Structural preferences in phosphanylthiolato platinum(II) complexes

The transition-metal complexes of heterotopic phosphanylthiolato ligands are useful in various reactions which depend on the stereochemistry of the complexes. Bis-chelate complex [Pt(SCH₂CH₂PPh₂-κ²P,S₂)] (1) was obtained in good yields by direct base-free substitution reaction of the corresponding phosphanylthiol (HSCH₂CH₂PPh₂) with K₂PtCl₄ or by oxidative addition of the same phosphanylthiol to Pt(PPh₃)₄. In agreement with the antisymbiosis rule, complex 1 shows a cis -P,P arrangement in solid state crystallizing in the monoclinic system (C2 /c). Density functional theory (DFT) calculations on 1 reveal the right characteristics for the preferred cis -P,P arrangement, rationalizing its formation. Direct base-free reaction of [PtCl₂(1,5-cyclooctadiene)] with one equivalent of the same phosphanylthiol produce the trinuclear complex [PtCl(μ-SCH₂CH₂PPh₂-κ²P,S)]₃ (2) instead of the binuclear structure common in palladium and nickel derivatives. Crystals of 2 are triclinic (P ) showing a sulfur-bridging edge-sharing cyclic trinuclear complex with square-planar coordination geometry around the platinum atoms and a Pt₃S₃ cycle in skew-boat conformation. This preference for the trinuclear structure was rationalized mechanistically and through conceptual DFT.