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.

Graphical abstractLithiation of phosphine-amine or (thio)phosphorane-amine mainly led to dissociation giving imine and P-based anion. Combined experimental and theoretical study allowed the isolation of a stable phosphine-amido ligand which was coordinated as well as its neutral counterpart to Rh(I) metal centre.Figure optionsDownload full-size imageDownload as PowerPoint slide