PALLADIUM-CATALYZED DISILANE METATHESIS REACTIONS OF 1,2-DISILACYCLOBUTANES

3,4-Bis(isopropylidene)-1,1,2,2-tetraalkyldisilacyclobutanes (1) were prepared by intramolecular reductive coupling of the corresponding 3,4-bis(chlorodialkylsilyl)-2,5-dimethyl-2,4-hexadiene. In the presence of a Pd catalyst, 3,4-bis(isopropylidene)-1,1,2,2-tetramethyl-1,2-disilacyclobutane (1a) afforded 3,4,7,8-tetrakis(isopropylidene)-1,1,2,2,5,5,6,6-octamethyl-1,2,5,6-tetrasilacyclootane (2a) as the disilane metathesis product in 93% yield. A highly selective cross-metathesis occurred between 1a and 3,4-benzo-1,1,2,2-tetramethyl-1,2-disilacyclobutene (1c) and gave 3,4-benzo-7,8-bis(isopropylidene)-1,1,2,2,5,5,6,6-octamethyl-1,2,5,6-tetrasilacyclooct-3-ene (3) accompanied by only small amounts of homo-disilane metathesis products 2a and 2c. The structures of the products (2a, 2c, and 3) and 11 were characterized by X-ray diffraction studies.