Synthesis of mono- and trinuclear palladium(II) complexes via oxidative addition of a bulky hexathioether containing a disulfide bond to palladium(0)

The oxidative addition reactions of a bulky hexathioether containing a disulfide bond, TbtS(o-phen)S(o-phen)SS(o-phen)S(o-phen)STbt (1) (Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, o-phen = o-phenylene), to a palladium(0) complex were studied. In the reaction of 1 with 3 molar amounts of [Pd(PPh3)4], a trinuclear palladium(II) complex, [Pd3{S(o-phen)S}2{(o-phen)STbt}2(PPh3)2] (2), was formed via three-step palladium insertion reaction including unusual C(aryl)–S bond cleavages. On the other hand, the reaction of 1 with an equimolar amount of [Pd(PPh3)4] afforded mononuclear palladium(II) complex having a pseudo-octahedral structure, [Pd{S(o-phen)S(o-phen)STbt}2] (3). The hexa-coordinated geometry for the palladium center in 3 was confirmed by the atoms in molecule (AIM) analysis, which revealed the presence of the bond critical points between the central Pd atom and the S atoms at the axial positions. In contrast to the bulky system, the reaction of Ph-substituted hexathioether, PhS(o-phen)S(o-phen)SS(o-phen)S(o-phen)SPh (4), with an equimolar amount of [Pd(PPh3)4] gave a palladium(II) complex having square-planar structure, [Pd{S(o-phen)S(o-phen)SPh}2] (5). Theoretical calculations revealed that there is no remarkable difference among the energies of isomers of [Pd{S(o-phen)SPh}2], 6a-syn, 6a-anti, 6b-syn, and 6b-anti. This result suggests that a reason for the preference of the trans-anti-conformation in 3 is the steric repulsion between the bulky Tbt groups, and that of the cis-syn-conformations in 5 and 6 is the intermolecular interactions.

Tripalladium(II) complex 2 was formed by the reaction of bulky hexathioether 1 with 3 molar amounts of [Pd(PPh3)4] via the S–S and the unusual aryl C–S bond cleavages. On the other hand, the reaction of 1 with an equimolar amount of [Pd(PPh3)4] affords monopalladium(II) complex 3 having pseudo-octahedral structure.Figure optionsDownload as PowerPoint slide