This paper investigates the required properties of Ru-coordinated ligands of a Ni–Ru based hydrogenase mimic. A series of ligands, including MeCN, pyridine, H2O and OH− were coordinated to Ru, with H2O being the only ligand to promote H2-activation. In addition, a tethered pyridyl moiety was synthesised and found to completely inhibit H2-activation. We conclude, therefore, that H2O is the ideal ligand for this mimic as a result of both its mild basicity and the availability of two lone pairs for simultaneous binding to Ru and H2.