Isolable Silylenes and Their Diverse Reactivity

A considerable number of isolable silylenes, silicon divalent compounds, have been synthesized and great efforts have been made of the discovery of their distinctive structural and physical properties and their characteristic reactions over the last three decades. While many reviews have been published on the isolable silylenes until now, the present review uniquely focuses on the differences in the properties and reactivities among the known stable silylenes including those dialkyl-, diamino- and amino(alkyl)-silylenes that are sterically and/or electronically stabilized. Some extra-coordinated silylenes reported are discussed subsidiarily. In a brief introduction are discussed the remarkable substituent effects on the 29Si NMR chemical shift of the silylene silicon nucleus, the UV–vis absorption maxima and MO properties revealed by the DFT calculations. Then, the diverse reactions of the silylenes reported, their mechanisms, and the substituent effects on the reactivity are discussed. The reactions of the silylenes surveyed here are those with (i) σ bonds like X-H (X = H, C, O, N, Si, etc.), CCl, SiCl, etc., (ii) unsaturated π bonds like CC, CO, CN, NN, CN, etc., (iii) alkali metals affording the corresponding radical anions via one-electron transfer, and (iv) transition metal complexes of copper, silver, nickel, palladium and platinum.