Reactions of titanium tetrachloride with carboxylic acids. Crystal and molecular structure of the dinuclear titanium oxo compound [{TiCl2(O2CBut)(ButCO2H)}2O]

Abstract

Reaction of TiCl₄(1 mol) with 2,2-dimethylpropanoic acid (2.5 mol) at room temperature yields the dinuclear oxo-bridged species [{TiCl₂(O₂CBu^t)(Bu^tCO₂H)}₂O]1 which has been fully characterised by an X-ray crystal structure analysis. The two metal atoms are bridged by the oxo and two carboxylate groups, which with a co-ordinated acid molecule and two chlorine atoms on each titanium gives a slightly distorted octahedral environment around each metal centre. At 40 °C compound 1 decomposes to the trinuclear species [Ti₃Cl₃(O₂CBu^t)₅O₂], and at higher temperatures (100–120 °C) to another dinuclear oxo derivative [{TiCl(O₂CBu^t)₂}₂O] which can also be obtained from the action of 2,2-dimethylpropanoic anhydride on TiCl₄ in refluxing toluene. Acetic acid produces a similar, but less soluble, species to 1. Aromatic acids react differently; para-substituted aryl acids generally yield trinuclear compounds [Ti₃Cl₃(O₂CC₆H₄X-p)₅O₂](X = Cl or Br) although the p-Bu^t acid forms [{TiCl(O₂CC₆H₄Bu^t-p)₂}₂O]. In contrast the ortho-and meta-substituted acids react to give either [Ti₃Cl₄(O₂CR)₄O₂](R = C₆H₄Cl-o or -m) or [Ti₄Cl₅(O₂CR)₇O₂](R = C₆H₄Me-o) derivatives.