Methylation of [Pt₂(μ-SR) (μ-S) (PPh₃)₄]: en route to mixed-thiolato bridged complexes

Abstract

Sequential and independent alkylation of [Pt₂(μ-SR) (μ-S) (PPh₃)₄] by RX followed by methylation with Me₂SO₄ led to the first successful isolation of novel diplatinum complexes [Pt₂(μ-SR) (μ -SCH₃) (PPh₃)₄](PF₆)₂ (3) (R= CH₂C₆H₅(a), CH₂CHCH₂ (b), C₅H₁₀CO₂CH₂CH₃(c), C₂H₄CO₂- CH₂CH₃(d), CH₂CH₂CN (e), C₂H₄CH-(O)₂C₂H₄ (f), and C₂H₄SC₆H₅(g)) with asymmetric thiolato bridges. The synthetic methodology can tolerate a range of electronically and sterically contrasting thiolate substituents with different chemical functionalities. The X-ray crystal structures of 3 a–c, g confirm the unusual heterodialkylation with two different thiolato bridging ligands in a syn–exo conformation. A secondary product [Pt₂(μ-SC₂H₄SC₆H₅) (μ-SCH₃)(PPh₃)₃](PF₆)₂ (4), which arises from intramolecular phosphine displacement by the thio pendant at the neighboring SC₂H₄SC₆H₅bridge, has been trapped and characterized. This is an unusual diplatinum complex with three different bridging thio ligands and three different phosphines. The heteroalkylation is screened in situ by ESI-MS, and the resultant spectral data provide a convenient guide for one-pot syntheses of {M₂(SR) (SR’)} from {M₂S}. The isolation and X-ray crystal structure of a homoalkylated analogue [Pt₂(μ-SCH₃)₂(PPh₃)₄](PF₆)₂ (6) is included for comparison.