Synergism between Cyclopentadienyl and Amidinate Ligands Affording the Anionic Scandium Terminal Imido Complexes

Terminal rare-earth imido complexes containing metal nitrogen double bonds have received more attention in recent years due to their importance in group transformation and catalytic reactions. However, due to the large difference in orb ital energy between rare-earth metals and nitrogen, their synthesis is difficult and the product is easy to polymerize. Here we use the combination of Cp* and amidine ligands to inhibit the tetramerization and provide exclusively the first anionic rare-earth(III) terminal imido complexes with both electro-donating and electron-withdrawing groups. The chemical bond analysis further confirms the double bond character and the strong polarity of the RE=N bond, which could be described as three orbital interactions, is primarily contributed from the imido nitrogen, while the contribution from rare-earth metal is limited. The mechanistic study by DFT calculations shows the formation of the RE=N bond undergo the activation of two N– H bonds. Furthermore, the anionic rare-earth(III) terminal imido complex shows some interesting and unique reactivity towards isocyanate, isonitrile, phenylsilane, and W(CO)6. The work extends the multiple bond chemistry between rare-earth metals and main group elements, and is expected to inspire the development of rare-earth organometallic chemistry and related fields.