Synthesis of rhodium-primary thioamide complexes and their desulfurization leading to rhodium sulfido cubane-type clusters and nitriles

Article abstract of DOI:10.1021/om500714c

Although molecular thioamide complexes of late-transition metals have been prepared since 1979, the chemistry of primary thioamide complexes remains relatively unexplored. To shed light on this area, we have investigated synthesis, structures, and reactiv

Full text of DOI:10.1021/om500714c

Article
pubs.acs.org/Organometallics
Synthesis of Rhodium−Primary Thioamide Complexes and Their
Desulfurization Leading to Rhodium Sulfido Cubane-Type Clusters
and Nitriles
Yuichiro Mutoh,*,†,‡ Masahiro Sakigawara,† Ippei Niiyama,† Shinichi Saito,‡ and Youichi Ishii*,†
†Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-3-27 Kasuga, Bunkyo-ku, Tokyo
112-8551, Japan
‡Department of Chemistry, Faculty of Science, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
S
* Supporting Information
ABSTRACT: Although molecular thioamide complexes of
late-transition metals have been prepared since 1979, the
chemistry of primary thioamide complexes remains relatively
unexplored. To shed light on this area, we have investigated
synthesis, structures, and reactivities of simple rhodium
organometallic complexes with a primary arenecarbothioamide
ligand [Cp*RhCl2{SC(Ar)NH2-κ1S}] (Cp* = η5-C5Me5).
Intra- and intermolecular hydrogen bonding in the thioamide
1
complexes is discussed on the basis of H NMR spectroscopy
and X-ray analysis. When these rhodium complexes were treated with a large excess amount of Et3N, desulfurization of the
thioamide ligand took place to give arenecarbonitriles (ArCN) in high GC yield and the cubane-type cluster [(Cp*Rh)4(μ3-S)4]
(3) in good yield as the organometallic product. Use of a smaller amount (2.4 equiv) of Et3N followed by treatment with
NaBArF (ArF = 3,5-(CF3)2C6H3) led to the isolation of the cationic clusters [(Cp*Rh)4(μ3-S)4](BArF ) or [(Cp*Rh)4(μ3-
4
4
S)4](BArF )2 in low yield. Reaction mechanisms of the desulfurization of the coordinated thioamides and the formation and one-
4
or two-electron oxidation of 3 during the desulfurization are discussed.
Although molecular thioamide complexes have been known
for more than 30 years1−12 and have attracted considerable
attention as described above, fundamental chemistry of primary
thioamide complexes with late-transition metals remains
unexplored; only one organometallic ruthenium complex7a
and very few coordination compounds of nickel1a,b and
cobalt4a,b were crystallographically characterized. Now we
have synthesized a series of simple rhodium complexes with a
primary arenecarbothioamide ligand [Cp*RhCl2{SC(Ar)-
NH2-κ1S}]. Inspired by the formation of molecular sulfido
complexes on desulfurization of thiophenes with late-transition
metals,23 we also envisioned that the desulfurization of the
thioamide complexes produces nitriles and rhodium sulfido
species, the latter of which can spontaneously be assembled
into rhodium sulfido cubane-type clusters. The Rh4S4 clusters
have been known in the literature, but their properties,
particularly their solid-state structures, have not been
described.24 Only preparative methods and cyclic voltammetric
analysis are mentioned very briefly23a,c,25a,b in contrast to the
well-documented iridium and ruthenium sulfido cubane-type
complexes.25,26 Consequently, we also describe desulfurization
of thioamide complexes obtained leading to arenecarbonitriles
(ArCN) and the rhodium sulfido cubane-type cluster
INTRODUCTION
■
Thioamides, sulfur analogues of carboxamides, act as versatile
and interesting ligands in coordination chemistry, because they
and their deprotonated species, thioamidate anions, can take
various coordination geometries such as S-bonded,1−8 N,S-
chelating,9 N,S-bridging,5a,10 and S,S-bridging (Chart 1).10a,11
Among those, thioamide-based pincer-type ligands have been
received considerable attention in recent years.12,13 Some
thioamide complexes of palladium and rhodium show catalytic
performance in reactions such as cross-coupling13h,14,15 and
asymmetric hydrogenation of carbonyl compounds.9e,16 Since
the sulfur atoms in thioamides are less prone to be oxidized in
comparison with commonly used organophosphorus ligand,
thioamide-based palladium complexes can serve as a good
catalyst even under aerobic conditions for Suzuki−Miyaura
cross-coupling and Mizoroki−Heck reaction.15a,b
Meanwhile, investigation into the coordination chemistry of
thioamides may help to bring fundamental insight into the
activation of carbon−sulfur bonds in organosulfur com-
pounds.17 The carbon−sulfur double bond cleavage reaction
of thioamides, i.e., desulfurization of thioamides, has also
received attention. The desulfurization of thioamides has been
achieved by using metals18,19 or some organic oxidants.20−22 In
this process, primary thioamides are converted into the
corresponding nitriles, providing one of the practical methods
for preparation of organonitriles.18,19d,20
Received: July 12, 2014
Published: September 23, 2014
© 2014 American Chemical Society
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a
Chart 1. Selected Precedents of Late-Transition Metal
Complexes
Table 1. Synthesis of Thioamide Complexes 2
b
entry
1
R
2
yield (%)
1
2
3
4
5
6
1a
1b
1c
1d
1e
1f
H
2a
2b
2c
2d
2e
2f
82
78
93
78
97
71
OMe
Me
Cl
CF3
NO2
a
Reaction conditions: a mixture of [Cp*RhCl2]2 (1 equiv) and 1 was
b
stirred in CH2Cl2 at room temperature for 0.5 h. Isolated yields.
[(Cp*Rh)4(μ3-S)4] along with its mono- and dicationic
derivatives [(Cp*Rh)4(μ3-S)4]1+/2+, providing the first com-
plete series of cuboidal species of rhodium with and without a
metal−metal bonding interaction.
RESULTS AND DISCUSSION
■
Synthesis and Structures of Rhodium Complexes with
a Primary Thioamide Ligand. When [Cp*RhCl2]2 was
allowed to react with thiobenzamide (1a) in CH2Cl2 at room
temperature, a dark red solid started to precipitate in a few
minutes. The solid was recrystallized from hot MeOH to give
the rhodium complex [Cp*RhCl{SC(C6H5)NH2-κ1S}] (2a)
in 82% yield as dark red crystals (Table 1, entry 1).
Arenecarbothioamide complexes with electron-donating (2b
and 2c) and -withdrawing groups (2d−2f) at the para position
[Cp*RhCl{SC(Ar)NH2-κ1S}] were also prepared by a
similar procedure (entries 2−6). In the 1H NMR, the
characteristic signals due to the N−H protons of 2 are
observed at δ 10.23−10.48 and 7.63−8.96 (1H each), which
were shifted downfield compared to the corresponding signals
of the starting thioamides 1 (at around δ 7.7 and δ 7.2). The
remarkable downfield shift and separation of the chemical shit
in the 1H NMR suggest the presence of hydrogen bonding in 2.
Molecular structures of 2 were confirmed by X-ray studies.
Complex 2a was revealed to possess intra- and intermolecular
NH···Cl hydrogen bondings between the two chlorido ligands
and thioamide N−H groups, forming a dimeric 12-membered
ring structure in the crystal (Figure 1). Unlike 2a, thioamide
complexes 2d−f are helically linked through intra- and
intermolecular NH···Cl hydrogen bonding in the crystal to
form tubular structure (Figure 2). These results are in good
accordance with the observation of two distinct downfield
Figure 1. Intermolecular interaction of 2a to form the dimeric
structure (50% thermal probability). Carbon-bound hydrogen atoms
are omitted for clarity.
1
signals in the H NMR of 2. The C−S bond length in 2a is
longer than that in 1a (2a, 1.702(3) Å; 1a, 1.68 Å (mean)),
whereas the C−N bond distance in 2a is shorter than that in 1a
(2a, 1.297(3) Å; 1a, 1.32 Å (mean)).27
Desulfurization of 2 Leading to Rhodium Sulfido
Cubane-Type Complexes. Next, we undertook investigation
into the base-promoted desulfurization of thioamide of 2.
Formation of a stable rhodium sulfido covalent bond could be a
driving force. When thiobenzamide complex 2a was treated
with 20 equiv of NEt3 for 1 h in benzene, the red color of the
solution quickly changed to dark brown (Table 2). GLC
analysis of the reaction mixture indicated that benzonitrile was
formed in 76% GC yield, indicating that desulfurization of 2a
smoothly took place as expected. From the reaction mixture,
the neutral rhodium sulfido cubane-type cluster [(Cp*Rh)4(μ3-
S)4] (3), which shows a sharp singlet at δ 1.73 in the 1H NMR,
was isolated in 32% yield (entry 1). With longer reaction time
the yield of 3 was improved to 93% (entry 2). Similar reactions
of thioamide complexes 2 having various substituents afforded
3 and the corresponding ArCN (entries 3−6), though there
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Figure 2. (a) Molecular structure of 2d (50% thermal probability). Carbon-bound hydrogen atoms and solvents are omitted for clarity. (b)
Hydrogen-bonded infinite helical motif formed in 2d. (c) Perspective representation of 2d along the c axis.
a
and the cubane-like cluster with a thiobenzamidato ligand
Table 2. Desulfurization of 2 Leading to 3 and ArCN
[(Cp*Rh)4(μ3-S)3{μ2-SC(Ph)NH-κ2S:κ1N}](BArF
)
4
(6(BArF )) were isolated from the reaction in CH2Cl2, albeit in
4
low yields. Complex 6(BArF ) was characterized only by a
4
preliminary X-ray study, which revealed that the thiobenzami-
dato ligand acts as a μ3-NHCS-κ1N,κ1S,κ1S ligand, bridging two
rhodium atoms through the sulfur atom and the third rhodium
through the deprotonated nitrogen.28 Obviously cluster
6(BArF ) is viewed as an incomplete desulfurization product
4
of 2. As for the cationic cubane-type clusters, it has been known
that related dicationic iridium and ruthenium sulfido clusters
[(Cp*M)4(μ3-S)4]2+ (M = Ir, Ru) are readily formed by
oxidation of neutral cubane-type complexes [(Cp*M)4(μ3-S)4]
with hydrogen chloride added or liberated in situ.25c,26c These
facts imply that the use of a large excess amine prohibits the
oxidation of neutral cluster 3 by quenching proton in the
reaction mixture. Indeed, treatment of 3 with an acid induced
the formation of the mono- and dicationic clusters (vide infra).
Chemical Oxidation of Neutral Rhodium Sulfido
Cluster 3. Rauchfuss and co-workers briefly noted the
preparation of 3 and its mono- and dication clusters.23a Hidai
and co-workers described that such oxidized rhodium sulfido
cubane-type clusters are observed in the electrochemical
measurement of 3.25c However, properties and structures of
this series of cubane-type clusters remain unreported. To
rationalize the formation of 4+ and 52+, as well as to uncover
their properties, we have examined the synthesis of these
mono- and dicationic clusters by chemical oxidation of 3 (Table
3). Initially, when 3 was treated with 1 equiv of [Cp2Fe]-
(BArF ) in CH2Cl2, the monocationic cluster 4(BArF ) was
b
c
entry
2
R
time (h) yield of 3 (%) yield of RC6H4CN (%)
1
2
3
4
5
6
7
2a
2a
2b
2c
2d
2e
2f
H
1
4
4
4
4
4
4
8
32
93
50
77
71
55
d
76
93
64
98
63
76
55
2
H
OMe
Me
Cl
CF3
NO2
e
8
1a
a
Reaction conditions: a mixture of 2 (1 equiv) and Et3N (20 equiv)
was stirred in benzene at room temperature. Isolated yields. GLC
yields. Complex mixture. 1a was used instead of 2a with 2.4 equiv of
b
c
d
e
Et3N.
was not observed a clear trend of electronic substituent effects.
Unfortunately 3 was not observed in desulfurization of 2f with
NO2 group (entry 7). Since thioamide 1a is inert under weakly
basic conditions and remains unchanged even after prolonged
reaction time (entry 8), the coordination of sulfur to rhodium is
considered to play a key role in the present base-induced
desulfurization of thioamides.
4
4
obtained in 73% yield (entry 1). By using 2 equiv of
[Cp2Fe](BArF4), the dicationic rhodium cluster
[(Cp*Rh)4(μ3-S)4](BArF )2 (5(BArF )2) was also synthesized
4
in high yield (entry 2). Salts of 52+4 with other counterions,
[(Cp*Rh)4(μ3-S)4](PF6)2 (5(PF6)2) and [(Cp*Rh)4(μ3-S)4]-
(BF4)2 (5(BF4)2), were synthesized in high yields by similar
two-electron oxidation of 3 (entries 3 and 4). A silver salt was
also able to be used in the oxidation reaction; reaction of 3 and
2 equiv of AgOTf afforded the dicationic complex
[(Cp*Rh)4(μ3-S)4](OTf)2 (5(OTf)2) in 36% yield (entry 5).
As already mentioned, the iridium analogue cluster
[(Cp*Ir)4(μ3-S)4] is readily oxidized by HCl to give the
dicationic complex [(Cp*Ir)4(μ3-S)4]2+.26c However, use of
In contrast, when 2.4 equiv of Et3N was used, a complex
mixture of organometallic species was formed, though PhCN
was formed in 70−82% yields. When NaBArF was added into
4
the crude product, several new tetrarhodium clusters related to
3 were obtained (Scheme 1). Thus, the monocationic cubane-
type cluster [(Cp*Rh)4(μ3-S)4](BArF ) (4(BArF )) was recov-
4
4
ered from the reaction conducted in benzene, whereas the
dicationic analogue [(Cp*Rh)4(μ3-S)4](BArF )2 (5(BArF )2)
4
4
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a
Scheme 1. Formation of Various [Rh4S4] Clusters and Molecular Structure of 6+
a
PhCN was formed in 70−82% GLC yields in each reaction. Thermal ellipsoids are drawn at 50% probability. For clarity, carbon-bound hydrogen
atoms and solvates are omitted, and Cp* ligands are shown in a capped-sticks style.
a
Unfortunately, only a small amount (<1%) of hydrogen
evolution was detected by GC analysis of these reaction
mixtures, and the fate of proton is unclear. Alternatively, a part
of 3 may be converted into a hydridorhodium or a hydrosulfido
species during the reaction.29
Table 3. Chemical Oxidation of 3
In the 1H NMR at room temperature, monocation 4+
displays a very broad signal at δ 8.61 with W1/2 = 857 Hz,
whereas the dicationic cluster 52+ shows one singlet signal at
around δ 1.70.
Structural Elucidation of a Series of Rh4S4 Clusters. All
of the cubane-type clusters obtained here have been
unambiguously confirmed by X-ray studies (Table 4), providing
the first structural characterization for the [Rh4S4] cubane-type
cluster series. Neutral 3 has a typical 72e cubane-type cluster
structure, in which six Rh···Rh distances are similar to each
other (3.5302(6)−3.5617(3) Å), whereas in monocationic
b
entry
oxidant (equiv)
product
yield (%)
1
2
3
4
5
[Cp2Fe](BArF ) (1)
4(BArF )
73
87
90
70
36
4
4
[Cp2Fe](BArF ) (2)
5(BArF )2
4
4
complex 4(BArF ) inequivalent Rh−Rh distances (3.3824(4)−
4
[Cp2Fe](PF6) (2)
[Cp2Fe](BF4) (2)
AgOTf (2)
5(PF6)2
3.5783(4) Å) are observed, which reflects the 71e configuration
5(BF4)2
of 4+.
5(OTf)2
decomp
c
It should be mentioned that different molecular structures
are observed with 52+ depending on the counterion. Judging
from the 70e configuration of 52+, there is an expected Rh−Rh
bonding interaction in the dications. In fact, a short Rh−Rh
6
HCl/Et2O (5)
TFA (5)
d
7
e
5(CF3CO2)2
52
16
8
TFA (1)
4(BArF )
4
a
Reaction conditions: a mixture of 3 and an oxidant was stirred in
CH2Cl2 at room temperature for 1 h unless otherwise noted. Isolated
distance is found in 5(PF6)2 (2.7541(5) Å) and 5(BArF )2
b
4
c
d
e
(3.0827(6) Å), respectively. In contrast, only relatively large
Rh−Rh separations (3.3080(5) Å or longer) were found in
5(CF3CO2)2. To evaluate the difference of metal−metal
bonding interactions variable-temperature NMR spectra of
these salts in CD2Cl2 were measured in a range of −90 to 25 °C
(Figure 3). In each case a sharp signal due to the Cp* protons
finally broadened at around −80 °C, but there was observed a
clear dependence on the anion. The signal for 5(CF3CO2)2
starts to split at −90 °C. These observations indicate that Rh−
Rh bonding in 52+ is mobile even at −80 °C, being in sharp
contrast to the fact that the migration of the metal−metal bond
in the iridium analogue [(Cp*Ir)4(μ3-S)4](PF6)2 is sufficiently
yield. Reaction time was for 2 h. Reaction time was for 8 h. The
reaction was carried out in the presence of NaBArF (1 equiv).
4
HCl as the oxidant for 3 led to decomposition products (entry
6). Instead, reaction of 3 with CF3COOH (TFA, 5 equiv)
successfully afforded the two-electron oxidation product
[(Cp*Rh)4(μ3-S)4](CF3CO2)2 (5(CF3CO2)2) in 52% yield
(entry 7). Similar reaction of 3 with an equimolar amount of
TFA in the presence of NaBArF (1 equiv) gave the
4
monocation 4(BArF ), albeit in lower isolated yield (entry 8).
4
These results indicate that neutral cluster 3 undergoes
oxidation in the presence of an appropriate proton source.
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a
Table 4. Rh−Rh Bond Lengths Determined by X-ray Studies for 3, 4(BArF ), 5(PF6)2, 5(BArF )2, and 5(CF3CO2)2
4
4
cluster
space group
electron configuration
shortest Rh−Rh distance [Å]
other Rh−Rh distances [Å]
3
P-1
72e
71e
70e
70e
70e
3.5236(2)
3.3824(4)
2.7541(5)
3.0827(6)
3.3080(5)
3.5303(4)−3.5617(3)
3.4005(5)−3.5783(4)
3.5022(5)−3.6288(5)
3.3567(5)−3.5463(7)
3.5121(5)−3.5701(4)
4(BArF )
P2/n
P-1
4
5(PF6)2
5(BArF )2
P-1
4
5(CF3CO2)2
C2/c
a
Thermal ellipsoids are drawn at 50% probability. For clarity, hydrogen atoms and solvates are omitted, and Cp* ligands are shown in a capped-
sticks style.
differences between the solid-state structure of 52+ is
attributable mainly to the packing effects by the counterions.
Reaction Pathway for the Desulfurization of 2
Leading to a Series of Clusters 3, 4+, and 52+. A plausible
mechanism for the formation of the clusters is shown in
Scheme 2. Initially, one molecule of HCl is eliminated by the
action of the base to give the thioamidato complex [Cp*RhCl-
{SC(Ph)NH-κ1S:κ1N}] (7). This type of N,S-chelating
thioamidato ligand has some precedents.9 Subsequent depro-
tonation of the N−H in 7 produces the corresponding nitrile
along with the highly unsaturated terminal sulfido complex
[Cp*Rh(S)(NCPh)]. Repeated dimerization of the sulfido-
rhodium species leads to the neutral cubane-type cluster
3,23c,25a,b which can be oxidized to cationic cubane-type clusters
4+ and 52+ by proton as an oxidant. When an insufficient
amount of the base was used as shown in Scheme 1, complex 7
is not consumed completely and provides another coordina-
tively unsaturated cationic species [Cp*Rh{SC(Ar)NH-
Figure 3. Selected region of the variable-temperature 1H NMR spectra
of 52+ in CD2Cl2.
κ1S:κ1N}](BArF ) (8). Coupling of 8 with [Cp*RhS] gives
4
slow at −40 °C in the 1H NMR time scale.26c Consequently, an
expected metal−metal bonding in 52+ is considered to be
delocalized over its rhodium sulfido framework, and the
rise to the dinuclear species [(Cp*Rh)2(μ2-S){μ2-SC(Ph)
NH-κ1S:κ1N}](BArF ) (9), which further transformed to 6+ by
4
coupling with 9 with [(Cp*Rh)2(μ2-S)2].
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Scheme 2. A Plausible Pathway for the Formation of 3, 4+, 52+, and 6+
NMR spectra were recorded on a JEOL ECA-500 or a Bruker
AV600 spectrometer. IR spectra were recorded on a JASCO FT/IR-
4200 spectrometer by using KBr pellet. GLC analyses were performed
on a Shimadzu GC-2014 instrument equipped with an FID detector
and a capillary column (Agilent Technologies, DB-5, 30 m × 0.25
mm). Elemental analyses were performed on a PerkinElmer 2400
series II CHN analyzer. Amounts of the solvent molecules in the
crystals were determined not only by elemental analyses but also by 1H
NMR spectroscopy.
Synthesis of the Rhodium Thioamide Complexes
[Cp*RhCl2{SC(Ar)NH2-κ1S}] (2). A solution of [Cp*RhCl2]2 and
ArCSNH2 (2.0−2.3 equiv) in CH2Cl2 was stirred at room temperature
for 0.5 h. The red solution quickly changed to a reddish suspension.
The resulting suspension was dried in vacuo to give a reddish powder.
This powder was dissolved in MeOH at 60 °C, and the resulting
solution was cooled at −20 °C overnight to give the corresponding
thioamide complexes 2.
CONCLUSIONS
■
In this study, we have synthesized a series of rhodium
complexes with a primary thioamide ligand and investigated
their base-promoted desulfurization. The X-ray and the H
1
NMR analyses of the rhodium thioamide complexes revealed
that there is intra- and intermolecular NH···Cl hydrogen
bonding between the chlorido and thioamide N−H groups.
The thioamide complexes undergo desulfurization with Et3N at
room temperature to give arenecarbonitriles in high yields.
When the thioamide complexes are treated with a large excess
amount of amine, the neutral rhodium sulfido cubane-type
cluster [(Cp*Rh)4(μ3-S)4] is obtained selectively. Use of a
smaller amount of the base gave rise to the oxidation of the
cubane cluster. Oxidation of the cuboidal cluster with
[Cp2Fe]1+ or proton and the molecular structures of the
cubane-type clusters have been established.
This study clearly demonstrated that activation of thioamides
is accomplished by coordination to a late-transition metal
center. In other words, arenecarbothioamides can be used in
the synthesis of sulfur clusters as a molecular sulfur source.
Further investigation into late-transition metal complexes with
carboxamides and their sulfur and selenium analogues,
thioamides and selenoamides, will be reported in due course.
[Cp*RhCl2{SC(C6H5)NH2-κ1S}] (2a). Following the general
procedure, 2a was synthesized from [Cp*RhCl2]2 (566.7 mg, 0.917
mmol) and PhCSNH2 (1a; 251.6 mg, 1.83 mmol) in CH2Cl2 (20 mL).
2a was isolated as dark red crystals (689.8 mg, 1.50 mmol, 82% yield).
1H NMR (CDCl3, 500 MHz): δ 10.36 (br s, 1H, NH), 7.80 (d, J = 7.5
Hz, 2H, o-Ph), 7.63 (br s, 1H, NH), 7.52 (t, J = 7.5 Hz, 1H, p-Ph),
7.42 (t, J = 7.5 Hz, 2H, m-Ph), 1.69 (s, 15H, Cp*). 13C{1H} NMR
(CDCl3, 126 MHz): δ 196.6 (CS), 137.4 (Ar), 132.9 (Ar), 128.9
(Ar), 127.1 (Ar), 96.2 (d, JRhC = 8.4 Hz, Cp*), 9.0 (Cp*). IR (cm−1):
3448 (νNH), 3220 (νNH), 1560 (νSCN). Anal. Calcd for
C17H22Cl2N1Rh1S1: C, 45.76; H, 4.97; N, 3.14. Found: C, 45.66; H,
4.88; N, 3.05.
EXPERIMENTAL SECTION
■
[Cp*RhCl2{SC(4-MeOC6H4)NH2-κ1S}]·MeOH (2b·MeOH).
Following the general procedure, 2b was synthesized from
[Cp*RhCl2]2 (49.5 mg, 0.080 mmol) and 4-MeOC6H4CSNH2 (1b;
29.0 mg, 0.173 mmol) in CH2Cl2 (4 mL). 2b·MeOH was isolated as
dark red crystals (59.6 mg, 0.117 mmol, 73%). 1H NMR (CDCl3, 600
MHz): δ 10.23 (br, 1H, NH), 7.79 (d, J = 8.9 Hz, 2H, Ar), 7.50 (br,
1H, NH), 6.91 (d, J = 8.9 Hz, 2H, Ar), 3.86 (OMe), 3.49 (s, MeOH),
1.70 (s, 15H, Cp*). 13C{1H} NMR (151 MHz, CDCl3): δ 194.3 (C
S), 163.6 (Ar), 129.6 (Ar), 129.1 (Ar), 114.1 (Ar), 96.1 (d, JRhC = 7.7
Hz, Cp*), 55.7 (OMe), 9.0 (Cp*). IR (cm−1): 3117 (νNH), 1256
(νSCN). Anal. Calcd for C18H24Cl2N1O1Rh1S1·MeOH: C, 44.89; H,
5.55; N, 2.76. Found: C, 44.65; H, 5.46; N, 2.71.
General Considerations. All reactions were carried out under a
dry nitrogen atmosphere by using standard Schlenk techniques unless
otherwise specified. [Cp*RhCl2]2,30 p-MeOC6H4CSNH2 (1b),31 p-
NO2C6H4CSNH2 (1f),31 NaBArF ·2H2O,32 [Cp2Fe](PF6),33 [Cp2Fe]-
4
(BF4),33 and [Cp2Fe](BArF )34 were prepared according to the
4
literature methods. CH2Cl2 (P4O10), acetone (CaSO4), MeOH (Mg),
EtOH (Mg), and Et3N (KOH) were dried and distilled over
appropriate drying reagents indicated. Trifluoroacetic acid was dried
over activated MS4Å. CDCl3 and C6D6 were degassed by freeze−
pump−thaw cycles and stored over activated MS4Å. Dehydrated-grade
solvents (benzene and ether) and other reagents were commercially
obtained and used as received.
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[Cp*RhCl2{SC(4-MeC6H4)NH2-κ1S}]·MeOH (2c·MeOH). Fol-
lowing the general procedure, 2c was synthesized from [Cp*RhCl2]2
(133.5 mg, 0.216 mmol) and 4-MeC6H4CSNH2 (73.9 mg, 0.489
mmol) in CH2Cl2 (8 mL). 2c·MeOH was isolated as red needles
(165.5 mg, 0.336 mmol, 78%). 1H NMR (CDCl3, 500 MHz): δ 10.25
(br, 1H, NH), 7.77 (br, 1H, NH), 7.71 (d, J = 8.0 Hz, 2H, Ar), 7.21
(d, J = 7.4 Hz, 2H,), 3.48 (s, MeOH), 2.38 (s, 3H, Me), 1.68 (s, 15H,
Cp*). 13C{1H} NMR (CDCl3, 126 MHz): δ 195.4 (CS), 143.8
(Ar), 134.4 (Ar), 129.5 (Ar), 127.7 (Ar), 96.1 (d, JRhC = 8.4 Hz, Cp*),
21.7 (Me), 9.0 (Cp*). IR (cm−1): 3073 (νNH), 1278 (νSCN). Anal.
Calcd for C18H24Cl2N1Rh1S1·MeOH: C, 46.35; H, 5.73; N, 2.85.
Found: C, 46.07; H, 5.66; N, 2.82.
crystals of 4(BArF ) suitable for X-ray diffraction study were prepared
4
1
by recrystallization from CH2Cl2/THF/hexanes. H NMR (CD2Cl2,
500 MHz): δ 8.61 (br, W1/2 = 857 Hz Hz, Cp*), 7.72 (s, 8H, o-ArF),
7.56 (s, 4H, p-ArF). Anal. Calcd for C72H72B1F24Rh4S4: C, 44.48; H,
3.73. Found: C, 44.59; H, 3.61.
Synthesis of the Dicationic Complexes [(Cp*Rh)4(μ3-S)4]X2
(5X2). To a solution of 2a in CH2Cl2 was added a solution of
[Cp2Fe]X (2 equiv) in CH2Cl2, and the mixture was stirred at room
temperature for 1 h. The resulting solution was dried in vacuo. The
residue was washed with hexanes and benzene to give the dicationic
cubane-type complexes 5X2.
[(Cp*Rh)4(μ3-S)4](BArF ) (5(BArF ) ). Following the general
4 2
4 2
procedure, 5(BArF )2 was synthesized from 2a (43.5 mg, 0.040
[Cp*RhCl2{SC(4-ClC6H4)NH2-κ1S}]·MeOH (2d·0.5MeOH).
Following the general procedure, 2d was synthesized from
[Cp*RhCl2]2 (44.2 mg, 0.072 mmol) and 4-ClC6H4CSNH2 (1d;
27.0 mg, 0.157 mmol) in CH2Cl2 (5 mL). 2d·0.5MeOH was isolated
as reddish brown needles (53.3 mg, 0.111 mmol, 78%), which were
suitable for an X-ray study. 1H NMR (CDCl3, 500 MHz): δ 10.36 (br,
1H, NH), 7.94 (br, 1H, NH), 7.77 (d, J = 8.6 Hz, 2H, Ar), 7.40 (d, J =
8.6 Hz, 2H, Ar), 3.49, MeOH), 1.69 (s, 15H, Cp*). 13C{1H} NMR
(151 MHz, CDCl3): δ 194.5 (CS), 139.3 (Ar), 135.6 (Ar), 129.1
(Ar), 128.6 (Ar), 96.3 (d, JRhC = 7.7 Hz, Cp*), 9.0 (Cp*). IR (cm−1):
3054 (νNH), 1311 (νSCN). Anal. Calcd for C17H21Cl3N1Rh1S1·
0.5MeOH: C, 42.32; H, 4.67; N, 2.82. Found: C, 42.08; H, 4.77; N,
2.72.
4
mmol) in CH2Cl2 (25 mL) and [Cp2Fe](BArF ) (79.3 mg, 0.0756
4
mmol) in CH2Cl2 (16 mL) and isolated as a brown powder (92.8 mg,
0.0331 mmol, 87%). Single crystals of 5(BArF )2·0.55hexane·
4
0.45acetone suitable for X-ray diffraction study were prepared by
recrystallization from acetone/hexanes. 1H NMR (CD2Cl2, 500 MHz):
δ 7.72 (s, 16H, o-ArF), 7.56 (s, 8H, p-ArF), 1.70 (s, 60H, Cp*). Anal.
Calcd for C104H84B2F48Rh4S4: C, 44.50; H, 3.02. Found: C, 44.32; H,
2.94.
[(Cp*Rh)4(μ3-S)4](PF6)2 (5(PF6)2). Following the general proce-
dure, 5(PF6)2 was synthesized from 2a (80.2 mg, 0.074 mmol) in
CH2Cl2 (85 mL) and [Cp2Fe](PF6) (48.7 mg, 0.147 mmol) in
CH2Cl2 (30 mL) and isolated as a brown powder (92.0 mg, 67.1 μmol,
91% yield). Single crystals of 5(PF6)2·2CH3COCH3 suitable for X-ray
diffraction study were prepared by recrystallization from acetone/
[Cp*RhCl2{SC(4-CF3C6H4)NH2-κ1S}]·0.5CH2Cl2 (2e·
0.5CH2Cl2). Following the general procedure, 2e was synthesized
from [Cp*RhCl2]2 (132.3 mg, 0.214 mmol) and 4-CF3C6H4CSNH2
(1e; 97.1 mg, 0.473 mmol) in CH2Cl2 (6 mL). Recrystallization from
CH2Cl2/hexanes gave 2e·0.5CH2Cl2 as red needles (213.1 mg, 0.383
mmol, 89%), which were suitable for an X-ray study. 1H NMR
(CDCl3, 500 MHz): δ 10.36 (br, 1H, NH), 7.95 (br, 1H, NH), 7.78
(d, J = 8.6 Hz, 2H, Ar), 7.40 (d, J = 8.6 Hz, 2H, Ar), 5.32 (s, CH2Cl2),
1.69 (s, 15H, Cp*). 13C{1H} NMR (151 MHz, CDCl3): δ 194.4 (C
1
hexanes. H NMR (CD2Cl2, 500 MHz): δ 1.86 (br, 60H, Cp*). Anal.
Calcd for C40H60F12P2Rh4S4: C, 35.05; H, 4.41. Found: C, 35.14; H,
4.33.
[(Cp*Rh)4(μ3-S)4](BF4)2 (5(BF4)2). Following the general proce-
dure, 5(BF4)2 was synthesized from 2a (36.9 mg, 0.034 mmol) in
CH2Cl2 (40 mL) and [Cp2Fe](BF4) (18.6 mg, 0.0685 mmol) in
CH2Cl2 (20 mL) and isolated as a brown powder (29.8 mg, 0.0238
1
mmol, 70% yield). H NMR (CD2Cl2, 500 MHz): δ 1.80 (br, 60H,
S), 139.9 (Ar), 133.8 (q, JFC = 32.9 Hz, Ar), 128.4 (Ar), 125.6 (q, JFC
=
Cp*). Anal. Calcd for C40H60B2F8Rh4S4: C, 38.30; H, 4.82. Found: C,
38.11; H, 4.52. Molecular structure of 5(BF4)2 was also confirmed by a
preliminary X-ray study.
3.3 Hz, Ar), 125.5 (q, JFC = 272.3 Hz, CF3), 96.3 (d, JRhC = 7.7 Hz,
Cp*), 9.0 (Cp*). IR (cm−1): 3044 (νNH), 1322 (νSCN). Anal. Calcd for
C18H21Cl2F3N1Rh1S1·0.5CH2Cl2: C, 39.91; H, 3.98; N, 2.52. Found:
C, 39.87; H, 3.89; N, 2.48.
[(Cp*Rh)4(μ3-S)4](CF3CO2)2 (5(CF3CO2)2). To a solution of 2a
(17.8 mg, 0.016 mmol) in CH2Cl2 (4 mL) was added CF3COOH (6.5
μL, 0.085 mmol, 5 equiv) at room temperature, and the mixture was
stirred for 8 h. The color of the solution gradually changed from
brown to dark brown. The resulting solution was dried in vacuo and
washed with hexanes and benzene. The resulting brown powder was
recrystallized from CH2Cl2/hexanes to afford 5(CF3CO2)2 (11.1 mg,
8.5 μmol, 52% yield) as dark red crystals, which were suitable for an X-
ray study. 1H NMR (CD2Cl2, 500 MHz): δ 1.76 (br, 60H, Cp*). Anal.
Calcd for C44H60F6O4Rh4S4: C, 40.44; H, 4.63. Found: C, 40.27; H,
4.50.
[(Cp*Rh)4(μ3-S)4](OTf)2 (5(OTf)2). To a solution of 2a (12.3 mg,
0.011 mmol) in CH2Cl2 (2 mL) was added AgOTf (8.8 mg, 0.0342
mmol, 3 equiv) at room temperature, and the mixture was stirred for 1
h. The brown solution gradually changed to a dark brown suspension.
The resulting suspension was filtered through a plug of Celite. The
filtrate was dried in vacuo, and the residue was recrystallized from
CH2Cl2/ether to afford 5(OTf)2 (5.6 mg, 4.06 μmol, 36% yield) as
dark red plates. 1H NMR (CD2Cl2, 500 MHz): δ 1.77 (s, 60H, Cp*).
Anal. Calcd for C42H60F6O6Rh4S6: C, 36.58; H, 4.39. Found: C, 36.56;
H, 4.18.
X-ray Diffraction Studies. All diffraction data except for 1a were
collected on a Rigaku Mercury CCD area detector with graphite-
monochromated Mo Kα radiation (λ = 0.71070 Å) at −150 °C for the
2θ range of 6−55°. Intensity data were corrected for Lorenz-
polarization effects and for empirical absorptions (REQAB).35 The
structure solution and refinements were carried out by using the
CrystalStructure36 crystallographic software package and Yadokari-XG
2009.37 For 1a, diffraction data were collected on a Bruker Apex II
Ultra at −173 °C, and intensity data were processed using Apex2
software suit. The position of the non-hydrogen atoms were
determined by direct methods (SHELXS-9738 for 1a, 3, and
[Cp*RhCl2{SC(4-NO2C6H4)NH2-κ1S}]·MeOH (2f·MeOH). Fol-
lowing the general procedure, 2f was synthesized from [Cp*RhCl2]2
(65.5 mg, 0.106 mmol) and 4-NO2C6H4CSNH2 (44.6 mg, 0.245
mmol) in CH2Cl2 (5 mL). 2f·MeOH was isolated as red needles (74.2
1
mg, 0.142 mmol, 67%). H NMR (CDCl3, 500 MHz): δ 10.48 (br,
1H, NH), 8.96 (br, 1H, NH), 8.25 (d, J = 8.8 Hz, 2H, Ar), 8.08 (d, J =
8.8 Hz, 2H, Ar), 3.48 (s, MeOH), 1.67 (s, 15H, Cp*). 13C{1H} NMR
(CDCl3, 126 MHz): δ 193.6 (CS), 150.0 (Ar), 142.3 (Ar), 129.0
(Ar), 123.8 (Ar), 96.6 (d, JRhC = 7.2 Hz, Cp*), 9.0 (Cp*). IR (cm−1):
3032 (νNH), 1346 (νSCN). Anal. Calcd for C17H21Cl2N2O2Rh1S1·
MeOH: C, 41.31; H, 4.82; N, 5.35. Found: C, 41.29; H, 4.53; N, 5.40.
Desulfurization of 2 and Isolation of [(Cp*Rh)4(μ3-S)4] (3). To
a suspension of 2a (302.7 mg, 0.678 mmol) in benzene (37 mL) was
added NEt3 (1.90 mL, 13.7 mmol), and the mixture was stirred at
room temperature for 4 h. The red-brown color of the suspension
quickly changed to dark red. GLC analysis of the reaction mixture
(internal standard, dodecane) indicated the generation of benzonitrile
in 93% yield. The resulting suspension was filtered through a Celite
pad, and the filtrate was dried in vacuo. The residue was washed with
hexanes and ether to give 3 as a dark red powder (170.1 mg, 0.157
mmol, 93% yield). Single crystals of 3 suitable for X-ray diffraction
study were prepared by recrystallization from CH2Cl2/EtOH. 1H
NMR (C6D6, 500 MHz): δ 1.73 (s, 60H, Cp*). Anal. Calcd for
C40H60Rh4S4: C, 44.45; H, 5.60. Found: C, 44.68; H, 5.51.
Synthesis of the Monocationic Complex [(Cp*Rh)4(μ3-S)4]-
(BArF ) (4(BArF )). To a solution of 2a (29.1 mg, 26.9 μmol) in
4
4
CH2Cl2 (20 mL) was added a solution of [Cp2Fe](BArF ) (26.3 mg,
4
25.1 μmol) in CH2Cl2 (10 mL), and the mixture was stirred at room
temperature for 1 h. The resulting dark brown solution was dried in
vacuo. The residue was washed with hexanes and benzene to give
4(BArF ) as a brown powder (35.7 mg, 18.4 μmol, 73% yield). Single
4
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Organometallics
Article
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4
4
4
0.55hexane·0.45acetone, 5(CF3CO2)2, and 6(BArF )·0.5hexane) and
subsequent Fourier syntheses (DIRDIF-99).40 All non-hydrogen
atoms were refined on F2 by full-matrix least-squares techniques
(SHELXL-97 and SHELXL-201438) with anisotropic thermal
parameters except for the several carbon and fluorine atoms with
nonpositive definite anisotropic displacement parameters, which are
refined with isotropic thermal parameters. All hydrogen atoms were
placed using AFIX instructions. Severely disordered solvent molecules
were treated with PLATON/SQUEEZE41 for 2d, 2e, and 2f. Although
there are some alerts of type A and B due to the disorder of some of
the Cp* and CF3 groups, they do not affect the results of the structural
determination. Details of the X-ray diffraction study are summarized in
Supplementary Tables S1−S3.
(8) [Ru], [Os]: Meier, S. M.; Hanif, M.; Adhireksan, Z.; Pichler, V.;
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ASSOCIATED CONTENT
* Supporting Information
■
S
Figures, tables, and CIF files giving NMR charts and
crystallographic data. This material is available free of charge
via the Internet at http://pubs.acs.org.
Kristallogr. - New Cryst. Struct. 2002, 217, 551−553. (d) Alagoz, C.;
̈
Brauer, D. J.; Mohr, F. J. Organomet. Chem. 2009, 694, 1283−1288.
(e) Ahlford, K.; Ekstrcm̧ , J.; Zaitsev, A. B.; Ryberg, P.; Eriksson, L.;
Adolfsson, H. Chem.Eur. J. 2009, 15, 11197−11209.
(10) (a) Song, L. C.; Mei, S.-Z.; Feng, C.-P.; Gong, F.-H.; Ge, J.-H.;
Hu, Q.-M. Organometallics 2010, 29, 5050−5056. (b) Hossain, M. I.;
Chosh, S.; Hogarth, G.; Kabir, S. E. J. Organomet. Chem. 2013, 737,
53−58.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: ymutoh@rs.tus.ac.jp.
*E-mail: yo-ishii@kc.chuo-u.ac.jp.
Notes
■
(11) Brunner, H.; Bugler, J.; Nuber, B. Tetrahedron: Asymmetry 1996,
̈
7, 3095−3098.
The authors declare no competing financial interest.
(12) For reviews, see: (a) Kuwabara, J.; Kanbara, T. J. Photopolym.
Sci. Technol. 2008, 21, 349−353. (b) Odinets, I. L.; Aleksanyan, D. V.;
Kozlov, V. A. Lett. Org. Chem. 2010, 7, 583−595.
ACKNOWLEDGMENTS
This research was partially supported by a Research Fund of
Tokyo University of Science for young chemists.
■
(13) For recent examples, see: (a) Kuwabara, J.; Munezawa, G.;
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(b) Koizumi, T.; Teratani, T.; Okamoto, K.; Yamamoto, T.; Shimoi,
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(c) Aleksanyan, D. V.; Kozlov, V. A.; Nelyubina, Y. V.; Lyssenko, K.
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been compared to reveal considerable contribution of the
iminothiolate form (S−CNH) to the thiobenzamidato ligand in
6+ in the solid state; the C−S bond distances are elongated in the
order of 1a (1.68 Å (mean)) < 2a (1.702(3) Å) < 6+ (1.756(12) Å),
while C−N bond lengths are shortened in the order of 1a (1.32 Å
(mean)) > 2a (1.297(3) Å) > 6+ (1.276(15) Å). Similar structural
parameters are observed in related iminothiolato complexes with μ2-
SCN-κ2S coordination mode [Rh{μ2-SC(Ph)NCHMePh-κ2S}
(cod)]2, (C−S, 1.83 Å (mean); C−N, 1.26 Å (mean))11 and
[Fe{μ2-SC(Ph)NPh-κ2S}{μ2-C(Ph)NPh-η1C:κ1N}(CO)3]2 (C−
S, 1,819(4) Å; C−N, 1.267(5) Å).10a
́
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dx.doi.org/10.1021/om500714c | Organometallics 2014, 33, 5414−5422