Topology-Dependent Synthesis, Structures, and Bonding Interactions of Uranium Polyarene Complexes

Metal polyarene complexes have attracted great attention in recent years because of their appealing electronic structures and readily tunable properties and reactivity. While main group and transition metal polyarene complexes have been well studied with various degrees of reduction and different coordination modes, f-block metal polyarene complexes are rare. Here we report the synthesis of a series of uranium polyarene complexes supported by ferrocene diamide ligands. X-ray crystallography shows that the structures of uranium polyarene complexes are dependent on the topology of polyarenes. While linear polyarenes form mononuclear compounds, nonlinear polyarenes prefer an inverse-sandwich structure with a mu-eta 6,eta 6-coordination mode. Combined experimental and computational studies unveil that mononuclear uranium polyarene complexes are best described as bidentate with a three-center two-electron (3c-2e) sigma bond, whereas inverse-sandwich uranium polyarene complexes are bound through two delta bonds. The correlation between the topology of polyarenes and the coordination mode of uranium polyarene complexes can be rationalized by the electronic structures and bonding interactions as well as the relative energies of coordination isomers.