Stereochemistry of Disilanylene-Containing Cyclic Compounds. Palladium-Catalyzed Reactions of cis- and trans-3,4-Benzo-1,2-diisopropyl-1,2-dimethyl-1,2-disilacyclobut-3-ene with Ethylene

The reaction of cis-3,4-benzo-1,2-diisopropyl-1,2-dimethyl-1,2-disilacyclobut-3-ene (1a) with ethylene in the presence of a catalytic amount of tetrakis­(triphenylphosphine)­palladium(0) in benzene at room temperature proceeded stereospecifically to give a 1:2 adduct, 3,4,9,10-dibenzo-1,2,5,8-tetrasilacyclodeca-3,9-diene (3a), consisting of two molecules of 1a and one molecule of ethylene, in 58% yield, along with a 1:1 adduct, cis-2,3-benzo-1,4-diisopropyl-1,4-dimethyl-1,4-disilacyclohex-2-ene (2a), in 7% yield. The reaction of trans isomer 1b with ethylene under the same conditions afforded two types of 1:2 adducts, 3b,c (64% combined yield), whose configurations at the silicon atoms were maintained, in a ratio of 1:1, together with the 1:1 adduct 2b (5% yield) with trans configuration. The reaction of a 1:1 mixture of 1a,b with ethylene in the presence of a catalytic amount of palladium­(II) dichloride under the same conditions also gave the 1:2 adducts 3a–c (3a:3b:3c = 3:1:1) in 63% combined yield, together with 2a,b (2a:2b = 1:3) in 16% combined yield. The structures of 3a,b were determined by crystallographic analysis. Treatment of a mixture consisting of 1a and 2a with a tetrakis­(triphenylphosphine)­palladium(0) catalyst in benzene at room temperature did not produce 3a; instead, 1a and 2a were recovered unchanged.