Structure, substitution and hydrolysis of Bis(trifluorobenzoylacetonato-O,O′)dichloro titanium(IV) : an experimental and computational study

Abstract

The chlorine coordinated ligands in [Ti(tfba)2Cl2] (Htfba = 4,4,4-trifluoro-1-(phenyl)-1,3-butanedione = PhCOCH2COCF3) are very susceptible to hydrolysis and even with trace amounts of water, the formation of hydrolysed complexes, dinuclear {Ti(tfba)2Cl}2(μ-O) or tetranuclear [Ti(tfba)2(μ-O)]4, take place, whereas with an excess of water, decomposition to TiO2 occurs. Substitution of the chloro-ligands in [Ti(tfba)2Cl2] with H2biphen (H2biphen = 2,2′-dihydroxybiphenyl or biphenol) leads to [Ti(tfba)2biphen] with enhanced water stability. Experimentally, two steps were observed for the substitution [Ti(tfba)2Cl2] + H2biphen. Computational chemistry calculations reveal that each step involves several transition states, with formation of a 7-coordinated intermediate in the first reaction half. Location of this intermediate is dependent on inclusion of empirical dispersion-corrections in the functional. The three geometrical cis-isomers of [Ti(tfba)2biphen] were observed in solution using low temperature 1H and 19F NMR, whereas in the solid state, two of the isomers, cis-cis-trans and cis-trans-cis, crystallized in the same unit cell. The crystal structure of the hydrolysed tetranuclear complex [Ti(tfba)2(μ-O)]4 is composed of four identical cis-cis-trans isomers of [Ti(tfba)2Cl2]. The eight β-diketonato backbones and the four bridging oxygens have a S4 molecular symmetry.