Negishi's reagent and Rosenthal's reagent are the two most important zirconium sources for the formation of zirconacyclopentadienes and further zirconium precursors. In this study, we compared both regarding yield, reaction time, and stability of the product in the reaction mixture. In total, Rosenthal's zirconocene was much more efficient in all three categories. A further advantage of Rosenthal's zirconocene was the easy handling and the stability of this reagent compared to Negishi's reagent, which is formed in situ; Rosenthal's reagent has stabilizing ligands so that it can be isolated in pure form by crystallization. More information can be found in the Full Paper by A. Staubitz et al. on page 13318.