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

• New series of cyrhetrenyl hydrazones were synthesized and characterized.
• All complexes adopted an (E)-configuration in solution and solid state.
• Cyrhetrenyl hydrazones, are compared to their ferrocenyl, cymantrenyl or phenyl analogues.
• DFT calculations were carried out to rationalize the influence of the substituents.

The synthesis of novel cyrhetrenyl hydrazones of general formula [Re{(η5-C5H4)C(R1) = NNHR2}(CO)3] {with R1 = H and R2 = 4-NO2C6H4 (4a), C6H5 (4b) or H (4c) or R1 = Me and R2 = 4-NO2C6H4 (5a), C6H5 (5b) or H (5c)} is described. Compounds 4a–4c and 5a–5c were characterized by mass spectrometry and IR spectroscopy. 1H and 13C{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 -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 R3 of [R3CH = NNH(4-NO2C6H4)] (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.

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