Synthesis of N-Heterocyclic Carbenes and Their Complexes by Chloronium Ion Abstraction from 2-Chloroazolium Salts Using Electron-Rich Phosphines

N‐Heterocyclic carbenes (NHCs) are commonly prepared by deprotonation of azolium salts using strong anionic bases. This reaction is often unselective, yielding alkali metal NHC complexes or dimerized NHCs. Alternatively, free NHCs are obtained by the dechlorination of 2‐chloroazolium salts using electron‐rich phosphines. PPh₃, PCy₃, and PtBu₃ are unsuitable for Cl⁺ abstraction, while the sterically encumbered tris(1,3‐tert‐butylimidazolidin‐2‐ylidenamino)phosphine 1 selectively removes Cl⁺ from 2‐chloroazolium salts. Since bulky 1 does not bind to metal complexes, it was used for the preparation of NHC complexes via in situ Cl⁺ abstraction from 2‐chloroazolium salts. The dechlorination was employed for the site‐selective monometallation with Ir^I, Ir^III, Rh^I, Rh^III, and Ru^II of a bis‐NHC precursor composed of a 2‐chlorobenzimidazolium and a 2‐chlorobenzimidazole group, followed by the preparation of the heterobimetallic Ir^III/Pd^II complex [18](BF₄)₂ by a dechlorination/oxidative addition reaction sequence.

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

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.

Strategy for the Construction of Diverse Poly-NHC-Derived Assemblies and Their Photoinduced Transformations

A series of supramolecular assemblies of types [Ag₈ (L)₄ ](PF₆ )₈ and [Ag₄ (L)₂ ](PF₆ )₄ , obtained from the tetraphenylethylene (TPE) bridged tetrakis(1,2,4-triazolium) salts H₄ -L(PF₆ )₄ and Ag^I ions, is described. The assembly type obtained dependends on the N-wingtip substituents of H₄ -L(PF₆ )₄ . Changes in the lengths of the N4-wingtip substituents enables controlled formation of assemblies with either [Ag₄ (L)₂ ](PF₆ )₄ or [Ag₈ (L)₄ ](PF₆ )₈ stoichiometry. The molecular structures of selected [Ag₈ (L)₄ ](PF₆ )₈ and [Ag₄ (L)₂ ](PF₆ )₄ assemblies were determined by X-ray diffraction analyses. While H₄ -L(PF₆ )₄ does not exhibit fluorescence in solution, their tetra-NHC (NHC=N-heterocyclic carbene) assemblies do upon NHC-metal coordination. Upon irradiation, all assemblies undergo a light-induced, supramolecule-to-supramolecule structural transformation by an oxidative photocyclization involving phenyl groups of the TPE core, resulting in a significant change of the luminescence properties.

Multicomponent Porphyrin-Based Tetragonal Prismatic Metallacages and their Photophysical Properties

Multicomponent coordination-driven self-assembly has proved to be a convenient approach to prepare advanced supramolecular coordination complexes (SCCs), especially for those with three-dimensional structures. Herein, we report the preparation of three tetragonal prismatic cages via the self-assembly of Pt(PEt₃)₂(OTf)₂, three different linear dipyridyl ligands and porphyrin-based sodium benzoate ligands. Due to the efficient charge separation in the coordination process of Pt(PEt₃)₂(OTf)₂ with pyridine and carboxylic acid and the directionality of metal-coordination bonds, these cages were prepared in high isolated yields (more than 90%). The absorption and emission properties as well as the singlet oxygen quantum yields of these cages were also studied, showing their potential applications as contrast agents for bio-imaging and photosensitizers for photodynamic therapy.