While many transition metal imido complexes are stable and unreactive, some exhibit high reactivities towards electrophiles, nucleophiles, or both. Nucleophilic imido ligands tend to be associated with the early transition metals (and more strongly polarized M-N bonds), while later transition metals exhibit more covalent metal-nitrogen bonding and less nucleophilic imido nitrogen centers. The bonding model described above suggests that bending of the imido ligand should lead to a reduced metal-nitrogen bond order and localization of a lone pair on nitrogen. This should lead to increased nucleophilicity of the imido nitrogen atom and increased reactivity of the complex due to a weaker, and more exposed, Ta=N bond.
Contrary to these expectations, our studies of compound 2 indicate that it is rather stable and not very reactive, as shown in the reactivity scheme below. The methyl derivative 3 was obtained by reaction with MeMgBr. Reaction of 3 with xylyl isonitrile gave the insertion product 4, which was structurally characterized.
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