DIANION DIALKALI METALS OF 2,2',5,5'-TETRASILABICYCLOPENTYLIDENE - SYNTHESIS AND CRYSTAL-STRUCTURES

The intramolecular bissilylation of 7,7,10,10-octamethyl-3,6,7,10-tetr asilacyclodecyne (4a) at 110 degrees C with a catalyst of Pd(OAc)(2)/1 ,1,3,3-tetramethylbutyl isocyanide under 5000 bar produced 2,2,2',2',5 ,5,5', '-octamethyl-2,2',5,5'-tetrasilabicyclopentylidene (5a). -Octam ethyl-2,2',5,5'-tetragermabicyclopentylidene (5b) was also synthesized by the same method. The reaction of 5a with alkali metals (Li, Na, K, Rb, and Cs) in THF gave the corresponding dianion dialkali metals. Th e structures of 5a, (2,2,2',2',5, icyclopentylidene)bis[(tetrahydrofur an)lithium(I)] (6a), and (2,2,2',2',5, 5,5',5'-octamethyl-2,2',5, bicy clopentylidene)bis[(tetrahydrofuran)sodium(I)] (6b) were studied by X- ray crystallography as well as NMR spectroscopic means. The central an ionic C-C bond is not twisted for 6a, whereas it is twisted by 17.1 de grees for 6b.