Oxygenextrusion from amidate ligands to generate terminal TaO units under reducing conditions. How to successfully use amidate ligands in dinitrogen coordination chemistry

Abstract

A series of mixed Cp* amidate tantalum complexes Cp*Ta(RNC(O)R′)X₃ (where R = Me₂C₆H₃, ⁱPr, R′ = ^tBu, Ph, X = Cl, Me) have been prepared via salt metathesis and their fundamental reactivities under reducing conditions have been explored. Reaction of the tantalum chloro precursors with potassium graphite under N₂ or Ar leads to the stereoselective formation of the terminal tantalum oxo species, Cp*TaO(η²-RNCR′)Cl. This represents the formal extrusion of oxygen from the amidate ligand to the reduced tantalum center and is accompanied by the formation of the iminoacyl fragment bound to Ta(V). Amidate dinitrogen complexes, [Cp*TaCl(RNC(O)^tBu)]₂(μ-N₂) (where R = Me₂C₆H₃, ⁱPr) were synthesized via salt metathesis from the known [Cp*TaCl₂]₂(μ-N₂) precursor, establishing that amidate ligands can support dinitrogen complexes, but not the reduction process often necessary for their synthesis.