Metallo 2,3-Disulfidothienoquinoxaline, 2,3-Disulfidothienopyridine, and 2-Sulfido-3-oxidothienoquinoxaline Complexes: Synthesis and Characterization

Article abstract of DOI:10.1021/ic961428v

The 2,3-disulfidothienoquinoxaline complexes of Cp₂Mo and dppePd and the 2,3-disulfidothienopyridine complexes of Cp₂Mo were obtained as products from the S₈ oxidation of the corresponding metallo-1,2-enedithiolate complexes. The analogous 2-sulfido-3-oxidothienoquinoxaline complexes of Cp₂Ti, Cp₂Mo, dppPd, and dppePt were prepared from 1-(quinoxalin-2-yl)-2-bromoethanone and the corresponding polysulfido complex. Both Cp₂Mo{S₂C₁₀H₄N₂S} and Cp₂Mo{SOC₁₀H₄N₂S} have been characterized crystallographically. These complexes contain an extended planar ring where the metal is bound to substituents at the 2and 3-positions of the thiophene ring. The oxidation products of the Cp₂Mo derivatives all have EPR g values near 1.98 and ^97.95Mo hyperfine of ≤ 8.5 G. All of UK complexes have a visible band assigned to an intraligand transition (IL). The excitation of a room-temperature DMSO solution of dppePt{SOC₁₀H₄N₂S} leads to an emission at 690 nm with a φ = 0.005. Lifetime measurements were best fit as the sum of two exponential decays with lifetimes of 6 and 0.3 ns.

Full text of DOI:10.1021/ic961428v

2406
Inorg. Chem. 1997, 36, 2406-2412
Metallo 2,3-Disulfidothienoquinoxaline, 2,3-Disulfidothienopyridine, and
2-Sulfido-3-oxidothienoquinoxaline Complexes: Synthesis and Characterization
Sharada P. Kaiwar,† John K. Hsu,† Anthony Vodacek,† Glenn Yap,‡ Louise M. Liable-Sands,‡
Arnold L. Rheingold,‡ and Robert S. Pilato*,†
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742,
and Department of Chemistry, University of Delaware, Newark, Delaware 19711
ReceiVed NoVember 27, 1996X
The 2,3-disulfidothienoquinoxaline complexes of Cp2Mo and dppePd and the 2,3-disulfidothienopyridine complexes
of Cp2Mo were obtained as products from the S8 oxidation of the corresponding metallo-1,2-enedithiolate complexes.
The analogous 2-sulfido-3-oxidothienoquinoxaline complexes of Cp2Ti, Cp2Mo, dppPd, and dppePt were prepared
from 1-(quinoxalin-2-yl)-2-bromoethanone and the corresponding polysulfido complex. Both Cp2Mo{S2C10H4N2S}
and Cp2Mo{SOC10H4N2S} have been characterized crystallographically. These complexes contain an extended
planar ring where the metal is bound to substituents at the 2- and 3-positions of the thiophene ring. The oxidation
products of the Cp2Mo derivatives all have EPR g values near 1.98 and 97/95Mo hyperfine of e 8.5 G. All of the
complexes have a visible band assigned to an intraligand transition (IL). The excitation of a room-temperature
DMSO solution of dppePt{SOC10H4N2S} leads to an emission at 690 nm with a φ ) 0.005. Lifetime measurements
were best fit as the sum of two exponential decays with lifetimes of 6 and 0.3 ns.
Introduction
oxidation was accompanied by the formation of a five-
membered thiophene ring. The analogous metallo-2-sulfido-
3-oxidothiophenes were available from the reaction of a
polysulfido complex with the R-bromo ketone, 1-(quinoxalin-
2-yl)-2-bromoethanone.
The synthesis of several metal derivatives of 2,3-disulfi-
dothienoquinoxaline, 2,3-disulfidothienopyridine, and 2-sulfido-
3-oxidothienoquinoxaline are described, and an overview of the
chemistry of these metal complexes is provided. The rather
unique features of these complexes include ligand-centered
oxidation, low-lying ligand-centered electronic transitions, and
luminescent Pt derivatives.
Metallo-1,2-enedithiolates, M{S2C2(R)(R′)}, have been used
as models for the molybdenum cofactor,1-5 as components in
conducting materials,6-9 and, in the case of platinum-1,2-
enedithiolates, as room-temperature solution lumiphores.10-13
While there are many reasons to study metallo-1,2-enedithi-
olates, few studies have focused on the reactivity of the metal-
bound ligand. While many 1,2-enedithiolate complexes undergo
reversible one electron oxidation of the metal or ligand, those
complexes with R ) H should undergo chemical oxidation. In
this paper, the reactions of complexes containing R ) H and
R′ ) heterocycle14,15 with S8 are described. The products from
these reactions are metallo-2,3-disulfidothiophenes. These
complexes were the result of a formal oxidation of both the
1,2-enedithiolate ligand and the appended heterocycle. This
Experimental Section
Materials. Cp2Mo{S2C2(2-quinoxaline)(H)},14 Cp2Mo{S2C2(2-py-
ridine)(H)},14 Cp2Mo {S2C2(3-pyridine)(H)},14 Cp2Mo{S2C2(4-pyridine)-
(H)},14 dppeM{S2C2(2-quinoxaline)(H)} (M ) Pd, Pt; dppe ) diphen-
yldiphosphinoethane),15 Cp2MoS4,16 dppePdS4,17 dppePtS4,17 Cp2TiS5,18
Cp2Mo(SH)2,19 dppePd(SH)2,20 and 1-(quinoxalin-2-yl)-2-bromoetha-
none21 were prepared according to the literature procedures. The 54%
† University of Maryland.
‡ University of Delaware.
X Abstract published in AdVance ACS Abstracts, May 1, 1997.
(1) Pilato, R. S.; Gea, Y.; Eriksen, K. A.; Greaney, M. A.; Stiefel, E. I.;
Goswami, S.; Kilpatrick, L.; Spiro, T. G.; Taylor, E. C.; Rheingold,
A. L. In ACS Symposium Series, Molybdenum Enzymes, Cofactors,
and Models Systems; Stiefel, E. I., Coucouvanis, D., Newton, W. E.,
Eds.; American Chemical Society: Washington, DC, 1993; Vol. 635;
pp 83-97.
(14) (a) Hsu, J. K.; Bonangelino, C. J.; Kaiwar, S. P.; Boggs, C. M.;
Fettinger, J. C.; Pilato, R. S. Inorg. Chem. 1996, 35, 4743-51. (b)
Kaiwar, S. P; Hsu, J. K.; Liable-Sands, L. M.; Rheingold, A. L.; Pilato,
R. S. The Synthesis of Heterocyclic Substituted-1,2-enedithiolates of
Nickel, Palladium, and Platinum. Submitted for publication.
(15) Kaiwar, S. P.; Vodacek, A.; Blough, N. V; Pilato, R. S. Protonation
State Dependent Luminescence and Excited State Electron Transfer
Reactions of 2-and 4-Pyridine(ium) Substituted Metallo-1,2-enedithi-
olates. Submitted for publication.
(16) Ko¨pf, H.; Kahl, W.; Wirl, A. Angew. Chem., Int. Ed. Engl. 1970, 9,
801-2.
(17) Chatt, J.; Mingos, D. M. P. J. Chem. Soc. A 1970, 1243-5.
(18) McCall, J. M.; Shaver, A. J. Organomet. Chem. 1980, 193, C37-
C39.
(2) (a) Subramanian, P.; Burgmayer, S.; Richards, S.; Szalai, V.; Spiro,
T. G. Inorg. Chem. 1990, 29, 3849-53. (b) Soricelli, C. L.; Szalai,
V. A.; Burgmayer, S. J. N. J. Am. Chem. Soc. 1991, 113, 9877-8.
(3) Das, S. K.; Chaudhury, P. K.; Biswas, D.; Sarkar, S. J. Am. Chem.
Soc. 1994, 116, 9061-70.
(4) Kilpatrick, L.; Rajagopalan, K. V.; Hilton, J.; Bastian, N. R.; Stiefel,
E. I.; Pilato, R. S.; Spiro, T. G. Biochemistry 1995, 34, 3032-9.
(5) Ueyama, N.; Oku, H.; Kondo, M.; Okamura, T.; Yoshinaga, N.;
Nakamura, A. Inorg. Chem. 1995, 35, 643-50.
(6) Veldhuizen, Y. S. J.; Veldman, N.; Spek, A. L.; Faulmann, C.;
Haasnoot, J. G.; Reedijk, J. Inorg. Chem. 1995, 34, 140-7.
(7) Fourmigue, M.; Lenoir, C.; Coulon, C.; Guyon, F.; Amaudrut, J. Inorg.
Chem. 1995, 34, 4979-4985.
(8) Schrauzer, G. N. Acc. Chem. Res. 1969, 2, 72-80.
(9) Clemenson, P. I. Coord. Chem. ReV. 1990, 106, 171-203.
(10) Cummings, S. D.; Eisenberg, R. J. Am. Chem. Soc. 1996, 118, 1949-
60.
(19) Green, M. L. H.; Lindsell, W. E. J. Chem. Soc. A 1967, 1455.
(20) (a) Schmidt, M.; Hoffmann, G. G.; Holler, R. Inorg. Chim. Acta 1979,
1
32, L19-L20. The H NMR resonance for the hydrosulfido ligands
of 3 was improperly assigned: 3, (dppe)Pd(SH)2: 1H NMR (CDCl3)
δ -0.55 (second-order multiplet, 2H, SH, line spacings ) 11 and 6
Hz).
(11) Cummings, S. D.; Eisenberg, R. Inorg. Chem. 1995, 34, 3396-403.
(12) Bevilacqua, M. J.; Eisenberg, R. Inorg. Chem. 1994, 33, 2913-23.
(13) Kaiwar, S. P.; Vodacek, A.; Blough, N. V.; Pilato, R. S. J. Am. Chem.
Soc. 1997, 119, 3311-16.
(21) (a) Rowe, D. J.; Garner, C. D.; Joule, J. A. J. Chem. Soc., Perkin
Trans. 1 1985, 1907-10. (b) Gardini G. P.; Minisci, F. J. Chem. Soc.
C 1970, 929.
S0020-1669(96)01428-0 CCC: $14.00 © 1997 American Chemical Society

Metallo Sulfidothienoquinoxaline Complexes
Inorganic Chemistry, Vol. 36, No. 11, 1997 2407
HBF4 etherate was purchased from Fluka Chemika and was used as
received. All reactions were performed under an atmosphere of nitrogen
using standard Schlenk line techniques. Neutral activated alumina, 80-
325 mesh, was purchased from EM Science, Cherry Hill, NJ, and treated
with 6% H2O by weight to generate the Brockmann activity 3 material
used throughout the study. Workups were performed in air unless stated
otherwise. Dichloromethane, acetonitrile, and pentane were dried over
calcium hydride and distilled under nitrogen. Diethyl ether, tetrahy-
drofuran, and dioxane were dried over sodium/benzophenone and
distilled under nitrogen. Triethylamine was dried over potassium
hydroxide and vacuum distilled.
11. Anal. Calcd for C17.5H14NS3MoCl: C, 45.12; H, 3.03; N, 3.01.
Found: C, 45.24; H, 3.28; N, 2.78. 1H NMR (CDCl3): δ 8.64 (s, 1H,
C5H3N), 8.17 (d, 1H, C5H3N, JH-H ) 6 Hz), 7.37 (d, 1H, C5H3N, JH-H
) 6 Hz), 5.39 (s, 10H, C5H5). Mass spectrum [m/z (EI)]: 425 (M+),
360 (M+ - C5H5), 228 (M+ - C7H3S3N). UV-vis [(abs) CH2Cl2,
nm; λmax (ꢀ)]: 358 (3950), 529 (660).
12. Anal. Calcd for C17.5H14NS3MoCl: C, 45.12; H, 3.03; N, 3.01.
Found: C, 45.52; H, 3.32; N, 2.83. 1H NMR (CDCl3): δ 8.20 (d, 1H,
C5H3N, JH-H ) 5 Hz), 7.60 (d, 1H, C5H3N, JH-H ) 8 Hz), 7.12 (dd,
1H, C5H3N, JH-H ) 5 Hz; JH-H ) 8 Hz), 5.39 (s, 10H, C5H5). Mass
spectrum [m/z (EI)]: 425 (M+), 360 (M+ - C5H5), 228 (M+
-
C7H3S3N). UV-vis [(abs) CH2Cl2, nm; λmax (ꢀ)]: 296 (7900), 376
(3110), 531 (820).
Physical Measurements. NMR measurements were made on either
a Bruker AF 200 or a Bruker AM 400. EPR measurements were made
on a Bruker ES-D 200. UV-vis measurements were made on a Perkin-
Elmer λ-2S UV-visible spectrometer. IR spectra were collected on
either a Perkin-Elmer 1600 Series FT-IR spectrometer or a Nicolet 5
DXL FT-IR spectrometer. Mass spectral data were collected on a
Magnetic Sector VG 7070E. All electrochemical experiments were
conducted on a BAS-50 in either CV or OSW modes with 0.1 M [Bu4N]-
[PF6] as the supporting electrolyte. In all electrochemical experiments,
the electrodes used were a carbon working, platinum auxiliary, and
Ag/AgCl reference. Under these conditions, the ferrocene/ferrocenium
couple (DMF) was found at 511 mV. All values reported in the text
are relative to SCE and were adjusted using the ferrocene/ferrocenium
couple. Chemical analyses were performed by M-H-W Laboratories,
Phoenix, Az.
Cp2Mo{S2C5H3NS} (13). Complexes 13 was prepared as described
for 11 and 12 using Cp2Mo{S2C2(2-pyridine)(H)} (0.070 g, 0.178 mmol)
in place of Cp2Mo{S2C2(3-pyridine)(H)} and S8 (0.012 g, 0.045 mmol).
Complex 13 was isolated as a purple solid in 4% yield (0.003 g, 0.007
mmol) upon eluting the column with dichloromethane and the removal
of the eluent. 1H NMR (CDCl3): δ 8.46 (d, 1H, C5H3N, JH-H ) 6
Hz), 7.68 (d, 1H, C5H3N, JH-H ) 6 Hz), 7.89 (dd, 1H, C5H3N, JH-H
)
6 Hz, JH-H ) 6 Hz), 5.39 (s, 10H, C5H5). Mass spectrum [m/z (EI)]:
425 (M+), 360 (M+ - C5H5), 228 (M+ - C7H3S3N). UV-vis [(abs)
CH2Cl2, nm; λmax (ꢀ)]: 378 (3890), 521 (1050).
Cp2Mo{SOC10H4N2S} (19). To a DMF solution (5 mL) of Cp2-
MoS4 (0.175 g, 0.50 mmol) was added 1-(quinoxalin-2-yl)-2-bromo-
ethanone (0.378 g, 1.50 mmol). The reaction mixture was heated at
90 °C for 30 min to give a violet solution. The DMF was removed,
and the solid was washed with 3 × 20 mL of diethyl ether. The solid
was dissolved in dichloromethane (3 mL) to which three drops of
triethylamine was added to give a purple-red solution. The solvent
was removed in air, and the solid was chromatographed on a 1 × 20
cm alumina column. Complex 19 was isolated as a purple solid in
57% yield (0.131 g, 0.285 mmol) upon eluting the column with 1:2
hexane/dichloromethane and the removal of the eluent. Crystallization
from dichloromethane/pentane gave analytically pure material. Anal.
Calcd for C20H14N2OS2Mo: C, 52.40; H, 3.06; N, 6.11. Found: C,
52.23; H, 3.30; N, 6.29. 1H NMR (CD2Cl2): δ 7.92 (m, 1H, C8H4N2),
7.54 (m, 1H, C8H4N2), 7.23 (m, 1H, C8H5N2), 7.15 (m, 1H, C8H4N2),
5.58 (s, 10H, C5H5). Mass spectrum [m/z (EI)]: 460 (M+), 228 (M+
- C10H4N2OS2). UV-vis [(abs) CH2Cl2, nm; λmax (ꢀ)]: 332 (15053),
536 (3508).
Cp2Ti{SOC10H4N2S} (20). To a DMF (5 mL) solution of Cp2TiS5
(0.030 g, 0.100 mmol) was added 1-(quinoxalin-2-yl)-2-bromoethanone
(0.075 g, 0.300 mmol). The reaction mixture was heated at 90 °C for
2 h to give a purple solution. The DMF was removed, and the solid
was washed with three 20 mL portions each of pentane, diethyl ether,
and CCl4. The black solid was dissolved in CH2Cl2 to a give a purple
solution that was washed with H2O until the CH2Cl2 was orange-red.
The CH2Cl2 was removed in vacuo to give 20 in 42% yield (0.052 g,
0.124 mmol) as an orange solid. 1H NMR (CDCl3): δ 8.17-8.11 (m,
2H, C10H4N2), 7.86-7.79 (m, 2H, C10H4N2), 6.62 (s, 10H, 2C5H5). High-
resolution mass spectra (EI): Calcd for C20H14OS2N248Ti, m/z 410.002 72;
found, m/z 410.003 59. UV-vis [(abs) CH2Cl2, nm; λmax (ꢀ)]: 328
(8320), 429 (1840), 482 (sh 1000), 562 (sh 340).
dppePd{SOC10H4N2S} (21). To a DMF solution (5 mL) of
dppePdS4 (0.126 g, 0.200 mmol) was added 1-(quinoxalin-2-yl)-2-
bromoethanone (0.151 g, 0.600 mmol), and the reaction mixture was
heated at 90 °C in an oil bath for 30 min to give a violet solution. The
DMF was removed under vacuo, and the solid was dissolved in
dichloromethane and washed with water. The dichloromethane was
removed in vacuo, and the solid was chromatographed in air on a 1 ×
20 cm alumina column. 21 was isolated as a red solid in 51% yield
(0.075 g, 0.102 mmol) upon eluting the column with 1:2 hexane/
dichloromethane and the removal of the eluent. Crystallization from
CH2Cl2/pentane gave analytically pure material. Anal. Calcd for
C36H28N2OP2S2Pd: C, 58.70; H, 3.80; N, 3.80. Found: C, 58.79; H,
4.10; N, 3.69. 1H NMR (CD2Cl2): δ 8.10-8.09 (m, 1H, C10H4N2),
8.07-8.04 (m, 4H, C6H5P), 7.94-7.92 (m, 1H, C10H4N2), 7.90-7.88
(m, 1H, C8H5N2), 7.87-7.81 (m, 4H, C6H5P), 7.62-7.60 (m, 1H,
C8H5N2), 7.59-7.50 (m, 12H, C6H5P), 2.73-2.42 (m, 4H, PC2H2).
31P{1H} NMR (CD2Cl2): 58.86 (d, JP-P ) 22 Hz), 49.19 (d, JP-P ) 22
Hz). Mass spectrum [m/z (FAB)]: 737 (M+), 504 (M+ - C10H4OS2N2).
Synthetic Procedures. Cp2Mo{S2C10H4N2S} (9). To a DMF
solution (3 mL) of Cp2Mo{S2C2(2-quinoxaline)(H)} (0.050 g, 0.112
mmol) was added S8 (0.0070 g, 0.027 mmol) and 54% HBF4 etherate
(0.1 mL). The reaction was heated for 12 h at 90 °C. The purple
solution was cooled, and NEt3 was added dropwise until the solution
became red. The DMF was removed in vacuo, and the solid was
chromatographed in air on a 2 × 15 cm alumina column. The product,
9, eluted with 1:4 pentane/dichloromethane and was obtained as a red
solid in 67% yield (0.036 g, 0.082 mmol) upon the removal of the
eluent. Anal. Calcd for C20H14N2S3Mo: C, 50.63; H, 2.95; N, 5.91.
Found: C, 50.51; H, 3.24; N, 5.69. 1H NMR (CD2Cl2): δ 8.00 (m,
1H, C8H4N2), 7.63 (m, 1H, C8H4N2), 7.23 (m, 1H, C8H5N2), 7.15 (m,
1H, C6H4), 5.43 (s, 10H, C5H5). Mass spectrum [m/z (EI)]: 476 (M+),
228 (M+ - C10H4N2S3). UV-vis [(abs) CH2Cl2, nm; λmax (ꢀ)]: 334
(13 825), 371 (sh) (6017), 532 (3541).
dppePd{S2C10H4N2S} (10). To a DMF solution (3 mL) of dppePd-
{S2C2(2-quinoxaline)(H)} (0.066 g, 0.100 mmol) was added S8 (0.0080
g, 0.031 mmol) and 54% HBF4 etherate (0.1 mL). The solution was
heated to 90 °C for 24 h. The DMF was removed under vacuum, and
the solid was dissolved in dichloromethane and washed with water.
The dichloromethane was removed in vacuo, and the solid was
chromatographed in air on a 1 × 20 cm alumina column. The column
was eluted with 1:2 hexane/dichloromethane, and 10 was isolated as a
red solid in 48% yield (0.036 g, 0.048 mmol) upon the removal of the
eluent. Anal. Calcd for C36H28N2P2S3Pd: C, 57.45; H, 3.72; N, 3.72.
Found: C, 57.30; H, 3.74; N, 3.39. 1H NMR (CDCl3): δ 8.17-8.15
(m, 1H, C10H4N2), 7.96-7.93 (m, 1H, C10H4N2), 7.90-7.84 (m, 1H,
C8H5N2), 7.83-7.76 (m, 8H, C6H5P), 7.60-7.57 (m, 1H, C8H5N2),
7.55-7.41 (m, 12H, C6H5P), 2.63-2.47 (m, 4H, PC2H2). 31P{1H}
NMR (CDCl3): 55.47 (d, JP-P ) 27 Hz), 53.86 (d, JP-P ) 27 Hz).
Mass spectrum [m/z (FAB)]: 753 (M+), 504 (M+ - C10H4S3N2). UV-
vis [(abs) CH2Cl2, nm; λmax (ꢀ)]: 326 (10280), 376 (6820), 476 (5610).
Cp2Mo{S2C5H3NS}‚0.5CH2Cl2 (11, 12). To a DMF solution (3
mL) of Cp2Mo{S2C2(3-pyridine)(H)} (0.058 g, 0.148 mmol) was added
S8 (0.010 g, 0.04 mmol) and 54% HBF4 etherate (0.1 mL). The solution
was heated to 90 °C for 12 h. To the cooled red solution was added
several drops of NEt3. The solvent was removed in vacuo, and the
solid was chromatographed in air on a 1 × 20 cm alumina column.
The column was eluted with 1:4 pentane/dichloromethane to yield 12
in 24% yield (0.016 g, 0.035 mmol) upon the removal of the eluent.
The column was then eluted with dichloromethane to yield 11 in 15%
yield (0.010 g, 0.022 mmol) upon the removal of the eluent. Both
1
compounds are red crystalline solids that consistently included a /2
molecule of CH2Cl2 as determined by 1H NMR and elemental analysis.

2408 Inorganic Chemistry, Vol. 36, No. 11, 1997
Kaiwar et al.
UV-vis [(abs) CH2Cl2, nm; λmax (ꢀ)]: 332 (30 590), 358 sh (9380),
370 sh (6470), 518 (5420).
lifetimes. The procedure provided lifetimes, fractional photon contribu-
tions, and ø2 for the least-squares fit.
dppePt{SOC10H4N2S} (22). This was prepared as described for
21 by replacing dppePdS4 with dppePtS4 (0.075 g, 0.100 mmol) and
using 1-(quinoxalin-2-yl)-2-bromoethanone (0.075 g, 0.300 mmol).
Complex 22 was isolated in 46% yield (0.038 g, 0.051 mmol) as a red
solid. Anal. Calcd for C36H28N2OP2S2Pt: C, 52.36; H, 3.39; N, 3.39.
Found: C, 52.47; H, 3.70; N, 3.22. 1H NMR (CD2Cl2): δ 8.11-8.10
(m, 1H, C10H4N2), 8.09-8.05 (m, 4H, C6H5P), 7.97-7.95 (m, 1H,
C10H4N2), 7.88-7.85 (m, 1H, C8H5N2), 7.86-7.81 (m, 4H, C6H5P),
7.65-7.62 (m, 1H, C8H5N2), 7.58-7.50 (m, 12H, C6H5P), 2.63-2.39
(m, 4H, PC2H2). 31P{1H} NMR (CD2Cl2): 42.31 (d with platinum
satellites, JP-P ) 12 Hz, JP-Pt ) 2170), 34.17 (d with platinum satellites,
JP-P ) 12 Hz, JP-Pt ) 2110). Mass spectrum [m/z (FAB)]: 826 (M+),
597 (M+ - C10H4N2OS2). UV-vis [(abs) CH2Cl2, nm; λmax (ꢀ)]: 327
(32 700), 357 sh (9410), 370 sh (8150), 501 (6270).
Results and Discussion
It was found that the 2,3-disulfidothienoquinoxaline (DSTQ)
complexes, 9 and 10, could be prepared in two steps from
1-(quinoxalin-2-yl)-2-bromoethanone, 1 (eq 2). The metallo-
Structural Determination of Cp2Mo{S2C10H4N2S} (9). Crystal,
data collection, and refinement parameters are given in Table 1. The
systematic absences in the diffraction data are uniquely consistent for
the reported space group. The structure was solved using direct
methods, completed by subsequent difference Fourier syntheses, and
refined by full-matrix least-squares procedures. Semi-empirical absorp-
tion corrections were not required because of the <10% variation in
the integrated ψ-scan intensities. All non-hydrogen atoms were refined
with anisotropic displacement coefficients. Hydrogen atoms were
treated as idealized contributions.
1,2-enedithiolates, 4 and 5, are generated in the first step. The
synthesis of 4 and 5 is a nonredox process that is similar to the
synthesis of organic-1,4-dithiins from R-substituted ketones and
dimercaptanes (eq 3).24 The details of the synthesis of 4 and 5
All software and sources of the scattering factors are contained in
the SHELXTL 5.3 program library.22
Structural Determination of Cp2Mo{SOC10H4N2S} (19). Crystal-
lographic data are collected in Table 1. Crystals were photographically
characterized and determined to belong to the orthorhombic crystal
system. Systematic absences in the diffraction data uniquely determined
the space group. Azimuthal scans indicated that no correction for
absorbance was required; Tmax/Tmin < 1.1. The structure was solved
by direct methods, completed from difference Fourier maps, and refined
with anisotropic thermal parameters for all non-hydrogen atoms except
those associated with the Cp rings to conserved data. Hydrogen atom
contributions were idealized. All computations used SHELXTL 5.3
software.22 Attempts to solve the structure as a racemic twin did not
improve the refinement.
Luminescence Measurements of 22. Room-temperature excitation
and emission spectra were acquired with a SLM AB2 fluorescence
spectrometer. Emission spectra were corrected for instrumental
response using factors supplied by the manufacturer. Luminescence
measurements were made on 10-5 M solutions of 22 (see eq 6) that
were deoxygenated by three freeze-pump-thaw N2-backfill cycles in
a fluorescence cell equipped with a reservoir and a Teflon valve.
Quantum yields, φs, were calculated relative to Zn(tpp) {φstd ) 0.04}23
(tpp ) tetraphenylporphyrinato) under Ar using eq 1, where F is the
have been described elsewhere.14,15 In the second step (eq 2),
complexes 4 and 5 were treated with S8 under acidic conditions
to produce the disulfidothienoquinoxaline complexes 9 and 10.
These complexes are air stable in solution and were purified
by column chromatography.
The formation of the DSTQ complexes requires a four-
electron oxidation of the 1,2-enedithiolate complex that is
accompanied by the loss of two protons. The electrons are
transferred to sulfur generating both the thiolate of the thiophene
and H2S. This reaction is similar to the four-electron sulfur
oxidation of 1,4-dienes and styrenes that produces thiophenes
and benzothiophenes, respectively (eqs 4 and 5).25 Since the
sulfur oxidation of 4 and 5 did not involve an oxidation state
change of the metal or a change in the number of metal
heteroatom bonds, these reactions can be classified using the
degree of oxidation state method (DOX).25a,b The oxidation of
FsAstdηs2φstd
φs )
(1)
2
FstdAsηstd
(24) (a) Caputo, R.; Ferreri, C.; Palumbo, G. Synthesis 1991, 223-4. (b)
Caputo, R.; Ferreri, C.; Palumbo, G. Tetrahedron 1986, 42, 2369-
76. (c) Wood, W. In Trends in the Chemistry of 1,3-Dithioacetal,
Organosulfur Chemistry, Synthetic Aspects Page, P., Ed.; Academic
Press: San Diego, CA, 1995; pp 133-224.
integrated luminescence, A is the absorbance at the excitation wave-
length, and η is the refractive index of the solvent. The subscripts “s”
and “std” refer to the sample and the standard, Zn(tpp), respectively.
The lifetimes of 22 were determined with an ISS K2 digital
frequency-domain spectrofluorometer. The excitation source was a 300
W Xenon lamp, and the bandpass of the excitation monochromator
was 16 nm. Sample and reference solutions were contained in 1 cm
quartz cells at room temperature. A scattering solution of glycogen in
Milli-Q water was used as the reference for 22. Single channel
detection at 90° was employed, with longpass filters used to block the
excitation line and Raman scatter from the sample. Lifetimes were
determined from the frequency dependence of the signal phase shifts
and demodulation, relative to the reference, using the ISS least-squares
analysis software. The minimization procedure assumed discrete
(25) (a) Klemm, L. H. J. Heterocycl. Chem. 1996, 33, 569-74. (b) Klemm,
L. H. J. Heterocycl. Chem. 1995, 32, 1509-12. (c) Gronowitz, S.
The Chemistry of Heterocyclic Compounds; Thiophene and its
DeriVatiVes; Gronowitz, S., Ed.; Interscience Publication, John Wiley
and Sons: New York, 1960; Vol. 44; Part 1, pp 4-10 and references
found within. (d) Broun, A. S.; Voronkov, G.; Shlyakhter, R. A. Chem.
Abstr. 1949, 43, 5392. (e) Arbuzov, B. A.; Kqtajev, E. G. Dokl. Akad.
Nauk. SSSR 1954, 96, 983-5. (f) Klemm, L. H.; Louris, J. N.; Boisvert,
W.; Higgins, C.; Muchiri, D. R. J. Heterocycl. Chem. 1985, 22, 1249-
52. (g) Klemm, L. H.; Pou, S.; Detlefsen, W. D.; Higgins, C.;
Lawrence, R. F. J. Heterocycl. Chem. 1984, 21, 1293-6. (h) Klemm,
L. H.; Karchesy, J. J.; McCoy, D. R. Phosphorus Sulfur 1979, 7, 9-22.
(i) Klemm, L. H.; Karchesy, J. J. J. Heterocycl. Chem. 1978, 15, 561-
3. (j) Klemm, L. H.; Karchesy, J. J.; Ross, R. J. Heterocycl. Chem.
1978, 15, 773-5. (k) Klemm, L. H.; Karchesy, J. J J. Heterocycl.
Chem 1978, 5, 281-4. (l) Klemm, L. H.; McCoy, D. R.; Klopfenstein,
C. E. J. Heterocycl. Chem. 1971, 8, 383-89. (m) Klemm, L. H.;
McCoy, D. R. J. Heterocycl. Chem. 1969, 6, 735.
(22) (a) Gabe, E. J.; Le Page, Y.; Charland, J. P.; Lee, F. L.; White, P. S.
J. Appl. Crystallogr. 1989, 22, 384. (b) Sheldrick, G. M. Acta
Crystallogr. 1990, A46, 467.
(23) Harriman, A. J. Chem. Soc., Faraday Trans. 1 1980, 76, 1978-85.

Metallo Sulfidothienoquinoxaline Complexes
Inorganic Chemistry, Vol. 36, No. 11, 1997 2409
radical.25,26 This does assume that 13 and 14 are tolerant of
the reaction conditions, which we have shown to be the case in
separate experiments. The relatively high yields of the DSTQ
derivatives are also consistent with the susceptibility of the
3-position of a 2-substituted quinoxaline to radical attack.3,26b
In addition to the DSTQ and DSTP derivatives, the 2-sulfido-
3-oxidothienoquinoxaline (SOTQ) complexes, 19-22, were
prepared from the reactions of 1-(quinoxalin-2-yl)-2-bromo-
ethanone with the respective polysulfido complexes (eq 9). Like
4 and 5 has a ∆(DOX) ) 2 consistent with a formal four-
electron oxidation. The ∆(DOX) can be calculated by summing
the number of carbon heteroatom and carbon-carbon multiple
bonds in the starting materials and products. Using this method
the 1,2-dithiolate ligand has a DOX ) 12 (8 carbon-heteroatom
bonds + 4 carbon-carbon multiple bonds) while the DSTQ
ligand has a DOX ) 14 (10 carbon-heteroatom bonds + 4
carbon-carbon multiple bonds).
The S8 oxidation, eq 2, can be extended to the corresponding
3-pyridyl-substituted complex, 6 (eq 6). The 2,3-disulfi-
the corresponding DSTQ and DSTP derivatives, these com-
plexes were air stable and, with the exception of 20, were
purified by column chromatography.
dothienopyridine (DTTP) complexes, 11 and 12, were the results
of oxidation at the 2- and 4-positions of pyridinium, respectively.
Attempts to extend this reaction to the corresponding 2-pyridyl,
7, 4-pyridyl, 8 (eqs 7 and 8), and several phenyl-substituted
The conversion of the R-bromo ketone, 1, to the correspond-
ing metal derivatives of SOTQ is also a four-electron oxidation
that is accompanied by the loss of three protons and a bromide.
In these reactions, two electrons are again required to generate
the thiolate of the thiophene ring. The additional electrons and
two protons are accommodated by the reduction of 1, added in
excess. The product of this reduction, 1-(quinoxalin-2-yl)-2-
ethanone, 23, could be isolated from the reaction mixture.21b
The reduction of 1, rather than the reduction of sulfur generated
in these reactions, likely arises from the relative solubilities of
these possible oxidants in DMF, the reaction solvent. Decreas-
ing the moles of 1 lowers the yield of the SOTQ derivatives.
Like the reactions shown in eqs 2 and 4-8, the conversion
of 1 to 19-22 has a ∆(DOX) ) 2 consistent with a formal
four-electron oxidation.25a,b Summing the number of carbon
heteroatom and carbon-carbon multiple bonds, 1 has a DOX
) 12 while the SOTQ ligand of the products, 19-22, has a
DOX ) 14.
Given the reactivity of the quinoxaline-substituted metallo-
1,2-enedithiolate complexes (eq 2), a 1-sulfido-2-oxido deriva-
tive, 24, may be an intermediate in the the synthesis of 19-22
(Scheme 1). We would envision such a complex resulting from
an attack of the R-bromo ketone by a metal sulfido or
polysulfido complex. The reaction of 24 with sulfur and 1 equiv
of 1 (an electron acceptor) would generate the observed
products. Attempts to isolate 24 (on Cp2Mo) by limiting the
amount of 1 in the reaction mixture accompanied by the addition
of PPh3 as a sulfur scavenger were unsuccessful and resulted
in reduced yields of the SOTQ derivative.
1,2-enedithiolates (not shown) of Cp2Mo14 resulted in yields
of the thiophene-containing products that were e5%. In these
reactions (eqs 7 and 8) the starting material was consumed, over
24 h, and Cp2MoS4 was generated as the major metal-containing
product. No pyridine-containing compounds, other than the
small amounts of 13 and 14, were tolerant of neutralization and
alumina chromatography. Of these complexes, only the 2,3-
pyridyl derivative, 13 (eq 6), could be isolated in sufficient
quantity and purity to be properly characterized.
Consistent with studies directed at the synthesis of thienopy-
ridines and thienoquinolines where a sulfur radical is thought
to be involved in the heterocycle oxidation,25l,m the generation
of thiophenes from metallo-1,2-enedithiolates is dependent upon
the site of heterocycle oxidation (eqs 6-8). Since the 2- and
4-positions of pyridinium are more susceptible to nucleophillic
and radical attack than the 3-position, the yields of 13 and 14,
relative to the combined yield of 11 and 12, support attack of
the heterocycle by either a sulfur nucleophile or a sulfur-centered
(26) (a) Barnes, R. A.; Brody, F.; Ruby, P. R. In The Chemistry of
Heterocyclic Compounds; Pyridines; Klingsberg, E., Ed.; Interscience
Publishers, Inc.: New York, 1960; Vol. 1; pp 1-29. (b) Simpson, J.
C. E. In The Chemistry of Heterocyclic Compounds; Condensed
Pyridines and Pyrazines Rings; Weissberger, A., Ed.; Interscience
Publishers, Inc.: New York, 1953; pp 201-362.

2410 Inorganic Chemistry, Vol. 36, No. 11, 1997
Kaiwar et al.
Scheme 1
Figure 1. ORTEP drawing of 9 with the thermal ellipsoids drawn at
50% probability. Selected bond lengths (Å) and angles (deg) are as
follows: Mo-S(1), 2.4729(10); Mo-S(3), 2.4821(9); S(1)-C(11),
1.726(3); S(2)-C(11), 1.763(3); C(11)-C(12), 1.363(5); C(12)-C(14),
1.431(4); C(11)-S(3), 1.764(4); C(13)-S(2), 1.746(3); C(13)-C(14),
1.445(4); S(1)-Mo-S(3), 83.61(3); Mo-S(1)-C(11), 104.05(11);
Mo-S(3)-C(12), 104.09(11); S(1)-C(11)-C(12), 125.0(2); S(3)-
C(12)-C(11), 123.0(2); S(1)-C(11)-S(2), 120.4(2).
Table 1. Summary of X-ray Crystal Structure Data for Complexes
9 and 19
complex
9
19
formula
fw
cryst system
space group
a (Å)
b (Å)
c (Å)
C20H14MoN2S3
474.45
monoclinic
P21/c
10.766(1)
14.385(1)
11.983(1)
90
107.848(5)
90
C21H16Cl2MoN2OS2
543.32
orthorhombic
P21212
10.669(4)
19.797(3)
9.905(2)
90
90
90
2092.0(9)
4
1.726
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
Figure 2. ORTEP drawing of 19 with the thermal ellipsoids drawn at
50% probability. Selected bond lengths (Å) and angles (deg) are as
follows: Mo-O(1), 2.088(9); Mo-S(1), 2.468(5); S(1)-C(11), 1.75-
(2); O(1)-C(12), 1.29(2); C(11)-C(12), 1.28(2); C(12)-C(14), 1.45-
(2); C(11)-S(2), 1.77(2); C(13)-S(2), 1.74(2); C(13)-C(14), 1.47(2);
O(1)-Mo-S(1), 81.0(3); Mo-S(1)-C(11), 94.3(7); Mo-O(1)-C(12),
117.4(13); S(1)-C(11)-C(12), 120.2(2); S(1)-C(11)-S(2), 122.6(13).
1766.6(2)
4
1.784
F
calc (g/cm-3
T (K)
)
298
298
diffactometer
geometry
Siemens P4
4-circle goniometer
Mo KR
1.035
0.0792
0.0331
Siemens P4
4-circle goniometer
Mo KR
1.096
0.0930
0.0438
radiation, λ
(16)°.14 Similar differences in bond angles were seen in
vanadium thiophenol complexes27 and the platinum 1-enol-2-
selenate complex (PPh3)2Pt[OSeC2{Me}{C(O)Me}].28 The
thiophene rings in 9 and 19, while essentially planar, were
distorted in that the C(11)dC(12) bond distances at 1.363(5)
and 1.28(2) Å, respectively, were considerably shorter than both
the C(12)-C(13) and the C(13)-C(14) bonds that were both
≈1.45 Å.
abs coeff (mm-1
)
a
wR2
R1
a
GOFa
1.042
1.142
a Residuals R1 ) ∑[|Fo| - |Fc|]/∑|Fo|, wR2 ) {[∑w(Fo - Fc2)2}/
2
2
2
∑[w(Fo )2]}1/2, where w-1 ) [σ2(Fo ) + (0.0422P)2 + 3.865P] and P
2
2
) (max(Fo ,0) + 2Fc2)/3, w-1 ) [σ2(Fo ) + (0.1215P)2 + 0.49698P],
and GOF ) δ ) [∑[w((Fo2 - Fc2)2]/(n - p)]1/2, where n ) number of
reflections and p ) number of parameters.
UV-Visible Spectroscopy and Electronic Transitions. All
of the complexes prepared in this study have an acid-sensitive
band assignable to an intraligand (IL) transition. This transition
was thought to possess considerable thiolate to heterocycle π*
character and was similar to an ILCT transition in complexes
4-8.14,15 In complexes 9 and 19 this band is found at 532 nm
(18 800 cm-1) and 536 nm (18 660 cm-1), respectively (Figure
3). Upon protonation of the quinoxaline moiety, this band is
red-shifted by 3810 and 3390 cm-1, respectively (Table 2).
Like 9 and 19, the palladium complexes, 10 and 21, have
similar bands at 476 nm (21 010 cm-1) and 518 nm (19 310
cm-1) that are red shifted by 4671 and 3381 cm-1 upon
protonation, respectively. The energy of the IL transition is
nearly equivalent in the palladium complex, 21, and the platinum
complex, 22, supporting the IL assignment. If this transition
had considerable d to d, MLCT, or LMCT character, it would
be substantially more sensitive to the Pt for Pd exchange.29-33
X-ray Crystallographic Results for 9 and 19. Complexes
9 and 19 were the subject of single-crystal X-ray studies, the
results of which are presented in Table 1 and shown in Figures
1 and 2. Both 9 and 19 contain an extended planar thiophene
ligand with no atoms deviating from the least-squares plane by
more than 0.03 Å. In complex 19, the Mo-S and Mo-O bond
distances of 2.464(5) and 2.086(9) Å are best described as single
bonds. The C(11)dC(12) bond in 19 was 1.28(2) Å, while that
of the 2,3-dithiophene complex 9 was 1.363(5) Å and the
metallo-1,2-enedithiolate complex 4 was 1.339(7) Å.14 The
O(1)-C(12) bond of 19 is 1.29(2) Å. The O-Mo-S(1) bond
angle of 81.2(3)° in 19 was not significantly different from the
S-Mo-S bond angle of 83.65(3)° in 9 . However, the Mo-
O-C(12) angle of 116.5(13)° and the Mo-S(1)-C(11) bond
angle of 94.3(7)° of 19 were significantly different from the
Mo-S-C angles found in 9, which were 104.05(11) and
104.09(11)°, and those of 4, which were 105.68(18) and 106.62-
(28) Yamazaki, S.; Deeming, A. J. Polyhedron 1996, 15, 1847-52.
(29) Shupack, S. I.; Billig, E. C.; Williams, R.; Gray, H. B. J. Am. Chem.
Soc. 1964, 86, 4594-602.
(27) Klich, P. R.; Daniher, A. T.; Challen, P. R.; McConville, D. B.;
Youngs, W. J. Inorg. Chem. 1996, 35, 347-56.
(30) Gray, H. B.; Ballhausen, C. J. J. Am. Chem. Soc. 1963, 85, 260-4.

Metallo Sulfidothienoquinoxaline Complexes
Inorganic Chemistry, Vol. 36, No. 11, 1997 2411
Table 2. UV-Visible Absorption Bands of the Neutal and Protonated 2,3-Sulfidothiophene and 2-Sulfido-3-oxidothiophene Complexes
complex
λ
max (ꢀ) neutral complexes
λmax (ꢀ) protonated complexes
9
10
11
12
19
20
21
22
334 (13 830), 371 (sh) (6020), 532 (3540)
326 (10 280), 376 (6820), 476 (5610)
290 (sh, 4870), 358 (3950), 529 (660)
296 (7900), 376 (3110), 531 (820)
332 (15 050), 536 (3510)
328 (8320), 429 (1840), 482 sh (1000), 562 (sh 340)
332 (30 590), 358 sh (9380), 370 sh (6470), 518 (5420)
327 (32 700), 357 sh (9410), 370 sh (8150), 501 (6270)
381 (10 260), 414 (11 840), 681 (5790)
352 (8710), 432 (9980), 612 (7760)
305 (4550), 388 (2910), 490 (sh, 940)
334 (10530), 388 (3520), 532 (3050)
371 (11 930), 404 (11 840), 655 (5790)
344 (6220), 396 (sh 2620), 422 sh (2040), 526 (1440)
360 (15 070), 409 (12 810), 628 (7580)
356 (11 290), 415 (13 790), 614 (8870)
Figure 3. UV-vis absorption spectra of (A) 19 and 19H+ in DMSO
and (B) 9 and 9H+ in DMSO. Solid lines are the absorbance spectra
of the neutral complex, while the dashed lines are the absorbance spectra
of the protonated complexes.
On the basis of its acid sensitivity, the IL transition of 20 is
assigned to a band at 482 nm (20 750 cm-1). This band is red
shifted upon protonation by ≈1740 cm-1. Unlike the molyb-
denum, palladium, and platinum SHTQ derivatives, the IL
transition is not the lowest energy band of the Cp2Ti derivative.
The lowest energy band, at 560 nm, was assigned to a LMCT
transition.18,34
Like 20, the IL transitions of 11 and 12 (found at 358 and
376 nm, respectively) are not the lowest energy bands. These
findings are consistent with those of the 3-pyridyl-substituted
1,2-enedithiolate complex, Cp2Mo{S2C2(3-pyridine)(H)}, 6,14
where the lowest energy band was assigned to a LMCT
transition.
Luminescence Spectra of 22. Excitation of solutions of
dppePt{S2C2(heterocycle)(H)}, where heterocycle ) 2-quinoxa-
line13 and 2- and 4-pyridinium,15 lead to room-temperature
emissions. All of these complexes have as their lowest energy
band an ILCT transition. Consistent with these findings,
excitation of solutions of 22 lead to a broad emission with little
vibronic fine structure (Figure 4). The emission intensity was
linear with concentration, and the excitation profile was identical
to the absorption spectra of 22. The quantum yield and emission
maxima were both solvent sensitive (Table 3). The quantum
yield increased 50 times and the emission maxima red shifted
by ≈2000 cm-1 as the solvent polarity increased from CCl4 to
DMSO. This suggests that the excited states may have some
charge transfer character.
Figure 4. (A) UV-vis absorption spectra of 22 and 22H+ in DMSO.
(B) Air-free emission spectrum of 22 in DMSO. The solid lines are
the absorbance and emission spectra of the neutral complex, while the
dashed line is the absorbance spectra of the protonated complex.
Table 3. Solvent Dependence of the Luminescence Maxima,
Quantum Yield, and Lifetimes of 22
solvent
DMSO
φa
λ (nm)
τ (ns)
0.005
690
5.94 (3)
0.26 (8)
DMF
0.003
681
670
668
663
acetone
CH2Cl2
(CH2Cl)2
0.0009
0.0008
0.0008
5.67 (1)
0.27 (9)
dioxane
toluene
Et2O
0.0005
0.0003
0.0002
0.0001
651
648
611
602
CCl4
Electrochemistry and EPR Measurements. The molyb-
denum DSTQ and SOTQ complexes, 9 and 19, have reversible
electrochemistry with oxidation waves centered at 420 and 378
mV in CH2Cl2, respectively. The protonation of these com-
plexes lead to a positive shift in the E1/2 of ≈ 75 mV for both
complexes. The difference in the E1/2 values for 9 and 19 is
42 mV, a value typical for a thiolate-alkoxide ligand exchange
on a MoIV center.35,36 Complexes 11-13 also have reversible
electrochemistry with oxidation waves that were centered at 260,
272, and 389 mV, respectively. Protonation of the heterocycle
in these complexes shifts the E1/2 by 150-200 mV.
Luminescent lifetime measurements of deaerated solutions
of 22 provided frequency plots that were best fit as a sum of
two exponential decays with one lifetime in the 6 ns range and
one lifetime in the 0.3 ns range (Table 3).
Oxidation of complexes 9, 11, 12, and 19 with I2 (or Br2)
lead to the generation of 26-29, respectively (eqs 10-12).
(31) Werden, B. G.; Billig, E.; Gray, H. B. Inorg. Chem. 1966, 5, 78.
(32) Fackler, J. P., Jr.; Coucouvanis, D. J. Am. Chem. Soc. 1966, 88, 3913-
20.
(33) Bowmaker, G. A.; Boyd, P. D. W.; Campbell, G. K. Inorg. Chem.
1983, 22, 1208-13.
(34) Bolinger, C. M.; Rauchfuss, T. B. Inorg. Chem. 1982, 21, 3947-54.
(35) Roberts, S. A.; Young, C. G.; Kipke, C. A.; Cleland, W. E.;
Yamanouchi, K.; Carducci, M. D.; Enemark, J. H. Inorg. Chem. 1990,
29, 3650-6.
(36) Harlan, E. W.; Berg, J. M.; Holm, R. H. J. Am. Chem. Soc. 1986,
108, 6992-7000.

2412 Inorganic Chemistry, Vol. 36, No. 11, 1997
Kaiwar et al.
heterocycle generating the 2,3-sulfidothiophene ligand. These
reactions (eqs 2 and 5) are reminiscent of the four-electron (∆-
(DOX) ) 2) sulfur oxidation of 1,4-dienes and styrenes that
produce thiophenes and benzothiophenes, respectively (eqs 4
and 5). The reaction of the heterocyclic substituted 1,2-
enedithiolate with sulfur is sensitive to the position of the
heterocycle that is oxidized in the reaction. Product yields
suffered when the site of oxidation is not activated toward
radical attack. As such, the disulfidothiophene derivatives were
obtained in the best yields when the site of oxidation was either
two or four to the nitrogen of the protonated heterocycle. These
findings are consistent with studies directed at the synthesis of
thienopyridines and thienoquinolines that require attack of the
heterocycle by a radical center.25l,m
Many of the properties of the 2,3-disulfidothienoquinoxaline,
2,3-disulfidothienopyridine, and 2-sulfido-3-oxidothienoqui-
noxaline complexes were similar to those of 2,3-sulfidoqui-
noxaline complexes.11,38 The synthetic methods outlined in this
paper should allow a range of these complexes to be prepared
that include a variety of heterocyclic groups that may share these
general properties. Thus, the properties of these complexes
could be fine tuned, a particularly useful feature in the design
and synthesis of new lumiphores.10-13,15,38a The intraligand
transition in 22 serves as a luminescent chromophore, and 22
is a member of an emerging class of platinum thiolates that are
emissive at room temperature in solution.
In addition to serving as a chromophore, the 2-sulfido-3-
oxidothienoquinoxaline ligand, along with the 2,3-sulfidothieno-
quinoxaline and 2,3-sulfidothienopyridine ligands, stabilize the
radical generated by the oxidation of the corresponding mo-
lybdenum complexes. The small molybdenum hyperfine clearly
demonstrates that the semi-occupied molecular orbital in these
oxidized complexes is localized primary on the ligand and not
the metal center.
Complexes 26-29 were stable in deaerated solutions for several
hours and could be reduced to 9, 11, 12, and 19, respectively,
with Cp2Co in an overall yield for the two reaction steps of
g90%.
The room-temperature EPR spectra of 26-29 in CH2Cl2
solution were characterized by g values at ≈ 1.98 and 95/97Mo
hyperfines of e 8.5 G. While similar hyperfine couplings to
95/97Mo were observed for [Cp2Mo{S2C2(heterocycle)(C(O)-
Me)}]+ (heterocycle ) pterin and quinoxaline),1 these values
were much smaller than the 36 G hyperfine observed for [Cp2-
MoCl3]+.37 The small 95/97Mo hyperfine suggests that the
electron in 26-29 is substantially delocalized throughout the
ligand. The small hyperfine couplings to molybdenum supports
the description of 26-29 not as MoV complexes but as ligand-
centered radical cations. The lack of 14N hyperfine suggests
that the semi-occupied molecular orbital is primarily dithiolato-
thiophene- or thiolato-hydroxo-thiophene-based.
Acknowledgment. We are indebted to the donors of the
Petroleum Research Fund, administered by the American
Chemical Society (Grant No. 28499-G3), and the Exxon
Education Foundation for supporting this work.
Supporting Information Available: Tables listing data collection
details, crystallographic data, positional parameters, anisotropic thermal
parameters, and bond lengths and angles for 9 and 19 (13 pages).
Ordering information is given on any current masthead page.
Conclusion
IC961428V
Metallo-1,2-enedithiolates of the type {MS2C2(R)(H)}, where
R ) heterocycle, are susceptible to chemical oxidation by sulfur.
The product from this oxidation was trapped by an appended
(38) (a) Cummings, S. D.; Eisenberg, R. Inorg. Chem. 1995 34, 2007-14.
(b) Theriot, L. J.; Ganguli, K. K.; Kavarnos, S.; Bernal, I. J. Inorg.
Nucl. Chem. 1969, 31, 3133-40. (c) Boyde, S.; Garner, C. D. J. Chem.
Soc., Dalton Trans. 1991, 713-16.
(37) Cooper, R. L.; Green, M. L. H. J. Chem. Soc. A 1967, 1155-60.