Copper complexes of strongly electron rich and deficient salen ligands br

Three copper(II) salen compounds (Cu(SalR)) bearing strongly electron donating (Cu(SalNMe2)), electronically neutral (Cu(SaltBu)) and strongly electron withdrawing (Cu(SalNMe3)) para-substituents were prepared. Their geometric structures were evaluated by single crystal X-ray diffraction and supported by theoretical DFT cal-culations. The electronic spectra of Cu(SalR) revealed LMCT bands at 23 000 cm1-27 000 cm1 with varying para-substituents, while the d-d bands remain around 17 600 cm1. The electrochemical behaviour of Cu(SalR), evaluated by cyclic voltammetry, reveal the expected positive shift in redox waves for more electron deficient compounds (Cu(SalNMe2) (CH2Cl2): 0.08, 0.03, 0.55, 0.64 V; Cu(SaltBu) (CH2Cl2): 0.59, 0.74 V; Cu(SalNMe3) (DMF): 0.78 V versus ferrocene/ferrocenium). The additional reversible oxidative couples observed for Cu(Sal-NMe2) are likely due to the strongly electron donating NMe2 moieties that either enable additional oxidation events to occur, and/or shifting any additional oxidation events within the experimental electrochemical win-dow. One-electron oxidation of Cu(SalNMe2) and Cu(SaltBu) were monitored using low temperature UV-vis spectroscopy: characteristic spectra for metal oxidized [CuIII(SaltBu)]+and ligand oxidized [CuII(SalNMe2)center dot]+species were observed

Automated summary

In this study, three copper(II) salen compounds with different electron donating or withdrawing para-substituents were synthesized and their geometric structures, electronic spectra, and electrochemical behavior were evaluated. The results showed that the properties of these compounds were influenced by the electron properties of the para-substituents, including geometric structures, electronic spectra, and redox potentials.