Unravelling the Roles of Solvophobic Effects and π⋅⋅⋅π Stacking Interactions in the Formation of [2]Catenanes Featuring Di-(N-Heterocyclic Carbene) Building Blocks

A series of [2]catenanes has been prepared from di-NHC building blocks by utilizing solvophobic effects and/or π⋅⋅⋅π stacking interactions. The dinickel naphthobiscarbene complex syn-[1] and the kinked biphenyl-bridged bipyridyl ligand L² yield the [2]catenane [2-IL](OTf)₄ by self-assembly. Solvophobic effects are pivotal for the formation of the interlocked species. Substitution of the biphenyl-linker in L² for a pyromellitic diimide group gave ligand L³ , which yielded in combination with syn-[1] the [2]catenane [3-IL](OTf)₄ . This assembly exhibits enhanced stability in diluted solution, aided by additional π⋅⋅⋅π stacking interactions. The π⋅⋅⋅π stacking was augmented by the introduction of a pyrene bridge between two NHC donors in ligand L⁴ . Di-NHC precursor H₂ -L⁴ (PF₆ )₂ reacts with Ag₂ O to give the [Ag₂ L⁴ ₂ ]₂ [2]catenane [4-IL](PF₆ )₄ , which shows strong π⋅⋅⋅π stacking interactions between the pyrene groups. This assembly was readily converted into the [Au₂ L⁴ ₂ ]₂ gold species [5-IL](PF₆ )₄ , which exhibits exceptional stability based on the strong π⋅⋅⋅π stacking interactions and the enhanced stability of the Au-C_NHC bonds.