The research described in this thesis concerns the synthesis of transition metal coordination complexes and their activity in the controlled radical polymerisation (CRP) of styrene, methyl methacrylate and vinyl acetate. In the first, introductory chapter, the literature pertaining to the main reported CRP systems is reviewed. The second chapter focuses on a family of novel α-diimine Fe(II) complexes bearing a conjugated acenaphthene backbone. The ligand-dependent catalytic behaviour in the atom transfer radical polymerisation (ATRP) of styrene is discussed, and the reaction conditions are varied to shed light on the system features. In the Chapter 3 the synthesis, characterisation and screening for reverse ATRP of the Fe(III) trichloride derivatives, as well as of two monodentate imino Fe(III) trichloride complexes, are described. A relationship between measured spin state and catalytic behaviour is highlighted. The fourth chapter reports the synthesis of bis-salicylaldimino Cr(II) complexes and their activity in the controlled radical polymerisation of styrene and vinyl acetate. The observed rearrangement of the latter monomer in the presence of chromium complexes is also examined. The fifth and final experimental chapter extends the studies carried out on bissalicylaldimino Cr(II) complexes to other transition metals, namely iron and cobalt. Chapter 6 gives the experimental details for Chapters 2-4. Crystallographic data for all X-ray diffraction structures presented in this thesis are collated in Chapter 7.