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

The intramolecular bissilylation of 3,3,6,6,7,7,10,10-octamethyl-3,6,7,10-tetrasilacyclodecyne (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', 5'-octamethyl-2,2',5,5'-tetrasilabicyclopentylidene (5a). 2,2,2',2',5,5,5',5'-Octamethyl-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. The structures of 5a, (2,2,2',2',5, 5,5',5'-octamethyl-2,2',5,5'-tetrasilabicyclopentylidene)bis[(tetrahydrofuran)lithium(I)] (6a), and (2,2,2',2',5, 5,5',5'-octamethyl-2,2',5, 5'-tetrasilabicyclopentylidene)bis[(tetrahydrofuran)sodium(I)] (6b) were studied by X-ray crystallography as well as NMR spectroscopic means. The central anionic C-C bond is not twisted for 6a, whereas it is twisted by 17.1 degrees for 6b.