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

Reductive debromination of {N(SiMe(3))(2)}SiBr(3) with Rieke magnesium results in the formation of the five‐vertex silicon cluster with one bromine substituent Si(5){N(SiMe(3))(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′.