Synthesis of a rhenium(V) polysulfide complex and a study of its reactivity with hydrogen

Article abstract of DOI:10.1021/om000962e

The reaction of Cp′ReCl₄ (Cp′ = EtMe₄C₅) with 2-3 equiv of bis(trimethylsilyl)sulfide in chloroform in the presence of an oxidant results in the formation of Cp′Re(η²-S₃)Cl₂, 2. Complex 2 has been characterized by spectroscopic methods, and its structure has been confirmed by an X-ray diffraction study. Complex 2 reacts with hydrogen under mild conditions to form H₂S, HCl, and a rhenium product tentatively identified as (Cp′Re)₂S₄, 3. Complex 3 reacted with benzyl bromide to form [(Cp′Re)₂(μ-S₂) (μ-SCH₂Ph)₂]Br₂, 4 which has been completely characterized by spectroscopic studies and an X-ray crystal structure. The structures and reactions of the Cp′Re derivatives with sulfur ligands are compared to those of the related tetrasulfur-bridged CpMo derivatives.

Full text of DOI:10.1021/om000962e

1370
Organometallics 2001, 20, 1370-1375
Syn th esis of a Rh en iu m (V) P olysu lfid e Com p lex a n d a
Stu d y of Its Rea ctivity w ith Hyd r ogen
Sarah E. Hobert, Bruce C. Noll, and M. Rakowski DuBois*
Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309
Received November 13, 2000
The reaction of Cp′ReCl4 (Cp′ ) EtMe4C5) with 2-3 equiv of bis(trimethylsilyl)sulfide in
chloroform in the presence of an oxidant results in the formation of Cp′Re(η2-S3)Cl2, 2.
Complex 2 has been characterized by spectroscopic methods, and its structure has been
confirmed by an X-ray diffraction study. Complex 2 reacts with hydrogen under mild
conditions to form H2S, HCl, and a rhenium product tentatively identified as (Cp′Re)2S4, 3.
Complex 3 reacted with benzyl bromide to form [(Cp′Re)2(µ-S2)(µ-SCH2Ph)2]Br2, 4, which
has been completely characterized by spectroscopic studies and an X-ray crystal structure.
The structures and reactions of the Cp′Re derivatives with sulfur ligands are compared to
those of the related tetrasulfur-bridged CpMo derivatives.
In tr od u ction
In previous work we have found that dinuclear
cyclopentadienyl molybdenum complexes containing
sulfido ligands show exceptional reactivity at the sulfur
sites. For example, certain of the complexes react with
hydrogen under mild conditions to form products with
S-H ligands, and these S-H groups undergo further
addition reactions with unsaturated organic substrates
to ultimately give reduced products.12,13 Recently we
have begun a study of related molecular rhenium sulfide
derivatives in order to compare reactivity with that of
the molybdenum derivatives. The systems also provide
potential models for the respective metal sulfide sur-
faces. In this paper we report the synthesis of a
mononuclear rhenium complex containing a polysulfide
ligand and a study of its reaction with hydrogen.
Observed differences between cyclopentadienylrhenium
sulfide and molybdenum sulfide reactivity are discussed.
Heterogeneous rhenium sulfides are active catalysts
for a number of reactions including hydrogenations,
dehydrogenations, and hydrotreating processes.1,2 Com-
parisons of hydrodesulfurization activity of the rhenium
systems with that of the more economic commercial
molybdenum sulfide catalysts have shown that the
rhenium surfaces display significantly higher catalytic
activity.3,4 The lower ∆Hf value for ReS2 (42.7 ( 3 kcal/
mol) compared to MoS2 (65.8 ( 1 kcal/mol)5 and the
weaker Re-S bond strength relative to Mo-S have been
suggested to be important factors in the higher activity
observed for ReS2. It has been proposed that weaker
Re-S bond strengths allow facile hydrogenolysis of the
Re-sulfide moiety to generate more sulfur vacancies,
which correlate with higher catalytic activity.6 Discrete
rhenium sulfide or polysulfide complexes provide the
opportunity to better understand and model the reactiv-
ity and potential catalytic activity of sulfide-supported
metal centers, but few relevant reactivity studies of
rhenium sulfide derivatives with hydrogen and/or or-
ganic reagents have been carried out.7-11
Resu lts a n d Discu ssion
Rea ction s of Cp ′ReCl4 w ith (Me3Si)2S. In previous
studies we found that the reaction of Cp′ReCl4 with 2
equiv of (Me3Si)2S under nitrogen at room temperature
led to a mixture of products, but after the reaction was
refluxed briefly in dichloromethane, 1 was formed in
good yield, as shown in eq 1.10 This synthesis was
(1) Broadbent, H. S.; Slaugh, L. H.; J arvis, N. L. J . Am. Chem. Soc.
1954, 76, 1519.
(2) Chiang, L. Y.; Swirczewski, J . W.; Kastrup, R.; Hsu, C. S.;
Upasani, R. G. J . Am Chem. Soc. 1991, 113, 6574.
(3) Eijsbouts, S.; deBeer, V. H. J .; Prins, R. J . Catal. 1988, 109, 217.
(4) Ledoux, M.; Michaux, O.; Agostini, G.; Panissod, P. J . Catal.
1986, 102, 275.
(5) Harris, S.; Chianelli, R. R. J . Catal. 1984, 86, 400.
(6) Topsoe, H.; Clausen, B. S.; Topsoe, N. Y.; Norskov, J . K.; Ovesen,
C. V.; J acobsen, C. J . H. Bull. Soc. Chim Belg. 1995, 104, 283.
(7) Wei, L.; Halbert, T. R.; Murray, H. H.; Stiefel, E. I. J . Am. Chem.
Soc. 1990, 112, 6431.
(8) Massa, M. A.; Rauchfuss, T. B.; Wilson, S. R. Inorg. Chem. 1991,
30, 4667.
(9) Qi, J . S.; Schrier, P. W.; Fanwick, P. E.; Walton, R. A. Inorg.
Chem. 1992, 31, 258.
(10) Rakowski DuBois, M.; J agirdar, B. R.; Dietz, S.; Noll, B. C.
Organometallics 1997, 16, 294.
repeated several times in our laboratory with yields in
the range of 70-80%, but we found that the yield was
(11) (a) Dopke, J . A.; Wilson, S. R.; Rauchfuss, T. B. Inorg. Chem.
2000, 39, 5014. (b) Goodman, J . T.; Rauchfuss, T. B. J . Am. Chem.
Soc. 1999, 121, 5017. (c) Goodman, J . T.; Rauchfuss, T. B. Angew.
Chem., Int. Ed. Engl. 1997, 36, 2083. (d) Goodman, J . T.; Rauchfuss,
T. B. Inorg. Chem. 1998, 37, 5040. (e) Schwarz, D. E.; Rauchfuss, T.
B. J . Chem. Soc., Chem. Commun. 2000, 1123.
(12) (a) Lopez, L. L.; Bernatis, P.; Birnbaum, J .; Halitwanger, R.
C.; Rakowski DuBois, M. Organometallics 1992, 11, 2424. (b) Casewit,
C. J .; Coons, D. E.; Wright, L. L.; Miller, W. K.; Rakowski DuBois, M.
Organometallics 1986, 5, 951.
10.1021/om000962e CCC: $20.00 © 2001 American Chemical Society
Publication on Web 02/22/2001

Synthesis of a Re(V) Polysulfide Complex
Organometallics, Vol. 20, No. 7, 2001 1371
very sensitive to the source of the sulfide reagent and
to the reaction conditions. Equation 1 does not represent
a balanced equation, because the isolated product 1 is
oxidized by two electrons relative to the reactants.
Although the formal oxidation state of the rhenium
centers goes from +5 in Cp′ReCl4 to +4 in the product,
each of the sulfide ligands is oxidized by one electron
to form the disulfide bridges in the dication. The nature
of the oxidant in the original reaction was not identified,
but the complex nature of this reaction prompted us to
investigate the reaction of Cp′ReCl4 with (Me3Si)2S in
the presence of various oxidants. Reactions were carried
out using oxidants such as elemental sulfur or sulfur
dichloride or simply air. Although 1 was not the final
product in these reactions, the same new product was
prominent in each case. The reaction in the presence of
air was one of the cleanest and is described below.
Syn th esis a n d Ch a r a cter iza tion of Cp ′Re(η2-S3)-
Cl2, 2. The reaction of Cp′ReCl4 with 2-3 equiv of bis-
(trimethylsilyl)sulfide was carried out in chloroform
solution at room temperature with exposure to air.
Under these conditions the reaction solution underwent
several color changes and ultimately formed a deep red
color after a period of 2-3 days. The red product, 2, was
isolated in yields of 60-75% and characterized by a
combination of spectroscopic techniques and an X-ray
diffraction study. X-ray crystallography established that
2 is the rather unexpected mononuclear complex con-
taining a trisulfide ligand with the formula Cp′ReS3-
Cl2. An unbalanced reaction for the synthesis is shown
in eq 2.
F igu r e 1. Perspective drawing and numbering scheme for
Cp′Re(η2-S3)Cl2, 2. Thermal ellipsoids are shown at the 50%
probability level.
Ta ble 1. Selected Bon d Dista n ces a n d An gles for
(EtMe4C5)Re(η2-S3)Cl2, 2
Distances (Å)
Re(1)-S(1)
Re(1)-Cl(1)
S(1)-S(2)
Re(1)-C(1)
Re(1)-C(3)
Re(1)-C(5)
2.3052 (19)
2.4211 (17)
2.069 (3)
2.210 (6)
2.433 (6)
2.259 (6)
Re(1)-S(3)
Re(1)-Cl(2)
S(2)-S(3)
Re(1)-C(2)
Re(1)-C(4)
2.2945 (17)
2.4127 (15)
2.059 (3)
2.282 (6)
2.419 (6)
Angles (deg)
S(1)-Re(1)-S(3)
S(1)-Re(1)-Cl(2)
S(1)-S(2)-S(3)
77.07 (7)
82.02 (7)
Cl(1)-Re(1)-Cl(2)
83.06 (6)
81.77 (7)
S(3)-Re(1)-Cl(1)
87.92 (10) S(3)-Re(1)-Cl(2) 133.35 (6)
S(1)-Re(1)-Cl(1) 133.14 (7)
Re(1)-S(3)-S(2) 96.88 (9)
Re(1)-S(1)-S(2)
96.27 (10)
2 are given in Table 1. The η2-trisulfide ligand is
nonplanar, with S(2) bent out of the plane of Re, S(1),
and S(3) by a dihedral angle of 13°. The two Re-S bonds
are equivalent within experimental error, with an
average distance of 2.300(2) Å. The other bond distances
and angles are also within the normal range of values.
The pentamethylcyclopentadienyl analogue of 2 has
been reported previously, and the triselenide derivative,
Cp*ReCl2Se3, has been characterized by an X-ray dif-
fraction study.15 The latter complexes were prepared by
the reaction of Cp*ReCl4 with polychalcogenide ligands
Na2S4 and (NEt4)2Se6, respectively. Other related Cp or
Cp*Re complexes with sulfide or polysulfide ligands
have also been characterized.16-21
To better understand the sequence of this transfor-
mation, we have monitored the reaction in eq 2 in CDCl3
by NMR spectroscopy. The reaction involved initial
conversion of Cp′ReCl4 to the deep green complex Cp′Re-
14
(O)Cl2 and further slow reaction of this complex with
the sulfide reagent. The formation of 1 was observed
as a major product over a period of 15-20 h. Longer
reaction times led to the disappearance of 1 and the
formation of 2 in high yield. Formally, 2 is related to 1
by the addition of the oxidant sulfur monochloride, eq
3. However the reaction steps and intermediates in-
1
In the H NMR spectrum of 2, the ethyltetramethyl-
cyclopentadienyl ligands show two strong methyl sin-
glets (total intensity 12) at 2.03 and 1.92 ppm in
addition to the ethyl triplet and quartet. The chemical
volved in the conversion of 1 to 2 under the aerobic
conditions of eq 2 have not been established.
In the structural study of 2, two molecules are present
in the unit cell with similar bond lengths and angles. A
perspective drawing of one of the molecules is shown
in Figure 1, and selected bond distances and angles for
(15) Herberhold, M.; J in, G.-S.; Milius, W. Anorg. Allg. Chem. 1994,
620, 299.
(16) Herberhold, M.; J in, G. X.; Milius, W. Angew. Chem., Int. Ed.
Engl. 1993, 32, 85.
(17) Herberhold, M.; J in, G. X.; Milius, W. J . Organomet. Chem.
1993, 459, 257.
(18) Herberhold, M.; Reiner, D.; Ackermann, K.; Thewalt, U.;
Debaerdemaeker, T. Z. Naturforsch. 1984, 39b, 1199.
(19) Mu¨ller, A.; Krickemeyer, E.; Wittneben, V.; Bo¨gge, H.; Lemke,
M. Angew. Chem., Int. Ed. Engl. 1991, 30, 1512.
(20) Kulpe, J . E.; Herdtweck, E.; Weichselbaumer, G.; Herrmann,
W. A. J . Organomet. Chem. 1988, 348, 369.
(21) Herrmann, W. A.; J ung, K. A.; Herdtweck, E. Chem. Ber. 1989,
122, 2041.
(13) (a) Casewit, C. J .; Rakowski DuBois, M. J . Am. Chem. Soc.
1986, 108, 5482. (b) Bernatis, P.; Laurie, J . C. V.; Rakowski DuBois,
M. Organometallics 1990, 9, 1607.
(14) Herrmann, W. A.; Herdtweck, E.; Flo¨el, M.; Kulpe, J .; Ku¨st-
hardt, U.; Okuda, J . Polyhedron 1987, 6, 1165.

1372 Organometallics, Vol. 20, No. 7, 2001
Hobert et al.
shifts of the methyl singlets are significantly upfield
from those observed at 2.44 and 2.43 ppm for the
dicationic dimer 1.10 The EI mass spectrum of 2 showed
a weak pattern at m/z 502 that corresponded to the
parent ion and the base fragmentation pattern at m/z
438 that resulted from the loss of two sulfur atoms. In
the cyclic voltammogram of 2 a wide window of redox
stability was observed; an irreversible reduction wave
was present with Ep ) -0.975 V vs Fc, and an irrevers-
ible oxidation occurred with Ep ) 1.032 V.
Rea ctivity Stu d ies of 2. Complex 2 is formally a
16-electron complex of Re(V). The rhenium sulfide
distances in 2 are similar to those observed for single
Re-S bonds in rhenium(V) thiolate derivatives11,22,23
and do not indicate significant π donation from a sulfur
donor. Nevertheless 2 appears to be quite a stable
complex. No further reaction was observed between 2
and 2 equiv of (Me3Si)2S, either at room temperature
or in refluxing acetonitrile. Unlike the Cp* analogue,
which was reported to be hydrolyzed in moist solvents
to form Re-oxo derivatives,15 no reaction of 2 with 2
equiv of water in CDCl3 was observed over a period of
several days. Although polysulfide ligands often undergo
insertion reactions with acetylenes,24 no reactions were
observed between 2 and phenyl acetylene or dimethyl-
acetylene dicarboxylate.
Despite the redox stability of 2, the complex was found
to react with 1-2 atm H2 under mild conditions. When
the reaction was carried out in CDCl3 in a sealed NMR
tube at room temperature, the red color of the solution
changed to brown over a period of several days and a
single new Cp′Re product was observed with the two
Cp′-methyl singlets at 2.28 and 2.26 ppm. A singlet at
0.79 ppm was attributed to the formation of hydrogen
sulfide, and the integration of this resonance suggested
that approximately 1 equiv of H2S was formed per Cp′Re
unit. An additional broad resonance was observed near
7 ppm, and this was tentatively assigned to free HCl.
No intermediate species were detected during the course
of this reaction at room temperature.
reaction of 2 with H2 could involve a sequence of steps
that includes both hydrogen addition across a Re-S
bond and the formation of a dihydrogen adduct, since
vacant rhenium coordination sites are generated during
the reaction by the eliminations of H2S and HCl.
Dinuclear cyclopentadienyl molybdenum complexes
with sulfide and disulfido ligands have also been found
to react with hydrogen under similar mild conditions.12
In these systems, products with µ-SH ligands were
formed and evidence for H2S elimination was generally
not observed.26 This difference in reactivity between the
molecular CpMo- and Cp′Re-sulfides parallels the dif-
ferences in reactivity proposed for the heterogeneous
molybdenum and rhenium sulfide surfaces.
Syn th esis a n d Ch a r a cter iza tion of (Cp ′Re)2S4, 3,
a n d Der iva tives. To obtain more information about the
products of this hydrogen activation process, the reac-
tion of 2 with hydrogen was repeated on a preparative
scale at 40 °C using toluene as the solvent. In this case,
the solution changed from red to green-brown within
hours, and a green product, 3, was isolated after
removal of the solvent and recrystallization from CH2-
Cl2/hexanes. The NMR spectrum of 3 showed a single
product with Cp′-methyl singlets at 2.26 and 2.24 ppm.
In the EI mass spectrum a strong pattern centered at
m/z 798 is observed, and the isotope pattern closely
matches that calculated for the formulation (Cp′Re)2S4.
The infrared spectrum of 3 does not show a strong
absorption in the region 400-550 cm-1 that can be
assigned to a RedS stretch,11,27 and no NMR or IR
spectroscopic evidence for the formation of S-H ligands
was observed for the rhenium product. The structure
is therefore tentatively assigned as a dimer with four
sulfur bridges, eq 4. It is not possible to unambiguously
Hydrogen additions to other metal sulfide complexes
have been reported. A titanocene derivative with a
terminal sulfido ligand, Cp*2Ti(py)(S), was found to add
hydrogen at room temperature to form Cp*2Ti(SH)(H).25
The reaction was proposed to occur via pyridine dis-
sociation and formation of a four-centered transition
state, and a Ti-dihydrogen adduct was proposed as a
likely intermediate. The titanocene disulfide complex
Cp*2Ti(η2-S2) reacted with H2 at 70 °C to form Cp*2Ti-
(SH)2, and in this case initial addition of hydrogen
across a Ti-S bond was suggested as the likely path-
way.25 The reaction of the rhenium-trisulfide complex
2 with hydrogen differs from the above examples in that
free hydrogen sulfide is eliminated as a product. The
assign oxidation states to the sulfur ligands and the
metal ions on the basis of the spectroscopic character-
ization, and possibilities that are related by intra-
molecular electron transfer are shown below. Attempts
to obtain single crystals of 3 have been unsuccessful.
(22) (a) Lente, G.; Guzei, I. A.; Espenson, J . H. Inorg. Chem. 2000,
39, 1311. (b) J acob, J .; Guzei, I. A.; Espenson, J . H. Inorg. Chem. 1999,
38, 3266.
(23) (a) Herberhold, M.; J in, G. X.; Rheingold, A. L. J . Chem. Soc.,
Chem. Commun. 1996, 2645. (b) Herberhold, M. J in, G. X.; Milius, W.
J . Organomet. Chem. 1996, 512, 111.
(24) (a) Mu¨ller, A.; Diemann, E. Adv. Inorg. Chem. 1987, 31, 89. (b)
Herberhold, M.; J in, G. X.; Milius, W. Z. Anorg. Allg. Chem. 1994, 620,
1295. (c) Bolinger, C. M.; Rauchfuss, T. B. Organometallics 1982, 1,
1551. (d) Draganjac, M.; Coucouvanis, D. J . Am. Chem. Soc. 1983, 105,
129.
(25) Sweeney, Z. K.; Polse, J . L.; Bergman, R. B.; Andersen, R. A.
Organometallics 1999, 18, 5502.
The complex is quite air sensitive and also appears to
be unstable in solution over a period of time even when

Synthesis of a Re(V) Polysulfide Complex
Organometallics, Vol. 20, No. 7, 2001 1373
solutions are maintained under nitrogen. A similar
formulation, [Cp*ReS2]2, has been mentioned briefly in
previous work.28
To obtain more information about the structure of 3,
further reactions were carried out in attempts to
prepare a derivatized form of this complex. To obtain a
product with a protonated or methylated sulfur ligand,
the reaction of 3 with tetrafluoroboric acid or with
methyl triflate was carried out. Each of these reactions
led to the rapid oxidation of 3 and formation of 1, which
was identified by NMR spectroscopy, e.g., eq 5.
F igu r e 2. Perspective drawing and numbering scheme for
[(Cp′Re)2(µ-S2)(µ-SCH2Ph)2]Br2, 4. Thermal ellipsoids are
shown at the 50% probability level.
When 3 was reacted with benzyl bromide (2 equiv) in
dichloromethane, some of the oxidized product 1 was
formed (approximately 50%), but we also observed the
formation of a new alkylated derivative, 4, which was
isolated by chromatography on a silica gel column and
tentatively formulated as [Cp′Re(S)(SCH2Ph)]2Br2, eq
6. The composition of the product was confirmed by the
Ta ble 2. Selected Bon d Dista n ces a n d An gles for
[(EtMe4C5Re)2(µ-S2)(µ-SCH2P h )2]Br 2, 4
Distances (Å)
Re(1)-S(1)
Re(1)-S(3)
Re(1)-Re(2)
Re(2)-S(2)
Re(2)-S(4)
S(1)-C(23)
2.393 (2)
2.397 (2)
2.5887 (5)
2.421 (2)
2.396 (2)
1.829 (10)
Re(1)-S(2)
Re(1)-S(4)
Re(2)-S(1)
Re(2)-S(3)
S(2)-S(4)
2.401 (2)
2.410 (2)
2.379 (2)
2.389 (2)
2.074 (3)
1.839 (9)
S(3)-C(30)
Angles (deg)
S(1)-Re(1)-S(3)
S(2)-Re(1)-S(3)
S(3)-Re(1)-S(4)
Re(1)-S(1)-Re(2)
Re(1)-S(3)-Re(2)
73.58 (8) S(1)-Re(1)-S(2)
113.27 (8) S(1)-Re(1)-S(4)
81.89 (8) S(2)-Re(1)-S(4)
65.70 (6) Re(1)-S(2)-Re(2)
65.48 (6) Re(1)-S(4)-Re(2)
83.75 (8)
112.77 (8)
51.07 (8)
64.94 (6)
65.18 (6)
Re(1)-S(1)-C(23) 115.1 (4)
Re(2)-S(1)-C(23) 109.1 (3)
FAB+ mass spectrum, which showed a weak peak at
m/z 1060 for the cation with one bromide and several
fragmentation patterns consistent with the formula. In
the 1H NMR spectrum of 4, only one isomer was
observed with one singlet for the benzylic hydrogens
(relative intensity 4) at 4.2 ppm and the Cp-Me singlets
at 2.34 and 2.38 ppm.
Further information on the oxidation states of the
metal ions and the µ-sulfur ligands was obtained from
an X-ray diffraction study. Single crystals of 4 were
obtained from a CH2Cl2/hexanes solution. The product
was found to contain a dicationic dinuclear rhenium-
(IV) derivative with two bridging benzylthiolate ligands
in equatorial configurations and a µ-η2-disulfido ligand.
Two bromide counterions are also observed at nonbond-
ing distances (>4.9 Å) from the metal ions. A perspective
drawing of the dication is shown in Figure 2, and
selected bond distances and angles are given in Table
2. The Re(1)-Re(2) distance of 2.5887(5) Å is similar to
values in other Re(IV) dimers with multiple M-M bond
character,9,29 but the metal-metal distances in dimers
with four bridging sulfur ligands have been found to be
quite insensitive to metal oxidation state and are not a
good indicator of bond order.30 Only a single Re-Re
bond in 4 is necessary to reach an 18-electron count for
each metal ion. The average of the four Re distances to
the µ-S2 ligand is 2.407(2) Å, while the average Re-
S(thiolate) distance is slightly shorter at 2.390(2) Å. The
S(2)-S(4) distance is 2.074(3) Å. This value is quite
typical for a single bond in a disulfide ligand and is
significantly shorter than the unusually long S-S
distance (2.228(10) Å) reported for the closely related
dimer [(Cp′Re)2(µ-S2)]2(Cl)2, 1.10 Distances between the
bromide counterions and the sulfur atoms of the µ-S2
ligand were in the range 3.336-3.604 Å. These distances
are close to the sum of the van der Waals radii (3.65 Å)
and indicate much weaker interactions between the
halide and the disulfide ligand than those observed for
1.10
The structural characterization of 4 suggests that the
structure of 3 may be that shown above in structure 3b,
where two µ-sulfido ligands are susceptible to electro-
philic attack by the alkylating agent. However, definite
conclusions regarding the structure and oxidation states
(26) For an exception see: Rakowski DuBois, M.; VanDerveer, M.
C.; DuBois, D. L.; Haltiwanger, R. C. J . Am. Chem. Soc. 1980, 102,
7456.
(27) Tahmassebi, S. K.; Mayer, J . M. Organometallics 1995, 14,
1039.
(28) Hermann, W. A. Angew. Chem., Int. Ed. Engl. 1988, 27, 1297.
(29) Lente, G.; Shan, X.; Guzei, I. A.; Espenson, J . H. Inorg. Chem.
2000, 39, 3572.
(30) See for example: Miller, W. K.; Haltiwanger, R. C.; VanDerveer,
M. C.; Rakowski DuBois, M. Inorg. Chem. 1983, 22, 2973. Kaul, B. B.;
Noll, B. C.; Renshaw, S.; Rakowski DuBois, M. Organometallics 1997,
16, 1604.

1374 Organometallics, Vol. 20, No. 7, 2001
Hobert et al.
Ta ble 3. Cr ysta l Da ta for (EtMe4C5)ReS3Cl2, 2, a n d
MHz instruments. All chemical shifts are reported in ppm
relative to tetramethylsilane. Mass spectra were obtained on
a Hewlett-Packard 5989A electrospray ionization LC mass
spectrometer, on a VG Autospec with EI/CI sources and liquid
secondary ion MS capabilities, or on a Finnigan MATR LCQ
ion trap mass spectrometer. Infrared spectra were obtained
on KBr pellets using a Perkin-Elmer Model 1600 FTIR
spectrometer. Cyclic voltammetry experiments were carried
out under nitrogen on acetonitrile solutions containing 0.3 M
Bu4NBF4 with a Cypress Systems electrolysis system. Fer-
rocene was used as an internal standard, and all potentials
are referenced to the ferrocene/ferrocenium couple. Elemental
analyses were performed by Desert Analytical Laboratory,
Tucson, AZ. Ethyltetramethylcyclopentadiene was purchased
from Aldrich, and bis(trimeylsilyl)sulfide was purchased from
Strem, Aldrich, or Fluka and used without purification.
Cp′ReCl4 was synthesized from Re2(CO)10 (Strem) by a pub-
lished procedure.14
Syn th esis of Cp ′Re (η2-S3) Cl2, 2. Cp′ReCl4 (0. 34 g, 0.70
mmol) was dissolved in chloroform in air, and (Me3Si)2S (0.44
mL, 2.10 mmol) was added. The solution was stirred in air for
2-3 days, until the color had changed to deep red. The solvent
was evaporated, and the remaining solid was extracted with
toluene and filtered. The filtrate was dried to give the desired
product, which could be recrystallized from toluene/hexanes.
Yield: ca. 60%. Additional product could be isolated by
extraction of crude solid with THF and workup as described
above. 1H NMR (CDCl3): 2.04, 1.92 (2 s, each 6 H, CpMe); 2.10
(q, 2 H, CpCH2); 1.14 (t, 3 H, CpCH2CH3). 13C NMR (CDCl3):
11.26, 11.85 (CpMe); 14.40 (CH2CH3); 19.97 (CpCH2); 103.84,
105.47, 110.53 (Cp). IR (KBr): 417, 512 (med, νS-S). Mass
spectrum (EI): m/z 502 (weak, P+); 438 (Base, P-2S); 402
(P - 2S - Cl). Visible spectrum (CDCl3): 512 nm (ꢀ 3700 M-1
cm-1); 450 nm (sh). CV (CH3CN, V vs Fc): -0.975 (irr); 1.032
(irr.). Anal. Calcd for C11H17Cl2S3Re: C, 26.26; H, 3.41; S,
19.14. Found: C, 26.40; H, 3.43; S, 19.43.
for [(EtMe4C5Re)2(µ-S2)(µ-SCH2P h )2]Br 2, 4
2
4
formula
2(C11H17Cl2ReS3) C36H48Br2Re2S4
fw (amu)
cryst syst
unit cell dimens
a (Å)
b (Å)
c (Å)
1005.05
triclinic
1141.20
monoclinic
6.8496(2)
16.1733(4)
16.3060(4)
60.71
43.368(5)
9.3628(11)
20.084(2)
90
110.840(2)
90
7621.7(15)
C2/c
8
R (deg)
â (deg)
80.2160(10)
78.4330(10)
1538.02(7)
P1h
γ (deg)
volume, Å3
space group
Z
2
density, calcd, g/cm3
λ(Mo KR) (Å)
temp (K)
2.170
0.71073
154(2)
ω scans
1.46 to 31.05
9027
7618
8.632
0.0487
0.1303
1.989
0.71073
143(2)
ω scans
1.00 to 27.50
8754
6255
8.688
0.0488
0.0992
1.013
scan type
θ range (deg)
no. of ind reflns
no. of reflns obd
abs coeff, mm-1
Ra
b
Rw
GOF
1.036
largest peak in final diff 3.962 and -3.379 2.138 and -2.147
map (e/Å3)
R1 ) [∑||Fo| - |Fc||]/∑|Fo|. b wR2 ) {∑[w(Fo2 - Fc2)]/∑[wFo2)2]}1/2
.
a
of 3 cannot be made on this basis because facile
intramolecular electron transfers have been well char-
acterized for various rhenium sulfide/disulfide deriva-
tives.7,31
Su m m a r y a n d Con clu sion s. The reaction of Cp′-
ReCl4 with (Me3Si)2S in air results in the unexpected,
but clean formation of a complex with a η2-S3 ligand,
Cp′ReS3Cl2, 2. Although 2 is stable to air and moisture,
it reacts with hydrogen under mild conditions to gener-
ate H2S and a product formulated as (Cp′Re)2S4, 3.
Further reaction of 3 with benzyl bromide generates the
complex [(Cp′Re)2(µ-S2)(µ-SCH2Ph)2]Br2, 4. To our knowl-
edge the reaction of 2 with hydrogen is the first example
of the hydrogen-induced elimination of hydrogen sulfide
from a mononuclear metal polysulfide complex. While
dinuclear Cp-molybdenum sulfide complexes were found
to react quite generally with hydrogen to form S-H
ligands, examples of both dinuclear10 and now mono-
nuclear Cp-rhenium sulfide complexes have been found
to generate a vacant coordination site much more
readily by H2S elimination. This trend reflects the
relative metal-sulfur bond strengths proposed for the
heterogeneous molybdenum and rhenium sulfides. The
new entry into Cp′2Re2S4 derivatives reported here
should permit us to make further comparisons with the
chemistry of the reactive Cp2Mo2S4 complexes.
X-r a y Diffr a ction Stu d y of Cp ′Re (η2-S3) Cl2, 2. Red
crystals were grown from diffusion of hexanes into a concen-
trated chloroform solution. Several crystals were examined
under Exxon Paraton oil, and the specimen crystal was cut
successively from a larger cluster. After mounting and optical
alignment of the crystal on the Siemens SMART CCD diffrac-
tometer, a set of three series of 20 0.3° ω scans was collected
and used for preliminary cell determination. An arbitrary
sphere of data was collected to 0.69 Å resolution using 30 s
0.3° ω scans. Final cell dimensions were determined from 7928
reflections chosen with I > 10σ(I).
The structure was solved by direct methods in centrosym-
metric space group P1h. There are two crystallographically
independent molecules in the asymmetric unit. Hydrogens
were placed at calculated geometries and allowed to ride on
the position of the parent atom. All non-hydrogen atoms were
refined with anisotropic parameters for thermal motion.
Isotropic hydrogen thermal parameters for methyl hydrogens
were set to 1.5 times the equivalent isotropic U value of the
parent atom. Methylene hydrogens were 1.2 times the value
for the parent atom. Residual electron density peaks were
located near the rhenium atoms and were likely artifacts of
absorption. See Table 3 for details of the structural studies.
Rea ction of 2 w ith Hyd r ogen . NMR Sca le Rea ction .
Complex 2 (0.015 g, 0.03 mmol) was dissolved in CDCl3 in an
NMR tube, and the solution was degassed in two freeze-
pump-thaw cycles on a vacuum line. Hydrogen (42 cm) was
added at -196 °C, and the tube was flame sealed. The solution
was warmed to room temperature, and the reaction was
monitored by 1H NMR spectroscopy over a period of several
days. The resonances for 1 slowly decreased in intensity, and
new resonances were observed for a single new product. A color
Exp er im en ta l Section
Gen er a l P r oced u r es a n d Ma ter ia ls. Except where noted,
syntheses were carried out under nitrogen using Schlenk line
and vacuum line techniques and a Vacuum Atmospheres
glovebox. Dichloromethane and acetonitrile were distilled from
CaH2 prior to use. Tetrahydrofuran, toluene, and diethyl ether
were distilled from sodium/benzophenone. 1H and 13C NMR
spectra were recorded on Varian VXR-300 or Varian Inova 500
1
change from red to brown was observed. H NMR: 2.29, 2.28
(31) Murray, H. H.; Wei, L.; Sherman, S. E.; Greaney, M. A.;
Eriksen, K. A.; Carstensen, B.; Halbert, T. R.; Stiefel, E. I. Inorg. Chem.
1995, 34, 841.
(2 s, CpMe); 2.24 (q, CpCH2); 1.16 (t, CpCH2CH3). In the sealed
tube, a sharp singlet was also observed at 0.79 ppm (relative

Synthesis of a Re(V) Polysulfide Complex
Organometallics, Vol. 20, No. 7, 2001 1375
intensity, ca. 2 H, H2S), and a broad resonance at 7.12 was
assigned to HCl exchanging with water in the solvent.
Syn th esis of (Cp ′Re)2(µ-S)4, 3. CpReS3Cl2, 2 (0.050 g, 0.10
mmol), was dissolved in ca. 20 mL of toluene, and the solution
was freeze-pump-thaw degassed two times. Excess hydrogen
(40 cm) was added at -196 °C, the reaction tube was sealed
with a Teflon vacuum stopcock, and the solution was heated
at 45 °C overnight with stirring. The color changed to green-
brown. The solvent was evaporated, and the remaining solid
was recrystallized under nitrogen from toluene/hexane. The
hexane-soluble fraction was evaporated to give pure 3. Yield:
ca. 50%. 1H NMR (CDCl3): 2.24, 2.26 (2 s, 12 H each); 2.32 (q,
4 H); 1.13 (t, 6 H). Mass spectrum (m/z): 800 (Cp′2(187Re)2S4);
768 (P - S); 736 (P - 2 S). UV vis (CH3CN, nm (ꢀ, M-1 cm-1)):
730 (616); 474 (530). Elemental analyses were obtained under
nitrogen on independently prepared samples with identical
NMR spectra, but reproducible values were not obtained.
Syn t h esis of [(Cp ′R e)2(µ-S2)(µ-SCH2P h )2]Br 2, 4. [Cp′-
ReS2]2, 3 (0.050 g, 0.063 mmol), was dissolved in CH2Cl2, and
benzyl bromide (15 µL, 0.13 mmol) was added. The solution
was stirred overnight, and the resulting red or red brown
to a tapered copper mounting-pin. This assembly was trans-
ferred to the goniometer of a Bruker SMART CCD diffracto-
meter equipped with an LT-2a low-temperature apparatus
operating at 143 K.
Cell parameters were determined using reflections har-
vested from a series of three orthogonal sets of 20 0.3 ω scans.
Final cell parameters were refined using 8274 reflections with
I > 10σ(I) chosen from the entire data set. All data were
corrected for Lorentz and polarization effects, as well as for
absorption. The anisotropy of the crystal created some absorp-
tion artifacts in the final structure.
Structure solution in centrosymmetric space group C2/c
revealed the heavy atom positions. Carbon positions were
located after four cycles of least-squares refinement followed
with difference Fourier synthesis. Hdyrogen atoms were placed
at calculated geometries and allowed to ride on the position
of the parent atom. All non-hydrogen atoms were refined with
anisotropic parameters for thermal motion. Thermal param-
eters for hydrogen atoms were set to 1.2 times the equivalent
isotropic U of the parent. Each bromine atom is present at
multiple sites. Atom Br(1) is disordered across two sites, with
site occupancies of 0.852(3) and 0.147(3). Atom Br(2) is
disordered across three sites, the principle site, occupancy
0.889(4), and two minor sites, which are related by crystal-
lographic symmetry. Site occupancy at each of these equivalent
sites is 0.056(2). No other disorder is present. All peaks in the
final difference map are reasonably close to heavy atom sites
and are likely absorption artifacts.
1
solution was evaporated. The H NMR spectrum of the crude
product was somewhat broadened, but resonances for 1 were
observed as well as those of another product in ca. 1:1 ratio.
The mixture was eluted on a silica gel column with CH3CN/
MeOH. Complex 1 decomposed on the column to give several
fractions, but 4 was eluted in a red band. This was evaporated
to give the product in pure form. Yield: ca. 20%. 1H NMR
(CDCl3): 2.34, 2.38 (2 s, CpMe); 1.10 (t, 6 H, CpCH2CH3); 2.35
(q, 4 H, CpCH2); 4.19 (s, 4 H, SCH2); 7.30, 7.60 (2 m, 10 H,
Ph). 13C NMR (CDCl3): 12.70, 12.95, (CpMe); 15.26 (CpCH2CH3);
21.15 (CpCH2); 48.25 (SCH2); 105.37, 107.58, 109.70 (Cp);
128.25, 128.58, 129.68, 137.18 (Ph). FAB mass spectrum,
m/z: 1060 (very weak, P - Br); 982 (P - 2 Br); 889 (Cp′2Re2S4-
CH2Ph); 798 ((Cp′2Re2S4). Analysis of NMR sample isolated
Ack n ow led gm en t. This work was supported by the
Division of Chemical Sciences, Office of Basic Energy
Sciences, Office of Energy Research, U.S. Department
of Energy.
from CDCl3, calcd for 4 + 1/2 CDCl3: C36.5H48.5Re2S4Br2Cl1.5
:
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tal data, positional and thermal parameters, bond distances,
and bond angles for 2 and 4. This material is available free of
charge via the Internet at http://pubs.acs.org.
C, 36.50; H, 4.07; S, 10.68. Found: C, 36.46; H, 4.18; S, 10.05.
X-r a y Diffr a ction Stu d y of 4. Crystals of 4 were obtained
from a toluene/hexanes solution and manipulated under a light
hydrocarbon oil. The datum crystal was affixed with a small
amount of silicone stopcock grease to a thin glass fiber attached
OM000962E