A large number of chemicals are currently obtained by catalytic synthetic processes, but usually in most of these processes the catalyst remains in the reaction medium during the whole cycle. The catalyst cannot be easily recycled and the products are usually contaminated by metal contaminants, with economic and environmental consequences. Hydrosoluble catalysts provide an attractive solution to these issues. The water soluble complex [RuCpCl(PTA)2] was found to be an excellent and versatile catalyst. Its reaction mechanisms have been studied in detail, but traditional experimental techniques (e.g. NMR, IR, UV) do not provide sufficient information on how water participates in the process. Neutron diffraction in the 0.1-50 Å-1 range offers a unique insight in this aspect. We propose to measure the [RuClCp(PTA)2] compound in water at two concentrations.