Reactions of dithiolate ligands in mononuclear complexes of rhenium(V)

Article abstract of DOI:10.1021/ja020125z

The thermal reactions of the Re(V) dithiolate complex Cp′ReCl₂(SCH₂CH₂S), 1 (where Cp′ = EtMe₄C₅), and related derivatives have been studied. When 1 is heated in toluene in a sealed evacuated tube at 100°C, a dehydrogenation reaction occurs to form a new rhenium complex with a dithiolene ligand, Cp′ReCl₂(SCHCHS), 6, in ca. 40% yield. The structure of 6 has been confirmed by an X-ray diffraction study. Under the thermal conditions studied, 1 also undergoes an olefin extrusion reaction. Free ethene is detected in the NMR spectrum of the products, and insoluble rhenium products are also formed. When 1 is reacted with excess ethene under mild conditions, a new organic product, 1,4-dithiane, is formed. Complex 1 is also found to react with oxidants, such as O₂ and S₈, under mild conditions to form the dehydrogenation product 6. Kinetic studies of the thermal reaction of 1 and related derivatives have been completed, and possible mechanisms for the thermally induced dehydrogenation reaction are discussed.

Full text of DOI:10.1021/ja020125z

Published on Web 07/26/2002
Reactions of Dithiolate Ligands in Mononuclear Complexes of
Rhenium(V)
J. A. Kanney, B. C. Noll, and M. Rakowski DuBois*
Contribution from the Department of Chemistry and Biochemistry, UniVersity of Colorado,
Boulder, Colorado 80309
Received January 24, 2002
Abstract: The thermal reactions of the Re(V) dithiolate complex Cp′ReCl2(SCH2CH2S), 1 (where Cp′ )
EtMe4C5), and related derivatives have been studied. When 1 is heated in toluene in a sealed evacuated
tube at 100 °C, a dehydrogenation reaction occurs to form a new rhenium complex with a dithiolene ligand,
Cp′ReCl2(SCHCHS), 6, in ca. 40% yield. The structure of 6 has been confirmed by an X-ray diffraction
study. Under the thermal conditions studied, 1 also undergoes an olefin extrusion reaction. Free ethene is
detected in the NMR spectrum of the products, and insoluble rhenium products are also formed. When 1
is reacted with excess ethene under mild conditions, a new organic product, 1,4-dithiane, is formed. Complex
1 is also found to react with oxidants, such as O2 and S8, under mild conditions to form the dehydrogenation
product 6. Kinetic studies of the thermal reaction of 1 and related derivatives have been completed, and
possible mechanisms for the thermally induced dehydrogenation reaction are discussed.
e.g., eq 1.6 These reactions are related to the asymmetric cis-
Introduction
Metal dithiolate and metal sulfide complexes are related in
some systems by the reversible addition and elimination of
alkenes at the sulfur sites. For example, thermodynamic data
have been reported for the reversible reactions of olefins with
the sulfido ligands in ReS4-,1 and kinetic and thermodynamic
studies of alkene addition and elimination have been reported
for a series of dinuclear molybdenum complexes with µ-sulfur
ligands.2 Alkene interactions with nickel dithiolene complexes
have been known for many years,3 and reversible olefin binding
as a function of redox state has been examined recently.4,5
dihydroxylation of olefins catalyzed by derivatives of osmium
tetroxide,14 which has been extensively studied in both experi-
mental and theoretical approaches.15,16
In this paper we report the syntheses and characterizations
of new mononuclear Re(V) derivatives with 1,2-dithiolate
ligands and a study of their thermal reactivity. Complexes of
the formula Cp′ReCl2(dithiolate) are found to undergo reversible
alkene eliminations; but rather unexpectedly, a novel C-H
activation process within the dithiolate ligand is also observed,
and dehydrogenated complexes of the formula Cp′ReCl2-
(dithiolene) have been isolated and characterized. In addition,
1 reacts with alkenes and alkynes to undergo dithiolate ligand
displacement forming uncoordinated cyclic bis(thioether) de-
rivatives.
The addition of olefins to the terminal oxo ligands of a metal
complex and the reverse alkene elimination from metal diolate
complexes have also been observed for a number of high-valent
metal complexes6-13 and studied mechanistically in some cases,
(1) (a) Goodman, J. T.; Rauchfuss, T. B. J. Am. Chem. Soc. 1999, 121, 5017.
(b) Goodman, J. T.; Inomata, S.; Rauchfuss, T. B. J. Am. Chem. Soc. 1996,
118, 11674.
(2) Koval, C. R.; Lopez, L. L.; Kaul, B. B.; Renshaw, S.; Green, K.; Rakowski
DuBois, M. Organometallics 1995, 14, 3440-3447.
(3) (a) Wing, R. M.; Tustin, G. C.; Okamura, W. H. J. Am. Chem Soc. 1970,
92, 1935. (b) Schrauzer, G. N.; Mayweg, V. P. J. Am. Chem. Soc. 1965,
87, 1483.
(4) Wang, K.; Stiefel, E. I. Science 2001, 291, 106.
(5) Geiger, W. E.; Barriere, F.; LeSuer, R. J.; Trupia, S. Inorg. Chem. 2001,
40, 2472.
(6) (a) Gable, K. P.; Phan, T. N. J. Am. Chem. Soc. 1994, 116, 833-839. (b)
Gable, K. P.; Juliette, J. J. J. J. Am. Chem. Soc. 1995, 117, 955-962. (c)
Gable, K. P.; Juliette, J. J. J. J. Am. Chem. Soc. 1996, 118, 2625-2633.
(7) (a) Herrmann, W. A.; Marz, D.; Herdtweck, E.; Schafer, A.; Wagner, W.;
Kneuper, H. J. Angew. Chem., Int. Ed. Engl. 1987, 26, 462-464. (b)
Hermann, W. A.; Marz, D. W.; Herdtweck, E. J. Organomet. Chem. 1990,
394, 285.
(8) Thomas, J. A.; Davison, A. Inorg. Chim. Acta 1991, 190, 231-235.
(9) Gable, K. P.; AbuBaker, A.; Zientara, K.; Wainwright, A. M. Organome-
tallics 1999, 18, 173-179.
(10) Zhu, Z.; Al-Ajlouni, A. M.; Espenson, J. H. Inorg. Chem. 1996, 35, 1408.
(11) Cook, G. K.; Andrews, M. A. J. Am. Chem. Soc. 1996, 118, 9448-9449.
(12) Shrock, R. R.; Pedersen, S. F.; Churchill, M. R.; Ziller, J. W. Organome-
tallics 1984, 3, 1574-1583.
Results and Discussion
Syntheses and Characterization of 1,2-Alkanedithiolate
Derivatives of Re(V). The reaction of Cp′ReCl4 with 1 equiv
(13) Sharpless, K. P.; Umbreit, M. A.; Nieh, M. T.; Flood, T. C. J. Am. Chem.
Soc. 1972, 94, 6538-6540.
(14) Kolb, H. C.; VanNieuwenhze, M. S.; Sharpless, K. B. Chem. ReV. 1994,
94, 2483.
(15) Delmonte, A. J.; Haller, J.; Houk, K. N.; Sharpless, K. B.; Singleton, D.
A.; Strassner, T.; Thomas, A. A. J. Am. Chem. Soc. 1997, 119, 9907-
9908.
(16) (a) Pidun, U.; Boehme, C.; Frenking, G. Angew. Chem., Int. Ed. Engl. 1996,
35, 2817. (b) Dapprich, S.; Ujaque, G.; Maseras, F.; Lledos, A.; Musaev,
D. B.; Morokuma, K. J. Am. Chem. Soc. 1996, 118, 11660. (c) Torrent,
M.; Deng, L.; Durna, M.; Sola, N.; Ziegler, T. Organometallics 1997, 16,
13.
9
9878
J. AM. CHEM. SOC. 2002, 124, 9878-9886
10.1021/ja020125z CCC: $22.00 © 2002 American Chemical Society

Dithiolate Ligands in Mononuclear Re(V) Complexes
A R T I C L E S
Figure 2. Perspective drawing and numbering scheme for Cp′ReCl2-
(SCHCHS), 6. Thermal ellipsoids are shown at the 50% probability level.
Figure 1. Perspective drawing and numbering scheme for Cp′ReCl2(SCH2-
CH2S), 1. Thermal ellipsoids are shown at the 50% probability level.
Table 1. Bond Distances (Å) and Angles (deg) for
(EtMe4C5)ReCl2(η2-SCH2CH2S), 1
of ethanedithiol in THF proceeded cleanly to form the deep
green product Cp′ReCl2(η2-SC2H4S), 1, eq 2. In the 1H spectrum
Re-S(1)
2.2697 (17)
2.4192 (18)
1.835 (8)
2.309 (7)
2.278 (7)
Re-S(2)
2.3102 (19)
2.4022 (17)
1.835 (8)
2.252 (7)
2.371 (7)
1.443 (9)
1.432 (10)
1.448 (9)
Re-Cl(1)
S(1)-C(12)
Re-C(1)
Re-C(3)
Re-C(5)
C(2)-C(3)
C(4)-C(5)
Re-Cl(2)
S(2)-C(13)
Re-C(2)
Re-C(4)
2.385 (7)
1.442 (10)
1.426 (10)
C(1)-C(2)
C(3)-C(4)
C(5)-C(1)
S(1)-Re-Cl(1)
S(1)-Re-S(2)
Re-S(1)-C(12)
80.24 (7)
84.24 (7)
109.7 (3)
S(2)-Re-Cl(2)
Cl(1)-Re-Cl(2)
Re-S(2)-C(13)
80.39 (7)
80.27 (7)
104.6 (3)
Table 2. Bond Distances (Å) and Angles (deg) for
(EtMe4C5)ReCl2(η2-SCHdCHS), 6
Re-S(1)
2.2884 (9)
2.4186 (9)
1.711 (4)
2.408 (3)
2.255 (3)
2.272 (3)
1.439 (5)
1.448 (5)
Re-S(2)
2.2888 (9)
2.4111 (9)
1.720 (4)
2.401 (3)
2.202 (3)
1.414 (4)
1.447 (4)
1.445 (5)
Re-Cl(1)
S(1)-C(12)
Re-C(1)
Re-C(3)
Re-C(5)
C(2)-C(3)
C(4)-C(5)
Re-Cl(2)
S(2)-C(13)
Re-C(2)
Re-C(4)
C(1)-C(2)
C(3)-C(4)
C(5)-C(1)
of 1 an AA′BB′ pattern for the ethanedithiolate protons was
centered at 4.01 ppm (relative intensity 4), and in the 13C
spectrum the carbons of the chelated ligand were found to be
equivalent with a single resonance at 48.7 ppm. The FAB mass
spectrum showed peaks at m/z 498 and 463, which were
assigned to P+ and P+ - Cl. However in the EI mass spectrum
of analytically pure samples of 1, peaks with m/z ratios that
corresponded to dinuclear formulations, such as [Cp′ReS2]2,
were observed. To confirm the structure of 1, an X-ray
diffraction study was carried out.
S(1)-Re-Cl(2)
S(1)-Re-S(2)
Re-S(1)-C(12)
80.97 (3)
82.59 (4)
107.90 (15)
S(2)-Re-Cl(1)
Cl(1)-Re-Cl(2)
Re-S(2)-C(13)
80.16 (3)
81.88 (3)
108.05 (15)
complexes fall in the range 2.30-2.40 Å.17-19 The S1-Re-
S2 angle is 84.24°, and the other three angles in the piano stool
base are all near 80°. The S-C-C-S dihedral angle in the
dithiolate ligand is 39.9°. In the cyclopentadienyl ring the
carbons trans to S1 show the longest Re-C distances, Re-C4
) 2.371(7) Å and Re-C5 ) 2.385(7) Å, while the other three
carbons have Re-C distances ranging from 2.25 to 2.28 Å. The
C-C distances within the Cp ligand are equivalent within
experimental error. Asymmetric η3,η2 coordination of Cp* rings
has been observed previously in Re(V) derivatives containing
a strong π donor, such as a terminal oxo or imido ligand.20,21
The structural study confirms that 1 is a mononuclear piano
stool complex containing a single chelated ethanedithiolate
ligand as well as two chloride ligands. The dinuclear species
observed in the EI mass spectrum therefore appear to be formed
during the mass spectroscopy experiment via ethylene loss and
dimerization of the resulting fragment. A perspective drawing
of 1 is shown in Figure 2, and selected bond distances and angles
are given in Table 2. The dithiolate ligand is bound asymmetri-
cally with Re-S1 ) 2.2697(17) Å and Re-S2 ) 2.3102(19)
Å. The shorter distance suggests some π-donor properties for
S1, since many reported Re-S distances for Re(V) thiolate
(17) Herberhold, M.; Jin, G. X.; Milius, W. J. Organomet. Chem. 1996, 512,
111. (b) Herberhold, M.; Jin, G. X.; Milius, W. Z. Anorg. Allg. Chem.
1994, 620, 1295.
(18) (a) Lente, G.; Guzei, I. A.; Espenson, J. H. Inorg. Chem. 2000, 39, 1311-
1319. (b) Jacob, J.; Guzei, I. A.; Espenson, J. H. Inorg. Chem. 1999, 38,
3266-3267.
(19) Goodman, J. T.; Rauchfuss, T. B. Angew. Chem., Int. Ed. Engl. 1997, 6,
2083-2084.
9
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A R T I C L E S
Kanney et al.
In these cases the C-C distances within the ring were also
inequivalent. The longer Re-C distances to the η2-portion of
the ring have been attributed to the trans effect of the multiply
bonded oxo or imido group.20 The π-donor thiolate sulfur in 1
appears to exert a similar, but weaker trans effect than oxo or
imido ligands.
well as a competing elimination of olefin from the ligand, as
summarized in eq 3 below. The rhenium product proposed to
The reactions of Cp′ReCl4 with 1,2-butanedithiol and with
2,3-butanedithiol were carried out under similar conditions to
form the corresponding complexes with alkyl-substituted al-
kanedithiolate ligands, Cp′ReCl2(η2-SCH2CH(Et)S), 2, and
Cp′ReCl2(η2-SCH(Me)CH(Me)S), 3. Two diastereomers of 2
1
(in a 70:30 ratio) are observed in the H NMR spectrum, each
showing four inequivalent Cp methyl resonances. The major
isomer is assumed to be that with the ethyl substituent directed
1
away from the Cp′ ligand. In the H NMR spectrum of 3, two
isomers in a 70:30 ratio are also observed, and the major isomer
is assigned to a cis-Me derivative on the basis of the NMR data
for the dithiolate hydrogens. Again the exo isomer is assumed
to be favored. The spectrum of the second isomer shows
inequivalent methyls and hydrogens in the dithiolate ligand and
is therefore assigned as the trans isomer. Other spectroscopic
data for 2 and 3, detailed in the Experimental Section, are
consistent with their simple mononuclear formulations.
result from olefin elimination was not detected in the spectrum.
It either decomposes or reacts in some way to form the observed
insoluble material. Neither molecular hydrogen nor ethane was
observed in the sealed tube reactions.
In a previous report, the reaction of 2 equiv of Li2-
ethanedithiolate with Cp*WCl4 at 0 °C produced [Cp*W(S)3]-
in 82% yield.22 In contrast, we found that 2 equiv of ethanedithi-
ol reacted with Cp′ReCl4 in THF at room temperature to form
Cp′Re(SC2H4S)2, 4, which was isolated as a deep purple solid
and characterized by spectroscopic data. In the 1H NMR
spectrum for 4 the multiplets for the ethanedithiolate protons
centered at 3.22 ppm show a significant upfield shift relative
to those of 1. A related structure Cp*Re(SCRdCRS)2, where
R ) CO2Me, was synthesized previously by the addition of
dimethylacetylene dicarboxylate to a Cp*Re-polysulfide deriva-
tive.17b For comparative purposes, Cp′ReO(η2-SC2H4S), 5, was
Similar dehydrogenation and olefin elimination reactions were
observed for the alkanedithiolate derivatives, 2 and 3, when these
were heated in toluene at 100-110 °C. The products, Cp′ReCl2-
(η2-SCHdC(Et)S), 7, and CpReCl2(η2-SCMedC(Me)S), 8,
were isolated and characterized by spectroscopic techniques.
1
For example, in the H NMR spectrum of 7, a singlet at 8.9
ppm in CDCl3 (relative intensity, 1 H) is assigned to the
ethenedithiolate proton, while in the spectrum of 8, the
alkenedithiolate methyl groups appear as a singlet at 3.01 ppm.
Additional data for these products are included in the Experi-
mental Section. In addition the presence of 1-butene and cis-
and trans-2-butene were observed in the NMR spectra of 7 and
8, respectively, and some insoluble material was formed.
Although the Cp* analogue of 5 has been reported to lose
ethene when heated to 200 °C,7 in our studies no reactions were
observed for Cp′ReO(η2-SC2H4S), 5, or for Cp′Re(η2-SC2H4S)2,
4, in toluene under thermal conditions similar to those reported
above. Similarly, in a recent report, no ethylene extrusion was
observed for the related complex Tp′ReO(η2-SC2H4S).23 In
compounds 1-3, the electron-withdrawing character of the
chloride ligands appears to be important for the dehydrogenation
and elimination reactions to occur under these relatively mild
conditions. The electronic differences between the dichloro
complex 1 and its oxo analogue, 5, are reflected in the
electrochemical data for these two derivatives. Complex 5
undergoes an irreversible oxidation at a carbon electrode at 0.68
V vs Fc in acetonitrile solution and a reversible reduction at
-2.14 V. The high negative reduction potential reflects the
π-donating character of the oxo ligand. In contrast, the cyclic
voltammogram of 1 shows an irreversible reduction at a much
lower potential, -0.82 V, and additional waves are observed
at more negative potentials.
20
also prepared. It was synthesized by the reaction of Cp′ReOCl2
with ethanedithiol in dichloromethane. The Cp* analogue of
this derivative has been reported previously.7
Thermal Reactions of Re(V) 1,2-Dithiolate Complexes.
When 1 was heated to 100-108 °C in dry toluene-d8 under
vacuum in a sealed tube, the deep green color changed to brown,
and a single new rhenium complex, 6, was observed in the NMR
spectrum in yields that ranged from 30 to 50%. In addition, a
singlet at 5.26 ppm was confirmed as the resonance of ethene,
1
and some insoluble material was observed in the tube. The H
NMR spectrum of 6 showed resonances for the Cp′ ligand, but
the multiplets of the ethanedithiolate ligand were absent and a
new singlet (relative intensity ) 2) was observed at 8.4 ppm.
In the 13C NMR spectrum of 6 a new resonance was observed
at 165 ppm in CDCl3. The data suggested the presence of an
ethenedithiolate ligand, and 6 was formulated as Cp′ReCl2(η2-
SC2H2S). The formulation was supported by the mass spectrum
of the complex and confirmed by an X-ray diffraction study
(see below). The thermal reaction of 1 therefore appears to
involve the dehydrogenation of the alkanedithiolate ligand as
X-ray Diffraction Study of Cp′ReCl2(η2-SC2H2S), 6. Single
crystals of the dehydrogenation product, 6, were obtained by
diffusion of hexane into a toluene solution. A perspective
(20) Hermann, W. A.; Herdtweck, E.; Floel, M.; Kulpe, J.; Kusthardt, U.; Okuda,
J. Polyhedron 1987, 6, 1165.
(21) Herrmann, W. A.; Weichselbaumer, G.; Paciello, R. A.; Fischer, R. A.;
Herdtweck, E.; Okuda, J.; Marz, D. W. Organometallics 1990, 9, 489-
496.
(22) Kawaguchi, H.; Yamada, K.; Yang, J. P.; Tatsumi, K. J. Am. Chem. Soc.
1997, 119, 10346-10358.
(23) Tp′ ) tris(3,5-dimethylpyrazolyl)hydridoborate: Gable, K. P.; Chuawong,
P.; Yokochi, A. F. T. Organometallics 2002, 21, 929-933.
9
9880 J. AM. CHEM. SOC. VOL. 124, NO. 33, 2002

Dithiolate Ligands in Mononuclear Re(V) Complexes
A R T I C L E S
Table 3. Kinetic Data for Thermal Reactions of
Cp′ReCl2(SCHRCHR′S)
Table 4. Crystal Data for (EtMe4C5)ReCl2(SCH2CH2S), 1, and
(EtMe4C5)ReCl2(SCHCHS), 6
complex
T (K)
solvent
k (s-1
)
1
6
1
353
358
363
368
373
377
381
381
381
381
toluene-d8
4.89 × 10-7
9.94 × 10-7
1.58 × 10-6
1.88 × 10-6
4.36 × 10-6
6.23 × 10-6
1.37 × 10-5
1.27 × 10-5
1.98 × 10-5
3.71 × 10-6
formula
fw (amu)
cryst syst
unit cell dimens
a (Å)
C13H21Cl2ReS2
498.52
orthorhombic
C13H19Cl2ReS2
496.50
orthorhombic
8.4218(5)
13.4234(7)
13.7910(8)
90
90
90
1559.06(15)
P212121
4
13.5694(15)
14.764(2)
15.469(2)
90
90
90
3099.0(7)
Pbca
8
b (Å)
c (Å)
2
3
1
R (deg)
â (deg)
CD3CN
γ (deg)
volume, Å3
space group
Z
drawing of 6 is shown in Figure 2, and selected bond distances
and angles are given in Table 2. The complex is a simple
mononuclear piano stool structure with a chelating ethenedithi-
olate ligand. The C-C distance in the dithiolene ligand of 1.343
Å is significantly shorter than the corresponding C-C distance
in 1 (1.46 Å) and is consistent with double-bond character. In
addition, the S-C bond distances within the dithiolene ligand
(av ) 1.715(4) Å) are much shorter than those in the dithiolate
complex (1.835(8) Å), suggesting that a contribution from a
dithioglyoxal resonance form B is an important component of
6. This description is consistent with the downfield chemical
density, calcd
2.124
2.128
(mg/m-3
)
λ(Mo KR) (Å)
temp (K)
scan type
θ range
no. of ind reflns
no. of reflns obsd
abs coeff (mm-1)
0.71073
143(2)
ω-scans
2.12 < θ < 30.93
4643 (R(int) ) 0.0567) 4926 (R(int) ) 0.0680)
4552
semiempirical
from equivalents
0.0448
0.1269
1.114
0.71073
143(2)
ω-scans
2.43 < θ < 31.48
4258
semiempirical
from equivalents
0.0395
0.1110
1.033
Ra
b
Rw
GOFc
largest peak in final 2.118 and -3.651
2.573 and -4.982
diff map (e-/Å3)
2 2
a R ) R1 ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑[w(Fo2 - Fc2)2]/∑[w(Fo ) ]]1/2
.
2
2
c GOF ) S ) [∑[w(Fo - Fc )2]/(M - N)]1/2 where M is the number of
reflections and N is the number of parameters refined.
1
shift (8.4 ppm) observed for the dithiolene protons in the H
NMR spectrum.24 Unlike the dithiolate bonding for 1, the Re-S
distances of the ethenedithiolate ligand are equivalent at 2.29
Å. An unsymmetrical coordination of the Cp′ ligand is again
observed with long (2.40 Å) Re-C1 and Re-C2 distances,
which are opposite the dithiolate sulfurs, while the other Re-
CCp distances average 2.243(3) Å.
Kinetic Studies. Kinetic data for the thermal reactions of 1,
2, and 3 in toluene-d8 in evacuated sealed tubes were determined
by NMR spectroscopy by monitoring the disappearance of the
Cp′ resonances for the reactants over a period of several days.
The thermal reaction of 1, followed through 3 half-lives, was
found to be first-order in 1. Rate constants were determined
over a temperature range of 80-108 °C, and rate constants were
found to vary from 5 × 10-7 to 1 × 10-5 s-1, Table 3. An
Eyring plot, Figure 3, provided the following activation
parameters: ∆Hq ) 121 ( 5 kJ/mol and ∆Sq ) -24 ( 12
J/mol K. Perhaps coincidentally, these activation parameters are
very similar to those determined for ethene extrusion from
Cp*ReO(OCH2CH2O).6 The rates of disappearance of the major
isomers of 2 and 3 were monitored at 108 °C in toluene-d8.
The first-order rate constants (Table 3) were found to be quite
comparable to those of the parent complex, but increasing alkyl
substitution appears to promote the rate of olefin elimination
slightly.
Figure 3. Eyring plot for the disappearance of 1 in the absence of air over
the temperature range 80-108 °C.
3). The reaction proceeded in a similar way to form 6 (ca. 30%),
ethene, and some insoluble material. In addition a new soluble
rhenium complex was observed in the NMR spectrum (ca. 30%
yield). Spectroscopic data are provided in the Experimental
Section, but an X-ray diffraction study will be necessary before
a structural identification can be confirmed.25
The disappearance of the dithiolate complex may be described
by two competing first-order processes (Scheme 1). In this
scheme the dehydrogenation reaction is independent of olefin
extrusion, but relative yields suggest that the rate constants are
comparable. The dehydrogenation might proceed through an
The thermal reaction of 1 was also monitored in a polar
solvent, acetonitrile-d3, at 108 °C, and the rate in this solvent
was found to be significantly slower than that in toluene (Table
(25) Preliminary X-ray data from our lab suggest that “Cp′ReCl2S2” fragments
may react with 1 or 6 to form dinuclear products with (µ-S) and either
µ-dithiolate or dithiolene ligands.
(24) King, R. B.; Eggers, C. A. Inorg. Chem. 1968, 7, 340.
9
J. AM. CHEM. SOC. VOL. 124, NO. 33, 2002 9881

A R T I C L E S
Kanney et al.
Scheme 1
protons in these products. Additional yield and chemical shift
data are given in the Experimental Section.
The reactive intermediate “Cp′ReCl2S2” is proposed to be a
soluble discrete complex on the basis of the following experi-
ment. The insoluble material generated during the course of the
dehydrogenation of 1 was washed with toluene and then
combined with a solution of 4. When this reaction mixture was
heated at 105 °C for 24 h, dehydrogenation of the dithiolate
ligands of 4 was not observed. It therefore appears that
“Cp′ReCl2S2” is a soluble species that reacts with 4 as the former
is generated in solution.
Scheme 2
Unfortunately, the sulfido and hydrosulfido complexes pos-
tulated in Scheme 2 are not observed by NMR spectroscopy
after the high reaction temperatures required for olefin extrusion.
However precedents for the role of metal sulfides in C-H
cleavage reactions have been reported. In homogeneous systems,
quite extensive C-H activation reactivity has been characterized
for the conjugated Ru-S-S-Ru core in complexes of the type
[{Ru(P(OCH3)3)2(CH3CN)3}2(µ-S2)]OTf and related deriva-
tives.28 For example the allylic C-H bond in many alkenes adds
across the disulfide ligand to form new C-S and S-H bonds
under mild conditions. In a second example the complex
[(CpMoµ-S)2(S2CH2)]22+ served as an oxidant for the conversion
of benzylamine to benzylimine (hydrolyzed to benzaldehyde)
and of benzyl alcohol to benzaldehyde.29 In addition, hetero-
geneous rhenium and other metal sulfides function as dehydro-
genation (and hydrogenation) catalysts.30 Olefin hydrogenation
mechanisms that involve S-H groups have been proposed for
these surface reactions.31 Sulfide sites with activity toward C-H
activation should therefore also be considered in the mechanisms
of the reverse dehydrogenation pathways. Additional studies
were carried out to try to learn more about the formation of the
reactive rhenium disulfide intermediate.
initial â-hydrogen elimination, although this type of reaction is
not very favored for a five-membered chelate ring.26 In addition,
neither H2 nor HCl has been detected as a product in the sealed
tube reactions. A thermally induced â-hydrogen elimination
reaction has been characterized for the 1,3-propanedithiolate
analogue of 1, Cp′ReCl2(SCH2CH2CH2S). The rhenium product
contains a chelated thioaldehyde ligand, Cp′ReCl(η1,η2-SCH2-
CH2CHdS), and in this case HCl is also formed.27
A second possibility is that the two processes may be
sequential, as shown in Scheme 2. In this scheme, the olefin
extrusion reaction is proposed to produce a reactive Re-disulfide
or Re-bis(sulfido) intermediate, which serves as an oxidant for
the dithiolate complex. This scheme seems more consistent with
the observation that in the thermal reactions the formation of
the dithiolene complex, 6, is always accompanied by formation
of some ethene, and the yield of 6 is always less than 50%.
The reaction of 1 with Cp′Re(SC2H4S)2, 4, in toluene-d8 at 105
°C in a sealed NMR tube also provides support for the formation
of a reactive rhenium sulfide intermediate. As we reported
above, 4 does not react when heated in toluene at 105 °C for
several days. Control experiments also indicate that dithiolate/
dithiolene ligand exchange reactions do not occur under these
conditions. However when the mixture of 1 and 4 is heated for
1 day, we observe the formation of not only the dithiolene
derivative CpReCl2(SC2H2S), 6, but also a dehydrogenated
product of 4, CpRe(SC2H4S)(SC2H2S), 9, eq 4. The latter
Reactions of 1 with Alkenes and Alkynes. The thermal
reaction of 1 in toluene-d8 was carried out in the presence of
excess dry ethene in a sealed NMR tube in an effort to suppress
the olefin elimination. We hoped to determine whether the
dehydrogenation reaction occurred when competing olefin loss
was inhibited. However under these conditions a new reaction
was observed to compete with the dehydrogenation. After the
tube was heated at 105 °C for several hours, the NMR spectrum
showed the formation of a small amount (ca. 12%) of the
dehydrogenation product, 6. In addition, a new organic product
that displayed a singlet at 2.41 ppm was identified as 1,4-
dithiane by spectroscopic comparisons with an authentic sample.
The reaction with excess ethene was found to proceed even at
very mild temperatures, eq 5, and under these conditions no
dehydrogenation product was observed.
No other rhenium products were observed in the NMR spectra
for eq 5 provided that the ethene was thoroughly dried and
degassed. A brown precipitate that formed during the course
(28) (a) Sugiyama, H.; Lin, Y. S.; Hossain, M. M.; Matsumoto, K. Inorg. Chem.
2001, 40, 5547-5552. (b) Hossain, Md. M.; Lin, Y. S.; Sugiyama, H.;
Matsumoto, K. J. Am. Chem. Soc. 2000, 122, 172. (c) Sugiyama, H.;
Hossain, Md. M.; Lin, Y. S.; Matsumoto, K. Inorg. Chem. 2000, 39, 3948.
(d) Matsumoto, K.; Uemura, H.; Kawano, M. Inorg. Chem. 1995, 34, 658-
662.
(29) Rakowski DuBois, M.; Vasquez, L. D.; Ciancanelli, R. F.; Noll, B. C.
Organometallics 2000, 19, 3507-3515.
(30) (a) Chiang, L. Y.; Swirczewski, J. W.; Kastrup, R.; Hsu, C. S.; Upasani,
R. B. J. Am. Chem. Soc. 1991, 113, 6574-6584. (b) Broadbent, H. S.;
Slaugh, L. H.; Jarvis, N. L. J. Am. Chem. Soc. 1954, 76, 1519-1523.
(31) Kasztelan, S.; Guillaume, W. Ind. Eng. Chem. Res. 1994, 33, 203.
product is readily identified by its NMR spectrum, which
includes a new singlet at 8.3 ppm, characteristic of the dithiolene
(26) Miller, T. M.; Whitesides, G. M. Organometallics 1986, 5, 1473.
(27) Kanney, J.; Rakowski DuBois, M. Manuscript in preparation.
9
9882 J. AM. CHEM. SOC. VOL. 124, NO. 33, 2002

Dithiolate Ligands in Mononuclear Re(V) Complexes
A R T I C L E S
complex has not been reported previously. However, a similar
product has been trapped by the addition of an alkyne to the
reaction of a tungsten carbonyl derivative with thiirane.33 In a
somewhat related system, the sequential reactions of Cp*ReO3
with phosphine and an alkyne and then an oxidant were found
to form free furan rings.34
Further Studies of the Dehydrogenation Reactions. When
the thermal reactions of 1 were carried out in sealed evacuated
NMR tubes, the dithiolene product 6 was formed only at T >
80 °C. However in additional studies we have found that 1 reacts
with various oxidants under milder conditions to form 6. For
example, the reaction of 1 with excess dry oxygen (ca. 0.5 atm)
proceeded slowly in the dark at 40 °C to cleanly form 6 as
shown in eq 7. No intermediates were detected. Hydrogen
of this reaction in toluene-d8 was redissolved in CDCl3. The
NMR spectrum showed very broad resonances in the Cp′ region
over a temperature range of 25 to -50 °C, consistent with one
or more reduced paramagnetic rhenium species. Although
[Cp′ReCl2]2 is a known diamagnetic derivative,32 this product
was not detected in reaction 5, which was carried out in the
presence of a large excess of ethene. Rather, the EI mass
spectrum of the precipitate showed patterns at m/z ) 463 and
435, consistent with the formulation Cp′ReCl2(C2H4)n, where
n ) 1, 2. When the paramagnetic material was exposed to air,
the formation of Cp′ReOCl2 was observed by NMR spectros-
copy.
Complex 1 was also reacted with excess phenylacetylene at
60 °C. As shown in eq 6, the main rhenium-containing product
peroxide is proposed to be the second product, but it was not
identified in the NMR spectrum of the sealed tube reaction.
Although both the thermal dehydrogenation and the reaction
with oxygen form 6, the reactions appear to involve distinct
pathways. To confirm that trace oxygen was not responsible
for the thermal reactions, samples were subjected to extensive
freeze-pump-thaw cycles (see Experimental Section), and
kinetic studies at 108 °C were repeated. Kinetic data were found
to be completely reproducible with previous runs, with k ) 1.4
× 10-5/s.
In previous work, the reactions of certain Ni(II) and Pd(II)
thiolate complexes with O2 to form sulfonate and sulfoxide
derivatives have been characterized.35 The 1,2-diphenyldithiolate
ligand in an electron-rich platinum(II) diimine complex was
oxidized to the dithiolene complex under photochemical condi-
tions using O2 as the oxidant.36 The reaction was proposed to
proceed through singlet oxygen attack on the dithiolate sulfur
ligand. However, reaction 7 was quite unexpected, since the
cyclic voltammogram (see above) of the 16-electron Re(V)
complex, 1, suggests that the complex should be quite electro-
philic and much less electron rich than the previously studied
d8 complexes. Further work will be necessary to explore the
mechanistic features of reaction 7. The facile reaction with
oxygen does seem to establish that the dithiolate ligand in 1 is
was the 1-phenylethenedithiolate complex, 10, which was
isolated by column chromatography in 46% yield. A new
organic product was also isolated and identified as 2,3-dihydro-
5-phenyldithiin on the basis of its NMR spectrum and by
comparing its mass spectrum with that of a standard sample. A
second rhenium product that was isolated from the reaction
mixture by chromatograpy was identified as [Cp′ReCl(PhCCH)2]-
Cl by NMR and mass spectroscopy. Related Re(III) bis-alkyne
adducts have been reported previously.32a
The rates of the reactions of 1 with 2 and 10 equiv of
phenylacetylene were qualitatively compared by NMR spec-
troscopy, and the rates of formation of 10 and of the dithiin
product were both found to increase as the concentration of the
acetylene was increased. This suggests that both products are
formed by an associative process. However no evidence for an
intermediate in which the acetylene interacted with the sulfur
sites or with the metal ion was detected in the NMR spectra.
To our knowledge the formation of cyclic bis-thioethers by the
reactions of an alkene or alkyne with a discrete dithiolate metal
(33) Adams, R. D.; Queisser, J. A.; Yamamoto, J. H. J. Am. Chem. Soc. 1996,
118, 10674-10675.
(34) deBoer, E. J. M.; de With, J. J. Am. Chem. Soc. 1986, 108, 8271.
(35) (a) Farmer, P. J.; Soolouki, T.; Soma, T.; Russell, D. H.; Darensbourg, M.
Y. Inorg. Chem. 1993, 32, 4171. (b) Buonomo, R. M.; Font, I.; Maguire,
M. J.; Reibenspies, J. H.; Tuntulani, T.; Darensbourg, M. Y. J. Am. Chem.
Soc. 1995, 117, 963. (c) Grapperhaus, C. A.; Darensbourg, M. Y.; Sumner,
L. W.; Russell, D. H. J. Am. Chem. Soc. 1996, 118, 1791. (d) Mirza, S.
A.; Pressler, M. A.; Kuman, M.; Day, R. O.; Maroney, M. J. Inorg. Chem.
1993, 32, 977.
(32) (a) Herrmann, W. A.; Fischer, R. A.; Felixberger, J. K.; Paciello, R. A.;
Kiprof, P.; Hertweck, E. Z. Naturforsch. 1988, 43b, 1391-1404. (b)
Pawlicki, S. H.; Noll, B. C.; Rakowski DuBois, M. Manuscript in
preparation.
(36) Zhang, Y.; Ley, K. D.; Schanze, K. S. Inorg. Chem. 1996, 35, 7102-
7110.
9
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A R T I C L E S
Kanney et al.
0.3 M Bu4NBF4 using a Cypress Systems potentiostat. A glassy carbon
working electrode was used, and potentials are reported relative to the
ferrocene couple, which was used as an internal standard. Elemental
analyses were performed by Desert Analytics, Tucson, AZ.
Synthesis of Cp′ReCl2(dithiolate) Derivatives. The dithiolate
complexes were all synthesized by a similar procedure.
quite susceptible to oxidation. This may be attributed in part to
the stabilization resulting from the dithiolene/dithioglyoxal
resonance forms.
Complex 1 also reacted with excess elemental sulfur in
toluene-d8 at 70 °C to form 6 and H2S. A blank reaction of 1
heated under identical conditions in the absence of sulfur showed
no change. However, unlike the reaction of 1 with O2, the
reaction with sulfur also formed other rhenium products,
including Cp′ReCl2S3,37 and the possible role of these products
in the dehydrogenation process could complicate mechanistic
interpretations of this reaction. The reaction of zinc polysulfide
complexes with activated alkenes has been found to produce
zinc dithiolene derivatives.38 Initial formation of zinc al-
kanedithiolate complexes was proposed with subsequent ligand
displacement and oxidation by sulfur.
Cp′ReCl2(SCH2CH2S), 1. Cp′ReCl4 (0.097 g, 0.20 mmol) was
dissolved in ca. 20 mL of THF and treated with a THF solution
containing 1,2-ethanedithiol (18 µL, 0.21 mmol). The solution was
stirred for 20 h at room temperature, during which time it changed
from deep red to brown and finally to dark green. The solvent was
reduced to ca. 4 mL, a large excess of hexanes was layered on top,
and the solution was stored at 0 °C for several hours. The resulting
dark green precipitate was isolated from the solution and washed with
2 × 10 mL of cold hexanes. Yield: 0.063 g, 62%. 1H NMR (CDCl3):
4.01 (AA′BB′ pattern, 4 H, SCH2CH2S); 2.24 (q, 2 H, CpCH2); 2.19
1
(s, 6 H, CpMe); 2.04 (s, 6 H, CpMe); 1.03 (t, 3 H, CpCH2CH3). H
Conclusions. The dithiolate ligands in the complexes Cp′ReCl2-
(dithiolate) show an unusual reactivity that includes both olefin
extrusion and a dehydrogenation reaction at high temperatures.
The dithiolate ligands can also be dehydrogenated at mild
temperatures by reactions with certain oxidants. In addition the
dithiolate complex undergoes an associative reaction with
alkenes and alkynes under mild conditions to form free cyclic
bis-thioethers. We have been particularly interested in the
dehydrogenation reactions of the rhenium-dithiolates because
we believe these transformations raise some intriguing mecha-
nistic questions about the ease of C-H bond activation in
dithiolate ligands and about the role of a rhenium disulfide (or
bis-sulfido) complex in reactions with C-H bonds. Further work
in our laboratory will address the problems of synthetic access
to such derivatives and the scope of their reactions.
NMR (500 MHz, tol-d8): 3.39 (m, 4 H, SCH2CH2S); 1.90 (q, 2 H,
CpCH2); 1.79 (s, 6 H, CpMe); 1.61 (s, 6 H, CpMe); 0.62 (t, 3 H,
CpCH2CH3). 13C NMR (CDCl3): 12.97, 13.14 (CpMe); 14.89
(CpCH2CH3); 22.27 (CpCH2); 48.70 (SCH2CH2S); 102.86 (Cp); 105.19
(Cp); 112.58 (Cp). MS (FAB): 498 (P, 7%); 463 (P - Cl, 52%); 444
(base, Cp′ReO(SC2H4S)). UV/vis (λmax in CH3CN, nm (ꢀ in M-1 cm-1)):
654 (2200); 470 (2000); and 338 (5400). E1/2 or Ep (V vs Fc): +0.70
(∆E ) 158 mV, ia/ic ) 1.4); -0.83 (irrev); -1.52 (∆E ) 41 mV);
-2.13 (∆E ) 94 mV). Anal. Calcd for C13H21Cl2S2Re: C, 31.31; H,
4.25. Found: C, 31.65; H, 4.13.
Cp′ReCl2(SCH2CH(Et)S), 2. Yield: 70%. 1H NMR (tol-d8): 3.60
(m 2 H, SCH2CH(Et)S); 3.45 (m, 1 H, SCH2CH(Et)S); 1.96 (q, 2 H,
CpCH2); 1.821, 1.817, 1.636, 1.634 (4s, 3 H each, CpMe’s, major
isomer, ca. 80%); 1.85, 1.80, 1.66, 1.63 (4s, 3 H each, CpMe’s, minor
isomer, ca. 20%); 1.72 (m, SCHCH2CH3); 0.93 (t, 3 H, SCHCH2CH3);
0.64 (t, 3 H, CpCH2CH3). 1H NMR (CDCl3): 4.25, 4.15, 3.95 (3 m, 3
H, SCH2CH(Et)S); 2.38 (q, 2 H, Cp CH2); 2.23, 2.228, 2.074, 2.070
(4s, 3 H each, CpMe’s, major isomer, ca. 80%); 2.26, 2.23, 2.09, 2.07
(4s, 3 H each, CpMe’s, minor isomer, ca. 20%); 2.1 (m, SCHCH2-
CH3); 1.19 (t, 3 H, SCHCH2CH3); 1.08 (t, 3 H, CpCH2CH3). 13C NMR
(CDCl3) major isomer (ca. 80%): 12.95, 13.13, 15.38, 14.90 (CpMe);
22.63 (CpCH2CH3); 27.23 (CpCH2CH3); 22.65 (SCHCH2CH3); 29.73
(SCHCH2CH3); 52.64, 63.56 (SCH2CH(Et)S); 102.70, 102.78, 105.05,
112.50, 112.58 (Cp). MS (EI): 524 (P - 2H, 90%); 489 (P - 2H -
Cl, base). UV/vis (λmax in CH3CN, nm (ꢀ in M-1 cm-1)): 644 (2400);
472 (2300); and 340 (5400).
Experimental Section
All manipulations were carried out under a dry nitrogen atmosphere
using strandard Schlenk techniques or a nitrogen-filled glovebox.
Solvents were distilled under nitrogen from the appropriate drying
agents. Cp′ReCl4 was prepared from Cp′ReO3 according to the literature
report.20 Dithiols and 1,4-dithiane were purchased from Aldrich and
used without purification. Ethene was purified by a published proce-
dure39 by passage through a series of columns. The first column
contained Drierite, the next two contained concentrated H2SO4, the
fourth column contained KOH pellets, and the last contained activated
carbon. The ethene was then condensed in a n-pentane-liquid nitrogen
slush bath. When sufficient liquid ethene was collected, it was subjected
to three freeze-pump-thaw cycles on a high-vacuum line by alternat-
ing the pentane slush bath during the thaw cycle with liquid nitrogen
for the freeze cycle. After completion of these cycles, the ethene was
carefully allowed to warm to generate the desired pressure needed for
the NMR tube experiments and was transferred into the tube on the
vacuum line. Extra dry oxygen was supplied by Airgas and passed
through a dry ice/acetone trap immediately before use.
Cp′ReCl2(SCHMeCHMeS), 3. Yield: 66%. 1H NMR (CDCl3) exo-
cis isomer (70%): 4.25 (m, 2 H SCH); 2.2 (q, 2 H, CpCH2); 2.18,
2.02 (2 s, MeCp); 1.56 (m, 6 H, SCMe); 1.03 (t, 3 H, CpCH2CH3).
Trans isomer (30%): 3.9 and 3.2 (2m, 2 H, SCH); 2.22, 2.19, 2.05,
2.02 (4s, 12 H, CpMe); 2.25 (q, 2 H, CpCH2); 1.88, 1.82 (2d, 6 H,
1
SCMe); 1.04 (t, 3 H, CpCH2CH3). H NMR (tol-d8) exo-cis isomer
(70%): 3.82 (m, 2 H, SCH); 1.96 (q, 2 H, CpCH2); 1.82, 1.63 (2s,
MeCp); 1.31 (m, 6 H, SCMe); 0.64 (t, 3 H, CpCH2CH3). Trans isomer
(30%): 3.38 and 2.84 (2m, 2 H, SCH); 1.86, 1.81, 1.67, 1.57 (4s, 12
H, CpMe); 1.42, 1.56 (2d, 6 H, SCMe); 0.65 (t, 3 H, CpCH2CH3). 13
C
IR spectra were recorded on KBr pellets with a Nicolet Impact 410
spectrometer. 1H and 13C NMR spectra were recorded on a Varian Inova
500 spectrometer. Chemical shifts are reported relative to TMS. Mass
spectra were obtained on a VG Autospec with EI/CI sources and liquid
secondary ion MS capabilities or on a Hewlett-Packard 5989A
electrospray ionization LC mass spectrometer. Visible spectra were
recorded on a Perkin-Elmer Lambda 9 spectrophotometer. Cyclic
voltammograms were obtained on acetonitrile solutions containing
NMR (CDCl3) major isomer (ca. 70%): 12.96, 13.14 (CpMe); 14.83
(CpCH2CH3); 22.30 (CpCH2CH3); 58.54 (SCHMe); 102.5, 105.0, 112.8
(Cp). MS (EI) m/z: 526 (P+, 20%); 470 (P - C4H8, base). UV/vis
(λmax in CH3CN, nm (ꢀ in M-1 cm-1)): 636 (2200); 476 (2100); and
340 (5100). Anal. Calcd for C15H25Cl2S2Re: C, 34.21; H, 4.79.
Found: C, 34.60; H, 4.77.
Cp′Re(SC2H4S)2, 4. The procedure described above for 1 was
followed, except that Cp′ReCl4 was reacted with 2 equiv of ethanedithi-
ol. 1H NMR (CDCl3): 3.22 (2m, 8 H, SCH2CH2S); 2.29 (q, 2 H,
CpCH2); 2.08 (s, 6 H, CpMe); 2.01 (s, 6 H, CpMe); 0.95 (t, 3 H,
CpCH2CH3). 1H NMR (tol-d8): 3.15, 2.90 (2m, 8 H, SCH2CH2S); 1.81
(s, 6 H, CpMe); 1.65 (s, 6 H, CpMe); 0.65 (t, 3 H, CpCH2CH3). 13C
NMR (CDCl3): 12.16, 12.39 (CpMe); 14.07 (CpCH2CH3); 21.02
(37) Hobert, S. E.; Noll, B. C.; Rakowski DuBois, M. Organometallics 2001,
20, 1370-1375.
(38) Pafford, R. J.; Chou, J.-H.; Rauchfuss, T. B. Inorg. Chem. 1999, 38, 3779-
3786.
(39) Perrin, D. D.; Armarego, W. L. Purification of Laboratory Chemicals, 3rd
ed.; Pergamon Press: New York, 1988.
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9884 J. AM. CHEM. SOC. VOL. 124, NO. 33, 2002

Dithiolate Ligands in Mononuclear Re(V) Complexes
A R T I C L E S
(CpCH2); 41.53 (SCH2CH2S); 99.95 (Cp); 103.33 (Cp); 105.43 (Cp).
MS (EI): 520 (P, 47%); 492 (P - C2H4, 55%); 464 (base, Cp′ReS4).
UV/vis (λmax in CH3CN, nm (ꢀ in M-1 cm-1)): approximately 640 (sh);
538 (3650); 432 (1350); and 312 (3800). E1/2 or Ep (V vs Fc): -1.41
V (∆E ) 130 mV); Ea ) +0.41 (irrev). Anal. Calcd for 5 + 1/2THF
(THF observed in NMR spectrum of dried sample), C16H27O1/2S4Re:
C, 35.47; H, 4.99. Found: C, 35.38; H, 4.88.
Cp′ReO(SCH2CH2S), 5. Cp′ReCl4 (0.080 g, 0.0.17 mmol) was
dissolved in 15 mL of CH2Cl2 and treated with water (50 µL, 2.78
mmol). The solution was stirred for 12 h, then evaporated to dryness
under vacuum. The green residue (Cp′ReOCl2) was redissolved in 20
mL of CH2Cl2, then treated with 1,2-ethanedithiol (15 µL, 0.18 mmol)
and stirred for 24 h. The resultant brown solution was reduced to ca.
3 mL, then loaded on a silica gel column and eluted with CH3CN.
Yield: 0.062 g (83%). 1H NMR (CDCl3): 2.56 (2m, 4 H, SCH2CH2S);
2.28 (q, 2 H, CpCH2); 2.00 (s, 6 H, CpMe); 1.98 (s, 6 H, CpMe); 1.08
(t, 3 H, CpCH2CH3). 13C NMR (CDCl3): 110.91, 108.87, 108.08 (Cp);
43.96 (SCH2CH2S); 19.50 (CpCH2CH3); 14.77 (CpCH2CH3); 11.11,
10.85 (CpMe). MS (EI): 444 (P+, base). UV/vis (λmax in CH3CN, nm
(ꢀ in M-1 cm-1)): 698 (170); 464 (430); 366 (2000). E1/2 or Ep (V vs
Fc): +0.68 (irrev); -2.14 (∆E ) 74 mV). Anal. Calcd for C13H21-
OS2Re: C, 35.17; H, 4.77; S, 14.46. Found: C, 35.73; H, 4.74; S,
13.20.
NMR spectrum was recorded, and then the tube was heated at ca. 108
°C for 1 day. The NMR spectrum showed that all of 1 had reacted, but
approximately 50% of 4 remained. Two rhenium products were
observed in the spectrum: Cp′ReCl2(SC2H2S), 6, 24% based on initial
1, and Cp′Re(SC2H4S)(SC2H2S), 9, 30% based on initial 4. A singlet
for free ethene (5.26 ppm) was also observed. 1H NMR for 9 (tol-d8):
8.31 (s, 2 H, SC2H2S); 2.68, 2.38 (2m, 2 H each, SC2H4S); 1.515 (s, 6
H, CpMe); 1.504 (s, 6 H, CpMe); 0.60 (t, 3 H, CpCH2CH3).
In a second experiment, 1 (0.025 g) was dissolved in toluene, the
solution was degassed three times, and the tube was sealed. The solution
was heated at 100-105 °C for 1 day to form 6 and some insoluble
material. The solution was removed, and the remaining precipitate was
washed with toluene two times. A solution of 4 in toluene-d8 was then
added to the precipitate, and this solution was heated at 100-105 °C
for 1 day. No significant reaction was observed for 4. A small amount
(<10%) of 6 was formed and only a trace (<5%) of 9. These are
attributed to the presence of a small amount (<10%) of 1 left in the
precipitate after the washings.
Reaction of 1 with Ethene. In the glovebox a saturated solution of
1 in toluene-d8 was gravity filtered through a fritted funnel to remove
undissolved solids, then placed into a NMR tube equipped with a
Schlenk adapter. The apparatus was closed, removed from the box,
frozen with liquid N2, then evacuated on a high-vacuum line. After
thawing, the tube was charged with 0.6 atm of purified ethene. The
tube was then frozen and flame sealed. The sample was heated to 67
°C in a constant-temperature bath, and reaction progress was periodi-
cally monitored by NMR. The reaction was complete after 20 h of
heating, giving a pale solution and a brown precipitate. The only product
observed in the 1H NMR spectrum was p-dithiane. 1H NMR (toluene-
d8): 2.42 (s). 13C NMR (toluene-d8): 29.26. MS (EI, m/z): 120, P+.
NMR data were compared to those of an authentic sample of
p-dithiane: 1H NMR 2.42; 13C NMR 29.24. The solvent was removed
from the brown precipitate, and this solid was dissolved in CDCl3 under
N2. The NMR spectrum showed very broad resonances at 1.25, 1.6,
2.3, and 2.5 ppm. The resonances did not sharpen at lower temperatures
(-50 °C). MS (ES): 463 (Cp′ReCl2(C2H4)2); 435 (Cp′ReCl2(C2H4)).
(Additional MS patterns were observed in the dimer region, e.g., 834
and 806.) Upon exposure to air, Cp′ReOCl2 was rapidly formed and
identified by NMR spectroscopy. 1H NMR of Cp′ReOCl2 (CDCl3): 2.36
(q, 2 H, CpCH2); 2.21 (s, 6 H, CpMe); 2.13 (s, 6 H, CpMe); 1.23 (t,
3 H, CpCH2CH3). MS (EI) m/z: 444 (P).
Cp′ReCl2(dithiolene) Derivatives. Cp′ReCl2(SCHCHS), 6. Com-
plex 1 (0.090 g, 0.18 mmol) was dissolved in toluene, the solution
was freeze-pump-thaw degassed three times, and the stopcock was
closed. The reaction was heated in toluene for 24-48 h at 100-108
°C. The color changed from green to brown. The solvent was removed
and the remaining product extracted with THF, then recrystallized from
dichloromethane/hexanes. Analytically pure samples were obtained by
silica gel chromatography with CH3CN as the eluent. Yield: 0.034 g
1
(38%). H NMR (CDCl3): 9.18 (s, 2 H, SCH); 1.84, 1.81 (2s, 12 H,
1
CpMe); 1.78 (q, 2 H, CpCH2); 0.96 (t, 3 H, CpCH2CH3). H NMR
(toluene-d8): 8.42 (s, 2 H, SCH); 1.46 (q, 2 H, CpCH2); 1.41, 1.40
(2s, 12 H, CpMe); 0.56 (t, 3 H, CpCH2CH3). 13C NMR (CDCl3): 165.01
(SCH); 109.80, 102.47, 101.38 (Cp); 20.01 (CpCH2CH3); 14.23
(CpCH2CH3); 11.99, 11.31 (CpMe). MS (EI) m/z: 496 (P+); 461 (P -
Cl). UV/vis (λmax in CH3CN, nm (ꢀ in M-1 cm-1)): 478 (5100); 422
(2300); 346 (2400); 290 (3900); 226 (8900). Ep (V vs Fc): -1.15 (irrev).
Anal. Calcd for C13H19Cl2S2Re: C, 31.44; H, 3.86; S, 12.91. Found:
C, 31.56; H, 3.90; S, 12.00.
1
Cp′ReCl2(SCHC(Et)S), 7. Yield: 22%. H NMR (CDCl3): 8.94
Reaction of 1 with Phenylacetylene. Phenylacetylene was dried
by storage over molecular sieves prior to use. In a glovebox, 1 (0.060
g, 0.12 mmol) was dissolved in ca. 20 mL of dry THF in a Schlenk
tube. Phenylacetylene (75 µL, 0.72 mmol) was added by syringe, and
the tube was closed and removed from the box. The dark green solution
was stirred for 5 days at 60 °C, during which time the color changed
to deep red. The solution was reduced to ca. 5 mL and the product
purified by silica gel chromatography. Fraction 1 was a yellow band
eluted with toluene. The solvent was removed, and the solid was
(s, 1 H, SCH); 3.50 (m, 2 H, SCCH2); 1.80 (s, 6 H, CpMe); 1.78 (s, 6
H, CpMe); 1.75 (q, 2 H, CpCH2); 1.43 (t, 3 H, SCCH2CH3); 0.97 (t, 3
1
H, CpCH2CH3). H NMR (tol-d8): 8.30 (s, 1 H, SCH); 3.02 (m, 2 H,
SCCH2); 1.448, 1.454, 1.462 (12 H, CpMe); 1.57 (m, 2 H, CpCH2);
1.10 (t, 3 H, SCCH2CH3); 0.62 (t, 3 H, CpCH2CH3). 13C NMR (CDCl3)
(assignments based on DEPT experiments): 185.96 (SCEt); 159.70
(SCH); 109.27, 109.19, 102.35, 101.24, 101.16 (Cp); 29.84, 20.0 (CH2);
17.29, 14.26 (Me); 11.90, 11.22 (CpMe). UV/vis (λmax in CH3CN, nm
(ꢀ in M-1 cm-1)): 484 (3800); 420 (1400); 346 (1600); 292 (2900).
MS (EI) m/z: 524 (P, 90%); 489 (P - Cl, base).
1
identified as 2,3-dihydro-5-phenyldithiin. Yield: 25-30%. H NMR
(CDCl3): 7.64, 7.4, and 7.3 (m, Ph); 6.37 (s, 1 H, PhCCH); 3.26 (m,
4 H, SCH2CH2S). MS (EI) m/z: 194 (P, base); 166 (P - C2H4), 40%).
Fraction 2 was a dark red band eluted with 5:1 toluene/acetonitrile.
The solvent was removed, and the product was identified as Cp′ReCl2-
(SCHC(Ph)S, 10. Yield: 0.033 g, 46%. 1H NMR (CDCl3): 9.44 (s, 1
H, SCH); 7.77 (m, 2 H, Ph); 7.46 (m, 2 H, Ph); 7.40 (m, 1 H, Ph);
1.86 (s, 6 H, CpMe); 1.85 (s, 3 H, CpMe); 1.84 (s, 3 H, CpMe); 1.8
(m, CpCH2); 0.98 (t, 3 H, CpCH2CH3). 13C NMR (CDCl3) (assignments
were made on the basis of DEPT experiments): 180.21 (SCH); 160.25
(SCPh); 129.55, 128.57, 128.10 (Ph); 110.08, 109.79, 102.56, 101.57,
101.25 (Cp); 20.04 (CpCH2); 14.33 (CpCH2CH3); 12.04, 12.01, 11.41,
11.33 (CpMe). E1/2 or Ep (V vs Fc): -1.12 (irrev); -1.37 (irrev); -2.2
(∆E ) 74 mV). MS (EI): 572 (P+, 80%); 537 (P - Cl, base). Another
red-orange Cp′Re-containing product was eluted from the column with
acetonitrile and tentatively identified as [Cp′ReCl(PhCCH)2]Cl. 1H
Cp′ReCl2(SC(Me)C(Me)S), 8. Yield: 40%. 1H NMR (CDCl3): 3.01
(s, 6 H, SCMe); 1.78, 1.76 (2s, 12 H, CpMe); 1.71 (q, 2 H, CpCH2);
1
0.96 (t, 3 H, CpCH2CH3). H NMR (tol-d8): 2.50 (s, 6 H, SCMe);
1.450, 1.449 (2s, 12 H, CpMe); 1.58 (q, 2 H, CpCH2); 0.62 (t, 3 H,
CpCH2CH3). 13C NMR (CDCl3): 171.84 (SCMe); 109.19, 102.11,
100.86 (Cp); 22.93 (SCCH3); 19.93 (CpCH2CH3); 14.26, 11.84, 11.19
(CpMe). UV/vis (λmax in CH3CN, nm (ꢀ in M-1 cm-1)): 490 (1700);
402 (1100); 330 (2400); 232 (7100). MS (EI) m/z: 524 (P+, 85%);
489 (P - Cl, base). Anal. Calcd for C15H23Cl2S2Re: C, 34.34; H, 4.43.
Found: C, 34.17; H, 4.60.
Reaction of CpReCl2(SC2H4S), 1, with Cp′Re(SC2H4S)2, 4.
Complexes 1 and 4 were dissolved in toluene-d8 in a 2:1 ratio, and
p-dimethoxybenzene (2-3 mg) was added as an internal standard. The
NMR tube was freeze-pump-thaw degassed and sealed. The initial
9
J. AM. CHEM. SOC. VOL. 124, NO. 33, 2002 9885

A R T I C L E S
Kanney et al.
NMR (CDCl3): 1.76, 1.75 (2s, 12 H, Cp-Me’s); 1.91 (q, 2 H, Cp-
CH2); 1.08 (t, 3 H, CpCH2CH3); 7.39, 7.23, 6.85 (3m, 10 H, Ph). 13C
NMR (CDCl3): 10.6, 10.8, 13.3 (Cp-Me); 19.2 (CH2); 101.9, 103.7
(Cp); 127.0, 127.8, 130.0 (Ph). MS (ES): 610 (P, <5%); 575 (P - Cl,
base).
descriptions above. To check for oxygen contamination, the procedure
was repeated with more extensive degassing that included four freeze-
pump-thaw cycles. Identical products and rate constants were observed.
Reaction of Cp′ReCl2(SC2H4S) in CD3CN. The same procedure
was followed to determine the rate constant for thermal dehydrogenation
at 108 °C. The color of the solution changed from green to brown, and
a brown precipitate was observed. Soluble products were free ethene,
Cp′ReCl2(SC2H2S) (ca. 30%), and a new Re product (ca. 30%), not
yet identified.25 1H NMR of Cp′ReCl2(SC2H2S) (CD3CN): 9.24 (s, 2
Reaction of 1 with S8. Two NMR scale solutions of 1 in toluene-d8
were prepared in a glovebox as described above for the reaction with
ethylene. A large excess of S8 (ca. 25 mg) was added to one of the
tubes, the second serving as a blank. The tubes were closed, removed
from the box, freeze-pump-thaw degassed three times, and then sealed
under vacuum. The tubes were heated to 70 °C in a constant-temperature
1
H, SCH); 1.78 (s, 12 H, MeCp); 0.95 (t, 3 H, CpCH2CH3). H NMR
of unidentified product (CD3CN): 2.29, 2.24 (2s, 12 H, CpMe); 1.16
(t, 3 H, CpCH2CH3). MS (ES): 854 (Cp′ReSC2H2S)2; 826 (Cp′Re(S)-
SC2H4S)2; 800 (Cp′ReS2)2, base.
X-ray Diffraction Studies of Cp′ReCl2(SCH2CH2S), 1, and
Cp′ReCl2(SCHdCHS), 6. Crystals were examined under a light
hydrocarbon oil. Each selected crystal was mounted with silicone
vacuum grease to a thin glass fiber affixed to a tapered copper mounting
pin. This assembly was transferred to the goniometer of a Siemens
SMART CCD diffractometer equipped with an LT-2A low-temperature
apparatus operating at 142-143 K.
Cell parameters were determined using reflections harvested from
three orthogonal sets of 20 0.3° ω-scans. Final cell parameters were
refined using 6089 reflections chosen from 12 177 with I > 10σ(I)
from the entire data set for 1 and 7647 relections with I > 10σ(I) chosen
from 29 708 unmerged reflections in the entire data set of 6. An arbitrary
hemisphere of data was collected to 0.68 Å using 0.3° ω-scans exposed
for 30 s in two correlated 15 s exposures. All data were corrected for
Lorentz polarization and absorption.
Structure solution via direct methods in non-centrosymmetric space
group P212121 revealed the non-hydrogen structure of 1, and structure
solution via direct methods in centrosymmetric space group Pbca
revealed the non-hydrogen structure of 6. In each case, all non-hydrogen
atoms were refined with parameters for anisotropic thermal motion.
Hydrogen atoms were placed at calculated geometries and allowed to
ride on the isotropic thermal parameter of the parent atoms of 1.
Absolute structures were determined using the method described by
Flack.40 The Flack parameter refined to 0.008(11). Hydrogen atoms of
6 were located via Fourier difference map and freely refined in
subsequent cycles of least squares refinement. Significant features in
the final difference electron density maps of 1 and 6 are clustered about
the Re position and are likely to be absorption artifacts. Data are given
in Table 4.
1
bath, and reaction progress was monitored by H NMR spectroscopy.
Before heating, the NMR spectrum showed only the resonances for
the starting material. After several days of heating, the blank showed
no change, while the tube with S8 showed resonances for three rhenium
products: Cp′ReCl2(S3), 50%; CpReCl2(SC2H2S), 6, 30%; and an
unidentified dithiolate complex Cp′Re(SC2H4S)(Sx), 20%. A singlet at
0.19 ppm was assigned to H2S by comparison with an authentic sample.
A second singlet at 2.71 was tentatively assigned to free dithiolate,
but attempts to prepare a standard of this dianion in toluene-d8 were
unsuccessful. CpReCl2(S3): 1H NMR (toluene-d8): 1.99 (q, 2 H,
CpCH2); 1.56 (s, 6 H, CpMe); 1.42 (s, 6 H, CpMe); 0.67 (t, 3 H,
CpCH2CH3). Cp′Re(SC2H4S)(Sx): 1H NMR (toluene-d8): 2.82, 2.30
(2m, 4 H, SCH2CH2S); 1.64 (s, 6 H, CpMe); 1.50 (s, 6 H, CpMe);
0.72 (t, 3 H, CpCH2CH3).
Reaction of 1 with O2. Two NMR scale solutions of 1 in toluene-
d8 were prepared in a glovebox as described above. The tubes were
closed, removed from the box, and then freeze-pump-thaw degassed
three times on a high-vacuum line. To one of the tubes, 0.8 atm of dry
O2 was added, the other serving as a blank. The tubes were sealed and
protected from light with aluminum foil. The samples were heated to
40 °C in a constant-temperature bath, periodically monitoring reaction
1
progress with H NMR. After several days of heating, no change was
observed in the blank. The sample containing O2 steadily produced
Cp′ReCl2(SC2H2S), 6, over time. No other products were observed.
Kinetic Studies. All kinetic experiments were set up in a similar
manner. In a glovebox, a solution of Cp′ReCl2(dithiolate) in toluene-
d8 was placed in an NMR tube equipped with a Schlenk adapter. A
small amount of p-dimethoxybenzene (ca. 2-3 mg) was added to this
solution as an internal standard. The tube was closed, removed from
the glovebox, frozen with liquid N2, freeze-pump-thaw degassed one
or two times, and flame sealed. An initial NMR spectrum was recorded;
then the tube was heated in a constant-temperature bath. Reaction
progress was monitored periodically by 1H NMR spectroscopy by
integrating the CpMe resonances of the starting complex. NMR
integration values were referenced to the 4-H resonance of the p-DMB
internal standard. Reactions at higher temperatures were followed
through 3 half-lives, but for the slowest reactions at lower temperatures,
initial rates were determined. Plots of ln A/Ast vs time were linear with
correlation coefficients > 0.98; a sample plot is provided in the
Supporting Information. First-order rate constants are given in Table
3. The color of the solution changed from green to brown, and a dark
brown precipitate coated the sides of the NMR tube. Soluble products,
which were identified by 1H NMR spectroscopy, were Cp′ReCl2-
Acknowledgment. This work was supported by the Division
of Chemical Sciences, Office of Basic Energy Sciences, Office
of Energy Research, U.S. Department of Energy.
Supporting Information Available: Tables giving crystal
data, positional and thermal parameters, bond distances, and
bond angles for 1 and 6, a sample first-order kinetic plot of ln
[1]/[st] vs time, and control experiments to check for ligand
exchange reactions (PDF). This material is available free of
charge via the Internet at http://pubs.acs.org.
JA020125Z
1
(dithiolene) (yields, ca. 40%) and free alkene. H NMR data for the
reactants and products in toluene-d8 are included in the synthetic
(40) Flack, H. D. Acta Crystallogr. 1983, A39, 876-881.
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9886 J. AM. CHEM. SOC. VOL. 124, NO. 33, 2002