Metal-free NH-oxidative addition at phospha-Wittig reagents

Abstract

N-containing molecules are mostly derived from ammonia (NH3). Ammonia activation has been demonstrated for single transition metal centers as well as for low-valent main group species. Phosphinidenes, mono-valent phosphorus species, can be stabilized by phosphines, giving so-called phosphanylidenephosphoranes of the type RP(PR’3). We demonstrate the facile, metal-free NH3 activation using ArP(PMe3), affording for the first time isolable secondary aminophosphines ArP(H)NH2 through oxidative addition at a phosphinidenoid P atom. DFT studies reveal that two molecules of NH3 act in concert to facilitate an NH3 for PMe3 exchange. Furthermore, H2NR and HNR2 activation is demonstrated.

On the ambiphilic character of phosphanylidenephosphoranes and manipulation of phosphinidenoid reactivity with Lewis acids

“…Such condensation was also observed for the respective secondary aminophosphanes RP(H)NH2 (R = Mes*, Mes Ter) upon crystallization. [30] In 2:Mes*, the P=O atom distance is in good agreement with phosphine oxides and measures 147.50 (45) pm. The formation of the herein reported stable primary phosphine oxides is outstanding.…”

“…The NH-oxidative addition of a series of NH-containing molecules including NH3 was realized at ambient temperature. [30] This was a remarkable finding as NH3activation remains a challenge in transition metal chemistry due to the possible formation of unreactive Werner-type complexes. [31] However, another under-explored potential appears to be bond activation chemistry of phosphanylidene-σ4phosphoranes through their nucleophilic, yet weakly basic character.…”