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

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, H-1, C-13 and O-17 NMR spectroscopies and theoretical modelling. In the case of the previously described [Ti-3(mu(3)-O)(OPri)(4)(mu-OPri)(3){Me2C(O)CH=C(O)CH2C(O)Me-2}] 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 H-1 and C-13 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 [Ti-3(mu(3)-O)(mu(3)-OPri)(mu-OPri)(3)(OPri)(6)] (3) meets acetone molecules in their enol form, (3) + 3 CH2=C(OH)CH3 --> (2) + 3 HOPri, is proposed, explaining why exactly three acetone molecules should undergo aldol condensation and why new complexes such as [Ti-3(mu(3)-O)(mu(3)-OH)(OPri)(6)(mu-OPri)(3)] (4) or [Ti-3(mu(3)-O)(mu-OOCPh3)(2)(mu-OPri)(3)(OPri)(5)] (5) may be isolated and characterised.