Azide Addition To Give a Tetra-azazirconacycle Complex

Addition of the dilithium salt, ortho-(Me3SiNLi)2C6H4, to ZrCl4 affords
a base-free, D2d-symmetric complex ZrIV[ortho-(Me3SiN)2C6H4]2 (2),
with rigorously planar ortho-phenylenediamine ligands. Lewis acidic
2 readily coordinates donor ligands such as NHEt2 to give the
five-coordinate complex, ZrIV(NHEt2)[ortho-(Me3SiN)2C6H4]2 (3),
which is also accessible by the reaction of Zr(NEt2)4 with 2 equiv
of ortho-(Me3SiNH)2C6H4. Aryl azides react with 2 and 3 to give
an unusual tetra-azametallacycle complex, 4, via 1,2-addition of a
ligand N−Si bond to the organic azide. An X-ray crystal structure
of 4 reveals a planar, five-membered metallacycle comprising the
zirconium atom, one nitrogen atom of the ortho-(Me3SiN)2C6H4
ligand, and all three nitrogen atoms of the aryl azide.