Adsorption of two model fragments, Fe(CO)(4) and PdCl3-, on a cluster model of the Si(100) surface and disilene was studied by means of density functional calculations. The reconstructed silicon-silicon surface dimer forms a strong bond to metal fragments, analogous to ethylene pi-bond complexation to a transition metal complex. This bond can be described in terms of the Dewar-Chatt-Duncanson model. The Fe(CO)(4) fragment binds to the surface cluster model in two geometrical configurations-in a geometry in which the Si-Si bond is in the equatorial plane of an approximate trigonal bipyramid at Fe and another, less stable geometry with the Si-Si bond perpendicular to the equatorial plane. PdCl3- also binds well, forming a square planar complex with the Si-Si bond in the plane of the complex. Since the Cl- ligands in PdCl3- are labile, adsorption in a geometry with the Si-Si bond perpendicular to the plane of the square planar complex leads to two unusual structures in which Si-Cl bonds are formed. The possibility of formation of one-dimensional chains of transition metal fragments on the surface, using O2- and H- bridging ligands has been explored.