Copper(I) Complexes of Pyridine-Bridged Phosphaalkene-Oxazoline Pincer Ligands

The synthesis of enantiomerically
pure pyridine-bridged phosphaalkene-oxazolines
ArPC­(Ph)­(2,6-C5H3NOx) (1, Ar = Mes/Mes*, Ox = CNOCH­(i-Pr)­CH2/­CNOCH­(CH2Ph)­CH2) is reported.
This new ligand forms a κ­(P), κ2(NN) dimeric
complex with copper­(I) (7) that dissociates into a cationic
κ3(PNN) monomeric complex upon addition of a neutral
ligand {[1a·CuL]­OTf (8a–e): L = PPh3 (a), P­(OPh)3 (b), 2,6-lutidine (c), 4-DMAP (d), 1-methylimidazole (e)}. The P–Cu bond lengths
in 8 are influenced by the π-accepting/σ-donating
properties of L, and this can be observed by changes in the δ31PPC NMR shift. The donor–acceptor
properties in complexes of type 8 have also been investigated
by UV/vis spectroscopy and density functional theory calculations.