From Tetragermacyclobutene to Tetragermacyclobutadiene Dianion to Tetragermacyclobutadiene Transition Metal Complexes

The reaction of 3,4-dichlorotetragermetene derivative 2 with Na-2[Fe(CO)(4)] in THF produced a (tetragermacyclobutadiene)tricarbonyliron complex, [{eta(4)-((Bu2MeSi)-Bu-t)(4)-Ge-4}]Fe(CO)(3) 4, which has a slightly folded Ge-4 ring perhaptocoordinated to the Fe center. Structural and spectral characteristics of 4 show a remarkable pi-donating ability of the tetragermacyclobutadiene ligand toward the transition metal, surpassing that of tetrasilacyclobutadiene and cyclobutadiene ligands. Reduction of 2 with KC8 resulted in exclusive formation of the dipotassium salt of the tetragermacyclobutadiene dianion derivative 3(2-).[K+(thf)(2)](2), representing a rare example of a 6 pi-electron compound that, on the basis of its structural and magnetic properties, was recognized as a nonaromatic species. Reaction of 3(2-).[K+(thf)(2)](2) with CpCoI2(PPh3) produced a (cyclopentadienyl)(tetragermacyclobutadiene)cobalt complex, [{eta(4)-((Bu2MeSi)-Bu-t)(4)Ge-4}]CoCp 7, as the first example of a sandwich compound featuring an all-germanium-containing cyclic polyene ligand.