Lukman A. Solola

Structurally authenticated, terminal lanthanide–ligand multiple bonds are rare and expected to be highly reactive. Even capped with an alkali metal cation, poor orbital energy matching and overlap of metal and ligand valence orbitals should result in strong charge polarization within such bonds. We expand on a new strategy for isolating terminal lanthanide–ligand multiple bonds using cerium(IV) complexes.

The formation and stabilization of multiple bonds between a lanthanide cation and an anionic p-block element fragment are challenging, and only a few examples of such terminal complexes have been reported to date. Notably, all reported synthetic routes to lanthanide-imido moieties employed deprotonation as the key formation step. In the present report, we describe the generation of a Ce(IV) imido complex by a trimethylsilyl group transfer pathway.

A series of alkali metal capped cerium(IV) imido complexes, [M(solv) ][Ce?N(3,5-(CF ) C H )(TriNOx)] (M = Li, K, Rb, Cs; solv = TMEDA, THF, Et O, or DME), was isolated and fully characterized. An X-ray structural investigation of the cerium imido complexes demonstrated the impact of the alkali metal counterions on the geometry of the [Ce?N(3,5-(CF ) C H )(TriNOx)]? moiety. Substantial shortening of the Ce?N bond was observed with increasing size of the alkali metal cation.