The Knölker complex is an organoiron compound, which is a catalyst for transfer hydrogenation.

[1] The complex features an hydroxycyclopentadienyl ligand bound to an Fe(CO)2H centre.

It is generated by the corresponding cyclopentadienone tricarbonyl by treatment with base followed by acidification.

[2] It is named for Hans-Joachim Knölker [de] The compound is related to the organoruthenium compound called Shvo's complex, a hydroxycyclopentadienyl derivative that also functions as a catalyst for hydrogenation.

[3]