Synthesis of new triazolyl-oxazoline chiral ligands and study of their coordination to Pd(II) metal centers

We report an improved protocol for the synthesis of TryOx, a family of N,N chiral ligands in which a 1,2,3-triazol-4-yl moiety bears a chiral 2-oxazoline as the substituent in 4 position. TryOxs were successfully employed for the preparation of cationic Pd(II)-allyl complexes of formulation [Pd(allyl)(TryOx)]+ in which they behave as bidentate N,N chelating ligands. On the other hand, reaction of TryOxs with an equimolecular amount of [PdCl2(CH3CN)2] leads to the formation of neutral complexes which according to NMR, ESI-MS and molar mass determination (VPO) appear to be dimeric species of formulation [PdCl(µCl)(TryOx)]2 in which monodentate TryOxs link to palladium with the N atom of the oxazoline ring. X-rays diffraction studies show that upon crystallization these dimers transform into monomeric compounds of formulation [PdCl2(TryOx)], where the ligands behave as N,N chelating. Treatment of the [PdCl(µCl)(TryOx)]2 dimers with an equivalent of TryOx affords mononuclear neutral dichloro species of formulation [PdCl2(TryOx)2]. X-ray diffraction studies show that the two TryOx units are equivalent behaving as monodentate ligands coordinated to the metal through the oxazoline N atom.