Guideline for Analysis and Prevention of Contamination Catalysis.

Over the last decades, numerous efforts have been made to replace metal catalysts with cheaper and earth-abundant alternatives or to completely exclude metals from cross-coupling reactions while maintaining high efficiency in the target transformation. However, follow-up studies often revealed the role of metal impurities in the catalytic process. Thus, active metal impurities can lead to mechanistic misinterpretations, and these could initiate erroneous research directives and lead to severe reproducibility problems. Milestone precedents of the impurity effect in cross-coupling reactions are well documented in the literature. Interestingly, this fallacy has reoccurred repeatedly over the years due to a lack of thorough mechanistic studies and appropriate research study schemes for identifying impurity effects. Herein, we propose a guideline to elucidate the real catalyst of future catalytic transformations, aiming to reveal the correct mechanism and help exclude the role of impurities in novel catalytic processes. Although this guideline mainly focuses on problems related to trace transition metals, it also offers the basis for more general catalyst research.