This thesis describes the use of in situ infrared spectroscopy to investigate the kinetics and mechanism of Pd-catalysed arylcyanation. These studies probe the formation of small Pd nanoclusters in the Pd catalysed cyanation of aryl halides. Initially, an overview of the role of Pd nanoparticles and Pd nanoparticle precursor complexes in Pd-catalysed reactions is provided. The application of the established precatalyst in extensive kinetic studies of arylcyanation has revealed that there is clear evidence for heterogeneous catalytic behaviour (Chapter 4). A significant change in kinetic profile supports a change in precatalyst activation mechanism. Pd concentration and catalyst loading data, along with computational analysis, support a role for small Pd clusters in catalysis (Chapter 5).