Novel Imino Thioether Complexes of Platinum(II): Synthesis, Structural Investigation, and Biological Activity

The reactions of the nitrile complexes cis- and trans-[PtCl2(NCR)2] (R = Me, Et, CH2Ph, Ph) with an excess of ethanethiol,
EtSH, in the presence of a catalytic amount of n-BuLi
in tetrahydrofuran (THF), afforded in good yield the bis-imino thioether
derivatives cis-[PtCl2{E-N­(H)C­(SEt)­R}2] (R = Me (1), Et (2), CH2Ph (3), Ph (4))
and trans-[PtCl2{E-N­(H)C­(SEt)­R}2] (R = Me (5), Et (6), CH2Ph (7), Ph (8)). The imino thioether ligands
assumed the E configuration corresponding to a cis addition of the thiol to the nitrile triple bond. The
spectroscopic properties of these complexes have been reported along
with the molecular structures of 1, 2, and 7 as established by X-ray crystallography which indicated
that these compounds exhibit square-planar coordination geometry around
the platinum center. Four N–H···Cl intermolecular
contacts (N–H···Cl ca. 2.5–2.7 Å)
between each chlorine atom and the N–H proton of the imino
thioether ligand gave rise to “dimers” Pt2Cl4L4 (L = imino thioether) formed by two PtCl2L2 units. The cytotoxic properties of these new
platinum­(II) complexes were evaluated against various human cancer
cell lines. Among all derivatives, trans-[PtCl2{E-N­(H)C­(SEt)­CH2Ph}2] showed the greatest in vitro cytotoxic activity being able
to decrease cancer cell viability roughly 3-fold more effectively
than cisplatin.