 Titanocene methylidene

The reactive early-metal alkylidene $\mathrm{C}{\mathrm{p}}_2\mathrm{Ti}=\mathrm{C}{\mathrm{H}}_2$. carbonyl methylenation proceeds through an oxatitanacyclobutane; alkene capture gives a titanacyclobutane. Its oxygen affinity makes ester methylenation feasible.