Influence of phosphine macroligands in solid molecular ruthenium catalysts on the hydrogenation of CO2 to formate

Advances in the essential direct hydrogenation of CO2 to formic acid are strongly linked to the development of suitable catalytic systems. Here, we have followed the molecular tailoring of macroligands that can be achieved by the crosslinking of aryl phosphine units or of entire transition metal phosphine complexes. Besides the systematic investigation of the reaction parameters, the metal uptake of these macroligands is studied. The versatile crosslinking strategy allows the incorporation of a series of common diphosphines into the frameworks, serving as fixed coordination sites for immobilized ruthenium species. The investigation described here is not restricted to one catalyst, but compares the characteristics and catalytic activities of a wide range of different materials, focusing on their stability over several recycling runs. In particular, catalysts derived from xantphos and BINAP show excellent catalytic performances after a certain induction period. Hence, this study highlights the advantageous properties of rigid bidentate macroligands with spatially close coordination sites for the design of an active and stable solid catalyst in the CO2 hydrogenation to formates.