Catalysts, by definition, provide a lower-energy route to the product. Organometallic complexes react with organic molecules in ways that are very different than how organic molecules react with themselves. At the most basic level, this is because transition metals have d-orbitals that are involved in making and breaking chemical bonds. With additional orbitals that are of different symmetry than the s- and p-orbitals that are available to elements like carbon, nitrogen, and oxygen, organometallic complexes can accomplish feats that are just impossible (forbidden!) for other elements.