Synthesis, solution and solid state structure of titanium–maltol complex

The reaction of Cp2TiCl2 with two equivalents of maltol (3-hydroxy-2-methyl-4-pyrone) in water, at room temperature and pH of 5.4, leads to a complete replacement of Cp and chloride ligands affording, Ti(maltolato)2(OH)2. The complex has been characterized by IR, NMR and ESI-MS spectroscopic and cyclic voltammetry methods. In DMSO-d6 solution, the complex shows two isomers in a ratio of 4:1, in which one OH signal can be identified per isomer. This suggests that in solution the complex is monomeric, most likely a chiral cis-Ti(maltolato)2(OH)2 and trans-Ti(maltolato)2(OH)2. The monomeric nature of the complex (in water/methanol 1:1) was verified by ESI-MS spectroscopy, showing a parent peak at 329 m/z. Electrochemical behavior of Ti(maltolato)2(OH)2using cyclic voltammetry experiments showed the complex undergoes irreversible reduction in aprotic solvents. In D2O solution, at pH of 8.4, the 1H NMR spectrum of the complex shows a mixture of monomer and tetramer Ti(IV)–maltol complexes in a ratio of 1:1. The crystallization of Ti(maltolato)2(OH)2 at pH of 8.4 leads to the formation of [Ti4(maltolato)8(μ-O4)] · 18H2O. A single crystal of [Ti4(maltolato)8(μ-O4)] · 18H2O was analyzed by X-ray diffraction methods. Solid state structure determination of the Ti-maltol complex showed to be tetrameric, containing two bridging oxides (in cis position) and two bidentate maltol ligands per titanium in a pseudo-octahedral coordination geometry.