Catalytic nitrene transfer by a zirconium(iv) redox-active ligand complex

Abstract

Nitrene transfer catalyzed by a d⁰zirconium(IV) complex with a redox-active ligand is reported. The redox-active ligand, bis(2-isopropylamido-4-methoxyphenyl)amide ([NNN^cat]³⁻), afforded zirconium(IV) complexes, [NNN^cat]ZrClL₂ (1a, L = THF; 1b, L = CN^tBu; 1c, L = py), upon reaction with ZrCl₄(THF)₂. Complex 1a was oxidized by one and two electrons using PhICl₂, affording [NNN^sq•]ZrCl₂(THF) (2) and [NNN^q]ZrCl₃ (3), respectively. Aryl azides reacted with 1a to afford zirconium imide dimers, including the crystallographically characterized species {[NNN^q]ZrCl(μ₂-p-NC₆H₄^tBu)}₂ (4). The formation of 4 is the result of the addition of an aryl nitrene to the zirconium(IV) metal center. When 1b was reacted with organoazides, the dimer was not observed, but rather the nitrene group was transferred to the isonitrile to form a carbodiimide. In the presence of excess organoazide and isonitrile, catalytic carbodiimide formation occurred, showing that a redox-active ligand and a d⁰ metal center can work in concert to effect nitrene group transfer reactivity.