Your question is very general and I don't feel there is a complete answer to it.
Anyway, organic conversions take place usually in organic solvents and simple metal salts are often insoluble in such solvents. With the Schiff base (usually bis-Schiff base with extra donours such as salen ligand) you have a quite stable complex which is soluble. Also, with such ligands the coordination sphere of the metal is not saturated and catalysis is possible.
Yes. I partially accept your answer. The coordination site found in the unsaturated coordination sphere of the metal may provide the reaction platform for the organic conversations. But my question is that if the Schiff base metal complex is a heterogeneous catalyst in the reaction what may be the reason for its good catalytic activity?
Thank you for the answers, but its still not clear. So let me put my question in different way.
As a compound, Schiff bases may not be good catalysts and metals salts also may not be good catalysts but when they combine and form complexes, they become a good catalysts.So what could be this driving force? Forget about being soluble or insoluble because a catalyst can be heterogenous as well as homogenous.
Look around stability of these complexes. Also when coordination has taken place the oxidation state of the metal atom is affected. These can contribute to the driving force. Thank you.