Synthesis and Catalytic Applications of Heterobimetallic Carbene Complexes Obtained via Sequential Metalation of Two Bisazolium Salts

Article abstract of DOI:10.1021/acs.organomet.9b00120

A simple sequential metalation approach starting from the imidazolium/benzimidazolium salt 4(I)₂ yielded the heterobimetallic Rh^III/M (M = Pd^II, Ir^I, Au^I, Ru^II) complexes [6]-[9]. Alternatively, a symmetrical 1,3-imidazolium substituted benzene was used for the preparation of the heterobimetallic M′/Pd^II (M′ = Rh^III, Ir^III) complexes [12] and [13]. The versatile stepwise approach used for the preparation of complexes [6]-[9] involved the deprotonation reaction of the bisazolium salt 4(I)₂ in the presence of [RhCp?(Cl)₂]₂ to afford the monometallic complex [5]I featuring a chelating coordinated bidentate C_NHC^C_phenyl ligand. Complex [5]I was reacted with Ag₂O to give a nonisolated Rh^III/Ag^I complex which in a subsequent transmetalation reaction yielded the heterobimetallic Rh^III/M bis-NHC complexes (M = Pd^II [6], Ir^I [7], Au^I [8], Ru^II [9]). Similarly, heterobimetallic M′/Pd^II bis-NHC complexes [12] (M′ = Rh^III) and [13] (M′ = Ir^III) have been prepared from a symmetrical bisazolium salt by generating first the monometallic M′ complexes followed by a transmetalation reaction of the in situ generated M′/Ag^I complexes with [Pd(dmba)(μ-Cl)]₂. The Rh^III/Pd^II complexes [6] and [12] and the Ir^III/Pd^II complex [13] were used as catalysts for two orthogonal tandem reactions, namely, the Suzuki-Miyaura coupling/transfer hydrogenation and the Suzuki-Miyaura-coupling/α-alkylation of ketones. The catalytic activity of the heterobimetallic complexes was compared to mixtures of the related monometallic analogues [14]-[17], with the heterobimetallic complexes generally showing a higher catalytic activity. In addition, nBuOH was found to play a dual role as an alkylating and reducing agent in the Suzuki-Miyaura coupling/α-alkylation of ketones.

Full text of DOI:10.1021/acs.organomet.9b00120

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Synthesis and Catalytic Applications of Heterobimetallic Carbene
Complexes Obtained via Sequential Metalation of Two Bisazolium
Salts
†
,‡
†
†
̈
Maximilian Bohmer, Gregorio Guisado-Barrios,* Florian Kampert, Florian Roelfes,
Tristan Tsai Yuan Tan,† Eduardo Peris,*,‡ and F. Ekkehardt Hahn*,†
†Institut fu
Munster, Germany
̈
̈ ̈
̈
r Anorganische und Analytische Chemie, Westfalische Wilhelms-Universitat Munster, Corrensstraße 28-30, 48149
̈
‡
́
Institute of Advanced Materials (INAM), Centro de Innovacion en Química Avanzada (ORFEO−CINQA), Universitat Jaume I,
́
Avda. Vicente Sos Baynat s/n, Castellon, E-12071, Spain
S
* Supporting Information
ABSTRACT: A simple sequential metalation approach starting
from the imidazolium/benzimidazolium salt 4(I)2 yielded the
heterobimetallic RhIII/M (M = PdII, IrI, AuI, RuII) complexes [6]−
[9]. Alternatively, a symmetrical 1,3-imidazolium substituted
benzene was used for the preparation of the heterobimetallic
M′/PdII (M′ = RhIII, IrIII) complexes [12] and [13]. The versatile
stepwise approach used for the preparation of complexes [6]−[9]
involved the deprotonation reaction of the bisazolium salt 4(I)2 in
the presence of [RhCp*(Cl)2]2 to afford the monometallic
complex [5]I featuring a chelating coordinated bidentate
C
NHC^Cphenyl ligand. Complex [5]I was reacted with Ag2O to
give a nonisolated RhIII/AgI complex which in a subsequent
transmetalation reaction yielded the heterobimetallic RhIII/M bis-
NHC complexes (M = PdII [6], IrI [7], AuI [8], RuII [9]).
Similarly, heterobimetallic M′/PdII bis-NHC complexes [12] (M′ = RhIII) and [13] (M′ = IrIII) have been prepared from a
symmetrical bisazolium salt by generating first the monometallic M′ complexes followed by a transmetalation reaction of the in
situ generated M′/AgI complexes with [Pd(dmba)(μ-Cl)]2. The RhIII/PdII complexes [6] and [12] and the IrIII/PdII complex
[13] were used as catalysts for two orthogonal tandem reactions, namely, the Suzuki−Miyaura coupling/transfer hydrogenation
and the Suzuki−Miyaura-coupling/α-alkylation of ketones. The catalytic activity of the heterobimetallic complexes was
compared to mixtures of the related monometallic analogues [14]−[17], with the heterobimetallic complexes generally showing
a higher catalytic activity. In addition, nBuOH was found to play a dual role as an alkylating and reducing agent in the Suzuki−
Miyaura coupling/α-alkylation of ketones.
finding rational synthetic protocols for the preparation of
heterometallic complexes.
INTRODUCTION
■
Performing multiple reactions in a “one-pot” atom efficient
scenario constitutes one of the most attractive targets for
optimizing new catalytic transformations. Among one-pot
reactions, orthogonal tandem catalysis is a process in which
noninterfering, mechanistically distinct catalytic cycles are
combined in order to facilitate the synthesis of organic
molecules reducing both waste and time.1 Polymetallic
catalysis is based on the combined action of different metals
in a chemical transformation.2 Ultimately, the different
catalysts must be compatible, meaning that they must
accommodate the same reaction conditions and catalyst
lifetimes over the whole sequence of catalytic transformations.
If the two different metals are linked by a single-frame ligand,
the close proximity between the metals may provide favorable
conditions for the occurrence of improved catalytic proper-
ties.3 This forms the basis for the recent significant interest in
We have contributed to the field of multimetallic catalysis by
designing families of ditopic and tritopic N-heterocyclic
carbene ligands (NHCs) for the preparation of heterometallic
catalysts that were used in several orthogonal tandem
processes.3c,4 Among the combinations of metals that were
studied, we found that heterometallic Ir/Pd or Rh/Pd
complexes afforded highly versatile tandem catalysts, due to
the large number of mechanistically distinct catalytic processes
that could be combined.4a,c,e In particular, the combination of
reactions involving the borrowing-hydrogen processes (cata-
lyzed by Ir or Rh) with C−C coupling processes involving aryl
halides (facilitated by Pd) constitute efficient one-pot methods
Received: February 22, 2019
© XXXX American Chemical Society
A
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for the generation of complex organic molecules with potential
pharmaceutical applications. Inspired by these results and
aiming to find new effective methods for the preparation of
NHC-based heterometallic homogeneous catalysts, we now
report the synthesis of a family of M/RhIII complexes (M =
PdII, IrI, AuI, and RuII) supported by a new benzimidazolyli-
dene-imidazolylidene ligand. In addition, we describe two
novel heterobimetallic PdII/M′ (M′ = RhIII, IrIII) complexes
based on a benzene-bis(imidazolylidene) ligand. We also
disclose the catalytic activity of various PdII/M (M = RhIII,
IrIII) complexes in two different tandem transformations,
namely the Suzuki−Miyaura coupling/transfer hydrogenation
and Suzuki−Miyaura coupling/α-alkylation of para-bromoace-
tophenone.
We first attempted the monometalation of 4(I)2 by its
reaction with 1 equiv of NaOAc as a base followed by the
addition of 1 equiv of complexes [MCl2(Cp*)]2 (M = Rh, Ir)
and KI. KI was added to the reaction mixture in order to
support the formation of only one halogen containing species.
For M = Ir, this reaction led to a mixture of monometallic
iridium complexes. However, for M = Rh only the
monometalated complex [5]I was obtained. The metalation
of 4(I)2 with rhodium occurred selectively at the C2 position
of the deprotonated imidazolium group leading via a
subsequent orthometalation of the phenyl ring to the
metallacycle found in [5]I (Scheme 2). The benzimidazolium
Scheme 2. Site-Selective Monometalation of Bisazolium Salt
4(I)2
RESULTS AND DISCUSSION
■
Synthesis and Characterization of New Complexes.
For the synthesis of heterobimetallic complexes from a bis-
NHC precursor, the benzimidazolium/imidazolium salt 4(I)2
was prepared on the gram scale and in good yield following the
multistep procedure depicted in Scheme 1.
group stays intact. At this point we can only speculate about
the reasons for the differences in reactivity observed for IrIII
and RhIII in this monometalation. Rh−CNHC bonds are known
to be rather labile compared to the more inert Ir−CNHC
bonds.5 Thus, it is reasonable to assume that any undesirable
M−benzimidazolylidene complex can rearrange to the more
stable CNHC^Cphenyl chelate complex for M = Rh, while such a
rearrangement is less likely for M = Ir. We therefore assume
that the selective formation of monometalated rhodium chelate
complex [5]I is favored, but only for metals forming reasonably
labile M−CNHC bonds such as rhodium (and not IrIII) which
can rearrange to the most stable complex.
Scheme 1. Synthesis of bis-NHC Ligand Precursor 4(I)2
Complex [5]I was obtained in a high yield of 85% and
characterized by NMR spectroscopy, mass spectrometry, and
elemental analysis. The 1H NMR spectrum features the
resonance for the benzimidazolium N−CH−N proton at δ =
9.44 ppm only slightly upfield from the equivalent resonance in
4(I)2, while the resonance for an imidazolium N−CH−N
proton was no longer detected. Clear evidence for the
metalation by rhodium was provided by 13C{1H} NMR
The synthesis of 4(I)2 commenced with the preparation of 1
from 5-fluoro-2-nitroaniline and imidazole in 99% yield by a
nucleophilic aromatic substitution. This was followed by
reduction of the nitro group in 1 using hydrazine monohydrate
and a catalytic amount of Raney nickel to give the diamine 2.
The benzimidazol moiety was constructed by condensation of
the diamine 2 with ammonium chloride and triethyl
orthoformate to give 3. Finally, the triple N-alkylation was
performed in a stepwise fashion. Deprotonation of the
benzimidazole/imidazole derivative 3 with sodium hydride
followed by the addition of methyl iodide resulted in the
formation of di-NHC precursor 4(I)2 in 49% yield.
Salt 4(I)2 was fully characterized by NMR spectroscopy,
mass spectrometry, and elemental analysis. In addition, an X-
ray diffraction study confirmed the composition and molecular
structure of 4(I)2 (see the Supporting Information, Figure
S23). Bisazolium salt 4(I)2 was used as the starting material for
the preparation of heterobimetallic bis-NHC complexes. These
were prepared through the stepwise metalation of the NHC
donors obtained by the sequential deprotonation of the
azolium groups in 4(I)2.
spectroscopy showing the resonances for the rhodium bound
1
CNHC and Cphenyl carbon atoms at δ = 180.3 ppm (d, JC,Rh
=
54.2 Hz) and δ = 157.5 ppm (d, 1JC,Rh = 36.7 Hz), respectively.
The molecular structure of [5]I was determined by an X-ray
diffraction study (Figure 1). Cation [5]+ adopts the classical
piano-stool geometry. The rhodium center is coordinated by a
bidentate, orthometalated N-phenyl substituted imidazolyli-
dene ligand; a pentamethylcyclopentadienyl ligand; and an
iodo ligand. The CNHC^Cphenyl chelate ligand exhibits a rather
small bite angle (angle C2−Rh−C8 78.01(19)°), leading to
angles involving the iodo ligand (I−Rh−C2 91.70(15)° and I−
Rh−C8 92.80(14)°) which are both larger than 90°. In accord
with previous observations,6 a smaller N−C−N angle (N1−
C2−N3 105.4(5)°) was observed for the metalated diamino-
heterocycle in comparison to the protonated one (N13−C14−
N15 110.4(5)°). The Rh−C2 distance measures 1.993(5) Å
and thus falls in the range previously reported for rhodacycle
complexes bearing an CNHC^Cphenyl chelate ligand.7 The Rh−
C2 distance, however, is significantly shorter than the Rh−C8
separation of 2.049(5) Å. This situation was previously
suggested by 13C{1H} NMR spectroscopy where the longer
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complex was not isolated but used directly for the trans-
metalation reaction.
The RhIII/PdII complex [6] was synthesized in 61% yield by
transmetalation of the metalloligand from the AgI/RhIII-bis-
NHC complex to [Pd(μ-Cl)(dmba)]2 in dichloromethane
(Scheme 3). Complex [6] was obtained as an air stable mixture
of two isomeric complexes in the ratio 60:40. The NMR
spectra feature two sets of resonances (see the Supporting
Information, Figures S11 and S12) for the two atropisomers.
For example, the CNHC resonances were observed in the
13C{1H} NMR spectrum at δ = 181.9 ppm (d, 1JC,Rh = 54.6 Hz,
CNHC−Rh), δ = 181.3 ppm (CNHC−Pd) for isomer A, and at δ
= 181.6 ppm (CNHC−Pd), δ = 180.0 ppm (d, 1JC,Rh = 54.7 Hz,
CNHC−Rh) for isomer B. The two different atropisomers
apparently result from the hindered rotation about the Pd−
CNHC bond, which leads to two different orientations of the
{Pd(dmba)I} moiety relative to the Rh(Cp*) moiety.
Restricted rotation about the Pd−CNHC bond in palladium
complexes bearing the dmba ligand resulting in the formation
of atropisomers has been observed multiple times and is rather
common for such complexes.9
Figure 1. Molecular structure (50% displacement ellipsoids, hydrogen
atoms except for H14 have been omitted for clarity) of complex
cation [5]+ in [5]I·2.5CH2Cl2. The asymmetric unit contains two
essentially identical equivalents of [5]I, only one of which is depicted.
Selected bond distances (Å) and angles (deg): Rh−I 2.6903(5), Rh−
C2 1.993(5), Rh−C8 2.049(5), range Rh−CCp* 2.142(5)−2.269(5),
N1−C2 1.352(6), N3−C2 1.341(6), N13−C14 1.332(7), N15−C14
1.339(7); I−Rh−C2 91.70(15), I−Rh−C8 92.80(14), C2−Rh−C8
78.01(19), N1−C2−N3 105.5(4), N13−C14−N15 110.4(5).
1
Rh−C8 separation leads to a smaller JC,Rh coupling constant
of 36.7 Hz than the shorter Rh−C2 bond (1JC,Rh = 54.2 Hz).
The remaining bond distances and bond angles in [5]I fall in
the range observed previously for related rhodium complex-
es.7,8a
Similarly, complex [7] was prepared by transmetalation of
the metalloligand from the in situ generated AgI/RhIII-bis-NHC
complex to [IrCl(cod)]2 in dichloromethane in 39% yield. No
isomeric complexes were observed in the case of [7]. The
13C{1H} NMR spectrum features the resonances for the Ir−
CNHC carbon atom at δ = 188.4 ppm and for the Rh−CNHC
Compound [5]I appears to be a useful starting material for
the preparation of heterobimetallic complexes. It can act as a
metalloligand and become metalated at the benzimidazolium
site with a second metal. The rhodacycle in [5]I is stable
enough to tolerate the deprotonation/metalation of the
benzimidazolium group. Starting from [5]I, we have prepared
the heterobimetallic RhIII/M complexes [6]−[9] (M = PdII,
IrI, AuI, and RuII, Scheme 3) in moderate yields, which are
most likely caused by the two reactions (reaction with Ag2O
followed by transmetalation) performed in a one-pot synthesis.
1
carbon atom at δ = 182.1 ppm (d, JC,Rh = 54.7 Hz).
Crystals of composition [7]·CH2Cl2 were obtained by vapor
diffusion of diethyl ether into a solution of [7] in dichloro-
methane. The molecular structure of the heterodinuclear
complex (Figure 2) features a hexacoordinate RhIII and a
Scheme 3. Preparation of Heterobimetallic Complexes [6]−
[9] from [5]I
Figure 2. Molecular structure (50% displacement ellipsoids, hydrogen
atoms have been omitted for clarity) of complex [7]. Selected bond
distances (Å) and angles (deg): Ir−I2 2.6515(5), Ir−C14 2.024(5),
Ir−C28 2.113(7), Ir−C29 2.102(6), Ir−C32 2.203(6), Ir−C33
2.189(6), Rh−I1 2.6865(5), Rh−C2 1.992(5), Rh2−C8 2.038(5),
range Rh−CCp* 2.153(5)−2.268(6); I2−Ir−C14 89.09(15), I1−Rh−
C2 90.18(15), I1−Rh−C8 90.15(15), C2−Rh−C8 78.2(2), N1−
C2−N3 104.7(4), N13−C14−N15 106.0(5).
square-planar, tetracoordinate IrI atom. The metric parameters
of the complex fragment containing the rhodium atom do not
differ significantly from those found in the mononuclear
complex [5]I, indicating that the second metalation does not
affect the bond parameters involving the rhodium atom.
Metalation of the benzimidazolium site, however, changes the
metric parameters within the affected diaminoheterocycle
significantly. In accord with previous observations,6 the N−
C−N angle of the iridium−metalated benzimidazolylidene
shrinks to 106.0(5)° from 110.4(5)° in the benzimidazolium
The metalation of the benzimidazolim site in [5]I was
accomplished by transmetalation of the metalloligand from the
in situ generated AgI/RhIII-bis-NHC complex to PdII, IrI, AuI,
and RuII complexes. The AgI/RhIII-bis-NHC complex was
obtained from [5]I and Ag2O in dichloromethane. This
C
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unit of [5]I. The bite angle of the bidentate CNHC^Cphenyl
ligand measures 78.2(2)° and is thus very similar to the
equivalent bite angle in [5]I. The Ir−Ccod bond distances trans
to the NHC ligand (Ir−C32 2.203(6) Å, Ir−C33 2.189(6) Å)
are significantly longer than the Ir−Ccod bond distances trans
to the iodo ligand (Ir−C28 2.113(7) Å, Ir−C29 2.102(6) Å)
in accord with a long C28−C29 bond of 1.439(10) Å and a
shorter C32−C33 bond of 1.399(10) Å. This is most likely due
to the anionic iodo ligand being a better donor than the NHC
ligand.
Reaction of [5]I with Ag2O followed by transmetalation
with [AuCl(tht)] yielded the heterobimetallic AuI/RhIII
complex [8] (Scheme 3). This complex was characterized by
1H and 13C{1H} NMR spectroscopy, mass spectrometry, and
elemental analysis. The 13C{1H} NMR spectrum of [8]
features the characteristic resonances for the CNHC−Au carbon
atom at δ = 185.7 ppm and for the CNHC−Rh carbon atom at δ
Figure 4. Molecular structure (50% displacement ellipsoids, hydrogen
atoms have been omitted for clarity) of complex [9]. Selected bond
distances (Å) and angles (deg): Rh−I1 2.6878(7), Rh−C2 1.998(7),
Rh−C8 2.060(6), range Rh−CCp* 2.154(7)−2.260(7), Ru−I2
2.7282(9), Ru−I3 2.7583(9), Ru−C14 2.074(7); I1−Rh−C2
92.6(2), I1−Rh−C8 93.6(3), C2−Rh−C8 77.5(3), I2−Ru−I3
82.84(3), I2−Ru−C14 97.9(2), I3−Ru−C14 86.3(2), N1−C2−N3
104.9(6), N13−C14−N15 105.0(5).
1
= 182.7 ppm (d, JC,Rh = 54.7 Hz). The latter resonance is
almost unchanged when compared to the equivalent
resonances in [5]I and [7].
Crystals of [8]·1.25CH2Cl2 were obtained by vapor diffusion
of diethyl ether into a CH2Cl2 solution of [8]. The structure
analysis (Figure 3) shows the rhodium atom coordinated the
The preparation of complexes [6]−[9] illustrates the
suitability of the bisazolium salt 4(I)2 for the preparation of
a variety of heterobimetallic complexes. The coordination of
the three different metals (IrI, AuI, and RuII) to the
monometallic complex[5]I has little influence on the metric
parameters of the {Rh(Cp*)(NHC)I} moiety in the resulting
heterobimetallic complexes as illustrated by the almost
unchanged Rh−CNHC (1.993(5) in [5]I, 1.992(5) in [7],
2.003(5) in [8], and 1.998(7) Å in [9]) and Rh−Cphenyl
distances (2.049(5) in [5]I, 2.038(5) in [7], 2.051(5) in [8],
and 2.060(6) Å in [9]).
Next, we wanted to test the applicability of the
heterobimetallic complexes in orthogonal tandem catalysis.
We thought that complexes of type [6] would be perfect to
start this investigation given our previous experience in
designing tandem processes for the Ir/Pd and Rh/Pd
couples.4a,b,b,e In order to expand the number of Ir/Pd and
Rh/Pd catalysts used and aiming to perform a more detailed
comparative study, we also prepared two additional hetero-
bimetallic MIII/PdII (M = Rh, Ir) complexes based on a
benzene-bridged bis-imidazolylidene ligand. As shown in
Scheme 4, complexes [12] and [13] were prepared from the
monometallic MIII complexes [10] and [11], which recently
have been described.8a
The second metalation of the metalloligands [11] and [12]
with PdII was achieved by transmetalation of the in situ
generated AgI/MIII-NHC (M = Rh, Ir) complexes, generated
by the addition of Ag2O to [10] and [11], respectively, with
[PdCl(dmba)]2. The new complexes were characterized by
NMR spectroscopy, mass spectrometry, and elemental analysis.
The NMR spectra of complexes [12] and [13] display double
signal sets for all resonances (Figures S19−S22) indicative of
the formation of two atropisomers. These are present in ratios
of 55:45 [12] and 52:48 [13], respectively. The existence of
the two atropisomers is a consequence of the restricted
rotation about the Cphenyl−NNHC bond of the imidazolylidene
donor bound to PdII. Formation of similar atropisomers has
been observed for complex [6] and for additional palladium
NHC complexes bearing the dmba ligand.9
Figure 3. Molecular structure (50% displacement ellipsoids, hydrogen
atoms have been omitted for clarity) of [8]. The asymmetric unit
contains two essentially identical molecules of [8], only one of which
is depicted, and 2.5 CH2Cl2 molecules. Selected bond distances (Å)
and angles (deg): Au−I2 2.5309(4), Au−C14 1.988(5), Rh−I
2.6923(5), Rh−C2 2.003(5), Rh−C8 2.051(5), range Rh−CCp*
2.158(6)−2.261(5); I2−Au−C14 173.34(15), I1−Rh−C2
86.61(14), I1−Rh−C8 88.73(13), C2−Rh−C8 78.3(2), N1−C2−
N3 104.7(4), N13−C14−N15 106.2(4).
same fashion as previously observed for [5]I and [7]. The gold
atom is coordinated almost linearly (angle I2−Au−C14
173.34(15)°). All other metric parameters in [8] compare
well to equivalent parameters in [7]. The bonds involving the
gold atom fall in the range previously reported for related
gold(I) complexes.10
Finally, complex [5]I was metalated at the benzimidazolium
site with ruthenium(II) by reacting the monometallic complex
[5]I with Ag2O followed by transmetalation with [RuCl2(p-
cymene)]2 in 1,2-dichloroethane (Scheme 3). 1H and 13C{1H}
NMR spectroscopy indicate the formation of the hetero-
bimetallic complex [9]. Formation of [9] was confirmed by an
X-ray diffraction analysis (Figure 4) showing the two metals
coordinated in a piano-stool geometry. The bond parameters
are unspectacular, and the {Rh(Cp*)(NHC)I} moiety in [9] is
essentially unchanged when compared to the same moiety in
[7] and [8].
Catalytic Studies. The heterobimetallic Pd/M (M = Ir,
Rh) complexes [6], [12], and [13] were tested in two different
catalytic tandem transformations. These were the Suzuki−
Miyaura coupling/transfer hydrogenation and the Suzuki−
Miyaura coupling/α-alkylation of para-bromoacetophenone. In
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Scheme 4. Preparation of Heterobimetallic MIII/PdII Complexes [12] and [13]
order to determine if the heterobimetallic nature of the
complexes would generate any benefits compared to the
activity provided by mixtures of monometallic analogs, we also
prepared the known complexes [14],11 [15],12 [16],9a and
[17]9a (Scheme 5) using described synthetic procedures.
catalyst is very effective in this tandem reaction. The mixtures
containing [14] + [17] and [15] + [16] were less effective,
indicating that the optimum combination of catalysts for
promoting the tandem reaction involves the use of the
rhodium catalyst (rather than iridium) and the imidazolylidene
(rather than the benzimidazolylidene) palladium catalyst.
Next, the performance of the three heterobimetallic
complexes [6], [12], and [13] (entries 4−6) was evaluated
for the same process. The catalytic activity observed for the
heterobimetallic complexes [12] and [13] was comparable to
that displayed by the most active mixture [14] + [16](entry 2)
and superior to that shown by [6]. Interestingly, the PdII/IrIII
complex [13] (entry 6) showed somewhat higher activity than
the corresponding mixture [15] + [16] of two monometallic
complexes (entry 3). Finally, a blank reaction carried out in the
absence of any catalyst afforded only the hydrogenated
reaction product III in 54% yield.
Scheme 5. Monometallic Complexes Prepared for
Comparative Catalytic Studies
In order to get further insight into the catalytic process, the
time-dependent reaction profile of the Suzuki−Miyaura
coupling/transfer hydrogenation of p-bromoacetophenone
was studied (Figure 5). The reaction was carried out in 2-
propanol in the presence of Cs2CO3 at 100 °C using 2 mol %
of the most active catalyst [13]. As can be seen from the
reaction profile, the consumption of the p-bromoacetophenone
is accompanied by the immediate formation of I. The
subsequent reduction of the ketone affords the corresponding
alcohol derivative II in 84% yield after 24 h. The reaction
profile also shows that the palladium catalyzed C−C coupling
between the acetophenone and the boronic acid occurs almost
instantaneously. The reduction of the ketone, however, is a
These monometallic complexes feature virtually the same
stereoelectronic properties as the corresponding complex
fragments in complexes [6], [12], and [13].
First, we evaluated the activity of three mixtures containing
the monometallic complexes in the catalytic Suzuki coupling/
transfer hydrogenation of p-bromoacetophenone in isopropyl
alcohol (Table 1, entries 1−3) under standard reaction
conditions.4a The reaction mixture containing complexes
[14] + [16] (entry 2) produced compound II in high yield
(84%). Compound II resulted from the Suzuki−Miyaura C−C
coupling and the reduction of the ketone to an alcohol,
indicating that the combination of a rhodium and a palladium
a
Table 1. Catalytic Suzuki Coupling/Transfer Hydrogenation of p-Bromoacetophenone in Isopropyl Alcohol
b
yield %
entry
catalyst
time h
conversion %
I
II
III
1
2
3
4
5
6
7
[14] + [17]
[14] + [16]
[15] + [16]
[6]
[12]
[13]
20
20
20
20
20
20
20
98
99
98
99
99
99
70
36
15
25
46
17
15
0
62
84
73
53
82
84
0
0
0
0
0
0
0
54
none
a
Reaction conditions: 0.36 mmol of p-bromoacetophenone, 0.54 mmol of phenylboronic acid, 1.08 mmol of Cs2CO3, 2 mL of 2-propanol (as
b
reagent and solvent), 2 mol % catalyst loading, 100 °C, 20 h. Yields were determined by GC using anisole (0.36 mmol) as internal standard.
E
DOI: 10.1021/acs.organomet.9b00120
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Article
alcohol IV (entries 1 and 2). A blank experiment was carried
out in the absence of any catalyst (entry 3). While 54%
conversion was detected in this experiment, a mixture of
decomposition products was obtained, and none of the
compounds I−IV was detected. We then evaluated the
performance of the heterobimetallic complexes [12] and
[13] (entries 4 and 5). Of these, the heterobimetallic PdII/
RhIII complex [12] produced 24% of III and 40% of the
alcohol IV (entry 4), while the PdII/IrIII complex [13]
produced 37% of III and 13% of IV (entry 5). These results
indicate that both heterobimetallic complexes are significantly
more active than the respective mixtures of the monometallic
analogues and also showed that the heterobimetallic catalysts
are more active in the reduction of the ketone to the alcohol.
At this point, it should be mentioned that the alkylation of
the ketone to give III and subsequently alcohol IV proceeds
via the well-accepted steps for an α-alkylation process14
followed by reduction of the ketone by transfer hydro-
genation.15 This reaction sequence involves (i) hydrogen
transfer from n-butanol to iridium to give the aldehyde and the
iridium−hydride complex, (ii) base-catalyzed condensation
between the resulting butanal and the ketone to give the α,β-
unsaturated ketone, (iii) selective hydrogenation of the α,β-
unsaturated ketone to form ketone III, and (iv) reduction of
III by an iridium dihydride, again generated by reaction of the
catalyst and n-butanol. Obviously, the overall process implies
that butanal is produced in the reaction sequence, although we
were unable to detect it.
Figure 5. Time-dependent reaction profile of the Suzuki−Miyaura
coupling/transfer hydrogenation in 2-propanol using catalyst [13].
Reaction conditions: 0.36 mmol of p-bromoacetophenone, 0.54 mmol
of phenylboronic acid, 1.08 mmol of Cs2CO3, 2 mL of 2-propanol (as
reagent and solvent), 2 mol % catalyst loading, 100 °C, 20 h. Yields
were determined by GC using anisole (0.36 mmol) as an internal
standard.
much slower process and constitutes the rate-determining step
of the overall reaction. This situation also accounts for the
observation that no direct reduction of p-bromoacetophenone
to the alcohol III was observed in the presence of any catalyst
(Table 1).
In view of the results obtained for the Suzuki−Miyaura
coupling/transfer hydrogenation reaction, we next decided to
explore the performance of the heterobimetallic catalysts in the
Suzuki−Miyaura coupling/α-alkylation of p-bromoacetophe-
none.4a This model reaction has straightforward applications,
since the resulting biphenyl substituted ketones are known to
behave as nonsteroidal inhibitors of 5α-reductase, the enzyme
that catalyzes the conversion of testosterones to dihydrotes-
tosterone.13
We initially tested the activity of mixtures of [14] + [16]
and [15] + [16] (Table 2, entries 1 and 2), using a 2 mol %
catalyst loading in the presence of Cs2CO3 and n-butyl alcohol
both as a solvent and as an alkylating reagent. Although full
conversion was observed for both mixtures, only a small
amount of the alkylated biphenyl ketone III was obtained
together with a negligible amount of the biphenyl alkylated
In order to confirm that the reaction was homogeneously
catalyzed and that the activity of the catalysts was not due to
the formation of metal nanoparticles generated by decom-
position of the heterobimetallic complex, we carried out the
same reaction using catalyst [12] in the presence of a drop of
mercury (entry 6). We observed that both, the activity and
selectivity of the process was quasi-identical compared to the
performance in the absence of mercury (compare to entry 4),
and therefore the contribution of heterogeneous nanoparticles
to the catalytic process can be discarded.
The time dependent reaction profile of the Suzuki−Miyaura
coupling/α-alkylation is depicted in Figure 6. The reaction was
carried out in n-butyl alcohol in the presence of Cs2CO3 at 100
a
Table 2. Suzuki−Miyaura Coupling/α-Alkylation in n-Butyl Alcohol
b
yield %
entry
catalyst
time h
conversion %
I
II
III
IV
1
2
3
4
5
[14] + [16]
[15] + [16]
none
[12]
[13]
20
20
20
20
20
20
99
99
54
99
99
99
0
11
0
6
4
14
23
0
12
8
21
12
0
24
37
20
6
5
0
40
13
38
c
6
[12]
6
11
a
Reaction conditions: 0.36 mmol of p-bromoacetophenone, 0.54 mmol of phenylboronic acid, 1.08 mmol of Cs2CO3, 2 mL of n-butanol (as
b
reagent and solvent), 2 mol % catalyst loading, 100 °C, 20 h. Yields were determined by GC using anisole (0.36 mmol) as an internal standard.
c
The reaction was performed in the presence of a drop of mercury.
F
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Article
Figure 6. Time-dependent reaction profile of the Suzuki−Miyaura coupling/α-alkylation in n-butyl alcohol with catalyst [12]. Reaction conditions:
0.36 mmol of p-bromoacetophenone, 0.54 mmol of phenylboronic acid, 1.08 mmol of Cs2CO3, 2 mL of n-butanol (as reagent and solvent), 2 mol
% catalyst loading, 100 °C, 20 h. Yields were determined by GC using anisole (0.36 mmol) as an internal standard under aerobic conditions.
(Thermo Scientific, ESI) spectrometers. Elemental analyses were
carried out with an Elementar Vario EL III CHNS analyzer. The
metal precursors [RhCp*(Cl)2]2,16 [IrCp*(Cl)2]2,16 [AuCl(tht)-
Cl],10 [Ir(cod)Cl]2,17 [Pd(dmba)(μ-Cl)]2,9a and [Ru(p-cymene)-
Cl2]2 were prepared according to literature procedures.
Synthesis of 5-(1H-Imidazol-1-yl)-2-nitroaniline 1. A sample of 5-
fluoro-2-nitroaniline (5.00 g, 32.0 mmol) and imidazol (8.72 g, 128.1
°C using 2 mol % of catalyst [12]. As can be seen from the
profile, the consumption of p-bromoacetophenone proceeds
rapidly with concurrent formation of I, indicating that the
palladium catalyzed C−C coupling is faster than the rhodium-
catalyzed borrowing hydrogen processes. The formation of
compounds II and IV occurs at a similar rate, as both involve
the borrowing-hydrogen processes with a common rate-
determining step. The formation of IV as the major product
is only completed after 20 h of reaction time.
18
CONCLUSIONS
■
In summary, we have used bisazolium salts for the preparation
of a variety of heterobimetallic complexes with the metal
combinations Rh/Ru, Rh/Ir, Rh/Au, Rh/Pd, and Ir/Pd. The
easy-to-prepare bisazolium salts together with the high-yield
syntheses of the metal complexes illustrate that this methodol-
ogy can be used for the preparation of a much larger library of
heterobimetallic complexes. The Rh/Pd and the Ir/Pd
complexes prepared were tested as catalysts in two orthogonal
tandem reactions, namely, the palladium catalyzed Suzuki−
Miyaura coupling/transfer hydrogenation and the Suzuki−
Miyaura coupling/α-alkylation of ketones. Although the
activity of the heterobimetallic catalysts was not superior
compared to that found for related catalysts reported by us4a
and others,8b two important results emerged from our study:
(i) in general, the activity of the heterobimetallic complexes
was superior to the activity shown by mixtures of the related
monometallic analogues, suggesting that catalytic additivity or
cooperativity may play an important role in the process, and
(ii) n-BuOH was found to play a dual action as an alkylating
and reducing agent, thus constituting a novelty in this type of
process for which iPrOH is often needed in order to reduce the
ketone to alcohol. The reasons for the higher activity of the
heterobimetallic complexes compared to mixtures of mono-
metallic ones remain elusive and are subject to speculations, as
is the case with related reactions described in the literature.
mmol) were dissolved in DMF (40 mL), and the mixture was stirred
at 100 °C for 2 days. The solution was then allowed to cool to
ambient temperature, and H2O (100 mL) was added. A yellow
precipitate formed, which was isolated by filtration, washed with H2O
(2 × 100 mL), and dried in vacuo to give 1 as a yellow solid. Yield:
6.52 g (31.9 mmol, 99%). 1H NMR (400 MHz, DMSO-d6): δ (ppm)
8.27 (s, 1H, H2), 8.09 (d, 3JH,H = 9.3 Hz, 1H, H8), 7.68 (s, 1H, H4/
5), 7.53 (s, 2H, NH2), 7.19 (d, 4JH,4H = 2.4 Hz, 1H, H11), 7.15 (s, 1H,
3
H4/5), 6.95 (dd, JH,H = 9.3 Hz, JH,H = 2.4 Hz, 1H, H7). 13C{1H}
NMR (101 MHz, DMSO-d6): δ (ppm) 147.0 (C9), 141.8 (C10),
135.5 (C2), 130.5 (C8), 128.6 (C6), 127.8 (C11), 117.5 (C7), 108.1
(C4/5), 107.8 (C4/5). MS (EI, 20 eV): m/z (%) 204 (100, [1]+).
HRMS (ESI, positive ions): m/z (%) 205.0722 (100, calculated for
[1+H]+, 205.0726), 227.0542 (50, calculated for [1 + Na]+,
227.0545). MS (MALDI-TOF, matrix DHB): m/z (%) 205 (100,
[1+H]+). Anal. Calcd for 1: C, 52.93; H, 3.95; N, 27.44. Found: C,
52.22; H, 3.90; N, 27.16.
Synthesis of 4-(1H-Imidazol-1-yl)benzene-1,2-diamine 2. Com-
pound 1 (4.67 g, 22.9 mmol) and hydrazine monohydrate (4.44 mL,
91.5 mmol) were dissolved in MeOH (50 mL). The yellow solution
was cooled to 0 °C, and a catalytic amount of Raney nickel was added
dropwise. The dark suspension was stirred at ambient temperature for
12 h. The suspension was then filtered through Celite leading to a
colorless solution. The solvent was removed to yield a white solid.
EXPERIMENTAL SECTION
■
General Procedures. All manipulations were carried out under an
argon atmosphere unless stated otherwise. H and 13C{1H} NMR
Yield: 3.68 g (21.1 mmol, 92%). H NMR (400 MHz, DMSO-d6): δ
1
1
spectra were recorded at 298 K on Bruker AVANCE I 400 and Bruker
AVANCE III 400 spectrometers. Chemical shifts (δ) are expressed in
parts per million downfield from tetramethylsilane using the residual
protonated solvent as an internal standard. Coupling constants are
expressed in Hertz. For the assignment of the NMR resonances, see
the numbering in the molecular plots. Mass spectra were obtained
with Reflex IV MALDI TOF (Bruker) and Orbitrap LTQ XL
(ppm) 7.88 (s, 1H, H2), 7.39 (s, 1H, H4/5), 7.01 (s, 1H, H4/5), 6.67
(d, 4JH,H = 2.2 Hz, 1H, H11), 6.60−6.57 (m, 2H, H7/8), 4.77 (s, 2H,
NH2), 4.64 (s, 2H, NH2). 13C{1H} NMR (101 MHz, DMSO-d6): δ
(ppm) 135.8 (s, C9/10), 135.2 (C-2), 134.2 (s, C9/10), 128.9 (C8),
127.6 (C6), 118.3 (C11), 114.2 (C7), 109.6 (C4/5), 107.0 (C4/5).
MS (EI, 20 eV): m/z (%) 174 (100, [2]+). HRMS (ESI, positive
ions): m/z (%) 175.0976 (100, calculated for [2 + H]+, 175.0984),
G
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Article
197.0799 (30, calculated for [2+Na]+, 197.0803). MS (MALDI-TOF,
matrix DHB): m/z (%) 175 (100, [2 + H]+). Anal. Calcd for 2: C,
62.05; H, 5.79; N, 32.16. Found: C, 61.74; H, 5.81; N, 31.94
Synthesis of 6-(1H-Imidazol-1-yl)-1H-benzo[d]imidazole 3. Dia-
mine 2 (3.68 g, 21.1 mmol), ammonium chloride (226 mg, 4.2 mmol)
[Rh(Cp*)Cl2]2(30.9 mg, 0.05 mmol) was added acetonitrile (40
mL). The red suspension was heated to reflux for 2 days. The
resulting yellow suspension was filtered through Celite, and the filtrate
was brought to dryness under reduced pressure. The yellow residue
was purified by chromatography (silica gel, CH2Cl2/MeOH, 6:1) to
give compound [5]I as an orange, hygroscopic solid. Yield: 61 mg
1
(0.085 mmol, 85%). H NMR (400 MHz, DMSO-d6): δ (ppm) 9.44
3
(s, 1H, H13), 8.22 (d, JH,H = 2.1 Hz, 1H, H5), 8.18 (s, 1H, H11),
7.90 (s, 1H, H8), 7.61 (d, 3JH,H = 2.1 Hz, 1H, H4), 4.10 (s, 3H, H16/
17), 4.04 (s, 3H, H16/17), 3.84 (s, 3H, H15), 1.82 (s, 15H, Cp*-
CH3). 13C{1H} NMR (101 MHz, DMSO-d6): δ (ppm) 180.3 (d,
1
1JC,Rh = 54.2 Hz, C2), 157.5 (d, JC,Rh = 36.7 Hz, C7), 144.9 (s, C6),
and triethyl orthoformate (5.25 mL, 31.7 mmol) were dissolved in
MeOH (40 mL), and the mixture was heated to reflux for 2 days.
After cooling to ambient temperature, all volatiles were removed in
vacuo. The residue was dissolved in H2O (20 mL), and the solution
was extracted with EtOAc (10 × 80 mL). The combined organic
extracts were dried over MgSO4, and the solvent was removed in
128.8 (s, C9/10), 128.6 (s, C9/10), 124.4 (s, C4), 120.4 (s, C8),
115.9 (s, C5), 97.9 (d, 1JC,Rh = 4.8 Hz, Cp*-C), 95.4 (s, C11), 37.4 (s,
C15), 33.0 (s, C16/17), 32.8 (s, C16/17), 10.1 (s, Cp*-CH3). HRMS
(ESI, positive ions): m/z (%) 591.0485 (100, calculated for [5]+,
591.0492). MS (MALDI-TOF, matrix DHB): m/z (%) 591 (100,
[5]+). Anal. Calcd for [5]I·H2O: C, 37.52; H, 4.24; N, 7.61. Found:
C, 37.57; H, 4.16; N, 7.43.
1
vacuo to give 3 as a red solid. Yield: 3.56 g (19.3 mmol, 91%). H
NMR (400 MHz, DMSO-d6): δ (ppm) 12.68 (br, 1H, NH), 8.29 (s,
General Procedure for the Synthesis of Complexes [6]−[8].
To a mixture of the monometallic complex [5]I (72 mg, 0.10 mmol)
and Ag2O (23 mg, 0.10 mmol) was added CH2Cl2 (15 mL). The
reaction mixture was stirred at ambient temperature for 24 h under
exclusion of light. Subsequently, the second metal precursor ([Pd(μ-
Cl)(dmba)]2, 28 mg, 0.05 mmol or [Ir(μ-Cl)(cod)]2, 34 mg, 0.05
mmol, or [AuCl(tht)], 32 mg, 0.10 mmol) and KI (166 mg, 1.0
mmol) were added, and the reaction mixture was stirred for an
additional 24 h. The resulting suspensions were filtered through
Celite, and the solvent of the filtrate was removed under reduced
pressure.
1H, H2), 8.16 (s, 1H, H13), 7.84 (s br, 1H, H11), 7.73 (s, 1H, H4/
5), 7.71 (d, 3JH,H = 8.7 Hz, 1H, H8), 7.43 (dd, 3JH,H = 8.7 Hz, 4JH,H
=
2.0 Hz, 1H, H7), 7.10 (s, 1H, H4/5). 13C{1H} NMR (101 MHz,
DMSO-d6): δ (ppm) 143.6 (C13), 135.9 (C2), 131.8 (br), 129.5,
119.8 (br), 118.8, 115.7 (br), 112.4 (br), 111.1 (br), 104.2 (br). MS
(EI, 20 eV): m/z (%) 184 (100, [3]+). HRMS (ESI, positive ions):
m/z (%) 185.0819 (80, calculated for [3 + H]+, 185.0827), 207.0639
(100, calculated for [3 + Na]+, 207.0647). MS (MALDI-TOF, matrix
DHB): m/z (%) 185 (100, [3+H]+). Anal. Calcd for 3: C, 65.21; H,
4.38; N, 30.42. Found: C, 65.11; H, 4.50; N, 30.05.
Synthesis of [N-(6′-(1′, 3′-Dimethylbenzimidazolyl)-N′-methyl]-
imidazoliumdiiodide 4(I)2. To a solution of compound 3 (3.56 g,
Complex [6]. Analytically pure [6] was obtained as an isomer
mixture by column chromatography on aluminum oxide/CH2Cl2.
19.3 mmol) in dry THF (40 mL) was added sodium hydride (60%
dispersion in mineral oil, 1.00 g, 25.1 mmol) at 0 °C. The reaction
mixture was then stirred at ambient temperature until the gas
evolution had ceased. Subsequently, methyl iodide (1.33 mL, 21.3
mmol) was added dropwise, and the suspension was stirred for 12 h.
All volatiles were then removed in vacuo. Acetonitrile (50 mL) and
methyl iodide (4.81 mL, 77.2 mmol) were added to the residue, and
the solution was heated under reflux for 2 days. The resulting
precipitate was isolated by filtration, washed with a small amount of
acetonitrile, and dried in vacuo. The bisazolium salt 4(I)2 was
1
Yield: 58 mg (0.061 mmol, 61%). Isomer A (60%), H NMR (400
MHz, CDCl3): δ (ppm) 7.71 (s, 1H, H8), 7.47 (d, 3JH,H = 2.1 Hz, 1H,
H5), 7.15 (s, 1H, H11), 7.02 (d, 3JH,H = 2.1 Hz, 1H, H4), 7.06−6.99
(m, 1H, H22), 6.99−6.92 (m, 1H, H21), 6.72−6.67 (m, 1H, H20),
5.94−5.87 (m, 1H, H19), 4.13 (s, 3H, H16), 4.07 (s, 3H, H17),
4.02−4.00 (m, 1H, H24), 3.96 (s, 1H, H24), 3.90 (s, 3H, H15), 3.01
(s, 3H, H25/26), 2.99 (s, 3H, H25/26), 1.87 (s, 15H, Cp*-CH3).
13C{1H} NMR (101 MHz, CDCl3): δ (ppm) 181.9 (d, JC,Rh = 54.6
1
1
1
Hz, C2), 181.3 (s, C13), 152.9 (s, C18), 150.7 (d, JC,Rh = 36.1 Hz,
obtained as an off-white solid. Yield: 4.54 g (9.42 mmol, 49%). H
C7), 148.4 (s, C23), 141.2 (s, C6), 134.9 (s, C19), 133.0 (s, C9),
132.1 (s, C10), 125.8 (s, C20), 124.1 (s, C21), 122.6 (s, C4), 122.4
(s, C22), 118.9 (s, C8), 115.2 (s, C5), 98.1 (d, JC,Rh = 4.9 Hz, Cp*-
NMR (400 MHz, DMSO-d6): δ (ppm) 9.97 (s, 1H, H2), 9.86 (s, 1H,
H13), 8.65 (d, JH,H = 2.1 Hz, 1H, H11), 8.44 (s, 1H, H5), 8.35 (d,
4
1
3JH,H = 8.9 Hz, 1H, H8), 8.12 (dd, 3JH,H = 8.9 Hz, 4JH,H = 2.1 Hz, 1H,
H7), 8.05 (s, 1H, H4), 4.18 (s, 3H, H16/17), 4.15 (s, 3H, H16/17),
4.01 (s, 3H, H15). 13C{1H} NMR (101 MHz, DMSO-d6): δ (ppm)
145.5 (C13), 136.5 (C2), 132.7 (C6), 131.7 (C9), 131.9 (C10),
124.5 (C4), 121.2 (C5), 120.2 (C7), 115.4 (C8), 107.7 (C11), 36.3
(C15), 33.8 (C16/17), 33.7 (C16/17). HRMS (ESI, positive ions):
m/z (%) 355.0434 (100, calculated for [4 + I]+, 355.0420). Anal.
Calcd for 4(I2): C, 32.39; H, 3.35; N, 11.62. Found: C, 31.98; H,
3.37; N, 11.54.
C), 93.2 (s, C11), 71.9 (s, C24), 52.2 (s, C25/26), 51.9 (s, C25/26),
38.0 (s, C15), 35.5 (s, C17), 35.3 (s, C16), 10.6 (s, Cp*-CH3).
Isomer B (40%), 1H NMR (400 MHz, CDCl3): δ (ppm) 7.69 (s, 1H,
H8), 7.27 (s, 1H, H11), 7.22 (d, 3JH,H = 2.1 Hz, 1H, H5), 7.06−6.99
(m, 1H, H22), 6.99−6.92 (m, 1H, H21), 6.72−6.67 (m, 1H, H20),
3
6.67 (d, JH,H = 2.1 Hz, 1H, H4), 5.94−5.87 (m, 1H, H19), 4.17 (s,
3H, H16), 4.04 (s, 3H, H17), 3.98 (s, 2H, H24), 3.93 (s, 3H, H15),
3.01 (s, 3H, H25/26), 2.99 (s, 3H, H25/26), 1.85 (s, 15H, Cp*-
CH3). 13C{1H} NMR (101 MHz, CDCl3): δ (ppm) 181.6 (s, C13),
180.0 (d, 2JC,Rh = 54.7 Hz, C2), 153.4 (s, C18), 150.5 (d, 2JC,Rh = 35.9
Hz, C7), 148.7 (s, C23), 141.5 (s, C6), 134.6 (s, C19), 132.7 (s, C9),
132.1 (s, C10), 125.4 (s, C20), 124.0 (s, C21), 122.5 (s, C22), 122.2
(s, C4), 118.2 (s, C8), 115.4 (s, C5), 98.0 (d, 2JC,Rh = 4.8 Hz, Cp*-C),
94.4 (s, C11), 71.9 (s, C24), 52.1 (s, C25/26), 52.1 (s, C25/26), 38.4
(s, C15), 35.5 (s, C16), 35.3 (s, C17), 10.6 (s, Cp*-CH3). HRMS
(ESI, positive ions): m/z (%) 830.0424 (45, calculated for [6−I]+,
830.0431), 979.9371 (10, calculated for [6+Na]+, 979.9373). MS
(MALDI-TOF, matrix DHB): m/z (%) 830 (100, [6−I]+). Anal.
Synthesis of [5]I. To a mixture of 4(I)2 (96 mg, 0.20 mmol),
NaOAc (66 mg, 0.8 mmol), KI (133 mg, 0.8 mmol), and
H
DOI: 10.1021/acs.organomet.9b00120
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Calcd for [6]·CH2Cl2: C, 38.01; H, 4.06; N,6.72. Found: C, 38.33; H,
4.07; N, 6.35.
Complex [7]. Analytically pure [7] was obtained by extraction of
the raw product with Et2O (3 × 20 mL) and subsequent removal of
p-Cym-CH), 5.25−5.14 (m, 2H, p-Cym-CH), 4.27 (s, 3H, H16), 4.19
(s, 3H, H17), 3.92 (s, 3H, H15), 3.40−3.23 (m, 1H, p-Cym-
CH(CH3)2), 1.94 (s, 3H, p-Cym-CH3), 1.84 (s, 15H, Cp*-CH3), 1.31
(s, 3H, p-Cym-CH−CH3), 1.30 (s, 3H, p-Cym-CH-CH3). 13C{1H}
1
NMR (101 MHz, CDCl3): δ (ppm) 182.4 (d, JC,Rh = 51.5 Hz, C2),
1
181.7 (s, C13), 151.9 (d, JC,Rh = 35.9 Hz, C7), 141.6 (s, C6), 133.9
(s, C9), 133.0 (s, C10), 122.7 (s, C4), 119.0 (s, C8), 115.2 (s, C5),
1
111.1 (s, p-Cym-Cq), 99.4 (s, p-Cym-Cq), 98.2 (d, JC,Rh = 4.8 Hz,
Cp*-C), 92.9 (s, C11), 87.2 (s, p-Cym-CH), 87.1 (s, p-Cym-CH),
83.0 (s, p-Cym-CH), 82.8 (s, p-Cym-CH), 41.6 (s, C16), 41.6 (s,
C17), 38.0 (s, C15), 31.7 (s, p-Cym-CH(CH3)2), 23.0 (s, p-Cym-CH-
CH3), 22.9 (s, p-Cym-CH-CH3), 19.2 (s, p-Cym-CH3), 10.5 (s, Cp*-
CH3). HRMS (ESI, positive ions): m/z (%) 952.9605 (10, calculated
for [[9]−I]+, 952.9607). MS (MALDI-TOF, matrix DCTB): m/z
(%) 861 (53, [[9]+Cl−2I]+), 953 (100, [[9]−I]+). Anal. Calcd for
[9]·2H2O: C, 35.53; H, 4.16; N, 5.02. Found: C, 35.46; H, 3.78; N,
4.99.
General Procedure for the Synthesis of Complexes [12] and
[13]. The monometallic complexes [10] and [11] were prepared
according to published procedures.8a Samples of complexes [10]
(60.3 mg, 0.1 mmol) or [11] (69.3 mg, 0.1 mmol) and Ag2O (13.9
mg, 0.06 mmol) were suspended in CH2Cl2 (5 mL) and stirred for 1
h at ambient temperature under exclusion of light. After filtration
through Celite, the filtrate was added to a solution of ([Pd(μ-
Cl)(dmba)]2 (27.6 mg, 0.05 mmol) and KI (166 mg, 1.00 mmol) in
CH2Cl2 (5 mL). The reaction mixture was stirred for an additional 24
h. The suspension was filtered through Celite, and the filtrate was
evaporated to dryness.
the solvent from the extract in vacuo. Yield: 40 mg (0.039 mmol,
39%). 1H NMR (400 MHz, CDCl3): δ (ppm) 7.60 (s, 1H, H8), 7.44
3
3
(d, JH,H = 2.1 Hz, 1H, H5), 7.04 (s, 1H, H11), 7.02 (d, JH,H = 2.1
Hz, 1H, H4), 4.89−4.83 (m, 2H, cod-CH), 4.08 (s, 3H, H16), 4.03
(s, 3H, H17), 3.91 (s, 3H, H15), 3.04−2.89 (m, 2H, cod-CH), 2.32−
2.07 (m, 4H, cod-CH2), 1.88 (s, 15H, Cp*-CH3), 1.86−1.80 (m, 2H,
cod-CH2), 1.46−1.40 (m, 2H, cod-CH2). 13C{1H} NMR (101 MHz,
1
CDCl3): δ (ppm) 188.4 (s, C13), 182.1 (d, JC,Rh = 54.7 Hz, C2),
150.3 (d, 1JC,Rh = 36.1 Hz, C7), 140.7 (s, C6), 133.7 (s, C9), 132.7 (s,
C10), 122.6 (s, C4), 118.5 (s, C8), 115.0 (s, C5), 98.1 (d, 1JC,Rh = 4.4
Hz, Cp*-C), 92.8 (s, C11), 84.0 (s, cod-CH), 84.0 (s, cod-CH), 55.5
(s, cod-CH), 55.3 (s, cod-CH), 38.0 (s, C15), 34.1 (s, C16/17), 34.1
(s, C16/17), 33.0 (s, cod-CH2), 33.0 (s, cod-CH2), 30.3 (s, cod-
CH2), 30.3 (s, cod-CH2), 10.6 (s, Cp*-CH3). MS (MALDI-TOF,
matrix DHB): m/z (%) 891 (20, [7−I]+). Anal. Calcd for [7]·H2O:
C, 35.95; H, 4.09; N, 5.41. Found: C, 35.45; H, 3.85; N, 4.99.
Complex [8]. Analytically pure [8] was obtained by column
chromatography on silica gel/CH2Cl2. Yield: 34 mg, 0.04 mmol, 40%.
Complex [12]. Analytically pure [12] was obtained as an isomer
mixture by column chromatography on aluminum oxide using
1H NMR (400 MHz, CD2Cl2): δ (ppm) 7.74 (s, 1H, H11), 7.56 (d,
3JH,H = 2.1 Hz, 1H, H5), 7.23 (s, 1H, H8), 7.12 (d, 3JH,H = 2.1 Hz, 1H,
H4), 4.05 (s, 3H, H16/17), 3.98 (s, 3H, H16/17), 3.90 (s, 3H, H15),
1.85 (s, 15H, Cp*-CH3). 13C{1H} NMR (101 MHz, CD2Cl2): δ
(ppm) 185.7 (s, C13), 182.7 (d, 1JC,Rh = 54.7 Hz, C2), 154.7 (d, 1JC,Rh
= 36.2 Hz, C7), 143.6 (s, C6), 131.7 (d, 3JC,Rh = 2.0 Hz, C9), 130.9 (s,
C10), 123.6 (s, C4), 120.4 (s, C8), 115.6 (s, C5), 98.6 (d, 1JC,Rh = 4.7
Hz, Cp*-C), 94.2 (s, C11), 38.4 (s, C15), 35.0 (s, C16/17), 35.0 (s,
C16/17), 10.1 (s, Cp*-CH3). HRMS (ESI, positive ions): m/z (%)
936.9026 (30, calculated for [8 + Na]+, 936.9022), 952.8760 (90,
calculated for [8 + K]+, 952.8761), 1377.0490 (100, calculated for
[2[8]−Au−2I]+, 1377.0493). MS (MALDI-TOF, matrix DCTB): m/
z (%) 787 (75, [8−I]+), 1377 (39, [2[8]−Au−2I]+). Anal. Calcd for
[8]: C, 30.22; H, 3.09; N, 6.13. Found: C, 29.90; H, 2.99; N, 5.90.
Synthesis of Complex [9]. To a mixture of complex [5]I (72 mg,
0.1 mmol) and Ag2O (23 mg, 0.1 mmol) was added 1,2-
CH2Cl2/MeOH (6:1). Yield: 45.4 mg (0.047 mmol, 47%). Isomer
A (55%), 1H NMR (400 MHz, CDCl3): δ (ppm) 8.54 (d, 4JH,H = 2.2
3
3
Hz, 1H, H11), 7.61 (d, JH,H = 2.1 Hz, 1H, H5), 7.59 (d, JH,H = 8.0
3
3
Hz, 1H, H8), 7.29 (d, JH,H = 1.9 Hz, 1H, H16), 7.09 (d, JH,H = 1.9
Hz, 1H, H15), 7.01−6.94 (m, 2H, H4/H9), 6.89−6.80 (m, 2H, H22/
3
H23), 6.73−6.66 (m, 1H, H21), 5.87 (d, JH,H = 7.5 Hz, 1H, H20),
2
4.01 (s, 3H, H18), 3.88 (s, 3H, H17), 3.81 (d, JH,H = 13.9 Hz, 1H,
H25), 3.54 (d, 2JH,H = 13.9 Hz, 1H, H25), 2.88 (s, 3H, H26), 2.66 (s,
3H, H27), 1.72 (s, 15H, Cp*-CH3). 13C{1H} NMR (101 MHz,
1
CDCl3): δ (ppm) 182.5 (d, JC,Rh = 55.5 Hz, C2), 172.1 (s, C13),
157.0 (d, 1JC,Rh = 35.0 Hz, C7), 152.8 (s, C19), 147.7 (s, C24), 144.9
(s, C6), 138.2 (s, C8), 135.8 (s, C10), 134.7 (s, C20), 125.2 (s, C21),
123.5 (s, C22), 122.5 (s, C15), 122.5 (s, C4), 121.8 (s, C23), 121.8
(s, C16), 120.1 (d, 3JC,Rh = 1.2 Hz, C9), 115.8 (s, C5), 109.7 (s, C11),
97.8 (d, 1JC,Rh = 4.8 Hz, Cp*-C), 71.7 (s, C25), 52.2 (s, C26), 51.8 (s,
C27), 39.1 (s, C18), 37.8 (s, C17), 10.3 (s, Cp*-CH3). Isomer B
1
4
(45%), H NMR (400 MHz, CDCl3): δ (ppm) 8.45 (d, JH,H = 2.2
3
3
Hz, 1H, H11), 7.65 (d, JH,H = 8.0 Hz, 1H, H8), 7.54 (d, JH,H = 2.1
3
3
Hz, 1H, H5), 7.27 (d, JH,H = 1.9 Hz, 1H, H16), 7.10 (d, JH,H = 1.9
3
Hz, 1H, H15), 7.01−6.94 (m, 1H, H9), 6.95 (d, JH,H = 2.1 Hz, 1H,
dichloroethane (15 mL). The reaction mixture was stirred at ambient
temperature for 24 h under exclusion of light. Subsequently,
[RuCl2(p-cymene)]2 (31 mg, 0.05 mmol) and KI (166 mg, 1.0
mmol) were added, and the reaction mixture was heated to 60 °C for
24 h. The suspension was filtered through Celite, and the filtrate was
concentrated to 2 mL. The addition of 15 mL of Et2O resulted in the
formation of a precipitate. The precipitate was isolated by filtration,
washed with Et2O, and dried in vacuo. Yield: 53 mg (0.049 mmol,
49%). 1H NMR (400 MHz, CDCl3): δ (ppm) 7.88 (s, 1H, H8), 7.49
(s, 1H, H5), 7.07 (s, 1H, H4), 7.07 (s, 1H, H11), 5.73−5.62 (m, 2H,
H4), 6.89−6.80 (m, 2H, H22/H23), 6.73−6.66 (m, 1H, H21), 5.81
3
(d, JH,H = 7.5 Hz, 1H, H20), 4.01 (s, 3H, H18), 3.87 (s, 3H, H17),
3.68 (s, 2H, H25), 2.82 (s, 3H, H26), 2.62 (s, 3H, H27), 1.83 (s,
15H, Cp*-CH3). 13C{1H} NMR (101 MHz, CDCl3): δ (ppm) 182.2
1
1
(d, JC,Rh = 55.1 Hz, C2), 172.6 (s, C13), 156.6 (d, JC,Rh = 35.4 Hz,
C7), 152.9 (s, C19), 148.2 (s, C24), 145.2 (s, C6), 138.3 (s, C8),
135.7 (s, C10), 134.2 (s, C20), 125.4 (s, C21), 123.8 (s, C22), 122.4
(s, C15), 122.3 (s, C4), 122.2 (s, C23), 122.2 (s, C16), 120.0 (d,
1
3JC,Rh = 1.2 Hz, C9), 115.8 (s, C5), 109.8 (s, C11), 97.8 (d, JC,Rh
=
I
DOI: 10.1021/acs.organomet.9b00120
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
4.8 Hz, Cp*-C), 71.6 (s, C25), 52.3 (s, C27), 51.9 (s, C26), 39.0 (s,
C18), 37.8 (s, C17), 10.2 (s, Cp*-CH3). HRMS (ESI, positive ions):
m/z (%) 842.0429 (100, calculated for [[12]−I]+ 842.0431). Anal.
Calcd for [12]·2CH2Cl2: C, 36.88; H, 3.89; N, 6.15. Found: C, 37.03;
H, 3.86; N, 5.92.
Complex [13]. Analytically pure [13] was obtained as an isomer
mixture by column chromatography on aluminum oxide using
of 693 parameters against all |F2| with anisotropic thermal parameters
for all non-hydrogen atoms and hydrogen atoms on calculated
positions, R = 0.0546, wR = 0.1359 [I ≥ 2σ(I)], R = 0.0789, wR =
0.1555 (all data). The asymmetric unit contains two formula units of
[5]I and five molecules of CH2Cl2.
Crystal Data for [7]·CH2Cl2. Crystals suitable for an X-ray
diffraction study were obtained by slow diffusion of diethyl ether
into a concentrated solution of [7] in dichloromethane. Formula
C32H42N4Cl2I2IrRh, M = 1102.50, orange plates, 0.08 × 0.05 × 0.05
mm3, triclinic, space group P1
̅
, a = 10.7952(2), b = 11.3055(2), c =
14.3625(2) Å, α = 82.6630(10), β = 89.3780(10)°, γ = 88.1930(10),
V = 1737.62(5) Å3, Z = 2, ρcalcd = 2.107 g·cm−3, μ = 6.259 mm−1,
51 322 intensities measured in the range 3.8° ≤ 2Θ ≤ 61.1°, 10 606
independent intensities (Rint = 0.0495), 8448 observed intensities [I ≥
2σ(I)], semiempirical absorption correction (0.656 ≤ T ≤ 0.746),
refinement of 399 parameters against all |F2| with anisotropic thermal
parameters for all non-hydrogen atoms and hydrogen atoms on
calculated positions, R = 0.0454, wR = 0.1097 [I ≥ 2σ(I)], R =
0.0627, wR = 0.1196 (all data). The asymmetric unit contains one
formula unit of [7]·CH2Cl2.
Crystal Data for [8]·1.25CH2Cl2. Crystals suitable for an X-ray
diffraction study were obtained by slow diffusion of diethyl ether into
a concentrated solution of [8] in dichloromethane. Formula
C24.25H30.5N4Cl2.5I2AuRh, M = 1020.33, orange needles, 0.32 × 0.06
× 0.06 mm3, monoclinic, space group P21/n, a = 15.6991(3), b =
13.6300(3), c = 28.3902(6) Å, β = 98.7790(10)°, V = 6003.7(2) Å3, Z
= 8, ρcalcd = 2.258 g·cm−3, μ = 7.731 mm−1, 161 167 intensities
measured in the range 4.7° ≤ 2Θ ≤ 59.4°, 16 968 independent
intensities (Rint = 0.0610), 13 686 observed intensities [I ≥ 2σ(I)],
semiempirical absorption correction (0.504 ≤ T ≤ 0.746), refinement
of 656 parameters against all |F2| with anisotropic thermal parameters
for all non-hydrogen atoms and hydrogen atoms on calculated
positions, R = 0.0362, wR = 0.0794 [I ≥ 2σ(I)], R = 0.0528, wR =
0.0865 (all data). The asymmetric unit contains two formula units of
[8] and 2.5 molecules of CH2Cl2. One of the CH2Cl2 molecules is
located about a crystallographic inversion center between two
asymmetric units.
CH2Cl2/MeOH (6:1). Yield: 83 mg (0.078 mmol, 78%). Isomer A
(52%), H NMR (400 MHz, CDCl3): δ (ppm) 8.52 (d, JH,H = 2.2
1
4
3
3
Hz, 1H, H11), 7.52 (d, JH,H = 2.1 Hz, 1H, H5), 7.52 (d, JH,H = 8.0
3
3
Hz, 1H, H8), 7.28 (d, JH,H = 1.9 Hz, 1H, H16), 7.08 (d, JH,H = 1.9
Hz, 1H, H15), 7.00−6.92 (m, 2H, H4/H9), 6.88−6.79 (m, 2H, H22/
3
H23), 6.74−6.64 (m, 1H, H21), 5.87 (d, JH,H = 7.5 Hz, H20), 4.00
(s, 3H, H18), 3.85 (s, 3H, H17), 3.78 (d, 2JH,H = 13.8 Hz, 1H, H25),
2
3.54 (d, JH,H = 13.8 Hz, 1H, H25), 2.87 (s, 3H, H27), 2.64 (s, 3H,
H26), 1.78 (s, 15H, Cp*-CH3). 13C{1H} NMR (101 MHz, CDCl3): δ
(ppm) 172.0 (C13), 163.9 (C2), 152.9 (C19), 147.8 (C24), 145.7
(C6), 140.0 (C7), 136.9 (C8), 135.0 (C10), 134.7 (C20), 125.2
(C21), 123.5 (C22), 122.4 (C15), 121.9 (C16), 121.7 (C23), 121.6
(C4), 120.6 (C9), 115.3 (C5), 109.2 (C11), 91.4 (Cp*-C), 71.6
(C25), 52.2 (C27), 51.7 (C26), 39.0 (C18), 37.5 (C17), 10.1 (Cp*-
CH3). Isomer B (48%), 1H NMR (400 MHz, CDCl3): δ (ppm) 8.45
4
3
(d, JH,H = 2.2 Hz, 1H, H11), 7.58 (d, JH,H = 8.0 Hz, 1H, H8), 7.47
(d, 3JH,H = 2.1 Hz, 1H, H5), 7.27−7.26 (m 1H, H16), 7.09 (d, 3JH,H
=
1.9 Hz, 1H, H15), 7.00−6.92 (m, 2H, H4/H9), 6.88−6.79 (m, 2H,
3
H22/H23), 6.74−6.64 (m, 1H, H21), 5.80 (d, JH,H = 7.5 Hz, H20),
Crystal Data for Complex [9]. Crystals suitable for an X-ray
diffraction study were obtained by slow diffusion of diethyl ether into
a concentrated solution of [9] in dichloromethane. Formula
C33H42N4I3RhRu, M = 1079.38, red block, 0.10 × 0.09 × 0.06
mm3, monoclinic, space group P21/c, a = 15.4517(2), b = 15.9094(2),
c = 15.1420(2) Å, β = 105.1560(10)°, V = 3592.84(8) Å3, Z = 4, ρcalcd
= 1.995 g·cm−3, μ = 3.485 mm−1, 37 908 intensities measured in the
4.00 (s, 3H, H18), 3.84 (s, 3H, H17), 3.67 (s, 2H, H25), 2.80 (s, 3H,
H26), 2.62 (s, 3H, H27), 1.88 (s, 15H, Cp*-CH3). 13C{1H} NMR
(101 MHz, CDCl3): δ (ppm) 172.5 (C13), 163.6 (C2), 152.9 (C19),
148.1 (C24), 146.0 (C6), 139.7 (C7), 137.0 (C8), 135.0 (C10),
134.1 (C20), 125.3 (C21), 123.7 (C22), 122.3 (C15), 122.1 (C16),
122.1 (C23), 121.6 (C4), 120.4 (C9), 115.3 (C5), 109.4 (C11), 91.5
(Cp*-C), 71.6 (C25), 52.3 (C27), 51.8 (C26), 38.9 (C18), 37.5
(C17), 10.2 (Cp*-CH3). HRMS (ESI, positive ions): m/z (%)
932.0988 (100, calculated for [[13]−I]+, 932.0997). Anal. Calcd for
[13]·0.5CH2Cl2: C, 36.52; H, 3.75; N, 6.36. Found: C, 36.19; H,
3.40; N, 6.41.
X-ray Crystallography. Single crystals of [5]I·2.5CH2Cl2, [7]·
CH2Cl2, [8]·1.25CH2Cl2, and [9] were analyzed by X-ray diffraction
(for crystallographic data of 4(I)2, see the Supporting Information).
X-ray diffraction data were collected at T = 100(2) K with a Bruker
AXS APEX II CCD diffractometer equipped with a microsource using
graphite-monochromated Mo Kα radiation (λ = 0.71073 Å).
Semiempirical multiscan absorption corrections were applied to all
data sets.19 Structure solutions were found with SHELXT (intrinsic
phasing)20a and were refined with SHELXL20b against |F2| of all data
using first isotropic and later anisotropic thermal parameters for all
non-hydrogen atoms. Hydrogen atoms were added to the structure
models on calculated positions.
Crystal Data for [5]I·2.5CH2Cl2. Crystals suitable for an X-ray
diffraction study were obtained by slow diffusion of diethyl ether into
a concentrated solution of [5]I in dichloromethane. Formula
C25.5H34N4Cl5I2Rh, M = 930.52, orange needles, 0.40 × 0.07 ×
0.07 mm3, monoclinic, space group P21/c, a = 16.2748(6), b =
16.5838(6), c = 24.5442(9) Å, β = 92.699(2)°, V = 6617.1(4) Å3, Z =
8, ρcalcd = 1.868 g·cm−3, μ = 2.809 mm−1, 174 490 intensities
measured in the range 3.0° ≤ 2Θ ≤ 61.2°, 20 246 independent
intensities (Rint = 0.0788), 15 205 observed intensities [I ≥ 2σ(I)],
semiempirical absorption correction (0.566 ≤ T ≤ 0.746), refinement
range 2.7° ≤ 2Θ ≤ 58.5°, 9760 independent intensities (Rint
=
0.0425), 7388 observed intensities [I ≥ 2σ(I)], semiempirical
absorption correction (0.671 ≤ T ≤ 0.799), refinement of 390
parameters against all |F2| with anisotropic thermal parameters for all
non-hydrogen atoms and hydrogen atoms on calculated positions, R =
0.0567, wR = 0.1657 [I ≥ 2σ(I)], R = 0.0781, wR = 0.1837 (all data).
The asymmetric unit contains one formula unit of [9].
Catalytic Suzuki Coupling/Transfer Hydrogenation Studies.
In a Schlenk tube containing a stirring bar were placed p-
bromoacetophenone (71.7 mg, 0.36 mmol), phenylboronic acid
(67.1 mg, 0.54 mmol), Cs2CO3 (351.9 mg, 1.08 mmol), catalyst (2
mol %, 0.0072 mmol), and anisole (internal reference, 38.9 mg, 0.36
mmol). The mixture was dissolved in 2-propanol (2 mL, used as
reagent and solvent). The tube was sealed, and the reaction mixture
was stirred at 100 °C under inert conditions for the given reaction
time. The products (yields) were determined with a GC-2010
(Shimadzu) gas chromatograph equipped with a FID and a
Teknokroma (TRB5, 30 m, 0.25 × 0.25 mm) column.
Catalytic Suzuki−Miyaura Coupling/α-Alkylation in n-Butyl
Alcohol. In a Schlenk tube containing a stirring bar were placed p-
bromoacetophenone (71.7 mg, 0.36 mmol), phenylboronic acid (67.1
mg, 0.54 mmol), Cs2CO3 (351.9 mg, 1.08 mmol), catalyst (2 mol %,
0.0072 mmol), and anisole (internal reference, 38.9 mg, 0.36 mmol).
The mixture was dissolved in n-butanol (2 mL, used as reagent and
solvent). The tube was sealed, and the reaction mixture was stirred at
100 °C under aerobic conditions for the given reaction time. The
J
DOI: 10.1021/acs.organomet.9b00120
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
products (yields) were determined with a GC-2010 (Shimadzu) gas
chromatograph equipped with a FID and a Teknokroma (TRB5, 30
m, 0.25 × 0.25 mm) column.
Multistep Preparation of Functionalized Indoles from the Reaction of
Amino Alcohols and Alkynyl Alcohols. Chem. - Eur. J. 2010, 16,
13109−13115. (c) Zanardi, A.; Mata, J. A.; Peris, E. One-Pot
Preparation of Imines from Nitroarenes by a Tandem Process with an
Ir-Pd Heterodimetallic Catalyst. Chem. - Eur. J. 2010, 16, 10502−
10506. (d) Sabater, S.; Mata, J. A.; Peris, E. Hydrodefluorination of
Carbon-Fluorine Bonds by the Synergistic Action of a Ruthenium-
Palladium Catalyst. Nat. Commun. 2013, 4, 2553. (e) Gonell, S.;
Poyatos, M.; Mata, J. A.; Peris, E. Y-Shaped Tris-N-Heterocyclic-
Carbene Ligand for the Preparation of Multifunctional Catalysts of
Iridium, Rhodium, and Palladium. Organometallics 2012, 31, 5606−
5614.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.9b00120.
Crystallographic data for 4(I)2 and spectra of all new
complexes (PDF)
(5) (a) Allen, D. P.; Crudden, C. M.; Calhoun, L. A.; Wang, R.
Irreversible cleavage of a carbene-rhodium bond in Rh-N-heterocyclic
carbene complexes: implications for catalysis. J. Organomet. Chem.
2004, 689, 3203−3209. (b) Praetorius, J. M.; Crudden, C. M. N-
Heterocyclic carbene complexes of rhodium: structure, stability and
reactivity. Dalton Trans. 2008, 4079−4094. (c) Li, L.; Brennessel, W.
W.; Jones, W. D. C-H Activation of Phenyl Imines and 2-
Phenylpyridines with [Cp*MCl2]2 (M = Rh, Ir): Regioselectivity,
Kinetics, and Mechanism. Organometallics 2009, 28, 3492−3500.
(6) Hahn, F. E.; Jahnke, M. C. Heterocyclic Carbenes: Synthesis and
Coordination Chemistry. Angew. Chem., Int. Ed. 2008, 47, 3122−
3172.
Accession Codes
CCDC 1897003−1897007 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.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: guisado@uji.es.
■
(7) (a) Maity, R.; Koppetz, H.; Hepp, A.; Hahn, F. E.
Heterobimetallic Carbene Complexes by a Single-Step Site-Selective
Metalation of a Tricarbene Ligand. J. Am. Chem. Soc. 2013, 135,
4966−4969. (b) Maity, R.; Rit, A.; Schulte to Brinke, C.; Daniliuc, C.
G.; Hahn, F. E. Metal Center Dependent Coordination Modes of a
Tricarbene Ligand. Chem. Commun. 2013, 49, 1011−1013. (c) Maity,
*E-mail: eperis@qio.uji.es.
*E-mail: fehahn@uni-muenster.de.
ORCID
Tristan Tsai Yuan Tan: 0000-0001-5391-7232
Eduardo Peris: 0000-0001-9022-2392
F. Ekkehardt Hahn: 0000-0002-2807-7232
̈
R.; Rit, A.; Schulte to Brinke, C.; Kosters, J.; Hahn, F. E. Two
Different, Metal-Dependent Coordination Modes of a Dicarbene
Ligand. Organometallics 2013, 32, 6174−6177.
Notes
̈
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Peris, E.; Hahn, F. E. IrIII/AuI and RhIII/AuI Heterobimetallic
Complexes as Catalysts for the Effective Coupling of Nitrobenzene
and Benzylic Alcohol. Organometallics 2018, 37, 4092−4099.
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Heterobimetallic Complexes Bearing NHC Ligands: Application in
-Arylation of Amide, Suzuki-Miyaura Coupling Reactions, and
Tandem Catalysis. Eur. J. Inorg. Chem. 2019, 2019, 1810−1815.
(9) (a) Sabater, S.; Mata, J. A.; Peris, E. Chiral Palladacycles with N-
Heterocyclic Carbene Ligands as Catalysts for Asymmetric Hydro-
phosphination. Organometallics 2013, 32, 1112−1120. (b) Sabater, S.;
Mata, J. A.; Peris, E. Synthesis of Heterodimetallic Iridium-Palladium
Complexes Containing Two Axes of Chirality: Study of Sequential
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Role of Gold Acetylides as a Selectivity Trigger and the Importance of
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(11) Ghorai, D.; Choudhury, J. Exploring a Unique Reactivity of N-
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge financial support from the
Universitat Jaume I (UJI-B2017-07) and the Deutsche
Forschungsgemeinschaft (SFB 858 and IRTG 2027). We
́
́
thank the Serveis Centrals d’Instrumentacio Cientifica (SCIC-
UJI) for access to the spectroscopic facilities. G.G.-B. thanks
MINECO for a “Juan de la Cierva Fellowship” (GGB, IJCI-
2015-23407).
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