Transition metal imido complex


In coordination chemistry and organometallic chemistry, transition metal imido complexes is a coordination compound containing an imido ligand. Imido ligands can be terminal or bridging ligands. The parent imido ligand has the formula NH, but most imido ligands are have alkyl or aryl groups in place of H. The imido ligand is generally viewed as a dianion, akin to oxide.

Structural classes

Complexes with terminal imido ligands

In some terminal imido complexes, the M=N-C angle is 180º but often the angle is decidedly bent. Complexes of the type M=NH are assumed to be intermediates in nitrogen fixation by synthetic catalysts.
catalyst features imides as spectator ligands.

Complexes with bridging imido ligands

Imido ligands are observed as doubly and, less often, triply bridging ligands.

Synthesis

From metal oxo complexes

Commonly metal-imido complexes are generated from metal oxo complexes. They arise by condensation of amines and metal oxides and metal halides:
This approach is illustrated by the conversion of MoO2Cl2 to the diimido derivative MoCl22, precursors to the Schrock carbenes of the type Mo2.
Aryl isocyanates react with metal oxides concomitant with decarboxylation:

Alternative routes

Some are generated from the reaction of low-valence metal complexes with azides:
A few imido complexes have been generated by the alkylation of metal nitride complexes:

Utility

Metal imido complexes are mainly of academic interest. They are however assumed to be intermediates in ammoxidation catalysis, in the Sharpless oxyamination, and in nitrogen fixation.