Hydrogenation and carbon-sulfur bond hydrogenolysis of benzothiophene promoted by Re2(CO)10 and H4Re4(CO)12

Article abstract of DOI:10.1021/ic034035m

In the search for metal complexes that promote the cleavage of C-S bonds in thiophenes, we observe that the reaction of Re₂-(CO)₁₀ and benzothiophene (BT) under a hydrogen atmosphere gives the trinuclear cluster Re₃(μ-H)₂(μ₃-S-2- EtC₆H₄)(μ-2,3-DHBT)-(CO)₉ (1), which contains a hydrogenated BT ligand and a thiolate ligand resulting from the hydrogenation and cleavage of a C-S bond in BT. A detailed study of the reaction shows that Re₂(CO)₁₀ initially reacts with H₂ to give H₃Re₃(CO)₁₂, which subsequently converts to H₄Re₄(CO)₁₂, which finally reacts with BT to give 1.

Full text of DOI:10.1021/ic034035m

Inorg. Chem. 2003, 42, 2191−2193
Hydrogenation and Carbon−Sulfur Bond Hydrogenolysis of
Benzothiophene Promoted by Re2(CO)10 and H Re4(CO)12
4
Michael A. Reynolds, Ilia A. Guzei,† and Robert J. Angelici*
Ames Laboratory and Department of Chemistry, Iowa State UniVersity, Ames, Iowa 50011-3111
Received January 14, 2003
Scheme 1. Pathways Proposed for the Catalytic HDS of
Benzothiophene
In the search for metal complexes that promote the cleavage of
C−S bonds in thiophenes, we observe that the reaction of Re2-
(CO)10 and benzothiophene (BT) under a hydrogen atmosphere
gives the trinuclear cluster Re3(µ-H)2(µ3-S-2-EtC H )(µ-2,3-DHBT)-
6
4
(CO)9 (1), which contains a hydrogenated BT ligand and a thiolate
ligand resulting from the hydrogenation and cleavage of a C−S
bond in BT. A detailed study of the reaction shows that Re2(CO)10
initially reacts with H to give H Re3(CO)12, which subsequently
2
3
converts to H Re4(CO)12, which finally reacts with BT to give 1.
4
The hydrodesulfurization (HDS) of organosulfur com-
pounds that are present in petroleum feedstocks is an
important industrial process that uses heterogeneous catalysts
such as Co- or Ni-promoted MoS2 supported on alumina
under high temperatures (300 °C) and pressures (10-90 atm)
of H2, as shown for benzothiophene in Scheme 1.1,2 The
efficient HDS of thiophenic compounds, such as ben-
zothiophene (BT) and dibenzothiophene (DBT), continues
to be challenging.3 In an attempt to understand the HDS
process of these compounds, homogeneous transition metal
complexes have been investigated as models for the binding,
hydrogenation, C-S bond cleavage, and hydrogenolysis of
thiophenes on HDS catalysts.4,5 Many of these studies
involved single-metal or dinuclear complexes, but there are
few studies of C-S bond hydrogenolysis that are promoted
by metal clusters.6 The trinuclear Fe3(CO)12 reacts with BT
in refluxing benzene to give a dinuclear benzothiaferrole Fe2-
(CO)6(SC8H6).7 On the other hand, Ru3(CO)12 reacts with
BT in refluxing THF to give the cluster Ru3(CO)8(C8H6)8
containing the desulfurized BT, while the related Os3(CO)10-
(NCMe)2 reacts with BT to give trinuclear clusters containing
BT ligands in which C-H cleavage has occurred.9 Curtis10
showed that the homogeneous sulfido cluster Cp2Mo2Co2-
(CO)4S3 desulfurizes thiophene stoichiometrically (at 150 °C,
15 atm of H2) to give desulfurized organic products and the
cluster Cp2Mo2Co2(CO)4S4, which contains the extruded
sulfur, in 90% yield. Suzuki11 demonstrated that (Cp*Ru)3-
(µ-H)3(µ3-H)2 reacts with BT at 50 °C to give the µ3-sulfido-
µ3-alkylidyne cluster (Cp*Ru)3(µ-H)2(µ3-S)(µ3-CCH2Ph); the
reaction with DBT gives biphenyl quantitatively and the
sulfido-containing cluster (Cp*Ru)3(µ-H)3(µ3-S) in 84% yield
at 110 °C. In this communication, we report the hydro-
genolysis of BT upon reaction with Re2(CO)10 under 1 atm
of H2 pressure to give a trinuclear Re cluster containing
partially hydrogenated and hydrogenolyzed BT ligands. A
* Author to whom correspondence should be addressed. E-mail:
angelici@iastate.edu.
† Iowa State University Molecular Structure Laboratory.
(1) Topsøe, H.; Clausen, B. S.; Massoth, F. E. Hydrotreating Catalysis:
Science and Technology; Springer-Verlag: Berlin, 1996.
(2) Angelici, R. J. In Encyclopedia of Inorganic Chemistry; King, R. B.,
Ed.; John Wiley & Sons: New York, 1994; Vol. 3, pp 1433-1443.
(3) Whitehurst, D. D.; Isoda, T.; Mochida, I. AdV. Catal. 1998, 42, 345.
(4) (a) Sanchez-Delgado, R. A. Organometallic Modeling of the Hy-
drodesulfurization and Hydrodenitrogenation Reactions; Kluwer
Academic Publishers: Dordrecht, 2002. (b) Bianchini, C.; Meli, A.
J. Chem. Soc., Dalton Trans. 1996, 801-814.
(7) Ogilvy, A. E.; Draganjac, M.; Rauchfuss, T. B.; Wilson, S. R.
Organometallics 1988, 7, 1171.
(8) Arce, A. J.; De Sanctis, Y.; Karam, A.; Deeming, A. J. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 1381-1383.
(9) Arce, A. J.; Karam, A.; De Sanctis, Y.; Capparelli, M. V.; Deeming,
A. J. Inorg. Chim. Acta 1999, 285, 277.
(10) (a) Riaz, U.; Curnow, O.; Curtis, M. D. J. Am. Chem. Soc. 1991, 113,
1416-1417. (b) Riaz, U.; Curnow, O.; Curtis, M. D. J. Am. Chem.
Soc. 1994, 116, 4357-4363.
(11) (a) Matsubara, K.; Okamura, R.; Tanaka, M.; Suzuki, H. J. Am. Chem.
Soc. 1998, 120, 1108. (b) Okamura, R.; Tada, K.; Matsubara, K.;
Oshima, M.; Suzuki, H. Organometallics 2001, 20, 4772.
(5) Angelici, R. J. Organometallics 2001, 20, 1259-1275.
(6) 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.
10.1021/ic034035m CCC: $25.00 © 2003 American Chemical Society
Published on Web 03/06/2003
Inorganic Chemistry, Vol. 42, No. 7, 2003 2191

COMMUNICATION
Scheme 2. Reactions of Re2(CO)10 and H4Re4(CO)12 with BT under
H2
unique aspect of this reaction is the initial conversion of
Re2(CO)10 to H4Re4(CO)12, which subsequently reacts with
BT to give the cluster product containing hydrogenated and
hydrogenolyzed BT ligands.
When a decane solution of Re2(CO)10 and excess BT was
refluxed under a H2 atmosphere for 5 days, the off-white
complex Re3(µ-H)2(µ3-S-2-EtC6H4)(µ-2,3-DHBT)(CO)9 (1)
(2,3-DHBT ) 2,3-dihydrobenzothiophene) was produced in
80% yield (Scheme 2, reaction a).12 Recrystallization of 1
gave a mixture of colorless crystals and an off-white powder.
An X-ray diffraction study of the crystals (1a) hand-picked
from the mixture yielded the trimetallic structure (Figure 1)
containing three pseudo-octahedral Re atoms with relatively
long Re(1)-Re(2) (3.1020(4) Å) and Re(2)-Re(3) (3.1093-
(4) Å) bonds indicating the presence of bridging hydride
ligands that were not located in the X-ray refinement.
Rhenium complexes that contain a Re-Re single bond
typically have shorter Re-Re distances as observed in the
structures of Re2(CO)10 (3.0413(11) Å),13 Re2(CO)9(3-MeBT)
(3.0343(4) Å),14 and Re2(CO)8(PMe2Ph)2 (3.044(1) Å)15
compared to those Re complexes that have a bridging hydride
ligand such as Re2(CO)8(µ-H)(µ-2-S-naphthyl) (3.0934(10)
Å),16 [Re3(µ-H)(CO)12]2- (3.125(3) Å),17 and [Re3(CO)9(µ-
H)3(µ3-StBu)]- (average Re-Re distance of 3.091(1) Å).18
The presence of the bridging hydride ligands was supported
Figure 1. Molecular structure of 1a with 30% probability thermal
ellipsoids. Selected bond distances (Å) and angles (deg): Re(1)-Re(2),
3.1020(4); Re(2)-Re(3), 3.1093(4); Re(1)-S(1), 2.4673(16); Re(1)-S(2),
2.4765(16); Re(2)-S(1), 2.4188(17); Re(3)-S(1), 2.4693(16); Re(3)-S(2),
2.4823(16); S(2)-C(18), 1.835(6); S(1)-C(10), 1.763(4); C(18)-C(19),
1.534(8); Re(1)-Re(2)-Re(3), 76.463(9); Re(1)-S(1)-Re(2), 78.81(5); Re-
(1)-S(1)-Re(3), 102.27(5); Re(2)-S(1)-Re(3), 78.99(5); Re(1)-S(2)-
Re(3), 101.64(5); C(18)-S(2)-C(25), 91.9(3); Re(1)-S(2)-C(18), 114.4-
(2); Re(3)-S(2)-C(25), 114.7(2).
molecule, suggesting the presence of two isomers, formed
in approximately equal amounts, which could not be
separated by chromatography. The 1H NMR spectrum of the
hand-picked crystals allowed the assignment of peaks to
isomer 1a in the spectrum of the mixture. It also allowed
the assignment of peaks to the other isomer 1b. The similarity
of their 1H NMR spectra suggests that the structure of 1b is
very similar to that of 1a, whose structure was established
crystallographically (Figure 1). We therefore suggest that 1b
has a structure in which the arene ring of the 2,3-DHBT
ligand is directed away from S(1), rather than toward it as
in 1a.
During the reaction of Re2(CO)10 with BT and H2, a series
of intermediates were detected by IR spectroscopy. In the
initial stages of the reaction, νCO bands corresponding only
to Re2(CO)10 were observed (2070w, 2014s, 1976m cm-1),
but after ca. 2 h these bands were replaced with those
corresponding to H3Re3(CO)12 (2093m, 2030s, 2008s, 1982m
cm-1), which has been reported in the reaction of Re2(CO)10
with H2.19 After a further 24 h, the H3Re3(CO)12 cluster
converted into H4Re4(CO)12 (2041s, 1987s cm-1), which then
converted into 1 within 4 days. The formation of H4Re4-
(CO)12 was confirmed by its preparation from Re2(CO)10 and
H2 (1 atm), as previously reported.20 The observation that
H4Re4(CO)12 was formed in the step immediately preceding
the formation of 1 suggests that H4Re4(CO)12 is the species
that reacts with BT. Indeed, when H4Re4(CO)12 and BT were
1
by the H NMR spectrum of 1a in CD2Cl2 which showed
only one hydride signal (δ -11.05) indicating the rapid
interchange of these two bridging hydrides. The Re(1) and
Re(3) atoms are bridged by the sulfur atom of a 2,3-DHBT
ligand. The Re3 unit is capped nearly symmetrically by the
sulfur atom of a 2-ethylthiophenolate (2-EtC6H4S-) ligand.
1
A H NMR study12 of the crystal-powder mixture of 1
showed duplicate sets of signals for all of the protons in the
(12) Selected spectroscopic data for 1a: 1H NMR (CD2Cl2) 300 MHz: δ
7.68-7.22 (m, 8 H), 4.25 (t, 2 H, J ) 6.9 Hz), 3.55 (q, 2 H, J ) 7.5
Hz), 3.43 (t, 2 H, J ) 6.9 Hz), 1.61 (t, 3 H, J ) 7.5 Hz), -11.05 (s,
2 H, µ-H). For 1: IR (decane): νCO, cm-1 2057vw, 2037vs, 2024m,
1966m, 1941m. Anal. Calcd (found) for C25H19O9Re3S2: C, 27.65
(27.64); H, 1.76 (1.71).
(13) Churchill, M. R.; Amoh, K. N.; Wasserman, H. J. Inorg. Chem. 1981,
20, 1609.
(14) Reynolds, M. A.; Guzei, I. A.; Angelici, R. J. J. Am. Chem. Soc. 2002,
124, 1689-1697.
(15) Harris, G. W.; Boeyens, J. C. A.; Coville, N. J. J. Chem. Soc., Dalton
Trans. 1985, 2277-2282.
(18) Bonfichi, R.; Ciani, G.; D’Alfonso, G.; Romiti, P.; Sironi, A. J.
Organomet. Chem. 1982, 231, C35-C37.
(19) Flitcroft, N.; Huggins, D. K.; Kaesz, H. D. Inorg. Chem. 1964, 3,
1123.
(16) Egold, H.; Schwarze, D.; Florke, U. J. Chem. Soc., Dalton Trans.
1999, 3203.
(17) Ciani, G.; D’Alfonso, G.; Freni, M.; Romiti, P.; Sironi, A. J.
Organomet. Chem. 1978, 157, 199-208.
(20) Wang, S. R.; Wang, S.-L.; Cheng, C. P.; Yang, C. S. J. Organomet.
Chem. 1992, 431, 215-226.
2192 Inorganic Chemistry, Vol. 42, No. 7, 2003

COMMUNICATION
reacted under the same conditions as those in the reaction
of Re2(CO)10, BT, and H2, complex 1 was produced and the
reaction was complete within 48 h, confirming the interme-
diacy of H4Re4(CO)12 in the formation of 1 from Re2(CO)10,
BT, and H2 (Scheme 2).
was not detected spectroscopically or Re metal which perhaps
forms during the course of the reaction in unobservable
amounts.
In conclusion, we have demonstrated that the reaction of
BT with Re2(CO)10 under H2 proceeds through H3Re3(CO)12
and then H4Re4(CO)12, which reacts with BT to give the
trinuclear cluster Re3(µ-H)2(µ3-S-2-EtC6H4)(µ-2,3-DHBT)-
(CO)9 (1) containing BT molecules that have undergone
hydrogenation and C-S bond hydrogenolysis. These inves-
tigations suggest that other hydride clusters may be useful
models for the catalytic hydrodesulfurization of thiophenes.
In order to test for the possibility that the hydrogenolysis
of BT could occur catalytically, Re2(CO)12 was reacted with
100 equiv of BT in refluxing decane under 1 atm of H2.
Samples taken during the reaction contained unreacted BT
and the hydrogenated product 2,3-DHBT as determined by
GC. After 6.5 days, 3.47 mol of 2,3-DHBT was produced
for each mole of Re2(CO)10 used, and ethylbenzene was
detected in very low concentration (<0.1 mol %). Although
there is some catalytic formation of 2,3-DHBT, complex 1
is not part of the catalyst system. This was shown by the
observation that BT was not converted to DHBT or ethyl-
benzene when 1 was reacted for 6 days with excess BT under
reaction conditions identical to those used in the formation
of 1; also no new organometallic products were observed
by IR spectroscopy. Thus, the hydrogenation of BT to DHBT
must be catalyzed by either an unidentified Re complex that
Acknowledgment. This research 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.
Supporting Information Available: Crystallographic files for
the structure of 1a. Preparative details and spectroscopic data for
1. This material is available free of charge via the Internet at
http://pubs.acs.org.
IC034035M
Inorganic Chemistry, Vol. 42, No. 7, 2003 2193