Discrete metal clusters supported by heavier group-14-element ligands

The construction of discrete transition-metal clusters with characteristic structures and/or chemical properties, e.g., reactivity and catalytic performance, has attracted great attention recently, as such clusters can exhibit functions that cannot be achieved by mononuclear metal complexes. For the precise synthesis of metal clusters, a judicious choice of bridging ligands is crucial, and ligands based on group-15 and group-16 elements have often been used for this purpose. As compounds based on heavier group-14 elements (e.g., Si, Ge, and Sn) are prone to adopt hypercoordinated structures, they can act as effective bridging ligands to produce a series of novel metal clusters. In addition, the strong trans -influence and the σ-electron-donating nature of group-14-element ligands can provide highly coordinatively unsaturated and electron-rich metal clusters with high reactivity. In this review, synthetic methods for the formation of transition-metal clusters surrounded by group-14-element-based ligands are summarized; such clusters have been synthesized via E–H, E–C, and E–E (E = Si, Ge, Sn) bond activation, as well as via the use of group-14 anions or stabilized tetrylenes as ligand precursors. In addition, the unique catalytic activity of the obtained metal clusters is also summarized. • Compounds based on heavier group-14 elements act as effective bridging ligands to produce a series of novel metal clusters. • Metal clusters with unique structures as well as chemical functions are constructed by using group-14 elements-based ligands. • Clusters were synthesized via E–H, E–C, and E–E (E = Si, Ge, Sn) bond activation, and via the use of stabilized tetrylenes.