Carbene-Mediated Stabilization of Reactive Copper–Chalcogenide Clusters: Defining the Operational Limits of Strong-Field Ligands in Multinuclear Nanoassemblies

Abstract Atomic precision in metal–sulfur assemblies offers a transformative pathway to programmable nanomaterials, with applications spanning energy-efficient optoelectronics to highly selective CO2 reduction catalysis. However, the inherent lability of the metal–sulfur bond remains a formidable barrier to the rational design of robust frameworks. While strong-field ligands such as cyclic (alkyl)(amino)carbenes (CAACs) are gold-standard scaffolds for stabilizing reactive monometallic centers, their impact on the structural fidelity of multinuclear clusters remains elusive. Herein, we report a combined experimental and theoretical investigation of a CAAC-supported Cu8(μ3-S)4 cluster─a high-impact prototype for metal-chalcogenide systems with relatively weak metal–sulfur bonds. Through electrochemical and protonation studies, we demonstrate that while the potent σ-donor ability of the CAAC ligand successfully enforces solution integrity and thermal resilience, the structural boundaries of the multinuclear scaffold under chemical stress are ultimately governed by the core topology and metal–sulfur bond lability rather than local metal–ligand bonding. In-depth density functional theory (DFT) analysis demonstrates that while the CAAC ligands actively strengthen the peripheral Cu–S bonds via a pronounced inverse trans influence, the trigonal pyramidal (μ3-S) motifs remain vulnerable to proton-induced bond labilization and oxidative S–S coupling. Our findings establish that the design rules for multinuclear assemblies diverge fundamentally from monometallic species: whereas CAACs successfully passivate peripheral coordination sites to thermal decomposition, they do not preclude internal, core-mediated degradation pathways. These clear boundaries reveal that achieving structural durability in functional base metal–sulfur assemblies requires pairing strong local donors with supramolecular and/or multidentate ligand strategies designed explicitly to buttress the metal–sulfur core.