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.