Synthesis, characterization, crystal structures and computational studies on novel cyrhetrenyl hydrazones

The synthesis of novel cyrhetrenyl hydrazones of general formula [Re{(η⁵-C₅H₄[Formula presented]¹) = NNHR²}(CO)₃] {with R¹ = H and R² = 4-NO₂[Formula presented]₆H₄(4a), C₆H₅(4b) or H (4c) or R¹ = Me and R² = 4-NO₂[Formula presented]₆H₄(5a), C₆H₅(5b) or H (5c)} is described. Compounds 4a–4c and 5a–5c were characterized by mass spectrometry and IR spectroscopy.¹H and¹³C{¹H} 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(η⁵-C₅H₄)(CO)₃” and the -NHR²moieties and the existence of strong hydrogen bonds involving the [Formula presented] 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 R³of [R³CH = NNH(4-NO₂[Formula presented]₆H₄)] (R³ = 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.