The Left Hand, Right Hand

Metal complexes are used to speed up reactions in all other types of molecules. But they come with some baggage because the metals need to be well isolated. They don't work well in oxygen and moisture environments. The residual metals can end up in the products or the molecules that you're trying to make. And then they have to be catalyzed out as well. To achieve more complex molecules, some molecules need to go through many rounds of catalysis. Depending on the catalus being used in the molecule being modified, it can produce pairs of new molecules. These pairs of molecules are a mere, mere image of each other.