Rosenthals reagent is a metallocene bis(trimethylsilyl)acetylene complex with zirconium (CpZr) or titanium (CpTi) used as central atom of the metallocene fragment CpM. Additional ligands such as pyridine or THF are commonly used as well. With zirconium as central atom and pyridine as ligand, a dark purple to black solid with a melting point of 125–126 °C is obtained. Synthesizing Rosenthals reagent of a titanocene source yields golden-yellow crystals of the titanocene bis(trimethylsilyl)acetylene complex with a melting point of 81–82 °C. This reagent enables the generation of the themselves unstable titanocene and zirconocene under mild conditions.
The reagent is named after the German chemist  (born 1950) and was first synthesized by him and his co-workers in 1995.