A heterogenized rhodium complex, prepared by sol-gel processing of Rh(CO)Cl[PPh2CH2CH2Si(OEt)3]2 and Si(OEt)4, is shown to catalyze the conversion of the silanes H4-nSiPh„ (n = 1 - 3) or (HMe2Si)2O to (poly)siloxanes by air or water. Using THF as a solvent, the silanoles Ph3SiOH or Ph2Si(OH)2 are obtained instead. The reaction of phenylacetic acid or acetic acid with HSiPh3 to give silyl esters is catalyzed by the same compound.