Diastereoselectivity in dinuclear complexes of chiral tridentate ligands

Using a racemic mixture of two chiral tridentate ligands 2-((1-(2-pyridyl)ethylimino)methyl)phenolate ion (L1) and 2-((phenyl(2-pyridyl)methylimino)methyl)phenolate ion (L2) and Cu(II) or Ni(II) salts, complexes having formulae [Cu(L2)(μ-1,1-NO3)]2 (1), [Cu(L2)(μ-Cl)]2 (2), [Cu2(L2)2(μ-1,2-SO4)] (3), [Cu2(L1)2(μ-1,2-SO4)] (4) and [Ni2(L2)2(OAc)(N(CN)2)(MeOH)] (5) were synthesized and characterized. Determination of molecular structures of all the five complexes confirmed the presence of a dimetallic core constructed by monochelates of the ligands. Compound 1, 2 have NO3− and Cl− bridge between two copper centers and 3–5 have phenoxo as well as SO42- (3,4) and OAc− (5) bridges. Compounds 1 and 2 have center of inversion in the dicopper core and are heterochiral. Whereas, in 3–5 center of inversion do not lie in the dimetallic core and are homochiral. Compound 1 has a rare feature of μ-1,1-NO3− bridge between two copper centers.

Monochelates of end-capped racemic tridentate ligands show bridging ligand dependent chiral preference based on bridging ligand’s ability/inability to accommodate center of symmetry at dimetallic core.Figure optionsDownload as PowerPoint slideHighlights
► Bridging ligands play a role in diastereoselectivity of chiral ligand at dimetallic core.
► Dicopper core in 1 and 2 has center of symmetry thus resulting in RS combination.
► Dimetallic core in 3–5 do not have center of symmetry hence has RR/SS combination.
► Rare example of μ-1,1-NO3− bridge between two copper centers has been observed in 1.