Synthesis and characterization of novel 2-fluoro/chloro-3-pyridyl selenides: X-ray crystal structure of bis(2-fluoro-3-pyridyl) diselenide and bis(2-fluoro-3-pyridylseleno) methane

An efficient one-pot synthesis of bis(2-fluoro/chloro-3-pyridyl) diselenide has been successfully achieved under dry-ice/acetone bath temperature that involves deprotonation of corresponding 2-fluoro/chloropyridine at C-3 with lithium di-isopropylamide, insertion of elemental selenium followed by the subsequent aerial oxidation. A series of novel and synthetically important unsymmetrical 2-fluoro/2-chloro substituted alkyl/allyl/benzyl pyridyl selenium compounds and a diselenoacetal, bis(2-fluoro-3-pyridylseleno) methane have been prepared by the reductive cleavage of the titled bis(2-fluoro/chloro-3-pyridyl) diselenides with sodium borohydride followed by quenching with the appropriate alkylating agents. The same could be realized by the deprotonation of 2-halopyridine accompanied with the insertion of elemental selenium followed by addition of appropriate alkylating agents. The hitherto unknown compounds have been fully characterized by elemental analysis and various spectroscopic techniques i.e., FT-IR, multinuclear (1H, 13C, 19F and 77Se) NMR and mass spectrometry. The crystal structures of bis(2-fluoro-3-pyridyl) diselenide and bis(2-fluoro-3-pyridylseleno) methane have been determined by single crystal X-ray diffraction (XRD).