Rational Synthesis of a Family of Neutral Monomeric Heteroleptic Titanium Complexes Based on an Octahedral TiO₄N₂ Motif

Abstract

Abstract A rational approach leading to a novel family of monomeric heteroleptic titanium complexes formed with two biphenolate derivatives and six different bidentate nitrogenated chelates is proposed. Only one case of loss of structural predictability was observed in the case of a N , O ‐coordinating ligand and led to a structure containing two (μ‐O)‐bridged titanium centres. Diffusion‐ordered NMR spectroscopy (DOSY) measurements have been systematically used to prove that the complexes characterised in the solid state remain identical in the liquid phase. All ligands have also been classified quantitatively according to their electron‐withdrawal capabilities. A quantitative thermodynamic analysis using the PACHA software showed that the entropically favoured displacement of two monodentate‐coordinated alcohol molecules needs to be assisted by solvation of the η 2 ‐chelate product to overcome the enthalpically unfavourable replacement of two highly polar Ti–O bonds by less polar Ti–N bonds. The occurrence of dichloromethane molecules in the crystalline state and the existence of more than one crystallographically nonequivalent complex within the unit cell has been associated with a low dipolar moment of the complexes. Other complexes with large dipolar moments ( μ > 2 D) seem to have enough dipolar energy in the solid state to remove all the solvating dichloromethane molecules.