Synthesis of alcohol substrate for [3,3]- and [3,5]-sigmatropic rearrangements and indenyl yttrium complexes as models for olefin polymerization catalysts
Sigmatropic rearrangements are an important class of pericyclic reactions. These rearrangements can provide “clean” products as they can be easily carried out at relatively low temperatures and/or under photochemical conditions. Pericyclic reactions can be explained using several theories - Frontier Molecular Orbital (FMO) theory, Woodward- Hoffmann rules and Aromatic Transition State theory. In 1976, Lemal and co-workers coined the term “pseudopericyclic” for a class of rearrangements that were distinguished by the presence of “orbital disconnections”. Beginning nearly 20 years later, Birney and co-workers have further shed light on the nature of these rearrangements. The transition states observed in these reactions also differ from planar to almost planar which affects the degree of pseudopericyclic character. The exact nature of pseudopericyclic reactions, however, continues to be of interest to the scientific community. The first part of the thesis discusses the background and current work done on pseudopericyclic reactions. The second part of the manuscript discusses a series of [3,3]- and [3,5]-rearrangements that have been designed to further elucidate their pericyclic/pseudopericyclic character. These systems could have six- and eight- member transition structures via [3,3]- and [3,5]-sigmatropic rearrangements The synthesis involves making the acetate, trichloroacetimidate, dimethyl thiocarbamate, xanthate and vinyl ether of a substrate dienol. The synthesis of the dienol is also discussed. The third part of the thesis discusses the synthesis of a novel indenyl yttrium complexes used as a model for active catalyst in Group 3 olefin polymerizations. A number of ligands have been discussed and synthesized. Using these ligands as ancillary supports, we have synthesized an indenyl yttrium complex that mimics the active species in olefin polymerization. Specifically, attempts have been made to study the insertion of a Y-carbon bond into the indenyl benzo ring at different temperatures and the β-elimination step. One of the biggest potential drawbacks of the indenyl complexes is the deactivation of the catalyst via insertion into the ligands; which directly affects the chain length, stereochemistry and molecular weight of the polymer. This in turn can drastically impact the mechanical, chemical, and physical properties of the polymer.