Pyrene-appended fluorescent tweezers generated via the Weak-Link Approach and their halide recognition properties

Article abstract of DOI:10.1016/j.tet.2008.05.047

Through the Weak-Link Approach, fluorescent condensed and open Cu(I) tweezer complexes were prepared and characterized. These complexes exhibit fluorescence-sensitive binding properties for halide anions. The solid-state structure of a non-fluorescent Rh(I) tweezer analogue, determined by X-ray crystallography, shows that the counter anion, Cl^-, is trapped inbetween the two amide groups of the tweezer arms through hydrogen bonds. Although the tweezer binds Cl^-, the open complex also binds Cl^-, showing that the main role of the metal is to increase the local concentration of the pyrenyl amide moieties so that 2:1 binding can take place.

Full text of DOI:10.1016/j.tet.2008.05.047

Tetrahedron 64 (2008) 8428–8434
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Pyrene-appended fluorescent tweezers generated via the Weak-Link Approach
and their halide recognition properties
,
b
b
You-Moon Jeon a, Dongwoo Kim a, Chad A. Mirkin a , James A. Golen , Arnold L. Rheingold
*
a Department of Chemistry and the International Institute for Nanotechnology, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3113, USA
b Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, MC 0358, La Jolla, CA 92093-0358, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Through the Weak-Link Approach, fluorescent condensed and open Cu(I) tweezer complexes were pre-
pared and characterized. These complexes exhibit fluorescence-sensitive binding properties for halide
anions. The solid-state structure of a non-fluorescent Rh(I) tweezer analogue, determined by X-ray crys-
tallography, shows that the counter anion, Clꢀ, is trapped inbetween the two amide groups of the tweezer
arms through hydrogen bonds. Although the tweezer binds Clꢀ, the open complex also binds Clꢀ,
showing that the main role of the metal is to increase the local concentration of the pyrenyl amide moieties
so that 2:1 binding can take place.
Received 25 February 2008
Received in revised form 25 April 2008
Accepted 9 May 2008
Available online 14 May 2008
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
facilitated small molecule transport.1–4 Our group has shown that
one can prepare fluorescent cyclophanes5 via the Weak-Link Ap-
Over the past decade, supramolecular cyclophanes and tweezer
complexes have received a significant amount of attention due to
their encapsulating properties and potential applications in cata-
lysis, sensing, mixture separations, molecular electronics, and
proach (WLA) in high yield (Scheme 1).2,6 The strategically posi-
tioned weak ligand–metal interactions within these structures
allow one to use small molecules and elemental anions to re-
versibly open and close such structures, allowing one to chemically
Scheme 1. Schematic illustration of the Weak-Link Approach.
* Corresponding author. Tel.: þ1 847 491 2907; fax: þ1 847 495 5123.
E-mail address: chadnano@northwestern.edu (C.A. Mirkin).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.05.047

Y.-M. Jeon et al. / Tetrahedron 64 (2008) 8428–8434
8429
trigger significant changes in their recognition and catalytic
properties.2
The Rh(I) metal center is coordinated by two phosphines and two
thioethers in a distorted square-planar geometry with P(1)–Rh(1)–
S(1) and P(1)–Rh(1)–P(10) angles of 85.21ꢁ and 98.46ꢁ, respectively.
Each coordinating sulfur atom has a distorted trigonal pyramidal
geometry with C(14)–S(1)–Rh(1), C(14)–S(1)–C(15), and C(15)–
S(1)–Rh(1) angles of 105.7ꢁ, 102.0ꢁ, and 111.5ꢁ, respectively. Of
particular interest is the chloride anion, which is trapped between
the two amide groups through hydrogen bonds.10 The N(1)/Cl(1)
distance and the N(1)–H(1A)–Cl(1) angle are 3.24 Å and 162.4ꢁ,
respectively. The two bridging aromatic spacers have a twisted
configuration with a torsion angle of 74.5ꢁ owing to the trigonal
pyramidal configuration of the coordinating sulfur atom and the
coordination of the Clꢀ anion. Note the pyrenyl groups in 3a ex-
Herein, we demonstrate how the WLA can be used to prepare
a novel class of fluorescent tweezer complexes that incorporate
both recognition sites and fluorophores within the framework of
the ligand that makes up the tweezer arms. We compare the halide
binding properties of these novel structures with the open versions
of these structures.
2. Results and discussion
The pyrenyl group has been used as a signaling fluorophore,
since when it dimerizes in the presence of analytes, it forms
a characteristic excimer.7 We hypothesized that 2 equiv of such
a moiety, held together in a tweezer configuration in the context of
a coordination complex prepared via the WLA, could act as a char-
acteristic signaling fluorophore for analyte recognition. The new
pyrene-appended hemilabile phosphine ligand 2 was synthesized
in two steps (Scheme 2) and fully characterized by 1H, 31P{1H} NMR
spectroscopy, and mass spectrometry. The solid-state structure of 2
was confirmed via a single crystal X-ray diffraction study (Fig. 1).
hibit intermolecular
p–p stacking interactions in the solid-state
(the inter-planar distance of the two pyrenyl group is 3.7 Å,
Fig. S1).11
Upon reaction with CO (1 atm), the tweezer complex 3a opens
to form a neutral Rh(I) complex 4a (CD2Cl2/CD3OD¼3:1, Scheme
3).2,4,9 This reaction involves the displacement of the thioether
ligands of 3a with 1 equiv of CO and the Clꢀ counter ion. The 31P{1H}
NMR spectrum of 4a exhibits a resonance at
d
25.0 (d, JRh–P
¼
124 Hz) indicative of a complex with trans-coordination of the two
phosphorous atoms.2,4,9 Although complex 4a is stable under CO
(1 atm) at room temperature, exposure to high vacuum results in its
conversion to the cationic condensed Rh(I) tweezer 3a. The in-
terconversion between complex 4a and 3a is completely reversible
as evidenced by 1H and 31P{1H} NMR spectroscopy. Note that the
amide protons, which exhibit a resonance at
8.39 in 4a in a 3:1 mixture of CD2Cl2 and CD3OD (Fig. S2).
In an attempt to increase the solubility of the condensed Rh(I)
d 8.77 in 3a, appear at
d
tweezer 3a, the anion was changed from Clꢀ to BF4ꢀ (3b) and
B(C6F5)ꢀ4 (3c), respectively (Scheme 3). These complexes were
prepared by initially abstracting the Clꢀ from the Rh(I) precursor
with the appropriate reagent (AgBF4 and LiB(C6F5)4, respectively).
The chemical shifts and coupling constants for the phosphorus
atoms of 3b and 3c were nearly identical to those observed for 3a
Scheme 2. (a) K2CO3, 18-crown-6, CH3CN/H2O, reflux; (b) isobutylchloroformate/NEt3,
2-pyrenylmethylamine$HCl/NEt3, CH2Cl2, rt.
The Rh(I) tweezer complex 3a was synthesized by the reaction
of [Rh(NBD)Cl]2 (NBD¼norbornadiene) and hemilabile ligand 2 in
CH2Cl2 at room temperature in quantitative yield (Scheme 3). It is
insoluble in CH2Cl2 and forms as a yellow precipitate in the bottom
of the reaction vessel. All data, including 1H NMR spectroscopy in
a 3:1 mixture of CD2Cl2 and CD3OD, 31P{1H} NMR spectroscopy in
the same solvent mixture, and ESI-MS, are in full agreement with
the proposed structural formulation for 3a. For example, the
(3b:
d
64.8 (d, JRh–P¼161 Hz), 3c: 64.7 (d, JRh–P¼162 Hz)). Although
d
3a and 3b are not soluble in pure dichloromethane, 3c with
B(C6F5)ꢀ4 as the counter anion is highly soluble at room tempera-
ture. The ability of 3c to bind Clꢀ was studied by 1H NMR titration
experiments in CD2Cl2 solution at room temperature. In all exper-
iments, the chemical shift for the amide –NH resonance was
monitored as a function of Clꢀ concentration. As expected, the
amide proton signals shift downfield, indicative of strong in-
teractions with the Clꢀ (Fig. 3b). The Ka of 3c for Clꢀ is 2.48ꢂ
103 Mꢀ2 as determined by EQNMR techniques.12 The interaction
between Clꢀ and 3c is primarily with the tweezer arms. Indeed,
there is no evidence of Clꢀ interacting with the metal center as
31P{1H} NMR spectrum of 3a exhibits a doublet at
d
64.7 (JRh–P
¼
161 Hz) assigned to the equivalent phosphorous atoms. This
chemical shift and coupling constant are highly diagnostic of
a square-planar cis-phosphine, cis-thioether Rh(I) complex.2,8,9
Significantly, the amide hydrogen atoms are shifted downfield from
where they would normally appear (vide infra). This is likely due to
an interaction between those protons and the Clꢀ counter ion. The
ESI-MS spectrum of 3a exhibited a peak at m/z 1261.5 corre-
sponding to the loss of the Clꢀ counter anion (calcd for
[MꢀClꢀ]þ¼1261.3).
probed by 31P{1H} NMR spectroscopy. The doublet at
d 64 does not
change significantly even in the presence of excess Clꢀ without CO
(Fig. 3a). Interestingly, in the solution state, 3c forms a 2:1 rather
than a 1:1 complex with Clꢀ as determined by a Job plot (Fig. 4).
Similar differences in stoichiometry, depending upon the physical
state, have been observed with a bicycliccyclophane complex with
Clꢀ anion (1:1 in the solution state and 1:2 in the solid state).13
Since Rh(I) quenches the fluorescence associated with the pyr-
ene based ligand, we turned to Cu(I) as an alternative metal hinge.
Complex 3d, the Cu(I) analogue of the Clꢀ free Rh(I) tweezer
complexes 3b and 3c, can be synthesized by the reaction of
[Cu(CH3CN)4][PF6] and ligand 2 in CH2Cl2 at room temperature
(Scheme 4). This methodology is similar to that used for preparing
Cu(I) metallocyclophanes using the symmetrical 1,4-bis[2-(diphe-
nylphosphino)ethylthio]benzene ligands.14 All of the spectroscopic
data, including 1H NMR spectroscopy, 31P{1H} NMR spectroscopy,
and ESI-MS are in full agreement with the proposed formulation for
3d. For example, the 31P{1H} NMR spectrum of 3d exhibits a broad
The solid-state structure of 3a (Fig. 2), as determined by X-ray
crystallography, is consistent with its proposed solution structure.
Figure 1. ORTEP diagram for the crystal structure of 2. Thermal ellipsoids are drawn at
60% probability. Hydrogen atoms have been omitted for clarity.

8430
Y.-M. Jeon et al. / Tetrahedron 64 (2008) 8428–8434
Scheme 3. (a) CH2Cl2, rt; (b) AgBF4 for 3b and LiB(C6F5)4 for 3c; (c) CO/n-Bu4NCl, CH2Cl2, rt.
singlet at
d
0.15 due to the interaction of the phosphorus atoms
colorless cationic open Cu(I) tweezer 4d (Scheme 4). The open Cu(I)
tweezer 4d was characterized by 1H and 31P{1H} NMR spectroscopy,
ESI-MS, and elemental analysis. The complex exhibits a diagnostic
with the quadrupolar 63Cu and 65Cu nuclei (I¼3/2), indicative of
equivalent phosphorus atoms in the condensed Cu(I) tweezer
complex.3,14,15 Pyridine was chosen as a suitable N-donor for
opening the Cu(I) condensed intermediates since it works quite
well in the metallocyclophane cases.3,14,15 Successful displacement
of the Cu–S bonds in 3d was achieved via the addition of excess
pyridine, which results in the quantitative formation of the
resonance in its 31P{1H} NMR spectrum at
d
ꢀ3.52, which is similar
to what is observed for mono and binuclear open Cu(I) complexes
with two phosphines and two pyridines (shift from
d
ꢀ0.05 to
ꢀ4.60).3,14–16 Although complex 4d is stable in CH2Cl2 solution as
well as in solid state, under high vacuum, its ESI-MS spectrum
exhibited only a single peak at m/z 1221.6 corresponding to the loss
of two pyridine ligands and the PFꢀ6 counter anion (calcd for [Mꢀ2
pyridineꢀPFꢀ6 ]þ¼1221.3).
We investigated the absorption and emission properties of li-
gand 2, condensed Cu(I) tweezer 3d, and open Cu(I) tweezer 4d.
The Cu(I) complexes 3d and 4d in CH2Cl2 (with 5% DMF) and ligand
2 show nearly identical absorption spectra with lmax at 345 nm.
Emission spectra of 2, 3d, and 4d with excitation at 345 nm in the
same solvent system are different (Fig. 5a). The metal complexes
both exhibit broad and strong excimer bands at 475 nm, while the
ligand does not. Interestingly, the relative intensity of excimer to
monomer emission (IE/IM) is slightly larger in the open complex 4d
(IE/IM¼1.46) as compared with the condensed structure 3d (IE/
IM¼1.01). Presumably, the open structure provides the structural
flexibility for the two pyrene moieties to interact more strongly
than in the condensed structure. Open Cu(I) tweezer 4d interacts
with Clꢀ as evidenced by an increase in fluorescence intensity of the
excimer as a function of added chloride anion up to 1 equiv
(Fig. 5b). The data are consistent with the formation of a structure
analogous to crystallographically characterized 3a where the Clꢀ
enhances the interaction between the pyrene moieties via the ha-
lide induced chelation effect of the pyrene-appended two amide
groups. If the titration is continued, the excimer intensity steadily
decreases after 1 equiv until it disappears at 100 equiv. The first
Clꢀ can be trapped inbetween the two amide groups but the
additional anions tend to break the chelate conformation to make
individual hydrogen bonding complexes for each amide group,
which prohibits excimer formation. Condensed Cu(I) tweezer 3d
shows a similar recognition trend to that of 4d, showing that
Figure 2. ORTEP diagram for the crystal structure of 3a with 60% probability ellipsoids.
All but the amide hydrogen atoms have been omitted for clarity. Selected distances (Å)
and angles (ꢁ): Rh(1)–S(1) 2.330(5), Rh(1)–P(1) 2.232(3), Cl(1)/N(1) 3.241(4), P(1)–
Rh(1)–S(1) 165.92(3), P(1)–Rh(1)–P(10) 98.46(5), Rh(1)–S(1)–C(14) 105.70(11), Rh(1)–
S(1)–C(15) 111.50(11), C(14)–S(1)–C(15) 102.07(17), Cl(1)–H(1a)–N(1) 162.40(4).

Y.-M. Jeon et al. / Tetrahedron 64 (2008) 8428–8434
8431
Figure 3. Partial (a) 31P{1H} and (b) 1H NMR spectra of 3c (5.15 mM) in the presence of n-Bu4NCl in CD2Cl2 at rt (the signals labeled with ‘
*
’ represent the amide –NH protons).
local concentration of the pyrenyl amide moieties so that 2:1
binding can take place.
4. Experimental
4.1. General
All reactions were carried out under an inert atmosphere of
nitrogen using standard Schlenk techniques or an inert atmosphere
glove box unless otherwise noted.17 Diethyl ether, CH2Cl2, pentane,
and hexanes were purified by published methods.18 All solvents
were deoxygenated with nitrogen prior to use. 2-Chloro-
ethyldiphenylphosphine was purchased from Organometallics Inc.
and used as is. Deuterated solvents were purchased from Cam-
bridge Isotope Laboratories Inc. and used as received. [Rh(NBD)Cl]2
(NBD is norbornadiene) was purchased from Stem Chemical Inc.
and used as is. All other chemicals were used as received from
Aldrich. 1H NMR spectra were recorded on a Varian Mercury
300 MHz FT-NMR spectrometer and referenced relative to the re-
sidual proton resonances. 31P{1H} NMR spectra were recorded on
a Varian Mercury 300 MHz FT-NMR spectrometer at 121.4 MHz and
referenced relative to an external 85% H3PO4 standard. 19F{1H} NMR
spectra were recorded on a Varian Mercury 300 MHz FT-NMR
spectrometer at 282.47 MHz and referenced relative to an external
CFCl3 in CDCl3 standard. All chemical shifts are reported in parts per
million. Electrospray ionization mass spectra (ESI-MS) were
recorded on a Micromas Quatro II triple quadrapole mass spec-
trometer. Electron ionization mass spectra (EIMS) were recorded on
a Fisions VG 70-250 SE mass spectrometer. Fluorescent spectra
were recorded with a Hewlett Packard (HP) 8452a diode array
spectrometer. Elemental analyses were performed by Quantitative
Technologies Inc., Whitehouse, NJ.
Figure 4. Job plot for 3c (3.43 mM) and n-Bu4NCl (3.44 mM) in CD2Cl2 solution.
although the metal site is important for holding 2 equiv of ligand
within one complex, the orientation of the pyrenes in the tweezer
3d does not offer a significant advantage with respect to Clꢀ rec-
ognition. Note that consistent with this conclusion the free base
ligand 2 does not show any excimer formation in the presence of
Clꢀ (Fig. S3a). The condensed and open tweezers 3d and 4d exhibit
similar recognition trends with Brꢀ and Iꢀ (Figs. S3 and S4).
3. Conclusions
We have developed a method for rapidly assembling fluorescent
tweezer complexes from Cu(I) metal ion and the appropriate pyr-
ene-appended hemilabile ligands. These complexes exhibit fluo-
rescence-dependent binding properties for halide anions. X-ray
crystallography of a non-fluorescent Rh(I) analogue shows that the
Clꢀ ion interacts with the amide moieties flanking the pyrenyl
groups. Surprisingly, the pocket created by the condensed tweezer
3d does not confer significant advantages with respect to halide
binding or selectivity since the open structure 4d shows very
similar trend. Indeed, the main role of the metal is to increase the
4.2. Materials
4.2.1. Ph2PCH2CH2SC6H4CO2H (1)
A mixture of 4-mercaptobenzoic acid (2.0 g, 12.32 mmol), 2-
chloroethyldiphenylposphine (3.3 g, 13.14 mmol), potassium car-
bonate (6.0 g, 42.98 mmol), and 18-crown-6 (0.5 g, 1.89 mmol) in
acetonitrile/H2O (80:20 mL) was heated at reflux with vigorous
stirring overnight. The mixture was allowed to cool to room tem-
perature and concd HCl was added dropwise to make the solution

8432
Y.-M. Jeon et al. / Tetrahedron 64 (2008) 8428–8434
Scheme 4. (a) CH2Cl2, rt; (b) pyridine, CH2Cl2, rt.
acidic under ice-bath cooling. The precipitate was filtered and
washed with water, CH2Cl2, acetone, and diethyl ether successively
and dried in vacuo, which gave analytically pure white solid (3.7 g,
82%). 1H NMR (DMF-d7):
d
2.66 (m, 2H, –CH2PPh2), 3.32 (m, 2H, J¼
7.2 Hz, –CH2S–), 7.46–7.69 (m, 12H, –C6H4–, –P(C6H5)2), 8.07 (d, 2H,
–C6H4–). 31P{1H} NMR (DMF-d7):
d
ꢀ16.32 (s). MS (EI, m/z)¼366.1
(calcd for C21H19O2PS¼366.0). Elemental analysis for C21H19O2PS$
C4H10O calcd: 68.16% C, 6.64% H. Found: 68.29% C, 6.95% H.
4.2.2. Ph2PCH2CH2SC6H4CONHCH2(C16H9) (2)
Chloro iso-butylformate (0.1 mL, 0.72 mmol) was added drop-
wise to the CH2Cl2 (10 mL) solution of 1 (0.2 g, 0.55 mmol) and
triethylamine (0.1 mL, 0.72 mmol) under ice-bath cooling for 5 min
and stirred 1 h at room temperature. To the solution, 2-pyr-
enylmethylamine$HCl (0.17 g, 0.60 mmol) and triethylamine (3 mL,
21.52 mmol) in CH2Cl2 (10 mL) were added dropwise and stirred for
2 h at room temperature. Solvent was evaporated at reduced
pressure and the remaining solid was washed with acidic ethanol.
The desired product was isolated by filtration and dried under
vacuum (70 mg, 22%). 1H NMR (THF-d8):
d 2.36 (m, 2H, –CH2PPh2),
2.99 (m, 2H, –CH2S–), 5.31 (d, 2H, J¼5.7 Hz, –CH2N–), 7.17 (d, 2H,
J¼6.6 Hz, –C6H4–), 7.19–7.42 (m, 10H, –P(C6H5)2), 7.77 (d, 2H, J¼
6.6 Hz, –C6H4–), 7.96–8.20 (m, 8H, pyrene–H), 8.47 (d, 1H, J¼9.0 Hz,
pyrene–H). 31P{1H} NMR (THF-d8):
m/z)¼579.1790 (calcd for C38H30NOPS¼579.1786). Elemental ana-
lysis for C38H30NOPS$1/2CH2Cl2 calcd: 74.32% C, 5.02% H, 2.25% N.
Found: 74.40% C, 5.58% H, 1.82% N.
d
ꢀ15.92 (s). HRMS (EI,
4.2.3. [(Ph2PCH2CH2SC6H4CONHCH2(C16H9))2Rh][Cl] (3a)
The dichloromethane solution (20 mL) of ligand 2 (200 mg,
345.0 mmol) and [Rh(NBD)Cl]2 (40 mg, 85.9 mmol) was stirred
overnight at room temperature. Solvent was evaporated under
reduced pressure. The resulting yellow precipitate was washed
with THF and diethyl ether and dried in vacuo (215 mg, 96%). 1H
NMR (CD2Cl2/CD3OD¼3:1):
d 2.51 (m, 4H, –CH2PPh2), 2.70 (m, 4H,
–CH2S–), 5.06 (d, 4H, J¼5.5 Hz, –CH2N–), 7.19–7.34 (m, 24H, –C6H4–,
–P(C6H5)2), 7.51 (d, 4H, J¼6.6 Hz, –C6H4–), 7.88–8.06 (m, 16H, pyr-
ene–H), 8.15 (d, 2H, pyrene–H), 8.77 (br t, 2H, J¼9.3 Hz, –NH–).
Figure 5. (a) Fluorescence spectra of 2 (10.8 mM), 3d (5.4 mM), and 4d (5.4 mM). (b)
31P{1H} NMR (CD2Cl2/CD3OD¼3:1):
d
64.70 (d, JRh–P¼161 Hz). MS
Fluorescence spectral change of 4d upon titration with n-Bu4NCl in the CH2Cl2 con-
taining 5% DMF (excitation¼345 nm).
(ESI, m/z): [MꢀCl]þ¼1261.5 (calcd for [C76H60N2O2P2RhS2]þ¼

Y.-M. Jeon et al. / Tetrahedron 64 (2008) 8428–8434
8433
1261.2). Elemental analysis for C76H64N2O2P2RhS2Cl$1/2CH2Cl2
calcd: 68.56% C, 4.59% H, 2.09% N. Found: 68.37% C, 4.22% H, 2.11% N.
30 min at room temperature. Solvent was evaporated under re-
duced pressure and dried in vacuo overnight. Diethyl ether was
added and sonicated for 10 min. White precipitate was isolated by
filtration and dried under vacuum (97 mg, 92%). 1H NMR (CD2Cl2):
4.2.4. [(Ph2PCH2CH2SC6H4CONHCH2(C16H9))2Rh][BF4] (3b)
The dichloromethane solution of [Rh(NBD)Cl]2 (40 mg,
d 2.52 (br s, 4H, –CH2PPh2), 3.00 (br s, 4H, –CH2S–), 5.14 (br d, 4H,
85.9
m
mol) and AgBF4 (35 mg, 179.8
m
mol) was stirred for 10 min at
J¼4.8 Hz, –CH2N–), 6.74 (br d, 4H, J¼5.4 Hz, –C6H4–), 7.30–7.50 (m,
28H, –P(C6H5)2, pyridine, pyrene–H), 7.73 (t, 2H, J¼7.8 Hz, pyrene–
H), 7.91–8.24 (m, 18H, pyridine, pyrene–H), 8.42 (br s, 4H, pyridine).
room temperature. The filtered solution of Rh(I) precursor in
dichloromethane was added to dichloromethane solution of ligand
2 (200 mg, 345.0
mmol) dropwise and stirred overnight at room
31P{1H} NMR (CD2Cl2):
d
ꢀ3.52 (br s, –PPh2), ꢀ143.22 (m, PFꢀ6 ). MS
temperature. Solvent was evaporated under reduced pressure and
the resulting yellow precipitate was washed with THF and dried in
(ESI, m/z): [Mꢀ2pyridineꢀPFꢀ6 ]þ¼1221.6 (calcd for [C76H60N2O2P2-
CuS2]þ¼1221.3). Elemental analysis for C86H70CuF6N4O2P3S2 calcd:
67.68% C, 4.62% H, 3.67% N. Found: 67.35% C, 4.50% H, 3.53% N.
vacuo (189 mg, 81%). 1H NMR (CD2Cl2/CD3OD¼3:1):
d 2.56 (m, 4H,
–CH2PPh2), 2.78 (m, 4H, –CH2S–), 5.08 (s, 4H, –CH2N–), 7.25–7.56
(m, 28H, –C6H4–, –P(C6H5)2), 7.74–8.22 (m, 18H, pyrene–H). 31P{1H}
4.3. X-ray crystallography
NMR (CD2Cl2/CD3OD¼3:1): 64.78 (d, JRh–P¼161 Hz). MS (ESI, m/z):
d
[MꢀBFꢀ4 ]þ¼1261.6 (calcd for [C76H60N2O2P2RhS2]þ¼1261.2). Ele-
mental analysis for C76H60BF4N2O2P2RhS2$2CH2Cl2 calcd: 61.68% C,
4.25% H, 1.84% N. Found: 61.90% C, 4.21% H, 1.74% N.
4.3.1. Refinement
Crystals 2 and 3a were mounted on a CryoLoopÓ with Paratone-
NÓ oil and immediately placed under a liquid stream of N2 on
a Bruker SMART APEX CCD system, respectively. Data were col-
4.2.5. [(Ph2PCH2CH2SC6H4CONHCH2(C16H9))2Rh][B(C6F5)4] (3c)
The desired complex 3c was synthesized by similar method to
that of 3b using [Rh(COD)Cl]2 (40 mg, 79.5
(130.0 mg, 171.0 mol), and ligand 2 (185 mg, 319.1
product was washed with diethyl ether and dried under vacuum
(229 mg, 74%). 1H NMR (CD2Cl2):
2.49 (m, 4H, –CH2PPh2), 2.66 (m,
lected at ꢀ60 ꢁC with Mo K
a radiation and corrected for absorption
using the SADABS program. The structures were solved by a Pat-
terson map, developed by successive difference Fourier syntheses,
and refined by full matrix least squares on all F2 data. All non-
hydrogen atoms were refined as being anisotropic and hydrogen
atoms, except H1A on N1 in 3a were placed in calculated positions
with temperature factors fixed at 1.2 or 1.5 times the equivalent
isotropic U of the C atoms to which they were bonded. The position
of the hydrogen atom H1A was determined from a Fourier differ-
ence map and allowed to refine.
mmol), LiB(C6F5)4$Et2O
m
mmol). The
d
4H, –CH2S–), 5.07 (d, 4H, J¼5.7 Hz, –CH2N–), 7.20–7.45 (m, 28H,
–C6H4–, –P(C6H5)2), 7.88–8.15 (m, 18H, pyrene–H). 31P{1H} NMR
(CD2Cl2):
d
64.67 (d, JRh–P¼162 Hz). 19F NMR (CD2Cl2):
ꢀ133.49 (s),
d
ꢀ146.03 (t), ꢀ167.90 (d). MS (ESI, m/z): [MꢀB(C6F5)4]þ¼1261.5
(calcd for [C76H60N2O2P2RhS2]þ¼1261.2). Elemental analysis for
C
101H62BCl2F20N2O2P2RhS2$CH2Cl2 calcd: 59.87% C, 3.08% H, 1.38%
4.3.2. Crystallographic data
N. Found: 59.90% C, 2.72% H, 1.28% N.
For 2 (CCDC 675487): C38H30NOPS, monoclinic, space group
P2(1)/c,
b
a¼16.115(2) Å,
b¼9.778(1) Å,
c¼18.536(2) Å,
¼100.004(2)ꢁ, V¼2876.3(6) Å3, Z¼4, T¼213(2) K, qmax¼28.27ꢁ, Mo
4.2.6. [(Ph2PCH2CH2SC6H4CONHCH2(C16H9))2Cu][PF6] (3d)
To the suspension of ligand 2 (91 mg, 0.157 mmol) in dichloro-
methane (10 mL), dichloromethane solution of [(CH3CN)4Cu]PF6
(30 mg, 0.079 mmol) was added dropwise and stirred overnight at
room temperature. Solvent was evaporated under reduced pressure
and dried in vacuo overnight. Diethyl ether was added and soni-
cated for 10 min. White precipitate was isolated by filtration and
K
a
(
l
¼0.71073 Å), 17,252 measured reflections, 5059 independent
reflections [R(int)¼0.0450], R1¼0.0718, wR2¼0.1687, GOF¼1.172
([I>2 (I)]). For 3a (CCDC 675488): C76H60ClN2O2P2Rh1S2, mono-
s
clinic, space group C2/c, a¼13.065(2) Å, b¼19.762(3) Å,
c¼24.237(3) Å,
b
¼99.752(2)ꢁ, V¼6167.1(13) Å3, Z¼4, T¼213(2) K,
qmax¼28.27ꢁ, Mo K
a
(
l¼0.71073 Å), 23,331 measured reflections,
dried under vacuum (103 mg, 96%). 1H NMR (CD2Cl2):
d 2.69 (br s,
7246 independent reflections [R(int)¼0.0505], R1¼0.0585,
4H, –CH2PPh2), 3.21 (br s, 4H, –CH2S–), 5.21 (br s, 4H, –CH2N–), 6.80
(br s, 2H, –NH–), 7.09 (d, 4H, J¼6.6 Hz, –C6H4–), 7.32–7.45 (m, 20H,
–P(C6H5)2), 7.75 (d, 4H, J¼6.9 Hz, –C6H4–), 7.95–8.17 (m, 16H, pyr-
ene–H), 8.31 (d, 2H, J¼9.0 Hz, pyrene–H). 31P{1H} NMR (CD2Cl2):
wR2¼0.1254, GOF¼1.102 ([I>2
s(I)]).
4.4. NMR experiment
d
0.15 (br s, –PPh2), ꢀ143.20 (m, PFꢀ6 ). MS (ESI, m/z): [MꢀPF6ꢀ]þ¼
4.4.1. 1H NMR titration
1221.4 (calcd for [C76H60N2O2P2CuS2]þ¼1221.3). Elemental analysis
for C76H60CuF6N2O2P3S2$1.5CH2Cl2 calcd: 62.25% C, 4.25% H, 1.87%
N. Found: 62.25% C, 3.84% H, 1.52% N.
Proton NMR titration was performed at 298 K. The condensed
Rh(I) tweezer complex 3c (5.15 mM) was titrated with n-Bu4NþXꢀ
(X¼F, Cl, Br, and I) in CD2Cl2 by monitoring the changes in the
chemical shift of amide –NH protons.
4.2.7. [(Ph2PCH2CH2SC6H4CONHCH2(C16H9))2Rh(CO)Cl] (4a)
Tothesolutionofcomplex3aina3:1mixtureofCD2Cl2 andCD3OD
was charged with CO gas (1 atm) for 10 min, which gave a desired
4.4.2. Job plot
1
Stock solution of 3c (3.43 mM) and n-Bu4NþClꢀ (3.44 mM) were
prepared in CD2Cl2 solution separately. Eleven NMR samples ([3c]/
([3c]þ[n-Bu4NþClꢀ])¼0.0, 0.1, 0.2, ., 0.9,1.0) were prepared and 1H
NMR spectra were taken at room temperature.
open complex in quantitative yield. H NMR (CD2Cl2/CD3OD¼3:1):
d
2.68 (br m, 4H, –CH2PPh2), 2.90 (br m, 4H, –CH2S–), 5.20 (d, 4H,
J¼5.4 Hz, –CH2N–), 7.10 (d, 4H, J¼7.5 Hz, –C6H4–), 7.36–8.15 (m, 40H,
–C6H4–, –P(C6H5)2, –Pyrenyl–H), 8.28 (d, 2H, J¼9.0 Hz, –Pyrenyl–H),
8.39 (br t, 2H, –NH–). 31P{1H} NMR (CD2Cl2/CD3OD¼3:1):
d 25.06 (d,
JRh–P¼124 Hz). Alternatively, the complex 4a can be synthesized from
3b and 3c by the reaction of 1 equiv of n-Bu4NþClꢀ and CO gas (1 atm)
in CH2Cl2 at room temperature in quantitative yield.
4.5. Fluorescence measurement
4.5.1. Titration experiment
Stock solution of n-Bu4NþXꢀ (91.0 mM) and stock solution of 2,
3d, and 4d (0.36 mM) were prepared in CH2Cl2 containing 5% DMF.
For all measurements, excitation was carried out at 345 nm with
emission slit width of 3 nm. Fluorescence titration experiments
4.2.8. [(Ph2PCH2CH2SC6H4CONHCH2(C16H9))2Cu
(pyridine)2][PF6] (4d)
Excess amount of pyridine (1 mL) was added to the solution of
3d (95 mg, 69.0
mmol) in dichloromethane (10 mL) and stirred for
were performed with 5.4 mM solutions of 2, 3d, and 4d and various

8434
Y.-M. Jeon et al. / Tetrahedron 64 (2008) 8428–8434
concentrations of n-Bu4NþXꢀ (X¼F, Cl, Br, and I) in CH2Cl2 con-
5. Holliday, B. J.; Farrell, J. R.; Mirkin, C. A.; Lam, K. C.; Rheingold, A. L. J. Am. Chem.
Soc. 1999, 121, 6316–6317.
taining 5% DMF.
6. (a) Farrell, J. R.; Mirkin, C. A.; Guzei, I. A.; Liable-Sands, L. M.; Rheingold, A. L.
Angew. Chem., Int. Ed. 1998, 37, 465–467; (b) Farrell, J. R.; Mirkin, C. A.; Liable-
Sands, L. M.; Rheingold, A. L. J. Am. Chem. Soc. 1998, 120, 11834–11835; (c) Jeon,
Y.-M.; Heo, J.; Brown, A. M.; Mirkin, C. A. Organometallics 2006, 25, 2729–2732;
(d) Holliday, B. J.; Jeon, Y. M.; Mirkin, C. A.; Stern, C. L.; Incarvito, C. D.; Zakharov,
L. N.; Sommer, R. D.; Rheingold, A. L. Organometallics 2002, 21, 5713–5725; (e)
Brown, A. M.; Ovchinnikov, M. V.; Mirkin, C. A. Angew. Chem., Int. Ed. 2005, 44,
4207–4209; (f) Brown, A. M.; Ovchinnikov, M. V.; Stern, C. L.; Mirkin, C. A. J. Am.
Chem. Soc. 2004, 126, 14316–14317; (g) Khoshbin, M. S.; Ovchinnikov, M. V.;
Mirkin, C. A.; Golen, J. A.; Rheingold, A. L. Inorg. Chem. 2006, 45, 2603–2609; (h)
Khoshbin, M. S.; Ovchinnikov, M. V.; Mirkin, C. A.; Zakharov, L. N.; Rheingold,
A. L. Inorg. Chem. 2005, 44, 496–501; (i) Khoshbin, M. S.; Ovchinnikov, M. V.;
Salaita, K. S.; Mirkin, C. A.; Stern, C. L.; Zakharov, L. N.; Rheingold, A. L. Chem.
Asian J. 2006, 1, 686–692; (j) Ulmann, P. A.; Brown, A. M.; Ovchinnikov, M. V.;
Mirkin, C. A.; DiPasquale, A. G.; Rheingold, A. L. Chem.dEur. J. 2007, 13, 4529–
4534.
Acknowledgements
C.A.M. acknowledges the ONR, NSF, and ARO for supporting this
research and he is also grateful for a NIH Director’s Pioneer Award.
D.K. acknowledges the Korea Research Foundation Grant (KRF-
2007-357-C00053) funded by the Korean Government (MOEHRD)
for postdoctoral fellowship support.
Supplementary data
The crystallographic data for 2 (CCDC 675487) and 3a (CCDC
675488) can be obtained free of charge from the Cambridge Crys-
tallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found in the
online version, at doi:10.1016/j.tet.2008.05.047.
7. (a) Wegner, S. V.; Okesli, A.; Chen, P.; He, C. J. Am. Chem. Soc. 2007, 129, 3474–
3475; (b) Nagatoishi, S.; Nojima, T.; Juskowiak, B.; Takenaka, S. Angew. Chem.,
Int. Ed. 2005, 44, 5067–5070; (c) Kim, S. K.; Lee, S. H.; Lee, J. Y.; Lee, J. Y.; Bartsch,
R. A.; Kim, J. S. J. Am. Chem. Soc. 2004, 126, 16499–16506.
8. Bader, A.; Lindner, E. Coord. Chem. Rev. 1991, 108, 27–110.
9. (a) Dixon, F. M.; Eisenberg, A. H.; Farrell, J. R.; Mirkin, C. A.; Liable-Sands, L. M.;
Rheingold, A. L. Inorg. Chem. 2000, 39, 3432–3433; (b) Ovchinnikov, M. V.;
Brown, A. M.; Liu, X. G.; Mirkin, C. A.; Zakharov, L. N.; Rheingold, A. L. Inorg.
Chem. 2004, 43, 8233–8235.
References and notes
10. (a) Szemes, F.; Hesek, D.; Chen, Z.; Dent, S. W.; Drew, M. G. B.; Goulden, A. J.;
Graydon, A. R.; Grieve, A.; Mortimer, R. J.; Wear, T.; Weightman, J. S.; Beer, P. D.
Inorg. Chem. 1996, 35, 5868–5879; (b) Beer, P. D.; Hesek, D.; Nam, K. C.; Drew,
M. G. B. Organometallics 1999, 18, 3933–3943; (c) Mahoney, J. M.; Beatty, A. M.;
Smith, B. D. Inorg. Chem. 2004, 43, 7617–7621; (d) Suksai, C.; Leeladee, P.;
Jainuknan, D.; Tuntulani, T.; Muangsin, N.; Chailapakul, O.; Kongsaeree, P.;
Pakavatchai, C. Tetrahedron Lett. 2005, 46, 2765–2769.
1. (a) Fujita, M. Acc. Chem. Res. 1999, 32, 53–61; (b) Pease, A. R.; Jeppesen, J. O.;
Stoddart, J. F.; Luo, Y.; Collier, C. P.; Heath, J. R. Acc. Chem. Res. 2001, 34, 433–444;
(c) Kesanli, B.; Lin, W. B. Coord. Chem. Rev. 2003, 246, 305–326; (d) Lee, J. W.;
Samal, S.; Selvapalam, N.; Kim, H. J.; Kim, K. Acc. Chem. Res. 2003, 36, 621–630;
(e) Kovbasyuk, L.; Kramer, R. Chem. Rev. 2004, 104, 3161–3187; (f) Heath, J. R.;
Stoddart, J. F.; Williams, R. S. Science 2004, 303, 1136–1137; (g) Thanasekaran, P.;
Liao, R. T.; Liu, Y. H.; Rajendran, T.; Rajagopal, S.; Lu, K. L. Coord. Chem. Rev. 2005,
249, 1085–1110; (h) Gianneschi, N. C.; Nguyen, S. T.; Mirkin, C. A. J. Am. Chem.
Soc. 2005, 127, 1644–1645; (i) Amijs, C. H. M.; van Klink, G. P. M.; van Koten, G.
Dalton Trans. 2006, 308–327; (j) Heo, J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2006,
45, 941–944; (k) Oliveri, C. G.; Gianneschi, N. C.; Nguyen, S. T.; Mirkin, C. A.;
Stern, C. L.; Wawrzak, Z.; Pink, M. J. Am. Chem. Soc. 2006, 128, 16286–16296; (l)
Filby, M. H.; Steed, J. W. Coord. Chem. Rev. 2006, 250, 3200–3218; (m) Beer, P. D.
Acc. Chem. Res. 1998, 31, 71–80; (n) Gale, P. A.; Garcia-Garrido, S. E.; Garric, J.
Chem. Soc. Rev. 2008, 37, 151–190; (o) Wintergerst, M. P.; Levitskaia, T. G.;
Moyer, B. A.; Sessler, J. L.; Delmau, L. H. J. Am. Chem. Soc. 2008, 130, 4129–4139.
2. (a) Holliday, B. J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2001, 40, 2022–2043; (b)
Gianneschi, N. C.; Masar, M. S.; Mirkin, C. A. Acc. Chem. Res. 2005, 38, 825–837.
3. Masar, M. S.; Gianneschi, N. C.; Oliveri, C. G.; Stern, C. L.; Nguyen, S. T.; Mirkin,
C. A. J. Am. Chem. Soc. 2007, 129, 10149–10158.
11. Roesky, H. W.; Andruh, M. Coord. Chem. Rev. 2003, 236, 91–119.
12. (a) Hynes, M. J. J. Chem. Soc., Dalton Trans. 1993, 311–312; (b) The Ka of 3c for Brꢀ
and Iꢀ are 2.69ꢂ103 Mꢀ2 and 2.03ꢂ103
M
ꢀ2, respectively.
13. Bisson, A. P.; Lynch, V. M.; Monahan, M. C.; Anslyn, E. V. Angew. Chem., Int. Ed.
1997, 36, 2340–2342.
14. Masar, M. S.; Mirkin, C. A.; Stern, C. L.; Zakharov, L. N.; Rheingold, A. L. Inorg.
Chem. 2004, 43, 4693–4701.
15. Doel, C. L.; Gibson, A. M.; Reid, G. Polyhedron 1995, 14, 3139–3146.
16. (a) Del Zotto, A.; Nardin, G.; Rigo, P. J. Chem. Soc., Dalton Trans. 1995, 3343–3351;
(b) Ruina, Y.; Kunhua, L.; Yimin, H.; Dongmei, W.; Douman, J. Polyhedron 1997,
16, 4033–4038.
17. Errington, R. J. Advanced Practical Inorganic and Metalorganic Chemistry; Chap-
man and Hall: New York, NY, 1997.
18. Armarego, W. L. F.; Perrin, D. D. Purification of Laboratory Chemicals; Butter-
worth-Heinemann: Oxford, 1996.
4. Yoon, H. J.; Heo, J.; Mirkin, C. A. J. Am. Chem. Soc. 2007, 129, 14182–14183.