Functionalized SiO2-tethered rhodium complexes derived from Rh-4(CO)(12), RhCl(PPh3)(3) and RhHCl(PPh3)(3) have been studied by infrared spectroscopy (IR) and solid state P-31 NMR. Rh-4(CO)(12) and phosphinated or aminated SiO2 are suggested to form Rh-4(CO)(12-x)L-x (L: supported PPh2 or NH2; x = 2 or 3). Rh-4(CO)(12) reacts with thiolated SiO2 to give [Rh(mu-L)(CO)(2)](2) (L: supported SH). The reaction of RhCl(PPh3)(3) or RhH(CO)(PPh3)(3) with functionalized SiO2 is assumed to result in RhCl(PPh3)(2)L or RhH(CO)(PPh3)(2)L (L: supported PPh2 or NH2 or SH). The catalytic activity and stability of a tethered rhodium complex catalyst in cyclohexene hydroformylation shows the supported donor ligand and the catalyst precursor dependences. The aminated SiO2-tethered catalyst derived from Rh-4(CO)(12) or RhCl(PPh3)(3) displays good catalytic activity and good resistance to rhodium leaching. The thiolated SiO2-tethered catalyst derived from RhH(CO)(PPh3)(3) exhibits the highest catalytic activity and good resistance to rhodium leaching. The effects of supported donor ligands on the activity and stability of tethered rhodium complex catalysts for hydroformylation are described. (C) 2003 Elsevier B.V. All rights reserved.