Synthesis and Characterization of the Hemi‐Salen Ligands and Their Triboron Complexes: Spectroscopy and Examination of Anticancer Properties

The synthesis, spectroscopic properties, and in vitro cytotoxicity activity of a series of various salen‐based triboron complexes have been designed and prepared from hemi‐salen ( L ₁ H ₃  –  L ₄ H ₃ ) ligands and BF₃·Et₂O or BPh₃ under simple reaction conditions. The hemi‐salen ( L ₁ H ₃  –  L ₄ H ₃ ) ligands and their BF₂ or BPh₂ chelating triboron complexes were characterized by means of NMR (¹H, ¹³C, ¹⁹F, and ¹¹B) spectra, FT‐IR spectra, UV/VIS spectra, fluorescence spectra, mass spectra, melting point, as well as elemental analysis. The triboron [L _{(1  –  4)} (BF ₂ ) ₃ ] and [L _{(1  –  4)} (BPh ₂ ) ₃ ] complexes were investigated for their absorption and emission properties, and these complexes are also good chelates towards boron(III) fragments such as BF₂ or BPh₂ quantum yield in solution reaching up to 38%. The hemi‐salen ( L ₁ H ₃  –  L ₄ H ₃ ) ligands and their BF₂ or BPh₂ chelating triboron complexes were tested for the in vitro anticancer activity against various cancer and normal cells (HeLa, DLD‐1, ECC‐1, PC‐3, PNT‐1A, and CRL‐4010), and it was found that the cell viability of cancer cells was decreased while most of the healthy cells could still be viable. Also, the cytotoxicity studies showed that anticancer activity of hemi‐salen ( L ₁ H ₃  –  L ₄ H ₃ ) ligands is higher than that of triboron [L _{(1  –  4)} (BF ₂ ) ₃ ] and [L _{(1  –  4)} ( BP h ₂ ) ₃ ] complexes. The hemi‐salen ( L ₁ H ₃  –  L ₄ H ₃ ) ligands showing the strongest cytotoxic effect in PC ‐3 cells were found to exhibit anticancer activity with apoptosis by increasing the level of ROS in the PC ‐3 cells.