Synthesis and guest recognition of molecular cleft consisting of terpyridine-Pt(II) acetylide complexes

Article abstract of DOI:10.1016/j.tetlet.2012.08.116

The stable molecular clefts 1 consisting of inert Pt-acetylide moieties and a 1,1':30,100-terphenyl spacer were synthesized. Guest binding behavior of 1a was examined by 1H NMR spectroscopy to determine the association constants; naphthalene (Ka0M-1) < an

Full text of DOI:10.1016/j.tetlet.2012.08.116

Tetrahedron Letters 53 (2012) 6182–6185
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis and guest recognition of molecular cleft consisting
of terpyridine–Pt(II) acetylide complexes
⇑
Tatsuya Nabeshima , Yuki Hasegawa, Robert Trokowski, Masaki Yamamura
Graduate School of Pure and Applied Sciences, Tsukuba Research Center for Interdisciplinary Materials Sciences, University of Tsukuba,1-1-1 Tennodai, Tsukuba,
Ibaraki 305 8571, Japan
a r t i c l e i n f o
a b s t r a c t
0
0
00
Article history:
Received 23 July 2012
Revised 24 August 2012
Accepted 27 August 2012
Available online 12 September 2012
The stable molecular clefts 1 consisting of inert Pt–acetylide moieties and a 1,1 :3 ,1 -terphenyl spacer
1
were synthesized. Guest binding behavior of 1a was examined by H NMR spectroscopy to determine
–1
–1
–1
the association constants; naphthalene (K
a
ꢀ0 M ) < anthracene (10 M ) < pyrene (50 M ) < coronene
(3:1, v/v). 1a is stable enough to resist disassembly in the pres-
ence of anionic species. Thus, 1a shows a higher affinity to large electron-rich aromatic compounds. In
–1
(640 M ) in chloroform-d/acetonitrile-d
3
–
1
addition, anionic aromatic guests were bound more strongly by 1a (K
late) due to the electrostatic interactions, interactions, and the stable cleft scaffold.
Ó 2012 Elsevier Ltd. All rights reserved.
a
= 540 M for 1-pyrenecarboxy-
Keywords:
p–p
Molecular cleft
Terpyridine
Platinum
Acetylide
p–p Stacking
Molecular clefts and tweezers are employed as a structurally
flexible host, which shows selective molecular recognition via
hydrogen bonding,
interaction, etc.1 Bosnich and co-workers
We now report the synthesis and binding properties of a stable
molecular cleft having inert terpyridine–Pt(II) acetylide moieties
0
0
00
p
–p
and a 1,1 :3 ,1 -terphenyl spacer, which should provide a suitable
2
,4b
reported that a metallo-cleft, which has flat terpyridine Pt com-
binding space for aromatic planes.
In particular, the host
plexes as a recognition component of the cleft host, captured a pla-
nar Pt complex and an aromatic compound in the cleft. However,
showed a high affinity to a large aromatic compound, that is, cor-
onene. Compared to neutral aromatic compounds, the binding
strength was enhanced for the anionic aromatic guests due to
the electrostatic interactions and the inertness of the Pt–acetylide
linkage, which resists ligand exchange by the anions and does not
decompose the cleft structure.
2
the synthesis of the host requires laborious multi-step processes
because the scaffold of the host is maintained by covalent bonds.
In contrast, a metallo-host, whose framework is synthesized via a
spontaneous coordination bond formation under mild conditions,
is very useful and easy to prepare. In particular, a labile coordina-
tion bond has often been used to make a variety of macrocyclic
supramolecular systems, such as ionophores, receptors, cages, cap-
The terphenyl spacer 8 was prepared from 3-bromoanisole (2)
via a seven-step synthesis in a 26% total yield (Scheme 1). The cleft
molecules 1a and 1b were synthesized by the reaction of 8 with
3
8
sules, etc. Very recently, an acyclic metallo-cleft bearing terpyri-
terpyridine platinum complexes 9a and 9b in the presence of a
dine–Pt(II) acetylide unit has been synthesized based on
coordination bond formation strategy. The cleft bound terpyri-
dine–Pt(II) complexes as a guest in a 1:1 stoichiometry. Another
a
catalytic amount of CuI in DMF. The successive addition of NaBF
4
4
9,10
gave 1a and 1b in 39% and 55% yields, respectively (Scheme 2).
1
13
The identification of the clefts was performed by H NMR, C NMR,
IR spectra, mass spectral techniques, and elemental analysis. The
cleft 1b is only slightly soluble in most solvents except for DMSO,
while 1a is soluble in acetonitrile, DMSO, acetonitrile-chloroform,
and aqueous acetonitrile. The higher solubility of 1a is probably
due to the steric hindrance of the tert-Bu groups on the terpyridine
5
cleft-type Pt(II) host, which consists of two Pt(II)–thiolate
complex moieties, has a very flexible structure and showed a
6
high affinity to DNA. However, its detailed binding mode is
still ambiguous. In these hosts, less labile coordination bonds,
7
Pt(II)–acetylide and Pt(II)–thiolate bonds, can be used to make
6
b
the acyclic cleft scaffold because the host formation proceeds
without any undesired side reactions such as oligomerization,
which often takes place in typical macrocyclizations.
that inhibits intermolecular
p
–
p
stacking.
H NMR spectra of 1a were strongly dependent on the solvents
(Fig. 1). As the acetonitrile content in CDCl –CD CN increased, all
1
3
3
the signals were more broadened and the protons H1, H4, and
H5 on the terpyridine moiety were shifted upfield. The 1H NMR
spectra in 1:1 acetonitrile-d /D O (1:1, v/v) showed an even higher
3 2
⇑
Corresponding author. Tel./fax: +81 29 853 4507.
E-mail address: nabesima@chem.tsukuba.ac.jp (T. Nabeshima).
0
040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.08.116

T. Nabeshima et al. / Tetrahedron Letters 53 (2012) 6182–6185
6183
X
H
Br
O
O
i, ii
iii
vii
B
OMe
OMe
X
H
2
3
4
: X = OMe
: X = OH
8
iv
v
vi
5
6
7
: X = OTf
: X = C CTMS
Scheme 1. (i) (a) Mg, THF, toluene, (b) B(OMe)
Tf O, pyridine: 96%; (vi) trimethylsilylacetylene, [PdCl
2
3
: 80%; (ii) pinacol, toluene: >99%; (iii) dibromobenzene, Pd(PPh
3
)
4
, K
2
CO
3
, 1,4-dioxane: 41% (Ref.11); (iv) BBr
3
, CH
2
Cl
2
: 96%; (v)
n
2
(PPh
3
)
2
], CuI, Bu
4
3 2
NI, DMF, Et N: 89%; (vii) K CO
3
, THF, MeOH: 97%.
R
+
X–
R
R
N
2
2
+
R
N Pt Cl
N
N
BF4–
R
R
N Pt
N
R
t
9
9
a: R = Bu, X = Cl
R
,
CuI
NaBF4
b: R = H, X = BF4
8
N
N Pt
N
i
H O
2
DMF, Pr NH
2
R
t
1
1
a: R = Bu 39%
b: R = H 55%
Scheme 2. Synthesis of clefts 1.
t
-Bu
3 3
complex. In chloroform-rich solvents (3:1 or 1:1 CDCl –CD CN),
N
N Pt
the solvent effect of the signals is almost negligible. This result
suggests that self-recognition is considered not to occur in such a
less polar solvent. In order to neglect the contribution of the
self-recognition for analyzing the guest recognition, a less polar
t-Bu
N
t
-Bu
3
"
2"
1"
t-Bu
4
'
N
t-Bu
N
4
Pt
N
3'
3
solvent, chloroform-d/acetonitrile-d (3:1, v/v), was employed
5
1
1' 2'
for the guest binding studies because the cleft 1a exists in the
t
-Bu
2
14
1
'-3', 1", 2"
monomeric form.
5
CHCl3
4
The NMR titration experiments were carried out for different
1
CDCl 3/CD3CN(3/1)
CDCl 3/CD3CN(1/1)
CDCl 3/CD3CN(1/3)
CD 3CN
3"4' 2
aromatic guests in chloroform-d/acetonitrile-d
presence of 3.9 equiv of coronene, large upfield shifts of H1
d – 0.76 ppm), H4 ( d – 0.57 ppm), and H5 ( d – 0.68 ppm)
3
(3:1, v/v). In the
(D
D
D
were observed (Fig. 2). In addition, the signals of coronene were
shifted upfield by 0.12 ppm. These spectral changes are similar to
those of the self-recognition described above, indicating that the
recognition of the aromatic guests took place inside the cleft cavity.
This guest recognition mode by the cleft in the case of coronene
CD 3CN/D2O(1/1)
5
4
1
DMSO-d
6
1
1
was supported by the H– H NOESY spectrum of a mixture of 1a
9
8
7
6
Chemical Shift (ppm)
Figure 1. 1H NMR spectra of 1a (400 MHz, 25 °C, [1a] = 2.0 mM) in various solvents.
coronene only
[
coronene]/[1a]
0
00
3.9
upfield shift of the protons except for H4 and H3 inside the cleft
than in acetonitrile-d . The upfield shift of signals assigned to the
terpyridine units strongly suggested that 1a was aggregated in a
2.3
3
2.1
1.5
1
2
self-recognition way by p–p stacking in the polar medium. Under
these conditions, the terphenyl unit of a host is captured in the ter-
pyridine-based cleft cavity of another host. The significant concen-
tration and temperature effects of the NMR signals are also
indicative of the self-recognition (see Supplementary data,
Fig. S2); upfield shifts were observed at higher concentrations,
revealing that the chemical shift changes are based on the self-
assembly. VT-NMR studies showed a downfield shift at higher
temperatures due to the disassembly (Fig. S5). This self-recognition
property means a high binding ability of 1a toward the Pt(II)
1
0
0
.1
.64
.34
0
1
5
4'
4
3"
9
8
1
3
Chemical Shift (ppm)
Figure 2. 1H NMR spectra upon titration of 1a with coronene (400 MHz, 3:1 CDCl
CD CN (v/v), 25 °C, [1a] = 2.0 mM).
3
/
3

6
184
T. Nabeshima et al. / Tetrahedron Letters 53 (2012) 6182–6185
and coronene, in which the cross-correlation peaks between the
protons of 1a (H1, H4, H5, and H4 ) and that of coronene appeared.
guest and the electron-deficient terpyridine Pt units. Among the
heterocyclic compounds, the affinity to carbazole is higher than
those of acridine and TTF.
0
A Job plot for the complexation of 1a and coronene clearly
showed the 1:1 association (Fig. S8). The binding constants (K
of the cleft 1a with the aromatic guests were determined by a
non-linear least-squares analysis of the chemical shift change in
a
)
The binding affinity to anionic aromatic guests was also exam-
ined because the cationic terpyridine–Pt acetylide complexes
showed electrostatic interactions with anionic polyelectro-
1
6,17
H1. The K
a
values are summarized in Table 1. As the size of the aro-
lytes.
carboxylates (K
9-anthracenecarboxylate) are much higher than those of the corre-
a
Noteworthy is the fact that the K values for the aromatic
–
1
–1
matic guest planes becomes larger, the binding constants increased
a
= 540 M for 1-pyrenecarboxylate and 80 M for
–
1
–1
in the order of naphthalene (K
<
a
ꢀ 0 M ) < anthracene (10 M
)
–
1
–1
–1
–1
pyrene (50 M ) < coronene (640 M ). This order is probably re-
flected by the strength of the stacking interaction between the
cleft and guest. The K value for naphthalene-2,3-diol is slightly
a
sponding hydrocarbons (K = 50 M for pyrene and 10 M for
p
–p
anthracene). The drastic enhancement of the affinity is due to the
electrostatic interactions between the cationic cleft and the anionic
guests. In contrast, our preliminary experiment indicated that the
corresponding pyridine-coordinated host molecule was disassem-
bled by the addition of the carboxylate. The pyridine-platinum
a
higher than that of naphthalene. The cleft 1a showed no binding
ability for the halogenated aromatic guests.15 This selectivity can
be explained in terms of the interactions between the electron-rich
Table 1
The binding constants of cleft 1a with aromatic guests
t-Bu
t-Bu
2
2
+
2+
2BF4
N
N Pt
N
BF4–
N
N Pt
N
–
t-Bu
t-Bu
t-Bu
t-Bu
guest
CDCl /CD CN(3/1)
t-Bu
t-Bu
t-Bu
t-Bu
N
N Pt
N
3
3
N
N Pt
N
t-Bu
t-Bu
1a
1a·guest
Guest
K
a
(M–1)a
Guest
K
a
(M–1)a
I
I
—b
6
40 ± 90
I
5
1
0 ± 5
0 ± 1
—b
—b
I
Br
Br
Br
Br
Br
—b
—b
—b
OH
OH
S
S
2
0 ± 4
S
S
OH
OH
N
—b
4 ± 1
Cl
H
N
—b
50 ± 0.3
COO
COO
5
2
40 ± 60
—b
—b
COO
COO
20 ± 20
OOC
COO
COO
7
8
8 ± 1
0 ± 5
—b
COO
a
Determined by 1H NMR spectroscopic titration (400 MHz, 3:1 CDCl
Too low to be determined.
3 3
/CD CN (v/v), 25 °C, [1a] = 2.0 mM).
b

T. Nabeshima et al. / Tetrahedron Letters 53 (2012) 6182–6185
6185
t-Bu
+
BF4–
References and notes
1.
(a) Vögtle, F. Supramolecular Chemistry; Wiley: New York, 1991; (b) Cargill
Thompson, A. M. W. Coord. Chem. Rev. 1997, 160, 1–52; (c) Hofmeier, H.;
Schubert, U. S. Chem. Soc. Rev. 2004, 33, 373–399; (d) Eryazici, I.; Moorefield, C.
N.; Newkome, G. R. Chem. Rev. 2008, 108, 1834–1895; (e) Constable, E. C. Coord.
Chem. Rev. 2008, 252, 842–855; (f) Yam, V. W.-W.; Wong, K. M.-C. Chem.
Commun. 2011, 47, 11579–11592.
t-Bu
t-Bu
N
N
N
Pt
2.
(a) Sommer, R. D.; Rheingold, A. L.; Goshe, A. J.; Bosnich, B. J. Am. Chem. Soc.
2001, 123, 3940–3952; (b) Goshe, A. J.; Steele, I. M.; Ceccarelli, C.; Rheingold, A.
L.; Bosnich, B. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 4823–4829; (c) Goshe, A. J.;
Steele, I. M.; Bosnich, B. J. Am. Chem. Soc. 2003, 125, 444–451.
(a) Steed, J. W.; Atwood, J. L. Supramolecular Chemistry; John Wiley & Sons,
1
0
3
4
.
.
2009; (b) Nabeshima, T. Bull. Chem. Soc. Jpn. 2010, 83, 969–991.
Scheme 3.
(a) Lo, H.-S.; Yip, S.-K.; Wong, K. M.-C.; Zhu, N.; Yam, V. W.-W. Organometallics
2
2
006, 25, 3537–3540; (b) Tanaka, Y.; Wong, K. M. C.; Yam, V. W.-W. Chem. Sci.
012, 3, 1185–1191.
5
.
(a) Howe-Grant, M.; Lippard, S. J. Biochemistry 1979, 18, 5762–5769; (b) Wang,
A. H. J.; Nathans, J.; van der Marel, G.; van Boom, J. H.; Rich, A. Nature 1978, 276,
bond is labile enough to be cleaved by the carboxylate anion.
However, the acetylide-based Pt cleft is stable enough even in
the presence of the anionic guests because of inertness of the
acetylide–platinum bonds. Binding studies with three aromatic
carboxylates bearing a pyrene unit showed an apparent selectivity
471–474.
6. (a) McFadyen, W. D.; Wakelin, L. P. G.; Roos, I. A. G.; Hillcoat, B. L. Biochem. J.
1986, 238, 757–763; (b) McFadyen, W. D.; Wakelin, L. P. G.; Roos, I. A. G.;
Hillcoat, B. L. Biochem. J. 1987, 242, 177–183; (c) Kurosaki, H.; Yamakawa, N.;
Sumimoto, M.; Kimura, K.; Goto, M. Bioorg. Med. Chem. Lett. 2003, 13, 825; (d)
Glover, P. B.; Ashton, P. R.; Childs, L. J.; Rodger, A.; Kercher, M.; Williams, R. M.;
De Cola, L.; Pikramenou, Z. J. Am. Chem. Soc. 2003, 125, 9918–9919.
for 1-pyrenecarboxylate (K
etate (K = 220 M ) is higher than 1-pyrenebutyrate (K = 78 M ).
a a
a
= 540 M–1). The affinity to 1-pyreneac-
ꢁ1
–1
7
.
(a) Yam, V. W.-W.; Tang, R. P.-L.; Wong, K. M.-C.; Cheung, K.-K. Organometallics
001, 20, 4476–4482; (b) Yam, V. W.-W.; Wong, K. M.-C.; Zhu, N. J. Am. Chem.
Soc. 2002, 124, 6506–6507.
This result suggested that the short distance between the
aromatic core and carboxylate moiety increases the electrostatic
2
16
interactions. For compound 10, a much lower binding constant
8. Yang, L.; Wimmer, F. L.; Wimmer, S.; Zhao, J.; Braterman, P. S. J. Organomet.
Chem. 1991, 525, 1–8.
9
–
1
a
(K = 40 M ) for 1-pyreneacetate was obtained, when compared
.
Hasegawa, Y.; Trokowski, R.; Yamamura, M.; Nabeshima, T. Abstract, The 89th
Annual Meeting of the Chemical Society of Japan 3PB-131, March, 2009.
to that in the cleft 1a (Scheme 3). Thus, the two terpyridine Pt units
of 1a play an important role for the stronger binding.
10. Compound 1a: 1H NMR (400 MHz, DMSO-d
) d 1.43 (s, 36H), 1.53 (s, 18H), 7.48
dd, J = 7.5 Hz, J = 7.5 Hz, 2H), 7.54 (d, J = 7.5 Hz, 2H), 7.62 (t, J = 7.5 Hz, 1H),
6
(
The guest recognition was also confirmed by UV–vis and emis-
sion spectroscopy (Fig. S19 and S20). The cleft 1a showed an
absorption band in the 400–500 nm region, which was originally
attributed to the charge transfer (CT) excitation from an occupied
orbital of the Pt–acetylide bond to an unoccupied orbital delocal-
7
4
.69 (d, J = 7.5 Hz, 2H), 7.74 (d, J = 7.5 Hz, 2H), 7.84 (s, 2H), 7.89 (d, J = 5.8 Hz,
195
H), 7.96 (s, 1H), 8.71 (s, 4H), 8.73 (s, 4H), 9.07 (d, J = 5.8 Hz, 4H,
Pt satellites
13
were not observed due to broadening.); C NMR (100 MHz, CD CN) 28.9 (CH ),
3
3
2
(
1
9.2 (CH
CH), 124.2 (CH), 124.5 (CH), 124.8 (CH), 127.0 (C), 128.1 (CH), 128.6 (CH),
29.7 (CH), 129.9 (CH), 138.6 (C), 138.9 (C), 153.1 (CH), 153.2 (C), 157.7 (C),
3
), 35.5 (C), 36.5 (C), 97.9 (C), 102.7 (C), 120.6 (CH), 122.4 (CH), 123.3
1
8
ized on terpyridine. The CT band decreased in the presence of
-pyrenecarboxylate, while the UV–vis spectra of 10 showed al-
165.7 (C), 166.7 (C); IR (KBr)
m
2116 cmꢁ1 (C„C); ESI–MS m/z 734.30
Pt O = C76 OPt : 1C,
ꢂH
2+; Anal. Calcd for
C
H
H
84
1
[Mꢁ2BF
4
]
76
82
N
6
B
2
F
8
2
2
6
N B
2
F
8
2
54.95; H, 5.10; N, 5.06. Found: C, 54.60; H, 5.12; N, 4.98. Compound 1b:
H
most no change by the addition of the same guest. A degassed solu-
tion of 1a showed an emission (ca. 600 nm) with a 3.7% quantum
yield. The emission is attributed to phosphorescence because the
emission intensity was lowered in an aerated solution. The emis-
sion intensity decreased upon the addition of 1-pyrenecarboxylate.
These spectroscopic results again suggested the host–guest
complexation.
We synthesized stable molecular clefts 1 consisting of inert Pt–
acetylide bonds. 1a captured large electron-rich aromatic com-
pounds. Interestingly, the anionic aromatic guests were bound
NMR (400 MHz, DMSO-d ) d 7.46 (d, J = 7.4 Hz, 2H), 7.50–7.53 (m, 6H), 7.72 (t,
6
J = 7.7 Hz, 1H), 7.76 (d, J = 7.4 Hz, 2H), 7.85 (d, J = 8.6 Hz, 2H), 8.11–8.13 (m,
6H), 8.24 (s, 1H), 8.29 (d, J = 8.3 Hz, 4H), 8.40 (br s, 4H), 8.47 (t, J = 7.8 Hz, 1H),
8
1
.55(d, J = 7.8 Hz, 4H); 13C NMR (100 MHz, DMSO-d
6
) d 98.3 (C), 102.6 (C),
24.7 (CH), 124.8 (CH), 125.5 (CH), 125.6 (CH), 126.2 (CH), 127.1 (C), 129.0
(
CH), 129.5 (CH), 129.9 (CH), 130.0 (CH), 130.7 (CH), 139.7 (C), 139.9 (C), 141.8
(CH), 142.1 (CH), 152.9 (C), 153.3 (CH), 157.7 (C); ESI–MS m/z 566.06
2
+
[
Mꢁ2BF
4
] .
1
1
1. Han, P.; Zhang, H.; Qiu, X.; Ji, X.; Gao, L. J. Mol. Catal. A: Chem. 2008, 295, 57–67.
2. Leung, S. Y.-L.; Tam, A. Y.-Y.; Tao, C.-H.; Chow, H. S.; Yam, V. W.-W. J. Am. Chem.
Soc. 2012, 134, 1047–1056.
1
1
1
3. Based on a monomer-dimer equilibrium model, the dimerization constant,
2
–1
K
2
dim = [(1a) ]/[1a] , was determined to be 758 M (Fig. S3).
more strongly by 1a due to the electrostatic interactions,
p–p
3
4. No self-recognition of 1a in chloroform-d/acetonitrile-d (3:1, v/v) was clarified
interactions, and the stable cleft scaffold. We are currently investi-
gating larger supramolecular architectures based on the stable Pt–
acetylide bonds.
by the variable-concentration NMR spectra (Fig. S4).
5. (a) Trokowski, R.; Akine, S.; Nabeshima, T. Chem. Commun. 2008, 889–890; (b)
Trokowski, R.; Akine, S.; Nabeshima, T. Dalton Trans. 2009, 10359–10366; (c)
Trokowski, R.; Akine, S.; Nabeshima, T. Chem. Eur. J. 2011, 17, 14420–14428.
6. Yam, V. W.-W.; Chan, K. H. Y.; Wong, K. M.-C.; Chu, B. W. K. Angew. Chem., Int.
Ed. 2005, 44, 791–794.
1
1
1
Acknowledgments
7. Moriuchi, T.; Yamada, M.; Yoshii, K.; Hirao, T. J. Organomet. Chem. 2010, 695,
2562–2566.
This research was financially supported by Grants-in-Aid for
Scientific Research from the Ministry of Education, Culture, Sports,
Science, and Technology of Japan.
8. (a) Zhou, X.; Zhang, H.-X.; Pan, Q.-J.; Xia, B.-H.; Tang, A.-c. J. Phys. Chem. A 2005,
109, 8809–8818; (b) Shikhova, E.; Danilov, E. O.; Kinayyigit, S.; Pomestchenko,
I. E.; Tregubov, A. D.; Camerel, F.; Retailleau, P.; Ziessel, R.; Castellano, F. Inorg.
Chem. 2007, 46, 3038–3048.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2012.
0
8.116.