An anionic ruthenium sandwich complex featuring the tetrasilacyclobutadiene ligand, [η4-tetrakis(di-tert-butylmethylsilyl)tetrasilacyclobutadiene](η5-pentamethylcyclopentadienyl)ruthenium was synthesized and isolated as its potassium salt [(η4-R4Si4)RuCp*]−·[K+(thf)2] (R = SiMet-Bu2, Cp* = η5-Me5C5), 1−·[K+(thf)2], by the reaction of the tetrasilacyclobutadiene dianion dipotassium salt [R4Si4]2−·[K+(thf)2]2 with 0.25 equiv. of [Cp*RuCl]4 in THF. In its crystalline form, 1−·[K+(thf)2] features a nearly square-planar tetrasilacyclobutadiene ligand.
