Phosphine- and thiophosphorane-amine ligands: Lithiation and coordination to Rh(I)

A series of phosphine-amine and thiophosphorane-amine ligands (PR₂(X)CH₂NHR′, X = lone pair, S, R = Ph, Cy, R′ = tBu, Ph) differing by the nature of the phosphorus and nitrogen substituents were synthesized. Their lithiation, in order to generate the corresponding amido ligand mainly led to dissociation with formation of phosphide or thiophosphinite anion and imine. DFT calculations confirmed that this pathway is in most cases thermodynamically favoured. But for a phosphine-amido anion featuring alkyl substituents on the P atom and phenyl on the nitrogen, calculations showed that the dissociation is strongly disfavoured (ΔG = +24.3 kcal mol^-1). Actually, {PCy₂CH₂NPhLi} was isolated in high yield and fully characterized. This phosphine-amido ligand and the corresponding amine derivative were then coordinated to Rh(I) metal centre.