Poisonous Truth about the Mercury Drop Test: The Effect of Elemental Mercury on Pd(0) and Pd(II)ArX Intermediates
Ian C. Chagunda, Tiago Fisher, Makenna Schierling, J. Scott McIndoe
Abstract
The mercury drop test is a widely used method often regarded as decisive for discriminating between homogeneous and heterogeneous catalysis in organometallic systems. However, recent research has highlighted the limitations of this test due to the intrinsic reactivity of some organometallic compounds toward elemental mercury. In this study, we used real-time mass spectrometry to investigate the effect of elemental mercury on L n Pd 0 and Pd II ArX intermediates common in palladium-catalyzed cross-coupling reactions. Our findings demonstrate that mercury can interact with both species through redox-transmetallation and amalgamation processes, leading to inhibition of catalytic activity, which would often be misinterpreted as evidence for heterogeneous catalysis. This result further calls into question the widely held assumption that mercury reacts selectively with heterogeneous catalytic species. Therefore, it is important to carefully evaluate the results provided by the mercury drop test and incorporate alternative comprehensive kinetic analysis of the catalyst.