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Article

Selective Formation of a Self-Assembling Homo or Hetero Cavitand Cage via Metal Coordination Based on Thermodynamic or Kinetic Control

Masamichi Yamanaka,^† Yoshifumi Yamada,^† Yoshihisa Sei,^‡ Kentaro Yamaguchi,^‡ and Kenji Kobayashi*^†^§

Contribution from the Department of Chemistry, Faculty of Science, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan, Faculty of Pharmaceutical Sciences at Kagawa Campus, Tokushima Bunri University, Shido, Sanuki, Kagawa 769-2193, Japan, and PRESTO, JST, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan

J. Am. Chem. Soc., 2006, 128 (5), pp 1531–1539

DOI: 10.1021/ja0555365

Publication Date (Web): January 12, 2006

†

Shizuoka University.

‡

Tokushima Bunri University.

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

PRESTO.

, skkobay@ipc.shizuoka.ac.jp

Abstract

The selective formation of a homo or hetero cavitand cage composed of two molecules of tetra(4-pyridyl)-cavitand (1), tetrakis(4-cyanophenyl)-cavitand (2), or tetrakis(4-pyridylethynyl)-cavitand (3), and four molecules of Pd(dppp)(OTf)₂ (4) or Pt(dppp)(OTf)₂ (5) has been studied. A 1:1:4 mixture of 1 with more steric restriction, 2 with less coordination ability, and 4 or 5 specifically self-assembled into a hetero cavitand cage 6 or 7, respectively. In contrast, a 1:1:4 mixture of 2, 3, and 4 in CDCl₃ at room temperature assembled into the most labile homo cyanophenyl cavitand cage 8 and the most stable homo pyridylethynyl cavitand cage 9 in a 1:1 ratio. Upon heating at 50 °C, the thermodynamic equilibrium was shifted to a 1:1:1 mixture of 8, 9, and a hetero cavitand cage 10. When 1 equiv of 3 was added to 8 at room temperature, 8, 9, and 10 were formed initially in a 1:1:3 ratio and finally shifted to a 1:1:1 ratio. In the Pt-system, upon addition of 1 equiv of 3 to homo cyanophenyl cavitand cage 11 in CDCl₃ at room temperature, the ratio of hetero to homo cavitand cage (13/12) initially attained was 8.7 and remained above 5.6 at room temperature. Upon heating at 50 °C, 13 was finally converted to 11 and 12. Thus, the selectivity for the self-assembly of the homo or hetero cavitand cage is controlled by the balance between kinetic and thermodynamic stabilities of cages based on a combination of factors such as coordination ability and steric demand of the cavitands.