Haptotropic Rearrangements of Polyenyl Ligands and their Role in the Activation of Transition Metal Complexes

Cyclopentadienyl transition metal chemistry dates back to the synthesis and characterization of ferrocene in the 1950`s which resulted in the award of a Nobel prize for E. O. Fischer and G. Wilkinson in 1973. The cyclopentadienyl ligand (C5 H5 ) has since become one of the most extensively utilized ligands in organotransition metal chemistry serving as so called "spectator". There is, however, an increasing awareness of the importance of haptotropic rearrangement reactions of polyenyl ligands which become even facile processes provided that certain conditions are met. This feature is arguably a key property for understanding the catalytic efficiency of many C5 H5 and indenyl (Ind) complexes. This project is aimed at the understanding of electronic and steric factors that govern haptotropic rearrangements of C5 H5 Ind, and related h 5 -bound polyenyl ligands. Furthermore, its implications to the activation of the polyenyl ligands themselves (functionalizations via nucleophilic attack), and to transition metal complexes with respect to the activation of other molecules. Several model systems will be studied kinetically by means of stopped-flow spectrophotometry and NMR spectroscopy. From these studies we intend to obtain activation parameters of individual reaction steps in combination with rate constants and the rate Law.