The title compounds were prepared and were found to undergo ring opening and molecular rearrangement under mild conditions and no catalysis, forming a carbon-carbon bond and closing a new chelate ring. The rearrangement product depends on whether R-protons are present. Reactants and products are characterized by crystal structures.This communication describes the preparation of hexacoordinate silacyclobutane complexes and their facile uncatalyzed ring opening and skeletal rearrangement under mild conditions. The rearrangement leads to a neutral pentacoordinate silicon complex, involving carbon-carbon bond formation and closure of a new chelate-ring. Silacyclobutane chemistry 1 is of considerable interest, due to its facile ring opening and consequent reactivity in anionic polymerization. 2 Its thermal 3 and photochemical 3a,4,5 reactivity has been reported, forming silenes and disilacyclobutanes. 3 Silacyclobutanes undergo reactions with carbenes, 6 aldehydes, and epoxides. 7 However, all of these reactions require strong bases, thermolysis at elevated temperatures, or photochemical initiation. In contrast, the present work reports facile spontaneous silacyclobutane ring expansion.The transsilylation reaction 8 of 1,1-dichlorosilacyclobutane (1) with O-(trimethylsilyl)-N-(alkylideneimino)-hydrazides (2; 9,10 eq 1) in chloroform solution at room temperature leads smoothly to the neutral hexacoordinate silacyclobutane complexes 3. 11 To the best of our knowledge there has only been one previous report of a hexacoordinate silacyclobutane compound, with a substantially different structure (four phosphorus ligands). 12 Under mild conditions (7 h in boiling acetonitrile or several days at room temperature in chloroform) 3a,b rearrange, respectively, to 4a,b, neutral pentacoordinate complexes with a new carbon-carbon bond closing a new chelate ring, while the four-membered ring opens and forms an n-propyl ligand (eq 2). 13 This remarkable rearrangement, which proceeds without any catalysis, † Ben-Gurion University of the Negev. Nagai, A.; Kazama, T.; Takano, A.; Isono, Y. Macromolecules 2004, 37, 315. (d) Kozo, M.; Shimazu, H.; Deguchi, M.; Yamaoka, H. (b) Gusel'nikov, L. E., Volkova, V. V.; Buravtseva, E. N.; Redchin, A. S.; Auner, N.; Herrschaft, B.; Solouki, B.; Tsantes, G.; Ovchinnikov, Y. E.; Pogozhikh, S. A.; Dolgushin, F. M.; Negrebetsky, V. V.
