Reactivity of terminal imido complexes of group 4–6 metals: Stoichiometric and catalytic reactions involving cycloaddition with unsaturated organic molecules

Imido complexes of early transition metals are key intermediates in the synthesis of many nitrogen-containing organic compounds. The metal—nitrogen double bond of the imido moiety undergoes [2+2] cycloaddition reactions with various unsaturated organic molecules to form new nitrogen—carbon and nitrogen—heteroatom bonds. This review article focuses on reactivity of the terminal imido complexes of Group 4–6 metals, summarizing their stoichiometric reactions and catalytic applications for a variety of reactions including alkyne hydroamination, alkyne carboamination, pyrrole formation, imine metathesis, and condensation reactions of carbonyl compounds with isocyanates.