Self-Assembly and Dynamic Equilibrium of Trinuclear and Tetranuclear Cu(I) Supramolecules Featuring nido-Carborane-Supported N-Heterocyclic Carbene Ligands

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Abstract
The self-assembly of metallo-supramolecules has attracted considerable attention in recent decades. These discrete architectures are primarily driven by coordination interactions, typically involving M-N/O (Werner-type) or M-C (organometallic) bonding. However, the use of M-π interactions for constructing these multinuclear complexes remains largely unexplored. In this work, we report the self-assembly of trinuclear and tetranuclear copper(I) complexes driven by a combination of M-π and M-C coordination interactions. These multinuclear Cu(I)-NHC complexes were synthesized from the nido-carborane-supported N-heterocyclic carbene (NHC) precursors and Cu(I) ions. In solution, a dynamic equilibrium between the trinuclear and tetranuclear species was observed, as confirmed by the variable-temperature NMR spectrum. Van't Hoff analysis revealed that the equilibrium is endothermic (ΔHeq = 53.6 kJ mol-1) and entropically driven (ΔSeq = 158 J mol-1 K-1). The solid-state structures of both forms were elucidated through single-crystal XRD analysis. Density functional theory calculations showed that the Cu-CNHC bonds in these complexes are relatively weak (∼100 kJ mol-1, approximately one-third of the strength of typical Cu-CNHC bonds). This is attributed to the strong Coulombic attraction between positively charged Cu(I) and negatively charged nido-carborane ligands (M-π interactions), which significantly reduces the bond strength between Cu(I) and neutral NHC moieties (M-C bonding).
Funding Information
  • National Natural Science Foundation of China (22171063, 22471050)
  • Natural Science Foundation of Zhejiang Province (LY22B010002)

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