Concave hydrocarbon cyclophane π-prismands

Abstract

Small hydrocarbon cyclophanes, viz. [2.2.2]-, [2.2.1] and [2.2.0]cyclophanes, were designed and synthesised as possible hosts for silver cation complexation in order to study how small and strained hydrocarbon cyclophane can be and still act as π-prismand. In the present study sulphone pyrolysis was selected as a synthetic route and thiols and dibromides were chosen as starting materials for the high dilution synthesis. Four new π-prismands were found. X-ray crystallography was used to verify and to study the cyclophane structures. Some of the structures are the precursors of the synthesised π-prismands, so it was possible to follow the conformational changes in those structures along the synthesis route. ISE measurements were used to study the utilization of cyclophanes as selective binding reseptors. All-solid-state ion-selective electrodes (ISEs) were constructed by using cyclophanes as π-coordinating ionophores in solvent polymeric membranes. Four structuraily similar cyclophanes, i.e. [2.2.2]p,p,p-cyclophane (2), [2.2.2]m,p,p-cyclophane (47), [2.2.1]p,p,p-cyclophane (49) and [2.2.1]m,p,p-cyclophane (48) were studied as ionophores for Ag+. The selectivity pattern of the solid-contact ISEs was found to depend strongly on the structure of the cyclophane. The p,p,p-cyclophanes are more selective to Ag+ than the corresponding m,p,p-cyclophanes where one phenyl ring is coupled in the meta position. As an introduction a short review of the literature on the cyclophanes, and especially π-prismand cyclophanes, are presented from a supramolecular point of view and their behaviour as cation receptors is discussed.