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

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, Cu₁₈H₁₆ and Cu₄₀H₃₈, which exhibit similar layered structures and components, albeit differing in size. The larger-sized Cu₄₀H₃₈ with more hydrides was achieved through ligand-length modulation by replacing 1,2-bis(diphenylphosphino)ethane (dppe) in the synthesis of Cu₁₈H₁₆ with 1,5-bis(diphenylphosphino)pentane (dpppe). Cu₄₀H₃₈ 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 Cu₄₀H₃₈ 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.