Preparation of chromium complexes such as [Cr(en)3](ClO4)3, the typical starting material is CrCl3 6H2O. When combined with excess ethylenediamine in an appropriate solvent, the reaction proceeds slowly, however the addition of a small, catalytic piece of Zn rapidly accelerates the reaction. Discuss this reaction in terms of the role Zn as a catalyst and the relative labilities of the oxidation state (or states) of chromium involved.