Cavitand-Based Pd-Pyridyl Coordination Capsules: Guest-Induced Homo- or Heterocapsule Selection and Applications of Homocapsule to Protection of Photosensitive Guest and Chiral ….

A 2 : 4 mixture of tetrakis[4-(4-pyridyl)phenyl]cavitand (1) or tetrakis[4-(4-pyridyl)phenylethynyl]cavitand (2) and Pd(dppp)(OTf)(2)self-assembles into a homocapsule {1(2) . [Pd(dppp)](4)}(8+) . (TfO-)(8)(C1) or {2(2) . [Pd(dppp)](4)}(8+) . (TfO-)(8)(C2), respectively, through Pd-Npy coordination bonds. A 1 : 1 : 4 mixture of1,2, and Pd(dppp)(OTf)(2)produced a mixture of homocapsulesC1,C2, and a heterocapsule {1 . 2 . [Pd(dppp)](4)}(8+) . (TfO-)(8)(C3) in a 1 : 1 : 0.98 mole ratio. Selective formation (self-sorting) of homocapsulesC1andC2or heterocapsuleC3was controlled by guest-induced encapsulation under thermodynamic control. Applications of Pd-Npy coordination capsules with the use of1were demonstrated. CapsuleC1serves as a guard nanocontainer fortrans-4,4 '-diacetoxyazobenzene to protect against thetrans-to-cisphotoisomerization by encapsulation. A chiral capsule {1(2) . [Pd((R)-BINAP)](4)}(8+) . (TfO-)(8)(C5) was also constructed. CapsuleC5induces supramolecular chirality with respect to prochiral 2,2 '-bis(alkoxycarbonyl)-4,4 '-bis(1-propynyl)biphenyls by diastereomeric encapsulation through the asymmetric suppression of rotation around the axis of the prochiral biphenyl moiety.