Ansa-metallocene

The link prevents rotation of the cyclopentadienyl ligand and often modifies the structure and reactivity of the metal center.

[1] The term ansa-metallocene (ansa being Greek for "handle") was coined by Lüttringhaus and Kullick to describe alkylidene-bridged ferrocenes, which were developed in the 1950s.

[2] Often ansa-metallocenes are described in terms of the angle defined by the two Cp rings.

Specifically, the ansa bridge allows greater control of the stereochemistry at the metal centre.

For example, three distinct ansa-zirconocene dichloride catalysts used in the synthesis of polypropylene in the presence of methylaluminoxane (MAO) can be used to direct whether the product is syndiotactic, isotactic, or atactic.

Structure of a generic ansa -metallocene. X is the linker group, often (CH 2 ) n or R 2 Si (R = alkyl). L n refers to additional ligands that may reside on the metal M.