The use of the hydrides as reagents for building group IVB - transition metal complexes has been investigated. The reactions of the simple hydrides; Me₃GeH, Me₂GeH₂, MeGeH₃, GeH₄, Me₂SiH₂, Me₂SnH₂, MeSnH₃, and SnH₄, with Co₂(CO)₈ have been examined, and the effect determined of, reactant ratios and amount of CO present, on the products obtained. Limited evidence was obtained for the synthesis of the new compounds; MeGe[Co(CO)₄]₃, HGe[Co(CO)₄]₃, Me₂SiHCo(CO)₄ and (OC)₄CoMe₂SiOCCo₃(CO)₉. Me₂GeH₂ replaces a bridging CO group: Me₂GeH₂ + Co₂(CO)₈ → Me₂GeCo₂(CO)₇ + H₂ + CO Me₂GeH₂ + Me₂GeCo₂(CO) ₇ → (Me₂Ge)₂Co₂(CO)₆ + H₂ + CO In the reactions of the polygermanes; Me₃GeGeH₃, Me₃SiGeH₃, Ge₂H₆, Ge₃H₈ and (GeH₃)₂SiMe₂ with Co₂(CO)₈, the M'-Ge, (M' = Si or Ge) bonds were quantitatively cleaved, and the new compound Ge₂Co₆(CO)₂₀, was isolated. This compound is assigned the structure: on spectroscopic evidence. Me₂GeH₂ also replaces a bridging CO group in the germanium - cobalt carbonyl species, to produce the new compounds; Me₂Ge₂Co₄(CO)₁₃ and (Me₂Ge)₂Ge₂Co₆(CO)₁₈. An X-ray crystallographic study on Me₂Ge₂Co₄(CO)₁₃ although showing the: skeleton, failed to refine properly. The reactions of Me₂SiH₂ and Me₂SnH₂ with germanium - cobalt carbonyl species failed to give a similar result. MeGeH₃ and GeCo₄(Co)₁₄ produced initially the analogous Me(H)Ge₂Co₄(CO)₁₃. However when left for 6 months, an unexpected rearrangement yielded (MeGe)₂Co₄(CO)₁₁. X-ray crystallography showed an irregular square bipyramidal structure, containing 5-coordinated square pyramidal germanium. This is this first example of such a group IVB - transition metal cluster. The decarbonylation of Ge₂Co₆(CO)₂₀ yielded the new compound [(OC)₄CoGe]₂Co₄(CO)₁₁ : which was found by X-ray crystallography to have a similar square bipyramidal structure. The new tin hydrides; MeSnH₂Mn(CO)₅ and Me₂SnHMn(CO)₅, have been prepared by the established route : Me₍₃₋ₓ₎SnHₓCl + NaMn(CO)₅ → Me₍₃₋ₓ₎SnHₓMn(CO)₅ + NaCl (x = 1,2) and characterised spectroscopically.