C O M M U N I C A T I O N S
conformational alteration of the capsule. The outward-pointing
ureide groups are too far away to form hydrogen bonds directly,
so two ureide groups are connected through one triflate ion. This
In conclusion, we have demonstrated that multifunctionalized
C2V-cavitand 1 and Pt(dppp)(OTf)2 (2) self-assemble into a hybrid
capsule 3 through a hydrogen bond and metal-ligand coordination
bond. Capsule 3 encapsulates a neutral guest molecule with the
assistance of an anion. The kinetics of guest exchange is controllable
by the amounts and/or types of anions or other influences such as
the polarity of the solvent. Further studies on encapsulation by the
capsule are currently underway in our laboratory.
proposed structure shown in Figure 3 was supported by a CPK
molecular modeling study and Vilars’ report.15 Addition of PF6
,
-
NO3-, and TsO- ions was also effective in leading to encapsulation
of 4.12 Titration of a CDCl3 solution of 3 and excess 4 (30 equiv
to 3) with TBAOTs proved that 2 equiv of anions were necessary
to complete the encapsulation.12 A DOSY experiment on a 1:5:5
mixture of 3, 4, and TBAOTs showed similar diffusion coefficients
(D ) (4.35 ( 0.17) × 10-10 m2 s-1) for the cavitand part,
encapsulated 4, and two associated TsO- ions. Halide or acetate
ions were not suitable for the encapsulation of 4 because they caused
partial dissociation of the N-Pt coordination bonds.12
Acknowledgment. This work was supported in part by Grants-
in-Aid from the Ministry of Education, Science, Sports, Culture,
and Technology of Japan (No. 19750111).
Supporting Information Available: Synthetic procedures and
spectral data. This material is available free of charge via the Internet
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Figure 2. 1H NMR spectra (600 MHz, CDCl3) of (a) 1 alone at 298 K; (b)
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Figure 3. Structure of 4-encapsulated hybrid capsule 3 with anion
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Chemical exchange between encapsulated 4 and free 4 was
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release was estimated to be k-1 ) 0.038 s-1 by EXSY calculation.12,16
The guest exchange rate became fast upon addition of 20 equiv of
TBAOTf (k-1 ) 0.064 s-1) or 70 equiv of DMSO (k-1 ) 0.141
1
s-1), although their H NMR spectra remained almost unchanged.
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(12) See Supporting Information.
Metal-ligand coordination bonds strongly maintained the capsular
structure of 3, and external additives such as an anion or use of a
polar solvent had an effect on the ureide moieties and accelerated
the guest exchange. The type of anion influenced the rate of guest
exchange. Guest exchange in the presence of TBAPF6 was slightly
faster than in the original TBAOTf case; the rate constants for guest
release, k-1, was 0.045 s-1. The encapsulation complex with
TBANO3 reduced the guest exchange rate (k-1 ) 0.011 s-1). No
guest exchange was observed for the TBAOTs-containing encap-
sulation complex on the NMR time scale.
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even at 193 K.
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of 4 or TBAOTf.
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