal. 1986, 102, 275. (c) Bussell, M. E.; Somorjai, G. A. J . Phys.
Chem. 1989, 93, 2009.
(8) See, for example: (a) Yam, V. W.-W.; Lee, W.-K.; Lai, T.-F. J .
Chem. Soc., Chem. Commun. 1993, 1571. (b) Yam, V. W.-W.; Yeung,
P. K.-Y.; Cheung, K.-K. J . Chem. Soc., Chem. Commun. 1995, 256. (c)
Yam, V. W.-W.; Yeung, P. K.-Y.; Cheung, K.-K. J . Chem. Soc., Dalton
Trans. 1994, 12, 2197. (d) Yam, V. W.-W.; Lo, K. K.-W.; Cheung, K. K.
Inorg. Chem. 1996, 35, 3459. (e) Yam, V. W.-W.; Lo, K. K.-W.; Wang,
C.-R.; Cheung, K. K. Inorg. Chem. 1996, 35, 5116. (f) Yam, V. W.-W.;
Yeung, P. K.-Y.; Cheung, K.-K. Angew. Chem., Int. Ed. Engl. 1996,
35, 739. (g) Yam, V. W.-W.; Chan, C.-L.; Cheung, K.-K. J . Chem. Soc.,
Dalton Trans. 1996, 4019.
(5) See, for example: (a) Yam, V. W.-W.; Lau, V. C.-Y.; Cheung, K.-
K. J . Chem. Soc., Chem. Commun. 1995, 259. (b) Yam, V. W.-W.; Lau,
V. C.-Y.; Cheung, K.-K. Organometallics 1995, 14, 2749. (c) Yam, V.
W.-W.; Lau, V. C.-Y.; Cheung, K.-K. Organometallics 1996, 15, 1740.
(d) Yam, V. W.-W.; Wong, K. M.-C; Lee, V. W.-M.; Lo, K. K.-W.; Cheung,
K.-K Organometallics 1995, 14, 4034.
(9) Krebs, B.; Henkel, G. Angew. Chem., Int. Ed. Engl. 1991, 30,
769.
(6) See, for example: (a) Hawecker, J .; Lehn, J . M.; Ziessel, R. J .
Chem. Soc., Chem. Commun. 1984, 328. (b) Sullivan, B. P.; Meyer, T.
J . J . Chem. Soc., Chem. Commun. 1984, 1244. (c) Sullivan, B. P.;
Bolinger, C. M.; Conrad, D.; Vining, W. J .; Meyer, T. J . J . Chem. Soc.,
Chem. Commun. 1985, 1414. (d) Breikss, A. I.; Abruna, H. D. J .
Electroanal. Chem. 1986, 201, 347. (e) Luong, J . C. Ph.D. Thesis,
Massachusetts Institute of Technology, Cambridge, MA, 1981.
(10) See, for example: (a) Osborne, A. G.; Stone, F. G. A. J . Chem.
Soc. A 1969, 1143. (b) King, R. B.; Welcman, N. Inorg. Chem. 1969,
12, 2540. (c) Abel, E. W.; Harrison, W.; McLean, R. A. N.; Marsh, W.
C.; Trotter, J . J . Chem. Soc., Chem. Commun. 1970, 1531.
(11) See, for example: (a) Volger, A.; Kisslinger, J . Inorg. Chim. Acta
1986, 115, 119. (b) J uris, A.; Campagna, S. Bidd, I.; Lehn, J . M.; Ziessel,
R. Inorg. Chem. 1988, 27, 4007.
S0276-7333(96)00797-2 CCC: $14.00 © 1997 American Chemical Society

1730 Organometallics, Vol. 16, No. 8, 1997
Yam et al.
8.90 (dd, 4H, phen H’s), 9.45 (dd, 4H, phen H’s). IR (CH2Cl2,
cm-1): ν(CtO) 2033, 2021, 1931, 1915. Positive FAB-MS: ion
clusters at m/ z 1065 {M}+, 616 {M - [Re(phen)(CO)3]}+, 451
{M-[Re(phen)(CO)3(SC6H4-tBu-p)]}+. UV-vis [λ/nm (ꢀmax/dm3
mol-1 cm-1)]: CH2Cl2, 270 (41 345), 294 sh (23 630), 366 (6905),
438 sh (2280). Elemental analyses. Found: C, 41.12; H, 2.21;
N, 4.59. Calcd for 3‚1/2(CH3)2CO: C, 41.02; H, 2.57; N 4.50.
[{Re(p h en )(CO)3}2(µ-SC6H4-Cl-p)]OTf (4). The procedure
is similar to that described for the preparation of 1, except
4-chlorothiophenol was used in place of p-thiocresol to give
yellow crystals of 4. Yield: 123 mg, 65%. 1H NMR (300 MHz,
acetone-d6, 298 K, relative to TMS): δ 5.15 (dd, 2H, aryl H
ortho to S), 5.75 (dd, 2H, aryl H meta to S), 7.95 (dd, 4H, phen
H’s), 8.10 (s, 4H, phen H’s), 8.80 (dd, 4H, phen H’s), 9.25 (dd,
4H, phen H’s). IR (CH2Cl2, cm-1): ν(CtO) 2034, 2024, 1932,
1914. Positive FAB-MS: ion clusters at m/ z 1029 {M}+, 594
{M - [Re(phen)(CO)3]}+, 451 {M - [Re(phen)(CO)3(SC6H4-Cl-
p)]}+. UV-vis [λ/nm (ꢀmax/dm3 mol-1 cm-1)]: CH2Cl2, 278
(41 590), 286 sh (28 900), 366 (7700), 436 sh (2825). Elemental
analyses. Found: C, 37.69; H, 1.50; N, 4.70. Calcd for
4‚1/4(CH3)2CO: C, 37.52; H, 1.78; N, 4.64.
[{Re(p h en )(CO)3}2(µ-SC6H4-F -p)]OTf (5). The procedure
is similar to that described for the preparation of 1, except
4-fluorothiophenol was used in place of p-thiocresol to give
yellow crystals of 5. Yield: 124 mg, 65%. 1H NMR (300 MHz,
acetone-d6, 298 K, relative to TMS): δ 5.10 (dd, 2H, aryl H
ortho to S), 5.90 (dd, 2H, aryl H meta to S), 7.75 (dd, 4H, phen
H’s), 7.95 (s, 4H, phen H’s), 8.50 (dd, 4H, phen H’s), 8.95 (dd,
4H, phen H’s). IR (CH2Cl2, cm-1): ν(CtO) 2034, 2023, 1937,
1915. Positive FAB-MS: ion clusters at m/ z 1045 {M}+, 594
{M - [Re(phen)(CO)3]}+. UV-vis [λ/nm (ꢀmax/dm3 mol-1 cm-1)]:
CH2Cl2, 272 (44 810), 294 sh (26 520), 366 (7525), 440 sh
(2975). Elemental analyses. Found: C, 38.44; H, 1.44; N, 4.76.
Calcd for 5‚1/4(CH3)2CO: C, 38.04; H, 1.81; N, 4.70.
[{Re(bp y)(CO)3}2(µ-SC6H4-CH3-p)]OTf (6). The proce-
dure is similar to that described for the preparation of 1, except
[Re(bpy)(CO)3(MeCN)]OTf was used in place of [Re(phen)(CO)3-
(MeCN)]OTf to give yellow crystals of 6. Yield: 117 mg, 70%.
1H NMR (300 MHz, CDCl3, 298 K, relative to TMS): δ 2.10
(s, 3H, Me), 5.90 (dd, 2H, aryl H ortho to S), 6.35 (dd, 2H, aryl
H meta to S), 7.25 (m, 4H, bpy H’s), 8.05 (dd, 4H, bpy H’s),
8.20 (dd, 4H, bpy H’s), 8.50 (dd, 4H, bpy H’s). IR (CH2Cl2,
cm-1): ν(CtO) 2033, 2022, 1927, 1915. Positive FAB-MS: ion
clusters at m/ z 975 {M}+, 550 {M - [Re(bpy)(CO)3]}+, 427 {M
- [Re(bpy)(CO)3(SC6H4-CH3-p)]}+. UV-vis [λ/nm (ꢀmax/dm3
mol-1 cm-1)]: CH2Cl2, 290 (20 730), 310 sh (15 305), 368 (5590),
438 sh (2700). Elemental analyses. Found: C, 36.47; H, 1.95;
N, 4.94. Calcd for 6: C, 36.29; H, 2.05; N, 4.98.
[{Re(Me2-bp y)(CO)3}2(µ-SC6H4-CH3-p)]OTf (7). The pro-
cedure is similar to that described for the preparation of 1,
except [Re(Me2-bpy)(CO)3(MeCN)]OTf was used in place of [Re-
(bpy)(CO)3(MeCN)]OTf to give yellow crystals of 7. Yield: 122
mg, 65%. 1H NMR (300 MHz, acetone-d6, 298 K, relative to
TMS): δ 2.15 (s, 3H, methyl H’s para to S), 2.40 (s, 12H,
methyl H’s on Me2-bpy), 6.00 (d, 2H, aryl H ortho to S), 6.45
(d, 2H, aryl H meta to S), 7.95 (d, 4H, Me2-bpy H’s), 8.25 (d,
4H, Me2-bpy H’s), 8.50 (s, 4H, Me2-bpy H’s), 9.25 (dd, 4H, Me2-
bpy H’s). IR (CH2Cl2, cm-1): ν(CtO) 2030, 2020, 1922, 1913.
Positive FAB-MS: ion clusters at m/ z 1026 {M}+, 575{M -
[Re(Me2-bpy)(CO)3]}+, 453 {M - [Re(Me2-bpy)(CO)3(SC6H4-
CH3-p)]}+. UV-vis [λ/nm (ꢀmax/dm3 mol-1 cm-1)]: CH2Cl2, 316
(37 515), 328 sh (32 410), 374 (6375), 422 sh (4120). Elemental
analyses. Found: C, 38.45; H, 2.75; N, 4.56. Calcd for 7: C,
38.63; H, 2.63; N, 4.74.
ligands. The crystal structure of [{Re(bpy)(CO)3}2(µ-
SC6H4-CH3-p)]OTf has also been determined.
Exp er im en ta l Section
Ma ter ia ls a n d Rea gen ts. [Re(CO)5Cl] was obtained from
Strem Chemicals, Inc. 1,10-Phenanthroline (phen) and 2,2′-
bipyridine (bpy) were obtained from Aldrich Chemical Co. 5,5′-
Dimethyl-2,2′-bipyridine (Me2-bpy) was prepared by the slight
modification of a reported procedure.12 p-Thiocresol, 4-tert-
butylthiophenol, 4-methoxythiophenol, and 4-chlorothiophenol
were obtained from Lancaster Synthesis Ltd. 4-Fluorothiophe-
nol was purchased from Aldrich Chemical Co. Both acetoni-
trile and dichloromethane were distilled over calcium hydride
before use. Tetrahydrofuran was distilled over sodium ben-
zophenone ketyl before use. All other reagents and solvents
were of analytical grade and were used as received. [Re(L-
L)(CO)3(MeCN)]OTf (L-L ) phen, bpy, or Me2-bpy) were
prepared according to literature procedures.2c
Syn th eses of Rh en iu m Com p lexes. All reactions were
performed under anaerobic and anhydrous conditions using
standard Schlenk technique under an inert atmosphere of
nitrogen.
[{Re(p h en )(CO)3}2(µ-SC6H4-CH3-p)]OTf (1). To a stirred
suspension of [Re(phen)(CO)3(MeCN)]OTf (100 mg, 0.16 mmol)
in THF (20 mL) was added a solution of Et3NHSC6H4-CH3-p
(0.10 mmol) in THF (10 mL), prepared in situ from HSC6H4-
CH3-p (12.4 mg, 0.10 mmol) and excess Et3N, under an inert
atmosphere of nitrogen. The reaction mixture was stirred for
48 h, after which the solvent was removed under vacuum. The
product was then purified by column chromatography on silica
gel using dichloromethane-acetone (9:1 v/v) as eluent. The
first band gave the monomeric [Re(phen)(CO)3(SC6H4-CH3-p)],
while the second band gave the desired product. Recrystal-
lization by slow vapor diffusion of diethyl ether into an acetone
solution of the complex gave 1 as yellow crystals. Yield: 122
mg, 65%. 1H NMR (300 MHz, acetone-d6, 298 K, relative to
TMS): δ 1.85 (s, 3H, Me), 4.95 (dd, 2H, aryl H ortho to S),
5.75 (dd, 2H, aryl H meta to S), 7.70 (dd, 4H, phen H’s), 7.90
(s, 4H, phen H’s), 8.50 (dd, 4H, phen H’s), 8.90 (dd, 4H, phen
H’s). IR (CH2Cl2, cm-1): ν(CtO) 2033, 2022, 1929, 1916.
Positive FAB-MS: ion clusters at m/ z 1025 {M}+, 993 {M -
CO}+, 574 {M - [Re(phen)(CO)3]}+, 451 {M - [Re(phen)(CO)3-
(SC6H4-CH3-p)]}+. UV-vis [λ/nm (ꢀmax/dm3 mol-1 cm-1)]: CH2-
Cl2, 270 (49 670), 290 sh (30 765), 370 (7425), 440 sh (2620).
Elemental analyses. Found: C, 38.98; H, 1.86; N, 4.50. Calcd
for 1: C, 38.89; H, 1.96; N, 4.78.
[{Re(p h en )(CO)3}2(µ-SC6H4-OCH3-p)]OTf (2). The pro-
cedure is similar to that described for the preparation of 1,
except 4-methoxylthiophenol was used in place of p-thiocresol
to give yellow crystals of 2. Yield: 124 mg, 65%. 1H NMR
(300 MHz, acetone-d6, 298 K, relative to TMS): δ 3.45 (s, 3H,
OMe), 4.90 (dd, 2H, aryl H ortho to S), 5.40 (dd, 2H, aryl H
meta to S), 7.95 (dd, 4H, phen H’s), 8.05 (s, 4H, phen H’s),
8.75 (dd, 4H, phen H’s), 9.25 (dd, 4H, phen H’s). IR (CH2Cl2,
cm-1): ν(CtO) 2033, 2022, 1929, 1915. Positive FAB-MS: ion
clusters at m/ z 1041 {M}+, 590 {M - [Re(phen)(CO)3]}+, 451
{M - [Re(phen)(CO)3(SC6H4-OCH3-p)]}+. UV-vis [λ/nm (ꢀmax
/
dm3 mol-1 cm-1)]: CH2Cl2, 278 (4300), 286 sh (29 180), 364
(8180), 434 sh (3315). Elemental analyses. Found: C, 38.91;
H, 1.70; N, 4.73. Calcd for 2‚1/6(CH3)2CO: C, 38.56; H, 2.04;
N, 4.67.
[{Re(ph en )(CO)3}2(µ-SC6H4-C(CH3)3-p)]OTf (3). The pro-
cedure is similar to that described for the preparation of 1,
except 4-tert-butylthiophenol was used in place of p-thiocresol
to give yellow crystals of 3. Yield: 126 mg, 65%. 1H NMR
(300 MHz, acetone-d6, 298 K, relative to TMS): δ 1.10 (s, 9H,
tBu), 5.00 (dd, 2H, aryl H ortho to S), 5.95 (dd, 2H, aryl H
meta to S), 8.10 (dd, 4H, phen H’s), 8.15 (s, 4H, phen H’s),
P h ysica l Mea su r em en ts a n d In str u m en ta tion . UV-
visible spectra were obtained on a Hewlett-Packard 8452A
diode array spectrophotometer, IR spectra on a Bio-Rad FTS-7
Fourier transform infrared spectrophotometer (4000-400
cm-1), and steady state excitation and emission spectra on a
Spex Fluorolog 111 spectrofluorometer equipped with
a
Hamamatsu R-928 photomultiplier tube. Low-temperature
(77 K) spectra were recorded by using an optical Dewar quartz
(12) Sprintschnik, G.; Sprintschnik, H. W.; Whitten, D. G. J . Am.
Chem. Soc. 1977, 99, 4947.

Luminescent Binuclear Rhenium(I) Complexes
Organometallics, Vol. 16, No. 8, 1997 1731
Ta ble 1. Cr ysta l a n d Str u ctu r e Deter m in a tion Da ta for 6
-
formula
fw
Re2SO6N4C33H23+CF3SO3
1125.11
T, K
301
a, Å
b, Å
c, Å
10.488(2)
18.599(4)
10.173(2)
91.60(2)
100.21(2)
73.98(1)
1876.7(6)
yellow prism
triclinic
R, deg
â, deg
γ, deg
V, Å3
crystal color and shape
crystal system
space group
Z
P1h
2
F(000)
1072
1.991
Dc, g cm-3
crystal dimensions, mm
λ, Å (graphite monochromated, Mo KR)
µ, cm-1
0.30 × 0.25 × 0.25
0.710 73
66.31
2θmax ) 48°
(h, 0-11; k, -20 to 20; l, -11 to 11)
ω-2θ, 16.0
0.79 + 0.35 tan θ
6263
collection range
scan mode and scan speed, deg min-1
scan width, deg
no. of data collected
no. of unique data
5893
no. of data used in refinement, m
no. of parameters refined, p
Ra
4950
488
0.029
0.039
wRa
goodness-of fit, S
1.74
maximum shift, (∆/σ)max
0.03
+1.60, -1.07
residual extremes in final difference map, e Å-3
a
w ) 4Fo2/σ2(Fo2), where σ2(Fo2) ) [σ2(I) + (0.028 Fo2)2] with I g 3σ(I).
sample holder. 1H NMR spectra were recorded on a Bruker
solution of the complex. Crystal Data. {[Re2SO6N4-
DPX 300 Fourier transform NMR spectrometer with chemical
shifts reported relative to tetramethylsilane. Positive ion FAB
mass spectra were recorded on a Finnigan MAT95 mass
spectrometer. Elemental analyses of the new complexes were
performed by Butterworth Laboratories Ltd.
C
33H23]+CF3SO3-}; Mr ) 1125.11, triclinic, space group P1h (No.
2), a ) 10.488(2) Å, b ) 18.599(4) Å, c ) 10.173(2) Å, R ) 91.60-
(2)°, â ) 100.21(2)°, γ ) 73.98(1)°, V ) 1876.7(6) Å3, Z ) 2, Dc
) 1.991 g cm-3, µ(Mo KR) ) 66.31 cm-1, F(000) ) 1072, T )
301 K. A yellow crystal of dimensions 0.30 × 0.25 × 0.25 mm
was used for data collection at 28 °C on a Rigaku AFC7R
diffractometer with graphite monochromatized Mo KR radia-
tion (λ ) 0.710 73 Å) using ω-2θ scans with ω-scan angle (0.73
+ 0.35 tan θ)° at a scan speed of 16.0 deg min-1 (up to six
scans for reflection I < 15σ(I)). Intensity data (in the range
of 2θmax ) 48°; h, 0-11; k, -20 to 20; l, -11 to 11 and 3
standard reflections measured after every 300 reflections
showed no decay) were corrected for Lorentz and polarization
effects and empirical absorption corrections based on the
ψ-scan of four strong reflections (minimum and maximum
transmission factors 0.607 and 1.000). A total of 6263 reflec-
Cyclic voltammetric measurements were performed by using
a
CH Instruments, Inc. Model CHI 620 electrochemical
analyzer interfaced to an IBM-compatible 486 personal com-
puter. The electrolytic cell used was a conventional two-
compartment cell. The salt bridge of the reference electrode
was separated from the working electrode compartment by a
Vycor glass. A Ag/AgNO3 (0.1 mol dm-3 in CH3CN) reference
electrode was used. The ferrocenium-ferrocene couple was
used as the internal standard in the electrochemical measure-
ments in acetonitrile (0.1 mol dm-3 NBu4PF6).13a The working
electrode was a glassy carbon (Atomergic Chemetals V25)
electrode with a platinum foil acting as the counter electrode.
Treatment of the electrode surfaces was as reported prev-
iously.13b
tions were measured, of which 5893 were unique and Rint
)
0.017. A total of 4950 reflections with I > 3σ(I) were
considered observed and used in the structural analysis. The
centric space group was used on the basis of a statistical
analysis of the intensity distribution and the successful
refinement of the structure solved by Patterson methods and
expanded by Fourier methods (PATTY15a) and refinement by
full-matrix least squares using the software package TeXsan15b
on a Silicon Graphics Indy computer. A crystallographic
asymmetric unit consists of a univalent complex cation and a
CF3SO3 anion. A total of 54 non-H atoms were refined
anisotropically. A total of 23 H atoms at calculated positions
with thermal parameters equal to 1.3 times that of the
attached C atoms were not refined. Convergence for 488
Emission lifetime measurements were performed using a
conventional laser system. The excitation source was the 355-
nm output (third harmonic) of a Quanta-Ray Q-switched GCR-
150-10 pulsed Nd-YAG laser. Luminescence decay signals
were recorded on a Tektronix Model TDS-620A (500 MHz, 2
GS/s) digital oscilloscope and analyzed using a program for
exponential fits. All solutions for photophysical 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 Kontes quick-release Teflon stopper.
Solutions were rigorously degassed with no fewer than four
freeze-pump-thaw cycles. Luminescence quantum yields,
Φ
em, were measured at room temperature by the Parker-Rees
(14) (a) van Houten, J .; Watts, R. J . J . Am. Chem. Soc. 1976, 98,
4853. (b) Parker, C. A.; Rees, W. T. Analyst (London) 1962, 87, 83. (c)
Demas, J . N.; Crosby, G. A. J . Phys. Chem. 1971, 75, 991.
(15) (a) PATTY: Beurskens, P. T.; Admiraal, G.; Beursken, G.;
Bosman, W. P.; Garcia-Granda, S.; Gould, R. O.; Smits, J . M. M.;
Smykalla, C., 1992. The DIRDIF program system, Technical Report
of the Crystallography Laboratory, University of Nijmegen, Nijmegen,
The Netherlands. (b) TeXsan: Crystal Structure Analysis Package,
Molecular Structure Corp., 1985, 1992.
method using [Ru(bpy)3]2+ as a standard.14
Cr ysta l Str u ctu r e Deter m in a tion . Crystals of 6 were
obtained by slow diffusion of diethyl ether into an acetone
(13) (a) Gagne, R. R.; Koval, C. A.; Lisensky, G. C. Inorg. Chem.
1980, 19, 2854. (b) Che, C. M.; Wong. K. Y.; Anson, F. C. J . Electroanal.
Chem., Interfacial Electrochem. 1987, 226, 211.

1732 Organometallics, Vol. 16, No. 8, 1997
Yam et al.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for 6
Re(1)-S(1)
Re(1)-N(2)
Re(1)-N(1)
Re(1)-C(1)
Re(1)-C(3)
Re(2)-C(22)
2.525(2)
2.164(5)
2.175(5)
1.927(8)
1.913(7)
1.912(8)
Re(2)-S(1)
Re(2)-N(4)
Re(2)-N(3)
Re(1)-C(2)
Re(2)-C(21)
Re(2)-C(23)
2.530(2)
2.177(5)
2.166(5)
1.906(8)
1.914(8)
1.919(7)
Re(1)-S(1)-Re(2)
Re(2)-S(1)-C(14)
N(3)-Re(2)-N(4)
S(1)-Re(1)-N(2)
S(1)-Re(2)-N(3)
S(1)-Re(1)-C(2)
S(1)-Re(2)-C(21)
S(1)-Re(2)-C(23)
126.3(8)
110.5(2)
74.7(2)
90.8(1)
89.5(1)
87.8(2)
86.1(2)
73.3(3)
Re(1)-S(1)-C(14)
N(1)-Re(1)-N(2)
S(1)-Re(1)-N(1)
S(1)-Re(2)-N(4)
S(1)-Re(1)-C(1)
S(1)-Re(1)-C(3)
S(1)-Re(2)-C(22)
112.3(2)
74.4(2)
82.4(1)
80.6(1)
94.6(6)
174.8(2)
95.4(2)
varible parameters by least-squares refinement on F with w
) 4Fo2/σ2(Fo2), where σ2(Fo2) ) [σ2(I) + (0.009 Fo2)2] for 4950
reflections with I > 3σ(I), was reached at R ) 0.029 and wR )
0.039 with a secondary extinction coefficient of 3.319 23 e-6
and goodness-of-fit of 1.74. (∆/σ)max ) 0.03 for the complex
cation. The final difference Fourier map was featureless, with
maximum positive and negative peaks of 1.62 and 1.07 e Å-3
,
F igu r e 1. Perspective drawing of the complex cation of 6
with atomic numbering scheme. Thermal ellipsoids are
shown at the 35% probability levels.
respectively. Crystal and structure determination data for 6
are summarized in Table 1. The final agreement factors for 6
are given in Table 1. Selected bond distances and angles are
summarized in Table 2. The atomic coordinates and thermal
parameters are given as supporting information.
Ta ble 3. P h otop h ysica l Da ta for Com p lexes 1-7
quantum yield,a
complexes medium (T/K)
λ
em/nm (τo/µs)
Φem
Resu lts a n d Discu ssion
1
2
3
4
5
6
7
solid (298)
solid (77)
CH2Cl2 (298) 611 (0.11)
solid (298)
solid (77)
CH2Cl2 (298) 615 (0.11)
solid (298)
solid (77)
CH2Cl2 (298) 615 (0.10)
solid (298)
solid (77)
CH2Cl2 (298) 606 (0.14)
solid (298)
solid (77)
CH2Cl2 (298) 610 (0.14)
solid (298)
solid (77)
CH2Cl2 (298) 620 (0.14)
563 (1.42)
575
Reaction of [Re(L-L)(CO)3(MeCN)]OTf (L-L ) phen,
bpy, Me2-bpy) with substituted thiophenol HSC6H4-X-p
(X ) CH3, OCH3, C(CH3)3, Cl, F) in the presence of
triethylamine in THF at room temperature under an
inert atmosphere of nitrogen afforded the corresponding
monomeric and dinuclear complexes. Separation of the
products was achieved by column chromatography on
silica gel using dichloromethane-acetone (9:1 v/v) as
eluent. Subsequent recrystallization from slow evapo-
ration of diethyl ether into acetone solution of the
complexes gave crystals of [{Re(L-L)(CO)3}2(µ-SC6H4-
X-p)]OTf [L-L ) phen, X ) CH3 (1), OCH3 (2), C(CH3)3
(3), Cl (4), F (5); L-L ) bpy, X ) CH3 (6); L-L ) Me2-
bpy, X ) CH3 (7)] in good yield. All the newly synthe-
sized compounds gave satisfactory elemental analyses
and have been characterized by 1H NMR, IR, and
positive FAB-MS. The crystal structure of complex 6
has also been determined.
0.012
0.010
0.011
0.015
0.012
0.002
0.020
564 (0.15, 0.81)b
576
575 (0.2)
582
562 (0.40)
556
547 (1.42)
552
581 (0.14)
578
solid (298)
solid (77)
550 (0.18)
565
CH2Cl2 (298) 590 (0.15)
a
Quantum yield was measured at room temperature using
[Ru(bpy)3]2+ as a standard. From ref 14. Biexponential.
b
Figure 1 shows the perspective drawing of the com-
plex cation of 6 with atomic numbering scheme. The
structure of the complex cation consists of two rhenium
diimine moieties bridged by the thiolato ligand, µ-SC6H4-
CH3-p, with a Re(1)-S(1)-Re(2) bond angle of 126.32-
(8)°. The coordination geometry at each Re atom is
distorted octahedral with the three carbonyl ligands
arranged in a facial fashion. The S(1)-Re(1)-C(3) and
S(1)-Re(2)-C(23) bond angles of 174.8(2) and 173.3-
(2)° show a slight deviation from an ideal octahedral
geometry. Although the Re-S σ-bonds are free to
rotate, it is interesting to note that the planes of the
two bipyridyl ligands and the phenyl ring of the bridging
thiolato ligand show a stacked conformation, with
dihedral angles between the idealized planes of the
bipyridyl units and the phenyl ring of 14.57 and 14.58°.
For the Re(I) metal centers, the N(1)-Re(1)-N(2) [74.4-
(2)°] and N(3)-Re(2)-N(4) [74.7(2)°] bond angles are
substantially smaller than 90° as the result of the bite
distances exerted by the steric requirements of each
chelating bipyridyl ligand.5a-c The average bond dis-
tances of Re-S [2.527(7) Å] and Re-C [1.915(9) Å] are
found to be comparable to those observed in [Re-
(CO)3SR]4.10c
The electronic absorption spectra of complexes 1-7
show a high-energy absorption at ∼275 nm and low-
energy absorption shoulders at ∼430 nm in CH2Cl2. The
low-energy absorption shoulders are likely to arise from
a dπ(Re) f π*(R,R′-diimine) MLCT transition (Table 3),
as similar assignments have been suggested in previous
spectroscopic work on Re(I) R,R′-diimine systems.1-5
Excitation of all the complexes in the solid state and in
CH2Cl2 solution at λ > 350 nm at room temperature
resulted in intense yellow-green luminescence. The
photophysical data are summarized in Table 3. The
emission energies are similar to those observed in other
Re(I) R,R′-diimine systems.1-5 The higher emission

Luminescent Binuclear Rhenium(I) Complexes
Organometallics, Vol. 16, No. 8, 1997 1733
Ta ble 4. Excited Sta te P a r a m eter s for
Com p lexes 1-5a
Eem
×
kr ×
knr
×
complex 10-3/ cm-1 Φem
τo/ns 10-3/s-1 10-3/s-1 ln knr
1
2
3
4
5
16.37
16.26
16.26
16.50
16.50
0.012 110
0.010 110
0.011 100
0.015 140
0.012 140
109.09
90.91
110.00
107.14
85.71
8.98
9.00
9.89
7.04
7.06
16.01
16.01
16.11
15.77
15.77
a
knr is the radiationless decay rate, kr is the radiative decay
rate, Φem is the luminescent quantum yield, and Eem is the
emission energy maximum.
energy in 7 compared to 6, in accordance with the trend
in MLCT absorption energies, is due to the higher π*
orbital energy of Me2-bpy as a result of the electron-
donating effect of the methyl groups on the bpy ligand.
It is therefore suggested that the emissions of the
complexes are associated with a metal-to-ligand charge
transfer triplet excited state. Table 4 shows the excited
state decay parameters for Eem, Φem, τo, kr, and knr
measured in degassed dichloromethane solution for
complexes 1-5. The least-squares fit to the data of the
plot of ln knr vs Eem for complexes 1-5 gave a slope of
-10.20 e V-1 and an intercept of 35.56, which are close
to that of -11.76 e V-1 and 40.21, respectively, in a
related system of [Re(bpy)(CO)3L]+ reported by Caspar
and Meyer.4a The linearity of the plot shows that the
emissions of the closely related complexes in solution
more or less follow the energy gap law. The relative
insensitivity of the solution emission energies to the
nature of the thiolate ligands in complexes 1-5 may
F igu r e 2. Cyclic voltammogram showing (a) the oxidation
(scan rate, 100 mV s-1) and (b) reduction (scan rate, 20
mV s-1) of complex 1 in acetonitrile (0.1 mol dm-3 nBu4-
NPF6).
3
suggest a MLCT origin for the emission, although one
Ta ble 5. Electr och em ica l Da ta for Com p lexes 1-7a
E1/2d/V vs SCE(∆Ep/mV)
could not exclude the possibility of a mixed MLCT/LLCT
character, derived from a p(S) f π*(R,R′-diimine) ligand-
to-ligand charge transfer (LLCT) transition, in particu-
lar, in the solid state.
complexes
reductionb
oxidationc
1
-1.21 (67)
-1.42 (67)
+1.19 (66)
+1.46e
The cyclic voltammograms of complexes 1-7 in ac-
etonitrile (0.1 mol dm-3 nBu4NPF6) display an irrevers-
ible and two quasi-reversible oxidation couples (+1.17
to +2.00 V vs SCE) and two quasi-reversible reduction
couples (-1.21 to -1.55 V vs SCE). The cyclic voltam-
mograms showing the oxidation and the reduction of
complex 1 are shown in Figure 2a and b, respectively,
and the electrochemical data are summarized in Table
5. The first reduction couple was tentatively assigned
as an R,R′-diimine ligand-centered reduction,3b,6c,d as it
occurred at almost identical potential for complexes 1-5
with the same 1,10-phenanthroline ligand being in-
volved. The more negative reduction potential observed
in 7 relative to that in 6 is in accordance with the
reduced ease of reduction of 5,5′-Me2-bpy as a result of
its higher π*-orbital energy. The second reduction
process may involve either a diimine-centered reduction
or a metal-based Re(I) to Re(0) reduction as suggested
in related systems.6c,d Upon scanning to more negative
potential (-2.0 to -2.5 V), two to five additional
ill-defined irreversible reduction waves are observed.
Such additional reduction waves have also been ob-
served by scanning [Re(R,R′-diimine)(CO)3(MeCN)]+ to
such negative potential. The peak current ratios for the
first and third oxidation couples of 1.00-1.14 together
with the ∆Ep values of slightly larger than that of the
ferrocenium-ferrocene couple suggest the quasi-revers-
ible nature of the couples. In view of the similarity in
the peak current for the first oxidation couple to that
for the reductions which are believed to be one-electron
+1.78 (66)
+1.17 (69)
+1.55e
2
-1.23 (68)
-1.43 (68)
+1.78 (68)
+2.00e
+1.18 (62)
+1.43e
+1.78 (58)
+1.24 (66)
+1.50e
+1.78 (66)
+1.22 (62)
+1.47e
3
4
5
6
7
-1.22 (65)
-1.44 (68)
-1.21 (70)
-1.41 (63)
-1.21 (69)
-1.40 (68)
+1.78 (63)
+1.19 (69)
+1.43e
-1.25 (72)
-1.43 (66)
+1.77 (66)
+1.18 (66)
+1.42e
-1.36 (64)
-1.55 (68)
+1.76 (69)
In acetonitrile (0.1 mol dm-3 NBu4PF6). Working electrode:
a
b
glassy carbon; ∆Ep of Fc+/Fc ranges from 62 to 64 mV. Scan rate,
100 mV s-1
.
c Scan rate, 20 mV s-1
.
E1/2 ) (Epa + Epc)/2; Epa and
d
Epc are peak anodic and peak cathodic potentials, respectively.
e Peak anodic potential for the irreversible couple.
processes, the first oxidation couple was tentatively
assigned as a Re(I) to Re(II) oxidation process. Similar
oxidation waves have also been observed in related
rhenium(I) R,R′-diimine systems.3a,b,4b,c,6 It is interest-
ing to note that the third oxidation couple, following the
second irreversible wave, appeared at almost identical
potential for all the complexes. This, together with the

1734 Organometallics, Vol. 16, No. 8, 1997
Yam et al.
close resemblance of the potential value to those ob-
served in [Re(phen)(CO)3(MeCN)]+ and [Re(bpy)(CO)3-
(MeCN)]+, suggested the generation of the respective
[Re(L-L)(CO)3(MeCN)]+ species. It is likely that the
dinuclear rhenium complexes upon oxidation are un-
stable and decompose to give [Re(L-L)(CO)3(MeCN)]+
with the loss of the thiolate ligand. A similar decom-
position pathway has also been suggested in the related
chlororhenium system.6d,e
to explore their potential as precursors for heteroleptic
dimers of rhenium(I).
Ack n ow led gm en t. V.W.-W.Y. acknowledges finan-
cial support from the Research Grants Council and The
University of Hong Kong. K.M.-C.W. acknowledges the
receipt of a Croucher Studentship administered by the
Croucher Foundation.
Su p p or tin g In for m a tion Ava ila ble: Tables giving frac-
tional coordinates and thermal parameters, general displace-
ment parameter expressions (U), and all bond distances and
bond angles (13 pages). Ordering information is given on any
current masthead page.
Preliminary work shows that a related [Re(L-L)-
(CO)3(SC6H4-Cl-p)] monomer that emits at ∼720 nm can
act as a metalloligand to form a heteroleptic dimer.
Work is in progress to synthesize other monomers and
OM960797W