Novel Family of Nickel (II)-Cornered Molecular Cages with Bis-NHC Bridging Groups

Abstract

Metal-directed self-assembly has been widely studied in the last decades since Lehn and co-workers demonstrate the spontaneous self-assembly of dinuclear helicates from 2,2’-bipyridine and copper(I). Thereafter, a substantial number of different metallosupramolecular structures were reported. Some of these structures exhibit internal cavities suitable for encapsulating small molecules. This kind of interactions between host (metallosupramolecular structure) and guest (small molecule) are often evidenced by NMR spectroscopy. Pioneered by the works performed by Fujita’s group, many groups have been investigating this interesting topic, with important contributions made by Jin and Stang. Fujita was the first in synthesizing and studying in detail a Metal-Cornered Molecular Cage. This metallosupramolecular structure, was built up from end-capped Pd(II) ions and 4,4’-bipyridine building blocks.Fujita’s metallosupramolecular structure, and most other metal-based cages described to date are derived from polydentate ligands featuring either nitrogen or oxygen donor atoms coordinating to the metal centers.

While supramolecular assemblies built from polydentate Werner-type ligands are well documented, those made from ligands with carbon donors are quite rare, although some examples have been described. Most of the metal-based cages based from the use of N-heterocyclic carbenes have been described by the group of Hahn and coworkers