From Coordination of Free Imine

The synthetic equivalent of zirconocene, Cp2Zr [27], can react with an imine to yield a zirconaaziridine (Eq. 5) [28] - a reaction that reminds us that zircona- 

Zirconaaziridine synthesis via the Negishi reagent [22,24,28,31,32] is a particularly efficient approach for zirconaaziridines that cannot be prepared by the C-H activation pathway. For example, addition of a hydrazone to zirconocene yields an AT-amino-substituted zirconaaziridine (see Sect. 4.1). The ligand-free 2i, produced in low yield by the C-H activation pathway, can be prepared from zirconocene and an imine/enamine mix as shown in Eq. 6 [24]. 

With its tetrasubstituted carbon, the zirconaaziridine 2i remains ligand-free in THF, but in the presence of PMe3 it forms a PMe3 adduct. Complex 2j [33], prepared in a similar manner with the Rosenthal reagent 8 [34], is the only zirconaaziridine with a tetrasubstituted carbon that has had its structure determined by X-ray studies. The stability of its pyridine adduct reflects the fact that pyridine is a stronger donor ligand than THF. 

Zirconaaziridines prepared through the addition of imine to zirconocene are generally not of high purity and cannot be isolated in high yield reductive coupling of imines often competes. However, this method is preferred for preparing zirconaaziridines in situ for reaction with electrophiles that can be 

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