Hafnium complexes nitrogen ligands

In addition, the electronic structure, mainly determined by the central metal and Lewis-basic or Lewis-acidic substituents at the ligands, is a considerable aspect for the polymerization activity of metallocene and half-sandwich complexes." Complexes with a sterically accessible oxygen or a nitrogen atom (Lewis bases) coordinated to the central metal are not useful for good catalytic performance. Generally, hafnium metallocene and half-sandwich complexes exhibit lower polymerization activities due to a more stable hafnium—carbon bond," which lowers the insertion rate of the coordinated monomer into the growing polymer chain. 

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