This thesis describes the preparation of some silyl and germyl complexes of rhodium, iridium and platinum. Some silyl and germyl derivatives of rhodium RhY(CO)H(MHZX)(PEt3)Z (Y = Cl or I; M = Si or Go, and X = H, Cl or I) have been prepared by reaction of MH3X with RhY(C0)(PEt3)Z. When X = Cl or I the products were stable at room temperature; nevertheless when X = H evidence supported the formation of the rhodium(III) adduct only at low temperature. Similar results were obtained when the reactions were performed using H2MRZ (for M = Si: Z = H, R = -CH 3 or -CHs CH=CH3; Z = Cl or I, R = -CH 3- For H = Ge: Z = H, R = -CH 3); formation of the products occurred at low temperatures, but the adduct dissociated to the starting materials as the temperature was increased. Also, preparation of Rh(III) hydrides of molecular formulae RhYXH(CO)(PEt3)3 (X = Cl or I) is described. Some equilibrium and thermochemical data corresponding to the Rh(I) + H2MRfRh(III) conversion was measured and attempts are made in the text to account for the information obtained. Reactions using some organ-substituted silyl compounds H3SiR (R = -CH3)-C6"51 -C&=CH3 and -CH s-CH=CHZ) were carried out with IrY(CO)(PEt3)Z, t-PtHY(PEt3)2 and t-PtYZ(PEt3)3. The phenylsilane derivatives of iridium and platinum were reacted with the hydrogen halides (HCl or HI), but evidence supporting the breaking of the C-Si bond was not found. The complexes formed were characterised by IH and 31P n.m.r. spectroscopy at low or room temperature as appropriate, and where possible, by analysis for C and H.