Titanium oxo carboxylate compounds. Crystal and molecular structures of [{TiCl2(O2CEt)(ETCo2H)}2O] and [Ti3Cl3O2(O2CEt)5] and an unusual quantitative conversion of a Ti2O to a Ti3O2 oxo derivative

Abstract

Reaction of TiCl₄ with alkyl carboxylic acids RCO₂H (R = Me, Et or Bu^t) using a 1:1 (Ti:acid) molar ratio at 0°C yielded the dinuclear chloro carboxylates [Ti₂Cl₇(O₂CR)(RCO₂H)](R = Et or Bu^t). When a 1:2.5 ratio is used at 25°C oxygen abstraction occurs to yield [(TiCl₂(O₂CR)(RCO₂H)}₂O](R = Me, Et or Bu^t). When R = Et another product, [Ti₂Cl₃O(O₂CEt)₃(EtCO₂H)], was also obtained. At 40–70°C the oxo compounds (R = Et or Bu^t) decompose quantitatively to form the trinuclear species [Ti₃Cl₃O₂(O₂CR)₅], but the compound with R = Me remains unchanged up to 110°C. The co-ordinated acid in [(TiCl₂-(O₂CR)(RCO₂H)}₂O] is displaced by tetrahydrofuran (thf) to yield [{TiCl₂(O₂CR)(thf)}₂O](R = Me, Et or Bu^t), and in contrast to the former, these species are stable up to 110°C. The crystal structures of [{TiCl₂(O₂CEt)(EtCO₂H)}₂O] and [Ti₃Cl₃O₂(O₂CEt)₅] have been determined, and show [Ti(µ-O)-(µ-O₂CR)₂Ti] and [Ti₃(µ-O)(µ₃-O)] cores respectively. The comparative reactivity of alkyl and aryl acids towards TiCl₄ is discussed.