Evidence for the Existence of Group 3 Terminal Methylidene Complexes

Terminal group 3
methylidene complexes are generated by thermolysis
of monoanionic PNP-supported scandium and yttrium dialkyl complexes.
The reaction mechanism has been probed by deuterium-labeling experiments
and DFT calculations. Abstraction of a γ-hydrogen from one alkyl
group by the other affords a metallacyclobutane that undergoes [2
+ 2] cycloreversion, analogous to a key step in the olefin metathesis
reaction, to generate a methylidene complex and isobutene. The resulting
methylidene complex dimerizes in the case of scandium and decomposes
to a mixture of products in the case of yttrium.