Thermodynamic vs. Kinetic products
The difference between Thermodynamic and Kinetic products is the difference in activation energy and the difference in (Gibbs)-Free-Energy.
When the activation energy is low, the reaction proceeds fast, while the product might not have as low a Free-Energy as an other product (with higher activation energy). When the reaction conditions allow however, the thermodynamically more stable product (with lower Free-Energy) will be formed. Even though the kinetic product first forms, most complexes are form in equilibrium reactions. Therefore, the kinetic product reverts to starting materials and then, slowly forms the thermodynamic product. This thermo dynamic product, though it is also in equilibrium, will not revert to starting materials as easily as the kinetic product will, due to the lower Free-Energy.

To conclude: First, the kinetically favored product will form. Then, when the reaction conditions allow it, the equilibrium shifts towards the thermodynamic product.
Note that the equilibrium is essential for the thermodynamically favored product to form.