This Thesis reports the synthesis and reactivity of zirconium and hafnium borylimides. Synthetic routes to such complexes of these two metals and corresponding novel borylamines were targeted. Their reactions with small polar and non-polar compounds were explored. Chapter One provides a background on Group 4 imido and hydrazido complexes. Group 4 alkoxyimides are also reviewed, as well as the recently developed titanium and scandium borylimides. The Chapter focuses on the synthesis, structure, and stoichiometric and catalytic reactions of these complexes with unsaturated substrates. Chapter Two describes the synthesis and structures of new zirconium and hafnium borylimides and their reactions with C-H and H-H bonds. The electronic structures of these complexes are analysed by DFT and QTAIM studies. Chapter Three describes the reactions of Group 4 metallocene borylimides with terminal alkynes. The principal reaction outcomes are [2+2] cycloadditions and C-H bond activations, and attempts to catalyse the hydro-borylamination reaction are also described. Kinetic studies of some reactions are presented, and are supported by DFT, QTAIM and NBO studies. Chapter Four describes the reactions of Cp2Zr{NB(NAr'CH2)}(py) with polar compounds, with a particular focus being the reactivity of esters and their analogues with this complex, eliminating and self-trapping ketene. Kinetic studies of some reactions are presented, and are supported by further DFT studies. Chapter Five presents full experimental procedures and characterising data for the new complexes reported.