Hydride‐Richest Molecular Complex: Ligand‐Length Facilitated Cu ₄₀ H ₃₈ Nanoclusters Exhibiting High Catalytic Performance for Selective Hydrogenation

Abstract Copper hydride clusters are extensively studied for their significant potential catalysis. Although clusters with a high hydride content are particularly intriguing, they present considerable synthetic challenges. Herein, we report two copper hydride clusters, Cu 18 H 16 and Cu 40 H 38 , which exhibit similar layered structures and components, albeit differing in size. The larger‐sized Cu 40 H 38 with more hydrides was achieved through ligand‐length modulation by replacing 1,2‐bis(diphenylphosphino)ethane (dppe) in the synthesis of Cu 18 H 16 with 1,5‐bis(diphenylphosphino)pentane (dpppe). Cu 40 H 38 is remarkable for i) the highest number of hydrides among known molecular compounds, ii) the highest number of unligated copper atoms and the highest metal‐to‐ligand ratio in copper hydride clusters. Moreover, catalytic studies on the selective hydrogenation of α,β‐unsaturated carbonyl compounds demonstrate that Cu 40 H 38 is a promising catalyst and provide clear structural evidence that a less sterically hindered cluster surface, with a high metal‐to‐ligand ratio, is beneficial for high‐performance catalysis. The findings highlight the importance of surface composition and ligand coverage in catalytic efficiency and offer new avenues for designing high‐performance copper hydride cluster catalysts.