Self-assembly of cucurbit[7]uril based triangular [4]molecular necklaces and their fluorescence properties

Article abstract of DOI:10.1039/C6CC10328F

Self-assembly of rigid-rod dipyridine ligand 1 with M(en)(NO₃)₂ (M = Pd, Pt) affords triangular (3, 5) and square (4, 6) supramolecular coordination complexes (SCCs). The binding affinity of 1 toward CB[n]-type containers results in the formation of triangular [4]molecular necklaces ([4]MNs, 7-10) by either one-pot or post complexation approaches as evidenced by ¹H NMR, diffusion ordered spectroscopy, and ESI-MS.

Full text of DOI:10.1039/C6CC10328F

ChemComm
View Article Online
View Journal
COMMUNICATION
Self-assembly of cucurbit[7]uril based triangular
4]molecular necklaces and their fluorescence
[
Cite this:DOI: 10.1039/c6cc10328f
properties†
Received 31st December 2016,
Accepted 9th February 2017
Soumen K. Samanta, Kimberly G. Brady and Lyle Isaacs*
DOI: 10.1039/c6cc10328f
rsc.li/chemcomm
3 2
Self-assembly of rigid-rod dipyridine ligand 1 with M(en)(NO ) (M = Pd,
Pt) affords triangular (3, 5) and square (4, 6) supramolecular coordination
complexes (SCCs). The binding affinity of 1 toward CB[n]-type
containers results in the formation of triangular [4]molecular necklaces
(
[4]MNs, 7–10) by either one-pot or post complexation approaches as
1
evidenced by H NMR, diffusion ordered spectroscopy, and ESI-MS.
Pioneering work by the groups of Stoddart, Sauvage and Leigh
has resulted in an in depth knowledge of the nature of the
mechanical bond and utilisation of mechanically interlocked
1
molecules (MIMs) to create functional molecular devices. In
the intervening years, these groups and others have used MIMs
as the basis for advanced applications like molecular motors
and machines, nanoscale devices and smart materials for drug
2
delivery and imaging. Whereas MIMs comprise at least one
molecular ring threaded onto one molecular axle, a subset of
MIMs known as [n]molecular necklaces ([n]MNs) comprise n ꢀ 1
molecular rings threaded onto a macrocycle. The first example
Chart 1 Molecular structures of compounds used in this study.
of a [3]MN, also known as a [3]catenane, was reported by
3
Sauvage based on metal ion templation. In 1998, Stoddart been used to create chemical sensors, supramolecular materials,
reported the preparation of [4]MNs by templation based on molecules and materials for drug solubilisation, delivery, and
4
8
aromatic donor–acceptor interactions. More recently, Kim, reversal, and as promotors of biological dimerisation events.
Stang and others synthesized [n]MNs (n = 4, 5) by utilising Over the past two decades, the strategic combination of rigid
pairs of orthogonal (non)covalent interactions (e.g. metal–ligand ligands and metal-ions with well defined coordination geometries
5
9
coordination and host–guest complexation).
Since the discovery of cucurbit[n]uril homologues (CB[n] Furthermore, some scientists have sought to extend the abilities of
n = 5, 6, 7, 8, 10), Chart 1) in 2000, the supramolecular chemistry these systems by decorating them with molecular containers (e.g.
has led to the creation of a variety of functional self-assemblies.
(
6
5c,10
of CB[n]-type receptors has developed rapidly. In particular, the crown ethers, pillarenes).
However, the strategic merger of the
high binding affinities and selectivities that CB[n] display structural features of macrocyclic metal–organic assemblies
toward their guests along with the stimuli responsiveness (e.g. with the outstanding recognition properties of CB[n]-type receptors
11
pH, chemical, photochemical, electrochemical) of CB[n] complexes is relatively unexplored. Very recently, we reported a Fujita-type
have made them prime components for the preparation of metal organic cubooctahedron studded with 24 methyl viologen
6
a,b,e,7
complex functional systems.
For example, CB[n] have groups which non-covalently recruits CB[8] and doxorubicin
prodrugs by heteroternary complexation and its ability to deliver
doxorubicin to HeLa cells. To make robust multivalent systems
for imaging, delivery, and theranostic applications, namely those
whose CB[n] components cannot dissociate, requires that CB[n]
units be incorporated within MIMs. Herein, we report that ligand
Department of Chemistry and Biochemistry, University of Maryland, College Park,
MD, 20742, USA. E-mail: LIsaacs@umd.edu
12
†
Electronic supplementary information (ESI) available: Experimental procedures
and characterization data and additional NMR, UV/Vis, Fluorescence, and ITC
data. See DOI: 10.1039/c6cc10328f
This journal is ©The Royal Society of Chemistry 2017
Chem. Commun.

View Article Online
Communication
ChemComm
1
3 2
self-assembles with M(en)(NO ) (M = Pd, Pt) and CB[n]-type
receptors to form [4]MNs.
Chart 1 shows the structure of rigid-rod ligand 1 which
0
features two terminal monocationic 4,4 -bipyridinium units
1
3
and a central dicationic benzidinium unit. All three units
constitute binding sites for CB[n]-type receptors, but the central
dicationic benzidinium unit was expected to be preferred. The
synthesis of 1 was accomplished in two steps (ESI†). First,
0
reaction of 4,4 -bipyridine with 2,4-dinitrochlorobenzene gave
0
14
N-(2,4-dintrophenyl)-4,4 -bipyridine (2).
Next, the Zincke
1
5
reaction of 2 with benzidine followed by anion exchange gave
ꢀ
1
ꢁ(NO3 )2 in 40% yield.
First, we studied the complexation behavior of 1 with CB[7]
1
1
by H NMR and UV/Vis spectroscopy. The H NMR spectra
recorded at various 1:CB[7] stoichiometries (Fig. 1 and 2)
established that two different complexes (1ꢁCB[7] and CB[7]ꢁ1ꢁ
CB[7]) coexist depending on the stoichiometry. When r1 equiv.
of CB[7] is used, a single 1ꢁCB[7] complex is formed selectively.
1
Fig. 2 H NMR recorded (400 MHz, D
2
O, RT) for (a) 1 (0.3 mM) and (b–g)
with various equiv. of CB[7] – (b) 1.0, (c) 1.25, (d) 1.50, (e) 1.75, (f) 2.0, (g) 3.0.
1
The H NMR of 1ꢁCB[7] is shown in Fig. 2b and displays
Next, we studied the interaction between 1 and CB[8]. We
substantial upfield shifts for H & H (7.15 and 7.64 ppm) relative hoped that CB[8] would bind in a 1 : 1 fashion to the central
e
f
to free 1. Conversely, the resonances for H –H of 1 shift slightly benzidinium unit which would leave cavity volume available for
a
d
1
downfield upon complexation. The CB[7] cavity constitutes an ternary complex formation. Unfortunately, the H NMR titration
NMR shielding region whereas the region just outside the CQO at 1 : CB[8] ratios below 1 : 0.5 show the formation of the 1
ꢁCB[8]
portals is slightly deshielding region, which establishes that (ESI,† Fig. S8). Analysis of the complexation induced chemical
CB[7] binds to the benzidinium core of 1 whose geometry shifts for H –H (all upfield) with 1
2
6c
a
f
2
ꢁCB[8] suggests that the
(
1ꢁCB[7]) is shown in Fig. 1. Addition of more CB[7] (1 equiv.) benzidinium unit is the major binding site although other complex
to [1ꢁCB[7]] causes H and H to shift downfield whereas H –H
geometries may be populated as shown in Fig. 1. Further addition of
shift upfield indicating translocation of CB[7] from benzidinium CB[8] up to a 1 : 1 1: CB[8] ratio results in the disappearance of the
e
f
a
d
core to the terminal bipyridinium units to form 1ꢁCB[7] (Fig. 1). resonances for 1ꢁCB[8]
2
and the presence of broadened resonances
UV/Vis titration of 1 (6.6 mM) with CB[7] (0–17.4 mM) results in a which suggests the formation of a [1ꢁCB[8]] oligomer based on
decreased absorbance at l = 320 nm along with a bathochromic CB[8]-induced homodimerisation of the bipyridinium binding
2
n
1
6
shift. A plot of A320 versus [CB[7]] showed saturation at 2.0 molar sites. DOSY NMR measurements confirm that [1ꢁCB[8]]
n
ꢀ
11
2
ꢀ1
ꢀ1
ratio indicating tight 1 : 2 binding for the 1/CB[7] system in (D = 7.94 ꢂ 10
m s ) is substantially larger than 1
2
ꢁCB[8]
1
ꢀ10
2
agreement with the NMR results. H NMR competition experiments (D = 3.16 ꢂ 10
m s ). Our inability to obtain the 1 : 1 1ꢁ
between 1 and p-hexanediammonium ion for a limiting quantity CB[8] complex, suggested that the planned synthesis of [n]MNs
8
ꢀ1
of CB[7] allowed us to determine K = 8.6 ꢂ 10 M for 1ꢁCB[7] incorporating CB[8] might be challenging.
a
1
7
(ESI,† Fig. S36). Similarly, addition of M2 to 1 initially gives 1ꢁM2
Next, we prepared the unthreaded SCCs by heating ligand
(100 1C,
24 h). H NMR displayed resonances for two SCC’s (ratio = 86 : 14)
followed by translocation to the terminal bipyridinium sites 1 (5.5 mM) with an aqueous solution of Pd(en)(NO )
3 2
1
2
upon formation of 1ꢁM2 (ESI,† Fig. S13 and S14).
that were of different size as determined by diffusion ordered
spectroscopy (DOSY) analysis (Fig. 3 and ESI,† Fig. S18). Diagnostic
downfield shifts of H
a
were observed for 3 (Dd = 0.09 ppm) and for
2+
4
(Dd = 0.21 ppm), which establishes that the Pd center is bound
to the terminal pyridine groups. We attribute the low magnitude of
these shifts to the presence of the charged pyridinium substituent
17c
as previously observed by Quintela. We hypothesised that two
ꢀ
10
2
ꢀ1
products are triangle 3 (most abundant, D = 3.02 ꢂ 10
m s
)
ꢀ10
2
ꢀ1
and square 4 (D = 2.18 ꢂ 10
m s ). When [1] was reduced
from 5.5 to 2.5 mM, the relative abundance of 3 with respect to 4
increased upon dilution from 86% to 499% ([4] is below NMR
detection limit). When 3 was subjected to ESI-MS, molecular ion
5
3 7
+
4+
peaks at 466.2 ([Pd 1 ](NO ) ), 615.2 ([Pd 1 ](NO ) + 4H O )
3
3
3
3
3 8
2
3+
and 815.8 ([Pd
. Similar phenomena were observed during the preparation of
platinum complexes 5 and 6. A concentrated solution of 1 (5.6 mM)
3 3 3 9
1 ](NO ) ) were observed corresponding to triangle
3
Fig. 1 Complexation of 1 with CB[7] and CB[8].
and Pt(en)(NO
)
2
afforded a mixture 5 and 6 in a 80 : 20 ratio,
3
Chem. Commun.
This journal is ©The Royal Society of Chemistry 2017

View Article Online
ChemComm
Communication
3 2 3
of equimolar quantities 1, CB[7], and Pt(en)(NO ) in aq. NaNO
1
(
(
1.0 M) afforded [4]MN 8 (reflux, 5d) as evidenced by H NMR
ꢀ
10
2
ꢀ1
Fig. 4e). DOSY NMR showed that 8 (D = 1.58 ꢂ 10
m s )
diffuses at similar rate as 7 (vide supra). ESI-MS also exhibited
peaks for [4]MN 8. Acyclic CB[n]-type container M2 was
also able to self assemble with equimolar amounts of 1 and
M(en)(NO
for Pd) and 10 (for Pt) as shown in Fig. 3.
Next, we set out to synthesize [4]MNs incorporating CB[8].
3 2
Unfortunately, the direct self-assembly of 1, CB[8], and M(en)(NO )
3 2
) (M = Pd, Pt) to give the analogous clipped [4]MN 9
1
8
(
was unsuccessful likely due to the preferred formation of [1ꢁCB[8]]n
as described above. Attempts to form 1 : 1 : 1 heteroternary
complexes between CB[8], 1, and second guests (e.g. 2,6-dihydro-
0
xynaphthalene, 1,4-dihydroxynaphthalene, indole, 4,4 -diamino-
azobenzene) as building blocks for [4]MN formation were not
1
Fig. 3 Synthesis of [4]MNs from 1 with Pd(en)(NO
3
)
2
and Pt(en)(NO
3
)
2
to successful as monitored by H NMR. Nevertheless, we attempted
afford mixture of triangle and square. Using CB[7] or M2 give [4]MNs or
pseudo [4]MNs in water.
3 2
the direct self-assembly of 1, CB[8], second guest, and M(en)(NO )
but did not observe [n]MN formation. We conclude that 1 with its
central benzidinium unit must be redesigned to disfavor ternary
whereas a dilute solution of 1 (2.3 mM) afforded only triangle 5 complexation and promote [n]MN formation.
1
as evidenced by H NMR and DOSY (ESI†).
It is known that conformational restriction (e.g. rotational,
The kinetically labile nature of the Pdꢁ ꢁ ꢁpyridine interaction geometrical) of chromophores by inclusion within metal–organic
suggested that CB[7] could be threaded postsynthetically to give frameworks (MOFs) or SCCs or by host–guest binding can slow
the desired [n]MN. Addition of CB[7] (3.0 equiv.) to 3 followed down non-radiative decay of the excited state and thereby
1
5a,19
by refluxing at 100 1C for 24 h gave only [4]MN 7 ([Pd (1ꢁ enhance luminescence.
Accordingly, we next turned our
12) as evidenced by H, DOSY NMR and ESI-MS. attention to the photophysical properties of the [4]MNs and their
Diagnostically, H and H
undergo significant upfield shift components. Rigid-rod ligand 1 exhibits a high fluorescence
Dd = 0.55 and 0.86 ppm compared to 1) reflecting their quantum yield (F = 20%) in water. Addition of 1 equiv. of CB[7]
inclusion in the anisotropic shielding region of CB[7] (Fig. 4a results in a 20 nm blue shift of the fluorescence emission band to
and b). DOSY NMR shows the formation of a single species
max = 526 nm and the fluorescence emission intensity of 1ꢁCB[7]
) that diffuses slower than free its at this wavelength increases E2-fold due to the higher molar
3
1
3 3
CB[7]) ](NO )
e
f
(
l
ꢀ
10
2
ꢀ1
(
D = 2.24 ꢂ 10
m s
ꢀ
10
2
ꢀ1
components CB[7] (D = 5.0 ꢂ 10
m
s
) and triangle 3 extinction coefficient of 1ꢁCB[7]. The quantum yield measured for
m s ). ESI-MS provided final evidence of the 1ꢁCB[7] (F = 31%) is significantly higher than free 1 presumably
formation of [4]MN 7. A molecular ion peak at m/z = 813.7 was due to restricted rotation upon complexation. Triangular SCC 3
. One pot self-assembly of 1, CB[7] and triangular [4]MN 7 display broad absorption bands centered
also successfully at ca. 260 nm and 320 nm. As expected, platinum analogues 5
delivered [4]MN 7. The postsynthetic threading approach was not and 8 show red shifted absorption bands (303 and 351 nm)
successful for [4]MN 8 due to the kinetically inert Ptꢁꢁꢁpyridine relative to 3 and 7. The quantum yield measured for triangle 3
interaction. However, a one pot process involving the self-assembly (F = 22%) is similar to that measured for free ligand 1. In
contrast, the quantum yield of 5 is dramatically decreased (F =
ꢀ
10
2
ꢀ1
(D = 3.02 ꢂ 10
7
+
assigned to [Pd
and Pd(en)(NO
3
(1ꢁCB[7])
3
](NO
3
)
5
3
)
2
or CB[7]ꢁ1 and Pd(en)(NO
3 2
)
20
1
.6%) due to the heavy atom effect of Pt which promotes the
2
0
intersystem crossing leading to nonradiative decay. Threading
of CB[7] onto the ligands comprising 3 and 5 to give [4]MNs 7 and
8
conformationally restrict the chromophore and lead to 1.5-fold
and 8.8-fold (5 to 8) higher quantum yields (7: F = 32%; 8: F =
4%). Interestingly, the fluorescence emission was quenched in 9
1
and 10 due to charge-transfer interaction between the electron
rich dialkoxynaphthalene walls of M2 and ligand 1.
In conclusion, we prepared rigid rod ligand 1 which forms
stable inclusion complexes with CB[7], CB[8], and M2. An equimolar
mixture of 1 and M(en)(NO ) (M = Pd, Pt) gave triangular and
3
2
square SCCs. Under more dilute conditions, assembly of 1 and
M(en)(NO ) afforded only triangles 3 and 5. Threading of CB[7]
3
2
onto the SCCs to give [4]MNs 7 and 8 occurs by postsynthetic
transformation or by a one-pot approach for kinetically labile
Pd triangle 3 but only by the one-pot process for kinetically
1
Fig. 4 Partial H NMR (D
(
2
O, 600 MHz) recorded for (a) 1, (b) 3, (c) 5,
d) [4]MN 7, and (e) [4]MN 8.
This journal is ©The Royal Society of Chemistry 2017
Chem. Commun.

View Article Online
Communication
ChemComm
inert Pt triangle 5. Attempts to form MNs incorporating CB[8]
were unsuccessful due to ternary complex formation. The
fluorescence and quantum yields of 1, SCCs, and [4]MNs were
quite different due to complexation induced conformational
restriction and charge transfer processes. For this reason, we
believe that CB[n] derived MNs will perform well as components of
sensing arrays. Furthermore, when MNs incorporating larger CB[n]
8 (a) M. E. Bush, N. D. Bouley and A. R. Urbach, J. Am. Chem. Soc.,
2
005, 127, 14511; (b) J. Del Barrio, P. Horton, D. Lairez, G. Lloyd,
C. Toprakcioglu and O. Scherman, J. Am. Chem. Soc., 2013,
35, 11760; (c) G. Ghale and W. M. Nau, Acc. Chem. Res., 2014,
1
47, 2150; (d) R. Joseph, A. Nkrumah, R. J. Clark and E. Masson, J. Am.
Chem. Soc., 2014, 136, 6602; (e) F. Benyettou, X. Zheng, E. Elacqua,
Y. Wang, P. Dalvand, Z. Asfari, J.-C. Olsen, D. S. Han, N. I. Saleh,
M. Elhabiri, M. Weck and A. Trabolsi, Langmuir, 2016, 32, 7144;
( f ) J. Tian, Z.-Y. Xu, D.-W. Zhang, H. Wang, S.-H. Xie, D.-W. Xu,
Y.-H. Ren, H. Wang, Y. Liu and Z.-T. Li, Nat. Commun., 2016, 7, 11580;
(e.g. n = 8) become available we believe they will constitute robust
(
g) E. Cavatorta, M. L. Verheijden, W. van Roosmalen, J. Voskuhl,
plug-and-play scaffolds for imaging, targeted drug delivery, and
theranostic application. We will report on these possibilities in
due course.
We thank the National Institutes of Health (CA168365) for
financial support.
J. Huskens and P. Jonkheijm, Chem. Commun., 2016, 52, 7146;
(h) R. P. G. Bosmans, J. M. Briels, L.-G. Milroy, T. F. A. de Greef,
M. Merkx and L. Brunsveld, Angew. Chem., Int. Ed., 2016, 55, 8899.
(a) M. Fujita, J. Yazaki and K. Ogura, J. Am. Chem. Soc., 1990,
9
1
12, 5645; (b) P. Mal, B. Breiner, K. Rissanen and J. R. Nitschke, Science,
2009, 324, 1697; (c) C. J. Brown, F. D. Toste, R. G. Bergman and K. N.
Raymond, Chem. Rev., 2015, 115, 3012; (d) L. R. Holloway, H. H.
McGarraugh, M. C. Young, W. Sontising, G. J. O. Beran and R. J. Hooley,
Chem. Sci., 2016, 7, 4423; (e) S. K. Samanta, A. Rana and M. Schmittel,
Angew. Chem., Int. Ed., 2016, 55, 2267; ( f ) D. J. Tranchemontagne,
J. L. Mendoza-Cortes, M. O’Keeffe and O. M. Yaghi, Chem. Soc. Rev.,
2009, 38, 1257; (g) W. Wang, Y.-X. Wang and H.-B. Yang, Chem. Soc. Rev.,
2016, 45, 2656.
References
1
(a) M. C. Jimenez, C. Dietrich-Buchecker and J.-P. Sauvage, Angew.
Chem., Int. Ed., 2000, 39, 3284; (b) A. Coskun, J. M. Spruell, G. Barin,
W. R. Dichtel, A. H. Flood, Y. Y. Botros and J. F. Stoddart, Chem. Soc.
Rev., 2012, 41, 4827; (c) V. Marcos, A. J. Stephens, J. Jaramillo-Garcia, 10 Z.-Y. Li, Y. Zhang, C.-W. Zhang, L.-J. Chen, C. Wang, H. Tan, Y. Yu,
A. L. Nussbaumer, S. L. Woltering, A. Valero, J.-F. Lemonnier,
I. J. Vitorica-Yrezabal and D. A. Leigh, Science, 2016, 352, 1555.
X. Li and H.-B. Yang, J. Am. Chem. Soc., 2014, 136, 8577.
11 K. Kim, Chem. Soc. Rev., 2002, 31, 96.
2
(a) V. N. Vukotic and S. J. Loeb, Chem. Soc. Rev., 2012, 41, 5896; 12 S. K. Samanta, D. Moncelet, V. Briken and L. Isaacs, J. Am. Chem.
b) A. Goujon, G. Du, E. Moulin, G. Fuks, M. Maaloum, E. Buhler and Soc., 2016, 138, 14488.
(
N. Giuseppone, Angew. Chem., Int. Ed., 2016, 55, 703; (c) Z. Li, 13 Y. Song, X. Huang, H. Hua and Q. Wang, Dyes Pigm., 2017, 137, 229.
J. C. Barnes, A. Bosoy, J. F. Stoddart and J. I. Zink, Chem. Soc. Rev., 14 I. Yamaguchi, H. Higashi, S. Shigesue, S. Shingai and M. Sato,
2
012, 41, 2590; (d) B. L. Feringa, J. Org. Chem., 2007, 72, 6635;
Tetrahedron Lett., 2007, 48, 7778.
(
e) J. J. Gassensmith, J. M. Baumes and B. D. Smith, Chem. Commun., 15 (a) M. Freitag, L. Gundlach, P. Piotrowiak and E. Galoppini, J. Am.
2
009, 6329.
Chem. Soc., 2012, 134, 3358; (b) J. Li, Y. Yu, L. Luo, Y. Li, P. Wang,
L. Cao and B. Wu, Tetrahedron Lett., 2016, 57, 2306.
16 (a) K.-D. Zhang, J. Tian, D. Hanifi, Y. Zhang, A. C.-H. Sue, T.-Y. Zhou,
L. Zhang, X. Zhao, Y. Liu and Z.-T. Li, J. Am. Chem. Soc., 2013,
135, 17913; (b) Z. Huang, L. Yang, Y. Liu, Z. Wang, O. A. Scherman
and X. Zhang, Angew. Chem., Int. Ed., 2014, 53, 5351.
3
4
5
F. Bitsch, C. O. Dietrich-Buchecker, A. K. Khemiss, J. P. Sauvage and
A. Van Dorsselaer, J. Am. Chem. Soc., 1991, 113, 4023.
D. B. Amabilino, P. R. Ashton, J. F. Stoddart, A. J. P. White and
D. J. Williams, Chem. – Eur. J., 1998, 4, 460.
(a) D. Whang, K.-M. Park, J. Heo, P. Ashton and K. Kim, J. Am. Chem. Soc.,
1
998, 120, 4899; (b) S. P. Black, A. R. Stefankiewicz, M. M. J. Smulders, 17 (a) W. M. Bloch, Y. Abe, J. J. Holstein, C. M. Wandtke, B. Dittrich and
D. Sattler, C. A. Schalley, J. R. Nitschke and J. K. M. Sanders, Angew.
Chem., Int. Ed., 2013, 52, 5749; (c) S. Li, J. Huang, F. Zhou, T. R. Cook,
X. Yan, Y. Ye, B. Zhu, B. Zheng and P. J. Stang, J. Am. Chem. Soc., 2014,
G. H. Clever, J. Am. Chem. Soc., 2016, 138, 13750; (b) P. Howlader,
P. Das, E. Zangrando and P. S. Mukherjee, J. Am. Chem. Soc., 2016,
138, 1668; (c) M. Chas, D. Abella, V. Blanco, E. Pia, G. Blanco,
A. Fernandez, C. Platas-Iglesias, C. Peinador and J. M. Quintela,
Chem. – Eur. J., 2007, 13, 8572.
1
36, 5908; (d) M. Fujita, F. Ibukuro, H. Hagihara and K. Ogura, Nature,
1994, 367, 720.
6
7
(a) L. Isaacs, Acc. Chem. Res., 2014, 47, 2052; (b) Y. H. Ko, E. Kim, 18 F.-G. Klaerner and T. Schrader, Acc. Chem. Res., 2013, 46, 967.
I. Hwang and K. Kim, Chem. Commun., 2007, 1305; (c) E. Masson, 19 (a) F. Biedermann, E. Elmalem, I. Ghosh, W. M. Nau and
X. Ling, R. Joseph, L. Kyeremeh-Mensah and X. Lu, RSC Adv., 2012,
O. A. Scherman, Angew. Chem., Int. Ed., 2012, 51, 7739; (b) X.-L. Ni,
S. Chen, Y. Yang and Z. Tao, J. Am. Chem. Soc., 2016, 138, 6177;
(c) K. Lu, C. He and W. Lin, J. Am. Chem. Soc., 2014, 136, 16712;
(d) X. Yan, T. R. Cook, P. Wang, F. Huang and P. J. Stang, Nat. Chem.,
2015, 7, 342.
2
5
, 1213; (d) W. M. Nau, M. Florea and K. I. Assaf, Isr. J. Chem., 2011,
1, 559; (e) S. J. Barrow, S. Kasera, M. J. Rowland, J. del Barrio and
O. A. Scherman, Chem. Rev., 2015, 115, 12320.
(a) A. E. Kaifer, Acc. Chem. Res., 2014, 47, 2160; (b) M. A. Yawer, V. Havel
and V. Sindelar, Angew. Chem., Int. Ed., 2015, 54, 276; (c) S. Kaabel, 20 (a) J. B. Pollock, T. R. Cook, G. L. Schneider, D. A. Lutterman,
J. Adamson, F. Topic, A. Kiesila, E. Kalenius, M. Oreren, M. Reimund,
E. Prigorchenko, A. Lookene, H. J. Reich, K. Rissanen and R. Aav, Chem.
Sci., 2017, 8, DOI: 10.1039/C6SC05058A.
A. S. Davies and P. J. Stang, Inorg. Chem., 2013, 52, 9254;
(b) J. B. Pollock, G. L. Schneider, T. R. Cook, A. S. Davies and
P. J. Stang, J. Am. Chem. Soc., 2013, 135, 13676.
Chem. Commun.
This journal is ©The Royal Society of Chemistry 2017