Palladium and Ruthenium Catalyzed Reactions

Abstract

Part one of this thesis will discuss research which involves the direct comparison of the activity of commonly used precatalysts with the newly synthesized precatalyst, Pd(η5-C5H5)(η3-1-Ph-C3H4), for Sonogashira cross-coupling reactions. Sonogashira reactions are important as they provide a simple method for the formation of substituted alkynes, a commonly found functionality within important organic molecules. These reactions are generally believed to be catalyzed by a Pd(0)L2 species which are generated in situ from a palladium precatalyst and are often co-catalyzed by CuI although use of the latter is undesirable as it induces homocoupling in certain instances. The rate and quantity of active species generated is not known for the commonly used precatalysts and is a potential reason for decreased rates and yields. Norton et al. have recently demonstrated that the newly synthesized, easily handled compound Pd(η5-C5H5)(η3-1-Ph-C3H4) is a superior precatalyst as it generates the active Pd(0)L2 species more quickly than other commonly used palladium precatalysts. Part one of this thesis will discuss research which investigated the efficiencies of precatalysts used for Sonogashira cross-coupling reactions. Part two of this thesis will discuss research into the syntheses of a novel series of ruthenium complexes and their utilization as ester hydrogenation catalysts. Reduction of esters to the corresponding alcohols is normally carried out using LiAlH4, a stoichiometric type of reaction which produces large amounts of undesirable by-products. Ruthenium-based catalysts are known to hydrogenate a variety of functional groups and many catalytic systems have been developed for the hydrogenation of alkenes, ketones, etc. The recent literature also describes a small number of ruthenium catalyst systems which enable ester hydrogenation to the same types of alcohols produced by LiAlH4 reduction albeit catalytically, a much “greener” type of chemistry. This paper will discuss the syntheses of a series of Ru(acac)2(phosphine)1-2 complexes and their utilization as ester hydrogenation catalysts.