The catalytic reactivity of titanosilsesquioxanes and titanosiloxanes are investigated with ab initio electronic structure theory including electron correlation effects. The reactions examined are the oxidation of olefins and polymerization of ethylene. The titanium compounds are found to be promising effective catalysts for the oxidation reactions, with the catalytic activity increasing with the number of Ti-containing substituents. Ring and cage structures also enhance the catalytic ability of these compounds, whereas the addition of Si-containing substituents has the opposite effect. The same Ti compounds are predicted to be less effective as catalysts for ethylene polymerization.