In addition, evolved carbon monoxide cannot be detected in the gas phase of the first catalytic run of P-BINAP-Ru (Fig. ). Beside C-O vibration bands (1080 cm -1 -1120 cm -1 ) in all catalysts, the spent polyphosphines exhibit an enhancement of the P=O vibrations (1179 cm -1 ) over the catalysis, except for P-Xantphos-Ru. This increased oxidation of phosphines strongly affects the coordinative bond between Ru and the macroligand, reducing the catalytic reaction rate in the CO2 hydrogenation to formate. This oxidation process can be significantly observed for the alkylbridged diphosphines P-dppm-Ru, P-dppe-Ru and P-dppp-Ru, while it is less pronounced for the aryl-phosphines P-BINAP-Ru and P-PPh3 and almost absent for P-Xantphos-Ru. In order to evaluate the influence of oxidized phosphines on the catalytic performance, a macroligand analogous to P-PPh3-Ru but consisting of monomeric triphenylphosphine oxide (OPPh3) was synthesized. The resulting catalyst coincides with P-PPh3-Ru in terms of structural elements in the FTIR spectrum (Fig. ). However, only a small amount of Ru is immobilized on the oxidized polyphosphines (0.14 wt%) (Table ), indicating a less likely coordination bond between the oxidized phosphine centers and the Ru species, since sufficient accessibility of the macroligand