Task: Text Categorization
Input (English): The yield of these compounds can be increased through ball milling of some of their components, and one mode of operation of these compounds proceeds through a mechanism called enantiomorphic site control. A process for the operation of these compounds that proceeds through migratory insertions and obeys the "principle of least nuclear motions" was developed by Cossee and Arlman. Compounds such bis(cyclopentadienyl)titanium chloride and bis(indenyl)zirconium dichloride, known as metallocenes, have been developed as an alternative to the traditional compounds of this type. Those traditional initiators include vanadium trichloride and triethylaluminum, and the product of the application of these compounds to alkenes can result in syndiotactic, isotactic, or atactic products. For ten points, identify these stereoselective compounds used to initiate polymerization, named for a German and an Italian chemist.
Output (English): Science