Synthesis and platinum- and palladium-catalyzed reactions of benzo[1,2:4,5]bis(1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene)

Benzo[1,2:4,5]bis(1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene) (1) was synthesized in situ by the reaction of 1,2,4,5-tetrabromobenzene with magnesium in the presence of diethylfluorosilane in THF. The reaction of 1 with diphenylacetylene in the presence of a catalytic amount of (η²- ethylene)bis(triphenylphosphine)platinum(0) in refluxing benzene gave a 1:2 adduct, benzo[1,2:4,5]bis(1,1,4,4-tetraethyl-2,3-&phenyl-1,4- disilacyclohexa-2,5-diene) in 91% yield. Similar platinum(0)-catalyzed reaction of 1 with 3-hexyne and acetylene in refluxing benzene afforded the respective 1:2 adducts benzo[1,2:4,5]bis(disilacyclohexadiene) derivatives in excellent yields. Benzobis(disilacyclobutene) 1 also reacted with diphenylacetylene, 3-hexyne, and acetylene in the presence of a catalytic amount of tetrakis(triphenylphosphine)-palladium(0) to give the corresponding 1:2 adducts in excellent yields. Computational analyses of benzo[1,2:4,5] bis(disilacyclobutene) and its 1:1 and 1:2 adducts with acetylene were carried out using the B3LYP density-functional-theory method; the structures of these compounds were shown to be planar. The Si-Si bond in the disilacyclobutene ring appeared from computations to be effectively cleaved by a platinum(0) complex.