Quantitative Assay for the Direct Comparison of Platinum Catalysts in Benzene H/D Exchange

Abstract

This paper describes a protocol for the direct comparison of diverse Pt catalysts in the H/D exchange between C6H6 and TFA-d1, CD3CO2D, and TFE-d3 using turnover number (TON) as a standard metric. An initial survey of Pt complexes, including commercial Pt salts (PtCl2, K2PtCl4) and Pt chloride complexes containing bidentate and tridentate nitrogen donor ligands, has been conducted. These studies have established that the addition of AgOAc (in TFA-d1) or AgBF4 (in CD3CO2D and TFE-d3) displaces the Cl ligands on the Pt precatalyst, which leads to dramatically increased turnover numbers. In general, PtCl2 and K2PtCl4 provided the fewest turnovers, and species containing bidentate ligands afforded higher turnover numbers than those with tridentate ligands. A diimine Pt complex was found to be a top performing catalyst for H/D exchange with all deuterium sources examined. Interestingly, the relative reactivity of many of the catalysts varied dramatically upon changing the deuterium source, highlighting the need to thoroughly assay potential catalysts under a variety of conditions.