Titanium and manganese complexes supported by a xanthene-bridged bis(tripodal N2O2) ligand: isomerization, intramolecular hydrogen bonding and metal-binding ability

Abstract

A new bis(N₂O₂) ligand, L⁴⁻, in which two tripodal diamine-bis(phenolate) moieties are bridged by a xanthene backbone, was prepared. The reaction of H₄L with 2 equiv. of [Ti(OⁱPr)₄] produced C₂ and C_s symmetrical isomers of the dititanium(IV,IV) complex [Ti₂(L)(OⁱPr)₄]. The isolated C₂ isomer was slowly converted to the C_s isomer via Ti–N bond cleavage to form a 3 : 2 mixture in equilibrium. A similar dimanganese(III,III) complex [Mn₂(L)(OMe)₂(MeOH)₂] was synthesized from a 1 : 2 mixture of H₄L and manganese(II) perchlorate in the presence of triethylamine. An X-ray analysis of [Mn₂(L)(OMe)₂(MeOH)₂] revealed that two Mn–N₂O₄ octahedrons are connected by intramolecular hydrogen bonds as well as a xanthene bridge to form a C₂ symmetrical structure. The dimanganese(III,III) complex further reacted with manganese(II) acetate to form the mixed-valence trimanganese(III,II,III) complex [Mn₃(L)(μ-OMe)₂(μ-OAc)₂]. Electrochemical data of the trimanganese(III,II,III) complex indicated that the xanthene-bridged dimanganese(III,III) unit effectively binds a Mn^II ion in solution.