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

The preparation of a series of 4,4′,5,5′-substituted benzo-fused 1,2,5,6-tetrathiocins X 2 C 6 H 2 S 4 C 6 H 2 X 2 ( 1a-1g ) were prepared from the reaction of S 2 Cl 2 with 1,2-C 6 H 4 X 2 (X = OMe, OEt; X 2 = OCH 2 O, OCH 2 CH 2 O, OCH 2 CH 2 CH 2 O, MeNC(&z.dbd;O)NMe, O(CH 2 CH 2 O) 4 ). The oxidative addition of 1a-1g to zero-valent Pd 2 dba 3 or Pt 2 dba 3 (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 NaBPh 4 led to isolation of the 1 : 1 complexes in which the Na + cation is bound in the macrocyclic crown, [Na( 2g )(MeOH) 2 ][BPh 4 ] and [Na( 4g )][BPh 4 ] 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 + . Functionalized benzenedithiolate complexes of Pt and Pd were prepared by oxidative addition of a library of 1,2,5,6-tetrathiocins to M 2 (dba) 3 . The oxidation potentials of crown-ether derivatives were increased upon binding Na + ions.