A Hemilabile and Cooperative N-Donor-Functionalized 1,2,3-Triazol-5-Ylidene Ligand for Alkyne Hydrothiolation Reactions

Article abstract of DOI:10.1002/chem.201604567

A series of novel cationic and neutral Rh complexes with an N-donor-functionalized 1,2,3-triazol-5-ylidene (TRZ) ligand (in which the pendant N donor is NHBoc, NH₂, or NMe₂) is described. The catalytic activity of these complexes was

Full text of DOI:10.1002/chem.201604567

A Journal of
Accepted Article
Title: A hemilabile and cooperative N-donor functionalized 1,2,3-
triazol-5-ylidene ligand for selective and base-free rhodium(I)
catalyzed alkyne hydrothiolation reactions.
Authors: Ian Strydom, Gregorio Guisado-Barrios, Israel Fernandez,
David C Liles, Eduardo Peris, and Daniela Ina Bezuidenhout
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To be cited as: Chem. Eur. J. 10.1002/chem.201604567
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10.1002/chem.201604567
Chemistry - A European Journal
A hemilabile and cooperative N-donor functionalized 1,2,3-triazol-
5-ylidene ligand for selective and base-free rhodium(I) catalyzed
alkyne hydrothiolation reactions.
Ian Strydom,[a] Gregorio Guisado-Barrios,*[b] Israel Fernández,[c] David C. Liles,[a] Eduardo Peris,[b] and
Daniela I. Bezuidenhout*[a],[d]
Abstract: A series of novel cationic and neutral Rh-complexes with
an N-donor functionalized 1,2,3-triazol-5-ylidene (TRZ) ligand (where
H
H
H
SR
H
RS
R'
pendant N-donor is NHBoc, NH2 or NMe2 respectively) is described.
Their catalytic activity was evaluated towards the hydrothiolation of
alkynes. Among the catalysts, a neutral dicarbonyl complex featuring
the tethered-NBoc amido-TRZ ligand proved very selective for
alkyne hydrothiolation with an aryl thiol. Remarkably, the reaction
could be carried out in the absence of pyridine or base additive. In
addition, during the reaction course, no evidence for oxidative
addition of the thiol S-H was observed, strongly suggesting a
R'
R
SH
R'
SR
R'
H
β-Z
(anti-Markovnikov)
β-E
(anti-Markovnikov)
α
(Markovnikov)
RS
(a) Oxidative addition for thiol activation
H
SR
[Rh]
R'
R'
β-E / Z
H
R'
migratory insertion
[Rh]-SR
into
SR
[Rh]
H
reaction pathway whereby
a bifunctional ligand is involved.
RS
R'
R'
[Rh]
Experimental and theoretical mechanistic investigations suggest a
ligand-assisted deprotonation of substrate thiol, hemilabile
dissociation of amine from metal and thiolate coordination, which is
indicative of a different reaction mechanism to those previously
reported for related alkyne hydrothiolation reaction.
[Rh] SR
H
R
SH
H
α
[Rh] SR
H
migratory insertion
[Rh]-H
into
R'
SR
R'
H
[Rh] SR
R'
β-E / Z
H
(b) This work: Acid-base metal-ligand cooperative thiol activation
L
L-H
L-H
R'
Introduction
RS
R'
[Rh]
RSH
protonoly sis
R
SH
[Rh] SR
[Rh]
migratory insertion
into [Rh]-SR
R'
SR
H
α
The hydrothiolation of alkynes involves the atom-economical
addition of the sulfur and hydrogen atom from a thiol group
across a carbon-carbon unsaturated bond to generate vinyl
sulfides. The structural motifs of vinyl sulfides as building blocks
for biologically active compounds[1] and polymers[2] stimulate the
development of efficient and selective synthetic methods for
these valuable compounds. To this end, recent strategies have
included the metal-catalyzed hydrothiolation of unsaturated
carbon-carbon bonds, with the advantage of increased chemo-,
Scheme 1. Thiol activation strategies in rhodium-catalyzed alkyne
hydrothiolation.
stereo- and regioselectivity over metal-free approaches.[3]
Depending on the choice of the metal, the selectivity can be
directed towards either the anti-Markovnikov β-E/Z-isomers, or
the more challenging Markovnikov-type α-vinyl sulfide products,
(Scheme 1).[3] Specifically in the case of rhodium-based
catalysts, both α-[4] and β-isomers[2a,5] have been shown to be
accessible by subtle electronic parameterization of the
coordination sphere of the metal center, markedly influencing
the selectivity outcomes of the reaction. As noted in the
mechanistic review of hydrothiolation by Castarlenas, Oro and
co-workers, the so-called ‘chameleonic’ Rh complexes
generally allow oxidative addition of the thiol to yield a hydrido
thiolato species,[3d] unlike other metals such as palladium[5e,6] or
nickel,[7] for which only the thiolate ligands remain on the active
catalytic species.
[a]
[b]
I. Strydom, D. C. Liles, D. I. Bezuidenhout
Chemistry Department
University of Pretoria
Private Bag X20, Hatfield 0028, Pretoria, South Africa
G. Guisado-Barrios, E. Peris
Institute of Advanced Materials (INAM)
Universitat Jaume I
Avenida Vicente Sos Baynat s/n, 12071 Castellon, Spain
E-mail: guisado@uji.es
[c]
[d]
I. Fernández
Departamento de Química Orgánica I, Facultad de Ciencias
Químicas
Universidad Complutense de Madrid
28040 Madrid, Spain
D. I. Bezuidenhout
This particular behavior of rhodium catalysts provides the
opportunity for the ligand-based direction of the alkyne
migratory insertion into either the [Rh]-H or [Rh]-SR bonds for
rational control over regioselectivity (Scheme 1(a)). This
approach was elegantly illustrated by the use of 10 equivalents
excess of pyridine as a directing ligand for Rh-NHC complexes,
Molecular Sciences Institute, School of Chemistry
University of the Witwatersrand
Johannesburg 2050, South Africa
E-mail: daniela.bezuidenhout@wits.ac.za
Supporting information for this article is available via a link at the
end of the document.
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10.1002/chem.201604567
Chemistry - A European Journal
Dipp
Dipp
to give the branched Markovnikov-products in excellent yields
for the hydrothiolation of aryl alkynes with aryl thiols.[4c,d]
N
N
N
N
(i) 2.2 eq KHMDS
(ii) 0.5 eq [Rh(COD)Cl]2
OC
OC
N
Dipp
N
THF, -78 o
C
Dipp
CO (g)
DCM, r.t.
Rh
Rh
R = H, R' = Boc
In an effort to circumvent the use of additive pyridine, we
recently reported the synthesis of a donating, monoanionic
bis(1,2,3-triazol-5-ylidene)-based CNC-type pincer ligand with
flanking mesoionic carbene (MIC) moieties,[8] as supporting
scaffold for [RhI(CNC)(µ-O2)], an air-stable selective precursor
catalyst for the regioselective hydrothiolation of aliphatic alkynes
with alkyl thiols.[4a] However, similarly to the pyrazolylborate
rhodium complexes reported by Love et al., diminished
regioselectivity for the branched α-vinyl sulfides was seen when
aryl thiol and aryl alkynes were employed.[4h] It was reasoned
that a less encumbered bidentate ligand framework bearing a
N
N
Boc
Boc
Dipp
H
PF6
N
N
1
(84%)
4
(> 99 %)
N
Dipp
R'RN
Dipp
Dipp
PF6
PF6
A
B
C
R = H, R' = Boc
R = R' = H
N
N
N
N
R = R' = Me
N
CO (g)
DCM, r.t.
N
Dipp
(i) 1.2 eq KHMDS
(ii) 0.5 eq [Rh(COD)Cl]2
THF, -78 oC
OC
OC
Dipp
Rh
Rh
N
N
R = R' = H or Me
RR'
RR'
Dipp = 2,6-diisopropylphenyl
Boc = tert-butoxycarbonyl
COD = 1,5-cyclooctadiene
2
3
R = R' = H (79%)
R = R' = Me (85%)
5
6
R = R' = H ( > 99%)
R = R' = Me ( > 99%)
Scheme 2. Synthesis of N-donor functionalized triazolylidene Rh(I) complexes
1 – 6.
pendant nitrogen functionality could confer
a bifuntional
catalyst[9] behaving as directing group and hemilabile ligand.
First, negating the use of additive pyridine; and second, favoring
intramolecular activation through the heterolytic cleavage of the
thiol S-H bond over oxidative addition (see Scheme 1(b)) to
improve the regioselectivity of the aryl substrates of alkyne
hydrothiolation. Thus we set out to prepare a series of electron-
rich RhI complexes containing a tethered N-donor-TRZ ligand A,
B and C (Scheme 2)[10] (where N-donor is NHBoc, NH2 or NMe2
respectively; TRZ = 1,2,3-triazol-5-ylidene) in order to exploit the
possibility of both hemilability and ligand cooperativity for the
activation of the thiol S-H bond.
The IR spectra of 4–6 show the C-O stretching vibrations (1993,
2068 cm-1 for neutral complex 4; and 2027, 2090 cm-1 (5) and
2031, 2090 cm-1 (6), for the cationic complexes) within the range
of previously reported Rh-TRZ complexes.[14] Crystals suitable
for X-ray diffraction could be obtained of complexes 1–4 (2 and
4, Figure 1; and 1 and 3, SI, Figure S31), and display pseudo-
square planar geometry around the Rh(I) metal centre (Figure 1).
As seen for the carbonyl ligands, the Rh-Ccarbene bond lengths
(2.017(2) – 2.045(3) Å) for the structures of 1–4 are in
accordance with previously reported structures, and are
relatively insensitive to changes in the electronic structure
around the metal.[14] For the cyclometallated complexes,
however, the neutral amido complexes 1 and 4 display the
expected shorter Rh-N bond distances (2.130(2) and 2.0924(18)
Å, respectively), compared to the cationic amine complexes 2
and 3 (2.165(2) and 2.222(2) Å, respectively).
Results and Discussion
Synthesis and characterization of catalyst precursors
The new ligand precursor 1,3-diaryl-1H-1,2,3-triazolium salts A–
C[11] were prepared by cycloaddition of the corresponging
alkynes and 1,3-bis(2,6-diisopropylphenyl)triaz-1-ene according
to an adapted literature procedure.[12] The rhodium complexes
1–3 were prepared by reacting the free 1,2,3-triazol-5-ylidene
ligands[13] obtained after deprotonation of the corresponding
triazolium salt precursors A, B or C, respectively with potassium
hexamethyldisilazide (KHMDS) followed by addition to the metal
precursor [RhCl(COD)]2 (COD = 1,5-cyclooctadiene) (Scheme 2).
The neutral metallocyclic complex 1 [Rh(TRZ-NBoc)(COD)]
(84%), was obtained when 2.2 equivalents of base were added
to precursor A prior to metalation. Employing the amino- and
dimethylamine-functionalized triazolium salts as precursor
ligands (B and C, respectively) with 1.2 equivalents of base led
to the isolation of the cationic chelated complexes [Rh(TRZ-
NR2)(COD)]+ complexes 2, and 3. The dicarbonyl complexes
[Rh(TRZ-NBoc)(CO)2] (4) and [Rh(TRZ-NR2)(CO)2]PF6 (5, R =
H; 6, R = Me) were quantitatively prepared by treatment of the
Rh(COD) complexes 1, 2 and 3, respectively, with CO (g) in
dichloromethane (Scheme 2). The [Rh(TRZ-NBoc)(LL)] or
[Rh(TRZ-NR2)(LL)]PF6 (LL = COD or (CO)2) metal complexes 1–
6, are all air and moisture stable. The carbene resonances of the
cyclooctadiene complexes 1–3 are observed at 162.3 and 164.8
ppm, respectively. The 13C NMR spectra of the dicarbonyl
complexes 4–6 display the carbene carbon doublet resonances
at 164.8 and 169.7 ppm, respectively.
2
4
Figure 1. Solid-state structures of complexes 2 and 4 with 50% probability
-
ellipsoids. The PF6 counterion and hydrogens (except for the NH2 functional
group) were omitted for clarity. Selected bond lengths (Å) and angles (°) for 2:
C5–Rh1 2.029(2); Rh1–N4 2.165(2); Rh1–C31 2.205(2); Rh1–C32 2.173(2);
Rh1–C35 2.132(2); Rh1–C36 2.111(2); C5–Rh1–N4 79.22(8); C5–Rh1–C31
164.76(10); C5–Rh1–C32 156.13(10); C5–Rh1–C35 100.60(11); C5–Rh1–
C36 98.95(10); for 4: C5–Rh1 2.036(5); Rh1–N4 2.0924(18); Rh1–C36
1.896(3); Rh1–C37 1.837(3); C5–Rh1–N4 79.69(8); C5–Rh1–C36 175.00(11);
C5–Rh1–C37 94.08(10); C37–Rh1–N4 173.68(9).
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10.1002/chem.201604567
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Catalytic and mechanistic studies
was performed in the absence of K2CO3 (Table 1, entry 6 and
11). The presence of this coupled bis-vinyl sulfide products is
suggestive of a reaction pathway that includes the presence of
two thiolate ligands on the rhodium metal center, similarly as the
mechanism proposed by Mizobe et al. that follows oxidative
addition of two thiolate ligands and concomitant release of
molecular hydrogen.[4g]
The catalytic activity of catalysts 1–6 was first investigated
towards the 1-hexyne hydrothiolation with thiophenol, either in
the presence or absence of the weak base K2CO3 (2 % mol) at
o
80 C in deuterated benzene (Table 1). When the reaction was
performed in the absence of rhodium catalyst (entry 1, Table 1)
an almost 1:1 mixture of only the linear β-E and β-Z vinyl sulfide
was obtained. This result contrasted with the reaction carried out
with [RhCl(COD)]2 in the presence of base (entry 2, Table 1) for
which a mixture of the coupled products, the thio-substituted
dienes, was obtained (identified as a mixture of the bis-β-E,β-Z-
vinyl sulfide and the bis-β-Z,β-Z-vinyl sulfide, Figure S36).
However, if 2 mol % of the base was added (Table 1, entry 5
and 10), none of the coupled product was observed, and a
complete selectivity switch was seen to favor the formation of
the α-vinyl sulfide product. This is anticipated for a situation
where [Rh]-SR insertion of the alkyne is favored over [Rh]-H
insertion.[3d] To rule out the possibility of NH2-deprotonation of
the amino catalyst precursors 2 and 5 by the weak base to yield
the neutral amido complexes, the reactions were repeated with
the analogous dimethylamine complexes [Rh(TRZ-NMe2)(LL)]+
(LL = COD, 3 or (CO)2, 6). Similar conversions and selectivity
were seen for dimethylamine-complexes 3 and 6 (Table 1, entry
7 and 12) compared to the amino-complexes derivatives 2 and 5,
and the possible bifunctional role of the TRZ-NH2 ligand was
dismissed. Instead, base-promoted deprotonation of the
thiophenol, and coordination of the resultant thiolate with
concomitant de-coordination of the NR2 (R = H, Me) seemed
more likely. To test this hypothesis, stoichiometric reactions
were performed where 1 equivalent of thiophenol and K2CO3
was added to both complexes 5 and 6 (see SI). The FT-IR
spectra of these complexes displayed a shift of the N-H
stretching frequencies from 3331 and 3285 cm-1 for 5, to 3311
and 3240 cm-1, respectively, thus indicating dissociation of the
NH2-moiety; while for the NMe2-complex 6, the ν(CO) bands
shifted from 2030 and 2090 cm-1 to 2008 and 2076 cm-1,
respectively, more closely correlating with the carbonyl vibration
bands observed for the neutral RhI complex 4 (1993, 2068 cm-1).
In both cases, these results point to the hemilabile action of the
NR2-ligands of the cationic complexes, followed by coordination
of the deprotonated thiol to yield a neutral RhI intermediate. In
addition, no Rh-H upfield shift was observed in the 1H NMR
spectra, nor was the ν(Rh-H) vibration observed in the 2200 –
2300 cm-1 region in the IR spectra. This result was also
supported by computational calculations of the possible
pathways for 5, comparing (a) an N-donor function that does not
act in a cooperative or hemilabile fashion (SI, Figure S44); (b) a
possible N-H effect by deprotonation of the amine-group by the
Table 1. Selection of precatalysts in the presence or absence of
K2CO3 for the model hydrothiolation of 1-hexyne with thiophenol.
% Product Distribution
Conv.
Entry
[cat.][a]
Couple
d bis-
β,β
[c]
%
α
β-E
β-Z
1
2
K2CO3
84
100
62
-
4
52
18
34
19
3
48
18
4
-
60
-
[b]
[Rh(COD)Cl]2
3
1[b]
1
62
75
94
28
89
97
> 99
97
13
93
4
94
6
-
5
2[b]
2
73
3
-
6
87
6
9
57
-
7
3[b]
4[b]
4
58
7
4
8
69
2
1
-
9
34
-
-
-
10
11
12
5[b]
5
77
3
-
-
51[d]
54
24
5
2
24
-
6[b]
2
weak non-coordinating base combined with
a hemilabile
[a] aReactions performed at 80 °C with 2 mol% of [cat.] in 0.5 mL C6D6,
using anisole as internal standard. [b] 2 mol% of K2CO3. [c] Conversion
after 24 h calculated by NMR integration based on internal standard
anisole integration. [d] Unidentified precipitate observed.
functionality (SI, Figure S45); (c) deprotonation of the thiol by the
weak base, with no N-H effect and solely a hemilabile function
(SI, Figure S46), with oxidative addition of a second thiophenol
molecule, and finally, the most energetically favourable pathway:
(d) deprotonation of the thiol by the weak base, decoordination
of hemilabile –NH2 and substitution by thiophenolate (no
oxidative addition and no [Rh]-H intermediate formed) (SI,
Figure S47).
In contrast, for the neutral amido complexes 1 and 4 [Rh(TRZ-
NBoc)(LL)] (LL = COD or (CO)2, respectively), the formation of
the mixture of C-C coupled thio-dienes was not observed even
in the absence of base (Table 1, entry 4 and 9). Catalyst 4 was
proven to be the most selective towards the α-vinyl sulfide,
In contrast, the metal complexes 1–6 displayed excellent
selectivity towards the branched vinyl sulfides after 24 hours
when 2 mol % of K2CO3 was added (Table 1, entry 3, 5, 7, 8, 10
and 12), comparable to some of the best rhodium-
hydrothiolation catalysts to date.[4] In the case of the cationic
complexes 2 and 5 [Rh(TRZ-NH2)(LL)]+ (LL = COD or (CO)2,
respectively), the formation of the coupled thio-substituted
dienes, in conjunction with the formation of the desired α-vinyl
sulfide and the linear products, were seen when the reaction
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10.1002/chem.201604567
Chemistry - A European Journal
although lower conversions were obtained. A mercury drop-test
was performed on catalyst precursor
4 with no resulting
significant change in either the conversion or regioselectivity of
the catalyst, thereby indicating that a heterogeneous catalytic
mode of action can be excluded.[15]
(a)
In order to gain more insight about the reaction mechanism, we
decided to explore the stoichiometric reactivity of
4 with
substrate thiophenol to investigate the possibility of
a
cooperative[16] and/or hemilabile catalyst activation mechanism.
Both NMR and FT-IR spectra were recorded after addition of
first 1 equivalent of thiophenol, and excess thiophenol in a
separate experiment, to 4 [Rh(TRZ-NBoc)(CO)2] in the absence
of base, at room temperature (see SI, Figures S37 – S42). We
did not observe any evidence for the formation of Rh-hydride
species by NMR and IR spectra, even when recording the
1
spectra after heating at 80° C. In the H and 13C NMR spectra,
clear evidence for the protonation and dissociation of the
resulting –NHBoc moiety was seen, and coordination of the
thiolate ligand (see SI, Figures S39, S40). The NBoc-CH2
chemical shift, observed as a singlet peak at 4.71 ppm in Figure
2(a), resonates as a doublet at 4.64 ppm (J = 6.24 Hz),
corresponding to the protonated NHBoc-CH2 chemical shift after
thiophenol addition (INT2ꞌ, Figure 2(b)). Although the NHBoc
proton could not be unambiguously assigned in the 1H NMR
spectrum due to overlap with the aromatic protons, a 2D COSY
NMR experiment proved the coupling of the CH2-group with a
(b)
chemical shift (N-H) at 6.96 ppm (see SI, Figure S41). In the 13
C
NMR spectrum, a shift of the original Rh-Ccarbene (δ 170.6, d, J =
45 Hz) and CO resonances (δ 189.7, d, J = 63Hz; 189.9, d, J =
59 Hz) (SI, Figure S38) to δ(Rh-Ccarbene) = 168.2 (d, J = 41 Hz)
and δ(CO) = 186.0 (d, J = 65 Hz), 191.0 (d, J = 59 Hz) (SI,
Figure S40) is observed. In addition, the coordination of the
thiolate is confirmed by the downfield shifted thiophenolate Cipso
resonance of the phenyl ring observed at 155.5 ppm, and the
downfield shift of the o-CH of the phenyl resonating at 7.89 ppm
(d, J = 7.24 Hz) and 134.2 ppm, in the 1H and 13C NMR
spectrum, respectively. The reaction mixture was analyzed by
high resolution electrospray-ionization mass spectrometry, and
the molecular ion peak of the thiolate complex INT2ꞌ was
observed as [M-(CO)2]+ = [Rh(NHBoc-TRZ)(SPh)]+ = 729.2746
(calculated exact isotopic mass = 729.2788) (Figure S43, SI),
consistent with the fragmentation pattern/loss of carbonyl
ligands expected for carbonyl complexes during mass
spectrometry ionization.
Similarly, the IR spectrum of INT2ꞌ after addition of 1 equivalent
of thiophenol to 4, supported the protonation and dissociation of
the –NHBoc moiety, with coordination of the thiolate ligand. The
ν(CO) bands observed shifted from 1993, 2068 cm-1 to 1998,
2060 cm-1 after thiophenol addition, and a new broad N-H
stretching frequency is observed at 3367 cm-1 (absent from the
IR spectrum of 4). The small shift in the carbonyl stretching
frequencies indicate that no oxidation of the RhI metal center
had taken place, only exchange of the amido ligand for the
thiolato ligand. In addition, the C=O vibration of the Boc-group
shifted from 1624 cm-1 in 4, to 1720 cm-1 for INT2ꞌ after
thiophenol addition. This stretching frequency more closely
Figure 2. 1H NMR spectra of (a) complex 4 before thiophenol addition and (b)
after thiophenol addition (1 equivalent) to form Rh-thiolate intermediate INT2ꞌ.
resembles the C=O stretching frequency observed for the
precursor salt A (1715 cm-1), supporting the dissociation of the –
NHBoc moiety from the Rh(I) metal center and resultant higher
energy NH-stretching frequency. If a second equivalent or
excess of thiophenol was added, a mixture of unidentified
products was obtained, although no evidence of dithiolate
coordination or Rh-H bond formation was obtained in either the
measured NMR or IR spectra, even after heating the reaction
mixtures at 80 °C. Importantly, both the IR carbonyl stretching
frequencies and the 13C NMR carbene resonance are indicative
of a RhI metal center, and not a RhIII metal center as would be
expected as a result of oxidative addition.
Density Functional Theory (DFT) calculations were additionally
carried out to further evaluate the mechanism of the alkyne
hydrothiolation reaction catalyzed by rhodium(I) complex 4 (vide
supra). To this end, we computed the corresponding reaction
profile involving the PhSH and HC≡CMe reactants in the
presence of the model RhI catalyst 4M (where the bulky Dipp
substituents on the triazolylidene ring were replaced by phenyl
groups). The results are shown in Figure 3, which gathers the
corresponding relative free energies (∆G298, at 298 K) computed
at the dispersion corrected B3LYP-D3/def2-SVP level (see
computational details below).
From the data in Figure 3, it can be suggested that the process
begins with the formation of the initial intermediate INT1,
characterized by the occurrence of an intermolecular hydrogen
bond involving the PhSH reactant and the NBoc moiety of the
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10.1002/chem.201604567
Chemistry - A European Journal
catalyst. Once this initial intermediate is formed, facile
thiolate/NHBoc ligand displacement occurs to produce the Rh(I)
complex INT2. The ease of this ligand exchange becomes
evident in view of the high exergonicity (∆GR = –18.4 kcal/mol
Figure 3. Computed reaction profiles for the reaction of PhSh and HC≡CMe in
the presence of model catalyst 4M. Relative free energies (∆G298, at 298 K)
and bond distances are given in kcal/mol and angstroms, respectively. All data
have computed at the B3LYP-D3/def2-SVP level.
Figure 4. Proposed mechanism incorporating an acid-base metal-ligand
cooperative thiol activation, and two possible protonolysis pathways.
from the separate reactants) and the rather low activation barrier
(∆G≠ = 1.4 kcal/mol, via TS1) computed for this reaction step.
Endergonic replacement of a CO ligand by the alkyne occurs
next to produce intermediate INT3 (∆GR = 12.3 kcal/mol).[17]
From this intermediate, insertion of the thiolate ligand into the
coordinated alkyne takes place leading to the alkenyl-Rh(I)
complex INT4.This slightly endergonic step (∆GR = 4.1 kcal/mol)
(Path 1, Figure 4). Repetition of the stoichiometric reaction with
1 equivalent of K2CO3 yielded the same results.
Table 2. Scope of the base-free hydrothiolation of terminal alkynes with
thiophenol using catalyst precursor 4.[a]
occurs through the transition state TS2,
a saddle point
associated with the concomitant formation of the new C–S bond
and Rh–S cleavage (∆G≠ = 19.8 kcal/mol). Final protonolysis of
the Rh–C bond (very likely assisted by a new molecule of PhSH)
leads to the formation of the observed alkene regenerating the
catalyst by coordination of the previously released CO ligand.
The high exergonicity computed for this final step (∆GR = –20
kcal/mol) compensates for the previous endergonic insertion
reaction and drives the complete catalytic cycle forward.The
proposed reaction mechanism (without the consideration of
external base) given in Figure 4, therefore includes the
dissociation of the hemilabile protonated ligand and thiolate
coordination to the metal center to form INT2ꞌ.
The spectroscopic detection of this intermediate is compatible
with its computed thermodynamic stability (see above).
Subsequent alkyne coordination by replacing one of the
carbonyl ligands (INT3ꞌ), is followed by alkenyl binding to metal
center (INT4ꞌ) after the thiolate group migration. Finally,
protonolysis either by a second thiophenol molecule (Path 1,
Figure 4) or deprotonation of the pendant NHBoc ligand (Path 2,
Figure 4), yields product vinyl sulfide and catalyst. In a final
stoichiometric reaction, 1 equivalent of alkyne was added to the
stoichiometric reaction mixture (4 + HSPh → INT2ꞌ), but did not
lead to product formation, even after heating to 80 °C. For this
reason, it can be concluded that protonolysis of the alkenyl
complex INT4ꞌ by a second thiophenol molecule is more likely
% Product Distribution
Conv.
Entry
R
Rꞌ
[b]
%
α
> 99
93
β-E/Z
-
1
2[d]
3
Ph
Ph
43[c]
63
40
23
79
57
91
88
49
88
Ph
Ph
Ph
7
(CH2)4CH3
71
29
2
4
(CH2)4CH3
(CH2)4CH3
CH2NH2
CH2NMe2
CH2NHBoc
CH2OH
Mes
98
5
Ph
Ph
Ph
Ph
Ph
Ph
86
10[c]
18
16[d]
14
-
6
82
7
80
8
86
9
> 99
97
10
Fc
3
[a] Reactions performed at 80 °C with 2 mol% of [4], in 0.5 mL C6D6, and
anisole as internal standard. [b] Conversion calculated after 24 h based on
NMR integration of the internal standard anisole. [c] Unidentified precipitate
observed. [d] An additional 4% unidentified byproduct was observed. [d] 2
mol% of K2CO3 added.
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10.1002/chem.201604567
Chemistry - A European Journal
All air and moisture sensitive synthetic procedures were performed under
a N2 (g) or Ar (g) atmosphere using standard Schlenk techniques. All
solvents were purified and distilled over Na (s) (hexane, diethylether,
benzene and THF) or CaH2 (dichloromethane and acetonitrile) under N2
(g) atmosphere. A Bruker AVANCE III- 300.12 MHz or 400.21 MHz
spectrometer was used for NMR experiments. Chemical shifts are
reported as δ (in ppm) and reported downfield from TMS and referenced
to the residual solvent chemical shifts. Coupling constants (J) are
reported in Hz. The NMR spectra were analysed using MNova
(Mestrelab research) and the residual solvent chemical shifts were
chosen as the default reference shifts in the software. Solution FT-IR
In addition, a perusal of table 1 reveals that in the case of metal
complex 2, the lack of ligand-assisted deprotonation of the
thiophenol, can only be circumvented by using a catalytic amount of
base in order to have excellent regioselectivity. The evidence for
ligand-assisted deprotonation of the thiophenol by 4 prompted us to
widen the range of both aliphatic and aryl substrates with various
functional groups for the base-free hydrothiolation reaction (Table 2),
using complex 4 as catalyst. Again, no coupled bis-β,β-vinyl sulfide
products were observed, and the reaction was selective to the
branched α-vinyl sulfides, thus demonstrating the good functional
group tolerance exhibited by the catalyst. Addition of 2 mol% of
K2CO3 (entry 2, Table 2) leads to an increase in the yield of the
reaction, but as previously seen (Table 1, entries 8 and 9),
accompanied by a slight decrease in selectivity. Notably, the
strategy of using a bidentate, hemilabile ligand in a cooperative[16]
fashion to deprotonate and activate the substrate thiol (especially
thiophenol) proved successful in preventing Rh-H formation, so that
alkyne insertion into the resultant Rh-SR bond favors α-isomer
product formation.
spectra (ν(CO)) were recorded on
a
Bruker ALPHA FT–IR
spectrophotometer with a NaCl cell, using CH2Cl2 as solvent. The range
of absorption measured was from 4000–600 cm-1. Mass spectral
analyses were performed on a Waters Synapt G2 HDMS by direct
infusion at 5 µL/min with positive electron spray as the ionization
technique. The m/z values were measured in the range of 400-1500 with
acetonitrile as solvent for 1–4, and dichloromethane for 5 and 6. Prior to
analysis, a 5 mM sodium formate solution was used to calibrate the
instrument in resolution mode.
Preparation of complexes 1–3.
A Schlenk tube in the glove box was charged with the precursor
triazolium salt A[11] (1.40 g, 2.1 mmol) and 2.2 eq. KHMDS (0.93 mg, 4.6
mmol). Freshly distilled, deaerated THF (ca. 15 mL) was cannula
transferred into this Schlenk tube at -78 oC. The solution was stirred at
this temperature for ca. 30 min, before allowing to warm up to -50 oC.
The deprotonated NBoc-functionalized carbene was then slowly
transferred dropwise (via cannula) into a THF suspension of 0.5 eq.
[Rh(COD)Cl]2 (0.54 g, 1.1 mmol) at -78 oC. The reaction mixture was
stirred overnight whilst slowly allowing to warm up to RT. The solvent
was evaporated to complete dryness in vacuo followed by extraction with
hexanes, to yield of 1. Crystallization from a dichloromethane solution
layered with hexane, yielded crystals of 1 suitable for X-ray diffraction.
Conclusions
The performance of a range of cationic and neutral bidentate N-
donor functionalized 1,2,3-triazol-5-ylidene Rh(I) complexes as
catalyst precursors for the alkyne hydrothiolation reaction was
investigated. The strategy of combining an electron-donating
(TRZ) bidentate ligand with a tethered coordinating N-moiety
was followed, as a design approach to yield a catalyst that
activates the substrate thiol via deprotonation by the ligand. In
addition, direction of the site of attack of the incoming substrate
thiol, and insertion of substrate alkyne into resulting [Rh]-SR
bond for improved Markovnikov-addition regioselectivity of the
Cationic complexes 2 and 3 were prepared in a similar procedure as
described above, using ligand precursors B (1.00 g, 1.8 mmol) and 1.2
eq of KHMDS (0.43 g, 2.2 mmol); and C (1.10 g, 1. 9 mmol),[11] with 1.2
eq of KHMDS (0.46 g, 2.3 mmol), respectively.
hydrothiolation reaction, were targeted.
For the cationic N-
donor (TRZ-NH2) complexes 2 and 5, no evidence for a ligand-
assisted bifunctional reaction mechanism for the catalytic
hydrothiolation could be found, which is supported by the similar
results obtained for the dimethylamino-analogues 3 and 6.
Instead, stoichiometric and computational studies indicated only
the hemilabile action of the NR2-moiety. In contrast, the neutral
[Rh(TRZ-NBoc)(COD)] (1) Yellow powder. Yield: 1.30 g (84%). 1H
NMR[18] (300 MHz, CDCl3): δ = 7.47 (dd, 2H, J = 7.82 Hz, H9), 7.26, 7.23
(d, 2H, J = 7.80 Hz, H8,10), 5.38 (br, 2H, H20,23), 4.10 (s, 2H,H16) 3.35 (br,
2H, H20,23), 2.52 (sept, 2H, J = 6.75 Hz, H12,14), 2.25 (m, 2H + 2H, H21,22
+
amido complexes
1
and
4
demonstrate ligand-assisted
H12,14), 2.10, 1.80, 1.67 (br m, 6H, H21,22) 1.37 (s, 9H, H19), 1.35 (d, J =
6.79 Hz, 6H, H13,15), 1.23, 1.06, 1.03 (d, 18H, J = 6.78 Hz, 6.80 Hz, 6.90
Hz, H13,15). 13C{1H} NMR (75 MHz, CDCl3):[18] δ = 164.3 (C17), 162.3 (d, J
= 51.6 Hz, C5), 157.3 (C4), 145.2 (C7,11), 134.6, 131.1 (C9), 131.7, 131.6
(C6), 124.5, 123.6 (C8,10), 95.8, 65.5 (C20,23) 65.8 (C18), 49.7 (C16), 28.5
(C19), 28.7, 28.6 (C12,14), 31.7, 29.4, 28.9, 26.4. 23.8, 22.4 (C13,15, 21, 22);
HRMS: m/z: [M+H]+ calculated: 729.3615; observed: 729.3607;
activation of the thiol substrates to circumvent the use of
directing ligand pyridine or base in the hydrothiolation reaction.
A pathway that includes thiol deprotonation by the pendant
amido of the triazolylidene ligand, and hemilabile dissociation of
the ligand N-donor was postulated for catalyst precursor 4,
following spectroscopic and computational studies. Excellent
regioselectivity towards the branched vinyl sulfide products was
shown by catalyst precursor 4, yielding the notoriously harder-to-
come-by α-vinyl sulfides with aryl substituents, specifically for
the case when both substrate alkyne and thiol contains aromatic
substituents.
[Rh(TRZ-NH2)(COD)]PF6 (2) Yellow powder. Yield: 1.10 g, 79 %. 1H
NMR[18] (300 MHz, CD2Cl2): δ 7.63, 7.56 (dd, 1H, J = 7.85 Hz, 7.82 Hz,
H9), 7.41, 7.35 (d, 2H, J = 7.86 Hz, 7.83 Hz, H8,10), 4.63 (m, 2H, H21,22
)
3.89 (t, 2H, J = 6.13 Hz, H16), 3.68 (m, 2H, H21,22), 3.61 (bt, 2H, HN) 2.45
(sept, 2H, J = 6.79 Hz, H12, 14)), 2.22 (m, 4H+ 2H, H21,22 + H12,14), 1.89,
1.79 (m, 2H, H21,22), 1.43, 1.30, 1.15, 1.11 (d, 24H, J = 6.77 Hz, 6.83 Hz,
6.81 Hz, 6.89 Hz, H13,15). 13C{1H} NMR[18] (75 MHz, CD2Cl2): δ = 164.8 (d,
J = 51.9 Hz, C5) 156.8 (C4) 145.6, 145.5 (C7,11), 134.7, 130.4 (C9), 133.2,
132.3 (C6), 125.6, 124.7 (C8,10), 93.7 (d, J = 8.26 Hz, C20) 74.2 (d, J =
13.1 Hz, C23) 41.8 (C16), 32.2, 29.5 (C12,14), 25.7, 25.1, 23.9, 23.2
(C13,15,21,22). 31P NMR (121 MHz, CD2Cl2): δ = -144.5 ppm (hept, J =
Experimental Section
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10.1002/chem.201604567
Chemistry - A European Journal
711.1 Hz). 19F NMR (282 MHz, CD2Cl2): δ = -72.9 ppm (d, J = 711.2 Hz);
HRMS: m/z: [M-PF6]+ calculated: 629.3090; observed: 629.3089.
(CH2Cl2): ν(CO)
605.2363; observed: 605.2363.
=
2031, 2090 cm-1; HRMS: m/z: [M]+ calculated:
[Rh(TRZ-NMe2)(COD)]PF6 (3) Yellow powder. Yield: 1.30 g, 85 %. 1H
NMR[18] (300 MHz, CD2Cl2): δ = 7.67, 7.60 (dd, 1H, J = 7.84 Hz, 7.82 Hz,
H9), 7.41, 7.35 (d, 2H, J = 7.85 Hz, 7.83 Hz, H8,10), 4.55 (m, 2H, H18) 3.65
(s, 2H, H16), 3.62 (m, 2H, H21), 2.68 (s, 6H, H17) 2.28 (m, (2H + 2H) +
(2H+2H), H12, 14 + H19,20), 1.91, 1.77 (m, 2H+ 2H, H19,20), 1.48, 1.31, 1.17,
1.14 (d, 24H, J = 6.81 Hz, 6.86 Hz, 6.80 Hz, 6.88 Hz, H13,15). 13C{1H}
NMR[18] (75 MHz, CD2Cl2): δ = 164.8 (d, J = 52.1 Hz, C5) 152.2 (C4)
145.6, 145.3 (C7,11), 134.3, 129.9 (C6), 133.4, 132.6 (C9), 125.7, 124.9
(C8,10), 96.2 (d, J = 8.37 Hz, C18) 73.3 (d, J = 13.5 Hz, C21) 60.8 (C16),
50.2 (C17) 31.9, 29.1 (C19,20), 29.8, 29.6 (C12,14), 26.1, 25.5, 23.8, 22.8
(C13,15). 31P NMR (121 MHz, CD2Cl2): δ = -144.5 ppm (sept, J = 710.7
Hz). 19F NMR (282 MHz, CD2Cl2): δ = -73.2 ppm (d, J = 710.8 Hz);
HRMS: m/z:[M-PF6]+ calculated: 629.3090; observed: 629.3089.
Crystal structure determination
Single crystal X-ray diffraction data were collected on a Bruker Apex II-
CCD detector using Mo-Kα radiation (λ = 0.71073 Å). Crystals were
selected under oil, mounted on nylon loops then immediately placed in a
cold stream of N2 at 150 K. Structures were solved and refined using
Olex2 and SHELXTL. A satisfactory refinement of the crystal structure of
complex 4 was only obtained after squeeze methodology was applied in
order to eliminate residual electronic density of the solvent, which could
not be refined otherwise.[19] CCDC-1504559 (A), 1504560 (B), 1504561
(C), 1504562 (2) and 1504563 (4), contain the supplementary
crystallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Preparation of complexes 4–6.
Crystal data for compound 2
The dicarbonyl complexes 4,
5 and 6 were prepared from the
corresponding COD complexes 1 (0.54 g, 0.74 mmol), 2 (0.47 g, 0.61
mmol) or 3 (0.32 g, 0.40 mmol), respectively, by dissolving the precursor
metal complex in ca. 20 mL dichloromethane. CO (g) was bubbled
through the solution at room temperature for ca. 5 min until the colour of
the solution ceases to lighten. The solution was stirred for ca. 15 min in
the CO (g) atmosphere, before the solvent was evaporated. Subsequent
washing with hexanes yielded the pure complexes.
C
35H50N4F6PRh (M =774.67 g/mol): monoclinic, space group P21/n (no.
14), a = 11.6643(5) Å, b = 12.5642(6) Å, c = 24.8822(11) Å, β =
102.418(2)°, V = 3561.2(3) Å3, Z = 4, T = 150.15 K, µ(MoKα) = 0.586
mm-1, Dcalc = 1.445 g/cm3, 121530 reflections measured (4.664°≤ 2Θ ≤
52.924°), 7330 unique (Rint = 0.0460, Rsigma = 0.0151) which were used in
all calculations. The final R1 was 0.0330 (I > 2σ(I)) and wR2 was 0.0893
(all data).
[Rh(TRZ-NBoc)(CO)2] (4) Pale yellow powder. Yield: 0.50 g, 99%. 1H
NMR[18] (300 MHz, CD2Cl2): δ = 7.58 (dd, 2H, J = 7.98 Hz, H9), 7.39,
7.38 (d, 4H, J = 7.80 Hz, 6.97 Hz, H8,10), 4.17 (s, 2H,H16), 2.46, 2.31
(sept, 4H, H12,14), 1.45 (s,9H,H19), 1.36, 1.28, 1.16, 1.13, (d, 24H, J =
6.82 Hz, 6.75 Hz, 6.91 Hz, 6.73 Hz, H13,15). 13C{1H} NMR[18] (75 MHz,
CD2Cl2 ): δ = 189.4, 188.9 (d, J = 61.5 Hz, 59.2 Hz, C20,21), 169.7 (d, J =
44.4 Hz, C5), 163.0 (C4), 158.3 (C17) 146.0, 145.8 (C7,11), 135.1, 131.1
(C9), 132.7, 132.1 (C6), 125.9, 125.5 (C8,10), 81.2 (C18), 35.8 (C16), 29.9,
29.7, 28.4 (C19), 25.9, 24.9. 24.0, 22.9 (C13,15); FTIR (CH2Cl2): ν(CO) =
1624, 1993, 2068 cm-1, ѵ(NH) = 3367 cm-1; HRMS: m/z: [M-CO+MeCN]+
calculated: 725.7365; observed: 725.7384.
Crystal data for compound 4
C34H45N4O4Rh (M =676.65 g/mol): triclinic, space group P-1 (no. 2), a =
12.3738(6) Å, b = 12.4127(4) Å, c = 12.5387(6) Å, α = 73.281(4)°, β =
85.620(4)°, γ = 75.727(4)°, V = 1787.46(14) Å3, Z = 2, T = 293(2) K,
µ(MoKα) = 0.517 mm-1, Dcalc = 1.257 g/cm3, 55567 reflections measured
(5.882° ≤ 2Θ ≤ 51.994°), 7031 unique (Rint = 0.0708, Rsigma = 0.0338)
which were used in all calculations. The final R1 was 0.0328 (I > 2σ(I))
and wR2 was 0.0891 (all data).
DFT calculations
[Rh(TRZ-NH2)(CO)2]PF6 (5) Pale yellow powder. Yield: 0.44 g, 100%. 1H
NMR[18] (300 MHz, CD2Cl2): δ 7.66, 7.61 (dd, 1H, J = 7.87, 7.83, H9),
7.43, 7.40 (d, 2H, J = 7.59, 7.66, H8,10), 4.30 (b, 2H, HN) 4.09 (t, 2H, J =
5.88, H16), 2.36, 2.24 (sept, 2H, J = 6.86, 6.84, H12, 14), 1.36, 1.31, 1.17,
1.15 (d, 24H, J = 6.81, 6.82, 7.44, 7.15, H13,15). 13C{1H} NMR[18] (75 MHz,
CD2Cl2): δ = 185.6, 185.1 (d, J = 56.3, 72.5, CO17,18) 164.8 (d, J = 45.2,
C5) 156.6 (C4) 145.9, 145.6 (C7,11), 134.5, 130.3 (C6), 133.5, 132.8 (C9),
125.6, 124.7 (C8,10), 42.0 (C16), 29.8, 29.6 (C12,14), 25.7, 25.1, 24.0, 23.4
(C13,15). 31P NMR (121 MHz, CD2Cl2): δ = -144.4 ppm (sept, J = 712.4
Hz). 19F NMR (282 MHz, CD2Cl2): δ = -72.5 ppm (d, 712.3 Hz); FTIR
(CH2Cl2): ν(CO) = 2027, 2090 cm-1; ѵ(NH) = 3311, 3250 cm-1; HRMS:
m/z: [M-PF6]+ [M]+ calculated: 577.2050; observed: 577.2044.
All the calculations reported in this paper were obtained with the
GAUSSIAN 09 suite of programs.[20] Electron correlation was partially
taken into account using the hybrid functional usually denoted as
B3LYP[21] in conjunction with the D3 dispersion correction suggested by
Grimme et al.[22] using the double-Ϛ quality plus polarization def2-SVP
basis set[23] for all atoms. This level is denoted B3LYP-D3/def2-SVP.
Reactants and products were characterized by frequency calculations,[24]
and have positive definite Hessian matrices. Transition structures (TS’s)
show only one negative eigenvalue in their diagonalised force constant
matrices, and their associated eigenvectors were confirmed to
correspond to the motion along the reaction coordinate under
consideration using the Intrinsic Reaction Coordinate (IRC) method.[25]
[Rh(TRZ-NMe2)(CO)2]PF6 (6) Pale yellow powder. Yield: 0.30 g, 100%.
1H NMR[18] (300 MHz, CD2Cl2): δ = 7.62, 7.57 (dd, 1H, J = 7.80, 7.84, H9),
7.38, 7.34 (d, 2H, J = 7.86, 7.87, H8,10), 3.76 (s, 2H, H16), 2.95 (s, 6H,
H17) 2.23, 2.11 (sept, 2H, J = 6.90, 7.00, H12, 14), 1.30, 1.24, 1.12, 1.10 (d,
24H, J = 6.84, 6.85, 8.12, 7.13, H13,15). 13C{1H} NMR[18] (CD2Cl2, 54.0
ppm): δ = 185.7, 184.4 (d, J = 58.4, 72.3, CO18,19) 168.9 (d, J = 45.3, C5)
154.2 (C4) 145.5, 145.3 (C7,11), 134.0, 129.7 (C6), 133.8, 133.0 (C9),
125.7, 125.2 (C8,10), 60.9 (C16), 53.8 (C17), 29.9, 29.7 (C12,14), 25.4, 25.0,
23.9, 23.4 (C13,15). 31P NMR (121 MHz, CD2Cl2): δ = -144.5 ppm (sept, J
= 711.0). 19F NMR (282 MHz, CD2Cl2): δ = -72.8 ppm (d, 711.1 Hz); FTIR
Acknowledgements
The authors gratefully acknowledge Ms Madelien Wooding,
University of Pretoria, for the mass spectrometric measurements.
G. G.-B. thanks the MINECO for a postdoctoral grant (FPDI-
2013-16525) and Generalitat Valenciana (GV/2015/097) for
financial support. E.P and I.F. gratefully acknowledge financial
This article is protected by copyright. All rights reserved.

10.1002/chem.201604567
Chemistry - A European Journal
Kajitani, E. Nishinaka, M. Sonoda, A. Ogawa, J. Sulfur Chem. 2009, 30,
309–318; e) V. P. Ananikov, N. V. Orlov, I. P. Beletskaya, V. Khrustalev,
M. Y. Antipin, T. V. Timofeeva, J. Am. Chem. Soc. 2007, 129, 7252–
7253; f) A. Kondoh, H. Yorimitsu, K. Oshima, Org. Lett. 2007, 9, 1383–
1385; g) B. Gabriele, G. Salerno, A. Fazio, Org. Lett. 2000, 2, 351–352.
h) J.-E. Bäckvall, A. Ericsson, J. Org. Chem. 1994, 59, 5850–5851; i) H.
Kuniyasu, A. Ogawa, K.-I Sato, I. Ryu, N. Kambe, N. Sonoda, J. Am.
Chem. Soc. 1992, 114, 5902–5903.
support from the Spanish MINECO-FEDER (CTQ2014-51999-P
to E.P. and CTQ2013-44303-P and CTQ2014-51912-REDC to
I.F.), UJI (P11B2014-02 to E.P.). D.I.B and I.S. gratefully
acknowledge the National Research Foundation, South Africa
(NRF 87890, 103698 and 92521), and Sasol Technology R&D
Pty. Ltd., South Africa for financial support.
[7]
a) V. P. Ananikov, N. V. Gayduck, N. V. Orlov, I. P. Beletskaya, V. N.
Khrustalev, M. Y. Antipin, Chem. Eur. J. 2010, 16, 2063–2071; b) D. A.
Malyshev, N. M. Scott, N. Marion, E. D. Stevens, V. P. Ananikov, I. P.
Beletskaya, S. P. Nolan, Organometallics 2006, 25, 4462–4470; c) V. P.
Ananikov, L. P. Orlov, I. P. Beletskaya, Organometallics 2006, 25,
1970–1977; d) V. P. Ananikov, D. A. Malyshev, I. P. Beletskaya, G. G.
Aleksandrov, I. L. Eremenko, Adv. Synth. Catal. 2005, 347, 1993–2001;
e) L. -B. Han, C. Zhang, H. Yazawa, S. Shimada, J. Am. Chem. Soc.
2004, 126, 5080–5081.
Keywords: rhodium(I) • hydrothiolation • 1,2,3-triazol-5-ylidene
(TRZ) • mesoionic carbene (MIC) • hemilabile
[1]
For selected examples of vinyl sulfides with biological applications, see:
a) C. A. Dvorak, W. D. Schmitz, D. J. Poon, D. C. Pryde, J. P. Lawson,
R. A. Amos, A. I. Meyers, Angew. Chem., Int. Ed. 2000, 39, 1664–
1666; b) M. Ceruti, G. Balliano, F. Rocco, P. Milla, S. Arpicco, L. Cattel,
F. Viola, Lipids 2001, 36, 629–636; c) P. Johannesson, G. Lindeberg, A.
Johansson, G. V. Nikiforovich, A. Gogoll, B. Synnergren, M. LeGrèves,
F. Nyberg, A. Karlén, A. Hallberg, J. Med. Chem. 2002, 45, 1767–1777;
d) Á. Szilágyi, F. Fenyvesi, O. Majercsik, I. F. Pelyvás, I. Bácskay, P.
Fehér, J. Váradi, M. Vecsernyés, P. Herczegh, J. Med. Chem. 2006, 49,
5626–5630; e) M. C. Aversa, A. Baratucci, P. Bonaccorsi, F. Marino-
Merlo, A. Mastino, M. T. Sciortino, Bioorg. Med. Chem. 2007, 17, 1456–
1463.
[8]
[9]
D. I. Bezuidenhout, G. Kleinhans, G. Guisado-Barrios, D. C. Liles, G.
Ung, G. Bertrand, Chem.Commun. 2014, 50, 2431–2433.
For recent reviews, see: a) R. H. Morris, Acc. Chem. Res. 2015, 48,
1494–1502; b) J. R. Khusnutdinova, D. Milstein, D. Angew. Chem.
2015, 127, 12406–12445; Angew. Chem. Int. Ed. 2015, 54, 12236–
12273; c) T. Zell, D. Milstein, Acc. Chem. Res. 2015, 48, 1979–1994; d)
S. Kuwata, T. Ikariya, Chem. Commun. 2014, 50, 14290–14300; e) D.
Gelman, M. Sanaa, ACS Catal. 2012, 2, 2456–2466. f) B. Askevold, H.
W. Roesky, S. Schneider, ChemCatChem. 2012, 4, 307–320; g) W.
Kaim, Eur. J. Inorg. Chem. 2012, 343–348; h) W. I. Dzik, B. de Bruin,
Organometallic Chemistry 2011, 37, 47–78; i) C. Gunanathan, D.
Milstein, Acc. Chem. Res. 2011, 44, 588–602; j) H. Grützmacher,
Angew. Chem. 2008, 120, 1838–1842; Angew. Chem. Int. Ed. 2008,
47, 1814–1818.
[2]
For selected examples of vinyl sulfides as polymers, see: a) J. Liu, J.
W. Y. Lam, C. K. Jim, J. C. Y. Ng, J. Shi, H. Su, K. F. Yeung, Y. Hong,
M. Faisel, Y. Yu, K.S. Wong, B. Z. Tang, Macromolecules 2011, 44,
68–79; b) A. B. Lowe, J. W. Chan, in Functional Polymers by Post-
Polymerization Modification; P. Theato, H.-A. Eds. Klok, Wiley-VCH
Verlag GmbH & Co. KGaA: Weinheim, 2013, pp. 87–118; c) B. Yao, J.
Mei, J. Li, J. Wang, H. Wu, J. Z. Sun, A. Qin, B. Z. Tang,
Macromolecules 2014, 47, 1325–1333; d) I. -T. Trotuş, T. Zimmermann,
F. Schüth, Chem. Rev. 2014, 114, 1761–1782.
[10] a) R. Lalrempuia, N. D. McDaniel, H. Müller-Bunz, S. Bernhard, M.
Albrecht, Angew. Chem. Int. Ed. 2010, 122, 9959–9962; Angew. Chem.
2010, 49, 9765–9768; b) Cao, R.; Lai, W.; Du, P. Energy Environ. Sci.
2012, 5, 8134–8157; c) D. Canseco-Gonzalez, A. Petronilho, H.
Mueller-Bunz, K. Ohmatsu, T. Ooi, M. Albrecht, J. Am. Chem. Soc.
2013, 135, 13193–13203.
[3]
[4]
For recent reviews, see: a) J. A. Love, M. Wathier, Eur. J. Inorg. Chem.
2016, 23911–2402; b) A. Dondoni, A. Marra, Eur. J. Org. Chem. 2014,
3955–39659; c) R. Chinchilla, C. Nájera, Chem. Rev. 2014, 114, 1783–
1826; d) R. Castarlenas, A. Di Giuseppe, J. J. Pérez-Torrente, L. A.
Oro, Angew. Chem. 2013, 125, 223 –234; Angew. Chem. Int. Ed. 2013,
52, 211–222; (e) I. P. Beletskaya, V. P. Ananikov, Chem. Rev. 2011,
111–1636.
[11] The synthesis, spectroscopic characterization and single crystal X-ray
structures of the new triazolium salts A–C are reported in the
Supporting Information.
a) G. Kleinhans, G. Guisado-Barrios, D. C. Liles, G. Bertrand, D. I.
Bezuidenhout, Chem. Commun. 2016, 52, 3504–3507; b) S. Kankala, S.
Nerella, R. Vadde, C. S. Vassam, RSC Adv. 2013, 3, 23582–23588; c)
L. Palacios, M. J. Artigas, V. Polo, F. J. Lahoz, R. Castarlenas, J. J.
Pérez-Torrente, L. A. Oro, L. A. ACS Catal. 2013, 3, 2910–2919; d) A.
Di Giuseppe, R. Castarlenas, J. J. Pérez-Torrente, M. Crucianelli, R.
Sancho, F. J. Lahoz, L. A. Oro, J. Am. Chem. Soc. 2012, 134, 8171–
8183; e) J. Yang, A. Sabarre, L. R. Fraser, B. O. Patrick, J. A. Love, J.
Org. Chem. 2009, 74, 182–187; f) L. R. Fraser, J. Bird, Q. Wu, C. Cao,
B. O. Patrick, J. A. Love, J. A. Organometallics 2007, 26, 5602–5611;
g) Y. Misumi, H. Seino, Y. Mizobe, J. Organomet. Chem. 2006, 691,
3157–3164; h) C. Cao, L.R Fraser, J. A. Love, J. Am. Chem. Soc.
2005, 127, 17614–17615.
[12] J. Bouffard, B. K. Keitz, R. Tonner, G. Guisado-Barrios, G. Frenking, R.
H. Grubbs, G. Bertrand, Organometallics 2011, 30, 2617–2627.
[13] G. Guisado-Barrios, J. Bouffard, B. Donnadieu, G. Bertrand, Angew.
Chem. Int. Ed. 2010, 122, 4869–4872; Angew. Chem. 2010, 49, 4759–
4762.
[14] a) D. Mendoza-Espinosa, R. González-Olvera, G. E. Negrón-Silva, D.
Angeles-Beltrán, O. R. Suárez-Castillo, A. Álvarez-Hernández, R.
Santillan, Organometallics 2015, 34, 4529–4542; b) T. V. Q. Nguyen,
W.-J. Yoo, S. Kobayashi, Angew. Chem. 2015, 127, 9341–9344;
Angew. Chem. Int. Ed. 2015, 54, 9209–9212; c) X. Yan, J. Bouffard, G.
Guisado-Barrios, B. Donnadieu, G. Bertrand, Chem. Eur. J. 2012, 18,
14627–14631; d) M. T. Zamora, M. J. Ferguson, M. Cowie,
Organometallics 2012, 31, 5384–5395; e) A. Poulain, D. Canseco-
Gonzalez, R. Hynes-Roche, H. Müller-Bunz, O. Schuster, H. Stoeckli-
Evans, A. Neels, M. Albrecht, Organometallics 2011, 30, 1021–1029; f)
P. Mathew, A. Neels, M. Albrecht, J. Am. Chem. Soc. 2008, 130.
13534–13535.
[5]
a) H. Zhao, J. Peng, M. Cai, M. Catal. Lett. 2012, 142, 138–142; b) L. D.
Field, B. A. Messerle, K. Q. Vuong, P. Turner, Dalton Trans. 2009,
3599–3614; c) S. Shoai, P. Bichler, B. Kang, H, Buckley, J. A. Love,
Organometallics 2007, 26, 5778–5781; d) S. Burling, L. D. Field B. A
Messerle, K. Q. Vuong, P. Turner, Dalton Trans. 2003, 4181–4191; e)
A. Ogawa, T. Ikeda, K. Kimura, J. Hirao, J. Am. Chem. Soc. 1999, 121,
5108–5114.
[15] a) D. R. Anton, R. H. Crabtree, Organometallics 1983, 2, 855−859; b) J.
A. Widegren, R. G. Finke, J. Mol. Catal. A 2003, 198, 317−341.
[16] a) W. Wylie, A. J. Lough, R. H. Morris, Organometallics 2011, 30, 1236-
1252; b) W. Wylie, A. J. Lough, R. H. Morris, Organometallics 2012, 31,
2152–2165.
[6] a) R. Gerber, C. M. Frech, Chem. Eur. J. 2012, 18, 8901–8905; b) V. P.
Ananikov, N. V. Orlov, S. S. Zalesskiy, I. P. Beletskaya, V. N.
Khrustalev, K. Morokuma, D. G. Musaev, J. Am. Chem. Soc. 2012, 134,
6637–6649; c) T. Mitamura, M. Daitou, A. Nomoto, A. Ogawa, A. Bull.
Chem. Soc. Jpn. 2011, 84, 413–415; d) S. Kodama, A. Nomoto, A.; M.
[17] An alternative reaction mechanism involving a related INT3 having a
square pyramidal Rh(I) cannot be discarded. For related species, see:
a) L. D. Field, B. A. Messerle, K. Q. Vuong, P. Turner, Organometallics
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2005, 25, 42414250; b) W. Gil, A. M. Trzeciak, J. J. Ziolkowski,
Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R.
Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C.
Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski,
G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels,
Ö. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox,
Gaussian, Inc., Wallingford CT, 2009.
Organometallics 2008, 27, 4131−4138.
[18] See Supporting Information for full NMR spectra and atom numbering
scheme.
[19] a) O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard, H.
Puschmann, J. Appl. Cryst. 2009, 42, 339-341; b) M. C. Burla, R.
Caliandro, M. Camalli, B. Carrozzini, G. L. Cascarano, L. De Caro, C.
Giacovazzo, G. Polidori, D. Siliqi, R. Spagna, J. Appl. Cryst. 2007, 40,
609–613; c) G.M. Sheldrick, Acta Cryst. 2008, A64, 112–122.
[20] Gaussian 09, D.01. M. Frisch, G. Trucks, H. Schlegel, G. Scuseria, M.
Robb, J. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.
Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F.
Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O.
Kitao, H. Nakai, T. Vreven, J. J. A. Montgomery, J. E. Peralta, F.
Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N.
Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.
C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, N. J. Millam, M.
[21] a) A. D. Becke, J. Chem. Phys. 1993, 98, 5648–5652; b) C. Lee, W.
Yang, R.G. Parr, Phys. Rev. B 1988, 37, 785–789.
[22] S. Grimme, J. Antony, S. Ehrlich, H. Krieg, J. Chem. Phys. 2010, 132,
154104–154119.
[23] F. Weigend, R. Ahlrichs, Phys. Chem. Chem. Phys. 2005, 7, 3297–
3305.
[24] J. W. McIver Jr, A. Komornicki, J. Am. Chem. Soc. 1972, 94, 2625–
2633.
[25] C. Gonzalez, H.B. Schlegel, J. Phys. Chem. 1990, 94, 5523–5527.
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Entry for the Table of Contents
FULL PAPER
Cooperation in action!
Ian Strydom, Gregorio Guisado-Barrios*,
Israel Fernández, David C. Liles,
Eduardo Peris and Daniela I.
Bezuidenhout*.
Dipp
N
N
N
H
Dipp
Dipp
N
R' =Ar, Alkyl
N
Boc
H
N
Dipp
N
Boc
N
Boc
Ph
Rh
N
N
N
N
R'
H
H
R'
H
CO
OC
Ph SH
Dipp
Ph
S H
S
H
Dipp
Rh
Ph
S
Rh
migratory
inversion into
[Rh]-SPh
OC
Page No. – Page No.
C6D6, 80oC
CO
protonolysis
OC
OC
α
R'
S
Ph
Title A hemilabile and cooperative N-
donor functionalized 1,2,3-triazol-5-
ylidene ligand for selective and base-
free rhodium(I) catalyzed alkyne
hydrothiolation reactions.
A ligand-assisted acid-base thiol activation strategy for the
regioselective hydrothiolation of alkynes mediated by a RhI-
catalyst
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