Synthesis and Multinuclear NMR Characterizations of Some Diselena- and Tetraselenacyclophanes.

Article abstract of DOI:10.1016/S0040-4020(01)80024-7

Several symmetrical and unsymmetrical bis-selenacyclophanes were prepared and characterized by multinuclear (1H, 13C<1H> and 77Se<1H>) NMR.The symmetrical cyclophanes of phenyl, furyl, pyridyl and thiophenyl appear to exist in predominantly syn conformation in solution at room temperature.VT-1H NMR of some cyclophanes indicate that the equilibrium between the syn conformers which differ in the disposition of the bridge seleniums (symmetric about mirror plane <*> symmetric about inversion center) can be slowed at low temperatures.Interesting 13C<1H> shifts are observed in unsymmetrical cyclophanes containing 2,2'-biphenyl, pyridine and furan.The 77Se<1H> chemical shifts appear to be related to the size of the cavity of the cyclophanes.