Cali[4]arene containing ferrocene or nickel dithia diaza as anion sensor

Abstract

25,27-N,Ń -bis(mercaptoethyl)-1,5-diazacyclooctaneethyl-p-tent-butylcalix[4]arene (6) can be synthesized by 2 methods. In the first method, coupling reaction of dibromoethylcalix[4]arene (2a) and Ni(bme-daco) bearing Ni acting as a metal template in CH₃CN afforded Ni(bme-daco)calix[4]arene (4a.Br₂). Interestingly, synthesis of dibromoethylcalix[4]arene (2a) produced the large amount of the by-product of dimericcalix[4]arene (3). In the second method, the reaction of dichloroethyl-calix[4]arene (2b) and Ni (bme-daco) in the presence of NaI as a catalyst in CH₃CN provided the Ni(bme-daco)calix[4] arene (4b.I₂) and the by-product, BisNi(bmedaco)calix[4]arene (5). Ni(II) was removed by refluxing compound 4 with KCN in CH₃CN to provide compound 6. 5,7-Diamideferrocenyl-25,26,27,28-tetraalkylcalix[4]arenes (5a, 5b and 5c) were prepared by coupling reactions of tetraalkyldiaminocalix[4]arenes (4a, 4b and 4c) and 1,1-Bis(chlorocabonyl)ferrocene in dichloromethane with triethylamine as base. Elucidation of the structures by NMR spectroscopy found that 5a and 5b were in the equilibrium of cone and partial cone conformations while 5c was in cone conformation. Binding abilities were investigated by ¹H-NMR titrations, cyclic voltammetry and squarewave voltammetry in CH₃CN. Ligands 5a, 5b and 5c were found to bind carboxylate anions significantly better than H₂PO₄¯ and Cl¯. The binding ability order of ligands towards anions is 5c > 5a > 5b). Additionally, 5c can bind alkali metals at tetraethyl ester units as studied by electrospray ionization mass spectrometry.