Exploring the scope of a novel ligand class: Synthesis and catalytic examination of metal complexes with 'normal' 1,2,3-triazolylidene ligands

Article abstract of DOI:10.1021/ic400533u

Using new 'normal'-substituted 1,2,3-triazolylidene silver compounds as starting materials allowed for preparation of a series of molybdenum, ruthenium, rhodium, and palladium transition metal complexes bound to the new 1,2,3-triazolylidene ligand system. In this work, the first triazolylidene Mo compound is presented as well as the first structural investigation of a silver complex with a monodentate 1,2,3-triazolylidene. Furthermore, the triazolylidene Pd complex and the Mo complex were tested as precatalysts in Suzuki-Miyaura coupling and epoxidation catalysis, respectively.

Full text of DOI:10.1021/ic400533u

Article
pubs.acs.org/IC
Exploring the Scope of a Novel Ligand Class: Synthesis and Catalytic
Examination of Metal Complexes with ‘Normal’ 1,2,3-Triazolylidene
Ligands
†
†
̈
Lars-Arne Schaper, Lilian Graser, Xuhui Wei, Rui Zhong, Karl Ofele, Alexander Po
Bettina Bechlars, Wolfgang A. Herrmann,* and Fritz E. Kuhn*
̈
thig, Mirza Cokoja,
̈
Chair of Inorganic Chemistry/Molecular Catalysis, Catalysis Research Center, Technische Universitat
̈
̈
Munchen,
Ernst-Otto-Fischer-Strasse 1, D-85747 Garching bei Munchen, Germany
̈
*
S Supporting Information
ABSTRACT: Using new ‘normal’-substituted 1,2,3-triazolylidene silver
compounds as starting materials allowed for preparation of a series of
molybdenum, ruthenium, rhodium, and palladium transition metal complexes
bound to the new 1,2,3-triazolylidene ligand system. In this work, the first
triazolylidene Mo compound is presented as well as the first structural
investigation of a silver complex with a monodentate 1,2,3-triazolylidene.
Furthermore, the triazolylidene Pd complex and the Mo complex were tested
as precatalysts in Suzuki−Miyaura coupling and epoxidation catalysis,
respectively.
INTRODUCTION
1,2,3-triazolylidene compounds featuring a 1,2,4-substitution
12
■
(
pattern. Synthesis of the corresponding precursor salts does
not follow the established Cu-catalyzed click chemistry routes
but proceeds via a ring-closing procedure based on isocyanides
After the isolobal analogy between N-heterocyclic carbenes
NHCs) and phosphines was discovered, research on
utilization of NHCs as ligands in transition metal complexes
experienced an enormous boost. The first report on the
catalytic activity of NHC−metal complexes had a great impact
on development of NHC-ligated homogeneous catalysts for a
1
13
2
and hydrazonoylchlorides (Scheme 1). Apart from the
3
Scheme 1. Traditional Access to 1,3,4-Substituted 1,2,3-
8
Triazolylidenes and Recently Described Access to Their
1,2,4-Substituted Relatives, ‘Normal’ 1,2,3-Triazolylidenes
plethora of organic reactions. To date, not only have extremely4
1
2
weak NHC donors been identified, i.e., tetrazolylidene ligands,
5
but also highly nucleophilic examples were synthesized. The
first evidence of alternative, abnormal binding modes of
imidazolylidene ligands led to an amplified interest in donor
6
strength variation of this ligand class.
A young but steadily growing family of rather strong NHC
sigma donors are 1,2,3-triazolylidenes, which are by definition
considered to reveal an ‘abnormal’ binding mode due to their
7
1
,3,4-substitution pattern. After their initial discovery by
Albrecht and co-workers and after isolation of the first free
stable carbene congeners of this NHC class by Bertrand’s
8
group, a plethora of new compounds equipped with 1,2,3-
unprecedented behavior of the first triazolylidene−ammonia
adduct, this underexplored carbene class also revealed high σ-
triazolylidenes was characterized, reflecting strong recent
9
interest of the scientific community. The growing significance
donor strength when examined in the [Ir(CO) ClL] system. In
of triazolylidene ligands may be justified by their great potential
2
10
addition to the higher σ electron donation, the unsymmetrical
substitution pattern of our triazolylidene ligand may even
leverage benefits in enantioselective catalysis.
for catalytic applications as well as by their interesting
11
zwitterionic behavior.
In spite of the growing significance of ‘abnormal’ 1,2,3-
triazolylidenes (exhibiting a 1,3,4-substitution pattern), exam-
ples of ‘normal’ congeners with a 1,2,4-substitution pattern are
extremely rare. Only recently, our group reported ‘normal’
Received: March 2, 2013
Published: May 6, 2013
©
2013 American Chemical Society
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Inorganic Chemistry
Article
This work aims at enlarging the family of new ‘normal’
triazolylidene carbene ligands by exploring the silver carbene
access route in order to yield new examples of metal complexes
with differently substituted ligands. Furthermore, the catalytic
potential of this ligand class is examined.
corresponding Ag complexes as viable carbene transfer
reagents, the precursor triazolium salts were treated with
17
Ag O according to Wang and Lin. Using methyl-substituted
2
A, synthesis of Ag compound A1 proceeds analogously to
frequently applied reaction conditions in reasonable yields
(
Scheme 2).
RESULTS AND DISCUSSION
The reactivity of the cyclohexyl-substituted triazolium salt B
■
Synthesis of Ag−NHC Complexes. Precursor salts
was different. The Ag complex could not be generated by
applying the same reaction conditions as for A1, and only
complex mixtures were isolated. After studying a variety of
solvents and conditions, the optimum reaction conditions could
be identified but only allowed for synthesis of B1 in rather low
yields. The red color of the reaction solution, however, is an
indication of triazolium ring decomposition. Accurate charac-
terization of both isolated compounds led to unambiguous
identification as carbene compounds. First evidence was
applied in this work were synthesized from hydrazonoyl-
1
4
15
16
chloride E1 and isocyanides E2 or E3 (Scheme 2). With
Scheme 2. Synthesis of Methyl- and Cyclohexyl-Substituted
Triazolium Chlorides A and B As Described by Moderhack
et al. and Subsequent Synthesis of Corresponding Silver
13
a
Complexes A1 and B1
1
provided by H NMR spectroscopy. The proton resonances,
which are characteristic for triazolium salts (proton bound to
C5, 11.25 ppm for A [CDCl ], 11.79 ppm for B [CDCl ]),
3
3
disappeared after reaction with silver oxide. Furthermore, the
signal for the methyl group bound to N1 was shifted upfield
from 4.78 ppm in A (CDCl ) to 4.29 ppm in A1 (CDCl ). In
3
3
addition, the resonance for the proton bound to the ipso-C of
the cyclohexyl moiety was shifted upfield from 4.52 ppm in B
(
CDCl ) to 4.36 ppm in B1 (CDCl ), with both shifts
3
3
indicating subtle changes in the electronic environments of the
heterocycles. In both cases, C{ H} NMR gave further hints
for carbene formation, as characteristic downfield signals were
a
Reaction conditions: (a) 1.00 equiv of NEt , RT, 24 h, MeCN. (b)
13
1
3
For A1 0.50 equiv of Ag O, RT, exclusion of light, 2 h, DCM. For B1:
1
MeCN:DCM/1:1.
2
.50 equiv of Ag O, molecular sieves, RT, exclusion of light, 18 h,
2
observed at 170.6 ppm (CDCl ) for A1 and 163.80 ppm
3
(
CDCl ) for B1. In general, observation of a carbene resonance
3
suggests nonfluxional behavior (i.e., no alternating between
the starting materials synthesized, the ensuing ring-closing
reaction allowed for isolation of 1-methyl-2-phenyl-4-tolyl-
mono- and bis(carbene) Ag species [AgCl(NHC)] and
+
−
18
[Ag(NHC) ] [AgCl ] ). However, for A1 we were not able
2
2
1
1
,2,3-triazolium chloride A or 1-cyclohexyl-2-phenyl-4-tolyl-
,2,3-triazolium chloride B. According to the literature,
to confirm preference for one of these structures by mass
spectroscopy, since under FAB conditions a mixture of A,
+
+
however, this method remains limited to generation of 1-
alkyl-substituted triazolium salts. In order to generate the
[Ag(Acarb)] , and [Ag(A ) ] was observed. The same
carb 2
behavior was observed for B1.
Figure 1. ORTEP representation of (a) observed triazolylidene chloroform adduct (thermal ellipsoids are shown at a probability level of 50%).
Selected bond distances [Å] and angles [deg]: C1−C17 1.551(2), N1−C1 1.464(2), N3−C2 1.288(2), N2−N3 1.376(2), N1−N2 1.456(2), N1−
C1−C2 102.8(1). Torsion angles [deg]: N3−N2−N1−N16 111.16(13), N2−N1−C1−C17 108.80(12). (b) Linear triazolylidene Ag complex A1
(
2
thermal ellipsoids are shown at a probability level of 50%). Selected bond distances [Angstroms] and angles [degrees]: Ag1−Cl1 2.335(1), Ag1−C1
.084(4), N1−N2 1.361(4), N1−C1 1.332(4), N2−N3 1.321(3), N3−C2 1.340(4); Cl1−Ag1−C1 172.5(1), N1−C1−C2 102.9(3). Torsion angle
[
degrees]: N3−N2−N1−C16 4.3(3).
6
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The first crystallization attempts of A1 revealed interesting
bent linear structure with an C1−Ag1−Cl1 angle of 172.5(1)°.
behavior of the compound in CHCl solution. Instead of
Compared to other linear gold chloride compounds presented
3
1
0b
isolating single crystals of A1, we obtained crystals of the
chloroform adduct of free carbene A (Figure 1). Although
similar examples for adducts of saturated NHCs and chloro-
by Crowley et al.
[177.2(1)°] and by our group
12
[177.1(2)°], this deviation from an ideal linear structure is
slightly more pronounced. The C1−Ag1 bond distance of
2.084(4) Å is elongated compared to the analogous gold
1
9
form exist, triazolylidene examples of these compounds have
not been described and structural representations were also not
published before. Isolation of this type of potential carbene
precursor from a silver carbene is certainly not cost efficient but
provides a new alternative to the known access routes. For
directed synthesis of this chloroform adduct, we heated a
CDCl3 solution of A1 in NMR scale experiments and
1
2
compound [1.997(6) Å]. Nevertheless, it is in line with the
row of imidazolylidene−AgCl compounds presented by Nolan
23
et al. [2.056−2.094 Å]. On the basis of the observations made
for A1, we assume that cyclohexyl congener B1 will also
primarily exist in the mono-carbene complex form, since its
increased steric demand will further reduce dimerization
tendencies.
1
monitored the reaction by H NMR. No single product could
be observed, but in turn we saw mixtures of at least five
different products. ESI-MS suggested that the chloroform
adduct was obtained in traces only (4% in Supporting
Information). However, we did not focus on further elaboration
of this synthesis.
Synthesis of Rh− and Mo−Triazolylidene Complexes
by Transmetalation. Rhodium complexes A2 and B2 were
obtained in excellent yields by application of the respective Ag
compound as carbene transfer reagent (Scheme 3). Reaction
with dimeric precursor [Rh(COD)Cl] proceeds smoothly to
2
The crystal structure underlines the nonaromatic bond
character within the chloroform adduct’s heterocycle [C1−N1
completion within 2 h at room temperature.
1
.464(2) Å, N3−C2 1.288(2) Å, N2−N3 1.376(2) Å, N1−N2
.456(2) Å]. The value for the N1−N2 bond is astonishingly
Scheme 3. Syntheses Starting from Silver Carbenes A1 and
B1, Yielding the Corresponding Triazolylidene Rh and Mo
1
20
a
long compared to the single bond in hydrazine but in line
Complexes A2, B2, and A3
with observations made for the ammonia adduct [N1−N2
12
1
.457(2) Å] published by our group. Furthermore, the other
values are in good accordance to the values obtained for the
earlier described ammonia adduct [C1−N1 1.483(2) Å, N3−
12
C2 1.287(2) Å, N2−N3 1.383(2) Å]. Here, the shortened
C1−N1 bond length in the chloroform adduct gives evidence
for the increased electron density at C1 because of the −CCl
3
substituent. The torsion angle observed for N3−N2−N1−C16
[
111.16(13)°] of the chloroform adduct supports this
observation when compared to N3−N2−N1−C16
[
131.20(15)°] of the ammonia adduct.
By avoiding chloroform as solvent, single crystals suitable for
a
X-ray diffraction were grown by slow evaporation of a saturated
dichloromethane (DCM) solution of A1. Figure 1 depicts the
crystal structure of A1, which is, to the best of our knowledge,
the first structural characterization of a mono-1,2,3-triazolyli-
dene-ligated Ag complex.
In contrast to many structurally characterized imidazolyli-
Reaction conditions: (a) For A1 and A2 0.50 equiv of [Rh(COD)-
2
Cl] , RT, exclusion of light, 2 h, DCM; (b) only for A1 1.00 equiv of
[
Mo(CO) CpCl], 45 °C, exclusion of light, 16 h, DCM.
3
9f
Since the compound was earlier described by isolation
12
following an alternative access route, we were able to identify
A2 by checking agreement with spectroscopic data. In the case
of B2, H NMR suggested emergence of a new carbene
complex by a notable downfield shift of one of the toluene aryl
signals from 8.10 ppm in A2 (CD Cl ) to 8.80 ppm in B2
(CDCl ). Additionally, in the C{ H} NMR spectrum, the
carbene carbon peak appears as a doublet at 181.1 ppm ( J
= 45.7 Hz), suggesting C1−Rh coordination. Single crystals of
B2 suitable for X-ray diffraction were grown by slow diffusion
of pentane into a saturated solution of the complex in
chloroform. An ORTEP representation of the obtained crystal
structure of B2 is shown in Figure 2. According to a C1−Rh1−
Cl1 angle of 89.25(5)°, the symmetry of B2 is close to an ideal
square-planar coordination of the Rh center. The torsion angle
of N3−N2−N1−C16 (179.42°) is extremely flat, indicating
even higher convergence to an ideal conjugated heterocyclic
ring system than in A1. The C1−Rh1 bond distance of
2.030(2) Å is very similar to the abnormal triazolylidene Rh
dene silver complexes, A1 does not form polymeric or cluster
2
f,9f,21
1
structures in the solid state.
.414(1) Å lies just within the sum of the van der Waals radii of
17,23
The Ag···Ag distance of
3
2
2
both ions, implying only weak argentophilic interactions.
The crystal structure provides strong evidence that at least at
room temperature the mono-carbene species [Ag(A )Cl] is
2
2
13
1
3
1
carb
Rh−C
preferred over [Ag(Acarb)2]+[AgCl ] or [Ag(A ) ] Cl .
−
+
−
2
carb 2
Furthermore, the crystallographic data of A1 corroborate the
expected ‘normal’ 1,2,3-triazolylidene structure, featuring a
1,2,4-substitution pattern. Selected bond distances between
heterocyclic ring atoms (see caption of Figure 1) are nearly
equidistant, suggesting a conjugated ring system. In comparison
to the triazolylidene chloroform adduct, the N1−N2 bond
distance is now considerably shortened [1.361(4) Å]. A
conjugated ring system is further evidenced by a very flat
C1−N1−N2−C16 torsion angle of 4.8(3)°, contrasting the
angle of 59.1° observed in the already published structure of the
12
8a
nonconjugated ammonia adduct. The angle N1−C1−C2 of
02.9(3)° around the carbene carbon and its closest ring
members corresponds well to that observed in the abnormal
complex presented by Albrecht et al. [2.027(6) Å].
Analogously, the Rh1−Cl1 bond length in our compound B2
[2.388(1) Å] resembles the bond length in Albrecht’s
triazolylidene Rh compound [2.372(1) Å]. The Rh−C
bond distance values observed for the abnormal bis(1,2,3-
1
8a
1
,2,3-triazolylidene Pd complex analyzed by Albrecht et al.
carbene
[N1−C1−C2 103.0(12)°]. Compound A1 reveals a slightly
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Figure 3. ORTEP representation of the crystal structure data of A3
(thermal ellipsoids are shown at a probability level of 50%). Selected
bond distances [Angstroms] and angles [degrees]: Mo1−C1 2.221(4),
Mo1−C22 1.965(4), Mo1−C23 1.945(4), Mo1−Cl1 2.519(1), C1−
Mo1−C22 74.61(17), C1−Mo1−C23 113.3(2). Bond lengths for A3
2
4
and IBzMo are within the limits of triple standard deviation; hence,
no absolute differences can be determined.
or less similar in both compounds (1.955 Å for A3 and 1.954 Å
for IBzMo, Figure 3).
Figure 2. ORTEP representation of the crystal structure data of B2
(
thermal ellipsoids are shown at a probability level of 50%). Selected
In the case of cyclohexyl-substituted silver triazolylidene B1,
no Mo complex could be isolated, although the same reaction
conditions were applied as in the case of A3. Formation of a
bond distances [Angstroms] and angles [degrees]: Rh1−C1 2.030(2),
Rh1−Cl1 2.3877(5); Cl1−Rh1−C1 89.25(5), N1−C1−C2 102.7(1).
Torsion angle [degrees]: N3−N2−N1−C16 179.4(2).
1
supposed product was observable in H NMR, with a
characteristic shift of the Cp signals. However, only complex
mixtures were obtained.
triazolylidene) Rh compound structurally characterized by
Bertrand and co-workers [2.071(4) and 2.068(4) Å] are slightly
elongated, certainly attributable to their rigid bis(carbene)
Epoxidation Catalysis. Use of complexes of the general
5
type [Mo(η -C R )O X] in the epoxidation of olefins is well
5
5
2
established and has been extensively studied throughout the last
9
e
26
ligand design.
Mo(CO) CpCl] was reacted with A1 and gave the air- and
three decades. Several groups showed that carbonyl
5
[
precursors of general formula [Mo(η -C R )(CO) X] can be
3
5
5
3
moisture-stable complex A3 in good yields (Scheme 3).
Complex A3 is highly soluble in polar solvents such as
acetonitrile, DCM, or chloroform as well as in less polar
solvents such as benzene and toluene. It even exhibits partial
solubility in diethyl ether, which proved to be an ideal solvent
for recrystallization. To the best of our knowledge, we isolated
the first example of a group 6 metal coordinated to a 1,2,3-
triazolylidene. In contrast to the earlier published access route
directly used as catalyst precursors in the homogeneous
27
epoxidation of olefins. For these reasons, complex A3 was
tested as catalyst for epoxidation of several internal and
terminal alkenes using tert-butyl hydroperoxide (TBHP, 5.5 M
decane solution) as oxidant. Using cyclooctene as substrate,
optimal reaction conditions regarding solvent, temperature,
oxidant, and catalyst loading were evaluated. Results of the
solvent and temperature screening are summarized in Table 1.
24
to related compounds, relatively mild reaction conditions
were applied (40 °C, 16 h). Formation of a new compound was
Table 1. Epoxidation of Cyclooctene Utilizing A3 As
Precatalyst
1
a
confirmed by H NMR with the shift of the Cp signals from
5
.66 (CDCl ) to 5.13 ppm (CD Cl ). Furthermore, in the
3 2 2
1
3
1
C{ H} NMR spectrum only two carbonyl signals with the
same intensity could be observed at 258.8 and 253.2 ppm as
well as a characteristic carbene signal at 185.8 ppm. Further
evidence was provided by the IR spectrum, which showed a
strong shift for the carbonyl resonances, from 1964 and 2056
25
c
yield [%] after 4 h (24 h)
solvent
25 °C
55 °C
−1
−1
cm in [Mo(CO) CpCl] to 1944 and 1848 cm in A3.
b
3
CHCl3
24 (28)
25 (29)
19 (22)
32 (53)
<10 (<10)
<10 (<10)
41 (85)
46 (88)
45 (91)
43 (96)
27 (35)
31 (36)
25 (36)
38 (52)
<10 (<10)
<10 (<10)
55 (85)
64 (88)
52 (91)
74 (96)
Comparison to the elevated IR resonances in the analogous
b
CH CN
3
dibenzylimidazolylidene compound [Mo(CO) CpCl(IBz)]
b
2
toluene
−1
(
IBzMo) [1953 and 1872 cm (KBr)] described by Hor
b
decane
2
4
and Zhao indicates that in A3 increased electron density is
present at the metal center, suggesting the presence of the
stronger electron-donating triazolylidene. Single crystals
suitable for X-ray diffraction could be grown at 5 °C from a
saturated solution of A3 in diethyl ether. Spectroscopic data
obtained allows for comparison to the structure of IBzMo
b
THF
b
MeOH
+
−
b
[
[
[
[
C mim] Cl
4
+
−
b
C mim] [BF ]
4
4
+
−
b
C mim] [NTf ]
4
2
+
−
b
C mim] [NTf ]
2
4
8
2
(
Figure 3). Interestingly, the differences in the carbene
a
ligands are not reflected in the Mo−C bond length
carbene
Effects of solvent and temperature variation on conversion are
b
[
2.221(4) Å in A3 vs 2.221(3) Å in IBzMo]. Also, the average
displayed. Reactions were carried out using a ratio for catalyst:sub-
c
bond lengths between Mo and both carbonyl ligands are more
strate:oxidant of 1:100:200. Yield determined by GC.
6
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Comparison of different reaction media showed that the
imidazolylidene-based systems [MoBr(CO) Cp(NHC)] re-
ported by Hor et al., we synthesized the analogous chloride
2
24
highest conversions can be obtained using ionic liquid
+
−
[
C mim] [NTf ] at 55 °C (C mim = 1-methyl-3-octylimida-
compound [Mo(CO) CpCl(IMes)] following published pro-
8
2
8
2
zolium; NTf = bis(trifluoromethanesulfonyl)imide. No con-
cedures. Catalytic yields were slightly higher for the
triazolylidene-based system in MeCN as well as in
2
version of epoxide could be observed, neither in THF nor in
+
−
methanol, reflecting the coordinative nature of these solvents,
[C mim] [NTf ] (see Supporting Information for synthetic
8 2
28
as observed earlier. Therefore, all further experiments were
and catalytic details).
+
−
carried out in [C mim] [NTf ] at 55 °C.
Apart from testing the catalytic performance of A3 in
epoxidation of cyclooctene as standard reaction, we were also
interested in finding its limitations in terms of substrate scope.
For that purpose, more challenging starting materials were
chosen for catalytic examination. Although conversions were
low compared to the more reactive cyclooctene, moderate
yields could be obtained for epoxidation of 1-octene, trans-ß-
8
2
In all organic solvents, except for decane, the red color of the
reaction solution disappeared after 20 min and a fine, yellow
24
precipitate formed. Hor et al. observed an analogous behavior
for imidazolylidene-based precatalysts. The precipitate was
1
found to be soluble in DMSO only and characterized by IR, H
1
NMR, and ESI-MS. In the H NMR the Cp resonance at 5.1
+
−
ppm disappeared and a set of peaks at 3.7, 7.3, and 8.6 ppm
could be observed, which most likely represents decomposition
products of the Cp and triazolium ligands. Strong absorptions
methylstyrene, and cis-stilbene (Table 2) in [C mim] [NTf ] .
8
2
Table 2. Epoxidation of Various Substrates Utilizing A3 As
−1
−1
in the IR spectrum around 950 cm and 800 cm indicate
a
Precatalyst
several MoO vibration bands. The negative mode of the ESI-
b
−y
substrate
1-octene
yield after 4 h (24 h) [%]
MS spectrum shows different [Mo O ] species, as observed in
n
x
Hor’s work. By combining these results it was not possible to
43 (65)
24 (32)
38 (54)
fully interpret the nature of the solid based on the available
trans-ß-methylstyrene
cis-stilbene
+
y−
data. However, it is most likely that a [triazolium] [Mo O ]
n
x
24
a
b
species forms, just as presumed earlier.
Comparison between catalysis in CH Cl and in the ionic
liquid (IL) [C mim] [NTf ] shows that the activity of the
Effects of solvent and temperature variation on conversion. All
2
2
reactions were carried out using a catalyst:substrate:oxidant ratio
1:100:200 at a reaction temperature of 55 °C; yields determined by
NMR.
+
−
8
2
formed catalyst species is higher in the IL. Kinetic evaluations
were undertaken for epoxidation of cyclooctene in MeCN and
+
−
[
C mim] [NTf ] (Figure 4). Here, acetonitrile was chosen as
8 2
In order to probe the convenience of catalyst recycling in an
ionic liquid-based system as well as to test the stability of the
catalytic species, recycling experiments were undertaken in
+
−
[
C mim] [NTf ] . For this purpose, after one catalytic run the
8 2
upper solvent phase containing the product was removed from
the catalyst/IL phase by addition of 5 mL of n-hexane and
removal of the upper phase by cannulation and subjected to
workup procedures and GC analysis (see the Experimental
Section). Subsequently, a further batch of substrate and
oxidants was added to the remaining IL phase. Evaluation of
these recycling experiments suggests high stability of the
catalytically active species, since the observed conversions
remained comparably stable for six subsequent 24 h runs
(
Figure 5).
Figure 4. Kinetic profile for conversion of cyclooctene with TBHP (in
decane) at 55 °C using complex A3 as the catalyst precursor. Results
for epoxidation catalysis using MeCN as solvent (solid gray symbol) or
+
−
[
C mim] [NTf ] (■).
8 2
solvent to allow for better comparison to the results obtained in
24
related investigations. As shown in Figure 4, conversion of
cyclooctene reaches its maximum at around 35% when using
MeCN as a solvent, while in the IL epoxidation continues and a
conversion of 96% after 24 h is reached. Apparently, the polar
environment of the ionic liquid supports the emerging active
catalyst species, since no precipitate of Mo salts appears, as
24
observed in MeCN.
Although compound A3 shows moderate catalytic activity
only, it still appears to be slightly more active than the related
ansa-bridged Cp-functionalized NHC complexes. In order to
compare the catalytic activity of A3 with the related
Figure 5. Epoxide yield for 6 cycles after 24 h reaction time applying
A3 as catalyst. Cyclooctene was used as substrate and
29
+
−
[C mim] [NTf ] as solvent at a reaction temperature of 55 °C.
8
2
6
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Inorganic Chemistry
Article
9
c
The preceding paragraphs showed that the catalytically active
species derived from compound A3 has moderate catalytic
activity in a variety of olefin substrates as well as in recycling
experiments. However, due to the observed precipitate
formation, presumably a catalytically active Mo−polyoxo salt,
it seems that system A3 is not stable under oxidative
conditions, and further examination will be necessary to reveal
the intrinsically active catalyst system. Nevertheless, it is
important to continue the search for more stable NHC-based
oxidation catalyst systems, which are less prone to decom-
position, as these could be capable of controlling the
stereoselectivity in epoxidation products.
Synthesis of Ru and Pd Complexes Bearing 1,2,3-
Triazolylidene Ligands. Since the cyclohexyl triazolylidene
Ag complex B1 seems to exhibit only limited applicability in
carbene transfer reactions, further examinations focused on
methyl-substituted A1. As to date no examples for group 8 and
group 10 complexes bound to normal 1,2,3-triazolylidene
ligands are known, we tested the carbene transfer reaction with
Å]. The Pd−Cl bond length of the nonbonding Cl [Pd1−Cl1
2.2781(7) Å] is slightly shortened in comparison to Cl-bridged
saturated NHC homo-bimetallic Pd compound reported by
30
Chen, Liu, and co-workers [2.298(1) Å]. Since the obtained
yield in the synthesis of the observed bimetallic Pd species was
very low and rarely reproducible, we applied a different Pd
precursor for subsequent synthetic attempts.
The existence of compound A4 was quickly confirmed by
identification of a new set of signals for the allyl ligand via H
1
NMR spectroscopy as well as a characteristic carbene signal at
174.8 ppm (CDCl ). Furthermore, crystals suitable for X-ray
3
diffraction were grown by slow diffusion of pentane into a
saturated solution of A4 in chloroform. The structure of
complex A4 could be confirmed (Figure 4b), but unfortunately,
the comparatively low quality of the crystal prevents further
discussion of structural parameters. Successful synthesis of the
Ru complex A5 was evidenced by characteristic new signals for
1
the p-cymene ligand in the H NMR and a distinct carbene
signal in the 13C{ H} NMR spectrum (173.4 ppm in CDCl
1
).
3
A1 and common dimeric metal complexes [Pd(allyl)Cl] and
Further evidence was provided by elemental analysis. In an
attempt to analyze the structure of A5 by means of X-ray
crystallography, only crystals of the metal precursor [Ru-
2
[
Ru(p-cymene)Cl ] . Reactions with both precursors were
2 2
conducted at room temperature and allowed for facile isolation
of triazolylidene-substituted Pd−allyl complex A4 and the
related triazolylidene cymene Ru dichloride compound A5 in
good yields (Scheme 4). Both compounds exhibit good stability
to air and moisture.
(cymene)Cl ] were found, indicating reduced stability of A5
2 2
dissolved in chloroform under ambient light for days, as
observed for the Ag compound A1.
Suzuki−Miyaura Coupling Catalysis. The catalytic
activity of Pd precatalyst A4 in C−C cross-coupling reactions
was examined. A standard method to test the potential of Pd
catalysts is the Suzuki−Miyaura reaction. Accordingly, the rare
reports dealing with catalytic examinations of new ‘abnormal’
Scheme 4. Synthesis of New Pd and Ru Complexes with
a
Methyl-Substituted Triazolylidene Ligands
1
,2,3-triazolylidene Pd complexes explore their catalytic ability
31 9j
in this type of coupling reaction. Albrecht et al. synthesized
and tested 1,2,3-triazolylidene-substituted PEPPSI-type Pd
catalysts, while Fukuzawa et al. examined Pd allyl, crotyl,
9j
and cinnamyl compounds bound to ‘abnormal’ 1,2,3-
31b
triazolylidenes,
the latter covering catalysts very similar to
our Pd precatalyst A4.
When testing Pd complexes in Suzuki−Miyaura coupling
catalysis, it is certainly essential to consider earlier findings of
Pd nanoparticles or traces of metallic Pd in the used basic salts
being able to catalyze the reaction between arylbromides and
a
Reaction conditions: (a) 0.25 equiv of [Pd(OAc) ], −78 °C to RT,
2
1
6 h, THF; (b) 0.50 equiv of [Pd(allyl)Cl] , RT, exclusion of light, 16
32
2
boronic acids. In order to find optimum reaction conditions,
h, DCM; (c) 0.50 equiv of [RuCl (p-cymene)] , RT, exclusion of light,
2
2
2
we undertook preliminary catalytic examinations with 4-
bromoacetophenone as substrate. However, yields above 99%
were common in this reaction and thwarted distinction
between subtle improvements in yields through variation of
base or solvent. To allow for better distinction, we chose 4-
chloroacetophenone as substrate to find the best reaction
conditions (see Supporting Information).
With the supposedly ideal reaction conditions found, we
decided to shift our focus on using the more reactive
arylbromides as substrates for Suzuki−Miyaura coupling
under mild conditions. Table 3 provides an overview of the
tested substrates and obtained yields. 4-Bromoacetophenone
gave quantitative yields under the tested conditions and allowed
for a reduced reaction time of 12 h (Table 3, entry 7).
However, apart from this rather reactive congener, also less
reactive arylbromide substrates were tested and gave good to
quantitative yields within 12 h at a reaction temperature of 65
°C. In this comparison of substrates, lowest yields were
obtained for mesityl bromide (22%) and 4-bromoanisole (67%)
(Table 3, entries 3 and 4). The appearance of Pd nanoparticles
was tested by poisoning experiments using mercury (entry 8).
h, DCM.
In order to examine further access routes to metal complexes
with normal triazolylidenes, we tested reaction of triazolium
precursor A and [Pd(OAc) ], one of the most common paths
2
to generating Pd NHC complexes (Scheme 4). However,
published procedures at elevated temperatures did not yield the
desired product. Instead, a reaction protocol starting at −78 °C
had to be applied in order to generate a Cl-bridged homo-
bimetallic Pd triazolylidene complex. Single crystals of the Cl-
bridged homo-bimetallic Pd complex depicted in Scheme 4
could be grown by slow diffusion of pentane into a saturated
CHCl solution of the complex. An ORTEP representation of
3
the structural data obtained for this compound is depicted in
Figure 6a. The observed angles for Cl1−Pd1−C1 [88.15(6)°]
and Cl2−Pd1−C1 [91.97(6)°] prove that the Pd compound
exhibits an almost ideal quadratic planar structure. The Pd
carbene bond [C1−Pd1 1.963(2) Å] is in good accordance
with the data provided for the row of I-bridged Pd compounds
presented by Albrecht et al. [between 1.96(3) and 1.977(13)
6
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Inorganic Chemistry
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Figure 6. ORTEP representation (thermal ellipsoids are shown at a probability level of 50%) of the structure of (a) earlier described Cl-bridged
homo-bimetallic Pd complex. Selected bond distances [Å] and angles [deg]: C1−Pd1 1.963(2), Pd1−Cl1 2.278(1), Pd1−Cl2 2.334(1), Cl1−Pd1−
C1 88.15(6), Cl2−Pd1−C1 91.97(6). (b) Compound A4. Peaks of residual electron density could not be assigned adequately; therefore, no
geometrical parameters are discussed.
As a result, severely reduced yields were detected, suggesting
that the catalytically active species were at least in part Pd
nanoparticles and A4 exhibiting limited stability.
CONCLUSION
■
Hitherto underexplored ‘normal’ triazolylidenes are viable
ligands for transition metal complexes. Synthesis of new
metal compounds via the convenient silver carbene trans-
metalation route is possible and allows complex isolation in
high yields. Applications of newly isolated triazolylidene
compounds A3 (Mo) and A4 (Pd) in catalysis were examined,
for example, epoxidation catalysis of alkenes and Suzuki−
Miyaura coupling of aryl bromides and chlorides.
Reaction with chloride substrates gave a maximum of 56%
yield when using the comparably more reactive 4-chloroaceto-
phenone as substrate and using prolonged reaction times (even
a long time experiment over 48 h was conducted).
1
Furthermore, H NMR proved that unidentifiable side products
(
8%) were obtained in the reaction as well. On the basis of the
observed low yields in the examinations utilizing 4-
chloroacetophenone as substrate, we estimate that other, less
reactive, aryl chloride substrates would give even lower yields.
On that account, further examinations with these substrates
were not undertaken.
In the case of Pd-promoted Suzuki−Miyaura CC-coupling
catalysis, stability issues prevent more successful catalytic
application. Here, our examinations highlighted the drawbacks
of the present N1-alkyl ligand design. It is highly likely that a
triaryl substitution pattern will help to improve ligand stability
of ‘normal’ 1,2,3-triazolylidenes as it was described for
abnormal triazolylidenes in the literature. For this reason,
current research efforts in our laboratories focus on variation of
these novel ligands’ substitution pattern in order to reveal their
full synthetic and catalytic potential.
The results of our initial evaluations of a Pd complex with
normal 1,2,3-triazolylidene ligands in Suzuki−Miyaura coupling
catalysis allow for classification of A4 as a mediocre performing
catalyst. Observed formation of Pd nanoparticles and
incomplete conversion of the tested aryl chloride substrate
provides evidence for a limited stability of A4 under catalytic
conditions. Therefore, results obtained are likely to reflect the
EXPERIMENTAL SECTION
■
9j
observations made by Albrecht and co-workers. We also
observed that the catalytic performance of our compound in
the Suzuki−Miyaura coupling of aryl chlorides is closely related
to its stability under catalytic conditions. Accordingly, alkyl
substituents at the N1 position of the heterocyclic ligands are
not likely to improve stability, and therefore, they should be
excluded when designing new ligand generations. The report of
Materials. All preparations and manipulations were performed
under argon atmosphere using standard Schlenk techniques or in a
glovebox. All glassware was dried in an oven at 80 °C overnight and
further flame dried in vacuo before use. THF was dried over sodium/
benzophenone with subsequent distillation. All other solvents were
dried with a MBraun MB SPS purification system and degassed via
repeated freeze−pump−thaw cycles. All commercial compounds were
used without further purification. 1-Methyl-2-phenyl-4-p-tolyl-1,2,3-
triazolium-chloride and 1-cyclohexyl-2-phenyl-4-p-tolyl-1,2,3-triazo-
lium-chloride were prepared following procedures described in the
3
1b
Fukuzawa et al. provided evidence that a substitution pattern
containing aryl substituents at positions 1 and 4 of the
heterocyclic ligand drastically improves performance. This
1
3
literature.
1
13
1
10f
Instruments. H and C{ H} NMR spectra were recorded on a
observation was generally described by Bertrand and Grubbs.
4
00 MHz Bruker Avance III or a 400 MHz Bruker Avance DPX
Consequently, changing our substitution pattern to a 1,2,4-
triaryl substitution in combination with replacing the Pd-bound
allyl ligand to a cinnamyl ligand are both measures likely to
bring great improvements in terms of stability and hence
performance for prospective Pd catalysts.
spectrometer at a temperature of 298 K if not indicated otherwise.
Spectra were referenced in parts per million (ppm) with an internal
standard using the residual solvent shifts. Abbreviations for signal
multiplicities are singlet (s), doublet (d), triplet (t), quartet (q),
multiplet (m), broad (br). IR spectra were recorded on a Varian 670
6
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weighting scheme. Neutral atom scattering factors for all atoms and
anomalous dispersion corrections for the non-hydrogen atoms were
Table 3. Substrate Scope of A4 in Suzuki−Miyaura Coupling
Catalysis
3
7
taken from the International Tables for Crystallography. Images of the
3
8
crystal structures were generated by PLATON.
Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication numbers
CCDC-918410 (chloroform adduct), CCDC-918406 (A1), CCDC-
9
18408 (B2), CCDC-918407 (A3), and CCDC-918409 (bridged Pd
complex). Copies of the data can be obtained free of charge on
application to the CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K.
(
fax (+44)1223-336-033; e-mail deposit@ccdc.cam.ac.uk).
(
1-Methyl-2-phenyl-4-tolyl-1,2,3-triazol-5-ylidenyl)silver(I)
Chloride (A1). Under argon atmosphere, 20 mL of anhydrous
dichloromethane were added to a Schlenk tube charged with 1-methyl-
2
-phenyl-4-p-tolyl-1,2,3-triazolium chloride (0.500 g, 1.75 mmol, 1.00
equiv) and silver(I) oxide (0.203 g, 0.880 mmol, 0.50 equiv). The
reaction solution was stirred at room temperature under exclusion of
light for 2 h. Then, the mixture was filtered through Celite to give a
pale yellow solution. The solution was concentrated, and diethyl ether
was added to afford a white precipitate. After filtration, a white solid
(
0.42 g, 63.0%) was obtained.
H NMR (400 MHz, CDCl ) δ (ppm): 8.04 (d, J = 8.2 Hz, 2H,
1
3
3
HH
3
CH ), 7.72−7.64 (m, 3H, CH ), 7.59 (dd, J = 7.9, 1.8 Hz, 2H,
CH ), 7.20 (d, J = 8.0 Hz, 2H, CH ), 4.29 (s, 3H, NCH ), 2.37 (s,
3
ar
ar
HH
3
ar
HH
ar
3
13
1
H, CCH3). C{ H} NMR (101 MHz, CDCl ) δ (ppm): 170.6 (Ag−
3
C ), 157.0 (C ), 139.6, 135.5, 132.0, 130.4, 129.7, 127.7, 126.7, 126.5
trz
trz
(
all C ), 42.6 (NCH ), 24.5 (CCH ). MS (FAB) m/z (%): 355.8
ar 3 3
+
+
+
[
M] . MS (ESI) m/z (%): 356 [M] , 250.2 [Trz + H] . Anal. Calcd
for C H AgClN (391.00): C, 48.94; H, 3.85; N, 10.70; Cl, 9.03.
16
15
3
Found: C, 48.99; H, 3.87; N, 10.72; Cl, 8.5.
1-Cyclohexyl-2-phenyl-4-tolyl-1,2,3-triazol-5-ylidenyl)-
(
silver(I) Chloride (B1). Under argon atmosphere, 15 mL of a 1:1
mixture of acetonitrile and dichloromethane (anhydrous) were added
to a Schlenk tube charged with 1-cyclohexyl-2-phenyl-4-p-tolyl-1,2,3-
triazolium-chloride (0.096 g, 0.30 mmol, 1.00 equiv), silver(I) oxide
(
0.104 g, 0.45 mmol, 1.50 equiv), and 3 Å molecular sieves. The
a
Reaction conditions: 1.0 mmol of aryl halide, 2.0 mmol of arylboronic
reaction solution was stirred at room temperature under exclusion of
light for 18 h. After filtration, the brown solution was concentrated and
8 mL of diethyl ether was added to give a brown precipitate. The crude
product was washed with diethyl ether twice to obtain an off-white
solid (0.15 g, 25.0%).
b
acid, 2.0 mmol of Cs CO , 1 mol % A4, 65 °C, 12 h. NMR yields,
average of two runs. Isolated yield. 2 mol % A4 was used, 24 h. 2.0
mmol of Cs CO , 1.5 mL of dioxane, 1 mol % A4, 100 °C, 24 h. Same
reaction conditions as in entry 4, except that 3 g of mercury was added
after 5 min of reaction time.
2
3
c
d
e
f
2
3
1
3
H NMR (400 MHz, CD Cl ) δ (ppm): 8.10 (d, J = 8.1 Hz, 2H,
2
2
HH
3
CH ), 7.82−7.63 (m, 3H, CH ), 7.49 (d, J = 7.0 Hz, 2H, CHar),
7
NCH), 2.48 (pseudo-qd, JHH = 13.1, JHH = 3.7 Hz, 2H, CCH
2.41(s, 3H, CCH ), 2.09 (d, J = 11.3 Hz, 2H, CCH ), 1.99 (m, 2H,
ar
ar
HH
3
3
.31 (d, J = 8.0 Hz, 2H, CH ), 4.38 (tt, J = 11.6, 3.7 Hz, 1H,
HH ar HH
2
3
FT-IR Spectrometer. ESI-HRMS analysis was performed on a Thermo
Scientific LTQ Orbitrap XL by Thermo Fisher Scientific. Elemental
analyses were conducted by the microanalytical laboratory of the
Technical University of Munich.
Single-Crystal X-ray Structure Determinations. Data were
collected on an X-ray single-crystal diffractometer equipped with a
CCD detector (Bruker APEX II, κ-CCD), a fine focus sealed tube with
Mo Kα radiation (λ = 0.71073 Å), and a graphite monochromator
using the APEX 2 software package. Measurements were performed
on a single crystal coated with perfluorinated ether. The crystal was
fixed on the top of a glass fiber and transferred to the diffractometer.
The crystal was frozen under a stream of cold nitrogen. A matrix scan
was used to determine the initial lattice parameters. Reflections were
merged and corrected for Lorenz and polarization effects, scan speed,
2
),
3
3
HH
2
3
CCH ), 1.69 (d, J = 13.0 Hz, 1H, CCH ), 1.40−1.19 (m, 3H,
2
HH
2
13
1
CCH2). C{ H} NMR (101 MHz, CD Cl ) δ (ppm): 163.8 (Ag−
2
2
C ), 157.8 (C ), 140.3, 135.4, 132.7, 131.0, 130.2, 129.0, 127.4,
trz trz
127.3, (all C ), 62.5 (NCH), 35.86 (NCH ), 26.07 (CCH ), 25.2
ar
3
2
+
(CCH ), 21.6 (CCH ). MS (ESI) m/z (%): 742.5 [M − Cl + Trz] ,
2
3
+
+
423.8 [M − Cl] , 318.0 [Trz + H] .
33
(1-Methyl-2-phenyl-4-tolyl-1,2,3-triazol-5-ylidenyl)rhodium-
(I) Chloride (A2). Under argon atmosphere, 3 mL of anhydrous
dichloromethane were added as solvent to a Schlenk tube charged with
A1 (0.0500 g, 0.127 mmol, 2.00 equiv) and [Rh(COD)Cl] (0.0316 g,
2
0.064 mmol, 1.00 equiv). The reaction solution was stirred at room
temperature under exclusion of light for 2 h. Then the reaction
mixture was filtered to give an orange solution. The solution was
concentrated, and 5 mL of pentane was added to give a yellow
precipitate. The crude product was washed twice with pentane to
obtain a yellow solid (0.0586 g, 93.0%).
34
and background using SAINT. Absorption corrections, including
odd- and even-ordered spherical harmonics, were performed using
SADABS. Space group assignments were based upon systematic
34
absences, E statistics, and successful refinement of the structures, Table
12
4
. Structures were solved by direct methods with the aid of successive
Obtained data are in accordance with literature values.
33
difference Fourier maps and refined against all data using SHELXL-
(1-Cyclohexyl-2-phenyl-4-tolyl-1,2,3-triazol-5-ylidenyl)-
rhodium(I) Chloride (B2). Under argon atmosphere, 3 mL of
anhydrous dichloromethane were added to a Schlenk tube charged
with B1 (0.0500 g, 0.109 mmol, 2.00 equiv) and [Rh(COD)Cl]2
(0.0268 g, 0.054 mmol, 1.00 equiv). The reaction solution was stirred
at room temperature under exclusion of light for 2 h. Then the
35
36
9
7 in conjunction with SHELXL. If not mentioned otherwise, non-
hydrogen atoms were refined with anisotropic displacement
parameters. Hydrogen atoms were placed in ideal positions using
the SHELXL riding model. Full-matrix least-squares refinements were
2
2
c
2
35
carried out by minimizing Σw(Fo − F ) with the SHELXL-97
6
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Article
Table 4. Crystallographic Data for Compounds: CHCl Adduct, A1, A3, B2, and the μ-Chloro-Bridged Pd Complex
3
CHCl adduct
A1
A3
B2
μ-Cl Pd complex
3
formula
fw
C H Cl N
C H AgClN3
C H ClMoN O
C H ClN Rh
C H Cl N Pd
2
1
7
16
3
3
16 15
23 20
3
2
29 35
3
32 30
4
6
368.68
392.63
501.81
563.96
853.22
color/habit
pale yellow/fragment
0.20 × 0.20 × 0.20
orthorhombic
colorless/fragment
0.04 × 0.05 × 0.52
triclinic
orange-red/fragment
0.06 × 0.16 × 0.58
monoclinic
red/fragment
orange/fragment
0.04 × 0.13 × 0.25
monoclinic
3
cryst dimens (mm )
0.05 × 0.20 × 0.20
monoclinic
cryst syst
space group
a, Å
Pca2 (no.29)
P1 (no. 2)
5.9205(2)
12.1256(6)
12.4065(6)
115.183(2)
101.493(2)
90.792(2)
784.95(6)
2
P2 /c (no. 14)
1
P2 /c (no. 14)
1
P2 /n (no. 14)
1
1
20.6804(9)
8.2500(4)
10.0422(4)
90
14.9104(5)
11.4808(4)
14.0996(5)
90
10.1793(3)
19.8096(7)
13.1890(5)
90
11.9638(10)
11.5099(11)
24.084(2)
90
b, Å
c, Å
α, deg
β, deg
γ, deg
V, Å3
Z
90
115.127(1)
90
98.846(2)
90
95.061(4)
90
90
1713.33(13)
4
2185.21(13)
4
2627.90(16)
4
3303.5(5)
4
T, K
173
123
123
173
173
−
3
Dcalcd, g cm
μ, mm−
1.429
1.661
1.525
1.426
1.715
1
0.537
1.450
0.747
0.774
1.445
F(000)
760
392
1016
1168
1696
θ range, deg
1.97 − 25.32
−24 − 16, ± 9, ± 12
32 306
1.86 − 25.46
±7, ± 14; ± 14
16 030
1.51 − 25.38
±17, ± 13; −13 − 16
22 712
2.02 − 26.34
±12,-24 − 22;-15 − 16
50 409
1.70 − 25.35
±14, ± 13; ± 28
70 917
index ranges (h, k, l)
no. of reflns collected
no. of indep reflns/Rint
no. of obsd reflns (I > 2σ(I))
no. of data/restraints/params
3126/0.0251
3070
2872/0.0485
2302
3974/0.0630
2845
5347/0.0369
4683
6019/0.0359
5352
3126/1/272
0.0180/0.0482
0.0188/0.0489
1.084
2872/0/192
0.0297/0.0528
0.0494/0.0582
0.976
3974/0/273
0.0356/0.0671
0.0685/0.0774
1.021
5347/0/308
0.0220/0.0623
0.0288/0.0665
0.989
6019/0/401
0.0194/0.0451
0.0245/0.0477
1.050
a
R1/wR2 (I > 2σ(I))
a
R1/wR2 (all data)
GOF (on F2)
a
largest diff peak and hole (e Å−3)
+0.16/−0.16
+0.43/−0.38
+0.62/−0.64
+0.40/−0.40
+0.30/−0.33
a
R1 = Σ(∥F | − |F ∥)/Σ|F |; wR2 = {Σ[w(F − F ) ]/Σ[w(F ) ]} ; GOF = {Σ[w(Fo − F ) ]/(n − p)}1/2.
2
o
2
c
2
2
o
2
1/2
2
2 2
c
o
c
o
1
3
1
reaction mixture was filtered to give an orange solution. The solution
was concentrated, and pentane was added to give a red precipitate.
The crude product was washed twice with pentane to obtain a dark red
solid (0.0473 g, 77.0%).
3H, NCH ), 2.46 (s, 3H, CCH ). C{ H} NMR (101 MHz, CD Cl )
3 3 2 2
δ (ppm): 258.8 (CO), 253.2 (CO), 185.8 (Mo−C ), 159.4 (C ),
140.1, 136.4, 131.9, 131.4, 130.6, 130.5, 129.6, 126.5 (all C ), 96.48
(C ), 41.6 (NCH ), 21.72 (CCH3). IR (solid): ν = 1943, 1848
(ν(CO)) cm . MS (ESI) m/z (%): 468.0 [M − Cl] . Anal. Calcd for
C H ClMoN O (503.0): C, 55.05; H, 4.02; N, 8.37. Found: C,
trz
trz
ar
Cp
3
1
3
−1
+
H NMR (400 MHz, CDCl ) δ (ppm): 8.80 (d, J = 8.1 Hz, 2H,
3
HH
3
CH ), 7.68−7.53 (m, 3H, CH ), 7.39 (d, J = 7.3 Hz, 2H, CHar),
ar
ar
HH
23 20
3
2
3
3
7
.32 (d, J = 8.0 Hz, 2H, CH ), 5.44 (tt, J = 12.1, 3.2 Hz, 1H,
55.03; H, 4.27; N, 8.30.
HH
ar
HH
CCH), 5.24−4.98 (m, 2H, COD), 3.20−3.10 (m, 1H, COD), 3.07−
(1-Methyl-2-phenyl-4-tolyl-1,2,3-triazolylidenyl)-
allylpalladium(II) Chloride (A4). Under argon atmosphere, 5 mL of
anhydrous dichloromethane were added as solvent to allylpalladium-
(II) chloride (0.070 g, 0.191 mmol, 1.00 equiv) and A1 (0.150 g, 0.383
mmol, 2.00 equiv) in a Schlenk tube. The reaction was stirred at room
temperature under exclusion of light for 16 h. The reaction mixture
was filter through cannula with the Schlenk technique. All volatiles
were evaporated, and the residue was washed with hexane. An off-
white solid (0.060 g, 67.9%) was obtained after removal of hexane.
2
3
3
.00 (m, 1H, COD), 2.70 (pseudo-qd, J = 12.3, J = 3.5 Hz, 1H,
HH HH
2
3
CCH ), 2.54 (pseudo-qd, J = 12.5, J = 3.6 Hz, 1H, CCH ), 2.43
2
HH
HH
2
2
3
(
=
(
s, 3H, CCH ), 2.42−2.22 (m, 4H, COD), 2.13 (tdd, J = 15.8, J
3
HH
HH
11.0, 8.1 Hz, 2H, COD), 2.04−1.81 (m, 5H, COD and CCH ), 1.70
2
3
1
3
1
t, J = 13.0 Hz, 2H, COD), 1.52−1.09 (m, 4H, CCH ). C{ H}
HH
2
NMR (101 MHz, CDCl ) δ (ppm): 181.1 (Rh−C ), 155.7 (C ),
3
trz
trz
1
9
3
(
[
38.8 (C ), 137.4, 131.7, 129.9, 129.0, 128.9, 128.8, 127.8 (all C ),
t
r
z
a
r
6.7, 96.6, 96.5, 96.4 (all CCOD), 71.5, 71.3, 67.9, 67.8, 66.2, 66.0, 34.2,
3.3, 32.7, 32.6, 29.8, 28.7, 26.4, 26.3, 25.2, 21.6, 15.4. MS (FAB) m/z
1
3
H NMR (400 MHz, CDCl
) δ (ppm): 8.18 (d, JHH = 8.1 Hz, 2H,
3
+
+
+
3
%): 562.4 [M] , 527.5 [M − Cl] , 418.5 [M − COD − Cl] , 317.8
CHar), 7.78−7.60 (m, 3H, CHar), 7.53 (dd, JHH = 6.4, 3.0 Hz, 2H,
+
+
3
Trz + H] . MS (ESI) m/z (%): 528.0 [M − Cl] , 419.2 [M − Cl −
CHar), 7.23 (d, JHH = 8.0 Hz, 2H, CHar), 5.35 (m, 1H, allyl), 4.39 (s,
+
3
3
COD] . Anal. Calcd for C H RhClN (563.16): C, 61.76; H, 6.26;
3H, NCH
3
), 4.36 (d, JHH = 7.5 Hz, 1H, allyl), 3.38 (d, JHH = 13.6 Hz,
29
35
3
3
N, 7.45. Found: C, 61.89; H, 6.27; N, 7.33.
1H, allyl), 3.16 (d, JHH = 6.4 Hz, 1H, allyl), 2.39 (s, 3H, CCH
3
), 2.36
(d, JHH = 12.0 Hz, 1H, allyl). C{ H} NMR (101 MHz, CDCl ) δ
(ppm): 174.8 (Pd−C ), 156.9 (C ), 139.1, 135.8, 131.5, 130.3,
3
13
1
(
1-Methyl-2-phenyl-4-tolyl-1,2,3-triazol-5-ylidenyl)-
3
molybdenum Dicarbonylcyclopentadienyl Chloride (A3).
Under argon atmosphere, 20 mL of anhydrous dichloromethane
were added to a mixture of A1 (0.300 g, 0.764 mmol, 1.00 equiv) and
trz
trz
129.2, 128.7, 127.9, 126.4 (all C ), 115.1 (CCH ), 72.8(CCH), 50.3
ar
2
(CCH ), 41.0 (NCH ), 21.5 (CCH ). MS (FAB) m/z (%): 645.1 [M
2
3
3
+
+
+
[
Mo(CO) CpCl] (0.215 g, 0.764 mmol, 1.00 equiv) inside a Schlenk
− Cl + Trz] , 436.8 [M − Pd + 2allyl] , 395.0 [M − Cl] , 250.3
3
+
+
+
flask. The reaction was heated to reflux for 16 h under exclusion of
light. Then the reaction mixture was passed through Celite to give a
dark red solution. After concentrating the solution, hexane was added
to precipitate the crude product. A red solid (0.254 g, 63.9%) was
obtained by recrystallization from dichloromethane and hexane.
[Trz] . MS (ESI) m/z (%): 644.2 [M − Cl + Trz] , 395.5 [M − Cl] ,
+
249.9 [Trz + H] . Anal. Calcd for C H ClN Pd: C, 52.79; H, 4.66;
19
20
3
N, 9.72; Cl, 8.20. Found: C, 52.39; H, 4.74; N, 9.63; Cl, 8.7.
p-Cymene-(1-methyl-2-phenyl-4-tolyl-1,2,3-triazolylidenyl)-
ruthenium(II) Dichloride (A5). Under argon atmosphere, 5 mL of
1
H NMR (400 MHz, CD Cl ) δ (ppm): 7.67−7.59 (m, 3H, CH ),
anhydrous dichloromethane were added to a mixture of [RuCl (p-
2
2
ar
2
3
3
7
.51 (dd, J = 6.8, 2.9 Hz, 2H, CH ), 7.43 (d, J = 8.0 Hz, 2H,
CH ), 7.35 (d, J = 7.9 Hz, 2H, CH ), 5.13 (s, 5H, H ), 4.03 (s,
cymene)] (0.078 g, 0.127 mmol, 1.00 equiv) and A1 (0.100 g, 0.255
HH
ar
HH
2
3
mmol, 2.00 equiv) in a Schlenk tube. The reaction was stirred at room
ar
HH
ar
CP
6
150
dx.doi.org/10.1021/ic400533u | Inorg. Chem. 2013, 52, 6142−6152

Inorganic Chemistry
Article
temperature under exclusion of light for 2 h. The reaction mixture was
filtered through silica gel, and the complex was washed down with
acetone. Removal of acetone afforded the crude product. Then,
acetone was used for recrystallization to obtain a dark red solid (0.097
g, 68.7%).
was extracted by DCM (2 × 5 mL) and filtered. The solvent of filtrate
was removed in a rotary evaporator (40 °C, 100 mbar), and the crude
product was directly used for chromatographic separation or dissolved
by CDCl for 1H NMR analysis.
3
1
3
H NMR (400 MHz, CDCl ) δ (ppm): 7.98 (d, J = 8.0 Hz, 2H,
ASSOCIATED CONTENT
Supporting Information
Tables of crystal parameters, atomic coordinates, bond lengths,
3
HH
■
3
CH ), 7.69−7.58 (m, 3H, CH ), 7.52 (d, J
= 5.2 Hz, 2H, CHar),
ar
ar
HH
S
*
3
7
.25 (d, 2H, CH ), 5.20 (d, J = 5.8 Hz, 2H, cymene-CH), 4.93 (d,
ar HH
3
3
JHH = 5.7 Hz, 2H, cymene-CH), 4.41 (s, 3H, NCH ), 2.75 [dt, J
=
HH
3
bond angles, and thermal displacement parameters for A1, A3,
1
4.2, 7.2 Hz, 1H, cymene-C(CH ) ], 2.42 (s, 3H, CCH ), 2.01 (s, 3H,
3 2 3
3
13
1
B2, CHCl adduct, and the bridged Pd complex in .cif format as
3
CCH ), 1.18 [d, J = 6.9 Hz, 6H, cymene-C(CH ) ]. C{ H} NMR
3
HH
3 2
well as data for A4, for which the residual electron density is
too high for further analysis; additional synthetic and catalytic
experimental details, NMR spectra, as well as detailed
crystallographic information. This material is available free of
charge via the Internet at http://pubs.acs.org.
101 MHz, CDCl ) δ (ppm): 173.4 (Ru−C ), 160.75 (C ), 138.9,
3
trz
trz
35.8, 131.5, 130.8, 130.2, 130.1, 128.6, 126.6 (all C ), 106.6, 100.3,
ar
6.1, 84.3 (all Ccym), 42.2 (NCH ), 31.0 [C(CH ) ], 22.7 [2C,
3
3 2
3
2
3
3
+
+
+
+
+
+
HCl] . Anal. Calcd for C H Cl N Ru: C, 56.22; H, 5.26; N, 7.56;
26 29 2 3
AUTHOR INFORMATION
Corresponding Author
E-mail: wolfgangherrmann@ch.tum.de (W.A.H.); fritz.
■
*
kuehn@ch.tum.de (F.E.K.).
cis-Cyclooctene. Olefin (800 mg, 7.3 mmol) and catalyst (1 mol %,
3 μmol) dissolved in RTIL (0.5 mL) were added to the reaction
Author Contributions
Equally contributing coauthors.
Notes
†
7
vessel. Afterwards, the reaction was initiated by adding TBHP (2.65
mL, 5.5 m in n-decane). Analysis: The course of the reaction was
monitored by quantitative GC analysis. Samples taken were treated
with MgSO and MnO to remove water and destroy excess peroxide.
The authors declare no competing financial interest.
4
2
ACKNOWLEDGMENTS
Afterward, the sample was diluted with CH Cl and the resulting slurry
■
2
2
was filtered. A mixture of 4 mg/mL indane and p-xylol in isopropanol
used as external standard) and the filtrate was injected into a GC
The authors thank the Bavarian Network of Excellence:
NANOCAT and the TUM Graduate School for generous
financial support.
(
column. Conversion of cis-cyclooctene and formation of the respective
2
oxides were calculated from calibration curves (r > 0.999) recorded
prior to the start of the reaction.
REFERENCES
■
1
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̈
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(
1.0 mmol, internal standard), and catalyst (1 mol %, 0.01 mmol) were
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4
2
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3
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the sample was diluted with CH Cl and the resulting slurry was
̈
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2
filtered. A mixture of 4 mg/mL indane and p-xylol in isopropanol
used as external standard) and the filtrate was injected into a GC
(
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(
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dx.doi.org/10.1021/ic400533u | Inorg. Chem. 2013, 52, 6142−6152