Oxidative addition of tetrathiocins to palladium(0) and platinum(0): a route to dithiolate coordination complexes

Abstract

The preparation of a series of 4,4′,5,5′-substituted benzo-fused 1,2,5,6-tetrathiocins X₂C₆H₂S₄C₆H₂X₂ (1a–1g) were prepared from the reaction of S₂Cl₂ with 1,2-C₆H₄X₂ (X = OMe, OEt; X₂ = OCH₂O, OCH₂CH₂O, OCH₂CH₂CH₂O, MeNC(O)NMe, O(CH₂CH₂O)₄). The oxidative addition of 1a–1g to zero-valent Pd₂dba₃ or Pt₂dba₃ (dba = dibenzylideneacetone) in the presence of bis (diphenylphosphino)ethane (dppe) resulted in formation of the substituted mononuclear benzenedithiolate complexes M(L)(dppe) [L = dithiolate ligand; 2a–2g (M = Pd) and 3a–3g (M = Pt)] in 37–89% yield based on recrystallized material. Representative examples of M(L)(dppf) [dppf = bis-diphenylphosphinoferrocene; 4a, 4g (M = Pd) and 5g (M = Pt)] were prepared in a similar fashion. The structures of all derivatives were determined by X-ray diffraction, multinuclear NMR and elemental analysis. The reactivity of the two crown ether dithiolate complexes, 2g and 4g, with 1 equivalent of NaBPh₄ led to isolation of the 1 : 1 complexes in which the Na⁺ cation is bound in the macrocyclic crown, [Na(2g)(MeOH)₂][BPh₄] and [Na(4g)][BPh₄] whose structures were determined by X-ray diffraction. Electrochemical studies supported through DFT calculations on the crown ether derivatives revealed a series of ligand-based oxidation waves corresponding to the dithiolate ligand (and dppf for 4g and 5g) whose redox potentials were shifted by ca. +0.1 V on binding to Na⁺.