Titanium-carbon functionalities on an oxo surface defined by a calix [4] arene moiety and its redox chemistry

Abstract

Lithiation of [ p-Bu t-calix[4]-(OMe) 2(OH) 2] ( 1), followed by reaction with TiCl 3(thf) 3 or TiCl 4(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]TiCl 2] ( 3), respectively. Reaction of 1 with TiCl 4(thf) 2 results in demethylation of the calix[4]arene and the obtention of [ p-Bu t-calix[4]-(OMe) 2(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) 2Ti(R)] (R = Me ( 7); CH 2Ph ( 8), p-MeC 6H 4 ( 9) and [ p-Bu t-calix[4]-(OMe)(O) 3Ti(R)] (R = Me ( 10); CH 2Ph ( 11); p-MeC 6H 4 ( 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(CH 2Ph) 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) 3Ti] 2] ( 13): the reduction of 4 and the reaction of TiCl 3(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.