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

The reactions of the nitrile complexes <i>cis</i>- and <i>trans</i>-[PtCl₂(NCR)₂] (R = Me, Et, CH₂Ph, Ph) with an excess of ethanethiol, EtSH, in the presence of a catalytic amount of <i>n</i>-BuLi in tetrahydrofuran (THF), afforded in good yield the bis-imino thioether derivatives <i>cis</i>-[PtCl₂{<i>E</i>-N­(H)C­(SEt)­R}₂] (R = Me (<b>1</b>), Et (<b>2</b>), CH₂Ph (<b>3</b>), Ph (<b>4</b>)) and <i>trans</i>-[PtCl₂{<i>E</i>-N­(H)C­(SEt)­R}₂] (R = Me (<b>5</b>), Et (<b>6</b>), CH₂Ph (<b>7</b>), Ph (<b>8</b>)). The imino thioether ligands assumed the <i>E</i> configuration corresponding to a <i>cis</i> addition of the thiol to the nitrile triple bond. The spectroscopic properties of these complexes have been reported along with the molecular structures of <b>1</b>, <b>2</b>, and <b>7</b> 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, <i>trans</i>-[PtCl₂{<i>E</i>-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

Platinum(II) Complexes with Novel Diisocyanide Ligands: Catalysts in Alkyne Hydroarylation

A series of novel diisocyanide ligands (<i>o</i>-CNC₆H₄O)₂Y (diNC-1: Y = P­(O)­Ph; diNC-2: Y = <i>o</i>-C­(O)­C₆H₄C­(O); diNC-3: Y = <i>m</i>-C­(O)­C₆H₄C­(O); diNC-4: Y = C­(O)­C₂H₄C­(O); diNC-5: Y = <i>trans</i>-C­(O)­C₂H₂C­(O)) was successfully synthesized by reaction of lithium 2-isocyanophenate (generated in situ from benzoxazole and <i>n</i>-BuLi) and a diacylic or phosphonic dichloride. The corresponding platinum­(II) complexes of general formula [PtX₂(diNC)]_1,2 (X = Cl, Me; diNC = diisocyanide ligand) were isolated by simple substitution of 1,5-cyclooctadiene in the starting [PtX₂(COD)] complexes. The structure of the complexes, mononuclear or dinuclear, was confirmed by single-crystal X-ray analysis. A dinuclear complex of formula {(μ-diNC)­[<i>cis</i>-PtCl₂(PPh₃)]₂} could also be obtained with the diisocyanide ligand having a rigid fumaryl bridge and consequently the isocyanide moieties pointing in opposite directions. All the complexes were employed as catalysts in the hydroarylation of alkynes, showing generally good activity and selectivity toward the <i>trans</i>-hydroarylation product. With <i>N</i>-methylindole as aromatic substrate the major product was instead a heterocycle:alkyne 2:1 adduct

Platinum(II) Complexes with Novel Diisocyanide Ligands: Catalysts in Alkyne Hydroarylation

A series of novel diisocyanide ligands (<i>o</i>-CNC₆H₄O)₂Y (diNC-1: Y = P­(O)­Ph; diNC-2: Y = <i>o</i>-C­(O)­C₆H₄C­(O); diNC-3: Y = <i>m</i>-C­(O)­C₆H₄C­(O); diNC-4: Y = C­(O)­C₂H₄C­(O); diNC-5: Y = <i>trans</i>-C­(O)­C₂H₂C­(O)) was successfully synthesized by reaction of lithium 2-isocyanophenate (generated in situ from benzoxazole and <i>n</i>-BuLi) and a diacylic or phosphonic dichloride. The corresponding platinum­(II) complexes of general formula [PtX₂(diNC)]_1,2 (X = Cl, Me; diNC = diisocyanide ligand) were isolated by simple substitution of 1,5-cyclooctadiene in the starting [PtX₂(COD)] complexes. The structure of the complexes, mononuclear or dinuclear, was confirmed by single-crystal X-ray analysis. A dinuclear complex of formula {(μ-diNC)­[<i>cis</i>-PtCl₂(PPh₃)]₂} could also be obtained with the diisocyanide ligand having a rigid fumaryl bridge and consequently the isocyanide moieties pointing in opposite directions. All the complexes were employed as catalysts in the hydroarylation of alkynes, showing generally good activity and selectivity toward the <i>trans</i>-hydroarylation product. With <i>N</i>-methylindole as aromatic substrate the major product was instead a heterocycle:alkyne 2:1 adduct