All three polyphosphines are capable to take up ruthenium species, when the precursor [Ru(pcymene)Cl2]2 is immobilized by ligand exchange from solution (Scheme 2). Regarding the molar ratio of ruthenium (Ru) to phosphorus (Table ), only a fraction of the overall phosphine centers actually coordinates a Ru species, resulting either from an unfavourable modification of the ligating phosphine or from a limited accessibility of appropriate coordination sites for the metal complex. In accordance with an extending porosity at longer aromatic crosslinker units, the Ru uptake per phosphine center increases from P-DCE-Ru (1:12) to P-BP-Ru (1:4). Hence, it seems that the biphenyl unit provides a more porous framework in the swollen state, where a higher amount of ligating sites is accessible for the metal complex. In order to gain an understanding about these Ru-coordinating sites and their catalytic properties, we evaluated the catalyst in the hydrogenation of CO2 to formic acid (Scheme 3 and Fig. ). The nearly identical catalytic activities of P-BP-Ru, P-B2-Ru and P-DCE-Ru suggest the presence of comparable catalytically active species. Reference experiments of modified materials allow the drawing of a more assessing picture. The inactivity of the non-impregnated polyphosphine P-BP is owed to the absence of a transition metal species. The commercial heterogeneous Ru@C catalyst possesses a negligible activity. The examination of a phosphine-free Ru catalyst is complemented by the synthesis of a comparable HCP, consisting entirely out of biphenyl units without any phosphine moieties. After the post-synthetic immobilization of the Ru precursor, BCMBP-Ru exhibited a tenth of the catalytic activity of the Ru-loaded polyphosphines. While the molecular Ru(NO)(NO3)3 complex shows a minor activity, the addition of 3 equivalents of the tri-sulfonated derivative of PPh3 (TPPTS) led to the in-situ formation of an active homogenous catalyst. This survey of reference catalysts demonstrates the excellent performance of our Ru-impregnated macroligands. Moreover, it reveals the involvement of both species, the Ru metal as well as the phoshphine microenvironment, in the catalytically active species of the solid catalyst, which is apparently not affected by the variation of the crosslinker unit. Recycling experiments, in which the reaction solution is exchanged after each catalytic run, enable insights into the catalytic stability of P-BP-Ru, P-B2-Ru and P-DCE-Ru (Fig. ). In the first runs of the respective catalyst, a continuous decline of the catalytic productivity is observed, which is more noticeable for P-DCE-Ru than for P-B2-Ru and least pronounced for P-BP-Ru. Since the hydrogenation reaction is far away from thermodynamic equilibrium, this flattening of the kinetic curve can be attributed to a gradual degradation of the catalytic species. The leaching of the Ru species is not detectable in the filtrate (Table ), therefore it can be excluded as source of deactivation. According to previous works, the decreasing productivity most probably relates to electronical changes of the active metal species, the oxidation of the phosphine species and structural alterations of the solid catalyst, which are subject to examinations further below. Regarding the consecutive runs of P-BP-Ru, P-B2-Ru and P-DCE-Ru (Fig. ), the gradual degradation leads to a significant drop of the productivity after 5.5 hours, followed by a minor decrease of the reaction rate in the second and third run, until the productivities of the three catalyst approach each other at a steady-state level.