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

Abstract

The reaction of Cp 2TiCl 2 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- d 6 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 D 2O 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 [Ti 4(maltolato) 8(μ-O 4)] · 18H 2O. A single crystal of [Ti 4(maltolato) 8(μ-O 4)] · 18H 2O 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.