High-nuclearity Cu hydride nanoclusters of Cu22H19 and Cu20H13 consolidated by an N-containing triphosphine ligand: synthesis, characterization and catalysis

Abstract

The synthesis of copper hydride nanoclusters and the determination of their atomically precise structures are beneficial for gaining an in-depth understanding of the structure–property relationship. N,P-containing ligands with a combination of hard and soft donors exhibit versatile coordination modes which are promising for mediating the structures of Cu hydride nanoclusters and their properties. Herein, two Cu hydride nanoclusters, [Cu₂₂H₁₉(NP₃)₄(CH₃CN)₄]·(ClO₄)₃ (1) and [Cu₂₀H₁₃(NP₃)₄(CH₃CN)₃Cl₄]·(ClO₄)₃ (2), based on the tripodal N-containing triphosphine ligand of tris(diphenylphosphino-ethyl)amine (NP₃) are synthesized, and their compositions and structures are determined by ¹H NMR, high-resolution ESI-MS and single-crystal X-ray diffraction. The location of hydrides is established based on the optimized model obtained by DFT calculations. In cluster 1, the skeleton of 22 Cu can be described as a fusion of two distorted Cu₁₃ centred icosahedra by sharing four Cu atoms, and each NP₃ ligand exhibits a tridentate mode (P, P, P) to bind one Cu₃ triangular plane. The skeleton of 20 Cu in cluster 2 can be described as a Cu₁₃ centred icosahedron bridging a cap-shaped Cu₇ moiety, and the ligands exhibit two binding modes, the tridentate (P, P, P) and the tetradentate (N, P, P, P) modes, to consolidate these Cu atoms. The synthesis of clusters 1 and 2 is similar. The involvement of Cl⁻ anions and the flexibility of NP₃ play a synergistic role in mediating the construction of cluster 2, resulting in a structure distinct from that of cluster 1. Their deuteride analogues, 1_D and 2_D, are also synthesized for comparison. Cluster 2 exhibits better catalytic activity than cluster 1 for the reduction of 4-nitrophenol to 4-aminophenol.