Transition metal-based catalysts are one of the most powerful tools available to chemists
and the development of ligand systems with which to modify their activity is a constant
area of research. In the last twenty years N-Heterocyclic carbenes (NHCs) have established
themselves at the forefront of organometallic chemistry. To increase the lifetime of the
catalyst these ligands are increasingly being immobilised on supports as, this allows
recovery and reuse while attempting to retain the activity. Cleaner, greener and safer
processes are increasingly important and the recovery of the catalyst by simple separation
also removes contamination and enables the possibility of re-use. This thesis describes
the development of a new concept to immobilise transition metal complexes through an
N-heterocyclic carbene ligand.
The introductory Chapter provides an overview of transition metal catalysis, introducing
the use of supported catalysis including the use of magnetic nanoparticles to aid the
recovery of the catalyst systems. A discussion is included of N-heterocyclic carbene
ligands, including their synthesis, activity in catalysis as ligands for metal complexes as
well as attempts to support the systems and their use in various reactions.
Chapter 2 provides an in-depth introduction to palladium catalysis, focusing on
cross-coupling and dehalogenation reactions. The design of palladium catalysts,
concentrating on palladium–NHC complexes and covers the use of supported catalysts.
The synthesis and immobilisation of a novel palladium carbene complex is also described.
The supported and unsupported complexes were screened in the Suzuki-Miyaura reaction
and dehalogenation reaction. The activity and recycling properties of the supported
catalyst system are discussed.
The next Chapter outlines the use of copper-NHC complexes in the 1,3-dipolar
cycloaddition reaction of azides and alkynes to form 1,2,3-triazoles. The preparation and
characterisation of a novel N-heterocyclic carbene ligand is described, along with the
construction of the supported copper systems. These catalysts were then investigated in
the cycloaddition reaction and assessed for their activity and recovery. The scope of the
reaction is also explored, investigating functional group tolerance.
The final Chapter contains experimental procedures and characterisation data for
all compounds synthesised during this project.