Palladium-Catalyzed Reactions of 4,4,5,5-Tetramethyl-2,7- bis(trimethylsilyl)dithieno[3,2-<i>c</i>:2‘,3‘-<i>e</i>]disilacyclohexadiene with Alkynes

The reactions of the dithienodisilacyclohexadiene derivative (1) with diphenylacetylene, dimethyl acetylenedicarboxylate, and phenylacetylene in the presence of a palladium catalyst at 150 °C afforded the respective adducts 2−4, arising from insertion of a triple bond of the alkynes into the silicon−silicon bond of 1, together with a small amount of the oxygen-insertion product 5, derived from oxidation of the silicon−silicon bond of 1 by molecular oxygen. The oxidation reaction of 1 with trimethylamine N-oxide cleanly produced 5 in high yield. The absorption and emission maxima of 2−5 were markedly blue-shifted from those of 1. The optical band gaps taken from the absorption spectra of 2−5 agreed very closely with the HOMO−LUMO energy gaps of the model compounds (6−8) derived from MO calculations, at the level of B3LYP/6-31+G(dp). The structures of adducts 2 and 3 were determined by single-crystal X-ray crystallography.