IrIII/AuI and RhIII/AuI Heterobimetallic Complexes as Catalysts for the Coupling of Nitrobenzene and Benzylic Alcohol

Article abstract of DOI:10.1021/acs.organomet.8b00642

Two simple bisimidazolium salts derived from m- or p-bisimidazolebenzenes have been used as ligand precursors for the preparation of a series of heterobimetallic Rh^III/Au^I and Ir^III/Au^I complexes. All complexes have been fully characterized, and the molecular structures of selected derivatives have been determined by X-ray diffraction studies. These analyses showed that, regardless of the ligand used, the direct coordination environment of the metals is composed of identical donors (M^III: C_NHC, C_benzene, η⁵-Cp?, and I^- Au^I: C_NHC and I^-) and is rather similar in the heterobimetallic complexes. The catalytic activity of the heterobimetallic complexes in the coupling of nitrobenzene with benzylic alcohol has been investigated. In all cases, the performance observed for the heterobimetallic complexes was superior to that shown by mixtures of homometallic M^III/Au^I complexes, suggesting a cooperative effect between the two metal centers. In addition and in spite of the similarity of the donor groups of the two bis-NHC ligands used, the slightly different relative orientation of the two metals in the heterobimetallic complexes also plays a role in the catalytic conversion observed.

Full text of DOI:10.1021/acs.organomet.8b00642

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
III
I
III
I
Ir /Au and Rh /Au Heterobimetallic Complexes as Catalysts for the
Coupling of Nitrobenzene and Benzylic Alcohol
†
†
†
‡
Maximilian Bohmer, Florian Kampert, Tristan Tsai Yuan Tan, Gregorio Guisado-Barrios,
̈
,
‡
,†
Eduardo Peris,* and F. Ekkehardt Hahn*
†
Institut fu
8149 Mu
̈
r Anorganische und Analytische Chemie, Westfal
nster, Germany
̈
ische Wilhelms-Universitat
̈
Mu
̈
nster, Corrensstraße 28−30,
4
‡
̈
Institute of Advanced Materials (INAM), Universitat Jaume I, Avda. Vicente Sos Baynat s/n, Castellon
́
, E-12071, Spain
*
S Supporting Information
ABSTRACT: Two simple bisimidazolium salts derived from m- or
p-bisimidazolebenzenes have been used as ligand precursors for the
III
I
III
I
preparation of a series of heterobimetallic Rh /Au and Ir /Au
complexes. All complexes have been fully characterized, and the
molecular structures of selected derivatives have been determined by
X-ray diffraction studies. These analyses showed that, regardless of
the ligand used, the direct coordination environment of the metals is
III
5
−
composed of identical donors (M : CNHC, Cbenzene, η -Cp*, and I ;
I
−
Au : C
and I ) and is rather similar in the heterobimetallic
NHC
complexes. The catalytic activity of the heterobimetallic complexes in
the coupling of nitrobenzene with benzylic alcohol has been inves-
tigated. In all cases, the performance observed for the heterobime-
tallic complexes was superior to that shown by mixtures of homo-
III
I
metallic M /Au complexes, suggesting a cooperative effect between the
two metal centers. In addition and in spite of the similarity of the donor groups of the two bis-NHC ligands used, the slightly different
relative orientation of the two metals in the heterobimetallic complexes also plays a role in the catalytic conversion observed.
INTRODUCTION
We became interested in the preparation of NHC-based
heterometallic complexes. In most cases, these complexes
■
6
Nitrogen-containing compounds are abundant in natural pro-
ducts, and many of them show an interesting biological and
were obtained by the stepwise metalation of suitable ligand
precursors, but some recent reports describe the convenient
preparation of heterometallic complexes by a single-step site-
1
medical activity. However, the construction of C−N bonds
requires harsh reaction conditions or the use of expensive cata-
lysts. Finding ways for the production of nitrogen-containing
compounds using inexpensive starting materials and mild
reaction conditions is still a major challenge for synthetic
7
selective metalation of the polycarbene ligands. Many of the
heterometallic complexes prepared by us were used for tandem
catalytic processes, and we often found that these catalysts
outperformed the activity exhibited by mixtures of the related
2
chemists. Given that nitro compounds are inexpensive and
5
a,6e,k
homometallic catalysts.
With regard to the construction
easily available, the reductive coupling of alcohols and nitro-
arenes for the construction of C−N bonds through a metal-
catalyzed tandem reaction involving transfer hydrogenation is
highly desirable. Often, tandem processes involving at least one
C−N bond formation step can generate structurally complex
nitrogen-containing molecules. In addition, the use of one-pot
multistep reactions is arguably the most efficient method for
the production of nitrogen-containing compounds, since these
processes avoid the need of isolation or purification of inter-
mediates. One-pot reactions involving multiple catalytic
processes facilitated by one catalyst can be an interesting
III
II
of C−N bonds, we have prepared an Ir /Pd catalyst for the
generation of a variety of functionalized imines from nitro-
arenes and primary alcohols. The multistep reaction involved
the reduction of the nitroarene to an amine with the concom-
itant oxidation of the alcohol to an aldehyde followed by the
condensation of the aldehyde and the amine to form the imine.
6
g
III
I
We also observed that the combination of Ir and Au in a
heterometallic catalyst produced important benefits in the
reduction of nitroarenes with benzyl alcohol to produce
6
h
N-benzylideneaniline. The catalytic benefits resulting from
the introduction of the gold(I) metal center into hetero-
bimetallic catalysts can be related to the enhanced catalytic
activity provided by organogold complexes when combined
3
alternative to multistep protocols. A close proximity between
the catalytic active sites (the metals) often provides favorable
conditions for the occurrence of an enhanced catalytic
4
activity. This proximity can result from the use of catalysts
with metal−metal interactions or by designing suitable ligands
Received: September 3, 2018
5
for multimetallic catalysts.
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00642
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Scheme 1. Stepwise Preparation of M /Au Heterobimetallic Complexes
Article
III
I
8
9
10
11
with palladium, iron, nickel, and rhodium and serve as exam-
ples for dual catalysis.
The molecular structures of the monometallic complexes
[3], [4], and [5] were determined by X-ray diffraction studies.
The molecular structure of [3] is shown in Figure 1 (ORTEP
diagrams of [4] and [5] are depicted in the Supporting
Information).
On the basis of these previous results, we now describe the
III
I
III
I
preparation of a new series of Rh /Au and Ir /Au complexes
which we used as catalysts for the preparation of amines from
the reaction of nitrobenzene and benzyl alcohol. We also
describe evidence for dual catalytic action provided by the two
different metals in the heterobimetallic complexes.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of New Complexes.
We hypothesized that two simple bisimidazolium salts such
1
2
13
as 1 and 2 (Scheme 1) might constitute useful ligand pre-
cursors for the preparation of new heterometallic complexes.
Due to their structural similarity, the bisimidazolium salts
should also afford structurally related complexes which might
exhibit different catalytic properties. The different relative
orientation of the imidazolium units attached to the central
benzene ring may provide a simple way for modulating the
distance between two metal centers, while maintaining the
basic steric and electronic properties of the ligand. The
Figure 1. Molecular structure (50% displacement ellipsoids) of complex
[
3] in [3]·MeCN. Hydrogen atoms (except H14) and the iodide
counterion have been omitted for clarity. Selected bond distances (Å)
and angles (deg): Rh−I 2.6940(4), Rh−C2 2.015(4), Rh−C12
2
.031(4); I−Rh−C2 85.58(12), I−Rh−C12 90.58(12), C2−Rh−C12
III
I
preparation of the M /Au (M = Rh, Ir) heterobimetallic
complexes was achieved by the stepwise procedure displayed in
78.20(17), N1−C2−N3 105.5(4), N13−C14−N15 108.7(4).
III
III
Scheme 1. First, the monometallic Rh and Ir complexes
Complex [3] exhibits a pseudo-piano-stool geometry with
the orthometalated phenyl-substituted imidazolylidene ligand
and the iodo ligand forming the legs. The orthometalated
phenyl ring contains an additional methylimidazolium substit-
uent at the p-position relative to the metalated imidazolylidene.
The cationic charge of the complex is balanced by the presence
[
3]−[6] were prepared by the in situ deprotonation of the
bisimidazolium salts with a mixture of cesium carbonate and
sodium acetate in the presence of [MCp*Cl ] (M = Rh, Ir)
2
2
and potassium iodine. All four complexes were obtained in
very good yields (83−91%) and were characterized by NMR
spectroscopy, mass spectrometry, and elemental analysis.
The monometallic complexes [3]−[6] were subsequently
of an iodide counteranion. The Rh−C
distance measures
2.015(4) Å and is unexceptional, as are the other molecular
parameters.
NHC
III
I
used as precursors for the preparation of the Rh /Au and
III
I
Ir /Au heterobimetallic complexes [7]−[10]. The coordina-
Single crystals of the heterobimetallic complexes [7] and [8]
suitable for X-ray diffraction studies were obtained by vapor
diffusion of diethyl ether into saturated acetonitrile solutions of
the complexes. Their molecular structures are depicted in
Figure 2. These are very similar and confirm the coordination
I
tion of the second NHC donor to Au was achieved by trans-
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I
metalation of the in situ preformed M /Ag −NHC complexes
with [AuCl(tht)] (tht = tetrahydrothiophene) in CH Cl at
2
2
room temperature. The silver(I)−NHC complexes were gen-
III
erated by addition of Ag O to the metalloproligands [3]−[6].
of the M center (M = Rh, Ir) by one NHC ligand and the
2
III
Complexes [7]−[10] were obtained as air-stable compounds
in yields ranging from 21 to 56%. Details regarding the
characterization of complexes [3]−[10] can be found in the
Experimental Section.
orthometalation of the M center through the central phenyl
III
ring. This leaves the M center in a pseudo-piano-stool coor-
dination geometry composed of a Cp* ligand, a CNHC^Cphenyl
I
chelate ligand, and a iodo ligand. The Au center is coordinated
B
DOI: 10.1021/acs.organomet.8b00642
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 2. Monometallic Complexes [11]−[13] for
Comparative Catalytic Studies
The catalytic reactions were carried out using nitrobenzene
and benzyl alcohol (which also acted as solvent) in the pres-
ence of Cs CO at 100 °C with a 0.5 mol % catalyst loading.
2
3
From the results shown in Table 1, it can be concluded that
Table 1. Catalytic Tandem Condensation of Nitrobenzene
,
a b
with Benzyl Alcohol and Imine Reduction
yield (%)
entry
catalyst
conversion %
I
II
III
IV
1
2
3
4
5
6
7
8
9
[11] + [13]
[12] + [13]
[12]
[13]
none
[7]
[8]
[9]
98
74
59
74
67
6
5
5
33
34
0
6
0
0
5
16
5
4
22
26
25
6
18
4
57
56
44
8
18
8
5
0
0
5
Figure 2. Molecular structures of [7] in [7]·0.5Et O·MeCN (top)
2
100
74
62
55
34
14
23
40
30
13
7
and [8] in [8]·0.5Et O·MeCN (bottom, 50% displacement
2
ellipsoids). Hydrogen atoms and the iodo counterions have been
omitted for clarity. The asymmetric unit of both compounds contains
two essentially identical molecules, one of which is depicted. Selected
bond distances (Å) and angles (deg) for [7] [[8]]: M−I2 2.6664(17)
100
100
100
100
100
48
82
51
43
55
[10]
[10]
[10]
[10]
c
10
1
1
21
17
14
d
[
[
[
[
[
2.6819(4)], M−C9 2.048(17) [2.055(5)], M−C14 1.988(17)
1.996(5)], Au−I1 2.5493(15) [2.5512(4)], Au−C2 2.034(19)
1.997(6)]; I2−M−C9 92.8(4) [91.41(13)], I2−M−C14 85.1(5)
85.05(14)], C9−M−C14 77.1(7) [77.9(2)], I1−Au1−C2 176.5(6)
176.17(16)], N1−C2−N3 107.9(16) [105.2(5)], N13−C14−N15
1
2
0
0
e
a
The reaction produces benzaldehyde as a necessary side-product.
Reaction conditions: 0.3 mmol of nitrobenzene, 1 mL of benzyl
alcohol, 0.3 mmol of Cs CO , 0.5% catalyst loading, 100 °C, 22 h.
2
3
1
04.1(15) [104.6(4)]. The asymmetric unit contains two formula
b
Yields were determined by GC using anisol (0.3 mmol) as an internal
units for both compounds, one of which is shown.
c
d
e
standard. 0.25 mol % catalyst loading. 0.1 mol % catalyst loading. The
reaction was conducted in the presence of a drop of mercury.
by the second imidazolylidene donor, with an iodo donor
completing the linear arrangement about this metal center.
The bond lengths and angles around the rhodium or iridium
the outcome of the reaction is highly dependent on the catalyst
used in the reaction. First, we observe that the mixture of
monometallic complexes [11]/[13] and [12]/[13] (entries 1
and 2) afforded moderate yields of the imine III with yields
slightly over 55%. This result is interesting when compared
with the activity shown by the monometallic complexes [12]
and [13] alone (entries 3 and 4), for which we observed that
the iridium(III) complex [12] produced moderate amounts of
centers fall within the expected range, (Rh−C
= 1.988(17) Å,
bond distances mea-
NHC
Ir−C
= 1.996(5) Å). The Au−C
NHC
NHC
sure 2.034(19) Å for [7] and 1.997(6) Å for [8].
Catalytic Studies. The heterobimetallic complexes [7]−
10] were tested in the catalytic coupling between nitro-
[
benzene and benzyl alcohol. The reduction of nitroarenes
normally involves the use of molecular hydrogen and Pd/C.
This catalytic system is very active in the hydrogenation of
many functional groups, but the main drawback is the lack of
chemoselectivity. The mechanism of reduction of nitrobenzene
I
the imine, while the Au complex [13] mainly yielded the
azoxy (I) and azo (II) reaction intermediates. This latter
product mixture is about the same as what was obtained in the
absence of a catalyst (entry 5). The results obtained with the
14
leading to aniline is known to involve various intermediates;
III
thus, an effective new catalyst must not only generate the
products in high yield, but it should also be highly selective to
give only one product. For comparative purposes, we also
tested the activity of mixtures of monometallic complexes.
To this end, we prepared complexes [11]−[13] featuring the
metal centers in a stereoelectronic environment similar to that
observed in the dinuclear complexes [7]−[10] (Scheme 2).
monometallic complexes indicate that the M complexes
alone are not efficient in the coupling between the nitroarene
III
and the primary alcohol, but the combination of the Ir and
I
Au catalysts is beneficial when compared to the activity of the
III
M
complex alone. This result is also in agreement with our
III
I
previous findings showing the dual action of Ir and Au for
the same process.
6h
C
DOI: 10.1021/acs.organomet.8b00642
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Organometallics
Article
When comparing the performance of the heterobimetallic
catalysts, we observe that the type of ligand used for the
construction of these complexes has important ramifications
for their catalytic conversions. The conversions obtained with
the reaction all along the profile. As soon as the imine is
produced in a significant amount, the formation of the amine
becomes evident, although the rate of reduction of the imine is
clearly lower than the rate of reduction of nitrobenzene. This
observation is rather logical if we take into account that imines
are rather inert to reduction.
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Rh /Au catalysts [7] and [9] (entries 6 and 8) are identical;
however, [7] yields N-benzylideneaniline (III) as the major
product, while [9] catalyzes the formation of the benzylphenyl-
III
I
amine (IV) as the major product. Comparison of the Ir /Au
CONCLUSIONS
■
catalysts [8] and [10] (entries 7 and 9) reveals a higher total
conversion of [10] and similarly to the couple [7] and [9]
catalyst [8] (para-bis-NHC) produces imine (III) as the major
product, while [10] (meta-bis-NHC) produces the amine (IV)
in an excellent yield of 82%. Given that the coordination envi-
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I
In summary, we have prepared a series of Rh /Au and
III
I
Ir /Au heterobimetallic complexes by using two simple
bisimidazolium salts as bis-NHC ligand precursors. The
structural analysis of the new complexes shows that, regardless
of the ligand used, the individual coordination environments
III
ronments and donors for both metal centers M (M = Rh, Ir)
III
I
I
and the donors bound to the two metals (M and Au ) are
very similar. The catalytic properties of the heterobimetallic
complexes were tested in the coupling of nitrobenzene and
benzyl alcohol. From the results obtained, we can conclude
that (i) the cooperation of the two metals (M and Au ) is
supported by the fact that mixtures of homometallic M /Au
and Au are identical in catalysts [7]−[10], we believe that the
differences in selectivity observed for either [7] and [8] (imine
III as the major product) or [9] and [10] (amine IV as the
major product) may be ascribed to electronic differences
arising from the different bridging ligands.
III
I
III
I
Given the high activity of [10] in the production of the
amine IV, the catalyst loading was reduced from the initial
complexes provide better results than the use of the individual
monometallic complexes alone, (ii) the use of the hetero-
bimetallic complexes affords better results than the use of
mixtures of the related monometallic catalysts, particularly with
the complexes derived from the meta-bis-NHC ligands, and
0
.5 mol % to 0.25 and 0.1 mol %. For these lower catalyst loadings,
the production of the amine was reduced to 51 and 43%,
respectively, although the conversion (related to the consump-
tion of substrates) was complete in all cases. The mercury-drop
test was performed in order to test if the process is homo-
geneously catalyzed. The comparison of the results (entries 9
and 12) indicates that the addition of the mercury drop has a
small (but not negligible) influence on the percentage of
conversion, with the yield of the amine IV dropping from 82 to
(
iii) in spite of the similar coordination environment at the
15
metal centers provided by the two bis-NHC ligands used, the
complexes of the meta-bis-NHC ligands ([9] and [10])
outperform the complexes of the para-bis-NHC ligands ([7]
and [8]) regarding the production of the amine IV. Our study
provides a new example for the benefits associated with the use
of heterobimetallic complexes in facilitating complex organic
transformations. However, at this time, our study is mostly
phenomenological and the elucidation of the actual reaction
mechanism and the parameters associated with it require
further research.
5
5%. This would indicate that the reduction of the imine is
affected by the addition of the mercury drop. We assume that
10] can decompose to yield small gold nanoparticles, a pro-
[
cess that should not affect the overall outcome of the process
much, given the known activity of gold nanoparticles in the
16
reduction of imines to amines.
In order to get some insight into the mechanism of the
catalytic conversion, we decided to study the time-dependent
reaction profile of the coupling between nitrobenzene and
benzaldehyde (Figure 3). The reaction was carried out in
EXPERIMENTAL SECTION
1. General Procedures. All reagents and solvents were used as
received without further purification. H and C{ H} NMR spectra
were recorded at 298 K on Bruker AVANCE I 400 and Bruker
AVANCE III 400 spectrometers. Chemical shifts (δ) are expressed in
ppm downfield from tetramethylsilane using the residual protonated
solvent as an internal standard. Coupling constants are expressed in
Hertz. Mass spectra were obtained with Reflex IV MALDI TOF
■
1
13
1
(
Bruker) and Orbitrap LTQ XL (Thermo Scientific, ESI)
spectrometers. High resolution mass spectra (HRMS) were recorded
on a Q-TOF Premier mass spectrometer (Waters) with an electro-
spray source operating in the V-mode. Elemental analyses were
carried out with an Elementar Vario EL III or a TruSpec Micro Series
elemental analyzer. The two bisimidazolium salts 1 and 2 (Scheme 1)
1
2,13
were synthesized according to reported procedures.
The metal
17
17
18
precursors [RhCp*(Cl) ] , [IrCp*(Cl) ] , and [AuCl(tht)] and
the monometallic NHC complexes [11], [12], and [13] were
2
2
2 2
1
9
20
18
prepared according to literature procedures.
Figure 3. Time-dependent reaction profile of the reduction of
nitroarene with catalyst [10]. Reagents and conditions: nitrobenzene
2
. Synthesis of Complexes [3]−[6]. One of the ligand
precursors 1 or 2 (0.20 mmol, 2.00 equiv), Cs CO (0.15 mmol,
(
(
0.3 mmol), benzyl alcohol (as solvent and reagent, 1 mL), Cs CO3
0.3 mmol), anisole (as internal reference, 0.3 mmol), 100 °C, aerobic
2
3
2
1
.50 equiv), NaOAc (0.40 mmol, 4.00 equiv), [MCp*(Cl) ] (M =
2 2
Rh, Ir) (0.050 mmol, 0.50 equiv), and KI (0.60 mmol, 6.00 equiv)
were dissolved in MeCN (30 mL). The reaction mixture was heated
under reflux for 3 h and then allowed to cool down to ambient
temperature. The obtained suspension was filtered through Celite,
and the filtrate was brought to dryness in vacuo. The crude solid
product was purified by column chromatography on silica (eluent:
CH Cl :MeOH = 6:1) to give the desired complex as air and moisture
conditions. Yields were determined by GC analysis.
benzyl alcohol in the presence of Cs CO at 100 °C using
2
3
0
.5 mol % of [10]. As can be seen from the profile, the con-
sumption of nitrobenzene proceeds concomitant with the
formation of the imine and with negligible formation of the azo
and azoxy intermediates which remain as minor products of
2
2
stable solid.
D
DOI: 10.1021/acs.organomet.8b00642
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Organometallics
Article
2
.1. Characterization of Complex [3].
2.4. Characterization of Complex [6].
1
Yield: 66.1 mg, 0.091 mmol, 91%. H NMR (400 MHz, DMSO-d ): δ
6
3
1
(
ppm) = 9.62 (s, 1H, H13), 8.21 (t, J = 1.8 Hz, 1H, H16), 8.13
d, J = 2.1 Hz, 1H, H5), 7.95 (t, J = 1.8 Hz, 1H, H15), 7.77 (d,
Yield: 72.0 mg, 0.088 mmol, 88%. H NMR (400 MHz, DMSO-d ):
H,H
6
3
3
3
3
(
δ (ppm) = 9.71 (t, J = 1.7 Hz, 1H, H13), 8.25 (t, J = 1.7 Hz,
HH
H,H
H,H H,H
4
3
3
3
3
JH,H = 2.3 Hz, 1H, H10), 7.65 (d, J = 8.3 Hz, 1H, H7), 7.56 (d, J
1H, H16), 7.97 (d, J = 2.1 Hz, 1H, H5), 7.95 (t, J = 1.7 Hz,
H,H H,H
H,H
H,H
3
4
4
3
=
2.1 Hz, 1H, H4), 7.31 (dd, J = 8.3 Hz, J = 2.3 Hz, 1H, H8), 3.97
1H, H15), 7.91 (d, J = 2.4 Hz, 1H, H11), 7.73 (d, J = 8.1 Hz,
HH
HH
H,H H,H
3
3
(
s, 3H, N−CH ), 3.83 (s, 3H, N−CH ), 1.82 (s, 15H, CH −Cp*).
1H, H8), 7.56 (d, J = 2.1 Hz, 1H, H4), 7.21 (dd, J = 8.1 Hz,
H,H H,H
3
3
3
1
3
1
1
4
C{ H} NMR (101 MHz, DMSO-d ): δ (ppm) = 180.4 (d, J
=
JH,H = 2.4 Hz, 1H, H9), 3.96 (s, 3H, N−CH ), 3.84 (s, 3H, N−CH ),
6
C,Rh
3
3
1
13 1
5
(
4.4 Hz, C2), 160.3 (d, J
= 36.6 Hz, C11), 147.1 (s, C6), 135.3
1.87 (s, 15H, CH −Cp*). C{ H} NMR (101 MHz, DMSO-d ): δ
C,Rh
3
6
3
s, C10), 130.8 (s, C13), 130.1 (d, J
= 1.6 Hz, C9), 124.1 (s, C4),
(ppm) = 162.8 (s, C2), 147.4 (s, C7), 143.0 (s, C6), 137.9 (s, C8),
135.2 (s, C13), 129.3 (s, C10), 124.1 (s, C15), 123.1 (s, C4), 121.0
C,Rh
1
24.0 (s, C16), 121.2 (s, C8), 116.3 (s, C5), 115.9 (s, C15), 111.4
1
(s, C7), 97.7 (d, J
= 4.7 Hz, C −Cp*), 37.3 (s, N−CH ), 36.0 (s,
C,Rh
q
3
(s, C16), 117.0 (s, C9), 115.1 (s, C5), 104.3 (s, C11), 91.5 (s, C −
q
N−CH ), 10.1 (s, CH −Cp*). HR-MS (ESI, positive ions): m/z (%) =
3
3
Cp*), 37.1 (s, N−CH ), 36.0 (s, N−CH ), 9.9 (s, CH −Cp*). HR-
3
3
3
+
6
03.0483 (100) (calculated for [3−I] 603.0492). MS (MALDI-TOF,
MS (ESI, positive ions): m/z (%) = 693.1062 (100) (calculated for
+
matrix DCTB): m/z (%) = 603 (100) [3−I] . Anal. Calcd for [3]·H O:
C, 38.52; H, 4.18; N, 7.49. Found: C, 38.34; H, 4.16; N, 7.29.
+
2
[6−I] 693.1066). MS (MALDI-TOF, matrix DCTB): m/z (%) =
+
6
93 (100) [6−I] . Anal. Calcd for [6]: C, 35.17; H, 3.57; N, 6.84.
2
.2. Characterization of Complex [4].
Found: C, 34.88; H, 3.44; N, 6.71.
. Synthesis and Characterization of Complexes [7]−[10].
To a mixture of one of the monometallic complexes [3]−[6] (0.08 mmol,
.00 equiv) and Ag O (0.05 mmol, 0.60 equiv) was added CH Cl
3
1
2
2
2
(10 mL). The reaction mixture was stirred at room temperature under
exclusion of light for 1 h, and the resulting dark suspension was filtered
through a pad of Celite. A clear filtrate was obtained. To this was added
upon stirring at ambient temperature [AuCl(tht)] (0.08 mmol, 1.00
equiv) and KI (1.2 mmol, 15.00 equiv). Immediately, the formation of
a white precipitate was observed. The suspension was stirred for 18 h
at room temperature and subsequently filtered through a small pad of
Celite. After removal of the volatiles, the crude product was purified
1
Yield: 68.0 mg, 0.083 mmol, 83%. H NMR (400 MHz, DMSO-d ): δ
6
3
(
(
ppm) = 9.61 (s, 1H, H13), 8.20 (t, J = 1.8 Hz, 1H, H16), 8.05
H,H
3
3
d, J = 2.2 Hz, 1H, H5), 7.94 (d, J = 1.8 Hz, 1H, H15), 7.72−
H,H
H,H
3
7
.62 (m, 2H, H7, H10), 7.54 (d, J = 2.1 Hz, 1H, H4), 7.23 (dd,
H,H
3
4
JH,H = 8.3 Hz, J = 2.4 Hz, 1H, H8), 3.97 (s, 3H, N−CH ), 3.83
H,H
3
by column chromatography on silica (eluent CH Cl ) to give the
1
3
1
2
2
(
(
s, 3H, N−CH ), 1.88 (s, 15H, CH −Cp*). C{ H} NMR
3
3
desired complex as an air and moisture stable solid. Further puri-
101 MHz, DMSO-d ): δ (ppm) = 162.3 (s, C2), 147.8 (s, C6),
6
fication can be achieved by recrystallization from CH Cl /Et O.
2
2
2
1
(
42.9 (s, C11), 135.3 (s, C10), 130.5 (s, C9), 129.7 (s, C13), 124.1
s, C16), 123.0 (s, C4), 121.2 (s, C8), 115.4 (s, C5), 115.4 (s, C15)
3
.1. Characterization of Complex [7].
1
9
11.0 (s, C7), 91.5 (s, C −Cp*), 37.0 (s, N−CH ), 36.0 (s, N−CH ),
q
3
3
.9 (s, CH −Cp*). HR-MS (ESI, positive ions): m/z (%) = 693.1056
3
+
(
100) (calculated for [4−I] 693.1066). MS (MALDI-TOF, matrix
+
DCTB): m/z (%) = 693 (100) [4−I] . Anal. Calcd for [4]: C, 35.17;
H, 3.57; N, 6.84. Found: C, 34.91; H, 3.44; N, 6.77.
2
.3. Characterization of Complex [5].
1
Yield: 16.0 mg, 0.017 mmol, 21%. H NMR (400 MHz, CD Cl ): δ
2
2
3
(
ppm) = 7.78−7.76 (m, 1H, H10), 7.49 (d, J = 2.1 Hz, 1H, H5),
HH
3
3
7
.34−7.30 (m, 1H, H8), 7.26 (d, J = 2.1 Hz, H7), 7.23 (d, J
=
HH
H,H
2
.1 Hz, 1H, H16), 7.14−7.08 (m, 2H, H4, H15), 3.95 (s, 3H, N−
1
3
1
CH ), 3.89 (s, 3H, N−CH ), 1.89 (s, 15H, CH −Cp*). C{ H}
3
3
3
1
NMR (101 MHz, CD Cl ): δ (ppm) = 182.9 (d, J = 54.5 Hz,
2
2
RhC
1
C2), 181.0 (s, C13), 160.2 (d, J
= 36.2 Hz, C11), 146.9 (s, C6),
RhC
3
135.4 (s, C10), 135.3 (d, J
= 1.8 Hz, C9), 123.3 (s, C16), 122.9
C4), 121.8 (s, C15), 120.0 (s, C8), 115.6 (d, J
1
C,Rh
Yield: 65.5 mg, 0.090 mmol, 90%. H NMR (400 MHz, DMSO-d ): δ
ppm) = 9.73 (t, J = 1.7 Hz, 1H, H13), 8.26 (t, J = 1.7 Hz, 1H,
H16), 8.06 (d, J = 2.1 Hz, 1H, H5), 7.96 (t, J = 1.7 Hz, 1H, H15),
3
6
(
= 1.4 Hz, C5),
C,Rh
= 5.0 Hz, C −Cp*), 38.4
3
3
(
3
1
H,H
H,H
111.0 (d, J
= 1.4 Hz, C7), 98.6 (d, J
3
3
C,Rh
C,Rh
q
H,H
H,H
(
s, N−CH ), 38.3 (s, N−CH ), 11.2 (s, CH −Cp*). HR-MS (ESI,
4
3
3
3
3
7
(
1
.90 (d, J = 2.4 Hz, 1H, H11), 7.79 (d, J = 8.1 Hz, 1H, H8), 7.58
H,H H,H
3
3
4
positive ions): m/z (%) = 1401.0511 (100) (calculated for [2·7−
d, J = 2.1 Hz, 1H, H4), 7.28 (dd, J = 8.1 Hz, J = 2.4 Hz,
H,H H,H H,H
+
AuI ] 1401.0493). MS (MALDI-TOF, matrix DCTB): m/z (%) =
2
H, H9), 3.97 (s, 3H, N−CH ), 3.84 (s, 3H, N−CH ), 1.81 (s, 15H,
3
3
+
+
13
1
799 (25) [7−I] ; 1401 (100) [2·7−AuI
CH Cl : C, 29.70; H, 2.99; N, 5.54. Found: C, 29.53; H, 2.87; N, 5.40.
2
] . Anal. Calcd for [7]·
CH −Cp*). C{ H} NMR (101 MHz, DMSO-d ): δ (ppm) = 181.0
3
6
1
1
2 2
3
(
1
d, J
= 54.7 Hz, C2), 160.1 (d, J
= 36.1 Hz, C7), 147.4 (s, C6),
C,Rh
C,Rh
.2. Characterization of Complex [8].
39.2 (s, C8), 135.3 (s, C13), 130.1 (s, C10), 124.1 (s, C15), 124.1
(
9
1
s, C4), 121.0 (s, C16), 116.4 (s, C9), 115.6 (s, C5), 104.7 (s, C11),
1
7.7 (d, J
= 4.8 Hz, C −Cp*), 37.4 (s, N−CH ), 36.1 (s, N−CH ),
C,Rh
q
3
3
0.1 (s, CH −Cp*). HR-MS (ESI, positive ions): m/z (%) = 603.0487
3
+
(
100) (calculated for [5−I] 603.0492). MS (MALDI-TOF, matrix
+
DCTB): m/z (%) = 603 (100) [5−I] . Anal. Calcd for [5]·H O: C,
3
2
8.52; H, 4.18; N, 7.49. Found: C, 38.49; H, 3.90; N, 7.10.
E
DOI: 10.1021/acs.organomet.8b00642
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
Yield: 28.4 mg, 0.028 mmol, 34%. H NMR (400 MHz, CD Cl ): δ
3.46 (s, 3H each, 2 × N−CH for two compounds), 1.92 and 1.91
2
2
3
4
3
13
1
(
ppm) = 7.72 (d, J = 2.3 Hz, 1H, H10), 7.42 (d, J = 2.1 Hz,
H, H5), 7.29 (d, J = 8.2 Hz, 1H, H7), 7.25 (d, J = 1.8 Hz,
(s, br, 15H each, 2 × CH −Cp* for two compounds). C{ H} NMR
H,H
H,H
3
3
3
1
1
7
1
(101 MHz, CD Cl ): δ (ppm) = 183.5 (br, C13 and C13′), 164.6
H,H
H,H
2
2
3
4
H, H16), 7.15 (dd, J = 8.2 Hz, J = 2.3 Hz, 1H, H8), 7.11−
(s, C2), 164.5 (s, C2′), 147.3 (s, C6), 147.2 (s, C6′), 142.7 (s, C7),
142.6 (s, C7′), 138.1 (s, C8), 138.0 (s, C8′), 134.1 (s, C10), 134.1
(s, C10′), 122.9 (s, C15), 122.8 (s, C15′), 122.7 (s, C4), 122.7
(s, C4′), 122.6 (s, C16), 122.6 (s, C16′), 121.0 (s, C9), 120.9
(s, C9′), 115.8 (s, C5), 115.7 (s, C5′), 108.0 (s, C11), 107.9 (s, C11′),
92.1 (s, 2 × C −Cp*), 38.9 (s, N−CH ), 38.8 (s, N−CH ′), 37.9
H,H
H,H
.05 (m, 2H, H4, H15), 3.95 (s, 3H, N−CH ), 3.88 (s, 3H, N−CH ),
3
3
1
3
1
.94 (s, 15H, CH −Cp*). C{ H} NMR (101 MHz, CD Cl ): δ
3
2
2
(
1
ppm) = 181.0 (s, C13), 164.7 (s, C2), 147.7 (s, C6), 143.2 (s, C11),
35.9 (s, C9), 134.3 (s, C10), 123.0 (s, C16), 122.4 (s, C4), 121.8 (s,
C15), 119.1 (s, C8), 115.2 (s, C5), 110.6 (s, C7), 92.4 (s, C −Cp*),
q
q
3
3
3
8.4 (s, N−CH ), 38.0 (s, N−CH ), 11.0 (s, CH −Cp*). HR-MS
(s, 2 × N−CH ), 10.3 (s, 2 × CH −Cp*). HR-MS (ESI, positive
3
3
3
3
3
+
(
[
ESI, positive ions): m/z (%) = 1579.1635 (100) (calculated for
ions): m/z (%) = 1579.1621 (100) (calculated for [2·10−AuI ]
1579.1620). MS (MALDI-TOF, matrix DCTB): m/z (%) = 1579
(100) [2·10−AuI ] . Anal. Calcd for 10·CH Cl : C, 27.29; H, 2.75;
N, 5.09. Found: C, 27.45; H, 2.82; N, 4.89.
2
+
2·8−AuI ] 1579.1620). MS (MALDI-TOF, matrix DCTB):
2
+
+
+
m/z (%) = 889 (100) [8−I] ; 1581 (56) [2·8−AuI ] . Anal. Calcd
2
2
2
2
for [8]·CH Cl ·Et O): C, 29.65; H, 3.43; N, 4.77. Found: C, 29.47;
2
2
2
H, 3.03; N, 4.97.
.3. Characterization of Complex [9].
3
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acs.organomet.8b00642.
■
*
S
Spectra of the new complex, crystallographic data, and
details of the catalytic studies (PDF)
Accession Codes
CCDC 1858122−1858126 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Yield: 17.2 mg, 0.021 mmol, 26%. The NMR spectra of complex [9]
feature two sets of resonances caused by ligand redistribution at the
gold atoms in solution (formation of NHC−Au−NHC complexes
I
with a AuI counterion). This type of redistribution at Au has been
2
observed multiple times in the past with the same consequences for
21
the NMR spectra. If resolved, we report the resonances for the
complex [9] and those for the NHC−Au−NHC complexes obtained
1
by ligand redistribution. H NMR (400 MHz, CD Cl ): δ (ppm) =
2
2
AUTHOR INFORMATION
Corresponding Authors
E-mail: eperis@qio.uji.es.
*E-mail: fehahn@uni-muenster.de.
■
7
.93−7.72 (m, 6H), 7.32−7.02 (m, 8H), 3.91 (s, br, 6H, 2 × N−CH
3
for two compounds), 3.48 and 3.45 (s, 3H each, N−CH for two
3
*
compounds), 1.87 and 1.86 (s, br, 15H each, 2 × CH −Cp* for two
3
compounds). 1 C{ H} NMR (101 MHz, CD Cl ): δ (ppm) = 183.5
3
1
2
2
1
1
(
5
3
br, C13 and C13′), 182.7 (d, J
= 55.0 Hz, C2), 182.7 (d, J
= 35.5 Hz, C7), 159.5 (d, J
5.2 Hz, C7′), 146.4 (s, C6), 146.4 (s, C6′), 139.2 (s, C8), 139.2 (s,
=
=
ORCID
C,Rh
C,Rh
1
1
5.2 Hz, C2′), 159.6 (d, J
C,Rh
C,Rh
Eduardo Peris: 0000-0001-9022-2392
F. Ekkehardt Hahn: 0000-0002-2807-7232
Notes
C8′), 134.9 (s, C10), 134.9 (s, C10′), 123.6 (s, C15), 123.6 (s, C15′),
1
22.9 (s, C4), 122.9 (s, C4′), 122.6 (s, C16), 122.6 (s, C16′), 120.4
(s, C9), 120.4 (s, C9′), 116.4 (s, C5), 115.3 (s, C5′), 108.5 (s, C11),
The authors declare no competing financial interest.
1
1
1
4
08.5 (s, C11′), 98.3 (d, J
= 4.9 Hz, C −Cp*), 98.3 (d, J
=
C,Rh
C,Rh
q
.9 Hz, C −Cp*′), 38.9 (s, N−CH ), 38.9 (s, N−CH ′), 38.2 (s, N−
ACKNOWLEDGMENTS
q
3
3
■
CH ), 38.2 (s, N−CH ′), 10.6 (s, CH −Cp*), 10.6 (s, CH −Cp*′).
3
3
3
3
The authors gratefully acknowledge financial support from the
Deutsche Forschungsgemeinschaft (SFB 858 and IRTG 2027),
and the Universitat Jaume I. G.G.-B. would like to thank
MINECO for the “Juan de la Cierva Fellowship” (IJCI-2015-
23407).
HR-MS (ESI, positive ions): m/z (%) = 1401.0491 (100) (calculated
+
for [2·9−AuI ] 1401.0493). MS (MALDI-TOF, matrix DCTB):
2
+
+
m/z (%) = 799 (10) [9−I] , 1401 (60) [2·9−AuI ] . Anal. Calcd for
2
9
5
·CH Cl : C, 29.70; H, 2.99; N, 5.54. Found: C, 29.68, H, 2.81; N,
2 2
.47.
3
.4. Characterization of Complex [10].
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DOI: 10.1021/acs.organomet.8b00642
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