The effect of cyclopentadienyl ligands on reaction rates

[crazychemist]

Hi,

 

Im trying to find out what effect different cyclopentadienyl complexes have on the rates of reactions. Specifically, cyclopentadienyl, pentamethylcyclopentadienyl, flourenyl and indenyl.

 

Hope someone can help!

[Tartaglia]

The most important point here is the ability of the fluorenyl and indenyl ligands to go eta-3 rather than eta-5. This occurs because the aromatic stabilisation energy of the fused benzene ring(s) is returned. This gives rise to an associative mechanism which will be orders of magnitudes faster than the dissociative reactions that cp and cp* will give. Cp* makes the metal centre more electron rich and thus will give rise to complexes that differ in rates of substitution but probably not by more than one order of magnitude. It could increase or decrease rates depending on whether the other ligands are pi acceptors or pi donors. Also steric effects may differ cp is much smaller than cp* in terms of occupied cone angle