The curious cases of tetrahydrosalen-type ligands interacting with Ni(ii): structures and ligand-based oxidation reactions

Abstract

This work centers around the nickel complexes derived from two tetrahydrosalen-type proligands: N,N′-bis(2-hydroxybenzyl)-o-phenylenediamine (H₂salophan) and N,N′-bis(2-hydroxy-3-methylbenzyl)-o-phenylenediamine (H₂salophan_Me). The reaction of H₂salophan with Ni(OAc)₂·4H₂O generates a dinuclear complex Ni₂(Hsalophan)₂(OAc)₂ or Na[Ni₂(salophan)₂(OAc)] when NaOH is added to assist ligand deprotonation. The reaction of H₂salophan_Me with Ni(OAc)₂·4H₂O, however, yields a mononuclear complex Ni(Hsalophan_Me)₂. Unlike the corresponding salen-type nickel complexes, these tetrahydrosalen-type complexes are paramagentic and air sensitive (in solution). Oxidation by O₂ or peroxides results in dehydrogenation of the ligand backbone to form the salen-type complexes.