Synthesis and Structure of Heavy Alkali Metal Pentalenides

The solid-state structures of the first rubidium and caesium pentalenides [Rb(THF)]2[Ph4Pn] and [Cs(THF)]2[Ph4Pn] have been determined by single crystal X-ray diffraction. Both were found to be polymeric in the solid state through interactions of the cations with the phenyl substituents, in contrast to their lighter group 1 congeners which are monomeric for lithium and sodium, and THF-bridged for potassium. Both [Rb(THF)]2[Ph4Pn] and [Cs(THF)]2[Ph4Pn] displayed increased eta 8 coordination, demonstrating a shift towards higher hapticities down the group as previously predicted computationally for the parent M2[Pn] complexes (M=group 1 metal). The solid-state structures of the polydentate donor adducts [M(DME)x]2[Ph4Pn] (M=Li, x=1; M=Na, x=2) and [M(Me6TREN)]2[Ph4Pn] (M=K, Rb, Cs) were all monomeric and displayed increased metal-carbon distances and decreased ring slippage values relative to the THF adducts. image