Secondly, it is known that alkynes coordinate to metal complexes more strongly than alkenes, which has two opposing consequences for hydrogenation. For most catalysts, stronger binding of the alkyne results in a lower intrinsic rate of hydrogenation compared to that for the corresponding alkenes . However, when both are present in the reaction system, stronger binding of alkyne allows it to outcompete the alkene in binding to the catalyst, which can result in high selectivities toward alkene production in selective alkyne hydrogenation even at high alkyne conversions . This type of behavior can be seen in Fig. A number of experimental parameters determine how efficient the competition for the metal center between alkyne and alkene is, including hydrogen pressure and the alkyne/catalyst ratio . In particular, for higher H2 pressures the hydrogenation events proceed faster (cf. Fig. ), implying that the dimethyl maleate molecule which was just formed on the catalytic center and still remains bound to the catalyst has a larger probability to be hydrogenated further to dimethyl succinate before it is kicked out from the catalyst by a DMAD molecule. The onset of dimethyl succinate formation quite early in the DMAD hydrogenation reaction was observed, for instance, in a recent NMR study which used DMAD hyperpolarized by dissolution DNP . The DMAD/catalyst ratio in that study was ca. 5-fold lower compared to our work, and besides the catalyst was undergoing activation during the measurements.