Photochemistry of 1-aryl-4-pentamethyldisilanyl-1,3-butadiynes

Abstract

Some 1-Aryl-4-pentamethyldisilanyl-1,3-butadiynes which are very interesting class of organosilicon compounds were synthesized through several synthetic methods and photophysical and photochemical properties were investigated. All the 1-aryl-4-pentamethyldisilanyl-1,3-butadiynes show strong phosphorescence emissions. The triplet energies of these compounds lie around 52-62 kcal/mol above the ground states. 1-Aryl-4-pentamethyldisilanyl-1,3-butadiynes were irradiated with acetone to obtain site specific and regioselective two-atom insertion products (1, 2, 3, 4, and 5) via silacyclopropene intermediates. Irradiation of 1-aryl-4-pentamethyldisilanyl-1,3-butadiynes with DMFu gives [2+2] type photoadducts (6,7,8 and 10)and/or a two-atom insertion product(9). The photoadduct 7 is initially formed and prolonged irradiation of the solution results in decrease of 7 and formation of 8 indicating that 8 is a secondary photoproduct of 7. Oxygen quenching studies suggest that [2+2] type photocycloaddition reactions proceed via triplet excited states of 1-aryl-4-pentamethyldisilanyl-1,3-butadiynes and the two-atom insertion product (9) is formed via the triplet excited state of silacyclopropene intermedicates. A plausible photoreaction mechanism is proposed.