A rhomboid-shaped organic host molecule with small binding space. Unsymmetrical and symmetrical inclusion of halonium ions

Article abstract of DOI:10.1039/c3dt53629g

A shape persistent rhomboid-shaped organic host molecule having two pyridyl units was synthesized which induces size selective halonium inclusion. Cl ⁺ and Br⁺ are included to form unsymmetric and symmetric complexes, while I⁺

Full text of DOI:10.1039/c3dt53629g

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A rhomboid-shaped organic host molecule with
small binding space. Unsymmetrical and
symmetrical inclusion of halonium ions†
Cite this: Dalton Trans., 2014, 43,
6643
Yuji Suzaki, Takashi Saito, Tomohito Ide and Kohtaro Osakada*
A shape persistent rhomboid-shaped organic host molecule having two pyridyl units was synthesized
which induces size selective halonium inclusion. Cl+ and Br+ are included to form unsymmetric and sym-
metric complexes, while I+ does not form a stable complex. The difference among the haloniums was
ascribed to the matching (or mismatching) of the shape of the cavity and the guest ions. The complexa-
tion of the host molecule with other cations, such as Ag+, Pd2+, Zn2+ and H+, is also mentioned.
Received 4th January 2014,
Accepted 5th February 2014
DOI: 10.1039/c3dt53629g
www.rsc.org/dalton
Introduction
Macrocyclic organic host molecules, such as crown ethers,1
cryptands,2 calix arenes,3 pillararenes4 and cyclodextrins,5
bind guest molecules as well as ions to form inclusion com-
plexes. Metal cations are complexed with the host molecules
containing donor atoms or groups, such as dicyclohexano[18]-
crown-6-ether
and
[2.2.2]cryptand,
N(CH2CH2OCH2-
Scheme 1 Structure of bpeb, cpeb and Yoshida’s macrocycle.
CH2OCH2CH2)3N.6,7 Inclusion of various metal ions and alkyl-
ammonium was achieved by artificial design of the host mole-
cules.8 Halonium9 is proposed as the intermediate of halogen
addition reaction to alkene10 and halolactamization11 and con-
tributes as a component of square-shaped dinuclear Pt com-
plexes.12 Its isolation with the aid of inclusion using cyclic
host molecules has attracted much less attention than
inclusion of the metal cations. Resnati reported halogen
bonding in which donor atoms have a significant interaction
with halogen atoms of the compound and recognition of
guests based on it.13 Recently, fluoronium “F+” sources, such
as Selectfluor (a derivative from DABCO), N-fluorobenzenesulfo-
nimide (NFSI) and N-fluoro-2,4,6-trimethylpyridinium hexa-
fluorophosphate, have gathered attention as electrophiles in
the electrophilic fluoronation of arenes catalyzed by Pd and
Cu.14,15 1,2-Bis(2-pyridylethynyl)benzene (Scheme 1, bpeb),
having two pyridyl groups tethered by a 1,2-dialkynyl benzene,
functions as a trans bidentate ligand of transition metal com-
plexes16,17 and the complexes of bromonium ions.18,19
In this paper, we designed a cyclic organic host molecule
composed of two pyridyl and two 1,2-dialkyl benzene units
(cpeb) which is expected to have a similar N⋯N distance and a
rigid structure, suited for complexation with haloniums. Here
we report unique inclusion behavior of cpeb for the haloniums.
Results and discussion
Eqn (1) depicts the synthesis of cyclic pyridylethynylbenzene
(cpeb) by deprotection of the –SiMe2{(CH2)3CN} group of 1
under basic conditions followed by the intramolecular Sono-
gashira–Hagihara cross-coupling reaction. The palladium(II)
complex, Pd(OCOCF3)2(cpeb), was obtained by reaction of
Pd(OCOCF3)2 and cpeb in 70% yield. Fig. 1 shows molecular
structures of cpeb and its complex with the Pd(OCOCF3)2 guest
determined by X-ray crystallography. Cpeb has a crystal poly-
morph (orthorhombic, Cmce (no. 64) and Pbca (no. 61))
depending on the recrystallization conditions (Fig. 1a and b).
The crystal structure analyzed as Cmce (no. 64) has a 4-fold
symmetry axis in which all the atoms are located within a
single plane (Fig. 1a) while the two pyridine rings in the
structure analyzed as Pbca (no. 61) are parallel in the
molecule with a 2-fold axis (Fig. 1b). The molecular structure
of Pd(OCOCF3)2(cpeb) adopts a square planar molecular
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta,
Midoriku, Yokohama 226-8503, Japan. E-mail: kosakada@res.titech.ac.jp;
Fax: +81-45-924-5224
†Electronic supplementary information (ESI) available: Additional figures, UV
and NMR spectra as well as theoretical calculation. CCDC 973075, 973076 and
973077. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c3dt53629g
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ð1Þ
Fig. 2 (a) Absorption spectra of (i) cpeb (blue, [cpeb] = 1.0 × 10−2 mM),
(ii) cpeb + Cl+OTf − (red, [Cl+OTf −] = 1.0 × 10−2 mM), (iii) cpeb + Br+OTf −
(green, [Br+OTf −] = 1.0 × 10−1 mM) and (iv) cpeb + I+OTf − (black,
[I+OTf −] = 1.0 × 10−1 mM) and (b) emission spectra of (i) cpeb (blue,
[cpeb] = 1.0 × 10−3 mM), (ii) cpeb + Cl+OTf − (red, [Cl+OTf −] = 1.0 × 10−3
mM), and (iii) cpeb + Br+OTf − (green, [Br+OTf −] = 1.0 × 10−3 mM).
Photograph under irradiation at 365 nm is shown in the inset ((i) cpeb,
(ii) cpeb + Cl+OTf −, (iii) cpeb + Br+OTf −).
Fig. 1 Crystal structure of (a) cpeb (space group = Cmce (no. 64)), (b)
cpeb (space group = Pbca (no. 61)) and (c) Pd(OCOCF3)2(cpeb).
geometry where pyridine units are located at trans positions to
Pd(II). The Pd atom is located at the mid-point of the two nitro-
gen atoms. The distance between the nitrogen atoms of cpeb
is 4.30 Å in both the structures (N1–N1* in Fig. 1a and N1–N2 quantum yield from Cl+(cpeb) (φ = 0.12) is higher than that
in Fig. 1b). Yoshida et al. selected a macrocyclic molecule, a from Br+(cpeb) (φ = 0.05). The color change in light-emission
cyclyne-type azamacrocycle having two pyridine units and two before and after addition of X+OTf− (X = Cl, Br) to the solution
1,3-dialkyl benzenes as the host and found its light-emitting of cpeb is clear (Fig. 2b, inset, λex = 365 nm). The lifetime of
inclusion complex with Sb(V)Cl5.20 Cpeb is estimated to have emission from the mixture of cpeb and Br+OTf− (τ0 = 10 ns) is
much shorter N–N distance and smaller binding space than longer than that from cpeb (τ0 = 6.5 ns). The solid-state emis-
the meta-substituted cyclic host. The N1–N1* distance of sion from cpeb (λmax = 406 nm, φ = 0.14 (absolute)) is similar
Pd(OCOCF3)2(cpeb) (4.09 Å) is shorter than the corresponding to that from the solution while the solid obtained by the evap-
distance of cpeb, which is attributed to coordination of the oration of the mixture of cpeb and X+OTf− (X = Cl, Br) is not
Pd(II) ion.21
UV-vis spectroscopy measurements revealed a remarkable
emissive (φ < 0.01 (absolute)).
HR-ESI-MS spectra of the mixture of cpeb and Br+OTf− in
bathochromic shift of cpeb (λmax = 319 nm) upon addition of CH2Cl2 showed mass peaks assigned to Br(cpeb) (m/z =
Cl+OTf− (λmax = 357 nm) and Br+OTf− (λmax = 358 nm) (Fig. 2a, 483.029, calcd 483.032). HR-ESI-MS spectra of the mixture of
Table 1). The shoulder peaks are observed at ca. 400 nm in the cpeb and Cl+OTf− showed mass peaks at m/z = 509.0306 and
spectra of the mixture of cpeb and X+OTf− (X = Cl, Br). Negli- 913.1532 which are assigned to the hydrochloric acid adducts
gible change was observed in the reaction of cpeb and I+OTf−. of the complex, Cl(cpeb)(HCl)2 (calcd 509.0346) and
The Job’s plots of the absorption intensity at 410 nm of the Cl3(cpeb)2(HCl)2 (calcd 913.1505), respectively. 1H NMR
mixture of cpeb and Br+OTf− ([cpeb] + [Br+OTf−] = 1.0 × 10−2 spectra of the mixture of cpeb and X+OTf− (X = Cl, Br) in
mM, CH2Cl2, 25 °C) shows a maximum at a molar fraction CD2Cl2 showed a broad signal at δ 7.5–8.0 while free cpeb
close to 0.5, which indicates that cpeb and Br+OTf− form a showed clearly separated signals (δ 7.63 (C5H3N), 7.59 (C6H4),
1 : 1 complex in CH2Cl2 solution.
7.44 (C5H3N), 7.34 (C6H4)). It suggests equilibration of the
Emission spectra also show the bathochromic shifts upon complex formation of cpeb and X+OTf− (X = Cl, Br) on the
complexation of Cl+ and Br+. Excitation of the mixture of cpeb NMR time scale.
and Cl+OTf− at λex = 357 nm results in green emission (λmax
=
Similar complexation and bathochromic shifts are observed
508 nm) with a Stokes shift of 1.00 eV and a moderate for the mixture of cpeb with AgOTf, Pd(OCOCF3)2, Zn(OTf)2
quantum yield (φ = 0.12), while cpeb shows emission at λmax
and CF3COOH (Table 1). The reaction of cpeb with Pd-
403 nm with a smaller Stokes shift (0.81 eV) (Fig. 2b). The (OCOCF3)2 causes quenching of fluorescence in solution
=
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Table 1 Photochemical data of compounds
Emissionb
Absorptiona
Compound
λmax/nm
λmax/nm
ϕc
τ0/ns
Stokes shiftd/eV (nm−1
)
cpeb
319
357
358
332
330
332
353
403 (406)e
508 (−)e
503 (−)e
501
0.15 (0.14)e
0.12 (<0.01)e
0.05 (<0.01)e
0.03
6.5
—
10
—
—
5.7
9.7
0.81 (84)
1.00 (169)
0.99 (171)
1.25 (169)
—
1.27 (172)
1.00 (113)
cpeb + Cl+ k
cpeb + Br+ j
cpeb + Ag+ f
cpeb + Pd2+ g
cpeb + Zn2+ h
cpeb + H+ i
—
—
504 (485)e
495 (495)e
0.09 (0.15)e
0.16 (0.19)e
a [cpeb] = 1.0 × 10−2 mM, CH2Cl2, 25 °C. b [cpeb] = 1.0 × 10−3 mM, CH2Cl2, 25 °C, λex = λmax(absorption). c Quantum yield. d Stokes shift, Δλ =
λmax(absorption) − λmax(absorption). e Data in solid state. f AgOTf (2 equiv. to cpeb). g Pd(OCOCF3)2 (4 equiv. to cpeb). h Zn(OTf)2 (2 equiv. to
cpeb). i CF3COOH (1.0 mM). j Br+OTf− (1 equiv. to cpeb). k Cl+OTf− (1 equiv. to cpeb).
probably due to a heavy atom effect. The mixture of cpeb and
Zn(OTf)2 has similar emission both from the solution and
from the solid state (in solution, λmax = 504 nm, φ = 0.09; in
solid state, λmax = 485 nm, φ = 0.15 (absolute)). The complexa-
tion of CF3COOH and cpeb requires a large excess of
CF3COOH ([cpeb] = 1.0 × 10−3 mM, [CF3COOH] = 1.0 × 10−1
mM) to reach a saturation point in emission, which indicates a
relatively lower ability of cpeb for complexation with H+ than
other cations described above. The complex of cpeb and
CF3COOH shows also emission both from the solution and
from the solid state (in solution, λmax = 495 nm, φ = 0.16; in
solid state, λmax = 495 nm, φ = 0.19 (absolute)).
Fig. 4 Calculated potential energy curve and the N(1)⋯X distance in N
(1)⋯X⋯N(2) in (a) [Cl+(cpeb)] and (b) [Br+(cpeb)]. The energies for the
Fig. 3 illustrates the structure of a rhomboid-shaped cyclic
pyridylethynyl benzene (cpeb) employed in this study and its model structures of (X)(cpeb) were calculated at every 0.05 Å distance of
the rigid N(1)⋯X⋯N(2) unit (N(1)⋯N(2) = 4.19 Å) using the PBE38/TZVP
plausible structures in the inclusion complexes. The smaller
basis set.23
guest, such as Cl+ and H+, may form an unsymmetric inclusion
complex g(cpeb) in which the guest prefers unsymmetrical
coordination with one donor atom. The guest molecule, such
Cl(cpeb) and Br(cpeb) was calculated to have a double-well and
as Br+, Ag+, Pd2+ and Zn2+, whose size is similar to the cavity of
single-well potential system, respectively. The results indicate
the cpeb may form a symmetric inclusion complex G(cpeb)
that Cl+ in an N–X+–N system of Cl+(cpeb) prefers the position
(G = guest) in which the guest molecule (or ion) is located at
close to one nitrogen than the other. Br+ in the Br(cpeb)
the midpoint of the nitrogen atom. A larger size ion such as I+
system is located at the midpoint of N–X+–N with similar inter-
may not be included due to the shape-persistence of cpeb.
actions of Br+ and the two nitrogen atoms. Erdélyi investigated
Fig. 4 shows the calculated energy potentials for the posi-
the complexation of halonium and deuterated bis(2-pyridyl-
ethynyl)benzene by NMR spectroscopy as well as DFT calcu-
tion of halonium in an N–X+–N system in X(cpeb) (X = Cl+, Br+)
using the ORCA package (version 2.9.1).22 The diagram of
lation in which the bromonium cation is included at the
midpoint of the nitrogen atoms of two pyridyl groups.19 The
optimization calculation for I+(cpeb) did not converge well due
to the instability of the complex.24
These results can be rationalized by the fitting of the halo-
nium ions and the cavity of cpeb. The N1–N1* distance in
cpeb analyzed by X-ray crystallography is 4.30 Å which is
shorter than the corresponding N⋯N distance in bis(2,6-
dimethylpyridyl)iodonium dibromoiodate, [I(C5H3N-2,6-
Me2)]+[BrIBr]− (N⋯N = 4.588 Å),25 and slightly longer than that
in bis(quinoline)bromine perchlorate, [Br(quinoline)2]ClO4,
(N⋯N = 4.285 Å),26,27 indicating that the N⋯N distance in
cpeb is not long enough for inclusion of I+ and appropriate for
Br+ inclusion. A relatively smaller Cl+ tends to coordinate
Fig. 3 Structure of the inclusion complex of cpeb with (a) smaller (Cl+,
H+) and (b) larger (Br+, Ag+, Pd2+, Zn2+) guest ions.
strongly to one nitrogen to form an unsymmetric inclusion
structure. Similar analysis by calculation for the complex
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Experimental
General
1,2-Diethynylbenzene29 was prepared by literature methods.
1
Other chemicals were commercially available. H and 13C{1H}
NMR spectra were acquired on a Varian MERCURY-300
(300 MHz) and a Bruker AV-400M (400 MHz). Fast atom bom-
bardment mass spectra (FABMS) and HR-ESI-TOF-MS were
obtained on a JEOL JMS-700 (matrix, 2-nitrophenyl n-octyl
ether (NPOE)) and a micrOTOF II (Bruker) spectrometer
respectively. Elemental analyses were carried out with a
Yanaco MT-5 CHN autorecorder. UV-visible absorption spectra
were measured on a JASCO V-530 for 1.0 × 10−2 mM solutions
in CH2Cl2. Photoluminescence spectra were recorded for 1.0 ×
10−3 M solutions in CH2Cl2. Quantum yields were estimated by
comparison of the standard solution of quinine sulfate (1.0 M,
ϕ = 0.546). The lifetime of the emission from the compounds
was measured using the Time-Resolved Absorption and emis-
sion Spectra Analysis System (TRASAS) in our institute equipped
Fig. 5 The (a) HOMO and (b) LUMO of the ground state of Cl(cpeb) cal-
culated by DFT calculation (PBE38/TZVP).
X(cpeb) (X = H, Zn, Ag) suggests a symmetric structure for large
guest ions (Zn, Ag) and an unsymmetric structure for a relatively
smaller ion (H) which is also explained by the size of the guest
ions.
Fig. 5 shows the calculated HOMO and LUMO of the
ground state of Cl+(cpeb) which has an unsymmetric ground
state with a short distance between the Cl+ and one nitrogen,
as described above; LUMO orbital is localized from Cl+ to phe-
nylene units. Br(cpeb) was calculated to have a symmetric
ground state structure which has LUMO spread over the cpeb
molecule.
Since the emission from a symmetric structure (LUMO to
HOMO) is derived from a forbidden transition,28 the observed
emission from Br+(cpeb) probably involves formation of an
unsymmetric transition state generated by intramolecular
relaxation after excitation. The lower quantum yield of emis-
sion from Br+(cpeb) (ϕ = 0.05) than that from Cl+(cpeb) (ϕ =
0.12) and relatively longer lifetime of emission from Br(cpeb)
(τ0 = 10 ns) are ascribed to the large structural change from
the symmetric ground state structure of Br(cpeb) to the tran-
sition state with an unsymmetric structure. The absorption
shoulder peak at 400 nm observed in the mixture of cpeb and
Cl+OTf is assigned to charge transfer (CT)-type absorption by
TD-DFT (PBE38/TZVP) calculation suggesting that the emis-
sion of X+(cpeb) (calculated to be 504 nm with oscillator
strength f = 0.04 (for Cl) and 457 nm with f = 0.03 (for Br))
mainly consists of a transition from HOMO to LUMO. TD-DFT
(PBE38/TZVP) calculation suggests that the absorption peaks
of cpeb observed at 259, 318 and 340 nm mainly consist of a
transition from HOMO−1 to LUMO (calcd 285.9 nm), HOMO
to LUMO (calcd 304.8 nm), and HOMO to LUMO+1 (calcd
340.4 nm, forbidden transition) respectively.
with an Nd-YAG laser (λex
= 355 nm, [compound] =
0.00001 mM, in CH2Cl2). Solid state photoluminescence
spectra were recorded using an absolute PL quantum yield
measurement system (C9920-01, Hamamatsu Photonics K. K.)
equipped with a Xe light source, a monochromator, an inte-
grating sphere, and a CCD spectrometer.
Synthesis of 1,2-bis(6-bromo-2-ethynylpyridyl)benzene (2)
A THF solution (300 mL) of 2,6-dibromopyridine (19.0 g,
80 mmol) and Et3N (27.8 mL, 200 mmol) was degassed by
freeze–pump–thaw cycles. To the solution, CuI (190 mg,
1.0 mmol), PdCl2(PPh3)2 (702 mg, 1.0 mmol) and 1,2-diethy-
nylbenzene (2.52 g, 20 mmol) were successively added and
then the mixture was stirred for 48 h at 50 °C. After removal of
the solvent by evaporation, the organic products were dissolved
in CH2Cl2 (300 mL), and the solution was washed with sat.
NH4Cl(aq) (100 mL). The separated organic phase was dried
over MgSO4, filtered and evaporated to form a crude product
as a yellow oil. Purification by silica gel column chromato-
graphy (eluent: CH2Cl2–hexane = 2/1, Rf = 0.65) yielded 1,2-bis-
(6-bromo-2-ethynylpyridyl)benzene (2) (4.01 g, 9.15 mmol,
46%) as a yellow powder. Anal. Calcd for C20H10Br2N2, C:
54.83, H: 2.30, N: 6.39%. Found, C: 54.99, H: 2.22, N: 6.26%.
1H NMR (300 MHz, CDCl3, r.t.) δ 7.85 (d, 2H, 3-C5H4N, J =
8 Hz), 7.64 (dd, 2H, m-C6H4, J = 6, 3 Hz), 7.63 (t, 2H, 4-C5H4N,
J = 8 Hz), 7.47 (d, 2H, 5-C5H4N, J = 8 Hz), 7.40 (dd, 2H, o-C6H4,
J = 6, 3 Hz). 13C{1H} NMR (100 MHz, CDCl3, r.t.) δ 144.0, 141.8,
138.7, 132.3, 129.3, 127.7, 127.0, 125.6, 92.3 (CuC), 89.2
(CuC). HRMS (ESI-TOF-MS): calcd for C20H11Br2N2 438.9383;
Conclusion
We synthesized a facile shape-persistent azamacrocyclic mole- found, m/z 438.9253 [M + H+]+.
cule, cpeb, having two pyridyl units and observed its size selec-
Synthesis of C6H4-1,2-(CuC–H)(CuC–CPDMS)
tive inclusion of halonium ions, Cl+, Br+ and I+. Cl+ and Br+
form unsymmetric and symmetric inclusion complexes, A THF–MeOH (100 mL/100 mL) solution containing C6H4-1,2-
respectively, while I+ does not form an inclusion complex. The (CuC–TMS)2 (2.71 g, 10 mmol) and K2CO3 (6.9 g, 50 mmol)
different types of inclusion of cpeb for halonium as well as Ag, was stirred at room temperature for 12 h. The separated
Pd, Zn and H are ascribed to the matching and mismatching organic phase was dried over MgSO4 and evaporated to yield
of the size of guest ions and the cavity of cpeb.
C6H4-1,2-(CuC–H)2 which was dissolved in dry THF (80 mL).
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To the solution, EtMgBr (1 M solution in THF, 10 mL, 100 mL), and the solution was degassed by freeze–pump–thaw
10 mmol) was added at 0 °C, and then the mixture was stirred cycles. To the mixture, CuI (9.5 mg, 0.05 mmol) and
for 3 h. To the resulting solution ClSiMe2{(CH2)3CN} (1.49 g, PdCl2(PPh3)2 (35 mg, 0.005 mmol) were successively added,
11 mmol) was added at room temperature, and then the and the solution was stirred at 50 °C for 48 h. The resulting
mixture was stirred for 24 h. The product was extracted with mixture was concentrated by evaporation. The obtained
CH2Cl2 and washed with water. The separated organic phase organic product was dissolved in CH2Cl2 (200 mL) and the
was dried over MgSO4, filtered and evaporated to form a crude solution was washed with sat. NH4Cl(aq) (100 mL). The separ-
product as a yellow oil. Purification by silica gel column ated organic phase was dried over MgSO4, filtered and evapor-
chromatography (eluent: CH2Cl2–hexane = 1/1, Rf = 0.4) ated to yield a crude product as a black solid. Purification by
yielded C6H4-1,2-(CuC–H)(CuC–CPDMS) (2.31 g, 8.7 mmol, silica gel column chromatography (eluent: CH2Cl2–hexane =
87%) as a colorless oil. 1H NMR (300 MHz, CDCl3, r.t.) 2/1, Rf = 0.40) yielded cpeb (834 mg, 1.37 mmol, 34%) as a
δ 7.51–7.45 (m, 2H), 7.32–7.27 (m, 2H), 3.33 (s, 1H, uC–H), 2.44 brown powder. 1H NMR (400 MHz, CD2Cl2, r.t.) δ 7.34 (dd, 4H,
(t, 2H, CH2CN, J = 6.8 Hz), 0.86 (m, 2H, CH2), 0.27 (s, 6H, Me).
o-C6H4, J = 6, 3 Hz), 7.44 (d, 4H, 3-C5H4N, J = 8 Hz), 7.59 (dd,
4H, m-C6H4, J = 6, 3 Hz), 7.63 (t, 2H, 4-C5H4N, J = 8 Hz).
13C{1H} NMR (100 MHz, CD2Cl2, r.t.) δ 144.3 (2-C5H4N), 136.8
(4-C5H4N), 133.1 (o-C6H4), 129.5 (m-C6H4), 126.9 (3-C5H4N),
Synthesis of 1-(6-[{(3′-cyanopropyl)dimethylsilyl}acetyl]-2-
ethynylpyridyl)-2-(6-bromo-2-ethynylpyridyl)benzene (1)
A THF solution (20 mL) of 2 (1.75 g, 4.0 mmol) and Et3N 125.9 (ipso-C6H4), 93.3 (CuC), 87.6 (CuC). HRMS (ESI-
(40 mL, 290 mmol) was degassed by freeze–pump–thaw cycles. TOF-MS): calcd for C30H14N2 + Na: 425.1055, found: m/z =
To the solution, CuI (38 mg, 0.20 mmol), PdCl2(PPh3)2 425.1049 [M + Na+].
(140 mg, 0.20 mmol) and C6H4-1,2-(CuC–H)(CuC–CPDMS)
(1.06 g, 4.0 mmol) were successively added, and then the
mixture was stirred for 36 h at 50 °C. The resulting mixture
was concentrated by evaporation. The obtained organic
product was dissolved in CH2Cl2 (300 mL) and the solution
was washed with sat. NH4Cl(aq) (100 mL). The separated
organic phase was dried over MgSO4, filtered and evaporated
to form a crude product as a yellow oil. Purification by silica
gel column chromatography (eluent: CH2Cl2–hexane = 2/1, Rf =
Synthesis of Pd(OCOCF3)2(cpeb)
A CH2Cl2 solution of cpeb (50 mM, 10 mL, 5 μmol) was added
to the THF solution of CF3COOH (5.0 mM, 1.2 mL, 6.0 μmol),
and the mixture was stirred at 50 °C for 12 h. The separated
brown solid of Pd(OCOCF3)2(cpeb) was collected by filtration
(2.6 mg, 3.5 μmol, 70%). HRMS (ESI-TOF-MS): calcd for
C30H14N2Pd:
508.0182,
found:
m/z
=
508.0213
[M-2(OCOCF3)2]+. Low solubility of the compound prevented
NMR measurements. A similar reaction in CDCl3 without stir-
ring yielded Pd(OCOCF3)2(cpeb) as single crystals which were
subjected to X-ray structure analyses.
1
0.40) yielded 1 (834 mg, 1.37 mmol, 34%) as a brown solid. H
NMR (300 MHz, CDCl3, r.t.) δ 7.91 (d, 1H, C5H4N, J = 8 Hz),
7.85 (d, 1H, C5H4N, J = 8 Hz), 7.79 (t, 1H, p-C5H4N, J = 8 Hz),
7.63–7.66 (m, 2H, C6H4), 7.58 (dd, 1H, C6H4, J = 6, 3 Hz), 7.54
(t, 1H, p-C5H4N, J = 8 Hz), 7.49–7.53 (m, 2H, C6H4, C5H4N),
7.37–7.41 (m, 3H, C6H4, C5H4N), 7.34 (dd, 2H, C6H4, J = 6,
3 Hz), 2.34 (t, 2H, CH2, J = 7 Hz), 1.73–1.83 (m, 2H, CH2,
C5H4N), 0.80 (m, 2H, CH2), 0.23 (s, 6H, Me). 13C{1H} NMR
(100 MHz, CDCl3, r.t.) δ 144.0, 143.9, 143.7, 141.8, 138.8, 136.8,
132.6, 132.5, 132.2, 132.2, 129.3, 129.1, 129.0, 128.7, 127.7,
127.4, 127.2, 126.7, 125.9, 125.8, 125.5, 125.1, 119.9 (CN),
104.5 (CuC), 97.4 (CuC), 93.1 (CuC), 92.3 (CuC), 92.2
(CuC), 89.3 (CuC), 88.1 (CuC), 88.0 (CuC), 20.8 (CH2), 20.6
(CH2), 15.7 (CH2), −1.7 (Me). Anal. Calcd for C36H26BrN3Si, C:
71.05, H: 4.31, Br: 13.13, N: 6.90%. Found, C: 70.33, H: 4.24,
Br: 12.71, N: 6.60%. HRMS (ESI-TOF-MS): calcd for
C36H26BrN3Si + Na: 630.0977, found: m/z = 630.0970 [M + Na+].
X-ray structure analyses
Crystals of cpeb and Pd(OCOCF3)2(cpeb) suitable for X-ray
diffraction study were obtained by recrystallization from
CH2Cl2 (cpeb (Cmce (no. 64)), CH2Cl2/HCl(aq) (cpeb (Pbca (no.
61)) and CDCl3 (Pd(OCOCF3)2(cpeb)). All measurements were
made on a Rigaku AFC-10R Saturn or Bruker ApexII CCD diffr-
actometer with graphite monochromated Mo-Kα radiation.
Calculations were carried out using a program package Crystal
Structure™ for Windows.30 All hydrogen atoms were included
at the calculated positions with fixed thermal parameters.
Acknowledgements
Synthesis of cpeb
A THF–MeOH solution (THF–MeOH = 50 mL/50 mL) contain- We thank our colleagues in the Chemical Resources Laboratory
ing 1 (609 mg, 1.0 mmol) and K2CO3 (690 mg, 5.0 mmol) was of the Tokyo Institute of Technology for their technical
stirred at room temperature for 12 h. After removal of the support and discussions, Dr Yoshihisa Sei for X-ray crystallo-
solvent by evaporation, the obtained organic product was dis- graphy and life-time measurements in the Center for Advanced
solved in CH2Cl2 (300 mL) and the solution was washed with Materials Analysis of our institute, and Dr Takanori Fukush-
water (50 mL). The separated organic phase was dried over ima and Dr Yoshiaki Shoji for measurement of emission
MgSO4, filtered and evaporated to yield C6H4-1-(CuC– spectra (solid state). This work was supported by a Grant-Aid
C6H3N-6–CuC–C6H4-2–CuCH)-2-(CuC–C6H3N–Br) as a yellow for Scientific Research for Young Scientists from the Ministry
oil. The above product was dissolved in THF–Et3N (100 mL/ of Education, Culture, Sports, Science and Technology, Japan
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