Alkynyl- and phosphine-ligated quaternary Au2Ag2 clusters featuring an Alkynyl-AuAg motif for multicomponent coupling

Abstract

The coordination motif of alkynly with a metal atom is versatile and plays a pivotal role in tailoring the kernel configuration of the atomically precise metal nanoclusters. In this study, we synthesized a new mono-valent Au(I)₂Ag(I)₂(C₁₀H₆NO)₄(Ph₃P)₂ alloy cluster with a very high yield of >90%, which is well characterized by a serial of technologies, e.g. UV-vis, X-ray single crystal diffraction (SCXRD) and FT-IR. The SCXRD analysis shows the alloy cluster is composed of a quadrangular Au₂Ag₂ kernel protected by four alkynyl and two phosphine ligands. Intriguingly, a new divergent alkyne-metal coordination model is revealed in this cluster, the alkynyl ligands selectively bind to Au and Ag atoms via σ- and π-bond configurations and adopt a VI-shaped alkynyl-M motif. It is distinct from the convergent motif observed in big clusters featuring an IV- or V-shaped alkynyl-M motif due to the steric effect. Finally, the titanium oxide-supported Au₂Ag₂ cluster catalysts show good catalytic performance in the multicomponent coupling reaction of alkynes, aldehydes and amines.