Countercation Effect on CO₂ Binding to Oxo Titanate with Bulky Anilide Ligands

This work focuses on nucleophilic activation of CO₂ at the anionic terminal oxo titanium tris(anilide) complexes [(Solv)_n M][OTi(N[^t Bu]Ar)₃ ]_m with M=Li, Na, K, Mg, MgMe, AlCl₂ , AlI₂ ; Ar=3,5-Me₂ C₆ H₃ ; Solv=Et₂ O, THF, 12-crown-4, 2,2,2-cryptand; n, m=1-2. The CO₂ binding strength to the terminal oxo ligand of [OTi(N[^t Bu]Ar)₃ ]^- ([1]^- ) and the stability of the resulting carbonate moiety [O₂ COTi(N[^t Bu]Ar)₃ ]^- ([2]^- ) are highly dependent on the Lewis acidity of the countercation. We report herein on CO₂ binding as a function of countercation and countercation coordination environment, and comment in this respect on the bottom and upper limits of the cation Lewis acidity. Thermodynamic parameters are provided for oxo complexes with lithium as countercation, that is, [(Et₂ O)₂ Li][1] and [(12-c-4)Li][1].