Synthesis, Characterization, Crystal Structures and Computational Studies on Novel Cyrhetrenyl Hydrazones

The synthesis of novel cyrhetrenyl hydrazones of general formula [Re{(eta(5)-C5H4)-C(R-1) = NNHR2}(CO)(3)] {with R-1 = H and R-2 = 4-NO2-C6H4 (4a), C6H5 (4b) or H (4c) or R-1 = Me and R-2 = 4-NO2-C6H4 (5a), C6H5 (5b) or H (5c)} is described. Compounds 4ae4c and 5ae5c were characterized by mass spectrometry and IR spectroscopy. H-1 and C-13{H-1} NMR studies revealed that 4a-4c and 5a-5c adopt the anti-(E) configuration in solution. X-ray crystal structures of compounds 4a and 5c confirmed the trans-arrangement of the cyrhetrenyl "Re(eta(5)-C5H4)(CO)(3)" and the -NHR2 moieties and the existence of strong hydrogen bonds involving the -NH- unit. Molecular Orbital calculations at a DFT level have also been carried out in order to rationalize the influence of the nature of the substituent R-3 of [(RCH)-C-3 = NNH(4-NO2-C6H4)] (R-3 = ferrocenyl, (3a), cyrhetrenyl (4a), phenyl (6a) or cymantrenyl (7a) on the electronic delocalization, the nucleophilicity of the imine carbon, the polarizability and hyperpolarizability of these compounds, and computational studies using time-dependent density functional (TD-DFT) calculations have also been carried out in order to assign the bands detected in their electronic spectra and to explain the effect produced by the solvent. (C) 2016 Elsevier B.V. All rights reserved.