Reactive Cationic Zr(IV) and Ti(IV) Complexes Containing Labile Ligands

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Ziegler-Natta catalysts are used widely as industrial catalysts for the synthesis of polymers. The zirconium and titanium compounds which will be studied in this project are related to soluble Ziegler-Natta catalysts. This project is expected to provide a better understanding of how these catalysts function and to provide information needed to design more specific and more efficient catalysts for polymer synthesis. General methods for the synthesis and isolation of cationic organozirconium complexes of the type bis-Cp-Zr(R)(L) where L is a labile ligand have been discovered. The organozirconium complexes are highly reactive. Their Zr-R bonds undergo rapid insertion of ketones, nitriles and other polar unsaturated substrates, and the THF complexes polymerize ethylene in the absence of an Al cocatalyst. These observations support recent proposals that cationic Ti and Zr complexes are active species in soluble Ziegler-Natta catalyst systems. The cationic organozirconium complexes are also easily hydrogenated to synthetically useful cationic hydrides. The research plan is to synthesize an extensive series of Cp2M(R)(L) complexes (M = Ti, Zr) and to study the scope and mechanisms of their reactions with olefins and other unsaturated substrates, and with hydrogen. These novel compounds provide an opportunity to study the fundamental features of insertion reactions of M-R bonds (M = Ti, Zr) in the absence of the many complications caused by Al cocatalysts. Also included in this project is research to develop asymmetric organic syntheses based on chiral cationic Cp2M(R)(L) complexes.