Immobilised N-heterocyclic carbene metal complexes in catalysis

摘要

Transition metal-based catalysts are one of the most powerful tools available to chemistsudand the development of ligand systems with which to modify their activity is a constantudarea of research. In the last twenty years N-Heterocyclic carbenes (NHCs) have establishedudthemselves at the forefront of organometallic chemistry. To increase the lifetime of theudcatalyst these ligands are increasingly being immobilised on supports as, this allowsudrecovery and reuse while attempting to retain the activity. Cleaner, greener and saferudprocesses are increasingly important and the recovery of the catalyst by simple separationudalso removes contamination and enables the possibility of re-use. This thesis describesudthe development of a new concept to immobilise transition metal complexes through anudN-heterocyclic carbene ligand.udThe introductory Chapter provides an overview of transition metal catalysis, introducingudthe use of supported catalysis including the use of magnetic nanoparticles to aid theudrecovery of the catalyst systems. A discussion is included of N-heterocyclic carbeneudligands, including their synthesis, activity in catalysis as ligands for metal complexes asudwell as attempts to support the systems and their use in various reactions.udChapter 2 provides an in-depth introduction to palladium catalysis, focusing onudcross-coupling and dehalogenation reactions. The design of palladium catalysts,udconcentrating on palladium–NHC complexes and covers the use of supported catalysts.udThe synthesis and immobilisation of a novel palladium carbene complex is also described.udThe supported and unsupported complexes were screened in the Suzuki-Miyaura reactionudand dehalogenation reaction. The activity and recycling properties of the supportedudcatalyst system are discussed.udThe next Chapter outlines the use of copper-NHC complexes in the 1,3-dipolarudcycloaddition reaction of azides and alkynes to form 1,2,3-triazoles. The preparation andudcharacterisation of a novel N-heterocyclic carbene ligand is described, along with theudconstruction of the supported copper systems. These catalysts were then investigated inudthe cycloaddition reaction and assessed for their activity and recovery. The scope of theudreaction is also explored, investigating functional group tolerance.udThe final Chapter contains experimental procedures and characterisation data forudall compounds synthesised during this project.