Unravelling the Roles of Solvophobic Effects and ??? 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 pi & sdot;& sdot;& sdot;pi 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 pi & sdot;& sdot;& sdot;pi stacking interactions. The pi & sdot;& sdot;& sdot;pi 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 Ag2O to give the [Ag2L42]2 [2]catenane [4-IL](PF6)4, which shows strong pi & sdot;& sdot;& sdot;pi stacking interactions between the pyrene groups. This assembly was readily converted into the [Au2L42]2 gold species [5-IL](PF6)4, which exhibits exceptional stability based on the strong pi & sdot;& sdot;& sdot;pi stacking interactions and the enhanced stability of the Au-CNHC bonds. Different effects have been shown to control the formation of [2]catenanes with different bridges between pyridine donors. The formation of [2-IL](OTf)4 is aided by solvophobic effects and [3-IL](OTf)4 is stabilized by solvophobic effects and pi & sdot;& sdot;& sdot;pi stacking. The pi & sdot;& sdot;& sdot;pi stacking between the pyrene groups is essential for the formation of [4-IL](PF6)4 and [5-IL](PF6)4, where the enhanced stability of [5-IL](PF6)4 is based on the more stable Au-CNHC bonds.+image