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

Article abstract of DOI:10.1016/j.poly.2013.09.004

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)^- > (CH₃COCHCOCH ₃)^-, 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. . 2013 Elsevier Ltd. All rights reserved.