Synthesis, crystal structure, and cytotoxicity studies of titanacalix[4 and 8]arene complexes

Reaction of 5,11,17,23-tetra-tert-butyl-dihydroxy-26,28-bis(2-entoxy)calix[4]arene (L(OH)2(Opentyl)2) with [TiCl4] afforded the dichlorotitanoacalix[4]arene complex [TiCl2L(O)2(Opentyl)2] (1) in good yield. Hydrolysis of 1 led to the isolation of the complex {[TiL(O)3(Opentyl)]2(-OH)(-Cl)} (2). Reaction of 49,50,51,52,53,54,55,56-octapropoxycalix[8]arene (L/(Opropyl)8) with [TiCl4] in refluxing toluene afforded, following work-up, a 35:65 mixture (3) of the complex [Ti(NCMe)Cl]2[TiCl(-O)]2L/] and the silicone grease derived complex [Ti(NCMe)Cl]2[Ti(-O)]2[OSi(CH3)2OSi(CH3)2O]L/] in which the grease replaces two chloride ligands. The molecular structures of 1∙2MeCN, 2∙7¼MeCN, and 3∙10MeCN have been determined. The complexes were studied using in vitro cell assays and were found to have CC50 values in the range 111 - 186 µM, i.e. they have low toxicity.