Group 10 metal complexes with a tetradentate thiosemicarbazonate ligand: Synthesis, crystal structures and computational insights into the catalysis for C–C coupling via Mizoroki-Heck reaction

A series of mononuclear complexes has been synthesized by reactions of group 10 metal ions with bis(4-phenyl-3-thiosemicarbazone) (H2bPht), affording compounds of general formula [MII(bPht)] (M = Ni, Pd and Pt). Their characterization involved FTIR, UV–Vis, 1H NMR, CV, DPV and elemental analysis. Furthermore, the crystal structures of all complexes have been determined, showing that the thiosemicarbazonate ligand is coordinated as a tetradentate N,N,S,S-donor forming three five-membered chelate rings. The catalytic activity of [MII(bPht)] in Heck's C–C coupling reaction using styrene and iodobenzene to obtain stilbenes has been evaluated. It was verified that the NiII and PtII complexes present low catalytic activity, while the PdII complex showed a conversion of 99% within 24 h. Trans-stilbene was identified as the major product of the coupling reaction, up to 90%. DFT studies were also performed in order to better understand the catalytic behavior of these complexes giving support for a new route for Mizoroki-Heck reaction.