FUNCTIONALIZED UO2 SALENES - NEUTRAL RECEPTORS FOR ANIONS

A novel class of neutral receptors for anions that contain a unique co mbination of an immobilized Lewis acidic binding site (UO22+) and addi tional amide C(O)NH, groups, which can form a favorable H-bond with a coordinated anion guest, has been developed. X-ray analysis of free re ceptor 14b shows that it is organized in the solid state as dimers, th e fifth position of the uranyl being occupied by an oxygen atom of the amide group of a second molecule. Anion complexation has been demonst rated by conductometry, X-ray crystallography, cyclic voltammetry, H-1 and P-31 NMR spectroscopy, and FAB mass spectrometry. X-ray structure s of 1c.H2PO4- and 14e.H2PO4- reveal that anion binding is effected by coordination to the uranyl cation and additional H-bond formation. Th e 1c.H2PO4- complex is arranged in centrosymmetric pairs, the core of the dimer consisting of two H2PO4- anions connected by two short H-bon ds. In the case of the 14e.H2PO4- complex, the H2PO4- complexed to the uranyl forms a H-bonded associate with a second H2PO4- anion which it self is not complexed by the ligand. In the case of the preorganized l igands 14b, 14d, and 18, strong (K-ass > 10(5) M(-1) in MeCN-DMSO, 99: 1) and selective complexation of H2PO4- has been observed. Selectiviti es of >10(2) and >10(3) over Cl- and HSO4-, NO2- and SCN-, respectivel y, were obtained for receptor 14b. ''Naked'' UO2 salophenes 19a-c, in which the Lewis acidic binding center contains two vacant positions fo r guest coordination, have been designed for complexation of dianions like malonate and succinate with K values of 80-460 M(-1) in DMSO. Sal ophene 19a forms a 1:2 complex with H2PO4-. Its X-ray structure shows that the complex is organized as a H-bonded ribbon due to the facts th at the H2PO4- anions form H-bonded dimers and, in addition, two H2PO4- anions are complexed by one uranyl cation.