A Strategy for the Construction of Triply Interlocked Organometallic Cages by Rational Design of Poly-NHC Precursors

Three-dimensional (3D) triply interlocked
catenanes are a family
of chemical topologies that consist of two identical, mechanically
interlocked coordination cage components with intriguingly complex
structures. Although only a few successful constructions of 3D interlocked
catenanes have been achieved to date via metal-mediated assembly,
these complex structures have thus far only been targeted by metal–nitrogen/oxygen
coordination techniques. Here, taking advantage of rational ligand
design, we report the efficient construction of a series of 3D triply
interlocked [2]­catenanes of the formula [Ag3L2]2, wherein the metal ions exclusively form bonds to N-heterocyclic
carbene (NHC) units, and their subsequent transmetalation to the corresponding
[Au3L2]2 gold analogues. The formation
and transmetalation reactions proceed under mild conditions and are
generally applicable. A series of characterization techniques were
applied to confirm the formation and structure of the desired 3D triply
interlocked architectures: multinuclear NMR spectroscopy, ESI-MS,
and single-crystal X-ray diffraction analysis. The solid-state structure
of [Ag3(1a)2]2(PF6)6 unambiguously confirms the existence of a 3D
catenane that consists of two identical, mechanically interlocked
trinuclear hexacarbene cage components. The interlocking of two 3D
cages into a [2]­catenane is driven by the efficient π···π
stacking of triazine–triazine stacks with cooperative interactions
between imidazo­[1,5-a]­pyridine subunits. Notably,
the triply interlocked organometallic cages exhibit good stability
toward various organic solvents, concentrations, and temperatures,
and no disassembly occurred in the presence of coronene or pyrene.
The future construction of mechanically interlocked architectures
using metal–carbene bonds rather than metal–nitrogen
bonds may provide assemblies with interesting properties for as-yet-unimagined
applications in fields such as sensors and molecular electrical conductors.