Structural properties and inversion mechanisms of [Rh(dippe)(μ-SR)] 2 complexes

Article abstract of DOI:10.1016/j.ica.2003.11.026

Several new bis-thiolate complexes of the type [Rh(dippe)(μ-SR)] ₂ where R=H, methyl, cyclohexyl, o-biphenyl, and phenyl, or (SR) ₂=SCH₂CH₂CH₂S have been synthesized and characterized by NMR spectroscopy and single crystal X-ray diffraction. All [Rh(dippe)(μ-SR)]₂ complexes except [Rh(dippe)(μ-SPh)] ₂ exhibit bent geometries, while the orientation of the thiolato substituents changes with increasing steric bulk. ¹H and ³¹P NMR spectroscopies indicate that both ring inversion and sulfur inversion occur among the members of the series, which allows them to access several isomeric forms when they are in solution. ³¹P NMR spectroscopy indicates that sulfur inversion in [Rh(dippe)(μ-SH)] ₂, [Rh(dippe)(μ-Sbiphenyl)]₂, and [Rh(dippe)(μ-SPh)] ₂ is a non-dissociative process.

Full text of DOI:10.1016/j.ica.2003.11.026

Inorganica Chimica Acta 357 (2004) 1836–1846
www.elsevier.com/locate/ica
Structural properties and inversion mechanisms
of [Rh(dippe)(l-SR)]2 complexes
*
Stephen S. Oster, William D. Jones
Department of Chemistry, University of Rochester, Hutchinson Hall, Rochester, NY 14627, USA
Received 30 October 2003; accepted 22 November 2003
Submitted on the occasion of the 70th birthday of Prof. Helmut Werner
Abstract
Several new bis-thiolate complexes of the type [Rh(dippe)(l-SR)]2 where R ¼ H, methyl, cyclohexyl, o-biphenyl, and phenyl, or
(SR)2@SCH2CH2CH2S have been synthesized and characterized by NMR spectroscopy and single crystal X-ray diffraction. All
[Rh(dippe)(l-SR)]2 complexes except [Rh(dippe)(l-SPh)]2 exhibit bent geometries, while the orientation of the thiolato substituents
changes with increasing steric bulk. 1H and 31P NMR spectroscopies indicate that both ring inversion and sulfur inversion occur among
the members of the series, which allows them to access several isomeric forms when they are in solution. 31P NMR spectroscopy in-
dicates that sulfur inversion in [Rh(dippe)(l-SH)]2, [Rh(dippe)(l-Sbiphenyl)]2, and [Rh(dippe)(l-SPh)]2 is a non-dissociative process.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Crystal structures; Thiolate complexes; Dynamics
1. Introduction
M2S2 core is ring inversion, which is analogous to chair–
chair interconversion in cyclohexane. Another process,
which appears to have a higher energy barrier than ring
inversion, is sulfur inversion. Here, the sulfur lone pair
inverts at the M–(l-SR)–M linkage. This can occur by
either a dissociative or non-dissociative mechanism. In
the dissociative case, a dative bond is broken between the
sp3-hybridized sulfur and one metal atom. Rotation
about the remaining sulfur–metal bond is followed by
reformation of a Rh–S bond with a different pair of
electrons. In the non-dissociative case, the sulfur atom
proceeds through a planar transition state in which it is
sp2-hybridized. It is well known that sulfur also inverts
when it is attached to a metal center as part of a terminal
ligand and when it is part of an organic ring [9–15].
Recently, a study that investigated the structure, re-
activity, and fluxional behavior of [Ni(dippe)(l-S)]2 and
its reaction products has been reported [16]. Like other
sulfur-bridged transition metal complexes, they too
interconvert between their possible conformers by a
process that is most likely ring inversion, also called ring-
flip, of the M2S2 core. However, experimental evidence
suggested the presence of sulfur inversion, as well.
Moreover, Torrens and coworkers [17] also recently
The existence of binuclear metal complexes that
possess a M2S2 core is well established in the literature.
One salient feature is that they can exist in a number of
distinct conformations. For example, [M2(l-S)2L4]
complexes can exist as either planar or bent conformers.
The addition of R groups to the M2S2 core further ex-
pands the number of possible isomers. [M2(l-S)(l-
SR)L4] complexes, where R ¼ H, alkyl, or aryl, may be
found in a total of four, and [M2(l-SR)2L4] complexes
may be found in a total of six, distinct conformations.
Sulfur strongly prefers a pyramidal geometry, so the
bent complexes predominate in the structures that have
been characterized [1].
A second feature that is related to the first is that
complexes of the three bent-dialkyl type shown in
Scheme 1 are often fluxional on the NMR timescale
[2–8]. Consequently, all three classes of complexes in-
terconvert between at least some of their possible con-
formations. One fluxional process that involves the entire
* Corresponding author. Tel.: +1-585-275-5493; fax: +585-506-0205.
E-mail address: jones@chem.rochester.edu (W.D. Jones).
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2003.11.026

S.S. Oster, W.D. Jones / Inorganica Chimica Acta 357 (2004) 1836–1846
1837
to the signal of 85% H3PO4. [Rh(dippe)(l-Cl)]2 and
[Rh(dippe)(l-H)]2 have been previously synthesized and
fully characterized [18,19]. Details of the X-ray structure
determinations are given in the Supplementary Material.
R
S
R
R
S
R
S
S
Pri2
P
sulfur
Pri2
P
Pri2
P
Pri2
P
Rh
Rh
Rh
Rh
inversion
(rear)
P
P
P
Pri2
Pri2
P
Pri2
Pri2
bent-anti
syn-exo
2.1. Synthesis of [Rh(dippe)(l-SH)]2 (1)
sulfur
ring inversion
Pri2
ring inversion
Pri2
Ten equivalents of NaSH (192 mg, 3.4 mmol) was
added, all at once, to a stirred THF suspension of
[Rh(dippe)Cl]2 (274 mg, 0.34 mmol) in approximately 50
mL of THF. The mixture was stirred overnight and then
filtered through 80–200 mesh neutral alumina on a fine
glass frit to remove unreacted NaSH and NaCl. The
solvent was evaporated to dryness under vacuum. The
solid was extracted with 5 mL portions of hexanes,
which were combined and placed under vacuum to
evaporate the solvent and leave a yellow solid (169 mg,
61.3%). Crystals for X-ray structural analysis were
grown from a THF solution of the product at )30 °C.
1H NMR (400 MHz, THF-d8, 20 °C): d 2.07 (sext,
J ¼ 6:9 Hz, 8H), 1.38 (d, J ¼ 12:0 Hz, 8H), 1.30–1.25
(dd, J ¼ 7:1, 7.0 Hz, 24H), 1.20–1.06 (dd, J ¼ 6:8, 5.0
Hz, 24H), )1.37 (s, 2H). 13C NMR (100 MHz, THF-d8,
25 °C): 27.90 (m), 23.19 (m), 20.76 (s), 19.13 (s). 31P
NMR (162 MHz, THF-d8, 20 °C): d 93.16 (d,
inversion
(front)
Pri2
P
Pri2
P
P
P
R
sulfur
P
Pri2
P
P
Pri2
P
Rh
R
Rh
R
Rh
Rh
Pri2
S
R
Pri2
S
inversion
(rear)
S
S
bent-anti
syn-endo
Scheme 1.
reported the results of a study in which (Bu4N)2[Pt2-
(l-SC6F5)2(SC6F5)4], (Bu4N)2 [Pt2(l-SC6HF4)2(SC6
HF4)4], and (Bu4N)2[Pt2(l-p-SC6F4(CF3))2(p-SC6F4
(CF3))4] appear to undergo inversion at the bridging
sulfur atoms. Since then, in HDS studies, [Rh(dippe)(l-
S-2-biphenyl)]2 and [Rh(dippe)(l-SPh)]2 were indepen-
dently synthesized to determine if they occur as reaction
products, and in turn they became an interesting subject
in their own right. Several analogs of these two species
were then synthesized and studied. Herein is a report on
the synthesis, structural properties, and NMR spectral
characteristics of [Rh(dippe)(l-SR)]2 complexes, where
R ¼ H, alkyl, and aryl groups, and a comparison is made
among them, as well as to similar complexes that have
been documented in the literature.
J
¼ 176:6 Hz). Anal. Calc. (Found) for
ðP–RhÞ
C28H66Rh2P4S2: C, 42.21 (42.36); H, 8.35 (8.66)%.
2.2. Synthesis of [Rh(dippe)(l-SCH3)]2 (2)
Approximately 4.3 equivalents of NaSCH3 (118 mg,
1.69 mmol) was added, all at once, to a stirred THF
suspension of [Rh(dippe)Cl]2 (312 mg, 3.89 mmol) in
approximately 50 mL of THF. The mixture was stirred
overnight and then filtered through 80–200 mesh neutral
alumina on a fine glass frit to remove unreacted
NaSCH3 and NaCl. The solvent was evaporated to
dryness under vacuum to leave a yellow solid (119 mg,
37.1%). Crystals for X-ray structural analysis were
grown from a THF solution of the product at )30 °C.
1H NMR (400 MHz, THF-d8, 30 °C): d 2.23 (s, 6H),
2. Experimental
All operations were performed under a nitrogen at-
mosphere unless otherwise stated. C6D6, THF, THF-d8,
hexanes, and toluene-d8 were distilled from dark purple
solutions of benzophenone ketyl. Thiophenol and cy-
clohexanethiol were purchased from Aldrich Chemical
Co., and distilled from CaCl2. NaSH, and NaSCH3
were purchased from Aldrich Chemical Co. and used
without further purification. 2-Phenylthiophenol was
obtained from John C. DiCesare, Department of
Chemistry, University of Tulsa, Tulsa, Oklahoma, and
used without further purification. A Siemens-SMART
3-Circle CCD diffractometer was used for X-ray crystal
structure determinations. Elemental analyses were ob-
tained from Desert Analytics and Complete Analysis
2.14–2.05 (m, 8H), 1.35 (d, J
¼ 11:5 Hz, 8H), 1.34–
ðH–PÞ
1.28 (dd, J ¼ 7:4, 7.1 Hz, 24H), 1.13–1.09 (dd, J ¼ 7:0,
4.4 Hz, 24H). 13C NMR (100 MHz, THF-d8, 25 °C): d
27.55 (t, J ¼ 9:6 Hz), 22.87 (td, J ¼ 20:9, 3.6 Hz), 21.07
(s), 19.58 (s), 19.24 (s). 31P NMR (162 MHz, C6D6, 20
°C): d 90.83 (d, J
for C30H70Rh2P4S2: C, 43.69 (43.97); H, 8.56 (8.62)%.
¼ 172:2 Hz). Anal. Calc. (Found)
ðP–RhÞ
2.3. Synthesis of [Rh(dippe)(l-SC6H11)]2 (3)
Laboratories, Incorporated. All H, 13C, and 31P NMR
1
Approximately 2.05 equivalents of cyclohexanethiol
(0.069 mL, 0.57 mmol) was added via syringe to a stirred
hexanes solution (ffi25 mL) of [Rh(dippe)H]2 (202 mg,
0.28 mmol). A reaction immediately occurred as H2
evolved and the color of the solution turned from
spectra were recorded on a Bruker Avance 400 NMR
spectrometer. All 1H chemical shifts are reported
relative to the residual proton resonance in the deuter-
ated solvent. All 31P chemical shifts are reported relative

1838
S.S. Oster, W.D. Jones / Inorganica Chimica Acta 357 (2004) 1836–1846
emerald green to orange. The mixture was stirred for 15
min and then the solvent was evaporated to dryness
under vacuum to yield an orange solid. The solid was
washed twice with pentane to remove residual cyclo-
hexanethiol and then dried under vacuum (114 mg,
(825.5 mg, 1.13 mmol). H2 evolved as the solution color
changed to yellow, followed by the formation of a yel-
low precipitate. The solvent was removed via vacuum
filtration. The solid was washed twice with pentane and
dried overnight under vacuum (140.6 mg, 58.0%). Ap-
proximately 20 mg of 5 was dissolved in THF and
chilled to )30 °C to grow crystals that were suitable for
X-ray diffraction. 1H NMR (400 MHz, THF-d8, 25 °C):
d 2.77 (s, 4H), 2.27–2.07 (m, 10H), 1.39–1.34 (dd,
J ¼ 6:9, 6.5 Hz, 12H), 1.32 (bs, 8H), 1.26–1.21 (dd,
J ¼ 7:2, 7.1 Hz, 12H), 1.16–1.11 (dd, J ¼ 6:9, 5.5 Hz,
12H), 1.09–1.05 (dd, J ¼ 7:0, 4.2 Hz, 12H). 13C NMR
(100 MHz, THF-d8, 25 °C): d 40.99 (s), 34.68 (s), 28.27
(t, J ¼ 10:5 Hz), 26.96 (t, J ¼ 16.6 Hz), 23.25 (td,
J ¼ 20:6, 3.8 Hz), 21.56 (s), 20.20 (s), 19.77 (s), 18.82 (s).
31P NMR (162 MHz, THF-d8, 25 °C): d 88.09 (d,
J ¼ 171:7 Hz). Anal. Calc. (Found) for C31H70Rh2P4S2:
C, 44.14 (44.41); H, 8.37 (8.60)%.
1
43.6%). H NMR (400 MHz, C6H6, 20 °C): d 3.27 (bt,
J ¼ 11:2 Hz, 2H), 2.84 (bd, J ¼ 12:3 Hz, 4H), 2.31–2.22
(m, 6.9 Hz, 8H), 1.95 (bd, J ¼ 12:8 Hz, 4H), 1.85–1.71
(m, 8H), 1.58 (dd, J ¼ 7:0, 6.4 Hz, 24H), 1.36–1.22 (m,
4H), 1.15 (m, J ¼ 6:9, 4.5 Hz, 24H), 1.06 (d, J ¼ 12:5
Hz, 8H). 13C NMR (100 MHz, THF-d8, 25 °C): d 47.20
(s), 42.70 (s), 29.36 (s), 27.99 (m), 27.15 (s), 23.35 (m),
21.41 (s), 19.17 (s). 31P NMR (162 MHz, THF-d8, 20
°C): d 82.73 (d, J
for C40H86Rh2P4S2: C, 49.99 (49.86); H, 9.02 (9.04)%.
¼ 171:8 Hz). Anal. Calc. (Found)
ðP–RhÞ
2.4. Synthesis of [Rh(dippe)(l-SC12H9)]2 (4)
Approximately 2.05 equiv. of 2-phenylthiophenol
(50.9 mg, 0.27 mmol) in hexanes was added dropwise to
a stirred hexanes solution (50 mL) of [Rh(dippe)H]2
(97.7 mg, 0.133 mmol) as the color of the mixture im-
mediately changed from emerald green to orange. The
resulting solution was stirred for approximately 15 min
and then the solvent was evaporated under vacuum to
leave a rust colored solid (104 mg, 70.8%). The solid was
dissolved in a minimal amount of THF and chilled at
)30 °C to yield crystals that were suitable for X-ray
2.7. Synthesis of [Rh(dippe)(l-SC6H5)]2 (6)
Approximately 2.05 equivalents of benzenethiol (0.58
mL, 0.56 mmol) was added via syringe to a stirred
hexanes solution (25 mL) of [Rh(dippe)H]2 (201 mg,
0.27 mmol). A reaction immediately occurred as H2
evolved and the color of the solution turned from em-
erald green to yellow. The mixture was stirred for 15 min
and then the solvent was evaporated to dryness under
vacuum to yield a yellow solid. The solid was washed
three times with hexanes to remove residual benze-
nethiol and then dried under vacuum (222 mg, 85.4%).
1H NMR (400 MHz, THF-d8, 20 °C): d 7.94 (m, 4H),
6.81 (m, 6H), 1.81 (sept, J ¼ 6:9 Hz, 8H), 1.25 (d,
J ¼ 12:0 Hz, 8H), 1.19–1.01 (m, 48H). 13C NMR (100
MHz, THF-d8, 25 °C): d 137.05 (s), 131.98 (s), 126.67
(s), 123.68 (s), 119.97 (s), 65.75 (s), 26.97 (m), 22.54 (m),
20.69 (s), 19.06 (s). 31P NMR (162 MHz, THF-d8, 20
1
crystal diffractometry. H NMR (400 MHz, toluene-d8,
20 °C): d 9.91 (d, J ¼ 7:7 Hz), 8.93 (bs), 8.08 (bs), 8.01
(d, J ¼ 7:1 Hz), 7.36 (bs), 7.27 (bm), 7.17 (bm), 6.78 (m),
6.45 (m), 2.23 (bs), 1.86 (bs), 1.67 (bs), 1.49 (m), 1.30–
0.94 (m), 0.82 (m). 13C NMR (100 MHz, toluene-d8, 25
°C): d 131.12 (s), 130.38 (s), 127.49 (s), 126.01 (s), 27.46
(m), 26.85 (s), 21.45 (s), 19.07 (s), 18.92 (s). 31P NMR
(162 MHz, toluene-d8, 20 °C): d 91.22 (d, J
¼ 178:5
ðP–RhÞ
Hz), 89.02 (d, J
in a 1:2 ratio). Anal. Calc. (Found) for C52H82Rh2P4S2:
¼ 178:5 Hz) (two doublets appear
ðP–RhÞ
°C): d 89.45 (d, J
for C40H74Rh2P4S2: C, 50.63 (49.83); H, 7.86 (7.78)%.
¼ 173:6 Hz). Anal. Calc. (Found)
ðP–RhÞ
C, 56.72 (56.67); H, 7.51 (7.76)%.
2.5. Alternative synthesis of 4
2.8. Synthesis of lithium 2-phenylthiophenolate
Approximately 2.1 equiv. of lithium 2-phenylthio-
phenolate (180.0 mg, 0.93 mmol) was added all at once
to a hexanes suspension of [Rh(dippe)Cl]2 (354 mg, 0.44
mmol). The resulting mixture was stirred overnight. The
contents of the reaction flask were vacuum filtered
through 80–200 mesh neutral alumina to remove LiCl.
The solvent was then evaporated under vacuum to leave
4 (366 mg, 75.3%).
Approximately 1 equiv. of n-butyllithium in hexanes
(1.76 mL, 1.6 M) was added dropwise, over a two
minute period, to a stirred diethyl ether solution (50 mL)
of 2-phenylthiophenol (524.6 mg, 2.82 mmol). The re-
sulting solution was stirred for 4 h to produce a white
precipitate. The solvent was removed by vacuum filtra-
tion and the solid was dried under vacuum (510.1 mg,
93.3%).
2.6. Synthesis of [Rh2(dippe)2(l-S2C3H6)] (5)
2.9. X-ray structures of 1–6
Approximately 1 equiv. of 1,3-propanedithiol (0.57
mL, 1.977 M in hexanes) was added dropwise to a
stirred pentane solution (950 mL) of [Rh(dippe)H]2
A Siemens-SMART CCD area detector diffractome-
ter equipped with an LT-2 low temperature unit was used
for X-ray crystal structure determination. Single crystals

S.S. Oster, W.D. Jones / Inorganica Chimica Acta 357 (2004) 1836–1846
1839
Table 1
Summary of crystallographic data for 1–6
Crystal parameters
Chemical formula
1
2
3
4
5
6
C
28H66P4Rh2S2
C30H70P4Rh2S2
C40H86P4Rh2S2
C60H98P4Rh2S2
Á 2C4H8O2
1245.20
C31H70P4Rh2S2
C40H74P4Rh2S2
Formula weight
Crystal system
Space group, Z
796.63
824.68
960.91
836.69
triclinic
948.81
monoclinic
P21=n, 4
10.7900(6)
25.5880(13)
13.4002(7)
90
orthorhombic
P212121, 4
14.8813(10)
5.4204(10)
16.8552(11)
90
monoclinic
P21=n, 4
10.4590(6)
21.7196(13)
20.7150(12)
90
triclinic
ꢁ
orthorhombic
Cmca, 4
24.204(2)
9.1172(8)
20.0689(19)
90
ꢁ
P1, 2
P1, 2
ꢀ
a (A)
12.0877(11)
12.4401(11)
21.538(2)
96.901(2)
104.197(2)
95.162(2)
3093.0(5)
)80
9.9435(6)
13.1478(8)
15.8197(10)
82.8660(10)
86.3790(10)
71.3120(10)
1943.4(2)
)80
ꢀ
b (A)
ꢀ
c (A)
a (°)
b (°)
c (°)
102.6560(10)
90
3609.8(3)
90
90
97.4030(10)
90
4666.5(5)
90
90
3
ꢀ
Volume (A )
3867.9(4)
)80
1.416
4428.6(7)
)80
1.423
Temperature (°C)
)80
1.466
)80
1.368
qcalc (g cmÀ3
)
1.337
13957
1.430
12668
Number of of data collected
Number of unique data
23555
8673
14306
8139
361
29017
11070
449
12389
2708
124
8821
597
8938
352
Number of parameters varied 333
R1ðFoÞ, wR2ðFo2Þ, (I > 2rðIÞ)
R1ðFoÞ, wR2ðFo2Þ, all data
Goodness-of-fit
0.0387, 0.0755
0.0570, 0.0806
1.009
0.0209, 0.0437
0.0230, 0.0443
0.998
0.0483, 0.0933
0.0713, 0.1006
1.069
0.1260, 0.2148
0.1393, 0.2191
1.513
0.0242, 0.0663
0.0281, 0.0683
1.024
0.0376, 0.1359
0.0550, 0.1420
1.100
of 1–6 were mounted under Paratone-8277 on glass fibers
and immediately placed in a cold nitrogen stream at )80
°C on the X-ray diffractometer. The X-ray intensity data
were collected on a standard Siemens-SMART CCD
Area Detector System equipped with a normal focus
molybdenum-target X-ray tube operated at 2.0 kW. A
total of 1321 frames of data (1.3 hemispheres) were col-
lected using a narrow frame method with scan widths of
0.3° in x and exposure times of 5 s/frame using a de-
tector-to-crystal distance of 5.09 cm (maximum 2h angle
of 56.54°) for all of the crystals except 3 (30 s), 5 (30 s),
and 6 (60 s). Frames were integrated with the Siemens
located from the difference Fourier map and the posi-
tional and isotropic thermal parameters were refined.
There was nothing unusual about the solution or re-
finement of any of the structures, with the exception of 4,
which also contained two diffuse THF molecules within
the asymmetric unit that were refined isotropically.
Further experimental details of the X-ray diffraction
studies are provided in Table 1.
3. Results and discussion
ꢀ
SAINT program to 0.75 A for all of the data sets; how-
3.1. Structural characteristics of [Rh(dippe)(l-SR)]2
complexes
ever, weak data >46.6° were omitted from the refinement
of 5. The unit cell parameters for all of the crystals were
based upon the least-squares refinement of three di-
The bridging thiolate complexes of the type
[Rh(dippe)(l-SR)]2 are easily prepared either by reaction
of [Rh(dippe)(l-Cl)]2 with thiolate salt or by reaction of
thiol with [Rh(dippe)(l-H)]2 (Scheme 2). [Rh(dippe)(l-
SH)]2 (1) is the simplest derivative in this class of com-
plexes. Its 1H NMR spectrum at 20 °C indicates the
presence of two sulfhydryl groups, which appear as sin-
glet at d )1.37. Also, its 31P NMR spectrum at the same
temperature shows a doublet that corresponds to the
four equivalent phosphorus nuclei that are each coupled
to I ¼ 1=2 rhodium. The ORTEP diagram of 1, shown in
Fig. 1, illustrates the fact that it assumes a bent syn-endo
conformation in the solid state, with a hinge angle h of
136.0° and a substituent angle of displacement from the
1
mensional centroids of >5000 reflections. Data were
corrected for absorption using the program SADABS [20].
Space group assignments were made on the basis of
systematic absences and intensity statistics by using the
XPREP program (Siemens, SHELXTL 5.04). The struc-
tures were solved by using direct methods and refined by
2
full-matrix least-squares on F2. For all of the struc-
tures, the non-hydrogen atoms were refined with aniso-
tropic thermal parameters and hydrogens were included
in idealized positions giving data:parameter ratios
greater than 10:1. The sulfur-bound hydrogens in 1 were
1
It has been noted that the integration program SAINT produces cell
3
constant errors that are unreasonably small, since systematic error is
not included. More reasonable errors might be estimated at 10Â the
listed value.
S–S axis s of 36.05° (see Table 2).
P
P
2
τ
Using the SHELX 95 package, R1 ¼ ð kFoj À jFckÞ= jFoj,
P
P
R
2
2
1=2
3
fwR2 ¼ ½ ðwðFo2 À Fc2Þ Š= ½wðFo2Þ Þg Š, where w ¼ 1=½r2ðFo2Þ þ
The angles are defined as follows:
S
S
Rh
Rh
2
ðaPÞ þ bPŠ and P ¼ ½fðMaximum of 0 or Fo2Þ þ ð1 À f ÞFc2Š.
.
θ

1840
S.S. Oster, W.D. Jones / Inorganica Chimica Acta 357 (2004) 1836–1846
Cl
Cl
NaSR
Pri2
P
Pri2
P
R
S
Rh
Rh
Rh
Pri2
P
Pri2
P
S
R
P
P
Pri2
Rh
Rh
Pri2
P
P
Pri2
Pri2
H
Pri2
P
Pri2
P
H
Rh
R = H, 1 R = o-biphenyl, 4
R = Me, 2 R = CH2CH2CH2, 5
R = Cy, 3 R = Ph, 6
P
P
RSH
Pri2
Pri2
Scheme 2.
Fig. 2. ORTEP drawing of [Rh(dippe)(l-SCH3)]2 (2). Ellipsoids are
shown at the 30% probability level. All hydrogen atoms are omitted for
clarity.
prefer to be sp3-hybridized relative to oxygen, as cou-
lombic repulsion between paired electrons is less in 3p
orbitals than in 2p orbitals. This is reflected by the fact
that the distribution of the sum of the bond angles around
P
sulfur, , in M2SR groups, where R ¼ H, alkyl, is cen-
tered at approximately 310–320°, while the distribution
for M2OR groups is centered near 360° [1]. The other
factor responsible for the bent conformations of 1 and 2 is
that rhodium constitutes the metal centers of both com-
plexes. Rhodium orbitals are diffuse relative to transition
metals that are above and to the right of it in the periodic
table. This allows the metal centers of 1 and 2 to achieve a
weak net-bonding interaction, via their dz2 and pz orbi-
tals, and each complex bends along its S–S axis to create a
dihedral angle h that is less than 140°. Good r-donor li-
gands further improve the overlap of the rhodium orbitals
by enhancing dz2 –s orbital mixing. This leads to resultant
dz2 -orbitals that are more directed along the z-axes of the
two centers [21]. As a good r-donor, dippe should be
expected to favor bending in both 1 and 2, provided that
direct ligand–ligand steric repulsion is absent.
Fig. 1. ORTEP drawing of [Rh(dippe)(l-SH)]2 (1). Ellipsoids are
shown at the 30% probability level. All hydrogen atoms are omitted for
clarity, except those that are on the bridging sulfur atoms, except those
that are on the bridging sulfur atoms, which are shown in refined lo-
cations.
Substitution of the sulfhydryl protons by methyl
groups gives [Rh(dippe)(l-SCH3)]2 (2), whose X-ray
structure is shown in Fig. 2. This complex assumes a
bent-anti conformation in the solid state. This appears
to be the most stable conformation in solution, as well,
as the 31P NMR spectrum of 2 at )95 °C in toluene-d8
consists of a pair of doublet of doublets at d 90.83,
which is indicative of AA0BB0X spin system.
The observed geometries of 1 and 2 in the solid state
results from the preference of sulfur to pyramidalize, the
presence of metal–metal interactions, and the presence of
ligand–substituent and ligand–ligand repulsions (see
Table 2). To begin, both 1 and 2 exist as bent isomers,
primarily because their bridging sulfur atoms strongly
The two different geometries of 1 and 2 in the solid
state is probably due to the increase in the steric bulk of
the thiolate substituents in moving from proton to me-
ꢂ
thyl group. For example, Lledos, Alvarez, and co-
workers calculate that to replace the SH hydrogen
Table 2
Selected angles and sums of angles about sulfur in [Rh(dippe)(l-SR)]2 complexes
P
ꢀ
dRh–Rh (A)
Complex
Isomer
h (°)
s
[Rh(dippe)(l-SH)]2 (1)
syn-endo
bent-anti
syn-exo
302.52(4)°
136.0
124.6
126.4
126.3
129.1
180
36.05°
3.28
[Rh(dippe)(l-SCH3)]2 (2)
[Rh(dippe)(l-SC6H11)]2 (3)
[Rh(dippe)(l-SC12H9)]2 (4)
[Rh2(dippe)2(l-1,2-S2C3H6)] (5)
[Rh(dippe)(l-SC6H5)]2 (6)
297:57ð12Þ°endo=327:71ð13Þ°exo
83:2°endo=16:9°exo 3.30
306.87(6)°
86.05
85.75°
80.65°
77.8°
3.25
3.18
3.24
3.63
syn-exo
syn-exo
planar-anti
302.35(87)°
289.44(15)°
301.02(13)°

S.S. Oster, W.D. Jones / Inorganica Chimica Acta 357 (2004) 1836–1846
1841
atoms in [M(PH3)2(l-SH)]2 with methyl groups, while
the complex is in the bent syn-endo conformation, in-
creases ligand–substituent repulsion by approximately 3
kcal molÀ1 per substituent. Yet, substituent–substituent
repulsion increases by ꢀ5 kcal molÀ1 when the model
complex assumes the bent syn-exo conformation [1].
Consequently, 2 most likely adopts a bent-anti geometry
because that conformation attenuates the added ligand–
substituent repulsion of the methyl substituents relative
to the sulfhydryl substituents of 1, while it all together
avoids a substituent–substituent repulsion. Lastly, it is
worthwhile to note that 2 stands in contrast to the iso-
electronic complex, [Pt(PH3)2(l-SCH3)]22þ. While this
dication bears methylthiolate substituents as in 2, cal-
culations show that it prefers to be planar rather than
bent when those substituents are anti to each other,
which illustrates the important role that diffuse d-orbi-
tals play in determining geometry [22].
Members of this series with R ¼ cyclohexyl (3), bi-
phenyl (4), and CH2CH2CH2 (5) all adopt the bent syn-
exo isomer form (Figs. 3–5). The latter, with the
CH2CH2CH2 bridge, can only adopt this isomer due to
geometric constraints. As is the case for 1 and 2, these
complexes bend along the bridging sulfur axis due to
sulfurÕs preference to be highly pyramidalized and to the
presence of a weak net bonding rhodium–rhodium in-
teraction. However, the cyclohexylthiolato and biphe-
nylthiolato substituents are much more sterically
demanding than methyl, which may be the reason why
they are exo-oriented. It is possible that the energy cost
in terms of dippe-substituent repulsion that would be
demanded by a bent-anti conformation is greater than
the cost in terms of substituent–substituent repulsion
that would be demanded by a bent syn-exo conforma-
Fig. 4. ORTEP drawing of [Rh(dippe)(l-SC12H9)]2 (4). Ellipsoids are
shown at the 30% probability level. All hydrogen atoms are omitted for
clarity.
Fig. 5. ORTEP drawing of [Rh2(dippe)2(l-S2C3H6)] (5). Ellipsoids are
shown at the 30% probability level. All hydrogen atoms are omitted for
clarity.
tion. Stated differently, DG° may be more positive for
both 3 and 4 if they assume bent-anti geometry.
In the case of 4, it may be possible to invoke a fa-
vorable p-stacking effect between the a-rings of the bi-
phenylthiolato substituents as another reason why it
assumes the bent syn-exo conformation in the solid
state. For instance, Torrens and coworkers have re-
ported several polyfluorophenyl substituted Rh2S2
complexes that exist as bent syn-exo isomers. In two of
these – [Rh(l-SC6F5)(COD)]2 and [Rh(l-SC6HF4)
(COD)]2 – the distance between the two centroids is 3.45
ꢀ
ꢂ
and 3.48 A, respectively [23,24]. Lledos and coworkers
[1] point out that this is approximately the same distance
as the intermolecular distance between the C6F5 groups
in [Zn(C6F5)2]. However, the distance between the a-
Fig. 3. ORTEP drawing of [Rh(dippe)(l-SC6H11)]2 (3). Ellipsoids are
shown at the 30% probability level. All hydrogen atoms are omitted for
clarity.
ꢀ
ring centroids in 4 is 4.06 A. Consequently, a p-stacking
effect is most likely absent.

1842
S.S. Oster, W.D. Jones / Inorganica Chimica Acta 357 (2004) 1836–1846
An examination of the Rh–S and Rh–P bond lengths
In addition to packing effects, it is possible that 6 is
planar as a result of the withdrawal of electron density
away from the sulfur atoms into the phenyl groups via
lone pair to pà orbital delocalization, which would at-
tenuate their r-donating ability. This, in turn, would
destabilize the bent conformations. This is the argument
that has been put forward by Golen and coworkers in
explaining the observed geometrical differences between
certain dipalladium l-arylthiolato and l-alkylthiolato
complexes. They noted that cis-[Pd2Cl2(l-Cl)(l-SMe)
(PMe3)2] and cis-[Pd2Cl2(l-Cl)(l-SCMe3)(PMe3)2] exist
as bent molecules while cis-[Pd2Cl2(l-Cl)(l-SPh)
(PMe3)2], trans-[Pd2Cl2(l-SPh)2(PEt3)2], and trans-
[Pd2(SC6F5)(l-SC6F5)2(PPh3)2] are found to be planar.
Moreover, they point out that the Pd–S distances in cis-
[Pd2Cl2(l-Cl)(l-SPh)(PMe3)2] are on average about
and S–Rh–S and P–Rh–P angles of 3 and 4 indicates
that there is nominal elongation of the P4Rh2S2 moiety
in the latter to offset the potential for added ligand–
substituent repulsions that accompany its larger thiolato
substituents. Moreover, as Table 2 illustrates, there is
hardly any change in hinge angle-size between the two
complexes. It appears that the oblique orientation of the
biphenylate substituents to the Rh–Rh vector in 4
compensates for their steric bulk.
The complex [Rh2(dippe)2(l-1,2-S2C3H6)] (5) is
forced to assume a bent-exo conformation by its pro-
pylene linker. As Table 2 shows, the average sum of the
P
three bond angles around the bridging sulfur atom,
,
is ca. 289.4°. With the exception of the endo substituent
in 2, this makes the sulfur atoms of 5 the most highly
pyramidalized in the entire [Rh(dippe)(l-SR)]2 series.
The complex [Rh(dippe)(l-SC6H5)]2 (6), which is
shown in Fig. 6, stands in contrast to the other members
of the series of [Rh(dippe)(l-SR)]2, and also to the
similar complex [Rh(CO)2(l-SC6H5)]2 [25], in that it has
a planar rhodium–sulfur core. Its two phenyl substitu-
ents are oriented in an anti fashion, with an average s of
77.8°. This gives the complex nominal C2h symmetry. A
search of the Cambridge Structural Database indicates
that among [Rh2L4(l-XR)2] complexes, where L ¼ CO,
PR3 and X ¼ O, S, the only analogous structures contain
bridging oxygen atoms. Complex 6 possesses all of the
features that, stated above, favor a bent structure. Like
the other members of the series under study, its sulfur
bridges, rhodium centers, and terminal dippe ligands
should result in it having bent geometry. Consequently,
its planar-anti geometry in the solid state may be due to
ꢀ
0.033 and 0.045 A longer than they are in cis-[Pd2Cl2(l-
Cl)(l-SMe)(PMe3)2] and cis-[Pd2Cl2(l-Cl)(l-SCMe3)
(PMe3)2], respectively [26]. Yet, a significant increase in
Rh–S distance in going from 6 to 3 is absent; it is only
ꢀ
about 0.003 A longer in the former than it is in the
latter. Structural data simply fails to support the notion
that 6 assumes planar geometry as a result of the with-
drawal of electron density from the bridging sulfur at-
oms by the phenyl groups.
ꢂ
Lledos and coworkers [1] point out that a conse-
is that there is an
P
quence of the quasi invariance of
indirect relationship between the hinge angle h and the
angle of displacement s of the thiolato substituents from
the S–S axis. Complexes 3–6 bear this out. After taking
into account the geometrical constraints and steric ef-
fects that are imposed by the thiolate substituents, there
is a general trend of decreasing s as h becomes larger.
For example, compare the values of 4 to those of 6. The
former complex has a of 126.3° and a s of 85.8° while the
latter complex has values of 180° and 77.8°, respectively.
1
packing effects.
3.2. Dynamic NMR spectra of [Rh(dippe)(l-SR)]2
complexes
All members of the series of [Rh(dippe)(l-SR)]2
complexes in this study are fluxional on the NMR
timescale when they are in solution. In this respect, they
resemble [Ni(dippe)(l-S)]2, [Ni2(dippe)2(l-S)(l-SR)]þ,
[Ni(dippe)(l-SCH3)]22þ, and other sulfur-bridged tran-
sition metal complexes that have been reported in the
literature [16]. Yet, the variable temperature H and 31
1
P
NMR spectra of [Rh(dippe)(l-SR)]2 complexes neither
are uniform as a group nor do they differ from each
other in a manner that can be predicted from the
structural data.
It is worthwhile to consider what one would expect to
see in the 31P NMR spectra of the complexes. In both
bent syn-exo and syn-endo compounds, all phosphorus
nuclei are equivalent and therefore a single doublet (due
to Rh–P coupling, J ꢁ 170 Hz) should be seen for each
Fig. 6. ORTEP drawing of [Rh(dippe)(l-SC6H5)]2 (6). Ellipsoids are
shown at the 30% probability level. All hydrogen atoms are omitted for
clarity.

S.S. Oster, W.D. Jones / Inorganica Chimica Acta 357 (2004) 1836–1846
1843
isomer present. In the bent-anti structure, however,
there are two different types of phosphorus and there-
fore two separate resonances are expected, each a dou-
blet of doublets (JRh–P ꢁ 170 Hz, JP–P ꢁ 20 Hz). If the
bent syn-exo or syn-endo structures undergo a rapid
ring-inversion process, then the two isomers intercon-
vert and a single type of phosphorus (doublet) should be
observed. In the bent-anti structures, ring inversion will
interchange the two types of phosphorus nuclei, ren-
dering them equivalent. A simple doublet will be ob-
served. Consequently, the observation of simple
doublets (due to JRh–P) does not tell much about the
structure(s) present. In addition, sulfur inversion can
interconvert syn and anti structures as shown in Scheme
1, resulting in interchange of all three isomers. If all of
these dynamic processes are occurring, then a solution
containing a mixture of all three structures might dis-
play a single doublet for all of them!
of doublets due to coupling to the methine H and the
phosphorus. Only two sets of doublets of doublets are
observed from 50 to 10 °C. As the temperature is lowered
to )105 °C, all proton signals show broadening, which
prevents clear identification of separate isopropyl methyl
resonances. However, no sign of coalescence is indicated.
The 31P NMR spectra of 1 between 20 and )100 °C in
THF-d8 are shown in Fig. 7. The spectrum at 20 °C
consists of a doublet at d 93.16. As the temperature is
lowered to )80 °C, that doublet broadens and then re-
solves into two doublets, with one being twice the in-
tensity of the other. Both upfield and downfield signals
have nearly identical phosphorus–rhodium coupling
constants of 176.2 and 176.6 Hz, respectively. Lowering
the temperature still further to )105 °C results in slight
broadening of the two doublets, but solvent-imposed
limitations prevented further cooling.
When this same experiment is conducted in toluene-d8,
two doublets are observed that are nearly equal in in-
tensity. A reasonable scenario, is that at 20 °C, both ring
inversion and sulfur inversion are quite energetically ac-
cessible and the two processes allow 1 to interconvert
among all of its bent forms in a manner that is shown in
Scheme 1. As the temperature is lowered, sulfur inversion
is slowed, so that bent-anti and bent-syn structures no
longer rapidly interconvert. However, ring inversion is
still rapid (as seen in other systems [8]) so that the inter-
converting syn-exo and syn-endo complexes display one
doublet, whereas the two interconverting (but equivalent)
bent-anti structures display a second doublet. As the X-
ray structure shows the syn-endo structure, it appears
likely that the bent-anti isomer corresponds to the lower
intensity signal in the THF-d8 31P NMR spectrum.
Changing to toluene-d8 lowers the ground state energy of
the bent-anti isomer. Therefore, a larger percentage of the
population of 1 is ‘‘stranded’’ as the bent-anti isomer.
Similar arguments can be made concerning the dippe
1
methyl groups in the H NMR spectrum. The syn-exo
and syn-endo structures each have two different kinds of
diisopropyl group, those pointing into the ÔpocketÕ cre-
ated by the bent structure, and those pointing away
from the pocket. Since the methyl groups on each iso-
propyl are also inequivalent, this means that four types
of methyl are expected for each of these isomers. If the
structure is fluxional due to ring inversion, then the syn-
exo and syn-endo isomers are interconverting. However,
the two types of isopropyl group in one isomer inter-
convert with the two types of isopropyl group in the
other isomer, but in a pairwise fashion, and therefore
one expects there will still be two types of isopropyl
group in the time-averaged spectrum, each with two
distinct methyl resonances. In the less symmetrical bent-
anti structure, all four isopropyl groups are distinct so
that eight types of methyl are to be observed in the static
molecule. If the bent-anti structure undergoes rapid
ring-inversion, then two types of isopropyl group will be
observed, again because of a pairwise correlation in the
exchange. This would result in four distinct types of
methyl groups. Should sulfur inversion be occurring in
any of these complexes, then all isopropyl groups will be
rendered equivalent, and only two types of methyl will
be seen.
3.3. Dynamic NMR spectra of [Rh(dippe)(l-SH)]2
The conformations that 1 adopts in solution are most
likely limited to the bent form(s) as seen in the X-ray
structure, and variable temperature NMR spectra are
consistent with this. Evidence for the fluxionality of 1 is
provided by the signals of the dippe isopropyl substit-
1
uents in the H NMR spectrum and the phosphorus in
the 31P NMR spectra.
1
The H NMR spectrum of 1 at room temperature
displays only two types of methyl group, each a doublet
Fig. 7. 31P NMR spectra of 1 in THF-d8 from +20 to )100 °C.

1844
S.S. Oster, W.D. Jones / Inorganica Chimica Acta 357 (2004) 1836–1846
Further evidence for the above hypothesis comes from
examination of the dynamic spectra of 2.
complexes in the series. Unfortunately, the 31P NMR
spectra of 3 in THF-d8 fail to provide insight into what
those processes are since coalescence is never observed.
The spectra all display a single doublet that is centered
at approximately d 82.7, which does broaden slightly at
about )105 °C (Fig. 9).
3.4. Dynamic NMR spectra of [Rh(dippe)(l-SMe)]2
1
The H NMR spectra of 2 in THF-d8 show evidence
for at least two types of isopropyl methyl group, but as
before, broadening at low temperature prevents defini-
tive assignment of the number of species present. At +50
°C, however, the dippe methyl resonances clearly appear
more complex than four simple doublets of doublets,
suggesting that more than two types of isopropyl group
are present.
The 31P NMR spectra of 2 in THF-d8 at temperatures
from 60 to )100 °C are shown in Fig. 8. At the highest
temperature measured, the spectrum consists of a sharp
doublet, with JP–Rh ¼ 172:6 Hz, that is centered at d
90.80. With decreasing temperature, the doublet shifts
slightly upfield and broadens. At )70 °C, it coalesces to
a broad singlet and further cooling to )100 °C causes
the signal to sharpen into a pair of doublets of doublets
with JP–Rh ¼ 172:0 Hz and JP–P ¼ 21:8 Hz. This pattern
is consistent with a static bent-anti geometry for 2 as
observed in the solid state X-ray structure. The 31P
NMR data indicate that ring inversion occurs as the
temperature is raised, equilibrating the two types of
phosphorus but producing none of the syn isomers.
3.6. Dynamic NMR spectra of [Rh(dippe)(l-S-biphe-
nyl)]2
As with the other compounds, the 1H NMR spectrum
of complex 4 in toluene-d8 lacks detailed structure at
most temperatures at which it was measured. However,
while at +85 °C two doublets of doublets are seen, these
resonances coalesce and then separate as four broad
singlets at 20 °C.
The 31P NMR spectra vary considerably with tem-
perature (Fig. 10). At 90 °C, 4 produces a sharp doublet
that is centered at 91.41 with a J
¼ 180:3 Hz. This
ðP–RhÞ
signal broadens as the temperature is lowered, and at 50
°C it coalesces to a broad singlet at d 90.65. This singlet
then sharpens to yield two sharp doublets that, at 20 °C,
are centered at d 91.22 and 89.02, with the upfield signal
being approximately twice the intensity of the downfield
signal. Furthermore, both doublets have the same
phosphorus–rhodium coupling constant of J
¼
ðP–RhÞ
178:5 Hz. When the temperature is decreased below 20
°C, the upfield doublet begins to broaden as the down-
field doublet remains sharp. Moreover, the ratio be-
3.5. Dynamic NMR spectra of [Rh(dippe)(l-SCy)]2
The 1H NMR spectrum of complex 3 in THF-d8
lacks fine structure for all temperatures at which it was
measured. From 60 to )60 °C nearly all signals appear
as broad singlets, suggesting that fluxional behavior is
responsible for the broadness. At RT, the methyl pro-
tons of the isopropyl substituents give rise to two dou-
blets of doublets. Based on this data, it appears that 3 is
interconverting among several isomers by either one or
more processes like the other bent [Rh(dippe)(l-SR)]2
Fig. 9. 31P NMR spectra of 3 in THF-d8 from +60 to )105 °C.
Fig. 8. 31P NMR spectra of 2 in THF-d8 from +60 to )100 °C.
Fig. 10. 31P NMR spectra of 4 in toluene-d8 from +90 to )75 °C.

S.S. Oster, W.D. Jones / Inorganica Chimica Acta 357 (2004) 1836–1846
1845
tween the two signals changes; at 0 °C it is 1:4, and at
lower temperatures the ratio is ꢀ1:20. A second coa-
lescence of the larger of the doublets occurs at )25 °C to
produce a broad singlet at 88.39. This singlet begins to
resolve as the temperature is lowered further, and at )75
°C it becomes a pair of doublets of doublets with
J
¼ 19:8 Hz and J
¼ 177:0 Hz.
ðP–PÞ
ðP–RhÞ
The 31P NMR data suggest that both ring and sulfur
inversion processes are slowed in 4 as the temperature is
lowered from +90 to )75 °C. There is only one doublet at
the high temperature limit because both processes are
facile. 4 is interconverting among all of its isomers rapidly
enough to render equivalent all phosphorus atoms.
However, sulfur inversion begins to slow as the temper-
ature is lowered so that, at 20 °C, the population of 4 is
clearly distributed between bent-syn and bent-anti iso-
mers, with the latter corresponding to the more intense
upfield doublet. Ring inversion is still very fast, and so
that the phosphorus atoms in the bent-anti isomer are
equivalent, giving a doublet, and the syn-exo and syn-
endo isomers rapidly interconvert, giving a doublet as
observed in 1. Ring inversion slows and eventually shuts
down (on the NMR timescale) in the bent-anti isomer,
producing a pair of doublets of doublets at )75 °C. The
slowing down of ring inversion should also allow the syn-
exo and syn-endo isomers of 4 to be resolved, but the
process is still too rapid at low temperature to result in
anything other than broadening. The fact that the ratio of
bent-anti to bent-syn isomers becomes larger as the
temperature is lowered indicates that the former geome-
try is the most stable in solution. This runs counter to
what would be predicted based on the X-ray crystallo-
graphic result. Moreover, it makes it harder to rationalize
the bent-exo geometries of 3 and 4 in the solid state. The
31P NMR data are in agreement with the preference for
the bent-anti structure in 2 at low temperature.
Fig. 11. 31P NMR spectra of 6 in toluene-d8 from +90 to )75 °C.
downfield doublet corresponds to the bent-anti isomer.
Similar equilibria have been observed for [Pt2(l-
SC6F5)2(SC6F5)4]2þ, [Pt2(l-p-SC6HF4)2(p-SC6HF4)4]2þ
,
and [Pt2(l-p-SC6F4(CF3))2(p-SC6F4(CF3))4]2þ [17]. In-
terestingly, Torrens and coworkers reported that the
NMR data for [Rh(l-SC6HF4)(COD)]2, [Rh(l-
SC6H4F)(COD)]2, and [Rh(l-SCF3)(COD)]2 indicate
that these complexes most likely adopt a rigid syn
structure in solution, while the data suggest that [Rh(l-
SC6HF4)(CO)]2 and [Rh(l-SC6H4F)(CO)]2 are fluxional
[24]. It is possible that the replacement of COD with CO
is responsible for the change in behavior.
The free energy of activation (DGzri) for the ring in-
version process was calculated for 2 and 4, and the free
energy of activation for the sulfur inversion process
(DGzsi) was calculated for 1, 4, and 6 at their coalescence
4
temperatures. These values are listed in Table 3. Ring
inversion values for 2 and 4 are 16.5 and 19.7 kJ molÀ1
3.7. Dynamic NMR spectra of Rh2(dippe)2(l-SPh)
,
respectively. These values are in agreement with the
conclusion of two previous studies, namely, that DGz for
ring inversion in bent M2X2 complexes is always less
than 35 kJ molÀ1 [27]. Sulfur inversion values for 1, 4,
and 6 are 42.5, 61.4, and 32.1 kJ molÀ1, respectively.
These compare favorably with what Torrens and co-
workers [17] report for the polyfluorinated benzenethi-
olate-bridged platinum dimers that are cited above, and
with the values that Killops and Knox [5] report for l-
thio-bis[carbonyl(g-cyclopentadienyl)ruthenium] com-
plexes (Scheme 2).
1
The H and 31P NMR data for the planar complex 6
indicate that it undergoes sulfur inversion throughout
the measured temperature range, which extends from 60
to )105 °C. All proton spectra that were obtained dur-
ing variable temperature experiments are broad.
The 31P NMR spectrum of 6 in THF-d8 broadens
upon lowering the temperature from 25 to )105 °C as
shown in Fig. 11. Collapse of the doublet that is initially
centered at d 89.48 leads to formation of two broad
doublets that are centered at 90.29 and 86.51. Here, the
downfield signal is approximately 2.5 times as intense as
the upfield signal.
The 31P NMR spectral data are consistent with the
presence of both bent-anti and bent-syn isomers for 6 in
solution (or possibly planar-anti and planar-syn) and
that these isomers are involved in an equilibrium as
observed in 4. It is assumed that the more intense
4
From the separation of the resonances (Dm) in the low temperature
limit, k ¼ pDm=21=2
.

1846
S.S. Oster, W.D. Jones / Inorganica Chimica Acta 357 (2004) 1836–1846
Table 3
Free energy of activation DGz for ring inversion and sulfur inversion
Acknowledgements
Complex
Solvent
DGz ring
inversion
(kJ molÀ1
DGz sulfur
inversion
Financial support from the US Department of En-
ergy, grant FG02-86ER13569, is acknowledged.
)
(kJ molÀ1
)
[Rh(dippe)-(l-SH)]2 (1)
THF-d8
42.5
[Rh(dippe)-(l-SCH3)]2 (2)
[Rh(dippe)-(l-SC12H9)]2 (4)
[Rh(dippe)-(l-SC6H5)]2 (6)
toluene-d8 16.5
toluene-d8 19.7
THF-d8
References
61.4
32.1
ꢂ ꢂ
[1] G. Aullon, G. Ujaque, A. Lledos, S. Alvarez, Chem. Eur. J. 5
(1999) 1391.
[2] E.W. Abel, S.K. Bhargava, K.G. Orrell, Prog. Inorg. Chem. 32
(1984) 1.
4. Conclusion
[3] K.G. Orrell, Coord. Chem. Rev. 96 (1989) 1.
[4] G. Natile, L. Maresca, G. Bor, Inorg. Chim. Acta 23 (1977) 37.
[5] S.D. Killops, S.A.R. Knox, J. Chem. Soc., Dalton Trans. (1978)
1260.
With the exception of 6, [Rh(dippe)(l-SR)]2 com-
plexes exhibit a bent geometry in the solid state. How-
ever, the orientation of the bridging sulfur substituents
changes as their steric bulk increases, presumably to
attenuate both ligand–substituent and substituent–sub-
stituent interactions. It is unclear why 6 has a planar-
anti geometry in the solid state, although as pointed out
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by Lledos and coworkers [1], the energy difference be-
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1
While the H and 31P NMR spectra of [Rh(dippe)(l-
SR)]2 complexes are somewhat dissimilar, they do
indicate that both ring inversion and sulfur inversion
occurs in the members of this series. Consequently, they
can access several isomeric forms when they are in so-
lution. Sulfur inversion appears to have a larger barrier
than ring inversion and can be more easily frozen out.
From these studies, it is concluded that X-ray studies
have little predictive value upon the structure(s) adopted
in solution. Lastly, 31P NMR spectroscopy in toluene-d8
and THF-d8 suggests that sulfur inversion in 1, 4, and 6
operates according to a non-dissociative mechanism, as
coordinating solvent does not affect the rate of the
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Crystallographic data (excluding structure factors)
for the structures reported in this paper have been de-
posited with the Cambridge Crystallographic Data
Center as supplementary publications nos. CCDC-
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of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44-1223-336-033; e-
mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
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