Diarylplatinum(II) Scaffolds for Kinetic and Mechanistic Studies on the Formation of Platinacycles via an Oxidative Addition/Reductive Elimination/Oxidative Addition Sequence

Abstract

Oxidative addition and reductive elimination reactions are fundamental steps in processes related to synthetic chemistry involving organometallic compounds. In these reactions a metal in two available oxidation states (generally differing in two units) is needed, platinum centers being a very good example. The relative inertness of diamagnetic PtII and PtIV organometallic species (having, respectively, d8 square-planar or d6 octahedral arrangements), enables an easy monitoring of time-resolved reactivity, including its posterior kinetic analysis. Specifically, imine ligands containing C-X bonds have been observed to oxidatively add to {PtII(Aryl)2} moieties, which sequentially undergo C-C reductive elimination and C-H bond activation on the new ligand formed. These new species have been found to contain mostly seven-membered metallacycles, despite the obvious thermodynamic preference for five-membered cycles, which are found only in some rather specific instances. The kinetic preference of the complexes obtained has been studied from a kinetico-mechanistic perspective, that included obtaining thermal- and pressure-derived activation parameters, and a dramatic influence on the spectator halido ligands, and the substituents on the aryl groups has been established. To complete this kinetic and mechanism (kinetico-mechanistic) study, theoretical calculations have also been conducted to model the data collected and propose both the elementary steps and the factors determining the specificity of the full process.