Titanium-Carbon Functionalities on an Oxo Surface Defined by the Calix[4]arene Moiety and its Redox Chemistry

Lithiation of [p-Bu-t-calix[4]-(OMe)(2)(OH)(2)] (1), followed by reaction with TiCl3(thf)(3) or TiCl4(thf)(2), led to the corresponding titanium calix [4]arene complexes [p-Bu-t-calix[4]-(OMe)(2)(O)(2)TiCl] (2) and [p-Bu-t-calix [4] -(OMe)(2)(O)(2)TiCl2] (3), respectively. Reaction of 1 with TiCl4(thf)(2) results in demethylation of the calix[4]arene and the obtention of [p-Bu-t-calix[4]-(OMe) (O)(3)TiCl] (4),whose hydrolysis led to [p-Bu-t-calix [4] -(OMe) (OH)(3)] (6), The preparation of 6 can be carried out as a one-pot synthesis. Both 2 and 4 undergo alkylation reactions using conventional procedures, thus forming surprisingly stable organometallic species, namely [p-Bu-t-calix [4]-(OMe)(2)-(O)(2)Ti(R)] (R =Me (7); CH2Ph(8),p-MeC6H4 (9)) and [p-Bu-t-calix[4] -(OMe) (O)(3)Ti(R)] (R =Me (10); CH2Ph (11);p-MeC6H4 (12)). Complexes 7 and 9 undergo a thermal oxidative conversion into 10 and 12, occurring with the demethylation of one of the methoxy groups. A solid state structural property of 9 and 12 has been revealed by X-ray analysis showing a self-assembly of the monomeric units into a columnar polymer, where the p-tolyl substituent at the metal functions as a guest group for an adjacent titanium-calixarene, Reductive alkylation of 3 with Mg(CH2Ph)(2) gave 8 instead of forming the corresponding dialkyl derivative. Two synthetic routes have been devised for the synthesis of the Ti(III)-Ti(III) dimer [p-Bu-t-calix[4]-(OMe)(O)(3)Ti](2)(13): the reduction of 4 and the reaction of TiCl3(thf)(3) with the lithiated form of 6. A very strong antiferromagnetic coupling is responsible for the peculiar magnetic behavior of 13. The proposed structures have been supported by the X-ray analyses of 4, 9, 12 and 13.