Structural variety of zinc and copper complexes based on a 2,3-disubstituted 1,2,3,4-tetrahydroquinazoline ligand

Abstract

The ring-chain tautomerism of 2-(3-tosyl-1,2,3,4-tetrahydroquinazolin-2-yl)quinolin-8-ol (H₂L^ring) has been exploited to produce mononuclear complexes or, alternatively, dinuclear complexes, as desired, by varying the stoichiometry of the ligand. Cu²⁺ and Zn²⁺ stabilise the ring tautomeric form of the ligand in their mononuclear complexes M(HL^ring)₂. The structural characterisation of Zn(HL^ring)₂·2MeOH·0.5H₂O shows O,N-donor behaviour of the ring tautomer. The 1,2,3,4-tetrahydroquinazoline undergoes a ring-opening reaction upon formation of phenoxo-bridged dinuclear complexes M₂(L^chain)₂ in which the chain tautomer is acting as O,N,N,N-donor. The crystal structure of Cu₂(L^amide)(L^quinazoline)(MeOH)·2MeOH evidenced the sensitivity of H₂L^ring to the copper-mediated aerobic oxidation, which results in two derivatives of the ligand, a quinazoline and an amide. The quinazoline ligand is acting as monoanionic and mononucleating through its O,N,N binding site, while the amide ligand behaves as a trianionic and binucleating through its O,N,N,N and O,O binding sites in Cu₂(L^amide)(L^quinazoline)(MeOH)·2MeOH.