G. Newkome, A. Nayak, F. Fronczek
Aug 1, 1979
Citations
0
Influential Citations
24
Citations
Journal
Journal of the American Chemical Society
Abstract
The synthesis of I : I crown ether macrocycles containing a 2.2-bipyridyl subunit by nucleophilic displacement reac- tions by the dianion of oligonieric glycols is described. The NMR spectral data of these macrocycles indicate that the preferred conformations are ascertained by the size of the polyethereal bridge. Variable-temperature NMR studies of the penta- and hexaethylene glycol-bipyridyl macrocycles support a conformational rotation at diminished temperatures, in which the syn conformation is preferred at > -70 OC, whereas at room temperature the anti conformation is dominant. Detailed mathemati- cal analysis suggests that only about 5% of molecule 6 occupies the anti conformation at -100 "C. However, the crystal struc- ture determination of 6 was conducted, thus establishing its anti conformation in the solid state. Numerous chelating reagents have been designed and created for analysis of metal ions, but few have received more attention than those of the 2,2'-bipyridyl class (1). Blau's initial discovery3 of Fe(l1) and Fe(lI1) complexation by this ligand at the turn of this century has sparked the ingenuity of chemists to devise more selective ligands, which have been based on the metamorphosis of the Schiff-base moiety of these bipyridyls. In 1972, a second-generation bipyridyl ligand was designed in which the bipyridyl moiety was used as a subunit within a macrocyclic framew01-k.~ Ogawa et aL5 reported the inclusion of the 1 ,lO-phenanthroline subunit into a macropolyhetero- cyclic framework, whereas later Buhleier and Vogtle6 dem- onstrated the incorporation of either this same subunit or the bipyridyl moiety into a macrocycle via direct nucleophilic displacement of heteroaryl halides7 with alkoxides or mer- captides. Bridged Schiff-base macro cycle^^^^ have also recently been synthesized from either 6,6'-dihydrazino-2,2'-bipyridyl or 2,9-di(methylhydrazino)-l, IO-phenanthroline, macrocyclic bisamideslO from 2,2'-bipyridyl-6,6'-dicarboxylic acid chloride with diverse diamines, and macrocyclic bisesters' from 2,2'- bipyridyl-3,3'-dicarboxylic acid.) I Recently in our laboratories, the ring contraction of phosphorus macrocycles" and a ring- contractive decarbonylation of dipyridyl ketonesI3 afforded unexpected new routes to crown-ether macrocycles possessing the 2,2'-bipyridyl unit. We herein report our original more traditional approach to these bipyridyl macrocycles as well as their temperature-dependent conformational preferences and configuration within the crystal. These studies suggest that different modes of ion complexation of conformationally mo- bile ligands may be possible depending upon the rotamer dis- tribution at diminished temperatures. Results