Molecular templating using titanium(iv) (oxo)alkoxides and titanium(iv) (oxo)aryloxides

Abstract

Crystalline materials obtained by reacting titanium(IV) isopropoxide (1) with widely different ligands such as 1,3-propanediol, 2,2′-biphenol or triphenylacetic acid using acetone as a solvent have been characterised using single-crystal X-ray diffraction, ¹H, ¹³C and ¹⁷O NMR spectroscopies and theoretical modelling. In the case of the previously described [Ti₃(μ₃-O)(OPrⁱ)₄(μ-OPrⁱ)₃{Me₂C(O)CHC(O)CH₂C(O)Me₂}] complex (2), the importance of the simultaneous use of HSQC, HBMC and ROESY techniques for a full spatial attribution of all resonances was demonstrated. The optimised molecular structure of (2) and its associated dynamics have also been used to demonstrate that more shielded ¹H and ¹³C resonances and shorter relaxation times were expected for more rigid bridging OR groups relative to terminal ones. A templating effect linked to the steric decompression that may occur when the rather constrained molecular structure of [Ti₃(μ₃-O)(μ₃-OPrⁱ)(μ-OPrⁱ)₃(OPrⁱ)₆] (3) meets acetone molecules in their enol form, (3) + 3 CH₂C(OH)CH₃ → (2) + 3 HOPrⁱ, is proposed, explaining why exactly three acetone molecules should undergo aldol condensation and why new complexes such as [Ti₃(μ₃-O)(μ₃-OH)(OPrⁱ)₆(μ-OPrⁱ)₃] (4) or [Ti₃(μ₃-O)(μ-OOCPh₃)₂(μ-OPrⁱ)₃(OPrⁱ)₅] (5) may be isolated and characterised.