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.