N─H or O─H Bond Activation With a Bicyclic Si4 Ring Compound.

The bicyclic silicon ring compound Si4{N(SiMe3)Mes}4 (Mes = 2,4,6-trimethylphenyl), a heavier analogue of cyclobutadiene, was reacted with ammonia, water, and selected alcohols. This resulted in E─H (E = N, O) bond activation, yielding saturated Si4 rings with ─NH2/─H or ─OH/─H functionalities in the case of ammonia or water, respectively. With methanol, a mixture of a saturated Si4 ring compound with ─OMe/─H functionalities and an eight-vertex methoxy-functionalized siliconoid cluster was obtained; an ethoxy-functionalized analogue was obtained from the reaction with ethanol. In contrast, the reaction between Si4{N(SiMe3)Mes}4 and phenol gave a simple 1,3-addition product with only a trace of side products. The observed reactivity was rationalized with the help of mechanistic calculations performed using density functional theory.