The precursor solution for all experiments was 250 mM acetylene dicarboxylic acid monopotassium salt, 250 mM sodium sulphite and 7 mM ruthenium catalyst [RuCp*(CH3CN)3]PF6 in D2O, which was prepared by dissolving the solids with heating and sonication. The solution additionally contained 250 mM NaOH, to be equimolar with the starting material. The sodium sulphite is added to increase the rate of reaction as discussed in Ref. . Oxygen was removed from the solution by bubbling nitrogen through for 5 minutes. All chemicals were purchased from Sigma Aldrich.