Nitrides four-membered rings

The preparation of metal nitrides with N3 reagents typically employs d° metal complexes as starting materials. However, the reactions of r-butyl isocyanate with metal-oxo complexes of OsVI and RuVI represent rare examples of the use N3- reagents with d2-metals. It has been postulated that reaction of the isocyanate with metal-oxo 3 affords a four-membered ring intermediate 4, followed by the extrusion of carbon dioxide to yield r-butyl metal imide 5 (Scheme 1). Elimination of isobutylene from this complex then produces the metal nitride and the isobutylene. 

Only a few ternary silicon nitrides have been prepared in a pure form and characterized. The isotypic compounds MSiN2 (M = Be, Mg, Mn, Ca, Zn), with the same valence electron concentration of 4, can be considered as ternary substitution variants of AlN [247]. These compounds contain three-dimensional (3-D) infinite network structures, with SiN4 tetrahedra linked through all four vertices by comer-sharing, which forms condensed [SieNe] twelve-membered rings in MgSiN2 [248]. 

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