Preparative routes to luminescent mixed-ligand rhenium(I) dicarbonyl complexes

Article abstract of DOI:10.1021/ic050707s

A series of mixed-ligand 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) rhenium(I) dicarbonyl complexes that are emissive in fluid solution has been prepared, which includes a new class of the type cis-[Re(CO)₂(P-P)(N-N)]⁺ (where P-P is a chelating diphosphine and N-N is a chelating polypyridine ligand). The four synthetic routes that have been developed rely on either reactive triflate displacement or abstraction of labile chloro ligands, followed by the use of the strong trans-labilizing effect of P donors or direct use of the trans effect of P donors. The spectroscopic, photophysical, and electrochemical properties of these new complexes systematically vary with the net donor ability of the ligands in the coordination sphere, as shown by correlations with Lever's E _L parameters. Lifetimes and quantum yields of the bipyridine complexes encompass a broad range, 25-1147 ns and ca. 0.002-0.11, respectively.

Full text of DOI:10.1021/ic050707s

Inorg. Chem. 2006, 45, 2163−2174
Preparative Routes to Luminescent Mixed-Ligand Rhenium(I) Dicarbonyl
Complexes
Joanna L. Smithback, Jeffrey B. Helms, Erick Schutte, Stephen M. Woessner, and
B. Patrick Sullivan*
Department of Chemistry, UniVersity of Wyoming, Laramie, Wyoming 82071-3838
Received May 5, 2005
A series of mixed-ligand 2,2
are emissive in fluid solution has been prepared, which includes a new class of the type cis-[Re(CO)2(P
(where P P is a chelating diphosphine and N N is a chelating polypyridine ligand). The four synthetic routes that
′
-bipyridine (bpy) and 1,10-phenanthroline (phen) rhenium(I) dicarbonyl complexes that
−P)(N−
N)]+
−
−
have been developed rely on either reactive triflate displacement or abstraction of labile chloro ligands, followed by
the use of the strong trans-labilizing effect of P donors or direct use of the trans effect of P donors. The spectroscopic,
photophysical, and electrochemical properties of these new complexes systematically vary with the net donor ability
of the ligands in the coordination sphere, as shown by correlations with Lever’s EL parameters. Lifetimes and
quantum yields of the bipyridine complexes encompass a broad range, 25−1147 ns and ca. 0.002−0.11, respectively.
Introduction
This paper deals with our quest to prepare novel mixed-
ligand rhenium(I) dicarbonyls, which indeed possess long-
lived excited states. The four synthetic routes that we have
developed rely on a combination of triflate or chloride
labilization and the trans effect of phosphine ligands. For
example, trans-labilization of carbonyls yields a new class
of complex, cis-[Re(CO)2(P-P)(N-N)]+ (where P-P is a
chelating phosphine and N-N is a chelating polypyridine
ligand). For comparison purposes, we have included several
preparations of phosphonite and phosphite complexes of the
type cis-trans-[Re(CO)2(P)2(N-N)]+ (where P is a mono-
dentate phosphine, phosphonite, or phosphite and N-N is a
chelating polypyridine ligand). Some complexes presented
in this paper were previously communicated,7 and some
related Re(I) dicarbonyl complexes have been published by
Ishitani et al.8
Due to their favorable photophysical properties, such as
room-temperature luminescence1 from low-lying, tunable
metal-ligand charge transfer (MLCT) (dπ(M) to π*(L))
excited states, Re(I) diimine tricarbonyls have been applied
in solar-energy conversion schemes2, sensor development3,
and biological labeling.4 Their excited-state lifetimes are
largely controlled by the nonradiative rate-constant values
(knr) due to “energy-gap law” behavior.5,6 Spectral fitting5
and excited-state resonance Raman spectroscopy6 have sug-
gested that a high-frequency CO stretching mode may be
involved in the radiationless decay process as an accepting
mode. This suggests that the removal of a carbonyl to form
a dicarbonyl species could result in more-favorable photo-
physical properties, such as increased quantum yields and
lifetimes.
Experimental Section
General Procedures. Infrared spectra were obtained on a Perkin-
Elmer 1600 series FTIR. The solution spectra were taken in
* Author to whom correspondence should be addressed. E-mail: bpat@
uwyo.edu.
(1) Wrighton, M.; Morse, D. L. J. Am. Chem. Soc. 1974, 96, 998-1003.
(2) Meyer, G. J., Ed. Molecular Level Artificial Photosynthetic Materials.
Prog. Inorg. Chem. (Karlin, K. D., Ed.) 1996, 44.
(3) See, for example: (a) MacQueen, D. B.; Schanze, K. S. J. Am. Chem.
Soc. 1991, 113, 6108-6110. (b) Shen, Y.; Sullivan, B. P. Inorg. Chem.
1995, 34, 6235.
(7) (a) Schutte, E.; Helms, J. B.; Woessner, S. W.; Bowen, J.; Sullivan,
B. P. Inorg. Chem. 1998, 37, 2618-2619. (b) Woessner, S. M. Ph.D.
Dissertation, University of Wyoming, Laramie, WY, 1999.
(8) (a) Koike, K.; Tanabe, J.; Toyama, S.; Tsubaki, H.; Sakamoto, K.;
Westwell, J. R.; Johnson, F. P. A.; Hori, H.; Saitoh, H.; Ishitani, O.
Inorg. Chem. 2000, 39, 2777-2783. (b) Ishitani, O.; George, M. W.;
Ibusuki, T.; Johnson, F. P. A.; Koike, K.; Nozaki, K.; Pac, C.; Turner,
J. J.; Westwell, J. R. Inorg. Chem. 1994, 33, 4712-4717. (c) Koike,
K.; Okoshi, N.; Hori, H.; Takeuchi, K.; Ishitani, O.; Tsubaki, H.; Clark,
I. P.; George, M. W.; Johnson, F. P. A.; Turner, J. J. J. Am. Chem.
Soc. 2002, 124, 11448-11455.
(4) (a) Oriskovich, T. A.; White, P. S.; Thorp, H. H. Inorg. Chem. 1995,
34, 1629. (b) Connick, W. B.; Di Bilio, A. J.; Hill, M. G.; Winkler,
J. R.; Gray, H. B. Inorg. Chim. Acta 1995, 240, 169.
(5) Baiano, J. A.; Kessler, R. J.; Lumpkin, R. S.; Monley, M. J.; Murphy,
W. R., Jr. J. Phys. Chem. 1995, 99, 17680-17690.
(6) Shen, Y.; Sullivan, B. P. J. Chem. Educ. 1997, 74, 685.
10.1021/ic050707s CCC: $33.50
Published on Web 02/03/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 5, 2006 2163

Smithback et al.
methylene chloride using a 1-mm length KCl flow cell. Electronic
absorption spectra were acquired on a Hewlett-Packard 8452A diode
array spectrophotometer, scanning the 190-820 nm spectral region.
The samples were contained in 1.00-cm quartz cuvettes and
referenced against a solvent blank. Molar extinction coefficients
were averaged from absorbance measurements obtained at two or
three different concentrations. 1H and 31P{1H} NMR spectra were
recorded in acetonitrile on a Bru¨ker GSX400 spectrometer. 1H NMR
spectra were internally referenced to the solvent, whereas 31P NMR
spectra were externally referenced to 85% H3PO4. Electrochemical
measurements were acquired using cyclic voltammetry on a
Princeton Applied Research model 273A poteniostat/galvanostat
attached to a PC operating Princeton Applied Research model 270/
259 Research Electrochemistry Software. All measurements were
recorded with a Pt disk working electrode using a Ag/AgCl
reference electrode. Tetrabutylammonium hexafluorophosphate (ca.
0.1 M) was used as the supporting electrolyte, and each sample
was deoxygenated under N2 for 10 min prior to scanning. Emission
and excitation spectra were obtained in N2-purged CH2Cl2 on a
SLM 8000C photon-counting spectrofluorimeter with a 450 W
ozone-free arc-lamp excitation source equipped with a cooled
Hamamatsu R928 photomultiplier tube (PMT). Manufacturer-
supplied computer software carried out corrections for instrument
response. Emission quantum yields (Φem) were measured relative
to [Ru(bpy)3]2+ (φem ) 0.062 in N2-purged CH3CN) or fac-
[Re(CO)3(bpy)py](CF3SO3) (φem ) 0.012 in air-saturated H2O;
average atmospheric pressure 585 mmHg in Laramie, WY).
Excited-state lifetime measurements (τ) were acquired on either
(1) an Edinburg LP900S1 time-resolved absorption/emission spec-
trophotometer equipped with a Continuum Minilite Nd:YAG laser
or (2) an ISS K2 multifrequency phase and modulation spectrof-
luorimeter equipped with a dual-line (325 and 442 nm) continuous-
wave He-Cd laser. Samples were sealed in a 1-cm quartz
fluorescence cuvette and purged with N2 for 15 min prior to data
acquisition. Lifetimes reported are the average for three runs over
a frequency range of 1/τ. Lifetime measurements were referenced
to a glycogen scattering standard. X-ray crystallographic data were
collected at room temperature on a Siemens P4 diffractometer
containing a molybdenum tube (λ ) 0.71073 Å) and a graphite
monochromator. The data were corrected for Lorentz-polarization
effects and absorption. The structure was solved by Patterson
methods and refined by least-squares technique effects using the
SHELXTL program (Sheldrick, 1997). Elemental analyses were
provided by Atlantic Microlabs, Inc., Norcross, GA.
sieves prior to use. All other spectroscopic-grade solvents were
obtained from Spectrum Chemical Company.
Synthetic Procedures. Complexes of the type fac-Re(CO)3
(N-N)L and fac-Re(CO)3(P-P)L (where N-N is a chelating
polypyridine ligand, L is Cl- or CF3SO3-, and P-P is a chelating
phosphine) were prepared according to literature.7,9 The previously
reported cis-trans-[Re(CO)2(PPh3)2(bpy)]PF610 was synthesized by
a new method.7 mer-Re(CO)3(PPh3)2Cl was prepared by literature
procedures,11 except that the reaction time was 16-24 h in toluene
and the product was recrystallized from mixtures of CH
2Cl2/
CH3OH.
Method I: Synthesis from fac-Re(CO)3(N-N)(CF3SO3).
cis-[Re(CO)2(bpy)(dppm)](CF3SO3) (1a). fac-Re(CO)3(bpy)(CF3-
SO3) (0.244 g (0.389 mmol)) and dppm (0.182 g (0.473 mmol))
were placed in a round-bottom flask with ca. 8 mL of o-
dicholorobenzene (ODB). The resulting cloudy solution was purged
with N2 for 20 min. The reaction was stirred at reflux under N2 for
3-5 h. During this time, the reaction changed from a cloudy-yellow
to clear-yellow solution, finally resulting in a clear-orange solution.
After the reaction had cooled to room temperature, hexanes were
added to precipitate the yellow-orange product. The product was
collected by suction filtration and washed with hexanes and diethyl
ether before allowing to air-dry. The product was purified by
column chromatography on acidic alumina, starting with a 90:10
ratio of CH2Cl2/CH3CN and gradually increasing the amount of
CH3CN in the eluant. The product was reprecipitated from CH2Cl2
into stirring diethyl ether. Yield: 283 mg (78%). Elemental Anal.
Calcd for C38H30N2O5P2F3SRe: C, 48.98; H, 3.25; N 3.01. Found:
1
C, 48.84; H, 3.34; N, 2.97. H NMR (δ/ppm, CD3CN): 9.60 (d,
1H, J ) 5.5 Hz), 8.30 (d, 1H, J ) 8.1 Hz), 8.13 (m, 2H), 7.97 (d,
1H, J ) 5.5 Hz), 7.87 [7.92-7.80] (m, 3H), 7.53 (m, 14H), 7.18
(dt, 1H, J ) 1.5, 7.6 Hz), 6.95 [7.00-6.90] (m, 3H), 6.51 [6.55-
6.47] (m, 2H), 5.37 (dt, 1H, J ) 16.6, 9.6 Hz), 5.18 (dt, 1H, J )
16.6, 9.6 Hz). 31P{1H} NMR (δ/ppm, CD3CN): -15.5 (s), -27.5
(d, J ) 5 Hz). UV-visible (λ (nm), CH2Cl2) (ꢀ in M-1 cm-1):
282 (21900), 302 (sh, 15700), 346 (3730), 438 (3270). IR (CH2-
Cl2) (ν(CO), cm-1): 1950, 1884.
cis-[Re(CO)2(phen)(dppm)](CF3SO3) (1b). Synthesis and pu-
rification were the same as for 1a except that 0.208 g (0.346 mmol)
of fac-Re(CO)3(phen)(CF3SO3) and 0.157 g (0.408 mmol) of dppm
were used. Yield: 245 mg (74%). Elemental Anal. Calcd for
C40H30N2O5P2F3SRe: C, 50.26; H, 3.16; N 2.93. Found: C, 50.31;
H, 3.20; N, 3.03. 1H NMR (δ/ppm, CD3CN): 9.97 (d, 1H, J ) 5.0
Hz), 8.70 (d, 1H, J ) 8.1 Hz), 8.36 (d, 1H, J ) 8.6 Hz), 8.29 (d,
1H, J ) 5.0 Hz), 8.08 (d, 1H, J ) 8.6 Hz), 8.00 [8.04-7.96] (m,
3H), 7.91 (d, 1H, J ) 8.6 Hz), 7.53 [7.74-7.35] (m, 13H), 7.30
(dd, 1H, J ) 4.0, 5.5 Hz), 6.89 (dt, 1H, J ) 1.5, 7.6 Hz), 6.58 (dt,
2H, J ) 1.0, 7.6 Hz), 6.07 (dd, 2H, J ) 5.5, 8.1 Hz), 5.34 (dt, 1H,
J ) 16.6, 10.1 Hz), 5.02 (dt, 1H, J ) 16.6, 10.1 Hz). 31P{1H}
NMR (δ/ppm, CD3CN): -15.9 (d, J ) 5 Hz), -27.3 (d, J ) 5
Hz). UV-visible (λ (nm), CH2Cl2) (ꢀ in M-1cm-1): 262 (sh,
30300), 270 (33400), 292 (sh, 16600), 336 (sh, 4140), 384 (4380),
426 (4380). IR (CH2Cl2) (ν(CO), cm-1): 1950, 1885.
Materials. All chemicals were purchased commercially and used
as received unless otherwise noted. Re(CO)5Cl, bis(diphenylphos-
phino)methane (dppm), and cis-1,2-bis(diphenylphosphino)ethylene
(c-dppene) were obtained from Strem Chemical Co. or Sigma-
Aldrich. 1,2-Bis(diphenylphosphino)ethane (diphos) was obtained
from Alfa-Aesar. Triphenylphosphine (PPh3), triphenyl phosphite
(P(OPh)3), trimethyl phosphite (P(OCH3)3), methyldiphenyl-
phosphinite (P(OCH3)(Ph)2), and dimethylphenylphosphonite
(P(OCH3)2(Ph)) were obtained from Sigma-Aldrich. 4,7-Diphenyl-
1,10-phenanthroline (Ph2phen)was obtained from Lancaster. 2,2′-
Bipyridine (bpy), 1,10-phenanthroline (phen), o-dichlorobenzene
(spectroscopic grade) (ODB), and all other reagent-grade solvents
were obtained from Sigma-Aldrich. Tetrabutylammonium hexafluo-
rophosphate (TBAH) was purchased from Sigma-Aldrich, recrystal-
lized from CH3CN/Et2O, and dried in vacuo prior to use. Acidic
alumina was purchased from Fisher and Sigma-Aldrich. Acetoni-
trile-d3 (CD3CN) was purchased from Cambridge Isotope Labora-
tories. Acetonitrile (spectroscopic grade) was obtained from
Spectrum or Sigma-Aldrich and was dried over 4 Å molecular
(9) (a) Sullivan, B. P.; Meyer, T. J. J. Chem. Soc., Chem. Commun. 1984,
1244-1245. (b) Geoffroy, G. L.; Wrighton, M. S. Organometallic
Photochemistry; Academic Press: New York, 1979 and references
therein. (c) Hino, J. K.; Della Ciana, L.; Dressick, W. J.; Sullivan, B.
P. Inorg. Chem. 1992, 31, 1072-1080.
(10) (a) Caspar, J. V. Ph.D. Dissertation, University of North Carolina-
Chapel Hill, 1982. (b) Caspar, J. V.; Sullivan, B. P.; Meyer, T. J.
Inorg. Chem. 1984, 23, 2104. (c) Worl, L. A.; Duesing, R.; Chen, P.;
Della Ciana, L.; Meyer, T. J. J. Chem. Soc., Dalton Trans. 1991, 849.
(11) Bond, A. M.; Colton, R.; McDonald, M. E. Inorg. Chem. 1978, 17,
2842-2847.
2164 Inorganic Chemistry, Vol. 45, No. 5, 2006

Luminescent Rhenium(I) Dicarbonyl Complexes
[cis-Re(CO)2(bpy)(c-dppene)](CF3SO3) (1c). Synthesis and
purification were the same as for 1a except that 0.305 g (0.529
mmol) of fac-Re(CO)3(bpy)(CF3SO3) and 0.237 g (0.598 mmol)
of c-dppene were used. Yield: 402 mg (80%). Elemental Anal.
Calcd for C39H30N2O5P2F3SRe: C, 49.63; H, 3.20; N 2.97. Found:
chromatography, followed by reprecipitation from hot toluene.
Yield: 194 mg (65%). Elemental Anal. Calcd for C53H38N2O5P2F3-
SRe: C, 56.83; H, 3.42; N 2.50. Found: C, 56.63; H, 3.46; N,
2.45. 1H NMR (δ/ppm, CD3CN): 10.03 (d, 1H, J ) 5.5 Hz), 8.61
(dt, 1H, J ) 49.4, 8.6 Hz), 8.14 [8.20-8.08] (m, 2.5H), 7.98 [8.03-
7.91] (m, 3.5H), 7.68 [7.75-7.62] (m, 11H), 7.59 [7.62-7.56] (m,
3H), 7.46 [7.55-7.36] (m, 10H), 7.18 (d, 1H, J ) 5.5 Hz), 6.83 (t,
1H, J ) 7.1 Hz), 6.52 (dt, 2H, J ) 2.0, 8.1 Hz), 5.94 (t, 2H, J )
8.6 Hz). 31P{1H} NMR (δ/ppm, CD3CN): 53.2 (d, J ) 19 Hz),
42.6 (d, J ) 19 Hz). UV-visible (λ (nm), CH2Cl2) (ꢀ in M-1 cm-1):
278 (37900), 286 (38500), 318 (sh, 15400), 352 (9200), 380
(9680), 428 (sh, 7310). IR (CH2Cl2) (ν(CO), cm-1): 1958, 1889.
cis-trans-[Re(CO)2(PPh3)2(bpy)](CF3SO3) (1h). fac-Re(CO)3-
(bpy)(CF3SO3) (0.150 g (0.260 mmol)) and triphenylphosphine
(PPh3) (0.504 g (1.92 mmol)) were placed in a round-bottom flask
with ca. 10-15 mL of ODB. The resulting solution was purged
with N2 for 20 min. The reaction was stirred at reflux under N2 for
8 h. After the reaction had cooled to room temperature, 50 mL of
a 1:1 solution of diethyl ether/hexanes was added, precipitating a
greenish-yellow solid. The solid was collected via suction filtration
and washed with hot toluene and then diethyl ether to remove any
residual triphenylphosphine. The product was reprecipitated from
methylene chloride into a 4:1 mixture of diethyl ether/hexanes. The
product was collected on a fritted funnel and dried in vacuo over-
night. Purification was achieved by column chromatography on
acidic alumina, eluting with methylene chloride first the increasing
the polarity by gradual introduction of acetone. The solvent was
removed, leaving an oily yellow residue that was reprecipitated
again from methylene chloride in a 4:1 mixture of diethyl ether/
hexanes, resulting in a greenish-yellow product. Yield: 240 mg
(86%). Elemental Anal. Calcd for C49H38N2O5P2F3SRe: C, 54.90;
1
C, 49.74; H, 3.17; N, 3.05. H NMR (δ/ppm, CD3CN): 9.59 (d,
1H, J ) 5.5 Hz), 8.54 (dt, 1H, J ) 49.4, 8.6 Hz), 8.13 (m, 2.5H),
8.00 (m, 2.5H), 7.81 (d, 1H, J ) 8.1 Hz), 7.65 [7.71-7.59] (m,
7H), 7.50 [7.54-7.46] (m, 4H), 7.38 [7.44-7.33] (m, 5H), 7.10
(m, 1H), 6.83 (m, 3H), 6.18 (m, 2H). 31P{1H} NMR (δ/ppm,
CD3CN): 52.2 (d, J ) 19 Hz), 42.2 (d, J ) 19 Hz). UV-visible
(λ (nm), CH2Cl2) (ꢀ in M-1 cm-1): 272 (21400), 390 (3440). IR
(CH2Cl2) (ν(CO), cm-1): 1959, 1888.
cis-[Re(CO)2(phen)(c-dppene)](CF3SO3) (1d). Synthesis and
purification were the same as for 1a except 0.362 g (0.603 mmol)
of fac-Re(CO)3(phen)(CF3SO3) and 0.278 g (0.701 mmol) of
c-dppene were used. Yield: 584 mg (81%). Elemental Anal. Calcd
for C41H30N2O5P2F3SRe: C, 50.88; H, 3.12; N 2.89. Found: C,
1
50.86; H, 3.06; N, 2.99. H NMR (δ/ppm, CD3CN): 9.97 (d, 1H,
J ) 5.5 Hz), 8.69 (d, 1H, J ) 8.1 Hz), 8.58 (dt, 1H, J ) 49.4, 9.1
Hz), 8.23 (d, 1H, J ) 8.6 Hz), 8.01 [8.16-7.90] (m, 5H), 7.86 (d,
1H, J ) 5.0 Hz), 7.77 (d, 1H, J ) 9.1 Hz), 7.65 [7.69-7.61] (m,
5H), 7.44 [7.54-7.35] (m, 8H), 7.21 (dd, 1H, J ) 5.0, 4.0 Hz),
6.73 (dt, 1H, J ) 7.1, 1.5 Hz), 6.39 (dt, 2H, J ) 7.6, 1.5 Hz), 5.73
(dt, 2H, J ) 10.1, 2.5 Hz). 31P{1H} NMR (δ/ppm, CD3CN): 53.2
(d, J ) 19 Hz), 43.2 (d, J ) 19 Hz). UV-visible (λ (nm), CH2Cl2)
(ꢀ in M-1 cm-1): 266 (32700), 298 (sh, 12400), 344 (4570), 376
(5050), 420 (sh, 3960). IR (CH2Cl2) (ν(CO), cm-1): 1959, 1889.
cis-[Re(CO)2(bpy)(diphos)](CF3SO3) (1e). Synthesis and pu-
rification were the same as for 1a except that 0.182 g (0.316 mmol)
of fac-Re(CO)3(bpy)(CF3SO3) and 0.131 g (0.329 mmol) of diphos
were used with reaction times not exceeding 3 h. Yield: 215 mg
(72%). Elemental Anal. Calcd for C39H32N2O5P2F3SRe: C, 49.52;
1
H, 3.57; N 2.61. Found: C, 53.70; H, 3.64; N, 2.27. H NMR (δ/
ppm, CD3CN): 8.33 (d, 2H, J ) 8.5 Hz), 8.04 (d, 2H, J ) 5.2
Hz), 7.91 (t, 2H, J ) 7.7 Hz), 7.30 [7.35-7.26] (m, 30H), 6.96 (t,
2H, J ) 6.4 Hz). 31P{1H} NMR (δ/ppm, CD3CN): 24.6. UV-
visible (λ (nm), CH2Cl2) (ꢀ in M-1 cm-1): 298 (15700), 306
(13300), 422 (24500). IR (CH2Cl2) (ν(CO), cm-1): 1938, 1868.
cis-trans-[Re(CO)2(P(OPh)3)2(bpy)](CF3SO3) (1i). Synthesis
and purification were the same as for 1h except that 0.215 g (0.374
mmol) of fac-Re(CO)3(bpy)(CF3SO3) and 2 mL (7.63 mmol) of
triphenyl phosphite (P(OPh)3) were used. The product was greenish
yellow. Yield: 401 mg (92%) Elemental Anal. Calcd for
C49H38N2O11P2F3SRe: C, 50.39; H, 3.28; N, 2.40. Found: C, 50.51;
H, 3.34; N, 2.38. 1H NMR (δ/ppm, CD3CN): 8.20 (t, 2H, J ) 7.7
Hz), 7.72 (d, 2H, J ) 5.9 Hz), 7.62 (d, 2H, J ) 3.2 Hz), 7.45 (t,
2H, J ) 6.3 Hz), 7.22 (t, 12H, J ) 7.8 Hz), 7.13 (t, 6H, J ) 7.4
Hz), 6.85 (d, 12H, J ) 8.0 Hz). 31P{1H} NMR (δ/ppm, CD3CN):
104.2. UV-visible (λ (nm), CH2Cl2) (ꢀ in M-1 cm-1): 286 (10900),
320 (70300), 372 (31400). IR (CH2Cl2) (ν(CO), cm-1): 1985, 1914.
cis-trans-[Re(CO)2(P(OPh)3)2(phen)](CF3SO3) (1j). Synthesis
and purification were the same as for 1h except that 0.175 g (0.292
mmol) of fac-Re(CO)3(phen)(CF3SO3) and 2 mL (7.63 mmol) of
triphenyl phosphite (P(OPh)3) were used. The product was greenish
yellow. Yield: 320 mg (92%) Elemental Anal. Calcd for
C51H38N2O11P2F3SRe: C, 51.39; H, 3.21; N, 2.35. Found: C, 51.52;
H, 3.27; N, 2.41. 1H NMR (δ/ppm, CD3CN): 8.62 (d, 2H, J ) 7.2
Hz), 8.13 (t, 2H, J ) 3.0 Hz), 7.92 (d, 2H, J ) 5.6 Hz), 7.74 (d,
2H, J ) 5.9 Hz), 7.52 (t, 12H, J ) 8.2 Hz), 7.42 (t, 6H, J ) 8.6
Hz), 6.98 (d, 12H, J ) 9.1 Hz). 31P{1H} NMR (δ/ppm, CD3CN):
103.9. UV-visible (λ (nm), CH2Cl2) (ꢀ in M-1 cm-1): 302 (17700),
338 (35600), 378 (31400). IR (CH2Cl2) (ν(CO), cm-1): 1984, 1914.
cis-trans-[Re(CO)2(P(OCH3)3)2(bpy)](CF3SO3) (1k). Synthesis
and purification were the same as for 1h except that 0.215 g (0.374
1
H, 3.41; N 2.96. Found: C, 49.31; H, 3.42; N, 2.84. H NMR (δ/
ppm, CD3CN): 9.64 (d, 1H, J ) 5.5 Hz), 8.12 (m, 2H), 7.91 [7.96-
7.85] (m, 3H), 7.73 (t, 1H, J ) 8.1 Hz), 7.64 [7.68-7.60] (m, 5H),
7.57 (m, 4H), 7.46 [7.52-7.41] (m, 5H), 7.37 [7.41-7.74] (m, 1H),
7.09 (t, 1H, J ) 7.6 Hz), 6.82 [6.87-6.77] (m, 3H), 6.19 (t, 2H, J
) 10.1 Hz), 3.31 (m, 2H), 2.81 (m, 2H). 31P{1H} NMR (δ/ppm,
CD3CN): 44.5 (d, J ) 4 Hz), 35.7 (d, J ) 5 Hz). UV-visible (λ
(nm), CH2Cl2) (ꢀ in M-1 cm-1): 278 (21200), 344 (sh, 3430), 392
(3210), 430 (sh, 2790). IR (CH2Cl2) (ν(CO), cm-1): 1952, 1881.
cis-[Re(CO)2(Ph2phen)(dppm)](CF3SO3) (1f). Synthesis and
purification were the same as for 1a except that 0.274 g (0.364
mmol) of fac-Re(CO)3(Ph2phen)(CF3SO3) and 0.165 g (0.429
mmol) of dppm were used. Purification was done by column
chromatography, followed by repeated reprecipitation from CH3CN
into stirring diethyl ether. Yield: 194 mg (65%). Elemental Anal.
Calcd for C52H38N2O5P2F3SRe: C, 56.36; H, 3.46; N 2.53. Found:
1
C, 56.56; H, 3.54; N, 2.58. H NMR (δ/ppm, CD3CN): 10.03 (d,
1H, J ) 5.5 Hz), 8.38 (d, 1H, J ) 5.5 Hz), 8.07 (dd, 2H, J ) 5.5,
7.1 Hz), 7.97 (m, 2H), 7.80 (d, 1H, J ) 9.6 Hz), 7.64 [7.73-7.56]
(m, 15H), 7.44 [7.53-7.36] (m, 8H), 7.27 (d, 1H, J ) 5.5 Hz),
6.95 (t, 1H, J ) 7.1 Hz), 6.66 (dt, 2H, J ) 1.5, 7.6 Hz), 6.23 (dd,
2H, J ) 6.0, 8.1 Hz), 5.38 (dt, 1H, J ) 16.1, 10.1 Hz), 5.02 (dt,
1H, J ) 16.1, 10.1 Hz). 31P{1H} NMR (δ/ppm, CD3CN): -16.3
(d, J ) 5 Hz), -27.3 (d, J ) 5 Hz). UV-visible (λ (nm), CH2Cl2)
(ꢀ in M-1 cm-1): 286 (43700), 316 (sh, 17700), 350 (7910), 394
(7790), 426 (7690). IR (CH2Cl2) (ν(CO), cm-1): 1949, 1883.
cis-[Re(CO)2(Ph2phen)(c-dppene)](CF3SO3) (1g). Synthesis and
purification were the same as for 1a except that 0.200 g (0.266
mmol) of fac-Re(CO)3(Ph2phen)(CF3SO3) and 0.114 g (0.288
mmol) of c-dppene were used. Purification was done by column
Inorganic Chemistry, Vol. 45, No. 5, 2006 2165

Smithback et al.
mmol) of fac-Re(CO)3(bpy)(CF3SO3) and 2 mL (17 mmol) of tri-
methyl phosphite (P(OPh)3) were used. The product was light yellow.
Yield: 226 mg (76%) Elemental Anal. Calcd for C19H26N2O11P2F3-
SRe: C, 26.68; H, 3.29; N, 3.52. Found: C, 28.06; H, 3.32; N,
3.44. 1H NMR (δ/ppm, CD3CN): 10.22 (d, 2H, J ) 4.6 Hz), 9.79
(d, 2H, J ) 10.2 Hz), 9.43 (t, 2H, J ) 8.3 Hz), 8.87 (t, 2H, J ) 6.7
Hz), 2.62 (t, 18 H, J ) 22.3 Hz). 31P{1H} NMR (δ/ppm, CD3CN):
122.4. UV-visible (λ (nm), CH2Cl2) (ꢀ in M-1 cm-1): 282 (13100),
294 (13000), 318 (sh), 374 (39300). IR (CH2Cl2) (ν(CO), cm-1):
1961, 1888.
Spectroscopic data are the same as those for 1c. Elemental Anal.
Calcd for C38H30 N2O2P3 F6Re: C, 48.57; H, 3.22; N, 2.98.
Found: C, 48.33; H, 3.21; N, 3.01.
cis-[Re(CO)2(c-dppene)(phen)](PF6) (2d). Synthesis and puri-
fication were the same as for 2a except that 0.100 g (0.142 mmol)
of fac-Re(CO)3(c-dppene)Cl, 0.054 g (0.16 mmol) of TlPF6, and
0.028 g (0.16 mmol) of phen were used. Yield: 125 mg (91%).
Spectroscopic data are the same as those for 1d. Elemental Anal.
Calcd for C40H30N2O2P3 F6Re: C, 49.90; H, 3.14; N, 2.91. Found:
C, 49.93; H, 3.15; N, 2.83.
cis-trans-[Re(CO)2(P(OCH3)(Ph)2)2(bpy)](CF3SO3) (1l). Syn-
thesis and purification were the same as for 1h except that 0.115
g (0.200 mmol) of fac-Re(CO)3(bpy)(CF3SO3) and 2 mL (9.97
mmol) of methyldiphenylphosphinite (P(OCH3)(Ph)2) were used.
The product was light yellow. Yield: 176 mg (90%) Elemental
Anal. Calcd for C39H34N2O7P2F3SRe: C, 47.80; H, 3.50; N, 2.86.
Method III: Synthesis from mer-Re(CO)3(PPh3)2Cl via Phos-
phine Displacement. cis-Re(CO)2(PPh3)(c-dppene)Cl (3a).
mer-Re(CO)3(PPh3)2Cl (0.101 g (0.122 mmol)) and c-dppene (0.050
g (0.126 mmol)) were added to a round-bottom flask with ca. 20
mL of toluene. The solution was refluxed under N2 for 24 h, causing
the cloudy solution to become clear and pale yellow. After the reac-
tion cooled, the solvent was removed and the product was redis-
solved in a minimal amount of CH2Cl2. Approximately 10 mL of
methanol was added to the solution, and the methylene chloride was
slowly removed by rotary evaporation. The off-white precipitate
was collected by suction filtration and washed with methanol before
being allowed to air-dry. Yield: 102 mg (90%). Elemental Anal.
Calcd for C46H37O2P3ClRe: C, 59.00; H, 3.98. Found: C, 57.63; H,
4.15. 1H NMR (δ/ppm, CDCl3): 7.34 [7.80-6.89] (m, 35H), 3.51
(t, 2H, J ) 2.08 Hz). 31P{1H} NMR (δ/ppm, CDCl3): 49.6 (dd, J
) 186.5, 9.40 Hz), 29.8 (dd, J ) 21.01, 10.28 Hz), 12.1 (dd, J )
186.7, 21.38 Hz). UV-visible (λ (nm), CH2Cl2) (ꢀ in M-1 cm-1):
282 (51400), 290 (45500). IR (CH2Cl2) (ν(CO), cm-1): 1948, 1866.
cis-Re(CO)2(PPh3)(c-dppene)(CF3SO3) (3b). cis-Re(CO)2(PPh3)-
(c-dppene)Cl (0.103 g (0.110 mmol)) and AgSO3CF3 (0.034 g (0.13
mmol)) were added to a round-bottom flask with ca. 20 mL of
CH2Cl2. The solution was stirred for less than an hour before a
white precipitate, AgCl, was observed. The reaction was allowed
to proceed for 4 h. The AgCl was removed via gravity filtration
through diatomaceous earth. Solvent was removed via rotary
evaporation. The product was precipitated from CH2Cl2 with
hexanes, collected by suction filtration, and washed with CH3OH
and hexanes. Yield: 98 mg (82%). Elemental Anal. Calcd for
C47H37O5P3F3SRe: C, 53.71; H, 3.55. Found: C, 53.86; H, 3.99.
1H NMR (δ/ppm, CDCl3): 7.00 [7.70-6.30] (m, 35H), 1.26 (s,
2H). 31P{1H} NMR (δ/ppm, CDCl3): 49.4 (d, J ) 649.1 Hz), 37.6
(d, J ) 693.2 Hz), 18.0 (d, J ) 26.1 Hz). UV-visible (λ (nm),
CH2Cl2) (ꢀ in M-1 cm-1): 270 (68570), 276 (50790). IR (CH2Cl2)
(ν(CO), cm-1): 1981, 1922.
cis-[Re(CO)2(c-dppene)(bpy)](CF3SO3) (3c). cis-Re(CO)2-
(PPh3)(c-dppene)(SO3CF3) (0.053 g (0.050 mmol)) was stirred in
25 mL of acetonitrile with gentle heating for 36 h. Solvent was
removed, resulting in an oily residue (IR (CH2Cl2) (ν(CO), cm-1):
1971, 1904). The resulting [Re(CO)2(PPh3)(c-dppene)(CH3CN)]-
(SO3CF3) was combined with 10.3 mg (0.066 mmol) of 2,2′-
bipyridine in ca. 10 mL of toluene. The solution was purged with
N2 and refluxed for 4 h. Once the reaction cooled, the solvent was
removed by rotary evaporation. The orange-yellow solid was redis-
solved in a minimal amount of methylene chloride. The product was
reprecipitated by slowly adding the CH2Cl2 solution to cold, stirring
diethyl ether. The orange-yellow product was collected by suction
filtration and washed with several 10-mL aliquots of diethyl ether.
Yield: 40 mg (83%). Spectroscopic data are the same as those for 1c.
1
Found: C, 47.91; H, 3.54; N, 2.79. H NMR (δ/ppm, CD3CN):
8.54 (d, 2H, J ) 5.7 Hz), 8.28 (d, 2H, J ) 7.8 Hz), 8.03 (t, 2H, J
) 4.1 Hz), 7.35 (t, 4H, J ) 12.0 Hz), 7.22 (t, 2H, J ) 2.8 Hz),
7.16 (t, 8H, J ) 21.3 Hz), 6.68 (d, 8H, J ) 17.2 Hz), 3.61 (t, 6H,
J ) 8.6 Hz). 31P{1H} NMR (δ/ppm, CD3CN): 119.7. UV-visible
(λ (nm), CH2Cl2) (ꢀ in M-1 cm-1): 298 (15100), 406 (32700). IR
(CH2Cl2) (ν(CO), cm-1): 1949, 1879.
cis-trans-[Re(CO)2(P(OCH3)2(Ph))2(bpy)](CF3SO3) (1m). Syn-
thesis and purification were the same as for 1h except that 0.148
g (0.257 mmol) of fac-Re(CO)3(bpy)(CF3SO3) and 2 mL (12.6
mmol) of dimethylphenylphosphonite (P(OCH3)2(Ph)) were used.
The product was light yellow. Yield: 228 mg (90%) Elemental
Anal. Calcd for C29H30N2O9P2F3SRe: C, 39.24; H, 3.41; N, 3.16.
1
Found: C, 39.29; H, 3.44; N, 3.14. H NMR (δ/ppm, CD3CN):
8.54 (d, 2H, J ) 6.8 Hz), 8.18 (d, 2H, J ) 8.9 Hz), 8.03 (t, 2H, J
) 6.9 Hz), 7.33 [7.46-7.20] (m, 22H), 2.69 (t, 2H, J ) 18.0 Hz).
31P{1H} NMR (δ/ppm, CD3CN): 149.2. UV-visible (λ (nm), CH2-
Cl2) (ꢀ in M-1 cm-1): 294 (14100), 324 (sh), 394 (32700). IR (CH2-
Cl2) (ν(CO), cm-1): 1957, 1866.
Method II:
Synthesis from fac-Re(CO)3(P-P)Cl.
cis-[Re(CO)2(dppm)(bpy)](PF6) (2a). fac-Re(CO)3(dppm)Cl (0.100
g (0.145 mmol)), TlPF6 (0.053 g (0.15 mmol)), and bpy (0.025 g
(0.16 mmol)) were combined with ca. 5 mL of ODB in a round-
bottom flask covered with aluminum foil. The solution was refluxed
for 7 h under N2, undergoing a color change from white to yellow-
orange. A 15-mL scintered glass funnel was filled with a slurry of
diatomaceous earth in methylene chloride. The cooled reaction
mixture was passed through this slurry to remove the TlCl
precipitate. The filtrate was transferred to a round-bottom flask,
and the solvent was reduced to 15 mL via rotary evaporation.
Diethyl ether was added to precipitate the yellow-orange product,
which was isolated by suction filtration and washed with ether.
The product was dried in vacuo for 24 h. Yield: 113 mg (84%).
Spectroscopic data are the same as those for 1a. Elemental Anal.
Calcd for C37H30 N2O2P3 F6Re: C, 47.90; H, 3.26; N, 3.02.
Found: C, 47.94; H, 3.23; N, 3.05.
cis-[Re(CO)2(dppm)(phen)](PF6) (2b). Synthesis and purifica-
tion were the same as for 2a except that 0.100 g (0.142 mmol) of
fac-Re(CO)3(dppm)Cl, 0.054 g (0.16 mmol) of TlPF6, and 0.029 g
(0.161 mmol) of phen were used. Yield: 118 mg (86%). Spectro-
scopic data are the same as those for 1b. Elemental Anal. Calcd
for C39H30 N2O2P3 F6Re: C, 49.22; H, 3.18; N, 2.94. Found: C,
48.08; H, 3.22; N, 2.85.
cis-[Re(CO)2(c-dppene)(phen)](CF3SO3) (3d). Synthesis and
purification were the same as for 3c except that 0.057 g (0.054
mmol) of cis-[Re(CO)2(PPh3)(c-dppene)(CH3CN)]SO3CF3 and 12.8
g (0.071 mmol) of 1,10-phenanthroline were used and the resulting
cis-[Re(CO)2(c-dppene)(bpy)](PF6) (2c). Synthesis and purifica-
tion were the same as for 2a except that 0.100 g (0.142 mmol) of
fac-Re(CO)3(c-dppene)Cl, 0.053 g (0.15 mmol) of TlPF6, and 0.024
g (0.15 mmol) of bpy were used. Yield: 177 mg (88%).
2166 Inorganic Chemistry, Vol. 45, No. 5, 2006

Luminescent Rhenium(I) Dicarbonyl Complexes
product was orange. Yield: 46 mg (87%). Spectroscopic data are
the same as those for 1d.
Method I relies on the displacement of a labile triflate and
CO ligand by a phosphine donor, either monodentate (IA)
or bidentate (IB). Method II reverses the order of binding,
allowing the phosphine to bind first, followed by the use of
its trans-labilizing ability to bind a bpy or phen ligand.
Reaction conditions were generally mild, and column chro-
matography on alumina using methylene chloride and
acetonitrile easily yielded pure materials. Yields were
typically 70-90% after chromatography.
Method
IV:
The
“Melt
Method”.
cis-[Re(CO)2(bpy)2](CF3SO3) (4a). fac-Re(bpy)(CO)3(CF3SO3)
(0.320 g (0.555 mmol)) and a large excess of bpy were placed in
a 14 in. × 0.75 in. tube. The tube was capped with a septum and
purged with N2. The mixture was magnetically stirred and heated
until reflux. The reaction was continued for approximately 4 h,
when a red solid appeared. The product was cooled and then
dissolved in CH2Cl2 and transferred from the tube. Purification was
achieved by column chromatography on acidic alumina with CH2-
Cl2/CH3CN mixtures. Reprecipitation was accomplished from the
addition of methylene chloride into stirring diethyl ether. Yield:
317 mg (81%). Elemental Anal. Calcd for C23H16N4O5F3SRe: C,
For chelating diphosphine ligands with a weak net donor
effect, it is possible to displace the phosphine with a
polypyridine group. In this case, fac-Re(CO)2(P-P)L (where
-
L is Cl- or CF3SO3 ) was isolated, but further reaction with
1
39.26; H, 2.29; N, 7.96. Found: C, 39.43; H, 2.32; N, 7.91. H
polypyridines resulted in fac-Re(CO)3(N-N)L (where L is
NMR (δ/ppm, CD3CN): 9.45 (d, 2H, J ) 5.0 Hz), 8.48 (d, 2H, J
) 8.6 Hz), 8.40 (d, 2H, J ) 8.6 Hz), 8.15 (dt, 2H, J ) 1.5, 8.1
Hz), 8.02 (dt, 2H, J ) 1.5, 8.1 Hz), 7.63 (m, 2H), 7.41 (dd, 2H, J
) 1.0, 5.5 Hz), 7.34 (m, 2H). UV-visible (λ (nm), CH2Cl2) (ꢀ in
M-1 cm-1): 288 (47400), 364 (6100), 400 (6590), 492 (5320), 564
(sh, 3660). IR (CH2Cl2) (ν(CO), cm-1): 1922, 1852. FAB-MS+:
555.08.
Cl- or CF3SO3 ). It has also been observed that, once the
-
polypyridine group is bound, these weakly coordinating
ligands will not bind in the same manner as described above.
In this case, fac-Re(CO)3(N-N)L (where L is Cl- or
-
CF3SO3 ) was isolated, but further reaction with a chelating
phosphine resulted in no reaction. These attempts, under
various solvents (DCE, mesitylene, ODB, toluene, etc.) and
thermal conditions, resulted in the same product, fac-Re-
cis-[Re(CO)2(phen)2](CF3SO3) (4b). Synthesis and purification
were the same as for 4a except that 0.256 g (0.427 mmol) of fac-
Re(phen)(CO)3(CF3SO3) and an excess of phen were used and the
reaction time was reduced to 15 min. Continued heating resulted
in a product that was insoluble in common solvents. Yield: 276
mg (86%). Elemental Anal. Calcd for C27H16N4O5F3SRe‚1/2H2O:
C, 42.13; H, 2.36; N, 7.28. Found: C, 42.17; H, 2.31; N, 7.31. 1H
NMR (δ/ppm, CD3CN): 9.93 (dd, 2H, J ) 5.5, 1.0 Hz), 8.76 (dd,
2H, J ) 8.1, 1.5 Hz), 8.49 (dd, 2H, J ) 8.6, 1.5 Hz), 8.22 (d, 2H,
J ) 8.6 Hz), 8.10 (d, 2H, J ) 8.6 Hz), 8.03 (dd, 2H, J ) 8.6, 5.0
Hz), 7.58 (dd, 2H, J ) 5.0, 1.5 Hz), 7.46 (dd, 2H, J ) 8.1, 5.0
Hz). UV-visible (λ (nm), CH2Cl2) (ꢀ in M-1 cm-1): 266 (70600),
294 (sh, 20500), 358 (sh, 4930), 412 (8650), 476 (7030), 540 (5050).
IR (CH2Cl2) (ν(CO), cm-1): 1922, 1853.
-
(CO)3(N-N)L (where L is Cl- or CF3SO3 ), each time. This
led to a new approach for making complexes of the type
cis-[Re(CO)2(P-P)(N-N)]+. The combination of the com-
plex mer-trans-Re(CO)3(PPh3)2Cl and a strongly binding
polypyridine ligand as an entering group, leads to the
synthetic route shown in Scheme 2 that allows “customiza-
tion” of the trans-labilizing effect. By starting with a mer-
tricarbonyl species, it is easy to displace a CO due to the
trans-labilizing effect of the other CO. One of the PPh3’s is
also easily displaced due to the trans-labilizing effect of the
phosphine. This allows a chelating phosphine to bind easily,
forming cis-Re(CO)2(P-P)(PPh3)Cl. The chealting phosphine
then creates a trans-labilizing effect on the remaining PPh3
ligand. Finally, labilization of the Cl via triflate metathesis
followed by CH3CN displacement yields two additional
binding sites on the complex. This enables the polypyridine
ligand to enter the coordination sphere without displacement
of the chelating phosphine.
cis-[Re(CO)2(Ph2phen)2](CF3SO3) (4c). Synthesis and purifica-
tion were the same as for 4a except that 0.172 g (0.229 mmol) of
fac-Re(Ph2phen)(CO)3(CF3SO3) and an excess of Ph2phen were used
and the reaction time was reduced to 15 min. Continued heating
resulted in a product which was insoluble in common solvents.
Yield: 176 mg (73%). Elemental Anal. Calcd for C51H32N4O5F3-
SRe‚1/2H2O: C, 58.00; H, 3.05; N, 5.30. Found: C, 58.23; H, 3.23;
1
N, 5.33. H NMR (δ/ppm, CD3CN): 10.00 (d, 2H, J ) 5.5 Hz),
8.17 (d, 2H, J ) 9.6 Hz), 8.04 (d, 2H, J ) 9.1 Hz), 7.98 (d, 2H,
J ) 5.5 Hz), 7.82 (d, 2H, J ) 5.5 Hz), 7.75 (m, 4H), 7.68 (m, 6H),
7.53 (m, 6H), 7.48 (d, 3H, J ) 5.0 Hz), 7.44 (m, 3H). UV-visible
(λ (nm), CH2Cl2) (ꢀ in M-1 cm-1): 280 (83100), 298 (sh, 56300),
320 (sh, 24500), 368 (sh, 9190), 422 (13200), 498 (sh, 10690),
568 (sh, 7060). IR (CH2Cl2) (ν(CO), cm-1): 1917, 1850.
Here, the mer conformation of the carbonyls allows
simultaneous phosphine and carbonyl displacement for
binding the chelating phosphine. Removal of the chloride
ligand in CH3CN gives a complex that is susceptible to
polypyridine reaction via dissociation of the remaining PPh3
and CH3CN ligands to give products of the formulation cis-
[Re(CO)2(P-P)(N-N)]+. Products are usually isolated on
the basis of solubility and recrystallization, but in some cases,
they need to be purified by column chromatography on
alumina. Yields are typically 60-80%.
A reaction driven by harsh conditions is seen in Scheme
3 (Method IV), which utilizes a “melt” of a tricarbonyl-
diimine with excess diimine to produce complexes containing
two polypyridine ligands. This reaction proceeds efficiently
by heating the pure ligand (e.g., bpy) in a round-bottom flask
under nitrogen or, more conveniently, in a test tube in a
microwave oven open to the atmosphere. Reaction yields
Results and Discussion
Synthetic Methods. Earlier preparations of Re(I) with
polypyridine acceptors appear in the literature. Complexes
of the type cis-trans-[Re(CO)2(N-N)(PR3)3]+ (where N-N
is bpy or phen and R is Ph or OR) have been prepared by
thermal or photochemical means,9b and cis-[Re(CO)2(bpy)2]+
has been prepared in low yield by reaction of fac-Re(CO)3-
(bpy)Cl with excess bpy in refluxing ethylene glycol.10 Two
similar, straightforward approaches to these and the new class
of complex, cis-[Re(CO)2(P-P)(N-N)]+, are shown in
Scheme 1.
Inorganic Chemistry, Vol. 45, No. 5, 2006 2167

Smithback et al.
Scheme 1. Direct Synthesis of Phosphine-Diimine Dicarbonyls of Rhenium(I) Complexesa
a Two synthetic routes are shown (Method IA,B and Method II). The first is the addition of the chelating polypyridine ligand and labilization of the
ancillary ligand, followed by phosphine addition. The second method involves chelating the phosphine, followed by the addition of the polypyridine ligand.
are approximately 75-85% after the products have been
purified by chromatography on an alumina support.
phosphine trans to a CO and mutually cis to the other
phosphines in the system. On the basis of the peak position
of bound PPh3 (10.04 ppm) in the precursor molecule, mer-
Re(CO)3(PPh3)2Cl, the smallest splitting (J ) 9 Hz) on the
peaks at 29.8 and 49.6 ppm is caused by the PPh3. The peaks
at 12.1 and 29.8 ppm experience a coupling constant of 20
Hz, corresponding to the end of c-dppene that is trans to the
PPh3. The intraligand J-coupling for the c-dppene is too small
to be resolved.
Crystal Structure Data. X-ray crystallographic data for
cis-Re(CO)2(phen)2(CF3SO3)‚1/2CH3CN is also consistent
with the structural assignments of these compounds as cis-
dicarbonyls. The crystal structure data of cis-[Re(CO)2-
(phen)2](CF3SO3), cis-[Re(CO)2(c-dppene)(phen)](PF6), and
cis-trans-[Re(CO)2(P(Ph)2(OCH3))2(bpy)](CF3SO3), an ex-
ample from each of three of the classes of compounds, can
be found in Figure 2. There are several structural trans effects
consistent within these types of compounds. It is observed
that the Re-C(O) bonds trans to a polypyridine ligand,
ranging from 1.887(10) Å in cis-[Re(CO)2(phen)2](CF3SO3)
(Figure 2i) to 1.895(5) Å in cis-[Re(CO)2(c-dppene)(phen)]-
(PF6) (Figure 2ii), tend to be shorter than those trans to a
phosphine, which range from 1.910(5) Å in cis-trans-
[Re(CO)2(P(Ph)2(OCH3))2(bpy)](CF3SO3) (Figure 2iii) to
Characterization. Characterization of the complexes was
achieved by a combination of elemental analysis, IR spec-
troscopy, 31P NMR spectroscopy, and 1H NMR spectroscopy.
Two intense IR bands in the 1870-1890 and 1940-1960
cm-1 regions and the appropriate number of 31P NMR
spectral peaks are consistent with a mutually cis-CO
geometry for all of the compounds. As shown in Table 1,
by changing the chelate ligand, a relative assignment of the
ligand donor ability can be made for isostructural complexes.
The apparent trend is Ph2phen > bpy, phen > dppm >
diphos > c-dppene, corresponding to both CO modes
increasing in energy (see later section on substituent effects).
The 31P NMR patterns and shifts of the complexes tend
to be very simple and reflect the presence of a plane or the
absence of symmetry at the metal. In some cases, the cis
assignment can be made by through-bond J-coupling effects.
Figure 1 shows the 31P NMR of Re(CO)2(PPh3)(c-dppene)-
(Cl). The analysis of its J-coupling, described below, can
be used to identify the cis assignment. Each of the peaks is
a doublet of doublets, corresponding to three inequivalent
phosphines in the molecule. The peaks at 12.1 and 49.6 ppm
have a large J-coupling of 186 Hz. This corresponds to a
2168 Inorganic Chemistry, Vol. 45, No. 5, 2006

Luminescent Rhenium(I) Dicarbonyl Complexes
Scheme 2. Synthesis of Phosphine-Diimine Dicarbonyls of Rhenium(I) Complexes via Phosphine Displacementa
a Method III is an indirect route that can be used to bind poorly chelating phosphines. This route utilizes the built-in trans effect of two mutually trans-
triphenylphosphine ligands to bind the polypyridine ligand without interfering with the chelation of the entering diphosphine.
+
Scheme 3. Synthesis of cis-Re(CO)2(N-N)2 Complexes via the
and 2.3868(11) Å in cis-[Re(CO)2(P(Ph)2(OCH3))2(bpy)](CF3-
SO3)). Last, when both are trans to a CO, Re-P(phosphine)
bonds, 2.4578(13) Å in cis-[Re(CO)2(c-dppene)(phen)](PF6)
and 2.3868(11) Å in cis-trans-[Re(CO)2(P(Ph)2(OCH3))2(bpy)]
(CF3SO3), are shorter than Re-N(diimine) bonds, 2.210(4)
and 2.166(4) Å, respectively. It is also noted that CO bonds
trans to a Cl are distinctly shorter (0.877(22) Å in cis-
Re(CO)2(PPh3)(c-dppene)Cl) than other CO bonds, due to a
large back-bonding effect. A better net donor trans to a CO
would be expected to cause a weakening in the bond and an
increased bond length due to increased electron density into
the CO π* orbitals; however, the C-O bond lengths appear
to be the same, ranging from 1.145(6) to 1.168(6) Å, regard-
less of the trans ligand. In addition, bonds of a similar nature
are of equal length across the series of complexes. Re-C(O)
bonds trans to a polypyridine are typically 1.89 Å, whereas
those trans to a phosphine range from 1.91 to 1.93 Å. Re-P
bonds trans to a CO range from 2.39 to 2.46 Å, and those
trans to a polypyridine range from 2.36 to 2.41 Å. Re-P
bonds trans to another P range from 2.39 to 2.46 Å. Re-N
bonds trans to a phosphine range from 2.12 to 2.17 Å, where-
as the Re-N bonds trans to a CO range from 2.17 to 2.21 Å.
“Melt Method”a
a Method IV uses harsh conditions to bind a second polypyridine ligand
using fac-Re(CO)3(N-N)OTf as the precursor complex.
1.931(5) Å in cis-[Re(CO)2(c-dppene)(phen)](PF6). An ex-
ception to this is found in the dppm complex, where Re-
CO(N) ) 1.888(14) Å and Re-CO(P) ) 1.900(13) Å. Also,
Re-N(diimine) bonds trans to a diphosphine, 2.115(8) Å in
cis-[Re(CO)2(phen)2](CF3SO3) and 2.150(4) Å in cis-[Re(CO)2-
(c-dppene)(phen)](PF6), are shorter than those trans to a CO,
2.190(7) and 2.210(4) Å, respectively. Re-P bonds trans to
another phosphine, 2.4574(67) and 2.3852(60) Å in cis-
Re(CO)2(PPh3)(c-dppene)Cl, are similar to those trans to a
CO (2.4578(13) Å in cis-[Re(CO)2(c-dppene)(phen)](PF6)
All bond angles support a distorted octahedron geometry.
The N1-Re-N2 bond angles formed by the diimine are less
than 90°, ranging from 74.2(2)° in cis-trans-[Re(CO)2(P(Ph)2-
(OCH3))2(bpy)](CF3SO3) to 76.1(3)° in cis-[Re(CO)2(phen)2]-
(CF3SO3), as required by the bite angle of the chelating
diimine. The dihedral angles between the COs are consis-
tently lower than 90°: 88.8(2)° in cis-trans-[Re(CO)2(P(Ph)2-
Inorganic Chemistry, Vol. 45, No. 5, 2006 2169

Smithback et al.
Table 1. IR Spectral Bands and 31P NMR Shifts for the Bis(diimine) and Phosphine-Diimine Complexesa
31P NMR
compound
νCOb (cm-1
)
δ (ppm)
∆δc (ppm)
∆δavc (ppm)
cis-[Re(CO)2(bpy)2]+
1922, 1852
1922, 1853
1917, 1850
1950, 1884
1950, 1885
1959, 1888
1959, 1889
1952, 1881
1949, 1883
1958, 1889
1938, 1868
1985, 1914
1984, 1914
1961, 1888
1949, 1879
1957, 1886
1948, 1866
1981, 1922
-
-
-
-
-
cis-[Re(CO)2(phen)2]+
-
-
cis-[Re(CO)2(Ph2phen)2]+
-
-
cis-[Re(CO)2(bpy)(dppm)]+
-15.5, -27.5
-15.9, -27.3
52.2, 42.2
53.2, 43.2
44.5, 35.7
-16.3, -27.3
53.2, 42.6
24.6
104.2
103.9
122.4
119.7
5.0, -7.0
4.6, -6.8
73.2, 63.2
64.2, 54.2
55.5, 46.7
4.2, -6.8
74.2, 63.6
28.2
-1.0
cis-[Re(CO)2(phen)(dppm)]+
-1.1
cis-[Re(CO)2(bpy)(c-dppene)]+
cis-[Re(CO)2(phen)(c-dppene)]+
cis-[Re(CO)2(bpy)(diphos)]+
68.2
59.2
51.1
-1.3
68.9
cis-[Re(CO)2(Ph2phen)(dppm)]+
cis-[Re(CO)2(Ph2phen)(c-dppene)]+
cis-trans-[Re(CO)2(PPh3)2(bpy)]+
cis-trans-[Re(CO)2(P(OPh)3)2(bpy)]+
cis-trans-[Re(CO)2(P(OPh)3)2(phen)]+
cis-trans-[Re(CO)2(P(OCH3)3)2(bpy)]+
cis-trans-[Re(CO)2(P(OCH3)(Ph)2)2(bpy)]+
cis-trans-[Re(CO)2(P(OCH3)2(Ph)(bpy)]+
cis-Re(CO)2(PPh3)(c-dppene)Cld
cis-Re(CO)2(PPh3)(c-dppene)OTfd
28.2
-25.4
-25.4
-25.7
-19.4
3.5
-12.6
[16.4], [60.7]
[20.9], [64.5]
-25.7
-19.4
3.5
149.2
[12.8], [29.8, 49.6]
[17.3], [37.6, 49.4]
-12.6
[16.4], [50.8, 70.6]
[20.9], [58.6, 70.4]
a All complexes are the triflate salt unless otherwise noted. b IR data taken in methylene chloride. c ∆δ is the coordination shift, ∆δav is the average
coordination shift. ∆δ ) δ (coordinated phosphine) - δ (free ligand). Free ligand 31P NMR shifts in CD3CN versus 85% H3PO4 as external standard: dppm
(-20.5 ppm); c-dppene (-21.0 ppm); diphos (-11.0 ppm); PPh3 (-3.6 ppm); P(OPh)3 (129.6 ppm); P(OCH3)3 (141.8 ppm); P(OCH3)(Ph)2 (116.2 ppm);
P(OCH3)2(Ph) (161.8 ppm). d 31P NMR taken in CDCl3.
Figure 1. 31P NMR of Re(CO)2(PPh3)(c-dppene)Cl showing how through-bond J-coupling effects can be used for the determination of structural conformation.
This spectrum was taken in CDCl3 with an 85% H3PO4 external standard. Phenyl omitted for clarity.
(OCH3))2(bpy)](CF3SO3), 86.9(6)° in cis-[Re(CO)2(c-dppene)-
(phen)](PF6), and 85.6(2)° in cis-[Re(CO)2(phen)2](CF3SO3).
The trans groupings are less than 180°, also consistent with
distortion of the octahedral. In cis-[Re(CO)2(phen)2](CF3-
SO3), the N1-Re-N1A angle is 165.5(4)°, and the N2-
Re-C1A angle is 171.7(3)°. In cis-[Re(CO)2(c-dppene)-
(phen)](PF6), the C1-Re-N2 angle is 172.0(2)°, the C1-
Re-P1 angle is 173.71(14)°, and the N1-Re-P2 angle is
172.10(11)°. In cis-trans-[Re(CO)2(P(Ph)2(OCH3))2(bpy)](CF3-
SO3), the C-Re-N angles are 172.3(2) and 173.0(2)°. The
Re-C-O bond angles are also somewhat distorted from a per-
fectly linear system, ranging from 174.6(4)° in cis-[Re(CO)2-
(c-dppene)(phen)](PF6) to 189.9(6)° in cis-trans-[Re(CO)2-
(P(Ph)2(OCH3))2(bpy)](CF3SO3). It appears that the smaller
the bite angle of the chelating ligand, the larger the deviation
from a perfect octahedron. For example, bpy has a smaller
bite angle (74.2(2)°) than phen (75.78(14)°), causing the cis-
COs in cis-trans-[Re(CO)2(P(Ph)2(OCH3))2(bpy)](CF3SO3)
2170 Inorganic Chemistry, Vol. 45, No. 5, 2006

Luminescent Rhenium(I) Dicarbonyl Complexes
using a Pt button working electrode. In all cases, the
potentials were calculated versus a Ag/AgCl reference
electrode. As shown in Table 2, the general trend for the
cis-[Re(CO)2(P-P)(N-N)]+ and cis-[Re(CO)2(P)2(N-N)]+
complexes is to exhibit a single ligand-centered reduction
wave and a metal-centered oxidation wave (ReII/I), both of
which are chemically and electrochemically reversible for
the majority of the cases. For cis-[Re(CO)2(bpy)2]+ and
related complexes, two reduction waves and one oxidation
wave can be seen. When phen is the diimine ligand, the
reductive branch of the cylic voltammogram is complicated
by what appears to be adsorption phenomena.12 Figure 3
shows cyclic voltammograms for three complexes: (a) cis-
[Re(CO)2(Ph2phen)2](CF3SO3), (b) cis-[Re(CO)2(Ph2phen)-
(dppm)](CF3SO3), and (c) cis-[Re(CO)2(Ph2phen)(c-dppene)]-
(CF3SO3). Figure 3a shows two reversible reduction waves
and a quasi-reversible oxidation, whereas Figure 3b demon-
states a reversible first reduction and a partially reversible
second reduction with irreversible oxidation showing some
evidence of product formation. Figure 3c exhibits both
reductive and oxidative reversibility.
The potential of the oxidation wave in the reversible cases
can be explained by the relative donating/withdrawing nature
of the chelate, as predicted by the Lever parameters, EL.13
Lever and colleagues developed this parameter, which can
be used to describe the electrochemical potentials of certain
transition metal complexes based on their coordinating
behavior.14 This calculation invokes the summation of
determined values for the ligands, followed by substitution
into the equation: Eobs ) SM[∑EL(L)] + IM. In the case of
the Re(II)/Re(I) couple, SM ) 0.76 and IM ) -0.95. For our
systems, when the reversible oxidations are plotted alongside
calculated values, the result is a line described by the
equation: y ) 0.3503x + 0.8851 (R2 ) 0.9426). This can
be used to tune the electrochemical potential based on the
ligand sphere. Predicted electrochemical frequencies can also
be compared to other directly measured properties, such as
IR stretching frequencies. These relationships are shown in
Figure 4 (calculated values for electrochemical potentials are
found in Table 3). On the basis of the experimental values
of ν(CO) and the correlation to Lever parameters, it is also
possible to back-calculate the EL value of Ph2phen, which is
found to be 0.23(1). This is to be expected on the basis of
the electronic similarity with slightly more π donation than
bpy and phen (EL ) 0.259 and 0.26, respectively).
Figure 2. Crystal structures of (i) cis-[Re(CO)2(phen)2](CF3SO3),
(ii) cis-[Re(CO)2(c-dppene)(bpy)](PF6), and (iii) cis-trans-[Re(CO)2-
(P(Ph)2(OCH3))2(bpy)](CF3SO3). Counterions and hydrogens have been
omitted for clarity.
UV-Visible Spectroscopic and Photophysical Data. The
complexes exhibit yellow-orange to red coloration in the solid
and in solution due to MLCT transitions in the range of 380-
560 nm. The corresponding luminescence occurs in the 600-
700 nm range. Higher energy absorption features in the UV
portion of the spectrum are assigned to intraligand (IL, π-π*)
absorptions of the diimine groups and phenyl groups on the
phosphorus donors on the basis of the properties of similar
to be less distorted, 88.8(2)°, from 90° than in cis-[Re(CO)2-
(c-dppene)(phen)](PF6), 85.6(2)°.
A crystal structure for cis-Re(CO)2(PPh3)(c-dppene)Cl was
obtained, and although the overall refinement is very poor,
it confirms the structural assignment made from the 31P NMR
spectrum. A single molecule of acetonitrile also appears in
the structure.
Electrochemical Studies. Cyclic voltammetry was per-
formed in CH3CN solution with tetra-n-butylammonium
hexafluorophosphate (TBAH) as the supporting electrolyte
(12) (a) Chen, P.; Curry, M.; Meyer, T. J. Inorg. Chem. 1989, 28, 2271-
2280. (b) Yam, V. W.-W.; Lo, K. K.-W.; Cheung, K.-K.; Kong, R.
Y.-C. J. Chem. Soc., Chem. Commun. 1995, 1191-1193.
(13) Lever, A. B. P. Inorg. Chem. 1990, 29, 1271-1285.
(14) Kalyanasundaram, K. Photochemistry of Polypyridine and Porphyrin
Complexes; Academic Press: New York, 1992.
Inorganic Chemistry, Vol. 45, No. 5, 2006 2171

Smithback et al.
Table 2. Electrochemical Dataa vs SCE Obtained by Cyclic Voltammetry with Ferrocene Internal Standardb
c
complex
E1/2ox (V)
Eobs
E1/2red (V)
cis-[Re(CO)2(bpy)2]+
0.91 (r)
0.91 (r)
0.88 (q)
1.26 (i), 1.42 (r)
1.24 (i), 1.42 (r)
1.37 (r)
1.37 (r)
1.32 (r)
1.22 (i), 1.39 (r)
1.35 (r)
1.40 (q)
1.19 (i)
1.19 (i)
1.46 (q)
1.42 (i)
1.52 (i)
1.02 (r)
1.189
1.191
-
-1.30 (r), -1.51 (r)
cis-[Re(CO)2(phen)2]+
-1.32 (i), -1.52 (i)
-1.26 (i), -1.42 (i)
-1.33 (r), -1.63 (i)
-1.35 (i), -1.69 (i)
-1.35 (r)
cis-[Re(CO)2(Ph2phen)2]+
cis-[Re(CO)2(bpy)(dppm)]+
1.319
1.320
1.365
1.366
1.342
N/A
N/A
-
cis-[Re(CO)2(phen)(dppm)]+
cis-[Re(CO)2(bpy)(c-dppene)]+
cis-[Re(CO)2(phen)(c-dppene)]+
cis-[Re(CO)2(bpy)(diphos)]+
-1.38 (i)
-1.35 (r)
cis-[Re(CO)2(Ph2phen)(dppm)]+
cis-[Re(CO)2(Ph2phen)(c-dppene)]+
cis-trans-[Re(CO)2(PPh3)2(bpy)]+
cis-trans-[Re(CO)2(P(OPh)3)2(bpy)]+
cis-trans-[Re(CO)2(P(OPh)3)2(phen)]+
cis-trans-[Re(CO)2(P(OCH3)3)2(bpy)]+
cis-trans-[Re(CO)2(P(OCH3)(Ph)2)2(bpy)]+
cis-trans-[Re(CO)2(P(OCH3)2(Ph)(bpy)]+
cis-Re(CO)2(PPh3)(c-dppene)Cld
cis-Re(CO)2(PPh3)(c-dppene)OTfd
-1.29 (r), -1.57 (i)
-1.30 (r)
-1.31 (r)
-
-1.25 (r)
-
-1.23 (r)
-
-1.28 (r)
-
-1.33 (r)
-
-1.32 (r)
1.282
-
-
-
0.800 (q)
a All complexes are the triflate salt unless otherwise noted; (r) ) reversible, (i) ) irreversible, (q) ) quasireversible. b Scans (20 mV/s) were taken in
CH3CN with TBAH as the supporting electrolyte against a Ag/AgCl reference electrode. A Pt button was the working electrode, and a Pt wire was the
counter electrode. Peak splitting for ferrocene under these conditions ranged from 0.28 to 0.21 V. c Calculated oxidation values versus SCE for reversible
waves from Lever parameters. Ph2phen value is not given in ref 14. d Taken in CH2Cl2. All other conditions were the same.
Figure 4. Calculated electrochemical oxidation potentials from EL
parameters vs (a) observed oxidation potentials and (b) IR stretching
frequencies for Re(I) dicarbonyl complexes. Cyclic voltammetry data was
taken at 20 mV/s in CH3CN with a ca. 0.1 M TBAH supporting electrolyte.
Pt button was used as the working electrode with a Ag/AgCl reference
electrode. IR spectral data was taken in CH2Cl2.
Figure 3. Typical cyclic voltammograms for the dicarbonyls for (a) cis-
[Re(CO)2(Ph2phen)2](OTf), (b) cis-[Re(CO)2(Ph2phen)(dppm)](OTf), and
(c) cis-[Re(CO)2(Ph2phen)(c-dppene)](OTf). Scans were taken at 20 mV/s
in CH3CN with a ca. 0.1 M TBAH supporting electrolyte. Pt button was
used as the working electrode with a Ag/AgCl reference electrode.
d6 polypyridine complexes.14 This is further supported by
their insensitivity to ligand sphere composition. Lower-
energy UV bands are assigned to metal-ligand charge
transfer (MLCT) transitions on the basis of their similarity
to MLCT transitions in other complexes.14 This is supported
by their sensitivity to changes in composition of the
coordination sphere. The overall red-shift in MLCT maxima
of dicarbonyls compared to that of tricarbonyls can be
attributed to the reduction in ligand field strength by
destabilization of the dπ orbital set attained through CO
removal. Because the MLCT is dπ - π* in nature, destabi-
lization of the dπ orbitals by replacement of an accepting
2172 Inorganic Chemistry, Vol. 45, No. 5, 2006

Luminescent Rhenium(I) Dicarbonyl Complexes
Table 3. Bond Lengths and Angles of Interest for Different Classes of Rhenium(I) Dicarbonyl Species
cis-trans-[Re(CO)2(P(Ph)2(OCH3))2(bpy)]
cis-[Re(CO)2(phen)2](CF3SO3)
cis-[Re(CO)2(c-dppene)(phen)](PF6)
(CF3SO3)
Lengths (Å)
1.895(5)
N/A
Re-C1(N)
Re-C1(Cl)
Re-C2(P)
Re-P(CO)
Re-P2(N)
Re-P1(P3)
Re-P3(P1)
Re-N1(P)
Re-N2(CO)
C1-O1(N)
C1-O1(Cl)
C2-O2(P2)
1.887(10)
N/A
N/A
N/A
N/A
N/A
N/A
2.115(8)
2.190(7)
1.164(12)
N/A
1.893(5)
N/A
1.910(5)
2.3868(11)
2.4077(11)
N/A
1.931(5)
2.4578(13)
2.3647(13)
N/A
N/A
N/A
2.150(4)
2.210(4)
1.163(5)
N/A
2.172(4)
2.166(4)
1.168(6)
N/A
N/A
1.160(6)
1.145(6)
Angles (deg)
85.6(2)
75.78(14)
82.06(4)
175.7(4)
174.6(4)
N/A
C1-Re-C2
N1-Re-N2
P1-Re-P2
Re-C1-O1
Re-C2-O2
N1-Re-N1A
C1A-Re-N2
C1-Re-N2
C2-Re-P1
N1-Re-P2
C2-Re-N2
C1-Re-N1
86.9(6)
76.1(3)
N/A
176.7(8)
N/A
165.5(4)
171.7(3)
N/A
N/A
N/A
-
-
88.8(2)
74.2(2)
173.89(4)
179.5(4)
179.9(6)
N/A
N/A
N/A
172.0(2)
173.71(14)
172.10(11)
-
-
-
-
172.3(2)
173.0(2)
-
Table 4. UV-Visible Spectral Data of Dicarbonyls Obtained in CH2Cl2
λ
max (nm) (ꢀ × 10-3, M-1 cm-1
)
complexa
π - π*
MLCT (dπ - π*)
cis-[Re(CO)2(bpy)2]+
288 (47.4)
266 (70.6), 294 (sh)
280 (83.1), 298 (sh), 320 (sh)
282 (21.9), 302 (sh)
262 (sh), 270 (33.4), 292 (sh)
272 (21.4)
364 (6.11), 400 (6.59), 492 (5.32), 564 (sh)
476 (7.03), 540 (5.05)
368 (sh), 422 (13.2), 498 (sh), 568 (sh)
346 (3.73), 438 (3.27)
336 (sh), 384 (4.38), 426 (sh)
390 (3.44)
344 (4.57), 376 (5.05), 420 (sh)
344 (sh), 392 (3.21), 430 (sh)
350 (7.91), 394 (7.79), 426 (7.69)
352 (9.20), 380 (9.68), 428 (sh)
422 (2.45)
372 (3.14)
338 (3.56), 378 (3.14)
374 (3.93)
406 (3.27)
394 (3.27)
cis-[Re(CO)2(phen)2]+
cis-[Re(CO)2(Ph2phen)2]+
cis-[Re(CO)2(bpy)(dppm)]+
cis-[Re(CO)2(phen)(dppm)]+
cis-[Re(CO)2(bpy)(c-dppene)]+
cis-[Re(CO)2(phen)(c-dppene)]+
cis-[Re(CO)2(bpy)(diphos)]+
266 (32.7), 298 (sh)
278 (21.2)
cis-[Re(CO)2(Ph2phen)(dppm)]+
cis-[Re(CO)2(Ph2phen)(c-dppene)]+
cis-trans-[Re(CO)2(PPh3)2(bpy)]+
cis-trans-[Re(CO)2(P(OPh)3)2(bpy)]+
cis-trans-[Re(CO)2(P(OPh)3)2(phen)]+
cis-trans-[Re(CO)2(P(OCH3)3)2(bpy)]+
cis-trans-[Re(CO)2(P(OCH3)(Ph)2)2(bpy)]+
cis-trans-[Re(CO)2(P(OCH3)2(Ph)(bpy)]+
286 (43.7), 316 (sh)
278 (37.9), 286 (38.5), 318 (sh)
298 (15.7), 306 (13.3)
286 (10.9), 320 (7.03)
302 (17.7)
282 (13.1), 294 (13.0), 318 (sh)
298 (15.1)
294 (14.1), 324 (sh)
a All complexes are the triflate salt.
group with a more net-donating ligand results in a red-shift
in the absorption manifold (see Table 4).
these classes of complexes. The plot shows the relationship
between the change in knr (as ln(knr)) and the excited-state
energy (as Eem). Table 5 provides the data used for this plot.
The Re(I) dicarbonyls slope (-1.209 eV-1) is less steep
than that of the Re(I) tricarbonyls (-1.458 eV-1). This
difference is probably due to decreased vibrational overlap
between excited- and ground-state surfaces, resulting from
the loss of a high-frequency CO stretching mode, and thus
the corresponding changes to the Franck-Condon factors
relative to the tricarbonyl species. The y-intercept is also
markedly smaller (34.46 for dicarbonyls vs 40.16 for
tricarbonyls). This implies a decrease in the vibrationally
induced electronic coupling between the excited state and
ground state. Both of these considerations lead to longer
lifetimes by a comparatively slower radiationless decay.
By comparison, energy-gap law plots for Ru(II)16 and
Os(II)17 bipyridine complexes show similar results. For these
For the cis-[Re(CO)2(P-P)(N-N)]+ and cis-[Re(CO)2(N-
N)2]+ complexes, lifetimes and quantum yields vary from
25 to 3840 ns and ca. 0.002 to 0.12, respectively. Inspection
of the data in Table 5 reveals a variation of kr over an order
of magnitude, whereas knr varies over ca. 2.5 orders of
magnitude. On the basis of previous preparative and pho-
tophysical studies of Meyer et al.,10,15 it is predicted that the
absence of a high-frequency (>2000 cm-1) CO stretching
mode could result in less rapid nonradiative decay from the
lowest-lying MLCT excited state manifold. Indeed, the new
dicarbonyl complexes display relatively long lifetimes when
compared to those of similar energy-gap behavior;15 i.e., a
dicarbonyl complex of the same energy gap as that of a
tricarbonyl complex has a longer lifetime. An energy-gap
law plot (Figure 5) provides a visual comparison between
Inorganic Chemistry, Vol. 45, No. 5, 2006 2173

Smithback et al.
Table 5. Luminescence Properties for Phosphine-Diimine or Diphosphine-Diimine Complexes of Re(I)a
b
c
complex
λemb (nm)
Φem
τb (ns)
krc × 104 (s-1
)
knr × 106 (s-1
)
ln knr
cis-[Re(CO)2(bpy)2]+
704
712
642
644
612
603
624
620
568
556
614
618
610
637
634
0.0017
0.0032
0.020
0.031
0.033
0.12
0.027
0.039
0.11
25
126
768
2900
378
3840
325
6.80
7.91
2.60
1.07
8.73
3.20
8.31
5.03
9.59
2.47
4.53
8.28
6.40
7.33
7.04
39.9
7.91
1.28
0.334
2.56
0.228
2.99
1.24
0.776
0.0784
2.62
2.15
1.76
5.16
4.96
17.5026
15.8838
14.0592
12.7193
14.7547
12.3389
14.9121
14.0306
13.5619
11.2696
14.7787
14.5810
14.3808
15.4569
15.4159
cis-[Re(CO)2(phen)2]+
cis-[Re(CO)2(bpy)(dppm)]+
cis-[Re(CO)2(phen)(dppm)]+
cis-[Re(CO)2(bpy)(c-dppene)]+
cis-[Re(CO)2(phen)(c-dppene)]+
cis-[Re(CO)2(bpy)(diphos)]+
cis-trans-[Re(CO)2(PPh3)2(bpy)]+
cis-trans-[Re(CO)2(P(OPh)3)2(bpy)]+
cis-trans-[Re(CO)2(P(OPh)3)2(phen)]+
cis-trans-[Re(CO)2(P(OCH3)3)2(bpy)]+
cis-trans-[Re(CO)2(P(OCH3)(Ph)2)2(bpy)]+
cis-trans-[Re(CO)2(P(OCH3)2(Ph)(bpy)]+
cis-trans-[Re(CO)2(t-dppene)2(bpy)]+d
cis-trans-[Re(CO)2(dppm)2(bpy)]+d
775
1147
9700
375
447
547
0.24
0.017
0.037
0.035
0.014
0.014
191
199
a All complexes are the triflate salt. Spectra obtained in dearated CH2Cl2 at room temperature. b λem is the wavelength of maximum emission, Φem is the
emission quantum yield, and τ is the excited-state lifetime. c kr and knr are the radiative and nonradiative rate constants for excited-state decay, respectively.
d Data from ref 7b. t-Dppene is trans-1,2-bis(diphenylphosphino)ethylene.
Complexes of both Ru(II) and Os(II) are widely studied for
practical use as molecular probes, sensors, and photosensi-
tizers for solar energy conversion.17 This suggests that similar
applications are available for Re(I) dicarbonyl complexes.
Conclusion
A series of Re(I) dicarbonyls was synthesized and studied,
showing promising results to photochemical applications due
to their long-lived excited-state lifetimes and high quantum
yields. Four synthetic routes were developed to provide
flexibility in the synthesis of other dicarbonyl species with
mixed-ligand coordination spheres. The correlation to Lever
parameters acts as a predictor of electrochemical and spectral
properties of these systems and can be used to interpret the
properties of the individual ligands.
Figure 5. Energy-gap law plot for Re(I) diimine dicarbonyl complexes
(solid line) and Re(I) diimine tricarbonyl complexes (dashed line). ()) cis-
trans-[Re(CO)2(PPh3)2(bpy)]+ and (4) cis-[Re(CO)2(dppm)(bpy)]+, which
were omitted from the best-fit line. Data for the dicarbonyls can be seen in
Table 5. Data for the tricarbonyls were taken from ref 15.
complexes having emissive MLCT excited states, slopes are
found to be -7.49 and -7.54 eV-1 and intercepts are 28.05
and 29.17, respectively, when measured in CH3CN. In fact,
the photophysical properties for the lowest MLCT excited
state of cis-[Re(CO)2(c-dppene)(bpy)]+ in CH2Cl2 are similar
to those of [Ru(bpy)3]2+ (λem ) 606 nm, τ ) 488 ns, φ )
0.029)18 in CH2Cl2, and the photophysical properties of cis-
[Re(CO)2(Ph2phen)2]+ in CH2Cl2 are similar to those of
[Os(bpy)3]2+ in CH3CN (λem ) 746 nm, φ ) 0.00462).17
Acknowledgment. We thank Dr. Navamoney Arulasamy
and Dr. Patricia Goodson for their assistance with X-ray
crystallography and Dr. John Bowen for his assistance with
lifetime information. Funding for this research was provided
by the National Science Foundation (Grant NSFLOC4835).
Supporting Information Available: Crystallographic data in
CIF format. This material is available free of charge via the Internet
at http://pubs.acs.org.
(15) Caspar, J. V.; Meyer, T. J. J. Phys. Chem. 1983, 87, 952-957.
(16) Caspar, J. V.; Meyer, T. J. Inorg. Chem. 1983, 22, 2444-2453.
(17) Caspar, J. V.; Kober, E. M.; Sullivan, B. P.; Meyer, T. J. J. Am. Chem.
Soc. 1982, 104, 630-632.
IC050707S
(18) Caspar, J. V.; Meyer, T. J. J. Am. Chem. Soc. 1983, 105, 5583-5590.
2174 Inorganic Chemistry, Vol. 45, No. 5, 2006