Tuning the excited-state properties of luminescent rhenium(V) benzylidyne complexes containing phosphorus and nitrogen donor ligands

Article abstract of DOI:10.1021/om971054t

Efficient methods are developed for the synthesis of rhenium(V)-substituted benzylidyne complexes with various auxiliary ligands to facilitate the tuning of their excited-state properties. The electronic structures and spectroscopic and photophysical properties of [Re(≡CAr′)(pdpp)2Cl]⁺ (Ar′ = C₆H₂Me₃-2,4,6, pdpp = o-phenylenebis(diphenylphosphine), 2), [Re(≡CAr′)L₂(CO)(H₂O)Cl]⁺ (L = PPh₃, 3; P(C₆H₄OMe-p)₃, 4; PPh₂Me, 5), [Re(≡CAr′)(dppe)-(CO)₂Cl]⁺ (dppe = 1,2-bis(diphenylphosphino)ethane, 6), [Re(≡CAr′)(L-L)(CO)₂Cl]⁺ (L-L = 2,2′-bipyridine, 7; 4,4′-dichloro-2,2′-bipyridine, 8; 4,4′-dimethoxycarbonyl-2,2′-bipyridine, 9), [Re(≡CAr′)(TpO(CO)₂]⁺ (Tp′ = tris(3,5-dimethyl-1-pyrazolyl)borohydride, 10), and [Re(≡CC₆H₄-R)(pdPp)(CO)₂(O ₃SCF₃)]⁺ (13, R = OMe, a; Me, b; H, c; Cl, d; Br, e; CN, f) are studied and compared. The molecular structures of 7·CHCl₃, 10, 12f, 13a·CH₃OH·H₂O, and 13d·2CH₂Cl₂ are determined by X-ray crystallography and reveal Re≡C distances in the 1.766(8)-1.786(7) A? range. HF-SCF calculations on the model compounds [Re(≡CC₆H₅)(H₂-PCH=CHPH₂) ₂C1]⁺ (2m), [Re(≡CC₆H₅)(PH₃)₂(H ₂O)(CO)Cl]⁺ (3m), and [Re(≡CC₆H₅)(H₂-PCH=CHPH ₂)(CO)₂(OH)]⁺ (13m) suggest that the HOMO is π(Re≡C-Ph) and the LUMO is ?*(Re=C-Ph). CI-singles calculations on the excited state of optimized 2m indicate that the lowest energy UV-vis absorption of 2-6, 10, and 13 originates from a HOMO to LUMO spin-forbidden transition. This is identified as ³[π(Re≡CAr) → π* (Re≡CAr)], where d(Re) → p(≡C) MLCT character is apparent and the p(≡C) orbital and phenyl π system are conjugated. The UV-vis absorption spectra of 7-9 are significantly different, and their lowest energy absorption is assigned d(Re) → π*(X₂-bpy). The rhenium(V) benzylidyne complexes are highly emissive at room temperature and 77 K. The combination of spectroscopic studies and theoretical calculations suggest that the emitting state of 2-6, 10, and 13 is ³[π(Re≡CAr)→π*(Re=CAr)] but that of 7-9 is d(Re) →*(X₂-bpy). The emission energies in dichloromethane can be adjusted from 520 to 610 nm by variation of the benzylidyne and ancillary ligands. Their electrochemical behaviors are examined and provide further evidence to support the excited-state assignment.

Full text of DOI:10.1021/om971054t

1946
Organometallics 1998, 17, 1946-1955
Tu n in g th e Excited -Sta te P r op er ties of Lu m in escen t
Rh en iu m (V) Ben zylid yn e Com p lexes Con ta in in g
P h osp h or u s a n d Nitr ogen Don or Liga n d s
Wen-Mei Xue, Yue Wang, Michael Chi-Wang Chan, Zhong-Min Su,
Kung-Kai Cheung, and Chi-Ming Che*
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong
Received December 2, 1997
Efficient methods are developed for the synthesis of rhenium(V)-substituted benzylidyne
complexes with various auxiliary ligands to facilitate the tuning of their excited-state
properties. The electronic structures and spectroscopic and photophysical properties of [Re-
(tCAr′)(pdpp)2Cl]+ (Ar′ ) C6H2Me3-2,4,6, pdpp ) o-phenylenebis(diphenylphosphine), 2),
[Re(tCAr′)L2(CO)(H2O)Cl]+ (L ) PPh3, 3; P(C6H4OMe-p)3, 4; PPh2Me, 5), [Re(tCAr′)(dppe)-
(CO)2Cl]+ (dppe ) 1,2-bis(diphenylphosphino)ethane, 6), [Re(tCAr′)(L-L)(CO)2Cl]+ (L-L
) 2,2′-bipyridine, 7; 4,4′-dichloro-2,2′-bipyridine, 8; 4,4′-dimethoxycarbonyl-2,2′-bipyridine,
9), [Re(tCAr′)(Tp′)(CO)2]+ (Tp′ ) tris(3,5-dimethyl-1-pyrazolyl)borohydride, 10), and [Re-
(tCC6H4-R)(pdpp)(CO)2(O3SCF3)]+ (13, R ) OMe, a ; Me, b; H, c; Cl, d ; Br, e; CN, f) are
studied and compared. The molecular structures of 7‚CHCl3, 10, 12f, 13a ‚CH3OH‚H2O, and
13d ‚2CH2Cl2 are determined by X-ray crystallography and reveal RetC distances in the
1.766(8)-1.786(7) Å range. HF-SCF calculations on the model compounds [Re(tCC6H5)(H2-
PCHdCHPH2)2Cl]+ (2m ), [Re(tCC6H5)(PH3)2(H2O)(CO)Cl]+ (3m ), and [Re(tCC6H5)(H2-
PCHdCHPH2)(CO)2(OH)]+ (13m ) suggest that the HOMO is π(RetC-Ph) and the LUMO
is π*(RetC-Ph). CI-singles calculations on the excited state of optimized 2m indicate that
the lowest energy UV-vis absorption of 2-6, 10, and 13 originates from a HOMO to LUMO
3
spin-forbidden transition. This is identified as [π(RetCAr) f π*(RetCAr)], where d(Re)
f p(tC) MLCT character is apparent and the p(tC) orbital and phenyl π system are
conjugated. The UV-vis absorption spectra of 7-9 are significantly different, and their
lowest energy absorption is assigned d(Re) f π*(X2-bpy). The rhenium(V) benzylidyne
complexes are highly emissive at room temperature and 77 K. The combination of
spectroscopic studies and theoretical calculations suggest that the emitting state of 2-6,
10, and 13 is 3[π(RetCAr)fπ*(RetCAr)] but that of 7-9 is d(Re) f π*(X2-bpy). The emission
energies in dichloromethane can be adjusted from 520 to 610 nm by variation of the
benzylidyne and ancillary ligands. Their electrochemical behaviors are examined and provide
further evidence to support the excited-state assignment.
In tr od u ction
(dmpe)2Br][PF6], and examination of their electronic
absorption spectra at high resolution provided a direct
assignment of the frontier molecular orbitals.5 McEl-
wee-White reported the observation of the lowest excited
states of tungsten and molybdenum arylcarbyne com-
plexes by laser flash photolysis.6 A number of accounts
on alkylidyne/carbyne-based photochemical reactions
have appeared,7 although the nature of the excited
states remains elusive.
Fluid luminescence from metal alkylidyne complexes
was first observed in 1985.1 However, emissive com-
plexes containing a metal-carbon triple bond remain
rare. To our knowledge, the only reported examples are
the d2 species [W(tCPh)(L2)X(CO)2] (L2 ) tmen (N,N,-
N′,N′-tetramethylethylenediimine), (py)2, dppe (1,2-bis-
(diphenylphosphino)ethane); X ) Cl, Br, I),1 Cp(CO)-
[P(OMe)3]MtCR (M ) Mo, W; R ) Ph, o-tolyl),2 and
[Os(tCPh)(NH3)5](O3SCF3)33 and the d1 derivatives Re-
(tCAr′)(PPh3)(H2O)X3 (Ar′ ) 2,4,6-C6H2Me3; X ) Cl,
Br).4 Hopkins has studied the molecular structures of
the redox compounds W(tCPh)(dmpe)2Br and [W(tCPh)-
Following the work by Schrock and Williams on d2
rhenium benzylidyne complexes,8 our studies have
revealed that congeners bearing phosphine ligands
exhibit a long-lived emissive excited state in fluid
solution.9 We have continued to develop this theme
with the purpose of (1) defining the nature of the
emissive excited state in order to gain further insight
into the photochemistry of metal benzylidyne complexes
(1) Bocarsly, A. B.; Cameron, R. E.; Rubin, H. D.; McDermott, G.
A.; Wolff, C. R.; Mayr, A. Inorg. Chem. 1985, 24, 3976.
(2) Carter, J . D.; Kingsburg, K. B.; Wilde, A.; Schoch, T. K.; Leep,
C. J .; Pham, E. K.; McElwee-White, L. J . Am. Chem. Soc. 1991, 113,
2947.
(3) Trammell, S.; Sullivan, B. P.; Hodges, L. M.; Harman, W. D.;
Smith, S. R.; Thorp, H. H. Inorg. Chem. 1995, 34, 2791.
(4) Xue, W. M.; Chan, M. C. W.; Mak, T. C. W.; Che, C. M. Inorg.
Chem. 1997, 36, 6437.
(5) Manna, J .; Gilbert, T. M.; Dallinger, R. F.; Geib, S. J .; Hopkins,
M. D. J . Am. Chem. Soc. 1992, 114, 5870.
(6) Schoch, T. K.; Main, A. D.; Burton, R. D.; Lucia, L. A.; Robinson,
E. A.; Schanze, K. S.; McElwee-White, L. Inorg. Chem. 1996, 35, 7769.
S0276-7333(97)01054-6 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 04/14/1998

Luminescent Re(V) Benzylidyne Complexes
Organometallics, Vol. 17, No. 10, 1998 1947
Emission lifetimes were measured with a Quanta Ray
DCR-3 pulsed Nd:YAG laser system (pulse output 355 nm, 8
ns). The emission signals were detected by a Hamamatsu
R928 photomultiplier tube and recorded on a Tektronix model
2430 digital oscilloscope.
and (2) exploring the relationship between molecular
structure and excited-state properties, such as excited-
state energy, nonradiative and radiative decay rate
constants, and excited-state redox potentials. A key
component of this work is the convenient synthesis of a
series of rhenium(V)-substituted benzylidyne complexes
with different ancillary ligands. Rhenium alkylidyne
complexes are relatively rare compared to the group 6
analogues,10 and previous routes do not allow for the
modification of both the alkylidyne and auxiliary groups.
We now present synthetic strategies to two series of
luminescent rhenium(V) benzylidyne complexes: (1)
2,4,6-trimethylbenzylidyne species containing various
phosphorus or nitrogen donor ligands (2-10) and (2)
para-substituted benzylidyne derivatives supported by
o-phenylenebis(diphenylphosphine) (pdpp) (13a -f). De-
tailed spectroscopic investigations demonstrate that the
anticipated tuning of the excited-state properties in
these complexes is possible.
Cyclic Volta m m etr y. Cyclic voltammetry was performed
with
a Princeton Applied Research model 175 universal
programmer and a model 273 potentiostat. Glassy carbon was
used as the working electrode, with Ag-AgNO3 (0.1 mol dm-3
in acetonitrile) as the reference electrode and platinum wire
as the counter electrode. The supporting electrolyte was
n-tetrabutylammonium hexafluorophosphate (0.1 mol dm-3).
Ferrocene was added as an internal standard.
Ma t er ia ls. 4,4′-Dimethoxycarbonyl-2,2′-bipyridine ((Me-
O2C)2-bpy),12 4,4′-dichloro-2,2′-bipyridine (Cl2-bpy),12 and Re-
8
[C(O)Ar′](CO)5 were prepared by literature methods. All
other reagents were used as received. The synthesis of [Re-
(tCAr′)(CO)4Cl][O3SCF3] (1), [Re(tCAr′)(pdpp)2Cl][ClO4] (2),
[Re(tCAr′)L2(CO)(H2O)Cl]+ (L ) PPh3, 3; P(C6H4OMe-p)3, 4;
PMePh2, 5), and [Re(tCAr′)(dppe)(CO)2Cl][ClO4] (6) have been
reported previously.9 All manipulations were carried out
under a nitrogen atmosphere using standard Schlenk tech-
niques unless otherwise stated.
Exp er im en ta l Section
Syn th eses. Satisfactory elemental analysis and infrared
and mass spectral data were obtained for all complexes (see
Supporting Information).
Sp ectr oscop ic P r oced u r es. Infrared spectra were re-
corded with KBr disks on a BIO-RAD FTS165 FT-IR spectro-
photometer. Mass spectra were obtained on a Finnigan Mat
95 mass spectrometer. Elemental analyses were performed
by Butterworth Laboratory, U.K. 1H, 13C, and 31P NMR
spectra (ppm, in CDCl3 unless otherwise stated) were obtained
on a J EOL 270 or a Bruker DRX 300 or 500 multinuclear FT-
NMR spectrometer with tetramethylsilane (1H and 13C NMR)
and H3PO4 (31P NMR) as internal references. UV-vis absorp-
tion spectra were obtained on a Milton Roy Spectronic 3000
diode-array spectrophotometer.
Em ission Sp ectr a a n d Lifetim es. Steady-state emission
spectra were recorded on a SPEX 1681 FLOUROLOG-2 series
F111AI spectrometer and corrected for monochromator and
photomultiplier efficiency and xenon lamp stability. The
absolute emission quantum yield was measured by the method
of Demas and Crosby11 using quinine sulfate in 0.1 N sulfuric
acid as the standard, where the emission quantum yield is
0.546 with 355 nm excitation.
[Re(tCAr ′)(bp y)(CO)2Cl]ClO4 (7). A mixture of 1 (0.40
g, 0.65 mmol) and bpy (0.12 g, 0.78 mmol) in toluene (20 cm3)
was refluxed overnight. The resultant pale yellow precipitate
was filtered and dissolved in methanol (5 cm3). LiClO4 (0.5 g)
was added to the solution, and precipitation with diethyl ether
gave a yellow solid. Recrystallization from an acetonitrile/
chloroform mixture afforded golden yellow crystals. Yield:
0.11 g, 25%. 1H NMR (CD3CN) 2.31 (s, 3, p-Me), 2.35 (s, 6,
o-Me), 6.92 (m, 2, aryl H), 7.85, 8.44, 8.63, 9.34 (4 × m, 8, py
H); 13C NMR (CD3CN) 28.1 (p-Me), 30.2 (o-Me), 126.0-165.2
(py and aryl C), 207.4, 194.0 (CO).
[Re(tCAr ′)(X2-bp y)(CO)2Cl]ClO4 (X ) Cl, 8; MeO2C, 9).
A mixture of 1 (0.40 g, 0.65 mmol) and Cl2-bpy (0.18 g, 0.80
mmol) or (MeO2C)2-bpy (0.21 g, 0.77 mmol) in tetrahydrofuran
(40 cm3) was refluxed for 16 h. The solvent was removed in
vacuo, and the residue was dissolved in methanol (10 cm3).
The crude product was precipitated with LiClO4 (0.5 g) and
then diethyl ether. Recrystallization by diffusion of diethyl
ether into a chloroform solution gave yellow crystals. Yield:
8, 0.16 g, 34%; 9, 0.12 g, 24%.
For 8: 1H NMR (CD3CN) 2.16 (s, 3, p-Me), 2.25 (s, 6, o-Me),
6.89 (s, 2, aryl H), 7.93-8.82 (m, 6, py H); 13C NMR (CD3CN)
27.4 (p-Me), 30.9 (o-Me), 125.2-157.7 (m, py and aryl C), 194.4,
207.6 (CO).
For 9: 1H NMR 2.37 (s, 3, p-Me), 2.44 (s, 6, o-Me), 4.11 (s,
6, CO2Me), 6.83 (s, 2, aryl H), 8.16-9.38 (m, 6, py H); 13C NMR
25.1 (p-Me), 30.8 (o-Me), 54.4 (CO2Me), 124.2-157.6 (m, py
and aryl C), 164.5 (CO2), 194.8, 207.9 (CO).
(7) (a) Mayr, A.; Kjelsberg, M. A.; Lee, K. S.; Asaro, M. F.; Hsieh, T.
C. Organometallics 1987, 6, 2610. (b) Sheridan, J . B.; Pourreau, D.
B.; Geoffroy, G. L.; Rheingold, A. L. Organometallics 1988, 7, 289. (c)
Brower, D. C.; Stoll, M.; Templeton, J . L. Organometallics 1989, 8,
2786. (d) Mayr, A.; Bastos, C. M.; Chang, R. T.; Haberman, J . X.;
Robinson, K. S.; Belle-Oudry, D. A. Angew. Chem., Int. Ed. Engl. 1992,
31, 747. (e) Vogler, A.; Kisslinger, J . Z. Naturforsch. B. 1983, 38B, 1506.
(f) Carter, J . D.; Schoch, T. K.; McElwee-White, L. Organometallics
1992, 11, 3571. (g) Kingsbury, K. B.; Carter, J . D.; Wilde, A.; Park,
H.; Takusagawa, F.; McElwee-White, L. J . Am. Chem. Soc. 1993, 115,
10056. (h) McElwee-White, L.; Kingsbury, K. B.; Carter, J . D. Adv.
Chem. Ser. 1993, 238, 335.
(8) Williams, D. S.; Schrock, R. R. Organometallics 1994, 13, 2101.
(9) Xue, W. M.; Wang, Y.; Mak, T. C. W.; Che, C. M. J . Chem. Soc.,
Dalton Trans. 1996, 2827.
[Re(tCAr ′)(Tp ′)(CO)2][O3SCF 3] (10). A solution of 1 (0.20
g, 0.36 mmol) and KTp′ (0.14 g, 0.42 mmol) in THF (20 cm3)
was refluxed for 16 h to give a yellow precipitate. This was
filtered, washed with THF, and recrystallized by diffusion of
diethyl ether into an acetonitrile solution to yield yellow
crystals. Yield: 0.064 g, 22%. 1H NMR 2.04 (s, 3, p-Me), 2.40-
2.47 (m, 24, Tp′ Me and o-Me), 6.03 (s, 3, Tp′ H), 6.97 (s, 1,
aryl H), 7.05 (s, 1, aryl H); 13C NMR 11.5, 12.6, 12.8, 15.4,
15.9, 18.9 (Tp′-Me), 20.6 (p-Me), 22.6 (o-Me), 107.8-153.5 (m,
Tp′ and aryl C), 192.8 (CO).
(10) (a) Murdzek, J . S.; Schrock, R. R. In Carbyne Complexes;
Fischer, H., Hoffman, P., Freissl, F. R., Schrock, R. R., Schubert, U.,
Weiss, K., Eds.; VCH Verlagsgesellschaft: Weinheim, 1988; p 147ff.
(b) LaPointe, A. M.; Schrock, R. R. Organometallics 1995, 14, 1895.
(c) Toreki, R.; Vaughan, A.; Schrock, R. R.; Davis, W. M. J . Am. Chem.
Soc. 1993, 115, 127. (d) Almeida, S. S. P. R.; Frausto Da Silva, J . J .
R.; Pombeiro, A. J . L. J . Organomet. Chem. 1993, 450, C7. (e) Lemos,
M. A. N. D. A.; Pombeiro, A. J . L.; Hughes, D. L. R.; Richards, L. J .
Organomet. Chem. 1992, 434, C6. (f) Toreki, R.; Schrock, R. R.; Davis,
W. M. J . Am. Chem. Soc. 1992, 114, 3367. (g) Weinstock, I. A.; Schrock,
R. R.; Davis, W. M. J . Am. Chem. Soc. 1991, 113, 135. (h) Herrmann,
W. A.; Felixberger, J . K.; Anwander, R.; Herdtweck, E.; Kiprof, P.;
Riede, J . Organometallics 1990, 9, 1434. (i) Felixberger, J . K.; Kiprof,
P.; Herdtweck, E.; Herrmann, W. A.; J akobi, R.; Gu¨tlich, P. Angew.
Chem., Int. Ed. Engl. 1989, 28, 334. (j) Pombeiro, A. J . L.; Hills, A.;
Hughes, D. L.; Richards, R. L. J . Organomet. Chem. 1988, 352, C5.
(k) Pombeiro, A. J . L.; Carvalho, M. F. N. N.; Hitchcock P. B.; Richards,
R. L. J . Chem. Soc., Dalton Trans. 1981, 1629.
Re[C(O)C6H4R-p](CO)5 (11, R ) OCH3 (a ), CH3 (b), H (c),
Cl (d ), Br (e), CN (f)). A modified version of Schrock’s method
was used.8 Re2(CO)10 (1.0 g, 1.53 mmol) was added to freshly
(12) Cook, M. J .; Lewis, A. P.; McAnliffe, G. S. G.; Skarda, V.;
Thomson, A. J .; Glasper J . L.; Robbins, D. J . J . Chem. Soc., Perkin
Trans. 2 1984, 1293.
(11) Demas, J , N.; Crosby, G. A. J . Phys. Chem. 1971, 75, 991.

1948 Organometallics, Vol. 17, No. 10, 1998
Xue et al.
1
prepared sodium amalgam (0.1 g of Na, 4.4 mmol, 10 g of Hg)
in tetrahydrofuran (40 cm3), and the mixture was stirred for
12 h at room temperature. The resultant bright orange
solution was filtered, and p-R-C6H4COCl (3.06 mmol, R )
OCH3, 0.52 g; CH3, 0.40 cm3; H, 0.36 cm3; Cl, 0.40 cm3; Br,
0.67 g; CN, 0.50 g) was added to the filtrate. After 1 h of
stirring at room temperature, the mixture was filtered and
the solvent was removed in vacuo. Recrystallization of the
residue in dichloromethane/methanol afforded yellow crystals.
For 13a : yield 0.08 g, 32%; H NMR 3.89 (s, 3, CH3), 6.61
(d, 2, J HH ) 9.0, m-H), 6.71 (d, 2, J HH ) 9.0, o-H), 7.27-7.98
(m, 24, aryl H); 13C NMR 56.8 (CH3), 114.9 (CF3), 126.1-137.9
2
(m, aryl C), 166.6 (ipso-C), 185.6 (d, J CP ) 8.7, CO), 186.1 (d,
2J CP ) 8.4, CO), 301.5 (t, J CP ) 10.0, RetC); 31P NMR 39.7.
2
1
For 13b: yield 0.09 g, 35%; H NMR 2.35 (s, 3, CH3), 6.12
(d, 2, J HH ) 8.2, m-H), 6.94 (d, 2, J HH ) 8.2, o-H), 7.32-8.00
(m, 24, aryl H); 13C NMR 22.8 (CH3), 126.0-149.8 (m, aryl C),
2
2
185.2 (d, J CP ) 8.3, CO), 185.6 (d, J CP ) 8.4, CO), 300.4 (t,
2J CP ) 10.0, RetC); 31P NMR 39.5.
1
For 11a : yield 0.68 g, 48%; H NMR 3.86 (s, 3, CH3), 6.94
(d, 2, J HH ) 9.0, m-H), 7.56 (d, 2, J HH ) 9.0, o-H); 13C NMR
55.5 (OMe), 113.3, 129.6, 146.9, 162.1 (aryl C), 181.2 (ax-CO),
183.1 (eq-CO), 242.2 (CdO).
1
For 13c: yield 0.08 g, 32%; H NMR 6.20 (d, 2, J HH ) 7.3,
m-H), 6.94 (d, 2, J HH ) 7.3, o-H), 6.93-8.07 (m, 24, aryl H);
13C NMR 125.8-142.1 (m, aryl C), 184.9 (d, J CP ) 8.6, CO),
2
1
185.4 (d, 2J CP ) 8.6, CO), 299.7 (t, 2J CP ) 10.1, RetC); 31P NMR
For 11b: yield 0.66 g, 48%; H NMR 2.38 (s, 3, CH3), 7.23
(d, 2, J HH ) 8.0, m-H), 7.43 (d, 2, J HH ) 8.0, o-H); 13C NMR
21.3 (CH3), 127.0, 129.0, 141.5, 151.5 (aryl C), 181.2 (ax-CO),
183.0 (eq-CO), 244.6 (CdO).
39.4.
1
For 13d : yield 0.09 g, 36%; H NMR 6.12 (d, 2, J HH ) 8.5,
m-H), 7.05 (d, 2, J HH ) 8.5, o-H), 7.31-8.00 (m, 24H, aryl H);
For 11c: yield 0.58 g, 44%; 1H NMR 7.41-7.50 (m, aryl H);
13C NMR 126.3, 128.4, 130.9, 154.3 (aryl C), 181.1 (ax-COax),
182.9 (eq-CO), 246.0 (CdO).
13C NMR 125.9-143.7 (m, aryl C), 184.6 (d, J CP ) 8.2, CO),
2
185.1 (d, 2J CP ) 8.2, CO), 297.6 (t, 2J CP ) 10.3, RetC); 31P NMR
39.4.
1
For 11d : yield 0.69 g, 47%; H NMR 7.42 (m, aryl H); 13C
For 13e: yield 0.09 g, 34%; 1H NMR 6.06 (d, 2H, J HH ) 8.5,
m-H), 7.24 (d, 2H, J HH ) 8.5, o-H), 7.38-8.01 (m, 24H, aryl
NMR 127.8, 128.6, 137.2, 152.1 (aryl C), 180.8 (ax-CO), 182.7
(eq-CO), 244.1 (CdO).
H); 13C NMR 126.0-140.7 (m, aryl C), 184.6 (d, J CP ) 8.5,
2
1
For 11e: yield 0.77 g, 49%; H NMR 7.35 (d, 2, J HH ) 8.5,
2
2
CO), 185.1 (d, J CP ) 8.5, CO), 297.7 (t, J CP ) 10.2, RetC);
m-H), 7.58 (d, 2, J HH ) 8.3, o-H); 13C NMR 126.1, 128.3, 131.9,
132.8 (aryl C), 181.1 (ax-CO), 183.0 (eq-CO), 244.9 (CdO).
31P NMR 39.4.
For 13f: yield 0.08 g, 30%; 1H NMR (CD3CN) 6.74-8.06 (m,
1
For 11f: yield 0.61 g, 44%; H NMR 7.46 (d, 2, J HH ) 8.5,
aryl H); 13C NMR (CD3CN) 126.9-145.9 (m, aryl C), 183.4 (d,
m-H), 7.75 (d, 2, J HH ) 8.5, o-H); 13C NMR 113.8 (CN), 118.3,
125.6, 132.6, 157.0 (aryl C), 180.5 (ax-CO), 182.2 (eq-CO), 245.9
(CdO).
2J CP ) 8.0, CO), 183.8 (d, J CP ) 7.8, CO), 302.5 (t, J CP ) 9.8,
2
2
RetC); 31P NMR (CD3CN) 39.6.
St r u ct u r a l Det er m in a t ion . Intensity data for 10, 12f,
13a ‚CH3OH‚H2O, and 13d ‚2CH2Cl2 were collected at 301 K
on a Rigaku AFC7R diffractometer with graphite-monochro-
mated Mo KR radiation (λ ) 0.710 73 Å) using ω-2θ scans at
a speed of 16.0 deg min-1. Intensity data were corrected for
Lorentz and polarization effects. The structures were solved
by Patterson methods, expanded by Fourier techniques
(PATTY13), and refined by full-matrix least-squares using the
software package TeXsan14 on a Silicon Graphics Indy com-
puter.
Re[C(O)C6H4R-p](p d p p )(CO)3 (12, R ) OCH3 (a ), CH3
(b), H (c), Cl (d ), Br e), CN (f)). A mixture of Re[C(O)C6H4R-
p](CO)5 (11a -f, 0.87 mmol) and pdpp (0.39 g, 0.87 mmol) in
tetrahydrofuran (40 cm3) was refluxed for 12 h. The solvent
was removed in vacuo, and the residue was recrystallized in
dichloromethane to give yellow to orange crystalline solids.
For 12a : yield 0.51 g, 69%; 1H NMR 3.79 (s, 3, CH3), 6.72-
7.78 (m, 28, aryl H); 13C NMR 55.2 (CH3), 112.2 (p-C), 128.0-
2
148.9 (m, aryl C), 160.6 (ipso-C), 193.1 (d, J CP ) 4.6, ax-CO),
2
2
196.6 (d, J CP ) 10.7, eq-CO), 197.3 (d, J CP ) 10.7, eq-CO),
263.7 (CdO); 31P NMR 44.2.
Crystallographic data are summarized in Table 1. For
For 12b: yield 0.54 g, 74%; 1H NMR 2.28 (s, 3, CH3), 7.00-
7.79 (m, 28, aryl H); 13C NMR 21.2 (CH3), 127.2-141.9 (m,
complex 10, a crystallographic asymmetric unit consists of one
-
complex cation and one CF3SO3 anion. All 45 non-H atoms
2
were refined anisotropically, H(1) bonded to B(1) was located
in the difference Fourier synthesis and its positional param-
eters were refined, and 32 H atoms at calculated positions with
thermal parameters equal to 1.3 times that of the attached C
atoms were not refined. For complex 12f, all 49 non-H atoms
were refined anisotropically, and 28 H atoms at calculated
positions were not refined. For complex 13a ‚CH3OH‚H2O, all
65 non-H atoms were refined anisotropically and 31 H atoms
at calculated positions were not refined. The H atoms of the
methanol molecule and water molecule were not located. For
complex 13d ‚2CH2Cl2, all 53 non-H atoms of the complex
aryl C), 153.1 (ipso-C), 193.2 (t, J CP ) 5.4, ax-CO), 196.5 (d,
2J CP ) 10.7, eq-CO), 197.2 (d, J CP ) 10.7, eq-CO), 265.8 (t,
2
2J CP ) 10.7, CdO); 31P NMR 44.2.
For 12c: yield 0.50 g, 70%; 1H NMR 7.08-7.80 (m, aryl H);
13C NMR 126.6-141.8 (m, aryl C), 155.5 (ipso-C), 193.2 (t, 2J CP
2
2
) 5.3, ax-CO), 196.2 (d, J CP ) 10.7, eq-CO), 196.9 (d, J CP
10.7, eq-CO), 268.1 (CdO); 31P NMR 44.1.
)
For 12d : yield 0.57 g, 77%; 1H NMR 7.07-7.79 (m, aryl H);
13C NMR 127.4-141.8 (m, aryl C), 153.6 (ipso-C), 193.0 (ax-
2
2
CO), 196.1 (d, J CP ) 10.7, eq-CO), 196.9 (d, J CP ) 10.7, eq-
CO), 265.1 (CdO); 31P NMR 44.1.
-
cation, the S atom of the CF3SO3 anion, and the 4 Cl atoms
For 12e: yield 0.58 g, 74%; 1H NMR 7.04-7.80 (m, aryl H);
of the dichloromethane molecules were refined anisotropically.
The O, F, and C atoms of the anion and solvent molecules were
refined isotropically. A total of 33 H atoms at calculated
positions with thermal parameters equal to 1.3 times that of
the attached C atoms were not refined.
The crystal structures of 7‚CHCl3, 12a , and 12d have also
been determined and are presented in the Supporting Infor-
mation. The quality of the crystal data for 7‚CHCl3 was
relatively poor and resulted in large standard deviations;
nevertheless, its structural parameters are discussed.
13C NMR 123.7-141.6 (m, aryl C), 154.2 (ipso-C), 193.0 (ax-
2
2
CO), 196.3 (d, J CP ) 10.2, eq-CO), 196.7 (d, J CP ) 10.2, eq-
CO), 265.1 (CdO); 31P NMR 44.1.
For 12f: yield 0.53 g, 72%; 1H NMR 6.95-7.82 (m, aryl-H);
13C NMR 111.6 (CN), 119.1, 125.6-141.6, 158.7 (aryl C), 192.9
(d, 2J CP ) 9.1, ax-CO), 195.7 (d, 2J CP ) 10.7, eq-CO), 196.5 (eq-
CO), 266.3 (CdO); 31P NMR 43.8.
[Re(tCC6H4R-p)](p d p p )(CO)2(O3SCF 3)][O3SCF 3] (13, R
) OCH3 (a ), CH3 (b), H (c), Cl (d ), Br (e), CN (f)).
Trifluoromethanesulfonic anhydride (40 mm3, 0.23 mmol) was
added to complexes 12a -f (0.23 mmol) in dichloromethane (10
cm3) at -40 °C. After 30 min, the volume of the solution was
reduced in vacuo at 0 °C to 5 cm3 and diethyl ether (40 cm3)
was added to precipitate the product. Recrystallization in
dichloromethane/diethyl ether/methanol mixtures at -20 °C
afforded yellow crystals.
(13) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garcia-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C. The
DIRDIF program system; Technical Report of the Crystallography
Laboratory; University of Nijmegen: The Netherlands, 1992.
(14) Crystal Structure Analysis Package; Molecular Structure
Corp.: The Woodlands, TX, 1985 and 1992.

Luminescent Re(V) Benzylidyne Complexes
Organometallics, Vol. 17, No. 10, 1998 1949
Ta ble 1. Cr ysta llogr a p h ic Da ta
10
12f
13a ‚CH3OH‚H2O
13d ‚2CH2Cl2
formula
fw
cryst dimens, mm
cryst syst
space group
a, Å
C28H33N6O5BF3ReS
819.70
0.25 × 0.15 × 0.35
monoclinic
P21/c (No. 14)
10.988(2)
C41H28NO4P2Re
846.83
0.20 × 0.05 × 0.25
monoclinic
P21/c (No. 14)
15.110(5)
C43H37O11F6P2ReS2
1156.05
0.20 × 0.10 × 0.30
triclinic
P1h (No. 2)
12.447(2)
17.396(2)
11.595(2)
105.19(1)
102.67(1)
75.80(1)
2389.5(7)
2
C43H32O8Cl5F6P2ReS2
1280.27
0.20 × 0.10 × 0.30
monoclinic
P21/n (No. 14)
11.01(1)
25.74(1)
b, Å
c, Å
18.952(2)
16.413(3)
14.936(5)
16.773(2)
11.984(10)
R, deg
â, deg
102.44(2)
111.34(1)
93.29(7)
γ, deg
V, Å3
3338.4(9)
4
1.631
37.66
1624
3525(1)
4
1.595
35.82
1672
5090(7)
4
1.671
28.66
2520
Z
F
calcd, g cm-3
1.607
27.77
1148
abs coeff, cm-1
F(000)
no. of unique data collected
no. of obsd data with I g 3σ(I)
no. of variables
Ra
4928
3761
409
0.034
0.043
2.05
4819
3378
442
0.032
0.035
1.48
6248
5325
586
0.041
0.060
2.43
+1.40, -0.75
9169
6322
559
0.042
0.051
2.58
b
Rw
goodness-of-fit, Sc
∆F(max, min, e Å-3
)
+0.83, -0.69
+1.20, -0.58
+1.46, -0.92
a
b
2
R ) ∑(||Fo| - |Fc||)/∑|Fo|. Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2
.
c S ) [∑w(|Fo| - |Fc|)2/(n - p)]1/2
.
stable, plus the metrical parameters of the crystal data show
that [Re(tCAr′)(pdpp)2Cl]+ (2),9 [Re(tCAr′)(PPh3)2(CO)(H2O)-
Cl]+ (3),9 and [Re(tCC6H5Cl-p)(pdpp)(CO)2(O3SCF3)]+ (13d )
have virtual C2v, Cs, and Cs symmetry, respectively.
The main optimized bond distances (Å) and angles (deg) are
as follows: in 2m RetC 1.76, C-Ph 1.44, Re-Cl 2.54, Re-P
2.52, P-Re-P 81.25; in 3m RetC 1.76, C-Ph 1.43, Re-Cl
2.52, Re-C 1.99, Re-O 2.28; in 13m RetC 1.79, C-Ph 1.43,
Re-C 2.04, Re-O 2.01, Re-P 2.57, P-Re-P 80.38, C-Re-C
93.37.
The ab initio calculations utilized the quasirelativistic
effective core potential (ECP) developed by Hay and Wadt;18
only the outermost electrons of each atom were treated
explicitly. For the Re atom, this includes electrons in the 5s,
5p, 5d, and 6s orbitals, and for P and Cl, this includes 3s and
3p electrons. All the electrons were included for C, O, and H
atoms. The double-ú valence Gaussian basis set associated
with the pseudopotential is adopted. The basis sets were taken
as Re (8s6p3d)/[3s3p2d], P (3s3p)/[2s2p], Cl (3s3p)/[2s2p], C
(10s5p)/[3s2p], O (10s5p)/[3s2p], and H (4s)/[2s].
Figu r e 1. Geometry of the model molecule [Re(tCC6H5)(H2-
PCHdCHPH2)2Cl]+ (2m ).
Molecu la r -Or bita l Ca lcu la tion s. Hartree-Fock self-
consistent-field (HF-SCF)15 and single-excitation configuration
interaction (CI-singles)16 calculations were performed using the
Gaussian 94/DEF program package17 on a Silicon Graphics
Indigo 2 workstation.
The symmetry of the model compounds [Re(tCPh)(H2-
PCHdCHPH2)2Cl]+ (2m , Figure 1), [Re(tCPh)(PH3)2Cl(CO)-
(OH2)]+ (3m ; see Supporting Information), and [Re(tCPh)(H2-
PCHdCHPH2)(CO)2(OH)]+ (13m ; see Supporting Information)
may only be as high as C2v, Cs, and Cs for 2m , 3m , and 13m ,
respectively, depending on the orientation of ligands. These
symmetries were chosen for the calculations because full
optimizations for the models indicate that they are the most
Resu lts a n d Discu ssion
Syn t h esis a n d Ch a r a ct er iza t ion . The synthetic
strategy9 used to prepare the 2,4,6-trimethylbenzyli-
dynerhenium(V) complexes [Re(tCAr′)(pdpp)2Cl]+ (2),
[Re(tCAr′)L2(CO)(H2O)Cl]+ (L ) PPh3, 3; P(C6H4OMe-
p)3, 4; PMePh2, 5), and [Re(tCAr′)(dppe)(CO)2Cl]+ (6)
is also applicable for the synthesis of derivatives con-
taining nitrogen donor ligands: [Re(tCAr′)(X2-bpy)(CO)2-
Cl]+ (X ) H, 7; Cl, 8; CO2CH3, 9) and [Re(tCAr′)(Tp′)-
(CO)2]+ (10) are afforded by the treatment of [Re(tCAr′)-
(CO)4Cl]+ (1) with the corresponding diimine or KTp′.
They are the first examples of rhenium benzylidyne
complexes supported by nitrogen donors. The IR spec-
tra of 7-9 are similar, with two strong CO bands at ca.
2090 and 2030 cm-1 while the CO bands of 10 appear
(15) Roothan, C. C. J . Rev. Mod. Phys. 1951, 23, 69. (b) Pople, J . A.;
Nesbet, R. K. J . Chem. Phys. 1959, 22, 571. (c) McWeeny, R.; Dierksen,
G. J . Chem. Phys. 1968, 49, 4852.
(16) Foresman, J . B.; Head-Gorden, M.; Pople, J . A.; Frisch, M. J .
J . Phys. Chem. 1992, 96, 135.
(17) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.;
J ohnson, B. G.; Robb, M. A.; Cheeseman, J . R.; Keith, T.; Petersson,
G. A.; Montgomery, J . A.; Raghavachari, K.; Al-Laham, M. A.;
Zakrzewski, V. G.; Ortiz, J . V.; Foresman, J . B.; Cioslowski, J .;
Stefanov, B. B.; Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala,
P. Y.; Chen, W.; Wong, M. W.; Andres, J . L.; Replogle, E. S.; Gomperts,
R.; Martin, R. L.; Fox, D. J .; Binkley, J . S.; Defrees, D. J .; Baker, J .;
Stewart, J . P.; Head-Gordon, M.; Gonzalez, C.; Pople, J . A. Gaussian
94, Revision C.3; Gaussian, Inc.: Pittsburgh, PA, 1995.
at 2076 and 2010 cm-1
.
Efficient synthesis of the para-substituted benzyli-
dynerhenium(V) compounds [Re(tCC6H4R-p)](pdpp)-
(18) (a) Hay, P. J .; Wadt, W. R. J . Chem. Phys. 1985, 82, 270. (b)
Schwerdtfeger, P.; Dolg, M.; Schwarz, W. H. E.; Bowmaker, G. A.; Boyd,
P. D. W. J . Chem. Phys. 1989, 91, 1762.

1950 Organometallics, Vol. 17, No. 10, 1998
Xue et al.
Sch em e 1
(CO)2(O3SCF3)][O3SCF3] (13, R ) OMe, a ; Me, b; H, c;
Cl, d ; Br, e; CN, f) has been developed by modification
of Schrock’s method.8 The para-substituted benzoyl-
rhenium(I) complexes Re[C(O)C6H4R-p](CO)5 (11a -f)
are readily formed from Re2(CO)10, and substitution of
CO with pdpp yield the air- and moisture-stable species
Re[C(O)C6H4R-p](pdpp)(CO)3 (12a-f). Trifluoromethane-
sulfonic anhydride is subsequently used as an oxygen-
abstracting reagent to give the series of benzylidyne
derivatives 13a -f (Scheme 1).
F igu r e 2. Perspective view of [Re(CAr′)(Tp′)(CO)2]+ (10;
35% probability ellipsoids).
The IR spectra of benzoylrhenium(I) complexes Re-
[C(O)R](CO)5 (11a -f) are comparable and depict a sharp
peak at ca. 2135 cm-1 and a broad band in the 2055-
1975 cm-1 region for the CO stretching frequencies. In
the 13C NMR spectra, no systematic effect by the para-
substituents is observed upon the benzoyl resonances,
which are located at 242.2-246.0 ppm. The 13C NMR
signal for the CO ligand trans to the benzoyl group
appears at ca. 181 ppm, while those for the four
equatorial COs are found at ca. 183 ppm. The IR
spectra of Re[C(O)C6H4R-p](pdpp)(CO)3 (12a -f) con-
tains three CO bands at ca. 2010, 1940, and 1910 cm-1
,
which are consistent with a fac configuration at the
rhenium center. The 13C NMR shifts of the benzoyl
carbons (265-268 ppm) and axial (193 ppm) and
equatorial (196 and 197 ppm) CO groups are downfield
from those of the pentacarbonyl derivatives 11a -f. The
IR spectra of [Re(tCC6H4R-p)](pdpp)(CO)2(O3SCF3)][O3-
SCF3] (13a -f) show CO bands at ca. 2110 and 2070
cm-1, while their 13C NMR spectra reveal resonances
for the benzylidyne carbon in the 297.6-302.5 ppm
range.
F igu r e 3. Perspective view of Re[C(O)C6H4CN-p](pdpp)-
(CO)3 (12f; 40% probability ellipsoids).
Complexes 7-9 with substituted bpy ligands are
stable for ca. 1 month in air in the solid state but
decompose after only a matter of days in acetonitrile
solution. In contrast, 2-6 (containing phosphine ligands)
and 10 (with Tp’) can be stored in air for several months.
Complexes 13a -f are slightly air-sensitive and decom-
pose in aerobic dichloromethane after a few hours at
room temperature.
Cr ysta l Str u ctu r es. Perspective views of complexes
10, 12f, 13a ‚CH3OH‚H2O, and 13d ‚2CH2Cl2 are pre-
sented in Figures 2-5, respectively; those of complexes
7‚CHCl3, 12a , and 12d are given in the Supporting
Information. Selected bond distances and angles are
listed in Table 2.
The RetC distances in this work (Å; 1.772(7) for 7,

Luminescent Re(V) Benzylidyne Complexes
Organometallics, Vol. 17, No. 10, 1998 1951
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p lexes 10, 12f, 13a ‚CH3OH‚H2O, a n d
13d ‚2CH2Cl2
Compound 10
Re(1)-N(1)
Re(1)-N(3)
Re(1)-N(5)
Re(1)-C(1)
2.158(6) Re(1)-C(2)
2.142(5) Re(1)-C(3)
2.226(6) C(3)-C(4)
1.962(9)
1.972(9)
1.786(7)
1.424(10)
N(1)-Re(1)-N(3) 85.6(2)
N(1)-Re(1)-N(5) 83.3(2)
C(1)-Re(1)-C(3) 90.3(3)
C(2)-Re(1)-C(3) 91.4(3)
N(1)-Re(1)-C(3)
N(3)-Re(1)-C(3)
96.4(3)
96.9(2)
N(5)-Re(1)-C(3) 179.5(3)
Re(1)-C(3)-C(4) 178.8(6)
Compound 12f
2.425(2) C(4)-C(5)
1.952(9) Re(1)-C(4)
Re(1)-P(1)
Re(1)-C(1)
1.54(1)
2.199(9)
C(1)-Re(1)-C(4) 176.6(3)
P(1)-Re(1)-C(4)
P(2)-Re(1)-C(4)
90.5(2)
83.7(2)
C(2)-Re(1)-C(4)
C(3)-Re(1)-C(4)
89.5(3)
88.0(3)
Re(1)-C(4)-C(5) 116.7(6)
Compound 13a ‚CH3OH‚H2O
2.461(2) Re(1)-C(3)
2.231(6) C(3)-C(4)
Re(1)-P(1)
Re(1)-O(4)
1.769(10)
1.43(1)
P(1)-Re(1)-C(3)
P(2)-Re(1)-C(3)
93.5(3)
94.5(3)
C(1)-Re(1)-C(3)
C(2)-Re(1)-C(3)
89.8(4)
88.5(4)
O(4)-Re(1)-C(3) 175.6(3)
Re(1)-C(3)-C(4) 175.3(7)
Compound 13d ‚2CH2Cl2
2.472(2) Re(1)-C(3)
2.228(5) C(3)-C(4)
Re(1)-P(1)
Re(1)-O(3)
1.766(8)
1.43(1)
F igu r e 4. Perspective view of [Re(tCC6H4OMe-p)(pdpp)-
(CO)2(O3SCF3)]+ (13a ; 40% probability ellipsoids).
P(1)-Re(1)-C(3)
P(2)-Re(1)-C(3)
94.8(2)
94.6(2)
C(1)-Re(1)-C(3)
C(2)-Re(1)-C(3)
Re(1)-C(3)-C(4) 175.9(6)
89.2(3)
89.3(3)
O(3)-Re(1)-C(3) 177.3(3)
[Re(tCNH2)(dppe)2Cl][BF4] (1.802(4) Å).10k The RetC-
Cipso angles are all close to linearity as expected.
The substantial trans influence of the benzylidyne
ligand is illustrated in these structures. In complex 7,
a trans chloride group (C(3)-Re(1)-Cl(1) 174.7(4)°)
results in
a rather long Re(1)-Cl(1) distance of
2.485(2) Å, similar to that in 2 (2.497(2) Å).9 For 10
with the facial Tp′ ligand, the nitrogen atom N(5) trans
to the benzylidyne moiety (N(5)-Re(1)-C(3) 179.5(3)°)
is located further from the metal center (Å; Re(1)-N(5)
2.226(6), cf. Re(1)-N(1) 2.158(6), Re(1)-N(3) 2.142(5)).
For 13a and 13d , a relatively long Re-O contact to the
trans triflate group is revealed in each case (Å;
2.231(6) for 13a , 2.228(5) for 13d ).
The structures of the benzoyl complexes 12a , d , and
f are similar, and depict a distorted octahedral config-
uration. The benzoyl ligand is trans to one of the three
CO groups with virtually linear C(1)-Re(1)-C(4) angles
(176.5(2)° for 12a , 177.2(2)° for 12d , and 176.6(3)° for
12f). The angles around the benzoyl carbon C(4) ap-
proach 120°, as expected for sp2 hybridization (for
example, in complex 12f Re(1)-C(4)-C(5) 116.7(6)°,
Re(1)-C(4)-O(4) 128.2(7)°, C(5)-C(4)-O(4) 115.0(8)°).
F igu r e 5. Perspective view of [Re(tCC6H4Cl-p)(pdpp)-
(CO)2(O3SCF3)]+ (13d ; 40% probability ellipsoids).
1.786(7) for 10, 1.769(10) for 13a , 1.766(8) for 13d ) are
typical for rhenium-carbon triple bonds10 and are
comparable to those in the previously reported struc-
tures of 2 and 3 (1.802(5) and 1.784(8) Å, respectively).9
The distances from the benzylidyne carbon to the
neighboring ipso-carbon (Å; 1.49(2) for 7, 1.424(10) for
10, 1.43(1) for 13a , 1.43(1) for 13d ) are slightly shorter
than normal C-C single bonds and suggest π-electron
delocalization throughout the RetC-Ar moiety (Ar )
substituted phenyl). The RetC distances also approach
Absor p tion Sp ectr a a n d Electr on ic Str u ctu r es.
The UV-vis absorption data of the benzylidyne com-
plexes are summarized in Table 3. The absorption
spectra of [Re(tCAr’)(pdpp)2Cl]+ (2), [Re(tCAr’)(PR3)2-
(CO)(H2O)Cl]+ (3-5), [Re(tCAr’)(dppe)(CO)2Cl]+ (6),
[Re(tCAr’)(Tp′)(CO)2]+ (10), and [Re(tCC6H4-R)-
(pdpp)(CO)2(O3SCF3)]+ (13a -f) possess similar fea-
tures: an intense band in the 310-354 nm region and
weak absorption in the 370-430 nm range. The ab-
sorption spectrum of 13c is shown in Figure 6. We note
that complex 13a displays an intense peak at 351 nm,
but inexplicably, no other lower energy absorptions are
those in [Re(tCCH2 Bu)(dppe)2F][BF4] (1.772(7) Å),10j
t
[Re(tCNHMe)(dppe)2Cl][BF4] (1.798(30) Å),10k and

1952 Organometallics, Vol. 17, No. 10, 1998
Ta ble 3. UV-Vis Sp ectr a l Da ta of Ben zylid yn e Com p lexes a t Room Tem p er a tu r ea
Xue et al.
d
complex
2 [Re(tCAr′)(pdpp)2Cl]+
λ , )
max,c nm (ꢀmax dm3 mol-1 cm-1
318 (13 900), 410 (450)
321 (13 900), 410 (1380)
320 (13 100), 420 (320)
320 (12 100), 410 (470)
330 (7290), 430 (400)
231 (31 500), 260 (20 300)
313 (22 400), 320 (24 000)
340 (16 400)
262 (22 200), 310 (17 700)
318 (20 800), 346 (15 800)
253 (20 800), 330 (23 600)
337 (26 200), 390 (9560)
354 (15 400), 425 (970)
351 (25 200)
3 [Re(tCAr′)(PPh3)2(CO)(H2O)Cl]+
4 [Re(tCAr′){P(C6H4OMe-p)3}2(CO)(H2O)Cl]+
5 [Re(tCAr′)(PPh2Me)2(CO)(H2O)Cl]+
6 [Re(tCAr′)(dppe)(CO)2Cl]+
7 [Re(tCAr′)(bpy)(CO)2Cl]+ b
8 [Re(tCAr′)(Cl2-bpy)(CO)2Cl]+
9 [Re(tCAr′){(CO2Me)2-bpy}(CO)2Cl]+
10 [Re(tCAr′)(Tp′)(CO)2]+
13a [Re (tCC6H4OMe)(pdpp)(CO)2(O3SCF3)]+
13b [Re(tCC6H4Me)(pdpp)(CO)2(O3SCF3)]+
13c [Re(tCC6H5)(pdpp)(CO)2(O3SCF3)]+
13d [Re(tCC6H4Cl)(pdpp)(CO)2(O3SCF3)]+
13e [Re(tCC6H4Br)(pdpp)(CO)2(O3SCF3)]+
13f [Re(tCC6H4CN)(pdpp)(CO)2(O3SCF3)]+
326 (18 700), 425(300)
310 (14 800), 425 (580)
325 (19 200), 370 (1440)
329 (23 200), 375 (3170)
313 (18 900), 380 (860)
a
b
d
In CH2Cl2 unless otherwise stated. In MeCN. c Error (2 nm. Error (1 in last significant figure.
F igu r e 6. UV-vis absorption spectrum of [Re(tCC6H5)-
(pdpp)(CO)2(O3SCF3)]+ (13c) in CH2Cl2 at room tempera-
ture.
observed even at a concentration of 5 × 10-3 mol dm-3
.
Although it is difficult to precisely define the energy of
the lowest energy absorption shoulder, it is apparent
from Table 3 that the different electron-withdrawing
para-substituents in complexes 13d -f cause a gradual
blue shift (ca. 3500 cm-1).
F igu r e 7. HOMO (bottom) and LUMO (top) of 2m .
Coefficients are derived from the HF calculation.
Complex 10 containing Tp′ displays a significant red
shift to 354 nm for the high-energy band. Significantly,
the absorption spectra of 7-9 containing para-substi-
tuted bipyridine are different from the other benzyli-
dyne complexes in this work. A strong peak (ꢀ > 2 ×
104 dm3 mol-1 cm-1) centered at 320, 318, and 337 nm
for 7, 8, and 9, respectively, is observed and is ac-
companied by a higher energy shoulder. The lowest
energy absorption appears at ca. 340, 346, and 390 nm
for 7, 8, and 9, respectively, and is also intense (ꢀ > 1.5
× 104 dm3 mol-1 cm-1).
spectra, HF-SCF calculations15 have been performed on
the model molecules [Re(tCC6H5)(H2PCHdCHPH2)2-
Cl]+ (2m , Figure 1; x, y, z axis defined), [Re(tCC6H5)-
(PH3)2(CO)(H2O)Cl]+ (3m ; see Supporting Information),
and [Re(tCC6H5)(H2PCHdCHPH2)(CO)2(OH)]+ (13m ;
see Supporting Information). The calculated energy and
composition of the near frontier orbitals for 2m , 3m , and
13m are summarized in the Supporting Information and
reveal that the HOMO for each complex (for 2m , Figure
7 bottom) is the π(RetC-Ph) orbital with π bonding
between dxz(Re) and px(tC) (2m dxz 27.96%, px(tC)
6.93%, px(Ph) 34.94%; 3m dxz 32.65%, px(tC) 1.89%, px-
(Ph) 59.33%; 13m dxz 26.83%, px(tC) 4.03%, px(Ph)
35.63%). This is different from previous assignments
of the HOMO in related tungsten complexes to a metal
d orbital that is nonbonding with respect to the benz-
ylidyne ligand.4,5 The LUMO (for 2m , Figure 7 (top))
is a π*(RetC-Ph) orbital with antibonding between dxz-
(Re) and px(tC) (2m dxz 20.49%, px(tC) 21.19%, px(Ph)
In solvent-dependent UV-vis studies on complexes
2 and 10, no significant shifts were observed when the
solvent is changed from chloroform to acetonitrile. The
absorption spectra of 13e in different solvents showed
significant but irregular changes, and this is ascribed
to the activity of the coordinated triflate group.
A
solvent effect on the electronic absorption bands of this
class of Re(V) benzylidyne complexes is, therefore,
discounted.
As an aid to interpreting the electronic absorption

Luminescent Re(V) Benzylidyne Complexes
Organometallics, Vol. 17, No. 10, 1998 1953
Ta ble 4. Lu m in escen ce Da ta for Ben zylid yn e Com p lexes a t Room Tem p er a tu r ea
d
complex
λ
max, nmc
φem
τ, µsd
2 [Re(tCAr′)(pdpp)2Cl]+
573
580
588
611
567
555
575
580
585
520
527
530
536
537
559
0.042
2.08
2.25
1.76
0.95
3.35
0.43
0.07
0.61
1.48
0.02
0.22
0.53
2.18
2.42
4.84
3 [Re(tCAr′)(PPh3)2(CO)(H2O)Cl]+
4 [Re(tCAr′){P(C6H4OMe-p)3}2(CO)(H2O)Cl]+
5 [Re(tCAr′)(PPh2Me)2(CO)(H2O)Cl]+
6 [Re(tCAr′)(dppe)(CO)2Cl]+
0.0020
0.0067
0.0046
0.0035
0.00025
0.00012
0.0028
0.0027
0.00015
0.0018
0.0026
0.012
7 [Re(tCAr′)(bpy)(CO)2Cl]+ b
8 [Re(tCAr′)(Cl2-bpy)(CO)2Cl]+
9 [Re(tCAr′){(CO2Me)2-bpy}(CO)2Cl]+
10 [Re(tCAr′)(Tp′)(CO)2]+
13a [Re(tCC6H4OMe)(pdpp)(CO)2(O3SCF3)]+
13b [Re(tCC6H4Me)(pdpp)(CO)2(O3SCF3)]+
13c [Re(tCC6H5)(pdpp)(CO)2(O3SCF3)]+
13d [Re(tCC6H4Cl)(pdpp)(CO)2(O3SCF3)]+
13e [Re(tCC6H4Br)(pdpp)(CO)2(O3SCF3)]+
13f [Re(tCC6H4CN)(pdpp)(CO)2(O3SCF3)]+
0.011
0.016
a
b
d
λex ) 300-350 nm; in CH2Cl2 unless otherwise stated. In MeCN. c Error (2 nm. Error (10%.
49.02%; 3m dxz 21.56%, px(tC) 26.39%, px(Ph) 42.04%;
13m dxz 18.61%, px(tC) 26.30%, px(Ph) 43.31%). By
comparing the composition of these orbitals, we find that
the percentage of dxz in the LUMO is smaller than that
in the HOMO whereas the percentage of px(tC) in-
creases tremendously in the LUMO. Hence, if the
lowest energy transition involves these frontier orbitals,
then this can be formulated as π(RetC-Ph) f π*-
(RetC-Ph) with dxz f px(tC) MLCT character, where
the px(tC) orbital and phenyl π system are conjugated.
To aid in the assignment of the transitions in the
absorption spectra of these complexes, a CI-singles
calculation16 was performed on the excited states of the
optimized model molecule 2m (see Supporting Informa-
tion), where all the orbitals and electrons of the ground
state were included to take into account the electronic
correlation for the excited states. The calculated lowest
energy absorption at 461 nm (HOMO to LUMO triplet
transition, see Supporting Information) can be visual-
ized as a spin-forbidden transition of π(RetC-Ph) f
π*(RetC-Ph) (vide supra). From the absorption spec-
trum of 2, a weak shoulder at ca. 410 nm is assigned to
this transition. In addition, the calculated HOMO to
LUMO singlet transition at 290 nm correlates with the
318 nm band in the absorption spectrum.
these complexes resemble those for a series of rhenium-
(I) N-heterocyclic carbene complexes containing 4,4′-
substituted bipyridine ligands, [HNCH2CH2NHCRe(X2-
bpy)(CO)3]+, where the absorption peaks at 350-400 nm
1
are assigned to a [d(Re) f π*(X2-bpy)] MCLT transi-
1
tion, and a correlation between the MLCT transition
energy and the Hammett parameters (σ) of the substit-
uents X was demonstrated.19 We therefore tentatively
assign the lowest energy shoulders of complexes 7-9
to the [d(Re) f π*(X2-bpy)] 1MLCT transition. Electron-
withdrawing substituents such as CO2CH3 should lower
the π*(X2-bpy), and thus the absorption energy, and
correspondingly, the lowest energy absorption of com-
plex 9 containing (CH3O2C)2-bpy appears at ca. 390 nm
compared with that for 7 (340 nm) and 8 (346 nm).
Lu m in escen ce Stu d ies a n d Mod ifica tion of Ex-
cited -Sta te P r op er ties. All of the rhenium(V) ben-
zylidyne complexes emit in fluid solution at room
temperature upon excitation at 300-350 nm (Table 4).
The profile of their emission spectra are very similar:
a broad and structureless band which is indicative of a
large degree of vibrational coupling like the solution
emission of [Ru(bpy)3]2+ 20
The emission energies λmax
.
range from 520 to 610 nm, and the emission lifetimes
vary from 0.02 to 4.84 µs. The relatively long lifetimes
imply that the transitions involved are spin-forbidden.
The emitting states of these complexes are assigned to
the lowest energy transition. For 2-6, 10, and 13a -f,
the lowest energy excited states have been identified
as 3[π(RetCAr) f π*(RetCAr)] (vide supra). This
assignment predicts that the excited-state energy is
affected by the electronic properties of the benzylidyne
group, and changing the para-substituents would affect
both the π(RetCAr) and π*(RetCAr) energies. Electron-
donating substituents such as OCH3 and CH3 should
lower the energy of π(RetCAr) and raise that of π*-
(RetCAr) and consequently increase the energy gap.
Conversely, electron-withdrawing substituents such as
Cl, Br, and CN should reduce this gap. Thus, a
correlation between the emission energy of 13a -f and
the Hammett parameters (σ) of the benzylidyne para-
substituents is anticipated and indeed observed (Figure
8). This demonstrates that the emission energy of these
derivatives can be tuned and implies (1) association
On the basis of these calculations, the lowest energy
absorption for the rhenium(V) benzylidyne complexes
3
2-6, 10, and 13a -f can be assigned to a [π(RetCAr)
f π*(RetCAr)] transition and the higher energy band
1
to [π(RetCAr) f π*(RetCAr)]; both of these contain
notable d(Re) f p(tC) MLCT character, and the px(tC)
orbital and phenyl π system are conjugated. Further-
more, if this is correct, the energies of these two
absorption bands should be affected by substituents on
the benzylidyne ligand but relatively insensitive to
different auxiliary ligands. This is indeed consistent
with our observation that while the variation of phos-
phine ligands only alters the absorption bands of
complexes 2-6 to a small extent, the nature of the para-
substituents on the benzylidyne ligand in 13a -f sig-
nificantly affects the absorption energies (Table 3). The
fact that the absorption bands are not solvent-dependent
is consistent with the proposal that the electronic
transitions are not pure MLCT.
The UV-vis absorption spectra of complexes 7-9
containing 4,4′-substituted bipyridine ligands are dif-
ferent, and hence the above assignment of the electronic
transitions is not applicable. The spectral features of
(19) Xue, W. M.; Chan, M. C. W.; Su, Z. M.; Cheung, K. K.; Liu, S.
T.; Che, C. M. Organometallics 1998, 17, 1622.
(20) Lytle, F. E.; Hercules, D. M. J . Am. Chem. Soc. 1969, 91, 253.

1954 Organometallics, Vol. 17, No. 10, 1998
Xue et al.
F igu r e 8. Correlation plot of room-temperature emission
energy Eem vs Hammett parameters σ of the substituents
for complexes [Re(tCC6H4R-p)(pdpp)(CO)2(O3SCF3)]+ (13a-
f), R ) -0.99, slope ) -993 ( 49.
F igu r e 9. Corrected emission spectra of [Re(tCC6H4CN)-
(pdpp)(CO)2(O3SCF3)]+ (13f) in CH2Cl2 at room tempera-
ture (s) and in solid state at 77K (- - -), λex 310 nm,
emission intensities are normalized.
Ta ble 5. Electr och em ica l Da ta a
between the emitting state and the benzylidyne moiety
and (2) delocalization of π(RetC) and π*(RetC) into the
phenyl π system. The tunable range of the excited-state
complex
Eox, V
Ered, V
d,h
2b,c
3b
1.48
1.83,e 1.39
-1.31
-1.76
-1.72
d,h
f
f
f
energy is 1300 cm-1
. This is the first example of
4b
1.50,e 1.31d
1.78,e 1.51d
systematic modification of the excited-state energy of
metal benzylidyne complexes by variation of the benz-
ylidyne moiety.
5b
f
f
f
f
f
6
-1.20,g -1.54
-0.89,g -1.91
-0.81,g -1.84
-0.77,g -1.81
-0.75,g -1.80
13a
13b
13c
13d
13e
13f
In addition to effects on emission energy, the variation
of benzylidyne and the auxiliary ligands also influences
the emission lifetime and quantum yield. As shown in
Table 4, lifetimes in the 20 ns to 4.8 µs range and
quantum yields from 1.2 × 10-4 up to 4.2 × 10-2 are
observed, and these indicate that the nature of the
ligands has considerable influence on the excited-state
decay kinetics. For complexes 2-6 with the (tCAr′)
moiety, the nonradiative decay rate constants increase
as excited-state energies decrease, and this is consistent
with the energy-gap law as described previously.9,21
We have assigned the lowest energy transition and,
hence, the emitting state of complexes 7-9 containing
4,4′-substituted bipyridine ligands to d(Re) f π*(X2-bpy)
MLCT. The red shift of the emission bands from 7 (555
nm) to 8 (575 nm) and 9 (580 nm), which bear more
electron-withdrawing substituents, is consistent with
this. Mayr reported that replacing tmen by bipyridine
in the tungsten derivative [W(tCPh)(tmen)(CO)2Cl]
totally quenched the fluid solution emission.1
At 77 K, the Re(V) complexes [Re(tCCH2C6H4R-
p)(dppe)2Cl][BF4] (R ) H, Me)10j with unconjugated
alkylidyne groups were found to emit at 545 and 535
nm, respectively.22 These are comparable to the emis-
sion energies of the benzylidyne complexes (Table 4) and
hence this implies that the emitting state is associated
with the [RetC] moiety. The effect of different solvents
on the emissive behavior of complexes 2, 10, and 13e
were studied, but like the absorptions, no notable effects
were seen upon the emission energies, quantum yields,
and lifetimes for 2 and 10. An irregular effect on the
luminescence of 13e was observed, but again the activity
of the coordinated triflate is the likely cause.
-0.68,g -1.67,f -1.81
-0.53,g -1.51
f,h
a
Measured in CH2Cl2 vs SCE; error (0.02 V; irreversible (Epa
and Epc potentials for anodic oxidation and cathodic reduction
b
waves, respectively) unless otherwise stated. In MeCN. c Refer-
ence 9. Re(VI)/(V). e Phosphine oxidation. f Benzylidyne reduc-
d
g
h
tion. Re(V)/(IV). Reversible.
state at 77 K and in dichloromethane solution at room
temperature are shown in Figure 9. To our knowledge,
this is the first observation of vibronic emission in metal
alkylidyne complexes. Gaussian deconvolution of the
vibronic structured 77 K emission spectra can be used
to obtain the vibrational spacing pωM, excited-state
distortion SM, v′M ) 0 f vM ) 0 emission energy Eem
-
(0-0), and full-width at half-maximum of the individual
23
vibrational components ν˜1/2
.
The fitting results are
available in the Supporting Information and show
vibrational progression pωM between 1080 and 1218
cm-1 and excited-state distortion SM in the 1.21-1.72
range. The latter indicate that the emitting states are
not pure MLCT, for which SM values are typically ca.
1.0.24
Electr och em istr y. Cyclic voltammetry was used to
study the electrochemistry of the benzylidyne complexes
(Table 5). The cyclic voltammograms of 3-5 are similar
and reveal two oxidations and one reduction, all of
which are irreversible. The first oxidation is tentatively
assigned to Re(V)/Re(VI), and the second is assigned to
oxidation of the phosphine ligands. The reduction is
ascribed to occur at the benzylidyne ligand.
(23) Caspar, J . V.; Meyer, T. J . J . Am. Chem. Soc. 1983, 105, 5583.
(24) (a) Dressick, W. J .; Cline, J ., III; Demas, J . N.; DeGraff, B. A.
J . Am. Chem. Soc. 1986, 108, 7567. (b) Caspar, J . V.; Westmoreland,
T. D.; Allen, G. H.; Bradley, P. G.; Meyer, T. J .; Woodruff, W. H. J .
Am. Chem. Soc. 1984, 106, 3492. (c) Allen, G. H.; White, R. P.; Rillema,
D. P.; Meyer, T. J . J . Am. Chem. Soc. 1984, 106, 2613. (d) Casper, J .
V.; Meyer, T. J . Inorg. Chem. 1983, 22, 2444. (e) Lumpkin, R. S.; Meyer,
T. J . J . Phys. Chem. 1986, 90, 5307. (f) Kober, E. M.; Casper, J . V.;
Lumpkin, R. S. J . Phys. Chem. 1986, 90, 3722.
The 77 K emission spectra of the benzylidyne com-
plexes show well to poorly resolved vibrational struc-
tures. The corrected emission spectra of 13f in the solid
(21) (a) Englman, R.; J ortner, J . Mol. Phys. 1970, 18, 145. (b) Freed,
K. F.; J ortner, J . J . Chem. Phys. 1970, 52, 6272.
(22) Xue, W. M.; Che, C. M.; Pombeiro, A. J . L. Unpublished results.

Luminescent Re(V) Benzylidyne Complexes
Organometallics, Vol. 17, No. 10, 1998 1955
and auxiliary ligands can be conveniently modified, and
this has paved the way for exploring the excited-state
properties of these luminescent compounds. Data from
electronic absorption and emission spectra, electrochem-
istry, and molecular-orbital calculations provide compel-
ling evidence to suggest that the excited state is
[π(RetCAr) f π*(RetCAr)] with d(Re) f p(tC) MLCT
character, where the p(tC) orbital and phenyl π system
are conjugated. Significantly, the excited-state proper-
ties associated with this chromophore can be tuned by
varying the benzylidyne and auxiliary ligands. Hence,
the emission energy can be modified from 520 to 610
nm in CH2Cl2, a range of 2840 cm-1. The excited-state
lifetimes can be adjusted from 20 ns to 4.84 µs, many
of which are significantly longer than those in related
Mo, W,1,2 and Os3 alkylidyne systems, so that Stern-
Volmer kinetic experiments are possible.
F igu r e 10. Plot of room-temperature emission energy Eem
vs ground-state reductive potential E°[(CAr)0/-] for [Re(tC-
C6H4R-p)(pdpp)(CO)2(O3SCF3)]+ (13a -f), R ) -0.96, slope
) -3068 ( 422.
No oxidation wave is observed for complexes 6 and
13a -f, which contain two coordinated CO groups, even
up to 2.3 V vs SCE. Two irreversible reduction waves
(the second for 13f is reversible) are observed; they are
tentatively assigned to metal-centered (Re(V) f Re(IV))
and benzylidyne ligand reductions, respectively.
The electrochemical data of 13a -f provide further
support for the assignment of the π*(RetCAr) excited
state. Reduction of the benzylidyne group results in
addition of an electron into the π*(tCAr) orbital. If the
emitting state is associated with π*(tCAr), a linear
relationship should exist between the emission energy
(Eem) and the reductive potential for the benzylidyne
group (E°[(CAr)0/-], denoted with footnote f in Table 5).
This is indeed observed for complexes 13a -f (Figure 10).
Importantly, this correlation illustrates that the excited
state is associated with the benzylidyne group and that
emission in this system is occurring from states which
have a common electronic origin.
Ack n ow led gm en t. We are indebted to Prof. A. J .
L. Pombeiro for providing samples of [Re(tCCH2C6H4R-
p)(dppe)2Cl][BF4] (R ) H, Me) and for helpful discus-
sions. We thank The University of Hong Kong, the
Croucher Foundation, and the Hong Kong Research
Grants Council for financial support. M.C.-W.C. is
grateful for a University Postdoctoral Fellowship from
The University of Hong Kong.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, atomic coordinates, calculated hydrogen coordinates,
anisotropic displacement parameters, and bond distances and
angles for 7‚CHCl3, 10, 12a , 12d , 12f, 13a ‚CH3OH‚H2O, and
13d ‚2CH2Cl2, the HF-SCF calculated energy and composition
of the near frontier orbitals for 2m , 3m , and 13m , excited state
assignment of 2m by CI-singles calculation, analytical data
for all complexes, emission parameters calculated from Gauss-
ian deconvolution, and geometry of 2m , 3m , and 13m (99
pages). Ordering information is given on any current mast-
head page.
Con clu sion
Synthetic routes to rhenium(V) benzylidyne com-
plexes have been developed so that both benzylidyne
OM971054T