Effect of the rigidity and flexibility features of 2-pyridinyl or 8-quinolinyl based N–N∗ chiral ligands on the stereochemical properties of [Pd(N–N∗)Cl2] complexes

The [Pd(N–N∗)Cl2] complexes have been obtained, as yellow solids, in almost quantitative yields; N–N∗ indicate bidentate chiral ligands (Sa)-1, (Sa)-2, (S,S)-3, (R,R)-4, containing the rigid 2-pyridinyl or 8-quinolinyl building block skeleton and the C2-symmetric chiral framework trans-2,5-dimethylpyrrolidinyl or (S)-(+)-2,2′-(2-azapropane-1,3-diyl)-1,1′-binaphthalene. The ligands pairs have the same C2-symmetric chiral framework but different building block skeleton, beyond that for the basicity in the N-donor atoms, for rigidity and flexibility features. The N–N∗ ligands act as chelating ligands leading a square planar geometry. The compounds [Pd(S,S-3)Cl2] and [Pd(R,R-4)Cl2] have been also characterised by X-ray diffraction. The rigidity and flexibility features of (S,S)-3 and (R,R)-4 ligands induce a different orientation of the trans-2,5-dimethylpyrrolidinyl moiety with respect to the pyridinyl and quinolinyl plane. This work shows that intrinsic rigidity and flexibility are not enough to define the ligand properties and to preview the effects that they induce on the reactivity of the metal complex.

Graphical abstractThe [Pd(N–N∗)Cl2] complexes have been obtained, N–N∗ indicate bidentate chiral ligands (Sa)-1, (Sa)-2, (S,S)-3, (R,R)-4, containing the rigid 2- pyridinyl or 8-quinolinyl building block skeleton and the C2-symmetric pyrrolidinic and azepinic chiral framework. The compounds [Pd(S,S-3)Cl2] and [Pd(R,R-4)Cl2] have been characterised by X-ray diffraction. The rigidity and flexibility features of (S,S)-3 and (R,R)-4 ligands induce a different orientation of the trans-2,5-dimethylpyrrolidinyl moiety with respect to the pyridinyl and quinolinyl plane.Figure optionsDownload full-size imageDownload as PowerPoint slide