A computational comparison of NiII and PtII hydrido-tris(pyrazolyl)borate supported hydroarylation catalysis

As alkyl-arenes are important feedstock chemicals, synthetic methods more atom economical than traditional Friedel-Crafts and bond-coupling reactions are needed. PtII complexes have been experimentally demonstrated to facilitate olefin hydroarylation. A TpPtII catalyst model (Tp = hydrido-tris(pyrazolyl)borate) was selected for computational studies. Nickel's low cost prompted its evaluation as it is isoelectronic to platinum. Computational results indicate that nickel and platinum operate through different mechanisms. The TpPt catalyst model activates benzene through a two-step oxidative addition/reductive elimination mechanism with a PtIV intermediate. However, the TpNi catalyst forms ethylbenzene product and closes the catalytic loop via a single step (sigma-bond metathesis) mechanism. Despite these differences in mechanism, comparable energy barriers (differing by ca. 2 kcal/mol), are derived from density functional theory (DFT) simulations. The present results suggest that attempts to “reverse engineer” precious metal catalyst substitutes with Earth-abundant metals (e.g., Pt → Ni) may require reconsideration of typical structure–property relationships in catalyst design.

.Figure optionsDownload high-quality image (196 K)Download as PowerPoint slideHighlights
► TpNiII and TpPtII complexes had activation barriers within 2 kcal/mol of each other.
► TpNiII operated via a sigma-bond metathesis mechanism.
► TpPtII proceeded by an oxidative addition/reductive elimination mechanism.