Substitution reactions of dichlorobis(betadiketonato-O,O′)titanium(IV) complexes with aryl diolato ligands: An experimental and computational study

Substitution reactions of complexes Ti(β-diketonato)2Cl2, in which the two monodentate Cl− ligands are replaced by different bidentate aryl-diolato ligands (catechol, naphthol, biphenol, binaphthol, or methylenebinaphthol), produce remarkably hydrolytically stable titanium(IV) complexes with 5-, 7- or 8-membered chelating rings. The lability of the chlorine ligand in the parent compound is dependent on the strength of the electron donating properties of the spectator β-diketonato ligand around the titanium centre. The reactivity of Ti(RCOCHCOR′)2Cl2 complexes according to the β-diketonato ligand (RCOCHCOR′)− follows the order (PhCOCHCOPh)− > (PhCOCHCOCH3)− > (CH3COCHCOCH3)−, in line with results for other known transition metal complexes. Detailed substitution kinetics along with the X-ray crystal structure of a mono-chloride Ti(β-diketonato)2(Cl)(naphthol) reaction intermediate are reported. DFT calculations on the reaction of Ti(acac)2Cl2 with different aryl-diolato ligands reveal that chlorine substitution proceeds via a two-step interchange mechanism with the formation of two seven-coordinated transition states and one six-coordinated intermediate. The computed mechanism agrees very well with experimental kinetic and X-ray data.

The kinetics of substitution of a bidentate aryl-diolato ligand for the two monodentate Cl− ligands in Ti(β-diketonato)2Cl2 proceeds in two steps via a 6-coordinated intermediate according to an interchange mechanism.Figure optionsDownload as PowerPoint slide