Orsola A. Luongo: Development of zirconium hydride catalyzed migratory C-C cleavage and hydrosilylation reactions

Abstract

Catalysis based on earth-abundant early transition metals has emerged as a sustainable alternative to traditional late transition-metal catalysis. In this context, zirconium(IV) complexes stand out for their unique reactivity, enabling both functionalization and cleavage reactions. 

This thesis describes the development of two zirconocene-catalyzed methodologies together with the identification of a practical strategy for the in situ generation of the active zirconium hydride catalyst.

The first project focuses on the development of a new zirconium-catalyzed C-C bond cleavage reaction of unactivated alkenylcyclopropanes. Depending on the hydride source and conditions, the reaction yields either the corresponding open-chain product or its hydrosilylated derivative. By exploiting the “chain-walking” ability of zirconocene hydride complexes, cyclopropanes distant up to eight carbons from the alkene unit could be successfully converted into the corresponding products. 

The second project involves the development of a new zirconium catalyzed hydrosilylation reaction of terminal and internal alkenes. This method employs the commercially available precatalyst Cp2ZrCl2 together with LiOMe and silanes as mild catalyst activators, providing a practical alternative to existing late transition-metal based methods. Mechanistic investigations support a pathway involving a zirconium(IV) species. 

Interestingly, in both projects LiOMe and silane emerged as unifying activation strategy for accessing the catalytically active zirconocene hydride species, enabling both bond-forming and bond-cleavage transformations under operationally simple conditions.