Cycloadditions with a Stable Charge-Separated Cyclobutadiene-Type Amido-Substituted Silicon Ring Compound.

Reductive debromination of {N(SiMe3 )2 }SiBr3 with Rieke magnesium results in the formation of the five-vertex silicon cluster with one bromine substituent Si5 {N(SiMe3 )2 }5 Br, 1, and the cyclobutadiene analogue 2 in a 1:1 ratio. The latter features a planar four-membered silicon ring with a charge-separated electronic situation. Two silicon atoms in 2 are trigonal planar and the other two trigonal pyramidal. In cycloadditions with ethylene, diethylacetylene, 1,5-cyclooctadiene, and 2,3-dimethyl-1,3-butadiene cyclic unsaturated ring compounds (3-6) were formed at room temperature in quantitative reactions. Two of the products (3 and 6) show photochemical isomerization with LED light (λ=405 nm) to afford saturated ring compounds 4 e and 6'.