Cavitand‐Based Pd‐Pyridyl Coordination Capsules: Guest‐Induced Homo‐ or Heterocapsule Selection and Applications of Homocapsules to the Protection of a Photosensitive Guest and Chiral Capsule Formation

• Published in: Chemistry, an Asian journal Vol. 15; no. 14; pp. 2218 - 2230
• Main Authors: Nakamura, Munechika, Tsukamoto, Yoshimi, Ueta, Takuro, Sei, Yoshihisa, Fukushima, Takanori, Yoza, Kenji, Kobayashi, Kenji
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 16.07.2020
• Subjects: cage compounds; cavitands; Chemistry; Chirality; Coordination; Encapsulation; host-guest systems; Photosensitivity; self-assembly; supramolecular chemistry
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.202000603

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 {12 ⋅ [Pd(dppp)]4}8+ ⋅ (TfO−)8 (C1) or {22 ⋅ [Pd(dppp)]4}8+ ⋅ (TfO−)8 (C2), respectively, through Pd−Npy coordination bonds. A 1 : 1 : 4 mixture of 1, 2, and Pd(dppp)(OTf)2 produced a mixture of homocapsules C1, 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 homocapsules C1 and C2 or heterocapsule C3 was controlled by guest‐induced encapsulation under thermodynamic control. Applications of Pd−Npy coordination capsules with the use of 1 were demonstrated. Capsule C1 serves as a guard nanocontainer for trans‐4,4′‐diacetoxyazobenzene to protect against the trans‐to‐cis photoisomerization by encapsulation. A chiral capsule {12 ⋅ [Pd((R)‐BINAP)]4}8+ ⋅ (TfO−)8 (C5) was also constructed. Capsule C5 induces 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. Expanded pyridyl‐cavitands form Pd−Npy coordination capsules. These capsules have multiple functions: (1) control of self‐sorting on homo‐ or heterocapsule selection by guest‐induced encapsulation, (2) a guard nanocontainer for a photoresponsive guest, and (3) a chiral capsule that induces supramolecular chirality with respect to a prochiral guest.