Olefin metathesis is one of the most important industrial processes for the production of alkenes. In contrast, silicon versions of metathesis are unknown given the lack of available silylene transition-metal complexes suitable for [2 + 2] cycloaddition with unsaturated substrates. Here, we report the synthesis of 18-electron titanium silylene complexes featuring different Lewis base ligands and classified on the basis of structural, computational, and reactivity studies as Schrock-type silylene complexes. Because of the presence of loosely bound Lewis base ligands, such silylene complexes readily undergo reaction with simple unsaturated hydrocarbons, such as alkynes, forming the corresponding [2 + 2] cycloaddition products.

The first [2+2] cycloadduct of the transition metal silylene complex and nitrile was synthesized by the reaction of titanium silylidene and benzonitrile. Only one regioisomer was exclusively isolated, in which the C atom of the nitrile group was bound to titanium whereas the N atom was bound to sili- [a]

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Novel unsaturated four-membered ring disilene, 3,3-dichloro-1,2,4,4-tetrakis[di- tert -butyl(methyl)silyl]- 1 Δ-1,2,3,4-trisilagermetene, was synthesized by the ring expansion reaction of the three-membered ring 1-disilagermirene with the silylene–NHC complex Cl 2 Si–IPr. The mechanism of the unexpected formation of this compound was verified by high-level density functional theory computations, which revealed n Si:(HOMO) –π Si=Si(LUMO) * as the dominant orbital interaction.