Re2(CO)10-promoted S-binding, C-S bond cleavage, and hydrogenation of benzothiophenes: Organometallic models for the hydrodesulfurization of thiophenes

Article abstract of DOI:10.1021/ja011725l

In hydrodesulfurization model reactions of dinuclear metal complexes with thiophenes, we observe that ultraviolet photolysis of Re₂(CO)₁₀ and benzothiophenes (BT*) in hexanes solution produces the ring-opened BT* complexes Re₂

Full text of DOI:10.1021/ja011725l

Published on Web 02/01/2002
Re2(CO)10-Promoted S-Binding, C-S Bond Cleavage, and
Hydrogenation of Benzothiophenes: Organometallic Models
for the Hydrodesulfurization of Thiophenes
Michael A. Reynolds, Ilia A. Guzei,† and Robert J. Angelici*
Contribution from the Ames Laboratory and Department of Chemistry, Iowa State UniVersity,
Ames, Iowa 50011
Received July 16, 2001
Abstract: In hydrodesulfurization model reactions of dinuclear metal complexes with thiophenes, we observe
that ultraviolet photolysis of Re2(CO)10 and benzothiophenes (BT*) in hexanes solution produces the ring-
opened BT* complexes Re2(CO)7(µ-BT*) (1a-d) (BT* ) benzothiophene (BT) 1a, 2-methylbenzothiophene
(2-MeBT) 1b, 3-methylbenzothiophene (3-MeBT) 1c, and 3,5-dimethylbenzothiophene (3,5-Me2BT) 1d).
The η1(S)-bound BT* complexes Re2(CO)9(η1(S)-BT*) (2a-d), prepared from Re2(CO)9(THF) and BT*,
are readily converted into 1a-d in good yields (40-60%) during UV photolysis in hexanes solution, which
suggests that the η1(S)-bound complexes 2a-d are precursors to 1a-d in the reactions of Re2(CO)10 with
BT*. Irradiation of Re2(CO)10 and 3,5-Me2BT with UV light in decane solution under an atmosphere of H2
produces complex 1d and the partially hydrogenated BT* complex Re2(CO)7(µ-3,5-Me2BT-H)(µ-H) (3d).
Reactions of 1a with phosphines yield further ring-opened BT-Re complexes of the types Re2(CO)7(PMe3)3-
i
(µ-BT) (4) and Re2(CO)7(PR3)2(µ-BT) (R ) Me (5), Pr (6), Cy (7), and bis(diethylphosphino)ethane (8)).
Structures of 1d, 2c, 3d, and 6, which demonstrate various bonding modes of benzothiophene and its
C-S cleaved derivatives to two metal centers, were determined by X-ray crystallographic studies.
Introduction
organometallic complexes as models. Thiophene coordination
to metal centers of organometallic complexes has been studied
Hydrodesulfurization (HDS) is the transition-metal-catalyzed
process used for removing sulfur from organosulfur compounds
in petroleum feedstocks.1,2 This large-scale process is typically
performed at high H2 pressures (<200 atm) and temperatures
(300-450 °C) in the presence of sulfided metal-based catalysts
such as Ni- and Co-promoted MoS2 and WS2 supported on
alumina.1,2 The sulfur content in crude petroleum is typically
in the range of 0.1-5 wt % and is present in the form of thiols,
thioethers, disulfides, and thiophenes (T*). However, it is the
alkyl-substituted benzothiophenes (BT*)3 and dibenzothiophenes
(DBT*) that are among the most difficult to desulfurize during
the HDS process due to their greater molecular size and aromatic
character.1,2
by several groups as models of thiophene adsorption on HDS
catalysts and has been the subject of reviews.4-6 Several
reports6-9 also describe reactions of thiophenes in mononuclear
metal complexes that lead to cleavage of C-S bonds. However,
there are relatively few examples of C-S bond cleavage in
complexes that contain multiple metal centers.10-13 The com-
(4) (a) Angelici, R. J. Bull. Soc. Chim. Belg. 1995, 104, 265. (b) Angelici, R.
J. Coord. Chem. ReV. 1990, 105, 61. (c) Angelici, R. J. Acc. Chem. Res.
1988, 21, 387.
(5) Rauchfuss, T. B. Prog. Inorg. Chem. 1991, 21, 259.
(6) (a) Angelici, R. J. Polyhedron 1997, 16, 3073. (b) Angelici, R. J.
Organometallics 2001, 20, 1259.
(7) (a) Bianchini, C.; Meli, A. Acc. Chem. Res. 1998, 31, 109. (b) Bianchini,
C.; Meli, A. J. Chem. Soc., Dalton Trans. 1996, 801.
(8) (a) Jones, W. D.; Chin, R. M.; Crane, T. W.; Baruch, D. M. Organometallics
1994, 13, 4448. (b) Myers, A. W.; Jones, W. D. Organometallics 1996,
15, 2905. (c) Myers, A. W.; Jones, W. D.; McClements, S. M. J. Am. Chem.
Soc. 1995, 117, 11704. (d) Jones, W. D.; Dong, L. J. Am. Chem. Soc. 1991,
113, 1577. (e) Jones, W. D.; Vicic, D. A.; Chin, R. M.; Roache, J. H.;
Myers, A. W. Polyhedron 1997, 18, 3115.
One approach to studying the catalytic HDS of thiophenes
and benzothiophenes at transition metal centers is to use
* To whom correspondence should be addressed. E-mail: angelici@
iastate.edu.
(9) (a) Garcia, J. J.; Maitlis, P. M. J. Am. Chem. Soc. 1993, 115, 12200. (b)
Iretskii, A.; Adams, H.; Garcia, J. J.; Picazo, G.; Maitlis, P. M. Chem.
Commun. 1998, 61. (c) Churchill, D. G.; Bridgewater, B. M.; Parkin, G. J.
Am. Chem. Soc. 2000, 122, 178. (d) Mills, R. C.; Abboud, K. A.; Boncella,
J. M. Chem. Commun. 2001, 1506.
(10) Brorson, M.; King, J. D.; Kiriakidou, K.; Prestopino, F.; Nordlander, E. In
Metal Clusters in Chemistry; Braunstein, P., Oro, L. A., Raithby, P. R.,
Eds.; Wiley-VCH Verlag: Weinheim, Germany, 1999; Vol. 2, pp 741-
781.
†Iowa State University Molecular Structure Laboratory.
(1) (a) Topsøe, H.; Clausen, B. S.; Massoth, F. E. Hydrotreating Catalysis:
Science and Technology; Springer-Verlag: Berlin, 1996. (b) Whitehurst,
D. D.; Isoda, T.; Mochida, I. AdV. Catal. 1998, 42, 345.
(2) Angelici, R. J. In Encyclopedia of Inorganic Chemistry; King, R. B., Ed.;
Wiley: New York, 1994; Vol. 3, pp 1433-1443.
(3) The numbering scheme for benzothiophenes (BT*) is shown below:
(11) Curtis, M. D. Appl. Organomet. Chem. 1992, 6, 429.
(12) (a) Arce, A. J.; Karam, A.; De Sanctis, Y.; Capparelli, M. V.; Deeming,
A. J. Inorg. Chim. Acta 1999, 285, 277. (b) Arce, A. J.; Arrojo, P.; Deeming,
A. J.; De Sanctis, Y. J. Chem. Soc., Dalton Trans. 1992, 2423. (c) Arce,
A. J.; De Sanctis, Y.; Karam, A.; Deeming, A. J. Angew. Chem., Int. Ed.
Engl. 1994, 33, 1381.
(13) Palmer, M. S.; Harris, S. Organometallics 2000, 19, 2114.
9
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J. AM. CHEM. SOC. VOL. 124, NO. 8, 2002 1689

A R T I C L E S
Reynolds et al.
Scheme 1
plexes Mn2(CO)7(µ-T*),14-17 [Cp*Co]2(µ-T*),18 [(dippe)Ni]2-
(µ-T*),19 and Fe2(CO)6(µ-T*)20 (T* ) T and BT) represent some
of the bimetallic complexes that contain bridging, ring-opened
thiophenes. Recently, we found that Re2(CO)10 promotes C-H
cleavage of DBT to produce Re2(CO)8(µ-C12H7S)(µ-H) and
C-S cleavage of 2,5-dimethylthiophene (2,5-Me2T) to afford
Re2(CO)7(µ-2,5-Me2T) during UV photolysis (Scheme 1).21 We
also communicated our preparation of Re2(CO)7(µ-BT) and its
reactions with PMe3.22
Figure 1. Molecular structure of Re2(CO)7(µ-3,5-Me2BT) (1d). Thermal
ellipsoids were drawn at the 30% probability level. Selected bond distances
(Å) and angles (deg): Re(1)-Re(2), 2.9245(3); Re(1)-S(1), 2.4320(13);
Re(2)-S(1), 2.4995(13); C(4)-C(5), 1.403(7); S(1)-C(12), 1.787(5); C(5)-
C(7), 1.503(7); Re(1)-S(1)-Re(2), 72.73(3); C(4)-C(5)-C(7), 122.9(5);
Re(1)-S(1)-C(12), 101.38(18); Re(2)-S(1)-C(12), 102.31(17).
Scheme 2. Preparations of Re2(CO)7(µ-BT*) (1a-d)
Herein we report detailed studies of the Re2(CO)10-promoted
cleavage of Cvinyl-S bonds in alkyl-substituted benzothiophenes
(BT*) during UV photolysis to afford BT* complexes of the
type Re2(CO)7(µ-BT*). These new investigations also include
reactions of the Re2(CO)7(µ-BT*) complexes with phosphines
and H2 to produce unexpected dinuclear ring-opened and
partially hydrogenated BT* complexes.
Results and Discussion
Synthesis of Re2(CO)7(µ-BT*) Complexes (1a-d). Ultra-
violet irradiation of a Re2(CO)10 and 2-3 equiv of BT* (BT*
) BT, 2-MeBT, 3-MeBT, or 3,5-Me2BT) in hexanes solution
for 24 h produces the ring-opened BT* complexes Re2(CO)7-
(µ-BT*) (1a-d) in moderate yields (20-50%) (pathway a in
Scheme 2). Complexes 1a-d are air-stable, orange solids that
are soluble in most organic solvents including CH2Cl2, benzene,
and hexanes. In solution, 1a-d are stable for days at room
temperature if stored under an inert atmosphere. The molecular
structure for 1d (Figure 1) contains a ring-opened 3,5-Me2BT
ligand that has been cleaved regioselectively at the Cvinyl-S
bond and bridges the Re2(CO)7 backbone through the S atom
and the η1,η2-bonded vinyl group. Cleavage of the vinyl C-S
bond in the BT* ligands of 1a-d was unaffected even by a
methyl substituent at the 2-position of the BT* ligand. This is
in contrast to results reported for other systems6b including those
by Jones et al.8c for the reaction of 2-MeBT with Cp*Rh(PMe3)-
(Ar)(H) (Cp* ) η5-C5Me5; Ar ) Ph or 3,5-xylyl). In this system,
Rh metal insertion into the Cvinyl-S bond of 2-MeBT gave, as
the kinetic product, Cp*Rh(PMe3)(Cvinyl,S-2-MeBT) which
readily converted into the Caryl-S cleaved isomer Cp*Rh(PMe3)-
(Caryl,S-2-MeBT) upon heating (74 °C, 38 h) in C6D12 solution.
Complex 1a was not converted into a Caryl-S metal-inserted
isomer even after heating in refluxing toluene for 2 d.
Complexes 1a-d do not react with the electrophiles methyl
iodide, methyl trifluoromethane sulfonate (TfOMe), or TfOH.
1
In the H NMR spectra of 1a-d (in CD2Cl2), the chemical
shift for the terminal vinyl proton of 1a (δ 8.63, d, J ) 11.4),
1c (δ 8.22, s), and 1d (δ 8.20, s) is shifted to low field as
compared to that in the free BT* molecules (δ 7.95-7.00). This
significant downfield shift of the vinyl protons is consistent with
Cvinyl-S cleavage of the BT* ligands and η1-binding of the
terminal vinyl carbon to a Re metal center. In the iron complex
Fe2(CO)6(µ-BT),20 which contains a bridging ring-opened BT
ligand similar to that in 1a, a significant downfield shift for the
terminal BT vinyl proton (δ 8.99 in CDCl3) was also observed.
The chemical shift for the methyl protons of the 2-MeBT ligand
(CD2Cl2) in 1b (δ 3.16, s) is also downfield of that in free
2-MeBT (δ 2.60).
(14) (a) Dullaghan, C. A.; Sun, S.; Carpenter, B. W.; Sweigart, D. A. Angew.
Chem., Int. Ed. Engl. 1996, 35, 212. (b) Dullaghan, C. A.; Carpenter, G.
B.; Sweigart, D. A.; Choi, D. S.; Lee, S. S.; Chung, Y. K. Organometallics
1997, 16, 5688.
(15) Zhang, X.; Dullaghan, C. A.; Carpenter, G. B.; Sweigart, D. A.; Meng, Q.
Chem. Commun. 1998, 93.
(16) Zhang, X.; Dullaghan, C. A.; Watson, E. J.; Carpenter, G. B.; Sweigart,
D. A. Organometallics 1998, 17, 2067.
(17) Dullaghan, C. A.; Zhang, X.; Walther, D.; Carpenter, G. B.; Sweigart, D.
A. Organometallics 1997, 16, 5604.
(18) (a) Chin, R. M.; Jones, W. D. Organometallics 1992, 11, 2698. (b) Jones,
W. D.; Chin, R. M. J. Organomet. Chem. 1994, 472, 311.
(19) Vicic, D. A.; Jones, W. D. J. Am. Chem. Soc. 1999, 121, 7606.
(20) Ogilvy, A. E.; Draganjac, M.; Rauchfuss, T. B.; Wilson, S. R. Organo-
metallics 1988, 7, 1171.
Proposed Mechanism for the Formation of 1a-d. A
possible mechanism (Scheme 3) for the formation of complexes
1a-d by pathway a in Scheme 2 is similar to that proposed by
Brown and co-workers for the formation of alkenyl complexes
(21) Reynolds, M. A.; Guzei, I. A.; Angelici, R. J. Organometallics 2001, 20,
1071.
(22) Reynolds, M. A.; Guzei, I. A.; Angelici, R. J. Chem. Commun. 2000, 513.
9
1690 J. AM. CHEM. SOC. VOL. 124, NO. 8, 2002

Models for the Hydrodesulfurization of Thiophenes
A R T I C L E S
Scheme 3. Mechanism for the Formation of Complexes 1a-d
TEMPO has been used to trap M(CO)5 (M ) Mn or Re) radicals
during UV photolysis of M2(CO)10 to produce the neutral
M-N-O metallacycles of the type (TEMPO)M(CO)3.25 When
a hexanes solution (35 mL) containing Re2(CO)10 (0.238 mmol)
and BT (0.714 mmol) was irradiated with UV light (-5 °C) in
the presence of TEMPO (0.474 mmol), unreacted Re2(CO)10
and a trace of Re2(CO)7(µ-BT) (1a) was detected by IR
spectroscopy after 2 h. After 23 h, all of the Re2(CO)10 had
reacted, and the intensity of the ν(CO) bands corresponding to
1a had not increased. Although other Re products were not
identified, an IR spectroscopic analysis of the oily precipitate
resulting from the reaction did not reveal any ν(CO) bands that
corresponded to 1a or 2a. The inhibitory effect of TEMPO is
consistent with Re-Re bond homolysis as the major pathway
in the formation of 1a. The small amount of 1a detected in the
TEMPO experiment could likely result from the CO dissociation
pathway (eqs 1 and 2) which would not have been inhibited by
the TEMPO. However, since the ν(CO) bands corresponding
to 1a were very weak during the TEMPO reaction, this cannot
be a dominant pathway.
The formation of 1a-d from 2a-d in steps 1 and 3 of
Scheme 3 must also be promoted photolytically as this conver-
sion does not occur thermally under the conditions of the
reactions. Photolytic loss of a CO from the adjacent Re(CO)5
moiety in 2a-d with subsequent η2-binding of the BT vinyl
group would yield (step 2) a bridging BT* species Re2(CO)8-
(µ2-η1(S),η2-BT*). Subsequent CO loss and oxidative addition
of the vinyl C-S bond of BT* would produce the 1a-d
products. None of the proposed intermediates, including Re2-
(CO)9(η1(S)-BT*) (2a-d) and Re2(CO)8(η1(S)-BT*)2, were
observed during the formation of 1a-d; however, irradiation
of Re2(CO)9(η1(S)-3-MeBT) (2c) in hexanes solvent for 1-5 h
did produce 1c in good yield (>50%) as illustrated in reaction
c of Scheme 2. This conversion of 2c to 1c supports the proposal
that 2a-d are precursors to 1a-d.
of the type Re2(CO)8(µ-alkenyl)(µ-H).23 The first step (1), which
involves the formation of the Re2(CO)9(η1(S)-BT*) (2a-d)
complexes, is similar to that for the photochemical reaction of
Re2(CO)10 with donor ligands (L ) phosphines)24 to form
complexes of the type Re2(CO)9(L) and Re2(CO)8(L)2, which
can occur by two mechanisms: [1] CO dissociation from Re2-
(CO)10 to afford Re2(CO)9 species (eq 1) and [2] cleavage of
the Re-Re bond in Re2(CO)10 to generate •Re(CO)5 radicals
(eq 3). In the CO dissociation pathway, the Re2(CO)9 species
would react with BT* molecules to give the Re2(CO)9(η1(S)-
BT*) (2a-d) complexes (eq 2).24 In the Re-Re bond cleavage
pathway, •Re(CO)5 radicals would undergo thermal CO sub-
stitution by BT* to produce •Re(CO)4(η1(S)-BT*) radicals (eq
4). Coupling of these radicals with •Re(CO)5 (eq 5) or another
•Re(CO)4(η1(S)-BT*) (eq 6) would produce complexes 2a-d
or Re2(CO)8(η1(S)-BT*)2.
hν
Re2(CO)10
y
z Re2(CO)9 + CO
(1)
(2)
Synthesis of Re2(CO)9(η1(S)-BT*) (2a-d). The S-bound
complexes Re2(CO)9(η1(S)-BT*) (2a-d) were prepared by two
different routes. In method A, BT* was added to a THF solution
of Re2(CO)9(THF) prepared by UV photolysis of Re2(CO)10 in
THF (path b, Scheme 2). In method B, the Re2(CO)9(THF)
precursor was prepared by reaction of Re2(CO)10 with Me3-
NO,26,27 in a procedure similar to that used for the preparation
of Re2(CO)9(CH3CN). Both methods produced 2a-d in low to
moderate yields (10-40%). Complexes 2a-d are moderately
air-stable in the solid state and are soluble in CH2Cl2, benzene,
and hexanes solvents. The BT* ligands of 2a-d are labile as
demonstrated by the reaction of 2d with CO (1 atm) which
resulted in displacement of the 3,5-Me2BT ligand to give Re2-
(CO)10 in less than 2 min; this is the time required to record
the IR spectrum.
Re2(CO)9 + BT* h Re2(CO)9(BT*)
hν
Re2(CO)10
y
z 2Re(CO)5
(3)
(4)
(5)
(6)
Re(CO)5 + BT* h Re(CO)4(BT*) + CO
Re(CO)4(BT*) + Re(CO)5 h Re2(CO)9(BT*)
2Re(CO)4(BT*) h Re2(CO)8(BT*)2
The following experiments were conducted to provide sup-
porting evidence for either the CO dissociation or the Re-Re
homolytic bond cleavage pathways. When Re2(CO)10 (0.377
mmol) and excess BT (1.00 mmol) were irradiated with UV
light under CO (1 atm) for 42 h (15 °C) in hexanes solution
(35 mL), the Re2(CO)10 and BT remained unreacted. In this
experiment, the CO could inhibit both pathways by suppressing
eqs 1 and 4. If a Re(CO)5 radical pathway is involved, a radical
scavenger such as TEMPO (2,2,6,6-tetramethyl-piperidinyl-1-
oxy radical) should inhibit the formation of the 2a-d complexes.
The 1H NMR spectra of 2a-d indicate S-binding of the BT*
ligands; chemical shifts of the BT* protons are within (0.05-
0.30 ppm of those of free BT* (δ 7.95-7.00 in CD2Cl2). Similar
small chemical shifts were observed in 1H NMR spectra of the
S-bound BT complexes CpRe(CO)2(η1(S)-BT),28,29 M(CO)5(η1-
(25) Jaitner, P.; Huber, W.; Huttner, G.; Scheidsteger, O. J. Organomet. Chem.
(23) Nubel, P. O.; Brown, T. L. J. Am. Chem. Soc. 1984, 106, 644.
(24) (a) Meyer, T. J.; Caspar, J. V. Chem. ReV. 1985, 85, 187. (b) Moelwyn-
Hughes, J. T.; Garner, A. W. B.; Gordon, N. J. Organomet. Chem. 1971,
26, 373. (c) Lee, S. W.; Wang, L. F.; Cheng, C. P. J. Organomet. Chem.
1983, 248, 189. (d) Byers, B. H.; Brown, T. L. J. Am. Chem. Soc. 1975,
97, 3260.
1983, 259, C1.
(26) Koelle, U. J. Organomet. Chem. 1978, 155, 53.
(27) Ingham, W. L.; Leins, A. E.; Coville, N. J. S.-Afr. Tydskr. Chem. 1991,
44, 6.
(28) Choi, M.-G.; Robertson, M. J.; Angelici, R. J. J. Am. Chem. Soc. 1991,
113, 4005.
9
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A R T I C L E S
Reynolds et al.
thiophene ligand. More electron density on the metal center
increases π-back-bonding, which results in a larger tilt angle
and also a shorter M-S bond distance. Therefore, the relatively
electron-deficient Re center in 2c exhibits a smaller tilt angle
and longer Re-S bond distance as compared to these parameters
in the Cp*Re(CO)2(η1(S)-T*) (T* ) T or 3-MeBT)29,33 com-
plexes. The sulfur geometry in 2c is also described by the sum
of the angles around the sulfur (308.3°) which would equal 360°
if the S atom were planar (sp2-hybridized).
The C-S bonds in 2c (C(10)-S, 1.746(14) Å; C(17)-S,
1.737(7) Å) are significantly shorter than those in Cp*Re(CO)2-
(η1(S)-3-MeBT) (1.92(2) Å and 1.74(3) Å, respectively),29 but
similar to those (1.75(1) and 1.741(9) Å) in free 2,3-
dimethylbenzothiophene.35a The Re-Re bond distance (3.0343-
(4) Å) compares well with that in both Re2(CO)9(η1(S)-DBT)
(3.0389(2) Å)21 and Re2(CO)10 (3.0413(11) Å).35b
Photolysis Reaction of Re2(CO)10 and 3,5-Me2BT with H2.
When Re2(CO)10 and 3-5 equiv of 3,5-Me2BT are irradiated
with UV light in a H2-saturated decane solution (24-36 h, 10
°C), the complexes H2Re2(CO)8, Re2(CO)7(µ-3,5-Me2BT) (1d),
and the partially hydrogenated BT* complex Re2(CO)7(µ-3,5-
Me2BT-H)(µ-H) (3d) are produced (eq 7).
Figure 2. Molecular structure of eq-Re2(CO)9(η1(S)-3-MeBT) (2c). Thermal
ellipsoids drawn at the 30% probability level. Selected distances (Å) and
angles (deg): Re(1)-Re(2), 3.0343(4); Re(2)-S, 2.5220(18); Re(2)-C(9),
1.927(7); S-C(10), 1.806(9); S-C(17), 1.685(9); C(10)-C(11), 1.268(12);
Re(1)-Re(2)-S, 89.21(4); Re(2)-S-C(10), 106.3(3); Re(2)-S-C(17),
111.5(3); C(10)-S-C(17), 90.5(4); tilt angle (θ) ) 116.9°.
(S)-BT) (M ) Cr or W),30 and [CpFe(CO)2(η1(S)-BT)+].31 If
the BT* ligands were η2-bonded through the olefin moiety, then
the olefinic protons would be expected to shift to higher field
1
as observed in the H NMR spectrum of Cp*Re(CO)2(2,3-η2-
BT)29 (δ 4.25 and 3.96 ppm in CDCl3). Complexes of the type
Re2(CO)8(η1(S)-BT*)2 were not observed during the synthesis
of Re2(CO)9(η1(S)-BT) by either method.
In the structure of 2c (Figure 2), the Re-S bond distance
(2.5220(18) Å) is similar to those in the analogous DBT complex
Re2(CO)9(η1(S)-DBT)21 (2.5375(8) Å) and the thietane complex
Re2(CO)9(SCH2C(CH3)2CH2) (2.485(4) Å).32 However, as com-
pared to Re complexes which have more electron density on
the Re center such as Cp*Re(CO)2(η1(S)-T) (2.360(3) Å)33 and
Cp*Re(CO)2(η1(S)-3-MeBT)29 (2.349(2) Å), the Re-S distance
for 2c is significantly longer. The tilt angle (θ) for 2c, which is
defined as the angle between the Re-S bond and the vector
from the sulfur to the midpoint between the C(11) and C(12)
carbons of the 3-MeBT ligand, is used to describe the geometry
around the thiophene sulfur atom. In complex 2c, the value of
θ is 116.9°, which indicates that the 3-MeBT sulfur is pseudo-
sp3 hybridized, in contrast to a value of 180° which would
indicate a sp2 sulfur. The tilt angle for 2c is similar to that in
the analogous DBT complex Re2(CO)9(η1(S)-DBT) (θ )
113.6°)21 and comparable to that in other complexes which
contain electron-deficient metal centers such as (CO)5W(η1(S)-
DBT)30 (118.8°), (CO)5Cr(η1(S)-DBT) (121.8°),30 and [CpFe-
(CO)2(η1(S)-DBT)+] (119.4°).31 However, the tilt angle in 2c
is much smaller as compared to that in the electron-rich
complexes Cp*Re(CO)2(η1(S)-3-MeBT) (θ ) 131.0°)29 and
Cp*Re(CO)2(η1(S)-T) (θ ) 140.4°).33 Harris34 has proposed that
the tilt angle in S-bound metal-thiophene complexes can be
used as an indicator of π-back-donation from the metal to the
Complex 3d, obtained in low yield (6-18%), contains a
bridging ring-opened 3,5-Me2BT ligand that formally results
from the addition of H2 across the Re-C vinyl bond of 1d to
give an η2-bound vinyl group and bridging hydride. To
determine whether complex 3d was indeed formed from 1d, a
decane solution of 1d was irradiated with UV light (1 atm H2,
10 °C, 15-18 h) to give Re2(CO)7(µ-3,5-Me2BT-H)(µ-H) (3d).
Under the same reaction conditions, complex 1c also converted
into Re2(CO)7(µ-3-MeBT-H)(µ-H) (3c) in a similar fashion.
Complexes 3c and 3d are colorless solids that are soluble in
CH2Cl2, toluene, and THF, but only moderately soluble in
hexanes and decane. Both complexes are air-stable in the solid
state but in solution must be stored under an inert atmosphere.
1
The H NMR spectra of 3c and 3d are significantly different
from those of 1c and 1d. The chemical shift of the protons on
the η2-vinyl group of 3c (in CD2Cl2) are observed at δ 4.31
and 4.06 ppm which are upfield as compared to the terminal
proton on the vinyl carbon of 1c (δ 8.22 ppm). Similar
differences in chemical shifts were observed between the vinyl
protons of the partially hydrogenated 3,5-Me2BT ligand in 3d
(in CDCl3, δ 4.28 and 4.03 ppm) when compared to the shift
of the vinyl proton in 1d (δ 8.14 ppm). The hydride ligand
signals were observed in the spectra of 3c and 3d at δ -12.60
and δ -12.62, respectively.
(29) (a) Choi, M.-G.; Angelici, R. J. Organometallics 1992, 11, 3328. (b) Li,
H.; Yu, K.; Watson, E. J.; Virkaitis, K. L.; D’Acchioli, J. S.; Carpenter, G.
B.; Sweigart, D. A. Organometallics, in press.
(30) Reynolds, M. A.; Guzei, I. A.; Logsdon, B. C.; Thomas, L. M.; Jacobson,
R. A.; Angelici, R. J. Organometallics 1999, 18, 4075.
(31) Goodrich, J. D.; Nickias, P. N.; Selegue, J. P. Inorg. Chem. 1987, 26, 3426.
(32) Adams, R. D.; Perrin, J. L.; Queisser, J. A.; Wolfe, J. B. Organometallics
1997, 16, 2612.
In the molecular structure of 3d (Figure 3), the Re-Re bond
distance (3.1083(3) Å) is similar to that in other dirhenium
complexes that contain a bridging hydride ligand such as Re2-
(33) Choi, M.-G.; Angelici, R. J. Organometallics 1991, 10, 2436.
(34) (a) Harris, S. Polyhedron 1997, 16, 3219. (b) Harris, S. Organometallics
1994, 13, 2628.
(35) (a) Hogg, J. H. C.; Sutherland, H. H. Acta Crystallogr., Sect. B 1974, 30,
2058. (b) Churchill, M. R.; Amoh, K. N.; Wasserman, H. J. Inorg. Chem.
1981, 20, 1609.
9
1692 J. AM. CHEM. SOC. VOL. 124, NO. 8, 2002

Models for the Hydrodesulfurization of Thiophenes
A R T I C L E S
Scheme 4
Figure 3. Molecular structure of Re2(CO)7(µ-3,5-Me2BT-H)(µ-H) (3d).
Thermal ellipsoids are drawn at the 30% probability level. Selected bond
distances (Å) and angles (deg): Re(1)-Re(2), 3.1083(3); Re(1)-S, 2.4444-
(14); Re(2)-S, 2.4883(14); Re(1)-C(4), 2.417(6); Re(1)-C(5), 2.532(6);
S-C(12), 1.783(6); C(4)-C(5), 1.379(8); Re(1)-S-Re(2), 78.11(4); Re-
(1)-S-C(12), 104.6(2); Re(2)-S-C(12), 103.21(18); C(4)-C(5)-C(7),
120.3(5).
4 and the pale yellow complexes 5-8 are soluble in CH2Cl2,
toluene, and benzene but sparingly soluble in hexanes. Each
complex can be handled in air for short times (<1 h) and is
moderately stable in solution.
In the 1H NMR spectrum of 4 (in CD2Cl2), the chemical shift
for the vinyl proton in the 2-position of the BT ligand (δ 7.89,
dd, J ) 13.5, 3.9 Hz) is shifted upfield of that in the spectrum
of 1a (δ 8.63, d, J ) 11.4 Hz). However, the proton in the
3-position (δ 7.43, dd, J ) 7.8, 1.2 Hz) is shifted downfield as
compared to that of 1a (δ 7.00, d, J ) 11.4 Hz). The dd pattern
for the vinyl proton signals for 4 is due to coupling (JHP ) 3.9
(CO)8(µ-H)(SC6H11) (3.0934(10) Å)36 and Re2(CO)8(µ-H)(2-
S-naphthyl) (3.0909(8) Å).36 However, this distance is signifi-
cantly shorter than that in the C-H cleaved DBT complex
Re2(CO)8(µ-H)(µ-SC12H7) (3.345 Å)21 (Scheme 1). The vinyl
group in 3d is bound in a η2-fashion to the Re(CO)3 moiety as
evidenced by the Re(1)-C(4) (2.417(6) Å) and Re(1)-C(5)
(2.532(6) Å) bond distances.
1
Hz) to the PMe3 phosphorus. In the H NMR spectra of 5-7,
The reaction of Re2(CO)10 with 3-MeBT or 3,5-Me2BT and
H2 (eq 7) to form 3c and 3d likely involves Re2(CO)7(µ-BT*)
intermediates (1c and 1d) as noted above. Both the formation
of these intermediates and their subsequent conversion to the
products (3c and 3d) must be promoted by UV light as neither
of these steps occurs without light. The mechanism of formation
of 1c and 1d was discussed above. The mechanism for
converting 1c and 1d to 3c and 3d could involve photopromoted
dissociation of the olefin or cleavage of the Re-Re bond. Either
process would allow coordination of η2-H2 which could lead to
the product.
Reactions of 1a with Phosphines. In a recent communica-
tion,22 we reported the reaction of Re2(CO)7(µ-BT) (1a) with
an excess of PMe3 in toluene solution at room temperature to
produce the further ring-opened BT complexes Re2(CO)7-
(PMe3)3(µ-BT) (4) and Re2(CO)7(PMe3)2(µ-BT) (5) whose
structures were established by X-ray diffraction studies (Scheme
4). Complex 1a also reacts with PiPr3 (5 equiv) and PCy3 (2
equiv) to produce the Re2(CO)7(PR3)2(µ-BT) complexes 6 (R
) iPr) and 7 (R ) Cy) which are structural analogues of 5, but
no evidence for complexes analogous to 4 was observed in these
reactions. Also, 1a reacts with the bidentate phosphine bis-
(diethylphosphino)ethane (depe) to give Re2(CO)7(depe)(µ-BT)
(8) with the proposed structure below. The colorless complex
the proton in the 2-position of the BT ligand of 5 (8.06, dd, J
) 14.1, 2.4 Hz), 6 (δ 8.30, dd, J ) 14.4, 2.1 Hz), and 7 (δ
8.33, dd, J ) 14.0, 2.0 Hz) is upfield of that observed in the
spectrum of 1a (δ 8.63 d, J ) 11.4 Hz). The vinyl proton in
the 3-position of the BT ligand in 5 (δ 7.44, dd, J ) 14.1, 3.6
Hz), 6 (δ 7.43, dd, J ) 14.4, 3.0 Hz), and 7 (δ 7.46, dd, J )
14.4, 2.4 Hz) is downfield of that of 1a (δ 7.00, d, J ) 11.4
Hz). Again, the vinyl protons in the spectra of 5-7 are split by
coupling to each other and to the phosphine ligand on the same
Re.
In the structure of 6 (Figure 4), a BT ligand that is cleaved
at the Cvinyl-S position bridges the two Re metal centers through
the sulfur atom, and the η1-vinyl group is bonded to the Re-
(CO)3(PiPr3) moiety. Each Re in 6 also contains one coordinated
PiPr3 group similar to that reported for the structurally analogous
5 which contains PMe3 ligands. The sulfur in 6 bridges the two
Re centers nearly symmetrically with distances of 2.5296(15)
Å for Re(1)-S and 2.5499(15) Å for Re(2)-S. These distances
are slightly longer than those observed in the structure of 1a
(Re(1)-S, 2.506(2) Å; Re(2)-S, 2.431(3) Å) in which there is
a Re-Re bond. The CdC distance of the vinyl group in 6 is
1.343(10) Å which is the same as that in 5 (1.343(5) Å) and
slightly shorter than that in 1a (1.370(14) Å). The Re(1)-C(13)
distance of 2.173(6) Å is also similar to that observed in 5
(2.169(3) Å) but shorter than that in complex 1a (2.208(10) Å)
in which the vinyl group is bridging.
In the 1H NMR spectrum of complex 8 (in CD2Cl2), the vinyl
BT protons (δ 7.71 and 7.43 ppm) are observed as doublets
due to coupling between these protons. The absence of
phosphorus coupling to the vinyl protons in 8 indicates that the
(36) Egold, H.; Schwarze, D.; Florke, U. J. Chem. Soc., Dalton Trans. 1999,
3203.
9
J. AM. CHEM. SOC. VOL. 124, NO. 8, 2002 1693

A R T I C L E S
Reynolds et al.
Scheme 6. Proposed Mechanism for the Formation of
Re2(CO)7(PR3)2(µ-Bt) (5-7) According to Scheme 4
Figure 4. Molecular structure of Re2(CO)7(PiPr3)2(µ-BT) (6). Thermal
ellipsoids are drawn at the 40% probability level. Selected bond distances
(Å) and angles (deg): Re(1)-S, 2.5296(15); Re(2)-S, 2.5499(15); Re-
(1)-C(13), 2.173(6); C(13)-C(14), 1.343(10); C(14)-C(15), 1.492(9); Re-
(1)-P(1), 2.5467(14), Re(2)-P(2), 2.5316(14); Re(1)-S-Re(2), 116.69(5);
Re(1)-S-C(20), 108.8(2); Re(2)-S-C(20), 102.7(2).
the formation of 8 in the reaction of 1a with depe. Displacement
of the BT sulfur in the final step in Scheme 5 is proposed
because the bridging sulfur in 5 is stable and is not displaced
by PMe3 under the conditions of the reaction.
Scheme 5. Proposed Mechanism for the Formation of
Re2(CO)7(PMe3)3(µ-Bt) (4) According to Scheme 4
A possible mechanism for the formation of the Re2(CO)7-
(PR3)2(µ-BT) complexes 5-7 from 1a-d is shown in Scheme
6. A distinguishing structural feature in these complexes is that
the terminal BT vinyl carbon is η1-bound to the Re(CO)3 unit
and not to the Re(CO)4 unit as observed in 1a and also in 4. A
reasonable mechanism for the formation of 5-7 must account
for the η1-vinyl bond to the Re(CO)3 moiety in the structures
of the products. The first step in the proposed mechanism
(Scheme 6) is the migration of a CO ligand from the Re(CO)4
group in 1a to the Re(CO)3 moiety to afford the isomer 1a′.
1
Although 1a′ has not been observed in the H NMR spectrum
of 1a in solution, as shown by the absence of any change in
1
the H NMR spectrum of 1a in CD2Cl2 over the temperature
range from +20 to -50 °C, a variable temperature 13C NMR
study of 1a (in CD2Cl2 solution) did show evidence for rapid
CO migration between the Re metal centers. The 13C NMR
spectrum of 1a at -50.1 °C exhibits a signal for each of the
seven carbonyl ligands at δ 193.4, 192.6, 189.9, 185.6, 184.7,
184.3, and 177.6 ppm. This spectrum is consistent with the static
structure of 1a in the solid state which was established by an
X-ray diffraction study.22 However, at +20.1 °C, the seven
signals observed at -50.1 °C coalesce into three signals (at δ
189.1 br, 187.4 br, and 185.9 sh ppm), which suggests that the
carbonyl ligands of the Re(CO)3 unit and the Re(CO)4 unit of
1a are rapidly exchanging between the Re centers.
Although presumably formed in only low concentration,
isomer 1a′ is proposed to react with a PR3 ligand at either the
η2-vinyl group or the Re-Re bond (Scheme 6). Cleavage of
the Re-Re bond (step 2) seems more likely as the relatively
unhindered Re(CO)3 unit would be susceptible to attack by PR3.
Phosphine displacement of the η2-bound vinyl group on the Re-
(CO)4 unit in step 3 would give observed products Re2(CO)7-
(PR3)2(µ-BT) (5-7). Although this proposed mechanism rea-
sonably accounts for the formation of 5-7, neither of the
intermediates could be observed spectroscopically.
coordinated vinyl group is bound to the Re center that is not
coordinated to the phosphine ligand. Additional evidence that
the structure of 8 is different from that of 5-7 is found in the
different pattern and intensities of the CO stretching frequencies
in 8 (in CH2Cl2: 2079 w, 2029 s, br, 1974 s, 1964 s, br, and
1907 s, br, cm-1) as compared with those for 5 (in CH2Cl2:
2100 w, 2018 m, 2003 s, 1953 m, 1896 m, and 1873 m cm-1).
Scheme 5 shows a possible mechanism that accounts for the
formation of 4 from the reaction of complex 1a with PMe3.
The first step (1) of this mechanism involves cleavage of the
Re-Re bond upon reaction with PMe3 to give the intermediate
Re2(CO)7(PMe3)(µ-BT). Addition of a second PMe3 ligand to
the Re(CO)3(PMe3) unit results (step 2) in displacement of the
η2-bound vinyl group by PMe3 to produce the intermediate Re2-
(CO)7(PMe3)2(µ-BT). We propose that this intermediate, al-
though not observed directly, has a structure that is analogous
to Re2(CO)7(depe)(µ-BT) (8). In the final step, an additional
PMe3 displaces the sulfur ligand to produce 4. The order of
steps 1 and 2 could be interchanged since there is no
spectroscopic evidence (1H NMR) to support the existence of
either intermediate. Steps 1 and 2 also reasonably account for
The phosphines used in the preparations of complexes 6 and
7 were chosen for their larger cone angles (PiPr3, 160°; PCy3,
170°)37 and similar basicities as compared to PMe3 (118°).37
All three phosphines produce similar disubstituted phosphine
9
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Models for the Hydrodesulfurization of Thiophenes
A R T I C L E S
Experimental Section
complexes of the type Re2(CO)7(PR3)2(µ-BT) (5-7). However,
complex 1a reacts with PMe3 to also yield the trisubstituted
phosphine complex 4. Since the relative amounts of 4 and 5
formed are the same whether 1 or 5 equiv of PMe3 is used
(Scheme 4), the tris(phosphine) product 4 cannot be formed from
the bis(phosphine) product 5. Therefore, 4 and 5 must be formed
by independent pathways, as suggested in Schemes 5 and 6.
The observation that only complexes of type 5 are formed in
reactions of 1a with the bulky phosphines suggests that these
phosphines react faster with 1a′ (Scheme 6) than with 1a
(Scheme 5). Perhaps the less crowded Re(CO)3 unit in 1a′ is
more susceptible to attack by bulky phosphines than either Re
in 1a.
General Considerations. All reactions were performed under a
nitrogen or argon atmosphere in reagent grade solvents using standard
Schlenk techniques. The solvents, hexanes, methylene chloride, toluene,
and tetrahydrofuran (THF), were dried using the Grubbs solvent
purification system38 (Solv-Tek, Inc.). Benzene and decane were dried
and distilled over CaH2 prior to use. Deutero-methylene chloride
(Cambridge) and CDCl3 (Cambridge) were stored over 4 Å molecular
sieves. Rhenium carbonyl was purchased from Strem Chemicals Inc.
Benzothiophene (Aldrich Chemical Co.), 3-methylbenzothiophene
(Maybridge Chemical Co.), and 3,5-dimethylbenzothiophene (May-
bridge Chemical Co.) were used as received without further purification.
2-Methylbenzothiophene was prepared according to a literature
procedure.8c The preparation of Re2(CO)9(THF) was previously de-
scribed.21 Trimethylamine N-oxide (Me3NO) (Aldrich) was dried by
azeotropic distillation of water in dry benzene. Silica gel (40-140 mesh,
J. T. Baker) was dried and degassed under vacuum for 14 h at ambient
temperature and stored under argon. TEMPO (2,2,6,6-tetramethyl-1-
piperidinyloxy free radical) was purchased from Aldrich.
1H NMR spectra for all complexes were recorded using a Varian
VXR-300 MHz, a Bruker AC 200 MHz, or an in-house 400 MHz
spectrometer with the appropriate deutero-solvent used as both the
internal lock and the internal reference. Solution infrared spectra were
recorded on a Nicolet-560 spectrometer using NaCl cells with 0.1 mm
spacers. Elemental analyses were performed on a Perkin-Elmer 2400
series II CHNS/O analyzer. All photochemical reactions were carried
out in a 50 mL capacity quartz Schlenk photolysis tube fitted with a
coldfinger which was immersed into the reaction solution. All photolysis
experiments were performed using a Hanovia 450 W Hg medium-
pressure lamp inserted into a water-cooled quartz jacket. The reaction
temperature was controlled using an Isotemp 1013P refrigerated
circulating bath (Fisher Scientific) with circulation hoses connected to
the coldfinger.
Conclusion
Although the HDS of thiophenes and benzothiophenes is often
considered to occur by similar pathways, it is clear in the present
studies that each of these thiophenes reacts with Re2(CO)10 to
give different types of products. With 2,5-dimethylthiophene
under UV photolysis, Re2(CO)10 gives Re2(CO)7(µ-2,5-Me2T)
(Scheme 1) in which a C-S bond is cleaved but there is no
Re-Re bond.21 However, the reaction of Re2(CO)10 with
benzothiophene under the same conditions gives Re2(CO)7(µ-
BT) (1a) (Scheme 2) in which the C-S bond is cleaved but
there is a Re-Re bond. The presence or absence of a Re-Re
bond appears to be related to the availability of π-coordinating
olefinic groups in the bridging thiophene ligand. In Re2(CO)7-
(µ-BT) (1a), there is only one coordinating olefinic group which
allows the formation of the Re-Re bond in order to achieve an
18-electron count at both metal centers. In Re2(CO)7(µ-2,5-
Me2T), two olefins are capable of coordinating which obviates
the need for a Re-Re bond. The reaction of Re2(CO)10 with
DBT under UV photolysis gives quite different products.21 One
is the S-coordinated Re2(CO)9(η1(S)-DBT), while the other is
the C-H cleaved Re2(CO)8(µ-C12H7S)(µ-H) (Scheme 1). More-
over, DBT gives no products resulting from C-S cleavage.
Thus, Re2(CO)10 demonstrates unique reactivities with 2,5-
Me2T, BT, and DBT, which contrasts with reactions of these
thiophenes with other dinuclear complexes.18-20
In Re2(CO)7(µ-BT) (1a), the Re atoms can be partially
removed from the bridging C-S-cleaved BT ligand by reaction
with phosphines (Scheme 4). The resulting products arise from
the replacement of Re-Re, Re-olefin, and Re-S bonds in 1a
with Re-PR3 bonds. Complexes 1, 4, and 5-8 illustrate three
different ways in which C-S-cleaved BT can bridge two metal
centers, as may occur on an HDS catalyst surface.
When the Re2(CO)7(µ-BT*) complexes, where BT* )
3-MeBT or 3,5-Me2BT, are photolyzed under an atmosphere
of H2, 1 equiv of H2 is added to give Re2(CO)7(µ-BT*•H)(µ-
H) with a bridging 2-vinylthiophenolate ligand resulting from
the cleavage of a Re-C bond and partial hydrogenation of the
bridging BT (eq 7). This addition of H2 to a C-S-cleaved BT
ligand in a dinuclear complex may also be involved in the
hydrogenation37a of benzothiophene in the presence of [Cp*Ir-
(Cl)(µ-H)]2 under an atmosphere of H2 at 90° to give (Cp*IrCl)2-
(µ-H)[(µ-S(C6H4)(CH2CH3)], a complex in which a 2-ethylth-
iophenolate ligand bridges the Ir atoms through the sulfur.
Preparation of Re2(CO)7(µ-BT*) (1a-d). Re2(CO)7(µ-BT) (1a).
In a typical experiment, a hexanes (40 mL) solution of Re2(CO)10 (224
mg, 0.343 mmol) and BT (97.0 mg, 0.723 mmol) was prepared in a
quartz Schlenk photolysis tube containing a Teflon-coated magnetic
stir bar. A coldfinger (10 °C) was inserted into the solution, and the
tube was fitted with an oil bubbler. The solution was then irradiated
for 24 h with stirring under a slow, but constant, flow of N2 during
which time the solution gradually became orange and an orange
precipitate formed. The orange solution was transferred to a silica gel
column (1 × 9 cm) packed in hexanes, and an orange band was eluted
using a mixture of hexanes and CH2Cl2 (10:1). The orange band was
collected, and the solvent was removed in vacuo to afford 1a as an
1
orange microcrystalline solid (61.0 mg, 24% yield). H NMR (CD2-
Cl2, 300 MHz): δ 8.63 (d, 1H, J ) 11.4 Hz), 7.11 (m, 2H), 7.05 (dt,
1H, J ) 7.5, 1.5 Hz), 7.00 (d, 1H, J ) 11.4 Hz), 6.93 (dt, 1H, J ) 7.2,
1.5 Hz). 13C NMR (300 MHz, -50.1 °C, CD2Cl2): δ 193.4, 192.6,
189.9, 185.6, 184.7, 184.3, 177.6 (CO); 150.0, 144.7, 135.6, 129.7,
129.5, 128.0, 127.7, 115.8 (BT). IR (hexanes) νCO: 2099 (m), 2043
(s), 2027 (s), 1981 (s), 1977 (s), 1957 (m), and 1947 (s) cm-1. Anal.
Calcd for C15H6O7Re2S: C, 25.64; H, 0.86. Found: C, 25.54; H, 0.69.
Re2(CO)7(µ-2-MeBT) (1b). Complex 1b was prepared in a similar
fashion as 1a from a hexanes (30 mL) solution containing Re2(CO)10
(122 mg, 0.187 mmol) and 2-MeBT (61.0 mg, 0.412 mmol) (29.5 h,
15 °C). After purification and isolation as described for 1a, an orange
solid was obtained and characterized as 1b (50.1 mg, 37% yield based
1
on Re2(CO)10). H NMR (300 MHz, CD2Cl2): δ 7.09 (m, 2H), 7.01
(dt, 1H, J1 ) 7.5 Hz, J2 ) 1.2 Hz), 6.89 (dt, 1H, J1) 7.5 Hz, J2 ) 1.5
Hz), 6.36 (s, 1H), 3.16 (s, 3H, Me). IR (hexanes): 2096 (m), 2041
(vs), 2026 (s), 1980 (s), 1974 (vs), 1956 (m), 1944 (s) cm-1. Anal.
Calcd for C16H8O7Re2S: C, 26.81; H, 1.13. Found: C, 26.94; H, 1.20.
(37) (a) Vicic, D. A.; Jones, W. D. Organometallics 1997, 16, 1912. (b)
McAuliffe, C. A.; Mackie, A. G. In Encyclopedia of Inorganic Chemistry;
King, R. B., Ed.; Wiley: New York, 1994; Vol. 6, pp 2989-3010.
(38) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers,
F. J. Organometallics 1996, 15, 1518.
9
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A R T I C L E S
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Re2(CO)7(µ-3-MeBT) (1c). Complex 1c was prepared in a fashion
analogous to that for 1a from a hexanes solution (35 mL) containing
Re2(CO)10 (298 mg, 0.457 mmol) and 3-MeBT (282 mg, 1.90 mmol)
(24 h, 10 °C). Orange microcrystals of 1c (159 mg, 49% yield based
on Re2(CO)10) were isolated and purified as described for 1a. 1H NMR
(200 MHz, CD2Cl2): δ 8.22 (s, 1H), 7.37 (d, 1H, J ) 7.6 Hz), 7.00
(m, 3H), 2.58 (s, 3H, Me). IR (hexanes): ν(CO) cm-1 2097 (m), 2040
(vs), 2024 (s), 1979 (vs), 1973 (s), 1954 (w), 1941 (m). Anal. Calcd
for C16H8O7Re2S: C, 26.81; H, 1.13. Found: C, 26.71; H, 1.17.
Re2(CO)7(3,5-Me2BT) (1d). Complex 1d was prepared and isolated
from the reaction of Re2(CO)10 (238 mg, 0.365 mmol) and 3,5-Me2BT
(200 mg, 1.23 mmol) in a hexanes (36 mL) solution, as in the procedure
for the synthesis of 1a. The yield (112 mg) was 42% based on Re2-
(m), 1989 (s, br), 1963 (m), and 1931 (m) cm-1. Anal. Calcd for
C19H10O9Re2S: C, 29.01; H, 1.28. Found: C, 28.53; H, 1.13.
Method B. A THF solution (20 mL) of Re2(CO)10 (147 mg, 0.225
mmol) and Me3NO (27.0 mg, 0.360 mmol) was stirred for 1.5 h. The
volatiles were then removed in vacuo, and both THF (10-15 mL) and
3,5-Me2BT (112 mg, 0.691 mmol) were added with stirring (10 h).
Complex 2d (62.4 mg, 35% based on Re2(CO)10) was isolated and
recrystallized as described for 2a.
Photolysis of Re2(CO)10 and 3,5-Me2BT in the Presence of H2. A
decane (30 mL) solution containing Re2(CO)10 (288 mg, 0.441 mmol)
and 3,5-Me2BT (226 mg, 1.39 mmol) was irradiated in a quartz reaction
tube at 10-15 °C for 24 h under a steady flow of H2 which was bubbled
through the solution. During the reaction, the solution became yellow,
and an insoluble light-brown residue formed. The solution was then
transferred to a silica gel column (1 × 10 cm) packed in hexanes. A
yellow band corresponding to H2Re2(CO)8 (12% based on Re2(CO)10)39
was eluted with hexanes. An orange band that was eluted with CH2-
Cl2/hexanes (1:10) was then evaporated to leave an orange solid that
contained 1d (based on IR and 1H NMR spectroscopies) and a second
product. The orange solid was recrystallized from a toluene (1 mL)
solution layered with hexanes (5 mL) (-20 °C). After 1 d, orange
crystals of 1d and colorless crystals of the new product Re2(CO)7(µ-
3,5-Me2BT•H)(µ-H) (3d) were formed; crystals of these products were
separated by hand. The hand-picked crystals of 3d were then dissolved
in toluene (1 mL) and layered with hexanes followed by recrystallization
at -20 °C to afford pure crystals of 3d (1-2 d) which were dried in
vacuo (20-30 mg, 6-18% based on Re2(CO)10). 1H NMR (300 MHz,
CDCl3): δ 7.20 (d, 1H, J ) 8.1 Hz), 7.00 (m, 1H), 6.84 (s, 1H), 4.24
(s, 1H), 4.03 (d, 1H, J ) 2.1 Hz), 2.81 (s, 3H, Me), 2.30 (s, 3H, Me),
-12.62 (s, hydride). IR (hexanes): νCO 2100 (w), 2039 (vs), 2003 (s),
1
(CO)10. H NMR (300 MHz, CD2Cl2): δ 8.20 (s, 1H), 7.20 (s, 1H),
6.97 (d, 1H, J ) 7.8 Hz), 6.79 (d, 1H, J ) 7.8 Hz), 2.58 (s, 3H, Me),
2.27 (s, 3H, Me). IR (hexanes): ν(CO) cm-1 2097 (m), 2040 (vs), 2023
(s), 1978 (vs), 1972 (s), 1953 (m), 1940 (s). Anal. Calcd for C17H10O7-
Re2S: C, 27.94; H, 1.38. Found: C, 27.85; H, 1.16.
Preparation of Re2(CO)9(η1(S)-BT*) (2a-d). Re2(CO)9(η1(S)-BT)
(2a): Method A. Benzothiophene (79.0 mg, 0.589 mmol) was added
to Re2(CO)9(THF) prepared by UV photolysis of a solution of Re2-
(CO)10 (0.313 mmol) in 30 mL of THF. While being stirred, the yellow-
orange solution gradually became lemon yellow (1-2 h); it was stirred
for an additional 12 h at which time the solvent was removed in vacuo
to produce a yellow-brown oily residue. The residue was dissolved in
CH2Cl2 (1 mL) and layered with hexanes (5 mL) followed by cooling
overnight (-20 °C) to give pale yellow crystals of 2a (45 mg, 19%
yield based on Re2(CO)10) which were filtered and dried under vacuum.
1H NMR (300 MHz, CD2Cl2): δ 7.89 (m, 2H), 7.57 (m, 2H), 7.44 (d,
1H, J ) 5.7 Hz), 7.32 (d, 1H, J ) 5.7 Hz). IR (CH2Cl2): 2101 (w),
2045 (m), 1990 (s, br), 1967 (m), and 1931 (m) cm-1
.
1992 (vs), 1964 (vs), 1955 (w), 1943 (m) cm-1
.
Method B. A THF (15 mL) solution of Re2(CO)10 (327 mg, 0.501
mmol) was prepared under an inert atmosphere in a 50 mL Schlenk
flask containing a stir bar. Anhydrous Me3NO (40 mg, 0.523 mmol)
was then added with stirring to produce a yellow-orange solution that
was stirred for an additional 1 h. The volatiles (THF and NMe3) were
removed in vacuo, and the resulting yellow residue was again dissolved
in THF (10 mL). BT (258 mg, 1.92 mmol) was added, and the resulting
yellow-orange solution was stirred for 15-18 h. During this time, the
solution lightened to a pale yellow. The solvent was removed under
vacuum, and the yellow oily residue was dried under reduced pressure.
The crude residue was dissolved in toluene (1 mL) and layered with
hexanes (6-7 mL) followed by cooling (-20 °C) until 2a precipitated
as a yellow solid. The precipitate of 2a was then filtered and dried in
vacuo (42 mg, 11% yield based on Re2(CO)10). Complex 2a was
characterized as described in Method A.
Photolysis of 1c with H2. A decane solution (30 mL) of 1c (125
mg, 0.174 mmol) was prepared in a quartz photolysis tube equipped
with a magnetic stir bar. Hydrogen was bubbled through the orange
solution while it was UV-irradiated for 15-18 h at 10 °C. During this
time the solution became dark, and a dark brown precipitate formed.
The solution was filtered and chromatographed on silica gel (1 × 10
cm) using hexanes to remove the decane solvent. A solvent combination
of CH2Cl2 and hexanes (1:10) was then used to elute the complex Re2-
(CO)7(µ-3-MeBT•H)(µ-H) (3c) with careful monitoring of the eluents
by IR spectroscopy. The volatiles were removed under vacuum to give
1
3c as a white solid (15 mg, 12%). H NMR (300 MHz, CD2Cl2): δ
7.34 (td, 1H, J1 ) 7.8 Hz, J2 ) 0.9 Hz), 7.19 (m, 1H), 7.09 (m, 2H),
4.32 (s, 1H), 4.06 (d, 1H, J ) 2.1 Hz), 2.81 (s, 3H, Me), -12.60 (s,
hydride). IR (hexanes): 2102 (w), 2041 (vs), 2005 (s), 1994 (vs), 1966
(vs), 1958 (m), and 1946 (s) cm-1. Anal. Calcd for C16H10O7Re2S: C,
26.74; H, 1.40. Found: C, 26.69; H, 1.31.
Re2(CO)9(η1(S)-3-MeBT) (2c): Method A. A THF (30 mL)
solution of Re2(CO)9(THF) (0.342 mmol based on Re2(CO)10) and
3-MeBT (112 mg, 0.756 mmol) was stirred for 20 h. The yield of 2c
was 72 mg (27% yield based on Re2(CO)10).
Reaction of 1a with PMe3. To a toluene solution (3-5 mL) of 1a
(41.0 mg, 0.058 mmol) was added a toluene solution of PMe3 (0.31
mL, 0.31 mmol, in 1 M toluene solution). The solution color changed
immediately from orange to light yellow. After 35 min, the volatiles
were removed in vacuo, and the resulting yellow oil was dissolved in
CH2Cl2 (1 mL) and layered with hexanes (4-6 mL). Colorless crystals
of Re2(CO)7(PMe3)3(µ-BT) (4) and yellow crystals of Re2(CO)7(PMe3)2-
(µ-BT) (5) precipitated as a mixture from the solution overnight at -20
°C. After filtering and drying under vacuum, crystals of 4 and 5 were
partially separated by hand-picking the crystals of each complex from
the 30-40 mg mixture. For 4: 1H NMR (CD2Cl2, 300 MHz): δ 7.89
(dd, 1H, J ) 13.5, 3.9 Hz), 7.43 (dd, 1H, J ) 7.8, 1.2 Hz), 7.21 (d,
1H, J ) 7.2 Hz), 6.99 (dt, 1H, J ) 7.5, 1.5 Hz), 6.92 (m, 2H), 1.62
(m, 27H, 3PMe3). IR (CH2Cl2) νCO: 2079 (w), 2018 (s), 1978 (s, sh),
1972 (s), 1933 (s), and 1893 (s) cm-1. Anal. Calcd for C24H33O7P3-
Re2S: C, 30.97; H, 3.57. Found: C, 30.72; H, 3.47. For 5: 1H NMR
(CD2Cl2, 300 MHz): δ 8.06 (dd, 1H, J ) 14.1, 2.4 Hz), 7.44 (dd, 1H,
Method B. A THF solution (25 mL) of Re2(CO)10 (310 mg, 0.475
mmol) and Me3NO (35 mg, 0.460 mmol) was stirred for 1 h, followed
by addition of 3-MeBT (215 mg, 1.45 mmol) with further stirring for
15 h. Complex 2c (93 mg, 25% yield) was isolated following the
procedure used for 2a. 1H NMR (300 MHz, CD2Cl2): δ 7.90 (m, 1H),
7.80 (m, 1H), 7.61 (m, 2H), 6.96 (s, 1H), 2.53 (s, 3H, Me). IR (CH2-
Cl2): 2102 (w), 2043 (m), 1989 (s, br), 1967 (m), 1931 (m) cm-1
.
Anal. Calcd for C18H8O9Re2S: C, 27.98; H, 1.04. Found: C, 27.76;
H, 1.00.
Re2(CO)9(η1(S)-3,5-Me2BT) (2d): Method A. A THF (30 mL)
solution containing 3,5-Me2BT (505 mg, 3.08 mmol) and Re2(CO)9-
(THF) (0.314 mmol based on Re2(CO)10) was stirred for 18 h. Yellow
crystals of 2d (106 mg, 43% yield) were afforded after recrystallization
from CH2Cl2/hexanes (-20 °C). 1H NMR (300 MHz, CD2Cl2): δ 7.74
(d, 1H, J ) 8.1 Hz), 7.58 (s, 1H), 7.38 (d, 1H, J ) 8.1 Hz), 6.91 (s,
1H), 2.53 (s, 3H, Me), 2.47 (s, 3H, Me). IR (CH2Cl2): 2102 (w), 2042
(39) Andrews, M. A.; Kirtley, S. W.; Kaesz, H. D. Inorg. Chem. 1977, 16, 1556.
9
1696 J. AM. CHEM. SOC. VOL. 124, NO. 8, 2002

Models for the Hydrodesulfurization of Thiophenes
A R T I C L E S
J ) 14.1, 3.6 Hz), 7.26 (d, 1H, J ) 7.8 Hz), 7.00 (m, 2H), 6.87 (m,
1H), 1.87 (d, 9H, PMe3, J ) 9.3 Hz), 1.19 (d, 9H, PMe3, J ) 8.4 Hz).
IR (CH2Cl2) νCO: 2100 (w), 2018 (m, sh), 2003 (s), 1953 (m, br), 1896
(m, br), and 1873 (m, br) cm-1. Anal. Calcd for C21H24O7P2Re2S: C,
29.51; H, 2.83. Found: C, 29.24; H, 2.78.
solution (-5 °C) and isolated by filtration and dried in vacuo (32-40
mg). H NMR (300 MHz, CD2Cl2): δ 7.71 (d, 1H, J ) 13 Hz), 7.43
(d, 1H, J ) 13 Hz), 7.21 (d, 1H, J ) 7.8 Hz), 7.04 (m, 2H), 6.78 (m,
1H), 1.94-1.53 (m, 12H, 6CH2), 1.10 (m, 12H, 4Me). IR (CH2Cl2):
νCO 2079 (w), 2029 (s), 1974 (s, br), 1964 (s, br), and 1907 (s, br).
Anal. Calcd for C25H30O7P2Re2S: C, 33.04; H, 3.33. Found: C, 32.77;
H, 3.22.
Crystallographic Structural Determinations for Complexes 2c,
1d, 3d, and 6. Systematic absences in the diffraction data were uniquely
consistent for space group Pbca for 1d and also for the space groups
P1 and P1h for 2c, 3d, and 6. In the latter three cases, the E statistics
strongly suggested the centrosymmetric space group P1h that yielded
chemically reasonable and computationally stable results of refine-
ment.40 In all cases, the absorption corrections were based on fitting a
function to the empirical transmission surface as sampled by multiple
equivalent measurements.41 The structures were solved using direct
methods, completed by subsequent difference Fourier syntheses, and
refined by full-matrix least-squares procedures. All non-hydrogen atoms
were refined with anisotropic displacement coefficients. All hydrogen
atoms were treated as idealized contributions.
1
Reaction of 1a with PiPr3. To a stirred CH2Cl2 solution (6 mL) of
complex 1a (50 mg, 0.071 mmol) was added PiPr3 (0.069 mL, 0.36
mmol). The solution lightened within 5 min and was stirred for an
additional 2 h, followed by removal of the solvent in vacuo to produce
a pale yellow solid. The solid was then dissolved in benzene (1 mL)
and layered with hexanes (3-4 mL) (5 °C) to afford crystals of Re2-
(CO)7(PiPr3)2(µ-BT) (6) after 1 d. After filtering, washing with cold
hexanes (0 °C), and drying in vacuo, crystals of 6 (21-36 mg) were
1
isolated in 28-50% yield. H NMR (300 MHz, CD2Cl2): δ 8.30 (dd,
1H, JHH ) 14.4 Hz, JHP ) 2.1 Hz), 7.43 (dd, 1H, JHH ) 14.4 Hz, JHP
) 3.0 Hz), 7.19 (d, 1H, J ) 6.9), 6.94 (m, 2H), 6.79 (m, 1H), 2.77 (m,
3H, CH), 2.08 (m, 3H, CH), 1.42-0.86 (m, 36H, Me). IR (hexanes):
2100 (w), 2026 (m), 2007 (vs), 1949 (m), 1905 (m), and 1884 (m)
cm-1
.
Reaction of 1a with PCy3. A toluene solution (5 mL) of 1a (40.2
mg, 0.057 mmol) and PCy3 (36.0 mg, 0.128 mmol) was prepared in a
25 mL Schlenk flask. The color of the solution changed from orange
to pale yellow within 1 h, and the solution was stirred for an additional
7 h. The solvent was then removed in vacuo, and the yellow solid
residue was dissolved in toluene (1 mL); the solution was layered with
hexanes (6 mL), followed by cooling (-20 °C) overnight which
produced a yellow crystalline solid of Re2(CO)7(PCy3)2(µ-BT) (7).
Crystals of complex 7 (33.8 mg, 0.026 mmol, 46%) were filtered,
In the case of 1d, there are two symmetry-independent molecules
in the asymmetric unit; however, only one molecule is presented (Figure
1). For 3d, the Re-H bonds were constrained to ensure stable
refinement.
Acknowledgment. This work was supported by the U.S.
Department of Energy, Office of Science, Office of Basic
Energy Sciences, Chemical Sciences Division, under contract
W-7405-Eng-82 with Iowa State University.
1
washed with hexanes (2 × 4 mL), and dried under vacuum. H NMR
(400 MHz, CD2Cl2): δ 8.33 (dd, 1H, JHH ) 14.0 Hz, JHP ) 2.0 Hz),
7.46 (dd, 1H, JHH ) 14.4 Hz, JHP ) 2.4 Hz), 7.24 (m, 1H), 6.98 (m,
2H), 6.80 (m, 1H), 2.41-0.88 (m, 66H, Cy). IR (CH2Cl2): 2096 (w),
2016 (m, sh), 1999 (vs), 1944 (m, br), 1888 (m, br), and 1868 (m, br)
cm-1. Anal. Calcd for C51H72O7P2Re2S: C, 48.48; H, 5.74. Found: C,
48.94; H, 6.01.
Supporting Information Available: Crystallographic data
including atomic coordinates, bond lengths and angles, aniso-
tropic displacement parameters, and hydrogen coordinates for
1c, 1d, 2c, 3d, and 6 (PDF). This material is available free of
charge via the Internet at http://pubs.acs.org.
Reaction of 1a with Bis(diethylphosphino)ethane. Complex 1a
(49.0 mg, 0.070 mmol) and bis(diethylphosphino)ethane (depe) (0.017
mL, 0.073 mmol) were dissolved in toluene (6 mL) in a 50 mL Schlenk
flask. The solution was stirred for 1 h, followed by removal of the
volatiles in vacuo, yielding a pale yellow oil. Solid pale yellow Re2-
(CO)7(depe)(µ-BT) (8) was precipitated from a benzene/hexanes (1:6)
JA011725L
(40) Blessing, R. H. Acta Crystallogr. 1995, A51, 33-38.
(41) All software and sources of the scattering factors are contained in the
SHELXTL (version 5.1) program library (Sheldrick, G. Bruker Analytical
X-ray Systems, Madison, Wisconsin, 1997).
9
J. AM. CHEM. SOC. VOL. 124, NO. 8, 2002 1697