Array-Based Clusters of Copper with Largely Exposed Metal Sites for Promoting Catalysis

Most ligand-stabilized metal nanoclusters feature a core–shell or polyhedron-derived metal framework, in which the metal active sites would be blocked by either metal–ligand interfacial shells or surface passive units. We report, in this work, a strategy of largely exposing metal sites and thus promoting catalysis via constructing metal nanoclusters with array-based geometry. Exampled here are a pair of Cu 8 clusters with polyhedron-derived ([Cu 8 (RS) 6 (PPh 3 ) 4 (MeCN) 4 H] +, where RS is 3,5-bis(trifluoromethyl)benzenethiol) and array-based ([Cu 8 (Tf-dpf) 4 (NO 3 ) 2 ](NO 3 ) 2, Tf-dpf is N, N ′-di(5-trifluoromethyl-2-pyridyl) formamidinate) structure, respectively. In sharp contrast to the cubic Cu 8 cluster whose metal core has been totally covered by ligands, the array-based analogue displays largely uncoordinated metal sites. As a result, the array-based Cu 8 cluster exhibits significantly enhanced activity in catalytic hydrogenation reactions in comparison to the cubic one. In addition, the array-based Cu 8 cluster shows excellent catalytic performance in the “aldehyde–acetylene–amine” A 3 -coupling reaction for the synthesis of propargylamines. The reaction can be converted almost perfectly with a rather low amount of cluster, which further reflects its potential catalytic application.