Photochemistry of Cyclic Trisilanes: “Spring-Loaded” Precursors to Methylphenylsilylene

Graphical Abstract

Photolysis of two new cyclic trisilanes containing a SiMePh moiety in the central position leads to enhanced yields of the transient silylene SiMePh, and concomitant reductions in that of the corresponding silene, formed by 1,3-silyl migration into the phenyl ring. Laser photolysis of the compounds allows the UV/Vis spectrum of SiMePh to be measured, along with absolute rate constants for its reactions with selected substrates.

Abstract

Two new cyclic trisilanes containing a SiMePh moiety in the central position have been synthesized, and their photochemistries studied by steady-state and laser flash photolysis methods. The yield of the transient silylene SiMePh increases at the expense of that of the corresponding cyclic silene derivative (formed by photochemical 1,3-silyl migration into the phenyl ring) as the ring size is decreased from 7 to 6, facilitating the direct detection of the silylene by laser flash photolysis. The UV/Vis spectrum of SiMePh in hexanes solution (λ_max=270, 505 nm) and absolute rate constants for its reaction with methanol, triethylsilane, a terminal alkene, alkyne, and two aliphatic dienes at 25 °C are reported.