ON THE STRUCTURES OF 1-AZAPENTADIENYLLITHIUM COMPOUNDS

1-Azapentadienyllithium compounds 2-6 have been prepared by deprotonation of the alpha,beta-unsaturated imines 1 with lithium diisopropylamide. Their structures in THF solution at various temperatures have been studied by H-1- and C-13-NMR spectroscopy. All N-alkyl-substiuted derivatives 2-5 adopt W conformations of the 1-azapentadienyl unit. The N-tert-butyl-substituted compound 2 shows an (E)-configurated N = C-bond, whereas compounds 3-5 prefer (Z)-N = C configurations. According to NOE experiments, the triphenyl system 6 has a U-shape structure, probably because of steric interactions of the phenyl substituents. C-13-shifts of the 1-azapentadienyl carbon atoms are discussed in terms of HOMO coefficients. The experimental structural results are compared with theoretical data obtained by MNDO and ab initio calculations for the corresponding anions. MNDO results are also given for monomeric 1-azapentadienyllithium conformers 11.