Carbon-sulfur bond activation of dibenzothiophenes and phenoxythiin by [Rh(dippe)(μ-H)]2 and [Rh2(dippe)2(μ-Cl) (μ-H)]

Article abstract of DOI:10.1021/om1001815

The rhodium dimer [Rh(dippe)(μ-H)]₂ (1) reacts with dibenzothiophene to form the C-S cleavage product [Rh₂(dippe) ₂(μ-SC₁₂H₉)(μ-H)] (3). Complex 1 also reacts with 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene to form [Rh₂(dippe)₂(μ-S-MeC₁₂H₈)(μ-H) ] (4) and [Rh₂(dippe)₂(μ-S-Me₂C ₁₂H₇)(μ-H)] (6), respectively. Reaction with phenoxythiin forms [Rh₂(dippe)₂(μ-S-C₆H ₄OC₆H₅)(μ-H)] (8). In 3, rhodium addition to the ortho C-H bond of the β-ring of the biphenylthiolate substituent does not occur at 100 °C. The crystal structures of [Rh₂(dippe) ₂(μ-Cl)(μ-H)] (2), 4, 6, and 8 indicate that each complex contains a nearly planar Rh₂(μ-X)(μ-H) core. The ¹H NMR spectra of 3, 4, and 6 suggest that the pyramidal geometry at the sulfur atom is maintained in solution and that sulfur inversion is absent. Unreacted 1 catalyzes H/D exchange between C₆D₆ and the biphenylate substituent of 3 faster than it cleaves the remaining C-S bond to make free biphenyl. Complex 3 is unreactive toward excess dibenzothiophene, while [Rh ₂(dippe)₂(μ-Cl)(μ-H)] cleaves a C-S bond of DBT to form [Rh₂(dippe)₂(μ-Cl)(μ-SC₁₂H ₉)] (9).

Full text of DOI:10.1021/om1001815

Organometallics 2010, 29, 4923–4931 4923
DOI: 10.1021/om1001815
Carbon-Sulfur Bond Activation of Dibenzothiophenes and Phenoxythiin
by [Rh(dippe)(μ-H)]2 and [Rh2(dippe)2(μ-Cl)(μ-H)]†
Stephen S. Oster, Matthew R. Grochowski, Rene J. Lachicotte, William W. Brennessel, and
William D. Jones*
Department of Chemistry, University of Rochester, Rochester, New York 14627
Received March 8, 2010
The rhodium dimer [Rh(dippe)(μ-H)]2 (1) reacts with dibenzothiophene to form the C-S cleavage
product [Rh2(dippe)2(μ-SC12H9)(μ-H)] (3). Complex 1 also reacts with 4-methyldibenzothiophene
and 4,6-dimethyldibenzothiophene to form [Rh2(dippe)2(μ-S-MeC12H8)(μ-H)] (4) and [Rh2(dippe)2-
(μ-S-Me2C12H7)(μ-H)] (6), respectively. Reaction with phenoxythiin forms [Rh2(dippe)2(μ-S-C6H4-
OC6H5)(μ-H)] (8). In 3, rhodium addition to the ortho C-H bond of the β-ring of the biphenylthio-
late substituent does not occur at 100 °C. The crystal structures of [Rh2(dippe)2(μ-Cl)(μ-H)] (2), 4, 6,
and 8 indicate that each complex contains a nearly planar Rh2(μ-X)(μ-H) core. The 1H NMR spectra
of 3, 4, and 6 suggest that the pyramidal geometry at the sulfur atom is maintained in solution and
that sulfur inversion is absent. Unreacted 1 catalyzes H/D exchange between C6D6 and the
biphenylate substituent of 3 faster than it cleaves the remaining C-S bond to make free biphenyl.
Complex 3 is unreactive toward excess dibenzothiophene, while [Rh2(dippe)2(μ-Cl)(μ-H)] cleaves a
C-S bond of DBT to form [Rh2(dippe)2(μ-Cl)(μ-SC12H9)] (9).
Introduction
compounds that was developed by Fryzuk and co-workers in
the 1980s.6 They found that [Rh(dippe)(μ-H)]2 reacts with
olefins to produce vinyl, alkenyl, dienyl, and diene hydride
bridged dimers.7,8 This complex also was observed to react
with phenol, N-benzylideneaniline, H2, aldimines, silanes,
and other substrates to form a variety of products.9
In the past, the hydrodesulfurization of thiophenes using
[Ni(dippe)(μ-H)]2 and systems that utilize the [M(dippe)]
fragment (M = Pd, Pt) as a source of M(0) have been stu-
died.1-4 The former complex readily activates thiophenic
carbon-sulfur bonds and, in the reaction with dibenzothio-
phene (DBT), eventually produces four metal complexes.
Two of these complexes contain extracted sulfur. However,
attempts to make the system catalytic have failed in that
the regeneration of a reactive form of Ni(0) has proven to be
elusive.5 The latter systems that use palladium and platinum
are highly reactive, but many of the Pd(0) and Pd(II) species
easily degrade into colloidal metal and free ligand.
In light of the limitations of [Ni(dippe)(μ-H)]2 and [Pd-
(dippe)], a metal hydride was sought that was both reactive
and capable of cycling between two stable oxidation states
that are separated by two electrons. In regard to the homo-
geneous hydrodesulfurization of thiophenes, these two qua-
lities are desirable, as evidenced by the many examples
of thiophene C-S oxidative addition by complexes in which
they are found. This search led to an investigation of
[Rh(dippe)(μ-H)]2, which is one of a class of [L2Rh]n(μ-H)n
[Rh(dippe)(μ-H)]2 offers several advantages. First, the
rhodium centers can cycle between the stable Rh(þ1) and
Rh(þ3) oxidation states, allowing [Rh(dippe)(μ-H)]2 to
accommodate the two-electron oxidation that is necessitated
by the activation of a carbon-sulfur bond in DBT. Second,
[L2Rh]n(μ-H)n compounds are electronically unsaturated,
which aids their reactivity. Third, the smaller bite angle of
dippe, relative to chelating phosphines with propyl and butyl
backbones, forces the isopropyl moieties away from the Rh-
(μ-H) core. This reduces steric crowding around the rhodium
centers to further improve reactivity. Finally, it was probable
that [Rh(dippe)(μ-H)]2 would maintain itself as a dinuclear
species in the presence of DBT, which is a desirable feature in
a homogeneous system that attempts to model the bulk solids
that are used in heterogeneous catalytic hydrodesulfuriza-
tion. Indeed, evidence from the hydrogenation of 1-hexene
(6) Fryzuk, M. D. Can. J. Chem. 1983, 61, 1347.
(7) Fryzuk, M. D.; Jones, T.; Einstein, F. W. B. Organometallics 1984,
3, 185.
† Part of the Dietmar Seyferth Festschrift. This article is dedicated in honor
of Professor Dietmar Seyferth for his special service and inspiration to
organometallic chemists worldwide through his creation of this journal.
(1) Vicic, D. A.; Jones, W. D. J. Am. Chem. Soc. 1997, 119, 10855.
(2) Vicic, D. A.; Jones, W. D. J. Am. Chem. Soc. 1999, 121, 4070.
(3) Vicic, D. A.; Jones, W. D. J. Am. Chem. Soc. 1999, 121, 7606.
(4) Ates-in, T. A.; Oster, S. S.; Skugrud, K.; Jones, W. D. Inorg. Chim.
Acta 2006, 359, 2798.
(8) Fryzuk, M. D.; Piers, W. E. Polyhedron 1988, 7, 1001.
(9) (a) Fryzuk, M. D.; Jang, M. L.; Jones, T.; Einstein, F. W. B. Can.
J. Chem. 1986, 64, 174. (b) Fruzuk, M. D.; Piers, W. E. Organometallics
1988, 7, 2062. (c) Fryzuk, M. D.; Piers, W. E.; Einstein, F. W. B.; Jones, T.
Can. J. Chem. 1989, 67, 883. (d) Fryzuk, M. D.; Piers, W. E. Organome-
tallics 1990, 9, 986. (e) Fryzuk, M. D.; Piers, W. E.; Rettig, S. J. Can. J.
Chem. 1992, 70, 2381. (f) Fryzuk, M. D.; Rosenberg, L.; Rettig, S. J. Inorg.
Chim. Acta 1994, 222, 345. (g) Rosenberg, L.; Fryzuk, M. D.; Rettig, S. J.
Organometallics 1999, 18, 958.
(5) Torres-Nieto, J.; Brennessel, W. W.; Jones, W. D.; Garcia, J. J.
J. Am. Chem. Soc. 2009, 131, 4120.
r
2010 American Chemical Society
Published on Web 05/12/2010
pubs.acs.org/Organometallics

4924 Organometallics, Vol. 29, No. 21, 2010
Oster et al.
Figure 2. (a) 1H NMR spectrum and (b) 31P NMR spectrum of
[Rh2(dippe)2(μ-SC12H9)(μ-H)] (3).
Figure 1. (a) 1H NMR spectrum and (b) 31P NMR spectrum of
[Rh2(dippe)2(μ-Cl)(μ-H)] (2). The doublet that is located around
δ 102 corresponds to unreacted [Rh(dippe)(μ-Cl)]2.
system, which results from the long-range coupling of phos-
phorus nuclei surrounding the asymmetric Rh2(μ-Cl)(μ-H)
core.
Reaction between [Rh(dippe)(μ-H)]2 and DBT. At 100 °C,
the reaction between the rhodium hydride dimer 1 and 1 equiv
of DBT goes to completion within ∼10 days, to produce
exclusively [Rh2(dippe)2(μ-SC12H9)(μ-H)] (3; eq 1). Activa-
tion of only one C-S bond of the organosulfur substrate is
observed, despite the presence of a second metal and hydride
ligand.
using [Rh(iPr2P(CH2)nPiPr2)(μ-H)]2, where n=2, 3, suggests
that the smaller bite angle resulted in [Rh(dippe)(μ-H)]2 inter-
acting with substrate as a binuclear complex, whereas [Rh-
(dippp)(μ-H)]2 fragmented into monomers.10
In the course of this study, [Rh2(dippe)2(μ-Cl)(μ-H)] was
also synthesized and its reactivity toward dibenzothiophene
was investigated in conjunction with our study of [Rh(dippe)-
(μ-H)]2. The ability of these complexes to insert into the carbon-
sulfur bonds of dibenzothiophenes and phenoxythiin, to con-
vert them into molecules easier to desulfurize, was determined.
The results of this work are reported herein.
Results and Discussion
[Rh(dippe)(μ-H)]2 and [Rh2(dippe)2(μ-Cl)(μ-H)] Complexes.
The complex [Rh(dippe)(μ-H)]2 (1) has been synthesized by
Fryzuk and co-workers by the reaction of [Rh(COD)(η3-
allyl)] with dippe and H2.7 We have found that 1 can also be
synthesized directly by reaction of [Rh(dippe)Cl]2 with 2 equiv
of LiHBEt3. The chloro-hydrido-bridged dimer [Rh2(dippe)2-
(μ-Cl)(μ-H)] (2) forms if only 1/2 equiv of LiHBEt3 is emp-
loyed.11 The 1H NMR spectrum of 2 (Figure 1a) indicates the
presence of an asymmetric complex. There are a total of four
different doublets of doublets that correspond to the dippe
isopropyl substituents, and the hydride appears as a triplet of
triplet of triplets. The 31P NMR spectrum of 2 (Figure 1b)
highlights the fact that a plane of symmetry is lost when one
bridging hydride ligand in 1 is replaced with chloride. Whereas
the phosphorus signal of 1 is a simple doublet, the signals for
2 are asymmetric. This is consistent with an AA0BB0XX0 spin
While a crystal structure of 3 could not be obtained, the 1H
and 31P NMR spectra, as well as elemental analysis data, are
consistent with a biphenylthiolato-hydrido-bridged rho-
dium dimer. In the 1H NMR spectrum (Figure 2a), there is
a complex multiplet at δ -7.88, which converts to a triplet
upon broad-band phosphorus decoupling. This resonance is
consistent with a hydride (JH-Rh =22.2 Hz) that occupies a
bridging position between two identical rhodium centers.
Evidence of the biphenylthiolato moiety is found in the aro-
matic region of the spectrum. Here, there are seven distinct
resonances, with four R-ring protons and the para proton of
the β-ring corresponding to 1 H, while the ortho and meta
protons of the freely rotating β-ring correspond to 2 H. The
aliphatic region of the spectrum indicates that a second plane
of symmetry also has been lost and that sulfur inversion,
which would restore that plane in solution, is absent. That is,
there are four types of isopropyl substituents that are differ-
entiated according to whether they are syn or anti to the
(10) Fryzuk, M. D.; Piers, W. E.; Einstein, F. W. B.; Jones, T. Can. J.
Chem. 1989, 67, 883.
(11) Swartz, B. D.; Ates-in, T. A.; Grochowski, M. R.; Oster, S. S.;
Brennessel, W. W.; Jones, W. D. Inorg. Chim. Acta 2009, 363, 517.

Article
Scheme 1. Possible Mechanism for H/D Exchange
Organometallics, Vol. 29, No. 21, 2010 4925
product [Rh2(dippe)2(μ-S-MeC12H8)(μ-H)] (4) (eq 2). An
atmosphere of hydrogen was also found to accelerate the
hydrogenolysis reaction.
The use of excess 4-MeDBT is problematic, since com-
mercial sources typically contain about 4% dibenzothio-
phene as an impurity. Use of commercial 4-MeDBT resul-
ted in a mixture of 3 and 4, since 1 reacts rapidly with the
sterically unhindered DBT.15 4-MeDBT was therefore syn-
thesized in pure form by an alternative method that did not
use DBT as a precursor.16 Reaction of 1 with 4-MeDBT was
carried to completion in 6.5 days. 4 was purified by eluting
the sample through silica with pentane and then with 20/80
THF/pentane. This allowed 4 to be cleanly separated from
the excess 4-MeDBT as a golden yellow solid in 80% yield.
The 31P NMR spectrum of 4 is nearly identical with that of
3, with a set of doublets of multiplets similar to those seen in
thiolato substituent, as well as to whether they are cis or trans
to the bridging sulfur, resulting in the presence of eight dif-
ferent doublets of doublets for the isopropyl methyl groups.
The 31P NMR spectrum of 3 (Figure 2b) resembles the spec-
trum of 2. It too consists of two differing sets of multiplets,
consistent with an AA0BB0XX0 spin system that would result
from the long-range coupling of phosphorus nuclei in a com-
plex where one plane of symmetry has been lost upon the
substitution of a bridging hydride ligand in 1 with a thiolato
ligand.
1
Figure 2b. The H NMR spectra of 3 and 4 are also very
similar. The aryl methyl peak in 4 is observed as a singlet at
δ 2.93, and one less resonance was present in the aromatic
region. The hydride resonance of 4 shows the same splitting
as that observed in 3 but is shifted slightly upfield and is
centered at δ -8.29. A small impurity (approximately 2%)
was present in the isolated product and was determined by
independent synthesis to be the complex [Rh2(dippe)2(μ-S-2-
MeC6H4)(μ-H)]. The origin of this impurity derives from
reaction of 1 with di-o-tolyl disulfide, which is present as an
impurity in the synthesized 4-MeDBT (approximately 1%).
Crystals of 4 suitable for X-ray diffraction were grown
from a saturated solution of hexanes at -30 °C (see Figure 3).
The crystal structure shows that cleavage of the C-S bond
occurs exclusively at the less hindered side of 4-MeDBT. 4
consists of a nearly planar Rh2(μ-S)(μ-H) core with a pyr-
amidal geometry at sulfur. Each Rh(I) center has a slightly
distorted square planar geometry. The hydride is bridging
between both Rh centers, and the distance between the Rh
In the same manner as reported for 1,7 complex 3 exchan-
ges hydride for deuteride, which is obtained from the C6D6
solvent. The observed pseudo-first-order rate constant for
this isotopic exchange process in C6D6 is 1.67 ꢀ 10-6 s-1 at
100 °C. However, there is no incorporation of deuterium at
the ortho position of the biphenylate β-ring after 21 days at
100 °C, which indicates that 3 does not reversibly activate
that C-H bond by the process that is shown in Scheme 1.
This observation is of relevance to other H/D exchange
reactions seen with 3 under different conditions (vide infra).
Reaction between [Rh(dippe)(μ-H)]2 and 4-Methyldibenzo-
thiophene. Experimental evidence12 and theoretical calcula-
tions13 from other studies indicate that the activation of a
C-S bond of a thiophene by a metal center is preceded by the
formation of an η2(C,C)-bound thiophene-metal adduct,
which leads to an η2(C,S) adduct just prior to C-S addition.
Consequently, dibenzothiophenes that are substituted with
an alkyl group at the 4- or the 6-position, or both, are parti-
cularly refractory with respect to hydrodesulfurization;the
alkyl substituent blocks dibenzothiophene precoordination
in either in an η2 fashion or via a sulfur lone pair of electrons.14
Reaction of 1 with 4-methyldibenzothiophene (4-MeDBT)
was therefore anticipated to be more difficult than reaction
with dibenzothiophene.
˚
centers is 2.89 A, close enough to assume that bonding
between the Rh centers is occurring. The average Rh-P
˚
distance is 2.21 A.
The progress of the reaction was followed by 31P NMR
spectroscopy, during which time several intermediates were
observed. The identity of these intermediates could not be
determined, except for one. The disubstituted product
[Rh(dippe)(μ-S-MeC12H8)]2 (5) was found to form rapidly
in the reaction with impure 4-MeDBT (10 equiv). It consisted
of 14% of the reaction mixture (determined by integration of
the 31P NMR spectrum). In the reaction with purified
4-MeDBT (99%) it was sometimes observed in trace
amounts. The path for formation of 5 using the less pure
4-MeDBT remains uncertain but does not appear to form
from a secondary reaction of 4 with excess 4-MeDBT.
[Rh(dippe)(μ-S-MeC12H8)]2 is an orange crystalline solid
The same reaction conditions used for the reaction of DBT
with 1 were employed for 4-MeDBT activation (C6D6, 100 °C,
1 equiv of 4-MeDBT). After more than 3 months the reaction
had not gone to completion, and several unidentified reso-
nances were present by 31P NMR spectroscopy (vide infra).
When the reaction was carried out in toluene at 135 °C with
an excess of 4-methyldibenzothiophene (3 equiv), however,
the reaction went to completion within 1 week to give the
(12) Jones, W. D.; Vicic, D. A.; Chin, R. M.; Roache, J. H.; Myers, A.
W. Polyhedron 1997, 16, 3115.
(13) Ates-in, T. A.; Jones, W. D. Organometallics 2008, 27, 3666.
Ates-in, T. A.; Jones, W. D. Organometallics 2008, 27, 53. Ates-in, T. A.;
Ates-in, A. C.; Skugrud, K.; Jones, W. D. Inorg. Chem. 2008, 47, 4596.
Ates-in, T. A.; Jones, W. D. Inorg. Chem. 2008, 47, 10889.
(15) Commercial routes involve 4-lithiation of DBT followed by
methylation; either incomplete deprotonation or the presence of water
during the methylation can easily lead to DBT contamination of the
4-MeDBT produced by this route.
(16) Tedjamulia, M. L.; Tominaga, Y.; Castle, R. N.; Lee, M. L.
J. Heterocycl. Chem. 1983, 20, 1485–95.
(14) Myers, A. W.; Jones, W. D. Organometallics 1996, 15, 2905.

4926 Organometallics, Vol. 29, No. 21, 2010
Oster et al.
Figure 4. ORTEP drawing of [Rh(dippe)(μ-S-MeC12H8)]2 (5).
Ellipsoids are shown at the 30% probability level. All hydrogen
atoms are omitted for clarity.
Figure 3. ORTEP drawing of [Rh2(dippe)2(μ-S-MeC12H8)(μ-H)]
(4). Ellipsoids are shown at the 30% probability level. All hydro-
gens except for the bridging hydride are omitted for clarity.
forming [Rh2(dippe)2(μ-SMe2C12H7)(μ-H)] (6), characte-
rized by an almost identical set of doublet of multiplet reso-
nances centered at δ 99 and 93 in the 31P NMR spectrum.
that is insoluble in hydrocarbons and was isolated by extrac-
ting the reaction product with hexanes, leaving behind 5.
The 31P NMR shows a doublet centered at δ 89.93 (JRh-P
=
1
175 Hz). The H NMR shows an aryl methyl resonance at
δ 4.68. A crystal structure of 5 was obtained, as shown in
Figure 4. The structure belongs to the space group P21/c and
consists of a planar Rh2S2 core. The geometry around the
two Rh(I) centers is distorted square planar, with the two
bridging biphenyl thiolate ligands orientated anti to one
another. The Rh-P bond lengths in 5 are identical with
However, an additional product formed competitively
with 6 and also displayed the familiar AA0BB0XX0 splitting
pattern with resonances centered at δ 110 and 91 in the 31P
NMR spectrum. The product was assigned as [Rh2(dippe)2-
(μ-SH)(μ-H)] (7). 7 formed as the major product initially,
but as 1 was consumed an approximately 50:50 ratio of 6 and
7 formed. The 1H NMR spectrum of the mixture showed the
hydride resonance of 7 at δ -7.84 and the S-H resonance
at δ -0.02. A disordered X-ray structure of 7 was obtained
(see the Supporting Information for structure details). 7 was
generated independently when 3 was reacted with 1 without
the presence of dibenzothiophene.
The much slower rate of activation of 4,6-Me2DBT ex-
plains the appearance of 7. 7 was observed by 31P NMR
spectroscopy in the reaction of 4-MeDBT (1 equiv) with 1.
Formation of 7 in reactions of 1 with 4-MeDBT (excess) and
DBT does not occur, due to the much faster consumption
of 1 in these reactions compared to the reaction with 4,6-
Me2DBT. 7 is apparently formed from reaction of 1 with
μ-SR complexes such as 3, 4, and 6.
˚
those found in 4 (2.21 A); however, the Rh-S bond lengths in
˚
5 are elongated in comparison to those in 4 (2.47 vs 2.34 A).
˚
The Rh-Rh distance (3.694 A) is much longer than in the
μ-H compound 4, indicative of no Rh-Rh interaction.
Reaction between [Rh(dippe)(μ-H)]2 and 4,6-Dimethyldi-
benzothiophene. The activation of 4,6-dimethyldibenzothio-
phene (4,6-Me2DBT) remains a considerable challenge in
HDS chemistry. The two methyl groups on the ring are well
positioned to sterically block a metal surface from interact-
ing with the C-S bonds, making it the most difficult thio-
phene to activate.17 There are few examples in the literature
which have shown activation of 4,6-Me2DBT by a metal
complex.18
1 was found to react with 4,6-Me2DBT in a fashion similar
to that for DBT and 4-MeDBT (eq 3). For a typical reaction
17-20 equiv of 4,6-Me2DBT was used, and 1 atm of hydro-
gen was added to the reaction vessel. Hydrogen, as in the case
of 4-MeDBT, was found to accelerate the reaction. The C-S
bond activation of 4,6-Me2DBT was complete in 8.5 days,
7 was found to decompose after several days of heating
after the consumption of 1, leaving 6 as the main product of
the reaction. 6 was isolated in a manner similar to that for 4
by using silica gel to separate it from the excess thiophene.
An impurity was present that was consistent with a [Rh2-
(dippe)2(μ-SAr)(μ-H)] (Ar = aryl) complex (approximately
10% by 31P NMR spectroscopy). This species likely arose
from a small impurity present in the 4,6-Me2DBT and then
was magnified due to the large excess of 4,6-Me2DBT used in
the reaction. The isolated yield of 6 was 24%. The low yield
was attributed to the slow formation of 6 and an increase in
(17) (a) Topsøe, H.; Clausen, B. S.; Massoth, F. E. Hydrotreating
Catalysis; Springer-Verlag: Berlin, 1996. (b) Startsev, A. N. Catal. Rev. Sci.
Eng. 1995, 37, 353. (c) Topsøe, H.; Gates, B. C. Polyhedron 1997, 16, 3212.
(d) Sanchez-Delgado, R. A. Organometallic Models of the Hydrodesulfuriza-
tion and Hydrodenitrogenation Reactions; Kluwer Academic: Dordrecht, The
Netherlands, 2002; Catalysis by Metal Complexes Series Vol. 24.
ꢀ
(18) (a) Becker, S.; Fort, Y.; Vanderesse, R.; Caubere, P. J. Org.
Chem. 1989, 54, 4848. (b) Vicic, D. A.; Jones, W. D. Organometallics 1998,
ꢁ
ꢀ
17, 3411. (c) Arevalo, A.; Bernes, S.; García, J. J.; Maitlis, P. M. Organo-
metallics 1999, 18, 1680. (d) Yu, K.; Li, H.; Watson, E. J.; Virkaitis, K. L.;
Carpenter, G. B.; Sweigart, D. A. Organometallics 2001, 20, 3550.

Article
Organometallics, Vol. 29, No. 21, 2010 4927
Figure 7. ORTEP drawing of [Rh2(dippe)2(μ-S-C6H4OC6H5)-
(μ-H)] (8). Ellipsoids are shown at the 30% probability level.
All hydrogens, except for the bridging hydride, are omitted for
clarity.
[Rh2(dippe)2(μ-S-C6H4OC6H5)(μ-H)] (8) in 31% isolated
yield. The selectivity of 1 for C-S bond activation may be
due to the greater strength of the C-O bond, the lesser ability
of oxygen to precoordinate to a rhodium center, or both.
Each factor arises from the greater lone electron pair delo-
calization into the phenyl rings from oxygen as opposed to
sulfur, which is indicated by the crystal structure of phenox-
ythiin. Its C-O-C angle is around 117.4°, while its C-S-C
angle is around 97.7°.19
Figure 5. ORTEP drawing of [Rh2(dippe)2(μ-SMe2C12H7)(μ-H)]
(6). Ellipsoids are shown at the 30% probability level. All hydro-
gens except for the bridging hydride are omitted for clarity.
The 31P NMR spectrum of 8 consists of a set of complex
multiplets that are centered around δ 102 and 93.5 (Figure 6)
and that have the same pattern as the signals that correspond
to 2-4. Its 1H NMR spectrum indicates that, like 3 and 4, it is
a thiolato-hydrido-bridged dimer. The aromatic region
consists of five separate signals from δ 7.76 to 6.59, which
each integrate for one proton, and overlapping multiplets
that are centered around δ 7.23, which together integrate for
four protons. The hydride region consists of a multiplet that
is centered at δ -7.81. The aliphatic proton region of the
spectrum is somewhat broad. However, the appearance of
more than one isopropyl methine signal indicates that, as in
3, there is more than one type of isopropyl group in the dippe
ligand.
A single-crystal X-ray structure of 8 is shown in Figure 7
and resembles the structure of 4 in that, while the Rh2(μ-S)-
(μ-H) core is nearly planar, the bridging sulfur atom is
pyramidal with an exo-oriented phenoxythiolato substitu-
ent. Both C-O bond lengths and the C-O-C angle in that
substituent are similar to those in the parent phenoxythiin.19
Sulfur tends to be highly pyramidalized, relative to oxy-
gen, in both XR3þ and M2XR groups, where X = O, S and
R = H, alkyl, because its bonding molecular orbitals have
Figure 6. 31P NMR spectrum of [Rh2(dippe)2(μ-S-C6H4OC6H5)-
(μ-H)] (8).
decomposition (via 7) compared to 3 and 4. A crystal suitable
for X-ray diffraction was grown from slow evaporation of a
hexanes solution, and the structure is shown in Figure 5.
To the best of our knowledge, this is the first X-ray
structure obtained of a C-S activated 4,6-Me2DBT metal
complex showing complete C-S bond cleavage and hydro-
genation (the earlier platinum examples formed a metalla-
cycle18b-d). The structure is nearly identical with that shown
for 4, with the key structural difference being the presence of
the second methyl group on the bridging biphenyl thiolate.
˚
The Rh-Rh distance (2.859 A) is almost identical with that
in 4. The H NMR spectrum of 6 shows the two methyl
1
resonances present at δ 2.94 and 2.44 (C6D6). The resonance
at δ 2.94 is attributed to the methyl group attached to the
phenyl thiolate ring, since the resonance is identical with the
aryl methyl resonance found for 4.
Reaction between [Rh(dippe)(μ-H)]2 and Phenoxythiin.
Complex 1 was treated with phenoxythiin in order to deter-
mine its preference for activating C-S versus C-O bonds in
thiophenic molecules. As eq 4 illustrates, over 8 days at 82 °C
in C6D6, the rhodium hydride dimer is completely consumed
to produce exclusively the phenoxythiolato-bridged dimer
(19) Fitzgerald, L. J.; Gallucci, J. C.; Gerkin, R. E. Acta Crystallogr.,
Sect. C 1991, 47, 381.

4928 Organometallics, Vol. 29, No. 21, 2010
Oster et al.
Figure 8. GC-MS of the C6D6 solution from the reaction be-
tween 1 and 2 equiv of DBT.
more p-orbital character. For instance, the distribution of
the sum of the bond angles about the X atom, , in M2XR
P
Figure 9. ORTEP drawing of [Rh2(dippe)2(μ-Cl)(μ-SC12H9)]
(9). Ellipsoids are shown at the 30% probability level. All hydro-
gens, except for the bridging hydride, are omitted for clarity.
groups is centered near 315° for sulfur, while it is centered
around 360° for oxygen.20 The bridging sulfur atoms in both
P
4 and 8 demonstrate this tendency. With a
value of
approximately 306.8°, the 4-methylbiphenylthiolato sulfur
Scheme 2. Pathway for H/D Exchange in the Biphenylate
Substituent of 3 by 1 before Cleaving the Second C-S Bond
of 4 is slightly more pyramidalized than the average M2SR
for the phenoxythiolato sulfur of 8
P
sulfur. Remarkably,
is 284.9°, which is smaller than the calculated value of 286°
þ 20
for SH3
.
Production of Free Biphenyl. The analysis by GC-MS of
the C6D6 solution from the reaction between 1 and 2 equiv of
DBT indicated the presence of nondeuterated (m/z 154),
monodeuterated, multideuterated, and perdeuterated biphe-
nyl. As Figure 8 shows, highly deuterated biphenyls predo-
minate over mono-, di-, tri-, and tetradeuterated biphenyl,
with hepta- and octadeuterated biphenyls being the most
prevalent.
To determine if the biphenyl originated from DBT or if it
resulted from the coupling of solvent molecules, 1 was heated
at 100 °C for 26 days in C6H6, in C6D6, and in toluene.
1
Analysis of all three solutions by GC-MS and H NMR
spectroscopy demonstrated that no biphenyl was formed. In
contrast, a C6D6 solution of approximately a 2:1 mixture of
1 and 3 was heated for 4 days at 100 °C, and analysis by GC-
MS indicated that biphenyl was present. Moreover, after
1 and 8 were heated together at 100 °C in C6D6 for 5 days,
free diphenyl ether was detected by GC-MS. This time tri-
and tetradeuterated products were predominant. The reac-
tions between the hydride dimer and 3 and 8 indicate that the
completely desulfurized organic product most likely is pro-
duced via the cleavage of the C-S bond of the thiolato-
bridged rhodium complex by unreacted 1. The binuclear
rhodium complex [Rh2(dippe)2(μ-SH)(μ-H)] (7) can be iden-
tified in these reactions by 31P NMR spectroscopy.
[Rh(dippe)(μ-H)]2 H/D Exchange of the Thiolato Substi-
tuent of [Rh2(dippe)2(μ-SC12H9)(μ-H)]. The fact that the
biphenyl produced is deuterated to varying stages in the
reaction between 1 and 3 indicates that the former, which is
known to exchange hydride for deuteride with benzene
solvent, must undergo reversible C-H activation of the
biphenyl thiolate substituent and C6D6 solvent before cleav-
ing the C-S bond in a manner that is described in Scheme 2.
Effectively, 3 undergoes H/D exchange prior to the second
C-S cleavage. The distribution of deuterated biphenyls that
is observed by GC-MS suggests that 1 prefers to initiate
H/D exchange at the freely rotating β-ring as opposed to the
R-ring.
Reaction between [Rh2(dippe)2(μ-Cl)(μ-H)] and DBT. Com-
plex 2 activates the C-S bond in DBT to form [Rh2(dippe)2-
(μ-Cl)(μ-SC12H9)] (9) as the major product. The chloro-
hydrido-bridged rhodium dimer is less reactive than 1. For
instance, the reaction between 2 and 10 equiv of DBT in C6D6
at 100 °C takes 51 days to reach 97% completion. Moreover,
there is evidence of partial decomposition at that temperature
and duration of time. 9 can be prepared independently from the
reaction of 2 with 2-(phenylthio)phenol at 20 °C. A crystal
structure of 9 was obtained and is shown in Figure 9. The
complex is bent along the S-Cl axis with a dihedral angle θ of
134.9°, and the angle between the Rh1-S-Rh2 and Rh1-
Cl-Rh2 planes, φ, is 135.7°. The 31P NMR spectrum indicates
the presence of long-range coupling through the sulfur and
chloride bridges, as the phosphorus signals of 9 consist of two
doublets of doublets of doublets.
ꢁ
ꢁ
(20) Aullon, G.; Ujaque, G.; Lledos, A.; Alvarez, S. Chem. Eur. J.
1999, 5, 1391.

Article
Organometallics, Vol. 29, No. 21, 2010 4929
decomposition occurs when it is exposed to prolonged heat-
ing at 100 °C in C6D6 in the presence of DBT. However, 3
does form products with other substrates, which is illustrated
by Scheme 3. It reacts with 2 equiv of CH3Cl to produce
[Rh(dippe)(μ-Cl)]2, 2-biphenyl methyl sulfide, and CH4. The
addition of approximately 2 equiv of HCl to 3 also results in
the formation of [Rh(dippe)(μ-Cl)]2, but it is now accom-
panied by H2 and 2-phenylthiophenol. Finally, while it is
unable to cleave a second C-S bond of DBT, 3 activates
the thiol bond of 2-phenylthiophenol to make [Rh(dippe)-
(μ-SC12H9)]2 (10) and H2. 10 has been synthesized indepen-
dently from 1 plus 2-phenylthiophenol or from [Rh(dippe)-
Cl]2 and lithium 2-phenylthiophenolate, and as expected, its
single-crystal X-ray structure is very similar to that of the
methyl derivative 5.21
Conclusion
This study has demonstrated the ability of 1 to activate
C-S bonds in dibenzothiophenes and phenoxythiin. 3 is
unable to either activate a second molecule of DBT or com-
pletely extract sulfur from the substrate without the partici-
pation of additional 1. Hydrogen (1 atm) was found to acce-
lerate reactions with 4-MeDBT and 4,6-DMDBT, although
it is not required by the reaction stoichiometry, and catalytic
sulfur removal is not observed. In a competition between
aryl-S and aryl-O cleavage, only the former is observed.
Figure 10. Plots of (a) kobs versus [DBT] and (b) kobs versus [phen-
oxythiin] for the reactions between 1 and DBT and phenoxy-
thiin, respectively.
Scheme 3. Reactivity of [Rh2(dippe)2(μ-SC12H9)(μ-H)] (3)
Experimental Section
All operations were performed under a nitrogen atmosphere
unless otherwise stated. Benzene, THF, and hexanes were dis-
tilled from dark purple solutions of sodium benzophenone ketyl.
[Rh(COD)(μ-Cl)]2 was purchased from Strem Chemical Co.,
dibenzothiophene and sodium hydrosulfide were purchased
from Aldrich Chemical Co., and 2-phenylthiophenol was obta-
ined from the laboratory of John C. DiCesare, University of
Tulsa. All of these reagents were kept under vacuum overnight
before using. Chloromethane was purchased from Aldrich
Chemical Co., and dihydrogen was purchased from Air Pro-
ducts Co. 1,2-Bis(diisopropylphosphino)ethane was synthesized
according to a literature method.22 [Rh(dippe)(μ-H)]2 (1) and
[Rh2(dippe)2(μ-Cl)(μ-H)] (2) were synthesized as previously
reported.11 Neutral silica, 80-200 mesh, was heated to 200 °C
under vacuum for 2 days and stored under nitrogen. A Siemens-
SMART three-circle CCD diffractometer was used for X-ray
crystal structure determinations. Elemental analyses were obta-
ined by Desert Analytics or Robertson Microlit. All 1H, 31P, and
13C NMR spectra were recorded on a Bruker Avance 400 NMR
spectrometer. 1H chemical shifts are reported relative to the
residual proton resonance in the deuterated solvent. 31P chemi-
cal shifts are reported relative to the signal of external 85%
H3PO4. Mass spectra were recorded using a Shimadzu LCMS-
2010 instrument.
Kinetic Studies. Kinetic studies were conducted on the reac-
tions between 1 and DBT, between 1 and phenoxythiin, and
between 2 and DBT. However, good-quality data were obta-
ined only for the reactions that involved 1. The experiments
were conducted under pseudo-first-order conditions in C6D6 at
100 °C, and all plots of ln([1]0/[1]) were linear, which is con-
sistent with 1 reacting as a dimer with the substrate. The plots of
[DBT] versus kobs and [phenoxy] versus kobs are shown in parts
a and b of Figure 10, respectively. The second-order rate
constants for the reactions with DBT and phenoxythiin are
[2.43(13)] ꢀ 10-4 and [3.54(5)] ꢀ 10-4 M-1 s-1, respectively.
Comparison of [Rh2(dippe)2(μ-Cl)(μ-H)] (2) and [Rh2(dippe)2-
(μ-SC12H9)(μ-H)] (3). Despite the fact that 3 is isoelectro-
nic with 2, it does not activate a C-S bond of DBT. Only
Synthesis of [Rh2(dippe)2(μ-SC12H9)(μ-H)] (3). DBT (55.8 mg,
0.303 mmol) was dissolved in a 25 mL C6H6 solution along with
[Rh(dippe)(μ-H)]2 (0.222 g, 0.303 mmol). The reaction mixture
was placed in a 50 mL ampule that was sealed with a Teflon valve
and heated at 100 °C for approximately 10 days. The solution was
transferred to a 50 mL round-bottom flask, and the solvent was
removed under vacuum to leave a golden yellow solid. The solid
was dissolved in a minimal amount of hexanes, and the solution
was chilled to -30 °C to yield pure product (0.188 g, 67.8%). 1H
(21) Oster, S. S.; Jones, W. D. Inorg. Chim. Acta 2004, 357, 1836.
(22) Cloke, F. G. N.; Gibson, V. C.; Green, M. L. H.; Mtetwa, V. S.
B.; Prout, K. J. Chem. Soc., Dalton Trans. 1988, 2227.

4930 Organometallics, Vol. 29, No. 21, 2010
Oster et al.
NMR (C6D6, 25 °C): δ 8.22 (d, o-phenyl, J=7.7 Hz, 2H), 7.97 (d,
m-thiophenol, J=7.7 Hz, 1H), 7.53 (t, m-phenyl, J=7.5 Hz, 2H),
7.33 (t, p-phenyl, J=7.3 Hz, 1H), 7.26 (m, o-thiophenol, 1H), 6.95
(t, m-thiophenol, J=7.3 Hz, 1H), 6.84 (t, p-thiophenol, J=7.4 Hz,
1H), 2.44 (m, (CH3)CH, J = 6.9 Hz, 2H), 2.19 (bm, (CH3)CH,
4H), 2.06 (m, (CH3)CH, J = 7.1 Hz, 2H), 1.59-0.96 (m,
(CH3)2CH, 48H), 1.39-1.32 (m, P(CH2)2P, 8H), -7.88 (m, Rh-
H-Rh, J=22.0 Hz, 1H). 13C{1H} NMR (C6D6, 25 °C): δ 144.75
(m, m-thiophenol), 131.02 (s, o-phenyl), 129.52 (s, o-thiophenol),
127.13 (s, m-phenyl), 126.22 (s, p-phenyl), 124.43 (s, p-thiophenol),
123.90 (s, m-thiophenol), 28.49-27.47 (m, (CH3)2CH), 22.77 (m,
P(CH2)2P), 22.13 (m, P(CH2)2P), 21.63 (d, (CH3)2CH, J=7.8Hz),
21.35 (d, (CH3)2CH, J = 6.9 Hz), 20.66 (s, (CH3)2CH), 20.02 (d,
(CH3)2CH, J=19.9 Hz), 19.47 (d, (CH3)2CH, J=7.7 Hz), 19.34
(d, (CH3)2CH, J = 3.9 Hz), 18.65 (s, (CH3)2CH), 17.88 (d,
(CH3)2CH), J=21.1 Hz). Accidental overlap results in fewer sig-
nals than types of carbons. 31P{1H} NMR (C6D6, 25 °C): δ 102.47
(m), 101.40 (m), 94.30 (m), 93.20 (m). Anal. Calcd (found) for
C40H74Rh2P4S: C, 52.40 (52.03); H, 8.14 (8.09). APCI-MS (þ):
m/z 915.15 ([M - H]þ), 916.15 ([M]þ)
Synthesis of [Rh2(dippe)2(μ-S-MeC12H8)(μ-H)] (4). 4-Methyl-
dibenzothiophene (0.0117 g, 0.0590 mmol) and [Rh(dippe)(μ-H)]2
(0.0144 g, 0.0197 mmol) were dissolved in 1 mL of toluene and
placed in a J. Young NMR tube. The reaction mixture was heated
at 135 °C and monitored periodically by 31P NMR spectroscopy.
The reaction was complete after 6.5 days, as the solution color
changed from emerald green to dark red. The toluene was removed
by vacuum. The solid was dissolved in pentanes and eluted through
a Pasteur pipet containing glass wool and 2 in. of silica. A 10 mL
portion of pentanes eluent was collected as a fraction, containing
the excess thiophene. A 20/80 THF/pentanes solution was used to
elute 4, which was then evaporated to dryness to leave a golden
yellow solid (0.0147 g, 80%). 1H NMR (C6D6, 25 °C): δ 8.12 (d,
J=7.3 Hz, 2 H), 7.45 (t, J=7.6 Hz, 2 H), 7.29 (t, J=7.4 Hz, 1 H),
7.24 (m, 1 H), 7.03 (m, 2 H), 2.94 (s, CH3, 3 H), 2.38 (m, (CH3)CH,
2 H), 2.14 (bm, (CH3)CH, 4 H), 1.97 (m, (CH3)CH, 2 H),
1.49-0.61 (m, 56 H), -8.29 (m, Rh-H-Rh, 1 H). 13C{1H}
NMR (THF-d8, 25 °C): δ 147.17 (s), 145.76 (s), 145.63 (s),
142.97(s), 132.34 (s), 130.28 (s), 128.21 (s), 127.51 (s), 126.64 (s),
124.36 (s), 29.77-28.79 (m), 23.18 (m), 22.60 (d, J=7.8 Hz), 21.54
(d, J=6.9 Hz), 20.68 (d, J=5.3 Hz), 20.38 (s), 19.74 (s), 19.17 (m),
18.36 (d, J=3.2 Hz). 31P{1H} NMR (C6D6, 25 °C): δ 99.41 (dd,
J = 175, 27 Hz), 94.08 (m), 93.21 (m). Anal. Calcd (found) for
C41H76Rh2P4S: C, 52.90 (53.14); H, 8.23 (8.07). APCI-MS (þ):
m/z 929.15 ([M - H]þ), 930.15 ([M]þ).
Synthesis of [Rh(dippe)(μ-S-MeC12H8)]2 (5). The complex was
formed using an excess of 4-methyldibenzothiophene (10 equiv,
96% purity) relative to [Rh(dippe)( μ-H)]2, when heated in C6D6 at
100 °C for 1 week. The solid is formed as a minor product
(approximately 14% by 31P NMR). Due to its low solubility in
hydrocarbons, it can be isolated by extracting out 4 with hexanes.
1H NMR (THF-d8, 25 °C): δ 7.97 (d, J = 7.5 Hz, 4 H), 7.29 (m,
4 H), 7.19 (t, J=7.4 Hz, 4 H), 7.03 (d, J=7.3 Hz, 2 H), 6.94 (t, J=
7.4 Hz, 2 H), 4.68 (s, 6 H), 1.43 (m, 4 H), 1.19 (dd, J=7.2, 14.5 Hz,
12 H), 1.13 (m, 4 H), 1.02 (dd, J=7.0, 11.8 Hz, 12 H), 0.87 (m, 8 H),
0.66 (t, J = 7.5, 8.3 Hz, 12 H), 0.31 (dd, J = 7.0, 14.9 Hz, 12 H).
31P{1H} NMR (THF-d8, 25 °C): δ 89.93 (d, JRh-P =175 Hz).
Synthesis of [Rh2(dippe)2(μ-S-Me2C12H7)(μ-H)] (6). 4,6-Di-
methyldibenzothiophene (0.0545 g, 0.257 mmol) and [Rh(dippe)-
(μ-H)]2 (0.0108 g, 0.0147 mmol) were placed in a J. Young NMR
tube, and 1 mL of toluene was added. The sample was freeze-
pump-thaw degassed (3ꢀ) to remove nitrogen, and 1 atm of
hydrogen was then added. The reaction mixture was heated to
135 °C and monitored periodically by 31P NMR spectroscopy.
The reaction was complete after 8.5 days, as the solution color
changed from emerald green to dark red. The toluene was re-
moved by vacuum, and the dark red-gray residue was extracted
with hexanes (3 ꢀ 1 mL) and concentrated to dryness. The solid
was dissolved in a minimum amount of hexanes and eluted
through a Pasteur pipet containing glass wool and 2 in. of silica.
A 20 mL portion of hexanes eluent was collected as a fraction,
containing the excess thiophene. Benzene (5 mL) was used to
elute 6, which was then evaporated to dryness to leave a dark
yellow solid (0.0033 g, 24%). 1H NMR (THF-d8, 25 °C): δ 7.73 (m,
1 H), 7.47 (d, J=7.5 Hz, 1 H), 7.19 (t, J=7.4 Hz, 1 H), 7.01 (d, J=
7 Hz, 1 H), 6.89(d, J=7Hz, 2 H), 6.83(m, 2 H), 2.62 (s, CH3, 3 H),
2.37 (s, CH3, 3 H), 2.34 (m, (CH3)CH, 2 H), 2.16 (m, (CH3)CH,
4 H), 1.98 (m, (CH3)CH, 2 H), 1.51-0.62 (m, 56 H), -8.24 (m,
Rh-H-Rh, 1 H). 13C{1H} NMR (C6D6, 25 °C): δ 146.92 (s),
145.70 (s), 145.50 (s), 142.57(s), 136.40 (s), 133.17 (s), 132.66 (s),
132.26 (s), 127.84 (s), 127.56 (s), 127.24 (s), 124.45 (s), 29.70-28.46
(m), 22.84 (m), 22.44 (d, J=7.2 Hz), 22.04 (s), 21.38 (s), 20.69 (s),
20.35 (s), 19.62 (s), 19.23 (s), 19.07 (s), 18.38 (s). 31P{1H} NMR
(C6D6, 25 °C): δ 99.16 (dd, J=173, 28 Hz), 93.94 (m), 92.83 (m).
APCI-MS (þ): m/z 943.25 ([M - H]þ), 944.20 ([M]þ).
Synthesis of [Rh2(dippe)2(μ-SH)(μ-H)] (7). 7 could not be iso-
lated in pure form; all relevant data are taken from a mixture of
7, 6, and 4,6-Me2DBT. 1H NMR (C6D6, 25 °C): δ -0.02 (s, 1 H),
-7.84 (m, 1 H). 31P{1H} NMR (C6D6, 25 °C): δ 110.08 (dd, J=
181, 29 Hz), 91.52 (m), 90.56 (m). An X-ray structure
(disordered, modeled as a 50/50 cocrystallization of 1 and 7) is
reported in the Supporting Information.
Synthesis of [Rh2(dippe)2(μ-S-C6H4OC6H5)(μ-H)] (8). Phen-
oxythiin (40.3 mg, 0.20 mmol) and Rh(dippe)(μ-H)]2 (147.4 mg,
0.20 mmol) were dissolved in 25 mL of C6H6 and placed in a
50 mL Schlenk flask. The reaction mixture was heated to 80 °C
for 14 days. The solution was transferred to a 50 mL round-
bottom flask, and the solvent was removed under vacuum to
leave a dark yellow solid. The solid was dissolved in a minimal
amount of hexanes, and the solution was chilled to -30 °C to
yield pure product (58.2 mg, 31.0%). 1H NMR (C6D6, 25 °C):
δ 7.74 (dd, J=7.7, 1.2 Hz, 1H), 7.26-7.19 (m, 4H), 6.93-6.90
(m, 1H), 6.87-6.85 (m, 1H), 6.73 (td, J=7.1, 1.2 Hz, 1H), 6.62
(td, J = 7.1, 1.2 Hz, 1H), 2.46-1.80 (bm, 8H), 1.66-0.60 (m,
56H), -7.81 (m, 1H). 13C{1H} NMR (C6D6, 25 °C): δ 144.81 (s),
129.29 (s), 124.32 (s), 121.83 (s), 121.59 (s), 119.66 (s), 117.65 (s),
28.28 (s), 28.08 (s), 26.38 (s), 22.83 (m), 21.87 (m), 21.47 (s), 21.41
(s), 19.66 (s), 18.71 (s), 15.73 (s), 15.46 (s). 31P{1H} NMR (C6D6,
25 °C): δ 102.54-102.36 (m), 101.46-101.30 (m), 94.34-93.84
(m), 93.25-92.85 (m). Anal. Calcd (found) for C40H74Rh2P4OS:
C, 51.50 (51.44); H, 8.00 (8.32).
Synthesis of [Rh2(dippe)2(μ-Cl)(μ-SC12H9)] (9). Lithium 2-
(phenylthio)phenolate (0.095 g, 0.490 mmol) in THF was trans-
ferred by cannula to a stirred THF suspension of [Rh(dippe)(μ-Cl)]2
(0.392 g, 0.489 mmol). After approximately 0.5 h, the solvent
was reduced under vacuum and the solution was vacuum-filtered
through neutral alumina. The solution was chilled to -30 °C to
yield a yellow precipitate. The precipitate was separated from
the supernatant by vacuum filtration, washed three times with
1
hexanes, and then dried under vacuum (218.9 mg, 47.0%). H
NMR (C6D6, 25 °C): δ 9.98 (d, J=7.9 Hz, 1H), 8.04 (d, J=7.6
Hz, 2H), 7.33 (bt, J = 7.6 Hz, 2H), 7.26 (d, J = 7.3 Hz, 1H),
7.19-7.13 (m, 2H), 7.00 (t, J = 7.2 Hz, 1H), 2.53-0.46 (bm,
64H). 13C{1H} NMR (C6D6, 25 °C): δ 140.06 (s), 131.14 (s),
130.37(s), 126.79 (s), 125.77 (s), 125.72 (s), 123.83 (s), 27.36 (s),
27.14 (s), 22.93 (m), 21.03 (m), 18.70 (s). Accidental overlap
results in fewer signals than types of carbons. 31P{1H} NMR
(C6D6, 25 °C): δ 99.61 (ddd, JP-Rh(1)=200.2 Hz, JP-P=28.1 Hz,
JP-Rh(2)=5.5 Hz), 92.50 (ddd, JP-Rh(1)=172.9Hz,JP-P=28.1 Hz,
JP-Rh(2)=4.0 Hz). Anal. Calcd (found) for C40H73Rh2P4SCl: C,
50.50 (50.42); H, 7.74 (7.81).
Alternative Synthesis of [Rh2(dippe)2(μ-Cl)(μ-SC12H9)] (9).
Approximately 5 equiv of 2-(phenylthio)phenol (9.7 mg, 0.053
mmol) was dissolved in a C6D6 solution of 2 (8.1 mg, 0.011 mmol).
The resulting mixture was placed in a resealable NMR tube for
analysis. 9 forms immediately (43%) as the major product.
Alternative Synthesis of [Rh2(dippe)2(μ-Cl)(μ-SC12H9)] (9).
Approximately 10 equiv of dibenzothiophene (19 mg, 0.10 mmol)
in C6D6 was added to a resealable NMR tube that contained a
C6D6 solution of 2 (8.0 mg, 0.010 mmol). The contents of the

Article
Organometallics, Vol. 29, No. 21, 2010 4931
tube were heated at 100 °C for 55 days to completely consume 2
Supporting Information Available: Text, tables, and CIF files
giving details of the X-ray structure determinations and crystal
data for 4-9. This material is available free of charge via the
Internet at http://pubs.acs.org. The structures are available in
the Cambridge Crystallographic Database as CCDC #748860-
748863, 767419, and 767420.
and produce 9 in approximately 28% yield by integration of 31
NMR signals.
P
Acknowledgment. We acknowledge the NSF for finan-
cial support (Grant Nos. CHE-0414325 and CHE-0717040).