Self-Assembly of Benzimidazole-Derived Tris-NHC Ligands and AgI-Ions to Hexanuclear Organometallic Cages and Their Unusual Transmetalation Chemistry

Article abstract of DOI:10.1002/chem.202003937

Multi-ligand self-assembly to attain the Ag^I-N-heterocyclic carbene (NHC)-built hexanuclear organometallic cages of composition [Ag₆(3 a,b)₄](PF₆)₆ from the reaction of benzimidazole-derived tris(azolium) salts [H₃-3 a,b](PF₆)₃ with Ag₂O was achieved. The molecular structures of the cages were established by X-ray diffraction studies along with NMR and MS analyses. The existence of a single assembly in solution was supported by diffusion-ordered spectroscopy (DOSY) ¹H NMR spectra. Further, transmetalation reactions of these self-assembled complexes, [Ag₆(3 a,b)₄](PF₆)₆, with Cu^I/Au^I-ions provided various coinage metal-NHC complexes having diverse molecular compositions, which included the first example of a hexanuclear Cu^I-dodecacarbene complex, [Cu₆(3 b)₄](PF₆)₆.

Full text of DOI:10.1002/chem.202003937

Accepted Article
Accepted Article
Title: Self-Assembly of Benzimidazole Derived Tris-NHC Ligands and
AgI-ions to Hexanuclear Organometallic Cages and Their Unique
Transmetalation Chemistry
Authors: Arnab Rit and Rajeev C. Nishad
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To be cited as: Chem. Eur. J. 10.1002/chem.202003937
Link to VoR: https://doi.org/10.1002/chem.202003937
0
1/2020

Chemistry - A European Journal
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COMMUNICATION
Self-Assembly of Benzimidazole Derived Tris-NHC Ligands and
I
Ag -ions to Hexanuclear Organometallic Cages and Their Unusual
Transmetalation Chemistry
[a]
[a]
Rajeev C. Nishad and Arnab Rit*
Dedicated to Prof. F. E. Hahn on the occasion of his 65th birthday
[
a]
Mr. Rajeev C. Nishad, Dr. Arnab Rit
Department of Chemistry
Indian Institute of Technology Madras, Chennai - 600036
E-mail: arnabrit@iitm.ac.in
Supporting information (experimental details, characterization data, and DFT calculation details) for this article is given via a link at the end of the document
I
I
Abstract: Multi ligand self-assembly to attain the Ag -NHC built
hexanuclear organometallic cages of composition [Ag (3a,b) ](PF
from the reaction of benzimidazole derived tris(azolium) salts [H
a,b](PF with Ag O is presented. The molecular structures of the
possess common structural motifs of Ag -ions sandwiched
6
4
6
)
6
between two homoleptic polydentate ligands in which all the NHC
donors are free to rotate (Scheme 1a).[8c,12] This restricts, by
disfavouring the multidirectional self-assembly, the diversity of the
molecular architectures which could be obtained by this strategy
and thus limited only to the compositions [Ag
depending on the number of NHC donors in the ligand L).
3
-
3
)
6 3
2
cages are established by X-ray diffraction studies along with NMR and
mass spectrometric analyses. The existence of a single assembly in
L
2
]n+ (n = 2-8,
n
1
[8c,12,13]
solution is supported by the DOSY H NMR spectra. Further,
I
transmetalation reactions of these self-assembled complexes,
Moreover, the essentially linear geometry around the Ag -ions
I
I
I
[
6 4
Ag (3a,b) ](PF
)
6 6
, with Cu/Au -ions provide various coinage metal-
(CNHC-Ag -CNHC  180) insists the need of diversity in the ligand
NHC complexes having diverse molecular compositions which
topologies for the generation of diversified 3D structures.
I
include the first example of a hexanuclear Cu -dodecacarbene
6 4 6 6
complex, [Cu (3b) ](PF ) .
Over the last few decades, metallo-supramolecular assemblies[1]
have gained much interest among the synthetic chemists
because of their elegant molecular architectures, intriguing
physical/chemical properties, biomedical applications, and rich
host-guest chemistry.[2] Metal-controlled self-assembly of
appropriate ligands is considered to be the most convenient
approach to access these structures.[3] The first report of such
I
assembly from two poly-(bipyridine) ligands and Cu ions by Lehn
et al. in 1987 is recognized as the start of an era of this exciting
chemistry.[4] Looking back at the library of such known assemblies,
one can easily comprehend that majority of the ligand systems
employed to attain such structures feature the Werner-type
pyridyl-N or carboxylate-O donors.[5] Whereas the utilization of
ligands featuring carbon donors to construct such structures is
rather limited.[6] Nevertheless, N-heterocyclic carbenes (NHCs)[7]
have slowly started to emerge as a new class of carbon donor
ligands in this chemistry after the pioneering works by Hahn et
al.[8] New ligand systems having diverse topologies can be
designed easily which made them a potent alternative to the
Werner-type ligands for the generation of metallo-supramolecular
assemblies.[8c,9d-e]
I
Scheme 1. Overview of (a) the previous work on Ag -NHC based assemblies
and (b) this work.
Ligands featuring mixed NHC donors with confined rotational
flexibility could be one of the possible ligand types which might
lead to captivating architectures via self-assembly of more than
two NHC ligands (commonly not observed) in combination with
the Ag -ions. However, to the extent of our knowledge,
polynuclear Ag -NHC complexes of such ligand systems are not
known till date, which motivated us to design new types of poly-
NHC ligands possessing NHC donors with confined rotational
freedom. Herein, we report the synthesis of Ag -NHC built cages
of composition [Ag L
]6+ via self-assembly of specifically designed
6 4
I
For the construction of the aforementioned NHC-based
I
I
I
architectures, coinage metals (Ag and Au ) have predominantly
been utilized possibly because of their fixed linear geometry which
enables the formation of predicted structures based on the
employed ligand topology.[8c,9] Among coinage metals, Ag -based
I
I
structures are, by far, the most investigated ones because of their
facile synthesis via Ag
2
O route[10] and the ability of the Ag -CNHC
I
tris-NHC ligands featuring two types of NHC donors which can
lead the self-assembly in nearly two vertical directions (Scheme
1b). These hexanuclear complexes represent the unique
examples of discrete polynuclear self-assemblies, obtained via
bond to undergo transmetalation with other transition metals.[11]
A
closer look at the metallo-supramolecular structures, built on
I
exclusive Ag -NHC bond formations, readily reveals that they
1
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Chemistry - A European Journal
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COMMUNICATION
I
rational design, which feature more than two poly-NHC ligands
Therefore, to access new types of Ag -NHC based architectures,
we attempted the metalation of [H -3a,b](PF with Ag O (acts as
3
both base and metal source). Treatment of the salts [H -
I
that are connected by means of exclusive Ag -NHC bonds.
3
6
)
3
2
I
Further, transmetalation reactions of these Ag -NHC complexes,
6
+
I
I
[
Ag
6
L
4
] , with Cu/Au -ions deliver various coinage metal-NHC
3a,b](PF
6
)
3
with 1.5 equiv. of Ag
2
O in acetonitrile generated the
hexanuclear Ag -dodecacarbene complexes having the
I
complexes having diverse compositions including the first
I
example of a hexanuclear Cu -dodecacarbene complex.
composition of [Ag
6
(3a,b)
4
](PF
6
)
6
via self-assembly of four NHC
I
The mixed tris(azolium) salts [H
3
-3a,b](PF
6
)
3
, precursors for NHC
ligands 3a,b with six Ag -ions in 81-83% yields (Scheme 3). These
complexes were characterized by NMR, mass, and single crystal
X-ray diffraction studies. Complete absence of the azolium N-CH-
N protons (δ = 9.48-10.15 ppm) of the parent salts [H
in the 1H NMR spectra of the complexes [Ag
supports the formation of carbene centers. The attachment of
these generated NHCs to silver ions was established by the
C{ H} NMR spectra which exhibit the very characteristic CNHC
Ag 13C{ H}-NMR signals in the region of δ = 180.5-183.6 and
ligands, were synthesized following the multistep procedure as
shown in Scheme 2a. In the first step, the imidazole moieties were
installed on the benzimidazole core via standard Ullmann
coupling protocol[8b,14] by reacting the dibromo compounds 1a,b
with imidazole. Subsequent reactions with excess alkyl halides
result in alkylations of the imine moieties in 2a and 2b to yield the
3
-3a,b](PF
](PF
6
)
)
3
6
(3a,b)
4
6
6
1
3
1
tris(azolium) salts [H
Exchange of the halide counterions in these salts with non-
coordinating PF anions via salt metathesis using NH PF
provides the [H -3a,b](PF as off-white solids in 84-86% yield.
Poly(azolium) salt ([H -3a,b](PF
3
-3a]Br
3
and [H
3
-3b]I
3
,
respectively.
-
1
1
3
1
6
4
6
192.3-195.2 ppm. Notably, these
C{ H}-NMR resonances
3
6
)
3
exhibit the rarely detected coupling of the NHC carbons with both
the silver isotopes ( J(C- Ag)  181-184 Hz and J(C-109Ag) 
209-213 Hz; Figure S22 and S24) and this implies that the
dynamic equilibria, usually observed for the Ag -NHC complexes
1
107
1
3
6
)
3
) formations were confirmed by
1
the NMR and ESI-mass spectral analysis. In the H NMR spectra,
the characteristic azolium N-CH-N proton resonances were
I
in solution, are slow in the present complexes.[8b,10b,11b]
Furthermore, the presence of only three aromatic resonances
with the integration ratio of 2:2:2 in the 1H NMR spectra of the
complexes (Figure S21 and S23) signifies the symmetric nature
of the complexes.
detected at  = 10.14 and 9.58 ppm for [H
3 6 3
-3a](PF ) and at  =
1
0.01 and 9.48 ppm for [H -3b](PF . Appearance of a single
3
6 3
)
resonance for both the imidazolium N-CH-N protons indicates the
free rotation of the imidazolium units in solution which is
imperative to attain self-assembled discrete structures rather than
1
3
1
the polymeric structures. Further, the C{ H} NMR spectra
display resonances for the N-CH-N azolium carbon atoms in the
usual range of δ = 148.7-138.2 ppm.[15] Presence of the PF
ions
were confirmed by 31P and 19F NMR analysis. Single-crystal X-ray
analysis of [H -3a](PF (Scheme 2) finally established the
structures of the [H -3a,b](PF salts.
6
3
6 3
)
3
6 3
)
I
Scheme 3. Synthesis of the self-assembled hexanuclear Ag -NHC
3 6 3
complexes from the [H -(3a,b)](PF ) ligand precursors.
Scheme 2. (a) Synthesis of the benzimidazole-derived precursors for the NHC
3+
3 3 6 3
ligands 3a,b. (b) Molecular structure of the trication [H -3a] in [H -3a](PF ) .
Hydrogen atoms except N-CH-N and counterions are omitted for clarity. The N-
ethyl groups are shown in capped stick.
Poly-NHC ligand systems are reported to generate
supramolecular architectures with coinage metals.8
c,9d,11a
I
However, in most of the known poly-NHC based Ag -complexes,
I
Figure 1. (a) Molecular structure of [Ag (3a) ]6+ cation in 4. The hydrogen atoms
6 4
Ag -ions are generally found to be sandwiched between the two
are removed and the N-Et groups are shown in capped stick. (b) Contour line
homoleptic polydentate ligands.[8c,16] Polynuclear Ag -NHC
complexes other than the typical sandwich-type where each AgI-
ion is coordinated by only NHC donors are extremely rare. To the
extent of our knowledge, only Han et al. have recently reported
such structures via serendipitous alterations of the N-alkyl groups
of a 1,2,4-triazolinylidene based poly-NHC ligand.[17] However,
our present ligand system is designed in such a way that it has
the potential to deliver self-assembled architectures via
I
2
diagrams of the  (r). Solid pink lines connecting the atomic nuclei represent
1
the bond paths. Blue dots indicate the bond critical points (BCPs). (c) The
H
3
DOSY NMR in CD CN and (d) ESI-mass spectrum of 4.
Initial evidence for the generation of a discrete self-
assembled species of composition [Ag 3a ](PF via
6
(
)
4
6 6
)
I
association of four ligands and six Ag -ions was received
from the ESI-MS analysis showing the most intense peaks at
2
+
m/z = 1338.0883 (calcd. for [M-2PF
6
]
1338.0884) and
I
association of more than two poly-NHC ligands and Ag -ions.
843.7377 (calcd. for [M-3PF
6
]3+ 843.7377) with the proper
2
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Chemistry - A European Journal
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COMMUNICATION
I
isotopic distributions (Figure 1d). Furthermore, the diffusion-
ordered NMR spectroscopy (DOSY) ensures the existence
of a single assembly in solution having diffusion coefficient of
maintaining the overall structure as the Cu -poly(NHC) complexes
I
having nuclearity higher than three which feature exclusive Cu -
NHC bonds are not known.[
8c,9d]
In this line, complex 4 was
)Br], source for Cu -ion (Scheme
4). However, our efforts to isolate related hexanuclear Cu -NHC
complex were unsuccessful. The reaction always yielded an
inseparable reaction mixture; it was difficult to monitor the reaction
8
.90 x 10-11 m /s (Figure 1c). The H DOSY NMR and ESI-
2
1
reacted with 6 equiv. of [Cu(SMe
2
I
I
MS data of the complex [Ag
6
(3b
)
4
](PF
6
)
6
display similar
characteristics (Figure S31 and S37).
Unequivocal evidence for the formation of a hexanuclear Ag -
I
1
dodecacarbene complex
4
was provided by single crystal X-
outcome by H NMR due to its complex nature and the ESI-MS
ray diffraction analysis (Figure 1a) which shows that the
structure is symmetrical in nature as indicated by the NMR
analysis and each Ag -ion is connected to either two
analysis was found to be incompetent because of the sensitive
I
nature of the Cu -NHC complex. Therefore, we shifted our
I
I
attention towards the corresponding Au -complex and accordingly,
imidazolinylidene or benzimidazolinylidene donors. The Ag-
complex 4 was treated with 6 equiv. of [Au(SMe
Here also, we failed to obtain the related hexanuclear Au -NHC
complex. ESI-MS analysis of the reaction mixture revealed the
2
)Cl] (Scheme 4).
I
C
NHC bond lengths [in the range of 2.101(16)-2.099(15) Å] fall
I
in the range previously observed for the Ag -poly(NHC)
complexes.[
8c,11a]
Notably, the observed Ag-Ag distances
presence of
a
mixture of products having ambiguous
(
d
Ag3-Ag3* = 3.19 Å and dAg2-Ag1 = 3.23 Å) indicate the existence
compositions from which we could not isolate a single compound
in pure form. This is in line with the transmetalation chemistry of
[
18a-c]
of strong argentophilic interactions
significant deviation of geometry around the Ag-ions from
linearity ( NHC-Ag-CNHC = 165.20-171.15 ). The existence
of these Ag-Ag interactions in was assessed by using NBO
which have led to the
I
I
[Ag
NHC complexes of nuclearity other than six might also be forming,
the equiv. of [Au(SMe )Cl] used for the reaction was increased
6 4 6 6
(3a) ](PF ) as observed with Cu -ion. Reasoning that Au -
∠
C

4
2
analysis. The WBI values suggest that the interaction
between the Ag3-Ag3* (WBI = 0.148) is relatively stronger
than that of the Ag1-Ag2 (WBI = 0.121; Table S2), which is
consistent with the crystal structure analysis as mentioned
above. On contrary, the WBI between the imidazolinylidene
periodically and the product formation was monitored via ESI-
Mass analysis as it was found to be the best way for this system.
Finally, when 4 was reacted with 10 equiv. of [Au(SMe )Cl], ESI-
2
mass spectrum displayed the most intense peaks at m/z =
1851.1502 and 908.0906 (Figure S38) which provided the
I
coordinated Ag1-Ag1* ions (WBI = 0.135) in
5
was calculated
preliminary indication that a pentanuclear Au -NHC complex of
to be higher than the benzimidazolinylidene coordinated
Ag2-Ag2* ions (WBI = 0.113; Table S2). This is also in line
composition [Au
molecular structure of [Au
5
(3a)
2
Cl
4
]PF
6
is forming (Scheme 4). The exact
Cl ]PF was established by X-ray
5
(3a)
2
4
6
with the single crystal X-ray analysis of
5
(dAg1-Ag1* = 3.14 Å
analysis which uncovered an unusual structure featuring two
different types of NHC coordination around the Au -ions (NHC-Au-
I
and dAg2-Ag2* = 3.33 Å; Figure S34). This variation in
[
18d]
argentophilic interactions
between the complex
4
and
5
is
NHC and NHC-Au-Cl; Figure 2a) which has not been observed
before in a single molecule, to the best of our knowledge. The
crystal structure also reveals the presence of aurophilic
interaction (dAu-Au = 3.34 Å)[11a,20] which results in a collinear
possibly due to the subtle difference in the steric requirement
of the N-Et and -Me moieties. Further, the topological
analyses of complexes
4 (Figure 1b) and 5 (Figure S41)
I
I
I
reveal the bond paths between the Ag -Ag ions establishing
the presence of reasonably strong argentophilic interactions.
Additionally, bonding analysis at the DFT level provided the
optimized geometries along with the metric parameters
which agree well with the experimental values (see
supporting information).
arrangement of all the three Au -ions coordinated by the
imidazolinylidene donors ( ∠ Au1-Au2-Au1* = 180.0°). These
I
I
aurophilic (Au -Au ) interactions are also supported by the DFT
calculations; the topological analyses clearly display the bond
I
I
paths between the Au -Au ions validating the existence of such
interactions (Figure S42).
5 2 4
(3a) Cl
]+ cation in 6 (a) and 7 (b). Hydrogen
Figure 2. Crystal structures of [Au
atoms are removed and the N-Et groups are shown in capped stick.
Motivated from the above results, [Ag
treated with 12 equiv. of [Au(SMe )Cl] (one equiv. per NHC donor).
To our surprise, we found that the hexanuclear structure of
Ag (3a) ](PF was completely disintegrated and provided a
trinuclear complex of composition [Au (3a)Cl ], 7 in 80% yield via
elimination of 6 equiv. AgPF and SMe (Scheme 4). Formation of
6 4 6 6
(3a) ](PF ) was eventually
2
I
Scheme 4. Synthesis of various Au -NHC complexes via transmetalation from
[
6
4
6 6
)
[
6 4 6 6
Ag (3a) ](PF ) .
3
3
Silver-NHC complexes are established to be excellent carbene
transfer agents to access other metal NHC complexes.[
6
2
10a,11a,19]
7
was substantiated by NMR spectroscopy, ESI-Mass
1
I
spectrometry, and X-ray crystallography. H NMR spectrum
exhibits only three resonances for the aromatic protons with the
Therefore, we initially attempted to substitute all the six Ag -ions
by CuI to yield an analogous complex
in [Ag (3a) ](PF )
6 4 6 6
3
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COMMUNICATION
I
intensity ratio of 2:2:2 suggesting a symmetrical structure in
marginally higher than the corresponding Ag -complex 5 (D = 8.10
I
-10
2
solution (Figure S25) and constitution of the Au -NHC fragment is
x 10 m /s; Figure S31) in line with the lower atomic weight of
Cu. This suggests that the produced Cu -NHC complex 8 is also
1
3
1
23
I
revealed by the C{ H} NMR spectrum [δ(CNHC-Au) = 180.9 ppm
and 183.0 ppm; Figure S26]. Further, formation of a trinuclear
hexanuclear and having the composition of [Cu
6
(3b)
4
](PF
6
)
6
as of
I
[
Au
3
(3a)Cl
3
] complex was supported by the ESI-MS showing the
its parent Ag -NHC complex 5 which is also supported by the DFT
optimization studies (Figure S43).[ Further, it is to be noted that
24]
highest intensity signals at m/z = 1023.0575 and 514.5578 which
+
are readily assignable to [M-Cl] (calcd. = 1023.0598) and [M-
6 4 6 6
we could not obtain the related [Cu (3a) ](PF ) complex featuring
2Cl+CH
3
CN]2+ (calcd.
=
514.5590) molecular fragments,
the N-ethyl substituents as mentioned before and this could
possibly be attributed to the subtle difference in the steric
requirements of the ethyl and methyl groups. It is important to
respectively. Finally, the molecular structure was confirmed by the
single crystal X-ray analysis of the complex (Figure 2b) and the
complex 7 was observed to be present as a dimer in the solid-
mention that the complex [Cu
example of a hexanuclear Cu -dodecacarbene complex.
Interestingly, construction of the hexanuclear Ag -NHC cage
6
(3b)
4
](PF
6
)
6
represents the first
state via strong unsupported closed-shell d10….
d
10
aurophilic
I
interaction (dAu-Au = 2.993 and 3.234 Å; Figure S35b).[ The Au-
NHC and Au-Cl bond lengths fall within the limits observed for 6
20]
I
C
[Ag
6
(3a)
4
](PF
6
)
6
was observed to be reversible under certain
6 6
Cl to [Ag (3a) ](PF )
I
[20c,21]
conditions (Scheme 6). The addition of NH
4
6
4
and related Au -NHC complexes.
completely disintegrates the assembly via breakage of the Ag-
NHC bonds to provide the corresponding azolium salt with
chloride counterion and AgCl. Anion exchange with NH PF
4 6
cleanly yields the parent azolium salt [H3-3a](PF
6
)
3
(Figure S44).
Scheme 6. Reversible transformation of the [Ag
6
(3a) ](PF )
4 6 6
cage.
In conclusion, we have developed a straightforward approach to
I
access unique hexanuclear Ag -NHC derived organometallic
I
cages [Ag
6
(3a,b)
4
](PF
6
)
6
from the tris-NHC ligands and Ag -ions
via self-assembly. These complexes represent the rare examples
I
of Ag -NHC based discrete self-assemblies featuring multiple
NHC ligands which are obtained via rational design of the poly-
NHC ligands. Further, the N-wingtip groups have been observed
I
to influence the transmetalation reactions of these Ag -NHC
I
I
complexes and thus, various types of homopolynuclear Cu /Au -
I
NHC complexes including an unprecedented hexanuclear Cu -
I
dodecacarbene complex were obtained via substitution of the Ag
I
I
I
by Cu /Au -ions. Additionally, formation of the hexanuclear Ag -
NHC cages was found to be reversible under chemical stimulus.
Further studies towards the various applications of these Ag -NHC
I
cages are underway in our laboratory.
I
Scheme 5. Cu -NHC complex synthesis via transmetalation of 5. (a)
Acknowledgements
We gratefully acknowledge SERB, India (Grant ECR/2016/
13
1
Comparison of the C{ H} NMR spectra of 5 (Ag-complex) and 8 (Cu-complex)
1
in CD
3
CN (*). (b) The H DOSY NMR spectrum of 8 in CD
3
CN.
001272) and IIT Madras for the financial support. R.C.N. thanks
Next, we focused on the transmetalation of the methyl variant
IIT Madras for a research fellowship. We thank the department of
chemistry and SAIF, IIT Madras for the instrumental facility.
(5) to learn if the wingtip group has any impact.[22]
[
Ag (3b) ](PF )
6 4 6 6
Accordingly, 5 was treated with 6 equiv. of [Cu(SMe
2
)Br] (Scheme
1
5) at ambient temperature. To our delight, the H-NMR spectrum
Conflicts of interest
(
Figure S27) revealed the formation of a single complex and
displayed similar resonances, however, slightly upfield shifted, to
those of the parent Ag –NHC complex 5, which probably suggests
There are no conflicts to declare.
I
the retention of a hexanuclear structure. Further, the formation of
I
a Cu -NHC complex is clearly established from the 13C{ H} NMR
1
Keywords: N-Heterocyclic carbenes • self-assembly • DFT
studies • supramolecular chemistry • transmetalation
spectrum (Scheme 5a) of the complex showing the characteristic
singlet CNHC resonances at δ = 194.6 and 178.1 ppm and the
1
13
1
2
released SMe (2.08 ppm, H NMR and 18.1 ppm, C{ H} NMR).
1
2
For selected reviews, see: a) R. Chakrabarty, P. S. Mukherjee, P. J. Stang,
Chem. Rev. 2011, 111, 6810–6918; b) W. X. Gao, H. J. Feng, B. B. Guo,
Y. Lu, G. X. Jin, Chem. Rev. 2020, 120, 6288–6325.
For selected references, see: a) P. C. Purba, S. Bhattacharyya, M. Maity,
S. Mukhopadhyay, P. Howlader, P. S. Mukherjee, Chem. Commun. 2019,
55, 8309–8312; b) Y. W. Zhang, R. Das, Y. Li, Y. Y. Wang, Y. F. Han,
Chem. Eur. J. 2019, 25, 5472–5479; c) G. Yu, K. Jie, F. Huang, Chem.
Rev. 2015, 115, 7240–7303; d) R. Visbal, M. C. Gimeno, Chem. Soc. Rev.
Unfortunately, we could not obtain suitable single crystals for the
X-ray analysis. However, the 1H DOSY NMR spectrum of the
complex 8 reveals a single diffusion coefficient value (D = 8.72 x
2
1
0-10 m /s) for all the proton signals which implies that they all
belong to a single assembly (Scheme 5b) and this value is
4
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COMMUNICATION
2014, 43, 3551–3574; e) A. Pöthig, A. Casini, Theranostics 2019, 9, 3150–
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3
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(
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Stability of the complex 8 is also supported by the calculated HOMO-LUMO
-
1
-1
gap of 414 kJ mol which is similar to that observed for 5 (408 kJ mol ,
Figure S40).
5
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Entry for the Table of Contents
I
Reactions of the benzimidazole derived tris(azolium) salts [H
3
-3a,b](PF
6
)
3
with Ag
(3a,b) ](PF
Cu/Au -ions to produce various coinage metal-NHC complexes of diverse compositions depending on the N-wingtip group of the ligands
a,b.
2
O under self-assembly provide access to Ag -NHC
based unique hexanuclear organometallic cages of composition [Ag
6
4
6 6
) which undergo transmetalation reactions with
I
I
3
6
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