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

Abstract

Reaction of 5,11,17,23-tetra-tert-butyl-dihydroxy-26,28-bis(2-pentoxy)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(μ-OH)(μ-Cl)} (2). Reaction of 5,11,17,23,29,35,41,47-p-tert-butyl-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(μ-O)]₂L′ and the silicone grease derived complex [Ti(NCMe)Cl]₂[Ti(μ-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.