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The Kaminsky Catalyst
The first metallocene understood by chemists was ferrocene. The Fe2+ ion bonds to two cyclopentadienyl ions (each with a charge of -1) to give a neutral molecule.
A research student working for Walter Kaminsky at the University of Hamburg was using a modified Ziegler catalyst based on a titanium-based metallocene. Usually the polymerisation was slow, so Kaminsky did not expect much from the experiment. But the student obtained quite a lot of poly(ethene). This was a perhaps lazy, but honest, student. He admitted that he had not flushed the apparatus out with nitrogen at the start, as he should have done.

It took six months to sort out that it was water in the air, and not oxygen, which was responsible for the polymerisation.

When a 1:1 mixture of triethylaluminium and water was used along with the titanocene the rate of polymerisation went up a million times.

A group of organometallic materials was discovered in the early 1950's. these are the metallocenes, a large family of 'sandwich compounds' involving metals held between different ring systems.
















If the metal is bonded to bulky groups the rings are forced to tilt apart. The zirconium(lV) brings two chlorines into the sandwich to balance charges, forcing the rings apart.