Heteropolytopic Arsanylarylthiolato Ligands: Cis–Trans Isomerism of Nickel(II), Palladium(II), and Platinum(II) Complexes of 1-AsPh2-2-SHC6H4

Heteropolytopic arsanylthiolato ligands 1-AsPh2-2-SHC6H4 (AsSH), PhAs­(2-SHC6H4)2 (AsS2H2), and As­(2-SHC6H4)3 (AsS3H3) have been prepared by lithiation–electrophilic substitution procedures. The 2:1 reaction of AsSH with NiCl2·6H2O, Na2[PdCl4], and [PtI2(cod)] (cod = 1,5-cyclooctadiene) in the presence of NEt3 afforded the square-planar complexes trans-[Ni­{(AsS)-κ2S,As}2] (1), cis-[Pd­{(AsS)-κ2S,As}2] (2), trans-[Pd­{(AsS)-κ2S,As}2] (3), and cis-[Pt­{(AsS)-κ2S,As}2] (4). In the cases of nickel and platinum, only one isomer was isolated. With palladium, initially the cis isomer 2 is formed and undergoes slow isomerization to the trans isomer 3 in solution. Small amounts of the trinuclear complex [{PtI­(1-AsPh2-μ-2-S-C6H4-κ2S,As)}3] (5) are also formed besides the mononuclear platinum bis-chelate complex 4. Density functional theory calculations support a dissociative mechanism for the isomerization of the palladium­(II) complexes.