Homo- and Heterodinuclear Head-to-Head or Head-to-Tail Complexes of Rhodium(I) and Iridium(I) with C2,N3 or C8,N9 Bridging Azolato Ligands

Article abstract of DOI:10.1021/acs.organomet.9b00074

Reaction of in situ lithiated N-methylimidazole or 1,5,6-trimethylbenzimidazole with [M(cod)(μ-Cl)]₂ (M = Rh, Ir) led to the exclusive formation of the homodinuclear head-to-head complexes [2]-[5], where the metal centers are bridged by two C,N-coordinated azolato ligands. The two metal centers are each coordinated by one cod ligand and either two carbon or two nitrogen donors of the azolato ligands. Access to a heterodinuclear Ir/Rh complex [6] was achieved via the lithiated iridium complex [7] and addition of an equimolar amount of [Rh(cod)(μ-Cl)]₂. Deprotonation of caffeine with lithium diisopropylamide and addition of [M(cod)(μ-Cl)]₂ (M = Rh, Ir) led to mixtures of the head-to-head (M = Ir: [8_H-H]; M = Rh: [9_H-H]) and head-to-tail isomers (M = Ir: [8_H-T]; M = Rh: [9_H-T]) of the homodinuclear complexes. The molecular structures of the homo- and heterodinuclear complexes [3], [5]·2C₆H₅F, [6]·2C₆H₅F, and [9_H-T]·C₄H₈O have been determined by X-ray diffraction studies.

Full text of DOI:10.1021/acs.organomet.9b00074

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Homo- and Heterodinuclear Head-to-Head or Head-to-Tail
Complexes of Rhodium(I) and Iridium(I) with C2,N3 or C8,N9 Bridging
Azolato Ligands
̈
Steffen Cepa, Maximilian Bohmer, Florian Roelfes, Tristan Tsai Yuan Tan, Fabian Dielmann,
and F. Ekkehardt Hahn*
Institut fu
Munster, Germany
r Anorganische und Analytische Chemie, Westfalische Wilhelms-Universitat Munster, Corrensstraße 30, D-48149
̈ ̈
̈ ̈
̈
S
* Supporting Information
ABSTRACT: Reaction of in situ lithiated N-methylimidazole or 1,5,6-
trimethylbenzimidazole with [M(cod)(μ-Cl)]2 (M = Rh, Ir) led to the
exclusive formation of the homodinuclear head-to-head complexes [2]−
[5], where the metal centers are bridged by two C,N-coordinated
azolato ligands. The two metal centers are each coordinated by one cod
ligand and either two carbon or two nitrogen donors of the azolato
ligands. Access to a heterodinuclear Ir/Rh complex [6] was achieved via
the lithiated iridium complex [7] and addition of an equimolar amount
of [Rh(cod)(μ-Cl)]2. Deprotonation of caffeine with lithium diisopro-
pylamide and addition of [M(cod)(μ-Cl)]2 (M = Rh, Ir) led to mixtures of the head-to-head (M = Ir: [8H−H]; M = Rh: [9H−H])
and head-to-tail isomers (M = Ir: [8H−T]; M = Rh: [9H−T]) of the homodinuclear complexes. The molecular structures of the
homo- and heterodinuclear complexes [3], [5]·2C6H5F, [6]·2C6H5F, and [9H−T]·C4H8O have been determined by X-ray
diffraction studies.
1. INTRODUCTION
N-Heterocyclic carbenes (NHCs) and their transition metal
complexes have been studied extensively over the last decade.1
Due to their electronic and steric properties, NHCs have found
many applications as ligands in coordination chemistry,1,2 as
building blocks for metallosupramolecular complexes,3 as
organocatalysts4 and their transition metal complexes are
used in a broad array of catalytic applications.5 While transition
metal NHC complexes containing one metal center have been
thoroughly studied, there are only a few examples for NHC (or
azolato) ligands acting as a bridging ligands in dinuclear
complexes, where one metal is bound at the carbene (or
azolato) carbon atom and another one is bound at the
unsubstituted ring-nitrogen (A in Figure 1).6 Such structures
are possibly promising candidates as catalysts for unique
transformations through cooperative action of the two metal
centers.7 It has been shown that N-deprotonation of platinum
or palladium complexes bearing protic NH,NR-NHC ligands
leads to homodinuclear complexes (B in Figure 1) with a head-
to-tail (H−T) orientation of the bridging ligands.8 Similar
Figure 1. Selected dinuclear complexes with C,N-bridging azolato
dinuclear complexes of type B have been obtained from the
ligands.
oxidative addition of 2-chloro-N-methylbenzimidazole to
[Pt(PPh3)4]9 and by treatment of an iron(II)−di-NHC
complex with PhLi (C in Figure 1).10 The formation of
homodinuclear head-to-head (H−H) complexes has been
proposed for the reaction of [Ir(cod)(μ-Cl)]2 with lithium N-
after substitution of the two cod ligands for four CO ligands
was H−H complex D characterized by X-ray diffraction.11a
benzylimidazolate. However, the cod complexes could not be
Received: February 4, 2019
characterized conclusively by NMR spectroscopy and only
© XXXX American Chemical Society
A
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The reaction of the more bulky substituted N-mesityimidazole
with [Ir(cod)(μ-Cl)]2 yielded a mixture of H−H and H−T
complexes.11b Finally, a mononuclear ruthenium(II) complex
bearing a tridentate ligand with two protic pNHC donors can
bind a second metal center after deprotonation of the ring-NH
functions with n-BuLi (E in Figure 1).12
metalated 1,5,6-trimethylbenzimidazolate ligand in [5] is
indicated in the H NMR spectrum by the absence of a
1
resonance for H2 proton, which was recorded at δ = 7.70 ppm
in ligand precursor 1. In addition, the 13C{1H} NMR spectrum
of [5] exhibited the typical resonance for the metalated azolato
carbon atom at δ = 192.5 featuring a 1JC,Rh coupling constant of
1J = 49.8 Hz, which clearly indicates the presence of a complex
with a Rh−Cazolato bond.
We became interested in the preparation of homo- and
heterodinuclear complexes with μ-C,N bridging NHC ligands
and in a detailed NMR spectroscopic characterization of the
possible isomeric H−H and H−T isomers. Herein, we report
the preparation of homo- and heterodinuclear complexes of IrI
and RhI obtained from C2/8-deprotonated N-methylimida-
zole, 1,5,6-trimethylbenzimidazole and caffeine and their
Distinction between the head-to-head versus the head-to-tail
complexes can be made by spin correlation spectroscopy
(1H,1H-COSY) as has been suggested for related complexes.11a
For the head-to-tail complexes, featuring a C2-symmetry axis,
one spin system is expected with 12 resonances for the two
chemically equivalent cod ligands. In contrast, the head-to-
head complexes feature a mirror plane (CS) that cuts through
both of the chemically non-equivalent cod ligands. Thus, two
spin systems, each comprising six resonances for each 1/2 cod
1
detailed H NMR spectroscopic characterization.
2. RESULTS AND DISCUSSION
Two geometrical isomers can be formed if N1-alkylated, azoles
(imidazoles and benzimidazoles) are deprotonated and used as
C,N-bridging ligands for the generation of dinuclear
complexes. The bridging ligands could be orientated head-to-
tail (H−T, Figure 1, B,C) or head-to-head (H−H, Figure 1,
D). Reaction of in situ generated lithium N-methylimidazolate
or 1,5,6-trimethylbenzimidazolate with a stoichiometric
amount of [M(cod)(μ-Cl)]2 (M = Rh, Ir) in tetrahydrofuran
(THF) leads exclusively to the air-sensitive homodinuclear H−
H complexes [2]−[5] (Scheme 1). The formation of a mixture
1
ligand, are to be expected. The H,1H-COSY NMR spectrum
of [5] (Figure 2) does exhibit two separate spin systems,
Scheme 1. Synthesis of Complexes [2]−[5] and Possible
Geometric Isomers
Figure 2. 1H,1H-COSY NMR spectrum of complex [5]. The blue and
red lines are assigned to the two spin systems.
indicating the head-to-head arrangement of the azolato ligands.
3
Every CH group experiences JHH coupling to the protons of
its neighboring CH- and CH2-groups. For example, the
resonance at δ = 5.08 ppm, which was assigned to a CH-
proton, couples with the resonances at δ = 4.04 ppm (CH) and
δ = 2.85 and 2.05 ppm (CH2).
Furthermore, the head-to-head arrangement of the azolato
ligands in rhodium complexes [3] and [5] (Scheme 1) has
been established by X-ray diffraction analyses (Figure 3),
confirming the conclusions drawn from NMR spectroscopy.
Both complexes feature a boat conformation of the six-
membered Rh−C−N−Rh−N−C ring, and the two rhodium
atoms are coordinated in an approximately square-planar
fashion. Any intramolecular interaction between the rhodium
atoms can be excluded owing to the long Rh1···Rh2
separations of 3.288(2) and 3.195(1) Å found for [3] and
of dinuclear H−H and H−T complexes as described by
Braunstein for the reaction of lithium N-mesitylimidazolate
with [Ir(cod)(μ-Cl)]2 was not observed, most likely due to the
different steric bulk of the N1-substituents (methyl vs
mesityl).11b
Since complexes [2]−[5] are isostructural, the analytical
data are discussed exemplarily for dirhodium complex [5] (for
analytical data of [2]−[4], see the Experimental Section and
the Supporting Information). The presence of the doubly
B
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Scheme 2. Synthesis of Complex [6] from 1, [Rh(cod)(μ-
Cl)]2, and [Ir(cod)(μ-Cl)]2
Figure 3. Molecular structures of complex [3] (top) and of complex
[5] in [5]·2C6H5F (bottom). (50% displacement ellipsoids, solvent
molecules, and hydrogen atoms have been omitted). Selected bond
lengths (Å) and angles (deg) for [3] and [[5]·2C6H5F]: Rh1···Rh2
3.288(2) [3.195(1)], Rh2−N3 2.080(2) [2.101(2)], Rh2−N23
2.078(2) [2.098(2)], Rh1−C2 2.033(2) [2.024(3)], Rh1−C22
2.042(2) [2.024(3)], N3−Rh2−N23 87.30(7) [86.16(8)], C2−
Rh1−C22 84.83(8) [82.64(10)], N1−C2−N3 107.1(2) [109.1(2)],
N21−C22−N23 106.4(2) [108.7(2)].
[5], respectively.11b,13 The Rh2−N distances (2.080(2) and
2.078(2) Å) in complex [3] are unexceptional.11b,13 The Rh1−
Cazolato distances (2.033(2) and 2.042(2) Å) fall in the range
observed in RhI dicarbene complexes14 and the related head-
to-tail complex with bridging N-mesitylimadzolato ligands.11b
Dinuclear complex [5], featuring two bridging 1,5,6-
trimethylbenzimidazolato ligands, exhibits slightly longer
Rh2−N bond lengths than observed in [3]. The Rh1−Cazolato
bond lengths in [5] are similar to those found in complex [3].
The cod ligands in both complexes [3] and [5] adopt a slightly
twisted conformation.
Figure 4. Section of the 13C{1H} NMR spectra of complex [5] (top),
complex [4] (middle), and the mixture of complexes [4]−[6]
(bottom).
of the signals of the aromatic protons allows the conclusion
that complexes [4]−[6] were formed in a ratio of 0.4:0.3:1.
Head-to-head coordination of both azolato carbon atoms to
one iridium atom has been concluded from the 13C{1H} NMR
data of [6] showing no 1JRhC coupling for the resonance of the
coordinated azolato carbon atoms at δ = 188.1 ppm.
1
We next attempted to prepare heterobimetallic complexes
from N-methylbenzimidazole 1 and RhI and IrI complex
precursors. Treatment of 1 with n-BuLi followed by addition
and 0.25 equiv each of [Rh(cod)(μ-Cl)]2 and [Ir(cod)(μ-
Cl)]2 led to the formation of a complex mixture composed of
the heterodinuclear complex [6] (major) and the homodinu-
clear complexes [4] and [5] (minor, Scheme 2). The
heterobimetallic complex [6] could not be obtained by
reacting a homonuclear complex (e.g., iridium complexes [2]
or [4]) with a second metal complex such as [Rh(cod)(μ-
Cl)]2. This indicates some stability of the Ir(C-azolato)2 and
Rh(N-azolato)2 motifs. NHC transfer from IrI to RhI and vice
versa is also no common procedure.
Meanwhile, JRhC coupling was observed for the resonances
1
1
at δ = 78.9 (d, JCRh = 3.9 Hz) and 78.7 (d, JCRh = 2.6 Hz)
assigned to the CH groups of the cod ligand coordinated to the
rhodium atom (see the Supporting Information Figure S14).
These observations confirm that the rhodium atom in [6] is
not coordinated by the azolato carbon atoms but by two
nitrogen atoms instead in an H−H arrangement of the ligands.
Suitable crystals of [6]·2C6H5F for X-ray diffraction studies
were obtained from the reaction mixture by cooling a
concentrated solution of complexes [4]−[6] in fluorobenzene.
The molecular structure determination (Figure 5) confirms the
head-to-head arrangement of the two azolato ligands as
concluded from the NMR data. The position of the metal
center coordinated by the two nitrogen atoms of the azolato
ligands is occupied by disordered Rh and Ir atoms in a ratio of
Rh0.67/Ir0.33 indicating that complex [4] (homobimetallic
iridium complex) co-crystallizes together with [6].
1
The H NMR spectrum of the complex mixture [4]−[6]
exhibits three sets of signals, which can be been assigned to the
previously described homobimetallic complexes [4] and [5]
and the new complex [6] (Figure 4). Complexes [4] and [5]
in the complex mixture were identified by comparison with the
spectra of authentical samples previously prepared. Integration
Owing to the metal disorder, metric parameters for [6] are
not discussed in detail here. Formation of complex [6] as the
C
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Cl)]2 to complex [7] gave the heterodinuclear complex [6] as
the only product in 90% yield. The NMR spectra agree with
the resonances assigned to complex [6] present in the mixture
of complexes [4]−[6].
Finally, caffeine was tested as ligand for the synthesis of
homodinuclear C,N-azolato bridged complexes. This study was
initiated in order to investigate the influence of the electron
withdrawing backbone of caffeine on the complex formation
and particularly on the geometrical isomers (H−H or H−T)
obtained. While the influence of the N-substituents of azoles
on the geometry of the resulting complexes has been
demonstrated,11 the effect of the electronic situation within
the azole has not been studied previously. The conditions
employed for the deprotonation of the azoles used for the
preparation of [2]−[5] could not be used for the
deprotonation of caffeine as this leads to decomposition.
When the base was changed from n-BuLi to lithium
diisopropylamide, deprotonation of caffeine proceeded with
no problems and the subsequent addition of [Ir(cod)(μ-Cl)]2
or [Rh(cod)(μ-Cl)]2 gave the homodinuclear complexes [8]
and [9] as mixtures of the head-to-head [H−H] and head-to-
tail [H−T] isomers (Scheme 4). It was also tempting to
Figure 5. Molecular structure of complex [6] in [6]·2C6H5F. (50%
displacement ellipsoids, solvent molecules, and hydrogen atoms have
been omitted for clarity).
main product can be explained using the HSAB concept. A C-
azolato atom is a softer donor than the N-azolato donor.10 In
addition, the iridium(I) ion is a softer Lewis acid than the
rhodium(I) ion. Following HSAB rules, the coordination of the
azolato carbon atoms to iridium and of the azolato nitrogen
atoms to rhodium would lead to the most stable complex and
thus to the preferred formation of complex [6].
In order to prepare a pure sample complex [6] with no
homobimetallic complexes present, a different synthetic
approach, inspired by the work reported by Cossairt,12 was
used. This approach involved the initial preparation of the
lithiated complex [7] which was prepared by treatment of 1
with n-BuLi followed by addition of only 0.25 equiv of
[Ir(cod)(μ-Cl)]2 (Scheme 3). The subsequent addition of
[Rh(cod)(μ-Cl)]2 to complex [7] yielded the heterobimetallic
complex [6] by metalation of the nitrogen donor sites.
Scheme 4. Synthesis of Isomer Mixtures of Homodinuclear
Complexes [8] and [9]
Scheme 3. Selective Synthesis of Heterodinuclear Complex
[6]
prepare heterobimetallic complexes with bridging caffeine
ligands similar to [6]. However, no attempts were made to
react C8-deprotonated caffeine with an equimolar mixture of
[Rh(cod)(μ-Cl)]2 and [Ir(cod)(μ-Cl)]2. The homodinuclear
caffeine-bridged complexes already form as mixtures of H−H
and H−T isomers and a total of 4 complexes would be
expected. In addition, various isomers of the heterodinuclear
complex could form, ultimately leading to an inseparable
mixture of homo- and heterodinuclear complexes.
The overall yield for the mixture of the homodinuclear
iridium complexes [8H−H]/[8H−T] was 29% with an isomer
ratio of approximately 0.5:0.5 ([H−H]/[H−T]). The mixture
of the homodinuclear rhodium complexes [9H−H]/[9H−T] was
obtained in an overall yield of 39% with an isomer ratio of
approximately 0.3:0.7 ([H−H]/[H−T]). Determination of the
Formation of [7] was confirmed by matrix-assisted laser
desorption ionization (MALDI) mass spectrometry revealing a
peak for the cation [[7]−Li + 2H]+ at m/z = 621. The
13C{1H} NMR spectrum of [7] features only four signals at δ =
68.9, 67.0 (CH), 29.7, and 29.4 ppm (CH2) for the cod ligand,
indicating the existence of a mirror plane bisecting the complex
in solution. The signal assigned to the azolato carbon atom in
[7] was detected in the typical range at δ = 192.6 ppm. The
subsequent addition of an equimolar amount of [Rh(cod)(μ-
D
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isomer ratio is based on the integrals of the resonances for the
cod protons in the H NMR spectra of the complex mixtures
2D NMR spectroscopy and by X-ray diffraction studies with
dirhodium complexes [3] and [5]. The reaction of in situ
lithiated N-methylbenzimidazolate with an equimolar mixture
of [Rh(cod)(μ-Cl)]2 and [Ir(cod)(μ-Cl)]2 led to a mixture
composed of the heterodinuclear complex [6] as a major
reaction product and the two homodinuclear complexes [4]
and [5]. However, a stepwise reaction sequence via the
lithiated monoiridium complex [7] followed by metalation of
the two ring-nitrogen atoms with [Rh(cod)(μ-Cl)]2 allowed
the preparation of pure [6] in good yield. The lithiated
complex [7] constitutes a perfect precursor for the preparation
of additional heterodinuclear complexes that might possess
unique properties owing to the presence two different metal
centers in close proximity to each other.7,15 In addition,
mixtures of homodinuclear head-to-head and head-to-tail
complexes [8] and [9] have been synthesized by using caffeine
as the η2,μ-C,N-azolato ligand precursor and lithium
diisopropylamide as the base.
1
(see the Supporting Information, Figures S15 and S17).
Separation of the H−H from the H−T complexes was
impossible by chromatography and all corresponding attempts
led to decomposition.
NMR spectroscopy data revealed two sets of resonances for
each complex, which can be assigned to the different isomers
of complexes [8] and [9]. Resonances for the azolato carbon
atoms were recorded in the 13C{1H} NMR spectra at δ = 182.6
ppm ([8H−H]), 178.6 ppm ([8H−T]) and at δ = 188.7 ppm (d,
1
1JRhC = 50.0 Hz, [9H−H]), 183.2 (d, JRhC = 48.2 Hz, [9H−T
]
(see the Supporting Information, Figures S16 and S18).
Crystals of [9H−T]·C4H8O suitable for an X-ray diffraction
study were obtained by slow diffusion of n-hexane into a
saturated solution of the complex mixture [9H−T]/[9H−H] in
THF at ambient temperature. The molecular structure is
depicted in Figure 6. Any intramolecular interaction between
the rhodium atoms can be excluded due to long Rh(1)···Rh(2)
separation of 3.1878(2) Å.
4. EXPERIMENTAL SECTION
4.1. General Procedures. All preparations were carried out under
an argon atmosphere using conventional Schlenk techniques or in a
glovebox. Solvents were dried and degassed by standard methods
prior to use. Compound 1-methylimidazole was purchased from Alfa
Aesar, and [Rh(cod)(μ-Cl)]216 and [Ir(cod)(μ-Cl)]217 were prepared
as described in the literature. NMR spectra were recorded on a Bruker
AVANCE I 400 or a Bruker AVANCE III 400 NMR spectrometer.
Chemical shifts (δ) are expressed in ppm downfield from
tetramethylsilane or using the residual protonated solvent signal as
an internal standard. Coupling constants are expressed in Hertz. ESI-
HRMS spectra were obtained with an Orbitrap XL spectrometer.
MALDI spectra were obtained with a Bruker Reflex IV spectrometer.
Assignment of the proton NMR resonances was made via spin
correlation spectroscopy (COSY).
4.2. Synthesis of Compound 1. A sample of 5,6-dimethylbenz-
imidazole (1.90 g, 13.0 mmol) was dissolved in acetonitrile (40 mL).
An aqueous solution of NaOH (20 mL, 25 wt %) was added and the
mixture was cooled to 0 °C. Then, a solution of methyliodide (0.80
mL, 13.0 mmol) in acetonitrile (20 mL) was added slowly and the
reaction mixture was stirred at ambient temperature for 3 d. The
solvents were removed in vacuo and the resulting residue was
extracted with dichloromethane (3 × 20 mL). The combined organic
phases were dried over MgSO4 and the solvent was removed under
reduced pressure to give 1 as a white solid. Yield: 1.34 g (8.4 mmol,
65%). 1H NMR (400 MHz, CDCl3): δ (ppm) 7.70 (s, 1H, H2), 7.54
(s, 1H, H5), 7.12 (s, 1H, H8), 3.73 (s, 3H, H12), 2.38 (s, 3H, H11),
2.36 (s, 3H, H10). 13C{1H} NMR (101 MHz, CDCl3): δ (ppm)
142.7 (C2), 142.3 (C4), 133.0 (C9), 131.9 (C6), 130.7 (C7), 120.1
(C5), 109.4 (C8), 30.8 (C12), 20.4 (C11), 20.1 (C10). MS (MALDI-
TOF, matrix DCTB) m/z (%): 161 (100) [1 + H]+. Anal. Calcd for
1: C, 74.96; H, 7.55; N, 17.49. Found: C, 73.91; H, 7.36; N, 17.16.
4.3. General Procedure for the Synthesis of Complexes [2]
and [3]. A sample of 1,5,6-trimethylbenzimidazole (16.0 mg, 0.10
mmol) was dissolved in THF (5 mL) and cooled to −78 °C before n-
BuLi (0.08 mL, 0.13 mmol of an 1.6 M solution in n-hexane) was
added. The reaction mixture was stirred for 2 h at −78 °C. A sample
of complex [Ir(cod)(μ-Cl)]2 or [Rh(cod)(μ-Cl)]2 (0.05 mmol, 33.6
mg or 24.7 mg, respectively) was added and the solution was stirred
for 12 h while it was allowed to warm up to ambient temperature. The
solvent was removed in vacuo and the resulting residue was washed
with methanol (2 × 5 mL) and dried under reduced pressure.
4.3.1. Characterization of Complex [2]. Complex [2] was
Figure 6. Molecular structure of complex of [9H−T] in [9H−T]·C4H8O
(50% displacement ellipsoids, hydrogen atoms have been omitted for
clarity). Selected bond lengths (Å) and angles (deg): Rh1···Rh2
3.1878(2), Rh1−N21 2.133(2), Rh1−C8 2.021(2), Rh2−N9
2.134(2), Rh2−C20 2.023(2), N9−C8 1.372(2), N7−C8 1.357(2),
N19−C20 1.361(2), N21−C20 1.368(3); C8−Rh1−N21 82.95(7),
N9−Rh2−C20 84.44(7), N7−C8−N9 108.5(2), N19−C20−N21
108.5(2).
The formation of complex mixtures containing both
geometric isomers ([H−H] and [H−T]) when C8-deproto-
nated caffeine is used as bridging C,N-ligand must be caused
by the weaker σ-donor properties of the caffeine N9-atom
owing to the electron withdrawing backbone compared to the
N3-atom in the bridging azolato ligands in complexes [2]−[5].
As a result, a metal atom coordinated by two ring-nitrogen
atoms of the caffeine-derived bridging ligand is less stabilized
than one coordinated by one ring-nitrogen atom and a carbon
atom from the second bridging ligand, leading to the formation
of the H−T isomer next to the H−H isomer. This effect is
more pronounced for the rhodium complex, thus leading to a
larger ration of 0.7:0.3 (H−T/H−H) compared to the iridium
complex (0.5:0.5).
1
obtained as a red solid. Yield: 18 mg, 0.235 mmol, 47%. H NMR
3. CONCLUSIONS
(400 MHz, THF-d8): δ (ppm) 6.88 (d, 3JHH = 1.5 Hz, 1H, H4), 6.78
(d, 3JHH = 1.5 Hz, 1H, H5), 4.22−4.14 (m, 1H, cod-CH), 4.00−3.90
(m, 1H, cod-CH), 3.63 (s, 3H, H6), 3.58−3.57 (m, 1H, cod-CH),
3.33−3.26 (m, 1H, cod-CH), 2.39−2.25 (m, 4H, cod-CH2), 2.04−
1.97 (m, 2H, cod-CH2), 1.71−1.63 (m, 2H, cod-CH2). 13C{1H}
Four homodinuclear complexes [2]−[5] have been prepared,
possessing two bridging η2,μ-C,N-azolato ligands. The head-to-
head geometry and the different coordination environments of
the two metal centers of these complexes were confirmed by
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1
NMR (101 MHz, THF-d8): δ (ppm) 175.3 (C2), 125.7 (C4), 120.1
(C5), 70.8 (cod-CH), 70.4 (cod-CH), 64.8 (cod-CH), 59.6 (cod-
CH), 35.5 (s, C6), 33.3 (cod-CH2), 33.0 (cod-CH2), 32.7 (cod-
CH2), 32.6 (cod-CH2). HRMS (ESI, positive ions) m/z: 763.2086
[[2] + H]+ (calcd for [[2] + H]+ 763.2097).
a red solid. Yield: 64 mg (of the complex mixture). H NMR (400
MHz, THF-d8, only resonances for the main component [6] are
listed): δ (ppm) 7.39 (s, 1H, H5), 6.81 (s, 1H, H8), 5.13−5.02 (m,
1H, cod-CH), 4.46−4.40 (m, 1H, cod-CH), 4.02−3.92 (m, 2H, cod-
CH), 3.78 (s, 3H, H12), 2.89−2.80 (m, 1H, cod-CH2), 2.64−2.54
(m, 2H, cod-CH2), 2.50−2.42 (m, 1H, cod-CH2), 2.27 (s, 3H, H11),
2.21 (s, 3H, H10), 2.19−2.14 (m, 2H, cod-CH2), 2.07−2.01 (m, 1H,
cod-CH2), 2.00−1.93 (m, 1H, cod-CH2). 13C{1H} NMR (101 MHz,
THF-d8, only resonances for the main component [6] are listed): δ
(ppm) 188.1 (s, C2), 143.4 (s, C4), 137.1 (s, C9), 128.7 (s, C6),
4.3.2. Characterization of Complex [3]. Complex [3] was
1
obtained as an orange solid. Yield: 12 mg, 0.205 mmol (41%). H
NMR (400 MHz, THF-d8): δ (ppm) 6.70 (d, 3JHH = 1.1 Hz, 1H, H4),
6.57 (d, 3JHH = 1.1 Hz, 1H, H5), 4.51−4.45 (m, 1H, cod-CH), 4.28−
4.17 (m, 2H, cod-CH), 3.83−3.75 (m, 1H, cod-CH), 3.63 (s, 3H,
H6) 2.69−2.63 (m, 1H, cod-CH2), 2.59−2.51 (m, 2H, cod-CH2),
2.46−2.40 (m, 1H, cod-CH2), 2.21−2.13 (m, 2H, cod-CH2), 1.95−
1.85 (m, 2H, cod-CH2). 13C{1H} NMR (101 MHz, THF-d8): δ
1
128.2 (s, C7), 115.6 (s, C5), 109.9 (s, C8), 78.9 (d, JCRh = 3.9 Hz,
1
cod-CH), 78.7 (d, JCRh = 2.6 Hz), 73.6 (s, cod-CH), 72.0 (s, cod-
CH), 33.24 (s, cod-CH2), 33.22 (s, C12), 32.8 (s, cod-CH2), 32.3 (s,
cod-CH2), 32.0 (s, cod-CH2), 20.5 (s C11), 20.2 (s, C10). HRMS
(ESI, positive ions) m/z: 830.2405 [6]+ (calcd for [6]+ 830.2409).
4.6. Synthesis of Complex [7]. Compound 1 (16 mg, 0.10
mmol) was dissolved in THF (5 mL) and the solution was cooled to
−78 °C. Then, n-BuLi (0.13 mmol, 0.08 mL of a 1.6 M solution in n-
hexane) was added. The reaction mixture was stirred for 2 h at −78
°C. Then, [Ir(cod)(μ-Cl)]2 (16.8 mg, 0.025 mmol) was added and
the solution was stirred over night while it was allowed to warm up to
ambient temperature. The solvent was removed in vacuo and the solid
residue was dissolved in THF (2 mL). Addition of n-pentane led to
precipitation of a white solid. The suspension was filtered through
Celite and the solvent was removed from the filtrate under reduced
pressure to give complex [7] as a reddish solid. Yield: 23 mg, 0.037
1
(ppm) 180.6 (d, JCRh = 50.5 Hz, C2), 127.1 (s, C4), 119.1 (s, C5),
1
1
85.5 (d, JCRh = 7.7 Hz, cod-CH), 83.6 (d, JCR1h = 8.4 Hz, cod-CH),
1
80.4 (d, JCRh = 13.2 Hz, cod-CH), 77.0 (d, JCRh = 11.4 Hz, cod-
CH), 35.6 (s, C6), 32.4 (s, cod-CH2), 32.2 (s, cod-CH2), 31.9 (s,
cod-CH2), 31.8 (s, cod-CH2). HRMS (ESI, positive ions) m/z:
584.0518 [3]+ (calcd for [3]+ 584.0894).
4.4. General Procedure for the Synthesis of Complexes [4]
and [5]. Compound 1 (32.0 mg, 0.20 mmol) was dissolved in THF
(5 mL) and the solution was cooled to −78 °C. Then, n-BuLi (0.2
mmol, 0.13 mL of a 1.6 M solution in n-hexane) was added. The
reaction mixture was stirred for 2 h at −78 °C. Subsequently,
[Ir(cod)(μ-Cl)]2 (0.1 mmol, 67.2 mg) or [Rh(cod)(μ-Cl)]2 (0.10
mmol, 49.3 mg) was added and the solution was stirred for 12 h while
it was allowed to warm up to ambient temperature. The solvent was
removed in vacuo and the resulting residue was washed with
methanol (2 × 5 mL) and dried under reduced pressure.
4.4.1. Characterization of Complex [4]. Complex [4] was
obtained as a red solid. Yield: 41 mg, 45 mmol, 45%. 1H NMR
(400 MHz, THF-d8): δ (ppm) 7.40 (s, 1H, H5), 6.85 (s, 1H, H8),
4.82 (s br, 1H, cod-CH), 4.43 (s br, 1H, cod-CH), 3.85 (s br, 1H,
cod-CH), 3.80 (s, 3H, H12), 3.58 (s br, 1H, cod-CH), 2.68−2.60 (m,
1H, cod-CH2), 2.49−2.41 (m, 2H, cod-CH2), 2.36 (s, 1H, cod-CH2),
2.25 (s, 3H, H11), 2.22 (s, 3H, H10), 2.20−2.18 (m, 1H, cod-CH2),
2.15−2.13 (m, 1H, cod-CH2), 1.80−1.76 (m, 2H, cod-CH2). 13C{1H}
NMR (101 MHz, THF-d8): δ (ppm) 185.5 (C2), 142.2 (C4), 136.9
(C9), 129.0 (C6), 128.7 (C7), 115.6 (C5), 110.1 (C8), 74.4 (cod-
CH), 72.2 (cod-CH), 62.8 (cod-CH), 61.0 (cod-CH), 33.4 (C12),
33.0 (cod-CH2), 32.9 (cod-CH2), 32.8 (cod-CH2), 32.7 (cod-CH2),
20.3 (C11), 20.1 (C10). MS (MALDI-TOF, matrix DCTB) m/z: 918
[4]+.
1
mmol, 74%. H NMR (400 MHz, THF-d8): δ (ppm) 6.93 (s, 1H,
H5), 6.80 (s, 1H, H8), 3.93 (s, 3H, H12), 3.91 (m, 1H, cod-CH),
3.58 (m, 1H, cod-CH), 2.29 (m, 1H, cod-CH2), 2.22 (s, 3H, H11),
2.20 (s, 3H, H10), 2.05 (m, 1H, cod-CH2), 1.84 (m, 1H, cod-CH2),
1.72 (m, 1H, cod-CH2). 13C{1H} NMR (101 MHz, THF-d8): δ
(ppm) 192.6 (s, C2), 144.0 (s, C4), 134.6 (s, C9), 123.8 (C6), 123.1
(s, C7), 113.3 (s, C5), 105.6 (s, C8), 68.9 (s, cod-CH), 67.0 (s, cod-
CH), 30.3 (s, C112), 29.7 (s, cod-CH2), 29.4 (s, cod-CH2), 17.42 (s,
7
C11), 17.40 (s, C10). Li NMR (155 MHz, THF-d8): δ (ppm) 1.6.
MS (ESI, positive ions) m/z: 621.2566 [7−Li + 2H]+ (calcd for [7−
Li + 2H]+ 621.2570). MS (MALDI-TOF, matrix DCTB) m/z: 621
[7−Li + 2H]+.
4.7. Synthesis of Complex [6] from [7]. A sample of complex
[7] (27.7 mg, 0.04 mmol) was dissolved in THF (5 mL) and
[Rh(cod)(μ-Cl)]2 (10.8 mg, 0.02 mmol) was added as a solid. The
reaction mixture was stirred at ambient temperature for 12 h. The
solvent was removed in vacuo and the solid residue was washed with
methanol (2 × 5 mL) and dried under reduced pressure to give
complex [6] as a reddish solid. Yield: 29.9 mg, 0.036 mmol, 90%. 1H
NMR (400 MHz, THF-d8): δ (ppm) 7.38 (s, 1H, H5), 6.81 (s, 1H,
H8), 5.11−5.03 (m, 1H, cod-CH), 4.47−4.40 (m, 1H, cod-CH),
4.02−3.92 (m, 2H, cod-CH), 3.78 (s, 3H, H12), 2.87−2.81 (m, 1H,
cod-CH2), 2.62−2.55 (m, 2H, cod-CH2), 2.50−2.42 (m, 1H, cod-
CH2), 2.27 (s, 3H, H11), 2.21 (s, 3H, H10), 2.19−2.14 (m, 2H, cod-
CH2), 2.08−2.01 (m, 1H, cod-CH2), 1.99−1.93 (m, 1H, cod-CH2).
13C{1H} NMR (101 MHz, THF-d8): δ (ppm) 188.1 (s, C2), 143.4 (s,
C4), 137.1 (s, C9), 128.8 (s, C6), 128.2 (s, C7), 115.6 (s, C5), 109.9
4.4.2. Characterization of Complex [5]. Complex [5] was
1
obtained as an orange solid. Yield: 26 mg, 35 mmol, 35%. H NMR
(400 MHz, THF-d8): δ (ppm) 7.36 (s, 1H, H5), 6.77 (s, 1H, H8),
5.08 (s br, 1H, cod-CH), 4.79 (s br, 1H, cod-CH), 4.50 (s br, 1H,
cod-CH), 4.04 (s br, 1H, cod-CH), 3.82 (s, 3H, H12), 2.90−2.80 (m,
1H, cod-CH2), 2.78−2.71 (m, 1H, cod-CH2), 2.69−2.60 (m, 1H,
cod-CH2), 2.63−2.54 (m, 1H, cod-CH2), 2.37−2.29 (m, 2H, cod-
CH2), 2.25 (s, 3H, H11), 2.19 (s, 3H, H10), 2.08−2.02 (m, 1H, cod-
CH2), 2.02−1.95 (m, 1H, cod-CH2). 13C{1H} NMR (101 MHz,
1
THF-d8): δ (ppm) 192.5 (d, JCRh = 49.8 Hz, C2), 143.6 (s, C4),
1
1
136.5 (s, C9), 128.1 (s, C6), 127.6 (s, C7), 115.0 (s, C5), 109.2 (s,
(s, C8), 78.9 (d, JCRh = 3.9 Hz, cod-CH), 78.7 (d, JCRh = 2.6 Hz,
cod-CH), 73.6 (s, cod-CH), 72.1 (s, cod-CH), 33.24 (s, cod-CH2),
33.22 (s, C12), 32.8 (s, cod-CH2), 32.3 (s, cod-CH2), 32.0 (s, cod-
CH2), 20.5 (s C11), 20.2 (s, C10). MS (MALDI-TOF, matrix
DCTB) m/z: 831 [[6] + H]+.
1
1
C8), 87.2 (d, JCRh = 8.4 Hz, cod-CH), 86.6 (d, JCRh = 7.1 Hz, cod-
CH), 78.2 (d, 1JCRh = 10.2 Hz, cod-CH), 78.1 (d, 1JCRh = 8.9 Hz, cod-
CH), 33.4 (s, C12), 32.2 (s, 2 × cod-CH2), 31.9 (s, cod-CH2), 31.7
(s, cod-CH2), 20.3 (s, C11), 20.1 (s, C10). HRMS (ESI, positive
ions) m/z: 531.1989 [[5]−Rh(cod) + 2H]+ (calcd for [[5]−Rh(cod)
+ 2H]+ 531.1995).
4.8. General Procedure for the Synthesis of Complexes [8]
and [9]. Lithium diisopropylamide (16 mg, 0.15 mmol) was dissolved
in THF (4 mL) and the solution was cooled to −78 °C. The caffeine
(19.8 mg, 0.10 mmol) was added. The reaction mixture was stirred for
2 h at −78 °C. Subsequently, [Ir(cod)(μ-Cl)]2 (33.6 mg, 0.05 mmol)
or [Rh(cod)(μ-Cl)]2 (24.7 mg, 0.05 mmol) was added and the
solution was stirred for 12 h while it was allowed to warm up to
ambient temperature. The solvent was removed in vacuo and the solid
residue was washed with methanol (2 × 2 mL) and dried under
reduced pressure.
4.5. Synthesis of the Complex Mixture [4]−[6]. Compound 1
(32.0 mg, 0.20 mmol) was dissolved in THF (5 mL) and cooled to
−78 °C. Then, n-BuLi (0.2 mmol, 0.13 mL of a 1.6 M solution in n-
hexane) was added. The reaction mixture was stirred for 2 h at −78
°C. Subsequently, [Ir(cod)(μ-Cl)]2 (33.6 mg, 0.05 mmol) and
[Rh(cod)(μ-Cl)]2 (24.7 mg, 0.05 mmol) were added and the solution
was stirred for 12 h while it was allowed to warm up to ambient
temperature. The solvent was removed in vacuo and the resulting
residue was washed with methanol (2 × 5 mL) and dried under
reduced pressure. The mixture of complexes [4]−[6] was obtained as
4.8.1. Characterization of Complex [8]. Yield: 14 mg, 0.014
mmol, 28%, ratio [8H−H]/[8H−T] 50:50. H NMR (400 MHz, THF-
1
F
DOI: 10.1021/acs.organomet.9b00074
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
d8 for [8H−H]): δ (ppm) 4.67 (m, 2H, cod-CH), 4.22 (s, 6H, C-11),
4.04 (m, 2H, cod-CH), 4.03 (s, 6H, H-12), 3.60 (m, 2H, cod-CH),
3.56 (m, 2H, cod-CH), 3.15 (s, 6H, H-10), 2.50 (m, 2H, cod-CH2),
2.46 (m, 2H, cod-CH2), 2.45 (m, 2H, cod-CH2), 2.43 (m, 2H, cod-
CH2), 2.30 (m, 2H, cod-CH2), 2.28 (m, 2H, cod-CH2), 1.76 (m, 2H,
cod-CH2), 1.69 (m, 2H, cod-CH2). 13C{1H} NMR (101 MHz, THF-
d8 for [8H−H]): δ (ppm) 182.6 (C-8), 154.6 (C-6), 152.6 (C-2), 147.4
(C-4), 110.6 (C-5), 78.7 (cod-CH), 74.7 (cod-CH), 63.2 (cod-CH),
56.2 (cod-CH), 36.9 (C-12), 33.0 (cod-CH2), 32.8 (C-11), 32.5
(cod-CH2), 32.4 (cod-CH2), 32.1 (cod-CH2), 27.6 (C-10). 1H NMR
(400 MHz, THF-d8 for [8H−T]): δ (ppm) 4.53 (m, 2H, cod-CH),
4.17 (s, 6H, H-11), 4.17 (m, 2H, cod-CH), 4.09 (s, 6H, H-12), 3.92
(m, 2H, cod-CH), 3.56 (m, 2H, cod-CH), 3.15 (s, 6H, H-10), 2.60
(m, 2H, cod-CH2), 2.53 (m, 2H, cod-CH2), 2.42 (m, 2H, cod-CH2),
2.32 (m, 2H, cod-CH2), 2.21 (m, 2H, cod-CH2), 2.10 (m, 2H, cod-
CH2), 1.86 (m, 2H, cod-CH2), 1.76 (m, 2H, cod-CH2). 13C{1H}
NMR (101 MHz, THF-d8 for [8H−T]): δ (ppm) 178.6 (s, C-8), 154.6
(s, C-6), 152.6 (s, C-2), 147.4 (s, C-4), 110.7 (s, C-5), 81.2 (s, cod-
CH), 81.1 (s, cod-CH), 78.7 (s, cod-CH), 74.7 (s, cod-CH), 36.1 (s,
C-12), 35.6 (s, cod-CH2), 33.6 (s, cod-CH2), 32.6 (s, cod-CH2), 32.5
(s, C-11), 29.3 (s, cod-CH2), 27.6 (s, C-10). MS (MALDI-TOF,
matrix DCTB) m/z (%): 986 (100) [8]+.
parameters against all |F2| with anisotropic thermal parameters for all
non-hydrogen atoms and hydrogen atoms on calculated positions, R =
0.0292, wR = 0.0686 [I ≥ 2σ(I)], R = 0.0381, wR = 0.0715 (all data).
The asymmetric unit contains one formula unit.
4.9.2. Crystallographic Data for [5]·2C6H5F. Crystals suitable for
an X-ray diffraction study were obtained by cooling a concentrated
solution of [5] in fluorobenzene. Formula C48H56N4F2Rh2, M =
̅
932.78, red blocks, 0.22 × 0.14 × 0.12 mm3, triclinic, space group P1,
a = 10.5486(2), b = 11.5988(2), c = 17.9751(3) Å, α = 85.6760(10),
β = 80.7610(10), γ = 70.8570(10), V = 2050.10(6) Å3, Z = 2, ρcalcd
=
1.511 g·cm−3, μ = 0.853 mm−1, 38 697 intensities measured in the
range 6.0° ≤ 2Θ ≤ 63.9°, 13 127 independent intensities (Rint
=
0.0393), 10 400 observed intensities [I ≥ 2σ(I)], semiempirical
absorption correction (0.857 ≤ T ≤ 0.905), refinement of 489
parameters against all |F2| with anisotropic thermal parameters for all
non-hydrogen atoms and hydrogen atoms on calculated positions, R =
0.0399, wR = 0.1031 [I ≥ 2σ(I)], R = 0.0554, wR = 0.1132 (all data).
The asymmetric unit contains one formula unit of complex [5] and
two molecules of fluorobenzene. The fluorine atom of one molecule
of fluorobenzene is disordered over two positions (occupancies
80:20). The entire second fluorobenzene molecule is disordered over
two positions (occupancies 60:40) and the positional parameters for
this molecule were refined with isotropic displacement parameters.
No hydrogen positions were calculated for carbon atoms refined with
isotropic displacement parameters.
4.8.2. Characterization of Complex [9]. Yield: 16 mg, 0.020
1
mmol, 40%, ratio [9H−H]/[9H−T] 30:70. H NMR (400 MHz, THF-
d8 for [9H−H]): δ (ppm) 5.01 (m, 2H, cod-CH), 4.66 (m, 2H, cod-
CH), 4.33 (s, 6H, H-11), 4.32 (m, 2H, cod-CH), 4.06 (m, 2H, cod-
CH), 4.03 (s, 6H, H-12), 3.11 (s, 6H, H-10), 2.76 (m, 2H, cod-CH2),
2.73 (m, 2H, cod-CH2), 2.65 (m, 2H, cod-CH2), 2.62 (m, 2H, cod-
CH2), 2.40 (m, 2H, cod-CH2), 2.40 (m, 2H, cod-CH2), 1.98 (m, 2H,
cod-CH2), 1.97 (m, 2H, cod-CH2). 13C{1H} NMR (101 MHz, THF-
d8 for [9H−H]): δ (ppm) 188.7 (d, 1JRhC = 50.0 Hz, C-8), 153.8 (s, C-
6), 152.5 (s, C-2), 148.7 (s, C-4), 110.2 (s, C-5), 90.8 (d, 1JRhC = 8.3
Hz, cod-CH), 88.1 (d, 1JRhC = 7.0 Hz, cod-CH), 81.7 (d, 1JRhC = 13.5
Hz, cod-CH), 80.1 (d, 1JRhC = 11.8 Hz, cod-CH), 36.7 (s, C-12), 33.0
(s, cod-CH2), 32.1(s, C-11), 32.0 (s, cod-CH2), 31.7 (s, cod-CH2),
4.9.3. Crystallographic Data for [6]·2C6H5F. Crystals suitable for
an X-ray diffraction study were obtained by cooling a concentrated
solution of [6] in fluorobenzene. Formula C48H56F2Ir1.33N4Rh0.67, M =
1051.54, purple plates, 0.443 × 0.300 × 0.113 mm3, triclinic, space
̅
group P1, a = 10.5666(2), b = 11.5860(2), c = 17.9775(4) Å, α =
85.8891(10), β = 80.7144(10), γ = 70.7500(10), V = 2050.20(7) Å3,
Z = 2, ρcalcd = 1.703 g·cm−3, μ = 4.630 mm−1, 37 179 intensities
measured in the range 5.9° ≤ 2Θ ≤ 61.1°, 12 420 independent
intensities (Rint = 0.0347), 11 675 observed intensities [I ≥ 2σ(I)],
semiempirical absorption correction (0.002 ≤ T ≤ 0.020), refinement
of 559 parameters against all |F2| with anisotropic thermal parameters
for all non-hydrogen atoms and hydrogen atoms on calculated
positions, R = 0.0444, wR = 0.1162 [I ≥ 2σ(I)], R = 0.0460, wR =
0.1182 (all data). The asymmetric unit contains 1 formula unit of
complex [6], and two molecules of fluorobenzene. Complex [6] had a
Rh/Ir substitutional disorder (occupancies Rh/Ir, 67:33) and the
positional and anisotropic displacement parameters of the disordered
Rh and Ir atoms were constrained to be the same. The fluorine atoms
of both fluorobenzene molecules are disordered over two positions.
4.9.4. Crystal Data for Complex [9H−T]·C4H8O. Crystals suitable
for an X-ray diffraction study were obtained by slow diffusion of n-
hexane into a saturated solution of the complex mixture [9H−T]/
[9H−H] in THF. Formula C36H50N8O5Rh2, M = 880.66, orange
1
30.0 (s, cod-CH2), 27.3 (s, C-10). H NMR (400 MHz, THF-d8 for
[9H−T]): δ (ppm) 4.73 (m, 2H, cod-CH), 4.66 (m, 2H, cod-CH),
4.33 (s, 6H, H-11), 4.54 (m, 2H, cod-CH), 4.06 (s, 6H, H-12), 3.96
(m, 2H, cod-CH), 3.12 (s, 6H, H-10), 2.76 (m, 2H, cod-CH2), 2.69
(m, 2H, cod-CH2), 2.63 (m, 2H, cod-CH2), 2.55 (m, 2H, cod-CH2),
2.26 (m, 2H, cod-CH2), 2.16 (m, 2H, cod-CH2), 2.14 (m, 2H, cod-
CH2), 2.14 (m, 2H, cod-CH2). 13C{1H} NMR (101 MHz, THF-d8
for [9H−T]): δ (ppm) 183.2 (d, 1JRhC = 48.2 Hz, C-8), 154.0 (s, C-6),
152.6 (s, C-2), 148.5 (s, C-4), 110.2 (s, C-5), 95.8 (d, 1JRhC = 6.9 Hz,
cod-CH), 95.0 (d, 1JRhC = 7.5 Hz, cod-CH), 75.9 (d, 1JRhC = 14.4 Hz,
cod-CH), 72.2 (d, 1JRhC = 12.1 Hz, cod-CH), 35.8 (s, C-12), 33.0 (s,
cod-CH2), 32.9 (s, cod-CH2), 32.5 (s, C-11), 32.5 (s, cod-CH2), 29.8
(s, cod-CH2), 27.3 (s, C-10). MS (MALDI-TOF, matrix DCTB) m/z
(%): 808 (75) [9]+, 700 (100) [9−cod]+.
needles, 0.360 × 0.260 × 0.100 mm3, triclinic, space group P1
̅
, a =
4.9. X-ray Diffraction Studies. X-ray diffraction data were
collected at T = 153 K for [3], [5]·2C6H5F and [6]·2C6H5F and at T
= 100 K for [9H−T] using a Bruker AXS APEX II charge-coupled
device diffractometer equipped with a microsource using graphite-
monochromated Mo Kα radiation (λ = 0.71073 Å). Semiemperical
multiscan absorption corrections were applied to all data sets.18
Structure solutions were found with SHELXT (intrinsic phasing)19a
and were refined with SHELXL19b 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.
12.1104(5), b = 12.4776(5), c = 13.3350(5) Å, α = 76.316(2), β =
63.622(2), γ = 87.914(2), V = 1748.52(12) Å3, Z = 2, ρcalcd = 1.673 g·
cm−3, μ = 1.000 mm−1, 47 891 intensities measured in the range 6.5°
≤ 2Θ ≤ 59.2°, 9746 independent intensities (Rint = 0.0325), 8651
observed intensities [I ≥ 2σ(I)], semiempirical absorption correction
(0.673 ≤ T ≤ 0.745), refinement of 490 parameters against all |F2|
with anisotropic thermal parameters for all non-hydrogen atoms and
hydrogen atoms on calculated positions, R = 0.0274, wR = 0.0604 [I
≥ 2σ(I)], R = 0.0330, wR = 0.0627 (all data). The asymmetric unit
contains one formula unit of [9H−T] and one THF molecule.
4.9.1. Crystallographic Data for [3]. Crystals suitable for an X-ray
diffraction study were obtained by cooling a concentrated solution of
[3] in fluorobenzene. Formula C24H34N4Rh2, M = 584.37, orange
ASSOCIATED CONTENT
■
S
* Supporting Information
plates, 0.173 × 0.097 × 0.004 mm3, triclinic, space group P1
̅
, a =
9.8190(2), b = 9.9553(2), c = 12.5831(2) Å, α = 76.9880(10), β =
89.2410(10), γ = 70.0240(10), V = 1123.60(4) Å3, Z = 2, ρcalcd
1.727 g·cm−3, μ = 1.487 mm−1, 20 499 intensities measured in the
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.9b00074.
=
range 5.7° ≤ 2Θ ≤ 62.0°, 7005 independent intensities (Rint
=
1H NMR and 13C{1H} NMR spectra of all new
compounds (PDF)
0.0289), 5885 observed intensities [I ≥ 2σ(I)], semiempirical
absorption correction (0.824 ≤ T ≤ 0.890), refinement of 294
G
DOI: 10.1021/acs.organomet.9b00074
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Organometallics
Article
Ligands. Chem.Eur. J. 2008, 14, 10900−10904. (e) Hahn, F. E.;
Radloff, C.; Pape, T.; Hepp, A. A Nickel(II)-Cornered Molecular
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Accession Codes
CCDC 1895429−1895432 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.
CCDC 1895429−1895432 contain the supplementary
crystallographic 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.
(4) (a) Enders, D.; Niemeier, O.; Henseler, A. Organocatalysis by N-
Heterocyclic Carbenes. Chem. Rev. 2007, 107, 5606−5655.
AUTHOR INFORMATION
Corresponding Author
*E-mail: fehahn@uni-muenster.de.
■
́
(b) Marion, N.; Díez-Gonzalez, S.; Nolan, S. P. N-Heterocyclic
Carbenes as Organocatalysts. Angew. Chem., Int. Ed. 2007, 46, 2988−
3000. (c) Grossmann, A.; Enders, D. N-Heterocyclic Carbene
Catalyzed Domino Reactions. Angew. Chem., Int. Ed. 2012, 51,
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Heterocyclic Carbenes and Beyond. Chem. Soc. Rev. 2012, 41, 3511−
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Catalysis with N-Heterocyclic Carbenes under Oxidative Conditions.
Chem.Eur. J. 2013, 19, 4664−4678.
ORCID
F. Ekkehardt Hahn: 0000-0002-2807-7232
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
The authors gratefully acknowledge financial support from the
Deutsche Forschungsgemeinschaft (SFB 858 and IRTG 2027).
■
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