Preparation and characterization of nickel(II), copper(II) and palladium(II) complexes with 5,14-dihydro-7,16-diethyl-dipyrazo[b,i][1,4,8,11]tetraazacyclotetradecine

A novel macrocycle, 5,14-dihydro-7,16-diethyldipyrazob,i]1,4,8,11]tetraazacyclotetradecine, has been synthesized from 1,2-diaminopyrazine and 2-ethyl-3-ethoxyacrolein. The absorption bands appearing in the energy range greater than 20000 cm^?1 were attributable to the π → π transitions. The bands in the range of the 20100–23300 cm^?1 show more bathochromic shift and greater intensity than those observed for corresponding 5,14-dihydro-7,16-diethyldibenzob,i]1,4,8,11]tetraazacyclotetradecine and/or 5,14-dihydro-7,16-diethyl-(Z)-dipyridob,i]1,4,8,11]tetraazacyclotetradecine. The nickel(II), copper(II) and palladium(II) complexes of 5,14-dihydro-7,16-diethyldipyrazob,i]1,4,8,11]tetraazacyclotetradecine have been synthesized using a metal template reaction. In ¹H and ¹³C nmr spectra, the signals of annulene skeleton for metal-free ligand and its complexes were found to observe in the lower field than those of the dibenzoanalogue.