Synthesis, photochemical decomposition and DFT studies of 2,2,3,3-tetramethyl-1,1-bis(dimethylphenylsilyl) silacyclopropane

The compound, 2,2,3,3-tetramethyl-1,1-bis(dimethylphenylsilyl) silacyclopropane (1), is a potential photochemical source of silylenes either through a 2 + 1 fragmentation of the silacyclopropane ring core or through alpha-elimination from the aryltrisilane chain. Upon 254 nm photolysis, the silacyclopropane (1) exclusively undergoes 2 + 1 ring fragmentation with the formation of bis(dimethylphenylsilyl) silylene and tetramethylethylene. This clearly shows the heightened photoreactivity of the silacyclopropane ring compared with the aryltrisilane chain. The extruded bis(dimethyphenyl) silylene is intercepted with trapping agents such as triethylsilane, methoxytrimethylsilane and bis(trimethylsilyl) acetylene to form thermally stable adducts. Time Dependent-Density Functional Theory (TD-DFT) calculations at the B3LYP/6-31G* level reveal that an electron is excited from a Si-C sigma orbital of the silacyclopropane ring (HOMO) to empty pi* orbitals of phenyl group (LUMO). This weakens the Si-C bonds of the silacyclopropane ring which is believed to result in the observed 2 + 1 photofragmentation. (C) 2015 Elsevier B.V. All rights reserved.